Dynamic system modeling and simulation of a power-to-methanol process based on proton-conducting tubular solid oxide cells

The importance of methanol as a basic building block of the chemical industry and as a means of chemical energy storage of renewable energy sources (e.g. wind & PV) will steadily increase in the upcoming years. Based on renewable electricity and through the coupling of a proton-conducting steam electrolyzer for the generation of pure H2 with a heterogeneously catalyzed direct synthesis of methanol from anthropogenic CO2, an attractive method for the production of methanol can be provided. To enable an efficient and economic application of these so-called power-to-methanol processes, high system efficiencies as well as suitable concepts for system control as well as system and heat integration for alternating operating conditions are of particular importance. In this work, a transient and real-time capable system model of a power-to-methanol process based on tubular proton-conducting high temperature electrolyzers is presented. The obtained stationary simulation results reveal beneficial operational windows and system efficiencies (0.488 to 0.617) with respect to the chosen process design and heat integration concept. The power-to-methanol process model also incorporates a multitude of feedback control loops or controllers, to manipulate relevant operating parameters of all employed sub-processes in case of fluctuating power inputs. The presented studies assess the transient responses of the modeled power-to-methanol system to defined step changes of the apparent cell voltage under negative feedback control of crucial operational parameters.