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# Simulate Dynamic Process Without Control Valve

1 reply to this topic
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### #1 Halflight

Halflight

Brand New Member

• Members
• 7 posts

Posted 30 August 2022 - 10:03 AM

Hello,

I want to calculate the vessel venting rates with aspen hysys. The venting case is as below.

1. Vessel is filled with nitrogen and toxic gas at 5 barG.

2. Vessel has 3/4" nozzle and pipe bound for thermal oxidizer.

3. Length of the pipe is almost 50m (including fittings like an elbow)

4. Destination is 0.25 barG.

When we use dynamic simulation with hysys I have to set all lines with control valve but the venting line doesn't have control valve.

I'll estimate control valve's rated Cv(flow coefficient) to 50m of 3/4" pipe by hydraulic calculation. Is it okay? or do you guys have better ideas?

### #2 Fletch

Fletch

Veteran Member

• Members
• 37 posts

Posted 10 September 2022 - 09:39 AM

What is maintaining the pressure difference between your two vessels? 5barg down to 0.25barg?

It might not be a control valve, but there is likely a restriction in your system (manual valve, orifice etc or is the two systems isolated by a valve that you are opening to vent

Specify the piping in a normal pipe segment. The valve can be used for part of your model, see below;

If there is a restriction, then this is your control valve in your model, you can define the fully open Cv of the valve to represent your restriction. in your model, you then open up the valve to 100% and run the model

If its an isolation, you can specify the control valve with a large Cv to minimize the effects of the valve, and let the system hydraulics dictate the flow rate. Like above open the valve to 100% and run the model