Performance assessment of Fischer-Tropsch liquid fuels production by solar hybridized dual fluidized bed gasification of lignite

A novel solar hybridized dual fluidized bed (DFB) gasification process for Fischer-Tropsch liquid (FTL) fuels production is proposed and investigated here for the case with lignite as the fuel, although it is also applicable to biomass. The concept offers sensible thermal storage of bed material, the use of inert particles in the solar receiver to avoid the need for sealing, and a process that delivers a constant production rate and quality of syngas despite solar variability. This solar hybridized coal-to-liquids (SCTL) process is simulated using a pseudodynamic model that assumes steady state operation at each time step for a one-year, hourly integrated solar insolation time series. The annual energetic and environmental performance of this SCTL process is investigated as a function of the solar multiple (i.e., the heliostat field area relative to that required to meet the demand of the DFB gasifier at the point of peak solar thermal output), bed material storage capacity, the assumed char conversion in the bubbling fluidized bed gasifier (BFBG), and the solar resource. This revealed that solar energy can be stored in the bed material to increase both the solar share and output while decreasing the CO₂ emissions, with a commensurate increase in the heliostat field area. For a solar multiple of 3 and bed material storage capacity of 16 h, the annual solar share is 21.8% and the annually averaged utilization factor of the heliostat field is 40.8%, assuming that the char conversion in the BFBG is 100%. However, the solar share is also found to be strongly dependent on the char conversion in the BFBG, so that the solar share decreases to zero as the conversion is decreased to 57%. The sensitivity of the SCTL performance to the quality of the solar resource is also reported.