Joule-Thompson expansion cycle

The air feed is first compressed and heat of compression is removed from the stream by intercooling, aftercooling and direct water quench. The elevated pressure airstream is purified to remove water and other impurities and it is then expanded to a lower pressure to generate the reduced temperature necessary for liquefaction. Expansion takes place either across a valve (Joule-Thompson expansion) or through a turboexpander producing useful work. The compression, cooling and subsequent expansion of the air feed stream constitutes the refrigeration cycle. 

The expander cycle and its corresponding temperature-entropy diagram are shown in Figure 4. Notice that the expander cycle is similar to the simplified Joule-Thompson cycle, except that the Joule-Thompson expansion valve has been replaced by an expansion turbine. The performance of this cycle differs in several ways. The expansion of the gas is no longer isenthalpic, but with the expansion turbine, it is isentropic that is, there is a change in... 

This cycle is a variation of the Claude cycle. If air is the working fluid, the compressor discharge pressure is 200 bars (2885 psig) and the liquid fraction produced in the Joule-Thompson expansion is about 0.6, then the optimum temperature for the inlet to the expansion turbine is about ambi-... 

Figure 5.9 The Joule-Thompson cycle (Linde cycle). The gas is first compressed and then cooled in a heat exchanger, before it passes through a throttle valve where it undergoes an isenthalpic Joule-Thomson expansion, producing some liquid. The cooled gas is separated from the liquid and returned to the compressor via the heat exchanger.

The Linde cycle is a simple cryogenic process based on Joule-Thompson effect. It is composed of different steps the gas is first compressed, then preliminarily cooled in a heat exchanger using liquid nitrogen, finally it passes through a lamination throttle valve to exploit the benefits of Joule-Thomson expansion. Some liquid is produced, and the vapour is separated from the liquid phase and returns back to the compressor through the heat exchanger. A simplified scheme of the overall process is reported in Fig. 2.9. 

---