That's quite a neat design alright - A lot depends on how much space you have and the particular gas and liquid flows.
Slug catchers are never intended to be super effective at gas liquid separation, the intent is just to stop the first stage separators from getting overwhelmed with liquid flow from either start up, ramp up or pigging. Given that the flow of liquid can vary hugely for the same gas rate, sometimes up to 100 times the instantaneous flow over a 5 second period, then it is just a bit of judgement as to how to design these things, but always leave room to add another couple of fingers in case reality doesn't turn out the same as the theoretical calculation.
At the end of the day, if the slug catcher doesn't work as well as you want then the first stage separator just trips on HH level and the plant stops for a little while. The designer then just says that the composition and flowrate of the fluid coming in is different to what the design basis said....
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