PSV sizing for fire case
PSV sizing for fire case
(OP)
Hi, I want to size a PSV based on fire case scenario on a vessel. The vessel is used as compressor knocks out drum. Sizing information is as following:
Operating Temperature: 47 .C (Tn)
Operating Pressure: 9.4 barg (Pn)
Design Temperature: 165 .C
Design Pressure: 69.4 barg
Vessel Size: ID=2.0 m, T/T=4.0 m
The problem is that the relief temperature base on
API formula (T1= [P1/Pn] Tn) is very high.
Max. Gas temperature in the vessel cannot be more than 1100 .F (API recommendation). So since temperature corresponding to set pressure is about 2400 .C in this case never pressure in vessel goes high up to set Pressure. In my opinion, this vessel does not need any safety valve! Because I can not find any Scenarios which lead to opening of PSV. But on the other it is very odd a pressure vessel without a PSV. Can you help me in this regard?
Operating Temperature: 47 .C (Tn)
Operating Pressure: 9.4 barg (Pn)
Design Temperature: 165 .C
Design Pressure: 69.4 barg
Vessel Size: ID=2.0 m, T/T=4.0 m
The problem is that the relief temperature base on
API formula (T1= [P1/Pn] Tn) is very high.
Max. Gas temperature in the vessel cannot be more than 1100 .F (API recommendation). So since temperature corresponding to set pressure is about 2400 .C in this case never pressure in vessel goes high up to set Pressure. In my opinion, this vessel does not need any safety valve! Because I can not find any Scenarios which lead to opening of PSV. But on the other it is very odd a pressure vessel without a PSV. Can you help me in this regard?





RE: PSV sizing for fire case
RE: PSV sizing for fire case
If liquid vaporization doesn't bring you up to relieving pressure at a temperature below 1100F, it's a rare case indeed. If this is true, I would still consider using a relief device to deal with the issues of CYA and Murphy's Law.
RE: PSV sizing for fire case
SeanB & someguy79 have clearly pointed out that liquid accumulation in suction vessel and leads to liquid vaporisation case.
You may also have to looks at the compressor settle-out follow by external fire which may have different distributed relief load...
One last point, is the suction vessel design pressure is selected base on settle-out pressure with margin ? If not may consider to reduce the suction vessel design pressure...
RE: PSV sizing for fire case
JoeWong88, you are right, Design Pressure of compressor suction Drum normally is based on settle-out pressure with some margin, but in my case its design pressure is based on compressor discharge pressure with some margin. The vessel is already available and I want to size PSV only.
RE: PSV sizing for fire case
RE: PSV sizing for fire case
You may consider to reduce the Suction drum PSV set pressure to settle out pressure plus margin.
RE: PSV sizing for fire case
Doug