CV request choke valve

[justitia]

Hello at everyone,

I must to design a multiple orifice choke valve.
I have the following data at the maximum:

flow: 13500 MMSCFD
Inlet pressure: 1300 psig
Temperature: 200°F
Outlet pressure: 300 psig
Specific Gravity: 0,683
State of fluid: Vapor

How do I calculate the Cv request?
I tried in ISA 75.01 but I don't understand some parameters like xt and other.

I have confused ideas.
Someone help me please.

Thanks to all.

 

[dcasto]

Some standards only allow the pressure drop across a valve to be 50% of the inlet pressure so you'd go from 1300 psig to 650 psig to 325 psig to 300 psig. You could fudge and go 1300 to 600 to 300.

 

[PaoloPemi]

as first step you need to verify the conditions for critical flow (which in ISA S75 depends from xt , the pressure differential ratio factor), assume a xt of 0.6 (which could be just a starting point) and see, if (as suggested by dcasto) you'll find that dp (critical) is well below your design value (1300-300=1000 psig) you can redefine the design conditions or adopt a different solution,
Paolo

a free software for control/relief valves

http://www.prode.com/en/valves.htm

 

[PaoloPemi]

Just to add that I assumed the choke valve as a constant pressure control valve (the flow through the hole -port- could be at critical condition)

 

[justitia]

Thank you all for the answers

Another question on this topic. I have to calculate the noise with IEC 60534-8-3. My problem is the jet diameter Dj.
If I have a cage with holes calculated as per the rules: I find Fd, valve style, with the formula dh/d0, knowing the number and size of holes? If it's a positive or adjustable choke which is the jet diameter? corresponds to the bean?

There is also a way to know the size of the bean without first passing through tests or CFD analysis?

Thanks