Thermodynamic and environmental analysis of the hydrogen and combustible gas production in supercritical water partial oxidation system of coal

Supercritical water partial oxidation (SCWPO) is an eco-friendly coal treatment technology that lowers the temperature needed for complete coal gasification, promotes hydrogen output, enables targeted regulation of gaseous product composition, and eliminates gaseous pollutants. Current researches mainly focus on experiments and numerical simulations, with limited exploration in thermodynamics. The present study establishes an auto-thermal SCWPO cogeneration system for Hongliulin coal, employs sensitivity analysis to refine system parameters, and utilizes Life Cycle Assessment to evaluate the environmental impact of the hydrogen production system. When the outlet temperature of the SCWPO reactor increases, the preheating water flow and equivalence ratio (ER) enhance, the fraction of H₂ in the gas product rises; conversely, the fraction of the combustible gas (CH₄+CO + H₂) rises. The SCWPO system can be precisely tailored to yield high-purity hydrogen or combustible gas by modulating the amount of oxygen input. The system of combustible gas production is capable of generating 241.67 GJ h⁻¹ of energy and attaining a cold gas efficiency of 81.62 % when the ER is 0.25. The hydrogen production system can generate 1004.38 kg h⁻¹ of H₂ and 206 t h⁻¹ of steam at 0.5 MPa and 150 °C for an ER of 0.6. The optimized hydrogen production system achieved 90.97 % energy efficiency and 59.33 % exergy efficiency. The standard Global Warming Potential through carbon capture technology is 0.087 (kg H₂)⁻¹. The system developed in this paper benefits the industrial application of SCWPO and the optimization of subsequent processes.