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Biomass
Since the discovery of fire, humans have been burning biomass to produce heat and light. Today, biomass continues to be an important source of energy around the world. Biomass accounts for approximately 1.5% of the total electricity produced in the United States.
Biomass resources include plants, residues from agriculture and forestry, the organic component of municipal and industrial wastes and landfill gas. These resources are all considered renewable, as they can be replenished in a relatively short amount of time without depleting the earth's natural resources, unlike fossil fuels. Biomass facilities are also significantly cleaner than fossil fuel power plants.
In general, biomass facilities can be separated into four different categories: direct-firing, co-firing, gasification and landfill gas.
Direct firing
In direct firing facilities, biomass is burned in a conventional steam boiler. The steam is then captured by a turbine and converted to electricity. The feedstocks for this process generally include milling and logging residues and "energy crops" (i.e., fast-growing trees and shrubs). Direct firing produces no net carbon dioxide emissions since growing the biomass consumes the same amount of carbon dioxide that is released through the combustion process. These facilities also have low sulfur dioxide emissions. There is some concern over the particulate matter that is released - however, when pollution control technologies are employed this is not a problem. It is also very important that feedstocks are closely monitored as burning treated or pressurized wood releases hazardous emissions.
Co-firing
Biomass can also be burned as a supplementary source in existing power plants. Woody and herbaceous biomass can be co-fired in coal plants, while biogas can be co-fired with natural gas. Co-firing can significantly reduce the emissions of the existing plant, however there is concern that it may extend the life of a dirty fossil fuel plant that would otherwise have closed.
Gasification
At high temperatures biomass can be converted to a gaseous mixture of methane, carbon monoxide and hydrogen. This gas can then be converted to electricity using a gas turbine or fuel cell. The process is highly efficient and produces a fuel that can be easily used in conversion technologies. Currently, gasification is being tested at the McNeil Station in Burlington, VT.
Landfill Gas
Gas is produced as the garbage in our landfills decomposes. This gas is composed of 50% methane and 48% carbon dioxide. If released into the atmosphere landfill gas poses an explosion hazard, smells bad and contributes to global warming. Fortunately, the gas can be collected and converted into electricity using a gas turbine or fuel cell.
For more information on biomass:
www.eren.doe.gov/biopower
www.nrel.gov/clean_energy/biopower.html
www.crest.org/bioenergy
www.nesea.org/energy/info/biopower.html
For more information on landfill gas:
www.epa.gov/lmop
