EFFECTS OF TEMPERATURE AND RESIDENCE TIME ON THE THERMAL CRACKING OF BIO-OIL FOR SYNGAS PRODUCTION

Bio-oil, the valuable liquid product obtained from biomass through pyrolysis, may be either combusted to generate carbon-neutral electricity or converted to a synthesis gas from which chemicals or clean fuels can be produced Producing bio-oil from biomass and then converting the bio-oil to syngas has several advantages. The bio-oil may be generated in distributed or mobile plants and then shipped to a central facility for conversion to syngas, thus avoiding the expensive transportation of bulky and perishable biomass. The syngas produced from bio-oil is CO2 neutral and produces no net greenhouse gas emissions. Finally, valuable green chemicals may be extracted from the bio-oil before it is converted to syngas. The Institute for Chemicals and Fuels from Alternative Resources (ICFAR) has recently designed and implemented a fluidized bed reactor, operating in the bubbling regime, for the conversion of bio-oil to syngas. The reactor consists of a 3 inch I.D. bed, with an expanded freeboard, whose volume can be adjusted to vary the gas residence time. This reactor has been used to carry out either thermal or catalytic cracking/reforming of bio-oil. A gas-atomized injector has been especially developed to feed bio-oil, which may be viscous and contaminated with small ash and char particles, allowing it to remain cool until coming in contact with the fluidized particles inside the bed. This paper presents the product yields and compositions obtained by thermally cracking the bio-oil at various temperatures and gas residence times. The bed temperature was varied from 600 ºC to 700 ºC and the vapor residence time ranged from 8 to 27 seconds. The conversion of bio-oil to gas increased with increasing temperature and residence time. At 700 °C, the H2/CO molar ratio increased from 0.29 to 0.60 as the residence time was increased over the range investigated. Finally, the effects of steam addition and bed height were investigated