Thermodynamic-Certified Conceptual Design of a DMR Refrigeration System for the Natural Gas Liquefaction Process

The manufacturing process for liquefied natural gas (LNG) is a highly capital-intensive and energy-intensive process, whose design and operation need to be continuously optimized. In this paper, a new conceptual design with the operation for a dual mixed refrigerant (DMR) LNG liquefaction process coupling turbo expansion and Joule–Thompson expansion technologies has been developed, modeled, and analyzed. The new development uses ethane and propane as the mixed refrigerant in the precooling cycle and meanwhile employs a turboexpander to recover notable energy from the feed gas to support the main refrigeration cycle. Compared with the current propane-precooled mixed refrigerant process, the thermodynamic analysis employing the temperature and specific enthalpy diagram can certify the energy-saving opportunities of the new DMR LNG process. Based on rigorous modeling and simulation results, the comprehensive economic analysis demonstrates that the new DMR LNG process could save 12.9% of the total capital cost and 7.4% of the total operating cost compared with the base propane-precooled mixed refrigerant LNG process.