Biomass and Biogas

In addition to its uses as a feedstock or source of biofuels, biomass can be processed to provide electric power. With approximately 9 GW of installed capacity, biomass ranks among the largest sources of renewable electricity in the United States. Electric power can be generated from a variety of biomass sources and bi-products including wood waste and agricultural residues, municipal solid waste, and landfill gas.

There are four main types of biomass power-generating systems. Direct-fired systems burn biomass in a boiler to produce steam to turn a turbine the same way traditional plants burn fossil fuel sources. Most systems in use in the United States today are of this type. The second-most common use of biomass as a power source is in co-fired plants, in which biomass is substituted for a percentage of the coal in an existing coal plant. Gasifiers heat biomass into a flammable gas, which can be cleaned and filtered to reduce pollutants. The gas can also power combined cycle systems, which combine gas and steam powered systems for doubly efficient power generation. Modular systems are smaller systems specially fitted to power farms or small villages.

Biofuel gasifier connected to a coal-fired boiler
(Source: Tekes Info Bulletin "Growing power. Bioenergy technology from Finland")

Biogas can also be used alone to produce power. There are three main sources of biogas production: anaerobic digester systems configured to convert animal manure to methane gas; digester systems that operate in conjunction with water or sewer processing plants; and gas wells drilled into landfills that contain large quantities of biodegradable materials. Several large farms around the United States already employ this technology to produce electricity on-site.

Source:
Energy Efficiency and Renewable Energy program in the Department of Energy