Pumping aqueous ammonia with a positive displacement pmp 1

[5wp]

Hi:
I'm pumping 29% aqueous ammonia with a positive displacement pump. The ammonia is transported thru a 1/4" plastic pipe to its dispertion point.
Near the point of application I notice bubbles being formed in this plastic line. The length of the plastic pipe from the pump to the dispertion point is about 200 feet.
What's causing the formation of bubbles? How do I correct this?

 

[Latexman]

The ammonia is coming out of solution as a vapor. It could be because of temperature increase or pressure decrease or both. What's happening temperature-wise at the dispersion point? Are the bubbles in the tube a problem?

Good luck,
Latexman

 

[5wp]

Latexman:
Is the pressure of the ammonia that is being pumped actually being driven below the vapor pressure and therefore flashing and forming bubbles?
The bubbles are not a problem, but if I have alot of space in the pipe taken up as bubbles not liquid ammonia, then I'm not really feeding my intended doasage. At times flow comes to a near stop, I'm assuming because of the
amount of space being taken up by the bubbles. we then have to purge to feed pipe.
Also due to the fact that the ammonia is being applied to chlorinated water, we are getting a large precipitate build up of calcium/magnesium at the application point.
Thanks for your reply.
5wp

 

[cub3bead]

It is not uncommon, especially in hot climates, for 29% aqua ammonia to off gas. The problem usually occurs on the suction side of the PD pump which then causes the pump to lose prime.

One way around it is to lower the ammonia concentration. If you go to <20% you get out of the RMP reg's too.

The chlorinated water isn't the cause of the Ca/Mg scale build up. The high pH of the aqua ammonia is causing the precipitation. Once the ammonia is fully dispersed the pH falls back to near normal conditions but the damage is already done as far as the scaling.

 

[5wp]

cub3bead:
Is there a chart or formula where I can figure out what % of ammonia I can go to,to significantly reduce the scaling?
I would guess that it is probably not a simple proportion.
At 20% what is the reduction of hydroxide that would be available for precipitation of the Ca/Mg?
Thanks again.

 

[BenThayer]

there is not an easy way to confirm the % ammonia that would prevent the scaling. it is also a function of the hardness of your water.

better dispersion would help.

gave the "star" to cub3head since he got the ammonia gassing and the scaling.

look up in Perry's for the vapor pressure of the ammonia over water. yes, nominal 29% is the max for about 14.7 psia at 80°F if my memory serves me right.

btw, plastic for ammonia related service does not really impress me but i guess i am old school.

 

[cub3bead]

Check out:

http://www.rmtech.net/technical_information.htm

Lots of good info.

BenThayer is on the right track with the Perry's reference.

The <20% sol'n won't help you much with the scaling problem, it helps with the risk management planning. To mitigate the scaling you will have to use a carrying water stream to further dilute and then transport the ammonia to the point of application. The carrying water stream should be softened.

What are you using the ammonia for?

 

[5wp]

The ammonia is used with chlorine to create chloramine in a potable water plant. Thanks for the reference, I'll check it out.
5wp

 

[cub3bead]

You can avoid the aqua ammonia handling problems entirely by switching to liquid ammonium sulfate (LAS) solution.