Thermodynamic Assessment of a Geothermal-Driven CO2-to-Synthetic Gas System

Abstract

Geothermal energy is a reliable low-carbon source of baseload power, yet its potential is often limited to electricity generation while CO2 contained in geothermal non-condensable gases remains underutilized. This study proposes and analyzes an integrated geothermal-driven system combining an Organic Rankine Cycle, CO2 capture, a proton exchange membrane electrolyzer, and a multi-stage Sabatier reactor for synthetic methane production. The configuration enables simultaneous generation of electricity, hydrogen, and methane within a unified thermodynamic framework. A steady-state energy and exergy analysis evaluates the effects of production well temperature, ORC operating conditions, Sabatier reactor pressure, and electrolyzer power input on system performance. Results show that increasing production well temperature from 420 K to 500 K raises net power output from approximately 2500 kW to 5500 kW, while exergy destruction increases from 6800 kW to 15,500 kW, reducing overall efficiencies. A Sabatier reactor pressure of 15 bar provides a suitable methane-hydrogen fuel mixture applications.