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CHAPTER 2 -- CARBON SEQUESTRATION THROUGH BIOMASS ENERGY 22
CHAPTER 2 -- CARBON SEQUESTRATION THROUGH BIOMASS ENERGY
United States agriculture could sequester of large amounts of carbon in another way - by
producing corn and other sources of biomass that would serve as a source of energy. Biomass would
be carbon-neutral because it would sequester carbon while the plant matter was growing and then
would release approximately the same amount of carbon as the biomass was converted into energy.
The combined effect of the original sequestration and the subsequent release of carbon would
approximate a zero net release of carbon into the atmosphere. Compared to the large net releases of
carbon in the burning of conventional fossil fuels, conversion to use of biomass as an energy source
would offer a large overall reduction in the net amounts of carbon dioxide (CO
2
) released into the
atmosphere per unit of energy.
The ability of biomass resources to meet the energy needs of the United States is still being
investigated. Private companies, mostly lumber mills and paper companies, using their wood waste
products, are already using biomass to generate energy. Estimates of energy capacity generated from
biomass range from 7000 to 10,000 MW. Increased competition in the energy industry and
technological advances in biomass power generation are likely to increase the potential amounts of
energy from biomass. If these increases in biomass capacity replace some of the energy supplied by
fossil fuels, CO
2
emissions can be avoided. Fossil fuels emit 1,634 MMTCE every year (DOE,
1997). Generating power from biomass, rather than fossil fuels, will help the United States meet
the Kyoto reduction requirement of 577 MMTC per year.
Biomass must prove economically viable before companies will begin their own projects.
Establishing comparative prices is difficult because costs rely heavily on site-specific factors such as
energy demand, the availability of suitable biomass, and proximity of the power plant to the biomass
source. Current estimates of cost range from $1.95 - $3.50 per million British thermal Unit (Btu)
(Moore, 1996) to $0.05 - $0.08 per kilowatt-hour (kWh) for heat and $0.08 - $0.15 per kWh for
electricity (IEA). The price and competitiveness of biomass energy could be affected by subsidies,
working both for and against it, and other price mechanisms designed to charge energy users for their
emissions. Federal legislationthe Public Utilities Regulatory Policy Act (PURPA)mandates
renewable energy purchases among electric utilities. Another federal law, the Energy Policy Act,
grants income tax credits of 1.5 cents / kWh for renewable energy generation and 10% for businesses
with solar and geothermal technology equipment. Renewable energy subsidies fall short of
conventional energy subsidies, but the gap is closing. In 1989, total subsidies for energy were $38
billion, with 58% allocated to fossil fuels and two percent to renewable energy. In 1992, energy
subsidies were $9 billion ($1995), with 23% allocated to electricity, 22% to natural gas, 14% to coal,
12% to oil, 11% to nuclear, eight percent to conservation, six percent to ethanol, and five percent to
other renewables (Sissine, 1996).
Biomass crops grown for energy have many environmental benefits as well as drawbacks.
Biomass energy generation requires large amounts of land for growing crops to supply adequate
amounts of fuel. According to the DOE, a 150 MW advanced biomass power station would
require energy crops grown on 100 square miles or 25,000 hectares of land. Therefore, 50,000
MW would require 33,000 square miles or over 8,300,000 hectares of landapproximately one
percent of the total land area of the United States (Patterson, 1994). Intensive agricultural 23
practices could also result in decreased diversity and soil degradation which could lead to heavy
chemical use, further degrading the soil quality. Using conservation techniques when growing
energy crops, though, would stabilize agricultural soils, protecting them from erosive forces and
contributing to the organic matter content in the soil. Energy crops will also help improve water
quality by slowing runoff of soils (and chemicals) into nearby water sources and by filtering the
water that percolates through the ground.
Taking account of all these factors, biomass appears a promising means of sequestering large
amounts of carbon at a cost less than energy reduction or energy substitution. Indeed, production of
biomass is today gaining more attention as an energy option.
I. A Brief History Of Biomass
Biomass is already being used to a limited extent but where it is being applied it is not for
purposes of carbon sequestration. Indeed, biomass was the first energy source. Humans burned wood
to heat homes and cook food. Many developing countries still depend on biomass to supply most of
the energy needed for heating and cooking. As industrialized civilization advanced, humanity moved
from using renewable biomass to non-renewable fossil fuels. Both biomass and fossil fuels, such as
coal, oil, and natural gas, are pools of stored carbon. But fossil fuels are considered non-renewable
because of the time required to regenerate their supply. Patterson illustrates this energy potential well,
commenting, If you leave appropriate biomass for a few million years under suitable temperatures and
pressures, it becomes coal (Patterson, 1994).
Worldwide, biomass accounts for 15% of the energy supply. But, biomass is much more
significant as a power supply in developing nations than in industrial nations. Biomass supplies 70-
90% of the energy needs of Africa; in China, 32% (BRIC, 1999); in Brazil, 33% (Patterson, 1994). In
contrast, the United States gets only four percent of its energy from biomass (BRIC, 1999). But, in the
United States technology could increase the feasibility and efficiency of growing biomass as an energy
crop and converting biomass to a more carbon neutral energy supply.
The United States currently has the ability to produce 10,000 MW of generating capacity with
the wood and agricultural waste that is already available. If the production of energy crops on unused
farmland were added to the existing supply of biomass, the potential may exceed 50,000 MW of
generating capacity in the 2-3 decades (Moore, 1996). This would avert the release of 90 MMTC
from the burning of conventional fossil fuels. Such a reduction of carbon emissions would equal 8
percent of the total current annual additions to world carbon dioxide from the United States (Moore,
1996).
Biomass comes from organic material, mainly plants. Plants, through photosynthesis, take up
carbon. The plants convert carbon dioxide into organic carbon, which provides plants with the energy
to grow. The more they grow, the more carbon dioxide they absorb. When the plant dies, bacteria and
fungi decompose the plant, converting the organic carbon back into its inorganic formcarbon
dioxide. If the plant material can be harvested before it falls to the ground or dies, then the carbon
remains stored in the plant material. This stored carbon has energy potential, available for human use.
Once the plants are harvested, biomass can be converted to energy by burning the dried plant material 24
directly (or turning it into a gas) to generate electricity or heat. Additionally, biomass can be converted
into a gas or a liquid fuel for powering automobiles or other types of engines (see Figure 2.1).
Energy crops that could be grown specifically for use in bioenergy processes include alfalfa,
wheat, corn, sugar cane, soybeans, grasses, and short-rotation woody crops (SRWC)which are fast
growing trees like willow and poplar. It is possible to use plants from the water, along with the plants
from the land, as energy sources. Algaelike land plantssequester carbon through photosynthesis.
Algae can be found in the ocean or in freshwater lakes, ponds, and streams. Algae also can be grown,
or farmed, in man-made ponds.
II. Agricultural Sources Of Biomass
More research has been focused on biomass as a fossil fuel substitution technique than as a
carbon management or sink technique, but biomass techniques have great potential for increasing the
carbon sequestration both in the United States and internationally. Idle cropland or surplus agricultural
land can be planted with biomass energy crops, creating a new sink not only in the growing plant
material but in the soil as well. Agricultural residues, left behind through conservation tillage practices,
also can be gathered and used as a biomass fuel source. Even if only five percent of the above-ground
residues were used (about 25 MMT residues or 10 MMTC), 1,093 MMT of (above and below)
ground residues (437 MMTC) would remain available for soil C-sequestration (Lal, 1998).
Currently there are about 14 million hectaresabout 15% of the total cropland in the United
Statesof idle, surplus, or fallow agricultural land in the United States (Moore, EPRI). Much of this
land is purposely not planted by farmers, who are paid by the federal government not to plant. Some
of this land is classified as highly erodable or environmentally