Catalytic tar decomposition in a slip stream of an 8 MV dual fluidised bed biomass steam gasifier

"Gasification of biomass is an attractive technology for combined heat and power production as well as for chemical synthesis. However, the tar content in the product gas, which can cause plugging in the colder parts of the plant, is still a barrier for the commercial breakthrough for this technology. Catalytic hot gas cleaning is considered as very promising cleaning method due to the complete destruction of the tars instead of creating a waste stream which is difficult to dispose. Based on experiments in laboratory scale a 100 scm/h slip stream reactor at the biomass combined heat and power plant in Guessing/Austria, using a dual fluidized bed gasifier, has been designed and erected summer 2006. The producer gas contaminated with tar is sucked off from the freeboard of the gasifier, fed into the catalytic reactor, and discharged back to the product gas line between the gasifier and the gas cooler. Tar amounts and composition as well as gas composition are measured before and after the reformer. Despite the low operating temperature of the reformer (840 instead of 910 °C) tar conversion rates of more than 80 % were found, whereas the tar composition was hardly influenced. The reformer was in operation continuously for 36 hours."