Gas Blow By Versus Upset Flow of Flashing Condensate

[ChemEngSquirrel]

In a gas blow by relief case where level is lost in a two phase vessel allowing gas to flow via the LCV, I normally size the PSV for the gas rate via the 100% open LCV.

If the liquid displaced pre gas blow has significant amount of flashing in the LP vessel, is it possible to say with certainty that the vapour relief load in a vessel will always be greater for the gas blow by case or could it be larger for the case that happens pre gas blow by when condensate flows via the 100% open LCV & flashes.

Assume no liquid accumulation in the vessel - only interested in vapour relief.

Thanks.

 

[met11]

It could certainly be higher for the condensate blow-by case (higher density liquid = higher mass flowrate through valve, which then flashes in downstream pipe). Definitely don't try to rationalize something "with certainty" when it comes to relief sizing. Always:

- go through relief contingency table and identify all cases
- size for all cases
- take no shortcuts