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Fire Case Psv Requied For Reflux Drum?


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#1 SJ28

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Posted 06 June 2018 - 07:16 AM

Hi All,

In my system I have a reflux drum in an open path to its column overhead while the column overhead already has a PSV set at the design pressure of the column and reflux drum.  Assuming that my reflux drum is in a fire zone, do I need to have a dedicated fire case PSV for the reflux drum, even though the drum is in an open path to the column overhead PSV?  Also, please give a reference to any code where the same has been specified, if any.


Edited by Art Montemayor, 08 June 2018 - 01:22 PM.
spelling, grammar


#2 Saml

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Posted 06 June 2018 - 08:06 AM

The first code to look is your local regulator code. That has preeminence over any code of practice.

Then you have to verify to what code is the equipment built, may be American ASME, European PED, Japanese, Chinese codes...

 

Now, assuming that is built to ASME (a big IF)

 

You have to demonstrate that the existing valve is able to relieve the demand of a fire case. If it is already built and operating, it should have been done by the designer. The cases considered for design should be available (although in many places that information is buried in a project binder in the back of a documentation room, where you have to clear the spiderwebs before opening them)

 

If you find that the valve is not capable of relieving the required capacity in case of fire, you may have to add a supplementary valve exclusively for the fire case 

 

See API Section VIII Div 1 UG-125 and followings, the Appendix M of the same Code, API 520 Parts 1 and 2, and API 521.

The first one (ASME) if the actual code requirements (where that code is used)

The last one is where you will find information  on how to get there.


Edited by Saml, 08 June 2018 - 06:50 AM.


#3 fallah

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Posted 08 June 2018 - 05:50 AM

In general, if there is an open path between the column and drum the PSV on the column overhead can handle the relief load due to fire case of the drum provided that this case had already been considered among credible scenarios in the PSV sizing and also the effect of pressure drop between column and drum on PSV relief being well evaluated.

#4 SJ28

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Posted 08 June 2018 - 08:05 PM

Thanks.

I was also of the same view. But somebody raised question that as per ASME we need to provide a separate PSV irrespective of whether the Vessel  is in open loop with the column overhead PSV or not.

Any ways, Thanks for your quick responses.



#5 Bobby Strain

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Posted 08 June 2018 - 10:18 PM

It is quite unusual to have an open path between the column and the reflux drum. I think there is something that you have not conveyed to us. So, if I were you, I wouldn't be too comfortable with the responses you received. You didn't provide enough information to get a reasoned response. Which is often the case.

 

Bobby



#6 SJ28

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Posted 09 June 2018 - 07:23 AM

@Bobby Strain I have described the condition as it is actually. The condenser is a partial condenser so we don’t have an isolation (control valve) between condenser and reflux drum. It’s all in a single loop with PSV at column overhead. Let me know if you still feel something is missing from my end.

#7 fallah

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Posted 10 June 2018 - 02:58 AM

SJ28,

 

Is there any isolation/control valve between the column and the condenser?



#8 SJ28

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Posted 10 June 2018 - 03:17 AM

Fallah,
No, it’s all open from column overhead all the way to Reflux Drum.

#9 fallah

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Posted 10 June 2018 - 05:12 AM

SJ28,

 

Code (ASME Sec. VIII Div.1, UG-133 ©) allows to protect multiple vessels with a single PSV's if they are connected without the possibility of any blockage along the interconnecting lines provided that the pressure drop from the farthest vessel to be taken into account during the relief. Hence you can proceed with this concept but respecting the conditions have to be followed to meet the code requirements.


Edited by fallah, 10 June 2018 - 05:16 AM.





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