Simulation calculation and exergy analysis on liquefaction processes of natural gas with expander.

The energy consumption and exergy loss of external refrigeration cycle under different fraction of methane are calculated firstly. The results show the methane content has significant effect on the power consumption, and there is turning point near 50% mol content of methane at which the power consumption reaches its minimum. Then the simulation calculation of exergy loss and power consumption based on three typical flows for liquefying natural gas is carried out. Three flows selected in this study are “Nitrogen-methane single-stage expansion liquefying cycle with propane pre-cooling system” (Solution 1) and two kinds of “Two-stage expander nitrogen-methane refrigerant” (Solution 2 & 3). Simulations under steady-state are undertaken to ensure each process was compared on an identical basis. The results show the solution 1 has lower exergy loss than those of others. To be specific, solution 1 saves energy expense 1.5% and 7.7% than solution 2 and solution 3 respectively.