Optimal design of self-recuperative single mixed refrigerant cycle for small-scale LNG production: Balancing thermodynamics, sustainability, and economics

This study presents a highly energy-efficient closed-loop self-recuperative mixed refrigerant cycle for natural gas liquefaction. Three distinct process configurations were developed using carefully selected mixed refrigerants and optimized using the multivariate Coggin's optimization algorithm. Among these, proposed case III emerged as the most efficient, achieving the lowest specific energy consumption (0.2712 kWh/kgNG), surpassing proposed cases I and II by 27.61 % and 34.11 %, respectively. Exergy analysis validated this superior performance, confirming that proposed case III had the lowest exergy destruction (10,073 kW). Although the sustainability assessment revealed that proposed case I achieved the highest sustainability index (SI = 9.97), proposed case III offered the best overall balance of energy efficiency, thermodynamic performance, and sustainability. Economic analysis further identified proposed case III as the most cost-effective design, with the lowest operating cost ($10.49 million/year) and a favorable total annualized cost. These findings underscore the potential of the proposed closed-loop self-recuperative mixed refrigerant cycle to significantly enhance both thermodynamic efficiency and economic viability. Furthermore, the study advances the objectives of the United Nations Sustainable Development Goal 7 (Affordable and Clean Energy), providing valuable insights for researchers and industry professionals aiming to implement self-recuperative mixed refrigerant cycles in commercial natural gas liquefaction and other industrial applications.