(99a) Process Analysis and Optimization for Transportation Liquid Fuel Production by BTL (Biomass to Liquids) Process

Biomass, that is carbon neutral and a renewable resource, becomes attractive after the decision of Biomass-Nippon strategy in Japan. A process to produce transportation liquid fuel from biomass is also attractive. In this study, BTL (Biomass to Liquids) process was considered from viewpoints of economics and environmental. The process comprises gasification of biomass, gas cleaning, compression of syngas, FT synthesis and distillation. That is, in the process, biomass is converted into syngas at first. Then syngas is cleaned and is pressurized. The pressurized syngas is synthesized into hydrocarbons. Finally, FT diesel is obtained by distillation. We are studying the economic and environmental evaluation based on process simulation and process analysis. The process requires thermal energy in gasification and distillation and electricity in compression. In this study, the effect of CO2 mitigation when the requirements were fulfilled by fossil fuel or biomass was considered. Consequently, the combustion of a part of a biomass as a heat source decreased the total CO2 emission though the partial combustion decreased the feedstock biomass and the yield of FT diesel. Further, the power generation using biomass was not useful if the efficiency was low. In other words, a process that does not depend on a fossil fuel is not necessarily effective. In the process, much amount of off-gas was discharged after FT synthesis. The off-gas had approximately a half of heating value of feedstock biomass. Therefore, the combustion of the off-gas and the recycle of the off-gas for effective utilization of the off-gas were examined. Consequently, it was found that the combustion of the off-gas as a heat source was effective for CO2 mitigation. On the other hand, the recycling of the off-gas to the gasifier where hydrocarbons were reformed into CO and H2 remarkably increased the yield of FT diesel. However, it increased power to compress the syngas and the consumption of electricity because of the increase of syngas flow rate. Accordingly, effect of CO2 mitigation decreased in this case. The compression capacity strongly affected CO2 mitigation. Furthermore, it was also strong factor in economics. That is, in the process, the cost of compressors accounted for 1/3 of the construction cost. In an improvement of the economics, the compressor section is sensitive. Therefore, a pressurized gasification that requires no compressor was examined and was compared with the atmospheric gasification. In this case, the cost of the pressurized gasifier increased because it had to be constructed heavily to endure high pressure. However, exclusion of compressors more strongly affected the economics than addition of the pressurized gasifier and the economics was improved.