Mixed refrigerant cycle liquefaction process for coalbed methane with high nitrogen content

摘要

The liquefaction process adopting a mixed refrigerant cycle (MRC) for coalbed methane (CBM) with a high proportion of nitrogen is discussed in this paper. For CBM feed gas with nitrogen content ranging between 0 and 70 mol.%, the composition of the mixed refrigerant is optimised to minimise the system unit product liquefaction power consumption, and the corresponding system performance is obtained and compared. Meanwhile, the effects of the other two important technical indexes (liquefaction rate and methane recovery rate) are also studied. The results are compared with former researches about CBM liquefaction by adopting nitrogen expansion cycle with propane precooling and MRC with propane precooling. It is indicated that nitrogen content has great influences on the parameters and the performance of the CBM liquefaction processes. The results also show that the MRC liquefaction process is an efficient way for CBM liquefaction if the nitrogen content is not too high.