5 replies to this topic

[kasri]

dear all,
I need to depressurisation calculation for a system which contains only minimal vapor fraction in normal operating pressure.When I set the corresponding stream to its initial pressure for doing depressurisation using depressurisation utility in hysys , it wont accept the stream becuase while I set the stream pressure to its initial depressurisation pressure the stream is fully liquid there is no vapor fraction.
Please advice how to do depressurisation calculation for this system and to find the BDV relieving load.
thanks .
kasri

[Erwin APRIANDI]

Hi Kasri,
HYSYS depressuring utility can be used to simulate the depressurisation of gas, gas-liquid filled vessels, pipelines and systems with several connected vessels or piping volumes depressuring through a single valve.

So I would not recommended to use HYSYS depressuring utility to do this, but I am also thinking whether the case that you mentioned is really applicable or not. Since if it is fully liquid how can it gets the pressure if there's no such thing as power to push the liquid (Like traped gas or pump)

[kasri]

dear erwin,
Thanks for your response.In that system during normal operation a small fraction of gas is there but during depressuraisation intial pressure , there is no vap. fraction that stream.
But in that system,BDV is provided for depresurisation.Hence I had confused to get the clear idea how to do depressurisation and find the load.
Regards.

Edited by kasri, 05 March 2012 - 12:43 AM.

[Erwin APRIANDI]

Hi Kasri,

Can you elaborate more regarding to the system condition
P & T of Initial depressuring, the fluid composition and also where the BDV is located. Volume of vessel and etc.

and what will be the depressuring time, is it 15 minute to 100 psig or 50% of PV design pressure (API STD 521).

I will try to look up my archieve for this matter, I remember I have quite similar problem before and I remember we develop some spreadsheet for this.

Edited by erwin.apriandi, 05 March 2012 - 01:30 AM.

[kasri]

Dear Erwin,
thanks for your response.This system is second stage separator which contains only minimum gas in operating condition;during depressurisaton pressure there is no vapor in the stream.
Please provide your procedure how you handled earlier.

[Erwin APRIANDI]

Hi Kasri,

The spreadsheet is develop inhouse only for the company application,
I can not distributed since it is part of company secrecy

I may can help you by providing the results, but I will need more data such as
1. Fluid composition
2. Initial condition P & T
3. Volume of inventory (SDV to SDV vol)
4. Scenario of blowdown to be considered

However, I'm still wondering why you said the gas will be minimum
since you may operate the liquid level inside the Second Stage Separator by using a level control valve
and I'm sure you may also control the pressure inside the vessel by a pressure control valve
which means you will have a gas inside the vessel, occupying the area between the liquid level and vessel tangent.
And if you provide a blowdown valve at upper section of the vessel, when it open it will release the gas and not the liquid. Enless the vessel is completely filled with liquid, which I'm sure it will not be the case.

So if this is the case, I think you can still use HYSYS depressuring package
but try to make a dummy stream combining your current stream + expected gas inside the vessel
and make the flowrate of gas at appropriate ratio with gas-liquid condition inside the vessel
after that use the mixed stream for depressuring calculation

Edited by erwin.apriandi, 12 March 2012 - 09:10 PM.