Optimization of Natural Gas Liquid (NGL) Recovery processes

Abstract

Natural gas liquid (NGL) is mainly composed of ethane. The demand for ethane is increasing continuously as it is used in the manufacturing of ethylene. A review of the major turboexpansion processes is provided in addition to some related work on the optimization of ethane recovery and profit obtained with several turboexpansion processes. The Cold Residue Recycle (CRR) process was simulated on Aspen HYSYS using lean and rich feed streams at three different demethanizer pressures, namely: 100 psia, 215 psia and 450 psia. The present work aimed at investigating the effect of the split ratios and other design variables on the profit. The optimization of the profit revealed that the Gas Subcooled Process (GSP) is superior to the CRR process in all cases except for lean gas at 100 psia and high NGL to gas price ratio. The external refrigeration requirement was also studied. The findings suggest that external refrigeration is required in all cases except for a lean feed gas operated at 100 psia where self-refrigeration is sufficient in providing the low temperature requirements of the turboexpander process. The flow rate of the splitted streams were included in the optimization. The results also suggest eliminating one splitter in case lean feed is used in the process. Further, the ethane recovery was calculated in all cases confirming that the optimum ethane recoveries available in literature matched the ethane recoveries at optimum profit as well in all cases except for the lean feed at 100 psia where the recovery is slightly below the one available in literature. Furthermore, the effect of CO2 was studied for all of the GSP cases. The CO2 tolerance of CRR and GSP was considered at a demethanizer pressure of 100 psia. The findings suggest that CRR is more CO2 tolerant than GSP.