Innovative single-mixed refrigerant in integrated LNG/NGL process to improve energy efficiency

Abstract

This study aims to propose an energy-efficient integrated process of extracting natural gas liquids (NGL) and producing liquefied natural gas (LNG). To achieve lower energy consumption, three integrated NGL recovery and natural gas liquefaction processes, base, refluxed, and thermally coupled distillation (TCD), are investigated and optimized using a modified vortex search optimization algorithm by adjusting the compositions of mixed refrigerants. The results indicate that the TCD configuration achieves the most efficient energy performance, with a specific energy consumption (SEC) of 0.276 kWh/kgLNG and a specific reboiler duty (SRD) of 0.187 kWh/kgNGL. In comparison, the base case exhibits identical SEC but higher SRD (0.259 kWh/kgNGL), while the refluxed case shows significantly higher SEC (0.387 kWh/kgLNG) with an SRD of 0.195 kWh/kgNGL, which is comparable with TCD case. Furthermore, in the hot-cold composite curve of refluxed, the smallest gap between the hot and cold curves and the flat and low Delta T curve indicates its high energy efficiency compared to other cases. Consequently, as shown in this study, the comprehensive approaches combining mixed refrigerant cycle, process intensification, and optimization highly improve energy efficiency and lead to determining TCD configuration as the bestperforming LNG/NGL process in terms of energy.