Summer 1993
U.S. Department of Energy
Bioenergy Feedstock Development Program at
Oak Ridge National Laboratory
Energy Crops Forum was published periodically by the Bioenergy
Feedstock Development Program, Environmental Sciences Division, Oak Ridge
National Laboratory, managed by UT-Battelle, LLC., for the U.S. Department of
Energy under Contract No. DE-AC05-00OR22725.
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Table of Contents
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Robin Graham; BFDP
Using biomass from energy crops for electric power plants or liquid fuel
conversion facilities will cause major shifts in the use of agricultural land.
Energy crops, like other crops, require agricultural-quality land for good
yields. As a rule of thumb, a 100 MW power plant operating at baseload capacity
(10,000 Btu/Kwh heat rate; 100% capacity) will require approximately 500,000
dry tons of biomass per year, or 100,000 acres of agricultural-quality land
dedicated to energy crops, provided the average delivered yield from that land
is 5 dry tons/acre/year. Liquid fuel facilities will also require large amounts
of biomass and, correspondingly, large acreages of energy crops.
The environmental effects of dedicating large acreages of cropland to energy
crop production will depend on the soil quality and slope of the land, the
conventional crops that are displaced, the landscape surrounding the energy
crops, and the management regime of the energy crops. If one assumes that
energy crops will be located where they can be procured at the least cost to a
power plant or liquid fuel facility and at the greatest profit to farmers, then
economics will determine the amount and type of land to be converted to energy
crop production. Thus, projecting the environmental impacts of energy crop
production requires an understanding of the economic factors that will
influence the location of energy crops.
An approach for projecting the probable environmental impacts of growing energy
crops at the regional scale is under development. The approach considers both
economic and environmental factors. A breakeven model is used to project where
energy crops could be grown least expensively (see Downing's
article below). A U.S. Department of Agriculture simulation model of crop
growth and soil processes is used to predict the environmental changes
associated with switching from conventional crops to energy crops.
To test this approach, an analysis of the probable environmental changes
(specifically erosion, evapotranspiration, nitrate in runoff, and phosphorous
fertilizer use) associated with growing switchgrass (Panicum virgatum)
is being conducted in two subregions within the Tennessee Valley Authority
region.
The analysis shows that switchgrass production will have different impacts in
each subregion as a result of differences in the initial land use and soil
conditions in the subregions. Erosion, evapotranspiration, and nitrate in
runoff are projected to decrease in both subregions as switchgrass displaces
the current crops. Phosphorous fertilizer applications are likely to increase
in one subregion but decrease in the other due to initial differences in the
types of conventional crops grown in each subregion. Overall, the predicted
changes portend an improvement in water quality and soil conservation in both
subregions with the production of switchgrass.
The results of this study should not be viewed as definitive or necessarily
reflective of what might be projected elsewhere. Each location will have unique
environmental and land use attributes that will affect both the economics and
environmental impacts of energy crop production. Furthermore, model projections
are only as good as the basic data that underlie them. Energy crops have not
been widely grown in many regions. More field studies are needed to
characterize both the energy crops themselves and their likely environmental
impact. Nonetheless, the model allows projections of at least the first-order
environmental changes that might accompany the introduction of energy crops
into a region.
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Roger K. Conway; Director, Office of Energy, U.S. Department of Agriculture,
Washington, D.C.
Development and implementation of the National Energy Policy Act, passage of the
Clean Air Act Amendments of 1990, and recent advances in science and technology
create expanding opportunities for liquid fuels derived from renewable
resources produced by America's farmers and foresters. The U.S. Department of
Agriculture (USDA) is committed to working with the Department of Energy (DOE),
the Environmental Protection Agency (EPA), and the private sector to accelerate
the development of markets for economically-competitive biofuels.
Our goal is to increase the use of biofuels made from domestic renewable farm
and forestry resources, thus creating jobs, economic activity, reducing
dependence on foreign oil, and reducing air pollution.
The objectives of the USDA Biofuels program are to: (1) increase the efficiency
of converting biomass to liquid fuels; (2) improve and expand feedstocks
available for conversion to liquid fuels; (3) develop high-value coproducts
form unused feedstock materials; (4) accelerate the identification and
demonstration of new conversion technology; and (5) expand market opportunities
for biofuels through the development of engine technology and fuel formulations
that maximize the environmental and technical benefits of biofuels.
Reprinted with permission from "Biographies & Abstracts," Forest Product
Society 47th Annual Meeting, June 20-23, 1993, Clearwater Beach, Florida.
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Mark Downing; BFDP
BFDP staff have developed a regional biomass feedstock supply model. The work,
done cooperatively with the Tennessee Valley Authority (TVA) and The University
of Tennessee, predicts the amount of dedicated biomass feedstock that could
potentially be produced in any of the counties in the Tennessee Valley region.
Using county level data on cropland and soils and projected energy crop yields
(5 dry tons/acre), the model projected the amount of land capable of supporting
energy crops (nearly 27 million acres in the region) and the cost and supply of
biomass from that land.
Results suggest that a breakeven farmgate price of at least $43/dry ton will be
needed to generate substantial supplies of feedstocks. At this price, 25
million dry tons/year might be grown. In reality, a farmer's decision to plant
or not plant energy crops would be more complex than a simple profitability
decision. The farmer would consider relative risk factors as well as farm level
constraints, time frames for production, and government programs. For this
study, however, the simple case of relative profitability was used because it
captures most of the cost and supply dynamics of producing biomass feedstocks
from energy crops.
The geographically specific information on woody biomass cost and supply is
being combined with information on the location, quantity, and cost of mill and
logging wood residues in a transportation network model of the TVA region as a
precursor to a geographic information system. The transportation network model
will be used to determine the least cost supply of wood to existing TVA
coal-fired plants that are being considered for cofiring. This will assist TVA
in determining which plants are most suited for cofiring and the associated
costs.
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Lynn Wright and Gregg Marland; BFDP
The United States has established a goal of stabilizing greenhouse gas emissions
at 1990 levels by the year 2000. Although energy conservation is likely to
provide the most immediate reductions in CO2 emissions, biomass
energy is one of the few energy production options currently available for
displacing fossil fuels. Several sources of biomass are available, but not all
offer the same level of environmental benefits.
Wastes and residues are potentially the most accessible source of biomass for
fuel within the next few years. The use of wastes and residues can be very
economical and environmentally beneficial. If left to decay, CO2 (and
possibly methane) is released to the atmosphere. When wastes and residues
displace fossil fuels, CO2 emissions are still produced but the
fossil carbon stays in the ground. Drawbacks include the potential for
undesirable contaminants in the wastes and excessive removal of crop residues
from the fields. It is also likely that the rate of residue use might exceed
the normal rate of decay. Recycling of the carbon into new growth, while
possible, is not assured.
Existing forest resources are another potential source of biomass. Stands that
are susceptible to fire hazard, disease, or decay would be good candidates as
are stands now being planted for carbon sequestration. Drawbacks include loss
of wildlife habitat, visual impacts, and soil erosion on sloping land. The
harvesting of mature trees results in an immediate loss of carbon that is not
quickly offset by new growth. Good forest management can, however, include
environmentally sound harvesting techniques and sustainable growth. Efficient
energy production may ultimately be the best use of some forest stands now
being planted for long-term carbon sequestration.
Dedicated energy crops grown on land depleted of soil carbon offer the most
environmentally beneficial and largest biomass resource for displacing fossil
fuel use. While all the various types of energy crops being
considered--short-rotation woody crops (SRWC), perennial grasses, and annual
grasses--provide a positive net CO2 emission reduction benefit when
converted to energy, SRWC offers the greatest net carbon benefit. SRWC stands
provide some carbon sequestration benefit as well as a fossil fuel offset. When
established on previously cropped soils, both SRWC and perennial grasses can
increase the carbon stored in the soil as well as reduce soil erosion.
Using efficient conversion processes to maximize the amount of fossil fuel
displaced is extremely important for increasing the carbon benefits of all
biomass resources. Unfortunately, many biomass energy systems operating today
are highly inefficient. High efficiency steam plants that can be modified for
cofiring of wood and coal offer one opportunity for more efficient biomass use
by 2000. The Whole Tree Energy concept is another acceptable option but the
first such facility is yet to be built. Combined cycle gas turbines may be
available within 10-15 years.Given these limitations, how can biomass energy
systems assist the United States in meeting CO2 emission reduction
goals by the year 2000? The biomass energy option that would offer the greatest
CO2 reduction per unit of land area harvested, that of using SRWC in
high efficiency conversion to electricity, is limited by the 5-10 year required
growth period of the trees. To reduce 1990 CO2 levels by 3% by 2000
would require replacing 25,000 MWe of coal-fired electric power production with
biomass-based power production at a net conversion efficiency of 33% or better
and the immediate planting of at least 15 million acres of SRWC within 2 years.
While these efforts should be started, such a rapid deployment of new
technology is not feasible. The use of annual or perennial grasses as biomass
fuels could expand the planting window up to 6 years to meet year 2000 goals.
However, in either case, there are significant sociological and political
constraints to converting large amounts of land and biological constraints to
acquiring sufficient high-quality planting material and seeds. Existing forest
wastes, residues, and forest thinning are the most feasible near-term biomass
feedstock supply alternative. Environmentally suitable and sustainable waste,
residue, and forest resources are limited however. It is unlikely that their
use could achieve greenhouse gas emission reductions of more than 1 or 2% per
year. Thus, efforts must be initiated to expand the biomass resource base. If
incentives were in place to plant dedicated energy crops now, the CO2
from waste and residue utilization could be recycled into a valuable resource
that would support the expansion of biomass energy commercialization soon after
the year 2000.
Realizing the tremendous potential that biomass energy offers for greenhouse gas
emission reduction within the next 20 to 30 years requires immediate action by
both the public and private sector. These actions should include: (1) improving
biomass energy technologies through research, development, and demonstration;
(2) investing in high-efficiency biomass conversion facilities; and (3)
developing agricultural and energy policies that facilitate production and use
of energy crops.
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Parrish, D. J., D. D. Wolf, and W. L. Daniels. 1993. Perennial species for
optimum production of herbaceous biomass in the Piedmont (Management study
1987-1991). Final Report. ORNL/Sub/85-27413/7. Oak Ridge National Laboratory,
Oak Ridge, Tennessee.
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Mosjidis, J. A. 1993. Variability for biomass production and plant composition
in Sericea Lespedeza
Germplasm. Final report on a field and laboratory research program for the
period September 30, 1990 to December 31, 1991. ORNL/Sub/90-SG301/1. Oak Ridge
National Laboratory, Oak Ridge, Tennessee.
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Wright, L. L., R. L. Graham, A. F. Turhollow, and B. C. English. 1992. The
potential impacts of short-rotation woody crops on carbon conservation. pp.
123-56. In N. Sampson and D. Hair (eds.) Forests and Global Change. Vol. 1:
Opportunities for Increasing Forest Cover. American Forests, Washington, D.C.
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Wright, L. L., and E E. Hughes. 1993. U.S. carbon offset potential using
biomass energy systems. Water, Air, Soil Pollut. (in press).
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