hi
sorry but your query still isnt clear as to what you asking here.
you say you have a pool fire of propane entering the flare KO drum?
Firstly a pool fire exists in the plant either on the floor or on a supporting structure, not inside a drum. So i dont think we are clear here.
Are you saying that you have a vessel V1 , say, which is subject to a fire scenario where you have a propane pool fire around it. The PSV on V1 is set at 20barg and the relief temp is 60C , if so that seems low for a fire scenario.
As to the 2nd part, the pressure, and hence the temperature in the KO drum will depend on the back pressure in the drum, which in turn is dependent on the sum of the flow of this relief and any other co reliefs for the fire scenario.
The operating T & P in the drum will depend on several factors as above so whether you get 2 phase flow depends on the T&P as well as the composition of the fluid entering the drum. The drum should be sized to handle a certain droplet size , say 400mic for its design case. so if, as you say the pool fire scenario is not the governing case then the drum should be able to settle better than this.
You seem to be confused here a little and so i suggest you ask your supervisor for some guidance as with the information provided i surmise that non of us can really assist with your problem.
Flarenuf