Venting Water Storage Tank 2

[ziptron]

Hi All,

I am oversimplifying the set-up that I have, however I'm hoping for a simple answer.

I have a tank that is pressurized with water, lets assume the tank only has an outlet and is closed off to the atmosphere. If I draw water from this tank from the outlet at some rate, what sized vent do I need to prevent a vacuum from forming inside?

To throw some numbers in, I have a 6 in pipe drawing water at 1000 gpm. I know theoretically I need a 6 in vent to suck in the same volume of air as the water I remove, however can I do this through a 5 inch vent, a 4 inch vent, a 2 inch vent... ect? I know the velocity of the air coming in will increase as I lower the vent diamater.. but so what? Will it still work if its a 1 inch vent but make a lot of noise?

Can someone point me to a good source that I could use to figure out how to size my vent properly? The tank currently does have a vent on there, and I think its too small, but I want to back up my thoughts with some standards.

Thanks in advance,

 

[TD2K]

If you are drawing water out of the tank at 1000 gpm, you need to replace that same volume with air. The size of the vent depends on how much vacuum and therefore dP you have available to flow air into the tank.

If you have access to API 2000, that is a good reference. You can also check Protectoseal and Shand and Jurs, both sell tank vents and have information for this question.

API 2000 will also get into temperature effects which cause inbreathing and outbreathing requirements as well as fire.

 

[bimr]

An atomospheric vent is not common on a vessel used in a pressure application.

The starting place is the vessel design. What is the maximum and minimum design pressures? Next, you must determine the design operating conditions. With this information, you can size a vaccum breaker.

You can use the information in this link to size a vacuum breaker or call the manufacturer.

http://www.tycovalves-usa.com/ld/Tech Sem Manual.pdf

 

[BENSMIL]

Hi ziptron,

I did some quick calculations with the assumption that the tank can withstand a vacuum of 0.25 kPA which is the case for API 650 tanks generally.
The vent line equivalent length was calculated considering two elbows and a metre of straight length. (assuming a goose neck vent)
Pressure drop calculations indicated that a 3" vent will suffice for your case. 2" vent will be undersized.

Verify the assumptions made above and do your own calculation to get the answer you are looking for.

regards,
Benoy

 

[lukman143]

Does this tank has a continuous inlet flow? You need to specify this before making any sizing.

You can refer to the following guidance:

http://www.acterragroup.com/Downloads/Petro/MorrisonVentGuide.pdf

http://engineeringchecks.wiki-site.com/index.php/Tanks

http://chemicalengineeringmagazine.com,

Free Chemical Engineering Magazine Subscription