An innovative vortex-tube turbo-expander refrigeration cycle for performance enhancement of nitrogen-based natural-gas liquefaction process

Liquefied natural gas (LNG) has attracted global attention as a more ecological energy source when compared to other fossil fuels. The nitrogen (N-2) expander liquefaction is the most green and safe process among the different types of commercial natural gas liquefaction processes, but its relatively low energy efficiency is a major issue. To solve this issue, an energy-efficient, safe, and simple refrigeration cycle was proposed to improve the energy efficiency of the N-2 based natural-gas liquefaction process. In the proposed refrigeration cycle, vortex tube as an expansion device was integrated with turbo-expander in order to reduce the overall required energy for LNG production. A well-known commercial simulator Aspen Hysys (R) v9 was employed for modeling and analysis of proposed LNG process. The hybrid vortex-tube turbo-expander LNG process resulted in the specific energy requirement of 0.5900 kWh/kg LNG. Furthermore, the energy efficiency of the proposed LNG process was also compared with previous N-2 expander-based LNG processes. The results demonstrated that the proposed hybrid configuration saved up to 68.5% (depending on feed composition and conditions) in terms of the overall specific energy requirement in comparison with previous studies.