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# How to obtain a pressure drop ?

## How to obtain a pressure drop ?

(OP)
I'm running a dynamic model in HYSYS for the following upstrem gas system:
wellhead - Choke - Export pipeline - 100mm Hole(leakage)

The boundary specifications are set as
Pressure drop=fixed         for the choke valve
Press @ pipe outlet=fixed   for the pipeline end

The choke results in a controlled Pressure and Flow at the inlet of the pipeline.

The leakage is modelled by appropriate size and setpoint of a PSV.

QUESTION: Since I expect the hole will result in a significant pressure drop upstream the pipe inlet, but what I obtain is a constant pressure instead, how to make HYSYS recognize that 100mm leak MUST result in a pressure drop upstream the hole?

thanks!

### RE: How to obtain a pressure drop ?

You HAVE to understand how HYSYS works (assuming you are dealing with SS)

You specify the pressure drop - you dont calculate it!

Think about it - what determines the pressure downstream? Its actually NOT the choke but the pressure control in the separator - the choke dosnt _control_ anything its just an adjustable orifice! It limits flow. What would happen if you bean up the choke? Well assuming sufficient capacity downstream control valves would counter that.

So i all cases a valve in HYSYS is not a common component - and you only use it if you need to know some downstream properties - eg for sizing!

Best regards

Morten

### RE: How to obtain a pressure drop ?

(OP)
I found the solution meanwhile.

You'r right: the pressure is determined by the resistance due to friction losses downstream (a Pressure-Flow problem is close to a Capacitor-Resistance problem for an electric network...)

Just one thing: since the flow from the well is critical (i.e. choked) it means that the velocity is constant through the choke valve orifice and subsequenctly the flowrate is constant in the pipe. This means that you can control the desired flow by adjusting the choke pressure drop.

at least, this is the matching result from my HYSYS runs with the actual measured data.

thanks Morten for support
A.

### RE: How to obtain a pressure drop ?

Once you move to transient then "real" pressure flow correlations are established in HYSYS and this is actually the difficult thing moving into transient in process simuation - along with hold-up, control etc

Best regards

Morten

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