Improvement of tar removal performance of oil scrubber by producing syngas microbubbles

This paper investigated the feasibility of a low-cost and highly effective tar removal technique using venturi oil scrubber enhancing the absorption surface area by producing microbubbles for tar removal in biomass pyrolysis/gasification processes. The basic experiment was carried out by utilizing a laboratory-scale fixed bed pyrolyzer, and then the achievements were implemented in a commercial-scale bubbling fluidized bed gasifier. In the laboratory-scale experiment, the absorption surface area was evaluated based on the mean diameter and the yield of microbubbles. The venturi tubes with various throat diameter ratios (0.17, 0.42 and 0.67) and inverter frequencies (40, 50 and 60 Hz) were tested to show that the throat diameter ratio of 0.42 and the inverter frequency of 60 Hz were the optimum conditions. Furthermore, it was found that up to 97.7% of gravimetric tar was removed by the venturi scrubber, while naphthalene and phenol were completely removed, which markedly improved the performance comparing with other conventional scrubbers. The 20-h operation of the commercial-scale gasifier also showed that the gravimetric tar removal efficiency of the venturi scrubber was 87.1% on average and there were no naphthalene and phenol observed at the exit of the venturi scrubber as well. Totally, 99.2% of gravimetric tar was removed by using only physical methods comprised of the following: a series of cyclone, ceramic filter, air cooler, water coolers, venturi scrubber and packed bed adsorber, which achieved the syngas quality requirement for internal combustion engines.