Biomass - Energy Policy Analysis: A Conceptual Framework - page 159

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Biomass
Whether crop or forest residues, urban and mill wastes, or energy crops, energy in the form of
organic materials—biomass—of one kind or another is available in most areas of the United
States. Plant material and animal waste are the raw materials of biomass energy, which can be
used with a variety of technologies to either generate electricity or provide fuel for transportation
and other uses. Generally we refer to biomass generation of electricity as biopower, and biomass
fuel for other uses such as transportation as biofuels. Biomass ultimately is another form of solar
energy, stored in plants in the form of carbohydrates through the process of photosynthesis, and
released through various technologies. In effect, biomass functions as a sort of natural battery for
storing solar energy (UCS 2010). A study done for the U.S. Department of Energy in 2005 found
that the United States has the technical potential to produce more than 1 billion tons of biomass
per year for energy use, which could have met about 42 percent of our electricity needs in 2007
(Perlack et al. 2005).
BIOPOWER
Biomass can be processed in a variety of ways to produce solid, gaseous, or liquid fuels that may
be used to generate electricity. Biomass fuels suitable for generation of electricity include forest
harvest residues such as tree tops and branches; bark, sawdust, “black liquor,” and other by-products
of milling timber and making paper; shavings produced during manufacture of wood products, often
in the form of wood chips; bagasse, the fibrous matter that remains after sugarcane or sorghum
stalks are crushed to extract their juice; corn stover residue of corn cultivation; prairie grasses;
dried manure; urban wood waste such as tree trimmings, shipping pallets, and clean, untreated,
leftover construction wood; rice hulls; oat hulls; barley malt dust from brewing of beer; the clean,
biodegradable portion of municipal garbage such as unrecycled paper; and woody yard waste
(Brower 2002). Methane can be captured from landfills or produced in the operation of sewage
treatment plants. All are routinely used to generate electricity, although wood chips account for
the greatest portion by far of biomass energy production in the United States.
Direct combustion of biomass produces heat that can be used to heat buildings, for industrial
processes, and to produce steam for turbine generation of electricity. Forest and crop residues,
switchgrass, and urban wood residues can be made into pellets and sold for residential wood stove
combustion or burned directly in power plants to generate electricity. Biomass can be mixed with
coal and burned at a power plant designed for coal—a process known as cofiring (UCS 2010).
BIOFUELS
Biomass can be converted into liquid fuels or cooked in a process of gasification to produce
combustible gases, which reduces some emissions from combustion, especially particulates. By
heating biomass in the presence of a carefully controlled amount of oxygen under pressure, it
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