99/00547 Scale-up of a dedicated biomass feedstock system for production of ethanol and electricity

Abstract

The effects of H2/CO ratio in syngas from a biomass gasifier, the type of a Fischer-Tropsch (FT) catalyst, addition of a reformer in a recycle mode, efficiency of CO2 removal, and co-feeding of biomass and natural gas on the overall thermal efficiency and costs for the production of FT liquid fuels from the biomass-derived syngas were analyzed using an Aspen Plus®-based process model. The overall thermal efficiency for biomass-fed processes was in a range of 41.3–45.5%. A cobalt catalyst-based FT process achieved slightly higher efficiency than an iron-based FT process mainly owing to the absence of water-gas shift activity on a cobalt FT catalyst. A proper amount of CO2 in the syngas can inhibit the amount of CO2 generated via the water-gas shift reaction in a FT reactor with an iron-based catalyst which yields a similar efficiency to a cobalt-based FT process. The lowest production costs were around $28.8 per GJ of FT liquids for the biomass fed processes with a reformer. However, the addition of a reformer in the gas recycle loop can improve the economics only when the operation of the plant is optimized for maximum fuel production rather than co-generation of fuels and power. A process with co-feeding of natural gas into the reformer can achieve more attractive economics than a solely biomass fed process. Co-feeding of biomass and natural gas each at 200 MWth for a total feedstock thermal energy input of 400 MWth reduced the costs of FT liquid production by about 30% to $19–$20 per GJ of FT liquids. However, production of FT biofuels would be economically viable only at very high oil price or if some premiums are considered for the production of green fuels and power. At an oil price of $60/barrel, production of FT biofuels in the process configurations considered in this study wouldn’t be economically feasible.