TECHNO-ECONOMIC AND LIFE CYCLE ASSESSMENTS OF BIOFUEL PRODUCTION FROM WOODY BIOMASS THROUGH TORREFACTION-FAST PYROLYSIS AND CATALYTIC UPGRADING

Biofuel production through fast pyrolysis of biomass is a promising conversion route in the production of biofuels compatible with existing technology. The bio-oil produced from fast pyrolysis is a versatile feedstock that can be used as a heating oil or upgraded to a transportation hydrocarbon biofuel. Comparative study of a one-step, fast pyrolysis only pathway and a two-step torrefaction-fast pyrolysis pathway was carried out to evaluate the effect of torrefcation on (i) the minimum selling price of biofuel and (ii) the potential life cycle GHG emissions of the biofuel production pathway. To produce bio-oil which can serve as a substitute for heating oil from loblolly pine biomass feedstock, torrefaction at three different temperatures of 290, 310 and 330°C were investigated while fast pyrolysis occurred at 530°C. Three scenarios of producing process heat from natural gas, internal by-products biochar or torrefaction condensate were also investigated. Economic assessment showed more favorable economics for the two-step bio-oil production pathway relative to the one-step bio-oil production pathway. The lowest minimum selling price of $1.04/gal was obtained for a two-step pathway with torrefaction taking place at 330°C. The environmental impact assessment also showed more the two-step bio-oil production pathway to be more environmentally friendly. The lowest GWP of about -60g CO2eq was observed for the two-step pathway at torrefaction temperature of 330°C while GWP of about 36g CO2eq was observed for the one-step pathway. Relative to heavy fuel oil, the one-step and two-step pathways are more environmentally friendly with lower GWP. To produce hydrocarbon biofuel by the catalytic upgrade of bio-oil derived from fast pyrolysis of loblolly pine, three torrefaction temperatures of 290, 310 and 330°C were investigated with fast pyrolysis taking place at 530°C. Three scenarios of producing process heat from natural gas, internal by-products biochar or torrefaction condensate were investigated. The effect of heat integration was also examined. The economic assessment showed equal minimum selling price for the one-step hydrocarbon biofuel production pathway and a two-step pathway with torrefaction occurring at 290°C. A minimum selling price of $4.82/gal was estimated while higher torrefaction temperatures showed less favorable economics. The environmental impact assessment however showed the two-step pathway to be more environmentally friendly when compared with the one-step pathway. GWP of about -66g CO2eq was observed for the two-step pathway with torrefaction taking place at 330°C compared to a GWP of about 88g CO2eq obtained for the one-step. Further reduction in minimum selling price and GWP were observed with heat integration. A minimum selling price of about $4.01/gal was estimated for the one-step and two-step pathway with torrefaction taking place at 290°C while GWP of about -144 g CO2eq was observed for the two-step hydrocarbon biofuel with torrefaction temperature of 330°C