Simultaneous maximization of the char yield and volatility of oil from biomass pyrolysis

This study proposes continuous biomass pyrolysis featuring internal recycling of a heavier portion of bio-oil (HBO) that evaporates, leaving solid residue when reheated. The recycling of HBO enables the selective production of light bio-oil (LBO) that is free from residue after evaporation, and also the maximization of the char yield. The performance of the proposed pyrolysis has been examined experimentally by employing an originally designed simulator of a vapor-solid countercurrent moving bed reactor, which provides the zone for pyrolysis at 120-550 C (PZ) and the zone for capture of HBO by the parent biomass at 120 C (CZ) in series. The HBO recycling increases the char yield from the pyrolysis of pine sawdust from 0.25 to 0.36 kg/kg of dry feedstock while producing LBO, in which the organic compounds have carbon numbers no greater than 13. Such a large increase in the char yield is caused by two different events. HBO is captured by the parent biomass in CZ and undergoes self-charring and/or co-carbonization in PZ. The vapor of HBO is decomposed over the surface of pyrolyzing solid (char) in PZ and then converted into a portion of char, LBO, and/or gas.