Concept of a solid oxide electrolysis-molten carbonate fuel cell hybrid system to support a power-to-gas installation

Abstract

This study outlines a concept for improving a power-to-gas (P2G) system through the implementation of highly efficient high-temperature electrolysis combined with a molten carbonate fuel cell (MCFC) as a CO2 capture unit for a power plant. Laboratory scale experiments demonstrate that the MCFC could be used for CO2 separation, opening the way to capture of CO2 from flue gases at coal-fired power stations, while maintaining both high electric efficiency and a high CO2 separation factor. Improved energy efficiency can be achieved by the lower electricity requirement of high temperature electrolysis compared to other technologies. Results obtained from experimental investigations show that a CO2 separation rate in excess of 90 % is achievable through adjusting the cathode inlet flow. It should be noted that flue gas must be mixed with air before delivery to the MCFC. Controlled flow of inlet gases to the anode can raise electric efficiency to above 35 % for both laboratory-size and full-scale MCFC. The benefits of the concept are manifested by lower power consumption of the system and no energy penalty for the CO2 capture process. Additionally, the system enjoys good thermal management because all devices run at elevated temperatures (Sabatier reactor at 300 °C, MCFC at 650 °C, solid oxide electrolyzer at 700–800 °C). The proposed improvements increase the system's competitiveness relative to alternative P2G systems and reduce the price of substitute natural gas. Secondly, it will eliminate the consumption of heat from the host coal-fired power plant. Thirdly, the entire system will be more straightforward, compact, and modular, allowing any future scale-up to be implemented without technological difficulties. Finally, the amount of energy required to produce hydrogen will decline by around 25 %.