Wensheng Lin

CBM Liquefaction Processes Integrated With Adsorption Separation of Nitrogen

Coalbed methane (CBM) is a kind of important energy resources in the world. Liquefaction is a good option for recovery of CBM. Generally, CBM consists of a lot of nitrogen besides methane, which is usually required to be separated by adsorption before liquefaction, or by distillation after liquefaction. For the CBM adsorption-liquefaction processes, two novel processes are proposed, which integrate the two parts of adsorption and liquefaction together by utilizing the residue pressure of the waste nitrogen: the released nitrogen expanded directly to precool CBM, or further compressed and then expanded to liquefy CBM. Taking the unit product liquefaction power consumption as the major index and nitrogen content of CBM feed gas together with residue pressure of waste nitrogen as variables, the system performance of these two integrated processes is studied and compared with that of the nitrogen expansion liquefaction process without integration. By simulation and calculation with HYSYS, it is confirmed that system power consumption can be reduced by both methods to utilize the residue pressure, and for CBM with high nitrogen content, the energy conservation effect is considerable, furthermore, it is better to use waste nitrogen to precool CBM than to liquefy it.Copyright

Analysis of Heat Transfer Characteristics in Liquefaction Processes of CBM With High Nitrogen Content

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.© 2011 ASME