Assessment of integrated energy systems for the production and use of renewable methanol by water electrolysis and CO2 hydrogenation

The conversion of renewable hydrogen and recycled CO2 to valuable fuels in power-to-liquids (PtL) systems could be a key solution to reduce CO2 emissions. Within this context, methanol is a promising candidate, both as an energy carrier and a chemical feedstock. This paper is focused on renewable methanol production and its use in a PtL integrated system based on a water electrolysis process fed by renewable energy sources (RES), a methanol synthesis and purification section and a high temperature solid oxide fuel cell. In particular, an analysis and comparison of two power-to-methanol integrated systems based on different electrolysis technology, i.e. the commercially mature alkaline electrolysers and the innovative high temperature solid oxide cells, was carried out. A thermal energy storage system based on a phase change material and an organic Rankine cycle engine can also be included, depending on the chosen electrolysis process. Detailed models of the main sections were developed and implemented by using Aspen Plus. A comprehensive analysis through mass and energy balances was carried out to evaluate performance indices of each section and of the overall plant for the two different configurations. A global efficiency of the overall system slightly lower than 0.35 was obtained for both systems.