PSV located on side of a tower

[sshep]

My Friends,

Generally relief valves are positioned at the top of a tower either on the top vapor line, reflux drum, etc. Top location means that the vapor flow in a relief case through the tower is upward in the normal vapor flow direction.

Sometimes relief valves are located on the side of a tower. In this case I think that some relief scenarios could result in vapor downflow through trays or beds to reach the relief valve. This abnormal flow direction seems like it could cause internal damage if not properly considered.

Are there any references for side mounted relief on towers. I cannot find anything in API about such configurations although some sites I have worked at use side mounted relief alot. Any references would be very helpful.

best wishes,
sshep

 

[owg]

A serious relief, like water in the bottom of an oil tower, will rip out all the trays on its way out of a top relief valve anyway. Trays are usually clamped down quite lightly so they will lift given a little persuasion. Side relief may not work for all relief scenarios. I would not want to have side only relief on any of my towers.

HAZOP at

http://www.curryhydrocarbons.ca

 

[SNORGY]

Pressure is pressure; the relief valve is there to relieve excessive pressure, primarily. At least, I *think* so.

I'd rather come off the side of a tower under a mesh pad, for example, than off the top of the tower downstream of the mesh pad.

But, owg is correct; each case warrants evaluation on its own merits.

Does the dynamic mode of Aspen have the capability of modeling the problems that one might face either way?

Regards,

SNORGY.

 

[owg]

Good point Snorgy, those pads could easily lift sections and at least partially plug the relief nozzle.

HAZOP at

http://www.curryhydrocarbons.ca

 

[SNORGY]

Or at least contribute to that magic 3% rule...

Regards,

SNORGY.

 

[koba78]

I am not quite understand where the location "side" of tower of the relief valves are positioned pointed by sshep.


I always see that reflux failure or pump around failure case on the sidestream reflux to the column
due to the loss of cooling to the condenser or loss of power to pump motor or control failure.

Therefore, is the side of tower means that the sidestream reflux from bottom pump to column ?

Thanks.

 

[sshep]

My Friends,

FYI, since I posted this I found 2-3 pages of reference to considerations about these two locations in Kister's book "Distillation Design". Henry cites the consideration I mention about the downflow of vapor in a relief scenario which can collapse trays above the relief valve, but also has some other guidence. He credits the side configuration as having some possible advantages in heavy fouling service.

The downflow of vapor is one of those things which is difficult to model quantitatively when there is liquid on the trays. I guess that internal damage is simply a secondary consideration to protection of the vessel from overpressure.

thanks and best wishes,
sshep