Novel approach to tar removal from biomass producer gas by means of a nickel-based catalyst

Abstract

The nickel-based catalyst was exposed to the raw gas from gasification of woody biomass with air in a fluidized-bed. After dust removal on a barrier filter and sulphur compounds capture, namely H2S, on an active sorbent made of CuO and ZnO, higher hydrocarbons as tar components were decomposed/reformed on a Ni-catalyst. Steam reforming reactions led to decomposition of tar and all hydrocarbons higher than CH4into mainly H2 and CO which further underwent reaction with steam via the water gas shift reaction to CO2. The reforming reactions caused approximately 10-20 % decrease in the lower heating values of the producer gas from the inlet values 5.0-6.5 MJ m-3. The gas yield increased from values 2.4-2.6 m3 kg-1 to values 2.8-3.0 m3 kg-1 on dry biomass basis. The chosen tar removal concept based on combination of dolomite in the fluidized-bed with the secondary catalytic reactor was proved by 20 hours long experiment in which the final tar content below 30 mg m-3 was attained corresponding to more than 97 % tar conversion. H2S content in producer gas was expected to be below 100 vol. ppm, bulk of which was captured on the sorbent. Only limited deactivation of the catalyst by sulphur compounds was found in the front of the catalyst bed where sulphur content was determined as high as 173 wt. ppm compared to 22 wt. ppm in the fresh sample.