Process Design for the Offshore Production of Liquefied Natural Gas with Nonflammable Refrigerants

In this paper, a conceptual process design for a novel natural gas liquefaction plant developed especially for offshore application is presented. Onshore liquefied natural gas (LNG) production usually utilizes mixed refrigerant (MR)-based cycles for high efficiency, in terms of operating cost. This paper proposes a cascade process that uses nitrous oxide and nitrogen refrigerants. The liquefaction process can be subdivided into a precooling section in the vapor phase, a condensation section, and a subcooling section in the liquid phase. The vapor compression refrigeration cycle of nitrous oxide is applied to the precooling and the condensation sections, whereas the gas compression refrigeration cycle of nitrogen is applied to the subcooling section of LNG. The proposed process shows enhanced efficiency, compared to the conventional turbine-based processes with the specific power comparable to the MR processes.