Biomass

Biomass Energy Resources

Biomass is plant material used as an energy resource. Plant materials are composed of carbohydrate compounds that store chemical bond energy. Combustion releases this stored energy. Some biomass materials are usable directly as fuel, but others need to undergo physical or chemical processing first. Biopower generally refers to the generation of electricity directly from biomass.. Biomass includes forest and wood waste, agricultural waste, and dedicated energy crops. Biofuels include methane gas from landfills, wastewater treatment processes, and animal manure processing. Biogenetic fuels (biofuels) are generally refined fuels created from biomass, such as ethanol or biodiesel, but they are not in the scope of this study.

Three sources of biomass-derived methane (landfill gas, wastewater treatment and animal manure processing) are included as informational layers in the Energy Zones Mapping Tool. These sources are important as they mitigate what might otherwise be environmental impacts from methane emissions or other effects.

In 2012, 57.6 terawatt hours (TWh) of biopower generation came from about 11 gigawatts (GW) of capacity, making biopower the third-largest form of renewable electricity generation after hydropower and wind energy (Augustine et al. 2012)¹. Of this capacity, 7.0 GW was generated from forest product industry residues and agricultural residues, and 3.7 GW was from municipal solid waste (MSW), including landfill gas. In 2010, 5.8 GW of the biopower capacity in the electric power sector represented approximately 0.6% of the total electric sector generating capacity; the 5.1 GW of end-use generation capacity represented approximately 17.0% of total end-use sector capacity.

Biomass Energy Technologies

Nearly all dedicated biomass-fueled electric generating plants employ direct combustion. The biomass material is transported and put into the steam generating furnace as the primary fuel. The production of steam occurs in a conventional steam turbine cycle. The steam turbine drives an electric generator. Biomass usually has a high moisture content, which reduces the power generating efficiency of direct-fired plants. The addition of dryers in the pretreatment of biomass materials and the incorporation of more complex steam cycles can raise the efficiency of direct combustion systems (McGowin 2007).

Another technology currently used is the co-firing of biomass materials in power plants that use coal as the primary fuel. Because biomass materials have a lower sulfur content, coal-fired power plants that co-fire biomass can have reduced sulfur dioxide emissions. As the biomass materials have lower and more variable heating value than most coals and may have high moisture content, the design of the power plant needs to accommodate these differences. Coal-fired power plants have an efficiency ranging from 32 to 38%, which is greater than that of dedicated biomass plants, but the biomass feed is limited to only 3 to 15% of the fuel energy input.

References

Augustine, C., R. Bain, J. Chapman, P. Denholm, E. Drury, D.G. Hall, E. Lantz, R. Margolis, R. Thresher, D. Sandor, N.A. Bishop, S.R. Brown, G.F. Cada, and F. Felker, 2012, Renewable Electricity Futures Study: Renewable Electricity Generation and Storage Technologies, TP 6A20-52409-2, Vol. 2, National Renewable Energy Laboratory, Golden, CO.

EIA (Energy Information Administration), undated, Biomass for Electricity Generation. http://www.eia.gov/oiaf/analysispaper/biomass.

Lopez, A., B. Roberts, D. Heimiller, N. Blair, and G. Porro, 2012, U.S. Renewable Energy Technical Potentials: A GIS-Based Analysis. NREL/TP-6A20-51946. National Renewable Energy Laboratory. July. http://www.nrel.gov/analysis/re_futures/.

McGowin, C., 2007, Renewable Energy Technical Assessment Guide, TAG-RE:2007, Electric Power Research Institute, Palo Alto, CA.

NREL (National Renewable Energy Laboratory), 2000, Biomass Cofiring: A Renewable Alternative for Utilities. NREL Biopower Factsheet DOE/GO-102000-1055. June. www.nrel.gov/docs/fy00osti/28009.pdf.

Perlack, R., L. Wright, A. Turhollow, R. Graham, B. Stokes, and D. Erbach, 2005, Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply. ORNL/TM-2005/66. Oak Ridge National Laboratory. Oak Ridge, Tenn.