Study on the carbon migration from fossil fuel to liquid methanol by integrating solar energy into the advanced power system

Abstract

Coupling advanced systems with carbon dioxide (CO2) capture and CO2-to-methanol technologies is a possible solution for both greenhouse gas emissions and low-carbon use of fossil energy. In view of this, this study further develops an advanced molten carbonate fuel cell (MCFC)/steam turbine (ST) hybrid system. The existing single pressurized liquefaction for storing CO2 is expanded to co-exist with liquid methanol synthesis for storing CO2. In detail, the valid thermodynamic models are presented, and the evaluation criteria for energy conversion are described. The case study shows that the energy efficiency of the referenced MCFC/ST system reaches about 62.60%, without cutting down this performance, the photovoltaic methanol efficiency is in the range of about 54% to 63%, which is at a current leading level. This study also investigates the effect of oxygen purity in cryogenic air separation unit (ASU), hydrogen production pressure of proton membrane electrolytic cells (PEMEC), and incident irradiation on CO2-to-methanol conversion. The results indicate that O2 purity of 0.97 in ASU, H2 production pressure of 13.6 bar in PEMEC and a dual-axis tracking method is recommended. These findings provide theoretical guidance for improving the CO2-to-methanol performance and providing a possible solution to the storage of intermittent renewable electricity.