| Developing trend of liquefaction technology is large scale natural gas liquefaction process,the focus of our paper is decreasing unit power consumption with the increase of single train capacity.MFC and AP-X processes that both comprise three refrigeration cycles are simulated and analyzed by software Aspen HYSYS.Quantitative analysis is conducted for MFC process with the variation of water-cooler outlet temperature,the factor that has greatest effect on process performance is indentified.The combination of pure nitrogen and high operation pressure level is recognized as the most efficient to create the cold temperature required for the sub-cooling section of the AP-X process.Then,the characteristic of excellent numerical calculation and user friendly interface of MATLAB and powerful thermo-physical property package of Aspen HYSYS is combined,and genetic algorithm is invoked to optimize the MFC and AP-X processes globally.After optimization,the unit power consumption can be reduced to 4.655kW·h/kmol and 4.337 kW·h/kmol respectively,13.15% and 15.56% energy saving are achieved compared with that of base case.Furthermore,configuration optimization are conducted for both MFC and AP-X processes,optimal configuration is selected in terms of unit power consumption,exergy losses and complexity.Meanwhile,this paper also proposes a novel three stages natural gas liquefaction process,which more efficiently provides refrigeration over pre-cooling,liquefaction and sub-cooling temperature range for feed gas.The unit power consumption of the novel 3X process can be decreased to 4.145kW·h/kmol,which is 5.15% and 4.42% less than that of optimized MFC and AP-X processes,and the corresponding exergy efficiency increases to 53.20%.Furthermore,different liquefaction rate task can be easily accomplished only by adjusting operation parameters of sub-cooling cycle,and the high exergy efficiency of the novel liquefaction process indicates good adaptability to varying natural gas compositions. |
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