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

[Display omitted] •An innovative vortex tube based N2 expansion refrigeration cycle.•Vortex tube is hybridized with turbo-expander for LNG production.•The overall energy requirement for the LNG process is reduced significantly.•The proposed refrigeration cycle can be implemented to other cryogenic processes. Liquefied natural gas (LNG) has attracted global attention as a more ecological energy source when compared to other fossil fuels. The nitrogen (N2) 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 N2 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® 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 N2 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.