Recapturing evaporative losses from cooling towers 1

[picsta]

Does anyone have any tips on how to recapture evaporative losses from cooling towers for use elswhere? Looking at reducing water use is shopping centres.
Any suggestions will be most appreciated

 

[Montemayor]

picsta:

I'm not sure your mean "evaporative" losses; but I'll have to take you at your word.

A water cooling tower does its cooling by evaporating a % of the feed water to the atmosphere. This is the key to the whole operation of "cooling". No evaporation - no cooling (& no foolin'). A cooling tower works on the principles of simultaneous heat and mass transfer. The mass transfered is the evaporated water. This evaporated water is not a "loss". Rather, it's the price you pay for the ride.

Now entrainment and "mist" losses, that's another story. These should not occur in a well designed tower. But if you're short of water in your shopping centers, then the cooling could have been designed to employ air-fin cooled condensers for your A/C system (I assume that's the load being imposed by the shopping center).

Recapturing the water evaporated is going to take energy and investment. And, as they say in my wife's native Peru, "the price of the price of the laundry bill is going to exceed the price of a new shirt". Once the water is diffused into the atmosphere, it's next to hell to try to get it back. It's like trying to seed a rain cloud, hoping it'll rain - and with little or no chance that it will. I frankly have never heard of anyone even debating any attempt to recover evaporation losses.

Sorry.

 

[quark]

Excellent summary by Mr Montemayor as usual.

There is more to this Herculean task than simply cooling the moist air and condensing it, as quoted elsewhere in these forums. The process you describe is just like keeping your refrigerator door open and trying to cool down the goods inside. In other words, it leads to violation of II law of thermodynamics. Google about Kelvin-Planck's statement of second law. Come back if you have any doubts.

Regards,

 

[katmar]

I really like the analogy of the shirt! I must remember that one.

I have also never seen anyone try to recover evaporated water from a cooling tower. Any method to do this would have to involve cooling, and by definition would have to be a non-evaporative method. As it would require removing the same amount of heat as was removed in the tower, it would be better to simply apply this non-evaporative cooling method directly to the original duty. This will save capital and running costs by transferring the heat only once.

If you are really tight on water then you may get some small savings by minimizing the entrainment with better demisters, or by reducing blowdown with better chemical treatment. But frankly, these consumptions are very small in relation to the evaporative losses and I believe you would be better off looking at replacing the evaporative towers with air-cooled fin-tube units - remembering that these will probably use a lot more electrical power than your evaporative towers do.

regards
Katmar