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 for the coproduction of liquefied natural gas (LNG) and natural gas liquids (NGL) based on the mixed fluid cascade (MFC) refrigeration systems, as one of the most important and popular natural gas liquefaction processes. To carry out this analysis, at first, the proposed process is simulated, and then the exergy analysis of the process equipment is performed; finally, an economic model is used for the exergoeconomic analysis. The results include cost of exergy destruction, exergoeconomic factor, exergy destruction, and exergy efficiency. The results of the exergy analysis demonstrate that the exergy efficiency of the proposed process is around 53.83%, and its total exergy destruction rate is 42617.5 kW at an LNG and NGL production rates of 68.99 kg/s and 27.41 kg/s respectively. The results of exergoeconomic analysis indicate that the maximum exergoeconomic factor, which is 69.53%, is related to the second compressor in the liquefaction cycle and the minimum exergoeconomic factor, which is 0.66%, is related to the fourth heat exchanger in the liquefaction cycle. In this process, demethanizer tower holds the highest relative cost difference 100.78) and the first air cooler in liquefaction cycle has the lowest relative cost difference (1.09). One of the most important exergoeconomic parameters is the cost of exergy destruction rate. The second heat exchanger has the highest exergy destruction cost (768.91 $/Gj) and the first air cooler in the liquefaction cycle has the lowest exergy destruction cost (19.36 $/Gj). Due to the high value of fuel cost rate (as defined in exergoeconomic analysis) in heat exchangers, their exergy destruction cost is much higher than other devices.