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[jprocess]

Dear All,
As you all know the API 521 proposed method is one of the most convenient methods that used for flare KOD sizing.GPSA also recommends this method in its chapter 7,section "Separators without Mist Extractors".
But I recently read SHELL company's DEP that about this method states:
"In API 521 the vessel sizing method is based on the settling of droplets, assuming a horizontal and uniform vapour flow.
However, in reality the vapour flow is far from uniform, especially if a small feed nozzle with no feed inlet device is used.
Also, in reality, the vapour flow contains a vertical component, in particular in the vicinity of the vapour outlet.Due to these two effects, the API 521 method results in vessels that are too small"
Your valuable comments are appreciated.
Cheers.

[pleckner]

And this is why you will find company standards and methods that are developed for their particular use. API is a good start, for the most part, but is not necessarily the best, something I've been saying for many years.

The API committee has published procedures in the past that are questionable but in their defense, these were developed because there was either nothing out there to begin with or what was out there had no good engineering basis. I suspect there may be some upgrades to their procedure for sizing KO drums in the next revision.

In the meantime, look for articles, etc. The CCPS has a procedure in their book, "Guidelines for Pressure Relief and Effluent Handling Systems", a book I've been pushing for quite some time. The procedure in the book has a slightly different way of determining terminal velocity and checks for possible entrainment from the liquid surface if the vapor velocity is too high.