hi,

could i know what is the typical pressure drop across a JT valves? In one of the site i visited (which i was unable to find it now) it was mentioned that JT valves work best at around 10 - 11 bar pressure drops. it this fact true o should the pressure outlet be varied to get the desired pressure at the equipemnnt downstream.

thanks,
Andy Lum

Andy,

The J-T valve can be designed for any pressure drop. The idea is to get a desired Temperature by dropping the pressure.

abhishek

I agree with abhishek , since JT is adiabatic (delta H=0) by trial and error you calculate the outlet temperature.

I dont know it there are any typical values of pressure drop across JT valve.It depends on your required outlet temprature.Factors affecting how much you can let down across the JT are your inlet gas pressure/and required sales gas pressure.Depending on your gas compositions/properties and required chilling,hydrate formation can also be of concern.Typical values of chilling ie.temperature reduction per unit of pressure drop can be estimated from a simulator if you have details of the gas.Many a time in natural gas processing operators have to shift from JT to refrigeration with decline in reservoir pressures and changes in contract clauses (or new contracts) w.r.t HC dewpoint etc.

Thx

Andy:

I strongly suggest that you read this article about the Joule-Thomson effect so that you have a better understanding of that effect:

http://en.citizendium.org/wiki/Joule-Thomson_effect

Milt Beychok

Very good point by Milton,

Somehow I had an impression that many people consider gas expansion as self-cooling process in 100% cases, regardless of initial fluid conditions. Taking into account the maximum inversion temperature, it is obvious that expansion process sometimes can result in heating rather than cooling.

Very good example is pure hydrogen, which has the maximum inversion temperature of -68C: it needs to be cooled below this temperature if any further cooling is to be achieved by throttling.

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