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

Abstract

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