Mixed Refrigerant Self-Precooling Recuperator-Assisted Refrigeration Cycle for Energy-Efficient and Cost-Effective Natural Gas Liquefaction

Abstract

This study proposes an energy efficient closed-loop self-recuperative mixed refrigerant cycle for the liquefaction of natural gas. Three distinct cases were developed, employing a combination of high-boiling and low-boiling refrigerants and optimized using multi-variate Coggin’s optimization algorithm. The study reveals that the proposed case III exhibits the lowest specific energy consumption, registering at 0.2712 kWh per kilogram of natural gas. This performance is notably superior, outperforming proposed cases I and II by 27.61% and 34.11%, respectively. The exergy analysis also underscores the energy-efficient nature of proposed case III, as indicated by its minimal exergy destruction of 10,073 kW. Further, proposed case III is also found to be the most thermo-economic viable case, with its lowest operating cost ($10.49 million per annum) and relatively lower total annualized cost. The results highlight the potential of the proposed closed-loop self-recuperative mixed refrigerant cycle in improving process thermodynamics and economics, adding value to the United Nation’s Sustainable Development Goal 7 (Clean and affordable energy). Further, the findings also empower researchers and industry professionals with valuable insights for implementing self-recuperative mixed refrigerant cycles in commercial natural gas liquefaction and similar industrial processes.

Keywords: Self-recuperative precooling, Offshore LNG process, Multivariate Coggins optimization, LNG process optimization, Natural gas transportation