Hybridization of solid oxide electrolysis-based power-to-methane with oxyfuel combustion and carbon dioxide utilization for energy storage

Abstract

The storage of excess or low-carbon electricity in the form of synthetic gas using power-to-gas technologies is a promising approach to enable high shares of renewables in power generation and reduce the fuel carbon content. However, the efficiency of standalone, low-temperature electrolysis-based power-to-methane (PtM) processes is presently limited. As a way of enhancing the potential of this technology to support the decarbonization of energy systems, this study investigates a high-temperature electrolysis-based PtM process and its integration with oxyfuel combustion to co-generate synthetic methane, heat and power. The system incorporates in-situ heat, oxygen, carbon dioxide (CO₂) and water recycling. The energy and exergy-based performance of the compound system and its main structures are investigated using an overpotential-based electrochemical model. Depending on electrolysis operating temperature (800–1000 °C) and pressure (1–10 bar), overall energy and exergy efficiencies range from 75.8% to 79.3% and 64.5% to 67.4%, respectively. In quasi-continuous operation, a 6.4 MW_e (AC input) hybrid PtM system would avoid approximately 1.9 GWh_e of electricity consumption for oxygen-air separation, and sink 6.6 kt of CO₂ from the oxyfuel co-generation plant annually. In parallel, 3.1 MW_th of heat could be recovered from the pre-methanation compressor and oxyfuel conversion products for use in external applications. Based on a carbon balance evaluation from initial resource extraction to SNG conversion, the PtM-oxyfuel hybridization investigated could effectively contribute to raise the electricity greenhouse gas (GHG) emission threshold below which SNG could environmentally compete with natural gas, relative to low-temperature electrolysis-based PtM and conventional post-combustion CO₂ capture.