Rika,

We have this exact setup, except a bit worse (29.6% ammonium hydroxide). I hate it. With high summer temperatures, you will off-gas ammonia through your conservation vent, especially if you are padding with N2. This will mean your 25% will turn into 24%, or 23%, or whatever equilibrium is required such that P(N2) + P(NH3) + P(H20) = conservation vent setpoint pressure. If you do not have an N2 blanket, then your tank will equilibrate at such a point that P(NH3) + P(H2O) = conservation vent setpoint, meaning you will lose less ammonia to off-gassing.

For us, this variability causes issues with neutralization in the plant, where operators have to account for "fresh" or wintertime ammonia being stronger, with less required than during summertime.

If you connect a tanker truck vent return that is naturally at 5 psi or whatever pressure due to NH3 vapor pressure, you will off-gas a large amount of ammonia through your conservation vent due to the pressure. Your vent line will not return any of the vapor space back to the T/T until the tanker pressure is less than the conservation vent setpoint, at which point the vapor can balance back to the tanker.

Ammonia hydroxide manufacturers recommend obtaining a 30 psig-rated storage tank to avoid this issue. If your client insists on an atmospheric tank, you should vent the conservation vent through some type of scrubber or stack so as to appropriately disperse the vapors. If you just vent to atmosphere it will be difficult to breathe within 50' of the tank when it is being filled...

Lastly, depending on where your client is located, be aware of regulatory thresholds for ammonium hydroxide. For the USA, ammonia is a regulated chemical under RMP, but only the active part of the solution is considered for the threshold - i.e. if the threshold quantity for RMP is 20,000 lbs of ammonia, then you can store up to 79,999 lbs of 25% ammonium hydroxide without entering RMP status. Check your local regulations to see if a similar logic applies. You may avoid future regulatory headaches with a small adjustment to tank size.

Hi,
Consider this handbook, you should find what you are looking for, with storages rated at 30 PSI (below and above).
Pierre

• https://files.engineering.com/getfile.aspx?folder=47ea2c4b-8e2b-4384-94b1-6

Thanks for the reply.
Degassing/ concentration decreasing is not acceptable. the storage tank is well insulated and an external cooler is installed to maintain the temperature lower than 28ºC. Vent is connected with a acid scrubber.

Because NH3 gas is flammable, N2 blanket is a hard request according to their regulation. I am wondering if O2 sensor is critical. The 2nd question actually comes from the unloading pump calculation. When temperature is high in the summer time, the ammonia solution is boiling, the pump is being cavitated. Or normal centrifugual pump is not an option?

@ pierre, I can't open the attachment. would you please upload it again? Many thanks.

Depends how the system is set up. If you have enough NPSH then it's ok, but my guess is that you'll need a can pump to get the required head.

A pump sitting on the ground next to a road tanker will almost certainly cavitate as you normally need min 2.5 to 3 m head going in.

And yes, boiling of the liquid in the tanker could overpressure your tank if the tanker is comin in super heated.

Atmospheric pressure tank in this instance looks like the wrong choice and maybe your client needs to think again.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

rika kose,

I could not open the attachment either. I'm guessing Pierre may have attached it from https://www.tannerind.com/PDF/green-aqua-amm.pdf

That website has always been very helpful when I have worked on aqueous ammonia or anhydrous ammonia projects.

Good Luck,
Latexman

The attachment has an "&" in the name which the forum software can upload, but won't download. If you manually replace that in the copy/pasted link with "%26" you can download it. If I leave it with the https:// at the start the forum software replaces it with "&" and it's back to something that doesn't work, hence the decapitated version below.

files.engineering.com/getfile.aspx?folder=47ea2c4b-8e2b-4384-94b1-69d313991fe8&file=Aqua_ammonia_S_%26_H_-_Tanner.pdf

Hi, Sorry I 've no access to my laptop, thanks to Latexman for seconding me.
Pierre

Your N2 pad pressure lower limit of -10mbarg seems too low - the vac mech design pressure limit of API650 tanks is (-)2.5mbarg. Vacuum RV may start to simmer at 80% of set, so N2 pad pressure must always be higher than (-)1.8 to (-)2mbarg to prevent air ingress through the VRV.

Hi,
In addition to my previous reply, consider the document attached
Pierre

• https://files.engineering.com/getfile.aspx?folder=8505be30-58c8-4aab-b6d5-c

Rika,

The need for an O2 sensor is a risk-based decision. An N2 pad does not always necessitate an O2 monitor. 25% ammonia at 28C has an absolute pressure (combined pressure of ammonia and water) of 10 psi. At ~36C, the solution has a vapor pressure equal to atmospheric pressure. If your tanker is coming in hotter than that, you are going to have issues.

If you are planning on controlling off-gassing via internal cooling coils or external cooling loop, be aware of the filling rate from the tanker truck. Your cooling system and heat exchange area needs to be able to keep up with whatever thermal load is coming in from the tanker. If the tanker is coming in hot (above 36 C) and offloads quickly, you'll end up blowing a lot of ammonia to your scrubber and you tank concentration will drop.

AirGas has some excellent data if you wish to peruse their technical publications more:

https://airgasspecialtyproducts.com/category/techn...