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.