Pressure Drop accross a fully open choke valve

[occasionallurker]

I am trying to get an approximate estimate of what the pressure drop would be across a fully open (on-plot located) choke valve.
Its for an Onshore Field that is in decline, and I need to estimate arrival pressure downstream of choke valve for rough sizing of a gas compressor. Some details below.

Pin = 650 psi
Pout = ? psi
Valve = 100% open
Flow = 20 MMscfd raw gas (multiphase stream with water and condensate) with a gas fraction is 0.98.
Temp = 205oF

Thanks

Joe

 

[JLSeagull]

The choke manufacturers have calculation programs with data for various models. Some fixed chokes were designed in the 1930's and have "generic" beans. Typically the beans are available with the bore increasing by 1/64th inches. Fully open suggests an adjustable choke. You need to know the fully open coefficient or bore.

 

[DrillerNic]

you omit teh kwy peice of information: the equasion for flow through a choke just uses the choke diamter, not the anount it's open... so a fully open 1" choke is the same as a half open 2" choke (for some reason it's always measured in 64ths of an inch, so if someone talks about a 32 choke, they mean the orifice or bean size is 32/64", ie 1/2").

For liquid flow the critical flow region:

Q = C * Cd * D * ((P1 - P2)/density)^1/2
Where:

Q = flowrate
C= a units constant
Cd = choke flow coefficient (ask the choke manufacturer)
D = diameter of the choke opening
P1 = upstream pressure
P2 = downstream pressure

For gases critical flow is when P1/P2 = ~1.6 (roughly)