CBM Nitrogen Expansion Liquefaction Processes Using Residue Pressure of Nitrogen From Adsorption Separation

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 the nitrogen content of CBM feed gas together with the 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.