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topic 12269

Atmosphere Evaporators for wastewater


 

I am considering getting an atmospheric evaporator to reduce my waste water volume. There is very little information available on evaporator rate reduction versus humidity. I am located in Kentucky and summer time the humidity can be high for long periods of time. I would like know from people who use atmospheric evaporators how much does outside humidity impact the evaporation rate? What kind waste water volume reduction is gained by atmospheric evaporator? Also, what are the other pit falls of atmospheric evaporators?

Karl Weyermann
- Lebanon, Kentucky


 

Hi Karl,

Firstly you'd know full well that internet sites give quite a bit of info on these evaporators.

It seems you have two options. One where you just allow the ambient air to (hopefully) evaporate and the other where you need a BTU heat assist, i.e., definite operating costs!

The former is the simplest but less efficient especially in winter time.

Personally, I'd opt for the former. I've seen a highly diluted chrome waste rejuvenated, so-to-speak, using a crude system of conventional (mass transfer) packing onto which, just as crudely BUT simply, a weir overflow distributes the liquid (i.e., no jets to plug up), the fan being a standard metal centrifugal blasting into the packing horizontally and then an ordinary but VERY efficient horizontal flow mist eliminator to take out the droplets.

I emphasize horizontal flow because any vertical flow blade type eliminator fights gravity and is not nearly as efficient and has to be much larger, too! Some people may, for all I know, suggest using a vertical flow mesh eliminator. Ah! Beware! These can be extremely good but operate at very low speeds (i.e., very bulky) but are highly prone to build-up.

To me, the K.I.S.S. principle is paramount. The eliminator is of prime importance. Munters have excellent T-l00 blades, Harrington Plastics makes complete units and in Canada (Vancouver area) there's Allanco Environmental which makes superb units.

Oh, before I forget, when at a trade show some years ago in the USA, I had a fully operating mist eliminator (horizontal airflow!) with the normal low gpm spray jets. This was in a clean building but after a few hours the water level in the make-up tank dropped and became scummy. At another trade show there was no cold water available so I had to use fairly hot water. HOWEVER, the return water from the eliminator drain outlet was dead cold! Isn't that an example of a good adiabatic reaction?

Unfortunately I never had the opportunity to design an atmospheric evaporator ... and if I did, I might have just used a two stage horizontal blade type mist eliminator JUST BY ITSELF and would have sized it to accept a high gpm rate of liquid flow.


 

If you have high ambient relative humidity, passive evaporation will be very slow or non-existent. That's why humid conditions are so uncomfortable. Your sweat does not evaporate from your skin and cool you, it just drips off. The same goes for evaporating waste water. If the air is saturated with water already, the water won't evaporate on it's own. You have to boil it off with heat input.

Guy Lester
plating co. - Ontario, California



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