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

Abstract

The production of synthetic fuels from CO2 and water, by using renewable power sources for hydrogen production, is one approach to defossilize the “difficult-to-electrify” sectors. In the Power-to-Liquid process the CO2 is activated at high temperature via reverse water-gas shift reaction (RWGS). The produced syngas is then converted to hydrocarbons via Fischer-Tropsch synthesis (FTS). In this work the influence of the operating conditions in the RWGS reactor on the Power-to-Liquid process is investigated. The evaluation of the optimum operating conditions is not straightforward. On the one hand, increasing the RWGS temperature and decreasing the RWGS pressure leads to a higher CO2 conversion and less CH4 formation, thus higher CO yield. On the other hand decreasing the pressure leads to an increase in power consumption due to additional compression work, while higher temperatures require additional high temperature heat. The effect of this variation is assessed and discussed. A process model is set up in Aspen Plus®. Temperature and pressure in the RWGS reactor are varied and the optimum operating conditions, in terms of high Power-to-Liquid / Hydrogen and Carbon efficiency, will be presented. Additionally, sensitivity studies are conducted to systematically address the influence of for example varying electrolyzer efficiencies and FT operating conditions on the optimum RWGS operating conditions. Major impacts on the efficiencies will be outlined and quantified.