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Blowdown Valve For Closed Drains Drum?


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#1 andybud

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Posted 30 April 2019 - 09:50 AM

Dear Sirs,

 

I am designing a closed drains system. Please see attached a basic sketch! I want to know if it requires a blowdown valve or not.

 

The drum (design pressure of 10 barg) is connected to upstream headers at different ratings and the off-gas collected in the closed drain drum goes to a vapour recovery unit.

 

Because of this, the vessel has PSVs. My question is, although the drum normally operates at very low pressure (0.1 barg), does it require a blowdown valve?

 

My thanks in advance for your thoughts

 

Andy

 

 

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#2 Perumal M

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Posted 30 April 2019 - 10:25 AM

Hi sir,

Basically we will provide BDV to increase the life of vessel when it is exposed to pool fire. Sometimes BDV will be provided at low pressure systems, only for maintenance purpose. For Drain systems BDV is not required. For Closed Drain vessel, PSV or a line with ball valve and globe valve shall be provided which will be floating with flare header.


From my experience, BDV is not recommended for Closed Drain vessel.

Thanks,
Peru

Edited by Perumal M, 30 April 2019 - 10:28 AM.


#3 Perumal M

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Posted 30 April 2019 - 10:34 AM

Do you think closed drain will receive that much gas from various places?
You are having vapour recovery line in vessel.
Drain line will collect only liquids. Pls anyone explain this system.
Regards,
Peru

Edited by Perumal M, 30 April 2019 - 10:34 AM.


#4 AlertO

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Posted 29 May 2019 - 02:25 AM

Hi Andy

 

API 521 has given the typical guideline for the requirement of emergency depressuring facilities at operating pressure of 250 psi or above. However, it also depends the equipment size as well as the consequence of the rupture on each equipment.

In my opinion, manual depressuring valve is sufficient for your system.



#5 fallah

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Posted 29 May 2019 - 10:15 AM


 

 

 

Hi Andy,

 

Is the drum above ground or installed under ground?

 

Is the fire case applicable for this drum?

 

If so, can the drum be isolated in case a fire happens?



#6 andybud

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Posted 07 June 2019 - 10:10 AM

Hi Fallah,

 

The drum is located on the sub-cellar deck of an offshore platform, likely to be grated decking as well. I envisage no automatic isolation upon fire and gas detection either, as fire risk is not a realistic case i believe.

 

AlertO, thank you for your input. Your thoughts sound correct to me, i shall add a manual depressurisation device instead.

 

Thank you all for your thoughts, much appreciated.



#7 fallah

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Posted 07 June 2019 - 10:53 AM

 

The drum is located on the sub-cellar deck of an offshore platform, likely to be grated decking as well. I envisage no automatic isolation upon fire and gas detection either, as fire risk is not a realistic case i believe.

 

AlertO, thank you for your input. Your thoughts sound correct to me, i shall add a manual depressurisation device instead.

 

If the offshore platform has to be operated unmanned, the depressurization should be performed automatically...



#8 Sharma Varun

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Posted 10 June 2019 - 12:21 AM

well i have worked in one such project for an offshore platform my observations are-

You don't need PSVs 

You don't even need depressurization system

Just work on upstream relieving scenarios and if there is any gas blow by case size the vent line for same.






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