Rupture Disk under PSV on Vacuum Tower

[sshep]

My Friends,

I am in a P&ID review where some members of the team have suggested that PSV's protecting vacuum distillation towers should have a rupture disk to guard against the PSV (set at 51psig) leaking backwards from the flare into the process.

As the operations engineer, I do not like to have unneccesary rupture disks under relief valves if they are not needed. Normally we have only used rupture disks under relief valves to protect them from fouling or corrosive service. This is clean service. Many vacuum columns in my experience do not have an RD-PSV combination, and there have never been any problems.

In your experience, is this vacuum system RD-PSV combination something which is common? Are there any industrial practices (API, etc) which reference RD-PSV in equipment running under vacuum.

best wishes,
sshep

 

[bljnv]

How about trying a resilient seat valve here provided the fluid is compatible.
How are the rupture disc/valve and rupture disc/vacuum column sealed.
Everything depends on the decay tolerance provided for the vacuum system.

 

[TD2K]

Hi Sshep,

I've only had to install 1 PSV on a vacuum tower (because it didn't have one) and the client insisted that we provide a rupture disk for the same reasons that you quoted, to avoid air leakage into the tower and additional load on the vacuum system.

If your experience is that these aren't needed, I would strongly push back. They have to be monitored for pressure between the disk and the PSV, they are expensive, they are a pain to replace as on a vacuum tower I expect they will be a reasonable size, etc. etc.