A Process Synthesis Approach to Natural Gas Liquefaction

A new approach to the design of natural gas liquefaction processes, which could significantly reduce their energy consumption, is proposed. A graphical technique based on exergy and enthalpy is used to determine optimal paths for refrigeration systems. The analysis reveals that keeping refrigeration cycles in the two-phase region, including compression and heat removal, is the most efficient way of supplying the work required to remove heat from sub-ambient processes. The approach is validated using an Aspen Plus simulation of a natural gas liquefaction process with pure refrigerant in cascade; it is shown that work efficiency higher than 90% can be achieved when the process fluid as well as the working fluids in the cascade cycles are kept in the two phase region at every stage.