Lowering Gasifier Tars and Particulates Using Heated Dololmite Catalyst and a Particulate Filter

Abstract

For this study, a fixed-bed, down-draft gasifier was designed to investigate the effect of a dolomite catalytic bedon tar removal. Pine pellets and wood chips (cypress) were used to produce syngas from the down-draft gasifier. For the gas conditioning, a combination of a heated dolomite (bed temperature at 850?C for catalytic cracking of tars) and a particulate filter (for particulate removal) was used. Investigation of temperature effects on dolomite activity between 650?C and 950 C bed temperatures, showed optimum catalytic efficiency at approximately 850?C. At the optimum conditions, gravimetric tar and particulate concentrations in syngas produced from pine pellets were 0.85 g/Nm3 (±0.16) and 4.75 g/Nm3 (±0.07), respectively before gas conditioning, and 0.09 g/Nm3 (±0.02) and 2.01 g/Nm3 (±0.13), respectively after gas conditioning. Syngas from wood chips contained 1.63 g/Nm3 (±0.45) and 3.84 g/Nm3 (±1.16) of tars and particulates, respectively before gas cleaning and 0.19 g/Nm3 (±0.02) and 2.27 g/Nm3 (±0.27) tars and particulates, respectively after gas conditioning. The combustible portion of the gas constituted carbon monoxide (12% - 14%), hydrogen (11% - 12%), and methane (~2%). These results suggest that syngas produced from gasification of pine pellets and wood chips in a down-draft biomass gasifier can be effectively cleaned using a heated catalyst bed and a particulate filter. However, the benefits of gas conditioning will be offset by the need to maintain a heated catalyst bed for tar cracking.