Joule-Thomson throttling process

Thus we conclude that in a Joule-Thomson throttling process the enthalpy is conserved. Therefore, the temperature of an ideal gas does not change as the heat capacity Cp and thus the enthalpy H do not depend on pressure. The change of temperature of a real gas during such an isenthalpic expansion is characterized by the Joule-Thomson coefficient... 

If high wellhead pressures are available over long periods, cooling can be achieved by expanding gas through a valve, a process known as Joule Thomson (JT) throttling. The valve is normally used in combination with a liquid gas separator and a heat exchanger, and inhibition measures must be taken to avoid hydrate formation. The whole process is often termed low temperature separation (LTS). 

Gas expanders are used to recover energy from high pressure process gas streams in a plant when the lower pressure is adequate for further processing. Power calculations are made in the same way as those for compressors. Usually several hundred horsepower must be involved for economic justification of an expander. In smaller plants, pressures are simply let down with throttling valves (Joule-Thomson) without attempt at recovery of energy. 

Joule-Thomson expansion Expression representing an isenthalpic throttling process. 

The temperature of the gas thus falls. The cooled air enters the chamber E from below and then goes up as shown. Thus, the gas cools the portion of the compressed air passing down the coil CE. This chilled gas then passes through a jet or throttle J and is further cooled by Joule-Thomson effect on account of expansion. This process goes on till the gas is converted into the liquid state. 

The quantity dT/dP)u is called the Joule-Thomson coefficient, and is represented by the symbol mj.t. it is equal to the rate of change of temperature with the pressure in a streaming process through a plug or throttle. According to equation (9.11), dH/d2 )p is the heat capacity of the gas at constant pressure, i.e., Cp, so that (11.4) is equivalent to... 

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. 

In the Heatric process, the warm wet pressurised gas from the inlet separator is pre-cooled in the PCHE and then throttled in a Joule-Thomson (JT) valve to a lower pressure. The drop in pressure produces a cooling effect and both hydrocarbon liquids and water condense out of the gas. The two-phase stream passes to a separator where the liquids are removed. The cold dry gas from the separator is returned to the exchanger to chill the incoming warm, wet gas (Figure 9.3). Refrigeration... 

For further cooling of a fluid, a common procedure is to use a continuous throttling process in which the fluid is forced to flow through a porous plug, valve, or other constriction that causes an abrupt drop in pressure. A slow continuous adiabatic throttling of a gas is called the Joule-Thomson experiment, or Joule-Kelvin experiment, after the two scientists who collaborated between 1852 and 1862 to design and analyze this procedure. ... 

We can determine the change in temperature that results as the pressure decreases in the isenthalpic throttling process if we know the derivative, dT/dP)h- We call this relation the Joule-Thomson coefficient, /x.jt-... 

Ethylene is liquefied by a Joule-Thomson expansion. It enters the throttling process at 50 bar and 0°C and leaves at 10 bar. What is the fraction of the inlet stream that is liquefied ... 

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