Biopower technologies convert renewable biomass fuels into heat and electricity using processes similar to those used with fossil fuels. There are three ways to release the energy stored in biomass to produce biopower: burning, bacterial decay, and conversion to gas/liquid fuel.
Most electricity generated from biomass is produced by direct combustion. Biomass is burned in a boiler to produce high-pressure steam. This steam flows over a series of turbine blades, causing them to rotate. The rotation of the turbine drives a generator, producing electricity. Biomass can also serve as substitute for a portion of coal in an existing power plant furnace in a process called co-firing (combusting two different types of materials at the same time).
Bacterial Decomposition (Anaerobic Digestion)
Organic waste material, such as animal dung or human sewage, is collected in oxygen-free tanks called digesters. Here, the material is decomposed by anaerobic bacteria that produce methane and other byproducts to form a renewable natural gas, which can then be purified and used to generate electricity.
Conversion to a Gas or Liquid Fuel
Biomass can be converted to a gaseous or liquid fuel through gasification and pyrolysis. Gasification is a process that exposes solid biomass material to high temperatures with very little oxygen present, to produce synthesis gas (or syngas)—a mixture that consists mostly of carbon monoxide and hydrogen. The gas can then be burned in a conventional boiler to produce electricity. It can also be used to replace natural gas in a combined-cycle gas turbine.
Pyrolysis uses a similar process to gasification but under different operating conditions. In this scenario, biomass is heated at a lower temperature range but in the complete absence of oxygen to produce a crude bio-oil. This bio-oil is then substituted for fuel oil or diesel in furnaces, turbines, and engines for electricity production.