Power generated from our nation’s waste products and domestically grown plants is one of the most promising sources of renewable electricity. There are four ways to turn biomass into electricity: digestion, combustion, gasification and pyrolysis. Currently, most biopower is generated through combustion, with smaller projects utilizing primarily digestion and gasification.

Research and development efforts are rapidly bringing improved methods and new technologies into the marketplace, maximizing the potential and efficiency of biopower. The Harvesting Clean Energy program is most interested in biopower projects which displace existing uses of petroleum and coal, generate public benefits, create rural jobs, and/or demonstrate emerging technologies.


Digestion

By using bacteria to break down organic wastes from livestock or food processing, anaerobic digestion produces methane gas that can be burned in a boiler to produce steam and electricity, or stored in microturbines or fuel cells. Anaerobic digestion is particularly effective because it produces renewable energy while simultaneously solving the problem of waste disposal and odor control.

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Combustion

Combustion, whether direct-firing of raw materials or co-firing with other fuel sources such as coal, produces hot air, hot water, and steam for power generation. A wide variety of biomass feedstocks can be converted into energy through combustion, including wood, grass, agricultural residue and municipal solid waste. Direct combustion is the simplest and most developed biopower technology.

Gasification

Gasification converts biomass into a mixture of hydrogen, carbon monoxide and methane gas using high temperatures and an oxygen-starved environment. The gas is then used to power a turbine and create electricity. Current efforts in the Northwest are focused on using straw and wood waste as biogas feedstocks. New technology is also capturing methane from landfills after the waste naturally decays.

Pyrolysis

Pyrolysis turns low-moisture biomass into liquid oil by forcing decomposition of organic matter with high temperatures in the absence of oxygen. The resulting bio-oil is then condensed into a fuel or refined and converted into different chemical products. Pyrolysis can convert biomass into all three of the types of bioenergy – biopower, biofuels and bioproducts – but is still in development.