Integrated Process Design and Optimization of a Nitrogen Recovery in Natural Gas Processing with Varying Feed Composition

In this study, two cryogenic nitrogen recovery processes integrated with natural gas liquefaction and NGL (Natural Gas Liquid) recovery are optimized using a commercial chemical process design simulator, gProms Processbuilder v.1.1 which is powerful at complex optimization problem. The difference of each process is the way the nitrogen is removed from product LNG: Stand-alone and integrated one for nitrogen removal unit. These two processes are compared with each other in teens of plant specific energy (kWH/kg(LNG)) with respect to varying nitrogen content in the feed gas. In order for clear comparison, each process would meet the same product specification of flowrate and composition for NGL, LNG, and vent N-2 stream and nitrogen contents in the feed gas vary from 0 to 20mol%. Consequently, as the nitrogen content in the feed increases, the specific energy also increases for both processes while the integrated configuration becomes more efficient than the other after around 13 mol%. It should be noted that all of the optimization results for each process configuration are improved compared with those from other researches which have the similar configuration. From this study, we could be ready for a recent trend occurring in natural gas processing. This trend would last for more than decades and the way this study aimed could be reasonable guidelines for other chemical process designs.