Optimization of Inorganic Refrigerants in Cascade LNG Liquefaction Systems: A Response Surface Methodology Approach for Enhanced Energy Efficiency and Sustainability

The global energy transition has intensified the demand for sustainable liquefied natural gas (LNG) production, necessitating advanced refrigeration systems with minimal environmental impact. This study presents a comprehensive thermodynamic optimization of inorganic refrigerants (xenon, argon, krypton, nitrogen) in cascade LNG liquefaction cycles using response surface methodology (RSM). Through Aspen HYSYS modeling and I-optimal design experiments, key performance metrics—coefficient of performance (COP), cooling capacity, specific work, exergetic efficiency, and overall thermal efficiency—were evaluated across varying evaporating temperatures (−50°C to −30°C) and pressure regimes (10–30 bar). Results demonstrate that xenon achieves superior performance, with a COP of 3.6 and exergetic efficiency of 89% at optimal conditions (−44.5°C, 10.78 bar), outperforming conventional mixed refrigerants (C3MR) by 16.6% in specific energy consumption. Exergy analysis reveals that xenon minimizes irreversibility in compression and heat exchange stages, reducing exergy destruction by 21% compared to nitrogen. However, economic constraints due to xenon’s high cost highlight the trade-offs between efficiency and scalability. This work advances sustainable LNG production by identifying energy-efficient refrigerant alternatives while providing a robust RSM framework for industrial process optimization.