Exergoeconomic Evaluation of LNG and NGL Co-production Process Based on the MFC Refrigeration Systems

In this paper, exergy and exergoeconomic analysis is performed on the recently proposed process forthe coproduction of liquefied natural gas (LNG) and natural gas liquids (NGL) based on the mixedfluid cascade (MFC) refrigeration systems, as one of the most important and popular natural gasliquefaction processes. To carry out this analysis, at first, the proposed process is simulated, and thenthe exergy analysis of the process equipment is performed; finally, an economic model is used for theexergoeconomic analysis. The results include cost of exergy destruction, exergoeconomic factor,exergy destruction, and exergy efficiency. The results of the exergy analysis demonstrate that theexergy efficiency of the proposed process is around 53.83%, and its total exergy destruction rate is42617.5 kW at an LNG and NGL production rates of 68.99 kg/s and 27.41 kg/s respectively. Theresults of exergoeconomic analysis indicate that the maximum exergoeconomic factor, which is69.53%, is related to the second compressor in the liquefaction cycle and the minimumexergoeconomic factor, which is 0.66%, is related to the fourth heat exchanger in the liquefactioncycle. In this process, demethanizer tower holds the highest relative cost difference (100.78) and thefirst air cooler in liquefaction cycle has the lowest relative cost difference (1.09). One of the mostimportant exergoeconomic parameters is the cost of exergy destruction rate. The second heatexchanger has the highest exergy destruction cost (768.91 $/Gj) and the first air cooler in theliquefaction cycle has the lowest exergy destruction cost (19.36 $/Gj). Due to the high value of fuelcost rate (as defined in exergoeconomic analysis) in heat exchangers, their exergy destruction cost ismuch higher than other devices.