Experimental study on catalytic cracking of model tar compounds in a dual layer granular bed filter

To simplify the purification process of hot effluent gases produced by biomass and/or coal gasification, an integrated technique employing dual layer granular beds for the simultaneous removal of particulates and tar at high temperature (750–850°C) has been proposed. Compared to the well studied process of particulate removal, investigations for the catalytic cracking of tar are inadequate. The present work conducted an experimental study of the catalytic cracking of tar based on two model compounds: toluene and methylnaphthalene. The experiments were conducted on a granular bed filter with an inner diameter of 40mm and a height of 1000mm. The catalytic cracking performances on an expanded perlite granule layer, an olivine granule layer, and a dual layer granular bed comprised of an upper layer of expanded perlite granules and a lower layer of olivine granules were investigated individually. It was found that the expanded perlite granule layer alone was effective for toluene cracking, and the efficiency was increased with increasing reaction temperature and gas residence time. The olivine granule layer provided excellent catalytic activity for toluene cracking. Furthermore, olivine granules exhibited significantly improved catalytic activity when calcinated at temperatures greater than 900°C, or impregnated with NiO. The conversion efficiencies of toluene and methylnaphthalene attained values as great as 98.89% and 79.33%, respectively, at a temperature of 800°C over a dual layer granular bed comprised of a 150mm thick upper layer of expanded perlite granules and a 50mm thick lower layer of 3wt% NiO impregnated olivine granules.