Fire case audit of existing PSV
Fire case audit of existing PSV
(OP)
This is my first time at doing such an audit to ensure adequate orifice area per a HazOp study recommendation. This PSV is on a fractionator originally designed as a deethanizer but is now being used as a depropanizer. The feed to the column is mostly butanes with some propane. It is operated on total reflux and overhead propane ends up in our fuel system while the bottom butanes in LPG. The PSV is set at 550 psig per its original function.
1. In a fire scenario, assuming 100% n-butane the relief conditions become very close to its critical poperties ~ 565 psig and 305 F.
2. Ignoring the above and performing the calculations per Consolidated's API Fire Sizing for liquid hydracarbons the required orifice area is less than the actual.
How should I proceed from here to determine the adequacy of the PSV?
Thanks.
1. In a fire scenario, assuming 100% n-butane the relief conditions become very close to its critical poperties ~ 565 psig and 305 F.
2. Ignoring the above and performing the calculations per Consolidated's API Fire Sizing for liquid hydracarbons the required orifice area is less than the actual.
How should I proceed from here to determine the adequacy of the PSV?
Thanks.





RE: Fire case audit of existing PSV
Good luck,
Latexman
RE: Fire case audit of existing PSV
RE: Fire case audit of existing PSV
You may want to examine the loss of power scenario and, also, the loss of cooling scenario, especially since you indicate that the required orifice size for the external fire scenario is less than what is required. I've found in many columns that the worst credible overpressure scenario is not the external fire scenario, but either the loss of distillate cooling or the loss of electric power.
RE: Fire case audit of existing PSV
Latexman - I am trying to download the article.
dcasto - I was concerned about the validity of API method at supercritical conditions.
gene2007 - You are right, I was planning to evaluate lowering the set point if I did not get guidelines for sizing relief valves for supercritical fluids (The column normally operates @ 180 psig). At this point, I don't plan on examining the loss of power/cooling scenarios since the recommendation came from a HazOp study specifically recommending audit of the fire case.
Regards.
RE: Fire case audit of existing PSV
RE: Fire case audit of existing PSV