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Overhead Drum With Deep Pipe


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#1 MacProcess

MacProcess

    Junior Member

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  • 14 posts

Posted 29 January 2018 - 01:40 AM

Hi.

 

We have a column system which has a PSV on the overhead vapor line.

PSV protects column and overhead drum in external fire case.

There is no block valve between column and drum.

 

However, overhead drum has inlet with deep pipe.

 

Someone told me that PSV cannot protect overhead drum in external fire case

because inlet pipe is submerged in liquid. Vapor cannot go through inlet line when fire case.

Equalizing line of drum is too small to relieve the external fire relieving rate.

 

Is there other solution to protect column and drum without adding PSV or increasing equalizing line size?

 

Thank you.

 



#2 fallah

fallah

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Posted 29 January 2018 - 06:37 AM

MacProcess,

 

The configuration you described in which a deep pipe containing permanent liquid static head isn't a normal one to play the role of PSV inlet line as protection device of a vessel against overpressure due to either case such as fire case; as the vapor has to go through a liquid column to reach the PSV and in this way not only has to overcome additional pressure of static head but also may entrain liquid droplets toward the PSV create a two phase flow conditions. Hence it mostly might the PSV cannot release the nominated load properly leading to over pressurization of the relevant vessel. 

 

In such cases, in my opinion, considering a small length vent line with a size at least equal to the PSV inlet nozzle size on the top of the incoming deep pipe inside the vessel can lead to prevent passing the relieving vapor through the liquid column which has been by passed following to such modification.






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