Novel sintered metal filter elements: Performance evaluation in biomass gasification conditions

Filtration is an essential step in biomass gasification processes. In synthesis gas applications, where full removal of gas contaminants is required, the filter unit is typically placed upstream the catalytic reformer in the purpose of shielding the reformer from dust deposits and preventing plugging of the catalytic layer. In state-of-the-art biomass gasification concepts, the raw product gas is cooled down to ca. 500 °C prior to filtration. This results in increased oxygen consumption in the reformer as the gas must be reheated after filtration to reach the targeted reforming temperatures of 850-950 °C. To improve the biomass-to-fuel conversion efficiency of biomass gasification-synthesis plants, the latest R&D efforts in this field have been targeted at operating the filter unit at gasifier outlet temperature (750-850 °C), which would eliminate the intermediate cooling and reheating steps. According to VTT’s estimate, the overall efficiency from biomass to Fischer-Tropsch liquids could increase from 53% to 58 %, if the filter temperature was raised from the conventional 550 °C level to 850 °C.Filter elements that are currently available for hot gas filtration at temperatures up to 1000 °C are manufactured from metal alloys, high temperature insulation wool or fine ceramic granules. However, these state-of-the-art filter elements have certain restrictions, such as low ductility, high pressure drop or deficient corrosion resistance. With the aim to generate a metal-based filter material withstanding mechanical loads and corrosive conditions, GKN has developed innovative filter elements out of a modified Iron-Chromium-Aluminium powder (material No. 1.4767 mod.). The focus of this work was on evaluating the performance and corrosion resistance of these novel filters in biomass gasification conditions at temperatures up to 750 °C.