Exergetic optimisation of a production process of Fischer-Tropsch fuels from biomass

An exergy analysis of Biomass Integrated Gasification-Fischer-Tropsch process is presented. The process combines an air-blown, atmospheric gasifier, using sawdust as feedstock, with a Fischer-Tropsch reactor and a steam-Rankine cycle for electricity generation from the Fischer-Tropsch tail gas. Results show that the rational (exergetic) efficiency is 36.4%, consisting of 34.5% efficiency to Fischer-Tropsch diesel and wax, and 1.9% efficiency to electricity. The largest exergy losses take place in biomass gasification and in generation of electricity from the Fischer-Tropsch tail gas. Recommendations are given for process improvements, which increase the rational efficiency to 46.2%.