Design and optimization of nitrogen expansion liquefaction processes integrated with ethane separation for high ethane-content natural gas

Abstract

Compared to ordinary natural gas, ethane has higher market value. Thus, recovery of ethane can increase the economic value of high ethane-content natural gas. This paper proposes a new liquefaction method for high ethane-content natural gas. Natural gas liquefaction and cryogenic distillation are combined to separate high-purity liquid ethane (no less than 99.95%) in the process of producing liquefied natural gas (LNG), which maximizes the economic benefits. And self-supply of the required heat of the distillation column is achieved by heat integration. For this new method, three nitrogen expansion processes are designed, and each process is simulated and optimized by HYSYS and genetic algorithm. Based on the optimization results, the specific power consumption and exergy efficiency of the three processes are analyzed. The results show that the specific power consumption of the three processes decrease with the increase of the ethane content. When the ethane content is 10% ~ 40%, the specific power consumption of the three processes is 0.5969 ~ 0.6060 kWh/Nm3 (NG), 0.5371 ~ 0.5592 kWh/Nm3 (NG), 0.5015 ~ 0.5403 kWh/Nm3 (NG), respectively, and the exergy efficiency of the proposed three processes is 33.3 ~ 35.4%, 37.1 ~ 38.3%, 39.7 ~ 39.9%, respectively.