Investigation of renewable methanol production from CO2 hydrogeneration based on spectral splitting and heat integration

Abstract

This study concerns a green hybrid system of methanol production via CO2 hydrogeneration, where the full spectrum solar energy is separated by spectral beam splitter to generate high temperature heat and electrical energy for solvent regeneration in CO2 capture unit and water electrolysis in proton exchange membrane electrolyzer, respectively. Then, heat integration is conducted among the whole system to recover the internal waste heat and minimize the total energy requirement. Thus the intermittency solar energy can be efficiently stored into the transportable methanol product through energy carrier of H2. The entire integrated scheme is simulated using Aspen Plus, while energy, exergy and environmental performances are investigated comprehensively to reveal the improvements of proposed system. Results show that with the electrolytic power of 60 MW, methanol synthesis condition of 250 °C and 100 bar, space velocity lower than 10 m3/kgcat·h, the overall efficiency of the proposed system reaches up to 41.61% (MSCH). Through system-level heat integration and solar energy supplement, the heating and cooling utility is reduced by 60.38% and 42.10%, which significantly improves the overall efficiency to 54.31% in winter (MSCH-HI-W) and 81.77% in summer (MSCH-HI-S), with the largest energy loss obtained at electrolysis cell. From the standpoint of exergy, the overall exergy efficiency is 53.14% in winter (MSCH-HI-W) and 79.75% in summer (MSCH-HI-S). Consequently, 210.59 kmol/h of CO2 is taken in by the proposed system and ends up in valuable methanol of 170.15 kmol/h, highlighting the strong potential of heat integration for overall performance enhancement and providing guidelines for future development of renewable energy utilization and storage under low carbon vision.