Hydromethane generation through SOE electrolyser: advantages of H2O-CO2 co-electrolysis

This paper aims to investigate a system based on Solid Oxide Electrolyser (SOE) and multistage methanation unit for "hydromethane" production. The presented solution can contribute to mitigate environmental issues related to CO2 reuse and critical issues linked to RES plants interconnection to the grid, beyond that to limit their curtailment. The produced gas mixture, a blend of CH4 and H2, is considered particularly suitable for transportation applications and it can be seen as an interesting energy storage solution. An accurate model of SOE-methanation integrated system was developed in Aspen Plus environment. It allowed to deeply analyse system performance, including the cases of co-electrolysis/steam electrolysis, relative to SOE, and methanation from CO/CO2. A sensitivity analysis, varying the amount of CO2 sent to SOE and methanator, has allowed to determine the most convenient operation mode and the related optimized plant layout, leading to the maximization of advantages. In particular, up to contextual 60.2% and 21.9 MJ/Sm3 of overall efficiency and hydromethane LHV are obtainable by applying SOE technology, in co-electrolysis mode, for hydromethane generation from RES. These impacts are particularly relevant in consideration of the possible exploitation of hydromethane in the transport sector.