System Optimization for Fischer-Tropsch Liquid Fuels Production via Solar Hybridized Dual Fluidized Bed Gasification of Solid Fuels

A new configuration of solar hybridized dual fluidized bed (DFB) gasification process is proposed with char separation for the production of Fischer-Tropsch (FT) liquid fuels from solid fuels of biomass and/or coal. The addition of carbon capture with sequestration and FT reactor tail-gas recycle configurations is also assessed. The studied FT liquid fuels production systems are simulated by using a pseudodynamic model incorporating a year long, hourly averaged solar insolation time-series. For the case with a 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) of 2.64 and bed material storage capacity of 16 h, the calculated annual solar share of the solar hybridized coal-to-liquids system can be increased from 12.2 to 20.3% by the addition of the char separation for a char gasification conversion of 80%. To achieve the well-to-wheel greenhouse gas emissions for FT liquid fuels parity with diesel derived from mineral crude oil, a calculated biomass fraction of 58% is required for the nonsolar coal case, also with a char gasification conversion of 80%. This fraction can be reduced to 30% by carbon capture and sequestration and further reduced to 17% by the integration of solar energy, based on a solar multiple of 2.64 and bed material storage capacity of 16 h. This reduction is significant given that biomass is much more expensive than coal. However, because of the higher content of light hydrocarbons content in the syngas produced with the studied biomass gasification, the specific FT liquids output per unit feedstock of the system decreases with an increase in the biomass fraction. As the biomass fraction is increased from 0 to 100%, this specific output is decreased from 59.6 to 48.3% but can be increased to 71.5 and 70.9%, respectively, by incorporating tail-gas recycle.