(537b) Gas Cleanup Technologies Suitable for Biomass Gasification to Liquid Fuels

Nexant Inc., with support and funding from the US Department of Energy's National Renewable Energy Laboratory, recently completed work to identify commercial technologies that are suitable for synthesis gas cleanup for biomass gasification. Currently, there are various types of technologies available. Technologies selection for a specific system is generally determined by the composition of the syngas, which is influenced by the biomass feedstock and the operating conditions of the gasifier, the cleanup requirements for the intended use of the syngas, and economic considerations.

The cleanup requirements will vary for different syngas applications. For example, the cleanup required for syngas that will ultimately be fed to a reciprocating engine is much less than for syngas used in chemical synthesis. This study examined relevant technologies that could be required for syngas that will be used for Fischer-Tropsch (FT) liquids and alcohol synthesis.

Typical contaminants from biomass gasification include particulates, tars, alkali, nitrogen, and sulfur compounds. In most biomass feedstocks, the sulfur concentration is low; however, the sulfur impurities need to be removed from syngas that will be used for synthesis of alcohol and Fischer-Tropsch (FT) liquids. Additionally, some biomass feedstocks may contain halides or trace metals. Contaminants are undesirable since they can present emissions problems, damage downstream equipment, or deactivate catalysts. Gas cleanup technologies can be used to control the level of contaminants in the syngas. For example, technologies such as cyclone separators, barrier filters, and electrostatic precipitators are routinely used for solid particulate removal. Catalytic tar crackers are employed to destroy tars and nitrogen contaminants. Wet scrubbers are used to remove a number of contaminants such particulates, alkali, halides, soluble gases, and condensable liquids. Acid gas removal technologies encompass a large selection of processes including amine-based, physical solvent, liquid phase oxidation, and catalytic absorbent.

For this presentation, the discussion will focus on the operating size ranges and conditions, materials of construction, and cleanup parameters for technologies to remove particulates, tars, acid gas, ammonia, alkali, and halides from biomass derived syngas. Application of this analysis will be demonstrated in developing a cleanup configuration for low- and high-pressure gasifiers with a wood feed rate of 2,000 tonnes per day. The cleanup configuration will comprise of a combination of technologies that will achieve syngas specifications required for producing a variety of liquid fuels as part of a biomass refinery.