Comparative energy, economic, and environmental analyses of power-to-gas systems integrating SOECs in steam-electrolysis and co-electrolysis and methanation

The integration of solid oxide electrolysis cells (SOEC) and methanation as a power-to-gas system is a promising technology for renewable energy storage and CO2 utilization. SOEC can operate in both modes: water electrolysis for hydrogen production and water/carbon dioxide co-electrolysis for syngas production. The operating conditions and performance of the integrated systems between the methanation and SOECs with both modes are different. To study the direct and indirect utilization of CO2 in the methanation integrating SOEC with both modes, this study focuses on the comparative analysis of two integrated systems between the methanation and SOECs with water electrolysis mode and co-electrolysis mode for green natural gas production from fermentation waste in all aspects such as energy and economic analyses. Additionally, heat integration of both integrated systems with pinch analysis is studied. Results indicate that the methane yield of mixed CO and CO2 methanation is higher than that of CO2 methanation. The integrated system between the methanation and SOEC with co-electrolysis mode achieves a higher system efficiency, compared to that of a system using SOEC with water electrolysis mode. The efficiency of both systems can be improved by heat integration which increases by 4.60–6.09%. Moreover, the levelized cost of the product in the system using SOEC with water electrolysis of 201.35–211.86 $/MWh is lower than that of the system using SOEC with co-electrolysis mode. The CO2 emission intensities of the system using SOEC with co-electrolysis mode by power consumption sources from the wind turbine are the lowest about 1.37 kgCO2,e/kWh.