A quantitative investigation of the influence produced by the J-T valve replacement with nitrogen gas expander in Rectisol process

The gas expanders of nitrogen (N₂) are introduced to the Rectisol process to replace conventional Joule-Thompson (JT) valves so as to enhance the energy and cost efficiency in the refrigeration cycles. The introduction of N₂ gas expanders may influence the process operation of Rectisol process, but the influential mechanism hasn't yet been reported and remained unclear. This paper presents a quantitative investigation on replacing the JT valve with the N₂ gas expander in the Rectisol process by means of thermodynamic, economic, and sensitivity analyses within the ASPEN frame. The results show that the application of N₂ expander (Cases 1–3) decreases the system energy consumption by 1.01 %, 0.56 %, and 1.58 %, respectively. The aforementioned benefits mainly rise from the green electricity output of N₂ gas expander and lower expander outlet temperature. The influence mechanism has been revealed through the energy footprint analysis. The expected payback periods of Cases 1–3 are 0.76 years, 1.28 years, and 0.90 years, respectively, and the lifetime profits are 22, 13, and 18 folds of the initial investment. Sensitivity analysis indicates that as the expander isentropic efficiency increases, the expander output power, cold utility saving, exergy efficiency, and life cycle profit increase approximately linearly. In Cases 1–3, for every 1 percentage point increase in the expander isentropic efficiency, there will be a 37.76 k$, 13.14 k$, and 51.00 k$ increase in the life cycle profit, respectively.