vapor pressure

[terry100]

the vapor pressure of ammonia and water increases with temperature. if this solution is in a metal tank in the sunlight, and the solution temperature rises, will the actual tank pressure increase with the vapor pressure?

 

[Latexman]

Yes! Perry's has data on the total vapor pressure of various concentrations at various temperatures. It is not unusual for 28% NH3 solution in a tank to be at it's boiling point in the summer. That's why aqueous ammonia storage tanks should be pressure vessels.

Good luck,
Latexman

 

[IFRs]

Would it be true that until the ammonia boils, the tank remains at atmospheric pressure?

 

[Latexman]

It really depends on how the tank's venting is set up, but most likely the answer is yes. I've seen pressure vessels that "ride the bubble" and those would be in a vacuum.

Good luck,
Latexman

 

[ash9144]

If the tank is vented freely with no back pressure it will stay at atmospheric pressure even at boiling point. Think of a pot of boiling water.

If the tank has no vent then the tank pressure will be equal to the vapor pressure of the solution inside for the given temperature.

 

[maddocks]

And conversely, the tank pressure will rise and fall in accordance with ambient temperature swings.

 

[JimCasey]

But if it's vented freely, you won't have any ammonia in the tank when you need it, and all the grass around the tank will be really really green.

 

[MJCronin]

terry....

Aqueous ammonia tanks with solutions >19% do indeed exist and this is a well known technology.

As I recall, the typical tank is a coded pressure vessel designed to ~30 psig.

Lower concentrations can be handled by a "flat-bottomed" API-650 type tank with a conservation vent.

-MJC