psv - set pressure higher critical pressure

[r0b3rt0p]

we have a vessel to protect by overpressure during a fire, the fluid has a critical pressure below the set pressure of the PSV so there isn't true latent heat.
How must the flowrate of fire contingency be set?

Tx for replies

 

[moltenmetal]

Treat this vessel as if it is gas filled, because in a sense, it is. You need to protect it by means that either don't reseal (rupture disk or buckle pin etc), or thermally.

 

[don1980]

It's important to understand that safety valves are generally incapable of protecting a vessel from fire exposure unless that vessel is at least partly filled with liquid, and that liquid will boil at a temperature that is not too excessive.

Moltenmetal provided real good advice - treat this supercritical fluid as if it's a gas - a very high density gas. If you're going to rely entirely on a relief device to protect a gas filled vessel from fire, then a non-reclosing device is what you need. A safety valve will not prevent the vessel from failing.

I just wanted to add that there's an alternate solution, if you hate rupture disks as much as I do. Whenever you use disks, you have to worry about premature disk failure, and that in itself can have some pretty unacceptable consequences. The alternative is to use a safety valve, but rely on other means to provide real protection. That is, use one, or any combination of the following protective measures, depending on the severity of the hazard: (1) auto depressurization, (2) water spray, (3) fire resistant insulation.

 

[moltenmetal]

...or a fusible plug, which is what I meant by "thermally".

 

[mpritchett]

Ryan Ouderkirk published a paper "Rigorously Size Relief Valves for Supercritical Fluids" in CEP August 2002 that may provided a method for this case.