Regenerative reverse-flow reactor system for cracking of producer gas tars

The gas produced in a biomass gasifier contains high amounts of tars which have to be removed prior to downstream utilization. Calcined dolomite is catalytically active for tar cracking reactions and resistant to sulfur poisoning. In this study, calcined dolomite was used as bed material in a reverse-flow reactor for cracking of tars in a model synthesis gas. 1-methylnaphthalene was used as model tar compound at a concentration of 15,000 mg/Nm3. The reactor system was operated at temperatures between 700 and 850 °C in the active zone. Total tar conversion was over 95 % for the system under reverse-flow conditions at the highest temperature. Already at the lowest temperature, up to 78 % of the 1-methylnaphthlene was converted, but mainly to other more stable tar compounds such as naphthalene and benzene, reaching a total tar conversion of only 23 %. To produce tar-free gas, higher temperatures are thus needed. The use of very high temperatures does, however, lead to a significant decrease in the specific area of the dolomite, as shown by BET surface measurements. The dolomite was further characterized with x-ray diffraction and energy dispersive spectroscopy.