Energy and exergy analyses of a zero emission power plant for coproduction of electricity and methanol

In this study, we study and evaluate a zero emission integrated system, as taken from the literature, for coproduction of electricity and methanol. The investigated integrated system has three subsystems: Water electrolysis, Matiant power plant (oxy-fuel combustion of pure methane), and methanol production unit. The system and its components are analyzed energetically and exergetically. The rates of exergy destructions, relative irreversibilities, and sustainability indexes of each subunit of each subsystem, as well as the overall system are analyzed to identify the greatest exergy losses and possible future research directions. The total rate of exergy destruction of the overall system is calculated to be around 280 MW. The greatest rate of exergy destruction, therefore the greatest irreversibility, occurs within the power plant unit (about 60 % of the total rate of exergy destruction). The energy efficiencies of electrolysis, power plant, and methanol synthesis unit are found to be 30 %, 76 %, and 41 %, respectively. The exergy efficiencies of electrolysis, power plant, and methanol synthesis unit are found to be 30 %, 64 %, and 41 %, respectively. Depending on the utilization of the heat rejected from the different units of each subsystem, the overall system could have energy and exergy efficiencies up to 68 % and 47 %, respectively.