Gas Cleaning and Tar Conversion in Biomass Gasification

Abstract

Producer gas, derived from biomass gasification, contains a wide variety of compounds organic as well as inorganic, apart from the gas species and particulate matters. The hydrocarbon compounds present in the raw gas, which have comparatively lower molecular weights, act as fuel in gas turbine or gas engines. Hydrocarbons with higher molecular masses are collectively called tars. Relatively simpler tars often polymerize into more complex structures. These heavier species quickly condense, some even solidify, and choke the particulate filters and other restrictions and valves in the gas paths, causing serious obstruction to continuous operation of the application components. Some other impurities, like sulphides and halides, too cause damages to the materials of downstream equipment. It is, therefore, essential to remove the tars and impurities in the product gas to the extent possible. Tars also pollute the environment if discharged untreated. If, however, tars could be cracked and converted to permanent gas species, the producer gas calorific value could be improved substantially. Tars can be eliminated or effectively converted or their production rates can be reduced by certain measures. They include installing separation devices, modifying the conditions and parameters of gasification, modifying the gasifier design, using additives and catalysts. This chapter discusses these measures or processes that are aimed at tackling the tars.