Humidification with pure water and corrosion

[greg87]

We had an application which used steam generated from a "clean steam" generator for humidification. The steam generator used DI water as feed. After a relatively short (?)period of time, the galvanizing on the ductwork downstream of the humidifier was almost gone. There had been some problems with the humidifcation valve being open when it should not have been; however, the corrosion took place so quickly that the conclusion was that the water was "too" pure. I understand that high purity water can be be ion hungry, but I have never seen sources on humidification warn against too high a quality water or state a high end specification? Could high purity be the issue here, and if so any thoughts on what the max purity should be?

 

[ChasBean1]

Greg, that sounds like a reach. I would guess the problem would be more related to a high limit humidistat (or one not located well or set too high), too high a steam pressure creating excessive vapor trail, or impingement due to vapor trail obstruction.

I would think that less clean steam might have more volatiles entrained in the water vapor which would tend to accelerate corrosion, not reduce it. The way to treat a steam system and reduce corrosion is to add a volatile pH additive like morpholine, but you definitely don't want a volatile additive in a humidification system.

Replace the rotted section of duct with stainless. Look at the drainage, high limit humidistat, steam pressure, an vapor trail path. Good luck with this, -CB

 

[quark]

Greg!

Check the dryness of the steam. IMO you should not have a problem unless your steam is wet. Run the humidifier and check for traces of water (or moisture) on the duct internals.

Check

http://www.armstrong-intl.com

website for humidifier handbook. They specified a method of jacketing steam supply pipe to reduce wetness.