Simulation and Optimization of LNG Production Unit for Energy Conservations

The prospect of LNG could become a major global energy source is one of the most debated issues. The Liquefied Natural Gas (LNG) supply chain and the properties that make this fuel environmental friendly is in high demand for energy supply. In this paper, at first, the process of converting the natural gas to LNG was simulated; then, the process is optimized to archive minimum energy consumption per ton of LNG produced. Using a three stage exchanger is the best way for minimization of energy consumption in LNG production unit. Outlet pressure from the compressor and also type of refrigerant in cooling system is very effective on rate of energy conservations. The best mass fraction for refrigerants in liquefaction cycle are 0.88 for methane and 0.12 for ethane. For subcooling cycle that fraction is defined as 0.6 for methane and 0.4 for nitrogen. The optimized pressure in outlet of compressors in liquefaction cycle is 650 kPa; also, for the subcooling cycle is 1800 kPa. The amount of consumed energy was 14.91 kW per ton of produced LNG.