2003 Volume 36 Issue 12 Pages 1440-1448
Production of tar constitutes one of the most pressing challenges in the development of low-temperature biomass gasification. As one solution to this problem, we suggest utilizing the capacitance effect of porous particles for tar-free gasification. In the present work, in order to clarify the fundamental characteristics of the capacitance effect for biomass gasification, tar yields in sawdust pyrolysis with and without porous particles were measured at 873 K and 1073 K in a lab-scale fixed bed reactor.
Employment of porous particles substantially reduced the tar yield from biomass pyrolysis. Within the range studied, the tar yield without porous particles is nearly equal to the yield of carbon deposition on porous particles at 873 K. This finding indicates that porous particles can capture and hold all tar. That is, tar produced from pyrolysis is instantaneously absorbed on the surfaces of porous particles, and the residence time of tar in a gasification furnace is prolonged and then tar is pyrolyzed, carbonized and fixed on porous particles, so high tar reduction is achieved. The results of gas yield measurement show that employment of porous particles increases hydrogen yields by three times or more. There are two reasons why hydrogen yield increased. One is that the catalytic effect promotes dehydrocyclization of lower molecular weight organic gases. Another is promotion of cyclized (poly-)condensation of aromatic compounds held on porous particles. Therefore, use of porous particles is also beneficial for improving gas properties.