Tank Vent Size

[olmedo]

How do we size the vent of a water storage tank to prevent overpressure during filling and vacuum during discharging?
The aboveground storage tank has a a capacity of 1000 cubic meters.

 

[GregLamberson]

olmedo

You might consult API 2000, there is a table that will give you venting capacity's of various size tanks (don't have the table reference in front of me).

As far as overpressure or vacuum, you might consider a pressure-vacuum valve. P-V valves are used to protect from either over-pressure or excessive vacuum. A P-V valve has two pallets (1 for pressure relief and 1 for vacuum relief), each weighted to open at a pre-set pressure or vacuum setting. You can mount them weither in-line mounting or at the endo f the line.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[gerhardl]

Forgetting all the detailed stuff (temperature, density, pressure) this is relatively simple.

1. Calculate, guess or estimate maximum filling and emptying rate of water to the tank,including emptying by bursting line, and including max filling obtainable rate even if this is above 'normal allowed'.

2. Check max allowed over and underpressure for the tank. Note:careful about underpressure, tank constructions are weaker for this than for overpressure. (Tank collapsing in industry by sudden vacuum by steam condensation without air inlet is a well-known phenomen)

3. Water in or out (in cubic/timeunit) equals air in or out at max or rater below max pressure. Ask vent supplier for capacity at rate at or below given max over/underpressure out/in. (May be different capacities)for the venting valve.

4. Check the air speed the vent supplier uses for calculations. Should be 'reasonable' and allow for extra safety from 20% -50%.

5. Different vent types on the market commercially easily available.

 

[JStephen]

For shop-fabricated vents, they are typically the same size as the largest inlet or outlet. Upsizing these kinds of vents is relatively cheap.

If you size per API-2000 or water flow rates, you may come up with very small vents.

If sizing based on actual flow rates, include some allowance for partially clogged screens or screens being replaced with less-open screens in the future.