Clean Heat and Power Using Biomass Gasification for Small- to Medium-Scale Industrial and Agricultural Projects
Carolyn Roos, Washington State University, Extension Energy Program, July 2009
The use of biomass to generate heat and power is crucial in achieving energy independence and increasing our use of renewable energy sources. In our transition to renewable energy, gasification promises to play a major role in large part because its products can make use of existing infrastructure and equipment associated with fossil fuel use. This guidebook is intended for use by the forest products and food processing industries. It can also be used by farmers, ranchers and others who have access to biomass materials.
Gasification is a thermal conversion process in which both heat and a combustible product gas are produced. Combustion, in contrast, produces only heat, most commonly in a boiler to generate steam for production of electricity using a steam turbine. With gasification, generation of a combustible gas is key to its importance. A gaseous fuel makes the use of reciprocating engines, gas turbines and fuels cells possible in the generation of electricity, thereby increasing electrical efficiency. Gasification also makes possible a highly efficient configuration for generating electricity, referred to as an integrated gasification combined cycle (IGCC). Further, gasification can facilitate the use of biomass for heat and power because gaseous fuels can be distributed by pipeline from a gasification plant for use in other locations, either on site or off.
Gasification of biomass and the use of the product gas in boilers and furnaces have a long and proven history. However, using the product gas for efficient electricity generation with engines, turbines and fuel cells has been hampered until recently by technical difficulties in removing tars from the product gas. Tar removal technologies have advanced in recent years and have now been successfully demonstrated and proven reliable. With these advances, biomass gasification for generation of heat and power has now emerged into commercialization. In the U.S., construction will begin in 2009 on a 42 MWe commercial-scale project in Tallahassee, Florida, and another 28 MWe gasifier is planned for Forsythe, Georgia. Around the world, more than 100 biomass gasifier projects are operating or ordered.
In addition to heat and power, there is a wide array of co-products possible with gasification. This can improve the cost effectiveness of a gasification project. The product gas can be used as a feedstock to produce hydrogen and liquid hydrocarbons, such as ethanol and chemical feedstocks. Biochar has several potential markets and also gives gasification the potential of a carbon neutral or carbon negative energy solution. Both combustion and gasification produce ash, which also can be marketed.
This guide is a practical overview of gasification on the small (