Fuel gas produced by gasifying biomass feedstocks will be expected to meet the general specifications for corrosive and particulate impurities set by the gas turbine manufacturers before being approved for use. The extent to which impurities are present in the fuel gas will be a function of the process used to produce the gas, as well as the type of feedstock from which the gas is derived. Experiences from various biomass gasification trials and hot gas filtration testing to assess the types and amounts of impurities that are likely to be present in the delivered gas during normal operation of the gasification/hot gas cleanup process and upset conditions are reviewed. Overall, it appears that biomass fuels can be separated into two classes: those derived from grass-based biomass and those from wood. Of these, the grasses have the potential to be the more troublesome since they contain the largest amounts of alkalis and total solids and have a significant excess of chlorine over sulfur species. A possible mitigating factor is that it may be possible to lower the alkali metal species (Na + K) to levels considered acceptable by operating the filters at temperatures below 500°C. There is concern that larger amounts of particulate matter than allowed in current gas turbine fuel specifications may pass through the hot gas clean-up systems in biomass gasification processes. These particles may also carry condensed alkali deposits. Therefore, it is considered essential that detailed characterization of the size and type of these particles be obtained so that their potential to cause deposition, erosion, or corrosion problems can be better assessed.

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