Solid wastes and residues: Conversion by advanced thermal processes

Solid Wastes and Residues Conversion by Advanced Thermal Processes Jerry L . Jones and Shirley B. Radding, EDITORS SRI International

A symposium sponsored by the Division of Environmental Chemistry at the 175th Meeting of the American Chemical Society, Anaheim, California, March 13-17, 1978.

ACS SYMPOSIUM SERIES 76 AMERICAN

CHEMICAL

SOCIETY

WASHINGTON, D. C. 1978

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Library of Congress CIP Data Solid wastes and residues. (ACS symposium series; 76. ISSN 0097-6156. Includes bibliographical references and index. 1. Refuse and refuse disposal—Congresses. 2. Pyrolysis—Congresses. 3. Fuel—Congresses. I. Jones, Jerry L., 1946. II. Radding, Shirley B., 1922. III. American Chemical Society. Division of Environmental Chemistry. IV. Series: American Chemical Society. ACS symposium series; 76. TD796.7.S64 ISBN 0-8412-0434-9

604.6 ACSMC8

78-16293 76 1-136 1978

Copyright © 1978 American Chemical Society A l l Rights Reserved. The appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating new collective works, for resale, or for information storage and retrieval systems. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN THE UNITED STATES OF AMERICA

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

ACS Symposium Series Robert F. G o u l d , Editor

Advisory Board Kenneth B. Bischoff

Nina I. McClelland

Donald G . Crosby

John B. Pfeiffer

Jeremiah P. Freeman

Joseph V . Rodricks

E. Desmond Goddard

F. Sherwood Rowland

Jack Halpern

Alan C. Sartorelli

Robert A . Hofstader

Raymond B. Seymour

James P. Lodge

Roy L. Whistler

John L. Margrave

Aaron Wold

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

FOREWORD The ACS SYMPOSIU

a medium for publishin format of the SERIES parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published in the ACS SYMPOSIUM SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

PREFACE A lthough the word "advanced" was used in the title of the symposium, the reader should be aware that the practice of producing fuel gases from wastes and residues is not new. During the early part of the 20th century, Crossley Brothers Limited of Manchester, England, was selling gasifiers worldwide that produced a low-Btu fuel gas from agricultural or forestry residues. During World War II, many vehicles in Sweden were retrofitted with low-Btu gas producers fueled by wood or charcoal. Therefore, some individuals may consider some of the research and development work describe the gasification field. In other cases, though, the processes have been conceived only within the last decade and are concerned with concepts new to the processing of wastes and residues. (However, some of the processes may have been applied previously to the conversion of fossil fuels such as coal or oil shale. ) The first two chapters present overview discussions of the feedstocks, technologies, and economics for producing fuels from wastes and residues. Chapter One briefly describes alternative technologies, including combustion and biochemical conversion processes, and also presents waste and residue quantities and a method for categorizing pyrolysis, thermal gasification, and liquefaction processes. Chapter Two discussed the production of low-Btu and medium-Btu fuel gases and the relative advantages to the product, which has a higher heating value. The next section of the book contains six chapters that describe verticle flow packed-bed reactor (or fixed-bed reactor) processes. The feedstocks included in these chapters are municipal solid waste, municipal wastewater treatment sludge, scrap tires, agricultural residues (such as peanut shells, corn cobs, cotton gin trash, walnut shells), and wood residues. Two of the process reactors are designed to operate with oxygen, whereas the other four are air-blown. The reactor products described include low-Btu gas (which is immediately combusted in a secondary combustion chamber), a medium-Btu gas, pyrolytic oil, and char. The third section contains three papers describing processes with multiple-hearth-type staged reactors. Although this type of reactor has been used for many years for ore roasting and sludge combustion, a great deal of development work has been done recently to lower the fuel requirements for processing high-moisture feedstocks, such as sludge or

vii In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

manure. The methods developed include operating in a starved-air combustion mode and changing the conventional gas flow between stages. Processes with horizontal or inclined-flow rotary reactors are described in the fourth section. Municipal sludge and solid waste, wood, and scrap tires are the respective feedstocks for the three processes discussed. The products include char, electric power, carbon black, and a pyrolytic oil. All of the rotary reactors described use indirect heat transfer. The last section of the book describes a flash pyrolysis process based on the use of a transport reactor, a new concept in fluidized-bed design, and research work being funded by the Environmental Protection Agency on topics such as a molten salt pyrolysis reactor that will accept whole (unshredded) scrap tires and a process for producing polymer gasoline from wastes. The last chapters also discuss a multiple reactor system that can produce a high methane content gas with a heating value of 370 Btu/scf, a high-pressure catalytic liquefaction process that is currently being developed to produce oil from wood, and the processing of char (from municipal soli water treatment. Special recognition and appreciation is given to the authors whose efforts made this publication possible. We also wish to acknowledge the assistance of the officers of the Environmental Chemistry Division of the ACS, and of Linda Deans, who coordinated the Environmental Chemistry Division programs at Anaheim. SRI

International

JERRY L . JONES

Menlo Park, C A 94025

SHIRLEY B. RADDING

Received June 2, 1978

viii In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

CONTRIBUTORS Alderstein, Joseph K., Syngas Inc., Suite 1260 East, First National Center, Oklahoma City, OK 73102 Bailie, Richard, Chemical Engineering Dept., West Virginia University, Morgantown, W V 26505 Beck, Steven R., Department of Chemical Engineering, Texas Tech Uni­ versity, Lubbock, T X 79409 Bowen, M . D., Tech-Air Corp., Atlanta, GA 30341 Brunner, Paul H . , E A W A G , Swiss Federal Institutes of Technology, C H 8600, Dubendorf, Switzerlan Coffman, J. Α., Wright-Malta Corp., Malta Test Station, Plains Rd., Ballston Spa, NY 12020 Cone, Eugene J., Occidental Research Corp., 1855 Carrion Rd., La Verne, CA 91750 Davidson, Paul E., Andco-Torrax Division, Andco Inc., 25 Anderson Rd., Buffalo, NY 14225 Farrell, J. B., U.S. E.P.A., M E R L , Cincinnati, O H 45268 Feldman, Herman F., Battelle-Columbus Laboratories, 505 King Ave., Columbus, O H 43201 Funk, Harald F., 68 Elm St., Murray Hill, NJ 07974 Garrett, Donald E., Garrett Energy Research and Engineering Co., Inc., 911 Bryant Place, Ojai, C A 93023 Goss, J. R., University of California, Davis, Agricultural Engineering Dept., Davis, C A 95616 Hoang, Dinh Co, Garrett Energy Research and Engineering Co., Inc., 911 Bryant Place, Ojai, C A 93023 Hooverman, R. H., Wright-Malta Corp., Malta Test Station, Plains Rd., Ballston Spa, NY 12020 Huffman, George L., U.S. Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, O H 45268 Huffman, William J., Department of Chemical Engineering, Texas Tech University, Lubbock, T X 79409 Jenkins, B., University of California, Davis, Agricultural Engineering Dept., Davis, C A 95616 Jones, Jerry L., SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025 Knight, J. Α., Engineering Experiment Station, Georgia Institute of Tech­ nology, Atlanta, GA 30332

ix In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Leckie, James Ο., Department of Civil Engineering, Stanford University, Stanford, C A 94305 Liberick, Walter W., Jr., U.S. Environmental Protection Agency, Indus­ trial Environmental Research Laboratory, Cincinnati, O H 45268 Lindemuth, T. E., Research and Engineering, Bechtel National, Inc., 50 Beale St., San Francisco, C A 94119 Lucas, Theodore W., Jr., Andco-Torrax Division, Andco Inc., 25 Ander­ son Rd., Buffalo, NY 14225 Mann, Uzi, Department of Chemical Engineering, Texas Tech Univer­ sity, Lubbock, T X 79409 Mehlschau, J. J., University of California, Davis, Agricultural Engineer­ ing Dept., Davis, C A 95616 Mikesell, Ritchie D., Garrett Energy Research and Engineering Co., Inc., 911 Bryant Place, Ojai, C A 93023 Moses, C . T., Union Carbide Corp., Linde Division, Tonawanda, NY 14150 Mudge, L . K., Battelle-Northwest, P.O. Box 999, Richland, W A 99352 Negra, John S., Nichols Engineering & Research Corp., Homestead and Willow Rds., Belle Mead, NJ 08502 Purdy, K. R., Engineering Experiment Station, Georgia Institute of Tech­ nology, Atlanta, GA 30332 Ramming, J., University of California, Davis, Agricultural Engineering Dept., Davis, C A 95616 Richmond, C. Α., Wheelabrator Incineration, Inc., 600 Grant St., Pitts­ burgh, PA 15219 Roberts, Paul V., Department of Civil Engineering, Stanford University, Stanford, C A 94305 Rohrmann ,C. Α., Battelle-Northwest, P.O. Box 999, Richland, W A 99352 Schulman, B. L., Tosco Corp., 18200 West Highway 72, Golden, C O 80401 Shelton, Robert D., BSP/Envirotech, One Davis Dr., Belmont, C A 94002 Sigler, John E., 2839 Tabago Place, Costa Mesa, C A 92626 Smyly, E. D., Tech-Air Corp., Atlanta, GA 30341 Stern, G., U.S. E.P.A., M E R L , Cincinnati, O H 45268 von Dreusche, Charles, Nichols Engineering & Research Corp., Home­ stead and Willow Rds., Belle Mead, NJ 08502 White, P. Α., Tosco Corp., 10100 Santa Monica Blvd., Los Angeles, C A 90067 Williams, R. O., University of California, Davis, Agricultural Engineering Dept., Davis, C A 95616 Wong, Ho-Der, Department of Chemical Engineering, Texas Tech Uni­ versity, Lubbock, T X 79409 Young, K. W., Union Carbide Corp., Linde Division, Tonawanda, NY 14150

χ

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1 Overview of Solid Waste and Residue Generation, Disposition, and Conversion Technologies JERRY L . JONES SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025

This discussion o to the materials that ar cluded are municipal refuse, scrap t i r e s , a g r i c u l t u r a l residues, and forestry residues as well as organic sludges (mainly from wastewater treatment). The d i s t i n c t i o n between the terms " s o l i d waste" and "residue" may be made precise by d e f i n i t i o n . Residues are defined here as s o l i d by-products that have some positive value or represent no cost for disposal. These materials that represent a disposal cost are defined as solid wastes. These definitions, however, do not allow simple c l a s s i f i c a t i o n . For many types of materials, l o c a l market conditions are quite v a r i able and the material may fall into both categories depending on the specific s i t e , the season of the year, or the state of the economy. The conversion processes to be discussed at this symposium are those that may be described as pyrolysis, thermal g a s i f i c a tion, or liquefaction processes. The products from these so-called advanced thermal processes may be gaseous or l i q u i d fuels, a synthesis gas for use as a chemical feedstock, or a carbon char. In some cases, a gaseous fuel generated from p a r t i a l combustion containing condensible tars may be immediately combusted i n a second stage. In others, a fuel product may be transported o f f s i t e for use. The process types included i n the advanced processes category are not a l l necessarily new, but their application to the conversion of s o l i d wastes and residues i s new or has been l i t t l e used i n the past. This paper provides some background on the types, quantities, and current disposition of wastes and residues as well as some information on other existing and developing processing options that are not included i n this symposium. The method used to c l a s s i f y the processes to be discussed by the symposium speakers w i l l also be described.

0-8412-0434-9/78/47-076-003$05.00/0 © 1978 A m e r i c a n C h e m i c a l Society

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4

SOLID WASTES AND RESIDUES

SOLID WASTE AND RESIDUE QUANTITIES GENERATED AND DISPOSITION More than 500 m i l l i o n tons (dry b a s i s ) of organic s o l i d wastes and r e s i d u e s are c u r r e n t l y generated y e a r l y i n the United S t a t e s . These m a t e r i a l s represent a p o t e n t i a l energy resource equivalent to more than 5 quads.* Estimates of the q u a n t i t i e s of these m a t e r i a l s by type are summarized i n Table I . The f i g u r e s have been presented on a dry b a s i s to a l l o w comparison i n cons i s t e n t u n i t s . In f a c t , these m a t e r i a l s vary g r e a t l y i n moisture content and other p h y s i c a l and chemical p r o p e r t i e s (bulk d e n s i t y , p a r t i c l e s i z e , p a r t i c l e s i z e d i s t r i b u t i o n , i n o r g a n i c ash c o n t e n t ) . The use of a s p e c i f i c m a t e r i a l as a feedstock to an energy recovery process depends on many f a c t o r s r e l a t e d to the cost to c o l l e c t and d e l i v e r the m a t e r i a l to the s i t e of the conversion r e a c t o r , and the p h y s i c a l d chemical p r o p e r t i e f th m a t e r i a l that a f f e c t the conversio f o r i n s t a n c e , o f t e n determines the extent o preprocessing r e q u i r e d . A major cost i n c e r t a i n m u n i c i p a l r e f u s e processing systems i s the f r o n t end processing to reduce the p a r t i c l e s i z e and to separate out metals and g l a s s before the thermal conversion step. By-product wood bark, a pulp and paper m i l l s r e s i d u e , on the other hand i s o f t e n q u i t e homogeneous and r e q u i r e s minimal preprocessing. Such a d i f f e r e n c e i n preprocessing cost may be p a r t i a l l y o f f s e t , however, by the dumping fee paid to the conv e r s i o n p l a n t f o r the r e f u s e or by s a l e of the recovered m a t e r i a l s such as f e r r o u s metals and aluminum. The moisture content of m a t e r i a l s may a l s o a f f e c t the c o s t s of the preprocessing (dewatering and drying) or f u e l product s e p a r a t i o n (dehydration of a f u e l gas). Where a r e a c t o r product gas contains condensible organics and r e q u i r e s dehydration, the dehydration o p e r a t i o n can represent a major cost because of poss i b l e t a r fog removal and water p o l l u t i o n problems. The moisture contents of some common s o l i d wastes and residues are shown i n Table I I . I t may be p r e f e r a b l e to predry r a t h e r than to attempt to process a wet m a t e r i a l i n the r e a c t o r . (See reference 8 f o r a more extensive d i s c u s s i o n of t h i s t o p i c . ) The d i s p o s i t i o n of the s e v e r a l c a t e g o r i e s of m a t e r i a l s l i s t e d i n Table I has been estimated i n Tables I I I and IV. The estimates shown i n Table I are based on an exhaustive study by SRI I n t e r n a t i o n a l , whereas those shown i n Table IV are merely crude a p p r o x i mations. One t h i n g i s obvious from a l l these estimates: A l a r g e

A quad i s 1015 Btu. more than 75 quads.

Current y e a r l y U.S.

energy consumption i s

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.

JONES

5

Overview of Solid Waste and Residue

Table I APPROXIMATE TONNAGES OF SELECTED ORGANIC RESIDUES AND SOLID WASTES IN THE UNITED STATES IN 1975 (Dry Weight B a s i s )

Type of M a t e r i a l " Agricultural crop manures

Quantity Generated ( m i l l i o n s of dr tons)

Data Sources (references)

residues ^ 278* 2>26*

1 1

Forestry residues

2>125*

1

M u n i c i p a l refuse

-100

2

Industrial sludges

wastewater

treatment 5,6

(Food p r o c e s s i n g , pulp and paper, p l a s t i c s and s y n t h e t i c s , organic chemicals, t e x t i l e s and petroleum r e f i n i n g ) M u n i c i p a l wastewater sludges Scrap t i r e s

treatment

-5.3

3,4

3 £546

Quantity c o l l e c t e d during normal operations or r e a l i s t i c a l l y collectible.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

6

SOLID WASTES AND RESIDUES

Table I I MOISTURE CONTENT OF SELECTED SOLID WASTES AND RESIDUES Moisture Content S o l i d Wast Wood r e s i d u e s Fresh manure (with u r i n e ) Rice h u l l s

^45 85 5-10

Bagasse

~ 50

Municipal refuse

20-35

Wastewater treatment sludges G r a v i t y thickened Centrifuged Vacuum f i l t e r e d F i l t e r pressed ( p l a t e and frame f i l t e r )

95 80-85 75-80 60-70

Scrap t i r e s

Negligible

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Source:

To s o i l

Reference 1

12.3

12.2

52,389,318

52,636,074

Total

Percent of t o t a l

52,142,254 — 247,064

11,266,626 37,449,165 3,920,283

Fed

Crop Forestry Manure

Sold

4.9

21,060,223

1,741,990 19,301,797 16,436

Fuel

52.1

223,445,115

205,599,417 — 17,845,698

Returned

18.5

79,150,181

6,810,630 67,909,684 4,429,867

Wasted

T o n s — D r y Weight

100.0%

428,680,911

277,560,917 124,660,646 26,459,348

Total

CROP, FORESTRY, AND MANURE RESIDUE DISPOSITION—COTERMINOUS UNITED STATES (1975)

Table I I I

100.0%

64.7% 29.1 6.2

Percent of T o t a l

I

Co

ο

CO

Ο

M

Ο

8

SOLID WASTES AND RESIDUES

Table IV ORGANIC SLUDGE AND MUNICIPAL REFUSE DISPOSITION IN THE UNITED STATES

D i s p o s a l Technique

Municipal Sludges

Percent of T o t a l Industrial Refuse Sludges

Landfill Land a p p l i c a t i o n

25-30

Onsite lagoons

small

Thermal conversion

25-30

Ocean Dumping

15

£90

small small

4-5

Recycled

Quantity ( m i l l i o n s of d r y tons/year)

10

5-6

9

Small number of u n i t s w i t h energy recovery. Sources: References J2_, 3> 4,, _5..

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

100

1.

JONES

Overview of Solid Waste and Residue

9

amount of s o l i d waste and r e s i d u e m a t e r i a l i s s t i l l p o t e n t i a l l y a v a i l a b l e ( a t some p r i c e ) as feedstock to energy recovery processes. I n the case of sludge d i s p o s a l , a primary c o n s i d e r a t i o n i s not to recover energy, but r a t h e r , to dispose of the m a t e r i a l f o r the lowest cost p o s s i b l e w i t h minimal energy use.

ENERGY RECOVERY OPTIONS The major process o p t i o n s f o r energy recovery from s o l i d wastes and r e s i d u e s have been described p r e v i o u s l y (see F i g ure 1 ) . ^The most w i d e l y used processes f o r energy recovery from wastes and r e s i d u e s have been d i r e c t combustion i n a furnace or c o f i r i n g of the m a t e r i a l s w i t h a f o s s i l f u e l f o r steam generat i o n . A recent use of s o l i cement k i l n s . I t has bee i n the United States w i l l be a b l e to burn c o a l . v i ' I n many of these u n i t s , r e f u s e - d e r i v e d f u e l (RDF) and a g r i c u l t u r a l or f o r e s t r y r e s i d u e s can be s u b s t i t u t e d f o r the c o a l . The more advanced thermal processes of p y r o l y s i s , thermal g a s i f i c a t i o n , and l i q u e f a c t i o n (PTGL)* may produce l i q u i d , gaseous, or s o l i d char products. I n some i n s t a n c e s , the gases l e a v i n g the r e a c t o r a r e immediately combusted f o r steam generation. One advantage of t h i s approach over c o n v e n t i o n a l i n c i n e r a t i o n i s that the s o l i d waste or r e s i d u e can be burned w i t h l e s s excess a i r , which means lower gas volumes f o r c l e a n i n g (and perhaps lower p a r t i c u l a t e l o a d i n g i n the combustor f l u e gas) and a higher thermal e f f i c i e n c y ( l e s s heat l o s s out o f the s t a c k ) . Biochemical conversion processes i n c l u d e methane fermentation (anaerobic d i g e s t i o n ) f o r p r o d u c t i o n of a f u e l gas (up to 70% C H 4 and the remainder mostly C O 2 ) and fermentation of sugars to e t h y l a l c o h o l . The fermentable sugars may be produced by a c i d o r enzymatic h y d r o l y s i s of c e l l u l o s e . T h i s paper focuses on the advanced thermal processes; however, to provide a p e r s p e c t i v e on the a p p l i c a t i o n s f o r the newer processes, i t a l s o presents some i n f o r m a t i o n on the use of combustion and biochemical conversion t e c h n o l o g i e s .

For d e f i n i t i o n of terms see reference 8.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978. ' Solid Waste

Unprocessed

r - — — - · > Use as Aggregate

DISPOSAL

LAND

Steam

a

WITH S T E A M GENERATION^

BOILER

INCINERATION

INDUSTRIAL

UTILITY OR

—ι

a

Η

ι

·>

JL

Soil Conditioner

PROCESSES*

CONVERSION

BIOCHEMICAL

Fuel

Gaseous

R D F may be used as a supplemental fuel for sludge incineration

Char

Liquid Fuel

•

I I

PROCESSES*

PTGL

!

F o r district heating, industrial process heating, electric power production, water desalting

6

1 1 <

PREPROCESSING SUCH AS DRYING. SHREDDING OR D E N S I F I C A T I O N

Figure 7. Energy recovery processes

* M a y be preceded by hydrolysis in case of cellulose fermentation

t p T G L : Pyrolysis, thermal gasification,and liquefaction processes

Recovery

Resource

To Nonenergy

COLLECTION

GAS

METHANE

CEMENT KILN

COMBUSTION

Recovered Materials

S O L I D W A S T E OR R E S I D U E

1.

JONES

Overview of Solid Waste and Residue

11

USE OF DIRECT COMBUSTION AND BIOCHEMICAL CONVERSION D i r e c t Combustion For many decades, energy has been recovered from s o l i d wastes and r e s i d u e s by d i r e c t combustion. As e a r l y as 1900, numerous m u n i c i pal r e f u s e i n c i n e r a t o r s i n the United States were generating steam for e l e c t r i c power p r o d u c t i o n . These i n c i n e r a t i o n u n i t s were of the r e f r a c t o r y - w a l l e d design, which was the b a s i c type used i n t h i s country u n t i l about 1970. Energy recovery, however, was not common w i t h the r e f r a c t o r y - w a l l e d i n c i n e r a t i o n i n s t a l l a t i o n s . Only about 20% of the more than 200 r e f r a c t o r y - w a l l e d i n c i n e r a t o r systems i n s t a l l e d before 1965 i n the United States i n c l u d e d heat recovery b o i l e r s f o r steam generation.(12) Refractory-walled incinerators have become s t e a d i l y l e s s popular, and the w a t e r - w a l l furnace i s now p r e f e r r e d . While c a p a c i t y f i g u r e s vary depending on the source, the more than 20 50 tons per day) i n e x i s t e n c 1960s(13_> 14) had a combined process c a p a c i t y of l e s s than 10% of the t o t a l m u n i c i p a l r e f u s e generated. By the mid-1970s, only about 160 of these r e f u s e i n c i n e r a t o r s were o p e r a t i n g i n the United States.(15) Since 1970 at l e a s t s i x w a t e r - w a l l furnaces f o r r e f u s e have been i n s t a l l e d i n the United States (16) f o r energy recovery.* The combined c a p a c i t y of these u n i t s i s approximately 1 m i l l i o n tons/year. These water w a l l u n i t s were i n i t i a l l y developed i n Europe and r e q u i r e only 50 to 100% excess a i r f o r combustion compared w i t h 150 to 200% f o r r e f r a c t o r y w a l l furnaces. This f a c t o r makes a s u b s t a n t i a l d i f f e r e n c e i n f l u e gas volume and improves thermal e f f i c i e n c y . Whereas the o l d e r i n c i n e r a t o r s r e c e i v e d a great d e a l of adverse p u b l i c i t y concerning a i r p o l l u t i o n problems, the modern u n i t s , which are equipped w i t h high energy scrubbers, e l e c t r o s t a t i c p r e c i p i t a t o r s , o r f a b r i c f i l t e r s , have been a b l e t o meet s t r i n g e n t p a r t i c u l a t e standards. (17, 18) Even though r e f u s e combustion w i l l probably continue to p l a y a r o l e i n the s o l i d waste management f i e l d , p r o d u c t i o n of RDF f o r c o f i r i n g i n b o i l e r s i s c u r r e n t l y r e c e i v i n g a great d e a l of a t t e n t i o n i n regions where c o a l i s f i r e d i n u t i l i t y b o i l e r s . Of the 47 e l e c t r i c u t i l i t y f e a s i b i l i t y s t u d i e s ( i n v o l v i n g r e f u s e use) under way i n the United States during 1976, 29 (62%) were concerned w i t h the use of shredded waste; 4 ( 8 % ) , the combustion of raw waste i n i n c i n e r a t o r s ; 3 ( 6 % ) , the use of a p e l l e t i z e d f u e l ; 6 (13%), the use of a powdered f u e l ; and 5 (11%), the use of a pyrolysis fuel,(i?) A number of p r o j e c t s based s o l e l y on m a t e r i a l s recovery (not f u e l ) from m u n i c i p a l r e f u s e are now being planned. Nevertheless, most a c t i v i t y i n the f u t u r e w i l l focus on systems that i n c l u d e energy recovery. Energy s a l e s account f o r 50% of the revenues f o r a system t h a t a l s o recovers aluminum and f e r r o u s metals. The d i s p o s a l fee may represent about 25% of the u n i t ' s revenue.

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Another s o l i d waste problem f o r many c i t i e s i s the d i s p o s a l of sludges from wastewater treatment p l a n t s . Sludges from wastewater treatment p l a n t s i n the United States have been combusted i n m u l t i p l e hearth furnaces s i n c e the 1930s and i n f l u i d i z e d bed u n i t s s i n c e the 1960s. C u r r e n t l y , about 25 to 30 percent or more of the sludge generated i s i n c i n e r a t e d . ( 3 , 4) Energy recovery from the i n c i n e r a t o r f l u e gases by use of waste heat b o i l e r s has only r e c e n t l y become common p r a c t i c e , however. Co-disposal of m u n i c i p a l r e f u s e and sludge i n thermal conversion processes i s c u r r e n t l y a t o p i c of great i n t e r e s t to m u n i c i p a l i t i e s . An EPA c o n t r a c t o r r e c e n t l y reported that c o - i n c i n e r a t i o n of sludge and r e f u s e " w i l l have lower o v e r a l l cost than separate i n c i n e r a t i o n of sludge and r e f u s e " (^0); although t h i s approach has met w i t h v a r i e d degrees of t e c h n i c a l and economic success i n the p a s t , i t may represent a f u t u r e s o l u t i o n f o r c e r t a i n s i t e s where r e f u s e d i s p o s a l by thermal conversion processes can be economically j u s t i f i e d . I i n the near term, however s i d i e s a r e o f f e r e d to l o c a l government agencies. For a f u r t h e r d i s c u s s i o n of t h i s t o p i c , see reference 21. As mentioned e a r l i e r , cement k i l n s o f f e r another o p p o r t u n i t y for use of RDF because many a r e near l a r g e p o p u l a t i o n c e n t e r s . Government-supported p r o j e c t s are under way i n the United S t a t e s , Canada and the United Kingdom to determine the e f f e c t of u s i n g RDF on cement q u a l i t y . ( 2 2 . > 2 3 ) A g r i c u l t u r a l r e s i d u e s a l s o r e p r e sent a f u e l source f o r these k i l n s . At S t u t t g a r t , Arkansas, r i c e h u l l s , which have a h i g h s i l i c a content, a r e now being used as a f u e l f o r a cement k i l n . While use of organic r e s i d u e s as a f u e l by a nonproducer of the r e s i d u e s may be new, the use of r e s i d u e s as f u e l i s n o t . Combustion of wood wastes and bagasse f o r steam production c u r r e n t l y represents a major energy source f o r the pulp and paper i n d u s t r y , lumber m i l l s , and sugar cane processors.(^5) The combined consumption of these r e s i d u e s f o r f u e l s represents c l o s e to one quad of energy f o r these i n d u s t r i e s . D i r e c t combustion of whole scrap t i r e s f o r energy recovery has not been w i d e l y p r a c t i c e d i n the United States but use of a Lucas C y c l o n i c Furnace f o r t h i s purpose was reported i n 1974 f o r a Goodyear T i r e and Rubber Company P l a n t i n Jackson, M i c h i gan. (^6, 27) Use of shredded scrap t i r e s as a supplemental f u e l i n c o a l f i r e d i n d u s t r i a l b o i l e r s has been p r a c t i c e d a t s e v e r a l sites.(27) Biochemical Conversion Anaerobic d i g e s t i o n of sludges from wastewater treatment p l a n t s has been p r a c t i c e d i n the United States f o r over 50 years. According to the EPA, (?§) there are c u r r e n t l y approximately 6000 anaerobic d i g e s t i o n f a c i l i t i e s a t treatment p l a n t s i n the United S t a t e s . I n the p a s t , a p o r t i o n of the f u e l gas produced by these u n i t s has been f l a r e d and the main purpose of the process was t o s t a b i l i z e the p u t r e s c i b l e s o l i d s . Now, more and more %

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p l a n t s are u s i n g the product gas as a f u e l f o r i n t e r n a l combust i o n engines to d r i v e pumps and compressors. Such d i g e s t e r s , however, do not produce l a r g e q u a n t i t i e s of f u e l gas. The amount of energy i n the product gas ranges from 300 to 600 Btu/day per person served by the treatment p l a n t (approximately 2000 B t u / l b of dry s o l i d s processed). Since the e a r l y 1970s, research has been under way t o develop an anaerobic d i g e s t i o n process to produce methane from a mixture of m u n i c i p a l r e f u s e and sludge.(29) The f i r s t demonstrat i o n p l a n t w i l l process about 100 tons per day of r e f u s e and sludge and i s scheduled to begin o p e r a t i o n during 1978 i n Pompano Beach, F l o r i d a , under Department of Energy sponsorship.(^0) p r o j e c t e d net gas y i e l d w i l l be about 1700 B t u / l b of dry s o l i d s processed or more than 5000 Btu/day per person served by the plant. P r o j e c t s to tap th methan produced fro th i s i t aerobic d i g e s t i o n at l a n d f i l during t h i s decade. Reserv S y n t h e t i Company Angeles County S a n i t a t i o n D i s t r i c t are r e c o v e r i n g methane a t the Palos Verdes l a n d f i l l , and the P a c i f i c Gas and E l e c t r i c Company i s r e c o v e r i n g gas from the Mountain View, C a l i f o r n i a , l a n d f i l l . ( 3 1 ) Numerous p r o j e c t s are a l s o under way to produce methane from c a t t l e manure by anaerobic d i g e s t i o n . Net gas y i e l d s are equival e n t to as high as 2000 B t u / l b of dry s o l i d s processed. A l a r g e p l a n t (processing 1000 dry tons of manure s o l i d s / d a y ) can produce approximately 4 m i l l i o n s c f of methane per day.(32) A process development program p a r t i a l l y funded by the United States Department of Energy i s c u r r e n t l y under way a t Kaplan I n d u s t r i e s , Incorporated, o f Bartow, F l o r i d a , under the d i r e c t i o n of Hamilton Standard (Windsor Locks, C o n n e c t i c u t ) . The process development u n i t w i l l a n a e r o b i c a l l y d i g e s t the manure from an environmental f e e d l o t w i t h 10,000 head of c a t t l e . Other a c t i v e Department of Energy-sponsored anaerobic d i g e s t i o n programs are under way a t C o r n e l l U n i v e r s i t y , the U n i v e r s i t y of I l l i n o i s , the U.S. Department of A g r i c u l t u r e , and Stanford U n i v e r s i t y . Carbohydrate c o n t a i n i n g m a t e r i a l s can a l s o be used as a feedstock to fermentation f o r the p r o d u c t i o n of ethanol f o r use as a t r a n s p o r t a t i o n f u e l . Ethanol production from g r a i n i s being a c t i v e l y i n v e s t i g a t e d by the S t a t e of Nebraska.(33) One of the economic problems w i t h the use of c e l l u l o s i c wastes and r e s i d u e s as a feedstock f o r ethanol production i s the cost f o r h y d r o l y s i s of the c e l l u l o s e to fermentable sugars. The conversion of carbohydrates to sugars by h y d r o l y s i s i s a very a c t i v e area of r e s e a r c h , which i n c l u d e s enzymatic h y d r o l y s i s . Enzymatic h y d r o l y s i s has been s t u d i e d a c t i v e l y by the U.S. Army Laboratory i n N a t i c k , Massachusetts, L o u i s i a n a S t a t e U n i v e r s i t y , the U n i v e r s i t y of C a l i f o r n i a a t Berkeley, Rutgers U n i v e r s i t y , the U n i v e r s i t y of Pennsylvania, the General E l e c t r i c Company, and the Massachusetts I n s t i t u t e of Technology. U n l i k e enzymatic h y d r o l y s i s technology, h y d r o l y s i s of c e l l u l o s e i n

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d i l u t e a c i d has been known f o r w e l l over a hundred years and has been p r a c t i c e d commercially. Some b e l i e v e that a c i d h y d r o l y s i s o f f e r s a more economical approach than does enzymatic h y d r o l y s i s . (_34) A c i d h y d r o l y s i s i s c u r r e n t l y under study a t Dartmouth C o l l e g e , New York U n i v e r s i t y , and Purdue U n i v e r s i t y . ADVANCED THERMAL CONVERSION PROCESSES Reasons f o r Development Based on the previous d i s c u s s i o n of a v a i l a b l e conversion t e c h n o l o g i e s , the f i r s t q u e s t i o n one might ask about the advanced thermal processes (PTGL processes) i s — w h y do we need them? Numerous answers a r e given but the most common ones a r e : (1) PTGL processes can produce gaseous or l i q u i d f u e l products that can be burned more e f f i c i e n t l y (low excess a i r ) i secondar combustio chamber used as f u e l f o designed to bur ga y minor m o d i f i c a t i o n s r e q u i r e d . ( 2 ) U n l i k e steam generated from a combustion process, l i q u i d or char f u e l products a r e s t o r a b l e — a medium Btu gas may a l s o be s t o r a b l e a t a reasonable cost. This second answer i s important because a t many s i t e s , no market e x i s t s f o r steam, and e l e c t r i c power cannot be generated economically because of the s m a l l s i z e of the e l e c t r i c a l generator. In other cases, i t i s uneconomical to s h i p the s o l i d waste or residue and the area where the m a t e r i a l i s l o c a t e d o f f e r s no market f o r the product f u e l s . Thus, the o n l y way to u t i l i z e the m a t e r i a l i s to produce a h i g h v a l u e shippable f u e l . The products a l s o may a l s o f i n d nonfuel uses. The char m a t e r i a l produced from some processes can be used as feedstock to produce a low cost adsorbent f o r wastewater treatment. This may be a t t r a c t i v e to both m u n i c i p a l i t i e s and i n d u s t r y . The r e a c t o r product gas (which i s mainly CO and H 2 from an oxygen blow r e a c t o r ) can be used as s y n t h e s i s gas to produce s t o r a b l e h i g h v a l u e products l i k e methanol or ammonia. Product o i l s may r e p r e sent a source of chemicals, but because of the h i g h l y oxygenated nature of the compounds (organic a c i d s ) , the o i l s may not be suitable f o r processing i n conventional r e f i n i n g u n i t s . Another reason o f t e n c i t e d f o r developing PTGL t e c h n o l o g i e s i s t h a t they may r e q u i r e lower investments f o r environmental cont r o l equipment. This statement may not be v a l i d i n a l l cases, as was discussed p r e v i o u s l y by t h i s author i n r e f e r e n c e 8.

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C a t e g o r i z a t i o n of Processes Numerous ways are a v a i l a b l e to c a t e g o r i z e PTGL processes, such as by: * Feedstock Type Refuse, t i r e s , sludge, a g r i c u l t u r a l and f o r e s t r y residues, etc. * Product D i s t r i b u t i o n Maximized char y i e l d Maximized f u e l gas y i e l d Maximized l i q u i d o r g a n i c s y i e l d * Product Use D i r e c t combustion of gases from r e a c t o r ( i . e . , furnaces o p e r a t i n g i n a s t a r v ed a i r o r p a r t i a l combustion mode to supply gas to a boiler) Clean f u e l gas f o r i n d u s t r i a l uses Synthesis ga Oil for offsit * S p e c i f i c Process Operating C h a r a c t e r i s t i c s Slagging versus nonslagging A i r blown versus oxygen blown * Fundamental Process Reactor C h a r a c t e r i s t i c s Solids flow d i r e c t i o n Conditions of s o l i d s i n r e a c t o r Type of r e a c t o r v e s s e l Heat t r a n s f e r method Relative gas/solid flow d i r e c t i o n The l a s t o p t i o n appears to be the most l o g i c a l approach t o analyze conversion processes and i s the approach used i n previous work.(8, 35) The b a s i c process c a t e g o r i e s are l i s t e d i n Table 5. (Reference j$ i n c l u d e s drawings showing the d i f f e r e n t types o f r e a c t o r s ). SYMPOSIUM PAPERS The other 22 speakers scheduled to p a r t i c i p a t e i n t h i s sym­ posium w i l l d e s c r i b e a wide v a r i e t y of thermal conversion process development and demonstration programs w i t h * Equipment s i z e s ranging from bench s c a l e to commercial scale. * Many types and q u a l i t i e s of f e e d s t o c k s . Numerous product types, q u a l i t i e s and uses, and * More than a dozen r e a c t o r types. Most of the papers w i l l i n c l u d e not only t e c h n i c a l d e t a i l s concerning process design and t e s t i n g , but a l s o estimates of the investment and o p e r a t i n g c o s t s . The papers have been organized f o r p r e s e n t a t i o n by process r e a c t o r type as p r e v i o u s l y d e s c r i b e d . The e x c e l l e n t response o f process developers to p a r t i c i p a t e i n t h i s symposium i s g r a t i f y i n g . β

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Table V PTGL PROCESS CATEGORIES* I

VERTICAL FLOW REACTORS D i r e c t Heat Transfer • Moving packed bed (shaft furnaces) • Moving staged s t i r r e d bed ( m u l t i p l e hearth furnaces) • Entrained bed (transport reactors)

II

III

FLUIDIZED BED REACTORS D i r e c t Heat Transfer

V VI

I n d i r e c t Heat Transfer ( r e c i r c u l a t i n g heat

HORIZONTAL OR INCLINED FLOW REACTORS D i r e c t Heat Transfer * Tumbling s o l i d s bed (rotary k i l n s ) * A g i t a t e d s o l i d s bed (on conveyer)

IV

I n d i r e c t Heat Transfer * Moving packed bed ( s h a f t furnaces) * Entrained bed ( r e c i r c u l a t i n g heat carrier)

I n d i r e c t Heat Transfer •Tumbling s o l i d s bed - Rotary c a l c i n e r s - Rotary v e s s e l s (recirculating heat c a r r i e r ) • A g i t a t e d s o l i d s bed (on conveyer) • S t a t i c s o l i d s bed (on conveyer)

MOLTEN METAL OR SALT BATH REACTORS Numerous flow and mixing options MULTIPLE REACTOR SYSTEMS Numerous flow and mixing options BACK-MIX FLOW REACTORS For s l u r r i e s and melts

Some r e a c t o r s may be designed w i t h numerous s o l i d s and gas f l o w regimes (countercurrent, cocurrent, s p l i t flow, c r o s s f l o w ) . A l s o known as f i x e d bed r e a c t o r s .

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With few e x c e p t i o n s , the e n t i r e range of the technology i s represented. Every type of process r e a c t o r l i s t e d i n Table V (except the two that are checkmarked) w i l l be d i s c u s s e d . The r o t a r y k i l n r e a c t o r ( d i r e c t l y f i r e d ) i s the type being used a t the demonstration p l a n t i n B a l t i m o r e , Maryland. Information on that process may be obtained from many sources, such as r e f e r ences 36 and 37. The h o r i z o n t a l f l o w , s t a t i c s o l i d s bed r e a c t o r i s now being proposed o n l y f o r t i r e p y r o l y s i s and has not been described i n the open l i t e r a t u r e .

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LITERATURE CITED 1.

SRI International, Menlo Park, California, "Crop, Forestry and Manure Residue Inventory--Continental United States" (June 1976), report prepared for the U.S. Energy Research and Development Administration, Contract Ε(04-3)-115.

2.

"Fourth Report to Congress--Resource Recovery and Waste Reduction" (1977), U.S. Environmental Protection Agency, Report SW-600.

3.

Jones, J. L., Bomberger, D. C., and Lewis, F. Μ., "Energy Usage and Recovery i n Sludge Disposal," Water and Sewage Works (July 1977) 124(7), 44-47.

4.

Jones, J . L., et al., "Municipal Sludge Disposal Economics" (October 1977), Environmenta 11(10), 968-972.

5.

Jones, J . L., unpublished SRI International data (October 1977).

6.

Moore, J . G., J r . , "Wastewater Requirements Multiply Solids Problems, Hydrocarbon Processing (October 1976), 55(10), 98-101.

7.

Beckman, J. Α., et al., "Scrap Tire Disposal," Rubber Reviews--Rubber Chemistry and Technology (July 1974) 47, 597-627.

8.

Jones, J . L., "Converting s o l i d wastes and residues to fuel," Chemical Engineering (January 2, 1978), 85(1), 87-94.

9.

"Conversion to Coal F i r i n g Picks Up Steam" (February 14, 1977), Chemical Engineering, 84(4), 40, 42, 44.

10.

Venable, Ν. Μ., "Burning Refuse for Steam Production," Garbage Crematories in America, John Wiley and Sons, New York, 1906.

11.

Venable, E., "Burning Issues--Letter to the Editor," Chemical Engineering Progress (January 1977).

12.

Stephenson, J . Ν., and Cafeiro, S. Α., "Municipal Incinera­ tor Design Practices and Trends," Paper presented at the 1966 National Incinerator Conference (ASME) at New York, New York, May 1966.

13.

Combustion Engineering, Inc., Techno-Economic Study of Solid Waste Disposal Needs and Practices, U.S. Department of Health, Education and Welfare, Public Health Service (1969), SW-7c, PHS 1886.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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14.

"Nationwide Inventory of A i r Pollutant Emissions," 1968, U.S. National A i r Pollution Control Administration (1970), AP-73.

15.

"Present Status of Municipal Refuse Incinerators," American Society of Mechanical Engineers (January 1975).

16.

"Refuse to Energy Plant Uses F i r s t Von R o l l Incinerators i n United States," Environmental Science and Technology (August 1974) 8(8), 692-694.

17.

"Hard Road Ahead of City Incinerators," Environmental Science and Technology (November 1972), 6(12), 992-993.

18.

Weinstein, N. J . , and Toro, R. F., "Control Systems on Municipal Incinerators," Environmental Science and Tech­ nology (June 1976), 10(6), 545-547.

19.

" E l e c t r i c Utilities Recovery and Energ

20.

Niessen, W., et al., "A Review of Techniques for Incineration of Sewage Sludge with Solid Wastes (December 1976), EPA-600/2 EPA-600/2-76-288.

21.

Jones, J. L., "The Costs for Processing Municipal Refuse and Sludge" (1978), paper presented at the F i f t h National Conference on Acceptable Sludge Disposal Techniques, Orlando, Florida (January 31 to February 2, 1978). Pro­ ceedings to be published by Information Transfer, Inc., Rockville, Maryland, Spring 1978.

22.

"Garbage: New Fuel for Making Cement," Business Week (April 12, 1976), 720.

23.

News Release of the Ontario Ministry of the Environment, Toronto, Ontario, Canada (December 1976).

24.

"A Rice Hull Foundation for Cement," Business Week (April 12, 1976), 72Q.

25.

Tillman, D. Α., "Combustible Renewable Resources," Chemtech (1977), 7(10), 611-615.

26.

Gaunt, A. R., and Lewis, F. Μ., "Solid Waste Incineration i n a Rotary Hearth, Cyclonic Furnace," paper presented at the 67th Annual Meeting of the American Institute of Chemical Engineers, Tulsa, Oklahoma (March 1974).

27.

"Decision-Makers Guide i n Solid Waste Management" (1976), Environmental Protection Agency Report SW-500.

28.

Cost Estimates for Construction of Publicly Owned Wastewater Treatment Facilities--Summaries of Technical Data, Cate­ gories I-IV, 1976 Needs Survey(February 1977), Environmental Protection Agency Report 430/9-76-011.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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29.

Pfeffer, J. T., "Reclamation of Energy from Organic Waste, U. S. Environmental Protection Agency, EPA-670/2-74-016 (1974).

30.

"Refuse Conversion to Methane-Pompano Beach, Florida"(1977), Waste Management Inc., Oak Brook, Illinois.

31.

Parkinson, G., "Short on Gas? Use L a n d f i l l " (February 13, 1978), Chemical Engineering, 85(4), 68, 70.

32.

Varani, F. T., Burford, J . , and Arber, R. P., "The Design of Large-Scale Manure/Methane Facility" (June 1977), Report from Bio Gas of Colorado, Inc., Arvada, Colorado.

33.

Scheller, W. Α., and Mohr, B. J . , "Gasoline Does, too, Mix with Alcohol" (1977), Chemtech, 7 (10), 616-623.

34.

Klee, J . , and Rogers, C. J . , "Biochemical Routes to Energy Recovery from Municipal " (1977) Proceeding f th Second P a c i f i c Chemica

35.

Jones, J . L., et al., "Worldwide Status of Pyrolysis, Thermal Gasification, and Liquefaction Processes for Solid Wastes and Residues (as of September 1977)," paper to be presented at the 1978 ASME National Solid Waste Processing Conference, Chicago, Illinois (May 1978).

36.

"Baltimore Demonstrates Gas Pyrolysis" (1974), U. S. Environ­ mental Protection Agency Report EPA/530/SW-75d.i.

37.

Weinstein, N. J . , Municipal Scale Thermal Processing of Solid Wastes, Environmental Protection Agency Report EPA/530/SW-133e (1977), available through NTIS, PB-263 396.

MARCH 3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2

Economics Associated w i t h Waste or Biomass Pyrolysis Systems RICHARD BAILIE Chemical Engineering Department, West Virginia University, Morgantown, WV 26505 C. A. RICHMOND Wheelabrator Incineration, Inc., 600 Grant Street, Pittsburgh, PA 15219 In the early dats used as the primary f u e l nations wood was soon replaced by fossil fuels. Wood could not compete economically with these fossil fuels. U n t i l recent times, these fossil fuels were low in cost and available i n what seemed to be an endless supply. Recently, costs have risen and are expected to rise even further in the future. I t i s becoming more apparent that this supply of fuel is limited. Wood remains an alternative f u e l . Unlike fossil f u e l , wood i s not found i n large amounts i n concentrated areas. I t is available i n limited amounts spread over a wide area and is renewable. Consideration is being given to once again making more use of wood as a fuel source. In addition to wood, all plant life (biomass) can be used for its f u e l value. In the discussion to follow, wood represents but one type of biomass that may soon see use as a fuel. During the time that has elapsed since wood was widely used, several important changes have occurred. Two of these changes are: 7.

Energy consumption (both t o t a l and per capita) has increased dramatically.

2.

Size of energy conversion systems have increased. These large systems have achieved "economies of scale."

In terms of e l e c t r i c power generation, a 50 Mw power station i s extremely small and cannot achieve the thermal e f f i c i e n c i e s and economics that are attributed to larger systems. Even this size u t i l i t y would require 1,000 tons/day of biomass or 365,000 tons per year on a continuing basis. The Department of Energy has a study underway (1) to determine i f this amount of fuel can be obtained on a continuing basis i n a l o c a l area i n the Northeast. Wood may be burned d i r e c t l y to provide for generation of steam or e l e c t r i c i t y or i t may be converted to a more attractive fuel form such as gas or l i q u i d that may be transported to a central 0-8412-0434-9/78/47-076-021$05.75/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

22

SOLID WASTES AND RESIDUES

s i t e where generation of steam or e l e c t r i c i t y occurs. The f i n a l judgement as to what form biomass can most e f f e c t i v e l y be used as a f u e l must r e s t on economics. I t i s not l i k e l y t h a t there i s a s i n g l e conversion process that w i l l be p r e f e r r e d f o r a l l biomass f u e l s i n a l l s i t u a t i o n s . The most common process f o r conversion i s d i r e c t combustion of biomass. Burning of wood and bagasse to produce steam has been an e s t a b l i s h e d p r a c t i c e . There are many s i t u a t i o n s where d i r e c t combustion may not be the most a t t r a c t i v e a l t e r n a t i v e . This paper d e s c r i b e s one a l t e r n a t i v e to d i r e c t combustion of biomass. Biomass may be converted to a medium energy f u e l gas t h a t i s l a t e r burned. The paper makes the case f o r c o n s i d e r a t i o n of generating medium energy f u e l gas, desc r i b e s a system that can accomplish the conversion of gas at a moderate s c a l e , d i s c u s s e s the economics of t h i s system, and p r o v i d e s some examples as to how the medium energy gas compares to d i r e c t combustion. Reasons to Consider Mediu I f a power p l a n t operator were given a choice of n a t u g a l gas, petroleum, or c o a l as a f u e l ( a l l at the same cost i n $/10 Btu); n a t u r a l gas would be p r e f e r r e d . Some of the reasons f o r t h i s preference are: 1.

N a t u r a l gas can be burned i n an environmentally acceptable manner without a i r p o l l u t i o n c o n t r o l equipment.

2.

The s i z e of the furnace i s s m a l l e r . B e c h t e l i n a r e p o r t f o r the e l e c t r i c power i n d u s t r y (2) gave the r a t i o of 1.0/1.35/1.85 f o r gas, o i l and c o a l f u e l systems.

3.

There i s a lower maintenance f o r the gas systems.

fired

F i g u r e 1 i s a schematic that compares s o l i d f u e l and gas f u e l b o i l e r s . The area of the furnace b l o c k represents the s i z e . The n a t u r a l gas furnace r e q u i r e s no p o l l u t i o n c o n t r o l equipment. Both of these f a c t o r s r e l a t e d i r e c t l y to c o s t s . I t i s cheaper to conv e r t n a t u r a l gas than s o l i d f u e l to steam or e l e c t r i c i t y i n a u t i l i t y b o i l e r . In a d d i t i o n to these f a c t o r s , f a v o r i n g gas f i r e d systems, the hog f i r e d b o i l e r s and bagasse b o i l e r s have a lower t h e r mal e f f i c i e n c y . The s i z e of these biomass b o i l e r systems are much l a r g e r than these f o r f o s s i l f u e l s of the same c a p a c i t y . Based on these f a c t s , i t can be seen that n a t u r a l gas i s much more v a l u a b l e (on a Btu b a s i s ) than i s biomass f u e l . Biomass may be converted to a medium Btu f u e l gas. B e c h t e l Corporation i n t h e i r r e p o r t to the E l e c t r i c Power Industry (2) prov i d e d curves of the thermal e f f i c i e n c y , the a i r r e q u i r e d and the

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

Economics Associated with Waste

23

combustion products produced f o r gases of v a r y i n g f u e l v a l u e s . They are shown i n Figures 2 and 3. These curves show that a 300 Btu gas has a higher e f f i c i e n c y , lower a i r requirements and pro­ duce l e s s combustion product. This i n d i c a t e s that a 300 Btu gas could be burned as e f f e c t i v e l y as n a t u r a l gas. I f a 300 Btu gas can be exchanged f o r a n a t u r a l gas, then the statement regarding the d e s i r a b i l i t y of n a t u r a l gas can apply to t h i s f u e l gas. I t f o l l o w s that a 300 Btu gas would be p r e f e r r e d over biomass f u e l s i n their natural state. Figure 4 provides a r e p r e s e n t a t i o n of the f u e l costs and a l l other y e a r l y costs to o b t a i n steam or e l e c t r i c i t y from wood, c o a l , or a 300 Btu gas. The costs of o p e r a t i n g a wood f i r e d p l a n t i s higher than a c o a l f i r e d p l a n t . To produce e l e c t r i c i t y at the same c o s t , the b a s i c f u e l cost must be l e s s as shown i n Figure 4. The y e a r l y cost of o p e r a t i n g a gas p l a n t i s considerably l e s s (about 1/2) than f o r a c o a l p l a n t . I to Δ i n Figure 4 then woo e l e c t r i c i t y at the same p r i c e as c o a l . The s u b s t i t u t i o n of biomass f o r f o s s i l f u e l i n an e x i s t i n g f a c i l i t y i s seldom p o s s i b l e . The s i z e of a furnace i s l a r g e r f o r systems using a biomass f u e l than f o r f o s s i l f u e l s . Figure 5 shows a h i e r a r c h y of s u b s t i t u t i o n s that are p o s s i b l e . Gas may be s u b s t i t u t e d f o r petroleum, c o a l , and wood; p e t r o ­ leum may be s u b s t i t u t e d f o r c o a l and wood; and c o a l may be sub­ s t i t u t e d f o r wood. S u b s t i t u t i o n s cannot normally be made i n the reverse d i r e c t i o n without major r e t r o f i t and/or d e r a t i n g of the boiler. N a t u r a l gas i s p r e d i c t e d to be the f i r s t form of f o s s i l f u e l to become depleted (estimates p r e d i c t as l i t t l e as eleven years of n a t u r a l gas remain). Industry has already f e l t c u r t a i l m e n t and i t may be s a f e l y p r e d i c t e d that i t w i l l be i n d u s t r y that w i l l be f i r s t to f e e l any e f f e c t s o f dwindling s u p p l i e s . Experience over the l a s t two years shows i n d u s t r y i s the f i r s t to f e e l the e f f e c t s o f c u r t a i l m e n t . What w i l l happen to i n d u s t r i a l and u t i l i t y b o i l e r s b u i l t to f i r e gas? Many of these are r e l a t i v e l y new and many were i n s t a l l e d to meet environmental r e g u l a t i o n s . They are h i g h l y e f f i c i e n t and are i n e x c e l l e n t o p e r a t i n g c o n d i t i o n , but cannot be switched to o i l o r c o a l . In such a s i t u a t i o n a customer w i l l be w i l l i n g to pay a premium p r i c e f o r a gas that may be sub­ s t i t u t e d f o r n a t u r a l gas and use t h i s f a c i l i t y . The a l t e r n a t i v e would be to r e t i r e the present system and commit the c a p i t a l t o b u i l d a new (and expensive) furnace. In such a s i t u a t i o n , a 300 Btu gas becomes an a t t r a c t i v e f u e l . Economics of Medium Energy Gas

Production

2 Two processes are a v a i l a b l e that can produce a 300-400 Btu/ f t f u e l gas from biomass that have been demonstrated i n p i l o t plant s i z e operations.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

Clean-Up

Solid Fuel

Furnace

Natural Gas ,

- • Steam or Electricity

Furnace

- Steam or Electricity

Figure

1,000

800

Flue Gas per 10,000 Btu of Fuel Fired

Theoretical Air Required to Burn 10,000 Btu of Fuel

ο 600h

05 400

200 J 0

2

4

J 6

I 8

I 10

I 12

L 14

16

Pounds

Figure 2.

Theoretical air and flue gas

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

25

Economics Associated with Waste

100 h

90

80

70 I

J_ 200

400

600

800

J 1000

Figure 3.

Gas Fuel Btu/Cu. Ft.

Wood-Gas

Wood

Unit efficiency

Coal

Unit Cost of Electricity (KWH)

Basic Fuel Cost I All other yearly costs.

J

Figure 4.

Cost breakdown for electricity from coal, wood, or wood^gas

Gas

i Petroleum

c

°

a l

I

Wood or Bagasse

Figure 5. Fuel substitution hierarchy

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

26

SOLID WASTES AND RESIDUES

1.

Purox - Union Carbide has operated a 200 ton/day p i l o t f a c i l i t y i n I n s t i t u t e , West V i r g i n i a ( 3 ) . The major system components are a s h a f t k i l n and an Oxygen p l a n t .

2.

Pyrox - K i k a i K u n i i has operated a 50 ton/ day p i l o t f a c i l i t y i n Japan. Some r e s u l t s have been reported by K u n i i ( 4 ) .

Both of these systems have used m u n i c i p a l waste to produce an i n t e r mediate Btu gas and the Pyrox u n i t has been operated on biomass. Since the organic p o r t i o n of m u n i c i p a l waste i s p r i m a r i l y c e l l u l o s e , comparable performance should be expected from s o l i d waste or biomass. Both processes p y r o l y z e the organic p o r t i o n present i n the s o l i d f u e l . To produce an i n t e r m e d i a t e Btu gas, i t i s necessary that the gas i s not d i l u t e t h i s i s accomplished by an a i r s e p a r a t i o n p l a n t . In the s i n g l e s h a f t k i l n r e a c t o r , both a combustion r e a c t i o n and p y r o l y s i s occur. In the Pyrox Process the combustion r e a c t i o n and the p y r o l y s i s take p l a c e i n separate f l u i d i z e d bed r e a c t o r s . S o l i d s c i r c u l a t e between the two beds to prov i d e the heat needed f o r the p y r o l y s i s r e a c t i o n . In the United States market, the p y r o l y s i s process developed by B a i l i e and a v a i l a b l e through Wheelabrator I n c i n e r a t i o n , I n c . , i s comparable to the Pyrox system. This process was the one sel e c t e d f o r t h i s paper because the authors are more f a m i l i a r w i t h the process economics and i t i s more compatible w i t h the modest s i z e d f a c i l i t y needed f o r most biomass conversion s i t e s . In a recent r e p o r t by B a t t e l l e i n a study of sugar cane as a f u e l crop (5) the f o l l o w i n g comment was made: Commercialization of r e l a t i v e l y s m a l l s y n t h e s i s gas p l a n t s needs a process such as P r o f e s s o r R. C. B a i l i e (1972) has suggested so t h a t the expense of an oxygen f a c i l i t y can be avoided. . . .The process i s admittedly s p e c u l a t i v e but i t s t r i k e s d i r e c t l y at a major drawback of the processes d i s c u s s e d a b o v e — t h e need f o r an e n e r g y - i n t e n s i v e oxygen p l a n t . F i g u r e 6 i s the b a s i c schematic of the two f l u i d i z e d bed process. The s o l i d f u e l i s fed i n t o a p y r o l y s i s r e a c t o r at about 1500 F. This r e a c t o r i s composed of hot i n e r t sand. Heat t r a n s f e r to the s o l i d feed i s r a p i d and p y r o l y s i s occurs. The r a p i d heat t r a n s f e r leads to h i g h gas y i e l d s ( 6 ) . The f u e l gas goes to a cyclone where the char i s removed. The char i s fed along w i t h a i r to a second f l u i d bed h e l d at about 1800 F. Combustion takes p l a c e and provides the energy needed f o r the p y r o l y s i s r e a c t i o n . This energy i s t r a n s f e r r e d to the p y r o l y s i s bed by a sand c i r c u l a t i o n system between the two r e a c t o r s .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 6.

CHAR

SAND

FUEL GAS + CHAR

PYROLYZER

1500°F

FUEL GAS

.

SOLID WASTE OR BIOMASS

FUEL GAS RECYCLE

Schematic flow diagram of two-reactor system: temperature—1800°F, 1500°F; feed—char —unsorted waste or biomass; products—fuel gas + char + solid waste

COMBUSTOR

1800°F

COMBUSTION GASES

- •

28

SOLID WASTES AND RESIDUES

Stanford Research I n s t i t u t e r e c e i v e d a c o n t r a c t from West V i r g i n i a U n i v e r s i t y to make an economic e v a l u a t i o n of the two f l u i d bed system to produce an intermediate Btu f u e l gas from s o l i d waste ( 7 ) . B e c h t e l Corporation working f o r the C i t y of C h a r l e s t o n , West V i r g i n i a , i n preparing a grant a p p l i c a t i o n to EPA provided a second economic e v a l u a t i o n of the two f l u i d bed system ( 8 ) . They confirmed the economics and process flow sheet given i n the SRI study. These s t u d i e s were made i n 1972 at a C. E. cost index of 135. For t h i s paper, the c o s t s are updated to a C. E. index of 210. The process flow sheet provided by Stanford Research I n s t i t u t e i s d i v i d e d i n t o three s e c t i o n s : f u e l p r e p a r a t i o n , p y r o l y s i s , and gas clean-up and a d e t a i l e d equipment l i s t . The totajL c a p i t a l i n v e s t ­ ment i n 1977 d o l l a r s i s estimated to be 18.2 χ 10 as shown i n Table 1. The annual opergting c o s t s were taken as 1.5 times the costs i n 1972 or $3.0 χ 10 /year produced from m u n i c i p a l s o l i The product gas composition developed by S.R.I, i s given i n Table 3 and the m a t e r i a l balance i n Table 4. The energy y i e l d i s defined as: Energy Value = Higher Heating Value of Gas Higher Heating Value of F u e l g y

was

77%. Chiang, Cobb and K l i n z i n g (11) have j u s t completed a study f o r Resources of the Future where they estimate the cost of f u e l gas from refuse u s i n g m u n i c i p a l waste. They based t h e i r values on the same S.R.I, study p r e v i o u s l y c i t e d ( 7 ) . These authors assumed t h a t between 1972 and 1977, the c a p i t a l costs e s c a l a t e d by a f a c t o r of 4 and the o p e r a t i n g costs doubled. Under these assump­ t i o n s and using economic c r i t e r i a s i m i l a r to "low debt economics" they c a l c u l a t e d t h a t the gas would cost $6.14/10 Btu w i t h no drop charge. The S.R.I, study cost estimate was made based upon s i z i n g and c o s t i n g a l l of the major equipment items. I t would seem t h a t the C. E. cost index between 1972 and 1977 (210/135 = 1.56) would be a more a p p r o p r i a t e procedure to update the c a p i t a l c o s t . I f a f a c t o r of 1.56^were used i n p l a c e of 4.00, the f u e l gas cost be­ comes $2.60/10 Btu which i s i n s u b s t a n t i a l agreement w i t h the cost of $2.28/10 Btu shown i n Table 2. In a more recent cost estimate by B a t t e l l e (5) the cost of gas produced i n a two f l u i d bed system i s given i n Table 5. In c o n v e r t i n g t o t a l c a p i t a l c o s t s to annualized c a p i t a l charges the r a t i o of annualized c a p i t a l costs to c a p i t a l c o s t s obtained from the c o s t s of the two bed system f o r the p y r o l y s i s of bagasse obtained by B a t t e l l e were used. The r a t i o s used were: (1) 0.167 f o r low debt economics and (2) 0.09 f o r high debt economics.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BAILIE AND RICHMOND

Economics Associated with Waste

Table (lOOO ton/day y Municipa D o l l a r Amounts i n M i l l i o n s Feed P r e p a r a t i o n Pyrolysis Product Recovery Total Utilities General F a c i l i t i e s Total Land Start-up Working C a p i t a l Total T o t a l Working C a p i t a l

) ^-8 6.1 2· j+ 13-5 2.2 0*8 3.0 2

· .8 «8 1-8 18.2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

30

SOLID WASTES AND RESIDUES

Table I I . Annual Operating Costs and Gas Costs Low Debt* Economics Operating Costs Annualized C a p i t a l Charge Total (

$3.0xl0 2.8 T75

6

High Debt* Economics (l.l8) (l.lO) (2.28)

3-0 1.6 Ο

(l.l8) (0*63) (1.81)

) φ per 10 B t u

* These are t h e economics developed and used by B a t t e l l e i n t h e i r r e c e n t study f o r D.O.E. and g i v e n i n Appendix A.

Table I I I .

Composition o f Product Gas from Two-Reactor System ( i n Mole P e r c e n t )

CO

co

H

2

Dry, C0 -Free

27.1# 1^.7

31.TS6 0.0

kl.J

2

c%

C2 unsaturates C H6 C3 unsaturates 3 8 Total 2

C

Dry Gas

H

7.7 7.1 0.7 0.6 0Λ 100.0$

h3.9 9.0 8.3 0.9 0.7

°Λ

100.0$ 529

Gross h e a t i n g value ( B t u / s c f ) Y i e l d o f gas, s c f / l b dry r e f u s e

2

9-3

8.0

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Depreciation Schedule

Investment Tax C r e d i t

0.0142 0.2355 Ο.Ο683

0.0261 0.2355 0.1052

3.0

0.2k

3.0

0.2k

O.3O O.7O Ο.Ο85 0.15 O.5O 20.0 11.0

Other

0.30 0.70 Ο.Ο85 0.15 O.5O 25.Ο 25.Ο

Steam P l a n t

Low Debt Economics

, t

Values f o r Economic Parameters

0.1k

0.0191 0.1645 O.067O

0.50 25.0 25.0 0.24 3.0

0.60 0.40 0.0875

Steam P l a n t

TT

0.0329 0.1645 0.1029

0.60 0.40 0.0875 0.l4 O.5O 20.0 11.0 0.24 3.0

Other

High Debt Economics

a

2k

12

1

0.05tL 0.0906 SL Ο.Ο889 0.0535 SL 0.1052 O.067O 0.1029 Ο.Ο683 SYD 12 0.0729 0.1047 0.1077 0.0715 0.0871 0.1224 Ο.Ο85Ο SYD 2k 0.1187 0.1046 0.0688 0.1046 0.0681 DDBSL 12 0.0829 0.1192 0.0823 DDBSL 2k 0.1173 A s t r a i g h t l i n e d e p r e c i a t i o n (SL) schedule was assumed f o r the values presented i n the upper p o r t i o n of Table A - I . I f a sum-of-the-year s d i g i t s (SYD) d e p r e c i a t i o n schedule and/or a 12 percent i n v e s t ­ ment t a x c r e d i t had been assumed the impact on t h e "Constant f o r ( F ) b e a r i n g the symbol L" would be t a b u l a t e d as i n the lower p o r t i o n o f Table A - I . S i m i l a r l y , values a r e shown f o r computations u s i n g a double d e c l i n i n g balance w i t h a s h i f t t o s t r a i g h t l i n e ( i n t h e n/2 year) d e p r e c i a t i o n schedule DDBSL i n the lower p o r t i o n o f Table A - I . (Constants f o r (Τ-W) and (τ) a r e n o t s u b j e c t t o change.)

A

J Κ L

Constant f o r (Τ-W) Constant f o r (τ) Constant f o r ( F )

E/T

i I R Ν η Ρ Y

D/T

Symbol

Debt f r a c t i o n Equity f r a c t i o n Interest rate Return on e q u i t y Tax r a t e P r o j e c t l i f e , years D e p r e c i a t i o n l i f e , years Investment t a x c r e d i t Years f o r t a x c r e d i t

Term

Table A - I .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2

2

3

H

8

6

Note:

Total

C

2

2

H CJ% C2H C % C H 3 6 C H Liquids Ash Char

co

Feed CO

3.81* vt#

—

values.

22.32 -Wtfo

--

(0.12)

--

22.32 Wt/o 10.68 11.52

3.81* wt#

2.05 0.76 0.27 0.l6 0.11 (0.09) (0.O8) (O.32)

0

H

Parentheses i n d i c a t e estimated

30.85 vtjt

7.35

2.25 3.22 0.95 0.1*3 (0.52) (0.35) 3^5

—

3Ο.85 vtjt 8.01 1+.32

c

(0.1) (O.l) Wt/o

(ô~3)

( ο Λ ) vt/o

--

—

--

—

—

---

( O . l ) Vt/o

s

(0.1)

—

---

--

—

--

( 0 Λ ) wt/o

Ν

Table IV. Y i e l d s from P y r o l y s i s o f Refuse (Dry B a s i s - Weight Percent)

1+2.1*9 Μή$

--

—

1*2.1*9

--

—

--

—

1*2Λ9 wt#

ASH

100.00vt$

100.00vt$ I8.69 15.81* 2.05 3.01 3.^9 1.11 0.5^ 0.61 0.1*3 3.99 1*2.1*9 7.75

Total

to

2.

BAILIE AND RICHMOND

Table V.

Product Cost f o r a P l a n t of 1530 Tons/day

Raw M a t e r i a l Costs ( $ 1 . 0 0 / l 0 Operating Costs Annualized C a p i t a l Charge

($/l0

6

Btu)

7-9 3.9 3.6 15 Λ

Total 6

33

Economics Associated with Waste

(l.2) (0.6) (0.6) (2Λ)

7-9 ( l . 2 ) 3.9 ( 0 . 6 ) 2.0 ( 0 . 3 ) 13-8

Btu)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

(2.l)

SOLID WASTES AND RESIDUES

34

These same r a t i o s were used throughout t h i s paper to convert t o t a l c a p i t a l cost to annualized c a p i t a l c o s t s . The b a s i s B a t t e l l e used f o r these two cases i s given i n Appendix A. The values provided by B a t t e l l e (5) were modified to r e f l e c t an energy y i e l d of 80% r a t h e r than the 62% used i n that study. Wheelabratog I n c i n e r a t i o n , Inc. (9) r e c e n t l y provided an estimate of $2.00/10 Btu f o r producing a gas from wood waste i n a p l a n t of 250 tons c a p a c i t y . In p r e p a r i n g the cost e s t i m a t e , B a t t e l l e used the gas compositions shown i n Table 6. The cost of f u e l produced i s not s e n s i t i v e to p l a n t s i z e . The cost a n a l y s i s f o r both SRI and B a t t e l l e were f o r dual t r a i n s fed 500 to 750 tons/day of s o l i d feed and there i s l i t t l e cost d i f f e r e n t i a l i n s i z e s above 500 tons/day. The cost estimates given above provide evidence that biomass can be^converted to a medium Btu gas at a cost of $2.00 to $2.50 per 10 Btu w h i l e m u n i c i p a l waste w i l l produce e g s e n t i a l l y the same q u a l i t y gas f o r abou timates assume that the cost at the s i t e was zero f o r m u n i c i p a l waste and $1.00/10 Btu f o r biomass. For m u n i c i p a l waste there would be a drop charge. This would decrease the cost of the gas produced. For biomass, there i s a cost a s s o c i a t e d w i t h t r a n s p o r t i n g the biomass from the l o c a t i o n i t was harvested to the p l a c e where i t i s to be converted to a gas. The cost a s s o c i a t e d w i t h the t r a n s p o r t a t i o n of the b i o mass and f u e l gas are not considered i n these estimates. System A p p l i c a t i o n s In t h i s s e c t i o n s e v e r a l a p p l i c a t i o n s u s i n g intermediate energy gas made from biomass are described and some economics developed. Application 1 The Department of Energy i s supporting a study on the f u e l i n g of a 50 Mw e l e c t r i c p l a n t w i t h wood. The most s t r a i g h t forward approach i s to burn the f u e l i n a power p l a n t . An a l t e r n a t i v e to t h i s approach i s to produce a gas (to be c a l l e d wood-gas) and f i r e t h i s gas i n a gas f i r e d power p l a n t . There are s e v e r a l advantages to t h i s approach. These i n c l u d e : a)

Lower power p l a n t c o s t s - A gas f i r e d power p l a n t costs about one h a l f as much as a s o l i d f u e l e d plant.

b)

Higher combustion e f f i c i e n c y - A gas f i r e d system uses l e s s excess a i r and combustion i s more complete than i n a wood f i r e d system.

c)

E n v i r o m e n t a l l y a t t r a c t i v e - A gas f i r e d p l a n t needs no s t a c k clean-up to meet environmental standards.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BAILIE AND RICHMOND

Table V I .

Economics Associated with Waste

Estimated Composition o f Output Gas — Process fro

Bailie

Mole Percent Dry B a s i s Bagasse co co Ho C% C hydrocarbons C3 hydrocarbons H2O ( i f wet) Net Heating Value 2

2

23.29 23.01* 35.38 8.53 8.66 1.10 (25.56) lk.96 MJ per scm (1*01 B t u per s c f ) (dry)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

36 d)

Lower maintenance - A gas f i r e d p l a n t has much l e s s maintenance than a s o l i d f u e l e d p l a n t .

The disadvantages i n c l u d e the cost of the p l a n t needed to generate the f u e l gas and the l o s s of heating value r e s u l t i n g from the a d d i t i o n a l processing. In comparing the d i r e c t wood f i r e d system to the wood-fuel g a s - e l e c t r i c p l a n t , the f o l l o w i n g assumptions were made: 1.

C a p i t a l cost and operating cost of a wood f i r e d e l e c t r i c generating p l a n t i s twice that of a n a t u r a l gas f i r e d system.

2.

To produce 1 Kw-hr o f e l e c t r i c i t y from wood r e q u i r e s 12,750 B t u and from n a t u r a l gas i s 11,000 Btu. This i s f o r a 55 Mw system

3.

F u e l gas can

A study by M i t r e (9) estimated the c a p i t a l cost of a 55 Mw b o i l e r f i r i n g wood i s $55 χ 10^ and the operating cost i s $3.6 χ 10 /year. The previous s e c t i o n provided estimates of f u e l costs from wood t o be 2.1 χ 1 0 Btu and 2.4 χ χ 1 0 Btu f o r low debt and high debt economics. Using these values and the assumptions given above, i t i s p o s s i b l e to compare d i r e c t wood f i r e d systems to woodgas f i r e d systems. The r e s u l t s are summarized i n Table 7. The r e s u l t s shown i n Table 7 i n d i c a t e : 6

6

a)

The cost of e l e c t r i c i t y from d i r e c t wood f i r i n g are equal t o or more expensive than wood gas f i r i n g systems.

b)

The cost i s s t r o n g l y a f f e c t e d by the method of financing.

c)

For low debt f i n a n c i n g e l e c t r i c i t y from wood gas i s about 20% l e s s than d i r e c t wood f i r i n g . For high debt f i n a n c i n g the cost i s comparable.

F i g u r e 7 shows the e f f e c t of the raw m a t e r i a l costs ( b a s i c wood cost) on the cost of e l e c t r i c i t y . The d i f f e r e n t i a l between the two a l t e r n a t i v e s remains constant w h i l e the percentage d i f f e r ­ ence decreases w i t h f u e l c o s t . Application 2 I t was suggested e a r l i e r that the conversion of wood to a f u e l gas would be p a r t i c u l a r l y important i f there was an e x i s t i n g f a c i l i t y that would be shut down i f n a t u r a l gas was c u r t a i l e d . The i n d u s t r y would not only pay the cost of a new wood burning

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

Table V I I .

Economics Associated with Waste

37

Comparison o f E l e c t r i c Costs f o r Wood-Electric and Wood-Gas-Electri

6

F u e l Costs (Wood @ $ l / l 0 ) Operating Costs ($106/yr) Annualized C a p i t a l Costs Mlll/Kw-hr

Wood-- E l e c t r i c

Wood-• G a s - E l e c t r i c

High Debt

High Debt

k.l 3-6 k.Q 12.5 m

Low Debt

k.l 3-6 8.5 1ÏÏT2 (58)

8Λ 1.8 2.k 1275" (ko)

Low Debt

8.k 1.8 k.2 1O (k6)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLED WASTES AND RESIDUES

38

f a c i l i t y , but would be f o r c e d to pay the annualized c a p i t a l cost f o r the i d l e n a t u r a l gas p l a n t . Figure 8 shows the e l e c t r i c c o s t s f o r a new wood f i r e d p l a n t and f o r wood-gas used i n an e x i s t i n g n a t u r a l gas p l a n t as a f u n c t i o n of wood f u e l c o s t . The only d i f f e r e n c e i n t h i s f i g u r e and that shown i n F i g u r e 7 i s the annuali z e d c a p i t a l cost f o r the i d l e gas p l a n t i s added to the cost of a new wood burning p l a n t . For e i t h e r f i n a n c i n g scheme, the wood gas p l a n t provides e l e c t r i c i t y a t a s i g n i f i c a n t l y lower cost than the d i r e c t f i r e d ^ s y s t e m . For the case where the b a s i c wood f u e l c o s t s are $1.00/10 B t u , the d i f f e r e n t i a l s are 15.6 and 35.7%, r e s p e c t ively. Application 3 The economies of s c a l e are s i g n i f i c a n t i n u t i l i t y power s t a t i o n s . The M i t r e report (10) provides cost estimates f o r p l a n t s using 850, 1700 and 340 converted to annualized v i o u s l y d e s c r i b e d . I n comparing c o s t s i t was assumed that the cost of the wood to gas conversion f a c i l i t y d i d not b e n e f i t from economies of s c a l e . This i s not true f o r other types of convers i o n f a c i l i t i e s . For example, the Union Carbide Process b e n e f i t s g r e a t l y from an i n c r e a s e i n s c a l e . This i s because the economies r e s u l t i n g from the l a r g e r oxygen p l a n t needed i n t h i s process. There are some s m a l l economies of s c a l e that would lower the curves f o r the wood gas systems a t l a r g e r c a p a c i t y . The curves i n F i g u r e 9 r e f l e c t the i n c r e a s e i n t r a s n p o r t a t i o n c o s t s f o r l a r g e r p l a n t s . In e v a l u a t i n g the t r a n s p o r t a t i o n costs the f o l l o w i n g assumptions were made: 1.

Cost of t r a n s p o r t a t i o n i s $0.10 per t o n m i l e .

2.

The average d i s t a n c e t r a v e l e d f o r v a r i o u s s i z e p l a n t s were: 850 tons/day 1700 tons/day 3400 tons/day

35 m i l e s 46.7 m i l e s 66 m i l e s

In F i g u r e 9 the cost of e l e c t r i c i t y i n d i r e c t f i r e d p l a n t s are seen t o cross the wood-gas f i r e d curves f o r h i g h c a p a c i t y . This i s a d i r e c t r e s u l t of not b e n e f i t i n g from economies of s c a l e for the wood-gas generators. Since there i s no cost advantage i n l a r g e r gas generating f a c i l i t i e s , i t would be more a t t r a c t i v e to l o c a t e the p l a n t s c l o s e r t o the wood source and p i p e l i n e the gas to a l a r g e c e n t r a l gas f i r e d u t i l i t y . This would reduce the d i s tance the wood i s hauled and the cost a s s o c i a t e d w i t h moving the wood t o a c e n t r a l p l a n t . This would reduce the cost below those shown i n F i g u r e 9 f o r the gas f i r e d systems. I n Figure 9 the wood-gas curves do not r e f l e c t e i t h e r the s m a l l but r e a l economies

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BAILIE

A N D RICHMOND

Economics Associated with Waste

Figure 7. Electric cost comparison between woodfiredand wood gasfired:( ) woodfired;( ) wood/gas fired

Debt Economics

Economics

$1.00

$3.00

$2.00 6

Basic Cost of Wood $ / 1 0 Btu

Figure 8. Cost comparison of electricity betweenfiringwood gas in existing plants and building new directfiredplants: ( ) new woodfiredphnts; ( ) existing plantfiredwith wood gas

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLED

40

Figure 9.

WASTES

AND

Economies of scale

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

2.

BAILIE

A N D RICHMOND

Economics Associated with Waste

41

of s c a l e o r the lower t r a n s p o r t a t i o n c o s t s . The s i t u a t i o n f o r wood gas would be b e t t e r than that shown i n F i g u r e 9. Application 4 The f i n a l h y p o t h e t i c a l s i t u a t i o n considers the use of m u n i c i p a l waste t o provide a f u e l gas t o a l a r g e m a l l , group of commerc i a l establishments o r i n d u s t r i a l park. Table 2 provided e s t i mates f o r the cost of f u e l gas from m u n i c i p a l waste. I n t h i s t a b l e no charge was made f o r the f u e l . For the case of m u n i c i p a l waste, a drop charge i s imposed i n order t o leave the waste a t the f a c i l i t y . E i g h t d o l l a r s per ton i s considered t o be a reasonable charge. I f four d o l l a r s of t h i s could be assigned t o s u b s i d i z e the wasteto-gas process, a c r e d i t of $0.79 per 10^ Btu i s r e a l i z e d . This reduces the gas cost to $1.06 t o $1.53 per m i l l i o n Btu. A t t h i s p r i c e i t becomes a h i g h l y c o m p e t i t i v e f u e l . This f u e l gas can be transported by p i p e l i n f i r e d equipment. This become c a p i t a l cost between gas f i r e d equipment t o s o l i d f i r e d equipment i s o f t e n as low as 1/6 f o r s m a l l commercial u n i t s . Conclusions 1.

Biomass and m u n i c i p a l waste can be converted t o an intermediate energy gas.

2.

The gas produced i n the twin f l u i d i z e d bed can s u b s t i t u t e f o r n a t u r a l gas i n e x i s t i n g equipment.

3.

The energy l o s t i n the biomass t o gas conversion system i s l a r g e l y made up i n higher combustion e f f i c i e n c y i n the power p l a n t .

4.

The cost of the wood-gas i s i n the p r i c e range of $2.00 t o $3.00 per 1 0 B t u . 6

5.

The economic choice between d i r e c t f i r e d o r wood gas f i r e d i s h i g h l y dependent on the method of f i n a n c i n g . I f there i s an advantage, i t would appear t o be w i t h wood-gas.

6.

Wood gas systems producing intermediate gas have not seen commercial o p e r a t i o n and has no t r a c k r e c o r d . D i r e c t f i r e d systems are o p e r a t i n g commercially but have a s p o t t y r e c o r d .

7.

When o p e r a t i n g n a t u r a l gas f i r e d u n i t must be r e p l a c e d by a wood f i r e d u n i t , i t becomes more a t t r a c t i v e t o convert wood t o gas and use the existing f a c i l i t y .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

42

SOLID

WASTES

AND

RESIDUES

8.

For power generating systems, economies of s c a l e are s i g n i f i c a n t f o r d i r e c t f i r e d systems. The wood gas to e l e c t r i c system i s l e s s s e n s i t i v e to s c a l e because the wood gas generating system i s i n s e n s i t i v e t o s c a l e . M u l t i p l e u n i t s are b u i l t f o r l a r g e s i z e a p p l i c a t i o n s . For the Union Carbide Purox system economies of s c a l e are achieved and t h i s c o n c l u s i o n would not apply i f t h i s u n i t were s e l e c t e d to produce wood-gas.

9.

M u n i c i p a l waste can produce a f u e l gas a t a lower cost because there i s no charge f o r the feed and the system w i l l r e c e i v e a subsidy through a drop charge.

The paper has emphasized wood which was s e l e c t e d to represent biomass. Other biomas bed system w i l l more r e a d i l d i f f e r i n g p h y s i c a l c h a r a c t e r i s t i c s than the Purox system or d i r e c t f i r e d b o i l e r s . I f i t i s not p o s s i b l e to provide assurances of the economic advantages that may be obtained from wood gas there i s l i t t l e doubt that the economics of today show t h i s o p t i o n i n a more f a v o r a b l e l i g h t than the economics of a few years ago. The longest c o a l s t r i k e i n h i s t o r y i s underway. I t shows how dependent the n a t i o n i s on c o a l . The cost of c o a l w i l l without q u e s t i o n r i s e s i g n i f i c a n t l y under any new c o n t r a c t . This w i l l see a f u r t h e r s h i f t toward f a v o r a b l e economics f o r biomass u t i l i z a t i o n

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

Economics Associated with Waste

43

REFERENCES 1Study for the United States Department of Energy, prepared by Wheelabrator Clean Fuels Corporation. 2E.P.R.I., "Fuels from Municipal Refuse for Utilities: Tech­ n i c a l Assessment." E.P.R.I. Report 261-1, March 1975 (Prepared by Bechtel Corporation). 3Fisher, T. F., Kasbohn M. L. and J . R. Riverο, "The Purox System," presented at the 80th National Meeting of the American Institute of Chemical Engineers, September 9, 1975. 4Hasegawa, Μ., Fukuda, J. and D. Kunii, "Research and Develop­ ment of Circulating System Between Fluidized Beds for Application of Gas-Solid Reactions, Congress, Denver, Augus 5

B a t t e l l e Columbus, "Fuels from Sugar Crops," BMI Report 1957A, Volume 1 through 5, March, 1977. 6Douglas, Ε., M. Webb and E. Daborn, "The Pyrolysis of Waste and Product Assessment," paper presented at Symposium on Treatment and Recycling of Solid Wastes, Manchester, England, January, ]974. (Available through Warren Spring Laboratory, Department of Industry.) 7

A l b e r t , S. B., et. al., "Pyrolysis of Solid Waste: A Techni­ c a l and Economic Assessment," P.B. 218-231, September, 1972. 8Bechtel Corporation, "West V i r g i n i a Recycle Resource Recov­ ery Center," Technical and Economic Review for City of Charleston, July 15, 1972. 9 B a i l i e , R. C. and C. A. Richmond, "New Technology and Pyroly­ s i s of Wood and Wood Waste." paper presented at the 1978 Regional Tappi Conference i n Portland, Oregon. 10Mitre Corporation, "Siloculture Biomass Farm," Mitre Techni­ c a l Report Number 7347, Volume 1 through 5, May 1977. 11Chiang, S. H., J . T. Cobb and G. E. Klinzing, "A Critical Analysis of the Technology and Economics for the Production of Liquid and Gaseous Fuels from Wastes," paper presented at the 85th National Meeting of the American Institute of Chemical Engineers, Atlanta, Georgia, February 27, through March 2, 1978. APRIL 7,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3 The Andco-Torrax High-Temperature Slagging Pyrolysis System P A U L E . D A V I D S O N and T H E O D O R E W . L U C A S , JR. Andco-Torrax Division, Andco Incorporated, 25 Anderson Road, Buffalo, N Y 14225

The Andco-Torrax syste process known technically solid waste is a relatively new innovation, pyrolysis processes have been used for years by industry. Typical examples are found in the production of char and methanol from wood and coal gasification. Pyrolysis, commonly referred to as destructive distillation, is defined as an irreversible chemical change brought about by the action of heat in an oxygen deficient atmosphere. The pyrolysis of organic material causes the volatile fraction to distill, forming combustible liquids and vapors. The vapors are composed primarily of methane, hydrogen, carbon monoxide, carbon dioxide, water and the more complex hydrocarbons such as ethane, propane, oils and tars. The exact components in percent composition of these gases formed by pyrolysis of municipal waste cannot accurately be predicted in that, in a real system, the complex multi-component fractions would be converted to more stable gases such as ethylene through a continuing pyrolysis action and are a result of complex time/temperature kinetic reactions. The material remaining after pyrolysis is char, a charcoal-like substance consisting primarily of fixed carbon residue. In the Andco-Torrax system, the char remaining from the pyrolyzed material is burned to carbon monoxide and carbon dioxide using high temperature air, thus releasing sufficient heat energy to convert all non-combustibles contained in the solid waste to molten slag and to further pyrolyze incoming waste material. PROCESS DESCRIPTION The" principal components of the Andco-Torrax system are the gasifier, secondary combustion chamber, primary air preheating equipment, waste heat boiler, and gas cleaning system. These components are shown in Figures 1 and 2. These figures illustrate the primary air preheating system as a regenerative tower system, although other alternatives may be used which could include a heat recuperator or a fossil fuel fired air preheater. The gasifier and secondary combustion chamber comprise the main process 0-8412-0434-9/78/47-076-047$05.00/0 © 1978 American Chemical Society American Chemical Society Library In Solid 1155 Wastes and Jones, 1 6 tResidues; h S t . X. W . J., et al.; ACS Symposium Series; American Chemical DC, 1978. Washington, D . C . Society: 2 0 0 3 Washington, 6

SOLID

48

Figure 1.

Figure 2.

WASTES

AND

Andco-Torrax system

Andco-Torrax system schematic

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

3.

DAVIDSON

A N D LUCAS

High-Temperature Slagging Pyrolysis System

49

components and are shown in Figure 3. Gasifier A crane with grapple bucket removes refuse from the refuse pit without pretreatment other than the shearing of oversize items to approximately one meter dimensions. The refuse is directed into a hopper from which it is fed into the top of the gasifier by either a reciprocating ram or a v i brating feeder. The gasifier is a vertical shaft furnace so designed that the descending refuse burden and the ascending high temperature gases become an effective countercurrent heat exchanger. The gasifier shaft is 12-15 meters (40'-50') in overall height, 1.8-2.7 meters (6'-9') in diameter, and is fabricated from mild steel with refractory lining in the lantern and hearth areas only. The main stack between the lantern and hearth is externally cooled over its length by a jacketed water cascade. The hopper has a loose sealing mechanism to decrease the infiltration of air into the top of the gasifier. As the zones are encountered - drying function of the drying zone is to evaporate the moisture in the refuse and to act as a plug to further restrict the in-flow of air during charging. Refuse entering at the top of the gasifier moves downward past the gas offtake plenum (lantern). From this point down, the refuse dries and then, in the pyrolysis zone, is heated from 260-1093°C (500-2000°F) in a reducing atmosphere where the rate of decomposition to pyrolysis products increases with temperature. Various oils formed in the low temperature region of pyrolysis continue to pass down and are cracked into gases and char at the higher temperatures. These particles of char and oil that are entrained in the hot gases are to a large extent scrubbed out by the descending refuse and are recycled down into the higher temperature zone. The heat for drying and pyrolyzing the refuse is supplied by the combustion of the carbon char with preheated air in the primary combustion zone. The preheated air at 1037°C (1900°F) is directed from the regenerative towers through a hot blast main into a circular bustle pipe. The air then passes through several downcomer-tuyere assemblies radially into the gasifier hearth where it is used to combust the char. The heat generated by this combustion process (up to 1650°C or 3000°F) also transforms the non-combustible materials to a molten slag. The temperature profile through the refractories results in the formation of a coating of solidified slag over the refractories in the hearth area. This coating assists in protecting the refractories from the high temperatures and corrosive action of the molten slag. The molten slag is drained continuously through a sealed slag tap into a water quench tank to produce a black, glassy, sterile aggregate. The sealed slag tap arrangement allows removal of the frit while maintaining pressures in the hearth slightly above atmospheric. The slag formed in the hearth of the gasifier and in the secondary combustion chamber accumulate in a common slag agitation/holding tank, and several

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

50

SOLID

WASTES

A N D RESIDUES

methods are available for transporting it from the tank. At the demonstration plant in Orchard Park, the material flowed into a slag pit and a front-end loader was used to manually carry it to a stockpile for later removal by truck. One automatic method uses drag and belt conveying equipment, with drag conveyors removing slag from the main slag pit and depositing it at a continuous rate on horizontal or inclined belt conveyors feeding a vertical bucket elevator. The bucket elevator directs the material to external storage bins or stockpiles for removal by transportation vehicles. Another method used is slurry pumping of slag from the main slag pit to dewatering tanks. The suspended solids quickly settle out in the dewatering tank for removal by grapple bucket or drag conveyor system. The conveying liquid may be pumped back through the system from the dewatering tanks for reuse in the quench tanks. Volume reduction from the raw refuse to the slag residue is approximately 95-97 percent and on the inert fraction In th present physica chemical properties of the slag residue produced at the Orchard Park demonstration plant. At least 90% of the energy content of municipal refuse is contained in the gas stream which leaves the gasifier. This energy is in the form of combustible gases, vapors, and entrained particles and as sensible and latent heat. The temperature of this gas is approximately 400°C-500°C (752°F-932°F). The complete combustion of this gas stream produces about the same volume of products of combustion per unit of heat released as would be the case with other gaseous fuels. The composition and properties of the combustible gas stream are dependent, of course, on the refuse mix. The heating value of the gas will normally be in the range of 937-1593 kcal/nm (100-170 Btu/scf). Although this combustible gas stream, with or without cleaning to remove entrained material, has potential application as an energy source where close coupling of the gasifier with the recipient combustion device (such as kilns, boilers, etc.) is possible, the present commercial AndcoTorrax plants employ a secondary combustion chamber to burn this gas to completion. Secondary Combustion Chamber The offgas exits from the gasifier via the lantern, and is drawn into the secondary combustion chamber through a refractory lined cross-over duct by the system's induced draft fan. At the inlet to the secondary combustion chamber, the offgas is mixed with air in a high energy burner and is admitted to the chamber in a tangential fashion for a high turbulence, spiral flame. A small quantity of excess air is normally used to maintain the exit temperature from the secondary combustion chamber between 1150°C and 1250°C (2100-2280°F). The secondary combustion chamber is a vertical, refractory lined vessel in which temperatures up to 1400°C 3

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

DAVIDSON

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High-Temperature Slagging Pyrolysis System

TABLE 1 -S LAG RESIDUE CHARACTERISTICS Constituent Si0 A1 0 2

2

3

T1O2 Fe 0 2

3

FeO MgO CaO MnO Na 0 2

κ ο 2

Cr 0 2

CuO ZnO Trace Oxides

3

(by weight) 45 10 0.8 10 15 2 8 0.6 6 0.7 0.5 0.2 0.1 1.1 100.0 Dry Bulk Density True Residue Density

Range % 32.00- 58.00 5.50- 11.00 0.48- 1.30 0.50 - 22.00 11.00-21.00 1.80- 3.30 4 . 8 0 - 12.10 0 . 2 0 - 1.00 4 . 0 0 - 8.60 0 . 3 6 - 1.10 0.11 - 1.70 0.11 - 0.28 0.02- 0.26

— 1.40 gm/cc 2.80 gm/cc

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

52

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(2550°F) are realized, and where sufficient residence time, up to 1.7 seconds, is maintained to assure complete combustion. The particulate matter entrained in the offgas from the gasifier is burned and the inert portion is fused, melted and slagged out of the stream. This slag is also water quenched and is approximately 10% of the total residue produced in the process. Air Preheating System As discussed previously, there are a number of possible methods for the preheating of primary combustion air by utilizing the energy from the hot combustion products which exit from the secondary combustion chamber or by burning fossil fuel. One such equipment system which has been built at both the SIDOR (Luxembourg) plant and the Frankfurt plant is shown in Figures 1 and 2. This system employs two regenerative towers, a system successfully used for many years in the steel and glass industries for preheating air. Regenerative taining a high heat capacit aligned flues which readily absorbs the heat from the hot products of combustion passing through them. During the heating cycle, approximately 10% of the total products of combustion from the secondary combustion chamber are introduced into the top of the regenerative towers. The heat from these gases is transferred to the refractories, bringing them up to temperature levels of approximately 1150°C (2100°F) at the top and 260°C (500°F) at the base. The waste gas exiting the regenerative tower subsystem is returned to a duct at the inlet of the gas cleaning system. A modulating damper valve in the boiler exit duct controls the amount of gas used in heating the regenerative tower refractory. During the "blast" cycle, the combustion products from the secondary combustion chamber are diverted to the second regenerative tower to heat its refractory. Ambient process air is introduced at the base of the fully heated regenerative tower and passes up through the refractory absorbing the stored heat. The exit temperature of the air from the tower ranges from 1037°C (1900°F) to 1110°C (2030°F). A constant primary air, or blast, temperature is maintained by blending the heated air with ambient air before introduction into the gasifier. A second method for preheating the primary combustion air employs a heat recuperator as used in the Grasse and Creteil plants. The metallic recuperator recovers heat from a portion of the products of combustion from the SCC exit and produces preheated air at a temperature of 600°C. The additional 400°C temperature differential is achieved through the use of a supplementary oil or gas fired burner. A third method for preheating the primary combustion air employs a fossil fuel fired silicon carbide cross flow shell-and-tube heat exchanger similar to that used in the demonstration plant in Orchard Park, New York. While this unit proved reliable during operation, the cost and availability

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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of liquid or gaseogs fossil fuels makes such a unit unattractive for commercial plants. Using a regenerative or recuperative type of heat exchanger results in both energy and cost savings. Waste Heat Boiler With regenerative towers as the method of air preheating, approximately 90% of the gas flow exiting the secondary combustion chamber is directed to the energy recovery system, a waste heat boiler. Typically, the waste heat boiler is of the combination radiation-convection type and is designed with certain Andco-Torrax process characteristics in mind. These characteristics are high temperature inlet gases (from 1150°C to 1250°C), constant temperature input, homogeneity of inlet gases and absence of unburned material, low volumetric gas flow, and low particulate loading. Gases leave the boiler at approximately 290°C (554°F). Gas Cleaning Equipment At the exit of the wast regenerative towers (or alternativ the exiting flow from the waste heat boiler and are ducted to the gas cleaning system. The gas cleaning system is typically a hot gas electrostatic precipitator of conventional design which can effect an outlet particulate loading of less than 100 gm/nm (.04 grains/SCF). DEMONSTRATION PLANT The development of the Andco-Torrax process began in early 1969 with the formation of a company called Torrax Systems, Inc. which was jointly owned by Andco Incorporated and the Carborundum Company. The purpose of Torrax Systems, Inc. was to acquire and develop all necessary technology for a new type of high temperature slagging pyrolysis process for disposal of municipal solid waste and then to make the necessary arrangements to build a prototype plant and to operate it successfully to prove out the technology. On July 1, 1969, Torrax Systems, Inc. entered into a contract with the County of Erie, a municipal corporation of the State of New York, to build and operate a 75-ton-per-day demonstration plant in Orchard Park, a suburb of Buffalo. This new plant program was made possible largely through the support of the U.S. Environmental Protection Agency acting under the Solid Waste Disposal Act of 1965 which provided a program of demonstration grants for the development and evaluation of new solid waste disposal technology. Other funds for the program were provided by New Ycrk State, Erie County, the American Gas Association, the Carborundum Company, and Andco Incorporated. Ground breaking ceremonies for the demonstration plant were held in July of 1970 and operation commenced in the second quarter of 1971. Between 1971 and 1973, the plant operated as an engineering development facility to evaluate and prove system design features. During that period of time, the plant operated for 2316 hours and processed 7664 tons of municipal solid waste. The longest period of continuous operations was 120 hours. Although 3

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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the plant design capacity was 3.1 tons per hour, the equipment operated at throughput rates as low as 1.3 tons per hour and as high as 4.7 tons per hour. In addition to normal municipal refuse, the Andco-Torrax demonstration plant handled other wastes, particularly those from industry. These wastes were mixed with municipal refuse and minor changes were made to the equipment and the operating procedures. Some of the tests at the demonstration facility included the following: Sewage Sludge. Undigested sewage sludge with 78 percent water conten t"waTcTîârgedrwith the municipal refuse in quantities averaging 28.5 percent of the total 3.8 TPH charge. Waste O i l . Waste automotive lubricating oil was charged with municipal refuse in average quantities of 6.1 percent of the 4.4 TPH charge. Combined Sludge and O i l . A test combining sewage sludge with waste oil and municipal refuse wa TPH of which 30.1 percen Tires. Unshredded automotive tires were charged by bucket with the normal refuse. The average addition was 30 tires per hour or about 10 percent of the total 3.3 TPH consumption. Polyvînylchlorîde (PVC). Bags filled with PVC plastic waste were charged with municipal refuse in quantities averaging 7 percent of the 3.2 TPH charge. In all cases no significant changes to the process operation were encountered. In these tests, changes in the process parameters (flows, temperatures, gas composition) were evident and were related to the changes in the input refuse heating value and composition. The Orchard Park plant employed equipment which for the main part was similar to that used in commercial Andco-Torrax plants. However, as discussed, the demonstration plant used a natural gas fired heat exchanger, rather than regenerative towers, to supply the high temperature primary combustion air. Other differences between the demonstration plant and commercial plants include the following: Refuse was charged into the top of the gasifier through an open cone without any type of hopper feed. The residue was removed from the slag quench area with a front end loader rather than automatically as is the case in commercial plants. A wet scrubber was used rather than an electrostatic precipitator. MARKET DEVELOPMENT It was decided by Carborundum and Andco in early 1973 that the original objectives of Torrax Systems, Inc. had been successfully concluded. Since then the demonstration plant has only operated for sales demonstration purposes. In 1973, agreements were executed between Carborundum and Andco giving Andco commercial rights to the process in Canada,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Australia and Europe. A further agreement was executed in 1976 which expanded Andco's commercial rights to the process to include the United States, the USSR, Japan, New Zealand, Indonesia, and countries in Polynesia, Latin America, Africa, and the Middle East. Commercial Plants Orders for four commercial Andco-Torrax systems have been received to January 1978. One order was placed in 1975 with Antox Wurth, Andco's West German licensee, by the City of Frankfurt. The unit capacity is 200 metric tons per day (220 TPD) and the system is located within an existing conventional incineration facility. Another order was placed in 1975 with Caliqua S.A. by the municipality of Grasse, France. The construction of the new 168 metric ton-per-day (185 TPD) plant is under the authority of Caliqua for use by the "Syndicat Intercommunal pour le Traitement et l'enlèvement des Ordures Ménagères et des Déchets Urbains de la Region de Grasse." Th initial start-up phase and th in the first quarter of 1978. A third plant, with a capacity of 400 metric tons per day (440 TPD), is being built in Creteil, France, and will be completed in 1979. The first order for a commercial Andco-Torrax System was awarded to S . A . Paul Wurth, Andco's Benelux licensee, in January 1974. This system has a 192 metric-ton-per-day (211 TPD) capacity, and is owned and operated by the Syndicat Intercommunal pour la Destruction des Ordures des Cantons de Luxembourg, Esch, et Cappellen, (SIDOR), a group of 35 municipalities in Luxembourg. Process design and sizing of the hardware components for this system were based largely on prior demonstration plant experience gathered at the Orchard Park facility, correlation with specific refuse analysis data for Luxembourg, and utilization of a process simulation computer program. The design point refuse composition, expressed in weight percent, for the SIDOR Andco-Torrax System is: Refuse Composition Proximate Analysis Ultimate Analysis Combustibles 51.4 Fixed Carbon 9TÔ Carbon 29.3 Water 23.7 Volatiles 42.4 Hydrogen 3.6 Ash-lnerts 24.9 Oxygen 18.5 This refuse analysis corresponds to a lower heating value of 2500 kcal/ kg (4500 Btu/lb). Although the plant was designed for 2500 kcal/kg refuse, actual refuse quality as received is closer to 1600 kcal/kg (2880 Btu/ lb). Mass and heat balances for these two operating points are presented in Table II. The differences in system efficiencies and steam production per unit of refuse for these two points are noteworthy. The over-all SIDOR plant consists of two conventional grate-type incinerators built by CNIM (Constructions Navales et Industrielles de la Mediteranee) and one 192 ton-per-day Andco-Torrax unit built by S. A . Paul Wurth. The Andco-Torrax equipment includes the refuse feeder,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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TABLE II - HEAT AND MASS BALANCES ANDCO-TORRAX (S.I.D.O.R.) SYSTEM Refuse Qualify

1600 kcalAg Refuse (2880 Btu/lb.) Heat Mass (kcalAg) (kgAg)

2500 kcalAg Refuse (4500 Btu/lb.) Heat Mass (kcal/kg) (kgAg)

Input Refuse 1600 1.00 2500 1.00 Auxiliary Fuel 69 Combustion Air 3 3.49 4 6.26 Feedwater 244 1.74 408 2.90 Electrical — Power 69 — 69 Total 6.24 1985 10.17 3050 Output Steam 1323 1.74 2206 2.90 Slag & Flyash 92 0.29 82 0.27 Exhaust Gases 296 4.21 464 7.00 — Losses 369 — 393 Total 2080 6.24 3145 10.17 Steam Production 1.7 kg steam/kg refuse 2.9 kg steam/kg refuse System Efficiency* 62% 68% *System Efficiency = ( Steam-Feedwater ) JQQO/ (Refuse + Fuel + Electrical Power) v

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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gasifier, secondary combustion chamber, regenerative towers, waste heat boiler, steam condensation unit, electrostatic precipitator, induced draft fan, chimney, water cooling plant, controls system, and all secondary equipment for compressed air, auxiliary fuel and waste oil subsystems. Figure 4 shows the SIDOR Andco-Torrax gasifier, Figure 5, the system. The greater portion of the hot gases exiting from the SIDOR AndcoTorrax secondary combustion chamber is fed to a waste heat boiler, where the sensible heat content is used to generate steam. The boiler has been designed for a maximum gas throughput of 36,800 rirn^/h (21,660 scf/min.), a maximum gas inlet temperature of 1370°C (2500°F) and a nominal gas in­ let temperature of 1250°C (2280°F). The boiler is a 3-pass, vertical, com­ bination radiation/convection boiler, with the first of the three passes com­ prising the radiation section. The boiler has a super heater at the end of the radiation section and an economizer in the third pass. With a feedwater temperature of 140° maximum of 60,000 Ib/hr o a temperature of 385°C (725°F). The steam produced by all three refuse conversion units is directed to a 7 MW turbine generator producing electricity at 10 kV. The turbine gen­ erator is designed for a throughput lower than the plant's corresponding re­ fuse capacity of 600 metric tons per day, in that the amount of waste cur­ rently generated and available to the plant is lower than the total design capacity. A second turbine generator will be installed as refuse production increases. Theoretically, 1 kg (2.2 lb) of 2000 kcalAg (3600 Btu/lb) refuse can be converted to 1.22 Kwh of electricity. However, due to practical tur­ bine efficiencies, line losses, and flue gas losses, the final conversion fac­ tor of refuse to electrical power is approximately 0.48 Kwh per kg of re­ fuse. Assuming the availability of the system as 85%, the total amount of electricity produced per year from the Andco-Torrax system will be approxi­ mately 28.6 χ 10° Kwh. Since the Andco-Torrax system electrical require­ ments are about 80 Kwh/ton of refuse, the total amount of electricity available to the local power distribution company is about 23.8 χ 10° Kwh per year. The waste gases from the boiler at 290°C (554°F) are combined with the exhaust gases from the regenerative towers and enter the electrostatic pre­ cipitator. The two field precipitator is designed to produce particulate emissions no greater than 100 mg/nm , corrected to 7% C 0 2 . The cleaned gases then pass through the induced draft fan to a triple flue stack, 80 meters in overall height. ECONOMICS Since 1973, Andco Incorporated and its licensees have been involved in several studies and have made qualitative and firm bids for refuse conver­ sion plants. Four such bids have resulted in the sale of Andco-Torrax 3

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

Figure 3.

WASTES

AND

Andco-Torrax unit

Figure 4. A 192-metric TPD SIDOR gasifier

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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systems to municipalities in Europe. An estimate of 1977 capital and operating costs are presented in Table III. It may be noted that construction costs for Andco-Torrax equipment alone range from a low of $22,000 per daily ton of plant capacity for a 1500 ton-per-day plant to a high of $30,000 per daily ton of capacity for a plant with a capacity of 250 tons per day. Net disposal costs per ton for plants of 250, 500, 1000 and 1500 tons respectively are $17.51, $11.90, $3.30 and $2.20. These net disposal costs after energy credits are currently competitive with other commercially available waste-to-energy technologies. The graph in Figure 6 utilizes the cost information presented in Table III with variable tipping (disposal) fees, and variable product credits. The family of curves thus generated depict Andco-Torrax plant economics for tipping fees ranging from zero dollars per ton of refuse to $20.00 per ton of refuse. Thus for any plant capacity and for a tipping fee between zero and $20.00 per ton, breakeven estimates for plan the vertical axes. For example per ton tipping fee has breakeven plant costs of $20.00 per ton without energy credits. If plant costs are to be covered by product sales, then steam must be sold at $4.00 per thousand pounds or electricity must be sold at 48 mîlls/Kwh. CONCLUSION The Andco-Torrax System has been proven through successful development and operation of a 75-ton-per-day demonstration plant in the United States over a four-year period. The first two commercial Andco-Torrax Systems have recently commenced operation in Luxembourg and Grasse, France. The third unit, located in Frankfurt, is scheduled for start-up in the second quarter of 1978. The fourth plant, in Creteil, France, will be completed in early 1979. The Andco-Torrax high-temperature slagging pyrolysis system accomplishes the three objectives required of modern refuse conversion units: 1. Maximum Volume Reduction - Volume reduction in the AndcoTorrax System is 95-97%. Future tests at the Frankfurt plant will be made to determine what further volume reduction can be achieved with conventional incinerator residue by adding varying amounts of incinerator residue to the Andco-Torrax System. 2. Inert Residue - The fritted, glassy aggregate residue is completely sterile and inert, consisting entirely of oxidized material as a result of the high-temperature process conditions. 3. Resource Recovery - The production rate of energy in the form of steam and/or electrical power is high as a result of all of the combustible material in the refuse being totally consumed. The economics of an AndcoTorrax energy recovery plant are similar to those of other commercially available, competitive waste-to-energy technologies.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Figure 5. SIDOR plant—Luxembourg: Andco Torrax equipment train

Figure 6. Andco-Torrax system net disposal/product costs

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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TABLE III - ANDCO-TORRAX SYSTEM ECONOMICS (1977) 250 TPD 500 TPD 1000 TPD 1500 TPD No. of Andco-Torrax Units 2 5 1 3 Annual Refuse Throughput (TPY) 82125 164000 329000 492750 CAPITAL COSTS ($000 omitted) 33000 Andco-Torrax Equipment 14900 20000 7500 14420 Buildings & Utilities 8080 12860 5800 4030 Interest During Construction 1953 2793 1130 Start-up Expense 1730 740 850 1080 1375 Working Capital 466 672 980 Total Capital Costs 15636 54555 26455 37713 Amortization Cost/Ton 11.94 11.53 19.83 16.80 (8-1/2% interest, 20 year plant life) OPERATING COSTS ($/Ton Labor & Administration (No of Personnel) Maintenance, Power & Utilities Total Operating Costs/Ton

9.64 16.58

8.52 14.00

6.70 10.26

6.49 9.37

Total Plant Costs/Ton

36.41

30.80

22.20

2Ô.9Ô

CREDITS Steam

18.90

18.90

18.90

18.90

NET DISPOSAL Cost/Ton

17.51

n.9o

3.30

2.20

6.94(19)

5.48(30)

3.56(39)

2.88(47)

ASSUMPTIONS: 1· A 1000 TPD plant will have 3-330 TPD units. A 1500 TPD plant will have 5-300 TPD units. 2. Plant availability is 90%. 3. No escalation of capital cost to completion of project. 4. Interest during construction is estimated at 8 i % of construction costs. 5. Start-up expense is estimated at 3%-6% of construction costs. 6. Working capital is estimated at 3% of construction costs. 7. Average total wages and benefits per employee per annum is $28,000. 8. Annual maintenace costs are 4% of capital (equipment and buildings} 9. Plant electrical consumption is 80 KWH/ton of refuse. Power costs 20 Mills/KWH. 10. Auxiliary fuel usage is 2.5 nm (88.3 ft ) natural gas/ton. Natural gas costs $3.00/1000 f t . 11. Refuse is assumed to have an LHV of 2275 kcalAg (4100 Btu/lb.). Steam produced will be 2.7 kgAg refuse. Steam credits will be $3.50/1000 lb. 3

3

3

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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ABSTRACT In our society today, the disposal of municipal solid waste poses ever increasing social and technical problems. During recent years, widespread attention has been focused on both real and potential scarcities of conven­ tional fossil fuels. The search for economically attractive solutions to these two problems has given rise to the development of different systems to pro­ cess municipal solid waste by thermal and chemical techniques to provide alternate energy sources. This paper describes one such system called the Andco-Torrax System which is used to convert municipal solid waste into useful energy and a granulated slag byproduct by the pyrolysis and primary combustion of organic materials and by the melting of non-combustible materials at temperatures up to 1650°C (3000°F). LITERATURE CITED 1. Andco Incorporate General Informatio of Solid Refuse (1975) 2. Legille, E., Berczynski, F. Α., Heiss, Κ. G . A Slagging Pyrolysis Solid Waste Conversion System (1975). Conversion of Refuse to Energy - First International Conference and Technical Exhibition IEEE Catalog Number 75CH1008-2 CRE 3. Davidson, P. E. Andco-Torrax: A Slagging Pyrolysis Solid Waste Conversion System (1977) Canadian Mining and Metallurgy Bulletin, July 1977 MARCH

3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4 Co-Disposal of Sludge and Refuse in a Purox Converter C . T . M O S E S and K . W . Y O U N G Union Carbide Corporation, Linde Division, Tonawanda, N Y 14150 G. STERN

and J. B. F A R R E L L

U.S. E.P.A., M E R L , Cincinnati, OH

45268

The development of the PUROX System for the conversion of municipal refuse into a and an inert slag stream (1,2,3). The key element in this system is the converter which is basically an oxygen-fed shaft furnace in which solid waste is dried, pyrolyzed, combusted, and the inorganic residues slagged. The operation of the converter is supported by several subsystems: a feed material storage and preparation system, a gas cleaning system, a wastewater treatment system, and an oxygen generating system. Figure 1 presents a mass balance indicating the general process flow and typical material rates for operation with municipal refuse. One mass unit of as-received refuse undergoes shredding and magnetic separation of ferrous material. The magnetically separated, shredded material is combined with 0.22 mass units of oxygen and is converted into 0.7 mass units of product gas saturated with water at ambient condition, 0.28 mass units of wastewater, and 0.22 mass units of slag. In the S. Charleston, WV demonstration plant a small amount of natural gas is injected with the oxygen into the slagging zone to provide preheating of the entering oxygen prior to contacting the molten slag pool. In a commercial installation this heat input would be provided by recycle of a portion of the product gas stream. Figure 2 presents an energy balance for the generalized process described above. Over 70% of the entering energy is converted into product gas. The product gas is a medium-Btu fuel with its major constituents being CO, CO2 and CH4 having a heating value of 350 Btu/S f t . A natural extension of the solid waste processing capability of the PUROX System was the use of dewatered sewage sludge cake as a feed material in combination with municipal refuse. This combined processing scheme has the potential advantage of 3

0-8412-0434-9/78/47-076-063$06.25/0 This chapter not subject to U.S. copyright. Published 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

WASTES

AND

RESIDUES

6

J

ο PC

a.

> UJ ΰ Μ Ι / 1 Σ LU Ζ)

u

IL

(Λ LI U

< α α

h -

ο .

Η

·

~

«

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 2. Typical PUROX System energy balance In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

66

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disposing of sludge and refuse with a net production rather than the net consumption of energy in conventional incineration techniques. Also, the positive environmental features of slagging the inorganic residues in a non-leaching, glassy matrix suggests a major environmental improvement in thermal processing techniques for sludge disposal. Following some preliminary analysis and pilot scale testing of the concept of sludge/refuse codisposal in the PUROX System, Union Carbide Corporation proposed through the Sanitary Board of the City of South Charleston, WV, to the U . S . Environmental Protection Agency that a large scale testing program be conducted utilizing the PUROX System demonstration plant in South Charleston. The EPA approved the proposed program and construction work began in the fall of 1976. Construction was completed in February of 1977 with the test program starting in mid April. The testing was conducte discussion of the test program and its results is presented below. Figure 3 presents an isometric view of the South Charleston PUROX System facility arranged for codisposal of sludge and refuse. Major pieces of processing equipment are described in the legend on the figure. The front end system consisting of the refuse storage building, the vertical-shaft, hammermill-shredder, and the drum magnetic separator was expanded to provide a dewateredsludge-cake processing capability by the following additions. Dewatered sludge cake from the wastewater treatment plant was delivered in dump trucks and stored in a sludge inventory area for subsequent use. Sludge cake was periodically loaded into a livebottom metering hopper from which it was steadily metered into the shredded refuse stream going to the converter. The mixture of sludge cake and refuse was fed into the converter where it underwent the drying, pyrolysis, combustion, and slagging steps to convert it into product gas, slag, and wastewater. The inorganic residues (slag) left the converter as a continuous molten stream which was quenched in a water tank and discharged into a storage dumpster. The products of the drying, pyrolysis and combustion reactions passed overhead through the gas cleaning system which consisted of a scrubber tower, electrostatic precipitator, and condenser. Wastewater was collected from the scrubbing and condensing operations. The product gas was continuously flared in a combustor. Figures 4 and 5 provide additional views of the actual sludge handling operation showing the sludge filter cake in the storage area being placed in the metering hopper for discharge onto the belt conveyor.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Figure 3. PUROX System facility for sludge/refuse codisposal in South Charleston, West Virginia.

PUROX System: (1) PUROX System leveling conveyor; (2) PUROX System pelletizing feeder; (3) PUROX System converter; (4) PUROX System slag quench system: (a) PUROX System slag quench tank, (b) PUROX System slag conveyor; (5) PUROX System scrubber; (6) PUROX System gas liquid separator; (7) PUROX System electrostati precipitator; (8) PUROX System condenser; (9) PUROX System combustor; (10) PUROX System solid liquid separation system: (a) PUROX Systemfiltratetank, (b) PUROX System vacuum filter, (c) PUROX System vacuum pumps, (d) PUROX System vacuum receivers; (11) PUROX System char conveyors. Front End (not PUROX System): (A) refuse storage building; (B) refuse weigh bridge and load ramp; (C) refuse feeder pit a shredder feed conveyor; (D) shredder; (E) shredder discharge conveyor; (F) magneti separator; (G) magnetic material conveyor; (H) sludge metering hopper with augers (I) sludge feed conveyors.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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68

Figure 4.

Figure 5.

WASTES

AND

Sludge cake at dumping station

Front loader scooping sludge cake

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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69

Codisposal Test Program Two types of dewatered sludge cake were selected for testing in this program. Raw primary sludge cake with a nominal moisture content of 25% solids, a volatiles content of'V 45% and a heating value of 5000 Btu per lb of dry solids, was available in sufficient quantity from the wastewater treatment plant at the City of Huntington, WV. Raw mixed sludge cake was not readily available in the South Charleston environs. It was necessary to go to the Alleghany County Sanitary Authority Waste Treatment Plant in Pittsburgh, PA to obtain a sufficient supply of dewatered, raw mixed sludge. This sludge was a mixture of 60% raw primary and 40% secondary which had been dewatered to^20% solids. The mixed sludge had a volatiles content of^60%, and a heating value of 6500 Btu per lb of dry solids. These two types of refuse from the S. Charleston area. The refuse was typical mixed municipal refuse with a moisture content of 25-35%, a dry inert content of v25%, and a heating value of 5000 Btu/lb. As noted above, the refuse was shredded and magnetic separation of the ferrous components was carried out prior to combination with the sludge. The test program consisted of a series of seven tests during which comprehensive sampling and analysis of the process streams entering and exiting the system were conducted. Test A was a baseline operating condition using refuse-only which was con­ ducted to provide a reference point for comparison of results from the codisposal tests. The converter operating rate averaged 81 tons per day for this test. Test Β was a combination of primary sludge and refuse in a sludge-dry-solids (SDS) to as-received refuse (ARR) ratio of 0.016. The plant was operated at an average rate of 61 tons per day (TPD) of refuse and 3.7 TPD of 26% solids primary sludge for a total operating rate of 64.7 TPD. Test C was conducted using primary sludge at an SDS/ARR ratio of 0.021. The plant operated at an average rate of 85 TPD of asreceived refuse and 5.6 TPD of 32.4% solids primary sludge for a total operating rate of 90.6 TPD. Test D was conducted using primary sludge at an SDS/ARR ratio of 0.027. The plant operated at an average rate of 83 TPD of refuse and 8.1 TPD of 27.5% solids sludge for a total operating rate of 91.1 TPD. Test Ε was conducted using primary sludge at an SDS/ARRratio of 0.052. The plant operated at an average rate of 95 TPD of refuse and 22.2 TPD of 22.3% solids sludge for a total operating rate of 117.2 TPD. /

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

70

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Test F was a combination of mixed secondary sludge and refuse with an SDS/ARR ratio of 0.027. The plant operated at an average rate of 86 TPD of refuse and 11.6 TPD of 20.3% solids mixed sludge for a total operating rate of 97.6 TPD. Test G was conducted using raw mixed sludge at an SDS/ARR ratio of 0.031. The plant operated at an average rate of 67.3 TPD of refuse and 10 TPD of 21% solids mixed sludge for a total operating rate of 77.3 TPD. Table I presents a summary of the test conditions described above. Summary tables of the mass flows, energy flows, product gas and slag analyses for each of these tests are presented in Tables II - V. As can be noted from the tables, there was no major departure from the baseline refuse-only results in the quantities reported. The slight variations that do appear are in part the result of changes in refuse composition that occur in a ramdomly varying fashion. Mechanical problem late recycle system throughout the test program. This resulted in an inability to recycle particulate from the electrostatic precipitator and scrubber to the converter and the loss of representative wastewater samples due to the use of substantial amounts of makeup water in the scrubbing system. During subsequent plant operation with refuse-only, stable operation of the particulate recycle system was achieved. A model was developed for projecting the codisposal data to the performance obtained during particulate recycle. The projected results for refuse-only (Test A) were in good agreement with the experimental data from the particulate recycle period which gave the projection model results for the codisposal period a measure of credibility. The mass flows in Table II are presented on a per-unit-offeed basis to aid in illustrating the general similarity of the codisposal results with those obtained for refuse only. The energy flows in Table III are based on the total quantity of energy leaving the system since it was not possible to obtain reliable measurements of the energy in the input refuse stream. The mass and energy flows were also adjusted to the recycle case where particulate is returned to the converter. In examining these results, test G appears to be the only period that differs significantly from the refuse-only and other codisposal results for key parameters such as oxygen usage and conversion to product gas. These differences are the result of mechanical problems encountered using the existing feeding equipment to blend the sludge and refuse. Improper blending produced a variable porosity condition in the converter bed which permitted a high heat loss condition to develop resulting in elevated oxygen consumption and heat loss factor while

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

78.0 (86.0) 61.0 (67.3)

20.25 21.01

P/MS

P/MS

F

G

-

86.2 (95.0)

22.32

H/RP

Ε

P/MS

75.3 (83.0)

27.47

H/RP

D

-

77.1 (85.0)

32.38

H/RP

C

H/RP

55.3 (61.0)

26.23

H/RP

Β

9.1 (10.0)

10.5 (11.6)

20. 1 (22.2)

7.4 (8.1)

5.1 (5.6)

3.4 (3.7)

-

0.098

0.066

0.061

-

70. 1 (77.3)

88.5 (97.6)

0.149

0.135

106.3 (117.2) 0.234

82.7 (91.1)

82.2 (90.6)

58.7 (64.7)

73.5 (81.)

0.031

0.027

0.052

0.027

0.021

0.016

-

Sludge/Refuse Wet SDS/ARR

Secondary sludge from Pittsburgh, Pennsylvania mixed with primary sludge in approximate ratio of 60% raw primary, 40% secondary

Raw primary sludge from Huntington, West Virginia

73.5 (81.0)

-

-

A

Feed Rate Mg/d (ton/d) Refuse Sludge (Wet) Total

Sludge % Solids

Source/Type

Test #

TABLE I. SLUDGE CODISPOSAL TEST SERIES

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.0 0.016 0.205 1.221 0.051 0.571 0.258 0.341 1.221

1.0 0.029 0.241 1.270 0.043 0.645 0.176 0.406 1.270

1.0

0.023

0.236

1.259

0.084

0.605

0.242

0.328

1.259

Refuse-Sludge Feed

Fuel Gas

Oxygen

Total In

Metal

Product Gas

Wastewater

Total Out

Slag

Ç

Β

A

1.237

0.325

0.248

0.614

0.050

1.237

0.223

0.014

1.0

p

1.237

0.423

0.191

0.586

0.039

1.239

0.223

0.016

1.0

Ε F

1.237

0.405

0.213

0.576

0.043

1.237

0.217

0.020

1.0

TABLE II. PROJECTED MASS FLOW (PER UNIT OF TOTAL FEED)

1.295

0.450

0.193

0.616

0.036

1.295

0.277

0.018

1.0

G

C/î

Θ

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

**

*

100%

100%

100%

100%

15.0

6.5

3.7

74.8

100%

100%

18.2

6.7

6.0 15.4

3.9

71.2 4.2

74.3

Exiting streams are given as a % of total energy leaving.

Since it was not possible to obtain representative measures of the input energy streams, the output energy flows were measured.

100%

13.7%

Heat Losses

13.4

5.2

5.9

4.7%

Wastewater 14.5

5.0

5.2

3.2

4.1

Slag

16.1

4.8

75.1

74.8

76.8

D

77.0%

Product Gas

Β

(Referenced to 60 deg. F)

PROJECTED ENERGY FLOW* BASED ON TOTAL ENERGY EXITING THE PROCESS

Exiting Streams**

TABLE III.

74

SOLID

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TABLE IV. SUMMARY OF PRODUCT GAS ANALYSES Mole Percents Test A Test Β Test C Test D Test Ε Test F Test G Vol. % Vol. % Vol. % Vol. % Vol. % Vol. % Vol. %

Com­ ponent H

2

CO

C

° 2

CH. 4 C

2

H

2

C

2

H

4

C

2

H

6

C

3

H

6

C

3

H

8

°4* C

5

+

C

6

H

6

HHC*

H

2

S

CH^OH

°2

Ar

28.14

29.64

31.25

29.62

26.81

25.30

30.32

37.28

33.74

36.24

36.80

34.19

36.72

31.56

23.07

25.58

23.52

23.85

26.85

25.01

28.86

6.21

5.89

4.46

5.02

6.12

6.48

4.82

0.46

0.52

0.25

0.41

0.72

0.60

0.48

1.90

1.91

1.32

1.68

2.19

2.26

0.68

0.44

0.34

0.33

0.32

0.40

0.46

0.23

0.32

0.27

0.27

0.23

0.28

0.39

0.20

0.23

0.12

0.25

0.18

0.19

0.21

0.02

0.40

0.28

0.47

0.34

0.40

0.44

0.23

0.29

0.22

0.35

0.27

0.36

0.31

0.17

0.24

0.26

0.17

0.25

0.34

0.26

0.22

0.26

0.17

0.32

0.29

0.37

0.23

0.12

0.02

0.02

0.00

0.04

0.03

0.02

0.01

0.11

0.04

0.14

0.08

0.09

0.11

0.12

0.03

0.04

0.05

0.03

0.04

0.26

0.24

0.59

0.61

0.62

0.59

0.63

0.95

0.74

* C4 is a composite of butanes, butènes, butadiene, vinyl acetylene and diacetylene + C5 is a composite of pentanes, pentenes, isoprene, and cyclopenetadiene + HHC are higher hydrocarbons C6 and above excluding benzene

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Co-Disposal of Sludge and Refuse

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TABLE V .

75

S U M M A R Y O F S L A G ANALYSES

Major Test Components A

Test Β

Test C

Test D

Test Ε

Test F

Test G

1.8

0.8

1.0

0.8

0.4

0.9

0.2

61.5

56.1

60.0

59.8

56.8

66.5

64.0

AT 0 2 3 C Ο a FeO MgO

11.6

9.7

10.0

11.9

9.3

10.5

11.0

9.8

8.5

12.0

10.5

11.3

9.9

12.1

8.0

14.6

8.1

8.1

8.3

6.3

6.7

0.9

1.9

1.9

0.9

1.0

1.6

1.2

ΡΟ 2 5 BaO

0.6

0.

0.1

0.1

0.2

0.2

0.2

0.1

0.1

MnO

0.2

0.3

0.2

0.1

0.2

0.2

0.3

Cr O 2 3 TiO,

0.5

0.5

0.05

0.1

0.5

0.5

0.05

0.7

0.6

0.51

0.52

0.6

0.6

0.56

0.05

0.05

0.3

0.2

0.1

0.05

0.05

93.72

90.4

97.95

96.86

C (wt. %) SiO Λ

n

N i

o

95.75 93.55 95.16

Trace Components Cd (ppm)

5

5

10

10

5

5

6

Cr

342 0

342 0

891

645

3420

342 0

363

Cu

4000

3400 4300

4000

3300

2860

3800

48800

53000

0.05

0.01

Fe

61970 113100 55000

53000 64300

Hg

0.03

0.02

0.010.01

0.15

Mn

1600

1300 1200

1700

1400

1140

1400

Ni

305

959 2700

1300

1500

150

145

Pb

94

75

119

119

243

120

128

Zn

309

404

455

482

1100

350

456

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

76

SOLID

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A N D RESIDUES

depressing overall conversion to useful fuel gas. This condition was corrected as noted in the results for Test F in which similar operating rates with similar sludge were used. Careful control of the sludge-refuse blending conditions in Test F resulted in normal performance. The environmental effects of the codisposal process were the key measurements to be made during these tests. The process product streams - product gas, wastewater, and slag were carefully monitored. In addition to the overall composition of the product gas reported earlier, sampling and analysis of the particulate remaining in the product gas after cleaning were conducted. Isokinetic samples of the product gas were collected, and the particulate obtained was thoroughly analyzed for key trace metal contaminants. Since the exiting gas leaves the system at/^100 deg. F, it seemed likely that any significant amounts of trace metal vapor would be presen particulate. Table VI presents a summary of the product gas particulate levels It should be noted that these levels are for gas prior to combustion. Since the particulate regulation is based on combustion products at standard conditions with 12% CO2/ these numbers must be converted. Table VII presents the calculated particulate levels in product gas combustion products converted to 12% CO2. All the levels reported are well below the regulated value of 0.08 grains per standard cubic foot at 12% (Χ>2· Table VEII reports the average trace metal levels found in the particulate material during the codisposal test period. Levels are reported on a combustion product basis for both the refuse-only and codisposal operation. The apparent improvement in trace metal levels of the codisposal period relative to the refuse-only period is misleading. At the time the refuse-only data were collected, the electrostatic precipitator in the gas cleaning system was operating unreliably which resulted in non-optimum gas cleaning performance. In general the trace metal levels during refuse-only operation should be very comparable to those observed during codisposal tests. A comparison of these combustion product levels is also made with time-weighted-average (TWA) threshold-level-values (TLV) proposed by the American Conference of Industrial Governmental Hygienists. In the absence of more complete emission regulations, these work­ place regulations, although not specifically applicable, give an indication of regulated levels for these materials.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

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77

Co-Disposal of Sludge and Refuse

TABLE VI. PRODUCT GAS PARTICULATE LEVELS Test Period

Type Feed

g/Nm

3

Particulate Loading gr/Sft

A

Refuse

0.0176

0.007

Β

Refuse + Primary Sludge

0.0223

0.009

Refuse + Primary Sludge

3

No samples taken

Refuse + Primary Sludg Refuse + Primary Sludge

0.0449

0.018

Refuse + Mixed Sludge

0.0201

0.008

Refuse + Mixed Sludge

0.0188

0.008

TABLE VII. CALCULATED PARTICULATE LEVELS IN PUROX SYSTEM GAS COMBUSTION PRODUCTS AT 12 PERCENT C 0 * 2

Test Period

Particulate Level gr/Sft g/Nm

A (Refuse) Β (Primary) C (Primary) D (Primary) Ε (Primary) F (Mixed) G (Mixed)

0.0031 0.0034

3

3

0.0013 0.0014

-

-

0.0056 0.0063 0.0029 0.0031

0.0023 0.0026 0.0012 0.0013

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

78

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RESIDUES

TABLE VIII. TRACE METAL CONCENTRATIONS IN PRODUCT GAS COMBUSTION PRODUCTS Combustion Product Concentration (mg/m , dry @ 12% CO J * Metal

Refuse + Sludge

Refuse +

Cd Cr Cu Fe Hg Mn Ni Pb Zn

+

(^L/5% sludge (ds)/refuse)+

0.0022 mg/m

3

0.0090 0.079 1.62 0.0084 0.012 0.058 0.038 0.047

3

TLV-TWA # (mg/m ) 3

0.05 mg/m

3

0.0001 mg/m 0.0007 0.0097 0.03 0.0004

0.5 0.2 5 0.05 5

0.009

5

below detection limit

* Computed from metal content in isokinetically collected particulate in the product gas. + Refuse-only with particulate recycle and non-optimum gas cleaning. Φ Based on average of measurements using primary and mixed sludges with more optimum gas cleaning performance. #(4) ACGIH, National Safety News, pp. 83-93, September 1977.

TABLE IX. PUROX SYSTEM WASTEWATER TREATABILITY DATA Wastewater Analysis

Reactor Operating Conditions

1321 ppm

BODs/da^ MLVSS t , days

1.18

Τ COD

3078 ppm

MLVSS, ppm

1684

S COD

3012 ppm

So (TBOD ), ppm

1350

2.28

Se (SBOD ), ppm

59

5

1350 ppm

5

TBOD SBOD

COD/BO D

5

'

d

5

5

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

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Co-Disposal of Sludge and Refuse

79

The wastewater production is obviously strongly affected by the moisture content of the feed material. The strength of the wastewater is related to the quantity produced. In general it has been found that the wastewater can be readily treated to a level sufficient for discharge into a municipal sewer system. A 95% reduction in biological oxygen demand can be achieved by diluting at a ratio of 20 to 1 with municipal sewage to provide nutrients and control for the biological process. Table IX summarizes the wastewater treatability data. Table X presents a summary of trace metal concentrations measured in the wastewater during operation of the particulate recycle system with refuse-only. Pretreatment requirements that are also given in the table are an estimate of the current status of regulations that are now being formulated. As can be seen from the table, the raw wastewater exceeds some of the projected standards. However problem can be obtained The small amount of precipitate could then be disposed of in an environmentally acceptable fashion. TABLE X. WASTEWATER METAL CONCENTRATION FROM REFUSE ONLY OPERATION WITH PARTICULATE RECYCLE Metal Cd Cr Cu Fe Pb Mn Ni Zn Hg

Raw Wastewater 0.22 ppm <0.07 0.12 39.9 43.0 19.9 0.11 83.7 < 0.02

Wastewater and Precipitation* 0.07 ppm < 0.04 <0.04 0.04 < 0.05 1.0 < 0.04 < 0.03 < 0.003

Pretreatment Requirement 0.1 ppm 1.0 0.5 20.0 0.5 1.0 5.0 5.0 0.02

* These values are essentially the detection limits for these metals where a < sign is used. Based on solubility calculation for hydroxides at pH 10. The trace metal content of the slag was reported in the earlier summary tables. The slag analysis do not reflect significant differences for the major constituents. The trace components, particularly zinc and lead, show an increase with increasing proportion of sludge. To evaluate the leaching potential of the

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

<: î . o < 1.0 < 1.0 < 0.1

< 0.1 < 0.05 0.5 < 0.1 < 0.1 < 1.0 <0.1

< 1.0 < 1.0 < 1.0 < 0.1

< 0.1 < 0.05 0.4 < 0.1 < 0.1 < 0.1 < 1.0 < 0.1

0.10 0.03 0.02 X 0.04

< 0.04 < 0.003 0.05 < 0.05 0.04 < 0.04 < 0.03 0.1

< 1.0
0.1 τ 0.1 <: 0.1

<·ο.ι * 1.0 <0.1

0.09

<0.03 0.02

^ 0.04

* 0.04

CO.003 0.04

< 0.05 0.05 0.05

<: 0.03 0.1

< 0.03

^ 0.03

0.02

< 0.04

<0.04


0.18

< 0.05

<0.02

<0.04

<0.03

0.1

Ba

Be

Cd

Cr

Cu

Hg

Fe

Pb

Mn

Ni

Zn

Ag

< 0.1

< 0.1

< 0.1

< 0.1

<. 0.1

< 0.1

As <

1.0

1.0

0.6

2.0

0.7

0.2

Ρ

<0.1

4.0

3.0

4.0

4.0

- ppm

4.0

- ppm

7.9

Test G

18.0

0.08 ppm

- ppm

0.06 ppm

0.07 ppm

F

7.7

Test F

Cl

7.9

Test Ε

-

Test D

7.8

Test Β

7.7

Test A

PH

Analysis

TABLE XI. SLAG LEACHATE ANALYSIS

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slag, a simple test procedure was devised in the absence of a standard method for such a test. A 375 gram representative slag sample was placed in a beaker with 1500 ml of distilled water. The beaker was gently agitated for at least 48 hours. The water was then analyzed for trace metals. Table XI summarizes the results of these analyses. An essentially negligible amount of material has leached from the slag. Table XII gives an overall summary of the disposition of trace metals in the three process effluent streams during refuse-only operation with particulate recycle. Hg, Cd, Zn and Pb show more volatility than the bulk of the metals; however, over 75% of these four end up in the slag. Except for mercury, over 99% of these metals are captured in the slag or wastewater. As the particulate loadings presented earlier indicate, the amounts that escape in the product gas are exceptionally low. Even Hg, which has the highest percentage loss, is in absolut below the regulated level cited in Reference (4). TABLE XII. TRACE METAL DISPOSITION IN PROCESS EFFLUENT STREAMS

Metal Cd Cr Cu Fe Pb Mn Ni Zn Hg

Percent of Total Metal Emitted in Product Gas Before Combustion 0.50 percent 0.05 0.04 0.05 0.30 -

0.60 0.80 15.0

Percent of Total Metal Emitted in Slag 96.4 percent 99.92 99.95 99.85 77.60 99.20 99.30 88.70 82.50

Percent of Total Metal Emitted In Wastewater* 3.10 percent 0.03 0.01 0.10 22.10 0.80 0.10 10.50 2.50

* Trace metals would be precipitated prior to wastewater treatment. The mechanism of capture of volatile metals in the slag as indicated in the data here is believed to be related to the formation of relatively stable inorganic salts which become phsico-chemically bonded within the silicate matrix of the slag. The high removal of mercury in the slag is especially impressive because this represents permanent removal from the environment.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

82

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Projected Economics of the Codisposal Process The economics of codisposal of sewage sludge and refuse in the PUROX System are strongly dependent upon the allowable cost of refuse disposal. If a relatively high tipping fee ($15/ton) can be charged for refuse disposal, then an attractive net sludge disposal cost can be developed. However, if low cost ($5/ton) refuse disposal alternatives are available, then the net sludge disposal cost will appear less attractive since a relatively small quantity of sludge must carry a larger portion of the total system cost. Processing alternatives can also have a substantial effect upon sludge disposal costs. The degree of dewatering strongly affects the size and cost of equipment required to handle a given amount of sludge dry solids. Since the process is a capitalintensive operation, improve mixing the sludge with refuse can generally result in reduced total capital cost. Four cases have been developed to examine these effects. Case A is based on thickened sludge at 3% solids dewatered to 20 percent solids and delivery of the 20 percent sludge cake to the PUROX facility. Case Β is based on 3% solids sludge dewatered to 25 percent solids and delivery of the sludge cake to the PUROX facility. For these cases, the PUROX facility is operated in a similar manner to the test program in which separately dewatered sludge is fed to the converter along with municipal refuse. Economics and practical considerations favor removing as much moisture as is reasonable in a combination of dewatering and drying steps before introduction of the sludge with refuse into the PUROX converter. This minimizes use of the PUROX converter and gas cleaning capacity for processing moisture. It maximizes the use of the PUROX System capacity for the critical task of producing energy and disposing of the sludge solids. Cases C and D are included in the projections of sludge disposal costs to reflect improvements in the codisposal process compared to that which was practiced at South Charleston. Case C is based on delivery of 3 percent sludge solids to the PUROX facility. At the facility, the 3 percent sludge solids would be combined with the PUROX System scrubber slurry and jointly dewatered to 35 percent solids with a belt filter press. The scrubber slurry contains particulate, pro­ duced from the pyrolysis of refuse and sludge, which enhances the dewatering characteristics of sludge. Bench scale evaluations of the dewaterability of the particulate and sludge mixture have shown significantly reduced polymer requirements from that of separate sludge dewatering and substantially higher cake solids following the filtering process.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

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Co-Disposal of Sludge and Refuse

83

Case D is based on codewatering of 3% solids sludge and particulate to 35 percent combined solids as in Case C and drying the 35 percent cake solids in a separate dryer to approximately 70 percent solids. In Cases C and D the particulate/sludge mixture, after dewatering (and drying in Case D), is fed into the converter together with municipal refuse. To properly compare these cases, all costs associated with dewatering from 3 percent solids and ultimately disposing of the sludge have been included. Dewatering costs associated with separate dewatering were taken from published literature as $55 to $66 per dry Mg ($50 to $60 per dry ton) for dewatering from 3 percent to 25 percent solids (5). Figures 6 and 7 illustrate the effect of refuse tipping fee and extent of dewatering upon sludge disposal costs at the national per capita sludge-to-refuse ratio of 0.05. Sludge disposal costs range from several hundre to a potential net credit for very large plants with drying and a $15/ton refuse tip fee. The situation specific nature of the system economics is readily apparent from these curves. Many municipalities may require higher sludge-to-refuse ratios than the national per capita due to the diversified nature of the refuse supply and the centralized wastewater treatment plant. To examine this case, economics for a Case D type system with codewatering and drying of sludge at a sludge to refuse ratio of 0.3 have been prepared in Table XIII. The plant would have a nameplate capacity of ^2000 tons per day of sludge/refuse mixture at the specified ratio. Capital equipment costs, amortization of capital, annual operating costs and revenues are presented to develop a net sludge disposal cost for processing 400 tons per day of sludge dry solids. The resultant sludge disposal cost of $40/ton of dry sludge is only meant to be illustrative. It is based on a budgetary economic projection. Site and project-specific costs such as: financing costs, capital escalation, interest during construction, land cost, insurance cost, consulting fees and miscellaneous legal fees are not included. In conclusion, individual site requirements will strongly affect project economics. At very low dry sludge-to-refuse ratios, refuse disposal economics (the available refuse tipping fee) will control rather than sludge related costs. If a refuse-only facility can be economically supported then, sludge at the national per capita ratio of sludge-to-refuse can be processed in the facility with very attractive disposal costs. If refuse only operation does not appear viable, then the relatively small amount of sludge processed

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 6.

Estimated net sludge disposal cost with tip fee of $15/ton of refuse: 0.05 dry sludge to refuse ratio; $15.00/ton of refuse

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I

CO

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1

0

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In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 7.

Estimated net sludge disposal cost with tip fee of $5/ton of refuse: 0.05 dry sludge to refuse ratio; $5.00/ton of refuse

88

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1

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86

SOLID

TABLE XIII.

Design Capacity

WASTES

A N D RESIDUES

ESTIMATED ECONOMICS PUROX SYSTEM CODISPOSAL FACILITY =

400 tons per day of sludge dry solids 0.3 sludge dry solids/refuse

Capital Costs (in thousands of 1977 dollars) PUROX System, Oxygen Plant, Wastewater Pretreatment System Front End System Site Facilities Buildings and Site Improvements Codewatering and Drying Equipment

$ 57,000 15,000 13,000 4,000 22,000

Total

$111,000

Annual Operating Costs (in thousands of 1977 dollars) Facility Operation and Maintenance Facility Power @ $0.03/KWH and Production Materials Levelized Amortization of Capital @ 7% for 20 years

$

6,370

Total

$ 24,200

7,330 10,500

Annual Revenues (in thousands of 1977 dollars) Refuse Disposal @ $15/ton of as-Received Fuel Gas @ $2.35/million Btu Ferrous Metal @ $40/ton

$

Total

$ 18,340

Net Sludge Disposal Cost (in 1977 dollars)

7,870 9,000 1,470

$40/ton of dry sludge

cannot appreciably alter the economics without developing unreasonable sludge disposal fees. At higher sludge to refuse ratios the sludge disposal fee carries a larger portion of the total project cost thus presenting potentially more favorable economics.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

MOSES

E T

AL.

Co-Disposal of Sludge and Refuse

87

ABSTRACT CODISPOSAL OF SLUDGE AND REFUSE IN A PUROX CONVERTER Combinations of dewatered sewage sludge and shredded, magnetically separated municipal refuse were processed in the slagging, oxidative pyrolysis process incorporated in Union Carbide's PUROX System. Both raw primary sludge at a solids content of ^25% and mixtures of primary and secondary sludge at a solids content of ^v20% were tested. Sludge dry solids-to-as received refuse ratios varied from 0.016 to 0.052 in the program. The general conclusion of the testing was that codisposal in this fashion does not produce any significant changes from operation experienced with refuse only. The environmental effects of this process are of particula significant improvement in the handling of heavy metals from sludge disposal. Economics of this process are very situation specific and are strongly tied to refuse disposal costs. LITERATURE CITED 1.

Anderson, J. E . , "The Oxygen Refuse Converter", Proceedings of the 1974 National AS ME Converence, Incinerator Division, pg. 337, April 1974.

2.

Fisher, T. F . , Kasbohm, M . L., and Rivero, J. R., A . I . C h . E . 80th National Meeting, September 1975.

3.

Moses, C . T., and Rivero, J. R., "Design and Operation of the PUROX System Demonstration Plant" , Fifth National Congress on Waste Management Technology and Resource Recovery, Dallas, Texas, December 1976.

4.

ACGIH, National Safety News, pp 83-93, September 1977.

5.

Van Note, R. H., et al, "A Guide to the Selection of Cost Effective Wastewater Treatment Systems," EPA-430/9-75002, July 1975.

MARCH 31,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5

T h e Caloricon Process for Gasification of Solid Wastes

HARALD F. FUNK

1

68 Elm Street, Murray Hill,NJ07974

Solid waste managemen burning and uncontrolled l a n d f i l l s are now being banned in most areas. Even incinerators which are not equipped with adequate pollution control devices have been or are going to be shut down. The new approach i s to recover usable portions of s o l i d waste such as metals, glass and even paper while the remainder goes to l a n d f i l l s or i s burned in modern incinerators which may be furnished with moving grates, water walls for steam generation, e l e c t r i c precipitators, secondary combustion chambers, scrubbers and high stacks. Unfortunately most of the incinerator models are not geared to process industrial waste because of the higher heating value of such materials or the pollution problems resulting from the combustion. Saarberg Fernwaerme, a division of Saarbergwerke A.G. in Saarbruecken, Germany owns and operates several incinerators, which y i e l d steam for either d i s t r i c t heating or power generation. Since they are aware of the shortcomings of incinerators they wanted to build a p i l o t plant for waste gasification as an improvement. The West-German Federal Ministry of Research and Technology decided to carry 60% of this 5 m i l l i o n dollar project for reasons of energy conservation and pollution control. A p i l o t plant was b u i l t for an intake capacity of one ton per hour of s o l i d waste, which by now has been in operation for more than 2 months. The technical f e a s i b i l i t y has been established and now the design criteria have to be studied. This system consists of the following stages of operation as can be seen in F i g . 1. Sorting of metals and glass, Size reduction to maximum lump size of 2", Gasification in a shaft furnace applying an autothermic process combined with a carburetting effect by recycling Current Address: A-5084 Grossgmain, 44, Austria 0-8412-0434-9/78/47-076-088$05.00/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5.

FUNK

The

89

Caloricon Process

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The Caloricon Process (U.S. Patent No. 3,970,524)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

90

SOLID WASTES AND RESIDUES

t a r s and o i l s , Condensation s e c t i o n to separate t a r s , o i l s and condensate and compress the cooled gas, P u r i f i c a t i o n s e c t i o n applying a cryogenic technique to physically retain impurities, N e u t r a l i z a t i o n to a n n i h i l a t e undesirable components by chemical treatment. A U.S. Patent No. 3,970,524 has been granted f o r t h i s type of process. U t i l i z a t i o n of the clean gas, This closed system i s designed to y i e l d a gas of r e l a t i v e l y high heating value. In comparison w i t h an i n c i n e r a t o r which sends 200,000 SCF of stack gas per ton of s o l i d waste to a scrubber using a minimum of 120 G a l . of water f o r the p u r i f i c a t i o n , the C a l o r i c o n Process counts on an output of 20,000 SCF of gas at a lower heating value of 475 BTU/SCF, w h i l e only 4,000 to 6,000 SCF of i m p u r i t i e s are discharged to a neutralization unit. g a s i f i c a t i o n p l a n t processe stack gas discharged from an i n c i n e r a t o r . This i s one reason why a cryogenic method was adopted f o r gas p u r i f i c a t i o n . The other reason was to a l l o w f o r a synthesis gas prepa r a t i o n combined w i t h t h i s p u r i f i c a t i o n system. Then carbon monoxide and hydrogen can be fed to a methanol synthesis p l a n t which provides an i d e a l use of the gas. A s h a f t furnace has been chosen f o r t h i s autothermic process i n i t i a t e d by a p a r t i a l o x i d a t i o n of the s o l i d waste. The oxygen or oxygen enriched a i r i s preheated as well as the steam which has to be charged i f the m a t e r i a l i s too dry or the r e a c t i o n becomes too hot. The s o l i d waste i s charged to the top of the f u r n a c e ; i t s l i d e s down through locks which prevent the escape of gas and passes through the various zones of h e a t i n g , d r y i n g , c a r b o n i z i n g , reducing and p a r t i a l combustion. Enough oxygen i s i n j e c t e d to maintain a temperature of at l e a s t 800°C but not more than 1000°C to prevent slagging which would not o n l y a f f e c t the g r a t i n g but consumes too much of the carbon and lowers the e f f i c i e n c y of the furnace. There i s a c e r t a i n f l e x i b i l i t y i n t h i s operation s i n c e the gas c a r r i e s more methane and C2 f r a c t i o n s i f the temperature i s maintained at a lower l e v e l , w h i l e a water gas r e a c t i o n i s favored i n the higher temperature range which might be p r e f e r a b l e i f the gas i s used f o r s y n t h e s i s gas makeup. The oxygen consumption ranges from 10% to 17% per ton of s o l i d waste as charged to the r e a c t o r . Based on the f o l l o w i n g assumption of m a i n t a i n i n g an e x i t temperature of gas and s o l i d s at a maximum of 300°C and a feed of 80% municipal and 20% i n d u s t r i a l waste ( i n t h i s case rubber t i r e s ) i s charged to the r e a c t o r , the thermal e f f i c i e n c y was c a l c u l a t e d to be 81%. I f the l i g h t o i l s , however,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5.

FUNK

The

Caloricon Process

are added to recoverable heating value the e f f i c i e n c y increases to 87% of heating value charged w i t h i n s o l i d waste. Deducting the energy consumption of the process i t w i l l r e s u l t i n an o v e r a l l heat recovery of b e t t e r than 70%. The average elemental a n a l y s i s shows a composition of carbon at 56.3%, hydrogen 6.7%, oxygen 33.9%, n i t r o g e n 1.4% and s u l f u r w i t h other i m p u r i t i e s 1.7%. This m a t e r i a l i n comparison w i t h coal which contains only 4% to 5% hydrogen i s more s u i t a b l e f o r g a s i f i c a t i o n . The gas emerging from the r e a c t o r i s cooled to ambient temperature and separated from t a r , o i l and condensate. The l a t e n t heat of the vapors and steam can be u t i l i z e d f o r d i s t r i c t heating i f f a c i l i t i e s are a v a i l a b l e . In t h i s phase of the o p e r a t i o n , a l l the water i s recovered which i s charged to the r e a c t o r i n form o f moisture or steam. Then the gas i s compressed to about 30 PSIG and passed on to the p u r i f i c a t i o n s e c t i o n 3 phases: 1. The l o a d i n g phase 2. The subgas recovery phase 3. The c o o l i n g down phase In the f i r s t phase, the gas i s cooled down to at l e a s t minus 120°C i n one run. The heavier components, mainly c o n s i s t i n g of i m p u r i t i e s are r e t a i n e d i n the vessel w h i l e the pure gas passes on to an expansion t u r b i n e where i t i s cooled f u r t h e r by means of a d i a b a t i c expansion. This c o l d e r gas i s returned through the l a s t regenerator i n a r e t u r n flow thus preparing i t f o r the next phase, the l o a d i n g p e r i o d . The heavier components which were r e t a i n e d during the l o a d i n g phase are recovered by means of a vacuum at an absolute pressure of 1.5 PSIA and t h i s stream i s d i v e r t e d to the n e u t r a l i z a t i o n s e c t i o n f o r chemical treatment. The c y c l e s are s w i t c h i n g i n periods o f 6 to 8 minutes. The regenerators are very e f f i c i e n t heat exchangers and the temperature d i f f e r e n c e s between i n and outgoing streams i s kept between 2° and 3°C. This e x p l a i n s the low power consumption to compensate f o r the l o s s of r e f r i g e r a t i o n . The clean gas can be used f o r various purposes: A. Heating b o i l e r s , B. D r i v i n g a gas t u r b i n e f o r power g e n e r a t i o n , C. As a reducing gas i n m e t a l l u r g i c a l processes, D. For synthesis gas p r e p a r a t i o n to produce methanol, E. For peak shaving to convert methanol to pure methane. Methanol as such can be converted to a high octane g a s o l i n e as suggested by Mobil O i l Corporation which has d e v e l oped such a process. Methanol can be used as f u e l f o r v e h i c l e s , gas t u r b i n e s or b o i l e r s . Methanol can be the b a s i c raw m a t e r i a l f o r a chemical process i n d u s t r y i f a c e t i c a c i d or formaldehyde has to be

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

91

92

SOLID WASTES A N D RESIDUES

§ 8 A*

o

U

g

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5.

FUNK

The

Caloricon Process

produced. C i t i e s w i t h a d a i l y c o l l e c t i o n r a t e of about 5000 t o n s , f o r instance P i t t s b u r g h , Cleveland or Toronto could produce between 600 and 1000 tons per day of methanol i f a l l s o l i d waste was to be g a s i f i e d . Such a q u a n t i t y of methyl alcohol would enable a c i t y to f u e l a l l i t s own v e h i c l e s and i t could support a chemical complex. An economic e v a l u a t i o n could be made only a f t e r opera t i n g c o n d i t i o n s have been defined from the p i l o t p l a n t , but i t seems to be j u s t i f i e d to a s s e r t t h a t such a g a s i f i c a t i o n p l a n t which does not r e q u i r e moving g r a t e s , e l e c t r i c p r e c i p i t a t o r s , secondary combustion chambers, scrubbers, and a stack should not cost more than i n c i n e r a t o r s but can o f f e r a b e t t e r u t i l i z a t i o n of the gas e i t h e r f o r heating or f o r use as base product f o r chemicals, p l a s t i c s or pharmaceuticals M ARCH 31,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

6 A Vertical-Bed Pyrolysis System M . D . B O W E N and E . D . S M Y L Y T e c h - A i r Corporation, Atlanta, G A 30341 J. A . K N I G H T and K. R. P U R D Y Engineering Experiment Station, Georgia Institute of Technology, Atlanta, G A 30332

The initial work o at the Georgia Institut approximately ten years ago. At that time the disposal of agricultural wastes due to new and impending a i r pollution regulations was a serious problem and a study was i n i t i a t e d to design a small, cheap incinerator which would meet emissions regulations and be suitable for use by small and intermediate sized, agricultural businesses. An evaluation of the inherent combustion characteri s t i c s of these ligno-cellulosic wastes indicated that such an incinerator would be large and very expensive. For example, an agricultural waste l i k e peanut hulls, when heated i n anairstream w i l l first decompose emitting gases from the s o l i d particles. These gases will burn i n the gas phase i n an envelope around each particle preventing oxygen from reaching the s o l i d . This process continues u n t i l the peanut hulls have decomposed to pieces of char containing practically all of the sand imbedded i n the o r i g i n a l hulls and the other ash. The combustion of a piece of char i s limited by the diffusion of oxygen to the s o l i d surface. This results i n a significant residence time and large excess air requirements for complete burning. Further, although the gases produced during decomposition of the hulls are gases with r e l a t i v e l y low heating value, they have a low a i r to fuel ratio at stoichiometric conditions and, consequently, the flame temperatures observed are surprisingly high. I t was clear from this and other early problems that a different approach to the disposal problem should be considered. Historically, ligno-cellulosic materials have been used to produce chars f o r many different uses by means of thermal decompos i t i o n , or pyrolysis. This approach appeared to offer a number of advantages over incineration and resulted i n thinking about the waste materials more i n terms of u t i l i z a t i o n rather than d i s posal. This can significantly affect the economics of a particular case when the cost of pollution controls and fuel values are considered. Generally, pyrolysis can be considered as one very e f f i c i e n t means of increasing the options available for u t i l i z i n g 0-8412-0434-9/78/47-076-094$08.00/0 © 1978 A m e r i c a n C h e m i c a l Society

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

6.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

95

waste materials. In this case the wastes are converted into more readily useable, and environmentally more acceptable, fuels — char, gas, and o i l . The f i r s t pyrolysis unit b u i l t i n this program was a retort approximately five feet high with a single a i r tube, an e l e c t r i c starter, and a movable grate for periodic char removal. The retort was b u i l t and operated with dry agricultural wastes i n the late I960 s. Information on the process and potential products obtained from this work was used as the basis for designing and building at the Georgia Institute of Technology the f i r s t continuous p i l o t plant i n 1970. This unit was designated Blue I and i s shown i n Figure 1. Some information on the p i l o t plant work has been reported e a r l i e r by Knight and Bowen (1, 2). The p i l o t plant was designed for a short l i f e and minimum cost. The system incorporated a v e r t i c a l bed, gravity fed, counter flow pyrolysis chamber with a continuously operating char output system. The input feed system consiste front of the picture, a roto - l i f t and an input chute feeding the top of the rectangular shaped pyrolysis chamber. Two leveling screws running the width of the chamber were used to distribute the material fed i n at the chute. In this system the process was i n i t i a t e d by means of a natural gas burner and sustained by bleeding a small amount of a i r low i n the bed. The system was operated s l i g h t l y above atmospheric pressure with the off-gases being taken o f f at the top of the chamber and burned i n four f l a r e stacks shown at the rear of the picture. Blue I was operated for approximately one year at temperatures below 1600°F, on dry agricultural wastes. This plant demonstrated that the process could be operated continuously with simple means of control and, most important, that the mechanical char output system was r e l i a b l e . Information obtained on the process showed the importance of distributing the process a i r within the bed and the wide variations i n char yields which could be obtained without producing slag. The i n t e r i o r surfaces of the pyrolysis chamber were eventually damaged by overheating while operating at high temperatures. This was not surprising i n view of the i n i t i a l design c r i t e r i a and the materials of construction used i n Blue I. The results of this f i r s t p i l o t plant program were very encouraging and led to the construction i n 1971 of the second p i l o t plant, Blue I I , shown i n Figure 2. This system used some of the components from the e a r l i e r unit, but was designed for a longer l i f e with refractory walls and more instrumentation. The input system consisted of a bin, a covered belt conveyor, and a rotary a i r lock. The off-gas system was changed significantly by i n s t a l l i n g an a i r cooled condenser, an off-gas control fan, and a refractory lined, swirl chamber for combustion of the non-condensed gases. The off-gas fan permitted the pyrolysis chamber to be operated at sub-atmospheric pressure and allowed the i n s t a l l a t i o n of simple, weighted doors for pressure r e l i e f on each component i n the system. 1

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

Figure 1.

WASTES

AND

Pilot phnt—Blue I, 1970-1971

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

6.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

97

Blue II was operated for approximately four years on a wide variety of feedstocks. These included bark, sawdust, wood chips, cotton gin trash, various nutshells, automobile shredder wastes and municipal wastes. In each case, significant variations i n processing characteristics and i n the quality of the different products, char, o i l and gas were observed. In 1971, based on the technology represented by Blue I I , Tech-Air Corporation designed two f i e l d test units, each with a nominal capacity of two tons per hour. These systems were b u i l t and installed at a peanut shelling plant i n Georgia. These two units are shown i n Figure 3 while i n operation. No provision was made for char storage and handling since these were test systems. For the most part the products were either l a n d f i l l e d or burned. However, one truckload of char was sold to the b r i quette industry for evaluation purposes. The two pyrolysis units were operated for approximately one year and resulted i n a greatly improved a i r injection system better safety interloc into the scaling and material handling problems associated with this type of equipment. The successful operation of these units, although on a test and development basis, and using only dry agricultural wastes, resulted i n a decision by Tech-Air Corporation to design and build a (commercial prototype plant to process wood wastes. This decision was not surprising i n view of the fact that 160,000 tons of peanut shells are produced each year i n Georgia compared with several m i l l i o n tons of wood wastes. This design work was i n i t i a t e d i n 1972. Early i n this work i t became apparent that i n the past attention had been focused primarily on the pyrolysis unit and the material handling, the metering and the drying problems required considerable work, particularly the drying of wood wastes. TechA i r Corporation undertook the development of a coirpartmented, conveyor type dryer during this same period which could use waste heat or low temperature gases for drying. Consequently, the commercial prototype plant included the development of a completel y new piece of major equipment i n the system. This development work significantly extended the t o t a l time which otherwise would have been required for the f i r s t wood waste system. The commercial prototype plant was installed i n a small lumber m i l l i n Cordele, Georgia i n 1973 and was operated intermittently for approximately two years. During this period the dryer was developed and successfully demonstrated, the char sold to the briquette industry and work performed on burning the o i l on a demonstration basis i n several commercial applications. I t should be noted that the servicing requirements of the off-gas system were high, but acceptable, for this plant operating intermittently on a one s h i f t basis. Each morning prior to start-up the off-gas system which was cool after standing i d l e for sixteen hours could be opened and the accumulated solids and tars removed. Later, after placing the plant on a twenty-four hours per day,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

Figure 2.

Pilot plant—Blue II, 1971-1974

Figure 3.

Field test units, 1971-1972

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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BOWEN ET AL.

A Vertical-Bed Pyrolysis System

99

seven days per week basis, this servicing problem became very d i f f i c u l t and resulted i n considerable down time f o r the system. By this time pyrolysis was being considered by several companies for a variety of different materials or applications. The American Can Company through their resource recovery business unit, Americology, was involved i n processing municipal refuse through a resource recovery system. American Can Company recognized the potential value of a pyrolysis system i n this area to produce more readily acceptable fuel fractions, to reduce the volume of material, and to allow development of new char-based products. This interest resulted i n the design and construction of a t h i r d p i l o t plant, nominally rated at one ton per hour, for processing municipal refuse. This p i l o t plant was designated Blue III and i s shown i n Figure 4. Ihis system was significantly different from the e a r l i e r ones due to the differences lock was used at the top were installed i n the pyrolysis chamber, a s t i r r e r s p e c i f i c a l l y designed to level and s l i g h t l y compact the refuse was installed i n the pyrolysis chamber and the output feed system was modified to pass large chunks, or pieces, of charred material. Blue III has been i n operation since 1974 processing a wide variety of materials. Approximately fifty-nine runs have been made on municipal refuse alone. These runs included l i g h t fraction, heavy fraction(with and without metals), whole garbage, sewage sludge blended with l i g h t fraction and l i g h t fraction blended with shredded t i r e s . These runs demonstrated that the technology developed for agricultural and forestry wastes could be applied successfully to processing municipal refuse and sewage sludge. Work i n this area of application i s currently continuing, particularly i n new product development and the next step for the municipal refuse application i s a f i e l d test program for at least one year duration. In 1975 Tech-Air Corporation became a wholly owned subsidiary of The American Can Company. At that time two different efforts were i n i t i a t e d to carry forward the work of commercializing the wood waste system and to establish a continuing research and development program at the Georgia Institute of Technology to support the area of waste u t i l i z a t i o n . F i r s t , a s i x month program was carried out to upgrade and extend the capacity of the commercial prototype plant and to permit a long term, around-theclock operation. Second, a fourth, smaller p i l o t plant was constructed for further study and development of the process. This fourth p i l o t plant was designated Blue IV and i s shown i n Figure 5. The commercial prototype plant, known as the Cordele plant, i s shown i n Figure 6. The weak links i n the material handling system were i d e n t i f i e d early at the Cordele plant with around-the-clock operation. These were not major problems but they did require some beefingup of certain conveyors and the establishment of a routine

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

Figure 4.

Figure 5.

Pilot plant—Blue III, 1974-present

Pilot plant—Blue IV, 1975-present

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

Figure 6. Cordele plant, 1973-present

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

102

SOLID WASTES AND RESIDUES

servicing program. As mentioned e a r l i e r the largest problem encountered involved servicing or cleaning the off-gas system which resulted i n considerable down time for the plant. Ihis down time was d r a s t i c a l l y changed by the i n s t a l l a t i o n of a scrubbing system using a portion of the pyrolysis o i l condensed from the off-gases. This technique was f i r s t considered i n 1972 i n the prototype design but the unquestionable requirement for i t s use accompanied the around-the-clock operation of the Cordele plant. The Cordele plant was operated on a twenty-four hours per day basis for eighteen months u n t i l June of 1977. A l l the products, char and o i l , produced at Cordele were sold during this period i n the bulk char and fuel o i l markets. With this successful demonstration the value of pyrolysis i n waste u t i l i z a t i o n and resource recovery has been established. In retrospect i t was indeed fortuitous that the direction of this e f f o r t started from a disposal standpoint which required the development of less complex and less expensiv Wood Waste System Plant Description. The process flow diagram for a 7 dry tons per hour wood waste system i s shown i n Figure 7. The system receives wet waste which has been hogged. The size of the hogged feed i s not c r i t i c a l but a maximum p a r t i c l e size on one inch i s desirable. The hogged wood waste i s received i n a metering bin which supplies a metered feed rate to the dryer. The dryer operates with some of the gaseous fuel generated i n the process and pyrolysis o i l can be used as a back-up. The dryer was designed by Tech-Air Corporation and i s a compartmented, screw conveyor dryer. The i n l e t temperature to the dryer operates within the range of 400 to 600°F with a bulk exhaust temperature of 130 to 140QF. The dryer reduces the moisture content from a nominal value of 50 percent to a f i n a l value below 7 percent. The dried feed i s conveyed to the storage bin which supplies feed to the pyrolysis unit on demand and provides surge capacity. The dried feed from the storage bin i s fed through a rotary a i r lock into the pyrolysis chamber where i t i s thermally decomposed into a char and a hot gas. The char i s discharged at the bottom of the unit and the pyrolysis gases flow upward through the v e r t i c a l bed and exit at the top of the unit. The rate of char discharge controls the throughput rate and a bed height sensing device i s used to control the input to the chamber. The char i s discharged into a sealed conveyor, cooled with a water spray and fed through a rotary airlock into a char conveyor. The char i s conveyed to a storage bin from which i t i s retrieved by gravity flow for subsequent shipment. The char bin incorporates a pressure-relief deck and low pressure, self-closing, r e l i e f doors. The pyrolysis gases leave the top of the converter at a temperature ranging from 350 to 500°F and at a pressure near at-

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

DRYER FAN FINES COLLECTOR HOGGED

33,600 LB/HR @50% MOISTURE METERING BIN

(MAXIMUM) 18,000 LB/HR @ 7% MOISTURE i S j GASEOUS HT FUEL 15,000 LB/HR @ 7% MOISTURE

DRIED κκκη SURGE BIN

- 0 GASEOUS FUEL DIRTY OIL

AIR BLOWER

SCRUBBING OIL

FILTER CAKE

CHAR STORAGE BIN

â\ 0

PRODUCT MASS AND ENERGY YIELDS FOR A MIXTURE OF BARK AND SAWDUST

®

®

CHAR

OIL

CHAR y TFT.π

CASE

©

®

GASEOUS FUEL GASEOUS FUEL TO DRYER TO PROCESS (LBS/ LB DRY MASS MASS ENERGY ENERGY ENERGY MASS ENERGY MASS FEED) (LB/HR) (MMBTUH) (LB/HR) (MMBTUH) (LB/HR) '(MMBTUH) (LB/HR) (MMBTUH)

MAXIMUM CHAR

.35

MAXIMUM OIL INCREASED GAS

4900

60.2

.25

3500

.20

2800

8.3

8116

24.6

4842

16.7

7132

24.6

7118

29.3

5976

24.6

2520

22.8

2738

46.2

3150

28.7

37.8

2660

24.4

NOTE - USED AVERAGE PROCESSING RATE THROUGH DRYER OF 15,000 LB/HR

"Figure

7. Wood waste pyrolysis system—7 dry tons/hi

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

104

SOLID WASTES AND RESIDUES

mospheric. The gas stream contains non-condensible gases, o i l vapors, water vapor and entrained particulates. These gases are iitinediately sprayed with cooled pyrolysis o i l i n a scrubbercondenser which serves to remove the particulates and cool the gas stream to a temperature between 180 and 200°F. The cooling process i s controlled to condense pyrolysis o i l and l i m i t the amount of water vapor condensed. The cooled gases flow through a rotary demister which removes the small l i q u i d droplets from the gas stream. The unfiltered pyrolysis o i l from the scrubber and demister i s discharged through a rotary valve directly into a continuous f i l t e r . The f i l t e r e d o i l i s pumped to a small holding tank from which the o i l i s recirculated through a cooler back to the scrubber. As the o i l level i n the holding tank increases due to condensation, o i l i s pumped to bulk storage. The f i l t e r cake, which has a dry appearance even though i t contains about 30 percent solids, i s conveyed back to the input feed system and reinjected into the pyrolysi cake, most of the o i l i a l i g h t gas, water vapor, and char. The pyrolysis gases leaving the demister contain water vapor and some low boiling point fractions i n addition to the non-condensible gases and this mixture i s nearly saturated. Hence, i t i s desirable to u t i l i z e these gases close to the pyrolysis plant. An induced draft fan controls the pressure i n the pyrolysis chamber and directs the flow of gases through the off-gas system from the converter. A portion of the gases leaving the fan are piped to a burner supplying heat f o r drying the feed. The remainder of the gases are supplied to a burner which provides heat for a boiler or, other heat device. A f l a r e stack i s used to burn the gases during start-up or i n case of a rapid change i n gas demand. Mass and Energy. The Tech-Air pyrolysis unit can be operated to provide a variable y i e l d of char from the feed material with a corresponding variation i n the gas and o i l yields. For a given feedstock, the char y i e l d i s affected primarily by the maximum bed temperature which i s controlled by the a i r to feed r a t i o . For purposes of presentation, the distribution of energy among the three products has been correlated versus char y i e l d and i s shown i n Figure 8 for a mixture of pine bark and sawdust. These curves are based on data obtained at the Cordele plant. The Cordele plant has been operated at char yields ranging from 19.5 to 38.6 percent and the p i l o t plants have been operated at char yields from 8 to 45 percent. The heating values of the three products vary with the char y i e l d as shown i n Figure 9. The energy recovered i n the form of char continuously increases as the char y i e l d increases with a corresponding decrease i n the energy i n the gaseous f u e l . Note that a constant amount of energy i s shown to provide the

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

105

Figure 8. Energy distribution vs. char yield for product of pyrolysis from blend of pine sawdust and bark

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

BASED ON TOTAL ASH IN INPUT FEED

AT 30% MOISTURE

AIR/FEED RATIO = 0.25 LB. AIR/LB. OF DRY FEED

10

15

20

25

30

35

40

CHAR YIELD - PERCENT OF DRY FEED

Figure 9.

Higher heating value of pyrolysis products from pine bark-sawdust mixture

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

6.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

107

energy for drying the wood. The drying energy was approximately 1600 BTU per pound of water removed. The energy i n the net gaseous fuel i s that available after the drying requirement has been s a t i s f i e d . The energy recovered as pyrolysis o i l increases s l i g h t l y as the char y i e l d increases from 10 to 25 percent and then decreases. The gross energy recovery i n the form of products i s approximately 95 percent of the energy i n the dry feed. The higher heating value normally associated with a mixture of pine bark and sawdust i s 8700 BTU per pound. Note i n Figure 8 that the sum of the energies of the products at 10 percent char y i e l d i s 8000 BTU per pound of dry feed and at 35 percent char y i e l d i s 8260 BTU per pound of dry feed. The energy distribution curves shown i n Figure 8 point out the f l e x i b i l i t y of the system. The process can be controlled to maximize those products of greatest value and to match the system to on-site energ The distribution o energy g products and gas also varies with the type of feed material. Data are presented i n Table 1 for pine tree top chips, pine bark, and a mixture of pine bark and sawdust. These data are from measurements at the Cordele plant and the Blue III and Blue IV p i l o t plants. Shown are the heating values of the input feeds, mass yields and energy yields. The portion of the energy contained i n the char i s approximately the same for a l l of the feeds at the same char y i e l d . However, at a char y i e l d of approximately 20 percent, the energy recovered as pyrolysis o i l was highest for the chips and lowest for the bark and, as expected, the value for the mixture of sawdust and bark l i e s between these two. Also, the highest char y i e l d obtained to date of 45.7 percent was from bark feed. An i n i t i a l study has been performed on the ndnimum char y i e l d obtainable while operating the unit as a non-slagging, pyrolysis system. The data from t h i s study, obtained from a 72 hour Blue IV p i l o t plant run, are presented i n Table 2. The feed material used was pine chips. Two modes of operation were used. In the once-through mode the material made a single pass through the unit as i s normal. In the recirculation mode, the char output was increased to an equivalent 20 percent y i e l d and screened. The coarse particles were reinjected into the unit with the feed material and the fine char and ash passing the screen were removed. A char y i e l d of 8.2 percent was obtained i n the once-through mode. With recirculation of char, the net y i e l d (fines passing the screen) was lowered to 3.8 percent. Even at the low char yields the unit was operated as a pyrolysis system with an o i l y i e l d only s l i g h t l y below that obtained on pine tree top chips (see Table 1) at a 20 percent char y i e l d . Char recirculation simply offers another option with pyrolysis, the e f f i c i e n t conversion of the wastes to gas and o i l only. This techniques can also be used to avoid slagging conditions i n the bed and obtain low char yields when the ash i s high.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20.5 25.6 20.5

2h.k

38.2

18.9 ^5.7

5.7 5.8

l.k 7.5 13.5 12.2

8935 8935

8837 8609 8663

8912 8801

Pine Bark-Sawdust Pine Bark-Sawdust Pine Bark-Sawdust

Pine Bark Pine Bark

7.8 12.8

19.2 23.7 17.5

3^.6 31.9

116 88

103 103 111

76 71

MASS YIELD (PERCENT OF DRY FEED) PERCENT Fuel MOISTURE Gas Char Oil

P i n e Tree Top Chips Pine Tree Top Chips

MATERIAL

HIGHER HEATING VALUE (DRY) (BTU/LB.)

5738

2k22

k66k

2768 3311

2631 3^12

1235

2179 22U9 1076

3^98 317^

5250 1316

3067 2953 2222

2^70 1987

ENERGY YIELD (BTU PER LB. OF DRY FEED) Fuel Gas Oil Char

SUMMARY OF MASS AND ENERGY DATA FOR PYROLYSIS OF SEVERAL WOOD FEEDSTOCKS

TABLE 1

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

.56 • 69

.92

Once Through Once Through

Recirculation of Screened Char Into Feed

OPERATIONAL MODE

AIR INPUT (Lbs. per Lb. o f Dry Feed)

2065

1865 1885

(°F)

MAXIMUM BED TEMPERATURE

3.8

10.9 8.2

Char

30.7

25.3 32.3

Oil

MASS YIELD ( Percent o f Dry Feed)

56.8

50.7

Gas

5Λ

16.7 12.2

28.0 36.1

33.2

Char

Oil

k.6

k.6 k.6

Heat Losses

ENERGY DISTRIBUTION (Percent o f Energy i n Dry Feed)

SUMMARY OF DATA FOR MINIMUM CHAR YIELD TESTS ON PINE CHIPS

TABLE 2

110

SOLID WASTES AND RESIDUES

Municipal Refuse System Plant Description. A system to process municipal refuse i s somewhat more complex than a system for wood waste. The additional complexity results from the added d i f f i c u l t y i n the handling and preparation of municipal refuse for pyrolysis feed. In a full-scale resource recovery f a c i l i t y the refuse i s shredded and a i r c l a s s i f i e d into heavy and l i g h t fractions. The heavy fraction i s processed further for the removal of ferrous metals, aluminum, and glass. Whether or not a l l of these operations are performed depends upon the quantity of refuse to be processed and i t s compos i t i o n . P i l o t plant runs have been made on l i g h t fraction, heavy fraction, single shredded whole refuse with the metals removed and on the co-pyrolysis of l i g h t fraction with both sewage sludge and shredded t i r e s . Although not limited to t h i s , the municipal refuse system described herein i s on insufficient waste quantitie recovery f a c i l i t y . Toward this end the system i s designed to require minimum processing of the refuse as preparation for pyrolysis feed. Of course, the pyrolysis system can be e f f i c i e n t l y used for the l i g h t and heavy fractions from a complete f a c i l i t y . The process flow diagram envisioned for a system to process limited quantities of refuse i s shown i n Figure 10. The refuse i s delivered to a receiving floor, placed i n a conveyor and processed tJirough a shredder. After the shredding operation the ferrous metals are magnetically separated. The shredded refuse with ferrous removed i s then placed i n storage. From storage the feed material i s fed at a metered rate to a dryer i n which the moisture i s reduced to approximately ten percent. The dried material i s screened to remove glass and debris. The process flow diagram given i n Figure 10 includes the input of sewage sludge for co-pyrolysis with the dried refuse. This sludge addition i s an optional feature which appears feasible i f the quantity of sludge i s small relative to the quantity of refuse. Data w i l l be presented which were obtained on the Blue III P i l o t plant for the co-pyrolysis of l i g h t fraction and a larger percentage of sludge than that shown i n the figure. The mass and energy values given i n Figure 10 are based on the copyrolysis of dried refuse and sludge. I f the system i s operated as shown without the addition of the sludge the average steam output w i l l increase from 47,000 to 48,000 pounds per hour. The pyrolysis portion of the system i s very similar to the system for wood waste. There are differences i n equipment design details, materials of construction, and the conveying and handling of the refuse, but the process functions are the same. Mass and Energy. Mass and energy data for the pyrolysis of dried municipal refuse are presented i n Figures 11 and 12, respectively. The data i n these figures were obtained on the

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 10.

10.76 TPH

DUAL-FUEL BURNER

l«

DRYER

NET OIL 0.706 TPH 14.5 MMBTUH

PYROLYSIS UNIT

GLASS 0.81 TPH

SCREEN

I CHAR 2.95 TPH 23.1 MMBTUH

TOTAL HEAT LOSSES 5.2 MMBTUH

AIR 3.10 TPH

2

8.30 TPH (§13.9% H o 104.7 MMBTUH

2

SEWAGE SLUDGE (OPTIONAL) 0.463 TPH @80%HO

8.45 TPH 76.4 MMBTUH

8.65 TPH

GAS CLEAN-UP 7.74 TPH 61.9 MMBTUH

OIL STORAGE

6.68 TPH 53.5 MMBTUH

STORAGE

24 HRS/Day @ 7 DAYS/WK & 90% UPTIME

Small community municipal refuse pyrolysis system—350 tons/day

FERROUS METALS 24.5 TPD

SHREDDER & FERROUS SEPARATOR

10 HRS/DAY @5 DAYS/WK

STEAM 36,300 LB/HR MINIMUM ON FUEL GAS 10,900 LB/HR FROM NET OIL 47,200 LB/HR AVERAGE

RECEIVING FLOOR

RECEIVE 350 TONS/DAY (25% H2O)

1

Ci)

I

CO

s-

3 f

a-

V"

a

2

1

112

SOLID WASTES AND RESIDUES

PERCENT MOISTURE

7.6

LIGHT FRACTION - TUBE FURNACE DATA LIGHT FRACTION - BLUE I I I PILOT PLANT

Y///////X V//////A

DATA

WHOLE REFUSE, METALS REMOVED BLUE I I I PILOT PLANT DATA

7.6 5-3

120

PYROLYSIS OIL RECOVERED

Figure 11.

PYROLYSIS

GAS

Mass balance for dried municipal refuse

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

Figure 12. Energy balance for dried municipal refuse

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

114

SOLID WASTES AND RESIDUES

l i g h t fraction of municipal refuse and on single-shredded, dried, whole refuse with the metals removed. For the l i g h t fraction, both tube furnace data and data obtained i n the Blue III p i l o t plant are shown. For the single shredded, whole refuse with metals removed, data obtained i n Blue III are presented. In the tube furnace, e l e c t r i c a l heating i s used and the material i s pyrolyzed with no a i r input. The Blue III p i l o t plant operates on the same p a r t i a l oxidation principal as the Gordele System. The mass balance data i n Figure 11 give the y i e l d of char, the y i e l d of o i l actually condensed from the gases, and the y i e l d of gas including the non-condensed o i l . Approximately the same y i e l d of char was obtained for the l i g h t fraction i n the tube furnace and i n Blue III. Further, the y i e l d of char from the single-shredded, whole refuse was approximately the same as the y i e l d from the l i g h t fraction. The values shown for the recovered o i l show the t o t a l o i l y i e l d broken down into water and dry o i l , which i s the moisture-fre a very high moisture conten a cold-trap as opposed to the p i l o t plant operation which sought to ininimize water condensation with the o i l . The o i l from the single shredded, whole refuse contained more water than the o i l from the p i l o t plant run on l i g h t fraction because of poor control. The o i l y i e l d on a later run i n the p i l o t plant with single-shredded, whole refuse was 19.5 percent with only 11.3 percent water. The gas yields shown i n Figure 11 represent the t o t a l vapor stream after the condensation of the recovered o i l . The muffle furnace gas y i e l d was the lowest since there was no a i r input. The higher yields for the p i l o t plant runs r e f l e c t the a i r input. The energy yields are more d i f f i c u l t to define than the mass yields. For the mass balances the quantities of feed material, char, condensed pyrolysis o i l and a i r input were measured directly. Thus, the quantity of gaseous fuel could be d i r e c t l y determined by difference. From an energy standpoint the energy associated with the char and o i l could be reasonably well characterized since representative samples could be obtained. For the gaseous vapors, the non-condensible portion could be accurately determined from gas chromatograph analysis of representative samples; however, the quantity of aerosols or low-boiling point fraction were extremely d i f f i c u l t to measure accurately. Again, the energy i n this fraction can be calculated by difference i f the heating value of the input feed i s accurately known. Experience has shown that i t i s very d i f f i c u l t to accurately sample the input feed for heating value measurements. Experimental data for the higher heating value of dry municipal refuse i s plotted i n Figure 13 as a function of ash content. Note that there was a wide variation i n the ash content of the samples taken. In treating the experimental data from the p i l o t plant, the average heating value measured on samples of the input feed was adjusted to the ash content calculated from the char

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

115

is I—I

«

4000

te

2000·

LIGHT

FRACTION

LIGHT

FRACTION

WHOLE REFUSE, METALS REMOVED HEAVY

5

10

15

FRACTION

20

25

30

PERCENT TOTAL ASH IN DRY FEED

Figure 13. Higher heating value of dry municipal refuse correlated vs. total ash content

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

116

y i e l d and ash content of the char. This value was then used to calculate the energy i n the condensible fraction which remained i n the gaseous vapors. The heat losses were calculated by assuming that each pound of input a i r released 1333 BTU which was l o s t as sensible or latent heat. The energy data for l i g h t fraction and single-shredded, whole refuse with metals removed are presented i n Figure 12. The heating value f o r the dry feed was 5700 BTU per pound for the singleshredded, whole (metals removed) refuse and approximately 6900 B1U per pound for the l i g h t fraction. For the p i l o t plant run the energy was reasonably well distributed among the products for the l i g h t fraction, with values of 1750 BTU per pound of dry input for the gas, 1850 BTU per pound of dry feed for the o i l , and 2200 BTU per pound of dry input for the char. For the single-shredded, whole (metals removed) refuse the gas contained the largest fraction of the energy, 2650 BTU per pound of dry input, and the o i l contained the least, 120 subsequent run made on single-shredded removed) refuse, which was mentioned e a r l i e r , the o i l contained 11.3 percent moisture and approximately 2300 BTU per pound of dry input. Data from p i l o t plant runs i n Blue III on the co-pyrolysis of l i g h t fraction with sewage sludge and l i g h t fraction with shredded rubber t i r e s are presented i n Table 3. The average moisture content of the feed material for the run with l i g h t fraction and sewage sludge was 16.2 percent. This high moisture content required a significant increase i n process a i r which increased the mass y i e l d of gaseous fuel. The energy y i e l d of the char was 2400 BTU per pound of dry input for the l i g h t fraction-sludge blend and 2808 BTU per pound of dry input for the l i g h t fractionrubber blend. The energy recovered as o i l was 674 BTU per pound of dry input for the l i g h t fraction-sludge blend and 1002 BTU per pound of dry input for the l i g h t fraction-rubber blend. The energy y i e l d of gaseous fuel was 2516 BTU per pound of dry feed for the l i g h t fraction-sludge blend and 3048 BTU per pound of dry feed for the l i g h t fraction-rubber blend. Pyrolysis Products from Wood Waste Characterization. Typical average heating values of the char, o i l , and gaseous fuel from the pyrolysis of a mixture of pine bark and sawdust are given i n Figure 9 at various char yields. Generally, measured heating values have ranged from 12,300 to 13,500 BTU per pound. The elemental carbon content of the char can be as high as 90 percent. The bulk density of char from hogged wood waste i s normally within the range of 10 to 13 pounds per cubic foot. The v o l a t i l e content has been measured within the range of 3 to 26 percent, depending upon operating conditions and feed material. Typical heating values for the gaseous fuel are shown i n

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3

)

6.0

16.2

U5.T

U7.5

17.2

10.9

83

136

MASS YIELD (Percent o f Dry Feed) Fuel Char Gas Oil

2808

2U00

1002

6lk

30U8

25l6

ENERGY YIELD (BTU per l b . o f Dry Feed) Fuel Char Oil Gas

2.

Based on ash i n char, h e a t i n g value o f l i g h t s was estimated t o be 6000 BTU/Lb. Heating value o f shredded rubber was measured t o be 12,600 BTU/Lb. These values were used t o c a l c u l a t e t h e average h e a t i n g value o f t h e i n p u t .

Notes : 1. Measured h e a t i n g value was 7631 BTU/Lb. at average ash content o f 20.1%, Ash cont e n t o f feed c a l c u l a t e d t o be 31 percent based on char y i e l d and ash content i n char. Heating value c o r r e c t e d t o 31 percent ash.

7391(2)

1

Dried Light Fraction w i t h 20 Percent Shredded Rubber T i r e s 1/15/75

(

6590

Dried Light Fraction v i t h 13 Percent Wet Sewage Sludge (80% Water) 5/21/75

MATERIAL

HIGHER PERCENT HEATING MOISTURE VALUE (BTU/Lb)

SUMMARY OF MASS AND ENERGY DATA FOR CO-PYROLYSIS OF SEWAGE SLUDGE WITH LIGHT FRACTION MUNICIPAL REFUSE AND SHREDDED RUBBER TIRES WITH LIGHT FRACTION OF MUNICIPAL REFUSE

TABLE

118

SOLID WASTES AND RESIDUES

Figure 9 at various char yields. The heating value decreases as the char y i e l d increases. Normally/ the gas i s at a temperature of approximately 200°F and the density i s approximately 0.05 pounds per cubic foot. At low char yields, the volumetric higher heating value w i l l generally be on the order of 225 B1U per actual cubic foot at 200° F and at a moisture content of approximately 30 percent by weight. Typical data for the pyrolysis o i l are presented i n Table 4. Note that the moisture content i s 26 percent. Normally, the condensation process i s operated to provide an o i l with a moisture content of about 20 percent. This quantity of moisture serves to lower the viscosity for improved handling and atomization and appears to enhance combustion. At 26 percent moisture as shown i n the table, the heating value i s 9081 BTU per pound or approxi­ mately 90,000 BTU per gallon which i s 60 percent of the heating value of No. 6 Fuel O i l . The viscosity of the o i l can be reduced below 100 SSU by heatin places i t i n the Code 1 highly corrosive to mild steel, but the corrosive rate i s a fraction of a mil per year for 304 stainless steel and copper. Uses. The char from the pyrolysis of wood waste i s widely used i n the manufacture of charcoal briquettes. In addition, i t has fuel value as a low sulfur coal extender or substitute and can be used to produce a water grade activated carbon. The combustion of pulverized char from wood waste produced by the Tech-Air system was studied i n a joint program by EPA and EPDA (3). Carbon (combustion efficiencies were 97.3 to 98.6 percent i n a pulverized coal f i r e d test f a c i l i t y and ΝΟχ emissions were much lower than those obtained with coal. Also, blended with coal, the SO emissions were much lower than the coal alone. A blend of pulverized char and pyrolysis o i l combined with No. 6 fuel o i l performed well. Char produced from wood waste at the Cordele plant has been activated i n the laboratory to produce a water grade activated carbon. In addition, laboratory studies have demonstrated the effectiveness of the activated char i n the removal of color from kraft m i l l effluents. The pyrolysis o i l has been demonstrated as a fuel. I t also has a potential as a chemical raw material. The o i l has been sold cjommercially for use as a fuel i n a cement k i l n , a power boiler and a lime k i l n . In the cement k i l n , several months production from Cordele was f i r e d as a 20 percent blend with No. 6 °ϋ· The remainder of the o i l produced has been sold as a fuel which was f i r e d i n p a r a l l e l with several No. 6 fuel o i l guns i n a power boiler and also directly f i r e d i n a lime k i l n . Prior to these applications the o i l was test f i r e d i n a Trane Thermal Vortex burner (4) and at KVB (5) i n a test boiler system. The burner used at Trane Thermal performed equally well with a i r or steam as the atomizing media. The maximum o i l pressure required was 3 psig. 0

f u e l

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

TABLE h TYPICAL DATA FOR PYROLYSIS OIL FROM PINE BARK-SAWDUST

ITEM

UNITS

CHEMICAL COMPOSITION CARBON HYDROGE OXYGEN NITROGEN WATER ASH VISCOSITY

g 68°F g 100°F g 150°F

VALUE

19.Τ 0.16 26.0 O.OU

SSU It It

276 11U 90

HIGHER HEATING VALUE

BTU/LB

9081

DENSITY

LB/GAL

9.88 t o 10.27

Op

262 t o 305

FLASH POINT (Open Cup) POUR POINT

o

F

+

2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

TABLE 5 TYPICAL DATA FOR PRODUCTS FROM PYROLYSIS OF SINGLE SHREDDED, DRIED MUNICIPAL REFUSE WITH METALS REMOVED

OIL HIGHER HEATING WATER CONTENT DENSITY

(Wt. P e r c e n t ) (Lb./Gal.) -

30 9-5

FUEL GAS COMPOSITION (Wt. Percent) Water Vapor Pyrolysis O i l "Dry" Gas HIGHER HEATING VALUE (BTU/Lb.) DENSITY g 200°F ( L b . / F t . ) HIGHER VOLUMETRIC HEATING VALUE g 200°F (BTU/ACF)

26 13 6l 308l 0.05

3

15^

CHAR HIGHER HEATING VALUE TOTAL ASH ACID INSOLUBLE ASH DENSITY

(BTU/Lb.) (Wt. Percent) (Wt. Percent) (Lb./Ft. ) 3

- 3972 69 60 20

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

6.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

121

The unburned hydrocarbons were measured to be 11 ppm at 6 percent excess a i r and the combustion chamber temperature was measured at 2520°F. In the tests at KVB the carbon monoxide level was about 15 ppm, and the Ν 0 level was about 110 ppm at 4.5 percent excess a i r . The o i l , also, has a potential use as a fuel for a hot gas turbine. Research work along these paths i s expected to be per­ formed i n the near future. Work done i n the laboratory has indicated the potential of the pyrolysis o i l as a raw material for the production of phenolic resins and rubber t a c k i f i e r s . Other work has shown that i t may be used as a substitute for wood tars produced by other methods. The gas from the pyrolysis system i s useful as a fuel. At the Gordele plant, the gas i s burned as a fuel to supply heat to the dryer. Preliminary studies have been made of the use of the gas as a fuel for an internal combustion engine. A dry gas mix­ ture which simulated the composition of the non-condensible pyrolysis gas fraction wa study {6). The higher heatin per cubic foot. The power output of the engine was s l i g h t l y over 60 percent of the output with gasoline. Calculations have shown that i t i s reasonable to expect that the heating value of the gas can be increased to around 400 BTU per cubic foot so that engines already developed for sewage gas can be used. These modifications would involve removing a l l of the condensible fractions from the gas and reducing or eliminat­ ing the process a i r . Preliminary estimates have indicated only a small penalty i n energy with incineration of the low-energy content l i q u i d effluent produced i n this case. χ

Pyrolysis Products from Municipal Refuse Characterization. The products of pyrolysis from municipal refuse are char, o i l , and gas. The yields and the properties of the products are related to the make-up of the input feed, the degree of shredding, the moisture content of the feed, and the pyrolysis conditions. Classification of the refuse prior to pyrolysis i s one direct means of influencing the quality of the products. For example, a char which can be readily upgraded and improved can be produced from l i g h t fraction. With whole garbage i t i s more d i f f i c u l t to u t i l i z e char except as a f i l l e r or color­ ing material for brick and similar products. The o i l obtained from single-shredded garbage i s usually more viscous than that obtained from wood. Its heating value ranges between 10,000 and 11,000 BTU/pound (at 30 percent moisture content), which i s higher than the heating value of o i l from wood. The density of both o i l s i s very similar, approximately 9.5 pounds per gallon. The fuel gas produced from garbage w i l l vary due to the physical characteristics of the refuse as well as the composition of the refuse. For example, the permeability of a bed of single-

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

122

SOLID WASTES AND RESIDUES

shredded refuse i s very low compared to wood wastes and usually results i n operating at higher air-to-feed ratios, which directly affects the heating value of the off-gas. Both agitation of the bed and improvement i n the distribution of the injected a i r can be used to improve this situation. Generally, the gas w i l l contain some non-condensed o i l and water vapor with the bulk being a non-condensible fraction. Its heating value usually l i e s i n the 3000 to 4000 BTU/pound range resulting i n volumetric values from 150 to 200 BTU per actual cubic foot. The char produced from refuse i s usually very high i n ash content, particularly acid insoluble ash. Its heating value usually i s below 4000 BTU/pound with a t o t a l ash of 65 percent or higher. This char w i l l contain l i t t l e or no slag, w i l l be relatively free flowing and dusty, and have a bulk density of 20 pounds per cubic foot or higher. Uses. O i l productio low air-to-feed ratios in order to have a suitable scrubbing medium, and this i s the i n i t i a l use of the o i l . In addition, the o i l from garbage i s a storable, transportable fuel o i l and has a potential use i n the production of carbon black, but l i t t l e has been done i n this area to date. Classification of the refuse into specific fractions i s probably the more r e a l i s t i c approach to producing an o i l from garbage that would have value outside the fuel area. This i s not meant to suggest that i t s fuel o i l value i s low. To the contrary, energy production from garbage at the present time i s the largest, single, economic factor involved. The fuel gas from garbage, although i t s heating value i s low, i s an acceptable fuel suitable for use i n the v i c i n i t y of the plant. The gas has a very low air-to-fuel requirement for combustion which results i n an attractive ratio of t o t a l pounds of combustion products per unit of heat released which i s not too different from the more common fuels. Also, since i t i s a scrubbed fuel gas i t can be readily adapted for use i n many d i f ferent heat devices. Further, i t i s well known that low BTU gas can be used i n an internal combustion engine. However, because of the derating involved, and the p o s s i b i l i t y of variable loading, i t s use directly for this purpose without drying, or upgrading, i s questionable. At the present time reduction of the a i r requirements and moisture removal from the gases appear to offer the best approach to producing a gas suitable for an internal combustion engine. Research work i n this area i s being conducted by Tech-Air Corporation and the Georgia Institute of Technology at the present time. An additional potential use of the gas can be suggested i n view of the low air-to-fuel r a t i o characteristic. A clean, dry fuel gas can be compressed for e f f i c i e n t use i n a hot gas turbine provided the compressor work on the fuel can be offset with a

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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123

similar, or larger, reduction i n a i r compression work. This appears to be possible with gases produced i n the pyrolysis process. Char produced from municipal refuse, generally, i s not considered of significant value. For this reason a pyrolysis system operating on refuse i s primarily aimed at gas and o i l production, ndnimizing the energy loss i n the char. Research work has been done on upgrading char from light fraction refuse, and i t holds significant promise i n the area of sewage treatment. Generally a carbon with an acceptable adsorptive capacity can be produced from the light fraction. Research work i n this area has been underway by Tech-Air for some time. This effort i s expected to intensify and increase i n the future. Discussion The development o b r i e f l y traced from th y through the construction and operation of four p i l o t plants, two large scale f i e l d test systems and one large, commercial prototype plant, the Cordele plant. This work was accomplished over a ten year period and culminated i n 1977 with the successful demonstration for eighteen continuous months of a commercial prototype plant operating on wood waste. The Tech-Air process i s based on a v e r t i c a l bed, gravity fed, counter flow pyrolysis chamber which probably gives the best heat balance attainable. To accomplish this process the distribution of the a i r and the permeability of the bed are very important. The a i r i s injected i n a manner so that p a r t i a l oxidation of the gases occurs rather than complete burning i n a small region. The result i s the a b i l i t y to produce char yields equivalent to that obtained i n the complete absence of a i r . Another important feature of this process i s the mechanical feedout mechanism for the char. The device, o r i g i n a l l y designed for Blue I, has proven very r e l i a b l e and adaptable to municipal refuse systems which occasionally require the passage of large chunks. This one device permits considerable automation to be introduced into the process. An output rate can be fixed by selecting the rotation rate of the output mechanism and with a bed level sensor controlling the input rate directly, the throughput rate i s effectively controlled by the one device. To complete the process control the a i r input can be controlled within predetermined limits by temperature sensing at points within the bed. An alternative to this arrangement i s to select an output rate and the desired off-gas temperature and vary the bed level continuously to maintain this temperature. This technique has been used successfully i n both the p i l o t plant operations and at the Cordele plant. This technique i s easily accomplished since the off-gases can be rapidly changed by raising or lowering the bed level. Approximately 40°F change i n off-eras temperature occurs

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

124

SOLID WASTES AND RESIDUES

with a change of only one inch i n bed l e v e l . This procedure, however, results i n a greater departure from what could be called equilibrium bed conditions. On f i r s t inspection, drying the wastes i n a separate step may appear to be undesirable, but experience with this system has shown that the added complexity i s more than off-set by the gains. The latent energy associated with the moisture w i l l be extracted with any process or device. I f this moisture i s evolved within a device u t i l i z i n g the energy i n the s o l i d there are additional penalties involved. I f i t i s being burned, as i n a bark boiler, additional a i r must be supplied to overcome the decrease i n oxygen concentration due to the presence of the moisture. The i n crease i n the mass of the flue gas due to the moisture and the additional a i r results i n an increase i n the sensible heat losses in the flue gases. Further, the increased mass results i n higher velocities through the boiler which, i n practice, results i n operation well below rated accomplished at approximatel moved, there w i l l be l i t t l e or no net energy penalty involved with a separate drying step. On the other hand, the gains to be had with dry feed material are significant i n pyrolysis, as well as other processes. The throughput i s greatly increased, the temperature control of the process i s easier and the products produced are of higher heating value. The Tech-Air pyrolysis process i s a low temperature, nonslagging process which produces char, o i l and gas. In cases of high ash feedstocks, or i f i t i s desirable to produce o i l and gas only, i t has been demonstrated that the process can handle the feed and gasify the char by the simple expedient of raising the a i r to feed r a t i o and recirculating char, but maintaining a s i g n i ficant char output from the bed. This technique has demonstrated that 90 percent of the energy i n the dry feed can be recovered i n the form of gas and o i l . In view of these data, considering the much higher net thermal efficiencies achievable with o i l and gas compared to burning a wet s o l i d , the value of pyrolysis i n waste u t i l i z a t i o n becomes clearer.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

6.

BOWEN ET AL.

A Vertical-Bed Pyrolysis System

125

Literature Cited 1.

2.

3. 4.

5. 6.

Knight, J.A. et al., "Pyrolytic Conversion of Agricultural Wastes To Fuels". Presented at 1974 Annual Meeting of American Society of Agricultural Engineers, Oklahoma State University, Stillwater, Oklahoma, June 1974. Knight, J.A. and Bowen, M.D., "A Method For Conversion Of Forestry Wastes To Useful Fuels". Presented at Fall Meeting of American Pulpwood Association, Atlanta, Georgia, November, 1975. Demeter, J.J.; McCann, C.R., et al., "Combustion of Char From Pyrolyzed Wood Waste", Pittsburgh Energy Research Center, PERC/RI-77/9, July, 1977. Paolucci, S. and Rafferty, J . P . , "Feasibility of Burning Wood Pyrolysis and Garbage Pyrolysis Waste Oil in a Thermal Vortex Burner". Engineering Test Report by Trane Thermal to TechAir Corporation, No Muzio, L.J., and Arand Oil Made from the Tech-Air Process". KVB Report KVB-12010-460 to Tech-Air Corporation, June, 1976. Tatom, J.W., Colcord, A.R., et al., "Development of a Prototype Mobile System for Pyrolysis of Agricultural and/or Silvicultural Wastes into Clean Fuels". EPA Report (In Review) on Grant No. R803430-01, Program Element No. EHE-624, June, 1977.

MARCH 3, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

7 Gasification of Solid W a s t e Fuels i n a F i x e d - B e d Gasifier L. K. MUDGE and C. A. ROHRMANN Battelle-Northwest, P.O. Box 999, Richland, WA 99352

Gasification of solid fuels i s a technology that has been around for many years. The process of solids gasification with a i r i s as old as steel. Industrial use of combustible gas produced from organic solids started with blast furnaces during the industrial revolution. Probably the original gas generator was the blast furnace, in which iron was smelted in the presence of coke. The combustible gases produced from the coke were used f o r various heating purposes by the year 1800. By the year 1840 gases generated by the partial oxidation of coal, charcoal and peat were used f o r heat generation. Gas generators were in operation in Europe f o r the specific purpose of producing combustible gases. Research and development studies on solids gasification at Battelle Northwest were i n i t i a t e d under private sponsorship in 1969 f o r the development of a process to recover s i l v e r from photographic f i l m . In a subsequent one-year study sponsored by EPA and the City of Kennewick, Washington, the process was applied to the conversion of municipal refuse to a low Btu gas. Recent studies have been sponsored by DOE and a number of private concerns. In these studies, a variety of materials, including wood, agricultural residues, shredded rubber, and mixtures of plastics with c e l l u l o s i c wastes, have been processed in a small-scale fixed bed g a s i f i e r . This paper describes the gasification process and equipment used f o r conversion of a variety of solid materials to a low Btu gas. Operating results obtained in the studies are presented. Preliminary economics f o r processing of municipal refuse are estimated. Process Description Gasification of solid waste fuels as practiced in the Battelle Northwest studies occurs in a c y l i n d r i c a l , vertical 0-8412-0434-9/78/47-076-126$05.00/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

7.

MUDGE AND ROHRMANN

Gasification of Solid Waste Fuels

127

r e t o r t . Processes t h a t occur i n the r e t o r t a r e i l l u s t r a t e d i n Figure 1. Waste feed m a t e r i a l enters through a lock hopper atop the r e t o r t and g r a v i t a t e s through zones o f i n c r e a s i n g temperature. As i t passes through the r e t o r t , the waste i s f i r s t d r i e d and pyrolyzed to y i e l d a char. The char i s then g a s i f i e d and combusted to leave an ash r e s i d u e . Gases pass countercurrent t o the f l o w of s o l i d s . An a i r - s t e a m b l a s t preheated t o about 150°C enters the r e t o r t through openings i n the g r a t e and passes through an ash zone. The ash zone serves the dual purpose of p r o t e c t i n g the grate from the high temperatures of the combust i o n zone and o f d i s t r i b u t i n g the gases over the r e t o r t ' s cross s e c t i o n . Oxygen i n the a i r r e a c t s w i t h carbonaceous r e s i d u e i n the combustion zone generating heat r e q u i r e d f o r the process. The s e n s i b l e heat i n the oxygen-depleted gases from the combustion zone s u s t a i n s the endothermic g a s i f i c a t i o n r e a c t i o n s o f steam and CO2 with carbonaceou G a s i f i c a t i o n reaction rate tures below 700°C. S e n s i b l e heat i n gases from the g a s i f i c a t i o n zone i s used t o p y r o l y z e and dry the incoming waste feed material. P y r o l y s i s o f t h e s o l i d waste feed m a t e r i a l produces CO, H 2 , CO2, hydrocarbons, and condensibles t h a t are c a r r i e d i n the product gas and carbonaceous r e s i d u e . The carbonaceous r e s i d u e r e a c t s with gas phase c o n s t i t u e n t s according t o the f o l l o w i n g reactions: C + 0

2

+ CO2

(1)

C + C02 -> 2C0 C + H 0 •* CO + H 2

(2)

(3)

2

C + 2H2 •> CH4

(4)

The o x i d a t i o n of char by r e a c t i o n (1) i s h i g h l y exothermic, extremely r a p i d and proceeds t o completion w i t h r e s p e c t t o oxygen disappearance. The endothermic water gas r e a c t i o n and Boudouard r e a c t i o n , r e a c t i o n s ( 2 ) and (3) r e s p e c t i v e l y , a r e thermodynamically favored a t temperatures over 700°C. These endothermic r e a c t i o n s a r e slow and r a r e l y a t e q u i l i b r i u m i n coal char systems a t temperatures below 1100°C. Reaction (4) i s h i g h l y exothermic and thermodynamically favored a t temperatures below 600°C. This r e a c t i o n i s o f n e g l i g i b l e importance in the system discussed i n t h i s r e p o r t . The f o l l o w i n g r e a c t i o n , the water gas s h i f t r e a c t i o n , i s a l s o important i n t h i s system: CO + H 0 + C 0 + H 2

2

2

(5)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

128

SOLID WASTES AND RESIDUES

This reaction appears to involve a heterogeneous phenomemon on the surface of the f u e l . ( J ) Equilibrium is approached as a function of steam decomposition, although other factors such as fuel reactivity and catalytic activity of the ash constituents should be considered. Detailed discussions of gasification reaction thermodynamics and kinetics are contained in several sources.(1,2,3,4,5) A hypothetical scheme showing mass and energy flows in the reactor is illustrated in Figure 2. Equilibrium concentration based on reactions (1) through (4) at some temperature may occur in the combustion gasification zone. The compositions and flows shown in Figure 2 are based primarily on yields actually obtained but are not experimental data. The actual product includes a condensible fraction similar to pyroligneous acids. Data are presented in a later section for processing different feedstocks. The experimental equipment used in the majority of the studies is illustrated i usually flared in a close-couple recovery of tars and o i l s was effected in a water 60oled condenser. Product gases were sampled and analyzed to determine compositions. Description of Testing Program Studies were conducted in pilot plant f a c i l i t i e s that include a three-foot diameter reactor (6) and a one-foot diameter reactor ( 7 ) . The three-foot diameter unit was a simple, v e r t i cle shaft"with an operating depth of up to 10 f t . The small scale unit with an operating depth of up to 5 f t was equipped with a mechanical agitator for distribution of the charged solid waste fuels. A rotary grate for ash discharge was also provided. A schematic of the one-foot diameter reactor is shown in Figure 4. Photographs of the one-foot diameter reactor and three-foot diameter reactor are shown in Figures 5 and 6 respectively as they exist today. Feedstocks that have been processed in the BNW f a c i l i t i e s include municipal refuse, wood wastes, agricultural residues, shredded t i r e s , and simulated wastes from nuclear processing f a c i l i t i e s . Properties of these materials and products obtained from their gasification are presented below. Shredded municipal refuse obtained from the City of Vancouver, Washington, and wood chips from the Boise-Cascade plant at Wallula, Washington, were gasified in the three-foot diameter reactor. Composition of the municipal refuse is shown in Table I. Ultimate and proximate analyses of this refuse are given in Table I I . Density of the shredded refuse ranged from 38 to 50 l b / f t 3 (600 to 800 kg/m3). The wood chips (Western soft wood) were mostly 5/16 to 1 inch in size and had a dry c a l o r i f i c value of 8500 Btu/lb. Moisture content of wood chips processed in the three-foot unit ranged from 20 to 45%.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MUDGE AND ROHRMANN

Figure 1.

Gasification of Solid Waste Fuels

Schematic of Battelle process

gasification

16.9% H , 18.3% CO, 16.5% H^O, 11.4% C0 , 4.1% CH . 32.8% N 98 g-moles TOTAL 2

1 kg WOOD. 20 WT% H 0 3830KCAL POTENTIAL ENERGY

2

4

?

~100°C 3210KCAL POTENTIAL ENERGY

2

19.1% H , 20.7% CO, 5.8% HpO, 12.8% C 0 , 4.6% CH , 37%N 87 g- moles TOTAL ~300°C

0.8 kg DRY WOOD

2

3830KCAL POTENTIAL ENERGY

2

4

2

PYROLYSIS ZONE

\%Η-β,

10* H-. 29% CO. 5%C0 . 55% N 58 g-moles TOTAL ~700°C 1550KCAL POTENTIAL ENERGY

0.24 kg C 1880KCAL POTENTIAL ENERGY

2

2

GASIFICATIONCOMBUSTION ZONE

ASH

Figure 2.

AIR-13VOL%STEAM 47 g- mol es TOTAL

Typical mass and energy flows for wood gasification

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

130

SOLID WASTES AND RESIDUES

SECONDARY BURNER

CONDENSER

LJ

ι

GAS I FIER

DEMISTER

V

TRAP

CONDENSATE CONDENSATE

ASH

Figure 3.

Schematic of experimental equipment

Figure 4.

Schematic of small gasifier

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

MUDGE AND ROHRMANN

Gasification of Solid Waste Fuels

Figure 5.

Small gasifter

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

132

Figure 6.

Three-foot gasifier and hot gas clean up pilot plant

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

7.

MUDGE AND ROHRMANN

TABLE I.

Gasification of Solid Waste Fuels

133

Refuse Composition Weight Percent

Component Paper Fines (Mostly paper and d i r t , some g l a s s ) Rubber and Leather Wood Metals other than Aluminum Aluminum Plastic Cloth Glass Food

38.5 34.2 2.0 5.3 7.0 0.6 1.7 5.7 5 Trace

TABLE I I Ultimate Analysis Moisture Carbon Hydrogen Oxygen Nitrogen Sulfur Chlorine Ash

% by Weight 5.08 45.91 7.06 28.82 4.19 0.10 0.32 14.18

Proximate A n a l y s i s Moisture V o l a t i l e a t 950°C Ash Btu/lb

5.08 80.74 14.18 7203

G a s i f i c a t i o n of the wood chips proceeded without d i f f i c u l t y and r e s u l t e d i n a gas product w i t h a heating value of 170 B t u / f t ^ , o r g r e a t e r . Processing of municipal r e f u s e was hampered by development o f a i r channels around the bed o f r e f u s e i n t h e r e t o r t . This i s i l l u s t r a t e d by the data i n Table I I I . These data were obtained i n a run t h a t was i n i t i a t e d by processing wood chips a t about 200 lb/hr f o r 15 hrs and then s w i t c h i n g t o the municipal waste as feed m a t e r i a l a t an average r a t e o f 180 l b / h r . An a i r - s t e a m b l a s t (0.2 l b steam/lb a i r ) preheated t o 350°C was used to g a s i f y the waste streams. As can be seen from examination of the data i n Table I I I , gas q u a l i t y begins to d e t e r i o r a t e about 5 hrs a f t e r s w i t c h i n g to the shredded municipal r e f u s e . At t h i s t i m e , none o f the wood chips feed remains i n the r e t o r t . Continued operations w i t h municipal r e f u s e r e s u l t s i n f u r t h e r d e t e r i o r a t i o n of gas

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

19.8

20.3

R.

R.

Wood Chips

S t a r t municipal1 refuse feed

R.

Wood Chips

Municipal Refuse

Municipal

Municipal

Municipal

Municipal

Municipal

Municipal

Municipal

13

14

14.6

16

18

19

20

21

22

27

33

R.

R.

R.

R.

23.9

Wood Chips

10 3.0

21.1

0.15

0. 10

1.1

7.3 5.4

11.4

5.1

1.5

0.13

0. 15

1.5

15.1

16.5 0. 18

0.17

0.24

0.12

1.3

15.6

17.8

0.35

17.9

0.13

0. 13

1.3

0. 12

0.27

0. 15

1.6

1.8

21.0

0.13

0.31

0. 25

0. 15

0.29

0.27

0.09

0. 23

0. 35

0. 16

0.15

16.4

2.0

23.5

2.7

2.8

20.2 23.7

2.2

22.6

6

0. 17

2

Gas Composition, vol C2H4 C H

20.9

22.1

21.6

21.0

25.2

Wood Chips

6

4

2.2

CH 2

0.7

0.4

Trace

Trace

Trace

Trace

Trace

Trace

0

0

0

0

0.35

o

17.8 19.9

61.0 66.5

15.8

50.8

58

80

129

135

137 13.8

168 13.8

172

11.8 11.6

186

189

10.3

12.4

180

14.6

51.1

50.1

43.5

43.3

42.9

40.3

41.0

191

192

180

Btu/ft

14.0

37.6

37.6 38.5

11.8

2

co 41.8

Gas Compositions f o r Run S t a r t e d w i t h Wood Chips and Completed w i t h Municipal Refuse

22.0

22.2

CO

Wood Chips

2

5

H

Feed

Time, Hr

TABLE I I I .

3

CO

7.

MUDGE AND ROHRMANN

135

Gasification of Solid Waste Fuels

q u a l i t y . F i n a l l y a f t e r 33 hours, operations were terminated when the feed r a t e could not be maintained a t 100 l b / h r . I n d i c a t i o n s of c h a n n e l i n g , other than d e t e r i o r a t i o n of gas q u a l i t y and reduced throughput, i n c l u d e increases i n the product gas temperature and i n w a l l temperatures i n the upper zone of the r e t o r t . Results of the operations i n the t h r e e - f o o t u n i t made i t obvious t h a t non-free f l o w i n g feed could not be expected to g r a v i t a t e through a v e r t i c a l r e t o r t a t design c o n d i t i o n s . Free f l o w i n g feeds such as wood chips were found t o be s u i t a b l e f o r processing i n a v e r t i c a l r e t o r t . M a i n t a i n i n g an open s t r u c t u r e i n the bed of r e f u s e to a l l o w f o r gas p e r c o l a t i o n was found to be e s s e n t i a l f o r s a t i s f a c t o r y o p e r a t i o n . Experience w i t h the t h r e e - f o o t diameter u n i t l e d to the c o n s t r u c t i o n of the u n i t shown s c h e m a t i c a l l y i n Figure 4 f o r processing o f simulated wastes from the nuclear i n d u s t r y Composition of these waste The high p l a s t i c s and p a r t i c u l a r l y troublesome f o r processing i n a f i x e d bed g a s i f i e r . TABLE IV.

Simulated Waste Composition

Component

Weight %

Paper Rags Wood Latex Rubber Hypalon Rubber Neoprene Rubber PVC Polyethylene

15 15 10 5 10 10 20 15

The simulated waste w i t h the composition shown i n Table IV was shredded to l e s s than 4 i n . pieces f o r processing i n the small g a s i f i e r . P y r o l y s i s of some of the components i n the simulated feed does not y i e l d a carbonaceous r e s i d u e . For example, polyethylene simply d i s t i l l s when heated and increases the y i e l d of t a r s from the process. C h a r a c t e r i s t i c s of some of the components i n the simulated waste from nuclear processing are given i n Table V. TABLE V. Component

C h a r a c t e r i s t i c s of Feed Components

wt % Moisture

Paper & Rags Latex Rubber PVC Neoprene Polyethylene

3.4 — — —

wt% C a l o r i f i c Value Ash Btu/lb kj/kg 0.8 1.4 1.8 28.5 —

7,170 18,760 8,970 8,690 19,790

16,700 43,600 20,900 20,200 46,000

Decomposition Mode Endothermic a t 320°C Exothermic Endothermic a t 260°C Exothermic a t 340°C Endothermic a t 420°C (Melting s t a r t s 80°C)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

136

Proper o p e r a t i o n of the d i s t r i b u t o r mechanism permitted processing of the simulated nuclear waste composition shown i n Table IV. The d i s t r i b u t o r mechanism r o t a t e d and moved a x i a l l y to d i s t r i b u t e the waste i n the r e f u s e bed. P e n e t r a t i o n a t the center of the bed w i t h an extended prong was found to be benef i c i a l f o r i n c r e a s i n g bed p o r o s i t y and pushing the r e f u s e outward a g a i n s t the w a l l s of the g a s i f i e r . The longest run made w i t h the simulated waste was 50 hours. Gas compositions 24 hours and 48 hours a f t e r i n i t i a t i o n of t h i s run are shown i n Table VI. Average processing r a t e during t h i s run was 25 l b / hr « 2 . TABLE VI. Time A f t e r Startup, Hour H2

Gas Composition from Simulated Waste Run

Volum CO

%

C2H

24

7.5

21.0

0.4

0.2

1.5

0.1

9.5

0.5

59.3

126

48

8.7

24.8

0.9

0.3

1.9

0.3

8.0

0.4

54.6

162

Y i e l d s of t a r s and o i l s were high when g a s i f y i n g the simul a t e d wastes. Condensate c o l l e c t e d was about 20% of the weight of the waste g a s i f i e d . C o l l e c t i o n of the condensate i n the condenser and t a r t r a p was not complete and t a r d r o p l e t s were c a r r i e d to the secondary combustion chamber. I t i s estimated t h a t the a c t u a l t a r y i e l d i s about 30 wt %. These t a r s had v i s c o s i t i e s ranging from 100 cp to 750 cp a t 55°C and had a c a l o r i f i c value of 16,900 B t u / l b . Other feedstocks t e s t e d i n the small g a s i f i e r , Figures 4 and 5 , i n c l u d e shredded corn s t a l k s , cubed corn s t a l k s , cubed grass straw, pressed planer shaving, and a mix of pressed planer shavings and shredded rubber t i r e s . C h a r a c t e r i s t i c s of these feedstocks are given i n Table V I I . Shredded corn s t a l k s could not be s a t i s f a c t o r i l y processed even w i t h use of the mechanical d i s t r i b u t o r . F i n e l y d i v i d e d r e s i d u e , s i m i l a r to lampblack, was formed and deposited i n the offgas l i n e s . This m a t e r i a l had an ash content of about 30 wt% and a c a l o r i f i c value of about 8400 B t u / l b . S a t i s f a c t o r y o p e r a t i o n could not be achieved w i t h 100% shredded rubber e i t h e r . In t h i s case, the rubber melted, hung to the w a l l s , and could not be pushed through the r e t o r t . A l l cubed m a t e r i a l , corn s t a l k s , grass straw, and pressed planer shavings gave h i g h l y s a t i s f a c t o r y o p e r a t i o n s . A mix of shredded t i r e s (20% by wt) w i t h pressed planer shaving a l s o gave h i g h l y s a t i s f a c t o r y results. Gas compositions obtained from processing the feedstocks shown i n Table VII are presented i n Table V I I I . These composit i o n s were obtained about 12 hours a f t e r i n i t i a t i o n of o p e r a t i o n s . An a i r - s t e a m b l a s t (about 0.1 l b steam/lb a i r ) preheated

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

5980 8920 (c)

Cubed Grass Straw

Pressed Planer Shavings

Shredded T i r e s

0.3

1.0

5.7

17.9

Shredded T i r e s

20% Shredded T i r e s / 80% Pressed Wood 19.7

7.0

0.7

0.4

0.8

14.4

Pressed Planer Shavings

18.4

14.9

Cubed Grass Straw

0.3

4.3

1.9

5.2

2.9

3.1

0.4

0.3

21.9

0.2

0.3

24.5

16.6

Cubed Corn S t a l k s

1.6

4

0.1

0.2

6

4.6

2

Volume % CH C H

7.0

Shredded Corn S t a l k s

Feedstock 4

2

2

C H

H

—

5.1

25

— 7.5

—

0.1

23^

— 8.8

wt % AshU)

0.4

— —

0.1

—

0.1

3

C H8

2

13.5

17.0

15.2

13.3

11.4

21.3

C0

0.7

1.0

0.6

200

90

66.1 42.5

190

170

180

60

Btu/ft

45.0

45.8

43.3 0.4

0.6

2

64.2

N 0.9

02_

2 in. to 6 in. s t r i p s of shredded passenger t i r e s

1 1/2 in. r i g h t c y l i n d e r s of pressed wood

3

1 3/4 in. s q , 2 to 6 in. long

3 i n t o 1 in. cuts 1 3/4 i n . sq, 2 to 6 i n . long

Size

Gas Compositions f o r D i f f e r e n t Feedstocks

—

20,700

13,900

16,500 16,500

CO

TABLE V I I I .

(a) Dry basis (b) Impregnated w i t h NaOH (c) C a l o r i m e t e r t e s t s not conducted

7085 7085

wt % Moisture

Feedstock C h a r a c t e r i s t i c s

Calorific V a l u e ^ Btu/lb kj/kg

Corn S t a l k s Shredded Cubed

Feedstock

TABLE VII.

138

SOLID WASTES AND RESIDUES

to 150°C was used as the g a s i f y i n g medium. Y i e l d s and processing r a t e s f o r the d i f f e r e n t feedstocks are shown i n Table IX. Condensate y i e l d s vary w i t h time over the d u r a t i o n of the run. I n i t i a l l y y i e l d s are high u n t i l the g a s i f i e r has reached steady s t a t e thermal c o n d i t i o n s . Y i e l d s a l s o can be expected to vary w i t h the depth of the beds of waste i n the g a s i f i e r . Operation w i t h a shallow bed depth i s p r e f e r r e d to reduce the q u a n t i t y of condensate generated. P r o x i m i t y of the high tempera t u r e zone r e s u l t s i n c r a c k i n g of the high molecular weight o r g a n i c s . A l k a l i metal c a t a l y s t s present w i t h the cubed grass straw were observed to be e f f e c t i v e i n reducing condensate y i e l d s . A l k a l i metals are reported to be e f f e c t i v e g a s i f i c a t i o n c a t a l y s t s f o r coal by Cox e t a l . (8) The condensate obtained during g a s i f i c a t i o n of pressed planer shavings and cubed a g r i c u l t u r a l r e s i d u e was a s i n g l e phase aqueous s o l u t i o g a n i c s . The condensat obtained during wood d i s t i l l a t i o n . An important c o n s i d e r a t i o n i n determining the s u i t a b i l i t y of a feedstock f o r processing i n a f i x e d bed g a s i f i e r i s the ash p r o p e r t i e s . The residues from the cubed grass straw was p r i m a r i l y Na2C03 which melts a t 850°C. A f t e r about 8 hours of o p e r a t i o n , the r o t a r y grate s i e z e d up and became i n o p e r a b l e . No ash could be discharged during the run. Examination of the g a s i f i e r a f t e r the run showed t h a t the r e s i d u e has f r o z e n i n t o a l a r g e clump around the g r a t e impeding i t s r o t a t i o n . Residue from other feedstocks d i d not i n t e r f e r e with operation of the g r a t e . Ash content of the other waste feeds was u s u a l l y so low t h a t the grate was used i n f r e q u e n t l y . Process

Economics

Economics were determined f o r the processing of municipal r e f u s e to generate a low Btu gas f o r f i r i n g a b o i l e r . (6) The flowsheet f o r the process i s shown s c h e m a t i c a l l y i n Figure 7. C a p i t a l and operating c o s t estimates f o r the system shown i n Figure 7 are presented i n Figure 8 f o r systems w i t h a capac i t y of 50 to 1000 tons/day. Costs have been r e v i s e d to r e f l e c t mid year 1977 d o l l a r s . I f a gas p r i c e of $1.10/10° Btu could be o b t a i n e d , p l a n t s w i t h a c a p a c i t y of 400 tons/day would operate a t a p r o f i t . The costs assume t h a t value obtained f o r recovered scrap j u s t o f f s e t s costs f o r d i s p o s a l of ash r e s i d u e . The operating costs assume s a l e of municipal bonds with a 25 year payback at 6% i n t e r e s t . Revenue from the low Btu gas assumes t h a t the r e f u s e has a c a l o r i f i c value of 7200 Btu/lb so t h a t 10 X 10° Btu of gas can be obtained from each ton of refuse.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

63 23 (c)

35 20-35 32

60 42 (c)

20% Shredded T i r e s / 80% Pressed Planer Shavings

Simulated Nuclear Waste

Shredded T i r e s

( f ) No steam i n b l a s t

(e) B l a s t contained 0.2 l b steam/lb a i r

(d) As r e c e i v e d wt basis

(c) Steady o p e r a t i o n not achieved

(b) B l a s t i s a i r - s t e a m w i t h 0.1 l b steam/lb a i r

e

s(> (c)

3

f

2. ( )

1.

e

1.8< >

b

63

24

70

Pressed Planer Shavings

3

i. ( )

13

58

A i r Required, lb a i r / l b f e e d ^ 0. 9(b)

69

(a) Energy i n low Btu gas d i v i d e d by energy i n p u t to process

d

110

Cubed Corn S t a l k s

—

2

Processing R a t e , ( ' lb/hr f t

69

Condensate, wt% of Feed

Cubed Grass Straw

Feedstock 3

Y i e l d s and Processing Rates Obtained with D i f f e r e n t Feedstocks

Conversion. . Efficiency^ '

TABLE IX.

140

SOLID

WASTES

A N D RESIDUES

HEAT EXCHANGER HOT AIR

1/

CONVEYOR

TIPPING AREA

STORAGE

RES I DUE TO SALVAGE OR LANDFILL

Figure 7. Gasification

35

30

25

20

5 h 100

200 300

400 500

600 700 800 900 1000

PLANT CAPACITY, TONS /DAY

Figure 8. Capital and operating costs for gasification plant to provide boiler fuel

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

7. MUDGE AND ROHRMANN

Gasification of Solid Waste Fuels

141

If a market exists for low Btu gas, a region with a population of more than 100,000 people could dispose of their soild waste by gasification at costs less than landfill. Natur­ al gas costs of $1.50 to $2.00/10 Btu are currently quite common. Similar prices for low Btu gas as a replacement for natural gas appear to be reasonable. 6

LITERATURE CITED 1.

Von Fredersdorff, C. G., Elliott, Μ. Α., "Coal Gasification", In: Chemistry of Coal Utilization, Η. H. Lowry, Editor, Supplementary Vol., John Wiley and Sons, Inc., New York, NY, pp 892-1022 (1963).

2.

Wen, C. Y., Editor, "Optimization of Coal Gasification Processes", R&D Repor Dept. of the Interior D.C., USGP0, Washington, D.C., Various paging (1972).

3.

Bituminous Coal Research, Inc., "Gas Generator Research and Development - Phase II. Process and Equipment Development", R&D Report No. 20, Final Report, U.S. Dept. of the Interior, Office of Coal Research, Washington, D.C., USGP0, Washington, D.C., Various paging (March, 1971).

4.

Blackwood, J . D., McCarthy, D. J., "The Mechanism of Hydro­ genation of Coal to Methane", Australian Journal of Chemistry 19, 797-813 (1966).

5.

Cox, J . L., "Catalysis for Coal Conversion", Paper presented at the Symposium on Clean Fuels from Coal, sponsored by the Institute of Gas Technology, Chicago, IL, 31 p (1973).

6.

Hammond, V. L., et a l . , "Pyrolysis - Incineration Process for Solid Waste Disposal", EPA Grant No. 1-G06-EC-00329, December 1972.

7.

Mudge, L. K., et a l . , "Pyrolysis - Incineration of Simulated Combustible Alpha Wastes", BNWL-1945, UC-70, October 1975.

8.

Cox, J . L., "The Direct Production of Hydrocarbons from CoalSteam Systems", R&D Report No. 80, OCR, Dept. of Interior, 1975.

MARCH 3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8

Development of Pilot Plant Gasification Systems for the Conversion of C r o p a n d Wood Residues to T h e r m a l and Electrical Energy R. O. WILLIAMS , J. R. GOSS, J. J. MEHLSCHAU, B. JENKINS, and J. RAMMING 1

University of California, Davis Agricultural Engineering Department, Davis, CA 95616

A noteworthy observation on the energy crisis, such as it existed i n America i n 1906, can be found i n "A Treatise on Producer-Gas and Gas Producers" by Samuel S. Wyer, M.E.(l). According to Mr. Wyer, "One of the most serious problems of the near future will be that of fuel supply. We are even now returning to mines that were abandoned several years ago and are beginning to rework them with an economy unknown before; and coal seams, formerly regarded as being too thin or too poor to work, are being investigated and purchased i n large areas. Brown coal, l i g n i t e , peat, sawdust and other refuse are now being used i n European Gas Producers, and these low-grade fuels must soon be used extensively i n this country." On the future of natural gas Mr. Wyer stated that "While natural gasisnow piped long distances and utilized i n manufacturing industries where the use of a gaseous fuel i s imperative, yet the states that have gas wells will soon enact laws that will prevent piping the gas outside the state or using it for anything except domestic service." And on the use of gas producers, Mr. Wyer continued, "On account ofitshigh fuel economy, producer gas will be one of the best means of c u r t a i l i n g the useless waste of f u e l , utilizing low-grade fuels, and presenting a substitute for natural gas." This statement appropriately describes the motivation behind the research discussed here. Futhermore, with renewed interest being shown i n coal, the price of indigenous natural gas in dispute and general acceptance of residue-derived fuel as a potential contributor to our energy needs, Mr. Wyer's opinions are equally applicable today - 70 years after the publication of his Treatise. Agriculture and related industries account for 12 to 20 percent of the national energy consumption - depending on the d e f i n i 1

Current Address: Biomass Fuel Conversion Associates, Inc., Yuba City, CA 0-8412-0434-9/78/47-076-142$05.25/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

WILLIAMS

E T

AL.

Pilot Plant Gasification Systems

143

t i o n of the food c h a i n ( 2 ) . At the same time, l a r g e amounts of energy are a v a i l a b l e i n the form of crop, food p r o c e s s i n g and f o r e s t i n d u s t r y r e s i d u e s (biomass). To f a c i l i t a t e the s u c c e s s f u l u t i l i z a t i o n of t h i s energy a t the farm, processing p l a n t or lumber m i l l a simple, low-cost method of r e c o v e r i n g thermal and e l e c t r i c a l energy from these r e s i d u e s i s r e q u i r e d . Downdraft g a s i f i c a t i o n i s one such method. T h i s concept has been under i n v e s t i g a t i o n a t the A g r i c u l t u r a l Engineering Department, U n i v e r s i t y of C a l i f o r n i a , Davis f o r 2 1/2 y e a r s . The work i s supported by p r i v a t e and government funding. The downdraft producer i s a moving, packed bed, v e r t i c a l - f l o w r e a c t o r employing cocurrent gas flow. A b a t c h - f i l l e d , l a b o r a t o r y - s c a l e producer ( c a p a c i t y of 40 to 90 f u e l l b - h r ~ l ) has been used to study the g a s i f i c a t i o n c h a r a c t e r i s t i c s of r e s i d u e s and t o t e s t d i f f e r e n t designs of g r a t e and f i r e b o x . The r e s u l t s of t h i s work are a v a i l able elsewhere (3) ( 4 ) A 10 K engine-generator s e t f u e l e d w i t h producer gas, has been demonstrated p e r i o d s up to 4 hours. Two p i l o t p l a n t producers systems were designed and c o n s t r u c t ed to demonstrate g a s i f i c a t i o n i n a c t u a l a p p l i c a t i o n . One u n i t i s supplying 10 m i l l i o n B t u - h r ~ l as hot, p a r t i c u l a t e - f r e e gas, t o the burner i n a steam b o i l e r , r e p l a c i n g n a t u r a l gas. A second u n i t generates f u e l gas from corn cobs which i s cleaned, cooled and s u p p l i e d to a 180 Hp d u a l - f u e l , turbo-charged, i n t e r c o o l e d d i e s e l engine that i s d i r e c t - c o u p l e d to a 100 Kw generator. G a s i f i c a t i o n Reactions The term " g a s i f i c a t i o n " , as used here, i s the r e a c t i o n of s o l i d f u e l s w i t h a i r and steam t o y i e l d a low-Btu gas which i s s u i t a b l e f o r use as a source of energy. The p r i n c i p l e components of the product gas a r e formed by a combination of r e a c t i o n s between the carbon i n the f u e l , oxygen i n the a i r b l a s t , and steam d e r i v e d from the f u e l . In an o r d i n a r y s o l i d f u e l combustion process, due to the comparatively s h a l l o w l a y e r of incandescent carbon and a r e l a t i v e l y h i g h a i r v e l o c i t y , carbon d i o x i d e i s formed and the g r e a t e s t number of a v a i l a b l e heat u n i t s i s obtained from the combustion of the f u e l . C + 0 + ( n i t r o g e n ) — * C 0 + (nitrogen) + 174,000 Btu ...1 2

2

A greater depth of f u e l g i v e s r i s e to the f o r m a t i o n of carbon monoxide w i t h corresponding l o s s of the a v a i l a b l e s e n s i b l e heat u n i t s . With a s u f f i c i e n t t h i c k n e s s of h i g h l y heated carbon, r e l a t i v e t o the a i r v e l o c i t y , carbon monoxide alone may be the f i n a l product, w i t h o n l y t r a c e s of carbon d i o x i d e . 2C + 0

+ ( n i t r o g e n ) — • 2C0 + (nitrogen) + 103,500 Btu ...2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

144

SOLID

WASTES

AND

RESIDUES

The a c t i o n of oxygen on carbon r e s u l t s i n the simultaneous f o r mation of carbon d i o x i d e and carbon monoxide but, w i t h a s u f f i c i e n t t h i c k n e s s of f u e l , the carbon d i o x i d e r e a c t s w i t h excess carbon producing carbon monoxide ( 5 ) . Reactions 1 and 2 are exothermic and the producer temperature w i l l continue to r i s e f o r g i v e n a i r input r a t e u n t i l c o u n t e r - b a l anced by heat l o s s e s i n the gas, s o l i d r e s i d u e , undecomposed steam, and by r a d i a t i o n . I n p r a c t i c e a l i m i t i s reached by the l i a b i l i t y of the s o l i d r e s i d u e to form c l i n k e r and by the maximum temperature which the producer w a l l s can w i t h s t a n d . Biomass f u e l s c o n t a i n s u b s t a n t i a l q u a n t i t i e s of moisture and elemental oxygen. Both the c e l l u l o s e and the l i g n i n that make up the m a j o r i t y of the biomass f u e l s c o n t a i n i n t h e i r s t r u c t u r e hydrogen and h y d r o x y l (OH) groups. Under the c o n d i t i o n s i n the producer, as the f u e l i s fed down i n t o the r e a c t i o n zone, when the temperat u r e reaches about 150°F (65°C) f r e e water or moisture i s r a p i d l y e x p e l l e d i n t o the produc at about 450°F (232°C), groups, and the hydrogen r e a c t , producing water. T h i s r e a t i o n i s exothermic; however, the f u l l heat v a l u e of s t o c h i o m e t r i c combust i o n of hydrogen i s not a v a i l a b l e as much of the hydrogen i s combined i n t o the h y d r o x y l group. In a downdraft system a i r i s forced r a d i a l l y i n t o a packed bed of f u e l through tuyeres which are l o c a t e d near the top of the f i r e b o x . Producer gas e x i t s the bed through the g r a t e below the firebox. The approximate l o c a t i o n s of the r e a c t i o n zones are shown i n F i g u r e 1. Neither the l o c a t i o n of the v a r i o u s zones nor the temperatures shown are r i g i d l y d e f i n e d . The diagram should only be used as a guide to the r e a c t i o n s i n a producer. Chemically produced steam along w i t h the steam from f r e e moisture moves down thru the hot f u e l bed. There are t r a c e s of steam introduced as water vapor i n the a i r b l a s t . The steam r e a c t s w i t h the incandescent carbon a c c o r d i n g to the f o l l o w i n g equations : ...3 ...4 Reaction 3 r e q u i r e s temperatures of at l e a s t 1650°F (900°C); r e a c t i o n 4 predominates at lower temperatures (930°F) (500°C). By the simultaneous a c t i o n of a i r and f u e l - d e r i v e d steam, a thermal balance i s set up between the exothermic a i r - c a r b o n r e a c t i o n and the endothermic steam-carbon r e a c t i o n . Depending on the r e l a t i v e p r o p o r t i o n s of a i r and steam, a constant temperature i s maintained and, corresponding w i t h t h i s temperature, a d e f i n i t e composition of the mixed gas i s obtained which, i n turn depends on the r e l a t i v e p a r t s played by r e a c t i o n s 2, 3 and 4.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

WILLIAMS

E T A L .

145

Pilot Plant Gasification Systems

Fuel

I

H 0 ( m o i s t u r e ) - V H 0 (steam) 2

Drying Zone 150°F Tar Formation Steam Formation

A i r + Water Vapor

Oxidation Zone +2000°F Primary Reduction Zone

2

H + OH->-H 0 (steam)

^-Air ^

c + o -> co 2

2

C + H 0->-CO + H 2

C + 2H 0—yC0 2

2

2

+ 2H

2

+ H

C + C0 -^±:2CO 2

1500°F Secondary

C + C0 "^2CO

Reduction Zone

CO + H 0 ^ C 0

2

2

2

S o l i d Residue and Gas 1000°F

1 lL Figure 1.

Reaction zones in a downdraft producer

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2

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The endothermic nature of r e a c t i o n s 3 and 4 c o n s t i t u t e another l i m i t on the maximum o b t a i n a b l e producer temperature. Furthermore, the presence of too much steam c h i l l s the combustion zone to a p o i n t where carbon d i o x i d e i n c r e a s e s , carbon monoxide decreases, and hydrogen i n c r e a s e s to a peak v a l u e and then decreases. The v o l a t i l e matter i n the f u e l i s decomposed d u r i n g preheati n g ; producing methane, higher hydrocarbons, pyroligneous a c i d s , and other r e l a t e d compounds. Biomass f u e l s c o n s i s t mostly of c e l l u l o s e and l i g n i n and the thermal decompostion of these compounds i s very complicated. Large volumes of higher hydrocarbons of t a r s are produced. As i n the case of steam, i n a downdraft system the t a r s are exposed to incandescent carbon before they e x i t from the producer. A s i g n i f i c a n t p o r t i o n of the t a r i s broken down i n t o gaseous hydrocarbons i n these hot zones. A p o s s i b l e a n a l y s i s of the gas obtained from a downdraft r e s i d u e - f u e l e d producer would be 1 0 % C 0 2 2 0 % CO 5% C H 18% H 2 1% O 2 , and 46% N£. Carbo r e a c t i o n s not being complete introduced i n the combustion a i r . The gas may a l s o c o n t a i n from 1 0 to 2 0 percent by volume of undecomposed steam, depending on the moisture content of the f u e l . Hydrocarbons are present i n the gas over a wide range of homologues. The 5% C Hy i n c l u d e d i n the a n a l y s i s above c o n s i s t s of methane, ethane, and other permanent gases. Some higher hydrocarbons or t a r s escape i n t o the gas stream where they form heavy vapors and a e r o s o l s . T h e i r dew p o i n t covers a wide temperature range. Although t a r s add to the h e a t i n g v a l u e of the produced gas, t h e i r presence i s u n d e s i r a b l e s i n c e they d e p o s i t on c o l d s u r faces i n p i p i n g , gas clean-up and combustion systems. The f o l l o w i n g a d d i t i o n a l r e a c t i o n s remain to be considered. In the a i r - c a r b o n r e a c t i o n , i f a l l the oxygen has combined w i t h carbon, hot carbon, carbon d i o x i d e and carbon monoxide e x i s t simultaneously. T h e i r p r o p o r t i o n s are c o n t r o l l e d by the f o l l o w ing r e v e r s i b l e reaction: x

C + C0 « 2

...5

> 2C0

High temperatures and maximum contact time favor the formation of carbon monoxide. Since hydrogen and steam are a l s o p r e s e n t , the f o l l o w i n g r e a c t i o n occurs: CO +

H0 2

2

.· ·6

T h i s i s considered to be a f u e l s u r f a c e phenomenon, w i t h v e r y l i t t l e r e a c t i o n i n the gas phase. I t approaches e q u i l i b r i u m gene r a l l y as a f u n c t i o n of steam decompostion and f u e l bed t h i c k n e s s at a g i v e n temperature although f u e l r e a c t i v i t y and c a t a l y t i c a c t i v i t y of the f u e l ash a l s o p l a y a p a r t ( 6 ) .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

WILLIAMS

E T A L .

Pilot Plant Gasification Systems

147

G a s i f i e r Design, Specif i c Rate of G a s i f i c a t i o n and Process V a r i a b l e s A s e c t i o n of the p i l o t p l a n t gas producer i s shown i n F i g u r e 2. E x c l u d i n g the f u e l feed and ash removal systems, i t s net weight i s about 4 tons and i t s o v e r a l l height i s 17 f e e t . A i r i s d i s t r i b u t e d t o the f i x e d f u e l bed w i t h an i n t e r n a l c y l i n d r i c a l plenum and e i g h t n o z z l e s o r tuyeres. The plenum c o n s i s t s o f two c o n c e n t r i c s t e e l c y l i n d e r s , the i n s i d e c y l i n d e r being the f i r e b o x w a l l . Gas e x i t s through the base and s i d e s o f the g r a t e . Designs are discussed l a t e r . A v a r i a b l e head o f f u e l i s maintained i n the f u e l hopper. I t passes down i n t o the r e a c t i o n zones i n the f i r e box under the i n f l u e n c e o f g r a v i t y . The r a t e o f burning f u e l o r " s p e c i f i c r a t e o f g a s i f i c a t i o n " i s expressed i n pounds o f d r y f u e l per square f o o t and hour, l b ( f t - h r ) " ' . When c o n s i d e r i n g the i n s t a l l a t i o n o f , o r the working r e s u l t s o f a gas producer p l a n t , s p e c i f i c r a t e has an important b e a r i n g on the t e c h n i c a question. For a given therma discussed i n terms o f other process design and o p e r a t i n g v a r i a b l e s . S p e c i f i c r a t e i s d i r e c t l y a f f e c t e d by both f u e l consumpt i o n r a t e and a i r i n p u t r a t e , s i n c e both o f these o p e r a t i n g v a r i ables are s t o i c h i o m e t r i c a l l y r e l a t e d . F u e l consumption r a t e i s mechanically c o n t r o l l e d by movement o f the grate. Grate a c t i o n c o n t r o l s s o l i d s - f l o w through the v e r t i c a l r e a c t o r and s p e c i f i c r a t e can be increased u n t i l t h i s c o n t r o l i s l o s t . Grate c o n f i g u r a t i o n i s a s i g n i f i c a n t design v a r i a b l e . I n a d d i t i o n t o supporting the f u e l bed and e n a b l i n g s o l i d r e f u s e t o be c o n t i n u o u s l y removed from the bottom of the bed, the grate must a l s o present s u f f i c i e n t open area f o r the gas t o escape through and, when necessary, provide s u i t a b l e b e d - a g i t a t i o n . I f s o l i d r e f u s e removal i s too r a p i d , the r e a c t i o n zones are subj e c t e d t o undue d i s t u r b a n c e . Raw f u e l r e p l a c e s char i n the reduct i o n zone producing l a r g e volumes o f t a r i n the gas and char streams. The r o t a t i n g e c c e n t r i c grate shown i n F i g u r e 3, which has seen widespread use i n u p d r a f t producers, has been used successf u l l y w i t h many f u e l s . I t c o n s i s t s o f f l a t , c i r c u l a r , s t e e l p l a t e r i n g s mounted one above the other w i t h t h e i r edges overl a p p i n g . S o l i d r e f u s e must pass h o r i z o n t a l l y between the p l a t e s and t h i s motion i s imparted t o the r e f u s e by r o t a t i o n of the grate. The grate p l a t e s are e c c e n t r i c w i t h the center support so r o t a t i o n f o r c e s r e f u s e between them and a l s o imparts a g r i n d i n g a c t i o n t o any c l i n k e r s which may form. These are crushed between the edges o f the p l a t e s and the s i d e s o f the f i r e b o x . Another grate design shown i n F i g u r e 2 i n v o l v e s the use o f s h o r t , h o r i z o n t a l lengths o f s t a i n l e s s - s t e e l tube-augers mounted i n s i d e a truncated c o n i c a l basket which extends below the f i r e box. The auger f l i g h t s are mounted i n opposing s e t s on each o f three s h a f t s and discharge on opposite s i d e s o f the basket where s o l i d r e f u s e drops down t o the ash p i t . The auger s h a f t s extend o u t s i d e the producer through packing glands, so the d r i v e mechanism 2

1

American Oiemlcal

Society Library 1155 16th St. N. w. Washington, D. C. Jones, 20036J., et al.; In Solid Wastes and Residues; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

Figure 2.

WASTES

AND

RESIDUES

Cross section of downdraft pilot plant gas producer—January, 1978

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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WILLIAMS

E T

AL.

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Pilot Plant Gasification Systems

i s i n a c l e a n atmosphere. S p e c i f i c r a t e i s l i m i t e d by an acceptable a i r input r a t e and consequent gas f l o w r a t e . I f the v e l o c i t y o f the produced gas, immediately below the g r a t e , i s g r e a t e r than the s e t t i n g v e l o c i t y of the s o l i d r e f u s e , p a r t i c l e s are e n t r a i n e d , r e s u l t i n g i n an over­ load on the downstream gas clean-up system. I f the a i r input r a t e i s too r a p i d , s u f f i c i e n t r e s i d e n c e time may not be a v a i l a b l e t o the gas i n the r e d u c t i o n zone, r e s u l t i n g i n incomplete formation of CO. I n p r a c t i c e , however, t h i s i s r a r e l y a l i m i t i n g f a c t o r . The f i r e b o x should be designed t o g i v e maximum f u e l depth t o pro­ v i d e f o r adequate r e s i d e n c e time. S p e c i f i c r a t e can be l i m i t e d by the p h y s i c a l and. chemical p r o p e r t i e s o f t h e feedstock. Moisture and t o t a l ash content can l i m i t feedstock from being g a s i f i e d without s u i t a b l e p r e p r o c e s s i n g , but the e f f e c t of these two parameters on s p e c i f i c r a t e i s not as pronounced as that o f f u e l p a r t i c l e s i z e and f u s i o n p r o p e r t i e s Fuel p a r t i c l e siz d i f f e r e n t i a l across the input m a t e r i a l s , such as sawdust and r i c e husks, present a h i g h r e s i s ­ tance t o the passage o f a i r and gas due t o the low voidance of f i x e d beds composed of these m a t e r i a l s . Α Δρ o f 5" w.g. was r e ­ corded over a bed o f sawdust one f o o t deep f o r a s u p e r f i c i a l v e l o c i t y o f 110 f t - m i n " . With s i m i l a r beds of broken corn cobs, wood c h i p s , and bark, a Δρ of 0.5" w.g. was obtained f o r the same a i r v e l o c i t y . F i n e feedstocks must be d e n s i f i e d (cubed o r p e l l e t i z e d ) , t o i n c r e a s e i n d i v i d u a l p a r t i c l e s i z e , before they can be g a s i f i e d i n a f i x e d bed downdraft system. The h i g h pressures r e ­ quired t o f o r c e the combustion a i r i n t o the bed, tend t o blow m a t e r i a l through the g r a t e . D e n s i f i c a t i o n a l s o improves the m a t e r i a l h a n d l i n g p r o p e r t i e s of feedstocks such as c o t t o n g i n waste and c e r e a l straw. F u r t h e r ­ more, without d e n s i f i c a t i o n these m a t e r i a l s b r i d g e i n the f u e l hopper s e c t i o n o f the g a s i f i e r . Fusion temperature o f the i n o r g a n i c matter (ash) i n the feed­ stock determines the formation o f c l i n k e r from the ash i n the o x i d a t i o n zone (+2000°F). The ash components form e u t e c t i c mix­ t u r e s of lowest m e l t i n g p o i n t which melt out from the whole mass. Cotton g i n n i n g waste i s p a r t i c u l a r l y prone t o c l i n k e r formation and must be cleaned t o remove as much f i n e i n o r g a n i c matter as p o s s i b l e p r i o r t o g a s i f i c a t i o n . C a r e f u l temperature c o n t r o l i n the r e a c t o r i s e s s e n t i a l w i t h c l i n k e r - p r o n e f e e d s t o c k s . T o t a l ash content i n the feedstock i s important, s i n c e i t i s u s u a l l y present a t the expense o f carbon. Most biomass f u e l s have ash contents w i t h i n the range o f 1 t o 5 percent by weight. Rice 1

h u s k s , w i t h up t o 21$

ash, mostly

silica,

a r e an

exception.

G a s i f i c a t i o n o f r i c e husks r e s u l t s i n unavoidably low thermal e f f i c i e n c y due t o s e n s i b l e heat l o s s e s i n the s o l i d r e f u s e . Water, from moisture i n the f u e l and water o f redaction, i s converted t o steam which, i n a downdraft r e a c t o r , must: then pass through the r e a c t i o n zones. Too much steam, from very wet

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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feedstocks, c h i l l s the r e a c t i o n zone, reducing gas q u a l i t y and thermal e f f i c i e n c y . Wet f u e l (>30% by weight moisture) must be d r i e d . Where the feedstocks a l s o r e q u i r e s d e n s i f i c a t i o n , these two requirements can be met i n one o p e r a t i o n . Temperature r e s i s t a n c e p r o p e r t i e s of the f i r e b o x w a l l m a t e r i a l s would be expected t o l i m i t the s p e c i f i c r a t e . I n the downdraft producer, a l a y e r of char b u i l d s up around the i n s i d e of the f i r e b o x , i n s u l a t i n g the w a l l m a t e r i a l , t u y e r e s , and choke p l a t e from the h i g h temperatures i n the o x i d a t i o n zone. Formation of t h i s l a y e r i s not a f f e c t e d by s p e c i f i c r a t e . A n c i l l a r y Systems In a d d i t i o n to the g a s i f i e r , a gas producer system i n c l u d e s a f u e l feed system w i t h a storage b i n , s o l i d r e f u s e removal dev i c e s and d i s p o s a l means and a s u i t a b l e gas clean-up t r a i n Where i t i s d e s i r e d to r e p l a c a producer gas burner mus product i s e l e c t r i c a l power, an engine-generator (or t u r b i n e generator) has to be provided. F u e l feed and ash removal have to be accomplished through a i r l o c k s s i n c e the producer i s operated e i t h e r a t a low pressure (1 to 5 p s i g ) or under a s l i g h t vacuum. For f u e l f e e d , a r o t a r y v a l v e mounted below e i t h e r a k n i f e gate or b u t t e r f l y v a l v e (to p r o v i d e p o s i t i v e s e a l when the system i s not c y c l i n g ) has been found to g i v e s a t i s f a c t o r y performance. F u e l i s conveyed from the storage b i n to the top of the feed v a l v e u s i n g tube augers f o r m a t e r i a l s such as corn cobs, or a b e l t conveyor f o r wood c h i p s . A r o t a r y v a l v e can be used to discharge s o l i d r e f u s e from the base of the g a s i f i e r . L e v e l i n d i c a t o r s must be provided to c o n t r o l the opera t i o n of the f u e l feed and s o l i d r e f u s e discharge. T o t a l l y automatic o p e r a t i o n of both systems i s e a s i l y achieved. Coarse p a r t i c u l a t e s ( s o l i d r e f u s e carry-over) should be r e moved from the produced raw gas as c l o s e as p o s s i b l e to the g a s i f i e r . Cyclones are w e l l s u i t e d to t h i s task. Accurate cyclone design i s made d i f f i c u l t by a f l u c t u a t i n g raw gas flow so h i g h e f f i c i e n c i e s are not achieved. The cyclone should be designed to accommodate maximum f l o w ; the o b j e c t i v e should be to r e l i e v e the load on down-stream clean-up components. A c o n v e n t i o n a l baghouse, employing f i b e r g l a s s bags has been used to remove the remaining f i n e p a r t i c u l a t e s . A c l u s t e r of f i b e r g l a s s bags i s shown i n F i g u r e 4. To avoid the d e p o s i t i o n of e i t h e r t a r or water i n the cyclone and baghouse, the gas must be maintained above the dew p o i n t (about 225°F) of the condensable vapors. Heat l o s s e s should be minimized by i n s u l a t i n g the c y c l o n e , baghouse, and connecting pipework ( F i g u r e 5 ) . A f t e r removal of coarse p a r t i c u l a t e s , the gas i s s u i t a b l e f o r combustion i n a steam b o i l e r . A d i v e r t i n g v a l v e should be provided to route the gas to a f l a r e e i t h e r i n an emergency shut-down or when low f i r e i s c a l l e d f o r i n the b o i l e r combustion chamber.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

WILLIAMS

E T

AL.

Pilot Fiant Gasification Systems

Figure

Figure 4.

Fiberglass filters

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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A c e n t e r - f i r e type gun i s g e n e r a l l y proposed f o r use w i t h producer gas i n a b o i l e r f i r e b o x . I t should have a l a r g e gas o r i f i c e as insurance a g a i n s t t a r b u i l d - u p and h i g h pressure drop. I f the gas i s t o be used as f u e l i n an i n t e r n a l combustion engine, i t r e q u i r e s f u r t h e r c l e a n i n g and a l s o c o o l i n g . A f i n n e d tube heat exchanger has been used t o remove condensables from the gas and t o i n c r e a s e i t s d e n s i t y . A fan i s used t o c o o l the tubes w i t h ambient a i r . Although d i r e c t contact between the gas and a c o o l i n g f l u i d ( g e n e r a l l y water) i s a more e f f i c i e n t method of c o o l i n g , d i s p o s a l o f the c o o l i n g water i s u s u a l l y an environmental problem. A constant speed, p o s i t i v e displacement blower was placed i n the system between the gas clean-up equipment and the d i e s e l - e n g i n e gas t h r o t t l e v a l v e . The blower i s r a t e d a t 300 cfm and w i t h a s e t of v a l v e s and pressure r e g u l a t o r s performs two f u n c t i o n s . During producer s t a r t - u p and f l a r e o p e r a t i o n the blower s u p p l i e s p r e s s u r i z e d a i r t o the producer are p r e s s u r e i z e d to aroun s u p p l i e d t o the d i e s e l engine, the blower i s v a l v e d such that below atmospheric pressure e x i s t s i n the producer and gas clean-up s y s tem. A i r i s drawn i n t o the producer from p o r t s v a l v e d t o the atmosphere. The blower draws producer gas from the producer, through the gas clean-up system, and p r o v i d e s a p r e s s u r i z e d , regul a t e d gas supply t o the t h r o t t l e v a l v e on the d i e s e l engine a i r i n t a k e stack. A complete t r a i l e r - m o u n t e d energy conversion p l a n t , comprising g a s i f i e r f u e l b i n , g a s i f i e r , clean-up t r a i n , and 100 KVA enginegenerator i s shown i n F i g u r e s 5 and 6. A schematic o f the process i s shown i n F i g u r e 7. Dual F u e l i n g and Performance o f a Standard Turbo-charged Cooled D i e s e l Engine

Inter-

A d i e s e l engine w i t h a 100 kw 12 w i r e a l t e r n a t o r mounted on the t r a i l e r was used t o supply the necessary e l e c t r i c a l power t o the onboard equipment and t o generate e l e c t r i c i t y u s i n g producer gas as the main source o f energy. The engine i s a 6 c y l i n d e r , 4 s t r o k e , d i r e c t i n j e c t i o n d i e s e l engine w i t h 531 i n ^ displacement and a compression r a t i o o f 14.5 t o 1. I t i s turbo-charged, i n t e r cooled, has^ a power r a t i n g o f 202 bhp i n t e r m i t t e n t , 172 bhp continuous a t 1800 rpm, and i s equipped w i t h a Bosch i n l i n e i n j e c t i o n pump and Bosch v a r i a b l e speed governor (type RSV). C o n s i d e r a t i o n s f o r Dual F u e l Conversion. I n order that d i e s e l engines can operate s u c c e s s f u l l y on producer gas, the f o l l o w i n g c h a r a c t e r i s t i c s a r e considered important. A minimum of d i e s e l f u e l should be used t o m a i n t a i n i g n i t i o n o f the producer gas. T h i s w i l l i n d i c a t e the a b i l i t y o f a d i e s e l - p r o d u c e r gas system t o econ o m i c a l l y operate i n a s i t u a t i o n where abundant c e l l u l o s i c matter i s present f o r g a s i f i c a t i o n but d i e s e l f u e l i s i n s h o r t supply

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Figure 5. Gas

clone and filters

Figure 6. Complete energy conversion system (100 KVA engine-generator is in foreground)

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>

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Figure 7. Schematic of portable 100 w farm power plant In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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and/or c o s t l y . I t i s d e s i r a b l e t o r e t a i n the accuracy and f a s t response t o load changes that are achieved w i t h d i e s e l engine governors on new engines. T h i s w i l l a l l o w d i e s e l - p r o d u c e r gas generator s e t s to supply r e g u l a t e d e l e c t r i c a l power i f r e q u i r e d . Present day d u a l f u e l engines n o r m a l l y are s u p p l i e d w i t h a p r e s s u r i z e d gas supply. Gas input response i s dependent s o l e l y on the response of the gas t h r o t t l e v a l v e to governor s i g n a l s . With the gas coming from a l o c a l gas producer, gas input response w i l l be dependent on the o p e r a t i n g c h a r a c t e r i s t i c s of the producer and s u p p o r t i n g equipment upstream of the engine. Poor response w i l l r e s u l t i n l a r g e speed v a r i a t i o n s d u r i n g changes i n engine l o a d . T h e r e f o r e , i t i s unacceptable to f i x the d i e s e l i n j e c t i o n q u a n t i t y and a l l o w the engine governor t o only operate the gas t h r o t t l e v a l v e , as i s c u r r e n t l y done w i t h many d u a l - f u e l systems. Safety c o n s i d e r a t i o n s a r e of prime importance w i t h r e s p e c t to both the personnel o p e r a t i n i t s e l f . Normal s a f e t y f e a t u r e ing system. The main s a f e t y problem r e s u l t i n g from u s i n g producer gas t o d u a l - f u e l the engine, i s one of an e x p l o s i o n hazard w i t h i n the exhaust system i f unburned producer gas i s exhausted from the combustion chamber. The s o l u t i o n i s to ensure t h a t complete comb u s t i o n occurs under a l l o p e r a t i o n c o n d i t i o n s and that the producer gas i s purged from the i n t a k e and exhaust system, p r i o r to engine shut-down. M o d i f i c a t i o n s and A d d i t i o n s t o Standard D i e s e l - E n g i n e . The only a l t e r a t i o n s made t o the p r o d u c t i o n model d i e s e l engine were to the Bosch governor and were minor i n n a t u r e . The governor housing was m o d i f i e d to a l l o w the a d d i t i o n of an a d j u s t a b l e , m i n i mum stop f o r the d i e s e l f u e l r a c k , and a sensor which i n d i c a t e d the a b s o l u t e p o s i t i o n of the f u e l rack. The f u e l rack stop d i c t a t e d the minimum q u a n t i t y of f u e l that was i n j e c t e d from the f u e l pump. T h i s f u e l r a c k stop i s s o l e n o i d c o n t r o l l e d and when d i s engaged, the o p e r a t i o n of the governor and f u e l pump t o engine speed v a r i a t i o n s i s no d i f f e r e n t from the unmodified d i e s e l engine. The f u e l stop i s set at the minimum q u a n t i t y of d i e s e l f u e l r e q u i r e d t o m a i n t a i n continuous i g n i t i o n of the producer gas. This q u a n t i t y i s about h a l f t h a t consumed at no load i d l e (1800 rpm) on f u l l d i e s e l . The stop ensures t h a t complete combustion w i l l be maintained under a l l o p e r a t i n g c o n d i t i o n s , thus, r e d u c i n g the exp l o s i o n hazard. The f u e l rack p o s i t i o n sensor has a r e s o l u t i o n of .001 i n c h and i s used i n the gas t h r o t t l e v a l v e c o n t r o l c i r c u i t . The sensor i s a wire-wound l i n e a r motion potentiometer and has l i t t l e e f f e c t on the governor's performance. The f a c t t h a t no other a l t e r a t i o n s to the d i e s e l engine were r e q u i r e d i s a good i n d i c a t i o n that minimal c a p i t a l w i l l be needed to develop s u c c e s s f u l producer g a s / d u a l - f u e l d i e s e l engines manuf a c t u r e d under mass p r o d u c t i o n techniques. Equipment added to the

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d i e s e l engine c o n s i s t e d o f a gas t h r o t t l e v a l v e , i t s a c t u a t o r and e l e c t r o n i c c o n t r o l and l o g i c c i r c u i t and the f o l l o w i n g s a f e t y equipment: 1) emergency i n t a k e a i r s h u t - o f f v a l v e , 2) over-speed sensors, 3) emergency k i l l b u t t o n , and 4) producer gas snap-off v a l v e upstream of the t h r o t t l e v a l v e (low o i l pressure and h i g h water temperature sensors were standard equipment). Engine Performance R e s u l t s o f Dual F u e l Operation on Producer Gas. A f t e r the gas producer system had been brought up to operati n g temperature, the d i e s e l engine was s u p p l i e d w i t h producer gas generated from broken corn cobs f o r d u a l f u e l running. Producer gas composition was assumed t o be 20.1% CO, 16.3% H , 5.0% THC w i t h a heat content o f 162 B t u / f t ^ a t STP. These average v a l u e s are from gas analyses data obtained w i t h d r y broken corn cobs a t another l o c a t i o n . R e s i s t i v e heater panels provided an e l e c t r i c load up t o 100 Kw (150 Bhp) i n 6 Kw increments. For most of the t e s t i n g the q u a n t i t y o was maintained a t t h a t q u a n t i t i d l e . Load was added o r s u b t r a c t e d i n 6 Kw increments and the gas t h r o t t l e v a l v e manually a d j u s t e d t o m a i n t a i n the i d l e q u a n t i t y of d i e s e l f u e l . Zero t o 60 Kw l o a d was d e l i v e r e d by producer gas w i t h no problems being experienced. I n f a c t l e s s exhaust smoke and q u i e t e r running were experienced when producer gas was being used. T h i s i s a t t r i b u t e d t o more complete combustion o f the outer s u r f a c e o f the i n j e c t i o n spray and t o the slower combustion chara c t e r i s t i c s of the low-Btu gas. Producer gas could not p i c k up more than 60 Kw o f load without d e t o n a t i o n appearing. By i n c r e a s i n g the d i e s e l f u e l being i n j e c t e d , a l t e r n a t o r output could be increased beyond 60 Kw. One hundred Kw output was e a s i l y achieved w i t h 60 Kw b e i n g s u p p l i e d from producer gas. T h i s demonstrated that a i r had not become a l i m i t i n g f a c t o r to i n c r e a s i n g the l o a d p i c k e d up w i t h producer gas. The e f f e c t o f low amounts o f i n j e c t e d d i e s e l f u e l was i n v e s t i g a t e d . The d i e s e l engine has an i n d i c a t e d demand o f 40 hp a t 1800 rpm no load i d l e . The a l t e r n a t o r output was s e t a t 46 Kw (70 Bhp) and the gas t h r o t t l e v a l v e s l o w l y opened. As producer gas flow r a t e i n c r e a s e d , the governor reduced the q u a n t i t y o f d i e s e l f u e l b e i n g i n j e c t e d . As the p o s i t i o n o f the minimum f u e l rack s e t t i n g was approached, d e t o n a t i o n appeared, and about 60 Kw of energy was being s u p p l i e d by producer gas. Up t o t h i s p o i n t i t has been the q u a n t i t y o f producer gas that caused d e t o n a t i o n , because enough d i e s e l was being i n j e c t e d t o ensure c o n s i s t e n t i g n i t i o n . T h i s procedure was repeated w i t h l e s s than 40 Kw l o a d on the a l t e r n a t o r . The f u e l rack stop was disengaged and the i n j e c t i o n q u a n t i t y of d i e s e l f u e l was allowed t o pass below t h i s s e t t i n g . J u s t below the minimum s e t t i n g severe m i s f i r i n g began t o occur. Approximately 6 1/2 l b / h r of d e i s e l f u e l was b e i n g i n j e c t e d when m i s f i r e occurred. Producer gas q u a n t i t y was then v a r i e d between c o n d i t i o n s of m i s f i r e and d e t o n a t i o n over a l l 6 Kw incremental s e t t i n g s of a l t e r n a t o r l o a d . The engine o p e r a t i n g performance was observed w i t h no i n c r e a s e i n 2

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the

exhaust smoke noted a t anytime. I t was observed t h a t the o n l y f a c t o r c o n t r i b u t i n g t o detonat i o n was the q u a n t i t y o f producer gas b e i n g used i n the engine. Whenever the producer gas c o n t r i b u t e d more than 60 Kw of l o a d , d e t o n a t i o n would appear. Except f o r the q u i e t running o f the engine when b u r n i n g low-Btu gas, i t was i m p o s s i b l e t o t e l l that i t was running i n a dual f u e l mode. R a t i o s o f gas t o d i e s e l energy up t o 4.5 t o 1 were experienced. Detonation o r m i s f i r e prevented h i g h e r r a t i o s from o c c u r i n g . The engine i n t e r c o o l e r was s u p p l i e d w i t h engine c o o l a n t and r e s u l t e d i n an i n d u c t i o n m i x t u r e temperature of about 170°F. Detonation occurred mainly because o f the hydrogen content of the producer gas and the r e l a t i v e l y h i g h i n d u c t i o n mixture temperature. I n j e c t i o n pump t i m i n g was not s e t a t optimum f o r d u a l f u e l operat i o n and could have added p o s s i b l y 5 Kw p r i o r t o onset o f detonat i o n . The use o f tap water i n the i n t e r c o o l e r would lower the tendency o f the produce the load c o u l d be s u p p l i e C a l c u l a t i o n s i n d i c a t e that s u f f i c i e n t combustion a i r i s a v a i l able f o r f u l l l o a d o p e r a t i o n . Unless d e t o n a t i o n appears p r i o r t o 100 Kw l o a d s , the d i e s e l engine should not be derated f o r 100 Kw (150 Bhp) f o r producer gas o p e r a t i o n . Thus, c l e a n c o o l gas i s necessary f o r r e l i a b l e continuous d u a l - f u e l o p e r a t i o n . Although i n these t e s t s d e t o n a t i o n l i m i t e d producer gas output to 60 Kw (90 Bhp), minor m o d i f i c a t i o n s w i l l a l l o w the producer gas power t o i n c r e a s e and l i k e l y to the f u l l r a t e d output o f 100 Kw output f o r the a l t e r n a t o r . P i l o t P l a n t G a s i f i e r Performance. The p i l o t p l a n t produced low-Btu gas from k i l n dry hog wood c h i p s t o f u e l a low-pressure (10 p s i ) n a t u r a l - d r a f t b o i l e r o f about 151 b o i l e r horsepower c a p a c i t y (4370 l b steam/hr @ 1157 B t u / l b e n t h a l p y ) . The b o i l e r steam was used p r i m a r i l y f o r space h e a t i n g i n a s i n g l e s t o r y concrete c o n s t r u c t i o n b u i l d i n g housing the S t a t e o f C a l i f o r n i a p r i n t i n g f a c i l i t y . The wood c h i p f u e l had a c a l o r i f i c h e a t i n g v a l u e of 8814 B t u / l b dry f u e l b a s i s and contained about 13.7 percent moist u r e on a wet b a s i s . With n i g h t t i m e ambient temperatures between 52 and 56°F, a g a s i f i c a t i o n r a t e o f 1105 l b dry wood chips/hour was adequate t o meet the b o i l e r h e a t i n g l o a d . The average combust i b l e -gas contents by volume a t ambient temperature and p r e s s u r e were: CO - 23.4%, H - 13.2%, and THC ( t o t a l hydro carbon) - 9.2%. The net t o t a l energy per c u b i c foot of low-Btu gas f o r these volume percentages was 205.7 Btu based on B t u / f t ^ h e a t i n g v a l u e s of 321.8 f o r CO, 275.0 f o r H , and 985.9 f o r THC (90% CH @ 913.1 and 10% C H @ 1641.0). Assuming an 85% f u e l thermal e f f i c i e n c y for the gas producer, 8.278 m i l l i o n Btu o f low-Btu gas was produced h o u r l y w i t h an average o f f - g a s temperature o f 780°F. Excess gas not r e q u i r e d by the b o i l e r was burned a t f l a r e s i n s t a l l e d i n the heat gas l i n e . A f t e r s t e a d y - s t a t e gas p r o d u c t i o n was achieved, there was 2

2

2

4

6

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n e g l i g i b l e condensate c o l l e c t e d ( l e s s than 1 q t / h r ) . The average dry char productive r a t e was 8.27 percent of the dry f u e l input r a t e . For the 4-foot diameter p i l o t p l a n t producer f i r e b o x , the s p e c i f i c d r y f u e l r a t e was 87.9 l b / f t * hour. Proximate analyses of char from the same f u e l a t a considerably higher moisture content but g a s i f i e d a t a d i f f e r e n t time contained 5.0% v o l a t i l e comb u s t i b l e matter, 92.28% f i x e d carbon and 2.70% ash (% a r e by weight dry b a s i s o f the c h a r ) . Cost P r o j e c t i o n s Cost p r o j e c t i o n s f o r g a s i f i e r a p p l i c a t i o n s a r e made d i f f i c u l t by t h e i r s i t e - s p e c i f i c nature. P r o j e c t e d f u e l c o s t s , f u e l t r a n s p o r t a t i o n , and r e s i d u e a v a i l a b i l i t y a r e p a r t i c u l a r l y d i f f i c u l t t o p r e d i c t . I n the f o l l o w i n g h y p o t h e t i c a l s i t u a t i o n a s u i t a b l e residue w i t h a heating value of 7,500 B t u - l b " (moisture content o f 10%) i s assume ton d e l i v e r e d t o the produce c r i b e s a water pumping a p p l i c a t i o n . In some s e c t i o n s o f the U.S. the cost and a v a i l a b i l i t y of energy f o r pumping i r r i g a t i o n water has increased t o s e r i o u s l y l i m i t the p r o f i t a b i l i t y of i n t e n s i v e cropping. I n p a r t s of the world experts a r e now recommending a draw-down o f i r r i g a t i o n w e l l s of as much as 98 f e e t (30 meters) t o o b t a i n the water r e q u i r e d f o r crops to support the l o c a l p o p u l a t i o n (7). Every year, i n the C e n t r a l V a l l e y o f C a l i f o r n i a and i n other western areas that use underground water f o r i r r i g a t i o n , the water t a b l e i s lower and the r e q u i r e d pumping l i f t t h a t much more t o provide the water. For the purpose o f t h i s study, a C e n t r a l V a l l e y ranch has been s e l e c t e d not as a s t a t i s t i c a l average but as an i l l u s t r a t i v e example. The ranch has 900 acres i n c u l t i v a t i o n w i t h crops that need 30 inches o f water per year of s o i l moisture which i s about 42 inches of i r r i g a t i o n water, a l l o w i n g f o r l o s s e s and i n e f f i c i e n c i e s . The i r r i g a t i o n water comes from four w e l l s and the depth to water t a b l e r e q u i r e s a t o t a l dynamic l i f t by the pumps of 120 f e e t . The pumps work 200 days per year, 12 hours per day, to pump the r e q u i r e d i r r i g a t i o n water o f 3150 a c r e - f e e t . The f i v e year average cost of n a t u r a l gas has been p r o j e c t e d i n the f o l l o w i n g manner: Present c o s t , per m i l l i o n Btu (10 therms) -$2.20 1978 season c o s t , w i t h i n d i c a t e d 30 percent i n c r e a s e 2.86 1979 season c o s t , estimated 15 percent increase 3.29 1980 season c o s t , estimated 15 percent i n c r e a s e 3.78 1981 season c o s t , estimated 10 percent i n c r e a s e 4.16 1982 season c o s t , estimated 10 percent i n c r e a s e 4.58 Average c o s t , f i v e years, o f $3.73 per m i l l i o n Btu Quantity o f water r e q u i r e d per day and w e l l : 1

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Volumetric demand on each w e l l : 3.937 acre f e e t χ 3.259 χ 10"* g a l l o n s per acre f t . 12 χ 60 = 1782 gpm/well Horsepower requirements of each w e l l : 1782 gpm χ 8.34 l b s / g a l , χ 120 f t . of l i f t = 54 hp 33,000 The thermal e f f i c i e n c i e s of the pump and engine are assumed to be 0.5 and 0.2 r e s p e c t i v e l y . Required energy i n p u t to each i n s t a l l a t i o n : 54 hp χ 42.42 Btu/mi 0.5 χ 0. I t i s assumed that a n a t u r a l gas engine has been a v a i l a b l e t o d r i v e the pump. The n a t u r a l gas w i l l be replaced by r e s i d u e d e r i v e d producer gas. D a i l y n a t u r a l gas requirements of engine: 22,907 Btu/min χ 60 χ 12 = 16.49 χ 1 0

6

Btu/day

N a t u r a l gas c o s t s per day f o r each w e l l : 16.49 χ 1 0

6

Btu/day χ $ 3 . 7 3 / m i l l i o n Btu = $61.5

Quantity of r e s i d u e r e q u i r e d t o f u e l g a s i f i e r : 22,907 Btu/min χ 60 _ 0.65 χ 7500 -

/u„ .

2 8 2

1K 11T l b / h o u r

(The thermal e f f i c i e n c y o f the g a s i f i e r i s assumed t o be 0.65). Hourly cost of r e s i d u e f u e l : 282 χ 15 2000

6 o =

1 Ί 2

n

$ - /

h o u r

A gas producer w i t h a 24 i n c h diameter f i r e b o x and g r a t e i s r e q u i r e d to g a s i f y the r e s i d u e at a f u e l r a t e of 282 l b / h o u r . The s p e c i f i c r a t e of t h i s producer i s 90 l b / f t hour which i s an a c c e p t a b l e d e s i g n f o r a downdraft producer. The purchase p r i c e (PV) of a 24 i n c h producer system i s as­ sumed t o be $25,000. T h i s i n c l u d e s the f u e l feed, s o l i d r e f u s e removal and gas clean-up equipment. The PV funds are assumed t o be a v a i l a b l e as proceeds from a s e l f - a m o r t i s i n g loan payable i n monthly increments over 5 years a t 2

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9% r a t e of i n t e r e s t . The monthly payments are c a l c u l a t e d to be $518.96. cost of producer:

RESIDUES

Total

$418.96/mo. χ 60 = $31,137.60 Hourly cost of producer: 31,137.60 5x200x12=

, , $2.59/hour

6 o

Q/

T o t a l o p e r a t i n g c o s t s of the g a s i f i e r system: $2.59 + 2.11 Savings:

$

= $4.7/hour - $4.7

= $0.42 per o p e r a t i n g hour

$0.42 χ 12 χ 200 χ The f o l l o w i n g example considers the use of producer gas as replacement f o r n a t u r a l gas at a h y p o t h e t i c a l r i c e m i l l . The g a s i f i e r has to supply the f o l l o w i n g l o a d s : 24 hrs/day and 360 days per year One 200 Bhp Steam B o i l e r Two 250 Bhp Steam B o i l e r One 350 Bhp Steam B o i l e r B o i l e r usage =0.65 (65%) B o i l e r e f f i c i e n c y - 0.75 Gas i s to be generated from r i c e h u l l s . These are assumed to have a h e a t i n g value of 7,200 B t u / l b . A g a s i f i e r thermal e f f i c i e n c y of 0.65 i s a l s o assumed. To meet peak demand of the b o i l e r s the f o l l o w i n g f u e l consump­ tion rate i s required: λ

1050 Bhp χ 3.352 χ 10 Btu/hr/Bhp 0.75 χ 0.65 χ 7,200 B t u / l b

1 Λ =

1 0

n 0 7

'°

2 7

-, l b / h r

F i v e g a s i f i e r s , each w i t h 60 i n c h f i r e b o x and grate are r e ­ q u i r e d . S p e c i f i c r a t e of g a s i f i c a t i o n : 1 Q

2

2

o c = 100 l b . per f t hour 5c χ ^ 6.25π r

Cost of gas producer system: F i v e 60 i n c h downdraft g a s i f i e r s w i t h c o n t r o l s and hot cyclones Feedstock p r e p a r a t i o n (2 p e l l e t i z e r s w i t h m a t e r i a l h a n d l i n g equipment) Feedstock bunkerage M o d i f i c a t i o n s to e x i s t i n g burners and c o n t r o l s

$500,000 125,000 50,000 40,000

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.

WILLIAMS

E T

AL.

161

Fïlot Plant Gasification Systems

T o t a l equipment c o s t s I n s t a l l a t i o n (30% of equipment cost) T o t a l c a p i t a l i z e d cost

715,000 214,500 929,500

P r o j e c t e d Costs of N a t u r a l Gas. The c u r r e n t cost o f n a t u r a l gas t o the r i c e m i l l i s $2.68 per m i l l i o n B t u . This i s i n c r e a s i n g a t a r a t e o f $0.03 per month. Since the g a s i f i c a t i o n system i s t o be p a i d f o r over a 10 year p e r i o d , the p r e d i c t e d cost f i v e years from now w i l l be used. T o t a l i n c r e a s e i n 5 years = 5 χ 12 χ 0.03 = $1.80 P r e d i c t e d cost i n 5 year time = $4.48 per 1 0 B t u 6

N a t u r a l gas consumption i n terms o f B t u : 1050 χ 3.352 χ 1Q

4

Ô7T5

B

t

u

/

h

At 65% b o i l e r usage, annual energy consumption: 4

1050 χ 3.352 χ 1Q . , l l _ , 75 χ 24 χ 360 χ 0.65 = 2.6 χ 10 Btu/yr. 0 /

o c r k

0

l

n

Annual c o s t of n a t u r a l gas : 1 1

2.6 χ 1 0 τ 10°

χ 4.48

_ = $1,180,700 per year 6 1

1 Q n

n n

Cost o f c a p i t a l : 9.75% s e l f - a m o r t i z i n g 10 year l o a n , monthly payments, ex­ pressed as an annual cost t o the producer. Monthly payments: $12,155.09 Annual c o s t o f g a s i f i e r : $145,861 Other Operating Costs: $ Per year Two men t o operate feedstock p r e p a r a t i o n system, s i n g l e s h i f t , 5 days (2 χ$17,000) $34,000 Three men t o operate g a s i f i e r , three s h i f t 7 days ( e q u i v a l e n t , 3 χ $20,000) 60,000 Maintenance and p a r t s (5% of c a p i t a l cost) 46,475 Insurance and taxes ( 5 % o f c a p i t a l cost) 46,475 P e l l e t i z i n g a t $5/ton 216,000 G r i n d i n g a t $2/ton 86,400 G a s i f i e r System 145,861 Total operating costs $635,211 Savings:

$1,180,700 - 635,211 = $545,489/yr.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

162

Literature Cited 1. 2. 3.

4. 5. 6. 7.

Wyer, Samuel S. A Treatise on Producer-Gas and Gas-Producers. The Engineering and Mining Journal, 1906. Page 53. Energy Use i n Agriculture Report #68. Council for Agriculture Science and Technology, August 1977. Williams, R. O., and Horsfield, B. Generation of Low-Btu Fuel Gas from A g r i c u l t u r a l Residues & Experiments with a Laboratory Scale Gas Producer. 9th Annual Conference on Food, Fertilizer, and A g r i c u l t u r a l Residues. Cornell University, Syracuse, New York, April 1977. Williams, R. O. and Goss, J . R. An Assessment of the G a s i f i cation Characteristics of some Agricultural and Forest Industry Residues. Submitted to Resource, Recovery and Conservation. Brame and King. Fuel, Solid, Liquid and Gaseous. St. Martin's Press, 1967. Lowry, H. H. Chemistr 1963. Ambroggi, Robert P. Underground Reservoirs to Control the Water Cycle. S c i e n t i f i c American, May 1977.

MARCH 3, 1978·

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9 Stagewise Gasification i n a M u l t i p l e - H e a r t h Furnace ROBERT D. SHELTON BSP/Envirotech, One Davis Drive, Belmont, CA 94002

The thermal reformatio nologies i n the world. On able to people of the world was the reformation of the physical and chemical characteristics of solids v i a the application of heat. Today, ore roasting, incineration, gasification and carbon production and activation are common examples of thermal reformation processes. Gasification is a thermal reformation technology with one of the most prominent h i s t o r i c a l roles. The thermal gasification of wood was known to the Pharaohs of Egypt and it produced charcoal i n Europe through the Middle Ages. It supplied the majority of wood alcohols and acetone f o r the Western Hemisphere until the early 1900's and it harnessed the energy of coal, wood and peat f o r industry and transporation i n Europe from the 1930's until the 1950's. Today, gasification i s emerging as a prominent technology f o r the conversion of carbonaceous wastes to energy. There are a huge assortment of carbonaceous solids i n todays world, by-products of people and industries, which are c l a s s i c a l l y identified as wastes. Municipal sewage sludge, garbage, industrial sludges, agricultural residues and food processing wastes are examples of such solids. In the past, these have generally been disposed of at the lowest possible cost. Today, stringent environmental requirements, increasing disposal costs, and limitations on the a v a i l a b i l i t y of natural resources have encouraged the u t i l i z a t i o n of these carbonaceous s o l i d wastes as renewable resources. Municipal sewage sludge provides a good example of the changing waste disposal situation i n this country. Most communities are faced with the problem of sludge disposal. Sewage sludges are becoming an especially d i f f i c u l t problem because of their escalating quantities and decreasing disposal options. It i s estimated that disposal methods w i l l have to deal with 23,000 dry tons of sewage sludge per day by 1985 i n the United States. In addition, methods of disposal available today w i l l not be legal or practical i n the years ahead. The 0-8412-0434-9/78/47-076-165$06.50/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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EPA has assured the end o f ocean dumping, a technique which p r e s e n t l y deals w i t h approximately 15% o f the sludge produced and the e s c a l a t i o n o f f u e l costs has made the economic f u t u r e o f sludge i n c i n e r a t i o n untenable f o r some communities and u n c e r t a i n for o t h e r s . A l r e a d y , sludge i n c i n e r a t o r s are s i t t i n g unused i n many communities, even though they are an environmentally acceptable d i s p o s a l method. I n c i n e r a t i v e d i s p o s a l p r e s e n t l y handles 35% of the present sludge o u t f a l l , but t h i s f r a c t i o n w i l l c e r t a i n l y decrease as communities become unable or u n w i l l i n g to pay the e s c a l a t i n g f u e l c o s t s . The l a n d f i l l i n g of sludge and the land a p p l i c a t i o n of sludge are d i s p o s a l options t h a t pose an i n t e r e s t i n g c o n t r a d i c t i o n . The present Resource Conservation and Recovery Act (RCRA) mandate i s t h a t sewage sludge, when l a n d f i l l e d , must be t r e a t e d as a hazardous waste. This i s because sewage sludges may c o n t a i n heavy m e t a l s , pathenogens and sometimes p e s t i c i d e s and h e r b i c i d e s . The presence o f these element a p o t e n t i a l hazard f o r p l a n t s q u a l i t y . According to RCRA, these hazardous p r o p e r t i e s of sludge make i t imperative t h a t the r e l e a s e of the harmful substances i n t o the environment be c o n t r o l l e d . The EPA, on the other hand, has endorsed land a p p l i c a t i o n of sludges as a s o i l c o n d i t i o n e r and f e r t i l i z e r . The extent of the danger t h a t t h i s land a p p l i c a t i o n o f sludges may pose, both i n the long and s h o r t term, has y e t to be determined, but the present EPA recommendat i o n s are i n s t a r k c o n t r a c t to the RCRA d e s i g n a t i o n of sludge as a hazardous m a t e r i a l . Obviously, there are c o n s t i t u e n t s i n sludge which could a i d i n s o i l c o n d i t i o n i n g but t h e i r b e n e f i t s w i l l have to be weighed a g a i n s t the p o t e n t i a l dangers of a l l o w i n g s i g n i f i c a n t q u a n t i t i e s o f the hazardous c o n s t i t u t e n t s i n t o p l a n t s and animals, s p e c i f i c a l l y , and the environment, i n g e n e r a l . The d i s p o s a l and u t i l i z a t i o n s i t u a t i o n with sludge i s a n a l ogous to the o t h e r municipal and i n d u s t r i a l s o l i d waste problems o f today. The c h i e f c o n s i d e r a t i o n s i n a l l wastes are the costs a s s o c i a t e d w i t h d i s c h a r g i n g or d i s p o s i n g of the s o l i d s and the l i a b i l i t y t h a t i s assumed because of t h a t d i s p o s a l . The p e c u l i a r t o x i c i t y of c e r t a i n i n d u s t r i a l sludges i s a constant l i a b i l i t y for manufacturing and process i n d u s t r i e s . Although thermal reformation v i a i n c i n e r a t i o n of these t o x i c s o l i d s reduces the environmental l i a b i l i t y , i t does so by exchanging l i a b i l i t y f o r high c o s t s . Municipal s o l i d wastes such as garbage are not n e a r l y as t o x i c as some i n d u s t r i a l counterparts but the options for d i s p o s a l are decreasing w h i l e the costs are e s c a l a t i n g . For a l l s o l i d wastes the problem i s one o f implementing d i s p o s a l technologies to deal w i t h the increased q u a n t i t i e s of waste i n the face of f l u c t u a t i n g d i s p o s a l options and a general u n c e r t a i n t y as to t h e i r value and place i n the environment. The g r e a t e s t p o t e n t i a l f o r the handling o f these wastes l i e s i n the capture of t h e i r value r a t h e r than i n t h e i r d e s t r u c t i o n . Across the f u l l range o f wastes, from municipal garbage to i n d u s t r i a l

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

SHELTON

Gasification in a Multiple-Hearth Furnace

167

sludge, e f f o r t s are being mounted to recapture some of the inherent worth contained i n these s o l i d s . Not only does t h i s r e c a p t u r i n g provide an increased m a t e r i a l s u t i l i z a t i o n e f f i c i e n c y , i t can a l s o r e s u l t i n a n u l i f i c a t i o n o f some or a l l of the detrimental a t t r i b u t e s of the waste. The reformation o f wastes i n t o usable forms can be a d i f f i c u l t t a s k , though, when faced w i t h present environmental, t e c h n i c a l and economic c o n s t r a i n t s . However, the g a s i f i c a t i o n of these carbonaceous s o l i d s i n t o energy has been demonstrated to provide a d i r e c t , c o s t - e f f e c t i v e , a v a i l a b l e , and environmentally sound method of d i s p o s a l . G a s i f i c a t i o n provides a technology which transforms the discarded and o f t e n dangerous components o f s o c i e t y and i n d u s t r y i n t o renewable energy s u p p l i e s . The m u l t i - h e a r t h furnace can g a s i f y carbonaceous wastes i n t o u t i l i t y energy, and the technology i s w e l l proven. The development o f the m u l t i p l e hearth g a s i f i c a t i o n system (MHGS) grew out of a long h i s t o r y of s o l i d s thermal reformation e x p e r i e n c e , beginning i n 1900. To dat i n c i n e r a t i o n , ore r o a s t i n g more r e c e n t l y , waste conversion to energy. The design and operation of the m u l t i p l e hearth furnace has shown i t to be capable of handling a wide range of s o l i d feedstocks and f o r c o n t r o l l i n g process c o n d i t i o n s so t h a t s p e c i f i c product q u a l i t i e s can be a t t a i n e d . The same t e c h n o l o g i c a l c a p a b i l i t i e s which make i t p o s s i b l e to groom the thermal reformation of wood, c h a r , and a c t i v a t e d carbon make i t p o s s i b l e to reform the carbonaceous wastes of i n d u s t r y or m u n i c i p a l i t y i n t o usable energy, w i t h a high degree o f e f f i c i e n c y and q u a l i t y c o n t r o l . For the m u l t i p l e hearth i t i s a r a t h e r s h o r t hop from producing charcoal and gas from wood wastes to producing char and f u e l gas from sludges and s o l i d wastes. There are immense compositional ranges of s o l i d s which are amenable to thermal r e f o r m a t i o n . Some of these s o l i d s have a composition which can s u s t a i n g a s i f i c a t i o n w i t h a net energy gain w h i l e others r e q u i r e a f u e l input to g a s i f y the s o l i d . Envirotech has e x p e r i m e n t a l l y and commercially g a s i f i e d a wide range of feedstocks and has developed a general c o r r e l a t i o n between the feedstock p r o p e r t i e s and the energy which can be derived from a given feedstock composition. The best c h a r a c t e r i z a t i o n of a f e e d s t o c k ' s energy p o t e n t i a l u t i l i z e s the r a t i o of i t s c a l o r i f i c value t o i t s water content, expressed as the a v a i l a b l e BTU per pound of water i n the feedstock. The r a t i o a u t o m a t i c a l l y takes i n t o account the inherent feedstock c a l o r i f i c value and the d i l u t i n g e f f e c t which feedstock moisture has on energy p r o d u c t i o n . Figure 1 d e p i c t s the r e l a t i o n s h i p between a f e e d s t o c k ' s BTU/lb water r a t i o and i t s energy p o t e n t i a l . 3500 BTU/lb water i s the autothermic p o i n t where the inherent c a l o r i f i c value of the s o l i d s i s j u s t s u f f i c i e n t to o f f s e t the water d i l u t i o n . At lower BTU/lb water r a t i o s the c a l o r i f i c value of the feedstock i s i n s u f f i c i e n t to evaporate the contained water and f u e l must

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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be u t i l i z e d to augment the evaporation and g a s i f i c a t i o n . Above 3500 BTU/lb water i s the autothermic region where the c a l o r i f i c content of the feedstock i s s u f f i c i e n t l y high to evaporate the feedstock moisture and produce energy. As the f e e d s t o c k ' s BTU content increases w i t h respect to i t s moisture content there i s more energy a v a i l a b l e which can be converted to energy. A t y p i c a l municipal sewage sludge w i l l c o n t a i n 20% s o l i d s . 65% o f these s o l i d s are combustibles with a heating value of 10,000 BTU/lb. Figure 2 d e p i c t s t h i s t y p i c a l sludge and shows t h a t i t contains only 1625 BTU/lb water, c o n s i d e r a b l y below the autothermic r e g i o n . T r a d i t i o n a l l y , sewage sludge has been disposed o f v i a i n c i n e r a t i o n and i t s compositional BTU/water r a t i o has r e q u i r e d the i n p u t o f f u e l . In c o n t r a s t , t y p i c a l municipal refuse contains over 20,000 BTU/lb water, high enough to generate s i g n i f i c a n t amounts of energy. The problem w i t h municipal refuse i s i t s heterogeneous composition, i n c l u d i n g l a r g composition of a t y p i c a w i t h a v a i l a b l e technology, the combustible f r a c t i o n o f the r e f u s e , refuse d e r i v e d f u e l (RDF), can be separated. Figure 4 i n d i c a t e s the compostion of RDF and shows t h a t i t contains 27,200 BTU/lb water. This places RDF w e l l i n t o the autothermic process region and marks i t as a good f u e l producer. The RDF and sludge provide an example of the range of waste p r o p e r t i e s which must be d e a l t w i t h . In the p a s t , some of the municipal refuse and sludge have been disposed of v i a separate i n c i n e r a t i o n without any heat recovery. While i t i s t h e o r e t i c a l l y p o s s i b l e to capture the heat of i n c i n e r a t i o n from these wastes, p r a c t i c a l c o n s i d e r a t i o n s , such as s o l i d s c l i n k e r i n g , l i m i t t h i s possibility. The major r e s t r i c t i o n on heat recovery from i n c i n e r a t i o n i s the low gas temperatures of the process. I n c i n e r a t i o n i s capable of producing such high temperatures (2000°F) t h a t the s o l i d s can fuse together. To p r o h i b i t t h i s , l a r g e amounts of excess a i r are used to quench the r e a c t i o n . By comparison g a s i f i c a t i o n of these s o l i d s l i b e r a t e s the f u e l p o t e n t i a l of the feedstock as a gas w i t h s o l i d s temperatures a t 1500°F or below. The gas i s combusted in a separate chamber from the s o l i d s . This allows f o r high gas temperatures and high heat recovery e f f i c i e n c i e s without s o l i d s agglomeration problems (see F i g u r e 5 ) . Figure 6 i s a graph which represents the p o s s i b l e compositional makeup of a l l combustible s o l i d waste feedstocks. The graph shows t h a t the composition can be c h a r a c t e r i z e d by three b a s i c elements, non combustibles, water and combustibles. This t r i p a r t i t e r e p r e s e n t a t i o n o f the s o l i d ' s composition allows f o r a comparison of the f u l l range of s o l i d wastes amenable to thermal reformation as w e l l as a d i s c u s s i o n of the r o l e and e f f e c t of the three compositional components. The shaded p o r t i o n s of the graph i s the autothermic region and i t represents range of compositions, which i n h e r e n t l y c o n t a i n enough energy i n t h e i r combustibles

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

SHELTON

Gasification in a Multiple-Hearth

2

169

Furnace

M Btu/Lb of Wet Feed —

Energy Generated

'

H 1

1

1

1

1

2 3/ 4 5 M Btu/Lb of Water in Feed

! 6

1 7

Fuel Expendedy

-1

-2-

Figure 1.

•

Rule of thumb

1625 Btu/Lb of Water Figure 2. Sludge

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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A N D RESIDUES

Aluminum & NF Metals

Figure 3.

Municipal refuse

27,200 Btu/Lb of Water Figure 4.

RDF

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SHELTON

Gasification in a Multiple-Hearth Furnace

HEARTH NO.

GAS TEMPERATURE, °F

Figure 5.

Operating range

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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RESIDUES

f r a c t i o n to o f f s e t the d i l u t i n g e f f e c t s of the moisture and i n e r t f r a c t i o n . This f i g u r e i s analogous to Figure 1 but i n t h i s case the noncombustible f r a c t i o n of the feedstock i s represented as w e l l as the water f r a c t i o n . The autothermic region represented here appears to be constant f o r a l l combustible feedstocks near 9000 BTU/lb combustibles, and has been e s t a b l i s h e d by t e s t i n g a wide range o f s o l i d s i n c l u d i n g RDF, sewage sludge, walnut s h e l l s , wood, ferro-manganese s o l i d s and onion s k i n s . The compositional l i m i t s of a u t o t h e r m i c i t y run between 70% water and 60% non combustibles. In the region bounded by the curve between these two points, the s o l i d s are capable of s u s t a i n i n g g a s i f i c a t i o n without f u e l a d d i t i o n . At the higher combustible f r a c t i o n and BTU contents a net energy gain can be produced from the s o l i d s . In Figure Τ the thermal reformation of the 40% water, 40% combustibles, 20% non combustibles feedstock i s represented by the pathway between the feedstock composition and the s o l i d product. The pathway represent stock composition t h a t ar of the s o l i d . The feedstock, on i n i t i a l exposure to the hot environment of the thermal reformer, increases i n temperature u n t i l the water f r a c t i o n of the feedstock begins to evaporate. The s o l i d s remain at approximately 100°C throughout the g r e a t e r p o r t i o n o f the d r y i n g stage and do not increase u n t i l the l a r g e s t p o r t i o n of the water has been evaporated. The l o s s of feedstock moisture i s represented by the segment of the pathway l a b e l e d 'DRYING'. In a l l feedstocks the i n i t i a l s o l i d t r a n s f o r m a t i o n i s the evaporation of the feedstock moisture. As the l a s t of the moisture i s d r i v e n from the s o l i d , the s o l i d s temperature increased to 3 0 0 d r i v i n g o f f the lower molecular weight v o l a t i l e s and the l a s t remaining water. As the s o l i d s temperature increases even f u r t h e r to 400°C the heavier weight v o l a t i l e s are d r i v e n o f f and the i n c r e a s i n g thermal f l u x e s l i b e r a t e s some o f the f i x e d carbon from the s o l i d . This second reformation phenomenon i s represented by the 'VOLATILIZATION' segment o f the r e a c t i o n pathway. The f i n a l stage of the thermal reformation i s the r e d u c t i o n of the l a s t remaining combustibles i n the s o l i d s . Here the f i x e d carbons are reduced to produce a gaseous product which i s reclaimed f o r i t s s e n s i b l e and l a t e n t heats of combustion i n the downstream process combustor. The s o l i d may be reacted to completion which would r e s u l t i n a 100% non combustibles product. However, the v o l a t i l i z a t i o n of low l e v e l s o f f i x e d carbons i s s u b j e c t to deminishing r e t u r n s f o r energy recovery and some carbon i s u s u a l l y l e f t i n the s o l i d product. This carbon i s not wasted because i t helps r e t a i n c e r t a i n components ( i . e . heavy metals) i n the s o l i d f r a c t i o n which would be detrimental to the environment i f they were allowed to escape. These three sub phenomena of g a s i f i c a t i o n s t r o n g l y a f f e c t the e f f i c a c y o f various g a s i f i c a t i o n r e a c t o r t e c h n o l o g i e s . The m u l t i p l e hearth g a s i f i c a t i o n system developed by Envirotech e

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

SHELTON

Gasification in a Multiple-Hearth Furnace

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

173

174

SOLID

WASTES

A N D RESIDUES

provides the greatest accommodation of the gasification phenomena for carbonaceous solids. Figure 8 depicts the operation of the multiple hearth gasifier. Feedstock solids are introduced into the top section of the furnace. The furnace is segmented into discrete process stages, called hearths, where the sequential thermal reformations are carried out. The solids are constantly mixed and transported across each hearth by air cooled mixing arms located on a central shaft. The solids drop from one hearth to the lower hearth after they have been mixed and reformed for the specified residence time on the hearth. The gases evolved in the reformation process flow counter currently to the down flowing solids. This counter current flow provides for efficient heat transfer from the hot gas to the solids. The solids exit the reactor at the bottom, essentially free from combustibles and the low c a l o r i f i c gases exit at the top of the reactor where they are transported to an afterburner and heat recovery system. The heart regions for each of the Each hearth provides a platform for the solids to undergo the sequential thermal reformations. The constant solids s t i r r i n g on each hearth overcomes the problems of stagnant reaction areas and the low velocity, countercurrent gas contacting provides e f f i c i e n t heat transfer without solids entrainment. The importance of constant agitation of the solids should not be overlooked. In a commercial demonstration f a c i l i t y i t was shown that a cessation of mixing decreased the gas production rate by nearly an order of magnitude. Not only does this mixing prohibit stagnant zones but i t promotes the solids particle breakdown which exposes fresh reaction surfaces and f a c i l i t a t e s the solids transfer from one stage to another. A temperature profile increasing from top to bottom is maintained i n the m u l t i p l e hearth g a s i f i e r . This p r o f i l e accommodates the reaction requirements of each of the three subphenomena. The heat for drying, volatilization and fixed carbon reduction is generated in the gasification zone of the lower hearths where air is admitted in sub stoichiometric quantities. This allows for combustion of some of the fixed carbon and the associated heat release v o l a t i l i z a t i z e s the remaining fixed carbon. In addition to a i r , steam can be used to gasify the fixed carbon via the water-gas shift reaction (see F i g u r e 9 ) . The hot gases from the gasification zone flow upward into the pyrolysis zone. The sub-stoichiometric quantities of a i r are consumed by the fixed carbon in the lower stages so the rising gases are reductive. In the pyrolysis zone the volatiles and some fixed carbon are thermally reformed in the reductive environment. The drying zone u t i l i z e s the heat remaining in the liberated gases to drive off the moisture. As can be seen, the sequential drying, volatilization and reduction phenomena of gasification are accommodated and individually controlled in the integrated,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

SHELTON

Gasification in a Multiple~Hearth Furnace

Figure 8.

Multi-hearth gasifier

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

175

176

SOLID

Figure 9.

WASTES

AND

Air requirements

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

9.

SHELTON

Gasification in a Multiple-Hearth

Furnace

177

staged and countercurrent multi hearth gasifier. The low BTU gases evolved from the solids are normally 130 BTU/SDCF but strongly depend on the feedstock. The gas is burned in an external afterburner which maximizes the u t i l i z a t i o n of the fuel value of the gas via an Envirotech temperature/oxygen control system. The control system maximizes the afterburner combustion temperature thereby increasing the heat recovery efficiency without producing solids agglomeration problems. The Envirotech control system also provides for control of the temperature/ oxygen profile throughout the gasification reactor. This maximizes the rate of reaction as well as the c a l o r i f i c value of the reformed gases. Gasification has been termed "destructive d i s t i l l a t i o n " because of its irreversible separation phenomena. In fact, there is some merit in the d i s t i l l a t i o n analogy based on experience gained by Envirotech with the MHGS The stage wise counter current, mixed, and temperatur Envirotech MHGS bear a striking liqui columns. The d i f f i c u l t y of transporting and contacting solids makes gasification significantly different from liquid d i s t i l l a t i o n but the analogy is generally valid. What has been found to affect control, operation, cost and product quality for liquid d i s t i l l a t i o n has its counterpart in the^destructive d i s t i l l a t i o r ï O f solids. The overall process control variables for gasification are listed in Table 1. The process control system uses these variables to maximize energy generation, protect the equipment and provide stable operation even with fluctuating feedstock characteristics. In addition, the patented temperature/air control system provides the special zonal control which efficient gasification requires. The total MHGS is depicted in F i g u r e s 10,11. Both sludge and RDF a r e shown as feedstocks i n what is described as co-gasification. The high moisture sludge is fed into the uppermost hearth to take advantage of gas drying while the drier RDF is introduced at a lower hearth. Combination of feedstocks in this manner has definite process advantages. F i g u r e 12 shows the combined BTCj/lb water r a t i o f o r RDF and sludge (3:1). The three to one RDF to sludge ratio was chosen because i t represents typical municipal generation rates of RDF and sludge. The mixture is significantly above the autothermic region for gasification, as is even a 1:1 ratio mixture. Thus, both wastes can be disposed of with a net energy gain via co-gasification. Incineration does not offer this option since moisture induced control problems in the burning region limit sludge additions to small quantities.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

SLUDGE

WASTES

A N D RESIDUES

Cyclone 800°

RDF

V

Scrubber

- AB

1000 1500° MHP

Air

ENERGY

Boiler Ash

Figure 10.

Turbine Generator

The MHP system

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

SHELTON

Gasification in a Multiple-Hearth Furnace

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

WASTES

AND

20,800 Btu/Lb of Water Figure 12.

RDF and sludge (ratio 3:1 )

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

9.

SHELTON

Gasification in a Multiple-Hearth

Furnace

181

TABLE I CONTROL VARIABLES FEED RATE fEEDSTOCK BTU/POUND WATER COMBUSTIBLES/AIR RATIO TEMPERATURE PROFILE MAXIMUM PROCESS TEMPERATURE PARTICLE SIZE AND DENSITY RESIDENC AFTERBURNER AIR/FUEL GAS RATIO The commercial scale co-gasification of sludge and RDF has been accomplished by Envirotech in an EPA sponsored demonstration at Concord, California. Varying ratios of the wastes were gasified to produce energy in a 144 TPD, 16' diameter six hearth furnace. The system, shown in Figure 1 3 , was constructed around an existing multi-hearth sludge incinerator which was modified to process specifications. The system processed a wide range of sludge/RDF mixtures as well as 100% sludge and RDF. The data showed that the energy recovery, pollutant emissions and operating s t a b i l i t y of the co-gasification was constantly superior to incineration. Table 2 presents some of the test data from the Concord tests. As can be seen, a wide range of feedstock compositions were evaluated. Even non-autothermic sludge was gasified u t i l i z i n g auxilliary fuel. In the other instances, autothermic mixtures were gasified without auxiliary fuel. F i g u r e d presents the material balance for a typical feedstock evaluation and Figure 15 presents the analogous heat balance. These demonstrations prove the capability of the Envirotech MHGS to process a wide range of feedstocks as well as the capability to accommodate instantaneous changes in feedstock composition without process upsets. In fact, the gasification process appeared less sensitive to moisture increases in the solids than did incinerative disposal. The environmental consequences of co-gasifying sludge and refuse in a MHGS were shown in the demonstration at Concord, California to be less than those of incineration. In fact, the Envirotech multiple hearth system surpassed both EPA and San Francisco Bay Area Pollution Control Board (SFBAPC) standards for gasification process emissions (see Figurel6). The s t r i c t control of the temperatures and the oxygen concentrations not only

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 13. Concord commercial demonstration system

>

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to

00

G α

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

SHELTON

Gasification in a Multiple-Hearth Furnace

183

Table I I . Furnace Operating Data f o r Test number

RDT/ sludge (wet b a s i s )

Total wet feed, lb/hr

Percent solids i n t o t a l feed

T o t a l feed h i g h heat v a l u e , B t u / l b of wet solids

19H1 26L 2TM 29N 30 0 31P 33 3^ 35 36 37 38 39

2.1/1 1.2/1 l/O 1.1/1 0/l 1.5/1 2.3/1 ι.ι/ι 1/2.1 2.9/1 l / l . 3 2.5/1 l . l / l

5,408 5,562 3,822 5,Ma 4,11 6,21 6,189 5,605 3,981 6,818 7,304 8,716 7,457

56 Λ 51.7 8Ο.9 45.8

4,249 3,862 5,865 3, toi

59.2 ^9.7 to.8 51.8 to.2 58.5 U3.7

4,310 3,682 3,384 3,to2 2,028 3,881 3,068

S

13

a

V i s t a = V i s t a Chemical and F i b e r Products. CRS/UCB=Cal Recovery Systems/University o f C a l i f o r n i a a t B e r k e l e y . High heat value (gross heat of combustion) determined by ASTM Standard 0240-64 (burning weighed sample i n an oxygen bomb calorimeter). Includes any n a t u r a l gas added t o e i t h e r the furnace o f the ^ afterburner. Includes l a t e n t heat, s e n s i b l e heat and heat value of unburned combustibles. Includes l a t e n t heat and s e n s i b l e heat. Computed as the r a t i o o f B t u s / h r i n t o furnace d i v i d e d by Btu's/hr out of a f t e r b u r n e r . c

e

f

!

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

184

SOLID

WASTES

A N D RESIDUES

S e l e c t e d M a t e r i a l and Heat Balances Auxiliary fuel , Btu/hrxlO c

None None None None 1.83 None None None None None None None None

Furnace o f f gas , Btu/hr x l O

Afterburner o f f gas , ^ Btu/hr χ 1 0

Process ^ efficiency percent

13.50 17 Λ 6 l8.kk 15.01 7.05 15.59 19.58 18.36 10.67 21.16 18.51 2k.18 16.99

13.36 17 Λ 18.2k Ik.8k 8.8 15-^ 19-k8 18.2I4. 10.51 21.09 18.35 2k.12 l6.8l

58 81 8l 80

d

6

6

e

b

73 88 78 89 89 71 73

β RDF f e e d r a t e f o r t e s t numbers 19H and 191 (see Table U - l ) averaged f o r heat and m a t e r i a l b a l a n c e s . ^ Preprocessed V i s t a RDF used. Note 1: L a t e n t heat r e f e r s t o the l a t e n t heat o f v a p o r i z a t i o n o f water, o r t h a t heat absorbed when water i s evaporated ( o r r e l e a s e d when evaporated water i s condensed). I t i s normally taken a t 60°F. and ik.J p s i a and i s about 1000 B t u / l b a t these conditions. Note 2: S e n s i b l e heat i s d e f i n e d as the s p e c i f i c heat i n a gas o r l i q u i d o r a l l heat a v a i l a b l e above the l a t e n t heat o f v a p o r i z a ­ t i o n o f water i n the gas. Note 3 Mean o f p y r o l y s i s mode e f f i c i e n c i e s i s 79 percent. :

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

30.04

W A T E RA D R Y R I3 7.40

W A T E R MM V O L A T L I E S O L D I S 268 X IE O 0 N IF E R TSCARBON 9 S6 TOTAL 2.8»

REEFR U SE D FUEV LIED

Figure 14.

FURNACE PRODUCT A ISHI

t

Typical material balance

W A *tIT V O L A LIECARBSO O L D IS F X I E D N N ISO EL R T S IS TO MEAT ANO A RIO 37.40GAS AFTERBURNER 81.18 TOTAL y~ H *EARTM ULT PL IE H FUR NA CE V O A ITLIECARBSO OL O IS IE D N IFX ER TS N NOTE.ALL VALUES N I LB/HR

C OM N BIED FEED W A T E R V O LAT LIE SOL D IS FIX IE N EO RTSCARBON TOTAL

ΛΛΛΛΛ.

W A ERT 0 V O LTA LIECARBO SO L D IB S.I5 83 3 F X I E O N 2 9 6 N ITO ET R TL S 30.3323 4 A

WATER 40.41 GAS TO 8U R N E 0 C O M B U S B T L I E C O M BU O STIN ARI 19 0 18S..4S3I23.94" SCRUBHt E X C E S A R I V LAT LIECARBSO O L O IS 1Τ FX IO E D N N IT E R T S OTAL 264.3774

W ATER 16 1..5 04 2 A R I 2 TOTAL 17 3.56

si

Ci

2

M

CO

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

AUDOE AND RDF

NOTE 1. NOTE 2: NOTE 3;

4

5

6

1550*F

1500"F RADIATION 129.800 SHAFT AIR 96U.bOO

- MULTIPLE HEARTH FURNACE

TOTAL HEAT

OTHER HEAT LOSSES

17.461.100

1 Γ 7 J 7(»0 SfcNSIBLE HE.AT MEAT VALUE Of UN BURNED COMBUSTIBLES 1? 654 400

2 (,Η', OiK) 84Η.υυο

RADIATION LOSSES

I

8 074,600 4.304.200 17.384.800

TOTAL HEAT

2.88S 600 2.121.000

MOISTURE LATENT HEAT SENSIBLE HEAT DRY GAS SENSIBLE HEAT COM 8 US ION GASES SENSIBLE HEAT EXCESS AIR

Figure 15.

Typical material balance

ALL VALUES IN BTU/HR MOISTURE INCLUOES FREE WATER IN FEED AIR. COMBlNFD WATER IN FEED. WATER PRODUCED BY COMBUSTION OF REMAINING HYDROGEN IN FEED. EXCESS AIR IS AIR ADDED IN ADDITION TO STOICHIOMETRIC AIR REQUIRED FOR COMPLETE COMBUSTION

FURNACE PROOUCT (ASH|

3

900* F

900* F

13S0*F

1

2

620* F

MOISTUHI LA Τ t Ν Τ HtAT SENSIBLE Η LA Γ DRY GAS

GAS TO SCRUBBER

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w

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5

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BAAPCB

EPA

PYROLYZING FljRNACES

10 MG/φ

Γ

|

TES

'/////

y\

VJ

////

////

/ / / / /

50 PERCENT OF STANDARD

25 PPM

Figure 16. Emission standards

25

fi

225 PPM

1

2

N0

300 PPM

C - C

2

S0

.05 GR/DAY

3200 GR/DAY

\

Y/////////////

V//////////

Hg

75

1

V//////////////////////

CO

'/////////////////////A*/, ' '' Τ

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100%

188

SOLID

WASTES

A N D RESIDUES

provides e f f i c i e n t energy recovery from the solids but i t also minimizes their detrimental effects on the environment. In general, solid wastes make good renewable fuel sources but their composition may include significant amounts of detrimental substances such as heavy metals. The low solids temperatures of the MHGS minimize the metal volatilization rates and promote their fixation in the carbon matrices of the char product. This retention is characterized by the gas emission of less than 1600 grams per day of mercury into the atmosphere. The low velocity gas contacting, made possible and e f f i c i e n t by the s t i r r i n g of the solids, promotes a low particulate loading of the gas stream. A reduction in the particulates is effected in the afterburner and in downstream gas scrubbing. Sulfur dioxide and hydrocarbon emissions were less than one quarter of the standards and obviously pose no environmental threat. The exceptionally low nitrogen dioxide emission levels are unique to gasification contain significant amount nitroge compounds these nitrogen compounds are almost a l l reduced to ammonia. The presence of ammonia in the afterburner, in conjunction with any nitrous oxides and oxygen, promotes the formation of diatomic nitrogen, N and limits NO production. Thus, a potentially noxious pollutant is transformed into an inert gas by the reductive/oxidative staged environment of the MHGS. The economics of waste gasification can be quite attractive as an environmentally sound disposal option and as means of developing renewable energy source. The projected economics of sludge/RDF co-gasification are presented in Table 3 as an example. The RDF/sludge ratio is varied from 3:1 down to 100% sludge to provide a comparison of feedstocks. These figures are derived from the Concord commençai demonstration studies and based on the data from that project a new disposal f a c i l i t y is being constructed at the Central Contra Costa Sanitation District in California. The design is based on a combined RDF/sludge rate of 888 TPD at 60% solids. The superheated steam produced will drive the in-house machinery and generate e l e c t r i c i t y . One of the important realizations to emerge from the studies was the economic benefit which could be accrued from combining wastes for co-gasification. In particular, the low BTU/lb water ratio of sludge could be offset with the high BTU/lb water ratio of RDF with very profitable results. In essence, the RDF is acting as a very inexpensive auxiliary fuel to aid in the gasification of sludge and the energy potential of both feeds are captured. The economic benefits of combining feedstocks for co-gasification are attainable with a multiple hearth gasification system. The gasification of carbonaceous wastes in an Envirotech MHGS has several advantages over other disposal systems. It is immediately available and i t is not an environmental threat. In addition, i t is an economically attractive disposal technology because i t s major product is 2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9.

Gasification in a Multiple-Hearth

SHELTON

Furnace

D (

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189

5Η

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In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

190

SOLID

WASTES

A N D RESIDUES

inexpensive energy, either for in-house use in place of expensive fuels or for sale. Also, the co-gasification of wastes, possible with MHGS, has the added advantage of being an integrated solution to the solid waste disposal dilemma. The hearth by hearth control, countercurrent flows and stirred characteristics of the Envirotech multiple hearth gasification system provide the best control and optimum process conditions for the conversion of carbonaceous wastes to energy. The Envirotech MHGS is capable of meeting today's solids disposal and energy supply needs with a technology that is commercially proven and cost effective. MARCH

3,

1978,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10 P y r o l y z e r Design Alternatives a n d E c o n o m i c Factors for P y r o l y z i n g Sewage Sludge i n M u l t i p l e - H e a r t h Furnaces CHARLES VON DREUSCHE and JOHN S. NEGRA Nichols Engineering and Research Corporation, Homestead and Willow Roads, Belle Mead, NJ 08502 While multiple commercially i n ten large plants for p y r o l y s i s of bark and sawmill waste to charcoal for briquette manufact u r e , used commercially for p y r o l y s i s of paper and p l a s t i c laminates on aluminum foil to recover the foil, (1) and demonstrated experimentally for p y r o l y s i s of RDF alone (2) and for c o - p y r o l y s i s of RDF and sludge,(3) t h i s paper will be l i m i t e d to considering p y r o l y s i s of sewage sludge alone. Many sewage treatment plants are equipped with multiple hearth furnaces for sludge i n c i n e r a t i o n . This transforms an offensive and dangerous waste into a safe and inoffensive ash, and s a t i s f i e s various purposes l i s t e d i n Table I . The need f o r t h i s transformation i s l i k e l y to continue since sewage sludge i s the one most l i k e l y place to f i n d , perhaps as an unrecognized by-product of o r ganic synthesis, organic substances that are found to be dangerous and non-biodegradable, perhaps long a f t e r t h e i r initial appearance. Thermal conversion of the complex organics to simple inorganic form i s the only way to insure that a dangerous substance i s not widely d i s t r i b u t e d as a sewage plant product. Most of the many multiple hearth incinerators now use oil or gas to supply the heat needed to evaporate 2 to 4 pounds of water received with each pound of dry sewage sludge s o l i d s and heat t h i s water along with 100% excess a i r from combustion of the organics to a l e g a l l y required 1400 ° F afterburner exhaust gas temperature.

0-8412-0434-9/78/47-076-191$06.50/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

192

WASTES

A N D RESIDUES

TABLE I Reasons for Thermal Destruction of Sewage Sludge A.

Change Physical Properties 1. 10:1 weight reduction from 30% s o l i d s , 33% ash dry basis to ash. 2. 5:1 volume reduction 3. Sticky slime to powder or granules

100%

B.

Public and Employee Safety and Aesthetics Promoted by E l i m i n a t i n g : 1. Odor 2. P o t e n t i a l odor by decomposition 3. Pathogens 4. P o t e n t i a l pathogen m u l t i p l i c a t i o n i f contaminated. 5. Support for larvae, rodents, etc. 6. Organic Toxins - i n c l u d i n g those which may be u n i d e n t i f i e d or whose t o x i c i t y may be currently unrecognized.

C.

Energy Conserved 1. Less trucking and l a n d f i l l operating f u e l (a) because of volume and weight reduction (b) because nearer s i t e l i k e l y to be acceptable.

D.

Reduced Handling and Disposal Cost 1. Acceptable land disposal may be much nearer 2. Reduced transport quantity and distance from plant 3. No cover d i r t required 4. Leachate control may not be required 5. Smaller land f i l l area to buy or longer l i f e of e x i s t i n g l a n d f i l l

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

V O N DREUSCHE

A N D NEGRA

Pyrolyzing Sewage Sludge

193

By considering simultaneous a p p l i c a t i o n of pyr o l y s i s and modern sludge dewatering p r a c t i c e s , i t is possible to accomplish the destruction of sludge organics without the need of any a u x i l i a r y f u e l , and substantial energy w i l l be a v a i l a b l e for recovery. Substitution of refuse derived f u e l i s another means of conserving gas and o i l . However, RDF costs money to prepare from r e f u s e . The cost depends on volume through-put. Large scale uses,needed to j u s t i f y RDF preparation p l a n t s , w i l l no doubt govern plant l o c a t i o n and market p r i c e . A high p r i o r i t y f u e l requirement that j u s t i f i e s pyrolyzing a large amount of RDF for i t s f u e l value i n conjunction with the sludge may on the other hand make c o - p y r o l y s i s ver A population o erate about 800 tons of refuse per day. The corresponding 40 MGD wastewater treatment plant would require about 24 tons RDF per day to make up the f u e l d e f i c i e n cy for p y r o l y s i s of t h e i r sludge i f they are able to dewater the sludge to only 25% s o l i d s . The f a i r p r i c e of the RDF, plus transportation, plus storage and metering costs for t h i s bulky, odoriferous b a c t e r i a l l y decomposable f u e l plus incremental furnace size r e quired to burn the RDF may make t h i s unattractive i n some circumstances. How t y p i c a l the 40 MGD plant i s i n s i z e , since i t w i l l be c a r r i e d through t h i s paper as an example, may be judged by reference to Table I I . The magnitude of energy a v a i l a b l e , energy demand and energy d o l l a r worth may also be judged from this Table. It is foreseen that energy may be recovered i n 3 ways. The hot gas e x i t i n g an afterburner on the pyr o l y s i s operation can be used to generate steam. Energy can be recovered from a 25% carbon/75% ash char produced by p y r o l y s i s . The char so produced need not be consumed i n the sewage treatment p l a n t , and i f i t i s , i t need not be consumed at the instantaneous rate that i t i s generated from sludge. A t h i r d p o s s i b i l i t y for heat recovery i s the generation of methane from d i g e s t e r s , made economical by the opportunity created by improved dewatering plus p y r o l y s i s , to safely destroy the energy depleted sludge produced by digesters without purchased f u e l and to return to the digesters

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8

399,000 525,000

67 133 175 2)

201,000

28

28

289

125

59

84,000

7

21,000

MAXIMUM * * $/YR.

5

MILLION BTU/YEAR (IN THOUSANDS) AVAILABLE IN * REQUIRED SLUDGE/WTP (NET) PER WTP

* * BASIS $3 PER MILLION BTU.

*BASIS OF EXPECTATION - SLUDGE AT 40% SOLIDS (SEE FIG.

83

180

20 - 50

50 &

267

10 - 20

12761

NUMBER PLANTS

494

d

5-10

5

m

PLANT CAPACITY

EXISTING PLANTS

ESTIMATED ENERGY - SEWAGE SLUDGE (10)

TABLE II

ο

•

Si

CD 0^

10.

V O N DREUSCHE

A N D NEGRA

Pyrolyzing Sewage Sludge

195

heat they r e q u i r e . Digester gas i s r e l a t i v e l y simple to produce, and to clean for transmission, and i t i s a high BTU gas. It i s not the purpose here to examine i n depth the many a l t e r n a t i v e uses for the surplus energy generated by improved e f f i c i e n c y i n thermal destruction of sludge, nor to question how l i k e l y the actual u t i l i z a t i o n of such energy may be. I t must be noted however that i n many plants where digester gas i s produced, the gas i s wasted. The exhaust gas of i n c i n erator afterburners i s also at 1400 °F and i n larger volume than w i l l r e s u l t under the proposed scheme of improved dewatering plus conversion to p y r o l y s i s ; yet only about 20 p l a n t s , including 12 yet to come on stream, a c t u a l l y practic believed that p y r o l y s i s , by providing more f l e x i b i l i t y as to the form of recovery, plus the opportunity to store energy as carbon and recover heat from that, at times of peak energy demand, w i l l make such recovery more p r a c t i c a l . Pyrolysis of sludge alone without a u x i l i a r y f u e l has been demonstrated and explored over a t o t a l of 400 hours operation i n a 3 ton per day p i l o t operation u t i l i z i n g two d i f f e r e n t raw sludges and one digested sludge. The p i l o t furnace i s shown i n Figure 1. The program was c a r r i e d out i n the p i l o t plant of Nichols Engineering and Research Corporation for the Interstate Sanitation Commission of New York, New Jersey and Connecticut as part of a program funded by the U . S . Envirommental Protection Agency. Release of the r e port of that program i s expected soon. Meanwhile one f u l l scale u n i t for the p y r o l y s i s of sludge and the recovery of carbon from a 40 MGD i n d u s t r i a l wastewater treatment plant is now coming on stream and the f i r s t municipal contract for two units pyrolyzing sludge alone has been b i d and Nichols expects award of the contract momentarily. In focusing on the p y r o l y s i s of sludge alone, i t is the viewpoint of t h i s paper that i n - p l a n t e l i m i n a t i o n of sludge organics i s the primary aim of the operation. E l i m i n a t i n g the purchase of valuable fuels such as RDF, o i l , gas or c o a l , i s the f i r s t step to economy and conservation. The recovery of heat from use of the char w i l l follow i n an increasing number of

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

WASTES

AND

RESIDUES

a. Ο

3»

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

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A N D NEGRA

Pyrolyzing Sewage Sludge

197

instances. The conversion of e x i s t i n g units to p y r o l y s i s seems eminently p r a c t i c a l but f i r s t some choices must be made between process design a l t e r n a t i v e s leading to d i f f e r e n t products. These choices depend on the i n d i v i d u a l plants requirements, opportunities for energy recovery and the nature of i t s sludge. Pyrolysis Process Description and Operating Modes The P y r o l y s i s Process. The thermal destruction of sludge by p y r o l y s i s i n a multiple hearth furnace i s a process by which s o l i d s are raked along the f l o o r of successive compartments while a larger vapor space exists above th of a i r are properly introduced into the vapor space the oxygen reacts with the organic vapors present and there i s starved a i r combustion (not p y r o l y s i s ) of these vapors. The oxygen does not, i n the proposed designs, p e r s i s t through the vapor space and reach the s o l i d s . The s o l i d s receive heat by r a d i a t i o n . They are shielded from contact with oxygen by a stagnant f i l m of organic vapor or water or both leaving the s t i r r e d bed of s o l i d s . Adding to the protection i s the fact that the l i m i t e d amount of a i r admitted has i t s oxygen consumed r a p i d l y i n the organics r i c h vapor phase. This is p y r o l y s i s with respect to the s o l i d s . Hot products of starved a i r combustion from the middle hearths provide the required heat for drying the wet incoming sludge on the upper hearths. Combustion of the gaseous products i s completed i n an afterburner. The e s s e n t i a l point of the p y r o l y s i s process i n reducing or e l i m i n a t i n g f u e l requirements i s the e l i m i n a t i o n of large excess a i r requirements common to incinerators. The middle hearths of the multiple hearth incinerator receive and burn sludge that has been predried on the upper hearths. Approximately 100% excess a i r i s required to d i l u t e the temperature of combustion of t h i s sludge to the 1800 °F upper l i m i t for which normal multiple hearth construction i s s u i t a b l e , as can be shown by a heat balance around t h i s portion of an i n c i n e r a t o r . P y r o l y s i s eliminates t h i s

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

198

SOLID

WASTES

A N D RESIDUES

need for excess a i r by postponing the completion of combustion u n t i l a f t e r p a r t i a l l y burned organic vapors have passed over the wet incoming sludge where they w i l l c o o l , pick up water vapor and may p i c k up add i t i o n a l organic vapors, steam d i s t i l l e d toxins, or odors. The organic vapors provide f u e l i n the a f t e r burner to r a i s e the temperature of water evaporated i n the upper hearths to the required 1400 ° F f i n a l combustion temperature. Low Temperature Char Operating Mode, The organics i n the sludge have undergone destructive d i s t i l l a t i o n g i v i n g o f f almost a l l the organic vapors that can be released, when the s o l i d s have been heated to 1200 to 1300 ° F . The proces point and the char discharged. This would be low temperature char (LTC operating mode). The product i s a s t e r i l e , b l a c k , charcoall i k e free flowing mixture of powder and granules having a bulk density of approximately 16 pounds per cubic foot and containing 75% ash. It contains a l l of the ash of the feed sludge plus amorphous carbon and some non-putrescible unleachable material akin to the v o l a t i l e content of c o a l . It i s believed that t h i s material could be s a f e l y l a n d f i l l e d s a t i s f y i n g the objectives of Table I. This material has been observed to have retained the l e a d , zinc and cadmium content of sludge to an extent not usual i n other modes of p y r o l y s i s operation nor i n i n c i n e r a t i o n . Allowing the s o l i d s temperature to exceed 1200 to 1300 °F seems to i n i t i a t e v o l a t i l i zation of these substances to a fume which i s d i f f i c u l t or impossible to capture i n most a i r p o l l u t i o n abatement equipment. Under development are methods to recover these metals from the low temperature char. One h a l f percent t o t a l l e a d , z i n c , cadmium content i n the char i s not uncommon for sludge i n i n d u s t r i a l areas (5). Recovery i s the one way to avoid putting the 80,000 pounds per year (more or l e s s ) of these metals, that a 40 MGD plant might have, into either the land, the water, or the a i r .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

V O N DREUSCHE

A N D NEGRA

Pyrolyzing Sewage Sludge

199

High Temperature Char Operating Mode. For high temperature char, the char can be brought to temperatures of 1600 ° F or higher either by allowing a high gas temperature i n the l a s t hearth of the p y r o l y s i s zone, or by very l i m i t e d contact of the char with a i r on a hearth at the end of the p y r o l y s i s zone. The product i s about 25 pounds per cubic foot and contains only ash and carbon. The carbon content can be estimated from the data i n Table I I I . It ranges from 7 to 18% of the organics i n the sludge and w i l l vary from about 10% to about 40% of the product depending on the kind of sludge and the r a t i o of ash to organics i n the sludge. Lack of r e s t r i c t i o n i n applying high gas phase temperatures, i f on the char above 1300 ° F , allows a greater heat transfer rate throughout the furnace. Thus the furnace for operation i n t h i s mode can be of minimum size for a given throughput capacity. Also r a i s i n g the temperature to t h i s l e v e l does reduce the heating value of the char discharged, making more heat a v a i l a b l e i n the furnace or afterburner. Char Burning Operating Mode. The char r e s u l t i n g from p y r o l y s i s i n the middle hearths can be converted to ash on the lower hearths, (CBA operating mode).An oxygen free atmosphere can be maintained as i n the p y r o l y s i s hearths and the carbon reacted with CO2 and H2O to produce CO and H2. This requires a temperature of at least 1600 °F to obtain p r a c t i c a l reaction rates (6). A l t e r n a t i v e l y a i r , or a i r plus steam (7), can be c i r c u l a t e d across these lower hearths and substant i a l l y vented from the side of these lower hearths to avoid an excess of a i r entering the middle p y r o l y s i s hearths. An excessive amount of oxygen entering the hearths where maximum organic vapor release occurs, r i s k s development of temperatures there i n excess of the 1800 ° F that normal multiple hearth furnace cons t r u c t i o n can withstand. The oxygen containing gases vented from the side of the lower hearths are brought by a separate external duct to the afterburner where these gases serve as preheated a i r for combustion, thus u t i l i z i n g the heat obtained from the carbon to r a i s e the afterburner temperature.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

AVERAGE

8

62

71

59-67

5,

6, 7

48-66

63

12

8

11-17

6-12

18

COMBUSTIBLES - % VOLATILES FIXED CARBON

2, 3, 4

1

SAMPLE NUMBER

26

21

18-24

28-40

19

% ASH

AERATED PRI.

WAS + PRIMARY

ANAEROBIC DIGEST

AEROBIC DIGEST

TYPE SOLIDS

SOME COMPOSITIONS OF VARIOUS SEWAGE SLUDGE SOLIDS TESTED

TABLE III

10.

V O N DREUSCHE

A N D NEGRA

Pyrolyzing Sewage Sludge

201

The advantage of reacting away the carbon r e s u l t ing from the p y r o l y s i s zone of the furnace i s to avoid a loss of heat from the process i n the form of unburned f u e l value as carbon i n the material produced. The material produced consists e n t i r e l y of ash and has a bulk density of approximately 33 pounds per cubic f o o t . Comparison of modes. Table IV shows the reasons for s e l e c t i n g one mode of operation as compared to another. It should be pointed out that a single furnace sized large enough to react away a l l of the f i x e d carbon, can be operated i n any of the three modes, LTC, HTC, or CBA, by simple v a r i a t i o n i n control settings. This i s importan the p o s s i b i l i t y of s t o r i n g and refeeding char product. Carbon Y i e l d s and Reaction Rates. It should however be pointed out that maximum energy production from a given quantity of sludge, by reacting away a l l of the f i x e d carbon formed i n p y r o l y s i s , does require a d d i t i o n a l hearth area. The extra hearth area required can be found by estimating the pounds per hour of f i x e d carbon l i k e l y to be formed from the organics i n the sludge, and d i v i d i n g by a rate of r e a c t i o n . Some t y p i c a l carbon reaction rates are shown i n Table V. T y p i c a l f i x e d carbon y i e l d s found for various sludges are indicated i n Table I I I . The importance of t h i s factor may best be shown by example. The 40 MGD plant c a r r i e d through this paper as an example, pyrolyzing 5000 pounds of sludge s o l i d s (dry b a s i s ) per hour at 25% s o l i d s ( a l t e r nately 40% s o l i d s ) requires 1,333 square feet ( a l ternately 833 square feet) to reach the HTC stage of product. This area requirement can be calculated from the usual heat transfer equations i n the form of q (heat transfer to solids)=U(a c o - e f f i c i e n t of t r a n s f e r ) X Area X gas to Solids Temperature D i f ference. Based on a t y p i c a l 12% f i x e d carbon y i e l d and 0.6 pounds reacted per square f o o t , the o x i dation of the 600 pounds of f i x e d carbon formed r e quires that an a d d i t i o n a l 1000 square feet be added

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Minimum

Intermediate 25

Maximum 16

L a n d f i l l Volume

Bulk Density

lbs/ft3

Maximum

Intermediate

Minimum

Heat Recovery

lbs/ft3

A l i a s Cr+3

33

lbs/ft

3

A l i t t l e may remain oxidized s t i l l under study

Less

A l l as Cr+3

Less

Chrome as Cr+3

CBA 9 lbs/Hr-SF

Maximum

HTC lbs/Hr-SF.

Heavy Metals Retention

13

10

Loading rate (approx.)

LTC lbs./Hr-SF,

Comparison of P y r o l y s i s Modes of Operation

TABLE IV

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

0

MODERATE

MODERATE

HIGH

1596

1608

1588

1599

LOW MODERATE HIGH

IN GAS

MODERATE

1742

^CONCENTRATION

0

_°2 0 4 9

LOW

MODERATE

MODERATE

HIGH

MODERATE

HIGH

CONCENTRATION IN GAS* 02 CO9 + STEAM

1823

TEMPERATURE GAS - ° F

_C0

CARBON GASIFICATION RATE

TABLE V

2

16 25 - 30 42 - 47

+ STEAM

(VOL.7o)

0.40

0.25

0.30

0.30

0.67

0.86

2

RATE CARBON GASIFICATION LB/HR. - F T

204

SOLID

WASTES

A N D RESIDUES

to the furnace s i z e . Similar consideration of hearth area to eliminate f i x e d carbon from s o l i d s accounts f o r the e a r l i e r statement that RDF i s a f u e l that needs hearth area i n a multiple hearth furnace while gas or o i l burners do not. Heat Balance Results Presentation of Fuel Requirements and Energy Recovery P o t e n t i a l . In Figure 2, the f u e l r e q u i r e ments (where any e x i s t ) and the heat a v a i l a b l e f o r recovery, are both plotted against the sludge chara c t e r i s t i c s expressed i n terms of higher heating value per u n i t of wate consumes heat i n the furnace and f u e l value of the organics that must provide the heat or be supplemented with purchased f u e l . The ash hardly matters except that i t c a r r i e s water with i t at any given feed s o l i d s content. It i s not possible to simply r e l a t e f u e l r e q u i r e ment to f i l t e r cake moisture content without assuming a figure f o r sludge ash content and f o r heating value of the sludge organics. Ash content of sludge varies from 20 to 50%. Heating value per pound of organic content varies from 8,000 to 14,000 BTU. Variations over about h a l f as wide a range as that j u s t s t a t e d , occur within many plants from season to season i f not from week to week. The two supplementary scales on Figure 2 show the s o l i d s content to which sludge must be dewatered to provide the corresponding f u e l c h a r a c t e r i s t i c f o r two d i f f e r e n t sludges. The range has been i n t e n t i o n a l l y narrowed to keep the scale on the page. Sludge at 40% s o l i d s shown to range from 3600 BTU/lb. water ( i f i t has 40% ash content and the nonash portion has a heating value of 9000 BTU/lb) to 6000 BTU/lb water ( i f i t has 25% ash content and the non-ash portion has a heating value of 12,000 BTU/lb. Impact of Cake Ash Content, Heating Value of Organics and Water Content. These two supplementary scales c e r t a i n l y emphasize the importance of cons i d e r i n g sludge ash content and heating value of

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

VON

DREUSCHE

Figure 2.

AND

NEGRA

Pyrolyzing Sewage Sludge

Heat recoverable and required with respect to sludge characteristics

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

206

SOLID

WASTES

A N D RESIDUES

sludge organic content when comparing d i f f e r e n t f i l t e r cake moisture contents as feed to a furnace. O i l y or greasy sludges are frequently d i f f i c u l t to dewater to high s o l i d s content, but the high BTU per pound of organics may well r e s u l t i n the wetter cake being equally acceptable for p y r o l y s i s or i n c i n e r a t i o n . High dosages of lime and f e r r i c s a l t s for coagulation before f i l t e r i n g sometimes gives a d r i e r cake than polymer f l o c c u l a t i o n but i f the cake i s not a l o t d r i e r , may increase cake ash content as to r e s u l t i n no improvement i n b u r n a b i l i t y . The graph also makes i t clear that small f l u c tuations i n moisture content plus fluctuations i n ash content and heating value of organics w i l l normally cause considerable v a r i a t i o i s t i c s of what is being fed to the pyrolyzer or incinerator. This w i l l become important when cons i d e r i n g storage and return of char to the furnace. Ir

,f

Conclusions from Figure 2, r e : P y r o l y s i s . The graph makes i t clear that : A. P y r o l y s i s i n the CBA mode increases recoverable heat by 10% as compared to i n c i n e r a t i o n , only when considering sludge feed of more than 5,000 BTU higher heating value per pound of water. Otherwise recoverable heat i s r e duced 33%, because with lower heating value i n the sludge feed the i n c i n e r a t i o n base of comparison uses purchased f u e l s . B.

The desirable aspect of p y r o l y s i s from an energy economy viewpoint, i s reduction or e l i m i n a t i o n of requirement for a u x i l i a r y fuel.

C.

P y r o l y s i s can be f u e l l e s s (including f u e l l e s s afterburner) with sludge dewatered to the range of 29 to 39% s o l i d s for most sludge compositions as compared to 42 to 52% s o l i d s required for i n c i n e r a t i o n to be f u e l less and provide a 1400 °F exhaust temperature. Being able to dewater sludge to 42 to 52% s o l i d s range i s quite uncommon, i n fact the authors know of

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

V O N DREUSCHE

A N D NEGRA

Pyrolyzing Sewage Sludge

207

no commercial piece of equipment that could be depended upon to do t h i s r e g u l a r l y on t y p i c a l sludges, although perhaps the new membrane plate f i l t e r presses w i l l get well into t h i s range on some sludges. A range of 29 to 39% s o l i d s for dewatering both sludges is something one would very confidently expect from 3 kinds of dewatering equipment: recess tray f i l t e r presses, b e l t f i l t e r presses equipped with squeezing devices and most confidently membrane plate f i l t e r presses. It seems apparent that r a i s i n g the sludge f u e l content per pound of water content from the r e s u l t s usually obtained by dewatering to 20 to 30% s o l i d s content i s necessary to make p y r o l y s i s a f u e l l e s s operation; and that p y r o l y s i s i s necessary to keep the extent of dewatering required down to a l e v e l that can be p r a c t i c a l l y depended upon from normal equipment. Raising sludge f u e l content per pound of water content depends p r i m a r i l y on improved dewatering of the sludge since one has no c o n t r o l over the heating value of the organic content and l i t t l e or no c o n t r o l over the ash content. Improved Dewatering Much i s r e l a t i v e l y new i n t h i s important area. F l o c c u l a t i o n . Polymer flocculants have become cost competitive with f e r r i c - l i m e coagulation. Some sludges coagulate and dewater best with f e r r i c and lime, some with one polymer, some with another. It i s not easy to be sure the choice of f l o c c u l a n t made during a t e s t period i s s t i l l the best f l o c c u l a n t choice during subsequent weeks of operation when sludge c h a r a c t e r i s t i c s may have v a r i e d . But i n creasingly systems are being designed for easy change from one f l o c c u l a n t to another. The increased f l e x i b i l i t y can r e s u l t i n better f u e l c h a r a c t e r i s t i c s i n the sludge f i l t e r cake i f due allowance i s made for the e f f e c t of f e r r i c and lime on sludge ash content, instead of seeking simply the highest s o l i d s content.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

208

SOLID

WASTES

A N D RESIDUES

F i l t e r i n g Equipment. The recessed plate f i l t e r press and b e l t f i l t e r s that squeeze the cake, both introduced to the sewage treatment f i e l d within the past few years, have r a i s e d cake s o l i d s content from the 2 0 to 3 0 7 o s o l i d s range to the 3 5 to 4 5 % s o l i d s range. Now i n t e r e s t i s s h i f t i n g to expandable membrane f i l t e r presses. This i s a concept patented some years ago by Ciba-Geigy ( 8 ) and licensed to Moseley Rubber Company Limited of England. That company a f t e r several years of developing and improving f a b r i c a t i o n methods for such plates i s now introducing them to sewage works i n England and i n this country ( 9 ) . In these the compartments containing a p a r t l y or f u l l y formed cak panding the face of the trays as shown i n Figure 3 . This squeezes the cake transversely whereas i n the older recessed tray plates pressure i s applied to the cake only by the force of new sludge coming i n through the feed entry p o r t . The older fixed plate presses therefore apply pressure only edgewise to the center of the cake and t h i s pressure i s soon l o s t to f r i c t i o n of the cake against the two adjacent f i l t e r c l o t h s . The cake can be squeezed by the expandable membrane tray for any desired time period and a t h i n cake i s squeezed as hard or harder than a t h i c k cake. The expandable membrane feature can be used to reduce i n i t i a l c a p i t a l cost of f i l t e r presses by r e ducing t o t a l cycle time. T y p i c a l l y , for the standard recess p l a t e , 7 5 % of the sludge volume enters the press i n the f i r s t 2 5 % of the press cycle a f t e r which sludge input rates d r a s t i c a l l y slow. By expanding the membranes with compressed a i r at t h i s p o i n t , a given s i z e press produces 7 5 % of the normal cake weight and with squeezing time allowed may require only 3 0 to 3 5 % of the normal cycle time. This i n essence doubles press c a p a c i t y . Besides producing a d r i e r cake i n normal operation due to the transverse d i r e c t i o n of the squeezing forces and the time for which squeezing forces can be a p p l i e d , and the thinner cake that i s produced, the membrane plate eliminates production of occasional "wetter than normal" cake. An i n completely f i l l e d press has f u l l squeezing pressure

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

VON

DREUSCHE

AND

NEGRA

Pyrolyzing Sewage Sludge

Figure 3. Flow scheme expandable membrane filter press

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

209

210

SOLID

WASTES

A N D RESIDUES

applied to each cake. Also an occasional upset i n coagulation may be l a r g e l y o f f s e t by slow i n i t i a l f i l t r a t i o n giving a thinner than normal cake during the time allowance for press f i l l i n g but that t h i n cake w i l l be squeezed dry while c o r r e c t i o n i s made to coa g u l a t i o n . The cake can be p r o f i t a b l y l e f t to squeeze for as much cycle time as safety factor i n the i n i t i a l i n s t a l l a t i o n of the presses and any under-capacity of actual operation compared to planned operation may a l low i n the f i l t e r c y c l e . F i l t r a t i o n Results with Membrane P l a t e s . The performance of such membrane plates i s described i n a B r i t i s h p u b l i c a t i o n (9) from which Table VI has been borrowed. Conditione pumped to a standard recessed plate press and s i multaneously to a membrane plate press. Cakes were formed, squeezed and then a d d i t i o n a l sludge pumped i n and squeezed, a procedure which accounts for there being a f i r s t and second feed time and a f i r s t and second squeeze time. Press capacity seems to be about doubled and comparative cake s o l i d s content increased from an average of 26.2% s o l i d s to 34.3% - a change from 2.8 l b s . water/lbs. s o l i d s to 1.9 l b s . water/lbs. solids. Such membrane plates were purchased for the Nichols p i l o t plant press which uses 4 f t . by 4 f t . plates. The main object of t h e i r use was to f a c i l i tate cake preparation for p y r o l y s i s t e s t s . But when only 1 tray was a v a i l a b l e f o r the f i r s t such campaign, i t was i n s t a l l e d i n a stack of regular r i g i d recessed trays and t r i e d . When the diaphrams were expanded they squeezed the cake on e i t h e r side of t h i s one t r a y . Though some s l i g h t sludge movement out of the two squeezed compartments occurred, perhaps preventing f u l l pressure development, the r e s u l t s i n Table VII were obtained. It i s believed that i t i s now possible to depend on dewatering most sludges to 35 to 50% s o l i d s i n a cost competitive system and obtain sludge cake that w i l l generally exceed 5000 BTU a v a i l a b l e per pound of water contained. This i s an important part of the system for pyr o l y s i s of sludge alone since the f i r s t aim a f t e r

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

TABLE

VI

11.6 12.7 106 106 8.6 8.6 13.0 13.0 10.0 100 11.7 11.9

25.8 28.0 283 28.3 22 0 22.0 31.2 31.2 21.4 21.4 26.0 28.4

621 621 621 621 621 621 621 621 621 621 621 621

180 180 180 180 180 180 180 180 150 150 150 150

mins

Maximum Feed Pressure kPa

Feed Time

8 10 10 10 10 10 10 10 10 10 10 10

Possible No. of Cycles per day

11.0 8.6 10.8 10.2 8.2 10.0 10.0 10.4 10.6 11.5 10.9 11.0

36.7 31.2 35.4 30.9 29.7 34.1 34.3 33.4 34.3 36.3 34.9 40.9

, '

Dry Solids Applied kg

Cake Dry Solids %

ι t

80 55 55 55 55 55 60 60 60 60 60 60

mins

Total Time

1st 45 20 20 20 20 20 30 30 30 30 30 30

mins 2nd "10 15 15 15 15 15 10 10 10 10 10 10

Feed Time

The output consideration is based on a day's operation at the Brockhurst Works ie a shift system with attendance hours 07.30 to 22.00h Monday to Friday.

27 29 30 31 32 33 34 35 36 37 38 39

Test No

Table A — Brockhurst sludge. 1 No. Membrane Chamber 1130mm χ 1075mm χ 32mm

%

Dry Solids Applied kg

Cake Dry Solids

Membrane

Table A — Large test press. 1 No. Recess Chamber 1220mm χ 1220mm χ 32mm

621

ι 10 10 10 10 10 10 10 10 10 10 10

kPa

ι ι

j ' !

io—t

2nd

mins

Squeeze Time

kg 88 86 108 102 82 100 100 104 106 115 109 110

Total Dry Solids per day

Press

1st 15 10 10 10 10 10 10 10 10 10 10 10

Per chamber

Possible No. of Cycles per day

=

90

1st 317 310 310 310 310 310 310 310 310 310 310 310

psi

2nd 310 310 310 310 317 310 310 310 310 310 310 310

Maximum Feed Pressure kPa

5 5 5 5 5 5 5 5 5 5 5 5

system

Maximum Squeeze Pressure kPa 1st 2nd 517 517 414 483 379 434 414 414 448 448 386 483 485 503 448 414 455 455 448 414 414 414 621 586

kg 58 63 53 53 43 43 65 65 50 50 58 59

Total Dry Solids per day

Recess Press

Output comparison — 2 shift

22 25 25 25 25 25 22 22 25 25 25 19

mm

Cake Thickness

52 37 104 92 91 133 54 60 112 130 88 86

Increase obtained by use of Membrane

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

26.2 34.3

MEMBRANE PLATES

7o SOLIDS

RECESS PLATES (STD.)

TYPE

10

5

PER DAY

MEMBRANE PLATES

VS.

STANDARD RECESS PLATES

FILTER COMPARISON SUMMARY

TABLE VI-A

103

55

DRY SOLIDS (AVERAGE) PER DAY - KG

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

40.2 37.4

35.8 34.3

2

3

45.7 46.8

29.8 43.5

19

20

LIME-FERRIC CHLORIDE CONDITIONED SLUDGE

34.4

31.9

POLYMER CONDITIONED SLUDGE 1

PRESS RUN

CAKE SOLIDS - % UNCOMPRESSED COMPRESSED CAKE CAKE

TABLE VII NICHOLS PILOT PLANT TEST RESULTS ON FILTER PRESS

214

SOLID

WASTES

A N D RESIDUES

thermal destruction of the organics must be to e l i m i n ate the use of purchased f u e l . Char as Supplemental F u e l . Variations i n sewage sludge dewaterability, i n ash content and BTU per pound of organics, and occasional upsets i n coagulant choice and a p p l i c a t i o n must be expected. Supplementation of the heating value of the sludge i t s e l f , by return of previously produced char i s one way to overcome t h i s problem. For a 40 MGD wastewater treatment plant producing approximately 5000 pounds of sludge s o l i d s per hour, f u e l l e s s operation i n the LTC or HTC mode to produce char would b has more than 5000 BT This w i l l be most i f not a l l of the time, judging from the conversion scales at the bottom of the graph i n Figure 2 and from the performance expected of the Moseley membrane p l a t e s . Assuming 30% ash i n the feed and 12% y i e l d of f i x e d carbon from organics, the char produced would consist of 600 pounds per hour of c a r bon plus 1500 pounds per hour of ash and be about 140 cubic feet per hour. A 14,000 cubic foot storage b i n f o r example would therefore hold about 100 hours production, or 60,000 pounds of carbon - 900 m i l l i o n BTU of heat value i n easy to store and handleable form. The furnace f o r p y r o l y s i s could be sized at 1833 square feet of hearth area as indicated e a r l i e r i n t h i s paper, to burn away a l l of the f i x e d carbon from the normal feed r a t e . S e l f - s u s t a i n i n g operation would then be maintained through any deviations i n sludge ash content, or heating value per pound of organics contained, or cake moisture content that reduced the f u e l chara c t e r i s t i c of the sludge to as l i t t l e as 3400 BTU per pound of water contained. Extreme high sludge ash content or low heating value of sludge organic content, reducing sludge heating value below 3900 B T U / l b . , could be offset by the return of char from the storage b i n . Low sludge a v a i l a b i l i t y i n r e l a t i o n to heat demand could be met i n the same way.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10.

V O N

DREuscHE

A N D NEGRA

Pyrolyzing Sewage Sludge

215

A temporary excessive sludge moisture content, for example change from 40% moisture to 25% moisture for 8 hours would require feeding the furnace half the usual s o l i d s r a t e . This 10,000 l b s / h r . wet cake feed would be pyrolyzed and the carbon burned away i n 1200 square feet leaving 600 square feet for burning of supplemental char added from the storage b i n , 360 pounds per hour of carbon or 5,000,000 BTU/hr. or 2,000 BTU/lb. of dry sludge s o l i d s fed could be added i n t h i s way; maintaining f u e l l e s s operation although reducing energy recovery from exhaust gases from 2750 BTU recovered per ton sludge s o l i d s to 2500 BTU recovered. These numbers are quickly worked out from the graphs and tables given e a r l i e r i n t h i s paper. The char storag used for stand-by f u e l to keep the multiple hearth furnace hot when sludge i s not a v a i l a b l e , or to provide start-up f u e l . Conelusions Pyrolysis of sludge alone can be r e l i e d upon to eliminate a l l use of purchased f u e l s . This requires the use of modern dewatering equipment, which now has become commercially a v a i l a b l e . Heat recovery i n the range of 2,000 to 3,000 BTU per pound of dry sludge s o l i d s seems e a s i l y f e a s i b l e . Energy recovery i n the form of increased use of digesters to generate methane, while s t i l l avoiding a f u e l cost to thermally destroy the organics i n the r e s u l t i n g energy depleted sludge may i n some cases be a preferred use. Energy recovery as a char ash mixture to be treated f o r the e l i m i n a t i o n of heavy metals, converted to active carbon, or used as a f u e l at other locations than the sewage treatment p l a n t , may also develop as the preferred form. It i s believed that much work remains to be done i n finding valuable uses, preferably i n - p l a n t , for the carbon ash mixture that can be produced from sewage sludge and for the heat a v a i l a b l e from the gases exhausting from the afterburner. Steady improvement in dewatering equipment and i n thermal destruction energy e f f i c i e n c y w i l l increase the a v a i l a b i l i t y of

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

216

SOLID WASTES AND RESIDUES

these products and thus b r i n g about increasing e f f o r t s to u t i l i z e them. The p y r o l y s i s of sludge alone i n conjunction with better dewatering p r a c t i c e s , w i l l eliminate a l l f u e l cost; and generate enough steam from the exhaust gas to run the exhaust gas fan (the only major power consumer on the p y r o l y s i s unit)and aeration blowers for the waste activated sludge process, by steam t u r b i n e . It w i l l at the same time provide for the production of char, thus laying a base for eventual heavy metals recovery. This should make i t much more cost e f f e c t i v e than heretofore to carry out the e s s e n t i a l function of converting offensive and dangerous sludge organics to safe and inoffensiv "Literature Cited" 1. Patent U . S . 3,650,830 (1972) Nichols Engg. & Res. (Mathis, E . A . ) 2.

Nichols Engineering & Research Report, "Pyrolysis of Refuse Derived F u e l " for Aenco, Inc. July 1,1976

3.

S i e g e r , R . B . and Bracken, B . D . , AIChE Symp.Ser., (1977), vol.73 (143-149)

4.

Jacknow, J., "Environmental Aspects of Municipal Sludge Incineration", WEMA, Jan. 1978.

5.

Camp Dresser & McKee, Alexander Potter A s s o c . , Phase 1 Report for I . S . C . of N.Y.,N.J., Conn. June, 1975.

6.

von Dreusche, C . J r . "Process Aspects of Regeneration in a M u l t i p l e Hearth Furnace AIChE A u g . , 1974.

7.

Patent, U.S. 4,046,085 (1977) Nichols Engg. & Res. (Barry, L.T. etal.)

8.

Patent U . S . 3,289,845 (1966) CIBA-GEIGY,(Weber,O.)

9.

Edmondson, B . R . , and Brooks, D . R . , Water Services (May 1977)

10. EPA-430/9-77-011, "Energy Conservation i n Munic i p a l Wastewater Treatment". MCD-32. (March, 1977) APRIL 18, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11 A Thermal Process for Energy Recovery from Agricultural Residues RITCHIE D. MIKESELL, DONALD E. GARRETT, and DINH CO HOANG Garrett Energy Research and Engineering Co., Inc., 911 Bryant Place, Ojai, CA 93023

In May, 1976, a one-yea was l e t by the U. S. Energ tion to Garrett Energy Research and Engineering Co., Inc. to study the thermal decomposition of biomass materials in a bench scale pilot plant of the multiple hearth reactor type. In October, 1977, this contract was extended by DOE for 18 months for operation in a larger, process development unit (PDU) pilot plant. This unit will have a six ton/day, four-foot diameter, four hearth reactor. The program to date has consisted of vacuum drying, direct contact drying, pyrolysis, the char-steam reaction, and combustion experiments. The results of these studies are reported in the following paper. GERE Process The proprietary Garrett Energy Research and Engineering Company biomass process is based upon a multiple-hearth furnace. This type of equipment has been successfully employed for continuous high temperature processing in the chemical and metallurgical industries for over 100 years. There are several vertically stacked compartments with a common central shaft. Rabble teeth are mounted on arms attached to the central shaft whose slow rotation imparts a positive mechanical motion to the solid material on each hearth. Downcomers through which the solid drops onto the hearth below are located alternately near the inner and outer periphery. They may have star valves for good sealing, and the conditions on each hearth may be optimized for i t s desired function. Since the solid is spread in a thin layer with constant raking and tumbling action, the residence time is adjustable, and efficient solid-gas heat- and mass-transfer are achieved. The multiple-hearth furnace is well suited for processing materials that are moist, fibrous, sticky, or susceptible to ash fusion at high temperature. In the GERE process, Figure 1, the raw material may be first chopped and mechanically dewatered if necessary, and then conveyed 0-8412-0434-9/78/47-076-217$05.25/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 1.

Multiple Hearth Reactor

Water

I—wvW*-

—/ΛΛΛΧ

.Manure Feed

GERE multiple hearth pyrolysis process

Ash

F l u e Gas

» Medium BTU Gas P r o d u c t

11.

MIKESELL

E T

AL.

Energy Recovery from Agricultural Residues

219

to the top of the multiple-hearth reactor by means of a jacketed screw conveyor. The material is partially dried under vacuum by moist flue gas flowing countercurrently through the conveyor jacket and screw, and condensing inside. The conveyor has star valves at each end to maintain a good seal. Following the vacuum drying the remaining approximately half the water is removed by direct contact with hot flue gas on the f i r s t , or drying hearth. This water is then partially condensed in the vacuum screw feeder to provide multiple effect economy. Because biomass usually contains a great deal of moisture, i t is very important that this moisture be removed as e f f i c i e n t l y as possible. The biomass, after drying to the desired moisture content, then f a l l s to the pyrolysis hearth. Here i t is heated by hot char from the steam-char reaction, and also by the hot gases accompanying the char. The char is introduced through an external steam l i f t in which synthesis gas is formed as the char reacts with superheated steam the gaseous products o (H HpS, NHL, COS) are cooled and condensed. The condensed tar is recycled to the pyrolysis zone. Char from the pyrolysis hearth drops onto the combustion hearth where i t is partially burned to generate steam and process heat. The hot flue gas preheats the incoming air in an external heat exchanger, and then goes to the drying section. Some of the hot char is reacted with steam in the steam l i f t and then sent to the pyrolysis zone, while an ash-bleed stream drops to the cleanup burner where i t is completely burned. The ash then drops to the lowest hearth where i t is cooled by incoming air and discharged from the reactor. The gas leaving the condensate collector may either be u t i l ized directly or sent to a scrubber in which hLS, C0 and moisture are removed. This product gas may be piped for use at a nearby industrial plant, or blended into a natural gas pipeline. 2

Experimental Biomass Feed. The GERE pilot plant work is done in Hanford, California, an agricultural community, with steer manure as the f i r s t pilot plant feed. The moisture content of fresh manure is about 80%, although the moisture content of piled manure ranges from about 10 wt_% {]_) to about 50 wt % (2) depending on the climate and length of storage. A typical ultimate analysis of bovine manure is given by Schlesinger, Sanner, and Wolfson (3) in Table I. For the pilot plant work, the moisture content of the feed manure was adjusted to 50 wt %.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

220

SOLID

Table I.

WASTES

A N D RESIDUES

Bovine Manure, Typical Ultimate Analysis 41.2 wt % 5.7 33.3 2.3 0.3 17.2 100.0 wt %

C H 0 Ν S Ash Total dry

Pilot Plant Equipment. During the f i r s t phase of this work a single-hearth reactor was used. Each process--direct contact dry­ ing, pyrolysis, water gas char gasification, and combustion—was studied in turn in this hearth. Figure 2 shows a schematic of the reactor; detailed description of the equipment is given in Refer­ ence (4). Laboratory Experimentation manure pyrolysis showed that over the temperature range 25-700 C, the reaction is slightly exothermic and that the use of NaoCOj had l i t t l e i f any effect on the reaction rate. It was found that flue gas as hot as 180 C could be used to dry manure without burning i t . Manure can be decomposed (pyrolyzed) at a temperature as low as 250 C, though the product gas at this temperature is mostly C0 . If the tar produced in pyrolysis is i t s e l f pyrolyzed, more gas is produced. In particular, the hydrocarbon gas production is en­ hanced. Manure ash begins to fuse at about 950 C. Manure drying experiments were f i r s t conducted in a laborato­ ry oven. The data were correlated using the relationship 2

fj=

4.27-M-exp -

2474

(1)

According to Reid, Prausnitz, and Sherwood (5), the exponential term is associated with the moisture d i f f u s i v i t y . Hot a i r was passed through a small, well insulated, fixed bed of manure in order to dry i t . Since the drying rate ought to depend upon the superficial gas velocity to the 0.8 power, and on the moisture diffusivity to the 0.56 power, the data were correlated as Μ'ΰτ

27·

G 150.8 V

•exp -

1385

(2)

This relationship is consistent with Equation (1) and represents the laboratory data to within ± 20%. Using bed thicknesses com­ parable to those used in the pilot plant (about 3 cm) and super­ f i c i a l gas velocities close to those used in the pilot plant (about 150 cm/min), i t was found that the gas and solids temperatures very rapidly came together. This was taken to mean that the pro­ duct of the heat transfer coefficient and the heat transfer area,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11.

MiKESELL

E T A L .

Energy Recovery from Agricultural Residues

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

221

222

SOLID

UA, for the bed is essentially i n f i n i t e . with

Equation (2) together (3)

( C ) . ^ - λ . ^ = (C ) .((T ) p

A N D RESIDUES

T Q = T<*

Thermal Equilibrium Heat Balance

WASTES

s

Moisture Balance

γ

p

G

s

i n

- y

(4)

- Μ . ^ = W{H - H. } (5) ο οτ b in make a system of relationships that describe the drying process. The problem was programmed on an HP-67 and numerically integrated. The model predicts drying rates about 20% higher than experienced in the laboratory. This probably reflects the fact that the model does not consider the heat losses ς

r

Pilot Plant Experimentatio Vacuum Drying. The small jacketed screw feeder was used to measure heat transfer coefficients. The screw in this feeder was not hollow, no vacuum was used, and saturated steam was fed to the jacket. The data are shown in Table II. Table II. Feed Moisture

Screw Speed

wt %

RPM

37.34 37.34 37.34

1 2 3

50.0 50.0 50.0

1 2 3

Screw Conveyor Heat Transfer Data for Vacuum Drying Manure Solids Residence Time, τ„ κ min. 25.7 15.0 9.4 50.4 27.5 15.1

Overall Heat Transfer Coefficent, U

u. ρο:τ β k

cal/miη cm^°C

dimensionΤ

1.0l(lO" ) 2.00 2.55

1.23 1.86 1.87

0.55 1.61 1.81

0.50 1.08 0.90

2

Direct Contact Drying. Moist manure was fed to the single hearth through the screw feeder. The rabble teeth swept the ma­ terial across the baseplate from the center to the outside where i t f e l l through a single hole into a receiver. The baseplate contained 1/8 i n . holes spaced about 2-1/2 i n . apart, and hot flue gas was passed upward through these holes and then through the moving bed of manure. Long solids residence times were obtained by using low rabble arm speeds and by turning the rabble teeth almost parallel to their direction of motion. The moisture con­ tents of the feed and product, the solids feed rate, the holdup

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11. MiKESELL E T A L .

Energy Recovery from Agricultural Residues

223

volume, the inlet and outlet solids temperatures, the rabble arm rotation rate, the rabble tooth angle, and the hot flue gas inlet and outlet temperatures and humidities and i t s flow rate were measured for each run. Equations (2) through (5) describe direct contact drying in the pilot plant as well as in a fixed bed, so long as i t is un­ derstood that time, τ, in the model corresponds t o £ d r / u in the pilot plant and that the outlet gas temperature in the pilot plant is the same as

in the model. Pilot plant data for three experimental runs are compared with results of numerically integrating Equations (2) through (5) in Table III The model does no outlet solids and gas temperatures are higher than measured, and the predicted outlet solids moisture content is lower. The mea­ sured outlet solids temperatures were obtained by immersing a thermometer in the solids after they had fallen from the reactor. As the solids accumulated in the receiving bag, they probably cooled down. Thus, the measured outlet solids temperatures in Table III seem unreasonably low. In the future this temperature will be measured inside the reactor by a thermocouple attached to one of the rabble teeth. Pyrolysis. In these experiments, manure samples having d i f ­ ferent moisture contents were pyrolyzed at moderate (600-750°C) temperatures. The data show that a substantial part of the carbon was gasified by the steam. Here, then, pyrolysis and steam gasi­ fication occurred together in the same reactor at only moderate temperatures. I n i t i a l l y the reactor was empty while the baseplate was heated from below by natural gas burners. Argon was used to purge the reactor. At time zero the feeder was turned on, and after a few minutes the argon flow was turned off and the temperatures stabilized. At 10-minute intervals, the pyrolysis gas flow rate was measured, pyrolysis gas samples were taken, the baseplate tem­ perature, the solids temperature near the i n l e t , and the solids temperature near the outlet were recorded. The solids tempera­ tures were measured by thermocouples attached to the rabble teeth. These temperature measurements showed that the solids are very nearly isothermal as they are swept across the reactor floor. The pyrolysis gas samples were analyzed by a Beckman Gas Chromatograph 2A. At the end of the experiment the remaining char was cooled under argon. The amount of char remaining that can be swept out by the rabble teeth (the dynamic holdup), and f i n a l l y the rest of the char in the reactor (the static holdup) was removed and weighed. The moisture content, the volatile content (750°C), the residual carbon, and the residual ash of the product char, the

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

G

S

in

T

G

d T

bà

°K

gm HoO/gm dry solids

M

T

.390 348°

358°

320°

386° .310

Meas.

Calc.

27.84

mi η

°K

R

.6234

gm H20/gm dry solids

.025

gm r^O/gm dry gas

344°

.416

353°

Calc.

332°

.507

320°

Meas.

19.04

.6234

376°

.500

380°

Calc.

340°

.545

319°

Meas.

7.39

.6234

.025

423°

421°

417°

°K .033

.7592

.3079

138.3

.4021

138.3

589

gm dry gas/(min)(gm dry solids)

138.3

cm/mi η

S

T

M. in

H

(Vin

G

W /M

V

1452

Comparison of Model With Pilot Plant Data

1112

Direct Contact Drying of Manure:

gm dry solids

Table III.

11.

MIKESELL

Energy Recovery from Agricultural Residues

E T A L .

225

dynamic holdup char, and the static holdup char were measured using the laboratory muffle furnace. The steam and tar in the pyrolysis gas were condensed and weighed. Later these samples of condensate will be analyzed for their water contents. The condensed tar can, of course, be re-pyrolyzed to produce a hydrocarbon-rich gas. Some representative data are shown in Table IV. These data are for the pyrolysis of two manure samples at about 650 C. The moisture content of the f i r s t sample was 43.2 wt %; the moisture content of the second was 5.2 wt %. In these pyrolysis experiments, Reactions (6), (7), and (8) also occurred. C + H 0 + H + CO

(6)

CO + H O i H + co

(7)

CH + H 0 Î 3H + CO

(8)

2

2

2

4

2

2

Carbon and methane can also be oxidized by C0 at these temperatures, but probably at slower rates. In the pyrolysis of Sample 1, the steam content of the pyrolysis gas in the reactor was quite high, and so the reactions above were driven further to the right. Reactions (7) and (8) are far from equilibrium for the data of Table IV. These reactions as well as Reaction (6) are probably almost, but not quite, frozen at these temperatures. Even i f the feed manure were completely dry, Reactions (6) through (8) would occur to some extent, because rLO is one of the products of pyrolysis. Water Gas Reactions. Nitrogen was used to purge the reactor as the baseplate was heated by natural gas burners. Pyrolysis char and superheated steam were fed to the reactor and the n i t r o gen flow was turned off. At 15-minute intervals gas samples were taken. The condensate, which contained very l i t t l e tar, was c o l lected and weighed after each run. At the end of the run, n i t r o gen was passed through the reactor until i t had cooled. The reactor holdup, dynamic and static together, was weighed, but this char was not analyzed. The ultimate analyses of the inlet and product chars were determined, but the volatiles (750 C) and residual carbon were not. The baseplate temperature, the gas temperature, and the temperature of the char as i t f e l l from the reactor were measured. In the future the solids temperature will be measured by a thermocouple attached to one of the rabble teeth In Table V the solids temperatures were probably in the 600-700 range. These runs lasted only about as long as one solids residence time, so the char remaining in the reactor at the end of each experiment is important to the material balance. In the next set of experiments the dynamic and static holdup chars will be weighed and analyzed. 2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

226

SOLID

Table IV. Sample 1.

Pyrolysis of Moist Manure:

WASTES

A N D RESIDUES

Pilot Plant Data

Solids 635°C; Pyrolysis gas 437°C; 45 min solids residence time. Feed 3170 gm/hr

Product Char 390 gm/hr

H0

.4316 wt. fract.

.018 wt. fract.

Volatile (750°C)

.2353

.159

Carbon

.0954

.183

Ash

.2377

.640

2

1.000 wt. fract.

1.000 wt. fract.

Dynami H0

.016 wt. fract.

.015 wt. fract.

Volatile (750°C)

.107

.090

Carbon

.174

.146

Ash

.703

2

.749

1.000 wt. fract.

1.000 wt. fract.

Condensate (H 0 + Tar) 1304 gm/hr 2

Gas 772 gm/hr H

.471 vol

2

fract.

37.1 gm/hr

.035 gm/gm DAF

CO

.112

123.6

.118

co

.308

533.1

.509

.089

56.1

.054

.015

16.5

.016

2

CH

4

2 4 C H C

H

2

6

.005

5.9

1.000 vol. fract.

772.3 gm/hr

Overall mass balance closure Overall ash balance closure Carbon (750°C) gasified Pyrolysis gas heating value (low) (including C0 but not H 0) 2

.006 .738 gm/gm DAF 97.9% 94.7% 42.9% 272.5 Btu/SCF

2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11.

MiKESELL

E T

AL.

Energy Recovery from Agricultural Residues

Table IV.

Pyrolysis of Moist Manure:

Sample 2.

Solids 657°C; Pyrolysis gas 460°C; 23 min solids residence time.

Pilot Plant Data (Cont.)

Feed 2700 gm/hr

Product Char 600 gm/hr

H0

.052 wt. fract.

.011 wt. fract.

Volatile (750°C)

.385

.113

Carbon

.2262

.304

Ash

.3368

.572

2

1.0000 wt. fract.

1.000 wt. fract.

Dynamic Holdu .012 wt. fract.

.009 wt. fract.

Volatile (750°C)

.073

.063

Carbon

.270

.233

Ash

.645

.695

H0 2

1.000 wt. fract.

1.000 wt. fract.

Condensate (H 0 + Tar) 466 gm/hr 2

Gas 875 gm/hr H

.352 vol

fract.

27.6 gm/hr

.017 gm/gm DAF

2

CO

.177

194.3

.118

co

2

.309

533.1

.323

CH

.126

79.2

.048

.021

23.4

.014

4

C H 2

C

4

2 6 H

.015

17.7

1.000 vol. fract.

875.3 gm/hr

Overall mass balance closure Overall ash balance closure Carbon (750°C) gasified Pyrolysis gas heating value (low) (including C0 but not H 0) 2

227

.011 .531 gm/gm DAF 97.6% 99.5% 37.3% 319!2°Btu/SCF

2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

228

SOLID

Table V. Run 6.

Steam-Carbon Rea

Baseplate 810°C; Gas outl residence time.

ion:

WASTES

A N D RESIDUES

Pilot Plant Data

425°C; 115 min solids

C

H

0

Ash

Total

.250

.025

.148

.497

.920

-_

.038

.302

-

.340

.250

.063

.450

.497

1.260

.074

.197

-

.271

CO, kg/hr

.013

.018

-

.031

CH , kg/hr

.003

.001

-

-

.004

Char Out, kg/hr

.127

.014

.024

.497

.662

Total, kg/hr

.217

.041

.239

.497

.994

Char In, kg/hr Steam Consumed, kg/hr Total, kg/hr Output Gas C0 , kg/hr 2

H , kg/hr 2

4

Overall mass balance closure

78.9%

Overall carbon balance closure

86.8%

Carbon gasified

36.0%

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11. MiKESELL E T A L .

Table V. Run 7.

Energy Recovery from Agricultural Residues

Steam-Carbon Reaction:

229

Pilot Plant Data (Cont.)

Baseplate 860°C; Gas outlet 415°C; 90 mi η solids residence time. C

Char In, kg/hr

Η

0

Ash

Total

.685

1.268

.344

.035

.204

Steam Consumed, kg/hr

-_

.052

.418

^_

.470

.344

.087

.622

.685

1.738

C0 , kg/hr

.094

-

.250

-

.344

H , kg/hr

-

CO, kg/hr

.022

-

.029

-

.051

CH , kg/hr

.003

.001

-

-

.004

Char Out, kg/hr

.148

.010

.042

.685

.885

Total, kg/hr

.267

.034

.321

.685

1.307

Total, kg/hr Output Gas 2

2

4

Overall mass balance closure

75.2%

Overall carbon balance closure

77.6%

Carbon gasified

34.6%

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

230

SOLID

WASTES

A N D RESIDUES

Char Combustion. Char from the water gas experiments was fed to the reactor. Combustion air was pushed through the base­ plate and through the hollow rabble teeth. A 2 cm ash layer was maintained on the reactor floor. The reactor was not lined with f i r e brick. Typical data are shown in Table VI. Table VI.

Char Combustion:

Pilot Plant Data

Char feed rate Carbon feed rate

67.7 gm/min 2.10 gm mol/miη

Air flow

11 SCFM

0

2

flow

0 /C ratio in feed 2

3.70 gm mol/miη 1.76

Carbon burned 63.1 The heat losses from the reactor were very large. In the work to follow, the combustion chamber will be well insulated and the combustion efficiencies should be higher. Commercial Biomass Processing Plant Based Upon the GERE Process Plant Sizing. It is assumed that each pyrolysis plant would serve an individual feedlot (or perhaps a group of feedlots con­ centrated in a sufficiently small area that they can conveniently use the same manure repository s i t e ) . To factually determine a reasonable plant size i t is necessary to review s t a t i s t i c a l data on feedlot sizes, as reported in Reference 4. Based upon this data, 2 ton/day (dry basis) plant for small feedlots (730 head @ 5.5 l b . per head), 100 ton/day (dry basis) plants for large feedlots (36,000 head), or very large plants of 250,000 t/yr. serving several feedlots could a l l be considered. However, the 2 ton/day plant proved to be prohibitively expensive in a preliminary anal­ y s i s , so detailed cost analyses were not considered j u s t i f i e d and only the larger plant sizes were reviewed. In each case a medium Btu gas was the only product considered. Economic Analysis. A detailed process design and economic analysis based upon the data from this study was then made. It indicated that the capital cost for a 100 t/d (on a dry feed ba­ sis) manure processing plant would be about $1.9 m i l l i o n , and the cost of gas $2.84/MM Btu after depreciation and a 10% pretax pro­ f i t . 1.7 MM SCF/day of about 500 Btu/cu.ft. gas would be genera­ ted. The break-even gas price would be $2.1/MMBtu. The plant would have a small ash disposal problem, but the ash may have some f e r t i l i z e r value so no charge was made against i t . The plant would generate a l l of its own heat and power, and have a net energy recovery of greater than 70% from the original feed

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11.

MiKESELL

E T

Energy Recovery from Agricultural Residues

AL.

231

material. The capital investment summary is given in Table VII, and the operating cost in Table VIII. The proposed process flow-sheet is shown in Figure 3. It assumes that the biomass, in this case manure, is delivered to the plant f a i r l y regularly, and dumped by the producer on a con­ crete storage pad. As described in an earlier section (GERE pro­ cess), the manure is dried, pyrolyzed, and then burned to produce a medium-Btu gas. The operating conditions in each hearth of the reactor are indicated in Figure 3. The pyrolysis and water gas product passes to a quench tank and then to COo, HpS, and water removal equipment. A clean, dry, medium Btu gas (400-500 Btu/cu.ft.) is produced for direct sale or use as a synthesis gas. Any condensate from the quench tank is reinjected into the pyrolysis section to be cracked into gas. Very thorough heat exchange is practiced on a l l entering and exit­ ing streams. The e l e c t r i c i t y required for the plant is generated internally from the hig Literature source Table VII, except the multiple hearth furnace, which is a quota­ tion from a manufacturer based upon past installations of essen­ t i a l l y turn-key plants for sewage sludge incinerators, including gas cleanup equipment, elevators, feeders, instrumentation, etc. Some of the assumptions used in sizing the equipment are: 1) the heating value for dry manure is 6240 Btu/lb; 2) the plant operates for 300 days/yr; 3) the total net energy recovery is 70%. The yearly energy production for the 100 ton/day plant i s : (6240 Btu/lb) χ (2000 lb/ton) χ (100 tons/day) χ (300 operating days/yr) χ (0.7) = 2.62 χ 10 MMBtu/yr, or 1.7 MM SCF/day of 500 Btu gas. A complete amine-glycol gas purification system was estimated to cost $150,000 as a skid-mounted package, which includes an ab­ sorption tower, stripper-régénérator column, reboiler, two coolers and pumps, instrumentation and controls. If the presence of carbonyl sulfide (COS) or carbon disulfide (CS ) becomes a problem, diethanolamine could replace monoethanolafnine. If the moisture content of the product gas exceeds the specified levels, an additional drying column would be required. An additional cost analysis has been made comparing the GERE process with a similar pyrolysis process studied by others. Their "best" pyrolysis case (Purox) was used, and the GERE process scaled from 100 t/d to 250,000 t/yr by means of the 0.6 power ratio. It is seen that the GERE process produces gas for $2.06/ MM Btu, compared to their $6 or $7/MM Btu. The difference is due primarily to their much higher plant capital investment (their oxygen plant, front end drying f a c i l i t y , much more complex reactor, e t c . ) , and the purchase of outside u t i l i t i e s (power). At either plant size the GERE process looks to be especially attract i ve. 5

2

Conclusion Biomass can obviously be processed to recover energy, but

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

232

SOLID

Table VII.

WASTES

Capital Investment, 100 T/day (dry basis) Manure Biomass Plant

Flow Chart Symbol CP-1

A N D RESIDUES

Direct Equipment Cost Concrete Storage Pad, 625m (25m χ 25m), 15cm thick with 15cm sub-base. 20cm χ 2m high walls on 3 sides. 2

$ 25,000

FEL

Front End Loader

40,000

R-l

Ramp with Guard Walls

15,000

H-l

Feed Hopper 12m with Grizzly; 3

stainless LB-1

Lump Breaker

SV-1

Rotary Valve, 10" χ 48", teflon coated rotor Vacuum Dryer-Screw Conveyor, 14" dia.

C-l

20,000

χ 60 f t . , jacketed shell and flights

5,000 66,000

SV-2

Rotary Valve

5,000

E-l

Condenser, 250 s q . f t . , carbon steel

5,000

E-2

Heat Exchanger, Cooler for quench f l u i d , 100 f t , carbon steel

4,000

2

3

P-l QV-1

MHF

Vacuum Pump, 50m /hr at 350mm Hg absolute Quench Column, 4' dia. and settling drum, carbon steel construction Total Pyrolysis Equipment Cost

5,000 10,000 $215,000

Factored Costs of Installed Equipment; 215%, including service f a c i l i t i e s , i n ­ strumentation and controls, piping, e l e c t r i c a l , land, yard improvements, engineering and construction overhead, contingencies

462,000

Multiple Hearth Furnace, 18* o.d. - 12 hearths (cost includes installation and a l l other costs)

960,000

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11.

MIKESELL

E T

AL.

Table VII.

Energy Recovery from Agricultural Residues

233

Capital Investment, TOO T/day (dry basis) Manure Biomass Plant (Cont.)

Total Capital Investment for Pyrolysis (Gasification) Plant $ 1,637,000 Gas Purification Equipment Reciprocating compressor, 2000 SCFM, 100 psig discharge pressure, complete with 250 HP motor drive, intercooler, other auxiliary equipment, installation

100,000

Amine Glycol gas purification system for HpS, COo, and H-O removal, complete as a packag skia h absorptio column, stripper-regenerato boiler, two coolers, instrumentation and control, carbon steel construction

150,000

Total TOTAL INITIAL INVESTMENT

$ 250,000 $ 1,890,000

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

234

SOLID

Table VIII.

WASTES

A N D RESIDUES

Annual Operating Costs, 100 t/d (dry basis) Manure Biomass Plant Capital Cost:

$1.89MM $/yr

$/MM3tu

Labor 8 operators (2 per s h i f t ) , 24 hrs/day, 365 days/yr, $8/hr 2 mechanics at $20,000/yr

140,000 40,000

0.802

1 superintendent Plant overhead cost, 25 and supervision

40,00 52,000

Outside maintenance materials, 4% of i n i t i a l investment

76,000

Outside maintenance labor, 1.5% of total i n i t i a l investment

28,000

0.397

Insurance, 2% of total i n i t i a l investment

37,000

0.141

Return on investment (10%) and depreciation (7%), 17% of total i n i t i a l investment

320,000

1.221

20,000

0.076

$743,000/yr

2.835

U t i l i t i e s (other than s e l f generated), power, water, etc. Total i f manure is free Manure @ $7/ton (dry basis)

0.198

0.801 TOTAL

$ 3.636/MMBtu

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2

?

B-l BOILER C-l CONVEYOR-VACUUM DRYER CY-1 CYCLONE C/W COOLING WATER E-l BAROMETRIC OR SURFACE CONDENSER E-3 QUENCH TOWER COOLER E-4 AMINE-GLYCOL COOLER E-5 REBOILER E-6 GAS COOLER FEL FRONT END LOADER H-1 FEED HOPPER LB-1 LUMP BREAKER MHF MULTIPLE HEARTH PYROLYSIS REACTOR P-1 VACUUM PUMP P-2 COMBUSTION AIR BLOWER P-3 PUMP P-4 RECIPROCATING COMPRESSOR R-l RAMP S-l SETTLING DRUM SV-1 STAR VALVE SV-2 STAR VALVE T-l QUENCH TOWER T-2 C0 , H S ABSORBER T-3 STRIPPER-REGENERATOR

Figure 3.

GAS PURIFICATION SYSTEM

GERE projected commercial-scale biomass process

ASH TO DISPOSAL

236

SOLID

WASTES

A N D RESIDUES

there appears to be no existing technology available that will allow an economical recovery. Nevertheless, the potential does exist for a correctly designed and engineered process which solves the problems of high moisture content, d i f f i c u l t feedstock handling, and generally low tonnage biomass a v a i l a b i l i t y at any one location. The GERE process shows promise in economically achieving this potential. The bench scale pilot plant study pro­ gram indicates a technical f e a s i b i l i t y for simple, low cost pro­ duction of medium-Btu gas from biomass in modest sized plants. Nomenclature (Cp) Y

= r

b

(C ) p

s

specific heat of the gas, cal/°C gm dry gas. A function of H. = specific heat of the solids, cal/°C gm dry solids. A function of M

H H

=

in

=

humidity of th h u n r i d i t

y

o f r

t

h

e

inlet gas, gm H 0/gm dry gas 2

k

=

thermal conductivity, cal/cm mi η °C

M

=

moisture content of solids, gm H 0/gm dry solids

Μ·

=

moisture content of inlet solids, gm H 0/gm dry solids

=

dry weight of fixed bed, gm dry solids

Ί

η

r

=

Τ G ^ G^in S

2

2

radius measured from the center of the rotating shaft, c m

= = =

temperature of the outlet gas, Κ temperature of the inlet gas, °K temperature of the solids, °K

r

=

local radial solids velocity across the baseplate, cm/mi η

U

=

overall heat transfer coefficient, cal/miη cm °C

Vç

=

superficial gas velocity, cm/mi η

Wç

=

gas mass flow, gm dry gas/mi η

T

T

u

2 α λ

γ

τ τ

ρ

=

thermal d i f f u s i v i t y , cm /miη

=

latent heat of evaporation, cal/gm water evaporated

=

time, min

=

solids residence time, min

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

11.

MIKESELL ET AL.

237 Energy Recovery from Agricultural Residues

Literature Cited 1. Huffman, W. J., Peterson, R. L., and Halligan, J . E., "Ammonia Synthesis Gas Generation from Cattle Feedlot Manure," Dept. Chem. Eng., Texas Tech. Univ., given at ACS Symposium on Clean Fuels from Biomass, Orlando, Fla. (Jan. 1977), p. 11. 2. Walawender, W. P. and Fan, L. T., "Pyrolysis of Dried Feedlot Manure in a Fluidized Bed," Private communication from Dept. Chem. Eng., Kansas State Univ. (Jan. 1976), p. 2. 3. Schlesinger, M. D., Sanner, W. S., and Wolfson, D. E., "Energy from the Pyrolysis of Agricultural Wastes," "Symposium: Processing Agricultural and Municipal Wastes," pp. 93-100, Avi Publishing Co., Westport, Conn., 1973. 4. Garrett, D. E., "Conversion of Biomass Materials into Gaseous Products," Report SAN/1241-77/1, prepared for ERDA Contract No. E(04-3)-1241 (1977) 5. Reid, R. C., Prausnitz Properties of Gases an Liquids, p , , , 1977. MARCH 3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

12

Activated C a r b o n and F u e l f r o m Sewage Solids

JOHN E. SIGLER 2839 Tabago Place, Costa Mesa,CA92626

Under a NASA development program for a source of carbon for i n s u l a t i o n , Marshall Humphrey of Jet Propulsion Labs, (1) Pasadena, Ca., conceived a new process for t r e a t i n g wastewater. A f t e r bench t e s t i n g , a trailer mounted unit was brought to the County Sanit a t i o n D i s t r i c t s of Orange County, C a l i f o r n i a . After t e s t i n g t h i s 10,000 gallon per day unit plus some tests on reactors i n Belle Meade, New Jersey, Springf i e l d , Ohio and L o u i s v i l l e , Kentucky, the Sanitation D i s t r i c t s decided the system had enough promise to j u s t i f y a p i l o t plant scale t e s t . Much of t h i s j u s t i f i c a t i o n was the elimination of a sludge disposal problem with which all present wastewater treatment systems are confronted. With the approval of the C a l i f o r n i a State Water Resources Control Board, the Environmental Protection Agency, and the Sanitation D i s t r i c t s Board of Directors, a p i l o t plant was b u i l t and operated to obtain data for design of a full scale p l a n t . The one m i l l i o n gallon a day (MGD) size was considered an intermediate step between the .01 MGD trailer mounted unit and the full plant size of 175 MGD. Process Description Hydraulics. The treatment system i s a two-stage counter-current adsorption process using activated carbon produced from the sewage s o l i d s . The flow diagram i n F i g . 3 i l l u s t r a t e s the 0-8412-0434-9/78/47-076-241$05.00/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

242

SOLID

Figure 1.

WASTES

AND

RESIDUES

A 10,000 gallon/day demonstration plant—trailer mounted

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

12.

siGLER

Activated Carbon and Fuel

Figure 2.

The 1 MGD pilot plant

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

243

244

SOLID

WASTES

A N D

RESIDUES

c o u n t e r - c u r r e n t movement o f t h e carbon w i t h r e s p e c t t o the wastewater. F r e s h carbon i s added b e f o r e the s e c ondary c l a r i f i e r where t h e a c t i o n i s e s s e n t i a l l y a d s o r p t i o n o f d i s s o l v e d o r g a n i c s on t h e c a r b o n . The p a r t i a l l y used carbon i s removed from t h e secondary c l a r i f i e r and mixed w i t h t h e i n c o m i n g wastewater. In the p r i m a r y s t a g e t h e a c t i o n o f t h e carbon i s as a s e t t l i n g a i d but some a d s o r p t i o n a l s o o c c u r s . Chemi c a l a d d i t i o n s o f F e r r i c C h o l o r d e and polymers were used t o a i d t h e s e d i m e n t a t i o n i n t h e c l a r i f i e r s . A sand f i l t e r was i n s t a l l e d on t h e e f f l u e n t but the main t h r u s t o f t h e work was d i r e c t e d toward obt a i n i n g a s a t i s f a c t o r y e f f l u e n t from t h e s e c o n d a r y clarifier. M i x i n g o f t h e carbon w i t h t h e wastewater b e f o r e each c l a r i f i e r was a c c o m p l i s h e d i n two s t e p s a 2 minute f a s t mix and 3

S o l i d s Dewatering and D r y i n g .

While t h e s o l i d s removed from t h e s e c o n d a r y s t a g e were r e t u r n e d t o t h e p r i m a r y s t a g e ^ s o l i d s from t h e p r i m a r y s t a g e were removed from t h e h y d r u a l i c system. These s o l i d s a r e o f a m i x t u r e o f a c t i v a t e d carbon and sewage s o l i d s i n about a 5 t o 3 r a t i o . The s l u d g e s o l i d s removed from t h e c l a r i f i e r were about 1 0 $ d r y s o l i d s . S t o r i n g and d e c a n t i n g i n c r e a s e d the s o l i d s c o n t e n t t o about 1 5 $ b e f o r e f e e d i n g t o t h e f i l t e r press. The f i l t e r p r e s s r e g u l a r l y produced cakes which were g r e a t e r t h a n 5 0 $ s o l i d s c o n t e n t . F u r t h e r d r y i n g was a c c o m p l i s h e d i n a f l a s h d r y e r which can produce s o l i d s w i t h o n l y 2 o r 3 $ m o i s t u r e ^ but t h e p r o d u c t i s d u s t y and f l u f f y . At 1 0 to 1 5 $ moisture content^ the product i s i n a b e t t e r c o n d i t i o n for feeding t o the reactor. Reactor.

The r e a c t o r used was an i n d i r e c t l y f i r e d , r o t a r y k i l n known as a c a l c i n e r . The tube was 3 0 i n c h e s i n d i a m e t e r and had a h o t zone o f 3 0 f e e t . This i s a s t a n d a r d u n i t as manufactured by Combustion E n g i n e e r i n g except t h e tube was o f ^ i n c h I n c o n e l 6lJ p l a t e r o l l e d and welded t o shape. F i f t e e n burners> d i v i d e d i n t o 3 zones f o r tempe r a t u r e c o n t r o l ^ were used t o s u p p l y the heat t o t h g reactor. The most common temperature used was l 6 0 0 F i n a l l t h r e e zones but some runs were made w i t h a

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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245

temperature p r o f i l e o f 1 1 0 0 - 1 3 5 0 - 1 5 0 0 ° F from f e e d t o p r o d u c t end. Feed was d e p o s i t e d w e l l i n t o the f i r s t zone by a screw f e e d e r which a l s o m a i n t a i n e d a gas s e a l . Product d i s c h a r g e d from t h e tube i n t o an end b e l l and then t h r o u g h a r o t a r y v a l v e which m a i n t a i n e d t h e s e a l on t h e d i s c h a r g e end. Three t h i n g s were t o be a c c o m p l i s h e d i n t h e r e actor. 1. Complete t h e d r y i n g o f t h e f e e d . 2. P y r o l y z e t h e sewage s o l i d s . 3. A c t i v a t e t h e carbon w i t h superheated steam. Superheated steam was f e d i n t o the l a s t zone o f the tube t o a c c o m p l i s h t h e a c t i v a t i o n and r e a c t i v a t i o n of t h e carbon. I t was g e n e r a l l y a c c e p t e d t h a t t h e p y r o l y s i s gas was e v o l v e d i n t h e c e n t e r s e c t i o n o f the r e a c t o r while the dryin end zone. Naturally,, a i r was e x c l u d e d from t h e r e a c t o r tube by t h e use o f r o t a r y s e a l s connected t o b e l l o w s on each end. A l l gas was taken from t h e r e a c t o r a t t h e f e e d end and washed i n a s p r a y s c r u b b e r t o remove any p a r t i c l e s c a r r i e d from the r e a c t o r . I t was o r i g i n a l l y i n t e n d e d t h a t t h i s gas be used t o f i r e t h e f l a s h d r y e r . However,, a few days o p e r a t i o n proved t h e f l a s h d r y e r c o u l d o p e r a t e u s i n g t h e hot s t a c k gases from t h e r e a c t o r . The next l o g i c a l p l a c e t o use t h i s gas was t h e r e a c t o r f i r e b o x but t h e p i l o t p l a n t was n o t plumbed t o a l l o w t h i s usage. A f t e r c l e a n i n g ^ t h e gas was compressed> metered, a n a l y z e d ^ and f l a r e d . Mi s c. Equipment.

An a f t e r b u r n e r t r a i n c o n s i s t i n g o f an a f t e r b u r ner^ p r e - c o o l e r ^ v e n t u r i s c r u b b e r ^ and f a n were i n s t a l l e d on the exhaust l i n e from t h e f l a s h d r y e r . However^ t h e v e n t u r i s c r u b b e r performed w e l l enough t o meet t h e a i r q u a l i t y s t a n d a r d s so t h e a f t e r b u r n e r and p r e - c o o l e r were n o t o p e r a t e d . D i s c h a r g e o f d r y carbon from t h e r e a c t o r i s conveyed t o a quench t a n k where i t i s c o o l e d and s l u r r i e d w i t h water f o r t r a n s p o r t i n g back t o the carbon feed tanks. Pyrolysis

Reactor

Reactor Operating C o n d i t i o n .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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W h i l e numerous p r o f i l e s were used throughout t h e p i l o t p l a n t o p e r a t i o n ^ t h e most runs wege made w i t h the t e m p e r a t u r e s c o n t r o l l e d around ΐβΟΟ F i n a l l t h r e e zones o f t h e f i r e b o x . This allows the r e a c t o r t o es­ t a b l i s h i t s own l e n g t h s n e c e s s a r y t o a c c o m p l i s h t h e d r y i n g ^ p y r o l y s i s and a c t i v a t i o n . A r o t a t i o n a l speed o f 1 . 6 rpm gave a r e s i d e n c e time i n the r e a c t o r o f about 4 0 minutes. Steam was superheated e x t e r n a l l y t o about 9 0 0 ° F and f e d a t r a t e s o f 2 0 ^ 5 0 ^ and 7 5 pounds p e r hour. D e s c r i p t i o n o f Feed t o R e a c t o r .

The r e a c t o r feed was a d r i e d cake which was about 5 p a r t s o f used r e a c t o r p r o d u c t and 3 p a r t s o f sewage solids. The f e e d s ha Analysis

o f Feeds

on Dry B a s i s

Ash

29-45$

V o l a t i l e Organics F i x e d Carbon

12-21$ 37-58$

Feed r a t e s were v a r i e d d r y f e e d p e r hour.

from 2 2 0 t o 4 8 0 pounds o f

Reactor Products.

The d r y s o l i d s d i s c h a r g e d from the r e a c t o r worked up t o an a s h c o n t e n t around 5 0 $ i n t h e l a s t r u n s . This ash content i s n e c e s s a r i l y a f u n c t i o n of the ash l o s s e s i n t h e system as a whole as w e l l as the r e a c t o r operating conditions. The a c t i v i t y o f t h e carbon^ as measured by t h e i o d i n e number^ f i n a l l y s t a b a l i z e d i n t h e range o f 3 0 0 to 3 5 0 mg o f i o d i n e p e r gram o f c a r b o n . A b e t t e r measure o f a c t i v i t y o f t h e carbon f o r use on t h i s p r o c e s s i s an e q u i l i b r i u m curve where t h e removal o f t h e a c t u a l contaminants i s measured. Figure 4 i s a p l o t of s e v e r a l of these isotherms comparing r e a c t o r p r o d u c t s w i t h commercial c a r b o n s . The carbons produced i n 1976 tended t o match Nuchar w h i l e t h e l a t e s t carbons o f Aug. 77 matched Calgon PC but were n o t as good as Calgon RB i n a d s o r b i n g T0C from sewages. A f t e r water washing^ p y r o l y s i s gas had t h e following analysis: Constituent $ V/V H 38-46 2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

siGLER

Activated Carbon and Fuel

Figure 3. Flow schematic of activated carbon treatment system

EQUILIBRIU 1-0. //!. / /

Calgon

Calgon

' ////

RB-7 J 11 I / // P C

/~~f

Nuchar 8/20/77-

/

η / //

19 76

2 12 Hi•hi -H 2/22 -11/26 -11/24 I

Figure 4. Equilibrium plots of total organic carbon adsorption of commercial carbons and re­ actor products

.01 10 100 TOTAL ORGANIC CARBON mg/L

Q

w.40f CO CO

io.30[

GAS PRODUCED STEAM R A T E S kg/hr

S

o23 • 34 /_ ο

O-20J Ο

GM

.20 .30 VOLATILES/GM

.40 ASHLESS FEED

Figure 5. Gas production of the reactor com­ pared with volatile matter fed at various rates of steam addition. > Λ

American Uliemical Sociaty Library

In Solid Wastes Residues; J., et al.; 41Wand1£th Si Jones, M W ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

248

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WASTES

A N D RESIDUES

10-22

17-27 4-8

T h i s gas had a c a l c u l a t e d n e t h e a t i n g v a l u e o f 3 0 0 - 4 0 0 BTU/ft^. A comparision o f the v o l a t i l e matter f e d t o the r e a c t o r v s . the p y r o l y s i s gas produced shows t h a t ; except a t t h e lowest steam r a t e s ; t h e v o l a t i l e s i n t h e f e e d a r e accounted f o r i n t h e p y r o l y s i s g a s . Material

Balances.

Around t h e r e a c t o r i d e a l l y on an 8 hou checks on the i n p u t v s . t h e o u t p u t were found when t h e ash b a l a n c e was c o n s i d e r e d . However^ a check on t h e e n t i r e system showed t h e p r o c e s s has a c t u a l l y gained 1 , 0 0 0 pounds i n f i x e d c a r bon i n t h e system over a 3 0 day p e r i o d o f s u s t a i n e d operation. T h i s i s t h e i m p o r t a n t f a c t s i n c e even w i t h the l o s s e s i n h e r e n t t o any p i l o t s c a l e o p e r a t i o n ; t h e system produced enough a c t i v a t e d carbon t o s u s t a i n t h e system as a whole. Energy B a l a n c e .

The p i l o t p l a n t d i d n o t a c t u a l l y produce enough gas f o r t h e r e a c t o r t o s u s t a i n i t s e l f . There were s e v e r a l reasons f o r t h i s which c o u l d n o t be c o r r e c t e d i n t h e time a l l o t e d . The b u r n e r s s u p p l i e d w i t h t h e r e a c t o r were s i z e d so t h a t t h e excess a i r used i n the combustion c o u l d not be reduced below 1 2 0 $ . T h i s meant e x c e s s i v e heat l o s s e s i n t h e s t a c k gases. The i n s u l a t i o n f o r t h e r e a c t o r f i r e b o x was des i g n e d i n a p e r i o d when energy was cheap. These l o s s e s w i l l have t o be s u b s t a n t i a l l y reduced i n t h i s p e r i o d o f energy c o n s e r v a t i o n . F o r example; t h e r e a c t o r r u n n i n g a t temperature b u t w i t h no l o a d r e q u i r e d 1 5 0 0 t o 1 7 0 0 c u b i c f e e t p e r hour o f n a t u r a l g a s . When o p e r a t i n g ; t h e gas consumption was i n the range o f 1 7 0 0 t o 2 0 0 0 c u b i c f e e t p e r hour. A n o t h e r a r e a o f energy s a v i n g can be found i n t h e d e w a t e r i n g by t h e f i l t e r p r e s s . Some s m a l l s c a l e t e s t i n g showed t h a t t h e use o f h i g h e r p r e s s u r e s w i t h a

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

12.

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Activated Carbon and Fuel

249

change i n c l o t h s c o u l d produce cakes i n the range o f 5 8 to 6 0 $ s o l i d s . In t h i s range an i n c r e a s e from 5 0 $ s o l i d s t o 6 0 $ s o l i d s means a r e d u c t i o n of 1 / 3 o f a pound o f water t o be removed p e r pound o f d r y s o l i d s or a r e d u c t i o n i n d r y i n g l o a d o f 3 3 $ . While the system was a c t u a l l y s e l f - s u s t a i n i n g i n a m a t e r i a l sense^ t h e r e were s t i l l l o s s e s o f f i x e d carbon. These l o s s e s o f carbon r e p r e s e n t energy which c o u l d be r e c o v e r e d i n a water-gas type r e a c t i o n . When the above energy c o n s e r v a t i o n measures a r e c a l c u l a t e d , the r e a c t o r system t h e n becomes s e l f - s u s t a i n i n g on a energy b a s i s . R e a c t o r Damage.

The r e a c t o r s u s t a i n e areas. The f i r s t develope the s e a l s n e a r each end of the r o t a t i n g t u b e . Changing the m a t e r i a l s o f c o n s t r u c t i o n from 3 0 4 s t a i n l e s s s t e e l y t o 6 0 1 I n c o n e l j t o 3 1 6 s t a i n l e s s s t e e l was not the answer. A c o a t i n g of Dow C o r n i n g S i l a s t i c 8 3 4 was the o n l y temporary measure t h a t c o u l d p r e v e n t the p i n h o l i n g and f a i l u r e o f t h e s e b e l l o w s . The second f a i l u r e was i n the r e a c t o r tube when a weld i n the c e n t e r o f the 3 f i r i n g zone f a i l e d . There was e v i d e n c e o f s u l f i d e a t t a c k i n t h i s weld material. In I n c o n e l 6 1 7 the weld m a t e r i a l i s a c t u a l l y the m a t e r i a l i t s e l f puddled w i t h an i n e r t gas arc. T h i s means the weld i s e s s e n t i a l l y a c a s t mat e r i a l whereas the p l a t e s are a r o l l e d m a t e r i a l . A r e a s o f p i t s were found i n s i d e the tube^ away from the welds> which showed e v i d e n c e o f s u l f i d e a t t a c k of the m e t a l . The r e p a i r was a c c o m p l i s h e d by c u t t i n g out bad a r e a s and r e p l a c i n g e n t i r e s e c t i o n s of the tube w i t h new m a t e r i a l . The s m a l l e r spots were ground and r e f i l l e d w i t h new weld m a t e r i a l . A f t e r 6 weeks of ope r a t i o n the r e p a i r e d a r e a s showed no s i g n s of a t t a c k . Comparisions W i t h Other Systems Cost e s t i m a t e s were made,, by our c o n s u l t i n g eng i n e e r s ^ f o r a 1 0 MGD s i z e d p l a n t f o r the A c t i v a t e d Carbon system compared w i t h A c t i v a t e d Sludge and Trickling Filters. These are shown i n F i g u r e 8 . The c o n s t r u c t i o n c o s t s match t r i c k l i n g f i l t e r s and are about 1 2 $ l e s s than a c t i v a t e d s l u d g e . Since a m u l t i p l e h e a r t h f u r n a c e i s a known s u b s t i t u t e f o r the c a l c i n e r as the reactor,, a c o s t e s t i m a t e was made

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

250

SOLID

Figure 6.

Construction $

O&M $/MG Energy $/MG

Figure 8.

Failed weld of reactor tube

COMPARISONS ACTS ACT.SL

COSTS

0

A N D RESIDUES

Pitting

Figure 7.

1

WASTES

14.4(Kii ) n

16.3

TR. FT. 144

15.6(Hearth)

212

260

37.30(50%cake)61.26

180

25.44

24.30(60%cake)

Comparison of cost estimates at a 10-MGD plant size

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

12.

Activated Carbon and Fuel

siGLER

251

on t h a t system as w e l l . The 0 & M c o s t s a r e "between t h e a c t i v a t e d s l u d g e and t h e t r i c k l i n g f i l t e r c o s t s . Energy c o s t s a r e s e n s i t i v e t o t h e d r y n e s s o f t h e cake i n t h e a c t i v a t e d c a r b o n system b u t c a n be t h e l o w e s t o f t h e t h r e e . B o t h t h e a c t i v a t e d s l u d g e and t h e t r i c k l i n g f i l t e r systems r e c e i v e d c r e d i t f o r gas t h a t c o u l d be gene r a t e d from d i g e s t i o n o f sewage s o l i d s . D i f f e r e n t e f f l u e n t s were used i n t h e systems e v a l u a t e d f o r c o m p a r i s o n . These a r e t a b u l a t e d below. ACTS Effluent SS mg/1 BOD mg/1 Grease mg/1

25 50

ACTS Sludge

25

Trickling Filter 40

8

I t s h o u l d be n o t e d t h a t t h e BOD o f t h e c a r b o n system does n o t match t h e e f f l u e n t from a c t i v a t e d s l u d g e a t t h e p r e s e n t s t a t e o f t h e a r t . More work w i l l have t o be done on r e a c t o r o p e r a t i n g c o n d i t i o n s t o produce a c a r b o n w h i c h w i l l remove more o f t h e BOD from w a s t e w a t e r . A complete r e p o r t o f a l l o p e r a t i o n a l d a t a has been p u b l i s h e d . (2_) Literature 1.

2.

MARCH

Cited

Humphrey, M.F., et al, "Carbon Wastewater T r e a t ment P r o c e s s . " Paper p r e s e n t e d a t Intersociety Conference on E n v i r o n m e n t a l Systems, Seattle, W a s h i n g t o n , July 2 9 - A u g . 1, 1974. " A c t i v a t e d Carbon Treatment System for M u n i c i p a l Treatment S y s t e m s . " County Saintation Districts of Orange C o u n t y , California, November, 1977. 3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

13 Power from Wastes via Steam Gasification J. A. COFFMAN and R. H. HOOVERMAN Wright-Malta Corporation, Ballston Spa, NY 12020

The Wright-Malt ranging a n a l y t i c a l an means of generating power from " d i f f i c u l t " fuels l i k e s o l i d waste and sewage sludge. The system was born complete, rather than growing from research findings or e x i s t i n g product l i n e s . It has changed in d e t a i l with refinement i n conceptual design, and will undoubtedly change again as the p i l o t plant is designed, b u i l t , and operated. However, the basic rotary k i l n g a s i f i e r - g a s turbine-recuperator-feedback system and c y c l e have weathered many reviews and appear to be sound and v i a b l e . Projected Power Plants An a r t i s t ' s conception of a single unit plant i s shown i n Figure 1. For perspective, i t might be noted that the pressurized (300 psi) rotary kiln is projected to be 5 ft. in diameter and 150 f t . in length. The plant would consume 200 tons/day of s o l i d waste and 300 tons/day of l i q u i d (97% water) sewage sludge and produce 10 megawatts of e l e c t r i c power. Plant operation can perhaps best be described by following material through it. Solid waste is delivered by compactor trucks, i s coarsely shredded but not c l a s s i f i e d , passes through lock hoppers to a metering auger where i t mixes with sewage sludge and alkaline catalyst. In the k i l n , the material rotates and tumbles, moving forward at about 3 ft/minute. During i t s slow steady t r a v e l to the hot ( 1 1 0 0 ° F ) end of the k i l n , the organic m a t e r i a l , mostly c e l l u l o s i c , p a r t i a l l y dries and pyrolyzes into gases, v o l a t i l e l i q u i d s , and char. The l i q u i d s and tars then steam-reform into a d d i t i o n a l gas; the char undergoes catalyzed steam g a s i f i c a t i o n to y i e l d still more gas. The 0-8412-0434-9/78/47-076-252$05.50/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

COFFMAN

AND

HOOVERMAN

Figure 1.

Steam Gasification

Single-unit power plant

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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r e s i d u e , m o s t l y cans, broken g l a s s , and o t h e r i n o r g a n i c d e b r i s , i s d i s c h a r g e d through a r o t a t i n g t r i a d of l o c k v a l v e s ; the steam-laden f u e l gas (125 B t u / s c f ) e x i t s through a f i l t e r and a s m a l l d i a m e t e r r o t a r y s e a l assembly. The whole p r o c e s s i s c a l l e d steam gasi f i c a t i o n and d i f f e r s from o r d i n a r y g a s i f i c a t i o n i n the absence o f o x i d a t i o n . Most o f the hot f u e l gas f l o w s t o the combustion chamber of the gas t u r b i n e , burns, d r i v e s the t u r b i n e g e n e r a t o r , and g i v e s up i t s r e s i d u a l heat i n a heat recovery b o i l e r (recuperator). Steam so r a i s e d and super-heated i s super-heated f u r t h e r i n a g a s - f i r e d u n i t at the hot end of the k i l n , and then, f l o w i n g through passages i n the k i l n w a l l , g i v e s most o f i t s heat t o the g a s i f i c a t i o n p r o c e s s . The condensate e x i t s the k i l n a t the c o o l end g i v e s i t s r e m a i n i n g heat t o the incoming sewage recuperator. Recovery o f i r o n and s t e e l from the r e s i d u e i s made easy by the absence o f b u l k y o r g a n i c m a t e r i a l . Cans a r e prime s c r a p : c l e a n , u n o x i d i z e d , d e t i n n e d . The remainder of the r e s i d u e i s u s a b l e as dense, s t e r i l e f i l l f o r c o n s t r u c t i o n purposes. A W-M p l a n t o f t h i s s i z e would s e r v e the homes, commercial e s t a b l i s h m e n t s , and i n d u s t r i e s o f a commun i t y of about 40,000 p e o p l e , consuming t h e i r s o l i d , l i q u i d , and hazardous wastes, and p r o v i d i n g o n e - q u a r t e r of t h e i r e l e c t r i c i t y . U n i t s as s m a l l as o n e - t e n t h t h i s s i z e would s t i l l be p r a c t i c a l i f a t t a c h e d t o p l a n t s h a v i n g o p e r a t i n g and maintenance crews w i t h a p p r o p r i a t e skills. L a r g e r c i t i e s would use g r o u p i n g s of k i l n s and turbines operating i n p a r a l l e l . S t i l l larger c i t i e s would have s e v e r a l p l a n t s s t r a t e g i c a l l y l o c a t e d t o keep waste haulage t o a minimum. New York C i t y , f o r examp l e , might have t h i r t y 1000 ton/day 50 MWe plants tucked i n t o a p p r o p r i a t e s p o t s i n a l l f i v e boroughs. Such d e c e n t r a l i z e d g e n e r a t i o n of power and d i s p o s a l o f waste i s more e c o n o m i c a l , e f f i c i e n t , and e n v i r o n m e n t a l l y a t t r a c t i v e than huge r e g i o n a l systems. Power C y c l e In F i g u r e 2 i s shown the W-M power c y c l e f o r a 10 MWe p l a n t f u e l e d by 200 ton/day of s o l i d waste and 300 ton/day of sewage s l u d g e . Two major flow streams are evident: t h e primary power stream c o n s i s t i n g of s o l i d waste and s l u d g e , hot f u e l gas, v e r y hot combustion p r o d u c t s , and somewhat c o o l e r , but s t i l l hot, exhaust gases; and the feedback l o o p of s u p e r h e a t e d steam and water which r e t u r n s r e c o v e r e d exhaust heat t o the

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gasifier. The w i d t h o f the c h a n n e l s denotes the magn i t u d e o f energy f l o w through each p a r t o f the system. The diagram i s l a r g e l y s e l f - e x p l a n a t o r y , p a r t i c u l a r l y when c o n s i d e r e d i n c o n j u n c t i o n w i t h the p l a n t d e s c r i p t i o n i n the p r e v i o u s s e c t i o n , but these comments might be made. The abundance of steam i n the hot f u e l gas e x i t i n g the k i l n means t h a t a l e s s than n o r mal amount of d i l u t i o n a i r i s r e q u i r e d i n the combustor. T h i s makes p o s s i b l e a s m a l l e r compressor and l a r g e r g e n e r a t o r than normal, e.g., a 7.5 MW t u r b i n e d r i v i n g a 5 MW compressor and a K> MWe g e n e r a t o r . The t u r b i n e i s r e a l l y a p a r t i a l steam t u r b i n e s i n c e i t d e r i v e s a s i g n i f i c a n t p o r t i o n of i t s power from the steam r a i s e d i n the k i l n . Thermodynamically, the c y c l e i s s i m i l a r t o t h a t i n the combined gas t u r b i n e / s t e a m t u r b i n e system and the e f f i c i e n c i e s a r e s i m i l a r , about 40%. F o r comparison p l a n t s f u e l e d by p e t r o l e u The c y c l e i s a t t r a c t i v e as drawn but s t i l l has room f o r improvement. One change f o r the b e t t e r might be t o p l a c e the s l u d g e p r e - h e a t e r i n the lower end of the t u r b i n e exhaust, t h e r e b y e l i m i n a t i n g a s t e p i n the t r a n s f e r of heat and p u l l i n g the exhaust temperature down by, say, a n o t h e r 50°F. I t i s p r o b a b l e , too, t h a t f u r t h e r development work w i l l l e a d t o r e d u c t i o n i n the energy c o n t e n t of the k i l n r e s i d u e , from 200 MBtu/day t o , say, 100 MBtu/day. The c y c l e e f f i c i e n c y c a l c u l a b l e from the diagram i s c o n s e r v a t i v e because i t i s based on p r e s e n t e x p e r i m e n t a l d a t a and performance c h a r a c t e r i s t i c s of p r e s e n t t u r b i n e s and does not take i n t o account improvements t h a t a r e l i k e l y t o r e s u l t as the system matures. Expérimentâtion-MinikiIn W-M r e s e a r c h on steam g a s i f i c a t i o n o f o r g a n i c s o l i d m a t e r i a l s has been performed i n two t y p e s o f equipment: a b a t c h - t y p e m i n i a t u r e k i l n ( m i n i k i l n ) and a c o n t i n u o u s f e e d biomass g a s i f i e r ( b i o g a s s e r ) . The m i n i k i l n r e s e a r c h a p p a r a t u s i s shown i n F i g u r e 3, i n s t a l l e d i n the t e s t bay of the g a s i f i c a t i o n l a b . It i s , i n e f f e c t , a r o t a t i n g autoclave, intended to s i m u l a t e , by t u m b l i n g a c t i o n , g r a d u a l i n c r e a s e i n temp e r a t u r e , and change i n gas c o m p o s i t i o n , the slow t r a v e r s e o f a charge of m a t e r i a l through a l o n g , p r e s surized rotary k i l n . There i s p r o v i s i o n f o r steam i n j e c t i o n d u r i n g the c o u r s e of a run and c o n t r o l l e d r e l e a s e of gas. There a l s o i s p r o v i s i o n (not shown) f o r c o n d e n s a t i o n of water and o r g a n i c l i q u i d s from the e f f l u e n t gas, and a n a l y s i s of t h e f i x e d gas by chroma-

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tograph. F o r p e r s p e c t i v e , i t might be noted t h a t t h e i n n e r b a r r e l o f t h e m i n i k i l n i s about 3 | f t . i n l e n g t h by 1 f t . i n d i a m e t e r . In a t y p i c a l run, 10 l b s o f c o a r s e l y shredded s o l i d waste, 2 g a l l o n s o f l i q u i d s l u d g e ( i n m i l k c a r t o n s ) , and \ l b o f sodium c a r b o n a t e a r e p l a c e d i n t h e minikiln. The door i s b o l t e d on, t h e thermocouple l e a d s a t t a c h e d , and r o t a t i o n and h e a t i n g s t a r t e d . Steam i s i n j e c t e d as needed t o h o l d t h e d e s i r e d waterto-waste' r a t i o . Waste d e c o m p o s i t i o n s t a r t s a t about 350°F and r e a c h e s i t s peak a t about 500°F ( m o s t l y CO2, CO, and H 0 ) . Methane s t a r t s e v o l v i n g a t about 500°F, hydrogen a l i t t l e h i g h e r ; bv 900°F, t h e f l o w o f CO has stopped. From 1000 t o 1100°F, t h e gas i s m o s t l y hydrogen and CO2 i n a r a t i o o f about n i n e t o f o u r . 2

4CH

5

(char)+8H

D u r i n g t h e p e r i o d from about 400 t o 900°F, l i q u i d s and t a r s a r e a l s o b e i n g e v o l v e d and a r e caught i n t h e condenser. I t i s e s t i m a t e d t h a t perhaps a h a l f o f t h e o r g a n i c waste i s v o l a t i l i z e d as c o n d e n s a b l e l i q u i d s . And so t h e gas a n a l y s i s does not g i v e a t r u e p i c t u r e o f the c o m p o s i t i o n t h a t would be r e a l i z e d i n a c o n t i n u ous p r o c e s s , where gases from s t e a m - r e f o r m i n g o f t h e l i q u i d v o l a t i l e s would combine w i t h t h o s e from t h e i n i t i a l p y r o l y s i s and t h e c h a r g a s i f i c a t i o n . An a p p r o x i m a t i o n was, however, o b t a i n e d by r u n n i n g the m i n i k i l n as a bomb w i t h no r e l e a s e o f gas, s t a r t i n g w i t h a s u f f i c i e n t l y s m a l l charge o f wood, water, and c a t a l y s t so t h a t p r e s s u r e l i m i t s were not exceeded. In a r u n t o peak p r e s s u r e and temperature o f 400 p s i and 1100°F, t h e gas had t h i s c o m p o s i t i o n : CH. 4 C Hg e t c . 2

18% 8% 28% 1% 45%

Note t h a t t h e CO had almost e n t i r e l y water g a s - s h i f t e d t o C 0 , but t h a t t h e methane and r i c h ethane were unaffected. The l i q u i d s and t a r s , which must have been p r e s e n t a t i n t e r m e d i a t e t e m p e r a t u r e s , had steamreformed c l e a n l y , j u d g i n g by t h e f a c t t h a t t h e r e was no soot i n t h e r e s i d u e and i t s weight was s l i g h t l y l e s s than normal. On t h e graph i n F i g u r e 4 a r e shown c h a r w e i g h t s , 2

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Figure 3. Minikiln research apparatus

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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as p e r c e n t a g e s o f d r y paper s t a r t i n g w e i g h t s , a f t e r r e a c t i o n w i t h water/steam t o t h e temperatures shown. Note t h a t the weight, which i s d r o p p i n g s t e e p l y w i t h paper d e c o m p o s i t i o n , s t a r t s t o l e v e l o f f , then drops a g a i n w i t h the onset o f c h a r g a s i f i c a t i o n . Note a l s o t h a t t h e c a t a l y s t e x e r t s an i n f l u e n c e from the lowest temperature. I t i s p r o b a b l e t h a t the c a t a l y s t o p e r a t e s by s e v e r a l mechanisms: h y d r o l y s i s a t the lowest temp e r a t u r e s , t h e n d e c a r b o x y l a t i o n and d e h y d r o x y l a t i o n , then r e a c t i o n w i t h b e n z y l i c a c i d i t y , and f i n a l l y , r e a c t i o n w i t h f r e e r a d i c a l s i n the c h a r and promotion of r i n g opening by steam. F i g u r e 5 shows r e s i d u a l c h a r weight of wood c h i p s a f t e r h e a t i n g t o 1100°F a t the p r e s s u r e s shown. Again the e f f e c t of the c a t a l y s t i s marked and apparent from the lowest steam p r e s s u r e and the c u r v e s t i l l seems t o have a s u b s t a n t i a l s l o p temperature c u r v e s appea g i v e s the d e s i g n e r some degree o f freedom t o p i c k the c o m b i n a t i o n o f p r e s s u r e , temperature, f e e d r a t e , and r e s i d u e which i s most e c o n o m i c a l . E x p e r i m e n t a l work on c o a l showed that both l i g n i t e and bituminous a r e s u b s t a n t i a l l y more r e f r a c t o r y than i s s o l i d waste. There was some r e a c t i o n o f c o a l w i t h steam, but under c o n d i t i o n s where waste was e s s e n t i a l l y consumed, the r e s i d u e s from both types of c o a l were o n l y about o n e - t h i r d l e s s than i f they had been pyrolyzed. More s t r e n u o u s c o n d i t i o n s may s u f f i c e , and i f they do so, c o a l can be c o n s i d e r e d as a s u p p l e m e n t a l f u e l i n a W-M waste-to-power system. S e v e r a l experiments on p o l y c h l o r i n a t e d b i p h e n y l s (PCB's) were made t o determine the e f f i c a c y o f W-M r e a c t i o n c o n d i t i o n s f o r d e s t r o y i n g PCB s i n municipal and i n d u s t r i a l wastes. Bomb runs were employed t o prevent the escape o f any m a t e r i a l ; t y p i c a l charges were e q u a l p a r t s by weight of PCB's, water, paper, and sodium c a r b o n a t e i n amounts s u f f i c i e n t t o g e n e r a t e about 400 p s i a t 1100°F. The d a t a a r e shown i n F i g u r e 6. I t i s e v i d e n t t h a t a time-temperature o f about an hour a t 1100°F i s n e c e s s a r y and s u f f i c i e n t t o complete the PCB d e c o m p o s i t i o n . By i n f e r e n c e , s i n c e P C B s a r e among the most s t a b l e o r g a n i c m a t e r i a l s known, any hazardous o r g a n i c waste would be consumed i n a W-M p l a n t a t l i t t l e c o s t and no d e t r i m e n t t o the e n v i r o n ment . One o t h e r f i n d i n g might be mentioned b e f o r e l e a v ing the m i n i k i l n work. The apparent a c t i v a t i o n energy f o r char-steam g a s i f i c a t i o n a t 200-400 p s i i n the temperature range o f 1050-1100°F was c a l c u l a t e d t o be o n l y o n e - h a l f (30 k c a l / m o l e ) t h a t a t one atmosphere T

T

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, pyrolysis at

, I

ι

I5(latm)

,

I

,

200

,

RESIDUES

1 400

I atm

STEAM P R E S S U R E - p s i

Figure 5.

Residual char of wood as function of pressure: peak temperature 1100° F

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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25%

800

900

PEAK

Figure 6.

1000

TEMPERATURE -

1100 e

F

Residual PCB vs. temperature

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(60 k c a l / m o l e ) . I t i s p r o b a b l e t h a t t h e lowered a c t i v a t i o n energy i s due t o the presence o f a condensed aqueous f i l m on the c h a r p a r t i c l e s , which promotes r e a c t i o n between water and c h a r . I t i s probable, too, that the hygroscopic nature of the c a t a l y s t helps t o c r e a t e t h e condensed phase and s u s t a i n i t t o h i g h e r temperatures. Expérimentâtion-Biogasser R e s e a r c h on g a s i f i c a t i o n o f biomass has product i o n o f f u e l gas as i t s u l t i m a t e purpose, and m a t e r i a l t r a n s p o r t w i t h i n the g a s i f i e r i s by auger r a t h e r than k i l n action. However, the c h e m i s t r y i s e s s e n t i a l l y the same, and the e x p e r i m e n t a l f i n d i n g s a r e d i r e c t l y a p p l i c a b l e t o the waste-to-power program The b i o g a s s e r i construction i n Figur the f u e l r e s e r v o i r , the i n s u l a t e d r e a c t o r w i t h p r o t r u d i n g thermocouple c o n n e c t i o n s s l a n t s back through the c e n t e r o f the p i c t u r e , and i n the background a r e the r e s i d u e t r a p and gas r e l e a s e v a l v e s . The condens e r and g a s / l i q u i d s e p a r a t o r a r e a l o n g the lower right-hand s i d e of the r e a c t o r . For perspective, i t might be noted t h a t the biomass s l u r r y r e s e r v o i r i s about 6 i n . ID and 6 f t . i n h e i g h t , the s l a n t e d r e a c t o r i s 1.75 i n . ID and 10 f t . i n l e n g t h , and the r e s i d u e t r a p i s about 3 i n . ID and 3 f t . i n h e i g h t . The equipment i s s t a i n l e s s s t e e l t h r o u g h o u t . I t s o p e r a t i o n can be d e s c r i b e d by moving through the sequence of a t y p i c a l r u n . The cap and p i s t o n a r e l i f t e d from the f u e l r e s e r v o i r , the r e s e r v o i r i s f i l l e d w i t h sawdust o r o t h e r shredded biomass, water, and c a t a l y s t , and the p i s t o n and cap r e p l a c e d . Then t h e h e a t e r s a r e turned on, the h y d r a u l i c pump d r i v i n g the p i s t o n down i s s t a r t e d as i s t h e auger d r i v e motor, and the s l u r r y moves s l o w l y down out o f the r e s e r v o i r and up the s l o p e o f the r e a c t o r . Temperatures r i s e u n t i l the d e s i r e d p r o f i l e i s reached, t y p i c a l l y 100°F a t the f e e d end and 1200°F a t t h e t r a p and r e d u c i n g v a l v e ; the p r e s s u r e r i s e s t o the d e s i r e d f i g u r e (up t o 3200 p s i ) by e v o l u t i o n o f gas and f o r m a t i o n o f steam, and then t h a t p r e s s u r e i s m a i n t a i n e d by c o n t r o l l e d r e l e a s e o f gas t o t h e condenser. As t h e gas i s r e l e a s e d , the condensate i s m o n i t o r e d f o r l i q u i d s and t a r s , and the non-condensing gas i s a n a l y z e d by chromatograph. At the end o f the r u n , the r e a c t o r and t r a p a r e examined f o r r e s i d u e . In s a t i s f a c t o r y s t e a d y s t a t e o p e r a t i o n , the g a s i f i c a t i o n i s r e a s o n a b l y complete, the condensate c o n t a i n s l i t t l e o r g a n i c l i q u i d o r t a r ,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Figure 7.

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Biogasser in itsfinalstages of construction

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and

the r e s i d u e i s e s s e n t i a l l y i n o r g a n i c . In the graph of F i g u r e 8 a r e shown data on r e s i dues as a f u n c t i o n of p r e s s u r e from the b i o g a s s e r ( t r i a n g l e s ) and the m i n i k i l n ( c i r c l e s ) . The m i n i k i l n data show how the c h a r r e s i d u e d e c r e a s e s r a p i d l y w i t h p r e s s u r e i n the range of 0-400 p s i and how the e f f e c t of p r e s s u r e i s g r e a t e r i n the presence of added N 2C03 catalyst. The r e s i d u e s from b i o g a s s e r runs at one atmosphere and 300 p s i l i e s l i g h t l y below the c o r r e s ponding m i n i k i l n c u r v e s because the b i o g a s s e r was o p e r a t e d a t a s l i g h t l y h i g h e r temperature; otherwise the b i o g a s s e r data seem c o n s i s t e n t w i t h the m i n i k i l n d a t a i n t h i s r e g i o n and show a c a t a l y s t e f f e c t of the same magnitude. By 600 p s i , however, the e f f e c t of the c a t a l y s t seems t o have d i s a p p e a r e d ; the r e s i d u e from the c a t a l y z e d b i o g a s s e r run c a t a l y z e d run. And c l e a r l y h e a v i e r than those at lower p r e s s u r e s . The exact shape of the c u r v e i s not w e l l - d e f i n e d by t h e s e experiments because of d i f f i c u l t i e s i n m a i n t a i n i n g the same peak temperatures i n runs a t d i f f e r e n t p r e s s u r e s . N e v e r t h e l e s s , i t i s e v i d e n t t h a t the t r e n d s i n the l o w e r - p r e s s u r e m i n i k i l n data may not be e x t r a p o l a t e d to h i g h e r p r e s s u r e s . Q u a l i t a t i v e l y , t h e r e i s a l s o a change i n the n a t u r e of t h e r e s i d u e at h i g h e r p r e s s u r e s . In both the m i n i k i l n and b i o g a s s e r runs a t p r e s s u r e s up t o 300-400 p s i , the c h a r r e s i d u e i s l o o s e and g r a n u l a r . In the b i o g a s s e r runs a t 600 and 1000 p s i , much of the r e s i d u e i s s t u c k t o g e t h e r i n hard lumps. T h i s type of c a k i n g and i n c r e a s e i n r e s i d u e become p r o g r e s s i v e l y more apparent as the p r e s s u r e i n c r e a s e s , a t l e a s t t o 3200 p s i . The o b s e r v a t i o n s suggest t h a t t h e r e a r e two p r e s s u r e i n f l u e n c e s working i n o p p o s i t e d i r e c t i o n s . In the lower range, i n c r e a s e i n p r e s s u r e promotes r e a c t i o n by i n c r e a s i n g the c o n c e n t r a t i o n of steam and f o r m a t i o n of aqueous f i l m s . But above 300-400 p s i , t h i s e f f e c t i s swamped out by an i n c r e a s i n g tendency toward f o r m a t i o n o f c o k e - l i k e m a t e r i a l , presumably from c h e m i c a l c o n d e n s a t i o n of v o l a t i l i z e d l i q u i d intermediates. The l a t t e r e f f e c t i s c o n s i s t e n t w i t h LeChatelier s principle. I t i s c o n c l u d e d t h a t f o r maximum c o n v e r s i o n of s o l i d s t o f u e l gas, t h e r e i s an optimum i n r e a c t o r p r e s s u r e i n the neighborhood o f 300-400 p s i . T h i s f i n d i n g i s s i g n i f i c a n t t o f u r t h e r development of the W-M p r o c e s s , i n t h a t i t i s now e s t a b l i s h e d t h a t t h e r e i s no advantage i n g o i n g t o h i g h e r r e a c t o r p r e s s u r e . a

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In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Figure 8.

Residual wood char vs. pressure, minikiln and biogasser

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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I t i s f o r t u n a t e t h a t the optimum p r e s s u r e c o i n c i d e s w i t h t h a t deemed most d e s i r a b l e f o r k i l n o p e r a t i o n f o r other reasons: gas t u r b i n e o p e r a t i o n , l o n g gas d w e l l time i n the k i l n , low p a r t i c u l a t e , heat t r a n s f e r , e t c . Gas c o m p o s i t i o n d a t a from the b i o g a s s e r s u p p o r t e a r l i e r work i n the m i n i k i l n , the p r o p o r t i o n s of hydrogen, methane, c a r b o n d i o x i d e , e t c . b e i n g s i m i l a r t o those i n m i n i k i l n bomb r u n s . Under c o n d i t i o n s o f e s s e n t i a l l y complete c o n v e r s i o n o f s o l i d s t o f u e l gas (1150°F, 300 p s i ) , the f i x e d gases had an i n t e g r a t e d hydrogen-to-oxygen r a t i o of two t o one, the same as i n c e l l u l o s e and water. A t l e s s than complete c o n v e r s i o n , the r a t i o f e l l below t h i s f i g u r e , because the oxygen tends t o come o f f f i r s t , as CO2 and C0> and the hydrogen tends t o s t a y behind i n the c h a r and l i q u i d s . Use o f t h i s gas measuring and i n t e g r a t i n g t e c h n i q u e enabled the g a t h e r i n of c o n v e r s i o n v e r s u would have been p o s s i b l e by measure of r e s i d u e w e i g h t s . The graph i n F i g u r e 9 shows the hydrogen t o oxygen r a t i o (times J) as a f u n c t i o n o f r e a c t o r t e m p e r a t u r e s . I t i s t o be noted t h a t the temperatures a r e maximum w a l l temperatures as measured by thermocouples embedded i n the r e a c t o r w a l l . I t i s e s t i m a t e d t h a t the c o r r e s p o n d i n g gas temperatures a r e about 200°F lower. The bend i n the c u r v e , t h e r e f o r e , comes a t about 1150°F, c o r r e s p o n d i n g to complete g a s i f i c a t i o n as judged by r e s i d u e and c o n d e n s a t e . C a l c u l a t i o n s have been made from heats o f format i o n t o determine e q u i l i b r i u m gas c o m p o s i t i o n s as a f u n c t i o n o f water/wood r a t i o , temperature, and p r e s sure. These c a l c u l a t e d e q u i l i b r i a have been found t o c o r r e s p o n d r e a s o n a b l y w e l l t o e x p e r i m e n t a l composit i o n s above 1150°F; below t h a t temperature, the exp e r i m e n t a l c o m p o s i t i o n s d e v i a t e i n f a v o r of the f i r s t formed p r o d u c t s . T h i s f i n d i n g has t h e o r e t i c a l s i g n i f i c a n c e but l i t t l e p r a c t i c a l u t i l i t y i n the k i l n power system where parameters l i k e water-to-waste r a t i o a r e f i x e d by c y c l e c o n s i d e r a t i o n s . However, i n the b i o mass g a s i f i c a t i o n system, the water/wood r a t i o can be v a r i e d t o maximize the u t i l i t y o f the product gas t o ward i t s i n t e n d e d use: medium B t u f u e l gas, s y n t h e s i s of methanol o r ammonia, o r methanation t o p i p e l i n e q u a l i t y gas. Pilot

Plant

Gasifier

The t r a n s i t i o n from bench s c a l e r e s e a r c h t o p i l o t p l a n t w i l l be a c c o m p l i s h e d i n s t a g e s , the f i r s t b e i n g g a s i f i e r d e s i g n . A s c h e m a t i c i s shown i n F i g u r e 10.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Figure 9.

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The hydrogen to oxygen ratio as a function of reactor temperatures

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

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The p i l o t p l a n t g a s i f i e r i s p r o j e c t e d t o be 60 f t . i n l e n g t h and 2\ f t . i n d i a m e t e r at the c o o l end, and thus has about o n e - t e n t h the volume of the p r o d u c t i o n unit described e a r l i e r . I t s nominal throughput i s 20 tons/day of s o l i d waste and 30 tons/day o f l i q u i d sewage s l u d g e , and i t s product gas, consumed i n a gas t u r b i n e , would g e n e r a t e 1 MWe. There a r e s i g n i f i c a n t d i f f e r e n c e s between t h i s d e s i g n and t h a t d e s c r i b e d e a r l i e r , t h e s e r e f l e c t i n g the c o n t i n u i n g e v o l u t i o n o f the W-M system. Feed. G r a v i t y - f e e d l o c k hoppers have been d i s carded i n f a v o r of a p o s i t i v e p i s t o n - f e e d system. C o a r s e l y shredded but u n c l a s s i f i e d s o l i d waste i s d e l i v e r e d from the l e f t by w e i g h i n g conveyor and dep o s i t e d i n t o the open t h r o a t of a c y l i n d r i c a l c a v i t y The m a t e r i a l i s tampe c y l i n d e r sealed wit i n n e r s t r u c t u r e r o t a t e s n i n e t y degrees, and the waste i s pushed from the c a v i t y i n t o the k i l n by a second piston. At the c o m p l e t i o n of t h i s p i s t o n s t r o k e , the i n n e r s t r u c t u r e b a c k - r o t a t e s to t h e v e r t i c a l p o s i t i o n , the tamping p i s t o n l i f t s , the i n n e r p i s t o n drops, and the c y c l e i s r e p e a t e d . L i q u i d s l u d g e i s pumped cont i n u o u s l y through i t s p r e - h e a t e r i n t o the t h r o a t of the k i l n , m i x i n g t h e r e w i t h the s o l i d waste. Homogen i z a t i o n w i l l o c c u r i n the f i r s t few f e e t of the k i l n . The f e e d system i s h e l d i n p l a c e a g a i n s t k i l n p r e s s u r e by a t h r u s t rod, t h r u s t r i n g assembly working a g a i n s t the f r o n t f l a n g e of the k i l n , and r e q u i r e s no external bracing. The feed support s t r u c t u r e i s mounted on r o l l e r s so t h a t the feed system can be unb o l t e d and moved away f o r maintenance of the f r o n t r o t a t i n g s e a l s , which a r e i n s i d e the t h r u s t r i n g and independent of i t . K i l n Support. The f i x e d p o i n t f o r the k i l n i s e s t a b l i s h e d through the t h r u s t assembly a t the f r o n t end. T h i s means t h a t the f r o n t end t r u n n i o n r o l l assembly and the m i d d l e one a r e n o n - f l a n g e d and nontracking . The e n t i r e n o n - r o t a t i n g assembly a t the hot end of the k i l n i s mounted on a support c a r r i a g e on r o l l e r s . I t s p o s i t i o n r e l a t i v e t o the k i l n i s determined by having t h i s end of the k i l n s u p p o r t e d by a t r a c k i n g trunnion. Movement o f the support c a r r i a g e w i t h t h e r mal e x p a n s i o n and c o n t r a c t i o n o f the k i l n means no a l l o w a n c e f o r a x i a l t h e r m a l motion i s r e q u i r e d i n the r o t a t i n g s e a l assembly.

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Stepped K i l n . The o u t e r b a r r e l o f the k i l n has a u n i f o r m , s l i g h t l y g r e a t e r than 2\ f t . diameter t h r o u g h out i t s l e n g t h . The i n n e r s h e l l , which c o n t a i n s t h e waste and on which t h e steam h e a t i n g tubes a r e wrapped, i s 2^ f t . i n d i a m e t e r f o r t h e f i r s t 30 f t . , then dec r e a s e s t o 2 f t . f o r t h e next 15 f t . , and d e c r e a s e s f u r t h e r t o \\ f t . f o r the f i n a l 15 f t . The space between the steam c o i l and t h e o u t e r b a r r e l i s p r e s s u r e e q u a l i z e d and f i l l e d w i t h t h e r m a l i n s u l a t i o n . This reduces the temperature o f the o u t e r b a r r e l a t t h e hot end t o about t w o - t h i r d s o f what i t would be i f the b a r r e l were immediately a d j a c e n t t o t h e steam t u b e s . T h i s means t h a t the b a r r e l can more r e a d i l y c a r r y i t s p r e s s u r e l o a d and can be l e s s massive than i f t h e i n n e r s h e l l were not stepped down A n o t h e r b e n e f i t o f t h e stepped d e s i g n i s the slowing o f the forward movemen diameter decreases. have been l o s t by the time i t reaches t h e m i d - p o i n t , and t h e k i l n w i l l not dam up a t the s t e p . The r e s u l t i n g i n c r e a s e i n d w e l l time w i l l a i d i n c o m p l e t i n g steam g a s i f i c a t i o n of the char. Steam H e a t i n g . The steam h e a t i n g system w i l l o p e r a t e a t 600 p s i , a p p r o x i m a t e l y t w i c e k i l n gas p r e s sure. T h i s w i l l ensure an adequate temperature d i f f e r e n t i a l between the condensing zone i n t h e steam c o i l s and t h e e v a p o r a t i n g zone w i t h i n the k i l n . The b o i l e r and s u p e r h e a t e r w i l l be f i r e d by a p o r t i o n o f the gas from the k i l n , i n c l u d i n g the low p r e s s u r e gas from t h e dump v a l v e s ; t h e remainder w i l l be f l a r e d . Gas w i l l l e a v e and steam w i l l e n t e r the r o t a t i n g s t r u c t u r e through a s m a l l diameter s t u f f i n g box s e a l , o f t h e type c o n s t r u c t e d f o r t h e m i n i k i l n and proved s a t i s f a c t o r y t h e r e . The condensate w i l l e x i t t h e k i l n through the c e n t e r o f t h e f a c e s e a l a t the f r o n t end and, by v i r t u e o f i t s h i g h e r p r e s s u r e , p r o v i d e a s s u r ance a g a i n s t gas leakage. Gas F i l t e r . Because o f the h i g h h u m i d i t y i n t h e k i l n , the r e l a t i v e l y low gas v e l o c i t y , and t h e g e n t l e t u m b l i n g a c t i o n , l i t t l e entrainment o f p a r t i c u l a t e i n the gas i s a n t i c i p a t e d . N e v e r t h e l e s s , a gas f i l t e r i s provided i n the e x i t l i n e . I t has a convex f a c e which i s c o n t i n u o u s l y wiped from behind as i t r o t a t e s by a j e t o f steam from a s t a t i o n a r y f i n g e r , shaped t o the contour of the f i l t e r . D i r t thus d i s l o d g e d f a l l s i n t o the d i s c h a r g e c a v i t y .

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Residue D i s c h a r g e . The dump v a l v e s a r e f u l l - b o r e b a l l v a l v e s a r d the c h a n n e l s above and between t h e v a l v e s have the same d i a m e t e r as t h e channels* w i t h i n the v a l v e s ; t h e r e a r e no s h o u l d e r s on which m a t e r i a l w i l l lodge. The v a l v e s swing w i t h the k i l n . At the bottom o f the f i r s t swing, t h e t o p v a l v e opens and the accumulated m a t e r i a l drops through the v a l v e s i n t o the c a v i t y between them. Then the v a l v e c l o s e s , and as i t swings, t h e c a v i t y i s s l o w l y d r a i n e d o f i t s f u e l g a s . At t h e bottom o f t h e second swing, t h e bottom v a l v e opens and drops the r e s i d u e i n t o t h e r e c e i v i n g container. Then t h e v a l v e c l o s e s and t h e c y c l e i s r e peated . Controls. The c o n t r o l system w i l l be designed f o r manual o r a u t o m a t i c o p e r a t i o n F o r automatic opera tion, the p r e d i c t i v maintain the apparatu o p e r a t o r w i l l have the a b i l i t y a t any time t o o v e r r i d e the p r e d i c t i v e c o n t r o l l e r o r t o r e - s e t i t s l i m i t s . Because o f t h e slow t r a v e r s e o f m a t e r i a l through t h e k i l n and hence the s l u g g i s h n e s s o f response t o changes i n q u a l i t y and q u a n t i t y o f feed m a t e r i a l , the c o n t r o l system w i l l have a n t i c i p a t o r y c h a r a c t e r , s e n s i n g the r a t e o f change as w e l l as the a c t u a l v a l u e s o f c o n t r o l parameters. When o p e r a t e d w i t h a gas t u r b i n e i n l a t e r phases of development, t h e g a s i f i e r p r e s s u r e w i l l be s e t about 50 p s i h i g h e r than t h a t r e q u i r e d a t the t u r b i n e combustion chamber i n l e t . The k i l n thus becomes a s m a l l surge tank, and i t s p r e s s u r e f l u c t u a t i o n s w i l l m i l i t a t e a g a i n s t changes i n f u e l v a l u e o f t h e waste b e i n g f e l t as s u r g e s on the power l i n e . (That, and a smart o p e r a t o r . ) Economics Economic a n a l y s i s work t o date assumes u t i l i t y ownership and o p e r a t i o n , w i t h d i s t r i b u t i o n o f t h e g e n e r a t e d power through t h e u t i l i t y g r i d . (A W-M p l a n t i s t o be thought o f as a power p l a n t f u e l e d by waste r a t h e r than a waste d i s p o s a l p l a n t w i t h e l e c t r i c i t y as a b y - p r o d u c t . ) The m u n i c i p a l i t y would have r e s p o n s i b i l i t y f o r c o l l e c t i o n and d e l i v e r y o f s o l i d waste t o the p l a n t , d e l i v e r y o f l i q u i d sewage sludge, and removal and d i s p o s a l o f p l a n t r e s i d u e s . Putting the i n t e r f a c e between u t i l i t y and m u n i c i p a l i t y a t t h e u n l o a d i n g dock would seem t o be t h e most r e a s o n a b l e a l t e r n a t i v e because i t p r e s e r v e s t h e t r a d i t i o n a l r o l e of each. Other arrangements a r e p o s s i b l e , o f c o u r s e :

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m u n i c i p a l o p e r a t i o n and d i s t r i b u t i o n o f power, munic i p a l o p e r a t i o n w i t h s a l e o f power t o t h e u t i l i t y , t h i r d p a r t y o p e r a t i o n , e t c . They would e n t a i l d i f f e r ent assumptions r e g a r d i n g t a x and i n t e r e s t r a t e s , and would y i e l d d i f f e r e n t r e s u l t s . The c a p i t a l c o s t o f t h e b a s i c 10 MWe, 200 ton/day s o l i d waste, 300 ton/day sewage s l u d g e p l a n t i s e s t i mated t o be $9 m i l l i o n o r $900/KW. The a n n u a l d i r e c t o p e r a t i n g c o s t i s e s t i m a t e d a t $850,000. To t h i s must be added d e p r e c i a t i o n , i n t e r e s t on d e p r e c i a b l e i n v e s t ment, l o c a l t a x e s , and income t a x e s . I f one assumes t i p p i n g c h a r g e s o f $8/ton f o r s o l i d waste and $10/ton f o r l i q u i d sewage s l u d g e , and v a l u e s o f 2, 3, and 4
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Steam Gasification

273

Environmental C h a r a c t e r i s t i c s The p o s i t i v e e n v i r o n m e n t a l c h a r a c t e r i s t i c s o f the W-M system a r e e v i d e n t : i t s a b i l i t y to c o n v e r t s o l i d , l i q u i d , and hazardous wastes i n t o power. I t s negative a s p e c t s appear t o be m i n i m a l . A W-M power p l a n t w i l l use no c o o l i n g water, nor w i l l t h e r e be any aqueous d i s c h a r g e from gas p u r i f i c a tion . The s t a c k gases a r e l i k e l y t o be c l e a n e r than those of c o n v e n t i o n a l gas t u r b i n e o r steam p l a n t s o p e r a t i n g on n a t u r a l gas o r o i l . The k i l n gas i s r i c h i n hydrogen and steam and w i l l burn about 600°F c o o l e r than u s u a l , t h e r e b y m i n i m i z i n g f o r m a t i o n of N0 . Complete o x i d a t i o n of CO t o CO2 w i l l a l s o be a i d e d by the h i g h steam c o n t e n t . C h l o r i n e and most of the s u l f u r w i l l be caught b c u l a t e w i l l be w i t h i be t o a v o i d t u r b i n e e r o s i o n . ) W i t h r e g a r d t o hazardous m e t a l s , k i l n c o n d i t i o n s a r e so m i l d , compared t o i n c i n e r a t i o n o r p a r t i a l o x i d a t i o n g a s i f i c a t i o n , t h a t t h e i r v o l a t i l i z a t i o n i s unl i k e l y t o be a problem. Most hazardous m e t a l s w i l l wind up i n the r e s i d u e as p a r t i a l l y h y d r a t e d o x i d e s and c a r b o n a t e s . The f a t e of mercury i s u n c e r t a i n and w i l l be i n v e s t i g a t e d . X

Acknowledgements The W-M g a s i f i c a t i o n / p o w e r program has been supp o r t e d by t h e s e a g e n c i e s : Empire S t a t e E l e c t r i c Energy R e s e a r c h Corp (NYS u t i l i t i e s ) f o r c o n s t r u c t i o n o f the m i n i k i l n ; US E n v i r o n m e n t a l P r o t e c t i o n Agency f o r e x p e r i m e n t a t i o n t h e r e i n on s o l i d waste and sewage s l u d g e ; New York S t a t e ERDA f o r c o a l experiments; US ERDA-Conservât i o n Research & Technology, now DOE-Power Systems D i v . f o r a n a l y s i s of the power c y c l e ; and D0ES o l a r f o r c o n s t r u c t i o n of and e x p e r i m e n t a t i o n w i t h the biogasser. MARCH

15,

1978,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

14 Pyrolysis of Scrap Tires Using the Tosco II Process—a Progress Report B. L. SCHULMAN and P. A. WHITE

1

Tosco Corporation, 18200 West Highway 72, Golden, CO 80401

During the cours pyrolyzing oil shale, Tosc cess to other organic materials such as coal, tar sands, municipal waste and scrap tires. Initially, the processing of scrap tires became of interest because of the high oil yield obtained from the decomposition of the rubber — about 150 gallons per ton, compared to 30-35 gallons per ton for oil shale. At that time, carbon black had approximately the same value as oil and, although it was known that the carbon black was recovered in good quality, its contribution to the potential economics was modest. In 1974, both carbon black and oil prices rose sharply, and later operations focused more closely on the carbon black product. After a series of pilot plant investigations, The Goodyear Tire & Rubber Company and Tosco entered into a program to define the commercial potential of the tire program. A major part of this effort was to construct and operate a 15 ton a day pilot plant specifically designed for pyrolyzing scrap tires and develop the appropriate techniques to recover the valuable liquid and carbon black materials in a suitable commercial form. Generally, the goals of the program were to define the methods for improving the process efficiency in three areas: 1. Optimize process conditions for maximum plant capacity and process yields. 2. Demonstrate best techniques for recovery of the carbon black with an acceptable commercial quality. 3. Demonstrate new mechanical hardware which could improve product recovery or lower total plant investment. 'Current address: Tosco Corporation, 10100 Santa Monica Blvd., Los Angeles, CA 90067

0-8412-0434-9/78/47-076-274$05.00/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

14.

SCHULMAN

A N D WHITE

Pyrolysis of Scrap Tires

275

Pyrolyzing Scrap Rubber Showed Surprising Yield — Polymer Cracks Easily With No Coke Formation The pyrolysis of rubber tires was found to be surprisingly different from processing other organic materials in that the materials making up the tires decomposed in a "cleaner" manner than other organic materials . Scrap tires consist of many elements which can roughly be categorized into four elements: 1. Synthetic rubber (butadiene-styrene copolymer) 2 . Extender oils 3. Organic cord and inorganic belting 4. Carbon black and fillers Analysis of the pyrolysis products which form at 900 to 1000°F showed that the organic polymers simply decomposed into liquid and gas with no cok black, fillers and inorganic belting remain behind as a solid residue. The form of the residue is essentially the same as the original materials used in the tire. For example, fiberglass cord may unravel into single strands; steel (as belting or bead wire) will show up as single or tangled strands; and the carbon black, together with the fillers, will appear as individual particles or loose agglomerates less than one micron in diameter. The major technical advantage of this controlled pyrolysis is that the carbon black is recovered in a "virgin form" — its reinforcing properties are the same as those of the mixture of the various grades of the carbon black which is used in the initial formulation of the tire. The inorganic additives are indicated by the ash content — the typical tire char will show an ash content in the range of 13-16%, as illustrated in Table I. The ash consists mostly of zinc, silica and titanium, with varying amounts of other elements as shown in Table II. Standard rubber formulation tests, together with the use in making tires has shown that the carbon black can be re-used in portions of the tire according to the char's grade. The Key To A Successful Process Is To Maximize Capacity And Maintain Carbon Black Quality The general TOSCO II process description has been well documented. (i) A simplified flow diagram of the process is illustrated in Figure 1. The shredded scrap tires are dried and fed to the rotary pyrolysis drum. Hot ceramic balls from a ball heater flow to the drum, also, where the mixing action raises the reaction temperature to 9 0 0 - 1 0 0 0 ° F . The organic materials decompose

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.33

0.24 2.1*6

0.25

2.3^

Chlorine, #

Sulfur, $

13-71 100.00

15» 36

100.00

100.01

0.18

Ο.13

0.17

$

Nitrogen,

Ash, $

0.27

0.75

Ô.7U

Hydrogen, Ο.85

81Λ9

82.66

Fiberglass-Belted

81.15

$

Steel-Belted

Carbon, $

Moisture,

Non-Belted

Table I . U l t i m a t e A n a l y s i s o f a T y p i c a l T i r e Char

0.25 0.60 2.5Ο ΙΛΟ Ο.36

0.l8 0.25 I.50 0.80 0.32 19.09

0.l6

0.27

2.3Ο

1.60

Ο.38

19.62

Lead

Barium

Magnesium

Phosphorus

Potassium

5.Ο6 2.77

6.0k

2.67

CaO

Sulfur

2

1^.27

Ti0

11.99

ZnO

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.27

6.08

10.28

to

CO

crap

21.31

8-

Pyro\

52.33

2.00

1.10

2.00

Iron

> HITE

S1O2

0.l6

0.13

0.15

Chromium

2Λ0

I.5O

2Λ0

^0.03

Fiberglass-Belted (Ash 13.7 v t 1o)

Aluminum

i)

<0.03

Steel-Belted (Ash 15.0 v t

<0.03

Non-Belted (Ash 15 Λ wt 1o)

Chemical A n a l y s i s of a T y p i c a l T i r e Char Ash (Average of S e v e r a l Samples)

Antimony

Element (wt i)

Table I I .

CHULMA

CO

i Figure 1.

The Tosco II process

CO

1 a

00

P

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

14.

SCHULMAN

A N D WHITE

Pyrolysis of Scrap Tires

279

into oil and gas vapor and pass out the top of the accumulator vessel into a fractionator. The oil is condensed into various fractions and separated from the gas. The gas, after sulfur removal, can be used as ball heater fuel. The mixture of balls and solid residue is separated by allowing the fine residue to fall through a fine rotating screen, called a trommel. The warm balls are collected separately and returned to the heater. The hot residue is cooled and treated to remove extraneous materials such as steel, fiberglass, stones and other material from the carbon black. For ease of handling, the carbon black is pelletized for shipment to the consumer. The key to a successful process is the efficienct handling of the feed material into the pyrolysis system and maintaining good recovery of the carbon black from the process. For example, due to its fineness, carbo fraction, which represents an economic loss. Similarly, it is important that carbon black be effectively separated from the steel and fiberglass contaminants without a loss on the less valuable materials. Such efficient handling, together with the prevention of carbon black being emitted to the atmosphere, is a key part of the process development. The recovery of the liquid product is also an important factor since the oil should have many valuable uses. It is very fluid liquid containing about 1% sulfur and can be used directly as an industrial heating o i l . Typical properties are shown in Tables III and IV. The gas produced is highly olefinic, containing substantial amounts of ethylene, propylene and butylène — as illustrated in Table V. Depending on the economic situation, the process can be run at high temperature to maximize gas and minimize liquids. If the temperature is kept at the low range, gas yield is minimized and liquid yields increase. At the same time, the lower temperature provides a large increase in capacity so that careful economic judgments must be superimposed on the processing results to define the optimum conditions. In addition to the capacity, a key item is to keep carbon black yield high and maintain its good quality. Our initial results show this can be done. The impact of the carbon black on product realization is significant, as shown in Table VI.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

280

SOLID

WASTES

A N D RESIDUES

Table I I I . I n s p e c t i o n Data f o r T i r e O i l and Condensate (Average o f f o u r samples o f o i l and f o u r samples o f condensate)* Tire O i l Whole O i l API G r a v i t y , @ 60 F* S p e c i f i c G r a v i t y , @ 60 F TCC F l a s h P o i n t , @ 76Ο mm*

14.8 0.9674

38.9 O.83IO

T y p i c a l No.6 Fuel O i l

1

12.4 0.9833 208 F

100 F 20 F

Pour P o i n t *

Condensate

- - -

60 F

Ash, v t 1o* V i s c o s i t y , @ 100 F, c S t *

8.54

V i s c o s i t y , @ 210 F, c S t *

1.96

Heating Value, Gross B t u / l b R e i d Vapor Pressure, p s i g

18,030

- - -

0.2

0.2

ppm

0.8

3

—

Conradson Carbon, v t °/ο

3.41

BaP Content, ppm*

6-20

Saturates, v o l

1

3

Olefins, vol #

4

5

95

92

vol $

- - -

95.0

Research Octane Number

Aromatics,

18,283

Positive

Doctor Test Mer captans,

118.7

10.35

S c h m i d t , P a u l F.,"Fuel O i l Manual, " I n d u s t r i a l Près s, I n c . 1969.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

14.

SCHULMAN

A N D WHITE

Pyrolysis of Scrap Tires

281

Table IV. I n s p e c t i o n Data f o r T i r e O i l and Condensate (Average elemental a n a l y s i s o f f i l t e r e d t i r e o i l and condensate) T y p i c a l No. 6

Tire O i l

Carbon, wt $

8T.II

Hydrogen, wt

86.85

86 Λ

10.67

12.9

N i t r o g e n , wt °/o

0.59

0.25

—

Oxygen, wt

1.07

Ο.76

---

S u l f u r , wt

1.014-

Ο.76

1.20

A r s e n i c , ppm

1.1

---

Copper, ppm

0.2

I r o n , ppm

133

N i c k e l , ppm

0.3

Sodium, ppm

27.5

Vanadium, ppm

---

—

-

—

0.8

'Schmidt, P a u l F., "Fuel O i l Manual," I n d u s t r i a l P r e s s , I n c . , 1969.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

282

SOLID

WASTES

AND

Table V TYPICAL PILOT PLANT PRODUCT GAS YIELD Gas Yield (lb/ton) H

1.49

2

CO co

2

41.24

HS

1.82

2

C

l

24.39

c

2

18.50

c -

22.76

2

C

3

C

3-

i-C

9.24 24.27

N-C c 4

2.19

4

4

2.28 61.59 222.02

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

14.

SCHULMAN

A N D WHITE

Table V I .

283

Pyrolysis of Scrap Tires

Gross R e a l i z a t i o n f o r T i r e P y r o l y s i s (Basis

Item

Production

Product V a l u e *

Revenue

Oil

3 t o k bbls

$l4.00/bbl

$49.00

Carbon B l a c k

575 t o 700 l b s

$ 0.095/lh

$60.00

Steel

85 t o 100 l b s

$4ο.οο/τ

$ 2.00

Fiberglass

70 t o 80 l b s

-0-

-0-

Gross R e a l i z a t i o n - U.S. $111

1

These are T0SC0 s estimates o f the market value f o r these products. The values shown have been discounted t o r e f l e c t p o t e n t i a l marketing p e n a l t i e s .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

284

SOLID

WASTES

A N D RESIDUES

Demonstration Program is Continuing The 15 ton a day pilot plant has been operating since early 1977 in various stages. A series of tests has been made in key areas to define the key operating parameters and critical elements in several areas which can affect the process economics: 1. Tire shredding, including separation of steel from rubber feed 2 . Pyrolysis operations 3. Oil recovery 4 . Carbon black recovery and handling This series of tests has identified major leads to improving the various areas to maintain product quality, increase capacity and maintain high carbon black recovery of good quality. Several simplifications of the mechanica handling have been made to the unit. Operations are continuing in 1978 to define optimum process conditions, demonstrate long term equipment operability and make large tonnage samples of carbon black for commercial evaluation. Literature Cited 1.

MARCH

Haberman, Charles Ε., "Pyrolysis of Scrap Tires Using the TOSCO II Process" , prepared for The Rubber Division, American Chemical Society, Chicago Symposium, May 3-6, 1977. 3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

15 Disposal of Sewage Sludge and Municipal Refuse by the Occidental Flash Pyrolysis Process EUGENE J. CONE

1

Occidental Research Corporation, 1855 Carrion Road, La Verne, CA 91750

For the last severa has been interested in gas by pyrolysis of "waste" organic materials. Within the last two years, this interest has extended to disposal of sewage sludge and sewage sludge/municipal solid waste mixtures by pyrolysis. The emphasis of the current work has been on defining and optimizing product yields (i.e., controlling the mix of liquid, gas, or char products) and on controlling their composition. System variables being investigated include temperature, pressure, and residence time. Objectives 1.

2. 3. 4.

Specific objectives of the research program are as follows: Demonstrate in small pilot scale equipment that pyrolysis of sewage sludge can be accomplished by the Occidental Research Corporation Flash PyrolysisTM process as practiced with municipal solid waste at El Cajon, San Diego, with only minor modification to existing equipment. Define any interaction or "nonlinear" effects caused by copyrolysis of sewage sludge/municipal solid waste as compared to separate pyrolysis of the materials. Define variables controlling product mix (liquid, gas, char). Optimize product quality.

Experimental Apparatus The pyrolysis system used in the experiments reported here was based on transport of sewage sludge or municipal solid waste through an electrically heated one inch nominal diameter pipe. Typical solids feed rates were 2 kg/hr, and typical carrier gas rates were 6.6 standard cubic meters per hour. 1

Current Address: Envirotech, One Davis Drive, Belmont, CA 94002 0-8412-0434-9/78/47-076-287$05.00/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

288

SOLID

WASTES

A N D RESIDUES

The system components consisted of a modified screw feeder, a 7 m long U-shaped section of e l e c t r i c a l l y heated pipe, two cyclones, a glass fiber packed f i l t e r , a liquid product conden­ sing section, and a gas flow sampling and metering section. Schematics of the system are shown in Figures 1 and 2. Products leaving the system were passed through a thermal oxidizer to eliminate any possible a i r pollution. Two different liquid recovery systems have been used in our pyrolysis experiments. The f i r s t (Figure 1) consisted of two externally cooled "knockout pots", and the second (Figure 2) used direct contact spray quenching with an immiscible hydro­ carbon l i q u i d , followed by phase separation and product recovery. This second method of product recovery models the technology now in use at Occidental's municipal solid waste demonstration plant at El Cajon, in San Diego County, California; however, all data actually discussed here were taken with the f i r s t system Discussion of Experimenta The two feed materials used in these experiments were finely shredded municipal refuse as obtained from the "front end" of the Occidental Resource Recovery system, (1,2) and sewage sludge as obtained from the San E l i j o , CA sewage treatment plant. The municipal refuse was usually reground in a hammer mill before pyrolysis so as to increase ease of handling in the small scale equipment used. The sewage sludge was a i r dried and then ground in the same m i l l . Typical particle size distribution for the pyrolysis feed materials are as shown in Table I. TABLE I PYROLYSIS FEED-PARTICLE SIZE DISTRIBUTION Screen Opening, μίτι

Municipal Solid Waste - Percent Throuqh Screen

Sewage Sludge - Percent Through Screen

841

96.8

297

90.4

77.0

149

82.4

54.4

105

77.2

50.6

75

66.4

36.2

45

44.0

26.8

37

36.6

20.2

100

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 1. Pyrolysis pilot plant initial design In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 2. Pyrolysis pilot plant with improved product collection system In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

15.

CONE

Occidental Flash Pyrolysis Process

291

Clearly the sewage sludge particles used in these experi­ ments tend to be larger than the corresponding municipal solid waste particles. Thus, the median sewage sludge particle is about 100 ym whereas the median municipal solid waste particle is about 50 ym. This should tend to make the sewage sludge used here more d i f f i c u l t to pyrolyze, but the exact magnitude of the effect has not been determined. Typical feed compositions are as shown in Table II. TABLE II PYROLYSIS FEED COMPOSITION Weight Percent

Municipal Solid Waste

Sewage Sludge

C H

6.3

5.0

Ν

0.5

2.5

S

0.3

1.0

Cl

0.4

0.1

Ash

12.4

44.0

H0

4.0

6.0

38.2

18.4

2

0 (by difference)

Note that the significant difference in ash content between municipal solid waste and sewage sludge makes i t necessary to compare product yields in terms of moisture and ash free (MAF) materials. Figure 3 shows a plot of o i l y i e l d as a function of tempera­ ture for pyrolysis of sewage sludge and municipal solid waste. Data i s , of course, on a MAF basis for both feed and products. Note that the o i l yield for sewage sludge is about 10% lower than that for municipal solid waste at 900°F, but essentially the same over the rest of the temperature range investigated. Figures 4 and 5 show similar plots for gas and char yields, respectively. Gas yield for sewage sludge is about the same at 900°F and about 10% lower over the rest of the temperature range. Char y i e l d for sewage sludge is about 10% higher over most of the pyrolysis temperature range, but only about 4% higher at 1600°F. Composition of pyrolytic o i l is shown in Table III. Again, data is on an MAF basis. Note that the sewage sludge o i l formed

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

292

SOLID WASTES AND

RESIDUES

Ο SEWAGE SLUDGE • 50

MSW

r

TEMPERATURE,*F

Figure 3.

Yield of oil vs. temperature for pyrolysis of sewage sludge and municipal solid waste (MSW) (data based on MAF oil and feed)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

CONE

Occidental Flash Pyrolysis Process

Figure 4. Yield of gas vs. temperature for pyrolysis of sewage sludge and municipal solid waste (MSW) (data based on MAF feed)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

294

Figure 5.

SOLID

WASTES

AND

RESIDUES

Yield of MAF char vs. temperature for pyrolysis of sewage sludge and municipal solid waste (MSW) (data based on MAF feed and char)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

78.0 10.3

1600

6.5

64.2

7.6

60.7

1400

7.0

52.4

60.1

6.6

54.3

900

1200

6.8

C

Pyrolysis Temperature, °F

3.1

0.3

18

7.8 12.6

65.0

17080

7.6 11.9

70.5 1.0

1.5

7.9 12.5

69.7

1.9

1.3

1.4

8.4 11.9

66.3

17

11394

1.3

0.2

2.0

0.8

9.5

28 26 31 32 27

14736 13206 13635 13588 12579

0.2

0.1 0.1 0.3

0.3

36 13211 1.1

9.4

0.1

0.2

0.5

6.6

29

14501

35

0.1

0.6

6.4

24

13372

Run No.

13114

0.2

0.7

5.7

7.1

69.9

0.4

19

8.4

66.4

11243

0.1

0.8

9.5

69.2

8.6

9.9

Oil From Sewage Sludge HHV H Ν S Cl (BTU/lb)

62.6

65.7

6

5

C

7

1.0

0.2

1.3

8684

9286

Run No.

10781

0.2

0.1

0.7

0.2

0.1

0.6

Oil From Municipal Solid Waste HHV (BTU/lb) S Cl H J L

TABLE III PYROLYTIC OIL PROPERTIES (MAF OIL)

296

SOLID

Ο Ο VO

Ο Ο

O Ο

ο ο

Ο

σ>

00

00

CO OsJ

CVJ Γ­

ο

ο

ΙΟ

LO

CVJ

00 CVJ

CO

^-

LO

CVJ

CVJ CO

CT>

AND

CO CO

ο

00

CVJ

Γ­

ο ο

c

ΟΟ r— r—

CVJ

CT>

LO

CT»

ο

cvj CO

00

Ο

WASTES

LO

LO

i— Ο

ο

ο ο

αϊ ο.

CT»

«s*

CV1 ι—

Γ—

m

LO

CVJ

r—

r— r—

r— CO

CO CO

ο ο

cvi

ο

ο ο CVJ

•"3

CO ι—ι CO

Ο

ο Cd >-

0Û < 5C|

CO

cvj

00 CVJ

CVJ

CO

CVJ

ο

«3-

cr>

vo CO

CO

«vt-

ΟΟ

oo

oô

ο

ο

00 CVJ

00

ο ο en

vo

ο

ο

>-J Q_

CO

LO ι—

CO

ο

LO CO

ο

Ο CO

ο ο

2

r—

CO

:
cvj

LO

VO r—

00 VO

cvj

ο ο

SI

Ο

CO

LO

Ο

co

cvj

CO

Ο

CVJ

Γ­

CVJ

-3-

cvj

ω CO S•r- 3 t0

4->

>> fO r - S-

IL.

ο eu S- Q_

Ο

CVJ

Ο

ο ο

CVJ

Ο

CVJ

eu ο ο ω c to eu Ό

— . -ι— co (Ο

co

Ο)

Ε

Q J T

CD S- -Μ

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

15.

297

Occidental Fhsh Pyrolysis Process

CONE

TABLE V CONCENTRATION OF MAJOR COMPONENTS IN PRODUCT GAS FROM PYROLYSIS OF MUNICIPAL SOLID WASTE Pyrolysis Temperature, °F

900

900

1200

1200

1400

1600

4.7

6.7

13.0

9.5

15.4

19.6

33.6

34.5

49.3

50.7

49.7

48.4

0.3

2.7

8.5

7.5

10.4

12.0

5.0

1.1

4.8

4.0

7.3

7.9

Gas/oil residence time (sec.)

0.5

0.5

0.5

0.3

0.3

0.3

Run number

5

6

7

Volume % H

2

CO co

CH

4

C H 2

55.2

2

4

19

17

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

18

298

SOLID

WASTES

A N D RESIDUES

in the 900-1200°F range is generally higher in carbon and hydrogen than the corresponding municipal solid waste o i l , and thus is apparently a high quality o i l . The nitrogen content might be considered a problem but blending with municipal refuse o i l and fuel oil can produce a composite fuel with nitrogen content below 1%. Table III also shows the higher heating value of pyrolytic o i l from municipal solid waste and sewage sludge c a l culated from the Dulong-Petit equation. As would be expected from the relatively large percent of carbon and hydrogen in the sewage sludge o i l , its higher heating value compares favorably with that of municipal solid waste o i l for oils formed at or below 1400°F. Table IV shows the concentration of the major components in the product gas from pyrolysis of sewage sludge, and Table V, similar data for municipal solid waste. Figures 6-10 present this data graphically. Examination of thes pected, gas composition perature. Variation in, and absolute value of hydrogen and methane concentrations are seen to be about the same for sewage sludge and municipal solid waste over the entire temperature range investigated. Carbon monoxide concentration is seen to be about 20% lower for sewage sludge, and carbon dioxide concentration is about 15% lower in the 900-1200°F range, and several percent lower in the 1400-1600°F range. Ethylene concentration is considerably higher for sewage sludge gas, particularly at higher pyrolysis temperatures. Table VI compares the calculated average gross heating value for product gas from the two feed materials. It should be noted that these values appear higher than might be expected because of the presence of several percent C5+ in the gas stream. TABLE VI PYROLYSIS PRODUCT GAS GROSS HEATING VALUE Temperature, °F

Municipal Solid Waste (BTU/SCF)

Sewage Sludge (BTU/SCF)

900

260

410

1200

680

960

1400

670

880

1600

600

960

Tables VII and VIII show product recoveries for sewage sludge, and municipal solid waste, respectively. It is particul a r l y interesting to note that overall, carbon, hydrogen and ash material balances generally close to within tl0%.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

15.

CONE

Occidental Flash Pyrolysis Process

299

Ο MSW • SEWAGE SLUDGE 26

r

Figure 6.

Volume percent of H in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW) 2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

300

SOLID WASTES AND RESIDUES

Figure 7. Volume percent of CO in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

CONE

Occidental Fhsh Pyrolysis Process

Figure 8. Volume percent of C0 in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW) 2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

302

SOLID

ι 0

900

1000

WASTES

AND

ι

ι

ι

ι

ι

1100

1200

1300

1400

1500

RESIDUES

1 1600

TEMPERATURE, *F

Figure 9.

Volume percent of CH in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW) k

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 10. Volume percent of C H in pyrolysis product gas for pyrolysis of sewage sludge and municipal solid waste (MSW) 2

h

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Pyrolysis temperature, °F Weight % MAF o i l based on MAF feed Weight % gas based on MAF feed Weight % MAF char based on MAF feed Water of pyrolysis--% Weight % dry o i l based on as used feed Weight % gas based on as used feed Weight % dry char based on as used feed Weight % water based on as used feed Run number Nominal gas/oil residence time (sec.) % Overall recovery % C recovery % H recovery % Ash recovery 900 43 .4 10 .7 32 .6 7 .0 20 .2 5 .0 62 .1 8 .3 29 2 95 .7 104 .9 97 .1 97 .0

900

36.3

6.9

40.8 5.3

18.5

3.5

60.7

8.5 24

2 91.2 89.1 86.6 92.4

0.3 92.6 86.4 95.7 91.1

11.4 35

65.9

2.6

12.8

39.1 16.0

6.4

32.3

900

0.3 88.0 87.4 83.7 96.0

6.2 28

51.4

11.1

19.3

17.8 3.2

21.7

37.5

1200

0.3 91.9 98.6 99.6 90.0

9.5 36

59.1

10.3

13.0

27.2 11.6

24.8

29.8

1200

0.,3 89.,1 94.,2 93.,0 98..6

10.,0 26

49.,2

31. 1

8.,9

14. 1 7.,9

40.,8

17.,2

1400

0.5 96.5 100.1 109.7 94.2

10.3 31

60.8

16.2

9.3

23.1 12.6

40.4

23.0

1400

TABLE VII PYROLYTIC PRODUCT RECOVERY FOR SEWAGE SLUDGE PRYOLYSIS

0 .5 97 .6 104 .0 98 .3 95 .7

9 .3 32

59 .5

17 .6

11 .2

29 .9 3 .5

46 .2

29 .2

1400

2 91.3 92.1 108.6 91.8

10.0 34

55.7

21.9

3.7

16.6 11.8

53.5

8.9

1400

0.3 92.5 90.3 99.9 97.4

9.9 27

47.4

30.7

4.5

11.6 8.4

59.3

8.6

1600

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

8.8 31.5 14.5 29.9 7.3

11.4 27.5 14.4 39.5 9.6

Weight % gas based on MAF feed

Weight % MAF char based on MAF feed

Water of pyrolysis--MAF feed

Weight % dry o i l based on as used feed

96.8

% H Recovery

105.8

97.6

% C recovery

% Ash Recovery

98.0

0.5

Nominal gas/oil residence time (sec.)

% Overall recovery

5

16.1

Weight % water based on as used feed

Run number

33.1

Weight % dry char based on as used feed

72.0

98.9

96.5

98.3

0.5

6

16.1

35.1

47.6

46.1

Weight % MAF o i l based on MAF feed

Weight % gas based on as used feed

900

900

Pyrolysis temperature, °F

15.9

14.1

102.0

96.3

98.4

95.9

0.5

7

15.8

20.5

29.6

99.9

105.4

99.3

96.3

0.3

19

93.6

103.7

99.0

98.9

0.3

17

19.1

18.2

19.9 19.0

47.3

14.4

15.1

10.4

57.0

17.0

1400

24.1

33.4

11.1

13.2

29.9

28.9

39.9

35.8 35.4

1200

1200

TABLE VIII PYROLYTIC PRODUCT RECOVERY FOR MUNICIPAL SOLID WASTE PYROLYSIS

306

SOLID

W A S T E S A N D RESIDUES

The conclusion from a l l the above is that copyrolysis of sewage sludge and municipal solid waste seems quite possible. The sludge pryolyzes quite readily during Flash P y r o l y s i s ™ to give apparently reasonable products. No special problems in the pyrolysis of sewage sludge are apparent at this time. Abstract Air-dried and ground municipal sewage sludge, and municipal solid waste have been pyrolyzed in a 2 kg/hr pilot plant. An e l e c t r i c a l l y heated vertical flow transport reactor with short residence time was used. Temperatures in the range 755-1144 Κ (900-1600°F) were investigated. O i l , gas, and char yields and composition varied appreciably with pyrolysis temperature. The results presented here suggest that the Occidental Flash P y r o l y s i s ™ process can be applied successfully to the codisposal of municipal sewag Literature Cited 1. 2.

APRIL

Levy, S.J., "San Diego County Demonstrates Pyrolysis of Solid Waste," SW-80d. 2, U.S. Environmental Protection Agency, (1975). Preston, G.T., "Resource Recovery and Flash Pyrolysis of Municipal Refuse," Institute of Gas Technology Symposium "Clean Fuels from Biomass, Sewage, Urban Refuse and Agricultural Wastes," Orland, Florida, (1976). 7,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

16 Variable Velocity Fluidized Bed for Pyrolysis of Biomass STEVEN R. BECK, WILLIAM J.HUFFMAN,1UZI MANN, and HO-DER WONG Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409

Current interest i to l i q u i d and gaseous product many new technologies and the resurrection of some old technologies. One such technology i s pyrolysis i n a f l u i d i z e d bed to produce gas that can be used as fuel or as a feedstock for petrochemical products. Processes utilizing f l u i d i z e d bed technology are i n varying stages of development for coal g a s i f i c a t i o n , oil shale gasification and biomass gasification (1, 2, 3, 4, 5). Most of these processes employ steam and a i r or oxygen as the f l u i d i z i n g medium. In the v i c i n i t y of the distributor, part of the s o l i d i s combusted to provide the heat to pyrolyze the remaining s o l i d . The pyrolysis zone in the reactorisgenerally above and separate from the combustion zone. At the top of the reactor i s an expanded disengaging section to prevent excessive solids entrainment i n the produced gas. A f l u i d i z e d bed designed for p a r t i a l oxidation of s o l i d hydrocarbons presents some interesting design problems. The different reactions which occur throughout the bed can lead to severe longitudinal temperature p r o f i l e s unless the bed i s very well mixed. In addition, the pyrolysis of solids results i n an increase i n the s u p e r f i c i a l mass flow rate of gas as the reaction proceeds. The combination of these effects leads to a f l u i d i z e d bed i n which the gas velocity varies throughout the bed even i n the constant diameter section of the column. Add to this the reduction i n gas velocity due to an increase in diameter i n the disengaging section and the resulting problems i n scale-up of the process are enormous. Figure 1 i l l u s t r a t e s how the gas velocity can vary i n a f l u i d i z e d bed used for pyrolysis. Synthesis Gas From Manure Process At Texas Tech University, the Synthesis Gas From Manure (SGFM) Process has been under development for seven years (6, 7, 1

Current Address: Battelle Memorial Institute, Columbus, O H

0-8412-0434-9/78/47-076-307$05.00/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

WASTES

A N D

RESIDUES

* PRODUCT GAS

DISENGAGING ZONE (LOW VELOCITY)

SOLIDS FEED

\ >

PYROLYSIS ZONE co + C 2CO 2

C +

H 0 2

CO + H

0

(INCREASING VELOCITY)

COMBUSTION ZONE C +

o -» co 2

2

(HIGH TEMPERATURE) SPENT SOLIDS

"Figure 1.

Fluidized bed pyrolysis reactor

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

16.

BECK ET AL.

Pyrolysis of Biomass

309

8). The o r i g i n a l o b j e c t i v e o f t h i s p r o j e c t was t o develop a pro­ cess by which c a t t l e f e e d l o t manure could be converted t o a syn­ t h e s i s gas s u i t a b l e f o r ammonia p r o d u c t i o n . This would provide a means by which the n i t r o g e n content o f the manure could be t r a n s ­ ported f o r f e r t i l i z e r a p p l i c a t i o n s a t l o c a t i o n s f a r d i s t a n t from the f e e d l o t . The p r o j e c t i s now i n v e s t i g a t i n g thermochemical g a s i f i c a t i o n o f other biomass feedstocks t o produce a medium-BTU (1.12 χ 1 0 t o 1.86 χ 1 0 J/m ) gas s u i t a b l e f o r d i r e c t combus­ tion or further synthesis. The SGFM process i s based on a counter-current f l u i d i z e d bed f o r p y r o l y s i s o f the biomass. The s o l i d feed i s i n t r o d u c e d a t the top o f the r e a c t o r and i s f l u i d i z e d by a i r and steam i n j e c t e d at the bottom o f the r e a c t o r as shown i n F i g u r e 2. This process i s c u r r e n t l y i n the p i l o t p l a n t stage o f development. The r e ­ a c t o r shown i n F i g u r e 2 has a c a p a c i t y o f ~500 Kg/day manure feed and was scaled-up from a 2.5 cm χ 45 cm l a b o r a t o r y r e a c t o r This p i l o t p l a n t has been o p e r a t i o n a s i g n data base was develope manure. A complete d e s c r i p t i o n o f the p i l o t p l a n t has been pre­ v i o u s l y reported ( 9 ) . 7

7

3

I n t e r n a l Gas Samples As p a r t o f the data base development f o r the SGFM p i l o t p l a n t , a s e r i e s o f i n t e r n a l r e a c t o r samples were taken t o d e t e r ­ mine gas c o n c e n t r a t i o n p r o f i l e s w i t h i n the r e a c t o r . These sam­ p l e s were obtained by i n s e r t i n g sample probes a t 30.5 cm i n t e r v a l s along the l e n g t h o f the r e a c t o r . The sample probe was 0.64 cm (0.5 cm ID) tubing w i t h t w e n t y - f i v e p o r t s along one s i d e o f the tubing. The probe s e c t i o n w i t h p o r t s t r a v e r s e d the e n t i r e d i a ­ meter o f the r e a c t o r . Hence, each sample i s thought t o represent an average, r a d i a l c o n c e n t r a t i o n . During sampling, the probe was connected t o a condenser t o remove steam and l i q u i d s . The d r i e d sample was then routed through a rotameter which was f o l l o w e d by a gas sample b o t t l e . The f i r s t step i n o b t a i n i n g a sample was t o purge the e n t i r e sample system and sample b o t t l e w i t h helium. The sample v e l o c i t y was a l s o set using helium. Then, the a c t u a l sample was obtained by opening a b a l l v a l v e . The gas was allowed t o purge through the sample b o t t l e f o r three t o s i x residence times. As the gas sample purged the sampling system, the gas v e l o c i t y would tend t o decrease due t o plugging i n the probe and l i n e s . The gas v e l o c i t y was adjusted t o the d e s i r e d r a t e by use o f a needle v a l v e j u s t p r i o r t o the sample b o t t l e . Two gas samples were obtained a t each l o c a t i o n t o check the r e p r o d u c i b i l i t y o f the sampling and gas ana­ lysis. The sample v e l o c i t y r e l a t i v e t o the i s o k i n e t i c sample v e l o ­ c i t y and residence time i n the sampling system were areas o f con­ cern i n regard t o the accuracy o f the r e s u l t s . The residence time of the gas sample i n the hot s e c t i o n (>400°C) o f the sample probe

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

BIOMASS FEED

STAR . FEEDER

PRODUCT GAS

61.0 cm 20.3 cm

κ

a

15.2 cm ^ 15.2 cm^j

ELECTRIC HEATERS TO MINIMIZE HEAT LOSS

182.9 cm . ^Ν|Γ

AIR

+ STEAM

CHAR

Figure 2.

SGFM pilot plant reactor

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

16.

BECK

E T

AL.

Pyrolysis of Biomass

311

was l e s s than 0.2 seconds which minimized r e a c t i o n s i n the probe. To determine the e f f e c t of sample v e l o c i t y r e l a t i v e t o i s o k i n e t i c v e l o c i t y , samples were taken a t d i f f e r e n t r a t e s . Table I shows some t y p i c a l r e s u l t s obtained i n these t e s t s . The sample v e l o ­ c i t y appeared to have n e g l i g i b l e e f f e c t s on the gas compositions. The complete r e s u l t s of the i n t e r n a l sample data w i l l be r e ­ ported a t a l a t e r date. For t h i s paper, the n i t r o g e n concentra­ t i o n throughout the r e a c t o r i s reported. F i g u r e 3 shows the n i ­ trogen c o n c e n t r a t i o n as a f u n c t i o n of height i n the p i l o t p l a n t r e a c t o r f o r f i v e runs. Since n i t r o g e n does not r e a c t , the de­ crease i n n i t r o g e n c o n c e n t r a t i o n can be r e l a t e d t o an i n c r e a s e i n t o t a l gas mass flow r a t e due t o p y r o l y s i s gas formation. I n a d d i ­ t i o n t o the v a r y i n g gas flow r a t e , the SGFM r e a c t o r shows a wide v a r i a t i o n i n temperature along the r e a c t o r as shown i n F i g u r e 4. P a r t o f t h i s temperature p r o f i l e i s due t o the f a c t that the lower heater on the r e a c t o r (see F i g 2) was i n o p e r a b l e Con sequently, very h i g h hea of the r e a c t o r w h i l e th r e a c t o r was minimized by the upper e l e c t r i c heater. Even i f both heaters were operable, a s i g n i f i c a n t l o n g i t u d i n a l temperature gradient would have been present. The change i n mass f l o w r a t e of gas and the temperature p r o f i l e r e s u l t s i n the gas v e l o c i t y i n c r e a s i n g 2-4 times i n the r e a c t o r as shown i n F i g u r e 5. The w i d e l y v a r y i n g gas v e l o c i t i e s i n the SGFM r e a c t o r p r e ­ sent problems i n t r y i n g t o scale-up the r e a c t o r . F l u i d i z e d beds are extremely d i f f i c u l t t o scale-up and s t i l l be able t o p r e d i c t the bed performance even when the v e l o c i t y i s constant. I n the case o f the SGFM r e a c t o r , no methods t o scale-up a v a r i a b l e v e l o ­ c i t y a r e known t o be completely r e l i a b l e . For t h i s reason, a program was i n i t i a t e d t o study a v a r i a b l e v e l o c i t y f l u i d i z e d bed. V a r i a b l e V e l o c i t y F l u i d i z e d Bed The o b j e c t i v e of t h i s p r o j e c t was t o b u i l d and operate an ambient temperature, non-reacting, g a s - s o l i d f l u i d i z e d bed t o i n ­ v e s t i g a t e the c h a r a c t e r i s t i c s of a v a r i a b l e v e l o c i t y f l u i d i z e d bed r e a c t o r such as the SGFM p i l o t p l a n t r e a c t o r . To o b t a i n the d e s i r e d v a r i a t i o n i n v e l o c i t y , the bed could have been constructed w i t h a changing c r o s s - s e c t i o n a l area and f l u i d i z e d by a constant v o l u m e t r i c gas flow r a t e or a constant diameter v e s s e l could have been operated w i t h a subliming s o l i d o r a porous s o l i d c o n t a i n i n g a v o l a t i l e s o l v e n t . The former method was chosen due t o i t s ease of o p e r a t i o n and the l a c k o f mass t r a n s f e r e f f e c t s between phases which would have complicated the a n a l y s i s of the r e s u l t s . This approach should be considered as a f i r s t attempt t o g a i n an under­ standing of the phenomena i n v o l v e d and must be f o l l o w e d by s t u d i e s i n a constant diameter bed u s i n g a v o l a t i l e component. The equipment used f o r t h i s study was a two-dimensional, P l e x i g l a s bed as shown i n Figure 6. The i n l e t o f the bed i s 7.5 cm χ 45.7 cm and decreases t o 7.5 cm χ 15.2 cm a t the h i g h v e l o c i t y R

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

cm

28.2

0.24-0.6 29.3

29.4

0.5-0.8

~ 0.25

24.3

37.8

0.7-1.2

~ 0.6

33.6

1.0-1.1*

2

38.4

N

0.7-1.2

Sample Rate, £/min

13.6

14.7

13.4

12.6

18.2

17.9

17.8

17.6

A r e a c t o r upset occurred w h i l e t h i s sample was being obtained.

8.3

8.7

25.0

24.6

4.6

4.9

4.8

25.2

8.4

4.8

26.5

3.6

3.4

8.2

27.2

H

2 4

3.6

C

27.6

16.6

8.1

2

28.4

co

5.1

6.4

4

20.8

C H

7.3

2 6.3

H

14.3

7.8

CO

The i s o k i n e t i c sample r a t e i s estimated t o be 0.6 £/min.

152.4

45.7

Height â Distrd

TABLE I . EFFECT OF SAMPLING VELOCITY ON INTERNAL GAS CONCENTRATIONS, RUN 19 H

2 2

0.5

0.4

0.5 0.5

0.4

0.5

0.6

0.5

0.6

°2

0.5

0.4

0.5

0.7

0.6

C

CO

S

%

CO

ί c/>

!

co ι—< to

16.

BECK

0

E T

AL.

40

Pyrolysis of Biomass

80

120

313

160

200

240

EXIT

H E I G H T A B O V E D I S T R I B U T O R , cm

Figure 3.

Nitrogen concentration in the SGFM reactor: O , Run 19; A, Run 20; Run 21; V, Run 23

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Q

314

SOLID WASTES AND RESIDUES

1000 ι

|

LOWER HEATER

{

t

UPPER HEATER

EXPANDED . SECTION ,

t

900 \

\ /θ

800

\

/

\ 1

Ο

700 J

o/

CC

600

500 .

\

400 .

300„

200 50

100

150

200

250

300

HEIGHT ABOVE DISTRIBUTOR, cm

Figure 4.

Temperature profile in the SGFM reactor: O, Run 20; Δ, Run 21; {J Run 22; V, Run 23 y

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BECK

ET

Pyrolysis of Biomass

AL.

50

? ι

45

/

\ \ \

/

Ρ

/

\

40

/

35

(Λ <

30

ϋ

25

0 1 I

/

ι

I

/

rfî

/

•

I

20

15

/ / / / f

Ό - - ^ -

REACTOR DIA. = 15.2 cm

^

0

^REACTOR PI A. =^0.3 cm

_L

101 100

200

300

HEIGHT ABOVE DISTRIBUTOR, cm

Figure 5.

Typical gas velocity profile in the SGFM reactor, Run 22: O , gas velocity; •, mass flow rate

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 6. Cold model, variable velocity, fluidized bed In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

16.

BECK

E T

AL.

Pyrolysis of Biomass

317

s e c t i o n . The upper p o r t i o n o f the bed expands t o 7.5 cm χ 53.3 cm a t the e x i t . Pressure taps are placed a t approximately 5 cm i n t e r v a l s along the bed. Pressure drop i s measured by both v e r ­ t i c a l U-tube and i n c l i n e d manometers. The d i s t r i b u t o r p l a t e i s P l e x i g l a s w i t h 1/32" holes on a 1/2 i n c h t r i a n g u l a r spacing. F l u i d i z i n g a i r i s s u p p l i e d by a Hybon Model HB-50 compressor w i t h a maximum flow of 1700 £/min a t 1 atm and 15°C which corresponds to a s u p e r f i c i a l gas v e l o c i t y i n the bed of 70.9 cm/sec a t the entrance depending on pressure. The a i r f l o w r a t e i s measured by pressure drop across a 1.87 cm o r i f i c e i n a 1 i n . , Sch. 40 pipe which was c a l i b r a t e d w i t h a t u r b i n e meter. The l o n g i t u d i n a l v e l o c i t y p r o f i l e created by t h e v a r y i n g c r o s s - s e c t i o n a l area i s very s i m i l a r to t h a t measured i n the SGFM p i l o t p l a n t r e a c t o r . This mode of o p e r a t i o n may have c e r t a i n ad­ vantages i n p y r o l y s i s r e a c t o r s . This gas v e l o c i t y w i l l be r e ­ l a t i v e l y low i n the combustio f th r e a c t o r h i g h i th p y r o l y s i s zone and low o c i t y i n the p y r o l y s i s zon the hydrocarbon gases produced and minimize reforming o r c r a c k i n g of these gases. This should r e s u l t i n a gas product w i t h a h i g h ­ er h e a t i n g v a l u e . Another advantage o f t h i s system could be three d i s t i n c t f l u i d i z a t i o n regimes i n the r e a c t o r . The low gas v e l o c i t y zones a t the top and bottom would r e s u l t i n dense phase f l u i d i z a t i o n and the high v e l o c i t y p y r o l y s i s zone would be a d i l u t e phase f l u i d i z e d bed. This concept, shown i n Figure 7, has been q u a l i t a t i v e l y i n ­ v e s t i g a t e d i n the c o l d model f l u i d i z e d bed. R

Results I n i t i a l f l u i d i z a t i o n t e s t s were conducted w i t h 1.2 cm s t y r o foam cubes i n the bed. This was chosen as the s o l i d phase be­ cause i t was r e a d i l y f l u i d i z e d and the l a r g e p a r t i c l e s were easy to observe. The p r e l i m i n a r y r e s u l t s a r e q u a l i t a t i v e , but do i n ­ d i c a t e that the concept of a three-stage f l u i d i z e d bed i s f e a s i ­ ble. To conduct each t e s t , a batch of s o l i d s was loaded i n the bed t o a predetermined s t a t i c bed h e i g h t . The a i r flow was then g r a d u a l l y increased u n t i l the bed was f u l l y f l u i d i z e d and p a r t i ­ c l e s began e n t e r i n g the h i g h v e l o c i t y s e c t i o n of the equipment. This flow was maintained u n t i l the lower and upper s e c t i o n s of the bed reached a s t e a d y - s t a t e s o l i d s content determined by v i s u a l o b s e r v a t i o n . Figure 8 shows the s t e a d y - s t a t e s o l i d s d i s t r i b u t i o n i n the system that developed from a 53.3 cm s t a t i c bed h e i g h t . Figure 8 i s an e x c e l l e n t example of the staged, f l u i d i z e d bed concept. The lower s e c t i o n o f the bed behaves as a dense phase, g a s - s o l i d f l u i d i z e d bed. As can be seen i n the p i c t u r e , the high v e l o c i t y , center p o r t i o n of the bed contains very few s o l i d p a r t i c l e s . The upper p o r t i o n of the bed i s the most i n t e r ­ e s t i n g . The s o l i d s content i s very s i m i l a r to a dense phase

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

WASTES

A N D RESIDUES

LOW VELOCITY DENSE PHASE (SPOUTING BED) GOOD HEAT TRANSFER

ο

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Three-stagefluidizedbed concept

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

16.

BECK

E T A L .

Pyrolysis of Biomass

Figure 8. Steady-state solids distribution for styrofoam showing three distinct fluidization regimes

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f l u i d i z e d bed, but there i s no d i s t r i b u t o r p l a t e h e l p i n g to supp o r t the bed. In f a c t , t h i s upper p o r t i o n behaves more l i k e a spouting bed w i t h s o l i d s moving downward near the w a l l and being e n t r a i n e d i n the center of the bed. This behavior i s l i k e a spouted bed except t h a t no d r a f t tube, downcomer or d i s t r i b u t o r p l a t e i s present. This proves that a dense phase, f l u i d i z e d bed can be supported by a high v e l o c i t y a i r stream. The geometrical c o n f i g u r a t i o n of the expanded top s e c t i o n of the apparatus could have c o n t r i b u t e d to t h i s spouting bed e f f e c t . However i n a more c o n v e n t i o n a l type design, the t r a n s i t i o n s e c t i o n between the lower s e c t i o n and upper, disengaging s e c t i o n of a f l u i d i z e d bed w i l l have sloped w a l l s . This would mean that a spouted bed could be e s t a b l i s h e d even i n a f l u i d i z e d bed of s t a n dard design. F o l l o w i n g the styrofoam experiments, manure was placed i n the bed. The p a r t i c l e s were much s m a l l e r (<2 mm) which created many problems. The f i r s broad p a r t i c l e s i z e range p a r t i c l e s were e l u t r i a t e d and the l a r g e p a r t i c l e s d i d not f l u i d i z e . This i s a p o t e n t i a l problem which must be considered when designing f l u i d i z e d bed p y r o l y s i s r e a c t o r s . To a l l e v i a t e t h i s problem, the manure was screened to narrow p a r t i c l e s i z e f r a c t i o n s and a d d i t i o n a l t e s t s were conducted on a p a r t i c l e s i z e of -0.50 mm + 0.25 mm. The manure e x h i b i t e d the same staged, f l u i d i z e d bed behavior as the styrofoam w i t h an a d d i t i o n a l phenomenon observed. The spouted bed formed i n the upper s e c t i o n of the r e a c t o r , but some of the manure r e c i r c u l a t i n g downward on the w a l l s cont i n u e d to f a l l down the w a l l s of the h i g h v e l o c i t y s e c t i o n and returned to the lower s e c t i o n of the bed. This can be seen i n Figure 9. I t i s f e l t t h a t the manure was able to f a l l down the w a l l s due to the low gas v e l o c i t y i n the boundary l a y e r . This was not observed w i t h the styrofoam which i s probably because the p a r t i c l e s were too l a r g e and were exposed to higher v e l o c i t i e s on the outer edge of the boundary l a y e r . These manure experiments demo n s t r a t e d that there was s o l i d c i r c u l a t i o n from the bottom bed to the top and back to the bottom. This i s very c r i t i c a l to the SGFM r e a c t o r because s o l i d s are fed to the top of the r e a c t o r and must be able to reach the lower s e c t i o n of the r e a c t o r i n order to r e a c t . The c o l d bed s t u d i e s i n d i c a t e that t h i s i s p o s s i b l e . Conclusions & D i s c u s s i o n The r e s u l t s reported i n t h i s paper have been q u a l i t a t i v e i n nature. When the p r o j e c t was i n i t i a t e d , there was no way to r e l i a b l y p r e d i c t the bed behavior and the f i r s t step i n the study was to determine i f the concept of a v a r i a b l e v e l o c i t y , staged, f l u i d i z e d bed was f e a s i b l e . Consequently, the experiments were designed to o b t a i n a maximum of q u a l i t a t i v e i n f o r m a t i o n i n order

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

16.

BECK

ET

AL.

Pyrolysis of Biomass

Figure 9. Steady-state solids distribution for manure showing manure from upper bed "raining" down into lower bed

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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to plan the second phase of the project which i s quantitative i n nature. The conclusions of the f i r s t phase are as follows: 1. The three-stage (dense phase, dilute phase, dense phase) f l u i d i z e d bed concept i s feasible. 2. Solid p a r t i c l e s can f a l l through the high velocity por­ tion of the SGFM p i l o t plant reactor and thus reach the lower section of the f l u i d i z e d bed. The study of variable velocity, f l u i d i z e d beds i s continuing at Texas Tech University. The goal of this study i s to obtain s u f f i c i e n t information to develop the correlations required to scale-up pyrolysis reactors with some degree of r e l i a b i l i t y . This w i l l reduce the time required to develop a process from the lab­ oratory scale to a commercial plant. Acknowledgements The authors wish to thank the U. S. Department of Energy for supporting this work under Contract No. EY-76-S-04-3779. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8.

9.

Feldman, H. F., Wen, C. Υ., Simons, W. Η., Yavorsky, P. Μ., "Supplemental Pipeline Gas from Coal by the Hydrane Process," 71st National AIChE Meeting, Dallas, February 20-23, 1972. Jewell, W. J . , Editor, "Energy Agriculture and Waste Manage­ ment," 373-396, Ann Arbor Science, Ann Arbor, 1975. Haynes, W. P., Forney, A. J . , "The Synthane Process," Clean Fuels from Coal Symposium II, Chicago, June 23-27, 1975. Bodle, W. Ν., Vyas, K. C., "Clean Fuels From Coal-Introduction to Modern Processes," Clean Fuels From Coal Symposium II, Chicago, June 23-27, 1975. Engler, C. R., Walawender, W. P., Fan, L. T., "Synthesis Gas From Manure, Conceptual Design Study and Economic Analysis," Environ. S c i . & Tech., (1975), 13(9), 1152-1157. Halligan, J. E., Sweazy, R. Μ., "Thermochemical Evaluation of Animal Waste Conversion Processes," 72nd National AIChE Meet­ ing, St. Louis, May 21-24, 1972. Halligan, J. E., Herzog, K. L., Parker, H. W., "Synthesis Gas From Bovine Wastes," Ind. Eng. Chem., Proc. Des. Dev., (1975), 14(1), 64-69. Huffman, W. J . , Halligan, J. Ε., Peterson, R. L., de l a Garza, Ε., "Ammonia Synthesis Gas and Petrochemicals From Cattle Feedlot Manure," Symposium on Clean Fuels from Biomass," Orlando, January 27, 1977. Peterson, R. L., "A P i l o t Plant Study of Synthesis Intermed­ iates From Feedlot Waste," Masters Thesis, Texas Tech Uni­ versity, Lubbock (1975).

MARCH 3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

17 E P A ' s R & D P r o g r a m i n P y r o l y t i c Conversion of Wastes to F u e l Products GEORGE L. HUFFMAN and WALTER W. LIBERICK, JR. U. S. Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, OH 45268

Only in recent years have we become properly concerned about the f i n a l disposition or utilization of the large volumes of wastes generated by our everyday a c t i v i t i e s . Many environmental insults have resulted from improper disposal; for example, the obvious insults from open burning, leaching from dumps, and improper discharges to surface and groundwaters. These insults l e d to passage of the 1965 S o l i d Waste Disposal Act and the subsequent Amendments that mandate the Federal Government (EPA) to support research, development, and demonstrations and applications of new and improved technologies for processing and recovering materials and energy from s o l i d wastes. This mandate, coupled with recent concerns about our dwindling energy supply, has focused our attent i o n on the utilization of these wastes as sources of energy. Although recovering energy-from-waste has been practiced i n Europe for many years, this technology has not been pursued in the United States u n t i l recently. Many options to utilize these wastes as an energy resource have been investigated. Options have varied from combustion i n waterwall incinerators, to c o - f i r i n g of prepared wastes with coal i n utility b o i l e r s , to the thermochemical conversion of wastes into usable fuel products.

0-8412-0434-9/78/47-076-323$09.00/0 This chapter not subject to U.S. copyright. Published 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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This paper focuses on c u r r e n t e f f o r t s being supported by EPA to develop new concepts o f thermochemical (or p y r o l y t i c ) convers i o n o f wastes t o energy. More s p e c i f i c a l l y , t h i s paper discusses f o u r EPA p r o j e c t s t h a t are i n v e s t i g a t i n g b a s i c r e a c t i o n k i n e t i c s and ways t o enhance the y i e l d and q u a l i t y o f p y r o l y s i s end-products; these are: •

S u b p i l o t - s c a l e p y r o l y s i s of mixed wastes t o f u e l gas, f u e l o i l and char i n a 500 l b / h o u r f l u i d i z e d bed r e a c t o r (by the Energy Resources Company, ERCO);

•

Bench-scale steam g a s i f i c a t i o n o f a g r i c u l t u r a l and f e e d l o t wastes t o energy products (by P r i n c e t o n University);

•

Laboratory t e s t s on a process t h a t converts a troublesome waste and other product s a l t c a t a l y t i c technique (by the U n i v e r s i t y o f Tennessee); and,

•

I n t e g r a t e d bench-scale development o f a nonc a t a l y t i c process t h a t transforms p y r o l y s i s off-gases i n t o polymer g a s o l i n e ( r e s e a r c h b e i n g conducted v i a Interagency Agreement w i t h China Lake, C a l i f o r n i a , Naval Weapons Center).

S u b n i l o t - S c a l e Conversion o f Mixed Wastes t o F u e l (ERCO) The o b j e c t i v e s o f t h i s p r o j e c t are t o i n v e s t i g a t e the k i n e t i c s o f the p y r o l y s i s o f s o l i d wastes and t o develop a data base t h a t w i l l a l l o w design engineers t o s e l e c t p y r o l y s i s system operat i n g c o n d i t i o n s f o r commercial systems t h a t w i l l p r o v i d e a p r e determined mix o f f u e l product y i e l d s . To accomplish these object i v e s , t h i s p r o j e c t i s d i v i d e d i n t o the f o l l o w i n g t a s k s : 1.

P l a n and Experimental Study. The i n i t i a l t a s k i n c l u d e d a l i t e r a t u r e study t o determine the p h y s i c a l and chemical p r o p e r t i e s of the wastes t o be u t i l i z e d and t o determine the r e a c t o r v a r i ables which would have a s i g n i f i c a n t i n f l u e n c e on product q u a l i t y and y i e l d s . From t h i s study, the p r o j e c t team determined the experiments t o be run and the data necessary t o model the r e s u l t s . This t a s k i n c l u d e d r e a c t o r and support equipment design.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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2.

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Equipment Procurement, Assembly and Check-Out. This task i n c l u d e d the f a b r i c a t i o n of the t e s t apparatus (a f l u i d i z e d bed r e a c t o r ) and i t s check-out. During t h i s t a s k , s e v e r a l m o d i f i c a t i o n s were made t o i n c r e a s e system operating r e l i a b i l i t y .

3.

Subpilot Plant Testing. This task i n c l u d e d a c q u i s i t i o n o f data on s e v e r a l waste components, some of which were taken during t e s t s run i n d i f f e r e n t o p e r a t i n g modes. These data were comp i l e d f o r use i n modeling the t e s t r e s u l t s of t h i s project.

k.

Development of the P r e d i c t i o n Model Based on th c a l model was developed to p r e d i c t the y i e l d s t o be expected from a known waste composition under v a r i o u s pyr o l y s i s o p e r a t i n g c o n d i t i o n s . The t h e o r e t i c a l model was then v e r i f i e d w i t h the experimental data.

5.

Chemical Conversion. In a d d i t i o n t o the v a r i a b l e p y r o l y s i s o p e r a t i n g modes i n v e s t i g a t e d , an e f f o r t was undertaken t o l o o k at p a r t i a l o x i d a t i o n and steam g a s i f i c a t i o n e f f e c t s .

6.

Product C h a r a c t e r i z a t i o n . D e t a i l e d product c h a r a c t e r i z a t i o n t e s t s were conducted on samples of the o i l and char products.

7.

Trace Metals I n v e s t i g a t i o n . A m a t e r i a l balance f o r t r a c e metals was completed f o r s e v e r a l of the runs on d i f f e r e n t waste components.

An extensive l i t e r a t u r e search was conducted t o : ( l ) p h y s i c a l l y and chemically c h a r a c t e r i z e s o l i d waste; (2) determine the parameters which would a f f e c t p y r o l y s i s y i e l d s ; and (3) determine the t h e o r e t i c a l k i n e t i c s t o be used i n modeling the r e a c t i o n s . The l i t e r a t u r e search provided the data contained i n Table I . These average chemical compositions of m u n i c i p a l s o l i d waste were s e l e c t e d as a b a s e - l i n e f o r t h i s study {l). A c t u a l analyses were of course used i n the m a t e r i a l balances throughout the work.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Pyrolytic Conversion of Wastes

327

To d e t e r m i n e t h e p a r a m e t e r s t h a t w o u l d a f f e c t p r o d u c t y i e l d s , s e v e r a l e f f o r t s r e p o r t e d i n t h e l i t e r a t u r e were r e v i e w e d (l). T a b l e I I i s a summary o f t h i s w o r k . I t was d e t e r m i n e d t h a t r e a c t i o n temperature i s the dominant parameter i n most s y s t e m s . A l s o , u l t i m a t e y i e l d s seem t o v a r y f r o m one t y p e o f r e a c t o r t o another ( f i x e d b e d , e n t r a i n e d f l o w , and f l u i d i z e d b e d ) . Another c o n c l u s i o n was t h a t s e c o n d a r y r e a c t i o n s ( r e a c t i o n s o c c u r r i n g i n t h e gas p h a s e f o l l o w i n g i n i t i a l p y r o l y s i s ) h a v e a s i g n i f i c a n t i m p a c t on f i n a l y i e l d s . I t i s suspected t h a t the secondary r e a c t i o n s t a k e t h e form o f a f u r t h e r breakdown o f t h e t a r s i n t o c h a r and g a s e s . A f t e r a n a l y s i s o f t h e r e s u l t s o f p r e v i o u s w o r k , i t was d e t e r m i n e d t h a t t h e f l u i d i z e d b e d r e a c t o r w o u l d be i d e a l f o r s t u d y i n g c h e m i c a l k i n e t i c s b e c a u s e i t s e x c e l l e n t h e a t and mass t r a n s f e r c h a r a c t e r i s t i c s r e s u l t i n good t e m p e r a t u r e u n i f o r m i t y . The c o n c l u s i o n t h a t s e c o n d a r y r e a c t i o n s w e r e i m p o r t a n t i n u l t i m a t e y i e l d s forced the i n v e s t i g a t o r t ERCO ( a n d t h e i co-worker t MIT) t o i n c l u d e t h e s e r e a c t i o n B a s e d on t h e l i t e r a t u r e s e a r c h , i t was d e t e r m i n e d t h a t t h e r e a c t i o n k i n e t i c s s h o u l d be c o n t r o l l e d b y t h e c o m p o s i t i o n o f t h e s o l i d waste and i t s t e m p e r a t u r e / t i m e h i s t o r y w h i l e u n d e r g o i n g pyrolysis. The w a s t e s i n v e s t i g a t e d i n t h e ERCO p r o j e c t a r e shown i n T a b l e s I I I and I V . The i n d e p e n d e n t v a r i a b l e s f o r t e s t i n g a r e shown i n T a b l e V . The r e s u l t i n g t e s t p l a n s f o r p y r o l y s i s a r e shown i n T a b l e s V I a n d V I I . The t e s t p l a n f o r p a r t i a l o x i d a t i o n , s t e a m g a s i f i c a t i o n a n d c a t a l y t i c e f f e c t s r u n s i s shown i n T a b l e VIII. T a b l e I X summarizes t e s t s conducted d u r i n g t h e i n i t i a l p h a s e o f t h i s p r o j e c t (l_). The e x p e r i m e n t s were c o n d u c t e d i n two r e a c t o r s ( a b a t c h t y p e a n d a f l u i d i z e d b e d ) . The b a t c h r e a c t o r ( s e e F i g u r e l ) was u t i l i zed e a r l y i n the program t o : ( l ) p e r f o r m p r e l i m i n a r y r u n s on d i f f e r e n t wastes t o i d e n t i f y p o t e n t i a l problems b e f o r e assembling the f l u i d bed; (2) d e v e l o p s a m p l i n g a n d a n a l y s i s t e c h n i q u e s ; (3) compare d a t a w i t h v a l u e s r e p o r t e d i n t h e l i t e r a t u r e ; a n d (k) meas u r e v a r y i n g p r o d u c t y i e l d s (l_). A f t e r g a i n i n g experience w i t h the b a t c h u n i t , a f l u i d i z e d bed r e a c t o r was c o n s t r u c t e d ( s e e F i g u r e 2 ) . The r e a c t o r was d e s i g n e d t o accommodate 200 K g / h r o f f e e d w a s t e m a t e r i a l s w i t h t h e c a p a b i l i t y t o measure t h o s e p a r a m e t e r s n e c e s s a r y t o d e t e r m i n e r e a c t i o n kinetics. The s y s t e m c o n s i s t e d o f : ( l ) a h e a t s o u r c e ; (2) an i n e r t gas s u p p l y t o m a i n t a i n an o x y g e n - f r e e e n v i r o n m e n t ; (3) i n e r t f l u i d i z i n g m e d i a ; {k) a gas d i s t r i b u t i o n a n d b e d s u p p o r t s y s t e m ; (5) a c o n t i n u o u s f e e d e r ; (6) t h e p r o d u c t c o l l e c t i o n s y s t e m ; (7) a gas c l e a n u p a n d a f t e r - b u r n i n g f a c i l i t y ; (8) s a m p l i n g a n d a n a l y s i s e q u i p m e n t ; and (9) s a f e t y a n d c o n t r o l e q u i p m e n t . Figure 3 shows a s c h e m a t i c o f t h e f l u i d m e d i a s e c t i o n o f t h e r e a c t o r .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978. Sewage Sludge Tires

Folks, et a l . ( 8 )

Firestone ( 9 )

Retort

Retort

Itoh, et a l . (12.)

Imperial College (13)

West Virginia Univ. (lU)

Combustion Gas

Hot Nitrogen Gas

Combustion Gas

MSW, Sawdust, Sludge and Others

MSW Sawdust, Cellulose, Sucrose

Univ. of Calif. (Berkeley)(11) Wood, MSW

Freefall

Fluidized Bed

Garrett Research Corp. (10)

Recirculation of Hot Char

Rice Hulls, Manure, Bark, Straw

MSW

Retort

Entrained Flow

Georgia Inst, of Tech. ( 5 , 6 ) Bark, Sawdust

MSW

Cities Service Oil Co. (h)

U. S. Bureau of Mines (T.)

MSW

Hoffman and Fit ζ (J3)

Retort

Retort

Retort

Newspaper

MATERIAL

Kaiser and Friedman (g)

INVESTIGATOR

Retort

Fixed Bed

REACTOR TYPE

SUMMARY OF PREVIOUS WORK

TABLE II

1280 F to 1520"F

ii50°C to 850°C

900°F to 1800°F

800°F to 1000°F

900°F to 1T00°F

1100°F to l8k0°F

900°F to 1T00°F

Ambient to 150C°F

900°F, 1200°F, 1500°F, 1T00°F

Ambient to 1500 F

TEMPERATURE RANG

3

17.

H U F F M A N

AND

Pywlytic Conversion of Wastes

LD3ERICK

329

TABLE III SEGREGATED WASTES

WASTE COMPONENT

MATERIAL

SOURCE

Wood

Pine Sawdust

Local Dealer

Wood

Pine Woodchips (1/2-1 in. long)

Local Dealer

Agri cultural Wastes

Ground Corncobs (20-hO mesh)

Local Dealer

Agricultural Wastes

Manure

Local Dealer

Paper

Punches (l/8-ΐΛ in. ) from Notebook Manufacture

Courtesy of National Blank Book Co. , Springfield, Mass.

Textiles

Shredded Cotton Cuttings

Local Dealer

Plastics

Polyethylene Beads (1/8 χ 3/8 in.)

Local Dealer

Tires

Metal and Fabric Free Shredded Tires—2 Sizes (-10 mesh and -h+10 mesh)

Solid Conversion Systems, Inc. Burlington, N.J.

Waste Oil

Automobile Crankcase Oil

Local Dealer

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

35/65

Corncobs + Manure

N a t i o n a l Center f o r Resource Recovery, Washington, D. C., g l a s s and metal f r e e , p e l l e t i z e d Sewage treatment p l a n t , C i t y o f Marlborough, Mass.

M u n i c i p a l S o l i d Waste

Sewage Sludge

SOURCES

50/50

Paper + P l a s t i c s

ACTUAL WASTES

50/50

APPROXIMATE COMPOSITION

Paper + Sawdust

SYNTHETIC MIXTURE

WASTE MIXTURES

TABLE IV

Ο

8

17.

H U F F M A N

A N D

LiBERiCK

Pyrolytic Conversion of Wastes

331

TABLE V IΚDEPENDENT VARIABLES

VARIABLE

NUMBER OF VALUES

BATCH REACTOR Feed Material Compositio Reactor Temperature

3

Heating Rate

3

Particle Size

2

TOTAL POSSIBLE COMBINATIONS

32k

FLUIDIZED BED REACTOR Feed Material Composition

18

Reactor Temperature

3

Liquid Recycle

2

Fluidization Velocities

2

Particle Size

2

Bed Height

2

TOTAL POSSIBLE COMBINATIONS TOTAL COMBINATIONS FOR TWO REACTORS

86U 1,188

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

tv

tioa I

Eei KeJ £ht Lev High

165 Tf6

6

733

P

700^ 900/

[όδΟ

6501

710/

580

,u

v

550 560t 4Ïcr 9oo/

500

) 375

|\ΐ63 ^5π> ιοο;

U70

U85

535

I185

185

550

j

780

7001 750

853

750

770

525

555

ί*10

600

6l0_

780

770

600

605

830

795

frOO U20 760

760 787

6><5

1/^90 1550

725

692

ί510 (730

801 800

7Γ0

732

t

657

760

789 770

710

670

680

753

Σ>2 mi

728

COVERAGE

825\ 370/

800

705

χιρ_\ 800

600

530

Î610

Γ

6 »5

635.

76Ο

mx

/ \550

725.

SÏ0

l

880/ 760 >if>7 7>i0 705_ 5^0 ~ 600 j Û10

872

550 750

675

610 770

753

575

560

8?5 750

705

b21 2bl 2ii£. (520

Taper

Suvdutît

Tenr>?ratnres ( Man. i i o l i d M i x t u r e 1: Waste 1 P a c e r and Sawdust

PARAMETERS AND TESTS ON MATERIALS REQUIRING COMPLETE

|/633,^6U0__.671)

Feed Rate Low Kighl

TABLE VI TEST PLAN

§21/

672 \

331

923/

ml

0

ούΟ

655

Coo

— —

ÎI2

g s

co CO to

17.

H U F F M A N A N D LiBERiCK

333

Pyrolytic Conversion of Wastes

TABLE V I I

TEST

PLAN

S C R E E N I N G RUNS USING A D D I T I O N A L

MATERIALS

FLUIDIZATIONS MATERIAL

Manure

Low High

Tires,

Small

Low High

Tires,

Large

Low High

Wood C h i p s

{1%

Moisture)

Fixed

UT5 723

6l8

809

8ÔT

921

500 ii5i

h^h 630

810

930

5I46 517

6ll* 595

727

932"

610

671

825

866

7^0

8U7

856

916

550

92c

935 Wood C h i p s

(17%

Moisture)

Fixed

57-1

Wood C h i p s

{2k%

Moisture)

Fixed

Ghi

Textiles

Fixed

Plastics

Fixed

863

781

6ho

690

706

770

800

Mixt.

H2 ( P a p e r

+

Textiles)

Fixed

Mixt.

/Π ( P a p e r

+

Plastics)

Fixed

620

650

715

760

765

Mixt.

f/U ( C o r n c o b s

Fixed

550

675

757

875

2ÏL

Mixt.

#5

(Paper

+

+ Manure) Plastics

Fixed

+ Sawdust) Mun.

Solid

Sludge

H2

Waste

tl2

Fixed Fixed

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

877

334

SOLID WASTES AND RESIDUES

VAULT vu τ ΉΜΤ

PLAN

PARTIAL OXTDAITOK, ST?AM CAST Π CATION AND CATALYTIC iSFFJSCT RIKS

PALTIAL OXIDATION Run Conditions Oxygen/Feed Ratio Material

Low Vrlr.h

Low

m

Β Δ

ν

Δ

Low

High

ν

0

Kif-)

V

Δ

Ο

•

Δ

668

0

V

0

Τ 30

•

Δ

6k0

0

Τ

0

790

ο

Α

650

7

•

—

827

•

Λ

1*23

•

•

0

8Ô5 —

Sawdust ϋ Δ

• Δ *

0 0 A

• A V

ν

·

•

88ο

670

Pape r •

Δ

Τ

t

a Δ τ

t

1*76

lits. 1*73

705

833

STEAM GASIFICATION AT 35-50/0 STEAM CONTENT Material

Oxygen

Content

Sawdust

•

τ

è

•

g

ν

Paper

•

τ

à

•

g

γ

Teed Rate Low High a

a

9 a υ

?

1

7 α

τ i γ

α

ν

ά

Temperatures, °c φ Q γ

556 5 3 8 667 61*3 6 0 0 5<J5 8υ·'* 790 7 i 5 ]

Wi 6^0

5.15 680 7 J 0 53 0

"j'iii ΪΖι ^I9_ ÏÎ2P-

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

705

720

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Waste O i l

Ten metals each

l6 3^5

16 3^5

Combustion

(a)

23

23

20

Oxidation

Partial

ication

20

2k

Pyrolysis

Steam G a s i -

2β2

262

Conditions

2k

Material and Energy Balances

Number of Runs

63

2

8

*+3

2

2

k

0

11

3

35

Char Analysis

39

Oil Analysis

SUMMARY OF TESTS

TABLE IX

26

0

3

0

9

lk

Trace Metal Samples ^

336

SOLID WASTES AND RESIDUES

Ο u i ο

K5

.tdO

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 2. Energy resources pilot plant for fluidized bed pyrolysis of solid waste

CONGUSTOR FLAME

TENSOR

PRCBÇS

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

SX

Ο

4 <*>

I

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

17.

H U F F M A N

AND

LD3ERICK

Pyrolytic Conversion of Wastes

339

The o p e r a t i n g procedure f o r each t e s t i s r e l a t i v e l y simple. The f l u i d i z a t i o n v e l o c i t y i s c o n t r o l l e d by r e g u l a t i n g the f l o w o f n a t u r a l gas and a i r t o the gas burner. Waste m a t e r i a l i s f e d i n t o the bed w i t h a screw feeder. The sampling apparatus i s operat e d d u r i n g s t e a d y - s t a t e c o n d i t i o n s f o r 2 or 3 minutes. At the end o f each run, excess a i r i s i n t r o d u c e d t o the r e a c t o r t o burn out the char accumulated i n the bed. The data r e s u l t i n g from a run are f e d i n t o a computer program f o r appropriate conversions and manipulation r e s u l t i n g i n a t y p i c a l p r i n t o u t and i s e v e n t u a l l y r e p o r t e d i n t a b u l a t i o n s s i m i l a r to t h a t i l l u s t r a t e d i n Table X (l). The major c o n c l u s i o n to be d e r i v e d from t h i s p r o j e c t concerns the i n f l u e n c e of secondary r e a c t i o n s on product y i e l d s i n the pyr o l y s i s mode. As an example w i t h sawdust the secondary r e a c t i o n s begin t o dominate because of the secondar the primary decomposition i s f u r t h e r broken down i n t o a d d i t i o n a l gas and char. This c o n c l u s i o n a p p l i e s t o a l l the feedstocks t e s t e d i n some 3^5 data runs and shows the predominant e f f e c t s of r e a c t i o n temperature on product y i e l d s . Concurrent w i t h the ERCO p r o j e c t , EPA i s a l s o s u p p o r t i n g a s m a l l e f f o r t t o evaluate the f e a s i b i l i t y o f multi-waste g a s i f i c a t i o n . This e v a l u a t i o n i s being done by Monsanto Research Corporat i o n . One o f the systems being analyzed i s the proposed ERCO system. Based on very p r e l i m i n a r y i n f o r m a t i o n , the economics of the ERCO-like system appear t o be a t t r a c t i v e . An a n a l y s i s was done f o r three d i f f e r e n t s i z e s o f systems. Tables XI and X I I i l l u s t r a t e the p r o j e c t e d economics (15). The P y r o l y s i s of Organic Wastes i n I n e r t and Reactive Steam Atmospheres ( P r i n c e t o n U n i v e r s i t y ) Over the past y e a r , the Environmental P r o t e c t i o n Agency has a l s o been supporting an i n v e s t i g a t i o n at P r i n c e t o n U n i v e r s i t y t o determine o p t i m a l g a s i f i c a t i o n c o n d i t i o n s f o r producing usable f u e l products by the p y r o l y t i c conversion of s o l i d waste i n a r e a c t i v e steam atmosphere. This p r o j e c t i s complementary t o our Energy Resources Corporation (ERCO) p r o j e c t . P r i n c e t o n , t o o , i s i n v e s t i g a t i n g the chemical phenomenon t a k i n g p l a c e i n a steam environment, but t h e i r bench-scale research w i l l l o o k at the i n f l u ence o f e l e v a t e d pressures on r e a c t o r y i e l d s as w e l l . The research at P r i n c e t o n has shown t h a t the steam g a s i f i c a t i o n o f organic wastes i s a two-step process. At r e l a t i v e l y low temperatures (300° t o i+00°C), organic wastes l o s e most of t h e i r v o l a t i l e matter content by p y r o l y s i s r e a c t i o n s . Because of the low temperatures at which p y r o l y s i s o c c u r s , the r a t e s of these

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

h5 hi

133

112

69

97

137

lk3

139

50

^7 1+8

1+8

463 570

700

730

550

500

560

670

670

710

900

i+80

500

555

680

700

68

66

75

71

69 6k

67

72

83

87

78

77

65

73

81+

63

Kg/hr

kk

0.1

0.61+

0.63

0.1+9

0.52

0.51

0.37 0.1+1

0.36

0.30

0.29 0.28

0.30

0.2

0.3

0.7

0.1

0.1

0.1

0.1

0.1

0.2

0.1

0.1

0.5

0.3

0.38

0.2 0.2

0.27

1+8

2 2

19.5

19.k

19.5 19.0

19.5

19.5

19.5

19.5

19.5

19.5 19.6

19.1

19. k

19.5

19.5

19.6

H 0*

GASES

o%

0.31

0.2k

1+1

(m/s)

VEL.

RATE

°C

FUJIDIZING

FLUID.

FEED

TEMP.

FILE

NO.

60 59

0.6

22

20

20

67

1+6

k3

35

15 20

18

61

kk

23

17

GAS

7 8

25 20

35

5

16

20

19

20

36

36

9 6

18

22

OIL

9

8

18

16

15

9

10

12

13

20

13

16

9

15

2.1

27

CHAR

YIELD,

O F SAWDUST

Χ

MATERIAL

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

0.6

HT.

BED

PYROLYSIS

TABLE

%

25 21+

39 39

29

20

28

25

31+

39

36

29

25

32

37

35

WATER

77

1+1+

19

10

11

81

61+

63

33

18

6

16

91

W

19

8

GAS

15

12

hi 38

67

8

30

38

36

38

68

68

10

17

35

1+1

OIL

11+

12

25 28

21+

13

16

19

20

33

20

25

ll+

2k

31+

1+3

CHAR

ENERGY Y I E L D ,

%

H U F F M A N

A N D LD3ERICK

Pyrolytic Conversion of Wastes

341

TABLE XI. CAPITAL AND OPERATING COST REQUIREMENTS, ERCO PROCESS (15.) Procès• sing capacity, tons/day 2250 1500 750

System ERCO

9.9M il il

Total capital investment, $ Capital cost per yearly ton, $ Unit operating cost, $/ton

16

17-2M a li|

2U.1M 3 6

3 8

a

a iU

Values are identical du process scale-up. ^Includes no byproduct credits. M = millions of dollars.

TABLE XII. FERROUS METALS, ALUMINUM, FUEL GAS, & DROP CHARGE REVENUES IN $/T0N, ERCO PROCESS (15) a

Gas_price, $/M Btu

Drop

0

charge, $/t'on 5 10

15-

ERCO 1.50

12.0

17.0

22.0

27.0

1.75

13.1

18.1

23.1

28.1

1Π.3

19.3

25.0

30.0

2.00

b

a

Revenues from ferrous metals and aluminum assumed at $5.01/ton.

kprice currently charged by some u t i l i t i e s to industrial natural gas consumers.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

a

342

SOLID WASTES AND RESIDUES

r e a c t i o n s are not a f f e c t e d by the presence o f steam as a g a s i f i c a ­ t i o n medium (ΐβ). A t h i g h e r temperatures (500° t o 700°C) , the vo­ l a t i l e p y r o l y s i s products r e a c t w i t h the steam producing a medium B t u s y n t h e s i s gas composed p r i m a r i l y o f CO, Η , CO^, CH^, C^H^, and h i g h e r hydrocarbons. During the past y e a r , research a t P r i n c e t o n has focused on experimental s t u d i e s and mathematical modeling o f the k i n e t i c r a t e s o f the primary p y r o l y s i s r e a c t i o n s and the secondary gas phase r e a c t i o n s . The Dupont 990 Thermal A n a l y s i s System has been used t o mea­ sure the primary p y r o l y s i s r a t e s o f r e a c t i o n o f c e l l u l o s e , news­ p r i n t from The New York Times and The Wall Street Journal, hard­ wood and s o f t wood sawdust, and cow manure at nominal h e a t i n g rates o f 5°, 10°, 20°, 50°, and 100°C/minute. F i g u r e h gives a weight l o s s vs. temperature curve f o r cow manure f o r these f i v e heating r a t e s . Curves such as these can be s i m u l a t e d using the r a t e equation: n

i g . = k(V* - V ) (1) dt where k - A exp(-E/RT). I n Eq. ( l ) , the v o l a t i l e weight f r a c t i o n of the organic m a t e r i a l i s V*, t h e r a t e o f weight l o s s (on a mass f r a c t i o n b a s i s ) i s dV/dt, Κ i s the temperature dependent r a t e constant, Τ i s the temperature, R the u n i v e r s a l gas constant, A the frequency f a c t o r , Ε the a c t i v a t i o n energy, and η the r e a c t i o n order. F i g u r e 5 p o r t r a y s a t y p i c a l f i t o f the mathematical model given by Eq. ( l ) w i t h the experimental r e s u l t s f o r a newsprint p y r o l y s i s experiment ( l j ) . Gas phase r e a c t i o n s o f the v o l a t i l e p y r o l y s i s products w i t h steam are being s t u d i e d i n a t u b u l a r quartz p l u g flow r e a c t o r designed and f a b r i c a t e d at P r i n c e t o n . A schematic o f the e x p e r i ­ mental l a y o u t i s given i n F i g u r e 6. A s m a l l (O.lg) sample o f organic m a t e r i a l i s r a p i d l y heated (100 t o 200°C/min.) and pyrol y z e d i n the p y r o l y s i s r e a c t o r . Evolved v o l a t i l e s are c a r r i e d by the steam flow i n t o the preheated, i s o t h e r m a l gas phase r e a c t o r , where they r e a c t w i t h the steam t o produce s y n t h e s i s gas. Rates o f p r o d u c t i o n o f 13 gaseous species are measured at 15 d i f f e r e n t times during the experiment u s i n g the 6 p o r t and 3^ port v a l v e s combined w i t h a Hewlett Packard 583*+a Gas Chromatograph. R e s u l t s o f these experiments w i l l be used t o develop mathe­ m a t i c a l models d e s c r i b i n g the e f f e c t s o f feedstock composition, h e a t i n g r a t e , f i n a l temperature, and residence time on the gase­ ous product composition. Although P r i n c e t o n s modeling e f f o r t i s not yet complete, data obtained from t h e i r r e a c t o r has already demonstrated the c r i t i c a l e f f e c t o f temperature on the gas phase chemistry. The r e s u l t s o f three experiments w i t h c e l l u l o s e u s i n g i d e n t i c a l o p e r a t i n g c o n d i t i o n s except a v a r i a t i o n i n the tempera­ t u r e o f the gas phase r e a c t o r are summarized as f o l l o w s (17): 1

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

H U F F M A N

AND

LiBERicK

Pyrolytic Conversion of Wastes

343

Figure 4. Cow manure in nitrogen—weight loss vs. temperature: +, 5.360; · 10.960; X, 22.930; *, 49.360; TRI, 138.400.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

344

SOLID

WASTES

AND

RESIDUES

DflTE-TIΜ Ε 0530771200

h- ο

530771200

co

UJ 2

0.00005 100.00

200.00

300.00

TEMPERATURE

Figure 5.

400.00

5C2.C0

IN DEGREES

BOO.DO

700.00

B00.00

CENTIGRADE

New York Times in nitrogen—weight loss vs. temperature (theoretical vs. experimental): +, 22.100; ·, 22.100,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

N

2

I Furnace 2

Gas Purge

E:

Temperature Controlers

Movable Pyrolysis Furnace

Gas Purge

HP Terminal

Liquid Ni trogen

Gas Phase Reactor Furnace

Furnace 3

Condenser

HP 5834a Gas Chroma tographl

Bag

Schematic of the Princeton University tubular quartz reactor experiment

8 Thermocouple Leads

Steam Superheater

Furnace 1

Steam Generator

Parastaltic Pump

Figure 6.

πϋΐίΞΓ

IT}

Chart Recorder

Purge

Ro tome te

TracerCarrier

34 Port Valve

-Vent

6 Port Valve

346

SOLID WASTES AND

Gas Phase Reactor Temperature lus) 500 600 TOO

Volume o f Combustible Gas Produced (cc/g) 9^ 318 821+

RESIDUES

C a l o r i f i c Value r of Gas ( l 0 B t u / M e t r i c Ton), b

1.0 6.0 15.0 U

I n the experiment w i t h the gas phase furnace at 700 C, l e s s than the 2% o f the sample weight was converted t o condensible products ( t a r s ) and the gas had a h e a t i n g value o f about 500 B t u / s c f . These r e s u l t s i n d i c a t e t h a t 90% o f t h e weight o f o r g a n i c wastes can be converted i n t o a medium-Btu gas w i t h a h e a t i n g value e s s e n t i a l l y equal t o t h a t of the feedstock. The remaining 10% o f the waste weight i s a char i n the form o f a c t i v a t e d carbon. Princeton i s usin c a l models t o design a organic wastes. T h e i r design a c t i v i t i e s w i l l be p u b l i s h e d at a f u t u r e meeting of the I n t e r n a t i o n a l S o l a r Energy S o c i e t y . Economic p r o j e c t i o n s o f P r i n c e t o n ' s g a s i f i c a t i o n r e a c t o r system were p r e sented at the I n t e r n a t i o n a l Symposium on A l t e r n a t i v e Energy Sources h e l d i n B a r c e l o n a , Spain ( l 8 ) . Chemical Reclamation of Scrap Rubber ( U n i v e r s i t y o f Tennessee) For the past y e a r , the Environmental P r o t e c t i o n Agency has been s u p p o r t i n g a p r o j e c t at the U n i v e r s i t y of Tennessee t o i n v e s t i g a t e and v e r i f y the t e c h n i c a l f e a s i b i l i t y o f a concept t o recover f u e l products and carbon b l a c k from scrap rubber. The proposed concept, shown s c h e m a t i c a l l y i n F i g u r e 7, u t i l i z e s molten s a l t as the heat s i n k t o d r i v e the p y r o l y s i s r e a c t i o n . Some major p r o j e c t e d advantages o f t h i s concept are: ( l ) i t s a b i l i t y t o accept whole t i r e s r a t h e r than shredded t i r e s ; and (2) the p h y s i c a l i n t e g r i t y o f the recovered carbon b l a c k should make i t d e s i r a b l e f o r re-use i n the rubber i n d u s t r y . The i n v e s t i g a t o r s at the U n i v e r s i t y are now b e g i n n i n g t o conduct experimental runs w i t h the bench-scale u n i t (see F i g u r e 8) (19). The apparatus c o n s i s t s o f molten s a l t r e s e r v o i r s , a f l o w through r e a c t i o n chamber, necessary p i p i n g and f l o w c o n t r o l , and necessary sampling p o r t s w i t h r e q u i r e d r e c o r d i n g equipment. The molten s a l t ( z i n c c h l o r i d e ) i s u t i l i z e d at U00°C. The c a p a c i t y o f the r e s e r v o i r allows molten s a l t f l o w d u r a t i o n s i n the range of 10 t o 30 minutes. This i s w e l l w i t h i n the r e a c t i o n times e s t i mated t o be necessary to complete the p y r o l y s i s r e a c t i o n i n the b a t c h - f e d r e a c t o r . S t a r t - u p t e s t s on the system are being conducted at t h i s t i m e , consequently, no data are a v a i l a b l e as y e t .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

H U F F M A N

AND

LiBERiCK

Pyrolytic Conversion of Wastes

GAS AND OIL "^PRODUCT TREATMENT

GASEOUS HYDROCARBONS RUBBER INPUT "

REACTO

SOLIDS

•

-

CARBON BLACK

ZnC1 SALT 2

RECYCLE LOOP Figure 7. The University of Tennessee project—laboratory tests on a tire pyrolysis process that uses a molten salt catalytic technique

American Chemical Society Library 1155 16th St. N. W. Washington, D. Jones, C. 20036 In Solid Wastes and Residues; J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

WASTES

A N D RESIDUES

Figure 8. Bench-scale tire pyrolyzer at the University of Tennessee

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

17.

H U F F M A N

AND

LiBERiCK

Pyrolytic Conversion of Wastes

349

The data t o be obtained i n these t e s t s can h o p e f u l l y be u t i l i z e d i n making d e c i s i o n s concerning the u n i t processes necessary f o r any l a r g e r - s c a l e system (e.g., feedstock p r e p a r a t i o n , materials handling, materials separation, e t c . ) . I t i s f e l t that the most f a v o r a b l e s e t t i n g f o r such a p l a n t would be next to e x i s t i n g ethylene p l a n t s . This would a l l o w the s a l e of a t i r e - d e r i v e d gas and l i q u i d feedstock t o the ethylene p l a n t and t h i s supplemental feed would have no s i g n i f i c a n t impact on the p l a n t capac i t y . Assuming 175 m i l l i o n t i r e s are scrapped i n the U n i t e d States annually and t h a t 85$ o f these could reach Molten S a l t Process P l a n t s , i t i s p r o j e c t e d t h a t the gross annual revenues f o r the products could range from $22^.2 t o $501.6 m i l l i o n (gases $2.3 t o $37.6 m i l l i o n , l i q u i d s $57-9 t o $380.0 m i l l i o n , and s o l i d s $164.0 m i l l i o n ) . No o p e r a t i n g and c a p i t a l cost estimates are p r o j e c t e d at t h i s time so t h a t no estimate of net p r o f i t i s available. Additional k t h i projec w i l l includ l economic a n a l y s i s (19) Conversion o f S o l i d Waste t o Polymer Gasoline .China Lake)

(The Navy at

Over the past three y e a r s , EPA has been supporting a p r o j e c t conducted by the Naval Weapons Center, China Lake, C a l i f o r n i a , to i n v e s t i g a t e and develop a system capable o f converting s o l i d wastes (organic m a t e r i a l s ) i n t o s y n t h e t i c petroleum products ( p r i m a r i l y g a s o l i n e and o i l ) . This e f f o r t has r e s u l t e d i n a bench-scale system capable o f t e c h n i c a l l y accomplishing the s t a t e d conversion. The system u t i l i z e s p y r o l y s i s t o g a s i f y the s o l i d waste t o a gas t h a t i s r i c h i n r e a c t i v e , unsaturated hydrocarbons. These gases are compressed and p u r i f i e d . The p u r i f i e d hydrocarbons are then t h e r m a l l y polymerized t o form the l a r g e r molecules of g a s o l i n e and o i l . The crude polymer product has been shown t o be 90$ g a s o l i n e w i t h an unleaded ASTM motor octane r a t i n g o f 90. A f t e r simple d i s t i l l a t i o n , t h i s product can be s t o r e d , handled and u t i l i z e d l i k e any petroleum-derived g a s o l i n e . The process i s p r o j e c t e d t o produce 0.21 l i t e r o f s y n t h e t i c petroleum product per Kg of s o l i d waste (minimum o f 70$ organic c o n t e n t ) , which t r a n s l a t e s t o about 50 g a l l o n s of g a s o l i n e per ton o f s o l i d waste (20). Experiments t o date have been conducted i n v a r i o u s p y r o l y s i s r e a c t o r c o n f i g u r a t i o n s . Figure 9 d e p i c t s one of the most recent c o n f i g u r a t i o n s u t i l i z e d t o g a s i f y the s o l i d waste feedstocks. An i n i t i a l a n a l y s i s of s e v e r a l feedstocks was made t o determine i n i t i a l composition (see Table X I I I ) . For ease of h a n d l i n g and f e e d i n g , ECO I I " f u e l " has been u t i l i z e d as the p r i n c i p a l feedstock. U t i l i z a t i o n of ECO I I f u e l i n p y r o l y s i s t e s t s r e s u l t e d i n data o f the type i l l u s t r a t e d i n Table XIV. Many runs o f t h i s type have been done and have r e s u l t e d i n the o p t i m i z a t i o n o f a p y r o l y s i s system t h a t produces the maximum q u a n t i t i e s o f g a s o l i n e

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

350

SOLID WASTES AND RESIDUES

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

12.0

12.0

h3.3

0

Altoona, PA

Dry cellulose

IBM computer cards

+12% ash

0.68

9.73

0.91

ECO II (drum T-51)

3.8

12.U6

1.69

ECO II (composite NWC)

ECO II (drum T-UT)

Ash

11.87

Weight % moisture

3.82

Sample

1*3.21

39.11

1*7.6

1*9.6**

6Λ6

5.U

1+9.1+5

1*3.1*5

32.9

0.023

...

... 0.10

0.3

l.ol*

0.98

0.73

s

1.2

0.22

6.1*0 32.38 6.0

0.27

...

...

...

Ν

6.20 31*. 22

0

H

C

...

...

... ... O.080

270ym

l88um

...

0.59

0.37

0.70

Cl

Particle size, average

Pyrolysis Feed Analysis ( 2 0 )

Weight % , dry basis

TABLE XIII.

(9,550)

3,920 (7,056)

3,677 ( 6 , 6 1 8 )

U.7U8 (8,51+6)

5,306

1*,726 (8,507)

(8,558)

Dry basis heat of combustion HHV, cal/g (Btu/lb)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

.h

850

815

0.10

815

0.10

790

0.15

760

Pyrolysis Te:.'p. ,

0.10

0.01+

.'•'Dis t a r e

2

16

a

H

a

100

'At le £

2

ko

100

100

a

CO

3

0.30

0.25

0.39

0.89

0.55

M /kdry feed

2

0.2

0.2

0.?

0.1

0.1

2

C H

TABLE XTV.

7.8

U.3

7.'»

11.6

8.2

2 U

Ho. U i s s u s p e c t e d

0.5

0.2

0.7

l.U

1.8

0.1

0.1

0.3

8.8

h.l

8.6

10.8

2

o.u

co 6.7

8

0.5

u

t-C H

0.2

O.U

0.6

0.2

0.3

8.8

U.l

6.6

6.7

2.3

t o have h a d a l e a k o f p y r o l y s i s gases s i n c e t h e gaseous p r o d u c t weights a r e a l l v e r y low.

0.6

0.2

0.6

1.0

1.0

2»6

18.6

15.0

15.7

23.7

21*. 0

Char

9.2

5.1

9.3

15.0

12.0

Irvjse runs were made w i t h ECO I I (drum T-51) as f e e d . A f t e r r u n No. 1, t h e r e were two t u r n s o f 3/U-inch t u b i n g (110 i n c h e s ) p r i o r t o the f e e d e n t e r i n g t h e c y c l o n e s e p a r a t o r . The l o s s o f c a r r i e r gas i s thought t o have o c c u r r e d i n a l l runs.

r;-:

c

Grams n e t p r o d u c t 100 grams d r y f e e d

P y r o l y s i s Summary (£0)

Trilr; c a r r i e r gas was a p o o r l y mixed 20$ H , h0% CO, U0/» CH^ m i x t u r e .

11/1V75

11/12/75

2

3

11/5/75

1

Zate

o r r,n

8.2

6.5

7.0

6.3

7.5

2 u

9.3

7.5

8.U

7.5

9.9

Vol m e % i n g r o s s gases

17.

H U F F M A N

AND

LiBERiCK

353

Pyrolytic Conversion of Wastes

p r e c u r s o r s (most n o t a b l y , e t h y l e n e ) . I t has been determined t h a t i n order t o maximize hydrocarbon p r o d u c t i o n during p y r o l y s i s i t i s necessary t o : ( l ) have a v e r y r a p i d h e a t i n g r a t e t o temperat u r e s i n the range o f 700°C; (2) a p y r o l y s i s environment which keeps the f r e e r a d i c a l p a r t i a l pressure low t o prevent these r a d i c a l s from r e a c t i n g t o form t a r s ; and (3) a short residence time t o prevent the formation of secondary r e a c t i o n products. A c h i e v i n g these c o n d i t i o n s r e s u l t s i n a gas stream w i t h the a p p r o p r i ate hydrocarbon content necessary f o r g a s o l i n e p o l y m e r i z a t i o n . A f t e r being generated i n the p y r o l y s i s o p e r a t i o n , the gases are compressed, s t o r e d , and then p u r i f i e d . The p u r i f i c a t i o n s y s tem c o n s i s t s o f a water scrubber which removes carbon d i o x i d e along w i t h w a t e r - s o l u b l e organics ( a c e t i c a c i d , e t c . ) and a hydrocarbon absorber and s t r i p p e r system which u t i l i z e s r e c i r c u l a t i n g benzene. The p u r i f i c a t i o syste take th o f f - g a s e fro th p y r o l y s i s system and provide benzene s t r i p p e r to th g a s o l i n p o l y m e r i z a t i o The p o l y m e r i z a t i o n u n i t i s designed t o operate at temperat u r e ranges o f 750° t o 950°F and at pressures of 700 t o 1000 p s i . These ranges are c u r r e n t l y employed commercially i n t h i s type of process i n the petroleum i n d u s t r y . Table XV shows experimental r e s u l t s from e a r l y t e s t s u t i l i z i n g pure ethylene as a feedstock

(20).

An i n t e g r a t e d system ( i . e . , p y r o l y z e r o f f - g a s f e e d i n g the p u r i f i c a t i o n / p o l y m e r i z a t i o n s e c t i o n ) has been b u i l t and i s c u r r e n t l y being debugged. I t i s planned t h a t a d d i t i o n a l experiment a l data w i l l be a v a i l a b l e i n the near f u t u r e . A p r e l i m i n a r y economic a n a l y s i s o f t h i s system was completed by the p r o j e c t s t a f f at China Lake. M u n i c i p a l f i n a n c i n g was assumed w i t h a 25 y e a r , 6.5 percent i n t e r e s t , a m o r t i z a t i o n c o s t . The s o l i d waste was assumed to c o n t a i n 60.2 percent o r g a n i c mat e r i a l , 27 percent m o i s t u r e , 5.5 percent i r o n , 0.5 percent a l u minum, 6.6 percent g l a s s and 0.2 percent o t h e r m a t e r i a l s . I t was assumed t h a t h6 g a l l o n s o f l i q u i d product would be produced per ton of s o l i d waste and t h a t the per c a p i t a g e n e r a t i on o f s o l i d waste was 5 pounds per day. F i g u r e 10 i n d i c a t e s the net operat i n g costs per ton of s o l i d waste as a f u n c t i o n o f p o p u l a t i o n w i t h negative c o s t s i n d i c a t i n g a p r o f i t (20). A more complete economic a n a l y s i s i s c u r r e n t l y being done by an independent, " t h i r d - p a r t y " c o n t r a c t o r o f the EPA, Dow Chemical. Dow s a n a l y s i s w i l l be based upon t h e i r experience w i t h the u n i t processes necessary t o accomplish the r e q u i r e d conversions and a c t u a l exp e r i m e n t a l data b e i n g generated on the l a t e s t i n t e g r a t e d , benchs c a l e u n i t at China Lake. ?

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

9/25/75

9/26/75

5

6

775

765

975

850

60

2C0

26Ο

26Ο

11/1-/75

820

12/3/75

1>

260

15/5/75

18

875

81.0

2β0

11/13/75

17

26θ

835

26Ο

U/18/75

11/13/75

->

:i/5/75

>:

-*

810

il/5/75

800

1,015

1,015

895

970

1,01*5

1,035

785

785

765

515

815

890

2β0

260

11Λ/75

:o

600

725

515

765

1,065

1,015

90 0.91

7

1.0U

30 k5

0.83

?

0.91

0.38

0.89

1.22

0.80

1.16

0.02

0.30

U60

150/600

500

150

600/300

600

0

600

600

600

600

600/1,200

0

0

0 0

?

Gas o u t , s t d cc/min

?

r/min ?

9.5

9

7.7

9 Λ

ν conv.

? 39.7

31.3

U3.8

51.8

hh.6

79.0

85.5

7.5

23.3

15.8

U6.h

(TheoretJ

uu.o

?

21.1

?

20.2

1*2.7

11.7

1*2.0

0

9

?

?

?

% conv. to g a s o l i n e

89.Ο

38.0

56.Ο

72.0

17.3

8.U ?

32.5

15.7

1*3.3

8.0

38.5

0

1.8

25.8

Ul.O

lh.2

c.c/hr

Gasoline production,

17.7

3.0

5.3

5.7

h.5

?

75.6

8.0

?

η

Residence time, mi

P o l y m e r i z a t i o n T e s t Data Summary ( 2 0 ) Ethylene input,

h5

h5

^5

120

65

90

U5

90

90

270

120

120

135

ππ η

TABLE XV. Run Coil p r e s s u r e , time, psia

30

26θ

10/30/75

10/2-/75

3

7

910

875

80

80

8U0

80

*

9/23/75

9/15/75

3

85Ο

Op

Bath rature,

δο

crr.

Coil vol ·ατ.'.·, J

Leak

Plugged, leak

Plugged

Remarks

17.

H U F F M A N

A N D LD3ERICK

Pyrôlytic Conversion of Wastes

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

356

SOLID

WASTES

AND

RESIDUES

Conclusion f

The p r o j e c t s d i s c u s s e d i n t h i s paper are examples o f EPA s current e f f o r t s i n the area o f b a s i c and a p p l i e d r e s e a r c h , and o f t h e i r i n v e s t i g a t i o n o f new and i n n o v a t i v e concepts , as they r e l a t e t o t h e thermochemical o r p y r o l y t i c conversion o f s o l i d waste i n t o usable f u e l s . These e f f o r t s have the prime o b j e c t i v e o f p r o v i d i n g process developers and p o t e n t i a l technology users w i t h i n f o r m a t i o n necessary t o make sound t e c h n i c a l assessments o f these concepts. Other more advanced waste p y r o l y s i s concepts supported by EPA that are c u r r e n t l y underway i n c l u d e the development of a prototype mobile p y r o l y s i s system f o r a g r i c u l t u r a l / i n d u s t r i a l wastes (co-funded w i t h S t a t e o f C a l i f o r n i a S o l i d Waste Management Board) and demonstration p r o j e c t s such as t h e Occident a l Process at E l Cajon, C a l i f o r n i a , and Monsanto-Landgard P r o cess at B a l t i m o r e , Maryland I t i s intended t h a t the data gener ated by our more b a s i c h e r e i n ) w i l l l e a d t o ne t h i s EPA r e s e a r c h w i l l provide s o l i d waste d i s p o s e r s w i t h new, e n v i r o n m e n t a l l y , t e c h n i c a l l y , economically f e a s i b l e o p t i o n s f o r converting t h e i r wastes i n t o b e n e f i c i a l f u e l products.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

17.

HUFFMAN AND

LiBERiCK

Pyrolytic Conversion of Wastes

357

Literature Cited 1.

Howard, J. Β . , R. H. Stephens, et al, "Subpilot-Scale Pyroly­ tic Conversion of Mixed Wastes to F u e l , " Draft Interim Report for EPA Contract No. 68-03-2340, September, 1977.

2.

Kaiser, E. R . , and S. G. Friedman. "The Pyrolysis of Refuse Components," Combustion, 31-36, 1968.

3.

Hoffman, D. R . , "Pyrolysis of S o l i d Municipal Wastes," Con­ tract No. EP-00266 (TIS PB-222-015), San Diego Utilities Department, Report to U. S. Environmental Protection Agency, July 1973.

4.

Rosen, B. H., R. G. Evans, P. C a r a b e l l i , and R. B. Zaborowski, "Economic Evaluation of a Commercial Size Refuse Pyroly sis Plant." In: Proceeding Waste Management Conference, y , of S o l i d Waste Management, March 1970. pp. 393-405.

5.

Knight, J. Α., J . W. Tatom, M. D. Bowen, A. R. Colcord, and L. W. Elston, "Pyrolytic Conversion of A g r i c u l t u r a l Wastes to Fuels," Paper No. 74-5017, 1974 Annual Meeting, American So­ ciety of A g r i c u l t u r a l Engineers, S t i l l w a t e r , Oklahoma, June 1974.

6.

Tatom, J. W., J. A. Knight, A. R. Colcord, L . W. E l s t o n , and P. H. Har-Oz, "A Mobile P y r o l y t i c System for Conversion of Agricultural and Forestry Wastes into Clean Fuels," Georgia Tech Engineering Experiment Station, Atlanta, Georgia.

7.

Walters, J. G . , and D. E. Wolfson, "Conversion of Municipal and Industrial Refuse into Useful Materials by Pyrolyzers," RI 7428, U. S. Bureau of Mines, August 1970.

8.

Folks, Ν. E., R. A. Lockwood, B. A. Eichenberger, F. R. Bowerman, and Κ. Y. Chen, "Pyrolysis as Means of Sewage Sludge Disposal," J . of the Environmental Engineering D i v i s i o n , Pro­ ceedings of the American Society of Civil Engineers, V o l . 101, No. EE4, August 1975.

9.

Beckman, J. A. and J. R. Laman, "Destructive Distillation of T i r e s , " In: Proceedings of National Industrial S o l i d Wastes Management Conference, University of Houston and Bureau of S o l i d Waste Management, March 24-26, 1970. pp. 388-392.

10.

Occidental Research Corporation (formerly Garrett Research and Engineering Company, I n c . ) , Draft Report to U. S. EPA on Grant S-801202 covering work completed as of March 1975.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

358

SOLID WASTES AND RESIDUES

11.

McFarland, J . M., D. L. Brink, C. R. Glassey, S. A. K l e i n , P. H. McGauhey and C. G. Goleuke, "Comprehensive Studies of Solid Wastes Management," VCB-ENG-2907, USPHS-2RD1EC 00260-05, Final Report to EPA on Standard Service Agreement, Sanitary Engineering Research Laboratory, College of Engineering and School of Public Health, University of C a l i f o r n i a , Berkeley, SERL Report No. 72-3.

12.

Itoh, K, "The Pyrolysis Equipment with Two Circulating Flui­ dized Beds," Kankyo Sozo 6:42-46, 1974. As reviewed by T. Y. Chen, E. Kojima, W. P. Walamender and L. T. Fan, "A Review of Waste Gasification Technology Development i n Japan," Systems Institute Report. Kansas State University, Manhattan, Kansas, Department of Chemical Engineering, 1975.

13.

Barooah, J . Μ., and V D t i o n of Some Carbonaceou 55:116-120, A p r i l 1976

14.

Burton, R. S., III, and R. C. Bailie, " F l u i d Bed Pyrolysis of Solid Waste Materials," Combustion, 1974.

15.

Monsanto Research Corporation, unpublished progress reports on EPA Contract No. 68-03-2550 e n t i t l e d "Process Evaluation: Multi-Waste Gasification," 1977.

16.

Antal, M. J . , H. L. Friedman, and F. E. Rogers, "Kinetic Rates of Cellulose Pyrolysis i n Nitrogen and Steam," Fall Meeting, Eastern Section, the Combustion I n s t i t u t e , Hartford, Conn., November 1977.

17.

Princeton University, unpublished First Annual Progress Report to EPA on Grant No. R804836-01-0, February, 1978.

18.

Antal, M. J., "The Conversion of Urban Wastes," International Symposium on Alternative Energy Sources, Barcelona, Spain, October 1977.

19.

University of Tennessee, unpublished progress reports on EPA Grant No. R804321 e n t i t l e d "Chemical Reclamation of Scrap Rubber," 1977.

20.

Naval Weapons Center, China Lake, C a l i f o r n i a , unpublished progress reports on EPA Interagency Agreement No. D7-0781 e n t i t l e d "Conversion of S o l i d Waste to Polymer Gasoline," 1975-1977.

MARCH 3,

Long "Rates of Thermal Decomposi

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

18 T h e Syngas Process HERMAN F. FELDMANN Battelle-Columbus Laboratories, 505 King Ave., Columbus, OH 43201 JOSEPH K. ADLERSTEIN Syngas, Inc., Suite 1260 East, First National Center, Oklahoma City, OK 73102 The Syngas Process development have been published.(1,2 i s to present additional information on calculated material b a l ances for an integrated process, projected oxygen consumption, as w e l l as to present preliminary projections of the economics of producing an intermediate-Btu gas by the Syngas Process. B r i e f l y , the Syngas Process, Figure 1, consists of a two-stage reactor system with a zone between the two stages where separation of metal and glass from organic char is accomplished by e l u t r i a t i n g the r e l a t i v e l y l i g h t carbonaceous char from the dense metal and glass phase. In the first stage, incoming s o l i d waste contacts a hydrogen-rich synthesis gas generated from the gasification of residual carbonaceous char. In this first stage, the incoming waste is devolatilized and hydrogasified and the residual char is then gasified to produce the hot synthesis gas. Our experimental studies suggest that the product d i s t r i b u t i o n (namely CH4 versus organic liquids) is influenced by the hydrogen/ s o l i d waste feed r a t i o more than by the hydrogen p a r t i a l pressure and, therefore, there i s considerable flexibility i n the selection of the system pressure. Overall Material Balances Overall material balances for the Syngas Process utilize experimental data generated i n our small process development unit (PDU) to determine the key factors influencing carbon conversion and product d i s t r i b u t i o n i n the first stage methane production reactor (MPR). The char produced in the MPR is then fed to a second stage entrained g a s i f i e r where it is completely gasified with oxygen and steam. Because the char fed to the second stage is mostly devolatilized, the performance of the entrained gasifiers was simulated using published data for entrained systems feeding coal or coal char.(3) Figure 2 shows a material balance calculated on the above basis. By separation of the MPR from the gasification zone, the 0-8412-0434-9/78/47-076-359$05.00/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

Shredded Waste

Product Gas Lock Hopper (Drying) System

Quench

W

Recovery

Ash Slurry to Settling

Methane Production Reactor Hot Syn Gas Char + Metal/Glass -

Char-Metal/Glass Separation Zone

Char Gasifierl

Char Oxygen

|Metal/Glass Water Quench Metal/Glass

-

Figure 1.

txH

Simplified block diagram—Syngas reactor system

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

18.

F E L D M A N

AND

ADLERSTEIN

The

StjngdS

361

PrOCeSS

Shredded S o l i d Waste

Product Gas

70 l b s "Organics" 30 l b s Moisture —

Constituent H

=

2

CH4

Methane Production Reactor

CO C02

C H C6H 2

6

= = = = =

Amount (lb-moles)

1.134 0.612 0.567 1.394 0.034 0.011

Metal/Glass 17.8 l b s Char

Steam 23.8 l b s -

Steam Oxygen [Gasification

2700 F Synthesis Gas C o n s t i t u e n t - Amount (lb-moles) CO H C0 H2O 2

2

= = = =

0.795 0.512 0.243 0.899 2.449

Oxygen 13.24 l b s

Total

Ash Figure 2.

Material balance for the Syngas process

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

362

SOLID

WASTES

AND

RESIDUES

f o l l o w i n g key advantages c r i t i c a l to the o v e r a l l process economics are achieved. (1) M e t a l and g l a s s can be recovered i n a r e s a l a b l e s t a t e without b e i n g slagged or without r e q u i r i n g a complex f r o n t end s e p a r a t i o n and c l e a n i n g system. I f the metal and g l a s s entered the g a s i f i e r , f u s i o n and p o s s i b l e o x i d a t i o n of metal would r e s u l t . (2) Methane y i e l d s are i n c r e a s e d because the methane i s prevented from e n t e r i n g the g a s i f i e r where i t would be reformed or combusted. (3) Oxygen requirements are minimized because only the char from the MPR, a s m a l l f r a c t i o n of the o r i g i n a l s o l i d feed, i s g a s i f i e d and because the char e n t e r s the g a s i f i e r a t a temperature of 1000 to 1200 F. In a d d i t i o n , the o v e r a l l process heat requirements are minimized because of the h i g h methan type of stage As mentioned, the balances shown i n F i g u r e 2 are based upon experimental data generated i n the PDU s t u d y i n g the MPR. Ci) For the steam/oxygen g a s i f i e r , experimental data presented by Von F r e d e r s d o r f f and E l l i o t t Q ) f o r an IGT e n t r a i n e d g a s i f i e r was used. A comparison of the IGT e n t r a i n e d g a s i f i e r data w i t h that from o t h e r e n t r a i n e d g a s i f i e r s i n d i c a t e d e x c e l l e n t c o n s i s t e n c y and i t i s t h e r e f o r e f e l t that the r e s u l t s are t y p i c a l . Because the char from the MPR enters the g a s i f i e r at 1000 to 1200 F, oxygen consumption should be l e s s than t h a t c a l c u l a t e d based on the above g a s i f i e r t e s t s because the c o a l used i n these t e s t s was not preheated. I t should be s t r e s s e d t h a t experimental data f o r an e n t r a i n e d g a s i f i e r was used and the g a s i f i e r was s m a l l compared to commercial s i z e . Thus, these r e s u l t s i n c l u d e the e f f e c t s of heat l o s s e s and c o n s e r v a t i v e l y represent the performance of a l a r g e r system. A f t e r c o o l i n g and quenching, the product gas from the Syngas r e a c t o r w i l l have the approximate composition and the y i e l d shown below. F u e l Gas Y i e l d and Composition from Syngas Reactor System F u e l Gas Composition, volume percent H2 = 30.3 CH4 = 16.4 Heating Value = 329 Btu/SCF CO =15.1 Y i e l d , SCF/lb-dry " o r g a n i c s " =20.3 37.3 CO2 C H 0.9 100.0 2

6

The major u n c e r t a i n t y i n the above gas composition i s the d i s t r i b u t i o n between H2, CO and CO2 which i s determined by the water gas s h i f t . The composition above i s based on assuming an H2/CO r a t i o approximately 2 because of the h i g h steam content of

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

18.

FELDMAN

AND

ADLERSTEiN

The Syngas Process

363

the gas. However, the Purox process r e p o r t s an H2/CO r a t i o s l i g h t l y l e s s than 1 i n s p i t e of h i g h steam c o n c e n t r a t i o n s i n the gas. A lower v a l u e f o r the H2/CO r a t i o w i l l i n c r e a s e the h e a t i n g value of the d r i e d product gas because the l e s s water-gas s h i f t o c c u r r i n g the lower the CO2 content of the gas and the h i g h e r the H2O content which i s removed by d r y i n g w h i l e CO2 i s not. Because oxygen consumption i s important i n determining gas p r o d u c t i o n c o s t s , the oxygen consumption p r o j e c t e d f o r the Syngas Process should be compared w i t h those r e p o r t e d f o r other g a s i f i c a t i o n processes. A comparison between p r o j e c t e d oxygen consumption f o r the Syngas P r o c e s s , the Purox P r o c e s s , and the L u r g i Process (for c o a l g a s i f i c a t i o n ) i s given i n Table 1. TABLE 1. OXYGEN REQUIREMENTS PER MILLION BTU OF RAW PRODUCT GAS

Process Syngas Purox(l>2) Lurgi(3)

(tons oxygen/MM B t u , raw product

gas)

0.014 0.029 0.019 (For a high-oxygen western c o a l )

(1) S o l i d Waste D i s p o s a l Resource Recovery, Brochure P u b l i s h e d by Union C a r b i d e s Environmental Systems. (2) Anderson, J.E., "The Oxygen Refuse Converter A System f o r Producing F u e l Gas, O i l , Molten M e t a l and S l a g from Refuse, 1974 N a t i o n a l I n c i n e r a t o r Conference, Miami, F l o r i d a (May 12-14, 1974). (3) E l g i n , D.C. and H. R. P e r k s , " R e s u l t s of American Coals i n L u r g i Pressure G a s i f i c a t i o n P l a n t at W e s t f i e l d , S c o t l a n d " , Proceedings of the S i x t h S y n t h e t i c P i p e l i n e Gas Symposium, pp 247-265, American Gas A s s o c i a t i o n , Chicago, I l l i n o i s (October 1974). 1

Thus, the Syngas Process o f f e r s the p o t e n t i a l of a very subs t a n t i a l r e d u c t i o n i n oxygen requirements over the Purox P r o c e s s , which employs a f i x e d - b e d s l a g g i n g g a s i f i e r . Reactor Design Concepts. E x p e r i m e n t a l l y , we operated the MPR as both a f r e e - f a l l and moving-bed r e a c t o r . However, these t e s t s e s t a b l i s h e d t h a t the conversion r a t e was l i m i t e d o n l y by heat t r a n s f e r t o the p a r t i c l e and t h a t the conversion l e v e l was d e t e r mined by the H2 "seen" by the waste. Thus, there i s c o n s i d e r a b l e f l e x i b i l i t y i n r e a c t o r design. For the purposes of e s t i m a t i n g r e a c t o r throughput, a f r e e f a l l system i s assumed. One major advantage of a f r e e - f a l l MPR i s t h a t there should be no problems w i t h b r i d g i n g of s o l i d waste. (For example, we were able t o operate even our 2.8 i n c h I.D. MPR

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

364

SOLID

WASTES

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RESIDUES

i n the f r e e - f a l l mode without b r i d g i n g problems.) The presence of metal and g l a s s should provide a d d i t i o n a l impetus f o r m a i n t a i n i n g f l o w through the f r e e - f a l l zone. Another advantage of the f r e e - f a l l system i s the i n c r e a s e d u t i l i z a t i o n of s e n s i b l e heat i n the product gases, which a l l o w feeding higher moisture content waste. Crude measurements of the f r e e - f a l l v e l o c i t y of shredded paper, which w i l l have the lowest t e r m i n a l v e l o c i t y of any s i g n i f i c a n t f r a c t i o n of s o l i d waste, i n d i c a t e that i t s f r e e - f a l l v e l o c i t y i s about 4 f t / s e c . Operating t h i s system i n the f r e e - f a l l mode a t a gas v e l o c i t y l i m i t e d t o 3 f t / s e c a l l o w s a gas p r o d u c t i o n r a t e i n the MPR e q u i v a l e n t t o about 7 m i l l i o n B t u / h r - f t 2 (1100 l b s dry organic material/hr-ft2). This s p e c i f i c Btu p r o d u c t i o n r a t e i s q u i t e h i g h compared t o most c o a l g a s i f i c a t i o n processes e s p e c i a l l y f i x e d or moving-bed systems. For example, th Galusha c o a l g a s i f i e r ha B t u / f t 2 - h r . d) A f t e r the char/metal/glass mixture f a l l s through the f r e e f a l l zone, the char w i l l be s t r i p p e d from the metal/glass mixture by a stream of steam and the char w i l l be blown i n t o an e n t r a i n e d g a s i f i e r i n t o which oxygen i s i n j e c t e d t o complete g a s i f i c a t i o n of the char. Before a d e t a i l e d design of the system i s p o s s i b l e , a d d i t i o n a l data w i l l have t o be generated. For example, i t w i l l be necessary to make more accurate measurements of entrainment v e l o c i t i e s of v a r i o u s s o l i d waste c o n s t i t u e n t s a f t e r primary shredding. I n a d d i t i o n , the d r y i n g r a t e s of s o l i d waste w i l l have to be d e t e r mined i n order to evaluate whether p r e d r y i n g i s necessary of i f f l a s h d r y i n g can be c a r r i e d out i n the top of the MPR i t s e l f . I n t e g r a t i o n of the MPR and g a s i f i e r should provide no t e c h n i c a l problem but w i l l r e q u i r e more d e t a i l e d engineering a n a l y s i s . P r e l i m i n a r y Cost Estimates. Because we do not y e t have a d e t a i l e d r e a c t o r d e s i g n , i t i s i m p o s s i b l e t o do a d e t a i l e d cost estimate. By u t i l i z i n g p u b l i s h e d c o s t s f o r s i m i l a r c o a l g a s i f i c a t i o n processes, i t i s p o s s i b l e t o determine a reasonable estimate of what gas c o s t s are l i k e l y t o be. U n f o r t u n a t e l y , most of the p u b l i s h e d cost data on c o a l g a s i f i c a t i o n i s f o r base load p i p e l i n e gas p l a n t s which a r e f a r l a r g e r than i s p r a c t i c a l f o r a p l a n t u t i l i z i n g m u n i c i p a l s o l i d wastes. However, the C u l b e r t s o n , Kasper d i s c u s s i o n on the economics of s m a l l c o a l gasifiers(£) provides a means of examining cost f e a s i b i l i t y f o r p l a n t s i z e s of g r e a t e s t i n t e r e s t i n g a s i f y i n g m u n i c i p a l s o l i d waste as w e l l as other biomass feeds. Economic f e a s i b i l i t y was evaluated f o r a c a t t l e manure feeds t o c k i n a d d i t i o n to the s o l i d waste. Chemically, both a r e s i m i l a r except that c a t t l e manure i s probably more r e a c t i v e , more homogeneous, and, i n many areas, a v a i l a b l e a t a p r i c e that makes i t s

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

18.

FELDMAN

A N D

The Syngas Process

ADLERSTEiN

365

u t i l i z a t i o n f o r conversion t o gas economically a t t r a c t i v e . The cost p r o j e c t i o n s a r e the u t i l i z a t i o n of commercially a v a i l a b l e Wellman-Galusha a g i t a t o r type g a s i f i e r s 10 f e e t i n diameter. Though the Syngas system i s d i f f e r e n t than the WellmanGalushaR g a s i f i e r , the higher throughput p o s s i b l e w i t h the Syngas system makes the u t i l i z a t i o n of Wellman-Galusha cost data reasonable and probably c o n s e r v a t i v e . Included i n the t o t a l c a p i t a l requirements are: (1) Estimated i n s t a l l e d cost of both o n - s i t e and off-site facilities, (2) P r o j e c t contingency of 15 percent of f a c i l i t y c o s t , (3) I n i t i a l charge o f c a t a l y s i s and chemicals, (4) Paid-up r o y a l t i e s , (5) Allowance f o r funds used during c o n s t r u c t i o n , (6) Start-up c o s t s and (7) Working c a p i t a l The estimated gas f o l l o w i n g assumptions o u t l i n e d i n the ERDA Gas Cost G u i d e l i n e s . (1) 20-year p r o j e c t d u r a t i o n . (2) 20-year s t r a i g h t - l i n e d e p r e c i a t i o n on p l a n t investment, allowance f o r funds used d u r i n g c o n s t r u c t i o n , and c a p i t a l i z e d p o r t i o n of start-up costs. (3) Debt/equity r a t i o o f 75/25. (4) 15 percent r e t u r n on e q u i t y . (5) 9 percent i n t e r e s t on debt. (6) F e d e r a l income tax r a t e o f 48 percent. The major s e c t i o n s o f the p l a n t a r e : (1) Coal storage and h a n d l i n g , (2) Coal g a s i f i c a t i o n , (3) P a r t i c u l a t e removal, (4) Tar removal and d i s p o s a l , (5) Water treatment and d i s p o s a l , (6) Ash d i s p o s a l , and (7) Oxygen p l a n t ( f o r the intermediate-Btu gas case). The only m o d i f i c a t i o n s o f the above cost p r o j e c t i o n s that were made were the f o l l o w i n g . (1) The e x t e r n a l oxygen consumption f o r producing intermediate-Btu gas from manure was adjusted f o r the d i f f e r e n c e i n oxygen consumption between s o l i d waste and c o a l . (2) The d i f f e r e n c e i n h e a t i n g value between manure and s o l i d waste and c o a l was compensated f o r i n determining the manure requirements t o produce an e q u i v a l e n t B t u output. (3) The c o a l cost c o n t r i b u t i o n was i s o l a t e d t o a l l o w separate assessment o f the e f f e c t of f u e l c o s t . R

R

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

366

SOLID

WASTES

AND

RESIDUES

Manure Case. No advantage was taken of the much h i g h e r react i v i t y of s o l i d waste and manure compared to c o a l , the f a c t that these feeds do not agglomerate, the h i g h e r ethane y i e l d s r e s u l t ing from t h e i r p y r o l y s i s and the h i g h e r throughputs a n t i c i p a t e d f o r the Syngas Reactor System. Thus, these cost p r o j e c t i o n s summarized below should be regarded as c o n s e r v a t i v e . Comparison of Average Gas P r i c e s Produced from Manure and Coal from a S i n g l e 1 0 f t I.D. Fixed-Bed G a s i f i e r

T o t a l C a p i t a l Requirements, m i l l i o n s Manure or C o a l Requirement, tons/day Gas P r o d u c t i o n , 109 Btu/day Cost C o r r e c t i o n f o r Reduced Manure Oxygen Requirements Average Gas P r i c Manure Cost, $/MM Btu Average Gas P r i c e Coal = $35/ton, Manure = $2.50/ton, $/MM Btu

Coal

Manure

5.44 132 2.27

5.44 254 2.27

2.49

2.17

4.53

2.45

These cost f i g u r e s e s t a b l i s h that an i n t e r m e d i a t e - B t u gas can be produced from manure at a cost that i s c u r r e n t l y competitive w i t h imported LNG ( p r i c e d at 2.50 to 3.50/MM Btu) and No. 2 h e a t i n g o i l ( p r i c e d at $2.70/MM Btu as of Summer 1977) and at a c o n s i d e r a b l y lower p r i c e than i t can be produced from c o a l . Wherever manure can be combined w i t h s o l i d wastes, the c o s t s w i l l be even more a t t r a c t i v e because of the lower cost to the p l a n t of s o l i d waste compared to manure and the l a r g e r p l a n t s i z e . Of course, other biomass can a l s o be combined to a l l o w l a r g e r p l a n t s . The q u a n t i t a t i v e e f f e c t of combining other forms of b i o mass w i l l depend on i t s cost r e l a t i v e to manure. Solid-Waste Case. Conversion of m u n i c i p a l s o l i d waste to e i t h e r an intermediate or low-Btu gas w i l l be extremely cost e f f e c t i v e because a nominal l a n d - f i l l fee can be charged to d i s pose of the s o l i d waste and the contained metal and g l a s s can be recovered i n r e s a l a b l e form by the Syngas Process. In the p r o d u c t i o n of i n t e r m e d i a t e - B t u gas, another important f a c t o r i n costs i s oxygen consumption. As p r e v i o u s l y pointed out, the Syngas Process should a l l o w a r e d u c t i o n of approximately $0.32/MM Btu compared to c o a l (because of the h i g h e r oxygen content of c e l l u l o s i c type m a t e r i a l s compared to c o a l ) . As mentioned, a g r a v i t a t i n g , f i x e d - b e d , s l a g g i n g bottom g a s i f i e r such as the Purox w i l l r e q u i r e s u b s t a n t i a l l y more oxygen a c c o r d i n g to publ i s h e d oxygen consumption data.(5) In a d d i t i o n to the increased oxygen consumption, the f u s i o n of metal and g l a s s to s l a g reduces the revenue that could o t h e r wise be obtained from t h e i r s a l e . For the s l a g g i n g g a s i f i e r case,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

18.

FELDMAN

A N D

ADLERSTEiN

The Syngas Process

367

i t i s assumed that t h e i r i s no net value f o r the s l a g and f o r the Syngas Process a net value of $3.00 MM/Btu i s assumed because metal and g l a s s a r e recovered i n r e s a l a b l e form. In order t o maintain these cost p r o j e c t i o n s on as common a b a s i s as p o s s i b l e , the same investment costs were assumed f o r the s l a g g i n g g a s i f i e r and the Syngas Process w i t h an adjustment made i n oxygen consumption, which f o r the c o a l case i s estimated by Culbertson and K a s p e r ( i ) t o c o n t r i b u t e about $1.00/MM B t u of product gas. The o v e r a l l thermal e f f i c i e n c y of both the Syngas Process and the s l a g g i n g g a s i f i e r i s assumed the same (approximately 72 percent) as estimated by Culbertson and Kasper f o r the c o a l g a s i f i c a t i o n case. No low-Btu gas cost p r o j e c t i o n s a r e made f o r the s l a g g i n g g a s i f i e r because i t i s impossible t o achieve s l a g g i n g temperatures w i t h an air-blown g a s i f i e r unless e x c e s s i v e l y high a i r preheat temperatures a r e employed requires a u x i l i a r y f i r i n A l s o , f o r the solid-waste cases, i t was a r b i t r a r i l y decided to i n c r e a s e the investment cost by 20 percent over the c o a l case to account f o r the greater hetrogeneity of s o l i d waste compared to c o a l or manure. The gas p r i c e s presented i n the f o l l o w i n g t a b l e are: (1) The average gas p r i c e w i t h c o a l as a feedstock. (2) A base case gas p r i c e f o r both the Syngas and Slagging G a s i f i e r Systems which assumes that waste, already shredded a t v a r i o u s t r a n s f e r s t a t i o n s , i s d e l i v e r e d t o the g a s i f i c a t i o n p l a n t s . The d i s p o s a l charge f o r t h i s waste i s assumed t o be $2.00/ton. For both Syngas and the s l a g g i n g g a s i f i e r a 20 percent i n c r e a s e i n p l a n t i n v e s t ment was assumed f o r the same Btu output. (3) A gas p r i c e assuming a net r e c y c l e value of $3.00/ton f o r recovered metal and g l a s s i s c a l c u l a t e d f o r the Syngas Process. The j u s t i f i c a t i o n i s that the Syngas Process recovers the metal and g l a s s i n a r e s a l a b l e form as p a r t of the g a s i f i c a t i o n process. (4) P r i c e s f o r low-Btu gas are presented only f o r the Syngas Process because i t can operate a i r blown as w e l l as oxygen blown. These cost p r o j e c t i o n s i n d i c a t e : (1) That e i t h e r s o l i d wastes or manure can produce intermediate and low-Btu gas a t p r i c e s that are e i t h e r c u r r e n t l y competitive or substant i a l l y cheaper than other c l e a n f u e l s and, i n the case of a solid-waste feedstock, even cheaper than c o a l ( c o a l a t $35/ton i s a p p r o x i mately $1.46/MM B t u ) .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

No. of Gasif1er8

8.20

390

11.35

660

1.64

2.27

132

78

Gas Output 109 Btu/day

Coal Reg. tpd

Oxygen Blown

COST PROJECTIONS FOR INTERMEDIATE AND LOW-BTU GAS FROM SOLID WASTES

2.62

3.44

3.75

4.53 1420

284

839

168

0.86

1.68

0.55

1.37

1.99

0.52

1.47

Air Blown

2.77 1.30

Slagging Gasifier $2/ton Solid Waste Fee No additional Value for Metal and Glass

2.25

Syngas Gas Price $3/ton Metal and Glass Value $/MM Btu

Coal Cost Contribution - $1.66/MM Btu Gas Heating Value - 158 Btu/SCF

Gas Price Coal Feed $/MM Btu

Equivalent Solid Waste Requirements tpd

Syngas Base Case Gas Price g $2.00/ton Solid Waste fee $/MM Btu

Coal Cost Contribution - $2.03/MM Btu Gas Heating Value - 285 Btu/SCF for coal; about 400 Btu/SCF from solid waste

Table II.

18.

FELDMAN AND ADLERSTEIN

The SyrigOS PfOCeSS

369

(2)

That the oxygen reduction made possible by the Syngas Process allows a very significant reduction i n gas price over a slagging g a s i f i e r . (3) The additional net revenue because of the separation of metal and glass that accrues to the Syngas Process i s an extremely important factor i n process economics. (4) That a plant producing low or intermediateBtu gas from manure or s o l i d waste need not be a giant to be economic. In fact, i f lowBtu gas i s produced, plant sizes capable of serving small communities (170 tpd) are economically very attractive. This greatly increases the s o l i d waste and manure that i s economically available for gasification. (5) Because one can produce a low-Btu gas from s o l i d waste a available fo efficiency of 88 percent, one should seriously examine the option of s e l l i n g this gas as supplementary fuel to a larger f o s s i l fuel power plant rather than c o - f i r i n g waste and refuse. Obviously the combination of attractive economics, an a b i l i t y to u t i l i z e a currently wasted resource, and the solution of a growing envionmental problem make the Syngas Process attractive for commercialization. These economic projections also indicate that gasification of waste and transportation of the gas to end users who can u t i l i z e the gas i s probably a much more attractive option than using the s o l i d waste d i r e c t l y . For example, the option of gasifying the waste and using the intermediate-Btu gas i n u t i l i t y boilers w i l l probably be a more attractive option than f i r i n g waste d i r e c t l y . For larger plants (^-3000 tpd), the production of SNG from the raw product gas may also present an attractive option i n many locales. Literature Cited (1)

Feldmann, H. F., G. W. Felton, H. Nack and J. Adlerstein, (Pipeline Gas from Solid Wastes by the Syngas Recycling Process", paper presented at Fuel Division Symposium, American Chemical Society New York Meeting (April 4-9, 1976). (2) Feldmann, H. F., G. W. Felton, H. Nack and J . Adlerstein, "Syngas Process Converts Waste to SNG", Hydrocarbon Processing, p 201-204 (November 1976). (3) VonFredersdorff, C. G. and M. A. Elliott, "Coal Gasification", Chemistry of Coal U t i l i z a t i o n , Chapter 20, pp 892-1022 (1963). (4) Culbertson, R. W., and S. Kasper, "Economic Advantages and Areas of Application of Small Gasifiers", Presented at 4th Internat'l Conf. on Coal Gasification, Liquefaction and

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

370

SOLID WASTES AND RESIDUES

Conversion to Electricity, University of Pittsburgh (August 2-4, 1977). (5) Anderson, J.E., "The oxygen Refuse Converter - A System for Producing Fuel Gas, Oil, Molten Metal and Slag from Refuse", National Incinerator Conference, Miami (May 12-14, 1974). MARCH 3,

1978

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

19 Investigations of the PERC Process for Biomass Liquefaction at the Department of Energy, A l b a n y , O r e g o n Experimental Facility T. E. LINDEMUTH Research and Engineering, Bechtel National, Inc., 50 Beale Street, San Francisco, CA 94119 Background of the Project Earliest efforts in rently practiced at the Albany experimental facility took place during the late 1960's and early 1970's at the U.S. Bureau of Mines Pittsburgh Energy Research Center (PERC). The study there showed that a wide variety of biomass materials, including wood municipal solid waste and cattle manure, could be turned into an oil-like material by reaction with carbon monoxide in the presence of an alkaline catalyst under conditions of moderate temperature and high pressure.1-3 This work was an outgrowth from earlier experiments of coal liquefaction using a similar reaction scheme. On the basis of the PERC results, the flow scheme for both a commercial size plant and what was to eventually become the Albany facility was developed in 1973.4 Figure 1 shows the process portion of the Albany experimental facility. Detailed engineering specifications were prepared in 19745 and construction of the facility proceeded soon thereafter. In late 1976 Bechtel National, Inc. was contracted to monitor the completion of construction and then to commission the facility. The following paper describes some of the activities involved with commissioning of the facility as well as the initial results and preliminary economic assessments of the process. Objectives The major objectives in the first year's activities at Albany were to verify, as well as possible, the original process data, to evaluate the process equipment involved, and to develop a preliminary conceptual design and economic assessment. The plant itself is located within the city limits of Albany, Oregon immediately adjacent to the U.S. Bureau of Mines Metallurgical Research Center. This facility is set in the middle of a residential area instead of the more isolated setting that one might expect. The location has created a special concern for new adverse environmental effects. In addition to the PDU shown in Figure 1, the site has a modern control room, an office building for technical and administrative staff, a repair and maintenance shop, a small process 0-8412-0434-9/78/47-076-371$05.25/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

Figure 1.

WASTES

AND

Albany, Oregon biomass liquefaction PDU

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

19.

LiNDEMUTH

Biomass Liquefaction

373

c o n t r o l l a b o r a t o r y , and simple p o l l u t i o n c o n t r o l f a c i l i t i e s . Figure 2 i s a s i m p l i f i e d flow scheme f o r the Albany f a c i l i t y as i t was o r i g i n a l l y b u i l t . In the o r i g i n a l process scheme, wood i n the form of wood c h i p s , such as are used i n the manufacture of pulp and paper, are brought to the p l a n t and conveyed i n t o a storage hopper. F i r s t , moist wood chips are d r i e d i n a r o t a r y drum d r i e r . Here, the moisture content i s reduced from 50 percent down to 3 percent or 4 percent. A f t e r d r y i n g , the wood i s ground i n a hammer m i l l to approximately 50 mesh. T h i s gives the m a t e r i a l the consistency of ordinary f l o u r . In order to b r i n g the wood i n t o the r e a c t i o n system, i t i s f i r s t blended with p l a n t r e c y c l e d o i l i n a multibladed continuous blender, s i m i l a r to those used i n making bread dough or compounding rubber. The wood/oil s l u r r y , c o n t a i n i n g approximately 25 percent wood f l o u r i s then pumped up to the r e a c t i o n system pressure which i s i n the range of 100 to 250 atmospheres. The s l u r r y i s then routed to a scraped s u r f a c e heat exchanger where i t i s heated to approximately 350°C. At tha sodium carbonate i s added s t i r r e d autoclave. In the autoclave the mixture i s f u r t h e r heated to 370°C and contacted with carbon monoxide gas. T h i s gas i s prov i d e d from storage tanks and d e l i v e r e d by multistage diaphragm comp r e s s o r s . Both the preheater and s t i r r e d tank r e a c t o r are e l e c t r i c a l l y heated. Offgases from the r e a c t o r c o n t a i n i n g carbon monoxide, carbon d i o x i d e , and hydrogen are cooled, condensed, and combusted in a flare. The l i q u i d mixture that remains from the CSTR i s f i r s t cooled and then depressurized f o r removal of water and noncondensible gases. These gases are also routed to the f l a r e system. L i q u i d from the f l a s h tank i s sent to a c e n t r i f u g e f o r the removal of water and s o l i d sludge. From the c e n t r i f u g e , p a r t of the o i l i s r e c y c l e d to the wood/oil blender, thus completing the process loop. The remaining o i l i s removed as product. Plant Commissioning Before any process t e s t i n g could begin, the e n t i r e f a c i l i t y had to be checked out and each i n d i v i d u a l p i e c e of equipment commissioned. To give you an i d e a of the o v e r a l l complexity of the p l a n t , Table 1 l i s t s the number of major process items i n the p l a n t , each of which r e q u i r e d some s o r t of check-out. To f u r t h e r i l l u s t r a t e the complexi t y of the f a c i l i t y , Figure 3 shows the c e n t r a l c o n t r o l panel. During the commissioning of the p l a n t a number of d i f f i c u l t i e s were encountered with the process equipment i t s e l f . This i s not unusual f o r the f i r s t development u n i t i n a new process. Table 2 highl i g h t s the areas where most d i f f i c u l t i e s were encountered. Of part i c u l a r importance were pump and a g i t a t o r shaft s e a l s on high pressure equipment. In order to use t h i s equipment, many m o d i f i c a t i o n s had to be made i n t h i s area. In a d d i t i o n , problems showed up with the gas compressors, wood handling equipment, and the preheater scraper. To i l l u s t r a t e the magnitude of some of the problems, F i g u r e 4

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 2. Albany PD U schematic (as built)

HOT GASES

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

LiNDEMUTH

Biomass Liquefaction

Figure 3. Albany PDU control panel

Figure 4. Reactor head seal

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

376

SOLID

WASTES

AND

RESIDUES

shows m o d i f i c a t i o n work on the head to s h e l l c l o s u r e of the s t i r r e d tank r e a c t o r . This v e s s e l i s approximately 600 m i l l i m e t e r s i n diameter, and designed f o r pressures of up to 300 atomospheres. The problems uncovered r e q u i r e d complete removal of the o r i g i n a l s e a l mechanism, replacement of the v e s s e l l i n i n g , and remachining f o r a new s e a l r i n g . A l l of the work was done i n p l a c e , i n c l u d i n g the machining of the r e a c t o r head, which weighs over 1,000 kilograms and was l o cated 15 meters above the ground. The i n i t i a l operation of the preheater uncovered d i f f i c u l t i e s w i t h i n t e r n a l coking and eventual damage to the scraper blades themselves. Figure 5 i l l u s t r a t e s the before and a f t e r c o n d i t i o n of some of the 50 scraper blades that are used i n t h i s heat exchanger. Degradation of polymeric m a t e r i a l s caused numerous problems i n the p l a n t . The product o i l or the anthracene v e h i c l e o i l which was used f o r startup r a p i d l y attacked gaskets, s e a l p a r t s , and 0-rings, as i l l u s t r a t e d i n Figure i n almost every s e a l and On the b a s i s of information acquired during the commissioning, a number of equipment and process m o d i f i c a t i o n s were made. Figure 7 i l l u s t r a t e s the changes that were made i n the flow scheme as f o l l o w s : •

The s t i r r e d tank r e a c t o r was bypassed due to cont i n u i n g problems with the a g i t a t o r shaft s e a l

•

The preheater v e s s e l alone was ing and r e a c t i o n

•

Carbon monoxide and c a t a l y s t s o l u t i o n were i n t r o duced ahead of the preheater

•

L i q u i d e f f l u e n t bypassed the c e n t r i f u g e s i n c e the c e n t r i f u g e was unable to handle the r e a c t o r e f f l u e n t

Process

then used f o r heat-

Results

In s p i t e of o b s t a c l e s that were encountered, v a l u a b l e operating time has been logged - r e c e n t l y , exceeding 50 percent — and important process r e s u l t s are being accumulated. The f i r s t area studied was r e a c t i o n c h a r a c t e r i s t i c s which included the e f f e c t s of system temperature, pressure, carbon monoxide concentration, residence time, and c a t a l y s t use. These have been evaluated f o r t h e i r e f f e c t on wood conversion, o v e r a l l y i e l d , and product q u a l i t y . Figure 8 i l l u s t r a t e s p r e l i m i n a r y r e s u l t s on the r a t e of wood conversion per pass through the preheater v e s s e l .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

19. L i N D E M U T H

Biomass Liquefaction

Figure 5.. Reheater scraper blades

Figure 6. Decomposed reactor rubber seal material

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

377

Figure 7. Albany PD U schematic (modified) In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

19.

LINDEMUTH

Biomass Liquefaction

379

Wood conversion, K, i s d e f i n e d as: Κ = where

Cf - Co χ 100 Cf

Κ i s wood conversion i n % Cf i s the undissolved s o l i d s i n the feed Co i s the undissolved s o l i d s i n the o u t l e t .

I t should be noted that conversion does not n e c e s s a r i l y mean o i l production but simply the disappearance o f wood. Residence time i s the o v e r a l l residence time i n the preheater and not time a t temp­ e r a t u r e . I t should be noted t h a t the temperature range i n the pre­ heater i s from 100° t o approximately 350°C. As F i g u r e 8 i l l u s t r a t e s , at approximately 25 minutes residence time, 70 percent conversion per pass i s u s u a l . Sinc th s l u r r i r e c y c l e d approximat 5 p a r t s r e c y c l e to one p a r i s over 90 percent. Unde , approx imate c a p a c i t y o f the p l a n t i s 1,000 kilograms a day o f wet wood feed w i t h 400 to 500 kilograms of o i l produced. This i s shown s c h e m a t i c a l l y i n F i g u r e 9, which i l l u s t r a t e s the o v e r a l l p l a n t mass balance. As shown, the main r e a c t a n t s are carbon monoxide and wood w h i l e the main products are o i l and f l u e gases. I n a commercial s i z e d p l a n t , as w i l l be i l l u s t r a t e d l a t e r , only wood would be used as a r e a c t a n t . To date, the product o i l that has been produced has been q u i t e viscous and resembles heavy h e a t i n g o i l i n i t s c o n s i s t e n c y . Table 3 i l l u s t r a t e s a few of the more important p r o p e r t i e s of the product o i l i t s e l f . At times, i n c r e a s i n g v i s c o s i t y of the product o i l has n e c e s s i t a t e d t e r m i n a t i o n o f t e s t runs. Methods t o c o n t r o l t h i s phenomenon are now being examined and w i l l have h i g h p r i o r i t y i n f u t u r e experiments. As can be seen, the h e a t i n g value i s s i m i l a r to a bunker f u e l o i l . The elemental a n a l y s i s shows that the oxygen content i s approximately 8 percent as compared t o the wood f l o u r used t o feed which has over 40 percent oxygen. The net e f f e c t o f conversion i s that the h e a t i n g value i s approximately twice as high as wood on a weight b a s i s and over f o u r times as high on a volume b a s i s . Commercial P l a n t Concepts With the i n f o r m a t i o n learned a t Albany, a p r e l i m i n a r y conceptual design has been developed. Some o f the c r i t e r i a that have been i n ­ corporated i n t o t h i s conceptual design are the amount of carbon monoxide consumed, the use o f the s l u r r y r e c y c l e o p e r a t i o n , the technique of CO a d d i t i o n ahead o f the preheater, and a knowledge of the s l u r r y and o f f - g a s c h a r a c t e r i s t i c s . Figure 10 i l l u s t r a t e s the main f e a t u r e s o f a commercial flow scheme. While the carbon monoxide gas i s brought i n t r u c k s t o the A l ­ bany p l a n t , a commercial f a c i l i t y w i l l use a s y n t h e s i s gas c o n t a i n -

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

Table I . •

Equipment Commissioning and Proof T e s t i n g PRESSURE VESSELS

7

PUMPS

•

15

HEAT EXCHANGERS

WOOD HANDLING

•

UNITS

ELECTRIC MOTORS

40

CONTROLS

60

Table I I PUMP A N D A G I T A T O R S H A F T S E A L S GAS

COMPRESSORS

E L E C T R I C A L PROCESS HEATING WOOD HANDLING

EQUIPMENT

REACTOR HEAD SEAL PREHEATER SCRAPER

Table I I I .

BLADES

Product O i l P r o p e r t i e s

VISCOSITY

200-1000 cp

SPECIFIC G R A V I T Y

1.05-1.10

B O I L I N G POINT

280OC

HEATING V A L U E

15,000 Btu/lb

ELEMENTAL

%C

ANALYSIS

77.2

% H

6.5

% Ν

0.4

%0

8.4

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

LiNDEMUTH

100

Biomass Liquefaction

381

h

0

5

10

15

20

25

O V E R A L L RESIDENCE TIME, MINUTES

Figure 8.

Rate of wood conversion

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

382

SOLID WASTES AND RESIDUES

Figure 10. Biomass liquefaction conceptual commercial process

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

19.

LiNDEMUTH

383

Biomass Liquefaction

ing both hydrogen and oxygen. A synthesis gas plant and a product separation system have been added to the commercial f a c i l i t y design. The synthesis gas i s produced i n an oxygen blown g a s i f i e r and i s t r e a t e d f o r removal o f water and carbon d i o x i d e . The synthesis gas a l s o t r e a t s the c a t a l y s t s o l u t i o n f o r recovery of the a l k a l i . In a commercial p l a n t about h a l f the wood that i s introduced as feed goes f o r synthesis gas production. The other h a l f of the wood i s t r e a t e d by drying and g r i n d i n g and then blending with r e c y c l e d o i l p r i o r to pumping i n t o the r e a c t o r system as i n the Albany p l a n t . A h e l i c a l c o i l preheater followed by a holdup tank i s a l s o c u r r e n t l y part of the design. The preheater i s heated by combustion of system o f f g a s e s . A f t e r pressure letdown from the r e a c t o r hold tank, some of the s l u r r y i s r e c y c l e d to the blender while the product p o r t i o n i s routed f o r p u r i f i c a t i o n . Here the product, c o n t a i n i n g some unreacted wood as w e l l as water and c a t a l y s t , i s f i r s t d i l u t e d with a l i g h t s o l v e n t . A f t e r d i l u t i o n , the mixture i s f i l t e r e d f o r the removal of s o l i d s l u t e d w i t h water to was s o l i d s and the aqueous waste stream are routed to the synthesis gas r e a c t o r f o r treatment. The organic stream i s sent to a f r a c t i o n a l column f o r recovery of the s o l v e n t . At t h i s point the s t i l l bottom becomes the product. Figure 11 i s an a r t i s t ' s rendering o f a commercial plant env i s i o n e d i n a P a c i f i c Coast s e t t i n g . In the foreground a l a r g e p i l e o f wood chips i s shown. These are assumed to be prepared i n the f o r e s t . From the p i l e , the wood i s d i s t r i b u t e d by conveyors to the synthesis gas r e a c t o r s and to the d r i e r - g r i n d e r apparatus. In a d d i t i o n to the major f a c i l i t i e s f o r o i l production, administrat i o n b u i l d i n g r e p a i r shops, c o o l i n g towers and wastewater f a c i l i t i e s are a l s o i l l u s t r a t e d . I t i s important to note that the l i q u e f a c t i o n p l a n t should be an environmentally good neighbor. Some of the h i g h l i g h t s of the design w i l l serve to i l l u s t r a t e : •

Biomass and a i r are the only raw m a t e r i a l s

•

O i l i s the only product

•

The e f f l u e n t s c o n s i s t of only water, clean f l u e gases, and i n e r t ash

•

The process i s e f f i c i e n t from an energy

standpoint

C a l c u l a t i o n s to date show that o v e r a l l y i e l d f o r a commercial plant should be approximately 35 percent wood to o i l , while energy balance would i n d i c a t e approximately 54 percent, as i l l u s t r a t e d i n Figures 12 and 13. Economic A n a l y s i s In order to develop operating and c a p i t a l c o s t s , s e v e r a l p l a n t s i z e s were costed out. Figure 14 i l l u s t r a t e s the e f f e c t of p l a n t

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

384

SOLID

Figure 11.

WASTES

AND

RESIDUES

Artist's rendering of a commercial biomass liquefaction plant

TRACE

Figure 12.

Biomass liquefaction mass balance

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

LiNDEMUTH

Biomass Liquefaction

TRACE

Figure 13.

Biomass liquefaction energy balance

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

386

SOLID

20

h

10

h

0 I Ο

1

L_

0.5

1.0*

WASTES AND

I

I

1.5

2.0

PLANT CAPACITY, THOUSAND TONS/DAY

Figure 14.

Effect of plant size on production cost

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

Ι ­

2.5

19.

LiNDEMUTH

Biomass Liquefaction

387

s i z e on product c o s t . As can be seen, due to the p l a n t complexity, the economies o f s c a l e a r e q u i t e strong. I t would appear that only l i q u e f a c t i o n p l a n t s of l a r g e production ( i n excess of 1,000 tons per day) w i l l be a t t r a c t i v e . F i g u r e 14 i l l u s t r a t e s the r e l a t i v e p o r t i o n o f p l a n t c a p i t a l a t t r i b u t a b l e to the major process s e c t i o n s of a commercial p l a n t . This breakdown was based on a plant of approximately 1,000 metric tons of oven-dried wood a day. The costs of the wood handling and synthesis gas p l a n t are the l a r g e s t s i n g l e items i n the p l a n t . The p o r t i o n of the p l a n t cost f o r the high pressure r e a c t i o n equipment i s only 16 percent of the t o t a l . This would tend to i n d i cate that f u t u r e development work should center on r e d u c t i o n i n the s i z e of the s y n t h e s i s gas p l a n t and a s i m p l i f i c a t i o n of wood handling. Based on a p l a n t of t h i s s i z e , Figure 15 shows the r e l a t i v e cost p o r t i o n s of the product that can be a l l o c a t e d to a m o r t i z a t i o n of c a p i t a l , feed stock, e l e c t r i and consumables. Amortizatio tor followed by the cost of feed stock. In t h i s instance, wood i s assumed to c a r r y a value o f $20 per oven-dried ton. O v e r a l l , t h i s r e s u l t s i n a breakeven production cost of j u s t under $35 per b a r r e l . Future A c t i v i t i e s 1

The past y e a r s e f f o r t s and the development of the f i r s t conc e p t u a l designs have shown a number of areas of f r u i t f u l continued e f f o r t s as i l l u s t r a t e d i n Figure 16. The o v e r a l l production costs are very s e n s i t i v e to p l a n t y i e l d and c a p i t a l cost. In the f o l l o w i n g program s u b s t a n t i a l e f f o r t s w i l l be aimed a t reducing the amount of s y n t h e s i s gas r e q u i r e d , r a i s i n g o v e r a l l y i e l d and e f f i c i e n c y , and reducing energy input. F i g u r e 17 i s a p r o j e c t i o n of the e f f e c t of f u t u r e a c t i v i t i e s on the o v e r a l l cost of biomass produced o i l . It i s expected that continued developments at the Albany f a c i l i t y w i l l y i e l d improvements that should show a r e d u c t i o n i n p r o j e c t ed product p r i c e to approximately $25 a b a r r e l . T h i s should take place over the next 2-1/2 years. At t h i s point i t i s suggested that a p i l o t p l a n t of approximately 100 to 300 tons per day c a p a c i t y be b u i l t and operated. This p i l o t p l a n t would have a l l the f a c i l i t i e s now envisioned f o r a commercial p l a n t but o f much smaller s i z e . I n formation gained by the o p e r a t i o n of t h i s p l a n t should reduce the product cost as expressed i n constant 1978 d o l l a r s to $20 per b a r r e l . T h i s would take approximately f i v e years. The f i n a l step i n the development would be the design and c o n s t r u c t i o n of a demonstration plant u t i l i z i n g f u l l - s i z e process t r a i n s . Information gained here should provide the means to be commercially competitive by approximately 1990.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

388

SOLID WASTES AND RESIDUES

Figure 15. Capital cost breakdown—commercial biomass liquefaction plant

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

LiNDEMUTH

Biomass Liquefaction

Figure 16. Oil production (break-even) costs—commercial biomass liquefaction plant

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

390

40

WASTES

AND

h

1980

1985

1990

YEAR

Figure 17.

Projected process economics

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

19. LiNDEMUTH

Biomass Liquefaction

391

Summary Investigations to date have led the authors to be optimistic about the possibilities of oil production from biomass. While difficulties in bringing the current facilities on-stream have somewhat limited information to date, i t is felt that a vigorous activity in the future can eventually provide a new source of energy for the country in the form of o i l from biomass. References 1.

Appell, H.R., Wender, I., and Miller, R.D., Chem & Ind.(London) Vol. 47, 1703 (1969).

2.

Appell, H.R., Fu, Y.C., Friedman, S., Yavorsky, P.M., and Wender, I., "Convertin Mines, RI 7560, 1971

3.

Appell, H. R., Fu, Y.C., I l l i g , E.G., Steffgen, F.W., and Miller, R.D., "Conversion of Cellulosic Wastes to Oil," U.S. Bureau of Mines, RI 8013, 1975.

4.

Dravo Corporation, Blaw-Knox Chemical Plants Division, "Economic Feasibility Study for Conversion of Wood Wastes to Oil," prepared for U.S. Bureau of Mines, June 1973.

5.

The Rust Engineering Co., "U.S. Bureau of Mines Wood-to-Oil Pilot Plant — Final Design Report," prepared for U.S. Bureau of Mines, February 1974.

MARCH 15, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20 Pyrolysis for the P r o d u c t i o n of Activated C a r b o n f r o m Cellulosic Solid Wastes PAUL V. ROBERTS and JAMES O. LECKIE Department of Civil Engineering, Stanford University, Stanford, CA 94305 PAUL H. BRUNNER EAWAG, Swiss Federal Institutes of Technology, CH 8600 Dübendorf, Switzerland Municipal s o l i d waste ceous, s o l i d char (1). Such a char potentially could be activated to generate a product with large internal surface area and favorable adsorptive properties. The production of activated carbon i n this manner offers the combined benefits of reducing the volume of s o l i d wastes with a minimum ofairpollutant emissions and producing a valuable product for a growing market i n water and wastewater treatment. Presently, carbonaceous raw materials such as bituminous coal, l i g n i t e and peat are used i n the manufacture of activated carbon (2). The properties of the f i n a l product are strongly influenced by the chemical composition and physical structure of the raw material (2, 3). If s o l i d wastes are to be used as raw materials for activated carbon manufacture, it is important to understand the effects of waste composition, pyrolysis conditions, and activation conditions on the y i e l d and properties of the intermediate product, char, and the f i n a l product, activated carbon. Municipal s o l i d wastes vary widely i n composition both geographically and temporally (4, 5). Their potential for activated carbon preparation can be gauged crudely from their content of organic material. Municipal s o l i d wastes contain from 50 to 75 percent organic material, the primary constituent being paper (5). Thus, cellulose i s a l o g i c a l choice for a model substance to investigate the behavior of s o l i d wastes i n pyrolysis. The elemental composition of the organic fraction of s o l i d wastes can be given approximately asC6H10O4(4,5,6), which agrees closely with the empirical formula for cellulose (C6H10O5)n

(

6)·

Objectives This work was undertaken to: 1. Determine the effects of pyrolysis and activation conditions on the yields and properties of char and activated carbon prepared from cellulose and municipal s o l i d waste. 0-8412-0434-9/78/47-076-392$05.00/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20.

ROBERTS

2. 3.

4.

E T

A L .

Activated Carbon from Cellulosic Solid Wastes

393

A s c e r t a i n the i n f l u e n c e o f the composition o f the educt on the p r o p e r t i e s and y i e l d o f the f i n a l product. Evaluate the e f f e c t i v e n e s s o f a i r c l a s s i f i c a t i o n i n r e ­ moving i n o r g a n i c i m p u r i t i e s and improving the q u a l i t y o f the f i n a l product. Evaluate the f e a s i b i l i t y o f producing from m u n i c i p a l s o l i d waste an a c t i v a t e d carbon comparable i n q u a l i t y to commercially a v a i l a b l e products.

Experimental

Procedure

Twenty-gram samples o f p u r i f i e d α-cellulose were p y r o l y z e d i n a 500-ml quartz g l a s s r e t o r t which was p l a c e d i n a temperaturec o n t r o l l e d m u f f l e furnace and purged w i t h argon ( 6 ) . Two a n a l y t i c a l grade c e l l u l o s e products were compared: Merck m i c r o c r y s t a l l i n e c e l l u l o s e f o r packing o f chromatographic columns (designated here­ a f t e r as C e l l u l o s e A ) , an paper f o r p r e p a r a t i v e chromatograph The c h a r a c t e r i s t i c s o f the two α-cellulose products are given i n Table I . The samples were f i r s t d r i e d a t 65°C. The ash content was estimated as the r e s i d u e a f t e r h e a t i n g a t 550°C f o r 24 hours. The metal contents were determined a f t e r d i g e s t i o n w i t h p e r c h l o r i c acid. The char formed by p y r o l y s i s o f c e l l u l o s e was a c t i v a t e d i n a steam-C02 atmosphere a t temperatures i n the range o f 700 t o 1000°C. Char samples weighing one to three grams were placed on a g l a s s f r i t i n the neck o f an i n v e r t e d 750-ml quartz b o t t l e , which was heated i n the same furnace used f o r p y r o l y s i s . Table I C h a r a c t e r i s t i c s o f C e l l u l o s e Used i n P y r o l y s i s (Reference 6) Cellulose A

Cellulose Β

Merck microcrystalline chromatographic cellulose

S c h l e i c h e r and S c h u e l l 2181 filter paper

44.4 6.2

44.3 6.2

Carbon content, % w/w Hydrogen content, % w/w Ash content, ppm Na Ca Mg Κ

Experiments

not

65 determined II II II

750 175 67 21 5

Particle size

90% w/w <100 ym

4.6 mm t h i c k x 10.5 mm square

D e n s i t y , g/cm

0.38

0.69

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

394

SOLID

WASTES

AND

RESIDUES

Thermoanalytic i n v e s t i g a t i o n s of c e l l u l o s e p y r o l y s i s were conducted w i t h a M e t t l e r Thermoanalyzer, Model 1, which s i m u l t a neously r e g i s t e r e d s i g n a l s f o r thermogravimetry (TG), d i f f e r e n t i a l thermogravimetry (DTG) and d i f f e r e n t i a l thermal a n a l y s i s . I n these experiments, 40 mg of sample were heated i n an argon atmosphere a t a c o n t r o l l e d r a t e of 0.5°, 1.5°, or 4°C/min to a temper a t u r e of 550°C. Mixed s o l i d waste from the C i t y of Schweinfurt, Germany, was p y r o l y z e d and the char was a c t i v a t e d under the c o n d i t i o n s described above f o r comparison w i t h c e l l u l o s e ( 6 ) . This s o l i d waste was chosen by v i r t u e o f i t s r e l a t i v e homogeneity, owing to i t s prepar a t i o n t h a t i n c l u d e d hand and magnetic s o r t i n g , shredding, and s c r e e n i n g through a s i e v e having 50-mm diameter openings. The s o r t e d and screened waste contained 23.9 percent carbon, 3.2 percent hydrogen, and 51.2 percent ash on a dry weight b a s i s . The water content was 38.6 percent. Air-classified soli f o r n i a , was chosen f o r stud t i o n of o r g a n i c m a t e r i a l . The average ash content was s l i g h t l y l e s s than 20 percent on a dry weight b a s i s . Large sample s i z e s (approximately 1 kg) were a n e c e s s i t y because of the heterogeneity of the m a t e r i a l . P y r o l y s i s was c a r r i e d out i n a s t a i n l e s s s t e e l r e t o r t heated i n a n i t r o g e n atmosphere. The o r g a n i c content of the char was then b e n e f i c i a t e d by a i r c l a s s i f i c a t i o n i n the appar a t u s shown i n F i g u r e 1 (_7) . The a i r - c l a s s i f i e d char was then act i v a t e d i n an atmosphere of steam and/or CO2 i n the same apparatus used f o r p y r o l y s i s Ç 7 ) . The a c t i v a t e d carbon prepared from a i r c l a s s i f i e d s o l i d waste was ground i n a b a l l m i l l and screened through a 100-mesh s i e v e before being c h a r a c t e r i z e d . The s p e c i f i c s u r f a c e s of char and a c t i v a t e d carbon samples were estimated by^B.E.T. a n a l y s i s of n i t r o g e n a d s o r p t i o n data obtained w i t h a S t r o h l e i n Area Meter i n the experiments w i t h c e l l u l o s e and u n c l a s s i f i e d waste (6). Products d e r i v e d from c l a s s i f i e d s o l i d waste were c h a r a c t e r i z e d by means of an Orr Surface Area and Pore S i z e A n a l y z e r , Model 2100 ( 7 ) . R e s u l t s and D i s c u s s i o n P y r o l y s i s of C e l l u l o s e and S o l i d Waste. The e f f e c t of p y r o l y s i s temperature and r a t e of h e a t i n g on the y i e l d , composition and s p e c i f i c s u r f a c e area of char was i n v e s t i g a t e d ( 6 ) . The o b j e c t i v e of these experiments was to f i n d a set of p y r o l y s i s c o n d i t i o n s r e s u l t i n g i n a f a v o r a b l e combination of y i e l d and p r o p e r t i e s of char, c o n s i d e r i n g i t as an i n t e r m e d i a t e product to be a c t i v a t e d . The char y i e l d i s shown as a f u n c t i o n of p y r o l y s i s temperat u r e i n F i g u r e 2A. The behavior of s o l i d waste as w e l l as c e l l u l o s e can be represented by sigmoid curves, w i t h a sharp decrease i n y i e l d between approximately 225°C and 375°C. This agrees w i t h observations t h a t c e l l u l o s e undergoes dehydration and c l e a v i n g of -(OH) and -(CH 0H) groups at temperatures below 250°C, f o l l o w e d by 2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20.

ROBERTS

E T A L .

Activated Carbon from Cellulosic Solid Wastes

îî CLASSIFIED MATERIAL OUT ν = 3.4 m/s

ΓΙ tI 61 cm

ι

I tI v = 2.1 m/s

SEPARATED MATERIAL OUT

Figure 1. Configuration of and air velocities in the modified zigzag air classifier used for separation of inerts from char

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

395

396

SOLID WASTES AND RESIDUES

depolymerization i n the range o f 250°C to approximately 370°C ( 8 , 9). A c c o r d i n g l y , the carbon content o f the char i n c r e a s e s most r a p i d l y w i t h i n c r e a s i n g temperature between 250°C and 370°C, as shown i n F i g u r e 2B. Above 400°C, the r i n g s t r u c t u r e s r e s u l t i n g from d e p o l y m e r i z a t i o n are f u r t h e r dehydrated and condensed to 6-member r i n g s w i t h a C/H r a t i o o f 2.5 ( 8 ) . Above 550°C, g r a p h i t i z a t i o n proceeds, r e s u l t i n g i n a r i s e i n the C/H r a t i o to values i n excess o f t e n a t 750°C ( 8 ) . The o r g a n i c f r a c t i o n o f s o l i d waste behaves s i m i l a r l y to c e l l u l o s e , as seen i n F i g u r e s 2A and 2B. The p r i n c i p a l d i f f e r e n c e s are that the onset o f p y r o l y s i s of s o l i d waste occurs a t a s l i g h t l y lower temperature and the y i e l d o f char i s h i g h e r than f o r c e l l u l o s e a t temperatures above 500°C. Of course, the y i e l d of char from s o l i d waste on a t o t a l weight b a s i s i s s u b s t a n t i a l l y h i g h e r than from c e l l u l o s e because o f the d i f f e r e n c e i n ash cont e n t . However, when compared u s i n g the weight o f v o l a t i l e s o l i d s as a measure o f p o t e n t i a l l y i e l d s are o n l y s l i g h t l Furthermore the carbon content o f the char d e r i v e d from s o l i d waste shows much the same dependence on temperature as i s the case for c e l l u l o s e c h a r s , a f t e r adjustment f o r the d i f f e r e n c e i n v o l a t i l e s o l i d s content o f the educt. The carbon content o f the v o l a t i l e s o l i d s i n unpyrolyzed s o l i d waste i s higher than i n c e l l u l o s e . This accounts f o r the r e l a t i v e l y h i g h carbon content o f the s o l i d waste "char" a t temperatures below 300°C. The h i g h e r carbon content (on an a d j u s t e d b a s i s ) o f the s o l i d waste char compared t o c e l l u l o s e chars above 600°C may be e x p l a i n e d by b i a s i n t r o d u c e d i n u s i n g the weight o f v o l a t i l e s o l i d s as a b a s i s . A p o r t i o n o f the m a t e r i a l remaining as " i n e r t r e s i d u e " i n the 550°C i g n i t i o n o f the v o l a t i l e s o l i d s d e t e r m i n a t i o n i s a c t u a l l y decomposed t o v o l a t i l e products d u r i n g p y r o l y s i s a t temperatures above 600°C. The most d i r e c t measure o f the e f f i c i e n c y o f p y r o l y s i s i n c o n v e r t i n g carbonaceous m a t e r i a l s i n t o an a c t i v a t e d char i s given by the y i e l d based on carbon. The percent y i e l d s based on carbon for c e l l u l o s e and s o l i d waste are shown i n F i g u r e 2C. The y i e l d s are comparable below 400°C, but a t temperatures above 600°C the carbon y i e l d from s o l i d waste i s g r e a t e r than from c e l l u l o s e by a f a c t o r o f two. To a s c e r t a i n the e f f e c t o f the r a t e o f h e a t i n g d u r i n g p y r o l y s i s , experiments were conducted w i t h a c o n t r o l l e d r a t e o f temperat u r e r i s e . The r e s u l t s are summarized i n Table I I . Increasing the h e a t i n g r a t e r e s u l t e d i n reduced y i e l d s expressed as e i t h e r t o t a l weight o r weight o f carbon, and i n approximately the same p r o p o r t i o n s . The carbon y i e l d i n c e l l u l o s e p y r o l y s i s was reduced by h a l f when the h e a t i n g r a t e was i n c r e a s e d by a f a c t o r o f 100, whereas the carbon y i e l d from s o l i d waste was l e s s s t r o n g l y a f f e c t e d . The f r a c t i o n o f carbon i n the char was not a f f e c t e d app r e c i a b l y by changing the h e a t i n g r a t e . The dependence o f char y i e l d on h e a t i n g r a t e i s shown i n F i g u r e 3. F o r c e l l u l o s e , a l i n e a r r e l a t i o n s h i p was found of the f o l l o w i n g form:

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20.

ROBERTS

Vj

Activated Carbon from Cellulosic Solid Wastes

E T AL.

' " 2 0 0

^ 4 0 0

600

397

800

TEMPERATURE, °C

100 of < X

80 60

S W * ^ / M 3 A and CB σο—S-srtf°D

--^OT

40 20

ο ο

2 6

200

S

400

600

T E M P E R A T U R E , °C

800

Figure 2. Dependence of char yield (2A), carbon content of char (2B), and carbon yield (2C) on the pyrolysis tem­ perature. Data are shown for Cellulose A (CA, O); Cellulose Β (CB, and unclassified solid waste on the basis of total weight (SW, A) as well as ad­ justed to the weight of volatile solids (SW*, Α λ expressed as g volatile solids in char per g volatile solids in educt in Figure 2A or g C per g volatile solids in char in Figure 2B. These data were ob­ tained in batch pyrolysis experiments conducted at a high heating rate, φ « 100°C/min.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

398

SOLID WASTES AND RESIDUES

Table I I E f f e c t of Heating Rate on the Y i e l d and Composition o f Char (Reference 6) Y i e l d , îI Based on

Carbon Γ*

*·

Educt

rinai Temperature °C

Heating Rate, °C/min

Total Weight

Carbon

Cellulose A

540

0.13 0.14 0.48 0.89 1.59 2.20

31.1 31.9 29.3 28.4 26.6 26.5

61.9 65.0 61.4 59.7 55.8 54.7

88.5 90.6 93.0 93.5 93.3 91.6

Cellulose A

710

max 0.2 0.42 1.2 1.7 43.0 max

29.2 27.0 25.9 24.7 12.2 13.0

62.2 57.3 56.4 53.3 25.7 27.3

94.8 94.2 96.7 95.9 94.3 93.5

Cellulose Β

710

-°* max

23.7 21.9 20.3 12.3 10.2

52.9 47.3 43.1 26.4 20.6

99.4 95.8 94.6 95.2 89.6

0.2 0.5 1.1 32.0·

65.3 65.4 64.4 63.2

47.2 46.9 42.3 39.6

16.9 16.8 15.4 14.7

0.5 1.7 5.35 7 8

Unclassified S o l i d Waste

710

4-

uontent of Char, % w/w

Samples were heated t o the p y r o l y s i s end temperature a t the maximum p o s s i b l e r a t e by i n t r o d u c i n g them i n t o the furnace a f t e r i t had been preheated to the designated temperature. The i n i t i a l h e a t i n g r a t e was approximately 100°C/min.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20.

ROBERTS

E T

Activated Carbon from Cellulosic Solid Wastes

A L .

399

y = -2.4 I n φ + C where y = weight o f char expressed as percent o f educt φ = h e a t i n g r a t e , °C/min C = e m p i r i c a l constant = 27.9 f o r C e l l u l o s e A a t 540°C end temperature =25.3 f o r C e l l u l o s e A a t 710°C = 22.9 f o r C e l l u l o s e Β a t 710°C. The s p e c i f i c s u r f a c e o f the char was l i k e w i s e found t o be de­ pendent on both end temperature and h e a t i n g r a t e . Data f o r C e l l u ­ l o s e A are shown i n F i g u r e 4. The s p e c i f i c surface i n c r e a s e s w i t h i n c r e a s i n g temperature above 400°C, reaching a maximum o f a p p r o x i ­ mately 350 to 400 m /g a t 700°C. Above 700°C, the s p e c i f i c s u r ­ face d e c l i n e s w i t h f u r t h e r increases i n temperature. The d e c l i n e i s more pronounced a t hig h e a t i n heatin For chars d e r i v e d from s o l i was approximately 10 m per gram o f char, o r 30 to 80 m per gram of v o l a t i l e s o l i d s . The k i n e t i c s o f p y r o l y s i s were i n v e s t i g a t e d using thermograv­ imetry (10, 11). I n t e r p r e t a t i o n o f o v e r a l l r a t e data from complex systems o f s o l i d phase r e a c t i o n s i s p e r i l o u s ; however, the compar­ i s o n o f a c t i v a t i o n energies so d e r i v e d i s p e r m i s s i b l e among experments that are conducted under comparable c o n d i t i o n s as i n t h i s work (11). The r e s u l t s were i n t e r p r e t e d by the approach suggested by Freeman and C a r r o l l (10, p. 44, 12), who proposed that the ac­ t i v a t i o n energy and order o f a decomposition r e a c t i o n can be e s t i ­ mated using the equation 2

3[ln(da/dt)] 3T

=

3[ln(l - a)] 3T

_ Ε 3(1/T) R 3T

where a i s the f r a c t i o n a l weight l o s s ; Τ i s the absolute tem­ p e r a t u r e ; R i s the gas constant; η i s the order o f r e a c t i o n ; and Ε i s the a c t i v a t i o n energy. The a c t i v a t i o n energy can be obtained from p l o t s o f Δ

log(da/dt) Δ l o g ( l - a)

„ a

ê

Β Ί Η Β |

a i n s t

.

Δ(1/Τ) Δ l o g ( l - a)

The a c t i v a t i o n energies f o r p y r o l y s i s o f c e l l u l o s e and s o l i d waste are summarized i n Table I I I . The values i n t h i s work range from 20 t o 70 k c a l / m o l , agreeing approximately w i t h a c t i v a t i o n energies p r e v i o u s l y reported f o r p y r o l y s i s o f c e l l u l o s e (13, 14, 15, 16). The h e a t i n g r a t e was found t o have no e f f e c t on a c t i v a t i o n energy. The a c t i v a t i o n energies d i f f e r e d s u b s t a n t i a l l y f o r the d i f f e r e n t educts. The h i g h e s t value was found f o r the educt having the low­ est ash content, C e l l u l o s e A, w h i l e the educt w i t h h i g h e s t ash content, i . e . the s o l i d waste, e x h i b i t e d the lowest a c t i v a t i o n energy. The d i f f e r e n c e s i n a c t i v a t i o n energies presumably can be a t ­ t r i b u t e d t o a c a t a l y t i c e f f e c t o f i n o r g a n i c i m p u r i t i e s present i n

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

400

SOLID WASTES AND RESIDUES

PYROLYSIS TEMPERATURE

Figure 4. Specific surface of char prepared from Cellulose A, expressed as m per g of char: —·—, ~ 1 ° C/min; - - Ο - -. > > 1 ° C/min 2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20.

ROBERTS

Activated Carbon from Ceïlulosic

E T A L .

Solid Wastes

401

Table I I I A c t i v a t i o n Energies f o r P y r o l y s i s (Reference 6)

Educt and Ash Content Cellulose A (65 ppm ash)

Cellulose Β (750 ppm ash)

Unclassifie S o l i d Wast (51.2% ash)

Heating Rate, °C/min.

Activation Energy kcal/mol

4.0 1.5 0.5

69.9 Ί

4.0 1.5 0.5

38.3 Ί o ο I average

70.0 71.8 J

7

Â:î

a

=

V

^ ·

7 0

f

a

6

ι = -° 38

1f £ f

0.5

20.1 21.7 J

Z J

-*

U

the educt. The a d d i t i o n o f i n o r g a n i c substances that are Lewis acids or bases has been shown to reduce the a c t i v a t i o n energy f o r p y r o l y s i s ÇL3, 14, JL6, .17, 18). I t has been p o s t u l a t e d that such a d d i t i v e s promote the r a t e o f dehydration of c e l l u l o s e compared to d e p o l y m e r i z a t i o n , consequently i n c r e a s i n g the y i e l d o f char a t the expense of v o l a t i l e p y r o l y s i s products (18). When the concentrat i o n o f a d d i t i v e s i s r a i s e d , a s a t u r a t i o n l i m i t i s reached beyond which there i s no incremental c a t a l y t i c e f f e c t (17). No f u r t h e r r e d u c t i o n i n a c t i v a t i o n energy and i n c r e a s e i n char y i e l d were observed when the a d d i t i v e content was increased from two to e i g h t percent (18). This e x p l a n a t i o n a l s o may account f o r the h i g h e r y i e l d o f carbon from s o l i d waste compared to c e l l u l o s e , as was observed a t temperatures above 600°C i n F i g u r e 2 C . The i n o r g a n i c matter p r e s ent i n s o l i d waste contains a p p r e c i a b l e amounts o f phosphorus, aluminum, potassium, sodium and other elements that might have a c a t a l y t i c effect (4). A c t i v a t i o n . A c t i v a t i o n o f p y r o l y s i s chars w i t h steam and C O 2 r e s u l t e d i n an i n c r e a s e i n s p e c i f i c s u r f a c e a t temperatures above 700°C, as shown f o r c e l l u l o s e - d e r i v e d chars i n F i g u r e 5. The r i s e i n s p e c i f i c s u r f a c e i s more pronounced i n the case o f C e l l u l o s e Β than f o r C e l l u l o s e A. The s p e c i f i c s u r f a c e o f a c t i v a t e d carbon d e r i v e d from C e l l u l o s e Β a t an a c t i v a t i o n temperature o f 950°C was 1550 m per gram, n e a r l y twice as great as f o r a c t i v a t e d carbon made from C e l l u l o s e A. The corresponding value f o r a c t i v a t e d car­ bon from u n c l a s s i f i e d s o l i d waste was comparable to that from C e l ­ l u l o s e A when compared on the b a s i s o f carbon content, i . e . , ap­ proximately 850 m per gram carbon. 2

2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

402

SOLID WASTES AND RESIDUES

The weight l o s s during a c t i v a t i o n i n c r e a s e s s h a r p l y between 700°C and 950°C, as i s evident i n F i g u r e 6. A t 950°C and a c t i v a t i o n times o f 30 minutes o r more, the weight l o s s exceeded 50 percent. F o r the a c t i v a t i o n o f c e l l u l o s e chars under the c o n d i t i o n s i n t h i s work, the optimum combination o f temperature and time o f a c t i v a t i o n appears to be approximately 850 to 900°C and 30 to 60 minutes. I n t h i s range the weight l o s s i s 35 to 55 percent and the s u r f a c e area i s 800 to 1100 m /g. The a c t i v a t i o n y i e l d f o r char d e r i v e d from u n c l a s s i f i e d s o l i d waste was much higher than f o r c e l l u l o s e when compared on a gross weight b a s i s . A lower l i m i t on the y i e l d from s o l i d waste was imposed by the ash content o f the char, approximately 80 to 85 percent by weight. At a c t i v a t i o n temperatures above 800°C, the c a r bon content o f the a c t i v a t e d product from u n c l a s s i f i e d s o l i d waste was l e s s than t e n percent by weight. 2

Air Classification A i r c l a s s i f i c a t i o n o f both raw, wet s o l i d waste and o f p y r o l y s i s char was evaluated as a means o f s e p a r a t i n g out i n o r g a n i c components that are not amenable t o c a r b o n i z a t i o n and a c t i v a t i o n , w i t h a view t o i n c r e a s i n g the carbon content and s p e c i f i c s u r f a c e of the a c t i v a t e d product (7). A i r c l a s s i f i c a t i o n segregated approximately h a l f of the i n o r ganic m a t e r i a l i n the raw wet waste. The o r g a n i c content o f the r e j e c t m a t e r i a l was approximately ten percent by weight. A i r c l a s s i f i c a t i o n o f the char achieved a f u r t h e r r e d u c t i o n o f 60 percent by weight o f the ash remaining a f t e r p y r o l y s i s . The i n e r t f r a c t i o n segregated i n a i r c l a s s i f i c a t i o n o f the char contained approximately 90 percent ash, as d i d that from raw waste c l a s s i f i cation. The y i e l d based on carbon was approximately 40 percent by weight i n p y r o l y s i s a t 700°C. The y i e l d based on carbon i n a c t i v a t i o n w i t h steam and CO2 a t 910°C and an a c t i v a t i o n time o f 20 minutes was 40 percent by weight. These y i e l d s are v i r t u a l l y i d e n t i c a l to those observed w i t h u n c l a s s i f i e d s o l i d waste a t the same c o n d i t i o n s . N e v e r t h e l e s s , the p r o p e r t i e s o f a c t i v a t e d carbon prepared from s o l i d waste were improved markedly by u t i l i z i n g a i r c l a s s i f i c a t i o n . The ash content was reduced from 90 percent t o 60 percent by weight. The s p e c i f i c s u r f a c e was i n c r e a s e d from 80 m per gram gross weight to 350 m per gram. The s p e c i f i c s u r f a c e s of a c t i v a t e d carbons d e r i v e d from both c l a s s i f i e d and u n c l a s s i f i e d s o l i d wastes were approximately equal when compared on the b a s i s of carbon content, 800 m per gram o f carbon. The e f f i c a c y o f a i r c l a s s i f i c a t i o n i n reducing the f r a c t i o n of i n o r g a n i c i m p u r i t i e s i n waste-derived a c t i v a t e d carbon i s demo n s t r a t e d i n Table IV. The o v e r a l l y i e l d o f carbon i n p y r o l y s i s and a c t i v a t i o n i s the same, approximately 25 p e r c e n t , r e g a r d l e s s of whether o r not a i r c l a s s i f i c a t i o n i s p r a c t i c e d . N e v e r t h e l e s s , the carbon content o f the f i n a l product i s 40 percent w i t h a i r 2

2

2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

ROBERTS

E T A L .

Activated Carbon from Cellulosic Solid Wastes

200

400

600

800

1000 °C

ACTIVATION TEMPERATURE

Figure 5. Effect of activation conditions on the specific surface of activated carbons pre­ pared from cellulose. Specific surface is ex­ pressed as m per g of activated carbon. Cellu­ lose A,( ); Cellulose B, ( ); 0,15 min; X,30 min; A, 60 min. 2

ACTIVATION TEMPERATURE

Figure 6. Weight loss during activa­ tion of chars derived from cellulose. Cellulose A, ( ); Cellulose B, ( ); O , 15 min; X , 30 min; Δ , 60 min.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

10

-6

16

-10

26

-58

84

n.a. 41 -6.5 34.5

-1 8 -4 4

15 -9 6 -0 6

-59

9

-0

41

100

19.8 -11

15

n.a.

-0.2

-15

-16

100

20

30

100

Total Weight,

n.a. 9 -4.5 4.5

30 -0 30

9

-11

20

n.a.

20

Carbon, g

n.a.

30

-0

30

n.a.

30

Ash, g

(CgHxoO^); and 30% w/w

n.a.: not a p p l i c a b l e .

45% i n p y r o l y s i s

ash.

and 50% i n a c t i v a t i o n .

100 g of raw, wet waste: 30% w/w H2O; 40% w/w v o l a t i l e matter w i t h an e m p i r i c a l formula

Activation

Air Classification

Pyrolysis'

Air Classification

Process

Assumed y i e l d s based on carbon:

Basis:

A c t i v a t e d Carbon

B e n e f i c i a t e d Char

Char

A i r - C l a s s i f i e d Waste

Raw, wet waste

Material

Carbon, g

Ash, g

Without A i r C l a s s i f i c a t i o n

Total Weight, g

With A i r C l a s s i f i c a t i o n

Weight and Change i n Weight, g

Table IV Y i e l d s and Product Compositions i n P y r o l y s i s and A c t i v a t i o n o f A i r - C l a s s i f i e d and U n c l a s s i f i e d S o l i d Waste

20.

ROBERTS

Activated Carbon from Ceïlulosic

E T A L .

Solid Wastes

405

c l a s s i f i c a t i o n o f raw waste and char, compared t o only 13 percent without a i r c l a s s i f i c a t i o n . Comparison w i t h Conventional Activated-Carbon Products. Powdered a c t i v a t e d carbon d e r i v e d from a i r - c l a s s i f i e d s o l i d waste was compared t o s e v e r a l commercially a v a i l a b l e , powdered a c t i v a t e d carbons i n terms o f s p e c i f i c s u r f a c e , ash content, and e m p i r i c a l measures o f a d s o r p t i o n c a p a c i t y . The r e s u l t s are shown i n Table V. Table V P r o p e r t i e s o f Powdered A c t i v a t e d Carbon

Activated Carbon Carbon from Air-Classified S o l i d Waste*

Ash Content % w/w

60

Aqua Nuchar A

3.5

Calgon BL

8

Darco M

16.5

Relative COD Methylene Reductio

Surface

350

500

15

120

1.00

625

560

28

150

1.00

1100

920

30

280

0.95

630

455

21

125

0.95

* A c t i v a t e d w i t h steam and CO2 a t900°C. t See d e f i n i t i o n i n t e x t . The waste-derived m a t e r i a l e x h i b i t e d a s u b s t a n t i a l l y higher ash content and lower s p e c i f i c s u r f a c e than any o f the commercial products t e s t e d . Moreover, i t was r a t e d i n f e r i o r according t o c o n v e n t i o n a l l y accepted c r i t e r i a f o r a d s o r p t i o n c a p a c i t y such as the phenol and methylene blue numbers. However, the waste-derived carbon proved e q u i v a l e n t t o the others when judged a c c o r d i n g t o the c r i t e r i o n o f r e l a t i v e c a p a c i t y o f r e d u c t i o n o f chemical oxygen demand (COD) i n p r i m a r y - t r e a t e d m u n i c i p a l wastewater. The r e l a t i v e c a p a c i t y f o r COD removal was d e f i n e d o p e r a t i o n a l l y as g COD removed from Palo A l t o primary e f f l u e n t (COD = 60 mg/1) per gram of adsorbent, averaged over a range o f carbon dosages from 400 to 1200 mg/1 and normalized w i t h respect t o Aqua Nuchar A as a r e f e rence product ( 7 ) . The s a t i s f a c t o r y performance of the s o l i d waste carbon d e s p i t e i t s low s p e c i f i c s u r f a c e i s s u r p r i s i n g . The apparent anomaly can be e x p l a i n e d i n p a r t by d i f f e r e n c e s i n pore s i z e d i s t r i b u t i o n . The waste-based carbon contains a higher prop o r t i o n o f i t s i n t e r n a l v o i d volume i n l a r g e - s i z e d pores. A comp a r i s o n w i t h the reference carbon, Aqua Nuchar A, can be made w i t h the data i n Table VI. Because o f the r e l a t i v e l y low p r o p o r t i o n o f

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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SOLID WASTES AND

RESIDUES

Table VI D i s t r i b u t i o n o f Pore Volume Percent o f Pore Volume Activated Carbon

Pore Radius <25 x 10"" m 10

Pore Radius <50 x 1 0 " m

Pore Radius <100xl0" m

Pore Radius <500xl0" in

10

10

10

Derived from Classified S o l i d Waste

15

30

45

75

Aqua Nuchar A

85

90

98

99

1 0

s m a l l pores (< 2 5 x l 0 ~ m ) , the carbon from waste has a low spec i f i c s u r f a c e , and hence a low c a p a c i t y f o r a d s o r p t i o n of s m a l l molecules such as phenol volume i n the t r a n s i t i o n a assures that the mass t r a n s p o r t r e s i s t a n c e w i l l be low compared to that i n carbon such as Aqua Nuchar A that has only a s m a l l f r a c t i o n of such l a r g e r pores. This i s an important f a c t o r a f f e c t i n g the extent and r a t e o f a d s o r p t i o n from s o l u t i o n o f l a r g e molecules such as a r e represented by the COD content of wastewater. Accordi n g to the data of Dewalle and Chian (19), n e a r l y s i x t y percent o f the s o l u b l e o r g a n i c matter i n b i o l o g i c a l l y t r e a t e d e f f l u e n t s l i e s i n the range of molecular weight greater than 500. Substances of such h i g h molecular weight a r e hindered i n t r a n s p o r t through pores of r a d i u s l e s s than 25 x 1 0 ~ m , s i n c e the dimensions of the molec u l e are of the same order of magnitude as those o f the space through which i t i s d i f f u s i n g . 10

F e a s i b i l i t y of A c t i v a t e d Carbon from S o l i d Waste I t has been shown i n t h i s work that the q u a l i t y o f a c t i v a t e d carbon prepared from u n c l a s s i f i e d m u n i c i p a l s o l i d waste i s so poor i n terms of s p e c i f i c surface that f u r t h e r i n v e s t i g a t i o n i s scarcel y j u s t i f i e d . On the other hand, there i s promise that an a c t i vated carbon of acceptable q u a l i t y can be made from m u n i c i p a l r e f use i f the carbon content i s enhanced by a s e l e c t i v e s e p a r a t i o n technique such as a i r c l a s s i f i c a t i o n . In order f o r an a c t i v a t e d carbon to be considered o f h i g h q u a l i t y f o r water treatment use, the ash content should be l e s s than 15 percent by weight. The corresponding maximum a l l o w a b l e ash content i n the educt can be estimated. O p t i m i s t i c a l l y assumi n g a 55 percent carbon y i e l d i n p y r o l y s i s and 70 percent i n a c t i v a t i o n , the l i m i t i n g ash content i n the educt would be 3.3 percent based on dry weight i f there were no s e p a r a t i o n of i n e r t m a t e r i a l from the char. I f a 60-percent r e j e c t i o n of the i n e r t m a t e r i a l i n the char could be achieved by a i r c l a s s i f i c a t i o n or some other means, the p e r m i s s i b l e ash content of the educt would be 8 percent.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20.

ROBERTS

E T

A L .

Activated Carbon from Cellulosic Solid Wastes

407

Thus, i f i t i s d e s i r e d t o produce from s o l i d waste an a c t i vated carbon that w i l l be considered e q u i v a l e n t t o the h i g h e s t q u a l i t y products a v a i l a b l e f o r water and wastewater treatment, a t t e n t i o n should be centered on s o l i d wastes having an ash content of 10 percent o r l e s s . An a c t i v a t e d carbon o f acceptable q u a l i t y can be produced from s o l i d waste having an ash content as h i g h as 20 percent o f dry weight, provided that i n e r t m a t e r i a l s are removed from the char. P i l o t p l a n t s t u d i e s o f a i r c l a s s i f i c a t i o n o f a l a r g e number o f m u n i c i p a l wastes i n d i c a t e t h a t the i n o r g a n i c content can be e a s i l y reduced t o 20 percent ( 4 ) . Combining e x t e n s i v e preshredding w i t h a i r c l a s s i f i c a t i o n , an ash content o f l e s s than 10 percent by weight i s a t t a i n a b l e (20). I t i s t o be a n t i c i p a t e d that p y r o l y s i s systems f o r the general purpose o f m u n i c i p a l s o l i d waste management w i l l be designed f o r maximum r e d u c t i o n o f waste volume and maximum p r o d u c t i o n o f energy values i n the form of gaseou an approach based on r a p i w i l l r e s u l t i n lower carbon y i e l d s than were obtained i n t h i s work u s i n g low h e a t i n g r a t e s . H i g h l y e f f i c i e n t p r e c l a s s i f i c a t i o n of the s o l i d waste i s a p r e r e q u i s i t e f o r o b t a i n i n g chars w i t h even a modest p o t e n t i a l f o r a c t i v a t e d carbon manufacture from an o p e r a t i o n o r i e n t e d toward volume r e d u c t i o n and gas p r o d u c t i o n . Hence, the chars obtained from p y r o l y s i s o f m u n i c i p a l s o l i d wastes under the c o n d i t i o n s t h a t probably w i l l be used i n p r a c t i c e are not i d e a l f o r conversion t o a c t i v a t e d carbon having p r o p e r t i e s s u i t a b l e f o r water and wastewater treatment. S p e c i a l a t t e n t i o n must be devoted t o the s e l e c t i o n o f the educt and the o v e r a l l proc e s s i n g scheme should be optimized w i t h a c t i v a t e d carbon i n mind. Conclusions C e l l u l o s e was found t o be a s u i t a b l e model compound t h a t behaves s i m i l a r l y t o the o r g a n i c f r a c t i o n o f s o l i d waste d u r i n g pyr o l y s i s and a c t i v a t i o n . Conversely s o l i d waste behaves i n a genera l way as expected f o r a mixture o f c e l l u l o s e and an i n o r g a n i c ash. The maximum s p e c i f i c s u r f a c e o f c e l l u l o s e char was 350 t o 400 m /g a t 710°C. A c t i v a t i o n o f c e l l u l o s e char w i t h steam and C02 r e s u l t e d i n a product w i t h a s p e c i f i c s u r f a c e as l a r g e as 1650 m /g. An acceptable combination o f a c t i v a t i o n temperature and time was found i n the range of 850°C t o 900°C and 30 t o 60 minutes, where a product having a s p e c i f i c s u r f a c e o f 800 t o 1000 m /g was obtained w i t h a y i e l d of 50 percent by weight. The o v e r a l l y i e l d o f carbon i n p y r o l y s i s and a c t i v a t i o n was approximately 25 percent. Inorganic c o n s t i t u e n t s a t low c o n c e n t r a t i o n i n the educt appear t o have a c a t a l y t i c e f f e c t enhancing p y r o l y s i s and a c t i v a t i o n . The i n o r g a n i c i m p u r i t i e s i n c e l l u l o s e and s o l i d waste c o n t a i n cons t i t u e n t s t h a t r a i s e the char y i e l d and i n c r e a s e the r a t e of p y r o l y s i s . Hence, i n o r g a n i c i m p u r i t i e s present a t l e v e l s o f a few percent are b e n e f i c i a l f o r producing a c t i v a t e d carbon. However, concentrat i o n s o f i n o r g a n i c m a t e r i a l g r e a t e r than ten percent i n the educt 2

2

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SOLID WASTES AND RESIDUES

adversely affect the properties of the final product, causing high ash content and low specific surface. The yield and composition of char from unclassified solid waste were similar to those from cellulose when adjusted for the differing contents of inert ash. However, because of the high ash content of the educt, the activated carbon prepared from municipal solid waste without segregation of the inert material has a compo­ sition that is unacceptable for water and wastewater treatment. The carbon content of the final product is ten percent or less and the specific surface is less than 100 m^ per gram. Air classification of solid waste and char has a significant, beneficial effect in enhancing the carbon content of the final product. Activated carbon so prepared has a carbon content of 40 percent and a surface area of 350 m^/g. It is comparable in qual­ ity to several low-priced commercial products for reduction of chemical oxygen demand in wastewater Manufacture of activate feasible under certain conditions for low ash content, heating during pyrolysis should be gradual, and inert material should be segregated from the char by air clas­ sification or an equivalent method. The char thus prepared can be activated by conventional thermal techniques. The optimization of pyrolysis for maximum volume reduction and gasification of solid waste at a minimum cost conflicts with the manufacture of highquality activated carbon. Acknowledgement s The experimental work concerning pyrolysis and activation of air-classified solid waste was conducted by M. K. Stevenson. The financial support of the U.S. Environmental Protection Agency, Contract Νο CPE-70-129 and Grant No. R-803188, as well as the Canton of Zurich is gratefully acknowledged. R. Braun, P. Erni, P. Grabner, and J . Wetzel of the Swiss Federal Institutes of Tech­ nology and D. M. Mackay of Stanford University provided helpful advice. Λ

Abstract The preparation of activated carbon by pyrolysis and thermal activation of municipal solid waste was investigated. The organic fraction of the solid waste behaves similarly to cellulose. Sat­ isfactory yields and specific surface were obtained by pyrolysis at 700°C and a heating rate of l°C/min, followed by activation at 900°C with steam and CO2. The overall yield based on carbon was 25 percent. The surface area of the activated product was 800 m per gram carbon. Segregation of inert material by air classifica­ tion of the municipal solid waste and its derivative char improved the carbon content of the activated product from ten to forty per­ cent and increased the specific surface from 80 to 350 m /g. The 2

2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20.

ROBERTS ET AL.

Activated Carbon from Cellulosic Solid Wastes

409

activated carbon so prepared was comparable to commercially a v a i l ­ able, powdered activated-carbon products in removing COD from wastewater. Literature Cited 1. 2. 3. 4.

5. 6.

7.

8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

18. 19.

Hoffman, D. Α., and R. A. F i t z , Environ. Sci. Technol. (1968) 2 (11), 1023. Hassler, J. W., " P u r i f i c a t i o n with Activated Carbon," Chemi­ cal Publishing Co., New York, 1974. Smisek, Μ., and S. Cerny, "Active Carbon," Elsevier, New York, 1970. Klumb, D. L., and P. R. Brendel in Energy and Resource Recov­ ery from Industrial and Municipal Solid Wastes, G. F. Kroneberger (ed.), A. I. Chem. E. Symposium Series #162, Vol. 73 (1977). Niessen, W. R., an Proceedings of th York, 1970. Brunner, P., Beitrag zur Pyrolyse von Cellulose f ü r die Herstellung von Aktivkohlen aus Abfallstoffen (1976), Doctoral Dissertation No. 5705, Swiss Federal Institutes of Technology, Zürich. Stevenson, M. K., J . O. Leckie, and R. Eliassen, Preparation and Evaluation of Activated Carbon Produced from Municipal Refuse (1972), Technical Report No. 157, Dept. of Civil Engineering, Stanford University. Losty, H. H. W., and H. D. Blakelock, Second Conference on Industrial Carbon and Graphite (1965), 29, London. Tang, Μ. Μ., and R. Bacon, Carbon (1964) 2, 211. Keatch, C. J . , and D. Dollimore, "An Introduction to Thermo­ gravimetry," 35-55, Heyden, London, 2nd ed., 1975. Garn, P. D., CRC Critical Reviews i n Analytical Chemistry (1972) 3 (1), 65. Freeman, E. S., and B. C a r r o l l , J . Phys. Chem. (1958) 62, 394. Akita, Κ., Rep. of Fire Research Industry of Japan (1959) 9, 1. Akita, Κ., and M. Kase, J . Polymer Sci. (1967) 5, 833. Tang, W. Κ., unpublished Ph.D. Dissertation, Univ. of Wiscon­ s i n , 1964. Stamm, A. J . , Indust. and Eng. Chem. (1956) 48, 413. Parker, W. J . , and A. E. Lipska, A Proposed Model for the Decomposition of Cellulose, U.S. Naval Radiological Defense Laboratory, San Francisco, C a l i f . , Rept. No. AD 701 957 (May 1969). Tang, W. Κ., and W. K. Neill, J . Polymer Sci. (1964) 6(C), 65. Dewalle, F. Β., and E. S. K. Chian (1974), "Removal of Organic Matter by Activated Carbon Columns," J . Envir. Eng. Div. ASCE, 5, 1089.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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Preston, G. T., "Resource Recovery and Flash Pyrolysis of Municipal Refuse," Symposium on Clean Fuels from Biomass, Sewage, Urban Refuse, and Agricultural Wastes, Institute of Gas Technology, Orlando, Florida, January 1976.

MARCH 3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

INDEX A Activated carbon(s) from cellulosic solid wastes, pyro­ lysis for the production of fuel from sewage solids production, experimental proce­ dure for pyrolysis products, conventional properties of powdered from solid waste, feasibility of specific surfaces treatment system Activation energies for pyrolysis Afterburner train Agricultural wastes disposal Air -carbon reaction exothermic classification classified, unclassified solid waste, activation of input rate preheating system requirements -to-fuel requirement for combustion velocities in modified zigzag air classifier Albany biomass liquefaction plant changes process results PDU control panel design highlights economic analysis equipment commissioning, prooftesting future activities mass balance mechanical difficulties product oil properties projected process economics schematic (as built) schematic (modified) synthesis gas plant Aluminum for E R C O process Anaerobic digestion methane from of sludge Ancillary systems

392 241 393 40 40 406 402 247 401 245 94 146 144 402 404 149 52 176 122 395 372 376 376 375 383 383 380 387 382 380 380 390 374 378 383 341 13 13 12 150

Andco-Torrax demonstration plant tests equipment train, S I D O R plant Luxembourg high-temperature slagging pyro­ lysis system process, development of

system economics of equipment net disposal/product costs unit Ash content, heating value of dry municipal refuse removal zone

54 54 60 47 53

47,48 57,61 55,57 60 58

115 150 127

Β Back-mix flow reactors 16 Baghouses 150 Bailie process from pyrolysis of bagasse 35 Batch reactor 327,336 Battelle gasification process 129 Bed reactors, fluidized 16 Bellows seal on reactor, pitting damage 250 Belt filter presses 207 Bench-scale steam gasification of agricultural wastes 324 steam gasification of feedlot wastes tire pyrolysis at the University of Tennessee 348 Biochemical conversion 12 processes 9 Biogasser 256,263 catalyzed 264 experimentation 262 runs, minikiln 264 Biomass 219 boiler systems 22 direct combustion of 22 feed 219 feedstocks 309 fuels 144,146 gasification 307

411

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

412

SOLID

Biomass (continued) liquefaction conceptual commercial process .... 382 energy balance 385 mass balance 384 P D U , Albany, Oregon 372 P E R C Process 371 Process, Garrett Energy Research and Engineering Company (GERE) 217 processing plant, commercial 230 processing plant, economic analysis 230 projected commercial-scale 235 pyrolysis systems, economics associated with 21 Blast cycle 52 Blue I 95 pilot plant 96 II 95,9 pilot plant 9 III 99 co-pyrolysis data 117 pilot plant 100,107 IV pilot plant 99,107 char yield 107 Boiler fuel, capital operating costs for 140 Boiler fuel, gasification process 140 Boudouard reaction 127 Bovine manure, typical ultimate analysis of 220

C Cake ash content 204 Calciner 244 Caloricon Process 88, 90,92 stages of operation 88, 90 Capital cost breakdown—commercial biomass liquefaction plant 388 investment of manure biomass plant 232 operating costs for boiler fuel 140 Carbohydrate conversion by hydrolysis 13 Carbon 201 black , 275 content of char 397 dioxide formation 143 gasification rate 203 monoxide formation 143 on the pyrolysis temperature 397 reaction rates 201 waste-derived 405 yield in cellulose pyrolysis 396 Carbonaceous residue 127 Carbonaceous solids 165

WASTES

A N D RESIDUES

Catalytic effects 334 Cellulose 407 hydrolysis of 13 pyrolysis 394 carbon yield 396 rate, effect of activation conditions on the specific surface activated carbons 403 solid wastes, pyrolysis for the production of activated carbon .... 392 used in pyrolysis experiments, characteristics 393 Cement kilns 12 Char 47,94,214 burning operating mode 199 combustion 230 conveyor 102 fuel products 14 gasification 257

output system pyrolysis specific surface steam gasification yield Blue IV pilot plant effect of heating rate during pyrolysis on for pyrolysis product on the pyrolysis temperature Chemical oxygen demand ( C O D ) .... China Lake project operating costs Chips municipal refuse, gas compositions for wood Clinker formation Coal, cost breakdown for electricity from Co-dewatering C O D (Chemical oxygen demand) .... Co-disposal process, environmental effects of .... process, projected economics of test program Co-firing Co-gasification Co-incineration of sludge and refuse .. Coke formation Combustion, air-to-fuel Combustion chamber, secondary Commercial biomass liquefaction plant artist's rendering capital cost breakdown oil production costs plants Concord commercial demonstration system

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

95 225 400 259 104 107 400 105 397 405 350 355 134 149 25 83 405 76 82 69 9 177 12 275 122 50

384 388 389 55 182

413

INDEX

Condensate inspection data 280 Condensate yields 138 Conversion processes 3 Co-pyrolysis 110 data of Blue III 117 Cordele plant 99,101,107 Corn cobs 156,329 Cost projections for gasifier applications 158 Cost of refuse disposal 82 Cotton gin waste 149 Counterflow pyrolysis chamber 123 Cow manure in nitrogen 343 Crop residue ( s ) disposition 7 to electrical energy, conversion 142 to thermal energy, conversion 142 Cyclones 150

D Decarboxylation Dehydroxylation Demonstration plant Andco-Torrax tests Purox System Dense-phase fluidization Densification Dew point Dewatering drying solids Diesel engines additions of modifications of turbo-charged intercooled Digester gas Direct combustion of biomass contact drying of manure spray quenching fired plants, cost of electricity in .... Distributor mechanism Down time Downdraft gasification pilot plant gas producer, crosssection producer, reaction zones of reactor residue-fueled producer Downstream gas clean-up system Drop charge revenues for E R C O Process Drying solids dewatering

259 259 53 54 54 66 317 149 146 82 244 155 155 152 195 9,11 22 222 224 288 38 136 102 143 148 145 149 146 149 341 f 244

Dual fuel conversion Dual fuel operation, engine performance results Dulong-Petit Equation D u m p valves Dupont 990 Thermal Analysis System

152 156 298 271 342

Ε Eccentric grate, rotating E C O II fuel Economic analysis of biomass processing plant Economics of scale Electric power industry Electrical energy, conversion of crop residues to Electrical power, conversion factor of

151 349 230 40 22 142

cost(s) of building new direct-fired plants 39 of firing wood-gas in existing plants 39 of wood-fired plants 39 of wood-gas-fired plants 39 Endothermic steam-carbon reaction .. 144 Endothermic water gas reaction 127 Energy balance 248 biomass liquefaction 385 for dried municipal refuse 113 Purox System 65 consumption 21,142 conversion system, complete 153 conversion system size 21 distribution 105 for a mixture of pine bank and saw dust 108 for pine bank 108 for pine tree top chips 108 flow(s) 70,128 for wood gasification 129 projected 73 recovery 193 from agricultural residues, thermal process 217 options 9 resources pilot plant for fluidizedbed pyrolysis of solid waste .... 337 value 28 Envirotech 172 temperature/oxygen control system 177 Enzymatic hydrolysis 13 Equipment commissioning, prooftesting at Albany P D U 380

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

414

SOLID

ERCO cost requirements 341 Process aluminum 341 drop charge revenues 341 ferrous metals 341 fuel gas 341 Estimated net sludge disposal cost 84,85 Ethanol through fermentation, production of 13 Exothermic air-carbon reaction 144 Expandable membrane filter press .... 209 Extender oils 275

F Failed weld of reactor tube 250 Farm power plant, portable 100 W .... 154 Feed components, characteristics of 135 particle size distribution, pyrolysi to reactor, description of 24 Feedstock(s) 167,275 characteristics 137 drying 172 ethylene 353 evaluation, material balance 185 gas compositions for 137 manure 371 municipal solid waste 371 solid waste 188 suitability, determination 138 thermal reformation 172 volatilization 172 wood 371 yields processing rates 139 Ferrous metals for E R C O Process 341 Fiberglass filters 151 Field test units 98 Filter cake 104 Filter comparison summary 212 Filtering equipment 208 Filtration results with membrane plates 210 Firebox 246 Firing wood-gas in existing plants, electricity costs of 39 Fixed-bed gasifier of solid waste fuels 126 Flocculation 207 Flow reactor(s) back-mix 16 horizontal 16 inclined 16 vertical 16 Flue Gas 219 Fluidization 317 bed pyrolysis 307 reactor 16,308,327,338 cold model variable velocity .... 316 concept, three-stage 317,318

WASTES

A N D RESIDUES

reactor (continued) nitrogen concentration of variable velocity Forestry residue disposition Fossil fuel-fired silicon carbide crossflow shell-and-tube heat exchanger Fuel combustion consumption rate E C O II feed system gas for E R C O Process gas, maximum conversion of solids product separation costs production costs from sewage solids, activated carbon substitution hierarchy

311 311 7

52 143 147 349 150 341 264 4 34 241 25

G Garrett Energy Research and Engineering Company ( G E R E ) biomass process 217 Gas (es) cleaning equipment 53 compositions for different feedstocks 137 from simulated waste run 136 for wood chips municipal refuse 134 filter 270 -fired power plant 34 producer of reactor 247 advantages of 34 disadvantages of 36 flow rate 149 fuel boilers 24 phase reactions of the volatile pyrolysis products 342 producer system 150,153 purification 91 of varying fuel value 24 yield, pilot plant 282 yield for sewage sludge 293 Gasification catalysts 138 downdraft 143 limitations of specific rate 149 in a multiple-hearth furnace 165 process 126 of rice husks 149 of solid waste(s) 88 Battelle 129 for boiler fuel 140 control variables 177

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

415

INDEX of solid wastes (continued) emissions 187 variables 147 reaction(s) 143 thermodynamics 128 of solid waste fuels in a fixed-bed gasifier 126 specific rates 147,160 systems, development of pilot plant 142 Gasifier 49 applications, cost projections 158 design147 I G T entrained 362 performance, pilot plant 157 pilot plant 268 T P D SIDOR 58 Gasoline polymerization 353 GERE multiple-hearth pyrolysis process .... 218 projected commercial-scale biomas process 23 single-hearth, bench-scale pilot plant unit 221 Goodyear Tire & Rubber Company .... 274 Grate configuration 147 Gravity-feed lock hoppers 269

H Heat balance(s) 184,186 of Andco-Torrax S I D O R System 56 results 204 exchanger, fossil fuel-fired silicon carbide cross-flow shell-andtube 52 exchanger, natural gas-fired 54 recovery 193 recuperator 52 transfer, indirect 16 Heating value 204 of dry municipal refuse ash content 115 Heavy fraction refuse 110 High-temperature char operating mode 199 Horizontal flow reactors 16 Hot fuel bed 144 Hot gas clean-up pilot plant 132 Hydraulic system 244 Hydrocarbon emissions 188 Hydrocarbon production during pyrolysis 353 Hydrolysis carbohydrate conversion by 13 of cellulose 13 enzymatic 13

I I G T entrained gasifier

362

Inclined flow reactors Indirect heat transfer Industrial sludges Internal gas concentration, effect of sampling velocity on Internal gas samples

16 16 166 312 309

Κ Kaplan Industries Kiln reactor, single-shaft Kiln support Knock-out pots

13 26 269 288

L Leaching potential LeChatelier's Principle

79 264

Ligno-cellulosic wastes Liquefaction Liquid recovery systems Lock hoppers, gravity-feed Low-temperature char operating mode

94 3 288 269 198

M MAFchar 294 M A F oil 295 Manure 320,329 biomass plant, annual operating costs 234 biomass plant, capital investment.... 232 direct contact drying 224 drying experiments 220 feedstock 371 process, synthesis gas ( S G F M ) 307 residue disposition 7 steady-state solids distribution of .... 321 Mass balance 63 Albany P D U 382 of Andco-Torrax ( S I D O R ) system 56 biomass liquefaction 384 for dried municipal refuse 112 Purox System 64 Mass flow(s) 70,128 projected 72 for wood gasification 129 Material balance(s) 248 overall 359 for the Syngas Process 361 handling system 99 Medium energy gas (es) 22 production, economics of 23

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

416

SOLID

Membrane plate ( s ) filter presses 207 filtration results 210 performance 211 Methane from anaerobic digestion 13 fermentation (anaerobic digestion) 9 production reactor ( M P R ) , firststage 359 Mettler thermoanalyzer 394 M G D pilot plant 243 1 0 - M G D pilot plant size, comparison of cost estimates 250 M H G S (multiple-hearth gasification system) 167 M H G S process efficiencies 179 M H P system 178 Minikiln 256 biogasser runs 264 experimentation 25 research apparatus 25 Moisture and ash-free materials (MAF) 291 Molten metal reactors 16 salt 346 catalytic technique 324 Muffle furnace 225 Multiple-hearth furnace(s) 191 gasification 165 system ( M H G S ) 167 gasifier 174 Municipal refuse 99,170 ash content, heating value of dry 115 disposal of sewage sludge 287 disposition in the U.S 8 energy balance for dried 113 gas compositions for wood chips 134 mass balance for dried 112 process economics 138 pyrolysis of dried 110 pyrolysis products 121 pyrolysis system, small community Ill system, plant description 110 sewage sludge 165 solid waste( s ) ( M S W ) 166,294,392 average chemical composition .... 326 C H in pyrolysis product gas for pyrolysis 303 C H in pyrolysis product gas for pyrolysis 302 C O in pyrolysis product gas for pyrolysis 300 C 0 in pyrolysis product gas for pyrolysis 301 feedstock 371 2

4

2

4

WASTES

A N D RESIDUES

solid waste ( s ) ( continued ) oil yield product gas from pyrolysis pyrolysis, pyrolytic product recovery unclassified

292 297 305 406

Ν Natural gas 22,142 -fired heat exchanger 54 five-year average cost 158 requirements of engine 159 Nichols pilot plant test results on filter press 213 Nitrogen concentration of the fluidized-bed pyrolysis reactor 311 concentration in the S G F M reactor 313

Ο Occidental Flash Pyrolysis Process .... 287 Off-gas system 97,102 Oil 191 production costs of commercial bio­ mass liquefaction plant 389 shale 274 yield 114 for municipal solid waste 292 for sewage sludge 292 Organic(s) carbon adsorption equilibriom plots 247 cord 275 residues, approximate tonnage of .... 5 sludge disposition in the U.S 8 wastes in inert, reactive steam atmospheres 339 water content 204 Outlet gas temperature 223 Outlet solid temperature 223 Output gas, estimated composition of 35 Oxygen-fed shaft furnace 63 Ρ P C B residual PCB's polychlorinated biphenyls P D U pilot plant P E R C process for biomass liquefaction P T G L process (es) categories categorization of P T G L ( pyrolysis, thermal gasification, and liquefaction processes)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

261 259 217 371 14 16 15 9

417

INDEX

Pilot plant equipment experimentation gas yield gasification systems development.... gasifier performance unit, G E R E single-hearth, benchscale Pine bank, energy distribution of bank and saw dust, energy distributions of tree top chips, energy distribution of Pitting damage of Bellows seal on reactor Plant(s) control system of W - M description size on production cost, effec sizing Polychlorinated biphenyls (PCB's) ... Polymer gasoline, conversion of solid waste to Polymerization test data summary Pore volume, distribution of Positive piston-feed system Power cycle Power plants, projected Preprocessing costs Press capacity Primary combustion air, preheating of zone Princeton University research Princeton University tubular quartz reactor experiment Process development unit pilot plant (PDU) effluent streams, trace metal disposition in product streams Processing rates for feedstocks, yields Product cost for a plant of 1530 tons/day .... gas analyses, summary of combustion products, trace metal concentrations in particulate levels oil properties at Albany P D U Production cost, effect of plant size on Purification system Purox converter sludge/refuse codisposal in a process

196 220 222 282 142 268 157 221 108 108 108 250 271 10 230 259 349 354 406 269 254 252 4 210 49 52 49 342 345

217 81 76 139 33 143 74 78 76 380 386 353 82 63 26

Purox (continued) System 63,82 codisposal facility, estimated economics of 86 demonstration plant 66 energy balance 65 facility for sludge/refuse codisposal 67 gas combustion products, calculated particulate levels in .... 77 mass balance 64 sludge/refuse codisposal in the .. 66 wastewater treatability data 78 Pyrolysis 3,47,49,94,223 for activated carbon production, experimental procedure 393 activation energies 401 of bagasse, Bailie Process from 35 of biomass, variable velocity

of cellulose, solid waste chamber, counterflow char activation of dried municipal refuse feed analysis feed composition in a fluidized bed modes of operation, comparison of moist manure of municipal solid waste, product gas oil data uses of wood waste pyrolysis char of organic wastes in inert, reactive steam atmospheres pilot plant with improved product collection system pilot plant initial design process description operating modes G E R E multiple-hearth Occidental Flash product(s) gas gross heating value heating value from municipal refuse from wood waste for the production of activated carbon from cellulosic solid waste reactor operating condition of refuse, yields from of rubber tires of sawdust of scrap tires of sewage sludge, product gas

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

394 123 225 401 110 351 291 307 202 226 297 118 119 118 339 290 289 26 197 218 287 298 106 121 116

392 245 32 275 340 274 296

418

SOLID

Pyrolysis (continued) of solid waste feed material summary system, non-slagging system, vertical-bed temperature dependence on carbon content of char dependence on carbon yield dependence on char yield test plans tests, summary thermal gasification and liquefaction processes ( P T G L ) of tires Pyrolytic oil properties Pyrolyzer design alternatives Pyrolyzing sewage sludge, economic factors Pyrox

127 352 107 94

397 397 397 332 335 9 346 295 191

Radiation-convection waste heat boiler 53 R C R A (Resource Conservation and Recovery Act) 166 R D F (refuse-derived fuel) .9,168,170,180 Reaction exothermic air-carbon 144 kinetics control 327 zones in a downdraft producer 145 Reactive steam atmospheres, pyrolysis of organic wastes in inert 339 Reactor damage 249 gas producer 247 head seal 375 products 246 tube, failed-weld 250 Recess tray filter presses 207 Recessed-plate filter press 208 Refractory wall furnaces 11 Refuse analysis of 133 composition 133 derived-fuel ( R D F ) 9,168 substitution of 193 disposal, cost of 82 to electrical power, conversion factor of 57 energy balance for dried municipal 113 heavy fraction 110 incinerators 11 light fraction 110 pyrolysis of dried municipal 110 pyrolysis products from municipal .. 121 single-shredded 122 yields from pyrolysis of 32

A N D RESIDUES

Regenerative towers Regenerators Reheater scraper blades Residual char Residue(s) discharge moisture content of Resource Conservation and Recovery Act ( R C R A ) Resource Recovery System Rice husks, gasification of Rotation eccentric grate Rubber, chemical reclamation of Rubber seal material, decomposed reactor Rubber tires, pyrolysis of

52 91 377 258 3 271 6 166 99 149 151 346 377 275

S

191 2

R

WASTES

Scrap rubber 275 Scrap tires, pyrolysis of 274 Screw conveyor dryer 102 Screw conveyor heat transfer data for vacuum drying manure 222 Scrubber condenser 104 Scrubbing system 102 S D S / A R R (sludge-dry solids to asreceived refuse ) ratio 69 Secondary combustion chamber 50 Sewage sludge 194,330 C H in pyrolysis product gas for pyrolysis .' 302 C H in pyrolysis product gas for pyrolysis 303 C O in pyrolysis product gas for pyrolysis 300 C 0 in pyrolysis product gas for pyrolysis 301 compositions of 200 gas yield of 293 H 0 in pyrolysis product gas for pyrolysis 299 municipal refuse, disposal of 287 oil yield of 292 particles 291 product gas from pyrolysis 296 pyrolytic product recovery 304 reasons for thermal destruction of 192 solids, activated carbon fuel 241 treatment plants 191 SGFM pilot plant reactor 310 reactor nitrogen concentration of 313 temperature profile of 314 velocity profile of 315 4

2

4

2

2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

419

INDEX Shaft furnace 90 oxygen-fed 63 SIDOR Andco-Torrax secondary com­ bustion chamber 57 plant Luxembourg: Andco-Torrax equipment train 60 Singlehearth reactor 220 shaft kiln reactor 26 shredded refuse 122 unit power plant 253 Slag analyses, summary of 75 leachate analysis 80 residue 50 characteristics 51 Sludge(s) 165,169,180 anaerobic digestion of 12 cake at dumping station 6 raw mixed 69 raw primary 69 characteristics 205 co-disposal tests 71 disposal 12,166 estimated net 84, 85 thermal processing techniques for 66 dry-solids to as-received refuse ( S D S / A R R ) ratio 69 incinerators 166 industrial 166 municipal sewage 165 -to-refuse ratios 83 /refuse blending conditions 76 co-disposal in a Purox converter .. 63 co-disposal in the Purox System .66,67 solids 244 Solid(s) dewatering 244 drying 244 fuel boilers, comparison of gas and 24 -to-fuel gas, maximum conversion of 264 waste 3 air-classified 394 disposal of 166 Disposal Act of 1965 53,323 energy resources pilot plant for fluidized-bed pyrolysis 337 feed material, pyrolysis of 127 feedstocks 188 fuels in a fixed-bed gasifier, gasification of 126 to polymer gasoline, conversion of 349 pyrolysis of cellulose 394 gasification of 88 moisture content of 6 municipal 166

Specific rate of gasification, limita­ tions of 149 Spouting-bed effect 320 Spray quenching, direct contact 288 Steady-state solids distribution for manure 321 Steady-state solids distribution for styrofoam 319 Steam -carbon reaction 228 endothermic 144 decomposition 128 gasification 252,254,334 heating system 270 Steer manure 219 Stepped kiln 270 Stripper system 353 Styrofoam, steady-state solids distribu­ tion of 319

of wastes to fuel, independent variables of 331 of wastes to fuel, summary of previous work 328 pyrolysis of mixed wastes 324 Subpilot-scale Sulfur dioxide 188 Syngas process 359 Syngas reactor system 360 Synthesis gas from manure process .... 307 Synthesis gas plant at Albany P D U .... 383 Synthetic rubber 275

Τ Tech-Air Corporation 97,102 Pyrolysis System, development of .. 123 pyrolysis unit 104 System uses 122 Test boiler system 118 Thermal conversion processes, advanced 14 destruction of sewage sludge, reasons for 192 energy, conversion of crop residues to 142 energy, conversion of wood residues to 142 gasification 3 of wood 165 processing techniques for sludge disposal 66 reformation, feedstock 172 reformation processes 165 Thermochemical conversion of wastes to energy 324

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

420

SOLID

Thermogravimetry Three-stage, fluidized-bed reactor Threshold-level values ( T L V ) Tire(s) char analysis char ash chemical analysis disposal oil inspection data program goals pyrolysis process pyrolyzer at the University of Tennessee, bench-scale T L V (threshold-level values) Tosco II Process 274, T P D S I D O R gasifier Trace metal concentrations in product gas combustion products disposition in process effluen streams levels Transportation costs of larger plants .. Trommel Tubular quartz plug flow reactor Tubular quartz reactor experiment, Princeton University Two-fluid bed reactor system annual operating costs of composition of product gas from .... economic parameters for estimated capital investment of flow diagram of gas costs of process

399 317 76 329 276 277 274 280 274 283 347 348 76 274 278 58

7 81 76 40 279 342 345 30 30 31 29 27 30 26

U Unclassified solid waste Union Carbide Process Unit efficiency University of Tennessee bench-scale tire pyrolyzer University of Tennessee project

404 38 25 348 347

V Vacuum drying manure Variable velocity fluidized-bed reactor cold model Velocity profile in the S G F M reactor Vertical bed pyrolysis system Vertical flow reactors Volatile pyrolysis products, gas-phase reactions of

222 222 311 316 315 94 16 342

WASTES

A N D RESIDUES

W W-M Plant(s) control system economic analysis of environmental characteristics power cycle waste-to-power system Walnut shells Waste(s) composition, simulated derived carbon economics associated with to energy, thermochemical conversion of to fuel, independent variables of subpilot conversion of to fuel products, pyrolytic conver-

254 271 271 273 254 259 172 135 405 21 324 331

gasification pilot plant 88 heat boiler 53 radiation-convection of 53 mixtures 330 oil 329 segregated 329 Wastewater metal concentration from refuse .... 79 production 79 treatability data, Purox System 78 treatment 241 plants 12 Water content 204 gas reactions 225 wall furnaces 11 Weight loss during activation of chars derived from cellulose 403 Wells, horsepower requirements of .... 159 Wells, volumetric demand of 159 Wood 172,329 char, residual 265 conversion rate 381 cost breakdown for electricity from 25 electric system, electric costs for .... 37 feedstock 371 -fired plants, electricity cost of 39 gas 34 cost breakdown for electricity from 25 electric system, electric costs for 37 -fired plants, electric cost of 39 residual char 260 residues to thermal energy, conversion of 142

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

INDEX

Wood (continued) thermal gasification of hogged pyrolysis products of pyrolysis system Wright-Malta System

165 102 116 99,102 252

Ζ Zigzag air classifier, air velocities modified Zigzag air classifier, configuration of modified o

f

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.