Help 1

[9706]

Dear All,
Background: A closed vessel(3'X 10' horizontal, initial pressure is 520psig,30degC, sweet gas, will be released to flare within 5 mins and finial pressure is 320psig. How to determine the relif pipe size.
The problem i have is when the relief valve open, the inlet stream is closed and th evessel is a closed vessel which means there is no constant flow rate coming to the vessel, only the relief valve is opening. Of course, if there is a constant flow stream continues to feed to the vessel, that's a simple one, but for this closed vessel, pls give any tips.
Thanks in advance

 

[katmar]

The best advice I can give you at this stage is to put a better title to your questions. Imagine what confusion we would have if every post was headed "Help". People do not have time to read every post and will only get involved with posts where the title looks interesting and relevant to their knowledge and experience.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Latexman]

This is commonly called a "blowdown problem".

Good luck,
Latexman

 

[Latexman]

Here's an excellent reference for you:

http://www.air-dispersion.com/feature2.html

If you label your post properly, Milton Beychok may answer you personally.

Good luck,
Latexman

 

[mbeychok]

9706:

For sizing a relief valve, you may want to use the instaneous initial flow rate (which is the worst case). In that event, instead of the article referred to by Latex, it is very much simpler to use:

http://www.air-dispersion.com/usource.html#Gas Discharge

(in USA units)

http://www.air-dispersion.com/usource.html#Gas Discharge

(in metric units)

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[Latexman]

mbeychok,

I wondered about that, but the OP was pretty precise about stopping at 320 psig within a 5 minute duration, so I wasn't real sure if he wanted a PSV or something else and he didn't explain it fully.

Good luck,
Latexman

 

[mbeychok]

Latexman:

You are right, the original poster really needs to give us more explanation. What happens after the 5 minutes and the vessel pressure is reduced to 320 psig?

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[zdas04]

He logged back on yesterday, I don't know why he didn't answer any of the plethora of questions posed for him, maybe his handle represents his birthday instead of his graduation?

David

 

[9706]

Dear All,
sorry for delay to provide all details about this thread and appreciate all nice peopel here for great help indeed! Actally, this is a As-build equip rennovation project, the question is coming from process' request, which meams when the inlet stream is closed, the separator shall be isolated and consequently a control valve in the existing 2" line will open to release the gas to the flare. However, the condition are (1)the opening of the control valve will maintain within 5 mins to lowdown the pressure from 520psig to 220psig, (2) as long as the pressure reach to 220psig, the control valve shall be closed. (3) the interesting point here is time, they require about 5 mins to do the job. is it interesting? so, initially, i think this is a simple question, however, while i think about it carefully, i realize this is a quite tough questuion. during the release period, the inside pressure will reduce accordingly, which meams the flow rate will reduce accordingly. it's like a puzzle. this is why i post the thread to ask for help. Now, i calculate the result is 1/4" opening of the control valve can satify the requirement. But, i am still wondering the result. Might be 1/8" opening is ok.
Thanks for all here!