Closed loop cooling water system maximum return temperature

[DoraeS]

Hi, I have a question related to closed loop cooling water system. In many projects I have seen the cooling water return temperature is fixed at 45degC or max 50 degC. I believe that this has something to do with scaling in cooling water system. But can anyone tell me more as why is the maximum return temperature to be designed at 50 degC?

Thanks in advance.

 

[ash9144]

Once you start going over 50 C (122 F) you begin to precipitate out CW treatment chemicals which will foul your exchangers

 

[jacksora]

While you can "design" for anything - there are a number of poblems that start to surface when you start running a "hot water" return in your cooling water system.

1. Scaling (as you mentioned)
2. Corrosion
3. Materials of construction - beyond scaling and corrosion worries and not just the piping or exchanger materials. You would need to look at the entire system including the cooling tower (you might start exceeding the temperatures of the commonly non-metalic distribution / contacting components)
4. Personal Safety (having to look at your cooling water system as a burn hazard due to the high temperature)

You can start to see why "although possible" it would take some interesting economic drivers to justify running the design temperature much higher than 50 C.

 

[786392]

It is a great deal to do with ambient conditions and Dry,Wet bulb temperatures prevalent.

However Combined CW return to cooling tower approaching anywhere above 48 Celsius becomes difficult in many ways to safely/easily handle.

Best Regards
Qalander(Chem)

 

[FFV5]

Environmental regulations as well. You do not wanna heat up the fishes especially if you are using a seawater cooling system

 

[MJCronin]

This is an excellent question to ask...

For the average cooling tower water system in the average chemical process plant, it was my understanding that the maximum inlet temperature is set by the cooling tower materials.

Other systems would, of course, have different maxima.

I believe that scaling is the primary reason for the maximum temperature.

-MJC

 

[FredExergy]

My recollection is that scaling in the heat exchangers is the main concern above 40-45°C Tube wall temperature. You could also get scaling and plugging of the spray nozzles in the cooling tower.
I think this issue will also depend on the number of concentration cycles and the hardness of the makeup water. Calcium and Magnesium carbonate solubility is anomalous and decreases with increase in temperature - thus leading to scaling risk.