energy from biological processes: volume ii—technical and environmental analyses

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Energy from Biological Processes: Volume II—Technical and Environmental Analyses

September 1980

NTIS order #PB81-134769



Library of Congress Catalog Card Number 80-600118

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 Stock No. 052-003-00782-7



Energy From Biological Processes Advisory Panel

Thomas Ratchford, ChairmanAssociate Executive Director, American Association for the Advancement of Science

Henry ArtCenter for Environmental StudiesWilliams College

Stanley BarberDepartment of AgronomyPurdue University

John BenemannSanitary Engineering LaboratoryUniversity of California, Richmond

Paul F. Bente, Jr.Executive DirectorThe Bio-Energy Council

Calvin BurwellOak Ridge National Laboratory

Robert HodamCalifornia Energy Commission

Kip HewlettGeorgia Pacific Corp.

Ralph KienkerMonsanto Co.

Dean KlecknerPresidentIowa Farm Bureau Federation

Kevin MarkeyFriends of the Earth

Jacques MaroniEnergy Planning ManagerFord Motor Co.

Michael NeushulMarine Science Institute

University of California, Santa Barbara

William SchellerDepartment of Chemical Engineering

University of Nebraska

Kenneth SmithOff ice of Appropriate TechnologyState of California

Wallace TynerDepartment of Agricultural EconomicsPurdue University

Robert HirschEXXON Research and Engineering Co.

-NOTE. The Advisory Panel provided advice and comment throughout the assessment, but the members do not necessarily approve,

disapprove, or endorse the report for which OTA assumes full responsibility

Working Group on Photosynthetic Efficiencyand Plant Growth

One BjorkmanCarnegie Institution

Stanford University

Gl e n n B u r t o nSouthern Region

U.S. Department of Agriculture

Ga r y H e i c h e lNorth Central Region

U.S. Department of Agriculture

University of Minnesota

Edgar LemonNortheastern Region

U S. Department of AgricultureCornell University

Contractors and Consultants

The Baham Corp.

Charles Berg

California Energy Commission

Otto Doering IllDouglas Frederick

Charles Hewett

1 E Associates

Larry JahnRobert Kellison

Neushul Mariculture, Inc.

Participation Publishers

Princeton University, Department of

Aerospace and Mechanical Sciences

Purdue University, Departments of

Agricultural Economics, Agricultural

Engineering, and Agronomy

Santa Clara University, Department ofMechanical Engineering

State of California, Office of AppropriateTechnology

T B Taylor, AssociatesTexas A&M University, Departments of

Agricultural Economics and AgriculturalEngineering

Texas Tech University, Department of

Chemical Engineering

R i c h a r d R a d m e rMartin-Marietta Laboratory

University of California at Davis, College of

Agricultural and Environmental Sciences

University of California, Richmond FieldStation

University of Pennsylvania, Department of

Chemical and Biochemical Engineering

University of Texas at Austin, Center for

Energy StudiesUniversity of Washington, College of

Forest Resources

RonaId Zweig

iv



Energy From Biological Processes Project Staff

Lionel S. Johns, Assistant Director, OTAEnergy, Materials, and International Security Division

Richard E. Rowberg, Energy Program Manager

Thomas E. Bull, Project Director

A. Jenifer Robison, Assistant Project DirectorAudrey Buyrn*

Steven Plotkin, Environmental Effects

Richard Thoreson, Eco nomics

Franklin Tugwell, Policy Analysis

Peter Johnson, Ocean Kelp Farms

Mark Gibson, Federal Programs

Administrative Staff

Marian Growchowski Lisa Jacobson

Lillian Quigg Yvonne White

Supplements to Staff

David Sheridan, Editor

Stanley Clark

OTA Publishing Staff

John C. Holmes, Publishing Officer

Kathie S. Boss Debra M. Datcher Joanne Mattingly

*Project director from April 1978 to December 1978



Acknowledgments

OTA thanks the fo l lowing people who took t ime to provide in formation or review part or a l l o f the study

Don Augenstein, Flow Laboratories

Edgar E. Bailey, Davy McKee Corp.

Richard Bailie, Environmental Energy

Engineering, Inc.

Weldon Barton, U.S. Department of

Agriculture

Charles Bendersky, Pyres, Inc.

Edward Bentz, National Alcohol Fuels

CommissionBeverly Berger, U.S. Department of Energy

Brian Blythe, Davy McKee Corp.

Hugh Bollinger, Plant Resources Institute

Diane Bonnert, Soil Conservation ServiceCarroll Bottum, Purdue University

Robert Buckman, U.S. Forest Service

Fred Buttel, Cornell University

James Childress, National Alcohol Fuels

Commission

Raymond Costello, Mittlehauser Corp.

Gregory D’Allessio, U S Department of

Energy

Ray Dideriksen, Soil Conservation Service

Richard Doctor, Argonne National

Laboratory

James Dollard, U.S. Department of Energy

Warren Doolittle, U.S. Forest ServiceErnest Dunwoody, Mittlehauser Corp.

Ed Edelson, Pacific Northwest Laboratory

Eugene Eklund, U.S. Department of Energy

George Emert, University of Arkansas

John Erickson, U.S. Forest Service

William Farrell, EXXON Research andEngineering Co

Winston C. Ferguson, Conservation Con-

sultants of New England

Kenneth Foster, University of Arizona

Douglas Frederick, North Carolina State

University

Ralph E C. Fredrickson, Raphael Katzen

Associates

Tim Clidden, Dartmouth College

Irving Goldstein, North Carolina State

University

John Goss, University of CaliforniaRoy Gray, Soil Conservation Service

Loren Habegger, Argonne National

Laboratory

John Harkness, Argonne National

Laboratory

Sanford Harris, U.S. Department of Energy

Marilyn Herman, National Alcohol Fuels

Commission

Edward Hiler, Texas A&M University

Dexter Hinckley, Flow Resources Corp.

Wally Hopp, Pacific Northwest Laboratory

John Hornick, U.S. Forest Service

William Jewell, Cornell (University

Fred Kant, EXXON Research and Engineer-ing Co,

J L. Keller, Union Oil of California

Don Klass, Institute of Gas Technology

J. A. Klein, Oak Ridge National Laboratory

Al Kozinski, Amoco Oil Co

Suk Moon Ko, Mitre Corp.

Kit Krickensberger, Mitre Corp.

Barbara Levi, Georgia Institute ofTechnology

Les Levine, U.S. Department of Energy

Edward Lipinsky, Battelle Columbus

Laboratory

William Lockeretz, Northeast Solar Energy

Center

Dwight Miller, U.S. Department of

Agriculture

John Milliken, U.S. Environmental Protec-

tion AgencyLarry Newman, Mitre Corp.

Edward Nolan, General Electric Co

John Nystrom, Arthur D. Little, Inc.

Ralph Overend, National Research Council

of Canada

Billy Page, U.S. Forest Service

R. Max Peterson, U S. Forest Service

David Pimentel, Cornell University

L. H. Pincen, U.S. Department of

AgricultureHarry Potter, Purdue University

T. B. Reed, Solar Energy Research Institute

Mark Rey, National Forest Products

Association

Robert San Martin, U.S. Department of

Energy

Kyosti Sarkanen, University of Washington

John Schaeffer, Schaeffer and Roland, Inc.

Rolf Skrinde, Olympic Associates

Thomas Sladek, Colorado School of Mines

Research Institute

Frank Sprow, EXXON Research and

Engineering Co.

George Staebler, Weyerhauser Corp.Terry Surles, Argonne National Laboratory

Robert Tracy, U.S. Forest Service

R Thomas Van Arsdall, U.S. Departmentof Agriculture

R. I Van Hook, Oak Ridge National

Laboratory

Thomas Weil, Amoco Chemicals

Donald Wise, Dynatech R&D

Robert Wolf, Congressional Research

Service

Robert Yeck, U S Department ofAgriculture

John Zerbe, U S. Department of

Agriculture

vi



Contents

Chapter Page

Part 1: Biomass Resource Base

1.2.3.4.

5.

Introduction and Summary . . . . . . . . .5

Forestry . . . . . .Agriculture. . . .UnconventionalBiomass Wastes

9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Biomass Production. . . . . . . . . . . . . . . .111. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

91

Part II: Conversion Technologies and End Use

6.

7.8.9.

10.11.

12.

Introduction and Summary . . . . . . . . . . . . . . . . . . . . . ..................119

Thermochemical Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 123Fermentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159Anaerobic Digester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181

Use of Alcohol Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....201Energy BaIances for Alcohol Fuels. . . . . . . . . . . . . . . . . . . . . . . . ..........219

Chemicals From Biomass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

vii



Part I.

Biomass Resource Base



Chapter 1

INTRODUCTION AND SUMMARY



Chapter 1


The biomass resource base potentially in-cludes hundreds of thousands of differentpIant species and various animal wastes. Inprinciple, plants can be cultivated anywherethere is a favorable climate with sufficientwater, sunlight, and nutrients. In practice,there are numerous limitations, and the mostimportant of these appears to be the soil typefor land-based plants and cultivation and har-vesting techniques for aquatic plants.

The largest area of underutilized land that iswelI suited to plant growth is the Nation’s for-

estland. Through more intensive forest man-agement— particularly on privately ownedlands–the supply of wood for energy, as wellas for traditional wood products, could be sub-

stantially increased. However, haphazardwood harvest could cause severe environmen-

tal damage and reduce the available supply ofwood.

The highest quality land suitable for inten-sive cultivation of plants is the Nation’s crop-Iand. The best cropland is dedicated to foodproduct ion, but there is some underutilizedhayland and pastureland as well as land thatcan be converted to cropland. To a certain ex-tent, grains—especially corn — can be grownfor ethanol production and the distillery by-

product used as an animal feed to displacesoybean production. More grain can then begrown on the former soybean land. As the etha-nol production level grows, however, the ani-mal feed market for the distillery byproductwill become saturated and grass productionquickly will become a more effective energyoption for the cropland. To a certain extent,environmental damage appears to be practi-cally unavoidable with grain production, butgrass cultivation is more environmentallybenign.

The candidates for bioenergy crops are nu-

merous, but crop development directed to-

ward energy production is needed to comparethe options and to establish cultivation re-quirements and yields.

In addition to energy crops, substantialquantities of crop residues can be collectedand used for energy without exceeding crop-Iand erosion standards.

The third major land category is rangeland,

which vary from highly productive wetlands todeserts. Cultivation and harvesting techniques

and plant growth are uncertain, and in drierregions the lack of water will Iimit yields unlessthe crops are irrigated. However, irrigationgreatly increases the energy needed for farm-ing and it is uncertain whether it will be social-ly acceptable to use the available water forenergy production.

Aside from natural wetlands, there are otherareas where freshwater plants might be grownand there are vast areas of ocean in whichocean farms might be built. Cultivation andharvesting techniques and crop yields arehighly uncertain.

In addition to crop cultivation and residuesthere is biomass potential from processing andanimal wastes. * Most processing wastes cur-rently are used for energy, animal feed, or

chemical production, but much of the remain-der could be used for energy. Moreover, mostof the manure from animals in confined live-stock operations could be used for energy.

These biomass sources and various otheraspects of the resource base are considered inthe following chapters.

*Wastes are defined as byproducts of biomass processing that

are not dispersed over a wide area and therefore need not be col-

lected Residues must be collected

5



Chapter 2

FORESTRY



Chapter 2.- FORESTRY

PageIntroduction q 9Present Forestland. . . . . . . . . . . . . . . . . . . . . . . . 10Present Cutting of Wood. . . . . . . . . . . . . . . . . . . 10

Forest Products Industry Roundwood

Harvesting . . . . . . . . . . . . . . . . . . . . . . . . . 11household Fuelwood. . . . . . . . . . . . . . . . . . . 13Stand improvements . . . . . . . . . . . . . . . . . . . 13Clearing of Forestland . . . . . . . . . . . . . . . . . . 14Summary of Current Cutting of Wood . . . . . . 14

Present lnventory of Forest Biomass. . . . . . . . . . . 14Noncommercial Forestland . . . . . . . . . . . . . . 14Commercial Forestland. . . . . . . . . . . . . . . . . 15Quantity Suitable for Stand Improvement. . . 15

Present and Potential Growth of Biomass inU.S. Commercial Forestso . . . . . . . . . . . . . . . . . 16

Forest Biomass Harvesting. . . . . . . . . . . . . . . . . . 18Factors Affecting Wood Availability . . . . . . . . . . . 21

Landownership . . . . . . . . . . . . . . . . . . . . . . . . 21

Alternate Uses for the Land . . . . . . . . . . . . . . 22Public Opinion . . . . . . . . . . . . . . . . . . . . . . . . 22Alternate Uses for Wood . . . . . . . . . . . . . . . . 22Other Factors and Constraints . . . . . . . . . . . . 23

Net Resource Potential . . . . . . . . . . . . . . . . . . . . 23Enviromental Impacts. . . . . . . . . . . . . . . . . . . . . 25

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 25Environmental Effects of Conventional

Silviculture . . . . . . . . . . . . . . . . . . . . . . . . . 27Potential Environmental Effects of

Harvesting Wood for Energy . . . . . . . . . . . 32Controlling Negative Impacts . . . . . . . . . . . . 41Potential Environmental Effects–Summary. 45

R&D Needs q **,.**. . . . . . . . . . ...***,., 46

TABLESPage

l. Logging Residues Estimate—summary . . . . 122. Logging Residue Estimates. . . . . . . . . . . . . . 13

Page

3. Fuelwood Harvests in 1976. . . . . . . . . . . . . . 134. Current and Expected Annual Stand

Improvements . . . . . . . . . . . . . . . . . . . . . . . 145. Estimated Above ground Standing Biomass of

Timber in U.S. Commercial Forestland. . . . . 156. Assumptions for Whole-Tree Harvesting

Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Annual Whole-Tree Chipping System Costs. 198. Assumptions for Cable Yarding Equipment . 209. Cable Logging System Costs. . . . . . . . . . . . . 20

10. Factors Affecting Logging Productivity . . . . 2111 . Potential Environmental Effects of Logging

and Forestry . . . . . . . . . . . . . . . . . . . . . . . . . 2812. Environmental impacts of Harvesting

Forest Residues . . . . . . . . . . . . . . . . . . . . . . 3413, Control Methods . . . . . . . . . . . . . . . . . . . . . 43

FIGURES

Pagel. Forestland as a Percentage of Total Land

Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112. Area of Commercial Timberland by Region

and Commercial Growth Capability as ofJanuary 1,1977. . . . . . . . . . . . . . . . . . . . . . . 12

3. Forest Biomass inventory, Growth, and Use. 17

4. Supply Curve for Forest Chip Residues forNorthern Wisconsin and Upper Michigan . . 21S. Materials Flow Diagram for Felled Timber

During Late 1970’s . . . . . . . . . . . . . . . . . . . . 246. Environmental Characteristics of Forest

Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33



Chapter 2

FORESTRY

Introduction

The use of wood for fuel is at least as old as

civilization. Worldwide, wood is still a very im-portant source of energy. The U.N. Food andAgricultural Organization estimates that thetotal annual world harvest of wood in 1975 was90 billion ft3 (about 25 Quads) of which nearlyone-half was used directly for fuel. ’ Much ofthe wood that is processed into other productsis available for fuel when the product is dis-carded from its original use, and indeed largebut unknown quantities are used in this man-ner.

Wood has been a very important fuel in the

United States, having been used for home

heating and cooking, locomotive fuel, the gen-eration of electricity for home, business, andindustrial use, and for the generation of steamfor industry. According to Reynolds and Pier-

son, more than half of the wood harvestedfrom U.S. forests for the 300 years of Americanhistory preceding 1940 was used as fuel. z Con-sumption of wood fuel reached its peak in theUnited States in 1880 when 146 million cords(2.3 Quads) were used according to Panshin, etal.

3The same authors report that per capita

consumption of wood fuel peaked in 1860 at4.5 cords/yr. During the past 100 years, the

direct use of wood for fuel declined in theUnited States to about 30 million cords/yr (0.5Quad/yr). It was used primarily as a fuel by the

forest products industries, which used manu-facturing residues, and for home fireplacesand outdoor cooking, which created demandfor charcoal and hardwood roundwood.

There have, however, been periodic revivals

of fuelwood use to replace conventional fuelsin the United States. They have usually oc-

curred during times of crises, such as World

1 Yearbook of Forest Produc ts 1%4-1975 (Rome: Food and Agri-

culture Organization of the United Nations, 1977)‘R V Reynolds and A. H. Pierson, “Fuelwood Used In the U.S.

16301930, ” USDA Clr. 641, 1942

3A J Panshin, E. S H arrar, J S Bethel, and W. J. Baker, Forest

Products (New York: McGraw-Hill, 1962)

Wars I and 11, when conventional fuels became

scarce. After the crises abated fuelwood usedwindled rapidly, even though the reemerg-ence of the same conditions in the near futuremay have been expected.

During 1917-18, for example, the Eastern

United States suffered a shortage of coal. FueI-wood was used whenever possible to replacecoal, as were sawdust briquettes and othercombustible biomass. Individual towns in New

England organized “cutting bees” and “cut acord” clubs for gathering wood fuel to offsetthe shortage of coal. Between 1916 and 1917the price of fuelwood increased by about 20 to

30 percent.

The U.S. Forest Service prepared a publica-

tion explaining, among other things, how woodcould be used as fuel to conserve coal.4

It was

thought at the time that coal reserves in theUnited States were dangerously low and thatthe war-induced shortage of 1917-18 had mere-ly emphasized the inevitable need to conservethem. This publication advocated a broadGovernment policy for development of a fuel-wood industry. The role that cutting fuelwoodcould play in forest management was consid-

ered, and an analysis of the economics of cut-ting and gathering, etc., was given. The reportconcluded that a fuelwood industry could beprofitable and could benefit the forest in otherways as well. The document was publishedMarch 10, 1919, by which time the war hadended, and the Nation’s fuel situation was al-ready beginning to return to prewar condi-tions. There is no evidence that any of the rec-ommendations were folIowed.

Since World War 11, the major emphasis onwood use has been for lumber and paper pulp.The annual harvest of commercial wood (woodappropriate for the forest products industry)

grew by 22 percent between 1952 and 1976.During this same period, the net growth of

‘USDA Bulletin 753, Forest Service, Mar 10,1919

9



10 q VOI. II—Energy From Biological Proc esses

commercial wood (total growth of commercialtimber less mortality of commercial timber) in-creased by 56 percent. In only one region inthe country, the Pacific Coast, did the inven-tory of live commercial wood on commercialforestlands decline. In the Pacific Coast re-gion, however, the growth, as a percentage of

the standing inventory, is the lowest in thecountry due to the old age of the timber. Na-tionwide the inventory of commercial timber

Present

Forestland is defined as land that is at least10-percent stocked with forest trees or hasbeen in the recent past and is not permanentlyconverted to other uses. The forestlands aredivided into two categories: commercial and

noncommercial. Commercial forestland is de-fined as forestland that is capable of produc-ing at least 20 ft3/acre-yr (0.3 dry ton/acre-yr) ofcommercial timber in naturally stocked standsand is not withheld from timber production(e.g., parks or wilderness areas). The rest istermed noncommercial.

The forest regions of the United States and

the percentage of the total land area of eachState that is forestland are shown in figure 1.Currently, there are 740 million acres of forest-Iand in the United States, with about half in

the East (i.e., North plus South) and half in theWest. About 490 million acres are classified ascommercial forestland and nearly three-quar-ters of this are in the East. The productivepotential of commercial forestlands is shownin figure 2.

In addition, there are 205 million acres of

noncommercial forestland, which are classi-fied this way because of their low productive

potential (i. e., less than 20 ft3/acre-yr). Prac-

tically all of the noncommercial forestland is

increased by 20 percent from 1952 to 1976.

Thus, increased harvests of wood do not neces-sarily imply that the forests are being depleted.

The growth of wood depends not only on theclimate and soil type, but also on the type and

age of trees and the way the forest is managed.In this chapter, the potential for fuelwood pro-

duction from the Nation’s forests is examined.

Forestland

in the West. Despite the low-productivity clas-

sification, however, timber is harvested frommany areas of land in this category.

Most of the forestland in the East is privately

owned, while about 70 percent of the western

forestland is publicly owned and managed bythe Federal Government or State and localauthorities.

The U.S. Department of Agriculture (USDA)projects that the forestland area will decreaseby 3 percent by the year 2030 (about 0.4 mil-lion acres/yr or a total of 20 million acres). s In

the 1980’s, a significant portion of the declinewill result from conversion to cropland, par-ticularly in the Southeast. USDA projects thatin the 1990’s, most of the conversion will be toreservoirs, urban areas, highway and airport

construction, and surface mining sites.

However, about 32 million acres of potentialcropland are now classified as forestland (seech. 3). Consequently, if a strong demand de-

velops for cropland, then the decrease in forestarea will be somewhat larger than USDA’s pro-jection.

‘An Assessment of the Forest and Range Land Situation in the

United States, review draft, USDA Forest Service, 1979.

Present Cutting of Wood

Forest wood is currently being cut for four dustry roundwood, 2) production of household

purposes: 1) production of forest products in- fuelwood, 3) timber stand improvements, and



Ch. 2—Fores t ry q 1 1

Figure 1.— Forestland as a Percentage of Total Land Area

SOURCE Forest Service u S Department of Agriculture

4) clearing of timberland for other uses. Each

of these produces wood that can be or is usedfor energy.

Forest Products IndustryRoundwood Harvesting

Currently, the forest products industry is har-vesting 200 million dry ton/yr (3.1 Quads/yr) forlumber, plywood, pulp, round mine timber,etc.). During the processing of this wood, 90million ton/yr of primary and secondary manu-facturing wastes are produced. These wastes

are discussed later under “Biomass ProcessingWastes” in chapter 5.

In addition, the process of harvesting thewood generates considerable logging residue.The logging residue consists of the material

left at the logging site after the commercial

roundwood is removed. These residues arebranches, small trees, rough and rotten wood,tops of harvested trees, etc.

The statistics on logging residues reportedfor 1970 and 1976 by the Forest Service under-estimate the total quantity of residues gener-ated by harvesting activities. The Forest Serv-ice data only include wood logging residuesfrom growing stock trees. *

Not reported are:

1. bark — most studies of logging residue pre-

sent volumes without bark;2. residues from:q nongrowing stock trees on logged-over

areas,‘Commercial stock trees that are 1 ) at least 5-inch diameter at

breast height (dbh) and 2) not classified as rough or rotten



12 q Vol. I I -Energy From Biological P rocesses

Figure 2.—Area of Commercial Timberland byRegion and Commercial Growth Capability

as of January 1, 1977

No. of acres

(millions) s

180

170

160

150

140

130

120

110

100

90

80

70

6050

40

30

20

10

N = North

S = South

PC = Pacific Coast. Alaska, HawaiiR M = R o c k y M o u n t a i n a n d G r e a t P l a i n s

From various sources’ 78 and OTA estimates,the ratios of growing stock residues to totalbiomass residues were derived. ’ Using theseratios and the Forest Service data for growingstock residues, the quantity of logging residueswas estimated to be about 84 million dry tons(1.3 Quads) in 1976. The regional breakdown is

shown in table 1, and a more detailed break-down is shown in table 2.

Table 1.–Logging Residues Estimatea –Summary(in million dry tons)

Region Softwood Hardwood Totalb

North . . . . . . . . . . . . . . . . . 2.9 13.2 “ 16.0South . . . . . . . . . . . . . . . . 17.6 15.2 32.8

2050 50-85 85120 120 + T o t a l

Growth capability

(ft3 commercial timber/acre-yr)

SOURCE Data from Forest Statistics, 1977, Forest Service, U S Department o fAgriculture, 1978

trees of growing stock species and qual-ity, but less than 5-inch diameter atbreast height,trees that would be growing stock treesexcept that they are classified as roughor rotten, andtrees of noncommercial species;

3. tops and branches; and4. stumps.

All of these logging residue components, aswell as the residue presented in the aforemen-tioned reports, are potentially usable as fuel. *

*In this report, the stumpwood component IS not considered

Total b . . . . . . . . . . . . . . . 54.5 29.5 84.1

aFrom a Ig76 harvest of 130 mllllon dry tons of softwood and 54 mllllon dry tom Of hardwoodbsurns may not agree due to round off error

SOURCE J S 8ethel, et al,, “Energy From Wood, ” College of Forest Resources, University of

Washington, Seattle, contractor report to OTA, April 1979.

There is some uncertainty as to whether var-ious logging residue studies are in agreement

as to what constitutes nongrowing stock log-ging residue. Loggers may avoid cutting non-growing stock trees that hold little or no eco-nomic value. This practice would be commonin selective logging. In many logging residuestudies, it is unclear whether or not such uncuttrees were considered residue. Some of the differences observed in logging residue factors re-ported by various authors in the same region

may be due largely to these methodologicaldifferences. There is a danger that if uncutnongrowing stock is counted as a logging resi-due, it might again be counted as part of thebiomass that should be removed by various sil-vicultural stand improvements. Every effortwas made to avoid this type of double count-ing.

‘J O Howard, “Forest Residues– Their Voiume, Vaiue and

Use, ” Part 2: Vo lume of Residues From Logging Forest Industries,

98(1 2), 1971

‘R L Weich, “Predicting Logging Residues for the Southeast, ”

USDA Forest Service Research Note SE-263, 1978“J. T Bones, “Residues for Energy in New Engiand,” Northern

Logger and Tmer Processor 25(1 2), 1977

‘j S Bethei, et al , “Energy From Wood, ” Coiiege of Forest Re-

sources, University of Washington, Seattle, contractor report to

OTA, Apni 1979



Ch. 2—Forestry . 1 3

Table 2.–Logging Residue Estimates (thousand dry tons)

From growing stock From nongrowing stock

Tops andHarvest branchesin 1976 Wood Bark Total Wood Bark Total incl. bark Total

Softwoods North. . . . . . . . . . .

South. . . . . . . . . . . .W.Pine . . . . . . . . .Coast . . . . . . . . . . . .

7,448

6303116,500

43,190

823

3,7561,5487,496

393181876

908

4,1491,7298,372

15,158

597

2,6972,0228.117

64

314236949

1,563

661

2,9932,2589,066

1,323

10,4153,000 9,668

24,406

2,892’

17,5576,98727,106

54,5421,535 13,433Total. . . . . . . . . . .Hardwoods N o r t h . . . . . . . . . . . .South. . . . . . . . . . . .W.Pine . . . . . . . . . .Coast . . . . . . . . . . . .

130,169 13.623 14,978

24,54627,974

341,094

53,648

4,2144,984

3345

313381

—

36

4,5275,275

3381

10,186

1,4101,637

2255

100123

—

27

250

1,5101,760

2282

7,1478,185

11458

15,801

13,18415,220

161,121

29,541Total . . . . . . . . . . . 9,456 730 3,304 3,554

SOURCE J S Bethel, et al, ’’Energy From Wood, “Coll ege of Forest Resources, University of Washington, Seattle, contract or reporf to OTA, April 1979

space for the higher quality trees. These cut-ting activities are generally referred to as stand

improvements, and include stand conversions*and thinning operations. Wood from these ac-tivities or sources is suitable for fuel.

The data on the amount of current stand im-provement activity are very limited and do notallow a detailed analysis. During the 1968-71period, various practices, such as precommer-cial and commercial thinning, species conver-sion, weed control, and other stand improve-ments were carried out on a total of 1.4 millionacres. This represents only 0.3 percent of thecommercial timberland. Generally these prac-

tices are carried out irregularly, or on a when-and where-needed basis. Undoubtedly most ofthe activity is carried out on industry landswhere intensive forest management is most ad-vanced. A recent survey of forest industryfirms that manage their own lands revealed the

current level of these practices. ’ These aresummarized in table 4.

In addition, there are timber stand improve-ments (excluding thinnings), species conver-sion, and weed control items, on about 1.7 mil-lion acres of low-quality stands per year. Yieldswould vary tremendously among these prac-

*Stand conversion is the practice of eliminating tree species

currently occupying a stand and replacing them with other

species.

‘ID S DeBell, A P Brunette, and D C Schweitzer, “Expecta-

tions From Intensive Culture on Industrial Forest Lands,” ). For.,

January 1977

Household Fuelwood

The harvest of roundwood for use as house-hold fuel was estimated in 1976 to be 657 mil-lion ft3, or approximately 10 million dry tons(0.16 Quad). These figures are similar to theresults reported by EIlis, who found that 600mill ion ft

3of roundwood, excluding bark, were

harvested for fuelwood. ’” Allowing a IO-per-cent increase for bark, this becomes 660 mil-lion ft3. The regional breakdown is shown intable 3. The quantity harvested in more recentyears is considerably larger, however,

Table 3.–Fuelwood Harvests in 1976 (in million dry tons)

Region Softwood Hardwood Totala

North, ., ... . . . . . . 0.05 3.7 3.8South . . . . . . 1.3 4.2 5.7R o c k y M o u n t a i n s 0.43 0.01 0.44Pacific Coast. . . . . . . 0. 33 0.11 0.39

Total . . . . . . . . . 2.3 8.2 10.2

asums may not agree due to round off errors

SOURCE J S Bethel et al Energy From Wood, ‘ College of Forest Resources, Umverslty ofWashmgtorr Seattle contractor report toOTA Aprd f979

Stand Improvements

In normal forestry operations, there may be

several times during the growth of a stand oftrees that malformed, rough, or otherwise un-desirable trees are cut to make more growing

‘OT H EIIIs, “FuelwoOd,” unpublished manuscript, 1978



14 q Vol. I I—Energy From Biological Pr ocesses

Table 4.–Current and Expected AnnualStand Improvements

Percent ofPercent of firms expectingIndustry Estimated to maintain or

lands acres increase levelTreatment treated treateda of treatment

Precommercial thinning ., 0.2 135,000 53

Timber standImprovement, . 1 8 1,212,000 69

Commercia l thron ing . . . 25 1,684,000 92Species conversion 04 269,000 65Weed control . . ., 0.3 202,000 50

aPercenl 01 lands treated hmes toial acreage owned by industry

S O U R C E O S OeBell A P Brunel[e and O C Schwe i t ze r Expec tat ions Fr om IntensweCulture on Induslnal Forest Lands J For January 1977

tices, but assuming 17 dry ton/acre (as derivedby Bethel for rough, rotten, and salvageabletrees in the South), this amounts to 29 milliondry ton/yr.

Thinnings were also carried out on 1.8 mil-lion acres, but there is little information re-

garding the amounts of residue produced.Yields have been reported of 2.2 dry ton/acrein 4-year-old Ioblolly pine thinning, 12 and 17 to

28 dry ton/acre in pole timber hardwoods inthe North. ” If a national average of 10 ton/

acre is assumed, thinning would provide 18milIion dry ton/yr of residue.

‘ ‘Si/ vicu/ ture Biomass Farms (McLean, Va The MITRE Corp ,

1977)

‘‘F E Blltoner, W A Hlllstrom, H M Stelnhlll, and R M Gad-

mar, USDA Fore$t Service Research Paper NC-1 37, 1976

Combining these two sources results in 47million ton/yr (0.7 Quad/yr) of residues fromstand improvements.

Clearing of Forestland

Clearing of forest land for other uses can pro-vide a temporary, but potentially significant,local supply of wood. The yield per acre har-vested varies widely with the locality. Assum-ing 30 ton/acre cleared, then USDA projectionsfor forestland clearing would provide about0.2 Quad/yr to 2030. If the forestland with ahigh and medium potential for conversion to

cropland is all cleared over the next 15 years,then this would provide 1 Quad/yr of wood for

these 15 years. Most of this would occur in theSoutheast (see ch. 3).

Summary of Current Cutting of Wood

The forest products industry currently har-vests about 200 million dry ton/yr (3.1 Quads/yr) of wood for lumber, plywood, paper pulp,and other products. The process generates anadditional 84 million ton/yr (1.3 Quads/yr) oflogging residues. Another 10 million dry tons(0.2 Quad/yr) are harvested for fuelwood, andabout 47 dry ton/yr (0.7 Quad/yr) are cut duringstand improvements. This results in a total har-vest of about 340 million dry ton/yr or the eqiv-a lent of 5.3 Quads/yr. Another 0.2 Quad/yr is

obtained from clearing and converting forest-Iands to other uses.

Present Inventory of Forest Biomass

It is not a simple matter to derive the total base, the present inventory of forest biomass

forest biomass inventory from the Forest Serv- can only be estimated.

ice surveys. As noted earlier, this lack of anadequate” census base stems from the tradi-

tional practice of evaluating the wood in a for-Noncommercial Forestland

est only in terms of what is assumed to be mer- As mentioned above, of the one-quarter bil-

chantable, rather than on a whole-tree or lion acres of noncommercial land, 24 millionwhole-biomass basis. Furthermore, the Forest acres (about 10 percent) are so classified be-Service does not survey noncommercial forest- cause they are recreation or wilderness areas,lands (about one-third of the total forest area). or are being studied for these uses. These landsAs a result of this inadequate information are not included in the inventory of standing




timber. Approximately 205 million acres are

classified as noncommercial because they areconsidered incapable of producing as much as20 ft3 of commercial wood per acre-year. Thiscriterion, is an arbitrary one, however, and

timber is, in fact, harvested from many areasof land in this category. For this reason, the lat-

ter category of noncommercial forestlands isincluded in the inventory of standing timber.

Assuming that these 205 million acres pro-duce an average of 10 ft

3/acre-yr of commer-cial wood, that they are mature stands (80years old or more), and that the abovegroundbiomass is 1.5 times the amount of commercial

timber, the inventory of these noncommerciallands is 3.7 billion dry tons (57 Quads).

In addition, 23 million acres, mostly inAlaska, were classified in 1978 as noncommer-cial because they were considered inaccessi-

ble. Assuming a production capability of 35ft3/acre-yr and the same assumptions as above,the inventory from these lands is 1.4 billion drytons (22 Quads).

These two categories result in an inventoryon 1978 noncommercial lands of about 5 bil-lion dry tons (80 Quads).

Commercial Forestland

Approximately 488 million acres of forest-land are classified by the Forest Service as

commercial forestland for purposes of report-ing a national forest survey. It is possible toestimate a fuel inventory from commercial for-estland, using national forest survey data, withmuch more precision than was the case fornoncommercial lands.

Two options were considered for developingestimates of total biomass on commercial for-estland based on the national forest survey.One procedure involved the assumption ofmultipliers that would convert the basic prod-uct inventory data to whole-stem biomass esti-

mates. A second method involved the use ofstand tables from the national forest survey

and allometric regression equations for esti-mating biomass for various tree components. 4

“llethel, op clt

For the purposes of this study, an estimate

of total whole-stem biomass for the UnitedStates was developed, based on Forest Statis-

tics for the United Sta tes, 1977.5 Table 5 showsthe result of this analysis for commercial for-estland. The details of these computations andmore extensive tables are given in OTA’s

tractor report “Energy From Wood. ”16

Table 5.-Estimated Above-ground StandingBiomass of Timber in U.S. Commercial Forestland

(excluding foliage and stumps, in billion dry tonsa)

con-

Region Hardwood Softwood Total

N o r t h . 5.2 1,3 6.5South . . . : : : : : ., 4.6 2,3 6.9R o c k y M o u n ta i n s . , 0.2 2 4 2.6Pacific Coast, ., 06 4 2 4 8Alaska, ., ., 0.08 1,3 1 4

Total ., . . 10.6 11 5 221

asum~ may noI agree due to round off errors

SOURCE J S Bethel, et al Energy From Wood College of Forest Resources Umverslty ofWashmgfon Seaftle contractor reporl to OTA April 1979

Adding commercial and noncommercialland inventories gives 27 billion tons (430Quads), which is estimated to be the inventoryof biomass in U.S. forests, excluding stumps,foliage, and roots and the biomass in parks and

wilderness areas, or areas being consideredfor these uses. *

Quantity Suitable for

Stand ImprovementOf the 27 billion tons of standing biomass,

some of the wood is of the type that would beremoved in stand improvements. This wouldinclude brush, rough, rotten, salvageable dead

wood, and Iow-quality hardwood stands occu-pying former conifer sites. In Alaska, there areroughly 330 miIIion tons of this type of wood.

7

In the rest of the Pacific Coast region, there are565 million tons, and in the Rocky Mountainregion, 324 million tons. The North and Southhave 822 million and 978 million tons, respec-

1‘Forest Statfstlcs of the U S . J 977, USDA Iorest Service, re-

view draft‘013ethel, Of) clt* For the purpose> of this report, ~turnps, root$, and follage are

exc I uded from who le-~tenl b Iom as~

‘‘1 bld



16 q VOI. Il—Energy From Biological processes

tively. 18 The total is 3.1 billion tons (49 Quads) or all of the cuttings that could be used to con-

of wood that would be appropriate for remov- vert stands of one kind of trees to a more pro-

al in stand improvements on commercial for- ductive type. Consequently, this is a conserva-

estlands. This figure does not include foliage tive estimate of the biomass available from

‘“lbd stand improvements.

Present and Potential Growth of Biomass in U.S. Commercial Forests

Current gross annual biomass growth incommercial U.S. forests has been estimatedfrom Forest Service data to be 570 million dryton/yr, of which 120 million ton/yr are mortali-

ty, and 450 million ton/yr net growth. * The

usual method of determining the productivityof a particular stand occupying a site is by ref-erence to normal yield tables. These tables aremodels used to predict growth of active nat-ural stands, and are based on stands of “full”

or “normal “ stock.Because of the utilization assumptions built

into normal yield tables, however, productivity

may consistently be assigned a low, and mis-leading rating. For example, when the actualgrowth in 131 Douglas-fir plots scatteredthroughout western Washington and Oregonwas compared with Forest Service BuIIetin nor-mal yield tables for Douglas fir, it was foundthat the yield tables consistently underesti-mated the actual growth. Actual growth insome age-site combinations was more thandouble the normal yield table value, and the

overall average growth exceeded the yieldtable by nearly 40 percent.20 Furthermore, inparts of the Rocky Mountains where ForestService and industry lands are co-mingled, in-dustry representatives report that measure-ments of actual growth are two to three times

the productivity assigned by normal yieldtables” Because of the errors associated withestimating tree types, their number, and theirsize from normal yield tables, OTA estimates

‘“H Wahlgren an d T EIIIs, “Potential Resource Avallablltty

With Whole Tree Uttllzatlon, ” TAPPI, VOI 61, No 11, 1978

q The 120 million tons of annual mortallty are from growingstock trees only Mortallty from nongrowtng stock trees IS no t

known Under Intensive management, much of the mortality loss

cou Id potentla I Iy be captured for product Ive use“)Bethel , Or) Clt

J ‘ I bld

that the actual current biomass growth oncommercial forestland is one to two times thevalues derived from normal yield tables, or 570million to 1,140 million dry ton/yr (9 to 18Quads/y r). (See figure 3.)

These estimates do not take into account

the productive potential of the forestland. For-est site productivity is estimated on the basisof the vegetation currently occupying the areaat the time of the survey. But over 20 million

acres of commercial forestland are unstocked,and much more land is stocked with speciesthat are growing more slowly than could beachieved with species better suited to the site.The forest survey indicates that, due to thesefactors, current growth is about half thegrowth that could be achieved with full stock-ing of highly productive tree types (i. e., currentgrowth is estimated by the Forest Service at 38ft 3/acre-yr while the land capability is esti-mated by USDA at 74 ft3/acre-yr). OTA there-fore estimates the potential growth to be

about two to four times that derived from nor-mal yield tables, or 1.1 billion to 2.3 billion dryton/yr (18 to 36 Quads/yr) with full stocking ofproductive tree species on commercial forest-Iand. This corresponds to slightly more than 2to 4 ton/acre-yr on the average.

Beyond the potential growth with unfertil-ized timber, studies in the Southeast indicate

that fertilizers and genetic hybrids could in-crease the ‘biomass growth by 30 percent.

22

However, not all of the potential growth isphysically accessible or economically attrac-

tive as discussed below.




Figure 3.—Forest Biomass Inventory, Growth, and Use (billion dry tons with equivalent values in Quads)

land/

trees

4 b i l l i o n d ry to n s / —

64 Quads /

/ ’

O 01 billion dry tons

I mortalitybillion dry tons \

0.45-0.90 billion dry tons

Commercial 7.0-14.0 Quads

f o r e s t l a n d

I n d u s t r i a l

w o o d c u t t i n g

/

/

SOURCE Off ice of Technology Assessment



18 q VOI. II—Energy From Biological Processes

Forest Biomass Harvesting

Variations on the current harvesting tech-niques (described below) are likely to be com-mon with fuelwood harvests and stand im-provement activities that produce residuessuitable for fuel. Nevertheless development of

new techniques and equipment designed forfuelwood harvests and stand improvements

could lower the cost.

Intensive forest management might typical-ly consist of the following: The stand would be

clearcut, and the slash (or logging residue) re-moved. The stand would then be replantedwith the desired trees. After 5 to 20 years thestand would be thinned so as to provide morespace for the remaining trees. The stand wouldthen continue to be thinned at about 10-yearintervals, by removing diseased, rough, rotten,

and otherwise undesirable trees and brush. Invery intensively managed stands, the treesmight also be pruned to avoid the formation oflarge knots in the stem of the tree (e.g., forveneer). These periodic thinnings and (possi-

ble) prunings would continue until the stand isagain clearcut and the entire cycle repeated.

For each operation mentioned above (exceptthe replanting), some woodchips suitable forenergy could be made available. The methodchosen for harvesting the fuelwood would de-pend on a number of site-specific factors. The

primary objective would be to fell and trans-port the selected trees or to transport the slashin the most cost-effective manner, while doing

a minimum of damage to the remaining stand.

Currently there are four basic methods oflogging, each of which is designed to accom-modate a number of physical and economicfactors peculiar to the logging site. Once thetree is felled: 1 ) it can be skidded (dragged) to aroadside as a who/e tree, 2) it can be delimbedand the top cut off, and the entire stem or treelength skidded to the roadside, 3) it can be de-

Iimbed, topped, and cut (bucked) into longlogs which are skidded, or 4) it can be cut intoshorter logs or short wood which are skidded.The whole-tree skidding brings out the most

biomass. However, if the limbs cannot be used

they represent a disposal problem. Also thewhole-tree and tree length methods tend to domore damage to the timber being skidded andto the residual stand. If there is thick under-brush, the who/e-tree method may be difficult

or impossible. A weighing of the various fac-

tors appropriate to the site being logged resultsin the method used. If markets for the limbsdevelop, however, then more who/e-tree skid-ding may be used than is now the case.

Once the wood is at the roadside, it can becut and loaded or loaded directly into trucksfor transport to the mill or conversion site.Alternatively, the wood can be chipped at theroadside with the chips being blown into a vanfor transport.

Two large-scale harvesting systems consid-ered here are whole-tree harvesting and cablelogging. In the whole-tree chip system, thetrees are felled by a vehicle called a feller-buncher, which grabs the tree and uses a hy-draulic shear to cut the tree at its base. Thetree is then lowered to the ground for skidding.This method is most appropriate for relativelyflat land and smaller trees (i.e., less than 20-inch diameter).

In the cable logging method, cables are ex-

tended from a central tower and the felledtrees are dragged to a central point, where they

are sorted and skidded to the roadside. Thismethod is used primarily on terrain with steep

slopes and large trees. Estimates for the equip-ment and annual operating costs of these two

systems are shown in tables 6 to 9. There areother logging systems, but these two methodsare fairly representative of the range of exist-ing systems.

The major difference between the harvest-ing of various categories of wood (e. g., resi-dues from logging, stand improvements, or pri-mary logging) is the quantity of wood that can

be removed from a site per unit of time, i.e.,the logging productivity. Several factors affectthe logging productivity, and the most impor-tant of these are shown in table 10. The pro-duction of the logging operations discussed




above might range from 15,000 to 75,000 greenton/yr, leading to harvesting costs from about$5 to $30/green ton. In addition, transporta-tion, possible roadbuilding, and stumpage fees(fees paid to the landowner for the right to har-vest the wood) must be included. Transporta-tion ranges from $0.06 to $0.20/ton-mile, and

where road building is necessary, the costs willbe considerably higher. Stumpage fees forfuelwood have been estimated at $0.40 to$1 .00/green ton in New England, *J but thesewill change with the market.

The costs of whole-tree chipping 33 stands innorthern Wisconsin and the Michigan penin-sula have been modeled by computer simula-tion.

24In each case, the center of the country

was assumed to be the destination for thewood. The supply curve for these stands isshown in figure 4, exclusive of stumpage fees.

The cost average varies from $6 to $1 5/greenton ($1 2 to $30/dry ton) in 1978 dollars. Therange of delivered costs included relogging oflogging residues ($16.50 to $20.30/green ton),

thinning ($10.00 to $1 3.80/green ton), and inte-grated logging for lumber and residue chipping

($9.75 to $12.30/green ton). An equalizing fac-

tor in the delivered cost is the stumpage fee.

I K Hewett, school of Forestry, Ya Ie Unlversltv, Private com-

munication14j A Mattson, D P Bradley, and E M Carpenter,

“Harvesting Forest Residues for E r-serrgy,” Proceedings of the Sec-

ond Annual Fue/s From B/orna s$ S yrnposiurn (Troy, N Y Rensse-

laer Polytechnic Institute, June 20-22, 1978)

Table 6.–Assumptions for Whole-TreeHarvesting Equipment

Initial Salvagecost value Life Labora

Equipment (do l lars) (percent) years $/hour

Whole-tree chipper380 hp . . . . . . . . . . . . $115,000600 hp . . . . . . . . . . . 132,000

Feller-buncher . . . . . . 100,000Skidder (each) . . . . . . . 55,000Used skidder . . . . . . . . . 10,000Lowboy trailer. . . . . . . . . 10,000Used crawler . . . . . . . . 30,000Equipment moving

truck . . . . . . . . . . . . . 1,680/yr3 /4-ton crew cab pickup . . 8,400/yr1 / 2 .ton pickup . 7,862/yrChain saws (3) . . . . . . . . 3,024/yrOther labor

deck hands (2) . . . . .foreman ... ... . . .supervisor . . . . .

20 5 $4.62 20 5 4.62 20 5 4.62 20 4 4.20 10 3 10 1020 5

7.20 8.40 2.81

aSouth, includes payroll benefits

SOURCE J S Bethel et al , Energy From Wood College of Forest Resources Umverslty of

Washington, Seattle, contractor report to OTA April 1979

Where logging, transportation, and other costsare low, stumpage fees will be high and viceversa. The market will determine these fees, aswell as the quantity and types of wood that

can be economically harvested.

The 1979 delivered cost of fuel chips wasabout $12 to $18/green ton in New England. 25 Adetailed national cost curve, however, wouldrequire a survey of all potential logging sites,

1’Connectl~ ut Valley Chipping, P l y m o u t h , N H , L W

Hawhensen, president, letter to Conservation Consultants of

New Eng[dnci, Dec 20, 1979

Table 7.–Annual Whole-Tree Chipping System Costs

Annual costs to pay all expenses and earn 15% aftertax ROI, shown in thousands of dollars (values in columns are shown only when a change occurs).

Annual Fuel, Local taxes MiscellaneousRegion capital cost Maintenance lube, etc. and insurance Labora

equipmentb Total

System based on 380-hp chipperInitial investment: $375,000

North. ., . . . . $221 $35 $44 $7 $ 8 3 $21 $442S o u t h 221 — — — 62 — 390West ... . . . . . . . 221 — — — 104 — 432

System based on 600-hp chipperInitial investment $447,000

North. . . . . . . . 264 40 50 9 94 21 478South . . . . . . . ., . 264 — — — 70 — 454

West ., ... . . . 264 — — — 118 — 502

alncludes foreman and superwsorbplckup trucks chamsaws elc

SOURCE J S Bethel et al Energy From Wood College of Forest Resources Unwersl!y of Washington Seattle contractor report to OTA April 1979



20 . VoI. II-Energy From Biological Processes

Table 8.–Assumptions for Cable Yarding Equipment which is not available. Nevertheless, somefuelwood can be had for as little as $10/green

Initial Salvagecost value Life Labora ton ($20/dry ton) plus stumpage fees.26 In un-

foreman . . ... ...supervisor (1/3 time).

20 0

20 20 20 20 101020

84

55463

105

10.29 —

7.767.767.06

10,64

47,84

(5 men)14, 11

4.72

Equipment ( do ll ar s) ( pe rc en t) y ea rs $/hour f a v o r a b l e c i r c u m s t a n c e s , t h e w o o d c o u l d c o s t

Yarder wi th 50-f t tower $180,000 20 8 $10.29 as much as $30/green ton ($60/dry ton for relog-Yarder with 90-ft tower 228,000Radio and accessories . . . 11,386Whole-tree chipper

380 hp . . . . . . . . . 115,000600 hp . ., ., . . . 132,000

Skidder (each) . . . ., 55,000Hydraulic loader . . . . 207,000Used sk idde r . .. . . . 10,000L ow bo y t ra i l er , . , . , 10,000Used c raw le r . , . , . , 30,000Equipment moving

truck ., ., . . . . . . . 1,680/yr3/4-ton crew cab pickup 8,400/Yr

7,862/yr1/2-ton pickup

Chain saws (3) . . . . . 3,024/yrOther labor

yard ing crew. . . .

ging of logging-residues in the Northwest).

27

Thus, fuelwood chips may vary in price from

about $20 to $60/dry ton which is in substantialagreement with the cost estimates based onharvesting costs.

In each category of wood there will be small

businesses or individuals who are willing towork at lower rates, who are figuring onlymarginal costs, and/or who own the land andassign a zero stumpage fee. In other words,there will always be limited supplies of woodbelow the average market price.

‘(’C Hewett, The A va l / ab i / l t y of LVood for a 50 MW Wood F/red

Power P/ant In Northern Vermont, report to Vermont State Fn-

erg~ Off Ice under grant No 01-6-01659‘i IK ,P Hewlett, ‘~eorgla Paclf IC Corp , At Ianta, (;a , Prlvat@awest, includes payroll benehts

SOURCE Off Ice of Technology Assessmentcommun lca t ion, 1979

Table 9.-Cable Logging System Costs

Annual requirement to pay all expenses and earn 15% aftertax ROI (thousands of dollars)

Annual Localcapital Fuel, taxes and Miscellaneous

Equipment cost Maintenance lube, etc. insurance Labora

equipment Total50-ft tower/ 380-hp chipper

investment: $466,000 ., . . . . $200 $43 $44 $ 9 $158 $21 $47590-ft tower/600-hp chipper

$531,000 . . . . . . . . . . . . 228 61 47 11 158 21 526

alnlcudes foreman and SupervisorbplCkup trucks chamsaws e[c

SOURCE Olflce of Technology Assessment




Table 10.–Factors Affecting Logging Productivity

Road space.Slope and slope changes-slope steepness and whether logging is uphill

or downhill.Size and shape of landing.Skidding distances–both loaded and return if different, affected by the

tract shape and its relation to the road systemSkid trail preparation.

Timber character–Species–Especially hardwood v. softwood.Volume and number of trees per acre to be removed–The size of trees

and logs IS a very Important consideration.Quality– More defective timber IS likely to result in more breakage, in-

creasing materials handling problemsResidual stand, if any, m terms of number of trees and volume per

acre This IS prescribed by the silvicultural method.Cutting policy–appropriate for the standFelling and logging methods–whole tree, shortwood, tree length, etc.Brush height and density.Condition and number of windfalls,Drainage and stream crossings.Season.Crew size and aggressiveness.Wage plan.

old stumps, and slash per acre.

Figure 4.—Supply Curve for Forest Chip Residuesfor Northern Wisconsin and Upper Michigan

20

15

10

5

1 I I I I I5 10 15 20 25 30

SOURCE:

Cumulat ive vo lume—mi l l ions of tons

J. A. Mattson, D. P Bradley, and E M. Carpenter, “Harvesting ForestRestdues for Energy, ” Proceedings of the Second Annual 13!omass

Sympos/um ( T r o y , N . Y . : R e n s s e l a e r P o l y t e c h n i c I n s t i t u t e ) ,

June 20-22, 1978.

Equipment types, functions, and balance–especially the number of

places handled per cycle,Maintenance policy.Environmental regulations–may prescribe certain practices or preclude

certain equipment from areas with sensitive mixes of soils, slopes,and/or drainage thereby reducing production or Increasing costs Inthe West these regulations have caused a shift in the mix of tractor v.cable Iogging as well as shifts within each of these general categories

SOURCE J S Bethel et al Energy From Wood College of Fores! Resources Un[verslty of

Wasmngton Seatlle conlracfor report 10 OTA April 1979

Factors Affecting Wood Availability

The presence of nearby roads, the concen-

tration of wood on the logging site, and the ter-rain (steepness of the slope) are the most im-

portant physical factors affecting the econom-ics, and thus the availability, of harvestedwood, Nevertheless, landownership, alternateuses for the land, taxation, and some sub-sidiary benefits and constraints also play animportant role in wood availability. Theseother factors are discussed below.

Landownership

One of the more important features distin-guishing the various forest regions in the coun-try is landownership. In New England 2 percentof the commercial forestland is federallyowned, and public ownership accounts for

only 6 percent. In the East as a whole, 14 per-

cent of the commercial forestland is publicly

owned, while 7 percent is federally owned.Ownership patterns in the West are reversed,with 68 percent of the commercial forestlandbeing publicly owned (96 percent in Arizona)and 58 percent in Federal ownership.

Although patterns in the West permit log-ging firms to deal with a limited number oflarge landowners, other restrictions may be

placed on the logging operations. One exam-ple is the Federal requirement that loggingresidues be removed from or otherwise dis-

posed of on national forests in the West, tomin imize the risks of forest fires.

Logging firms in the East must deal with alarger number of landowners, and in the North-



22 . VOI. II-Energy From Biological Processes

east, forestlands are often owned for recrea-tional or investment purposes. It may be dif-ficult to determine who owns the land, to con-

tact the owner, or to interest the owner in usingthe land for logging. In the South this is less ofa problem. Large areas of forestland owned byrelatively small landowners are managed by

the forest products industry and are availablefor logging.

Alternate Uses for the Land

The fact that a tract of land is forested anddesignated commercial does not necessarilymean that it can be logged. The owner mayhave esthetic objections to logging, may usethe land for recreational purposes, or, in thecase of an investor, may feel that it would bemore difficult to sell the land after logging. in

New Hampshire and Vermont, for example, arecent study concluded that only 6 percent ofthe owners of commercial forestland consid-ered timber production as a reason for owningforestland, and only 1.3 percent listed it as themost important reason. 28 (This 6 percent owns21 percent of the commercial forestland in thetwo States). Nevertheless, 10 percent of theprivate owners (representing 53 percent of theforestland) intended to harvest their timber

within 10 years and over one-third of theowners (representing 87 percent of the land) in-tended to harvest “some day. ” About half of

the landowners (owning 9 percent of the land)indicated that they would not harvest the land

because of its scenic value or because theirtracts were too small.

Public Opinion

While proper management of a forest can

improve the health and vitality of the trees, im-proper management can have severe environ-mental consequences. (See “EnvironmentalImpacts”. ) In any event, an intensively man-aged forest will look like it is being managed.

IJN p Klng+y and T W Birch, “The Forest-Land Owners of

New Hampshire and Vermont, ” USDA Forest Service Resource

Bulletln NE-51, 1977

There will be fewer overmature trees, the trees

will be more uniform in appearance and spac-ing, and the forest floor will have less debrisand “extraneous” vegetation. The managedforest will not look like a natural forest, andthe difference in appearance can be quitelarge.

This change in appearance, together withvarious environmental uncertainties (see “En-vironmental Impacts”), leads to widely varying

opinions about the benefits of forest manage-ment. If the citizenry affected by increasedmanagement cannot effectively participate in

the process of deciding where and how inten-sively the forests will be managed, and if busi-ness and Government officials are not sensi-tive to the concerns of the citizenry, then thepolitical atmosphere surrounding forest man-agement for energy could become polarized.

Public opposition could then seriously restrictthe use of forests for energy.

Forest management, however, is not an ab-solute. There are many ways to manage forest-Iands, from wood plantations to the occasion-al gathering of fallen trees and branches. Theability of political leaders to convey this factto the public, and the ability of Government toaid in striking an equitable balance betweenenvironmental and esthetic concerns and theeconomics of wood harvesting, may prove tobe one of the most significant factors affecting

an increased availability of wood for energyoutside of the forest products industry.

Alternate Uses for Wood

Much of the wood that will be used for en-ergy in the near future is less suitable for ma-terials (e. g., particle board or paper) than thewood currently used for these products. Ifthere is a strong demand for wood products,however, some of this lower quality wood willbe drawn into the materials market. Similarly,technical advances in wood chemistry maycreate an additional demand for wood to be

processed into chemicals.

It must be remembered that a strong wood

energy market would provide an incentive to




increase the number of stand improvements.This will result in an increased supply of whatis considered commercial-grade timber. Fur-

thermore, some stands that cannot now be har-vested economically for only lumber or pulp-wood will become economically attractive fora combined harvest of lumber, pulpwood, and

wood chips for energy.

In the very long term, competition for woodmay develop between the energy and materi-

als/chemicals markets. For the next 20 years,however, a wood energy market–properlymanaged—will increase the supply of woodfor other uses over what would occur in itsabsence, and indeed this situation is likely toprevail for at least 50 to 60 years.

Other Factors and Constraints

As noted previously, the Forest Service re-

quires that logging residues on national forests

be disposed of to minimize the risks of forestfires. Stumpage fees for logging national for-

estlands are therefore lower than for compara-ble private lands in the region, in order tocover the cost of disposing of the residues. Inthe early 1970’s, as a result of a strong demandfor paper, some of these residues were col-

lected and chipped for paper pulp. Currently,however, the residues (about 0.2 Quad/yr) aredisposed of onsite by burning and other tech-

niques. If a strong energy market existed, muchof this could be chipped and used for energy.

It has been common practice in site prepara-tion to use herbicides to kill unwanted plantsso that preferred trees could regenerate eithernaturally or artificially. Increasingly, however,the use of herbicides for this purpose is beingrestricted and in some cases banned (e. g., 2, 4,5-T). A strong energy market would provide an

additional incentive to harvest the brush andother low-quality wood and thereby minimizethe use of these controversial chemicals.

Net Resource Potential

There is no simple way to assess accurately

the impacts of the various and sometimes con-

tradictory factors affecting the availability ofwood for energy. Many of the important fac-tors, such as public opinion, the way the for-

ests are managed, and the presence of roads,will depend on actions taken in the future. As-suming, however, that 40 percent of the growthpotential of the U.S. commercial forestland iseventually accessible, 450 million to 900 mil-lion dry ton/yr (7.3 to 14.6 Quads/yr) could be

available for harvest.

In terms of energy, the forest products in-dustry currently cuts 5.1 Quads/yr of wood, in-cluding logging residues (1.3 Quads/yr) andstand improvement cutting (0.7 Quad/y r). Ofthis total, 1.7 Quads/yr are converted intoproducts sold by primary or secondary manu-

facturers, and 1.2 Quads/yr, supplied by woodwastes, satisfies over 45 percent of the in-

dustries direct energy needs. This leaves about2.2 Quads/yr of wood that are currently being

cut but not used (see figure 5), and there is atleast 40 Quads (total) of unmerchantable

standing timber.

Assuming that the demand for traditionalforest products doubles by 2000, then 3.4

Quads/yr will be needed for finished woodproducts, and 3.9 to 11.2 Quads/yr could beused for energy, provided increased forestmanagement occurs. If, however, the forestproducts industry becomes energy self-suffi-

cient by 2000, it could require as much energyas the lower limit of available wood energy,but three factors will probably alter this simpleprojection. First, the increased demand forwood products is likely to increase the numberof stand improvements. Second, the energy ef-ficiency of the forest products industry willprobably increase as a result of higher energy

prices and new processes (such as anthraqui-none catalyzed paper pulping). Third, if theforest products industry requires most of the

available output of 40 percent of the commer-



24 . Vol. Il—Energy From Biological Processes

cial forestlands to supply its needs, then addi- These estimates are admittedly approxi-tional roads would be built to access more tim- mate, but a more precise estimate would re-berland. Additional wood that is not of high quire a survey of potential logging sites, landenough quality for lumber, veneer, paper pulp, capability, road availability, and the costs ofetc., would therefore become available. In harvesting.light of these factors, it is likely that significantquantities of wood will become available for The results of such a survey could change

energy uses outside of the forest products in- these estimates, but 5 to 10 Quads/yr is OTA’sdustry, but this industry could be the major best estimate of the energy potential from ex-user isting commercial forestland

Figure 5.—Materials Flow Diagram for Felled TimberDuring Late 1970’s (Quads/yr)

F e l l e d t i m b e r

F o r e s t p r o d u c t s

i n d u s t r y h a r v e s t

3.1

R e tu r n e d t o s o i l

b y b a c te r i a l

d e c o m p o s i t i o n o r

b u r n e d i n f o r e s t

2 .0

P u l p w o o d h a r v e s t s

Primary and

secondarymanufacturing 0.7 Paper and pulp

, Residues of primarya n d s e c o n d a r y

m a n u f a c t u r i n g

Total left in forest 2.0 Quads/yr

Total used as energy 1.5 Quads/yr

U n u s e d r e s i d u e s 0 .1 4 Qu a d / y r

T o t a l p r o d u c t s 1 .7 Qu a d s / y r

SOURCE Off ice of Technology Assessment



Ch. 2—Forestry . 2 5

Environmental Impacts

Introduction

A forest may be perceived as:

q

q

q

q

q

q

q

q

q

a natural ecosystem deserving protection;a source of materials — renewable or oth-erwise;

a physical buffer to protect adjacentareas from erosion, flood, pollution, etc.;a source of esthetic beauty;a wiIdlife preserve;a source of recreation — hiking, hunting,etc.;a temporary land use;a place to retreat from civiIization; or

an obstacle to another desired land usesuch as mining or agriculture.

This range of perceptions is complicated by

the fact that individuals do not perceive allforests to be alike, and few would attach thesame perspective—or value— to all forests.Thus, the keenest environmentalist may com-fortably accept a managed, single-aged pineforest in the same terms as he accepts a wheat-field, while a lumber company president mayview a preserve of giant Sequoias with as much

reverence as a Sierra Club conservationist.

These perceptual differences make an eval-

uation of the environmental effects of a wood-for-energy strategy difficult, because many of

the effects may be valued by some groups aspositive and by others as negative. In otherwords, although some potential effects of

growing and harvesting operations (e.g., ef-fects such as impaired future forest productivi-

ty or extensive soil erosion) are clearly nega-tive or (in the case of restoration of landsdamaged by mining) positive, other effects aremore ambiguous. Changes in such forest char-acteristics as wildlife mix, physical appear-ance, accessibility to hikers, and water storagecapabilities may be viewed as detrimental orbeneficial depending on one’s objectives or

esthetic sense. For instance, measures that in-crease forest productivity by substituting soft-wood for hardwood production would be con-

sidered as strongly beneficial by those whovalue the forest mainly for its product output,

but may be perceived as detrimental by thosewho cherish the same forest in its originalstate. Hence, it is likely that a wood-for-energystrategy that increases the areal extent or in-tensity of forestry management will promote a

wide range of reactions . . . even if the physical impacts are fully predictable and if forecasts of

these physical changes are believed by all par-

ties.

Environmental evaluation is further compli-cated both by difficulties in predicting thephysical impacts and by the strong possibilitythat even those predictions that c an be accu-rately made will not be accepted as credibleby all major interest groups.

The problem of credibility stems largely

from the history of logging activities in the

United States and the negative impact it hashad on public perceptions of logging. Theadaptation of the steam engine to loggingaround 1870 began an era (lasting into the 20thcentury) when America’s forest resource wasmined and devastated .29 The dependence of

logging on the railroads and on cumbersomesteam engines— capital-intensive equipment

that could not easily be moved from site tosite–led to the cutting of vast contiguousareas. There was virtualIy no attention to refor-estation. In fact, it was then thought that most

of this land would be used for agriculture, andthat clearcutting enhanced the value of theland. It also was thought that the timber re-source was essentially unlimited and that itwas unnecessary to worry about regeneration.

Massive cutting followed by repeated firesled to the destruction of tens of millions ofacres of hardwood (in the South and East) andsoftwood (in the Lake States, Rockies, and partof the Northwest) forest and their replacementby far less valuable tree types or by grassland.This massive destruction led to a considerablepublic revulsion towards logging, much of

which still survives. It also led to a revulsion

29M Smith, “Appendix L, Maintaining Timber Supply in a

Sound Environment” In Report of th e Presidents Advisory Pane/orI Tmber and the .Environment (Washington, D C Forest Serv-

ice, U S Department of Agriculture, 1973)

67-968 0 - 80 - 3



26 . Vol. II-Energy From Biological Processes

against clearcutting and even-aged manage-ment within the forestry profession whichlasted for 20 years; 30 although clearcutting (at

least the very limited version used today,

which involves very much smaller areas thanwere routinely cut in the past) is now an ac-cepted and even popular practice in the pro-

fession, the attitudes formed by attempts atpublic education about forest values in the1930’s and 1940’s linger on. Furthermore, therehave been enough reports of unsound forestmanagement and widely publicized environ-mental fights over such management in the in-

tervening decades to create a sizable constitu-ency that is generally very skeptical about log-ging practices. As a result, assessments thatfocus on the potential positive effects of in-creased forest management may be greetedwith skepticism by large segments of the pub-lic.

The prediction of environmental changes

that might occur in American forest areas if de-mand for wood energy grows is extremely diffi-cult. The potential for wood energy identifiedpreviously is based on a “scenario”-a visionof a possible future—that assumes an in-creased collection of wood residues that arenow left to rot in the forest as well as an as-sumed intensification of silvicultural manage-ment on suitable land that would increasegrowth rates and timber quality, increasing the

supply of nonenergy wood products while pro-

viding a steady supply of wood fuel. This typeof strategy could lessen harvesting pressureson wilderness areas and other vulnerable for-estlands. It probably would be perceived bymany groups as environmentally beneficial, al-though it would lead to esthetic and ecosys-tem changes on those lands where manage-ment was intensified. Given the present institu-

tional arrangements, however, there is no guar-antee that this assumed “scenario” will unfoldas outlined. Instead, a combination of Federal,State, business, and other private interests willrespond to a complex market amid a variety of

institutional constraints. In order to predict theenvironmental outcome of such a response,the following factors must be understood:

‘“I bid

1.

2

3

The environmental effects that occurwhen different kinds of silvicultural oper-ations (including different kinds and in-

tensities of cuts, regeneration practices,roadbuilding methods, basic managementpractices, etc.) are practiced on differentforest types and land conditions.

The kinds and amounts of Iand likely tobe harvested and their physical-environ-mental condition.The types of practices, controls, etc., like-ly to be adopted by those harvesting thisland.

There is an extensive literature describingfactor #1. However, the range of forest ecosys-

tems and possible silvicultural practices is fargreater than the range of existing research, andthere are as well substantial gaps in the knowl-edge of some important cause-effect relation-

ships such as the effect of whole-tree removaland short rotations on nutrient cycling, or,more generally, the ecosystem response tophysical pollutants such as sediments and pes-

ticides.

Identification and characterization of theland base most likely to be affected by in-creased wood demand (#2) are complicated bya lack of good land resource data, the lack ofinformation on the precise nature of the futurewood market, and the complexity of incentives

that affect the decisionmaking of small wood-

land owners.Predicting the types of practices and envi-

ronmental controls likely to be adopted (#3) is

difficult because State and local regulatorycontrols generally do not specify or effectivelyenforce “best management practices. ” Thus,existing regulations cannot be used as a guide

to actual practices. Also, although knowledgeabout the present environmental performance

of the forest industry might provide a startingpoint for gaining an understanding of what toexpect in the future (because most wood-for-energy operations are more intensive exten-

sions of conventional forestry), it is surprising-ly difficult to produce a clear picture of howwell the forestry industry is performing. Withthe exception of a few isolated State surveysand a detailed survey of erosion parameters




(percentage of bare ground, compaction, etc.)in the Southeast,31

there appears to be a severe

lack of surveys or credible assessments of ac-tual forestry operations and their environmen-

tal impacts. As a result, a critical part of thebasis for an adequate environmental assess-ment is unavailable.

Because of these limitations, this discussion

generally is limited to a description of poten-

tial impacts, although a few of the impactsdescribed are inevitable. The economic and

other incentives that influence the behavior ofthose engaging in forestry are examined todetermine how probable some of these im-pacts are. The types of controls and practicesavailable to moderate or eliminate the nega-tive impacts also are described.

As discussed above, wood for energy may be

obtained from several sources. With the

growth of a wood-for-fuel market, the residueof slash from logging may be removed andchipped. Thinning operations may becomemore widespread because the wood obtainedwill have considerable value as fuel. Standconversions— clearing of low-quality trees fol-lowed by controlled regeneration–as well asharvesting of low-quality wood on marginallands may increase, also because of the in-

creased value of the fuelwood gained. Newharvesting practices such as whole-tree remov-al may become more common. Waste woodfrom milling and other wood-processing opera-tions will certainly be more fully utilized.Finally, wood “crops” may be grown on largeenergy farms.

Many of these activities are similar to(though usually more intensive than) conven-tional logging. In addition, other activities as-sociated with using wood as a long-term ener-gy supply — including tree planting, pesticideand fertilizer application, etc. — are similar oreven identical to “ordinary” silvicultural activ-ities. This section, therefore, first discusses thegeneral impacts of silviculture and then de-

scribes any changes or added effects associ-

“C Dlssmeyer and K Stump, “Predicted Erosion Rates forForest Management Actlvltles and Conditions Sampled In the

Southeast,” USDA Forest Service, April 1978

ated with alternative wood-for-energy systems.In each case, the discussion will attempt to

draw a distinction between clearly positive ornegative pollution and land degradation andrestoration impacts and the more ambiguousecosystem and esthetic impacts. Because theenvironmental effects of silviculture are ex-

ceedingly varied and complex and because anumber of good reviews are available, the dis-cussion highlights only the major and mostwidespread impacts. It is stressed that few ifany of the environmental relationships de-scribed in the discussion are applicable to allsituations.

Environmental Effects ofConventional Silviculture

The practice of silviculture can have both

positive and negative effects on the soils,wildlife, water quality, and other components

of both the forest ecosystem and adjacentlands. Table 11 provides a partial list of thepotential environmental effects of convention-al silviculture. The magnitude of these impactsin any situation, however, depends almost en-tirely on management practices and on thephysical characteristics of the site, i.e., type oftrees and other vegetation, age of the forest,soil quality, rainfall, slope, etc. It is also impor-tant to remember that most of the negative im-pacts generally are short term and last only a

few years (or less) over each rotational cycle.Erosion has always been a concern in silvi-

culture, especially in logging operations (andparticularly in road construction). Undisturbedforests generally have extremely small erosionrates — often less than 75 lb of soil per acre per

year32 — and in fact tree planting is often used

to protect erosion-prone land. * Increased ero-sion caused by logging, however, varies fromnegligible (light thinning and favorable condi-

‘zEnvironmenta/ Implications of Trends in Agriculture and $Ilvi-

cu/ ture, Vo /ume 1 Trend Identifica tion and Evac uation (Washing-

ton, D C Environmental ProtectIon Agency, December 1978),E PA-600/3 -77-l 21

*However, from a historical perspective, all land forms go

through natural erosional cycles that produce much htgher rates

of soil loss These rates are often drwen by natural catastrophic

events Including wildfire and storms



28 . Vol. II—Energy From Biological Processes

Table 11.-Potential Environmental Effects ofLogging and Forestry

Water q

q

q

q

q

q

Air .q

q

q

Land q

q

q

q

q

q

q

q

q

increased flow of sediments into surface waters from logging ero-sion (especially from roads and skid trails)clogging of sfreams from logging residueleaching of nutrients into surface and ground waterspotential improvement of water quality and more even flow from for-

estation of depleted or mined landsherbicide-pesticide poll ution from runoff and aerial application (froma small percentage of forested acreage)warming of streams from loss of shading when vegetation adjacentto streams is removed

fugitive dust, primarily from roads and skid trailsemissions from harvesting and transport equipmenteffects on atmospheric CO2 concentrations, especially if forestedland is permanently converted to cropland or other (lower biomass)use or vice-versaairpollution from prescribed burning

compaction of soils from roads and heavy equipment (leading to fol-lowing two impacts)surface erosion of forest soils from roads, skid trails, other disturb-ances

loss of some long-term water storage capacity of forest, increasedflooding potential (or increased water availability downstream) untilrevegetation occurschanges in fire hazard, especially from debrispossible loss of forest to alternative use or to regenerative failurepossible reduction in soil quality/nutrient and organic level fromshort rotations and/or residue removal (inadequately understood)positive effects of reforestation–reduced erosion, increase in waterretention, rehabilitation of strip-mined land, drastically improvedesthetic quality, etc.slumps and landslides from loss of root support or improper roaddesigntemporary degrading of esthetic quality

Ecological q changes in wildlife from transient effect of cutting and changes in

forest typeq temporary degradation of aquatic ecosystems q change in forest type or improved forest from stand conversion

SOURCE Office of Technology Assessment

tions) to hundreds of tons per acre per year(poorly managed clearcuts on steep slopes inhigh rainfall areas) .33

A recent Environmental Protection Agency(EPA) report suggests the loss of 7 or 8 tons ofsediment per acre per year as a mean value forrecently harvested forests, although the varia-

tion around this mean is very large. ” To placethis rate in perspective, the continuous sheet

“ Environmenta l Read iness Docum ent, Wood Commerc ia l iza-

tion, draft (Washington, D.C : Department of Energy, 1979).J4Envlronmenta/ /mp/;ca(/on5 of T rends in Agriculture and SIIVI-

cuhure, vol. 1, op cit

and rill erosion rate on intensively managedagricultural land averages 6.3 ton/acre-yr.

Most forestland is harvested at most once

every several decades and the increased ero-sion generally lasts only a year or two on themajority of the affected acreage. Increased

erosion from poorly constructed roads, how-ever, may last longer.

The processes involved in erosion of forest-Iand are stream cutting, sheet and gully ero-sion, and mass movement of soil. Erosion dan-ger increases sharply with the steepness of thelandscape, and the most common form of thiserosion is mass movement. Mass movement“includes abrupt or violent events such aslandslides, slumps, flows and debris ava-lanches, as well as continuous, almost imper-ceptible creep phenomena."

35Occurrence of

mass movements is most often associated with

steep slope conditions where the forest soil isunderlaid with impermeable rock. 36 Thesemovements are natural processes associatedwith the downwearing of these steep slopes,

but they can be triggered by man’s activities.In contrast, sheet and gully erosion are rare in

undisturbed forests, but they can be triggeredby soil disturbances caused by careless roadconstruction or logging practices.

The major causes of erosion problems inforestry operations are the construction anduse of roads and other activities that may com-

pact or expose soil or concentrate water.

37

Thecompaction caused by the operation of heavymachinery can reduce the porosity and water-holding capacity of the soil, encouraging ero-sion and restricting vegetation that eventuallywould reduce erosion. Roads and skid trailscomprise up to 20 percent of the harvestarea, 38 and the total area that may be com-pacted at a site may range up to 29 percent in

“Earl Stone, “The Impact of Timber Harvest on Soils and

Water, ” Report of the Presiden t’s Advisory Pane l on Timb er and

the Environment (app M, Washington, D C Forest Service, U S

Department of Agriculture, April 1973)

“Environme ntal Imp lica tions of Trends in Agriculture and Si/ vi-cu/ ture, vo/ . 1., op cit

“Stone, op cit

“ Draft 208 Preliminary Non-Point Source Assessment Report

(Augusta, Maine Land Use Regulatory Commission, State of

Maine, 1978




some instances. 39 Although in most areas thethawing and freezing cycle allows compactedsoil to recover in 3 to 10 years, recovery takes

far longer when, as in parts of the Southeast,

this cycle does not occur.40 Also, when com-paction is very severe, recovery may take con-

siderably longer than 10 years; old loggingroads are still visible in the Northeast, evenwith the frost cycle.

The vulnerability of logging roads to erosionis related to topography and soil type as wellas to road design. Roads developed on gentleto moderate slopes in stable topography posefew problems with the exception of carelessmovements of soil during construction. Large

areas of forestland served by such roads drawlittle attention or criticism.

41

The great majority of difficulties and haz-

ards arise, however, when roads are con-structed on steep terrain, cut into erosive soils

or unstable slopes, or encroach on streamchannels. Steep land conditions present adilemma for road development, and criteriafor location, design, and construction that aresatisfactory on even moderate slopes may leadto intolerable levels of disturbance on steeplands. Building a road on a slope involves cut-ting into the slope to provide a level surface.The soil removed from the cut is used as fill ordumped. The steeper the slope, the more soilthat must be disposed of and the more difficult

is the job of stabilizing this soil. In the absenceof proper attention to soil and geology, roaddesign (especially alinement and drainage),and other factors, surface erosion from roadand fill surfaces can continue for years. Road-building on steep slopes may also removeenough support from the higher elevations to

cause mass failures; problems created by theroad cut may be aggravated by inadequatedrainage allowing further cutting away of sup-porting soil.

Aside from roads, the movement of logs

from the harvest site to loading points maypresent considerable erosion potential. “Skid-

“ fnvlronmental Implications of Trends in Agriculture and Silvi-

cu//ure, vo/ 1 , o p clt

‘“lbd“S tone , OP clt

ding” logs may expose the subsoil, or compactthe soil. Exposing the surface is a problemwhen the soil is highly erosive or when waterconcentrates, but is usually not a major ero-sion problem. The deeper disturbances of com-

paction and of cutting into the soil create

more significant erosion problems, especiallywhen they occur parallel to the flow of water.Most surveys of logging have concluded thatthe hauling or skidding of logs “generally doesnot lead to appreciable soil erosion or im-paired stream quality;”

42however, the same

surveys conclude that “exceptions are com-men, ” and logging in vulnerable areas, underwet weather conditions, or with inappropriateequipment are thought to be important prob-lems in the industry.

Erosion caused by the actual cutting of the

trees generally is considered to be relativelyunimportant. Vegetation usually regeneratesquickly and reestablishes a protective cover onthe land, preventing surface erosion except inareas where other components of the loggingoperation have damaged the soil. “Many ob-servations and several studies on experimentalwatersheds demonstrate that sheet and gullyerosion simply do not occur as a result of treecutting alone, even on slopes as steep as 70percent. ”43

However, land that is vulnerable to massmovements may be damaged by tree cutting.

The decay of the old root systems will removecrucial support from a vulnerable slope fasterthan it can be replaced by the root systems ofnew growth; within 4 to 5 years after tree cut-ting (or fire), mass movement potential may in-crease dramatically. Forests in the NorthwestUnited States and coastal Alaska are the mainareas for this type of damage potential .44

The method of clearing for forest regenera-

tion may also affect erosion potential. Inten-sive mechanical preparation of land beforetree planting (i.e., use of rakes, blades, and

other devices to reduce a forest to bare groundto favor reproduction of pine) can cause very

“lbld‘Jlbld“’lbld



30 . VOI. II—Energy From Biological Processes

serious erosion problems. This practice is oc-curring on hilly sites in the South that havebeen depleted by intensive cotton productionin the past; it “may foster a dangerous cycle oftopsoil and nutrient loss and increased sedi-ment loading in streams. ”

45Poorly managed

raking may have adverse effects on forest pro-ductility. ” Area burning can also badly dam-age forest soils if managed improperly or ifused on improper soils. Although suitable forhighly porous, moist soils (where much of thesurface cover is not consumed), poorly man-aged burning may consume most of the coverand leave the soil exposed to surface erosion.(However, area burning is considered to have alesser potential to degrade productivity than

raking.”) Burning may also represent a signifi-cant local source of air pollution. On the otherhand, “controlled” burning may reduce future

fire hazard by reducing slash buildup and mayfavor regeneration on the site of fire-resistanttrees.

The sediment resulting from the erosion de-scribed in this section is “the major cause ofimpaired water quality associated with log-ging.” 48 These sediments are directly responsi-

ble for water turbidity, destruction of streambottom organisms by scouring and suffoca-tion, and the destruction of fish reproductivehabitat. Sediments also carry nutrients fromthe soil. Nutrient pollution is further increasedby increased leaching and runoff as increasedsolar radiation reaches the forest floor andwarms it, microbial activity (which transformsnutrients to soluble forms) accelerates and nu-

trient availability increases (this soil heating ef-fect also has been known to retard regenera-

tion, especially on south-facing slopes, by kill-ing off seedlings). The increased nutrient load-ing of streams may have a variety of effects, in-

cluding accelerated eutrophication and oxy-gen depletion. Fortunately, the increased nutri-

45 Environrrrenta/ Effec ts of Trends, vo/. 2 (Washington, D C En-

vironmental Protection Agency, December 1978), E PA-600/

3-77-121“Stone, op clt“lbld

4“Silviculture Act iv i t i es and Non-Point Pollution Abatement: A

Cost-Effectiveness Ana/ysis Procedure (Washington, D C Forest

Service, US Department of Agriculture, November 1977),E PA-600/8-77-Ol 8

ent loading is usually short-lived, because re-vegetation of the site slows runoff and leach-ing, increases nutrient uptake, and, by shadingand cooling the soil, slows the decompositionof organic material and consequent nutrientrelease.

The effects of nutrient enrichment are ag-gravated by the decomposition of organic mat-

ter from slash that is swept into streams, andby any water temperature increases caused byloss of streambank shading* (the temperatureincreases speed up eutrophication and furtherreduce oxygen content of the water). Tempera-

ture increases may also directly harm somefreshwater ecosystems by affecting feeding

behavior and disease incidence of cold waterfish.

Logging operations affect water supply and

may decrease a watershed’s ability to absorbhigh-intensity storm waters without flooding(although this problem may have been exag-gerated somewhat in the past).

The possibility of increased flooding stemsfrom two causes. First, cutting the forest re-

duces the very substantial removal by trans-piration of water from underground storage.

During the period before substantial revegeta-tion has taken place, the amount of this long-term “retention storage” capacity available toabsorb floodwaters will be lessened and peakstream flows may rise. For example, increasesin peak flows of 9 to 21 percent in the East and30 percent in Oregon following clearcuttinghave been reported. These increases are usual-ly observed only during or right after the grow-ing season, where continual drawdown of stor-age would be occurring had the trees not beencut (floods occurring during the winter, as inthe Northwest, may be unaffected or less af-fected because drawdown would not normallybe occurring). This decrease in storage capaci-ty apparently is not significant unless at least20 percent of the canopy is removed.49 Second,

*The extent of any Increases depends on stream volume,

degree of removal of understory vegetation, and several other

factors In many cases, no significant effects occur

“An Assessment of the Forest and Range Land Situation in the

United States (Washington, D C Forest Service, U S Depart-

ment of Agriculture, 1979), review draft



Ch. 2—Forestry q 3 1

damage to forest soil increases runoff and in-

hibits the action of even the temporary “deten-

tion storage” potential wherein water is tem-

porarily stored in pores in the upper soil layers

and can be delayed from reaching streams foranywhere from several minutes to severaldays. Although treecutting, even clearcutting,

is not likely to affect this temporary storagecapacity, compaction of the soil by roadbuild-ing, log skidding, and operation of heavy ma-

chinery may reduce the infiltration of waterinto the soil if the compaction occurs over a

wide area50

and thus drastically reduce stor-age. Area burning on coarse-textured soils cancreate a water-repellant layer that would alsodecrease this infiltration and thus reduce thesoils’ capacity for detention storage. 51

The reduction of transpiration that is caused

by timber harvest may be beneficial by in-

creasing stream flow and groundwater suppliesin water short areas. Also, carefully structured

cuts can be used to trap and maintain snowaccumulation, greatly reducing evaporationlosses, It is claimed that by using such tech-niques, water yield from commercial forest-Iand in the West could be increased, supplyingmillions of additional acre feet at a cost of afew dollars per acre foot. 52

Large-scale forestry operations often dras-

tically alter local ecosystems, even for the longterm. Wetlands in the South are being drained

and pine forests are being created with the aidof substantial applications of phosphate fertil-izers. In the process, aquatic ecosystems arebeing replaced by terrestrial ones and somecritical wildlife habitats, especially for water-fowl, are being destroyed.

53In the Pacific

Northwest, old stands of Douglas fir are beingreplaced by single-aged plantings of the samespecies. EIsewhere, mixed hardwood forestsare being replaced by plantations of conifers.In many cases, however, the ecosystems beingreplaced are themselves the result of past log-

“’Stone, op clt“R M Rice, et al , “Erosional Consequences of Timber Har-

vesting An Appraisal, ” Wate r s hed jr-i Trarrs/t/on, (Urbana, I l l

American Water Res Assoc Proc Ser 14, 1972)

“An As~essment of the Fore$t and Range Land S/ fuat/on In the

Un/ted State \ , o p ci t

5‘Vo/ //, fnv(ronmenta/ Effects of Trend\ , op clt

ging and agriculture as well as “unnatural” for-est fire suppression that gradually replacedconifer forests with mixed hardwoods.

All types of replanting are accompanied bymajor changes in habitats available for wild-life. In the short term, any wood-harvesting

operation, other than large area clearcutting,usually increases wildlife populations becausemature forests normally do not support asgreat a total population of wildlife as do younggrowing forests. Many species require both

cleared and forested area to survive, and thus,the “edges” created by logging operations areparticularly attractive to deer and other spe-cies. Other species dependent on subclimaxhabitats (such as eastern cottontails) will alsoincrease following logging, while species de-pendent on mature climax forests (e. g., wolver-ine, pileated woodpecker) will decline.

54

Although the desirability of the ecosystem

changes caused by logging may always be sub-ject to one’s point of view, different forestrypractices tend to have varying effects that may

be judged unambiguously from the standpointof wildlife diversity and abundance:

F o r e s t m a n a g e m e n t p r a c t i c e s t h a t r e d u c e

s t r u c t u r a l d i v e r s i t y o f h a b i t a t , s u c h a s e x t e n -

s i v e o l d g r o w t h c l e a r c u t t i n g , t h e r e m o v a l o f

s n a g s t h a t p r o v i d e w i l d l i f e f o o d a n d n e s t i n g

s i t e s , a n d c o n v e r s i o n t o p l a n t a t i o n m a n a g e -

ment wi l l genera l Iy reduce wi ld l i fe a b u n d a n c e

and diversity by reducing habitat essential tomany species. Conversely, animal diversityand wildlife abundance generally will be in-creased by opening up dense stands, makingsmall patch cuts, or by conducting other tim-ber management activities that increase struc-

tural diversity and provide a wide mix of hab-itat types. 55

Current pesticide and fertilizer use in U.S.forests is low, In 1972, insecticides were usedon only 0.002 percent of commercial forest-Iands, and fertilizers were used on less than500,000 acres. 5’ Because long-rotation logging

and removal of only boles generally do not“An Assessment of the Forest and Range Land Sltuatlon In f~e

United States, op clt

“lblci

‘6Vo/ 1 Errvironmenta/ lrnpllcatlon~ o f Trends In Agrlcu/ture

and S\lv/cu/ture, op c(t




deplete nutrients from forest soils, the mostimportant use of fertilizers is on soils that arenaturally deficient in nutrients or that havebeen depleted by past farming practices. Forexample, intensive cotton production in the

Southeast seriously depleted soils and much ofthis land was abandoned long ago. Phosphate

fertilization has allowed this land to becomeproductive in the growth of softwood forests.Pesticides generally are used in forest manage-ment to control weed vegetation during refor-estation or to combat serious outbreaks of in-sect pests. There is considerable controversyover aerial spraying of insecticides to controlthe gypsy moth and other damaging insects.Also, circumstantial evidence exists that cer-

tain herbicides in recent use may have causedoutbreaks of birth defects and other damagewhen inadvertently sprayed over populatedareas. Although the existence of these effectshas been vigorously denied by the manufactur-ers, and although pesticide use in forests is atiny fraction of the use in food production andis likely to remain so,

57

this use is likely to con-tinue to be a source of disquiet accompanyingintensive management of forests.

Silvicultural activities, and especially inten-sive harvesting operations, strongly affect theesthetic appeal of forests. The immediate af-termath of intensive logging is universally con-sidered to be visually unattractive, especiallywhere large amounts of slash are left on the

site. Therefore, wood harvesting has a strongpotential to conflict with other forest usessuch as recreation or wiIderness.

The significance of any negative effects de-pends on the nearness of logging sites to activi-ty areas or to scenic vistas, the rapidity of re-vegetation, and the extensiveness of the oper-ation. Therefore, the Forest Service seeks toroute trails away from active harvesting sites,

to avoid interrupting vistas, and to plan the ex-tent and shape of the areas to minimize visualimpacts.

The negative effect on the esthetic and rec-reational quality of forests caused by loggingmay be aggravated by a negative public per-

“lbld

ception of the environmental effects of clear-cutting in particular and logging in general. Asnoted earlier, this perception has been exag-

gerated by a number of factors including thegrim history (1870-1930) of forest exploitationin the United States, the former revulsion

against clearcutting practices within the for-

estry profession itself during the 1930’s and1940’s, and continued attacks against loggingby the environmental community. Although alogged-over area may be no uglier, objectivelyspeaking, than a harvested field, the publicperception of the two vistas is vastly different.

All reviews of logging and general forestryimpacts stress the importance of regional dif-

ferences –as well as extensive site-specific dif-ferences – in determining the existence andmagnitude of environmental effects. Figure 6presents a summary of those characteristics of

U.S. forest regions that are most relevant topotential silvicultural impacts. Because thedescriptions in figure 6 are, of necessity, muchoversimplified, they are meant to give someperspective of the general range of environ-mental conditions and problems in Americanforestlands and should not be considered asfully representing all of the major conditionsand problems in these lands.

Potential Environmental Effects ofHarvesting Wood for Energy

This section discusses the activities— har-vesting logging residues, whole-tree removal,intensifying and expanding silvicultural man-agement, and harvesting for the residentialspace-heating market — which are characteris-tic of an expansion in the use of wood as anenergy source.

Harvesting Logging Residuesand Whole-Tree Removal

The harvesting of logging residues for an en-

ergy feedstock has potential for both positiveand negative environmental impacts depend-ing on the nature of the forest ecosystem andthe previous manner of handling these resi-dues.



34 q Vol. II—Energy From Biological Processes

In forests where wood residues–tops, limbs,

and possibly leaves and understory — are rou-tinely gathered into piles for open burning (thisis required in forest fire prone areas of theWest), residue use for energy production is en-vironmentally beneficial. It eliminates the airpollution caused by this burning and has essen-

tially no additional adverse impacts exceptthose incurred in physically moving the residueout of the forest (and burning it, with controls,in a boiler). In forests where residues would

otherwise be broadcast burned, physical re-moval prevents some of the potential adverse

effects of burning — especially destruction of aportion of the organic soil layer. The removaldoes, however, subject the soil to compactionor scraping damage by the mechanical remov-al process that would otherwise be avoided.Also, broadcast burning is, at times, used to

control weed vegetation, and in some circum-

stances herbicide use may be substituted ifburning cannot be practiced.

Where logging residues are normally left inthe forest, institution of a residue removal pro-gram will have mixed environmental effects

which are summarized in table 12.

A worrisome effect of residue removal is the

increased potential for long-term depletion of

nutrients from the forest soils and consequentdeclines in forest productivity. These effectsare not well understood and although nutrientcycling in natural and managed forests has

been extensively studied, few of these studieshave included the effects of residue removal.

58

The existing studies indicate that short-rota-tion Southern forests may be more susceptibleto depletion than longer rotation Northernforests, and that marginal sites suffer far more

heavily than forests with fertile soils.59 60 61 62

“C. J. High and S E. Knight, “Environmental Impact of Har-

vesting Noncommercial Wood for Energy Research Problems, ”

Thayer School of Engineering, Dartmouth College paper DSDNo. 101, October 1977.

“E H White, “Whole-Tree Harvesting Depletes SOII Nutri-

ents, ” Ca n 1. Forest. Res. 4.530-535,1974

‘“ J R Jorgensen, et al., “The N utrient Cycle Key to Con-

tinuous Forest Production, ” /. Forestry 73.400-403, 1975.

“ J R Boyle, et al , “Whole-Tree Harvesting. Nutrient Budget

Evaluation, ” ). Forestry 71 760-762

“C F Weetman and B Webber, “The Influence of Wood Har-

vesting on the Nutrient Status of Two Spruce Stands, ” Can. / . For-

est. Res. 2 351-69, 1972

Table 12.-Environmental Impacts ofHarvesting Forest Residues

Water decrease in clogging of streams caused by entry of slashincreased short-term flow of sediments into streams because of loss oferosion control provided by residues, soil damage caused by removaloperations; somewhat counteracted by decline in broadcast burning,which at times destroys surface cover and causes erosion potential to

increasepossible changes in long-term flow of sediments where residueremoval affects revegetation; this effect is mixedchanges in herbicide usage–on the one hand, chemical destruction ofgrowing residues (valueless trees) will cease; on the other, broadcastburning no longer effective in retarding vegetative competition to newtree growth, herbicide use may increaseincreased short-term nutrient l eaching because of increased soil tem-peratures, accelerated decomposition

Air q reduction in air pollution from forest fires q reduction in air pollution from open burning of residues (if the residues

normally are broadcast burned or burned after collection)q dust from decreased land cover, harvesting operations

Land q potential depletion of nutrients and organic matter from forest soils and

possible long-term loss of productivity (inadequately understood)q short-term increase in erosion and loss of topsoil, possible long-term

decrease or increaseq reduction in forest fire hazard q short-term decreased water retention, increased runoff (and flooding

hazard) until revegetation takes place; aggravated by any soil compac-tion caused by removal operation

Other q change in wildlife habitat—bad for small animals and birds, good for

large animals unless serious erosion resultsq changes in tree species that can regrowq esthetic change, usually considered beneficial when slash is heavyq reduction in bark beef/es and other pathogens that are harbored by

residues

SOURCE Office of Technology Ass essment.

Further study and careful soil monitoringwould allow the use of fertilizers to compen-sate for nutrient depletion, but fertilizer ap-plication is energy intensive; it may increase

the flow of nutrients to neighboring streams,and its correct use may be difficult to ad-minister for smaller stands. Also, successful

application may be difficult unless the nutri-ent depletion is a simple one involving only

one or a few nutrient types <

Residues serve a number of ecological func-tions in addition to nutrient replenishment,

and their removal will eliminate or alter thesefunctions. They provide shelter and food to

small mammals and birds, provide a temporaryfood supply for deer and other larger mam-mals, moderate soil temperature increases that




normally occur after logging, provide someprotection to the forest floor against erosion,and are a source of organic matter for forestsoils. Thus, removal of residues will reduce cer-tain wildlife habitats and may expose the for-est floor to some additional erosion above andbeyond that caused by conventional logging.

Higher soil temperatures resulting from loss ofthe shade provided by residue cover will accel-

erate organic decomposition activity and maylead to a period of increased nutrient leachingbefore revegetation commences. Also, the in-

creased rate of organic decomposition cou-pled with the removal of a primary source oforganic matter may lower the organic contentof forest soils. Declines in soil organic matterare expected to be accompanied by declines innitrogen-fixing capacity, soil microbial activityrates, and cation exchange capacity, all con-

sidered to be important determinants of long-

term forest health. 63 64 The present scientificunderstanding of organic matter removal is,however, insufficient to allow a determinationof the significance of these possible effects.

The extensive residue left on the forest floorafter cutting dense stands can inhibit revegeta-

tion, especially in softwood forests. To the ex-tent that residue removal may promote newvegetation, this will counteract the removal’sshort-term negative erosion and nutrient-leach-ing effect (as long as removal is not so com-plete as to eliminate the light mulch necessary

to shade the surface and maintain soil mois-ture).

Residues also provide a habitat for disease

and pest organisms such as the bark beetleand, when washed into neighboring streams,may clog their channels and degrade waterquality. They add considerably to the inci-dence and intensity of forest fires, especially inthe West. Also, the esthetic impact of residues

*‘E L Stone, “Nutrient Removals by Intensive Harvest— Some

Research Gaps and Opportunttles, ” Proceedings Impact of Har-

vesting on Forest Nutr \ en t Cycle (Syracuse, N Y State Unlverslty

of New York, College of Environmental Science and Forestry,

1 979)“E H Wh/te and A E Harvey, “Modlficatlon of Intensive

Management Practices to Protect Forest Nutrient Cycles, ” Pro

ceedlngs /rnpact of Har\,e$t/ng on Forest Nutr/ent Cyc/e [ S y r a -

cuse, N Y State Untverslty of New York, College of Environ-

mental Science and Forestrv, 1979)

is generally considered to be negative when

they are left at the logging site; when denselyforested areas are cut, residues will completelycover the ground with several feet of unsightlyslash. Therefore, removal of residue will, in apositive sense, reduce the number and severityof forest fires and pest infestations, improve

esthetics, and reduce the potential for streamclogging.

“Whole-tree harvesting” is really a variationof residue removal with the bole and “resi-d u e ” - branches, leaves, twigs– removed inone integrated operation. It is most likely tooccur when the entire tree is to be chipped forfuel or some other use.

The problems of long-term nutrient and or-

ganic matter depletion from whole-tree har-vesting are basically the same as those ofresidue removal, and whole-tree logging simi-

larly removes far greater nutrients and organicmatter from forest soils than do other conven-tional methods. Whole-tree removal of Nor-way spruce, for example, results in a loss of 2to 4 times more nitrogen, 2 to 5 times morephosphorus, 1.5 to 3.5 times more potassium,and 1.5 to 2.5 times more calcium than conven-

tional Iogging.65 In addition, ground disturb-

ance from the actual tree removal is likely tobe worse with whole-tree harvesting when thefully branched trees are dragged off the log-ging site, eradicating understory vegetation inthe process. This disturbance, besides promot-

ing erosion, will accelerate organic matter de-composition. As noted previously, however,the effects of these organic matter and nutri-ent removals on long-term forest productivity

are poorly understood.

Intensifying and ExpandingSilvicultural Activities

The creation of new energy markets forwood will have a significant effect on the eco-nomics of managing forested land, includingland not currently considered to be high-grade

“E Malkonen, “The Effects of Fuller Biomass Harvesting on

SOI1 Fertlllty, ” SyrnposIurn on the Harvest~ng of a Larger Parf of

the Forest Biomass (Hyvlnkaa, Finland E conomlc Commlsslon

for Europe, Food and Agriculture Organlzatlon, 1976)




forest. New lands will be harvested and silvi-cultural practices will intensify.

One effect will be the expansion of loggingonto lands that are not now in the wood mar-ketplace. The operational costs of loggingsome of these lands cannot, at present, be re-couped through increased property values, the

sale of the harvested wood, or the value of fu-ture growth of a regenerated forest. Additionallands that currently are economically attrac-

tive targets for logging activities (stand conver-sion, clearing for nonforest use, etc.) are with-held by their owners for a variety of reasons

(their higher valuation of the land’s recre-ational potential, fear of environmental dam-age, etc.). As an energy market for wood devel-ops, however, harvesting part or all of thewood resource on these lands will become in-creasingly attractive.

The logging of some forests that wouldotherwise be untouched (or, perhaps morerealistically, that would only be logged at

some later time) may be viewed as beneficialby some groups. Most reviews depict Americanforests as being characterized by “overmaturestands of old-growth timber, especially in theWest, and . . . many stands, mainly in the Eastand South, that were repeatedly mined of goodtrees in earlier, more reckless times. ”

66Conver-

sion of such stands is often characterized as astep towards a healthier forest, because treegrowth generally is enhanced and more “desir-

able” tree species are introduced. Wherewhole-tree harvesting or residue removal ispracticed, the forest may become more acces-sible to hikers and may be more estheticallyappealing. The extent to which all this is con-sidered a benefit depends heavily on one’s per-spective, however, and optimizing commercialvalue is not necessarily synonymous with opti-

mizing other values such as ecosystem mainte-

nance or wildlife diversity.

As discussed later, expansion of silviculturalmanagement onto suitable lands, combined

with an increase in the intensity of manage-ment on existing commercially managed lands,

“Smith, op . cit

may provide important environmental benefitsin the form of decreasing logging pressures onlands that combine high-quality timber with

competing values that would be compromisedby logging. Unfortunately, a decrease in log-ging pressures on one segment of America’sforests may be coupled with an undesirable in-

creased pressure on another segment.A particular fear associated with the rise in

demand for “low quality” wood is that mar-ginal, environmentally vulnerable lands withstands of such wood may become targets forlogging. Much of this land that may be vulner-

able to logging for energy, although “poor”from the standpoint of commercial productivi-ty, is valuable for esthetic, recreational, water-shed protection, and other alternative forestuses. These forest values may be lost or com-promised by permanent clearing or by harvest-ing on sites where regeneration may be a prob-lem. For example, forests in areas with margi-

nal rainfall —e. g., in the Southwest— may be

particularly vulnerable to regeneration failuresand thus may be endangered by a growth inwood demand. On lands with poor soils andsteep slopes, clearcutting and other intensiveforms of harvesting create a high potential fornutrient depletion, mass movement, and otherproblems as described earlier. Because, as dis-cussed later, the Federal Government main-tains supervisory control over forest opera-

tions on federally owned lands, this potential

problem is likely to be concentrated on privatelands. The overall danger is somewhat miti-gated, therefore, by the Federal Government’sownership of a significant percentage of themost vulnerable land.

It is difficult to predict whether wood-for-energy operations will tend to gravitate to the

poorer quality and more vulnerable lands. Theseveral factors that will determine the tenden-cy of wood-for-energy harvesting to gravitate

to vulnerable lands include:

1. The d irec t c ost of w ood ha rvesting, – De-

velopment of more versatile harvestingequipment can lower the cost of operat-ing on steep slopes and promote harvest-ing on vulnerable lands.



38 . VOl. II-Energy From Biological Processes

be beneficial to the forest. Thinning allows in-creased growth in the remaining trees, esthetic-ally and physically “opens up” the forest, andmay allow some additional growth of under-story vegetation if the thinning is extensiveenough. If heavy machinery is used, however,resulting soil compaction can cause adverseimpacts, and care must be taken during thethinning operation to avoid damaging the treesthat remain.

A critical argument in favor of thinning and

other logging operations is that these activitiesresult in increased wildlife populations and di-versity. The definition of “diversity” is criticalto this argument. There is a substantial differ-ence between maximizing diversity in a singleforest stand and maximizing it in the forest

system composed of many forest stands in aregion. The first definition may be well served

by more intensive management because suchmanagement provides more “edges” and un-

derstory vegetation for browse. On the otherhand, many species will suffer from such man-agement. A great many species depend fortheir food and shelter on “unhealthy” –dead,dying, rotten —trees that would be removed ina managed forest, and other species cannot

tolerate the level of disturbance that would becaused by thinning operations. Maintaining di-versity in a forest system must include protect-ing these species by deliberately leaving un-

managed substantial portions of the forest or apercentage of the individual stands within theentire system. in regions where officially desig-nated wilderness areas or other protectivemeasures are adequate, intensive managementon the remaining stands may be considered(even by environmental groups) as benign orbeneficial if good management practices arecarefully followed. In other regions, especiallyin the East, intensive management may con-ceivably work to the detriment of species di-versity although it may increase the total wild-life population. Even in these regions, how-

ever, there is a possibility that large numbersof property owners may choose to leave theirlands unmanaged because of personal prefer-ences. This would serve to protect diversity.

The potential for added growth of high-quality timber from stand conversions of low-

quality forest and the increased use of thinningon commercial forestlands may have, as itsmost important effect, a decrease in the pres-sures to log forests that have both high-valuetimber and strong nontimber values —recrea-tion, esthetic, watershed protection, etc. — and

that may be quite vulnerable to environmentaldamage. Analysts such as Marion Clawson ofResources for the Future have long argued thatthe management of American forestland is ex-tremely inefficient, that by concentrating in-tensive management practices on the most ,

productive lands we could increase harvestyields while withdrawing from silviculture lessproductive or more environmentally vulner-able lands. 69 70 An expansion of wood use forenergy and the consequent creation of a strongmarket for “low quality” wood may have thisbeneficial effect.

OTA estimates that placing 200 millionacres of commercial forestland into intensivemanagement (full stocking, thinnings every 10years, 30- to 40-year rotations) could allowwood energy use to reach 10 Quads annuallywhile the availability of wood for nonenergyproducts might double its 1979 value. Alter-natively, the same result might be achieved byusing less intensive management on a largeracreage. The nature of any actual benefits,however, are dependent on the following con-siderations:

q Major effects on the availability of high-quality timber probably would not occurfor a number of years. Some additionalhigh-quality wood might be available im-mediately from stand conversions andharvest of noncommercial timber, andsome in about 20 years from timber

growth in stands that required only thin-ning for stand improvement. The quan-tities would not peak, however, beforeabout 30 to 40 years as stands that hadbeen cleared and replanted began toreach harvesting age, By this time, most of

the old-growth stands accessible to log-ging already may have been harvested, al-

“M. Clawson, “The National Forests, ” Science, VOI 20, Febru-

ary 1976

‘“M Clawson, “Forests in the Long Sweep of American His-

tory, ” Science, VOI 204, June 15, 1979




though significant benefits from reducinglogging pressures on other valuable orfragile lands would still be available.

q Although the increased availability ofhigh-quality timber might negate argu-ments that these valuable or fragiIe standsmust be cut to provide sufficient wood to

meet demand, there is no guarantee thatthe wood made available from intensifiedmanagement will be less expensive than

that obtainable from these stands, andeconomic pressure to harvest them mightcontinue.

Although the long-range economic goals ofintensive management provide an incentiveagainst poor environmental practices, carelesslogging and regeneration practices will still oc-

cur on a portion of the managed sites. Poormanagement may be practiced on a smaller

proportion of sites than would have been thecase without an expansion of wood for energy,but the effects of such management may beaggravated with such an expansion because:

q more acreage wilI be logged each year,q most affected sites will have fewer years

to recover before they are logged again,and

q the removal of maximum biomass andsubsequent soil depletion may reduce thesites’ ability to recover.

Thus, the impacts associated with conven-

tional logging— including erosion and soil deg-radation, damage to water quality, esthetic

damage, and other impacts–are likely to oc-

cur with even greater severity on a portion ofthose lands devoted to wood production forenergy. Unfortunately, because of the lack ofdata on logging practices and the very mixednature of the incentives for good management,it is impossible to make a good quantitativeprediction of the size of this portion.

A basic— and difficult to resolve— issueconcerning the wisdom of moving to a very

high level of intensive management of U.S. for-estland is the possibility that the long-termviability of these forests may be harmed. The

possibility of soil depletion is only one aspectof this. The cycles of natural succession oc-

curring in an unmanaged forest give that forestsubstantial resilience, because the diversity ofvegetation and wildlife of the more mature

states of the forest cycle as well as the diversi-ty created by the heterogeneous mix of stagestend “to buffer the system against drasticchange as by diluting the effects of pests on

single species.’’” Ecologists often have arguedthat man pays a significant price in moving toofar from this natural state:

The whole history of agriculture, and later,forestry, is basically a continuous effort to

create simplifed ecosystems in which special-ized crops are kept free of other species whichinterfere with the harvest through competi-tion . . . diversified systems have built-in insur-ances against major failures, while the simpli-fied systems need constant care. ’z

In relation to human needs, the human strat-

egy can be viewed as a reversal of the succes-sional sequence, creating and maintaining

early successional types of ecosystem wheregross production exceeds community respira-tion. Such . . . ecosystems, despite their highyield to mankind, carry with them the disad-vantages of all immature ecosystems, in par-ticular they lack the ability to perform essen-tially protective functions in terms of nutrient

cycling, soil conservation and population reg-ulation. The functioning of the system is thus

dependent upon continued human interven-

tion. 73

There are, of course, counterarguments to

the thesis that this simplification of ecosys-tems places these systems under significantrisk. One argument is that much of silvicultureduplicates natural events, and purposely so;for example, clearcutting, sometimes followed

by broadcast burning, is said to duplicate theeffects of severe storms or catastrophic fires. 74Another is that professional silviculturalistscan compensate for any tendency towards a

“Smith, op cit

“A H Hoffman, “Comprehensive Planning and Management

of the CountrVslde A Step Towards Perpetuation of an Ecologi-

ca l Balance, ” C / oba / Perspectives on Eco/ ogy , Thomas C Em-

mel, ed (May field Publlshlng Co , 1977)‘‘R Manners, “The Environmental Impacts of Modern Agricul-

tural Technologies, ” Perspectives o rI Environment, I R Manners

and M W Mlkesell, eds (Association of American Geographers,

1974), publication No 1374 Smith, op clt



40 . VOI. II-Energy From Biological Processes

decline in resiliency. In its extreme, this argu-ment is particularly unacceptable to thosewho are skeptical of placing too great a faithin science:

We ought to believe that we can excel overnature; and if we do, we should not be re-stricted to blind imitation of her methods

. . . we have the chance to sift nature’s truths,and recombine them into a new order in whichnot only survival, but enhanced productivity

are the ruling criteria . . . (we) must look tonear-domestication of our forests . . . we mustmove forestry close to agriculture. 75

The strongest argument that can be made,however, is that past forestry experience hasdemonstrated that temperate forests can ab-sorb an unusual amount of stress without suf-fering long-term damage. For example, largeacreages in Europe as well as the United Statesthat today are densely forested were intensely

exploited as agricultural land in the past. Inmany instances, foresters can point to inten-sive management practices in European for-ests that have continued to provide high pro-

ductivity of lumber for a hundred or moreyears. In counterpoint to these arguments,some environmentalists are worried about thefuture of Europe’s forests and point to increas-ingly high external costs in terms of pollutedwater and increasing incidence of disease epi-demics.76 Also, insufficient data is available toindicate whether or not small but significantdrops in long-term productivity may have oc-

curred because of such past practices.

A similar argument rages about high-yield

agriculture: yield levels in the Western coun-tries have climbed steadily over the past cen-tury, with temporary setbacks that have thusfar been dealt with by further adjusting the sys-tem, but environmentalists as well as manyagronomists are worried about increasing num-bers of pesticide-resistant insects and rising en-vironmental costs.

Pursuit of the evidence on both sides of thisargument may be worthwhile, but it is beyond

‘% Staebler, “The Forest and the Railroad, ” brochure pub

Ilshed by Weyerhaeuser Co , December 1975“Goldsmith, “The Future of Tree Diseases, ” The Eco/og is t , No

4[5, July-August 1979

the resources of this assessment. Also, the highlevel of emotional commitment that is at-tached to the alternative views of how farnature can be safely manipulated makes it un-likely that such a gathering of evidence will

change many minds. However, it is at /eastclear that a substantial increase in intensive

management must be accompanied by a thor-ough research program stressing examinationof such critical factors as nutrient cycling, therole of soil organic material vis-a-vis resistanceto tree disease, and other factors affecting sys-tem resiliency. The possibility that forest via-bility might be at excessive risk if hundreds ofmillions of acres in the United States wereplaced in intensive management should not beautomatically rejected, even though some de-gree of success in such management appar-ently has been achieved elsewhere.

Harvesting for the Residential MarketThe rapidly expanding demand for wood

fuel for residential use currently is satisfied

largely by harvesting of wood by homeowners

and by local entrepreneurs. The high price ofwood for residential use is an incentive forlarger scale loggers to enter the market, and atrend in this direction probably should be ex-pected in the future. The identity of the sup-plier may be an important component in deter-mining the environmental effects of satisfyinga high residential demand for wood fuel.

An expansion of the residential wood marketrepresents an opportunity for improved forestmanagement because of the value it places onlower quality wood, which in turn should stim-

ulate an increase in thinning activities. Thepotential benefits are the same as those de-scribed for the increase in intensive manage-ment: an increase in productivity and timbervalue on the affected lands. This opportunity

exists on woodlands ranging from smalI privatewoodlots to federally- and State-managed for-ests. The latter could use homeowners as a“free” work force to harvest selected trees, a

practice that is already in operation in manyareas.

Unfortunately, a rising demand for woodwill bring with it a potential for significant




Table 13.–Control Methods

Mitiaativea Preventive

Surface protection: q Access: seeding, mulching, riprap, or mat on cut-and-fill slopesq Timber harvest: maintenance of vegetative cover; distribution of slashq Cultural treatments: seeding; planting; fertilization

Flow diversion and energy:

q Access: berms above cut slopes; benches on cut slopes; checkdamsin ditches; drop structure at culvert ends; water bars on road surface;flow diversion from potential mass failures or at mid-slope

q Timber harvest: buffer strips; water bars on skid trailsq Cultural practices: plowing, furrowing, bedding

Access design modification

System design and maintenance: q Access: minimize cuts and fills, roadway widths and slopes; control

road densityq Timber harvest: minimize soil compaction from equipment operation;

use site-compatible log removal system; control harvested volume

within a watershed; limit harvest on unstable slopes; shape openingsfor minimum esthetic impact, avoid cutting next to recreational activityareas

q Cultural treatments: minimize reentry disturbances; fire control

Timing: q Access: closure of temporary roads; limited access; closure during

adverse conditionsq Timber harvest: limit operation during adverse climatic conditions; site

preparations during favorable conditionsq Cultural treatments: intensity and number of thinnings

acontrol~ can be described as preventive’ or ‘‘mltlgal[ve” according to the mode of applications Preverrwe COfIfrO/S apply to the prelmplementatlon Phase Of an oPeratlon These controls involve stopping

or changing the actwlty before the sod-dlsturbmg actlwty has a chance fo occur Mmgalwe corwok include vegetatwe or chemical measures or physmal structures which alter the response of the soIl dls-

turbmg achwty after t has occurred

SOURCE S/lvlcullureAcl/vll/es and NonpovMPo//ul/onAb aternent A Cost-E/(ecOvenes sAna/ys/s Procedure (Washington, D C Forest Serwce, USDA, November 1977)

along the shoreline may be sufficient toprovide shading and some sediment pro-tection to the body of water.

q Selection of harvesting system. — Controlof erosion, esthetic, and other impactscan be achieved by matching the harvest-ing system to the site conditions. For ex-

ample, the type of forest regenerated at

the site can be controlled by the harvest

system, because different degrees of dis-turbance favor different tree species.Clearcutting and residue removal favorspecies that need maximum disturbance

to grow (e. g., Douglas fir, jack and lodge-pole pine, paper birch, red alder, and cot-tonwood 81) and shelterwood cutting(which leaves residual trees in sufficientnumbers to shade new seedlings) favorsspecies (such as true firs, spruces, andmaples) that require light shade to thrive.The harvesting system may also be used toavoid some of the negative effects towhich the site is particularly vulnerable.

Clearcutting, for example, would be in-dicated for old, decrepit stands in whichresidual trees would be likely to blow

down in the first severe storm followingharvest. Shelterwood cutting would be ap-

propriate for stands important to scenicviews. A light selection cut may be the

“Smith, op clt

q

The

only harvesting allowed on soils subject tomass movement.Erosion/sediment control measures. — Al-

though a certain amount of erosion fromsoil compaction and mineral soil exposureis inevitable in logging operations, it can

be reduced by using lighter equipment to

avoid compaction, by using overhead oreven aerial (balloon or helicopter) log col-lection methods (although these methodsare economically feasible only for veryhigh-quality timber), by properly design-ing roads and minimizing their overall

length, by mulching the site, and by avariety of other methods. Furthermore,

the erosion that cannot be controlled can

be prevented from damaging water quali-

ty by using buffer strips, sediment traps,

and other means.

Institutional Climate forEnvironmental Control

Despite the generally resilient nature of theforests and considerable scientific knowledge

of forest ecology and regeneration, forest en-vironments may be threatened in the future be-cause certain market forces or institutionalconstraints discourage adequate environmen-tal protection. These problems include a lackof expertise in the logging community, a vola-tile market that hinders adequate planning in



—

44 . VOI. //—Energy From Biological Processes

certain segments of the industry, and a lack ofsufficient incentives to practice environmen-tally sound management.

1.

I

2.

Lack of expertise. –Although the majority of

negative impacts may occur because offailure to follow well-recognized guidelines,

others occur because of failures of judg-ment; forest environments are extremelycomplex and often require expert judgmentabout site conditions to select correctharvesting strategies. Some important im-pacts can be avoided only if the logger canrecognize subtle clues to the existence ofvulnerable conditions. For example, many

unstable soil conditions may be recogniz-able only to a soils expert. This type of ex-pertise usually is not available to the smalloperator, except possibly where local andState governments offer preoperation in-

spections and guidance (e. g., in Oregon].This poses a special problem if the residen-

tial market for wood expands considerably,because small operators may be expected tosatisfy much of this new demand.Insuff icient t ime for proper planning. – I n

current mill operations in Maine, many “millmanagers commonly call on short notice for

a certain volume of a given type of productfrom the firms’ logging division . . . A com-mon result is that a considerable amount of

the haul road construction is done on shortnotice . . . (without) . . . proper planning and

correctly installed and maintained drainagestructures. ”82 It is not clear that problems of

this nature will be as severe for wood har-vesting for energy, because demand for thewood as a feedstock may be more uniformand predictable than the demand for tradi-tional forest products (it also is not certainthat the Maine experience is widely ap-plicable). Nonetheless, most operations willcombine lumber and energy feedstock oper-ations— removing the high-quality wood,

and then clearing to harvest the remainderof the biomass for energy users. To the ex-tent that the timing of these operations de-

pends on the demand for the (higher value)lumber, this problem may remain.

‘*”A Survey of Erosion and Sedimentation Problems Associ-

ated With Logging in Maine, ” op cit

3. Lack of incentive. —These are four reasons

why a logger would pay strict attention to

minimizing environmental damages:

q personal environmental or esthetic ideal-ism,

q economic incentive,q regulatory controls, orq public relations

Idealism–and the role of education in fos-tering it—should not be ignored in predictingimpacts and attempting to mitigate them. Thestrengthening of existing programs to educate

potential wood harvesters about the adverseenvironmental effects of careless harvestingmay be useful in tapping the vein of environ-mental idealism in the United States. Idealismis clearly insufficient to assure environmentalprotection, however, and more selfish incen-tives are needed.

The long time period needed to recoup the

benefits of protective measures and the tend-ency of many of the benefits to accrue to adja-cent landowners or the general public reducethe economic incentive of environmental pro-tection. The shorter rotation periods that maybe used for obtaining wood for energy may en-hance the economic incentive, especially for

owners of large tracts of land (because they are

the “adjacent landowners”). Also, some “bestmanagement” measures do yield immediatereturns to loggers, for example, measures that

minimize road length or that prevent roadbedsfrom washing away.

Finally, to the extent that poor managementof logging does long-term physical and estheticdamage to the forest, the value of forestedland as a recreational and esthetic asset offers

a strong incentive to the landowner to insist onsound practices. This incentive will be partic-ularly strong in areas that have seen recent in-creases in market value because of their envi-ronmental value. This incentive will be effec-tive, however, only where the landowner main-

tains close supervisory control over the logger.

Regulatory control of wood harvesting oper-

ations in the United States is very uneven. Al-though the Forest Service can exert considera-ble control of logging operations on Federal




lands, logging on private lands is largely un-controlled or very loosely controlled.

The 1976 National Forest Management Actincludes requirements that federally owned

timber “be harvested only where soil or . . .water conditions will not be irreversibly dam-

aged, that harvests be on a sustained yield ba-sis, that silvicultural prescriptions be written toensure that stands of trees will generally not beharvested until they are mature (although thin-ning and other stand improvement work is per-mitted), that clearcutting meet certain stand-ards, and that land management plans be writ-ten with public participation. ”

83The Multiple

Use Act of 1960, by defining environmentallyoriented uses (such as wildlife protection) aslegislated uses of the national forests, requiresmanagement practices in these forests to con-

sider environmental protection as a direct re-

quirement. In response to these mandates, theForest Service enforces strict standards forharvesting lumber on Federal lands.

The degree of control exerted on non-Fed-

eral forests — especially privately owned for-ests — is noticeably weaker. Water quality im-pacts from wood harvesting theoreticallyshould be regulated through the developmentof nonpoint source control plans under section208 of the Federal Water Pollution ControlAct. As discussed in volume 1, however, im-plementation of section 208 generally hasbeen disappointingly slow, and the eventualeffectiveness of the 208 plans is highly uncer-tain. Also, few States have comprehensive for-est practices legislation or the manpower toenforce such legislation. A major problem fac-ing States wishing to control forest practices isthe complexity and site-specific nature of theenvironmental impacts, forcing the difficultchoice of using either a substantial force ofhighly trained foresters enforcing loosely writ-

ten performance guidelines or else a more(economically) manageable agency enforcingrigid — and perhaps impractical — rules. This

n IE ~ “lronmenta/ Readjne55 D o c u m e n t , wood CommerC/a /;~a-

tlon, op clt “

problem is discussed with insight in Brown1976: 84

The difficulty is that rules specific to thewide variety of situations encountered wouldoften be difficult to write and cumbersome toenforce for a great many problem areas, par-

ticularly within the context of our present

state of technology. Field personnel recognizethe dilemma of rules so vaguely written that

they provide no control versus rules so spe-cific that they prohibit flexibility and preventforest practice officers and operators from ad-justing methods to meet complex or highlyvarying situations. Given the option, most fieldpeople prefer to have flexibility at the risk oflosing some control.

Finally, many State forestry agencies have

concentrated their attention on forest fireprevention and control and not on forest man-agement. Hence, the experience, interest, and

expertise of present State forestry personnelmay not provide a good base on which to builda strong management-oriented program.

The public’s increasing awareness of envi-ronmental problems and willingness to actmay serve as a strong incentive for the largerforest products companies to consider thepublic relations implications of their decisions.Companies like Weyerhaeuser spend largesums of money explaining their activities insophisticated advertisements; presumably, thisawareness of the importance of public approv-

al affects their decision making and operations.

Environmental Effects—Summary

wood as an energy feedstock

Potential

The use ofholds considerable potential for reducing the

adverse impacts associated with fossil fueluse. It also offers the potential for some impor-

tant environmental benefits to forests, includ-ing:

q decreased logging pressures on some envi-

ronmentalIy valuable forests;

‘“Brown, et al , Meet/rig Water Qua//ty Objecr/~es Through the

Oregon Fores t Pract/ces Act, (Ore g o n S ta te De p a r tme n t o f

Forestry, 1976)




q

q

improved management of forests thathave been mismanaged in the past, withconsequent improvements in productivi-ty, esthetics, and other values; andreduced incidence of forest fires.

There is considerable uncertainty, however,about the extent to which a significant in-crease in the use of wood for energy will ac-tually result in these benefits and avoid thenegative impacts that could also accompany

such an increase. There are important econom-ic incentives for good management, includingincreased production of high-value timber andavoidance of losses in land values. There are anumber of factors, on the other hand, thatmust be interpreted as warning signals:

1.

2.

3.

4.

Environmental regulation of forestry oper-ations, especially on private lands, gen-eralIy is weak or nonexistent.

Some of the existing economic incentivesmay induce cutting of vulnerable lands or

neglect of best management practices.Important gaps in the knowledge of theeffects of intensive silvicultural activity—for example, of the nutrient and organicmatter changes in the soil caused bywhole-tree logging — may deter environ-

mentally sound choices from being made.The complexity and site-specificity of theharvesting choices that “must be mademay complicate adoption of environ men-

R&D

The primary R&D needs in the area of woodsupplies from forests fall into the categories ofharvesting technology, growth potential, en-vironmental impacts, and surveys. Traditionalharvesting technologies are geared toward re-moving large pieces of wood in a way that isappropriate for lumber or paper pulp produc-tion. The wood that can be harvested for fuel,however, is considerably more varied, involv-

ing brush, rough and rotten timber, and thesmaller pieces associated with logging resi-dues. Although the whole-tree chip methodseems to work well on relatively flat land,

tally sound harvesting plans, especially bysmalI operators.

If careful environmental management is notpracticed, the result might be:

q

q

q

q

q

increased erosion of forest soils and con-sequent degradation of water quality,

significant losses in esthetic and recrea-tional values in forested areas,

possible long-term drop in forest produc-tivity,decline in forested area, andreduction of forest ecosystem diversityand loss of valued ecosystems and theirwiIdlife.

Because the quality of forest management

and the capacity for environmental regulationcurrently span the entire range from very low(or nonexistent) to high, the expected result of

a “business as usual” approach to wood-for-energy environmental management would un-doubtedly be a complex mix of the above im-pacts and benefits —with the marketplace de-termining the balance between positive andnegative effects. Government action — includ-ing improved programs for local management

assistance, increased research on the effects ofintensive management, and increased incen-tives (economic or regulatory) for good man-agement — may be capable of shifting this bal-

ance more towards the positive.

Needs

there is a need to develop low-cost techniquesand equipment for harvesting smaller pieces ofwood and brush on more varied terrains and atgreater distances from roads.

Most research into forest growth potential isaimed at producing large straight trees suit-able for the traditional forest products in-dustry. Although some of this is research ap-

plicable to the production of wood for energy,the conditions and techniques for enhancingcommercial timber growth are not the same asthose for enhancing total biomass growth. As



Ch. 2—Forestry . 47

an example, thinning of tree stands reduces thetotal leaf surface and, with it, the amount ofsunlight that is being captured by plants. Thisreduces the total biomass growth on the stand,although it tends to increase the growth ofcommercial timber. If a strong wood energymarket develops, the ideal forest composition

could involve a mix of tree types, sizes, andqualities. Various strategies for achieving in-tegrated and economical energy-commercialtimber operations need to be investigated.Tree hybrids, for example, should be devel-oped with both commercial timber productionand biomass production as dual goals.

There are a number of uncertainties regard-ing the environmental impacts of increasedlogging for energy. The nutrient balance inforests, as noted, needs to be better under-stood in order to better define the types and

quantities of wood that can be removed with-out depleting the soil’s nutrients. The effectsof high biomass removal on soil carbon con-tent and any subsequent long-term impacts onproductivity or on forest viability require con-siderable research. The relationship between

the diversity of tree and understory species in aforest and the forest’s resilience to environ-

mental stresses must be better understood be-fore highly intensive management is allowedto expand to a majority of the commercial for-est acreage. Alternative harvesting techniquessuch as strip cutting (or the cutting of strips of

trees through the forest rather than clearcut-ting a large area) should be pursued in order to

provide a repertoire of techniques that can beused where soil erosion may be a problem,such as in steeper slope terrains. Harvestingtechniques that decrease the degree of soilcompaction should also be developed. Further-more, the entire forest ecosystem needs to bebetter understood if the environmental im-

pacts of various types of forest activities are tobe appropriately managed.

The national forest survey is primarily in-tended as a survey of commercial timber. Theassumptions as to what is commercial shouldbe separated from the survey of the biomassinventory and growth potential, in order tohave an accurate assessment of the quantitiesavailable for all uses. The survey should in-corporate noncommercial forest lands which

are classified that way because of low growthpotential.

A thorough assessment of the energy poten-tial of the forests should also include a qualita-tive assessment of the conditions of the stock-ing on forestlands and the silvicultural activ-ities (e. g., stand improvements) that could be

carried out to increase the yield. The surveydata should include environmental conditionssuch as soil types, rainfall, and other parame-ters. Finally, the size of tract is an importantfactor affecting the availability of the wood.

Consequently, the farm and miscellaneous for-est landowner classifications in forest surveys

should be subdivided according to tract sizeand ownership.



Chapter 3

AGRICULTURE



Chapter 3.— AGRICULTURE

Page Introduction . . * . . * * . . . * * * . . . . . . . . . . . . . . . 51Plant Growth, Crop Yields, and Crop

Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Theoretical Maximum Yield. . . . . . . . . . . . . . 51

Historical Yield Trends. ., ., . . . . . . . . . . . . . 53Record Yields . . . . . . . . . . . . . . . . . . . . . . . . . 54Future Yields . . . . . . . . . . . . . . . . . . . . . . . . . 54

land Availability . . . . . . . . . . . . . . . . . . . . . . . . . 54Types of Crops . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Current Agricultural Practices and Energy andEconomic Costs. . . . . . . . . . . . . . . . . . . . . . . . . 61

Energy Potential From Conventional Crops . . . . . . 64Energy Potential From Crop Residues . . . . . . . . . . 67

Environmental impacts of Agricultural BiomassProduction .0.,... . . . . . . . . q . . . . . . . ..*** 70Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 70The Environmental lmpacts of American

Agriculture. .,...... . . . . . . . . . . . . . . . . 70

1973-74: A Case Study in IncreasedCropland Use . . . . . . . . . . . . . . . . . . . . . . . 75Potential impacts of Production of Biomass

for Energy Feedstocks . . . . . . . . . . . . . . . . 76

Environmental lmpacts of Harvesting AgriculturalResidues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

R&D Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

TABLESPage

14. Photosynthetic Efficiency Summary . . . . . . 5215. Factors Limiting Plant Growth . . . . . . . . . . . 5216. Cropland Use in 1977 . . . . . . . . . . . . . . . . . . 56

17. Potential Cropland. . . . . . . . . . . . . . . . . . . . 5818. Cropland Balance Sheet . . . . . . . . . . . . . . . . 58

19. Cropland Available for Biomass Production 59

20. Annual Production and Disposition ofCorn for Grain in the United States, 1966-75. 60

21. Annual Production and Disposition ofWheat in the United States, 1966-75. . . . . . . 60

22. Estimated per Acre Production Costs inlndiana, 1979 . . . . . . . . . . . . . . . . . . . . . . . . 62

23. Energy lnputs for Various Crops . . . . . . . . . . 6224. Energy inputs and Outputs for Corn in U.S.

Corn Belt . . . . . . . . . . . . . . . . . . . . . . . . . . . 6225. Estimated Costs of Producing Grass

Herbage at Three Yield Levels . . . . . . . . . . . 6326. Total Crop Residues in the United Statesfor 10 Major Crops. . . . . . . . . . . . . . . . . . . 65

27. Total Usable Crop Residue by Crop . . . . . . . 6828. State Average Estimated Usable Group

Residue Quantities and Costs. . . . . . . . . . . . 69

29. Environmental impacts of Agriculture, . . . . 7030. 1977 Cropland and Potential Cropland

Erosion Potential . . . . . . . . . . . . . . . . . . . . . 7731. Mean National Erosion Rates by

Capability Class and Subclass . . . . . . . . . . . 7732. Agricultural Production Practices That

Reduce Environmental Impacts . . . . . . . . . . 7933. Enviromental Pollution Effects of

Agricultural Conservation Practices . . . . . . . 8134. Ecological Effects of Agricultural

Conservation Practices. . . . . . . . . . . . . . . . . 8335. Environmental impacts of Plant Residue

Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

FIGURES

Page 7. U.S. Average Corn Yield . . . . . . . . . . . . . . . . 538. U.S. Average Crop Output . . . . . . . . . . . . . . 549. Farm Production Regions of the

United States . . . . . . . . . . . . . . . . . . . . . . . . 5510. Cropland as a Percentage of Total LandArea by Farm Production Region ..,...... 56

11. Present Use of Land With High andMedium Potential for Conversion to

Cropland by Farm Production Region . . . . . 5712, Net Displacement of Premium Fuel per

Acre of New Cropland Brought IntoProduction . . . . . . . . . . . . . . . . . . . . . . . . . . 66



Chapter 3

AGRICULTURE

Introduction

Agriculture was originally developed to pro-

vide a reliable source of food. Later feed wasincluded in farm production and animals pro-vided large parts of the population’s energyneeds. Although animals are rarely used for en-ergy on U.S. farms today, agriculture has ex-panded to include the production of nonfoodcommodities, including cotton, tobacco, paintsolvents, specialty chemicals, and various in-dustrial oils. In 1977, these nonfood products

accounted for over 13 percent of total farm

production.

Many of the food and feed crops as well asfarming byproducts can also be used to pro-duce fuels or be combusted directly. In thischapter, the technical aspects of conventionalagriculture are considered, leading to esti-mates of its potential for supplying energy.

Plant Growth, Crop Yields, and Crop Production

Harvested yields of many crops have in-

creased dramatically over the past 30 years asa result of the development of genetically im-proved crop strains, as well as increased use offertilizers and irrigation. Also, increased ap-

plication of chemicals for control of insects,diseases, and weeds; further mechanization so

that operations can be timely; improved tillageand harvesting operations; and other forms ofimproved management have also helped toraise yields.

Photosynthesis is the basic process provid-

ing energy for plant growth. Solar energy is ab-sorbed by the green chlorophyll in the leaf andused to combine carbon dioxide (CO2) from theair with water from the soil into stored chemi-cal energy in the form of glucose. Glucose isused in the formation of compounds like aden-osine triphosphate which provides energy for

the synthesis of the various materials neededin the plant such as cellulose and Iignins forcell walls and the structural parts of the plantand various amino acids (protein components).Glucose is respired to provide energy for pro-

duction of other compounds, plant growth,and absorption of nutrients from the soil. Asthe plant matures, carbohydrates are stored inthe seed to provide energy for the growth ofnew plants.

Sixteen nutrients are essential for plantgrowth and two or three more may increaseyields but are not essential for the plant tocomplete its growth cycle. Of the 16, nitrogen,phosphorus, and potassium are the 3 main nu-

trients needed in large quantities to supple-ment the soil supply in order to obtain highcrop yields. Calcium and magnesium are ap-plied where needed as finely ground lime-stone. Sulfur is added as elemental sulfur or assulfates when needed. Carbon, hydrogen, andoxygen come from the air and water and the re-

maining seven are used in extremely smallamounts and are absorbed from the soil. All ofthese nutrients play essential roles in thegrowth processes within the plant.

Theoretical Maximum Yield

The theoretical maximum photosynthetic ef-ficiency can be estimated as follows:

Ten percent of the light striking a leaf isreflected. Only 43 percent of the light that

penetrates the leaf is of a proper energy tostimulate the chlorophyll. The basic chemical

reactions (10 photon process) which use stimu-lated (“excited”) chlorophyll to convert CO 2

and water to glucose have an overall efficien-

51



52 q Vol. I/—Energy From Bi olog ical Processes

cy of 22.6 percent. The net result of these fac-tors is, in theory, a maximum photosyntheticefficiency of about 9 percent. A summary ofthe various cases of photosynthetic efficiencyis presented in table 14.

Table 14.–Photosynthotic Efficiency Summary

Average PSEaduringgrowth cycle

(percent)

Maximum theoretical . . . . . . . . . . . . . . . . . . .Highest laboratory short-term PSEa . . . . . . . .Laboratory single leaves, high CO2or

low O2, C-3 plants, c 7% full sunlight. . . . .Same as above, for C-4 plants. . . . . . . . . . . . .Corn canopy, single day, no respiration . . . . .Record U.S. corn (345 bu of grain/acre,

120-day crop) . . . . . . . . . . . . . . . . . . . . .Record sugar cane (Texas) . . . . . . . . . . .Record Napier grass (El Salvador) ... . . . . . .Record U.S. State average for corn (128

bu/acre, Illinois, 1979). . . . . . . . . . . . . . . .Record U.S. average for corn (108

bu/acre, 1979 . . . . . . . . . . . . . . . . . . . . .

8.7- 9

6.34.45,0

3. 03. 02. 5

1.1

0. 9

apSE.pholo5ynthetlc efficiency

SOURCE OftIce of Technology Assessment

An efficiency approaching the theoreticalmaximum appears to have been achieved for ashort time under laboratory conditions usingan alga or single-celled water plant. Theseresults are controversial, however, and in prac-tice there are always several other factors thatlimit the efficiency of photosynthesis, and the

transformation of glucose into plant material.The most important of these factors, many ofwhich are interdependent, are listed in table15. For example, light saturation can be influ-enced by the CO2 concentration, which is af-fected by other things. The key factors arelight saturation, soil productivity (its ability tohold water, supply oxygen, release nutrients,and allow easy root development), weather(amount and timing of rainfall, absence of se-vere storms, length of growing season, temper-ature and insolation during the growing sea-son), and plant type (leaf canopy structure,

longevity of the photosynthetic system, sensi-tivity to various environmental stresses, etc.).

‘V C Coedheer and J W Klelnen Hammans, Nature, VOI 256,

p 333, 1975

Table 15.–Factors Limiting Plant Growth

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

Water availability,Light saturation–a tendency for the photosynthetic efficiency to dropas the incident light intensity increases above values as low as about10% of peak solar radiation intensity.Ambient temperature, especially wide fluctuations from ideal.Mismatch between plant growth cycle and annual weather cycle.Length of photoperiod (hours of significant illumination per day).

Plant respiration,Leaf area index–completeness of coverage of illuminated area byleaves or other photosensitive surfaces.Availability of primary nutrients–especially nitrogen, phosphorus, andpotassium,Availability of trace chemicals necessary for growth.Physical characteristics of growth medium.Acidity of growth medium.Aging of photosynthetically active parts of plants.Wind speed.Exposure to heavy rain or hail or icing conditions.Plant diseases and plant pests.Changes in light, absorption by leaves due to accumulations of waterfilm, dirt, or other absorbers or reflectors on surfaces of leaves or anyglazing cover.Nonuniformity of maturity of plants in crop.Toxic chemicals in growth medium, air, or water, such as pollutants

released by human activity.Availability of CO2.Adjustment to rapid fluctuations in insolation or other environmentalvariables —i. e., ‘‘inertia’ of plant response to changing conditions.

SOURCE. Off Ice of Technology Assessment

In an untended system, the environmentalfactors are left to chance. Consequently, inany given year, some areas of the country willexperience a favorable combination of factors,resulting in more plant growth, while in otherareas environmental factors will be unfavor-able, resulting in less plant growth. The exact

places where the growth is favorable or unfa-vorable will also change from year to year, aswill the exact growth at the most favorablearea in each year. In the absence of long-rangeenvironmental changes, however, such asweather changes or soil deterioration, the aver-age growth over a very large area and for manyyears will remain relatively constant.

Some of the environmental factors can becontrolled, while others cannot within thepresent state of knowledge. Managing a plantand soil system consists of artificially main-

taining some of the environmental factors,such as nutrients or water, at a more favorablelevel than would occur naturally. The many re-maining factors, however, are still left tochance. Furthermore, there is a limit to how



Ch. 3—Agriculture . 53

much plant growth (or other characteristics

such as grain yield) can be influenced bychanges in given environmental factors. Oncesome of the factors have been optimized forplant growth (or, e.g., grain yield) the plant’sperformance will not be improved by furtherchanges of these factors. Too much water or

fertilizer, for example, could actually inhibitgrowth rather than increase it.

Because plants vary in their sensitivity to

growth-limiting factors yields can be improved

by selecting or breeding for plants that are

relatively insensitive to environmental factors

that cannot be controlled and/or that respond

well to factors that can.

A dramatic example of the success of breed-

ing and management is corn. The history of

U.S. average corn yields from 1948-78 is shownin figure 7. While the national average yieldshave not been analyzed in detail, Duvick hasanalyzed the changes in yields from hybridsgrown in various Midwestern locations.

2H e

Figure 7.—U.S. Average Corn Yield

A . .

1940 1950 1960 1970 1980 1990 2000Year

SO URCE. ~gr~cultura~ S~at~stKs (Washington, D C: U S Department of Agri-culture. 1978)

‘D N Duvick, Mayd~ca XXII, p 187,1977

concluded that 60 percent of the increase on

these plots was due to genetic improvementswhile 40 percent was attributed to improvedmanagement. The management tends to re-duce the environmental stresses, while hybridswere developed that are less sensitive to ad-verse environmental factors and more respon-

sive to the factors that can be controlled (e. g.,fertilizers, weed control, insect control, etc.).

Historical Yield Trends

Past yield trends can be used as a guide forprojection of future yields. A period of at least15 years should be considered because ofweather fluctuations since the desired value isthe yield trend if weather remained constant. Aperiod of dry years from 1973 to 1976 tendedto exert some influence on data variability.

During the 1948-78 period, corn yields in-creased an average of 2 bu/acre-yr giving a1978 yield just over 100 bu/acre. Similarlysoybean yields showed an increase of about0.4 bu/acre-yr and a 1978 yield of 29.2 bu/acre.National wheat yields are somewhat morevariable since wheat is grown primarily inareas that are more affected by drought thanis corn. Nonetheless, the yield trend indicatesan increase of 0.5 bu/acre-yr and a 1978 aver-age yield of 31.6 bu/acre. The U.S. Departmentof Agriculture (USDA) has calculated a sum-mary of all crop yields per acre using a relative

value of 100 for the 1967 yield. The trend forincrease over this period was 1.4 units per year,but the uncertainty in this number is large (seefigure 8).

Yield increases in the future as in the pastwill come from a combination of improvedcrop varieties and improved cultural practices.Since current fertilization practices havereached near optimum rates, increases in yielddue to increases in fertilization rates will beless than for the past 20 years. As yield poten-tials of varieties are increased, however, in-

creased rates of fertilization will be needed tokeep pace with the increased yields. Since

yield increases result from a combination ofpractices, it is difficult to attribute yield in-

creases to any one practice.



54 . Vol. II—Energy From Biological processes

II

Figure 8.—U.S. Average Crop Output

12 0

11 0

10 0

90

o 1965 1970 1975 1980

Year SOURCE: Agricultural Statistics (Washington, D. C.: U.S. Department of Agri-

culture, 1978).

Record Yields

Projection of yields and determination ofwhere yield increases will diminish may bejudged on the basis of yields that have beenobtained. For example, the average U.S. cornyield has reached over 100 bu/acre, but the

average yield in Illinois in 1979 was 128bu/acre and in Iowa in 1979 it was 127 bu/acre. * If county averages within a State are ex-

amined, average yields are found to approach140 bu/acre. If individual farms of 500 acres of

corn are considered, yields of 175 bu/acre haveoccurred. And on selected areas of 2 or 3 acres

yields of 345 bu/acre have been noted.

Future Yields

Over the past 30 years corn yields have in-creased at an average rate of about 2 bu/acre-yr. One would not expect this rate of increase

to rise, and it may decline. Therefore, in pro-jecting corn yields in the year 2000, 140 bu/acre would be optimistic. A less optimistic pro-jection, based on annual average yields in-creasing at one-half the rate that they have inthe recent past, is 120 bu/acre in 2000. A studyby the National Defense University in 1978gave a projected corn yield for 2000 of 132

bu/acre.

Future increases in the yields of other cropsare also expected, but each crop together withthe cropland on which it will be grown must beconsidered separately. Dramatic increases,such as a doubling in crop yields by 2000, how-ever, are not expected for conventional crops.

*The weather in 1979 was ideal for corn growing

Land Availability

Cropland is land used for the production ofadapted crops for harvest, alone or in a rota-tion with grasses and legumes, and includesrow crops (e. g., corn), small grain crops (e. g.,wheat), hay crops, nursery crops, orchard

crops, and other similar specialty crops. Crop-Iand is generally categorized into the agricul-tural production regions shown in figure 9.

Of the U.S. total land area of 2.3 billionacres, 413 million or 467 million acres are cur-rently classified as cropland depending onwhether one uses the Soil Conservation Service(SCS) or the other USDA classification system.

The second is a broader classification that in-cludes some land not currently cropped that isrotated into cropland but may now be in pas-ture or other use. The percentage of the totalland area of each State that is cropland isshown in figure 10 and the cropland used in1977 is shown in table 16. Both of these arebased on the more restrictive SCS classifica-tion of cropland.

Cropland, however, is not a static category.The location of cropland may shift eventhough the quantity of cropland remains rela-



Ch. 3—Agriculture . 55

Figure 9.— Farm Production Regions of the United States

SOURCE S O iI Conservation Service, U S Department of Agriculture

tively constant. Over time there are both addi-tions and deletions to the cropland inventory.

The quality of land and cropping systemsmay shift as well. One such change has beenthe increase in irrigation, in areas like the

Texas high plains, from 1.2 million acres in1948 to 6.4 million acres in 1976. This repre-sents both a trend in improving the productivi-ty of existing cropland and a trend towardsopening new, marginal land that is only pro-ductive and economic with irrigation. To someextent, the United States has been replacingrainfed arable land that is lost to agriculturewith irrigated land in dry areas. This trend,

however, is likely to change due to increasingenergy costs and depletion of some Westernground water.

Over time, the content of a land inventory

can be influenced by the way that a given sta-

tistic is enumerated. For example, up to 1964the agricultural census was personally enu-

merated and in 1969 it was done by mail. Ac-cording to the broader USDA classification,cropland pasture increased by over 30 millionacres between these surveys, and the suspicionis that the farmer applied a less strict defini-tion to cropland pasture which resulted in theinclusion of 30 million acres of pasturelandand grassland into the cropland pasture cate-gory even though the actual usage had notchanged.

One strong influence on the land inventoryhas been the Government’s agricultural pro-grams. The land retirement programs of the

1960’s reduced planted cropland and had thenet effect of moving less productive land out

of crop production temporarily or even perma-nently in the case of very low-quality land. As




Figure 10.—Cropland as a Percentage of Total Land Area by Farm Production Region

Table 16.-Cropland Use in 1977(thousand acres)

OccasionallyRow crops Close-grown crops Rotation hay improved hayland

Region Irrigated Nonirrigated Irrigated Nonirrigated Irrigated Nonirrigated Irrigated Non irrigated

Northeast ., . . . . . . . . . . . . 254 6,771 1,033 9 3,339 5 3,286Appalachian. ... ... . . . . 349 14,445 33 543 7 1,248 10 3,151Southeast . . . . . . . . . . . . . . 1,681 12,108 23 342 24 74 8 604Delta States. . . . . . . . . . . . . 2,294 15,358 1,489 285 170 299 0 397Corn Belt. . . . . . . . . . . . . . 1,035 70,291 31 7,228 8 5,987 4 4,116Lake States. . . . . . . . . . . . . 799 20,930 80 9,140 36 7,753 2,802Northern Plains ... . . . . . . 8,641 18,062 920 40,007 690 5,387 325 3,885Southern Plains . . . . . . . . . . 5,935 13,908 2,354 15,784 33 802 286 725Mountain. ... . . . . 4,117 962 3,316 14,021 2,269 380 3,821 1,276Pac if ic. . . . . . . ., ., . . . . . 4 ,477 132 2,757 5,556 1,124 502 1,092 295

Totala. ... . . 29,750 173,493 11,025 93,865 4,398 25,818 5,559 20,839

Native hay Orchards, etc. All cropland

Region Irrigated Nonirrigated Summer fallow Irrigated Nonirrigated Other Irrigated Nonirrigated

Northeast . . . . . . . . . . . . . 0 789 24 84 508 493 372 16,534A p p a l a c h i a n , . . . . . . 0 86 112 0 149 690 406 20,339Southeast . . . . . . . . . . . . . . 0 0 54 699 661 1,324 2,449 15,053Delta States. . . . . . . . . ., 0 84 179 6 136 489 3,979 17,207Corn Belt. . . . . . . . . . . . . . . 0 117 749 22 72 876 1,115 88,739Lake States. . . . . . . . . . . . 0 719 466 42 291 1,073 972 43,167Northern Plains . . . . . . . . . . 33 2,493 13,825 0 15 268 10,790 83,733Southern Plains . . . . . . . . . . 0 405 1,061 33 153 755 9,011 33,223Mountain. . . . . . . . . . . . . . . 1,460 320 9,449 0 641 17,208 26,111Pacific. . . . . . . . . . . . . . . . . 261 208 4,082 2,242 183 277 12,261 10,927

Totala. . . . . . . . . . . . . . . . 1,754 5,221 28,319 3,295 2,225 6,806 57,647 355,520

aAlsO Includm Canbbe.an and Hawall

SOURCE SoIl Conservation Serwce, U SOeparlment of Agriculture



Ch. 3—Agr i c u l t u re q 5 7

programs were terminated in the early 1970’s,some of these acres came back into crop pro-duction.

USDA’S SCS surveyed non-Federal lands in1977 and identified the land that potentially

could become cropland. 3 The survey classified

potential croplands according to whether theland was judged to have a high, medium, low,or zero potential for conversion. Figure 11summarizes the quantities of land that have a

Figure 11 .—Present Use of Land With High andMed ium

N o r t h e a s t

L a k e

S t a t e s

C o r n B e l t

N o r t h e r n

P l a i n s

A p p a l a c h i a n

S o u t h e a s t

D e l t a S t a t e s

S o u t h e r n

P l a i n s

M o u n t a i n

P a c i f i c

Potential for Conversion to Croplandby Farm Production Region

Q 5 10 15 20 ( m i l l i ons o f ac r es )

F o r e s t

P a s t u r e a n d n a t i v e l a n d s

R a n g e l a n d

O t h e r

SOURCE: 1977 National ErosIon Inventory Preliminary Estimates, Soil Conser.

vation Service, U.S. Depar tment of Agr icul ture, Apr!l 1979.

319775011 Conservation Service National Erosion Inventory Es-

t imate (Washington, D C SoIl Conservation Service, U S De-

partment of Agriculture, December 1978)

high or medium potential for conversion tocropland. Of the total potential cropland in1977, 40 million acres have a high probabilityto be converted and another 95 million acresare classified as having medium probability. *

The breakdown of the potential cropland

into high and medium potential for conversionis an attempt to define a crude cost curve for

the availability of new cropland. It was judgedby SCS that the land with a high potential willenter agriculture as a matter of course, if pricerelationships are somewhat more favorable tothe farmer than the 1976 prices on which thesurvey was based. The medium potential, how-ever, is a category involving lands with a widevariety of problems but which cannot be cate-

gorically excluded from conversion if farm-land prices increase sufficiently.

The SCS survey, however, does not include aquantitative measure of the price increasesnecessary to bring potential cropland undercultivation. A conservative approach would beto assume that only land with high potentialcan be included in the cropland base withoutexcessive inflation in food prices above thatwhich would occur normally due to increaseddemand for food. A more optimistic approachwould be to include those types of medium-po-tential land that probably will be consideredhigh potential in the future, as increased de-mand for food raises cropland prices. This is

the approach that was taken.Two major factors, mentioned above, that

affect crop productivity are water availabilityand soil quality. Therefore, land was includedfrom the medium-potential category that hasgreater than 28 inches of annual rainfall andpotentially has good productivity (capabilityclasses 1 and 2 of the eight agricultural landcapability classes). These land types are themost Iikely to be brought into cultivation if de-mand exceeds the high-potential category.

With these assumptions, the potential crop-

I and is shown in table 17. This together with ex-isting cropland provides the cropland base, to-

*As of November 1979, these numbers were 36 million and 91

million acres, respectively

67-968 o - 80 - 5



Ch. 3—Agriculture q 5 9

NIRAP high and low productivity (yield/acre)

estimates to determine plausible ranges of de-mand for cropland for food and feed produc-

tion and thus the ranges of land available forbioenergy production. These estimates areshown in table 19.

Table 19.–Cropland Available for Biomass Production

Million acres

1984 From cropland pasture . . . . . . . . . . . . . . . .From high potential . . . . . . . . . . . . . . . . . .From medium potential . . . . . . . . . . . . . . . .

10

10

10

Range of uncertainty, . . . . . . . . . . . . . . .1990From cropland pasture . . . . . . . . . . . . . . . .From high potential . . . . . . . . . . . . . . . . . .From medium potential . . . . . . . . . . . . . . . .

Range of uncertainty . . . . . . . . . . . . . . . .2000From cropland pasture . . . . . . . . . . . . . . . .From high potential . . . . . . . . . . . . . . . . . .From medium potential . . . . . . . . . . . . . . . .

30

30-70

2555

35 9-69

10

NANA

Range of uncertainty. . . . . . . . . . . . . . . .10

0-65

NA=none available

SOURCE” Otfo C Ooerlng Ill, “Cropland AvallabMy for Biomass Production, ” contractor report toOTA, August 1979

It should be emphasized that these are notpredictions, but rather plausible estimatesgiven the current state of knowledge. Theranges are less than &10 percent of the crop-

Iand base, so it is unlikely that more accurateestimates can be made. Furthermore, unex-pected increases in crop productivity, in worldfood demand, or in demand for cropland fornonagricultural uses could increase or de-crease the quantity of cropland available forbioenergy production beyond the rangesshown. Also, since this only refers to cropland

capable of producing more or less convention-al crops, the development of unconventionalcrops could open new land categories not con-sidered here.

In addition to the physical availability ofcropland, one must consider the cost of bring-ing it into production. Four major factors in-

fluence this cost. First the land is currently be-ing used for some purpose that the owner con-siders to be more valuable. than crop produc-

tion. Second an investment is sometimes nec-essary to convert the land to crop production,

such as installation of drainage tiles or remov-ing trees occupying the site. These costs canvary from virtually nothing to as much as

$600/acre.’ Third, the land that can be brought

into production is generally less productive, onthe average, than cropland currently in pro-duction. Finally, this land also typically suffersfrom problems of drought or flooding thatmake crop yields extremely sensitive to weath-

er (particularly the rainfall pattern). Conse-quently, farming this land involves a largercost and risk than with average cropland; and,from the national perspective, using it will in-crease the year-to-year fluctuations in foodsupplies and prices.

As a result of these added costs and risks,farm commodity prices will have to rise beforeit will be profitable to bring new land into crop

production. Eventually this raises the cost ofall farmland, the cost of farming, and foodprices. The exact price rise needed to increase

the cropland in production by a given amountis unknown, but some things can be deducedfrom this analysis. During the next few years,bioenergy production from cropland is notlikely to be constrained by the availability ofcropland. However, the quantity of land that

can be devoted to energy production withoutreducing food production is likely to decrease

in the future. Furthermore, since the marginalcost of bringing new cropland into productionincreases as the quantity of cropland in pro-duction expands, the added cost in terms ofhigher food prices needed to keep a givenamount of cropland in energy production islikely to increase with time. In other words, it is

likely to be increasingly expensive to produceenergy crops, even if the energy output re-mains constant.

The above comments are particularly appli-

cable to grains and sugar crops. Considerablequantities of land, however, already are de-voted to forage grass production and the yieldscan be raised through increased fertilization(see below). Furthermore, grass yields tend to

be less sensitive to poor soil quality than grains

Cl bid




and sugar crops. Consequently, the economic Nevertheless, in the long term, there may be

barriers to increased grass production are con- Iittle cropland suitable for food/feed produc-

siderably lower than for increased grain or tion that can be devoted to energy, and any

sugar production, and one would expect the in- energy crops would have to be grown on land

direct costs of grass production to be less than totally unsuited to food and feed production.

those of grains and sugar crops.

Types of Crops

There are over 300,000 plant species in theworld, but less than 100 are grown as crops inthe United States. Of the various crops, three

basic types are currently of interest for imme-diate energy production: starch, sugar, and for-age.

The major starch crops are corn (for grain)and wheat, accounting for 21 percent each of

the total acreage of harvested crops, or about70 million acres each. The annual productionand disposition of corn and wheat are shown intables 20 and 21. In addition, oats, barley,grain sorghum, and rice are other important

starch crops.

The main sugar crops currently grown in the

United States are sugarcane and sugar beets.About 760,000 acres are devoted to sugarcane(in Florida, Louisiana, Texas, and Hawaii) andsugar beets were grown on 1.2 million acres in1977. Also, a smaller acreage is devoted to

sweet sorghum production, primarily for sor-ghum syrup. The sugar yields averaged about

3.7 ton/acre for sugarcane (some growing sea-

sons were 18 to 24 months) and 2.6 ton/acre forsugar beets. The very limited commercial acre-age of sweet sorghum has yielded about 1.9ton/acre of sugar, however, the acreage is toosmall to accurately reflect the yields thatwould occur from large-scale production ofthis crop.

Forage crops are grown for feed and bed-

ding. Including alfalfa, the area under foragecrop production is about 60 miIIion acres.

7For-

age crops include orchard grass, brome grass,tall fescue, alfalfa, clover, and reed canary-

7Agr icu/ tura/ Stati stics (Washington, D C.: U S Department of

Agriculture, 1978).

Table 20.–Annual Production and Disposition of Corn for Grainin the United States, 1966-75 (million bushels)

DomesticYear Production consumption ExPorts Stocks

1966 . . . . 4,167 3,697 487 8261967 . . . . 4,860 3,885 633 1,1691968 . . . . 4,450 3,966 536 1,1181969 . . . . 4,687 4,189 612 1,0051970 . . . . 4,152 3,977 517 6671971 . . . . 5,641 4,387 796 1,126

1972 . . . . 5,573 4,733 1,258 7061973 . . . . 5,647 4,631 1,243 4831974 . . . . 4,664 3,641 1,149 3591975 . . . . 5,797 4,049 1,711 398

SOURCE Agr~cullural Stafrstlcs 1977( WashmgIon, D C U S Department of Agriculture, 1977)

Table 21.-Annual Production and Disposition of Wheatin the United States, 1966-75 (million bushels)

DomesticYear Production consumption Exports Stocks

1966 . . . . 1,967 683 771 5131967 . . . . 2,202 626 765 6301968 . . . . 2,188 740 544 9041969 . . . . 2,350 764 603 983

1970 . . . . 2,336 772 741 8231971 .., . 2,442 848 610 9831972, . . . 2,530 798 1,135 5971973, . . . 2,305 748 1,217 3401974 . . . . 2,140 686 1,019 4351975 . . . . 2,572 735 1,173 664

SOURCE Agr/cu/tura/Stat/sl(cs 1977( Washington, D C U S Department of Agriculture, 1977)

grass. Yields average about 1.5 to 2.5 ton/acrebut could be increased to 4 to 5 ton/acre by rel-atively straightforward changes in manage-ment practices.

Most crops can be grown in several different

areas of the country. However, each crop hasunique characteristics that enable it to do wellunder certain combinations of soil type, grow-ing season, rainfall, etc. Since these parame-ters vary widely throughout the United States,it is unlikely that any one crop could prove to




be the correct energy crop for a given product. The crops mentioned here do not exhaust

Rather, the available cropland can best be uti- the possibilities, even for starch, sugar, andlized for energy by growing various different cellulosic products. Other crops may be supe-

crops suited to the various soil types, climates, rior to these under certain circumstances. But

and other conditions. Nevertheless, there are these crops do serve to illustrate U.S. agricul-

some striking differences when national aver- ture’s energy potential, costs, and impacts.

age yields are compared. (See “Energy Poten-tial From Conventional Crops” below.)

Current Agricultural Practices and Energy and Economic Costs

As mentioned above, the purpose of manag-ing a plant system is to provide an artificiallyfavorable environment for plant growth. Since

increasing the intensity of management costsmoney, there is always a tradeoff between theincreased cost and the expected increase inyields. As price relationships change, the inten-

sity of management will also change. A sum-mary of some current agricultural practices

and their costs and energy usage is given be-low.

Aside from weather and soil type, the plant-

ing date, planting density, weed, disease, and

insect control, and tillage practices can all af-fect crop yield. Different plants have differentsensitivities to these various factors. Practicesalso have to be suited to the climate and soil

type that is being farmed. Consequently, thedirect costs of farming will vary depending on

the crop and region. There can even be signifi-cant differences for the same crop within agiven region (e. g., erosion control measures,irrigation, etc.).

A “typical” farming operation for annual

crops such as corn and soybeans, however,might be as follows: After harvest of the cropin the fall the residues are chopped or the soilis disked to reduce the size of the residues andto level the soil. Phosphate and potassium fer-tilizer are broadcast and the residues and fer-tilizer are plowed under. In the spring, surface

tillage to level the soil is done soon after thesoil becomes suitable for tillage. Nitrogen fer-tilizer — anhydrous (dry) ammonia, etc. — ifneeded, is applied to the soil. Five to ten dayslater the soil is surface tilled with a cultivator

or disk and the crop planted. During plantingsome additional fertilizer may be added, an in-secticide may be applied, and herbicides maybe broadcast on the soil surface. The crop may

be cultivated for weed control once or twicewithin the first month of growth. No additional

operations occur until the crop is harvested

with a harvestor that separates the grain andleaves the residue on the field. If the grain hasa moisture content above that needed for stor-age without spoilage, it is dried. The grain maybe fed on the farm, stored and sold later, or

sold directly to a grain company at harvest.

Minimum or reduced tillage operations are

used to reduce soil erosion. With their use thesoil may be chisel-plowed rather than mold-board-plowed so that much of the residue re-mains in the surface. Herbicides may be usedto give complete weed control so that no fur-

ther cultivation is needed.

Forage crop management is considerably

simpler. Since forage crops are usually peren-nials, crop planting is done only once every 4to 5 years, or longer. Aside from planting, theonly management is the application of fer-tilizers and the harvesting of the forage crop.

The estimated costs for producing corn (arow crop) and wheat (a close-grown crop) are

shown in table 22. These costs are fairly repre-sentative of what can be expected for the pro-duction costs per acre for annual crop produc-

tion, with intensive agriculture. Costs will varyfrom place to place, but where costs otherthan land costs are higher and/or yields arelower, the land will be worth less and landcosts will be lower.



Ch. 3—Agr icu l ture . 63

tion and the fuel used for irrigation. Examples

of energy-intensive crops range from corngrown in Nebraska which is irrigated withground water brought to the surface by elec-tric pumps and is dried with liquefied petro-leum, to grain sorghum which has relativelylow yields compared to energy inputs through-

out the United States. Other crops, such asrice, can be even more energy intensive (7.8

million Btu/ton, U.S. average).

For most corn cultivation, over half of theenergy input comes from fertilizer, principallynitrogen. However, without nitrogen fertil-izers, average corn yields would drop fromabout 100 bu/acre to less than 30 bu/acre. Inthe example in table 23, the energy used wouldincrease from 3.0 million to 4.9 million Btu/tonif nitrogen fertilizers were not used, assuming

the above yield change.

The other big energy input for some areas—irrigation —can have the opposite effect. Inthe example given in table 24, the use of irriga-tion raises the energy input from 2.2 million to3.4 million Btu/ton. And in some areas (e.g.,west Texas and southern Arizona), the energy

required for pumped irrigation is more thantwice that shown in table 24.

8In all, 85 percent

of the 58 million acres of irrigated croplandare in the West (Northern Plains, SouthernPlains, Mountain, and Pacific farm productionregions) and 94 percent of the 0.26 Quad/yrused for pumped irrigation in the United States

in 1974 was in the West. 9 On the average, theenergy needed to pump the equivalent of 22inches of rainfall in the West is 6 million

Btu/acre. Consequently, this is a reasonableaverage figure for the energy input due to irri-gation.

Another possible type of energy crop is for-age grass. Currently, little or no fertilizer isused to cultivate forage grass; and yields areabout 2 ton/acre. However, if fertilizers wereused and the crops harvested more times per

year, additional biomass could be obtained.

Table 25 shows the costs of producing grass

“D, Dvoskin, K, Nicol, and E. O. Heady, “ Irrigation Energy Re-

quirements in the 17 Western States,” Agrku/ture and Energy, W,

Locheretz, ed. (Academic Press, 1977)

%. Sloggett, “Energy Used for Pumping Irrigation Water in the

United States, 1974,” Agrku/ture and Energy, W. Locheretz, ed

(Academic Press, 1977).

Table 25.–Estimated Costs of Producing Grass Horbage at Three Yield Levels

Yield level (ton/acre)

2 3 4

Growing costs ($/acre)

Fertilizer . . . . . . . . . . . . . . . . . — 1 9 .4 5b

- 24.42C

41.59d

- 50.70e

Seed and seeding . . . . . . . . . . . 2.30 2.30 2.30Interest and miscellaneous. . . . . 0.22 2.07 - 2.54 4.17 - 5.04

Total. . . . . . . . . . . . . . . . . . . 2.52 23.92 - 29.26 48.06 - 58.04Harvest costs ($/acre)Machine operating. . . . . . . . . . . 8.00 12.00 16.00Interest and miscellaneous . . . . . 0.76 1.14 1.52Machine investment. . . . . . . . . . 34.06 34.06 34.06Hay storageg. . . . . . . . . . . . . . . 0 - 8.72 0 - 13.08 0 - 17.44Labor @ $4/hrh. . . . . . . . . . . . . 3 .68 -11.04 5.52 - 16.56 7.36 - 22 .0 8

Total. . . . . . . . . . . . . . . . . . . 46.50 -62.58 52.72 - 76.84 58.94 - 91.10Total non-land costs $/acre . . . . . . . . . . . . . . . . . . . 4 9 .0 2 - 6 5,1 0 76.54 -106.10 107.00 -149.14$/ton

i. . . . . . . . . . . . . . . . . . . . 27.23 -32.55 28.35 - 35.37 29.72 - 37.29

alncludes cost of apphcatlonb60 lb nitrogen< 20 lb phosphorous pentoxide, 50 lb potassium monoxide/acre.

c&I lb nitrogen, 30 lb phosphorous pentoxlde, 90 lb potassium rnonoxideiacredlso lb nitrogen, 30 It) phosphorous errtoxtde, 60 lb potassiummonoxidelacre

e150 b nitrogen,50 lb phosphorous pentoxide, 150 lb potassium rnmoxldejacre.

‘9-percent interest = O 5% miscellaneous costsgRange from no cost If iarge hay package stored outside to new barn costs for rectangular baleshHlgh labor values for rectangular bale handled by hand, low labor bales for lar9e hay Pa*a9esIAssumes 10% additional storage loss If hay stored outside (average st0ra9e period).

SOURCE. Barber, et al , “The Potential of Producing Energy From Agricult ure, “ Purdue University, contractor report to OTA, May 1979




herbage at various levels of fertilization andgrass production. The additional production is

estimated to cost $28 to $37/dry ton. Noteparticularly that no land charges are includedin these cost calculations, because the use of

the land has not changed. Only the output hasbeen increased. Nevertheless, some farmerprofit in addition to the labor charge may beneeded to induce farmers to increase produc-tion. Furthermore, obtaining the full potential

1OS. Barber, et al., “The Potential of Producing Energy From

Agriculture,” Purdue University, contractor report to OTA, May

1979.

from this resource would require a 50- to 100-percent increase in fertilizer use in agriculture.

With no fertilization the energy used to pro-

duce the grass is about 0.1 million Btu/ton ofgrass at the present estimated level of 2 ton/

acre. At 3 and 4 ton/acre, the additional energy

use is about 1.9 million Btu for the third and2.4 million Btu for the fourth ton. About 0.1million to 0.2 million Btu/ton should be added

to these energy inputs for a 15-mile transportof the grass.

‘}Ibid

Energy Potential From Conventional Crops

Aside from crop residues, the two majornear- to mid-term sources of bioenergy from

conventional crops are grains and sugar cropsfor liquid fuels production and increasedforage grass production, On the land capable

of supporting grain and sugar crop production,grasses could also be grown; and a comparisonof these choices is considered first.

The mechanism through which food andfuel production compete is the increase infarm commodity prices. Since farm commodi-ty prices must rise in order to make it profit-able for farmers to increase the quantity ofland under intensive production, it is impor-

tant to examine the net quantities of premiumfuels that can be displaced, through liquidfuels production, by each of the alternativeswhen new cropland is brought into production.(For details of the energy balances, see ch. 11.)

The calculations for sugar crops and grassesare relatively straightforward, since these feed-stocks have very little protein in them and,

consequently, the byproduct probably has lit-tle value as an animal feed (see “Byproducts”in ch. 8). The distillation of grains, in contrast,

produces a protein concentrate byproduct thatcan displace significant quantities of soybean

meal and thus soybean production. Additionalgrains could then be grown on the land former-ly devoted to soybean production. Estimatesof the effect of this substitution are calculatedbelow.

First, let X represent the number of acres ofaverage soybean production that can be dis-

placed by growing 1 acre of average corn pro-duction, converting the corn to ethanol, and

feeding the byproduct to livestock. Assuming

that the corn yield on marginal cropland (i.e.,the new cropland that can be brought into pro-duction) is y times as great as on average crop-Iand, then 1 acre of marginal cropland grownwith corn for ethanol production results in abyproduct that can displace yX acres of soy-bean production. Planting this yX acres withcorn for ethanol and using the distillery by-product for animal feed displace an additionalyX2 acres of soybeans, etc. In all, the total acre-

age of average soybean production displacedby this marginal acre of corn is:

yx + yx2 + yx3 . . . . = YX (1)1 - x

If Nm and Na are the net premium fuels dis-placement per acre of marginal and average

corn production, then the total net premiumfuels displacement attributable to bringing 1marginal acre into corn production is:

N = N m + N a

( )

y X (2)

1 - x

The ideal crop switching technique wouldbe where X =1, i.e., where one can simplyswitch to another crop which produces all ofthe products of the first crop and liquid fuelsas well, without expanding the acreage under



Ch. 3—Agr icu l ture q 6 5

intensive cultivation. Several imaginative sug-gestions for crop switching have achieved thisideal but none are proven.

2The closest to this

ideal that has been demonstrated is the corn-soybean switch, in which X = 0.77, based onnational average yields of the respectivecrops. * 1 3

Nevertheless, even this switch is

limited by the quantity of land suitable forcorn production and the fact that the corn dis-tillery byproduct is not a perfect substitute forsoybeans in all of its uses. As a fuel ethanol in-dustry is first developing, however, these limi-tations are probably of minimal importance.

Assuming, then, that the distillery byproductis fully utilized and that marginal cropland

produces 75 percent of the yield of average

cropland, OTA has calculated the net premiumfuels displacement per acre of marginal (new)

cropland brought into production for various

liquid fuels options. These include ethanolfrom various grains and sugarcane and bothmethanol and ethanol from grass. The energyinputs were assumed to be national average

energy inputs for the various grains and sugar-cane and 1 million Btu/dry ton for grass** andthe alcohols are assumed to be used as octane-boosting additives to gasoline. The results areshown in figure 12. Although the exact num-bers cannot be taken too literally because of

the various assumptions required to derivethem, the relative values are fairly insensitiveto the assumptions chosen, provided the alco-

hols are used as octane-boosting additives. *Also, utilization of crop residues does not sub-stantially change the results.

Among the grain and sugar crops, corn ap-pears to be the best choice, as long as the dis-

‘2R Carlson, B Commoner, D Freedman, and R Scott, “inter-im Report on Possible Energy Production Alternatives in Crop-

Llvestock Agriculture, ” Center for the Biology of Natural Sys-

tems, Washington University, St. LouIs, Mo , Jan 4, 1979

q The byproduct of 1 bu of corn can displace the meal from

about O 25 bu of soybean. See “Byproducts” under “Fermenta-

tion “‘ ‘Improving SoI/s With Organic Wastes, op . cit

* *One-half that denved above for Increased grass production,

because here it is assumed that the entire grass production goes

to energy

*If the alcohols are used as standalone fuels, the relative val-

ues are similar, but the net displacement is about half that shownIn figure 12

tillery byproduct is fully utilized to displacesoybeans. 1 n this calculation, 2.5 acres of aver-age soybean land plus 1 acre of marginal land,all grown in corn for ethanol production, canproduce an equivalent amount of animal feedprotein concentrate as 2.5 average acres grownwith soybeans, and provide the ethanol as

well. However, as the utilization (i. e., X inequation 2) drops, then grass quickly becomesa superior alternative. If, for example, 1 lb ofdistillery byproduct displaces 0.5 lb of soybeanmeal instead of the maximum of 0.67 lb (seech. 8), then grass and corn would be roughlyequivalent. Similarly if grass yields increase to8 dry ton/acre-yr, then grass would be as goodor better than corn regardless of the byproductutilization. (It should be noted, however, thatthese calculations do not take the economicsof producing ethanol from grass or the diffi-culties of using methanol as an octane-boost-ing additive into consideration. )

Sugarcane appears to be roughly equivalentto grass, but sugarcane can be grown on only alimited amount of U.S. cropland and the etha-nol produced from it would be considerably

more expensive than corn-derived ethanol.Other sugar crops have considerably loweryields than sugarcane.

The exact point where the byproduct utiliza-tion will drop is unknown. Some analyses haveput it at 2 billion to 3 billion gal/yr of ethanolwhen distillers’ grain is the distillery byprod-uct. ‘4 Producing corn gluten meal could, how-

ever, increase this to as much as 7 billion

gal/yr, based on the total domestic use of soy-bean meal for animal feed. ’s As mentionedabove, however, the byproduct is not equiva-lent to the soybean products, so it is unlikelythat one can reach this level with full byprod-uct utilization to displace other crops. For thepurposes of these estimates, it is assumed that2 billion to 4 billion gal/yr of ethanol from corn

“R C. Meekhof, W E. Tyner, and F. D Holland, “Agricultural

Policy and Gasohol,” Purdue University, May 1979. This refer-ence reports a 3-billion-gal limit based on a 2-lb substitution of

distillers’ grain for 1 lb of soybean meal. Other studies, however,

have put the feed ratio at 1 5:1, which would reduce the limit to

2.25 billion gal/yr

“improving Soi/ s With Organic Wastes, op cit.




(about 0.2 to 0.4 Quad/yr) can be producedwhile utilizing the byproducts fully. This wouldrequire about 2 million to 5 million additionalacres in intensive crop production and expan-sion of corn production by over three timesthis acreage. It is not certain that cropland will

be available for energy production by 2000;but if it is, it is assumed that any further pro-duction above this level will use grass as theenergy crop.

In the near to mid-term, increased produc-

tion of forage grass can be obtained on about100 million acres of hayland, cropland pasture,and noncropland pasture. Assuming a 1- to 2-ton/acre-yr increase in yields, this would resultin 100 million to 200 million tons of grass or

about 1.3 to 2.7 Quads/yr. Deducting the ener-gy needed to cultivate and transport the grassreduces the output to about 1.1 to 2.2 Quads/yr.

By 2000 anywhere from zero to 65 million

acres could be used for energy crops. Assum-ing that grasses with average yields of 6 dryton/acre-yr on this cropland have been devel-oped, then the energy potential would be zero

to 5 Quads/yr.

Although adding this to the ethanol yieldfrom corn involves a small amount of double

counting, the uncertainty in the actual crop-Iand availability and future grass yields is toogreat to warrant a detailed separation. Conse-quently, OTA estimates that 1 to 3 Quads/yrcan be obtained in the near to mid-term andzero to 5 Quads/yr in the long term from theproduction of conventional crops for energy.

The above mix of corn and grass was chosenas the one that appears to be the least infla-

tionary to food prices in the long term per unitof liquid fuel produced. However, if 65 millionacres are available for energy production in2000, one could conceivably produce over 15billion gal of ethanol from corn* or about 1.3Quads/yr of liquid fuel. Grass production, on

the other hand, would yield about 2.5 Quads/yr** of liquid fuel from this same cropland andwith the same or lower inflationary impact.

Judging when the emphasis should shiftfrom corn to grass is likely to be difficult. As afallible rule of thumb, however, any significantincrease in corn prices relative to the othergrains would be an economic signal to distil-lers and/or animal feeders to use grains otherthan corn, which would make grass a superioroption for energy production. Similarly a sig-nificant drop in the price of distillery byprod-uct, relative to the alternatives, would be aneconomic signal that the distillery byproductsare not being fully utilized and, again, grasswould be superior. Consequently, if there is asignificant rise in corn prices or drop in distil-lery byproduct prices, relative to the alterna-tives, then these could be indications that thecropland could better be utilized by producinggrass.

*Seven billion gal with complete substitution of soybean meal

and requiring about 10 million of the 65 million acres. The re-

maining 55 million acres, with yields of 65 bu/acre, could pro-

duce an additional 9 billion gal/yr of ethanol.

**5 Quads/yr of grass could yield slightly less than 25

Quads/yr of methanol

Energy Potential From Crop Residues

Crop residues are the plant material left in of soil organic matter. (See also “Environmen-

the field after a crop harvest. Their major func- tal Impacts.”)tion is to protect the soil against wind and wa-ter erosion by providing a protective cover,and they have a modest fertilizer value

16and a Barber, et al., have calculated the total

soil-conditioning value through maintenance quantities of residues by multiplying the crop

“Residues are about O 7 percent nitrogen, O 2 percent phos- yields reported by USDA by residue factors,phorus, and 4 percent potash See Barber, et al., op cit. i . e . , t h e r a t i o o f r e s i d u e t o t h e y i e l d o f t r a d i -



68 . Vol. Ii—Energy From Biological Processes

t ional crop for the various types of crops. ’7The results of these calculations are shown in

table 26. The total quantity of residues gener-ated is about 400 million ton/yr or about 5Quads/yr.

Table 26.-Total Crop Residues in the United States for10 Major Crops (based on 1975-77 average production)

Acres Total residuek acres k tons

Corn. . . . . . . . . . . . . . . . . . . . . 69,530 171,084Wheat . . . . . . . . . . . . . . . . . . . 68,789 99,890Soybeans . . . . . . . . . . . . . . . . . 53,616 67,556Sorghum . . . . . . . . . . . . . . . . . 14,714 21,123Oats. ., . . . . . . . . . . . . . . . . . . 12,831 20,677Barley . . . . . . . . . . . . . . . . . . . 8,772 13,341Rice. . . . . . . . . . . . . . . . . . . . . 2,515 8,584Cotton . . . . . . . . . . . . . . . . . . . 1 0,990 3,578Sugarcane . . . . . . . . . . . . . . . . 660 4,700Rye . . . . . . . . . . . . . . . . . . . . . 715 708

U.S. Total . . . . . . . . . . . . . . . 243,132 411,240

SOURCE. Barber, etal , “ThePotentialofProducingEnergy From Agriculture,’’ Purdue lJnwershIy, contractorreporttoOTA, May1979

During fall plowing many farmers turn under

the residues, rendering them useless as a pro-tection against erosion. These residues couldbe collected and used for energy without wor-sening the erosion on these lands. However,

current agriculture policy is to encouragefarming practices that Iimit soil erosion to thesoil-loss tolerance levels, or the levels of ero-sion that are believed not to impair the long-

term productivity of the land (see “Environ-mental Impacts”). Consequently, a more de-

tailed consideration of crop residues is ap-propriate.

Using data supplied by Dr W. Larson,’* thetotal crop residues were calculated for each ofthe major land resource areas or subregions ofStates. Using standard equations for soil ero-sion,’ the quantities of residues that could beremoved without exceeding standard soil-loss

tolerance values were calculated. These werethen modified to take into consideration thequantities that can be physically collectedwith current harvesting equipment (about 60

percent in field trials at Purdue University). In

171 bid

“W. E. Larson, “Plant Residues–How Can They Be Used

Best,” paper No. 10585, Science Journal Series, SEA-AR/USDA,

1979

q Universal soil-loss equation and wind erosion equation.

addition, a 15-percent storage loss was as-sumed. The results of these calculations areshown in table 27 as the usable crop residues,which are about 20 percent of the total crop

residues.

Table 27.–Total Usable Crop Residue by CropAmount Harvestable acres Average yield

Crops (k tons) (k acres) (ton/acre)

Corn. . . . . . . . . . 37,098 39,122 0.95Small grains . . . . 33,623 36,324 0.93Sorghum. . . . . . . 1,452 4,100 0,35Rice . . . . . . . . . . 5,457 2,516 2.17Sugarcane. . . . . . 590 331 1.78

Total ... , . . . . 78,220 82,393 0.95

SOURCE Barber, et al., “The Potential of Producing Energy From Agriculture, ” Purdue IJnlversl-ty, contractor reporl to OTA, May 1979

H a r v e s t i n g c r o p r e s i d u e s w o u l d t y p i c a l l y

c o n s i s t o f m o v i n g t h e r e s i d u e s i n t o w i n d r o w s ,

or long thin piles of residues. The windrowswould then be collected with baling machinery

and the bales dumped at the roadside. Thewindrows would be collected and transportedto a place where they would be stored or used.

Crop residues typically contain 40- to 60-per-cent moisture 2 days after the grain harvests.In favorable weather conditions, the residues

dry to about 20-percent moisture in 18 days. ”With these moisture contents, bacteria willgradually consume the residues. If the residuebales are compacted too tightly, the heat gen-

erated from the bacterial action can cause thematerial to spontaneously combust. However,with relatively loose bales, the bacterial heat-ing will dry the material to a moisture contentat which the bacteria do not consume the ma-terial. Some loss, however, is inevitable (15-percent loss has been assumed in table 27).

The extra fertilizers necessary to replace thenutrients in the residues removed cost about

$7.70/ton of residue removed.

In addition, one of the main problems withharvesting residues is that it delays the fall

ground preparation. If winter rains come toosoon, there may not be sufficient time to col-lect the residues and prepare the ground for

the spring planting. The spring planting is then

“Barber, et al., op. cit.




delayed and yields for the following year maysuffer. Using computer simulations of farming

operations and the actual weather conditionsin central Indiana between 1968 and 1974, itwas found that residue harvests reduced cornyields by an average of 1.6 bu/acre-yr.

20If this

cost is attributed to the residues, then it raises

the residue costs by $2.70/ton. This factor isless of a problem with most other grains, how-ever, since they are less sensitive to the exactplanting time.

Adding these various costs and assuming a

markup of 20 percent above costs gives theState average costs for various residues (table28). Care should be exercised when using thistable, however, since the costs within a Statecan vary considerably. In favorable cases the

’01 bid

Table 28.–State Average Estimated Usable GroupResidue Quantiti es and Costs

Total usable crop Delivered costa

residues (million ($/ton) (estimatedState tons/yr) uncertainty: 20%))

Corn Illionois . . . . . . . . . . .Indiana . . . . . . . . .lowa ., . . . . . . . . . . .Minnesota . . . . . . . . . .Nebraska. ., . . . . . . . .Ohio ., . . . . . . . . . . .

Small grains California. . . . . . . . . .

Illinois. . . . . ...Minnesota ., . . . . . . . .South Dakota . . . . . .W a s h i n g t o n . . . . .Wisconsin . . . . . . . .

Sorghum grain Colorado . . . . . . . . . .Kansas . . ., . . . . . . .Missouri . . . . . . . .

Rice Arkansas, . . . . . . . . .California. ., . . . . . . . . .Texas . . . . . . . . . . . . . .

Sugarcane Florida. . . . . . . . . . . . . .

8.04.66.94.21.82.6

1.8

1 . 06.11.83.02.0

0.120.720.28

1.91.11.2

0.53

32.1632.4232.7738.6741.6835.18

28.29

31.5330.5433.0531.0126.93

35.60 57.62 36.87

36.3234.8236.08

30.93

costs might be as low as $20/dry ton and, in un-favorable cases, as high as $60/dry ton or more.

Crop residues contain about 13 million Btu/ton. The energy costs for harvesting and trans-porting the residues are about 0.9 millionBtu/ton for a 15-mile transport and 1.8 million

Btu/ton for a 50-mile transport. (With inte-grated residue and crop harvests the energycosts would be slightly less, but this may notbe a practical alternative because it delays theharvest.) In addition, the energy content of the

additional fertilizer needed to replace the nu-

trients lost in the residues is about 0.6 millionBtu/ton. Thus, the total energy use associatedwith collecting and transporting the residues isabout 1.5 million to 2.5 million Btu/ton of resi-due.

National average crop yields can fluctuateby ±± 5 percent or more from year to year and

the usable crop residues will fluctuate by

about ± 10 percent, since an absolute quantityof residue should be left regardless of the cropyield. On a local basis, usable crop residuescan vary considerably. Within a county lo-cated in a humid region of the country, thefluctuation may be ± 20 percent and for cropsthat are not irrigated in dry regions, the year-to-year variations can reach ± 100 percent.The areas with the largest fluctuations, how-

ever, also have the lowest quantities of usableresidues.

In summary, the total crop residue produc-tion in the United States is about 5 Quads/yr,of which about 3 Quads/yr can be collectedwith current harvesting equipment. The quanti-ty that can be collected while maintaining cur-rent soil erosion standards is about 1 Quad/yr.

Considerations of a reliable supply, however,would reduce this to roughly 0.7 Quad/yr* ofreliable feedstock, if soil erosion standards arestrictly adhered to. By 2000, increases in cropproduction could raise this by 20 percent to 0.8to 1.2 Quads/yr.

alncludmg 15-rnlle transport, labor at $5/hr, $0 80/gal diesel fuel, y!eld Penalty of $2 70/lon of

residues for corn, adctmonal ferlhzers for $7 70/ton of residues, and profit of 20 percent ot

costs

SOURCE Barber, et al , < ‘The Potential of Producing Energy From Agriculture, Purdue Unlversl-ly, contractor report to OTA, May 1979

q Calculated by assuming that the total quantity of residue canfluctuate by ± 20 percent at the local level; i.e , by subtracting

20 percent of the total residues from the usable residues on a

State-by-State basis




Environmental Impacts of Agricultural Biomass Production

Introduction Table 29.-Environmental Impacts of Agriculture

American agriculture, with its astonishingproductivity and reliability, bestows criticallyimportant benefits on the economy and gener-

al well being of the United States. Unfortu-nately, it also has serious negative environ-mental impacts. Any substantial increase inland cultivation or intensification of presentcrop production to produce energy crops—biomass–will cause an extension and intensi-fication of many of the impacts of the present

system.

There are substantial uncertainties in the

understanding of the consequences of relyingon agricultural feedstocks for energy produc-tion. These uncertainties stem from a lack of

complete understanding of present impacts,the potential for changes in crop productionmethods in the future, and uncertainty as to

the pace of development. This section at-tempts to place the potential impacts of large-scale biomass production from agriculture into

perspective by briefly describing what isknown of the impacts of food crop production

(the energy feedstock production systemshould resemble the food production system),describing how the pace of development mayintensify impacts, and finally identifying thosedifferences between food and energy feed-

stock production that are most critical indetermining impacts.

The Environmental Impacts ofAmerican Agriculture

Agriculture is a major source of pollutionand causes serious environmental impacts.Table 29 lists the major environmental impactsassociated with present forms of large-scalemechanized agricultural production. Most ofthe impacts apply to the majority of farming

situations (although with varying magnitude),but some impacts are negligible or nonexistentin certain situations. Also, most of the impacts

are more or less controllable, but for a varietyof reasons (a high perceived cost or negative

Water use (irrigated only) that can conflict with other uses or causeground water mining.Leaching of salts and nutrients into surface and ground waters, (and

runoff into surface waters) which can cause pollution of drinking watersupplies for animals and humans, excessive algae growth in streamsand ponds, damage to aquatic habitats, and odors.Flow of sediments into surface waters, causing increased turbidity,obstruction of streams, filling of reservoirs, destruction of aquatic hab-itat, increase of flood potential.Flow of pesticides into surface and ground waters, potential buildup infood chain causing both aquatic and terrestrial effects such as thinningof egg shells of birds.Thermal pollution of streams caused by land clearing on stream banks,loss of shade, and thus greater solar heating. -

Air • Dust from decreased cover on land, operation of heavy farm machin-

ery.q Pesticides from aerial spraying or as a component of dust.q Changed pollen count, human health effects.q Exhaust emissions from farm machinery.

Land q

q

q

q

q

q

Erosion and loss of topsoil from decreased cover, plowing, increasedwater flow because of lower retention; degrading of productivity.Displacement of alternative land uses–wilderness, wildlife, esthetics,etc.Change in water retention capabilities of land, increased flooding po-tential.Buildup of pesticide residues in soil, potential damage to soil microbialpopulations.Increase in soil salinity (especially from irrigated agriculture), degrad-ing of soil productivity.Depletion of nutrients and organic matter from soil.

Other q Promotion of plant diseases by monoculture cropping practices.q Occupational health and safety problems associated with operation of

heavy machinery, close contact with pesticide residues and involve-ment in spraying operations.

SOURCE Office of Technology As sessment

effect on crop yields are almost certainly themost important) many control techniques arerarely used.

Water pollution and land degradation dueto erosion are American agriculture’s primaryproblems, and the two impacts are intimatelylinked. The action of wind and water stripsfarmland of its productive topsoil cover, and

much of this soil ends up in the Nation’s water-ways. Thus, estimates of soil erosion are criti-cal to understanding the effects of agriculture

on both soil productivity and on water ecosys-tems.




SCS has recently revised downward its esti-mates of cropland erosion. Its 1977 NationalErosion Inventory estimates average annualsheet and rill erosion from all cropland to be4.77 ton/acre-yr (or a total of about 2 billionton/y.

21Previously, it had estimated cropland

sheet and rill erosion at about 9 ton/acre-yr,22

and other sources had estimated total erosion(including wind erosion) from croplands to be

as high as 12 ton/acre-yr.23

SCS attributes thedecrease to the greatly improved data base re-

cently made available by the 1977 Inventory.

Also, the original 9-ton/acre-yr estimate appar-ently referred only to land in row crops, close-grown crops, and summer fallow, whereas themore recent estimate includes lands that are inless intensive (and less erosive) uses such asrotation hay and pasture, or native hay.

Data from the 1977 Inventory has only re-

cently begun to be released to the general pub-lic, and it seems likely to generate contro-versy — especialIy because its estimate of aver-age erosion is under the 5 ton/acre-yr that SCSgenerally considers to be a tolerable level (i. e.,a level that wilI not affect long-term produc-tivity) for much U.S. cropland. However, thelower estimate is not especially comforting fora number of reasons:

q National (sheet and rill) erosion rates forcropland in intensive production are esti-mated by SCS to be 6.26 ton/acre-yr.

q

The national estimate tends to hide sever-al important food-producing areas withuncomfortably high erosion rates (e. g.,Missouri averages 11.38 ton/acre-yr; Iowaaverages 9.91 ton/acre-y r).

q The estimates do not include wind erosion

and alternative forms of water erosion.

Cropland wind erosion in 10 westernStates averages 5.29 ton/acre-yr. Thus, al-though Texas cropland has a sheet and rillerosion rate of only 3.47 ton/acre-yr, its to-tal erosion rate is greater than 18 ton/acre-yr because of wind erosion.

“1977 SCS Natfona/ Erosion Inventory Estimate, op. cit.

’21 bld“D Plmentel, et al , “Land Degradation, Effects on Food and

Energy Resources, ” Science, VOI 194, Oct 8, 1976

q

q

q

Although SCS generally considers 5 ton/

acre-yr as an (average) annual erosion atwhich long-term productivity on goodsoils will not suffer, it is not certain thatsoil is actually replaced this fast. Authori-tative estimates of soil replacement ratesdo not exist, but average rates of as low as

1.5 ton/acre-yr have been claimed. z’ How-ever, the SCS rates do represent the gener-al consensus of the agronomy community.Even the new lower erosion rate implies

that about a billion or more tons of sedi-ment from croplands are entering the Na-tion’s waterways each year.25

Erosion rates from croplands are manytimes higher than those of natural ecosys-tems. Forests typically erode at a rate ofless than one-tenth of a ton/acre-yr, andgrassland at less than half a ton/acre/yr.

26

As a result of the mismatch between erosionand soil replacement, the United States haslost a considerable portion of its topsoil and,some have claimed, its production potential.Pimentel estimates that U.S. cropland has lostabout one-third of its topsoil and 10 to 15 per-cent of its production potential over the last200 years.

z’ Bennett estimates that, during the

period prior to 1935, 100 million acres of crop-I and were lost to erosion and an additional 100

million acres were stripped of more than halfof their topsoil .28 At best, however, these val-ues represent extremely rough estimates, and

the new SCS erosion inventory may cause theirdownward revision.

It appears likely that the process of land

degradation will continue for the immediatefuture. Although USDA has spent nearly $15billion in its soil conservation programs sincetheir inception in 1935,29 only 36 percent of the

“Ibid

“Environmental Implications of Trends in Agric ulture and Slvi-

cu/ture– Vo /ume 1: Trend Identific ation a nd Evo/ ution (Washing-

ton, D C Environmental Protection Agency, October 1977),

EPA-60013-77-I 21‘61 bid

*7D Pimentel, op cit

“H H Bennett, So;l Conservat ion (New York. McGraw-Hi l l ,1939),

“TO Protect Tom orrow ’s Foo d Supp/y , Soi/ Conservation Needs

Priority Attention (Washington, D C : General Accounting Of-

fice, Feb 4, 1977), CED-77-30




472 million acres of cropland in 1967 werejudged to have adequate conservation treat-ment30 and the programs have been criticizedas inadequate by the General Accounting Of-fice.31

A reason for the inability of USDA conserva-

tion programs to satisfy their critics may be thedifficulty of demonstrating to the farmer (in allbut the more severe cases) the benefits of addi-tional conservation measures. Because an inchof topsoil weighs about 150 ton/acre, a net lossof 5 ton/acre-yr would result in a loss of 1 inchof soil every 30 years. During that time, farm-ing procedures would be gradually changing,

obscuring the effects of any soil loss. For exam-ple, during the past 30 years, more intensiveuse of fertilizers, pesticides, and other inputs,better information on future weather andother critical factors, and improved crop varie-

ties more than compensated for erosion-caused losses on most lands. Also, the actualeffect on productivity may not be large insome circumstances because the effect of soil

loss is very sensitive to soil conditions: whileloss of soil from a very shallow soil over rock inKentucky may cause the land to be withdrawnfrom production, on some deep Ioess soils oflowa, the loss of several inches of topsoil mayhave little effect on productivity. Few if anyagricultural scientists would argue that net soilloss can continue indefinitely without majorlosses in productivity. However, on many lands

the damages of erosion may never become vis-ible to the farmer; rather they will be perceived

by his children or grandchildren. Moreover,short-term economic constraints may compel afarmer to discount the future benefits of con-servation by much more than he would person-ally prefer.

Aside from the long-term consequences inland degradation, soil erosion represents a

severe water pollution problem. Not only issoil itself a serious pollutant, it also acts as acarrier of other pollutants: phosphorus, pesti-

cides, heavy metals, and bacteria.

32

The soil

‘“’’Potential Cropland Study, ” Statistical Bulletin No. 578, Soil

Conservation Service, U.S. Department of Agriculture, 1977.31 T. protect Tom orrow ’s Food SUPp / Y, OP. cit.

Jl~nvjronmental /mp/ications of Trends, OP. cit.

lost to agricultural erosion represents morethan half of the sediment entering the Nation’ssurface waters. 33 34 Sediment causes turbidity,fills reservoirs and lakes, obstructs irrigation

canals, and destroys aquatic habitats. Yearlymaterial damages have been estimated at over

$360 million,35

not including damage to aqua-

tic habitats and other noneconomic costs.Adding the flooding damage caused by the de-

crease in storage capacity of reservoirs andstreams would increase annual costs to over $1billion.

36

The effects on aquatic ecosystems of the

enormous flow of sediments into the Nation’swaterways have never been satisfactorily esti-mated. Research on the impacts of “nonpoint”sources of water pollution—agriculture, con-struction, etc. –has not been given a high pri-ority within the Environmental Protection

Agency (EPA) or USDA, and the result is a scar-city of information from which to draw conclu-sions about either present impacts or futureimpacts associated with the devotion of mil-

lions of additional cropland acres to biomass

production.

The other major water pollution problems ofagriculture involve the toxic effects of pesti-cides and inorganic salts and the nutrient in-flux into the Nation’s waterways associatedwith American agriculture’s increasing use offertilizers.

Pesticide use in American agriculture hasgrown from 466 million lb in 197137 to 900million lb in 1977.38 By 1985, American farmersare expected to be using as much as 1.5 billion

lb.39 Much of this increase can be traced to thegrowth in minimum tillage practices40 which

substitute increased herbicide use for tillage tocontrol weeds. These practices include leavingcrop residues on the soil surface, and theseresidues harbor plant pests and pathogens and

generally increase pesticide requirements (al-

‘]Ibid.

“Pimentel, op. cit.357977 SCS Nationa/ Erosion /nventOry f5t;mafe, 0p. cit.

“Ibid.

“ Environmenta l /mp / i ca t i ons of Trend s, op. cit.‘S7977 SCS National Erosion Inventory Estimate, op cit.

‘;l bid,

40[nvironmenta/ Implications of Trends, op. cit.




though they offer substantial benefits in ero-sion control). Recent growth in the practice ofsingle- and double-cropping may also accountfor some of the increase. Although less than 5

percent of the pesticides enter the surface andground water systems, ” pesticide use has beenassociated with fish kills and other damage toaquatic systems as well as reproductive fail-ures in birds and acute sickness and death inanimals. Under conditions of high exposure—in accidental spills, improper handling by ap-plicators, etc. —pesticides have been associ-ated with the sickness and death of humans.Recent research has implicated some widely

used pesticides as possible carcinogenicagents when ingested or inhaled, and EPA hasremoved certain of these— including Aldrin,Dieldrin, and Mirex–from the marketplaceunder the Federal Insecticide, Fungicide, andRodenticide Act (FIFRA). Amendments toFIFRA have considerably tightened the require-ments for testing and registering pesticides.However, the tremendous variety of pesticidecompounds [“1 ,800 biologically active com-pounds sold domestically in over 32,000 dif-ferent formulations”42

) and the difficulty ofdetecting damages in human populations andin the environment will greatly complicate suc-cessful enforcement of the Act. At present, thelong-term impacts of pesticides on the environ-ment and on man are poorly understood.

The problems of pesticide use in agriculture

are becoming particularly visible because ofa recent rash of instances where pesticidesthought to be safe have been accused of caus-ing severe injuries — including birth defects,miscarriages, and other acute physical disor-ders–and death to exposed populations, Thecontroversy surrounding the use of the her-bicide 2, 4, 5-T in Oregon and its suspension byEPA is a widely publicized– but by no meansunique —example of rising national concern.Resolution of the conflicting claims about thesafety (or lack of it) of these pesticides is wellbeyond the scope of this report. Based on cur-

rent interest, however, it is likely that a majorpublic concern associated with any large in-

4’ I bid421977 SCS Nat;ona/ Erosion Inventory Estimate, op. cit .

crease in crop cultivation will be the concur-rent increase in pesticide use on the new lands.There is a distinct possibility that rising public

concern over pesticide usage could put a se-vere constraint both on the continuing in-crease in this usage and on the expansion ofcrop production for energy feedstocks.

Salinity increases caused by irrigated agri-culture present another substantial impact. lr-rigated land produces one-fourth of the totalvalue of U.S. crops, mostly in the 17 western

States. ’J Increased salinity in streams in theseareas is caused by the salts added to irrigationwater from upstream farms and by the concen-trating effect of the high evaporation rates inarid climates (evaporation leaves the salts be-hind). The same mechanisms can lead to in-creasing salt concentrations in the soils ofdownstream farms unless sufficient water can

be obtained to periodically flush excess saltsout of the soil profile. Damages associatedwith increased salinity of soils and irrigationwater include reduced crop yields, inability togrow salt-sensitive crops, increased industrialtreatment costs, and adverse effects on wild-life, domestic animals, and aquatic ecosys-tems. Trends in irrigated agriculture are lead-ing to improvements in irrigation efficiencyand decreased salt loadings in streams, but

these trends could be overwhelmed by sub-stantial increases in irrigated acreage either togrow crops for energy or to compensate for

competition between food and biomass pro-duction in other areas.

Fertilizer use is of extreme importance incalculating the environmental impacts of agri-

culture. Large amounts of energy— one-thirdof the energy consumed by the agriculturalsector and its suppliers— are needed to pro-duce fertilizer. The Haber-Bosche process forthe synthesis of anhydrous ammonia fertilizerrequires around 21 ft3 of natural gas to pro-duce 1 lb of nitrogen in fertilizer (and more forother forms of nitrogen);44 current U.S. nitro-

gen fertilizer production is 10 million metric4’1 bid

“C. H. Davis and G M Blouin, “Energy Consumption In the

U.S. Chemical Fertilizer System From the Ground to the

Ground,” Agriculture and Energy, W. Lockeretz, ed. (New York:Academ~c Press, 1977), pp 315-371

67-968 0 - 80 - 6




tonnes per year consuming 3 percent of totalU.S. natural gas production. If current trendsof increased rates of fertilizer applicationscontinue and food demands increase by 3 per-cent per year, natural gas requirements for fer-tilizer production will triple by 2000.45

The application of large quantities of chemi-cal fertilizers also represents a water pollutionproblem because much of the nutrient valueends up in the Nation’s waterways. Wittwerestimates that only 50 percent of the nitrogenand less than 35 percent of the phosphorus andpotassium applied as fertilizer are actually re-covered by crops;46 other estimates for nitro-gen range from 46 to 85 percent. 47 Although a

portion of that which is lost is due to volatiliza-tion (and consequent loss to the atmosphere),much is lost to surface and ground waters viarunoff, leaching, and erosion processes. The

amount of nitrogen and phosphorus (potassi-um is not considered to have significant en-vironmental impacts48) entering the waterwaysfrom agricultural lands in the early 1970’s hasbeen estimated at 1,500 million to 15,000 mil-lion lb/yr and 120 million to 1,200 million lb/yr,respectively.49

This nutrient pollution from fertilizers maybe toxic to humans and wildlife in high concen-trations; nitrate poisoning of wells from con-taminated ground water is not unusual in someagricultural areas. The more common impact,however, is to speed up eutrophication of

streams and the problems of oxygen demandand algae growth associated with eutrophica-tion.

The remaining major water-associated im-

pact of agriculture is water use. The appropria-tion water rights system in the West offers lit-tle incentive to use water efficiently. * The

45S. H Wittwer, “The Shape of Things to Come, ” l?io/ogy of

Crop Productivity, P. Carlson, ed. (New York: Academic Press,1978),

*bIbid

47Environmenta/ /mp / i ca t i ons of Trends, op. cit.

‘al bid,

“Ibid.*For an excellent review of Western water law see E, Radose-

vitch, “Interface of Water Quantity and Quality Laws in the

West, in Proceedings of the Nat iona / Conference Irrigation Return F/ow Quantity Management, J. P. Law and G V. Skogerboe,

eds. (Fort Collins, Colo.: Colorado State University, 1977).

combination of artificially low prices for waterand the requirement of the appropriation doc-trine that the holder of a water right mustmaintain that right through use (“use or lose”)has led to the cultivation of water-intensivecrops in arid climates. This has led to watershortages in many Western basins and to ag-

gravation of salinity problems in several majorrivers.

Several water use trends will affect agricul-tural production capabilities in the near fu-ture. First, large-scale energy development—especially electrical generating stations and,possibly, synthetic fuel plants–will consumesubstantial quantities of water and, in somecases, compete directly with agricultural inter-ests for the limited supply. Second, expandedacreage for food production will occur, in-cluding projects on Indian land that may have

priority rights to the limited water supply. Onthe other hand, improvements in irrigation effi-ciency will have some conserving effect on wa-ter consumption even though this is not a pri-mary goal of efficiency increase (the primary

goal is to reduce water withdrawals and ‘returnflows and to improve water quality rather thanto reduce consumptive use). For example, SCSestimates that irrigated acreage in the criticalUpper Colorado River Basin could increasefrom 1,370,000 acres in 1975 to 1,442,000 acresin 2000 while water consumption declines by93,000 acre-ft with a concerted program to im-

prove irrigation practices.

so

Further decreasesin water consumption are possible by “cropswitching” — shifting to less water-intensivecrops where markets are available—and re-moving marginal, low-productivity land fromcultivation.

51 Also, substantial potential for

water conservation exists in energy produc-tion.

Much of the agricultural land in the UnitedStates was’ obtained by forest clearing or plow-ing native grasslands, and the consequent re-placement of natural ecosystems with inten-sively managed monoculture must be consid-

50Conservation Needs Inventory (Washington, D. C.: Soil Con-

servation Service, U.S. Department of Agriculture, 1976).

51S. E Plotkin, H. Gold, and 1. L. White, “Water and Energy inthe Western Coal Lands,” Water Resources Bu//e t in , vol. 15, No.

1, February 1979.




ered a major environmental impact of agricul-tural production. (This process is not a one-waystreet. A combination of changing crop pat-terns, alternative producing areas, increasingaverage productivity, and, especially in the

South, depletion of soils has led during thiscentury to the abandonment of considerablefarmland acreage and, in many cases, rever-sion to second-growth forest. Principle areasinvolved in this transformation include thePiedmont areas of the Southeast, the hillier

areas of the Northeast, and the upper lakeStates. However, farm abandonment no longerappears to be a significant force.52) Aside fromthe loss of esthetic and recreational values,this replacement represents a substantial de-cline in wildlife diversity, loss of watershedprotection, and the loss of the alternativewood (or other) resource. At present, this loss

involves a bit over 400 million acres of desig-nated cropland53

and will probably increaseunless crop production efficiency can keeppace with the rising demand for food. Also, be-cause millions of acres of cropland are losteach year to roadbuilding and urban develop-ment, merely the maintenance of the statusquo demands continued clearing of unman-aged and lightly managed lands for crop pro-duction.

1973=74: A Case Study inIncreased Cropland Use

54

In 1973, USDA told American farmers thatthey would be free to plant as many acres ofwheat, corn, and feed grains as they wishedduring the 1973-74 season. In response, 8.9million additional acres were planted andharvested during that season:

. 3.6 million acres from grassland,

• 0.4 million acres from woodland, andq 4.9 million acres from idle cropland and

set-aside land.

The results of this new agricultural produc-

tion may provide a basis on which to predict

‘2M Clawson, “Forests in the Long Sweep of American His-

tory, ” Science, VOI 204, j une 15, 1979

5JPotentia/ Crop/a nd Study, op cit

“Adapted from K E Grant, Erosion 1973-74: The Rec ord and

the Cha/ /enge,

the potential impact of a surge in productioncaused by incentives to grow crops for biomassenergy production.

Of the 8.9 million acres, SCS estimated that5.1 million acres had inadequate conservation

treatment and water management, and 4 mil-

lion acres had inadequate erosion control.These problems in land selection and environ-mental planning were soon translated intosevere erosion losses. Although poor weatherconditions (fall and winter drought in thesouthern high plains, spring floods in the north-ern Great Plains, torrential spring rains fol-lowed by drought in the Corn Belt) aggravated

these losses, most observers appear willing toplace a major blame on the farmers’ land se-lection and inattention to erosion control prac-tices.

Soil losses on the additional acreage duringthe 1973-74 season averaged over 6 ton/acreover and above expected losses without pro-duction. Those lands designated as sufferingfrom inadequate conservation treatment lost

an average of more than 12 ton/acre above ex-pected losses. First-year erosion losses are ex-pected to be lighter than subsequent years be-cause the root structures of the original covercrops are not totally destroyed by tilling andprovide some protection to the soil until theydecompose; thus, erosion rates would be ex-pected to rise still further unless conservation

practices were begun.

The hardest hit of the agricultural regionswere the Corn Belt (390,000 acres, 15 to 100

ton/acre additional soil loss on the new land),western Great Plains— North Dakota, Mon-tana, Wyoming, eastern Colorado (325,000acres, 5 to 40 ton/acre), eastern Great Plains —Nebraska, Kansas, South Dakota (260,000acres, 5 to 55 ton/acre). Great Lakes (195,000acres, 5 to 55 ton/acre), and the southernCoastal Plains of Florida, Georgia, Louisiana,Alabama, and Mississippi (210,000 acres, 5 to

70 ton/acre). In addition, a number of otherproducing regions experienced high soil losseson the additional acreage.

High as these soil losses were, however, theyare not unusual when compared to losses suf-




fered by land in continuous production. Asnoted previously, many areas that are criticallyimportant to U.S. grain production routinely

lose soil at rates well above the 5-ton/acre-yrmaximum recommended by SCS. Assumingthat much of the converted land was taken outof relatively nonerosive uses (the 4 millionacres of grassland and woodland, nearly halfthe total, would have suffered virtually noerosive losses if left undisturbed), the erosionexperienced on the additional acreage was

only slightly worse than the average erosionrates on all U.S. cropland. On the other hand,the lands designated as inadequately pro-tected did have much higher erosion than aver-age. The conclusion appears to be that a rapidincrease in land under production will not nec-essarily cause proportionately more erosionthan our current experience would lead us to

expect, but that conservation planning andtreatment will be required to keep erosionrates from escalating beyond current rates.

Potential Impacts of Production ofBiomass for Energy Feedstocks

Most proposals for using the agricultural sys-

tem to produce energy feedstocks do not con-template growing and harvesting systems thatappear to be radically different from currentlarge-scale mechanized food-growing systemsfound in the Corn Belt and other centers of

American agriculture. Proposals centeringaround gasohol, for example, assume that atleast the near-term feedstock (after foodwastes and spoiled grains are used up) will becorn and other conventional starch or sugarcrops. Even the more radical systems—for ex-ample, tree plantations — can be viewed as var-iations of common agricultural systems.

The key to identifying the impacts of imple-

menting the various approaches to energyfeedstock production is to identify those dif-ferences from today’s systems that are most

critical to causing differences in the impacts.These differences in impacts primarily depend

on differences in:

quality and previous use of the land,

q production practices, andq type of crop grown.

Land Quality and Previous Use

The land available for growing biomass

crops consists of cropland that is presently notin intensive use— for instance, land used togrow native hay— and land currently in range,

forest, or other use that can be converted tocropland. Table 30 presents SCS estimates of

cropland not currently being utilized to itsmaximum production potential, and landavailable for conversion to cropland in 1977.(The acreage “not in intensive use” includesland where the current use meshes with thefarmers’ desired mix of livestock and crops and

thus is unlikely to be converted to more inten-sive use; thus, the table may overestimate the

acreage available for switching to biomass pro-duction.) Table 31 presents SCS estimates ofthe rates of erosion on these lands, by Iand useand capability class.

The data shows that there is a very substantialamount of land available for biomass productionthat could be cultivated with few environmentalproblems. For example, table 30 shows well

over 3 million acres of the highest quality

(class I) land with high and medium conversionpotential. Over 10 million acres of high-qualityclass I I (for brief definitions, see table 30) land

requiring some drainage correction is avail-able. However, there currently is no guaranteethat land for biomass production will be selectedfor its environmental characteristics. Erosion po-tential, which is of critical environmental im-portance, is only one of several characteristics

used by farmers to decide whether to put landinto production. Characteristics such as con-tiguity of land, current ownership, and the costof conversion may be the deciding factors.

According to table 30, farmers currentlyhave biased their choice of land for row cropcultivation somewhat in favor of the lesserosive lands. Over 11 percent of land in row

crops is prime class I land with both high pro-ductivity and minimal erosion. In contrast,

other land uses typically have about 4 or 5 per-




Table 30.–1977 Cropland and Potential Cropland Erosion Potential (in thousand acres, % of total acreage)

Present croplandnot in intensive use

(rotation hay and

Present cropland in intensive usepasture, occasionally

improved/native Potential cropland

Class Row crops Close-grown crops hayland) High potential Medium potential

1. Excellent capability, few restrictions. . . . . . . . . . . . . . . . 23,034(11.3)

Il. Some limitations, require moderate conservation practicesErosive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45,954

(22.6)Other problems ... ... . . . . . . . . . . . . . . . . . . . . . 58,657

(28.9)Ill. Severe limitations, reduced crop choice and/or special

conservation practices requiredErosive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28,054

(13.8)Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27,676

(13.6)IV. Severe limitations, more restricted than above

Erosive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9,159(4.5)

Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5,436(2.7)

V-VIII. Generally not suited. . . . . . . . . . . . . . . . . . . . . . . . 5,728(2.6)

Total, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203,243Percent of land that is erosive . . . . . . . . . . . . . . . . . . . . . . 40.9

4,471(3.4)

23,463(22.4)22,762(21 .7)

26,997 (25.7)10,811(10.3)

9,324(8.9)2,933(2.8)

345(0.3)

104,89057.0

2,389(4.2)

11,718(20.8)9,855

(1 7.5)

12,561(22.3)6,557

(1 1.6)

5,701(10.1)3,154(5.6)4,479(7.9)

2,186(5.5)

10,543 (26.3)8,278 (20,7)

7,893(19.7)4,797

(12.0)

1,896(4.7)1,601(4.0)2,888(7.2)

1,412(1 .5)

13,921(14.8)10,750(11 .3)

25,142(26.7)12,703(13.4)

11,531(12,3)7,210(7.6)

12,248(13.0)

56,414 40,08253.1 50.7

94,91753.4

SOURCE 1977S011 Corrsewahon Serwce Naflona/Eros~on /rrventory Eshrrale (Washington, D C SoIl Conservation Service, U S Department of Agriculture, DecemtNr 1978)

Table 31 .–Moan National Erosion Rates by Capability Class and Subclass (rates are in ton/acre-yr)

Potential

Class/subclass Row crop Close grown Nonintensive

Class 1. Excellent capabil ity, few restrictions . . . . . . . . . 3.46” 1.75 0.66

Class Il. Some limitations, require moderate conservationpractices/erosive . . . . . . . . . . . . . . . . . . . . . . . . . . 6.51 3.67 0.96Class n/other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.46 2.55 0.43Class Ill. Severe limitations, reduced crop choice and/or

special conservation practices required/erosive . . . 12.39 6.62 1.51Class Ill/other. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.41 2.51 0.51Class IV. Severe limitations, more restricted than

I ll /erosive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.88 12.20 2.93Class IV/other. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.52 1.85 0.45Classes V-VIII. Generally not suited/erosive . . . . . . . . . 46.82 19.61 5.42Classes V-Vlll/other. . . . . . . . . . . . . . . . . . . . . . . . . . 14.26 3.27 0.80

High Medium

0.31 0.35

0.67 0.710.30 0.31

1.08 1.280.21 0.28

2.01 2.280.46 0.432.38 4.151.51 0.38

SOURCE 1977 Sod Conservaflori Serwce Naf~ona/ Erosion Irwentory Estmate (Washington, DC SoIl Conservation Service,U SOepaflment of Agriculture, December 1978)

cent of their land classified as class 1. In land towards use of less erosive land is not surpris-

quality classes I through IV, 43 percent of the ing.row-cropped acreage is erosive, whereas over50 percent of every other land use category is Close-grown crop cultivation is considerably

erosive. Because row crop cultivation is gener- Iess erosive than row cropping. Apparently in

ally the most vulnerable to erosion, this bias response to this, farmers have placed close-



78 q VOl. II—Energy From Biological Processes

grown crops on lands that are more vulnerable

to erosion; 60 percent of close-grown croplandacreage is erosion-prone.

It is important to look beyond these overallpercentages and examine the percentage ofland in each land use capability class. The

erosivity of lands categorized as E (erosive] bySCS appears to be a strong function of thecapability class. For example, the average 1977 annual sheet and rill erosion rates on erosivecroplands in intensive use were estimated tobe (from table 31 ):

Class I . . . . . . . . . . . . . . . . . . . 3.18 ton/acre-yrClass IIE. . . . . . . . . . . . . .....5.55Class IIIE . . . . . . . . . . . . .....9.56Class IVE . . . . . . . . . . . . ....15.02Class V-VIIIE . . . . . . . . . ....34.70

Thus, the erosion danger appears to increase

markedly as land capability declines. If theerosive portions of the land with future bio-mass potential (present cropland not in inten-sive use and land with switching potential)were skewed towards the lower quality classes,then an examination of the overall erosivepotentials would underestimate the erosiondanger presented by massive shifts to intensive

cultivation. An examination of table 30 in-dicates that the erosive portions of the presentcropland not in intensive use and the high-potential land are somewhat skewed towardsthe lower quality lands when compared with

present cropland, but the differences do notappear to be substantial. For example, whereas53 percent of erodible land in intensive use isclass I I I E or below, 60 percent of erodible landwith high biomass potential is in this erosivityrange.

The surprising implication of the statisticspresented in table 30 is that the land availablefor agricultural biomass production is not radical-ly different in its erosion qualities from land cur-rently being utilized for intensive agricultural pro-duction. Although clearly some selection hasbeen made in utilizing the best lands and keep-ing idle the worst, this selection process ap-

pears to have been skewed by other physical

attributes and economic and social factorsthat are as important or more important than

erosion potential. It appears that erosion prob-

Iems will be significant in adding new lands tointensive agricultural production, but it doesnot appear on a national basis that these prob-Iems will be very much worse than those thatcould be predicted by extrapolating from cur-rent erosion rates.

It is possible to estimate quantitatively thegeneral erosion danger from an expansion of

intensive production by utilizing the data intables 30 and 31 and by making the followingsimplifying assumptions:

q

q

q

The 1977 erosion rate for land under inten-sive production, for each land capabilitysubclass, is representative of the erosionthat would occur if additional land in thatsubclass were to be put into intensive pro-duction.

Given a desire to place additional land

into intensive production, farmers will se-lect land mainly from cropland not now inintensive production and “high potential”land, and their selection will be random

(this is probably a “worst case” assump-tion but may not be seriously in error judg-ing from the discussion above).

A mix of row and close-grown biomass

crops will be grown, with the mix beingabout the same as the 1977 food crop mix.

Under these conditions, the average erosion

rate on the new land put into intensive produc-

tion will be about 7.5 ton/acre-yr. For compari-son, the 1977 erosion rate on intensively culti-vated lands was 6.26 ton/acre-yr. In otherwords, erosion from additional acres devotedto growing biomass crops may be about 20 per-cent worse than similar acreages of food cropsin production today (this assumes no Govern-ment action to improve land selection). Given

the substantial uncertainties in this estimate,the 20-percent differential is well within therange of possible error. It is, however, consist-ent with what is known about agricultural landselection and the quality of available (but un-

developed) farmland.

Because land quality is affected by net rath-er than gross erosion — i.e., by the differencebetween erosion and soil replacement–the ef-fect on the land of relatively small changes in




erosion rates may be greater than would be ap-parent at first glance. For example, if the aver-age topsoil replacement rate is 5 ton/acre-y r,*the 7.5 ton/acre-yr biomass erosion rate yieldsa 2.5 ton/acre-yr net soil loss, versus 1.26ton/acre-yr net loss from food production.Thus, while a large-scale expansion of acreage

for biomass production may have effects onwaterways that are similar in magnitude to theeffects of present intensive agriculture, thisacreage may lose its topsoil layer at twice therate of current agricultural land. However, itshould be noted that the rate of loss is (on theaverage) fairly low.

Aside from new biomass cropland’s capabili-

ty to resist erosion and its productive poten-tial, an important factor determining the en-vironmental impact of the conversion to inten-sive production is the nature of the previous

land use. For example, the conversion of landin rotation hay and pasture to intensive cropproduction would clearly be valued differentlyfrom a conversion from forest. Because differ-ent groups value alternative land uses differ-ently, it is difficult to place more or less weighton the conversion of one land use relative to

another. It seems likely, however, that most en-vironmentally oriented groups would prefer tosee the conversion of lands that are manmademonoculture (e. g., improved haylands) beforemore natural and diverse ecosystems wereconverted.

The cost of conversion will play an impor-tant role in determining which lands will bechosen. At the present time, conversion of pas-tureland and hayland is likely to be less expen-sive than conversion of forest, and land con-versions may be expected to be skewed awayfrom forests. Least expensive of all to convertare lands currently in set-aside, and these arelikely to be the first to be taken. The cost offorest conversion may, however, be loweredsignificantly if the demand for wood-for-ener-gy rises with the demand for energy crops (be-

cause the value of the now-worthless cullwood and slash can be traded off against clear-ing and site preparation costs). Thus, there is

‘This IS almost certainly very optlmlstlc, but SCS guidelines

def Ine 5 ton/acre-yr as an acceptable rate for many lands

no guarantee that forests—which make upabout one-quarter of the high- and medium-po-tential cropland55 — will not be cleared in sig-

nificant quantities if large-scale conversion tobiomass crop production occurs.

Production Practices

A variety of practices are available to con-

trol the erosion and other impacts of farming.These range from crop rotation to conserva-

tion tillage to scouting for pest infestations.Table 32 provides a partial list of these prac-

Table 32.–Agricultural Production PracticesThat Reduce Environmental Impacts

Runoff and erosion control Contour farming or contour stripcroppingTerraces and grass waterwaysMinimum tillage and no-tillCover crops

Reducing fall plowing

Reducing chemical pollution Scouting (monitoring for pest problems)Disease- and insect-resistant cropsCrop rotationIntegrated pest managementSoil analysis for detecting nutrient deficienciesNitrogen-fixing cropsImproved fertilizer and pesticide placement, timing, and amountImproving irrigation efficiency-trickle irrigation, etc.Incorporating surface applications into soil

SOURCE Office of Technology As sessment

tices. Their future use will play a critical role indetermining the environmental impacts of bio-mass energy production.

The availability of these controls should not

be confused with the probability that impactswill not occur. in fact, it is unwise to assumethat the use of many of the practices listed intable 32 will be widespread. There are a num-ber of reasons for this.

First, the costs of the controls may consid-erably exceed the farmer’s perceived benefits.The effects of erosion on water quality arelargely “external” effects; although the farmer

may benefit from the control efforts of others,he is unlikely to benefit from any water quality

improvements caused by his own efforts. This

55 Natjona/ ~rosjon Inventory Estimate, op c It



80 q Vol. 11—Energy From Biological Processes

problem of “external” benefits is endemic to

American agricultural practices. It is, in fact,

merely one aspect of the “tragedy of the com-mons” that hinders voluntary environmentalcontrol in virtually all of man’s activities. Also,any success in delaying or preventing produc-tivity declines from erosion effects may be

masked by improvements in other productionpractices and in any case would be very longterm in nature. The farmer must balance thesebenefits against very high erosion controlcosts. SCS has examined the effects on farmproduction costs of requiring reductions incurrent erosion rates on croplands. For exam-ple, requiring a 10-percent reduction in each of105 producing areas would raise corn produc-

tion costs by $0.07/bu in 1985. Requiring allacreage to conform to a maximum allowableerosion rate of 10 ton/acre-yr (twice the “noproductivity loss” rate) would cost $0.31/bu ora 16-percent increase over the projected 1985cost without controls. Further constraintscould raise costs astronomically (a 5-ton/acre-yr constraint leads to a $23.70/bu productioncost) because heroic efforts must be made onsome acreage in order to meet the con-straints.

56 Although these estimates are sharply

dependent on a number of critical assump-tions (e.g., the role of Federal soil conservationassistance is ignored), they demonstrate thelarge potential cost (and price) increases thaterosion control requirements could cause.

Second, there are substantive scientific dis-agreements about the actual environmentalbenefits achieved by these controls. Some ofthe controls may reduce one environmentalimpact at the expense of increasing others. A

primary example of this is the effect of someerosion controls— reductions in fall plowingand conservation tillage —on pesticide use.These controls leave crop residues on the sur-face, and the residues in turn act to break theforce of raindrops on the soil and drasticallydecrease erosion and runoff. Because the resi-dues harbor plant pathogens and insect pests,

pesticide requirements will go up sharply.Also, increased applications of herbicides are

used for weed control to compensate for the’66. English, lowa State University, personal communication,

June 15,1979.

reduced tillage. The net effect on the environ-ment is not entirely clear because a largesource of pesticide entry into surface waters —adsorption on soil particles and transport inrunoff — is considerably reduced by the con-trols, but EPA has identified increased pesti-cide use with conservation tillage as a signifi-

cant problem .57 Tables 33 and 34 identify ingreater detail the environmental tradeoffs in-volved in erosion controls.

Third, some of these controls may appear to

be incompatible with the present agriculturalsystem and may not be accepted by farmers.For example, the use of nitrogen-fixing crops,

cover crops, and crop rotations conflict withtoday’s large-scale, highly mechanized, chemi-cal-oriented farming although they were wide-ly practiced in the past. Although some scien-tists argue that the economic advantages of

present methods will evaporate (or have al-ready evaporated) in the face of rising pricesfor energy and energy-intensive agricultural

chemicals, and that the long-term environmen-tal viability of the methods is questionable, therelative advantages and disadvantages of thepresent system and its alternatives are a sub-ject of intense controversy in the agriculturalcommunity— with defense of the present sys-

tem having the upper hand at present. It ap-pears virtually certain that in the absense ofGovernment intervention the provision offeedstocks for energy production will rely pri-

marily on a mechanized, chemical-orientedphilosophy modified only by any economicpressures arising from increases in energyprices. Any substantive changes from this phi-losophy would represent essentially a revolu-

tion from established practice and would beunlikely because the present system has clear-ly succeeded in providing a reliable supply offood at (comparatively) moderate prices.

Crop Types

The environmental impacts of growing and

harvesting agricultural crops for energy willvary strongly with the type of crop grown,since different crops have different fertilizerand pesticide requirements, water needs, soil

57 Environmenta/ /mp / i ca t i ons of Trend s, op . cit.



Table 33.-Environmental Pollution Effects of Agricultural Conservation Practices

Pollutant changes m Pollutant changes m

media: surface water media: ground water– Po ll ut an t c han ge s m Po ll ut an t ch an ges i n

Extensiveness Resource use sediment Nutrients Pesticides nut r ients–pest i c ides media: soi l media: air

Contour farming/co ntour stripcropping

Acreage of crops farmed Fertizer and herbicideon the contour or strip- use remain constant

cropped decreased 25% Insecticideuse will re-between 1964 and main constant to very1969 and continued to slight increases.decrease slightly to1976, Contour farmingis more widely used innonirrigated crop pro-duction than m irrigatedcrop production.

Terraces and grass waterways

Sediment loss can be re-duced substantially onmoderate slopes, butmuch less on steepslopes, Reductions upto 50% are possible,but average reductionswill be about 35%.Contour stripcroppingcan reduce sedimentlosses more than con-tour alone. (Note: re-search shows substan-tial loss can occur withcontour watershedswith some soil types,with long slopes and/orwith steep slopes. )

Terraces and-grass wa- Fertilizer, herbicide, and Substantial reductions interways are not impor-tant in irrigated produc-tion, but are Importantfor nonirrigated crops.However, only 6% of all

acres in 1969 had ter-races The acres withterraces in 1976 couldhave increased or de-creased slightly.

insecticide use is not sediment and runoffexpected to increase can usually be ex-

(fertilizer could increase pected.if production percropped acre is ex-

pected to increase tocompensate for landtaken out of produc-tion). However, terracepractices will not re-quire more fertilizers.Costs and maintenanceincrease for terraces,

Nutrients associated with Pesticlie reductions will Loss of nutrients and Erosion losses can be re- Pesticide losses throughs edi ment wi ll be re - be l es s t han t ha t f or pest ic ides t hr ough duced up t o 50% wi th volatilization will de-duced, but reductions nutrients since a great- ground water will re- average reductions of crease if they are incor-may be proportional to er amount of pesticide main constant or de- 12Y0 (see conclusions porated into the soil bythe amount of sediment IS lost through surface crease slightly. How- on sediment). mechanical meanslost, water than bound to ever the amount of N

sediment. leached IS small com-pared to amount thatcan be lost in runoffand loss of pesticides toground water IS minorwith proper applicationrates.

Reductions in nitrates Reduction of pesticide N m ground water may Substantial reductions m No change.and phosphates are ex- residues in surface be reduced, based on erosion can result.pected with decreased water could be substan- limited research data.soil loss and surface tial with terrace sys- Leaching of pesticides IS

runoff. Reductions terns, since both sur- not likely to result incould be substantial face runoff and soil loss significant loss with

with some soils and are reduced. normal applicationscropping systems. rates

SOURCE U S Enwronmental Protection Agency, ErWlrOnmenfal /mPllCaf10/ts of Trencfslfr ~gricu/(ure and Si/v~cu/ture, Vo/urne // &wlronrnerrla/Ef feck of Trends, EPA-600/3-78-102, December 1978



Table 33.–Environmental Pollution Effects of Agricultural Conservation Practices-continued

Pollutant changes m Pollutant changes inmedia: surface water media: ground water— Pollutant changes m

Extensiveness Resource use sediment Nutrients Pesticides nutrients—pesticides media: soil

Conservation tillage; no-till Approximately 2.6% of Fertilizer and herbicide Sediment reductions of While Iarqe soil loss re- Effect of no-till on pesti- Niall cropped land was use increases by 15%, 50 to 90% will result. ductions will tend to re-no-till in 1977. While insecticide use by 11%. duce nutrient losses,this Practice is expected “An estimated 5 million fertilizer use will in-to increase to Iimiteduse in 2010, currentprojections (up to 55%of crops under no-till in2010) seem high. Ex-tensiveness may onlybe 10 to 20% in 2010.

acres of land could be crease by 15%. Thereshifted to crop produc- will probably still tendtion with no-till and re- to be reductions in totalduced-till methods. La- nutrient loss, but re-bor costs are reduced, duction will not be pro-More water will be con- portional to reductionsserved with no-till, asmuch as 2 inchesperyear.

Conservation tillage; reduced tillage In 1977, an estimated Fertilizer use will in-58.8 million acres (19%of total cropped acres)will be reduced tilled.An additional 40 millionacres will be classifiedas less tilled. Less tillincludes chisel plowing,disking once instead oftwice, and planting inrough ground.

In 2010, a total of 40%of all cropland may beclassified as reducedtilled.

crease slightly. Herbi-cide use is up (0.6%)and insecticide use in-creases by 8.6%. Anestimated 5 millionacres of land will beshifted to crop produc-tion with reduced andno-tillage methods. La-

bor output will de-

in soil loss. N contentof soil may also in-crease from weatheringof crop residues.

cide losses is not welldocumented. Loss tosurface water is greaterwhen the compound issurface applied and notincorporated in the soil,and 11‘Yo more insecti-cides and 15% moreherbicides will be usedfor no-till. While reduc-tions of pesticides insurface water could oc-cur, current researchdoes not prove this. In-creased use and sur-face application, evenwith reduced soil losswith no-till, could evencause slight increasesin pesticide losses.

Sediment will be reduced There will probably be Effect of reduced tillagean average Of 14%. Re- reductions in total nutri- on pesticide loss IS notduced tillage is less ef - ent loss to surface wa- well documented. Lossfective than no-til l in ter, but reduction wil l to surface water iscontrolling soil loss, not be proportional to greater when a pesti-

reductions in soil loss cide is surface applied(14%), and total pesticide use

IS 9% greater for re-duced till. While reduc-tions of pesticides insurface water could oc-

crease. Energy to plant cur, there is notcrops decreases, but enough research data toincreased energy will be support this.used in manufacture ofincreased fertilizers andinsecticides. Some soilmoisture will be con-served with reducedtillage.

titrates in ground water Erosion losses will be de-will show no change to creased 50 to 90%.slight increases. Pesti- Crop residues will in-c ide loss to ground crease which may resultwater will not be signifi- in increased N loss tocantly changed with no- the soil or available fortill practices. runoff. Additionally,

residues may provide ahiding place for pestsand increase the in-cidence of pests.

Nitrates in ground water Erosion losses decreasewill show no change to an estimated 14%.slight increases. Pesti- Wind erosion losses willcide levels in ground also decrease slightly.water will not be signifi- Crop residues increase,cantly changed with re- which lead to increasedduced ti llage. N available to the soil

for leaching and runoff.Residues on soil alsoincrease the incidence

of pests.

With some pesticides, in-increased volatilizationwill occur with surfaceapplications. The vaporpressure, molecularweight, and other prop-erties of a pesticide willdetermine the extent ofvaporization.

Surface applications ofsome pesticides typesleads to increased vola-tilization losses. Thevapor pressure, molecu-lar weight, and otherchemical properties of apesticide will determinethe extent of vaporiza-tion.

SOURCE U S. Enwronmental ProtectIon Agency, Envlmnmen?a/ /mp/icaf/onso( Trends lnAgncu/ture and Sl/vlcu/ture, Vo/urrre //: Environmenfa/ Eflecfsot Trends, EPA-600/3-78-102, Oecember 1978.




Table 34. -EcoIogical Effects of Agricultural Conservation Practices

Contour farming/contour stripcropping Extensiveness of contouring in 1985 (over 1976 use) will be low, but will increase by 2010. Beneficial aquatic effects result from decreased turbidity and

pesticide residues in surface water. Species diversity will also increase in the aquatic ecosystem. Decreased erosion and retention of soil nutrient cycleswill have long-term beneficial terrestrial effects. Since pesticide residues at current levels in drinking water are not known to be a human health hazard,reduction of pesticide residues will have no significant human health effects. However, if pesticide residues are later determined to be dangerous at cur-rent levels, then human health effects would be beneficial.

Terraces and grass waterways

Terraces are more effective than contouring in reducing pollutants, but extensiveness of use is tower for terraces. Aquatic effects are decreased turbidity,increased species diversity, and decreased pesticide residues. Terrestrial effects are beneficial, resulting from increased vegetation on terraces andgrass waterways, increased diversity of wildlife, and more pathways for animal populations to travel. Valuable topsoil will also be retained. Based onpresent knowledge, there is no known human health effect. Decreased sediment in water might result in an unpleasant taste or odor in drinking water.

Reduced tillageReduced tillage (with crop residues remaining) is less effective than no-till in reducing soil loss, but extensiveness of reduced tillage will be greater. There-

fore, the intensity of ecological effects are comparable for the two practices. Sediment reductions will reduce turbidity and increase species diversity.However, the potential for increased pesticide residues in surface water could have adverse effects on the aquatic ecosystem. Crop residues remainingon the soil and decreased soil loss are beneficial to the terrestrial system, but increased pesticide use will have adverse effects on nontarget organisms.Human health effects will not be significant.

No-tillAquatic and terrestrial effects are both beneficial and adverse. Aquatic systems will benefit from reduced turbidity and increased species diversity. How-

ever, pesticide residues in surface water could potentially be increased with no-till and create adverse effects in the aquatic ecosystem. Increased pesti-cide use can also have adverse effects on nontarget terrestrial life. Retention of crop residues and reductions in erosion will have beneficial terrestrial ef-fects. Human health effects will not be significant since pesticide residue in surface water should still be within safety limits even if they increase slightlywith no-till.

SOURCE U S Enwronmental Protection Agency, Hrwromnerrfal lrnpllca(~orrs of Trerrds m Agrlcullwe arrd Sf/wmdLve, I/ohmre // Errvrorrrnerrta/ Hfeck of Trends, EPA-600/3-78-102, Oecember 1978

preparation methods, harvesting times, andother factors that may potentially affect im-pact. Some of the more important crop-deter-mined factors are:

q Annual or perennial, — Perennial crops

(trees, sugarcane, perennial grasses, etc.)offer a substantive environmental advan-

tage over annuals because their roots andunharvested top growth protect the soilfrom erosion year round, while annuals of-

fer protection only during the growing

q

season and require seasonal tilling (unlessno-till is used) and planting.

q Row or close-grown crops. — Row crop cul-

tivation is generally more erosive than cul-

tivation of close-grown crops. For exam-ple, the average erosion rates of close-grown crops are significantly lower thanthose of row crops in every land capabili-ty class and subclass shown in table 34. Ingeneral, the rates of the close-grown cropsappear to be about half those of the rowcrops.

In the previous calculation of the ex-pected average erosion rates from new

biomass production, a mix of row andclose-grown biomass crops (in the same

tion) would be expected to have an aver-age (sheet and gully) erosion rate of about7.5 ton/acre-yr compared with about 6.3ton/acre-yr for food production. If the en-tire biomass crop were a row crop (e. g.,corn for large-scale alcohol production),

the average erosion rate from the biomassacreage is estimated to be 9.3 ton/acre-yr— almost 50 percent higher than the ero-sion rate from food production.Water requirem ents. — High irrigation wa-

ter use means greater competition for wa-ter among competing uses, greater draw-down of streams and consequent loss ofassimilative capacity, potential for entryof more salts into surface and ground wa-ters, depletion of aquifers (ground watermining), and energy use for pumping.There are substantial differences in waterconsumption among different crops. Forexample, irrigation requirements for cropsin Arizona during a dry year58 are:

Water use, acre-ft/ton of crop

W h e a t . . . . . . . . . . . . . . 0 . 9O a t s . . . . . . . . . . . . . . . 1 . 6

B a r l e y . . . . . . . . . . . . . . 1 . 3A l f a l f a . . . . . . . . . . . . . 0 . 7

proportion as existed in 1977 food produc- sacon~~rvat;on NeecjS Inventory, OP. Cit




q

q

q

Most discussions of biomass energyassume that irrigation generally will notbe used in growing feedstocks. However,an extension of the types of irrigationwater subsidies now available to Westernfarmers, however unlikely, could lead to

such use.

Soil requirements. —The ability to utilizemarginal lands can avoid the problem ofcompetition with food production that isa major environmental and social/eco-nomic issue in evaluating biomass fuels.As discussed elsewhere in this chapter,however, the potential for high biomassyields under marginal soil, temperature,and water conditions has been exagger-ated.

Pesticide requirements. —The importance

of reducing pesticide applications is a

matter of considerable controversy. How-ever, crops that have low pesticide re-

quirements will be perceived as more en-vironmentally benign. In some instances,present pesticide use may be a poor in-

dicator of future requirements for energycrops because cropping practices andland characteristics may be altered signifi-cantly in going to a crops-for-energy sys-tem. For example, regulatory restrictionson soil erosion could force virtually uni-versal use of conservation tillage and con-sequent increases in herbicide and (to a

lesser extent) insecticide applications. Thelack of esthetic requirements for biomassfeedstocks might also lead to some de-crease in pesticide requirements, but thiseffect may be small because minor insectdamage can lead to further damage byfungal and viral infections (especially dur-ing storage). Finally, although pesticide re-

quirements for grasslands currently arevery low, pest problems conceivably may

accelerate if productivity is pushed by ex-

panded use of fertilizers.

Fertilizer requirements. – In general, highfertilizer requirements are an environmen-tal cost because of the energy used to pro-duce the fertilizer and the nutrient runoffthat results from applications. However,

q

crop requirements for very high levels ofnitrogen may be an environmental advan-tage; some high-nitrogen crops are com-patible with land disposal of sewagesludge and effluents and thus can be animportant component of urban sewage

treatment strategy.

Yield. — Because yield per acre determines

the amount of land necessary to producea unit of energy, it is one of the most im-portant factors determining impact. Meas-

urements of input requirements (water,fertilizer, pesticides, etc.) and measurable

damages (such as erosion) on a “per acre”basis are inadequate measures of relativeenvironmental impact because of thelarge variation in biomass yields fromcrop to crop. For example, corn is widelyperceived as an extremely energy- and wa-

ter-intensive crop, but its very high yieldsessentially cancel its high “per acre” fer-tilizer, pesticide, and water needs; it is, infact, a relatively average crop on an “en-

ergy per ton of product” basis.

The importance of these factors in determin-ing environmental impacts is extremely siteand region specific. For example, water re-quirements clearly are more important in thearid West than in the wet Southeast, while fac-tors affecting sheet and rill erosion potentialare more or less important in the reverse order.

Much of the data needed to assess the differ-ent potential crops are not available, and thusit is premature to suggest which crops wouldbe the most environmentally benign in each re-gion or subregion. There are sufficient data,

however, to draw some rough sketches of someof the possible advantages or disadvantages ofseveral of the suggested biomass crops.

Corn has been most often mentioned as theprimary candidate for an ethanol feedstock. Itis an annual row crop and thus a major contrib-

utor to erosion, but much of the land on whichit is grown is relatively flat, a factor that limitsthe erosion rate. Corn’s high yield rate—cur-rently about 100 bu/acre, or about 260 gal/acreof ethanol —will minimize the land use impact




of additional production, although yields onnew lands will not be as high as the current av-erage, and the land displaced would be of high

quality.

Because the protein-rich residue from thefermentation (ethanol producing) process is a

substitute (although not necessarily a perfectone) for soybean meal in cattle feed, switchingexisting cropland from soybean to corn pro-duction may allow large quantities of ethanolto be produced using far less acreage thanwould be needed if corn for ethanol produc-tion were planted only on new acreage. As dis-cussed in the section on “Energy PotentialFrom Conventional Crops,” corn’s effectiveyield per acre of new land could grow by over300 percent (i.e., about three-fourths of thecorn used for ethanol would be grown on landformerly planted in soybeans with no loss in

national food and feed values) as long as thesoybean meal market remained unsaturated.

Significant uncertainties concerning the cornresidue’s nutritive value, potential corn yields

on soybean land, soybean market response,and other factors must be overcome, however,before this crop-switching scenario can be ac-cepted as valid. In the absence of the neces-

sary research, the higher estimate of new land

required for each gallon of ethanol producedshould be used as a pessimistic measure of po-tential impact. At low levels of production, themore optimistic, lower acreage requirements

are likely to be accurate, but the requirementsmay increase as production increases. Above 2billion to 7 billion gal of ethanol produced an-nually, feed markets would be saturated evenunder the most optimistic assumptions and ad-ditional ethanol production would requirecropland conversion at the higher rate.

Sweet sorghum has been praised as a crop ofhigh biomass potential for fermentation andalcohol production. Although ethanol yields of260 to 530 gal/acre have been projected, theseprojections are based on minimal — and clearly

inadequate — experience. However, these highyields, if confirmed, would limit displacementof alternative land uses. Sweet sorghum maybe more tolerant of marginal growing condi-

tions than corn, which could lead to a lower

level of displacement of the most productiveecosystems.

Sugarcane has been suggested as a biomass

crop for alcohol production in Hawaii and theGulf Coast. Because its cellulosic content ishigh enough to supply all of the heat energy

necessary to ferment the sugar and distill alco-hol from it, no coal or other fossil fuel usewould be necessary to power the system.Sugarcane requires high-quality land and thusmay displace particularly valuable alternativeland uses.

Perennial grasses can be supplied in largequantities by increasing yields on present acre-age with more intensive harvesting and fertili-zation; the present average yield is 1½ to 2

ton/acre, and this can be increased to 3 to 5tons. Because perennials provide excellent ero-

sion control, and because no additional acre-age would have to be converted from alterna-

tive uses, the environmental impact of a grass-based biomass strategy should be far less thanthat of a strategy based on annual crops. Envi-ronmental impacts of some significance could

occur because of the expanded use of fertilizer(150 lb N, 30 to 50 lb P2O5, 80 to 150 lb K2 foran incremental production of 78 gal of ethanolon each acre) and pesticides. Recovery ofadded fertilizer is very high for grasses, how-ever, so the potential for water pollution willbe less than for annual crops. Also, there is

uncertainty about changes in susceptibility todisease and insect damage because of the in-tensification of production, and substantialnew use of pesticides conceivably could be re-quired. Finally, the frequent harvesting andgreater use of chemicals may disrupt the popu-lations of wildlife that now flourish in the lessintensively maintained grasslands.

Trees may be grown plantation-style and har-vested by coppicing to supply significant quan-tities of biomass. A carefully designed treeplantation should have few problems of ero-

sion unless cultivation is practiced (which ap-pears unlikely); however, harvesting may con-ceivably create an erosion problem unless low-bearing-pressure machines are used to avoiddamaging the soil. Tree plantations present



86 . Vol. II—Energy From Biological P r oc e s e s

basically the same ecological problems as do from weeds– and consequently larger herbi-

agricultural monocultures — higher potential cide requirements –but the sheltering effect

for disease attack and displacement of alterna- of the tree canopy and the greater ability of

tive ecosystems. The spacing necessary for tree some tree species to compete for water may

growth may also allow greater competition counterbalance this effect.

Environmental Impacts of Harvesting Agricultural Residues

The residues from agricultural productionhave a number of significant effects –benefi-cial or otherwise—when left on the land. Un-derstanding these effects is critical to under-standing the potential environmental impactsof the collection and use of these residues asan energy feedstock.

The effects of residues left on the land in-

clude (table 35):

q

q

q

q

Control of wind and water e ros ion . –

Retention of residues as a surface cover isa major erosion control mechanism onerosion-prone lands. For example, residueretention on land that is conventionallytilled (i.e., plow-disk-harrow) can cut ero-sion in half.59

Retention of plant nutrients. – Residuesfrom the nine leading crops in the UnitedStates contain about 40, 10, and 80 per-cent as much nitrogen, phosphorus, andpotassium, respectively, as in total fertil-izer use in U.S. agriculture.

60

Enhanced retention of water by soils andmaintenance of ability of soil surfaces to

allow water infiltration.Maintenance of organic matter levels (nec-essary to maintain soil structure, ion ex-

change capacity, water retention proper-ties) in soils. –Croplands in the UnitedStates have lost major portions of their or-ganic content. Reductions (in North Cen-tral and Great Plains soils) of one-half totwo-thirds of what was present under na-tive grassland have been cited.61 Reten-

tion of crop residues is a critical factor inmaintaining organic matter levels.

“W. E. Larson, et al., “Residues for Soil Conservation, ” paper

No. 9818, Science Journal Series, AR S-USDA, 1978.

‘“I bid.

“Ibid.

Table 35.–Environmental impacts of Plant Residue Removal

Water q

q

q

Increased erosion and flow of sediments into surfacewaters if restric-tions on removal are not observed, causing increased turbidity,obstruction of streams, filling of reservoirs, destruction of aquatichabitat, increase of flood potential; under circumstances where con-servation tillage is encouraged by removal of a portion of the residues,erosion and its consequences will decrease,Increased use of herbicides and possible increased flow into surfaceand ground waters if conservation tillage is required for erosion con-trol; in some situations, removal of a portion of the residues would in-crease herbicide efficiency and greater use may not occur.

Increased flow of nutrients if more runoff results from decreased waterretention of soil and greater erosivity of soil; if more fertilizer is appliedto compensate for nutrient loss, flow of nutrients will change but thenet affect is not certain.

Air q Dust from decreased cover on land, operation of residue harvesting

equipment (unless integrated operation).q Added herbicides from aerial spraying or as a component of dust.q Decreased insecticides, fungicides.q Reduction in pollution from open-burning of residues, where formerly

practiced.

Land q Erosion and loss of topsoil, degrading of productivity if restrictions on

removal are not observed; the opposite, positive effect if conservationtillage is encouraged by residue removal.

q Decrease in water retention capabilities of land, increased floodingpotential if restrictions are not observed.

qDepletion of nutrients and organic matter from soil (nutrients may easi-ly be replaced),

Other • Reduction in plant diseases and pests (if lowering of soil organic mat-

ter does not adversely affect this factor) because residues can harborplant pathogens.

SOURCE: Office of Technology Assessment.

q A number of negative effects depending

on the type of crop and amount of resi-d u e – ” poor seed germination, stand re-duction, phytotoxic effects, nonuniformmoisture distribution, immobilization ofnitrogen in a form unavailable to plants,

and increased insect and weed prob-lems."

62In all cases, the residues harbor

crop pests; this can be a particularly sig-

6z /mprov ;ng Soils With Organic Wastes, OP. c it.



Ch. 3—Agr icu l ture . 87

nificant problem if single cropping is prac-ticed (the same crop is grown in consecu-tive years). Because the residues shield thesoil, they may hinder soil warming and de-lay spring planting (causing reduced yieldsin corn).

When the problems associated with crop res-idues outweigh the benefits, farmers will phys-ically remove the residue (this practice is nec-

essary in rice cultivation) or plow it under inthe fall (a common practice in the Corn Belt).The collected residues may be burned, al-

though they have alternative uses such as live-stock bedding. Where removal is normallypracticed, use of the residues as an energyfeedstock is at worst environmentally benign

and possibly beneficial (if air pollution fromopen burning is prevented). Because fall plow-ing negates much of the residues’ value as an

erosion control, collection of a portion of theresidue is usually considered benign (fullremoval may affect soil organic content, theimportance of which is somewhat in debate).Because an excess of residue may inhibit theeffectiveness of herbicide treatments — espe-cially preemergence and preplant treatments — and also leave large numbers of weed seeds

near the soil surface, removal of a portion ofthe residues on land where they are in excessmay promote the use of reduced tillage byallowing more effective chemical weed con-trol, and thus be considered environmentally

beneficial.

When residues are normally left on the soilsurface as an erosion control, their removal po-tentially may be harmful. However, where sub-stantial quantities of residue are produced onflat, nonerosive soils, a portion of these resi-dues may be removed without significantly af-fecting erosion rates. SCS and the Science andEducation Administration –Agricultural Re-

search have sponsored extensive research de-signed to compute the effects of residue re-moval practices and other practices on soil

erosion. USDA believes that it can identify thequantity of residues that can be safely re-moved from agricultural lands in all parts ofthe United States. Although controversy existsover the rate of creation of new topsoil, and

thus the erosion rate that will maintain produc-tivity over the very long term, it seems likely

that errors in these computations will notcause significant harm as long as SCS main-tains its monitoring efforts at the current level.

The key to preventing significant environ-

mental damage while harvesting large quanti-ties of residues is for the agricultural system toact in accordance with USDA’s knowledge.The discussion of the impacts of U.S. agricul-

ture presented previously seems to indicate awillingness among farmers to ignore warningsabout using erosive practices or cultivatingfragile land, in order to gain short-term bene-fits. In the absense of additional constraints, asignificant number of farmers might be willingto remove their crop residues even when ad-verse erosion effects would occur. (interest-ingly enough, some farmers may ignore USDA

with the opposite effect—they may be reluc-tant to remove any residues because of theirfear of erosion and other negative conse-quences). Under these circumstances, the es-tablishment of a market for crop residuescould result in additional erosion from crop-Iands that cannot afford it and add to the al-ready significant sediment burden on surfacewaters caused by current farming practices.

Although the negative effects of any in-crease in erosion are straightforward, other ef-fects that have been associated with residue

removal are more ambiguous. For example, theremoval of pIant nutrients in the residues maybe compensated for by the return of the con-version process byproducts or by chemical fer-tilizers (both of which may have some adverseeffects on water quality). The removal of or-ganic content has been identified as a signifi-cant impact

63and soil scientists have long

thought that soil organic content is a criticalvariable of the health of the agricultural eco-system (e. g., increasing the organic content ofsoils can stimulate the growth and activity ofsoil micro-organisms that compete with pIant

pathogens). However, despite a variety of pa-pers in the agronomy literature that treat yield

‘)Pimentel, et al., op cit.




as a function of soil carbon level, there is insuf-ficient experimental evidence to establish thatany significant effects on crop yields would oc-cur. Also, the much higher yields of today’s ag-riculture means that removal of half of the res-

Considerable research has been and is di-rected at improving agriculture for food, feed,and materials production. While much of thisresearch is applicable to energy production,

the specific goal of producing various types ofenergy crops has not been adequately ad-dressed. Changing the emphasis to energy orenergy and food production and the environ-mental concerns with agriculture suggest sev-eral R&D problems. Some examples are listed

below.q

q

q

A wide variety of crops that are not usedas food or feed crops could, potentially,

be good bioenergy crops. The promisingvarieties should be developed. From a the-

oretical point of view, grasses appear tobe promising candidates for high biomassproducers and on marginal cropland (seech. 4): and arid Iand and saline tolerantcrops may enable the economic use oflands and water supplies that are other-wise unsuited for agriculture.

Food and feed crops are usually quite spe-cific as to their use. Corn, for example, isnot interchangeable with wheat. Many dif-ferent types of crops, however, can pro-

duce the same or interchangeable bio-mass fuels. Consequently, extensive com-

parative studies between various cropsare needed to determine the promisingbioenergy crops for the various soil typesand climates.

If both the residues and the grain can besold, then the optimum plant may not be

the one that produces the most grain.

Farming practices and hybrids that canchange the relative proportions of grain toresidue in the plant while maintaining ahigh overall yield should be investigated.

idue will leave the same amount of organicmaterial as would have occurred 25 years agoif all of the residue had been left on the land.This is an area that clearly deserves further re-

search.

Needs

q Various crop-switching possibilities thatinvolve fuel production should be investi-

gated further to determine the extent towhich they can provide fuels and the tra-ditional products from agriculture with-.

out expanding the quantity of cropland

cultivated. The extent to which the corn-soybean switch actually takes placeshould be studied, as should novel possi-bilities such as sugar beets used for ani-

mal fodder. Included in this should be in-vestigations of the effect of substituting

current feed rations with varying amountsof forage-distillers’ grain, forage-corn glu-ten mixtures, and other feeds that may beinvolved in the crop-switching schemes.

q Large-scale biomass development will re-quire the placement of millions of acresof land — now in low-intensity agriculture(e.g., pasture), forest, or other uses– intointensive production, coupled in many

cases with very high rates of removal oforganic matter. Environmental R&D that

should accompany, and preferably pre-cede, such development includes:

–further investigation of long-term ef-fects of reduction in soil organic mat-

ter, –determination of pesticide require-

ments for high-yield grasses in intensiveproduction,

— intensification of breeding programsfor insect/disease-resistant strains of

crops with high biomass potential, –determination of economically opti-

mum strategies for minimization of soil

erosion, and –development of effective/ programs to

improve farmer (environmental) behav-ior.



Chapter 4

UNCONVENTIONAL

BIOMASS PRODUCTION



Chapter 4.— UNCONVENTIONAL BIOMASS PRODUCTION

Page Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Genetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Crop Yields . * . . . . . . . . . . . . . . 92Unconventional land-Based Crops. . . . . . . . . . . . 95

Lignocellulose Crops . . . . . . . . . . . . . . . . . . . 95Vegetable Oil and Hydrocarbon Crops . . . . . 96Starch and Sugar Crops . . . . . . . . . . . . . . . . . 97General Aspects . . . . . . . . . . . . . . . . . . . . . . . 97

Aquiculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98Mariculture q . . * * * * * * * * . . . . . . . . . . . * . * * * * * 101

Other Unconventional Approaches . ..........105Multiple Cropping . . . . . . . . . . . . . . . . . . . . .105

Chemical Inoculation. . .................105Energy Farms . . . . . . . . . . . . . . . . . . . . .. ...105Biophotolysis. . . . . . . . . . . . . . . . . . . . . ....106Induc ing N i t rogen F ixa t ion in P lan ts . . . . . . .107Greenhouses . . . . . . . . . . . . . . . . . . . . .. ...108

TABLESPage

36. Optimistic Future Average Crop Yields forPlants Under Large-Scale Production . . . . . . 94

37. incomplete List of CandidateUnconventional Bioenergy Crops . . . . . . . . . 95

38. Optimistic Cost Estimates forUnconventional Crops. . . . . . . . . . . . . . . . . 97

FIGURE

Page 13. Macrocystis Pyrifera . .................102



Chapter 4

UNCONVENTIONAL BIOMASS PRODUCTION

Introduction

A number of unconventional approaches to

biomass energy production have been pro-posed. Several nontraditional crops that pro-duce vegetable oils, hydrocarbons, and otherchemicals or cellulosic material are under in-vestigation. Both freshwater and saltwaterplants are being considered, and various other

approaches to biomass fuel production arebeing examined. A common feature to all ofthese approaches is that the full potential ofindividual plants proposed as fuel-producers

cannot be fully assessed without further R&D.A description of some general plant character-

istics, however, can aid in comparing the vari-

ous possible types of energy crops.

The general aspects of farming, plantgrowth, and the efficiency of photosynthesisare considered in chapter 3. Since future cropyields will depend on these factors and on thedevelopment of hybrids for energy production,the possibilities for genetic improvements areconsidered here. Following this, crop yieldsand various unconventional bioenergy cropsand approaches to farming them are discussed.

Genetics

There are two major areas of genetics. Thefirst, which plant breeders have used most ef-

fectively to date is the classical Mendelian ap-proach (introduced by Gregor Mendel in the19th century). It involves selecting and cross-

breeding those plants with desired characteris-tics (e.g., biomass yield, grain yield, pest re-sistance). The process is continued througheach succeeding generation until a hybrid, or

particularly favorable strain, is isolated.Strains with unique and desirable propertiesare often crossbred to produce hybrids thatoutperform the parents. Hybrid corn is an ex-ample. This technique is limited, however, bythe variability of characteristics that existnaturally in plants or mutations that occurspontaneously during breeding. One can iso-late the best, but one cannot produce betterthan nature provides.

The second approach to genetics, moleculargenetics, is a recent development that involves

manipulating the genetic code more or less di-rectly. Three types of potential advances from

molecular genetics can be distinguished: 1 ) im-provements in the efficiency or rate of biologi-cal conversion processes (e.g., fermentation,anaerobic digestion), 2) introducing specific

characteristics into specialized cells such as

the ability to produce insulin,1 and 3) improve-ments in photosynthetic efficiency, plantgrowth, and crop yields. The complexity of the

tasks increases greatly as one goes from 1) to3), as described below.

The first type involves subjecting single cellsto chemicals or radiation that cause mutationsin the celIs’ genes. The way these mutations oc-

cur is not well understood and the effects aregenerally unpredictable. The result is to in-crease the diversity of cell types over what oc-curs naturally; and in favorable cases one mayproduce a cell that performs a particular func-tion “better” than naturally occurring cells.This method has been applied successfully tothe production of antibiotics, in biologicalconversion processes,

2and in increasing the

tolerance of plants to certain diseases; but it isgenerally a “hit and miss” proposition.

‘A Elrich, et al , Science, VOI 196, p, 1313, 1977

‘ F o r e x a m p l e , s e e G H E i n e r t a n d R . K a t z e n , “ C h e m i c a l s

F r om B iomas s by I mpr ov ed Enz y me T ec hno logy , ” p r es en t ed a t

the Biomass as a Non-Fossi/ tue/ Source, ACS/CSJ Joint ChemicalCongress, Honolu lu, Hawall, April 1979

91



92 q Vol . n-Energy From Bio logica l Processes

The second type involves identifying the

genes responsible for a particular function inone cell and transferring these genes to anoth-er cell. This transfer does not always require adetailed knowledge of how the gene producesthe desired characteristic. One can draw fromthe pool of naturally occurring characteristics,

but the conceptual link between the gene andthe characteristic must be relatively direct.

The third type probably would involve alter-

ing a complex set of interdependent processesin the plant. Although some plant physiologists

believe that some improvements in photosyn-thetic yield can be achieved by suppressingprocesses like photorespiration (a type of plantrespiration that occurs only in the presence oflight), this belief is highly controversial amongspecialists in the field. It is generally believedthat the processes involved in plant growth

and photosynthesis and their relation to specif-ic genes are too subtle and poorly understoodat present to know what biochemical proc-esses should or can be altered to improve plantgrowth and crop yields.

Some additional near- to mid-term advancesare likely in the area of biological conversionprocesses and with gene transfers in the area

of synthesizing high-value chemicals, like in-sulin, that would be either impractical or im-possible to synthesize by other means. Thecomplexity of plant growth and photosynthet-

ic efficiency, however, reduces the chances ofimproving ‘these characteristics in plantsthrough molecular genetics in the near future.Although the possibility cannot be precluded

that a scientist will alter a crucial process inplant growth despite the lack of knowledge,there are few grounds for predicting that thiswill occur before the fundamental biochemi-cal processes involved in plant growth andphotosynthesis and the way that environmen-tal factors limit them are better understood.There is a great deal of controversy surround-ing this subject, but most arguments— both

pro and con– are based on intuition ratherthan demonstrated fact.

Crop Yields

Current knowledge and theories of plant

growth do not enable one to predict the cropyields that can be achieved with unconven-tional crops. Nevertheless, because of the im-portance of biomass yields in determining theeconomics of production, it is important tohave an idea of the approximate magnitude ofthe yields of various options that may be possi-ble.

To this end, corn – a highly successful exam-ple of crop development– is used as the basisfor these estimates. Corn has the highest pho-tosynthetic efficiency of any plant cultivatedover large areas of the United States. As dis-cussed in chapter 3, an optimistic estimate foraverage corn grain yields would be about 140

bu/acre (3.9 tons of grain/acre) by 2000. Manyfarmers routinely exceed this yield, as do ex-

perimental plot yields. This number, however,is quite optimistic for average yields from cul-

tivation on millions of acres of average U.S.

cropland. Furthermore, since cropland thatcould be devoted to energy crops is generally ofpoorer quality than average cropland, using thisas a basis for estimates may be overstating thepotential.

A yield of 140 bu/acre for corn correspondsto a photosynthetic efficiency of about 1.2 per-cent over its 120-day growing season. Perennialcrops, however, probably will have somewhatlower efficiencies during the cold weather at

the beginning and end of their growing sea-sons. Consequently, it is assumed that peren-nials can achieve an average photosyntheticefficiency of 1.0 percent. With these assump-

tions, and the others stated below, the follow-ing yields may be possible.

qDry matter yield.— With an 8-month growing

season in the Midwest, biomass productioncould yield 15 ton/acre-yr of dry plant mat-ter. For the Gulf Coast (12-month growing



Ch. 4—Unconventional Biomass Production q 9 3

q

q

q

q

q

season), the yields could reach 21 ton/acre-

yr.

Grain yields.– Based on corn yields, average

gra in product ion f rom some p lants cou ld

yield 3.9 ton/acre-yr.

Sug a r yields.– Goo d suga r crop s are 40- to

45-percent sugar on a dry weight basis (e.g.,

sugarcane, sweet sorghum). In the Midwest,

sugar crops wi l l p robably be annual crops

l e a d i n g t o p o s s i b l e y i e l d s o f 4 t o n s o f

sugar/acre-yr. Along the Gulf Coast, there is

a lo n g e r se a so n . C u rre n t a v e ra g e su g a r

yields are 4 ton/acre-yr. As with corn, the

yields could conceivably be increased by 40

percent to 5.6 ton/acre-yr.

Aquatic plant yie lds.– Estimates for water-

based p lants are more d i f f icu l t to der ive ,

since there is considerably less experience

and app l i cab le i n fo rma t ion . Wate r p lan ts

have a continuous supply of water and arenever water stressed. For maximum produc-

t iv i ty , nutr ients and carbon d iox ide (CO,)

(for submerged plants) would be added to

the water and cou ld be ava i lab le cont inu-

ously a t ne a r -op t imum leve ls. The w a te r

wou ld p reven t rap id changes in tempera -

ture. All of these factors favor plant growth,

a n d i f o t h e r p r o b l e m s w i t h c u l t i v a t i n g

aquatic plants can be solved, yields may be

quite high (see “Aquicul ture” and “Maricul-

ture”). Nevertheless the uncertainty is too

g r e a t t o m a k e a m e a n i n g f u l c o m p a r i s o n

wi th the land-based p lants . As wi th o therplants, experimental yields wil l probably not

be rep resen ta t i ve o f commerc ia l l y ach iev -

able yields.

Y ie lds i n g reenhouses .– Y ie lds i n g reen-

houses are also very uncertain, due to a lack

o f su f f i c ien t da ta and po ten t ia l p rob lems

such as fungal a t tacks on p lants , root ro t ,

and o ther prob lems wi th extremely humid

envi ronments. I f these and o ther prob lems

are so lved, then crop y ie lds approach ing

those estimated for the milder cl imates may

be achieved.

Vegetable oil or hydrocarbon yields. – In ad di-t i on to so l i d ma te r ia l , p lan t b iomass in -

cludes oils. New seed oil crops typically con-

tain 10-to 15-percent vegetable oil, and in

sunflowers the oi l comprises up to 50 per-

q

q

c e n t o f t h e s e e d w e i g h t .3 A s s u m i n g th a t

p lants which are 50-percent seed conta in

seeds that are 50-percent oil, the oil content

may reach 25 pe rcen t o f the to ta l p lan t

weight .

Assuming the b iochemica l react ion pro-

ducing the oil is 75 percent as efficient as

that which produces ce l lu lose, then for 1-

p e r c e n t p h o t o s y n t h e t i c e f f i c i e n c y t h e o i l

p roduc t ion wou ld be 16 bb l /ac re -y r fo r a

plant that is 25-percent oi l . For an oi l -pro-

ducing react ion that is 50 percent as e f f i -

cient as the reaction that results in cellulose,

the yield would be 12 bbl/acre-yr.

Plant material stored as hydrocarbons has

a lso been proposed as a source o f l iqu id

fuels. Eucalyptus trees and milkweed, for ex-

ample, contain up to 12-percent hydrocar-

bons. Assuming that th is content cou ld be

doubled, the same yields as for oi l cropswould apply.

Ar id land crop y ie lds.– Another impor tant

and somet imes l im i t i ng fac to r i n b iomass

produc t ion i s wa te r . Genera l l y p lan ts w i l l

grow well without irrigation in areas of the

United States where the rainfall is 20 to 30

inches or more. For high biomass-producing

crops in relatively humid cl imates ( l ike the

Midwest), the minimum water necessary for

p l a n t g r o wth i n o p e n f i e l d s i s a b o u t 2 0 0

w e i g h t s o f w a t e r f o r 1 w e i g h t o f p l a n t

grow th. There ha s b ee n interest, how eve r, in

plants that can grow under more arid condi-tions. In desert regions with very low humidi-

t ies, requirements are more typical ly 1,000

we igh ts o r more o f wa te r pe r 1 we igh t o f

p lant g rowt h. (Som e p lant s survive fo r long

periods of t ime without water, but they do

not grow. ) Assuming the 1,000:1 figure, the

max imum p lan t g rowth tha t cou ld be ex -

pected in a region with 5 inches of rain and

no i r riga t ion is 0 .6 to n/ a c re-yr. Oi l y ie lds

would be correspondingly low or less than 1

bbl/acre-yr.

Natural systems. — In addition to agriculture,

there has also been interest in using biomassproduced by plants in their natural state. In

‘D. Gilpin, S Schwarzkopf, j. Norlyn, and R. M. Sachs, “Ener-

gy From Agriculture– Unconventional Crops,” University of Cal-

ifornia at Davis, contractor report to OTA, March 1979.



94 q Vol. i i—Energy From Biological Processes

the natural state, most of the nutrients are

returned to the soil as the leaves drop off

or the plant dies and decays. Harvesting of

some of the biomass removes some of the

nutr ients , a l though an imal excre t ions and

the natural breakdown of minerals in the soil

p rovide new nutrients. The ra te of replenish-

ment varies considerably from area to area,however, and this determines the rate that

biomass could be removed from natural sys-

tems without depleting the soil.

The p ote ntial growth o f bioma ss in c ont in-

uously harvested natural systems has appar-

ently not been studied. (Forestlands are an

exception, al though the emphasis there has

been on the product ion o f commerc ia l t im-

ber rather than on total biomass.) It has been

estimated, however, that some natural wet-

l ands p roduce more than 5 ton /ac re -y r o f

growth, and that 11.4 million acres of range-

Ia n d p r o d u c e m o r e th a n 2.5 t o n /a c r e - y r . 4

Whi le no est imates for the product ion o f

natural systems can be given, they wil l cer-

ta in ly permi t less harvestab le growth than

intensively managed systems on comparable

soil.

In evaluating the possible yields for biomass

produc t ion , a l l o f the y ie ld es t ima tes he re

should be treated with extreme caution. None

of these yields has been achieved under large-

scale cultivation (i. e., mill ions of acres) and the

estimates for oi l-producing plants are particu-

lar ly uncertain. Experimental p lot yie lds, on

the other hand, exceed these yields for many

plants.

Moreover, several factors operate to prevent

average yields from reaching these estimates

fo r la rge -sc a le p rod uc t ion o f b ioma ss. The

most important are the less than ideal soils of

most potent ia l crop land and the fundamenta l

l i m i t a t i o n s o f p l a n t g e n e t i c s w i t h c u r r e n t

knowledge. On the o ther hand, management

pract ices improve wi th t ime and increased

costs for farm products may eventually justify

more extensive management practices, such as

addit ional fert i l izers, extensive soi l treatment,and expanded irrigation. *

*“An Assessment of the Forest and Range Land Situation in the

United States, ” Forest Service, U S Department of Agriculture,

review draft, 1979

q It is unclear whether Irrigation WIII be socially acceptable for

Each plant is, to a certain extent, a special

c ase. The e xperienc e w ith large-sc a le c ultiva -

tion of crops is l imited to a few food, animal

feed , f i be r , and chemica l c rops . Many p lan t

sc ient is ts argue that maximum food produc-

t i on imp l ies max imum b iomass p roduc t ion .

However , few genet ic and deve lopment pro-

grams have been speci f ical ly aimed at max-im iz ing b iomss ou tpu t fo r c rops su i tab le to

large a rea s of t he United Sta tes.

These c ontrad ic tory fac tors me an tha t the

potential for biomass production is uncertain.

And the uncertainty of the estimated yields is

judged to be at least 50 percent. Consequently,

the yields could easily vary anywhere from 0.5

to 1.5 times the numbers reported.

It is highly unlikely, however, that average

U.S. yield s for c orn w i ll exce ed 140 b u/ a c re

before 2000, and perhaps not after then. And

corn is one of the best biomass producers forthe U.S. cl ima te know n to m a n. Conseq uent ly,

the numbers repor ted represent reasonable

l imits in terms of what is known today. Any

large-scale production of biomass that signifi-

cantly exceeds these yields would represent a

major breakthrough. Estimates that are based

o n p r o j e c te d y i e l d s s i g n i f i c a n t l y e x c e e d i n g

those in table 36 either: 1) are l imited to the

relatively small acreage of the best U.S. soils,

Table 36.–Optimistic Future Average Crop Yields for PlantsUnder Large-Scale Productiona

Plausible average yieldb

Region Product (ton/acre-yr)

Midwest Dry plant matter 15Gulf Coast Dry plant matter 21Midwest Sugar 4

Gulf Coast Sugar 5.6Midwest Grain 3.9Midwest Vegetable oil or 1.7- 2.2

hydrocarbons (12 -16 bbl)Area with 5 inches rainfall

per year and noirrigation. . . . . . . . . . . Dry plant matter 0.6

Area with 5 inches rainfallper year and noirrigation. . . . . . . . . Vegetable oil or 0.1

hydrocarbons (0.7 bbl)

aln thl~ ~Ont~xt, lar~~.~~al~ @UC(iOfl means cultivation On mllllotls 01 acres of average U S

croplandbEstlmaled Uricerfamly 250 percent

SOURCE Otflceot Technology Assessm@

energy production or whether the necessary water WIII be avail-

able




2) rely on technologies that do not

and are not anticipated in the near

3) r e q u i r e e x te n s i v e m a n a g e m e n t

now exist

future, or

pract ices

Unconventional

A la rge number o f p lan ts no t now g rown

c om me rc ially in the United Sta tes a re p ote n-

tial ly energy c rop c an dida tes. Som e a re rela -

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

could provide a source of a variety of chemi-

cals that could be used as fuel or as chemical

feedstocks. Unl ike conventional crops, these

crops cou ld be considered pr imar i ly for the i r

value as fuel. (However, see also ch. 10.)

Assessing and comparing potential yields for

the unconvent iona l crops f rom l i te ra ture re-

ports are extremely di ff icul t, s ince these re-

ports often do not give dry yields, the plants

often are grown on unspecified soils and in dif-

ferent climates, and the water and nutrient in-

puts often are not given. Furthermore, it is a

wel l -known fact that experimental p lot yie lds

are larger than those achieved with large-scale

commercial cultivation. For these reasons, the

yields reported below should be treated with

extreme skept ic ism. Comparat ive cu l t iva t ion

exper imen ts and c rop deve lopment w i l l be

needed in the various regions and soil types in

order to estab l ish which crops are , in fact ,

suitable or superior for bioenergy production.In broad terms, the categories include: 1 ) ligno-

ce l lu lose, 2) vegetab le o i l and hydrocarbon,

a nd 3) starch and sugar crops. Each group is

considered brief ly below, and an incomplete

list of candidate bioenergy crops is shown in

table 37.

Lignocellulose Crops

Various species of hardwood trees (e.g., red

alder, hybrid poplar) and grasses (e. g., kenaf,

Bermuda grass, Sudan grass, big bluestem) are

candidates for crops grown primarily for their

high dry matter yields (Iignocellulose crops).

Theo ret ica l ly , one w ould expe c t pe renn ia l

crops (like trees and some grasses) to be su-

pe r io r b iomass p roducers to annua l c rops ,

that are not l ikely to be cost effective unless

there are dramatic increases in the prices for

farm commodit ies,

Land= Based Crops

Table 37.–incomplete Lis t o f CandidateUnconventional Bioenergy Cropsa

Lignocellulose crops American sycamore Red alderBermuda grass Russian thistleBig bluestem Salt cedarGum tree (eucalyptus) Sudan grassKenaf SwitchgrassNapier grass TamarixPoplar Tall fescueReed canarygrass

Vegetable oil and hydrocarbon crops Crambe MilkweedGuayule Mole plant (euphorbia)Gum tree (eucalyptus) SafflowerJojoba Turnip rape

Starch and sugar crops Buffalo gourd Kudzu vineChicory Sweet potatoesFodderbeets Sweet sorghumJerusalem artichoke

asome of these crops are produced commercially today on a hmlted scale, but fIOt for their ener9Yvalue

SOURCE D Gdpm, S Schwarzkopf, J Norlyn, and R M Sachs, “Energy From Agrlculture–Unconventional Crops, ” Unwersity of Cahforrua at Davis, contractor report to OTA.March 1979, S Barber, et al , “The Potential of Producing Energy From Agriculture, ”Purdue Unwerslty, contractor report to OTA, and J S Bethel, et al , “Energy From

Wood, ” UnwersNy of Washington, contractor report to OTA

since the perennials develop their leaf cover

sooner in the spring and do not need to gener-

ate a complete root system each year. Onewould also expect grasses to be superior bio-

mass producers to trees because of their larger

leaf area per acre of ground, * but considerable

attention has been focused on trees, since the

te c h n o l o g i e s f o r u s i n g wo o d a r e m o r e a d -

vanced. Experimental plot yields for short-rota-

tion trees are 5 to 20 ton/acre-yr .5 Yields of as

much as 10 to 15 ton/acre-yr may be achieved

for la rge-sca le cu l t iva t ion o f some of these

c rop s in g oo d soil (see “ Crop Yields” sec tion)

but are likely to be 6 to 10 ton/acre-yr in poorer

soils. Since farming costs could be similar to

corn, this could result in biomass for about $20to $50/ton.

“Thereby reducing Ilght saturation, which lowers photosyn-

thetic efficiency

5Cllpin, et al , op clt



96 q Vol. I/—Energy From Biological Processes

The t ree s wo uld typ ica lly be grow n for 6 to

10 yea rs be fo re ha rves t , wh i l e the g rasses

would be harvested several times a year. With

fewer harvests for the trees, each harvest could

be considerably more expensive and consume

more energy than grass harvests without unfa-

vorably affecting the economics or net energy

balance. However , t ree crops would requ i rethat the land be dedicated to the crop for sev-

e ra l yea rs and conver t i ng the land to o the r

uses would be more expensive, due to the de-

veloped root system. Also, if a disease were to

kil l the crop, reestablishing a tree crop would

b e m o re e xp e n siv e . Bo t h t r e e s a n d so m e

grasses are perennial crops and, consequently,

would require fewer herbicides and would re-

duce eros ion on eros ion-prone land as com-

pared to annual crops. Grasses, having a more

complete soi l cover, would be more effective

in preventing soil erosion.

Vegetable Oil and Hydrocarbon Crops

Vegetable oils and hydrocarbons are chemi-

ca l ly qu i te d i f fe rent f rom petro leum o i l . Nev-

er the less, most vegetab le o i ls and hydrocar-

bons can be burned and might prove to be a

subst i tu te for fue l o i ls or , wi th re f in ing, for

other l iquid fuels. However, appropriate meth-

ods for extracting the oi l from the plant and

for refining the oil are not well defined at pres-

ent.

A number of edible and inedible vegetableo i ls are current ly produced commerc ia l ly .6 In

add i t ion, unconvent iona l crops such as gum

t r e e ( e u c a l y p tu s ) , m o l e p Ia n t ( e u p h o r b i a s ) ,

guayule, mi lkweed, and others could be used

as vegetable oil and hydrocarbon crops (or for

na tural rub b er). The m a ximum c urrent yie lds

of commercial o i l p lants are in the range of

100 to 200 gal/acre (2.5 to 5 bbl) of vegetable

oil and/or hydrocarbon. Reports of 10 bbl/acre

(420 gal) for euphorbia were apparently based

on measurements of plants on the edge of a

field, which were 1.5 times larger than interior

p lants . A lso, in some cases, 16 months o f

growth were used to obtain “annual” yields, ’

6Agricu/tura/ Statistics (Washington, D. C.: U.S. Department of

Agriculture, 1978).

‘Gilpin, et al., op. cit.

The theo ry of hydroca rbo n a nd vegeta ble oil

production in plants is not adequate to predict

possible yields. However, from other consid-

erations (“Crop Yields” section) there may be a

significant potential for improvement. Further-

more, some of these crops (e. g., guayule) may

do well on land where there is slightly less wa-

ter available than would be needed for con-ventional crops. a

Others, such as mi lkweed,

can be grown with brackish water which would

be unusable for convent iona l food crops. ’

Compara t i ve tes ts under comparab le cond i -

t i ons wi l l be necessary to de te rm ine wh ich

plants show the most promise for energy pro-

duc t ion .

Because o f the h ighe r p r i ces tha t can be

paid for chemicals and natural rubber, the fact

tha t these p roduc ts a re economic i n some

cases does not in any way imply that energy

production from vegetable oi l and hydrocar-

bo n plants will be ec ono mic. Some prop onent s

of hydrocarbon plant development have failed

to distinguish between these end uses, a fact

that has led to considerab le confus ion and

misunderstanding.

Cri t ics of the development of vegetable oi l

and hydrocarbon plants for energy argue that

the production of these products by plants is

considerably less efficient than normal chemi-

cal synthesis (e.g., to produce methanol or eth-

an o l f rom d ry p lant ma tter ) . They a lso p o in t

out that the plant often must be subjected to

stress (drought or cold) to produce hydrocar-

bons, and this lowers the photosynthetic effi-

c iency. Consequently, they contend that the

high yields being predicted (e.g., 26 bbl/acre10),

will not be achieved in the foreseeable future.

At present, however, the theory of and ex-

perience with these types of plants is inade-

quate to make a meaningful judgment.

‘K. E. Foster, et al., “A Sociotechnical Survey of Guayule Rub-

ber Commercialization, ” Office of Arid Land Studies, Universityof Arizona, Tucson, Ariz., prepared for the National Science

Foundation under grant PRA 78-11632, April 1979.

‘W. H, Bollinger, Plant Resources Institute, Salt Lake City,

Utah, private communication, 198o.

‘“J D. Johnson and C. W Hinman, “Oils and Rubber From AridLand Plants,” Science, VOI 280, p. 460,1980.




Starch and Sugar Crops

Sta rch a nd sug a r c rop s a re of interest since

they can b e used to p rod uce e thanol with com -

mercial technology. Current corn grain yields

can be processed into about 260 gal of ethanol

per acre cultivated and sugar beets (usually ir-

r igated) can produce about 350 ga l /acre , on

the average. Irrig a te d c o r n, h o we v e r, wo u ld

match the sugar beet yield. Furthermore, ex-

perimental p lot yie lds for corn produce about

430 gal/acre-yr and record yields exceed 850

gal/acre. In addition to the conventional starch

and suga r c rops, seve ra l o the r p lan ts have

been proposed as ethanol feedstocks including

sweet sorghum and Jerusalem artichokes.

Experimental plot yields for sweet sorghum

could be processed into about 400 gal of etha-

nol per acre year. Furthermore, this crop pro-

duces large quantities of residues that are suit-a b le fo r use a s a d ist i lle ry bo i le r fue l . The

yields for large-scale cultivation, however, are

still unknown, and concern has been expressed

that droughts during parts of the growing sea-

son could reduce sugar yields significantly.

Experimental p lot yie lds for Jerusalem art i -

chokes have produced about twice the sugar

yields of sugar beets under the same growing

conditions in Canada. Whether this result can

be applied to other regions is not known. Jeru-

salem artichoke, l ike the sugar beet, is a root

crop. Harvesting it, therefore, causes extensivesoil disturbance which increases the chances

of soiI erosion.

“Gllpln, et al , op clt

Other plants such as fodderbeets, sweet po-

tatoes, and Kudzu vine are also potential etha-

nol crops. Comparative studies are necessary

to determine which crops are best in each soil

typ e a nd reg ion of the United Sta tes. As wa s

emphas ized in chap te r 3 , th i s compar i son

s h o u l d i n c l u d e t h e d i s p l a c e m e n t o f o t h e r

crops that ca n be ac hieved b y the byproducts

o f e th a n o l p r o d u c t io n . Th i s f a c to r t e n d s to

favor grains, but other possibilities do exist. ’2

General Aspects

I n t e n s i v e c u l t i v a t i o n o f u n c o n v e n t i o n a l

crops may cost about the same as corn, or $200

to $400/ a c re-yr in the Midw est. These c osts,

together with the yield estimates given above,

al low an approximate comparison of the costs

for var ious unconvent iona l land crops, which

is show n in ta ble 38. Since the exac t c ultiva -tion needs have not been established, a more

deta i led compar ison is not warranted a t th is

t ime. These c osts estima te s, ho we ver, sho w

that unconvent iona l crops may be economic

ene rgy sou rce s. The u ltima te c osts will d ep en d

to a large extent on the yields that can actually

be a t ta ined wi th in tens ive management and

the success of developing crops that can be

cultivated on land that is poorly suited to food

produc t ion .

The c rop s tha t a re now grow n in U.S. ag ric ul-

ture were selected for properties that are unre-I IR Carl son, B commoner, D Freedman, and R Scott, “Inter-

Im Report on Possible Energy Production Alternatives In Crop-

Livestock Agriculture, ” Center for the Biology of Natural SVs-

tems, Washington University, St Louis, Mo , Jan. 4, 1979

Table 38.-Optimistic Cost Estimates for Unconventional Cropsa

Product Ultimate fuel Yield of ultimate fuel per acre cultivated Contribution of feedstock to fuel costb

Dry plant matter Combustible dry matter 15 ton (195 106Btu) $20/ton ($1 .53/ 10

6Btu)

Dry plant matter Methanol 1,500 gale (95 106 Btu) $0.20/gal ($3.15/10 6 Btu)

Dry plant matter Ethanol 1,300 gald (107 106 Btu) $0.23/gal ($2.80/10’ Btu)

Grain Ethanol 364 gal (31 106 Btu) $0.82/gale ($9.89/10’ Btu)

Sugar (Midwest) Ethanol 540 gal (46 106 Btu) $0.56/gal ($6.50/10’ Btu)

Vegetable oil or hydrocarbon crop Vegetable oil or hydrocarbon 504-670 gal ( 63 -8 4 106 Btu) $0.45-$0.60/gal ($3.60-$4.70/10’ Btu)

aBased on yields m table 36bAssumlng $3i)o/acre cuttwatlon and harvest costs, does nOt include COnver510n costscAssumlng yw,lds of 100 gal/ton of btornassdAssumes yields of 85 galiton of biomasse~s not ,n~lude by Droduct credit for distillers’ grain H byproduct Credits Included, the Sltuatlon becomes more complex as described m ch 3, in the section on

“Energy Potential From Conventlonai

Crops ‘‘ The bypro&ct credit would reduce the costs by roughly one-thtrd

SOURCE Otflce of Technology Assessment



98 q Vol. Ii—Energy From Biological Processes

Iated to energy. It ‘ is l ikely, therefore, that

other plants wil l prove to be superior to con-

ventional crops for energy production. Beyond

the yields of these crops, properties like insen-

si t iv i ty to poor soi ls, mult ip le products (e.g.,

vegetab le o i l , sugar , and/or s tarch p lus dry

p lan t he rbage) d i sp lacement o f o the r c rops

with crop byproducts (e. g., corn disti l lery by-

product), the energy requirements to cul t ivate

the crop, the energy needed to convert i t into a

form that can be stored (especially for sugar

and starch crops), tolerance to adverse weath-

er conditions, ease of harvesting and conver-

s ion to fue ls , and the env i ronmenta l impacts

of growing the crop are all factors that should

be considered when choosing energy crops. In

s h o r t , a n a l y s e s o f t h e n e t p r e m i u m f u e l s

displacement per new acre cul t ivated (as was

done for various conventional crops in ch. 3),

the cost, and the environmental impacts areneeded to compare the options. Due to the di-

ve rsi ty o f U.S. so i ls a nd c l ima te s, d i f fe rent

crops will no doubt prove to be superior in dif-

ferent regions. Many of the possible unconven-

t iona l crops appear promis ing, but the u l t i -

mate decisions wil l have to come from experi-

me nt a nd expe rience . (Typica lly it requires 10

to 20 years to develop a new crop.) Neverthe-

less, some general aspects of plants can be ex-

pected to hold for the unconventional crops.

Roo t p lan ts (e .g . , Jerusa lem ar t ichokes,

sugar beets, pota toes, sweet pota toes) wi l l

cause the most soil erosion. Annual crops will

be next, and perennial grasses can vir tual ly

eliminate soil erosion.

So i l st r uc tu re a n d c l im a te a r e d o m i n a n t

features contro l l ing p lant growth and thesecan be control led by man only to a very l im-

ited extent. Plants vary as to their sensitivity to

these factors and to the presence of nutr ient

so lub i l i z ing mycorrh izae in the so i l , ’3 but

yields will decrease on going to poor soils and

climates. Crops grown in arid cl imates without

i r r igat ion or an underground supply o f water

wi l l g ive low yields; and social resistance to

using water for energy production in the West

c o u l d p r e c l u d e i r r i g a te d e n e r g y c r o p s , a l -

though some people maintain that this resist-

ance will not extend to crops.

Finally, any crop that grows very well in an

a r e a w i t h o u t i n p u t s f r o m m a n i s l i k e l y t o

spread and become a weed problem.

“J. M. Trappe and R. D. Fogel, “Ecosystematic Functions of

Mycorrhizae,” reproduced from Range Sci. Dep Sci., series No,

26, Colorado State University, Fort Collins, by U S. Department

of Agriculture.

Aquiculture

Aquat ic p lants co mpr ise a d iversity o f types, systems for energy product ion. ’4 The genera l

from the single-cel led microalgae to the large conclusions were that the production of aqua-

marsh p lants such a s ca t ta ils and even some t ic b iomass has near-term potent ia l in con junc-

trees such as mangroves. Considerable interest tion with wastewater treatment and high-value

e x ist s i n t h e c u lt i va t io n o f m a n y d if f e re n t c h e m ic a ls p ro d u c t io n . Ho we v er, t he d e ve lo p -

aquat ic p lants as energy sources. Examples are ment o f la rge-sca le “ energy farms” ba sed on

th e p r o d u c t i o n o f c a t ta i l s i n t h e e x te n s i v e aqua t i c p lan ts i s l ess p romis ing a t p resen t ,

marshes of Minnesota, the cultivation of water from both an economic or a resource potential

h y a c in th s o n wa ste w a t e r s in M i ssissip p i o r v ie wp o in t . Ne ve rth e le ss, a q u a t ic p la n ts h a v e

Flor id a , and the e sta b l ishm ent in the Sou th- cer ta in un ique a t t r ibutes, the key one be ing

west o f la rge-sca le brack ish water ponds for h i g h a c h i e v a b l e b i o m a s s p r o d u c t i o n r a te sm i c r o a l g a l p r o d u c t i o n o f c h e m i c a l f e e d s t o c k s . -

OTA has prepa red a d eta iled review of the p o-“ J. Benemann, “Energy From Aquiculture Biomass Systems:

Fresh and Brackish Water Aquatic Plants, ” Ecoenergetics, Inc ,tential of fresh and brackish water aquiculture Vacaville, Cal if , contractor report to OTA, April 1979




which justify continued research on a variety

of app roac hes to the development of aq uac ul-

ture energy systems.

H i g h e r a q u a t i c p l a n ts g r o w i n g i n o r o n

water are not, as a rule, water limited — a com-

mo n a nd nat ura l sta t e o f land p lant s. Thus,

they are capable of higher rates of photosyn-thesis by keeping their stomata (plant pores)

open longer than land plants* thereby, increas-

ing C02 a b sorp tion . Thus, p lan ts suc h a s the

water hyacinth and cattai ls exhibi t very high

rates of biomass production, often exceeding

2 0 t o n / a c r e - y r . Th i s h i g h p r o d u c t i v i t y i s

ach ieved , however , by evapora t ion o f l a rge

amounts o f water , exceeding by a factor o f

two to four that t ransp i red by land p lants .

Thus, cultivation of w a ter plant s c a n only be

considered where ample supplies of water ex-

ist or where the systems are covered, such as in

greenhouse structures.

Some aq uatic p lants, howeve r, do no t exhib-

it very high biomass production rates. For ex-

amp le , the common duckweed (Lemna sp . )

covers a water surface very rapidly; however,

once this is achieved, further growth in the ver-

tica l direc tion is minima l. Thus, the p rod uc tivi-

ty of such plants is relatively low when com-

pared to plants such as water hyacinths and

marsh plants which extend their shoots up to

several feet into the air. Indeed, the high leaf

area index (the ratio of the total leaf area to

the ground area), sometimes exceeding 10, ofthese plants, accounts, along with high trans-

piration rates, for their high productivity.

Another type of aquatic plant that exhibi ts

re la t i ve l y l ow p roduc t i v i ty i s the sa l t marsh

p l a n t Sp a rt in a , wh ic h d o e s n o t p ro d u c e a s

much biomass as its freshwater analogues such

a s Typ ha (c a tta ils) o r Phrag mite s (bullrush). The

high salt co nc entrat ion tolera ted b y Spa rtina

also results in a decrease of transpiration and

p ro d uc t iv it y. Ev e n a m o n g t h e f re sh w a t e r

marsh plants, b iomass productiv i t ies are l im-

i ted by both the seasonal growth patterns ofthe p lan ts i n the tempera te c l ima te o f the

‘Somata are closed to conserve water, but this also prevents

carbon dioxide from entering the leaf

‘ ‘Ibid

United State s and the large frac tion o f b ioma ss

present in the root system which may be diffi-

cul t to rec over. The subm erged aq uatic p lants

such as the notorious weed Hydrilla, are also

not remarkable for their biomass productivity.

Adaptation to the l ight-poor environment fre-

quently encountered below the water surface

has made these plants poor performers at the

high light intensities that would be the norm in

a biomass production system.

Finally, the case of the microalgae must be

considered. Being completely submerged they

also are subject to signi f icant l ight losses by

reflection from the water surface (at low solar

angles) and scattering of light. More important-

ly, in a mixed algal pond, the cells near the sur-

face tend to absorb more l ight than they can

use in photosynthesis, resulting in a significant

waste of solar energy. However, if a microalgal

production system is designed to enhance mix-ing, then rapid adjustment by the algae occurs,

thus overcoming, to some extent, the handicap

inherent in inef f ic ient sun l ight absorpt ion by

microa lgal c ultures. Therefore, m icroalga l c ul-

tures could be considered in a biomass produc-

tion system. A review of the rather sparse pro-

ductiv i ty data avai lable, together with consid-

eration of the basic photosynthetic processes

involved, suggest that green algae and diatoms

are promising candidates for mass cultivation,

probably with achievable production rates of

at least 20 ton/acre-yr, wi th blue-green algae,

part icular ly the ni trogen-f ix ing species, con-

siderably less productive.

It must be noted that the available data on

aqua t i c p lan t p roduc t i v i ty a re too l im i ted to

a l low conf ident extrapo la t ions to la rge-sca le

systems. Most ava i lab le data are based on

natural systems where nutrient limitations may

have depressed p roduc t i v i ty o r sma l l - sca le ,

short- term experimental systems where edge

effects and other errors may have increased

product iv i ty . Actua l year ly b iomass produc-

tion rates in sufficiently large-scale managed

systems must be considered uncertain for anyaquat ic p lant , par t icu lar ly i f factors such as

stand establishment, pest control, optimal fer-

ti l izer supply, and harvesting strategy are con-

c erned . Thus, to a c on side rab le exte nt, a ssess-




ing the potent ia l of aquat ic p lants in energy

f a r m i n g , l i k e t h a t o f o t h e r u n c o n v e n t i o n a lcrops, involves more uncer ta in ty than speci f ic

deta i led knowledge.

Among the uncertainties are the economics

of the product ion system, inc lud ing the har-

vesting of the plants. Detai led economic anal-yses are not avai lable; those that have been

carr ied out are based on too many optimistic

a s s u m p t i o n s t o b e c r e d i b l e o r u s e f u l . O f

course each type o f p lant wi l l requ i re a d i f -

ferent cultivation and harvesting system. How-

ever, in all cases, these appear to be signifi-

cantly more expensive per acre in both capital

and operat ions than the costs o f te r restr ia l

p lants. This increa sed c ost p er ac re ca n on ly b e

just i f ied by an increased b iomass product ion

rate or a specific, higher valued product. Be-

cause the productivity and economics of aqua-

tic plants are, to a large degree, unknown, thep o te n t i a l f o r a q u a t i c p l a n t b i o m a s s e n e r g y

farming is in doubt.

One approach to improve the economics of

such systems is to combine the biomass energy

system with a wastewater treatment function.

As aquatic plants are in int imate contact wi th

water, they can perform a number of very im-

p o r ta n t wa s te t r e a tm e n t f u n c t i o n s — o x y g e n

production (by microalgae) which al lows bac-

terial breakdown of wastes, settl ing and fi l tra-

t ion o f suspended so l ids, uptake o f organ ics

and heavy metals, and, perhaps most impor-

tantly, uptake of the key nutrients that cause

po l lu t ion. The re la t ive ly h igh c onc entra t ions

of ni trogen and phosphorus in aquatic plants

(e.g., about 10 percent nitrogen and 1 percent

phosphorus in microalgae and 3 percent ni tro-

gen and 0.3 percent phosphorus in water hya-

cinths), makes these plants particularly useful

i n nu t r i en t remova l f rom was tewa te rs . Re-

search in wastewater aqu icu l ture is wel l ad-

vanced, a l though some cr i t ica l prob lems re-

main to be elucidated, and several large dem-

onstration projects are being initiated through-

out t he United Sta tes. For exam p le, wa ter hya-cinths are being used in wastewater treatment

plants in Coral Gables and Walt Disney World,

Fla., in projects which involve fuel recovery by

anaerobic digestion of the biomass. Microalgal

ponds have been used for several decades in

many wastewater treatment systems through-

out the Uni ted Sta tes. More str inge nt w at er

qua l i ty s tandards are resu l t ing in a need for

be t te r m ic roa lga l ha rves t ing techno logy and

present ing an oppor tun i ty for fue l recovery

from the ha rvested microa lga e. Seve ra l p ro j -

ec ts throug hout the United Stat es have de mon-strated the beneficial effects of marsh plants

in wastewater. treatment. In all cases, waste-

wa te r aqu icu l tu re appears more economica l

and less energy in tens ive than convent iona l

technolog ies. 16 However , the to ta l po ten t ia l

imp ac t of wa stew at er aq uiculture on U.S. en-

ergy suppl ies, even when making favorab le

market penetration assumptions, is minimal —

about 0.05 to 0.10 Quad/yr.17

For aquatic plants to make a more signifi-

c a n t c on t r ib u t i on to U.S. ene rg y resourc es,

other types of aquatic biomass energy systemsmust be developed. One alternative is the con-

version to fuel of aquatic plants already har-

vested from natural, unmanaged stands. Exam-

ples are water hyacinth weeds removed by me-

chanical harvesters from channels in Flor ida

an d othe r south ern Sta tes and c at ta ils or bull-

rushes cut periodical ly in natural marshes in

M i n n e so t a o r So u t h C a ro l in a t o i m p ro v e

w i l d fo w l h a b i t a t s . Ho we v e r , t h e i n f r e q u e n t

occurrence o f such harvests , the smal l b io-

mass quanti t ies involved, and transportation

d i f f icu l t ies make energy recovery f rom such

sourc es essen t ia l ly imp rac t i ca l . The c onv er -sion, if practiced, of natural marsh systems to

large-scale managed (planted, ferti l ized, har-

vested) plantations wil l present significant eco-

logical problems and, even if these are ameli-

ora ted or overcome, opposi t ion by env i ron-

men ta l g roups. None the less, la rge a reas o f

ma rshes do exist in the United Sta tes and they,

in the long term, may become resources that

could be exploited on a multipurpose and sus-

tained yield basis like the national forests. In

the near te rm, however , the techno logy fo r

aquatic plant biomass energy systems must be

developed with presently unused or “margin-

“’Ibid

“Ibid

“Ibid.




a l ” l a n d a n d wa te r r e s o u r c e s . I n a d d i t i o n ,

relatively high-value biomass energy products,

specifically chemicals and liquid fuels, should

be produced by such systems. Examples of

such systems include the production of alco-

hol fuels from cattails (either by hydrolysis of

the area l par ts or d i rect ly f rom the s tarches

stored in the roots) or the production of hydro-carbon fuels and specialty chemicals from mi-

croalgae.

Microalgae are known to produce a variety

of usefu l chemica ls . However , the deve lop-

ment o f such product ion technology is on ly

just now beginning, and the potential resource

base (land, water, nutrients) available for such

syste ms is no t ye t q ua ntified . Thus, the futu re

c ont r ib ution t o U.S. fuel sup p l ies of a q ua tic

plant biomass energy systems cannot be pre-d i c ted . However , su f f i c ien t poss ib i l i t i es and

promise exist to warrant further R&D efforts.

Mariculture

This sec tion d esc rib es p rob lems a nd op p or-

tun i t i es assoc ia ted wi th deve lop ing fu tu re

ocean farms which might use the g iant ke lp

( m a c r o c y s t s ) a s a f u t u r e b i o m a s s e n e r g y

source. Other macroalgae have also been pro-

posed as potentia l marine biomass crops. Byexamin ing the poss ib i l i t i es o f ke lp and a l so

no ting o the r prop osals, OTA ho p es to illustrate

the s ta tus o f th is technology in genera l , i ts

fu ture potent ia l , the prob lems invo lved, and

the Federal role in this segment of alternative

energy research.

Macroalgae are harvested around the world.

About 2 million wet metric tonnes are now cut

annual ly, and estimates are that the total po-

tential worldwide crop is 10 times this much—

about 20 miIlion wet tonnes. 9

In recent decades seaweed cul t ivation hasrapidly become more successful and has sub-

stantial ly added to annual harvest figures. For

example, as of 1970 there were 130,000 acres

o f s e a s u r fa c e u n d e r c u l t i v a t i o n i n J a p a n ,

a b out 25,000 a c res in The Peo p les Rep ub lic of

C h in a , a n d a d d i t io n a l a c re a g e in Ta i w a n ,

Korea, the Phil ippines, and elsewhere. None of

the current annual world harvest is being used

for energy production.

In the Uni ted Sta t es, whe re wi ld sea we ed

beds have been harvested for many years, the

poss ib i l i t y i s beg inn ing to be s tud ied o f i n -

creasing production through ocean farm cul-

‘9G Michanek, Seaweed Resources of the Ocean, U.N, Food

and Agriculture Organization, Rome, 1975,

tivation techniques. A small test farm has been

installed along the California coast. 20

Large ocean kelp farms could theoretical ly

supp ly s ign i f i can t quan t i t i es o f na tu ra l gas

(methane) . L inked to a me thane p roduc t ion

sys tem, fo r examp le , and assuming se r ioustechnical problems are solved, a l-mil l ion-acre

kelp farm could produce enough gas to supply

1 pe rcen t o f c urrent U.S. ga s nee ds.

It would be no easy matter to farm such vast

tracts of ocean. Much still needs to be learned

about macroa lgae cu l t iva t ion. But ser ious re

search is reducing the areas of ignorance and

seaweed may some day become a biomass pro-

ducer.

A l g a e a r e a m o n g th e s i m p l e s t a n d m o s t

pr imi t ive of p lan ts. The la rge r ma c rosc op ic

algae are commonly referred to as seaweeds or

macroalgae. Large seaweeds are the dominant

plant in most shallow coastal waters including

those off California and Mexico, where they at-

tach themselves to rocks or some other hard

substrate under water.

To d a te , t h e se a we e d s a p p a re n t l y m o st

adap tab le to human cu l t i va t i on a re the red

and the brown a lgae. People have eaten red

algae variet ies for thousands of years, espe-

cially in countries such as Japan and China.

2“A. Flowers, statement before the House of Representatives

Committee on Merchant Marines and Fisheries, Subcommittee

on Oceanography, p. 18, committee report serial No , 95-4, June

7,1978.



102 q Vol. /l—Energy From Biological Processes

The b row n a lga e g roup inc lud es the g iant

kelp Macrocystis (figure 13), already harvested

Figu re 13.—Ma c roc ystis Pyrife ra

(A: 1/64 natural size; B: 1/4 natural size.) The Giant Kelp isshown in the left part of the plate in a natural pose with thelong lea fy stipe s rising to the sea surfac e from the ma ssiveholdfast. On the right is one of the leaf-like fronds showing

the gas-filled float bladder at its base and the distinctiveteeth along the margin (Anon. 1954).

SOURCE: Velco, Inc.

in the Unite d Sta tes from w i ld a nd sem icul t i -

vated beds and considered at present as the

b e s t c a n d i d a te f o r i n te n s i v e c u l t i v a t i o n o f fCalifornia and as a possible fuel producer. z’

z ‘Neushal, et al., “Biomass Production Through the Cultiva-

tion of Macroalgae in the Sea, ” p 100, Neushul Mariculture,Inc , for OTA, Oct 6, 1978

Kelp may grow in length as much as 2 ft/day

or increase its weight by 5 percent per day un-

d er op timum c ond itions. The p la nts form nat u-

ral beds up to 3 miles wide and several miles

long in sou the rn Ca lifo rnia. This kelp is no w

harvested and put to a variety of uses, prin-

cipal ly in the food-processing industry. Fuels

have never been produced from kelp except inminute quantities as part of research testing.22

Unfortunately, there is no consensus among

the experts who have made projections as to

th e p o te n t i a l o f o c e a n e n e rg y fa rm s. Th e i r

estimated costs vary widely and are based on

such very sparse data that they cannot be used

to ei ther support or reject ocean farm propos-

als. Estimates of production rates vary by fac-

tors of as much as 100. Better experimental

data and more complete b io log ica l eng ineer-

ing tests will allow for better estimates in the

future. The estima tes used here l ie a p p rox-

imately in the middle of responsible optimistic

and pessimistic projections for a 400,000-hec-

tare (1 million acre) ocean kelp farm:

q average p roduc t i v i ty = 20 d ry ash f ree

(DAF) tons per acre per year, and

q a v e r a g e a n n u a l e n e r g y p r o d u c e d = 0.2Qua d (1 p erce nt of U.S. ga s c onsump tion

of 20 Quads/y r).

Suc h a system , if b ui lt , wo uld p rovide t he

equivalent in energy supply of one large LNG-

impor t i ng p lan t such as the one loca ted a t

Cove Point, Md. It would, of course, be a do-mestic rather than an imported fuel, however.

Exper imen ts a re underway in to the bes t

laboratory- reared seaweed farms. Eventua l ly ,

some researchers hope to p roduce a “ped i -

greed” kelp bred specifically for high methane

production, fast growth, and hardiness.

A k e y p r o b l e m fa c e d b y p o te n t i a l o c e a n

kelp farmers is to deliver enough nutrients to

the p lants to fert i lize the m. This is b ec a use,

whi le the deep waters o f the ocean conta in

many necessary nu t r i en ts , su r face wa te r i s

often as devoid of nourishment as a desert is

ZZM. Neushal, “The C)cmnesticatlorl of the C iant Kelp, ~acro

cystis as a Marine Plant Biomass Producer, ” presented at the Ma- rine Biomass of the Pacific Northwest Coast Symposium, Oregon

State University, Mar. 3,1977



Ch. 4—Unconventional Biomass Production q 103

devoid of water. One fert i l iz ing technique be-

ing tr ied is art i f ic ia l upwel l ing of seawater,

wh i c h i n v o l v e s p u m p i n g n u t r i e n t - r i c h , d e e p

ocean water to the surface to benefit the kelp

p lants . 23

Current research on marine plants can be di-

vided into two categories.

The first c at eg ory, fund ed by seve ral Fed eral

agencies to a total of about $1 million in 1979,

generally includes research projects aimed at a

bet ter understand ing o f mar ine p lants , the i r

c u l t i v a t i o n , a n d p o te n t i a l n e w u s e s o f t h e

plants.

The o ther “ c at eg ory” is a c tua lly just on e

project: the Marine Biomass Research Program

jointly funded by the Gas Research Insti tute

(GRI) and the Depar tment o f Energy (DOE),

which has funded over $9 mil l ion of directed

research as of 1979.

Th is ong o ing ma r ine b ioma ss p ro jec t i n -

c lude s a test fa rm o f f Ca l ifo rn ia . The fa rm

began artificial upwell ing experiments late in

1978, but was forced to suspend operations in

ea rly 1979 d ue to sto rm da ma ge . This p roto-

type is meant to prov ide b io log ica l in forma-

t i on and research c lues needed to opera te

much larger culture farms. It also aims at ex-

perimental work into cultivation of giant kelp

on m oo red structures in the o p en o c ea n. The

test farm, may lead to the actual operation of

a full-scale ocean farm.

There is c on sidera b le d i ff ic ul ty a t th is t ime

i n e v a l u a t i n g t h e a p p r o p r i a t e n e s s o f t h e

Marine Biomass Research Program because lit-

t le has been produced. I t i s impor tant that

research results on the cultivation of kelp on

ocean farms be reported in a comprehensive

way and subjected to critical review if a future

large program is to be justified.

Kelp and other seaweeds are potential ly a

highly productive source of biomass for fuels.

Estimates can vary drastically as to what may

be possible for future large ocean farms, but

OTA’s eva luation of a hypo thetica l oc ea n kelp

fa r m i n d i c a te s p r o d u c t i v e n e s s c o u l d r a n g e

from a low value of 6 DAF ton/acre-yr to a high

value of 30. I n comparison, this country’s aver-

age corn harvest is 6 DAF ton/acre-yr and Ha-

waiian sugarcane averages 14 DAF ton/acre-yr.

OTA e stimate s tha t if a bo ut 1 m illion a c res

were ever farmed, the gross energy production

c ould a mo unt to 0.2 Quad . This is eq ua l to a p -

proxima tely 1 pe rc ent of c urrent U.S. nat ural

ga s c onsump tion. These p rod uc tion estimate s

should be treated with caution since there are

no ocean ke lp energy farms and nobody has

ever p lan ted a nd ha rvested a m ac roa lga e

energy crop.

Actual gross energy production from such a

huge hypothet ica l ocean ke lp p lanta t ion has

been projected by other researchers to range

f rom 10 t ime s OTA’ s est ima te to on ly on e-

te n th t h a t f i g u re . Th e e n t i re p ro j e c t m i g h t

simply prove impossible, others caution. Years

of exper iments wi l l be necessary before any

projections can be confirmed.

The re is ev en less d a ta to d raw on in esti-

ma t ing ne t ene rgy poss ib i l i t i es . In a repo r t

prepared for DOE by the Dynatech R&D Corp.,

net energy outputs were estimated to range

anywhere from a negative number to about 70

percent of crop energy .24

Much of the technology to construct pres-

ent concepts of open ocean farms is already

w ell kno w n. Similar pla tfo rms, struc ture s, and

moorings have been built for the offshore oil

industry and the existing seaweed industry uses

mechanical harvesting techniques.

Less certain areas of ocean farm engineering

at present include nutrient distribution, disper-

s ion character is t ics o f upwel led water , and

s p e c i f i c c o n f i g u r a t i o n o f t h e s t r u c t u r e t o

wh ich ke lp p lan ts w i l l be a t tached . A ma jo r

p rob lem fo r cu l t i va ted ke lp beds may be to

supply an ocean farm with proper nutrients in

c orrec t q ua nti t ies. The e xtrem e d i ff ic ul t ies of

noting the delicate balance of nutrients found

in a natural environment and reproducing this

in a cultivated one are well known to research-

ers.

24Dynatech R&D Co , “Cost Analysis of Aquatic Biomass Sys-terns, ” prepared for the Department of Energy, contract NoHCP/ET-400-78/I



104 . Vol. II —Energy From Biological Processes

Test farms will up we ll d ee p o c ea n wa ter to

supply kelp with proper nutrients. Reservations

about this procedure are twofold among skep-

tic s. They wo rry that d ee p w ate r co uld b ec ome

stagnan t under the fa rms, o r tha t , once up -

welled, the water would dilute too rapidly and

sink again.

As previously mentioned, this country’s ma-

jor ocean biomass project is jointly supported

by C R I and DOE. The p roject ma y be c ome the

most heavily funded biomass program of the

1980’S, with grants projected to grow to over

$50 million yearly by 1983. Plans for this proj-

ect have been developed mainly by GRI, al-

though regular DOE approval for phases of the

project is mandatory.25

GRI estimates imply that ocean kelp farming

could be a commercially viable project for this

c ou ntry. The Insti tute ’ s fue l p rod uc tion c ost

est imates for methane generat ion f rom ke lprange from $3 to $6/million Btu.

The p rev iously ment ioned Dynate c h repo rt

on fuels from marine biomass comes to a dif-

fe ren t conc lus ion . I ts es t ima tes range f rom

$7/mi l l ion Btu up to several hundreds of dol-

lars per mi l l ion Btu, should productiv i ty prove

low and design costs high.

Som e c ritics of the GRI marine b ioma ss p ro-

gram contend that there is not enough data

ava i lab le to just i fy the leve l o f expendi tures

for the biological test farm.

Critics have stated that the open ocean test

farm is an inappropriate and perhaps prema-

ture step in a long, logical process of devel-

oping future deep sea operations. Considera-

t ions which may be over looked by th is test

farm approach include:

the need fo r be t te r i n fo rma t ion on ke lp

growth and productiv i ty and l imit ing fac-

tors in natural beds;

the need for additional basic research into

nutrients and productivity (much research

‘sGeneral Electric Co., briefing, “Energy From Marine Biomass

Project, Program Review, ” for the Gas Research Institute, New-

port Beach, Cal if., March 1978.

q

q

q

is also needed on plant diseases, preda-

tors, and water movement and quality);

the poss ib i l i ty o f deve lop ing sha l low wa-

ter kelp farms ei ther in areas of natural

upwell ing or in conjunction with other fer-

tilizing techniques (see ch. 10);

hard data on net energy expectations is

lacking; andno plans are being readied at present as

alternatives to ferti l ization by upwell ing.

Since plan s for future oc ea n b ioma ss farms

call for the use of mil l ions of acres of ocean

surface, there will be conflicts with other tradi-

tional users. The d ed ic a tion of large area s of

open ocean surface for a single commercial

pu rpose such as th i s i s unp receden ted . I t

wo u l d r e q u i r e c o m p l e x , s p e c i a l r e g u l a t i o n

after review of current local, national, and in-

ternational laws.

Even though the ocean space within the 200-mile zone surrou nd ing the United Sta te s is 1½

bi l l ion acres, confl icts can be expected with

such t rad i t iona l ocean users as commerc ia l

shipping, the navy, commercial and sport fish-

ing, offshore oil and gas operation, and recrea-

t iona l boa ting. To da te, no de tai led investiga -

tion of legal or institutional approaches to re-

solving c onfl ic ts ha s be en a c c om plished . This

issue will need analysis prior to any large-scale

initiative in ocean farming, and will have a ma-

jor impact on feasibil i ty, productivity, and cost

of marine biomass in the future. Analyses of

specific sites and siting problems will be cru-

cial to the ocean question.

OTA ha s found tha t Fed era l resea rc h p ro-

grams directed toward energy problems have

not been adequately coordinated with simi lar

research directed toward production of food,

chemicals, or other products.

Much research i s needed to deve lop any

su i tab le mar ine p Ian t cu l tu re regard less o f

whethe r the end produc t is food or fuel. Such

basic research could be better supported and

coord inated by a l l in terested agencies. Pro-

grams supp orted b y Sea Grant and the Nation-

al Scienc e Found ation have tend ed to foc us on

b a s i c b i o l o g i c a l e f f o r t s o r f o o d p r o d u c t i o n

goals while DOE programs are focused on pri-




ma ry fuel prod uc tion. Since DO E now ha s the in de ep wa te r, op en o c ea n fa rms. This p ossibili-

major funds ava i lab le for seaweed research, ty would mean coordination of several existing

the tendency has been to create programs fo- research efforts; expanding some, developing

cused on fuel produc tion. The enc ourage ment s o m e n e w o n e s , and genera l ly in tegrat ing

o f fu r the r d i ve rs i ty i n ex i s t i ng seaweed re - many efforts focused on basic biological ques-

search efforts is essentia l to a long-term im- t ions and food product ion as wel l as energy

provement in the knowledge and capabil i ty of p roduc t ion .

deve lop ing fu ture mar ine p lant cu l ture pro-grams.

One approach to conduct ing a systemat ic

program for developing ocean farms would be

to expand research in natural seaweed beds

and shallow water farms prior to experiments

Other Unconventional

There a re seve ra l othe r unc onve ntional ap -

proaches to b iomass product ion. Because o f

the complexity of plant growth, it is l ikely that

many approaches wi l l be tr ied and fai l . How-

ever, this complexity also gives rise to signifi-

cant possibil i ties. While all unconventional ap-

proaches cannot be covered here, a few are

discussed below.

Multiple Cropping

MultipIe cropping consists of growing two or

more crops on the same acreage in a year.

Growing winter wheat on land that produced a

summ er crop is one exam p le. The w inter wh ea tcan delay spring planting, so i ts use is ap-

p l icab le on ly for land where cer ta in summer

crops are to be grown. However, this is basical-

ly a conventional approach.

The unc onventional mult ip le c rop ping c on-

sists of growing more than one summer crop

on an acreage by harvest ing the f i rs t crop

before i t matures or deve lop ing species that

ma ture rap idly. Since sta rche s, sug a rs, veg et a -

ble oils, and hydrocarbons are generally pro-

d u c e d i n t h e g r e a te s t q u a n t i t i e s i n m a tu r e

plants, th is approach would probably reduce

the overall yields of these products. Also, the

time between the harvest of the first crop and

the development of a full leaf cover in the sec-

ond crop wil l be a time when sunlight is not

Approaches

c a p tu r e d b y th e p l a n ts a s e f f e c t i v e l y a s i t

could. Consequently, this approach would also

be expected to reduce the total biomass yields.

Chemical Inoculation

By subjecting some plants to herbicides like

paraquat or 2,4-D, hydrocarbon or vegetable

o i l p roduct ion can somet imes be increased.

Th e se c h e m i c a ls b l o c k c e r ta i n b i o c h e m ic a l

pathways, thus promoting greater production

o f o th e r p r o d u c ts . Pre l im ina ry resu l ts w i th

guayule, for example, indicate that 2,4-D may

cause a doubling of the natural rubber content

o f th i s p lan t .26

While it is too soon to assessthis approach, it may prove to be an effective

way of improving yields of these products.

Energy Farms

E n e r g y fa r m s h a v e b e e n p r o p o s e d27 a s a

means of providing a reliable supply of large

quan t i t i es o f b iomass fo r l a rge convers ion

fa c i li t ies l oc a ted on o r nea r the fa rm. The

basic idea is to have a large tract of land (tens

‘6Gilpin, et al,, op. cit.

“See, e.g., G, Szego, “Design, Operation, and Economics ofthe Energy Plantation, ” Proceedings Conference on Capturing the Sun Through 6ioconversion (Washington Center for Metropoli-

tan Studies, 1976); G C. Szego and C C Kemp, “Energy Forests

and Fuel Plantations,” Chemtech,p. 275, May 1973; and Si/vicu/-ture Biomass farms (McLean, Va.: MITRE Corp., 1977).

67-968 0 - 80 - 8



106 q Vol. Il—Energy From Biological Processes

of thousands of acres) dedicated to growing

the biomass feedstock for a nearby conversion

facility. Although this is technically possible, a

number o f pract ica l and economic considera-

t ions probably wi l l l imi t investment in energy

farms. Moreover, this approach ignores the ef-

fect that bioenergy production has on related

sec tors. Som e o f the m ore imp ortant of the sepoints are:

q

q

q

q

Land. – Th e l a n d a v a il a b l e f o r e n e r g y

farms has often been estimated to be sev-

e r a l h u n d r e d m i l l i o n a c r e s .2829 O TA ’ s

analysis, however, indicates that consider-

ably less land is available for biomass pro-

duction (see ch. 3). Furthermore, there

would be pract ica l d i f f i cu l t ies wi th buy-

ing la rge con t iguous t rac ts o f the s i ze

needed for large conversion facilities (tens

to hundreds of thousands of acres).

If cultivation on very poor or arid land

proves to be feasible or i f i r r igation for

energy production is social ly acceptable

and the water is available, then these lim-

i tat ions could be somewhat less severe

than they appear to be at present.

Crop yields.– Est imates o f fu ture y ie lds

from short-rotation tree farms have been

as h igh as 30 ton /ac re -y r ,30 w h i c h O TA

considers to be highly unreal ist ic. Yields

of 6 to 10 ton/acre-yr are more realistic for

the poorer soil that could be available for

energy farms.

Initial investment.– I f short-rotation treesare used as the energy crop, there would

be a 6- to 10-year Ieadtime before the first

harvest c ou ld b e m ad e. Th is wo uld b e

p r o h i b i t i v e l y l o n g f o r m a n y i n v e s t o r s .

Grasses, however, would reduce the lead-

time to a fraction of a year. In either case,

the cost of acquir ing the land would in-

crease the initial investment substantially.

Risk.— Using short-rotation trees as the en-

ergy crop would give yields that are less

sensi t ive to weather than grass because

the growth would be averaged over sev-

‘%zego, op . cit.29s; /v;cu/ ture/3;c3fnass Farms, op . cit.

‘OJ. A Allich, Jr., and R E Inman, “Effective Utilization of

Solar Energy to Produce Clear Fuel, ” Stanford Research insti-

tute, final report No NSF/RANN/SE/Cl 38723/FR/2 , 1974

q

q

eral years. A pest infestation, however,

could destroy the entire crop in which an

average of 3 to 5 years’ cul t ivation had

been invested, and this could be financial-

ly disastrous. If grass is the energy crop,

or the t ime between t ree harvests is re-

duced, the loss f rom a pest in festa t ion

would be considerably less, but the yieldswould f luctuate more from year to year,

mak ing i t necessary to re l y on ou ts ide

sources of biomass in years with low har-ves ts o r t o se l l surp luses in years w i th

bumper harvests.

Competition with other uses for the land. – Because o f the uncer ta in ty abou t fu -

ture cropland needs for food production,

it would be unwise to assume that tens of

mi l l ions of acres could be devoted to a

conversion facility for 30 years without af-

fec t i ng the p r i ce o f fa rm land and thus

food .Preclusion of nonenergy benefits. -OTA’sanalysis indicates that bioenergy harvests,

i f properly integrated into nonenergy sec-

tors, can provide benefi ts beyond the en-

ergy, such as increased growth of timber

suitable for paper and lumber. Attempting

t o i s o l a t e b i o e n e r g y p r o d u c t i o n f r o m

these other sectors would preclude some

of the potential benefits.

A l though none o f these fac to rs i s i nsu r -

mountab le , taken together they make energy

farms appear considerably less attractive than

numerous other bioenergy options. Particular-

ly because of the r isk and the in i t ia l invest-

ment, it is more likely that bioenergy crops will

be grown as one o f the many crop cho ices

a v a i l a b l e t o f a r m e r s , r a th e r t h a n o n l a r g e

tracts dedicated solely to energy production.

There is, howeve r, no te c hnica l reason w hy en-

ergy farms cannot be constructed.

Biophotolysis

Biophoto lys is is genera l ly def ined as the

process by which cer ta in microscopic a lgaecan produce hydrogen (and oxygen) from wa-

te r a nd sunlight. Two d istinc t me c ha nisms a re

known by which microalgae can carry out bio-

photo lys is : 1) through a “hydrogenase” en-



Ch. 4—Unconventional Biomass Production . 107

zyme (biological catalyst) which is activated or

induced by keeping the microalgae in the dark

w i th o u t o x y g e n fo r a p e r i o d o f t i m e ; o r 2 )

through the “ni trogenase” (ni trogen-f ix ing) en-

zyme which normally allows some types of mi-

croalgae (the “blue-green” algae) to fix atmos-

pher i c n i t rogen to ammon ia bu t wh ich a l so

can be used to produce hydrogen by keepingthe algae under an inert atmosphere such as

argon gas.

In the case o f b iophoto lys is wi th hydroge-

nase the key problem is that when simultane-

ous oxygen product ion occurs, the hydroge-

nase enzyme reaction is strongly inhibited and

the enzyme i tsel f inactivated. Al though i t was

recently demonstrated that simultaneous pro-

duction of oxygen and hydrogen does occur in

such algae,31 it is uncertain whether it will be

possible to sustain such a reaction in a prac-

tica l syste m. This d iffic ulty ha s led to p rop os-als for separation of the reactions either by de-

veloping an algal system which alternates oxy-

gen and hydrogen production, (possibly on a

day-night cycle) or by developing a two-stage

p roc ess. Suc h syste ms a re still at t he c on c ep -

tua l s tage , a l though cons ide rab le knowledge

exists about the basic mechanisms involved.

Some wha t bette r de veloped is a b iop hoto ly-

sis process based on nitrogen-fixing blue-green

algae. I n these algae the oxygen-evolving reac-

tions of photosynthesis are separated from the

oxygen-sensitive nitrogenase reaction by their

segregation into two cell types — the photosyn-

thetic vegetative cells and the nitrogen-fixing

heterocysts. Heterocysts receive the chemicals

necessary to produce hydrogen from vegeta-

t i ve ce l l s bu t a re p ro tec ted f rom oxygen by

the i r heavy ce l l wa l l and act ive resp i ra t ion.

Using cultures of such algae from which nitro-

gen gas was removed, a sustained biophotoly-

sis reaction was demonstrated: about 0.2 to 0.5

percent of incident solar energy was converted

to hydrogen gas over a l -month period. How-

ever, significant problems stil exist in the de-

velopment of a practical system —1 O times

higher conversion e ffic ie nc ie s m u st b e

ach ieved, a goa l which may not be reached

“ E Greenbaum, Bioengineering Biotechnology Symposium,VOI 9, In press

due to the high energy consumption of the ni-

trogenase reaction. Also, the mixture of hydro-

gen and oxygen generated by such a system

may be expensive to separate.

W h i c h e v e r b i o p h o t o l y s i s m e c h a n i s m s o r

processes are eventually demonstrated to be

capable of efficient and sustained solar energy

conversion to hydrogen fuel from water, they

must take place in a very low-cost conversion

system . The d eve lopm ent o f an e ng inee red

biophotolysis conversion uni t must meet str in-

gent capital and operational cost goals. As bio-

photolysis wi l l be l imited by the basic proc-

esses of photosynthesis— probably no more

than 3 to 4 percent of total solar energy con-

version to hydrogen fuel —this sets an upper

l imit to the allowable costs of the conversion

unit. In principle, the algal culture—the cata-

lyst which converts sunlight and water to hy-

d r o g e n a n d o x y g e n – c a n b e p r o d u c e d v e r ycheaply; however, the required “hardware” to

contain the algal cul ture and trap the hydro-

gen produced may be relatively expensive.

Biophotolysis is still in the early stages of

deve lopment . No pa r t i cu la r mechan ism, con -

verter design, or algal strain appears to be in-

he ren t l y super io r a t th i s s tage . C la ims tha t

near-term practical applications are possible,

that genetic engineering or strain selection can

result in a “super” algae, or that biophotolysis

is inherently more promising than other bio-

mass energy opt ions are present ly not war-

ranted. A relatively long-term (10 to 20 years)

basic and app l ied research e f for t wi l l be re-

quired before the practical possibil i ties of bio-

photolysis are established.

Inducing Nitrogen Fixation in Plants

The b iologic a l p roc ess of ni trog en f ixa tion,

the conversion of nitrogen gas (not a fertilizer)

to ammonia (a ferti l izer) has only been found

to occur in bacteria and the related blue-green

a lga e. The se p rimitive org a nisms ma intain the

ecological nitrogen cycle by replacing nitrogenlost th roug h va r iou s na tura l proc esses. The

capabi l i ty for n i t rogen f ixa t ion expressed by

many pIants (soybeans, al fa l fa, peas) is due

so le ly to the i r ab i l i ty to I ive in a symbiot ic



108 q Vol. Ii—Energy From Biological Processes

association with certain bacteria (of the genus

Rhizobia), which form the character ist ic “root

nodules.” A certain fraction of the photosyn-

thetic products of these plants are transferred

to the roots where they are used (as “fuel”) by

the bacteria to fix nitrogen to ammonia which

is then sent (in bound form) to the protein syn-

thesizing parts of the plant.

This p roc ess is, in p rinc iple, e ne rgy inte n-

sive, wi th each ni trogen atom (f ixed) reducing

th e b i o m a s s p r o d u c t i o n b y s e v e r a l c a r b o n

atoms (about 2 to 3).32 In pract ice , s ign i f icant

inefficiencies in the process are often noted,

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

some Rhizobia bacteria in root nodules waste

a large fraction of the “fuel” suppl ied by the

plant in the form of hydrogen gas.33 By using

Rhizobia stra ins that can e f fect ive ly recyc le

the hydrogen gas, this loss may be overcome.

A l th o u g h b i o l o g i c a l n i t r o g e n f i x a t i o n c a nsubstitute, to a large extent, for the fossil-fuel-

derived ni trogen fert i l izers currently used in

ag r i cu l tu re , the t radeo f f may be an ove ra l l

reduction in biomass yields. In an era of de-

creasing fossil fuel availability, such a tradeoff

may be desirable, particularly as the price of

commercial fert i l izers is a l imit ing economic

factor in many biomass production proposals.

However , nutr ient recyc l ing cou ld be pre fer-

ab le to de novo p roduc t ion , as i t p robab ly

wou ld be less cos t l y and energy in tens ive .

Al ternat ive ly to b io log ica l n i t rogen f ixa t ion,

the rmochemica l convers ions o f b iomass tosynthesis gas and their catalytic conversion to

ammonia are feasible. Whether this is more fa-

vorable both in terms of economics and energy

efficiency is uncertain.

A number of scientists have proposed that,

through genetic engineering, they could trans-

fer the n i t rogen- f ix ing genes d i rect ly to the

plant. However, such proposals face technical

barriers. For example, the nitrogen-fixing reac-

tion is extremely oxygen sensitive and is unlike-

ly to be able to take place in the highly oxygen-

rich environment of a plant leaf. In principle,

there would only be a relatively minor advan-

tage for a plant to directly f ix ni trogen rather

than do so symbiot ica l ly . Much more bas ic

knowledge in many areas of plant physiology,

genetics, biochemistry, etc., as well as devel-

opments in genetic engineering and plant t is-

sue culture wil l be required before the poten-t ia l for practical appl ications of such concepts

can be evaluated.

Greenhouses

It is well known that increasing the C02 c o n -

cen t ra t i on in the air results in signific a ntly im-

proved plant growth for some plants. Depend-

ing on the specific plant and the specific con-

ditions of the experiments, a 50-to 200-percenti n c r e a s e i n b i o m a s s p r o d u c t i o n h a s b e e nnoted . Greenhouses have the add i t i ona l ad-

v an t ages o f p rov i d i ng a “ c on t r o l l ed env i r on -ment” where pest contro l , water supp ly , and

ferti l ization can be better managed, resulting

in po tent ial ly high yields. The higher te mp era-

ture in greenhouses allows extended growing

seasons in temperate cl imates. Greenhouse

agriculture is rapidly expanding thoughout the

wor ld to meet the demands o f a f f luent coun-

tries for out-of-season vegetables and horticul-

tu ra l p roduc ts . Ho we v e r , t h e h i g h c o s t o f

greenhouse agr icu l ture and i ts h igh energy

consumption make production of staple c rops

unfeasible and proposals for biomass energy

p r o d u c t i o n u n r e a l i s t i c a t p r e s e n t . A l t h o u g h

significantly lower cost greenhouse technology

is feas ib le i n p r inc ip le , b iomass p roduc t ion

costs in Arizona, for example, would still be 10

times as expensive as open-field biomass crops

grown in the Midwest.34 A signi f icant inf lat ion

i n f a r m c o m m o d i t y , f a r m l a n d , a n d w a t e r

prices could make greenhouse systems more

attractive. At present and in the foreseeable

fu tu re , however , g reenhouses do no t appear

economica l ly feas ib le for b ioenergy produc-

t ion.

‘2K. T Shanmugan, F. O’Gara, K. Andersen, and P C. Valen-

tine, “Biological Nitrogen Fixation,” Ann. Rev. Plant Physio/. 29,p. 263,1978.

“Ibid.

“L. H. de Bivort, T. B. Taylor, and M, Fontes, “An Assessment

of Controlled Environment Agriculture Technology, ” report by

the International Research and Technology Corp. to the National

Science Foundation, February 1978.



Chapter 5.— BIOMASS PROCESSING WASTES

Page

Introd uc tion . . . . . . . . . . ... , . . . . . . . . . . . . .. 111

Wood-Processing and Paper-Pulping Wastes .. ..111

Ag ric ultura l Wastes . . . . . . . . . . . . . . . . . . . . .. .112A n i m a l M a n u r e . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 4

TA BLESPage

39. The Ten Ma jor Ag ric ultural Wa ste s WithPotential to Produce Energy. . ...........113

Page40. Energy Potential From Animal Manure on

Confined Animal Operations . . . . . . . . . . . .114

FIGURES

Page 14. Material Flow Diagram for Forest

P ro d u c ts I n d u s t r y . . .. . . . . . . . . . . . . . . . . . 1 1 115. Tota l Energy Ava ila b le From Ma nure b y

Farm Size . . . . . . . . . ..................114



Chapter 5

BIOMASS PROCESSING WASTES

Introduction

There a re a numb er o f b yprod uc ts assoc i-

ated with growing biomass and processing itinto finished prod uc ts. The b yprod uc ts tha t a re

not general ly col lected in one place, such as

logging or crop residues, are termed residues

and are d ea lt with in c hap ters 2 and 3. The b y-

products that are col lected in one place are

termed processing wastes for the purposes of

this report and are considered in this chapter.

The three m a in type s of w a stes c onsid ered a re

th e p r i m a r y a n d s e c o n d a r y m a n u fa c tu r i n g

wastes of the forest products industr ies, and

the wastes associated with the processing ofa g r i c u l t u r a l p r o d u c ts a n d a n i m a l m a n u r e s .

W a s t e p a p e r , c a r d b o a r d , a n d u r b a n w o o d

wastes are not considered in this report, since

they fall into the category of municipal solid

wa ste s, whic h is the sub jec t of a p revious OTA

r e p o r t .

IMateria/s and Energy From Municipal Waste [Washington,

D C.: Office of Technology Assessment, July 1979), OTA-M-93

Wood-Processing and Paper= Pulping WastesBased on published surveys and discussions

wi th people fami l ia r wi th the forest products

industries, the fraction of wood feedstock that

appears as residue was estimated for the vari-

ous types of processes and regions of the coun-

try. The se fra c tions a nd the U.S. Dep a rtmen t

of Ag ric ulture’ s Forest Sta tistics* w ere used to

estimate the quantities of residues generated

by wood-processing and paper-pulping indus-

tries. The re is, how ev er, som e un c erta inty in

these figures, since published data usually are

repor ted in board fee t o r cub ic fee t ( ra the rt h a n d r y t o n s ) a n d o f t e n t h e b a r k i s n o t

counted. Fur thermore, mois ture loss dur ing

drying must be accounted for, Every effort was

made to avoid these potentia l problems and

adjust for the shrinkage.

Current data on the use of the manufactur-

ing residues are not complete. In some cases

da ta are a vailab le for only a few State s or for

some of the industries. In other published data,

regional surveys are extrapolated to the entire

c oun t ry . The e st ima te s p resen t ed he re a re

based on several surveys,

3

but are neverthelessba sed on incom plete data .

‘Forest Statistics for the United 5tates, 1977 (Washington, D C :

Forest Service, U.S. Department of Agriculture, 1978)

‘J S. Bethel, et al., “Energy From Wood,” contractor report to

OTA, April 1979.

Figure 14 shows an approximate materia ls

f l ow d iag ram fo r the ha rves ted wood p roc -

esse d b y th e fo rest p rod uc ts ind ustry. This is a

nationa l average diag ram . There are, howe ver,

Figure 14.—Material Flow Diagram for ForestProducts Industry (in energy units, Quads/yr)

Forest productsindustry harvest

3.1Pulpwood harvests

Primary andsecondary

manufacturing 0.7 Paper and pulp2.0 1.8

Residues of primaryand secondarymanufacturing

Unused Energy Energy0.14 0.3 1.0

Total wastes used as energy: 1.2 to 1.3 Quads/yr

Unused waste 0.1 to 0.2 Quad/yrEnergy and unused 1.4 Quads/yr


111




s ign i f i can t va r ia t i ons be tween the reg ions ,

with the unused fraction being about twice as

large in the East as in the West.

The large st user of b ioma ss ene rgy in the

United Sta tes is the pu lp an d pa pe r ind ustry.

This ind ustry is c urre nt ly 45 - t o 5 5 -p e rc e n t

energy sel f-suff ic ient, up from 37 p e r c e n t i n

1967.4 A major reason for the use of wood en-

ergy in the forest products industry is that the

p r o c e s s u s e d to r e c o v e r t h e p a p e r - p u l p i n g

chemicals in most of the pulping processes in-

volves burning the sp en t p ulping l iq uor. This

ac co unts for ab out 0.8 Qua d/ yr. The rema ining

0.2 Quad/yr of bioenergy used in the pulp and

paper industry comes from the bark of the har-

vested wood and reject woodchips.

The p r ima ry ma nu fa c tu r ing indust ry p ro -

duc es lumb er, p lywo od , po les, e tc . The sec -

ondary industry produces furni ture, prefabri -c a te d ho using, et c . The se ind ustries a re 20- to

40 -pe rcen t ene rgy se l f - su f f i c ien t . sA b o u t 5 0

percent (40 mil l ion dry ton/yr) of the primary

‘E, P Gyftopoulos, L J Lazarides, and T. F Wldmer, Potential

Eue/ Effectiveness in Industry (Cambridge, Mass : Balllnger Pub-

lications).5S. H Spurr, Renewable Resources for Energy and Industrial

Materials (Austin, Tex LBJ School of Public Affairs, University

of Texas, 1978)

manufacturing wastes and 40 percent (4 mil-

l ion dry ton/yr) of the secondary manufactur-

ing wastes go to paper pulping. Another 20 per-

cent of each of these industries’ residues goes

to particle board and various other uses. About

20 million dry ton/yr (0.3 Quad/yr) of wood are

used for energy; 9 mi l l ion dry ton/yr (about0.14 Quad/yr) are unused.

The m ain rea sons that t he unused po rtion is

not used appear to be the very low quality of

these wastes and a geographical mismatch be-

tween the source and potent ia l users o f the

waste. However, e i ther a strong wood energy

market or cooperative agreements with elec-

tric uti l i ties for cogeneration could bring these

wastes into energy use.

There a re a l ternative uses for som e o f the

wastes other than for energy. If the demand for

forest products increases and other fuels areavailable, then more of the pr imary and sec-

o n d a r y m a n u fa c tu r i n g b y p r o d u c t m a y b e d i -

verted from energy use to part ic le board and

p a p e r a n d p u l p p r o d u c t i o n . I n a d d i t i o n , a

s m a l l f r a c t i o n o f t h e s p e n t p u l p i n g l i q u o r

could be used to produce ethanol and I ignin

products (as one Georgia Paci f ic Corp. plant

does) instead of simply burning the spent l iq-

uor to recover the pulping chemicals.

Agricultural WastesWi th th e e x c e p t i o n o f o r c h a r d p r u n i n g s ,

agr icu l tura l waste byproducts are genera l ly

not collected at the place where the crops are

grown. Rather, the wastes usual ly occur as

byproduc ts to the ag r i cu l tu ra l p roduc t -p roc -

essing industr ies. About 50 to 70 percent of

these byproducts are sold as animal feed or for

chemica l p roduc t ion a t p r i ces tha t p roh ib i t

the ir use fo r ene rgy. ’ The w a ste b yprod uc ts not

being used for other purposes are considered

in this sec tion.

The va riou s a gricul tural p rodu c t-proc essing

industr ies were surveyed 7 t o d e t e r m i n e t h e

quanti t ies and types of waste byproducts that

‘R. Hodam, “Agricultural Wastes,” Hodam Associates, Sacra-

mento, Calif., contractor report to OTA.

‘Ibid.

are p rod uc ed . Tab le 39 show s the 10 major

types o f agr icu l tura l wastes and the energy

po tentia l of e ac h. These 10 wa stes rep resent

ove r 95 pe rcen t o f a l l ag r i cu l tu ra l was tes

available for energy. Of these 10, about 90 per-

cent are materia ls relatively low in moisture,

and suitable for thermal conversion (combus-

tion o r ga sifica tion). The rema ining 10 perce nt

ap pea r to be a cc epta ble for ana erob ic d iges-

tion or possible fermentation to ethanol in the

case of fruit and vegetable wastes and cheese

whey.

In addition, there is an unknown quantity of

spoiled and substandard grain. One source8 e s-

OM. T Danz iger, M, P, Steinberg, and A. I Nelson, “Storage of

High Moisture Field Corn,” Illinois Research, fall 1971



Ch. 5—Biomass Processing Wastes q 1 13

Table 39.–The Ten Major Agricultural Wastes WithPotential to Produce Energy

Wastes Btu/yr x 1012

Orchard pruningsa. . . . . . . . . . . . . . . . .

Cotton gin trasha . . . . . . . . . . . . . . . . . . . .Sugarcane bagasse

a. . . . . . . . . . . . . . . .

Cheese wheyb . . . . . . . . . . . . . . . . . . . . . .Tobacco (burley)a. . . . . . . . . . . . . . . . . . . .

Rice hullsa. . . . . . . . . . . . . . . . . . . . . .Tomato pumice

b. ., ., . . . . . . . . . .

Potato peel and pulpb . . . . . . . . . . .Walnut shella. . . . . . . . . . ., . . . . . . .Citrus rag and peel

b. . . . . .

Total . . . . . . ., . . . . . . . . . . . . .

30-6120-31

4-84- B c

2.3

2.2 1.3-1.81.0-1.1

0.90.3-1.0

66-117

asultable for combustion or gaslflcatlonbsultable for anaerobtc dtgestlon or fermentationc~sed on starch content of milk and the volume of cheese production frOrTl ~rJrlCUhJh3/ .%?tEflCS

(Washmgfon, D C U S Department of Agriculture, 1978)

SOURCE Off Ice of Technology Assessment, and R Hodam “Agricultural Wastes, ” Hodam

Assoclales, contractor report to OTA, 1979

timated corn spoilage from mold at 250 million

bu/yr , but th is number should be v iewed asspeculative. Furthermore, much of the spoiled

grain may be accessible only as a supplement

to existing distillery feedstocks because its oc-

currence is dispersed and unpredictable.

Th e f o u r m a j o r so u r c e s o f a g r i c u l t u ra l

wastes are orchard prunings, cotton gin trash,

sugarcane bagasse, and cheese whey. Most

Sta tes have f ru it o r nu t o rc ha rds, w i th the

largest crops occurring in Arizona, California,

Flor id a , Texa s, New York, and Wa shing to n.

Cotton gin trash is generally localized to the

southern third of th e United Sta tes and Ca lifor-nia. Suga rca ne is proc essed p rimarily along the

Gul f Coast , in Hawai i , and in New England.

The m ajor ity o f c hee se w hey is prod uc ed in

Wisconsin, Minnesota, New York, lowa, and

Ca l ifornia, but 30 Sta te s ha ve som e c he ese

produc t ion .

Orchard prun ings are genera l ly co l lected

and burned onsite. A few growers disk whole

prunings into the soi l , a l though this is not a

preferred practice for growers. With a strong

energy market, much of this could be used for

en ergy. The m a jor exp en se is tran sp orting th e

prunings to the place they are used.

Cotton gin trash is another potential source

of ene rgy. Texas c ot to n g ins prod uc e a bo ut

five times as much energy in gin trash as they

c onsume (mo stly electricity). The ma jor prob-

lems with using the trash for energy seem to be

the difficulty of handling the trash, the season-

al nature of the ginning operations, and the dif-

f i cu l ty i n es tab l i sh ing coopera t i ve ven tu reswith the electr ic uti l i t ies. In addi t ion, in the

areas where the cotton plants are ki l led with

arsenic acid prior to harvest, such as in much

of Texa s, sp ec ial prec a utions will b e n ec essa ry

to burn the trash in an environmentally accept-

able way.

Suga rc ane b ag a sse is wide ly used in Ha wa ii

a s a source of e ne rgy. The suga r refineries ha ve

long-standing cooperative agreements with the

electric utilities. Cogeneration is used to gener-

ate and export electricity to the utiIities and to

produce the process steam used by the sugarre f ine r ies. The e lec t r ic g ene ra t ing fa c i li t ies

range in size from 1.5- to 33-MW electric. Most

of the Hawaiian sugar refineries are 99- to 100-

percent energy self-sufficient.

The New Eng land an d Sout hern sug ar refin-

eries should be analyzed in detail for the po-

tentia l to dupl icate the Hawai i experience, in-

c l u d i n g th e p o te n t i a l t o p u r c h a s e o r c h a r d

prunings or wood wastes which are found in

the same area in some cases.

OTA’ s a na lysis indic a te s tha t c he ese whe y is

the largest source o f food-process ing wastesu i tab le for convers ion to e thanol , a l though

other studies have indicated that citrus wastes

are a larger source.9 Based on total cheese pro-

d u c t i o n , 10 OTA e stima te s tha t 50 m illion to 100

mi l l i on ga l /y r o f e thano l cou ld be p roduced

from cheese whey. Current product ion f rom

this source is about 5 million gal/yr.

‘The Report of the A/coho/ Fue/s Po/Icy Review (Washington,

D C : Department of Energy, June 1979), GPO stock No 061-

(XX3-OO31 3-4,

‘“The Out/ook for Timber in the U.S. (Washington, D C : Forest

Service, U S Department of Agriculture, 1974), report No. 24;

and Agricu/tura/ Statistics (Washington, D C U S Department of

Agriculture, 1978)



114 q Vol. II—Energy From Biolog ica l Proc esses

Animal Manure

The m a jor sou rce s of a nima l ma nures suit-

able for energy are from dairy cows, cattle on

feed, swine, chickens (broilers and layers), and

turkeys. Only animals in confined animal oper-

ations are considered. However, i t has been

estimated that 48 percent of all manure voidedfrom livestock (primarily sheep and cattle), is

on open range. ” Th is op en ra nge ma nure

would requ i re co l lect ion and, therefore , wi l l

not be economic in the foreseeable future.

The inventory o f onfa rm c onf ined an ima ls

was derived from inventory numbers for ani-

mals that remain onfarm for more than a year

and from sales numbers and the average time

the animal spends on the farm for animals on

fa rm for less tha n a yea r. ’z These invento ry

numbers were converted to the common basis

of the number of animal units, or the equiv-

alent of a 1,000-lb animal (defined in figure 15).The q uantities of ma nure w ere ca lculated and ,

assuming that the manure is anaerobically di-

gested to produce biogas (60 percent methane,

40 percent carbon dioxide), the energy equiv-

alent was derived.

Ta ble 40 show s the e nergy p ote ntia l from

each type of animal operation, and f igure 15

shows the percent of this energy potential that

is present on conf ined an imal operat ions o f

various sizes (expressed in animal units). Cur-

rently most of this manure is used as nitrogen

fertilizer and soil conditioner or is unused.

The to tal energy p otential from ma nure p ro-

duced in confined animal operations is about

0.3 Quad/yr. From one-third to one-half of this

manure is currently allowed to wash away with

rain or is allowed to dry which makes it unsuit-

able for anaerobic digestion. However, if it be-

comes economica l ly a t t ract ive to d igest the

manure, then most o f these operat ions can

change the i r manure-handl ing techn iques to

accommodate anaerobic digestion.

Figure 15 shows that over 75 percent of the

energy potential occurs on farms with less than

1‘D. Van Dyne and C, C ilbertson, Estimating U.S. Livestock andPoultry Manure and Nutrient Production (Washington, DC.: U.S.

Department of Agriculture, 1978), ESCS-12.

“1974 Census of Agriculture (Washington, D C : Bureau of the

Census, U S. Department of Commerce), vol. 1-50

1,000 animal units and that about 45 percent

of the potential is on farms with less than 100

animal un i ts . L a r g e fe e d l o t s ( g r e a te r t h a n

10,000 animal units) only account for about 15

percent of the total . Consequently, any tech-

nology development that is aimed at ful ly uti-lizing the potential for energy from animal ma-

nure wi l l have to concentra te on re la t ive ly

small-scale conversion units.

Figure 15.—Total Energy Available From Manure byFarm Size (confined animal operations)

16.2% I6.6%

30.9%

41.7%

4.6%

50 ”/0

10,000 + animal units IPercent of energy

100-999

10-99

0.1-9.0

4 0 %

3 0 %

2 0 %

10%

1 animal unit =

250 chickens250 broilers50 turkeys

1.25 cattle on feedFarm size in animal units

0.83 dairy cow6.25 swine

SOURCE: K D, Smith, J. Philbin, L. Kulik, and D. Inman, “Energy From Agri-culture: Animal Wastes,” contractor report to OTA, March 1979.

Table 40.–Enorgy Potential From Animal Manureon Confined Animal Operations

Total energy potential PercentType animal Btu x 1012 /yr or total

Dairy cattle. . . . . . . . . . . . . . . . . . . . .Cattle on feed . . . . . . . . . . . . . . . . . . .Swine . . . . . . . . . . . . . . . . . . . . . . . .Chicken (broilers) . . . . . . . . . . . . . . . .Chicken (layers) . . . . . . . . . . . . . . . . .Turkeys. . . . . . . . . . . . . . . . . . . . . . .

Total energy potential from allmanures . . . . . . . . . . . . . . . . . . .

90 3380 3032 12

30 11

25 9

18 6

274 100

SOURCE K D. Smtth, J Phdbm, L Kuhk, and D. Innran, “Energy From Agriculture. AnimalWastes, contractor report to OTA, March 1979.



Part II.

Conversion Technologies andEnd Use



Chapter 6




Chapter 6


Most bioenergy currently comes from direct

combustion of solid biomass for space heating,

process steam, and a small amount of electric

generation. As chemically stored solar energy,

biomass can be converted to a number of gas-

eous and liquid fuels, which can be used for a

variety of energy purposes not suited to direct

combust ion.

Th e r m o c h e m i c a l c o n v e rsio n , o r c h e m i c a l

processes induced by heat, is currently the

most sui table process for the major biomass

feeds tocks–wood and p lan t he rbage . As ide

from direct combustion, these processes in-

clude gasification and l iquid fuels production.

Various types of gasifiers are being developed

wh i c h could be used for process h e a t a n d r e t -

rofits of oil- and na tural-ga s-fired b oilers. Suit-

able gasifiers may be commercially available

in less than 5 years wi th adequate deve lop-

ment support. Methanol synthesis is the near-

term option for l iquid fuels production. Wood-

to-methanol plants can be constructed imme-

d ia te ly , wh i le herbage- to-methanol processes

need to be demonstrated. Various other proc-

esses are being developed, and thermochemi-

cal conversion of biomass offers considerable

promise for improved processes and new appli-

cations for fuel and chemical syntheses.

Fermentation is the biological process usedto convert grains and sugar crops to ethanol –

cu r ren t l y the on ly l i qu id fue l f rom b iomass

used in the United Sta tes. The byp rod uc t o f

distillery grains can be used as an animal feed,

th e r e b y r e d u c i n g th e c o m p e t i t i o n b e twe e n

foo d a nd fuel uses for the g ra in. Som e fa rmers

a re p roduc ing e thano l on fa rm, bu t w i th cu r -

ren t techno logy the p rocesses a re no t eco -

nomic unless they are heavily subsidized or the

onfarm product ion leads to increased gra in

pr ices—thereby enabl ing the farmer to earn

more on the crops he/she sells for feed. How-

ever, process development could decrease thec osts. Seve ral p roc esses for prod uc ing et ha no l

from wood and herbage are being developed,

but the costs are highly uncertain.

Anaerobic digestion is a biological process,

which produces a gas containing methane (the

principal component of natural gas) and car-

b on d ioxide . Suitab le feed stoc ks include m an y

wet forms of biomass, such as animal manure

and some aquatic plants. For the near to mid

term, d igesters for onfarm product ion o f gas

from animal manure appear to hold the great-

est promise. Not only can this technology serve

as a waste disposal process, but it also could

make most confined animal operations energy

self-sufficien t. The re is a ne ed to d em on strat e

a va r ie ty o f d iges te rs us ing d i f fe ren t feed -

stocks to gain operating experience. Because

the major cost is the in i t ia l investment, pol-

icies designed to lower capital charges wil l in-

crease market penetration of the technology.The a lcoho ls mo st e asily prod uc ed from bio-

mass—ethanol and methanol —are not total ly

compatible with the exist ing l iquid fuels sys-

tem and auto mob ile f leet. These a lco hols ca n

be used in gasol ine blends or as standalone

fue ls , bu t me thano l b lends wi l l have more

problems than ethanol blends unless sui table

addit ives are included with the methanol. Al l

of the problems regarding the alcohols’ incom-

patib i l i ty wi th the exist ing system have mult i -

ple solutions, but it is unclear which strategies

will prove to be the most cost effective.

The e nergy ba lanc e for etha nol from grains

and sugar crops has been the subject of consid-

erable controversy, because the farming and

process ing energy consumpt ion together are

approx ima te l y the same as the energy con -

tained in the ethanol. A net displacement of

premium fue ls—oi l and natura l gas—can be

assured with ethanol, however, if: 1 ) distilleries

do not use premium fuel for their boilers and

2) the ethanol is used as an octane-boosting ad-

di t ive to gasol ine. Fai lure to fu l f i l l e i ther of

these criteria could lead to ethanol production

a nd use inc reasing t he U.S. co nsump tion ofp r e m i u m fu e l s , a l t h o u g h th e r e wo u l d b e a

smal l net d isp lacement o f premium fue ls in

most cases. Failure to comply with both crite-

119



Chapter 7

THERMOCHEMICAL CONVERSION



Chapter 7

THERMOCHEMICAL CONVERSION

Introduction

During the 1980’s, the conversion processes

with the greatest potential in terms of both thegross energy use and the largest possible dis-

placement of oil and natural gas are the ther-

mochemical processes, or processes involving

h e a t -in d u c e d c h e m ic a l r e a c t io n s. C u rre n t ly

about 1.5 Quads/yr of biomass are combusted

directly for process steam, electric generation

(mostly cogeneration), and space heat. lnter-

mediate-Btu gasifiers currently under develop-

ment wil l be useful in retrofitting oil- and gas-

fired boilers to biomass fuels and for crop dry-

ing and o ther process heat needs. Deve lop-

ment of medium-Btu gasifiers is also underway

and various processes for producing alcoholsand other liquid fuels can be or are being de-

veloped. Also, methanol synthesis from wood

can probably be accompl ished wi th commer-

c ia lly a va i lab le tec hno log y , wh i le p roc esses

producing methanol f rom p lant herbage can

probably be demonstrated fairly rapidly. More-over, there are good theoretical reasons for be-

l ieving that the flexibil i ty, efficiency, and use-

fu lness o f thermochemica l processes can be

sign i f icant ly improved through basic and ap-

plied research into the thermochemistry of bio-

ma ss.

Som e g ene ric aspe c ts o f b iom a ss thermo-

chemistry and generic reactor types are given

first, fol lowed by a discussion of the optimum

size of some thermochemical conversion facil-

i t i e s a n d a m o r e d e ta i l e d c o n s i d e r a t i o n o f

select processes including densification, directcombust ion, gas i f ica t ion, and d i rect and in-

d i rect l iquefact ion. Fina l ly , the env i ronmenta l

impacts and research, development, and dem-

onstration (RD&D) needs are presented.

Generic Aspects of Biomass Thermochemistry

Possible feedstocks for the thermochemical

convers ion p rocesses inc lude any re la t i ve l y

dry plant matter such as wood, grasses, and

c rop residue s. Som e c onv ersion p roc ess d e-signs accept a wide range of feedstocks, while

others wil l be more suited to a specific feed-

stock. A l though th is is somet imes dependent

on the chemica l p roper t i es o f the feeds tock

(e.g., manure), i t more often depends on the

physical properties of the material, such as its

tendency to c log o r b r idge the reac to r , the

ease with which it can be reduced to a small

particle size, and the materials’ density.

Classification systems that provide informa-

tion for assist ing the designer of conversion

equipment are not presently avai lable for bio-ma ss fee d sto c ks. Sta nd a rd me tho d s for bio-

mass analysis or assays do not exist, although

it is customary to use coal analyses (ultimate

and proxima te) for bioma ss. Som e o f the prop -

ert ies of some biomass materia ls using coal

analyses are shown in tables 41 and 42. As a

fu l le r understand ing o f b iomass thermochem-

istry is developed, however, new classification

schemes and methods of analysis are likely tobe necessary.

Despi te the d i f fe rences in feedstocks, the

gener ic thermochemica l process consis ts o f

the fol lowing steps:

q moisture removal;

q hea t ing the ma te r ia l to and th rough the

temperature where i t decomposes (about

4000 to 8000 F);

q decomposition to form gases, l iquids, and

sol ids; and

q secondary gas phase reactions.

The drying p roc ess ab sorbs the he a t ne c es-

sa ry to e va p ora te the wa te r. This results in a

decrease in the net usable heat from the feed-

sto c k as sho wn in figure 16. I n th is figure, the

n e t h e a t c o n te n t p e r p o u n d o f d r y wo o d i s

123



124 . Vol. I/—Energy From Biological Processes

Table 41 .–Proximate Analysis Data for Selected Solid Fuels and Biomass Materials (dry basis, weight percent)

Volat ile mat ter F ixed carbon Ash Reference

CoalsPittsburgh seam coal. . . . . . . . . . . . . . . . . . .Wyoming Elkol coal, . . . . . . . . . . . . . . . . . . .Lignite . . . . . . . . . . . . . . . . . . . . . . . . . . . .Oven dry woodsWestern hemlock . . . . . . . . . . . . . . . . . . . .Douglas fir. . . . . . . . . . . . . . . . . . . . . . . .White fir . . . . . . . . . . . . . . . . . . . . . . . . . . .Ponderosa pine. . . . . . . . . . . . . . . . . . . . . . .Redwood . . . . . . . . . . . . . . . . . . . . . . . . . . .Cedar . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Oven dry barks Western hemlock . . . . . . . . . . . . . . . . . . . . .Douglas fir.. . . . . . . . . . . . . . . . . . . . . . . . .White fir . . . . . . . . . . . . . . . . . . . . , . . . . . .Ponderosa pine. . . . . . . . . . . . . . . . . . . . . . .Redwood . . . . . . . . . . . . . . . . . . . . . . . . . . .Cedar . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Mill woodwaste samples -4 mesh redwood shavings . . . . . . . . . . . . .-4 mesh Alabama oakchips . . . . . . . . . . . . .Municipal rufuse and major components National average waste . . . . . . . . . . . . . . . . .Newspaper(9.4% of average waste) . . . . . . . .Paperboxes (23.4%) . . . . . . . . . . . . . . . . . .Magazine paper (6.8%) . . . . . . . . . . . . . . . .Brownpaper (5.6%). . . . . . . . . . . . . . . . . . .Pyrolysis chars Redwood (790°to 1,020 F) . . . . . . . . . . . . .Redwood (800°to 1,725 F) . . . . . . . . . . . . .Oak (820°to 1,185 F) . . . . . . . . . . . . . . . . .Oak (1,060°F). . . . . . . . . . . . . . . . . . . . . . .

33.944.443.0

55.851.446.6

10.34.2

10.4

Bituminous Coal Research 1974Bituminous Coal Research 1974Bifumirtous Coal Research 1974

84.886.284.487.083.577.0

15.013.715.112.816.121.0

0.20.10.50.20.42.0

Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977

74.370.673.473.471.386.7

24.027.224.025.927.913.1

1.72.22.60.70.80.2

Howlett and Gamache 1977Hewlett and Gamache 1977Hewlett and Gamache 1977Hewlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977

76.274.7

23.521.9

0.33.3

Boley and Landers 1969Boley and Landers 1969

65.986.381.769.289.1

9.112.212.9

7.39.8

25.01.55.4

23.41.1

Klass and Ghosh 1973Klass and Ghosh 1973Klass and Ghosh 1973Klass and Ghosh 1973Klass and Ghosh 1973

30.023.925.827.1

67.772.059.355.6

2.34.1

14.917.3

Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977Howlett and Gamache 1977

SOURCE M Graboskland R Barn, ’’Propertiesof Biomass Relevant lo Gasification, “ in A Swveyo/8/orrrass Gas/ficaf/on (vol. 11: Golden, (Mo, Solar Energy Research Institute, July 1979), TR-33-239

Table 42.–Ultimate Analysi s Data for Selected Solid Fuels and Biomass Materials (dry basis, weight percent)

Higher heatingMaterial C H N S O Ash value (Btu/lb) Reference

Pittsburgh seam coal ., . . . . . . . . ., , , , , . 75.5 5.0 1,2 3.1 4 .9 1 0 .3

West Kentucky No. 11 coal . . . . . . . . . . . . . 74.4 5.1 1.5 3.8 7.9 7.3Utah coal . . . . . . . . . . . . . . . . . . . . . . . . . 77.9 6.0 1.5 0.6 9.9 4.1Wyoming Elkol coal . . . . . . . . . . . . . . . . . . 71.5 5.3 1.2 0.9 16.9 4.2Lignite . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.0 4.2 0.9 1.3 19.2 10.4Charcoal. , . . . . . . . . . . . . . . . . . . . . . . . . 80.3 3.1 0.2 0.0 11.3 3.4Douglas f ir . . . . . . . . . . . . . . . .. . . . . . . 52.3 6.3 0 .1 0 . 0 40 .5 0 .8Douglas fir bark. . . . . . . . . . . . . . . . . . . . . 56.2 5.9 0.0 0.0 36.7 1.2Pine bark ., ., . . . . . . . . . . . . . . . . . . . . . 52,3 5.8 0.2 0.0 38.8 2.9Western hemlock. . . . . . . . . . . . . . . . . . . . 50.4 5.8 0.1 0.1 41.4 2.2Redwood. ... , . . . . . . . . . . . . . . . ... , . . 53,5 5.9 0.1 0.0 40.3 0,2Beech. . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.6 6.3 0.0 0.0 41.5 0.6Hickory. . . . . . . . . . . . . . . . . . . . . . . . . . . 49.7 6.5 0.0 0.0 43.1 0.7Maple. . . . . . . . . . . . . . . . . . . . . . . . . . . . 50.6 6.0 0.3 0.0 41,7 1.4Poplar. . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.6 6.3 0.0 0.0 41.5 0.6Rice hulls . . . . . . . . . . . . . . . . . . . . . . . . . 38.5 5.7 0.5 0.0 39.8 15.5Rice straw. . . . . . . . . . . . . . . . . . . . . . . . . 39.2 5.1 0,6 0.1 35.8 19.2

Sawdust pellets. . . . . . . . . . . . . . . . . . . . . 47.2 6.5 0.0 0.0 45.4 1.0

Paper. . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.4 5.8 0.3 0.2 44.3 6.0Redwood wastewood . . . . . . . . . . . . . . . . 53.4 6.0 0 .1 3 9 .9 0.1 0.6Alabama oak woodwaste. . . . . . . . . ., . . . . 49.5 5.7 0.2 0.0 41.3 3,3Animal waste. . . . . . . . , . . . . . . . . . . . . . . 42.7 5.5 2.4 0.3 31.3 17.8Municipal solid waste ... , . . . . 47.6 6.0 1.2 0.3 32.9 12.0

13,650

13,46014,17012,71010,71213,370

9,0509,5008,7808,6209,0408,7608,6708,5808,9206,6106,5408,814

7,5729,1638,2667,3808,546

Tillman 1978

Bituminous Coal Research 1974Tillman 1978Bituminous Coal Research 1974Bituminous Coal Research 1974Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tillman 1978Tiliman 1978Tillman 1978Wen et al. 1974

Bowerman 1969Boley and Landers 1969Boley and Landers 1969Tillman 1978Sanner et al. 1970

C = carbon H = hydrogen N = nitrogen S = sulfur O = oxygen

SOURCE M Graboskl and R Barn, “Properties of Biomass Relevant to Gastf!catlon, ” m A .%rwyof Llornass Gas/f/caf/err, (VOI 11, Golden, Colo Solar Energy Research Institute, July 1979), TR-33-239



Ch. 7—Thermochemical Convers ion q 12 5

Figure 16.— Effect of Moisture on theHeat Content of Wood

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

o 10 20 30 40 50 60

Moisture content

(% of fresh weight)

SOURCE: Off Ice of Technology Assessment,

sho w n for va riou s mo isture c on te nts. The h ea t

content per pound of moist material, however,decreases much more rap id ly wi th mois ture

c o n te n t , d u e to t h e fa c t t h a t p a r t o f e a c h

pound is water and not combustib le materia l .

(Nevertheless, the price of the moist feedstock

wi l l vary wi th the moisture content , so that

$1 5/ton material at 50-percent moisture con-

tent is roughly equal to $30/ton of dry material.

In this report, the feedstock costs are generally

expressed as dollars per ton of dry material, so

that variations in cost and heat content per ton

are kept at a mini mum.)

There is a lso a sec ond a ry effe c t o f the mo is-ture content of the feedstock. If moist feed-

stocks are combusted to produce steam, the

boiler efficiency wil l usually drop if the feed-

stock moisture content is not that for which

the boiler was designed. Aside from the heat

lost in evaporating the water in the feedstock,

high-moisture feedstocks have a lower flame

temperature in direct combustion, which can

resul t in part iculate and creosote emissions

(which escape wi thout be ing complete ly com-

busted, if considerable excess combustion air

is not used). (1 n poorly designed wood stoves or

boilers, simply feeding excess air may not besufficient to suppress these emission s.) In prin-

ciple, a reac tor ca n be de signed to ac co mmo-

da te th i s excess combus t ion a i r , vapor i zed

moisture , and lower f lame temperature wi th-

out a drop in efficiency, but in practice the ef-

ficiency is likely to drop.

A theoretical example of how the boiler effi-

c iency drops with feedstock moisture content

is shown in figure 17. Care should be exercisedin applying these results to any given situation,

s i n c e s o m e fa c to r s wh i c h wo u l d v a r y w i thmoisture content (e. g., excess air) are held con-

stant in the calculations, but i t does i l lustrate

the point.

Wi th gas i f i ca t i on , the s i tua t ion i s s l i gh t l y

different. In this case the feedstock is decom-

po sed into a fue l gas be fore c om bu stion. The

energy needed to vaporize the feedstock mois-

ture is still lost, but the fuel gas can easily be

mixed with the combustion air, so that excess

air is not required, and the feedstock moisture

is already vaporized, so the flame temperature

can be high. Consequently, it may be possible

to maintain the eff ic iency of gasi f ication-com-

bustion processes over a variety of feedstock

moisture contents better than with direct com-

bust ion. Depending on reactor des ign, how-

ever, it may be necessary to limit the feedstock

moisture in order to produce a flammable gas,

and this point needs further investigation.

The rate t ha t the b ioma ss is hea ted to a nd

through i ts decomposi t ion temperature is a

c r i t i c a l f a c to r i n d e te r m i n i n g th e p r o d u c ts .

Many reactor designs are being developed to

achieve high heating rates, as described below.

(The he ating rate is also d ete rmined by t he p ar-ticle size— small particles heating faster— and

moisture content. ) Depending on the products

desired, however, one may want th is heating

rate to be slower.

The d eta i ls of b ioma ss d ec om p osit ion a re

not well understood, but one can surmise the

following. As the material is heated, the large

biomass molecules (cel lu lose, hemicel lu lose,

and Iignin) begin to break down into intermedi-

ate-sized molecules. If the material stays in the

heating zone long enough, the intermediate-

s ize molecu les decompose in to s t i l l smal lermolecules, such as hydrogen, methane, carbon

monoxide (CO), ethane, ethylene, acetylene,

and other chemicals. If the heating rate is too

slow relative to the time the material is in the




Figure 17.—Effect of Feedstock Moisture Content on Boiler Efficiency

90

80

70

60

50

0 10 20 30 40 50 60

Moisture content (o /o )

SOURCE: R. A. Arola, “Wood Fuels – How Do They Stack Up?” Energy and the Wood Products Industry, Forests Products Research Society, Proceeding No. 76-14,

NOV. 15-17, 1976.

heat ing zone, the intermediate-sized mole-

cules wi l l escape and later condense as oi ls

a nd ta r. (This ma y a lso invo lve som e inte rmed i-

ate reactions that are not wel l understood at

present. ) It also appears that a slow heating

rate e nc ourag es the fo rmation o f c ha r. Thus, a

slow heating rate (either by design or due to ex-

cess moisture in the feedstock) will lead to the

formation of varying amounts of char, tar, oi l ,

and gas. With rapid heating, however, virtually

the entire biomass goes to a gas with only the

ash remaining.

Finally, the gases and vaporized tars and oils

can react in the gas phase to form a new or

modified set of products. Very Iittle is under-

stood about these secondary gas phase reac-

tions, but they are of considerable importancein thermochemica l processes. Depending on

the oxygen and moisture content, the rate the

b iomass was decomposed, the temperature ,

the p ressu re , an d o t he r va r iab les no t fu l ly

understood, the resul tant gas can vary from

almost pure carbon dioxide (C02) and water to

gases with relatively high contents of materialssuch as hydrogen, methane, or ethylene (see

ch. 12), or the gas can contain considerable

quan t i t i es o f pa r t i cu la te , va r ious hyd roca r -

bons, CO, and other pollutants.

Depending on the conditions chosen and the

design of the reactor, the product(s) can be

heat as in direct combustion, an intermediate-

or medium-Btu gas suitable for oil- or gas-fired

boi lers and process heat, a gas sui table for

chemical synthesis, oils, and/or char. But con-

siderable research into the thermochemistry of

biomass will be needed, before engineers willhave the necessary information to design reac-

tors that can achieve the full potential for the

thermochemical conversion of biomass.



Ch. 7—Thermochemical Conversion q 12 7

Reactor-

Type

Most commercial biomass reactors used for

d i rect combust ion or gas i f ica t ion are modi f i -

c a tions of c oa l tec hnolog y. The reac tors p ro-

posed for d i rect l iquefact ion and densi f ica-

t ion, however , do not fa l l in to th is category

and are considered in the sections dealing with

these topics.

Al though the technology for coal combus-

tion and gasification is considerably more ad-

vanced than for biomass, it is generally agreed

that grasses, wood, and crop residues are more

rea dily ga sified tha n c oa l or cha r. The b ioma ss

gasifies at a lower temperature and over a nar-

rower temperature range than does coal, as il-

lustrated in f igures 18 and 19, Both of these

p r o p e r t i e s f a v o r r a p i d g a s i f i c a t i o n . W h i l e

these advantages of biomass over coal are par-

t ia l ly offset by biomass’ higher heat capaci ty(the amount of heat needed to raise the materi-

Figure 18.—A Comparison of Pyrolytic Weight Loss(on a mass fraction basis) v. Temperature

for Coal and Cellulose1.0

0.9

0.8

0.4

0.3

0.2

Cellulose

0.1100 300 500 700 900

Temperature, “C

SOURCE: M J Antal, Biomass Energy Enhancement—A Report to the Presl.dent’s Counc// on Errv/ronrnental Oua//ty (Princeton, N.J PrincetonUnlverslty, July 1978)

al ’s temperature a given amount) ’ coal gasi f i -

cation in advanced reactors wi l l u l t imately be

l imited by the rate that oxygen, CO2, steam,

etc., can diffuse to and into the surface of coal

particles. Biomass gasification and decomposi-

t i on , on the o the r hand , do no t requ i re the

reaction of two or more separate species. Con-

sequently, b iomass gasi f ication probably wi l l

be l imited by the rate that heat can be trans-

ferred to the biomass.

In ba lance, these d i f fe rences po in t to the

conclusion that there is the potential for build-

ing b iomass reactors that have considerab ly

higher rates of throughput and thus lower costs

than wi l l be achieved with coal or has been

achieved for e i ther mater ia l so far . On the

other hand, the most rapid heat transfer occurs

when the feedstock particles are pulverized orof relatively small size. Most coals can readily

be pulverized, but the fibrous nature of many

types of biomass makes it difficult to reduce

the particle size. Biomass densification (see

below) makes i t fa i r ly easy to pulverize the

biomass, but this and other pretreatments add

to the costs . At present i t i s impossib le to

predict whether the di ff icul ty and expense of

reducing the biomass part ic le size or the in-

herent l imitations in the rate that coal reacts

wi l l domina te the economic d i f fe rences be -

tween the two types of fuel reactors. Neverthe-

less, it is clear that dramatic improvements inbiomass reactors are possible and that achiev-

ing this ful l potential wil l require RD&D spe-

c i f ica l ly a imed at address ing and exp lo i t ing

the unique features of biomass. Furthermore,

s ince b iomass cha r i s more l i ke coa l than

wood, grasses, or crop residues, achieving this

potent ia l advantage o f b iomass wi l l invo lve

reactors that produce Iittle or no char.

General ly, the biomass reactors are classi-

fied according to the way the feedstock is fed

into them. Although there are numerous varia-

tions, the major types are moving grate, mov-

‘M Graboskl and R Baln, “Properties of Biomass Relevant to

Caslflcatton, ” m A S u r v e y o f L?iorTra55 Gas// icat ion ( V O I 1 1 ,

Golden, Colo Solar Energy Research Institute, July 1979),TR- 13-239



128 q Vol. n-Energy From Biological Processes

q These curves represent the derivative of curves similar to those given in figure 18. They were obtained by heating asmall sample of solid material at a given rate and recording fractional weight loss v. temperature. The peak of each

differential weight-loss curve (i.e., for cellulose the value is 15% per 10°C at 315 “C) is indicative of the individual

material’s pyrolysis kinetics — a higher heating rate would displace all the curves to higher temperatures and would

“sharpen” each peak. Thus the position of each peak is not related to “optimum” operating conditions. The curves

simply show that biomass materials pyrolyze much more rapidly at much lower temperatures than coal.

SOURCE: H. H. Lowry, Chemistry of Coal Ufi/ization Supplementary Vo/ume (New York: John Wiley and Sons, Inc. 1963)

ing be d, fluidized be d , and e ntrained flow. Thera te o f hea t t rans fe r genera l l y fo l lows the

order given, with the moving-grate reactors be-

ing the slowe st. (There a re, howe ver, othe r

classification schemes which can be useful as

well. )

Moving-grate reactors consist of a grate that

carries or moves the biomass through the zone

whe re it is hea ted and de c om po ses. The hea t

transfer is relatively inefficient and slow, so an

excess of heat must be generated to sustain the

rea c tion. Therefore this type of rea c tor is ge n-

erally best suited to direct combustion wherethe biomass is completely reacted and releases

vir tual ly al l of i ts heat in the decomposit ion

zone.

A s l ight ly faster ra te of heat t ransfer isachieved wi th moving-bed reactors. In these

the bed, or clump of biomass, moves in a ver-

tical direction as it is decomposed. Additional

biomass is added at the top, which then grad-

ua l ly works i t s wa y d ow n the rea c to r . Two

types of moving-bed reactors exist : updraf t

and downdraft.

The up draf t mo ving-bed rea c tors have a

stream of air moving up through the bed of

biom ass. The ho ttest p art of t he b ed is at the

bot tom. As the hot gases move through thebed , however , they cause re la t i ve ly la rge

amounts of tars and oils to form, which can

condense causing maintenance problems and



Ch. 7—Thermochemical Conversion q 129

which may make i t more di ff icul t to burn the

resultant gas without forming particulate.

The d ow ndraft mo ving-bed rea cto rs have a

s t ream o f a i r mov ing downward th rough the

b ed of b ioma ss. Tars an d oils are fo rme d nea r

the middle of the bed (where the air is injected)

and subsequent ly move through a re la t ive lylarge hot zone which gives them time to fur-

ther d ec om p ose. The ne t result is a fuel ga s

with fewer tars and oils, thereby making gas

c leanup eas ie r and reduc ing the amoun t o f

particulate that form when the gas is burned.

Another type is the fluidized-bed reactor. In

this case, gas is blown through the bed of solid

fue l so rap id ly that the bed o f b iomass lev i -

tates and churns as if it were fluid. In coal-fed

flu idized-bed reactors, the f lu id bed may con-

tain l imestone particles to react with and re-

mo ve sulfur from th e c oa l. Since b ioma ss usu-

a l l y does no t con ta in s ign i f i can t l eve ls o f

sulfur, sand can be used as a fluidizing medi-

um or one can rely solely on the biomass itself,

with no sep arat e fluid izing me dium. San d ha s

the advantage, however, of helping to retain

heat in the bed, thereby increasing the rate

that new pieces of fuel heat up in the bed.

Fluidized-bed reactors have a considerably

faster heating rate than moving-bed or travel-

ing-g ra te rea ct ors. The c hurn ing in the be d ,

however, enables material at al l stages of de-

composi t ion to be found throughout the bed.

Consequently, there may be a tendency for oils

and ta rs to escape f rom the hea t ing zone

before they can be fully decomposed.

The last typ e o f rea c tor co nsidered here is

the suspension or entrained-f low reactor. In

th i s type , sma l l pa r t i c les o f feeds tock a re

suspended in a stream of gas which moves rap-

id ly into and through the decomposit ion zone.

This type ha s the mo st rap id rate of he at ing,

but the feedstock particles must be reduced toa relatively smal l s ize. As mentioned above,

th is would add to the to ta l convers ion costs

and the detai ls of th is economic tradeoff are

sti l l uncertain.

Optimum Size for Thermochemical Conversion Facilities

Electr ic generat ing p lants fue led wi th nu-

clear power or fossil fuels are generally quite

large in order to take advantage of economies

of sca le. The sa me is true o f mo st p rop osals for

synthe tic fuel p lants. The op timum size o f abiomass-fueled electric powerplant or synthet-

ic fuels plant, on the other hand, is determined

by a tradeoff between this economy of scale

and the cost of transport ing the feedstock to

the conversion plant. Under favorable circum-

stances this optimum size could be several

hundred megawatts electric (see app. A), and

some paper-pulping mills do have wood inputs

that would be suf f ic ient for fac i l i t ies o f th is

size. z U n d e r m o r e c o m m o n c i r c u m s t a n c e s ,

however , the loca l ava i lab i l i ty o f feedstock

m a y I i m i t t h e s i z e o f b i o m a s s c o n v e r s i o n

2KIp H e w l e t t , Georg!a Pactflc Corp , pr i vate communlcat lon,

1979

faci l i t ies to the equivalent of 10- to 60-MW

elec tric o r less.

The e c ono my o f sc a le , how eve r, is o f te n

matched by the cost savings associated withmass producing a large number of small units.

Furthermore, in many industr ia l appl ications

(e. g., process heat or steam boilers) the size is

determined by the needs o f that industr ia l

plant rather than a potential economy of scale

for the boiler or heat needs.

Large-scale facilities are technically feasible

under some circumstances, particularly where

the biomass arises as a waste byproduct in a

large ma nufac turing plant. The num be r of sites

where large quantities of biomass are avaiIable

to a single plant on a continuing basis, how-

ever, may be l imited. Consequently, the ful lest

utiIization of the biomass resource for thermo-

chemical conversion wil l require the develop-

ment of small-scale, mass-produced units.




Biomass Densification

Freshly harvested biomass usually contains

considerable moisture, has a relatively large

volume per unit of energy (making it expensive

to transport) , and is f ibrous (making i t often

d iffic ult to red uc e the p a rtic le size). The se d if-

ficulties can be partial ly overcome by densify-

ing the biomass.

There a re seve ra l type s o f d ensi f ic a t i on

p rocesses inc lud ing pe l l e t i z ing , cub ing , b r i -

que t t i ng , ex t rusion , and ro l ling -com pressing .

Pelletizing typifies the advantages and disad-

vantages of densification processes and is con-

sidered in more detail here.

Pelletization consists of drying the biomass,

heating it unti l the Iignin melts, and compress-

ing th e m a te ria l into p el lets. The p el lets a re

denser than the biomass, more easily ground,and easier to handle and feed into reactors.

Due to the i r lower mois ture content , pe l le ts

usual ly burn more eff ic iently in boi lers than

does green biomass.

At present there are only commercial pelleti-

za tion p roc esses for woo d . The Iignin c onte nt

in wood is general ly high enough to bind the

pellets so that no additional adhesives are re-

qu i red. Densi f ied crop res idues or grasses,

however , may requ i re the add i t i on o f adhe-

sives to achieve the necessary binding strength

to prevent the pellets from disintegrating to a

powder; and the costs for this are uncertain.

The w oo d pe lletiza tion p roc ess ha s an ene r-

gy efficiency* of about 90 percent if one starts

wi th wood having 50-percent mois ture con-

tent. Furthermore, wood pellets would burn in

the bo i l e r dep ic ted in f i gu re 17 to p roduce

steam with an eff ic iency of about 83 percent

as compared with an efficiency of 65 percent

for wo od c hips with 50-p erce nt mo isture. Thus

the ove ra l l e f f i c i ency (50 -pe rcen t mo is tu re

woodchips to steam) is increased from 65 per-

cent to perhaps 75 percent by including a pel-

Ie t iza t ion process. Th is e f f ic ien c y inc rea secould also be achieved by predrying the wood-

*E fficlency is defined here as the lower heating value of the

product divided by the lower heating value of the feedstock

chips with heat escaping out the burner’s chim-

ne y. The e xac t num b ers wi l l va ry, how eve r,

depend ing on the spec i f i c bo i l e r be ing con -

s idered. I f the bo i le r is des igned to accept

high-moisture woodchips, then there may be

no eff ic iency improvement with wood pel lets.

Wood pellet costs are shown in table 43 for

various feedstock costs. Whi le the costs are

Table 43.–Cost of Pelletized Wood

Wood feedstock cost (dollars/green ton)

$6.50 $10.00 $20,00

Dollars/ton of pellets sold

Wood. ... ., . . . . . . . $14.39 $22.13 $44.26Operation and

maintenance . . . . . , . . 7.95 7.95 7.95Capital charges. . . . . . . . 5.14(30%Of total investment

5.14 5.14

per year)

Total . . . . . . . . . . . . . $27.48 $35.22 $57.35Dollars/ IO” Btu. ... , . . . $1.72 $2.20 $3.58

Input: 540 ton/d of wood (50% moisture)Output: 244 ton/d of pellets (10% moisture) for sale and 56 ton/d of

pellets used to fuel the plant.Load 330 operating days per year

SOURCE OffIce of Technology Assessment, and T B Reed, et al, “Technology and Economics ofClose-Coupled Gaslflers for Relrof!ttmg Gas/Od Combustion Uruts to Biomass Feed-

stocks , In Retrof/f ’79, Proceedings 0/a Workshop on M Gas#mal/on, sponsored bythe Solar Energy Research Instltule, Seattle, Wash , Feb 2, t979

considerably higher than those for woodchips,

the pellets’ higher energy density allows them

to be transported at a lower cost than green

w oo d c hips. This c ost sa vings in the t ransp orta -

t ion pays for the pel let ization process i f the

fuel is to be transported more than 50 to 150

mi les depend ing on the t ranspor t and wood

feedstock costs and the in i t ia l mois ture con-

tent of the wood (see app. B for details of the

ca lcu la t ion) . However , th is ca lcu la t ion does

not include the added cost of transporting very

bu lky mater ia l such as p lant herbage where

t h e v o l u m e r a t h e r t h a n t h e w e i g h t o f t h e

material determines the transport cost.

The m ost c om mo n a nd least expe nsive use

of fue lwood, however , is l i ke ly to be in theregion where it is harvested. Consequently, the

use of densification processes may be l imited.

On the other hand, the increased ease of han-

dl ing and burning pel lets may make them at-



Ch. 7—Thermochemical Conversion . 131

tractive in applications where the process has wi l l have to dec ide whe the r the h ighe r fue l

to be extremely automated such as in very c ost is justified in te rms of the lab or sa vings.

small industrial applications or where the feed- For the remainder of this chapter, it is assumed

s tock i s pa r t i cu la r l y unwie ldy such as wi th that raw biomass rather than pellets are being

plant herbage. In each appl ication, the user used.

Direct Combustion of

Biomass can be burned together with coal

( te rmed cocombus t ion ) to p roduce p rocess

steam or e lectr ic i ty . Current ly however , the

largest amounts of energy produced from bio-

mass come from the combustion of wood and

food-p rocess ing wastes such as sugarcane ba-

gasse by themselves. Another important use of

direct combustion is in home heating. Each of

these applications is considered below.

Cocombustion of Biomass

Currently, outdated — and therefore unusa-

b l e – s e e d c o r n i s b e i n g c o c o m b u s te d w i th

coal by the Logansport, lnd., Municipal Uti l i ty.

Co c o m b u s t i o n o f wo o d w i th c o a l h a s a l s o

been successfully demonstrated by the Grand

Haven, Mich., Board of Light and Power. ’ And

several assessments of the cocombustion of

crop res idues wi th coa l concluded that i t i s

techn ica l ly feas ib le .4

Abdullah has estimated that the added costs

at an electric powerplant needed to modify the

boilers and handle the crop residues is $0.20 to

$0.50/ million Btu. 5 Consequently, for coal cost-

ing $1.50 to $2.00/miIlion Btu ($30 to $45/ton),

crop residues costing $13 to $24/ton would be

ec onom ica lly coc omb usted . Some c rop resi-

dues may be ava i lab le for these pr ices, but

general ly del ivered crop residue prices are

IPlerre Heroux, Supplemental Wood Fue/ Experiment, report to

Crand Haven Board of L ight and Power (Crant Hav en , Mich J

B Sims Generating Stat Ion, 1978)

‘See, e g , Wesley t3uechele, D/rect Combustion of Crop /?es-

/dues In FurnaceBo//ers

(Ames, Iowa Agriculture and Home E co-nomlcs Experiment Stat Ion), paper No J8791

‘Mohammed Abdul Iah, “ E conomles of Corn Stover as a Coa

Supplement In Steam Electrlc Power Plants in the North Central

United States, ” ph D thesis, Agricultural Economics Depart-

ment, Ohio State Unlverslty, Columbus, Ohio, 1978

l ikely

Biomass

to be h ighe r. Higher coa l p rices, how-

ever, will make residue cocombustion more at-

t ract ive

Cocombustion can also be used to lower sul-

fur emissions som ew ha t. Sinc e th e b iom a ss

general ly contains negl ig ible amounts of sul-

fur, the quantity of sulfur being released in the

combust ion (per mi l l ion Btu o f heat) wi l l de-

crease with the percentage of biomass, typical-

ly 20 to 30 pe rcent . The ec ono mic sa vings asso-

c iate d w ith this will b e hig hly site spec ific . The

most advantageous si tuation would be where

coal-fired boiler emissions are only marginally

above the emissions standards without the use

of su l fur remo val eq u ipm ent. Sinc e the b io-

mass costs, a ir pol lut ion benefi ts, and feed-

stock availability are site specific, the econom-

ics of cocombustion wiII have to be deter-

mined through s i te-speci f ic economic ana ly-

ses. The p rinc ipa l de termina nt, ho we ver, wi ll

probably be the availabil i ty of a reliable sup-

ply of low-cost biomass feedstock.

Combustion of Biomass

Direct combust ion o f b iomass for produc-

tion of electricity or steam or for cogeneration

(simultaneous production of steam and ei ther

e l e c t r i c i t y o r m e c h a n i c a l s h a f t p o we r ) h a s

commercial ly ready technology for wood, sug-

arcane bagasse, and many other feedstocks.

There a re also c om me rcially a va ila b le susp en-

sion burner retrofits for oi l-fired boilers of 4.5

mi l lion Btu/ hr or large r. The latte r ret rofi t ted

boilers can return to oil i f the biomass feed-

stock is temporari ly unavailable, but they re-

quire a biomass feedstock that is quite dry (less

than 15-percent moisture) and relatively small



132 . Vol. //—Energy From Biological Processes

in size (less than 1/8” x 1/2’’ -3/4’’). sA few types

of biomass, however, involve special problems

(e.g., the high si l ica content in rice hulls and

residues) and boilers for these are not availa-

ble.

In many appl ications today, feedstocks with

40- to 50-percent moisture content are used,resulting in boiler efficiencies of 65 to 70 per-

c e n t . ( Th e r e t ro f i t u n it m e n t i o n e d a b o v e ,

which is restricted to low-moisture feedstock,

achieves an estimated 75-percent efficiency). 7

There ha s be en little inc entive to dry the feed -

stock in most current applications, since they

usual ly invo lve re la t ive ly inexpensive waste

products. As the use of biomass for direct com-

bustion becomes more widespread and the av-

erage feedstock costs increase, however, pre-

dry ing o f the feedstock is l i ke ly to be more

c o m m o n .

As wi th cocombust ion, the feedstock cost

a n d a v a i l a b i l i t y o f a r e l i a b l e s u p p l y o f t h e

feedstock are major determinants of the eco-

nomics of using biomass as a fuel. While these

costs vary considerably from site to site, an av-

erage feedstock cost of $30/dry ton ($1 5/green

ton) results in the costs of electric generation,

cogeneration, and steam production shown in

table 44. (More detailed cost calculations are

given in ap p . B.) The c osts for prod uc ing o nly

e lectr ic i ty or on ly s team are a lso shown for

various feedstock costs in figures 20 and 21.

‘Peabody, Cordon-Piatt, Inc , Wlnfleld, Kan , e g , offers sus-

pension burner retrofits to oll-fired boilers ranging from 45 mll-

Ilon Btu/hr and up. The retrofit cost IS slightly higher than for gas-

Iflers, but where dry, small particle feedstock (e g , sawdust) IS

available at low prices, the system is competitive with fuel 011

Prwate communication with Delvln Holdeman, Solld Fuels Mar-

keting Dlvlslon, Peabody, Gordon-Platt, November 1979

‘Ibid

Figure 20.—Cost of Electricity From Wood forVarious Wood Costs (field-erected

generating station)

Low 1

I20

10 t I0 $5 $10 $15 $20 $25 $30

Wood cost (dollars/green ton at 500/ . moisture


Obviously, where the feedstocks can be ob-

tained inexpensively enough, biomass is com-

pet i t ive wi th coa l fo r generat ing e lectr ic i ty

and with oil for process steam. 1 n the case of

electricity, the investment costs are about the

same as for coal-f i red powerplants; but wood-

fired boilers cost about three times that of oi l

or natural gas boilers.8

Wood Stoves and FireplacesWood stoves and fireplaces have long been

used as a means of space heating in residences,

but f i replaces are more often used today for

‘A Survey of Biomass Gas/f/cat/on ( VO I 1, Golden, Colo SolarEnergy Research Institute, July 1979)

Tab le 44.–Cost of Elec tric Gene ration, Coge nerarion, and Stea m Produc tion From Wooda

Wood cost (dollars/green ton, delivered

Product Plant size at 50% moisture) Product cost

Electricity 60 MW (field erected) 15 50-70 mill/kWh

Steam 50,000 lb/hr (package boiler) 15 $3.50-$6.00/1 ,000 lbSteam and electricity 390,000 lb/hr 15 $4-$6/1 ,000 Ibb

21,4 MW (field erected) 109-30 mills/kWhb

aSee delafls In app BbAs the steam COSI increases, the electric cost decreases

SOURCE Ofhceot Technology Assessment



134 q Vol. ii—Energy From Biological Processes

In general wood stove and furnace heating

require more labor than oil or natural gas heat.

The fu el req uires mo re ha nd ling , ashe s must b e

removed, and the systems must be regu lar ly

serviced to maintain eff ic ient and safe opera-

tion. This is less of a p rob lem if wo od pellets or

well-dried wood is used or if the wood is used

only as a solar bac kup. The use o f wo od hea t-

ing exclusively, however, is likely to be limited

to those people who consider this type of ac-

tivity enjoyable or wish to use wood to achieve

some degree of energy self-sufficiency. A larg-

er number o f people are l ike ly to purchase

wood stoves as insurance against oil or natural

gas shortages or as a supplement to more con-

ventional systems.

Gasification of Biomass

Gasif ication is the process of turning sol id

biomass into a gas suitable for use as a fuel or

for c he mic a l synthe sis. The re a re seve ral typ es

of thermal gasification processes, or gasifica-

tion induced by heat. Gases produced in blast

furnaces or by the water gas process are low-

Btu g a ses (80 to 180 Btu/ std ft3). Other gasifiers

use pure oxygen and partial combustion of thefeedstock to produce a medium-Btu gas (300

to 5 0 0 Btu / std f t3) su i tab le fo r reg iona l i n -

d ustrial p ipe line s o r ch em ica l synth esis. Sti l l

others (pyrolysis gasifiers) provide an external

source of heat to produce a medium-Btu gas

(e.g., dual fluidized bed gasifier described in

the next section).

The g a sifiers d isc ussed in d et a il in this sec -

tion a re the a irb low n g a sifiers. This typ e b lows

air through the feedstock to part ia l ly combust

it. The h ea t g ene ra ted is used to g asify the re-

ma ining m a te ria l . The resul tan t ga s from up -

draft and downdraft airblown gasifiers (termed

intermediate-Btu gas) has a lower heat content

(120 to 250 Btu/stdft3) than with oxygen or py-

rolysis gasification, due to the dilution effect

o f the n i t rogen conta ined in the a i r . (A i r is

about 78 percent nitrogen and 21 percent oxy-

ge n.) This lower hea t c onte nt m akes the ga s un-

sui table for regional pipel ine distr ibution, but

i t is not a disadvantage i f the gasi f ier is at-

tached directly to the boi ler being f i red (so-

called close-coupled gasifier) or used directly

for process or space heat. Gases with heat con-

tents of 250 to 400 Btu/stdft

3

, however , havebeen p roduced f rom an exper imen ta l f l u id -

ized-bed a i rb lown gasi f ie r , but the gas con-

tains considerable tar and oil.

‘ ‘Steven R Beck, Department of Chemical Engtneerlng, Texas

Tech Unlverslty, Lubbock, Tex , private communlcatlon, 1979

C l o s e - c o u p l e d a i r b l o w n g a s i f i e r s y s t e m s

have the potentia l for higher eff ic iencies than

d i r e c t c o m b u s t i o n w h e n a v a r i e t y o f f e e d -

s tocks wi th d i f fe ren t mo is tu re con ten ts a re

used (see “ Ge neric A sp ec ts of Bioma ss The r-

mochemistry”), and can be used for process

heat. Moreover, they are likely to be more effi-

cient and less expensive, in most applications,than oxygen-blown or pyrolysis gasi f iers (due

to the energy loss and cost associated with the

added equ ipmen t needed to p roduce oxygen

or the external supply of heat). Nevertheless,

for methanol synthesis, these gasifiers would

be necessary. Moreover, there may be some

ci rcumstances where reg iona l industr ia l natu-

ral gas pipelines could be converted wholly or

part ia l ly to gasi f ied biomass. Consequently,

cost calculations for two medium-Btu gasifiers

are included in appendix B.

Airblown (and other) gasifiers have the flex-

ibility of being able to be used together with or

as a substitute for oil or natural gas in indus-

tr ia l boi lers for crop drying, and for process

hea t. Th is me an s tha t eve n w here b iom ass

feedstocks are not ava i lab le in la rge quan-

tities, those that are available can be used to

displace oi l and natural gas to the extent of

their availabil i ty; and (barring regulations pro-

h ib i t i ng i t ) the use rs cou ld re tu rn to o i l o r

natural gas i f the biomass is temporari ly un-

available or in short supply. (It should be noted

that the suspension burner retrofit mentioned

in the last section also has this advantage butthe types of feedstocks it will accept are more

restr icted than for gasi f ies. ) Furthermore, in

prop erly de signed c lose-c oup led ga sifiers, the

fue l gas needs on ly minor c leanup (cyc lone

p rec ipita to r a nd p erha p s fibe rglass filte r). This



136 . Vol. n-Energy From Biological Processes

Figure 22.—Schematic Representation of Various Gasifier Types

aNote that other schemes such as moving grate gasifier also exist

SOURCE: From R. Overend, “Gasifiation An Overview, ” Retrofit 79, Proceedings of a Workshop on Air Gasification, Seattle, Wash.,SER1/TP-49-183, Feb. 2, 1979.




Figure 23.— Boiler Efficiency as a Function of theBtu Content of the Fuel Gas

Gas fuel Btu/ft3

S OURCE : Fuels From Munic ipal Refuse for Ut i l i t ies : Technical Assessment (Electric Power Research Institute, March 1975), EPRI report 261-1,

prepared by Bechtel Corp.

how to obtain it requires further experimenta-

t i on and a be t te r unders tand ing o f b iomasscombus t ion chemis t ry . Never the less, some

downdraft gasi f iers have produced gases ap-

proach ing 200 Btu /s td f t3 from wood with l i ttle

oil formation, 18 and there appears to be no fun-

damental reason why the optimum energy con-

tent (see f igure 23) wi th low tars cannot be

reached with additional gasifier development,

The ot her fac tor de termining the ove ra ll ef-

ficiency of gasifier-boiler systems is the effi-

c ienc y of t he ga sifier itself. Since b oth the sen-

sible heat* and the chemical energy in the gas

can be uti l ized with a close-coupled gasifier,the only gasification losses are the heat radi-

ated from the gasifier, that lost during fuel gas

cleanup, and the fuel value lost in condensed

tars, oils, or char. Gasifiers have achieved effi-

ciencies of 85 to 90 percentl920 and wel l - insu-

lated gasifiers designed to minimize char, oil,

and tar formation should be able to reach effi-

c ienc ies of 90 pe rce nt o r b et te r. This wo uld

ra ise the overa l l e f f ic iency o f feedstock to

steam to 85 percent or higher and provide high

efficiencies for process heat needs.

‘‘j R Gos~, “The Downdraft Gasifler, ” Retrofit ’79, Proceed- /rigs of a W’orkshop on A/r Ca\/f/cat/on, sponsored by the Solar

Energy Research Institute, Seattle, Wash , Feb 2,1979‘Sensible heat IS the energy contained In the gas by virtue of

Its be I ng hot, I e , It If the heat that can be sensed or felt directly

“Goss, Op Clt

“’Reed, op clt

Airblown Gasifier Costs

It has been estimated that oil- or gas-fired

boilers can be retrofitted with mass-produced

airblown biomass gasifiers for $4,000 to $9,000/

million Btu/hr ($5 to $1 2/lb of steam/h r), with

gasifiers ranging from 14 mil l ion to 85 mil l ion

Btu/hr .21 Retrofit costs, however, can vary con-s i d e r a b l y d e p e n d i ng on the d i f f i cu l ty o f ac -

cessing the boiler and the possible need for an

additional building, to house the gasifier. Voss,

for example, has estimated the cost at $20,000/

mil l ion Btu/hr when new buildings and founda-

tions are nee de d .22

The fa vorab le ca se c ost estimate s are c om -

pared with the costs of new oil/gas- and wood-

fired package boilers in figure 24 (similar prob-

Figure 24.—Comparison of Oil/Gas Package BoilerWith Airblown Gasifier Costs

o Air gasifiers

o Oil/gas package boilers ‘ \

---Forest product laboratory summary

Field-erectedwood-fired

Package wood-fired boilers

boilers

10 20 30 40 50 60 80 100

Boiler size

(1,000 lb of steam/hr)

SOURCE: T B. Reed, D E Jantzen, W P Corcoran, and R Wltholder, “Technol-ogy and Economics of Close. Coupled Gastffers for RetrofittingGas/Oil Combustion Units 10 Biomass Feedstocks, ” Retrofit ’79, Pro-ceedings of a Workshop orI A/r Gas/~/cat/on, sponsored by the Solar

Energy Research institute, Seattle, Wash , Feb 2.1979

“ C i t e d In I b i d

“G D Voss, Amer i c an Fyr-Feeder Eng i nee rs , Des Plalnes, Ill ,

private communication, 1979




Iems wi th insta l la t ion can occur wi th these

boilers as well). It can be seen that the capital

investment for a gas i f ie r re tro f i t i s roughly

twice that for a new o i l /gas- f i red bo i le r , but

on ly two- th i rds o f that for a new wood- f i red

boiler. From these preliminary estimates, it ap-

pears that a new gasifier-oil/gas boiler combi-

nation costs roughly the same as a new wood

package boiler but more refined data on gasifi-

ers are needed before accurate comparisons

can be made .

With c o sts o f $4,000 to $9,000/ million Btu/ hr

and wood fuel at $30/dry ton ($21/air dry ton,

30-percent moisture) the resultant gas is esti-

mated to cost about $2.70 to $2.90/mil l ion Btu

( s e e ta b l e 4 6 ) . I n t h e u n fa v o r a b l e c a s e o f

$20,000/million Btu/hr, the cost could be $3.35/ million Btu with this feedstock cost.

Table 46.–Cost Estimate for Fuel Gas From Wood Usinga Mass-Produced Airblown Gasifier

$4,000-$9,000 per 106

Fixed investment Btu/hr of capacity

Dollars/lOaBt u

Wood ($21 /ton, 30% moisture,i.e., $30/dry ton). ., . . . . . . . . $2.38

Labor, electricity . . . . . . . . . . . . . . . . 0.20Capital charge (30% of fixed investment

p e r y e a r ) 0.150-0.34

Total ., . . . . . . . . $2,73-$2,92Estimated range ($20-$60/dry ton wood) . $ 2 - $ 6

Input: 38 to 230 tons of air-dried wood (30% moisture) per day

Output: 14 to 85 10

6

Btu/hr of intermediate-Btu gasLoad: 330 operating days per year

SOURCE: Office of Technology Assessment

Obviously from table 46, the dominant cost

is the feedstock cost. If waste byproducts are

used to fuel the gasifier, the gas could cost less

than $1/million Btu. For the larger quantities of

wood, grasses, and residues costing $20 to $60/

dry ton, the gas pr ice is est imated to range

from $2 to $6/m illion Btu. These c osts a re c om -

p e t i t i v e w i th f u e l o i l a t $ 6 .5 0 /m i l l i o n B tu

($0.90/gal), but less so with natural gas at about

$3.50/m illion Btu. To a c hieve t he fu ll p ot en tial

of gasifiers, however, units in the range of 0.1

million to 10 million Btu/hr should also be de-

ve loped.

F i e l d - e r e c t e d g a s i f i e r s a r e c o n s i d e r a b l y

mo re expensive (see ap p. B). They m ay be ec o-

nomic, however , in cases where very la rge

quant i t ies o f a low-cost feedstock are ava i l -

able. Al ternatively, package gasi f iers of sev-

era l hundred mi l l ion Btu /hr cou ld be deve l -

oped, which, together wi th smal ler gas i f ie rs ,

would cover most situations involving biomass

feedstocks.

Gasifiers for Internal Combustion Engines

Wood and charcoal gasifiers were used dur-

ing the 1930’s and 1940’s in Europe to fuel

automobi le and truck engines. After some de-

velopment, the gasifiers operated satisfactori-

ly , but even under favorab le c i rcumstances,

operation and maintenance required an esti -

mated 1 hour per day of operation .23 Because

of this and the 30-percent power loss associ-

a ted wi th swi tch ing to the gas ,24 it is unlikelythere would be a la rge market for gas i f ie rs

used in automobiles, except under cases of ex-

treme shortages of gasol ine. Gasi f iers could,

how eve r, be used to fuel remo te ICES for irriga -

tion water pumping or electric generation.

The p rinc ipa l d i ffe renc e b etw ee n ga si fy ing

for close-coupled boi ler operation and process

hea t a nd for ICES is tha t the la tte r a p plica tion

requires that the gas be cooled before entering

the eng ine and requ i res par t icu lar ly low tar

and ash c ontent. The c oo ling is req uired to en-

able sufficient gas to be sucked into the cylin-der to fuel the engine and to prevent misfiring.

The c a reful ga s c lea nup is req uired to p reve nt

fouling or excessive wear in the engine.

These p rob lem s we re a lleviat ed for cha rcoa l

and low-mo is tu re wood by us ing downdra f t

gasifiers and various gas cooling and cleanup

schemes in Europe before and dur ing Wor ld

War 11.25 (Charcoal tended to form more ash,

whi le wood more tar , so somewhat d i f fe rent

syste ms we re req uired .) The a p p l ic a b i li ty of

these gasifiers to other feedstocks, however, is

uncertain.

*] Swedish Academy of Engineering, Generator Gas– The

Swedish Experience from 7939-1945, Genera lstabens Litograf iska

Anstalts Forlag, Stockholm, 1950, translated by the Solar Energy

Research Institute, Golden, Colo , 1979

“IbidZSlbld



Ch. 7—Thermochemical Conversion 139

Gasifiers could be used as the sole fuel for

spark ignition (e. g., gasoline) engines or togeth-

er with reduced quantities of diesel fuel in die-

sel engines (by fumigation, i.e., replacing the

air inta ke w ith an a ir-fuel ga s mixture). The en-

ergy lost in cooling the gas and removing the

tar and the added cost o f the coo l ing equ ip-

ment are l ikely to more than double the gascos ts ove r tha t fo r c lose -coup led gas i f i e rs .

(This is b a sed on c a lculat ions b y Ree d , z’ in

wh ich i t i s es t ima ted tha t abou t ha l f o f the

c lose-c ou p led g a s ene rgy is sen sible he a t. The

actual value, however, wilI vary with the gas-

ifier. )

With waste byproducts having no value or

giving a disposal credit, the gas would be com-

*’Reed, OP clt

petitive with electric irrigation, gasoline, diesel

fuel, and, probably, natural gas. With crop resi-

dues costing $30/dry ton, the gas cost with con-

vent iona l technology is l i ke ly to be over $7/

mil l ion Btu, which is competitive with electric

i r r igat ion and wi l l soon be compet i t ive wi th

gasoline and diesel fuel, but is more expensive

than natural gas at present.

Ga sifiers suitab le fo r ICES c ou ld p rob a b ly be

manufactured immediately, but improvements

in the gasifier efficiency and reliabil i ty could

improve the appl icabi l i ty of gasi f iers to ICES

for crop irriga tion a nd othe r uses. The d eve lop-

ment cou ld para l le l the deve lopment o f o ther

gasi f ie rs , and improved un i ts cou ld probably

be available in 2 to 5 years.

Liquid Fuels From Thermal Processes

Numerous l iqu id fue ls can be made from

biomass through thermal processes and chemi-

c a l synthe sis. The Iiquid fue ls c on side red he re

are methanol, pyrolytic oil, and ethanol. Cost

estimates for the production of these fuels are

shown in table 47, with further details given in

appendix B. Each of the processes is discussed

below.

Methanol

Methano l ( “wood a l coho l ” ) was f i r s t p ro -

duced from biomass as a minor byproduct of

c h a r c o a l m a n u f a c t u r in g . Th i s p r o c e ss f o r

methanol synthesis, however, is no longer eco-

nomic. Most methanol today is produced from

na tural ga s. The na tural ga s is reac ted with

steam and CO2 to produce a CO-hydrogen mix-

ture. The ga s c om po sition is then a djusted to

the correct ratio of these components and the

resultant gas is pressurized in the presence of a

c a ta l y s t t o p r o d u c e m e th a n o l . F i n a l l y , t h e

c rude methano l may be d i s t i l l ed to p roduce

pure methanol.

Methanol can be produced from biomass by

gasifying the biomass with oxygen or through

p y r o l y t i c g a s i f i c a t i o n to p r o d u c e th e CO-

hydrogen mixture, wi th the remainder of the

process being identical to the processes which

use na tural g a s. The oxyg en -blow n g a sifier sys-

tems can be built today, whereas pyrolysis gas-

ifiers require further development.

Cost estimates for an oxygen-blown gasifier

used to produce methanol are given in table 48

and a flow diagram of the process is shown in

figu re 25. The c ost is estima te d a t $0.75 to

Table 47.–Summary of Cost Estimates for Various Liquid FuelsFrom Wood via Thermochemical Processes

Commercial facilities couldFuel $/bbl $/gal $/millIon Btu be available by.

Methanol ., $28-$56 $ 0 .6 7 - $ 1 .3 3 $ 1 0 .5 0 - $ 2 0 .9 0 NowP y r o l y s i s o i l 30“ 50 0.70-1.20 7 “ 12 Mid to late 1980’sEthanol ., 2 3 - 6 8 0.55-1.62 6.50-19.10 1990’s

SOURCE Off Ice of Technology Assessment




Table 48.–1979 Cost of Methanol From WoodUsing Oxygen Gasification

Fixed investment (field erected) . . ., ., ., $80 millionWork ing capital (10% of fixed investment ) . , 8 million

Total investment . . , . . $88 million$/bbl

Wood ($15/green ton) . . . . . . . . . . . . . . . . . 10.35

Labor, water, chemicals. ., . . . . . . . . . . . . . 1.10Electr ic i ty (3 .8 kWh/gal , $0.04 kWh) 6.40Capital charges (15-30% of total

investment per year). ., ., ... . . . . $13.80-$27.60

Total, ., . . ... ., ., ., ... ., $31.65-$45.45($0.75-$1 .08/gal)

Estimated range:. ., . . . . . . . ... ., ., . $28-$ 56/bbl($10-$30/green ton wood) ($0.67-$1 .33/gal)

($10.50 -$20.90/10 6 Btu)

Input: 2,000 green ton/d of wood (50% moisture)Output: 2,900 bbl/d methanol (40 million gal/yr)Load: 330 operating days per year

SOURCE Off Ice of Technology Assessment and based on J H Rooker, Davy McKee, Inc.,Cleveland Ohio private commumcahon May 1980 A E Hokanson and R M Rowell,

Methanol From Wood Waste A Techmcal and Economic Study Forest Products Lab.oratory Forest Serwce, U S Oeparfment of Agriculture general technical report

FPL12 June 1977 and E E Badey manager Coal and Biomass Conversion, OavyMcKee Corp Cleveland Ohio, private communication, 1979

$1 .08/gal from $30/dry ton wood, and the capi-

tal investment is about $2.00 for each gallon

per year of capacity, which is somewhat more

expensive than grain ethanol distilleries.

Comparable cost calculations are given for a

dual f lu id ized-bed pyrolysis gasi f ier in appen-

dix B. In this gasifier, the fluidizing medium isheated in one fluidized-bed reactor which

burns biomass and it is transferred to another

fluidized bed where it gasifies biomass in the

absence of air or oxygen, Although dual fluid-

ized-bed gasifiers are not ful ly developed, the

ca lcu la t ions in appendix B ind icate that th is

method may produce methanol a t somewhat

lower costs than using oxygen-blown gasifiers,

pr inc ipa l ly because i t e l iminates the equ ip-

ment needed to produce oxygen. A more accu-

rate comparison, however, must await devel-

opmen t and demons t ra t i on o f dua l f l u id i zed -

bed and other pyrolysis gasifiers.

Figure 25.—Block Flow Diagram of Major Process Units

Wood hand. WoodWood

logsgasification

and prep.

plant

oil ILightends Methanol Crude Methanol Acid gasto distillation

MeOHsynthesis

synthesisremoval

fuel gas

Product Purge gasstorage to fuel

SOURCE: J H. Rooker, &fethano/ V/a Wood Gas/ficat/on (Cleveland, Ohio: Davy Mckee, Inc , 1979)



Ch. 7—Thermochemical Convers ion q 1 41

The on ly p a r t o f m e th a no l syn the sis, fo r

which there is any uncertainty is the operation

of and yield from the gasifier. Oxygen-blown

wo o d g a s i f i c a t i o n c a n p r o b a b l y b e a c c o m -

pl ished with commercial f ixed-bed gasi f iers,27

but a large part of the gasi f ier cost would be

associated with cleaning tars, oi ls, and other

compounds f rom the gas. Consequent ly , the

costs would be reduced somewhat by develop-

ing advanced oxygen gasifiers that maximize

the CO-hydrogen yields and reduce the tar and

oi l formation.

With plant herbage as the feedstock, addi-

tional problems may arise from the handling of

this material and possible clogging of the gasi-

f ier. These p roblem s p roba b ly c a n be solved

with a relatively straightforward development

of suitable gasifiers.

Methanol yie lds from wood would vary de-

pending on the type of wood, but have been

estimated at 120 gal/dry ton in a plant that pur-

c h a s e s i t s e l e c t r i c i t y .28 I f the e lec t r i c i ty i s

cogenerated onsi te the y ie ld would be about

100 gal/dry ton. ” The se yield s c orresp on d t o

conversion efficiencies of 48 and 40 percent,

respectively. Yields from plant herbage are not

available, but based on the above efficiencies,

they may be 100 or 80 gal /ton depending on

whether the electricity is purchased or gener-

ated onsi te. In nei ther case would addi t ional

bo i le r fue l be needed. In theory, however ,

these yields can be increased significantly.Accessing a large part of the potentia l b io-

mass resource would be aided by the develop-

ment of smal l , inexpensive package methanol

p lan ts . However , because sma l l cen t r i fuga l

compressors c a n n o t a c h i e v e th e p r e s s u r e s

needed for methanol synthesis, plants smaller

than about 3 mi l l ion to 10 mi l l ion ga l /yr o f

me thano l wou ld requ i re a d i f fe ren t type o f

compressor, e.g., rec ip roca l compresso r .30 31

‘7 J H Rooker, A4ethano/ Via Wood Gasification [C leve lan d ,

Ohio Davy McKee, Inc , 1979)I~E E Bailey, Manage r , Coal and Biomass conversion, Davy

McKee Corp , Cleveland, Ohio, private communication29A E Hokanson an d R M Rowell, “ M e t h a n o l F r o m Wood

Waste A Technical and Economic Study,” Forest Products Labo-

ratory, Forest Service, U S Department of Agriculture, general

technical report FPL 12, June 1977

\OBalley, op c it

“J H Rooker, Davy McKee, lnc , Cleveland, OhJo, private

communlcatlon, May 1980

This c ould increa se the p lant c ost ab ove t ha t

r e s u l t i n g f r o m t h e n o r m a l d i s e c o n o m y o f

sca le , but eng ineer ing deta i ls and costs are

uncertain at present.

There is l ittle do ub t that m etha nol ca n be

synthesized f rom wood wi th ex is t ing technol -

og y. Since the only unc erta inty is with the ga si-fier, the cost estimates are probably accurate

to within 20 p erce nt. This wo uld p ut the c ost

per Btu o f methanol f rom wood at about the

same leve l as e thanol f rom gra in . However ,

both alcohols are l ikely to be more expensive

than methanol from coal, due primari ly to the

e c o n o m y o f s c a l e t h a t c a n b e a c h i e v e d b y

building very large coal conversion facil i ties.

Pyrolytic Oil

P y r o l y t i c o i l c a n b e p r o d u c e d b y s l o w l y

heating biomass under pressure and in the

p resenc e o f a c a ta lyst. The p ressure sup presses

gas formation and the catalyst aids the forma-

tion of the oi l . Other possibi l i t ies, however,

such as rapid heating and cooling can also pro-

duce pyrolytic oils.

The p roc ess involving slow h ea ting is c ur-

rently under development and a pi lot p lant in

Albany, Oreg., has produced a small quantity

of oi l, fol low ing e a rlier difficu lties. The oil is

about 30 percent lower in heat content (per

gal lon) than petroleum fuel oi l and i t may bec orrosive b ut it c on ta ins ne gligible sulfur. The

oil is said to be roughly equivalent to a low-

grade fuel oil, but further testing is necessary

to determine how well the oil stores and what

modif ications in boi lers may be necessary to

use this oil as a boiler fuel.

Since the pyro lyt ic o il is ma de f rom feed -

stocks that could be used in close-coupled, air

gas i f ie rs and would have some of the same

uses as the gasifier fuel gas, pyrolytic oil pro-

duction should be compared to close-coupled

g a sifiers. The p yrolyt ic o il is less exp e nsive totransport than raw biomass and it is p r o b a b l y

well suited to fulIy automatic boiler operation.

It may also be possible to refine the oi l to

higher grade l iquid fuels. At present, never-

theless, the costs appear to be high in relation




to air gasifiers and the efficiency of using the

biomass feedstock in this way is considerably

lower than with gasification, but the oil may be

comparab le in cost to some other synthet ic

fuels. Consequently, if gasifiers become widely

available, markets for the pyrolytic oils may be

limited to those users who are wil l ing to pay

for complete automation of their boi lers.

Various other thermal processes are possible

for the production of oi ls from biomass (see

app. C), including processes which do not try

to minimize oil production during gasification

and co l l ec t the o i l as one o f the p roduc ts .

These latte r type s prod uc e g as, oil, a nd c ha r

products.

The m ulti p rod uc t system s, while b eing tec h-

nically easier to develop, have decreased oil

y ie lds (since part of the biomass is not con-

ver ted to o i l ) and the management and eco-

nomics are more complicated due to the need

to sell each of the various products. A tech-

nical solution to these problems being studied

is to slurry the char with the oil. Although the

char contains ash and the oil is corrosive and

may de te r io ra te under s to rage , the Depar t -

ment of Energy (DOE) is funding a feasibility

study for burning this slurry of oil and char in

g a s turb in e s. j’ Sin c e c o n v e n t i o n a l t u rb i n e s

may not be able to tolerate gases with sodium

and potassium the project proposes to use tur-

bine combustion technology developed from

miIitary programs. 34It would seem, however, to be more tech-

n i ca l l y and economica l l y sound to deve lop

convers ion processes which produce l i t t le or

no char and which produce only as much gas

as can be uti l ized by the conversion facil i ty.

‘ ]] W Blrkeland and C 13endersky, “Status of Biomass Waste

and Residue Fuels for Use In Directly Fired Heat Engines, ” pre-

sented at the Conference on Advanced Materia/s for A hernateFuel Capable Direct/y Fired Heat Engines, sponsored by the Elec-

tric Power Research Institute and the Department of Energy,

Maine Marltlme Academy, Castine, Maine, August 1979J iTeledyne CAE, Toledo, OhIO~ “Gas Turbine Demonstration

of Pyrolysls-Derived Fuels, ” Department of Energy contractE778-C-03-1839

“Btrkeland and Bendersky, op clt

Co nseq uently, OTA ha s not an alyzed the m ul-

tiproduct l iquefaction systems in detail.

St i ll an o th e r type o f li que fac t i on p roc ess

would subject medium-Btu gas to pressure in

the presence of a catalyst (the biomass analog

of t he Sou th A fric a n SASOL proc ess fo r p ro-

du c ing ga soline from c oa l). The c ap ital invest-ment, however, appears to be quite high,35 a n d

further development wi l l be needed to lower

these costs.

Ethanol

C o n c e p t u a l l y , e t h a n o l c a n b e p r o d u c e d

f rom b iomass th rough rap id gas i f i ca t i on to

prod uc e et hylene. The e thylene is the n sep a-

rated from the other gases and converted to

ethanol using commercial technology.

The c r it i ca l fac tor in de termin ing the ec o-nomics is the ethylene yield from rapid gasi-

f i ca t i on . P resen t exper imen ta l y ie lds have

reached 6 percent (by weight) from biomass, 36

but som e resea rch ers’ be l ieve that y ie lds as

high as 30 percent (by weight) may be possible.

If so, then this process could produce fuel eth-

anol at prices considerably below those for the

fermentat ion o f I ignoce l lu los ic mater ia ls and

at costs (per mil l ion Btu) comparable to those

projected for methanol from coal, or roughly

$0.65/gal of ethanol.

The p roc ess, how eve r, nee d s c onsid erab le

research to determine i f and how such ethyl-

ene yields can be achieved. Even under favor-

able circumstances, it is unlikely that commer-

cial processes could be available before the

1 990’s.

“DOW Ctremlcal, U S A , Freeport, “Technical, Economic, and

Environmental Feaslblllty Study of China Lake Pyrolysts Sys-

tern, ” report to the Environmental Protection Agency, 1978“S Prahacs, H C Barclay, and S P Bhada, “A Study of the

Possiblllties of Producing Synthetic Tonnage Chemicals From

Llgnocellulosld Residues,” Pulp and Paper Magazine of Canada,

VO I 72, p 69, 1971J 7See e ~, M j Anta 1, Biomass Energy Enhancement — A ‘e-

port to the President’s Council on Environmental Qua/it y (Prince-

ton, N J Princeton Unwerslty, July 1978)



144 • Vol. Il—Energy From Biological Processes

Table 50.–Estimates of Total B(a)P Emissions(metric tons/year)

Major sources Minimum Maximum

Burning coal refuse banks. . . . . . . . . . . 280 310Residential fireplaces . . . . . . . . . 52 110Forest fires . . . . . . . . . . . . ., . . . . . ., . 9.5 127Coal-fired residential furnaces . . . . . . . . . . . 0.85 740Coke production. . . . . . . . . . . . . . . . . . . . . 0.05 300

SOURCE Energy and Environmental Analysts, Inc ‘‘Prehmmary Assessment of the Sources,Control and Population Exposure to Airborne Polycyclic Organic Matter (POM) as indi-cated by benzo(a)pyrene [B(a) P], November 1978

to travel 60 miles (100 km) or farther from their

source .4] How eve r, source s that are far f rom

population centers are less dangerous than ur-

ban sources both because o f the d ispers ion

that occurs with distance and because POMs

even tua l l y can be degraded to l ess ha rmfu l

forms by photo-oxidative processes. ”

POMs are dangerous for a number of rea-

sons. First, because of their physical nature,

they are more l ikely than most substances tore a c h v u ln e ra b le h u m a n t i ssu e s. Th e y a r e

formed in combustion as vapors and then con-

d ense o nto pa rtic les in the flue ga s. The sma ll-

e r p a r t i c l e s a d s o r b a p r o p o r t i o n a te l y h i g h

a m o u n t b e c a u s e t h e y h a v e l a r g e s u r f a c e /

we ight ra tios. The se sma ller p a rtic les a re bo th

less l ikely to be captured by particulate con-

t ro l equ ipmen t and more l i ke l y to pene t ra te

de ep in to the lungs i f b rea thed in . Sec ond ,

several of the POM compounds produced by

combustion are “the same compounds that, in

pure form, are known to be potent animal car-

cinogens. “45

POM is suspected as a cofactor(contributor) to the added lung cancer risk ap-

p a rently run b y urba n reside nts. ” Finally, POM

is suspec ted o f caus ing o r con t r i bu t i ng to

added inc idence o f chron ic emphysema and

asthma. 47

“ C Lunde and A Blorjeth, “PolycyclIc Aromatic Hydrocar-

bons In Long-Range Transported Aerosols, ” Nature, 268, 1977,Pp 518-519 “M J Svess, “The Environmental Load and Cycle of Polycy-

CIIC Aromatic Hydrocarbons, ” The Scien ce of t he Tota/ Environ-

m e n t , 6 , 2 3 9 , 1 9 7 9

4’J O Milliken, “ Airborne Emissions From Wood Combus-

tion, ” presented at the Wood Heating Seminar IV, Portland,

Oreg , sponsored by the Wood Energy Institute, Mar 22-24,1979

“J O Mllllken and E G Bobaleck, Po/ycyc/ic Or gan ic Ma t t e r : Review and Analysis (Research Triangle Park, N C Special

Studies Staff, Industrial Environmental Research Laboratory, En-

vironmental ProtectIon Agency, 1979)

“K L Stemmer, “Cllnical Problems Induced by PAH,” In Car-cinogenesis, Volume 1. Polynuclear Aromat ic Hydrocarbons:

Chem~stry, Metabolism, and Carcinogenests (New York. RavenPress, 1976)

Because POM and other organic emissions,

as well as CO, are the products of incomplete

combustion, the new airtight stoves, which are

beginning to take an increasing market share,

wi l l have to be eva luated carefu l ly for the i r

emission character ist ics, especial ly under im-

proper operat ion. A i r t ight s toves ach ieve a

h igher ove ra l l hea t ing (bu t no t necessar i l y

combustion) eff ic iency by slowing down com-

b u s t i o n , t r a n s fe r r i n g m o r e o f t h e h e a t p r o -

duced into the room rather than up the f lue,

and avoiding the establishment of an airflow

from the room into the stove and up the flue.

The red uc t ion o f exce ss a i r a l low ed in to the

combustion zone increases the emissions of

CO and unburned hydrocarbons. Ideally, these

pol lutants wi l l be burned in a secondary com-

bustion zone fed with preheated air (air that is

f i rs t routed through the pr imary combust ion

chamber). However, if the air fed into this zone

is too cool, secondary combustion wil l not oc-

cur; under these circumstances, airtight stoves

would be substantial ly more polIuting than or-

d inary s toves. A lso , the lower a i r f l ow and

cooler exit gases of these stoves cause them to

deposi t more of their organic emissions– in

the form of creosote—on the interior of their

ch imneys . Depos i ts o f c reoso te f rom wood

stoves and fireplaces have always been a fire

hazard; this hazard will be increased by great-

er use of airtight stoves. An added safety prob-

l e m a s s o c i a te d w i th a i r t i g h t s to v e s i s t h e

p o t e n tia l fo r “ b a c k -p u f fin g ” —surge back off l a m e s – wh e n th e s to v e i s o p e n e d . B o th o f

these safe ty hazards are contro l lab le by, re-

spect ive ly , hav ing the f lue c leaned regu lar ly

and increasing the intake airflow before open-

ing the stove.

Utility and Industrial Boilers

Large wood-fired boilers should be more ef-

ficient energy converters than small units and

therefore should have less problems with CO

and unburned hydrocarbons. However, the po-

tential exists to generate significant quantitiesof these pol lutants, and some exist ing large

boilers are fairly inefficient and thus fulfill this

potential. (For example, emissions of CO from

industr ia l boi lers range from 1 to 30 g/kg of

wood, compared to 60 to 130 g/kg from small



Ch. 7—Thermochemical Conversion • 145

wo od stove s. )48 Inefficient boilers will generate

the same dangerous organic compounds— in-

cluding species of POM — as do small residen-

tial sto ves and firep lac es. These orga nics a re

m o s t l y “ l o w- m o l e c u l a r - we i g h t h y d r o c a r b o n s

and alcohols, acetone, simple aromatic com-

pounds, and severa l shor t-cha in unsatura ted

compounds such as o le f i ns .49

Som e o f the seemiss ions a re pho tochemica l l y reac t i ve , a l -

though the amounts in quest ion should not

contr ibute s ign i f icant ly to smog prob lems. As

the price of wood and wood waste increases,

strong incentives for greater combustion effi-

c iency should work to min imize the organ ic

emission problem.

Sul fur d iox ide (SO 2) emissions should be

minimal because of wood’s low sulfur content.

An exception to this is the combustion of black

liquor in the pulp and paper industry; some of

the se b o i le rs sho u ld req u i re SOX s c r u b b i n gunder Federal regulations. 50

Although particulate emissions generated by

wood-f i red boiIers can be high (6 g/kg, or about

as high per uni t of energy as a wood stove),

e f f ic ient contro ls are ava i lab le for the larger

units. Available devices or combinations of de-

vices include multi cyclones coupled with low-

energy wet scrubbers, dry scrubbers, electro-

sta tic p rec ipita to rs (ESPs), o r b a g ho uses (fab ric

f i l te rs) . A l though ESPs are the most wide ly

used con t ro l mechan ism fo r u t i l i t y bo i l e rs ,

they have been said to be less practical for

wood-f i red boilers because of the very low re-

sistivity of both the flyash and unburned car-

bon part ic les from wood combustion .5’ How-

ev er , ESPs ha ve b ee n succ essfu l ly used on

some wood-fi red boi lers, and the problem of

low resistivity apparently can be handled with

appropriate precipi tator design.

C u r r e n t r e g u l a t i o n s f o r e m i s s i o n c o n t r o l

from pollution sources do not distinguish par-

ticulates by their size. Most control devices in

4* Mllllken, “Airborne E mlsslons From Wood Gaslflcatlon, ” op

c It

“M D Yokell, op clt50~n “I ron menta / ~eadjness Documen t , W o o d COmmercia/iza-

rIorI (Department of Energy, 1979), draft

5 ’ Wood Combu~t /on S y s t e m s A n Assessment of Env/ ronmenta /

Concerns (Mlttelhauser Corp , July 1979), draft, contractor report

to Argonne National Laboratory

current use suffer from a severe drop in effi-

ciency in controlling the finer, more dangerous

particles. Baghouses appear to be the only fea-

s ib le contro l dev ices current ly ava i lab le that

are capable of collecting particles below a few

microns in size with 99-percent eff ic iency or

greater. I t appears qui te probable that emis-

sion standards for the finer particulate even-tua l ly wi l l be promulgated; these standards

would almost certainly lead to extensive use of

baghouse controls.

Cu r r e n t E P A e m i s s i o n fa c to r s s h o w NOX

emissions from wood combustion to be com-

parab le to emiss ions f rom coa l combust ion.52

If these factors were correct, large boilers sub-

ject to Federal new source performance stand-

ards would require NOX reductions of 40 per-

c ent. This wo uld p ose a p rob lem in the short

term, because there is virtually no experience

in reduc ing NOX e m i s s i o n s f r o m wo o d - f i r e d

b o ilers. Tec hniq ue s used fo r fossil fue l bo ilers

that may be appl icable to wood are:

q low excess air firing,

. staged combustion, and

q flue gas recirculation.

Recent measurements conducted by Oregon

State Universi ty” a nd TRW54 show actua l NOX

emissions from test boi lers to be one-third or

less than those predicted by using the current

e m i ssio n fa c to rs. Th e se m e a su re m e n ts a r e

much more in I ine with the lower combustion

temperatures in wood boi lers and wood’s low

nitrog en c ont ent , EPA a nd DOE resea rche rsare convinced that the current emission fac-

tors are in er ror55 56and it appears l ikely that

the factors wilI soon be revised.

In the past , wood bo i le rs have never a t-

tained the size normally associated with large

coa l - f i red bo i l e rs , Whereas coa l - f i red u t i l i t y

boi lers are typical ly a few hundred megawatts

52 Cornp l /a t ion of Air Po/ /u tant Em/ss/on f ac t o r s Rev / sea l (Wash-ington, D c Office of Al r Programs, E nvlronmental Protect Ion

Agency , February 1972), publ i cat ion No AP-42

“ M e m o r a n d u m f r o m P a u l A B o y s , Al r Surve i l l ance and lnves-

tlgatlon Section to George Hofer, Chief, Support and Special

Projects Sect[on, U S Environmental, ProtectIon Agency, “Com-

parison of Emlsflons Between Oil Fired Boilers and WoodwasteEloilers, ” November 3, 1978

“J O Mllllken, Envlronrnental Protect Ion Agency, ResearchTriangle Park, N C , private communlcatlon, June 6, 1979

“Mllllken, Oct 26, 1979, op clt

“J Harkness, Argonne National Laboratory, private communl-

catlon, Oct 26, 1979



148 q Vol. Il—Energy From Biological Processes

put capaci ty. An addit ional l imit may be pre- content of the biomass may cause condensa-

sented by the addit ional volume of combustion problems in the stack unless the biomass

tion gases that would be generated if the bio- content is l imited, stack temperatures are in-

ma ss is fed mo ist into the b oi ler. These c on - creased (by removing less energy from the gas

straints do not apply when the energy output and thus lower ing system ef f ic iency) , or the

required is much lower than the boiler’s rated biomass is f i rst dr ied (which may also lower

capaci ty , or when the system is speci f ica l ly system efficiency).

designed for cofi r ing. Also, the high-moisture

Environmental Impacts of Gasification

Gasif ication technologies have a number of

potentia l a ir and water impacts. Because few

such gasifiers are in operation, quantification

of the se imp ac ts is prema ture. The low c onc en-

trations of trace metals and sulfur in the bio-

mass feedstocks and the lack of extreme tem-

perature and pressure condi t ions imply that

impacts should be substantially less than those

associa ted wi th coa l gas i f ica t ion. However ,

sc ien tists w o rking fo r DOE’ s Fue ls from Bio-

m a s s B r a n c h p r o fe s s to b e u n s u r e a s to

whether th is supposed b iomass “advantage”

actually exists, especially in the water effluent

stream; although the hydrocarbons present in

b iomass gas i f i ca t i on was tewa te r shou ld be

more amenable to b io log ica l t reatment than

coal gasi f ication hydrocarbons (they are more

oxygenated), they may be produced in greater

quantities and have a higher biological oxygen

demand than those o f a coa l sys tem.57 Also,

the potentia l for prol i feration of smal l -scalebiomass gasifiers may present monitoring and

enforcement prob lems that would not ex is t

with a few la rge c oa l ga sifiers. Therefore, b io-

mass gasification may require as much atten-

tion and concern as coal gasification.

The q ua ntity and mix of a ir polluta nts pro-

duced by biomass gasification plants wil l de-

pend in large part on the combustion/gasifica-

tion conditions maintained as well as the en-

vironmental controls and the chemical make-

up o f the feed stoc k. For exam ple, the co nc en-

tra t ion o f hydrogen in the react ion chamber

and of suIfur and nitrogen in the feedstock wilI

i n f l u e n c e t h e f o r m a t i o n o f a m m o n i a ( N H3) ,

‘7 Richard Doctor, Science Appllcatlons, Inc , prwate commu-

nlcatlon, November 1979

hydrogen sulfide (H2S), and hyd rog en c yanide

(HCN). Other products of the gasification proc-

ess include c a rbo nyl sulfide (C OS) an d c arbo n

disu l f ide (CS2) as wel l as phenols and poly-

nuc lear aromat ic (PNA) compounds.58 Gasifi-

cation processes that are closer in their nature

to pyrolysis and that produce considerable by-

product char wil l have lower nitrogen and sul-

fur-derived emissions; about half of the origi-

nal sulfur and nitrogen in the biomass should

remain in the char. 59

The g as prod uce d wi ll e ither be burned on-

site (producer gas) or cleaned and upgraded to

pipeline gas. Either process should eliminate or

reduce most of the more toxic pollutants, with

the onsite burning oxidizing them to CO2, SO 2,

N O 2, and water. Recent tests of a close-cou-

p led gas i f ie r /bo i le r combinat ion us ing wood-

chips for fuel showed emissions of CO, particu-

Ia tes, and hydrocarbons–which are o f major

concern in wood combustion — to be well be-low emiss ions expec ted f rom a d i rec t - f i red

wo o d b o i l e r , a l t h o u g h a fu e l o i l b o i l e r r e -

placed by such a gasifier would have had con-

s iderab ly lower par t icu la te and hydrocarbon

emissions. NO X emiss ions f rom the gas i f ie r /

boi ler combination were lower than those ex-

pected from either oil- or wood-fired boilers. 60

“ Solar Program Assessment: Environmental Factors, Fuels From

B/ornass (Washington, D C Energy Research and Development

Administration, March 1977), ERDA 77-47/7

“lbld“’Ca[ifornla Al r Resources Board, “source Test Report NO C-G-

O(I2-C, Source Test of Exhaust Gas From a Boiler Fired by Produc-

tion Gas Generated From an Experimental Gaslfler Unit Using

Wood Chips for Fuel, ” Stationary Source Control Dlvlslon,March 1978




Wood Oi l Gasifier boiler boiler

Carbon monox ide ( lb /h r ) . 0 1.8-54 0 .3 3Part icu la tes ( lb /hr) 0 7 0 4 5 - 1 3 5 0 1 3H y d r o c a r b o n s ( l b / h r ) 0 . 9 0 6 3 0 0 7Nitrogen ox ides ( lb /h r ) 039 9 1.46

These results c a nnot b e rea dily extrap olate d

to other situations, but they imply that the useof gasi f iers may offer a less pol Iut ing al ter-

native to direct combustion of biomass when a

sh i f t to renewab le ( f rom o i l ) i s be ing con -

templated.

Leaks of raw product gas represent a poten-

tial for significant impacts, especially on those

in the imme d iate v icin i ty of the g a si f ier. The

probabil i ty of such leakage is not known. Al-

though impact analyses of high-pressure coal

gasification technologies have identified fugi-

t ive hydrocarbon emissions as a l ikely prob-

lem, it is not clear that similar problems would

occur with (lower pressure) biomass gasifiers.

The c omb ustible c har produc ed by the ga si-

fication process is another potential source of

air pollution. It may be used as a fuel source

elsewhere or else used to heat the bed in a flu-

idized-bed gasifier. In either case, its combus-

t ion wi l l p roduce NOX, flyash, and SOx as well

as trace metals either adsorbed on the flyash

(potassium, magnesium, sodium, i ron, boron,

ba r ium, cadmium, ch romium, copper , l ead ,

strontium, and zinc) or in gaseous form (beryl-

l ium, arsenic compounds, f luorides).61 62

Because most biomass feedstocks used

gasification processes have concentrations

6’So/ ar Program Assessment, op clt

“Doctor, op clt

in

o f

trace elements, ash, and sulfur that are sub-

stant ia l ly lower than concentra t ions found in

c o a l , c o m b u s t i o n o f t h e c h a r s h o u l d e m i t

l o we r c o n c e n t r a t i o n s o f r e l a te d p o l l u ta n ts

than wou ld coa l combus t ion . Depend ing on

the farming and harvesting techniques, how-

ever, the feedstock may be somewhat contami-

nated wi th pest ic ides, fer t i l i zers , and so i l ,

wh ich should add to combust ion po l lu tants ,

A lso , some fo rms o f b iomass—for examp le ,

cot ton t rash, wi th 1 .7 percent— have su l fur

levels comparable to levels in coal.

As ide f rom wa te r impac ts caused by con -

struction activities and leaching from biomass

storage piles, gasification facilities will have to

contro l potent ia l impacts f rom d isposa l and

storage o f process wastes and byproducts .

Water in i t ia l ly present in the feedstock and

that formed dur ing the combust ion accompa-

nying gasi f ication should provide signi f icantamoun ts o f e f f l uen t requ i r i ng d i sposa l (a l -

though in c lose -coup led sys tems, the mo is tlow-Btu gas may be fed directly into the boil-

er). Air polIutants identified above may appear

also as water contaminants: NH3 (as ammoni -

um hydroxide), HCN and its ionized form, phe-

no ls , and t race e lements found in the ash.

Leaching from byproduct chars may be a prob-

lem i f the char is ( incomplete ly carbon ized)

brown char a l though (carbon ized) b lack char

shouId be similar to charcoal and far less likely

to be polluting. Finally, the tars produced by

gasi f ication may wel l be carcinogenic; as yetno d a ta c onf i rm th is p ote nt ia l . These w at er

contaminants present a potential occupational

as wel l as ecological and publ ic heal th con-

cern, because plant operators may be exposed

unless stringent “housekeeping” is enforced.

Research, Development, and

Thermo c hem ica l c onv ersion inc lude s the

least expensive, near-term processes for using

the major biomass resources — wood and plantherbage. Moreover, R&D is likely to lead to in-

teresting new possibi l i t ies for the production

of fue ls an d c hem ica ls from b iom ass. Som e o f

the more important areas are:

Demonstration Needs

q Thermochemistry of biomass. — Basic and

appl ied research into the thermochemis-

t ry o f b iomass, inc lud ing secondary gasphase reactions, is needed to better define

the possibil i ties for fuel synthesis and to

aid engineers in designing advanced reac-

to rs. The resea rch sho uld inc lude stud ies




q

q

of the effects of the various operating pa-

rameters on the nature and composit ion

of products and ways to maximize the

yields of various desirable products such

as CO and hydrogen, ethylene, methane,

and other Iight hydrocarbons.

Gasifier development and demonstration. –Gasifiers should be developed further and

demonstrated, so as to improve their relia-

bi l i ty, eff ic iency, and f lexibi l i ty wi th re-

spect to feedstock type and moisture con-

ten t. This shou ld includ e a irb lown g a si f i-

ers for process heat, boiler retrofits, and

ICES, and oxyg en-blow n and p yrolysis gas-

i f iers for methanol synthesis. I t should

also include the demonstration of gasifi-

ers suitable for converting pIant herbage

to me thano l and shou ld i nves t iga te the

tradeoff between densi fy ing herbage be-

fo re gas i f i ca t i on ve rsus gas i f i ca t i on o fherbage directly. Each of the uses for gasi-

fiers will have unique requirements, which

p robab ly w i l l d i c ta te separa te deve lop -

ment and demonstration efforts.

Compressor development.– One of the

m a j o r c o s ts o f p r o d u c i n g m e th a n o l i n

small plants is the relativley high price of

sma ll c om p ressors. The c ost of me tha no l

synthesis from biomass would be lowered

substant ia l ly i f smal l , inexpensive com-

pressors suited to the process are devel-

oped .

Each of the new biomass conversion tech-

nologies will require environmental assesment

to ensure the development of appropriate con-

trol technologies and incorporation of environ-

mental considerations in system design, siting,

and operation. In general, the larger scale tech-

nologies are I ikely to be assessed as part of

n o r m a l E P A a n d D O E e n v i r o n m e n t a l p r o -

g ram s. The sma ller te c hno log ies g en era lly will

not come under Federal new source perform-

ance standards (speci f ica t ions o f a l lowable

emissions), but there is growing recognition in

EPA and DOE of the potential environmental

dangers of smal l -scale technologies such as

wood stoves.

Key env i ronmen ta l R&D a reas in the rmo-

chemical conversion are:

q

q

q

q

q

deve lopment o f wood s tove des igns (o r

controls) that achieve complete combus-

tion and minimize emissions of unburned

hydrocarbons;development of combustion controls that

wil l al low efficient — and pollutant mini-

m i z i n g — th e r m o c h e m i c a l r e a c t i o n s r e -

gardless of feedstock characteristics;

assessment of the potential health effects

of emissions from wood stoves and other

biomass conversion technologies, wi th a

f o c u s o n p a r t i c u l a t e w i t h a h i g h u n -

burned hydrocarbon component;

evaluation of toxici ty and carcinogenici ty

of b iom a ss g a sifier/ p yrolysis ta rs a nd oils;

and

design of controls for gasifier/pyrolysis ef-

fIuent streams.



Ch. 7—Thermochemical Conversion . 151

Appendix A. —Optimum Size for a Wood-Fired Electric Powerplant

The annual cost, C, of producing electricity in awood-fired electric powerplant can be expressed

as:

c = cc + Cf + ct (1)

Where CC represents the capital and other fixed

charges, Cfrepresents the fuel and other variablecosts, and Ctthe cost of transporting the fuel.

Letting S represent a dimensionless scaling pa-

rameter

c c = CcoS 0.7

(2)

Here CC

O represents the fixed charges for a base

case and it is assumed that these charges scale witha 0.7 scaling factor. Furthermore, the variable costsare:

Cf = CfoS [3)

Where Cf

O represents the base case.Assuming the fuel is collected from a circular

area surrounding the powerplant, the transport

costs can be expressed as:

C t = C t

O Q o S r (4)

Where Ct

O is the transport cost per ton-mile, Qo is

the annual quantity of wood transported in thebase case, and r is the average transport distance.

For a given scaling parameter S, the quantity ofwood transported is:

Q = Q OS = enr2 (5)

where e is the average availability of fuel wood col-lected in dry tons per square mile year and r is theradius of the circle from which wood is collected.

If one assumes that the actual transport distance

from a harvest site to the powerplant is J2 timesthe direct Iine distance,

Taking the derivative of C with respect to S and set-

ting it to zero (in order to find the minimum costper kilowatthour) yields

(9)

This represents the optimum size for the power-

plant.Evaluating the parameters for the base case

given in appendix B results in:

S = 11.7 Q06)5 (lo)where Q is in dry tons per acre year, the base case

corresponds to a 62-MW powerplant, and the trans-port costs are assumed to be $0.20/dry ton-mile

($0.10/green ton-mile).As expected, the higher the density of biomass

availability, e, the larger is the optimum-sized pow-erplant. IronicalIy, however, as Q increases, the av-

erage transport distance decreases. I n other words,it is more economic to keep the powerplant size

smaller than to transport large quantities of woodfor greater distances.

If one assumes that Q = 0.5 dry ton/acre-yr, then

the optimum powerplant size is over 500 MW andthe radius of the collection circle is about 50 miles.With Q = 0.05 dry ton/acre-yr, the optimum size is110 MW and the circle radius is 75 miles. If the

transport charges double, then for these values of

e, the optimum sizes are reduced to 200 and 50

MW, respectively, with collection radii of 30 and 50miles, respectively,

In principle, then, large-scale biomass conver-sion facilities are not unrealistic. The values as-

sumed for Q are probably less than what can beachieved in a region where the infrastructure forfuelwood harvests is fully developed. In practice,

however, it is likely to be difficult to develop amature harvest-supply infrastructure devoted to a

single conversion facility. As the infrastructure isbeing developed, many small users are likely tocompete for the fuelwood and the resultant availa-

bility to a single user may never reach the hundreds

of thousands or milIions of dry tons per year neces-sary for the larger faciIities.

Clearly biomass farms dedicated to a single con-version facility would overcome these problems of

obtaining a large feedstock source, It is unlikely,however, that these farms will be developed as de-scribed in the section on “Unconventional Biomass

Product ion.”




Appendix B.— Analysis of Break-Even Transport Distance forPellitized Wood and Miscellaneous Cost Calculations

Two ways for producing 1 million Btu of steam

from woodchips containing 50-percent moistureare presented in figure B-1. In the first case 389 lb

of greenwood are transported to the boiler andburned direc tly; in the sec ond 339 lb of g reenw oo dare pelletized first and then transported to the

boiler for burning.In the first case the cost of the fuel needed to

prod uc e this stea m is:

C = C W W W + C t W W d (1)

where CW is the cost per ton of wood at a central

yard, WW is the weight of wood to be transported,Ct is the transport cost per ton-mile, and d is the dis-

tance from the yard to the boiler.I n the second case:

C = CP W P + C t W P d (2)

when C is the cost of the pellets at the pellet mill,

W Pis the weight of pellets to be transported andthe other symbols are as before (assuming the pel-let mill is located at the wood yard).

Setting these two costs equal to one another andusing the weights of wood and pellets as above,

one finds that:

d = (0.65 CP – 1.65 CW) / Ct (3)With transport costs of $0.10/ton mile and the

wood and pellet costs given in the text, the break-even transport distance varies from 43 to 71 miles.If, however, the original wood is 40-percent mois-

ture, only 324 lb are needed in the boiler (with thesame efficiency) and the break-even transport dis-

tance becomes 123 to 134 miles. If the transportcharges are lower, the break-even distance will in-crease. Conversely, where transport is more expen-

sive, the break-even distance wilI be less. Numer-ous other local variables can also change the re-sults.

Miscellaneous Cost CalculationsFollowing are estimates for the costs of variousthermochemical conversion processes.

Figure B-1.-Two Ways to Produce 106Btu Steam From Wood

I 1

q

Pellet mill Wood boiler

Case 2339 lb wood 153 lb

1 x 106

Btu steam(50% moisture) 9(3% efficiency pellets83% efficiency

Table B-1 .-Electricity From Wood by Direct Combustion Table B-2.-Steam From Wood by Direct Combustion

Input 2,000 green ton/d of wood (50% moisture)

output 62-MW electricityLoad 300 operating days per year

Fixed investment (field erected) $50 millionWorking capital (10% of fixed

Investment) 5 million

Total Investment $55 million

Mills/kWh Million $/yr

Wood ($15/green ton) 20 9 0Labor and water 9 4 0

Capital charges (15’%o of totalInvestment per year) 19 82 5

Total 48 21 3Estimated range 45-70 mills/kWh

(package boiler)

Input: 270 green ton/d of wood (50% moisture)

output, 50,000 lbaof steam/hr

Load 330 operating days per year

Fixed investment (package boiler) $600,000

$1,000 lb steamW o o d ( $ 1 5 / g r e e n t o n ) 338L a b o r ( $ 7 5 , 0 0 0 / y r ) 0 1 9Capital charges(15-30’%0 of fixed

Investment per year) O 23-0.46

T o t a l 380-403E s t i m a t e d r a n g e : $350-$6 00/

1,000 lb steam

($2 ‘O-$4 80/106Btu)

‘1 ,O@I lb of steam = 1 25 mllllon Btu of steam

SOURCE OTA from A Survey of B/omam Gas/f (car/on (Golden, Colo Solar EnergyResearch Institute, July 1979)



Chapter 8.– FERMENTATION

Introduction . . . . . . . . . . . . . . . . . . . . . . . . .

Ethanol From Starch and Sugar Feedstocks . . .Energy Consumption . . . . . . . . . . . . . . .,Process Byproducts . . . . . . . . . . . . . . . . .

Ethanol Production Costs. . . . . . . . . . . . .Onfarm Distillation . . . . . . . . . . . . . . . . .

Cellulosic Feedstocks. . . . . . . . . . . . . . . . . . .Generic Aspects and Historical Problems

With Pretreatment . . . . . . . . . . . . . .Processes Currently Under DevelopmentGeneric Economics of Lignocellulosic

Materials to Ethanol. . . . . . . . . . . . . . .

Environmental lmpact of Ethanol Production. .Process Innovations. . . . . . . . . . . . . . . . . . . .

Crain and Sugar Processing ..., . . . . . . .Fermentation . . . . . . . . . . . . . . . . . . .

Distillation. , . . . . . . . . . . . . . . . . . . . . . .

Producing Drv Ethanol. . . . . . . . . . . . . . .

Page . . . 159. . . 160. . . 160 52. . . 162

. . . 164 53166

. . . 167 5455

. . . 169

. . . 169

. . . 172

. . . 173

TABLESPage

Energy Consumption in a DistilleryProducing Fuel Ethanol From Corn . ......161

Early 1980 Production Costs for EthanolFrom Grain and Sugar Crops. . . . . . . . . ....165

Cost of Ethanol From Various Sources. ....165Plausible Cost Calculation for FutureProduction of Ethanol From Wood,Classes, or Crop Residues . .............173

FIGURES

Page . . . 175 26. Process Diagram for the Production of. . . 175 Fuel Ethanol From Grain . ..............160

. . . 175 27. Process Diagram for the Production of

176 Fuel Ethanol From Sugarcane or Sweet. . .

. . . 176 Sorghum. . . . . . . . . . . . . . . . . . . . . . ......160



Chapter 8

FERMENTATION

Introduction

Etha no l, or “ gra in alco hol,” is a versa ti le

and commercial ly important l iquid which hasbeen used for a variety of purposes for centu-

ries. Ethanol is the intoxicant in alcoholic bev-

erages and, prior to the industrial age, society’s

most common contact with ethanol was as an

ingredient of beer, wine, or liquor.

Beverage alcohol is a major i tem of com-

merce and a source o f substant ia l tax reve-

nues. In addition, ethanol is also a key industri-

al chemical and is used as a solvent or reactant

in the manufacture of organic chemicals, plas-

tics, and fibers. Ethanol has a long history as acombus t ib le fue l fo r t ranspor ta t i on veh ic les

and space heating. Except under unusual cir-

cumstances (e. g., wartime Europe), ethanol has

been little used for these purposes in the 20th

century, having been largely displaced by pe-

troleum-based motor and boiler fuels.

Beverage alcohol is usually produced by fer-

mentation processes, but the processes are de-

signed to achieve various qualities of taste and

aroma which are irrelevant to fuel alcohol pro-

duct ion. Most industr ia l e thanol is produced

from ethylene, a gas derived from petroleum

or natural gas l iquids. Rising oil prices have

m a d e b i o m a s s - d e r i v e d e th a n o l c o m p e t i t i v e

with ethanol derived from petroleum but i t is

u n c l e a r wh e th e r t h e c h e m i c a l i n d u s t r y w i l l

turn to biomass or coal for i ts supply of etha-

nol.

All processes for the production of ethanol

th rough fe rmen ta t i on cons is t o f fou r bas ic

steps: 1 ) first the feedstock is treated to pro-

duce a sugar solution; 2) the sugar is then con-

verted to ethanol and carbon dioxide (CO2) b y

yeast or bacteria in a process called fermenta-

tion; 3) the ethanol is removed from the fer-

men ted so lu t i on by a d i s t i l l a t i on* p rocess

which yields a solution of ethanol and waterthat cannot exceed 95.6 percent e thanol (a t

normal pressures) due to the physical proper-

ties of the ethanol-water mixture; and 4) in the

final step, the water is removed to produce dry

et ha no l . Th is is a c c om p l ishe d b y d ist i ll ing

once again in the presence of another chemi-

cal.

The ma in distinctions amo ng the proc esses

using different feedstocks are the differences

in the p retrea tme nt step s. Sug a r crop s suc h a s

sug a rc a ne , sw e e t so rg h u m , a n d su g a r b e e t s

yield sugar directly, but the sugar often must

b e c o n c e n t r a te d to a s y r u p o r o th e r w i s e

treated for s torage or the sugar wi l l be de-

stroyed “ by ba c teria. Starch feed stoc ks such as

corn and o ther gra ins requ i re a ra ther mi ld

treatment with enzymes (biological catalysts)

or acid to reduce the starch to sugar. And. cel-

Iu losic (cel lu lose containing) feedstocks such

as crop residues, grasses, wood, and municipal

wastepaper require more extensive treatment

to reduce the more inert cellulose to sugar.

Processes utilizing each of the ethanol feed-

stock types are considered below. I n addition,

the env i ronmenta l e f fects o f e thanol d is t i l l -e r ies are d iscussed as are var ious process

changes that could lower costs. Although etha-

nol is emphasized in this chapter, it should be

remembered that other alcohols (e. g., butanol)

a n d c h e m i c a l s c o u l d b e p r o d u c e d f r o m th e

sugar so lu t ions, but techn ica l and economic

uncer ta in t i es a re too g rea t to i nc lude a de -

ta i led considerat ion o f these a l ternat ives a t

present.

*Distillation consists of heating the ethanol-water solutionand passing the vapor through a column in which the vapor con-

densed and revaporized numerous times, a process that succes-

sively concentrates the ethanol and removes the water

159



160 Ž Vol. II—Energy From Biological Processes

Ethanol From Starch

Ethanol ca n be p rod uce d from starch and

sugar feedstocks with commercially available

tec hno logy. Sta rch fee d sto c ks are p r ima rily

grain crops such as corn, wheat, grain sor-

ghum, oats, etc., but also include various roo t

p Ia nts suc h a s p ota toe s. The sug a r fee d sto c ks

are plants such as sugarcane, sweet sorghum,

sug a r be et s, an d Jerusa lem a rtic ho kes. Since

these feedstocks are all crops grown on agri-

cultural lands under intensive cultivation and

can be converted with commercial technology,

they are considered together.

The p roc esses for prod uc ing et ha nol from

starch and sugar feedstocks are shown sche-

ma tica lly in figu res 26 and 27. The ene rgy c on-

sumption of these processes is discussed next,

fol lowed by a description of process byprod-

ucts, cost calculations, and onfarm processes.

Figure 26.—Process Diagram for the Production ofFuel Ethanol From Grain

and Sugar Feedstocks

Figure 27.—Process Diagram for the Production ofFuel Ethanol From Sugarcane or Sweet Sorghum

Energy Consumption

Mo st e tha no l distilleries in th e United Sta tes

today were designed for beverage alcohol pro-

duction, with l i ttle emphasis on energy usage.

A fuel ethanol distillery can take advantage of

newer technology and the low puri ty require-

ments of fuel ethanol to reduce its energy con-

sumption. Nevertheless, both the type of fuel

used and the amount of energy consumed at

the disti l lery wil l continue to be important de-

terminants of the eff icacy of fuel ethanol pro-duction in displacing imported fuels.

In the plant currently producing most of the

fuel ethanol today, the germ (protein) in theSOURCE Office of Technology Assessment



Ch. 8—Fermentat ion . 161

corn feedstock is removed in a separate feed

processing plant. Consequently, the dist i l lery

receives a more or less pure starch from the

grain processing plant and the waste sti l l age

(mate r ia l l e f t i n the fe rmen ta t i on b ro th a f te r

the ethanol has been removed) is fed into a

municipal sewage system, so that the energy

needed to pretreat the corn and to process the

waste stream is not included in the dist i l lery

energy usage. Nevertheless, the distillery con-

sumes 30,000 Btu/gal of ethanol and 96.5 per-

cent of this is in the form of natural gas.1 If all

p rocess ing energy inputs are inc luded, fue l

consumption is about 65,000 to 75,000 Btu/gal

of ethanol (exclusive of the energy needed for

was te s t ream t rea tmen t ) . z Furthermore, the

economics of this process are predicated on in-

come from process byproducts, such as corn

oil, for which the markets are uncertain if large

volumes are produced.OTA’ s a na lysis indica te s tha t th e fuel used

at the distillery cannot soon be reduced to an

insigni f icant fraction of the energy contained

in the etha nol. Thus, if the d isp lac em ent of im-

ported fuels (oil and natural gas) is to be max-

imized, fuel ethanol distiIIeries should be re-

quired to use abundant or renewable domestic

fuels such as coal or solar energy ( including

biomass).

A distillery that might be more common in a

large-scale ethanol program has been designed

b y Ra p ha el Katzen Assoc iat es. ’ This d isti l lerywould produce a dry an imal feed byproduct ,

known as distillers’ grain (DC) (see next section

on byp roduc ts ) . A l though the d i s t i l l e ry uses

some equipment to dry the DC which is not in

common use in ethanol dist i l ler ies, al l of the

eq uipme nt is c om me rc ially ava ilab le. The d e-

sign reduces the number of dist i l lat ion col-

umns to the minimum using conventional tech-

nology (two columns: one to produce 95 per -

cent ethanol and one to produce dry ethanol)

‘ R Strasma, “Domestic Crude 011 Entitlements, Application

for Petroleum Substitutes, E RA-03° submitted to the Department

of Energy by Archer Danlels Midland, Co , Decatur, Ill , May 17,1979 update

* I b}d

‘Raphael Katzen Associates, Grain Motor Fuel Alcohol, Tech-

n / c a / a nd Econorn(c Assessment Study (Washington, D C Assist-

ant Secretary for Pol Icv Evaluation, Department of Energy, June

1979), CPO stock No 061-000-00308-9

and uses “vapor recompress ion” evaporat ion

fo r drying t he DG. The d isti l lery is c oa l-fired

and consumes 42,000 Btu of coal and 13,000

Btu of purchased electr ic i ty* to produce 1 gal

of ethanol which has a lower heating value of

76,000 Btu. ** The e ne rgy b rea kdo wn fo r the

Katzen design is shown in table 52.

Table 52.–Energy Consumption in a DistilleryProducing Fuel Ethanol From Corn

Thousand Btu ofProcess step coal/gal of ethanol

a

Receiving, storage, and milling, . . . . . . . . . . . . 0.8Conversion to sugar (including enzyme production). 16.0Fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.6Disti llat ion . . . . . . , . . . . . . . . 24.8Disti llers’ grain recovery . . . . . . . . . . . . . . . . . . . . 6.2Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 .6

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55.0

aA55ume5 10,000 Btu of cod per kllowatthour of electricity

SOURCE Raphael Katzen Assoclales, Gram Molor Fuel Alcohol, Technical and Econorrvc Assess.rrml Study (Washington, D C Assistant Secretary for Policy Evaluation, Departmentof Energy, June 1979), GPO stock No 061-000 .00308-8

At first thought, one might expect the energy

demand of a disti l lery using sugar plant feed-

stocks to be less than that for s tarch feed-

stocks, since the energy needed to reduce the

sta rch to sug a r is no long er req uired . The situ-

a tion is, in fa c t, quite the op po site. The p roc -

esses for extracting the sugar from the feed-

stock and concentrating i t to a syrup (highly

concentrated sugar solution) are qui te energy

intensive. The a verag e e nergy usa ge for a sug a r

f e e d s t o c k ( b a s e d o n s u g a r c a n e ) w o u l d b eabout 85,000 Btu of coal per gal Ion of ethanol

p roduced on the ave rage , ’ o r s l i gh t l y more

than the energy content in the ethanol. If the

bagasse, i.e., p lant matter left over after the

sugar is extracted, is used to fuel the boiler,

then 110,000 Btu of bagasse would be needed

to p rod uc e 1 ga l of e tha nol. (This a ssume s a 70-

percent bo i le r e f f ic iency for bagasse, as op-

posed to 90 percent for coal.)

For both the gra in and sugar feedstocks,

crop res idues cou ld be used to fue l the d is-

ti l leries. In b ot h c a ses the re is suffic ient resi-

*1O,OOO Btu/kilowatthour

* *Lower heating value is measured when water vapor iS the

product of combustion The higher heat value, when liquid water

iS the product, iS 84,000 Btu/gal

‘Ibid




fuel alcohol, resulting in a 0.7-percent increase

in the quantity of fuel produced.

C O 2 i s a l s o a b y p r o d u c t o f f e r m e n ta t i o n

which is used in carbonated beverages, dry ice,

and, to a small extent, in chemical processes.

Moreover, CO2 has many interesting properties

that are currently being researched and recov-

ery may eventual ly become more widespread

and profi table.

Ethanol Production Costs

Raphael Katzen Associates has performed a

detailed cost calculation on a 50-mil l ion-gal/yr

coal-fired distillery that purchases its electrici-

ty from an electric utility. 14 Including coal-han-

dl ing and pol lut ion control equipment and al-

lowing the production of dr ied DC, the total

distillery would cost an estimated $53 million.

Inflating this to early 1980 dollars (20 per-

cent) results in a disti l lery investment of $64

million. (The se figu res d o no t inc lude en gine er-

ing fees which could be small if a large number

of d is t i l le r ies are bu i l t , but which are est i -

mated at $6 mil l ion, in 1978 for a single dis-

ti l lery.)

A disti l lery designed solely for sugar crop

feedstocks would cost considerably more. As

mentioned above, the sugar has to be concen-

trated to a syrup for storage, since the feed-

stock is available for only part of the year, dur-

ing and somewhat after the harvesting season.Hence, the pretreatment equipment has to be

able to handle a larger capacity than the distil-

lery for part of the year, while standing idle for

part of the year. In addition storage tanks are

needed for the syrup. if the bagasse and crop

residues are used as fuel, however, then some

of the pol lut ion control equipment needed to

remove sul fur emissions can be el iminated,

d u e to t h e v e r y l o w s u l f u r c o n te n t o f t h e

b iom a ss. In a l l, a 50-miI lion-g a l / yr dist i l lery

for sugarcane or sweet sorgham would cost an

es t ima ted $100 mi l l i on i n 197815 16 o r $ 1 2 0

‘“Raphael Katzen Associates, op clt

‘Slbid

“F C Schaffer, Inc , in E S Llplnsky, et al , Sugar Crops as a

Source of Fuels, Vol // Processing and Conversion Research,final report to Department of Energy, Aug 31, 1978

mi l l ion in 1980, assuming the feedstock is

avai lable for hal f of the year and hal f year’s

syrup sto rag e is req uired . The se a ssum p tions

about the length o f t ime that the feedstock

wil l be available may be somewhat optimistic

for Midwestern grown sweet sorghum, how-

ever, and the cost could be higher. If the raw

feedstock is avai lable for only 3 months peryea r, OTA estima te s the d isti l lery wo uld c ost

about $140 million in 1978 dollars.

Although it might be possible to avoid con-

centra t ing the extracted sugar so lu t ion to a

syrup by using antib iotics or various chemi-

cals, a major cost of the pretreatment is the

equipment needed to remove the sugar solu-

tion from the raw plant material. Furthermore,

storage of large quantities of dilute sugar solu-

t ion would be expensive. Consequent ly , im-

provements in the economics o f us ing sugar

feedstock will require methods for storing the

raw sugar feedstocks inexpensively and in a

way that the sugar need not be removed and

concen t ra ted . Poss ib i l i t i es i nc lude p re t rea t -

ment with chlor ine gas, ammonia, or sul fur

dioxide (to change the acidi ty and provide a

toxic e nvironm ent for ba c ter ia). OTA is un-

aware, however, of any work in this area that

would serve as a basis for cost calculation.

An alternate approach is to build a distillery

capable o f handl ing e i ther s tarch or sugar

feedstocks. Katzen has calculated that this 50-

mil lion-g a l/yr d isti llery wo uld c ost $93 mil lion

in 1978 dolIars.17

The e thano l costs are influenc ed by the ca p-

ital investment in and financing of the disti l-

l e ry , the d i s t i l l e ry opera t ing cos ts , and the

byproduct credits. For a coal-fired 50-mill ion-

gal/yr distillery using starch feedstock, the cap-

ital charges are about $0.21 to $0.42/gal of eth-

ano l , depend ing on the f i nanc ing a r range-

me nts. These ch a rges, how eve r, c a n va ry sig-

ni f icantly wi th interest rates, depreciation al-

lowances, tax credits, and other economic in-

centives.

The m ajor op erat ing expe nse is the feed -

stock cost less the byproduct credit. For corn

at $2.50/bu, the feedstock costs $0.96/gal of

1 ‘Raphae l Katzen Associates, op clt




tank t rucks, but as product ion volume growsother forms of t ranspor tat ion, such as bargeshipments, rai l tank cars, and petroleum prod-uct pipelines, * could decrease the transporta-

tion cost to as low as $0.03 to $0.05/gaI under

favorable circumstances.)

A s s h o wn in tables 53 a n d 5 4 t h e m a j o r

tradeoff between starch and sugar feedstocks

is that the starch-fed dist i l ler ies require con-

siderably less investment than the sugar-fed

ones, but the ethanol yield per acre cultivated

may be larger wi th the sugar feedstocks. As

noted in chapter 3, however, these yield figures

are highly unreliable for sweet sorghum, and

sugarcane cannot be grown on most cropland

potentia l ly avai lable for energy crop produc-

t ion. I f comparat ive s tud ies o f potent ia l e th-

anol feedstocks grown under comparable con-

ditions show that certain sugar crops produce

more ethanol per acre than the starch crops,then there may be a tendency to turn to sugar

feedstocks as farmland prices rise. Moreover,

i f the gra in byproducts are d i f f icu l t to se l l ,

then economics could favor sugar crop feed-

stocks. For now, however, the lower capital in-

ves tmen t requ i red fo r g ra in - fed d i s t i l l e r i es

gives them an advantge over sugar-fed disti l-

leries.

Onfarm Distillation

Apart from commercial distilleries, consider-

able interest has been expressed in individualfarmers or farm coops producing e thanol . A

number o f factors , however , cou ld l imi t the

prospects of such production.

Tec hnology for produc ing 90 to 95 percent

ethanol (5 to 10 percent water) is relatively sim-

ple. Seve ral farmers are o r have c onstructe d

their own distilleries for this purpose. In addi-

‘Various strategies can be used to eliminate potential prob-

lems with the water sometimes found in petroleum pipelines. If

ethanol is being transported, the total volume of ethanol in the

batch can be kept large enough so that the percentage of water

in the delivered ethanol iS within tolerable limits If gasohol is

transported, it can be preceded by a few hundred barrels of etha-

nol which will absorb any water found in the pipeline, thereby

keeping the gasohol dry. Other strategies also exist or can be de-

veloped 18

‘8L J Barbe, Jr , Manager of Otl Movements, EXXON Plpellne

Co , Houston, Tex , private communication, August 1979

tion prefabricated disti l leries for producing 9 0to 95 percent ethanol are available both at thefarm size (15,000 gal/yr)19 and coop size (sev-eral hundred thousand gallons per year) 20 for a

cost of about $1 for each gallon per year of ca-

pacity, but there is insufficient onfarm operat-

ing experience to establish the reliability or ex-

p ec te d o p era ting life o f the se d istilleries. OTAis not aware of smaller distilleries, but there is

no fundamenta l reason why they canno t be

bui lt . There wi ll , how ever , be a t rade off b e-

tween the cost of smal l d ist i l ler ies and the

amount of labor required to operate them.

A farmer must consider a number o f s i te -

specific factors before deciding to invest in an

onfa rm sk il l. Som e o f the mo re imp or tant o f

these are:

q

q

q

q

q

q

Investment. – How much does the still and

related equipment cost?

Use of the ethanol. –Will the ethanol beu s e d o n fa r m o r s o l d ? Wh a t e q u i p m e n t

m o d i f i c a t i o n s a r e n e c e s s a r y ? W i l l t h e

farmer be dependent on a single buyer,

such as a large distillery that will upgrade

95 percent ethanol to dry ethanol?

Labor. – Does the farmer have access to

cheap, qualified labor, or is it better tomake a larger investment for an automat-ic distillery?Skill.– Although ethanol can be producedeasily, the process yield—and thus thecost — as well as the safety of the opera-

tion can depend critically on the skil l of

the operator.

Equipment lifetime.– Less expensive distil-

le r ies may be constructed o f mater ia ls

that are destroyed by rust a f ter a few

years’ operation.

Fuel.– Does the farmer have access to

wood, grass, or crop residues and combus-

t ion equipment that can use these fuels?

Can re l iab le , inexpensive so lar s t i l l s be

constructed for the distiIlation step?

If oil or natural gas is used in the distil-

Iery, would it be less expensive to use this

“Paul Harback, United International, Buena Vista, Ga , pri-

vate communication, October 1979ZORobert Chambers, president, ACR Process Corp , Urbana, Ill ,

private communication, September 1979



Ch. 8—Fermentat ion q 1 6 7

q

q

fuel directly as a diesel fuel supplement in

a retrofitted diesel engine?

Byproduct. – Can the farmer use the wet

byproduct on his/her farm? Wil l th is un-

duly complicate the feeding operations or

make the animal operation dependent on

an unreliable still? What will drying equip-

men t cos t and how much energy wi l l i tconsume?

Water. – Does the farmer have access to

sufficient water for the distiIIery?

Under favorable circumstances, it might be

possible to produce 95 percent ethanol for as

little as $1/gal* plus labor with a labor-inten-

sive distillery. If the ethanol is used in a diesel

t rac to r , the e thano l wou ld be equ iva len t to

diesel fuel costing $1.70/gal, or about twice the

current diesel fuel pr ices, Under unfavorable

circumstances, the cost could be several times

as great. Due to a lack of experience with on-farm distilleries, however, these cost estimates

may be low.

Onfarm or coop product ion o f dry e thanol

cou ld become compet i t ive wi th commerc ia l ly

dist i l led ethanol, however, i f re latively auto-

mat ic , mass-produced d is t i l le r ies capable o f

us ing fue ls found onfarm and producing dry

ethanol and dry DC could be sold for about $1

fo r each ga l l on pe r yea r o f capac i ty and i f

fa rmers c ha rge little fo r their la b or. OTA is no t

aware of any package distiIIeries for producing

dry ethanol that are available at this price.

*Assuming equipment costs of $1 for each gallon per year of

capacity, the costs per gallon of ethanol are: $0.58 for net feed-

stock cost, $0.20 for equipment costs (operated at 75 percent of

capacity), $020 for fuel (assuming $3/m million Btu and 67,000

Btu/gallon), and $0.05 for enzymes and chemicals, resulting in$1 03/gal of ethanol or $0.98/gal of 95 percent ethanol

Cellulosic

The fe ed stoc ks with the largest p ote ntial for

ethanol production –both in terms of the ab-

solute quantity of ethanol and in terms of the

q u a n t i t y o f e t h a n o l p e r a c r e o f c u l t i v a t e dland– are the cellulosic, or cellulose contain-

ing, fee d stoc ks. These include wo od , c rop resi-

dues, and grasses, as well as the paper fraction

of municipal solid waste.

Mee t ing th i s p r i ce goa l fo r au tomat i c , on -

fa rm, d ry e thano l p roduc t ion fac i l i t i es w i l l

probably require process innovations, particu-

larly in the ethanol-drying step, and could well

involve the use of small, inexpensive comput-

ers (microprocessors) for monitoring the proc-

ess. A major constraint, however, could be the

cost o f sensors, automat ic va lves, e tc . thatwould be required.

For some farmers, however, the cost or labor

required to produce ethanol may be of second-

ary imp ortance . The va lue o f some de gree o f

l iquid fuel sel f-suff ic iency and the abi l i ty to

d i v e r t l i m i t e d a m o u n ts o f c o r n a n d o th e r

grains when the market price is low may out-

weigh the inconvenience and/or costs. 1 n other

words, farmers may consider the technology to

be an insurance against diesel shortages and

hope that it will raise grain prices. Although

insurance against diesel shortages certainly canbe achieved by purchasing large diesel storagetanks at a cost below an ethanol distillation andstorage system, increased grain prices for the en-tire crop would make the economics consider-ably more favorable to farmers but would be avery expensive way for the nonfarm sector toprovide fuel to farmers. As evidence of the inter-

est, the Bureau o f Alcoh ol, Tob ac c o, a nd Fire-

arms had received over 2,800 applications for

on fa rm d is t i l l a t i on pe rmi ts by m id -1979 and

they expected 5,000 by the end of the year. 2’

As a profitable venture in the absence of large

subsidies or grain price increases, however, on-farm production of ethanol is, at best, margin-

al with current technology.

1’Wllllam Davis, Bureau of Alcohol, Tobacco, and Firearms,

U S Treasury, Washington, D C , private communlcatlon, July

1979

Feedstocks

Wood, grasses, and crop residues contain

c ellulose, he mic ellulose, a nd lig nin. The c ellu-

lose can be reduced, or hydrolyzed, to sugars

that c an b e fermented to alcohol. The hemicel-Iulose can also be reduced to sugars capable

of being converted to ethanol with other types

of b ac teria. The Iignin, howe ver, does not c on-

vert to alcohol and can be used as a source of




chemicals or dried and used as a fuel. General-

ly , paper is pr imar i ly ce l lu lose wi th vary ing

amounts of partial ly broken Iignin.

The remo va l of hem icel lu lose from wo od ,

grass, or crop residues and i ts reduction to

sugar are relatively straightforward. In fact,

hemice l lu lose f rom b iomass is the pr in icpa l

s o u r c e o f t h e c h e m i c a l f e e d s to c k fu r fu r a l .Although hemicellu lose is not now used as a

source of ethanol, the fermentation step can

probably be developed without excessive dif-

f icu l ty .

The c e l lu lose , o n the o the r hand , is em -

bedded with Iignin, which protects it from bio-

logical, but to a much lesser extent chemical,

a t ta c k . Thus, the red uc t ion o f c e l lu lose in -

volves treating the IignocelIulose material with

acid or pretreating the materia l e i ther chem-

ically or mechanically to make it susceptible

to biological reduction with enzymes.What was apparently the first acid hydroly-

sis of wood was described in a German patent

issued in 1880.22 Modifications of this processwere used to produce animal fodder in several

countr ies (mostly for the sugar) during World

War 1. At the end of the war, the economic ba-

sis became obsolete. Between World Wars 1

and 11, however, other acid hydrolysis proc-

esses were used mostly in Germany to produce

sugar and alcohol, partly because of materials

shortages but partly in an attempt at self-suffi-

c i e n c y . 23 Oth er p lants were a lso b uilt in Swit-

zerland and Korea.

During World War 1, pilot plants were built

i n the Un ited Sta tes fo r p roduc ing e tha no l

from wood wastes. Acid hydrolysis processes

underwen t a se r ies o f mod i f i ca t i ons du r ing

Wor ld War I l . Fo l lowing Wor ld War I I , how-

ever , v i r tua l ly a l l o f the wood-ethanol p lants

were c losed for economic reasons. * Tod ay

commercial wood sugar plants are in opera-

tion on ly in the U.S.S.R. and in Jap an b ut sever-

Z~H F J wenz I ~~e Chemica / Tec/?nO/ogy of wood, t r a n s -

lated by F E Braun’s (New York: Academic Press, 1970).

~ ‘Ibid

*One ethanol plant that uses the sugar-containing wastestream of a sulfite paper-pulping plant IS still in operation. It is,

however, primarily a waste treatment plant and less than 10 per-

cent of the paper-pulping processes used in the United States

produce a suitable waste stream

al other countr ies have expressed interest in

developing the technology, and one plant in

Switzerla nd is a ga in be ing used for p ilot stud -

ies. 24

Clearly it is technically possible to produce

ethanol from Iignocellulosic feedstocks today.

The fa ilure of th ese p roc esses to rem a in ec o-

nomically viable except under special circum-stances has been due, in large part, to the rela-

tively low costs of petrochemicals and ethyl-

ene-derived ethanol. With oil prices rising, the

primary competi tor is l ikely to be grain- and

sug a r-d erived e tha nol. There a re, how eve r, im-

provements and developments in the l ignocel-

Iulose processes which can make them com-

petitive with the current costs of ethanol from

these o the r feeds tocks . A l te rna t i ve l y , l a rge

rises in farm commodity prices could make the

cellulosic processes competitive without tech-

nical developments.

While there are processes whose economics

rely on large byproduct credi ts or special f i -

nancing that could be in commercial operation

before 1985, the key to achieving economic

competitiveness without these conditions is to

develop processes which:

q produce high yields of ethanol per ton of

biomass,

q do not require expensive equipment,

q allow nearly complete recovery of any ex-

pensive process chemicals, and

q do not produce toxic wastes.

No processes currently in existence fully satis-

fy all of these criteria, although there are proc-

esses that satisfy two and sometimes three of

the criteria. Nevertheless, R&D currently un-

derway could yield significant results in 3 to 5

years. With a normal scaleup of 5 years, one or

more processes satisfying these criteria could

become commercial by the late 1980’s.

The ge neric aspe c ts an d historica l problems

wi th producing sugars f rom I ignoce l lu los ic

feedstocks are now discussed, fol lowed by a

Sl igh tly more d eta i led d esc ript ion of va rious

processes currently under investigation. Final-

24) L Zerbe, Program Manager, Forest Service Energy Re-

search, U S Department of Agriculture, Forest Products Labora-tory, Madison, WIS , private communication, 1980



Ch. 8—Fermentation q 169

Iy, a generic economic analysis is presented for

a hypothetical advanced dist i l lery for produc-

ing ethanol from IignocelIulosic feedstocks.

Generic Aspects and HistoricalProblems With Pretreatment

As mentioned above, Iignocellulosic materi-

als consist of cellulose, hemicellulose, and lig-

n in . Typ ica l ly , suc h ma te r ia l wo uld f i rst b e

treated with dilute acid to remove the hemicel-

Iu lose, which then would be fermented in a

sep a rate step to e tha nol. The rema ining lignin-

ce l l u lose comb ina t ion wou ld be t rea ted wi th

concentra ted ac id a t low temperatures (per-

hap s 100° to 110° F) or dilute a cid a t high te m-

peratures (300 0 to 4000 F) to either dissolve the

cellulose from the Iignin or to cause the mate-

rial to swell, thereby exposing the cellulose for

hydrolysis. Al ternatively, the materia l can beexposed to a number of di fferent chemical or

mechan ica l p re t rea tmen ts wh ich render the

c ellulose susc e p tib le to h yd rolysis. The h yd rol-

ysis is then accomplished by further exposure

to acid or by the action of enzymes (biological

catalysts).

The relat ive am ou nts of c el lu lose, hem ice l-

Iulose, and Iignin can vary considerably among

the various Iignocellulosic materials. If pure

cellulose is converted completely to ethanol,

however, the theoretical maximum yield is 170

ga l of etha nol pe r ton of c ellulose. The yields

per ton of hemicel lu lose are simi lar. Conse-

quently for a Iignocellulosic material that is so

percent ce l lu lose, 20 percent hemice l lu lose,

and 25 percent Iignin, the theoretical yield is

about 120 gal/dry ton of biomass fermented. A

yield of 85 to 90 percent of this is a reasonable

practical goal, which would result in yields of

100 to 110 gal of ethanol per ton of biomass

fermente d. The expe c ted yield, how eve r, will

vary with the exact composit ion of the feed-

stock. For municipal sol id waste (29 percent

paper and 21 percent yard wastes and wood

p a c k a g i n g 25), the average yield could be about

60 gal of ethanol per ton assuming a 90-per-

cent overall conversion efficiency.~ ~~a ~erla / ~ a n~ f ~e fgy ~rorn MU njclpa/ Waste (VOI 1, wa sh lng-

ton, D C Office of Technology Assessment, 1979), GPO stockNo 052-001-00692-8

The histo ric a l proc esses have g ene rally used

a c id hydrolysis. The dilute a c id me thod s (Mod -

i f ied Rheinau, Sc ho l ler -Torne sc h, Ma d ison ,

Ten ne ssee Va lley Auth ority, and Russian Mo d i-

f i ca t i on o f Pe rco la t i on p rocesses) a l l su f fe r

f rom a s imi lar a i lment,26 Th e h i g h t e m p e r a -

tures and acidic conditions needed in the proc-

esses cause the resultant sugars to decompose,thereb y lowe ring the ove ra ll etha nol yield. The

concentrated acid processes (Rheinau-Bergius

and Hokkaido), on the other hand, have re-

sulted in go od prod uc t yields. The e c ono mics,

however, have historically suffered due to the

loss of large quantities of acid in the processes,

Nevertheless, one of the oldest concentrated

acid processes (Rheinau-Bergius) is currently

being reexamined to see if this economic con-

clusion necessarily pertains today (see below).

Pub lic a tions over the p ast 20 yea rs in the So-

v ie t Un ion have repor ted good exper imen ta lresults with impregnating wood with acid fol-

lowe d b y mec ha nica l grind ing. The d eta ils for

an assessment o f the commerc ia l v iab i l i ty o f

th is process, however , are not ava i lab le . On

the o ther hand, a mechanica l pre treatment is

also involved in the Emert ( formerly Gulf Oi l

Chemicals) process discussed below. Histori-

ca l l y , the mechan ica l p re t rea tmen ts needed

have been quite expensive, but the researchers

ind icate that th is is not a prob lem wi th the

Eme rt p roc ess. 27 F i n a l l y , a v a r ie t y o f o t h e r

processes or combinations of processes aimed

at exposing the cellulose to hydrolysis are cur-rently b eing resea rche d . The mo st imp orta nt of

these are considered below.

Processes Currently UnderDevelopment

Emert Process

The d eve lop me nt o f this proc ess sta rted in

1971 under Gulf Oil Chemicals Corp., but was

transferred to the University of Arkansas Foun-

1~1 Gold5teln D~partm~nt of Wood and Paper Science, North

Carollna State Unwerstty, Ralefgh, N C , private communlcatlon,

1979

“G H Emert and R Katzen, “Chemicals From Biomass by lm -proved Enzyme Technology, ” presented In the fymposlum f3iGm a s s a s a Non-Fue/ S o u r c e , sponfored b y t h e A C S/CSJ Joint

Chemical Congress, Honolulu, Hawal}, Apr 1-6, 1979

67-968 0 - 80 - 12




dation for scaleup (the transfer reportedly oc-

curred bec ause Gulf had ma de a manage ment

decision to concentrate i ts efforts on fossi l

fue ls). This p roc ess is the mo st a d va nc ed of the

enzymatic hydrolysis methods and, with prop-

er financing, can probably be brought to com-

mercial-scale operation by 1983-85.

The me thod c onsists of a p retrea tme nt d e-

veloped for this process which involves grind-

ing and heating the feedstock fol lowed by hy-

dro lys is wi th a mutant bacter ium a lso deve l -

oped for this purpose. A unique feature is that

the hydrolysis and fermentation are performed

simultaneously in the same vessel, thereby re-

ducing the t ime requirements for a separate

hydrolysis step, reducing the costs and increas-

ing the yield (since a sugar buildup during hy-

dro lys is cou ld s low the hydro lys is and de-

crease the overall yield). Also the process does

not use ac ids, which would increase equ ip-

me nt c osts. The sug a r yield s from t he c ellulose

are about 80 percent of what is theoretical ly

achievable, 28 but the small amount of hemicel-

Iulose in the sawdust is not being converted.

The p roce ss ha s be en b rought t o the p ilot

p l a n t s ta g e a n d fu n d s a r e c u r r e n t l y b e i n g

sought for a demonstration (1 million gaI/yr) fa-

cility as part of the scaleup process. Based on

the pilot plant experience, Emert estimates the

sell ing price for the ethanol to be $1 .49/gal

(1983 do l l a rs , 100 -pe rcen t p r i va te equ i ty f i -

nancing, and 10-year amort iza t ion) .29 With 80-

pe rcen t mun ic ipa l bond f i nanc ing , he es t i -mates the sell ing price to be $1.01/gal (1983

dollars, 20-year amortization).

These c ost estimate s are b a sed on a fee d-

stoc k of So-p erce nt “ air classified” municipa l

solid waste (i. e., the paper and plastic fraction)

at $14/ton, 25-percent saw mil l waste at $21/

ton, and 25-percent pulp mill waste at $14/ton.

These c osts are a ll on the low end of e stimates

for 1978-79 prices and consequently represent

optimistic estimates. Furthermore, by 1983, in-

flation would increase these costs. More realis-

t ic 1983 feedstock costs (50 to 100 percenthigher than those cited) would raise the etha-

nol cost by about $0.10 to $0.20/gal.

“lbtd“lbld

The c ost estima te s a lso a ssum e a large b y-

p roduc t c red i t fo r d r ied fe rmen ta t i on yeas t

and hydro lys is bacter ia ($0.40/ga l e thanol ) .

Most of this comes from the hydrolysis bacte-

r ia and an animal feed value for th is materia l

has not been estab l ished. In add i t ion, la rge-

sca le p roduc t ion cou ld l ead to a sa tu ra ted

animal feed market similar to that with graindisti l lation and subsequent loss of the byprod-

uct credit.

Furthermore, p r o b l e m s e n c o u n te r e d w i th

scaling up a process virtually always lead to

cost increases above those estimated. Conse-

quently, these cost estimates could be too low

by $0.20 to $0.70 or more per gallon of ethanol.

Never the less, wi th munic ipa l bond f inancing,

th is process cou ld wel l be compet i t ive wi th

ethanol produced from corn in a pr ivately f i -

nanced distillery by 1983. (Assuming 7-percent

annual in f la t ion as apparent ly was done in

Emert’s calculations, $1 .10/gal ethanol in 1979

would sell for about $1 .45/gal in 1983).

Whi le no cost est imates are ava i lab le for

this process using woodchips, grasses, or crop

residues as feedstocks, Emert reports that ex-

per iments have shown that modi f ica t ions in

the thermal-mechanical pretreatment enables

ethanol y ie lds o f 70 to 75 ga l / ton o f feed-

sto c k .30 The inc rea sed c osts for the se fe ed -

stocks ($40 to $50/ton in 1983 up from $30 to

$40/ton in 1979) would add $0.30 to $().45/gal

to the ethanol pr ice. Consequently, i t is less

likely that this process using these feedstockswould be competi t ive with corn-derived etha-

nol , unless corn and other grain pr ices r ise

more rapidly than general inflation.

In sum, it appears that this process could be

competi t ive with grain-derived ethanol i f mu-

nicipal wastepaper is used as a feedstock and

the distillery receives special financing. A re-

l iab le determinat ion o f the compet i t ive pos i -

tion of other feedstocks and financing arrange-

ments are less certain and probably cannot be

determined unt i l a fu l l -sca le p lant has been

built.

‘“G H Emert, private ~ommunlcation, October 1979



Ch. 8—Fermentation q 171

Reexamination ofRheinau-Bergius Process

Much o f the de ta i l ed i n fo rma t ion on the

Rhe ina u-Berg ius p roc ess ha s b ee n lost. Sinc e

the acid hydrolysis of wood involves subtle

chemical processes which can change dramat-

ically with small changes in the process condi-tions, the detailed process chemistry of hydrol-

ysis with concentrated hydrochloric acid is be-

ing reexam ined a t North Ca rolina Sta te Univer-

sity. The re sea rch should p rovid e a b a sis fo r

reevaluating the process as a source of ethanol

and chemicals and determining whether suffi-

cient quantities of the acid can be recovered

to make the process economic at today’s

prices.

Tsao Process

This p roce ss is b eing d eve lope d a t Purd ue

Universi ty wi th the major emphasis on crop

residues as a feedstock and is currently pro-

g r e s s i n g to t h e p i l o t p l a n t s ta g e . A l t h o u g h

there have been numerous changes in the proc-

ess as the research has proceeded, in the cur-

rently preferred process hemicel Iulose is re-

moved first with dilute acid and then, the cel-

lulose and Iignin are dissolved in concentrated

(70 p erce nt) sul furic a c id. The a c id is rec ov-

ered by precipitating the celIulose-lignin from

the ac id th rough the add i t i on o f me thano l ,

then the methanol is removed from the acid by

d is t i l l a t i on . Fo l l owing th i s p re t rea tmen t , en -

zymes hydrolyze the cellulose.

The use o f me thano l to a id in reco vering the

acid is a novel aspect of this process. As the

recovery has been proposed, however , the

methanol is l i ke ly to react to form tox ic by-

p roduc ts such as d ime thy l su l fa te , d ime th -

y l e ther , d imethy l su l fox ide, and o ther com-

p ou nd s. The loss of p roc ess me tha no l as we ll

as the disposal of these toxic wastes would in-

crease the costs. I n addition, there are several

places in the process where more expensive

equipment wi l l be needed than has been in-

cluded in most cost calculations due primarilyto t h e c o r r o s i v e e f f e c t s o f t h e a c i d .31 32 A l -

though novel acid recovery processes of this

‘‘I?aphael Katzen Associates, op clt

’11 Goldsteln, op clt

type should be thoroughly investigated, it has

not yet been satisfactor i ly demonstrated that

the process proposed would be economical ly

competitive as a source of fuel ethanol.

University of Pennsylvania—General Electric Process

In this process, woodchips are heated in an

alkaline solution containing water, sodium car-

bo nate , and buta nol (a higher alco hol). Since

butanol is only part ly soluble in water, the

solution consists of two phases (similar to oil

floa ting o n w at er). The h em icellulose g oe s to

the water phase, the Iignin dissolves in the bu-

tanol , and the cel lu lose remains undissolved.

Following removal of the cellulose, and clean-

ing to remove traces of butanol, it can be hy-

drolyzed either with acid or enzymes and the

hemice l l u lose can be conver ted to e thano l

without removing it from solution. The b uta nolis then cooled, which causes the Iignin to pre-

cipi tate from solution, the solution is f i l tered,

and the butanol recycled to the process.

Clearly the process economics wil l depend

heavi ly on the cost of producing the process

butanol and the quantity of butanol lost to the

waste stream. On the other hand, the butanol-

water sod ium carbonate so lu t ion is consider-

ably less corrosive than other chemicals used

to remove Iignin and therefore could result in

lower equipment costs. At this stage, however,

the processes are not wel l enough defined to

provide a meaningful cost calculation.

U.S. Army —Natick Laboratories

Work done at th is laboratory has contr ib -

u te d s u b s ta n t i a l l y t o t h e b a s i c k n o w l e d g e

about the enzyme system that converts cellu-

lose to sugar. ’3 The se resea rch ers first ide nti-

fied the three-enzyme system involved in the

hydrolysis and have developed fungus mutants

w i th i m p r o v e d e n z y m e p r o d u c t i v i t i e s . N o t

only is this research applicable to ethanol pro-

duct ion, but i t a lso prov ides in format ion for

those interested in retarding cellulose degrada-tion such as that which occurs with jungle rot.

“E T Reese, “History of the Cellulose Program at the U SArmy Natlck Development Center, ” Biotechnology a nd B/oener -

gy Syf71POS/Uf?l, No 6, p 9, 1976



Ch. 8—Fermentation . 173

R&D currently underway could fulfill these

criteria. If so, the production costs might look

something like tho se in ta b le 55. The se c osts

represent plausible cost goals for the produc-

tion of ethanol from IignocelIulosic materials.

D is t i l l e r i es can and may be bu i l t be fo re

these criteria are fulfi l led, but the economicswi l l depend on favorable f inancing and atypi-

calIy low feedstock costs or in securing a mar-

ket fo r che mica l byp rod uc ts. Som e d isti lleries

based on these circumstances are likely to be

built before the late 1980’s. It is unl ikely, how-

ever, that such circumstances wi l l sustain a

large fuel ethanol industry.

Table 55.-Plausible Cost Calculation for Future Productionof Ethanol From Wood, Grasses, or Crop Residues

(in a 50-million-gal/yr distillery, early 1980 dollars)

Dollars

Fixed investment ... , ... ., ., ... ., ... $120 millionWorking capital ... . . ., ., . . ., . . ., 12 million

Total investment ... . . ., ., ... . . ... . . $132 million

$/gallon

Labor, chemicals, fuel ., ., ., . . . ., . . $0.30Feedstock ($30/ton, 110 gal/ton) ., ., ., . . . 0.27Capital charges (15 to 30% of total investment) . . . . . 0.36-0.72

Total . . ... . . ., ., . . . . . . . ., ., ... $0.93-$1.29

SOURCE : Office of Technology Assessment

Environmental Impact of Ethanol Production

The m a jor p ote ntial ca uses of e nvironm en-

ta l impac ts f rom e thano l p roduc t ion a re the

emissions a s s o c i a t e d w i t h i t s s u b s t a n t i a l

energy requirements, wastes from the distilla-

tion process, and hazards associated with the

use o f tox i c chemica ls (espec ia l l y i n sma l l

plants). A variety of controls and design alter-

nat ives are ava i lab le to reduce or e l iminate

adverse e f fects , however , so actua l impacts

wi l l depend more on design and operation of

the p lan ts than on any inev i tab le p rob lems

with the production process.

Ne w large energy-efficient ethanol plants

probably will require at least 50,000 Btu/gal ofethanol produced to power corn milling, d is-

t i l l ing , s t i l l age dry ing, and o ther operat ions

(see “ Energ y C on sum p tion” d isc ussion). Sma l l

plants wil l be less efficient. Individual disti l l-

eries of 50-milIion-gal/yr capacity wilI use

slightly more fuel than a 30-MW powerplant; *

a 10-billion-gal/yr ethanol industry (the ap-

p rox ima te requ i remen t fo r a 10 percent alco-

hol blend in all autos) will use about the same

amount of fuel needed to supply 6,000 to 7,000

MW of electric power capacity.

New source performance standards have notbeen formulated for industrial combustion fa-

ci l i ties, and the degree of control and subse-

qu ent em issions are not pred ic ta ble. The mo st

* Assuming 1 (),0()() Btu k Ilowatthour

l i ke l y fue l s fo r these p lan ts w i l l be coa l o r

biomass (crop residues and wood), however,

and thus the most l i ke ly source o f prob lems

wi l l be their part iculate emissions. Coal and

biomass combustion sources of the size re-

qu i red for d is t i l le r ies —especial ly dist i l ler ies

designed to serve smal l local markets–must

be careful ly designed and operated to avoid

high emission levels of unburned part iculate

h y d r o c a r b o n s ( i n c l u d i n g p o l y c y c l i c o r g a n i c

matter). Fortunately, most disti l leries wil l be

located in rura l areas; th is wi l l reduce to ta l

p o p u l a t i o n e x p o s u r e to a n y h a r m fu l p o l l u t -

ants . Par t icu la te contro l equ ipment wi th e f f i -c iencies of 99 percent and greater are avai l -

ab le , espec ia l l y fo r the la rge r p lan ts . I f a l l

energy requirements are provided by a single

boiler, high efficiency control would be easier

to p rovid e. This is a lso t rue fo r a ny sulfur oxide

(SO x) controls (scrubbers) that may be required

if the faciIity is fueled with high-sulfur coal.

Other air emissions associated with ethanol

production include fugi t ive dust from raw ma-

ter ia l and product handl ing; emissions of or-

ganic vapors from the disti l lation process (as

much as 1 percent of the ethanol, as wel l as

other volatile organics, may be lost in the proc-

ess); and odors from the fermentation tanks.

The se e missions ma y b e t ightly c on trol led b y

water scrubbing (for odors and organics) and

cyclones (for dust).




The “ sti ll ag e” — the waste p rod uct from the

f i rst st i l l (o r “ b ee r st i l l’ ’ )–wi ll be extrem ely

h igh in organ ic mater ia l wi th h igh b io log ica l

and chemical oxygen demand, and wi l l a lso

conta in inorgan ic sa l ts , and poss ib ly heavy

metals and other pollutants. When corn is the

biomass feedstock, the stillage is the source of

d r i e d DC, wh i c h i s a v a l u a b l e c a t t l e f e e dwhose byproduct value is essential to the eco-

no mic s of t he p roc ess. Thus, it w ill be rec ov -

ered as an integral part of the plant operation

a n d d o e s n o t r e p r e s e n t a n e n v i r o n m e n ta l

hazard. On the other hand, sugarcane sti l lage

has far lower economic potential as a byprod-

uct; i ts recovery is unl ikely except as a re-

sponse to regulation.

The sti llage an d othe r wa stes from a ll etha -

nol plants have severe potentia l for damaging

aquat ic ecosystems i f they are mishandled.

The high biolog ica l and c hemica l oxygen de -mand levels in the stillage, which would result

in oxygen depletion in any receiving waters,

wi l l be the major prob lem. 35 Contro l tech-

niques are available for reducing impacts from

these wastes. B io log ica l t reatment methods

(activated sludge, biological fi l ters, anaerobic

digestion, etc.] and land disposal techniques

used in the brewing industry are sui table for

e thanol product ion, but contro ls for s t i l lages

from some crop materia ls wi l l require further

deve lopment and demonstra t ion.

Because fermentation and disti l lation tech-

nologies are available in a wide range of sizes,

smal l -sca le onfarm a lcohol product ion may

pla y a role in a na tiona l ga soho l p rogram . The

scale of such operations may simplify water ef-

f l u e n t c o n t r o l b y a l l o w i n g l a n d d i s p o s a l o f

wastes. On the other hand, environmental con-

trol may in some cases be more expensive be-

cause of the loss of scale advantages. Current

experience with combustion sources indicates

that h igh emiss ions o f unburned par t icu la te

h yd ro c a rb o ns, in c l u d in g p o l y c y c lic o r g a n i c

m a t t e r , a r e a m o r e c o m m o n p r o b l e m w i t h

JsCarjbbean Rum Stud y,. Effec ts of Distillery Wastes on (he Na -

rine Environment (Washington, D C Off Ice of Research and De-

velopment, Environmental Protect Ion Agency, April 1979)

smaller units. Because smaller units are unlike-Iy to have highly efficient particulate controls,

th i s p rob lem w i ll be a gg rava ted . A lso , SOX

scrubbers are impractical for small boilers, and

e f fe c t i ve SO X con t ro l may be ach ieved on ly

with clean fuels or else forgone. Because local

coals in the Midwest tend to have high sulfur

contents (5 percent sulfur content is not unusu-al), small distiIIeries in this region may have ob-

j ec t i ona b ly h igh SOX emission rates. Final ly,

smal l p lants wi l l be less eff ic ient than large

plants and will use more fuel to produce each

gallon of alcohol.

The d ec entra l iza t ion o f ene rgy proc essing

and conversion faci l i t ies as a rule has been

viewed favorab ly by consumer and envi ron-

mental interests. Unfortunately, a proliferation

of many smal l ethanol plants may not provide

a favorab le set t ing for care fu l moni tor ing o f

environmental condit ions and enforcement ofenvironmental protection requirements. Regu-

la to ry au tho r i t i es may expec t to have p rob -

lems with these facilities similar to those they

run into with other small pollution sources. For

example, the attempts of the owners of late-

m o d e l a u to m o b i l e s t o c i r c u m v e n t p o l l u t i o n

contro l systems conce ivab ly may prov ide an

analog to the kinds of problems that might be

expected from smal l d ist i l ler ies i f their con-

tro ls prove expensive and/or inconvenient to

operate.

The sa me ma y be true for co nsiderations of

oc cup a t iona l sa fe ty . The cu r ren t tec hno logy

f o r t h e f i n a l d i s t i l l a t i o n s t e p , t o p r o d u c e

anhydrous (water-free) alcohol, uses reagents

such as cyclohexane and/or ether that could

pose severe occupational danger (these chemi-

cals are toxic and highly flammable) at inade-

qua te l y ope ra ted o r ma in ta ined d i s t i l l e r i es .

Simila r prob lems ma y exist b ec a use o f the use

of pressurized steam in the distillation process.

Al though a l ternat ive (and safer) dehydrat ing

technologies may be developed and automatic

pressure/leak controls may eventually be made

a v a i l a b l e ( a t a n a t t r a c t i v e c o s t ) f o r s m a l lplants, in the meantime special care wil l have

to be taken to ensure proper design, operation,

and maintenance of these smaller plants.



176 • Vol. Il—Energy From Biological Processes

Distillation

The d istilla tion process in the corn- to- fue l -

ethanol disti l lery considered above consumes

nearly half of the energy used at the distillery.

Lowering the energy requirements for separat-

ing the ethanol from the mash is desirable for a

fue l e thanol fac i l i ty in any case, but the in-creased equipment costs for advanced ethanol

separation techniques could counter part or all

of the potential cost savings from lower fuel

use and smal ler boi ler and fuel-handl ing re-

quirements. Consequently, R&D into this area

must address both the energy use and the

equipment cost.

One way to lower the energy requirements

of d is t i l la t ion is to produce a mash wi th an

ethanol concentration higher than the usual 10

percent. This would require development of

yeast or bacteria that are tolerant of the high

alcohol concentrations. Since it would be ex-

pected that any yeast or bacteria producing

ethanol would produce it more slowly at the

higher ethanol concentrations, this might re-

quire longer fermentation times with a conse-

quent increase i n the cos t o f fe rmen ta t i on

equipment. I t may be poss ib le , however , to

c o m b i n e t h i s w i t h a d v a n c e d f e r m e n t a t i o n

methods to provide an overall savings.

Seve ra l me tho d s ha ve b ee n sug ge sted for re-

mo ving the e tha nol from t he w a ter. These in-

clude:

q

q

q

membranes using reverse osmosis (some-

thing l ike a super f i l ter that al lows the

water or ethanol to pass through the mem-

brane whi le preventing the other compo-

nent from doing so);

absorption agents (solids which selective-

ly absorb the ethanol are then separated

from the solution, with the ethanol finally

being removed from the solid); and

liquid-l iquid extraction (extracting the eth-

anol into a l iquid that is not soluble in

water, physical ly separating the l iquids,

and removing the e thanol f rom the o therl iquid).

All of these processes, however, are likely to

require that the yeast and grain sol ids be re-

moved from the mash first, so that they do not

interfere with the ethanol concentration step

(e.g . , by c logg ing the membrane) . L i t t le re-

search has been done in producing a clarified

so lu t ion f rom the mash, hence, the costs for

these methods are highly uncertain.

Numerous other suggestions exist, and re-search in these areas may eventually produce

usable results. One example is the use of super-

cr i t ical CO 2. When gases are subject to high

pressures at suitable temperatures, they form a

f lu id wh ich i s ne i the r gas no r l i qu id , bu t i s

c a l led a sup erc r it ica l f lu id. The p rope rt ies of

supercr i t ical f lu ids are largely unresearched,

but there are propr ie tary c la ims that super-

c r i t i ca l CO 2 could be su i tab le for extract ing

eth a no l from th e m a sh. The p ressure wo uld

then be lowered, the CO2 would b ecome a g as,

and the ethanol would Iiquefy.

Another possibility is the use of phase sep-a rat ing salts. Sa lts, wh en d issolve d in a liqu id

change the l iquid’s structure and properties. It

has been suggested that there may be sal ts

which would attract the water (or ethanol) so

v igorously and se lect ive ly that the e thanol -

water mixture wouId separate into two phases,

wi th one be ing predominant ly water and the

other predominantly ethanol.

These nove l a p p roac hes sho uld b e investi -

gated, but it is not possible to predict when or

if results applicable to commercial fuel etha-

nol production will emerge.

Producing Dry Ethanol

In a large, commercial distillery, the produc-

tion of dry ethanol only costs $0.01 to $0.03/gal

(of ethanol) more than the production of 95

p erce nt et ha nol .40 (The d ifferenc e in the selling

price per gallon of 99.5 percent ethanol and 95

percent e thanol is due pr imar i ly to the fact

that the latter contains 4.5 percent less ethanol

per gallon of product.) Furthermore, with mod-

ern heat recovery systems, the production of

dry ethanol requires very l i ttle additional ener-gy. Consequent ly , l i t t le economic or energy

savings are available here.

‘“I bid



Chapter 9

ANAEROBIC DIGESTION



Chapter 9.–ANAEROBIC DIGESTION

Page

Introduction . . . . . . . . . . . . . . . . . . . . . .181

Generic Aspects of Anaerobic Digestion. . .181Basic Process . . . . . . . . . . . . .181F e e d s t o c k s . . . . . . . . . . . . . 1 8 2

Byproducts. . . . . . . . . . . . . . . . . . ....182Reactor Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

Single-Tank Plug Flow . . . . . . . . . . . . . . .184Multitank Batch System. . . . . . . . . . . . . 184

Single-Tank Complete Mix. . . . . . . . . . . .184Anaerobic Contact, . . . . . . . . 184

Two or Three Phase . . . . . . . . . ...187Packed Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188Ex pa nde d B e d . . . . . . . . . . . . . . . . . . . . . 1 8 9Variable Feed. . . . . . . . . . . . . . . . . . . . . .189

Existing Digester Systems . . . . . . . . . ..................191

Economic Analysis. . . . . . . .. . . . . . ......................191Environmental lmpacts of Biogas Production:

Anaerobic Digestion of Manure. . . . . . . .........,195

Research, Development, and DemonstrationNeeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..198Microbiology . . . . .198Engine e r ing . . . . . . . . . . . . . . . . . . 1 9 8Agriculture. . . . . . . . . . .. . . . . . . . . . . . . . 98

TABLESPage

56. Suitability of Various Substrates for

Anaerobic Digestion. . . . . . .183

Page

57. Anaerobic Digester Systems. . . . . . . . . . ...18558. investment Cost for Various Anaerobic

Digester System Options . ..............19259. Anaerobic Digestion: Energy Balance, or

the Energy Production Potential andEnergy Consumption Potential ofindividual Farms in Major Producing States. 193

60. Cost of Various Digesters With ElectricGenerating Capabilities . . . . . . . . . . . . . . .194

61. Annual Costs and Returns From DigesterEnergy Only . . . . . . . . . . . . . . . . . . . . ....194

62. Economic Feasibility of AnaerobicDigestion , . . . . . . . . . . . . . . . . . . . . . . . . . 195

FIGURES

Page

28. Chinese Design of a Biogas Plant. . . . . ..185

29. Diagram of a Gobar Gas Plant . ..........18630. Plug Flow Digestion System . , . . . . . . . . . .186

31, Single-Tank Complete Mixed Digester .. ...18732. Two-Stage Digester . . . . . . . . . . . . . . . . ..187

33. Two-Phase Digestion of Cellulosic Feed. ...188

34. Packed-Bed Digester . . . . . . . . . . . . . . . . .18935. Expanded-Bed Reactor. . . . . . . . . . . ..19036. Variable Feed Systems . . . . . . . . . .190



Chapter 9

ANAEROBIC DIGESTION

Introduction

Anaerob ic ( “wi thout a i r ” ) d igest ion is the

process that occurs when various kinds of bac-teria consume plant or animal material in an

a irtight c onta iner c alled a d igester. Tem pe ra-

tures between 950 and 140°F favor bacteria

that release biogas (50 to 70 percent methane

— essentially natural gas — with most of the re-

mainder as carbon dioxide — CO2). The bacte-

ria may be present i n the o r ig ina l ma te r ia l

when charged (as is the case with catt le ma-

nure) or may be placed in the digester when it

is initially c ha rge d . The ga s ha s the hea t va lue

of i ts methane component, 500 to 700 Btu /

s td f t 3, and can be used directly as a heat fuel

or in internal combustion engines. I n somecases there is enough hydrogen sul f ide (H2S)

present to cause corrosion problems, particu-

larly in engines. H2S ca n be remo ved by a sim-

ple, inexpensive, existing technology. CO2 c a n

be removed by a somewhat more complex and

expensive technology, which would need to be

employed if the gas is to be fed into a natural

gas pipeline.

The a na erob ic d igestion p roc ess is esp ec ial-

ly well adapted to slurry-type wastes and has

environmental benefits in the form of treating

wastes to reduce pollution hazards and to re-

duce odor nuisances. Furthermore, the residual

from the process can be returned to land, ei-

ther directly or through animal refeeding tech-

nologies, and thus retain nitrogen and organic

levels of soil. Most other biomass energy con-

version processes more nearly total ly destroythe input material.

Generic Aspects of Anaerobic Digestion

The a na erob ic dige stion process involves a

number of different bacteria and a digester’s

performance depends on a large number of

variables. The basic process is considered first

and then the feedstocks and byproducts of the

process.

Basic Process

Not all of the bacteria involved in anaerobic

digestion have been identi f ied and the exact

b iochemica l p rocesses a re no t fu l l y under -

stood. Basically, however, the process consists

of three steps: 2 1 ) decomposition (hydrolysis)

of the plant or animal matter to break it down

to usable-sized molecules such as sugar, 2)

conversion of the decomposed matter to or-

1 j j WOIIS, Arner lcan /ourna/ 01 C / i n l ca l Nutrit ion, 27 (11), p

1120, 1974

‘E C Clausen and I L Caddy, “Stagewlse F e r m e n t a t i o n o ff310mass to Methane, r’ Department of Chemical E nglneerlng,

Unlverslty ot Ml~~ourl, Rolla, Mo , 1977

ganic acids, and 3) conversion of the acids to

methane. Accompl ish ing these steps invo lves

at least two different types of bacteria.

The rate at whic h the biog a s forms will d e-

pend on the temperature (higher temperature

usually gives a faster rate) and the nature of

the substrate to be digested. Cellulosic mate-

ria ls, suc h a s c rop residue s and mun icipa l solid

waste, produce biogas more slowly than sew-

age sludge and animal manure. Disturbances

of the digester system, changes in temperature,

feedstock composition, toxins, etc., can lead

to a buildup of acids that inhibit the methane-

p roduc ing bac te r ia . Genera l l y , anaerob ic d i -

gest ion systems work best when a constant

t e m p e r a t u r e a n d a u n i f o r m f e e d s t o c k a r e

maintained.

When a d igester is s tar ted, the bacter ia l

composition is seldom at the optimum. But if

the feedstock and operating conditions are

held constant a process of natural selection

181




takes p lace un t i l the bac te r ia bes t ab le to

metabolize the feedstock (and thus grow) dom-

inate. Biogas production begins within a day or

so, but complete stabil ization sometimes takes

months.

Numerous sources for good anaerobic bac-

teria have been tried, though the process is ba-sica l ly on e o f hi t a nd miss. The p ot en tia l for

improvement cannot be assessed at this time.

Future deve lopments cou ld produce super ior

genet ic s tra ins o f bacter ia , but too l i t t le is

known about the process to judge i f or when

this can be accomplished. It is quite possible

that if such strains are to be effective, the in-

put material may first require pasteurization.

Biogas yields vary considerably with feed-

s tock and opera t ing cond i t i ons . Opera t ing a

digester at high temperatures usually increases

the rate at which the biogas is formed, but rais-

ing the temperature can actually decrease the

net fuel yie ld as more energy is required to

hea t the d igester. The op timum c ond itions for

biogas yields have to be determined separately

fo r each feeds tock o r comb ina t ion o f feed -

sto c ks.

Feedstocks

A wide range of plant and animal matter can

be anaerobical ly digested. Both the gas yields

and rates of digestion vary, Generally materi-

als that are higher in Iignin (e. g., wood and

crop residues3) are poor feedstocks because

the Iignin protects the cellulose from bacterial

attack. Pretreatment could increase their sus-

ceptibi l i ty to digestion. ’ However, even then

digestion energy efficiencies generally do not

exce ed 50 to 75 pe rc ent . Thus, more usa ble e n-

ergy can genera l ly be obta ined through com-

bustion or thermal gasification of these feed-

stocks (see ch. 5).

The b est fee dstoc ks for ana erob ic d igestion

usually are wet biomass such as fresh animal

‘See also, J T Pfeffer, “131010 glcal Conversion of Crop Resi-

dues to Methane, ” In Proc eed ings of the Sec ond A nnua l S ympo~i -

urn on Fue/\ fo r Bioma \ s, Troy, N Y , June 20-22, 1978

4P L McC~rty, et al , “Heat Treatment of Biomass for increas-

ing Blodegradabllity, ” In Proceeding~ of t he Third Annua l Bio-

mass Energy System s Co nferenc e, sponsored by the Solar Energy

Research Institute, Golden, Colo , June 1979, TP-33-285

manure, various aquatic plants, and wet food-

processing wastes such as those that occur in

the cheese, potato, tomato, and frui t-process-

ing ind ustries. See ta b le 56 for a summ a ry of

the suitability of various feedstocks for diges-

t ion.

The d igester

well as most of

Byproducts

e f f l uen t con ta ins bac te r ia as

the undigested materia l in the

feedstock (mostly Iignocellulose) and the solu-

b ilized nutrients. The p roc ess ha s the p ot en tial

for ki l l ing most disease-causing bacter ia, but

volati le losses of ammonia may increase with

anaerobic digestion. 5

The m ost g enerally ac ce pted technology for

disposal of the effluent is to use it as a soil con-

di t ioner ( low-grade fert i l izer). Animal manure

is already used widely for this but there is somecontroversy over whether the digester effluent

is a better source of ni trogen than the undi-

gested manure. * The a c tua l add ed va lue ( if

any) as a ferti l izer, however, wil l have to be

determined experimentally and is l ikely to be

h igh ly feed stoc k sp ec if ic . The e f f luent m a y

also be used as fertilizer for aquatic plant sys-

tems. In one case the effluent is dewatered and

used as animal bedding in place of sawdust. G

Another potential use of the effluent is as an

animal feed. It has been claimed that the pro-

tein mix in the cake obtained from dewateringthe effluent is superior to that of undigested

m a n u r e . 7 Biogas of Colorado has concluded a

successful animal feeding trial of digester cake

and Ham ilton Stand ard ha s also d one feed ing

tr ia ls.8

‘J A. Moore, et al , “Ammonia Volatilization From Animal Ma-

nures, ” in Biomass Uti/ lzat ion in Minnesota, Perry Black shear,

ed , National Technlcai Information Service

q The nitrogen IS more concentrated In the effluent, but It IS

also more volatile

‘John Mart[n, Scheaffer and Roland, Inc , Chicago, Ill, private

communication, 1980

‘B G Hashlmoto, et al , “Thermophllllc Anaerobic Fermenta-

tion of Beef Cattle Residues, ” In Symposium on Energy From Bio-

mass and Wastes, Institute of Gas Technology, Washington,

D C , Aug 14-18, 1978

‘D J Llzdas, et al , “Methane Generation From Cattle Resi-

dues at a Dirt Feedlot, ” DOE report COO-2952-20, September

1979



Ch. 9—Anaerobic Digestion q 1 83

Table 56.-Suitability of Various Substrates for Anaerobic Digestion

Feedstock Availability Suitability for digestion Special problems

Animal wastes Dairy . . . . . . . . . . . .Beef cattle ., ., .,

Swine . . . . . . . .

Chicken . . . . . . . . .

Turkey. . . . . . . .

Municipal wastes Sewage sludge . . . . .Solid wastes . . . . . . .

Crop residues W h e a t s t r a w . .

Corn stover. . . . . . . .

GrassesK e n t u c k y b l u e .

O r c h a r d g r a s s .

Aquatic plants Water hyacinth . . . . .

Algae. . . . . ., . . .Ocean kelp . . . . . . .

Various woods. . . .

Kraft paper. . . . . . . .

Small- to medium-sized farms, 30-150 headFeedlots, up to 1,000-100,000 cattle

100-1,000 per farm

10,000-1,000,000 per farm

30,000-500,000 per farm

All towns and citiesAll towns and cities

Same cropland

Same cropland

Individual home lawns

Midwest

Southern climates, very high reproductionratesWarm or controlled climatesWest coast, Pacific Ocean, large-scale kelp

farmsTotal United States

Limited

ExcellentExcellent

Excellent

Excellent

Excellent

ExcellentBetter suited to directcombustion

Poor, better suited todirect combustion

Poor, better suited todirect combustion

Very good

Fair

Very good

GoodVery good

Poor, better for directcombustion or pyrolysis

No major problems, some systems operating.Rocks and grit in the feed require degritting, some

systems operating.Lincomycin in the swine feed will inhibit

digestion–full-scale systems on university farms.

Degritting necessary, broiler operations need specialdesign due to aged manure, tendency to sour.

Bedding can be a problem, manure is generally aged, nocommercial systems operating.

Vast experience.Designed landfill best option

Particle size reduction necessary, low digestibility, nocommercial systems.

No commercial systems, no data available, particle sizereduction necessary.

Distribution of feedstock disperse, no commercialsystems.

No commercial systems, no data on sustainability ofyields.

No commercial operations, needs pregrinding.

Longer reaction time than for animal wastes.Full-scale operations not proven, no present value foreffluent.

Will not digest.

Excellent, need to evaluate Premixing watering necessary.recycle potential andother conversion

SOURCE TomAbeles and David Ellsworth, ‘‘Blologlcal Production of Gas, contractor report to OTA by I E Associates, Inc., Minneapolis, Minn. , 1979

Although most of the disease-causing bacte-

ria are killed by digestion of the manure, sev-

eral questions about refeeding of digester ef-

fluents need to be resolved. Buildup of toxic

materials, development of resistance to antibi-

otics by organisms in the cake, permissible

quant i t ies o f cake in the d ie t , s torage, and

product quality are all issues that have been

raised . There is no firm evid enc e tha t th ese will

present significant problems, however.

To avo id som e o f these prob lems, the Foo d

and Drug Administration has generally favoredcross-species feeding, but has not sanctioned

its use as a feed or feed ingredient.9 The use o f

digester effluents as an animal feed, however,

would greatly improve the economics of ma-

nure digestion. Consequently, the value, use,

and restrictions on using digester effluents as

an ima l feeds shou ld be tho rough ly i nves t i -

gated. Moreover, the animal feed value of ef-

fluents from the digestion of feedstocks other

than manure should also be investigated.

9T P Abeles, “Design and Englneerlng Conslderatlons In Plug

Flow Farm Digesters, ” In Symposium on C / c a n Fue/s From Bio-ma ss, Institute of Gas Technology, 1977



184 . Vol. Ii—Energy From Biological Processes

Reactor Types

The re are nu me rous p ossible d esig ns fo r a n-

aerobic digesters, depending on the feedstock,

the avai labi l i ty of cheap labor, and the pur-

po se o f the d ige stion. The m ost c omp lex and

expensive systems are for municipal sewage

sludge digestion, but the pr imary purpose ofthese has been to stabilize the sludge and not

to produce biogas.

Digester processes have been classified into

three types, depending on the operating tem-

perature: 1 ) psychrophilic (under 680 F), 2) mes-

ophi l ic (680 to 1130 F), and 3) thermophi l ic

(11 30 to 150° F). The c ost, co mp lexity, an d en-

ergy use of the systems increase with the tem-

perature, as does the rate of gas production.

The am oun t o f gas p roduce d p e r po und o f

feedstock, however, can either increase or de-

crease with temperature. Retention time is alsoan important consideration, wherein maximum

gas production per pound of feedstock is sacri-

ficed for reduced size and cost of the digester.

Anaerobic digesters in the mesophilic and ther-

mophilic ranges have used agricultural wastes,

residue s, a nd gra sses, to p rodu c e b ioga s. The

optimum temperature appears to be both si te

an d fee d stoc k sp ec i f ic . There a re st i ll unre-

solved technical questions about the tradeoffs

between mesophi l ic and thermophi l ic d igest-

ers, but most onfarm systems have been meso-

philic.

Other design parameters include continuousversus batch processes, mixed versus unmixed

rea c tors, and othe r fea tures. Som e o f the m a-

jor types are summarized in table 57 and dis-

cussed briefIy.

Single-Tank Plug Flow

This syste m is the simp lest a d a p ta t ion o f

Asian anaerob ic d igester technology ( f igures

28-30). The fe ed sto c k is p ump ed or allow ed to

flow into one end of a digester tank and re-

moved at the other. Biogas is drawn off from

the to p o f the d igester tank. The fee d rate is

chosen to maintain the proper residence time*

q The time the feedstock remains in the digester

in the digester and the feed or digester con-

tents can be heated as needed. Depending on

the placement of the heating pipes, some con-

vective mixing can also occur.

Multitank Batch System

This syste m c o nsists of a se rie s o f t a nks o r

chambers which are f i l led sequentia l ly wi th

biomass and sealed. As each unit completes

the digestion process, i t is emptied and re-

c ha rged . This typ e o f rea c tor is b est suited to

opera t ions where the feeds tock a r r i ves i n

batches, for example, grass or crop residues

that are collected only at certain times of the

year or turkey or broi ler operations that are

c leaned on ly when the f l ocks a re changed .

This digester system, however , is re la t ive ly

labor intensive.

Single-Tank Complete Mix

The single-ta nk c om p lete mix syste m (fig ure

31) has a single r ig id digester tank which is

heated and mixed several times a day. It has

been argued that mixing enhances the contact

o f bacter ia wi th the feedstock and inh ib i ts

scum format ion, which can in ter fere wi th d i -

gester operat ion. Theo retica l c alculations, ’ ”however, indicate that the mixing does not im-

prove bacterial contact, and these calculations

have been conf i rmed exper imenta l ly in one

c a s e . Single-tank co mp lete-mixed d igesters

are used to treat municipal sewage sludge and

have been used in the larger anaerobic digester

syste ms (exc lusive of lan d fills).

Anaerobic Contact

The single-tan k c om p lete-mix system eff lu-

ent can be transferred to a second unmixed

‘(’P C Augensteln, “Technical Prlnclples of Anaerobic Diges-tion, ” Dynatech R&D CO , presented at course f l /o techno/ogy for

Ut//izat/on o f o r g a n i c Wastes, Unlversldad Autonoma Metropoll-

tana, Iztapalapa, Mexico, 1978

“K D Smith, et al , “Destgn and First Year Operation of a50,000 Gallon Anaerobic D[gester at the State Honor Farm Dairy,

Monroe, Washington, ” Department of Energy contract EG-

77-C-06-1016, ECOTOPE Group, Seattle, Wash , 1978



Ch. 9—Anaerobic Digestion 185

Table 57.–Anaerobic Digester Systems

Type of system Application and inputs Scale a Stage of development Advantages Disadvantages

Landfill

municipal solid wastes,sewage sludge, warmclimates

All types of organics, farmand feedlot operations

Low cost, tanks not re- Gas generation may Iast onlywaste and up landfills, controlled land quired, high loading rates 10 years in “as is” land-(28-acreIandfill)

Small to large

filling in pilot stages

Commercial

possible, no moving parts

Low cost, simple designcan run high solids

wastes, can have gravityfeed and discharge

Simple, low maintenance,low cost, complete diges-

tion of materials

Proven reliability, workswell on all types ofwastes

Smaller tank sizes,operation not overlycritical

Allows more completedecomposition, greatergas yields, greater load-ing rates, lower retentiontimes

High loading ratespossible, short retentiontimes

High loading rates, lowtemperature digestion,high quality gas, shortretention times

Fast throughput, highloading rates, highersolids input than packedbeds

Allows seasonal peaking of

fills, gas usage onsite maypresent problems

Low solids wastes maystratify

Single-tank plugflow

Multitank batchsystem

Can accept all types ofwastes, limited applicationcrop residues, grasses,chicken broilers, turkeys

All types of organics sewagetreatment, farm and feedlot,municipal solid wastes

Sewage sludge and otherorganics, limited apphcation(see variable feed)Celluloslc feedstocks

Small to large Commercial, in Asia Gas generation notcontinuous, labor-intensive

feed and discharge, low gasproduction per day

Greater input energy to runmixers, higher cost thanplug flow

Two tanks necessary

Single-tankcomplete mix

Anaerobic contact

Small to large Commercial

Commercial, for sewagetreatment

Pilot scale

Medium tolarge

Medium tolarge

Two or three phase Feed rates vary withfeedstocks, have not beenattempted full scale, requiretight controls and manage-ment of the operation

Tends to clog with organicparticles, Iimited to dilutewastes

Packed bed Dilute organics–sewage,food-processing wastes,very dilute animal wastes—Industrial and commercial

Dilute organics-sewage,food-processing wastes,very dilute animal wastes

Medium tolarge

Commercial, as wastetreatment technology

LaboratoryExpanded bed Undetermined Not developed, high energyinput to operate pumps, nooperating data

Tends to clog, high pumpingenergy input no operatingdata

Feed-discharge may requireextra pump

Mixed bed

Variable feed

Sewage sludge, animalwastes, food-processingwastes–fairly dilutemixtures

All types of organics, farmsand feedlots

Small to large Pilot scale

Small to Conceptual–combinesmedium plug flow wi th anaerobic gas product ion, pre-

contact serves nutrient value ofmaterial, low cost

ascaje def[ned as small–o to 30,000 gal med!um–30 000 to 80000 gal. andlarge–over 80,000 gal

SOURCE Tom Abeles and David Ellsworth Blologlcal Produchon of Gas ‘‘ contractor report to OTA by I E Associates Inc M!nneapohs, Mlnn 1979

Figure 28.—Chinese Design of a Biogas Plant

Gas ventpipe Outlet C o v e r Gas outlet pipeInlet

S l u d g ec h a m b e r

Over-flow

Base

SOURCE: K. C. Khandeleval, “Dome-Shaped Biogas Plan,” Compost Science, March/Apr!l 1978.




Figure 29.—Diagram of a Gobar Gas Plant (Indian)

rr y

pit

All dimensions in meters

SOURCE: R. B. Singh, “Biogas Plant,” Gobar Gas Research Station, Ajitmal, Etaweh (V.P.), India, 1971

Figure 30.-Plug Flow Digestion System

Cross section

Gas utilization system

SOURCE: W. J. Jewell, et al., “Low Cost Methane Generation on Small Farms,” presented at Third Annual Symposium on Biomass Energy Systems, Solar EnergyResearch Institute, Golden, Colo., June 1979



Ch. 9—Anaerobic Digestion . 187

Figure 31. —Single-Tank Complete Mixed Digester

Digester gast

Raw Active

sludge 4 zone

exchanger

Digested sludge

SOURCE Environmental Protection Agency, “Process Design Manual, Sludge

Treatment and Disposal,” EPA 625/1-29-001, September 1979

and unheated storage tank. Here the biomass

undergoes further digestion and sol ids sett le

out (figure 32). In other words, by adding a sec-

ond, inexpensive digester tank gas yields can

be improved. These systems have been us e d

extensively in sewage treatment and may re-

ceive wide appl ication where preservation of

the eff luents nutr ient value requires covered

lagoons or in short throughput systems located

in warm climates.

Two or Three Phase

As mentioned previously under “Generic As-

pects of Anaerobic Digestion, ” the basic proc-

ess c on sists of a series of b ioc hemic a l ste ps in-

volving different b ac teria. The ide a be hind the

multitank systems is to have a series of digest-

er tanks (figure 33) each of which is separatelyoptimized for one of the successive digestion

ste p s. The ration a le b eh ind suc h syste m is the

hypothesis that they: 1 ) can accept higher feed-

s to c k c o n c e n t r a t i o n s w i th o u t i n h i b i t i n g th e

reactions in successive stages, 2) have greater

process s tab i l i ty , 3) produce h igher methane

concentra t ions in the b iogas, and 4) requ i re

lower retention times in the digester than with

mo st sing le-pha se d igesters. The ma jority o f

the work on this approach has been on munici-

pal sewage sludge, although the Institute for

Ga s Tec hnolog y hop es to eve ntua lly t ransfer

the te chnique to kelp d ige stion. The ne ed for

uniform feed rates and controls may l imit the

use of two or muItiphased systems to larger or

extremely wel l -managed operat ions; but th is

type of reactor should be careful ly examined

for other anaerobic digestion appl ications be-

cause of its potentialIy high efficiencies.

Figure 32.—Two-Stage Digester

Digester

Primary digester

Transfer

gas

Supernatant

sludge

1 Digested

sludge -

Secondary digester

SOURCE Environmental Protect Ion Agency, “Process Design Manual, Sludge Treatment and Disposal,” EPA 625/29-001, September 1979




Figure 33.—Two-Phase Digestion of Cellulosic Feed

Gas

SOURCE S Ghos and D. L Klass, “Two Phase Anaerobic Digestion,” Symposium on Clean Fuels f rom Biomass ( Inst i tute of Gas Technology, 1977)

Packed Bed (Anaerobic Filter)

In this system a dilute stream of feedstock is

fed up through a verticle column packed with

small stones, plastic balls, ceramic chips, or

other inert materials (figure 34). Because the

bacteria attach themselves to the inert mate-

rial, i t is possible to pass large quantities of

feedstock through it while maintaining a high

ba c ter ia l c onc entra t ion in the d igester . The

system is best suited to municipal sewage (and

other d i lu te feedstocks) . More concentra ted

feedstocks tend to clog the column.

Analyses of bench-scale laboratory resul ts

on the AN FLOW system indicate that the sys-

tem could produce enough energy to make this

sewage treatment step energy self-sufficient. 12

‘JR K Genung and C D S c o t t , “ A n Aneroblc Bloreactor

(A N F1.OW) for Wastewater Treatment and Process Appl(ca-tlons, ” briefing presented to the Subcommittee on E nergv and

Power, HOLJJ(J I nter$tate and Foreign Commerce Committee,

Nov 1, 1979

As it now exists, however, it is not well suited

to energy production.

L i ke the packed and expanded bed , the

mixed-bed systems are intended to provide an

inert substance to which the bacteria can at-tach, thereby preventing them from being

flushed out with the effluent. The digester

maintains a higher bacteria population. Vari-

ous designs include netting,13

strips of plastic,

and rough porous digester walls. In all cases,

the inert substance increases the resistance to

flow and thus the energy needed for pumping

increases too, but it decreases the necessary

rea c tor size. Suffic ient d a ta are no t yet a vail-

able for a detailed analysis of this tradeoff.

‘ ‘S A St’rfl Ing and C Alsten, “An I nt~gratd, Controlled E nvl-ronment A q u i c u l t u r e Lagoon Proce\\ t o r S e c o n d a r y o r Ad-vanced Wastt>water Treatment ,“ Sol ar Aqua\ y\tem\, I nc , En -clnltas, Cal If , 1978



Ch. 9—Anaerobic Digestion q 189

Figure 34.—Packed-Bed

System gas

p r e s s u r e

Digester

Process gas

chromatographyGa s p u m p

F l o w Magne t i c

contro l va lve f l o w

pH and

temperatureprobes

composite

samp les

5 ft diax

10 ft highpackedsection

gas meter

pH and

temperature

probes

Weir box composite

flow meter samplers

Bar screens

SOURCE R K Genung. W W Pitt, Jr , G M Davis, and J H Koon, “Energy Conservation and Scale-Up Studies for a Wastewater Treatment System Based on a Fixed-Film, Anaerobic Bioreactor,” presented at 2nd Symposium on Biotechnology in Energy Production, Gatlinburg, Term Oct 2-5, 1979

Expanded Bed

A var ia t ion on the packed-bed concep t i s the

expanded-bed reacto r ( f igu re 35 ) . I n th is case

the co lumn pack ing is sand o r o the r ve ry sma l l

p a r t i c l e s . T h e f e e d s t o c k s l u r r y i s f e d u p

through the column and the bed of inert mate-

r i a l e x p a n d s to a l l o w th e m a te r i a l t o p a s s

through. A semiflu idized state resul ts, reduc-

i n g th e p o te n t i a l f o r c l o g g in g wh e n re l a t i ve l y

co n ce n t ra te d m a te r i a l i s f e d i n to th e re a c to r ,

Th e process has been found to be qu i te s tab le

wi th h igh o rgan ic inpu ts , shor t res idence t imes

in the digester, and relatively low temperatures

(50° to 70° F).

14

Th e stu d y d i d in d i c a te , h o w -

ever, that the process would not be a net ener-

gy producer due to the energy required to ex-pand the bed.

Variable Feed

The ide a be hind va riable fe ed system s (fig-

ure 36) is to store undigested manure in times

of low gas demand for use during periods of

high d em an ds. The key is to b e a b le to store

the manure for long periods (e. g., 6 months)

without exce ssive de terioration. The e ffec t o f

long- term storage is be ing invest igated,15 b u t

the systems may be limited to areas with cool

summers or to operations in which the gas is

used to generate electricity for export during

the peak electric demand periods in summer.

‘ “ W J Jewel 1, ( .orn[~l I Un Iveriitp, I t ha( ,1, N } , {)rlv,ltt> c onlnjLl-

nlc,l tlon, 1978




Existing Digester Systems

Fourteen experimental and prototype digest-

ers of animal manure were identified as opera-

tional in 1978. ’6 The capacity of these plants

varies from less than 1,500 gal to 4 million gal.

Two of the prototypes are owned by individualfa rmers a nd a re sized for fa rm use. The 12

others are owned by private firms, universities,

or the Federal Government.

Since then, how ever, the f ie ld o f a nae rob ic

digestion has been advancing rapidly, and any

l i s t o f ex i s t i ng opera t ions wou ld be qu ick l y

outd at ed . Seve ral c om p an ies c urrently design

and sell digesters and the support equipment.

Most systems are currently designed for cattle

manure. One example of an apparently suc-

cessful digester system is on a dairy farm in

Penn sylvania . The d ige ste r is fed b y 700 hea d“D L Klass, “Energy From Biomass and Wastes, ” In Syrnposi-

urn on Energy from L?lom assand Waste, I nstltute of Gas Technol-ogy, Washington, D C , Aug 14-18, 1978

Economic

Aside from the paper and other digestable

matter in municipal solid waste (which is not

included in this report), the best feedstocks for

anaerobic digestion are animal manure, some

types of grasses, aquatic plants, and various

p ro c e ssin g w a st e s. Th e su p p l y o f a q u a t i c

plants is likely to be small in the next 10 years

a n d l i t t l e i n f o r m a t i o n i s a v a i l a b l e o n t h e

digester requirements for grasses. Furthermore,

with grass at $30/dry ton, the feedstock cost

alone would be $4.50/milIion Btu. More energy

a t a lower cost can usually be produced from

grass by thermal gasification or combustion.

Hence, an imal manure and some process ing

w a s t e s a r e t h e m o s t p r o m i s i n g n e a r - t e r m

sou rce s of b iog a s b y fa r. The la rger of t he se

two sources is animal manure.

More than 75 percent of the animal manureresource is

tions that h

equiva lent

250,000 ch i

located on confined animal opera-

ave less than 800 dairy cows or the

we i g h t o f o th e r a n i m a l s ( e . g . ,

ckens). Large feedlots account for

of catt le and has been functioning since late

fa ll 1979. The b iog a s is fed i n to a d u a l - f u e l

diesel engine and supplies about 90 percent of

the eng ine’s fuel need s. The eng ine d rives a

125-kW generator (for peak electric demands)and the generator has an average output of 45

kW. The syste m sup p lies essen tia l ly a l l of t he

operation’s direct energy needs.

Other systems are operational or are l ikely

to become operational soon. Nevertheless, op-

era t ing exper ience is l imi ted and su i tab le d i -

gesters for all types of manures and combined

animal operations are currently not available.

Consequently, commercial ization of the tech-

no logy cou ld be he lped by demons t ra t i ng a

wide range of digester systems in a variety of

conf ined an imal operat ions so as to prov ideoperating experience and increase the number

of operations for which sui table digester sys-

tems exist.

Analysis

less than 15 percent of the resource or less

than 0.04 Quad/yr (see ch. 5 in pt. l). Sinc e it is

relatively expensive to transport manure long

distances, this economic analysis concentrates

on digesters appropriate for onfarm use.

The syste m a na lyzed c on sists of a p lug flow

digester ope rating a t 700 to 90° F, with a fe ed -

stock pond and e f f luent res idue storage p i t .

(See top sc hem at ic, figure 36.) Afte r rem ova l of

t h e h y d r o g e n s u l f i d e ( H2S), the b iog a s is

burned in an in terna l combust ion eng ine to

ge nerate elec tric ity. The elec tric ity is used on

the farm (replacing retai l e lectr ic i ty) and the

excess is sold wholesale to the electric utility.

The w aste he at from the g enerato r engine is

also used onfarm, but any excess heat goes to

waste. On the average,15 percent of the ener-

gy produced is used to heat the manure enter-ing the digester and for the other energy needs

of the digester (e. g., pumping). (Other systems

vary from 10 to 40 percent, depending on the

type of digester and the operating conditions.)




The re is suff ic ient g a s sto rag e c a p a c i ty to

l imit electric generation to those times of the

day when the u t i l i ty or the farmer has peak

electr ic demands; and the feedstock storage

al lows for seasonal variat ions in the average

d a i ly e ne rgy p rodu c tion. Therefo re, th is sys-

tem can be used either as a peakload or base-Ioad electric generating system. In a mature

system, the e lectr ic u t i l i ty would be ab le to

call for more or less electric generation from

onfarm units by sending coded signals along

the electric powerlines.

Other systems are possible, including one in

wh i c h th e wa te r i n t h e d i g e s te r e f f l u e n t i s

largely removed (dewatered) and the resultant

materia l sold as a fert i l izer or animal feed.

Tab le 58 sho ws the c ost of v a riou s syste ms; the

basic digester cost represents the sum of the

cos ts fo r d iges te r , pumps, p ipes , ho t wa te rboilers, H2S sc rubb er, low -pre ssure g a s c om -

p ressor, hea t e xcha ng ers, an d ho using. The

cost o f the manure premix ing equ ipment is

also included with tanks larger than 40,000 gal.

However, these costs should be viewed as pre-

l iminary and approximate.

Removal of the CO2 and sales of the gas to

natural gas pipelines were assumed not to be

feasible in small operations because: 1) the gas

pipel ines often are not readi ly accessible, 2)

the cos t o f CO 2 r e m o v a l e q u i p m e n t i s h i g h ,

and 3) revenues from the gas sales would prob-ably be relatively low. In very large systems,

though, production of pipeline quality gas may

be feasible.

Tab le 59 gives the e nergy that c ould b e p ro-

duced with onfarm digesters. It also shows the

quanti t ies that could be used onfarm and ex-

ported for various animal operations in some

of the m a jor prod uc ing Sta tes if farm ene rgy

use stays at 1974-75 levels or if it decreases 25

p e r c e n t due to energy conservation. In mostcases, the digester energy output is sufficient

to meet the energy needs of the Iivestock oper-

ation and in more than half of the cases con-

sidered, it also fills the farmer’s home energy

needs and enables a net export of e lectr ic i ty.

With conservation, the situation is even more

favo ra ble w ith resp ec t to ene rgy expo rts. The

lower revenue that the farmer rece ives for

surplus energy as opposed to the replacement

of retail energy, however, makes conservation

less economically attractive unless the farmer

is not energy self-sufficient without conserva-

t ion. In other words, i t is more economical lyattractive to replace retai l e lectr ic i ty than to

generate surplus electricity for sales at whole-

sale rates.

The d igester size, c a p i tal investme nt, a nd

operating costs for anaerobic digester-electric

generation systems for these various opera-

tions are shown in table 60. Assuming the farm-

ers can displace retai l e lectr ic i ty costing 50

m i l l/ k Wh , se l l wh o l e sa l e e l e c t r ic i t y f o r 25

mi l I /kWh, and d isp lace heat ing o i l used on-

farm costing $6/mi l l ion Btu, the returns from

the digester system are shown in table 61. Also

shown are the farmer’s costs for two assumed

capital charges: 1 ) where

charges are 10.8 percent 01

Table 58.–investment Cost for Various Anaerobic Digester System Options

th e

th e

annual cap i ta l

investment, i.e.,

Median capital costs ($1 ,000)

Options

Tank size (gallons) Basic digester Dewatering Electric generator Feedstock IagoonbResidue pitc

10,000 . . . . . . . . . . . . . $ 19.6 $34.0 $ 4 . 0 $ 6.7 $ 0 . 420,000 . . . . . . . . . . . . . 33.7 34.0 5.0 13.4 0.840,000 . . . . . . . . . . . . . 48.1 34.0 6.0 26.9 1.6

80,000 . . . . . . . . . . . . . 65.6 45.0 12.0 53.7 3.2200,000 . . . . . . . . . . . . 98.8 60.0 45.0 133.0 7,5400,000 . . . . . . . . . . . . 143.6 90.0 70.0 268.3 15.2

aGeRerator IS In operation 12 hours each daybStorage for 6 monthscStorage for 9 months.

SOURCE Tom Abeles and Dawd Ellsworlh, ‘Biological ProductIon of Gas, ” contractor repofl 10 OTA by I E Associates, Inc , Mmneapolls, Mmn , 1979



Ch. 9—Anaerobic Digestion q 193

Table 59.–Anaerobic Digestion: Energy Balance, or the Energy Production Potential and Energy Consumption Potentialof Individual Farms in Major Producing States

Methane energy Demands of l ivestock Household use Excess energy Excess energyoptions operation (1975 levels) (1974 levels) (25% conservation

Direct Electrici ty 1974 levels 25% conserv. Direct Electricity Direct Electricity

use Waste use Waste use Wasteonly heat only heat on ly heat

1974 livestock average number sold 1,000 1,000 1,000 1,000 1,000 1,000(inventory )/farm Btu 106 kWh Btu 10 6Btu 106 kWh Btu 10 6 kWh Btu 10 6 kWh Btu 10 6 kWh Btu 10 6Btu 106 kWh Btu 10 6

Turkeys Minnesota (124,000). . . . . ., 14,914 877California (98,000) . . . . . . .. . ..11,787 693North Carolina (89,000 . . . . . . . . . . . . .. .10,705 630Broilers Minnesota (52,000), . . . . . . . . 522 31

(198,000). .. . . . . . . . . . . . . . . . . . . . 1,986 117California (56,000) . . . . . . . . . . . . . 562 33

( 1 ,3 7 7 ,0 0 0 ) . . . . . . . . . . 1 3 ,8 1 2 8 1 2Arkansas (63,200) ., ., ., . . 634 37

(186,000) . . . . 1,866 110Swine lowa . , . , .. . ., . .. . , 325a 19Missouri . . 32 5a 19

North Carolina (500) ., . . . . . 325a 19Dairy cows Wisconsin (36) ., ., . . . . . ., ., 261 15New York (71) . , ., . , 521 31California (337) . . . . . . . . . . . . . . . 2,459 145Laying hens Minnesota (13,000). ., . . . ., 846 50

(41,000) . . . . . . . . . . 2,670 157Georgia (14,000) . . . . . . . . . . . . 912 54

(41,000) . . . . . . . . . . . . . . . . . . . . . . 2,670 157California (14,000) . . . . 912 54

(105,000) . . . . . . . . 6,838 402Beef(500) . . . . . . . . . 1,527 90

9,545 8,7547,544 4,7146,851 1,931

248147160

6,5593,5361,448

186 326110 180120 128

161622

5,835 6136,893 5308,646 448

465 8,029

2,650 8,071

4,792 9,129

675567488

2,6603,8285,275

11 16341 163

8 90183 180

7 10720 107

888

1699

2 9457 54122 15

5,026 552213 19822 74

-186 91- 2 5 8 7 9 9

-80 21054 7,178

- 1 5 291150 1.056

126817

6132181

- 9 784

82,206

63384

334 3571,271 1,366

360 3508,840 8,606

406 3141 , 1 9 4 9 3 7

14

5510

2449

27

2681,024

2626,454

236703

208 147208 69

208 29

2822

13

11052

22

21 15516 136

10 64

88

11

2 3 - 1 71 2 0 - 1 1

232 -5

-94 603 137

115 239

– l o- 5

- 2

- 5 720

123

-5 92182 376934 1,911

- 2188

1,026

167 11333 25

1,574 370

1633

133

819

278

12 16125 126

100 270

88

24

89 -93 7 0 - l o

1 ,8 1 9 - 1 2

- 5- 221

541 2131 , 7 0 9 6 7 2

584 1401 , 7 0 9 4 1 0

584 2244,376 1,680

977 –

34106349855

414 —

160504105308168

1,260 —

26 16380 16326 7274 7241 90

310 180 — 160

88

10108

1610

470 81,835 43

700 102,188 49

598 -94 ,9 7 8 – 2 81.427 80

165 523874 2,003372 735

1,227 2,290270 654

2,516 5,398817 –

16691873

576

—

2181,042’ 4 0 7

1,329326

2,936 —

alncludes breeding stockAssumptions 15% of blogasused lorun digester system electrrc generational 20% effmency,and80% of the engmewaste heatcanbe recaptured

SOURCE Tom Abelesand David Ellsworth “Bloloqlcal ProducNon o f Ga s c on t ra ct o r reporl to OTA by I E Associates Inc , MmneaDohs, Mlnn 1979, Enerayafld L/ S Awrcu/ture, 1974 Da/a Base (Washington DC Energy Research and_Development AdmmlstraNon, 1974)

9-percent interest loan with 20-year amoritiza-

tion, and 2) where the annual capital charges

are 15 percent of the investment.

The p rincipa l cost fa cto r in a nae rob ic diges-

tion is the capital charge, or the cost of the di-

gester i tsel f—thus, favorable f inancing is the

most effective way of reducing the cost to the

farmer.

Financing aside, the anaerobic digestion op-

erations that are most economical ly attractive

a re re la t i ve l y l a rge pou l t ry , da i ry , bee f , o r

swine opera t ions (enab l i ng an economy o f

scale) which are also relatively energy inten-

s ive (enabl ing the d isp lacement o f re la t ive ly

Iarge quantities of energy at retail prices) For

example, anaerobic digestion on a broiler farm

“.

with 198,000 birds in Minnesota is more eco-

nomical ly attractive than an equivalent oper-

ation with only 52,000 birds (see table 61). On

the other hand, the 52,000-bird broi ler farm

(equivalent to 250 head of catt le in terms of

the quant i ty and qua l i ty o f manure) is more

economically attractive than a 500-head cattle

feed lo t , because the pou l t ry ope ra t ion con -

s u m e s c o n s i d e r a b l y m o r e e n e r g y , a n d th u s

could better uti l ize the digester output within

its own enterprise.

Based on 1978 fuel prices, the feasibility of

anaerobic digestion was assessed for various

types of farm animal operations in the various

reg ions o f the country . I t was found that i t

would be feasible to digest so percent of the




Table 60.–Cost of Various Digesters WithElectric Generating Capabilities

Table 61 .–Annual Costsand Returns From Digester Energy Only

Return from1974 livestock Capital Annualaverage number sold Digester size investment operating costs(inventory )/farm (1,000 gal) ($1 ,000) ($1 ,000)

energydisplacement Digester costs

and sales of (operating + capital) ($1,000)

1974 livestock electricity 10.8% annual 15% annual(inventory )/farm ($1,000) capital charge capital charge

Turkeys Minnesota (124,000).

California (98,000) . . . .North Carolina (89,000). .

Broilers Minnesota (52,000) . . . .

(198,000). . . .California (56,000) . . . . .

(1 ,377,000). . .Arkansas (63,200) . . . . .

(186,000) . . . .

Swine Iowa (500). . . . . . . . . . .Missouri (500) . . . . . . .North Carolina (500) ... ,

Dairy cows Wisconsin (32). . . . . . . .New York (64) . . . . . . . .

California (337). . . . . . . .Laying hens Minnesota (13,000) . . . .

(41,000) . . . .Georgia (14,000) . . . . . .

(41,000) . . . . . .California (14,000) . . . . .

(105,000) . . . .

Beef(500).. . . . . . . . .

300

250225

220

195182

4.6

3.93.7

Turkeys Minnesota (124,000). . . .California (98,000) . . . . .North Carolina (89,000)..

Broilers Minnesota (52,000) . . . .

(198,000) . . .California (56,000) . . . . .

(1,377,000). . .Arkansas (63,200) . . . . .

(186,000) . . . .

Swine lowa (500). . . . . . . . . . .Missouri (500) . . . . . . . .North Carolina (500) . . . .

Dairy cows

Wisconsin . . . . . . . .NewYork (64) . . . . . . . .California (337) . . . . . . .

Laying hens Minnesota (13,000) . . . .

(41,000) . . . .Georgia (14,000) . . . . . .

(41,000) . . . . . .California (14,000) . . . . .

(105,000) . . . .

600/(500) . . . . . . . . .. . .

81 2851 2536 12

38333112

4513

3001440

256227

2202859

0.92.60.94.41.02.6

3,3 3.612 9.33.4 3.8

80 283.8 4.09.9 9.0

4.712

5.037

5.21110

1010

272727

0.80.80.8 2.2 3.7

2.2 3.71.5 3.7

4.94.94,910

10

80

2430

92

0.60.8

1.6 1.8 3.22.5 4.0

11 12

4.25.3

153410034

10035

250

20

5010350

10351

169

43

1.61.71.61.71.63.0

0.7

4.6 712 133.7 7.9.5 134.6 7.1

31 21

3.2 5.3

9.1179.1

179.3

28

7.2SOURCE SOURCE Tom Abeles and David Ellsworth, ’’Biological Production of Gas,’’ contractorreport to OTA by l. E Associates, lnc ,Minneapolis, Minn. ,1979

animal manure to produce electr ic i ty and on-

site heat if the effective annual capital charges

were 6.6 percent of the investment. (Digestion

was deemed feasible i f the returns from dis-

placing onsite energy use and wholesaling ex-

cess electr ic i ty were greater than the capi tal

and operating costs for the anaerobic diges-

t i on en ergy system .) Th is e f fe c t i ve c a p i ta l

charge cou ld be ach ieved by a 9-percent in -

terest, 20-year loan with 4.2-percent annual tax

writeoff. Other possible credits could be avail-

a b l e t h r o u g h c o m b i n a t i o n s o f A g r i c u l t u r a l

Sta b i li za t i on a nd Co nserva t ion Serv ic e p o l -

lu t ion abatement cost shar ing, so i l conserva-

t ion distr ict cost sharing, energy credi ts, and

other incent ives, a l though these are not in -cluded in the feasibil i ty calculations. In table

62, the percent of the manure resource that

would be feasible fo r ene rgy p roduc t ion wi th

the 6 .6-percent cap i ta l charge is shown for

various manure types and regions. Also shown

SOURCE SOURCE Tom Abeles and David Ellsworth, “Biological Production of Gas, ” contractorreport to OTA by I E Associates, Inc. , Minneapolis, Minn., 1979.

are the quantities of manure that would be fea-

sible if the digester effluent were dewateredand sold as a fertilizer at $1 O/dry ton over the

revenues available from sales of the raw ma-

nure as a fertilizer. Furthermore, if the dewa-

tered eff luent could be sold for feed, higher

credits may be possible based on the protein

content o f the e f f Iuent .17 Although the feasibil-

ity of these higher credits is unproven as yet,

the selling of digester effluent as feed or fertil-

i zer would substant ia l ly expand the quant i ty

o f manure tha t cou ld be d iges ted economi -

cally.

Turkey farms tend to b e the most ec ono micbecause of their rather large average size and

17Blogas of Colorado, “Energy Potential Through Bloconver-

sion of Agricultural Wastes, ” Phase //, Fina / Report to the Four

Corners Regiona/ Commission, demonstration pro]ect FCRC No

672-366,002, Arvada, Colo , 1977




Table 62.–Economic Feasibil ity of Anaerobic Digestion (percent of total manure resource that can be utili zed economicall ya)

Total usableRegion manure problem Layers Broilers Turkeys Cattle on feed Dairy Swine

Northeast . . . . . . . . . . . . . . . . . 52% 68% 82% 98% 6% 43%Southeast . . . . . . . . . . . . . . . . . . . .

—

65 54 75 90 45 80Appalachia . . . . . . . . . . . . . . . . . . .

—

47 51 85 89 8 26Corn Belt . . . . . . . . . . . . . . . . . . .

—

17 38 67 89 9 19 8%

Lake States . . . . . . . . . . . . . . . . . . 30 50 90 98 6 23 8North Plains . . . . . . . . . . . . . . . . . . 39 37 46 96 55 12Delta . . . . . . . . . . . . . . . . . . . . . . .

—

69 68 82 86 21 37South Plains . . . . . . . . . . . . . . . . . .

—

82 76 87 94 90 49Mountain. . . . . . . . . . . . . . . . . . . .

—

75 82 44 95 83 49Pacific . . . . . . . . . . . . . . . . . . . .

—

88 78 97 98 90 89Alaska. . . . . . . . . . . . . .

—

69 0 0 0 0 82Hawaii. ..., . . . . . . . . . . . . .

—

70 35 82 0 89 99 —

National totals 49 + 20b

With fertilizer enhancement59 81 94 61 41 5

assumption of $10/dry ton . . . . . 69 + 30b 85 95 99 72 60 35

Investment Also assumes 1978 energy costs as follows home healing $3 80/mdhon Btu, farming heat $5 40/mlHlon Blu, retadelectrlclty accordlngto DOE, Typca/Hectm Ms . .larruary 1978, October1978, and wholesale elecrrlclty 25 mdl/kWh

bEstlmated uncertainty These correspond to weighted average per cen tages

SOURCE Tom Abeles and Dawd Ellsworfh, ‘Blologlcal Produchon of Gas, ‘‘ contractor report to OTA by I E Associates, Inc , Mmneapolls, Mmn , 1979

the relatively large amount of thermal energy

c onsume d b y them. Swine op erat ions, how-

ever, are usually too small to be economically

attractive, for the energy alone, but because of

odor problems these may also be attractive.

If 50 percent of the animal manure on con-

fined a nimal op erations in the United Sta tes is

converted to electr ic i ty and heat, about 7 bi l -

l ion kWh of electricity per year (equivalent to

about 1,200 MW of electric generating capaci-

ty) and about 0 .08 Quad/yr o f heat would beproduced by 0.12 Quad/yr of biogas. At 70- per-

cent utilization, electricity equivalent to about1,600 MW of electr ic generat ing capacity

would be produced along with 0.11 Quad/yr of

heat.

In ei ther case some of the heat would be

wa sted in the system s d esc ribed ab ove . There

is, however, the possibi l i ty of expanding the

operation to use the excess heat, for example,

b y b ui ld ing g reenho uses. This c ould improve

the economics, but i t would require major ad-

justments in the farmer’s operation. In the end ,

site-specific economics and the inclination of

the ind iv idua l farmer wi l l determine whether

such options are adopted.

Care should be exercised when using these

da ta. They are ba sed on a num be r of ap proxi-

mations and they cannot be taken too Iiterally.

They d o, thoug h, indica te the ge neral trend s as

to economic feasibi l i ty and they show that a

substantia l quanti ty of the manure produced

on livestock operations could be used econom-

ically to produce energy, if the effective capi-

ta l charges are reduced through various eco-

nomic incentives.

Environmental Impacts of Biogas Production:Anaerobic Digestion of Manure

Anaerob ic d iges t ion o f feed lo t manure i snure (which often represents a substantial dis-

cons ide red to be an env i ronmen ta l l y bene f i - p o s a l p r o b l e m ) i n to a m o r e b e n i g n s l u d g e

cial technology because it is an adaptation of waste. Where the manure was used as a fertil-

a po llution c ontrol proc ess. The e nergy p rod - izer and soil amendment, the digestion wastes

u c t– b i o g a s – i s b a s i c a l l y a b y p r o d u c t o f t h e can substitute for the manure while eliminat-

control process, which converts the raw ma- ing some of its drawbacks.




The e nvironm enta l ben efits assoc iated with

reducing feed lo t po l lu t ion are extremely im-

po rta nt . The runoff f rom c at t le fee d lo ts is a

source of high concentrations of bacteria, sus-

pended and dissolved solids, and chemical and

bio log ic a l oxygen d em an d (CO D/BOD). Th is

type of runoff has been associated with: large

and ex tens ive f i sh k i l l s because o f oxygen

deple t ion o f rece iv ing waters; h igh n i t rogen

concentrations in ground and surface waters,

which can contr ibute to the ag ing o f s t reams

and to n i t ra te po ison ing o f in fants and l ive-

stock; transmission of infectious disease orga-

nisms (including salmonella, leptospirosis, a n d

coliform a nd enterococci bacteria) to man,

livestock, a nd w il dl if e; a nd c ol o ri n g o f

streams. 8Other problems associated with

feedlots include attraction of flies and obnox-

ious odors.

Because anaerobic digestion is a relativelysimple process not requiring extreme operating

condit ions or exotic controls, b iogas faci l i t ies

may be designed for very small (10 cow) oper-

a tions a s we ll a s large fee d lots. The en viron -

mental impacts wil l vary accordingly. For ex-

ample, recycl ing of wastewater may be possi-

ble for the larger operations; it is not likely to

be possible for the small onfarm digesters be-

ca use o f high w ate r trea tment c osts. The p rod -

uct gas from the smal ler uni ts is l ikely to be

used onsite and, depending on its use, may or

ma y not b e sc rub be d o f its HIS an d a mm onia

(N H,) content ; the product f rom very la rge

units may be upgraded to pipel ine qual i ty by

removing these pollutants as well as the 30 to

40 percent of the CO, fraction in the biogas.

The m ajor prob lem a ssoc iated with the d i-

gestion process is waste disposal and the asso-

ciated water pol Iut ion impacts that could re-

su l t . As noted above, anaerob ic d igest ion is

basically a waste treatment technology, but al-

though i t reduces the o rgan ic po l l u t i on con -

tent o f m a nure it d oe s not e l iminate it . The

combination of l iquid and solid effluent from

the digester contains organic solids, fairly high

concentra t ions o f inorgan ic sa l ts , some con-

c e n t r a t i o n s o f H2S a n d NH3, a n d v a r i a b l e

amounts o f potent ia l ly tox ic meta ls such as

boron, copper, and iron. For feed lot operations

where the manure is co l lected on ly in termi t -

tently, small concentrations of pesticides used

for fly control may be contained in the manure

and passed through to the waste stream.

A variety of disposal options for the l iquid

and sludge wastes exist. Generally, wastes will

be ponded to allow settling to occur. The liq-

uid, which is high in organic content, can be

pumped into tank trucks (or, for very large

operations, piped directly to fields) to be used

for i rr ig a t ion a nd fe r t il iza t ion . The h igh sa l t

content and the smal l concentrations of met-

als in the fluid make it necessary to rotate land

used for this type of disposal. Large operations

may conceivably treat the water and recycle it,

but treatment cost may prove to be prohibi-tive. Other disposal methods include evapora-

t ion ( in ar id c l imates) , d ischarge in to water-

ways (although larger operations are l ikely to

be subject to zero discharge requirements by

the Environmental Protection Agency), and dis-

cha rge in to pub l i c sewage t rea tmen t p lan ts .

In all cases, infi l tration of wastewater into the

ground water system is a possibility where soils

are porous and unable to puri fy the eff luent

through natural processes. As with virtually all

disposal problems of this nature, this is a de-

sign and enforcement problem rather than a

technological one; if necessary, ponds can be

lined with clay or other substances for ground

water pro tect ion.

The orga nic co ntent o f the eff luent, which

varies according to the efficiency of the digest-

er, wil l represent a BOD problem if al lowed to

enter surface waters that cannot dilute the ef-

fluent sufficien tly. Simila r p rob lems c a n oc c ur

wi th organ ics leached f rom manure s torage

pi les. However , th is prob lem ex is ts in more

severe form in the original feedlot operation.

The sludg e p rod uct c an be dispo sed of in a

landf i l l , but i t appears that the s ludge has

1 ‘Env i ronmenta l Impllcation$ o t [rends In Agriculture and S/ lvi-

culture, Volume I I En vlronmenta I t ffect~ of Trencfj (Wa shlngton,

D C Environmental Protection Agency, December 1978), E PA-

600/ 1-78-102

‘ v Solar Program A~se$$ment Environmental factors, Fue/s From

Biomass (Washington, D C Energy Research and Development

Acimlnlstratlon, March 1977), ERDA 77-477




ard opera t ing p rac t i ce ” wou ld e l im ina te th i s

safety factor.

The insti tut iona l prob lems a ssoc iate d with

assuring that there is adequate control of di-

gester impacts are very similar to those of eth-

a n o l p l a n ts : t h e r e i s a n a t t r a c t i o n to wa r d s

smaller size (“on farm”) plants which may havesome advantages (mainly ease of locating sites

for waste disposal and smaller scale local im-

pacts) but which cannot afford sophisticated

waste t reatment, are un l ike ly to be c lose ly

moni tored, and may be operated and main-

tained by untrained (and/or part- t ime) person-

nel . Some of the po tentia l safe ty and hea lth

prob lems probably wi l l respond to improved

system designs i f smal l onfarm systems be-

come popular and the size of the market justi-

fies increased design efforts on the part of the

ma nufac turers. The e ase o f bu ild ing hom e-made systems, however, coupled with farmers’

t rad i t i ona l i ndependence shou ld p rov ide po -

tent competi t ion to the sale of manufactured

(and presumably safer) systems.

Research, Development, and Demonstration Needs

Below, the more important research, devel-opment, and demonstration needs for anaero-

bic digestion are divided into the general areas

of microbiology, engineering, and agriculture.

Microbiology

The w hole rang e o f stud ies relate d t o ho w

a n a ero b ic d ig e st io n w o rk s sh o u l d b e a d -

d ressed . This includ es ide ntifying the b a c te ria

and enzymes involved, studying the bacter ia ’s

n u t r i e n t r e q u i r e m e n t s ( i n c l u d i ng t r a c e e l e -

ments), identifying optimum conditions for the

various conversion stages, and investigating

why some feedstocks are superior to others.

Much of this is in the realm of basic research

needed to understand the processes involved

so that the yields, rates, control, and flexibility

of anaerobic digestion can be improved.

Engineering

A large number o f d i f fe rent d igester types

need to be demonstrated to aid in optimizing

the safety and rel iabi l i ty of d igester systems

while reducing the cost for onfarm use or for

large -sc a le syste ms. The uniqu e p rob lems a nd

opportunities of various types of animal opera-

tions should also be addressed by the various

d ige ste r syste ms. There a re a lso num erous de -

sign alternatives that could lower the digester

costs, and these should be thoroughly exam-

ined.

Elec tric po we r ge neration a nd the related

f e e d s t o c k p u m p i ng is a weak area in digester

systems, particularly with respect to reliabiIity,

maintenance, and efficiency of the engine-gen-

erator uni ts. Development work for smal l en-

gines intended to use biogas and the related

pumps cou ld lead to improvements in these

areas, and fuel cells capable of using biogas

shou ld be deve loped . Deve lopment work i s

also needed into the best ways the farm gener-

ator can supply the electric uti l i ty grid during

periods of high demand without undue incon-venience for the Iivestock operation.

Agriculture

More needs to be known about the di ffer-

ence between d igested and und igested ma-

nure. The d ige sted ma nure should be investi-

gated in order to determine its value as a fertil-

izer, animal feed, and nutrient source for aqua-

tic plants. High-value uses for the digester ef-

f luent, proved through thorough testing, could

significantly improve the economics of anaer-

obic digestion.



Chapter 10

USE OF ALCOHOL FUELS



Chapter 10.–USE OF ALCOHOL FUELS

Page

Introduction . . . . . . . . . . . . . . . . . . . . . .......201Spark Ignition Engines–Ef

and Blends . . . . . . . .Gasohol . . . . . . . . .

Ethanol. . . . . . . . .Methanol-Gasoline BMethanol . . . . . . .

Summary . . . . . . . . .

ects From Alcohols. . . . . . . . . . . . . . . . . . . 201. . . . . . . . . . . . 203

, . . . . . . . . 206ends. . . . 207

. . . . . . . . . . . . 208

. . . . . . . . . . . . . . 208

D i e s e l E n g i n e s . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 9Environmental impacts of Automotive Use of

B i o m a s s F u e l s . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 0Air Pol lu t ion— Spark Ignition Engines. .. ...210

Air Pollution—Diesel Engines . . 213

Occupational Exposures to Fuels and

Emissions . . . . . 213

Safety Hazards. . . . . . . . . . . . . . . . . . . . . ...214

E n v i r o n m e n t a l E f f e c t s o f S p i l l s . . . . . . . . . . . 2 1 4

H a z a r d s t o t h e P u b l i c . . . . . . . . . . . . . . . . . . . 2 1 4

Page

Ga s Tur b ine s . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 5Air Pollution Effects of Alcohol Fuel Use in

63.

64.

37

Gas Turbines. . . . . . . . . . . . ....215

TABLESPage

Various Estimates of Refinery Energy

Savings From Use of Ethanol as Octane-Boosting Additive. . . . . . . . . . . . . . . . . . ..205

Emission Changes From Use of AlcoholFuels and Blends. . . . . . . . . . . . . . . . . . . . . 211

FIGURE

PageEfficiency, Power, and Emissions as aFunction of Equivalence Ratio. . .........202



Chapter 10

USE OF ALCOHOL FUELS

Introduction

Liquid fuels have some unique advantages

over sol ids and gases that make them impor-ta nt fue ls in som e a pp lic at ions. They c onta in a

la rge amoun t o f ene rgy pe r un i t vo lume (as

compared to gases) and their combustion can

easi ly be contro l led (as compared to so l ids) .

However , the re a re subs tan t ia l d i f fe rences

among Iiquid fuels. At one end of the spectrum

is residual fuel oi l , which can produce consid-

erable emissions when burned and is generally

best suited as a boiler fuel (an application also

open to solid fuels). At the other end are light

d istilla te o ils, ga so line s, an d a lco ho l fuels. The

oils and gasolines are superior to alcohols with

respect to their energy content per unit weight(ethanol has two-thirds and methanol one-hal f

of the energy per gal lon of gasol ine), which

ma kes them be tte r suited for aviat ion. The a l-

cohols are superior to oils with respect to their

lower particulate emissions and higher octane

va lues. These prop ert ies ma ke the m p a rt ic u-

larly useful for marine and ground transporta-

tion where energy density is not critical and for

gas turbines used for peak load electric genera-

tion, the applications considered here.

Whi le both e thanol and methanol are a lco-

hols, they have different physical and chemi-cal properties. Of the two, methanol is less sol-

ub le in gaso l ine, separates eas ier , and can

more easily damage certain plastics, rubbers,

and metals used in current automobi les. Fur-

thermore, methanol requires more heat to va-

porize it. Both alcohols, as contrasted to gas-ol ine, contain oxygen and conduct electr ic i ty.

These p rope rties a re imp ortant whe n c onsid er-

ing the use of alcohol fuels.

Whi le oi l and hydrocarbon (HC) crops may

s o m e d a y p r o d u c e fu e l s f o r t r a n s p o r ta t i o n ,

their costs and yields are highly uncertain at

this time. For the near to mid-term, the most

l ikely biomass substitutes for gasoline, diesel,

and light fuel oil are the alcohol fuels.

Biomass is the only solar technology for pro-

du c ing l iqu id fuels. The b iom ass c an be c on-ver ted to methanol ( “wood a lcoho l ” ) th rough

t h e r m o c h e m i c a l c o n v e r s i o n o r t o e t h a n o l

( “ g r a i n a l c o h o l ” ) t h r o u g h f e r m e n t a t i o n o r ,

poss ib ly , thermochemica l convers ion. Ethanol

production from sugars and starches is current-

ly commercial technology. Wood-to-methanol

p lants can be bu i l t wi th ex is t ing technology,

although none currently exists, and plant-herb-

age-to-methanol technology needs to be dem-

onstrated.

Most cost calculations indicate that metha-

nol from coal will be less expensive than eitheralcohol from biomass. Unti l and unless a do-

mestic l iquid fuels surplus develops, however,

this cost difference is not l ikely to exclude the

biomass alcohols from the market.

Spark Ignition Engines— Effects From Alcohols and Blends

Alcoho ls make exce l l en t fue l s fo r spa rk -

ign i ted eng ines which are des igned for the i r

use. However, when considering alcohol or al-

cohol-gasoline blend use in gasoline engines,

there are four specific factors that are of over-

riding importance. One factor is the material

from which the engine is constructed. Another

is the ratio of air to fuel (A /F ratio) in the mix-

ture that is burned in the engine. A third is

proper fue l d is t r ibut ion among the cy l inders,

and a fourth is cold-starting ability.

Som e m a te ria ls in som e a uto mo b iles a re in-

compatible with alcohols. Contact wi th alco-

hols can damage some gaskets, fuel pump dia-

phragms, and other plastic and rubber parts. If

these parts are adversely affected or fai l , the

engine is l ikely to malfunction. Furthermore,

201

67-968 0 - 80 - 14




some electr ic fuel pumps are mounted in the

fue l tank . E lec t r i c cu r ren ts i nduced in the

alcohol fuels by these motors may cause the

protective terneplate coating on fuel tanks to

dissolve and leave the tank susceptible to cor-

rosion. The re ma y a lso b e a fire haza rd a ssoc i-

ated with electrical shorting. Under certain cir-

cumstances, not totally understood at present,

the a lcoho ls or b lends can a lso chemica l ly

r e m ov e the te r ne p la te c oa t ing .12 3 F i n a l I y ,

alcohols can cause some deposits in the fuel

tanks and lines to loosen and dislodge, leading

to a blockage in the fuel filter or carburetor.

Three major classes of automobiles are in

use today: pre-1 975 cars, oxidation (two-way)

catalyst cars (most post-1 975 cars in States

other than Cal i fo rn ia) , and Cal i fo rn ia three-

wa y c a ta lyst c a rs. The ra nge of A/ F ratios* in-

tended for each class of cars is shown in figure

37 together with the effect of this ratio on theengine power, efficiency, and emissions. If the

A/ F ratio extends beyond the ranges of this fig-

ure, most engines will hesitate or stall. (Strati-

fied-charge engines like the Honda CVCC and

Ford Proco have somewhat wider ranges.)

Since the pre-1975 c a rs an d o xida tion ca ta -

lyst cars usual ly have carburetors with f ixed

fuel metering passageways, the alcohol blend

fuels, which require less air per volume of fuel

than gasoline, will make the effective fuel mix-

ture leaner (i. e., move the effective A/F ratio to

less fuel and more air) . Cal i fornia three-waycatalyst cars, however, have a sensor that ad-

justs the fue l de live ry syste m t o the A/ F va lue

in tended by the manufacturer . Never the less,

exha usts from a lco hol fue ls “ foo l” th is sen sor

somewha t , so the compensa t ion i s no t com-

‘K R Stamper, “50,000 Mile Methanol/Gasollne Blend Fleet

Study– A Progress Report, ” in Proceeding of the Alcohol Fuels

Tec hno log y Third /nterr-tat iona/ Syrrrposlum, Asllomar, Callf (Bar-

tlesvllle, Okla Bartlesvllle Energy Technology Center, Depart-

ment of Energy, May 1979)

‘S. Gratch, Director of Chemical Science Lab, Ford Motor Co ,

Dearborn, Mlch , private communlcatlon, 1979

‘j L Keller, G M Nakaguckl, and j C Ware, “Methanol Fuel

Modlflcatlon for Highway Vehicle Use, ” Union 011 Co ofCalifornia, Brea, Callf , final report to the Department of Energy,

contract No FY 76-04-3683, j uly 1978

q The ftgure shows the equivalence ratio which is found by di-

viding the stolchlometnc A/F rat to which IS exactly sufficient to

completely burn all of the fuel by the actual AIF ratio used In the

car Leaner mixtures are to the left and richer to the right

Figure 37.—Efficiency, Power, and Emissions as aFunction of Equivalence Ratio

1 1

0.85 0.90 0.95 1.0 1.05

Stoichiometric Rich

Equivalence ratio (+ )

The equivalence ratio is the ratio of the A/F ratio which is exactlysufficient to completely burn all of the fuel to the actual A/F ratioused in the car. Leaner mixtures have an excess of air, while richerones have an excess of fuel.

SOURCE: H Adelman, et al., “End Use of Fluids From Biomass as Energy Re-sources in Both Transportation and Nontransportation Sectors, ” Uni-versity of Santa Clara, Santa Clara, Cal If., contractor report to OTA,1979

plete. 4 Consequently, while the difference be-

tween the A/F ratio for alcohol fuels and pure

gasoline is less for California three-way cata-

lyst cars than for other cars, the A/F ratio is still

somewhat leaner with alcohol fuels compared

to gasoline.

Fo r pu re a l coho ls the fue l me te r ing ra te

must be increased significantly relative to gas-

01 inc . This inc reased rate c a n result in strea m-

ing flow rather than well-disbursed droplets asthe fuel enters the air stream when carburetors

are re tro f i t ted for a lc oho l fue l . Th is c ha nge

‘Gratch, private communlcatlon, op clt



Ch. 10—Use of Alcohol Fuels q 20 3

can seriously aggravate the variation in the A/F

ratio among the cylinders which in turn can re-

duc e performanc e and e co nomy and increase

emissions. Proper design of the fuel delivery

s y s te m a n d i n ta k e m a n i fo l d c a n a v o i d t h i s

penalty.

The a lco hols do not inherently p rovide go odcold engine starting. Below 400 F, special at-

tent ion must be pa id to avo id co ld-s tar t ing

problems with alcohol. Aids such as electr ic

h e a t i n g i n t h e i n t a k e m a n i f o l d , b l e n d i n g

agents such as gasoline, butane, or pentane

added to the a lcoho ls , or aux i l ia ry co ld-s tar t

fuel are providing solutions to this problem in

the alcohol vehicle fleets now in operation.

Gasohol

Materials Compatibility

Gasohol is a mixture of 10 percent ethanol

and 90 pe rce nt unlea de d g asoline. The etha nol

blended in gasohol must be dry (anhydrous) or

the blend will separate into two phases or lay-

ers und er ce rtain c ond it ions. Typ ica l ly, ga so-

hol can hold more water than gasol ine, but i t

can contain no more than about 0.3 percent if

separation is to be avoided down to –400 F.

Various additives have been tried to improve

the water tolerance of gasohol, but none have

proved satisfactory to dates

A l th o u g h th e u s e o f a n h y d r o u s e th a n o ls h o u l d m i n i m i z e wa te r t o l e r a n c e p r o b l e m s

with gasohol, phase separation has been ob-

se rved to occu r i n fou r se rv i ce s ta t i ons in

Iow a . ’ This p ha se-sep a ra ted b lend wa s sold t o

some customers and caused their vehicles to

stal l . Both the vehicle tanks and the service

station tanks were drained and up to 0.3 per-

cent by volume water was found in the mix-

ture, but the origin of the water contamination

is not known.

5 H Adelman, et al , “End Use of Flu Ids From Biomass as Ener-

gy Resources In Both Transportation and Non-Transportation

Sectors, ” University of Santa Clara, Santa Clara, Callf , contrac-

tor report to OTA, 1979,

‘Douglas Snyder, lowa Development Commission, private

communication, 1979

Gasohol does not appear to signi f icantly af-

fect engine wear as compared to gasoline but

more experience with gasohol is needed before

a definitive statement can be made. However,

an unknown fract ion o f ex is t ing automobi les

have speci f ic components that are not com-

patible with gasohol, which can result in some

fuel system failures.

As older cars are replaced with newer ones

warranted for gasohol use and as experience

develops in handling ethanol-gasoline blends,

these problems should gradually disappear.

Thermal Efficiency

The lea ning effec t of ga soho l relative to ga s-

oline wiII affect the three classes of cars some-

what differently. For precatalyst and oxidation

catalyst cars, the thermal efficiency can either

increase or decrease with gasohol dependingon the origina l A/ F set ting (see figure 37). In

general, automobiles that operate rich wil l in-

crease in eff ic iency, whi le those that operate

lean wi l l decrease in thermal e f f ic iency wi th

gasohol.

Th e Ne b r a sk a “ t w o m i l l io n m i le ” t e st

showed a large average mi leage increase (7

percent) with gasohol. ’ However, the spread of

data points is so large that the uncertainty in

this difference is greater than the difference

itself. * This is a g en eric p rob lem in trying to

deduce small differences in mileage with road

tests.

Laboratory tests , however , ind icate an in-

crease in thermal eff ic iency of 1 to 2 percent

‘W A Scheller, Nebraska 2 Million Mile Gasohol Road Test

Program, Sxth Progress Report (Lincoln, Nebr Unlversit~ of Ne-

braska, January 1977)

*Taking data from figure 4 of Scheller, OTA has analyzed the

uncertainty in the average mileage difference Using a standard

statistical test (“t” test) reveals that the spread In data points

(standard deviation) IS so large that the mileage difference be-

tween gasohol and regular unleaded would have to be more than

30 percent (two times the standard deviation) before OTA would

consider that the test had demonstrated a difference In mileageWhile more sophisticated statistical tests might Indicate that the

measured difference in mileage is meaningful, the validity of

these statistical methods IS predicated on all the errors being

strictly random, and the assumption of random errors IS suspect

unless the number of vehicles in the test fleet is orders of magni-

tude larger than any tests conducted to date




with gasohol in precatalyst and oxidation cata-

l ys t ca rs , wh ich i s w i th in the measuremen t

errors. 8 The c ha ng es in therma l efficienc y with

three-way catalyst cars wil l be less and there-

fore negligible.

Since ga soho l co nta ins 3.5 p erce nt less ene r-

gy per gallon than gasoline, precatalyst and OX-

idation catalyst cars are expected to experi-

ence about a zero- to 4-percent decrease in

miles p er ga llon . Three-w a y c a ta lyst c a rs a re

expected to experience about a 3- to 4-percent

decrease in mileage. Probably neither of these

decreases would be not iceab le by motor is ts

and, as stated above, wil l depend on the A/F

setting of the automobile for all but the three-

way catalyst cars.

These conclusions are in complete agree-

ment with the results of an American Petrole-

um Insti tute study released in the spring of1980, 9 in which al l avai lable data on gasohol

mileage were compared, averaged, and treated

sta t is t ica l ly to determine the s ign i f icance o f

the results.

Drivability

Post -1970 n o n c a t a l y s t a n d o x i d a t i o n c a t a l y s t

cars that are set at lean A/F ra t ios on gaso l inecan exper ience dr i vab i l i t y p rob lems s u c h a s

stumbl ing, surg ing, hes i ta t ion, and sta l l ing

wi th gasohol due to fur ther mixture lean ing.

Whi le no dr ivab i l i ty prob lems have been re-

ported for precatalyst cars, laboratory tests on

1978 and 1979 oxidation catatlyst cars sug-

gested sl ight deter ioration in dr ivabi l i ty . ’” I f

the percentage of ethanol is increased beyond

10 percent, more and more cars are expected

to experience drivabil i ty problems due to the

leaning effect.

Since t hree-wa y ca ta lyst c ars la rge ly c om -

pensate for the leaning effect of gasohol, no

‘R K Pefley, et al., “Characterization and Research investiga-

tion of Methanol and Methyl Fuels, ” University of Santa Clara,

Santa Clara, Calif , contractor report to the Department of

Energy, contract No FY 76-5-02-1258, 1979‘Mueller Associates, Inc , “A Comparative Assessment of Cur-

rent Gasohol Fuel Economy Data, ” commissioned by the Amer-

ican Petroleum Institute, 1980

‘“R Lawrence, “Gasohol Test Program, ” Technology Assess-

ment and Evaluation Branch, Environmental Protection Agency,

Ann Arbor, Mlch , December 1978

dr ivab i l i ty prob lems are expected wi th gaso-

hol, as long as the mixture does not go beyond

the capabil i ty of the compensation mechanism

in these cars.

In most cars there may also be some minor

problems with vapor lock, if the vapor pressure

of the blend is not adjusted properly by remov-ing some butanes from the gasoline.

Octane

Addition of ethanol to gasoline increases the

octane* for the mixture over that of the gaso-

line. The e xac t increa se w ill d ep end on the ga s-

oline, of which there is a great variety. On the

average, for the range of 5 to 30 percent etha-

nol, each percent of ethanol added to one base

unleaded regular gasoline (88 octane) raised

the octane number by 0.3. However, the oc-

tane increases per unit alcohol are larger forlower percentages of ethanol and lower octane

gasolines and level off at higher alcohol per-

centages and gasol ine octane. A 10-percent

blend would raise the octane by about 2 to 4

using an “average gasoline. ”

The oc tan e-bo ost ing prop er t ies o f e tha nol

can be exploited in either of two ways to save

energy: 1 ) by reducing the oil refinery energy

by producing a lower octane gasoline or 2) by

increasing the octane of all motor fuels so that

au tomob i le manu fac tu re rs can inc rease the

compression ratios and thus the efficiency of

new cars.

There is c onsiderab le unc ertainty a nd va ria-

bi l i ty in the amount of premium fuel that can

be saved at refineries by using ethanol as an

octane-boosting additive. As shown in table 63,

repor ted or der ived va lues vary f rom near ly

zero to more than 60,000 Btu/gal of ethanol,

depending on the average octane of the refin-

ery gasoline pool, the octane boost assumed

f rom e thano l , the type o f gaso l i ne and the

ratio of gasoline to middle disti l lates produced

by the refinery, the refinery technology used,

and other specifics.

*Octane here refers to the average of research octane and

motor octane.

‘ ‘Keller, Nakagucki, and Ware, op cit




The o the r possibility is to u se th e e tha no l na -

t ionwide to gradual ly increase the octane of

motor fuels. Auto manufacturers could use the

increased octane to improve engine eff ic ien-

cies by increasing the compression ratios in

aut om ob i le eng ines. The ene rgy sav ings per

gallon of ethanol would be comparable to that

calculated above, but there would be Iittle sav-ings before h igher octane fue ls were read i ly

avai lable and older automobi les had been re-

placed with the newer, more efficient engines.

Som e strati f ied -cha rge e ng ines (e.g ., Ford

Proco) do not require high-octane fuels and the

benefits from a high-octane fuel would be sub-

stantially less than for conventional engines. If

these or other such engines are used extensive-

ly, the octane-boosting propert ies of ethanol

would be of l i t t le value, but i t is l ikely that

large numbers of automobiles wil l need high-

octane fuels well into the 1990’s.

Value of Ethanol in Gasohol

The va lue o f etha nol or the price at which it

becomes competitive as a fuel additive can be

c a l c u l a t e d in seve ral wa ys. Two a l ternatives

are presented here.

At the oi l ref inery, each gal lon of ethanol

used as an octane booster saves the refinery

the equivalent of 0.4 gal of gasoline by allow-

ing the production of a lower octane gasoline

(see section on octane above). in addition, 1

gal of ethanol will displace about 0.8 gal ofgasoline when used as a gasohol blend (i.e.,

gasohol mileage is assumed to be 2 percent

less than gasol ine mi leage). At the refinery

gate, unleaded regular costs about 1.6 t imes

the crude o i l p r ice . Assuming that the fue ls

saved by the octane boost, which are of lower

value than gasol ine, cost about the same as

crude oil, the ethanol is valued at about (gaso-

line saved) x (gasol ine pr ice) + (refinery fuel

saved) x fuel pr ice = 0.8 X 1.6 + 0.4 X 1.0 =

1.7 times the crude oil price. *

‘This IS in agreement with the value of 16 to 1 8 times thecrude oil price that can be calculated using Bonner an d

Moore’s” estimates based on $12 25/bbl crude 011

“ A Formu/a fo r Estimating Refinery Cost Changes Associated

With Motor Fue/ Reformation (Houston, Tex Bonner and Moore

Associates, Inc., Jan 13, 1978)

If the gasoline retailer blends the gasohol,

the value of the ethanol is somewhat different.

Gaso l i ne re ta i l e rs bough t regu la r un leaded

gasoline for about $0.70/gal in July 1979 and

sold gasohol for a rough average of $().()3/gal

more tha n regular unlea de d. (The di fferenc e

between this and the retail price of gasoline is

due to taxes and service station markup, whichtotal about $0.29/gal.) One-tenth gallon of eth-

anol displaces $0.07 worth of gasoline and the

mixture sold for $0.03/g a l mo re. The refore, 0.1

gal of ethanol was valued at $0.10 or $1 .00/

g a l. This is 2.5 time s the July 1979 a ve rag e

crude oil price of $0.40/gal.

Both o f these est imates are approx imate,

and changing price relations between crude oil

and gasoline couId affect them. Moreover, sev-

eral other factors can change the estimated

value of ethanol. If a special, low-octane, low

vapor pressure gasol ine is sold for blending

with ethanol, at low sales volumes the whole-

saler might assign a larger overhead charge per

gallon sold. Also, the refinery removes relative-

ly inexpensive gasoline components in order to

lower the vapor pressure* of the gasoline, and

this increases its cost. On the other hand, in

areas where gasohol is popular, the large sales

vo lumes lower serv ice s ta t ion overhead per

g a llon t hus raising e tha no l’s va lue. The se fa c -

tors can change the va lue o f e thanol by as

much as $0.40/gal in ei ther direction ( i . e.,

$0.04/gal of gasohol) and the pricing policies of

oil refiners and distributors will, to a large ex-tent, determine whether ethanol is economi-

calIy attractive as an octane-boosting additive.

Ethanol

If pure ethanol is used, carburetors have to

be modif ied to accommodate this fuel . New

e n g i n e s d e s i g n e d fo r e th a n o l c o u l d h a v e

*The more’ volatile components of gasoline (e.g., butanes) may

be removed to decrease evaporative emissions and reduce the

possibility of vapor lock Although these components can be

used as fuel, removing them decreases the quantity of gasoline

and the octane boost achieved by the ethanol Consequently, theadvantages of having a less volatile gasoline must be weighed

against the resultant decrease in the gasoline quantity and the

value of the ethanol This IS a matter of business economics in

each refinery and there are no simple rules which would be uni-

versally applicable




are to be expected. The se p rob lem s sho uld d is- cause of the energy saved by allowing refiners

appear with time, however, as more experience to p rod uce a low er oc tane ga soline. The situa-

is gained at handl ing and using the alcohol tion with methanol is less clear because of the

fue ls and as o lder automobi les are rep laced greater d i f f i cu l t ies associa ted wi th methanol

with vehicles designed for use with these fuels. blends and the possible need for cosolvents.

The use of methanol both in blends and as aFor ethanol the preferred use probably is as

straight fuel is currently being pursued.an oc tane-boos t ing add i t i ve to gaso l i ne be -

Diesel Engines

A l c o h o l s h a v e o n l y l i m i t e d v o l u b i l i t y i n

diesel fuel , making diesel-alcohol blends im-

p r a c t i c a l a t p r e s e n t . * I f “ i g n i t i o n a c c e l e r -

a to rs” * * a re d i sso l v e d i n t h e a l c o h o l s t o

enable them to ignite in diesel engines, they

can be used as a replacement for diesel fuel,

but the fuel metering system would have to be

modified to provide the fuII range of power forwhich the engine was designed and some pro-

visions made for the decreased lubricity of the

alcohols.

Al ternat ive ly , the a lcoho ls can be used in

dual fuel systems, i.e., where the alcohol and

diesel fuel are kept in separate fuel tanks and

sep a rate fue l met ering syste ms are used . The

two main possibil i ties are fumigation and dual

injection. In a fumigation system, the alcohol

is passed through a carburetor or injected into

the air intake stream and the alcohol-air mix-

ture replaces the intake air. In dual injection,

each fuel is in jected separately into the com-

bustion chamber.

Most diesel engines are speed governed, i.e.,

more or less diesel fuel is injected automatical-

ly to maintain a constant engine speed for a

g iven acce le ra to r se t t i ng . If alcohol is fumi-

gated into the cylinder, the diesel injection

decreases automatically when the eng ine i s

not at ful l power to compensate for the addi-

t ional power from the alcohol. At fu l l power,

the a l coho l w i l l g i ve the eng ine add i t i ona l

power. Consequently, once a fumigation sys-

tem i s i ns ta l l ed , a l coho l usage i s op t iona l ,

since the engine wil l run normally without the

alcohol present, but the higher power at fu l l

power can cause additional engine wear if the

engine is not designed for th is power. Al ter-

natively, the diesel injection can be modified

to allow less fuel to be injected, but it would

have to be returned to its original state when

alcohol is not being used. Dual injection sys-tems also can be designed to run with or with-

out a lcoho l , but the in ject ion contro ls would

probably be more complicated.

If the fuel systems are separate, alcohol con-

taining up to 20 percent water probably can be

used. However, the diesel engines must be

mod if ied to a cc omm od ate the a lco hols. The

modifications for alcohol fumigation are rela-

tively simple and can be performed for an esti-

mated $150 if, for example, a farmer does it

h imself and uses mostly spare parts. ” Costs

could range up to $500 to $1,500 if installed by

a mechanic using stainless steel fuel tanks and

al l new parts.40 Cost estimates for modifying

engines for dua l in ject ion are not ava i lab le ,

however, but would be more expensive. In ei-

ther case the long-term effects, such as possi-

bly increased engine wear, are unknown at the

present time.

Fumigation systems will generally be limited

to 30 to 45 percent ethanol or about 20 percent

methanol, because evaporation of the alcohol

cools the combustion air and the cooling from

higher concentra t ions is suf f ic ient to prevent

the diesel fuel from igniting. However, consid-

*E mulslons are possible, but still In the R&D phase

qq Although alkyl nitrates have generally been used as Ignltlon

accelerates, sunflower 5CW! 011 and other vegetable OIIS have

btwn suggested for biomass-derived ethanol

“Pefley, et al , op cit

‘(’lbld




companied by design changes that would

take advantage of the different properties

of t he se fu els. Thus, extra p ola tion s from

current test data may be overly pessimis-

tic, at least for the long run.

Aside f rom test resu l ts , emiss ion changes

can be explained in great part by the depend-ence of emissions on the operating conditions

of the engine. Emissions of CO, HC, NOX, and

a l d e h y d e s a r e s t r o n g l y i n f l u e n c e d b y th e

“equ iva lence ra t i o @“ (stoichiometric A/F ra-

tio/actual A/F ratio) and the emission control

system (none, oxidation catalyst, etc.). Figure

37 shows how CO, HC, NOX, and aldehydes are

likely to vary with @.

Both methanol (6.4:1 ) and ethanol (9:1) have

lower stoichiometr ic A/F ratios than gasol ine

(14. s: I). Thus, b lend s of eithe r alc ohol fue l re-

sult in lower equivalence ratios (“leaner” oper-

ation) if no changes are made in the fuel meter-

ing d ev ices. Examin ing f i gu re 37 , emissions

changes can be predicted qualitatively by ob-

serving that adding alcohol pushes the equiva-

lence ratio to the left. For an automobi le nor-

mal ly operat ing “lean,” CO may be expected

t o r e m a i n a b o u t the same, HC rema in the

same or increase slightly, and NOX d e c r e a s e .

For ou t -o f - tune au tomob i les , wh ich usua l l y

operate in a “fuel rich” mode, CO and HC may

be expected to decrease while NOX increases.

Vehic les equ ipped wi th three-way cata lysts

have feedback-controlled systems that operate

to maintain a predetermined value of @ a nd

thus should be less affected by the blend lean-

ing effect of the alcohol fuels. However, thisfeedback system is usual ly overr idden during

cold starting to deliver a fuel-rich mixture; dur-

ing this time period, HC and CO are more like-

l y t o d e c r e a s e a n d N OX t o i n c r e a s e w i t h

alcohol fuels. Also, catalysts with oxygen sen-

sors can be foo led in to ad just ing to leaner

operation because the exhaust emissions from

alcohol blends oxidize faster than gasol ine-

based exhausts and drive down the oxygen lev-

el in the exhaust stream (giving the appearance

of overly fuel-rich operation);47 th is sho uld a lso

tend to decrease HC and CO and increase NOX

emissions when alcohol blends are used in ve-

hicles equipped with such catalysts.

Ta ble 64 provides a summ a ry of the t ype of

emissions changes that may be expected by

combining knowledge of test results and the

47 Cratch, op cit

Table 64.–Emission Changes (compared to gasoline) From Use of Alcohol Fuels and Blends

Pollutant/fuel Methanol Methanol/gasoline Ethanol Ethanol/gasoline ‘‘gasohol’

Hydrocarbonor unburnedfuels

Carbonmonoxide

Nitrogenoxides

Oxygenatedcompounds

Particulate

Other

About the same or slightly higher, May go up or down in unmodifiedbut much less photochemically vehicles, unchanged when @

reactive, and virtual elimination remains constant. Compositionof PNAs; can be catalytically changes, the, and PNAs gocontrolled down. Can be controlled. Higher

evaporative emissionsAbout the same, slightly less for Essentially unchanged if@

rich mixtures; can be catalytically remains constant, lower ifcontrolled; primarily a function -

of @1/3 to 2/3 less at same A/F ratio,

can be lowered further by goingvery lean; can be controlled

Much higher aldehydes, particu-larly significant with precatalyst

vehiclesVirtually none

No sulfur compounds, no HCN orammonia

leaning is allowed to occur

Mixed; decreases when is heldconstant, but may increase fromfuel ‘‘leaning’ effect in unmodi-fied vehicles

Aldehydes increase somewhat,most significant in

precatalyst vehiclesLittle data

Unknown

Not very much data, should be May go up or down in unmodifiedabout the same or higher but less vehicles, about the same when +

reactive. Expected reduction in remains constant; compositionPNA may change, expected reduction

in PNAs. Evaporative emissionsup

About the same, can be controlled ;Decrease in unmodified vehiclesprimarily a function of * (i.e., leaning occurs), about the

same when @ remains constant

Lower, but not as Iow as with Slight effect, small decrease whenmethanol; can be controlled 4 is held constant, but may

increase or decrease further fromfuel ‘‘leaning’ effect inunmodified vehicles

Much higher aldehydes, particu- Aldehydes increase, most signifi-Iarly significant with precatalyst cant in precatalyst vehicles

vehiclesExpected to be near zero Lit tle data, no sign if icant changeexpected

No sulfur compounds No data

SOURCE Office of Technology Assessment




q

q

The effec ts of bo th ac ute a nd c hronic ex-

posure to e thano l a re cons ide red to be

much less disruptive than methanol and,

therefore, gasoline.

The a u to mo t i ve e xhaust e missions tha t

are most dangerous in an enclosed space

— such as a garage without adequate ven-

t i la t ion —are CO from gaso l ine and COand fo rma ldehyde f rom methano l . I f a

f l ee t o f me thano l -powered ca rs i s com-

p a r e d d i r e c t l y t o a f l e e t o f g a s o l i n e -

powered cars, CO will be the most danger-

ous pol lutant (and equal ly dangerous for

both f leets, because methanol should not

substant ia l ly change CO emiss ions)—so

long as three-way catalysts are used. With-

ou t ca ta l ys ts , fo rma ldehyde emiss ions

could be more dangerous than CO in the

methanol-powered fleet.

It is interesting to observe that, for the

catalyst-equipped methanol f leet, formal-

dehyde will act as a “tracer” for CO; if eye

and respiratory i rr i tat ion from formalde-

hyde becomes acute, th is wi l l be an al-

most sure sign that CO is at dangerous lev-

els.

Safety Hazards

The risks of fire an d e xplosion a p p ea r to b e

lower wi th a lcoho l fue ls than wi th gaso l ine,

although evidence is mixed:

q

q

q

q

q

gasoline has a lower flash point and igni-

t ion temperature and is more f lammableand explosive in open air than either etha-

nol or methanol, 64

alcohols are the greater hazard in closed

areas, 65

h igher e lec t r i ca l conduc t i v i ty o f a l coho l

lessens danger of spark ignition,

h i g h v o l u b i l i t y i n wa te r m a k e s a l c o h o l

fires easier to fight than gasoline fires, and

alcohol fires are virtually invisible, adding

to their danger (but addition of trace ma-

terials could overcome this drawback).

Alcohol blends wi l l be simi lar to gasol inebut they may be more ignitable in open spaces

and less ignitable in closed containers when

“CRC Handbo ok of Laborato ry Safety, op clt

“lbd

the blends have higher evaporation rates than

th e p u re g a so lin e . D ie se l f u e ls a n d d i e se l

alcohol emulsions are considered to be safer

than gasoline or alcohol fuels. 66

Environmental Effects of Spills

To the extent tha t do me stic alco hol prod uc-

tion substitutes for significant quantities of im-

por ted o i l , a reduct ion in fue l t ranspor ta t ion

and a consequent reduction in spills can be ex-

pected. If alcohol is shipped by coastal tanker,

t h e p o s s i b i l i t y o f l a r g e a l c o h o l s p i l l s i s a

real ist ic one, and the effects of such spi l ls

should be compared to the effects of oilspilIs.

Alcohol fuels appear to be less toxic than oil

in the initial acute phase of the spill and have

fewer long-term effects. Except in areas where

alcohol concentrations reach or exceed 1 per-

cent, the immediate effects of a spill should bem i n i m a l . Fo r e x a m p l e , a c o n c e n t r a t i o n o f

about 1 percent methanol in seawater is toler-

a ted by many common components o f in ter -

tidal, mud-flat, and estuarine ecosystems un-

less the a lcoho l is contaminated wi th heavy

metals. b ’ I n contrast, crude oil contains several

h igh ly tox ic water so lub le components that

can be damaging at low concentrations. Fur-

thermore, a lcoho ls are extremely b iodegrad-

able— toxic effects may be eliminated in hours

—whereas the effects of heavy fuel oi ls can

last for years.

Hazards to the Public

The w idesp rea d d istrib ution a nd u se o f alc o-

hol fuels wi l l resul t in the publ ic facing the

same potential dangers as exist in the occupa-

tional environment. A true assessment of etha-

nol and methanol public health risks must in-

corporate an ana lys is o f probable exposure,

however, and such an analysis is likely to show

that both alcohol fuels may have considerably

“M ELePera, “Fine Safe Diesel Emulsions, ’’Conference orI

Trarrsportation Synfue/s, sponsored by the Department of Energy,

San Antonio, Tex , November 1978

‘7P N D’E Iiscu, “Biological Effects of Methanol Spills Into

Marine, Estuarine, and Freshwater Habitats, ” in Proceedings of the International Symposium on Alcohol Fuel Technology, Meth- anol and Ethanol, Wolfsburg, West Germany, Nov 21-23, 1977




The most significant emission change should distillate fuels. ’z Ethanol, which has a combus-

be a substantial drop in NOx e m ission s, w hic h tion temperature intermediate between metha-

are typically quite high in gas turbines. Metha- no l and d is t i l la tes, shou ld ach ieve somewhat

nol has achieved 76-percent reductions in NOX smalIer reductions.

emissions in large turbines because it has a sig-

nificantly lower combustion temperature than ‘2JdrVlS, op clt



Chapter

ENERGY BALANCES FOR

ALCOHOL FUELS



Chapter 11.-ENERGY BALANCES FOR ALCOHOL FUELS

Page Page Ethanol From Grains and Sugar Crops.... . . . . . . 219 66. Net Displacement of Premium Fuels FromMethanol and Ethanol From Wood, Grasses, and Various Feedstocks and Two End Uses. . . . .221

crop Residues q q q q q q q q q q q q q q q q q 222 67. Net Displacement of Premium Fuels WithGeneral Considerations . . . . . . . . . . . . . . . . . . . . 223 Alcohol Production From Various Feedstocks

and Two End Uses . . . . . . . . . . . . . . . . .. ..22268. Net Displacement of Premium Fuel perTABLES Dry Ton of Wood for Various Uses. . . . . . . . 222

Page

65. Energy Balance of Gasohol From Corn: Oiland Natural Gas Used and Displaced. .. ...220

I

I



Chapter 11

ENERGY BALANCES FOR ALCOHOL FUELS

The energy objective of using alcohol fuels

from biomass is the displacement of foreign oil

and gas with domestic synthetic fuels. The ef-

fectiveness of a fuel alcohol program depends

on the energy consumed in growing and har-

vest ing the feedstock and conver t ing i t in to

alcohol, the type of fuel used in the conversion

process, and the use of the alcohol.

The major sources of biomass alcohol fuels

are grains, sugar crops, wood, grasses, and

crop residues. Ethanol from grains and sugar

crops is considered first, including a compar-

ison of various feedstocks and end uses. Meth-

anol and ethanol from the other feedstocks are

then considered, and the use of these feed-

stocks directly as fuels is compared with the

p roduc t ion o f a l coho ls f rom them. F ina l l y ,

some general considerations about the energy

balance of these fuels are given.

Ethanol From Grains and Sugar Crops

Corn is current ly a pr inc ipa l feedstock for

ethanol production, but other grains and sugar

crops could also be used. The energy balance

for gasohol from corn is discussed in detail

below, followed by a summary of the energy

balance for various possible feedstocks and

for use of the ethanol either as an octane

booster or as a standalone fuel.

For each gallon of ethanol derived from

corn, farming and grain drying consume, on

the average, the energy equivalent of 0.29 gal

of gasoline’ in the form of oil (for fuel andpetrochemicals) and natural gas (for nitrogen

fertilizers). (See ch. 3 in pt. l.) The exact

amount will vary with farming practices (e. g.,irrigation) and yields. I n general, however, the

farming energy input per gallon of ethanol pro-

duced will increase when the farmland is of

poorer quality (e. g., setaside acreage) and/or in

dryer or colder climates (i.e., most of the

western half of the country, excluding Hawaii).

The type of fuel used in the distillation proc-

ess is perhaps the most important factor in de-

termining the displacement potential of etha-

q Some authors have Included the energy used to manufacture

farming equipment and the materials from which they are madeas part of the farm energy inputs However, for consistency one

should aIso Include, as a credit, the energy used in manufactur-

ing the goods that would have been exported to pay for import-

ing the 011 displaced by the ethanol Because of the uncertainty

in these factors, and the fact that they are relatively small, they

are not incIuded in the energy balance caIcuIations

nol. Even under the most favorable circum-

stances, distillery energy consumption is sig-

nificant. The distillery producing most of the

fuel ethanol used today reportedly consumes

0.25 gal of gasoline equivalent (0.24 in the

form of natural gas) per gallon of ethanol pro-

duced. 1 This number, however, involves some

arbitrary decisions about what energy inputs

shouId be attributed to the faciIity’s food-proc-

essing operations. Total processing energy in-

puts in this plant amount to about 0.55 gal of

gasoline equivalent per gallon of ethanol (see

ch. 7).

Energy-efficient standalone fuel ethanol dis-

tilleries would consume the equivalent ofabout 0.45 gal of gasoline per gal Ion of ethanol

produced (see ch. 7). Because the energy con-

sumption of distilleries is not Iikely to be insig-

nificant in relation to the alcohol produced in

the foreseeable future, it is essential that dis-

tilleries use abundant or renewable domestic

energy sources such as coal, biomass, and/or

solar heat or obtain their heat from sources

that would otherwise be wasted. Reliance on

these fuels would reduce the total use of oil

and gas at the distillery to insignificant levels.

‘Archer Dantels Mtdland Co , Decatur, III , “Update of Domes-

tic Crude C)ll Entitlements, Application for Petroleum Substi-

tutes, ” ERA-O 1, submitted to the Department of Energy, May 17,

1979

21 9




The a mount o f petroleum d isplac ed by etha -

nol fuel also depends on the manner in which

it is used. As a standalone fuel, each gallon of

e thanol d isp laces about 0 .65 ga l o f gaso l ine

equivalent. As an additive in gasohol, each gal-

lon of ethanol displaces about 0.8 (± 0.2) galof gasoline. * (See ch. 10. ) If the oil refinery pro-

duces a lower grade of gasoline to take advan-tage of the octane-boosting properties of etha-

nol, up to 0.4 gal of gasoline energy equivalent

can be saved in refinery processing energy (see

ch. 10) for each gallon of ethanol used.

Addit ional energy savings are achieved by

us ing the byp roduc t d i s t i l l e rs ’ g ra in as an

animal feed . To the e xtent tha t crop p rod uc-

tion is displaced by this animal feed substitute,

the energy required to grow the feed crop is

displaced.

Ta b le 65 summ a rizes the oil a nd na tural ga s

used and displaced for the entire gasohol fuelc yc le. The energy is expressed as gal lons of

gasoline energy equivalent for each ga l lon o f

ethanol produced and used in gasohol (i. e., 1.0

in the table represents 117,000 Btu/gal of eth-

anol, 0.5 represents 58,500 Btu/gal of ethanol,

etc.) The th ree c a ses p resente d c orrespo nd to:

1) two ways to calculate the present situation,

2) future production of ethanol from the less

productive land that can be brought into crop

production and using coal as a disti l lery fuel,

*The greater displacement results from the alcohol’s Ieaning

effect

a nd 3) the same as (2) except that the octane of

the gasoline is lowered to exactly compensate

for etha nol’s oc ta ne-b oo sting p rope rties. They

result in net displacements of: 1 ) from zero to

one- th i rd ga l , 2 ) about one-ha l f ga l , and 3)

slightly less than 1 gal of gasoline and natural

gas equivalent per gallon of ethanol used.

In a l l , the to ta l d isp lacement o f premium

fuels (oil and natural gas) achieved per gallon

o f e thano l can be near l y 1 ga l o f gaso l i ne

equ iva len t per gallon of ethanol if petroleum

and natural gas are not used to fuel ethanol

distilleries and 2) lower octane gasoline is used

in gasohol blends. Failure to take these steps,

however, can result in the fuel cycle consum-

ing sl ightly m o r e o i l a n d n a tu r a l g a s th a n i t

displaces leading to a net increase in oil and

gas consumption with ethanol production and

use. This is th e situa tion th a t is a llud e d to in

most debates over gasohol ’s energy balance,

but i t is a si tuation that can be avoided with

appropriate legislation.

Never the less i n the mos t favo rab le case

(case 3) and with an energy-efficient disti l lery,

the ra t i o o f to ta l ene rgy d i sp laced to to ta l

energy consumed is 1.5 ( ± 0.4), i.e., the energy

balance is positive (a ratio greater than 1). And

if the feedstocks are derived from more pro-

d u c t i v e f a r m l a n d , o r l o c a l c o n d i t i o n s a l l o w

energy savings at the distillery, e.g., not having

to dry the disti l lers’ grain, then the balance is

even more favorable. Al ternatively, an energy

Table 65.–Energy Balance of Gasohol From Corn: Oil and Natural Gas Used(+) and Displaced ( - )(in gallons of gasoline equivalent per gallon of ethanol produced and useda)

Set-aside and potential cropland

PresentCoal-fired distillery and

lowering of gasolineEntire plant Ethanol only Coal-fired distillery octane Uncertainty

Farming. . . . . . . . . . . . . . . . . . . . . 0 . 3b 0 . 3b

0.4c 0.4

C

?0.15Distillery . . . . . . . . . . . . . . . . . . . . 0.55 0.24 0

eOe

Distillery byproduct . . . . . . . . . . .

—

- 0 . 0 9 d o - 0 . 0 9d –0 .09d±0.03

Automobile. . . . . . . . . . . . . . . . . . . - 0 . 8 - 0 . 8 - 0 . 8 - 0 . 8 ± 0 .2Oil refinery. . . . . . . . . . . . . . . . . . . — — — - 0 . 4 ± 0.2

Total. . . . . . . . . . . . . . . . . . . . . . - 0 . 0 - 0 . 3 - 0 . 5 - 0 . 9 * 0 . 3

aLower heat content Of gasoline and ethanol taken to be 117,000 Btu/gal and 76,000 Btu/gal, resPectlve&bo 16 as nitrogen ferflhzer (from natural gas) and 0.13 tTI05tly as Petroleum ProductscEQlmated “nce~alnly of tO 15, assumes 75% of the yield achievable on avera9e cropland

dBa5~ on soy~an ‘Ultlvatlon and ~rushlng energy The byproduct of 1 gal of ethanol from corn displaces 12 lb of crushed soybeans, whtch requires 009 gal Of gasoline eqUIValenf tO produce private COM-

murrlcatlon with R Thomas, Van Arsdall, National Council of Farmer Cooperatese

55,

000BIU Ot COaI per gallon of ethanol

SOURCE Offtce of Technology Assessment



Ch. 11-Energy Balances for Alcohol Fuels q 221

cred i t cou ld be taken for the crop res idues,

which would also improve the calculated bal-

anc e. This ge neral app roa c h to the ene rgy b al-

ance, however, does not consider the different

values of Iiquid versus solid fuels.

The uncertainty factor in table 65 of ± 0.3

gal of gasoline per ga l lon o f e thanol is duepr imar i l y to i nhe ren t d i f fe rences in fa rm ing

practices and yields, errors in fuel eff ic iency

measurements, uncer ta in t ies in o i l re f inery

savings, and the magni fy ing e f fect on these

errors of the low (10 percent) ethanol content

of g asohol. These fa c tors ma ke mo re p rec ise

estimates unlikely in the near term.

Not only does the farming energy used for

grain or sugar crop production vary consider-

ab ly from State to State , but a lso the ave rag e

energy usage d isp lays some d i f fe rences be-

tween the various feedstocks. A more signifi-cant difference arises, however, between use

of the ethanol as an octane-boosting additive

to gasoline and as a standalone fuel, e.g., in

diesel tractors or for grain drying. As an oc-

tane-boosting additive, each gallon of ethanol

displaces up to 1.2 gal o f g a s o l i n e e n e r g y

equ iva len t i n the au tomob i le and a t the re -

finery (see table 65). * As a standalone fuel,

however, the displacement at the end use is

only 0.65 to 0.8 gal of gasoline energy equiv-

alent per gallon of ethanol.**

Ta b le 66 summ a rizes the net d isp lac em ent

o f p remium fue ls (o i l and na tu ra l gas ) fo r

various feedstocks and the two end uses. I n

each case it was assumed that the feedstocks

would be grown on marginal cropland with

yields that are 75 percent of those obtained on

average U.S. cropland.

The striking feature displayed in table 66 is

that use of ethanol as a standalone fuel is con-

siderably less eff ic ient in displacing premium

fuels than use of it as an octane-boosting ad-

ditive. In some cases, e.g., with grain sorghum

a n d i n a r e a s w i th p o o r y i e l d s o f t h e o th e r

*O 4 gal of gasoline equivalent IS due to the octam-boosting

properties of ethanol and () 15 gal 15 due to the leaning effect of

the a Icohol

q * Used as a standalone fuel in spark-ignition engines, alcohol-

fueled engines can have a 20 percent higher thermal efflclencv

than their gasollne-fuelwf counterparts (see ch 10)

Table 66.–Net Displacement of Premium Fuels (oil andnatural gas) From Various Feedstocks and Two End Uses

(energy expressed as gallons of gasoline equivalent per gallon

of ethanol produced and useda)

Ethanol used as an octane-boosting a dditive t o Ethanol used as a

Feedstock gasolineb standalone fuelc

Corn . . . . . . . . . . . . 0.9 0.4Grain sorghum . . . 0.7 0.1Spring wheat . . . . . . 1.0 0.5Oats. ., 1.0 0.5Barley ... ., ., . 1,0 0.4S u g a r c a n e 0.9 0.3

%ssut-mflg lower fl@ content of gasoline and ethanol to be 117000 Btu/gal and 76000 Btu/gal

respectwely, crops grown on margmal cropland wlfh yields of 75 percent of average croplandyields, distillers’ gram energy credts as In table 65 for all grams and no credit for sugars, dlst[l-Iers fueled with nonpremmm fuels, nahonal average energy Inputs S Barber et al The Po-tential of Producing Energy From Agriculture. contractor report 10 OTAbUncerfamty * O 3CUncertamfy t O 2

SOURCE Off Ice of Technology Assessment

grains, ethanol produced from grains and usedas a standalone fuel (e. g., onfarm as a diesel

fue l subst i tu te) may actua l ly lead to an in-

creased use of premium fuels, even if nonpre-

mium fuels are used in the disti l Iery. Conse-

quently, caution should be exercised if onfarm

ethanol production and use are encouraged as

a means of reducing the U.S. d e p e n d e n c e o n

imported fuels.

Fur thermore, the agr icu l tura l system is so

complex and interconnected that i t is vi r tual ly

impossible to ensure that large levels of grain

production for standalone ethanol fuel would

not lead to a net increase in premium fuel con-

sum p tion. Two exa mp les illustrat e this p oint. If

grain sorghum from Nebraska is used as an eth-

anol feedstock (to produce a standalone fuel),

the net displacement of premium fuels per gal-

lon of ethanol is similar to the national aver-

age for corn. A secondary effect of this, how-

ever, could be an increase in grain sorghum

produc tion on ma rginal crop land in Texas, and

the increased energy requ i red to grow th is

grain sorghum could more than negate the fuel

d isp lac ed b y the Ne b raska sorgh um. Simila rly,

ethanol production from corn could raise corn

prices and lead to some shift from corn to

grain sorghum as an animal feed. Depending

on where the shifts occurred, U.S. p r e m i u m

fuel consumption could either increase or de-

crease as a resuIt.



Ch. 11-Energy Balances for Alcohol Fuels q 223

Care should be exercised when interpreting boosting additives can be nearly as efficient in

tab le 68. The e thano l yields (pe r ton of wo od ) d isp lac ing premium fue ls as the d i rect com-

and the energy that wil l be required by wood- bustion or airblown gasification of wood. On

to-ethanol distilleries are still highly uncertain. the o ther hand, i f the a lcoho ls are used as

Nevertheless, this table does display the gener- standalone fuels, the premium fuels displace-

al feature that alcohol fuels used as octane- ment is considerably smaller.

General Considerations

The results p resen te d in ta b les 65 throug h 68

a re b a sed on O TA’ s estimate s of a verag e va l-

ues for the energy consumed and displaced by

the va riou s fee d sto c ks. The se fig ures, how eve r,

cannot be taken too l i terally since local vari-

at ions and changing circumstances can inf lu-

enc e th e resu l ts. Two of the mo re imp or tant

factors which inf luence the resul ts–the ener-

gy required to obtain the feedstock and the

end use of the fuel — are discussed below.

The ene rgy nee de d to grow , ha rvest , and

transport the feedstocks varies considerably,

depending on a number of site-specific factors

such as quantity of available biomass per acre,

terrain, soi l productiv i ty, p lant type, harvest-

ing techniques, etc. General ly, however, fac-

tors that increase the energy requirements also

increase the costs. For example, where the

quanti ty of col lectable crop residues per acre

is small both the energy used and the cost (per

to n of residue) will be higher than the average.

The e c on om ics wi l l the refore usua l ly dic ta te

that— locally, at least—the more energy-effi-

cient source of a given feedstock be used.

As the use of bioenergy increases, however,

the tendency wi l l be to move to less energy-

efficient sources of feedstocks, and large Gov-

e rnmen t i ncen t i ves cou ld l ead to the use o f

b i o e n e r g y th a t a c tu a l l y i n c r e a s e s d o m e s t i c

c onsump tion of p rem ium fuels. The d a nge r of

this is minimal with wood, but somewhat great-

er for grasses and crop residues due to the

larger amount of energy needed to grow and/or

c ollec t them . The d ang er is even great er when

grain or sugar feedstocks are used for the pro-

duction of standalone fuel ethanol.

Another important factor in the energy bal-

ance is the end use of the alcohol fuel. As has

been emphasized above, there is a significant

increase in the displacement of premium fuels

when the alcohol is used as an octane-boosting

additive. In the 1980’s, however, there could be

an increased use of automobile engines thatdo not require high-octane fuels and that have

automatic carburetor adjustment to maintain

the proper air to fuel ratio (see ch. 10). With

these engines, the octane-boosting propert ies

of the alcohols are essentially irrelevant. Con-

sequently, i f the automobile fleet is gradually

converted in th is way, there wi l l be a gradual

reduction in the fuel d isplacement per gal lon

of alcohol, unti l the energy balances derived

for standalone fuels p ertain. The sa me c onc lu-

s ion wou ld ho ld i f o i l re f i ne r ies conver t to

more energy-efficient processes for producing

high-octane gasoline.

A n o th e r c o n s e q u e n c e o f t h e s e p o s s i b l e

changes would be to increase the importance

of the energy required to obtain the feedstock.

For example, if ethanol only displaces as much

premium fue l as ind icated when used as a

s tanda lone fue l , then , as men t ioned above ,

cultivating and harvesting the grains or sugar

crops used as feedstocks may require more

premium fuel than is displaced by the ethanol.

The d a ng er o f th is is c on side rab ly less fo r

grasses and crop residues and virtually nonex-

is tent for forest wood used as feedstock for

alcohol production.



Chapter 12

CHEMICALS FROM BIOMASS

Introduction

Biomass is used as a source of several indus-

trial chemicals, including dimethyl sulphoxide,

rayons, vanillin, tall oil, paint solvents, tannins,

and specialty chemicals such as alkaloids and

essential oils. Biom a ss is a lso the sou rce o f fur-

fural which is used to produce resins and adhe-

sives and can be used in the production of ny-

ion. ’ Aside from paper production, biomass

currently is the source of cellulose acetates

and nitrates and other cellulose derivatives (4

billion lb annual ly) . Other chemica ls inc lude

tall oil resin and fat acid, Iignosulfonate chem-

icals, Kraft Iignin, bark chemicals, various seed

oils, and many more. Every petroleum-derived

chemica l current ly be ing used could be p ro -duced from biomass and nonpetroleum miner-

als, but some (e. g., carbon disulphide) would

require rather circuitous synthesis routes.

In the future biomass-derived chemicals

could play an increasing ro le in the petro-

c hem ica l industr ies. The ec on om ic de c isions

to use or not to use biomass will be based on

an assessmen t o f the ove ra l l p rocess f rom

feedstock to end product and i t wi l l probably

‘ I S Goldstein, “Potential for Converting Wood Into Plastics, ”S( /ence, vol 189, p 847, 1975

i nvo lve cons ide ra t i on o f va r ious a l te rna t i ve

synthe sis routes in mo st c ases. At present, how-

ever , too l i t t le in format ion is ava i lab le about

the relative merits of biomass-versus coal-de-

rived chemicals to expect widespread, new in-

dustrial commitments to biomass chemicals in

the nea r fu ture . Th is unc er ta in ty de pe nd s as

much on uncer ta in t ies surrounding the costs

and possibilities of coal syntheses as on those

surrounding biomass chemicals. Continued re-

search into both options is needed to resolve

the problem and it is l ikely (as has been the

case in the past) that a mix of feedstocks will

result.

B iomass-der ived chemica ls can be d iv idedinto two major areas: 1 ) those in which the

plant has performed a major part of the syn-

thesis and 2) those in which chemical industry

feedstocks are derived by chemical synthesis

from the more abundant biomass resources

suc h a s wo od , grasses, and c rop residue s. Som e

examp les of ea ch type are g iven b elow. The

possibi l i t ies are so enormous, only an incom-

plete sampling can be given here. A thorough

ana lys i s o f the op t ions fo r chemica ls f rom

biomass is beyond the scope of this study.

Chemicals Synthesized by Plants

Se v e ra l p l a n t sp e c ie s p r o d u c e re la t i ve l y h a ve p ro p e rly p la c e d c h em ic a l g ro up s w h ic h

large quantities of chemicals that can be used are susceptible to chemical attack so that they

to p r o d u c e p l a st ic s, p la st ic i ze r s, l u b ric a n ts, c a n b e re a d ily c on ve rted to th e ne e d ed ind u s-

coat ing products (e . g . , pa in ts) , and var ious trial c he mic a ls. The re is a lso t he pos s ib i l i t y o f

chemicals that can serve as intermediates in us ing b io log ica l Iy der ived chemica ls to pro-

the syn theses used f o r n u m e ro u s in d u st ria l d u c e p ro d u c ts ( su c h a s p la st ic s) wh ic h wo uld

products. 2be expected to have simi lar propert ies to the

The b iolog ica lly synthe sized c he mic a ls tha tproducts currently produced. For example, ny-

lon cou ld be made f rom ac ids and aminesare most easily

usedin the chemical industries

other than the six carbon acids and amines cur-are those that are either: 1 ) identical to existing

feedstock or intermediate chemicals, or 2 )rently used for nylon synthesis.

‘1 H Prlnc en, ‘ Potential Wealth Is New Crops . Research ancl

llevf~l(jpm[~nt ,“ ( ro p l?e~ource} ( N e w Y o r k Academic Pres$, S o m e p l a n t species producin g various1’977) c l a s s e s o f c h e m i c a l s a r e s h o w n in t a b le s 6 9

227



228 q Vol. I I -Energy From Bio logica l Processes

through 72. (Note that these l ists are incom-

plete and used only to i l lustrate some possi -

bilities.) Included are the following types:

q

q

q

l o n g - c h a i n f a t t y a c i d s w h i c h m i g h t b e

used for the product ion o f po lymers, lu -

bricants, and plasticizers;

hydroxy fatty acids which could displacethe imported castor oil currently used as a

supply of these fatty acids;

epoxy fatty acids which may be useful in

plastics and coating materials; and

Table 69.–Species With Long-Chain Fatty Acids in Seed Oil

Component inCommon name Species triglyceride oil

Crambe. . . . . . . . Crambe abyssinica 60% C22

Money plant . . . . Lunaria annua 40% C22, 20% C24

Meadowfoam. Limnanthes alba 95% C22 + C20

Selenia . . . . . . . Selenia grandis 58% C22

— Leavenworthia alabamica 50 % C22

Marshallia. . . . . . . . Marshallia caespitosa 44% C22

SOURCE : L. H. Prlncen, ‘‘Potenllal Wealth in New Crops Research and Development, Crop Re-sources (New York Academic Press, Inc. ), 1977

Table 70.–SpeciesWith Hydroxy and Keto Fatty Acids

Component inCommon name Species triglyceride oil

B ladde rpod .Consessi

H o l a r r h e n a .B i t t e r c r e s s . ,

Thistle . . . . . . .Bladderpod . . . .

BlueeyedCapemarigold. .

Myrtle Coriaria. . .

Lesquerella gracilis

Holarrhena antidysentericaCardamine impatiens

Chamaepeuce afraLesquerella densipila

Dimorphotheca sinuata

Coriaria myrtifolia

Cuspedaria pterocarpa

14-OH-C 20(70%)

9-OH-C, 8 (70%)Dihydroxy C22and C24

(23%)Trihydroxy C18(35%)12-OH-C 18diene (50%)

9-OH-C 18 conj. diene(67%)

13-OH-C18 conj. diene(65%)

Keto acids (25%)

SOURCE L H Prmcen, ‘‘Polenhal Wealth m New Crops Research and Oevelopmenl,Crop /?e.

sources (New York Academic Press, Inc ), 1977

Table 71 .–Potential Sources of Epoxy Fatty Acids

Epoxy acidCommon name Species content,%

Kinkaoil ironweed. . . . Vernonia anthelmintica 68-75%Euphorbia Euphorbia Iagascae 60-70Stokesia Stokesia Iaevis 75

— . . . . . . . Cephalocroton pueschellii 67 — Erlangea tomentosa 50

Hartleaf Christmasbush Alchornea cordifolia 50 (c20) — Schlectendalia Iuzulaefolia 45

SOURCE L H Prmcen, ‘‘Potenllal Wealth In New Crops Research and Development, Crop Re-


Table 72.–Sources of Conjugated Unsaturates

Common name Species Type of saturation

Common valeriana. . . . . . Valeriana officinalis 40% 9,11,13Potmarigold colendula . . . Calendula officinalis 55% 8,10,12Spurvalerian centrathus. .Centranthus macrosiphon 65% 9,11,13Snapweed . . . . . . . . . . . Impatiens edgeworthii 60% 9,11,13,15Blueeyed Capemarigold . Dimorphotheca sinuata 60% 10,12

( + hydroxy)Myrtle Coriaria . . . . . . . . Coriaria myrtifolia 65% 9,11

(+ hydroxy)

SOURCE L H Prmcen, ‘‘Potential Wealth m New Crops” Research and Development, Crop l?e-

q


conjugated unsaturates potential ly useful

as intermediates in the synthesis of vari -

ous industria l prod uc ts. (These c an a lso b e

obta ined f rom structura l modi f ica t ion o f

soybean and linseed fatty acids.3).

Othe r poss ib le new sources o f chemica ls

and materials include natural rubber from gua-

yule (Parthenium argentaturn),4 and possibly jo-

joba (Sirnmo ndia c h inensis) a nd pa pe r pu lp

f r o m k e n a f (H ib iscus cannab inus) .5 So m e o f

these plants have also received considerable

attention because i t may be possible to grow

them on marginal lands or land where the irri-

gation water is insufficient to support conven-

tional crops (see ch. 4). It is risky, however, to

extrapo la te unambiguous conclus ions about

their economic viabi l i ty from incomplete data

on the cultivation. In many cases they would

a lso compe te wi th food p roduc t ion fo r the

ava i lab le farmland. Never the less, cont inued

screening of plant species together with cul-

t ivation tests should provide numerous addi-

t i o n a l o p t i o n s fo r t h e c u l t i v a t i o n o f c r o p s

yielding chemicals for industrial use.

Another type of chemical synthesis involves

the use of specific bacteria, molds, or yeasts to

synthesize the desired chemicals or substance.

Commerc ia l product ion o f a lcoho l beverages

by fermentation is one example. Mutant bac-

te r i a d e s i g n e d to p r o d u c e i n s u l i n o r o th e r

‘W j De Jarlals, L E Cast, and j C Cowan, / Am , Oi/ Chem,

SOC., VOI 50, P 18, 1973

‘K E Foster, “A Sociotechnlcal Survey

ofEluyule

Rubber Com-mercla Iizat Ion, ” report to the National Science Foundation,

Dlvlslon of Policy Research and Analysis, grant No PRA

78-11632, April 1979

‘M O f3agby, “Kenaf A Practical Fiber Resource, ” TAPP/Press Report Non-Wood Plant Fiber Pulping Process Report, No

8, p 175, Atlanta, Ca , 1977



Ch. 12—Chemicals From Biomass . 229

drugs is another. ’ 7 Furthermore, other basic

biochemical processes such as the reduction

of nitrates to ammonia may also be used even-

t u a l l y .8

“Pe~r( e Wright, 1 Ime for Bug Valley, ” New Sc/ent/sL p 27,Julv 5, 1979

“’Where Genctlc Englneerlng Will Change Industry, ” f3usJness

Wee&, p 160, Oct 22, 1979

‘P Candan, C Manzano, and M Losada, “Bloconverslon of

Light Into Chemical Energy Through Reduction With Water ofNitrate to Ammonia, ” Nature, VOI 262, p 715, 1976

Further study into the details of photosyn-

thesis, the biochemistry of plants, and molecu-

lar genetics could lead to the development of

other plants or micro-organisms that could syn-

thesize specific, predetermined chemicals. The

options seem enormous at this stage of devel-

opment, but considerab le add i t iona l R&D is

needed be fo re the fu l l po ten t ia l o f th i s ap -proach can be evaluated.

Chemical Synthesis From Lignocellulose

The sec ond ma jor area o f c hem ic a ls f rom

biomass involves using the abundant biomass

resources of wood, grasses, and crop residues

(I ignocel lu losic materia l) to synthesize large-

volume chemical feedstocks, which are con-

verted in the chemical industry to a wide varie-

ty of more complex chemicals and materia ls.

The large (p olyme r) mo lec ules in lig no c ellulo-

s i c ma te r ia l s a re conver ted to the des i red

chemica l feeds tocks e i the r : 1 ) by chemica l

me a ns or 2) with hea t o r mic row av es. The d is-

t inct ion between these two approaches, how-

ever, is not always clear cut.

The c hemica l means include trea tment with

acids, alkaline chemicals, and various bacteri-

al processes. Pretreatments also often involve

some heating and mechanical grinding (see ch.

8). The three b a sic p olyme rs– Iignin, c ellulose,and hemicellulose — are reduced to sugars and

var ious benzene-based (so ca l led aromat ic)

chemicals, which can be used to synthesize the

chemical feedstocks by rather direct and eff i -

cient chemical synthesis or fermentation (see

figure 38). Some of the ma jor pe troc hemica l

feedstocks that can be produced in th is way

are shown in table 73, together with the quan-

tities of these chemicals (derived mostly from

petroleum) which were used by the chemical

industries in 1974.

The q uan t i t ies o f wo od tha t w ou ld b e re -q uired to sa tisfy the 1974 U.S. de ma nd for p las-

t ic s, synth et ic f ibe rs, a n d s y n th e t i c r u b b e r

from the above chemical feedstocks are shown

in table 74 for the various types of products.

The se e stima tes we re de rived b y Go ldste in’

using optimistic assumptions about the yields

of the sugars- and benzene-based chemicals

from wood. Obtaining these sugars- and ben-

zene-based compounds from wood is currently

the sub ject of c onsiderab le R&D. (See c h. 8.)

The y ie lds for the o ther c hem ica l rea ct ions

were based on establ ished experimental and

industrial data.

About 95 percent o f these synthet ic po ly-

mers (plastics, synthetic f ibers, and synthetic

rubbers) can be derived from wood or other

I i gnoce l l u los i c ma te r ia l s , a l though the c i r -

cui tous synthesis route required for some of

them might make such processes uneconomic

at this time. I n al 1, SIightly less than 60 million

d ry tons (ab ou t 1 Quad) o f wo od pe r yea r

could supply 95 percent of these synthetic pol-

ymer needs; and the ratio of cellulose to Iigninrequired (2:1) would be about the same as their

natural ab unda nce in wo od . This qua ntity of

wood is re la t ive ly modest in compar ison to

OTA est imate s o f the qu ant i t ies tha t c a n b e

made available, and in all cases it serves as a

d i rect subst i tu te for chemica ls der ived f rom

fossil fuels (mostly oil and natural gas). About

th ree to f i ve t imes as much wood wou ld be

n e e d e d t o s u p p l y a l l p e t r o c h e m i c a l n e e d s

using more or less establ ished chemical syn-

thesis routes,10 and again there appears to be

no technical barrier to supplying these quan-

tities of wood. In both cases, however, addi-

‘Goldsteln, op clt

1 “1 S Goldstein, Department of Wood and Paper Sc Ien( e,

No r th Carolln~ State Unlverslty, Raleigh, N C , prlvdte communi-

cdtlon, 1980



230 . Vol. I/—Energy From Biological Processes

Figure 38.—Synthesis Routes for Converting Lignocellulose Into Select Chemical Feedstocks

HydrolysisHydrogenation Phenolic C 6H 50 H C 6H 6

LigninPyrolysis Benzene

SOURCE: 1. S. Goldstein, “Chemicals From Lignocellulose,” Biotechnol. and Bioen. Symp. No. 6, (New York: John Wiley and Sons, Inc., 1976), p. 293.



Ch. 12—Chemicals From Biomass . 231

Table 73.–Major Petrochemicals That Can Be SynthesizedFrom Lignocellulose

1974 U.S. production(in billions of pounds)

Total Iignocellulose Ammonia ., . . . . . . . . . ., 31.4Methanol ., ., . . . . . . . . 6.9

Hemicellulose Ethanol. ., ., ., ... ., ., ., . . 2.0

cellulose Ethanol, . . . . . ., ., ., ... ., 2.0Ethylene . . . . . . . . . . 23,5Butadiene ., . . 3.7

Lignin Phenol . . . . . ., ., ... 2.3Benzene . . 11.1

SOURCE: From l. S. Goldstein Chemicals From Lignocellulose in Biotechnology and Bioener- gy Symposium No 6( John Wiley&Sons Inc. p 293 1976)

tional energy would be needed to provide heat

for the syntheses; and, in some cases, this is

more than the energy content of the chemical

f e e d s t o c k .11 As of 1976, the petrochemical in -

dustry consumed 1.2 Quads/yr of oil and natu-

ral gas for fuel and 2.3 Q u a d s / y r f o r f e e d -

sto c ks. 12

Another approach to chemicals from l igno-

cellulose involves heat, partial combustion, or

the use of microwave radiation to break the

natural polymers into smal ler molecules sui t-

able for the synthesis. Biogas derived from the

anaerobic digestion of biomass could also be

used in some of these processes, but the yields

are Iikely to be lower than for the more direct

p roc esses. Som e p ossible synthet ic route s a reshown in figure 39.

‘1 “ BIg Future for SVnthetlcs, ” Science, VOI 208, p 576, May 9,

1980

12G B Hegeman, Report to th e Petrochemical Energy G r o u p on 1976 Petrochem/ca/ /ndustry Prof//e (Cambridge, Mass Ar-thur D Little, Inc , June 28, 1977)

Table 74.–1974 Production of Plastics, Synthetic Fibers,and Rubber, and Estimated Lignocellulose

Raw Material Base Required

LignocelluloseProduction required a

Material (103 tons) (1 03tons)

Plastics

Thermosetting resinsEpoxies . . . . . . . . . . . . . . . . . .Polyesters ., ., .,Urea . . . . . . . . . . . . . . . . . . . .Melamine. . . . . . . . . . . . . . . . .Phenolic and other tar-acid resins

Thermoplastic resinsPolyamide . . . . . . . . . . . . . . . .Polyethylene

Low density. . . . . . . . .High density . . . .

Polypropylene and copolymersStyrene and copolymers, . ,P o l y v i n y l c h l o r i d e . ,Other vinyl resins . . . . . . . . . . .

125455420

80670

100

2,9851,4201,1252,5052,425

175

T o t a l p l a s t i c s . . , 12,485

Synthetic fibers CellulosicRayon . . . . . . . . . . . . . . . . . . .Acetate ... . . ... .,

NoncellulosicNylon. . . . . . . . . . . . . . .Acrylic, . . . . . . ... . .Polyester . . . . . . . . . . . . . .Olefin . . . . . . . . . . . . . . . . . . .

Total noncellulosic fibers,

Synthetic rubber Styrene-butadiene . . . . . . .

Butyl. . . . . . . . . . . . . . . . . . . . .Nitrile . . . . . . . . . . . . . . . . . . . .Polybutadiene . . . . . . . . . . . . . . .P o l y i s o p r e n e

E t h y l e n e - p r o p y l e n e . . ,Neoprene and others. . . . . . .

Total synthetic rubber. . . .

Total plastics, noncellulosic fibers,and rubber. . . . .

Obtainable from IignocelluloseCellulose drived (C). ., . . . . .Lignin derived (L) . . . . . . .

410190

1,065320

1,500230

3,115

1,615

18095

360100

140280

2,770

18,37017,490

355 (L)1,220 (L)

— —

1,915 (L)

285 (L)

11,940 (c)5,680 (C)4,500 (c)7,445 (L)4,225 (C)

440 (c)

— —

3,045 (L)640 (C)

4,020 (L)920 (C)

5,700 (c)1,920 (L)1,060 (C)

190 (c)2,120 (c)

—

825 (C) —

58,44538,240 (C)20,205 (L)

aEstlmated from Opllmlstlc approximate yields of monomers obtainable (C) cellulose derived (L)

hgmn derwed

SOURCE I S Goldstein. “Potential for Converrlng Wood Into Plasttcs, Science VO I 189, P

847, 1975




Figure 39.—Chemical Synthesis Involving Thermal Processes and Microwaves


The prod uction of amm onia’ 3 and methano l

from wo od c an be a cc omp lished with comme r-

cial technology (see ch. 7 for further details of

th e m e tha no l synt he sis). The Fisc he r Trop sc h

p roce ss i s c om me rc ia l in Sou t h A f r ic a (a l -

though the source of the synthesis gas is coal

ra the r tha n b iomss) . The e c ono mics o f the

processes other than methanol synthesis have

no t b ee n a ssessed b y OTA fo r this rep ort.

The ot he r proc esses yield ing va riou s c hem i-

c a ls a re c onside rab ly less d eve lope d . The

yields of some chemicals that have been pro-

duced in laboratory exper iments us ing rap idheating and gasification (pyrolysis) of various

1‘R W Rutherford and K Ruschln, “Product ion of AmmoniaSynthesis Ca$ From Wood Euel In Incfla, ” presented at a meeting

of the Institute of Chem Ica I E nglneers, London, Oct 11, 1949

types of biomass are shown in table 75. Pre-

sumably by learning more about pyrolysis, the

yields of select chemicals would be increased

to a level where it could be economical to ex-

tract that chemical from the gas. An example

might be the conceptual equation:

C 1 0H 1 4O 6- 3CO 2 + 3.5 C2H4

Wood Carbon dioxide Ethylene

(solid) (gas) (gas)

where 43 weight percent of the dry wood is

converted to ethylene (which is by far the Iarg-

est vo lume petrochemica l used for chemicalsynthesis in the world). If it becomes practical

to achieve relatively high (e. g., 30 weight per-

cen t ) y ie lds o f e thy lene , then th i s p rocess

could be competi t ive with petroleum-derived



Ch. 12—Chemicals From Biomass q 233

I

I I

I

1

I

I




References to Table 75

Antal, M. J., W. E. Edwards, H. C. Friedman, and F. E. Rogers, ‘‘A Study of the Steam Gasification of Organic Wastes, Environmental Protection AgencyUniversity grant No. R 804836010, final report, 1979.

Berkowitz-Mattuck, J, B. and T. Noguchi, “Pyrolysis of Untreated and APO-THPC Treated Cotton Cellulose During l-See. Exposure to Radiation Flux Lev-els of 5-25 cal/mc2 sec.1, J. App/ ied Po/ymer Sc ience , vol. 7, p. 709, 1963.

Brink, D. 1.., ‘ ‘Pyrolysis –Gasification–Combustion: A Process for Utilization of Plant Material, App lied Polymer Symp osium IVO. 28, p. 1377, 1976.Brink, D. L, and M. S. Massoudi, ‘‘A Flow Reactor Technique for the Study of Wood Pyrolysis. 1. Experimental, J. Fire and flammability T, p. 176, 1978.Diebold, J. P. and G. D. Smith, ‘‘Noncatalytic Conversion of Biomass to Gasoline, “ ASME paper No. 70-Sol-29, 1979.

Hileman, F. D., L. H. Wojeik, J. H. Futrell, and 1. N. Einhorn, ‘(Comparison of the Thermal Degradation Products of Cellulose and Douglas Fir Under Inertand Oxidative Environments, Therm a/ Uses and Properties o f Carbohydrates and LigninsSymposium, Shafizadek, Sarkenen, and Tillman, ed. (Aca-demic Press, 1976), p. 49.

Lewellen, P. C., W. A. Peters, and J. B. Howard, “Cellulose Pyrolysis Kinetics and Char Formation Mechanism, Sixteenth Symposium (International on Combustion (The Combustion Institute, 1976), p. 1471.

Lincoln, K. A., ‘‘Flash Vaporization of Solid Materials for Mass Spectrometry by Intense Thermal Radiation,na/ytica/ Chemistry, VOI 37, p. 541, 1965.Martin, S., “Diffusion-Controled Ignition of Cellulosic Materials by Intense Radiant Energy, ’ Tenth Symposium (/niernationa/) on Comb ustion (The Com-

bustion Institute, 1965), p. 877.P h S “P l i G ifi i f N C d B S P l i Li i AST R ’ Ad i Ch i t S i l 69 230