Thermodynamic design of natural gas liquefaction cycles for offshore application

•We perform a thermodynamic study for selecting offshore LNG cycles.•We propose closed Claude cycle to use natural gas (NG) itself as refrigerant.•The optimized NG Claude cycle is compared with C3-MR and nitrogen cycles.•The proposal is a good candidate from the point of efficiency and compactness.

A thermodynamic study is carried out for natural gas liquefaction cycles applicable to offshore floating plants, as partial efforts of an ongoing governmental project in Korea. For offshore liquefaction, the most suitable cycle may be different from the on-land LNG processes under operation, because compactness and simple operation are important as well as thermodynamic efficiency. As a turbine-based cycle, closed Claude cycle is proposed to use NG (natural gas) itself as refrigerant. The optimal condition for NG Claude cycle is determined with a process simulator (Aspen HYSYS), and the results are compared with fully-developed C3-MR (propane pre-cooled mixed refrigerant) JT cycles and various N2 (nitrogen) Brayton cycles in terms of efficiency and compactness. The newly proposed NG Claude cycle could be a good candidate for offshore LNG processes.