resistivity and humidity 1

[heieup]

I am currently working on a project to optimise our precipitator performance. We are aware that gas conditioning through the use of water sprays is very effective but don't really understand why !

There is a temperature resistivity effect that is well documentedIn additiong we are aware that as humidity increases then resistivty decreases, but don't know why !

Can someone please enlighten me as to the actual effect upon the dust of increasing humidity. The waste 'gas' is mainly air with a loading of very fine iron dust.

 

[joisy]

Is this electrical precipitator?

 

[heieup]

Sorry !

Yes a dry electrostatic precipitator at approx 72 C

 

[Dauden]

heiup,

The moisture you add to the gas stream doesn't really change the resistivity of the particulate matter itself (only temperature does, as you already noted). But the moisture present in the dust laden gas stream creates a thin conductive film on the SURFACE of the particles, thus decreasing the resistivity of the "blend" gas-dust.

The lower resistivity results in a more-conductive dust layer sitting on top of the collecting plates. So being, the voltage drop across this dust layer decreases, leaving more voltage available as measured between the Discharge Electrode and the Dust Surface.

The more voltage in that space, the stronger electrical field you will have, increasing Migration velocity and subsequently Precip efficiency.