Closed Cooling Tower System

[JHanson717]

In a closed loop cooling tower system, is there a "best practices" as far as if the pump should pump from the tower return to the heat exchangers, or pump to the tower and the tower returns through the heat exchangers?

It seems like it shouldn't matter, all components are rated for pressures well in excess of the discharge pressure, or is there another reason?

 

[MJCronin]

The pump should draw from the sump beneath the cooling towers and flow to the HXs.

The primary reason is the NPSHr requirements of the pump.

If you configure the system differently, the pump would be operating with a higher temperature liquid.....Less NPSHa

Furthermore, if the pump "pulls through" the HXs, it would be subject to cavitation if there is any fouling within the HXs.

-MJC

 

[SNORGY]

I guess I am not sure where the head would come from to drive the cooling water through the system if you arranged things to pump *into* the tower.

MJCronin is correct. Typically pump the cooled cooling water from the sump (small towers) or forebay basin (large towers) to the exchangers, then the hot water returns under pressure via return header to the flow distributors across the top of the cooling tower.

Regards,

SNORGY.

 

[JHanson717]

Thanks for the responses, I'm sorry, I guess I was less than clear about the tower. It is a closed loop system, i.e., just a finned coil with 4" flanged connections that the cooling system water flows through.
The sump is part of a separate spray system that just pumps water from the sump to the top of the tower, where it falls through the fill then across the a fore mentioned coil to cool the system water., here's a simplified pdf of the system if it helps.
Thanks in advance,
JH

 

[LUDPEKA1]

The “cooling tower” in your thread title got me thinking, like the previous responders, of a different type of closed loop cooling system that uses an unpressurized gravity cooling tower.

In theory it should not matter where you put the pump in your pressurized closed loop system.

When it comes to “best practices” two things come to mind. First, as it’s already been mentioned, the system temperatures it might make a difference in the pump design if it is installed after the cooling tower. I’m thinking pump seals and such. Second is purely the site conditions and what makes the best system for operations and maintenance.

 

[BigInch]

Snorgy, if the pump is before the tower, the tower is at pump discharge pressure - friction loss to get there. You can use that head equivalent in the tower to continue flowing out of it.



**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

If it was a closed tower.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[SNORGY]

Thanks BigInch. I was thinking - incorrectly - that it was a classic evaporative type cooling tower, and that "closed loop cooling tower system" was a misnomor.

I learn something every day. I have never seen this type of cooling tower before (as shown in the schematic by Jhanson717), whereas I imagine a lot of you folks see these things often, so a "closed loop cooling tower system" automatically makes perfect sense to you and you understand what it is. Up here (Alberta) you would typically see an API-661 air cooler and run it in warm air recirculation mode 9 months of the year.

Regards,

SNORGY.

 

[BigInch]

OK, we let you off the hook as you answered before he posted the diagram. It might be more customary to assume he meant closed except for an open cooling tower, but I took him at his word, closed system = totally closed system.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[hrsgguru]

I believe another term for this type of cooling tower is:

wet surface air cooler or WSAC

If anyone's interested in such an animal, there's some good info at this manufacturer's website:

http://www.niagarablower.com/wsac.htm

(I am in no way affiliated with this supplier, by the way).

I've used them in combined cycle plants where water usage is at a premium to help with auxiliary load cooling during the hottest months. The aux cooling system uses a fin-fan in series with a WSAC. During the cool days/months, the fin-fan does all the duty, but when the ambient gets up over 100F and we need 90 degree cooling water, we turn on the circ water for the WSAC and use it as a trim cooler to make 90F or less water. And just FYI, the main cycle cooling is done by a really big air cooled condenser 24-7.

Back to the point of the question, for all of the closed loop (auxiliary) cooling systems I've seen in combined cycle plants (which are directly analagous to the system in the sketch above), the circuit looks pretty much the same as what is in the sketch. Just make sure that your expansion tank is the highest point in the system.