API 2000 vent activation pressure

[IFRs]

When sizing API 2000 vents for a small anchored tank with a relatively high fill rate we have chosen vents that require 4 to 5 inches of water delta pressure to flow the required amounts. This is higher than the weight of the cone roof plates. Other than checking Appendix F are there any other considerations?

 

[MJCronin]

IFR,

For a small tank,4 to 5 inches of water is modest, but I would not hesitate to try to contact the original tank fabricator.

Ask him if a "standard air test" (1-2 psig) was performed on all tanks of your vintage.

-MJC

 

[JStephen]

How small is "small"?

Do you also have emergency venting? If so, can the emergency and regular vents be combined for the pressure case (assuming you don't also have large outflows)?

 

[IFRs]

The tank is 35' dia x 32' high. The fill rate is 50,000 BPH. We have emergency venting, which opens at 5 inches of water. The required outbreathing venting just for the filling rate is 50,000 x 12 = 600,000 CFM (crude oil with a possible flash point under 100 degF). Since the flash point is under 100 DegF we need flame arrestors on the vents. The cone roof will look like a forest of steel thingamajigs!!

 

[JStephen]

I was thinking that you didn't need flame arrestors with a pallet-type valve. In which case, you could possibly use the lifting-manway type vents for both standard venting and emergency venting.

Is that CFM? Or SCFH?

If the tank isn't built yet, possibly go to a self-supporting cone roof designed for higher pressure specifically for this reason.

 

[IFRs]

Good thought on using the pallet-type for normal venting - never done that but I guess it might be OK - I have to think about if I want the tank to experience 5" H2O for every venting need (thermal/filling/emptying/emergency). The calcs result in SCFM - I forgot to type the "S" (does it really matter???). The tank is built, being moved from another location. We are doing two of them.

 

[JStephen]

In my Table 1A, the air flow is SCFH, not SCFM, based on barrels/hour. IE, 50,000 barrels/ hour x 12 = 600,000 SCFH.

 

[IFRs]

My bad. You are correct.

 

[JoeTank]

Just a quick note to remind you that most pallet-type vents require 100% over-pressure to fully open and operate. If it has a set pressure of 4" it may require 8" at fully operation.

Joe Tank

 

[EGT01]

Just as a sanity check... 50000 BPH (35000 gpm) seems like a tremendous fill rate for your 35' dia x 32' high (5480 barrel) tank. That will fill a completely empty tank in less than 7 minutes. Besides your outbreathing concerns, I wonder about your overfill protection.

 

[IFRs]

Yes, it is unusually high...they are surge tanks protecting 24" and 36" pipelines. There are flow indicators after the surge valves to alert the inbounding operator. There are no overfill slots or pipes - if it happened the liquid would pour out the vents.