Production of Fischer-Tropsch Liquid Fuels from High Temperature Solid Oxide Co-Electrolysis Units

A model for high temperature co-electrolysis (HTCE) of carbon dioxide and water using solid oxide electrolytic cells (SOEC) for syngas production and subsequent conversion to liquid fuels by a Fischer-Tropsch (F-T) process is presented. The SOEC model is guided by experimental data from the literature, and the model is employed to explore the effect of temperature, pressure, and feedstock composition on syngas composition exiting the SOEC. The syngas is converted in a slurry bubble column F-T synthesis reactor in which the model approach of a once-through conversion of carbon monoxide is chosen, and the distribution of hydrocarbon products is determined by the Anderson-Schulz-Flory model. The overall system efficiency for liquid hydrocarbon fuels produced from electrical energy is found to be 54.8% HHV (51.0%-LHV). It is determined that operating the SOEC at low pressure (1.6 bar) versus higher pressure (5 bar) results in an efficiency gain of 2.6%. The economics of the production plant are evaluated for variations in electricity feedstock costs and operating capacity factors. The liquid fuels production costs range from 4.4 $/GGE to 15.0 $/GGE for electricity prices of 0.02 $/kWh to 0.14 $/kWh and a plant capacity factor of 90% to 40%, respectively.