Liquefaction is considered as one of the best methods for using coalbed methane (CBM). Unlike conventional natural gas, CBM usually contains a high proportion of nitrogen, so the liquefaction system performance, especially the heat transfer characteristics, differs from that of conventional natural gas liquefaction processes and depends on the nitrogen content. Irreversibility is an important aspect of the heat transfer charactenstics and reflects the potential for further optimization of the heat exchanger system. In this paper, four liquefaction processes for nitrogen/methane mixtures are evaluated. Heat exchanger irreversibilities in each of these four processes are analyzed and compared for CBM nitrogen contents ranging between 0 and 70% and a methane recovery rate of 95% on the basis of optimization results provided by previous studies. It is revealed that the irreversibility in the heat exchanger system decrease with the increase of nitrogen content, and it is higher for the mixed refrigerant system than for the nitrogen refrigerant system. The results provide a direction for improvement of the liquefaction system performance and a reference for the selection of liquefaction processes for CBMs with different nitrogen contents.