flare drum sizing basis

[ChemEngSquirrel]

I'm sizing a flare drum for an offshore platform. Does the following sound like a valid sizing case:

A blocked occurs in the LP separator (3 phase separator) oil outlet. The oil level builds up to fill the vessel. The vessel high level trip fails to act, Two phase oil / gas flow via the gas outlet PCV doesn't lead to a high pressure trip in the vessel (so only single trip failure).

LP flare drum sized for the calculated oil / gas flow.

Note: Other sizing cases have been considered. I simply want to confirm if this is a realistic case.

Thanks.

 

[MikeClay]

I've always used this case as a basis for Flare Scrubber sizing unless a SIL analysis shows that the shutdown system is reliable enought to stop the flow once high level/pressure has been reached.

Remember that the shutdown valves are probably the least reliable part of your shutdown. If the high level and high pressure trips both shut the same valves, then you don't have a second shutdown. You just have one shutdown with diverse sensors.

--Mike--