Biomass refers a wide range of biological materials used as sources of energy. While wood products are the most common form of biomass power, a host of feedstocks can be used for electricity generation, including a variety of crops, agricultural waste, yard clippings, and even municipal solid waste (MSW). In addition to producing electricity, biomass can also be used for space and domestic water heating, process heat, and the thermal portion of combined heat and power, as well as for transportation (see Biofuels).
A variety of processes convert biomass materials into electricity:
Incineration/Direct-Firing is the most common method of generation. The biomass feedstocks are burned directly to produce steam, which in turn rotates turbines to generate electricity.
Gasification refers to heating biomass while restricting the amount of oxygen and/or steam in the gasifier. This process produces a synthetic gas known as “syngas,” containing carbon monoxide and hydrogen. The syngas can be burned in gas engines, used to produce methanol and hydrogen, or transformed into a synthetic fuel via the Fischer Tropsch (FT) process.
Co-Firing is the burning of biomass in conjunction with a non-renewable feedstock (often coal) to reduce emissions and, in certain cases, increase output and efficiency. Nitrogen, sulfur oxides, and carbon dioxide emissions are considerably lessened by a biomass co-firing arrangement.
Anaerobic Digestion is a biological process in which microorganisms break down biomass and release biogas, which consists of methane, carbon dioxide, and certain other gasses. The biogas can be subsequently captured and combusted to generate electricity. Anaerobic digestion is used in a variety of locations as a way to manage waste, including at dairy farms, landfills, and wastewater and sewage treatment facilities.
Landfill gas is produced as a result of anaerobic digestion at landfills. Landfill operators collect the gas produced by the decomposition of solid waste and use it to generate electricity.
Pyrolysis is the process of heating biomass in the absence of oxygen. The result of the process is a substance known as pyrolysis oil, which then can be converted into biofuel or used to generate electricity.