Characterization and treatment of tars and biomass gasifiers

Biomass gasification and pyrolysis have the potential to make a significant impact on energy supplies in the United States and have demonstrated their commercial potential in many projects around the country. The environmental aspects of biomass gasification need to be defined to assure that the technology makes its maximum impact on energy supplies. One area that needs further development is characterization and treatment of the tar byproduct from gasifiers and pyrolyzers. This paper examines the effect of the type of gasifier/pyrolyzer and the processing conditions on the yield and properties of tars and condensates. End use limitations for tars are discussed. Wet scrubbing is the most common method of tar removal from gases. The scrub liquor will require treatment to remove organics before it can be disposed. Pacific Northwest Laboratory (PNL) is developing a catalytic tar destruction process that will treat the hot, raw gas from the gasifier and convert the tars to gas. The process increases the gas yield and cold gas efficiency of the gasification process, produces a clean gas that can be used for many applications, and produces a clean condensate that can be disposed with minimal treatment. 10 refs., 2 figs., 1 tab.