Calculating Relief Load for A PSV

[ELNG]

Hi there,

I need to calculate the relief load for a new feed gas inlet separator , when blocked outlet occurs. The gas comes from another upstream plant to the new separator, and upstream plant will trip when pressure reaches 88 bar g. Is it safe to asusme that whatever gas is trapped between pipe and separator at 88 bar needs to be relieved?

Can you please advise on how I determine the relief rate required?

Thank you
Nadia

 

[Latexman]

Is it safe to asusme that whatever gas is trapped between pipe and separator at 88 bar needs to be relieved?

Do you mean, is 88 barg my sizing pressure for the separator's blocked outlet scenario?

Can you please advise on how I determine the relief rate required?

Yes. In addition to the above clarification, what is the MAWP of the separator and what is the fluid?

Good luck,
Latexman

 

[VugarN]

Hi!

Yes,whatever gas which is traped between the upstream and downstream of separator to be relieved and pipng will be protected.

Also to determine the flowrat,you need to have a look to the inlet flow rates and base on this I think .Also you need use the API 520 part 1 for sizing..Check for the other scenarious as well.

Good luck

 

[Ashereng]

I would have thought that for the blocked flow case, the PSV would need to vent the flow rate of gas should the upstream plant "not" trip.

I would use the maximum capacity of the upstream plant as the volume to be relieved.

Hope I understood your question correctly.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[mkannans]

HI,
What is the maximum source pressure (from the upstream plant) ? if the equipment (separator) is designed for the maximum upstream pressure (say for example 88 barg) then your psv need not be sized for this case, probably only for fire case.

If your source pressure is more than your design pressure, then as Ashereng mentioned you have to size it for maximum flow rate, when your upstream plant is running.

 

[mark06]

Ashereng is correct. You do not credit the equipment "trip" unless it is as reliable as the PSV itself, i.e. redundant switches or a triconex type safety system.

Will this valve also protect the separator? If so, have you evaluated the fire case?

If blocked outlet is the limiting contingency, the relief rate is the material balance rate for the stream from the upstream plant to the separator.

 

[djack77494]

ELNG,
The situation you refer to, when
"gas is trapped between pipe and separator at 88 bar"
is vented is commonly called "Blowdown" and not "Relief". You might use a control valve or an automated On/Off valve for this purpose, but you would not use a PSV or Pressure Safety (relief) Valve.