Optimization of Syngas Quality for Fischer-Tropsch Synthesis

While fossil oil reserves have been receding, the demand for diesel and gasoline has been growing. In recent years, syngas of biomass origin has been emerging as a viable feedstock for Fischer-Tropsch (FT) synthesis, a process for manufacturing synthetic gasoline and diesel. This paper reports the optimization of syngas quality to match the FT synthesis requirement. The optimization model maximizes the thermal efficiency under the constraint of H2/CO≥2.15 and operating conditions of equivalent ratio (ER=0.0-1.0), steam to biomass ratio (SB=0.0-5.0), and gasification temperature (Tg=500°C-1300°C). The optimization model is executed using the optimization section of the Model Analysis Tools of the Aspen Plus simulator. The model is tested using eleven (11) types of municipal solid waste (MSW). The optimum operating conditions under which the objective function and the constraint are satisfied are ER=0, SB=0.66-1.22, and Tg=679-763°C. Under optimal operating conditions, the syngas quality is H2=52.38-58.67 mole percent, lower heating value LHV=12.55-17.15 MJ/kg, and N2=0.38-2.33 mole percent. From an economic point of view, 12.98% to 33.12% of biomass is used as fuel for steam generation, drying, and pyrolysis. The generalized optimization model reported could be extended to any other type of biomass and coal.