Integrated power to methanol processes with steam-assisted direct air capture

Carbon dioxide (CO2) generated from the combustion of fossil fuels has resulted in global warming. Utilizing CO2 from direct air capture (DAC) and green hydrogen to produce methanol is a potential method to reverse this process; however, its technical and economic feasibility remains controversial. In this study, three distinct power-to-methanol systems integrating adsorption-based DAC, alkaline water electrolysis, and thermochemical methanol synthesis were investigated. The modelling results showed that the energy consumption of the base case (PtM) was 49.58 GJ tCH3OH−1, which decreased to 45.89 GJ tCH3OH−1 using a steam-assisted DAC process (S-PtM). The heat-integrated S-PtM system (I-S-PtM) could further reduce the energy consumption to 37.84 GJ tCH3OH−1. In detail, high-grade waste heat (>100°C) was directly transferred to DAC and methanol distillation units via heat exchangers. Low-grade waste heat (>60°C) was upgraded and provided to DAC unit via heat pumps. In the I-S-PtM system, 93 % of the heat and 90 % of the cold demands could be satisfied, which achieved 23.7 % and 17.5 % reduction compared to that of the PtM and S-PtM systems. Consequently, the I-S-PtM system demonstrated a high total energy efficiency (53 %) and a low methanol production cost (801.79 $ tCH3OH−1) based on an electricity price of 60 $ MWh−1. Moreover, when powered by renewable electricity with the electricity price less than 41.3 $ MWh−1, the I-S-PtM is more cost-effective than the conventional fossil fuel-to-methanol process. In China, replacing gasoline with methanol from the I-S-PtM process using abandoned renewables could reduce gasoline consumption by 4.4 % and emissions by 8.47 MtCO2 per year.