Biomass as a Nonfossil Fuel Source 9780841205994, 9780841207615, 0-8412-0599-X

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.fw001

Biomass as a Nonfossil Fuel Source

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.fw001

Biomass as a Nonfossil Fuel Source Donald L. Klass, EDITOR

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.fw001

Institute

of Gas

Technology

Based on a symposium sponsored by the Division of Petroleum Chemistry at the ACS/CSJ Chemical Congress (177th ACS National Meeting), Honolulu, Hawaii, April 2, 1979.

ACS

SYMPOSIUM AMERICAN

CHEMICAL

WASHINGTON, D. C.

SERIES SOCIETY

1981

144

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.fw001

Library of Congress CIP Data Biomass as a nonfossil fuel source. (ACS symposium series; 144 ISSN 0097-6156) Includes bibliographies and index. 1. Biomass energy—Congresses. I. Klass, Donald L. II. American Chemical Society. Division of Petroleum Chemistry. III. ACS/CSJ Chemical Congress, Honolulu, 1979. IV. Series: American Chemical Society. ACS symposium series; 144. TP360.B586 ISBN 0-8412-0599-X

662'.8 ACSMC8

80-26044 144 1-564 1981

Copyright © 1981 American Chemical Society All 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 anyrightor 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. P R I N T E D I N THE U N I T E D

STATES

OF

AMERICA

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.fw001

ACS Symposium Series M . Joan Comstock, Series Editor

Advisory Board David L. Allara

James P. Lodge

Kenneth B. Bischoff

Marvin Margoshes

Donald D. Dollberg

Leon Petrakis

Robert E. Feeney

Theodore Provder

Jack Halpern

F. Sherwood Rowland

Brian M . Harney

Dennis Schuetzle

W. Jeffrey Howe

Davis L. Temple, Jr.

James D. Idol, Jr.

Gunter Zweig

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.fw001

FOREWORD The ACS SYMPOSIUM SERIES was founded in 1974 to provide

a medium for publishing symposia quickly in book form. The 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. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable since symposia may embrace both types of presentation.

PREFACE

E

xcluding most of the contribution made by biomass, which is defined as organic waste such as agricultural residues and urban refuse, and landand water-based plant material such as trees, grasses, and algae, the United States consumed about 78.2 quads (1 quad = 10 Btu) of primary energy in 1979. The contribution of each energy component was 37.1 quads for petroleum, 19.8 quads for natural gas, 15.2 quads for coal, 3.2 quads for hydroelectric power, 2.8 quads for nuclear electric power, and 0.1 quad for electric power production from wood and waste and geothermal sources. Few realize that the biomass contribution, in all its forms, for the production of heat, steam, electric power, and synfuels for 1979 was about 1.9 quads, or a contribution of about 2.3% to the total primary energy consumption. Thus, biomass energy consumption is equivalent to about one million barrels of oil per day, so it is obviously a commercial reality now. Indeed, as the costs of fossil energy increase and the available supplies shrink, especially petroleum and natural gas, we will begin to return to a renewable source of fixed carbon in the form of biomass to assure a continuous supply of organic liquid and gaseous fuels and chemicals. The concept of using biomass as a primary energy source is not new. Wood was a major source of primary energy and chemicals in the United States only a relatively few years ago. As late as 1880, over 50% of the U.S. energy demand was supplied by wood. After 1880, fossil fuels began to dominate as a primary energy supply and have continued to be our largest source of energy to the present time. In the 1970s, a major effort was launched in the United States to develop modern technology for the utilization of biomass energy. The symposium on biomass as a nonfossil fuel source, presented in Honolulu, Hawaii in April 1979 by the Division of Petroleum Chemistry at the American Chemical Society/Chemical Society of Japan Joint Chemical Congress, was devoted to this subject. Twelve basic and applied research papers were presented at this symposium on biomass energy. This book contains updated versions of ten of these papers and fifteen additional papers to balance the treatment of the subject. These are grouped into the categories of biomass production, liquid fuels, gaseous fuels, economics and energetics, and systems analysis. It will become apparent to the reader who is being introduced to the subject for the first time that there are many routes for the utilization of biomass energy and that many activities are underway to develop commercial processes and systems. Substitute natural gas in the form of methane from landfills, liquid alcohol

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.pr001

15

ix

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.pr001

fuels to replace gasoline, and direct biomass combustion for steam and electric power production are typical technologies now in use and under development. For the reader who already has been involved in biomass energy, many of the papers have extensive bibliographies that serve as a reference source. It should be emphasized that, though this book is edited and all the papers reviewed by independent referees, I have not attempted to convert an author's views with which I disagree to my own way of thinking. However, these instances are in the minority. Universal agreement on a given biomass subject does not exist necessarily among those who have been in the field, mainly because some of the work has not yet progressed to the point where the ultimate answers are in hand. Finally, I would like to briefly state my personal opinions on the present and future prospects of biomass energy. It is not a panacea for all of our energy problems, but it will find a logical place in the commercial energy market Further, suitable biomass energy supplies, because of their generally dispersed nature, will be used initially in small-scale, localized applications. Large-scale central utility systems and synfuel plants supplied with biomass raw materials will be the exception rather than the rule in the 1980s and are not expected to reach commercial status to any significant extent until after 1990. Nevertheless, biomass will continue to contribute more to our energy and chemical needs as time passes. Because of the multitude of organic residues and plant species, and the many processing combinations that yield solid, liquid, and gaseous fuels, the selection of the best technology and raw materials for specific applications seems very difficult. Many factors must be examined in depth to choose and develop systems that are technically feasible, energetically and economically practical, and environmentally acceptable. These factors are particularly important for large-scale biomass energy farms where continuity and efficiency of operation and synfuel production are paramount. The problem is not so intractable that it defies solution. But there are several major barriers to be overcome or at least reduced in size to facilitate commercial use of biomass energy technology on a scale that will satisfy a large portion of our energy demand. These barriers, none of which is insurmountable in my judgment, include such factors as excessive cost of biomass-derived synfuels, low or negative net energy production efficiencies for some systems, the problem of acquiring sufficient and suitable land for biomass production, conflicts with foodstuffs production, obtaining advance approvals and permits from state and federal agencies, and dependence on forgiven taxes and subsidies for economic success. At the present time, the commercialization of biomass energy is proceeding at the proverbial snail's pace. The excessive cost of synfuels from biomass in integrated growth, harvesting, and conversion systems, and from integrated waste collection and conversion systems, is the prime x

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.pr001

reason for the low commercialization rate. Although synfuel production capacity (plant size) andfinancingconditions impact directly on synfuel costs, the estimated and actual manufacturing costs of most biomassderived synfuels are not presently competitive with fossil fuels. Examples are SNG from manure and natural gas, and ethanol from sugarcane for gasohol and gasoline. As the price of crude oil continues to increase, I expect the cost of fuels and chemicals from biomass will become competitive with conventional petroleum derivatives. At this time, the major factor influencing synfuel costs from biomass is biomass cost itself; conversion and other associated costs are often a smaller part of the total cost. Plant biomass production costs are affected most by independent inputs such as the costs of planting, fertilization, irrigation, and harvesting. An incremental increase in biomass yield often cannot be justified based on the additional cost of achieving this yield improvement. For organic wastes that are debited against conversion process cost, the delivered cost of the waste, which includes the costs of collection and transport, is sometimes too high to justify synfuel manufacture. Credits must be taken for the by-products and if they cannot be sold at certain minimum prices, the operation is not profitable. Finally, alternative biomass uses such as those for materials of construction, foodstuffs, animal feeds, and soil conditioning that offer a higher profit margin than synfuel must be considered. The potential owners and operators of a biomass energy system cannot be expected to undertake a business venture to commercialize biomass energy if the profits are too small in comparison with other alternatives. Tax incentives and other forms of subsidy already have been suggested to reduce synfuel costs and thereby stimulate the investment of private capital. Whether or not this approach can be effective remains to be established. In any case, biomass costs should be reduced to help make commercial synfuel manufacture economically attractive on its own merits. I would like to express my appreciation to the Division of Petroleum Chemistry for sponsoring this somewhat "alien" symposium. (After all, biomass will displace a significant portion of petroleum if my projections are accurate.) I especially want to thank all of the speakers who somehow managed to be in Hawaii at the appointed time despite the airline travel problems prevalent during the symposium, and also all of the contributors of other articles that I requested to try to provide a more balanced treatment of biomass energy. The authors' individual efforts were indispensable in assembling a book of this type. Institute of Gas Technology Chicago, Illinois

DONALD

June 1980 xi

L.

KLASS

1 Industrial Development of Biomass Energy Sources GEORGE P. SCHAEFER

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

Booz-Allen & Hamilton, Incorporated, 4330 East-West Highway, Bethesda, M D 20014

A wide diversity of companies has entered into the development of biomass resources to solve non-energy and energy-related problems. These companies can be grouped as follows: • Companies currently utilizing or producing biomass or biomass-derived materials and products (e.g., paper, lumber, food, and distilled spirits) are attempting to recover and use greater amounts of the resources and by-products available to them to reduce costs, develop new products, and produce energy. • Companies which have large amounts of wastes (e.g., animal manures) are developing new ways of reducing and disposing of the wastes, reducing operating costs, and producing energy. • Manufacturers and entrepreneurs are conducting research and development, production, and marketing of equipment to convert biomass feedstocks into energy. The goal of these activities, primarily, is to develop new products and processes which can be marketed to potential biomass users. • Utilities which have large demands for fuels on a continuing basis are supporting the development of new, renewable, supply sources to help satisfy this demand.

0097-6156/81/0144-0003$05.00/0 © 1981 American Chemical Society

4

BIOMASS AS A NONFOSSIL FUEL SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

T h e c o m p o s i t i o n of these c o m p a n i e s a n d t h e i r m o t i v a t i o n s are i m p o r t a n t t o g o v e r n m e n t p o l i c y makers a n d c o m p a n i e s c o n s i d e r i n g e n t r y i n t o t h e i n d u s t r y , for t h e m o t i v a t i o n s p r o v i d e a f r a m e w o r k w i t h w h i c h t o e v a l u a t e a l t e r n a t i v e o p t i o n s . It is i m p o r t a n t t o k n o w , for e x a m p l e , t h a t t h e d e v e l o p m e n t of e n e r g y f r o m b i o m a s s is of s e c o n d a r y i m p o r t a n c e t o m a n y c o m p a n i e s w h e n d e v e l o p i n g a n e w m a r k e t i n g p l a n or t a x i n c e n t i v e p r o g r a m . In r e c o g n i t i o n of t h i s f a c t o r , t h e Office of Policy a n d A n a l y s i s w i t h i n t h e U.S. D e p a r t m e n t o f Energy (DOE) asked Booz. A l l e n & H a m i l t o n Inc. t o assess t h e n a t u r e of i n d u s t r i a l a c t i v i t i e s in t h e utilization of b i o m a s s for energy. This assessment, p e r f o r m e d in t h e s u m m e r a n d fall of 1 9 7 9 . f o c u s e d u p o n i d e n t i f y i n g t h e s t r u c t u r e of t h e i n d u s t r y , t h e t y p e s of c o m p a n i e s a c t i v e in t h e i n d u s t r y , w h a t t h e y are d o i n g , a n d w h a t t h e m o t i v a t i o n s are for these activities. Initially, an e x t e n s i v e literature research w a s p e r f o r m e d t o d e t e r m i n e t h e c o m p a n i e s a c t i v e l y p u r s u i n g b i o m a s s e n e r g y d e v e l o p m e n t , t h e issues critical t o t h e e x p a n s i o n of t h e i n d u s t r y , a n d m a r k e t p e r s p e c t i v e s w h i c h exist. Based u p o n t h e d a t a c o l l e c t e d . Booz. A l l e n i n t e r v i e w e d 1 0 0 e x e c u t i v e s of c o m panies n a t i o n w i d e t o d e t e r m i n e t h e s c o p e of p r i v a t e sector i n v o l v e m e n t in b i o m a s s e n e r g y d e v e l o p m e n t . These c o m p a n i e s , s h o w n in Figure 1. represent a cross s e c t i o n of c o m p a n i e s a c t i v e in t h e d e v e l o p m e n t of e n e r g y f r o m b i o m a s s a n d are representative of c o m p a n i e s in t h e field. T h e i n t e r v i e w s w e r e p e r f o r m e d by t w o - p e r s o n t e a m s u t i l i z i n g a standardized i n t e r v i e w f o r m d e v e l o p e d b y Booz. A l l e n a n d r e v i e w e d by t h e client. T h e y w e r e c o n d u c t e d on-site a n d w e r e c o n s i d e r e d c o n f i d e n t i a l . T h e i n t e r v i e w s f o c u s e d u p o n t h e c u r r e n t a n d p l a n n e d activities of t h e c o m p a n i e s in t h e d e v e l o p m e n t of e n e r g y f r o m b i o m a s s , t h e m o t i v a t i o n s for t h e i r activities, t h e financial c o m m i t m e n t s w h i c h the companies were making, and their market outlook. T h e d a t a c o l l e c t e d i n d i c a t e t h a t p r i v a t e sector i n v o l v e m e n t in biomass e n e r g y d e v e l o p m e n t is e x t e n s i v e d e s p i t e i n d u s t r y ' s p e r c e p t i o n t h a t federally s p o n s o r e d w o r k has had little i m p a c t . A n o t h e r key f i n d i n g w a s t h a t g o v e r n m e n t r e g u l a t o r y policies generally had a greater effect u p o n i n d u s t r y t h a n DOE a n d these policies o f t e n c o n t r a d i c t e d DOE's p o s i t i o n . INDUSTRY STRUCTURE There is no single biomass for t h e e n e r g y industry. Rather, m a n y c o m p a n i e s are a c t i v e in utilizing a variety of biomass resources. In m o s t cases, t h e p r i n cipal line of business of these c o m p a n i e s is not biomass d e v e l o p m e n t b u t a g r i c u l t u r a l p r o d u c t i o n , w o o d p r o d u c t s m a n u f a c t u r i n g , d i s t i l l i n g , a n d similar

1.

SCHAEFER

FOREST

PRODUCTS

COMPANIES

Boise-Cascade Chamoion Paoer Crown-Zcllcrbach AGRICULTURAL

. Georgia-Pacific . I n t e r n a t i o n a l Paper . I n t e r s t a t e Paper

PRODUCTS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

Diamond-Sunsweet F i r s t C o l o n y Farms Grain Processing Corporation Jack Daniels KaDlan Industries Kelco Corporation

AND

GAS

PETROLEUM

. General Electric . Halcyon . Hamilton-Standard . Johnson Energy Systems . Oneida Heater . PyroSol . Rexnard-Envirex

. Α . 0. S m i t h . A. E . S t a n l e y . Thermonetics . V e r m o n t * ood E n e r g y Corporation . Wheelabrator Clean-fuels . Yukon Industries

. P a c i f i c Gas & E l e c t r i c . S e a t t l e Power & L i a h t . Southern C a l i f o r n i a Edison . U n i v e r s i t y o f Oregon . N a t u r a l Gas P i o e l i n e

. San D i e g o Water and u t i l i t i e s Department . Southern C a l i f o r n i a Gas . U n i t e d Gas Pioeline

COMPANIES

AND

A m e r i c a n O i l Company Bohler Brothers

. Gulf O i l . MarCom I n d u s t r i e s

.

Fannon

. Mid-West

O i l &

A r t h u r D. Little CPR F o r e s t P r o d u c t s Energy Resources Company . G a r r e t t Energy R&D . Gas R e s e a r c h Institute . IE A s s o c i a t e s

. .

· Mobil O i l . Occidental

Petroleum

Solvents

ENGINEERING

. . .

.

7

DISTRIBUTORS

. .

TRADΓ

Land 0'Lakes National Distillers New L i f e Farm Pioneer Hi-Bred International . Publicker Distillers . S m i t h Bowman D i s t i l l e r s . Sunny Time Foods

UTILITIES

B o n n e v i l l e Power Administration Burlington Electric E u g e n e W a t e r and E l e c t r i c Board Lamar U t i l i t y Board

RESEARCH

. . . .

MANUFACTURERS

. American Can . American Fry-Feeder . Bio-Gas of Colorado . Bio-Solar R&D . Chromoloy Corporation . Combustion Power . Evans P r o d u c t s . Forest Fuels ELECTRIC

. Scott Paper . U n i o n Camp . Weyerhaeuser

COMPANIES

. Anheuser-Busch . Archer-Daniels-Midland . Brown & W i l l i a m s o n . Cajun Sugar C o o p e r a t i v e . C a s t l e and Cook . C. P. Brewer . Dekalb AgResearch

EQUIPMENT

5

Biomass Energy Resources

I n s t i t u t e o f Gas Technology Intertechnology Marelco, Inc. O a s i s 2000 SRI International Touche-Ross

WED Enterorises "right-Malta Bechtel Chemapac Ultrasystems

Northwest Pine Association W e s t e r n Wood P r o d u c t s Association Wood E n e r g y C o r p o r a ­ tion

Wood E n e r g y Institute

ORGANIZATIONS

Alternative Alcohol Fuels Institute Distilled Spirits C o u n c i l of the U.S. national Gasohol Cornmi s s i o n

Figure 1.

Companies interviewed for the study

BIOMASS AS A NONFOSSIL FUEL SOURCE

6

endeavors. In t h i s assessment, these c o m p a n i e s w e r e e x a m i n e d a c c o r d i n g t o t h e t y p e s of b i o m a s s e n e r g y p r o d u c t s w h i c h t h e y p r o d u c e . Based u p o n t h e d a t a a n d i n f o r m a t i o n c o l l e c t e d , t h e i n d u s t r y w a s d i v i d e d into f o u r p a r t s : • • • •

A l c o h o l fuels Thermal energy from w o o d Thermal energy from agricultural wastes Gaseous fuels.

Each s e g m e n t has a d i f f e r e n t set of f e e d s t o c k s , c o n v e r s i o n t e c h n o l o g i e s , a n d

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

p r o d u c t s associated w i t h i t as s h o w n in Figure 2. A l c o h o l Fuels T h e a l c o h o l fuels s e g m e n t is r e c e i v i n g s i g n i f i c a n t a t t e n t i o n f r o m t h e p u b l i c a n d p r i v a t e sectors at t h e present t i m e . T h e use of b i o m a s s resources — p r i m a r i l y h e r b a c e o u s c r o p s , s u c h as c o r n , w h e a t g r a i n s o r g h u m , a n d w o o d m i l l residues — is v i e w e d as a m e a n s for r e d u c i n g o u r d e p e n d e n c e o n i m p o r t e d oil a n d for u s i n g excess crops. T h e key c h a r a c t e r i s t i c s of t h e c o m p a n i e s a c t i v e in t h i s s e g m e n t are t h a t t h e y have: • • • •

Access to ethanol feedstocks A c c e s s t o e x i s t i n g gasoline m a r k e t i n g s y s t e m s Experience in d e s i g n i n g a n d b u i l d i n g f e r m e n t a t i o n u n i t s A n interest in r e d u c i n g d e p e n d e n c e u p o n o t h e r s for f u e l .

By u t i l i z i n g s t a n d a r d f e r m e n t a t i o n a n d d i s t i l l a t i o n processes, c o m p a n i e s in t h i s sector are p r o d u c i n g a n h y d r o u s e t h a n o l . It can be b l e n d e d w i t h u n l e a d e d gasoline t o f o r m g a s o h o l , w h i c h is c u r r e n t l y m a r k e t e d t h r o u g h o u t t h e n a t i o n , a l t h o u g h m o s t sales are in t h e M i d w e s t . Thermal Energy From W o o d M o r e b i o m a s s - d e r i v e d e n e r g y is p r o d u c e d f r o m w o o d t h a n a n y o t h e r source. T h e use o f w o o d f o r t h e r m a l e n e r g y p r o d u c t i o n is m o t i v a t e d p r i m a r i l y b y a desire t o r e d u c e w a s t e disposal p r o b l e m s a n d oil a n d gas usage. C o m p a n i e s a c t i v e in t h i s sector generally h a v e : e

Experience in h a n d l i n g b i o m a s s materials a n d / o r solid fuels

• • •

Access to w o o d and w o o d wastes Experience in b u i l d i n g a n d utilizing d i r e c t c o m b u s t i o n u n i t s External s u p p o r t for, or e n t r e p r e n e u r i a l interest i n , d e v e l o p i n g p a r t i c u l a r equipment.

AND ANIMAL

COLLECTION

Figure 2.

UTILITY SECTOR

AGRICULTURAL SECTOR

ENERGY

PETROCHEMICAL SUBSTITUTES

SECTOR

INDUSTRIAL

SECTOR

COMMERCIAL

RESIDENTIAL

SECTOR

TRANSPORTATION

MARKETS MARKETS

PROCESS

SOLID FUELS

GASEOUS FUELS

LIQUID FUELS

PRODUCTS PRODUCTS

Biomass overview (nonfossil, primary organic materials)

RESIDUES

MATERIAL PROCESSING

AGRICULTURE

THERMOCHEMICAL

BIOCHEMICAL

CONVERSION TECHNOLOGIES

RESIDUALS

FORESTRY,

BIOMASS

AQUATIC

AQUATIC

AND

BIOMASS

TERRESTRIAL

RESOURCE BASES

OPEN OCEAN

LAND BASED

SILVICULTURE

PRODUCTION TECHNOLOGIES

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8

BIOMASS AS A NONFOSSIL FUEL SOURCE

T h e d i r e c t c o m b u s t i o n of w o o d t o p r o d u c e t h e r m a l e n e r g y , w h i c h c a n be used as process s t e a m or heat, is t h e m o s t f r e q u e n t a p p l i c a t i o n in t h i s sector. S o m e research a n d d e v e l o p m e n t is b e i n g p e r f o r m e d in o t h e r areas, especially o n t h e g a s i f i c a t i o n of w o o d . Thermal Energy From Agricultural Residues

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

T h e use of a g r i c u l t u r a l residues for t h e r m a l e n e r g y is v e r y similar t o t h e t h e r m a l - e n e r g y - f r o m - w o o d s e g m e n t . C o m p a n i e s a c t i v e in t h i s s e g m e n t h a v e : •

A need t o dispose of a g r i c u l t u r a l process b y - p r o d u c t s a n d access t o a

• •

c e n t r a l l y l o c a t e d stock of residues or b y - p r o d u c t s A need for l o w - c o s t process heat or s t e a m Experience in b u i l d i n g or utilizing d i r e c t c o m b u s t i o n systems.

Gaseous Fuels T h e d e v e l o p m e n t of gaseous f u e l s f r o m b i o m a s s is t h e least d e v e l o p e d of t h e b i o m a s s i n d u s t r y sectors. M o s t efforts in t h i s sector are e x p e r i m e n t a l a n d t h e c o m m e r c i a l use of gases f r o m b i o m a s s is still years a w a y in t h e o p i n i o n of i n d u s t r y e x e c u t i v e s . C o m p a n i e s a c t i v e in t h i s area g e n e r a l l y h a v e : • A c c e s s t o a resource base — p r i m a r i l y m a n u r e s — w h i c h present a d i s posal p r o b l e m • Experience w i t h c o n s t r u c t i n g c o n v e r s i o n e q u i p m e n t , s u c h as anaerobic digesters • N e e d f o r gaseous fuels. T h e m o s t w i d e s p r e a d a p p r o a c h t o g a s i f i c a t i o n is t h e a n a e r o b i c d i g e s t i o n of m a n u r e s a n d land-based a q u a t i c biomass. T h i s c o n v e r s i o n process p r o d u c e s e i t h e r a m e d i u m - B t u gas, w h i c h can be used on-site, or in s o m e cases, u p g r a d e d t o a s u b s t i t u t e n a t u r a l gas (SNG). T h e b i o m a s s i n d u s t r y is c o m p o s e d of g r o u p s of c o m p a n i e s a c t i v e in t h e d e v e l o p m e n t of specific p r o d u c t s or uses for biomass. T h e f o c u s of t h e i r a c t i v i t i e s is g e n e r a l l y not t o d e v e l o p processes or e q u i p m e n t w h i c h c a n be used in a w i d e range of a p p l i c a t i o n s . Rather, i n d u s t r y has f o c u s e d its efforts o n p a r t i c u l a r a p p l i c a t i o n s s u i t e d t o their c i r c u m s t a n c e s . T h e specific t y p e s of c o m p a n i e s a n d t h e i r a c t i v i t i e s are d e s c r i b e d in t h e f o l l o w i n g s e c t i o n .

1.

SCHAEFER

Biomass Energy Resources

9

CORPORATE ACTIVITIES A N D OUTLOOK Corporate activities in biomass i n c l u d e a w i d e range o f efforts related t o m e e t i n g a n u m b e r o f internal needs a n d p r o b l e m s w h i c h , in m a n y cases, are not e n e r g y - r e l a t e d . In a d d i t i o n , m a n y c o m p a n i e s are a c t i v e in t h e d e v e l o p m e n t o f n e w p r o d u c t s a n d m a r k e t s f r o m biomass. W i t h i n t h e f o u r i n d u s t r y s e g m e n t s d e s c r i b e d above, v a r i o u s t y p e s o f activities are b e i n g p u r s u e d in t h e d e v e l o p m e n t o f biomass.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

A l c o h o l Fuels A l t h o u g h t h e a l c o h o l fuels s e g m e n t is in its infancy, m a n y c o m p a n i e s are a c t i v e in its d e v e l o p m e n t . A t t h e present t i m e , t h e r e is n o s i g n i f i c a n t vertical i n t e g r a t i o n in t h e i n d u s t r y . T h a t is, f i r m s are generally a c t i v e in o n l y one o f t h e t h r e e c o m p o n e n t areas d e s c r i b e d in Figure 2. C o m p a n i e s presently e n g a g e d in t h e large-scale p r o d u c t o n o f e t h a n o l generally have access t o a c o n t i n u i n g resource base w h i c h c a n be c o n v e r t e d t o e t h a n o l . These c o m p a n i e s are n o r m a l l y agriprocessors, f o o d processors, a n d distilleries. A t t h e present t i m e , o n e large agriprocessor, A r c h e r - D a n i e l s M i d l a n d , is p r o d u c i n g large q u a n t i t i e s o f e t h a n o l f r o m b y - p r o d u c t s g e n e r a t e d during the production of corn sweetener. Many of the other companies active in t h i s s e g m e n t are also e x p l o r i n g a l t e r n a t i v e means t o p r o d u c e e t h a n o l f r o m t h e i r f e e d s t o c k s , w a s t e s , or b y - p r o d u c t s b y t h e a d d i t i o n o f n e w d i s t i l l a t i o n u n i t s , as i n d i c a t e d in Figure 3. These large-scale p r o d u c e r s consider t h e m i n i m u m e f f i c i e n t size o f a n e t h a n o l plant t o be 10 m i l l i o n gallons a year, based u p o n c u r r e n t costs for f e e d s t o c k s , b y - p r o d u c t s a n d e t h a n o l . In v i r t u a l l y every case, these a c t i v i t i e s have been i n i t i a t e d w i t h i n t h e past t w o t o t h r e e years a n d represent n e w o p e r a t i o n s f o r t h e c o m p a n i e s in r e c o g n i t i o n o f t h e m a r k e t o p p o r t u n i t i e s w h i c h are d e v e l o p i n g in a l c o h o l fuels. S m a l l - a n d m e d i u m - s i z e d f a r m s are interested in t h e d e v e l o p m e n t o f s m a l l scale e t h a n o l p r o d u c t i o n facilities ( a p p r o x i m a t e l y 2 5 0 , 0 0 0 gallons per year) as a m e a n s o f d e v e l o p i n g a d d i t i o n a l uses f o r t h e i r crops, a n d as a m e a n s t o d e v e l o p i n d e p e n d e n c e f r o m oil suppliers. W h i l e , t o date, t h e r e has been little c o n s t r u c t i o n o f o n - f a r m u n i t s , t h e s e f a r m s represent a large p o t e n t i a l m a r k e t if c u r r e n t t r e n d s c o n t i n u e . A t h i r d g r o u p o f c o m p a n i e s in t h e a l c o h o l fuels s e g m e n t o f t h e biomass i n d u s t r y are a r c h i t e c t / e n g i n e e r i n g f i r m s , fuel d i s t r i b u t o r s , a n d oil c o m p a n i e s . These c o m p a n i e s are a t t e m p t i n g t o b u i l d u p o n their expertise in c o n s t r u c t i o n , f u e l h a n d l i n g a n d retailing t o d e v e l o p n e w markets for t h e i r p r o d u c t s . In m o s t cases, gasohol d i s t r i b u t o r s are i n d e p e n d e n t w h o l e s e l e r s a n d retailers.

BIOMASS AS A NONFOSSIL FUEL SOURCE

10

AGRIPROCESSING

WHY ARE THEY DOING IT?

WHAT ARE THEY DOING?

WHO IS INVOLVED?

•

FIRMS

PRODUCE ETHANOL FROM

•

AN ADDITIONAL REVENUE

WET CORN MILLING PLANTS

GENERATING PRODUCT

•

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

FOOD PROCESSING

•

FIRMS

PRODUCE AND MARKET

BY-PRODUCT STREAMS OF

WASTE STREAMS

PRODUCE AN ADDITIONAL REVENUE-GENERATING

PRODUCE ETHANOL FROM

PRODUCT •

ALLEVIATE WASTEHANDLING PROBLEMS

DISTILLERIES

ARCHITECTURE/ ENGINEERING

UTILIZE EXISTING PLANTS

POTENTIAL PROFITABLE

IN THE PRODUCTION OF

UTILIZATION OF EXCESS

ETHANOL

CAPACITY

•

SELL TURN-KEY FACILITIES

•

BLEND AND DISTRIBUTE

FIRMS

•

SALES EXPANSION

• FUEL DISTRIBUTORS

GASOHOL

DEVELOP MARKET FOR POTENTIAL RENEWABLE LIQUID FUEL • PUBLIC RELATIONS

PUBLIC RELATIONS MAJOR OIL

EXPERIMENTAL TEST

KEEP UP-TO-DATE IN

COMPANIES

MARKETING

CASE INDUSTRY EXPANDS RAPIDLY

PRODUCE FEEDSTOCKS BUILD ON-FARM ETHANOL PLANTS (PREDOMINATELY SMALL FARMERS)

Figure 3.

SEE ETHANOL PRODUCTION AS AN ADDITIONAL MARKET FOR THEIR CROPS ENERGY SUPPLY SECURITY. INDEPENDENCE FROM UTILITIES. "BIG OIL" (PRIMARILY SMALL FARMERS)

Overview of motivations for entry into the alcohol fuel/gasohol segment

1.

SCHAEFER

Biomass Energy Resources

11

a l t h o u g h large oil c o m p a n i e s , i n c l u d i n g A m o c o , Exxon, a n d Gulf, are b e g i n n i n g t o m a r k e t gasohol.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

I n d u s t r y e x e c u t i v e s a n t i c i p a t e t h a t t h e a l c o h o l fuels business w i l l g r o w m o r e rapidly in t h e next f e w years t h a n o t h e r s e g m e n t s of t h e i n d u s t r y . S y s t e m s c u r r e n t l y exist, or are e x p a n d i n g , in m a n y regions for c o l l e c t i n g t h e resource, c o n v e r t i n g it t o e t h a n o l , a n d t r a n s p o r t i n g a n d m a r k e t i n g it. In a d d i t i o n , curr e n t g o v e r n m e n t policies e n c o u r a g e t h e use o f gasohol. T w o major barriers t o a l c o h o l fuels are u n c e r t a i n t y r e g a r d i n g g o v e r n m e n t policies, i n c l u d i n g a p r o b l e m recently addressed in part b y President Carter, w h o proposed t h a t tax e x e m p t i o n s be e x t e n d e d t o t h e year 2 0 0 0 , a n d t h e lack o f a pipeline s y s t e m t o d i s t r i b u t e large v o l u m e s o f gasohol. Thermal Energy From W o o d T h e t h e r m a l e n e r g y f r o m w o o d s e g m e n t o f t h e biomass i n d u s t r y is c o m p o s e d of a broad m i x o f c o m p a n i e s t h a t are d o m i n a t e d b y t h e forest p r o d u c t s a n d p u l p a n d paper industries. These c o m p a n i e s are active in all t h e various c o m p o n e n t areas o f t h e i n d u s t r y f r o m o w n e r s h i p of t h e resource base t o t h e use of w o o d f o r p r o d u c t s a n d energy. Generally, t h e m a i n t h r u s t of these c o m panies is t o p r o d u c e p r o d u c t s f r o m w o o d rather t h a n t h e r m a l energy. Only small w o o d d i s t r i b u t o r s a n d h a r d w a r e - o r i e n t e d c o m p a i n e s are active in t h e d e v e l o p m e n t o f e n e r g y f r o m w o o d , as s h o w n in Figure 4. Forest resource c o m p a n i e s are a c t i v e l y p u r s u i n g t h e d e v e l o p m e n t of w o o d resources f o r a n u m b e r o f a p p l i c a t i o n s — t o increase t h e g r o w t h rate of w o o d , t o improve t h e efficiency of harvesting and collecting w o o d , t o d e v e l o p m o r e efficient c o m b u s t i o n systems. The p r o d u c t i o n o f energy f r o m w a s t e w o o d is g r o w i n g , a n d close t o 5 0 p e r c e n t of t h e t o t a l e n e r g y requirem e n t s of these c o m p a n i e s is p r o d u c e d f r o m biomass in t h e f o r m of heat, s t e a m , a n d c o g e n e r a t e d electricity. W o o d fuel d i s t r i b u t i o n s y s t e m s are b e g i n n i n g t o e m e r g e in m o s t regions of t h e c o u n t r y , a l t h o u g h m a n y p o t e n t i a l users indicate t h a t t h e y still have d i f f i c u l t y a c q u i r i n g w o o d d u e t o t h e lack o f a d e q u a t e d i s t r i b u t i o n systems. W i t h t h e e x c e p t i o n o f s o m e large d i s t r i b u t o r s in parts o f t h e Northeast, Southeast, a n d N o r t h w e s t , t h e e x i s t i n g d i s t r i b u t i o n s y s t e m of fuel w o o d f o r t h e industrial a n d residential m a r k e t s is c o m p o s e d of small operators. M o s t industrial users o f w o o d for e n e r g y are t r a n s p o r t i n g w o o d t h e m s e l v e s , or c o n t r a c t i n g f o r its t r a n s p o r t a t i o n . Large w o o d e n e r g y users i n c l u d e m a n u f a c t u r i n g f i r m s , utilities, a n d o t h e r facilities, s u c h as universities, w h i c h are b e g i n n i n g t o utilize w o o d as a cheaper, m o r e reliable source o f energy. These users are b u r n i n g w o o d b o t h

12

BIOMASS AS A NONFOSSIL FUEL SOURCE

WHO IS INVOLVED?

HARVESTING WOOD

FOREST

PRODUCING WOOD

RESOURCE

PRODUCTS

COMPANIES

BURNING WASTE WOOD

•

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

WHY ARE THEY DOING IT?

WHAT ARE THEY OOING?

•

USE A GREATER PERCENT OF THE HARVESTED WOOD

•

MEET ENVIRONMENTAL REGULATIONS

•

REDUCE ENERGY COSTS

DISTRIBUTING WOOD FROM FOREST RESOURCE

WOOD FUEL

•

CONSUMER DEMAND FOR WOOD FUEL

COMPANIES TO END

DISTRIBUTORS

USERS

UTILITIES

•

BURNING WOOD

BURNING

TO GENERATE

WOOD

ELECTRICITY

•

REDUCE ENERGY COSTS

•

PROVIDE EXTRA CAPACITY

t

PROCESS STEAM. HEAT,

FIRMS BURNING

•

ELECTRICITY

A

TECHNOLOGY

MEET ENVIRONMENTAL REGULATIONS

AND COGENERATED

WOOD

MEET ENVIRONMENTAL REGULATIONS

BURNING WOOD FOR

MANUFACTURING

CONDUCTING R&D OF

REDUCE ENERGY COSTS

•

NEW WOOD BURNING

DEVELOPERS/

•

PRODUCTS

• EQUIPMENT

MANUFACTURING AND •

BURNING EOUIPMENT •

PERSONAL CHALLENGE AND OPPORTUNITY

SELLING PROVEN WOOD-

WOOD-BURNING

FIRST TO THE MARKET WITH NEW PRODUCT

TECHNOLOGIES AND

INNOVATORS

MANUFACTURERS

•

INCREASE MARKET SHARE

IMPROVING THESE PRODUCTS

INDUSTRY ASSOCIATIONS AND AGENCIES

CONDUCTING STUDIES ON ISSUES OF CONCERN TO THE INDUSTRY LOBBYING PROVIDING A COMMUNICATIONS

•

INCREASED PUBLIC PERCEPTION AND INFORMATION REGARDING WOOD FOR ENERGY

FORUM

Figure 4.

Motivations for entry into the thermal energy from wood sector

1.

SCHAEFER

Biomass Energy Resources

13

alone o r w i t h coal t o l o w e r e m i s s i o n s f r o m their f u e l - b u r n i n g installations. A n o t h e r g r o u p o f c o m p a n i e s is a c t i v e in t h e d e v e l o p m e n t o f w o o d c o m b u s t i o n s y s t e m s t o m e e t t h e g r o w i n g d e m a n d f o r utilizing w o o d energy. C o m panies specializing in t h e d e v e l o p m e n t m a n u f a c t u r e a n d m a r k e t i n g o f w o o d b u r n i n g e q u i p m e n t f o r residential, c o m m e r c i a l , a n d industrial uses are e m e r g i n g in t h o s e regions w h e r e w o o d is m o s t heavily used.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

Business e x e c u t i v e s e x p e c t g r o w t h o f t h e w o o d - f o r - e n e r g y business t o o c c u r s l o w l y . W h i l e t h e means exist t o c o l l e c t a n d c o n v e r t w o o d into useful p r o d u c t s , t h e lack o f w o o d fuel d i s t r i b u t i o n s y s t e m s is p e r c e i v e d t o be a major barrier t o g r o w t h . A f u r t h e r c o n c e r n o f e x e c u t i v e s is t h e lack o f assurances r e g a r d i n g t h e l o n g - t e r m a v a i l a b i l i t y o f supplies. Thermal Energy From Agricultural Residues The s e g m e n t c o n c e r n e d w i t h t h e r m a l e n e r g y f r o m a g r i c u l t u r a l residues is small a n d localized at t h e present t i m e . Only a f e w t y p e s of a g r i c u l t u r a l residues, s u c h as n u t shells a n d c o r n c o b s , are being utilized f o r t h e p r o d u c t i o n o f energy. Corporate a c t i v i t i e s are f o c u s e d u p o n t h e use o f a g r i c u l t u r a l residues w h i c h are l o w in m o i s t u r e c o n t e n t , w h e r e t h e residues are a b y - p r o d u c t o f a n o t h e r o p e r a t i o n , a n d w h e r e t h e y are a c c u m u l a t e d in a central location. A g r i c u l t u r a l processing c o m p a n i e s are e n t e r i n g into t h i s s e g m e n t t o f i n d a m e a n s t o dispose o f their b y - p r o d u c t s a n d w a s t e s , as w e l l as t o d e v e l o p a c h e a p , i n d e p e n d e n t source o f e n e r g y , as s h o w n in Figure 5. T o m e e t this g r o w i n g d e m a n d , e q u i p m e n t m a n u f a c t u r e r s are d e v e l o p i n g boilers a n d o t h e r c o m b u s t i o n e q u i p m e n t w h i c h c a n be utilized easily b y a g r i c u l t u r a l processing c o m p a n i e s . M a n u f a c t u r e r s w i t h e x p e r i e n c e in h a r d w a r e d e v e l o p m e n t a n d f a b r i c a t i o n are a t t e m p t i n g t o s p i n o f f their experience in o t h e r markets t o t h i s n e w market. In a d d i t i o n t o t h e g e n e r a t i o n o f s t e a m a n d heat, a g r i c u l t u r a l processors are d e v e l o p i n g c o g e n e r a t i o n s y s t e m s t o p r o d u c e e l e c t r i c i t y w h i c h c a n be used on-site. In m o s t cases, these s y s t e m s generate m o r e e l e c t r i c i t y t h a n can be c o n s u m e d b y t h e processor. Local electric utilities in these cases m a y serve as m a r k e t s for t h i s p o w e r a n d s o m e c o m p a n i e s are p u r c h a s i n g this e l e c t r i c i t y f r o m t h e processor. In California, t w o m a j o r utilities are also e n t e r i n g into a g r e e m e n t t o p u r c h a s e s t e a m f r o m t h e processors t o g e n e r a t e electricity. Business e x e c u t i v e s see t h e barriers t o w i d e s p r e a d use of a g r i c u l t u r a l residues for t h e r m a l energy as similar t o t h o s e in t h e w o o d s e g m e n t . The lack of c o l l e c t i o n a n d d i s t r i b u t i o n s y s t e m s f o r t h e f e e d s t o c k is a key barrier, as is t h e c y c l i c a l nature of its availability.

14

BIOMASS AS A NONFOSSIL FUEL SOURCE

I M P A C T OF FEDERAL G O V E R N M E N T P R O G R A M S

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

T h e Federal G o v e r n m e n t has d e v e l o p e d n u m e r o u s p r o g r a m s d e s i g n e d t o accelerate t h e c o n v e r s i o n of b i o m a s s t o energy. In s o m e cases c i t e d by i n d u s t r y , t h e s e p r o g r a m s c o n f l i c t w i t h o n e another. Industry e x e c u t i v e s i n d i c a t e d t h a t Federal i n c e n t i v e s p r o g r a m s a n d r e g u l a t o r y policies are h a v i n g a m a j o r i m p a c t o n t h e g r o w t h of b i o m a s s activities, w h i l e DOE p r o g r a m s are h a v i n g little i m p a c t . A m a j o r f a c t o r t h a t affects t h e e c o n o m i c v i a b i l i t y of t h e a l c o h o l fuels i n d u s t r y is t h e c o n t i n u a t i o n of gasohol t a x e x e m p t i o n s p r o v i d e d b y Federal a n d s o m e state g o v e r n m e n t s . A t t h e present t i m e , g a s o h o l is e x e m p t f r o m t h e 4-cent per g a l l o n ($16.80 per barrel of alcohol) excise tax o n gasoline a n d state e x e m p t i o n s range f r o m 3 t o 9.5 c e n t s per gallon ($12.60 t o 3 9 . 9 0 per barrel of alcohol). Extension of t h e Federal tax e x e m p t i o n t o t h e year 2 0 0 0 has been p r o p o s e d ; t h i s is v i e w e d by e x e c u t i v e s as a m a j o r step t o w a r d s a c c e l e r a t i n g t h e d e v e l o p m e n t of t h e i n d u s t r y . T h e Bureau of A l c o h o l , T o b a c c o a n d Firearms (ATF) is responsible for m o n i t o r i n g a n d r e g u l a t i n g all processes w h i c h result in t h e p r o d u c t i o n of e t h a n o l or o t h e r a l c o h o l i c substances. Currently, r e g u l a t i o n s w h i c h a p p l y t o t h e p r o d u c t i o n of a l c o h o l for h u m a n c o n s u m p t i o n also a p p l y t o e t h a n o l p r o d u c e d for fuel a n d industrial uses. T h e r e g u l a t i o n s are c u m b e r s o m e a n d retard t h e d e v e l o p m e n t of t h e i n d u s t r y . D e v e l o p m e n t of s t r e a m l i n e d p r o c e d u r e s w o u l d help accelerate t h e d e v e l o p m e n t of t h e i n d u s t r y a c c o r d i n g t o industry executives. T h e U.S. Forest Service, t h r o u g h its c o n t r o l over p u b l i c forests a n d its policies, has a s i g n i f i c a n t i m p a c t o n t h e a m o u n t l o c a t i o n , a n d p r i c e of w o o d t h a t is available for all uses, i n c l u d i n g energy. Of greatest i m p o r t a n c e are t h e r e g u l a t i o n s r e g a r d i n g c u t t i n g , h a r v e s t i n g , and m a n a g e m e n t of t h e forest, especially t h e a m o u n t t h a t c a n be c u t . Clearer g u i d e l i n e s r e g a r d i n g t h e use of p u b l i c lands c o u l d help i m p r o v e t h e availability of w o o d for energy. T h e DOE has t h r e e m a j o r offices w h i c h are a c t i v e in b i o m a s s t e c h n o l o g y d e v e l o p m e n t a n d c o m m e r c i a l i z a t i o n . T h e Biomass Energy S y s t e m s Branch a n d W o o d C o m m e r c i a l i z a t i o n Program w i t h i n t h e Office of t h e A s s i s t a n t Secretary for Conservation a n d Solar A p p l i c a t i o n s are t h e m a j o r f u n d e r s of b i o m a s s projects in DOE. In a d d i t i o n , DOE provides f u n d s t o t h e Solar Energy Research I n s t i t u t e for b i o m a s s research a n d d e v e l o p m e n t activities. Presently. DOE f u n d i n g is f o c u s e d o n t h e p r o d u c t i o n , c o n v e r s i o n , a n d / o r u t i l i z a t i o n of b i o m a s s , rather t h a n on p r o g r a m s w h i c h f o c u s u p o n a p a r t i c u l a r t y p e of b i o m a s s or i n d u s t r y s e g m e n t . I n d u s t r y e x e c u t i v e s felt t h a t t h e i m p a c t of

1.

SCHAEFER

Biomass Energy Resources

15

Gaseous Fuels

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

A c c o r d i n g t o t h e i n t e r v i e w s p e r f o r m e d as part of t h e assessment o f t h e biomass i n d u s t r y , t h e g a s e o u s - f u e l s - f r o m - b i o m a s s i n d u s t r y is small. Corporate a c t i v i t i e s are f o c u s e d o n t h e anaerobic d i g e s t i o n of m a n u r e s t o p r o d u c e gaseous fuel. M i n i m a l activities are d i r e c t e d t o w a r d s t h e d e v e l o p m e n t of o t h e r f e e d s t o c k s a n d processes. Despite t h e c u r r e n t i n d u s t r y a t t e n t i o n t o these systems a n d their p o t e n t i a l t o m e e t site-specific needs, i n d u s t r y e x p e r i e n c e indicates t h a t t h e e c o n o m i c s of t h e a n a e r o b i c d i g e s t i o n o f m a n u r e s are n o t c o m p e t i t i v e a t t h e present t i m e . In f a c t , m a n y o f t h e c o m p a n i e s i n t e r v i e w e d i n d i c a t e d t h a t t h e refeed materials ( b y - p r o d u c t s w h i c h can be fed t o animals) p r o d u c e d b y anaerobic d i g e s t i o n have higher e c o n o m i c value t h a n t h e gas w h i c h is p r o d u c e d . Resource o w n e r s , s u c h as c a t t l e f e e d l o t operators, farmers, a g r i c u l t u r a l p r o cessors a n d w a s t e w a t e r t r e a t m e n t p l a n t operators, p r o d u c e large q u a n t i t i e s of w a s t e s t h a t c o u l d serve as feedstocks. T h e y are e x p l o r i n g w a y s t o c o n v e r t these w a s t e s t o e n e r g y as s h o w n in Figure 6. A n u m b e r of anaerobic digesters have been b u i l t at facilities s u c h as feedlots, b u t t h e results are m i x ed. Gaseous fuels are p r o d u c e d , b u t t h e a m o u n t is small a n d h i g h in cost. E q u i p m e n t c o m p a n i e s , industrial research organizations, a n d utilities are p r o v i d i n g s u p p o r t f o r research a n d d e v e l o p m e n t in t h i s s e g m e n t . M a n u f a c t u r e r s are a t t e m p t i n g t o d e v e l o p e q u i p m e n t w h i c h c a n c o n v e r t t h e f e e d s t o c k e c o n o m i c a l l y i n t o gases a n d are c u r r e n t l y b u i l d i n g d e m o n s t r a t i o n facilities. Utilities a n d industrial research o r g a n i z a t i o n s foresee t h e d e v e l o p m e n t of b i o g a s i f i c a t i o n as a p o t e n t i a l r e n e w a b l e source o f e n e r g y a n d are a c t i v e l y s u p p o r t i n g efforts in t h i s area. I n d i v i d u a l utilities have b u i l t anaerobic d i g e s t i o n facilities t o b e g i n t e s t i n g s y s t e m s , a n d t h e g a s i n d u s t r y is s u p p o r t i n g R&D o n n e w f e e d s t o c k p r o d u c t i o n a n d c o n v e r s i o n . Electric utilities foresee t h e possibility o f c o n v e r t i n g t h e p r o d u c t gas into e l e c t r i c i t y a n d are s u p p o r t ing d e m o n s t r a t i o n facilities t o test t h e e f f i c i e n c y of t h e process. T h e o u t l o o k f o r t h e gaseous fuels s e g m e n t is t h a t l i m i t e d d e v e l o p m e n t of t h e resource w i l l c o n t i n u e u n t i l c o m p a n y e x e c u t i v e s are c o n v i n c e d t h a t these fuels c a n be p r o d u c e d e c o n o m i c a l l y . S o m e u n c e r t a i n t y exists regarding t h e c o n v e r s i o n t e c h n o l o g y , w h i c h also hinders its d e v e l o p m e n t . In a d d i t i o n , if t h e p r o d u c t gases are n o t u p g r a d e d t o a h i g h - B t u gas, n e w d i s t r i b u t i o n systems m u s t be d e v e l o p e d .

16

BIOMASS AS A NONFOSSIL FUEL SOURCE

WHAT ARE THEY DOING?

WHY ARE THEY DOING IT?

FOOD AND AGRICULTURAL PROCESSING COMPANIES

COMBUSTION OF PROCESSING BY-PRODUCTS

• FUEL DEPENDABILITY • DISPOSAL • REDUCE ENERGY COSTS

CONVERSION AND MATERIALS HANDLING EQUIPMENT MANUFACTURERS

PROVIDING DEMONSTRATED TURNKEY SYSTEMS

TRANSFER EXISTING SKILLS AND CAPABILITIES INTO A NEW MARKET

ELECTRIC UTILITIES

PROVIDING A MARKET FOR GENERATED ELECTRICITY

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

WHO IS INVOLVED?

Figure 5.

• PUBLIC RELATIONS • EXTRA CAPACITY

Motivations for entry into the agricultural residues industry segment

WHO IS INVOLVED?

WHAT ARE THEY DOING?

WHY ARE THEY DOING IT? •

RESOURCE OWNERS

PRODUCE GAS FROM WASTE STREAM

• EQUIPMENT MANUFACTURERS

•

DEVELOP EQUIPMENT SELL TURN-KEY FACILITIES

SUPPORT R&D PROVIDE MARKET FOR PRODUCT GAS

Figure 6.

DEVELOP ENERGY SUPPLY INDEPENDENCE • REDUCE ENERGY COSTS

TRANSFER EXISTING SKILLS INTO NEW MARKETS

•

DEVELOP NEW SUPPLY SOURCES • IMPROVE PUBLIC RELATIONS

Motivations for entry into the gaseous fuels industry segment

1.

SCHAEFER

Biomass Energy Resources

17

these p r o g r a m s c o u l d be e n h a n c e d b y p l a c i n g m o r e e m p h a s i s o n t h e d e v e l o p m e n t o f near- a n d m i d - t e r m t e c h n o l o g i e s a n d a p p l i c a t i o n s .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch001

O t h e r Federal agencies, s u c h as t h e Federal Energy Regulatory C o m m i s s i o n (FERC) a n d t h e U.S. D e p a r t m e n t o f A g r i c u l t u r e , affect t h e g r o w t h of specific sectors. In s o m e cases. Federal p r o g r a m s have c o n t r a d i c t o r y i m p a c t s u p o n t h e i n d u s t r y . For e x a m p l e : •

DOE is e n c o u r a g i n g t h e d e v e l o p m e n t of c o g n e r a t e d electric p o w e r . H o w e v e r , FERC has n o t i m p l e m e n t e d regulations w h i c h w o u l d p e r m i t utilities t o b u y t h i s p o w e r f o r t h e i r c o n s u m e r s .

•

DOE's e n c o u r a g e m e n t t o utilize w o o d as a n e n e r g y source is n o t consist e n t w i t h Forest Service policies o n m a n a g i n g w o o d availability.

These f i n d i n g s s u g g e s t t h a t Federal policies c o u l d be m o r e effective if t h e y c o u l d be c o o r d i n a t e d t o e n h a n c e d e v e l o p m e n t of biomass energy. A reorganization of DOE's p r o g r a m a l o n g p r o d u c t lines w o u l d help t o i m p r o v e c o m m u n i c a t i o n s w i t h i n d u s t r y a n d w o u l d increase DOE's effectiveness. ACKNOWLEDGEMENT T h e f o l l o w i n g people p a r t i c i p a t e d in Booz, A l l e n ' s Biomass Industry Assessm e n t : J a m e s F. L o w r y , S c o t t D. Moeller, K e n n e t h G. Salveson, M i c h a e l R. S e d mak, Satish S u r y a w a n s h i .

RECEIVED M A Y 12, 1980.

2 Forest Biomass for Energy A Perspective R. L. SAJDAK, Y. Z. LAI, G. D. MROZ, and M . F. JURGENSEN

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Department of Forestry, Michigan Technological University, Houghton,MI49931

A primary challenge of the near future is the development of alternative energy sources to make this nation less dependent on imported oil. Increasing the use of wood for energy production has been suggested as one method of meeting this goal (1,2). There are a number of advantages for developing a wood-related energy base in this country. Most importantly, wood is a renewable resource and its production normally has a relatively low environmental impact. Wood can be burned and thus converted directly into energy. Used in this way, it is a relatively clean fuel and the residual ash is useful as a fertilizer. The technology also exists for converting wood into other energy forms such as oil, gas, alcohol, charcoal, and electricity. The forest resource of the United States can make a significant contribution toward meeting national energy needs. Forests occupy about one third of our land area and the wood inventory of this resource is enormous. Of the total annual biomass produced in these forests, only about thirty percent is presently used (3). Better utilization of our annual forest production could make significant quantities of wood material available for energy purposes. However, annual forest growth is well below what is currently possible. More intensive management systems could double the productivity of our forest lands within fifty years (4). Wood now supplies about two percent of total U.S. energy needs, primarily through the use of manufacturing wastes and mill residues for boiler fuel.

0097-6156/81/0144-0021$07.00/0 © 1981 American Chemical Society

22

BIOMASS AS A NONFOSSIL FUEL SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

V a r i o u s studies s u g g e s t w o o d c o u l d s u p p l y up t o 10 p e r c e n t of t h e Nation's c u r r e n t energy needs w i t h i n t h e next decade. D e p e n d i n g u p o n t h e strategies used, e v e n t u a l l y it m a y be possible t o s u p p l y 2 0 p e r c e n t of o u r t o t a l e n e r g y b u d g e t (5). H o w e v e r , t h e use of w o o d for e n e r g y p r o d u c t i o n m u s t be kept in p r o p e r perspective. W o o d is n o t t h e o n l y p r o d u c t of o u r forests. These lands play a v i t a l role in p r o v i d i n g various social a n d c u l t u r a l benefits s u c h as w i l d e r n e s s , o u t d o o r r e c r e a t i o n , w i l d l i f e , f i s h , a n d clean w a t e r . Therefore, no single resource or forest use can be e x a m i n e d in isolation f r o m t h e others. Energy uses w i l l have, t o be b a l a n c e d a g a i n s t t h e g r o w i n g d e m a n d on our forests for l u m b e r , fiber p r o d u c t s , a n d recreational o p p o r t u n i t i e s . This paper w i l l analyze t h e feasibility a n d i m p l i c a t i o n s of increased utilization of o u r forests as a source of energy. C o n s i d e r a t i o n w i l l also be g i v e n t o t h e p r o d u c t i o n of b i o m a s s f r o m intensively c u l t u r e d p l a n t a t i o n s as w e l l as t h e q u a l i t y of t h e b i o m a s s p r o d u c e d by d i f f e r e n t m a n a g e m e n t t e c h n i q u e s . T H E U. S. F O R E S T R E S O U R C E A b o u t 7 4 0 m i l l i o n acres or 3 3 p e r c e n t of t h e land area of t h e U n i t e d States is classified as forest land. In order t o be classified as forest, at least 10 p e r c e n t of t h e land m u s t be s t o c k e d w i t h trees of a n y size. A l s o in this c a t e g o r y are lands t h a t f o r m e r l y had tree c o v e r b u t have n o t been d e v e l o p e d for o t h e r purposes, as w e l l as lands w h o s e p r i m a r y use is not t i m b e r p r o d u c t i o n . Nearly t w o - t h i r d s of t h i s area, or 4 8 8 m i l l i o n acres, is classified as c o m m e r c i a l forest land. C o m m e r c i a l forests are d e f i n e d as f o r e s t e d land c a p a b l e of p r o d u c i n g at least 2 0 c u b i c feet of industrial w o o d per acre per year, a n d is not reserved for uses w h i c h are i n c o m p a t i b l e w i t h t i m b e r p r o d u c t i o n (6). T h u s , National Parks, w i l d e r n e s s areas, a n d o t h e r special use areas are n o t i n c l u d e d in this category. T o help deal w i t h t h e d i v e r s i t y a n d c o m p l e x i t y of v e g e t a t i o n a l a n d e n v i r o n m e n t a l differences in various parts of t h e c o u n t r y , t h e forest resource is discussed by f o u r major g e o g r a p h i c regions: N o r t h e r n , S o u t h e r n Rocky M o u n t a i n s — Great Plains, a n d t h e Pacific Coast. T h e N o r t h e r n Region i n c l u d e s M a r y l a n d , W e s t V i r g i n i a , K e n t u c k y . M i s s o u r i , a n d all states n o r t h a n d w e s t t o t h e Great Plains. T h e S o u t h e r n Region e n c o m p a s s e s V i r g i n i a . Tennessee, Arkansas, O k l a h o m a , and states t o t h e s o u t h . T h e Rocky M o u n t a i n s — Great Plains Region includes W e s t e r n S o u t h Dakota a n d all states w e s t of t h e Great Plains e x c e p t t h o s e b o r d e r i n g on t h e Pacific Ocean. T h e Pacific Coast Region has t h e f o u r states a l o n g t h e Pacific Ocean, including Hawaii.

2.

SAJDAK ET A L .

23

Forest Biomass for Energy

The Northern Forest Region This r e g i o n , w h i c h c o n t a i n s over o n e - h a l f of t h e Nation's p o p u l a t i o n (53 percent), is t h e s e c o n d m o s t densely forested area w i t h 3 5 p e r c e n t o f t h e t o t a l land in c o m m e r c i a l forests (Table I). It is also t h e o n l y region t o register an increase in c o m m e r c i a l forest acreage d u r i n g t h e period 1 9 5 2 - 1 9 7 7 . Private, n o n - i n d u s t r i a l land o w n e r s h i p in t h e states of N e w York, Pennsylv a n i a , a n d W e s t V i r g i n i a c o n t r i b u t e d t o m o s t of t h i s increase. This o w n e r s h i p makes u p 7 1 p e r c e n t of t h e forest h o l d i n g s in t h e N o r t h e r n Region. T a b l e I. D I S T R I B U T I O N O F C O M M E R C I A L F O R E S T L A N D I N T H E Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

U N I T E D S T A T E S B Y R E G I O N A N D B Y O W N E R S H I P C L A S S (6)

Ownership Region

Public

Industry

Private

(%)

(%)

(%)

170,769

35

19

10

71

188.433 South Rocky M o u n t a i n s — Great Plains 57.765

39

9

19

72

12

75

4

21

Pacific Coast

14

63

17

20

TOTAL

Distribution

6

(%) North

Area

8

70.758

6

487,725

a

T h o u s a n d acres.

b

Percentages o f t h e t o t a l U.S. c o m m e r c i a l forest land.

c

Percentages of t h e region.

T h e N o r t h e r n Region's forests vary c o n s i d e r a b l y as d o their uses. S e v e n t y - f i v e p e r c e n t of t h e t i m b e r v o l u m e is in h a r d w o o d s , w h i c h are utilized for f u r n i t u r e , veneer, p u l p , pallets, a n d railroad ties (Table II). S o f t w o o d v o l u m e is t h e smallest of any region (25 percent). The s t o c k i n g levels are t h e l o w e s t in t h e c o u n t r y a n d t h e average a n n u a l g r o w t h per acre is q u i t e l o w (Table III). It s h o u l d be n o t e d t h a t these v o l u m e figures are based o n c o m m e r c i a l - s i z e d t i m b e r a n d d o n o t i n c l u d e w o o d present in small, n o n - m e r c h a n t a b l e trees a n d in t h e t o p s a n d limbs o f m e r c h a n t a b l e trees.

24

BIOMASS AS A NONFOSSIL FUEL SOURCE

Table II. T I M B E R PRODUCTION O N UNITED STATES C O M M E R C I A L F O R E S T L A N D I N 1 9 7 7 (6)

Total Volume Region

(million c u . ft.)

(cubic feet)

(%)

(%)

200.337 230.037

1173

25

1221

43

75 57

112.405

1946

94

6

258.024

3646 1997

92

8

62

38

North South

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Rocky tains-

Average Volume Timber Type Per A c r e Softwood Hardwood

Moun-

Great Plains Pacific Coast TOTAL

800.803

Table III. NET A N N U A L G R O W T H A N D H A R V E S T O N C O M M E R C I A L T I M B E R L A N D S I N T H E U N I T E D S T A T E S (6) Average Growth Region

Growth Harvest ( 1 0 0 0 c u . ft.) ( 1 0 0 0 c u . ft.)

Per A c r e (cubic feet)

North South Rocky M o u n t a i n s — Great Plains

5.927.587 10.826.042 1.689.553

2.739.535 6.571,223 845.786

34.7 57.4 29.2

Pacific Coast TOTAL

3.431.151 21.874.333

4.278.868 14.425.230

48.5 44.8

The Southern Region T h i s r e g i o n is t h e m o s t densely forested in t h e N a t i o n w i t h 3 9 p e r c e n t of t h e land area in c o m m e r c i a l forests. It is also t h e s e c o n d m o s t d e n s e l y p o p u l a t e d . C o m m e r c i a l forest acreage d e c l i n e d d u r i n g t h e 2 5 year p e r i o d . 1 9 5 2 t o 1 9 7 7 . p r i m a r i l y d u e t o c o n v e r s i o n of forest lands t o a g r i c u l t u r a l uses. Forest o w n e r s h i p , as in t h e N o r t h , is p r i m a r i l y in private n o n - i n d u s t r i a l h o l d i n g s (72 percent). I n d u s t r y o w n e r s h i p is t h e largest of any region (19 percent) a n d p u b l i c o w n e r s h i p is t h e smallest (9 percent). S o u t h e r n forests are q u i t e e q u a l l y d i v i d e d b e t w e e n h a r d w o o d a n d s o f t w o o d tree species. Forty-three p e r c e n t of t h e t i m b e r v o l u m e is in s o f t w o o d s . A v e r a g e a n n u a l g r o w t h per acre of forest land is t h e h i g h e s t of any region. T h e S o u t h is p r o j e c t e d t o s u p p l y over o n e - h a l f of t h e Nation's s o f t w o o d r e q u i r e m e n t s by t h e year 2 0 3 0 . nearly d o u b l i n g its 1 9 7 6 o u t p u t .

2.

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25

Forest Biomass for Energy

The Rocky M o u n t a i n s - G r e a t Plains Region This region c o n t a i n s t h e smallest p e r c e n t a g e (12 percent) of this c o u n t r y ' s c o m m e r c i a l forests a n d is t h e least p o p u l a t e d . M o s t o f t h e forest land is in p u b l i c o w n e r s h i p (75 percent). D u r i n g t h e period 1 9 5 2 t o 1 9 7 7 , this region lost over 10 p e r c e n t o f its forest land, m o s t of w h i c h w a s e n t e r e d into t h e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

w i l d e r n e s s and National Park s y s t e m . These forests are p r e d o m i n a n t l y s o f t w o o d s w h i c h c o m p r i s e 9 4 p e r c e n t of t h e t i m b e r v o l u m e . A b o u t o n e - t h i r d o f t h i s v o l u m e is in t h e p i n y o n p i n e / j u n i p e r t i m b e r t y p e w h i c h is relatively u n i m p o r t a n t f o r w o o d p r o d u c t i o n . A n n u a l g r o w t h averages 2 9 c u b i c feet per acre per year, t h e l o w e s t o f all regions. These forests are very i m p o r t a n t f o r w a t e r s h e d , recreation, a n d livestock grazing. The Pacific Coast Region There is a t r e m e n d o u s a m o u n t o f d i v e r s i t y o f t h e forests in t h i s region. T h e c l i m a t e ranges f r o m arctic t o t r o p i c a l a n d s o m e of t h e m o s t

productive

forests in t h e w o r l d are f o u n d a l o n g t h e coast f r o m N o r t h e r n California t o W a s h i n g t o n . O n l y 1 4 p e r c e n t o f t h e t o t a l land area is in c o m m e r c i a l forests a n d like t h e Rocky M o u n t a i n Region, m o s t is in p u b l i c o w n e r s h i p . This region also recorded a d e c l i n e in c o m m e r c i a l forest land d u e t o transfers

into

w i l d e r n e s s areas a n d parks. M o s t of t h e t i m b e r v o l u m e is in s o f t w o o d s (92 percent) a n d t h e average a n n u a l g r o w t h is s e c o n d h i g h e s t in t h e N a t i o n . A v e r a g e g r o w i n g stock per acre is t h e h i g h e s t in a n y r e g i o n , a n d a n n u a l t i m b e r c u t is m o r e t h a n n e t i n g r o w t h . O v e r c u t t i n g is d u e t o t h e accelerated removal o f o l d g r o w t h , o v e r m a t u r e stands. This region n o w supplies over one-half o f o u r s o f t w o o d t i m b e r needs. T h e p r o j e c t i o n s are for t h i s region's s o f t w o o d o u t p u t t o d e c l i n e after 1 9 9 0 . FOREST P R O D U C T I V I T Y

ASSESSMENT

In e v a l u a t i n g t h e forest resource t o d e t e r m i n e h o w m u c h w o o d is available for e n e r g y p r o d u c t i o n , a m u l t i t u d e o f factors needs t o be c o n s i d e r e d . M o s t o f t h e c o m m e r c i a l forest land in t h e N o r t h e r n a n d S o u t h e r n Regions is in private, n o n - i n d u s t r i a l o w n e r s h i p . It is d i f f i c u l t t o assess t h e c o n t r i b u t i o n these lands w i l l m a k e t o w a r d s u p p l y i n g o u r e n e r g y needs. O b j e c t i v e s o f forest o w n e r s h i p vary c o n s i d e r a b l y a n d t i m b e r p r o d u c t i o n is o f t e n s e c o n d t o n o n - t a n g i b l e goals. Private forest lands are o f t e n m a n a g e d o n a n o p p o r t u n i s t i c basis w i t h little regard t o a r e g u l a t e d a n d s u s t a i n e d t i m b e r y i e l d .

26

BIOMASS AS A NONFOSSIL FUEL SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Therefore, it m a y be d i f f i c u l t t o o b t a i n a d e p e n d a b l e s u p p l y of w o o d f r o m a p a r t i c u l a r g e o g r a p h i c area. A l s o , m o s t private forest h o l d i n g s are small a n d t h e m o s t e f f i c i e n t t o t a l tree h a r v e s t - s y s t e m s c a n n o t o p e r a t e e c o n o m i c a l l y in s u c h situations. W h e n c o n d u c t i n g c o n v e n t i o n a l r o u n d w o o d harvests, t h e r e m o v a l of l o g g i n g residue f r o m s m a l l , w i d e l y scattered o p e r a t i o n s poses a difficult problem. T h e private forest resource c a n be very p r o d u c t i v e . A recent s t u d y i n d i c a t e d t h a t w o o d p r o d u c t i o n o n t h e s e lands w a s 6 1 p e r c e n t of c a p a c i t y u n d e r c u r r e n t m a n a g e m e n t p r a c t i c e . In c o n t r a s t , t h e N a t i o n a l Forests g r e w w o o d at 4 9 p e r c e n t of c a p a c i t y (7). I m p r o v e d m a n a g e m e n t of small forests for increased b i o m a s s p r o d u c t i o n m a y be t h e m o s t d i f f i c u l t p r o b l e m of all. Usually l a c k i n g is t h e w i l l i n g n e s s a n d c a p a c i t y of t h e small l a n d - o w n e r t o m a k e i n v e s t m e n t s for a r e t u r n w h i c h w i l l be 2 0 - 3 0 years a w a y (8). S u b s t a n t i a l increases in t h e s u p p l y of w o o d f r o m t h e s e o w n e r s h i p s can be a c h i e v e d o n l y t h r o u g h g o v e r n m e n t a l assistance, s u c h as c o s t - s h a r i n g a n d t e c h n i c a l assistance p r o g r a m s (9). C o n c e i v a b l y , m u c h of t h e w o o d f r o m p r i v a t e forests m a y be used for h o m e h e a t i n g purposes, p a r t i c u l a r l y in t h e m o r e p o p u l a t e d forested areas. A s t h e cost of h e a t i n g oil increases, h e a t i n g w i t h w o o d b e c o m e s m o r e a t t r a c t i v e a n d m o r e p r i v a t e forests w i l l be d e d i c a t e d for f u e l w o o d p r o d u c t i o n . In M a i n e , for e x a m p l e , over 5 0 p e r c e n t of t h e h o m e s are c u r r e n t l y b e i n g h e a t e d w i t h w o o d . T h e i m p a c t of t h i s t y p e of m a n a g e m e n t o n f u t u r e s u p p l i e s of h i g h v a l u e s a w l o g s in a p a r t i c u l a r region c o u l d be s i g n i f i c a n t . Increasing Timber Output W i t h b e t t e r m a n a g e m e n t . U.S. t i m b e r s u p p l i e s c o u l d be d r a m a t i c a l l y increased in t h e f u t u r e . A v e r a g e a n n u a l g r o w t h o n c o m m e r c i a l forest land in 1 9 7 6 w a s 4 5 c u b i c feet per acre. If t h e forests w e r e f u l l y s t o c k e d , average g r o w t h w o u l d average 7 5 c u b i c feet per acre per year. This increase in a n n u a l g r o w t h w o u l d r o u g h l y equal t h e t o t a l v o l u m e harvested f r o m all forests in 1 9 7 6 (6). T h e possibilities f o r i n t e n s i f y i n g m a n a g e m e n t exist for all o w n e r s h i p s a n d in all regions of t h e c o u n t r y e x c e p t for t h e Rocky M o u n t a i n s - G r e a t Plains. Preliminary results of t h e U.S. Forest Service a n d Forest Industries C o u n c i l s t u d i e s i n d i c a t e t h e r e are e c o n o m i c o p p o r t u n i t i e s for i n t e n s i f i e d m a n a g e m e n t o n 1 6 0 m i l l i o n acres of c o m m e r c i a l t i m b e r l a n d or a b o u t 3 4 p e r c e n t of t h e N a t i o n ' s t o t a l . T h e o p p o r t u n i t i e s are m o s t c o n c e n t r a t e d in t h e 1 1 3 m i l l i o n acres of t h e S o u t h e r n Region. A b o u t t h r e e - f o u r t h s of t h e t r e a t m e n t strategies involve regeneration of n o n - s t o c k e d areas, h a r v e s t i n g m a t u r e forests,

2.

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27

Forest Biomass for Energy

r e g e n e r a t i n g higher y i e l d i n g y o u n g stands, a n d c o n v e r t i n g e x i s t i n g stands t o m o r e p r o d u c t i v e species. T h e e s t i m a t e d t o t a l cost o f t r e a t i n g t h e S o u t h e r n acreage is $8.8 billion. This i n v e s t m e n t w o u l d increase a n n u a l g r o w t h in this region by m o r e t h a n 8.5 billion c u b i c feet. The National Forests, p a r t i c u l a r l y those in t h e W e s t , also have t h e c a p a b i l i t y o f s u p p o r t i n g larger harvests. Additional

investments

would

be needed

f o r road

construction,

stand

i m p r o v e m e n t , reforestation, a n d salvage (9). Increased forest yields c a n be o b t a i n e d b y using k n o w n a n d p r o v e n intensive c u l t u r e t e c h n i q u e s . Use of g e n e t i c a l l y i m p r o v e d p l a n t i n g stock can increase yields b y 10 t o 2 0 percent. Fertilization a n d t h i n n i n g p r o g r a m s , better tree Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

s p a c i n g , a n d increased fire, insect, a n d disease p r o t e c t i o n c a n all i m p r o v e yields s i g n i f i c a n t l y . T h e limits t o increasing w o o d yields b y intensive c u l t u r a l t e c h n i q u e s are n o t k n o w n . A reasonable e s t i m a t e is t h a t t h e g r o w t h c o u l d d o u b l e o n half o f t h e c o m m e r c i a l forest land in 5 0 years (3). Availability o f W o o d f o r Energy Production W e c a n o n l y s p e c u l a t e o n t h e t r u e size o f t h e t o t a l t i m b e r resource of t h e U n i t e d States. T o d a t e , all of t h e inventories a n d surveys o n a national scale have been based o n v o l u m e m e a s u r e m e n t s of t h e m e r c h a n t a b l e parts of trees. Tables I. II, a n d III reflect this. M e r c h a n t a b l e v o l u m e is a v a g u e t e r m , p a r t i c u l a r l y since m e r c h a n t a b i l i t y limits are rapidly c h a n g i n g . The c o n c e p t of w h o l e - t r e e utilization has reinforced t h i s c o n f u s i o n . W i t h t h e d e v e l o p m e n t o f w h o l e - t r e e h a r v e s t i n g m e t h o d s , previously n o n - m e r c h a n t a b l e parts o f t h e tree are c h i p p e d a n d used f o r p u l p a n d paper, c o m p o s i t e p r o d u c t s , a n d fuel. These n e w c o n c e p t s of utilization m a k e t h e w h o l e tree t h e basic u n i t of m e a s u r e m e n t . Since a c c u r a t e v o l u m e d e t e r m i n a t i o n is d i f f i c u l t o n irregular s h a p e d o b j e c t s , w e i g h t o f biomass is t h e n e w s t a n d a r d of measure for all tree components. There have been n u m e r o u s e s t i m a t e s m a d e o n t h e t o t a l biomass a n d biomass p o t e n t i a l o f o u r forests (3.1Ω). T h e i n v e n t o r y p r o c e d u r e used is based o n e s t i m a t e s a n d averages, a n d is fully d e s c r i b e d by W a h l g r e n a n d Ellis ( U ) . Forest surveys based o n biomass m e a s u r e m e n t t e c h n i q u e s are needed t o a c c u r a t e l y d e t e r m i n e t h e q u a n t i t i e s a n d l o c a t i o n of our w o o d resource. M a n y studies o n m e a s u r i n g t h e w e i g h t o f i n d i v i d u a l trees, a n d t o a lesser e x t e n t forest stands, have been made. T h i s w o r k has been s u m m a r i z e d b y Keays (12). a n d H i t c h c o c k a n d M c D o n n e l l (12). A s w o r k in forest b i o m a s s m e a s u r e m e n t is r e f i n e d , regional w e i g h t tables c a n be d e v e l o p e d a n d a c c u r a t e biomass inventories c o m p i l e d .

28

BIOMASS AS A NONFOSSIL FUEL SOURCE

W o r k has already b e g u n in this d i r e c t i o n . Pioneering w o r k i n i t i a t e d by Y o u n g a n d others in M a i n e has resulted in t h e c o m p l e t i o n of a forest biomass i n v e n t o r y o n nearly t w o m i l l i o n acres in t h a t state (14)· T h e next forest survey of M a i n e , t o be s t a r t e d in 1 9 8 0 . by t h e U.S. Forest Service w i l l be in t e r m s of b o t h m e r c h a n t a b l e v o l u m e a n d t o t a l w o o d biomass. I n f o r m a t i o n s u c h as t h i s , as w e l l as m e a s u r e m e n t of a n n u a l d r y m a t t e r p r o d u c t i o n , w i l l d e t e r m i n e t h e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

availability of w o o d supplies o n a regional basis for industrial a n d energy purposes. Biomass inventories m u s t also u n d e r g o e c o n o m i c assessments since in m a n y s i t u a t i o n s , t h e c o s t of c o l l e c t i n g , p r o c e s s i n g , a n d t r a n s p o r t i n g b i o m a s s materials w o u l d e x c e e d a n y reasonable v a l u e a n t i c i p a t e d for fuel or other products. Forest Residue Forest residue is d e f i n e d as t h e b i o m a s s left in t h e w o o d s after harvest a n d i n c l u d e s tree t o p s , l i m b s , c u l l m a t e r i a l , a n d all present a n d f u t u r e n o n m e r c h a n t a b l e trees. This differs f r o m m i l l residue s u c h as bark, e d g i n g s , a n d s a w d u s t , w h i c h is o f t e n f u l l y utilized as boiler f u e l . T h e a m o u n t of residue r e m a i n i n g after harvest w i l l v a r y a c c o r d i n g t o m e r c h a n t a b i l i t y s t a n d a r d s , m e t h o d of harvest, a n d forest s t a n d c o m p o s i t i o n a n d q u a l i t y . In a t y p i c a l h a r d w o o d s a w l o g harvest as m u c h as 5 0 p e r c e n t of t h e p o t e n t i a l usable b i o m a s s m a y be left as residue. If t h e s a w l o g s t a n d is o v e r m a t u r e or of poor q u a l i t y , a d d i t i o n a l residue m a y be left. In c o n t r a s t , if t h e s t a n d is w h o l e - t r e e c h i p p e d for p u l p m a t e r i a l , very little residue w i l l r e m a i n . T h r o u g h o u t t h e U n i t e d States t h e r e are a n u m b e r of o n g o i n g studies w h o s e o b j e c t i v e s are t o d e t e r m i n e , o n a regional basis, t h e real p o t e n t i a l a n d e c o n o m i c a v a i l a b i l i t y of w o o d y b i o m a s s for energy. T h e D e p a r t m e n t of Energy in c o o p e r a t i o n w i t h t h e U.S. Forest Service is in t h e process of d e v e l o p i n g a N a t i o n a l W o o d Energy Data S y s t e m . This s y s t e m w i l l i d e n t i f y a m o u n t s a n d locations of w o o d fuels in excess of c o m m e r c i a l needs. The i n f o r m a t i o n w i l l be d e l i n e a t e d by state a n d in s o m e cases d o w n t o t h e c o u n t y level. In a d d i t i o n , t h e l o c a t i o n of c u r r e n t a n d p o t e n t i a l large w o o d b u r n i n g s y s t e m s w i t h i n each u n i t w i l l be i d e n t i f i e d (14). T h e M a r y l a n d D e p a r t m e n t of N a t u r a l Resources r e c e n t l y c o m p l e t e d an assessment of t h e availability, cost, a n d reliability of w o o d fuels o n t h e D e l m a r v a Peninsula (14). T h e s t u d y c o n c l u d e d t h a t c u l l trees a n d t i m b e r harvest residue c o u l d p r o v i d e o v e r 1.9 m i l l i o n t o n s o f w o o d fuel a n n u a l l y at a cost t o users of $ 1 2 . 5 0 per green t o n . O t h e r studies in M i n n e s o t a , N e w York, O r e g o n , a n d W a s h i n g t o n are i n v o l v e d in similar utilization a n d biomass assessments t o d e t e r m i n e t h e availability of w o o d fuels for energy.

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29

Forest Biomass for Energy

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Recently, t h e N o r t h e r n W i s c o n s i n a n d U p p e r M i c h i g a n region w a s intensively s t u d i e d b y t h e U.S. Forest Service t o d e t e r m i n e t h e a m o u n t of residue available in t h e region U s i n g available forest s u r v e y i n f o r m a t i o n a n d c o m p u t e r s i m u l a t i o n , t h e harvest a m o u n t s a n d delivered cost of biomass w e r e d e t e r m i n e d . A " M a n a g e d H a r v e s t " p r o c e d u r e w a s used t o d e t e r m i n e t h e a m o u n t of w o o d p r o d u c t a n d residue t h a t s h o u l d be r e m o v e d each year for a 10-year period. O n l y t w o p r o d u c t s w e r e c o n s i d e r e d : s a w l o g s a n d w o o d chips. T h e a s s u m p t i o n w a s m a d e t h a t excess c h i p s n o t n e e d e d f o r paper p r o d u c t s w o u l d be available f o r e n e r g y purposes or m o r e s u c c i n c t l y , " p u l p t h e best a n d b u r n t h e rest." T h e overall o b j e c t i v e of t h e " M a n a g e d H a r v e s t " p r o c e d u r e w a s t o m o v e t h e forests t o a f u l l y - r e g u l a t e d a n d m o r e p r o d u c t i v e condition. Several h a r v e s t i n g strategies w e r e e x a m i n e d a n d s i g n i f i c a n t differences w e r e f o u n d t o exist in t h e deliverable cost a n d a m o u n t of recovered b i o m a s s a m o n g t h e h a r v e s t i n g s y s t e m s used. O n e h a r v e s t i n g strategy i n v o l v e d t h e m e c h a n i z e d t h i n n i n g o f o v e r s t o c k e d , small d i a m e t e r forest stands. Over three m i l l i o n d r y t o n s of b i o m a s s w a s p r o j e c t e d t o be deliverable f r o m t h e entire s t u d y area in 1 9 8 0 at a cost of $ 1 5 . 9 1 per t o n . This v o l u m e w o u l d also be available in each s u c c e e d i n g year. A s e c o n d s t r a t e g y i n v o l v e d t h e c l e a r c u t t i n g o f m a t u r e a n d o v e r m a t u r e stands a n d stands t o o poorly s t o c k e d t o be carried t o a n o r m a l c u t t i n g age. S a w l o g s w e r e r e m o v e d before t h e residual s t a n d w a s c h i p - h a r v e s t e d . This s t r a t e g y is used w h e r e e v e n - a g e d forest m a n a g e m e n t

is p r a c t i c e d a n d also

where

stands w o u l d be c o n v e r t e d t o a f u l l y - s t o c k e d s i t u a t i o n . Ten m i l l i o n t o n s c o u l d be p r o d u c e d a n n u a l l y , e x c l u s i v e o f s a w l o g s . at a n average cost o f $ 1 2 . 3 5 per t o n delivered. The costs per delivered t o n are averages f o r t h e entire t o n n a g e available. S u b s t a n t i a l v o l u m e s o f forest biomass are available at l o w e r costs, b u t as an a t t e m p t is m a d e t o recover increasing a m o u n t s of t h e biomass, t h e costs increase. The s t u d y c o n c l u d e d t h a t s i g n i f i c a n t forest biomass q u a n t i t i e s are available in t h i s r e g i o n . For b o t h N o r t h e r n W i s c o n s i n a n d Upper M i c h i g a n , 30.5 m i l l i o n dry t o n s a n n u a l l y w o u l d be deliverable at a 1 9 8 0 p r o j e c t e d cost of $ 1 6 . 0 7 per t o n . These biomass q u a n t i t i e s w o u l d be available each year f o r t h e next 1 0 years. A t t h e e n d of t h e 10-year p e r i o d , a n e w assessment w i l l have t o be made. The

costs

for w o o d y

residue

materials

will

change

as m o r e

efficient

h a r v e s t i n g e q u i p m e n t is d e v e l o p e d . Koch a n d N i c h o l s o n (1Q) d e s c r i b e d a

30

BIOMASS AS A NONFOSSIL FUEL SOURCE

m o b i l e c h i p p e r d e s i g n e d t o effectively harvest b i o m a s s o n relatively flat t e r r a i n . Their s t u d i e s s h o w t h a t if a m i n i m u m of 2 5 t o n s (green w e i g h t ) of b i o m a s s is available per acre, a b o u t 8 5 p e r c e n t of s u c h b i o m a s s c o u l d be recovered a n d d e l i v e r e d t o t h e forest roadside for a b o u t $ 1 1 . 8 2 per green t o n . This m a c h i n e w a s d e s i g n e d t o recover forest residue t h a t is o r d i n a r i l y b u l l d o z e d a n d b u r n e d d u r i n g t h e p r e p a r a t i o n of a site for p l a n t i n g .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

INTENSIVE PLANTATION CULTURE T r a d i t i o n a l p l a n t a t i o n c u l t u r e in t h i s c o u n t r y has a p p r o x i m a t e d w h a t o c c u r s in nature. In t h i s s i t u a t i o n trees are p l a n t e d at fairly w i d e s p a c i n g (6 feet or more) o f t e n w i t h little or no site p r e p a r a t i o n . Occasionally, t h e trees are released f r o m c o m p e t i n g v e g e t a t i o n a n d t h e p l a n t a t i o n m a y be t h i n n e d o n c e or t w i c e . T h e r o t a t i o n l e n g t h of these p l a n t a t i o n s m a y be 3 0 years or more, d e p e n d i n g o n t h e g r o w t h rate a n d e n d p r o d u c t desired. Coniferous trees, p a r t i c u l a r l y t h e pines, have been p l a n t e d far m o r e o f t e n t h a n h a r d w o o d s . Recently, interest has d e v e l o p e d in t h e i n t e n s i v e c u l t u r e o f p l a n t a t i o n s o n a short r o t a t i o n . H o w e v e r , t h i s c o n c e p t is n o w n e w . T h e Europeans have been m a n a g i n g p l a n t a t i o n s in t h i s m a n n e r for d e c a d e s a n d in t h e 1960's. M c A l p i n e a n d his c o w o r k e r s f u r t h e r d e v e l o p e d t h e c o n c e p t in t h e U n i t e d States w i t h s y c a m o r e (P/atanus occidentalis L ) (1Ζ)· Since t h a t t i m e , studies have been i n i t i a t e d w i t h o t h e r tree species t h r o u g h o u t t h e U n i t e d States a n d Canada. In c o n c e p t , t h e intensive c u l t u r e of p l a n t a t i o n s o n a short r o t a t i o n is essentially an a g r o n o m i c s y s t e m . Trees are p l a n t e d on prepared sites at close s p a c i n g (4 feet or less), c u l t i v a t e d , fertilized, a n d irrigated d u r i n g t h e r o t a t i o n . A g r i c u l t u r a l - t y p e forage e q u i p m e n t w o u l d t h e n harvest t h e c r o p at ages of less t h a n 10 years. T h e e n t i r e a b o v e g r o u n d p o r t i o n of t h e tree is utilized. Regeneration of t h e p l a n t a t i o n w o u l d be by c o p p i c e g r o w t h , t h e r e b y l i m i t i n g t h e p l a n t a t i o n s m a i n l y t o h a r d w o o d s w h i c h s t u m p or root s p r o u t after cutting. A n u m b e r of a d v a n t a g e s are e v i d e n t in t h e intensive c u l t u r e of p l a n t a t i o n s o n a short rotation w h e n contrasted to conventional plantation

(1S,12). These 1.

Higher yields per u n i t of land area, therefore less land w o u l d be needed t o p r o d u c e a g i v e n a m o u n t of biomass.

2.

management

are:

Early a m o r t i z a t i o n of p l a n t a t i o n e s t a b l i s h m e n t costs.

2. 3.

SAJDAK ET AL.

Forest Biomass for Energy

31

Increased e f f i c i e n c y o f m o s t c u l t u r a l a n d h a r v e s t i n g o p e r a t i o n s because of c o m p l e t e m e c h a n i z a t i o n .

4.

Reduced p l a n t a t i o n regeneration costs after t h e first r o t a t i o n .

5.

Genetically i m p r o v e d trees c a n be utilized q u i c k l y .

6.

T h e biomass p r o d u c e d w i l l be o f m o r e u n i f o r m q u a l i t y .

There are s o m e s i g n i f i c a n t d i s a d v a n t a g e s , h o w e v e r :

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

1.

Initial p l a n t a t i o n e s t a b l i s h m e n t a n d m a n a g e m e n t costs per acre are very h i g h , t h e r e b y increasing t h e f i n a n c i a l risk i n v o l v e d .

2.

Site l i m i t a t i o n s are i m p o r t a n t f o r t h i s t y p e of forest practice. T h e land m u s t be relatively flat a n d soil t e x t u r e , s t r u c t u r e , d r a i n a g e a n d stoniness w i l l be i m p o r t a n t c o n s i d e r a t i o n s .

3.

T h e relatively u n i f o r m g e n e t i c m a k e u p of t h e trees increase e p i d e m i c disease a n d insect hazards.

H a r d w o o d s have been preferred f o r intensive p l a n t a t i o n m a n a g e m e n t because o f their s p r o u t i n g c a p a b i l i t y a n d t h e fast g r o w t h of these s p r o u t s f o r t h e first 1 0 - 2 0 years, as c o m p a r e d t o conifers.There are e x c e p t i o n s , h o w e v e r , w h e r e conifers m a y be m o r e desirable. W i l l i f o r d et al. (20) reported loblolly pine {Pinus taeda L.) t o be superior in b i o m a s s p r o d u c t i o n o n m a n y sites in t h e s o u t h . Studies b y t h e U.S. Forest Service at Rhinelander, W i s c o n s i n , i n d i c a t e conifers m a y have a d v a n t a g e s u n d e r certain site c o n d i t i o n s (21.). For e x a m p l e , jack pine (Pinus banks/ana Lamb.) is w e l l a d a p t e d t o t h e N o r t h , has f e w serious insect a n d disease p r o b l e m s , a n d is less d e m a n d i n g of n u t r i e n t s and moisture than many hardwoods. N u m e r o u s species trials are u n d e r w a y in various parts of t h e c o u n t r y t o i d e n t i f y t h e best species f o r localized b i o m a s s p r o d u c t i o n (14). Several of t h e m o r e intensively s t u d i e d c a n d i d a t e species are discussed in m o r e detail as follows: American Sycamore This w a s t h e first species a d v o c a t e d f o r short r o t a t i o n intensive c u l t u r e . S y c a m o r e p l a n t a t i o n s are established u s i n g seedlings or f r o m c u t t i n g s . If c u t t i n g s are used, a clonal p l a n t a t i o n is established w h i c h results in a h i g h degree of tree u n i f o r m i t y . S y c a m o r e w o o d is m o d e r a t e l y dense w i t h a specific

32

BIOMASS AS A NONFOSSIL FUEL SOURCE

g r a v i t y of a b o u t 0.46 a n d a s a p w o o d m o i s t u r e c o n t e n t of 1 3 0 p e r c e n t o n an o v e n d r y basis (4Q).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

This species is m o s t p r o d u c t i v e o n rich alluvial land in t h e s o u t h . Plantations o n u p l a n d sites have y i e l d e d p o o r survival a n d u n a c c e p t a b l e levels of g r o w t h (22). H o w l e t t a n d G a m a c h e (18) r e v i e w e d n u m e r o u s studies on t h e biomass p r o d u c t i v i t y of s y c a m o r e in t h e s o u t h a n d f o u n d g r o w t h rates as h i g h as 9 d r y t o n s per acre per year. T h e average yield w a s a b o u t 4.5 d r y t o n s per acre per year a n d in s o m e studies yields w e r e as l o w as 2 t o n s per acre per year. Usually, higher initial s t a n d densities p r o d u c e d h i g h e r yields for r o t a t i o n ages of up t o f o u r years. H o w e v e r , d i r e c t c o m p a r i s o n s a m o n g sites are d i f f i c u l t because of t h e d i f f e r e n t c u l t u r a l t r e a t m e n t s a p p l i e d in t h e various studies. Poplars and C o t t o n w o o d V a r i o u s species a n d h y b r i d s of t h e g e n u s Populus are s o m e of t h e m o r e p r o m i s i n g c a n d i d a t e s for i n t e n s i v e b i o m a s s p r o d u c t i o n . This g r o u p has long been c u l t i v a t e d in Europe a n d m o r e r e c e n t l y in t h e Eastern U n i t e d States a n d Canada. Poplar h y b r i d s are easily d e v e l o p e d a n d t h e r e s u l t i n g p r o g e n y are p r o p a g a t e d v e g e t a t i v e l y using s t e m c u t t i n g s . C o n s e q u e n t l y , t h e r e are literally h u n d r e d s of n u m b e r e d or n a m e d clones e s t a b l i s h e d t h r o u g h o u t t h e Eastern U n i t e d States. T h e w o o d is m o d e r a t e l y l i g h t as i n d i c a t e d by specific g r a v i t y values of 0.32 t o 0.37 a n d t h e m o i s t u r e c o n t e n t of t h e s a p w o o d is a b o u t 146 p e r c e n t (4Q). Certain h y b r i d poplar c l o n e s s h o w e x c e l l e n t response t o i n t e n s i v e c u l t u r e t e c h n i q u e s . D a w s o n (21J r e p o r t e d a m e a n a n n u a l biomass yield of nearly 7 t o n s per acre on a 12 i n c h s p a c i n g d u r i n g t h e first r o t a t i o n . A n d e r s o n a n d Zsuffa (23) r e p o r t e d c o p p i c e d s t a n d s y i e l d i n g 8.5 t o n s per acre per year o n a t w o year r o t a t i o n . Eucalypts Species of Eucalyptus appear t o have p r o m i s e as c a n d i d a t e s for biomass p r o d u c t i o n in intensively c u l t u r e d p l a n t a t i o n s . H o w e v e r , a lack of c o l d hardiness w o u l d restrict t h e i r usage t o t h e s o u t h e a s t e r n states, California a n d H a w a i i . This e v e r g r e e n h a r d w o o d g e n u s c o n t a i n s over 5 0 0 species, m o s t of w h i c h are n a t i v e t o A u s t r a l i a . T h e e u c a l y p t s have been p l a n t e d t h r o u g h o u t t h e w o r l d a n d display a w i d e a d a p t a b i l i t y t o a variety of sites. Especially n o t e w o r t h l y is t h e i r c a p a b i l i t y t o t h r i v e o n d r o u g h t y a n d n u t r i e n t - d e f i c i e n t sites. A l t h o u g h p r i m a r i l y s u i t e d for frost-free areas, studies by industrial c o o p e r a t o r s in t h e s o u t h e a s t e r n states i n d i c a t e d t h a t c o n s i d e r a b l e v a r i a t i o n exists in resistance t o freezing t e m p e r a t u r e s . (24). T h e g e n e t i c v a r i a t i o n

2.

SAJDAK ET AL.

33

Forest Biomass for Energy

i n d i c a t e d w a s s u c h t h a t selection f o r freeze-tolerant e u c a l y p t u s species a n d races m a y be possible. L i m i t e d g r o w t h d a t a is available b u t it has s h o w n a m e a n a n n u a l biomass p r o d u c t i o n of over 4 t o n s per acre per year. Greater productivity from eucalyptus

plantations should

be possible w i t h

more

i n t e n s i v e c u l t u r e a n d g e n e t i c a l l y i m p r o v e d stock.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Nitrogen-Fixing Species N i t r o g e n is t h e m o s t l i m i t i n g m a c r o n u t r i e n t needed for tree g r o w t h o n m o s t forest sites. Concern over t h e h i g h cost o f n i t r o g e n fertilizers for intensive p l a n t a t i o n c u l t u r e has p r o m p t e d c o n s i d e r a b l e interest in plants c a p a b l e of using a t m o s p h e r i c n i t r o g e n . Zavitkovski et al. (25) r e v i e w e d t h e studies w h i c h p e r t a i n t o t h e use o f n i t r o g e n - f i x i n g w o o d y a n d herbaceous species f o r forestry purposes. A s s e s s m e n t s w e r e m a d e o n t h e possibility of using red alder (A/nus rubra Bong.) f o r b i o m a s s p r o d u c t i o n , t h e use of n i t r o g e n - f i x i n g trees in m i x t u r e s w i t h n o n - n i t r o g e n f i x i n g trees a n d t h e use of herbaceous l e g u m e s as nurse crops in intensively m a n a g e d p l a n t a t i o n s . This r e v i e w i n d i c a t e s s i g n i f i c a n t m a n a g e m e n t benefits are possible t h r o u g h t h e use o f n i t r o g e n - f i x i n g trees. Red alder biomass yields are c o m p a r a b l e t o o t h e r fast g r o w i n g species. T h e use o f n i t r o g e n - f i x i n g trees a n d herbaceous material has g i v e n s i g n i f i c a n t increases in biomass yields. Cost-benefit ratios have n o t been d e t e r m i n e d because of t h e variety o f s t u d y c o n d i t i o n s e n c o u n t e r e d . M u c h a d d i t i o n a l i n f o r m a t i o n is needed t o f u l l y assess t h e feasibility of using n i t r o g e n - f i x i n g species in s h o r t - r o t a t i o n i n t e n s i v e p l a n t a t i o n c u l t u r e . Economics of Intensive Plantation Culture T h e yields f r o m intensively c u l t u r e d p l a n t a t i o n s are c o n s i d e r a b l y greater t h a n t h o s e f r o m natural s t a n d s o f similar tree species. It m u s t be e m p h a s i z e d , h o w e v e r , t h a t m a n y o f t h e r e p o r t e d p l a n t a t i o n yields are f r o m small s t u d y plots a n d i n d i c a t e w h a t is b i o l o g i c a l y possible. T o project s u c h yields over a larger area m a y be i n a p p r o p r i a t e . Several studies in W i s c o n s i n , S o u t h Carolina a n d Georgia (26,27,28) are c u r r e n t l y u n d e r w a y t o d e t e r m i n e t h e feasibility of intensive p l a n t a t i o n c u l t u r e o n a large scale. Rose a n d DeBell (29) assessed t h e e c o n o m i c s o f intensive p l a n t a t i o n c u l t u r e for w o o d fiber p r o d u c t i o n . S p a c i n g o f trees a n d l e n g t h o f r o t a t i o n a p p e a r e d t o be particularly cost sensitive in d e t e r m i n i n g e c o n o m i c feasibility. W i d e s p a c i n g ( 4 X 4 feet a n d 1 2 X 2 feet) a n d longer c o p p i c e rotations (4 year a n d 10 year, respectively) appeared feasible w h i l e t w o year c o p p i c e rotations d i d not.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

34

BIOMASS AS A NONF OSSIL FUEL SOURCE

Using a d i f f e r e n t p e r s p e c t i v e . Eimers (30) e v a l u a t e d t h e e c o n o m i c s of i n t e n s i v e p l a n t a t i o n c u l t u r e as an e n e r g y source f r o m t h e s t a n d p o i n t of a c o m p a n y h a v i n g e x t e n s i v e e x p e r i e n c e in g r o w i n g a n d h a n d l i n g forest p r o d u c t s . His c o n c l u s i o n s w e r e t h a t fuel p l a n t a t i o n s are c u r r e n t l y u n e c o n o m i c a l . H o w e v e r , i n d i c a t i o n s are t h a t t h i s c o u l d c h a n g e if c e r t a i n costs w e r e r e d u c e d . T h e e c o n o m i c o u t l o o k for intensive m a n a g e m e n t s y s t e m s w o u l d i m p r o v e if h a r v e s t i n g costs c o u l d be r e d u c e d a n d e n e r g y c o n v e r s i o n costs l o w e r e d . The overall cost p i c t u r e m a y also be m o r e favorable if a dual p u r p o s e c r o p c o u l d be p r o d u c e d . For e x a m p l e , t h e biomass material p r o d u c e d f r o m p l a n t a t i o n s w o u l d be s o r t e d i n t o h i g h q u a l i t y c h i p s for fiber p r o d u c t s a n d l o w q u a l i t y c h i p s c o n v e r t e d i n t o energy. A d i r e c t parallel already exists in m a n y forest i n d u s t r i e s w h i c h c u r r e n t l y use residues f r o m t h e m a n u f a c t u r e of forest p r o d u c t s t o fire boilers. Eimers (30) also p o i n t s o u t t h a t p l a n t i n g at close s p a c i n g offers s o m e m a n a g e m e n t f l e x i b i l i t y w h e n t h i n n i n g is c o n s i d e r e d . T h a t is, t h i n n i n g f r o m i n t e n s i v e l y m a n a g e d p l a n t a t i o n s c a n be used for e n e r g y , w h i l e t h e r e m a i n i n g trees c a n be g r o w n for c o n v e n t i o n a l forest p r o d u c t s . T h e a d v a n t a g e t o this m a n a g e m e n t s t r a t e g y is t h a t d e c i s i o n s c o n c e r n i n g w o o d use can be deferred t o a f u t u r e date w h e n t h e e c o n o m i c s of e n e r g y s u p p l y m a y be less t u r b u l e n t t h a n at present. C H A R A C T E R I Z A T I O N OF B I O M A S S T h e p h y s i c a l a n d c h e m i c a l n a t u r e of b i o m a s s materials has a p r o f o u n d i n f l u e n c e o n t h e i r end-uses. For e x a m p l e , m o i s t u r e c o n t e n t a n d specific g r a v i t y are i m p o r t a n t properties for t h e p r o d u c t i o n of solid w o o d a n d paper p r o d u c t s , as w e l l as for c o n v e r s i o n into energy. O t h e r p h y s i c a l a n d m e c h a n i c a l properties of w o o d , s u c h as fiber l e n g t h , fibril a n g l e a n d s t r e n g t h of i n d i v i d u a l fibers, are n o t i m p o r t a n t for e n e r g y a p p l i c a t i o n s . T h e c u r r e n t t r e n d s t o w a r d w h o l e tree utilization a n d e n e r g y p l a n t a t i o n s t h r o u g h intensive m a n a g e m e n t can result in s u b s t a n t i a l c h a n g e s in t h e nature of w o o d resources available for i n d u s t r i a l a n d c o m m e r c i a l use. T h e effects of v a r i o u s intensive m a n a g e m e n t s y s t e m s o n w o o d properties have been reported in n u m e r o u s p u b l i c a t i o n s a n d w e r e r e c e n t l y s u m m a r i z e d in t h r e e articles (31.32,33). It w a s clearly i n d i c a t e d t h a t t h e m a j o r c h a n g e s in w o o d properties are associated w i t h shorter r o t a t i o n s , w h i c h result in a h i g h e r p r o p o r t i o n of j u v e n i l e w o o d . This y o u n g w o o d , as c o m p a r e d t o m a t u r e w o o d , c o n t a i n s a h i g h e r m o i s t u r e c o n t e n t , l o w e r specific g r a v i t y a n d a h i g h p r o p o r t i o n of r e a c t i o n w o o d . T h e effects of c h a n g i n g t h e s e w o o d properties on t h e solid w o o d p r o d u c t a n d paper i n d u s t r y have been e x t e n s i v e l y r e v i e w e d by Bendtsen (31.) a n d Einspaphr (32.33), respectively. In t h e

2.

SAJDAK ET AL.

following

35

Forest Biomass for Energy

s e c t i o n , those

wood

properties

which

are i m p o r t a n t

to the

c o n v e r s i o n of w o o d y biomass into e n e r g y uses are discussed.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Distribution of Tree Components Total a b o v e - g r o u n d tree biomass is generally d i v i d e d into foliage, b r a n c h , a n d s t e m c o m p o n e n t s . The b r a n c h e s a n d s t e m s can be separated f u r t h e r into bark a n d w o o d portions. The i m p o r t a n c e of branches a n d foliage t o total tree w e i g h t is d e p e n d e n t u p o n t h e age a n d / o r size o f t h e tree (34). It is e s t i m a t e d t h a t t h e a b o v e - g r o u n d biomass c u r r e n t l y p r o d u c e d o n c o m m e r c i a l forest land in t h e U n i t e d States is a p p r o x i m a t e l y d i s t r i b u t e d as w o o d (80 percent), bark (12 percent), a n d foliage (8 percent) (11). Table IV s h o w s s o m e representative d i s t r i b u t i o n s o f tree c o m p o n e n t s by species a n d age. T h e d a t a clearly s h o w t h a t y o u n g trees have a s u b s t a n t i a l l y h i g h e r c o n t e n t of foliage a n d bark b i o m a s s t h a n older, larger trees. These t w o c o m p o n e n t s are not desirable f o r t h e p r o d u c t i o n o f fiber related p r o d u c t s , s u c h as paper, b u t are desirable f o r e n e r g y p r o d u c t i o n d u e t o t h e i r h i g h e n e r g y c o n t e n t , part i c u l a r l y bark. T h e t r e n d t o w a r d s h o r t e r s t a n d r o t a t i o n or t h e e s t a b l i s h m e n t of e n e r g y p l a n t a t i o n s w o u l d increase t h e availability of y o u n g tree biomass f o r e n e r g y use. Moisture Content M o i s t u r e c o n t e n t is a p a r t i c u l a r l y i m p o r t a n t characteristic w h e n usine w o o d y biomass as f u e l , a n d is generally expressed as p e r c e n t of t h e d r y w e i g h t . W a t e r c o n t a i n e d in biomass a d d s t o t h e cost o f t r a n s p o r t a t i o n , a n d l o w e r s t h e e f f i c i e n c y o f e n e r g y c o n v e r s i o n b y a d i r e c t c o m b u s t i o n process, because of t h e e n e r g y required f o r e v a p o r a t i o n o f t h e w a t e r . It is e s t i m a t e d t h a t a b o u t 15 p e r c e n t o f t h e t o t a l available heat in a w o o d or bark fuel is required f o r m o i s t u r e e v a p o r a t i o n , a s s u m i n g a 1 0 0 p e r c e n t m o i s t u r e c o n t e n t (38). H o w e v e r , c o n v e r s i o n b y anaerobic d i g e s t i o n or f e r m e n t a t i o n m e t h o d s are m o r e efficient w h e n u s i n g h i g h - m o i s t u r e biomass materials. T h e p r o c e d u r e for e s t i m a t i n g e f f e c t i v e heat values f o r b o t h w o o d a n d bark fuels u n d e r v a r y ing m o i s t u r e c o n t e n t a n d f u r n a c e e n v i r o m e n t s has been s u m m a r i z e d b y Ince (39). The m o i s t u r e c o n t e n t of various forest biomass varies w i d e l y w i t h species, g e o g r a p h i c locations, g e n e t i c differences, tree c o m p o n e n t s used, a n d tree age. Published d a t a indicate t h a t m o i s t u r e c o n t e n t o f m a t u r e w o o d m a y range f r o m a b o u t 3 0 p e r c e n t t o m o r e t h a n 2 0 0 p e r c e n t (40). A l s o , m o i s t u r e c o n t e n t o f t h e s t e m s a p w o o d p o r t i o n is usually h i g h e r t h a n t h a t of t h e associated h e a r t w o o d . For y o u n g h a r d w o o d s p r o u t s (6 t o 15 years old), a n average

L.

Marsh.

Lamb.

—

— —

— — —

(29)

(27) (22)

(19)

67

64 68

68 b

10

22 16

—

—

(38)

— — —

—

— — — —

%

%

88

52 80

— — —

—

%

N u m b e r s in t h e parentheses are bark p e r c e n t a g e s of t h e tree c o m p o n e n t .

S u m of s t e m s a n d b r a n c h e s

40

6 40

2

3

2

2

%

(19)

(20) (10)

— — —

—

%

2

24 4

33

36 32

32

%

The d a t a clearly s h o w t h a t y o u n g trees have a s u b s t a n t i a l l y h i g h e r c o n t e n t of foliage a n d bark b i o m a s s t h a n older, larger trees. These t w o c o m p o n e n t s are n o t desirable for t h e p r o d u c t i o n of f i b e r - r e l a t e d p r o d u c t s , s u c h as paper, b u t are desirable for e n e r g y p r o d u c t i o n due t o t h e i r h i g h energy c o n t e n t , p a r t i c u l a r l y bark. T h e t r e n d t o w a r d s h o r t e r s t a n d r o t a t i o n or t h e e s t a b l i s h m e n t of e n e r g y p l a n t a t i o n s w o u l d increase t h e a v a i l a b i l i t y of y o u n g - t r e e biomass for e n e r g y uses.

b

a

Populus tremuloides M i c h x . (aspen)

(jack pine)

Pinus banksiana

Robinia pseudoaccacia L. (black locust)

(red maple)

Acer rubrum

(sugar maple)

%

Stems Total Bark Foliage

yr

Age,

W o o d y Biomass" Branches Bark Bark Total Total

Acer saccharum

Species

BIOMASS

T a b l e IV. TREE C O M P O N E N T S A S PERCENT OF A B O V E - G R O U N D

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2.

SAJDAK ET AL.

Forest Biomass for Energy

37

m o i s t u r e c o n t e n t o f 8 0 p e r c e n t w a s reported f o r nine species c o l l e c t e d in m i d s u m m e r , r a n g i n g f r o m 5 9 p e r c e n t f o r green ash (Frax/nus pennsylvanica Marsh.) t o 9 9 p e r c e n t f o r y e l l o w poplar (Liriodendron tuplipifera L.) (41).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

It has been s h o w n t h a t w o o d m o i s t u r e c o n t e n t has an inverse c o r r e l a t i o n w i t h tree age (35,42). In general, w o o d f r o m a y o u n g tree c o n t a i n s m o r e w a t e r t h a n w o o d f r o m a n older o n e o f t h e s a m e species (42). This is p r o b a b l y associated w i t h t h e v i g o r o u s g r o w t h a n d t h e h i g h p r o p o r t i o n of s a p w o o d in t h e y o u n g e r tree. There is n o general c o n s e n s u s c o n c e r n i n g a seasonal t r e n d of m o i s t u r e c o n t e n t in trees (43). S o m e researchers have reported larger seasonal variations w h i l e others have f o u n d very little. H o w e v e r , it appears t h a t t h e y o u n g trees or s p r o u t s , in c o n t r a s t t o m a t u r e trees, display a s i g n i f i c a n t seasonal v a r i a t i o n in m o i s t u r e c o n t e n t , p a r t i c u l a r l y for t h o s e g r o w i n g in n o r t h e r n c l i m a t e s . Figure I s h o w s seasonal variations in m o i s t u r e c o n t e n t f o r 3-year o l d s u g a r m a p l e (Acer saccharum Marsh) s p r o u t s (35) a n d 50-year old y e l l o w poplar (43). The m a p l e , g r o w n in t h e Upper Peninsula of M i c h i g a n , displays a m a r k e d seasonal v a r i a t i o n in m o i s t u r e c o n t e n t w h i c h reaches a m a x i m u m in J u n e . This w o o d m o i s t u r e p a t t e r n is essentially parallel t o s p r o u t g r o w t h a c t i v i t y . In c o n t r a s t , t h e m o i s t u r e c o n t e n t of m a t u r e y e l l o w poplar g r o w n in t h e S o u t h e r n A p p a l a c h a i n M o u n t a i n s of N o r t h Carolina does n o t vary s i g n i f i c a n t l y f r o m season t o season.

Specific Gravity Specific g r a v i t y indicates t h e a m o u n t of solid material in a g i v e n v o l u m e , a n d is usually c o n s i d e r e d t h e best single index of intrinsic w o o d q u a l i t y f o r fiber, w o o d p r o d u c t s , a n d e n e r g y p r o d u c t i o n . Specific g r a v i t y is inversely correlated w i t h w o o d m o i s t u r e c o n t e n t (44). T h u s , it also varies w i t h species, tree c o m p o n e n t s , a n d t h e age of t h e tree. In general, j u v e n i l e w o o d has a relatively l o w e r specific g r a v i t y t h a n m a t u r e w o o d . In s o m e species, t h e j u v e n i l e g r o w h t period m a y last f o r at least 10 years, d u r i n g w h i c h there is a steady increase in specific g r a v i t y (45). Therefore, y o u n g trees w i l l n o t p r o v i d e t h e s a m e yield o f solid material or fiber per u n i t v o l u m e of w o o d as c o m p a r e d t o older trees. Chemical Composition The c h e m i c a l c o m p o s i t i o n o f biomass materials is generally discussed in t e r m s o f cell w a l l p o l y s a c c h a r i d e s (cellulose a n d hemicelluloses), p h e n o l i c s (lignin a n d p o l y p h e n o l s ) , extractives, a n d ash c o n t e n t . W o o d n o r m a l l y c o n tains small a m o u n t s of ash (1 percent) a n d various q u a n t i t i e s of e x t r a c t i v e s

38

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

BIOMASS AS A NONFOSSIL FUEL SOURCE

FEB.

APRIL

JUNE

AUG.

OCT.

DEC.

MONTH

Figure 1. Season variation of moisture content of (O bark, · wood) 3-year-old sugar maple and (A bark, A wood) 50-year-old yellow poplar (43)

2.

SAJDAK ET AL.

Forest Biomass for Energy

39

d e p e n d i n g o n tree species (46). Extractive-free h a r d w o o d s have a lignin c o n t e n t b e t w e e n 18 p e r c e n t a n d 2 5 p e r c e n t ; it varies b e t w e e n 2 5 percent and 3 5 percent f o r t h e s o f t w o o d s . T h e r e m a i n i n g materials in t h e w o o d are t h e polysaccharides (46).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

There are d e f i n i t e c h a n g e s in t h e c h e m i c a l c o m p o s i t i o n of reaction w o o d . Compression w o o d has a s i g n i f i c a n t increase in lignin a n d a c o r r e s p o n d i n g decrease in polysaccharides as c o m p a r e d t o n o r m a l s o f t w o o d . Tension w o o d has j u s t t h e o p p o s i t e relationship. Since j u v e n i l e w o o d t e n d s t o c o n t a i n a h i g h level o f reaction w o o d , its c h e m i c a l c o m p o s i t i o n s h o u l d differ f r o m t h a t of m a t u r e w o o d . Other tree c o m p o n e n t s , s u c h as foliage a n d bark, c o n t a i n a s u b s t a n t i a l l y higher c o n t e n t of e x t r a c t i v e s , a n d a s l i g h t l y higher ash c o n t e n t t h a n w o o d . A l s o , bark has a h i g h e r c o n t e n t of p h e n o l i c s other t h a n l i g n i n , i n c l u d i n g p h e n o l i c acid a n d t a n n i n s as c o m p a r e d t o w o o d . C h e m i c a l c o m p o s i t i o n , as discussed in t h e next s e c t i o n , is closely related t o t h e caloric values of biomass, a n d also affects t h e efficiency of c o n v e r s i o n , particularly w h e n using a biological a p p r o a c h . For e x a m p l e , t h e presence of p h e n o l i c s , p a r t i c u l a r l y l i g n i n , presents a major roadblock f o r e n z y m a t i c c o n version o f p o l y s a c c h a r i d e s t o a l c o h o l . The c o n v e r s i o n of j u v e n i l e biomass has been s h o w n t o have a higher m o i s t u r e c o n t e n t a n d l o w e r specific g r a v i t y t h a n m a t u r e w o o d (47), a n d m a y respond m o r e f a v o r a b l y t o s u c h a t r e a t m e n t process. The energy c o n v e r s i o n o f j u v e n i l e biomass materials b y a t h e r m a l or biological m e t h o d s needs t o be e x p l o r e d . Caloric Values* The caloric value, or heat of c o m b u s t i o n , of a natural fuel o n w e i g h t basis is a f u n c t i o n o f t h e c h e m c i a l c o m p o s i t i o n . It has been s h o w n t h a t a linear relat i o n s h i p exists b e t w e e n t h e heat of c o m b u s t i o n a n d t h e c a r b o n c o n t e n t of t h e substrate (48). L i g n i n has a higher heat of c o m b u s t i o n t h a n t h a t of a p o l y s a c c h a r i d e ( 5 8 8 4 vs. 3 8 5 3 c a l / g ) , because of its l o w e r o x y g e n c o n t e n t . The extractives (terpenoid h y d r o c a r b o n s or resin) w i t h even l o w e r o x y g e n c o n t e n t s have still h i g h e r heat c o n t e n t s ( 8 1 2 4 and 9 0 2 7 cal/g) (49). In c o n trast h i g h e r ash c o n t e n t w i l l have a negative effect o n t h e calorific value. The caloric values of natural fuels reported in t h e literature have been s u m marized b y various a u t h o r s (38,29,41,48,50,51,52). The average values taken f r o m these reviews are listed in Table V. A n average heat c o n t e n t of 4 7 8 1 a n d

• A l l heating values discussed in this section are high heating values.

a

5177

— —

— —

5010

5197(13)

—

5 2 4 1 (3) 5 2 6 6 (9) 5 0 3 3 (24)

5149 (15)

Softwood Bark

5133(16)

— —

4886(16)

— —

Wood 8

5081

—

5016(1)

—

5145(1)

— — —

Needles

Figures in parentheses are t h e n u m b e r o f species e x a m i n e d .

Average

Ince Koch Neenam and Steinbeck

S u s o t t et al.

Harder a n d Einspahr Corder Corder

Harder a n d Einspahr

Author

4781

4 7 7 7 (9)

—

4 9 7 1 (13)

— —

4 5 9 6 (7)

—

Wood

4 6 3 1 (9) 4664

—

—

4 6 7 2 (9)

4 6 8 8 (21)

—

4613(15)

4715(9)

Hardwood Bark

T a b l e V. A V E R A G E C A L O R I C V A L U E S OF N A T U R A L FUELS (cal/g)

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

4759

5 0 4 7 (9)

— —

4 4 7 0 (4)

— —

Needles

2.

SAJDAK ET AL.

Forest Biomass for Energy

41

5 0 1 0 c a l / g w a s f o u n d f o r h a r d w o o d a n d s o f t w o o d , respectively. It appears t h a t little v a r i a t i o n in caloric values exists a m o n g various h a r d w o o d species. Larger variations have been o b s e r v e d a m o n g s o f t w o o d species because o f t h e m a r k e d differences in e x t r a c t i v e c o n t e n t . H o w e v e r , it c a n generally be c o n c l u d e d t h a t t h e caloric value for a g i v e n v o l u m e of biomass material is p r i marily d e t e r m i n e d b y its m o i s t u r e c o n t e n t a n d specific gravity. PERSPECTIVE The near t e r m a n d e x t e n d e d o u t l o o k of increasing use of w o o d f o r energy purposes is favorable. C o m m e r c i a l forests c o n t a i n a n a b u n d a n c e of biomass Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

for fuel a n d intensively c u l t u r e d p l a n t a t i o n s c o u l d a d d a d d i t i o n a l a m o u n t s . The q u e s t i o n is h o w m u c h a n d at w h a t cost? The use o f w o o d f o r e n e r g y w i l l c o m p e t e w i t h w o o d f o r material use. W o o d as a c o n s t r u c t i o n material is m u c h m o r e i m p o r t a n t in t h e Nation's energy b u d g e t t h a n as a fuel. T h e m a n u f a c t u r e of l u m b e r a n d p l y w o o d f r o m w o o d is much

less e n e r g y - i n t e n s i v e t h a n t h e m a n u f a c t u r e of m e t a l a n d plastic

p r o d u c t s . Also, t h e e n e r g y savings d u e t o t h e h i g h i n s u l a t i n g value of w o o d b u i l d i n g c o m p o n e n t s s h o u l d be n o t e d . Forest survey statistics i n d i c a t e w e harvest a n d use u p w a r d s o f 3 0 p e r c e n t o f c u r r e n t forest p r o d u c t i o n f o r c o n v e n t i o n a l forest p r o d u c t s . The r e m a i n i n g 7 0 p e r c e n t has been s h o w n t o be p o t e n t i a l l y available f o r various energy uses (3.10). H o w e v e r , before s u c h increased w o o d use o c c u r s , a n u m b e r of factors need t o be e x a m i n e d a n d h o p e f u l l y resolved. Conventional W o o d Needs It is a p p a r e n t t h a t increasing d e m a n d s f o r t r a d i t i o n a l forest p r o d u c t s w i l l require s o m e of t h e c u r r e n t b i o m a s s surplus. It is also a p p a r e n t t h a t s o m e of t h e s u r p l u s biomass m a y be unavailable f o r e c o n o m i c reasons o r u n h a r v e s t a ble d u e t o c o n s t r a i n t s i m p o s e d b y o t h e r forest users or e n v i r o n m e n t a l factors. C o n s e q u e n t l y , w h a t is t h e n left o f t h e surplus w o u l d be p o t e n t i a l l y available for e n e r g y use. A recent s t u d y f o r t h e A m e r i c a n P u l p w o o d A s s o c i a t i o n evaluated t h e w o r l d w o o d s u p p l y a n d d e m a n d s i t u a t i o n t o t h e year 2 0 0 0 (7). T h e U n i t e d States w a s i d e n t i f i e d as one o f t h e c o u n t r i e s w h i c h w i l l need m o r e w o o d t h a n it can s u p p l y . H o w e v e r , t h e s t u d y c o n c l u d e d t h a t w e have t h e p o t e n t i a l t o n o t o n l y e l i m i n a t e t h e e x p e c t e d d e f i c i t b u t also t o b e c o m e a n e t e x p o r t e r o f forest p r o d u c t s . T o a c c o m p l i s h this g o a l , w e w i l l need t o increase utilization o f c u r r e n t g r o w t h as w e l l as increase p r o d u c t i v i t y o n all available lands.

42

BIOMASS AS A NONFOSSIL FUEL SOURCE

Increasing Utilization

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

W o o d c u r r e n t l y u n u s e d because of p o o r m a r k e t s a n d h i g h utilization s t a n d a r d s w i l l help alleviate t h e p r o j e c t e d U.S. w o o d deficit. Smaller logs m u s t be harvested a n d t h e r e m a i n i n g p o r t i o n s of t h e trees c h i p p e d . High q u a l i t y c h i p s w o u l d likely be utilized for fiber p r o d u c t s w h i l e l o w q u a l i t y m a t e r i a l c a n be b u r n e d . I m p r o v e d b i o m a s s inventories are also n e e d e d t o i d e n t i f y t h e a m o u n t s , q u a l i t y , locations, a n d deliverable costs of t h e excess forest biomass. Increasing t h e utilization of forest b i o m a s s is p a r t i c u l a r l y cost-sensitive. A s greater a m o u n t s of forest residue are r e m o v e d f r o m a g i v e n area, t h e costs w i l l increase. In m a n y cases, it m a y not be e c o n o m i c a l l y feasible t o recover t h e residue g e n e r a t e d by small l a n d o w n e r harvest o p e r a t i o n s a n d t r a n s p o r t t h i s t o a large e n e r g y user. M o r e likely, t h i s residue a n d possibly h i g h e r value t i m b e r w i l l be i n c r e a s i n g l y used for h o m e h e a t i n g in a d i r e c t response t o rising c o n v e n t i o n a l h e a t i n g costs. Utilization w i l l p r o b a b l y be m o s t intense in t h e N o r t h e r n a n d S o u t h e r n Regions w h e r e m o s t of o u r p o p u l a t i o n exists a n d t h e forests are also m o s t diverse. Impact on Other Forest Uses Increasing t h e utilization of o u r forests w i l l have a d e f i n i t e i m p a c t o n o t h e r forest uses s u c h as w i l d l i f e , r e c r e a t i o n , a n d w a t e r . I n d e e d , s o m e s e g m e n t s of o u r s o c i e t y place t i m b e r p r o d u c t i o n s e c o n d a r y as is e v i d e n c e d by recent c o u r t d e c i s i o n s w h i c h l i m i t m a n a g e m e n t p r e r o g a t i v e s o n c e r t a i n National a n d State Forests. T h e m o s t efficient h a r v e s t i n g s y s t e m s , i.e.. c l e a r c u t t i n g w i t h w h o l e - t r e e c h i p p i n g , are especially in disfavor. H o w e v e r , it m u s t be n o t e d t h a t t h e i n h e r e n t n a t u r e of species like aspen (Populus) a n d j a c k pine requires t h a t c l e a r c u t t i n g be used for r e g e n e r a t i o n . T h e removal of t o p s , l i m b s , a n d cull trees in a selective log harvest, w h i l e i m p r o v i n g t h e visual i m p a c t , w i l l d e s t r o y t h e c o v e r n e e d e d for s m a l l a n i m a l s a n d birds. A m u l t i p l e use m a n a g e m e n t a p p r o a c h is necessary w h e n i m p l e m e n t i n g increased forest u t i l i z a t i o n , b u t at s o m e sacrifice in y i e l d . Not every acre can be utilized t o its fullest p o t e n t i a l for b i o m a s s p r o d u c t i o n . Impact on Site Quality M o r e i n f o r m a t i o n is n e e d e d t o d e t e r m i n e t h e i m p a c t t h a t increased utilization w i l l have o n site q u a l i t y s u c h as soil o r g a n i c m a t t e r c o n t e n t , w a t e r h o l d i n g c a p a c i t y a n d f e r t i l i t y levels. (53) It appears t h a t t h e m o r e intensive t h e harvest, t h e greater t h e o p p o r t u n i t y for soil d e t e r i o r a t i o n . The increased

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43

r e m o v a l o f leaves a n d small b r a n c h e s represents a s i g n i f i c a n t drain o f n u t r i e n t capital o n s o m e sites a n d m a y cause s o m e l o n g - t e r m r e d u c t i o n in site p r o d u c t i v i t y .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Increasing Forest Productivity A s stated earlier, m a n y forests are u n d e r s t o c k e d . S o m e of t h e biomass surplus w i l l need t o be left o n site t o increase t h e a m o u n t of g r o w i n g stock a n d therefore increase f u t u r e yields. T h e increasing d e m a n d f o r w o o d p r o d u c t s a n d f u e l w o o d presents a n o p p o r t u n i t y for forest i m p r o v e m e n t practices as never before. P r e - c o m m e r c i a l t h i n n i n g s a n d i m p r o v e m e n t c u t t i n g s m a y n o w be p r o f i t a b l e in s u p p l y i n g w o o d for e n e r g y uses w h i l e increasing t h e p r o d u c t i o n of q u a l i t y t i m b e r in t h e f u t u r e . It is e x p e c t e d t h a t t h e forest p r o d u c t s industries w i l l lead t h e w a y t o w a r d increasing forest p r o d u c t i v i t y . Industry lands are already t h e m o s t p r o d u c t i v e as c o m p a r e d t o private a n d p u b l i c lands. A t present, w i t h a b o u t 14 p e r c e n t of t h e c o m m e r c i a l forest land area, t h e forest industries p r o d u c e 3 3 p e r c e n t o f t h e w o o d in t h e U n i t e d States. Less certain is t h e e x t e n t t o w h i c h small private forests w i l l increase p r o d u c t i v i t y . The w o o d markets are assured b u t t h e i n v e s t m e n t required f o r forest i m p r o v e m e n t is u n a t t r a c t i v e f o r i n d i viduals, especially in t h e face o f rising land costs, interest rates a n d taxes, a n d increasing regulations. Public lands are least p r o d u c t i v e because o f l o c a t i o n , terrain a n d land use history a n d because o f t h e pressures f r o m o t h e r users. Large increases in g o v e r n m e n t a l f u n d i n g w i l l be needed a n d policy c h a n g e s i n i t i a t e d before s i g n i f i c a n t increases in p r o d u c t i v i t y can be realized. Biomass Energy Plantations Intensively c u l t u r e d s h o r t - r o t a t i o n p l a n t a t i o n s have been a d v o c a t e d as p r o v i d i n g a d d i t i o n a l sources o f b i o m a s s for e n e r g y use. The land base needed for t h e i m p l e m e n t a t i o n o f t h i s proposal o n a n extensive scale w o u l d seem t o present a nearly i n s u r m o u n t a b l e p r o b l e m . For e x a m p l e , Evans (54) c a l c u l a t e d t h a t a 1 0 0 m e g a w a t t electric f a c i l i t y w o u l d require a forest biomass p l a n t a t i o n nearly 2 0 0 square miles in size if o v e n d r y yields of five t o n s per acre per year c o u l d be a t t a i n e d . It m u s t be n o t e d t h a t t h e h i g h yields o b t a i n e d f r o m small plot studies m a y be d i f f i c u l t t o o b t a i n o n s u c h a large scale. Biomass e n e r g y p l a n t a t i o n s w o u l d m o s t likely be relegated t o s u b - m a r g i n a l a g r i c u l t u r a l lands or areas w h e r e forests are n o t n o r m a l l y f o u n d . T h e i n p u t s needed o n these lands t o achieve h i g h yields o f biomass m a y n o t be feasible or e c o n o m i c a l . A s i n d i c a t e d earlier, t h e l o w e r specific g r a v i t y a n d higher m o i s t u r e c o n t e n t o f s h o r t - r o t a t i o n b i o m a s s m a y affect t h e e n e r g y c o n v e r s i o n process.

44

BIOMASS AS A NONFOSSIL FUEL SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Natural n o r t h e r n h a r d w o o d s t a n d s in N o r t h e r n M i c h i g a n w e r e f o u n d t o p r o d u c e nearly t w o d r y t o n s of b i o m a s s per acre per year over a 5 0 - y e a r period. These yields w e r e o b t a i n e d w i t h no m a n a g e m e n t i n p u t s w h a t s o e v e r (35). Frederick a n d C o f f m a n (55) r e p o r t e d m e a n a n n u a l d r y w e i g h t p r o d u c t i o n of nearly 2.5 t o n s per acre in a 2 5 year o l d u n m a n a g e d red p i n e (Pinus resinosa Ait.) p l a n t a t i o n . Even greater yields are possible in t h e S o u t h a n d t h e Pacific N o r t h w e s t . A m o r e realistic a p p r o a c h m i g h t be t o use t h e k n o w l e d g e gained from the intensive culture studies and supply this to improved m a n a g e m e n t of c o n v e n t i o n a l forest p l a n t a t i o n s . In c o n c l u s i o n , w o o d w i l l play an increasingly i m p o r t a n t role in s u p p l y i n g a part of o u r Nation's e n e r g y needs. T o w h a t e x t e n t t h i s w i l l o c c u r is u n k n o w n a n d w i l l d e p e n d in part o n t h e costs of m o r e c o n v e n t i o n a l fuels. Using w o o d for e n e r g y is t h e least p r o f i t a b l e use of t h i s resource a n d t h e d i f f e r e n t i a l s h o u l d c o n t i n u e . T h e forest p r o d u c t s i n d u s t r y w i l l likely lead t h e w a y in increasing t h e use of w o o d for energy. This i n d u s t r y has had t h e expertise in g r o w i n g , h a n d l i n g , a n d utilizing w o o d b o t h for m a n u f a c t u r i n g p r o d u c t s a n d for energy. T h e use of w o o d in g e n e r a t i n g e l e c t r i c i t y w i l l increase b u t on a smaller scale as utilities take a d v a n t a g e of s u r p l u s w o o d in t h e heavily f o r e s t e d regions. It is a p p a r e n t t h a t t h e use of w o o d as a h o m e h e a t i n g fuel w i l l c o n t i n u e t o e x p a n d d r a m a t i c a l l y . T h e effects of t h e s e v a r i o u s w o o d e n e r g y uses o n t h e e n v i r o n m e n t are largely u n k n o w n . ACKNOWLEDGEMENT T h e a u t h o r s w i s h t o t h a n k t h e U.S. D e p a r t m e n t of Energy for t h e i r partial s u p p o r t of t h i s endeavor. A l s o a p p r e c i a t e d is t h e e n c o u r a g e m e n t received f r o m t h e E n v i r o n m e n t a l Sciences Division. Oak Ridge N a t i o n a l Laboratory.

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

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RECEIVED JUNE 20,

1980.

3 Production of Nonwoody Land Plants as a Renewable Energy Source A L E X G. A L E X A N D E R

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

University of Puerto Rico, P.O. Box H , Agricultural Experiment Station, Rio Piedras, PR 00928

Non-Woody Land Plants in Perspective Literally thousands of terrestrial plant species can be regarded as potential energy sources. A majority of these are herbaceous seed plants which complete their growth and reproductive processes within a single growing season of a few months duration. They are widely distributed from arctic regions to the tropics (1-3). They are equally diverse with respect to their growth and anatomical characteristics, their cultural requirements, and their physiological and biochemical processes (2-9). Yet all have the capacity to convert sunlight to chemical energy and to store this energy in the form of biomass. A n oven-dry ton of herbaceous biomass represents about 15 Χ 10 Btu's of stored energy. The direct firing of one such ton, in a stoker furnace with high-pressure boiler having a 70% conversion efficiency, would displace about two barrels of fuel oil. 6

In addition to their fibrous tissues, some species also produce sugar and starch in sufficient quantities to warrant extraction and conversion to ethanol. The latter can displace petroleum in the production of motor fuel or chemical feedstocks (10-13). Other species store additional energy in the form of natural hydrocarbons.

0097-6156/81/0144-0049$07.00/0 © 1981 American Chemical Society

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

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B I O M A S S AS A N O N F O S S I L F U E L

SOURCE

W h i l e it is not correct t o say t h a t herbaceous land plants have been overlooked as a d o m e s t i c energy resource, o n l y a small n u m b e r have been e x a m i n e d closely for t h i s purpose. A m o n g t h e latter are t r o p i c a l grass species of Zea, Sorghum, Saccharum. a n d Pennisetum w h i c h w e r e recognized for t h e i r h i g h yields of fiber a n d f e r m e n t a b l e solids long before t h e oil e m b a r g o of 1 9 7 3 . T h r o u g h o u t their history as c u l t i v a t e d crops, plants s u c h as c o r n , s w e e t s o r g h u m , s u g a r c a n e , a n d napier grass have e v o l v e d extensive t e c h n o l o g i e s for t h e i r c u l t i v a t i o n , harvest, post-harvest t r a n s p o r t a n d storage, a n d for their processing a n d m a r k e t i n g . Yet, even for t h e s e p l a n t s m a j o r c h a n g e s m u s t be m a d e in their m a n a g e m e n t if t h e y are t o serve e f f e c t i v e l y as e n e r g y crops (5.6.23.24). O t h e r t r o p i c a l p l a n t s h a v i n g very f i n e b o t a n i c a l or a g r o n o m i c a t t r i b u t e s a n d e n j o y i n g a y e a r - r o u n d c l i m a t e s u i t e d t o biomass p r o d u c t i o n have been generally i g n o r e d as e n e r g y resources. Pineapple, cassava, a n d a range of u n d e r u t i l i z e d t r o p i c a l species are a p p r o p r i a t e e x a m p l e s (4,8,13). A m a j o r i t y of h e r b a c e o u s l a n d plants have never b e e n c u l t i v a t e d for f o o d or fiber. In w a r m c l i m a t e s , w i l d grasses s u c h as Sorghum halepense (Johnson grass), Arundo donax (Japanese cane), a n d Bambusa species are b o r d e r l i n e cases w h e r e occasional use has been m a d e of t h e i r h i g h p r o d u c t i v i t y of d r y matter. In cooler c l i m a t e s , self-seeding plants s u c h as reed canary grass, c a t t a i l , w i l d oats, a n d o r c h a r d grass m a y be v i e w e d w i t h m i x e d f e e l i n g b y l a n d o w n e r s u n a b l e t o c u l t i v a t e m o r e v a l u a b l e f o o d or f o r a g e crops. Plants s u c h as r a g w e e d , redroot p i g w e e d , a n d l a m b s q u a r t e r s are recognized for t h e i r persistent g r o w t h habits w h i l e o t h e r w i s e regarded as c o m m o n pests. H o w e v e r , t h e v a l u e of s u c h species c o u l d rise d r a m a t i c a l l y as b i o m a s s assumes a role as a nonfossil d o m e s t i c e n e r g y resource. Prior S t u d i e s o n H e r b a c e o u s Plants as Energy S o u r c e s A s i d e f r o m s u g a r c a n e a n d " a l l i e d " t r o p i c a l grasses (6.7.13,23-25), relatively little a t t e n t i o n has been g i v e n t o herbaceous land p l a n t s specifically as sources of fuels a n d c h e m i c a l feedstocks. Studies w e r e initiated r e c e n t l y at B a t t e l l e - C o l u m b u s Laboratories o n c o m m o n grasses a n d w e e d s as p o t e n t i a l s u b s t i t u t e s for fossil e n e r g y (26). Plants s h o w i n g p r o m i s e as boiler fuels i n c l u d e perennial ryegrass, reed canarygrass, sudangrass, o r c h a r d g r a s s , bromegrass, K e n t u c k y 31 fescue, l a m b s q u a r t e r s , a n d others. A range of species have i n d i c a t e d s o m e p o t e n t i a l as sources of o i l , fats, p r o t e i n , dyes, alkaloids, a n d rubber. S u c h plants i n c l u d e g i a n t r a g w e e d , alfalfa, j i m s o n w e e d , c r a m b e , redroot p i g w e e d , d o g b a n , m i l k w e e d , a n d p o k e w e e d . Recently, a g o v e r n m e n t - s p o n s o r e d p r o g r a m w a s i n i t i a t e d t o screen herbaceous plants t o close t h e i n f o r m a t i o n g a p in this area of biomass e n e r g y d e v e l o p m e n t (27). This p r o g r a m has t w o phases: First, t o identify p r o m i s i n g

3.

ALEXANDER

Nonwoody Land Plants

51

species for w h o l e - p l a n t biomass p r o d u c t i o n in at least six different regions o f t h e U.S., a n d s e c o n d , t o p e r f o r m field e v a l u a t i o n s o n at least 2 0 species per region, w i t h a v i e w t o w a r d i d e n t i f y i n g t h o s e m o s t suitable f o r c r o p p i n g o n terrestrial e n e r g y p l a n t a t i o n s . A r t h u r D. Little, Inc., c o n d u c t e d Phase I (2).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

Six regions w e r e d e s i g n a t e d o n t h e basis of c l i m a t i c characteristics, land availability, a n d land resource d a t a p r o v i d e d b y t h e U.S. Soil Conservation Service (2). A list of 2 8 0 p o t e n t i a l species w a s prepared o n t h e basis of p u b l i s h e d literature a n d personal i n t e r v i e w s . These w e r e screened in a c c o r d a n c e w i t h b o t a n i c a l a n d e c o n o m i c characteristics, w i t h e m p h a s i s o n previously u n c u l t i v a t e d species. Certain a g r i c u l t u r a l plants w e r e also considered. Factors s u c h as yield p o t e n t i a l , c u l t u r a l r e q u i r e m e n t s , tolerances t o p h y s i o l o g i c a l stress, p r o d u c t i o n costs, a n d land availability w e r e c o n s i d e r e d in r a n k i n g t h e c a n d i d a t e species o f each region (2). Plants w i t h yields less t h a n 2.2 t o n s / a c r e (5 m e t r i c t o n s / h e c t a r e ) w e r e e l i m i n a t e d . For t h e p o t e n t i a l energy c r o p species, c o m p a r i s o n s w e r e d r a w n w i t h six categories of e c o n o m i c plants, i n c l u d i n g tall a n d short broadleaves, tall a n d short grasses, l e g u m e s , a n d tubers. S o m e 7 0 species w e r e r e c o m m e n d e d f o r c o n s i d e r a t i o n in t h e p r o g r a m ' s s e c o n d phase (field screening). S o m e o f these plants (redroot p i g w e e d , l a m b s q u a r t e r s . Colorado river h e m p , ragweed) have n o prior history as c u l t i v a t e d crops a n d their c u l t u r a l needs remain obscure. Other species (Bermuda grass. Kenaf. reed canary grass, s u d a n grass) have been i m p r o v e d a n d c u l t i v a t e d f o r decades (2). BOTANICAL A N D AGRONOMIC CONSIDERATIONS This initial p r o g r a m t o evaluate herbaceous land plants w i l l help t o clarify their value as a r e n e w a b l e e n e r g y source. H o w e v e r , a n e x t e n s i v e research effort is needed t o c o m p l e t e t h i s task even as it applies t o e x i s t i n g plant f o r m s already m a n a g e d as a g r i c u l t u r a l crops. A c o n t i n u i n g effort w i l l be needed over a period o f several decades in t h e areas o f n e w species e v a l u a t i o n , g e n e t i c i m p r o v e m e n t , herbaceous plant c r o p p i n g o n m a r g i n a l lands, a n d c r o p t a i l o r i n g t o c h a n g i n g e n e r g y needs. T h e r e m a i n d e r o f t h i s paper offers s o m e general g u i d e l i n e s a n d c o n s i d e r a t i o n s f o r d e a l i n g w i t h t h e vast pool o f e x i s t i n g herbaceous land plants.

52

BIOMASS AS A N O N F O S S I L F U E L

SOURCE

Botanical Considerations Photosynthesis: P h o t o s y n t h e s i s is t h e process by w h i c h t h e e n e r g y of s u n l i g h t is c o n v e r t e d t o c h e m i c a l e n e r g y by plants. Its reaction c a n be s t a t e d s i m p l y as:

radiant overall

Sunlight C0

2

+ H

2

0 • (CH 0) + 0 Green Plants 2

2

T h e a m o u n t of e n e r g y r e t a i n e d in t h e p h o t o s y n t h a t e ( C H 0 ) is a b o u t 4 6 8 2

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

kJ/mole. A l t h o u g h not an e f f i c i e n t process, it is t h e o n l y s y s t e m of solar e n e r g y c o n v e r s i o n o n e a r t h t h a t has o p e r a t e d at a n y a p p r e c i a b l e m a g n i t u d e a n d w i t h a n y a p p r e c i a b l e e c o n o m y for a n y a p p r e c i a b l e period of t i m e . A n e s t i m a t e d 1 3 5 0 J / m arrives at t h e earth's u p p e r a t m o s p h e r e in t h e f o r m of solar r a d i a t i o n , b u t o n l y a b o u t half p e n e t r a t e s t o t h e earth's surface (28). A t h e o r e t i c a l 8 p e r c e n t of t h i s r a d i a t i o n c o u l d be c o n v e r t e d p h o t o s y n t h e t i c a l l y ; h o w e v e r , a m a x i m u m c o n v e r s i o n e f f i c i e n c y of o n l y 4 p e r c e n t has been a t t a i n e d a n d t h i s u n d e r c o n d i t i o n s of l o w l i g h t i n t e n s i t y (29). A g r i c u l t u r a l plants average p e r h a p s 0.5 t o 1.0 p e r c e n t efficiency. L a n d plants o n a w o r l d w i d e basis p r o b a b l y average less t h a n 0.3 p e r c e n t efficiency. Nonetheless, t h e earth's p l a n t s store a n n u a l l y a b o u t 10 t i m e s m o r e e n e r g y t h a n is utilized, a n d s o m e 2 0 0 t i m e s m o r e t h a n is c o n s u m e d a n n u a l l y as f o o d (30). 2

P h o t o s y n t h e s i s consists of t w o phases: (a) Energy c a p t u r e , y i e l d i n g c h e m i c a l e n e r g y a n d r e d u c i n g p o w e r ; a n d (b). t h e r e d u c t i o n or " a s s i m i l a t i o n " of a t m o s p h e r i c C 0 . T h e c a r b o n r e d u c t i o n phase is a c c o m p l i s h e d by three d i s t i n c t p a t h w a y s ( C , C , a n d C A M ) . Each p a t h w a y is f o u n d a m o n g t h e w o r l d ' s h e r b a c e o u s land p l a n t s , b u t t h e C p a t h w a y is t h e m o s t w i d e l y d i s t r i b u t e d . C A M plants, w h i c h assimilate c a r b o n at n i g h t , are relatively less i m p o r t a n t even t h o u g h t h e i r utilization of w a t e r is generally m o r e efficient t h a n for C 3 species. The C p a t h w a y w a s at first t h o u g h t t o reside only in s u g a r c a n e a n d related t r o p i c a l grasses (31-33). It w a s soon f o u n d in o t h e r plants s u c h as Zea. Sorghum, a n d Amaranthus (34-38). T h e C species c o n s t i t u t e a k i n d of apex in p h o t o s y h t h e t i c p r o f i c i e n c y , a i d e d t o s o m e e x t e n t by a t t r i b u t e s s u c h as a l o w C 0 c o m p e n s a t i o n p o i n t , a " l a c k " of p h o t o r e s p i r a t i o n , a n d a c a p a b i l i t y t o utilize b o t h l o w e r a n d h i g h e r light intensities better t h a n C species (5.9,39-41}. 2

3

4

3

4

4

2

3

A n i m p o r t a n t aspect of p h o t o s y n t h e t i c e n e r g y c o n v e r s i o n o f t e n overlooked in h i g h e r plants is their " s p e c t r a l p r o f i c i e n c y " , t h a t is. t h e i r ability t o c o n v e r t

3.

ALEXANDER

53

Nonwoody Land Plants

d i f f e r e n t regions of t h e sun's spectral e n e r g y d i s t r i b u t i o n . W h e n

photo-

s y n t h e s i s b y a g i v e n leaf is m e a s u r e d at d i f f e r e n t w a v e l e n g t h s o f equal q u a n t u m f l u x , say f r o m 4 0 0 n m in t h e b l u e - v i o l e t t o 7 2 0 n m in t h e f a r - r e d . a p h o t o s y n t h e t i c a c t i o n s p e c t r u m is a t t a i n e d w h i c h tells us m u c h a b o u t t h e leaf's a b i l i t y t o " h a r v e s t " t h e entire package of visible light e n e r g y received f r o m t h e s u n . W i t h s u f f i c i e n t replications, an a c t i o n s p e c t r u m c h a r a c t e r i s t i c of t h e species is d e r i v e d , a kind o f spectral f i n g e r p r i n t c o m p l e t e w i t h peaks a n d depressions t y p i f y i n g t h a t species. Ironically, m o r e t h a n 6 0 p e r c e n t o f i n c o m i n g solar e n e r g y is received a t w a v e l e n g t h s shorter t h a n 5 5 0 n m , w h i l e (apparently) m o s t p l a n t s are p h o t o s y n t h e t i c a l l y a c t i v e at w a v e l e n g t h s longer t h a n 6 0 0 n m . There is s o m e e v i d e n c e t h a t Saccharum

and a f e w other

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

species have m a j o r p h o t o s y n t h e s i s a c t i v i t y in t h e blue-violet t o b l u e - g r e e n region (40,41). P h o t o s y n t h e t i c

a c t i o n s p e c t r a have been d e t e r m i n e d f o r

a p p r o x i m a t e l y 3 0 a g r i c u l t u r a l p l a n t s T h e vast m a j o r i t y o f h e r b a c e o u s land p l a n t s have n o t been e x a m i n e d in t h i s c o n t e x t . Photosynthesis in an Energy Crop Perspective:

A plant p h y s i o l o g i s t or

b i o c h e m i s t m e a s u r i n g p h o t o s y n t h e s i s in t h e laboratory usually d e t e r m i n e s t h e q u a n t i t y of C O 2 a s s i m i l a t e d per u n i t o f leaf area in a n hour or s o m e o t h e r c o n v e n i e n t t i m e interval (mg C 0 2 / c m - h r " 2

1

). It does n o t necessarily f o l l o w

t h a t superior a s s i m i l a t i o n rates n o t e d u n d e r these c o n d i t i o n s w i l l translate t o high

photosynthate

yields in t h e field. A m o r e c o n v e n i e n t

measure o f

p h o t o s y n t h e t i c p o t e n t i a l in b i o m a s s - c a n d i d a t e species is t h e q u a n t i t y of d r y m a t t e r p r o d u c e d per square m e t e r o f leaf surface per d a y (g D M / m - d a y ) . A 2

m a j o r i t y o f h e r b a c e o u s land p l a n t s w o u l d p r o d u c e on t h e order o f 2-8 g r a m s of o v e n - d r y material per square m e t e r per day, during growth

or tissue-expansion

the peak

of

their

phase. A yield of 15 g / m - d a y w o u l d be q u i t e

good and w o u l d typify some C

2

4

p a t h w a y species. Potential m a x i m u m y i e l d

e s t i m a t e s have been placed at 3 4 t o 3 9 g / m

2

-day f o r C

3

plants a n d 5 0 - 5 4

g / m - d a y for C plants (46). 2

4

To a n y e n e r g y

planter, t h e m o s t

meaningful

measure

of solar

energy

c o n v e r s i o n t o b i o m a s s is t h e n u m b e r o f k i l o g r a m s of d r y m a t t e r p r o d u c e d per hectare per year (or t o n s per acre per year). W h i l e p h o t o s y n t h e t i c processes per se r e m a i n a n i m p o r t a n t factor, e q u a l l y i m p o r t a n t are all other processes a n d c o n s t r a i n t s of p l a n t g r o w t h a n d d e v e l o p m e n t w h i c h c o m e into play as p h o t o s y n t h a t e is e l a b o r a t e d t o harvestable biomass. Each o f these factors f i n d s expression in t h e e n e r g y planter's gross yield of biomass. A n n u a l d r y m a t t e r yields in t h e order of 2 2 . 5 0 0 k g / h a (10 t o n s / a c r e ) are c o m m o n f o r a f e w species b u t t h e m a j o r i t y of herbaceous land plants p r o b a b l y yield less t h a n 4 5 0 0 k g / h a (2 t o n s / a c r e ) .

54

B I O M A S S A S A N O N F O S S I L FUEL SOURCE

T h e r e c k o n i n g of dry m a t t e r yields on an a n n u a l basis rather t h a n an h o u r l y or a daily basis m i g h t seem i n a p p r o p r i a t e t o n o n - w o o d y species w h o s e g r o w t h period lasts only a f e w w e e k s or m o n t h s . H o w e v e r , it is correct t o d o so since m a n y of t h e e n e r g y planter's expenses ( i n c l u d i n g land rentals, taxes, e q u i p m e n t d e p r e c i a t i o n , a n d land m a i n t e n a n c e ) are i n c u r r e d o n an a n n u a l basis (9,47.48). M o r e o v e r , s o m e herbaceous p l a n t species d o p r o d u c e dry m a t t e r c o n t i n u a l l y t h r o u g h o u t t h e year a n d o t h e r s c o u l d d o so if m a n a g e d as e n e r g y crops. A p l a n t s u c h as s u g a r c a n e p r o p a g a t e d as a 1 2 - m o n t h sugar c r o p c a n yield dry m a t t e r at t h e rate of 1 0 - 1 2 g / m -day, or a b o u t 10 t o n s / a c r e - y e a r . T h e h i g h e s t d r y m a t t e r yields a t t a i n e d t o d a t e b y t h e a u t h o r w e r e w i t h f i r s t - r a t o o n s u g a r c a n e m a n a g e d f o r t o t a l b i o m a s s rather t h a n sugar. These a m o u n t e d t o 36.6 t o n s / a c r e - y e a r , or 26.6 g / m - d a y , over a t i m e c o u r s e of 3 6 5 d a y s (49). 2

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

2

It is safe t o say t h a t for m o s t plants, t h e r e is no d i r e c t relationship b e t w e e n p h o t o s y n t h e t i c p o t e n t i a l , as d e t e r m i n e d in t h e laboratory, a n d t h e t o t a l dry b i o m a s s t o be harvested in t h e field. T h e p r i n c i p a l reasons for t h i s are a series of b o t a n i c a l a n d a g r o n o m i c factors w h i c h p r e v e n t t h e e l a b o r a t i o n of p h o t o s y n t h a t e t o b i o m a s s at rates c o m m e n s u r a t e w i t h t h e plant's c a r b o n r e d u c t i o n p o t e n t i a l . S o m e of these f a c t o r s are f u n d a m e n t a l c o n s t r a i n t s against g r o w t h a n d d e v e l o p m e n t essentially b e y o n d t h e c o n t r o l of t h e e n e r g y planter ( t h o u g h s o m e t i m e s c o n t r o l l a b l e by t h e p l a n t breeder). Other c o n s t r a i n t s are a r e f l e c t i o n of plant m a n a g e m e n t a n d c a n be e l i m i n a t e d t h r o u g h research a n d d e v e l o p m e n t of t h e species as an e n e r g y c r o p . It is also safe t o say t h a t s o m e n o n - w o o d y land plants w i l l be f o u n d t o have g o o d biomass p o t e n t i a l s b u t little prospect of ever b e i n g m a n a g e d as a g r i c u l t u r a l e n e r g y c o m m o d i t i e s . For s u c h plants, a decisive a t t r i b u t e w i l l be t h e i r ability t o s u r v i v e a n d p r o d u c e s o m e b i o m a s s w i t h t h e barest m i n i m u m of p r o d u c t i o n i n p u t s (8.9). Yet even in these instances one m u s t n o t overemphasize p h o t o s y n t h e s i s rate as an e n e r g y yield i n d i c a t o r ; t h e r e is s i m p l y t o o m u c h variability in t h e measured rates of p h o t o s y n t h e s i s and t o o little correlation w i t h m e a s u r e d biomass (5,33,50). A n e x a m p l e of t h i s w a s f o u n d in a series of " w i l d " sugarcanes (Saccharum species) w h o s e p h o t o s y n t h e s i s rates varied by a f a c t o r of 10 w h i l e t h e i r b i o m a s s yields varied by a f a c t o r less t h a n 2 (40). V a r i a t i o n is similarly h i g h a m o n g t h e h y b r i d sugarcanes of c o m m e r c e (33,51). ' g i v e n field of sugarcane, c o m p l e t e l y u n i f o r m as t o soil series, variety, p l a n t i n g d a t e , a n d c u l t u r a l m a n a g e m e n t , one can e x p e c t to f i n d p h o t o s y n t h e s i s a n d g r o w t h rates t h a t vary by a f a c t o r of 3 t o 5 a m o n g r a n d o m l y - s e l e c t e d s a m p l i n g sites (5). n

a

3.

ALEXANDER

55

Nonwoody Land Plants

Reduction State of t h e Primary Photosynthate: T o this p o i n t w e have c o n s i d e r e d biomass as " e l a b o r a t e d p h o t o s y n t h a t e " , c o n s i s t i n g m a i n l y o f cellulose, a n d lignin d e r i v e d f r o m g l u c o s e or p o l y g l u c o s i d e s h a v i n g t h e basic f o r m u l a ( C H 0 ) . This is q u a n t i t a t i v e l y t h e m o s t i m p o r t a n t f o r m o f biomass for b o t h w o o d y a n d herbaceous p l a n t species. H o w e v e r , as a f o r m of stored energy it has t h e l i m i t a t i o n of b e i n g o n l y partially r e d u c e d . T h e presence of o x y g e n in t h e s t r u c t u r e o f plant tissues, s t a r c h , a n d e x t r a c t a b l e sugars limits t h e e n e r g y c o n t e n t of s u c h materials t o a p p r o x i m a t e l y 1 4 - 1 6 Χ 1 0 Btu's per dry t o n . A l t e r n a t e l y , s o m e plant species store e n e r g y in m o r e h i g h l y r e d u c e d c o m p o u n d s h a v i n g progressively less o x y g e n in their s t r u c t u r e . Plant materials s u c h as isoprene p o l y m e r s , sterols, oils a n d w a x e s consist m a i n l y of c a r b o n a n d h y d r o g e n a n d c o n t a i n o n t h e order o f 4 0 - 5 0 X 1 0 Btu's per dry t o n . Calvin a n d others have a d v o c a t e d t h e s t u d y o f " h y d r o c a r b o n p l a n t s " as superior b i o m a s s e n e r g y sources (21.22.52). M a n y of these species have t h e a d d e d a d v a n t a g e of g o o d a d a p t a b i l i t y t o lands t h a t are s e m i - a r i d , r o u g h l y c o n t o u r e d , a n d o t h e r w i s e m a r g i n a l f o r t h e p r o d u c t i o n of more c o n v e n t i o n a l f o o d a n d e n e r g y crops (8.53.54). 6

1 2

6

6

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6

H y d r o c a r b o n - b e a r i n g plants i n c l u d e b o t h w o o d y a n d herbaceous species. S o m e of t h e b e t t e r - k n o w n e x a m p l e s , s u c h as t h e r u b b e r tree (Hevea brasiliensis) a n d g u a y u l e (Parthenium argentatum), are w o o d y perennials, w h i l e others, s u c h as Euphorbia a n d Calotropis species, are borderline cases t h a t c o u l d be m a n a g e d either as forest or a g r o n o m i c energy crops. M i l k w e e d species (Asclepidacea) are p r e d o m i n a n t l y herbaceous, b u t o n e m e m b e r f o u n d in t h e t r o p i c s , Calotropis procera (the " g i a n t m i l k w e e d " ) , is a w o o d y perennial r e a c h i n g h e i g h t s o f 9 t o 12 feet over a period of several years. In Puerto Rico it is regarded as a forest s p e c i m e n (55). b u t as an energy c r o p w o u l d m o s t likely be m a n a g e d as a f r e q u e n t l y reçut forage (56). Water Utilization Efficiency: W a t e r w i l l q u i t e d e f i n i t e l y be a decisive l i m i t i n g f a c t o r in t h e w o r l d w i d e e x p a n s i o n of a g r i c u l t u r e (9,54,57,58). It is therefore i m p o r t a n t t h a t w a t e r utilization e f f i c i e n c y be c o n s i d e r e d in t h e f u t u r e s c r e e n i n g a n d d e v e l o p m e n t o f herbaceous land plants as energy resources. Three factors m u s t be assessed f r o m t h e onset: (a) Utilization e f f i c i e n c y in p h o t o s y n t h e t i c processes; (b) w a t e r e x t r a c t i n g c a p a b i l i t y f r o m t h e c a n d i d a t e species' natural t e r r a i n ; a n d (c), t h e species c a p a c i t y for w a t e r c o n s e r v a t i o n b y a n a t o m i c a l means. Agronomic Considerations The p r o d u c t i o n of biomass involves t h e c o l l a b o r a t i o n of p h y s i o l o g i c a l , b i o c h e m i c a l , b o t a n i c a l , a n d a g r o n o m i c factors u n d e r any set o f c o n d i t i o n s . H o w e v e r , f o r t h e intensive m a n a g e m e n t of biomass p r o d u c t i o n , p a r t i c u l a r

56

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a t t e n t i o n m u s t be g i v e n to field-scale b e h a v i o r of plant masses in w h i c h an i n d i v i d u a l p l a n t or c r o w n c o m p l e x loses t h e i m p o r t a n c e w e a t t a c h t o it as a b o t a n i c a l or h o r t i c u l t u r a l e n t i t y . Several a g r o n o m i c c o n s i d e r a t i o n s c r i t i c a l t o successful biomass p r o d u c t i o n are herein d i s c u s s e d . G r o w t h Characteristics: T o a t t a i n m a x i m u m biomass o n a per a n n u m basis, o n e w o u l d ideally select a y e a r - r o u n d g r o w i n g season a n d p l a n t species c a p a b l e of g r o w i n g o n a y e a r - r o u n d basis. Certain t r o p i c a l grasses (sugarcane, napier grass. J o h n s o n grass, b a m b o o ) d o t h i s very nicely if p l a n t e d in t h e t r o p i c s . S o m e of t h e i r m e m b e r s p r o d u c e w e l l also in s u b t r o p i c a l or even t e m p e r a t e regions, b u t g i v e n equal m a n a g e m e n t , t h e y w i l l realize o n l y part of t h e i r f u l l y i e l d p o t e n t i a l w h e n g r o w t h is c o n s t r a i n e d for several m o n t h s by c o o l t e m p e r a t u r e s . It is i m p o r t a n t t o recognize also t h a t g r o w t h is a 2 4 - h o u r process as w e l l as a 1 2 - m o n t h process. T h e p h o t o s y n t h e t i c a n d t i s s u e - e x p a n s i o n s y s t e m s t h a t o p e r a t e each d a y are f u l l y d e p e n d e n t o n t h e n o c t u r n a l t r a n s p o r t a n d m o b i l i z a t i o n of g r o w t h - s u p p o r t i n g c o m p o u n d s . For t h i s reason, t h e t r o p i c s are a g a i n f a v o r e d by t h e i r w a r m n i g h t s for b i o m a s s p r o d u c t i o n . In a similar v e i n , t h e cool n i g h t s of t h e s o u t h w e s t e r n arid lands are p r o b a b l y as r e s t r i c t i v e for b i o m a s s as are t h e l i m i t e d m o i s t u r e supplies. Possibly t h e m o s t desirable g r o w t h c h a r a c t e r i s t i c of all for h e r b a c e o u s species is t h e a b i l i t y t o p r o d u c e n e w shoots c o n t i n u a l l y t h r o u g h o u t t h e year, year after year, f r o m an established c r o w n . This is a p r e d o m i n a n t c h a r a c t e r i s t i c of s u g a r c a n e a n d c e r t a i n o t h e r t r o p i c a l grasses b o t h related a n d u n r e l a t e d t o Saccharum species. S u c h p l a n t s d o n o t require t h e p e r i o d i c d o r m a n c y a n d rest intervals so i m p o r t a n t t o m o s t t e m p e r a t e species. Nor is t h i s c o m p e n s a t e d by t h e intensive f l u s h of M a y - J u n e g r o w t h by t e m p e r a t e p l a n t s ; over t h e course of a year t h e s l o w e r - g r o w i n g t r o p i c a l f o r m s w i l l o u t p r o d u c e t h e m by a f a c t o r of three or four. A less o b v i o u s b u t u t t e r l y c r i t i c a l f e a t u r e of t h e perennial c r o w n is its c o n t i n u a l u n d e r g r o u n d c o n t r i b u t i o n of d e c a y i n g o r g a n i c m a t t e r t o t h e soil. This process p r o c e e d s c o n c u r r e n t l y w i t h t h e c o n t i n u o u s r e n e w a l of u n d e r g r o u n d c r o w n a n d root tissues. For t h i s reason, t h e l o n g - t e r m harvest a n d r e m o v a l of a b o v e g r o u n d s t e m s , t o g e t h e r w i t h t h e b u r n i n g off of " t r a s h " , does n o t have an adverse effect o n s u g a r c a n e lands. There are soils in Puerto Rico t h a t have p r o d u c e d s u g a r c a n e m o r e or less c o n t i n u a l l y f o r f o u r c e n t u r i e s w i t h o u t d e s t r u c t i o n of t h e i r p h y s i c a l properties or n u t r i e n t - s u p p l y i n g c a p a b i l i t y . On t h e o t h e r h a n d , seasonal crops s u c h as field c o r n a n d grain s o r g h u m d o not d e v e l o p a perennial c r o w n . For these plants, a g o o d case can be m a d e a g a i n s t t h e r e m o v a l of a b o v e g r o u n d residues f r o m t h e c r o p p i n g site.

3.

ALEXANDER

Nonwoody Land Plants

57

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Tissue Expansion v s . Maturation: A c o m m o n m i s c o n c e p t i o n is t h a t b i o m a s s g r o w t h involves m a i n l y a visible increase o f size, a n d t h a t per acre t o n n a g e s of green m a t t e r are a reasonably a c c u r a t e i n d i c a t o r of a plant's yield p o t e n t i a l . It is also f r e q u e n t l y a s s u m e d t h a t t h e m o i s t u r e c o n t e n t o f plant tissues is essentially c o n s t a n t a t a r o u n d 7 5 percent, a n d t h a t dry m a t t e r yields c a n be c a l c u l a t e d rather closely f r o m green w e i g h t data. These a s s u m p t i o n s are n o t correct in a n y case, b u t are p a r t i c u l a r l y erroneous w i t h respect t o h e r b a c e o u s species. In v i r t u a l l y all s u c h plants " g r o w t h " consist o f discrete, d i p h a s i c processes o f tissue e x p a n s i o n f o l l o w e d b y m a t u r a t i o n . The tissue e x p a n s i o n phase p r o d u c e s visible b u t s u c c u l e n t g r o w t h c o n s i s t i n g m a i n l y o f w a t e r (on t h e order o f 8 8 - 9 2 p e r c e n t moisture). T h e m a t u r a t i o n phase c o r r e s p o n d s t o p h y s i o l o g i c a l a g i n g a n d senescence, t h a t is, t o f l o w e r i n g a n d seed p r o d u c t i o n , s l a c k e n i n g of visible g r o w t h , y e l l o w i n g a n d loss o f foliage, a n d h a r d e n i n g o f t h e f o r m e r l y s u c c u l e n t tissues. D u r i n g t h i s p e r i o d , t h e dry m a t t e r c o n t e n t w i l l increase b y a f a c t o r o f t w o t o four in a t i m e interval t h a t m a y be shorter t h a n t h a t of t h e t i s s u e - e x p a n s i o n phase. For e x a m p l e , t h e h y b r i d forage grass Sordan 7 0 A m o r e t h a n d o u b l e s its d r y m a t t e r yield in a t i m e - s p a n o f o n l y t w o w e e k s (23). i.e.. d u r i n g w e e k s 8 t o 1 0 in a 1 0 - w e e k g r o w t h a n d r e p r o d u c t i o n cycle. For this reason, t h e o p t i m a l period of harvest m u s t be d e t e r m i n e d w i t h care for each c a n d i d a t e species. A g a i n , as a rule o f t h u m b , t h e a l l o w i n g o f a d d i t i o n a l t i m e before harvest w i l l w o r k in favor of increased b i o m a s s yields f r o m herbaceous plants. For m o s t herbaceous plants, t h e p r o d u c t i o n of d r y m a t t e r can be p l o t t e d as an S-shaped c u r v e (Figure I). Dry m a t t e r c o n t e n t w i l l not ordinarily e x c e e d 10 t o 12 p e r c e n t d u r i n g t h e period o f rapid tissue e x p a n s i o n b u t w i l l b e g i n t o rise d r a m a t i c a l l y at s o m e p o i n t in t i m e t h a t is c h a r a c t e r i s t i c of t h e i n d i v i d u a l species. D r y m a t t e r w i l l rarely increase b e y o n d 4 0 p e r c e n t in herbaceous plants. A t t e m p t s t o hasten t h i s rise (by w i t h h o l d i n g w a t e r ) or t o delay it (by use o f g r o w t h s t i m u l a n t s ) have m e t w i t h l i m i t e d success in t r o p i c a l grasses (63). S o m e increase in t h e m a g n i t u d e of d r y m a t t e r a c c u m u l a t i o n has been a t t a i n e d over short periods o f t i m e w i t h t h e plant g r o w t h regulator Polaris (63). Harvest Frequency: O n c e t h e d i p h a s i c n a t u r e of biomass g r o w t h a n d m a t u r a t i o n is r e c o g n i z e d , t h e i m p o r t a n c e o f harvest f r e q u e n c y is also u n d e r s c o r e d . T h e o p t i m a l period f o r harvest in t h e m a t u r a t i o n c u r v e of one species w i l l differ e n o r m o u s l y f r o m t h e o p t i m a l harvest period of another, even a m o n g varieties w i t h i n t h e s a m e g e n u s a n d species. For t h i s reason, it is c o n v e n i e n t t o g r o u p c a n d i d a t e species i n t o d i s t i n c t categories based o n t h e t i m e interval t h a t m u s t elapse after p l a n t i n g t o m a x i m i z e d r y m a t t e r yield (63). The m a n a g e m e n t a n d harvest r e q u i r e m e n t s of each g r o u p w i l l also vary. On t h i s basis, it has been c o n v e n i e n t t o organize t r o p i c a l grasses i n t o " s h o r t - , i n t e r m e d i a t e - , a n d l o n g - r o t a t i o n " categories (Table I).

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T a b l e I. C A T E G O R I E S O F T R O P I C A L G R A S S E S A N D L E A D I N G CANDIDATE CLONES UNDER INVESTIGATION A S R E N E W A B L E ENERGY SOURCES IN PUERTO RICO*

Category I. Short Rotation

Harvest Interval (Months) 2-4

Candidate Clones Sordan 7 0 A

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

Sordan 7 7

b

b

Trudan 5 Millex 23 B e r m u d a Grass NK Hybrids Roma (Sorghum) II. I n t e r m e d i a t e Rotation

4-6

C o m m o n Napier Grass (Var. Meker) Napier H y b r i d PI 3 0 0 8 6 Napier H y b r i d PI 7 3 5 0 NK Hybrids Saccharum spontaneum: b

US 6 7 - 2 2 - 2 US 7 7 - 7 0 SES 2 3 1 S. spont. H y b r i d (Wild) Intergeneric Hybrids III. L o n g Rotation

12-18

Saccharum Hybrids NCo 3 1 0 PR 9 8 0 PR 6 4 - 1 7 9 1 Β 70-701 US 6 7 - 2 2 - 2 USDA Imports b

b

" b

DOE C o n t r a c t No. D E - A S 0 5 - 7 8 E T 2 0 0 7 1 . Leading c a n d i d a t e s for t h e i r catetory.

3.

ALEXANDER

Nonwoody Land Plants

59

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A s illustrated in Figure II. t h e tissue m a t u r a t i o n curves for t y p i c a l m e m b e r s of each c a t e g o r y vary greatly over a t i m e - c o u r s e o f 12 m o n t h s . Hence, t o harvest s u g a r c a n e at t h e 1 0 - w e e k intervals favorable t o Sordan 7 0 A w o u l d yield little d r y matter. Similarly, any delay of t h e Sordan harvest b e y o n d 12 w e e k s is a w a s t e of t i m e a n d p r o d u c t i o n resources. Napier grass, an " i n t e r m e d i a t e r o t a t i o n " species, is m o r e t h a n a m a t c h f o r s u g a r c a n e at t w o a n d f o u r - m o n t h s of age, a n d w i l l nearly equal s u g a r c a n e yields at six m o n t h s , b u t thereafter s u g a r c a n e w i l l easily o u t - p r o d u c e napier grass. In this c o n t e x t , a s h o r t - r o t a t i o n species s h o u l d be harvested four or five t i m e s per year, an i n t e r m e d i a t e - r o t a t i o n species t w o or three t i m e s per year, a n d l o n g - r o t a t i o n species n o m o r e t h a n o n c e per year. This need f o r careful a t t e n t i o n t o t h e m a t u r a t i o n profiles of c a n d i d a t e species is u n d e r s c o r e d b y yield data f o r sugarcane a n d napier grass harvested at variable intervals over a t i m e - c o u r s e of 12 m o n t h s (Table II). It is also e v i d e n t t h a t , w h i l e Sordan a n d napier grass attain rather level plateaus f o r d r y m a t t e r , s u g a r c a n e c o n t i n u e s t o increase in d r y m a t t e r b e y o n d 12 m o n t h s (Figure II). Sucrose a c c u m u l a t i o n profiles are very similar for sugarcane. For m a n y years, sugar planters have taken a d v a n t a g e of t h i s feature b y e x t e n d i n g t h e cane harvest interval b e y o n d 12 m o n t h s . Hence, t h e Puerto Rico sugar i n d u s t r y harvests t w o crops - t h e " g r a n c u l t u r a " (14 t o 16 m o n t h s b e t w e e n harvests) as o p p o s e d t o t h e p r i m a v e r a crop (10 t o 12 m o n t h s b e t w e e n harvests). In H a w a i i , s u g a r c a n e is c o m m o n l y harvested at t w o - y e a r intervals. E n e r g y C r o p R o t a t i o n s : From Figure II. one w o u l d s u r m i s e t h a t t h e e n e r g y p l a n t a t i o n m a n a g e r s h o u l d plant a herbaceous species s u c h as s u g a r c a n e a n d leave it there - u p t o 1 8 m o n t h s if possible — before harvest. In a d d i t i o n t o m a x i m u m fiber, he w o u l d also harvest f e r m e n t a b l e solids as a salable b y p r o d u c t . This reasoning w o u l d p r o b a b l y be c o r r e c t in a t r o p i c a l e c o s y s t e m suited t o Saccharum species a n d w h e r e a regional t r a d i t i o n exists f o r sugar p l a n t i n g . H o w e v e r , these c i r c u m s t a n c e s d o n o t exist in m a n y c o u n t r i e s h a v i n g an o t h e r w i s e g o o d p o t e n t i a l f o r g r o w i n g biomass. For e x a m p l e , there is n o region o f t h e U.S. m a i n l a n d s u i t e d f o r 1 2 - t o 1 8 - m o n t h c r o p p i n g of sugarcane, a l t h o u g h there are vast regions there suited t o s o m e f o r m o f t r o p i c a l grasses. Hence, a f u t u r e e n e r g y p l a n t e r in Florida, Louisiana, S o u t h e r n California, or S o u t h e r n Texas m i g h t seriously consider w h e t h e r he s h o u l d harvest a 6 t o 8 m o n t h c r o p o f s u g a r c a n e per a n n u m or t w o crops o f napier grass in t h e s a m e t i m e frame. Equally i m p o r t a n t is t h e fact t h a t s o m e c o u n t r i e s w i l l n o t be able t o afford a land o c c u p a t i o n o f 1 8 m o n t h s b y a single e n e r g y crop. This is especially t r u e of densely p o p u l a t e d , d e v e l o p i n g t r o p i c a l nations h a v i n g a n u r g e n t need f o r

60

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FUEL

SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

50k

AGE OF SPECIES

Figure 1.

A generalized representation of the maturation profile of herbaceous land plants

While no specific time-frame or plant form is depicted, the diphasic process of tissue expansion followed by maturation is typical of nonwoody plant species. With the visible growth phase essentially completed, the energy planter will gain much additional dry matter by allowing a brief additional time interval to elapse before harvest.

5θ\Sugarcane

AGE OF SPECIES (WEEKS)

Figure 2. Relative maturation profiles for Sordan 70A, napier grass, and sugarcane over one year. These plants are representative of the short-, intermediate-, and longrotation cropping categories, respectively.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

3.

ALEXANDER

61

Nonwoody Land Plants

Table II. DRY M A T T E R YIELDS OF S U G A R C A N E A N D NAPIER GRASS HARVESTED A T V A R I A B L E FREQUENCIES OVER A TIME-COURSE OF ONE Y E A R " Interval No. of (Months) Harvests Species 2

3

b

c

6

Cane" Napier

4

3

Cane Napier

6

2

Cane Napier

12

1

Cane Napier

0

Tons DM/Acre/Year

For—

Plant Crop

1st Ratoon Crop

6.5 12.7

3.3 11.9 11.9

11.1 22.6 16.6 25.6 25.5 19.3

DOE C o n t r a c t No. D E - A S 0 5 - 7 8 E T 2 0 0 7 1 . C o m p u t e d m e a n of t h r e e varieties a n d t w o r o w spacings. C o m p u t e d m e a n o f one v a r i e t y a n d t w o r o w spacings.

25.1 20.6 33.0 33.6 25.8

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

d o m e s t i c f o o d p r o d u c t i o n (64). In s u c h cases, a s h o r t - r o t a t i o n species s u c h as S o r d a n m a y be t h e p o p u l a r c h o i c e for e n e r g y p l a n t i n g since it c a n be s o w n as a s t o p - g a p b e t w e e n t h e harvest of one f o o d c r o p a n d t h e p l a n t i n g of another. In t h i s c a p a c i t y , it w o u l d also p r e v e n t soil erosion a n d w e e d g r o w t h w h i l e a c t i n g as a s c a v e n g e r for residual n u t r i e n t s left over f r o m t h e prior f o o d c r o p . Seasonal c l i m a t e c h a n g e s w i l l also be a f a c t o r in t h e r o t a t i o n of biomass e n e r g y species w i t h c o n v e n t i o n a l f o o d a n d fiber crops. S h o r t - r o t a t i o n t r o p i c a l grasses s u c h as Sordan are ideally s u i t e d t o t h e t r o p i c s , b u t t h e y can be g r o w n o n a seasonal basis d u r i n g t h e heat of s u m m e r in m o s t t e m p e r a t e regions. S u c h plants c o u l d be p r o p a g a t e d t o m a t u r i t y in a m i d - J u n e t o m i d A u g u s t t i m e f r a m e . In a g i v e n year, t h e s a m e site c o u l d p r o d u c e a cool season f o o d c r o p (a Brassica species, spinach), or a cool season forage (ryegrass, fall barley) b o t h p r e c e d i n g a n d f o l l o w i n g t h e b i o m a s s e n e r g y crop. HARVEST A N D TRANSPORTATION Perhaps t h e w e a k e s t p o i n t in c u r r e n t p r o d u c t i o n research for b i o m a s s is the lack of p r o v e n harvest e q u i p m e n t a n d m e t h o d o l o g i e s for t h e m a x i m i z e d s t a n d s of b i o m a s s t h a t each c o n t r a c t o r strives t o a t t a i n . This is m o s t e v i d e n t in w o o d y b i o m a s s scenarios w h e r e c o n v e n t i o n a l forest h a r v e s t i n g t e c h n o l o g y is either not a p p l i c a b l e or s i m p l y d o e s n ' t exist in t h e c o n t e x t of s i l v i c u l t u r e e n e r g y p l a n t a t i o n s . T h e o u t l o o k for h a r v e s t i n g herbaceous land plants is c o n s i d e r a b l y better b u t a g o o d deal of research remains o n harvest a n d p o s t - h a r v e s t t e c h n o l o g y , t o g e t h e r w i t h e q u i p m e n t redesign a n d modification. M o w i n g vs. Conditioning As Harvest Options T h e vast m a j o r i t y of herbaceous land plants can be harvested nicely w i t h the sickle-bar m o w e r (assuming t h a t land slopes and c o n t o u r s are o t h e r w i s e s u i t e d for m e c h a n i z e d operations). This i m p l e m e n t w a s d e s i g n e d m o r e t h a n a c e n t u r y ago as a r e p l a c e m e n t for t h e h a n d sickle a n d m a n u a l grass s c y t h e . As a h o r s e - d r a w n i m p l e m e n t , it r e v o l u t i o n i z e d t h e harvest of grain a n d forage crops. T o d a y it is usually o p e r a t e d f r o m t h e p o w e r take-off of Class I a n d II tractors. The original w o o d e n parts have been replaced, bearings and l u b r i c a t i o n systems have been i m p r o v e d , a n d it is no longer geared to t h e s l o w f o r w a r d pace of d r a f t animals. But it operates o n basically t h e same p r i n c i p l e as its h o r s e - d r a w n predecessors. There are t w o p r i n c i p a l l i m i t a t i o n s of t h e sickle-bar m o w e r as a harvest i m p l e m e n t for herbaceous biomass crops: (a) It is d e s i g n e d to operate in relatively l o w - d e n s i t y stands of plants, a n d (b). its c u t t i n g process is c o n f i n e d

3.

ALEXANDER

Nonwoody Land Plants

63

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t o a single slice near t h e base of u p r i g h t stems. In o t h e r w o r d s , it is a m e c h a n i z e d sickle f o r severing s t e m s rather t h a n a s t e m c o n d i t i o n e r . This m o w e r has a preference for d r y a n d u p r i g h t s t e m s w h o s e t o t a l mass does n o t exceed a b o u t 12 green t o n s per acre. It experiences real d i f f i c u l t y w i t h w e t and l o d g e d materials a n d w i t h plant stands in a n y c o n d i t i o n w h o s e mass exceeds 15 green t o n s per acre. Since its o p e r a t i o n is based o n a c u t t i n g p r i n c i p l e , t h e sickle m u s t be kept c o n t i n u a l l y sharp for effective p e r f o r m a n c e . Its e f f i c i e n c y is i m m e d i a t e l y l o w e r e d b y c o n t a c t w i t h m o l e hills, rocks, w i r e s , scrap m e t a l , and d u r a b l e o b j e c t s o f any kind e n c o u n t e r e d in t h e field. In t h e a u t h o r ' s experience, t h e m o d e r n sickle-bar m o w e r o p e r a t i n g in a t y p i c a l l y dense t r o p i c a l grass, s u c h as S o r d a n 7 0 A (about 2 0 - 2 5 green t o n s / a c r e ) , w i l l e x p e r i e n c e f r e q u e n t t r i p p i n g of its " f a i l - s a f e " m e c h a n i s m . This is a b u i l t - i n feature o f t h e i m p l e m e n t d e s i g n e d t o p r e v e n t its d e s t r u c t i o n w h e n s t r i k i n g unseen s t u m p s or o t h e r f i x e d o b j e c t s at operational speed. Nonetheless, t h e sickle-bar m o w e r is p r o b a b l y very a d e q u a t e for h a r v e s t i n g m o s t herbaceous land plants, t h a t is. t h o s e plants w h o s e s t a n d i n g green mass w i l l n o t exceed a b o u t 12 t o n s per acre at any g i v e n harvest interval. For h a r v e s t i n g s o m e w h a t higher densities o f herbaceous m a t e r i a l , a series o f " f l a i l " a n d " c o n d i t i o n e r " designs have p r o v e n t o be superior t o t h e sickle-bar m o w e r . S u c h i m p l e m e n t s d o n o t p e r f o r m o n a c u t t i n g p r i n c i p l e b u t rather break o f f t h e plant s t e m by striking it w i t h e x t r e m e force. Sharpness o f t h e c o n t a c t blades is n o t a decisive feature. In fact t h e y w i l l p e r f o r m fairly a d e q u a t e l y even w h e n dull f r o m long use. These m a c h i n e s require h i g h h o r s e p o w e r (90 t o 1 2 0 hp) a n d h i g h p o w e r - t a k e - o f f speed ( 1 0 0 0 rpm). The m o s t effective i m p l e m e n t of t h i s t y p e t e s t e d t o date in Puerto Rico is t h e M-C " r o t a r y s c y t h e - c o n d i t i o n e r " . T h e plant s t e m s are broken o f f by four lines of w h i r l i n g blades a n d are repeatedly s h a t t e r e d as t h e blades restrike t h e s t e m s at 3 - t o 5-inch intervals. T h e r e s u l t i n g " c o n d i t i o n e d " biomass is evenly d i s t r i b u t e d in a broad s w a t h b e h i n d t h e rotary s c y t h e . In this state, t h e s u b s e q u e n t d r y i n g a n d baling o p e r a t i o n s are m o r e easily p e r f o r m e d t h a n w i t h c o n v e n t i o n a l l y - m o w e d biomass, t h a t is. w i t h plant materials received in c l u m p s a n d m a t t s a n d w i t h o n l y one c u t surface t o facilitate w a t e r r e m o v a l . A n a d d i t i o n a l a d v a n t a g e of t h e rotary s c y t h e - c o n d i t i o n e r is its c a p a c i t y t o harvest plant densities r o u g h l y d o u b l e t h o s e h a n d l e d b y t h e sickle-bar m o w e r . A second a d d e d a d v a n t a g e is its a b i l i t y t o harvest lodged a n d w e t materials. Such plants are harvested a b o u t as readily as t h o s e in a d r y a n d u p r i g h t c o n d i t i o n . A t h i r d a v a n t a g e is its relatively t r o u b l e - f r e e o p e r a t i o n . The n u m b e r o f parts s u b j e c t t o m a l f u n c t i o n is purposely r e d u c e d t o a m i n i m u m .

64

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SOURCE

A t t h i s w r i t i n g , t h e rotary s c y t h e - c o n d i t i o n e r has g i v e n e x c e l l e n t

perfor-

m a n c e in p l a n t densities a m o u n t i n g t o a b o u t 2 2 g r e e n t o n s per acre (62). It is believed t h a t its u p p e r d e n s i t y l i m i t w i l l be o n t h e order of 4 0 g r e e n t o n s per

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acre (65). Plant yields c o n s i d e r a b l y h i g h e r t h a n 4 0 green t o n s per acre are a n t i c i p a t e d for a f e w h e r b a c e o u s species. S u g a r c a n e yields in excess of 9 0 g r e e n t o n s per acre year w e r e r e c e n t l y d e m o n s t r a t e d in Puerto Rico (49). M o s t s u g a r c a n e harvesters m a r k e t e d t o d a y b e g i n t o have d i f f i c u l t y w i t h c a n e densities in t h e range of 5 0 t o 6 0 s t a n d i n g g r e e n t o n s per acre (65). T h e m o s t e f f e c t i v e s u g a r c a n e harvester in Puerto Rico at present is t h e Class M o d e l 1400. O r i g i n a l l y d e v e l o p e d in East G e r m a n y , t h e Class is a s i n g l e - r o w , w h o l e cane harvester w h i c h e m p l o y s a p o w e r f u l air blast t o r e m o v e o r g a n i c trash a n d soil f r o m t h e cane at t h e p o i n t of harvest in t h e field. It has a c c o m m o d a t e d over 6 0 t o n s of green c a n e per acre. W i t h m o d i f i c a t i o n s , it m i g h t possibly harvest 8 0 t o 9 0 t o n s per acre (65). Solar Drying A c h a r a c t e r i s t i c d i f f i c u l t y w i t h b i o m a s s is its l o w d e n s i t y relative t o fossil e n e r g y a n d its h i g h w a t e r c o n t e n t w h i c h is c o s t l y t o t r a n s p o r t t o p r o c e s s i n g centers. W h e r e v e r possible, it is desirable t o r e m o v e m o s t of t h i s w a t e r at t h e harvest site by solar d r y i n g . O n e e x c e p t i o n t o t h i s is t h e use of " g r e e n " b i o m a s s for a n a e r o b i c d i g e s t i o n . A n o t h e r e x c e p t i o n is f o u n d in s u g a r c a n e . In t h i s case, t h e w h o l e green stalk is t r a n s p o r t e d t o a centralized m i l l for d e w a t e r i n g . T h e p l a n t ' s s o l u b l e f e r m e n t a b l e solids are recovered t h e r e f r o m t h e expressed j u i c e a n d sold as refined sugar or molasses. Very a d e q u a t e e q u i p m e n t for t h e solar d r y i n g of n o n - w o o d y land plants can be f o u n d in t h e c a t t l e f o r a g e i n d u s t r y . T h e rotary s c y t h e - c o n d i t i o n e r d e s c r i b e d a b o v e does m u c h t o prepare herbaceous p l a n t s for rapid d r y i n g in t h e s u n (66.67). O r d i n a r i l y t h e s e materials w o u l d be t u r n e d over o n c e or t w i c e in b r i n g i n g t h e m o i s t u r e c o n t e n t d o w n t o a b o u t 15 percent. Three w i n d r o w s w o u l d t h e n be c o m b i n e d into one s h o r t l y before b a l i n g . Each of these o p e r a t i o n s can be p e r f o r m e d w i t h s t a n d a r d side-delivery f o r a g e rakes o p e r a t i n g f r o m t h e p o w e r take-off of a Class I or II tractor. W h e n higher d e n s i t y b i o m a s s is t o be raked (Sordan or napier grass), a h e a v y - d u t y " w h e e l " rake m a y be m o r e suitable. These i m p l e m e n t s are also b e c o m i n g s t a n d a r d e q u i p m e n t for f o r a g e - m a k i n g o p e r a t i o n s .

3.

ALEXANDER

Nonwoody Land Plants

65

Compaction A n d Baling

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

Solar-dried biomass is rarely t r a n s p o r t e d t o its processing site t o d a y in a loose s t a t e , a l t h o u g h o n c e t h i s w a s s t a n d a r d practice. For e c o n o m y of space in t r a n s p o r t a n d storage, as w e l l as ease o f h a n d l i n g , s u c h materials are first c o m p a c t e d and t h e n b o u n d w i t h a suitable t w i n e or w i r e . T h e s t a n d a r d h a y " b a l e r " t o d a y is a c t u a l l y a c o m p a c t o r . It p r o d u c e s c o n v e n i e n t l y - s i z e d c u b e s h a v i n g a c o n t r o l l e d d e n s i t y range o f r o u g h l y 8 t o 2 0 p o u n d s per c u b i c foot. A t y p i c a l hay " b a l e " w o u l d w e i g h 6 0 or 7 0 p o u n d s a n d is easily h a n d l e d b y one m a n in t r a n s p o r t a n d storage p r o c e d u r e s or in c a t t l e - f e e d i n g operations. A d i f f e r e n t c o n c e p t in biomass b a l i n g has appeared in recent years. This is t h e " b u l k " or " r o u n d " baler w h i c h operates as a w i n d r o w w r a p p e r rather t h a n a c o m p a c t o r . This i m p l e m e n t p r o d u c e s large c y l i n d r i c a l bales w e i g h i n g u p t o 1 5 0 0 p o u n d s each (68,69). Since n o a p p r e c i a b l e c o m p a c t i o n is i n v o l v e d , t h e bale d e n s i t y is relatively low. o n t h e order o f 10 t o 12 p o u n d s per c u b i c foot. M o r e recent m o d i f i c a t i o n s enable t h i s m a c h i n e t o p r o d u c e

cube-shaped

bales w h i c h are more e c o n o m i c a l o f space d u r i n g t r a n s p o r t a n d storage. Both f r o n t - a n d rear-end loaders suitable f o r h a n d l i n g these bales are m a r k e t e d as c o n v e n t i o n a l t r a c t o r a t t a c h m e n t s (65). There are t w o t y p e s o f balers for s u g a r c a n e bagasse, t h e b a l i n g press a n d t h e b r i q u e t t i n g press (70). The first t y p e is a h y d r a u l i c press e m p l o y i n g t h e s a m e c o m p a c t i o n p r i n c i p l e used for hay. T h e bagasse is baled in a s e m i - g r e e n state a n d t h e f o r m e d c u b e s are t i e d w i t h t w i n e or w i r e s t o p r e v e n t t h e m f r o m ree x p a n d i n g . Their d e n s i t y w i l l range f r o m 2 5 t o 4 0 p o u n d s per c u b i c foot. Bales of t h i s t y p e m u s t be stacked c a r e f u l l y t o p r e v e n t s p o n t a n e o u s c o m b u s t i o n , t h a t is. w i t h s u f f i c i e n t space b e t w e e n t h e m t o a l l o w air c i r c u l a t i o n . T h e b r i q u e t t i n g press operates w i t h d r y bagasse h a v i n g a m o i s t u r e c o n t e n t of 8 t o 15 percent. This press provides h i g h pressures o n t h e order o f 5.000 t o 1 5 . 0 0 0 psi. U n d e r t h e s e c o n d i t i o n s , e x t r e m e l y c o m p a c t c u b e s are p r o d u c e d w h i c h retain t h e i r f o r m w i t h o u t t h e use o f t w i n e or w i r e s . Transport And Storage Herbaceous b i o m a s s t h a t has been solar-dried a n d baled can be t r a n s p o r t e d t o p r o c e s s i n g or storage sites w i t h o u t a p p r e c i a b l e d i f f i c u l t y w i t h e x i s t i n g e q u i p m e n t . H o w e v e r , t h i s c a n entail a s i g n i f i c a n t cost. Ordinarily s u c h materials w o u l d be loaded d i r e c t l y in t h e field o n a l o w - b e d truck. S t a n d a r d bales ( 6 0 - 8 0 pounds) c a n be loaded m a n u a l l y or w i t h m e c h a n i c a l loaders r e q u i r i n g o n l y o n e laborer on t h e t r u c k f o r final p o s i t i o n i n g o f t h e bales. Bulk bales w o u l d be stacked t w o layers d e e p o n t h e t r u c k b e d w i t h t r a c t o r m o u n t e d loaders. T h e s a m e t r u c k w o u l d t r a n s p o r t t h e biomass t o a final

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SOURCE

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p r o c e s s i n g or storage f a c i l i t y w i t h o u t i n t e r m e d i a t e t r a n s - s h i p m e n t o p e r a tions. In t h e case of s u g a r c a n e , t h e harvested w h o l e stalks or s t e m billets, w h a t e v e r t h e case m a y be. are hauled in carts t o t h e a d j a c e n t mil.. T h e same materials c o u l d be c a r t e d t o an i n t e r m e d i a t e reloading p o i n t for t r u c k delivery t o m o r e d i s t a n t sugar mills. Delivery costs w i l l vary c o n s i d e r a b l y w i t h t h e i n d i v i d u a l biomass p r o d u c t i o n o p e r a t i o n . In g e n e r a l , a 4 0 - t o n l o w - b e d t r u c k w i t h driver can be hired for a b o u t $ 1 8 0 per 2 4 - h o u r d a y at c u r r e n t rates. L o a d i n g e q u i p m e n t w i t h o p e r a t o r s m u s t be s t a t i o n e d at each e n d of t h e d e l i v e r y r u n . In an ideal b i o m a s s p r o d u c t i o n o p e r a t i o n , i.e., o n e m a n a g e d by a private f a r m e r for profit, t h e land o w n e r w o u l d p r o b a b l y o w n a n d help o p e r a t e t h e t r u c k a n d accessory e q u i p m e n t . A n e s t i m a t e d d e l i v e r y c o s t for solar-dried b i o m a s s on a 2 0 - m i l e run w o u l d be $ 6 . 0 0 t o $ 8 . 0 0 per t o n ( 1 9 8 0 dollars). PRODUCTION COSTS Published p r o d u c t i o n costs for b o t h h e r b a c e o u s a n d w o o d y biomass s h o w broad v a r i a t i o n s t h a t are b o t h u n d e r s t a n d a b l e a n d i n e v i t a b l e (3,6,7,48,58). A g i v e n c o n t r a c t o r w i l l w a n t t o present his speciality c r o p in t h e best possible l i g h t relative t o t h e dollar i n p u t s needed t o o b t a i n a m i l l i o n Btu's in biomass f o r m . This t o p i c has been r e v i e w e d in detail (48). It w a s c o n c l u d e d t h a t m o s t b i o m a s s researchers g r e a t l y u n d e r e s t i m a t e t h e cost of b i o m a s s p r o d u c t i o n , e x c l u d i n g f r o m t h e i r c a l c u l a t i o n s s i g n i f i c a n t i n d i r e c t costs, l o n g - t e r m repercussions o n e c o s y s t e m resources, f u t u r e c o m p e t i t i o n for land a n d w a t e r , a n d b o t h t h e cost a n d e f f i c i e n c y of b i o m a s s c o n v e r s i o n s y s t e m s . Obtaining Correct Cost Data A seriously m i s l e a d i n g t r e n d is t o base t h e p r o d u c t i o n costs of a biomass c a n d i d a t e on its p u b l i s h e d yield p e r f o r m a n c e as a c o n v e n t i o n a l f o o d or fiber crop. S u g a r c a n e is an a p p r o p r i a t e e x a m p l e . In Puerto Rico, s u g a r c a n e m a n a g e d for sucrose yields 2 5 t o 3 0 green t o n s per acre year; as an energy c r o p it can yield 8 0 t o 9 0 t o n s per acre year w i t h o n l y m o d e r a t e increases in p r o d u c t i o n costs (49). Napier grass data are similarly m i s l e a d i n g . There is a w e a l t h of p r i n t e d m a t t e r o n t h e yields of napier grass m a n a g e d as a t r o p i c a l f o r a g e c r o p , t h a t is, w h e n harvested repeatedly at f i v e - or s i x - w e e k intervals at m o i s t u r e c o n t e n t s a p p r o a c h i n g 9 0 percent. A s an energy c r o p , napier grass p r o d u c e s r o u g h l y t w o t o t h r e e t i m e s m o r e dry m a t t e r per a n n u m at less cost t h a n t h e c a t t l e forage (49).

3.

ALEXANDER

Nonwoody Land Plants

67

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P r o d u c t i o n C o s t s For T r o p i c a l G r a s s e s Since J u n e of 1 9 7 7 . considerable i n f o r m a t i o n has been g a t h e r e d o n p r o d u c t i o n costs for s u g a r c a n e a n d o t h e r t r o p i c a l grasses w h o s e a g r i c u l t u r e has been m a n a g e d f o r m a x i m u m d r y m a t t e r yield in a t r o p i c a l e c o s y s t e m (62,63). A b r e a k d o w n o f p r o d u c t i o n i n p u t charges f o r " e n e r g y c a n e " is presented in Table III. There d a t a pertain t o a p r i v a t e l y - o w n e d , 2 0 0 - a c r e o p e r a t i o n y i e l d i n g 3 3 o v e n - d r y t o n s o f biomass per acre-year. Total cost, i n c l u d i n g delivery t o t h e m i l l i n g site, is $ 2 5 . 4 6 per t o n or $ 1 . 7 0 per m i l l i o n Btus. U n d e r Puerto Rico c o n d i t i o n s , a b o u t 7 0 p e r c e n t o f this d r y m a t t e r w o u l d be b u r n e d as a boiler f u e l . The r e m a i n d e r w o u l d be e x t r a c t e d as f e r m e n t a b l e solids d u r i n g t h e cane d e w a t e r i n g process a n d later sold as c o n s t i t u e n t s o f h i g h - t e s t molasses. This is a solid credit t o t h e insular e n e r g y cane planter o w i n g t o Puerto Rico's precarious reliance o n f o r e i g n molasses as f e e d s t o c k for her r u m i n d u s t r y (7JJ. A s s u m i n g a market price of $ 0 . 7 5 per gallon f o r h i g h - t e s t molasses, t h e f e r m e n t a b l e solids f r o m one such t o n o f energy cane w o u l d be v a l u e d at m o r e t h a n $ 4 5 . 0 0 , or a b o u t $ 1 5 0 0 . 0 0 per acre. Cane m i l l i n g costs t o d a y in Puerto Rico are a b o u t $ 4 . 5 0 per t o n (72). P r o d u c t i o n costs f o r Sordan 7 0 A are presented in Table IV. A l t h o u g h Sordan's biomass yield is l o w e r t h a n t h a t of energy cane, p r o d u c t i o n i n p u t costs are also lower. T h e final cost o f an o v e n - d r y t o n of Sordan 7 0 A is a b o u t $ 1 4 . 0 0 , or $ 1 . 5 0 less t h a n a t o n o f e n e r g y cane. In this instance, there is no sale of f e r m e n t a b l e solids. P r o d u c t i o n costs f o r napier grass w o u l d be m o d e r a t e l y l o w e r t h a n Sordan 7 0 A o w i n g t o a m u c h higher yield per acreyear for napier grass (49,62). This c r o p similarly has no sales f o r f e r m e n t a b l e solids. M a n a g e m e n t A s A Production Cost Factor P r o d u c t i o n costs f o r e n e r g y cane listed in Table III i n c l u d e " m a n a g e m e n t " as 10 p e r c e n t of t h e cost s u b t o t a l . This is an i n d e f i n i t e t e r m c o v e r i n g t h e a d m i n i s t r a t i v e skills e x p e n d e d b y w a y o f g o o d a g r i c u l t u r a l t e c h n i q u e t o m a x i m i z e biomass y i e l d . It also reflects t h e m o r a l e (or profit i n c e n t i v e level) o f t h e i n d i v i d u a l g r o w e r or i n s t i t u t i o n in c h a r g e o f p r o d u c t i o n . The m a n a g e m e n t f a c t o r c o n t r i b u t i o n t o f u t u r e biomass p r o d u c t i o n scenarios can range f r o m very g o o d t o very b a d , b u t it w i l l have t h e p o t e n t i a l t o be decisive in all p r o d u c t i o n operations. A g a i n , u s i n g s u g a r c a n e as a c o n v e n i e n t e x a m p l e , it is c o m m o n k n o w l e d g e t h a t little profit is t o be m a d e a n y w h e r e in t h e w o r l d t o d a y b y p l a n t i n g sugar, b u t it is t h e w e l l - m a n a g e d o p e r a t i o n s t h a t w i l l m i n i m i z e losses a n d offer t h e best p r o s p e c t o f survival u n t i l sugar values are again equitable. A t one e x t r e m e , superior m a n a g e m e n t w i l l be f o u n d in

68

BIOMASS AS A NONFOSSIL F U E L

SOURCE

T a b l e I I I . D R Y M A T T E R P R O D U C T I O N C O S T S FOR FIRST-RATOON S U G A R C A N E M A N A G E D A S A N ENERGY CROP" Land Area: 2 0 0 Acres P r o d u c t i o n I n t e r v a l : 12 M o n t h s

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D M Y i e l d : 3 3 (Oven-Dry) S h o r t T o n s / A c r e : 6 , 6 0 0 T o n s Preliminary Cost Analysis Item 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

16. T o t a l C o s t / T o n ( 1 6 8 . 0 2 3 + 6.600): 17. Total C o s t / M i l l i o n Btu (25.46 -s- 15): 1

2

Cost ($/Year)

L a n d Rental, at 5 0 . 0 0 / A c r e S e e d b e d Preparation, at 1 5 . 0 0 / A c r e W a t e r (800 A c r e Feet at 15.00/ft) W a t e r A p p l i c a t i o n , at 4 8 . 0 0 / A c r e Year Seed (For Plant Crop Plus T w o Ratoon Crops 1 T o n / A c r e Year at 1 5 . 0 0 / T o n Fertilizer, at 1 8 0 . 0 0 / A c r e Pesticides, at 2 6 . 5 0 / A c r e Harvest, I n c l u d i n g E q u i p m e n t Charges, E q u i p m e n t D e p r e c i a t i o n , a n d Labor Day Labor. 1 M a n Year ( 2 0 1 6 hrs. a t 3 . 0 0 / h r ) C u l t i v a t i o n , at 5 . 0 0 / A c r e L a n d Preparation & M a i n t e n a n c e (Pre-& Post-Harvest) Delivery, at 7 . 0 0 / t o n / 2 0 miles of Haul Subtotal: Management: 10% Subtotal T o t a l Cost:

DOE C o n t r a c t No. D E - A S 0 5 - 7 8 E T 2 0 0 7 1 . Labor w h i c h is n o t i n c l u d e d in o t h e r costs

b

10,000 3,000 12.000 9,600 3.000 36.000 5,300 20,000 6,048 1.000 600 46,200 152,748 15.275 168.023 25.46 1.70

3.

ALEXANDER

Nonwoody Land Plants

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T a b l e IV. D R Y M A T T E R P R O D U C T I O N C O S T S FOR S O R D A N 7 0 A Land A r e a : 2 0 0 A c r e s Production Interval: 6 Months Sordan 7 0 A Y i e l d : 15 (Oven Dry) Short T o n s / A c r e , Total 3,000 Tons Preliminary Cost Analysis Item

C o s t ($)

1. 2. 3. 4. 5.

5.000 2.160 4,800 10.000 4,000 2,650 1,988 1,988 2,200 12,600 18,000 65,386 6,538 71,924 23.97 1.59

6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. a

Land Rental, at 5 0 . 0 0 / A c r e Year W a t e r (Overhead Irrigation), 3 6 0 A c r e Feet Seed, at 6 0 l b / A c r e Fertilizer Pesticides E q u i p m e n t D e p r e c i a t i o n (6 mo.) E q u i p m e n t M a i n t e n a n c e (75% o f Depreciation) E q u i p m e n t O p e r a t i o n (75% o f Depreciation) Diesel Fuel Day Labor ( 9 0 . 0 0 / D a y f o r 1 4 0 Days) Delivery, at 6 . 0 0 / T o n Subtotal: M a n a g e m e n t (10% o f Subtotal) Total Cost: Total C o s t / T o n (71,924 + 3.000): Total C o s t / M i l l i o n Btu (23.97 + 1 5 ) :

DOE C o n t r a c t No. D E - A S 0 5 - 7 8 E T 2 0 0 7 1 .

a

70

BIOMASS AS A NONFOSSIL F U E L

SOURCE

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p r i v a t e l y - o w n e d p l a n t a t i o n s w h i c h in s o m e c o u n t r i e s are still basically f a m i l y o p e r a t i o n s . Here t h e land o w n e r has an i n h e r e n t interest in his p r o p e r t y a n d c a p i t a l i n v e s t m e n t s a n d possesses t h e skills a n d i n c e n t i v e t o m a k e a g o o d l i v i n g f r o m a g r i c u l t u r e . S u c h i n d i v i d u a l s c a n still be f o u n d t o d a y , for e x a m p l e , in t h e Q u e e n s l a n d sugar i n d u s t r y . A t t h e o t h e r e x t r e m e is t h e g o v e r n m e n t o w n e d p r o d u c t i o n o p e r a t i o n . Historically, g o v e r n m e n t s have not m a d e g o o d farmers. A f a r m m a n a g e r w h o has little i n c e n t i v e t o m a k e a profit a n d w h o c a n n o t be held a c c o u n t a b l e for a loss w i l l u l t i m a t e l y have t h e inferior p r o d u c t i o n record. G o v e r n m e n t take-over of an a g r i c u l t u r a l c o m m o d i t y is s o m e t i m e s v i e w e d as a necessary i n t e r v e n t i o n in a free market w h e r e i m p o r t a n t social or p o l i t i c a l c o n s i d e r a t i o n s c o u l d n o t o t h e r w i s e be served (73). T h i s w a s t h e case w i t h s u g a r c a n e in Puerto Rico w h e r e a large a n d o t h e r w i s e u n e m p l o y a b l e labor force c o u l d no longer be s u s t a i n e d by p r i v a t e enterprise (64.79). A s a c o n s e q u e n c e it n o w costs a b o u t 2 8 c e n t s t o p r o d u c e a p o u n d of sucrose in Puerto Rico, at a t i m e w h e n its v a l u e o n t h e w o r l d sugar m a r k e t is o n l y a b o u t 14 c e n t s per p o u n d . It is fair t o say t h a t m a n a g e m e n t is n o t t h e o n l y f a c t o r c o n t r i b u t i n g t o h i g h p r o d u c t i o n costs — e n v i r o n m e n t a l q u a l i t y s t a n d a r d s have also had a n e g a t i v e i m p a c t o n t h e PR s u g a r i n d u s t r y (29) — b u t poor m a n a g e m e n t is clearly t h e m a i n c o n t r i b u t i n g factor. In a w e l l - m a n a g e d p r o d u c t i o n scenario for herbaceous terrestrial b i o m a s s s o m e s t r a i g h t - f o r w a r d steps w i l l need t o be t a k e n t o assure m a x i m u m returns f r o m p r o d u c t i o n i n p u t e x p e n d i t u r e s . These i n c l u d e : a) Correct land p r e p a r a t i o n , i n c l u d i n g land leveling a n d p l a n n i n g w h e r e n e e d e d ; b) correct d e s i g n a n d installation of t h e irrigation s y s t e m ; c) c o r r e c t seedbed (relative t o d e p t h , d e n s i t y or r o w s p a c i n g , a n d season); d) reseeding of v a c a n t space w h e n necessary; e) correct pest c o n t r o l p r o g r a m s ( i n c l u d i n g a d m i n i s t r a t i o n of c o n t r o l on w e e k e n d s a n d holidays w h e n required); f) m a i n t e n a n c e of c o r r e c t i r r i g a t i o n , fertilization, a n d c u l t i v a t i o n p r o g r a m s ; g) correct t i m i n g a n d s y n c h r o n i z a t i o n of harvest o p e r a t i o n s ; h) c o r r e c t selection a n d use of harvest e q u i p m e n t ; i) p o s t - h a r v e s t m a i n t e n a n c e of land a n d m a c h i n e r y . For m o s t biomass c r o p s , t h e cost of these measures w i l l a c c r u e w h e t h e r t h e y are p e r f o r m e d c o r r e c t l y or not. T h e decisive f a c t o r w i l l be t h e skill a n d m o t i v a t i o n of t h e o p e r a t i o n ' s field managers. Good m a n a g e m e n t c a n best be assured w h e n p r o d u c t i o n is retained in t h e c o n t e x t of p r i v a t e l y - o w n e d p l a n t a t i o n s t h a t are o p e r a t e d for personal profit.

3.

ALEXANDER

Nonwoody Land Plants

71

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch003

SUMMARY The n a t u r e of herbaceous land plants a n d their p o t e n t i a l usefulness as a f u t u r e energy resource is presented in broad outline. T h e large n u m b e r of herbaceous species f o u n d in b o t h cool a n d w a r m c l i m a t e s a n d in b o t h t h e w i l d a n d c u l t i v a t e d state s u g g e s t s t h a t at least a small p e r c e n t a g e of these c o u l d b e c o m e v a l u a b l e sources o f fuel. Extensive s c r e e n i n g w i l l be needed in a r a n g e o f e c o s y s t e m s t o b r i n g t h e n u m b e r o f c a n d i d a t e species t o a m a n a g e a b l e level. Both b o t a n i c a l a n d a g r o n o m i c features t o be e v a l u a t e d d u r i n g t h e s c r e e n i n g process are briefly discussed. S o m e of t h e p r o d u c t i o n a n d harvest o p e r a t i o n s required of herbaceous plants as a g r i c u l t u r a l c o m m o d i t i e s are also r e v i e w e d , t o g e t h e r w i t h partial cost analyses f o r t h e p r o d u c t i o n operations. M a n a g e m e n t of t h e energy crop is seen t o be t h e decisive cost input. This f a c t o r w i l l be o p t i m i z e d in p r i v a t e l y - o w n e d o p e r a t i o n s m o t i v a t e d b y a s t r o n g profit i n c e n t i v e .

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RECEIVED JULY 1,

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4 Biomass Production by Freshwater and Marine Macrophytes W. J. NORTH, V. A. GERARD, and J. S. KUWABARA

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

W. M . Keck Engineering Laboratories, California Institute of Technology, Pasadena, C A 91125

Biomass plantations for energy production in coastal and oceanic settings have several inherent attractions. Water requirements for aquatic plants may pose no serious limitations. Algal tissues do not contain high proportions of refractory materials such as lignin and cellulose (which might complicate processes for conversion to certain fuels). Many algal species show little or no seasonal changes in potential for growth and presumably can be maintained indefinitely. Photosynthetic conversion efficiencies are good. Space is abundant in the oceanic environment and environmental energy in waves and currents might be utilized for tasks such as obtaining and dispersing plant nutrients. Research on aquatic macrophytes as producers of biomass has been undertaken at Woods Hole Oceanographic Institution (WHOI) on the east coast and on the west coast by a group of collaborators in a joint effort known as the Marine Biomass Project. Studies at WHOI have focused on estuarine and coastal situations with some attention recently to freshwater plants. The Marine Farm Project has primarily been concerned with oceanic biomass production. A group at WHOI led by John H. Ryther has undertaken a wide variety of studies concerning aquatic macrophytes including nutrient uptake, growth,

0097-6156/81/0144-0077$05.50/0 © 1981 American Chemical Society

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yields, a n d e n v i r o n m e n t a l factors a f f e c t i n g yields. Joel C. G o l d m a n of W H O I has s u r v e y e d a q u a t i c biomass p r o d u c t i o n s y s t e m s o n a w o r l d w i d e basis a n d is c u r r e n t l y e x a m i n i n g t h e role of c a r b o n as a p o t e n t i a l l i m i t i n g n u t r i e n t in b i o m a s s c u l t u r i n g . T h e M a r i n e Farm Project is presently a t t e m p t i n g t o g r o w g i a n t kelp in offshore w a t e r s off s o u t h e r n California. O t h e r w o r k related t o a q u a t i c b i o m a s s p r o d u c t i o n i n c l u d e s an i n v e s t i g a t i o n at t h e U n i v e r s i t y of California, Berkeley, of m i c r o a l g a e in p o n d s . This paper w i l l emphasize d i s c u s s i o n of t h e kelp p r o d u c t i o n phases of t h e M a r i n e Farm Project because of t h e a u t h o r s ' d i r e c t i n v o l v e m e n t t h e r e i n . W e w i l l also briefly s u m m a r i z e a c t i v i t i e s by t h e g r o u p s at W H O I .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

MACROCYSTIS BIOLOGY T w o species of Macrocystis o c c u r a l o n g t h e w e s t coast of t h e U n i t e d States f r o m Baja. California t o t h e Gulf of Alaska. M. pyrifera prefers t e m p e r a t e w a t e r s (ca. 5 ° t o 25°C) a n d requires s o m e p r o t e c t i o n f r o m severe w a v e s a n d s t o r m s f r o m central California n o r t h w a r d s . A d u l t plants t y p i c a l l y o c c u r in t h e d e p t h range 8 t o 2 0 - 3 0 m. This species does n o t usually o c c u r m u c h b e l o w 2 0 m in t u r b i d w a t e r . M. integrifolia o c c u r s a l o n g t h e n o r t h e r n p o r t i o n of t h e range, b u t is not i n c l u d e d in t h i s paper. The Macrocystis life c y c l e involves a h e t e r o m o r p h i c a l t e r n a t i o n of g e n e r a t i o n s b e t w e e n m i c r o s c o p i c - s i z e haploid g a m e t o p h y t e s a n d m a c r o s c o p i c d i p l o i d s p o r o p h y t e s (Figure I). Our p r i m a r y c o n c e r n is w i t h t h e large s p o r o p h y t e . T h e a d u l t s p o r o p h y t e is a n c h o r e d t o t h e b o t t o m by t h e perennial holdfast o r g a n . Unlike t r u e roots, holdfasts are n o t specialized for a c c u m u l a t i n g minerals. Macrocystis a n d indeed m o s t seaweeds a c c u m u l a t e t h e i r dissolved m i c r o n u t r i e n t s across all exposed surfaces. A s t e m l i k e p r i m a r y stipe e m e r g e s f r o m t h e holdfast apex and soon d i v i d e s into a c o m p l e x b r a n c h i n g p a t t e r n . A m o n g t h e first branches are blades t h a t p r o d u c e spores, a n d in N o r t h Pacific m a t e r i a l , these are t e r m e d s p o r o p h y l l s . T h e basal b r a n c h e s s u p p o r t a n y w h e r e f r o m one t o h u n d r e d s of fronds. T h e m a t u r e Macrocystis f r o n d consists of a long vinelike stipe s u b t e n d i n g gas f l o t a t i o n b u l b s ( p n e u m a t o c y s t s ) t h a t in t u r n s u p p o r t leaflike blades. A n older f r o n d m a y display a b o u t 2 0 0 or m o r e blades and p n e u m a t o c y s t s , dispersed in a regular p a t t e r n a l o n g t h e stipe l e n g t h . The u p p e r m o s t blade is m e r i s t e m a t i c a n d c o n t i n u a l l y p r o d u c e s n e w blades, p n e u m a t o c y s t s . a n d m o r e stipe. Basal m e r i s t e m s are sources of j u v e n i l e f r o n d s . The y o u n g f r o n d s d e v e l o p rapidly, usually r e a c h i n g t h e surface in t w o t o f o u r m o n t h s . The u p p e r p o r t i o n s of t h e m a t u r i n g f r o n d s t h e n b e g i n c o n t r i b u t i n g t o t h e c a n o p y . Frond lifespan is o n l y a b o u t six m o n t h s (J_. 3). C o n s e q u e n t l y , senescing f r o n d s m u s t c o n t i n u a l l y be replaced by p r o d u c t i o n of y o u n g f r o n d s g r o w i n g up f r o m b e n e a t h . Plants, as a w h o l e , m a y survive m a n y years (3).

Figure 1. Important phases in the life history of Macrocystis. Developmental patterns among the basal branches are shown in detail for the juvenile sporophyte to illustrate production of fronds and and of basal meristems.

Sporophytt

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

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Dense Macrocystis canopies are able t o absorb 9 9 p e r c e n t or m o r e of s u n l i g h t e n t e r i n g t h e sea surface (4). T h u s j u v e n i l e f r o n d s exist in a d a r k e n e d e n v i r o n m e n t w h i c h has been s h o w n t o lie b e l o w t h e c o m p e n s a t i o n level [i.e. w h e r e p h o t o s y n t h e s i s balances respiration] (5, 6). L o b b a n (7) a n d Parker (8) d e m o n s t r a t e d existence of t r a n s l o c a t i o n processes in Macrocystis. Photos y n t h a t e p r o d u c e d in t h e Macrocystis c a n o p y is t r a n s l o c a t e d d o w n t h e stipes t o n o u r i s h j u v e n i l e f r o n d s . T h u s t h e s e y o u n g tissues are able t o g r o w rapidly, o v e r c o m i n g t h e self-shading p r o b l e m . T h e t r a n s l o c a t i o n c a p a b i l i t y enables Macrocystis t o f o r m very dense o p u l a t i o n s of h i g h biomass per u n i t area. T h e average s t a n d i n g c r o p of Macrocystis in s o u t h e r n a n d Baja, California is a r o u n d six f r o n d s per square m e t e r a n d c a n range u p t o t h i r t y fronde per square m e t e r (9). T h e average w e t w e i g h t of a f r o n d is a p p r o x i m a t e l y 1 t o 1.5 kg (10). N o r t h (JJJ s u m m a r i z e d results f r o m several e s t i m a t e s of p r o d u c t i v i t y in Macrocystis beds. Values r a n g e d f r o m 16 t o a b o u t 1 3 0 m e t r i c t o n s of d r y w e i g h t per hectare per year. Harvest yields, of course, are l o w e r b e c a u s e of inefficiencies in c u t t i n g a n d because o n l y u p p e r p o r t i o n s of p l a n t s ae r e m o v e d . T h e a n n u a l harvest f r o m California w a t e r s p r o v i d e s an average yield in t h e range of one t o t w o m e t r i c t o n s d r y w e i g h t per hectare per year. Values m a y be t w o t o f o u r t i m e s as h i g h for ore p r o d u c t i v e beds in areas w h e r e u p w e l l i n g is w e l l d e v e l o p e d . State l a w l i m i t s d e p t h of c u t t i n g by c o m m e r c i a l harvesters t o four feet b e l o w t h e surface. T h u s o n l y c a n o p y tissues are r e m o v e d . A l l apical m e r i s t e m s l y i n g w i t h i n t h e c a n o p y are also g a t h e r e d by harvesters. Hence t h e r e m a i n i n g p o r t i o n s of c u t f r o n d s c a n n o t s i g n i f i c a n t l y d e v e l o p further. T h e c a n o p y is essentially replaced f r o m g r o w t h by f r o n d s w h o s e apical m e r i s t e m s lie b e l o w t h e d e p t h of c u t t i n g . Usually, canopies regenerate in t w o t o f o u r m o n t h s so t h a t beds can be harvested t w o t o t h r e e t i m e s a n n u a l l y . Y o u n g Macrocystis plants m a y be raised f r o m t h e r e p r o d u c t i v e spores in t h e laboratory. A f t e r plants are 1 0 - 2 0 c m t a l l , t h e y can readily be t r a n s p l a n t e d t o t h e sea floor or t o artificial s t r u c t u r e s . T h e h o l d f a s t s are a t t a c h e d t o p r o j e c t i o n s by w i n d i n g r u b b e r b a n d s a r o u n d t h e m (12). A d u l t s m a y also be t r a n s p l a n t e d . T h e holdfast is first t h r e a d e d w i t h n y l o n line, t h e n p r i e d loose f r o m t h e b o t t o m , t h e p l a n t is m o v e d t o a n e w l o c a t i o n , a n d t h e h o l d f a s t is t h e n secured t o an a p p r o p r i a t e a n c h o r a g e (Figure II). A t t a c h m e n t t o solid s u b s t r a t e is n o t m a n d a t o r y . T h e holdfast c a n s i m p l y be m o o r e d by f a s t e n i n g it t o a rope. T r a n s p l a n t a t i o n t e c h n i q u e s are n o w used r o u t i n e l y by b i o l o g i s t s f r o m t h e State a n d f r o m t h e h a r v e s t i n g i n d u s t r y t o restore d e p l e t e d kelp beds in s o u t h e r n California.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

Towing

Transplants ara shiftad ta •srmanantly

.1 Τ J

T Î J T T T I ^

Β. Transplanting Operation

Figure 2. One of several techniques in use for transplanting adult Macrocystis: A. details of kelp needle and its use to weave nylon line between hapteral clumps in the holdfast; B. operations involved in moving transplants to new location, using chain for towing

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

EARLY STUDIES BY THE M A R I N E F A R M PROJECT Research o n oceanic f a r m s c o m m e n c e d in California a r o u n d 1 9 7 3 . T h e y w e r e m a n a g e d by t h e U.S. Navy, u n d e r t h e d i r e c t i o n of H o w a r d A. W i l c o x . A t a b o u t t h e s a m e t i m e , a g r o u p led by E d w a r d N. Hall at U n i t e d A i r c r a f t Research Laboratories in C o n n e c t i c u t w a s i n v e s t i g a t i n g m e t h a n e p r o d u c t i o n f r o m o r g a n i c materials a n d c o n s i d e r i n g t h e o r e t i c a l p r o b l e m s of m a r i n e biomass p r o d u c t i o n . In 1 9 7 6 , m a n a g e m e n t of t h e Navy p r o j e c t w a s a s s u m e d by General Electric C o m p a n y . T h e M a r i n e Farm Project c u r r e n t l y exists as a g r o u p of o r g a n i z a t i o n s g u i d e d by, or c o l l a b o r a t i n g w i t h , t h e General Electric g r o u p (Global M a r i n e D e v e l o p m e n t , Inc. — e n g i n e e r i n g ; I n s t i t u t e of Gas T e c h n o l o g y — m e t h a n e p r o d u c t i o n ; U.S. D e p a r t m e n t of A g r i c u l t u r e — kelp processing). T h e California I n s t i t u t e of T e c h n o l o g y has been separately f u n d e d by DOE b u t w o r k s in close c o l l a b o r a t i o n w i t h t h e General Electric part of t h e Project. Recently, responsibility for g o v e r n m e n t a l r e v i e w a n d m a n a g e m e n t w a s t r a n s f e r r e d f r o m DOE t o t h e Solar Energy Research Institute. A r e v i e w of t h e literature by J a c k s o n a n d N o r t h 0 3 ) e x a m i n e d c h a r a c t e r i s t i c s of n u m e r o u s s e a w e e d species t o i d e n t i f y likely c a n d i d a t e s f o r use on oceanic f a r m s . Giant kelp, Macrocystis pyrifera w a s selected as a h i g h l y s u i t a b l e s e a w e e d o n several c o u n t s . Macrocystis beds c a n be c o p p i c e d several t i m e s yearly by m e c h a n i c a l h a r v e s t i n g t e c h n i q u e s . T h e species is h i g h l y p r o d u c tive. A h a r v e s t i n g i n d u s t r y utilizing Macrocystis has been a c t i v e in s o u t h e r n California for a l m o s t 7 0 years. W e t h u s have available a w e a l t h of i n f o r m a t i o n c o n c e r n i n g h a r v e s t i n g a n d t h e o p e r a t i o n s i n v o l v e d . Extensive research has p r o d u c e d t e c h n i q u e s for t r a n s p l a t i n g , p r e d a t o r a n d c o m p e t i t o r c o n t r o l , c u l t u r i n g , a n d o t h e r m a n a g e m e n t tools w h i c h are presently utilized in s o u t h e r n California (14, 1_5). For all these reasons, Macrocystis is b e i n g used as t h e test o r g a n i s m in t h e c u r r e n t studies of oceanic f a r m i n g . Other s e a w e e d s m a y prove t o be q u a l l y suitable if t h e scope of t h e research is b r o a d e n e d at s o m e f u t u r e date. T h e first m a j o r a c t i v i t y u n d e r t a k e n by t h e M a r i n e Farm Project i n v o l v e d studies of Macrocystis t r a n s p l a n t s m o o r e d o n artificial s t r u c t u r e s in o c e a n i c e n v i r o n m e n t s . T h e largest of t h r e e s u c h e x p e r i m e n t s c o n s i s t e d of a t h r e e hectare s t r u c t u r e d e s i g n e d a n d installed by t h e Naval Undersea Center off San C l é m e n t e Island, a b o u t 1 0 0 k m f r o m t h e m a i n l a n d . T h e s t r u c t u r e c o n s i s t e d of a g r i d or n e t w o r k of ropes, d e p l o y e d 15 t o 2 0 m b e n e a t h t h e sea surface by a s y s t e m of cables, b u o y s , a n d a n c h o r s 0 6 ) . Overall w a t e r d e p t h r a n g e d f r o m a b o u t 7 0 t o 150 m. A p p r o x i m a t e l y 130 a d u l t Macrocystis t r a n s p l a n t s w e r e relocated o n t o t h e g r i d d u r i n g s u m m e r a n d fall, 1974. The source of t r a n s p l a n t s w a s a nearby kelp bed at San C l é m e n t e Island w h i c h

4.

NORTH

ET AL.

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w a s also used as a c o n t r o l f o r o u r m e a s u r e m e n t s . G r o w t h p e r f o r m a n c e s by test plants a n d c o n t r o l s y i e l d e d m e a n e l o n g a t i o n rates of 4.6 vs 7.6 p e r c e n t per d a y respectively, a m o n g j u v e n i l e f r o n d s . N i t r o g e n c o n t e n t of blade per tissues in t h e t r a n s p l a n t s fell t o 0.7 t o 0.8 p e r c e n t of t h e d r y w e i g h t c o m p a r e d t o a range of 0.9 t o 1.4 p e r c e n t d r y w e i g h t a m o n g t h e c o n t r o l s . T h e e x p e r i m e n t a l plants soon d i s p l a y e d u n u s u a l l y dense a c c u m u l a t i o n s o f bryozoan e n c r u s t a t i o n s . Presumably, t h e s p r e a d i n g rate of t h e bryozoan colonies e x c e e d e d e x p a n s i o n rate of t h e u n d e r l y i n g , s l o w l y g r o w i n g blade tissues. These general f i n d i n g s at t h e San C l é m e n t e Island f a r m w e r e c o n f i r m e d b y a d d i t i o n a l e x p e r i m e n t s at t w o o t h e r sites. W e c o n c l u d e d t h a t l o w c o n c e n t r a t i o n s o f dissolved n u t r i e n t s in oceanic surface w a t e r s w e r e a p p a r e n t l y unable t o sustain n o r m a l g r o w t h rates by kelp tissues. W e also n o t e d i m p r o v e m e n t in kelp g r o w t h d u r i n g periods w h e n natural u p w e l l i n g w a s intense a n d t h e n u t r i e n t - r i c h deep w a t e r m o v e d u p into s h a l l o w d e p t h s . W e f u r t h e r d e t e c t e d faster kelp g r o w t h d u r i n g e x p e r i m e n t s w h e r e w a t e r artificially u p w e l l e d f r o m d e p t h s of 3 0 t o 4 5 m w a s i n t r o d u c e d a r o u n d t h e e x p e r i m e n t a l plants ( V U A p p a r e n t l y , o b t a i n i n g h i g h biomass yields f r o m oceanic f a r m s necessitates fertilizing operations. Costs a n d energetic r e q u i r e m e n t s c o n n e c t e d w i t h d i s p e r s i n g c o m m e r c i a l fertilizers o n m a r i n e f a r m s have led analysts t o favor use o f artificially u p w e l l e d d e e p w a t e r as a source of n u t r i e n t s (V7). There has been c o n c e r n , h o w e v e r , t h a t t h e a m o u n t s of freely available metallic ions, s u c h as c o p p e r and zinc in deep w a t e r , m i g h t be s u f f i c i e n t t o i n h i b i t kelp g r o w t h . Likewise, d e e p w a t e r m i g h t n o t c o n t a i n a full c o m p l e m e n t o f required e l e m e n t s or t h e i r c o n c e n t r a t i o n s m i g h t n o t be in proper balance. W e a t t e m p t e d t o resolve these and other q u e s t i o n s t h r o u g h laboratory c u l t u r i n g studies c o m p a r i n g g r o w t h in deep a n d surface w a t e r m e d i a . W e have also a t t e m p t e d t o d e t e r m i n e t h e e l e m e n t a l r e q u i r e m e n t s of Macrocystis b y c u l t u r i n g g a m e t o p h y t e s a n d juveniles s p o r o p h y t e s in a c h e m i c a l l y d e f i n e d artificial s e a w a t e r k n o w n as A q u i l . S U M M A R Y OF LABORATORY FINDINGS Culturing W o r k in S e a w a t e r M e d i a M a n y m i c r o n u t r i e n t s in s e a w a t e r o c c u r at e x t r e m e l y l o w c o n c e n t r a t i o n s . A c c i d e n t a l c o n t a m i n a t i o n of laboratory w a r e can easily alter levels of s o m e critical e l e m e n t s q u i t e p r o f o u n d l y . For t h o s e w h o m i g h t w i s h t o repeat o u r e x p e r i m e n t s , s c r u p u l o u s cleanliness is m a n d a t o r y in all phases of t h e w o r k . Our c u l t u r i n g studies have utilized s e a w a t e r c o l l e c t e d f r o m a d e p t h range of 0 t o 8 7 0 m. M o s t e x p e r i m e n t s , h o w e v e r , w e r e c o n d u c t e d w i t h w a t e r f r o m 3 0 0 m deep, c o l l e c t e d a b o u t 5 k m offshore f r o m o u r laboratory headquarters

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

at Corona del M a r , California. T y p i c a l e x p e r i m e n t s i n v o l v e d b a t c h c u l t u r i n g c o n d i t i o n s u s i n g 4 0 - 1 aquaria (18). S m a l l Macrocystis s p o r o p h y t e s (wet w e i g h t s of 0.5 t o a b o u t 15 g) w e r e t h e test o r g a n i s m s . T h e e x p e r i m e n t a l d e s i g n m a d e it unlikely t h a t n i t r o g e n or p h o s p h o r u s w o u l d be l i m i t i n g w h e n u s i n g d e e p w a t e r 2 5 t o 3 0 μ M in nitrate. A n e x p e r i m e n t a l series e m p l o y i n g n o n e n r i c h e d 3 0 0 - m w a t e r as t h e m e d i u m y i e l d e d m e a n s p e c i f i c g r o w t h rates r a n g i n g f r o m a b o u t 8 t o 1 8 p e r c e n t daily w e i g h t increases w i t h i n a 1 3 - m o n t h p e r i o d of t e s t i n g (Figure III). T h e series c o m p r i s e d 4 8 i n d e p e n d e n t e x p e r i m e n t s e a c h e m p l o y i n g f r o m t w o t o nine plants. S o m e of t h e v a r i a b i l i t y in results u n d o u b t e d l y arose f r o m p h y s i o l o g i ­ cal differences a m o n g t h e plants. There w a s e v i d e n c e , h o w e v e r , t h a t c h a n g e s in c o m p o s i t i o n of t h e d e e p w a t e r in part c o n t r i b u t e d t o t h e f l u c t u a t i o n s seen in Figure III. For e x a m p l e , f r o m t i m e t o t i m e w e c o n d u c t e d a parallel c u l t u r i n g series w h e r e t h e 3 0 0 - m w a t e r w a s s u p p l e m e n t e d w i t h m a n g a n e s e t o g i v e 1 m i c r o m o l a r c o n c e n t r a t i o n s of M n in t h e m e d i u m . S i m u l t a n e o u s l y , b a c k g r o u n d M n c o n c e n t r a t i o n s in t h e n o n e n r i c h e d 3 0 0 - m w a t e r w e r e r o u t i n e l y d e t e r m i n e d by A A S . W e f o u n d t h a t s u p p l e m e n t i n g d e e p w a t e r w i t h Mn s t i m u l a t e d kelp g r o w t h d u r i n g periods w h e n b a c k g r o u n d M n fell b e l o w d e t e c t a b l e levels (Table I). Conversely, a d d i t i o n s o f M n c o u l d even be m i l d l y i n h i b i t o r y w h e n t h e A A S analyses revealed presence of t h e e l e m e n t in d e e p water. W e have similarly f o u n d t h a t s u p p l e m e n t i n g 3 0 0 - m w a t e r with F e m a y or m a y n o t s t i m u l a t e kelp g r o w t h . W e have never o b s e r v e d a clearly s t i m u l a t o r y response f r o m e n r i c h i n g d e e p w a t e r w i t h Z n or w i t h Cu . Occasionally, h o w e v e r , m i l d g r o w t h s t i m u l a t i o n a c c o m p a n i e d a d d i t i o n s of c o p p e r , at a p p r o p r i a t e c o n c e n t r a t i o n s , t o offshore surface w a t e r . Iron a n d m a n g a n e s e c o n c e n t r a t i o n s have a l w a y s a p p e a r e d e n t i r e l y a d e q u a t e in surface w a t e r s a l t h o u g h o u r t e s t i n g has been l i m i t e d . + 2

+ 2

+ 3

+ 2

+ 2

M a x i m a l g r o w t h by y o u n g Macrocystis s p o r o p h y t e s w a s o b t a i n e d in a f l o w i n g s y s t e m w h e r e t h e m e d i u m c o n s i s t e d of equal parts of surface a n d of w a t e r f r o m 8 7 0 m d e e p (16). It appears t h a t i n a d e q u a c i e s of d e e p w a t e r w e r e m e t by c o m p o n e n t s of surface w a t e r a n d v i c e versa. C o n s e q u e n t l y , at t h i s t i m e , o u r laboratory w o r k indicates t h a t m i x t u r e s of t h e t w o w a t e r t y p e s s h o u l d p r o v i d e a n e a r - o p t i m a l m e d i u m for fertilizing plants o n o c e a n i c farms. M o s t of o u r studies have been d o n e at l o w light intensities c h a r a c t e r i s t i c of t h e sea floor in kelp beds. Recent w o r k i n d i c a t e d t h a t specific g r o w t h rates increase at h i g h light intensities. Needs for n u t r i e n t s w i l l u n d o u b t e d l y be greater t o m a i n t a i n s u c h h i g h g r o w t h rates, so t h a t p r e v i o u s l y established n u t r i e n t resources m a y require réévaluation in t e r m s of t h e greater needs.

ND ND 3.6 17 4.3 3.6 4.0 1.6 ND

10/31/77 11/15/77 2/6/78 4/24/78 5/23/78 7/6/78 8/4/78 9/19/78 10/17/78 b

Background M n nM/f ND

Date of Sampling 5/5/77

A p p r o x i m a t e end of a severe rainy season.

Temporal relations between background concentration of M n in seawater from 3 0 0 m deep and the effect on kelp g r o w t h w h e n 300-m water w a s enriched w i t h M n at one μ Μ . This effect w a s taken as the difference between the mean specific g r o w t h rate s h o w n by plants in Mn-enriched water minus the mean rate in nonenriched 300-m water. Background M n w a s determined by atomic absorption spectroscopy. ND =• Not detected (i.e. concentration below one nM). Enrichment w i t h M n tended to stimulate g r o w t h (i.e. positive values for the differences between experimental and control g r o w t h rates) w h e n background M n w a s low. Enrichment w i t h M n inhibited g r o w t h w h e n background M n w a s high. Numbers of juvenile sporophytes involved given in parentheses.

-0.1 +4.7

13.3 (6) 15.0 (8)

13.4 (6) 10.3 (6)

10/22/78-10/29/78 11/5/78-11/12/78

-2.7 -0.3 -1.8

7.4 (5) 13.3 (5) 12.0 (5)

10.1 (8) 13.6 (5) 13.8 (5)

5/2/78-5/8/78 7/16/78-7/23/78 7/23/78-7/30/78

Dates of Testing 6/3/77-6/16/77 9/24/77-10/5/77 10/25/77-11/2/77 11/2/77-11/6/77 11/12/77-11/20/77 11/20/77-11/26/77 2/7/78-2/15/78

M e a n Specific Growth Rate Enriched Difference Nonenriched Medium Medium + 5.5 14.5 (3) 9Ό (5) 10.4 (6) 13.0 (3) +2.6 12.3 (6) +4.1 8.2 (5) 9.3 (3) 10.3 (3) -1.0 11.5 (3) -0.7 12.2 (3) 11.4 (3) 14.0 (3) -2.6 10.9 (5) 13.7 (5) -2.8

Table I. EFFECT OF M A N G A N E S E O N KELP G R O W T H *

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

86

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SOURCE

Culturing W o r k Using t h e Defined M e d i u m Aquil

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

A n artifical s e a w a t e r n a m e d A q u i l w a s devised b y M o r e l a n d associates f o r c u l t u r i n g m a r i n e o r g a n i s m s (19). Because A q u i l is a c h e m i c a l l y d e f i n e d s e a w a t e r m e d i u m , c h e m i c a l s p e c i a t i o n c a n be c o m p u t e d u s i n g a n e q u i l i b r i u m c o m p u t e r p r o g r a m called REDEQL2 (20). A q u i l c o n t a i n s eleven m a j o r c o m p o n e n t s in f i x e d a m o u n t s . These c o r r e s p o n d t o t h e p r i n c i p a l i n o r g a n i c c o n s t i t u e n t s of seawater. C o n c e n t r a t i o n s of m a c r o n u t r i e n t s , s u c h as n i t r a t e a n d p h o s p h a t e , a n d c e r t a i n t r a c e m e t a l s m a y be varied as desired for a g i v e n A q u i l f o r m u l a t i o n . W e have r e c e n t l y been able t o c u l t u r e spores f r o m Macrocystis through the entire g a m e t o p h y t i c p o r t i o n of t h e life c y c l e , t o e m b r y o n i c s p o r o p h y t e s as large as 3 0 t o 4 0 cells. A f t e r a t w o - w e e k c u l t u r i n g p e r i o d , v o l u m e s of t h e e m b r y o n i c plants w e r e b e t w e e n 2 0 0 t o 1 0 0 0 t i m e s greater t h a n t h e spores f r o m w h i c h t h e y arose. It seems unlikely t h a t s u c h large v o l u m e increases c o u l d have been entirely s u p p o r t e d b y reserves of n u t r i t i v e e l e m e n t s stored in t h e spores. A n a l t e r n a t i v e h y p o t h e s i s seems m o r e a t t r a c t i v e — n a m e l y , t h a t t h e f o r m u l a t i o n used c o n t a i n e d all e l e m e n t s required b y Macrocystis. A s i d e f r o m t h e m a j o r salts, o n l y nine n u t r i e n t e l e m e n t s w e r e a d d e d (Table II). W e w i l l be g r a t i f i e d if f u r t h e r studies c o n f i r m t h i s f i n d i n g because t h e n u m b e r of p o t e n t i a l l y l i m i t i n g c o m p o n e n t s a f f e c t i n g Macrocystis nutrition appears t o be relatively small. Table II. M E D I U M FOR K E L P G R O W T H * Amount Nutrient used Fe

+ 3

Mn Co Cu

+ 2

2

NO3PO4-

a

1

1

3

2

(%) (100)

1

ΜηEDTA

(65) (23)

0.04

MnCI CoEDTA

5

4

Present FeEDTA

10

+ 2

2

Major Species

7 x 10"

40

Mo0 " EDTA"

Free Ion Cone, η M

400

+ 2

Zn+

Γ

Added. n M

11

+

(99)

0.0000

CuEDTA

(99)

250

0.12

ZnEDTA

(100)

100

100 0.00007

CaEDTA FeEDTA

(89)

6.000 15.000 2.000

15.000 0.3

100

100

HPO4MgHP04

2

(6) (51) (47)

Nannomoles of nine inorganic nutrients and of EDTA added to the completely defined artificial seawater Aquil to yield a medium that sustained development by Macrocystis zoospores in petri-dish cultures completely through the gametophyte stage to embryonic sporophytes.

4.

NORTH E T A L .

Freshwater and Marine Macrophytes

87

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

PRESENT FIELD STUDIES Our laboratory w o r k t h u s s u g g e s t s t h a t w e can e x p e c t s t r o n g s t i m u l a t i o n of g r o w t h w h e n d e e p w a t e r is dispersed a m o n g plants o n a f a r m (e.g., c o m p a r e t h e level of average g r o w t h c a l c u l a t e d f o r small s p o r o p h y t e s in natural kelp beds w i t h values a c h i e v e d in 3 0 0 - m w a t e r , Figure 3). It is d i f f i c u l t , h o w e v e r , t o t r a n s l a t e o u r laboratory d a t a i n t o q u a n t i t i v e p r e d i c t i o n s o f yields f r o m a d u l t Macrocystis residing in artificially u p w e l l e d w a t e r . It is also risky t o i n t e r p o l a t e f r o m yield m e a s u r e m e n t s c o n d u c t e d a m o n g kelp beds. Product i v i t y in m o s t , if n o t a l l , of s o u t h e r n California's kelp beds appears t o be l i m i t e d f o r s u b s t a n t i a l p o r t i o n s of each year b y availability of n u t r i e n t s . N u t r i e n t supplies f r o m u p w e l l i n g a n d runoff are q u i t e variable a n d d i f f i c u l t t o define precisely. Nonetheless, reliable information c o n c e r n i n g yields e x p e c t e d f r o m a d u l t plants c o m p l e t e l y free of n u t r i e n t l i m i t a t i o n s is central t o assessing e c o n o m i c feasibility o f t h e m a r i n e f a r m c o n c e p t . T h e M a r i n e Farm Project presently is in t h e early stages of a large-scale field e x p e r i m e n t i n t e n d e d t o p r o v i d e k n o w l e d g e in t h i s critical area (Figure IV). One of our collaborators, Global M a r i n e D e v e l o p m e n t , Inc., revised t h e d e s i g n of a s t r u c t u r e , c o n c e i v e d at t h e Naval Ocean Systems Center, w h i c h w a s d e s i g n e d t o s u p p o r t a b o u t 1 0 0 a d u l t Macrocystis transplants and supply t h e m w i t h a b u n d a n t q u a n t i t i e s of w a t e r p u m p e d u p f r o m d e p t h s of a b o u t 4 5 0 m (Figure V). This "Test F a r m " w a s d e p l o y e d a b o u t 6 k m f r o m shore, near our laboratory h e a d q u a r t e r s , d u r i n g S e p t e m b e r 1 9 7 8 (Figure VI). W a t e r d e p t h at t h e site w a s a b o u t 5 5 0 m. In m i d - D e c e m b e r , a p r o t e c t i v e c u r t a i n w a s installed a r o u n d t h e w e s t e r n border o f t h e f a r m . This c u r t a i n w a s i n t e n d e d t o r e d u c e effects of c u r r e n t s , w h i c h are o f t e n greater t h a n 0.5 kt, o n t h e t r a n s p l a n t s a n d t o increase r e t e n t i o n t i m e of t h e artificially u p w e l l e d deep w a t e r w i t h i n t h e f a r m . T h e c u r t a i n w a s lost t o s t o r m s w i t h i n t h e f o l l o w i n g week. A n initial c r o p of 103 a d u l t Macrocystis f r o m local beds w a s t r a n s p l a n t e d t o t h e s t r u c t u r e d u r i n g N o v e m b e r - D e c e m b e r 1978. Our i n t e n t i o n w a s t o harvest a n d w e i g h u p p e r p o r t i o n s of t h e plants at a p p r o p r i a t e intervals t o d e t e r m i n e yields. W e m e a s u r e d g r o w t h rates a n d n u t r i e n t c o n c e n t r a t i o n s w i t h i n t h e tissues a n d in t h e w a t e r . W e also f o l l o w e d r e p r o d u c t i v e success o n solid substrates of t h e s t r u c t u r e , general health a n d appearance of t h e test plants, a n d t h e d e v e l o p m e n t of an associated c o m m u n i t y , as w e l l as other related p a r a m e t e r s (see Figure IV). T h e e x p e r i m e n t w a s s c h e d u l e d t o last f o r t w o years; h o w e v e r , all t r a n s p l a n t s had been d e s t r o y e d by t h e e n d of t w o m o n t h s , p r i m a r i l y d u e t o lack of p r o t e c t i o n f r o m c u r r e n t .

88

BIOMASS AS A N O N F O S S I L

FUEL

SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

20r-

I— Aug. 1977

1

Sept.

1

Oct.

ι Nov.

ι Otc.

I Jon. 1978

ι

ι Fab.

ι Mar.

ι Apr.

ι May

1

Junt

July

1

Aug.

4 Stpt.

Figure 3. Record snowing variation with time of mean specific growth rates ob­ tained from groups of juvenile Macrocystis sporophytes cultured in seawater pumped up from depths of 300 m. The batch cultures employed 40 L aquaria with the medium being renewed every other day.

fc

I d e n t i f y necessary inputs Amounts o f inputs needed I d e n t i f y c r i t i c a l species Determine uptake r a t e s Optimize inputs

OPERATIONAL SUPPORT STUDIES

Transplanting Plant maintenance F e r t i l i z i n g (juveniles) Mechanical monitoring Grazer c o n t r o l

OPERATIONAL ACTIVITIES

Growth assessments J u v e n i l e fronds Adult fronds Frond i n i t i a t i o n r a t e s Frond production r a t e s Harvest y i e l d s T i s s u e n u t r i e n t contents Nitrogen Trace metals General h e a l t h & appearance J u v e n i l e recruitment A s s o c i a t e d community

OUTPUT STUDIES

Biomass Juvenile plants A s s o c i a t e d species

OUTPUTS

Figure 4. Relationships between fluxes of energy and materials at the Test Farm and the principal groupings that constitute operation and monitoring of the Farm by staff of the California Institute of Technology

Biological Encrustations Diseases Competitors Grazers Nutrient r e c y c l i n g

Chemical Salinity Oxygen Nutrients Mean concentrations & s p e c i a t i o n Temporal v a r i a t i o n Vertical distributions H o r i z o n t a l d i s t r i b u t i o n (on farm)

Physical Water c l a r i t y Water temperature S t a b i l i t y o f deep water Water movements Entangling o f fronds Abrasion of t i s s u e s

ENVIRONMENTAL STUDIES

/

Sunlight Water Carbon d i o x i d e Mineral nutrients Toxicants or i n h i b i t o r s Substrate i n t e r a c t i o n s Biological interactions

INPUTS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

00 VO

s-

1

I 3*

a.

§

I

>

M H

S H Χ

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

BIOMASS AS A N O N F O S S I L

FUEL

SOURCE

W1 r s//

Figure 5.

\

\

\

The Test Farm structure with 100 adult Macrocystis transplants indicated diagrammatically

A 0.61-m-diameter polyethylene pipe tending down from the Test Farm supplies 30,000 L/min of nutrient-rich water from 450 m deep to fertilize the transplants. The deep water is discharged horizontally from three pipes 120° apart, just below the water line The striped cylindrical object is a buoy 17 m long that contains machinery and instrumentation. The plant holdfasts are at depths of 15-17 m. The radiating arms are about 32 m from tip to tip.

NORTH

ET

AL.

Freshwater and Marine Macrophytes

91

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

4.

Figure 6. Chart of the southern California coastline from Huntington Beach to Monarch Bay, showing locations of the Test Farm and other geographical features described in the text

92

BIOMASS AS A NONFOSSIL F U E L

SOURCE

To date, i n v e s t i g a t i o n s c o n c e r n e d w i t h biological o u t p u t s f r o m t h e Test Farm have e n c o m p a s s e d t w o d e f i n e d t i m e periods: A. D e c e m b e r 1 9 7 8 t o J a n u a r y 1 9 7 9 w h e n our a d u l t t r a n s p l a n t s existed at t h e F a r m ; B. M a y t o A u g u s t 1 9 7 9 w h e n dense p o p u l a t i o n s of j u v e n i l e plants a p p e a r e d , p r e s u m a b l y o f f s p r i n g arising f r o m spores liberated by t h e a d u l t t r a n s p l a n t s five m o n t h s previously. T h e m o s t i m p o r t a n t c o n c l u s i o n s a n d results f r o m o u r D e c e m b e r - J a n u a r y monitoring were:

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch004

1.

G r o w t h rates J u v e n i l e f r o n d s : A series of seven w e e k l y d e t e r m i n a t i o n s b e t w e e n D e c e m b e r 12 a n d J a n u a r y 2 9 y i e l d e d m e a n s t a n d a r d g r o w t h rates r a n g i n g f r o m 5.4 t o 7.4 p e r c e n t e l o n g a t i o n per day. These are w i t h i n t h e n o r m a l range for natural kelp beds at t h i s t i m e of year b u t t e n d t o lie p r i m a r i l y w i t h l o w e r p o r t i o n of t h e range. Percent of f r o n d s s h o w i n g a b n o r m a l l y s l o w g r o w t h rates a m o n g t a g g e d j u v e n i l e s ranged f r o m 6% t o 4 4 % of t h e t a g g e d recoveries, a relatively h i g h p r o p o r t i o n of a b n o r m a l juveniles. A b n o r m a l l y s l o w g r o w t h in j u v e n i l e f r o n d s o f t e n results f r o m severe d a m a g e t o or loss of t h e p a r e n t a d u l t f r o n d , t h a t nourishes g r o w t h of t h e j u v e n i l e t h r o u g h t r a n s l o c a t i o n of p h o t o s y n t h a t e . A d u l t f r o n d s : D a m a g e a n d m o r t a l i t y a m o n g a d u l t f r o n d s interferred w i t h assessment so t h a a statistically a d e q u a t e e v a l u a t i o n of g r o w t h rate w a s not possible. It w a s e s t a b l i s h e d , h o w e v e r , t h a t s o m e of t h e t a g g e d s p e c i m e n s g e n e r a t e d reasonable rates of p r o d u c t i o n of n e w blades.

2.

Plant M o r t a l i t y A b o u t 2 / 3 of t h e initial c o m p l e m e n t of t r a n s p l a n t s w e r e lost b e t w e e n D e c e m b e r 5 a n d J a n u a r y 5. M o r t a l i t y d u r i n g t h e n e x t 2 0 days d e c l i n e d , as o n l y a b o u t one t h i r d of t h e r e m a i n i n g plants d i s a p p e a r e d . A s h o r t b u t v i o l e n t squall o n J a n u a r y 3 0 d e s t r o y e d t h e last of t h e t r a n s p l a n t s . T a n g l i n g w i t h a n d abrasion on various parts of t h e test f a r m s t r u c t u r e w e r e t h e sole causes of plant m o r t a l i t y .

3.

N i t r o g e n c o n t e n t s of blade tissues Except for t h e final w e e k of J a n u a r y ( w h e n all of t h e r e m a i n i n g plants h a d suffered s i g n i f i c a n t d a m a g e ) , Ν c o n t e n t s r e m a i n e d a b o v e o n e p e r c e n t of t h e d r y w e i g h t . In our experience, t h i s represents a h e a l t h y n u t r i t i o n a l c o n d i t i o n . Of t h e 8 2 blade samples t a k e n , 7 1 % w e r e a b o u t 1.5% in Ν c o n t e n t . T h e h i g h e s t Ν c o n t e n t s w e r e a r o u n d 2.5% a n d c a m e f r o m c a n o p y blades d u r i n g t h e period w h e n t h e c u r t a i n w a s m o s t effective in r e t a i n i n g t h e u p w e l l e d w a t e r w i t h i n t h e f a r m . W e c o n c l u d e d t h a t , unlike our previous e x p e r i m e n t a l oceanic f a r m s , t h e t r a n s p l a n t s on t h i s test f a r m d i d not suffer f r o m i n a d e q u a t e n u t r i t i o n .

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D u r i n g January 1 9 7 9 , w e observed s o m e small j u v e n i l e Macrocystis a t t a c h e d t o several o f t h e p l a n t i n g buoys. Only a m o n t h had elapsed since t h e t r a n s p l a n t s had been i n t r o d u c e d . W e therefore p r e s u m e d t h a t these j u v e n i l e s reached t h e test f a r m as established m i c r o s c o p i c - s i z e d plants a n d d i d n o t arise f r o m spores liberated at t h e test f a r m . Usually at least t h r e e m o n t h s are needed f o r d e v e l o p m e n t of barely visible j u v e n i l e s f r o m settled kelp spores,

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and t h e t i m e m a y be longer if light or n u t r i e n t s are n o t o p t i m a l . In late A p r i l 1 9 7 9 , w e observed small plants d e v e l o p i n g near t h e ends o f t h e test f a r m dispersion hoses. By M a y , large n u m b e r s of juveniles w e r e a p p e a r i n g o n m o s t o f t h e solid surfaces of t h e test f a r m s t r u c t u r e d o w n t o d e p t h s as great as 3 0 m. C o n c e n t r a t i o n s w e r e sparse, h o w e v e r , b e l o w t h e level o f t h e t r a n s p l a n t i n g s u b s t r a t e (20 m). D e v e l o p m e n t b y most of these plants w a s p r o b a b l y s t i m u l a t e d n o t b y t h e artificially u p w e l l e d deep w a t e r b u t b y natural u p w e l l i n g w h i c h usually is m a x i m a l d u r i n g late s p r i n g . T h e j u v e n i l e recruits w e r e s t u d i e d intensively t o g a t h e r e c o l o g i c a l i n f o r m a t i o n t h a t m i g h t be useful f o r e n c o u r a g i n g a n d assisting kelp r e p r o d u c t i o n o n t h i s a n d o n o t h e r oceanic farms. Several n o t e w o r t h y results e m e r g e d . 1.

Total plant p o p u l a t i o n o n t h e substrate a r m s , cables, a n d p l a n t i n g b u o y s w a s e s t i m a t e d t o be 3 6 . 0 0 0 individuals.

2.

T e m p o r a l c h a n g e s in n i t r o g e n c o n t e n t s of kelp blades paralleled c h a n g e s in a m b i e n t nitrate c o n c e n t r a t i o n s (nitrate is a g o o d measure of natural u p w e l l i n g in this instance) a n d correlated w i t h c h a n g e s in rates of plant e l o n g a t i o n .

3.

Greatest plant m o r t a l i t y o c c u r r e d o n t h e s m o o t h p l a s t i c - c o a t e d cables. Plants w e r e p r o b a b l y easily d i s l o d g e d b y w a t e r m o v e m e n t s f r o m t h i s t y p e o f substrate. High m o r t a l i t y rates also o c c u r r e d a m o n g plants on t h e u p w e l l i n g hoses w h e r e barnacle e n c r u s t a t i o n s proliferated and c r e a t e d e x t r e m e l y abrasive surfaces. I n t e r m e d i a t e degrees o f m o r t a l i t y o c c u r r e d on t h e p l a n t i n g b u o y s a n d s u b s t r a t e arms. L o w e s t m o r t a l i t y appeared a m o n g plants a t t a c h e d t o t h e m o d e r a t e l y r o u g h surfaces p r o v i d e d b y polyester ropes.

4.

Tissue n i t r o g e n c o n c e n t r a t i o n a n d g r o w t h w a s e n h a n c e d s l i g h t l y b y " s p r a y i n g " a g r o u p of j u v e n i l e s o n a s u b s t r a t e a r m , t w i c e w e e k l y w i t h 1 M a m m o n i u m sulfate. Even greater e n h a n c e m e n t o c c u r r e d a m o n g plants close t o bags of O s m o c o t e pellets affixed t o t h e side of a substrate a r m . T h e pellets s l o w l y released n i t r o g e n a n d p h o s p h o r u s into t h e surrounding water.

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In s u m m a r y , perhaps t h e m o s t revealing result t h u s far f r o m t h e test f a r m e x p e r i m e n t w a s our failure t o observe increased g r o w t h rates a m o n g t h e j u v e n i l e f r o n d s d u r i n g t h e period w h e n t h e c u r t a i n w a s r e t a i n i n g t h e n u t r i e n t rich d e e p w a t e r a n d h i n d e r i n g effects by c u r r e n t s . This very p r e l i m i n a r y f i n d i n g s u g g e s t s t h a t g r o w t h of j u v e n i l e f r o n d s m a y be l i m i t e d b y t h e rate at w h i c h p h o t o s y n t h a t e c a n be t r a n s l o c a t e d d o w n w a r d f r o m t h e c a n o p y a n d not f r o m l i m i t e d availability of n u t r i e n t s (in t h i s p a r t i c u l a r case). W h i l e w e need m o r e e x p e r i m e n t a t i o n t o establish t h i s h y p o t h e s i s , t h e p o s s i b i l i t y has i m p o r t a n t i m p l i c a t i o n s for o p t i m i z i n g b i o m a s s p r o d u c t i o n . If t r a n s l o c a t i o n rate is i m p o r t a n t as a l i m i t i n g f a c t o r in j u v e n i l e f r o n d g r o w t h , t h e best s t r a t e g y w o u l d involve t r y i n g t o a c h i e v e a c o n d i t i o n w h e r e availability of l i g h t b e c o m e s t h e p r i n c i p a l l i m i t i n g factor. P r e s u m a b l y t h i s c o u l d be d o n e by increasing f r o n d d e n s i t y o n t h e f a r m (i.e. p l a c i n g t h e p l a n t s m o r e closely together). For t h e f u t u r e , o u r c o l l a b o r a t o r s at General Electric w i l l be i n s t a l l i n g a m o r e d u r a b l e p r o t e c t i v e c u r t a i n at t h e p e r i p h e r y of t h e test f a r m in late 1 9 7 9 . W e w i l l t h e n be able t o r e s u m e o u r studies m o n i t o r i n g health a n d m e a s u r i n g p r o d u c t i v i t y of a d u l t kelp plants b e i n g held in t h e artificially u p w e l l e d d e e p water. B I O M A S S STUDIES A T W H O I Studies by Ryther a n d c o - w o r k e r s of W H O I have been l o c a t e d for a b o u t three years at t h e Harbor Branch F o u n d a t i o n , Inc., f a c i l i t y in central Florida. The site has t h e a d v a n t a g e of a s u b t r o p i c a l l o c a t i o n w i t h access t o b o t h f r e s h w a t e r a n d m a r i n e e n v i r o n m e n t s . Earlier w o r k o n Neoagardhiella, Gracilaria. Hypnea, a n d o t h e r s e a w e e d s h a d been c o n d u c t e d d i r e c t l y at W H O I in M a s s a c h u s e t t s (20). Initial phases at t h e Florida site i n c l u d e d general surveys t o screen t h e m o s t p r o m i s i n g c a n d i d a t e species in t e r m s of ease of c u l t u r i n g and p e r f o r m a n c e in biomass p r o d u c t i o n . Of t h e 4 2 Floridanian seaweeds e x a m i n e d , Gracilaria tikvahiae s h o w e d greatest p r o m i s e (22). Effects on yields of f l o w rates, n u t r i e n t c o n c e n t r a t i o n s , w a t e r t e m p e r a t u r e , solar r a d i a t i o n , salinity, a n d plant d e n s i t y w e r e e x a m i n e d for Gracilaria a n d others ( 2 1 . 23). Yields by Gracilaria w e r e d e t e r m i n e d on a w e e k l y basis t h r o u g h o u t t h e year for plants held in f l o w i n g s y s t e m s e n r i c h e d w i t h a m m o n i u m or n i t r a t e (10 t o 1 0 0 μ M) a n d w i t h p h o s p h a t e (1 t o 10 μ M) a n d essential t r a c e metals. Cultures w e r e e x p o s e d t o a m b i e n t c o n d i t i o n s of full s u n l i g h t a n d t e m ­ perature. T h e m e a n a n n u a l yield for Gracilaria w a s 34.8 d r y g / m - d a y (25.4 d r y ash-free t o n s / a c - y r ) . Progress w a s m a d e in e p i p h y t e c o n t r o l by s h a d i n g infested plants, by w i t h h o l d i n g n u t r i e n t s for 5 t o 10 days, or by use of an 2

4.

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ET AL.

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e p i p h y t e - g r a z i n g snail, Costoanarchis avara. Preliminary a t t e m p t s t o raise s e a w e e d species, i n c l u d i n g Gracilaria, in a s e m i - o c e a n i c m e d i u m (a p o w e r plant's d i s c h a r g e candal) w e r e n o t successful. A p p a r e n t l y n u t r i e n t c o n c e n t r a t i o n s w e r e i n a d e q u a t e . Of f o u r f r e s h w a t e r a n g i o s p e r m s e v a l u a t e d , w a t e r h y a c i n t h , Eichhornia crassipes. w a s m u c h superior t o d u c k w e e d a n d Hydrilla a n d w e l l a b o v e p e n n y w o r t ( p e n n y w o r t , h o w e v e r , m i g h t be useful in c l i m a t e s colder t h a n t o l e r a t e d b y h y a c i n t h a n d t h e others). M e a n a n n u a l p r o d u c t i v i t y b y h y a c i n t h w a s 24.2 d r y g / m - d a y (range 5.3 t o 34.9 g / m - d a y ) or 2 8 d r y ash-free t o n s / a c - y r ) . Yields f r o m natural stands o f h y a c i n t h s a n d o t h e r f r e s h - w a t e r m a c r o p h y t e s gave values less t h a n 1/3 of those o b t a i n e d f r o m laboratory studies. O p t i m a l c u l t u r i n g d e n s i t y for h y a c i n t h s in t e r m s of biomass p r o d u c t i o n w a s in t h e range 10 t o 2 0 w e t k g / m w h i l e t h e range w a s l o w e r for Gracilaria, ca. 1 t o 4 k g / m . H y a c i n t h p r o d u c t i v i t y e s t i m a t e d b y n u t r i e n t uptake m e a s u r e m e n t s y i e l d e d m e a n values a b o u t 12 percent b e l o w similar d e t e r m i n a t i o n s b y t h e m e t h o d of w e i g h t gains. P r o d u c t i v i t y on a large p l a n t a t i o n c o u l d p r o b a b l y be e s t i m a t e d m o r e easily b y n u t r i e n t u p t a k e m e a s u r e m e n t s t h a n b y w e i g h t c h a n g e s . T h e presence of h y a c i n t h s increased e v a p o r a t i v e and t r a n s p i r a t i o n a l w a t e r losses f r o m t h e c u l t u r i n g c o n t a i n e r b y a b o u t 1.7 t i m e s a b o v e t h a t d u e t o s i m p l e e v a p o r a t i o n f r o m o p e n w a t e r . Studies e v a l u a t e d s u i t a b i l i t y as fertilizer f o r h y a c i n t h c u l t u r e o f residues f r o m digesters o p e r a t e d o n h y a c i n t h biomass. Residues s u p p o r t e d 5 4 p e r c e n t higher g r o w t h c o m p a r e d t o t h e c h e m i c a l l y - e n r i c h e d s t a n d a r d m e d i u m used in r o u t i n e c u l t u r i n g . Efficiency o f utilization of n i t r o g e n in t h e s y s t e m h y a c i n t h - d i g e s t e r r e s i d u e - h y a c i n t h w a s 3 1 percent. T h e digester p r o d u c e d 0 . 4 1 of gas (60 p e r c e n t m e t h a n e ) per g r a m volatile solids f r o m h y a c i n t h s . Similar studies w e r e progressing u s i n g Gracilaria as t h e e x p e r i m e n t a l plant. Dr. Ryther's g r o u p e x p e c t s t o e x p a n d t h e operational scales for c u l t u r i n g Gracilaria a n d Eichhornia, u l t i m a t e l y e x p e r i m e n t i n g w i t h p o n d s of o n e q u a r t e r acre size. 2

2

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2

2

Dr. Joel G o l d m a n is c u r r e n t l y i n v e s t i g a t i n g utilization of inorganic c a r b o n b y algae t o p r o v i d e f a c t u a l bases f o r e n s u r i n g t h a t c u l t u r e s never b e c o m e l i m i t e d b y this e l e m e n t a n d f o r e c o n o m i c analysis. Studies t h u s far have u t lized m i c r o a l g a e b u t t h e scope w i l l e v e n t u a l l y be e x p a n d e d t o i n c l u d e m a c r o p h y t e s . Studies i n c l u d e t h e role of c a r b o n d i o x i d e a n d of b i c a r b o n a t e as c a r b o n sources, effects of p H a n d o f m i x i n g , a n d d e f i n i n g c u l t u r i n g c o n d i t i o n s required for t h e m o s t e c o n o m i c a n d efficient means f o r s u p p l y i n g a d e q u a t e c a r b o n t o mass c u l t u r e s of algae (24). Tolerance t o a b n o r m a l l y l o w or h i g h p H values varied a m o n g algal species. Utilization of b i c a r b o n a t e as a c a r b o n source reduces t h e b u f f e r i n g c a p a c i t y of natural w a t e r s . The pH t e n d s t o rise because h y d r o g e n ions are assimilated a n d h y d r o x y l ions are liberated as b i c a r b o n a t e is utilized. G o l d m a n c o n t r o l l e d p H w i t h o r g a n i c buffers in o n e e x p e r i m e n t a l series w i t h Phaeodactylum tricornutum. This marine d i a t o m

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utilized b i c a r b o n a t e at efficiencies of 9 0 t o 100 p e r c e n t across c o n c e n t r a t i o n s r a n g i n g up t o m o r e t h a n f o u r f o l d above natural levels. G o l d m a n c o n c l u d e d t h a t b i c a r b o n a t e s h o u l d easily be able t o fulfill c a r b o n r e q u i r e m e n t s of p r o d u c t i v e species s u c h as Phaeodactylum, provided that m i x i n g a n d p H c o n t r o l are adequate. Bicarbonate w a s as g o o d a c a r b o n source as gaseous c a r b o n d i o x i d e for t h e f r e s h w a t e r C h l o r o p h y t e Chlorella vulgaris, b u t not for Scenedesmus obliquus. under batch conditions. G o l d m a n c o n c l u d e d t h a t t h e rate of s u p p l y of gaseous c a r b o n d i o x i d e c o n t r o l l e d its availability t o t h e plants, rather t h a n t h e c o n c e n t r a t i o n of c a r b o n d i o x i d e in t h e gas m i x t u r e b u b b l e d t h r o u g h t h e m e d i u m .

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ACKNOWLEDGEMENTS C u r r e n t research s u p p o r t f r o m t h e U.S. D e p a r t m e n t of Energy u n d e r Contract E(04-3)-1275 a n d f r o m t h e Office of Sea Grants u n d e r Grant No. 0 4 - 5 - 1 5 8 - 1 3 is g r a t e f u l l y a c k n o w l e d g e d , as w e l l as past s u p p o r t f r o m t h e U.S. N a v y a n d t h e National Science F o u n d a t i o n . A d v i c e f r o m Drs. M i c h a e l Barcelona, George J a c k s o n , J a m e s M o r g a n , a n d Clair Patterson, a n d f r o m M i c h a e l B u r n e t t w a s invaluable. Our t h a n k s are also d u e t o Drs. J o h n H. Ryther a n d Joel C. G o l d m a n for h e l p f u l discussions a n d for s u p p l y i n g us w i t h t h e i r m o s t recent i n f o r m a t i o n c o n c e r n i n g t h i e r studies. The a u t h o r s are especially g r a t e f u l t o Sylvia Garcia for t h e A A S d e t e r m i n a t i o n s . T h a n k s are d u e t o t h e Kerckhoff M a r i n e L a b o r a t o r y staff for assistance in all aspects of t h e w o r k : Peter A l l i s o n . Brian A n d e r s o n , Barbara B a r t h , Randall B e r t h o l d , Elliott Crooke, Henry Fastenau. Laurence Jones, V i c t o r i a Kromer, V i r g i n i a M a r t i n i , Frank Sager. T h o m a s S t e p h a n , a n d M a r y A n n W h e e l e r . In part, t h i s w o r k is a result of research s p o n s o r e d by N O A A Office of Sea Grants, D e p a r t m e n t of Commerce.

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REFERENCES 1.

Gerard, V. A. Ph.D. Thesis, University of California, Santa Cruz, Calif., 1976.

2.

Lobban, C. S. Phycologia 1978 17, 196-212.

3.

Rosenthal, R. J.; Clarke, W. D.; Dayton, P. K. Fish. Bull. 1974 72, 670-84.

4.

Neushul, M. In "Biology of Giant Kelp Beds (Macrocystis) in California"; W. J. North, Ed.; J. Cramer, : Lehre, Germany, 1971; pp 241-54.

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Sargent, M. C.; Lantrip, L. W. Am. J. Bot. 1952 39, 99-107.

6.

Clendenning, Κ. Α.; Sargent, M. C. In "Biology of Giant Kelp Beds (Macrocystis) in California"; W. J. North, Ed.; J. Cramer,: Lehre, Germany, 1971; pp 169-90.

7.

Lobban, C. S. Ph.D. Thesis, Simon Fraser University, Burnaby, Canada, 1976.

8.

Parker, B. C. In "Biology of Giant Kelp Beds (Macrocystis) in California"; W. J. North, Ed.,; J. Cramer: Lehre, Germany, 1971; pp 190-95.

9.

North, W. J. "Proceedings", Symposium on Chilean Algae, Universidad Catolica, Santiago, Chile, Nov. 1978.

10. North, W. J. In "Biology of Giant Kelp Beds (Macrocystis) in California"; W. J. North, Ed.; J. Cramer: Lehre, Germany, 1971; pp 1-97. 11.

North, W. J. "Proceedings", Fuels from Biomass Symposium, University of Illinois, Urbana-Champaign, 1977; pp 99-114.

12.

McPeak, R. H.; Fastenau, H.; Bishop, D. Pasadena, Calif., 1972-73, California Institute of Technology, Kelp Habitat Improvement Project, Annual Report 91125; pp 57-73.

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Jackson, G. Α.; North, W. J., China Lake, Calif., 1973, Final Report, Contract No. N60530-73-MV176. U.S. Naval Weapons Center.

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North, W. J., J. Fish. Res. Board Can. 1976 33, 1015-23.

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Wilson, K. C.; Haaker, P. L.; Hanan, D. A. "The Marine Plant Biomass of the Pacific Northwest Coast"; R. W. Krauss, Ed.; Oregon State University Press: Corvallis, 1977; pp 183-202.

16. North, W. J. "Proceedings of the Symposium on Biological Conversion of Solar Energy", University of Miami, 1977; Academic Press: New York, 1977; pp 347-61. 17. Ashare, E.; Augenstein, D. C.; Sharon, A. C.; Wentworth, R. L.; Wilson, E. H.; Wise, D. L. Cambridge, Mass., 1978, DOE Report 1738R.

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18.

North, W. J. "Symposium Papers", Clean Fuels from Biomass and Wastes; Institute of Gas Technology: Chicago, Ill., 1977; pp 128-40.

19. Morel, F. M. M.; Rueter, J. G.; Anderson, D. M.; Guillard, R.R.L. J. Phycol. 1979, 15, 135-41. 20.

McDuff, R. E.; Morel, F.M.M. Description and use of the chemical equilibrium program REDEQL2. Tech. Rpt. EQ-73-02, 1975, p 82.

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Ryther, J. H.; Lapoints, B. E.; Stenberg, R.W.; Williams, L. D. "Proceedings" Fuels from Biomass Symposium; University of Illinois Press: Urbana, Ill., 1977; pp 83-98.

22. Ryther, J. H.; Williams, L. D.; Hanisak, M. D.; Stenberg, R. W.; DeBusk, T. A. "Proceedings," Third Annual Biomass Energy Systems Conference; SERI: Golden, Colo., in press. 23. Ryther, J. H.; Williams, L. D.; Hanisak, M. D.; Stenberg, R. W.; DeBusk, T. A. "Proceedings," Second Annual Symposium on Fuels from Biomass; Rensselaer Polytechnic Institute: Troy, N.Y. 1978; pp 947-89. 24.

Goldman, J. C. Proceedings," Third Annual Biomass Energy Systems Conference; SERI: Golden, Colo., in press.

RECEIVED M A Y 19,

1980.

5 Energy from Fresh and Brackish Water Aquatic Plants JOHN R. BENEMANN

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

Ecoenergetics, Incorporated, 5691 Van Fleet Avenue, Richmond, CA 94804

The large-scale cultivation of aquatic plants and their conversion to fuels has often been suggested in recent years as a potential energy source. Large-scale systems for cultivation of microalgae (1,2), cattails (3,4), and water hyacinths (5,6) have been proposed without, however, sufficient supporting analysis. Historically, the concept of cultivating aquatic biomass for energy dates back twenty-five years when microalgae were suggested as a renewable source of methane (7). This concept was demonstrated experimentally a few years later (8) and subjected to a general analysis which, based on very favorable assumptions, concluded that the concept could be a low-cost future energy source (9). Recently, a more detailed analysis, also based on very favorable assumptions, again concluded that microalgae could be economically cultivated in large-scale systems and converted to fuels (10). A related study (11) using a similar design concept and analysis, concluded that emergent aquatic plants (e.g.. water hyacinths) would be favored over microalgae because they would not be limited by the availability of an enriched carbon dioxide source. All of these analyses and proposals were based on relatively superficial considerations of the requirements for cultivation, harvesting, and conversion of these aquatic plants. This review attempts to advance the concepts of aquatic biomass energy farming based on a more detailed review of the biological data base and the technical limitations and potentials for cultivating aquatic plants. This review is based, in part, on recent reports and publications by the author and colleagues (12,13).

0097-6156/81/0144-0099$05.75/0 © 1981 American Chemical Society

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A r e v i e w of t h e a q u a t i c plant literature (13) reveals t h a t s u b m e r g e d plants, brackish w a t e r m a r s h plants (Spartina). small f l o a t i n g plants ( d u c k w e e d ) , a n d b l u e - g r e e n algae are not as p r o d u c t i v e as e m e r g e n t f r e s h w a t e r m a r s h plants (cattails, bull rushes), w a t e r h y a c i n t h s , a n d p l a n k t o n i c g r e e n algae. T h u s , t h i s paper w i l l c o n s i d e r o n l y t h e latter plant t y p e s . Particular a p p l i c a t i o n s of these p l a n t s in c h e m i c a l p r o d u c t i o n a n d utilization of m a r g i n a l lands a n d w a t e r

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

resources are c o n s i d e r e d . Specific c o n c e p t u a l s y s t e m s are p r e s e n t e d for each t y p e of a q u a t i c plant. T h e p o t e n t i a l of h a r v e s t i n g n a t u r a l , u n m a n a g e d s t a n d s of m a r s h plants or a q u a t i c w e e d s (e.g.. w a t e r hyacinths) a n d c o n v e r t i n g t h e biomass t o fuels is c o n s i d e r e d small by this a u t h o r (12!). H o w e v e r , m a n a g e m e n t a n d h a r v e s t i n g of natural s t a n d s of a q u a t i c p l a n t s is t a k i n g place for a q u a t i c w e e d c o n t r o l (e.g.. w a t e r hyacinths) a n d for w i l d l i f e m a n a g e m e n t (marsh plants). T h u s , t h i s o p t i o n s h o u l d be c o n s i d e r e d t o a greater e x t e n t in t h e f u t u r e . It is not possible, at present, t o p r o v i d e either a d e t a i l e d resource base assessment (e.g.. p o t e n t i a l l y available w a t e r , l a n d , or n u t r i e n t resources), or a d e t a i l e d cost analysis of a q u a t i c p l a n t p r o d u c t i o n . T h u s , t h i s r e v i e w presents general c o n c e p t s of a q u a t i c biomass f a r m i n g e x e m p l i f i e d by t h r e e s y s t e m s — m i c r o a l g a e f a r m i n g for lipid fuel a n d c h e m i c a l s p r o d u c t i o n , cattail c u l t i v a t i o n for c o n v e r s i o n t o alcohol fuels, a n d g r o w i n g w a t e r h y a c i n t h s for m e t h a n e gas g e n e r a t i o n . W a s t e w a t e r a q u a c u l t u r e a p p l i c a t i o n s are not c o v e r e d in this r e v i e w nor are t h e a c t u a l c o n v e r s i o n processes by w h i c h a q u a t i c biomass w o u l d be c o n v e r t e d t o fuels. M I C R O A L G A E F A R M I N G FOR L I P I D S D u r i n g a n d after W o r l d W a r II. b o t h in G e r m a n y a n d t h e U.S.. t h e h i g h lipid c o n t e n t of m i c r o a l g a e (up t o 8 6 % for Chlorella) a t t r a c t e d a t t e n t i o n as a possible source of fats a n d oils (14-16). This led t o a c o n c e r t e d effort in t h e U.S. in t h e late 1940's a n d early 1950's t o d e v e l o p m i c r o a l g a e p r o d u c t i o n t e c h n o l o g y as a p o t e n t i a l source of f o o d . This w o r k , w h i c h c u l m i n a t e d in a pilot-scale p r o j e c t by t h e A r t h u r D. Little Co.. s u p p o r t e d by t h e Carnegie I n s t i t u t e , is r e p o r t e d in t h e book e d i t e d by B u r l e w e n t i t l e d Algae Cultivation from Laboratory to Pilot Plant (V7). A l t h o u g h n o t d i r e c t l y a c k n o w l e d g e d , t h e results of t h i s early w o r k w e r e not e n c o u r a g i n g ; t h e large plastic t u b e used for t h e pilot-scale algal c u l t u r e w a s s u s c e p t i b l e t o leaks a n d o v e r h e a t i n g . Harvesting p r o v e d q u i t e d i f f i c u l t , r e q u i r i n g expensive c e n t r i f u g e s . Recycling of t h e m e d i a appeared t o give s o m e p r o b l e m s . In general, costs far o u t w e i g h e d benefits in p r o t e i n or lipids p r o d u c t i o n .

5.

BENEMANN

Energy from Aquatic Plants

101

S u b s e q u e n t w o r k w a s c o n c e n t r a t e d m a i n l y in J a p a n , leading t o t h e d e v e l o p m e n t of very " h i g h t e c h n o l o g y " algal c u l t i v a t i o n systems, s o m e of w h i c h even g r e w t h e algae h e t e r o t r o p h i c a l l y (on acetic acid) u n d e r sterile f e r m e n t a t i o n c o n d i t i o n s (18). P r o d u c t i o n costs o f t h e algal biomass p r o d u c e d by s u c h s y s t e m s are very h i g h , e x c e e d i n g $ 1 0 , 0 0 0 / t o n (dry) d u e t o t h e use o f c e n t r i f u g e s , d r y i n g plants, a n d elaborate p o n d i n g systems. T h e algae are

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

used as a health f o o d a n d specialty feed (e.g.. f o r t r o p i c a l fish). In t h e 1960's. a n u m b e r of projects w e r e i n i t i a t e d for t h e use of m i c r o a l g a e in a q u a c u l t u r e f o o d c h a i n s (see l â f o r a review), f o r f o o d p r o d u c t i o n (particularly by t h e G e r m a n a n d Czechoslovakia g r o u p s , see (20), a n d f o r w a s t e w a t e r t r e a t m e n t a n d feed p r o d u c t i o n . H o w e v e r , at present, o n l y o n e c o m m e r c i a l p r o d u c t i o n s y s t e m is o p e r a t i n g t o date o u t s i d e o f t h e Far East — t h e Spirulina p r o d u c t i o n plant o f t h e Sosa T e x c o c o C o m p a n y near M e x i c o City (2JJ. T a k i n g a d v a n t a g e of t h e n a t u r a l l y favorable c o n d i t i o n s in s o m e areas o f t h e i r b i c a r b o n a t e e v a p o r a t i o n p o n d s , this c o m p a n y operates a 10 hectare Spirulina p r o d u c t i o n p o n d f o r t h i s f i l a m e n t o u s b l u e - g r e e n alga. H a r v e s t i n g is n o p r o b l e m , as t h e long f i l a m e n t s a l l o w easy r e m o v a l by relatively w i d e - m e s h screens. T h e s p r a y - d r i e d p r o d u c t sells f o r a b o u t $ 5 , 0 0 0 / t o n , m a i n l y t o t h e Japanese market. P r o d u c t i o n costs are u n k n o w n . The o t h e r major practical use o f m i c r o a l g a e w a s in w a s t e w a t e r t r e a t m e n t a p p l i c a t i o n s (22). M i c r o a l g a e are capable of p r o v i d i n g t h e dissolved o x y g e n required in m e e t i n g t h e biological o x y g e n d e m a n d of m u n i c i p a l a n d other w a s t e w a t e r s . S e w a g e o x i d a t i o n p o n d s have been used in t h e U.S. f o r m a n y d e c a d e s ; t h e y are s i m p l e e a r t h e n lagoons, one t o t w o meters deep, a n d u p t o f i f t y acres or m o r e in size. Several lagoons are usually o p e r a t e d in series t o effect w a s t e w a t e r t r e a t m e n t . T h e m i c r o a l g a e c u l t u r e is neither c o n t r o l l e d n o r h a r v e s t e d ; t h u s , n o t r u e c u l t i v a t i o n process is i n v o l v e d . O s w a l d in t h e early 1 9 5 0 ' s applied m o r e c o n t r o l l e d " h i g h r a t e " p o n d s t o w a s t e w a t e r t r e a t m e n t (23). These w e r e essentially s h a l l o w (20-50 c m ) , m e c h a n i c a l l y m i x e d , a n d baffled p o n d s w h i c h a l l o w e d m a i n t e n a n c e of a dense c u l t u r e of m i c r o a l g a e w h i c h c o u l d m o r e e f f i c i e n t l y p r o v i d e t h e o x y g e n required in w a s t e w a t e r t r e a t m e n t . A l t h o u g h these s y s t e m s w e r e s t u d i e d in detail b o t h in t h e U.S. (24) a n d m o r e recently in Israel (25), o n l y f e w p o n d s y s t e m s of this t y p e have been built. This is because t h e h i g h algae c o n c e n t r a t i o n makes h a r v e s t i n g i m p e r a t i v e , and m i c r o a l g a e h a r v e s t i n g w a s expensive. The a u t h o r , in association w i t h W . J . O s w a l d , over t h e past four years has s t u d i e d l o w e r cost algal p r o d u c t i o n a n d h a r v e s t i n g systems f o r a p p l i c a t i o n t o b o t h w a s t e w a t e r t r e a t m e n t a n d energy p r o d u c t i o n (26-28). The research has c o n c e n t r a t e d o n t h e p r o b l e m s o f m i c r o a l g a l harvesting a n d species c o n t r o l in e x p e r i m e n t a l a n d pilot-scale s e w a g e h i g h - r a t e p o n d systems. T h e first

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c o n c e p t s t u d i e d w a s t o harvest t h e algae by m i c r o - s c r e e n s — r o t a t i n g b a c k w a s h e d fine m e s h screening devices. T h e critical p a r a m e t e r is t h e screen o p e n i n g — a 2 6 m i c r o n screen size w a s c h o s e n as t h e m o s t cost effective. This required m a i n t a i n i n g in t h e p o n d s colonial t y p e s of algae as average single cell algae sizes range b e t w e e n 2 a n d 2 0 m i c r o n s . H o w e v e r it w a s e x p e r i m e n t a l l y d e t e r m i n e d t h a t relatively l o n g d e t e n t i o n t i m e s w e r e required t o a l l o w m a i n t e n a n c e of c o l o n i a l g r e e n algal c u l t u r e s w h i c h resulted in a s i g n i f i c a n t loss of b i o m a s s p r o d u c t i v i t y (about haJf of t h e total) (28). T h e e m p h a s i s s h i f t e d t o an even l o w e r c o s t m e t h o d of algal h a r v e s t i n g — s p o n t a n e o u s f l o c c u l a t i o n of t h e algae, f o l l o w e d by s e d i m e n t a t i o n of t h e m i c r o a l g a e c u l t u r e . T h e results of over t w o years of s t u d y , w i t h t h e last year b e i n g d e v o t e d t o pilot-scale (0.1 hectare) d e m o n s t r a t i o n of t h i s process, have s h o w n t h a t it is possible t o c u l t i v a t e y e a r - r o u n d a m i c r o a l g a l c u l t u r e t h a t exhibits both high productivity and good harvestability (flocculations e d i m e n t a t i o n ) (29). Data f r o m over o n e year of o p e r a t i o n is s h o w n in Table I. A l t h o u g h t h i s process remains t o be d e m o n s t r a t e d in p r a c t i c e , it appears t h a t l o w - c o s t algal h a r v e s t i n g is feasible. A n e c o n o m i c analysis of m i c r o a l g a l b i o m a s s p r o d u c t i o n m u s t be based o n a n u m b e r of a s s u m p t i o n s , o n l y one of w h i c h is t h e availability (and practicality) of a l o w - c o s t h a r v e s t i n g process. O t h e r a s s u m p t i o n s m u s t be m a d e a b o u t t h e specific d e s i g n a n d t h e c a p i t a l cost of t h e p o n d s y s t e m (e.g.. lined vs. u n l i n e d ) . t h e a v a i l a b i l i t y a n d q u a l i t y of w a t e r , t h e feasibility of r e c y c l i n g w a t e r , t h e n u t r i e n t utilization e f f i c i e n c y , t h e source a n d transfer e f f i c i e n c y of c a r b o n (carbon d i o x i d e ) , a n d t h e p r o c e s s i n g costs after t h e initial h a r v e s t i n g (defined as r o u g h l y t h e first 1 0 0 - f o l d c o n c e n t r a t i o n ) . M o r e i m p o r t a n t l y , a s s u m p t i o n s m u s t be m a d e a b o u t t h e a b i l i t y t o g r o w c e r t a i n algal species or t y p e s , p r e v e n t i n g c u l t u r e instabilities (e.g., z o o p l a n k t o n prédation), m a n a g e m e n t r e q u i r e m e n t s , a n d p r o d u c t i v i t y . T h e reason so m a n y d i f f e r e n t a s s u m p t i o n s are r e q u i r e d is t h e lack of d e t a i l e d a n d / o r available i n f o r m a t i o n , i n c l u d i n g p r o d u c t i v i t y d a t a . T h e Japanese a n d Far East s y s t e m s m e n t i o n e d a b o v e are not a g o o d g u i d e because no f i r s t - h a n d t e c h n i c a l d a t a are available; these are c o m m e r c i a l p r o p r i e t a r y projects. Similarly, t h e M e x i c a n Spirulina p r o d u c t i o n project is not d e s i g n e d for o p t i m a l p r o d u c t i o n , as it o n l y i m p r o v e s o n t h e natural s i t u a t i o n . H o w e v e r , an overall p r o d u c t i o n f i g u r e of 1 0 - 1 2 g / m - d a y averaged over 10 m o n t h s has been r e p o r t e d (21). T h e best p r o d u c t i v i t y d a t a for large-scale systems (above 100 m ) are available f r o m h i g h - r a t e s e w a g e o x i d a t i o n p o n d s as s u m m a r i z e d in Table II. Even in this case, serious short c o m i n g s of t h e data are a p p a r e n t w h e n r e v i e w i n g t h e original literature; s e w a g e solids, for e x a m p l e , are i n c l u d e d in these p r o d u c t i o n figures. H o w e v e r , based o n available d a t a , a biomass p r o d u c t i o n rate of 4 0 - 5 0 t / h a - y r appears feasible a n d p r a c t i c a l . 2

2

8.5 15.8 20.1 22.6 22.0 21.7 19.9 16.3

25.5 25.5 11.6 4.7 4.9 6.4

2

85 71 83 64 56 74 74 53 74 91 89 94 87 69 8.0 11.3 9.8 6.6 4.7 9.3 16.5 16.2 21.3 20.2 35.5 35.6 35.5 27.8 23.5 22.7 3.1 3.3 4.2 5.2 6.9 12.0 17.7 20.6 20.2 19.1 18.7 13.7

2

92 89 27 70 85 82 81 76 88 91 92 88 94 84

2

East Pond 24-hr Imhoff Cone* % removal

Total Production g/m -da y

Harvestable Production g/m -da y

W e s t Pond 24-hr Imhoff Cone* % removal

• Imhoff cone removals indicate t h e percentage of algal biomass that will spontaneously flocculate and settle

Sept 7 8 Oct Nov Dec Jan 7 9 Feb Mar Apr May Jun Jul Aug Sep Oct

Date

Total Production g/m - d a y

Table I. S U M M A R Y OF 0.1 H E C T A R E HIGH-RATE P O N D OPERATIONS A T RICHMOND, CALIFORNIA 1 9 7 8 - 7 9 . The two ponds were operated at variable detention times, depths, and mixing speeds, accounting for differences in productivity and harvestability (29).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

12 15

30 days summer 6 0 days Sep-Oct

5 days 2.6 days

variable

variable (semi-batch)

6 days 9.3 days

3 days fixed 4.5 days variable

3 days 3 days

Duration of Time

29

34

.32.

32

ai

.22

Ref.

*The productivities were generally not corrected for non-algal sewage solids (except for Shelef et al. 1977) and sometimes calculated indirectly from t h e data presented.

2500 1000

Richmond. Calif.

average of yearround experiments

-15-25

100

Manila. Philippines

1-2 week ave. summer

— 14-18

646

Southern California

30 days Mar 30 days A p r

14.3 17.4

2800

365 days 365 days

30.2 20.2

10 days A u g 2 mos. Nov-Dec

Productivity* Experiment

120 150

2

Scale g/m -day

25.3 12.2

2

70

m

Melbourne, Australia

Haifa, Israel

Richmond, Calif.

Location

Table II. PRODUCTIVITIES OF M I C R O A L G A L C U L T U R E S IN HIGH-RATE S E W A G E P O N D S

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

5.

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105

Energy from Aquatic Plants

D e p e n d i n g o n a s s u m p t i o n s , c a l c u l a t e d p r o d u c t i o n costs of m i c r o a l g a l biomass can a m o u n t t o as little as $ 5 0 / t o n or u p t o several t h o u s a n d dollars per t o n . One analysis, carried o u t b y this a u t h o r , w a s d e s i g n e d t o explore t h e l o w e r cost limits o f algal biomass p r o d u c t i o n at very large scales a n d arrived at a p r o d u c t i o n cost of $ 5 0 / d r y t o n . This cost analysis w a s based o n an u n l i n e d p o n d s y s t e m c o n s i s t i n g of very large i n d i v i d u a l p o n d s (100 acres), d i v i d e d into long s e r p e n t i n e c h a n n e l s b y baffles, m i x e d b y p a d d l e - w h e e l s , a n d harvested b y a 4 8 - h r c y c l e b a t c h s e t t l i n g p o n d . H o w e v e r , this analysis w a s n o t realistic nor detailed in a n u m b e r of specifics. It is d o u b t f u l t h a t a n y m i c r o a l g a l s y s t e m c o u l d p r o d u c e a c o n c e n t r a t e d slurry of 2 - 5 % algae at a cost of less t h a n $ 2 0 0 / t o n (dry w e i g h t basis), even if w a t e r a n d n u t r i e n t s w e r e s u p p l i e d free of c h a r g e or e f f i c i e n t l y r e c y c l e d . T h u s , c o n t r a r y t o m a n y assertions, m i c r o a l g a e d o n o t appear t o be a suitable c h o i c e f o r e n e r g y f a r m i n g , as a p r o d u c t i o n cost of at least $ 1 0 / 1 0 Btu f o r " r a w " biomass is foreseen. This does n o t d e t r a c t f r o m t h e p o t e n t i a l of m i c r o a l g a l w a s t e w a t e r t r e a t m e n t - e n e r g y p r o d u c t i o n systems, w h e r e w a t e r a n d n u t r i e n t s are p r o v i d e d free of c h a r g e a n d c r e d i t is t a k e n f o r w a s t e w a t e r t r e a t m e n t . T w o i n d e p e n d e n t analyses o f a m i c r o a l g a l w a s t e w a t e r t r e a t m e n t - e n e r g y p r o d u c t i o n s y s t e m (based o n a s s u m p t i o n s o f c a r b o n or n i t r o g e n as l i m i t i n g nutrients) c o n f i r m e d t h a t m u n i c i p a l w a s t e t r e a t m e n t s y s t e m s c o u l d c o m p e t i t i v e l y p r o d u c e fuel f r o m m i c r o a l g a l b i o m a s s if h a r v e s t i n g c o u l d be carried o u t b y a l o w - c o s t process s u c h as m i c r o s t r a i n i n g (35). However, m u n i c i p a l w a s t e w a t e r s are a l i m i t e d resource base; even c o n s i d e r i n g energy c o n s e r v a t i o n , a m a x i m u m e n e r g y c o n t r i b u t i o n of a b o u t 0 . 1 % of national energy needs can be foreseen f r o m all w a s t e w a t e r a q u a c u l t u r e s y s t e m s , m i c r o a l g a e b e i n g o n l y o n e o f these t e c h n o l o g i e s (12). 6

O t h e r p o t e n t i a l c o n t r i b u t i o n s of m i c r o a l g a e f o r energy p r o d u c t i o n are of interest. One possibility is t h e p r o d u c t i o n o f speciality c h e m i c a l s , w h e r e h i g h u n i t prices c o u l d defray h i g h p r o d u c t i o n costs. S u c h c h e m i c a l s i n c l u d e fats, h y d r o c a r b o n s , p i g m e n t s , proteins, a n d p o l y s a c c h a r i d e s . Glycerol is a g o o d e x a m p l e of s u c h a p r o d u c t . It w a s d i s c o v e r e d a n u m b e r o f years ago t h a t t h e Dead Sea m i c r o a l g a e Dunaliella w i l l p r o d u c e a h i g h f r a c t i o n of its t o t a l d r y w e i g h t as g l y c e r o l , as m u c h as 5 0 % , in response t o h i g h salt c o n c e n t r a t i o n s in its m e d i u m , as a m e t h o d o f m a i n t a i n i n g a n o s m o t i c e q u i l i b r i u m (36.37). T h e p r o d u c t i o n of Dunaliella has been p r o p o s e d (38,39), a n d t h e d e v e l o p m e n t o f a n a p p r o p r i a t e t e c h n o l o g y is u n d e r w a y in Israel (38). The c o n c e p t is t o c o - p r o d u c e p r o t e i n a n d c a r o t e n e p i g m e n t s w i t h t h e glycerol. T e c h n i c a l l i m i t a t i o n s a p p a r e n t l y i n c l u d e h a r v e s t i n g a n d c u l t u r e stability. E c o n o m i c a l l y , t h e process is c o m p e t i n g w i t h g l y c e r o l p r o d u c e d d u r i n g f a t r e n d e r i n g , w h i c h sells f o r a b o u t $ 1 / k g , b u t w h i c h c o u l d be s u b j e c t t o s i g n i f i c a n t d o w n w a r d price shifts. A l s o , t h e p r o d u c t i o n of this algae requires very h i g h - s t r e n g t h brines a n d t h e p r o d u c t has a l i m i t e d market.Thus, a l t h o u g h it is t h e process

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nearest t o c o m m e r c i a l i z a t i o n , g l y c e r o l p r o d u c t i o n f r o m m i c r o a l g a e s h o u l d be c o n s i d e r e d as o n l y o n e of m a n y t y p e s of m i c r o a l g a l c h e m i c a l s y s t e m s . U n d e r fairly o p t i m i s t i c a s s u m p t i o n s a n d c o n d i t i o n s , it m a y be possible t o p r o d u c e h i g h - v a l u e l i q u i d h y d r o c a r b o n fuels f r o m m i c r o a l g a e . either by c o n v e r s i o n of t h e lipids or by d i r e c t h y d r o c a r b o n p r o d u c t i o n (40). In s o m e cases, very h i g h lipid c o n t e n t s have been reported in m i c r o a l g a e u p t o 8 6 % (of d r y w e i g h t ) (mostly C - C o f a t t y acids) for t h e u n i c e l l u l a r algae Chlorella (16) a n d a similar a m o u n t of l o n g - c h a i n ( C 2 6 ) h y d r o c a r b o n s in t h e colonial Botryococous (41). H o w e v e r , t h e s e h i g h c o n c e n t r a t i o n s are o n l y a c h i e v e d at t h e e n d of a l o n g period of l i g h t or n i t r o g e n l i m i t a t i o n , w h i c h result in e x t r e m e l y l o w rates of lipid p r o d u c t i o n . W h e t h e r it is possible t o o p t i m i z e lipid c o n t e n t a n d p r o d u c t i v i t y is u n c e r t a i n . A b o u t 2 0 % lipids are present in s e w a g e - g r o w n m i c r o a l g a e ( A a r o n s o n . personal c o m m u n i c a t i o n ) . H o w e v e r , t h a t appears s o m e w h a t l o w for p r o c e s s i n g purposes. It m a y be possible t o d o u b l e t h i s a m o u n t by s t r a t e g i c s c h e d u l e s of p o n d o p e r a t i o n s a n d n u t r i e n t additions w i t h o u t significantly lowering total productivity. A high product i v i t y of Phaeodactylum tricornutum w i t h a b o u t 4 0 % lipids, u s i n g very s h a l l o w c u l t u r e s , has been r e p o r t e d (42).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

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If fuel is t o be p r o d u c e d f r o m t h e algae, s o m e t y p e of s u b s i d y is required even w h e n c o m p e t i n g against spot m a r k e t prices for oil. O n e specific e x a m p l e involves t h e use of m i c r o a l g a l p o n d s in t h e e v a p o r a t i v e disposal of brackish a g r i c u l t u r a l d r a i n a g e w a t e r s w h o s e m a n a g e m e n t a n d disposal is a serious p r o b l e m in m a n y areas. T h u s , in t h e Central Valley of California, elaborate d i s c h a r g e s y s t e m s t h r o u g h artificial marshes are b e i n g p r o p o s e d . T h e use for m i c r o a l g a l p r o d u c t i o n of brackish-saline w a t e r s u n s u i t a b l e for c o n v e n t i o n a l a g r i c u l t u r e is o n e of t h e m o s t i m p o r t a n t p o t e n t i a l a p p l i c a t i o n s of m i c r o a l g a l p r o d u c t i o n systems. In c o n c l u s i o n t h e r e are several, n e a r - t e r m a p p l i c a t i o n s of m i c r o a l g a e biomass s y s t e m s in e n e r g y p r o d u c t i o n . M u n i c i p a l w a s t e w a t e r t r e a t m e n t s y s t e m s are t h e m o s t i m m e d i a t e ones f o l l o w e d by s y s t e m s d e s i g n e d t o p r o d u c e speciality c h e m i c a l s s u c h as polyols (e.g., glycerol), lipids, p o l y s a c c h a r i d e s a n d p i g m e n t s . The w a s t e w a t e r t r e a t m e n t credits, a n d lack of alternative uses for a q u a t i c biomass g r o w n o n s e w a g e , or t h e h i g h u n i t prices for s o m e c h e m i c a l s a l l o w t h e relatively h i g h p r o d u c t i o n costs forecast for m i c r o a l g a l biomass. S u c h a p p l i c a t i o n s have, h o w e v e r , an a g g r e g a t e p o t e n t i a l i m p a c t o n U.S. e n e r g y supplies t h a t m u s t be characterized as. at best, rather minor. Larger i m p a c t s i n v o l v i n g l i q u i d fuels p r o d u c t i o n m a y be possible if m i c r o a l g a l b i o m a s s p r o d u c t i o n c o u l d be c o m b i n e d w i t h t h e m a n a g e m e n t or disposal of brackish-saline a g r i c u l t u r a l w a s t e w a t e r s or by s i g n i f i c a n t t e c h n o l o g i c a l b r e a k t h r o u g h s s u c h as a c o n t i n u o u s a n d s p o n t a n e o u s s e t t l i n g or f l o t a t i o n process for algal h a r v e s t i n g .

5.

BENEMANN

Energy from Aquatic Plants

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

M a r s h plants have been relatively little e x p l o i t e d by m a n . T h e i m m e n s e stands of Phragmites (bullrush) c o v e r i n g a b o u t 6 0 % of t h e D a n u b e Delta, over 3 m i l l i o n hectares, are, perhaps, t h e best e x a m p l e of large-scale m a n a g e m e n t a n d h a r v e s t i n g o f a n e m e r g e n t marsh plant s y s t e m (43). T h e plants are harvested o n a sustainable yield basis a n d are used as fiber f o r paper m a n u f a c t u r e , as w e l l as s o m e t r a d i t i o n a l uses (construction) a n d c h e m i c a l s . In t h e U n i t e d States, large areas o f fresh brackish w a t e r marshes are c u t on a m o r e or less regular basis b o t h in t h e N o r t h e r n Lakes area and o n t h e East Coast t o i m p r o v e t h e o p e n w a t e r s u r f a c e - t o - m a r s h plants ratio o p t i m a l f o r m i g r a t o r y birds (about half a n d half). T h e c o n c e p t of using this t y p e of biomass s y s t e m f o r e n e r g y p r o d u c t i o n has been p r o p o s e d , particularly in M i n n e s o t a (3,4). M a r s h l a n d s border t h e areas o f m o s t o f t h e inland and coastal w a t e r s o f t h e w o r l d a n d t h e U n i t e d States. Detailed statistics o n m a r s h l a n d areas w e r e n o t r e v i e w e d b y t h i s a u t h o r ; h o w e v e r , a g o o d e s t i m a t e is t h a t in t h e U.S. a b o u t 2 0 m i l l i o n hectares of marshes exist w i t h an equal a m o u n t already d r a i n e d or filled since t h e e s t a b l i s h m e n t o f t h e U.S. M a j o r areas w i t h marsh lands are in t h e Great Lakes area, s u c h as M i n n e s o t a w i t h 4 m i l l i o n hectares, t h e s o u t h e r n states (Louisiana h a v i n g 3 m i l l i o n hectares), t h e East Coast s u c h as t h e Carolinas a n d t o a lesser e x t e n t , t h e S a c r a m e n t o Delta region o n t h e W e s t Coast. H o w e v e r , e x i s t i n g natural m a r s h lands are n o t likely t o be used f o r e n e r g y p r o d u c t i o n purposes t o a great e x t e n t unless t h e y c a n be d e m o n s t r a t e d t o be c o m p a t i b l e w i t h preservation of e n d a n g e r e d plant a n d a n i m a l species, are c o n d u c i v e t o w i l d l i f e m a n a g e m e n t , a n d e n h a n c e e n v i r o n m e n t a l a n d c o m m u n i t y benefits. S u c h a c c o m m o d a t i o n s m a y be possible. For e x a m p l e , m a n y m a r s h s y s t e m s are essentially m o n o c u l t u r e s o f specific species s u c h as Phragmites communis (bullrush) or Typha augustifolia (cattail). Thus, o n e e c o l o g i c a l o b j e c t i o n o f e n e r g y f a r m i n g is o v e r c o m e . A n o t h e r f a c t o r t h a t m u s t be c o n s i d e r e d is t h a t t h e c u l t i v a t i o n of these a n n u a l plants m a y n o t a l l o w c o m p l e t e harvest because t h a t w o u l d p r e v e n t rapid regeneration w i t h o u t e x p e n s i v e r e p l a n t i n g . This w o u l d allay t h e o b j e c t i o n against c l e a r - c u t t i n g as in tree e n e r g y f a r m i n g . For m a x i m a l w i l d l i f e m a n a g e m e n t , partial c u t t i n g is already u n d e r t a k e n as m e n t i o n e d above. The U. S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y p o l i c y is t o m i n i m i z e " a l t e r a t i o n s " of q u a l i t y or q u a n t i t y of t h e natural w a t e r s t h a t affect w e t l a n d s (44). These w e t l a n d s are recognized as sensitive e c o l o g i c a l areas a n d . t h u s , a n y neart e r m use o f s i g n i f i c a n t areas m u s t be c o n s i d e r e d unlikely. This a u t h o r envisions t h a t in t h e n e a r - t e r m , m a r s h p l a n t - e n e r g y systems c a n be established o n a l r e a d y - d i s t u r b e d or m a r g i n a l w e t l a n d areas, or w h e r e

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p l e n t i f u l w a t e r resources a l l o w s u c h h i g h l y c o n s u m p t i v e use. In t h e longer t e r m (e.g., t w e n t y years), s u c h systems c o u l d e x p a n d i n t o n a t u r a l , n o n sensitive marsh areas. T h u s , e v e n t u a l l y , a s i g n i f i c a n t f r a c t i o n of t h e large w e t l a n d resources in s o m e states c o u l d b e c o m e available for biomass p r o d u c t i o n a n d be i n t e g r a t e d into t h e h i g h e r uses of w i l d l i f e m a n a g e m e n t , fisheries p r o d u c t i o n , e n v i r o n m e n t a l p r o t e c t i o n , a n d recreation. Even o n e t e n t h of all present m a r s h l a n d s (e.g.. 2 m i l l i o n hectares), a s s u m i n g a s u s t a i n e d yield of 3 0 t / h a - y r . w h i c h is relatively m o d e s t , c o u l d p r o v i d e a s i g n i f i c a n t a m o u n t of fuels, a b o u t o n e q u a d ( 1 0 Btu) of r a w biomass (higher h e a t i n g value basis).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

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Before s u c h p r o g n o s i s c a n be m a d e , h o w e v e r , t h e c u l t i v a t i o n a n d h a r v e s t i n g t e c h n o l o g i e s for s u c h plants m u s t be d e v e l o p e d . This requires c o n s i d e r a t i o n of t h e biological c h a r a c t e r i s t i c s of these plants. T h e first aspect t o c o n s i d e r is t h e seasonality of these plants. T h e y g r o w very rapidly in t h e s p r i n g t i m e , d r a w i n g o n t h e c a r b o h y d r a t e stored t h e p r e v i o u s fall in t h e i r root t u b e r s (rhizomes). T h e s h o o t s very rapidly a t t a i n a v e r y h i g h leaf area index, e x c e e d i n g 10 in several reports, w h i c h is h i g h e r t h a n a n y c r o p p l a n t , even sugarcane. T h e v e r t i c a l leaf a r r a n g e m e n t a l l o w s g r a d u a l light a t t e n u a t i o n a n d . t h u s , efficient light utilization. Relatively h i g h t r a n s p i r a t i o n rates a l l o w for m a x i m a l p h o t o s y n t h e s i s rates, similar t o t h o s e of t r o p i c a l grasses, a l t h o u g h t h e C p a t h w a y of c a r b o n d i o x i d e f i x a t i o n is usually absent. M o s t reports o n p r o d u c t i v i t y of these plants o n l y m e a s u r e d t h e areal parts of t h e p l a n t s , w h e r e a s a s i g n i f i c a n t f r a c t i o n of t h e p h o t o s y n t h a t e is t r a n s l o c a t e d t o t h e roots w h i c h m a y c o n t a i n u p w a r d s of 4 0 % of t h e t o t a l biomass. T h u s , t h e d a t a o n a c h i e v a b l e p r o d u c t i v i t y by these plants is a f f e c t e d by t w o critical p r o b l e m s — t h e seasonality of their g r o w t h a n d t h e t r a n s l o c a t i o n t o their e x t e n s i v e root s y s t e m s . 4

T h e root s y s t e m of m a r s h p l a n t s e v o l v e d t o tolerate t h e anaerobic c o n d i t i o n s in t h e b o t t o m layers of w e t l a n d areas. T w o basic a d a p t a t i o n s are f o u n d — internal air passages e x t e n d i n g f r o m t h e leaf bases t o t h e rhizomes. Rhizomes are enlarged roots w h i c h a l l o w for storage of c a r b o h y d r a t e s a n d t h e e x t e n s i o n of lateral roots a n d n e w shoots. A n a e r o b i c roots are c a p a b l e of anaerobic m e t a b o l i s m w i t h e t h a n o l (instead of t h e lactic a c i d f o u n d in a n i m a l tissues) as e n d p r o d u c t (45). It is u n c e r t a i n h o w h i g h a rate of e t h a n o l p r o d u c t i o n c a n be s u s t a i n e d , b u t it is not t o o f a r - f e t c h e d t o p o s t u l a t e t h e possibility of a p p l y i n g g e n e t i c selections t o this s y s t e m t o a level w h i c h w o u l d a l l o w d i r e c t e t h a n o l p r o d u c t i o n f r o m harvested rhizomes. S o m e a d v a n t a g e s of s u c h a s y s t e m are t h e h i g h solids (substrate) c o n c e n t r a t i o n feasible a n d t h e s i m p l i f i c a t i o n of t h e process. In t h i s c o n t e x t t h e areal part of m a r s h plants are l o w e r in l i g n i n c o n t e n t t h a n terrestrial land plants, m a k i n g t h e m m o r e suitable for e n z y m a t i c or c h e m i c a l hydrolysis and s u b s e q u e n t use

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch005

for e t h a n o l i c f e r m e n t a t i o n s . T h u s , o n b o t h a c c o u n t s , these plants c a n be c o n s i d e r e d p r o s p e c t i v e sources o f e t h a n o l . W h e t h e r their fruits, w h i c h also c o n s u m e a large a m o u n t o f p h o t o s y n t h a t e , c o u l d be f e r m e n t e d is n o t k n o w n . Of course, c o m b u s t i o n is a s t r a i g h t - f o r w a r d a n d m o r e efficient use o f t h e p l a n t f o r energy. H o w e v e r , t h e s i g n i f i c a n c e of e t h y l alcohol as a liquid fuel e x t e n d e r makes it t h e preferred c o n v e r s i o n route, even at a m u c h h i g h e r cost or l o w e r efficiency. The data o n p r o d u c t i v i t y o f cattails are s u m m a r i z e d in Table III a n d are l i m i t e d by t h e absence of t o t a l p r o d u c t i v i t y d a t a , b o t h a b o v e a n d b e l o w g r o u n d . S o m e o f t h e best data w e r e c o l l e c t e d in M i n n e s o t a as s u m m a r i z e d in Table IV, w h i c h s h o w s t o t a l , above, a n d b e l o w g r o u n d p r o d u c t i o n . It s h o u l d be n o t e d t h a t natural stands c a n have as h i g h , or higher, t o t a l p r o d u c t i v i t i e s t h a n m a n a g e d (fertilized) plots. Peat soils had s o m e w h a t l o w e r p r o d u c t i v i t i e s . In late s u m m e r , s h o o t d r y w e i g h t reaches a m a x i m u m , a n d roots start a c c u m u l a t i n g p h o t o s y n t h a t e . P r o d u c t i v i t i e s of 4 0 t / h a - y r have been e s t i m a t e d f o r cattails in M i n n e s o t a (51). A c h i e v a b l e p r o d u c t i v i t y w i l l d e p e n d o n d e v e l o p m e n t of a p p r o p r i a t e c u l t i v a t i o n a n d h a r v e s t i n g t e c h n o l o g i e s . T h e p r o d u c t i o n s y s t e m itself w i l l likely be relatively s i m p l e , c o n s i s t i n g o f large ( 1 0 - 1 0 0 hectares) level g r o w t h areas s u r r o u n d e d b y a l o w soil e m b a n k m e n t a n d p r o v i d e d w i t h i n l e t / o u t l e t s t r u c t u r e s . The actual o p e r a t i o n s w o u l d need t o be w o r k e d o u t : H o w m u c h a n d w h e n t o harvest; w h e t h e r o n l y a b o v e or also b e l o w g r o u n d biomass w o u l d be h a r v e s t e d ; h o w m u c h n u t r i e n t a n d h o w t o a p p l y it; h o w t o c o n t r o l possible pests; etc. A l t h o u g h t o t a l biomass p r o d u c t i v i t y in a w e l l - m a n a g e d s y s t e m w o u l d likely exceed 5 0 t / h a - y r , based o n t h e data in Table II. t h e a c t u a l harvestable p r o d u c t i v i t y is likely t o be s i g n i f i c a n t l y less, possibly in t h e range of t h e 3 0 t / h a - y r . T h e cost o f p r o d u c t i o n , h o w e v e r , s h o u l d be l o w if h a r v e s t i n g does n o t present t o o great a p r o b l e m a n d if n u t r i e n t s are available t o sustain h i g h p r o d u c t i v i t i e s . Typha a n d o t h e r similar a q u a t i c m a r s h plants have n u t r i e n t c o n c e n t r a t i o n s as % o f dry m a t t e r o f a b o u t 0.5-3% N. 0.1-0.3% P, a n d 1.6-3.5% Κ (13). T h e actual n u t r i e n t c o n c e n t r a t i o n d e p e n d s o n t h e part of plant analyzed, t h e season (or age of plant), a n d , m o s t i m p o r t a n t l y , o n t h e n u t r i e n t s u p p l y t o t h e plant. N u t r i e n t l i m i t a t i o n reduces light c o n v e r s i o n e f f i c i e n c y a n d p r o d u c t i v i t y . H o w e v e r , t h e m i n i m a l c o n c e n t r a t i o n s required t o m a i n t a i n h e a l t h y g r o w t h are n o t w e l l characterized. Critical n u t r i e n t tissue levels (at w h i c h n u t r i e n t d e f i c i e n c y sets in) are 0.09% f o r Ρ a n d 2.5% f o r Κ in a Typha h y b r i d (52); for n i t r o g e n it is likely b e t w e e n 0.5-1.0%. For s u p p l y of s u c h n u t r i e n t levels o n a large-scale a n u m b e r of sources can be c o n s i d e r e d — a g r i c u l t u r a l fertilizers, s e w a g e a n d a n i m a l w a s t e s , a n d recycled n u t r i e n t s f r o m a processing plant.

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch009

p r e h y d r o l y z e d w o o d w a s reacted w i t h 1.5 m l of d i l u t e s u l f u r i c acid in an a t m o s p h e r e of c a r b o n d i o x i d e . T h e reactors w e r e heated w i t h s u i t a b l e p r e c a u t i o n s in a m o l t e n salt b a t h a n d q u e n c h e d in w a t e r . A s s h o w n i n Figure III, p r e d i c t e d general i m p r o v e m e n t in yield w a s m a i n t a i n e d u p t o 2 6 0 ° C . A t t h i s p o i n t , t h e y i e l d w a s 5 4 % . T h e t i m e t o m a x i m u m y i e l d at 2 6 0 ° C w a s 0.45 m i n u t e s . T h e m o d e l p r e s u m e s i s o t h e r m a l reaction c o n d i t i o n s , b u t w i t h a r e a c t i o n t i m e o f 3 0 s e c o n d s , t h e average reaction t e m p e r a t u r e w a s m u c h b e l o w t h e b a t c h t e m p e r a t u r e , t h u s r e s u l t i n g in l o w e r yields. A n e x a m i n a t i o n o f t h e kinetics s h o w s t h a t if t h e l o w e r l i m i t o f p r a c t i c a l r e t e n t i o n t i m e is r e a c h e d , it is a d v a n t a g e o u s t o l o w e r t h e a c i d i t y a n d raise t h e t e m p e r a t u r e . It is also e v i d e n t t h e p r e t r e a t m e n t s w h i c h accelerate t h e rate o f h y d r o l y s i s a n d increase t h e heat o f a c t i v a t i o n are a d v a n t a g e o u s . M i c r o t e c h n i q u e s are n o w available w h i c h c a n establish yields o n m i l l i g r a m samples h e a t e d in glass capillaries w i t h reaction t i m e s o f a f e w s e c o n d s a n d internal pressure in excess o f a 1 0 0 0 l b s / s q in b u t t h e y have n o t y e t been a p p l i e d t o t h i s p r o b l e m . P u m p e d h y d r o c e l l u l o s e slurries c a n b e heated b y s t e a m i n j e c t i o n a n d q u e n c h e d b y release o f pressure, b u t t h e p r a c t i c a b i l i t y of s u c h a p r o c e s s i n g t e c h n i q u e has n o t been e s t a b l i s h e d . G r e t h l e i n r e c e n t l y c o n f i r m e d S a e m a n ' s m o d e l by r e p o r t i n g a y i e l d o f over 5 0 % sugar f r o m cellulose u s i n g 1 % s u l f u r i c a c i d a n d a c o n t i n u o u s - f l o w reactor w i t h a residence t i m e o f 0.22 m i n u t e s at a t e m p e r a t u r e o f 2 3 7 °C (6). Research seeking h i g h e r y i e l d s b y t h i s a p p r o a c h s h o u l d be f r u i t f u l . DILUTE

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Hydrolysis of Cellulose

Spano reported t h a t cellulose p r e t r e a t e d b y r o l l - m i l l i n g w i t h a n energy i n p u t of 0 . 2 5 k i l o w a t t p e r h o u r p e r p o u n d w a s e n z y m a t i c a l l y h y d r o l y z e d t o t h e e x t e n t o f 4 5 % in 2 4 hours. T h e results o f t h i s w e r e said t o b e e n c o u r a g i n g (13). E N Z Y M A T I C HYDROLYSIS OF CELLULOSE There is m u c h e x c e l l e n t basic w o r k u n d e r w a y o n t h e e n z y m a t i c hydrolysis o f cellulose. The key f a c t o r is t h e p r e t r e a t m e n t r e q u i r e d b y lignocellulose before it is a c t e d u p o n a t an a c c e p t a b l e rate. In p a r t i a l l y d e l i g n i f i e d p u l p s , t h e rate o f h y d r o l y s i s rises w i t h d e c r e a s i n g l i g n i n c o n t e n t , b u t p u l p i n g t h e s u b s t r a t e is Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch009

impractical. P r e t r e a t m e n t s m e n t i o n e d previously i n c l u d e irradiation, b a l l - m i l l i n g , a n d rollm i l l i n g . S o m e success in u p g r a d i n g r u m i n a n t f o d d e r has been a c h i e v e d w i t h s t e a m i n g , t r e a t m e n t w i t h d i l u t e alkali, a n d d i g e s t i o n w i t h a q u e o u s sulfur d i o x i d e solutions. Intensive w o r k d i r e c t e d t o t h e d e v e l o p m e n t o f inexpensive solubilization m e t h o d s f o r increasing t h e y i e l d o f sugar f r o m lignocellulose b y acid or e n z y m a t i c hydrolysis is in progress at Purdue University. A recent report s h o w e d t h a t c a d o x e n is e f f e c t i v e b u t c a d m i u m presents u n a c c e p t a b l e hazards (14). A n a p p r o a c h in w h i c h p r e h y d r o l y z e d lignocellulose is t r e a t e d w i t h 7 0 % sulfuric acid f o l l o w e d b y m e t h a n o l has also been r e p o r t e d (14). T h e f l o w c h a r t calls f o r r e c y c l i n g 2.5 parts o f s u l f u r i c a c i d a n d 5.5 parts o f m e t h a n o l for each part o f sugar p r o d u c e d . A n o t h e r a p p r o a c h (15) calls for t h e use o f a solvent c o n s i s t i n g o f s o d i u m tartrate, ferric c h l o r i d e , s o d i u m sulfite, a n d s o d i u m h y d r o x i d e . S u c h t r e a t m e n t s increase t h e accessibility o f e n z y m e s t o cellulose a n d increase t h e rate o f a c i d hydrolysis, t h e k : k ratio, a n d t h e y i e l d o f sugar. T h e cost o f r e c o v e r i n g t h e reagents, h o w e v e r , is a key factor. W h i l e t h e r e is w i d e s p r e a d e n t h u s i a s m f o r t h e e n z y m a t i c hydrolysis o f lignocellulose a n d many pretreatments facilitate the reaction, published process d a t a d o n o t p e r m i t e c o n o m i c assessment. }

2

CONCLUSIONS T h e o u t l o o k f o r fuels a n d c h e m i c a l s f r o m b i o m a s s is c l o u d e d because it d e p e n d s o n t h e o u t l o o k f o r energy. T h e m o s t p r o b a b l e o u t l o o k for e n e r g y in t h e n e x t d e c a d e is t h a t it w i l l be e x p e n s i v e b u t available, a n d c o n s u m p t i o n w i l l c o n t i n u e t o increase. W h i l e t h i s s i t u a t i o n m a y n o t c o n s t i t u t e a crisis, it is "crisis p r o n e . " This latter f a c t justifies a careful c o n s i d e r a t i o n of biomass as a source of fuels a n d c h e m i c a l s .

194

BIOMASS

AS A

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The price of b i o m a s s is critical in d e t e r m i n i n g its p o t e n t i a l . Because of lack of d e m a n d , c u r r e n t s p o t prices are o f t e n l o w . T h e price of a large q u a n t i t y of w o o d (a t h o u s a n d or m o r e t o n s / d a y ) for t h e life of a p l a n t (decades) is n o t l o w . Katzen in 1 9 7 5 (7) a s s u m e d t h a t a large q u a n t i t y of w o o d w i l l have a m i n i m u m v a l u e of $ 2 4 / t o n (dry basis) set b y its fuel e q u i v a l e n t , a n d t h e a d d i t i o n a l cost of assuring l o n g - t e r m s u p p l y w o u l d raise t h i s t o $ 3 6 / t o n . The cost of w o o d , t o g e t h e r w i t h labor a n d capital costs, w i l l of course rise as t h e cost of p e t r o l e u m rises. T h e best use of b i o m a s s f o r all purposes requires realistic, d i s c r i m i n a t i n g , a n d

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch009

selective s e t t i n g of priorities. W o o d c o n t r i b u t e s m o s t t o o u r e n e r g y b u d g e t w h e n it is used for t h e p r o d u c t i o n of s t r u c t u r a l a n d fiber p r o d u c t s , t h u s p r o v i d i n g a l t e r n a t i v e s t o e n e r g y - i n t e n s i v e materials. A t o n of w o o d in t h e materials s y s t e m c o n t r i b u t e s i n d i r e c t l y m a n y t i m e s as m u c h t o o u r n a t i o n a l e n e r g y b u d g e t as a t o n of w o o d in t h e fuel s y s t e m . T h e relative e c o n o m i c i m p o r t a n c e of forest p r o d u c t s w i l l increase as t h e e n e r g y s h o r t a g e w o r s e n s , a n d as forest p r o d u c t s i n d u s t r i e s accelerate t h e i r s u b s t i t u t i o n of l o w - g r a d e w o o d for fossil fuel. A f t e r s a t i s f y i n g t h e needs for an e n e r g y self-sufficient w o o d i n d u s t r y , t h e r e c o u l d still be available s o m e h u n d r e d or h u n d r e d s of m i l l i o n s of t o n s of b i o m a s s in t h e f o r m of w o o d , t o g e t h e r w i t h a similar q u a n t i t y of a g r i c u l t u r a l residues. T h e large-scale c h e m i c a l c o n v e r s i o n of s u c h r a w material w i l l p r o b a b l y i n v o l v e h y d r o l y s i s , b u t no available t e c h n o l o g y is c o n s i d e r e d e c o n o m i c a l l y viable. T h e key t o f u t u r e progress lies in basic s t u d i e s , a n d an e v o l u t i o n a r y a p p r o a c h t o possible large-scale i n t e g r a t e d c h e m i c a l utilization. Cellulose h y d r o l y s i s by m e a n s of e n z y m e s , s t r o n g a c i d , or d i l u t e acid is preferably p r e c e d e d by a p r e h y d r o l y s i s t o separate easily h y d r o l y z e d h e m i c e l l u l o s e c o n s t i t u e n t s . A s an e v o l u t i o n a r y s t e p , p r e h y d r o l y s i s itself m i g h t be a v i a b l e route for a l i m i t e d q u a n t i t y of special p r o d u c t s . Prehydrolysis Prehydrolysis is a s i m p l e a n d w e l l - k n o w n step r e q u i r i n g little f u r t h e r basic studies, b u t t h e r e are solvable t e c h n i c a l p r o b l e m s in o b t a i n i n g t h e p r e h y d r o l y z a t e s in f a v o r a b l e c o n c e n t r a t i o n . Prior t o t h e e s t a b l i s h m e n t of a f u l l y i n t e g r a t e d h y d r o l y s i s o p e r a t i o n , t h e r e m i g h t be o p p o r t u n i t i e s t o p r o d u c e a n d p u t t o use h a r d w o o d or c r o p - r e s i d u e prehydrolyzates. There are n o w in p r o s p e c t boiler p l a n t s w h i c h w i l l b u r n over 1,000 t o n s of w o o d / d a y . Preceding c o m b u s t i o n , w o o d can be p r e h y d r o l y z e d t o y i e l d a s t r e a m rich in pentoses for s u b s e q u e n t c o n v e r s i o n t o xylose, xylose

9.

SAEMAN

Hydrolysis of Cellulose

195

derivatives, f u r f u r a l , yeast, or o t h e r feed a n d f e r m e n t a t i o n p r o d u c t s 0 6 ) . T h e residual w o o d , a b o u t t h r e e - f o u r t h s o f t h e i n c o m i n g w e i g h t , c a n t h e n be b u r n e d f o r process s t e a m a n d a d d i t i o n a l s t e a m as a c o p r o d u c t . S u c h an o p e r a t i o n w o u l d be a n e v o l u t i o n a r y step t o w a r d an i n t e g r a t e d hydrolysis plant.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch009

Pretreatment for Enzymatic Hydrolysis W h i l e t h e r e has been m u c h progress in t h e s t u d y o f cellulases, t h e a p p l i c a t i o n s of s u c h t e c h n o l o g y have been l i m i t e d by a lack o f e c o n o m i c a l p r e t r e a t m e n t of t h e lignocellulose. W i t h o u t s u c h p r e t r e a t m e n t , hydrolysis is s l o w a n d i n c o m p l e t e . T h e v a l u e of e n h a n c e d e n z y m a t i c a t t a c k o n lignocellulose is n o t l i m i t e d t o t h e p r o d u c t i o n o f sugar a n d c h e m i c a l s . T h e same p r o c e d u r e s w o u l d be a p p l i c a b l e t o t h e increased d i g e s t i b i l i t y o f coarse fodder by ruminants. W h i l e g o v e r n m e n t - s u p p o r t e d research n o w emphasizes t h e p r o d u c t i o n o f l i q u i d fuels f r o m b i o m a s s , c o m m e r c i a l i z a t i o n m i g h t be reached sooner b y c o o p e r a t i o n w i t h t h o s e interested in cellulose d i g e s t i o n b y r u m i n a n t s . Experience in t h e practical u p g r a d i n g o f coarse f o d d e r w o u l d be d i r e c t l y a p p l i c a b l e t o t h e h y d r o l y s i s of b i o m a s s b y cellulases. The Strong Acid Hydrolysis o f Cellulose The h i g h yield a n d h e n c e h i g h e r p u r i t y o f sugar o b t a i n e d b y s t r o n g acid h y d r o l y s i s o f cellulose makes it a n a t t r a c t i v e process, b u t t h e lack of a recovery s y s t e m f o r s t r o n g acid c o m p l i c a t e s t h e outlook. T h e i m p r o v e m e n t o f m e m b r a n e t e c h n o l o g y w i l l p r o b a b l y p r o c e e d because o f p o t e n t i a l a p p l i c a t i o n s t o m a n y p r o b l e m s . A p p l i c a t i o n t o cellulose hydrolysis a d d s j u s t i f i c a t i o n for i n t e n s i f i e d w o r k in t h e field. The Dilute Acid Hydrolysis of Cellulose T h e r a p i d , h i g h - t e m p e r a t u r e h y d r o l y s i s o f cellulose seems t o g e t less a t t e n t i o n t h a n it deserves. T h e s e q u e n c e i n v o l v e d is s i m p l e ; t h e i n c o m i n g w e t m a t e r i a l need never be d r i e d . T h e c o n s e c u t i v e first-order reactions i n v o l v e d c a n b e s t u d i e d w i t h a d e q u a t e precision in very s i m p l e e q u i p m e n t . W h i l e t h e o u t l o o k f o r t h e process, based o n m e a g e r presently available d a t a , is m a r g i n a l , studies c a n be c o n d u c t e d t o increase t h e ratio o f t h e rate of sugar p r o d u c t i o n t o d e s t r u c t i o n a n d h e n c e t h e y i e l d , t o decrease t h e t e m p e r a t u r e a n d pressures i n v o l v e d , a n d t o increase t h e recovery o f c o p r o d u c t s .

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BIOMASS AS A NONFOSSIL FUEL SOURCE

REFERENCES

1. Sherrard, E. C.; Kressman, F. W. Ind. Eng. Chem. 1945, 37, 5. 2. Wenzl, H.F.J. "Chemical Technology of Wood"; Academic Press: New York, 1970. 3. Luers, H.Z. Angew. Chem. 1930, 43, 455; 1932, 45, 369.

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4. Saeman, J.F. Ind. Eng. Chem. 1945, 37, 43. 5. Kirby, A. M. M.S. Thesis, University of Wisconsin, 1949. 6. Grethlein, H. E. "Proceedings", the Second Annual Fuels From Biomass Symposium sponsored by Rensselaer Polytechnic Institute, June 1978; Rensselaer Polytechnic Institute: Troy, N.Y., 1978; Paper No. 26. 7. Katzen, R., Associates. NTIS Accession No. PB 262 489. Natl. Tech. Inf. Serv., Springfield, Va. 1975. 8. Saeman, J. F. "Symposium Papers", Clean Fuels from Biomass and Wastes Symposium sponsored by the Institute of Gas Technology, Orlando, Florida, 1977. Institute of Gas Technology: Chicago, 1977. 9. Gregor, H. P., and Jefferies, T. W. Annals of New York Academy of Sciences, 1979, pp 273-87. 10. Millett, Μ. Α.; Moore, W. E.; Saeman, J. F. Ind. Eng. Chem., 1954, 46 (7), 1493. 11. Saeman, J. F.; Millett, Μ. Α.; Lawton, E. L. Ind. Eng. Chem. 1952, 44 (12), 2848-52. 12. Millett, Μ. Α.; Effland, M. J.; Caulfield, D. F. Adv. Chem. Ser., in press. 13. Bungay, H. R. and Walsh, T. J., Eds. Fuels from Biomass Fermentation Newsletter. Rensselaer Polytechnic Institute: Troy, N.Y., April and July 1978. 14. Ladisch, M. R.; Ladisch, C. M.; Tsao, G. T. Science 1978, 201, 743.

9. SAEMAN Hydrolysis of Cellulose 15.

197

Tsao, G. T. "Proceedings", the Second Annual Fuels from Biomass Symposium sponsored by Rensselaer Polytechnic Institute, Troy, N.Y., June 1978; Rensselaer Polytechnic Institute: Troy, N.Y., 1978; Paper No. 30.

16. Harris, J. F. "Applied Polymer Symposium"; John Wiley & Sons, Inc.: New York, 1975; Vol. 28, pp 131-44.

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RECEIVED JUNE 18,

1980.

10 Perspectives on the Economic Analysis of Ethanol Production from Biomass 1

HARRY J. PREBLUDA and ROGER WILLIAMS, JR.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch010

Roger Williams Technical And Economic Services, Incorporated, P.O. Box 426, Princeton, NJ 08540

Our objective is to clarify the many misapprehensions pertaining to the practical use of ethanol from biomass to extend motor fuel. While one might agree that biomass can be a renewable resource for non-polluting safe fuels, press reports have questioned the practicality of making large quantities of ethanol as a fuel source not only from rice, cereal grains or tuberous roots, but also from agricultural by-products, such as molasses, timber wastes, cheese whey, pineapple, waste paper or even garbage. From the many articles, there has appeared a potpourri of facts and fallacies (1,2). At all levels of our Federal and State Governments as well as within the automotive and petroleum industries, people have taken sides on the alcohol question. Opposing views are often voiced within the same organization. A leading university economics professor disagreed with the engineering department and questioned the feasibility of alcohol for transportation fuel (3). However, we want to take a neutral position and point out some of the pitfalls in the thinking on this subject. Large-scale usage may some day correct the present day economic inequities. This will come from new breakthroughs in fermentation and engineering technology to increase yields and reduce costs.

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M o t o r Fuel A l c o h o l In 1 8 9 4 . Professor H a r t m a n at t h e Laboratory of t h e G e r m a n Distillery. D e u t s c h e n L a n d w i r t s h a f t s - G e s e l l s c h a f t . Leipzig. G e r m a n y , w a s a m o n g t h e first t o use a l c o h o l as a fuel in c o m p e t i t i o n t o p e t r o l e u m . In later years, scientists in o t h e r c o u n t r i e s f o u n d t h a t a l c o h o l / f u e l b l e n d s have s h o r t c o m ings. Storage t a n k m o i s t u r e c a n c o n t a m i n a t e t h e m i x t u r e so t h a t t h e r e is a l c o h o l a n d gasoline s e p a r a t i o n . Under c e r t a i n c o n d i t i o n s , i m p u r i t i e s in d e n a t u r i n g a g e n t s accelerate c o r r o s i o n . M e t h a n o l is a d é n a t u r a n t for e t h a n o l in m a n y c o u n t r i e s a n d usually c a n be used w i t h o u t i n t e r f e r i n g w i t h t h e effectiveness of fuel s y s t e m s . In s o m e parts of t h e w o r l d , i m p u r i t i e s in localarea gasoline c a n react w i t h small a m o u n t s of w a t e r in t h e a l c o h o l t o accelerate g a l v a n i c a c t i o n o n fuel s y s t e m s w i t h dissimilar metals. Henry Ford w a s o n c e q u e s t i o n e d as t o w h a t w o u l d h a p p e n t o his a u t o m o b i l e " b u g g y " business if p e t r o l e u m s u p p l i e s s h o u l d d w i n d l e . He said. " W e c a n g e t fuel f r o m f r u i t , f r o m t h a t of s u m a c by t h e roadside or f r o m apples, w e e d s , s a w d u s t — a l m o s t a n y t h i n g . There is fuel in every bit of v e g e t a b l e m a t t e r t h a t c a n be f e r m e n t e d . There is e n o u g h a l c o h o l in a year's yield of p o t a t o e s t o d r i v e t h e m a c h i n e r y necessary t o c u l t i v a t e t h e field for a h u n d r e d y e a r s . . . A n d it r e m a i n s for s o m e o n e t o f i n d h o w t h i s fuel can p r o d u c e d c o m m e r c i a l l y — b e t t e r fuel at a c h e a p e r price t h a n t h a t w e n o w k n o w . " Ford h o s t e d t h e Dearborn Conferences of A g r i c u l t u r e . I n d u s t r y a n d Science in t h e 1930's. This w a s t h e b e g i n n i n g of t h e Farm C h e m u r g i c C o u n c i l w h i c h p i o n e e r e d t h e use of r e n e w a b l e resources as i n d u s t r i a l r a w materials. F e r m e n t a t i o n a l c o h o l for m o t o r fuel w a s a major t o p i c at t h e Dearborn Conferences (4). A p l a n t at A t c h i s o n . Kansas soon f o l l o w e d in O c t o b e r 1 9 3 6 w i t h t h e first a t t e m p t t o m a r k e t an a l c o h o l / g a s o l i n e b l e n d in t h e U n i t e d States. D u r i n g 1 9 3 8 - 1 9 3 9 , t w e n t y m i l l i o n gallons of a l c o h o l / g a s o l i n e blends w e r e sold t h r o u g h i n d e p e n d e n t dealers a n d f a r m bureaus in t e n w e s t e r n a n d m i d w e s t e r n states (5). Nebraska alone had as m a n y as 2 5 0 dealers. A t a b o u t t h i s t i m e , A m e r i c a n a u t o makers w e r e s h i p p i n g vehicles a n d t r a c t o r s t o t h e Philippines w i t h special e n g i n e s d e s i g n e d t o use a l c o h o l f r o m s u g a r cane. T h i s e q u i p m e n t b e c a m e p o p u l a r in t h e Philippines w h e n gasoline prices w e r e too high. A u t o e n g i n e s b u r n i n g s t r a i g h t alcohols are p r o n e t o poor c o l d w e a t h e r s t a r t i n g . M u c h b a c k g r o u n d has been b u i l t u p for over 5 0 years on b o t h m e t h a n o l a n d e t h a n o l by r a c i n g car e n t h u s i a s t s u s i n g t h e s e b l e n d e d fuels in t h e i r special e n g i n e s (6,7). O n l y r e c e n t l y has t h e r e been serious t h o u g h t t o c h a n g i n g t h e d e s i g n of t h e a u t o m o b i l e e n g i n e for h a n d l i n g either m e t h a n o l or e t h a n o l . Prestart h e a t i n g of s o m e kind m a y have t o be used t o o v e r c o m e t h e s l u g g i s h p e r f o r m a n c e of special e n g i n e s for these fuels in c o l d climates.

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Gasohol in Brazil Currently. Brazil is leading t h e W o r l d in t r y i n g t o decrease d e p e n d e n c e o n i m p o r t e d fossil fuels. A b o l d g o v e r n m e n t p r o g r a m there centers a r o u n d t h e idea of c o n s t r u c t i n g 1 7 0 f e r m e n t a t i o n plants a n d distilleries. A f t e r w o r k i n g on a l c o h o l f o r over 5 0 years. Brazilian research h a d reached a standstill u n t i l t h e rise of oil prices in 1973. A l t h o u g h t h e e c o n o m i c s o n t h i s project are far f r o m favorable as y e t , Brazil is g o i n g f o r w a r d t o nationalize t h e " g a s o h o l " m o v e m e n t . T h e p o l i t i c i a n s in Brazil feel t h e i r f a r s i g h t e d n e s s s h o u l d p a y off w h e n oil prices g o u p . In t h e m e a n t i m e , t h e r e are m a n y n e w jobs f o r their u n e m p l o y e d . It s h o u l d be kept in m i n d t h a t Brazilian a l c o h o l cost w o u l d be m u c h h i g h e r if o u r U.S. w a g e scale w e r e used. Plans are also progressing in Brazil f o r intensive c u l t i v a t i o n of cassava (manioc). M o r e t h a n a dozen n e w a l c o h o l plants w i l l be b u i l t r e q u i r i n g cassava as a r a w material. This t u b e r o u s root can t h r i v e o n poor soil c o n d i t i o n s in Brazil w i t h l o w rainfall a n d is unlike cane since it c a n be harvested year r o u n d . Stillage b y - p r o d u c t f r o m m a n i o c c o u l d be used t o m a k e m e t h a n e or a h i g h p r o t e i n a n i m a l feed. Incidentally, cassava, b e i n g a p e r e n n i a l , c a n g r o w f o r several years w h i l e t h e roots a c c u m u l a t e starch. It differs f r o m sugar cane in t h a t cassava p r o c e s s i n g requires s o m e hydrolysis before f e r m e n t a t i o n . A l s o , sugar cane d e c o m p o s e s w h e n left in t h e fields t o o long. Because of starches a n d fibers, cassava is m o r e stable t o w e a t h e r i n g . It has n o t had m u c h o p p o r t u n i t y as y e t f o r g e n e t i c improvement. Brazilian officials have a p p a r e n t l y o v e r l o o k e d t h e possibility of using e t h a n o l or m e t h a n o l f o r c o n v e r s i o n t o h y d r o c a r b o n s s u c h as gasoline using t h e M o b i l process(8). This process c a n c o n v e r t e t h a n o l t o gasoline d i r e c t l y , t h u s a l l o w i n g t h e use of h y d r o c a r b o n fuel f r o m r e n e w a b l e resources in e x i s t i n g cars w i t h o u t e n g i n e m o d i f i c a t i o n . This s c h e m e w o u l d n o t require a separate ethyl alcohol/gasoline blend distribution system. Biomass N o t Complete Answer T h e o p i n i o n s of farmers, legislators a n d t h e p u b l i c o n t h e use of biomass f r o m a l c o h o l have been d e b a t e d a n d t h e oil c o m p a n i e s have had a d i f f i c u l t course t o steer(9). It is n o t generally realized t h a t oil c o m p a n i e s g e t into p r a c t i c a l l y all facets of energy. In a d d i t i o n t o coal a n d p e t r o l e u m d e v e l o p m e n t s , t h e y are in o t h e r activities s u c h as solar, w i n d , a t o m i c , tidal a n d r e n e w a b l e e n e r g y sources. They also w a n t t o k n o w h o w a l c o h o l can be best used as a source of energy. Some A m e r i c a n p e t r o l e u m c o m p a n i e s have taken a l o n g - r a n g e v i e w a n d m a d e b r e a k t h r o u g h s f o r h i g h a l c o h o l yields f r o m cellulosic w a s t e s using special f e r m e n t a t i o n technology.QO)

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The U.S. D e p a r t m e n t of Energy has been e v a l u a t i n g t h e pros a n d c o n s of a l c o h o l fuels (V\). DOE's m a i n c o n c l u s i o n has been t h a t b o t h e t h a n o l a n d m e t h a n o l can c o n t r i b u t e t o t h e e n e r g y resources of t h i s c o u n t r y by e x t e n d i n g l i q u i d fuel supplies. DOE appears t o be c o m m i t e d t o d e v e l o p i n g a l c o h o l fuel. If n a t i o n w i d e m a r k e t p e n e t r a t i o n of alcohol fuels takes place, present m a j o r fuel suppliers w i l l u n d o u b t e d l y have t o p a r t i c i p a t e . Over t h e long t e r m it is e x p e c t e d t h a t m e t h a n o l w i l l offer l o w e r cost possibilities t h a n e t h a n o l . A l t h o u g h t h e U.S. D e p a r t m e n t of A g r i c u l t u r e v i g o r o u s l y s u p p o r t s t h e d e v e l o p m e n t of g a s o h o l in t h e U.S.. it urges Congress t o be w a r y of proposals t h a t w o u l d c o m m i t h u g e a m o u n t s of U.S. feed grains t o gasohol (12). M e n t i o n s h o u l d be m a d e of o u r c o n c e r n a b o u t d i s t r i b u t i o n costs. T h e DOE p o s i t i o n papers gloss over d i s t r i b u t i o n costs of a l c o h o l / g a s o l i n e fuels. A l s o o v e r l o o k e d is t h e possible e c o n o m i c gain by g o i n g f r o m coal t o s y n t h e s i s gas t o m e t h a n o l t o gasoline u s i n g t h e M o b i l process for t h e latter route (8). This c o u l d a v o i d t h e p r o b l e m of n e w storage facilities a n d get a r o u n d t h e need for a n o t h e r fuel d i s t r i b u t i o n s y s t e m . Over 9 0 % of t h e present U.S.A. n o n - b e v e r a g e e t h y l a l c o h o l p r o d u c t i o n c o m e s f r o m p e t r o l e u m or n a t u r a l gas-derived e t h y l e n e synthesis. Less t h a n 1 0 % of t h e r e m a i n i n g a l c o h o l m a r k e t c o m e s f r o m f e r m e n t a t i o n of grains, f r u i t , a n d sulfite liquors. Using a r o u n d n u m b e r f i g u r e of 100 billion gallons of gasoline per year, t h e i n d u s t r i a l e t h a n o l p r o d u c t i o n in t h e U.S.A. a m o u n t s t o a b o u t o n e - t h i r d of one p e r c e n t of m o t o r fuel used by vehicles o n t h e h i g h w a y . It has been e s t i m a t e d t h a t if all t h e available f a r m l a n d w e r e used for g r o w i n g a g r i c u l t u r a l c r o p s in excess of t h o s e n e e d e d for f o o d p r o d u c t i o n , t h e e t h y l a l c o h o l p r o d u c e d f r o m these r e n e w a b l e crops a n d residues w o u l d m e e t o n l y 8 % of our nation's l i q u i d fuels e n e r g y needs for t r a n s p o r t a t i o n . Unless ethyl a l c o h o l f r o m b i o m a s s is subsidized for political reasons or for national s e c u r i t y purposes, it w i l l not be t h e fuel of c h o i c e t o be used in large q u a n t i t i e s (13,14). Of course, t h e r e w i l l be b r e a k t h r o u g h s in i m p r o v e d c r o p yields, processing t i m e a n d o t h e r e n e r g y savings. L i m i t e d use w i l l t a k e place in local g e o g r a p h i c areas w h e r e t h e f e r m e n t a t i o n of o f f - g r a d e grains t o e t h y l a l c o h o l can be s u p p o r t e d by s u b s i d y , tax c r e d i t s or loan guarantee. T h e U.S. has p l e n t y of c o r n i n v e n t o r y presently because of t h e e x c e l l e n t 1 9 7 8 c a r r y o v e r a n d i m p r o v e d o u t l o o k for t h e 1 9 7 9 crop. A t first g l a n c e , it appears t h a t a l c o h o l f r o m f e r m e n t e d g r a i n c o u l d leave us less d e p e n d e n t o n p e t r o l e u m supplies. Yet t h e r e are c a u t i o u s m e t e o r o l o g i s t s w h o e x p e c t t h e d r o u g h t c y c l e t o hit o u r c o u n t r y in t h e next f e w years. W e recall v i v i d l y t h e days of t h e d u s t s t o r m s a n d lack of rain in t h e corn belt. In a special U.S.D.A. report, it has been q u e s t i o n e d w h e t h e r w e c o u l d afford t o divert srzable q u a n t i t i e s of grain for m o t o r fuel purposes (1_3). It has been

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e s t i m a t e d t h a t s t a r t u p costs f o r plants a n d distilleries w o u l d be b e t w e e n $ 1 5 $ 1 7 billion f o r m a k i n g 1 0 0 billion gallons of gasohol b l e n d per year. This does not i n c l u d e a direct a d d e d s u b s i d y of $ 1 0 . 4 billion a year t o make t h e p r o d u c t c o m p e t i t i v e w i t h gasoline prices. A n e w m e t h o d (15) f o r e x t r a c t i n g w h e a t g l u t e n offers s o m e possibilities f o r

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alcohol f e r m e n t a t i o n of w h e a t s t a r c h b y - p r o d u c t s in g e o g r a p h i c areas w h e r e this g r a i n w o u l d be a d v a n t a g e o u s . T h e n e w t e c h n o l o g y called t h e "Raisio A l f a - L a v a l " process is d e s c r i b e d as a " u n i q u e closed s y s t e m f o r w h e a t f r a c t i o n a t i o n s u b s t a n t i a l l y increasing t h e yield of h i g h q u a l i t y starch a n d vital g l u t e n w h i l e p e r m i t t i n g p o l l u t i o n - f r e e p r o c e s s i n g . " W i t h h i g h beef prices a h e a d , t h e w o r l d d e m a n d for g l u t e n in h u m a n f o o d is e x p e c t e d t o increase. Gasohol and t h e Beef Industry T h e beef p r o d u c e r s feel t h a t t h e gasohol d e v e l o p m e n t in t h e U.S. c o u l d h u r t its i n d u s t r y 0 6 ) . A n a t i o n w i d e gasohol p r o g r a m w o u l d b r i n g higher prices a n d h i g h e r p r o d u c t i o n costs t o be passed a l o n g t o c o n s u m e r s . There w o u l d be a n a d d i t i o n a l cost t o p r o d u c e r s in t h e f o r m of higher taxes t o p a y f o r t h e large g o v e r n m e n t subsidies n e e d e d f o r t h e gasohol p r o g r a m . T h e beef p r o d u c e r s are also w o r r i e d a b o u t regional livestock p r o d u c t i o n shifts. S t o c k m e n w o u l d t r y t o relocate near distilleries t o be close t o a l o w - c o s t source of b y - p r o d u c t feed. The greater feed use of distillers grains c o u l d s l o w d o w n t h e livestock cycle. U.S.D.A. researchers t h i n k t h a t t h e h i g h fiber value of distillers feed m i g h t require a longer d i g e s t i v e phase a n d t h u s push c o n s u m e r beef prices higher. Overall livestock p r o d u c t i o n w o u l d be e x p e c t e d t o decrease. A l s o t h e e x p e c t e d 10 billion g a l / y r subsidized alcohol m a r k e t w o u l d sharply increase feed prices a n d f o o d grains. Incidentally, w h e r e w o u l d t h e subsidies c o m e f r o m ? W h o w o u l d p a y f o r t h e m ? T h e 3 5 m i l l i o n t o n s of d r i e d distillers feed grains f r o m t h e gasohol p r o g r a m each year w o u l d depress soybean meal prices in s u c h a w a y t h a t there w o u l d be radical c h a n g e s in t h a t i n d u s t r y . T h e soybean c r u s h i n g i n d u s t r y f o r a n i m a l feed w o u l d be s u p p l a n t e d p r i m a r i l y b y o n e p r o d u c i n g f o o d oils a n d special p r o d u c t s i n t e n d e d f o r h u m a n use in t h e e x p o r t market. A n o t h e r w o r r y of beef p r o d u c e r s — w h a t w o u l d h a p p e n in t h e event of short U.S. f o o d crops? Also, is t h e r e e n o u g h c a p a c i t y f o r b o t h f o o d a n d gasohol p r o d u c t i o n ? W h a t is t h e real a n s w e r t o these q u e s t i o n s ? Land Program Possibility J a w e t z (1_7) presented a n i n t e r e s t i n g idea as a r e n e w a b l e resource r a w material p o t e n t i a l f o r e t h a n o l . It offers t h e f a r m e r a n o p p o r t u n i t y t o g r o w specific crops u s i n g t h e m i l l i o n s o f acres in t h e Federal G o v e r n m e n t " s e t

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a s i d e " p r o g r a m in e x c h a n g e for g u a r a n t e e d m i n i m u m prices of f a r m crops. Instead of leaving t h e land f a l l o w a n d idle. J a w e t z has s u g g e s t e d g r o w i n g a c r o p t h a t c o u l d be used by a distiller t o m a k e a l c o h o l . T h e s u b s i d y w o u l d revert t o t h e distiller. Ethanol based o n $ 2 . 0 0 / b u s h e l of c o r n w o u l d t h e n c o s t o n l y $ 0 . 4 5 / g a l at t h e distillery after a l l o w i n g t h e distiller a s u b s i d y c r e d i t of a p p r o x i m a t e l y $ 0 . 5 4 / g a l of e t h a n o l f r o m t h e " s e t a s i d e " p r o g r a m a n d

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d i v e r t e d land. H o w e v e r , t h i s p r o g r a m m i g h t raise s o m e q u e s t i o n s b y c o n s e r v a t i o n i s t s . T h e y c o u l d c l a i m t h a t t h e c o n s t a n t p l a n t i n g of c r o p s o n land w o u l d have a t e n d e n c y t o run d o w n t h e soil unless there w a s heavy fertilization. W h i l e p o n d e r i n g a n s w e r s t o t h e s e q u e s t i o n s , let us e x a m i n e t h e possibilities of u s i n g o t h e r r a w materials s u c h as s u g a r c a n e or c a n e molasses f o r e t h a n o l p r o d u c t i o n . W e k n o w t h a t of t h e m a n y t y p e s of p l a n t material t h a t c a n be f e r m e n t e d , t h e greatest e n e r g y yield is o b t a i n e d w h e n sugar c a n e is f e r m e n t e d . T h e sugar cane p l a n t is c o n s i d e r e d t o be o n e of t h e m o s t e f f e c t i v e t o fix solar energy. If e t h a n o l is t o be m a d e f r o m a c a n e s o u r c e , it m u s t be p r o d u c e d in large q u a n t i t i e s f r o m available land t o m a k e it c o m p e t i t i v e a n d n o t have c o n s t r a i n t s w i t h o t h e r c o m p e t i n g crops. In t h e f u t u r e , t h e e c o n o m i c s c a n be i m p r o v e d by f e r m e n t i n g t h e h y d r o l y z e d bagasse fiber if it is n o t used d i r e c t l y as f u e l . It has also been s u g g e s t e d t h a t t o t a l f e r m e n t a b l e material in cane j u i c e be m a d e i n t o a l c o h o l w i t h o u t crystallizing sucrose. W h o l e Cane Process Rolz of G u a t e m a l a (1_8) r e p o r t e d o n t h e " E x - F e r m " process w h e r e b y e t h a n o l is f e r m e n t e d d i r e c t l y f r o m small pieces of w h o l e c h o p p e d cane. T h e a c c u m u l a t i o n of e t h y l a l c o h o l d u r i n g t h e f e r m e n t a t i o n leaches o u t o t h e r n o n sucrose c o m p o n e n t s a n d breaks d o w n t h e solid fibre m a t r i x of t h e cane. T h e s i m u l t a n e o u s e x t r a c t i o n a n d f e r m e n t a t i o n p r o v i d e s m a n y a d v a n t a g e s for t h e c a n e g r o w e r t o b e c o m e an a l c o h o l producer. Rolz p r o j e c t s a m a n u f a c t u r i n g c o s t of $ 0 . 6 4 3 / g a l of a l c o h o l vesus $ 0 . 7 9 5 / g a l for t h e c o n v e n t i o n a l s t a n d a r d t e c h n o l o g y e x c l u s i v e of c h a r g e s for return o n original i n v e s t m e n t . Sugar M a r k e t Implications V a c i l l a t i o n a n d m i s t r u s t in W a s h i n g t o n led t o t h e p l u m m e t i n g of s u g a r prices prior t o A u g u s t 1 9 7 8 . T h e c o m b i n a t i o n of record w o r l d s t o c k s of 3 0 m i l l i o n t o n s of sugar a n d l o w prices at t h e t i m e s t i m u l a t e d t h e t h i n k i n g of g o v e r n m e n t officials in c a n e - p r o d u c i n g , e n e r g y - b e l e a g u e r e d c o u n t r i e s t o be m o r e f a v o r a b l y d i s p o s e d t o m a k e a l c o h o l for fuel or gasohol p r o g r a m s . A n o t h e r f a c t o r has e n t e r e d t h e p i c t u r e for c o u n t r i e s basic in cane sugar a n d molasses p r o d u c t i o n . The large-scale d e v e l o p m e n t in t h e U.S. of h i g h

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f r u c t o s e c o r n s y r u p (HFCS) u s i n g g l u c o s e isomerase t o prepare s w e e t e n e r s f r o m c o r n starch is h a v i n g a d r a m a t i c effect o n cane sugar markets. HFCS w i l l p r o b a b l y replace m o s t of t h e cane sugar w e n o w i m p o r t . H o w e v e r , it w i l l n o t replace t h e beet a n d cane sugar w e n o w g r o w in t h e U.S. Indirectly, t h i s w i l l release cane acreage especially in t h e d e v e l o p i n g n a t i o n s w h i c h i m p o r t p e t r o l e u m (gasoline). These n a t i o n s are n o w t h i n k i n g of a l c o h o l p r o d u c t i o n f r o m their cane sugar or c a n e molasses. Currently, sugar p r o d u c t i o n is s h r i n k i n g in t h e U.S. T h e 1 9 7 9 c r o p is e x p e c t e d t o be d o w n b y as m u c h as 5 0 0 , 0 0 0 short t o n s a n d Congress is e x p e c t e d t o raise s u p p o r t prices.

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Attention t o By-Products Greater a t t e n t i o n is presently b e i n g g i v e n t o s o m e of t h e b y - p r o d u c t s of sugar processing a n d f e r m e n t a t i o n . W i t h rising fertilizer a n d labor costs, t h e sugar cane g r o w e r s in t h e State of Sao Paulo, Brazil have been r e t u r n i n g filter-press cake t o their g r o w i n g fields. Several mills have decreased usage of o r g a n i c fertilizers w h e n u s i n g filter-press cake. Brazilian e n v i r o n m e n t a l p r o t e c t i o n laws have recently p r o h i b i t e d a l c o h o l p r o d u c e r s f r o m d u m p i n g distillery slops or w a s t e s i n t o t h e rivers w h i c h t h e y have been d o i n g f o r s o m e t i m e . A p p l y i n g these w a s t e s t o t h e g r o w i n g fields a n d irrigation s y s t e m s is p r o v i n g beneficial. In Europe, b o t h beet a n d cane f e r m e n t a t i o n residues are e v a p o r a t e d t o a p p r o x i m a t e l y 6 5 % d r y m a t t e r a n d are referred t o as " v i n a s s e s " (19). W e s t e r n European p r o d u c t i o n of these materials in 1 9 7 8 w a s close t o 6 8 0 , 0 0 0 tons. A l c o h o l f e r m e n t a t i o n vinasses have been used in Europe f o r a n i m a l feed because of a p p e t i t e - s t i m u l a t i n g properties. There has also been a large-scale post-harvest use of vinasses o n fields. Prior t o W o r l d W a r II cane residues f r o m U.S. a l c o h o l f e r m e n t a t i o n w e r e i n c i n e r a t e d t o m a k e potash f o r fertilizer use. Both d u r i n g a n d after W o r l d W a r 11, m i l l i o n s of p o u n d s of d r y a n d also c o n d e n s e d molasses f e r m e n t a t i o n p r o d u c t s w e r e p r o f i t a b l y sold f o r speciality i n d u s t r i a l use o u t s i d e of t h e feed i n d u s t r y . These m a r k e t s have been n e g l e c t e d a n d c o u l d readily be established again o n a n e c o n o m i c basis t o r e d u c e overall e t h a n o l p r o d u c t i o n costs f r o m cane or beet molasses. In l o o k i n g at t h e fuel f a r m i n g p i c t u r e , one w o n d e r s j u s t h o w m u c h t i m e any of these processes c o u l d b u y in relation t o t h e life of o u r fossil fuel s u p p l y . Biomass c o n v e r s i o n t o fuel does n o t appear t o be a real i m m e d i a t e a n s w e r t o o u r l o n g - t e r m e n e r g y p r o b l e m because of t h e costs of t h e r a w m a t e r i a l ; nevertheless, s o m e b r e a k t h r o u g h s appear on t h e horizon. The need f o r a yearr o u n d s u p p l y o f r a w material necessitates u s i n g cellulose f r o m a g r i c u l t u r a l , forest or m u n i c i p a l solid w a s t e s as t h e f e e d s t o c k source. T h e h i g h cost of e t h a n o l f r o m grain or sugar c a n e is d u e p r i m a r i l y t o r a w material w h i c h

206

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AS A

NONFOSSIL

FUEL

SOURCE

represents a b o u t t w o - t h i r d s of alcohol p r o d u c t i o n costs. In t h e U.S., t h e r e are t r e m e n d o u s t o n n a g e s of cellulosic materials d e r i v e d f r o m various u r b a n a n d industrial o r g a n i c w a s t e s w h i c h can be o b t a i n e d at l o w cost. T o use t h i s b i o m a s s for f e r m e n t a t i o n , it is m o s t i m p o r t a n t t o have it c o l l e c t e d a n d available at a c e n t r a l l o c a t i o n . Biomass e n t h u s i a s t s o f t e n overlook t h e h i g h cost of b r i n g i n g these t y p e s of r a w materials t o t h e p r o d u c t i o n plant.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch010

Process Possibilities S i g n i f i c a n t b r e a k t h r o u g h s have recently t a k e n place w h i c h w i l l i m p r o v e t h e e c o n o m i c p i c t u r e for m a k i n g a l c o h o l f r o m solid w a s t e . Rutgers U n i v e r s i t y research (20) o n t h e r m o t o l e r a n t m u t a n t strains of o r g a n i s m s p r o d u c i n g cellulase of a h i g h e r order t h a n r e p o r t e d heretofore s h o u l d be m e n t i o n e d . I m p o r t a n t w o r k o n v a c u u m t e c h n o l o g y t o o v e r c o m e factors of a l c o h o l i n h i b i t i o n l i m i t i n g f e r m e n t a t i o n e f f i c i e n c y has b e e n r e p o r t e d by Cysewski a n d W i l k e (21) as w e l l as R a m a l i n g h a m a n d Finn (22). Cysewski a n d W i l k e s u g g e s t e d s o m e process d e s i g n f e r m e n t a t i o n s c h e m e s for c o n t i n u o u s cell recycle a n d also v a c u u m f e r m e n t a t i o n processes for m a k i n g 7 5 , 0 0 0 gallons of 9 5 % e t h a n o l / d a y . Using a reasonable yeast b y p r o d u c t credit of $ 0 . 1 0 / l b , their net e s t i m a t e d p r o d u c t i o n cost appeared t o be $ 0 . 8 2 3 / g a l for t h e c o n t i n u o u s cell recycle s y s t e m as c o m p a r e d t o $ 0 . 8 0 6 / g a l for t h e v a c u u m f e r m e n t a t i o n . This c o m p a r e s f a v o r a b l y w i t h t h e c u r r e n t price of s y n t h e t i c 9 5 % e t h a n o l selling a r o u n d $ 1 . 4 0 / g a l . Spano (23) at t h e U.S. A r m y Laboratories has reassessed t h e e c o n o m i c s of cellulose process t e c h n o l o g y for p r o d u c t i o n of e t h a n o l using u r b a n w a s t e as a cellulosic substrate. T h e results of t h i s s t u d y are e n c o u r a g i n g . W i t h i m p o v e d cellulose p r o d u c t i v i t y a n d b y - p r o d u c t c r e d i t s of $ 0 . 5 4 / g a l of e t h a n o l , S p a n o has been able t o get t h e l o w e s t e s t i m a t e d cost d o w n t o $ 0 . 8 9 / g a l of 9 5 % e t h a n o l using a unit cost of $ 0 . 1 1 / g a l of a l c o h o l for t h e cellulosic material. Hoge (24) has s u g g e s t e d a novel e t h a n o l process u s i n g steam-sterilized i m p u r e cellulosic f r a c t i o n s of solid m u n i c i p a l w a s t e s t r e a t e d w i t h a m i x t u r e of e n z y m e a n d yeasts. T h e c o m b i n e d e n z y m a t i c d i g e s t i o n of cellulose t o sugars a n d t h e f e r m e n t a t i o n of sugars t o alcohol takes place in a c o m m o n reaction vessel. T h e s y s t e m has several reactors o p e r a t i n g at a t m o s p h e r i c pressure. Each reactor is i n t e r m i t t e n t l y c o n n e c t e d t o a shared r e c i r c u l a t i o n s y s t e m h a v i n g a flash c h a m b e r f r o m w h i c h a l c o h o l is d i s t i l l e d f r o m t h e reaction mass. T h e reaction t e m p e r a t u r e of t h e f e r m e n t a t i o n is also c o n t r o l l e d b y t h e v a c u u m . The u n i q u e d e s i g n of t h i s process e x t e n d s t h e life of t h e e n z y m e a n d reduces cost. Repeated reuse of t h e e n z y m e also makes t h e process

10.

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AND WILLIAMS

Economics of Ethanol Production

207

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a t t r a c t i v e . Enzyme cost has been h o l d i n g back c o m m e r c i a l - s c a l e cellulose d i g e s t i o n . Ethanol cost in t h e Hoge process is e s t i m a t e d a r o u n d $ 0 . 4 0 / g a l , exclusive of selling expenses, a d m i n i s t r a t i v e costs and profits based u p o n an a n n u a l p r o d u c t i o n of 32.7 m i l l i o n gallons of e t h a n o l . Recent u n p u b l i s h e d data f r o m Cornell University s h o w e d t h a t v a c u u m removal of alcohol f r o m t h e Hoge process i m p r o v e d yields per unit of cellulase e n z y m e used. A n o t h e r n o t e w o r t h y d e v e l o p m e n t is g o i n g o n at Purdue University. A c o m b i n a t i o n of solvent p r e t r e a t m e n t a n d e n z y m e hydrolysis of cellulose is used t o o b t a i n a very h i g h yield of sugar f o r t h e p r o d u c t i o n of alcohol (25). This opens great o p p o r t u n i t i e s f o r m a k i n g use of t h e o n e billion t o n s of cellulosic residues available each year f r o m cornstalks, w h e a t s t r a w , sugar mill bagasse, s a w m i l l rejects, p a c k a g i n g residues, l o g g i n g residues, a n i m a l feedlot w a s t e s , c i t y t r a s h , e t c . There is no q u e s t i o n t h a t t h e d i m i n i s h i n g supplies of o u r n o n - r e n e w a b l e materials w i l l a c c e n t u a t e t h e d e m a n d f o r resources t h a t are r e n e w a b l e . W e s h o u l d be practical in o u r t h i n k i n g . Let us r e m e m b e r t h a t if a / / t h e c o r n g r o w n in t h e W o r l d a n d a / / t h e w h e a t a n d all t h e o t h e r w o r l d crops g r o w n b y farmers w e r e t o be c o n v e r t e d into a l c o h o l , it w o u l d be six t o seven p e r c e n t of t h e e n e r g y e q u i v a l e n t of t h e w o r l d c r u d e oil p r o d u c t i o n (Table I). The c a l c u l a t i o n s in Table I are based o n t h e a s s u m p t i o n t h a t u p o n f e r m e n t a t i o n , a p p r o x i m a t e l y half t h e energy of grain is c o n v e r t e d t o e t h a n o l . This is exclusive of natural gas or coal e n e r g y sources. The idea of r e n e w a b l e s o u n d s great u n t i l y o u p u t it into perspective a n d look at t h e e c o n o m i c s (Table II). M o s t ecologists j u s t d o n ' t . The e c o n o m i c d i s p a r i t y of f e r m e n t a t i o n alcohol as fuel at t h e service s t a t i o n p u m p c o m p a r e d t o gasoline at t o d a y ' s prices of a r o u n d $ 1 . 0 0 / g a l is self-evident w i t h o u t even g o i n g into Btu or p e r f o r m a n c e ratings. Yet in t h e m i d s t of t h i s p e s s i m i s m , t h e r e is s o m e h o p e t o at least make use of industrial a n d u r b a n w a s t e material t o e x t e n d o u r fuel supplies (26). W e feel t h a t o u r greatest o p p o r t u n i t i e s m a y y e t c o m e f r o m b r e a k t h r o u g h s i n v o l v i n g t h e cross d i s c i p l i n e s b e t w e e n t h e c h e m i s t , engineer, a g r i c u l t u r a l engineer, m i c r o b i o l o g i s t , g e n e t i c i s t , b i o c h e m i s t , a g r o n o m i s t a n d last b u t n o t least, t h e economist A s W i n s t o n Churchill o n c e said. " W e have n o t reached t h e b e g i n n i n g of t h e e n d . b u t perhaps w e have reached t h e e n d of t h e b e g i n n i n g . "

208

BIOMASS

AS A

NONFOSSIL

FUEL

SOURCE

T a b l e I. A N N U A L W O R L D G R A I N S U P P L Y A L C O H O L E Q U I V A L E N C E A N D CRUDE OIL USE

CRUDE OIL

1975

19.5x10 5.8X10

Total

6

barrels

9

Btu/barrel

113.1 X 1 0

Btu's

1 5

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113.1 Q u a d s CORN

1975

3 2 4 . 7 2 1 . 0 0 0 m e t r i c t o n s ( 3 5 8 x 1 0 short tons) 380 Kcal/100 grams 6859 Btu/lb

WHEAT

1975

3 5 5 . 9 8 5 . 0 0 0 m e t r i c t o n s ( 3 9 2 x 1 0 short tons)

6

6

330 Kcal/100 grams RICE

1975

SOYBEAN

1975

5957 Btu/lb

348,374.000 metric tons ( 3 8 4 x 1 0

6

s h o r t tons)

370 Kcal/100 grams

6679 Btu/lb

68.900.000 metric tons

(76 Χ 1 0

360 Kcal/100 grams

6498 Btu/lb

Btu .25198 K i l o g r a m - c a l o r i e Pounds — 4 5 4 grams

6

short tons)

3.97 B t u / . 2 2 lbs. 18.05 B t u / l b

CORN

716x10

9

Ibs.x6.859x10 - 4 . 9 X 1 0

WHEAT

784X10

9

Ibs.x5.957x10 = 4.7X10

1 5

Btu's = 4.7 q u a d s

RICE

768X10

9

Ibs.x6.679x10 = 5.1x10

1 5

Btu's =

5.1 q u a d s

SOYBEAN 152X10

9

Ibs.x6.498x10 -

1 5

Btu's-

.9 q u a d s

3

3

3

3

.9x10

1 5

Btu's

- 4.9 q u a d s

15.6 q u a d s

15.6x0.50 2J*

7.8 q u a d s -

a l c o h o l e q u i v a l e n t of W O R L D GRAINS

= 6.9% of CRUDE OIL USE

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10.

PREBLUDA

A N D WILLIAMS

209

Economics of Ethanol Production

Table I I . F E R M E N T A T I O N E T H A N O L A S FUEL

Φ/QAL

CORN

WOOD WASTE

SUGAR CANE

CASSAVA

56 20 30

68 33 36

Net R a w M a t e r i a l Cost Processing Cost

44 30

Capital Charges

40

68 40 82

114

190

106

137

5 8

5 8

5 8

5 8

127

203

119

150

SUB-TOTAL Distribution Dealer M a r g i n PUMP PRICE ( e x c l u d i n g taxes)

210

BIOMASS AS A NONFOSSIL FUEL SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch010

REFERENCES

1.

Anderson J. "Gasohol Gasohowl", NY. Daily News. July 5, 1978.

2.

Klass, D. L. "Symposium Papers", Energy from Biomass and Wastes Symposium sponsored by the Institute of Gas Technology, Washington, D.C., Aug 1978; Institute of Gas Technology: Chicago, 1978.

3.

Anderson, Ε. V. Chem. Eng. 1978,

4.

Reese, Κ. M. Chem. Eng. News 1979, 57 (35), 56.

56 (31), 8-12, 15.

5. Hind, J. D. Chem. Eng. News 1978, 56 (35), 43. 6. Williams, Roger, Jr. "Methanol — The Energy Chemical", presented to the World Trade Institute and Chemurgic Council on Renewable Resources, New York, May 1976. 7. Williams, Roger, Jr. "Methanol — Markets vs. Price". Testimony before State Affairs Committee, Alaska State Senate, Juneau, Alaska, 1976. 8. Smay, V. E. Popular Science 1978, June, pp 90-91; Weisz. P. B.; Marshall, J. F. "High Grade Fuels From Biomass — Analysis of Potentials and Constraints". International Symposium On Energy and Technology, International Association of Science and Technology for Development (I.A.S.T.E.D.), Montreux, Switzerland, June 19-21, 1979; Weisz, P. B.; Marshall, J. F. "Fuels From Biomass: A Critical Analysis of Technology & Economics"; Marcel Dekker: New York City, in press. 9. Pratt, H. T. Chem. Eng. News 1978, 56 (41), 2,55. 10. Gauss, William F.; Suzuki, S.; Takagi, M. U.S. Patent 3990944, 1976; Huff, George F.; Yata, N. U.S. Patent 3990945, 1976; Chemical Marketing Reporter 1979, 216 (8), 7. 11.

United States Department of Energy, "Position Paper on Alcohol Fuels", March 1978; United States Department of Energy, "The Report of the Alcohol Fuels Policy Review", June 1979.

12.

Milling and Baking News 1979, 58 (28), 59.

10. PREBLUDA AND WILLIAMS Economics of Ethanol Production 211

13.

United States Department of Agriculture, Economics, Statistics & Cooperatives Service, "Gasohol From Grain ... The Economic Issues". Prepared for the Task Force on Physical Resources, Committee of The Budget, U.S. House of Representatives, Washington, D.C., January 19, 1978.

14. Klosterman, H.J.; Banasik, O. J.; Buchanan, M. L.; Taylor, F. R.; Harrold, R. L. Farm Res. 1978, 35 (2), 3-8.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch010

15.

Kerkkonen, H. K.; Laine, Κ. M. J.; Alanen, M. R.; Renner, H. V. U.S. Patent 3951938, 1976.

16. Richter, J. Beef 1978, 72. 17. Jawetz, P. "Symposium Papers", Energy From Biomass and Wastes Symposium sponsored by the Institute of Gas Technology, Washington, D.C., Aug 1978; Institute of Gas Technology: Chicago, 1978; 14th InterSociety Energy Conversion Engineering Conference, Boston, Mass. Aug 1979; American Chemical Society, Division of Petroleum Chemistry, Washington, D.C., September, 1979. 18. Rolz, C. Meeting of the American Chemical Society, Miami, September 1978. American Chemical Society: Washington, D.C., 1978. 19. Lewicki, W.Process Biochemistry 1978, 78 (13), 12. 20.

Montenecourt, B. S.; Eveleigh, D. E. "Hypercellulolytic Mutants and Their Role in Saccharification"; Rensselaer Polytechnic Institute; Troy, N.Y., June 20-21, 1978.

21.

Cysewski, G. R.; Wilke, C. R. Biotechnol. Bioeng. 1977, 1978, 20, 1421.

22.

Ramalingham, Α.; Finn, R. K. Biotechnol. Bioeng. 1977, 19, 583.

23.

Spano, L. "Revised Economic Analysis of Cellulose Process Tech­ nology", Fuels From Biomass Fermentation Newsletter; Rensselaer Polytechnic Institute, Troy, Ν. Y., July 1978, Item 4, p 9.

24.

Hoge, W. H. U.S. Patent 4009075, 1977; Finn, R. K. to Hoge, W. H., private report on laboratory results, 1979; Hoge, W. H. to Prebluda, H. S., private communication, 1979.

19,

1125;

212

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25. Ladisch, M. R.; Ladisch, C. M.; Tsao, G. T. Science 1978, 201, 743. 26. Williams, Roger, Jr.; Rains, W. Α.; Prebluda, H. J. "Is Solid Waste a Viable New Jersey Raw Material?" New Jersey Academy of Science: Lawrenceville, N. J., April 7, 1979.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch010

RECEIVED JUNE 18, 1980.

11 Chemicals from Biomass by Improved Enzyme Technology 1

GEORGE H. EMERT

Gulf Oil Chemicals Company, P.O. Box 2900, Shawnee Mission, KS 66201

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

RAPHAEL KATZEN Raphael Katzen Associates, 1050 Delta Avenue, Cincinnati, OH 44208

PART I - CELLULOSE TO ETHANOL PROCESS Introduction Gulf's biochemical research program began in 1971 with a search for alternate feedstocks for petrochemicals manufacture. Practically all of the organic chemicals industry relies on chemicals derived from fossil fuels — petroleum, natural gas or coal. We had become concerned even before the Arab embargo that increasing prices of petroleum and petroleum feedstocks would eventually make many of the materials now supplied by the chemicals industry too expensive for general use. It was becoming imperative to have alternate feedstock sources available. Subsequent research led to the construction of a cellulose-to-ethanol pilot plant at Pittsburgh, Kansas. This pilot plant has a capacity of one ton of feedstock per day and has been in operation since January, 1976. Information gained from work done in our Merriam laboratories and the operation of the pilot plant has led us to recognize that renewable resources in the form of carbohydrates are an excellent source of a variety of chemicals now derived from fossil fuels. Our plans f o r t h i s t e c h n o l o g y in t h e very near f u t u r e i n c l u d e t h e process d e s i g n , p r o c u r e m e n t , f a b r i c a t i o n , c o n s t r u c t i o n a n d o p e r a t i o n of a 5 0 - t o n / d a y cellulosic w a s t e c o n v e r s i o n facility, f o l l o w e d b y a c o m m e r c i a l scale f a c i l i t y

1

Current address: 415 Administration, University of Arkansas, Fayetteville, A R 72701

0097-6156/81/0144-0213$05.00/0 © 1981 American Chemical Society

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utilizing 2.000 t o n s / d a y of cellulosic feedstocks t o be o p e r a t i o n a l by 1983. This b i o c o n v e r s i o n t e c h n o l o g y addresses itself t o t w o i m p o r t a n t national p r o b l e m s . One is t h e r e m o v a l or decrease in v o l u m e of solid w a s t e . S e c o n d l y , it provides e t h y l alcohol a n d o t h e r c h e m i c a l s w h i c h can be utilized t o s u p p l a n t fossil fuel sources as a feedstock.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

Direct Cellulose t o Ethanol Process The c e l l u l o s e - t o - e t h a n o l process has five basic steps as s h o w n in Figure I. T h e y are: f e e d s t o c k h a n d l i n g a n d p r e t r e a t m e n t , e n z y m e p r o d u c t i o n , yeast p r o d u c t i o n , s i m u l t a n e o u s s a c c h a r i f i c a t i o n / f e r m e n t a t i o n (SSF) a n d e t h a n o l recovery. Cellulose is t h e m o s t a b u n d a n t o r g a n i c material o n t h e earth. It is a n n u a l l y r e n e w a b l e , a n d not d i r e c t l y useful as a f o o d s t u f f . It is a p o l y m e r of g l u c o s e linked / M . 4 as c o m p a r e d w i t h t h e ο - 1 , 4 linked p o l y m e r starch w h i c h by c o n t r a s t is easily d i g e s t i b l e by m a n . There are t h r e e basic classes of p o t e n t i a l cellulose feedstocks. These are a g r i c u l t u r a l b y - p r o d u c t s , industrial a n d m u n i c i p a l w a s t e s , a n d special crops. T h e availability of t h e s e materials in t h e U.S. is s h o w n in Table I. For e c o n o m i c reasons, w e are c o n c e n t r a t i n g our efforts on t h o s e materials t h a t are c o l l e c t e d for s o m e o t h e r reason. W i t h respect t o c o n v e r s i o n t o e t h a n o l or o t h e r c h e m i c a l s , t h e r e are f o u r m a j o r f a c t o r s t o c o n s i d e r r e g a r d i n g t h e s u s c e p t i b i l i t y of n a t i v e cellulose t o b i o d é g r a d a t i o n . These are: its i n s o l u b i l i t y in w a t e r , p a r t i c l e size, e x t e n t of l i g n i f i c a t i o n , a n d c r y s t a l l i n i t y . L i g n i n , a p o l y p h e n o l i c , c e m e n t - l i k e m a t e r i a l , is f o u n d closely associated w i t h n a t u r a l l y o c c u r r i n g cellulose, a n d n o t o n l y i n h i b i t s access t o cellulose linkages b u t in s o m e cases is t o x i c t o m i c r o o r g a n i s m s . L i g n i n presence in kraft or sulfite p u l p e d cellulosics is not a p r o b l e m using our s y s t e m . T h e crystal s t r u c t u r e of cellulose has f i n i t e p h y s i c a l m e a s u r e m e n t s w h i c h d i s a l l o w t h e c e l l u l o l y t i c e n z y m e s access t o t h e 0 - 1 , 4 linkage. A w i d e variety of p o t e n t i a l f e e d s t o c k s has been t e s t e d at t h e pilot p l a n t level. These i n c l u d e c o t t o n g i n t r a s h , clarifier sludges, digester fines, digester rejects, s t r a w , bagasse, a n d m u n i c i p a l solid w a s t e . Several m i c r o b i a l , m e c h a n i c a l , a n d c h e m i c a l p r e t r e a t m e n t s have been t e s t e d . M i c r o b i a l pretreatments include: ligninase-producing organisms and xylanase-producing o r g a n i s m s . M e c h a n i c a l p r e t r e a t m e n t s t e s t e d i n c l u d e h a m m e r mills, rod mills, roller mills, ball mills, m u l l o r s . a n d attritors. C h e m i c a l p r e t r e a t m e n t s t e s t e d i n c l u d e a c i d . base, c a d m i u m o x i d e , d i m e t h y l s u f f o x i d e . e t h y l e n e d i a m i n e . t a r t r a t e , etc. O b v i o u s l y , t h e r e are specific particle sizes, degrees of m o i s t u r i z a t i o n , a n d lignin c o n t e n t s w h i c h are o p t i m u m for c o n v e r s i o n of t h e cellulose t o c h e m i c a l s .

11.

EMERT AND KATZEN

215

Chemicals from Biomass

Characterizations o f p o t e n t i a l feedstocks have been a c c o m p l i s h e d b y m e a s u r i n g p e r c e n t cellulose, l i g n i n , ash, a n d acid d e t e r g e n t - s o l u b l e materials as s h o w n in Table II. A s a n e x a m p l e , t h e c o m p o s i t i o n s of p u l p a n d paper w a s t e s s h o w a p p r o x i m a t e l y a 5 5 % average cellulose c o n t e n t . M o s t of these materials have been partially d e l i g n i f i e d a n d t h u s s h o w a m o d e r a t e lignin c o n t e n t . High ash c o n t e n t w o u l d be a d e t r i m e n t f o r processing purposes

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

since it is w e i g h t w h i c h has t o be m o v e d t h r o u g h t h e process along w i t h substrate, t h u s u s i n g excess energy. P r e t r e a t m e n t of f e e d s t o c k f o r subseq u e n t processing m a y i n c l u d e m i x i n g in w a t e r t o o b t a i n a u n i f o r m m i x t u r e a n d m o i s t u r i z a t i o n f o l l o w e d b y either pasteurization or sterilization as necessary. The s e c o n d step in t h e d i r e c t e t h a n o l process is t h a t of e n z y m e p r o d u c t i o n . The Gulf process utilizes a m u t a n t strain of Trichoderma

reesei.

grown

c o n t i n u o u s l y t o p r o d u c e a c o m p l e t e cellulase s y s t e m . T h e residence t i m e is 4 8 hours. Enzyme p r o d u c t i o n b e g i n s o n a spore plate w i t h s u b s e q u e n t scaleup t o t h e e n z y m e p r o d u c t i o n vessel size t o be used. Our pilot plant facility has 3 0 0 - g a l e n z y m e reactors. T h e cellulase s y s t e m consists o f /8-1,4-endoglucanase, a c e l l o b i o h y d r o l a s e a n d a /8-glucosidase. These activities are m e a s u r e d c o l l e c t i v e l y f o r their a b i l i t y t o e n z y m a t i c a l l y catalyze t h e d e g r a d a t i o n of crystalline cellulose t o glucose. T h e t r i p l e e n z y m e s y s t e m does n o t have t o be isolated or p u r i f i e d , b u t is used as a w h o l e b r o t h . The t h i r d step in t h e d i r e c t e t h a n o l process is t o p r o d u c e t h e yeast necessary for c o n v e r t i n g t h e g l u c o s e t o e t h a n o l . Varieties of o r g a n i s m s have been screened f o r c o m p a t i b i l i t y w i t h t h e Trichoderma reesei cellulase s y s t e m . The o p t i m u m t e m p e r a t u r e f o r t h e cellulase s y s t e m is 4 5 ° t o 50°C. M o s t yeasts have a t e m p e r a t u r e o p t i m a less t h a n t h a t , e.g., 3 0 ° t o 35°C. W e have t e s t e d a variety of strains, i n c l u d i n g Saccharomyces cerevisiae, S. carlsbergensis, and Candida brassicae. A t e m p e r a t u r e of 4 0 ° C has been i d e n t i f i e d as o p t i m u m for t h e c o m b i n e d cellulase a n d yeast systems. The f o u r t h step in t h e d i r e c t e t h a n o l process is c o n s i d e r e d t o be key t o t h e e c o n o m i c v i a b i l i t y o f t h e b i o c o n v e r s i o n of cellulose t o c h e m i c a l s . T h e pretreated cellulose slurry is s i m u l t a n e o u s l y c o n v e r t e d t o glucose a n d t h e g l u c o s e t o e t h y l alcohol in t h e same vessel in a c o n t i n u o u s or s e m i c o n t i n u o u s m o d e . The e n z y m e s a m p l e is t h e w h o l e c u l t u r e f r o m t h e e n z y m e p r o d u c t i o n vessel. T h e f e e d s t o c k is a slurry o f 7.5% t o 1 5 % cellulose. T h e yeast is either a d d e d as a cake or recycled as a c r e a m .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

216

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W h e n a c o m p a r i s o n is m a d e of s i m u l t a n e o u s s a c c h a r i f i c a t i o n / f e r m e n t a t i o n , a n d s a c c h a r i f i c a t i o n alone w i t h s u b s e q u e n t c o n v e r s i o n t o e t h y l alcohol of t h e g l u c o s e , one f i n d s a considerable e n h a n c e m e n t of e t h a n o l p r o d u c t i o n as s h o w n in Figure II. T h i s e n h a n c e m e n t a m o u n t s t o a 2 5 % t o 4 0 % increase in y i e l d a n d is d u e t o t h e r e m o v a l of p r o d u c t s f o r m e d d u r i n g s a c c h a r i f i c a t i o n w h i c h i n h i b i t t h e cellulase s y s t e m . Glucose a n d cellobiose are f e e d b a c k i n h i b i t o r s of e n z y m e s in t h e cellulase s y s t e m . In SSF, w h e n g l u c o s e is r e m o v e d as fast as it is p r o d u c e d , t h e r e is no p r o d u c t i n h i b i t i o n ; t h u s t h e e n z y m e s f u n c t i o n m o r e efficiently. Figure III s h o w s t h e p r o j e c t e d e t h a n o l p r o d u c t i o n w h e n paper a n d p u l p m i l l w a s t e is reacted w i t h a s t a n d a r d a m o u n t of e n z y m e as p r o t e i n w h i c h c o i n c i d e s w i t h a 1 0 % v / v i n o c u l u m of t h e e n z y m e p r o d u c t i o n m a t e r i a l . It is a s i m p l e m a t t e r t o raise t h e c o n v e r s i o n t o 9 0 % w i t h s l i g h t l y m o r e p r o t e i n , for e x a m p l e u s i n g a 2 0 % v / v i n o c u l u m . T h e last step in t h e d i r e c t e t h a n o l process is r e c o v e r y of e t h a n o l . To d o t h i s , a slurry s t r i p p e r w a s d e s i g n e d in w h i c h w e c o u l d d i r e c t l y p u m p t h e m a s h of SSF i n t o a s t r i p p i n g c o l u m n a n d strip t h e a l c o h o l u s i n g an u p w a r d f l o w of s t e a m . A p p r o x i m a t e l y 2 5 % by w e i g h t e t h a n o l c o n c e n t r a t i o n is o b t a i n e d in t h i s first step. This material can t h e n be u p g r a d e d t h r o u g h a n o r m a l r e c t i f i c a t i o n s y s t e m t o either i n d u s t r i a l grade, m o t o r grade, or p h a r m a c e u t i c a l grade ethyl alcohol. There are f o u r basic c h a r a c t e r i s t i c s of f e r m e n t a t i o n processes w h i c h c o m e t o m i n d w h e n c o m p a r i s o n s are m a d e w i t h c o n v e n t i o n a l p e t r o c h e m i c a l processing t e c h n i q u e s . These are t h a t f e r m e n t a t i o n o c c u r s at essentially a m b i e n t t e m p e r a t u r e s a n d pressures, incurs l o w c o r r o s i o n of e q u i p m e n t , i n h e r e n t l y involves l o w reaction rates, a n d results in l o w p r o d u c t c o n c e n t r a t i o n s . T h e first t w o c h a r a c t e r i s t i c s are a d v a n t a g e o u s a n d s u p p o r t u s i n g f e r m e n t a t i o n t e c h n o l o g y industrially. T h e s e c o n d — l o w rates a n d l o w c o n c e n t r a t i o n s — are d i s a d v a n t a g e o u s . It is t h e a b i l i t y t o m a n a g e or o v e r c o m e these w h i c h d e t e r m i n e s w h e t h e r or not a p a r t i c u l a r f e r m e n t a t i o n t e c h n o l o g y is a p p r o p r i a t e for c o m m e r c i a l use. S h o w n in Table III are t h e c o m b i n e d results i n d i c a t i n g progress m a d e in our research laboratories a n d pilot plant since 1 9 7 5 . T h e level of a c c o m p l i s h m e n t in e n z y m e p r o d u c t i o n a n d SSF e t h a n o l yield s h o w n for 1 9 7 8 w a s utilized for t h e e c o n o m i c e v a l u a t i o n a n d e n e r g y c a l c u l a t i o n s w h i c h are i n c l u d e d in t h i s paper. P A R T II - T E C H N I C A L A N D E C O N O M I C E V A L U A T I O N T h e basic f l o w s h e e t for t h e p r o p o s e d c o m m e r c i a l process is s h o w n in Figure IV.

11.

EMERT

217

Chemicals from Biomass

A N DKATZEN

Table L UQNO-CELLULOSE A V A L A B U T Y tons/year Coftected Municipal Solid Waste Pulp and Paper Mill Waste Selected Agricultural Waste

140,000,000 3.000.000 1.000.000

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

UncoMectBd Forest Residues W o o d Processing Agricultural Residues

145.000.000 20,000.000 300.000.000

Table L C O M O S F T O N OF C E L L U L O S C S % Dry Solids Wastes

Cellulose

Lignin

Ash

Ads

48 21 29 62 65 64 61 43

8 4 4 6 13 9 9 14

18 55 38 8 1 5 8 8

26 20 29 24 21 22 22 35

Primary clarifier sludge Secondary clarifier sludge Deinking sludge Super fines Digester rejects Digester fines Municipal solid waste RDF Bagasse

Table WL PROGRESS S U M M A R Y

Enzyme Production Residence Time Enzyme A c t i v i t y (Conversion of Cellulose) Saccharification-Fermentation Residence Time Cellulose Concentration Ethanol Production (Concentration)

1976

1976

1977

1978

Design

14 days

10 days 11%

4 days 51%

2 days 90%

2 days 90%

6 days 6% 1%

2 days 10% 1.8%

1 day 8% 3.6%

1 day 8% 3.6%

218

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

BIOMASS

Figure 2.

Comparison of simultaneous saccharification/fermentation (SSF) saccharification

and

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

11.

NUTRIENTS • WATER Of REACTION ( I K tons/day) Municipal Solid Waste (500 00 tons/day) Saw mil Waste (250 00 tons/day) Pulp Mill Waste (250 00 tons/day)

219

Chemicals from Biomass

EMERT AND KATZEN

f"""~TYEA!

RAW MATERIAL RECEIVING & STORAGE SECTION 100

MATERIAL PREPARATION

SIMULTANEOUS SACCHARIFICATION * FERMENTAT I Of.'

ENZYME PRODUCTION J

CO; VENTING^

SECTI

1,

ol Enzyee / Recycle

I

c 13.984 KW (424 00 tons/day)

: POWER 13.711 KW

"I

I

GENERAL UTILITIES t OfFSITES SECTION 700

Li

WASTE LIQUOR

A

CONDENSATE TREATMENT (EVAPORATION) SECTION 600

Dissolved Solids

ALCOHOL RECOVERY

Treated Waste Sludg (15 tons/day)-

Figure 4.

1000 TPD feedstock

,000 U.S. Gal/day] INDUSTRIAL (190°PR) ALCOHOL, (37.440 U.S. Gal/day) (TOTAL » 242 tons/day)

220

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N O N F OSSIL

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SOURCE

T h e n o m i n a l q u a n t i t i e s s h o w n are based on a s s u m e d availability of 1,000 t o n s / d a y (dry basis) of cellulosic w a s t e s , c o n t a i n i n g a p p r o x i m a t e l y 5 5 % cellulose. From t h e data s t u d i e d , p r o j e c t e d p r o d u c t i o n of 7 5 , 0 0 0 g a l / d a y of e t h a n o l (190° pr basis) is e s t i m a t e d . Also, b y - p r o d u c t / a n i m a l feed in t h e a m o u n t of 2 6 7 t o n s / d a y w o u l d be p r o d u c e d . Inherent in t h i s process is t h e separation of i n s o l u b l e solids, t h e o r g a n i c c o n t e n t of w h i c h , p r i m a r i l y l i g n i n

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

a n d u n c o n v e r t e d cellulose, w o u l d b e c o m e t h e basic fuel for t h e plant, p r o v i d i n g essentially all of t h e t h e r m a l e n e r g y a n d a m a j o r part of t h e m o t i v e (turbine-drive) energy. A m i x e d f e e d s t o c k of m u n i c i p a l solid w a s t e , p u l p mill w a s t e a n d s a w d u s t w a s used as t h e basis for these balances. This, of course, m a y be varied regionally, a n d m a y i n c l u d e a g r i c u l t u r a l w a s t e s a n d residues. T h e essentially s e l f - c o n t a i n e d process requires o n l y small a m o u n t s of fossil f u e l , a n d p u r c h a s e d e l e c t r i c p o w e r , w h i c h m a y be g e n e r a t e d f r o m fossil fuel. Energy balances based o n net fuel v a l u e of t h e r a w materials a n d p r o d u c t s ( i n c l u d i n g fuel used t o p r o d u c e electric p o w e r ) i n d i c a t e an overall e n e r g y e f f i c i e n c y of 5 1 % as i n d i c a t e d in Figure V. O n g o i n g i n v e s t i g a t i o n s have i n d i c a t e d a s u b s t a n t i a l e c o n o m i c a d v a n t a g e in c o n v e r t i n g 2 , 0 0 0 t o n s / d a y of cellulosic w a s t e t o 1 5 0 , 0 0 0 g a l l o n s of a l c o h o l . This a m o u n t of w a s t e m a t e r i a l appears t o be e c o n o m i c a l l y available at a n u m b e r of locations in t h e U.S. S u c h a c o m m e r c i a l facility, p l a n n e d for c o n s t r u c t i o n d u r i n g t h e p e r i o d 1 9 8 0 - 8 2 . has been e s t i m a t e d t o cost a p p r o x i m a t e l y $ 1 1 2 m i l l i o n (1981 costs). A s i n d i c a t e d in T a b l e IV. t o t a l p r o d u c t i o n c o s t o n a 1 0 0 % investor e q u i t y c a p i t a l basis is $ 0 . 7 0 / g a l of a l c o h o l . T h e p r o j e c t e d selling price d u r i n g t h e first p r o d u c t i o n year. 1 9 8 3 , is $ 1 . 4 4 / g a l e t h a n o l , after credit is taken for a n i m a l feed b y - p r o d u c t s a n d a l l o w a n c e s are m a d e for taxes a n d a 1 5 % after-tax return o n i n v e s t m e n t for a 10-year plant life. Since t h e f a c i l i t y is d i s p o s i n g of w a s t e materials, a n d m a y be c o n s i d e r e d a s o l u t i o n t o a g r o w i n g n a t i o n a l solids w a s t e disposal p r o b l e m — p a r t i c u l a r l y t h e need for e l i m i n a t i o n of landfills — t h e project m a y be c o n s i d e r e d as a w a s t e disposal f a c i l i t y a n d t h e r e b y m i g h t be f i n a n c e d t o a s u b s t a n t i a l e x t e n t by m u n i c i p a l tax-free b o n d s . A s s h o w n in Table V. o n t h e basis of 8 0 % m u n i c i p a l b o n d f i n a n c i n g over 2 0 years for t h e f i x e d i n v e s t m e n t , a n d e q u i t y capital f i n a n c i n g of t h e r e m a i n i n g f i x e d i n v e s t m e n t a l o n g w i t h b o r r o w e d w o r k i n g capital f r o m c o n v e n t i o n a l sources, after t a k i n g c r e d i t for t h e a n i m a l feed b y - p r o d u c t , t h e t o t a l o p e r a t i n g cost is $ 0 . 5 9 / g a l l o n of a l c o h o l a n d t h e p r o j e c t e d selling price for a 1 5 % aftertax return on investor's e q u i t y capital is $ 0 . 9 5 / g a l l o n in t h e year 1983. The 1 9 8 3 selling price is a t y p i c a l because t h e federal a n d state taxes are r e d u c e d d u e t o previous losses in interest p a y m e n t prior t o s t a r t u p of t h e plant.

11.

EMERT

221

Chemicals from Biomass

AND KATZEN

Flue Gas Energy Loss 1,786 MM Btu/D

±

STEAM AND POWER CO-GENERATION Purchased Fuel Oil Feedstocks

• 99 Bbl/D 594 MM Btu/D

! Steam 2,070 T/D Residue 4,800 MM Btu/D 419 T/D 6,369 MM Btu/D/ Electric Power & Turbine Drive 152,500 kwh/D 521 MM Btu/D

1,000 T/D (dry) 15,088 MM Btu/D

Fuel - 10,000 Btu/kwh 3,290 MM Btu/D

Alcohol

75,000 gal/D (190°Pr) 6,000 MM Btu/D

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

PROCESS Power Plant

329,000 kwh (Purchased) or 1,151 MM Btu/D

Animal Feed - 267 T/D (dry) 3,080 MM Btu/D Heat and Mechanical Energy Losses 5,967 MM Btu/D

Heat to Cooling Water & Stack 2,139 MM Btu/D

Overall Gross* Energy Efficiency, ( Overall Net Energy Efficiency, (Corrected for (•Neglecting Differences in Boiler

Figure 5.

Products ) Feedstocks & Power

* 48%

Boiler

= 51%

Efficiency Differences

Efficiencies among Various Fuels)

Cellulose alcohol process: energy balance, daily basis

B.OO-

4Λ0-

Curve A Β C D

Figure 6.

Code X

•

••

Process Raw Material Ethylene Com Cellulose Cellulose

Plant Capacity SO SO 50 SO

MM MM MM MM

Fixed Investment Method of Financing

GPY $50.6 MM GPY S63.1 MM GPY $112.2 MM GPY $112.2 MM

lOOt Co. Financed 1001 Co. Financed 100X Co. Financed 801 Municipal Bond Financing

Comparative ethanol economics, selling price for 15% ROI A Τ

222

BIOMASS

AS A NONFOSSIL

FUEL

SOURCE

Table IV. CELLULOSE ALCOHOL 2 0 0 0 T/D Commercial Plant Investment (1981 Costs) 50 UNI USGPY (190° Proof) Ethanol

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

1981 $ MM Section 100 - Raw Materials Receiving & Storage 2 0 0 - Raw Material Preparation 3 0 0 - Enzyme Production 400-SSF 500 - Alcohol Recovery 6 0 0 - W a s t e Liquor (feed molasses) & Condensate Treatment 7 0 0 - General Facilities a n d Offsites Including Dryer Boiler

8.95 11.65 8.34 16.80 10.42 13.98

Power Generation Power Distribution Scrubber Cooling Tower Wells Water Treatment Offsifes Office and Labs Maintenance & Stores Alcohol Storage and Shipping Fire Protection Yard Piping Miscellaneous Total Section 7 0 0

27.46 Total Installations + 1 5 % Contingency

$ 97.60 14.60 Total Investment

$112.20

(2102) 500 2948 100 550 550 000 620 4768

(0420) 0.100 0702 0000 0000 0000 0367 0367 1436

(21 02) 50 35 11 000 000 000 1830 1830 71 71

By Product Credit ($1?0/ton) Sales. Freight G&A0 ($0 10/gan Total Operating Coots

Interest on Working Capital (10%) Interest on Loan (6 5%) Previous Taxable Losses Paid Back Federal and State Taxes (50%) Net Profit After Taxes

Total tioorna and toting Prtoa

250 4550

1022

51 13

035 030

923 1.35 10.58

Total Production Cott

0185 0027 TOT

0007 0006 0037

9 23 1 35 ÏÏÏ5T

UtiPtioa Electric Power 2194 MM kwh at 042 $/kwh Fuel 64.000 bbl/yr at $21 00/bbl Subtotal

462 347 2.31 967 20.07

0093 0069 0046 0193 0401

035 0 30 185 250

4 62 347 231 968 2008

MSW - 1.000 OD T/D x 330 Dal $14 00/O D Τ SMW - 500 Ε D T/D x330 D at $21 00/0DT PMW - 500 0D T/D x 330 D at $1400/ODT Nutrients. Chemicals, etc Subtotal

5Θ1 0.01 449 224 12 35

0224 0000 0090 0045 0359

0954

0.020 0.110 0.110 0000 0.124

(0420) 0.100 0590

0.910

0.007 0.006 0.037 0.050

0.1 P5 0.027 0212

0.093 0.069 0.046 0193 0.401

0.112 0000 0.090 0.045 0.247

20 YIAA AMDPTBAT0N - 1ΜΙΉΡΜΟ •0HMUMCPAL 10ND PMAMB

Labor 8 - Supervisory staff ($43.750/yr) 11 - Lab and Office Staff ($27.275) 58 - Operators. Laborers ($31.900) Subtotal

11.22 002 449 224 17 97

Depreciation (D). Straight Line License Fees Maintenance. 4% of TFI Taxes & Insurance. 2% of TFI Subtotal

PJaad Charfw

10-VIA*. AMORTIZATION - WfTMPHOIY-PPOOUCT 100 H COMPANY 1•NANCNQ

OPWATPJO COST AMD ULUNQ PPJCI MTiMTlS (1IU) IA1I CAil - WTTM WNt EYMi PJCVCLI •0 MM U.I. QALLONi/YP. PRODUCTION

Tat* V. CILLULOfl ALCOHOL

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

224

BIOMASS

ASA NONFOSSIL

FUEL

SOURCE

10.15

0.126 0001 0.060 0JD26 0203

Table VI. SYNTHETIC AMD

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

Baata: SO MM US9PY (ISO* Ptaaeff) Etjoaxd)

Mil Total Fixed Investment (TFO (For Construction 1980-1962) Working Capital Read ( Depreciation (D). 10% of TR License Fees. (10 yr payout) Maintenance. 4% of TFI Taxes & Insurance. 2% of TR

Ethylene ($0.18/lb) Com ($3.00/bu) Other

Total Praduodan Coat (TFO

50.6 72 57A 5.6 02 Z0 10

1Z7 75B

8u8

0.112 0.004 O040 0O20 0.176

37.5

0.750

1.2

0.024

600 005

ooqi

11.9

0238

13.9

027B

03

0018 1030

23

By-product Credit (S120.00/T) Sales. Freight. G&AO ($0.10/gal)

6l3

006 2i 13

1200

7625

0046 1525

( - 200)

( - 0400)

50

0100

50

0100

Total Operating Coats

65.3

1.306

714

1428

Federal & State Taxes

a7

0.174

114

0228

a7

0.174

114

0228

82.7

1.654

942

1884

Net Profit

(15% ROI After Taxes)

11.

EMERT

AND

KATZEN

Chemicals from Biomass

225

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch011

Figure 6 s h o w s t h e p r o j e c t e d selling price for a 1 5 % r e t u r n on i n v e s t m e n t after taxes for t h e 5 0 , 0 0 0 , 0 0 0 g a l / y r Gulf cellulose alcohol plant a n d for f e r m e n t a t i o n corn a n d s y n t h e t i c e t h y l e n e - a l c o h o l plants of t h e same c a p a c i t y (Table VI). The e t h y l e n e costs are escalated at 9%, per i n d u s t r y p r o j e c t i o n s , cellulosics at 7%, a n d a c c o r d i n g t o U S D A p r o j e c t i o n s , c o r n at 5%. Feedstock costs used as a basis for these g r a p h s are (starting 1 9 8 3 as in Tables V a n d VI): M S W $ 1 4 . 0 0 / o v e n - d r i e d t o n (ODT). S M W $ 2 1 . 0 0 / O D T , Pulp mill w a s t e s $ 1 4 . 0 0 / O D T . Ethylene $ 0 . 1 8 / p o u n d a n d corn $ 3 . 0 0 / b u s h e l . Thus, t h e t o t a l feedstock cost per g a l l o n of e t h a n o l p r o d u c e d is $ 0 , 1 0 4 in t h e case of cellulose, $0.75 for e t h y l e n e , a n d $ 1 . 2 0 for c o r n . B y - p r o d u c t credits used escalated f r o m prices listed in 1 9 8 3 at a 7% rate. The t w o curves for cellulose a l c o h o l represent t h e e c o n o m i c s for 1 0 0 % investor e q u i t y capital a n d for m u n i c i p a l b o n d f i n a n c i n g . A l s o s h o w n o n t h e f i g u r e is t h e p r o j e c t e d selling price for e t h a n o l at 7% a n d 5% inflation rates. The cellulose alcohol c u r v e w i t h m u n i c i p a l b o n d f i n a n c i n g s h o w s t h e effect of interest losses prior t o t h e first o p e r a t i n g year. The t h i r d - y e a r selling price is m o r e representative of actual e c o n o m i c s . The t e c h n i c a l feasibility has been d e m o n s t r a t e d by t h e research w o r k carried o u t at t h e Gulf Oil C h e m i c a l s C o m p a n y . The c o m m e r c i a l process e c o n o m i c s , w h i c h are based on p r o d u c i n g 5 0 m i l l i o n g a l / y r of a l c o h o l , s h o w a m o r e favorable selling price t h a n grain f e r m e n t a t i o n a n d s y n t h e t i c alcohols w i t h 1 0 0 % investor e q u i t y capital f i n a n c i n g . W i t h m u n i c i p a l b o n d f i n a n c i n g , cellulosic w a s t e a l c o h o l yields m u c h greater p r o f i t a b i l i t y or m u c h l o w e r selling prices t o o b t a i n a 1 5 % return on investor e q u i t y . REFERENCES

1.

Mooney, J. R., Orange Disc, 1977 2.

2.

Emert, G. H.; Gum, E. G., Jr.; Lang, J. Α.; Liu, T. H.,; Brown, R. D., Jr. Adv. Chem. Ser. 1974, 136, 79.

3.

Dyess, S. E.; Emert, G. H. "Encyclopedia of Chemical Processing and Design"; Marcel Dekker: New York, 1978; Vol. 7, pp 499-58.

4.

Takagi, M.; Abe, S.; Emert, G. H.; Yata, N. "International Symposium on Bioconversion of Cellulosic Substrates"; Ghose, T. K., Ed.; Institute of Chemical Engineering: New Delhi, India, 1977; p 551.

5.

Blotkamp, P. J.; Takagi, M.; Pemberton, M. J.; Emert. G. H. "Proceed­ ings", the 84th American Institute of Chemical Engineers National Meeting; American Institute of Chemical Engineers: New York, 1978.

RECEIVED JUNE 18,

1980.

12 Methane Production by Anaerobic Digestion of Bermuda Grass DONALD L. KLASS and SAMBHUNATH GHOSH

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Institute of Gas Technology, 3424 South State Street, Chicago, IL 60616

It is now clear that every technically and economically feasible source of additional methane must be tapped to meet the growing demand for natural gas. One potentially large-scale source of methane is land- and water-based biomass which can be converted to substitute natural gas (SNG) by a variety of techniques. Because biomass is a renewable nonfossil carbon source that derives its energy from photosynthetic fixation of ambient carbon dioxide, the concept could lead to the development of perpetually available SNG supplies (1). Perennial grasses have been suggested as one category of land-based biomass suitable for conversion to methane (2). Most perennial grasses can be grown vegetatively, and they reestablish themselves rapidly after harvesting. Also, more than one harvest can usually be obtained per year. The warm-season grasses are preferred over the cool-season grasses because their growth rate increases rather than declines as the temperature rises to its maximum in the summer months (3). In certain areas, rainfall is adequate to permit harvesting every 3 to 4 weeks from late February into November, and yields between 18 to 24 metric ton/ac-yr (8 to 10 short ton/ac-yr) of dry grass equivalent are believed to be attainable in managed grasslands (3).

0097-6151/81/0144-0229$0.5.25/0 © 1981 American Chemical Society

230

BIOMASS

AS

A

NONFOSSIL

FUEL

SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Our initial e x p e r i m e n t a l w o r k t o s t u d y t h e c o n v e r s i o n of grass t o m e t h a n e a n d t h e feasibility of d e v e l o p i n g small-scale installations for on-site use by t h e i n d i v i d u a l h o m e o w n e r w a s d o n e w i t h c o m m o n l a w n grass, w h i c h c o n s i s t e d p r e d o m i n a t e l y o f K e n t u c k y bluegrass g r o w n in N o r t h e r n Illinois (4). E x p e r i m e n t s carried o u t in laboratory digesters s h o w e d t h a t t h e grass can be c o n v e r t e d d i r e c t l y t o h i g h - m e t h a n e gas u n d e r c o n v e n t i o n a l anaerobic d i g e s t i o n c o n d i t i o n s . M e t h a n e yields of 2.5 a n d 3.1 SCF/lb volatile solids (VS) a d d e d w e r e o b s e r v e d at m e s o p h i l i c t e m p e r a t u r e s a n d s e m i c o n t i n u o u s d i g e s t i o n c o n d i t i o n s . This c o r r e s p o n d e d t o e n e r g y recovery efficiencies as m e t h a n e of a b o u t 2 8 % a n d 3 4 % . Alkali t r e a t m e n t of K e n t u c k y bluegrass before d i g e s t i o n gave a m e t h a n e yield a n d e n e r g y recovery e f f i c i e n c y of 4.6 SCF/lb V S a d d e d a n d 5 1 % . This paper s u m m a r i z e s t h e p r e l i m i n a r y e x p e r i m e n t a l w o r k carried o u t w i t h t h e w a r m - s e a s o n grass Coastal B e r m u d a grass (Cynodon dactylon) t o s t u d y its c o n v e r s i o n t o m e t h a n e by anaerobic d i g e s t i o n . B e r m u d a grass is w i d e l y d i s t r i b u t e d t h r o u g h o u t t h e t r o p i c a l a n d s u b t r o p i c a l c o u n t r i e s of t h e w o r l d , a n d in t h e U n i t e d States, is best a d a p t e d t o t h e states s o u t h of a line c o n n e c t i n g V i r g i n i a a n d Kansas (5). Coastal B e r m u d a grass, w h i c h tolerates m o r e frost, makes m o r e g r o w t h in t h e fall, a n d r e m a i n s g r e e n m u c h later t h a n c o m m o n B e r m u d a grass, g r o w s tall e n o u g h t o be c u t for hay on a l m o s t any soil (5). From an overall s t a n d p o i n t of d i s t r i b u t i o n a n d g r o w t h c h a r a c t e r i s t i c s . Coastal B e r m u d a grass is a g o o d c a n d i d a t e for biomass e n e r g y a p p l i c a t i o n s . MATERIALS AND METHODS Digesters T h e d i g e s t i o n runs w e r e carried o u t in t h e s e m i c o n t i n u o u s m o d e in w h i c h s e q u e n t i a l w a s t i n g of a p o r t i o n of t h e d i g e s t e r c o n t e n t s a n d f e e d i n g of grass slurry w e r e p e r f o r m e d o n a daily basis u n d e r a n a e r o b i c c o n d i t i o n s . C u s t o m m a d e . 7 - / , c y l i n d r i c a l , f l a t - b o t t o m e d . L u c i t e digesters (7.5 in. ID) h a v i n g w o r k i n g v o l u m e s of 5 / w e r e e m p l o y e d . M i x i n g w a s p r o v i d e d by t w o 3-in. d i a m e t e r , stainless steel, p r o p e l l e r - t y p e impellers m o u n t e d on a single, t o p d r i v e n , stainless steel shaft p o s i t i o n e d in t h e c e n t e r of t h e vessel. The impellers w e r e m o u n t e d 3 in. a n d 6 in. f r o m t h e b o t t o m of t h e d i g e s t e r a n d w e r e d r i v e n by an e x t e r n a l l y m o u n t e d 1 / 8 - h p A C m o t o r at 1 3 0 r p m . Four internal L u c i t e baffles 6 in. x 3 in. X 1 in. s p a c e d 9 0 ° apart w e r e a t t a c h e d t o t h e d i g e s t e r w a l l at t h e 6 in. x 1/4 in. surface. T h e l o n g d i m e n s i o n of each baffle w a s p e r p e n d i c u l a r t o t h e f l a t b o t t o m a n d t o t a l l y i m m e r s e d in t h e c u l t u r e . T h e t o p of t h e digester w a s e q u i p p e d w i t h a t h e r m o m e t e r w e l l , a shaft seal on t h e stirring shaft, a n d f e e d , gas r e m o v a l , a n d gas s a m p l i n g ports. T h e b o t t o m of t h e digester c o n t a i n e d an effluent w i t h d r a w a l port.

12.

KLASS

A N D GHOSH

231

Methane from Bermuda Grass

T e m p e r a t u r e w a s c o n t r o l l e d b y m o u n t i n g t h e digesters in a c o n s t a n t t e m p e r a t u r e c a b i n e t in w h i c h preheated air w a s c o n t i n u o u s l y c i r c u l a t e d . T h e gas c o l l e c t i o n a n d m e a s u r i n g s y s t e m f o r each digester w a s m o u n t e d o u t s i d e t h e c o n s t a n t t e m p e r a t u r e c a b i n e t a n d w a s similar in d e s i g n t o t h a t d e s c r i b e d previously (6).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Digester Feeds Coastal B e r m u d a grass w a s o b t a i n e d f r o m t h e N o r t h Louisiana Hill Farm E x p e r i m e n t Station in Homer, Louisiana. T h e s t a t i o n reported t h a t t h e soil f r o m w h i c h t h e grass w a s t a k e n is classified as a S h u b u t a fine s a n d y l o a m , a soil t y p e c o m m o n t o t h e Coastal Plains region o f N o r t h Central Louisiana. The area w a s fertilized w i t h 3 0 0 lb per acre o f Ν as N H N 0 o n A p r i l 2 2 , 1 9 7 7 , a n d w i t h 6 0 lb of K 0 a n d 9 0 lb of P 0 / a c r e o n A p r i l 2 8 , 1977. T h e grass w a s harvested o n M a y 2 3 - 2 4 , 1 9 7 7 w i t h a sickle bar m o w e r , left o n t h e g r o u n d t h e first day, raked into w i n d r o w s t h e next day, a n d baled o n t h e t h i r d day. The yield for t h i s c u t t i n g w a s a p p r o x i m a t e l y 1.5 t o n / a c r e . A b o u t 1 4 0 0 lb (20 bales) w e r e s h i p p e d t o IGT b y t r u c k f r e i g h t a n d arrived o n J u n e 3 0 . 1977. T h e bales w e r e stored under a m b i e n t c o n d i t i o n s in an enclosed trailer. A s received, t h e grass c o n t a i n e d s t e m s a n d blades 3 in. or longer in l e n g t h . 4

2

2

3

5

A 3 0 0 - l b s a m p l e of t h e grass w a s g r o u n d t w i c e in a n Urschel Laboratory Grinder (Comitrol 3 6 0 0 ) e q u i p p e d w i t h a 0.030-in. c u t t i n g head, d r y - m i x e d in a r i b b o n blender, a n d stored in a c o v e r e d 2 0 - g a l plastic d r u m at r o o m t e m p e r a t u r e . A t y p i c a l particle size analysis of t h e g r o u n d grass is s h o w n in Table I, a n d t h e p h y s i c a l a n d c h e m i c a l properties of t h e as-received a n d g r o u n d grass as w e l l as t h e g r o u n d grass after r o o m - t e m p e r a t u r e storage f o r 3 m o n t h s are s h o w n in Table II. Feed slurries w e r e prepared fresh daily b y b l e n d i n g t h e required a m o u n t s o f g r o u n d grass a n d d e m i n e r a l i z e d w a t e r . T h e properties o f feed slurries prepared a b o u t 4 m o n t h s apart are presented in Table III. T h e p H o f t h e d i g e s t e r c o n t e n t s w a s m a i n t a i n e d in t h e 6.8 t o 7.2 range as m u c h as possible by a d d i n g a p r e - d e t e r m i n e d a m o u n t of 1.0 Ν NaOH s o l u t i o n t o t h e feed slurry before d i l u t i o n t o t h e required v o l u m e w i t h w a t e r . W h e n a d d e d n u t r i e n t s o l u t i o n s w e r e used, t h e c o m p o s i t i o n s o f w h i c h are s h o w n in Table IV. pre­ selected a m o u n t s w e r e also b l e n d e d w i t h t h e feed slurries before d i l u t i o n t o t h e final feed v o l u m e . Analytical Techniques M o s t analyses w e r e p e r f o r m e d in d u p l i c a t e ; several w e r e p e r f o r m e d in t r i p l i c a t e or higher m u l t i p l e s . T h e p r o c e d u r e s w e r e either A S T M , S t a n d a r d

232

BIOMASS

AS A NONFOSSIL

FUEL

SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Table L PARTICLE SIZE ANALYSIS OF GROUND G R A S S U.S. Sieve Size, mm

Grass Retained on Sieve. wt%

1.18 0.60 0.297 0.250 0.212 0.180 0.149 0.105 0.063

0 0 36.2 55.4 74.6 83.3 87.9 92.6 98.5

Table II. PHYSICAL A N D C H E M I C A L CHARACTERISTICS OF G R A S S

A s Received Ultimate Analysis, w t % C H Ν S Ρ Ca Na Κ Mg Μη Fe Sr Zn Proximate Analysis. w t % Moisture Volatile Matter Ash Organic Components. w t % Crude Protein Cellulose Hemicellulose Lignin High Heating Value. Btu/dry lb Btu/lb (MAF) Btu/lb C Bulk Density, l b / f t 3

9.26 95.3 4.73

After Grinding

After Storage and Grinding

47.1 6.04 1.96 0.21 0.24 0.30 0.08 1.6 0.14 0.01 < 0.005 < 0.001 < 0.005

47.5 6.12

5.15 95.0 5.05

6.26 95.1 4.90

12.3 31.7 40.2 4.1

4.70

8.185 8.616 17.378 23.76

8.162 8.583 17.183

12.

KLASS

A N D GHOSH

233

Methane from Bermuda Grass

Table ft C H A R A C T E R B T C S OF FEED SLURRY* Jury 2 3 . 1977 Density, g / m l at 25°C Total Solids. w t % of slurry Volatile Matter. w t % of slurry Total Alkalinity, m g / / as C a C 0 Bicarbonate Alkalinity, m g / / as C a C 0

0.944 1.59 1.51 211

3

137

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

3

PH Conductivity, μ m h o / c m Volatile Acids, m g / / Acetic Propionic Butyric Isobutyric

6.02 1.030 104 0 0 _0

Total A s Acetic Chemical Oxygen Demand, m g / / A m m o n i a N. p p m as Ν *

104 35.000 3.5

Formulated for loading rate of 0.1 lb V S / f t volume.

3

November 14, 1.59 1.50 240 143 6.11 1.060 115 24 0 _0 136 32.630 5.0

-day. 12-day detention time. 5 /

culture

Table IV. COMPOSITION OF A D D E D NUTRIENT SOLUTIONS M i x e d Nutrient Component NH CI NaH P 0 KI FeCI 4

2

4

3

MgCI CoCI NaMo0 CuCI MnCI 2

2

2

2

2

Ν

concentration. mg/ml

Formulation, g// 3.0 20.0 2.0 2.0 2.0 0.25 0.10 0.10 0.10

7.85

Ammonium Chloride Solution, g// 120.0

- -

31.42

234 Methods,

BIOMASS

or

special

techniques

as

AS A

reported

NONFOSSIL

previously

FUEL

(6).

SOURCE

Cellulose,

h e m i c e l l u l o s e , a n d l i g n i n in t h e grass a n d d i g e s t e d solids w e r e d e t e r m i n e d by t h e m e t h o d s of Goering a n d v a n Soist (7). Data Reduction Gas y i e l d , m e t h a n e y i e l d , volatile solids r e d u c t i o n , a n d e n e r g y recovery e f f i c i e n c y w e r e c a l c u l a t e d by t h e m e t h o d s d e s c r i b e d p r e v i o u s l y (6). A l l gas d a t a r e p o r t e d are c o n v e r t e d t o 6 0 ° F a n d 3 0 i n . of m e r c u r y o n a d r y basis.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Inoculum, Start-Up and Operation D e v e l o p m e n t of t h e m e s o p h i l i c i n o c u l u m for t h e grass digester runs w a s s t a r t e d o n J u n e 2 2 a n d 2 9 . 1 9 7 7 by a c c u m u l a t i n g d a i l y e f f l u e n t s f r o m e x i s t i n g l a b o r a t o r y d i g e s t i o n runs o p e r a t i n g o n g i a n t b r o w n kelp a n d o n m i x e d p r i m a r y - a c t i v a t e d s e w a g e sludge. T h e kelp a n d s l u d g e digesters w e r e o p e r a t e d at 3 5 ° C a n d d e t e n t i o n t i m e s of 18 a n d 5.6 d a y s , a n d l o a d i n g rates of 0.1 a n d 0.8 lb V S / f t - d a y . respectively. T h e e f f l u e n t s f r o m these digesters w e r e c o l l e c t e d in o t h e r digesters u n t i l 8 . 7 5 / o f t h e b i o m a s s c u l t u r e a n d 7 . 5 0 / of t h e s l u d g e c u l t u r e h a d been a c c u m u l a t e d . Each d i g e s t e r w a s t h e n o p e r a t e d s e m i c o n t i n u o u s l y for 10 d a y s t o stabilize its p e r f o r m a n c e . On J u l y 15. 1 9 7 7 . 1.75 / o f b i o m a s s c u l t u r e a n d 0.75 / o f s l u d g e c u l t u r e w e r e anaerobically t r a n s f e r r e d t o each of t w o B e r m u d a grass digesters w h i c h w e r e t h u s started w i t h 2.5 / of m i x e d i n o c u l u m . These digesters w e r e t h e n o p e r a t e d in t h e s e m i c o n t i n u o u s m o d e w i t h a d a i l y f e e d i n g a n d w a s t i n g s c h e d u l e d e s i g n e d t o increase c u l t u r e v o l u m e s b y 1 0 % per d a y t o a v o l u m e of 5 . 0 / w h i l e m a i n t a i n i n g t h e d e t e n t i o n t i m e a n d l o a d i n g c o n s t a n t at a b o u t 15 days a n d 0.1 lb V S / f t - d a y . T h e digesters w e r e fed w i t h kelp, s l u d g e , a n d grass. The ratio of kelp VS t o s l u d g e VS w a s m a i n t a i n e d at 7 0 : 3 0 . The p e r c e n t a g e s of t h e kelp a n d s l u d g e w e r e g r a d u a l l y decreased w h i l e t h e p e r c e n t a g e of grass w a s g r a d u a l l y increased d u r i n g t h i s t r a n s i t i o n . The c u l t u r e v o l u m e of 5 . 0 / w a s a t t a i n e d o n J u l y 2 3 . 1 9 7 7 a n d t h e kelp a n d s l u d g e w e r e c o m p l e t e l y d i s p l a c e d b y B e r m u d a grass b y A u g u s t 19. 1 9 7 7 . D i g e s t i o n w a s t h e n c o n t i n u e d at t h e selected o p e r a t i n g c o n d i t i o n s w i t h grass feed only. 3

3

Steady-state

digestion

was

defined

in t h i s

work

as o p e r a t i o n

without

s i g n i f i c a n t c h a n g e s in t h e gas p r o d u c t i o n rate, gas c o m p o s i t i o n , a n d e f f l u e n t characteristics. Usually, o p e r a t i o n for t w o or t h r e e d e t e n t i o n t i m e s e s t a b lished steady-state p e r f o r m a n c e . W i t h t h e e x c e p t i o n of Run 1, w h i c h d i d not achieve steady state, selected steady-state results are s h o w n in Table V. Run 1 is t h e e x p e r i m e n t started as i n d i c a t e d above t o establish a baseline w i t h o u t a d d e d n u t r i e n t s . Runs 5 and

12.

KLASS AND GHOSH

235

Methane from Bermuda Grass

Table V. SUMMARY Of SELECTED STEADY-STATE DATA Run 2

Run 3

Run 4

Run 5

Run 6

Run 7

Run 8

7 5

7 5

7 5

7 5

7 5

7 5

7 5

c

c

c

c

c

c

c

M D 0 35 68 0.10 12

M D MN 35 6.9 010 12

M D MN 35 6.9 010 12

7 5 C M D MN 35 69 0.10 12

M D Ν 35 6.8 0.10 12

M D Ν 35 6.8 010 12

M D Ν 35 6.8 0.10 12

M D Ν 55 6.4 0.10 12

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Run1 Operating Conditions Digester Volume. / Working Volume. / Agitation Schedule Agitation Type Feeding Frequency Nutrients Added Temperature. C pH Loading Rate, lb VS/ft -day Detention Time, day Total Solids in Feed Slurry. wt% Volatile Solids in Feed Slurry. wt% C/N Ratio in Feed Slurry Caustic Requirements, m- q/f Feed Gas Production Gas Production Rate. vol/vol-day Gas Yield. SCF/lb VS added Methane Yield. SCF/lb VS added Methane Concentration. mol% Coefficient of Variation. Methane Yield Efficiencies Volatile Solids Reduction. % Energy Recovered as Methane. % 3

9

3

3

e

b c

3

d

1 59

1 59

1 59

1.59

1.59

1.59

1.59

1 59

1.51 240 72

1.51 16 3 66

1 51 12.3 66

1.51 83 103

1.51 12.3 81

1.51 83 81

1.51 6.3 36

1.51 12.3 42

0313

0.459

0407

0.398

0.350

0.464

0.587

0527

587 351 59.8

527 2.73 51.8

0

Effluent Volatile Acids, m g / / as HOAc c

a

b

0

d

3 13 1 92 61.4

459 268 583

407 245 603

398 2.45 61.7

3.50 2.20 637

464 290 62.4

10

7

6

10

9

13

9

10

200 22 6

293 31 5

260 288

25.4 289

22.1 258

29.7 34.1

37.5 41.2

33.7 32.1

1.989

2.056

1.300

2.123

2.540

1.159

354

2.273

"C" denotes continuous agitation " M " denotes continuous mechanical mixing "D" denotes daily feeding and wasting cycles "Ο" denotes no nutrients added to feed slurry. "MN" denotes mixed nutrient solution added to feed slurry " N " denotes ammonium chloride solution added to feed slurry pH maintained in indicated range by periodic NaOH additions. Mean values. Did not achieve steady state

236

BIOMASS AS A NONFOSSIL F U E L

SOURCE

6. 7 w e r e s e q u e n t i a l l y d e r i v e d f r o m Run 1. Runs 2, 3, a n d 4 w e r e s e q u e n t i a l l y d e r i v e d f r o m a replicate of Run 1. T y p i c a l p e r f o r m a n c e of one of t h e runs (Run 7) over an e x t e n d e d t i m e is s h o w n in Figure 1. T h e r m o p h i l i c Run 8 w a s i n i t i a t e d by a n a e r o b i c a l l y a c c u m u l a t i n g t h e e f f l u e n t f r o m Run 7 u n t i l 5.0 / h a d been c o l l e c t e d . T h e c u l t u r e w a s m a i n t a i n e d in t h e b a t c h m o d e at 5 5 ° C for a f e w d a y s , a n d t h e n s e m i c o n t i n u o u s o p e r a t i o n w i t h grass w a s started at a d e t e n t i o n t i m e of 5 0 days a n d a l o a d i n g rate of 0.02 lb V S / f t - d a y . T h e a m m o n i u m c h l o r i d e n u t r i e n t s o l u t i o n (Table IV) w a s a d d e d t o t h e feed slurry at a rate of 1.0 m l of s o l u t i o n per 0.02 l b / f t - d a y l o a d i n g . The l o a d i n g rate w a s g r a d u a l l y increased at a c o n s t a n t d e t e n t i o n t i m e ; 0.1 lb V S / f t - d a y l o a d i n g rate w a s a t t a i n e d in 10 days. T h e d e t e n t i o n t i m e w a s t h e n g r a d u a l l y r e d u c e d t o 12.0 days over a 10-day period. O p e r a t i o n of Run 8 w a s t h e n c o n t i n u e d at t h e t a r g e t c o n d i t i o n s . 3

3

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

3

Dewatering Testa Gravity s e d i m e n t a t i o n tests w e r e c o n d u c t e d b y a m o d i f i e d AEEP m e t h o d (8) in w h i c h a 4 0 0 - m I s a m p l e of e f f l u e n t w a s e x a m i n e d in a 1 - / g r a d u a t e d c y l i n d e r g i v i n g a f l u i d d e p t h of 140 m m . T h e h e i g h t of t h e interface b e t w e e n t h e t h i c k e n e d s l u d g e a n d clarified s u p e r n a t a n t is p l o t t e d versus t i m e . V a c u u m f i l t r a t i o n tests w e r e c o n d u c t e d by a m o d i f i e d AEEP m e t h o d j 9 ) in w h i c h a 0.05 f t c i r c u l a r L u c i t e leaf c o v e r e d w i t h an Eimco No. N Y - 4 1 5 m o n o f i l a m e n t filter c l o t h w a s used in a 1 - / beaker c o n t a i n i n g 4 1 7 m l of e f f l u e n t sample. 2

DISCUSSION Feed Properties A l l of t h e d i g e s t i o n runs w e r e carried o u t w i t h small particle-size grass t o f a c i l i t a t e m a x i m u m gas yields a n d p r o d u c t i o n rates in t h e laboratory w o r k . S o m e m o i s t u r e loss w a s o b s e r v e d on g r i n d i n g as e x p e c t e d , and no s i g n i f i c a n t c h a n g e s w e r e d e t e c t e d on r o o m - t e m p e r a t u r e storage of t h e g r o u n d grass (Table III). Several c h a r a c t e r i s t i c s of t h e p a r t i c u l a r lot of grass a n d r e s u l t i n g feed slurries e x a m i n e d in t h i s w o r k i n d i c a t e d t h a t a n a e r o b i c d i g e s t i o n u n d e r c o n v e n t i o n a l c o n d i t i o n s m i g h t not p r o v i d e g o o d m e t h a n e f e r m e n t a t i o n . The mass ratios of C / N (24), C/P (196), C/Ca (157). a n d C / M g (336) in t h e d r y grass solids a n d t h e C O D / N ratio (105-112) in t h e feed slurry appear t o o h i g h w h e n c o m p a r e d w i t h t h e c o r r e s p o n d i n g ratios s u p p l i e d by suitable substrates s u c h as s e w a g e s l u d g e a n d g i a n t b r o w n kelp. T h e q u a n t i t i e s of a m m o n i a Ν (3.5 m g / / ) . Ca (48 m g / / ) , Na (13 m g / / ) , a n d M g (23 m g / / ) in t h e feed slurries f o r m u l a t e d t o m e e t t h e desired loading rate a n d d e t e n t i o n t i m e

12.

KLASS AND GHOSH

237

Methane from Bermuda Grass

c o n d i t i o n s are also less t h a n t h e s t i m u l a t o r y c o n c e n t r a t i o n s r e c o m m e n d e d for anaerobic t r e a t m e n t of w a s t e (10). The c o n c e n t r a t i o n s of N, P. Na, Ca, a n d Mg

might

thus

have

t o be a d j u s t e d

to promote

adequate

methane

p r o d u c t i o n . A l s o , t h e relatively l o w p H (6.0) a n d b i c a r b o n a t e alkalinity (137 mg//

as C a C O ^ of t h e feed slurry indicate poor b u f f e r i n g c a p a c i t y a n d

potential problems w i t h pH control during digestion.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Mesophilic Digestion Representative d a t a f r o m Run 1, w h i c h d i d n o t achieve steady state, as previously m e n t i o n e d , are s h o w n in Table V. This represents t h e baseline r u n w i t h o u t a d d e d n u t r i e n t s . It w a s f o u n d t h a t t o m a i n t a i n p H in t h e 6.8-7.2 range, 7 2 m e q N a O H / / o f feed slurry w a s r e q u i r e d ; this raised t h e s o d i u m ion c o n c e n t r a t i o n in t h e digester t o a b o u t 1 6 7 0 m g / / . Overall, t h e results o f Run I w e r e poor. The m e t h a n e y i e l d , volatile solids r e d u c t i o n , a n d energy recovery e f f i c i e n c y as m e t h a n e in t h e p r o d u c t gas w e r e l o w , a n d t h e volatile acids c o n c e n t r a t i o n in t h e digester e f f l u e n t w a s h i g h . T h e p e r f o r m a n c e of Run 1 a n d t h e c o m p o s i t i o n a l data i n d i c a t i n g possible n u t r i t i o n a l deficiencies led t o t h e e v a l u a t i o n of Runs 2, 3, a n d 4 at t h e s a m e o p e r a t i n g c o n d i t i o n s as Run 1 e x c e p t t h a t t h e m i x e d n u t r i e n t s o l u t i o n in Table IV w a s a d d e d t o t h e feed slurry t o raise t h e c o n c e n t r a t i o n s of t h e n u t r i e n t s . S u f f i c i e n t n u t r i e n t f o r m u l a t i o n w a s a d d e d t o reduce t h e C / N ratios of Runs 2. 3. a n d 4 t o 16.3. 12.3. a n d 8.3, r e s p e c t i v e l y Substantial i m p r o v e m e n t s w e r e o b s e r v e d in t h e p e r f o r m a n c e of these runs, b u t t h e volatile acids c o n c e n t r a t i o n s in t h e digester e f f l u e n t s w e r e still h i g h . Also, there d i d n o t seem t o be a correlation b e t w e e n gas p r o d u c t i o n a n d t h e concentration of added mixed nutrient solution. S i g n i f i c a n t i m p r o v e m e n t in digester p e r f o r m a n c e w a s also observed w h e n pure N H C I n u t r i e n t s o l u t i o n (Table IV) w a s a d d e d t o t h e feed slurry as s h o w n by t h e results in Table V f o r Runs 5. 6, a n d 7. In these e x p e r i m e n t s , t h e r e w a s a g o o d c o r r e l a t i o n of m e t h a n e y i e l d , volatile solids r e d u c t i o n , a n d energy recovery e f f i c i e n c y w i t h t h e c o n c e n t r a t i o n of a d d e d n i t r o g e n . The h i g h e r t h e a d d e d n i t r o g e n c o n c e n t r a t i o n u p t o t h e h i g h e s t c o n c e n t r a t i o n e v a l u a t e d (C/N ratio 6.3; c a l c u l a t e d a m m o n i a N, 1.190 m g / / ) . t h e h i g h e r t h e gas y i e l d . Figure 2. w h i c h i n c l u d e s t h e data f r o m Runs 1. 5, 6, a n d 7 as w e l l as d a t a f r o m t h r e e o t h e r runs n o t s h o w n in Table V, illustrates t h i s correlation. N o i n h i b i t i o n b y a d d e d n i t r o g e n w a s observed a l t h o u g h it m i g h t be e x p e c t e d at c o n c e n t r a t i o n s a b o v e 1.500 m g / / (JO). 4

Run 7 e x h i b i t e d t h e best m e t h a n e yield of 3.51 SCF/lb V S a d d e d a n d t h e h i g h e s t volatile solids r e d u c t i o n a n d e n e r g y recovery efficiencies o f Runs 1 t o 7. A l s o , t h e volatile acids c o n c e n t r a t i o n in t h e digester effluent is in t h e range

238

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

BIOMASS AS A NONFOSSIL F U E L SOURCE

Figure 2.

Effect of ammonium chloride added to feed slurry on methane yield: 35°C, 0.1 lb VS/ff-day, 12-day detention time

12.

KLASS AND GHOSH

239

Methane from Bermuda Grass

e x p e c t e d f o r b a l a n c e d d i g e s t i o n . T h e plot in Figure 2 s u p p o r t s t h e c o n c l u s i o n t h a t t h e particular lot o f Coastal B e r m u d a grass evaluated in this w o r k w a s n i t r o g e n - l i m i t e d u n d e r anaerobic d i g e s t i o n c o n d i t i o n s , a n d t h a t c o n t i n u e d a d d i t i o n o f a m m o n i u m c h l o r i d e u p t o t h e h i g h e s t c o n c e n t r a t i o n s t u d i e d (C/N ratio o f 6.3) appeared t o have a s t i m u l a t o r y effect o n m e t h a n e p r o d u c t i o n . Since it is k n o w n t h a t fertilization m e t h o d s a n d dosage rates affect t h e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

n i t r o g e n c o n t e n t of Coastal B e r m u d a grass (JJJ, a tradeoff analysis w o u l d have t o be p e r f o r m e d t o establish t h e i n c r e m e n t a l benefits of increased fertilization vs. n u t r i e n t a d d i t i o n if an i n t e g r a t e d p r o d u c t i o n - h a r v e s t i n g gasification system were designed t o manufacture methane. A reasonably g o o d linear c o r r e l a t i o n w a s f o u n d b e t w e e n energy recovery e f f i c i e n c y as m e t h a n e in t h e p r o d u c t gas a n d volatile solids r e d u c t i o n as s h o w n in Figure 3. This t y p e o f c o r r e l a t i o n has also been f o u n d t o exist f o r g i a n t b r o w n kelp after c o r r e c t i o n w a s m a d e f o r a n y h y d r o g e n in t h e p r o d u c t gas (6). Thermophilic Digestion One r u n . Run 8. w a s carried o u t t o s t u d y t h e effect of d i g e s t i o n at t h e r m o p h i l i c t e m p e r a t u r e s . T h e results s h o w n in Table V w e r e o b t a i n e d w i t h s u p p l e m e n t a l n i t r o g e n a d d i t i o n s at t h e same c o n c e n t r a t i o n as t h a t used in Run 5. Run 8 e x h i b i t e d a b o u t 5 0 % h i g h e r gas p r o d u c t i o n a n d volatile solids r e d u c t i o n t h a n Run 5. b u t d u e t o t h e l o w e r m e t h a n e c o n t e n t in t h e p r o d u c t gas, t h e e n e r g y recovery e f f i c i e n c y o f Run 8 w a s o n l y a b o u t 2 4 % higher t h a n t h a t o f Run 5. It is a p p a r e n t also t h a t t h e h i g h volatile acids c o n c e n t r a t i o n in t h e d i g e s t e r effluent o f Run 8 does n o t indicate b a l a n c e d d i g e s t i o n . Carbon a n d Energy Balancée It w a s d i f f i c u l t t o c a l c u l a t e c a r b o n a n d e n e r g y balances f o r t h e digester runs p e r f o r m e d w i t h Coastal B e r m u d a grass because o f t h e a d d i t i o n of relatively large q u a n t i t i e s of alkali f o r p H c o n t r o l a n d of n u t r i e n t s . These a d d i t i v e s c o n t r i b u t e d t o ash w e i g h t s . T w o t e c h n i q u e s w e r e used t o c i r c u m v e n t these p r o b l e m s . O n e a s s u m e d t h a t a d d e d NaOH w a s c o n v e r t e d t o N a H C 0 o n a s h i n g at 5 5 0 ° C a n d r e m a i n e d in t h e a s h , a n d t h a t a d d e d N H C I w a s c o m p l e t e l y volatilized o n a s h i n g . These a s s u m p t i o n s are p r o b a b l y n o t s t r i c t l y true. T h e o t h e r t e c h n i q u e relied u p o n e x p e r i m e n t a l m e a s u r e m e n t of ash a n d v o l a t i l e solids in t h e d r y d i g e s t e d solids. 3

4

T h e details of o n e set o f c a l c u l a t i o n s b y b o t h t e c h n i q u e s are illustrated in Chart 1 f o r Run 1 w h i c h w a s p e r f o r m e d w i t h o n l y a d d e d alkali. T h e best balance, 1 0 1 % c a r b o n a n d 1 0 0 % e n e r g y a c c o u n t e d for, w a s o b t a i n e d b y t h e

35°C, 0.10 lb VS/ft3-day, 12-day DT 40.0 meq NaOH/1. feed, 20.0% VS Reduction 0

Carbon 96.66 χ 0. 376 = 36.3 lb Energy 96.66 χ 6.237 = 602,900 Btu

Method 1* 72.09 lb VS 24.57 lb Ash 96.66 lb

Carbon 88.15 χ 0.376 = 33.1 lb Energy 88.15 χ 6.237 = 549,800 Btu

Method 2^ 72.09 lb VS 16.06 lb Ash 88.15 lb

Digested Solids

Carbon 0.744 χ 12.0 = 8.9 lb Energy 3.13 χ 0.614 χ 1,012 χ 90.11 = 175,300 Btu

282.0 + 379=0.744 mole gas

3.13 SCF gas/lb VS added x90.11 lb VS added =282.0 SCF gas

Gas

X

40.0 meq NaOH 0.417 1. feed 1. feed dajr 417 g feed 1.59 wt % TS in feed day 100 X

0.084 g NaHCOa formed meq NaOH 5.05 wt % ash in TS 100

/Ash and VS experimentally determined to be 18.22 wt % and 81.78% on dry digested solids.

4.74 lb original ash +

4.74 = 24.57 lb ash

•Ash calculated by assuming 40.0 meq NaOH added/1, feed slurry for pH control converted to NaHCCX; on ashing at 550°C and 0.417 1. feed equal 417 g feed. Thus:

Carbon 54.85 χ 0.471 = 44.7 lb Energy 94.85 χ 8,185 = 776,300 Btu

5.15 lb H2O 90.11 lb VS 4.74 lb Ash 100.00 lb

100 lb Grass

Accounted For: Feed Carbon 101%*, 94%/ Feed Energy 100%*, 93%^

Chart 1. Carbon and Energy Balance For Ron No. 1

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

3

>

>

>

δ

Ν) Ο

12.

KLASS AND GHOSH

241

Methane from Bermuda Grass

t e c h n i q u e t h a t a s s u m e d t h e a d d e d alkali w a s c o n v e r t e d t o b i c a r b o n a t e in t h e ash. T h e t e c h n i q u e t h a t relied o n e x p e r i m e n t a l ash a n d volatile solids d e t e r m i n a t i o n s gave results t h a t a c c o u n t e d f o r less t h a n t h e feed c a r b o n a n d energy. But t h i s d i d n o t o c c u r in t h e o t h e r c a l c u l a t i o n s , t h e results o f w h i c h are s u m m a r i z e d in Table VI. Higher a n d l o w e r d e v i a t i o n s f r o m 1 0 0 % o c c u r r e d w i t h each t e c h n i q u e .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Properties of Effluent and Digeated Solids A s already p o i n t e d o u t , t h e volatile acids c o n c e n t r a t i o n s in t h e effluents f r o m m o s t of t h e runs w e r e h i g h . T h e detailed b r e a k d o w n o f t h e i n d i v i d u a l acids a n d o t h e r properties are s u m m a r i z e d f o r t h e feed slurry a n d effluents f r o m Runs 1, 7. a n d 8 in Table VII. The effects of t h e a d d e d NaOH a n d N H C I o n t h e alkalinity, a m m o n i a n i t r o g e n , a n d specific c o n d u c t i v i t y are in t h e e x p e c t e d d i r e c t i o n s . The c o n v e r s i o n of n o n - a m m o n i a n i t r o g e n t o a m m o n i a n i t r o g e n in Run 1 , w h i c h w a s c o n d u c t e d w i t h o u t a d d e d N H C I , d u r i n g t h e d i g e s t i o n process is e v i d e n t ; t h e a m m o n i a n i t r o g e n increased f r o m 3.5 m g / / in t h e fresh feed slurry t o 7 6 m g / / in t h e effluent. 4

4

Gravity s e d i m e n t a t i o n a n d v a c u u m f i l t r a t i o n tests w e r e c o n d u c t e d o n t h e u n c o n d i t i o n e d e f f l u e n t f r o m Run 7. T h e e f f l u e n t e x h i b i t e d rapid s e t t l i n g velocities (Figure 4) a n d t h e f i l t r a t i o n c h a r a c t e r i s t i c s w e r e excellent (Table X). T h e properties o f t h e d i g e s t e d solids f r o m Runs 1, 7, a n d 8 are c o m p a r e d w i t h t h o s e o f t h e d r y feed solids in Table IX. For t h e t o t a l d i g e s t e d solids, c a r b o n c o n t e n t a n d h e a t i n g values decreased a n d t h e ash c o n t e n t increased as e x p e c t e d d u r i n g d i g e s t i o n . The h e a t i n g values of t h e d i g e s t e d solids per mass u n i t o f c a r b o n , h o w e v e r , d i d n o t e x h i b i t a general decrease o n d i g e s t i o n . On t h i s basis, t h e h e a t i n g value o f t h e d i g e s t e d solids f r o m Run 1 w a s s l i g h t l y less t h a n t h e c o r r e s p o n d i n g value of t h e feed solids, w h i l e t h e h e a t i n g values of t h e solids f r o m Runs 7 a n d 8 w e r e higher. These t r e n d s are p r o b a b l y t h e result o f different rates o f b i o d e g r a d a b i l i t y of t h e o r g a n i c c o m p o n e n t s in t h e grass, each o f w h i c h w o u l d be e x p e c t e d t o have d i f f e r e n t h e a t i n g values. To a t t e m p t t o a c q u i r e i n f o r m a t i o n o n t h e d e g r a d a b i l i t i e s o f t h e major classes of o r g a n i c c o m p o n e n t s in t h e grass, t h e c o n v e r s i o n data s u m m a r i z e d in Table X w e r e derived f r o m t h e c o m p o s i t i o n a l d a t a in Table IX b y a s s u m i n g t h a t a decrease in t h e c o n c e n t r a t i o n o f a n y o r g a n i c c o m p o n e n t w a s caused b y g a s i f i c a t i o n . This a s s u m p t i o n is n o t s t r i c t l y t r u e , b u t it p e r m i t s firsta p p r o x i m a t i o n c a l c u l a t i o n s of relative biodegradabilities. Hemicellulose, w h i c h w a s present in t h e h i g h e s t c o n c e n t r a t i o n , w a s c o n v e r t e d t o gas at t h e h i g h e s t yield w i t h o n e e x c e p t i o n , w h i l e t h e c r u d e protein f r a c t i o n a n d t h e l i g n i n f r a c t i o n gave t h e l o w e s t gas yields. T h e e x c e p t i o n appears t o be

242

BIOMASS AS A NONFOSSIL FUEL SOURCE Table VI. S U M M A R Y OF C A R B O N A N D ENERGY B A L A N C E S Accounted For Feed Carbon, % 94.0 .101 a

b

93.4 .100

b

Run 7

85.7 ,115

b

96.7 . 116

b

Run 8

107 ,116

a

a

a

a

106 . 116

b

a

b

Calculated from experimental determinations for moisture, volatile solids, ash. carbon, and heating values of feed and digested solids, a n d yield and composition of product gas. Volatile solids in digested solids calculated f r o m percent volatile solids reduction.

a

b Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Feed Energy, %

Run 1

Calculated from parameters in footnote " a " except that ash in digested solids estimated by assuming original ash in feed is in digested solids, that NaOH used for pH control is converted t o N a H C 0 on ashing at 500° C and remains in ash. that that N H CI. if added, is volatilized o n ashing. 3

4

Table VII. C O M P A R I S O N OF FEED A N D DIGESTER E F F L U E N T SLURRIES Parameter*

Feed

Run 1

Run 7

Run 8

pH

6.0 221

6.8 3.182

6.8 2.571

6.4 2.906

137 3.5 1.030

1.525 76 5.000

2.276 738 12.540

1.013 500 6.250

104 0 0 0 0 0 0 104

1.461 541 43 42 25 54 0 1.989

238 126 5 9 2 3 0 354

1.821 323 71

Total Alkalinity, m g / / as CaCU3 Bicarbonage CaC0

Alkalinity,

m g / / as

3

A m m o n i a Nitrogen, m g / / Specific Conductivity, μιτιηο/οπη Volatile Acids (Filtrate), m g / / Acetic Propionic Butyric Isobutyric Valeric Isovaleric Caproic Total A s Acetic *

125 72 18 14 2.273

Mean Values

Table VIII. VACUUM FILTRATION CHARACTERISTICS OF UNCONDITIONED DIGESTER EFFLUENT. RUN 7 TEST TEMPERATURE 26"C

TS.wt% 1

6

6

1

6

6

Effltftnt VS.wt%ofTS 788 78 8

Çjkj TS.wt% VS.wtttofTS 16 8 96 9 97 1 1

6

3

YirtdDry Cake, lb/ft -hr Filtrate, lb/lb dry cake 12.3 115 13.1 155 2

30 sec cycle time. 6 sec form time. 12 sec drying time. 12 sec removal time. 20 in. Hg.

KLASS A N D GHOSH

Methane from Bermuda Grass

243

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

12.

Figure 4. Interface height vs. time for gravity settling of unconditioned effluent from Run 7

244

BIOMASS AS A NONFOSSIL

FUEL

SOURCE

Table IX. C O M P A R I S O N OF DRY FEED A N D DIGESTED SOLIDS

Dry Feed

Run 1

Digested Solids* Run 8 Run 7

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Ultimate Analysis. w t % C H

47.1

37.6

30.2

43.9

6.04

5.43

Ν

1.96

4.78 2.34

6.65

5.50 2.34

81.8 18.2

78.8 21.2

80.2

14.6 17.7

15.9

37.9

13.6

19.5 13.6

Proximate Analysis, w t % 5.15 95.0

Moisture Volatile Matter Ash

5.05

19.8

Organic Components. w t % 12.3

Crude Protein (Kjeldahl Nx6.25) Hemicllulose

40.2 31.7

Cellulose Lignin

4.1

Heating Value Btu/dry lb

*

Btu/lb ( M A R

8.185 8.616

Btu/lb C

17.378

17.5 7.4

4.5

6.237

6.021

7.625 16.588

7.641 19.957

7.721 9.627 17.588

Prepared by evaporation of total effluent t o dryness o n steam bath, pulverization, and drying in an evacuated desiccator t o a constant weight.

Table X. C O M P A R I S O N OF ORGANIC C O M P O N E N T CONVERSION

Component

Hemicellulose Cellulose Crude Protein Lignin *

M a s s Ratio In Feed Solids

Run 1 Run 7 Gasified, Gasified, wt% Ratio* wt% Ratio* 1.0 0.63

0.30

55.1 43.8 0

0.10

0

0

1.0 0.79

Run 8 Gasified. Ratio* wt%

1.0 0.76

16.2

1.0

64.5

45.3

2.2

9.3

0.01

0

67.3

0 0

Expressed as mass of indicated component gasified per unit mass of hemicellulose gasified.

12.

KLASS A N D GHOSH

245

Methane from Bermuda Grass

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

t h e r m o p h i l i c Run 8, in w h i c h less h e m i c e l l u l o s e w a s c o n v e r t e d t h a n cellulose. The h i g h e r level of u n c o n v e r t e d h e m i c e l l u l o s e t h a n cellulose in Run 8 m a y be an artifact c a u s e d b y c o n v e r s i o n of cellulose at t h e r m o p h i l i c c o n d i t i o n s t o d e r i v a t i v e s w h i c h are d e t e c t e d in t h e h e m i c e l l u l o s e f r a c t i o n . T h e e x p e r i m e n t a l d a t a also i n d i c a t e t h a t a small a m o u n t o f t h e lignin f r a c t i o n w a s c o n v e r t e d in Run 7. Overall, t h e p o l y s a c c h a r i d e f r a c t i o n is m o r e b i o d e g r a d a b l e t h a n t h e p r o t e i n a n d lignin f r a c t i o n s . T h e l o w b i o d e g r a d a b i l i t y of l i g n i n u n d e r a n a e r o b i c d i g e s t i o n c o n d i t i o n s is e x p e c t e d , w h i l e t h e h i g h e r b i o d e g r a d a b i l i t y of t h e h e m i c e l l u l o s e m i g h t be p r e d i c t e d because it has a h i g h e r r e a c t i v i t y t o a c i d a n d alkali t h a n cellulose. The l o w e r b i o d e g r a d a b i l i t y of p r o t e i n w i t h respect t o t h e m o n o s a c c h a r i d e s a n d p o l y s a c c h a r i d e s in g i a n t b r o w n kelp has been r e p o r t e d (12). Thermodynamic Estimates T h e e n t h a l p y o f d i g e s t i o n , p r o d u c t gas c o m p o s i t i o n , a n d m e t h a n e yield f o r t h e lot of grass e x a m i n e d in t h i s w o r k w e r e e s t i m a t e d as s h o w n in Chart 2. T h e process is p r o j e c t e d t o be s l i g h t l y e x o t h e r m i c , — 1 7 3 B t u / l b grass reacted, w h i c h agrees w e l l w i t h t h e slight e x o t h e r m i c i t y r e p o r t e d f o r kelp (6). A s s u m i n g t h a t 2 0 % o f t h e c a r b o h y d r a t e f r a c t i o n a n d 7% o f t h e p r o t e i n present in t h e grass w o u l d be c o n v e r t e d t o n e w bacterial cells b y anaerobic f e r m e n t a t i o n a n d h e n c e n o t be available f o r m e t h a n e p r o d u c t i o n b y a single pass t h r o u g h t h e f e r m e n t o r , t h e m a x i m u m t h e o r e t i c a l yield of m e t h a n e is g i v e n b y (12): (1 lb VS a d d e d -

0.176 lb VS t o cells) f \0.95 7

9

2

S

C

-

F CH

M lb V S

/

6.87

S

C

F

C

h

4

lb VS-pass

T h e h i g h e s t e x p e r i m e n t a l yield o b t a i n e d in t h i s w o r k is 3.5 SCF/lb V S a d d e d (Run 7) or 5 1 % o f t h e t h e o r e t i c a l m a x i m u m value. T h u s , c o n s i d e r a b l e yield i m p r o v e m e n t s are still possible. Comparison W i t h Other Substrates T h e gas yields a n d volatile solids r e d u c t i o n a n d e n e r g y recovery efficiencies f r o m Coastal B e r m u d a grass are c o m p a r e d in Table XI w i t h t h o s e o b t a i n e d f r o m o t h e r substrates u n d e r similar m e s o p h i l i c d i g e s t i o n c o n d i t i o n s . T h e n i t r o g e n - s u p p l e m e n t e d B e r m u d a grass w a s c o n v e r t e d t o m e t h a n e a t a b o u t t h e s a m e efficiencies as g i a n t b r o w n kelp a n d p r i m a r y s e w a g e sludge. T h e n o n - s u p p l e m e n t e d B e r m u d a grass, h o w e v e r , afforded c o n s i d e r a b l y l o w e r m e t h a n e yields a n d efficiencies t h a n these substrates. U n t r e a t e d K e n t u c k y bluegrass w a s s o m e w h a t b e t t e r in p e r f o r m a n c e t h a n Coastal B e r m u d a grass.

246

BIOMASS AS A NONFOSSIL F U E L

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Chart 2.

Summary of Thennodynamk Calculations

I.

Crass Composition

C, 47.10 wt% H, 6.04 N, 1.96 S, 0.21 0, 39.64* Ash, 5.05

II.

E m p i r i c a l Formula

C

III.

SOURCE

3

q

2

(dry)

0 ^

^

N

S

Q u

Ashj , Mol. Wt. 100

Q Q Q J

Q

Heat of D i g e s t i o n , Gas Composition, Methane Y i e l d a.

Assuming Ν and S can be neglected and C1U and C 0 are the o n l y products 2

C

b.

3

H

92 5 99 °2 48

+

1

,

1

8

2 H

2

°

"

2

,

0

8

9

C

H

+

"

,

8

3

Gas composition:

53.3 moIX CH*,

Methane Y i e l d :

7.92 SCF CHw/lb grass r e a c t e d (max.)

For 1.00

l b dry grass r e a c t e d :

Input = 8,185

Btu

Output- 8,012

Btu

Heat of Reaction: *By d i f f e r e n c e .

46.7 molZ C 0

1

8,012

- 8,185

- -173

Btu

2

1C

°

2

12.

KLASS AND GHOSH

247

Methane from Bermuda Grass

Table XI. C O M P A R I S O N O F COMPOSITIONS A N D S E L E C T E D S T E A D Y - S T A T E ANAEROBIC DIGESTION RESULTS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

Compositional Parameter

Coastal Bermuda Grass

C. w t % H. w t % N. w t % Moisture. w t % Volatile matter. w t % Ash. w t % High heating value. Btu/dry lb High heating value. Btu/lb (MAR High Heating value. Btu/lb C Digestion Conditions Mechanical A g i t a t i o n Feeding Frequency Nutrients A d d e d Temperature. °C

47.1 6.04

45.8 5.9

1.96 5.15 95.0 5.05

8.052

4.620

8.537

8.616

9.309

7.977

11.620

17.378

17.581

16.619

19.513

0.313 3.13 1.92 61.4

d

Efficiencies Volatile Solids Reduction. % 20.0 Energy Recovered as Methane. % 22.6

c

d

e

f

9

Sludge

8.185

Gas Production Gas Production Rate, vol/vol-day Gas Yield. SCF/lb VS added Methane Yield. SCF/lb VS added Methane Concentration. mol%

b

f

4.8 7.8 86.5 13.5

Loading Rate, lb V S / f r -day Detention Time, day C/N Ratio in Feed Slurry

a

Brown Kelp

43.75 6.24

O 35 6.8 0.10 12 24.0

b

Primary

Giant 0

27.8 3.73 1.63 88.8 57.92 42.08

c D

3

a

Kentucky Bluegrass

C D N

C D 0

35 6.8 0.10 12 6.3

35 7.1

C D

3.16 94.12 73.47 26.53

C D 0

0.13 12 9.54

0 35 7.0 0.10 12 17.1

35 7.0 0.10 12 13.8

3.51 55.9-

0.55 4.20 2.54 60.4

0.662 6.62 3.87 58.4

0.78 7.8 5.3 68.5

37.5 41.2

25.1 27.6

43.7 49.1

41.5 46.2

e

0.587 5.87

9

" C " denotes continous agitation. " D " denotes daily feeding and wasting cycle. " O " denotes no nutrients added to feed slurry. " N " denotes a m m o n i u m chloride added t o feed slurry. RunBofRef.4. Run 1 of Table 5. Run 7 of Table 5. R u n 2 o f R e f . 12. Experimental data obtained w i t h primary thickened sewage sludge in laboratory digesters under standard high-rate conditions. Sludge obtained f r o m Metropolitan Sanitary District of Greater Chicago.

American Chemical Society Ubraiy

Ï1M 169 St N. W. ttllBglm, D. C. 2003·

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B I O M A S S AS A N O N F O S S I L F U E L

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch012

S U M M A R Y AND CONCLUSIONS B e r m u d a grass (Cynodon dactylon) is o n e of t h e h i g h - y i e l d w a r m - s e a s o n grasses t h a t has been s u g g e s t e d as a p r o m i s i n g r a w material for c o n v e r s i o n t o m e t h a n e . E x p e r i m e n t a l w o r k p e r f o r m e d w i t h laboratory digesters t o s t u d y t h e a n a e r o b i c d i g e s t i o n of Coastal B e r m u d a grass h a r v e s t e d in Louisiana a n d h a v i n g a C / N ratio of 2 4 is d e s c r i b e d . M e t h a n e yields of a b o u t 1.9 SCF/lb of v o l a t i l e solids (VS) a d d e d w e r e o b s e r v e d u n d e r c o n v e n t i o n a l m e s o p h i l i c high-rate conditions. W h e n supplemental nitrogen additions were made, t h e m e t h a n e yields increased. This o b s e r v a t i o n a l o n g w i t h t h e c o m p o s i t i o n a l d a t a c o m p i l e d o n t h e grass used in t h i s w o r k i n d i c a t e d t h a t t h e n i t r o g e n c o n t e n t of t h e u n s u p p l e m e n t e d grass w a s i n s u f f i c i e n t t o sustain h i g h - r a t e d i g e s t i o n at t h e h i g h e r y i e l d level. H o w e v e r as t h e C / N ratio w a s r e d u c e d by a d d i t i o n of a m m o n i u m c h l o r i d e , t h e m e t h a n e yield c o n t i n u a l l y increased up t o 3.5 SCF/lb a d d e d at t h e l o w e s t C / N ratio e x a m i n e d (6.3) even after relatively h i g h c o n c e n t r a t i o n s of a m m o n i u m n i t r o g e n w e r e m e a s u r e d in t h e effluent. It appears t h a t t h e a d d e d n u t r i e n t had a s t i m u l a t o r y effect on methane production above the point where nitrogen w a s not limiting. Thermophilic digestion w i t h supplemental nitrogen additions afforded m e t h a n e yields of a b o u t 2.7 SCF/lb V S a d d e d . Carbon a n d e n e r g y balances w e r e c a l c u l a t e d a n d t h e relative b i o d e g r a d a b i l i t i e s of t h e o r g a n i c s w e r e estimated. It w a s c o n c l u d e d f r o m t h i s w o r k t h a t Coastal B e r m u d a grass c a n be c o n v e r t e d t o h i g h - m e t h a n e gas u n d e r c o n v e n t i o n a l a n a e r o b i c d i g e s t i o n c o n d i t i o n s T h e p e r f o r m a n c e of t h e p a r t i c u l a r lot of grass s t u d i e d w a s s u b s t a n t i a l l y i m p r o v e d by s u p p l e m e n t a l n i t r o g e n a d d i t i o n s . A C K N O W L E D G E M EN Τ T h e a u t h o r s w i s h t o express t h e i r a p p r e c i a t i o n for t h e f i n a n c i a l s u p p o r t of t h e w o r k d e s c r i b e d in t h i s paper b y U n i t e d Gas Pipe Line Co.. a n d especially for t h e m a n y v a l u a b l e d i s c u s s i o n s a n d s u g g e s t i o n s p r o v i d e d by Dr. V i c t o r E d w a r d s a n d Robert C h r i s t o p h e r of U n i t e d . T h e a u t h o r s also a p p r e c i a t e t h e assistance s u p p l i e d by M i k e Henry. A l Iverson. Frank Sedzielarz. a n d Janet Vorres. w h o p e r f o r m e d t h e e x p e r i m e n t a l d i g e s t i o n s t u d i e s , a n d by J a m e s I n g e m a n s o n a n d Robert Stotz a n d t h e i r staff w h o p e r f o r m e d m a n y of t h e c h e m i c a l analyses. Special t h a n k s is g i v e n t o Mr. D a w s o n J o h n s of N o r t h Louisiana Hill Farm E x p e r i m e n t S t a t i o n for s u p p l y i n g t h e B e r m u d a grass a n d i n f o r m a t i o n on its p r o d u c t i o n .

12. KLASS AND GHOSH Methane from Bermuda Grass

249

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REFERENCES

1.

Klass, D. L. Chemtech 1974, 4, 161-68.

2.

Klass, D. L. 169th National Meeting, American Chemical Society, April 1975; Energy Sources 1977, 3 (2), 177-95.

3.

InterTechnology Corp. October 1975, American Gas Association Project IU-114-1, Final Report.

4. Klass, D. L.; Ghosh, S.; Conrad, J.R. "Symposium Papers", Clean Fuels From Biomass, Symposium sponsored by the Institute of Gas Technology, Orlando, Fla., January 1976; Institute of Gas Technology: Chicago, Ill., 1976, pp. 229-52. 5. Burton, G. W. In "Forages The Science of Grassland Agriculture"; Highes, H. D.; Heath, M. E.; Metcalfe, D. S., Eds.; The Iowa State College Press: Ames, Iowa; Chapter 24. 6.

Klass, D. L.; Ghosh, S. "Symposium Papers", Clean Fuels From Biomass and Wastes, Symposium sponsored by the Institute of Gas Technology, Orlando, Fla., January 1977; Institute of Gas Technology: Chicago, Ill. 1977; pp 323-51.

7.

Agricultural Research Service, Washington, D.C., December 1970, United States Department of Agriculture, Agriculture Handbook No. 379.

8.

Association of Environmental Engineering Professors, "Environmental Engineering Unit Operations and Unit Processes Laboratory Manual", O'Connor, J. T., Ed.,III-1-1,July 1972.

9.

Ibid., V-2.

10.

McCarty, P. L. Public Works 1964 (November), 91-4.

11.

Johns, D. M. "Fertilization of Coastal Bermuda Grass on a Coastal Plain Soil", North Louisiana Hill Farm Experiment Station, Homer, Louisiana.

12. Klass, D. L .; Ghosh, S.; Chynoweth, D. P. 175th National Meeting, American Chemical Society, Anaheim, Calif., March 1978. RECEIVED JUNE 18, 1980.

13 Advanced Digestion Process Development for Methane Production from Biomass-Waste Blends SAMBHUNATH GHOSH and DONALD L. KLASS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

Institute of Gas Technology, 3424 South State Street, Chicago, IL 60616

Biomass and organic wastes (discarded biomass or biomass-derived material) may supply up to 15% of the U.S. energy needs by the end of this century via gasification or other conversion schemes (1). One conversion process that is expected to play a role in producing methane from biomass and wastes is anaerobic digestion. Commercial production of substitute natural gas (SNG) and medium-Btu fuel gas by anaerobic digestion of waste materials has already started in the U.S. and other countries (2). Increased usage of the anaerobic digestion process for methane production is, however, hindered because of the low reaction rate and conversion efficiency of the conventional digestion process. New digestion techniques are needed to improve conversion rates and efficiencies so that the full potential of anaerobic digestion as a methane-producing process can be realized. Starting with the crude septic tank, a number of improved process configurations, including "standard-rate" digestion, stage digestion, "high-rate" digestion, and the anaerobic contact process, have evolved during the nearly 100 years of application of the anaerobic digestion process to sewage sludge stabilization. However, the design requirements of even one of the best anaerobic sludge stabilization modes, high-rate digestion, result in large expensive plants that are difficult to justify for commercial SNG production. An additional problem with the conventional digestion process is

0097-6156/81/0144-0251 $07.00/0 © 1981 American Chemical Society

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SOURCE

t h a t 4 0 t o 7 0 % of t h e feed o r g a n i c s r e m a i n u n c o n v e r t e d a n d m u s t be d i s p o s e d of at s u b s t a n t i a l cost. Considerable research, s u c h as t h a t r e p o r t e d by Pohland a n d Ghosh (3). Gavett (4), Ort (5,6). S w i t z g a b l e (7). Klass et al. (8). G h o s h et al. (9). G h o s h a n d Klass ( 1 0 , ] \ ) H a u g (12). a n d o t h e r s (13) has t h e r e f o r e been d i r e c t e d t o t h e d e v e l o p m e n t of better d i g e s t i o n m e t h o d s .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

t

Considerable w o r k has been d o n e at t h e I n s t i t u t e of Gas T e c h n o l o g y since 1971 t o d e v e l o p a d v a n c e d d i g e s t i o n m e t h o d s a n d process c o n f i g u r a t i o n s for t h e c o n v e r s i o n of various o r g a n i c feeds t o h i g h - B t u fuel gas (8-11). In t h i s paper, w e w i l l d e s c r i b e a f e w selected a d v a n c e d d i g e s t i o n c o n c e p t s a n d t h e results of t h e i r a p p l i c a t i o n t o b i o m e t h a n a t i o n of a m i x e d b i o m a s s - w a s t e b l e n d . T h e t e r m " a d v a n c e d d i g e s t i o n " as used in t h i s paper includes u n c o n v e n t i o n a l f e r m e n t a t i o n m o d e s a n d process c o n f i g u r a t i o n s for i m p r o v e d m e t h a n e p r o d u c t i o n rate a n d y i e l d . T h e research r e p o r t e d here c o n s i s t e d of a laboratory e v a l u a t i o n of several a d v a n c e d d i g e s t i o n m e t h o d s a n d a selected b i o m a s s - w a s t e b l e n d . T h e o b j e c t i v e of t h i s w o r k w a s t o search for an o p t i m u m b i o c o n v e r s i o n s y s t e m c o n f i g u r a t i o n , a n d t h e u l t i m a t e goal is t o a p p l y t h i s c o n f i g u r a t i o n t o t h e p r o d u c t i o n of SNG. Specifically, t h e a d v a n c e d d i g e s t i o n t e c h n i q u e s s t u d i e d w e r e d i g e s t i o n of p r e t r e a t e d f e e d , r e c y c l i n g of d i g e s t e r e f f l u e n t a n d p r o d u c t gas. aerobic p o s t t r e a t m e n t a n d r e c y c l i n g of d i g e s t e r e f f l u e n t , a n d t w o - p h a s e digestion. T h e e x p e r i m e n t a l p l a n c o n s i s t e d of: •

C o n v e n t i o n a l h i g h - r a t e d i g e s t i o n u n d e r baseline o p e r a t i n g c o n d i t i o n s of 3 5 ° C d i g e s t i o n t e m p e r a t u r e . 0.1 lb V S / f t - d a y l o a d i n g a n d a 12-day detention time. 3

•

M e s o p h i l i c (35°C) a n d t h e r m o p h i l i c (55°C) d i g e s t i o n of feed s u b j e c t e d t o m i l d alkaline (sodium hydroxide) p r e t r e a t m e n t w i t h r e c y c l i n g of spent c a u s t i c for fresh feed t r e a t m e n t a n d neutralization of t r e a t e d feed w i t h digester gas t o m i n i m i z e a c i d neutralizer r e q u i r e m e n t .

•

M e s o p h i l i c (35°C) d i g e s t i o n w i t h p r o d u c t gas r e c y c l i n g .

•

M e s o p h i l i c (35°C) d i g e s t i o n w i t h r e c y c l i n g of aerobically digester effluent.

•

Two-phase digestion.

posttreated

13.

GHOSH AND KLASS

253

Methane from Biomass-Waste

MATERIALS AND METHODS Digester Feeds Four f e e d s t o c k s , w a t e r h y a c i n t h (Eichhornia grass (8) (Cynodon

dactylon)

crassipes)

a n d Coastal B e r m u d a

i n d i g e n o u s t o t h e Gulf Coast, a n d s e w a g e

s l u d g e a n d m u n i c i p a l solid w a s t e ( M S W ) w e r e c o n s i d e r e d f o r b i o c o n v e r s i o n t o m e t h a n e . C o n v e n t i o n a l m e s o p h i l i c (35°C) h i g h - r a t e d i g e s t i o n of a b i o m a s s s l u d g e b l e n d p r e p a r e d w i t h t h e s e m a t e r i a l s s h o w e d t h a t t h e m i x e d feed w a s superior t o t h e single feeds in t e r m s o f n u t r i t i o n a l b a l a n c e a n d m e t h a n e y i e l d a n d p r o d u c t i o n rate (14-16). U t i l i z a t i o n o f a b i o m a s s - w a s t e b l e n d has several

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

a d v a n t a g e s . Use of a b l e n d f a c i l i t a t e s f e e d s t o c k s u p p l y o n a y e a r - r o u n d basis, a n d a m i x e d feed m a y be s u p e r i o r t o b i o m a s s alone in t e r m s o f process economics.

In a d d i t i o n ,

use of a b i o m a s s - w a s t e

blend

provides t h e

o p p o r t u n i t y f o r s i m u l t a n e o u s e n e r g y recovery a n d w a s t e s t a b i l i z a t i o n in an o p t i m i z e d i n t e g r a t e d s y s t e m . T h e feed used f o r t h e w o r k d e s c r i b e d in t h i s paper is a m i x t u r e of s e w a g e l a g o o n e f f l u e n t - g r o w n w a t e r h y a c i n t h , Coastal B e r m u d a grass, t h e c o m b u s t i b l e f r a c t i o n o f m u n i c i p a l solid w a s t e , a n d m i x e d a c t i v a t e d - p r i m a r y s l u d g e b l e n d e d in t h e mass ratio of 3 2 . 3 : 3 2 . 3 : 3 2 . 3 : 3 . 1 o n a volatile solids (VS) basis. T h i s p a r t i c u l a r ratio w a s selected based o n t h e p r o j e c t e d availability of these feed c o m p o n e n t s f o r a c o m m e r c i a l p l a n t in t h e Gulf States area. T h e b i o m a s s a n d M S W c o m p o n e n t s w e r e finely g r o u n d before b l e n d i n g . The m i x e d feed had a m e d i a n p a r t i c l e size of 0.25 m m . It had m o i s t u r e , VS, c a r b o n , n i t r o g e n , p h o s p h o r u s , sulfur, h y d r o g e n , c a l c i u m , s o d i u m , p o t a s s i u m , m a g n e s i u m , cellulose, h e m i c e l l u l o s e . l i g n i n . a n d c r u d e p r o t e i n c o n t e n t s a n d a h i g h h e a t i n g v a l u e o f 8 8 . 9 7 . 8 2 . 7 8 (of t o t a l solids). 4 3 . 1 4 , 1.64, 0.43. 0 . 3 1 , 5.60, 1.23. 0.78, 1.05, 0.22. 37.5. 31.8. 4.6. a n d 10.1 w t %. a n d 7.445 B t u / l b (dry), respectively. T h e m i x e d feed h a d t h e e m p i r i c a l f o r m u l a C3595 H5545 Ο1.979

N

0.117

p

o.oi4

S0.010 A s h

1 7 2

2

at a m o l e c u l a r w e i g h t of 100, a n d a

t h e o r e t i c a l m e t h a n e y i e l d o n a n a e r o b i c d i g e s t i o n o f a b o u t 6.4 SCF/lb V S a d d e d (14).* A l s o , it w a s d e t e r m i n e d b y l o n g - t e r m b a t c h d i g e s t i o n tests t h a t this m i x e d feed had a n u l t i m a t e a n a e r o b i c b i o d e g r a d a b i l i t y or v o l a t i l e solids d e s t r u c t i o n e f f i c i e n c y of 6 6 % (14). Digester feed slurries w e r e p r e p a r e d b y d i l u t i n g a w e i g h e d mass o f t h e feed a c c o r d i n g t o t h e l o a d i n g rate w i t h d i s t i l l e d d e m i n e r a l i z e d w a t e r t o a v o l u m e d e t e r m i n e d b y t h e h y d r a u l i c d e t e n t i o n t i m e o f t h e run. •

Assumes 30% of volatile solids converted to cells on one pass through the digester.

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Digesters T h e d i g e s t i o n runs w e r e c o n d u c t e d in c u s t o m - m a d e , f l a t - b o t t o m e d , c y l i n d r i c a l Plexiglas digesters h a v i n g f o u r vertical baffles m o u n t e d 9 0 ° apart o n t h e inside w a l l s t o p r e v e n t v o r t e x i n g of t h e c u l t u r e d u r i n g m e c h a n i c a l a g i t a t i o n by t w o stainless steel impellers at 1 3 0 r p m . T h e digesters w e r e h e a t e d by p l a c i n g t h e m in a c o n s t a n t - t e m p e r a t u r e c h a m b e r or by t h e r m i s t o r c o n t r o l l e d h e a t i n g tapes. A l l digesters w e r e g e o m e t r i c a l l y similar in c o n s t r u c t i o n . T h e c u l t u r e v o l u m e s of t h e v a r i o u s digesters are i n d i c a t e d in t h e t a b u l a t i o n s of t h e e x p e r i m e n t a l results. Except for t h e t w o - p h a s e s y s t e m , all digesters w e r e m a n u a l l y f e d o n c e per d a y after w i t h d r a w i n g an equal v o l u m e of digester e f f l u e n t . A s d e s c r i b e d later, t h e t w o - p h a s e s y s t e m w a s e q u i p p e d w i t h an a u t o m a t e d f e e d i n g s y s t e m . A D V A N C E D S Y S T E M CONFIGURATION A N D OPERATION Digestion of Pretreated Feed T h e m i x e d h y a c i n t h - g r a s s - M S W - s l u d g e feed w a s p r e t r e a t e d w i t h c a u s t i c soda s o l u t i o n at m i l d t e m p e r a t u r e s a n d pressures in an a t t e m p t t o i m p r o v e feed b i o d e g r a d a b i l i t y a n d m e t h a n e y i e l d . T r e a t m e n t t e m p e r a t u r e s (5°. 2 5 ° , 5 5 ° . 1 0 0 ° . 121°C) a n d pressures ( a t m o s p h e r i c a n d 3 0 psig) a n d d i l u t e c a u s t i c c o n c e n t r a t i o n s w e r e selected for t h e p r e t r e a t m e n t s t u d i e s for reasons of l o w e r reaction vessel costs, r e d u c e d e n e r g y a n d c h e m i c a l i n p u t s , a n d t o keep t h e salt c o n c e n t r a t i o n in t h e d i g e s t e r l o w . A l k a l i n e t r e a t m e n t u n d e r these c o n d i t i o n s is e x p e c t e d t o be a c o s t - e f f e c t i v e m e t h o d for increasing m e t h a n e p r o d u c t i o n f r o m cellulosic feeds (14.17). D i g e s t i o n of t h e c a u s t i c - t r e a t e d feed w a s c o n d u c t e d at selected m e s o p h i l i c (35°C) a n d t h e r m o p h i l i c (55°C) t e m p e r a t u r e s . Flow d i a g r a m s d e p i c t i n g t h e e x p e r i m e n t a l s e q u e n c e are p r e s e n t e d in Figures I a n d II. T h e p r o c e s s i n g steps i n c l u d e d m i x i n g of t h e u n d i l u t e d feed w i t h c a u s t i c s o l u t i o n , p r e t r e a t m e n t at t h e c h o s e n t e m p e r a t u r e , pressure, a n d t i m e ; d i l u t i n g t h e t r e a t e d feed w i t h d i s t i l l e d d e m i n e r a l i z e d w a t e r a n d neutralization of t h e digester feed slurry w i t h h y d r o c h l o r i c a c i d or digester g a s ; a n d d i g e s t i o n of t h e p r e t r e a t e d neutralized f e e d . In s o m e runs, t h e d i g e s t e r feed slurry w a s neutralized w i t h t h e d i g e s t e r gas t o r e d u c e neutralizer a c i d r e q u i r e m e n t a n d d i g e s t e r salinity, a n d t o increase t h e b i c a r b o n a t e alkalinity (buffer c a p a c i t y ) . In still o t h e r runs, t h e c a u s t i c - t r e a t e d feed w a s v a c u u m f i l t e r e d , a n d a p o r t i o n of t h e filtrate c o n t a i n i n g t h e spent c a u s t i c s o l u t i o n w a s r e c y c l e d for fresh feed pretreatm e n t . Filtrate r e c y c l i n g r e d u c e d t h e c a u s t i c r e q u i r e m e n t for feed pretreatm e n t . t h e acid r e q u i r e m e n t t o neutralize t h e pretreated feed, a n d t h e salt c o n c e n t r a t i o n in t h e feed slurry a n d digester.

13.

255

Methane from Bio mass-Waste

GHOSH AND KLASS

II-/

DIGESTER GAS

CAUSTIC

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

NoOH

ι

SOLUTION /

PRETREATMENT j j ^ "

MIXING

1

H 0 2

^

1

FEED S L U R R Y PREPARATION

NEUTRALIZATION EFFLUENT

Figure 1.

QAS COLLECTION

Experimental sequence for mesophilic digestion of caustic-treated feed

MIXING

PRETREATMENT IN 55"C/KX)*C INCUBATOR - ALTERNATE PATH

Figure 2 .

Experimental sequence for thermophilic digestion of caustic-treated feed

256

BIOMASS AS A NONFOSSIL F U E L SOURCE

Digestion W i t h Product Gas Recycling T h e s y s t e m used t o c o n d u c t t h e gas r e c y c l i n g studies is s h o w n in Figure III. Digester gas w a s c l e a n e d a n d d r i e d by passing it t h r o u g h a g l a s s - w o o l p a r t i c u l a t e t r a p , a w a t e r - c o o l e d c o n d e n s a t e t r a p , a n d a C a S 0 -filled gasd r y i n g c o l u m n . T h e c l e a n , d r y gas w a s r e c y c l e d at a selected recycle ratio (defined as t h e ratio of r e c y c l e d gas f l o w rate in d r y s t a n d a r d c u b i c feet at 6 0 ° F a n d 3 0 in. Hg t o t h e d i g e s t e r gas p r o d u c t i o n rate in d r y s t a n d a r d c u b i c feet) i n t o t h e d i g e s t i n g c u l t u r e t h r o u g h a glass diffuser. E x p e r i m e n t s w e r e c o n d u c t e d at gas recycle ratios r a n g i n g f r o m a b o u t 2 t o 125. T h e pressure d i f f e r e n c e across t h e gas p u m p c o r r e s p o n d i n g t o t h e s e recycle ratios r a n g e d f r o m a b o u t 1 t o 9 psi. Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

4

Digestion W i t h Recycling of Aerobically Posttreated Digester Effluent T h e p u r p o s e of t h i s s t u d y w a s t o e x a m i n e t h e effect of aerobic biological p o s t t r e a t m e n t of d i g e s t e r e f f l u e n t o n t h e b i o d e g r a d a b i l i t y of r e c a l c i t r a n t feed c o m p o n e n t s passing u n c o n v e r t e d or partially c o n v e r t e d t h r o u g h t h e digester. P r e s u m i n g t h a t aerobic t r e a t m e n t of t h e d i g e s t e r e f f l u e n t i m p r o v e d b i o d e g r a d a b i l i t y . r e c y c l i n g of t h e t r e a t e d solids w a s e x p e c t e d t o increase m e t h a n e p r o d u c t i o n rate a n d yield w i t h s i m u l t a n e o u s a n d e n h a n c e d r e d u c t i o n of t h e e f f l u e n t solids a n d soluble o r g a n i c s load d i s c h a r g e d f r o m t h e overall a n a e r o b i c - a e r o b i c s y s t e m . In t h e e x p e r i m e n t a l process c o n f i g u r a t i o n (Figure IV). d i g e s t e r e f f l u e n t w a s aerobically t r e a t e d in a 1 4 / c u l t u r e v o l u m e s e m i c o n t i n u o u s l y . or in a 2 / c u l t u r e v o l u m e b a t c h a c t i v a t e d s l u d g e unit. A e r a t i o n a n d m i x i n g w e r e a c c o m p l i s h e d by d i f f u s e d a e r a t i o n . Dissolved o x y g e n w a s m o n i t o r e d by a lead-silver g a l v a n i c p r o b e inserted in t h e c u l t u r e . T h e 1 4 / a c t i v a t e d s l u d g e u n i t w a s a t w o - c o m p a r t m e n t t a n k , t h e aeration c h a m b e r of w h i c h w a s separated f r o m t h e a d j a c e n t s e t t l i n g zone by a v e r t i c a l plate. This u n i t w a s used for s e m i c o n t i n u o u s o p e r a t i o n at aerator d e t e n t i o n t i m e s greater t h a n 2 days. Settled s l u d g e w i t h d r a w n f r o m t h e b o t t o m of t h e settler w a s r e c y c l e d t o t h e digester. T h e 1 4 / unit w a s o p e r a t e d at 3 5 ° C w i t h an air f l o w rate of 1 / / m i n . V a r i o u s runs w e r e c o n d u c t e d at selected aerator d e t e n t i o n t i m e s a n d s l u d g e recycle ratios (defined as t h e v o l u m e of recycle s l u d g e d i v i d e d by t h e v o l u m e of t h e d i g e s t e r feed). T h e 2 / b a t c h u n i t w a s o p e r a t e d u n d e r c o n d i t i o n s of l i m i t e d aeration (0.12 / / m i n ) at an a m b i e n t t e m p e r a t u r e of a b o u t 25°C). T h e f i l l - a n d - d r a w a c t i v a t e d s l u d g e u n i t w a s f e d d a i l y w i t h 1.667 m l of fresh digester e f f l u e n t after w i t h d r a w i n g an equal v o l u m e of m i x e d liquor aerated for 2 4 hours. Selected v o l u m e s of t h e aerator m i x e d liquor w e r e r e c y c l e d t o t h e d i g e s t e r t o

GHOSH AND KLASS

Methane from Biomass-Waste

257

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13.

Figure 4.

Recycling system for aerobically-posttreated digester effluent

258

BIOMASS AS A NONFOSSIL F U E L SOURCE

o b t a i n t h e desired recycle ratio (defined as t h e ratio of t h e v o l u m e of m i x e d liquor t o t h e v o l u m e of fresh feed). In s o m e e x p e r i m e n t s , t h e aerator feed (fresh digester effluent) w a s pretreated w i t h d i l u t e s o d i u m h y d r o x i d e s o l u t i o n for 2 4 hours at 100°C. T h e recycle s l u d g e w a s d e o x y g e n a t e d w i t h a h e l i u m p u r g e in s o m e runs before c h a r g i n g it t o t h e digester.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

Two-Phase Digester T w o - p h a s e d i g e s t i o n has c o n s i d e r a b l e p o t e n t i a l f o r increasing m e t h a n e p r o d u c t i o n rate a n d yield (3.10,18,^9). It is a m u l t i - s t a g e , h i g h - r a t e d i g e s t i o n process in w h i c h a c i d o g e n i c a n d m e t h a n o g e n i c f e r m e n t a t i o n s are o p t i m i z e d in separate digesters. T h e t w o - p h a s e s y s t e m used in o u r w o r k c o n s i s t e d of a c o m p l e t e l y m i x e d a c i d - p h a s e digester a n d a c o m p l e t e l y m i x e d m e t h a n e phase digester or a m e t h a n e - p h a s e a n a e r o b i c filter p a c k e d w i t h Raschig rings (Figure V). T h e a c i d digester w a s g r a v i t y fed f r o m a sealed o v e r h e a d feed reservoir h a v i n g a h e l i u m or a r g o n b l a n k e t a b o v e t h e feed slurry. Caustict r e a t e d feed w a s delivered t o t h i s d i g e s t e r in small slugs u p t o 7 0 t i m e s per d a y by a t i m e r - o p e r a t e d v a l v e t o o b t a i n o p e r a t i n g c o n d i t i o n s closely a p p r o a c h i n g t h o s e of c o n t i n u o u s f e e d i n g . Effluent f r o m t h e acid digester o v e r f l o w e d d i r e c t l y t o t h e c o m p l e t e l y m i x e d m e t h a n e - p h a s e digester. A l t e r n a t i v e l y , part of t h i s e f f l u e n t w a s v a c u u m f i l t e r e d , a n d t h e f i l t r a t e w a s f e d c o n t i n u o u s l y t o t h e a n a e r o b i c filter f r o m a c o n s t a n t - h e a d M a r i o t t e b o t t l e s u p p l i e d w i t h h e l i u m t o fill t h e reservoir gas phase. T h e p a c k e d - b e d anaerobic filter had a gross v o l u m e of 1 8 . 5 / a n d a v o i d ratio of 0.63. Filter e f f l u e n t w a s r e c i r c u l a t e d c o n t i n u o u s l y t o t h e inlet e n d at a r e c i r c u l a t i o n ratio of 5.1 (defined as t h e ratio fo t h e recycle f l o w rate t o t h e daily feed f l o w rate) t o d i l u t e t h e i n c o m i n g feed a n d accelerate t h e t r a n s p o r t of d i g e s t i o n p r o d u c t s o u t of t h e c u l t u r e . T h e filter h a d a h y d r a u l i c d e t e n t i o n t i m e of a b o u t 2 . 3 3 . d a y s (defined as t h e gross v o l u m e d i v i d e d by t h e daily feed f l o w rates). The t w o - p h a s e s y s t e m feed w a s s u p p l e m e n t e d w i t h external n i t r o g e n , p h o s p h o r u s , a n d m a g n e s i u m t o ensure t h a t feed hydrolysis, a c i d i f i c a t i o n , a n d gasification were not nutrient limited. RESULTS A N D DISCUSSION Conventional High-Rate Digestion Steady-state p e r f o r m a n c e of c o n v e n t i o n a l h i g h - r a t e m e s o p h i l i c d i g e s t i o n of t h e b i o m a s s - w a s t e b l e n d at t h e baseline loading a n d d e t e n t i o n t i m e is presented in Table I. The m e t h a n e yields f r o m replicate baseline runs ranged

Τ CAKES

Figure 5. Two-phase system for biomass-waste blend

EFFLUENT

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

to vo

* ΐ

20 0.18 9 0.868 58.7 2.88 6 29.9 32.4

0.570 60.7 3.45 27 34.5 38.8

0.550 63.9 3.53 35 33.6 39.7

0.550 62.0 3.40 42 33.3 38.3

Run 3MA/7

20 0.1 12

3MA/2

5 0.1 12

5

Baseline Runs* 6M

0.1 12

Runs 5M and 6M were replicates. Calculated by formula suggested by Klass and Ghosh (21).

3

Operating Conditions Culture Volume, t Loading. l b V S / f t - d a y Detention Time, days Gas Production Rate, std vol/vol culture-day Methane Content, m o l % Methane Yield. SCF/lb VS added Effluent Quality Volatile Acids, m g / f as acetic Efficiency VS Reduction. %* Energy Recovery in Collected Methane. %

6M

Table I. C O N V E N T I O N A L MESOPHILIC (3B°C) DIGESTION OF HYACINTH-GRASS-MSW-8LUDGE BLEND UNDER BASELINE A N D N O N - B A S E L I N E CONDITIONS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

to

H

ι

I

>

δ

ο

OS

13.

GHOSH AND KLASS

Methane from Biomass-Waste

261

b e t w e e n 3.4 a n d 3.5 SCF/lb V S a d d e d . These yields w e r e b e t w e e n 53.1 a n d 5 4 . 7 % o f t h e t h e o r e t i c a l m e t h a n e y i e l d . A s e x p e c t e d f o r digesters o f similar g e o m e t r y a n d m i x i n g c o n f i g u r a t i o n , c u l t u r e v o l u m e had n o d i s c e r n i b l e effect o n m e t h a n e p r o d u c t i o n (compare Runs 5 M , 6 M , a n d 3 M A ) . N u t r i t i o n a l studies, t h e details o f w h i c h w e r e p r e s e n t e d in a n earlier paper (14), s h o w e d t h a t c o n v e n t i o n a l d i g e s t i o n o f t h e b i o m a s s - w a s t e feed w a s n o t n u t r i e n t or growth-factor limited. The performance of subsequent advanced digestion runs w a s e v a l u a t e d w i t h reference t o t h e baseline p e r f o r m a n c e d a t a reported in Table I. M e t h a n e yield decreased t o 2.4 SCF/lb V S a d d e d (43.8% o f t h e o r e t i c a l yield) w h e n t h e l o a d i n g rate w a s increased t o 0.18 lb V S / f t - d a y a n d t h e d e t e n t i o n t i m e decreased t o 9 days (Table I). These d a t a i n d i c a t e t h a t c o n v e n t i o n a l d i g e s t i o n process e f f i c i e n c y w o u l d decrease s u b s t a n t i a l l y as t h e l o a d i n g rate is increased a n d t h e d e t e n t i o n t i m e is decreased b e y o n d t h e baseline values of these parameters. U n c o n v e n t i o n a l or a d v a n c e d d i g e s t i o n m e t h o d s are t h u s needed t o o v e r c o m e t h e l i m i t a t i o n s o f t h e c o n v e n t i o n a l h i g h - r a t e process.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

3

Digestion o f Pretreated Feed A s p o i n t e d o u t previously, o n l y a b o u t 6 6 % of t h e h y a c i n t h - g r a s s - M S W s l u d g e feed V S w a s d e t e r m i n e d t o be b i o d e g r a d a b l e u n d e r l o n g - t e r m b a t c h d i g e s t i o n c o n d i t i o n s . A b o u t 5 2 % o f t h e b i o d e g r a d a b l e o r g a n i c s a n d 3 2 % of t h e cellulose c o m p o n e n t o f t h e feed w e r e gasified at t h e baseline o p e r a t i n g c o n d i t i o n s of 0.1 lb V S / f t -day l o a d i n g a n d a 12-day d e t e n t i o n t i m e (14). These data s u g g e s t t h a t 3 4 % o f t h e feed o r g a n i c s resisted anaerobic d e g r a d a t i o n , a n d t h a t o n l y a b o u t one-half or less o f t h e b i o d é g r a d a b l e s c o u l d be gasified by c o n v e n t i o n a l h i g h - r a t e d i g e s t i o n . One p r o b a b l e e x p l a n a t i o n for t h e l o w b i o c o n v e r s i o n e f f i c i e n c y w a s t h a t hydrolysis a n d a c i d i f i c a t i o n l i m i t e d t h e d i g e s t i o n of t h e h i g h l y f i b r o u s l i g n o c e l l u l o s i c feed (14). If this is t h e case, t h e n considerable i m p r o v e m e n t w o u l d be e x p e c t e d w h e n t h e feed is p r e t r e a t e d c h e m i c a l l y t o hydrolyze t h e c o m p l e x p o l y m e r i c s u b s t a n c e s or t o c o n v e r t t h e m t o a f o r m s u i t a b l e f o r s u b s e q u e n t e n z y m a t i c hydrolysis. 3

A c i d or alkaline t r e a t m e n t s o f p a r t i c u l a t e feeds have been s h o w n t o i m p r o v e digester gas yields (17,22-25). A c i d hydrolysis w a s n o t used in o u r w o r k because severe reaction c o n d i t i o n s are r e q u i r e d , a n d there is considerable d e c o m p o s i t i o n o f t h e h y d r o l y t i c p r o d u c t s u n d e r these c o n d i t i o n s (26). Dilute alkaline p r e t r e a t m e n t w a s e v a l u a t e d because alkali w a s s h o w n t o be more e f f e c t i v e in p r o m o t i n g hydrolysis of cellulosic biomass t h a n acid (j_7,26). It is p o s t u l a t e d , for e x a m p l e , t h a t s o d i u m h y d r o x i d e breaks d o w n t h e cross-linked l i g n i n m a c r o - m o l e c u l e s s u r r o u n d i n g t h e cellulose fibers into alkali-soluble l o w e r - m o l e c u l a r - w e i g h t units. In t h i s w a y . t h e cellulose fibers are e x p o s e d f o r

262

BIOMASS AS A NONFOSSIL F U E L SOURCE

e n z y m a t i c hydrolysis d u r i n g anaerobic d i g e s t i o n . A l s o , it has been s u g g e s t e d t h a t alkali t r e a t m e n t hydrolyzes ester b o n d s b e t w e e n t h e uronic acids of h e m i c e l l u l o s e a n d l i g n i n (27), t h e r e b y e n h a n c i n g t h e b i o d e g r a d a b i l i t y of hemicellulose. A s already

mentioned, digestion

runs w i t h

caustic

t r e a t e d feed

were

c o n d u c t e d u n d e r a v a r i e t y of o p e r a t i n g c o n d i t i o n s . T h e results of a f e w selected runs w i t h p r e t r e a t e d feed are p r e s e n t e d in Table II. T h e d a t a in t h i s table s h o w t h a t t h e h i g h e s t m e s o p h i l i c (35°C) m e t h a n e y i e l d . 4.10 SCF/lb VS a d d e d , f r o m d i g e s t i o n of t h e p r e t r e a t e d feed at a l o a d i n g of 0.1 lb V S / f t - d a y a n d a 12-day d e t e n t i o n t i m e w a s o b t a i n e d w i t h w e t feed p r e t r e a t e d w i t h 3 w t % c a u s t i c s o l u t i o n . H o w e v e r , t h e m e s o p h i l i c m e t h a n e y i e l d (3.92 SCF/lb VS added) f r o m feed t r e a t e d w i t h 1 w t % NaOH s o l u t i o n w a s n o t s i g n i f i c a n t l y different. A l s o , neutralization of t h e p r e t r e a t e d feed or a d d i t i o n of e x t e r n a l n i t r o g e n t o t h e d i g e s t e r d i d n o t affect t h e m e s o p h i l i c m e t h a n e yield. These o b s e r v a t i o n s i n d i c a t e t h a t an increase in m e s o p h i l i c m e t h a n e y i e l d u p t o 2 0 % m a y be e x p e c t e d at a l o a d i n g of 0.1 lb V S / f t - d a y a n d a d e t e n t i o n t i m e of 12 days w i t h alkaline p r e t r e a t m e n t .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

3

3

T h e r m o p h i l i c (55°C) d i g e s t i o n of t h e c a u s t i c - t r e a t e d feed at 0.4 lb V S / f t - d a y loading a n d a 6-day d e t e n t i o n t i m e s h o w e d t h e s a m e m e t h a n e yield of a b o u t 4 SCF/lb V S a d d e d as o b s e r v e d d u r i n g m e s o p h i l i c d i g e s t i o n of t h e p r e t r e a t e d feed at a 0.1 lb V S / f t - d a y l o a d i n g a n d a 1 2 - d a y d e t e n t i o n t i m e (Run 5 T / 2 4 . Table II). H o w e v e r , t h e t h e r m o p h i l i c gas p r o d u c t i o n rate w a s 4 - 5 t i m e s t h e m e s o p h i l i c rate. A l s o , t h e c a u s t i c r e q u i r e m e n t for feed p r e t r e a t m e n t w a s l o w e r for t h e t h e r m o p h i l i c r u n o w i n g t o t h e r e c y c l i n g of t h e spent c a u s t i c solution. 3

3

A t h e r m o p h i l i c m e t h a n e yield of a b o u t 3.7 SCF/lb V S a d d e d , w h i c h w a s still larger t h a n t h e baseline y i e l d , w a s o b s e r v e d at a l o a d i n g rate of 0.43 lb V S / f t -day a n d a d e t e n t i o n t i m e of 5.5 days w h e n t h e c a u s t i c - t r e a t e d feed w a s neutralized t o p H 10 w i t h digester gas instead of t o p H 9 w i t h h y d r o c h l o r i c acid(Run 5 T / 2 6 . Table III). This r e d u c e d yield resulted f r o m increased l o a d i n g a n d decreased d e t e n t i o n t i m e . A s e x p e c t e d , a h i g h e r b i c a r b o n a t e alkalinity c o u l d be m a i n t a i n e d w h e n t h e d i g e s t e r w a s c h a r g e d w i t h p r e t r e a t e d feed neutralized w i t h d i g e s t e r gas. In a d d i t i o n , neutralization of t h e alkaline feed w i t h p r o d u c t gas e l i m i n a t e d t h e need for neutralizing acid a n d p r o v i d e d a m e t h o d of c a r b o n d i o x i d e r e m o v a l f r o m t h e digester gas. This t e c h n i q u e s h o u l d p r o v i d e a r e d u c t i o n in t h e cost of feed t r e a t m e n t a n d digester gas cleanup. 3

13.

263

Methane from Biomass-Waste

GHOSH AND KLASS

Table II. MESOPHILIC (3B C) AND THERMOPHILIC (55°C) DIGESTION OF HYACINTH-QRAS8-M8W-SLUDGE BLEND PRETREATED WITH CAUSTIC SODA 80LUTION

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

a

Neutralization Method Operating Conditions Culture Volume. I Loading, lb VS/ft -day Detention Time, days Qas Production Rate, std vol/vol culture day Methane Content, mol % Methane Yield. SCF/lb VS added Effluent Quality PH Volatile Acids. mg/f as acetic Total Alkalinity. mg/f asCaC03 Bicarbonate Alkalinity. mg/f asCaC03 3

VS Reduction. % Energy Recovery in Collected Methane. %

Mesophilic Run 6M A/13* No neutralization of caustictreated feed

Run •MA/22 Whole feed to pH 8-8.4 with acid. b

Thermophilic Digester Feed Run 5T/24 Run 5T/26 Mixed vacuum filter Mixed vacuum filter cakes plus filtrate to cakes plus filtrate pH 9 with acid. to pH 10 with acid. C

d

10 0.1 12

10 0.1 12

5 0.4 6.0

5 0.43 5.5

0.606 59.5

0.670 58 1

2.851 56.4

2.911 56.0

4.10

392

4.00

3.68

684

6.71

7.35

743

20

21

99

140

2618

2433

6075

6298

2592

2412

5993

6240

41 9

41.0

43.1

40.0

46 1

44.1

45.0

41.4

The fresh feed was treated with 140 ml of 3 wt % NaOH solution at 55°C for 24 hr The treated feed was not neutralized, and no N H 4 C I was added Feed pretreatment same as Run 6MA/13 except that 140 ml of 1 wt % NaOH solution was used at 25°C for 24 hr. The treated feed was neutralized with HCI to the indicated pH and supplemented with 10 ml of 120-g/l NH CI solution. Fresh feed was treated with 160 ml of 3 wt NaOH solution at 100°C for 24 hr. The treated feed was vacuum filtered, and about 158 g of filter cake and 200 ml of filtrate were fed to the digester after dilution to the proper volume and neutralization with HCI to pH 9. Fresh feed was treated in the same way as in Run 5T/24. except that the alkaline feed slurry was neutralized by bubbling a portion of the digester gas (Ave 9.2 f . range 7.19-11.55 f ) through it. The average pH of the digester feed after gas neutralization was 9.98 (range 9.31 -11.55). 4

d e o x y g e n a t i o n ; 2 5 7 vol % recycle.

VS added

recycled gas/std f

digester gas produced-day.

43.7

55.0

41.6

4645

4667

20

6.80

culture volume, batch, activated sludge unit operated

43.1

—

37.9

2819

2826

9

6.69

3.88

56.7

3.83

0.687

61.5

t h r o u g h it.

S a m e o p e r a t i n g c o n d i t i o n s as i n R u n 1 M A / 1 3 . e x c e p t t h a t t h e r e c y c l e a e r a t o r s l u d g e w a s d e o x y g e n a t e d b y b u b b l i n g h e l i u m

at a m b i e n t t e m p e r a t u r e . A v o l u m e o f 1 2 0 0 m l o f a e r a t e r c o n t e n t w a s r e c y c l e d w i t h 4 6 7 m l o f f r e s h f e e d d a i l y .

D a i l y d i g e s t e r e f f l u e n t w a s a e r a t e d (air f l o w r a t e 0 . 1 2 f / m i n ) i n a 2.0- f

R e c y c l e r a t i o is s t d f

Methane. %

44.4

39.7

Energy Recovery in Collected

39.7

Overall V S Reduction. %

3

VS Reduction. %

Efficiency

Bicarbonate Alkalinity, as C a C 0 3997

3997

mg/f

Total Alkalinity, as C a C 0

3

8

Volatile Acids, m g / f as a c e t i c

mg/f

7.06

PH

Effluent Quality

3.95

60.5

Methane Content, m o l %

Methane Yield. SCF/lb

0.596

Rate, s t d v o l / v o l c u l t u r e - d a y

0.630

12

12

12

Production

Detention Time, days

Gas

20 0.1

20 0.1

20

3

0.1

6

56 v o l % r e c y c l e .

8

recycle ratio.

Culture volume, f Loading, lb V S / f t - d a y

Operating Conditions

Run I M A / 1 8 A e r a t e d digester effluent after

Run 1 M A / 1 3 Aerated effluent;

MESOPHILIC

Run 2 M A / 1 1

BLEND

Digester Gas: 3 9 gas

(3B°C) DIGESTION OF H Y A C I N T H - G R A S S - M S W - 8 L U D G E

EFFECT OF PRODUCT QA8 A N D P08TTREATED EFFLUENT RECYCLING ON

Recycled Material and Amount

T a b l e III.

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ON

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265

T h e e x p e r i m e n t a l d a t a s u g g e s t t h e f o l l o w i n g s e q u e n c e of o p e r a t i o n s f o r improved digestion of the hyacinth-grass-MSW-sludge feed: 1.

Caustic t r e a t m e n t of u n d i l u t e d feed for 2 4 hr at 100°C w i t h 3 w t % NaOH a n d r e c y c l i n g of spent c a u s t i c s o l u t i o n . Fresh caustic is a d d e d at t h e rate of a b o u t 3 m e q per g r a m of VS. Spent c a u s t i c recycle f l o w rate is 7 5 v o l % o f t h e feed slurry f l o w rate.

2.

D e w a t e r i n g of t h e pretreated feed. D e w a t e r e d cakes a n d t h e balance of

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

t h e filtrate after r e c y c l i n g are fed t o t h e digester. 3.

Neutralization o f alkaline feed slurry w i t h digester gases.

4.

T h e r m o p h i l i c d i g e s t i o n o f t h e feed at a l o a d i n g rate of 0.4 lb V S / f t - d a y 3

a n d a d e t e n t i o n t i m e of 6 days. Digestion W i t h Product Gas and P o s t t r e a t e d Effluent Recycling T h e s e c o n d major a d v a n c e d s y s t e m w a s c o n c e r n e d w i t h t h e r e c y c l i n g of p r o d u c t gas a n d l i q u i d e f f l u e n t t o t h e digester. T h e effluent w a s p o s t t r e a t e d before r e c y c l i n g . The p r o d u c t gas w a s d e h y d r a t e d before r e c i r c u l a t i o n t o t h e d i g e s t i n g c u l t u r e . T h e a q u e o u s e f f l u e n t w a s s u b j e c t e d t o various f o r m s o f p o s t t r e a t m e n t i n c l u d i n g s o n i c a t i o n , s i m p l e heat t r e a t m e n t f o r 3 0 m i n at 2 7 0 ° F a n d 2 5 psig. a n d a c t i v a t e d s l u d g e t r e a t m e n t t o i m p r o v e t h e b i o d e g r a d a b i l i t y o f t h e u n d i g e s t e d solids. Recycling of s o n i c a t e d a n d heatt r e a t e d s l u d g e t o t h e digester d i d n o t increase m e t h a n e yield a b o v e t h e baseline yield. Gas r e c y c l i n g a n d a c t i v a t e d s l u d g e p o s t t r e a t m e n t w h i c h e f f e c t e d a higher s y s t e m V S r e d u c t i o n , w i l l be discussed here. Gas Recycling Recycling of p r o d u c t gases t h r o u g h t h e d i g e s t i n g c u l t u r e w a s e x p e c t e d t o increase m e t h a n e p r o d u c t i o n because of a d d i t i o n a l m e t h a n e f e r m e n t a t i o n f r o m increased r e d u c t i o n of c a r b o n d i o x i d e a n d because t h e s w e e p i n g a c t i o n of t h e recycled gas m i g h t be e x p e c t e d t o accelerate r e m o v a l o f t h e gaseous products surrounding the microorganisms thereby minimizing end-product repression. Digester gases w e r e r e c y c l e d at various recycle ratios f r o m 2 t o 125. T h e best m e t h a n e yield o f 3.95 SCF/lb V S a d d e d , w h i c h w a s a b o u t 1 5 % h i g h e r t h a n t h e baseline y i e l d , w a s o b s e r v e d a t a g a s recycle ratio o f 3 9 (Table III). T h e gas-phase d i l u t i o n rate at t h i s recycle ratio w a s a b o u t 0.2 hr"'. The e x i s t e n c e of an o p t i m u m gas recycle ratio is rationalized as f o l l o w s : A s t h e gas recycle

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ratio is increased, t h e o p p o r t u n i t y for c a r b o n d i o x i d e r e d u c t i o n a n d s w e e p i n g of t h e gaseous d i g e s t i o n p r o d u c t s o u t of t h e d i g e s t e r increases t h e r e b y s t i m u l a t i n g m e t h a n e p r o d u c t i o n . H o w e v e r as t h e gas r e c y c l i n g ratio is increased f u r t h e r , t h e c u l t u r e is increasingly s a t u r a t e d w i t h gaseous e n d p r o d u c t s ; t h i s w o u l d t e n d t o repress or i n h i b i t a d d i t i o n a l m e t h a n e p r o d u c t i o n . T h e o p p o s i n g effects of increasing gas recycle o n m e t h a n e p r o d u c t i o n e q u a l each o t h e r at t h e o p t i m u m gas recycle ratio w h i c h maximizes methane yield. It s h o u l d be n o t e d t h a t d u r i n g gas r e c y c l i n g , t h e test d i g e s t e r w a s m e c h a n i c a l l y m i x e d as in t h e baseline c o n t r o l runs so t h a t t h e effect of t h e r e c y c l e d gas o n test digester m e t h a n e p r o d u c t i o n c o u l d be e v a l u a t e d . Since m e c h a n i c a l m i x i n g alone w a s d e s i g n e d t o p r o v i d e c o m p l e t e m i x i n g of t h e d i g e s t e r c o n t e n t s , t h e beneficial effect of gas r e c y c l i n g m a y n o t be a t t r i b u t e d t o effects s u c h as s u b s t r a t e t r a n s p o r t a n d s u b s t r a t e - m i c r o o r g a n i s m c o n t a c t . M i l d m e c h a n i c a l m i x i n g also p r o v e d t o be beneficial d u r i n g gas r e c y c l i n g because s c u m f o r m a t i o n , w h i c h arises d u e t o gas f l o t a t i o n of d i g e s t e r solids, w a s s u r p r i s i n g l y n o t a p r o b l e m even at very h i g h gas recycle ratios. The reason for t h i s w a s t h a t m e c h a n i c a l a g i t a t i o n at a m i x i n g Reynolds n u m b e r of a b o u t 9,000 dispersed t h e surface solids a n d m o v e d t h e m d o w n i n t o t h e c u l t u r e by t h e f o l d i n g a c t i o n of t h e t w o propeller m i x e r s p l a c e d at h e i g h t s of one a n d t w o i m p e l l e r d i a m e t e r s a b o v e t h e digester b o t t o m . The results of t h e gas r e c y c l i n g e x p e r i m e n t s s h o w e d t h a t m o d e s t increases in m e t h a n e yield c a n be o b t a i n e d by r e c y c l i n g p r o d u c t gas at an o p t i m u m gas recycle ratio. Dual m e c h a n i c a l a n d gas m i x i n g e l i m i n a t e d t h e s c u m p r o b l e m associated w i t h gas m i x i n g alone. Aerobic Sludge Posttreatment of Digester Effluent T h e o b j e c t i v e of aerobic p o s t t r e a t m e n t is t o treat t h e " r e f r a c t o r y " e f f l u e n t o r g a n i c s t o render t h e m b i o d e g r a d a b l e , a n d t o increase m e t h a n e p r o d u c t i o n by r e c y c l i n g t h e p o s t t r e a t e d m a t e r i a l for f u r t h e r d i g e s t i o n . P o s t t r e a t m e n t m a y be preferred t o p r e t r e a t m e n t because it o n l y treats t h e recalcitrant residue r e m a i n i n g after t h e b i o d e g r a d a b l e material is gasified a n d not t h e t o t a l solids in t h e feed. T h u s , t h e o r g a n i c loading rate on t h e p o s t t r e a t m e n t process is s u b s t a n t i a l l y l o w e r t h a n t h a t for a similar p r e t r e a t m e n t process. A l s o , w h i l e i m p r o v i n g t h e b i o d e g r a d a b i l i t y of t h e r e c a l c i t r a n t f e e d f r a c t i o n , p r e t r e a t m e n t m a y adversely affect t h e d i g e s t i b i l i t y of feed c o m p o n e n t s t h a t are easily gasified in t h e i r o r i g i n a l f o r m s . P o s t t r e a t m e n t o b v i a t e s t h i s p r o b l e m . A e r o b i c b i o c h e m i c a l a n d c h e m i c a l - b i o c h e m i c a l p o s t t r e a t m e n t s w e r e invest i g a t e d because several species of f u n g i a n d aerobic o r g a n i s m s are k n o w n t o hydrolyze a n d d e g r a d e c o m p l e x lignocellulosic s u b s t a n c e s t o s i m p l e r

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13.

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Methane from Biomass-Waste

267

s u b s t a n c e s (26). Trichoderma viride. Cellulomonas, and Cytophaga hutchinsonii. Cytophaga vulgaris are e x a m p l e s o f aerobic m i c r o o r g a n i s m s t h a t m e d i a t e these reactions (28.29). Because s o m e aerobes c a n n o t e f f i c i e n t l y a t t a c k lignocellulosic cellulosic c o m p l e x e s (30,31). o n e r u n w a s also c o n d u c t e d in w h i c h t h e aerator feed (digester effluent) w a s p r e d i g e s t e d w i t h hot c a u s t i c t o m a k e t h e fibers available f o r aerobic d e c o m p o s i t i o n (28). Finally, a c t i v a t e d s l u d g e p o s t t r e a t m e n t o f t h e d i g e s t e d residue w a s also c o n d u c t e d u n d e r c o n d i t i o n s o f " l i m i t e d " aeration t o arrest cellulose b r e a k d o w n before t h e f o r m a t i o n of m o n o m e r i c p r o d u c t s (hexose, pentose, etc.) w h i c h are readily oxidized aerobically a n d , t h u s , b e c o m e unavailable f o r gasification), so t h a t t h e p r o d u c t s o f partial aerobic d i g e s t i o n c o u l d be gasified anaerobically u p o n r e c y c l i n g t o t h e digester. Evidence o f partial cellulose d e g r a d a t i o n b y l i m i t e d aeration w a s presented b y Kalnins (32), w h o s h o w e d t h a t Bacterium protoziodes d e c o m p o s e d cellulose t o dextrose w i t h an u n l i m i t e d s u p p l y of o x y g e n . H o w e v e r , w h e n t h e s u p p l y o f o x y g e n w a s l i m i t e d , dextrose p r o d u c t i o n w a s s t o p p e d , b u t t h e o r g a n i s m d e c o m p o s e d an increased q u a n t i t y of cellulose t o derive a n a m o u n t of e n e r g y e q u i v a l e n t t o t h a t o b t a i n e d d u r i n g d e g r a d a t i o n of cellulose t o dextrose. T h u s , t h e a d v a n t a g e of l i m i t e d aeration p o s t t r e a t m e n t is t h a t it s h o u l d l i m i t d e g r a d a t i o n of t h e residual solids t o f o r m s t h a t are lost b y o x i d a t i o n before r e c y c l i n g t o t h e digester. P o s t t r e a t m e n t studies o f digester e f f l u e n t c o n d u c t e d in t h e 1 4 - / m e s o p h i l i c (33°-34°C) aerobic s l u d g e u n i t at d e t e n t i o n t i m e s o f 2.4 a n d 5.3 days, a n d an air f l o w rate of 1 / / m i n p r o d u c e d settleable s l u d g e w h i c h , w h e n r e c y c l e d t o t h e d i g e s t e r at recycle ratios o f 5.3 a n d 33.7%, e f f e c t e d digester m e t h a n e yields based o n fresh-feed volatile solids r a n g i n g b e t w e e n 2.81 a n d 3.51 SCF/lb V S a d d e d . These yields w e r e l o w e r t h a n or equal t o t h e baseline m e t h a n e yield o b s e r v e d u n d e r t h e same d i g e s t e r o p e r a t i n g c o n d i t i o n s , w h i c h i n d i c a t e d t h a t aerobic biological p o s t t r e a t m e n t at long d e t e n t i o n t i m e s a n d a h i g h air f l o w rate ( p r o d u c i n g residual aerator dissolved o x y g e n c o n c e n t r a t i o n of 0.7 t o 2.8 m g / / ) d i d n o t e n h a n c e m e t h a n e p r o d u c t i o n . H o w e v e r , residue p o s t t r e a t m e n t in t h e 2 - / b a t c h unit o p e r a t e d u n d e r l i m i t e d aeration c o n d i t i o n s (no residual dissolved o x y g e n in aerator) w a s superior in t h a t r e c y c l i n g o f t h i s s l u d g e at a 5 6 % recycle ratio led t o a m o d e s t increase in t h e d i g e s t e r m e t h a n e yield (Run 1 M A / 1 3 . Table III). T h e m e t h a n e yield d i d n o t increase f u r t h e r w h e n t h e recycle s l u d g e w a s d e o x y g e n a t e d . t h e recycle ratio w a s increased f r o m 5 6 t o 2 5 7 % (Run 1 M A / 1 8 ) , or t h e feed t o t h e aerator w a s pretreated w i t h h o t caustic. It is i n t e r e s t i n g t o note t h a t t h e volatile solids r e d u c t i o n increased w h e n t h e aerobic p o s t t r e a t m e n t m e t h o d w a s used as s h o w n b y t h e overall V S r e d u c t i o n o f Run 1 M A / 1 8 .

268

BIOMASS AS A NONFOSSIL F U E L SOURCE

Two-Phase Digestion of Slurry Systems T w o - p h a s e studies w e r e u n d e r t a k e n t o d e v e l o p a m u l t i s t a g e h i g h - r a t e process superior t o c o n v e n t i o n a l d i g e s t i o n . Results of selected t w o - p h a s e runs are presented in Tables IV a n d V. T w o - p h a s e d i g e s t i o n of t h e u n t r e a t e d feed at an overall d e t e n t i o n t i m e of 7.6 days a n d a l o a d i n g rate of 0.26 lb V S / f t - d a y e x h i b i t e d a t o t a l gas p r o d u c t i o n rate of 1.35 s t d v o l / v o l of c u l t u r e d a y a n d an e f f l u e n t volatile a c i d c o n c e n t r a t i o n of a b o u t 19 m g / / (Run A 3 0 / M 1 6 . Table IV). T h u s , t h e t w o - p h a s e s y s t e m h a d a gas p r o d u c t i o n rate t h a t w a s a b o u t 2.5 t i m e s t h a t of c o n v e n t i o n a l baseline d i g e s t i o n , a n d y e t had a b o u t t h e s a m e e f f l u e n t v o l a t i l e acid c o n c e n t r a t i o n as t h a t o b s e r v e d d u r i n g c o n v e n t i o n a l d i g e s t i o n at a 12-day d e t e n t i o n t i m e . T h e m e t h a n e y i e l d for t h i s r u n . h o w e v e r , w a s a b o u t 2 SCF/lb V S a d d e d , a n d t h e volatile a c i d (VA) yield f r o m t h i s s y s t e m w a s e s t i m a t e d t o be 0.31 (mass of V A as a c e t i c d i v i d e d by mass of V S added), w h i c h i n d i c a t e d t h a t h y d r o l y s i s a n d a c i d i f i c a t i o n of t h e feed o r g a n i c s w e r e inefficient. T o i m p r o v e t h i s c o n d i t i o n . Run A 3 C / M 3 C w a s c o n d u c t e d w i t h c a u s t i c - t r e a t e d feed. Gas p r o d u c t i o n rate, m e t h a n e y i e l d , a n d a c i d yield f r o m t h i s run w e r e 1.5 s t d v o l / v o l of c u l t u r e - d a y . 3 SCF/lb VS a d d e d , a n d 0.49, respectively, all of w h i c h w e r e s u b s t a n t i a l l y h i g h e r t h a n t h o s e o b s e r v e d w i t h t h e u n t r e a t e d f e e d . T h e v o l a t i l e acid yield c o e f f i c i e n t of 0.49 for t h e solid b i o m a s s - w a s t e feed w a s l o w e r t h a n t h e acid yield of 0.73 r e p o r t e d by Ghosh a n d Pohland (33) for t w o - p h a s e d i g e s t i o n of t h e s i m p l e soluble sugar, g l u c o s e , s u g g e s t i n g t h a t it m a y still be possible t o i m p r o v e t h e V S - t o - a c i d c o n v e r s i o n e f f i c i e n c y b e y o n d t h a t realized b y c a u s t i c t r e a t m e n t . Further acid y i e l d or b i o d e g r a d a b i l i t y increase is e x p e c t e d t o be d i f f i c u l t t o a c h i e v e a n d m a y require m o r e severe feed p r e t r e a t m e n t .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

3

Run A 7 C / M 7 C in Table IV had t h e s a m e o p e r a t i n g c o n d i t i o n s as t h e t w o o t h e r runs d i s c u s s e d above, b u t received o n l y external n i t r o g e n instead of e x t e r n a l n i t r o g e n , p h o s p h o r u s a n d m a g n e s i u m . I n s p e c t i o n of t h e d a t a in Table IV s h o w s t h a t e l i m i n a t i o n of e x t e r n a l p h o s p h o r u s a n d m a g n e s i u m f r o m t h e feed d i d n o t affect t w o - p h a s e process p e r f o r m a n c e . This o b s e r v a t i o n correlated w i t h t h e results of t h e c o n v e n t i o n a l d i g e s t i o n runs w h i c h s h o w e d t h a t t h e b i o m a s s - w a s t e b l e n d used in t h i s w o r k w a s not n u t r i t i o n a l l y deficient. A l l t w o - p h a s e process feeds, h o w e v e r , w e r e f o r t i f i e d w i t h external n i t r o g e n t o g u a r d against a n y d e f i c i e n c y of t h i s e l e m e n t d u e t o loss t h a t c o u l d o c c u r d u r i n g c a u s t i c t r e a t m e n t of t h e f e e d . A d d i t i o n of e x t e r n a l n i t r o g e n w o u l d not be r e q u i r e d in a c o m m e r c i a l process utilizing a p r o p e r l y d e s i g n e d c o n t i n u o u s p r e t r e a t m e n t reactor. To test kinetic p o t e n t i a l of t h e t w o - p h a s e s y s t e m , a d d i t i o n a l runs w e r e c o n d u c t e d at decreased d e t e n t i o n t i m e s of 5 a n d 4 days, a n d increased loading rates (Table V). A t e m p e r a t u r e of 5 5 ° C w a s selected for t h e a c i d -

13.

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269

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Table IV. EFFECT OF FEED PRETREATMENT ON TWO-PHASE MESOPHILIC (35°C) DIGESTION OF HYACINTH-QRA88-MSW-8LUDGE BLEND

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

Untreated Feed Run AM/MI β Operating Condition*' Acid-Phase Culture Volume, t Methane-Phase Culture Volume. / Acid-Phase Loading. lbVS/ft -day Methane-Phase Loading. lbVS/ft -day Acid-Phase Detention Time, days Methane Phase Detention Time. days Overall Loading, lb VS/ft -day Overall Detention Time, days External Nutrient Additions to Acid-Phase Feed Gas Production Rate, std vol/vol culture-day Acid Phase Methane Phase Total Methane Content, mol % Acid Phase Methane Phase Total Gas Yield. SCF/lb VS added Acid Phase Methane Phase Total Total Methane Yield. SCF/lb VS added Effluant Quality PH Acid Phase Methane Phase Volatile Acids, mg/y as acetic Acid Phase Methane Phase Efficiency VS Reduction. % Energy Recovery in Collected Methane. % 3

3

3

16 45

Caustic Traatad Feed Run A3C/M3C Run A7C/M7C 16 45

16 45

1.0

10

10

0.32 2.0

0.32 2.0

0.32 2.0

5.6 0.26 76

5.6 0.26 76

5.6 0.26 76

N.P.Mg

N.P.Mg

Ν

1.346 0.924 1.035

1484

— 1.443

49 2 59.0 497

528

559

1.34 2.91 3.98

563

5.50

1 98

2.87

3.07

5.86 6.44

6 72 7.03

6 82 7.15

1047 19

2440 287

I860 148

24 2

34 2

33 4

22 3

33 4

34.5

" No alkali was used for digester pH control. The acid-phase feeds for Runs A3C/M3C and A7C/M7C were pretreated for 24 hr with 2.561 of 1 wt % NaOH solution in a total volume of 4 8 f under ambient conditions. The product gases from each phase were collected together for these two runs.

270

BIOMASS AS A NONFOSSIL F U E L SOURCE

Table V. THERMOPHILIC IBB'C) ACID-PHASE AND MESOPHILIC (3B"C) METHANE-PHASE DIGESTION OF PRETREATED HYACINTH-GRAS8-M8W-8LUDQE BLEND

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

Run A3B/M21 Operating Conditions' Acid-Phase .Culture Volume, f Methane-Phase Culture Volume. I Acid-Phase Loading, lb VS/ft -day Methane-Phase Loading, lb VS/ft -day Acid-Phase Detention Time, days Methane-Phase Detention Time, days Overall Loading, lb VS/ft -day Overall Detention Time, days External Nutrient Additions to Acid-Phase Feed Gas Production Rate, std vol/vol culture-day Acid Phase Methane Phase Total Methane Content, mol % Acid Phase Methane Phase Total Gas Yield. SCF/lb VS added Acid Phase Methane Phase Total Total Methane Yield. SCF/lb VS added Effluent Quality PH Acid Phase Methane Phase Volatile Acids, mg/f as acetic Acid Phase Methane Phase Efficiency VS Reduction. % Energy Recovery m Collected Methane. % 3

3

Run A37/M23

5 20 2.0 044 1.0 4.0 0.40 50

5 20 2.5 0.56 0.80 32 0.50 4.0

Ν

Ν

3.189 1 553 1.880

3.472 1.740 2.086

60.3 59.6 598

58.5 59.1 57.9

1.53 335 4.70 2.81

1.40 3.11 425 2.46

699 7.05

7.05 7.05

1734 347

2255 591

28.6 31.6

25.8 27.7

No alkali was used for digester pH control. The acid-phase digester feed was pretreated for 24 hr with NaOH solution at ambient conditions. The caustic concentration in the slurry was 142 meg/f

13.

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271

Methane from Biomass-Waste

phase digester because of t h e earlier o b s e r v a t i o n t h a t this t h e r m o p h i l i c t e m p e r a t u r e i m p r o v e d g a s i f i c a t i o n rates at higher loadings a n d shorter d e t e n t i o n t i m e s w i t h o u t s i g n i f i c a n t l y a f f e c t i n g m e t h a n e yield. A s s h o w n in Table V, an overall s y s t e m gas p r o d u c t i o n rate of 1.9 std v o l / v o l c u l t u r e - d a y , a m e t h a n e yield o f 2.8 SCF/lb V S a d d e d , a n d a n e f f l u e n t volatile acid c o n c e n t r a t i o n o f a b o u t 3 5 0 m g / / w e r e observed at a s y s t e m loading a n d d e t e n t i o n t i m e o f 0.4 lb V S / f t - d a y a n d 5 days, respectively. A s e x p e c t e d , gas p r o d u c t i o n rate a n d e f f l u e n t volatile acids c o n c e n t r a t i o n increased t o a b o u t 2.1 s t d v o l / v o l c u l t u r e - d a y a n d 6 0 0 m g / / , a n d m e t h a n e yield decreased t o a b o u t 2.5 SCF/lb V S a d d e d w h e n t h e s y s t e m d e t e n t i o n t i m e w a s decreased t o 4 days a n d t h e s y s t e m l o a d i n g w a s increased t o 0.5 lb V S / f t - d a y . Volatile acid yields at t h e 5- a n d 4 - d a y d e t e n t i o n t i m e s w e r e , h o w e v e r , a b o u t t h e same. 0.46 a n d 0.50, respectively. C o m p a r i s o n of acid p r o d u c t i o n yield c o e f f i c i e n t s f o r t h e runs in Tables IV a n d V i n d i c a t e d t h a t volatile solids c o n v e r s i o n t o volatile acids is s i g n i f i c a n t l y increased b y alkaline feed p r e t r e a t m e n t . F u r t h e r m o r e , it w a s o b s e r v e d t h a t , w h i l e t h e V S - t o - a c i d c o n v e r s i o n e f f i c i e n c y of t h e p r e t r e a t e d feed r e m a i n e d t h e same as t h e s y s t e m d e t e n t i o n t i m e w a s decreased f r o m 7.6 t o 4 days, t h e gas p r o d u c t i o n rate increased b y 5 0 % c o m p a r e d t o a 1 7 % decrease in m e t h a n e yield. These o b s e r v a t i o n s indicate t h a t it is desirable t o o p e r a t e t h e t w o - p h a s e s y s t e m at a d e t e n t i o n t i m e o f 4 days or less, a n d t o c o u p l e this s y s t e m t o a cell mass r e c y c l i n g d e v i c e (e.g.. anaerobic settler) t o p r e v e n t m e t h a n e yield r e d u c t i o n s a n d volatile acids a c c u m u l a t i o n associated w i t h short d e t e n t i o n t i m e s . It s h o u l d be n o t e d , h o w e v e r , t h a t s e t t l i n g of relatively c o n c e n t r a t e d d i g e s t e d b i o m a s s - w a s t e slurry a n d anaerobic settler o p e r a t i o n w e r e p r o b l e m a t i c a n d appeared i m p r a c t i c a l in light o f o u r e x p e r i e n c e w i t h c u s t o m - d e s i g n e d laboratory settlers. A n alternate a p p r o a c h , w h i c h has t h e same effect o f m a i n t a i n i n g higher cell d e n s i t y a n d increasing solids r e t e n t i o n t i m e (SRT) as in a settler, is a p a c k e d bed anaerobic filter. W i t h this reactor, it is be possible t o c o n d u c t d i g e s t i o n at short h y d r a u l i c r e t e n t i o n t i m e (HRT) a n d still o b t a i n h i g h m e t h a n e yield a n d l o w e f f l u e n t volatile acid c o n c e n t r a t i o n because o f t h e h i g h SRT. 3

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3

Packed-Bed Anaerobic Digester T h e p a c k e d - b e d anaerobic digester, c o m m o n l y referred t o as an anaerobic " f i l t e r " , w a s o p e r a t e d w i t h filtrates f r o m t h e v a c u u m f i l t r a t i o n of t h e a c i d digester effluent. Filtrate w a s used because u n f i l t e r e d a c i d - d i g e s t e r effluents t e n d e d t o c l o g t h e p a c k e d bed. T h e feed t o t h e p a c k e d - b e d digester h a d volatile acids c o n c e n t r a t i o n s b e t w e e n 1 5 0 0 a n d 2 0 0 0 m g / / as acetic a n d a solids c o n t e n t o f a b o u t 0.5 w t %. T h e d i g e s t e r w a s o p e r a t e d at a n HRT of a b o u t 2.3 days a n d a l o a d i n g rate o f a b o u t 0.15 lb V S / f t - d a y based o n t h e gross filter v o l u m e (1.5 days a n d 0.24 lb V S / f t -day w h e n based o n t h e v o i d 3

3

272

BIOMASS AS A NONFOSSIL F U E L SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

or c u l t u r e v o l u m e ) . Effluent r e c i r c u l a t i o n a n d c u l t u r e t e m p e r a t u r e had s i g n i f i c a n t effects on gas p r o d u c t i o n (Table VI). Recirculation of t h e e f f l u e n t f r o m t h e t o p t o t h e b o t t o m of t h e bed increased gas p r o d u c t i o n rate by 7 6 % , w h i l e also increasing t h e m e t h a n e yield by 4 5 % . M e t h a n e c o n t e n t w a s a b o v e 7 0 m o l % w i t h or w i t h o u t r e c i r c u l a t i o n . Increase in m e a n d i g e s t e r t e m p e r a t u r e f r o m 3 3 ° t o 3 8 ° C decreased gas p r o d u c t i o n rate by a b o u t 2 0 % a n d m e t h a n e yield by a b o u t 25%. D e p e n d i n g on t h e o p e r a t i n g c o n d i t i o n , volatile acids c o n c e n t r a t i o n s in t h e filter e f f l u e n t varied b e t w e e n 9 0 a n d 1 9 0 m g / / (Table VI), w h i c h w e r e still l o w e r t h a n t h o s e in t h e slurry m e t h a n e d i g e s t e r o p e r a t e d at a h i g h e r HRT of 5.6 days (Table V). It s h o u l d be p o i n t e d o u t t h a t t h e p e r f o r m a n c e of t h e p a c k e d - b e d m e t h a n e d i g e s t e r is m o r e d e p e n d e n t perhaps o n t h e i n f l u e n t v o l a t i l e acids c o n c e n t r a t i o n t h a n t h e overall VS l o a d i n g rate. T h u s , filter p e r f o r m a n c e w i t h a c i d - d i g e s t e r filtrate m i g h t be e x p e c t e d t o be better t h a n t h a t o b t a i n e d w i t h m e t h a n e - d i g e s t e r e f f l u e n t s h a v i n g c o m p a r a b l e volatile acids c o n t e n t . Hypothetical Multi-Stage Digestion Process T h e u l t i m a t e o b j e c t i v e of t h i s research w a s t o synthesize a h y p o t h e t i c a l b i o m a s s - w a s t e pilot process d e s i g n based o n t h e results of o u r i n v e s t i g a t i o n of p r o m i s i n g a d v a n c e d d i g e s t i o n m o d e s . T h e w o r k p r e s e n t e d here p r o v i d e d i n f o r m a t i o n o n t h e effects of alkaline p r e t r e a t m e n t alkali r e c y c l i n g , d i g e s t i o n t e m p e r a t u r e , a n d d i g e s t e r gas r e c y c l i n g ; h e a t s o n i c a t i o n , a n d aerobic p o s t t r e a t m e n t a n d r e c y c l i n g of d i g e s t e d s l u d g e u n d e r different a e r a t i o n , s l u d g e recycle, a n d aerator d e t e n t i o n t i m e c o n d i t i o n s ; slurry a n d p a c k e d - b e d d i g e s t i o n ; a n d t w o - p h a s e d i g e s t i o n . T h e results of t h i s w o r k are s u g g e s t i v e of an a d v a n c e d b i o m a s s - w a s t e d i g e s t i o n s y s t e m as d e p i c t e d in Figure VI. A d d i t i o n a l w o r k t o refine t h e pre- a n d p o s t t r e a t m e n t t e c h n i q u e s a n d t w o phase process o p t i m i z a t i o n is better c o n d u c t e d in a pilot s y s t e m similar t o t h a t of Figure V I . T h e h y p o t h e t i c a l s y s t e m is necessarily a m u l t i - s t a g e s y s t e m t o a c c o m o d a t e p r e t r e a t m e n t m u l t i - s t a g e phasic d i g e s t i o n , a n d d i g e s t e d residue p o s t t r e a t m e n t . T h e h y d r a u l i c residence t i m e in t h e t o t a l s y s t e m is a b o u t 6 days a l l o w i n g for 12 hr of d i l u t e c a u s t i c p r e t r e a t m e n t 1 2 - 2 4 hr of t h e r m o p h i l i c acid d i g e s t i o n . 2-5 days of slurry-phase m e s o p h i l i c m e t h a n e d i g e s t i o n . 2 days of m e s o p h i l i c p a c k e d - b e d m e t h a n e d i g e s t i o n , a n d 12 hr of l i m i t e d - a e r a t i o n b i o l o g i c a l t r e a t m e n t of t h e d i g e s t e d s l u d g e . Based o n t h e d a t a c o m p i l e d in t h i s w o r k , m e t h a n e yields u p t o 5.5 SCF/lb V S a d d e d are e x p e c t e d for t h i s t y p e of c o n f i g u r a t i o n .

27.0 34.3 45.9

31.7

6.86 68

6.86 131

6.73 186 34.3

0.698 68.7 3.05

0.872 72.3 4.08

0.495 73.5 2.82

23.3

38 0.16 2.34 510

Run 8MA/6

33 0.15 2.33 510

Run 8 M A / 5

35 0.13 2.30 0

Run 8MA/4

FED MESOPHILIC

The packed-bed digester had a gross v o l u m e of 18.5 f The bed had a void ratio of 0.63. Filtrate from a slurry-phase acid digester effluent having a volatile acid content of 1550-2000 m g / J as acetic acid and a solids content of about 0.5 w t % was used as feed. No pH control w a s used.

Efficiency VS Reduction, % Energy Recovery in Collected Methane, %

3

Operating Conditions* Temperature. °C Loading, lb V S / f t - d a y Detention Time, days Effluent Recycle Ratio, % Qas Production Rate, std v o l / v o l culture-day Methane Content, mol % Methane Yield. SCF/lb VS added Effluent Quality PH Volatile Acids, m g / j f as acetic

Table VI. S T E A D Y - S T A T E P E R F O R M A N C E OF C O N T I N U O U S L Y P A C K E D - B E D M E T H A N E DIGESTER

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

274 BIOMASS AS A NONFOSSIL F U E L SOURCE

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GHOSH AND KLASS

Methane from Biomass-Waste

275

SUMMARY

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch013

A series o f e x p l o r a t o r y anaerobic d i g e s t i o n e x p e r i m e n t s w a s p e r f o r m e d w i t h a m i x e d b i o m a s s - w a s t e feed t o search f o r d i g e s t i o n c o n f i g u r a t i o n s t h a t p r o v i d e i m p r o v e d p e r f o r m a n c e over t h a t o f c o n v e n t i o n a l h i g h - r a t e d i g e s t i o n . T h e t e c h n i q u e s s t u d i e d w e r e p r e t r e a t m e n t o f t h e feed w i t h caustic soda, p r o d u c t gas r e c y c l i n g t o t h e digester, r e c y c l i n g of aerobically t r e a t e d digester e f f l u e n t t o t h e digester, t w o - p h a s e d i g e s t i o n w i t h c o m p l e t e m i x a c i d - a n d m e t h a n e - p h a s e reactors, a n d p a c k e d - b e d . m e t h a n e - p h a s e d i g e s t i o n o f t h e e f f l u e n t f r o m an a c i d - p h a s e reactor. A m b i e n t - t e m p e r a t u r e p r e t r e a t m e n t of t h e feed b l e n d w i t h d i l u t e caustic a n d r e c y c l i n g of t h e p r o d u c t gas each a f f o r d e d higher m e t h a n e yields a n d volatile solids r e d u c t i o n efficiencies t h a n h i g h - r a t e d i g e s t i o n alone. It w a s f o u n d t h a t spent c a u s t i c c o u l d be r e c y c l e d for fresh feed p r e t r e a t m e n t a n d t h a t neutralization w a s n o t necessary before f e e d i n g t o t h e digester. T w o - p h a s e d i g e s t i o n in t h e c o m p l e t e - m i x reactors gave m e t h a n e yields a n d r e d u c t i o n efficiencies a b o u t t h e same as t h o s e of h i g h - r a t e d i g e s t i o n b u t at m u c h h i g h e r loadings a n d r e d u c e d d e t e n t i o n t i m e s t h e r e b y o f f e r i n g s i g n i f i c a n t r e d u c t i o n s in e q u i p m e n t size f o r t h e same t h r o u g h p u t s . The use o f a p a c k e d - b e d a n a e r o b i c filter as a m e t h a n e - p h a s e reactor also s h o w e d c o n s i d e r a b l e p r o m i s e f o r o p e r a t i o n at r e d u c e d d e t e n t i o n t i m e s w h e n t h e filter e f f f u e n t w a s r e c y c l e d t o t h e filter inlet. A n a l y s i s of t h e data f r o m t h e e x p e r i m e n t s c o n d u c t e d t o s t u d y each a d v a n c e d d i g e s t i o n t e c h n i q u e indicates t h a t a n i n t e g r a t e d series o f unit processes c o n s i s t i n g of dilute caustic pretreatment, thermophilic acid-phase digestion, mesophilic complete-mix and packed-bed methane-phase digestion, and limitedaeration aerobic t r e a t m e n t of t h e m e t h a n e - p h a s e effluents c o u p l e d w i t h r e c y c l i n g s h o u l d e x h i b i t d i g e s t i o n efficiencies a n d m e t h a n e yields near t h e u p p e r practical limits. ACKNOWLEDGEMENT This research w a s s u p p o r t e d b y U n i t e d Gas Pipe Line C o m p a n y (UGPL). H o u s t o n , Texas. T h e project w a s d o n e u n d e r t h e m a n a g e m e n t o f UGPL a n d is c u r r e n t l y m a n a g e d b y t h e Gas Research Institute. The g u i d a n c e a n d help of Mr. Robert C h r i s t o p h e r a n d Dr. V i c t o r E d w a r d s , b o t h o f UGPL, w e r e invaluable. The assistance of Dr. B. C. W o l v e r t o n of N A S A , M r . D a w s o n M. J o h n s of LSU. Mr. Robert Power o f W a s t e M a n a g e m e n t , Inc., a n d t h e staff of t h e M e t r o p o l i t a n Sanitary District o f Greater Chicago in p r o v i d i n g t h e feed samples is a p p r e c i a t e d . T h e a u t h o r s also a c k n o w l e d g e t h e efforts of Janet Vorres, M i c h a e l Henry, A l v i n Iverson, M o n a S i n g h , Frank Sedzielarz, Phek H w e e Y e n , a n d R a m a n u r t i Ravichandran in c o l l e c t i n g t h e e x p e r i m e n t a l data.

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BIOMASS AS A NONFOSSIL FUEL SOURCE

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Haug, R.T. J. Water Pollut. Control Fed. 1977, 49 (7), 1713.

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Klass, D.L. "Proceedings", Bio-Energy World Congress and Exposition, Atlanta, Ga., April 21-24, 1980; Bio-Energy Council: Washington, D.C., 1980.

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Ghosh, S.; Henry, M.P.; Klass, D.L. Second Symposium on Biotechnology in Energy Production and Conservation, Gatlinburg, Tenn., Oct. 3-5, 1979.

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Ghosh, S.; Klass, D.L. Process Biochem. 1978,

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Heertjes, P.M.; Van der Meer, R.R. Purdue University Industrial Waste Conference, West Lafayette, Ind. May 8-10, 1979; Ann Arbor Science Publishers, Inc.: Ann Arbor, Mich., 1979.

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RECEIVED JUNE 24, 1980.

14 Methane Production from Landfills An Introduction EDWARD J. D A L E Y , IRA J. WRIGHT, and ROBERT E. SPITZKA

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch014

Brown and Caldwell Consulting Engineers, Resource Recovery and Energy Conservation, 1501 North Broadway, Walnut Creek, C A 94596

The sanitary landfill process was developed to provide a means of disposal of wastes, particularly urban refuse and industrial solid wastes, in a manner that will not pollute the environment. In simple terms, this is accomplished by sealing the wastes to prevent interaction with the environment. Soil with low permeability provides the seal. The integrity of the seal is dependent upon the quality of the landfill operation, especially the cover soil compaction requirements. In a well-designed landfill, the movement of moisture and gas into or out of the interior of the landfill is significantly restricted to create a relatively closed environment for the wastes. Within this closed environment can be found an extremely wide variety of materials. Though waste composition differs widely from place-to-place and from season-to-season, a typical landfill can be expected to have a composition similar to that shown in Table I (1). The waste contains considerable moisture (about 25 percent by weight) and a high concentration of organics. As a result of the collection, unloading, spreading, and compaction of wastes during landfilling, the fill material will be heterogeneous with a large surface area-to-volume ratio. It will be under compression due to the weight of the compacted trash and earth above it. D u r i n g t h e l a n d f i l l i n g process, a c e r t a i n a m o u n t o f air w i l l be t r a p p e d in t h e landfill interior a l o n g w i t h t h e trash. T h e q u a n t i t y of air c a n n o t be d e t e r m i n e d , but c a n logically be e x p e c t e d t o be s i g n i f i c a n t . A small a m o u n t o f free w a t e r

0097-6156/81/0144-0279$05.00/0 © 1981 American Chemical Society

BIOMASS AS A NONFOSSIL F U E L SOURCE

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Φ Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

n

CRYSTAL DETECTOR

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MATCHNG (water)

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BIOMASS AS A NONFOSSIL F U E L SOURCE

Analytical Scheme

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

T h e so-called p e r m a n e n t gas f r a c t i o n w a s r o u t i n e l y analyzed o n a 6-ft X 1/8i n c h d i a m e t e r S u p e l c o Porapak Q c o l u m n u s i n g a Perkin-Elmer M o d e l 3 9 2 0 gas c h r o m a t o g r a p h (G.C.). T h e f l o w r a t e of t h e G.C. carrier, h e l i u m , w a s 3 0 m l / m i n . The b r i d g e c u r r e n t w a s set for 1 7 5 m A a n d t h e t h e r m a l c o n d u c t i v i t y d e t e c t o r t e m p e r a t u r e w a s m a i n t a i n e d at 2 0 0 ° C . CO a n d C O 2 peaks w e r e q u a n t i t a t i v e l y analyzed at r o o m t e m p e r a t u r e w h i l e t h e a s s y m m e t r y of t h e a c e t y l e n e peak necessitated e l u t i o n at 100°C. T h e presence of h y d r o g e n w a s d e t e r m i n e d o n a m o l e c u l a r sieve 1 3 X c o l u m n at r o o m t e m p e r a t u r e . Since a c e t y l e n e w a s n o t separated f r o m e t h y l e n e , c o n f i r m a t i o n of a c e t y l e n e w a s m a d e o n a S u p e l c o Porapak Τ c o l u m n (10 ft X % inch) at r o o m t e m p e r a t u r e . T h e l i q u i d f r a c t i o n , d i s s o l v e d in ether, w a s separated o n a S u p e l c o DEGS 5 0 ft x 1 6 - i n c h capillary c o l u m n (liquid l o a d i n g 10%). T h e s a m p l e w a s prepared b y d r y i n g o v e r M g S O * a d d i n g p a r a - b r o m o p h e n o l as a n internal s t a n d a r d a n d b r i n g i n g it a l m o s t t o d r y n e s s in a Danish Kaderna evaporator. A s a m p l e c h r o m a t o g r a m is s h o w n in Figure IV. C o n f i r m a t i o n of t h e major c o m p o n e n t s w e r e m a d e by an associated Hitachi Perkin-Elmer R M S - 4 mass s p e c t r o m e t e r . A d d i t i o n a l analyses are d e t a i l e d in Graef (46). A l i m i t e d n u m b e r of c h a r f r a c t i o n analyses w e r e c o n d u c t e d on a B e c k m a n I.R.-4 infrared s p e c t r o m e t e r . A s a m p l e size of 0.5 m g residual t o 8 0 0 m g KBr w a s f o u n d t o g i v e t h e best s p e c t r a (41). RESULTS Helium Plasma Product Characterization The m i c r o w a v e reactor p a r a m e t e r s distribution and thus, the conditions reaction c o n d i t i o n s . The a b s o r b e d m o n i t o r s a n d t h i s particular p o w e r c o n s i s t e n t l y stable d i s c h a r g e over an rates.

are e x p e c t e d t o affect t h e p r o d u c t in Table I w i l l be c o n s i d e r e d baseline e n e r g y is read d i r e c t l y f r o m p o w e r level w a s t h e l o w e s t t h a t p r o v i d e d a a c c e p t a b l e range of pressures a n d f l o w

T h e gross d i s t r i b u t i o n of p r o d u c t s f o r m e d f r o m lignin in a h e l i u m d i s c h a r g e are s h o w n in Table I. T h e values in parenthesis are t h o s e c a l c u l a t e d by e x c l u d i n g t h e residual f r a c t i o n . The u n c e r t a i n t y s u g g e s t e d by t h e u p p e r l i m i t ( < 1 0 % ) g i v e n for t h e volatile f r a c t i o n is a c o n s e q u e n c e of t h e d e p o s i t i o n of fine particle m a t e r i a l in t h e n i t r o g e n t r a p . T h e i n a b i l i t y t o dissolve this s u b s t a n c e in a v a r i e t y of solvents s u g g e s t s t h a t it s h o u l d be categorized w i t h t h e p o l y m e r i z e d f r a c t i o n , t h u s t h e l o w e r limit ( > 3 % ) given for t h e polymerized fraction.

GRAEF ET AL.

Acetylene from Biomass/Lignin

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

15.

Figure 4. Gas chromatograph of condensable volatiles

299

300

BIOMASS AS A N O N F O S S I L F U E L

SOURCE

T h e p l a s m a pyrolysis values presented in Table I can be c o m p a r e d w i t h t h e c o m p i l a t i o n by A l l a n and M a t t i l a (1_7) of t h e t h e r m a l pyrolysis p r o d u c t s of l i g n i n under solvent-free c o n d i t i o n s over a broad range of t e m p e r a t u r e s . The t w o p r o d u c t d i s t r i b u t i o n s are q u i t e dissimilar. T h e r m a l pyrolysis p r o m o t e s l i q u e f a c t i o n ( 7 8 % o n a residual-free basis) w h i l e p l a s m a p r o c e s s i n g is p r i m a r i l y a g a s i f i c a t i o n r e a c t i o n ( 8 1 % o n a residual-free basis). A s e x p e c t e d t h e p l a s m a reactions cause a m o r e severe d e g r a d a t i o n t o l o w e r m o l e c u l a r weight products. T a b l e I. O V E R A L L P R O D U C T D I S T R I B U T I O N

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

Representative Conditions Reaction Product Residual V o l a t i l e Fraction Permanent G a s e s

3 3 % (0%) < 10% ( 3 % (>4%)

4

Baseline Reactor Parameters H e l i u m Initial Pressure: 2 5 Torr M a x i m u m Pressure: — 1 0 0 Torr Forward Power: 5 5 0 w a t t s Batch Reaction T i m e : 10 m i n Total A b s o r b e d Energy: 7 5 w a t t - h o u r Carrier Flow Rate: 8 6 c m / m i n 3

2.

From Ref. 17. A l l a n a n d M a t i l l a

3. 4.

MW = 1 4 g/mole By d i f f e r e n c e a v e

Gas Fraction Characterization Detailed c h a r a c t e r i z a t i o n of t h e gas f r a c t i o n s of t h e respective

pyrolysis

processes s h o w n in Table II s u g g e s t s t h a t t h e d i s s i m i l a r i t y e x t e n d s b e y o n d t h e d i s t r i b u t i o n of t h e p r o d u c t s .

15.

GRAEF ET AL.

301

Acetylene from Biomass/Lignin

Table II. C O M P O S I T I O N OF P E R M A N E N T G A S E S

Carbon Monoxide Carbon Dioxide Hydrogen Methane Ethane Acetylene Higher H y d r o c a r b o n s Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

Sum

1

Helium Plasma

Thermal Pyrolysis

44% 2% 43% 2% Trace 14% Trace

50% 10% None 38% 2% None Trace

105%

3

100%

1. V o l u m e p e r c e n t 2. Reference 17 3. Indicates error in m e a s u r e m e n t s , ± 5 % The analytical s c h e m e f o r these studies p r e c l u d e d m e a s u r e m e n t of w a t e r . Both pyrolysis m e t h o d s evolve c a r b o n m o n o x i d e a n d c a r b o n d i o x i d e in c o m p a r a b l e a m o u n t s . H o w e v e r , plasma processing p r o d u c e s 4 3 % h y d r o g e n a n d 1 4 % acetylene o n a v o l u m e basis w h i l e t h e r m a l pyrolysis gases c o n t a i n neither c o m p o n e n t . Instead, t h e m a j o r h y d r o c a r b o n generated in t h e t h e r m a l pyrolysis s y s t e m is m e t h a n e (38%), w h i l e s a t u r a t e d h y d r o c a r b o n s are m i n o r c o m p o n e n t s in t h e plasma process. These differences illustrate t h a t t h e n a t u r e of c o n v e n t i o n a l pyrolysis reactions is radically different f r o m t h e m i c r o w a v e plasma pyrolysis reactions. Condensible Liquid Characterization The gas phase species w e r e s w e p t f r o m t h e plasma zone b y t h e carrier gas a n d a p o r t i o n o f t h e m c o n d e n s e d in a l i q u i d n i t r o g e n c o l d trap. S o m e of t h e major c o n d e n s i b l e volatiles w e r e i d e n t i f i e d w i t h G.C.-Mass s p e c t r o s c o p y as s h o w n in Figure IV. Q u a n t i t a t i v e d e t e r m i n a t i o n of several of t h e larger peaks is g i v e n in Table III f o r t h e h e l i u m plasma reactor baseline c o n d i t i o n s . C o m p a r i s o n of Table III w i t h t y p i c a l lignin pyrolysis p r o d u c t s f r o m A l l a n a n d M a t t i l a (17) s h o w n in Figure V reveals t h a t w h i l e guaiacol a n d t h e cresols are present in b o t h s y s t e m s , a variety of o t h e r p r o d u c t s , specifically t h e c o n d e n s e d a r o m a t i c s , are n o t c o n v e n t i o n a l pyrolysis p r o d u c t s . T h e major c o m p o n e n t s i d e n t i f i e d represent o n l y 4 % b y v o l u m e of t h e volatile f r a c t i o n w h i l e at least 5 0 a d d i t i o n a l c o m p o u n d s a c c o u n t f o r t h e r e m a i n i n g 96%. No a t t e m p t has y e t been m a d e t o o p t i m i z e or n a r r o w t h e p r o d u c t d i s t r i b u t i o n of t h e l i q u i d f r a c t i o n o b t a i n e d in a h e l i u m p l a s m a since t h e liquids represent only a b o u t 10 w e i g h t p e r c e n t of t h e t o t a l p r o d u c t s . A l t h o u g h c u r r e n t studies are addressing t h e issue of w h i c h e x p e r i m e n t a l variables n a r r o w t h e p r o d u c t

302

BIOMASS AS A NONFOSSIL F U E L SOURCE

COMPOUNO

I D E N T I F I E D AS MAJOR COMPONENTS IN CONDENSIBLE V O L A T I L E FRACTION OF

STRUCTURE

NAME

HELIUM MICROWAVE PLASMA PYROLYSIS

OH

phenol

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

o-cresol

è

y

OH

ér

OH

p-cresol

Φ

guaiacol

CH

j

CHs

y

OH Js^OCH

3

y

3

OH

2 , 4 dimethyl phenol ο ) (xylenol) 2-methoxy,4-methyl phenol

CH

OH ,OCH, 3

OH ,OCH

2-methoxy, 4 - e t h y l phenol 2-methoxy, 4 - p r o p y l phenol

CH, OH

CH -CH 2

OH

Ψ

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3

CH

p - v i n y l phenol

napthalene

3

CH=CH

anthracene

2

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3

2

-CH

3

y

β ί ο ] 2

C H » C H

y 2

y

styrene C = CH

phenyl acetylene

y

acenaphthcene

y

FigureS. Contrast between plasma and thermal pyrolysis condensable volatile fraction (tars) produced in solvent-free pyrolysis of lignin

15.

GRAEF ET A L .

303

Acetylene from Biomass/Lignin

d i s t r i b u t i o n (43,44), it is d i f f i c u l t t o generalize a b o u t t h e reactions f o r m i n g t h e c o n d e n s i b l e l i q u i d f r a c t i o n in t h i s reactor g e o m e t r y a n d q u e n c h zone c o n f i g u r a t i o n (44). Even if m o r e favorable yields of t h e a b o v e c o m p o u n d s c o u l d be a c h i e v e d , e c o n o m i c c o n s i d e r a t i o n s s u g g e s t t h e decreased diversity of t h e gas f r a c t i o n s h o u l d take p r e c e d e n c e a n d its c o m p o s i t i o n s h o u l d be optimized. Table III. COMPOSITION OF VOLATILES (Baseline Reactor Parameters)

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

Volume Fraction Major Components

of Tars, %

Styrene Phenyl A c e t y l e n e

0.5 0.5 0.9 0.2

Napthalene Guaiacol O-Cresol P-Cresol Acenaphthene Anthracene

1.0 0.4 0.1 0.5 4.1

Other* Methylphenylacetylene 1,2-Dimethoxybenzene Other unidentified components. 5 0

not quantitative 100%

* Unconfirmed Residual Analysis A n e l e m e n t a l analysis w a s p e r f o r m e d (42) o n t h e residual f r a c t i o n . T h e f o l l o w i n g w e i g h t p e r c e n t s w e r e o b t a i n e d o n t h e char: C. 8 3 . 9 2 % ; H. 2.09%; N, 0.45%; O, 8.5%; a n d remainder, 5.06%. T h e c h a r is a black, porous material w i t h a shape similar t o a n e x p a n d e d pellet. Infrared spectra (41) of t h e char f r a c t i o n s h o w e d v i r t u a l l y n o features a n d n o n e o f t h e original lignin f u n c t i o n a l g r o u p a b s o r p t i o n b a n d s , s u b s t a n t i a t i n g t h a t nearly c o m p l e t e reaction o c c u r r e d . A l t h o u g h f e w residual f r a c t i o n samples w e r e analyzed s p e c t r o s c o p i c a l l y , e a c h w a s v i s u a l l y i n s p e c t e d a n d it is believed t h a t t h e lack of f u n c t i o n a l i t y is representative o f all char fractions. Certain runs n o t reported here s h o w e d u n r e a c t e d l i g n i n in a zone c o n t i g u o u s w i t h t h e reactor w a l l . The p a t t e r n o f t h e reacted a n d u n r e a c t e d zones suggests t h a t t h e pellet

304

BIOMASS AS A NONFOSSIL F U E L SOURCE

was misaligned in the field shielding a portion of the lignin from electron bombardment. This phenomenon, together with short duration runs showing a distinct shell of reacted lignin, lends support to the explanation that the lignin is transformed primarily by electron bombardment, a surface phenomenon, the rate of which depends on the electron concentration and energy.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

Effects of Some S y s t e m Parameters on Acetylene Production

In order to evaluate the importance of the major system parameters on the product distribution and composition, experiments were conducted in which power, carrier gas composition, flowrate, and time were varied (41J. The variation of carrier composition and power are best described simultaneously since the effect of the input power is dependent on the carrier gas under consideration. This interaction exists since a change in either parameter alters the electron concentration and electron energy in the system (10). The power, expressed as energy absorbed over the 10-minute run. was varied in several experiments and its effect on acetylene production is shown in Figure VI for three carrier gases, helium, argon, and hydrogen. The effects on other products are reported elsewhere (46). The higher concentration of H when it serves as the carrier gas promotes an increase of roughly 1.5 times the acetylene produced in either inert carrier.

2

The mechanism for the homogeneous production of acetylene from the CO and H in the plasma has been suggested by Mertz, et al. (32) as follows: 2

H + e - — 2H- + e H- + CO — CH- + 0 · 2CH* C H 2

2

+

2

Although this mechanism can be expected to occur in H carrier gas experiments, a considerable volume fraction, 43%, of the gaseous products is H derived from the lignin itself (Table II). Thus the CH- radical is being generated directly from lignin and complex hydrocarbon fragmentation. Several studies (13.26,31) of coal plasma pyrolysis report acetylene production in somewhat smaller quantities than reported here consistent with the lower H to C ratio of coal. We suggest, however, that the acetylene production rate is a complex phenomenon dependent on the reactor geometry, local plasma temperature (47.48), plasma applicator configuration, quenching rate, and mass transfer limitations. This matter is under continued investigation. 2

2

15.

GRAEF ET AL.

305

Acetylene front Biomass/Lignin

DISCUSSION Devolatilization kinetics e x p e r i m e n t s (43,44) a n d pellet behavior in w h i c h t h e unreacted-reacted

interface is sharply m a r k e d i n d i c a t e t h a t t h e p r i m a r y

reactions w i t h i n t h e solid c a n be d e s c r i b e d b y a shell-progressive m o d e l of t h e t y p e discussed b y Carberry (45) a n d others. H o w e v e r , t h e e x p e c t e d s e c o n d a r y reactions d e s c r i b e d briefly b e l o w are q u i t e different f o r volatiles e s c a p i n g t o t h e gas phase plasma or volatiles r e m a i n i n g in t h e pellet or charresidual. T h e differences b e t w e e n plasma a n d t h e r m a l pyrolysis r e g a r d i n g p r o d u c t d i s t r i b u t i o n s s h o w n in Figure V a n d Tables II a n d III arise f r o m t h e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

n a t u r e of t h e secondary reactions. In t h e g a s phase, t h e p l a s m a reactor e n v i r o n m e n t c o n t a i n s e l e c t r o n s g e n e r a t e d a n d s u s t a i n e d b y t h e m i c r o w a v e field (10). T h e e l e c t r o n , b y v i r t u e of its c h a r g e a n d m i n u t e mass, is t h e p r e d o m i n a n t " c a r r i e r " by w h i c h this transfer of e l e c t r o m a g n e t i c e n e r g y t o kinetic energy is a c h i e v e d . Specifically, t h e e l e c t r o n , accelerated b y t h e rapidly o s c i l l a t i n g f i e l d , develops s u f f i c i e n t kinetic energy (1-2 KEV) or p s e u d o - t e m p e r a t u r e s (on t h e order of 1 0 °K) t o dissociate, excite, or ionize o t h e r m o l e c u l e s present in t h e gas. The e n e r g e t i c e l e c t r o n also f r a g m e n t s t h e surface lignin a n d o t h e r h y d r o c a r b o n s u p o n collision. Because of t h e relatively h i g h c o n c e n t r a t i o n o f free radicals a n d o t h e r e n e r g e t i c species, t h e p l a s m a gas reactions are characterized as h i g h t e m p e r a t u r e reactions o c c u r r i n g at rapid rates a n d p r o d u c i n g o t h e r e n e r g e t i c species. T h e p r o d u c t i o n of a c e t y l e n e in a m i c r o w a v e p l a s m a , as c o n t r a s t e d t o e t h a n e or m e t h a n e in c o n v e n t i o n a l pyrolysis, s u p p o r t s t h i s c o n c e p t o f t h e p l a s m a g a s as a h i g h e n e r g y zone, since as Figure VII f r o m Baddour a n d T i m m i n s (10) s h o w s , a c e t y l e n e is t h e r m o d y n a m i c a J l y stable at higher 4

t e m p e r a t u r e w h i l e m e t h a n e a n d e t h a n e are n o t . A l t h o u g h t h e r m o d y n a m i c a r g u m e n t s c a n n o t strictly be used in a m i c r o w a v e p l a s m a as a c o n s e q u e n c e of t h e i n e q u a l i t y of t h e e l e c t r o n t e m p e r a t u r e a n d t h e t e m p e r a t u r e o f t h e ions and molecules, the production of acetylene tends t o suggest that the electron c o n c e n t r a t i o n a n d v e l o c i t y d e t e r m i n e t h e e n e r g e t i c s o f t h e gas phase. Further details of t h e plasma gas reactions are discussed in Graef (41,46). A l t h o u g h e l e c t r o n b o m b a r d m e n t is rapid a n d t h e p r e d o m i n a n t f o r m of heat transfer in t h e gas phase, t r a n s p o r t processes w i t h i n t h e pellet are q u i t e d i f f e r e n t a n d m u c h slower. Increased c h a r yield a n d c o n d e n s e d a r o m a t i c s f o u n d in t h i s s t u d y are c o n s i s t e n t w i t h t h e f o l l o w i n g d e s c r i p t i o n of t h e processes o c c u r r i n g w i t h i n t h e pellet. U p o n collision w i t h t h e pellet surface, t h e f l u x of electrons relases large a m o u n t s o f heat w h i c h volatilizes a n d cracks t h e p o l y m e r i c l i g n i n . D e p e n d i n g o n t h e gas c o m p o s i t i o n as in Figure V I , t h e s t o i c h i o m e t r y (or C / O / H ratios) o f t h e biomass, a n d t h e mass t r a n s p o r t s i t u a t i o n , an a m o u n t of residual or char f o r m s i n w a r d f r o m t h e pellet surface, w h i l e t h e volatiles o u t f l o w increases t h e gas pressure near t h e pellet.

306

BIOMASS AS A NONFOSSIL F U E L SOURCE

PRODUCTION OF ACETYLENE vs ENERGY ABSORBED

140

1201

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

2

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3 80 >

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60fFigure 6. Acetylene evolved (standard ce) as a function of tubegrabed power absorbed over a 10-min experiment: (0) He, (A) Ar, and (+) H carriers; line is trend only 9

..J I 40 0 40 80 120 160 200 ENERGY ABSORBED (watt-hours)

25h /

2

o

15

υ

I 0 h

^

^ / ^ E T H Y L E N E CjH -| 4

^ / S > V - ^ACETYLENE CjHj

ETHANE

5

C H 2

METHANE C H

6

4

GRAPHITE ( S O L I D ) HYDROGEN(GAS)
1-10 m i n " ) t h a n one m i g h t predict f r o m electron p s e u d o t e m p e r a t u r e s in t h e gas p l a s m a . A f t e r a n initial period, these a p p a r e n t devolatilization rates are c o n s i s t e n t w i t h rates f o r c o n d u c t i o n in porous char (44,49). 1

3.

T h e porous interior of t h e pellet provides a resistance t o mass transfer, i.e., c o n f i n e s t h e volatiles, w h i c h increases reactive f r a g m e n t c o n c e n t r a t i o n s . This p r o m o t e s p o l y m e r i z a t i o n a n d c o n d e n s a t i o n reactions w h i c h f o r m t h e greater char f r a c t i o n a n d c o n d e n s e d a r o m a t i c s (Table III a n d Figure V) t h a n r e p o r t e d f o r c o n v e n t i o n a l pyrolysis.

D e p e n d i n g o n t h e carrier gas f l o w rate, v a c u u m p u m p c a p a c i t y , degree of c r a c k i n g a n d local plasma t e m p e r a t u r e , t h e j u s t - v o l a t i l i z e d higher m o l e c u l a r w e i g h t gases c a n be either s w e p t f r o m t h e plasma zone or u n d e r g o secondary plasma r e a c t i o n s . T h e s e g a s - p h a s e s e c o n d a r y r e a c t i o n s (described previously) o c c u r t o v a r y i n g e x t e n t s d u e t o t h e residence t i m e d i s t r i b u t i o n (laminar f l o w ) a n d spatially n o n u n i f o r m plasma p s e u d o t e m p e r a t u r e (48). T h e c o n d e n s i b l e volatile f r a c t i o n c o m p o n e n t s s u c h as guaiacol a n d cresol t h a t reflect t h e original lignin s t r u c t u r e are rapidly q u e n c h e d volatiles s u b j e c t e d t o short residence t i m e s or l o w - p l a s m a t e m p e r a t u r e s , perhaps f r o m t h e o u t e r m o s t pellet layer reacted. The d e s c r i p t i o n of t h e s e c o n d a r y reactions in t h e gas phase is f u r t h e r c o m p l i c a t e d b y t h e fact t h a t e l e c t r o n c o n c e n t r a t i o n a n d average electron v e l o c i t y or energy d o n o t remain c o n s t a n t f o r t h e entire e x p e r i m e n t because

308

BIOMASS AS A NONFOSSIL F U E L SOURCE

of n o n c o n s t a n t s y s t e m pressure a n d c o m p o s i t i o n . The e l e c t r o n c o n c e n t r a t i o n is inversely related t o pressure a n d h i g h l y d e p e n d e n t o n gas c o m p o s i t i o n via t h e ionization p o t e n t i a l of t h e c o m p o n e n t s (47). T h e a b s o r b e d p o w e r also c h a n g e s w i t h gas c o m p o s i t i o n , f u r t h e r c o u p l i n g t h e variables. T h u s , t h e volatiles o u t f l o w reduces t h e p l a s m a h e a t i n g rate as a f u n c t i o n of t h e rate a n d a m o u n t of pressure increase. E x p e r i m e n t s c o n d u c t e d w i t h increasing initial p o w e r as s h o w n in Figure VI s h o w a c o m p l e x d e p e n d e n c e o n p o w e r a n d e x p e r i m e n t s are b e i n g c o n d u c t e d t o u n c o v e r t h e m e c h a n i s m s . A s t r o n g effect of particle size is o b s e r v e d a n d d e s c r i p t i o n of t h e c o u p l e d t r a n s p o r t a n d reaction processes is r e p o r t e d e l s e w h e r e (43,44).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

SUMMARY Rapid, severe d e g r a d a t i o n has been s h o w n t o n a r r o w t h e reaction p r o d u c t d i s t r i b u t i o n in p l a s m a pyrolysis of t h e a r o m a t i c f r a c t i o n of b i o m a s s . l i g n i n . This paper reports o n l y f i v e c o m p o u n d s w i t h yields > 2 % if t h e tar (3% t o 10%) a n d char (33%) are c o n s i d e r e d t w o of t h e five. Primarily g a s i f i c a t i o n o c c u r s since yields of 51 w e i g h t p e r c e n t gases are f o u n d . These gases, are 17 w e i g h t p e r c e n t H (43 v o l u m e percent) a n d C H is 13 w e i g h t p e r c e n t (14 v o l u m e percent). Char y i e l d is r e d u c e d as s u g g e s t e d by L e w e l l y n because of c o n s u m p t i o n by increased radical c o n c e n t r a t i o n s , here, associated w i t h t h e p l a s m a . C o n d e n s e d a r o m a t i c s in a d d i t i o n t o p h e n o l - t y p e c o m p o u n d s are f o u n d in t h e tar f r a c t i o n , d u e p r e s u m a b l y t o mass t r a n s p o r t l i m i t a t i o n s in t h e pellet. Despite t h e n a r r o w p r o d u c t d i s t r i b u t i o n a n d h i g h h e a t i n g v a l u e of t h e gas p r o d u c e d , e n e r g y c o n s u m p t i o n for t h e process is h i g h d u e t o t h e necessity of m a i n t a i n i n g t h e p l a s m a a n d t o t h e large pellet size s l o w i n g t h e rate. Because of t h e p o t e n t i a l of very fast reactions in t h e p l a s m a , t r a n s p o r t c o n s i d e r a t i o n s , especially heat transfer, b e c o m e increasingly i m p o r t a n t and point the way to further improvements. 2

2

2

ACKNOWLEDGEMENTS This w o r k w a s s u p p o r t e d by t h e National Science F o u n d a t i o n u n d e r t h e Division of A d v a n c e d Energy a n d Resources Research a n d T e c h n o l o g y Grant No. 7 7 0 8 9 7 9 a n d t h e NSF Engineering Initiation Grant Program. M a r t h a Graef w i s h e s t o a c k n o w l e d g e f i n a n c i a l assistance f r o m t h e D e p a r t m e n t of C h e m i c a l E n g i n e e r i n g . U n i v e r s i t y of W a s h i n g t o n . T h e h e l p f u l s u g g e s t i o n s of Κ. V. Sarkanen, D. H a n s o n , D. E d e l m a n , B. H r u t f i o r d , a n d R. Chan are also g r a t e f u l l y acknowledged.

15. GRAEF ET AL. Acetylene from Biomass/Lignin

309

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

REFERENCES

1.

Sarkanen, Κ. V. Science 1976, 191, 773-76.

2.

Goldstein, I. S. Biotechnol Bioeng. Symp. Proc. 1976, (6), 293-301.

3.

Rydholm, S. A. "Pulping Processes"; Interscience Publishers: New York, 1965.

4.

Longwell, J. P. "Symposium Papers", 16th International Symposium on Combustion, sponsored by the Combustion Institute, Pittsburgh, 1976; Combustion Institute: Pittsburgh, 1976; 1-15.

5.

Anthony, D.; Howard, J. P.; Hottel, H. C.; Meissner, H. P. "Symposium Papers", 15th International Symposium on Combustion, sponsored by the Combustion Institute: Pittsburgh, 1975; Combustion Institute, Pittsburgh, 1975; 1303.

6.

Anthony, D. B.; Howard, J. B.; Hottel, H.; Meissner, H. P. Fuel 1976, 55, 121-28.

7.

Suuberg, F. M. "Rapid Pyrolysis and Hydropyrolysis of Coal", Ph.D. Dissertation, Massachusetts Institute of Technology, Cambridge, Mass., 1977.

8.

Lewellen, P.D.; Peters, W. Α.; Howard, J. B. "Symposium Papers", 16th International Symposium on Combustion, sponsored by the Combus­ tion Institute, Pittsburgh, 1977; Combustion Institute: Pittsburgh, 1977; 1471.

9.

Goheen, D.W.; Henderson, J. T. Cellulose Chem. and Tech. 1978, (3), 363-72,.

13

10.

Baddour, R. F.; Timmins, R. S. "The Application of Plasmas to Chemical Processing"; M.I.T. Press: Cambridge, Mass., 1967.

11.

Hollahan, J.R.; Bell, A. T. "Techniques and Applications of Plasma Chemistry"; John Wiley: New York, 1974.

12.

Bonet, C. Chem. Eng. Prog. 1976, 72 (12), 63-69.

13.

Nicholson, R.; Littlewood, K. Nature 1972, 236, 397.

310 BIOMASS AS A NONFOSSIL FUEL SOURCE

14.

Collins, J., U.S. Dept. of Energy, Washington, D.C., personal communica­ tion, 1978.

15.

Shafizadah, F.; Sarkanen, Κ. V.; Tillman, D. Α., eds. "Thermal Uses and Properties of Carbohydrates and Lignins"; Academic Press: New York, 1976.

16. Pearl, I.A. "The Chemistry of Lignin"; Marcel Dekker: New York, 1967; pp 276-83.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

17. Allan, G. G.; Mattila, T. In "Lignins"; Sarkanen, Κ. V.; Ludwig, C. H., Eds.; Wiley-Interscience Publishers: New York, 1971; p 575. 18. Shafizadah, F.; Fu, Y. L. Carbohydr. Res. 1973, 29, 113. 19. Shafizadeh, F.; McIntyre, C.; Lundstrom, H.; Fu, Y. L. Proc. Mont. Acad. Sci. 1973, 33, 65-96. 20.

Tran, D. Q.; Rai, C. Fuel 1978, 57, 293-98.

21.

Tillman, D. Α.; Sarkanen, Κ. V.; Anderson, L. L. "Fuels and Energy From Renewable Resources"; Academic Press: New York, 1977.

22. Shafizadeh, F.; Furneaux, R. H.; Cochran, T. G.; Scholl, J. P.; Sakai, Y., J. Appl. Polym. Sci. 1979, 23 (12), 3525-39. 23. Bradbury, A.G.W.; Sakai, Y.; Shafidzdeh, R. J. Appl. Polym. Sci. 1979, 23 (11), 3271-80. 24. Fairbridge, C.; Ross, R. Α.; Sood, S. P. J. Appl. Polym. Sci., 1979 22,497510. 25.

Goldstein, I.S. Appl. Polym. Symp. 1975, (28), 259-67.

26.

Che, S.C.L. Ph.D. Dissertation, University of Utah, Provo, Utah, 1974.

27. Bittman, R. Ph.D. Dissertation, University of California, Berkeley, Calif., 1966. 28. Fu, Y. C.; Blaustein, B.D. Chem. Ind. 1967, 1257 (London). 29. Fu, Y. C.; Blaustein, B. D. Fuel 1968, 47, 463.

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30.

Fu, Y. C.; Blaustein, B. D. Ind. Eng. Chem. Process Design Develop 1969, 8, 257.

31.

Fu, Y. C.; Blaustein, B. D.; Wender, I. In Flinn, J., Ed.; Chem. Eng. Prog. Symp. Ser. 1971, 67 (112), 47-54.

32.

Mertz, S. F.; Asmussen, J.; Hawley, M. C. IEEE Trans. Plasma Sci. 1975, 25 (Dec.), 297.

33.

Streitwieser, Α.; Ward, H. E. J. Amer. Chem. Soc. 1962, 84, 1065.

34.

Bosisio, R. G. J. Phys. E. 1973, 6, 628.

35.

Gehrling Moore, Inc. Palo Alto, California.

36.

Knapp, E. M.; Ellis, W. T. U.S. Patent 3 560 347, 1971; U.S. Patent 3 449 213, 1969.

37.

Grannen, Ε. Α.; Robinson, L. U.S. Patent 3 843 457, 1974.

38.

Bailin, L. J.; Sibert, M.; Jonas, L. Α.; Bell, A. T. Environ. Sci. Technol. 1975, 9, (3), 254.

39.

Zaitsev, V. M.; Piyalkin, V. N.; Isyganov, E. A. Gidroliz. Lesokhim. Promst. 1975, 3, 10-12.

40.

Work, D. W. M.S. Thesis, University of Washington, Seattle, Wash., 1977.

41. Graef, M. G. M.S. Thesis, University of Washington, Seattle, Wash., 1978. 42.

Swarzkopf Analytical Labs, New York, 1978.

43. Chan, R. C. M.S. Thesis, University of Washington, Seattle, Wash., 1979. 44. 45.

Wiggins, D. M.S. Thesis, University of Washington, Seattle, Wash., 1979. Carberry, J. J. "Chemical & Catalytic Reaction Engineering"; McGraw Hill: New York, 1977.

312

BIOMASS AS A NONFOSSIL FUEL SOURCE

46.

Graef, M. K; Krieger, Β. B., in preparation, 1979.

47.

MacDonald, A. D. "Microwave Breakdown in Gases"; John Wiley: New York, 1966.

48. Bonet, C.; Bell, A. T. "Plasma Chemistry — 2 Transport Phenomena in Thermal Plasmas"; Pergamon Press: Elmsford, N.Y., 1975.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch015

49. Russel, W.; Saville, D.; Greene, M. I. "A Model for Short Residence Time Hydropyrolysis of Single Coal Particles"; Amer. Inst. of Chem. Eng. J. 1979, 25 (Jan.), 65-80. RECEIVED JUNE 18, 1980.

16 The Effects of Residence Time, Temperature, and Pressure on the Steam Gasification of Biomass MICHAEL J. A N T A L , JR.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08540

The underlying science of thermochemical conversion of biomass materials to useful gaseous fuels is poorly understood. Recent experimental research in the U.S.A. (1) and Sweden (2) has offered new and important insights into the gasification process. The two research teams independently conclude that biomass gasification occurs in three steps: 1) pyrolysis. producing volatile matter and char; 2) secondary reactions of the evolved volatile matter in the gas phase; and 3) char gasification. Detailed understanding of the rates and products of these three steps offers important guidance for the improved design of biomass gasifiers. Pyrolysis of biomass materials occurs under normal conditions at relatively low temperatures (300° to 500°C), producing volatile matter and char. Very rapid heating causes pyrolytic weight loss to occur at somewhat higher temperatures. In general, the volatile matter content of cellulosic materials approximates 90% of the dry weight of the initial feedstock. Woody materials contain between 70% and 80% volatile matter, and manures contain 60% volatile matter. However, it is known (3) that cellulosic materials can be completely volatilized when subject to very rapid heating (>10,000°C/sec). Several relatively complete reviews of the mechanisms and kinetics of cellulose pyrolysis are available in the literature (4-7).

0097-6156/81/0144-0313$05.50/0 © 1981 American Chemical Society

314

BIOMASS AS A NONFOSSIL F U E L SOURCE

V o l a t i l e m a t t e r p r o d u c e d by pyrolysis of t h e biomass b e g i n s t o p a r t i c i p a t e in secondary, gas-phase reactions at t e m p e r a t u r e s e x c e e d i n g 6 0 0 ° C . These reactions o c c u r very rapidly a n d yield a h y d r o c a r b o n - r i c h syngas p r o d u c t . A s recognized by Diebold (8), these reactions resemble t h e h y d r o c a r b o n c r a c k i n g reactions e m p l o y e d in t h e m a n u f a c t u r e of e t h y l e n e a n d p r o p y l e n e by t h e p e t r o c h e m i c a l i n d u s t r y (9.10). T h e s e c o n d a r y gas-phase reactions d o m i n a t e t h e g a s i f i c a t i o n c h e m i s t r y of biomass. A t still higher t e m p e r a t u r e s ( > 7 0 0 C ) . p y r o l y t i c c h a r reacts w i t h s t e a m t o p r o d u c e h y d r o g e n , c a r b o n m o n o x i d e a n d c a r b o n d i o x i d e . Rates of g a s i f i c a t i o n of biomass-derived chars are k n o w n t o be h i g h e r t h a n coal-derived chars (2); h o w e v e r , m u c h higher t e m p e r a t u r e s are required t o a c h i e v e c h a r g a s i f i c a t i o n t h a n w e r e initially required for t h e pyrolysis reactions. Catalysis of c h a r g a s i f i c a t i o n has been reported (1_1.12) w i t h l i m i t e d success.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

e

Research d e s c r i b e d in t h i s paper focuses o n t h e s e c o n d step of t h e g a s i f i c a t i o n process, a n d details t h e effects of t e m p e r a t u r e a n d residence t i m e o n p r o d u c t gas f o r m a t i o n . Cellulose is used as a f e e d s t o c k for p y r o l y t i c volatiles f o r m a t i o n . Earlier papers (13.14) have d i s c u s s e d t h e effect of s t e a m o n cellulose pyrolysis kinetics. T w o recent papers (15.16) p r e s e n t e d early results on pelletized red alder w o o d p y r o l y s i s / g a s i f i c a t i o n in s t e a m . Future papers w i l l discuss results u s i n g o t h e r w o o d y materials, c r o p residues, a n d m a n u r e s (1_7.18). Research t o date i n d i c a t e s t h a t all biomass materials p r o d u c e q u a l i t a t i v e l y similar results in t h e g a s i f i c a t i o n reactor d e s c r i b e d in t h e f o l l o w i n g s e c t i o n of t h i s paper. Effects of pressure o n t h e heat of pyrolysis of cellulose are also d i s c u s s e d as a p r e l u d e t o f u t u r e papers d e t a i l i n g t h e m o r e general effects of pressure on reaction rates a n d p r o d u c t slates. EFFECTS O F T E M P E R A T U R E A N D

RESIDENCE T I M E O N THE SEC-

ONDARY. GAS-PHASE REACTIONS Experimental Procedure For t h e e x p e r i m e n t s d e s c r i b e d b e l o w , d r y W h a t m a n No.1 filter paper stored in a d e s i c c a n t b o t t l e w a s used as f e e d s t o c k material. T h e use of an o v e n t o o b t a i n " b o n e d r y " material w a s f o u n d t o be f u t i l e d u e t o t h e h y g r o s c o p i c n a t u r e of t h e cellulose. T h e cellulose w a s a s s u m e d t o have t h e c h e m i c a l c o m p o s i t i o n 0 . 4 4 4 C. 0.062 H, 0.494 0 o n a mass f r a c t i o n basis, a n d t h e c h a r c o m p o s i t i o n w a s d e t e r m i n e d t o be 0 . 7 8 3 5 C. 0.04 H. a n d 0 . 1 7 6 5 by an i n d e p e n d e n t laboratory. A specially d e s i g n e d quartz, t u b u l a r , p l u g - f l o w reactor w a s f a b r i c a t e d t o s t u d y t h e gas-phase reactions. Rates of gas f o r m a t i o n by species can be

16.

ANT AL

315

Steam Gasification of Biomass

m e a s u r e d u s i n g t h e reactor either in a differential or an integral m o d e . Results d e s c r i b e d here emphasize t h e integral aspects of t h e t u b u l a r reactor since t h e y are t h e easiest t o interpret. A s c h e m a t i c of t h e e x p e r i m e n t a l a p p a r a t u s is g i v e n in Figure I. A t y p i c a l experimental procedure was: 1) W i t h all three f u r n a c e s c o l d , a small (0.1 t o 0.5 g) s a m p l e of t h e material t o be pyrolyzed is placed in t h e c e n t e r of t h e pyrolysis reactor. 2) A n inert gas is bled t h r o u g h ports D a n d Ε t o cool t h e s a m p l e a n d p u r g e t h e reactor, w h i l e f u r n a c e s 1 a n d 3 b r i n g t h e s t e a m superheater Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

a n d t h e gas-phase reactor t o t h e desired t e m p e r a t u r e . 3) T h e peristaltic p u m p is a c t u a t e d a n d p u m p s w a t e r into t h e s t e a m generator at a m e a s u r e d rate. C o n c u r r e n t l y , a small a m o u n t of inert tracer gas (argon) is c c n t i n u o u s l y i n j e c t e d t h r o u g h port A into t h e rear of t h e reactor. 4) W h e n c o n d e n s e d w a t e r first b e g i n s t o appear in t h e pyrolysis reactor, f u r n a c e 2 ( w h i c h w a s p r e h e a t e d t o t h e desired

pyrolysis

t e m p e r a t u r e ) is m o v e d i n t o place a r o u n d t h e pyrolysis zone o f t h e reactor. 5) W h e n pyrolysis t e m p e r a t u r e s are r e a c h e d , t h e six-port V a l c o valve is s w i t c h e d a n d t h e 3 4 - p o r t V a l c o valve a u t o m a t i c a l l y takes 15 samples of t h e gas s t r e a m f o r later analysis in t h e H e w l e t t - P a c k a r d 5 8 3 4 a Gas C h r o m a t o g r a p h (HPGC). U n s a m p l e d g a s is c o l l e c t e d in a T e f l o n b a g f o r later analysis. 6) W h e n

all 15 samples

have been t a k e n , t h e six-port valve is

s w i t c h e d again a n d t h e samples are a u t o m a t i c a l l y analyzed b y t h e HPGC. Gases c o l l e c t e d in t h e T e f l o n bag are s a m p l e d using a gas t i g h t syringe a n d analyzed b y t h e HPGC. 7) T h e c h a r a n d tars p r o d u c e d d u r i n g t h e e x p e r i m e n t are c o l l e c t e d a n d w e i g h e d . W a t e r c o l l e c t e d in t h e c o n d e n s e r is also w e i g h e d . T e m p e r a t u r e s w i t h i n t h e reactor are c o n t r o l l e d controllers

and monitored

by Type

by various

Κ thermocouples

with

temperature continuous

r e c o r d i n g o n c h a r t recorders. M e a s u r e d t e m p e r a t u r e variations a l o n g t h e l e n g t h of t h e gas-phase reactor have been d e s c r i b e d in a n earlier p u b l i c a t i o n (1).

Chart Recorder

TracerCarrier Gas

"

u

H

.

f

a

o

t

e

_

r

Figure 1.

8 Thermocouple Leeds

ED

Temperature C o n t r ô l e r s

Movable Pyrolysis Furnace

Furnace 3

Condenser

HP 5834a Gas Chromatography

6as Phase Reactor Furnace

i l l

lir Furnace 2

Gas Purge

Gas Purge

HP Terminal

Schematic of the tubular quartz reactor experiment

Steam Superheater

Furnace 1

Steam Generator

Perl stal tic Pump

Liquid Nitrogen

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

34 Port Valve

Vent

ta

ο

ι

δ

16.

ANTAL

The

evolved

variation

317

Steam Gasification of Biomass gas c o m p o s i t i o n

during

t h e course

w a s observed

to undergo

of the experiment;

considerable

consequently

t e n gas

s t a n d a r d s w e r e a c q u i r e d t o calibrate t h e HPGC for q u a n t i t a t i v e analysis of t h e f o l l o w i n g gases: Ar, N . H , CO, C 0 . C H , C H . C H , C H , C H , C H 2

C H 5

1 2

, and C H

obscured

6

1 4

2

2

4

2

4

2

6

3

6

4

8

4

1 0

,

. I d e n t i f i c a t i o n of t h e h i g h e r h y d r o c a r b o n s (>C3> is

by t h e fact that some other

pyrolysis p r o d u c t s

have

similar

r e t e n t i o n times. A n a l y s e s g i v e n in this paper f o r light h y d r o c a r b o n s ( ^ C ) 3

have been c h e c k e d using a mass s p e c t r o m e t e r . The HPGC uses a Poropak QS column

in series

with

a Porosil

column

operating

between

— 5 0 °C

(cryogenic) and 2 0 0 ° C f o r gas analysis w i t h a t h e r m a l c o n d u c t i v i t y d e t e c t o r (TCD). T h e carrier gas is an 8.5% H

2

-

91.5% He m i x t u r e . A t y p i c a l gas

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

analysis takes 1 4 m i n u t e s . The c o m p l e t e recovery of m o i s t u r e a n d tars f r o m t h e reactor s o m e t i m e s poses d i f f i c u l t i e s . T h e m o i s t u r e is a b s o r b e d o n d r y paper t o w e l s a n d w e i g h e d ; w h e r e a s t h e tars c o n d e n s e o n a rolled piece of a l u m i n u m foil inserted in t h e condenser. Mass balances are a l w a y s better t h a n 0.8, b u t can be m i s l e a d i n g because m u c h m o r e w a t e r is used d u r i n g t h e course o f an e x p e r i m e n t t h a n solid reactant. T h e c a r b o n balance is a better measure of t h e e x p e r i m e n t ' s q u a l i t y , a n d c u s t o m a r i l y ranges b e t w e e n 0.7 a n d 1.0 for t h e results reported here. Our inability t o close t h e c a r b o n balance in part reflects t h e f o r m a t i o n o f w a t e r - s o l u b l e c a r b o n a c e o u s c o m p o u n d s w h i c h are n o t s u b j e c t t o analysis b y o u r e x i s t i n g i n s t r u m e n t a t i o n . Their presence is m a n i f e s t e d by t h e color a n d o d o r of t h e c o l l e c t e d w a t e r , w h i c h ranges f r o m clear w i t h an o d o r r e s e m b l i n g a u t o m o b i l e exhaust, t o deep a m b e r w i t h a stronger, m o r e n o x i o u s odor. A s d e s i g n e d , t h e reactor bears s o m e r e s e m b l e n c e t o a d i l u t e - p h a s e t r a n s p o r t reactor in t h a t t h e solids a n d volatile pyrolysis p r o d u c t s are present o n l y in l o w c o n c e n t r a t i o n s in t h e s t e a m reactant. D u r i n g pyrolysis.the c o m p o s i t i o n of gas in t h e gas-phase reactor u s i n g t h e l o w e s t s t e a m f l o w a n d a 0.1 g s a m p l e is n o m i n a l l y 6 8 % s t e a m , 2 8 % volatiles, a n d 4 % a r g o n carrier (on a v o l u m e p e r c e n t basis). S o m e w h a t larger samples, leading t o an increase in volatile c o n c e n t r a t i o n s , d o n o t m a r k e d l y affect t h e results reported here. Rates of gas p r o d u c t i o n c a n be m e a s u r e d using t h e reactor in either a differential or a n integral m o d e . T h e d i f f e r e n t i a l m o d e e m p l o y s t h e V a l c o valve s y s t e m t o o b t a i n f i f t e e n 0.6-ml samples o f gas e v o l v e d d u r i n g t h e course of t h e e x p e r i m e n t . W i t h A r tracer gas i n j e c t e d at a measured rate, t h e d i l u t i o n of t h e tracer gas s a m p l e c a n be d i r e c t l y related t o t h e " i n s t a n t a n e o u s " rate of volatile gas p r o d u c t i o n in t h e reactor. For e x a m p l e , w i t h a tracer gas f l o w of 5 m l per m i n . a d i l u t i o n of 5 0 % in t h e gas s a m p l e w o u l d c o r r e s p o n d t o a n " i n s t a n t a n e o u s " volatile gas p r o d u c t i o n rate of 5 m l per

318

BIOMASS AS A NONFOSSIL F U E L SOURCE

min.

Unfortunately,

(primarily

due

departures

to the

effect

from

of t h e

true

plug

condenser

flow on

within

the

gas f l o w )

reactor

make

the

differential mode experimental data more difficult to interpret than indicated a b o v e . Research r e p o r t e d here e m p h a s i z e s t h e i n t e g r a l a s p e c t s of t h e r e a c t o r design. W h e n used in t h e i n t e g r a l m o d e , t o t a l gas p r o d u c t i o n by species is m e a s u r e d u s i n g t e f l o n bags t o c o l l e c t all t h e reactor e f f l u e n t . T h e d e p e n d e n c e of t o t a l gas p r o d u c t i o n o n g a s - p h a s e r e s i d e n c e t i m e in t h e g a s - p h a s e zone of t h e r e a c t o r is d e t e r m i n e d u s i n g t h e c o m b i n e d d a t a of m a n y e x p e r i m e n t s . T h i s d a t a c a n be used t o infer rates of gas p r o d u c t i o n w i t h i n t h e g a s - p h a s e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

reactor. K i n e t i c

models

of g a s e o u s

species

formation

can

be

obtained

t h r o u g h a s t u d y of t h e e f f e c t s of b o t h t e m p e r a t u r e a n d r e s i d e n c e t i m e o n species p r o d u c t i o n . Kinetic Interpretation of Reactor Data Consider t h e p y r o l y s i s of a s m a l l s a m p l e of o r g a n i c m a t e r i a l in t h e p y r o l y s i s zone of t h e t u b u l a r reactor s y s t e m . A t a n y t i m e t. t h e rate of e v o l u t i o n of g a s e o u s v o l a t i l e m a t t e r ( r h ) f r o m t h e p y r o l y z i n g s a m p l e is g i v e n b y : v

m (t) v

m ^

-

mk[V -

V(t)] ; k -

A exp(-E/RT)

n

(1)

w h e r e m is t h e t i m e d e p e n d e n t s a m p l e mass, m j is t h e initial s a m p l e mass. m

f

is t h e final s a m p l e mass. V

= (mj —

m ) / m i . V = (mj — f

m ) / m j , A is t h e

p r e - e x p o n e n t i a l c o n s t a n t . Ε is t h e a p p a r e n t a c t i v a t i o n e n e r g y , R t h e Universal Gas C o n s t a n t . Τ is t h e t i m e - d e p e n d e n t a b s o l u t e t e m p e r a t u r e , a n d η is t h e a p p a r e n t o r d e r of t h e r e a c t i o n . T h e c o n c e n t r a t i o n of v o l a t i l e m a t t e r ( C ) in t h e v

f l o w i n g s t r e a m is g i v e n b y : C (t) -

—

v

m

where m

s

,

—

^

S'Ps +

, , . m /p v

(2)

v

is t h e m a s s f l o w of s t e a m in t h e t u b u l a r r e a c t o r a n d ρ

s

and ρ

v

are t h e d e n s i t i e s of s t e a m a n d v o l a t i l e m a t t e r (respectively). A s s u m i n g p l u g f l o w , t h e v o l a t i l e m a t t e r e v o l v e d at t i m e t e n t e r s t h e gas-phase reactor at t i m e t + θ =

Tj a n d leaves t h e g a s - p h a s e reactor at t i m e t +

r . The residence time 0

T . Tj of t h e v o l a t i l e s in t h e gas phase is g i v e n by: Q

0-L /J v(x)dx^crL/V ο 2

L

(3)

w h e r e L is t h e l e n g t h of t h e g a s - p h a s e reactor, ν is t h e s p a t i a l l y - d e p e n d e n t gas v e l o c i t y in t h e reactor. V is t h e v o l u m e t r i c f l o w of volatiles plus s t e a m in t h e reactor at t h e g a s - p h a s e reactor t e m p e r a t u r e T, a n d σ is t h e reactor's e f f e c t i v e cross s e c t i o n a l area.

16.

ANTAL

319

Steam Gasification of Biomass

S u p p o s e t h a t t h e rate of d i s a p p e a r a n c e of c o n d e n s i b l e volatiles (due t o c r a c k i n g , r e f o r m i n g , e t c . a n d t r e a t i n g t h e c o n d e n s i b l e volatiles as a single c h e m i c a l species) in a differential v o l u m e e l e m e n t ν δ τ of gas m o v i n g w i t h average v e l o c i t y ν = L / 0 satisfies a first order rate l a w : ^ dr w h e r e t h e rate c o n s t a n t r

v

-C r v

(4)

v

is g i v e n b y t h e A r r h e n i u s e x p r e s s i o n : r

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

-

v

- A

exp(-E /RT)

v

(5)

v

The t i m e variable τ c a n be t h o u g h t t o " t r a c k " t h e p o s i t i o n of t h e differential v o l u m e e l e m e n t w i t h initial v o l a t i l e c o n c e n t r a t i o n C ( t ) as it m o v e s t h r o u g h t h e gas-phase reactor. T h e p r o d u c t i o n of p e r m a n e n t gases p r o d u c e d b y c r a c k i n g / r e f o r m i n g reactions is also a s s u m e d t o satisfy a first order rate l a w : v

dCj -jf.

- C , ,

w h e r e η is t h e rate c o n s t a n t associated w i t h t h e j

(6) p e r m a n e n t gas a n d :

t h

rj - A j e x p ( - E j / R T )

(7)

A s a first a p p r o x i m a t i o n , t h e gas-phase zone c a n be treated as an i s o t h e r m a l reactor (however, see t h e f o l l o w i n g section), leading t o t h e expressions: C (t + T Q ) - C (t) e x p [ - r v

C

j(t

+

v

τ ) 0

— Cj(t)

-

J

°

T

C

v

v

(τ -

(t)rj e x p

[-r

(8)

TJ)]

0

(T-TJ)]CIT

v

Tj

-

C

v

(t)(rj/r ){l-exp[-r v

v

(τ 0

TJ)]}

(9)

w h e r e r a n d r j are c o n s t a n t (by a s s u m p t i o n of c o n s t a n t T), a n d it is also a s s u m e d t h a t t h e t e m p e r a t u r e of t h e pyrolysis zone is s u f f i c i e n t l y " c o l d " so t h a t t h e c r a c k i n g / r e f o r m i n g reactions d o n o t c o m m e n c e u n t i l t h e differential v o l u m e e l e m e n t enters t h e gas-phase reactor. v

The mass of species j in t h e differential v o l u m e e l e m e n t e m e r g i n g f r o m t h e reactor at t i m e t + τ js g i v e n b y : 0

a v ô t C j (t + τ ) 0

(10)

320

BIOMASS AS A NONFOSSIL F U E L SOURCE

a n d t h e t o t a l mass m; of species j p r o d u c e d d u r i n g t h e e x p e r i m e n t is g i v e n by: m j - crJv(t)Cj(t + T ) d t 0

=

vo-/Cj(t + r ) d t -

[vo-(rj/r )]{l-

0

exp [ - r ( T v

0

-

v

Tj)]}/C (t)dt v

+ V a J C j (t)dt

(11)

For s h o r t residence t i m e s [ r ( τ — Tj) < < 1 ] Equation (11) b e c o m e s : v

0

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

mj — ν σ η ( τ

0

-

TJ) J C ( t ) d t + v

vo-/Cj(t)dt

(12!

A p l o t of m j vs. residence t i m e ( τ — τ ) s h o u l d y i e l d a s t r a i g h t line w i t h t e m p e r a t u r e d e p e n d e n t slope ν σ η / C (t)dt — k j . A s u b s e q u e n t plot of / n ( k j ) vs. T " s h o u l d yield s t r a i g h t lines w h o s e slopes are t h e a p p a r e n t a c t i v a t i o n e n e r g y Ej associated w i t h t h e rate of p r o d u c t i o n of species j . T h u s , t h e d a t a o b t r a i n e d f r o m t h e t u b u l a r reactor are s u s c e p t i b l e t o kinetic interpretation. 0

(

v

1

It s h o u l d be n o t e d t h a t t h i s analysis o n l y p r o v i d e s an i n s i g h t i n t o t h e initial rates of t h e c r a c k i n g reactions. Tertiary gas-phase r e a c t i o n s t e n d t o o b s c u r e t h e i n t e r p r e t a t i o n of t h e kinetic data d e r i v e d f r o m t h e reactor. M o r e o v e r , t h e initial rate m e a s u r e m e n t s for t h e c r a c k i n g r e a c t i o n s are m e a n i n g f u l o n l y for short residence t i m e s [ r ( T — τ j )< < 1 ] . Because t h e c r a c k i n g reactions o c c u r rapidly, t h i s c o n s t r a i n t is d i f f i c u l t t o satisfy. v

0

Departures From an Ideal Isothermal Reactor T h e t u b u l a r q u a r t z reactor w a s d e s i g n e d a n t i c i p a t i n g t h e need t o p r o v i d e for long (5 s e c o n d s or more) gas-phase residence t i m e s in order t o r e f o r m the oily v o l a t i l e m a t t e r . S u r p r i s i n g l y , t h e o b s e r v e d reaction rates w e r e so h i g h t h a t residence t i m e s o n t h e order of 0.5 sec or less w e r e n e e d e d t o satisfy t h e c o n d i t i o n r ( 1 — τ j ) < < 1 . T o o b t a i n s u c h s h o r t residence t i m e s , large mass f l o w s w e r e r e q u i r e d w h i c h c a u s e d t h e reactor t o d e v i a t e f r o m its i n t e n d e d use as an ideal i s o t h e r m a l s y s t e m . In a d d i t i o n , t h e L i n d b u r g f u r n a c e s w e r e o b s e r v e d t o be less u n i f o r m in t e m p e r a t u r e t h a n e x p e c t e d . C o n s e q u e n t l y , heat transfer plays a c r i t i c a l role in d e t e r m i n i n g t h e residence t i m e of t h e volatiles at t e m p e r a t u r e . T h e f o l l o w i n g p a r a g r a p h s o u t l i n e o u r " f i r s t o r d e r " a p p r o a c h t o w a r d s r e c o g n i z i n g t h e affects of heat transfer o n t h e kinetic i n t e r p r e t a t i o n of t h e e x p e r i m e n t a l d a t a . v

0

16.

ANTAL

321

Steam Gasification of Biomass

A s i m p l e energy balance for laminar f l u i d f l o w in a long t u b e leads t o t h e equation: — dx

+ aT = a T

(13)

w

w h e r e « = π D h / m c . a n d T(x) is t h e bulk gas t e m p e r a t u r e along t h e l e n g t h p

χ of t h e t u b e . T

w

is t h e c o n s t a n t w a l l - t e m p e r a t u r e , D is t h e t u b e ' s d i a m e t e r , h

is t h e heat transfer c o e f f i c i e n t , m is t h e mass f l o w of t h e gas a n d c

p

is t h e

specific heat of t h e gas. Equation (13) c a n be solved t o d e t e r m i n e t h e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

distance f

required for t h e gas t o reach t e m p e r a t u r e T, w i t h t h e result:

,

(14l \

*-kN

N u D

\ t

J

w

— τ jy

where h = k N / D . k is t h e t h e r m a l c o n d u c t i v i t y of t h e gas. a n d t h e Nusselt number N = 3.7. N u D

N

u

d

In order t o o b t a i n an a p p r o x i m a t e residence t i m e ( τ — τ , ) for t h e volatiles in t h e gas-phase reactor, t h e l e n g t h f w a s c a l c u l a t e d a s s u m i n g T — Τ = 5°C. A n error of 5°C in t h e gas-phase t e m p e r a t u r e m e a s u r e m e n t gives rise t o a b o u t a 1 0 % error in t h e d e t e r m i n a t i o n of E, . T h e residence t i m e of t h e volatiles at t e m p e r a t u r e w a s t h e n c a l c u l a t e d using t h e f o r m u l a : 0

w

(L - Λ )σ T

° -

T

|

"

m /ps + m / p s

v

v

(15)

w h e r e L is t h e t o t a l l e n g t h of t h e gas-phase section of t h e reactor, a n d σ is t h e a p p a r e n t cross s e c t i o n a l area of t h e reactor. Table I lists values o f . / as a f u n c t i o n of T f o r a s t e a m f l o w of 0.34 g / m i n (used in t h e short residence t i m e kinetic e x p e r i m e n t s ) . From this d a t a , it is a p p a r e n t t h a t at t h e higher gas-phase t e m p e r a t u r e s , t h e volatiles s p e n d a b o u t 5 0 % of their t i m e in t h e gas-phase reactor b e i n g heated t o i s o t h e r m a l c o n d i t i o n s . C o n s e q u e n t l y , kinetic m e a s u r e m e n t s at t h e higher t e m p e r a t u r e s represent i n t e g r a t e d values of t h e rates at l o w e r t e m p e r a t u r e s , in a d d i t i o n t o t h e (assumed) c o n s t a n t rate at T . This result c l o u d s t h e kinetic i n t e r p r e t a t i o n of t h e reactor d a t a . A l t h o u g h m o r e effort c o u l d be m a d e t o e x p l i c i t l y a c c o u n t f o r t h e w a r m u p t i m e in t h e kinetic m o d e l for t h e reactor d a t a , w e have c h o s e n t o f o c u s o u r effort o n t h e d e s i g n of a " s e c o n d g e n e r a t i o n r e a c t o r " w h i c h w i l l p r o v i d e s u f f i c i e n t heat transfer rates t o ensure nearly i s o t h e r m a l c o n d i t i o n s f o r t h e shortest residence t i m e e x p e r i m e n t s . w

w

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

322

BIOMASS AS A NONFOSSIL F U E L SOURCE

T a b l e I. P A R A M E T E R S U S E D T O C A L C U L A T E G A S - P H A S E RESIDENCE T I M E Effective Reactor Volume, f , cm

w« °C 750 700 675 650

13.4 13.9 14.2 14.5 14.8 15.2 15.6 16.1 17.2

625 600 575 550 500 L « 29.2 c m σ - 3.474 c m

cm

3

46.4 48.1 49.2 50.2 51.3 52.7 54.0 55.8 59.6

2

Bulk v o l u m e of insert ^ 7 0 c m L e n g t h of insert 31.1 m C

3

Effective Insert V o l u m e , cm 3

30.2 31.3 32.0 32.6 33.3 34.2 35.1 36.2 38.7

16.

ANTAL

323

Steam Gasification of Biomass

S o m e efforts have also been m a d e t o e x p e r i m e n t a l l y measure t h e t e m p e r a t u r e rise of t h e s t e a m e n t e r i n g t h e gas-phase reactor. Q u a l i t a t i v e a g r e e m e n t w i t h t h e results of t h e heat transfer c a l c u l a t i o n s w a s f o u n d ; h o w e v e r , a brief c a l c u l a t i o n of t h e effect of radiation o n t h e t h e r m o c o u p l e ' s m e a s u r e m e n t of t h e gas t e m p e r a t u r e p o i n t e d t o a s i g n i f i c a n t error in t h e m e a s u r e m e n t . For e x a m p l e , w i t h a s t e a m f l o w of 0.12 g / m i n a n d a gas-phase

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

t e m p e r a t u r e of 6 0 0 ° C . t h e t h e r m o c o u p l e t e m p e r a t u r e w a s c a l c u l a t e d t o exceed t h a t of t h e gas b y 13°C. Carefully c o n s t r u c t e d radiation shields are needed t o e l i m i n a t e t h i s effect. Because o u r research effort in this area w a s d r a w i n g t o a close, it w a s d e c i d e d t o use t h e m e t h o d o l o g y d e s c r i b e d earlier (Equation 15) t o e s t i m a t e t h e residence t i m e of t h e volatiles at t e m p e r a t u r e . Departures From A n Ideal Plug-Flow Reactor Both t u r b u l e n c e a n d m o l e c u l a r d i f f u s i o n cause t u b u l a r reactors t o d e p a r t f r o m ideal p l u g - f l o w behavior. It is s t a n d a r d p r a c t i c e t o a c c o u n t f o r t h e t w o effects

b y a single

dimensionless

parameter

D / v L , called

t h e vessel

dispersion n u m b e r . This n u m b e r is usually d e t e r m i n e d e x p e r i m e n t a l l y , a n d its m a g n i t u d e indicates t h e degree of d e p a r t u r e of t h e reactor f r o m p l u g f l o w (2VvL) < 0 . 0 1 f o r p l u g f l o w ) . A g o o d d i s c u s s i o n of t h e effects of dispersed p l u g f l o w o n t h e kinetic i n t e r p r e t a t i o n of reactor data is g i v e n b y Levenspiel (19). T h e value Z)/vL = 0.122 w a s m e a s u r e d b y T. M a t t o c k s (V7). A l t h o u g h this value suggests s i g n i f i c a n t d e p a r t u r e s f r o m p l u g f l o w , w e believe m o s t of t h e dispersion o c c u r s in t h e c o n d e n s e r w i t h o u t a f f e c t i n g t h e kinetic measurem e n t s presented here. Results and Discussion Figures II. Ill, a n d IV display t h e d e p e n d e n c e of gas p r o d u c t i o n (g gas per g cellulose or % conversion) b y species o n gas-phase residence t i m e f o r various gas-phase reactor t e m p e r a t u r e s . For these e x p e r i m e n t s , t h e s t e a m superheater w a s m a i n t a i n e d at 3 5 0 ° C , a n d t h e pyrolysis f u r n a c e at 5 0 0 ° C . This latter s e t t i n g gave rise t o a m e a s u r e d s a m p l e h e a t i n g rate of 1 0 0 ° C / m i n . Residence t i m e s w e r e altered b y v a r y i n g t h e peristaltic p u m p ' s w a t e r f l o w rate b e t w e e n 0.06 a n d 0.34 g / m i n . a n d b y inserting a closed quartz c y l i n d e r into t h e gas-phase reactor t o reduce its a p p a r e n t v o l u m e . Data p o i n t s reported in Figures ll-V w e r e a c c u m u l a t e d m o n t h s using e x p e r i m e n t a l t e c h n i q u e s w h i c h evolved t h a t t i m e period. Data p o i n t s w i t h residence t i m e s of w e r e o b t a i n e d using a w a t e r f l o w rate of 0.34 g / m i n

over a period of e i g h t and improved during t w o t o three seconds f o r a 0.25 g sample.

324

BIOMASS AS A NONFOSSIL F U E L SOURCE

χ ο 0.08 0.0*

0

1

?

3

4

S

6

7

8

9

10

11

12

U

12

0.014 ρ

0.006

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

0.004 0.002

• 0

D 1

2

3

4

S

·

7

8

9

10

CO

•

9

°

Figure 2. Nonhydrocarbon gas production vs. residence time for various gasphase temperatures: Ο 500°, (A) 600°, (O) 650°, (·) 700°, (X) 750°C

0.08 0.07 0.06 0.05 0.04

0.03

0.02

Δ 0

1

2

3

4

5

6

Δ 7

8

9

10

U

12

0.014 0.012 0.010 Ι

0.006

-

0.004

-

Ο

0.002 _J

I

I

L_

Residence T 1 M (sec)

Figure 3. Paraffinic hydrocarbon gas production vs. residence time for various gas—phase temperatures: Ο 500°, (A) 600°, (O) 650°, (%) 700°, (X) 750°C

ANTAL

Steam Gasification of Biomass

325

o.os • -

0.04

0.03

-

0.0?

-

.

0.01

L É » .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

0

1

' D 0

3

2

4

• Πι

1

6

I

5J

ι

6

7

l

3

2

5

4 . 5

7

Residence T I M

Β

9

1 B

3

10

1

11

1

1

10

11

12

_à 12

(sec)

Figure 4. Olefinic hydrocarbon gas production vs. residence time for various gasphase temperatures: Ο 500°, (A) 600°, (0)650°, (·) 700°, (X) 750°C

CARBON

• —I Ο

EFFICIENCY

•

I

1

OXYCEN

ft

I 3

2

I

Ι­ S

6

7

8

9

10

11

12

i

6

7

8

9

10

11

12

EFFICIENCY

KO

*

Δ

•

SJ

0

1

Γ

HYDROGEN

EFFICIENCY

1

3

2

2

3

4

4

5

6

7

8

9

Residence Tine (sec)

Figure 5. Carbon, hydrocarbon, and oxygen efficiency vs. residence time for vari­ ous gas—phase temperatures: Ο 500°, (A) 600°, (O) 650°, (·) 700°, (X) 750°C

326

BIOMASS AS A NONFOSSIL F U E L SOURCE

Shorter residence t i m e s w e r e o b t a i n e d using a quartz insert to reduce t h e gas-phase reactor's a p p a r e n t v o l u m e . Longer residence t i m e s w e r e o b t a i n e d by r e d u c i n g t h e w a t e r f l o w rate a n d cellulose s a m p l e size p r o p o r t i o n a t e l y . T h u s , all t h e d a t a represents t h e same s t e a m f l o w / c e l l u l o s e w e i g h t ratio.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

Since cellulose pyrolysis o c c u r s in a b o u t one m i n u t e w i t h a h e a t i n g rate of 1 0 0 ° C / m i n . t h e data c o r r e s p o n d t o a s t e a m d i l u t i o n ratio of a b o u t 1.4 g s t e a m per 1 g cellulose feed. A v a i l a b l e e v i d e n c e s u g g e s t s t h a t h i g h e r s t e a m d i l u t i o n ratios have little affect on t h e g a s i f i c a t i o n results. Efforts are presently b e i n g m a d e t o m o r e f u l l y e l u c i d a t e t h e effects of d i l u t i o n ratio o n s t e a m g a s i f i c a t i o n products. Of t h e various gases represented in Figures ll-IV. t h e behavior of c a r b o n d i o x i d e is s i m p l e s t t o interpret, since it s h o w s t h e least d e p e n d e n c e on g a s phase residence t i m e or t e m p e r a t u r e . A p p a r e n t l y , t h e p r i m a r y m e c h a n i s m for C O 2 f o r m a t i o n rests in t h e initial pyrolysis process. S e c o n d a r y gas-phase reactions at t e m p e r a t u r e s of a b o u t 5 0 0 ° C c o n t r i b u t e less t o C O 2 f o r m a t i o n . In order t o increase g a s i f i c a t i o n e f f i c i e n c y by r e d u c i n g C O 2 f o r m a t i o n (each m o l e c u l e of C O 2 f o r m e d represents a net loss of c a r b o n f r o m t h e c o m b u s t i b l e p r o d u c t s of t h e process), t h e c o n d i t i o n s a f f e c t i n g t h e pyrolysis step of g a s i f i c a t i o n m u s t be carefully e x a m i n e d . For e x a m p l e , t h e use of h i g h h e a t i n g rate m a y r e d u c e C 0 f o r m a t i o n . 2

M e t h a n e f o r m a t i o n is also relatively easy t o interpret. Increasing t e m peratures a n d increasing residence t i m e s result in increased m e t h a n e f o r m a t i o n . T h e slope of t h e d a s h e d lines in Figure III gives t h e a p p a r e n t rate of m e t h a n e p r o d u c t i o n at t h e various t e m p e r a t u r e s s t u d i e d . The d e p e n d e n c e of t h i s p r o d u c t i o n rate on t e m p e r a t u r e is used later in t h i s section t o e s t i m a t e t h e a c t i v a t i o n energy for m e t h a n e f o r m a t i o n . Efforts t o e l u c i d a t e t h e m e c h a n i s m of m e t h a n e f o r m a t i o n (most p r o b a b l y t h e p y r o l y s i s / h y d r o g e n a t i o n of h i g h e r h y d r o c a r b o n s ) are p r e s e n t l y u n d e r w a y . Carbon m o n o x i d e a n d h y d r o g e n p r o d u c t i o n data behave similarly, a n d reach a m a x i m u m at a b o u t 5 sec residence t i m e a n d 7 0 0 t o 7 5 0 ° C . Data for C H p r o d u c t i o n s h o w s o m e s i m i l a r i t y t o t h a t of C H ; h o w e v e r . C 2 H p r o d u c t i o n reaches a m a x i m u m at t e m p e r a t u r e s of 6 5 0 ° t o 7 0 0 ° C a n d residence t i m e s of a b o u t 2 sec. C o m p e t i t i v e rates of f o r m a t i o n by pyrolysis a n d c o n s u m p t i o n by pyrolysis or d e h y d r o g e n a t i o n reactions p r o b a b l y e x p l a i n t h i s o b s e r v e d behavior. 0

2

4

6

6

Ethylene p r o d u c t i o n is m a x i m i z e d at t e m p e r a t u r e s of 7 0 0 ° t o 7 5 0 ° C a n d residence t i m e s of a b o u t 6 sec. w h e r e a s p r o p y l e n e f o r m a t i o n is f a v o r e d by l o w e r t e m p e r a t u r e s (650°C) a n d shorter residence t i m e s (2 sec).

16.

ANT AL

327

Steam Gasification of Biomass

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

In general, these results i n d i c a t e t h a t t h e gas-phase reaction t e m p e r a t u r e is t h e m o s t s i g n i f i c a n t parameter. T h e role of p r i m a r y pyrolysis c o n d i t i o n s a n d gas-phase residence t i m e s are m u c h less significant. Moreover, f o r t e m p e r a t u r e s a b o v e 6 5 0 ° C , t h e initial rates of species f o r m a t i o n are very h i g h , so t h a t m u c h of t h e gas f o r m a t i o n is c o m p l e t e in less t h a n 0.5 sec. These very h i g h rates of gas f o r m a t i o n d u e t o s e c o n d a r y reactions are of great s i g n i f i c a n c e f o r reactor d e s i g n . The p r e c e d i n g c o n c l u s i o n s are s u b s t a n t i a t e d b y Figure V, w h i c h s h o w s t h e effect of gas-phase t e m p e r a t u r e a n d residence t i m e o n t h e c a r b o n , h y d r o g e n a n d o x y g e n g a s i f i c a t i o n efficiencies (carbon e f f i c i e n c y = c a r b o n in gas-rf e e d s t o c k carbon). A g a i n , t h e gas-phase reactor t e m p e r a t u r e m o s t s i g n f i c a n t l y affects t h e c a r b o n a n d h y d r o g e n efficiencies of t h e s y s t e m . Under t h e best c o n d i t i o n s e x a m i n e d t o d a t e , 8 3 % of t h e feedstock's energy w a s retained by t h e gaseous p r o d u c t s of t h e process, a n d t a r p r o d u c t i o n w a s r e d u c e d t o 3 % of t h e f e e d s t o c k w e i g h t . T h e gas h a d a h e a t i n g value of 4 9 0 Btu/SCF. Other p e r t i n e n t statistics are g i v e n in Table II. Initial e x p e r i m e n t s in f l o w i n g a r g o n w i t h n o s t e a m present yield essentially t h e same results as t h e c o m p a r a b l e s t e a m runs. From this, it appears t h a t t h e g a s i f i c a t i o n process is d o m i n a t e d

by c r a c k i n g reactions a n d n o t s t e a m

r e f o r m i n g reactions. V a r i a t i o n s in h e a t i n g rate of t h e cellulose f r o m 5 0 ° C / m i n t o 2 0 0 ° C / m i n d o n o t m a r k e d l y affect results. Using gas-phase residence t i m e s of 0.46 t o 0.97 sec at t e m p e r a t u r e s of 7 5 0 ° a n d 5 0 0 ° C , respectively, a p p a r e n t rates of p r o d u c t i o n w e r e m e a s u r e d for seven gaseous species: C 0 . H . CO. C H , C H , C H a n d C H . Figures VI a n d VII are g r a p h s of log ( k j / m j ) vs. Τ " , w h e r e kj is t h e e x p e r i m e n t a l l y d e t e r m i n e d rate of p r o d u c t i o n of gas species j . A s i n d i c a t e d in Figures VI a n d VII, t h e slope of t h e lines c o n n e c t i n g t h e values of log (kj / m j ) gives t h e a p p a r e n t a c t i v a t i o n e n e r g y Ej associated w i t h t h e rate of p r o d u c t i o n of each species j . Values f o r each Ej are g i v e n in Table III. 2

2

4

2

4

2

6

3

6

1

Several c o n c l u s i o n s c a n be d r a w n f r o m Figures VI a n d VII. A t h i g h t e m p e r a t u r e s (and short residence t i m e s ) , t h e rate of c o n v e r s i o n of volatile m a t t e r t o e t h y l e n e is s e c o n d o n l y t o c a r b o n m o n o x i d e a n d m e t h a n e . T h u s , large yields of e t h y l e n e c a n be e x p e c t e d f r o m a w e l l d e s i g n e d biomass gasifier. In c o n t r a s t t o e t h y l e n e , t h e rate of p r o d u c t i o n of p r o p y l e n e peaks at 6 7 5 ° C a n d rapidly declines at h i g h e r t e m p e r a t u r e s . A s e x p e c t e d , t h e rates of p r o d u c t i o n of h y d r o g e n a n d c a r b o n m o n o x i d e are favored b y h i g h temperatures.

328

BIOMASS AS A NONFOSSIL F U E L SOURCE

T a b l e I I . S E L E C T E D G A S I F I C A T I O N R E S U L T S FOR C E L L U L O S E Steam Superheater Temperature Pyrolysis Reactor T e m p e r a t u r e Gas-Phase Reactor T e m p e r a t u r e Gas-Phase Reactor Residence T i m e Sample W e i g h t Char Residue W e i g h t

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

Char Residue W e i g h t Percent Tar Residue W e i g h t Tar Residue W e i g h t Percent Gas V o l u m e P r o d u c e d Gas H e a t i n g V a l u e Calorific V a l u e of Gases Calorific V a l u e of Char Calorific V a l u e of Tars Mass Balance Carbon Balance Gas A n a l y s i s (Vol %) CO H 2

co

2

CH

4

C H C H C3H6 Other 2

4

2

6

350°C 500°C 700°C 3.5 sec 0.125 g 0.012 g 10% 0.003 g 2% 8 4 ml 4 9 0 Btu/SCF 13.7 M M B t u / t o n 2.8 M M B t u / t o n 0.5 M M B t u / t o n 0.84 0.96 52 18 8 14 6 1 0.1 0.9

T a b l e I I I . A P P A R E N T L O W T E M P E R A T U R E ( 5 0 0 ° C s= Τ s= 6 7 5 ° C ) A C T I V A T I O N E N E R G Y (Ej) FOR V A R I O U S G A S S P E C I E S

Gas Species C0

(kcal/gmol) 21

2

H C H C2H4

35 38 55

C3H6 CO CH

55 60 67

2

2

6

4

329

Steam Gasification of Biomass

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

ANT AL

l.o

Figure 7.

l.i

looo/T ( · κ - ΐ )

,

I

I

I

I

I

I

I

750"C

700"C

675-C

ISOt

SXt

600*C

575*C

z

,

I 5S0'C

J

I 500*C

Arrhenius plot of the gas—phase production rate for various gas species: (X)C H„ (+) C H (O) C H t

t

kt

s

e

330

BIOMASS AS A NONFOSSIL F U E L SOURCE

T h e rate c u r v e s for m e t h a n e a n d e t h y l e n e " t r a c k " each o t h e r closely, s u g ­ g e s t i n g t h a t t h e s a m e m e c h a n i s m m a y be responsible for t h e f o r m a t i o n of t h e t w o gases. A l l t h e rates e x h i b i t a break at a b o u t 6 7 5 ° C , w i t h l o w e r a p p a r e n t Ej a b o v e 6 7 5 ° C . This m a y i n d i c a t e a c h a n g e in t h e c r a c k i n g m e c h a n i s m , or it m a y be an a r t i f a c t of poor heat t r a n s f e r in t h e gas-phase reactor. A m o r e e x p l i c i t m e c h a n i s t i c i n t e r p r e t a t i o n of t h e d a t a is m a d e d i f f i c u l t b y t h e effects of heat transfer a n d non-ideal p l u g f l o w o n t h e kinetic i n t e r p r e t a t i o n of t h e e x p e r i m e n t a l d a t a . Nevertheless, t h e d a t a are q u i t e useful for e n g i n e e r i n g d e s i g n purposes, a n d s u g g e s t s criteria t o be used for t h e d e s i g n of s e c o n d g e n e r a t i o n reactors i n t e n d e d t o p r o v i d e m o r e a c c u r a t e m e a s u r e m e n t s of gas-

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

phase c r a c k i n g rates. Finally, Figures ll-IV also e x h i b i t t h e f i t (dashed lines) of E q u a t i o n 11 t o t h e e x p e r i m e n t a l d a t a for a g a s - p h a s e t e m p e r a t u r e of 6 0 0 ° C . Values for ν σ / c j (t) d t a n d vo- ( r / r ) J c ( t ) d t at 6 0 0 ° C used in Equation 11 are listed in Table IV. v

v

T h e relatively g o o d a g r e e m e n t of t h e m o d e l e m b o d i e d in E q u a t i o n 11 w i t h t h e e x p e r i m e n t a l d a t a g i v e n in Figures ll-IV is n o t e n t i r e l y f o r t u i t o u s , b u t less g o o d at h i g h e r t e m p e r a t u r e s w h e r e t h e c o n s t r a i n t r

v

(τ

0

—

Τ | ) < < 1 is not

satisfied. A m e c h a n i s t i c i n t e r p r e t a t i o n of gas-phase p h e n o m e n a is n e e d e d t o i m p r o v e our a b i l i t y t o m a t h e m a t i c a l l y p r e d i c t t h e p r o d u c t s of g a s i f i c a t i o n u n d e r a v a r i e t y of c o n d i t i o n s . EFFECTS OF PRESSURE O N T H E P Y R O L Y S I S H E A T OF R E A C T I O N A c o m p r e h e n s i v e e x p e r i m e n t a l research p r o g r a m t o i n v e s t i g a t e t h e effects of pressure o n t h e p r o d u c t s of s t e a m g a s i f i c a t i o n of b i o m a s s is c u r r e n t l y u n d e r w a y . A stainless steel, t u b u l a r m i c r o r e a c t o r similar t o t h e q u a r t z reactor d e s c r i b e d earlier has been f a b r i c a t e d for t h e e x p e r i m e n t a l w o r k . T h e pyrolysis f u r n a c e used w i t h t h e q u a r t z reactor s y s t e m has been r e p l a c e d in t h e pressurized s t e a m s y s t e m by a Setaram Differential S c a n n i n g Calorimeter (DSC). The DSC provides for q u a n t i t a t i v e d e t e r m i n a t i o n of t h e effects of pressure on pyrolysis kinetics a n d heats of reaction. Figure VIII presents t h e results of t h r e e m e a s u r e m e n t s of t h e heat of pyrolysis of cellulose at d i f f e r e n t

pressures. A t

elevated

pressures, t h e

pyrolysis

r e a c t i o n b e c o m e s e x o t h e r m i c , a n d char p r o d u c t i o n increases f r o m a b o u t 1 2 % by w e i g h t of t h e cellulose f e e d s t o c k at 1 bar t o 1 6 % at 6 bars. Future research is e x p e c t e d t o refine this initial data a n d e x t e n d it over a broader range of pressures.

16.

ANTAL

331

Steam Gasification of Biomass

Table IV. N U M E R I C A L V A L U E S USED IN T H E GAS-PHASE

KINETIC

MODEL

co H

2

CO CH

4

C H

6

C H

4

2

2

3

H

6

w

T

= eocc

0.0145 0.0039 0.010

0.0035 0.0009 0.0 0.0002

0.0058

•

Figure 8.

w

0.046 0.0057 0.155

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

C

va(rj/r )/c (t)dt|

vo-/cj(t)dt 0.061 0.001 0.045

2

Cellulose ΔΗ p i i

yro ys s

I

Pressure (bars)

vs. pressure

332

BIOMASS AS A NONFOSSIL F U E L SOURCE

CONCLUSIONS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

Gas-phase, s t e a m c r a c k i n g reactions d o m i n a t e t h e c h e m i s t r y of b i o m a s s g a s i f i c a t i o n . A t t e m p e r a t u r e s a b o v e 6 5 0 ° C , these reactions p r o c e e d very r a p i d l y a n d g e n e r a t e a h y d r o c a r b o n rich syngas c o n t a i n i n g c o m m e r c i a l l y i n t e r e s t i n g a m o u n t s of e t h y l e n e , p r o p y l e n e , a n d m e t h a n e . Increased pressure appears t o i n h i b i t t h e g a s i f i c a t i o n process. These results i n d i c a t e t h a t b i o m a s s gasifiers s h o u l d be d e s i g n e d t o p r o v i d e for h i g h h e a t i n g rates a n d s h o r t residence t i m e w i t h gas-phase t e m p e r a t u r e s e x c e e d i n g 6 5 0 ° C . T r a n s p o r t reactors, characterized b y large t h r o u g h p u t s , h i g h h e a t i n g rates, m o d e s t pressures, a n d s h o r t residence t i m e s appear t o be ideally s u i t e d f o r t h i s purpose. Future b i o m a s s gasifiers s h o u l d rely o n s t e a m c r a c k i n g t o p r o d u c e fuels a n d c h e m i c a l s . ACKNOWLEDGEMENTS T h e assistance of Mr. W . E d w a r d s a n d Mr. T. M a t t o c k s in p e r f o r m i n g t h e t u b u l a r p l u g - f l o w reactor e x p e r i m e n t s is g r a t e f u l l y a c k n o w l e d g e d . The m e a s u r e m e n t of t h e heat of pyrolysis of cellulose at six bars w a s m a d e by Dr. P. Leparlouer w h i l e t h e a u t h o r v i s i t e d S e t a r a m Laboratory in L y o n . France. T h e assistance of Setaram in t h i s research is also g r a t e f u l l y a c k n o w l e d g e d . This project w a s f i n a n c e d by t h e U.S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y under Grant No. R 8 0 4 8 3 6 0 1 0 .

16. ANTAL Steam Gasification of Biomass

333

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REFERENCES

1.

Antal, M.J. "Symposium Papers", Energy From Biomass and Wastes, Symposium sponsored by the Institute of Gas Technology, Washington, D.C., August 1978; Institute of Gas Technology: Chicago, 1978.

2.

Rensfelt, E.; Blomkvist, G.; Ekstrom, C.; Engstrom, S.; Espenas, B.G.; Liinanki, L. "Symposium Papers", Energy From Biomass and Wastes, Symposium sponsored by the Institute of Gas Technology, Washington, D.C., August 1978; Institute of Gas Technology: Chicago, 1978.

3.

Lewellen, P.C.; Peters, W.A.; Howard, J.B. "Cellulose Pyrolysis Kinetics and Char Formation Mechanism", 16th International Symposium on Combustion, Cambridge, Mass., 1976.

4.

Mackay, G.D.M. Canada Department of Forestry and Rural Development, Publ. 1201, Ottawa, Ont., 1967.

5. Roberts, A.F. Combust. Flame 1970, 14, 261. 6.

Welker, J.R. J. Fire Flammability 1970, 1, 12.

7.

Beall, F.C.; Eickner, H.W. U.S. Forest Service, 1970, FPL-130.

8. Diebold, J; Smith, G. Naval Weapons Center, NWC Technical Publication 6022, April 1978. 9.

Hatch, L.F.; Matar, S. Hydrocarbon Process. 1978, March, 129-139, Part 8.

10.

Hatch, L.F.; Matar, S. Hydrocarbon Process. 1978, March, 129-139, Part 9.

11.

Feber, R.C.; Antal, M.J. U.S. Environmental Protection Agency, Report EPA-600/2-77-147, Cincinnati, Ohio, 1977.

12.

Appell, H.R.; Pantages, P. in "Thermal Uses and Properties of Carbohydrates and Lignin", Shafizadeh, F.; Sarkanen, K.; Tillman, D., Eds. Academic Press: New York, 1976.

13.

Antal, M.J.; Friedman, H.L.; Rogers, F.E. "Kinetic Rates of Cellulose Pyrolysis in Nitrogen and Steam", Eastern Section, The Combustion Institute Fall Meeting, Hartford, Conn., 1977.

334 14.

BIOMASS AS A NONFOSSIL FUEL SOURCE

Antal, M.J.; Friedman, H.L.; Rogers, F.E. Combust. Sci. Technol., in press.

15. Reed, T.B.; Antal, M.J. "Preprints", 176th National Meeting of the American Chemical Society, Miami, Fla., 1978. 16.

Antal, M.J.; Reed, T.B. "Preprints", 176th National Meeting of the American Chemical Society, Miami, Fla., 1978.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch016

17. Mattocks, T. M.S.E. Thesis, Princeton University, Princeton, N.J., 1979. 18. Antal, M.J.; Edwards, W.E.; Friedman, H.L.; Rogers, F.E. "A Study of the Steam Gasification of Organic Wastes", Final Progress Report to the U.S. Environmental Protection Agency, Princeton University, 1979. 19.

Levenspiel, O. "Chemical Reaction Engineering"; J. Wiley and Sons: New York, 1972.

RECEIVED JULY 28,

1980.

17 Gasification of Oak Sawdust, Mesquite, Corn Stover, and Cotton Gin Trash in a Countercurrent Fluidized Bed Pilot Reactor STEVEN R. BECK, MAW JONG WANG, and JAMES A. HIGHTOWER Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

Texas Tech University, Box 4679, Lubbock, T X 79409

Research on pyrolyzing manure and wood using a pilot scale, countercurrent, fluidized bed reactor to produce ammonia synthesis gas and hydrocarbons has been conducted by the Department of Chemical Engineering at Texas Tech University since 1970. Results have been encouraging and justify further study. This paper reports the results of a comparison of the gasification of various biomass residues in the Synthesis Gas From Manure (SGFM) pilot plant. The residues evaluated include oak sawdust, mesquite, corn stover, and cotton gin trash. The SGFM process is based on a countercurrent, fluidized bed reactor. In this system, biomass is fed to the top of the reactor. As a result, the fresh feed is partially dried by direct contact with hot product gas prior to entering the reaction zone. This process has been described in detail by various researchers (1-4). In t h e SGFM reactor, fresh feed enters t h e pyrolysis zone o f t h e reactor prior t o e n c o u n t e r i n g a n o x i d i z i n g a t m o s p h e r e . A s a result, s i g n i f i c a n t a m o u n t s o f o l e f i n i c c o m p o u n d s are f o r m e d a n d exit t h e reactor before t h e y c a n d e c o m p o s e . This also results in t h e f o r m a t i o n o f tars w h i c h present p r o b l e m s in d o w n s t r e a m p r o c e s s i n g .

0097-6156/81/0144-0335$05.00/0 © 1981 American Chemical Society

336

BIOMASS AS A NONFOSSIL F U E L SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

S G F M PILOT P L A N T T h e SGFM pilot plant w a s d e s i g n e d a n d c o n s t r u c t e d in 1 9 7 5 t o test t h e SGFM process in a c o n t i n u o u s s y s t e m a n d p r o v i d e data for d e s i g n a n d e v a l u a t i o n of a c o m m e r c i a l facility. A s c h e m a t i c d r a w i n g of t h e SGFM pilot p l a n t is s h o w n in Figure I. T h e heart of t h e pilot p l a n t is t h e reactor itself. The reactor is 15.2 c m in t h e l o w e r 1.5 m a n d 20.3 m in t h e u p p e r 1 m or d i s e n g a g i n g zone. T h e solids are f e d to t h e t o p of t h e reactor t h r o u g h a s c r e w feeder, w h i c h c o n t r o l s t h e feed rate, a n d fall by g r a v i t y i n t o t h e reactor itself. T h e a i r - s t e a m m i x t u r e w h i c h enters t h e b o t t o m of t h e reactor is p r e h e a t e d in an 8 - m l e n g t h of t u b i n g t h a t serves as a resistance heater. T h e c h a r is r e m o v e d f r o m t h e reactor t h r o u g h a c e n t e r p o r t o p e n i n g in t h e b o t t o m d i s t r i b u t o r plate. A h y d r a u l i c r a m is used t o p r e v e n t a n y b r i d g i n g of t h e c h a r in t h e d i s c h a r g e line. T h e gases exit t h e t o p of t h e reactor a n d pass into a c y c l o n e t h a t is o p e r a t e d at a p p r o x i m a t e l y 3 5 0 ° C . T h e c y c l o n e is heated to p r e v e n t c o n d e n s a t i o n of a n y of t h e reaction p r o d u c t s a n d a d e q u a t e l y r e m o v e s m o s t of t h e e n t r a i n e d solids. T h e gases l e a v i n g t h e c y c l o n e t h e n pass t h r o u g h a 3-stage i m p i n g e r s e q u e n c e w h i c h is o p e r a t e d at a b o u t 1 1 0 ° — 1 4 0 C . This serves t o c o n d e n s e t h e tar b u t m a i n t a i n s t h e w a t e r in a v a p o r state. F o l l o w i n g t h e i m p i n g e r s . t h e w a t e r is c o n d e n s e d in a d o u b l e - p i p e heat e x c h a n g e r a n d c o l l e c t e d in t h e d o w n s t r e a m i m p i n g e r s e c t i o n . T h e p r o d u c t gases are t h e n passed t h r o u g h a t u r b i n e m e t e r for f l o w rate m e a s u r e m e n t s a n d v e n t e d t o t h e a t m o s p h e r e . U s i n g this a r r a n g e m e n t , g o o d material b a l a n c e data has b e e n o b t a i n e d , b u t there are s o m e p r o b l e m s in o p e r a t i o n of t h e pilot plant. W i t h t h e s c r e w feeder, very f e w p r o b l e m s have been e n c o u n t e r e d in f e e d i n g t h e biomass. T h e tar c o l l e c t i o n s y s t e m is c u r r e n t l y t h e m a j o r p r o b l e m . Tar p r o d u c e d f r o m biomass feedstocks is a very v i s c o u s material a n d t e n d s t o c o n d e n s e o n all p i p i n g a n d also p l u g t h e i m p i n g e r s . For t h i s reason, t h e errors t h a t are a p p a r e n t in material balance are p r i m a r i l y d u e t o t h e inability t o c o l l e c t a n d measure all t h e tar p r o d u c e d . T h i s is a relatively m i n o r error because of t h e f a c t t h a t the tar p r o d u c t is only a b o u t 5% of t h e raw feedstock weight. e

FEEDSTOCKS T h e c o m stover used in t h i s s t u d y w a s a c q u i r e d f r o m area f a r m s in L u b b o c k C o u n t y , a n d w a s g r o u n d in a h a m m e r m i l l s u c h t h a t it w o u l d pass a 1 / 4 - i n c h screen. Because of t h e f i b r o u s nature of t h e c o r n stover, all of t h e particles w e r e not smaller t h a n 1/4 i n c h . S o m e of t h e particles w e r e greater t h a n 1 i n c h l o n g b u t o n l y a b o u t 1/16 i n c h in diameter. Figure II gives t h e particle size d i s t r i b u t i o n of t h e g r o u n d c o r n stover.

BECK ET AL.

Countercurrent Fluidized Bed Reactor

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

17.

Figure 1. Flowsheet of SGFM pilot plant

337

338

BIOMASS AS A NONFOSSIL F U E L SOURCE

T h e oak s a w d u s t used in t h i s s t u d y w a s o b t a i n e d f r o m M i s s o u r i . Figure III gives t h e particle size d i s t r i b u t i o n of t h e s a w d u s t . C o t t o n g i n trash w a s o b t a i n e d in pelletized f o r m f r o m A m e r i c a n C o t t o n G r o w e r s , C r o s b y t o n Gin Division in C r o s b y t o n , Texas. T h e g i n trash w a s pelletized w i t h n o b i n d e r a d d e d . Figure IV g i v e s t h e p a r t i c l e size d i s t r i b u t i o n of t h e c o t t o n g i n t r a s h .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

T h e m e s q u i t e used in t h i s s t u d y w a s o b t a i n e d f r o m L u b b o c k C o u n t y . It w a s g r o u n d in a h a m m e r m i l l a n d t h e n pulverized in a m i c r o - p u l v e r i z e r s u c h t h a t it w o u l d pass a 2 - m i l l i m e t e r screen. Figure V gives t h e particle size d i s t r i b u t i o n of t h e m e s q u i t e . T h e m o i s t u r e a n d ash c o n t e n t of t h e f e e d s t o c k s are s h o w n in T a b l e I a l o n g w i t h t h e h e a t i n g value of each material. T a b l e I. F E E D S T O C K P R O P E R T I E S

Feedstock Corn Stover Oak S a w d u s t C o t t o n Gin Trash Mesquite

Moisture Content, %

Ash Content, %

High Heating Value, as-received, Btu/lb

6.1 35 11.2 6.9

5.0 0.9 7.9 5.6

6,550 4,842 6,886 10.195

DISCUSSION Gas Yield T h e o b j e c t i v e of t h i s s t u d y w a s to d e t e r m i n e t h e t o t a l gas yield a n d gas c o m p o s i t i o n f r o m t h e v a r i o u s f e e d s t o c k s as a f u n c t i o n of reactor t e m p e r a t u r e , air-to-feed ratio, a n d s t e a m - t o - f e e d ratio. The gas c o m p o n e n t s of greatest interest are h y d r o g e n , c a r b o n m o n o x i d e , m e t h a n e , a n d e t h y l e n e . These c o m p o n e n t s c o n t r i b u t e n o t o n l y t o t h e gas h e a t i n g value, b u t also t o t h e value of t h e gas as c h e m i c a l synthesis feedstock. T h e gas yields as a f u n c t i o n of average reactor t e m p e r a t u r e are s h o w n in Figure VI for d r y s a w d u s t , green s a w d u s t , c o r n stover, c o t t o n g i n trash a n d m e s q u i t e . For c o m p a r i s o n , t h e gas yields f r o m c a t t l e f e e d l o t m a n u r e are also s h o w n in Figure V I (2). T h e gas y i e l d s for all t h e f e e d s t o c k s are greater t h a n for m a n u r e . It is a s s u m e d t h a t m u c h of t h e h e m i c e l l u l o s e a n d cellulose fed t o t h e c a t t l e w a s c o n s u m e d d u r i n g d i g e s t i o n . A s a result, t h e m a n u r e is l o w in cellulose and h i g h in l i g n i n , p r o t e i n , and fat. T h e biomass residues e v a l u a t e d

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

BECK ET AL.

Countercurrent Fluidized Bed Reactor

.02

.04

.06

.08

.10

.12

SCREEN OPENING, in. Figure 2. Particle size distribution of corn stover

.02

. 04

.06

.08

.10

.12

SCREEN OPENING, in. Figure 3. Particle size distribution of oak sawdust

.14

340

BIOMASS AS A NONFOSSIL F U E L SOURCE

ι

1

1

1

1

Γ

60 40 40

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

30 20 10 I Γ-ΠΓΓΊ

3

.02

Γ-ΓΊ

.04

. I

.06

II

.08

I

.

.10

.12

.14

SCREEN OPENING, in. Figure 4.

Particle size distribution of cotton gin trash

π

.02

1

1

r

.04

.06

.06

.10

.12

SCREEN OPENING, in. Figure 5.

Particle size distribution of mesquite

.14

17.

BECK ET A L .

Countercurrent Fluidized Bed Reactor

341

c o n t a i n relatively h i g h a m o u n t s of h e m i c e l l u l o s e a n d cellulose. Previous studies reported b y S t a m m (5) s h o w t h a t h e m i c e l l u l o s e a n d cellulose gasify at a m u c h higher rate t h a n does lignin. Therefore, u n a l t e r e d plant matter, w h i c h is h i g h in cellulose, s h o u l d p r o d u c e m o r e gas t h a n cattle m a n u r e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

w h i c h is l o w in cellulose. T h e f o u r runs w i t h g r e e n s a w d u s t are very i n t e r e s t i n g . T w o runs, 5 6 a n d 5 7 , w e r e m a d e w i t h n o s t e a m i n j e c t e d into t h e reactor. This resulted in a higher gas yield t h a n runs 5 4 a n d 5 5 w h i c h w e r e m a d e w i t h s t e a m i n j e c t i o n . It is felt t h a t t h e s t e a m served as a heat sink and r e d u c e d t h e reaction t e m p e r a t u r e of t h e particles. These results also indicate t h a t t h e s t e a m - c h a r reaction d i d n o t occur. Previous studies (6,_7) i n d i c a t e t h a t t h e reaction t e m p e r a t u r e m u s t e x c e e d 8 6 0 ° C in order f o r t h e s t e a m - c h a r reaction t o be significant. This c o n c l u s i o n is also s u p p o r t e d b y t h e gas c o m p o s i t i o n w h i c h w i l l be d i s c u s s e d later. T h e gas yields f o r corn stover are very similar t o t h o s e o b t a i n e d f o r t h e d r y s a w d u s t . Corn stover poses s o m e very d i f f i c u l t o p e r a t i n g p r o b l e m s however. These w i l l be d i s c u s s e d in t h e s e c t i o n o n o p e r a t i n g d i f f i c u l t i e s . The pelleted c o t t o n g i n trash b e h a v e d s o m e w h a t d i f f e r e n t l y t h a n t h e o t h e r feedstocks. The t o t a l gas yield w a s n o t greatly different, b u t it appeared t h a t t h e s t e a m - c h a r reaction d i d occur. T h e g i n trash w a s c o m p o s e d of s o m e large pellets a n d a s i g n i f i c a n t f r a c t i o n of fines a n d broken pellets. This greatly a f f e c t e d f l u i d i z a t i o n in t h e reactor. T h e w h o l e pellets p r o b a b l y d i d not fluidize u n t i l t h e y w e r e m o s t l y a s h . C o n s e q u e n t l y , t h e y w e r e able t o lay o n t h e d i s t r i b u t o r and u n d e r g o s t e a m g a s i f i c a t i o n at l o w t e m p e r a t u r e ( < 8 0 0 ° C ) a n d long residence t i m e . T h e c h a r e x i t i n g t h e b o t t o m of t h e reactor w a s light grey w h i l e t h e c y c l o n e fines w e r e black. W i t h all o t h e r feedstocks, b o t h t h e b o t t o m char a n d c y c l o n e fines w e r e black. T h e ash c o n t e n t of t h e char a n d c y c l o n e fines s u p p o r t s t h e c o n c l u s i o n t h a t t h e g i n trash char u n d e r w e n t s t e a m g a s i f i c a t i o n . Table II s h o w s t h e ash c o n t e n t f r o m t h e v a r i o u s runs. T h e h i g h ash c o n t e n t of t h e c h a r f r o m c o t t o n g i n trash indicates a h i g h degree of c o n v e r s i o n t o gas. The c o r n stover also s h o w e d a h i g h level of c o n v e r s i o n . This is p r o b a b l y d u e t o t h e very small d i a m e t e r of t h e particles w h i c h a l l o w s f o r rapid transfer. This results in h i g h g a s i f i c a t i o n rates.

heat

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BIOMASS AS A NONFOSSIL F U E L SOURCE

T a b l e II. A S H C O N T E N T OF C H A R A N D C Y C L O N E FINES Run No.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

51 60 71 72

Feedstock

73 74

Corn Corn Corn Corn Corn Corn

76 77

Mesquite Mesquite

78 79 67 68 69

Mesquite Mesquite C o t t o n Gin C o t t o n Gin C o t t o n Gin C o t t o n Gin

Trash Trash Trash Trash

Green Green Green Green

Sawdust Sawdust Sawdust Sawdust

70 54 55 56 57 64 65 *

Ash Content, %

Raw Stover Stover Stover Stover Stover Stover

Oak Oak Oak Oak

Green Oak S a w d u s t Green Oak S a w d u s t

Feed

Char

C y c l o n e Fines

5.0 5.0 5.0 5.0 5.0 5.0 5.6

88.8 89.5 69.4

57.8 51.7 56.7

46.6 70.5 86.5 19.6 17.3 24.0

72.8 46.1 28.9 29.9 31.4

18.6 67.7

20.5 31.9 28.7

5.6 5.6 5.6 7.9 7.9 7.9 7.9 0.9 0.9 0.9 0.9 0.9 0.9

82.8 84.3 90.3 11.1 9.0 8.7 2.2

·

34.1

39.1 29.3 29.8 28.4 31.6 19.6 5.6 7.1

No c h a r w a s o b t a i n e d .

A d d i t i o n a l e v i d e n c e i n d i c a t i n g lack of f l u i d i z a t i o n of t h e large g i n t r a s h pellets a p p e a r e d w h e n t h e b o t t o m f l a n g e of t h e reactor w a s r e m o v e d . W i t h m a n u r e , s a w d u s t , m e s q u i t e . a n d c o r n stover, t h e reactor w a s e m p t y at t h e c o n c l u s i o n of each r u n . W i t h pelleted c o t t o n g i n trash, a b u i l d u p of ash w a s f o u n d o n t h e d i s t r i b u t o r plate. This m e a n s t h a t t h e pelleted g i n trash c o u l d not be used in t h e SGFM reactor o n a c o n t i n u o u s basis. Gas C o m p o s i t i o n T h e yields of h y d r o g e n , c a r b o n m o n o x i d e a n d e t h y l e n e are i m p o r t a n t w h e n c o n s i d e r i n g use of biomass as a c h e m i c a l feedstock. H y d r o g e n is a v a l u a b l e p r o d u c t for c h e m i c a l synthesis a n d u p g r a d i n g l o w q u a l i t y fuels s u c h as coal a n d heavy oils. S h o w n in Figure VII is t h e u l t i m a t e h y d r o g e n yield f r o m t h e various feedstocks. This is c a l c u l a t e d as the s u m of t h e h y d r o g e n y i e l d a n d c a r b o n

17.

BECK E T AL.

Countercurrent Fluidized Bed Reactor

1 Ο Δ V • Ο

1.8

1

1

1.5

X Δ

1.2 Δ

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

r

Green Oak Sawdust Dry Oak Sawdust Corn Stover Cotton Gin Trash Mesquite

Δ

Δ

600

00

Δ

Δ

ο •

650

V

700

•

750

800

A V E R A G E R E A C T O R T E M P E R A T U R E , °C

Figure 6.

Ο Δ

1.0

• Ο

Total dry gas yield

1 Τ ι Green Oak Sawdust Dry Oak Sawdust Corn Stover £ Cotton Gin Trash Mesquite Δ Δ

Δ _

-

•

•8h-

•

ΔΟ

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BIOMASS AS A NONFOSSIL F U E L SOURCE

m o n o x i d e y i e l d . It is a s s u m e d t h a t all of t h e CO c a n be s h i f t e d to H a n d C 0 The c o t t o n g i n trash a n d oak s a w d u s t appear t o p r o d u c e t h e m o s t h y d r o g e n . In t h e case of g i n t r a s h , this is due to t h e s t e a m - c h a r reaction. For oak s a w d u s t , it is probably d u e to higher reactivity of t h e material. 2

2

A u n i q u e aspect of t h e SGFM reactor is t h a t e t h y l e n e is present in t h e gas at

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

s i g n i f i c a n t c o n c e n t r a t i o n s . Figure VIII s h o w s t h e e t h y l e n e yield o b t a i n e d f r o m t h e various feedstocks. T h e e t h y l e n e y i e l d f r o m all t h e feedstocks s t u d i e d is l o w e r t h a n for c a t t l e m a n u r e . In all cases, t h e e t h y l e n e c o n t e n t is b e l o w t h e l i m i t w h e r e recovery is e c o n o m i c . By o p e r a t i n g at h i g h e r t e m p e r a t u r e s a n d gas v e l o c i t y , it s h o u l d be possible to increase t h e y i e l d of e t h y l e n e . Gas Heating Value If t h e gas is t o be used for f u e l , t h e h e a t i n g value of t h e gas is c r i t i c a l . In Figure IX. t h e h i g h e r h e a t i n g v a l u e (HHV) o f t h e r a w gas is s h o w n as a f u n c t i o n of reactor t e m p e r a t u r e . In all cases, t h e gas has an HHV b e t w e e n 2 0 0 a n d 4 0 0 Btu/SCF. Feedstocks, s u c h as oak s a w d u s t , w h i c h p r o d u c e m o r e h y d r o c a r b o n gases, have a h i g h e r HHV. Thermal Conversion A relative measure of t h e t h e r m a l e f f i c i e n c y of t h e process is s h o w n in Figure X. T h i s s h o w s t h e t o t a l h e a t i n g value of t h e gas as a p e r c e n t a g e of t h e t o t a l h e a t i n g v a l u e of t h e f e e d . T h e relative values d e p e n d p r i m a r i l y on gas h e a t i n g value a n d t o t a l gas y i e l d . Comparison of Feedstocks Of t h e f o u r f e e d s t o c k s used in t h i s s t u d y , oak s a w d u s t p r o v e d t o be t h e easiest to w o r k w i t h as n o b r i d g i n g o c c u r r e d w i t h i n t h e feed h o p p e r a n d no p l u g g i n g o c c u r r e d b e t w e e n t h e s c r e w feeder a n d t h e reactor inlet. The p r o b l e m of tar removal a n d b u i l d u p in t h e i m p i n g e r s a n d d o w n s t r e a m lines w a s no greater t h a n t h a t c r e a t e d by t h e o t h e r feedstocks. M e s q u i t e a n d c o r n stover w e r e t h e s e c o n d a n d t h i r d m o s t desirable f e e d s t o c k s in t e r m s of ease of h a n d l i n g . M e s q u i t e required a d d i t i o n a l p r e p a r a t i o n in t h a t it had t o be pulverized t o p r e v e n t b r i d g i n g w i t h i n t h e feed h o p p e r a n d c l o g g i n g b e t w e e n t h e s c r e w feeder a n d t h e reactor inlet. Tar r e m o v a l p r o b l e m s w e r e c o m p a r a b l e t o t h o s e of oak s a w d u s t . Feeding d i f f i c u l t i e s w e r e e n c o u n t e r e d w i t h c o m stover, as it t e n d e d t o b r i d g e w i t h i n t h e feeder a n d t h e reactor inlet. Carry-over of fines in t h e p r o d u c t gas f r o m c o r n stover increased tar b u i l d u p in t h e i m p i n g e r s a n d d o w n s t r e a m lines. It is

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Countercurrent Fluidized Bed Reactor

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

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BIOMASS AS A NONF OSSIL F U E L SOURCE

t h e a u t h o r s ' o p i n i o n t h a t d i f f i c u l t i e s e n c o u n t e r e d in t h e use of c o r n stover c o u l d be e l i m i n a t e d if t h e f e e d s t o c k w a s pulverized t o r e d u c e t h e l e n g t h - t o d i a m e t e r ratio of t h e particles a n d an electrostatic p r e c i p i t a t o r w a s used t o knock o u t all solid fines in t h e p r o d u c t gas s t r e a m as it left t h e reactor.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

C o t t o n g i n trash w a s t h e least favorable of t h e f e e d s t o c k s in t e r m s of h a n d l i n g . T h e f o r m a t i o n of clinkers w i t h i n t h e reactor is a serious p r o b l e m , o n e w h i c h c a n n o t be s o l v e d in t h e present s y s t e m . T h e b o t t o m f l a n g e o f t h e reactor m u s t be t a k e n off in order t o remove clinkers f r o m t h e reactor. This s i t u a t i o n is n o t c o n d u c i v e t o a n y c o n t i n u o u s o p e r a t i o n process. P r o d u c t gas yields for t h e f o u r f e e d s t o c k s all increased as average reactor t e m p e r a t u r e increased. A h i g h air-to-feed ratio w a s f o u n d t o increase p r o d u c t gas y i e l d f o r oak s a w d u s t , corn stover, t h e v a l u e b e i n g 1.5 / / g D A F f e e d , a n d t h e l o w e s t f r o m m e s q u i t e , t h e v a l u e b e i n g 0.51 / / g DAF feed. T h e p e r c e n t a g e of corn stover a n d c o t t o n g i n trash c o n v e r t e d t o p r o d u c t gas w a s h i g h e r t h a n t h a t of oak s a w d u s t a n d m e s q u i t e . A s h c o n t e n t s of c h a r a n d c y c l o n e f i n e s f o r corn stover w e r e b e t w e e n 4 6 a n d 8 9 % a n d b e t w e e n 4 6 a n d 7 3 % , respectively, w h i l e t h o s e for c o t t o n g i n trash w e r e b e t w e e n 6 7 a n d 9 0 % a n d b e t w e e n 2 8 a n d 3 9 % . respectively. A s h c o n t e n t s of c h a r a n d c y c l o n e fines f r o m m e s q u i t e ranged f r o m 17.3 t o 2 4 % a n d f r o m 2 0 t o 3 4 % . respectively, a n d ash c o n t e n t s of c y c l o n e fines f r o m oak s a w d u s t w e r e 5.6 a n d 7 . 1 % . T h e d i f f e r e n c e in p e r c e n t a g e c o n v e r s i o n is d u e t o e i t h e r a d i f f e r e n c e in g a s i f i c a t i o n rates of t h e feedstocks, or a d i f f e r e n c e in residence t i m e . It is believed t h a t t h e h i g h p e r c e n t a g e c o n v e r s i o n of c o r n stover w a s c a u s e d by a h i g h pyrolysis a n d g a s i f i c a t i o n rate. Corn stover feed rates w e r e l o w , b u t h i g h in t e r m s of v o l u m e of feed because of t h e l o w bulk d e n s i t y of t h e feedstock. This s i t u a t i o n a l l o w e d for a greater heat transfer area per p o u n d of feed, t h e r e b y increasing c o n v e r s i o n rate. A s m e n t i o n e d previously, c h a r f r o m c o t t o n g i n trash c o l l e c t e d in t h e b o t t o m of t h e reactor, g i v i n g t h e f e e d s t o c k a l o n g residence t i m e . The effect of average reactor t e m p e r a t u r e on p r o d u c t gas yield f r o m c o t t o n g i n trash is n o t as p r o n o u n c e d as t h a t for t h e o t h e r feedstocks. Char b u i l d u p in t h e b o t t o m of t h e reactor creates this effect, as a l o n g residence t i m e a l l o w s f o r increased heat transfer a n d as a result, increased c o n v e r s i o n of t h e f e e d s t o c k t o p r o d u c t gas. L o w p r o d u c t gas yields f r o m m e s q u i t e at l o w t e m p e r a t u r e s are p r o b a b l y a result of a l o w g a s i f i c a t i o n rate. A s t e m p e r a t u r e is increased, p r o d u c t gas rate increases sharply. T h e sharp rise in p r o d u c t gas rate at elevated t e m p e r a t u r e is p r o b a b l y d u e t o t h e breakup of lignin w h i c h w a s not c o n v e r t e d t o p r o d u c t gas at l o w e r t e m p e r a t u r e s .

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

Product gas yields f r o m oak s a w d u s t w e r e higher t h a n those f r o m c o r n stover a n d m e s q u i t e a n d a p p r o x i m a t e l y t h e same as t h o s e f r o m c o t t o n g i n trash at t h e s a m e average reactor t e m p e r a t u r e s . A l t h o u g h gas yield is h i g h , a s h c o n t e n t o f c y c l o n e fines is relatively l o w in c o m p a r i s o n t o t h e o t h e r feedstocks. This indicates t h a t h i g h gas yields are p r o b a b l y a result o f t h e c o m p o s i t i o n o f t h e oak s a w d u s t . A s h c o n t e n t w o u l d have been greater if t h e h i g h p r o d u c t gas yield h a d been caused b y a long residence t i m e or h i g h g a s i f i c a t i o n a n d pyrolysis rates. It is p o s t u l a t e d t h a t at increased heat transfer rates, (i.e., elevated t e m p e r a t u r e s ) , p r o d u c t gas yields f r o m oak s a w d u s t a n d m e s q u i t e w o u l d c o n t i n u e t o increase w h i l e p r o d u c t g a s yields f r o m c o t t o n g i n trash a n d c o r n stover w i l l level o f f a n d remain c o n s t a n t . Increased heat transfer c o u l d be a c c o m p l i s h e d by a longer residence t i m e in t h e reactor, higher t e m p e r a t u r e s o r smaller particles. H o w e v e r , particle size m u s t be large e n o u g h t o p r e v e n t e n t r a i n m e n t . If t h e reactor w a s o p e r a t e d in t h e t e m p e r a t u r e range c o v e r e d in this s t u d y , char a n d c y c l o n e fines f r o m m e s q u i t e a n d oak s a w d u s t c o u l d b e r e c y c l e d , increasing t o t a l gas y i e l d per p o u n d of dry, ash-free feed. Very little a d d i t i o n a l gas c o u l d be o b t a i n e d w i t h t h e recycle of char a n d c y c l o n e fines f r o m c o r n stover and c o t t o n g i n trash. A s e m i q u a n t i t a t i v e rating s y s t e m f o r t h e various feedstocks w a s d e v e l o p e d . This w a s based o n o p e r a t i n g c o n s i d e r a t i o n s a n d p r o d u c t yields. This w i l l serve as a g u i d e l i n e f o r f u t u r e w o r k . Table III presents a w e i g h t e d c o m p a r i s o n of t h e four feedstocks used in this study. T a b l e III. W e i g h t e d C o m p a r i s o n o f Corn S t o v e r , O a k S a w d u s t Cotton Qin Trash, and Mesquite A 1. Corn Stover 2. Oak S a w d u s t 3. C o t t o n Gin Trash 4. M e s q u i t e A Β C Ε F

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch017

T h e availability a n d price of t h e f e e d s t o c k s is a major f a c t o r in d e t e r m i n i n g t h e feasibility of a p a r t i c u l a r feedstock. Values are not presented because t h e y w i l l vary d e p e n d i n g o n l o c a t i o n . O p e r a b i l i t y is a major c o n c e r n a n d is t h e r e f o r e w e i g h t e d heavily. Oak s a w d u s t is t h e best f e e d s t o c k as t o o p e r a b i l i t y because it feeds easily a n d requires very little t r e a t m e n t prior t o f e e d i n g . M e s q u i t e is rated l o w e r t h a n oak s a w d u s t because it m u s t be pulverized before f e e d i n g , w h i l e corn stover is rated even l o w e r because it m u s t be g r o u n d a n d has a t e n d e n c y t o p l u g a n d b r i d g e w i t h i n t h e hopper. Fine particles f r o m c o r n stover are also b l o w n o u t of t h e reactor because of its l o w bulk d e n s i t y , c a u s i n g p l u g g i n g in d o w n s t r e a m lines. C o t t o n g i n t r a s h is rated at zero because of c l i n k e r f o r m a t i o n w i t h i n t h e reactor. T h i s w i l l not a l l o w c o n t i n u o u s o p e r a t i o n in a s y s t e m s u c h as t h e o n e used in t h i s s t u d y . P r o d u c t gas y i e l d , t o t a l h y d r o c a r b o n y i e l d , a n d u l t i m a t e h y d r o g e n y i e l d are rated o n a scale of 1 t o 4 because d i f f e r e n c e s b e t w e e n f e e d s t o c k s are not great e n o u g h t o w a r r a n t a large d e v i a t i o n in values. Gas q u a l i t y is c o n s i d e r e d t o be of more i m p o r t a n c e t h a n C. D. a n d Ε a n d is t h e r e f o r e rated o n a scale f r o m 1 to 6. It is c o n s i d e r e d m o r e i m p o r t a n t because a h i g h e r gas q u a l i t y w i l l l o w e r gas s h i p p i n g costs. T h e calorific value of t h e gas per p o u n d of feed a n d t h e p e r c e n t a g e c o n v e r s i o n of r a w feed h e a t i n g value t o gas h e a t i n g value are b o t h of m a j o r i m p o r t a n c e a n d are rated o n a scale f r o m 1 t o 10. T h e calorific v a l u e of gas p r o d u c e d f r o m m e s q u i t e is l o w e r t h a n o t h e r f e e d s t o c k s at l o w t e m p e r a t u r e s , b u t increases t o h i g h values at h i g h t e m p e r a t u r e s . M e s q u i t e w a s g i v e n a h i g h rating because t h e p o t e n t i a l for h i g h e r yields of e n e r g y per p o u n d of feed at elevated t e m p e r a t u r e s exists. T h e p e r c e n t a g e c o n v e r s i o n of e n e r g y s t o r e d in t h e feed to e n e r g y in t h e gas is rated heavily because l o w p e r c e n t a g e c o n v e r s i o n s m i g h t i n d i c a t e t h a t h i g h e r e n e r g y yields c o u l d be o b t a i n e d in an a l t e r n a t e process. T h e p r a c t i c a l i t y of f l u i d i z e d bed g a s i f i c a t i o n is greatly r e d u c e d if a h i g h e r e n e r g y yield can be o b t a i n e d f r o m s o m e o t h e r process. SUMMARY T h e Synthesis Gas From M a n u r e (SGFM) process w a s d e s i g n e d t o c o n v e r t c a t t l e feed lot m a n u r e t o a m m o n i a synthesis gas. C u r r e n t w o r k is a i m e d at u s i n g a n y b i o m a s s f e e d s t o c k t o p r o d u c e e i t h e r m e d i u m - B t u gas or c h e m i c a l feedstocks. This paper presents a c o m p a r i s o n of t h e e x p e r i m e n t a l results c o m p i l e d o n g a s i f i c a t i o n of oak s a w d u s t , c o r n stover, m e s q u i t e . a n d c o t t o n g i n trash in t h e SGFM pilot plant. A w e i g h t e d c o m p a r i s o n of t h e p r o d u c t gas. h y d r o c a r b o n , a n d h y d r o g e n y i e l d s , gas q u a l i t y , calorific value of p r o d u c t gas. p e r c e n t a g e c o n v e r s i o n of raw feed h e a t i n g value t o gas h e a t i n g value, a n d o p e r a b i l i t y of each feed i n d i c a t e d t h a t oak s a w d u s t w a s t h e best feedstock.

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R EF E RE NCE S

1.

Beck, S. R. 3rd Annual Biomass Energy Systems Conference, Golden, Colo., June 5-7, 1979.

2.

Beck, S. R.; Huffman, W . J.; Landeene, B. C.; Halligan, J. E. Ind. Eng. Chem., Proc. Des. Dev. 1979 18, 328.

3.

Halligan, J. E.; Herzog, K. L.; Parker, H. W. Ind. Eng. Chem., Proc. Des. Dev. 1975 14 (1), 64-69.

4.

Halligan, J. E.; Sweazy, R. M. 72nd National Meeting of the American Institute of Chemical Engineers, St. Louis, May 21-24, 1972.

5.

Stamm, A. J. Ind. Eng. Chem. 1956 48(3), 413-17.

6.

Garrett, D. E. 70th Annual Meeting of the American Institute of Chemical Engineers, New York, November 16, 1977.

7.

Rensfelt, E.; Blomkuist, G.; Ekstrom, S.; Espenas, B. G.; Liinanki, L. Conference on Energy from Biomass and Wastes Sponsored by the Institute of Gas Technology, Washington, D.C., 1978; Institute of Gas Technology, Chicago, 1978; paper No. 27.

RECEIVED JULY 7,

1980.

18 Thermochemical Gasification of Woody Biomass H. F. FELDMANN, P. S. CHOI, H . N. CONKLE, and S. P. C H A U H A N

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch018

Battelle Columbus Laboratories, 505 King Avenue, Columbus, O H 43201

It is generally agreed that oil and gas supply problems can be partially met by the use of renewable resources such as forest products, agricultural materials, and urban wastes. The main advantage of renewable energy sources other than their renewable nature is that they are clean, i.e., low in sulfur and ash, and are highly reactive and nonagglomerating compared with fossil fuels. Gasification of renewable feedstock offers great potential particularly for retrofit of existing gas and oil-fired industrial boilers which represent about 84 percent of the boilers sold between 1963 and 1975 (1). Gasification can also be used for industrial dryers and furnaces and, on a larger scale, can be coupled in a combined-cycle system for power generation or used for the synthesis of transportation fuels. Although various types of gasification systems have been explored, there is a lack of steady-state data on the effect of various operating parameters including the use of catalysts to improve gasification reactivities, product distribution, and yields. The o b j e c t i v e of t h i s paper is t o present e x p e r i m e n t a l data o n effects of o p e r a t i n g parameters, i n c l u d i n g t h e c a t a l y t i c effects of w o o d ash, c a l c i u m o x i d e , a n d c a l c i u m c a r b o n a t e , o n w o o d g a s i f i c a t i o n in a c o n t i n u o u s reactor. These results w i l l be utilized t o g u i d e o p e r a t i o n o f a m u l t i - s o l i d f l u i d - b e d (MSFB) w o o d g a s i f i c a t i o n process w h i c h is b e i n g d e v e l o p e d by Battelle t o i m p r o v e t h e e c o n o m i c s of p r o d u c i n g a m e d i u m - B t u gas or synthesis gas f r o m w o o d a n d o t h e r b i o m a s s (2).

0097-6156/81/0144-0351$06.25/0 © 1981 American Chemical Society

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BIOMASS AS A NONFOSSIL F U E L SOURCE

E X P E R I M E N T A L S Y S T E M A N D PROCEDURES T h e c a t a l y t i c w o o d g a s i f i c a t i o n e x p e r i m e n t s w e r e carried o u t in a 2.8-inch I.D. pressurized c o n t i n u o u s reactor s y s t e m . T h e e x p e r i m e n t a l s y s t e m is s h o w n

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch018

s c h e m a t i c a l l y in Figure I a n d consists of t h e f o l l o w i n g sections. 1.

Hydrogen and steam feeding,

2. 3.

W o o d feeding, Gasifier,

4. 5.

Char w i t h d r a w a l , Liquid product collection, and

6.

Gas m e t e r i n g a n d analysis.

W o o d pellets are c h a r g e d t o t h e feed h o p p e r a n d t h e n t h e s y s t e m is sealed a n d pressurized w i t h h y d r o g e n or n i t r o g e n . T h e gasifier is t h e n b r o u g h t t o t h e desired r u n t e m p e r a t u r e . A f t e r e s t a b l i s h i n g t h e desired gas f l o w rates, w o o d f e e d i n g is i n i t i a t e d . T h e gasifier is 12 feet in overall h e i g h t w i t h 8 feet w i t h i n t h e heated zone. It operates w i t h t h e f l o w of gas c o u n t e r c u r r e n t t o t h e d o w n w a r d - m o v i n g w o o d . Char is c o n t i n u a l l y r e m o v e d f r o m t h e b o t t o m of t h e gasifier t o m a i n t a i n a c o n s t a n t bed h e i g h t a n d stored in t h e pressurized c h a r receiver. Hot gases e x i t i n g t h e reactor are c o o l e d in a c o n d e n s e r whe>e t h e l i q u i d p r o d u c t s are c o l l e c t e d . A f t e r r e m o v a l of t h e l i q u i d p r o d u c t s , t h e gas is f i l t e r e d , r e d u c e d in pressure, m e t e r e d , a n d f i n a l l y analyzed by a gas c h r o m a t o g r a p h a n d a c o n t i n u o u s m e t h a n e analyzer. DISCUSSION Experimental Results U l t i m a t e a n d p r o x i m a t e analyses of t y p i c a l w o o d feed materials are g i v e n in Table I. Ranges of t h e o p e r a t i n g c o n d i t i o n s are: Feed T y p e : Feed Rate: Gasifier T e m p e r a t u r e : Pressure: Residence T i m e :

W o o d pellets " Ib/hr 1 1 5 0 - 1 6 0 0 °F 1 0 - 2 1 6 psig 3 0 - 1 3 0 m i n (nominal) 4

1

2

S t e a m / W o o d Ratio: 0.10-0.56 l b / l b M A F Feed H y d r o g e n / W o o d Carbon Ratio: 0.24-0.58 I b M / l b M Catalysts: W o o d ash, CaO a n d C a C 0 incorpora t e d i n t o w o o d pellets 3

FELDMAN ET AL.

Gasification of Woody Biomass

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch018

18.

Figure 1. Continuous gasification unit

47.41 5.86 0.11 0.02 0.03 0.66 6.20 39.71

46.78 5.75 0.64 0.14 0.02 0.66 5.64 40.37

79.56 14.14 7897

Volatile Matter. % Fixed Carbon, % Heating Value, Btu/lb 81.13 12.01 8182

Hard, White None

BCL Pellet

Hard, White None

Californie Pellet

Type of Wood Catalyst Ultimate Analysis. % C H Ν S Cl Ash Moisture O (bal)

Item

78.05 12.63 7855

45.96 5.62 0.14 0.05 0.02 2.22 7.10 38.89

Hard. White 1.5% Ash

BCL Pallet

74.57 14.24 7515

44.56 5.60 0.11 0.07 0.02 4.95 6.24 38.45

Hard. White 5%CaO

BCL Pallet

3

74.86 13.07 7275

44.81 5.45 0.08 0.09 0.03 6.08 5.99 37.47

Hard, White 9%CaC0

BCL Pellet

75.98 13.00 7437

45.56 5.62 0.08 0.08 0.01 5.28 5.74 37.63

Hard. White 5% Ash

BCL Pellet

Table I. ANALY8I8 OF RAW AND CATALYZED WOOD FEED MATERIALS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch018

Hard. Mixed None 40.36 4.70 0.22 0.13 0.04 10.46 11.80 39.29 66.74 11.00 6881

37.22 4.68 0.14 0.15 0.03 15.22 9.33 33.23 61.60 13.85 6222

Tenn Pellet

Hard, White 20% Ash

BCL Pellet

FELDMAN ET AL.

Gasification of Woody Biomass

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AD F F AD F AD

4.87

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b

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9.00

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20.00

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2.75

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Key: AD - anaerobic digestion; F - fermentation. 1977 dollars in year 1985. Data source, SRI Detailed Analysis — Regulated Utility Financing. High by-product values and product yields. SNG « Substitute natural gas; IBG - Intermediate-Btu gas.

Cattle manure to I B G Cattle manure to S N G 100.000 head environmental feedlot 10.000 head environmental feedlot Wheat straw to ethanol Sugarcane to ethanol Kelp to SNG Algae to ethanol Wheat straw to IBG (40% conversion)

Route

Conversion" Process

Table II. DETAILED MISSION ANALY8I8 RE8ULT8: LARGE BIOCHEMICAL FACILITIES

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch019

c

b

a

0 0.41 4.17 0.87 5.66

0 0.13 1.10 0.04 1.27

0.21

0.61 3.46

0.04 0.74 0

0 0.40 2.32

0.13

2000

0 0.02 0.68

0

1985

Excludes existing biomass energy products. SNG - Substitute natural gas; IBG - Intermediate-Btu gas; LBG -Low-Btu gas. Assumes 18.3 million Btu/ton of ammonia.

c

b

OPTIMISTIC SCENARIO Gaseous products (SNG. IBG. LBG) Methanol/Ethanol Ammonia Process steam or steam/electric Pyrolytic fuel oils Total Quads

c

b

BASE CASE SCENARIO Gaseous products (SNG. IBG. LBG) Methanol/Ethanol Ammonia Process steam or steam/electric Pyrolytic fuel oils Total Quads

Year

1B

0.83 10.25

0 0.58 8.39

0.45

0.53 5.39

0 0.56 4.01

0.29

2020

Estimated Biomass-Derived Products" 10 Btu

Table III. MARKET PENETRATION - BIOMASS PRODUCTS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch019

394

BIOMASS AS A NONFOSSIL F U E L SOURCE

Mission Ranking

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch019

W e a s s u m e d t h a t a large d e v e l o p m e n t facility w o u l d be desirable t o d e m o n s t r a t e t h e feasibility of each h i g h p o t e n t i a l m i s s i o n a n d t o assure t h e a c h i e v e m e n t of f u t u r e c o m m e r c i a l c o n v e r s i o n operations. Table IV s h o w s a f i g u r e of m e r i t (cost-benefit ratio), c a l c u l a t e d by d i v i d i n g t h e p r o g r a m f u n d i n g r e q u i r e m e n t for e a c h m i s s i o n (based o n t h e cost of a large d e v e l o p m e n t f a c i l i t y o p e r a t i n g for five years) by t h e a n n u a l q u a d p e n e t r a t i o n in 2 0 2 0 . T h e results of t h i s analysis p r o v i d e t h e r a n k i n g of m i s s i o n s s h o w n in Table V. T h e m o d e l o u t p u t s a n d m a r k e t d e m a n d levels are e x t r e m e l y sensitive t o f e e d s t o c k scenario a s s u m p t i o n s * as i n d i c a t e d by t h e d o u b l i n g in p r o d u c t d e m a n d w i t h a c h a n g e f r o m base case t o o p t i m i s t i c scenario (see Table VI). H o w e v e r , s e p a r a t i n g SRI-generated m i s s i o n i n p u t d a t a f r o m d a t a g e n e r a t e d by o t h e r s resulted in o n l y a s l i g h t c h a n g e in m o d e l results (an increase in b i o m a s s f u e l p r o d u c t p e n e t r a t i o n f r o m 10.00 t o 10.25 q u a d s in t h e year 2 0 2 0 a n d a c h a n g e in t o t a l f e e d s t o c k d e m a n d f r o m 13.4 t o 13.6 q u a d s of biomass). A s i n d i c a t e d by t h e ratio of fuel p r o d u c t d e m a n d t o f e e d s t o c k d e m a n d , t h e overall c o n v e r s i o n e f f i c i e n c y p e r c e n t a g e is a b o u t 7 5 p e r c e n t , r e f l e c t i n g t h e s t r o n g i n f l u e n c e of d i r e c t c o m b u s t i o n m i s s i o n p e n e t r a t i o n . SUMMARY Biomass offers a s i g n i f i c a n t p o t e n t i a l for r e d u c i n g n a t i o n a l d e p e n d e n c e on i m p o r t e d fossil fuels t h r o u g h t h e c o n v e r s i o n of a r e n e w a b l e e n e r g y source t o useful l i q u i d a n d gaseous fuels, electric p o w e r , process s t e a m , a n d c h e m i c a l s . Several p r e v i o u s s t u d i e s have i n d i c a t e d t h a t feasible national goals c o u l d be t h e p r o d u c t i o n of a b o u t 5 q u a d r i l l i o n Btu (quads) of e n e r g y by t h e year 2 0 0 0 a n d 10 q u a d s of e n e r g y by t h e year 2 0 2 0 . T h e results of these s t u d i e s indicate t h a t these are realistic a n d a c h i e v a b l e goals p r o v i d e d Federal f u n d i n g levels for b i o m a s s d e v e l o p m e n t are increased a n d Federal i n c e n t i v e s are s u c c e s s f u l l y a p p l i e d t o increase biomass f e e d s t o c k availability. T h e s t u d y s u m m a r i z e d in t h i s paper i n v o l v e d t h e i d e n t i f i c a t i o n of over 1,100 possible missions (specific c o n v e r s i o n routes f r o m b i o m a s s f e e d s t o c k t o useful fuel a n d c h e m i c a l p r o d u c t s t o e n d - u s e markets) prior t o t h e selection of 15 missions for d e t a i l e d analysis.

* As well as other factors such as end use demand projections and foreign oil prices.

Wood Low moisture Wood Low moisture Subtotal

IBG SNG SNG IBG

Steam Steam Steam/electric Steam/electnc

1985 1985 1985 1980

(earlier than) 1975 1975 1975 1975

DetS*

11 14 97 74

94 94 109 109

61 61

78

135 65

170 86 151 116

c

10 13 50 58

59 59 60 60

52 52

111

170 107

96 59 113 15

21 27 147 132 327

153 153 169 169 644

113 113 226

189

305 172 477

266 150 264 131 811

0 15 0.02 002 001 020

1 21 1.01 336 281 839

0 68 0 15 084

0.11

0.11 0.15 026

005 0.47 003 001 0.56

c

• A Missions number 1 through 25 were evaluated by SRI Date estimated to reflect initial mission technical and economic feasibility for modeling purposes Demonstration plant costs assume largest design practicable - 500 to 3.000 dry tons per day of feedstock Source of cost data - Appendix A.

Anaerobic digestion 13 Manure 14 Manure 30 High moisture 39 High moisture Subtotal

9 10 24 25

Direct combustion

Pyrolysis — maximum liquids 18 Wood 19 Low moisture Subtotal Oil and Char Oil and Char

Ammonia LBG

Direct gasification — air blown/staged 31 Wood 42 High moisture Subtotal

Pyrolysis - maximum gas yield 28 Wood

SNG Ammonia IBG IBG

Direct gasification — oxygen blown 26 High moisture 32 High moisture 34 High moisture 35 Low moisture Subtotal

Mission" Feedstock e

0 14 1.35 735 13.20 1.64

0.13 0.15 0.05 006 008

0 17 0.75 027

1 72

2 77 1.15 1 83

532 032 880 13 10 1 45

Estimated Development Program Funding Required (millions of dollars) Development Feedstock Large Demo Total Cost-Benefit Demo Operation Total Quads Pilot Preparation Rato 1ant (B yeers) $ 2020 and Production (S/10

Table IV. RESEARCH AND DEVELOPMENT C08T-BENEFIT RATIO CALCULATIONS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch019

Feedstock

Process

SRI SRI

Anaerobic digestion Pyrolysis (maximum liquid yields)

Manure

Wood or low moisture

IBG

Oil and charcoal

High moisture Wood

High moisture

High moisture

High moisture

LBG SNG

SNG

IBG

IBG

SNG SNG IBG

Wood or high moisture Manure High moisture Low moisture

Ammonia

Gasification staged air/or oxygen blown Anaerobic digestion Anaerobic digestion Gasification (oxygen blown) Gasification (air blown) Pyrolysis (maximum gas yield) Gasification (oxygen blown) Gasification (oxygen blown) Anaerobic digestion

Others

Others

Others

Others Others

SRI SRI SRI

SRI

SRI

Combustion

Wood or low moisture

Steam

ther missions showing penetration (higher cost-benefit ratios)

SRI

Combustion

Wood or low moisture

Evaluated by

Process steam with electrical by-product

Highest ranking (mission with lowest cost-benefit ratios)

Product

Table V. MISSION RANKING

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch019

19.

SCHOOLEY ET AL.

Economies of Chemicals & Fuel from Biomass

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch019

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0.32 g lipid

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254 2398.4

p a l m i t i c acid in kcal (29) Heat of c o m b u s t i o n of 0.32 g p a l m i t i c acid in kcal

3.0

T h e o n l y w a y t o increase e n e r g y yield per hectare is t o increase e n e r g y c a p t u r e a n d t h e e f f i c i e n c y of c o n v e r s i o n t o c a r b o h y d r a t e . A more r a p i d g r o w i n g s t a n d , or a g g r e g a t i o n of trees, w i l l be more p r o d u c t i v e of energy, a s s u m i n g its c h e m i c a l c o m p o s i t i o n is u n c h a n g e d , t h a n a s l o w - g r o w i n g stand. Breeding p r o g r a m s in s o u t h e r n pines have been successful in increasing v o l u m e p r o d u c t i o n a b o u t 15% in t h e first g e n e r a t i o n and increases of 2 5 % seem reasonable for t h e s e c o n d g e n e r a t i o n (B. J. Z o b e l . pers. c o m m u n .

458

BIOMASS AS A NONFOSSIL F U E L SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch022

1978). T h e p h y s i o l o g i c a l basis for these gains is u n k n o w n a n d c o u l d reflect b e t t e r utilization of i n c i d e n t solar radiation because of i m p r o v e d c a n o p y a r c h i t e c t u r e , ability t o utilize m o r e of t h e g r o w i n g season, a n d e n h a n c e d rate c a r b o n d i o x i d e a b s o r p t i o n a n d f i x a t i o n , a l o w e r rate of respiration for tissue m a i n t e n a n c e , or a r e d u c t i o n in losses to p a t h o g e n s a n d stress f a c t o r s of a n o n a c u t e t y p e . M a x i m u m o b s e r v e d e f f i c i e n c y for p h o t o s y n t h e s i s of poplar u n d e r intensive c u l t u r e w a s 3.5% of t h e v i s i b l e s p e c t r u m (22), for Serbian s p r u c e 7.9% ( I S ) , for maize 10.9% (7). T h e goal of breeders is t o increase e n e r g y yields b y r e a c h i n g t h e m a x i m u m t h e o r e t i c a l e f f i c i e n c y of 12% (15i). O n t h e o t h e r side of t h e c o i n , b r e e d i n g c o u l d help t o r e d u c e d e p e n d e n c e o n e n e r g y i n p u t t h e r e b y also increasing net e n e r g y y i e l d a n d s u b s t a n t i a l l y i m p r o v i n g t h e e f f i c i e n c y ratio. Fertilization is o n e of t h e m o s t c o s t l y i t e m s in s i l v i c u l t u r a l s c h e m e s for f u e l b i o m a s s p r o d u c t i o n . M a n u f a c t u r e a n d t r a n s p o r t of fertilizers in t h e s h o r t - r o t a t i o n , intensive c u l t u r e s c h e m e of Z a v i t k o v s k i (22) c o u l d a c c o u n t for nearly half of t h e t o t a l e n e r g y i n p u t . In S m i t h a n d J o h n s o n ' s s c h e m e , (24) 70% of t h e t o t a l i n p u t f o r site p r e p a r a t i o n a n d c u l t i v a t i o n w a s for fertilization. M o s t or all of these i n p u t s are related t o n i t r o g e n fertilization. If b r e e d i n g c o u l d d e v e l o p t y p e s less d e p e n d e n t u p o n m i n e r a l fertilizers, it w o u l d result in a major i m p r o v e m e n t in t h e e n e r g y b a l a n c e sheet. In fact, t h e r e are major differences in g e n e t i c response t o f e r t i l i z a t i o n , a n d o f t e n t h e g e n o t y p e s m o s t responsive t o fertilization are t h o s e t h a t are poorest w i t h o u t fertilization (\χ). S o m e g e n o t y p e s have a relatively stable p e r f o r m a n c e , o f t e n equal t o t h e fertilizer-responsive t y p e s w h e n fertilized a n d b e i n g g r e a t l y superior w h e n g r o w n w i t h less t h a n o p t i m u m levels of n i t r o g e n . A n o t h e r b u t m o r e r e m o t e possibility for i m p r o v e m e n t is t h r o u g h i n c o r p o r a ­ t i o n of n e w s y m b i o n t s or n e w genes for n i t r o g e n f i x a t i o n in w o o d y plants. S o m e p l a n t s i m p o r t a n t t o a g r i c u l t u r e have n i t r i f y i n g bacteria, h o u s e d in special root s t r u c t u r e s , t h a t e x t r a c t gaseous n i t r o g e n f r o m t h e a t m o s p h e r e . T h e n i t r o g e n soon appears f i x e d in a m i n o a n d a m i d e f o r m s . L e g u m e s like alfalfa are t h e m o s t n o t a b l e e x a m p l e s of plants t h a t are host t o n i t r o g e n f i x i n g bacteria, a n d t h e y are o f t e n alternated w i t h o t h e r crops t o m a i n t a i n a n d i m p r o v e soil fertility. A m o n g w o o d y perennials, alders are c a p a b l e of c o n v e r t i n g a t m o s p h e r i c n i t r o g e n . T h r o u g h g e n e t i c e n g i n e e r i n g , it m a y s o m e d a y be possible t o i m p r o v e t h e g r o w t h of o t h e r a g r i c u l t u r a l a n d forest crops by t h e a d d i t i o n of n i t r i f y i n g c a p a c i t y . In t h e m e a n t i m e , proper c h o i c e of species or b r e e d i n g of trees w h i c h are e f f i c i e n t scavengers of soil n i t r o g e n m a y reduce t h e need for fertilization.

22.

LEDIG

Silvicultural Systems for Fuel from Biomass

459

W O O D PRODUCTS A N D RESIDUALS

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch022

Irrespective of h o w e f f i c i e n t l y forests c a n c a p t u r e e n e r g y is t h e q u e s t i o n o f w h e t h e r w o o d c a n be e c o n o m i c a l l y sold as fuel. A l l p r o j e c t i o n s s u g g e s t a c o n t i n u e d increase in d e m a n d f o r fiber a n d solid p r o d u c t s w h i c h w i l l be s u p p l i e d f r o m a d w i n d l i n g land base. N o t o n l y c o u l d w o o d increase in value relative t o a s u b s t i t u t e like c o a l , b u t t h e energy balance m i g h t be e n h a n c e d more b y p r o m o t i n g w o o d as a material t h a n as a fuel source. For e x a m p l e , f o r every B t u e x p e n d e d in c o n s t r u c t i n g a house o f w o o d , there w o u l d be 6 B t u for steel or 2 5 Btu f o r a l u m i n u m (23). Of course, this is t r u e for f u r n i t u r e or any o t h e r m a n u f a c t u r e d i t e m s in w h i c h material s u b s t i t u t i o n s are possible. T h u s , t h e best e n e r g y value o f w o o d m i g h t be its u t i l i t y f o r a diversity of p r o d u c t s t h a t are f r e q u e n t l y m a d e f r o m more energetically costly materials. A s a b y p r o d u c t of w o o d p r o c e s s i n g , extensive residuals are p r o d u c e d . Slabs, t h e r o u n d e d shell o u t s i d e t h e s a w n boards, a l w a y s c o n s t i t u t e d a h i g h p r o p o r t i o n of t h e log, b u t t h e t r e n d t o shorter, e c o n o m i c rather t h a n biologic rotations f o r c e d harvest o f smaller trees, a n d increased t h e p r o p o r t i o n of slab t o board. These residuals are already salvaged b y large mills. T h e y are c h i p p e d a n d sold f o r p u l p i n g or used t o s u p p l y heat a n d energy f o r mill o p e r a t i o n . O n a local scale, use of mill residuals m a y have a major i m p a c t . A n o t h e r class of residuals, a n d o n e n o t f r e q u e n t l y used, includes t h e branches, t w i g s , leaves, a n d roots left in t h e forest. Branches a n d leaves m a y c o n s t i t u t e a b o u t 3 5 % of t h e t o t a l biomass or an a m o u n t equal t o t h e s t e m biomass (2g). C h i p p i n g t h e t o p s in t h e forest is q u i t e practical and c o u l d have an i m p a c t o n local fuel needs. Roots represent 2 0 % of t h e a b o v e - g r o u n d biomass a n d c o n s t i t u t e a n o t h e r source of fuel. M e c h a n i z e d s y s t e m s f o r root e x t r a c t i o n are available, b u t t h e i m p a c t of root e x t r a c t i o n o n soil s t r u c t u r e a n d site p r o d u c t i v i t y m a y be u n f a v o r a b l e a n d . o f course, c o u l d not be used in systems of c o p p i c e regeneration. CONCLUSIONS P r o d u c t i o n of biomass b y forests is h i g h l y energy efficient. Purely e x p l o i t a t i v e s c h e m e s are more efficient t h a n h i g h l y intensive silviculture. H o w e v e r , n e t e n e r g y yield increases w i t h i n t e n s i t y of c u l t i v a t i o n , so silvicultural s y s t e m s a p p r o a c h i n g those o f a g r i c u l t u r a l c r o p p i n g s h o u l d be f a v o r e d f r o m a n energy p r o d u c t i o n s t a n d p o i n t . Efficiency c a n be f u r t h e r increased by b r e e d i n g , a n area n e g l e c t e d in forestry f o r c e n t u r i e s after it h a d b e c o m e a p r o v e n assist in a g r i c u l t u r e . T h e rate of p r o d u c t i o n o f biomass c a n be increased by b r e e d i n g for rapid g r o w t h . S i m u l t a n e o u s l y , it m a y be possible t o reduce e n e r g y i n p u t s by b r e e d i n g f o r trees t h a t d o n o t require s u p p l e m e n t a l fertilization or by e n g i n e e r i n g n e w s y m b i o t i c relationships w i t h n i t r o g e n - f i x i n g o r g a n i s m s .

460

BIOMASS AS A NONFOSSIL

F U E L SOURCE

T h o u g h p r o d u c t i o n of forest biomass is efficient, its c o n v e r s i o n to gaseous or l i q u i d fuels is not. Cellulose a n d lignin are m o r e d i f f i c u l t t o c o n v e r t t o alcohol or m e t h a n e t h a n sugars, a m a j o r c o m p o n e n t of biomass in some c r o p plants. Therefore, trees w i l l p r o b a b l y be used d i r e c t l y for b u r n i n g or perhaps in p y r o l i t i c c o n v e r s i o n , a process w h i c h holds s o m e p r o m i s e . M e r e l y increasing reliance o n w o o d in c o n s t r u c t i o n w i l l have a positive effect on w o r l d energy b u d g e t s because p r o d u c t i o n of s u b s t i t u t e s requires a h i g h e n e r g y e x p e n ­ d i t u r e . P r o d u c t i o n of w o o d p r o d u c t s i n e v i t a b l y p r o d u c e s residuals. These c a n a n d are b e i n g used in e n e r g y p r o d u c t i o n a n d m a y have a m a j o r i m p a c t o n a local scale.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch022

REFERENCES

1.

"Fuel Requirements for Harvesting Pulpwood"; American Pulpwood Association: Washington, D.C., 1975; p 15.

2. Blankenhorn, P. R.; Bowersox, T. W.; Murphy, W. K. Tappi 1978, 61, 5760. 3.

Boardman, Ν. K. "Proceedings", Fourth International Congress on Photosynthesis; Biochemical Society: London, 1977; 635-44.

4. Bowersox, T. W.; Ward, W. W. J. For. 1976, 74, 750-3. 5. Burks, J. E. "Proceedings"; 1978 Joint Conv. Soc. Am. For. and Can. Inst. For.; Soc. Am. For.: Washington, D.C., 1979; 146-48. 6.

Burwell, C. C. Science 1978, 199, 1041-8.

7.

Caldwell, Μ. Α.; Cooper, J. P., Ed. "Photosynthesis and Productivity in Different Environments"; Cambridge Univ. Press: Cambridge, 1975; 4173.

8.

Calvin, M. Science 1974, 184, 375-81.

9.

Federal Energy Administration. "Energy in Focus, Basic Data"; U.S. Federal Energy Administration: Washington, D.C., 1977; p 13.

10. Fege, A. S.; Inman, R. E.; Salo, D. J. J. For. 1979, 77, 358-61. 11. Goodard, R. E., et al., Eds. "Tree Physiology and Yield Improvement"; Academic Press: London, 1976; pp 449-62.

22. LEDIG Silvicultural Systems for Fuel from Biomass 461

12. Heichel, G. H. Am. Sci. 1976, 64, 64-72. 13. Ibrahim, Y. M. N.Y. Times 1978,

128 (44-070), A1, D6.

14.

Kira, T.; Cooper, J. P., Ed. "Photosynthesis and Productivity in Different Environments"; Cambridge University Press: Cambridge, 1975; 5-40.

15.

Ledig, F. T.; Linzer, D.I.H. Chemtech 1978, 8, 18-27.

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16. McCann, D. J.; Saddler, H.D.W. Search 1976, 7, 17-23. 17.

Noggle, G.R.; Fritz, G. J. "Introductory Plant Physiology"; Prentice-Hall: Englewood Cliffs, N.J., 1976.

18.

Pecoraro, J. M.; Chase, R.; Fairbank, P.; Meister, R. New England Federal Regional Council, Energy Resource Development Task Force, Wood Utilization Group: Boston, Mass., 1977; p 91.

19.

Penning de Vries, F.W.T.; Brunsting, A.H.M.; van Laar, H.H. J. Theor. Biolo. 1974, 45, 339-77.

20.

Pimentel, D.; Jewell, W. J., Ed. "Energy Agriculture, and Waste Management"; Ann Arbor Sci. Publ.: Ann Arbor, Mich., 1975; pp 5-16.

21.

Schreiner, E. J. U.S. For. Serv. Res. Pap. 1970, NE-174, p 32.

22. Shulze, E.-D; Fuchs, M.; Fuchs, M. I. Oecologia 1977, 30, 239-48. 23. Smith, D. M. Connecticut Woodlands 1978, 43 (2), 3-5. 24. Smith, D. M.; Johnson, E. C. J. For. 1977, 75, 208-10. 25.

Steinbeck, K.; McAlpine, R. G.; May, J. T. J. For. 1972, 70, 210-14.

26.

Szego, G. C.; Kemp, C. C. Chemtech 1973, 3, 275-84.

27.

Zavitkovski, J. "Proceedings", Joint Convention of the Society of American Forestry and Canadian Institute of Forestry; Washington, D.C., 1979; Society of American Forestry: Washington, D.C., 1979; 13237.

28.

Zavitkovski, J. submitted for publication in For. Sci..

29.

Weast, R. C., Ed. "Handbook of Chemistry and Physics"; Chemical Rubber Co.: Cleveland, Ohio, 1969.

RECEIVED JUNE 18, 1980.

23 Electric Power Generation from Wood Waste A Case Study RICHARD T. SHEAHAN

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

Hennington, Durham & Richardson, 5454 Wisconsin Avenue, Washington, D C 20015

The current "Energy Crisis" being experienced worldwide has directed attention to the development of alternate sources of energy. One of those alternatives is wood. Wood appears to have numerous attractive advantages; it is available and renewable, a "clean" fuel, and has potential positive impacts on the enhancement of good forest management practice. The availability of wood residue exists in all forested areas of the United States, including "Urban" wooded areas. It is renewable because it regenerates in a relatively short time after each harvest cycle unlike fossil fuels. Wood is a relatively "clean" fuel because it contains virtually no sulfur. Most forested areas in the United States are currently not properly managed. Typical harvesting operations will "high-grade" a forest, or cut mostly the strong and marketable specimens, leaving the weak and "weedy" tree behind. As any gardener knows, if you do not "weed" your garden it will eventually become a weedpatch. This phenomenon occurs in numerous forested areas throughout the country. In most of these areas, there is no environmentally sound method of disposing of the rough and rotten wood residue, nor are there economic incentives for its removal. Utilizing this residue as an energy source can create an environmentally sound and economically viable motivation for "culling-out" and disposing of this

0097-6156/81/0144-0465$05.00/0 © 1981 American Chemical Society

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BIOMASS AS A NONFOSSIL F U E L SOURCE

material. C o m b u s t i o n t e c h n o l o g y for g e n e r a t i n g e l e c t r i c i t y f r o m w o o d w a s t e s is w e l l e s t a b l i s h e d ; t h e major p r o b l e m area is t h e g a t h e r i n g a n d t r a n s p o r t i n g of t h e w o o d material in an e c o n o m i c a l l y a c c e p t a b l e fashion.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

A general o v e r v i e w of t h e r e q u i r e m e n t s necessary t o i m p l e m e n t a w o o d residue e n e r g y p r o g r a m is presented in t h i s article. A case s t u d y of a n a c t u a l 5 0 m e g a w a t t ( M W ) w o o d - f i r e d electric g e n e r a t i n g p l a n t in B u r l i n g t o n . V e r m o n t w i l l be p r e s e n t e d as a m o d e l . Each c o m p o n e n t necessary t o m a k e u p t h e entire w o o d e n e r g y s y s t e m w i l l be d i s c u s s e d in s u f f i c i e n t detail t o assist t h e reader in u n d e r s t a n d i n g t h e r e q u i r e m e n t s necessary t o e v a l u a t e a n y w o o d e n e r g y p r o g r a m , be it t h e r m a l , s t e a m , or e l e c t r i c g e n e r a t i o n . T h e e x p e r i e n c e of t h e B u r l i n g t o n p r o j e c t is based o n t h e results o f a c o n c e p t u a l e n g i n e e r i n g s t u d y c o n d u c t e d by H e n n i n g s o n . D u r h a m & Richardson. Inc.O) T h e a v a i l a b i l i t y of w o o d residue a n d s u p p l y , its e n e r g y c h a r a c t e r i s t i c s , harvesting methodology, transportation and handling, combustion equipment, institutional and environmental concerns, and economic considerat i o n s are d i s c u s s e d . W O O D SUPPLY Due t o t h e relative sparsity of t i m b e r i n v e n t o r y data it is d i f f i c u l t t o a c c u r a t e l y d e t e r m i n e the t o t a l a m o u n t of w o o d residue available in t h e U n i t e d States. H o w e v e r , e s t i m a t e s i n d i c a t e t h a t a p p r o x i m a t e l y t h r e e p e r c e n t of t h e t o t a l U n i t e d States e n e r g y d e m a n d c o u l d possibly be s u p p l i e d by w o o d residues (2). There are several sources of w o o d residues s u i t a b l e for f u e l . A p r i m a r y criteria is t h a t t h e material be of a n o n - c o m m e r c i a l nature a n d have a l o n g t e r m a n d reliable s u p p l y . The p r i m a r y sources of w o o d residue are forest a n d mill residue. T h e U.S. Forest Service publishes statistics w h i c h c a n p r o v i d e t h e basis for e s t i m a t i n g t h e p o t e n t i a l a m o u n t s of available w o o d residues. O t h e r state a n d regional organizations also p u b l i s h d a t a w h i c h are useful in e s t i m a t i n g t h e q u a n t i t y of available material(3). Forest Residue There are several sources of available w o o d residues f r o m c o n v e n t i o n a l l o g g i n g opearations t h a t are n o r m a l l y n o t utilized o n a c o m m e r c i a l basis. A large v o l u m e of material c a n be d e r i v e d f r o m t o p s , b r a n c h e s , leaves, roots, s t u m p s , etc. w h i c h are usually left on t h e forest floor f o l l o w i n g a t y p i c a l s a w log h a r v e s t i n g o p e r a t i o n . This material can represent f r o m 3 5 t o 4 5 p e r c e n t of t h e v o l u m e , a n d therefore t h e e n e r g y c o n t e n t , of a tree. It c a n be c h i p p e d in t h e forest as an a d j u n c t t o a n o r m a l h a r v e s t i n g o p e r a t i o n . Removal of s o m e of this w a s t e material c a n reduce forest fire risk a n d e n h a n c e w i l d life habitat. N o n - c o m m e r c i a l species of trees are also available for fuel. These i n c l u d e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

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t y p i c a l small size, poor f o r m , or inferior q u a l i t y trees w h i c h have little h o p e o f m a t u r i n g or d e v e l o p i n g into trees suitable f o r industrial a p p l i c a t i o n . These plants c o m p e t e f o r m o i s t u r e a n d n u t r i e n t s w i t h t h e p r i m a r y forest. Therefore, p r u d e n t removal o f t h i s m a t e r i a l , w h i c h o f t e n is categorized as w a s t e , c a n e n h a n c e t h e health o f an overall forest. A n o t h e r source o f w o o d w a s t e is cull i n c r e m e n t a n d r o u g h a n d r o t t e n trees. Cull i n c r e m e n t refers t o t h e q u a n t i t y of w o o d w h i c h a n n u a l l y b e c o m e s n o n - c o m m e r c i a l , or " c u l l " material, d u e t o i n s u f f i c i e n t c u t t i n g or o v e r m a t u r e t i m b e r stands. A c e r t a i n n o n g r o w i n g p o r t i o n o f trees in a n y forested area is classified as s t a n d i n g r o u g h - a n d r o t t e n . This material is n o n - c o m m e r c i a l because it is either r o t t e n , b r o k e n , or d e a d . A s in a n y aspect of life, g o i n g t o e x t r e m e s is generally incorrect. Likewise, in a forest harvest o p e r a t i o n , c u t t i n g o u t t o o m u c h o f t h e n o n m e r c h a n t a b l e material is also incorrect. A certain a m o u n t o f t h e material m u s t be left b e h i n d t o replenish t h e soil n u t r i e n t s t o ensure f u t u r e forest health a n d vitality. Therefore, in a n y w o o d p r o c u r e m e n t o p e r a t i o n , g o o d forest m a n a g e m e n t practices m u s t be f o l l o w e d t o ensure t h a t t h e proper a m o u n t of w a s t e w o o d material is left t o m a i n t a i n t h e forest e c o l o g i c a l balance. M i l l Residue M i l l residue is a s o u r c e o f w o o d w a s t e w h i c h c a n be d e r i v e d f r o m t h e w o o d p r o d u c t s industry. D e p e n d i n g o n t h e e f f i c i e n c y o f a m i l l , u p t o f i f t y p e r c e n t o f t h e i n c o m i n g material c a n b e c o m e w a s t e material in t h e f o r m o f bark, s a w d u s t , c u t slabs, etc. (4). This residue is a n e x c e l l e n t source o f f u e l ; h o w e v e r , f o r a l o n g - t e r m s u p p l y , it m a y d w i n d l e as m o r e e m p h a s i s is p l a c e d on utilizing it f o r " i n - h o u s e " e n e r g y uses by t h e w o o d p r o d u c t s industries. Supply Evaluation W h e n e v a l u a t i n g a w o o d residue s u p p l y , c e r t a i n a s s u m p t i o n s m u s t be m a d e t o q u a n t i f y t h e availability. Data p u b l i s h e d b y t h e U.S. Forest Service a n d o t h e r organizations are a g o o d s t a r t i n g p o i n t f o r f o r m u l a t i n g w o o d residue q u a n t i t y . H o w e v e r , a t h o r o u g h u n d e r s t a n d i n g of t h e local h a r v e s t i n g t e c h n i q u e s a n d c u s t o m s , access t o t r a n s p o r t a t i o n , p e r c e n t grade o f local t e r r a i n , land o w n e r a t t i d u e s , seasonal w e a t h e r c o n d i t i o n s a n d o t h e r c o n s i d e r a t i o n s m u s t be e v a l u a t e d . A s an e x a m p l e of t h e latter i t e m , t h e City of B u r l i n g t o n w i l l have t o s t o c k p i l e s u f f i c i e n t w o o d residue in t h e s p r i n g a n d fall d u e t o a s h u t d o w n of h a r v e s t i n g operations. In t h e s p r i n g , t h e " m u d s e a s o n " makes l o g g i n g roads impassable d u e t o m e l t i n g s n o w s . In t h e fall, t h e h u n t i n g season closes d o w n t h e forest t o m o s t h a r v e s t i n g operations. Culling o u t of t h e n o n - m e r c h a n t a b l e material s h o u l d a c t u a l l y increase t h e a n n u a l g r o w t h rate o f a forest because t h e residual-stock is healthier a n d

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faster g r o w i n g . H o w e v e r , it is m o s t i m p o r t a n t t h a t t h e a n t i c i p a t e d a n n u a l r e m o v a l rate of w o o d residue does not exceed t h e a n n u a l n e w g r o w t h rate of a forest. Burlington W o o d Supply

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

Based o n a reasonable e n e r g y balance a n d load f a c t o r for a 5 0 M W w o o d fired p o w e r plant, it w a s e s t i m a t e d t h a t t h e City of B u r l i n g t o n requires a p p r o x i m a t e l y 4 7 0 . 0 0 0 g r e e n t o n s of w o o d r e s i d u e / y e a r t o o p e r a t e t h e i r p o w e r plant. Several a s s u m p t i o n s w e r e m a d e t o d e t e r m i n e if t h a t q u a n t i t y of m a t e r i a l is available t o t h e City. •

T h e s u p p l y area w a s a s s u m e d t o be c i r c u l a r a n d a p p r o x i m a t e l y 8 0 miles in d i a m e t e r . B u r l i n g t o n is s i t u a t e d in t h e w e s t e r n regions of t h e c i r c u l a r area.

•

M i n i m u m parcel size for t h e h a r v e s t i n g o p e r a t i o n w a s a s s u m e d t o be 5 0 acres. This is a very c o n s e r v a t i v e e s t i m a t e since m a n y h a r v e s t i n g o p e r a t i o n s take place o n h o l d i n g s b e l o w 3 0 acres in size.

•

Timberland that was owned

by t h e forest i n d u s t r y w a s

considered

unavailable for c o m p e t i t i v e p u r c h a s e of w o o d . •

A n n u a l g r o w t h o n state a n d national forests w a s c o n s i d e r e d available.

•

It w a s a s s u m e d t h a t w o o d in t h e i m m e d i a t e v i c i n i t y of B u r l i n g t o n w a s not available; likewise, it w a s a s s u m e d t h a t no s u b s t a n t i a l s u p p l y of w o o d f r o m Canada or across Lake C h a m p l a i n is available.

Based o n these a s s u m p t i o n s , it w a s d e t e r m i n e d t h a t t h e total w o o d d e m a n d by B u r l i n g t o n Is m o r e t h a n a d e q u a t e l y s u p p l i e d f r o m t h e a s s u m e d area. W O O D FUEL C H A R A C T E R I S T I C S W h e n e v a l u a t i n g w o o d as a f u e l , c h a r a c t e r i s t i c s of t h e delivered material m u s t be e s t i m a t e d relative t o t h e w e i g h t e d average of energy c o n t e n t s for t h e v a r i o u s a n t i c i p a t e d species of w o o d . I m p o r t a n t c o m b u s t i o n c h a r a c teristics of w o o d are its h e a t i n g value, w h i c h is a f u n c t i o n of its m o i s t u r e c o n t e n t a n d d e n s i t y , a n d its ash c o m p o s i t i o n . F l u c t u a t i o n s of these values are p r i m a r i l y d u e t o d i f f e r e n t c o n c e n t r a t i o n s of l i g n i n a n d t h e presence of e x t r a c t i v e s in t h e w o o d s u c h as resins a n d t a n n i n s . H a r d w o o d s (i.e., oak, m a p l e , etc.) generally have an average h i g h h e a t i n g v a l u e b e t w e e n 8 5 0 0 and 8 6 0 0 B t u / o v e n dry p o u n d of w o o d . Resin has a m u c h greater h e a t i n g value

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469

t h a n w o o d ( a p p r o x i m a t e l y 1 7 , 0 0 0 B t u / l b ) . Therefore, soft w o o d s (i.e., m o s t l y pines) w h i c h have h i g h e r resin c o n t e n t s a n d p r o p o r t i o n s of l i g n i n have h i g h e r e n e r g y c o n t e n t s t h a n hard w o o d s a n d average a p p r o x i m a t e l y 9 0 0 0 B t u / o v e n d r i e d p o u n d o f w o o d . These average values vary o n l y 5 t o 8 p e r c e n t d e p e n d i n g o n specific w o o d s (5). Bark also has a higher e n e r g y c o n t e n t t h a n w o o d . T h e a c t u a l h e a t i n g value f o r w o o d decreases as m o i s t u r e increases, since w a t e r has no h e a t i n g value. T h e m o i s t u r e c o n t e n t o f " g r e e n " w o o d , or w o o d r e c e n t l y harvested a n d c h i p p e d , is a p p r o x i m a t e l y 5 0 p e r c e n t (on a w e t basis). Based o n this m o i s t u r e c o n t e n t , t h e average h i g h h e a t i n g values are approximately 4 3 0 0 Btu/lb for hardwoods and approximately 4 5 0 0 Btu/lb for s o f t w o o d s . The ash c o m p o n e n t is generally c o n s i d e r e d undesirable since it is inert a n d n o t c o m b u s t i b l e . A s h e i t h e r remains in t h e c o m b u s t i o n c h a m b e r or is e n t r a i n e d w i t h stack gases w h i c h m a y create p a r t i c u l a t e air e m i s s i o n p r o b l e m s . T h e average ash c o n t e n t of m o s t w o o d s ranges f r o m 0.1 t o 3 percent, w i t h m o s t species a v e r a g i n g less t h a n o n e percent. A possible increase in t h e ash c o n t e n t o f w o o d can c o m e f r o m t h e s k i d d i n g of harvested trees in t h e forest w h i c h o f t e n results in t h e c o l l e c t i o n of s o m e dirt and sand on t h e bark. Unless t h i s material is r e m o v e d , it c a n increase t h e t o t a l ash c o n t e n t o f t h e fuel. A s a p o i n t o f c o m p a r i s o n , m o s t coals have an average ash content substantially above 5 percent w i t h some reaching t h e 25 percent level. B u r l i n g t o n ' s Fuel C h a r a c t e l s t i c s Based o n a w e i g h t e d average o f t h e w o o d specie m i x in t h e s u p p l y area, it w a s e s t i m a t e d t h a t t h e average h i g h h e a t i n g value of t h e w o o d fuel t o B u r l i n g t o n w o u l d be a p p r o x i m a t e l y 4 7 5 0 B t u / l b . HARVESTING TECHNIQUES N u m e r o u s c o m b i n a t i o n s of h a r v e s t i n g scenarios are possible. A l l basically involve t h e t r a d i t i o n a l steps o f a n o r m a l h a r v e s t i n g a n d delivery process w h i c h includes f o u r separate a c t i v i t i e s : f e l l i n g , s k i d d i n g , y a r d i n g , a n d hauling. Felling — This step involves t h e c u t t i n g o f i n d i v i d u a l trees. T h e p r e v a i l i n g f e l l i n g e q u i p m e n t is t h e c h a i n s a w ; h o w e v e r , m o r e m e c h a n i z e d devices are available a n d b e i n g d e v e l o p e d . T h e fellerb u n c h e r is a m a c h i n e t h a t uses a h y d r a u l i c s y s t e m t o h o l d t h e s t a n d i n g tree w h i l e c u t t i n g it near g r o u n d level w i t h a m e c h a n i c a l shear. O n c e c u t , t h e trees are i n d i v i d u a l l y laid side by side.

470

BIOMASS AS A NONFOSSIL F U E L SOURCE

Skidding— The s k i d d i n g o p e r a t i o n involves d r a g g i n g t h e logs or trees f r o m their felled p o s i t i o n t o a general c o l l e c t i o n site called a l a n d i n g . T h i s is usually d o n e by large f o u r - w h e e l e d d r i v e , r u b b e r - t r i e d skidders. T o a l i m i t e d e x t e n t s k i d d i n g is d o n e by steel t r a c k e d c r a w l e r s or by horses. Skidders usually pull m o r e t h a n one log or tree at a t i m e , h o l d i n g t h e leading e n d s of t h e logs off t h e g r o u n d by use of steel cables a n d a

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

w i n c h , or by h y d r a u l i c g r a p p l e devices. Yarding— O n c e t h e logs or trees have been s k i d d e d t o t h e l a n d i n g , t h e y are prepared for s h i p m e n t t o t h e w o o d y a r d . This process is called y a r d i n g . A n i n t e g r a t e d o p e r a t i o n t h a t s u p p l i e s w o o d for a p o w e r p l a n t w o u l d p r o b a b l y skid either long logs or entire trees. A t t h e l a n d i n g , q u a l i t y s a w logs w o u l d be c u t . sorted a n d piled for s u b s e q u e n t l o a d i n g o n large t r u c k s for delivery t o t h e a p p r o p r i a t e m i l l . T h e balance of t h e trees or logs m a y t h e n be c h i p p e d a n d b l o w n i n t o e n c l o s e d trailers by w h o l e - t r e e c h i p p e r s . A w h o l e - t r e e c h i p p e r c a n be t o w e d by t r u c k t o t h e l a n d i n g area a n d q u i c k l y set up for o p e r a t i o n . A m e c h n i c a l a r m picks up t h e w h o l e tree or log a n d feeds one e n d i n t o a m o t o r i z e d c o n v e y o r s y s t e m w h i c h t h e n pushes t h e material t o w a r d s a set of h i g h s p e e d , r o t a t i n g knives. T h e w o o d c h i p s t h a t result are generally a b o u t t h e size of m a t c h b o o k s . If w h o l e - t r e e c h i p p e r s are n o t used, t h e logs w o u l d be c u t into c o n v e n i e n t l e n g t h s for loading i n t o t r u c k s . In a n o n c h i p p i n g o p e r a t i o n , t h e t o p s a n d b r a n c h e s w o u l d be left b e h i n d as w a s t e m a t e r i a l . Hauling — T h e c h i p s are t r a n s p o r t e d f r o m a l a n d i n g t o a p o w e r p l a n t b y tractor-trailer. S a w logs o n t h e o t h e r h a n d c a n be h a u l e d by e i t h e r s t r a i g h t t r u c k s or tractor-trailers. These log t r u c k s m a y be e q u i p p e d w i t h self-loading e q u i p m e n t . Burlington Harvesting Scenario In e v a l u a t i n g t h e c o s t of h a r v e s t i n g w o o d f u e l , t h e r e are i n f i n i t e c o m b i n a t i o n s of labor a n d e q u i p m e n t w h i c h c o u l d be utilized in p r o c u r i n g t h e w o o d w a s t e . M a n y factors m u s t be c o n s i d e r e d ; these i n c l u d e h a r v e s t i n g e q u i p m e n t , m a n p o w e r r e q u i r e m e n t s , slope of terrain, access t o l o g g i n g trails and t r a n s p o r t a t i o n roads, haul d i s t a n c e t o u l t i m a t e use, land o w n e r a t t i t u d e s a n d n u m e r o u s o t h e r c o n s i d e r a t i o n s . In e v a l u a t i n g t h e c o s t of fuel d e l i v e r e d t o B u r l i n g t o n , t h r e e w o o d fuel p r o d u c t i o n m o d e l s w e r e e x a m i n e d . T h e p r o d u c t i o n m o d e l s selected for e v a l u a t i o n w e r e j u d g e d t o be fairly representative of m e t h o d s c u r r e n t l y e m p l o y e d in t h e N e w England region. Model Number 1 — Traditional Round Wood - This m o d e l e x e m p l i f i e s m a n y small w o o d h a r v e s t i n g operations a n d consists of t w o m e n a n d one skidder. One m a n is responsible for felling a n d c u t t i n g t h e tree t o

23.

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471

Electric Power Generation

desired lengths. T h e o t h e r l u m b e r m a n skids t h e tree o u t t o a l a n d i n g . This h a r v e s t i n g s y s t e m requires a m o d e s t c a p i t a l i n v e s t m e n t a n d offers o p e r a t i n g f l e x i b i l i t y t o c o n f o r m t o local c o n d i t i o n s . It is t h e p r e d o m i n a n t h a r v e s t i n g s y s t e m c u r r e n t l y utilized in V e r m o n t ' s forest. Model

Number

2 — Chip Harvesting

(Moderate

Mechanization)-

This

represents a p o p u l a r e m e r g i n g h a r v e s t i n g t e c h n o l o g y in N e w England. " I n - t h e - w o o d s " c h i p p i n g offers a d v a n t a g e s of greater resource utilizat i o n a n d r e d u c e d t r a n s p o r t a t i o n cost. W h o l e trees are felled b y c h a i n s a w s a n d s k i d d e d t o a m e d i u m size (18 in.) c h i p p e r at t h e l a n d i n g area.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

Chips are b l o w n into tractor-trailers f o r t r a n s p o r t t o t h e p o w e r plant. Model Number 3 — Whole Tree Harvesting (Highly Mechanized)This s y s t e m utilizes a m e c h a n i c a l f e l l e r - b u n c h e r t o c u t trees utilizing m u l t i p l e skidders t o m o v e t h e m t o a large (22 in.) c h i p p e r located at t h e l a n d i n g area. T h e increased capital i n v e s t m e n t a n d higher o p e r a t i n g costs c o m b i n e d w i t h p r o b l e m s presented b y r u g g e d terrain have t o date e x c l u d e d t h e general use o f f e l l e r - b u n c h e r s in V e r m o n t . Generally, t h e y are restricted t o terrain h a v i n g slopes of 15 p e r c e n t or less (6). It is d o u b t f u l t h a t f e l l e r - b u n c h e r o p e r a t i o n s w i l l b e c o m e w i d e s p r e a d in V e r m o n t ' s forests d u e t o h i g h capital costs, u n c e r t a i n t y a b o u t p r o d u c t i v i t y in certain c u t s , a n d t h e i r l i m i t e d a d a p t a b i l i t y t o small a n d m e d i u m size parcels w h i c h are very c o m m o n in V e r m o n t . H o w e v e r , its p o t e n t i a l is very s i g n i f i c a n t in less r u g g e d a n d sloped terrain a n d large parcels of forested land. Economic

assumptions

a n d capital

and operating

costs

f o r t h e three

p r o d u c t i o n m o d e l s are p r e s e n t e d in Tables I a n d II. T o realistically evaluate t h e cost of p r o d u c i n g w o o d fuel f o r t h e B u r l i n g t o n plant, it w a s a s s u m e d t h a t o n l y p r o v e n h a r v e s t i n g t e c h n o l o l g y w o u l d be utilized. T h u s , a f e l l e r - b u n c h e r o p e r a t i o n , a l t h o u g h t e c h n i c a l l y possible, w a s not c o n s i d e r e d t o be a m a j o r c o n t r i b u t o r . It w a s a s s u m e d t h a t t h e p r e d o m i n a n t p o r t i o n o f t h e w o o d fuel w o u l d be s u p p l i e d by t r a d i t i o n a l r o u n d w o o d a n d m o d e r a t e l y m e c h a n i z e d c h i p h a r v e s t i n g operations. It w a s f u r t h e r a s s u m e d t h a t 7 0 p e r c e n t o f t h e fuel r e q u i r e m e n t s w o u l d be s u p p l i e d b y " i n t h e - w o o d s " c h i p p i n g a n d 3 0 p e r c e n t b y t r a d a t i o n a l r o u n d w o o d subseq u e n t l y c h i p p e d at a satellite facility or c o n c e n t r a t i o n y a r d . T h e w e i g h t e d average o f w o o d fuel cost (prior t o c h i p p i n g o f t h e r o u n d w o o d p o r t i o n a n d t r a n s p o r t a t i o n of t h e t o t a l p o r t i o n of t h e w o o d fuel) w a s e s t i m a t e d t o be $ 8 . 0 6 / t o n (1977 dollars).

472

BIOMASS AS A NONFOSSIL F U E L SOURCE

T A B L E I. P R O D U C T I O N M O D E L A S S U M P T I O N S (All c o s t s e x p r e s s e d in 1 9 7 7 dollars) Productivity: Estimate based on m a n u f a c t u r e r ' s i n f o r m a t i o n a n d national averages revised t o reflect V e r m o n t c o n d i t i o n s . A s s u m e 1,800 h r / y r o p e r a t i o n . Labor: Based o n 4 5 w e e k s per year at $ 2 2 0 / w e e k per person plus 2 5 % payroll benefits.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

Fuel a n d O i l : Fuel Diesel @ $ 0 . 5 0 / g a l Skidders Feller-buncher, c r a w l e r t r a c t o r Chipper — M e d . 1 8 " Lg. 2 2 "

Consumption 5.0 g a l / h o u r 6.0 g a l / h o u r 10.0 g a l / h o u r 12.0 g a l / h o u r

3 0 % of Fuel Cost M a i n t e n a n c e a n d Repair: Hourly D e p r e c i a t i o n (HD) = Purchase P r i c e / E x p e c t e d Life A s s u m e .70 x HD x 1 8 0 0 h r / y r = M a i n t e n a n c e a n d Repair Skidders — Dovers — Chippers —

7 , 5 0 0 hr e x p e c t e d life 10,000 hr e x p e c t e d life

$0.50/ton

Financing: A s s u m e 7 5 % Debt — 2 5 % Equity

12%, 5 years

Depreciation: A s s u m e 5 years s t r a i g h t line S t u m p a g e : (Payment to l a n d o w n e r for w o o d removed) A s s u m e average $ 0 . 7 5 / t o n Taxes: State a n d Federal Federal i n c l u d e s i n v e s t m e n t tas c r e d i t a m o r t i z e d over 5 years. Profit: Reflects o n assessment of r i s k - r e w a r d f a c t o r s a n d varies a c c o r d i n g t o size of capital i n v e s t m e n t , m a r g i n s are c o n s i d e r e d reasonable t o a c h i e v e desired p r o d u c t i o n levels.

23.

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473

Electric Power Generation

TABLE II. PRODUCTION MODELS -

CAPITAL A N D OPERATING COST

SUMMARY

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

(All c o s t s e x p r e s s e d in 1 9 7 7 dollars)

P r o d u c t i v i t y (tons/year) Labor (Men)

Moderately

Highly

Mechanized

Mechanized

Traditional Roundwood

Chip Harvesting

Chip Harvesting

8.440 2

33.750 6

54,000 9

1 1

2

$44,000

$242,000

1 2 2 1 1 $509,000

$67,112

$273,316

$526,639

$24,750 5.850 6.700 2.550 9.350 6.330

$74,250 23,000 29.000 14,000 48,500 25,000 7,825 21,676

$111,375 43.000 51.000 29.600

Equipment C r a w l e r Tractor Cable Skidders Grapple Skidders Feller-Buncher Chipper Capital I n v e s t m e n t

1

Revenues A n n u a l W o o d Sales Costs Labor Fuel & Oil M a i n t e n a n c e & Repair Interest Depreciation Stumpage Miscellaneous Taxes Net Profit Profit o n Sales (%) Return o n I n v e s t m e n t (%) U n i t Cost ($/ton)

2.775 3.706 5.371 8 12

30.065 11 12

7.95

8.10

100.000 38.000 12.000 62.733 78,931 15 15 9.75

474

BIOMASS AS A NONFOSSIL F U E L SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

T R A N S P O R T A T I O N , H A N D L I N G A N D PROCESSING There are e s t i m a t e s t h a t indicate o n a net zero e n e r g y basis for electric g e n e r a t i o n (i.e.. e n e r g y i n p u t r e q u i r e m e n t t o p r o d u c e a c o m p a r a b l e electrical o u t p u t derived f r o m w o o d chips), " g r e e n " w o o d c h i p s can be hauled by t r u c k for a p p r o x i m a t e l y 5 0 t o 100 miles d e p e n d i n g o n t h e average heat a n d m o i s t u r e c o n t e n t of t h e w o o d fuel (7). T h e c o m p a r a b l e d i s t a n c e for rail haul is m u c h greater. H o w e v e r , o n an e c o n o m i c basis, rail haul p r o v e d t o be u n a c c e p t a b l y m o r e e x p e n s i v e d u e t o t h e a d d i t i o n a l costs associated w i t h l o a d i n g a n d u n l o a d i n g of railroad cars. It w a s a s s u m e d t h a t all w o o d c h i p s w o u l d be hauled t o t h e p o w e r p l a n t b y t r u c k s . T r u c k i n g costs for r o u n d w o o d a n d c h i p s w e r e d e t e r m i n e d t h r o u g h analysis of rate s c h e d u l e s of w o o d haulers in t h e B u r l i n g t o n area. Generally, r o u n d w o o d is m o r e c o s t l y t o t r a n s p o r t t h a n c h i p s d u e t o r e d u c e d v e h i c l e p a y loads a n d h a n d l i n g p r o b l e m s . Therefore, a c o m p o s i t e average t r u c k i n g cost r e f l e c t i n g r o u n d w o o d a n d c h i p t r a n s p o r t w a s used. Rates w e r e s t r u c t u r e d t o p r o v i d e i n c e n t i v e s for utilization of efficient vehicles a n d t o a t t r a c t d i s t a n t supplies. It w a s a s s u m e d t h a t v e h i c l e s w o u l d average 3 5 m i l e s - p e r - h o u r a n d carry a p a y l o a d of f r o m t w e n t y t o t w e n t y five tons. T h e t r u c k t r a n s p o r t a t i o n costs w e r e d e t e r m i n e d by a p p l y i n g u n i t haul costs per m i l e t o t h e w e i g h t e d d i s t r i b u t i o n of w o o d e d area w i t h i n t h e s u p p l y area. T h e average t r u c k i n g c o s t w a s d e t e r m i n e d t o be $ 3 . 4 3 / t o n ( 1 9 7 7 dollars) f r o m t h e forest t o p o w e r plant. A n a d d i t i o n a l cost of $ 1 . 6 7 / t o n w a s d e t e r m i n e d for t h e cost of c h i p p i n g t h e plant's w o o d fuel r e q u i r e m e n t s d e r i v e d f r o m t h e r o u n d w o o d o p e r a t i o n . This cost w a s a p p l i e d t o 3 0 p e r c e n t of t h e t o t a l w o o d s u p p l y per t h e p r e v i o u s assumption. T h e f o l l o w i n g f i g u r e s indicate t h e t o t a l e s t i m a t e d c o s t in 1 9 7 7 dollars for w o o d fuel p r o c u r e m e n t for t h e B u r l i n g t o n P o w e r Plant. W o o d P r o d u c t i o n Costs Trucking C h i p p i n g of R o u n d W o o d (applied t o 3 0 p e r c e n t of w o o d supply)

$8.06/ton 3.43 0.50 $11.99/ton

FUEL H A N D L I N G A N D STORAGE Chip t r u c k s a r r i v i n g at t h e p o w e r p l a n t are w e i g h e d a n d t h e n u n l o a d e d by h y d r a u l i c t r u c k d u m p e r s . Chips f l o w by g r a v i t y f r o m t h e t r u c k s into liveb o t t o m receiving h o p p e r s ; a n d f r o m there, o n t o i n c l i n e d belt c o n v e y o r s w h i c h t r a n s p o r t t h e c h i p s t o storage. A m e c h a n i c a l - b e l t pile-builder d i s t r i b u t e s the chips evenly a r o u n d the p e r i m e t e r of t h e storage pile. A disk

23.

SHEAHAN

Electric Power Generation

475

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

screen a n d w o o d pulverizer are p r o v i d e d t o reduce oversized material t o p r e v e n t j a m m i n g o f material h a n d l i n g systems. Also, a m a g n e t i c ferrous recovery s y s t e m is necessary t o recover t r a m p m e t a l parts w h i c h c a n cause d a m a g e t o t h e c o n v e y i n g a n d c o m b u s t i o n systems (8.9). D u r i n g w i n t e r m o n t h s , vehicles a r r i v i n g at t h e u n l o a d i n g area m u s t be carefully i n s p e c t e d t o ensure t h a t massive loads o f frozen chips are n o t d u m p e d o n t o t h e r e c e i v i n g hoppers t h e r e b y c r e a t i n g a b o t t l e neck t o s u b s e q u e n t u n l o a d i n g operations. The e x p e r i e n c e o f c h i p h a n d l i n g facilities in Canada indicates t h a t t h e o n l y sure p r e v e n t i o n is t o establish a f i r m policy against delivery of frozen chips. M o s t freezing p r o b l e m s o c c u r w h e n c h i p s are loaded i n t o vans a n d left t o s t a n d over long periods o f t i m e prior t o delivery. Chips p r o d u c e d in t h e w o o d s a n d b r o u g h t p r o m p t l y t o t h e p o w e r plant s h o u l d n o t arrive solidly frozen. The a n t i c i p a t e d w o o d storage pile f o r t h e p o w e r plant is s e m i - c i r c u l a r in shape a p p r o x i m a t e l y 3 8 0 feet in d i a m e t e r w i t h a h e i g h t of 4 0 feet. It c o n t a i n s a p p r o x i m a t e l y 4 2 . 5 0 0 t o n s o f c h i p s o r a p p r o x i m a t e l y 21 days o f fuel s u p p l y for t h e p o w e r plant. T w o c h i p dozers w o r k t h e pile a n d share responsibility f o r m a n a g i n g t h e pile a n d r e c l a i m i n g w o o d . Chip pile m a n a g e m e n t is a n i m p o r t a n t task w h i c h i n c l u d e s responsibility f o r r o t a t i o n o f c h i p i n v e n t o r y , c h i p m i x i n g , d u s t c o n t r o l , a n d fire p r e v e n t i o n . T h e relatively h i g h m o i s t u r e c o n t e n t of w o o d fuel d i c t a t e s t h a t material be reclaimed o n a " f i r s t - i n firsto u t " basis t o m a i n t a i n freshness a n d i n h i b i t c h i p d e c o m p o s i t i o n . Chip i n v e n t o r y s h o u l d be c o m p l e t e l y rotated at least o n c e a year t o m i n i m i z e d e c o m p o s i t i o n . A c e r t a i n degree o f natural d e c o m p o s i t i o n w i l l o c c u r a n d t h e p o t e n t i a l f o r s p o n t a n e o u s c o m b u s t i o n fires exists. C o m p a c t i o n of t h e entire pile, especially a l o n g t h e o u t e r perimeter, reduces air f l o w w h i c h c a n feed " h o t s p o t s " in t h e pile. " H o t - s p o t s " , i d e n t i f i e d b y t h e presence of smoke, s h o u l d be u n c o v e r e d a n d a p p r o x i m a t e l y a t r u c k load of d r y ice a p p l i e d a n d the area r e c o m p a c t e d . Carbon d i o x i d e gas is d r a w n into t h e " h o t " area a n d causes it t o be e x t i n g u i s h e d . Before large w o o d c h i p inventories are a c c u m u l a t e d , a q u a n t i t y supplier o f d r y ice s h o u l d be i d e n t i f i e d . W o o d c h i p s are r e c l a i m e d f r o m t h e storage pile b y c h i p dozers and d e p o s i t e d in r e c l a i m hoppers a d j a c e n t t o t h e w o o d pile. Steel grates a b o v e t h e hoppers p r e v e n t frozen c h i p s or oversized o b j e c t s f r o m j a m m i n g c o n v e y o r s or o t h e r w i s e f o u l i n g h a n d l i n g e q u i p m e n t . Draft c o n v e y o r s installed beneath t h e hoppers discharge c h i p s t o i n c l i n e d belt c o n v e y o r s w h i c h elevate t h e w o o d fuel t o storage bunkers s i t u a t e d above t h e p o w e r plant boilers. Chips are c o n t i n u o u s l y f e d t o t h e boiler feeders t o provide a d e q u a t e fuel s u p p l y .

476

BIOMASS AS A NONFOSSIL F U E L SOURCE

ELECTRIC G E N E R A T I O N S Y S T E M W o o d is basically a cellulose fiber a n d its c o m b u s t i o n t e c h n o l o g y is w e l l e s t a b l i s h e d . T h e p a p e r a n d p u l p i n d u s t r y for years has been b u r n i n g bark; t h e l u m b e r i n d u s t r y b u r n s s a w d u s t ; a n d m a n y f o o d p r o c e s s i n g industries have years of e x p e r i e n c e in t h e c o m b u s t i o n of cellulosic fiber. T h e r e f o r e t h e

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p r i m a r y p r o b l e m in t h e large scale g e n e r a t i o n of e l e c t r i c i t y f r o m w o o d w a s t e is n o t c o m b u s t i o n , b u t t h e g a t h e r i n g a n d t r a n s p o r t a t i o n of t h e w o o d f u e l . T h e p r i m a r y c o n c e r n of w o o d fuel c o m b u s t i o n is t h a t it has a h i g h m o i s t u r e c o n t e n t w h i c h reduces h e a t i n g values a n d i n f l u e n c e s c o m b u s t i o n t e m p e r a tures a n d o t h e r f u r n a c e p a r a m e t e r s . T h e basic f u n d a m e n t a l s of w o o d w a s t e c o m b u s t i o n entail three c o n s e c u t i v e stages: t h e e v a p o r a t i o n of m o i s t u r e , t h e d i s t i l l a t i o n a n d b u r n i n g of volatile m a t t e r , a n d t h e c o m b u s t i o n of t h e f i x e d c a r b o n . In t h e f u r n a c e c o m b u s t i o n c h a m b e r , r a d i a t i o n a n d c o n v e c t i v e heat i n p u t evaporates t h e w o o d ' s m o i s t u r e a n d distills t h e v o l a t i l e matter. T h e e v a p o r a t i o n of m o i s t u r e t o s t e a m takes a p p r o x i m a t e l y 1 1 0 0 B t u / l b of m o i s t u r e . O n c e m o i s t u r e has been e v a p o r a t e d , heat is a b s o r b e d by t h e fuel particles t h u s d r i v i n g off v o l a t i l e matter. T h e v o l a t i l e m a t t e r b u r n s in a s e c o n d a r y c o m b u s t i o n r e a c t i o n w i t h i n t h e f u r n a c e c h a m b e r , b u t e x t e r n a l t o t h e a c t u a l w o o d fiber. Finally, t h e f i x e d c a r b o n of t h e w o o d b u r n s in t h e p r i m a r y c o m b u s t i o n reaction in c o n j u n c t i o n w i t h c o m b u s t i o n air. T h e m o s t e f f i c i e n t m e t h o d of w o o d w a s t e c o m b u s t i o n in t h e 5 0 M W p o w e r p l a n t size p r o p o s e d for B u r l i n g t o n is by use of a t r a v e l l i n g - g r a t e spreaderstoker boiler. A single u n i t is m o r e e f f i c i e n t t h a n m u l t i p l e units. Boiler m a n u f a c t u r e r s i n d i c a t e t h a t t h e largest stoker size available limits t h e i n p u t of b u r n i n g w o o d in a single u n i t t o a p p r o x i m a t e l y 7 5 t o n / h r or 1 8 0 0 t o n / d a y . A s s u m i n g a 7 5 p e r c e n t p o w e r p l a n t c a p a c i t y factor, t h i s fuel i n p u t e q u a t e s t o a n o m i n a l 5 0 M W c a p a c i t y . T h e c a p a c i t y f a c t o r of 7 5 p e r c e n t m e a n s t h a t t h e u n i t w i l l operate o n an average of 7 5 p e r c e n t of its rated c a p a c i t y o n an a n n u a l basis. T h u s the p l a n t w o u l d average 3 7 , 5 0 0 k W on an a n n u a l basis. A c t u a l l y t h e p o w e r plant w o u l d p r o d u c e on an average over 4 0 , 0 0 0 k W / h r for j u s t over 8 , 0 0 0 hr of t h e year. This a l l o w s for 3 0 days of d o w n t i m e for m a i n t e n a n c e d u r i n g t h e year. T h e e n e r g y i n p u t r e q u i r e d t o s u p p l y t h i s e l e c t r i c g e n e r a t i o n c a p a c i t y e q u a t e s on a Btu basis t o a p p r o x i m a t e l y 4 7 0 , 0 0 0 t o n s of " g r e e n " w o o d c h i p s per year. The p r o p o s e d B u r l i n g t o n p l a n t i n c l u d e s a 5 0 M W c o n d e n s i n g t u r b i n e generator u n i t ; a 5 2 5 , 0 0 0 I b / h r boiler; a c o m p l e t e c o m p l e m e n t of s t a t i o n auxiliary, m e c h a n i c a l , a n d electrical e q u i p m e n t ; a n d a p o w e r t r a n s m i s s i o n s u b s t a t i o n . S t e a m f r o m t h e boiler is s u p p l i e d t o t h e t u r b i n e at a pressure of 1,250 p o u n d s a n d t e m p e r a t u r e of 9 5 0 ° F . A h y d r a u l i c ash h a n d l i n g s y s t e m c o n v e y s t h e ash f r o m t h e stoker s i t t i n g s a n d ash h o p p e r to a s y s t e m w h e r e it is d e w a t e r e d and t r u c k e d to

23.

SHEAHAN

All

Electric Power Generation

landfill. W o o d has a n inherently l o w sulfur c o n t e n t a n d therefore poses n o p r o b l e m as a source o f sulfur d i o x i d e air emission. W o o d b u r n s at a l o w e r t e m p e r a t u r e t h a n fossil f u e l s ; a n d likewise, has a n i n h e r e n t l y l o w e r n i t r o g e n c o n t e n t t h a n fossil fuels. A s a result, w o o d c o m b u s t i o n p r o d u c e s l o w e r q u a n t i t i e s of n i t r o g e n oxides. T h e p r i m a r y air e m i s s i o n c o n c e r n f o r t h e w o o d fired p l a n t is p a r t i c u l a t e matter. M e c h a n i c a l c o l l e c t i o n a n d e l e c t r o s t a t i c p r e c i p i t a t i o n e q u i p m e n t is e x p e c t e d t o ensure c o m p l i a n c e w i t h p a r t i c u l a t e a n d s m o k e e m i s s i o n s t a n d a r d s (12.13). T h e s y s t e m operates o n a closed c o o l i n g s y s t e m a n d therefore t h e r e is n o t h e r m a l w a t e r d i s c h a r g e t o t h e a d j a c e n t river or nearby Lake C h a m p l a i n .

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COST ESTIMATES Estimates o f t h e c a p i t a l , o p e r a t i n g , a n d m a i n t e n a n c e costs of t h e p r o p o s e d 5 0 M W w o o d - f i r e d p o w e r p l a n t are p r e s e n t e d in Table III a n d are based o n c o n c e p t u a l d e s i g n c o n c e p t s . A l l costs are expressed in 1 9 7 7 dollars. The t o t a l c o n s t r u c t i o n cost e s t i m a t e w a s $ 4 6 , 2 2 7 , 0 0 0 .

T A B L E III. C A P I T A L C O S T E S T I M A T E FOR 50 M W WOOD-FIRED POWER PLANT A T BURLINGTON, VERMONT (All c o s t s e x p r e s s e d as $ 1 , 0 0 0 in 1 9 7 7 ) S t e a m Boiler Turbine System Mechanical Equipment

$8,820 3,870 3,660

Electrical E q u i p m e n t Piping Site D e v e l o p m e n t Building - Structural W o o d Handling System

3,300 2,900 1,275 10,500 2,039

Chimney Substation, Interconnect

1.200 1,010

C o n t i n g e n c i e s , E n g i n e e r i n g , Legal T o t a l Capital Cost

7,653 $46,227

478

BIOMASS AS A NONFOSSIL F U E L SOURCE

The p r o p o s e d p o w e r plant w i l l p r o d u c e a gross of 3 2 8 , 5 0 0 M W - h r a n n u a l l y or a net of 3 0 2 , 2 0 0 M W - h r (8 p e r c e n t i n - p l a n t use) o p e r a t i n g at a 7 5 p e r c e n t c a p a c i t y factor. It w i l l c o n s u m e a p p r o x i m a t e l y 4 7 0 , 0 0 0 green tons of w o o d c h i p s w h i c h is 100 p e r c e n t of t h e energy input. Based on t h e p r e v i o u s l y d e r i v e d cost of f u e l of $ 1 1 . 9 9 / t o n , t h e t o t a l a n n u a l fuel cost w i l l be a p p r o x i m a t e l y $ 5 , 6 3 5 , 0 0 0 . Plant o p e r a t i o n w a s e s t i m a t e d t o require a staff of 4 2 w i t h an a n n u a l payroll of $ 7 1 4 , 0 0 0 . A n n u a l m a i n t e n a n c e , c h e m i c a l a n d s u p p l y costs, a n d o p e r a t i o n a n d m a i n t e n a n c e for t h e fuel off l o a d i n g a n d h a n d l i n g s y s t e m w a s e s t i m a t e d t o be $ 7 2 7 , 0 0 0 / y r . T h e e s t i m a t e d t o t a l o p e r a t i n g a n d m a i n t e n a n c e c o s t for t h e p o w e r plant is $ 7 , 0 7 6 , 0 0 0 / y r .

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Annual Cost Projection It w a s a s s u m e d t h a t t h e p o w e r p l a n t w i l l be f i n a n c e d f r o m revenue b o n d i n g . Therefore, reasonable e s t i m a t e s w e r e m a d e for interest o n b o n d s , interest earned a n d e x p e n d e d d u r i n g c o n s t r u c t i o n , a n d b o n d d i s c o u n t s . W o r k i n g capital a n d t h e d e b t reserve f u n d w e r e a s s u m e d t o be capitalized. By p r o j e c t i n g all c a p i t a l a n d o p e r a t i n g costs w i t h reasonable escalation f a c t o r s , a life-cycle cost analysis w a s p e r f o r m e d . Results of t h a t analysis s h o w n b e l o w indicate an e s t i m a t e of required revenues t o offset all costs. These p r o j e c t e d costs are favorable w h e n c o m p a r e d t o a l t e r n a t i v e fossil fuel u n i t costs p r o j e c t e d for t h e N e w England region.

Year Unit Cost (cents/kWhr) 1982 1984 1986 1988 1990

5.1 5.5 5.9 6.4 6.9

INSTITUTIONAL CONSIDERATIONS A c c o r d i n g t o o u r analysis, t h e g e n e r a t i o n of e l e c t r i c i t y f r o m w o o d w a s t e is t e c h n i c a l l y feasible a n d e c o n o m i c a l l y a t t r a c t i v e . The m o s t d i f f i c u l t p r o b l e m in i m p l e m e n t i n g a w o o d - f i r e d p o w e r plant is perceived as being of i n s t i t u t i o n a l nature. These c o n c e r n s are p r i m a r i l y associated w i t h forest m a n a g e m e n t , t h e economy, and environmental considerations.

23.

SHEAHAN

Electric Power Generation

479

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Forest M a n a g e m e n t A forest is like a g a r d e n w h i c h needs t o be w e e d e d t o p r o m o t e a s o u n d a n d h e a l t h y s t a n d o f t i m b e r . Currently, there is no large-scale m e t h o d o l o g y t o remove n o n - c o m m e r c i a l w e e d trees w h i c h c o m p e t e f o r t h e s u p p l y o f w a t e r , n u t r i e n t s , a n d s u n l i g h t w i t h i n t h e forest. D e v e l o p m e n t o f a l o n g - t e r m w a s t e w o o d d e m a n d f o r electric g e n e r a t i o n c o u l d create a w a y t o better m a n a g e t h e forest's t i m b e r . A basic c o n c e r n t h a t a l w a y s a c c o m p a n i e s t h e d e v e l o p m e n t of any large forest-based i n d u s t r y is t h e p o t e n t i a l f o r abuse. It is therefore m a n d a t o r y t h a t a p o w e r plant n o t be s u p p l i e d w i t h w o o d at t h e expense of d e g r a d i n g or d e n u d i n g t h e forest. T o alleviate this c o n c e r n , it is r e c o m m e n d e d t h a t t h e personnel responsible f o r w o o d a c q u i s i t i o n m u s t be qualified professional foresters. In a d d i t i o n t o being in c h a r g e of w o o d w a s t e a c q u i s i t i o n , t h e y c o u l d also be available f o r private land o w n e r c o n s u l t a t i o n . This is p a r t i c u l a r l y i m p o r t a n t in V e r m o n t , since 9 0 p e r c e n t of t h e c o m m e r c i a l forest acreage is in private o w n e r s h i p . This t y p e of personnel a r r a n g e m e n t is similar t o t h e c o o p e r a t i v e assistance p r o g r a m s w h i c h are c o m m o n p l a c e in t h e p u l p a n d paper industry. T h e a c q u i s i t i o n personnel w o u l d be responsible for m o n i t o r i n g w o o d w a s t e deliveries t o a v o i d w a s t e f u l operations. T h e y w o u l d have t w o p r i m a r y c o n c e r n s . T h e first is t o ensure t h a t d i f f e r e n t i a t i o n is m a d e b e t w e e n h i g h q u a l i t y a n d l o w q u a l i t y material so t h a t q u a l i t y s a w t i m b e r a n d veneer logs are n o t c h i p p e d f o r fuel w o o d . T h e s e c o n d c o n c e r n is t o m a n d a t e t h a t small trees be carefully e v a l u a t e d before m a r k e t i n g f o r harvest. M a n y y o u n g trees m a y b e c o m e v a l u a b l e stock if g i v e n s u f f i c i e n t t i m e . In V e r m o n t , t h e p r i m a r y o w n e r s h i p o b j e c t i v e s o f t i m b e r land are recreation a n d place of residence; t i m b e r p r o d u c t i o n ranks t h i r d (14). Therefore, personnel responsible f o r w o o d w a s t e p r o c u r e m e n t s h o u l d recognize t h i s f a c t a n d p r e s c r i b e a n d e n c o u r a g e forest m a n a g e m e n t p r o c e d u r e s w h i c h m i n i m i z e a n y d i s r u p t i o n s t o t h e o w n e r s ' values a n d objectives. Economy T h e o p e r a t i o n o f a 5 0 M W w o o d - f i r e d p o w e r plant c o u l d have s i g n i f i c a n t a n d positive i m p a c t s o n V e r m o n t a n d t h e City of B u r l i n g t o n . The f o l l o w i n g are a f e w of t h e potential impacts: • The creation of a long-term and consistent demand for non-merchantable w o o d w a s t e c o u l d result in d r a m a t i c a l l y higher y i e l d f o r land parcels; therefore m a n y areas w h i c h previously h a d m a r g i n a l h a r v e s t i n g p o t e n t i a l c o u l d b e c o m e f i n a n c i a l l y viable.

480

BIOMASS AS A NONFOSSIL F U E L SOURCE

• T h e e x i s t i n g forest p r o d u c t i n d u s t r y c o u l d e x p e r i e n c e a l o n g - t e r m general u p g r a d i n g , faster g r o w i n g a n d healthier forest d u e t o t h e r e m o v a l of nutrient-depleting waste wood. • Private land o w n e r s c o u l d realize an i n c o m e f r o m t h e s t u m p a g e (price p a i d for t h e r e m o v a l of t h e w o o d ) w h i c h c o u l d help offset t h e effects of p r o p e r t y taxes.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

• V e r m o n t a n d t h e City of B u r l i n g t o n w o u l d b e c o m e m o r e self-sufficient in t h e i r e n e r g y resources, t h u s o f f s e t t i n g t h e r e q u i r e m e n t s for p r e d o m i n a n t l y i m p o r t e d fossil fuels. L i k e w i s e t h e s t a t e w i d e balance of p a y m e n t s w o u l d be i m p r o v e d by t h e r e d u c t i o n of i m p o r t e d energy. • T h e e c o n o m i c m u l t i p l i e r effect a p p l i e d t o t h e m o n e y kept in V e r m o n t , plus t h e general e x p a n s i o n of t h e forest-based i n d u s t r y c o u l d result in a s u b s t a n t i a l i m p a c t o n t h e City a n d State e c o n o m i e s . Environmental Concerns S o m e of t h e p r i m a r y e n v i r o n m e n t a l c o n c e r n s associated w i t h t h e h a r v e s t i n g of w o o d w a s t e f r o m a forested area i n c l u d e , b u t are not l i m i t e d t o , soil erosion, n u t r i e n t d e p l e t i o n , a e s t h e t i c d e g r a d a t i o n , r e d u c e d w a t e r q u a l i t y , a n d d e t e r i o r a t i o n of w i l d l i f e habitat. W i t h p r u d e n t h a r v e s t i n g m a n a g e m e n t p r o c e d u r e s , s u c h d a m a g e need n o t h a p p e n , a n d in fact, t h e e n v i r o n m e n t c o u l d be e n h a n c e d by t h e process. T h e forest is a l w a y s s u b j e c t t o insect a t t a c k s , disease infestations, a n d w i l d fire. Dense s t a n d s of o v e r m a t u r e trees are h i g h l y s u s c e p t i b l e t o insect or disease outbreaks. O n c e e s t a b l i s h e d , t h e y c a n spread easily t h r o u g h s u c h stands. Resistance of t h e forest d e p e n d s d r a m a t i c a l l y o n t h e species c o m p o s i t i o n , size d i s t r i b u t i o n , d e n s i t y , a n d general health of t h e tree. If trees are l a b o r i n g u n d e r o l d age a n d severe n u t r i e n t c o m p e t i t i o n caused by h i g h d e n s i t y , t h e general forest w i l l m o s t likely be seriously d a m a g e d . O n c e a s u b s t a n t i a l p o r t i o n of t h e t i m b e r is d e a d or r o t t e n , dry s u m m e r days c a n t r a n s f o r m t h e forest i n t o a h a v e n for disease o u t b r e a k a n d spread of fire. P r o v i d i n g a m a r k e t for l o w q u a l i t y m a t e r i a l c a n p r o v i d e a m e c h a n i s m for u p g r a d i n g t h e h e a l t h of t h e residual trees. F u r t h e r m o r e , l o g g i n g roads p r o v i d e access for p r o t e c t i o n as w e l l as recreation. W i l d l i f e needs an a d e q u a t e f o o d s u p p l y as w e l l as p r o t e c t i v e cover. Dense, o v e r m a t u r e trees m a y p r o v i d e p r o t e c t i o n a n d f o o d for s o m e b u t n o t m o s t of the w i l d l i f e species because t h e r e is relatively little p r o t e c t i o n of f o o d at g r o u n d level. S t u m p s , tree t o p s , a n d l i m b s w h i c h a c c o m p a n y c o n v e n t i o n a l h a r v e s t i n g o p e r a t i o n s are h a v e n s of p r o t e c t i o n for m a n y w i l d l i f e species. N e w g r o w t h t h a t f o l l o w s h a r v e s t i n g o p e r a t i o n s also represents an a b u n d a n t a n d c o n v e n i e n t f o o d source for w i l d l i f e . Therefore, it is i m p o r t a n t

23.

SHEAHAN

Electric Power Generation

481

t h a t in a h a r v e s t i n g o p e r a t i o n , a balance be p r o v i d e d b e t w e e n n e w g r o w t h a n d m a t u r e stands w i t h a s u b s t a n t i a l a m o u n t o f t r a n s i t i o n b e t w e e n t h e t w o . This is a desired w i l d l i f e m a n a g e m e n t o b j e c t i v e . T h e nature o f t h e w o o d d e m a n d o f a p o w e r plant is likely t o result in more m e c h a n i z e d harvesting operations, a n d e x p a n s i o n as a n t i c i p a t e d in t h e

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

p u r c h a s e a n d use o f w h o l e tree c h i p p e r s , a n d t o a lesser e x t e n t , m e c h a n i c a l h a r v e s t i n g e q u i p m e n t . Care m u s t be a p p l i e d in t h e selection a n d use o f this t y p e o f e q u i p m e n t o t h e r w i s e t h e large r u b b e r w h e e l s or tracks c o u l d b e c o m e a serious source of soil erosion. T h e n e g a t i v e c o n n o t a t i o n s associated w i t h t h i s t y p e o f p r o b l e m c o u l d q u i c k l y d i s c o u r a g e t h e c o o p e r a t i o n of private l a n d o w n e r s in a l l o w i n g w o o d w a s t e removal. SUMMARY Generation of e l e c t r i c i t y f r o m w a s t e w o o d is t e c h n i c a l l y , e c o n o m i c a l l y , a n d e n v i r o n m e n t a l l y feasible. A brief o v e r v i e w of p r i m a r y c o n c e r n s w h i c h a n y o r g a n i z a t i o n or c o m m u n i t y s h o u l d c o n s i d e r in i m p l e m e n t i n g s u c h a f a c i l i t y is presented. A s a n e p i l o g u e , t h e City of B r u l i n g t o n c o n d u c t e d a successful b o n d i n g r e f e r e n d u m f o r c o n s t r u c t i o n of t h e 5 0 M W w o o d - f i r e d p o w e r plant. By t h e s u m m e r o f 1 9 7 9 , d e s i g n w a s w e l l u n d e r w a y a n d plans f o r implementing construction were being formulated.

REFERENCES

1.

Henningson, Durham & Richardson, Inc. "Burlington, Vermont Refuse-Wood Power Plant, Aquaculture, Greenhouse - A Conceptual Study"; Washington D.C.; 1977.

2.

Ellis, T. Paper presented at the Forest Products Research Society Energy Workshop; FPRS Proceedings P-75-13; Denver, Colo., 1976.

3.

North Central Forest Experiment Station Forest Service; U.S. Department of Agriculture. Forest Residue Energy Program; St. Paul, Minn., 1978. Christensen, G. Paper presented at the Forest Products Research Society Energy Workshop; FPRS Proceedings P-75-13; Denver, Colo., 1976.

4.

5.

Corder, S. "Fuel Characteristics of Wood and Bark and Factors Affecting Heat Recovery"; ibid.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch023

482

BIOMASS AS A NONFOSSIL FUEL SOURCE

6.

Hewett, C. DSD No. 114; Thayer School Engineering, Dartmouth College: Hanover, NH, 1978.

7.

Blankenhorn, P.; Bowersox, T.; Murphey, W. Tappi 1978 61, 4.

8.

Towne, R. Paper presented at Forest Products Research Society Energy Workshop; FPRS Proceedings P-75-13; Denver, Colo. 1976.

9.

Hoff, E. "Abstracts of Papers:, the Conference on Energy and the Wood Products Industry sponsored by the Forest Products Research Society, Atlanta, Ga., 1976.

10.

Fernandes, J. "Wood Energy Systems, State of the Art and Developing Technologies"; Paper presented at the Future of Wood as an Energy Source Conference, Gorham, Maine, 1976.

11.

Johnson, N. "Wood Waste Burning on a Traveling Grate Spreader Stoker"; Paper presented at conference Hardware for Energy Generation in the Forest Products Industry, Seattle, Washington, 1979.

12.

Costle, D. "Standards of Performance for New Stationary Sources, Wood Residue-Fired Steam Generators"; 40 CFR Part 60; Federal Register 44, 12, Jan. 17, 1979.

13.

Phelan, J. "Review of Particulate Equipment for Power Plant Effluents"; Tappi 1977 60, 9.

14.

Kingsley, N.; Birch, T. "The Forest-Lane Owners of New Hampshire and Vermont. USDA Forest Service Resource Bulletin 1977, NE-51.

RECEIVED M A Y 12, 1980.

24 A Biomass Allocation Model Conversion of Biomass to Methanol Υ. Κ. A H N

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

Gilbert Associates, Incorporated, P.O. Box 1498, Reading, PA 19603

It has become apparent that the effects of the rapid rise in prices and dwindling supply of petroleum and natural gas are being felt by all of us in terms of the prices we pay for gasoline, electrical energy, and chemicals. Various alternative energy sources, both fossil and nonfossil, are being sought as substitutes for petroleum and natural gas. Fuels and petrochemi­ cals from biomass are considered to be promising alternatives. Biomass feedstocks under consideration include crops produced by agriculture or forestry, aquatic crops, agricultural and forest residues, and animal residues. The U.S. Department of Energy predicts the contribution of near-term systems to our domestic energy supply to be an additional 0.5 to 1.0 quad by 1985, (over the 1.0-1.5 quad now used) a displacement of 230,000 to 460,000 barrels of oil per day (1). Using published results as a data base (38,11), this paper illustrates how a deterministic model can be developed and utilized for the optimum allocation of biomass feedstocks. An example is presented for production and utilization of methanol from biomass. A m o n g t h e various p r o d u c t s t h a t c a n be synthesized f r o m biomass, m e t h a n o l w a s selected because o f its versatile a p p l i c a b i l i t y t o t h e electricity, t r a n s p o r t a t i o n , a n d c h e m i c a l sectors. Conversion of m e t h a n o l f r o m biomass is a c h i e v e d v i a o x y g e n - s t e a m g a s i f i c a t i o n f o l l o w e d by shift c o n v e r s i o n a n d m e t h a n o l synthesis. Three feedstocks w e r e selected f o r c o n v e r s i o n t o m e t h a n o l — w o o d residue, c o r n stover, a n d furfural residue. A v a i l a b i l i t y of

0097-6156/81/0144-0483$05.00/0 © 1981 American Chemical Society

484

BIOMASS AS A NONFOSSIL F U E L SOURCE

feedstocks is h i g h l y regional, a n d t h e state of Missouri w a s selected because of its a g r i c u l t u r e a n d forest w o o d land availability. M e t h a n o l w a s a s s u m e d t o be used for p o w e r g e n e r a t i o n by c o m b i n e d cycle, as a b l e n d i n g stock for gasoline, a n d as a c h e m i c a l . FEEDSTOCK SUPPLY A N D PRODUCT D E M A N D

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

Regional Selection T h e State of M i s s o u r i p r o d u c e s 10 m i l l i o n t o n per year (MMTPY) of a g r i c u l t u r a l residues, i n c l u d i n g 5.4 M M T P Y f r o m c o r n (2). It also has a p o t e n t i a l s i l v i c u l t u r a l p l a n t a t i o n c a p a b i l i t y of p r o d u c i n g , by c u r r e n t t e c h ­ n o l o g y , an average of 7 d r y t o n e q u i v a l e n t (DTE) per year-acre of h y b r i d poplar. A v a i l a b i l i t y of state land for d e v e l o p m e n t of s i l v i c u l t u r a l p l a n t a t i o n s is e s t i m a t e d t o be 11 t o 15 m i l l i o n acres for U.S. Forestry Service classification IIV sites (3). Feedstock Supply Of t h e 5.4 M M T P Y of c o r n p r o d u c e d , a p p r o x i m a t e l y 4 0 % consists of residue a n d t h e r e m a i n i n g 6 0 % is used as grain (4). Total a n n u a l f u r f u r a l c o n s u m p t i o n in t h e U n i t e d States is 150 m i l l i o n p o u n d s . For each p o u n d of f u r f u r a l processed, a p p r o x i m a t e l y 10 lb of residue is p r o d u c e d . T h e f u r f u r a l residue c o n t a i n s a p p r o x i m a t e l y 3 5 % m o i s t u r e (5). A v a i l a b i l i t y of t h e w o o d residue is e s t i m a t e d by a s s u m i n g t h a t o n l y 1 0 % of t h e class l-IV sites w i l l be used for h y b r i d poplar p l a n t a t i o n s a n d t h a t half of t h e w o o d p r o d u c e d w i l l be c o l l e c t e d as w o o d residue. A v a i l a b i l i t y of t h e t h r e e biomass f e e d s t o c k s is s u m m a r i z e d in Table I. T A B L E I. A V A I L A B I L I T Y O F F E E D S T O C K , F,

10

Heating Value, Btu/lb

i

Feedstock

1

Corn Stover

2.2

8.390

36.9

2

Furfural Residue

0.5

7.680

7.5

3

W o o d Residue

4.5

8.500

69.6

6

Btu/yr

10

6

Btu/Yr

Product Demand Total a n n u a l e n e r g y d e m a n d by t h e electric u t i l i t y sector in t h e State of Missouri is e s t i m a t e d t o be 3 5 8 . 4 χ 1 0 Btu (6). Of t h i s t o t a l d e m a n d . 64.9 X 10 Btu is oil a n d gas fired a n d is a p o t e n t i a l c a n d i d a t e for c o n v e r s i o n to o t h e r alternative fuels. It is e s t i m a t e d for t h e present s t u d y t h a t a p p r o x i 1 2

1 2

24.

AHN

485

Methanol from Biomass

m a t e l y 5% o f t h e oil a n d gas fired p o w e r g e n e r a t i o n , w h i c h is e q u i v a l e n t t o 7 0 M W , is s u b s t i t u t e d by m e t h a n o l f r o m biomass, m o s t l y f o r peaking services in gas t u r b i n e s . The t o t a l a n n u a l gasoline d e m a n d in t h e U n i t e d States is e s t i m a t e d t o be 1 1 5 , 0 0 0 Χ 1 0 gallons. If a 1 0 / 9 0 b l e n d o f m e t h a n o l / g a s o l i n e is c o n s i d e r e d as a gasoline s u b s t i t u t e , t h e t o t a l national m e t h a n o l d e m a n d w o u l d be 11,500 Χ 1 0 gallons. D e m a n d f o r t h e State of M i s s o u r i , prorated based o n p o p u l a t i o n , is 2 5 2 Χ 1 0 gallons. 6

6

6

The t o t a l a n n u a l d e m a n d for c h e m i c a l grade m e t h a n o l is e s t i m a t e d t o be 6 4 1 Χ 1 0 gallons. D e m a n d f o r t h e State of M i s s o u r i , again prorated based o n p o p u l a t i o n , is 14 Χ 1 0 gallons.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

6

6

The selling prices f o r e l e c t r i c i t y , c r u d e m e t h a n o l , a n d c h e m i c a l grade m e t h a n o l w e r e o b t a i n e d f r o m p u b l i s h e d studies (7). Table II summarizes t h e d e m a n d f o r each of t h e three c o n s u m i n g sectors a n d t h e p r o d u c t selling prices: T a b l e I I . P R O D U C T D E M A N D A N D S E L L I N G PRICES

j

Annual Demand, Dj S e l l i n g P r i c e , Sj Conventional Conventional Unit Unit 10 Btu $/10 Btu 70 M W 19Mills/kWh 6.37 3.245 10.45 2 5 2 M M Gal 0.6$/gal 14.449 10.75 0.805 14 M M Gal 0.150 $ / l b 1 2

1

Electricity

2

Transportation

3

Chemicals

6

BIOMASS CONVERSION Conversion o f Biomass t o Fuel Grade M e t h a n o l A block f l o w d i a g r a m f o r p r o d u c t i o n of fuel grade m e t h a n o l f r o m biomass is d e p i c t e d in Figure I. The g a s i f i c a t i o n step is based u p o n t h e Purox process a n d is f o l l o w e d by shift c o n v e r s i o n a n d gas p u r i f i c a t i o n steps. The clean gas, w h i c h is s h i f t e d t o a H / C O ratio of a p p r o x i m a t e l y 2 / 1 , is c o n v e r t e d t o m e t h a n o l in t h e ICI l o w - p r e s s u r e m e t h a n o l synthesis process. T h e process yields a p p r o x i m a t e l y 9 8 % pure m e t h a n o l w i t h t h e r e m a i n i n g 2 % c o n s i s t i n g of w a t e r a n d s o m e higher c a r b o n n u m b e r alcohols. 2

The m e d i u m - B t u gas f r o m t h e Purox process need not be desulfurized prior t o e n t e r i n g t h e shift reactor since a s u l f i d e d catalyst is used. The shifted gas goes t o t h e p u r i f i c a t i o n s y s t e m , w h e r e a h o t - c a r b o n a t e s c r u b b i n g s y s t e m is

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

486

BIOMASS AS A NONFOSSIL

^ ® ^

BIOMASS •

OXYCFN

U W fc|

r

GAS WASH - HEAT

BIOMASS

RECOVERY

GASIFICATION

SULFUR C02

F U E L SOURCE

SULFUR

RECOVERY

H2S - C 0 2

SHIFT

REMOVAL

CONVERSION

- •

COiPRESSION

Figure 1.

1500

PSIG

•ETHANOL

METHANOL

SYNTHESIS

PURIFICATION

PURGE

, FUEL GRADE METHANOL

Flow diagram for methanol via biomass gasification

24.

AHN

487

Methanol from Biomass

The fuel grade m e t h a n o l is 9 8 % pure a n d c o n t a i n s such i m p u r i t i e s as w a t e r , e t h a n o l a n d higher alcohols. T h e i m p u r i t i e s w o u l d have t o be r e m o v e d by d i s t i l l a t i o n t o p r o d u c e c h e m i c a l grade m e t h a n o l of 9 9 . 9 0 % p u r i t y c o n t a i n i n g e t h a n o l a n d w a t e r c o n t e n t s of n o more t h a n 9 0 0 p p m a n d 5 0 0 p p m respectively (7). It is e s t i m a t e d f o r t h e present s t u d y t h a t an a d d i t i o n a l 2 % t h e r m a l e f f i c i e n c y is lost for t h e d i s t i l l a t i o n o p e r a t i o n . The s y s t e m efficiencies f o r c o n v e r t i n g t h e three biomass feeds t o t h e three final p r o d u c t s are s u m m a r i z e d as f o l l o w s :

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

T a b l e III. S U M M A R Y O F T H E R M A L EFFICIENCIES Thermal Efficiency, %

i

Biomass

1

Corn Stover

2

Furfural Residue W o o d Residue

3

Conversion t o

System Efficiency, n j

Fuel Grade

j = 1 Elec.

j = 2 Trans.

j = 3 Chem.

21.7 21.7

47.0 47.0

46.0

20.5

44.3

{

Methanol 48.0 48.0 45.3

46.0 43.3

Conversion Economics The base capital a n d a n n u a l o p e r a t i n g costs t o m a n u f a c t u r e t h e final p r o d u c t s w e r e o b t a i n e d f r o m p u b l i s h e d date o n w o o d residue (7) and o n c o r n stover a n d furfural residue (8). T h e base data w e r e u p d a t e d t o 1979 p r i c i n g . The p r o d u c t costs w e r e c a l c u l a t e d f o r three fuel grade m e t h a n o l p r o d u c t capacities o f 6.550, 1 3 , 1 0 0 a n d 2 6 , 2 0 0 X 1 0 B t u / d a y . T h e base data w e r e a d j u s t e d using 0.7 scale factor f o r plant size. 6

The m e t h a n o l p r o d u c t i o n costs c a n be d i v i d e d into t w o m a i n unit o p e r a t i o n s — t h e g a s i f i c a t i o n s y s t e m i n c l u d i n g gas c l e a n i n g a n d t h e m e t h a n o l synthesis s y s t e m i n c l u d i n g shift a n d p u r i f i c a t i o n . T h e p r e l i m i n a r y cost e s t i m a t e s i n d i c a t e d t h a t a s i g n i f i c a n t p o r t i o n o f c a p i t a l cost is associated w i t h g a s i f i c a t i o n a n d gas c l e a n i n g systems. For t h e a n n u a l o p e r a t i n g costs, t h e f e e d s t o c k costs w e r e t h e m o s t c o s t l y e l e m e n t . Therefore, it is desirable t o investigate sensitivity of profit t o f e e d s t o c k cost. This is discussed in t h e results a n d c o n c l u s i o n section. T h e e s t i m a t e d m a n u f a c t u r i n g costs based o n t h e p u b l i s h e d f e e d s t o c k costs f o r t h e baseline case are s u m m a r i z e d in Table IV.

Product Electricity Transportation Chemical

b

C

Corn Stover, I = 1 l II III 15.31+A 13.05+A 11.46+A 16.08 13.70 12.03 16.53 14.09 12.38

Furfural Residue, I = 2 1 II III 9.95+A 7.51+A 6.76+A 10.45 7.89 7.50 10.75 8.11 7.71

W o o d Residue, I = 3 1 II III 10.64+A 9.1+A 8.13+A 11.71 8.54 9.56 11.49 9.83 8.78

a

0 7

Plant capacities of I - 6.550 M M Btu/day, II - 13.000 M M Btu/day and III - 26.200 M M Btu/day. A - ( D / 2 0 0 ) (0.4). where D - electricity demand in M W .

Based on raw material costs of $ 4 0 / t o n . $ 1 / M M Btu, $ 1 . 6 2 / M M Btu for corn stover, furfural residue, and w o o d residue, respectively.

j 1 2 3

Table IV. S U M M A R Y OF M A N U F A C T U R I N G C O S T , M,j, $ / M M B t u

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

24.

AHN

Methanol from Biomass

489

used t o reduce sulfides in t h e gases t o 10 p p m , a n d C O 2 t o 7%, so t h a t a ratio of 2.05 for H / ( C 0 4- 1.5 C 0 ) can be a c h i e v e d (7). 2

2

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

The p u r i f i e d gas is t h e n passed t h r o u g h a n iron s p o n g e d r u m a n d a sulfur g u a r d d r u m t o r e m o v e traces o f sulfur. F o l l o w i n g t h e g u a r d d r u m s , t h e gas, w h i c h is essentially sulfur free, is c o m p r e s s e d t o 1 5 0 0 psia. c o m b i n e d w i t h recycle gas, and passed t h r o u g h a f i x e d - b e d c a t a l y t i c ( h i g h l y - a c t i v e c o p p e r catalyst) c o n v e r t e r t o p r o d u c e c r u d e m e t h a n o l . The m e t h a n o l is c o n d e n s e d a n d separated f r o m t h e u n t r e a t e d gas, w h i c h is recycled t o t h e converter. The pressure is t h e n r e d u c e d , a n d dissolved gases are flashed f r o m t h e c r u d e m e t h a n o l . S o m e of t h e flash gas is p u r g e d for use as fuel t o c o n t r o l t h e c o n c e n t r a t i o n of inert c o m p o n e n t s in t h e c o n v e r t e r s y s t e m . T h e c r u d e m e t h a n o l is purified as required by d i s t i l l a t i o n t o p r o d u c e f u e l - g r a d e methanol. T h e r m a l efficiencies f o r c o n v e r t i n g c o r n stover (8), furfural residue (8), a n d w o o d residue (7) t o m e t h a n o l w e r e e s t i m a t e d f r o m t h e p u b l i s h e d data t o be 48.0, 48.0, a n d 4 5 . 3 % respectively. The e f f i c i e n c y data used f o r c o n v e r t i n g w o o d t o m e t h a n o l v i a t h e Purox process is also in g o o d a g r e e m e n t w i t h recently p u b l i s h e d data 0 2 ) . T h e Purox process m a y n o t have been t h e best c h o i c e f o r t h e g a s i f i c a t i o n (12), b u t process a n d e c o n o m i c data are available for all t h r e e feedstocks c o n s i d e r e d in this paper. C o n v e r s i o n o f Fuel Grade M e t h a n o l t o Final P r o d u c t s Conversion of fuel grade m e t h a n o l t o e l e c t r i c i t y is a c h i e v e d b y means of a combined-cycle configuration. The efficiency of a methanol-fueled c o m b i n e d c y c l e plant w a s e s t i m a t e d t o be 4 5 . 2 % (9). The use o f fuel g r a d e m e t h a n o l f o r gasoline-alcohol blends m a y require e n g i n e m o d i f i c a t i o n s , b u t t h i s paper is n o t c o n c e r n e d w i t h s u c h m o d i f i c a tions. Rather, it is l i m i t e d t o t h e p r e p a r a t i o n o f fuel grade m e t h a n o l suitable for gasoline b l e n d i n g . One r e q u i r e m e n t is t o r e d u c e t h e m o i s t u r e c o n t e n t t o a m a x i m u m o f 0.25 w e i g h t p e r c e n t t o avoid phase separation. Therefore, w a t e r m u s t either be e x l c u d e d f r o m t h e fuel g r a d e m e t h a n o l or o t h e r c o m p o u n d s m u s t be a d d e d t o i m p r o v e t h e w a t e r t o l e r a n c e of t h e m e t h a n o l - g a s o l i n e b l e n d . S o m e of t h e l o w e r m o l e c u l a r w e i g h t f r a c t i o n s o f t h e gasoline m a y have t o be r e m o v e d d u r i n g t h e s u m m e r t o c o u n t e r a c t t h e large nonideal increase in t h e v a p o r pressure o f t h e b l e n d . This c o u l d penalize t h e e c o n o m i c s o f b l e n d i n g gasoline a n d m e t h a n o l (V3). It is e s t i m a t e d for t h e present s t u d y t h a t 1 % t h e r m a l e f f i c i e n c y is lost t o refine suitable gasoline b l e n d i n g stocks.

490

BIOMASS

AS A

NONFOSSIL

FUEL

SOURCE

D E V E L O P M E N T OF A L L O C A T I O N M O D E L T h e p r o b l e m is t o d e t e r m i n e t h e o p t i m u m biomass a l l o c a t i o n p o l i c y in order t o m a x i m i z e t h e profit. A generalized linear p r o g r a m , SIMPLES (10), w a s used t o d e v e l o p t h e resource a l l o c a t i o n m o d e l . T h e m o d e l seeks t o m a x i m i z e t h e linear o b j e c t i v e f u n c t i o n (profit). Ν Ρ - Σ

Ν DjSj-Σ

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

j-1

j-1

Κ LnijfjjMjj i-1

1)

for Ν set of i n e q u a l i t y c o n s t r a i n t s Ν ZfjjSFj

i-1,2....K

j-1

2)

a n d Κ set of e q u a l i t y c o n s t r a i n t s Κ

Wu-Dj

j - 1.2....N

i-1

3)

a n d t h e n o n - n e g a t i v e restrictions of

Where: Ρ Dj Sj

= profit = d e m a n d for c o m m o d i t y j = selling price for c o m m o d i t y j

M j j — m a n u f a c t u r i n g cost for c o m m o d i t y j f r o m f e e d s t o c k i njj fjj Fj

= t h e r m a l e f f i c i e n c y of c o n v e r t i n g f e e d s t o c k i t o c o m ­ modity j = allocation of f e e d s t o c k i t o c o m m o d i t y j = availability of f e e d s t o c k i

24.

AHN

491

Methanol from Biomass

In t e r m s of t h e present m e t h a n o l s t u d y , t h e p r o b l e m seeks an o p t i m u m a l l o c a t i o n policy for c o r n stover (i — 1), furfural residue (i = 2), a n d w o o d residue (i = 3) t o p r o d u c e three c o m m o d i t y p r o d u c t s of e l e c t r i c i t y (j = 1), t r a n s p o r t a t i o n (j = 2), a n d c h e m i c a l s (j = 3) in t h e m o s t p r o f i t a b l e w a y . In pure m a t h e m a t i c a l t e r m s , w e are t o d e t e r m i n e fjj w h i c h m a x i m i z e s t h e profit f u n c t i o n . Equation 1 , w h e n t h e f e e d s t o c k availability a n d d e m a n d are c o n s t r a i n e d by Equations 2 a n d 3. respectively. The data base t o use w i t h Equations 1 t h r o u g h 4 is t a b u l a t e d in Table I f o r F Table II f o r Dj a n d Sj, Table III for n|j, a n d Table IV for My. ir

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

RESULTS A N D CONCLUSIONS Table V presents t h e result of t h e o p t i m u m allocation p o l i c y for t h e three biomass feedstocks in satisfying t h e d e m a n d of t h e three c o n s u m i n g sectors.

T a b l e V . O P T I M U M F E E D S T O C K A L L O C A T I O N P O L I C Y , fjj (BASELINE CASE)

Allocation of Feedstock i t o Consuming Sector j , 1 0 Btu/Yr 1 2

Feedstock Cost, i

Feedstock

1

Corn

$/10

6

Btu

j = 2

j = 3

Elec.

Trans.

Chem.

0

0

i - 1

Stover

2.38

0

2

Furfural Residue

1.0

0

3

Wood Residue

1.62

15.83

5.75 26.52

1.75 0

It is i n t e r e s t i n g t o note t h a t furfural residue alone w a s s u f f i c i e n t t o satisfy t h e d e m a n d of c h e m i c a l grade m e t h a n o l . This is d u e t o t h e fact t h a t all t h e available, least e x p e n s i v e fuel (furfural residue), w a s used t o m a n u f a c t u r e t h e m o s t expensive p r o d u c t (chemical grade m e t h a n o l ) . T h e t r a n s p o r t sector requires t h e second m o s t e x p e n s i v e m e t h a n o l fuel, a n d any furfural residue left over after c h e m i c a l grade m e t h a n o l w a s used f o r p r o d u c t i o n of t h e t r a n s p o r t a t i o n grade m e t h a n o l . T h e balance of t h e t r a n s p o r t a t i o n grade m e t h a n o l w a s s u p p l i e d by t h e w o o d residue, t h e s e c o n d least e x p e n s i v e feedstock. A l l t h e electric u t i l i t y d e m a n d w a s satisfied b y w o o d residue, a n d no c o r n stover w a s used.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

BIOMASS AS A NONFOSSIL F U E L SOURCE

Figure 2.

Sensitivity of feedstock costs on optimum profit

24.

AH Ν

493

Methanol from Biomass

Profit c a l c u l a t e d f r o m t h e o p t i m a l p o l i c y w a s $ 2 6 . 5 m i l l i o n per year i n d i c a t i n g t h a t various g r a d e m e t h a n o l s m a d e f r o m t h e three biomass feedstocks can be c o m p e t i t i v e w i t h t h o s e m a d e f r o m c o n v e n t i o n a l sources. The c a l c u l a t i o n w a s based o n t h e unit m a n u f a c t u r i n g cost d e t e r m i n e d f r o m a 2 6 , 2 0 0 X 1 0 / d a y m e t h a n o l plant c a p a c i t y (plant c a p a c i t y III in Table IV). T h e s t u d y , h o w e v e r , disclosed t h e fact t h a t t h e biomass f e e d s t o c k costs are t h e d o m i n a t i n g f a c t o r in t h e e c o n o m i c s of m e t h a n o l p r o d u c t i o n . It w o u l d therefore be i n t e r e s t i n g t o note h o w t h e o p t i m u m profits vary w i t h f e e d s t o c k cost. 6

Since m o r e t h a n one f e e d s t o c k is i n v o l v e d , d e v e l o p m e n t of a sensitivity curve for o p t i m u m profits vs. f e e d s t o c k cost requires use o f a w e i g h t - a v e r a g e d Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

f e e d s t o c k cost. T h e w e i g h t - a v e r a g e d f e e d s t o c k cost is d e f i n e d as:

3 Weight —

3

Averaged

Feedstock Cost

_

——1H

( $ / M M Btu)

j j-1

£

f j

.

i-i'

J

Cj = cost of f e e d s t o c k i in $ / M M B t u a n d fjj w e r e d e f i n e d previously. For t h i s s t u d y , t h e costs of t h r e e feedstocks w e r e varied f r o m 2 5 t o 5 0 % higher or l o w e r t h a n t h e p u b l i s h e d base case f e e d s t o c k costs. The o p t i m u m profits w e r e t h e n c a l c u l a t e d u s i n g t h e same f e e d s t o c k availability, p r o d u c t d e m a n d , a n d p r o d u c t selling prices as t h e base case. Figure II s u m m a r i z e s t h e results of t h e c a l c u l a t i o n . T h e f i g u r e indicates t h a t t h e o p t i m u m profits are indeed very sensitive t o f e e d s t o c k cost c h a n g e s a n d t h a t c o n t i n u e d i m p r o v e m e n t o f biomass p r o d u c t i o n a n d c o l l e c t i o n t e c h n i q u e s is very desirable t o i m p r o v e t o t a l profit. LIST OF S Y M B O L S Cj

Cost o f Feedstock i

Dj fjj Fj i

Demand for Commodity j A l l o c a t i o n o f Feedstock i t o C o m m o d i t y j A v a i l a b i l i t y o f Feedstock i Feedstock

j Mjj Ρ Sj njj

Commodity M a n u f a c t u r i n g Cost f o r C o m m o d i t y j f r o m Feedstock i Profit Selling Price f o r C o m m o d i t y j T h e r m a l Efficiency of C o n v e r t i n g Feedstock i t o C o m m o d i t y j

494

BIOMASS AS A NONFOSSIL FUEL SOURCE

REFERENCES

1.

U.S. Department of Energy, "Fuels from Biomass — Multiyear Program Plan", Washington, D.C., April 27, 1978.

2. Clausen, E.C.; Gaddy, J.L. "Preprints", 81st National Meeting, The American Institute of Chemical Engineers, Kansas City, Mo., April 1976. 3. Salo, D.J.; Inman, R.E.; McGurk, B.J.; Verhoeff, J. MITRE Technical Report for ERDA MTR-7347 (Vol. III), Mclean, Va., May 1977.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch024

4.

McClure, T.A. "Proceedings", Biomass — A Cash Crop for the Future? Kansas City, Mo., March 2-3, 1977; 145-77.

5. Sheppard, W.J. ibid; 178-204. 6.

"The Application of Near-Term Fossil Technologies to the Energy Supply/Demand Profiles of U.S. States and Regions", U.S. Department of Energy, January 1977, FE/2442.

7.

Bliss, C.; Blake, D.O. MITRE Technical Report for ERDA MTR-7347 (Vol. III), Mclean, Va., May 1977.

8.

Otis, J.L. "Proceedings", Biomass — A Cash Crop for the Future?, Kansas City, Mo., March 2-3, 1977; 219-36.

9.

Gilbert Associates, Inc. "Assessment of Fossil Energy Technology for Electric Power Generation", OPPA/ERDA, March 1977, GAI Report 1940.

10.

Walker, H.; Hall, L. "SIMPLEX, A Code for the Solution of Linear Programming Problems", UCRL-51820.

11.

SRI International, "Mission Analysis for the Federal Fuels from Biomass Program", U.S. Department of Energy, Report, Vol. II, 1978.

12.

Science Applications, Inc., "Biomass Based Methanol Processes", Presented at the Seventh Biomass Thermochemical Conversion Contractors Meeting, Roanoke, Va., April 24-25, 1979.

13.

Hagan, D.L., "Methanol — Its Synthesis, Use as a Fuel, Economics, and Hazards", Report prepared for ERDA, December 1976.

RECEIVED JUNE 20, 1980.

25 The Energy Plantation and the Photosynthesis Energy Factory M A L C O M D. FRASER, JOHN F. HENRY, LOUIS C. BORGHI, and NORMAN J. BARBERA

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

InterTechnology/Solar Corporation, 100 Main Street, Warrenton, V A 22186

The Energy Plantation In conventional forestry, trees are grown in plantations to produce the raw material for a variety of products such as lumber, plywood, pulp and others. In these plantations, the trees are generally widely spaced and grown to sizes large enough for the manufacture of the desired products. Achieving these commercial sizes may require long growing periods or rotations which may range from 30 to 80 years or more. As a result of these constraints — long rotations and planting densities of the order of a few hundred trees per acre towards the end of the rotation — the plantation site is only fully utilized for a short fraction of the rotation period. Average sustained yields over the rotation therefore rarely exceed about 1 oven-dry-ton of mechantable material per acre-year (1). Moreover, because of the size of the crop and the need to maintain its physical integrity, conventional single-tree harvesting and handling methods are generally used in forestry operations. Tree crops h o w e v e r c o u l d be g r o w n o n m u c h shorter rotations if t h e size a n d f o r m o f t h e crops w e r e n o t l i m i t i n g f a c t o r s in t h e e n d use o f t h e crop. S u c h is t h e case w h e n t h e desired p r o d u c t is w o o d c h i p s t o be used f o r p u l p , fuel, or f e e d s t o c k f o r c o n v e r s i o n t o s u b s t i t u t e fuels. S h o r t - r o t a t i o n tree f a r m i n g

0097-6156/81/0144-0495$ 12.50/0 © 1981 American Chemical Society

496

BIOMASS AS A NONFOSSIL FUEL SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

generally refers t o r o t a t i o n s of 2 0 years or less a n d is generally associated w i t h close s p a c i n g of t h e trees in order t o a c h i e v e full site utilization w i t h i n the rotation period. S h o r t - r o t a t i o n tree f a r m i n g for fiber p r o d u c t i o n has been p r o p o s e d by a n u m b e r of investigators (2-5). Early s h o r t - r o t a t i o n e x p e r i m e n t a l data i n d i c a t e d t h a t t h e biomass yields a c h i e v e d in s h o r t - r o t a t i o n p l a n t a t i o n s c o u l d far exceed t h o s e of c o n v e n t i o n a l forestry. A v e r a g e a n n u a l s u s t a i n e d yields of 5 t o 10 o v e n - d r y t o n s per acre-year (ODT/ac-yr) w e r e s h o w n t o be possible u n d e r s h o r t - r o t a t i o n c o n d i t i o n s (6,7). It also b e c a m e a p p a r e n t t h a t s u c h h i g h yields c o u l d be a c h i e v e d o n l y if intensive m a n a g e m e n t w e r e a p p l i e d t o t h e p l a n t a t i o n . In m a n y cases, t h e level of m a n a g e m e n t appears t o be c o m p a r a b l e t o t h a t required in t h e p r o d u c t i o n of a g r i c u l t u r a l c r o p s (8-10). T h e p o t e n t i a l of s h o r t - r o t a t i o n tree f a r m i n g for fiber p r o d u c t i o n i n d u c e d I n t e r T e c h n o l o g y / S o l a r C o r p o r a t i o n t o a d v a n c e t h e same c o n c e p t as a possible source of b i o m a s s for e n e r g y c o n v e r s i o n (11-13). O t h e r i n v e s t i g a t o r s have d e s c r i b e d similar c o n c e p t s (14,15). A s it is presently e n v i s i o n e d by I n t e r T e c h n o l o g y / S o l a r C o r p o r a t i o n , t h e Energy Plantation is a w o o d y biomass p r o d u c t i o n e n t i t y relying o n short r o t a t i o n a n d i n t e n s i v e m a n a g e m e n t t o p r o d u c e b i o m a s s e x c l u s i v e l y for its fuel a n d / o r f e e d s t o c k value. Energy Plantations offer a n u m b e r of p o t e n t i a l a d v a n t a g e s over c o n v e n t i o n a l forestry p l a n t a t i o n s : h i g h e r p r o d u c t i v i t y per u n i t land area, l o w e r land r e q u i r e m e n t s for a g i v e n biomass o u t p u t , earlier cash return o n t h e i n v e s t m e n t , e x t e n s i v e m e c h a n i z a t i o n similar t o t h a t p r a c t i c e d in a g r i c u l t u r e , a n d a b i l i t y t o assimilate c u l t u r a l a n d g e n e t i c i m p r o v e m e n t s q u i c k l y . S h o r t - r o t a t i o n c r o p s c a n also be c h o s e n a m o n g a v a r i e t y of species w h i c h regenerate by c o p p i c i n g , t h e r e b y e l i m i n a t i n g t h e need for r e p l a n t i n g after each harvest. Energy Plantations h o w e v e r d o have a n u m b e r of d i s a d v a n t a g e s : initial e s t a b l i s h m e n t costs a n d yearly m a n a g e m e n t costs per unit area are generally higher t h a n those for c o n v e n t i o n a l forest c r o p s ; o n l y sites a m e n a b l e t o m e c h a n i z e d o p e r a t i o n s can be u s e d ; a n d disease a n d insect p r o p a g a t i o n m a y be d i f f i c u l t t o c o n t r o l . S e c u r i n g t h e use of t h e land for e n e r g y c r o p s c o u l d also be a p r o b l e m in s o m e areas w h e r e c o m p e t i t i o n w i t h o t h e r uses (e.g., f a r m i n g , recreation) c o u l d occur. No full-scale Energy Plantation has yet been d e m o n s t r a t e d . It is therefore necessary t o use a c o n c e p t u a l d e s i g n of t h e Energy Plantation t o assess its economic and energy efficiency potential. Table I summarizes the design p a r a m e t e r s a d o p t e d in t h e ITC/Solar m o d e l of t h e Energy Plantation. T h e c r o p s are a s s u m e d t o be c h o s e n f r o m a v a r i e t y of h a r d w o o d s d i s p l a y i n g fast j u v e n i l e g r o w t h a n d c a p a b l e of regeneration by c o p p i c i n g . C a n d i d a t e crops i n c l u d e A m e r i c a n s y c a m o r e (Platanus occidentalis), h y b r i d poplars (Populus

25.

FRASER E T AL.

497

Photosynthesis Energy Factory

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

T a b l e I. D E S I G N P A R A M E T E R S U S E D I N T H E I T C / S O L A R M O D E L OF THE ENERGY P L A N T A T I O N Production

Variable, generally o f t h e order o f 2 0 0 , 0 0 0 O D T / a c - y r

Crop

F a s t - g r o w i n g h a r d w o o d s w i t h c o p p i c e regeneration

Productivity

5 t o 10 O D T / a c - y r

Planting Density

4 t o 16 square f t per plant, i.e., — 1 0 , 0 0 0 t o — 2 5 0 0 trees per acre

Lifetime

One f i r s t - g r o w t h r o t a t i o n f o l l o w e d b y five c o p p i c e r o t a tions

Management

Mechanical weed control Fertilization Irrigation (in s o m e m o d e s of o p e r a t i o n of t h e p l a n t a tion)

Harvesting

C o n c e p t u a l self-propelled h a r v é s t e r - c h i p p e r

Transportation

Green

woodchips

transported

to conversion

plant

located in c e n t e r o f t h e p l a n t a t i o n Support

Nursery o p e r a t i o n , e q u i p m e n t m a i n t e n a n c e a n d repair, supervision

Land

Plantation m a d e o f lots o f t h e size o f an average f a r m in t h e region d i s t r i b u t e d at r a n d o m w i t h i n a larger g e o g r a p h i c area

498

BIOMASS AS A NONFOSSIL F U E L SOURCE

sppj. Eastern c o t t o n w o o d (P. deltoïdes), black c o t t o n w o o d (P. trichocarpa). black alder (Alnus glutanosa). green ash (Fraxinus pennsylvanicum). Eucalyptus, a n d others. T h e selection of t h e c r o p is m a d e o n t h e basis of c l i m a t e , soil c o n d i t i o n s , a n d d e m o n s t r a t e d g r o w t h c h a r a c t e r i s t i c s of t h e c a n d i d a t e crop.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

F a s t - g r o w i n g h a r d w o o d s are generally s u g g e s t e d because of t h e i r c o p p i c i n g properties, w h i c h e l i m i n a t e t h e need for r e e s t a b l i s h m e n t of t h e p l a n t a t i o n after each harvest. Due t o t h e c l i m a t e a n d soil c o n d i t i o n s , pines m a y be better c r o p c a n d i d a t e s in s o m e s i t u a t i o n s , as s h o w n for instance in S o u t h e r n Georgia w h e r e loblolly pines d i s p l a y e d h i g h e r p r o d u c t i v i t y t h a n s y c a m o r e for r o t a t i o n s of a b o u t 6 years or m o r e (16). On an Energy P l a n t a t i o n , t h e p l a n t i n g d e n s i t y a n d r o t a t i o n d u r a t i o n , a n d their associated p r o d u c t i v i t y , are c h o s e n t o m i n i m i z e t h e c o s t of biomass p r o d u c t i o n . M a n y a u t h o r s have recognized t h a t a s t r o n g c o r r e l a t i o n exists b e t w e e n s p a c i n g a n d r o t a t i o n age for h a r d w o o d c r o p s g r o w n u n d e r intensive m a n a g e m e n t . O n c e a s p a c i n g has been a d o p t e d w h e n e s t a b l i s h i n g a f a r m , t h e r o t a t i o n age at w h i c h t h e m e a n a n n u a l b i o m a s s increase is o b t a i n e d m u s t be a d o p t e d t o m a x i m i z e t h e yield of t h e f a r m (17). T h e c h o i c e of t h e o p t i m u m r o t a t i o n is p a r t i c u l a r l y critical for close s p a c i n g s generally associated w i t h short rotations because t h e average p r o d u c t i v i t y decreases s i g n i f i c a n t l y once t h e o p t i m u m r o t a t i o n is e x c e e d e d . On t h e basis of d a t a available at present, s o m e a u t h o r s (6,18) favor r o t a t i o n s of 10 t o 15 years w h i l e others prefer shorter r o t a t i o n s (19-21). T h e d e s i g n p a r a m e t e r s a d o p t e d in Table I m i g h t t h e r e f o r e have t o be m o d i f i e d t o a c c o u n t for site-specific c o n d i t i o n s . The i m p a c t of c h a n g e s in s p a c i n g a n d r o t a t i o n d u r a t i o n has been e s t i m a t e d t h r o u g h sensitivity analyses (21). L a n d m a n a g e m e n t i n c l u d e s w e e d c o n t r o l t o e l i m i n a t e c o m p e t i t i o n for light, m o i s t u r e , a n d n u t r i e n t s ; fertilization t o ensure m a i n t e n a n c e of s u s t a i n e d p r o d u c t i v i t y ; a n d irrigation in s o m e m o d e s of o p e r a t i o n . Irrigation w i t h surface or w e l l w a t e r is p r o b a b l y not c o s t - e f f e c t i v e (22). H o w e v e r , irrigation w i t h m u n i c i p a l s e w a g e effluent c o u l d be c o s t - e f f e c t i v e as a result of the c r e d i t g e n e r a t e d t h r o u g h land t r e a t m e n t of t h e w a s t e s (23). This latter m o d e of o p e r a t i o n is analyzed in t h e P h o t o s y n t h e s i s Energy Factory d i s c u s s e d b e l o w . H a r v e s t i n g is a s s u m e d t o be p e r f o r m e d m e c h a n i c a l l y by a harvesterc h i p p e r w h i c h c o u l d be similar in d e s i g n t o a c o r n silage harvester a d a p t e d for t h e Energy Plantation crops. T h e green c h i p s , after field storage, are t r a n s p o r t e d t o t h e c o n v e r s i o n plant located ideally in t h e c e n t e r of t h e Energy Plantation area.

25.

FRASER E T AL.

Photosynthesis Energy Factory

499

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

T h e Energy Plantation is c o n c e i v e d as a s e l f - c o n t a i n e d industrial o p e r a t i o n i n c l u d i n g its o w n m a n a g e m e n t a n d s u p p o r t services. T h e Energy Plantation is a s s u m e d t o consist of parcels o f land of t h e size of an average f a r m in t h e region d i s t r i b u t e d w i t h i n a g e o g r a p h i c area s u r r o u n d i n g t h e c o n v e r s i o n plant. The land selected f o r e n e r g y f a r m i n g is preferably m a r g i n a l land n o t suitable for t h e p r o d u c t i o n o f m o r e v a l u a b l e crops. Using m a r g i n a l land h o w e v e r w i l l result in p r o d u c t i v i t i e s l o w e r t h a n t h o s e m e n t i o n e d earlier as achievable. O n t h e o t h e r h a n d , m a r g i n a l land c a n p r o b a b l y be o b t a i n e d at a l o w e r cost ( t h r o u g h leasing or purchase) t h a n t h e g o o d - q u a l i t y land o n w h i c h m a n y h i g h p r o d u c t i v i t y data have been g e n e r a t e d . T h e t y p e of land available for Energy Plantations w i l l therefore be d e t e r m i n e d b y t h e overall e c o n o m i c s o f biomass p r o d u c t i o n at i n d i v i d u a l sites. In its s i m p l e s t o p e r a t i o n a l schedule, t h e t o t a l p l a n t e d area o f t h e p l a n t a t i o n is d i v i d e d into a n u m b e r of equal m o d u l e s equal t o t h e r o t a t i o n d u r a t i o n (e.g.. four m o d u l e s , each equal t o o n e - f o u r t h of t h e p l a n t e d area f o r a four-year rotation). Each year, one of these m o d u l e s is harvested a n d t h e n regenerates t h r o u g h c o p p i c i n g t o s u p p l y t h e n e w c r o p at t h e e n d o f t h e next r o t a t i o n . A f t e r a n u m b e r of c o p p i c e crops have been harvested f r o m t h e original p l a n t i n g , t h e m o d u l e m u s t be r e p l a n t e d before progressive w e a k e n i n g o f t h e root s y s t e m results in r e d u c e d a n n u a l p r o d u c t i v i t i e s . In ITC/Solar's m o d e l , regeneration of a m o d u l e is a c c o m p l i s h e d b y p l a n t i n g of clones g a t h e r e d f r o m o t h e r (still operational) areas o f t h e p l a n t a t i o n . This m o d e of o p e r a t i o n ensures sustained a n n u a l p r o d u c t i o n of biomass o n a p e r m a n e n t basis. Other c o n c e p t u a l designs of energy f a r m s have been proposed w h i c h i n c l u d e t h e same basic features as t h e ITC/Solar m o d e l (19,20.24,25). Because of t h e lack of e x p e r i m e n t a l d a t a c o n c e r n i n g s o m e aspects of energy f a r m i n g , all designs i n c l u d e a c e r t a i n e l e m e n t of u n c e r t a i n t y . Sensitivity analyses are therefore needed t o e s t i m a t e t h e i m p a c t o f these u n c e r t a i n t i e s o n t h e p r o j e c t e d biomass p r o d u c t i o n costs a n d t o e s t i m a t e reasonable ranges of values f o r these p r o d u c t i o n costs. The Photosynthesis Energy Factory A n o t h e r alternate source of energy, w h i c h also offers t h e a d d i t i o n a l a d v a n t a g e of d e c r e a s i n g t h e e n v i r o n m e n t a l i m p a c t associated w i t h t h e disposal o f w a s t e w a t e r a n d residues, is t h e c o n c e p t of g r o w i n g algae in s h a l l o w ponds. A l g a e p o n d s are o p e n s h a l l o w p o n d s in w h i c h algae a n d bacterial p o p u l a t i o n s s y m b i o t i c a l l y utilize s u n l i g h t a n d n u t r i e n t s t o p r o d u c e cell mass. T h e earliest a p p l i c a t i o n of t h e algae p o n d c o n c e p t is t h e stabilization p o n d . Stabilization p o n d s have been used by small c o m m u n i t i e s for years as a means of t r e a t i n g d o m e s t i c w a s t e w a t e r . In c o n s t r u c t i o n a n d

500

BIOMASS AS A NONFOSSIL F U E L SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

o p e r a t i o n , these p o n d s are t h e essence of s i m p l i c i t y . The m a i n r e q u i r e m e n t s are land a n d a favorable, s u n n y c l i m a t e . Currently, t h e r e is a t r e n d t o w a r d t h e use of algae p o n d s as f i n i s h i n g p o n d s in i n t e g r a t e d m u n i c i p a l a n d w a s t e t r e a t m e n t . The p o n d s o p e r a t e in series t o " r e m o v e " b o t h BOD a n d p h o s p h o r u s by t y i n g up these c o m p o n e n t s in cell mass. In an algae p o n d s y s t e m for r e c o v e r y i n g e n e r g y f r o m v a r i o u s residues, t h e algae w o u l d be d i g e s t e d a n a e r o b i c a l l y t o y i e l d a m e t h a n e - c o n t a i n i n g gas, w h i c h w o u l d be processed into SNG. A s l o n g as 2 0 years a g o . w o r k w a s u n d e r t a k e n by Dr. W . J . O s w a l d a n d others at t h e U n i v e r s i t y of California at Berkeley t o d e v e l o p a s y s t e m u t i l i z i n g t h e algae p o n d c o n c e p t b o t h t o t r e a t w a s t e (26-29) a n d t o p r o d u c e fuels (30.31). Indeed, m i c r o a l g a e w e r e a m o n g t h e earliest " f u e l c r o p s " p r o p o s e d , t h e t e c h n i c a l p r o b l e m s w e r e essentially c o n c e r n e d w i t h i n t e g r a t i n g t h e c o m p o nents and optimizing their operation. The components themselves — the algae p o n d , t h e digester, a n d t h e s e d i m e n t a t i o n , s e p a r a t i o n , a n d f i n i s h i n g stages — w e r e already b e i n g used in w a s t e t r e a t m e n t . T h e w o r k over t h e last 2 0 years has c o n c e n t r a t e d in t h r e e areas: (1) i d e n t i f y i n g a n d q u a n t i f y i n g algal g r o w t h - l i m i t i n g f a c t o r s (nutrients, species c h a r a c t e r i s t i c s , a n d c l i m a t o l o g i c a l p a r a m e t e r s ) ; (2) m a x i m i z i n g gas p r o d u c t i o n f r o m anaerobic f e r m e n t a t i o n ; a n d (3) o p t i m i z i n g t h e s y s t e m w i t h respect t o gas p r o d u c t i o n , residue uptake, land utilization, a n d cost-effectiveness. S t a t e - o f - t h e - a r t r e v i e w s have been p u b l i s h e d r e c e n t l y r e g a r d i n g t h e e n g i n e e r i n g aspects (32) of m i c r o a l g a e p r o d u c t i o n a n d t h e p o t e n t i a l of m i c r o a l g a e as b i o c o n v e r s i o n s y s t e m s (33.34). O t h e r p u b l i c a t i o n s have r e p o r t e d recent research o n species c o n t r o l , algae h a r v e s t i n g , a n d t h e p o t e n t i a l of b l u e - g r e e n algae (35-39). Both t h e Energy Plantation a n d t h e algae p o n d c a n c o n t r i b u t e t o t h e s o l u t i o n of t h e p o p u l a t i o n , resources a n d e n e r g y p r o b l e m s f a c i n g us. Recently, it b e c a m e a p p a r e n t t h a t t h e y c o u l d perhaps better a c c o m p l i s h these missions w h e n t h e t w o are i n t e g r a t e d t o f o r m one c o m p o s i t e s y s t e m , as s h o w n in Figure I. In short, each b i o c o n v e r s i o n s y s t e m p r o d u c e s a b y - p r o d u c t t h a t can be used t o a d v a n t a g e by t h e other. The c a r b o n c o n t e n t of s e w a g e limits the p r o d u c t i o n of t h e algae p o n d , b u t c a r b o n d i o x i d e , a b y - p r o d u c t of c o m b u s t i o n of solid Energy Plantation fuel ( w h i c h c u r r e n t l y appears t o be t h e best w a y of u s i n g p l a n t m a t t e r as fuel), c a n be s u p p l i e d t o t h e algae p o n d t o increase its p r o d u c t i v i t y . T h e w a s t e heat f r o m t h e boiler c a n be used t o c o n t r o l t h e t e m p e r a t u r e of t h e algae digester. T h e s l u d g e g e n e r a t e d as a byp r o d u c t of t h e algae p o n d p r o v i d e s a source of inorganic n u t r i e n t s a n d w a t e r for t h e Energy P l a n t a t i o n , w h i c h t h u s provides an ideal disposal site for t h e sludge.

25.

FRASER E T AL.

Photosynthesis Energy Factory

501

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

T h e Photosynthesis Energy Factory (PEF) is a synergistic c o m b i n a t i o n of t h e d r y - l a n d Energy Plantation a n d t h e algae p o n d w h i c h c a n p r o d u c e o n a p e r p e t u a l l y r e n e w a b l e basis, n o n p o l l u t i n g a n d t o t a l l y d o m e s t i c fuels f r o m m a r g i n a l l y useful land, solar energy, a n d various residues. S i m u l t a n e o u s l y , f r o m different parts o f t h e PEF, c h i p p e d solid fuel is p r o d u c e d , f r o m w h i c h e l e c t r i c i t y is g e n e r a t e d , a n d m e t h a n e or SNG is recovered f r o m w a s t e C O 2 a n d m u n i c i p a l or industrial w a s t e w a t e r . I n c i d e n t a l e c o n o m i c benefits — w h i c h are s i g n i f i c a n t — i n c l u d e s e c o n d a r y or t e r t i a r y t r e a t m e n t of m u n i c i p a l a n d industrial e f f l u e n t s , a n d t h e c o m p l e t e e l i m i n a t i o n o f t h e need for a sanitary landfill f o r disposal of t h e resultant sludge. The PEF is n o t merely a c o m b i n a t i o n of c o n v e n i e n c e , b u t a t r u l y i n t e r a c t i v e utilization of materials a n d energy. Repeated a p p l i c a t i o n o f s l u d g e f r o m t h e algae p o n d c o u l d result in a progressive a c c u m u l a t i o n of s o m e t o x i c e l e m e n t s originally present in t h e w a s t e w a t e r s fed t o t h e p o n d . T h e rate of a c c u m u l a t i o n o f t h e t o x i c e l e m e n t s w i l l d e p e n d o n various site-specific factors s u c h as t y p e o f w a s t e w a t e r ( m u n i c i p a l w a s t e w a t e r is m u c h less likely t h a n industrial w a s t e w a t e r t o c o n t a i n p o t e n t i a l l y t o x i c e l e m e n t s ) , soil t y p e , t e x t u r e a n d p H . It has been e s t i m a t e d t h a t in m a n y areas o f t h e U n i t e d States, it w o u l d require 5 0 t o 8 0 years before t h e a c c u m u l a t i o n o f t o x i c e l e m e n t s reached levels c o n s i d e r e d d a n g e r o u s b y t h e EPA f o r land d e v o t e d t o f o o d c r o p p r o d u c t i o n (23). Exceeding these levels of t o x i c e l e m e n t s w o u l d e l i m i n a t e t h e possibility of u s i n g t h e land f o r f o o d crops at a later date. In t h e d i a g r a m of t h e PEF s h o w n in Figure I, t h e a s s u m p t i o n has been m a d e t h a t t h e w o o d y biomass is used as fuel f o r g e n e r a t i n g electricity. Biomass can of course be used as f e e d s t o c k f o r o t h e r c o n v e r s i o n processes t o p r o d u c e a w i d e variety of fuels or c h e m i c a l s . H o w e v e r , direct c o m b u s t i o n of w o o d y biomass is a n a c c e p t e d , c o m m e r c i a l t e c h n o l o g y , a l l o w i n g c o m p a r i s o n w i t h alternate m e t h o d s o f g e n e r a t i n g electricity, a n d t h e e m p h a s i s of t h e studies of t h e PEF w a s o n d e v e l o p m e n t o f t h e b i o m a s s p r o d u c t i o n processes a n d their i n t e g r a t i o n rather t h a n t h e s t u d y of biomass c o n v e r s i o n . A n y o t h e r process f o r c o n v e r s i o n of w o o d y biomass c o u l d be used in t h e PEF c o n c e p t . Description of Projects A n initial project w a s u n d e r t a k e n t o s t u d y t h e c o n c e p t of t h e PEF a n d its characteristics a n d a p p a r e n t benefits. T h e project w a s d i v i d e d into three parts or tasks. T h e o b j e c t i v e of o n e task w a s t o analyze t h e c o n c e p t of t h e PEF, w i t h particular e m p h a s i s o n t h e c o m p l e m e n t a r y a n d synergistic aspects of t h e s y s t e m . A s e c o n d task w a s c o n c e r n e d w i t h t h e analysis a n d selection

Wastewater

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s

+4-

R

Underflow

A i r Drying Beds

Primary Sol Ids

Green Wood Chips

Growth Ponds

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Gas Dryer

Sol Ids Recycle

Co Absorption S

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ing Water for Heating gesters „ζ£

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Flow diagram of photosynthesis energy factory

Digester

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Settled Sewage

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Solar Energy

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

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25.

FRASER E T A L .

Photosynthesis Energy Factory

503

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

of p o t e n t i a l sites. T h e final task w a s t o d e v e l o p p r e l i m i n a r y designs a n d associated cost e s t i m a t e s f o r p o t e n t i a l d e m o n s t r a t i o n systems at t h e best sites. In t h e PEF, various s t r e a m s of e n e r g y a n d materials f l o w b e t w e e n three major s u b s y s t e m s — t h e d r y - l a n d Energy Plantation, a w o o d - f i r e d p o w e r plant, a n d an algae p r o d u c t i o n s y s t e m . T o analyze t h e resultant i n t e r a c t i o n s b e t w e e n the subsystems, a comprehensive technoeconomic model was developed to d e s c r i b e t h e PEF's p e r f o r m a n c e a n d cost. M o d e l s of t h e three s u b s y s t e m s w e r e d e v e l o p e d w i t h t h e aid o f i n f o r m a t i o n a n d data t h a t w e r e already available as t h e result of previous studies. N e w d a t a and n e w c o n c e p t s w e r e i n t r o d u c e d into t h e m o d e l s w h e r e v e r possible. T h e University of California at Berkeley s u p p l i e d s t a t e - o f - t h e - a r t data o n algae p o n d p e r f o r m a n c e a n d costs. These s u b s y s t e m m o d e l s w e r e e n g i n e e r i n g m o d e l s d e v e l o p e d in s u f f i c i e n t detail t o represent t h e i m p o r t a n t variables a n d v a r i a b l e - p a r a m e t e r interact i o n s i n f l u e n c i n g s u b s y s t e m p e r f o r m a n c e a n d costs. Of t h e three s u b s y s t e m m o d e l s , t h e m o s t c o m p r e h e n s i v e a n d t h e m o s t c o m p l e x w a s t h e Energy Plantation m o d e l , w h i c h is a c o m p l e t e design m o d e l . For t h e t w i n purposes of d e f i n i n g t h e a p p l i c a b i l i t y of t h e PEF c o n c e p t a n d s e l e c t i n g t h e best site for a d e m o n s t r a t i o n PEF project, data w e r e g a t h e r e d o n t h e characteristics of land, t h e availability of m u n i c i p a l a n d industrial e f f l u e n t s a n d residues, a n d t h e s u p p l y a n d d e m a n d for e n e r g y at a w i d e v a r i e t y a n d n u m b e r o f p o t e n t i a l sites. A f o r m a t w a s d e v e l o p e d f o r h a n d l i n g t h i s data base, a n d a n u m b e r o f s u i t a b i l i t y indexes w e r e d e f i n e d f o r e v a l u a t i n g t h e site d a t a . Data w e r e o b t a i n e d f r o m a n u m b e r o f sources in t h e literature as w e l l as f r o m state e n e r g y offices. A s t h e result of this siteselection p r o c e d u r e , a n u m b e r o f sites w e r e c h o s e n for analysis b y m e a n s o f the technoeconomic model. T h e m o d e l w a s t h e n used t o d e s i g n a d e m o n s t r a t i o n PEF s y s t e m at each of t h e selected p o t e n t i a l sites. This p r e l i m i n a r y d e s i g n illustrated for a specific site t h e benefits a n d t h e i m p a c t t o be e x p e c t e d f r o m a d e m o n s t r a t i o n PEF project. Estimated costs w e r e p r o v i d e d also f o r each d e m o n s t r a t i o n PEF. C o m p a r i n g these p r e l i m i n a r y d e s i g n s a n d their costs w a s t h e n d o n e t o s h o w w h e r e a n d under w h a t c o n d i t i o n s a PEF w o u l d be e x p e c t e d t o be coste f f e c t i v e in r e c y c l i n g w a s t e s a n d p r o d u c i n g fuels f r o m biomass w h i c h w o u l d be c o m p e t i t i v e w i t h presently used fuels. T h e results of this initial project have been p u b l i s h e d (21). T h e analysis w h i c h w a s p e r f o r m e d in t h i s initial project i n d i c a t e d t h a t s o m e i n t e r a c t i o n s b e t w e e n t h e PEF s u b s y s t e m s are generally c o s t - e f f e c t i v e w h i l e o t h e r s are p r o b a b l y site-specific or can be i m p r o v e d u p o n . From these initial

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results, it w a s c o n c l u d e d t h a t certain r e f i n e m e n t s in t h e d e s i g n of a PEF s h o u l d be analyzed t o give t h e PEF greater a p p l i c a b i l i t y as w e l l as t o i m p r o v e its e c o n o m i c s . T h u s , it w a s d e c i d e d t o investigate in m o r e detail certain aspects of t h e d e s i g n a n d o p e r a t i o n of t h e d r y - l a n d Energy Plantation subsystem. One possible i n t e r a c t i o n w i t h i n a PEF w h i c h w a s n o t c o n s i d e r e d in t h e initial project is t h e c o n t r i b u t i o n of w a t e r f r o m t h e w a s t e w a t e r t r e a t m e n t s u b s y s t e m t o t h e d r y - l a n d Energy P l a n t a t i o n . One of t h e original s i g n i f i c a n t credits r e s u l t i n g f r o m t h e w e t l a n d s biological w a s t e w a t e r t r e a t m e n t s u b s y s t e m c a n a u g m e n t t h e available natural rainfall or even s u p p l y t h e entire w a t e r r e q u i r e m e n t of a PEF. T h u s , it m i g h t be possible t o site a PEF in s e m i - a r i d or arid l o c a t i o n s t o e x p a n d its a p p l i c a b i l i t y . T h e results f r o m t h e initial p r o j e c t i n d i c a t e d t h a t s u p p l y i n g t h e necessary n u t r i e n t s t o m a i n t a i n t h e p r o d u c t i v i t y of t h e land — p a r t i c u l a r l y n i t r o g e n — w a s a s i g n i f i c a n t cost i t e m in t h e e c o n o m i c s of p r o d u c i n g w o o d y biomass. Because of t h e i m p o r t a n c e of n u t r i e n t s , it w a s d e c i d e d t h a t t h e n u t r i e n t balance in t h e Energy Plantation m o d e l n e e d e d t o be refined t o p r e d i c t t h e required a m o u n t of n u t r i e n t s m o r e precisely. In particular, because t h e leaves c o n t a i n a h i g h p e r c e n t a g e of n i t r o g e n c o m p a r e d t o t h e w o o d , w o r k is b e i n g d o n e t o i n c l u d e in t h e n u t r i e n t balance t h e effect of n u t r i e n t r e c y c l i n g via leaf fall a n d a m o r e precise a c c o u n t i n g of n u t r i e n t l e a c h i n g . T r a n s p o r t a t i o n w a s a n o t h e r s i g n i f i c a n t cost i t e m w h i c h appeared t o have p o t e n t i a l for c o s t s a v i n g s t h r o u g h a m o r e d e t a i l e d analysis of alternative s y s t e m designs. T h u s , alternative m e t h o d s for h a n d l i n g a n d t r a n s p o r t i n g t h e w o o d y biomass are b e i n g analyzed, s u c h as p n e u m a t i c t u b e t r a n s p o r t , c h i p b a l i n g , a n d a l t e r n a t i v e m e t h o d s for d r y i n g t h e chips. In a d d i t i o n , t h e t r a n s p o r t a t i o n s y s t e m is b e i n g analyzed in greater detail t o see w h e r e cost savings m i g h t be a c h i e v e d t h r o u g h o p t i m i z a t i o n . T h e initial results f r o m s t u d y i n g t h e PEF c o n c e p t i n d i c a t e d t h a t t h e m o s t s i g n i f i c a n t c r e d i t r e s u l t i n g f r o m t h e w e t l a n d s biological w a s t e - w a t e r t r e a t m e n t s u b s y s t e m w a s t h e w a s t e w a t e r t r e a t m e n t credit itself rather t h a n t h e c r e d i t for t h e v a l u e of t h e gas p r o d u c e d . T h u s , it b e c a m e of interest t o look for b e t t e r w a y s of i n c o r p o r a t i n g t h e w a s t e w a t e r t r e a t m e n t f u n c t i o n w i t h i n t h e PEF t h a n via an algae p o n d . O n e w a y t h a t t h i s m i g h t be d o n e is t o a p p l y t h e w a s t e w a t e r d i r e c t l y t o t h e Energy Plantation. H o w e v e r , t h i s process has l i m i t a t i o n s , w i t h respect t o b o t h t h e particular location a n d local soil q u a l i t y , a n d t h e c o m p o s i t i o n of t h e w a s t e w a t e r . W o r k is therefore b e i n g d o n e t o collect t h e necessary data o n t e c h n i c a l l i m i t a t i o n s a n d EPA regulations a n d t o d e v e l o p a m o d e l for this process. In a d d i t i o n o t h e r w e t l a n d s biological

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species besides algae have been s u g g e s t e d for w a s t e w a t e r t r e a t m e n t a n d it w a s d e c i d e d t o investigate t h e possible use of these o t h e r plants t o p e r f o r m this function. Finally, a d d i t i o n a l w o r k is b e i n g d o n e in this s e c o n d project t o look for n e w a n d i m p r o v e d t e c h n o l o g y t o i n c l u d e in t h e p o w e r plant s u b s y s t e m m o d e l .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

A d d i t i o n a l p o t e n t i a l sites are also t o be i d e n t i f i e d w h e r e t h e n e w m o d e s o f o p e r a t i n g a PEF — e.g., w i t h irrigation or d i r e c t a p p l i c a t i o n of w a s t e w a t e r — w o u l d be applicable. T h e n e w c o m p l e t e PEF m o d e l w i l l t h e n be used t o c o m p a r e t h e various m o d e s o f o p e r a t i o n , a n d t o d e t e r m i n e t h e e c o n o m i c v i a b i l i t y of PEF systems f o r sites d i s p l a y i n g w i d e l y different local c l i m a t i c a n d site-specific c o n s t r a i n t s . T h e f o l l o w i n g sections of this paper w i l l describe t h e s u b s y s t e m m o d e l s w h i c h w e r e d e v e l o p e d in t h e initial project t o s t u d y t h e PEF a n d present s o m e o f t h e overall results o b t a i n e d by s i m u l a t i n g t h e p e r f o r m a n c e of t h e entire PEF s y s t e m . A d d i t i o n s t o t h e m o d e l w h i c h are b e i n g d e v e l o p e d as t h e result of w o r k in t h e s e c o n d project w i l l also be d e s c r i b e d , a n d s o m e results of t h e analysis o f these i m p r o v e d aspects of PEF d e s i g n a n d o p e r a t i o n w i l l also be presented. THE ENERGY P L A N T A T I O N S U B S Y S T E M Description of Initial M o d e l In t h e PEF c o n c e p t , t h e i n p u t s t o t h e Energy Plantation m o d e l are a d e s c r i p t i o n of t h e site b e i n g i n v e s t i g a t e d , s u p p l i e d b y t h e site-selection p r o c e d u r e , a n d t h e a m o u n t s o f n i t r o g e n a n d p h o s p h o r u s recycled t o t h e p l a n t a t i o n s u p p l i e d by t h e algae p o n d m o d e l . T h e major o u t p u t s of t h e p l a n t a t i o n m o d e l are t h e yearly a m o u n t o f biomass p r o d u c e d a n d its cost (green chips) delivered at t h e utilization point. These items c o n s t i t u t e t h e m a j o r i n p u t s t o t h e p o w e r plant m o d e l . M a n p o w e r a n d e q u i p m e n t r e q u i r e m e n t s ; species s u g g e s t e d for t h e p l a n t a t i o n ; a n d p l a n t i n g , h a r v e s t i n g , a n d o p e r a t i n g schedules f o r t h e p l a n t a t i o n are secondary o u t p u t s of t h e plantation model. This p l a n t a t i o n m o d e l is an e x t e n s i o n a n d generalization of w o r k d o n e in previous studies (40,41). T h e m o d e l i n c l u d e s a n u m b e r of s u b m o d e l s w h i c h are discussed b e l o w . These s u b m o d e l s i n c l u d e : (1) land resources. (2) data base o n plants. (3) r e c y c l e d i n p u t s . (4) species selection a n d c h a r a c t e r i z a t i o n , (5) plant g r o w t h m o d e l . (6) d a t a base f o r field operations, (7) field operations, (8) d a t a base f o r cost e s t i m a t e s , a n d (9) cost e s t i m a t e f o r biomass p r o d u c e d .

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

T h e land resources s u b r o u t i n e is t h e m a j o r i n p u t t o t h e m o d e l . T h e data g e n e r a t e d t h r o u g h t h e site-selection p r o c e d u r e are organized in three categories: land d e s c r i p t i o n , land c a p a b i l i t y , a n d land cost. The land available for p l a n t a t i o n o p e r a t i o n s is characterized by t h e p l a n t a t i o n d e n s i t y or ratio of t h e p l a n t a t i o n area t o t h e t o t a l g e o g r a p h i c area e n c o m p a s s i n g t h e p l a n t a t i o n a n d by t h e average size of t h e parcels m a k i n g u p t h e p l a n t a t i o n area. B o t h f a c t o r s have been s h o w n t o have a s i g n i f i c a n t effect o n t h e cost of t h e b i o m a s s p r o d u c e d . (42) T h e p l a n t a t i o n area w o u l d i n c l u d e t h e actual p l a n t e d area plus necessary service roads a n d irrigation lanes if w a r r a n t e d . T h e land q u a l i t y or ability t o s u p p o r t plant g r o w t h is characterized in t e r m s of t h e land classes used in t h e N a t i o n a l I n v e n t o r y of Soil a n d W a t e r C o n s e r v a t i o n Needs (43). A c o r r e l a t i o n w a s established b e t w e e n e x p e r i m e n t a l y i e l d data (ODT/ac-yr) a n d land classes o n w h i c h t h e data w e r e g e n e r a t e d (a linear relation w a s used, w h i c h had a c o r r e l a t i o n c o e f f i c i e n t > 0 . 7 5 ) . L a n d of Class III w a s a s s u m e d t o have an index of 1. t h e r e b y a l l o w i n g t h e p r o d u c t i v i t y of l a n d of o t h e r classes t o be e s t i m a t e d o n t h e basis of relative p r o d u c t i v i t y indexes. These p r o d u c t i v i t y indexes w e r e used t o w e i g h t t h e e x p e r i m e n t a l y i e l d data f r o m t h e literature t o a c c o u n t for t h e d i f f e r e n c e in land p r o d u c t i v i t y b e t w e e n t h e land c o n s i d e r e d in t h e analysis of specific sites a n d t h e land o n w h i c h t h e e x p e r i m e n t a l data w e r e g e n e r a t e d . This a p p r o a c h is s o m e w h a t similar t o t h e a p p r o a c h used by Marshall a n d Tsang (22) t o relate t h e relative v a l u e of t h e yields e x p e c t e d f r o m land of various classes s u b m i t t e d t o c o m p a r a b l e c u l t u r a l practices, t o land classes. T h e m e t h o d p r o p o s e d here t o e s t i m a t e yields at a g i v e n site on t h e basis of yields m e a s u r e d at e x p e r i m e n t a l sites s h o u l d be refined as more data b e c o m e available. T h e data base on plants c o n t a i n s d a t a d e s c r i b i n g t h e g r o w t h characteristics of t h e species of interest for p l a n t a t i o n a p p l i c a t i o n s . Plant g r o w t h a n d yields o n an Energy Plantation are p r e d i c t e d by m e a n s of a m o d e l d e s c r i b i n g j u v e n i l e plant g r o w t h w h i c h w a s d e v e l o p e d at I n t e r T e c h n o l o g y / S o l a r Corporation (21). The m o d e l c o n t a i n s several parameters w h i c h are characteristic of t h e species c o n s i d e r e d a n d are d e t e r m i n e d f r o m e x p e r i m e n ­ tal d a t a . T h e d a t a base c o n t a i n s t h e values of these c h a r a c t e r i s t i c p a r a m e t e r s w h i c h have been f o u n d for various species. T h e d a t a base also lists t h e forest regions, a n d soil classes a n d subclasses in w h i c h each of t h e species is expected to grow. In t h e s u b r o u t i n e d e s c r i b i n g t h e recycled i n p u t s , t h e n u t r i e n t value (Ν. Κ a n d P) of t h e ash a n d s l u d g e r e c y c l e d f r o m t h e boilers a n d digesters is e s t i m a t e d a n d c o m p a r e d t o t h e a m o u n t s required by the p l a n t a t i o n t o m a i n t a i n sustained yields.

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Photosynthesis Energy Factory

507

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

Species t o be i n c l u d e d in a p l a n t a t i o n are selected f r o m t h e data bank on t h e basis of t h e forest g r o u p , land class, a n d subclass t o w h i c h t h e p l a n t a t i o n land belongs. The c h a r a c t e r i s t i c p a r a m e t e r s o f each species retained are t h e n a d j u s t e d t o take into a c c o u n t t h e d i f f e r e n c e in soil q u a l i t y b e t w e e n t h e p l a n t a t i o n land a n d t h e land o n w h i c h t h e e x p e r i m e n t a l d a t a f o r each species were generated. In t h e plant g r o w t h s u b r o u t i n e , average a n n u a l s u s t a i n e d yields are e s t i m a t e d f o r each species f o r various h a r v e s t i n g cycles a n d p l a n t i n g densities b y m e a n s of t h e m o d e l d e s c r i b i n g j u v e n i l e plant g r o w t h . In m o s t cases, t h e d i s c r e p a n c y b e t w e e n c a l c u l a t e d values of these s u s t a i n e d yields a n d e x p e r i m e n t a l d a t a is of t h e order o f 5 t o 10 p e r c e n t o f t h e e x p e r i m e n t a l data. This level of precision is satisfactory as it is c o m p a r a b l e t o or smaller t h a n t h e observed f l u c t u a t i o n s in yield d u e t o yearly c l i m a t i c variations. S i g n i f i c a n t variations in field d a t a are o b s e r v e d , a n d t h e p r o p o s e d m o d e l w i l l have t o be revised or refined as m o r e data b e c o m e available. T h e y i e l d - c y c l e c o m b i n a t i o n s g e n e r a t i n g a m o u n t s o f biomass w i t h i n 5 or 10 p e r c e n t of t h e m a x i m u m p r e d i c t e d are retained f o r f u r t h e r analysis. Field o p e r a t i o n s in a n Energy Plantation i n c l u d e h a r v e s t i n g a n d c h i p p i n g , c u l t i v a t i o n , fertilization, c l o n e g e n e r a t i o n , r e p l a n t i n g of a f r a c t i o n o f t h e p l a n t a t i o n , a n d t r a n s p o r t a t i o n of t h e biomass t o t h e p o i n t o f utilization. These o p e r a t i o n s are s u p p o r t e d b y m a i n t e n a n c e a n d a d m i n i s t r a t i v e teams. For each of t h e y i e l d - c y c l e c o m b i n a t i o n s o f interest, t h i s s u b r o u t i n e establishes t h e i n v e n t o r y of t h e e q u i p m e n t , p e r s o n n e l , a n d supplies required t o m a i n t a i n t h e operation. In t h e c o s t - e s t i m a t i n g s u b r o u t i n e , t h e cost of biomass delivered in t h e f o r m of c h i p s at p o i n t of use is e s t i m a t e d o n t h e basis of t h e u t i l i t y ( 1 1 . 1 % average r e t u r n , i n c o m e t a x paid o n e q u i t y return) a n d m u n i c i p a l (6.375% r e t u r n , n o i n c o m e tax) m e t h o d s of f i n a n c i n g . T h e resultant o u t p u t of t h e s u b r o u t i n e s h o w s t h e various c o m p o n e n t s of t h e overall cost of biomass for b o t h m e t h o d s of f i n a n c i n g . Table II s h o w s t h e e c o n o m i c analysis f o r a particular site a n d a b r e a k d o w n of t h e capital a n d o p e r a t i n g costs i n v o l v e d in t h e Energy Plantation s u b s y s t e m o f a PEF. T h e d e p r e c i a b l e i n v e s t m e n t includes t h e capital cost of p l a n t a t i o n installation (land clearing) a n d s t a r t u p (planting stock). F o l l o w i n g this analysis, t h e major c o m p o n e n t of t h e total revenue is t h e cost o f n i t r o g e n fertilizer. T h e c o n t r i b u t i o n of fertilizers t o t h e cost of biomass p r o d u c t i o n has been n o t e d by o t h e r investigators (44). A s a result, m u c h e m p h a s i s has been g i v e n t o t h e p r o b l e m of n u t r i e n t r e q u i r e m e n t s in t h e e x p a n d e d version of t h e PEF m o d e l (see below). T h e final cost data used t o characterize t h e p o t e n t i a l o f a site f o r biomass p r o d u c t i o n w e r e averages of t h e data f o r each of t h e species c o n s i d e r e d f o r t h e site. This a p p r o a c h w a s a d o p t e d as Energy Plantations are a s s u m e d t o i n c l u d e a m i x of species.

508

BIOMASS AS A NONFOSSIL F U E L SOURCE

T a b l e I I . C O S T A N A L Y S I S FOR N A T C H I T O C H E S , L A , S I T E 3 6 , 0 0 0 acres of p l a n t a t i o n H y b r i d Poplar NE 3 8 8 4 f t / t r e e , harvest every 2 years 8.52 O D T / a c - y r Municipal financing

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

2

Annual Equivalent Cost, $* Depreciable I n v e s t m e n t Nondepreciable Investment Federal I n c o m e Tax A n n u a l O p e r a t i n g Costs Fuels L a n d Rental T o t a l Labor Administrative & Overhead Supplies — Nitrogen Phosphorus Potassium Lime Others M a i n t e n a n c e a n d Repair Local Taxes & Insurance T o t a l Revenue Required

938.700 49.300 0

16.7 0.9 0.0

140,100 1.113.100 972,200 194,400 1,365.000 43,000 361.100 8.900 81.200 322.600 39,600 5,629.200

2.5 19.7 17.3

Product Cost (Delivered in t h e f o r m of g r e e n chips) $/ODT 17.71 $/10 Btu 1.03 6

* 1 9 7 7 dollars.

Percent of Total Revenue

3.5 24.2 0.8 6.4 0.2 1.6 5.7 0.7

25.

FRASER E T A L .

509

Photosynthesis Energy Factory

Fifteen sites w e r e i d e n t i f i e d f o r f u r t h e r analysis of t h e PEF c o n c e p t . T h e selection criteria i n c l u d e d resource availability (land, w a s t e w a t e r , labor, climate) a n d m a r k e t for t h e PEF p r o d u c t s a n d services (electricity, natural gas, s t e a m , need f o r w a s t e t r e a t m e n t , a n d jobs). T h e 15 selected sites w e r e analyzed w i t h t h e p l a n t a t i o n m o d e l . Species i n c l u d e d h y b r i d (Populus spp.). Eastern c o t t o n w o o d (P. deltoïdes), plains c o t t o n w o o d (P. sargentii), silver m a p l e (Acer saccharinum). A m e r i c a n s y c a m o r e (Plantanus occidentalis) (southern a n d m i d l a t i t u d e sites), a n d Eucalyptus (Florida sites only). Proposed p l a n t i n g densities w e r e generally b e t w e e n 4 a n d 12 f t / t r e e w i t h harvests (first a n d coppice) o f 4 O D T / a c - y r (Maysville, KY) t o a b o u t 9 O D T / a c - y r (Bemidji. MN). Differences in cost o f biomass w e r e related t o a n u m b e r of factors, i n c l u d i n g t h e i n v e s t m e n t , land rental, t r a n s p o r t a t i o n costs, a n d a m o u n t of n u t r i e n t s r e c y c l e d t o t h e p l a n t a t i o n . The cost of biomass at t h e 15 p o t e n t i a l sites ranged f r o m $ 1 6 . 9 0 t o $ 2 3 . 5 9 per o v e n - d r y t o n ( m u n i c i p a l f i n a n c i n g ) . These costs are c o m p a r a b l e t o t h o s e e s t i m a t e d o n t h e basis of o t h e r tree f a r m designs f o r similar locations.

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

2

Nutrient Balance The n u t r i e n t balance m o d e l p r e d i c t s t h e a m o u n t of inorganic fertilizer required t o m a i n t a i n site fertility, a n d t h u s p r o d u c t i v i t y , of t h e p l a n t a t i o n . Fertilizer a p p l i c a t i o n is needed because o f t h e shorter rotations and t h e m o r e c o m p l e t e removal of biomass f r o m t h e site t h a t o c c u r s w i t h this t y p e of m a n a g e m e n t as c o m p a r e d t o c o n v e n t i o n a l forestry. A l t h o u g h t h e soil n u t r i e n t pool at a n y g i v e n site is a n u n k n o w n , m a i n t e n a n c e of site fertility is a s s u m e d t o be possible b y r e p l a c i n g t h e a m o u n t of n u t r i e n t s r e m o v e d in t h e harvested biomass plus a n a d d i t i o n a l a m o u n t f o r leaching a n d d e n i t r i f i c a t i o n losses. T h e m o d e l treats t h e soil n u t r i e n t pool as t h e s y s t e m of interest, t h e upper b o u n d a r y i n c l u d i n g a n y surface o r g a n i c horizons t h a t m a y be present, t h e l o w e r b o u n d a r y b e i n g t h e u n d e r l y i n g bedrock, a n d t h e laterial b o u n d a r i e s e x t e n d i n g t o t h e b o u n d a r i e s of t h e site. Inputs t o t h e s y s t e m i n c l u d e t h e a p p l i c a t i o n of inorganic fertilizer, r e t u r n of ash material f r o m t h e p o w e r plant c o m p o n e n t of t h e PEF, a p p l i c a t i o n of s l u d g e f r o m t h e algae p o n d , n i t r o g e n f i x a t i o n by cover crops or i n t e r p l a n t e d w o o d y n i t r o g e n - f i x i n g species, a n d t h e r e c y c l i n g of leaf material n o t r e m o v e d in t h e harvested biomass. O u t p u t s f r o m t h e s y s t e m i n c l u d e t h e g r o w t h of w o o d a n d leaf material, leaching a n d erosion losses, a n d d e n i t r i f i c a t i o n losses f o r soil n i t r o g e n . A l t h o u g h inputs f r o m a t m o s p h e r i c sources a n d t h e w e a t h e r i n g o f bedrock are operative a n d can be i m p o r t a n t over long periods o f t i m e (45-47), t h e y are n o t i n c l u d e d in t h e m o d e l because t h e m a g n i t u d e of their c o n t r i b u t i o n over t h e short

510

BIOMASS AS A NONFOSSIL F U E L SOURCE

d u r a t i o n of t h e rotations used in this t y p e of m a n a g e m e n t is a s s u m e d t o be small in c o m p a r i s o n t o t h e o t h e r i n p u t s .

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

In t h e original n u t r i e n t balance m o d e l t h e a n n u a l fertilizer r e q u i r e m e n t w a s c a l c u l a t e d on t h e basis of r e p l a c i n g t h e n u t r i e n t s r e m o v e d in t h e biomass harvested less n u t r i e n t credits o b t a i n e d f r o m r e c y c l i n g t h e s l u d g e f r o m t h e algae p o n d a n d t h e ash f r o m t h e boiler t o t h e Energy Plantation. Credits w e r e t a k e n o n l y for n i t r o g e n a n d p h o s p h o r u s in t h e s l u d g e a n d c a l c i u m in t h e ash. A l l o w a n c e w a s m a d e for loss of n u t r i e n t s by l e a c h i n g , a n d a p p l i c a t i o n of fertilizer w a s a s s u m e d t o o c c u r o n l y o n c e per r o t a t i o n . T h e n u t r i e n t s present in t h e b i o m a s s harvested w e r e c a l c u l a t e d o n t h e basis of tables d e v e l o p e d f r o m data o n (1) b i o m a s s d i s t r i b u t i o n in leaves, s t e m s , a n d b r a n c h e s of y o u n g trees as a f u n c t i o n of age, a n d (2) t h e n u t r i e n t c o m p o s i t i o n of leaves, s t e m s , a n d b r a n c h e s for y o u n g trees. T h e d a t a base used for (1) a b o v e w a s g e n e r a t e d in s h o r t - r o t a t i o n field trials of A m e r i c a n s y c a m o r e (Platanus occidentalis) (48), a n d t h a t used for (2) a b o v e c o n s i s t e d of averages of analyses p e r f o r m e d on a n u m b e r of o l d e r - g r o w t h h a r d w o o d species (49). It s h o u l d be n o t e d t h a t t h e r e are a n u m b e r of d i f f i c u l t i e s i n h e r e n t in t h e use of tissue analyses for p r e d i c t i o n of fertilizer r e q u i r e m e n t s (50,51). j u s t as there are d i f f i c u l t i e s a n d l i m i t a t i o n s i n v o l v e d w i t h t h e use of soil analyses (ΕΠ .52). T h e relative d i s t r i b u t i o n of b i o m a s s into s t e m , b r a n c h a n d leaf c o m p o n e n t s w i l l vary w i t h t h e species i n v o l v e d , t h e age of t h e tree (rotation l e n g t h ) , a n d t h e d e n s i t y ( n u m b e r of trees per u n i t area) of t h e p l a n t a t i o n . T h e c h e m i c a l c o m p o s i t i o n of t h e i n d i v i d u a l c o m p o n e n t s w i l l also vary w i t h species, age, site f e r t i l i t y , a n d t h e t i m e of year of s a m p l i n g (e.g., seasonal f l u x of Ν a n d Ρ f r o m leaves t o t w i g s ) (50). These differences are even m a n i f e s t e d w i t h i n t h e i n d i v i d u a l biomass c o m p o n e n t s . T h e variables used in t h e m o d e l are general d e s i g n variables t h a t c a n be easily m o d i f i e d t o o b t a i n better p r e d i c t i v e results either w i t h n e w d a t a f r o m field trials or site-specific i n f o r m a t i o n for a p a r t i c u l a r m a n a g e m e n t d e s i g n . Several o t h e r general c h a r a c t e r i s t i c s of t h e m o d e l s h o u l d be m e n t i o n e d . First, t h e m o d e l p r e d i c t s fertilizer r e q u i r e m e n t s for t h e p l a n t a t i o n o n c e steady-state c o n d i t i o n s have been a t t a i n e d . Steady-state is d e f i n e d as t h a t p o i n t at w h i c h t h e m a n a g e m e n t schedule's c y c l i c o p e r a t i o n results in t h e d e c o m p o s i t i o n (mineralization) of t h e o r g a n i c i n p u t s f r o m p r e v i o u s years in an a m o u n t equal t o t h e o r g a n i c i n p u t s for o n e year; t h i s is e q u i v a l e n t t o s a y i n g t h a t all of t h e a n n u a l i n p u t s are d e c o m p o s e d in o n e year, m e a n i n g t h a t t h e n u t r i e n t s c o n t a i n e d in t h e o r g a n i c m a t t e r b e c o m e available for u p t a k e by t h e plant in g r o w t h or loss in l e a c h i n g . A n n u a l i n p u t s t h u s equal a n n u a l o u t p u t s .

25.

FRASER ET AL.

Photosynthesis Energy Factory

511

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

T h e rate of b r e a k d o w n o f o r g a n i c material in natural stands is d e p e n d e n t u p o n e n v i r o n m e n t a l c o n d i t i o n s a n d t h e c h e m i c a l nature o f t h e s u b s t r a t e b e i n g d e c o m p o s e d . Litter half lives are in t h e range of one t o a f e w years f o r t e m p e r a t e d e c i d u o u s forests as a w h o l e (53). T e m p e r a t u r e a n d m o i s t u r e have been f o u n d t o be t h e m o s t i m p o r t a n t e n v i r o n m e n t a l parameters a n d t h e c a r b o n / n i t r o g e n (C/N) ratio a n d l i g n i n c o n t e n t t h e m o s t i m p o r t a n t c h e m i c a l parameters (54,55). T h e rate of d e c o m p o s i t i o n is a l m o s t a l w a y s l i m i t e d by t e m p e r a t u r e , m o i s t u r e , or n u t r i e n t deficiencies. T h e d e c o m p o s i t i o n rate s h o u l d be e x p e c t e d t o increase u n d e r m a n a g e m e n t s c h e m e s w h i c h i n c l u d e irrigation a n d f e r t i l i z a t i o n , p r o v i d e d t e m p e r a t u r e is n o t l i m i t i n g . From t h e s t a r t - u p o p e r a t i o n s of p l a n t a t i o n e s t a b l i s h m e n t t o t h e a t t a i n m e n t of steady state, t r a n s i t i o n c o n d i t i o n s prevail w i t h respect t o n u t r i e n t s . In this case, t h e a m o u n t o f o r g a n i c material d e c o m p o s e d w i l l n o t be equal t o t h e a n n u a l o r g a n i c i n p u t s . T r a n s i t i o n - p e r i o d fertilizer r e q u i r e m e n t s are e s t i m a t e d in c o n j u n c t i o n w i t h s t a r t - u p o p e r a t i o n r e q u i r e m e n t s a n d costs. T h e y w i l l be larger t h a n steady-state r e q u i r e m e n t s since full credit f o r t h e o r g a n i c i n p u t s c a n n o t be taken each year. S e c o n d , t h e m o d e l does not p r e d i c t t h e g r o w t h response t o fertilization above levels required t o c o m p e n s a t e f o r n u t r i e n t s r e m o v e d in t h e harvested material. The parameters f o r w o o d a n d leaf g r o w t h are c u r r e n t l y p u t into t h e n u t r i e n t balance m o d e l f r o m t h e g r o w t h m o d e l as i n d e p e n d e n t parameters. G r o w t h is only i n d i r e c t l y related t o t h e n u t r i e n t balance t h r o u g h t h e use of land class p r o d u c t i v i t y data in t h e g r o w t h m o d e l for t h e p r e d i c t i o n of biomass p r o d u c t i o n . A n y fertilization necessary t o raise t h e fertility o f t h e site t o a level required t o sustain a desired a m o u n t o f p r o d u c t i v i t y w o u l d be i n c l u d e d in t h e t r a n s i t i o n period costs. T h e necessary detailed d a t a required t o e s t i m a t e o p t i m u m fertilizer s c h e m e s are n o t presently available. T h e n u t r i e n t balance m o d e l c a l c u l a t e s t h e fertilizer r e q u i r e m e n t s f o r t w o separate m a n a g e m e n t designs, a p p l i c a t i o n of fertilizer yearly a n d a p p l i c a t i o n on a o n c e - p e r - r o t a t i o n basis. For t h e yearly a p p l i c a t i o n d e s i g n , t h e m o d e l p r e d i c t s t h e fertilizer r e q u i r e m e n t f o r t h e entire p l a n t a t i o n using s i m p l e l e a c h i n g losses. T h e yearly a p p l i c a t i o n d e s i g n c o r r e s p o n d s t o p l a n t a t i o n m a n a g e m e n t i n v o l v i n g t h e use of irrigation, t h e fertilizer b e i n g a p p l i e d in c o n j u n c t i o n w i t h irrigation w a t e r . For cases w h e r e irrigation w i l l n o t be used, a p p l i c a t i o n of fertilizer w i l l o c c u r o n c e per r o t a t i o n . This is e n v i s i o n e d t o o c c u r after harvest w h e n t h e site w i l l be m o s t easily accessible. This d e s i g n p r e d i c t s t h e fertilizer r e q u i r e m e n t f o r o n l y t h a t p o r t i o n o f t h e p l a n t a t i o n b e i n g harvested in a g i v e n year. Fertilizer r e q u i r e m e n t s are first e s t i m a t e d based u p o n biomass g r o w t h only a n d t h e n

512

BIOMASS AS A NONFOSSIL F U E L SOURCE

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

are p u t into e q u a t i o n s c o n t a i n i n g t h e o t h e r variables similar t o t h o s e used for t h e yearly a p p l i c a t i o n d e s i g n . These e q u a t i o n s c o n t a i n a n a d d i t i o n a l p a r a m e t e r t h a t d e t e r m i n e s t h e a m o u n t o f n u t r i e n t s t a k e n u p each year in g r o w t h as w e l l as t h e a m o u n t left over a n d s u b j e c t t o leaching a n d u p t a k e in s u b s e q u e n t years o f t h e r o t a t i o n . The e q u a t i o n s are solved b y a n iterative a l g o r i t h m . L e a c h i n g losses are c a l c u l a t e d as c o m p o u n d losses d u e t o t h e longer period b e t w e e n a p p l i c a t i o n s a n d are w e i g h t e d f o r t h e d i f f e r e n t r o t a t i o n l e n g t h s f o r first versus c o p p i c e g r o w t h cycles. T h u s , b o t h t h e l e a c h i n g values t h e m s e l v e s a n d t h e l e n g t h o f t h e r o t a t i o n w i l l have a s i g n i f i c a n t effect o n t h e p r e d i c t e d fertilizer r e q u i r e m e n t s w h e n a p p l i c a t i o n is o n a o n c e - p e r - r o t a t i o n basis. In t h e m o d e l , t h e a m o u n t o f n i t r o g e n fertilizer required yearly is t h e a m o u n t r e q u i r e d for g r o w t h (both leaf a n d w o o d g r o w t h — o b t a i n e d f r o m t h e g r o w t h model) m i n u s t h e a m o u n t s u p p l i e d b y s l u d g e f r o m t h e algae p o n d , t h e leaf recycle (calculated in t h e g r o w t h m o d e l as t h e d i f f e r e n c e b e t w e e n t h e leaf m a t e r i a l p r o d u c e d a n d t h a t harvested), a n d n i t r o g e n f i x a t i o n . There is no ash p a r a m e t e r in t h e n i t r o g e n e q u a t i o n because t h e n i t r o g e n present in t h e b i o m a s s is volatilized d u r i n g t h e c o m b u s t i o n process o c c u r r i n g a t t h e p o w e r plant. T h e o t h e r n u t r i e n t s o f interest, h o w e v e r , r e m a i n in t h e ash. so t h a t this p a r a m e t e r is i n c l u d e d in all e q u a t i o n s o t h e r t h a n t h o s e f o r n i t r o g e n . The n i t r o g e n f i x a t i o n t e r m in t h e n i t r o g e n e q u a t i o n a c c o u n t s f o r a t m o s p h e r i c n i t r o g e n b i o l o g i c a l l y f i x e d b y c o v e r c r o p s o r i n t e r p l a n t e d w o o d y species c a p a b l e o f f i x i n g n i t r o g e n (legume o r a c t i n o m y c e t e - n o d u l a t e d species) (5659). T h e m o d e l a l l o w s t h i s n i t r o g e n f i x a t i o n i n p u t o n l y for t h a t p o r t i o n o f t h e p l a n t a t i o n not harvested d u r i n g t h e g r o w i n g season, as e n e r g y d e r i v e d f r o m p h o t o s y n t h e s i s m u s t be s u p p l i e d t o drive t h e c h e m i c a l reactions i n v o l v e d . T h e o r g a n i c i n p u t s in t h e n u t r i e n t balance e q u a t i o n s are m u l t i p l i e d by o r g a n i c l e a c h i n g factors a n d t h e inorganic i n p u t s are m u l t i p l i e d b y inorganic l e a c h i n g f a c t o r s w h i l e t h e n i t r o g e n f i x a t i o n i n p u t p a r a m e t e r has n o associated leaching t e r m . N i t r o g e n f i x a t i o n is a s s u m e d t o be a s l o w , steady i n p u t t o t h e s y s t e m m o r e closely t i m e d t o t h e g r o w t h r e q u i r e m e n t s o f t h e plants a n d therefore less likely t o be s u b j e c t e d t o l e a c h i n g losses. T h e l e a c h i n g f a c t o r p a r a m e t e r s represent t h e o t h e r o u t p u t f r o m t h e s y s t e m besides g r o w t h . In t h e case o f n i t r o g e n , t h e l e a c h i n g parameters i n c l u d e losses d u e t o d e n i t r i f i c a t i o n . In t h e e q u a t i o n s for yearly a p p l i c a t i o n s , leaching is d e s c r i b e d as s i m p l e leaching losses. For t h e case o f a p p l i c a t i o n o n c e per r o t a t i o n , c o m p o u n d l e a c h i n g is used. T h e a c t u a l values o f t h e leaching p a r a m e t e r s w i l l d e p e n d u p o n s u c h site-specific f a c t o r s as c l i m a t e , soil t e x t u r e a n d c a t i o n e x c h a n g e c a p a c i t y (CEC). t h e presence or a b s e n c e o f v e g e t a t i v e cover for uptake of w a t e r a n d n u t r i e n t s (47.53,60). and t h e m e t h o d

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

of fertilizer a p p l i c a t i o n (banded versus broadcast). For t h e m o d e l , three sets o f values w e r e s u b j e c t i v e l y c h o s e n t o represent l o w , m e d i u m , a n d high l e a c h i n g losses. These values w e r e c h o s e n after r e v i e w i n g t h e literature for ranges o f general y e t representative n u m b e r s (53,61-64). It s h o u l d be n o t e d , h o w e v e r , t h a t a c t u a l values w i l l be h i g h l y site-specific. L e a c h i n g values are e n t e r e d as f r a c t i o n s , so t h a t t h e q u a n t i t y (1-leaching value) represents t h e a m o u n t available f o r g r o w t h after l e a c h i n g . Inorganic leaching values are s l i g h t l y higher t h a n o r g a n i c values because it is a s s u m e d inorganic i n p u t s are i m m e d i a t e l y available f o r g r o w t h or leaching. Different values are also used for each n u t r i e n t ; f o r e x a m p l e , t h e inorganic leaching value f o r Κ is larger t h a n t h a t f o r Ca since Κ is a m o r e m o b i l e i o n . For t h e yearly fertilizer a p p l i c a t i o n d e s i g n , s l u d g e a n d ash inputs are also a s s u m e d t o o c c u r yearly, a n d c r e d i t s for leaf r e c y c l i n g a n d n i t r o g e n f i x a t i o n are taken o n an a n n u a l basis. W h e n fertilizer is a p p l i e d o n c e per r o t a t i o n , s l u d g e a n d ash are a s s u m e d t o be applied o n a o n c e - p e r - r o t a t i o n basis. H o w e v e r , leaf r e c y c l i n g o c c u r s every year, so t h a t a n n u a l credits for t h i s i n p u t a n d f o r n i t r o g e n f i x a t i o n are t a k e n f o r b o t h a p p l i c a t i o n designs. Preliminary sensitivity analyses w e r e p e r f o r m e d t o d e t e r m i n e t h e i m p o r t a n c e of each of t h e variables in t h e e q u a t i o n s . These analyses w e r e run f o r a basecase d e s i g n for a p l a n t a t i o n in t h e S o u t h e r n U n i t e d States. T h e d e s i g n variables f o r this case i n c l u d e d : (1) 2 8 , 5 0 0 acres of p l a n t a t i o n ; (2) first a n d c o p p i c e g r o w t h cycles of 2 a n d 4 years, respectively; (3) 5 c o p p i c e g r o w t h s prior t o r e p l a n t i n g ; (4) a 1.8-million-gallon-per-day (MGD) w a s t e w a t e r t r e a t m e n t facility f o r t h e algae p o n d a n d t h e s l u d g e credit i n p u t ; (5) 180 days in t h e g r o w i n g season; a n d (6) average p r o d u c t i v i t y of 8.2 o v e n - d r y t o n s of biomass ( w o o d a n d leaf) per acre-year, or t o t a l p r o d u c t i o n of 2 3 3 , 7 0 0 ODT/year. Table III lists t h e results of these tests. T h e ranges s h o w n reflect values g e n e r a t e d over all three sets of l e a c h i n g rates. It can be seen t h a t r e c y c l i n g of leaf m a t e r i a l , t h a t is, r e s t r i c t i n g h a r v e s t i n g t o t h e d o r m a n t season, w i l l reduce t h e fertilizer r e q u i r e m e n t b y 8 - 1 6 % f o r Ν a n d P. A s t h e n u m b e r of days in t h e h a r v e s t i n g season increases, m o r e leaf material is r e m o v e d f r o m t h e site a n d less is r e c y c l e d , increasing t h e r e q u i r e m e n t o f inorganic fertilizer. These results agree fairly w e l l w i t h p u b l i s h e d values o f 1 5 - 3 0 % savings in fertilizer r e q u i r e m e n t s r e s u l t i n g f r o m h a r v e s t i n g o n l y in t h e d o r m a n t season (65). S l u d g e c o n t r i b u t e s a smaller a m o u n t t o t h e overall balance, a b o u t 2 - 4 % of t h e Ν a n d Ρ fertilizer r e q u i r e m e n t s , a n d appears t o be m o r e i m p o r t a n t for Ρ t h a n N. T h e largest savings, h o w e v e r , result f r o m t h e ash a n d n i t r o g e n f i x a t i o n inputs. D e p e n d i n g u p o n t h e level of return of ash t o t h e p l a n t a t i o n , f r o m 9 - 7 7 % of t h e Ρ fertilizer r e q u i r e m e n t can be replaced b y r e c y c l i n g of ash material.

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BIOMASS AS A NONFOSSIL F U E L SOURCE

N i t r o g e n f i x a t i o n c o n t r i b u t e s s i g n i f i c a n t savings t o t h e n i t r o g e n fertilizer r e q u i r e m e n t s . From o n e - t h i r d t o t h r e e - f o u r t h s of t h e Ν fertilizer r e q u i r e m e n t can be s u p p l i e d by t h i s i n p u t . Since o r i g i n a l PEF s y s t e m p e r f o r m a n c e analyses i n d i c a t e d t h a t n i t r o g e n fertilizer costs c o n t r i b u t e b e t w e e n 2 0 - 2 5 % of t h e t o t a l cost of t h e biomass p r o d u c e d , these savings represent a s i g n i f i c a n t decrease in t h e c o s t of p r o d u c t i o n . T h e levels of n i t r o g e n a c c r e t i o n f r o m f i x a t i o n used in Table III are readily a t t a i n a b l e u n d e r m i x e d p l a n t i n g m a n a g e m e n t (66). It s h o u l d be n o t e d t h a t s o m e decrease in overall p r o d u c t i v i t y c a n be e x p e c t e d because of t h e e n e r g y needed for f i x a t i o n ; t h i s has been e s t i m a t e d as a 1 2 - 1 5 % decrease (67).

Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

W a t e r Balance and Irrigation Even in areas of t h e U n i t e d States w h e r e natural rainfall is s u f f i c i e n t for h a r d w o o d g r o w t h (25 inches or more), periods of w a t e r stress m a y o c c u r d u r i n g t h e g r o w i n g season (68.69). Lack of a d e q u a t e m o i s t u r e m a y have disastrous c o n s e q u e n c e s o n t h e survival a n d e s t a b l i s h m e n t of clones or seedlings. It has also been s h o w n t h a t yields o f h a r d w o o d p l a n t a t i o n s c a n be increased by r e d u c i n g w a t e r stress d u r i n g t h e g r o w i n g season. A n irrigation s u b r o u t i n e has therefore been i n c l u d e d in t h e PEF m o d e l t o evaluate t h e costeffectiveness of irrigation for site-specific c o n d i t i o n s . Irrigation r e q u i r e m e n t s for a site are d e t e r m i n e d t h r o u g h a m o n t h - b y - m o n t h b a l a n c e analysis. T h e Blaney-Criddle m e t h o d as a d a p t e d by t h e Soil C o n s e r v a t i o n Service (70) is used in t h i s analysis. T h e m e t h o d first d e t e r m i n e s t h e w a t e r c o n s u m p t i v e needs of d e c i d u o u s p l a n t a t i o n s for local c l i m a t i c c o n d i t i o n s . T h e irrigation r e q u i r e m e n t s are t h e n e s t i m a t e d by c o m p a r i n g these needs t o e f f e c t i v e w a t e r i n p u t s f r o m rainfall. T h e m o n t h l y irrigation r e q u i r e m e n t s are i n p u t s t o t h e irrigation s u b r o u t i n e . T h e peak m o n t h l y r e q u i r e m e n t is used t o d e t e r m i n e t h e peak c a p a c i t y a n d c a p i t a l cost of t h e irrigation s y s t e m . It is a s s u m e d t h a t t h e irrigation required d u r i n g t h e m o n t h of h i g h e s t d e m a n d w i l l be s u p p l i e d t h r o u g h f o u r w e e k l y a p p l i c a t i o n s . T h e o p e r a t i o n costs are e s t i m a t e d on t h e basis of t h e t o t a l irrigation needs for t h e g r o w i n g season. Self-propelled t r a v e l i n g sprinklers f e d by u n d e r g r o u n d m a i n s are a s s u m e d in t h e m o d e l . This s y s t e m w a s c h o s e n because it has been e x t e n s i v e l y used for w a s t e w a t e r a p p l i c a t i o n (23). T r i c k l e - d r i p s y s t e m s are m o r e e n e r g y efficient, b u t their use w i t h w a s t e w a t e r s has resulted in c l o g g i n g d u e t o algae g r o w t h a n d t h e r e f o r e m a y require f l u s h i n g w i t h fresh w a t e r (7Yl. W a t e r c a n be s u p p l i e d f r o m w e l l s , river o r lake w a t e r , or e f f f u e n t s f r o m a w a s t e w a t e r t r e a t m e n t plant. T h e response of t h e p l a n t a t i o n is d e s c r i b e d by a relation of t h e f o r m y = ax + b w h e r e y = y i e l d , χ = n u m b e r of g r o w t h days w i t h s u f f i c i e n t m o i s t u r e , a n d a a n d b = c o n s t a n t s . T h e use of

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Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch025

T a b l e III. PERCENT S A V I N G S OF FERTILIZER R E Q U I R E M E N T S ATTRIBUTABLE TO VARIOUS INPUT PARAMETERS" Application Design Nutrient Input Parameter Leaf Recycle Sludge Ash Ash Ash Nitrogen Fixation Nitrogen Fixation' b

c

d

6

Rotation

Yearly Ν

Ρ

Ν

Ρ

%

%

%

%

8-13 2-4

12-15 4-6 18-24 36-48 57-77

14-16