"Dry" Nitrogen Gas Charging for Refrigeration Applications 1

[jsanders2008]

Our gas charging specification calls for "dry" nitrogen gas, but I don't know how "dry" the nitrogen needs to be. I know that different grades of nitrogen contain different amounts of water vapor; I was wondering if anyone could give me a specific dryness standard for nitrogen gas charging in refrigeration applications (e.g. < 1 ppm H2O).

 

[dcasto]

Dryness is typically in units of "dew point temperature", not ppm. So, a typical number used is -80F dew point N2.

 

[jsanders2008]

So dryness is not H2O content? All the gas suppliers I've looked at give H2O content for their gases, among other things, in ppm, and I just assumed that that was what "dryness" referred to. I'd still like to find a specific dryness standard for our purposes (refrigeration systems). Like I said, I don't know how "dry" our "dry" nitrogen needs to be. Thanks for the help, though.

 

[israelkk]

See the following federal standards avaiable freely at

http://www.assistdocs.com/search/search_basic.cfm

A-A-59155 NITROGEN, HIGH PURITY, SPECIAL PURPOSE
A-A-59503 NITROGEN, TECHNICAL

However, this is the quality of the supplied nitrogen from the factory. Some unique application will use added dryers (silica gel) to lower the water and hydrocarbon ppms.

 

[freonpeon]

nitrogen is probably being used for pressure testing and to prevent oxidation during the brazing process. refrigeration systems will all be evacuated with a vacuum pump. this will remove all moisture in the piping system.

 

[hfc]

I've been hearing that CO2 for leak checking is ok. And is <20 PPM.

 

[dcasto]

look at it this way, if the nitrogen is brought in as a liquid, it must be dry. Use liquified nitrogen source to purge. We do this reguarly before starting up our cryogenic plants (ie plants that liquify methane and nitrogen).

 

[dcasto]

oh, never use CO2 to dry a piece of equipment that will be chilled down because it may turn to dry ice in the process if not removed. Look at the process temps and press to verify.

 

[monkeydog]

If -40 deg nitrogen will work, why not use a Regenerative
Compressed Air Dryer?