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[jprocess]

Dear All:
We should do hydraulic calculation for some gas streams coming from some production stations in a gas gathering and NGL recovery project,to obtain pressure profile.
The gas streams pass through some compressor suction and dscharge drums.So the pressure drop across demister pads should be specified.A rule of thumb that can be found in GPSA says that give the demister pad pressure drop as 1 inch of water.But I think we can not use this value for all the drums.Any hint about pressure drop of gas streams passing through separators?
Another concern is pressure drop across control valves.A rule of thum says that begin from a source with given pressure upstream of control calve and calculate the pressure drop up to control valve inlet.20% of the calculated pressure drop should be considered for control valve pressure drop.Another approach is beginning from a source with given pressure downstream of CV,and back calculate up to CV outlet.Summation of downstream source pressure and calculated pressure drop is the CV outlet pressure but I think this approach can not be followed for every case and is limited to the piping layout.
Your valuable comments are appreciated.
Cheers.

[djack77494]

j,
I personally like the approach of using 1" W.C. as the dP across a demister. As always in engineering, one size never fits all, so if you have a good reason to want to allow more or less, you should move in that direction. For example, in vacuum systems a lower dP could well be more appropriate. Of course, you'll have to confirm that the demister can indeed do its job with a lower dP. Add an entry and exit loss for getting into & out of the drum.

For control valves, you need to take enough dP to achieve effective control. Without knowing what source & destination you're interested in, I can't offer much by way of comment. For a pumped circuit, I'd want the valve to take enough dP to effect movement along the pump curve. Then I achieve my ultimate objective which is to effect a change in flowrate through the pump. For a compressor minimum flow valve, essentially 100% of the dP occurs across the valve. So again, it's very difficult to make generalizations, and if you'd like a more definitive suggestion, please supply more specific information.

Doug