Multi-aspect assessment of a novel geothermal-driven polygeneration arrangement using water electrolyzer, methanol synthesis unit, and Goswami cycle

Abstract

Geothermal energy’s renewable nature with minimal emissions compared to fossil fuels has led to valuable polygeneration models in geothermal-rich regions, promoting energy sustainability. Key challenges include improving integrated structures due to these resources’ low/medium temperature nature and assessing the feasibility of producing essential products (e.g., hydrogen and methanol), typically produced in structures with substantial pollution. The proposed system’s innovations focus on reducing irreversibility through thermal integration, introducing a negative CO2 emission structure, and utilizing CO2 hydrogenation based on geothermal energy for methanol production. Hence, the system encompasses a geothermal power plant, a Goswami cycle, a direct hydrogenation methanol synthesis unit, and a proton exchange membrane electrolyzer. The findings show generating methanol at a rate of 0.85 kg/s, domestic hot water at a rate of 2.231 kg/s, chilled water at a rate of 3.931 kg/s, and electric power at a capacity of 21,530 kW. Hence, the system’s thermal, electrical, and exergy efficiencies are determined to be 7.54 %, 3.87 %, and 47 %, respectively. Furthermore, the sum unit cost of products and the levelized energy cost equal 0.0272 $/GJ and 0.17 $/kWh, correspondingly. Additionally, a net present value of 65.86 M$ and a total yearly cost of 37.52 M$ are the results of the economic assessment. The current research demonstrates a negative CO2 emission from an environmental standpoint. The attainment of negative CO2 emissions is due to using CO2 as input material in the system. Also, the system’s net present value surpasses the total annual cost by 1.75 times, mainly due to its ability to produce products like methanol, generating revenue to offset initial costs. The proposed system is ideal for geothermal energy sites near seawater, promoting environmental preservation by reducing pollutants. Finally, it is suggested that the system’s operation be optimized and an experiential setup be used for future research.