Is Vaccum breaker needed for Ammonia Hydroxide Storage Vessel?

[Chedork]

I've recently sized a PRD for a storage vessel that is rated for full vacuum. However, I noticed that there is no vacuum breaker or conservation vent installed on the tank. I questioned the owner of the equipment to see if the vacuum relief was somewhere else. Could it be possible for the vapor/liquid equilibrium to be adequate to relieve the vacuum when the tank is in operation?

 

[Latexman]

Chedork,

What's the pressure rating? About 50 psig or more? If so, the tank is probable set up, as you suspect, to "ride the bubble". It should still have a relief device if it's a Code vessel. We've got lots of tanks set up this way.



Good luck,
Latexman

 

[Chedork]

Latexman

The vessel is rated only for 25 psig and full vacuum.

Thank you for your help.

CheDork

 

[TD2K]

If the tank is designed for full vacuum, then there is no need for a vacuum breaker from the point of view of vessel protection. That doesn't mean a partial vacuum might not create a problem with getting the liquid out of the tank, that depends how you do that.

Overpressure is another case, at 25 psig you've got a pressure vessel which requires a PSV to be installed somewhere in the system to protect it (suggest you refer to ASME Section 8, Div 1, UG 125 to UG 129 for a more complete discussion). Potential cases would be protection against overfilling (unless the source pressure can't exceed the design pressure), a fire depending if there is a source of fuel in the area, external sources etc.

 

[Chedork]

The vessel is a ASME VIII coded vessel and has been sized with a PRV.

However, how would you then relieve any vacuum that is in the vessel when you refill the tank. Also wouldn't riding the vapor/liquid equilibrium cause fluctuations in the concentration of the aqeous solution as vacuum is pulled?

 

[Latexman]

Chedork,

When the tank is re-filling, the vapor space is getting compressed and is under less of a vacuum than when re-filling began, so I don't know what you mean by "how would you then relieve any vacuum that is in the vessel when you refill the tank". If the tank is good for full vacuum, there is no need to relieve the vacuum. It's designed to operate under a vacuum; hopefully the rest of your system is too.

During filling and emptying the VLE will cause changes to occur, but they'll be small compared to the mass in the liquid phase as long as you have a reasonable inventory when you re-fill.


Good luck,
Latexman