PSV for oil/gas separator

[furio2]

Hi all, I’m new in this field so I would like to know your opinion.

According to Client’s request (from which it’s difficult to obtain clarifications!), I sized the PSVs of four water/oil/gas separators connected in series (2 of which three-phases and 2 biphases) for “full flow rate” therefore for the mixture water/oil/gas entering on each separator (I used equations recommended in API RP 520 Appendix D valid for flashing multi-component systems): is it correct?

If the interpretation is correct:

1) It’s common practice to size PSV separators with this criterion? I think that the eventuality of all outlets blocked is rather remote. Moreover an ESDV should be closed when liquid level reaches LHH.

2) PSV discharges of all separators are collected in a manifold and then dispelled through a “cold flare”: but if PSVs are designed for full flow rate it’s needed a ko drum before flare, I cannot use another design criteria assuming that only gas is relieved. Is it correct?

I hope problem exposition is clear.

Thank you in advance for your attention.

Angela

 

[dcasto]

You need to size 1 psv on each vessel for a fire case. Then look at the set up of the separators. Can they be isolated such that all the flow can go through just 1 seperator?

If yes, the full flow can go through just one, you must design a relief for blocked flow. If the fire relief is big enough for blocked flow, you are finished. If the blocked flow case requires a larger relief, then you'll need the larger on each vessel.

If the blocked flow relief requires the fire relief vale to be the next size vale or larger, it may be less expensive to have just one blocked flow relief on the header going to all 4 seperators.