Proposal and simulation of a geothermal-driven water electrolysis unit integrated with a CO2 methanation process toward a novel sustainable framework

Abstract

This paper presents a novel multigeneration structure powered by geothermal energy, featuring a geothermal power plant, water electrolyzer unit, methanation reactor, fuel and utility production unit, supercritical-carbon dioxide cycle, and both high-temperature and low-temperature organic Rankine cycles. Simulated in Aspen HYSYS software and analyzed from energy, exergy, economic, and environmental (4E) perspectives, the process, under base operating conditions, is capable of producing 20,940 kW of power, 620.70 kg/h of hydrogen, 4,913 kg/h of oxygen, 12.35 kg/s of domestic hot water, 5.293 kg/s of chilled water, and 2.659 kg/s of carbon dioxide with over 99% mole purity. Efficiency assessments reveal energy, exergy, and electrical efficiencies of 10.69%, 48.53%, and 3.73%, respectively, with a total unit product cost of $3.11/GJ and a net present value of $67.40 million. The water electrolyzer unit, with an 88.94% exergy efficiency and a 10% contribution to total system irreversibility, is identified as the most efficient subsystem. The geothermal power plant accounts for the highest system irreversibility at 61%, while the combustor in the fuel and utility production unit contributes 11,250 kW of irreversibility. Environmentally, the system operates with zero emissions and significantly reduces annual CO2 emissions compared to coal, oil, biomass, and natural gas power plants by 453.14 × 106, 576.80 × 106, 111.92 × 106, and 344.10 × 106 kg, respectively.