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High Rho V2 Value In Psv Downstream


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#1 process chemical

process chemical

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Posted 07 August 2008 - 01:44 AM

I am working in Flare network design for Oil & Gas project.

In the PSV network, i am getting higher RHO V2 value in one of the PSV outlet . As per standard engineering practice, to reduce the higher RHO V2 value i am providing higher tail pipe size.

Eventhough i am providing higher tail pipe size to reduce the RHO V2 value, i am going to provide the expander at the downstream of PSV to match the PSV outlet nozzle size & the Tail pipe size.In this scenario the expander will face the higher RHO V2 value? Is it adviceable?

In the above scenario,Where do we need to provide PSV downstream isolation valve? i.e Upstream of Expander or Downstream of Expander? Can u elaborate more on this issue?

Thanks in advance.

#2 rxnarang

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Posted 09 August 2008 - 11:28 PM

1)If the reducer has a higher rhoV^2, no problem. Go ahead . You do not have a choice as the pipe has to be swaged up to meet the higher line size.

2) Placement of the reducer: I prefer it immediately downstream of the PSV, flange to flange. The problem with this is that the PSV isolation valve is the higher line sized, and hence costs more. It is possible to to use a valve which is PSV outlet sized , and then swage up. The only thing one has to be careful about is that if the flow is choked in the smaller valve size, then there are thermodynamic and physical uncertanties which crop in, and are difficult to therotically analyse. However, if the flow is not choked, then one can have the smaller valve size.

3) Please compute the STATIC back pressure at the PSV outlet carefully. If the reducer is placed at the PSV outlet flange, then it is conservative to ignore the reducer to compute the static back pressure.

4) If the isolation valve is the same size as the PSV outlet, then INCLUDE the reducer AND the isolation valve to correctly compute the static back pressure.

Regards

#3 process chemical

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Posted 11 August 2008 - 11:10 PM

Dear Rajiv,

Thank you very much for your prompt reply.

regards,
Process Chemical

QUOTE (rxnarang @ Aug 10 2008, 12:28 AM) <{POST_SNAPBACK}>
1)If the reducer has a higher rhoV^2, no problem. Go ahead . You do not have a choice as the pipe has to be swaged up to meet the higher line size.

2) Placement of the reducer: I prefer it immediately downstream of the PSV, flange to flange. The problem with this is that the PSV isolation valve is the higher line sized, and hence costs more. It is possible to to use a valve which is PSV outlet sized , and then swage up. The only thing one has to be careful about is that if the flow is choked in the smaller valve size, then there are thermodynamic and physical uncertanties which crop in, and are difficult to therotically analyse. However, if the flow is not choked, then one can have the smaller valve size.

3) Please compute the STATIC back pressure at the PSV outlet carefully. If the reducer is placed at the PSV outlet flange, then it is conservative to ignore the reducer to compute the static back pressure.

4) If the isolation valve is the same size as the PSV outlet, then INCLUDE the reducer AND the isolation valve to correctly compute the static back pressure.

Regards


#4 JoeWong

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Posted 20 August 2008 - 12:11 PM

Process Chemical

Rajiv has given some very good advices...

You may be interested in this post "Few Concerns & Recommendations of PSV Discharge Tail pipe ".

#5 process chemical

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Posted 22 August 2008 - 09:25 AM

QUOTE (JoeWong @ Aug 20 2008, 12:11 PM) <{POST_SNAPBACK}>
Process Chemical

Rajiv has given some very good advices...

You may be interested in this post "Few Concerns & Recommendations of PSV Discharge Tail pipe ".

Thank you very much




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