Methanol synthesis from renewable H2 and captured CO2 from S-Graz cycle – Energy, exergy, exergoeconomic and exergoenvironmental (4E) analysis

Thermodynamic, economic and environmental analyses of a combined CO ₂ capturing system, including, geothermal driven dual fluid organic Rankine cycle (ORC), proton exchange membrane electrolyzer (PEME), S-Graz cycle and methanol synthesis unit (MSU) were carried out. The presented zero emission system was designed based on the oxy-fuel combustion carbon capturing to produce power, hydrogen and methanol, while released CO ₂ can be captured. Generated renewable power by the ORC was utilized by the PEME to produce renewable hydrogen. Part of the produced hydrogen is fed to the MSU, while the rest was stored in hydrogen tanks. In fact, CO ₂ hydrogenation to produce methanol suggested via direct methanol synthesis in order to utilize the captured CO ₂ from the S-Graz cycle. Exergy efficiency of the system defined to analyze the system thermodynamically, while SPECO method utilized to evaluate system economically. Results revealed that the most important part of the system is the S-Graz cycle, from the viewpoint of capital investment. Also, the average product unit cost of 24.88 $/GJ obtained for the whole system.