Calcium oxide for CO2 capture: Operational window and efficiency penalty in sorption-enhanced steam methane reforming

Calcium oxide (CaO) is a material that is being widely investigated in the context of CO2 capture. One such application is as a CO2 sorbent in the sorption-enhanced steam methane reforming processes (SERP). CO2 is captured in an adsorption mode, where the conversion of CH4 to H2 is also enhanced, and released later in a separate desorption mode. This work presents an analysis of the relation between different process conditions and parameters during both adsorption and desorption modes. The interrelation between these conditions and the sorbent properties as well as the targeted carbon capture ratio is analysed. Conditions relevant for capturing 85% of carbon in the feed on CaO are determined and interlinked. A steam-to-carbon ratio of 4.2 has been determined to be relevant under 600 °C and 17 bar adsorption conditions. Similarly, process conditions relevant for regenerating the sorbent are determined and interlinked. For purge steam-to-CO2 ratio of 1.8 at a desorption pressure of 1 bar, relevant desorption temperature has been calculated to be 820 °C. System simulations under these adsorption and desorption conditions resulted in a system efficiency of 50.8%. Effect of tuning process operating conditions on system efficiency as well as the efficiency penalty associated with the regeneration of the sorbent are investigated by process simulations using Aspen Plus®. Possible system heat integration routes to reduce the efficiency penalty are proposed and the results of the process simulations are presented.