Modelling and Simulation of a CO2 System as a Replacement for Propane in the Pre-Cool Loop of a Propane-Mixed Refrigerant Cycle

Abstract To fulfil the energy needs of the nations where it is regasified and delivered via pipelines, specialist tankers transport liquefied natural gas (LNG), a reliable and efficient energy source, across the sea. To improve efficiency and environmental acceptability, research is being done on substituting carbon dioxide for propane in the precool loop of the propane-precooled mixed refrigerant cycle. The primary goal of the research is to compare carbon dioxide and propane as refrigerants for the precooling loop of a propane-mixed refrigerant (C3-MR) cycle, which is utilised to liquefy natural gas, utilising Aspen HYSYS to design the plants. The performance of CO2 and propane were examined in this study using various process factors that were discovered through sensitivity analysis. The study determined both refrigerants’ coefficients of performance (COP), which show how well they cool while consuming less energy. In comparison to propane, which had a COP of 3.555, carbon dioxide showed a slightly higher COP of 3.728, indicating that it was more effective at transmitting heat under the given circumstances. The impact of variations in the precooling refrigerant pressure and molar flow rate on the compressor's duty for the carbon dioxide and propane precooling cycles was also examined in this study. Both refrigerants demanded more effort from the compressors as the molar flow rate was raised, but carbon dioxide fluctuated in compressor duty a little more than propane. In a similar vein, both refrigerants showed reduced compressor workload with increasing pressure, with carbon dioxide once more exhibiting somewhat greater compressor duty changes. Based on the data gathered, the study came to the conclusion that carbon dioxide, with its greater coefficient of performance, superior heat transfer efficiency, safety advantages, and less environmental impact, was the best refrigerant for the precooling loop in the C3-MR cycle.