Design of an integrated CO2 methanation system with CO2 capture from flue gas and H2 production from water electrolysis

Abstract

As one of the important Power to X technologies, CO2 methanation realizes the storage of green hydrogen and the emission reduction of flue gas CO2. In this study, process modeling was applied for CO2 methanation coupled with CO2 capture and water electrolysis. Aspen Plus and HYSYS models of 400 kW water electrolysis were set up for integration. The heat exchange network and the reaction temperature and catalyst usage of two methanation reactors are optimized. The effects of step-wise evolution of H2 flow on stream flows and reactors are also studied. The results show a system energy efficiency of 42.3% using a high-temperature solid oxide electrolysis cell (SOEC) and 30% monoethanolamide solution (MEA). The heat-exchange network significantly improves the efficiency to 61.5%. Optimizing two-stage methanation reactors realizes 98% CO2 conversion at 10018 h-1 gas hourly space velocity. The optimized reaction temperatures are 390 and 325 °C, respectively. The Aspen HYSYS dynamic modeling shows that the flows reach stability within 10 min under 1 kmol/h step-wise evolution of H2 flow. Longer time is required to approach the stability of the methanation reactor. Sharp evolutions of H2 flow cause higher amplitudes and a longer time to reach stability. The H2 flow lower than 35% of the initial value would result in the unstable behavior of the methanation reactor.