Exergy Efficiency Analysis of a Power-to-Methane System Coupling Water Electrolysis and Sabatier Reaction

Abstract

Power-to-methane (PtM) systems coupling solid oxide electrolysis cell (SOEC) and Sabatier reactors offers an efficient and promising pathway to integrate the renewable/nuclear power with the existing natural gas network. SOEC operates at a higher temperature and yet produce hydrogen or syngas with a controllable H2/CO ratio with higher efficiency compared to low temperature electrolyzers. Besides, with the coupling of the SOEC and the Sabatier reactor, methane can be synthesized in one reactor from renewable energy. In this study, we firstly compared the power-to-hydrogen processes using the alkaline electrolysis cell (AEC), the proton exchange membrane electrolysis cell (PEMEC) and the SOEC. A factor of 38% is used to convert electricity to primary energy for first law efficiency analysis. Exergy efficiency analysis is also carried out to distinguish the qualities of the heat, electricity and gaseous fuels. The results show the PtM system using SOEC is more efficient than those using the other electrolysis technologies due to lower overpotential and better heat coupling. Particularly, the intermediate temperate SOEC exhibits a better heat coupling with the Sabatier reactor rather than the high temperature SOEC to further improve the system efficiency. Figure 1