"breathing" valve for ammonia tank

[csaba]

Hello again!

I would have a further question:

I have an NH4OH diluting and dosing tank. There are two phases of operation:

1. concentarted ammonia filling to the tank - breathing valve opens in one direction
2. diluted NH4OH pumping from the tank - breathing valve opens in the other direction
3. standby (no filling and pumping - breathing valve closed in both directions

Well, in order to avoid excessive pressure in the tank in the first phase, the ammonia gas/air should be let out of the tank. In the second phase however, in order to balance the negative pressure caused by pumping from the tank, one must let air go in the tank.

So far so good. Now the client asks that in the third phase the air outlet-inlet of the tanks should be automatically sealed that ammonia that evaporate unnecessarily.

In our practice up to now I solved this situation by 2 simple ball check-valves (no spring) built vertically at the top and bottom connection of a T-piece. The middle connection served for connecting the tank breathing stub. This worked well but are there some better/more nice/less expensive solutions? Do you know a valve type that is able for managing all the 3 phases of operation?

Thanks a lot!

Csaba (ProMinent hungary Co. Ltd. -

http://www.prominent.hu)

 

[Fizzhead]

csaba:

What you are looking for is normally called a P/V breather valve and these are commonly available. However, be careful to match the P/V range to your tank design.

I note that you do not describe a "third phase" in which water is added to the tank. I assume you must do that simultaneously with the concentrate addition. Either the valve arrangement you described, or the "breather valve" can handle all of these conditions without difficulty when correctly matched to process conditions and tank design constraints.

 

[BenThayer]

you don't mention any concentrations or what temperatures you are storing the solutions at but....

~30% wt. ammonia in water has a vapor pressure of about 14.7 psia at ~80°F. This is from memory but check it out in Perry's for details. The ammonia partial pressure certainly is dominating here.

Typically the ammonia does not evaporate off "unnecessarily" but is simply in equilibrium with its storage temperature. I agree with Fizzhead (love that name) that you need to be very careful with the settings and the design pressure of the tank. its very easy to get an upset with making ammonium hydroxide and get more ammonia than you wanted.

I worked at a plant for over 18 years where we made this with DI water and anhydrous ammonia. From a production/quality standpoint, very few batches would come back off-spec 'high' because all the excess ammonia could not stay in solution and would boil off. Wow what a way to clear your sinuses in the morning!

We piped several tanks together to minimize the collective 'breathing' when we were filling/transferring tanks. The common header then went to a small scrubber to capture the ammonia fumes. this water then was our make up water for the next batch.

hope this helps!

 

[abcmex]

Csaba,
you may find a lot of information in this site using the advanced search function (see top). Regarding ammonia + breathing valves I remember thread378-68541. If you are in Hungary you probably can locate a representative of Protego (

http://www.protego.de)

they are specialized in this field.

Kind regards

 

[csaba]

Thank you very much for you all! This has been my first attempt to get answers on this forum and you helped a lot.

Csaba

 

[Latexman]

csaba,

Another approach I've seen is have a tank rated for full vacuum (and whatever pressure rating this comes out to, probably ~ 50 psig) and not have a vent. We call it "riding the bubble". When it is started up, the inerts in the tank have to be eliminated. We do it by manually venting while filling the tank, then close the valve. We temporarily connect to our thermal oxidizer when we do this. After this, close the manual valve, disconnect from the vapor treatment system, install a blind flange, and the tank runs at the vapor pressure of the contents of the tank. You'll still need a relief device for credible emergency scenarios, but there is no normal venting. Now you have a zero discharge tank from an air emissions standpoint (not counting fugutive emissions)!

Good luck,
Latexman

 

[MJCronin]

Latexman,

I have heard of this method before

How do you get the liquid out of the tank ?

Is the liquid being pumped ? What type of pump ? Unless the tank is elevated ( you haven't stated this) you will run into cavitation on centrifugal pumps...

My opinion only...


MJC

 

[Latexman]

Liquid is pumped out. We have several pump designs in this application. One design uses a centrifugal pump. The tanks are not elevated, other than the usual few feet above grade. We also use vapor return on the shipping container (rail and truck) when unloading to the tank. The shipping container is pressurized with an initial few psi of N2 to prime the unloading pump, then switch to vapor return. Apparantly we keep just enough inerts in the system to not have cavitation problems. We have > 100 installations.


Good luck,
Latexman