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Blowdown Philosophy


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#1 Dilu

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Posted 04 September 2014 - 05:14 AM

Hi

 

I am working on Low temperature Seperator of capacity 122 MMSCFD of gas at 650 psig. For PSV sizing of Seperator there are two cases fire case and blocked discharge case for gas outlet side. By considering blocked discharge the orifice design comes out P which seems larger.

 

Is this orifice size oka..if not does it mean I have to size it for fire case???

 

If not ok can I use blowdown valve in case of blocked discharge in such a way that if it blocks blowdown valve opens until the process conditions become stable by opening of discharge valve (like PSV).?

 

What other options I have in this scenerio.



#2 fallah

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Posted 04 September 2014 - 12:32 PM

Dilu,

 

About the first query you should calculate the required orifice area for fire case and then select higher area for PSV sizing...

 

Your second query isn't so clear and needs to be clarified...



#3 Rahul Valimbe

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Posted 04 September 2014 - 10:41 PM

Dilu,

 

As Fallah rightly mentioned, You should size the PSV for Fire Case also and then select higher of the two cases.

 

As for the second query, I interpret that you feel, "P" orifice is on the higher side. Then, you can always use 2 PSV's of lower areas, by dividing the flow into half. The overpressure of one PSV will be 10% and other will be 16% (In blocked discharge case)

 

But, do check for fire case before going for the above solution.

 

Regards

 

Rahul



#4 Dilu

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Posted 05 September 2014 - 02:42 AM

Thanks Fallah and Rahul

 

For fire case the designation is D. So blocked discharge will be the governing scenario. 

 

Fallah

 

My 2nd point was that P designation was too large so by using blowdown valve and giving it a set pressure same as PSV , in such a way that at set pressure blowdown valve will atomatically open same as PSV and after conditions become stabilize it will shutdown the blowdown valve by control logic.



#5 fallah

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Posted 05 September 2014 - 05:08 AM

Dilu,

 

If the PSV is too large you can use two or three smaller valves in staggered configuration. A blowdown valve cannot act as a PSV and will be activated manually or automatically by F&G system...


Edited by fallah, 05 September 2014 - 05:09 AM.


#6 Dilu

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Posted 05 September 2014 - 06:09 AM

Thanks Fallah






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