Optimization of Small-Scale Natural Gas Liquefaction using Nitrogen Expander with Precooled Cycle

Nitrogen expander is the liquefaction process which suitable for small scale liquefied natural gas plant because its characteristic. However, the major issue of technology is low energy efficiency. In this study, optimization of small-scale natural gas liquefaction process using nitrogen expander with precooled cycles were conducted. The specific energy consumption is chosen as an objective function with decision variables are natural gas pressure after compression, nitrogen pressure after compression, inlet temperature of high pressure expander, evaporation temperature in precooling cycle, and type of precooling refrigerant. The refrigerant used for precooling cycle are propane, cyclopropane, isobutane, butane, and neopentane. The simulation and optimization processes are are performed by UniSim and GAMS software. The results show that integrating precooling cycle to the nitrogen expander system can reduce specific energy consumption up to 25, 24% and propane is the most effective precooling refrigerant.