CBM Liquefaction Process Integrated with Distillation Separation of Nitrogen

概要

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Coal-bed methane (CBM) is an important energy resource globally, and liquefaction is a good option for the recovery of CBM. Unlike ordinary natural gas, CBM usually contains a substantial proportion of nitrogen, which cannot be removed by ordinary purification technologies of liquefied natural gas engineering. Nitrogen can be separated from CBM by distillation after liquefaction, which is an efficient separation technology. A novel process that integrates liquefaction and distillation is proposed in this paper. In this process, a nitrogen expansion cycle is used to provide cold energy for both the liquefaction process and the condenser in the distillation column, and the cooling capacity of the re-boiler in the distillation column is used to cool CBM. The cold enriched nitrogen gas released from the top of the distillation column is introduced into the liquefaction process to recover its cold energy, while the enriched methane from the bottom of the distillation column is introduced into the liquefaction process to be further cooled, and thus liquefied natural gas at atmospheric pressure is produced. For CBM with a nitrogen content between 10 and 70%, the parameters of this integrated process are optimized to minimize the system unit power consumption. The corresponding system performance, including unit power consumption, product purity and methane recovery rate, is compared and analyzed for CBM with different nitrogen contents.