Liquefaction is suggested to be one of the best ways to utilize coalbed methane (CBM). Different from ordinary natural gas, CBM usually contains a high proportion of nitrogen, so the liquefaction system performance, especially the heat transfer characteristics, is different from that of the ordinary natural gas liquefaction processes, and will change along with the nitrogen content of CBM feed gas. Four liquefaction processes for nitrogen/methane mixture are evaluated. For the composition with nitrogen ranging between 0 and 70% and with the methane recovery rate of 95% as the restricted index, the heat transfer characteristics for the heat exchanger systems of these four processes are investigated and compared on the basis of the optimization results given by the previous studies. This investigation provides a direction for improvement of the liquefaction system performance, and gives reference for the selection of the liquefaction process for CBM with different nitrogen content.

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