Impact of the reverse water-gas shift operating conditions on the Power-to-Liquid process efficiency

Abstract

Fischer-Tropsch based fuels from renewable electricity and carbon dioxide provide one possibility to defossilise the transport sector, especially where long distances and high loads require fuels with high energy density. In this work, a stationary Power-to-Liquid (PtL) process model is set up in Aspen Plus®. The process involves CO2 absorption, water electrolysis, CO2 activation by reverse water-gas shift reaction (rWGS), an oxyfuel burner, Fischer-Tropsch synthesis, product separation and hydrocracking. The influence of the rWGS operating conditions (pressure and temperature) on the overall process performance in terms of PtL-efficiency and hydrogen/ carbon efficiency is investigated. The operating conditions are varied between 550 and 950 ° C and 1–25 bar. The temperature and pressure dependent methane formation in the rWGS is found to have major influence on the efficiencies. For the base case, a maximum Power-to-Liquid efficiency of ηPtL = 38.7 % is obtained at 5 bar and 825 ° C, while a maximum hydrogen efficiency of ηH = 28 % results at 1 bar and 725 ° C. The carbon efficiency is found to be constant (ηC = 88 %). Sensitivity studies show that the optimum operating conditions are not affected significantly by variation of the investigated process variables.