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What is Biomass? Can Today’s Agriculture Produce Both Food and Fuel? Biomass is defined briefly as organic matter of recent biological origin that can be converted to produce energy. Typical forms of biomass are agricultural crops, crop residues and forest products. Fossil fuels were also created from organic matter; however, fossil fuels are not considered biomass because they are not of recent biological origin. Most agricultural crops and crop residues are renewed on an annual or biennial basis. Forest products and forest residues are also considered biomass and are harvested on a 30-50 year basis. Other perennial crops such as switch grass and small-diameter woody species require less time to grow to usable size and may be harvested between one and five years. Biomass energy or bioenergy is considered to be a sustainable form of energy because the natural resource materials renew themselves at a frequent rate so that the ability of future generations to utilize bioenergy is not impacted. Biomass is really concentrated solar energy because it is based on the solar-powered photosynthesis process during the growth and development phases of the plant materials. Most biomass energy resources can be characterized as solid materials with low bulk density, high moisture content, low heat energy content, high oxygen content, relatively high ash content and varying energy values. They are often difficult to handle compared to the traditional fossil fuels. Because of the low bulk density characteristic of most solid biomass, capacity limitations for transportation and storage are often dictated by volume rather than weight. These disadvantages are offset by the fact that these resources are renewable, sustainable, are readily available and are often environmentally preferable. A common misperception is that crop residues are free. There are significant expenses associated with using crop residues. These expenses include harvesting, packaging, transportation, storage, further processing and handling. Densification of crop residues to produce pellets, cubes, discs or other concentrated forms is often necessary to address some of the handling challenges. Crop residues are biomass materials that can be utilized to produce energy resources now and in the future. Crop residues were once considered waste products, but their value as a coproduct has become apparent. Crop residues that remain in fields serve very beneficial purposes including:
Can Today’s Agriculture Produce Both Food and Fuel? The agricultural industry in the United States and throughout the world has a tremendous role and responsibility in the development of biomass resources that can be processed into renewable, sustainable energy supplies. Agriculture has traditionally provided the food and fiber for the six billion people of this world. The production and processing of food and fiber for the ever-increasing global population remains the most important role and responsibility of agriculture. Agricultural resources are also used to produce additional products, such as chemical feedstocks, pharmaceuticals, and fuel. Using agricultural resources to produce fuel not only presents economic opportunities and creates a renewable fuel, it also is friendlier to the environment than utilizing many fossil fuels. The four most common methods in which the biomass energy is utilized are:
Direct Combustion
The simplest method of utilizing crops and crop residues to produce thermal energy is through direct combustion. Successful systems are already in place for burning shelled corn and other agricultural materials in specially designed stoves, boilers and furnaces. Production of corn-burning units has tripled in the past two years, and it is anticipated that this practice will continue to increase in certain areas. Other direct combustion systems are based on burning crop residues such as corn stover, corn cobs, straw, switch grass, wood pellets, wood chips and other forest-based resources. There are several pilot projects of growing low-diameter wood species to be harvested every third year after establishment for direct combustion for heat and/or the generation of electricity. Production of fuel from crop seeds Production of ethanol and biodiesel from shelled corn and soybeans has become very popular in the United States and the demand for both ethanol and biodiesel will likely continue to increase, particularly as new technologies and markets emerge. Cellulosic conversion Cellulosic conversion of plant residues into ethanol and other fuel sources is still largely at the laboratory stage. However, it is anticipated that commercial production of ethanol and other fuels through cellulosic conversions of the crop residues will occur in the next several years. Methane production from animal manures Capturing methane from anaerobic digesters of animal manure and from landfills offers an additional method of utilizing biomass as fuel in certain site-specific areas. Animal manure digesters are most cost effective when the captured methane is utilized on-site to provide thermal energy needed for space heating and/or process heat. There is considerable interest in utilizing the methane to produce electricity to be sold back into the grid. On-site generation with sales into the grid may or may not be feasible economically depending on net-metering requirements of the electric utility company in that region.
Last updated December 03, 2007. |
