Performance Improvement of Propane Refrigeration Unit in a Liquefied Natural Gas Plant

The aim of this study is to improve the performance of the propane refrigeration unit for precooling in a liquefied natural gas plant. Energy and exergy methods were used to analyze the performance of the unit. Aspen HYSYS v10 and Microsoft excel v2016 were used to carry out the simulation and analysis. Results obtained show that the base scenario has a mass flow rate of 17509kg/h. However, sensitivity analysis results show that decrease in pressure from the expansion valves causes a decrease in temperature of the propane refrigerant which in turn causes an increase in the mass flow rate of the propane refrigerant from 17509kg/h to 17814kg/h. Further results obtained considering the base scenario on the effect of the operating parameter on the compressor power show that the compressor power obtained is 761.3 KW. However, sensitivity and graphical analysis show that decrease in pressure from the expansion valves causes a decrease in temperature of the refrigerant which in turn causes an increase in the mass flow rate of the refrigerant. This increase in the mass flow rate of the refrigerant makes the compressor to do less work thereby reducing its power consumption from 761.3 KW to 678.3 KW, the cooler duty from 135KW to 125KW, exergy loss in the air cooler increases from 12.74KW to 11.77KW, the exergy loss in the compressor increases from 27.45KW to 25.35KW, the exergy loss in the heat exchanger decreases from 15.1KW to 14.3KW, and the expansion valve’s energy loss goes from 28.66KW to 33.52KW. The results of exergy efficiency for the propane pre-cooling cycle reveal that Scenario 5 have the lowest exergy efficiency (34.67%), which suggests greater irreversibilities within the process. The process has a strong potential for improvement since Scenario 1 has the best exergy efficiency (40.03%) and COP rises by 20% compared to Scenario 5. The findings indicate that altering the propane evaporator’s working parameters causes a larger creation of entropy, which lowers the exergy efficiency.