set pressure of P/V valve for tank 1

[somayehn]

Hi
i design a covered floating roof for Benzene With capacity=7000 m3.
design pressure of tank is 20 mbar. waht is the best set point for pressure and vacuume valve for this tank and how can size?
Thank you

 

[IFRs]

According to API 650 Appendix H, covered floating roof tanks are freely vented and require two square feet of open area for each 10 feet of tank diameter. The only other option is to have the tank inerted - ie helium blanketed etc. Using a PV vent is only for an inerted tank and the set points are based on the inerting system and tank design. The floating roof has no impact on the set points. If you are not inerting the tank then PV vents are not needed because your tank is freely vented.

 

[somayehn]

Dear IFRs
thanks for your reply.Yes the tank has inerting (N2) and so PV is necessary for this tank. But i dont know what is the best pressure set point for the vaccum valve?

 

[Duwe6]

Unless there are calc's to support a higher vacuum [look at the external roof, and at the shell - empty], the industry standard in the US is 1/2 ounce per square inch, about 22mm water column.

Don't put too much work into picking/calculating the vacuum setpoint, as you are running under a slight positive pressure from your N2 purge. The vacuum relief is for unusual emergencies only.

 

[somayehn]

Duwe6
Hi
Thanks for your reply,its useful for me.
Best Regards