Design and analysis of a novel self-refrigerated natural gas liquefaction system integrated with helium recovery and CO2 liquefaction processes

Utilizing the high-pressure exergy of a pipeline gas is a route to overcome the challenge of high power consumption in liquefying natural gas. Through the expansion in city gate stations (CGSs), a notable cold duty is achieved that can liquefy a part of a natural gas feed. Based on this concept, the present research proposes a novel system for natural gas liquefaction utilizing pipeline exergy integrated with helium recovery and innovative carbon dioxide capturing and liquefaction. The process was evaluated by energy, exergy, economic, and exergoeconomic analyses. Results showed that the proposed system can co-produce LNG, liquid helium, and liquid CO2 products with low energy consumption, simplicity, and high profitability. The specific power consumption (SPC) and the exergy efficiency of the natural gas liquefaction system are 0.227 kWh/kgLNG and 64.24%, respectively, which shows a desirable performance as well as a notable potential for improvement. The process equipment of the helium liquefaction system also offers a higher total cost rate, mostly constituting an exergy destruction cost rate. The integrated system exhibits appropriate profitability by the internal rate of return of 47% and the payback period of 3.25 years.