Although the global energy sector is still driven by fossil fuels, renewable and more environmental friendly energy sources need to be explored due to the insecurity of crude oil supply and the environmental problems associated with fossil fuel consumption. The conversion of biomass to liquid transportation fuels is a promising alternative. A process is developed in ASPEN Plus to simulate the conversion of biomass to produce gasoline, diesel, and kerosene at varying design/operation conditions. Biomass is dried and gasified to generate synthesis gas, which is converted to a mixture of hydrocarbons via Fischer-Tropsch synthesis (FTS). Given the same biomass feedstock, three FTS technologies including conventional FTS, once-through FTS, and supercritical FTS are comparatively studied. Hydrocarbons from FTS are upgraded to liquid transportation fuels which meet all necessary physical property standards through several upgrading technologies (hydrocracking, hydrotreating, isomerization, catalytic reforming, and alkylation). In conventional FTS, the produced C1
light gas in the hydrocarbon upgrading process is reformed to produce additional syngas and then recycled back to the FTS reactor along with the fresh syngas to improve the overall carbon conversion rate. For once-through FTS, the C1
light gas from hydrocarbon upgrading process and the unreacted syngas from the FTS reactor are directed to a gas turbine for co-production of electrical power. For supercritical FTS, a supercritical fluid is used as the reaction medium to improve/tailor the performance of the FTS reactions.
This study first investigates the product distribution and CO2 emission of the biomass conversion processes associated with the three FTS technologies. Then heat and power integration is performed for these three biomass conversion process topologies and a given set of operating conditions. Finally, a detailed economic analysis is performed using Aspen Process Economic Analyzer and unit cost functions obtained from literature.