Dear all experts,
I'm studying the requirement of PSV on an "Instrument Air Receiver (IAR)". There are 2 more Air Receivers (AR) in the same plot area. Following are the design parameters:
Design pressure: 174 psig
Design temp.: 122 F
Volume of each AR: 1.5 m3
Each air receiver has a PSV of 1/2" x 1/2" which is a non-standard PSV as per API.
Now I'm contemplating 2 options:
1. Car seal open all the valves (as per the attached P&ID) to provide an open path for pressure relief from IAR to the connected vessels. This way I can avoid installing a PSV on IAR.
Only thing I need to ensure is that the PSVs on other two air receivers can relieve the entire load (of all 3 vessels) in case of fire exposure. As per my calculations, the exposed surface area is 15.2 m2 and calculated orifice area is 1.233 cm2. This gives me E orifice.
According to above calculations, PSVs on both ARs are under-sized and need to be replaced with higher orifice designation to relieve this load.
2. Since the air receivers have only dry air, fire exposure will result in vapor thermal expansion and a very negligible amount of relief will occur. If this is true, the installed PSVs (1/2" x 1/2") on ARs are adequate and it can even relieve the load from IAR when given an open path.For this, I need to support this with a calculation for relief load and orifice area for vapor thermal expansion. I can not find any calculation on API for this case. HYSYS safety analysis tool gives me 0.176 cm2 of orifice area. I did not provide any heat flux for this though.
Kindly give your suggestions to a way forward.
Thanks very much in advance!
Regards
Yogesh