10 replies to this topic

[prashamjain]

Hello,

 

I am working as an intern for a company and i have been given a project for water conservation.

My prime focus is on reducing the water consumption in the cooling tower.

 

The company has a zero blowdown: induced draft, counter flow cooling tower and it operates 3-4 times a week.

 

I  calculated the Cycle of concentration(COC) for the present situation and found it to be around 1.23

 

With the help of makeup water parameters, I was able to calculate the optimum COC level of the tower to be 3.67

 

I am really confused if it is giving any relevant inference, as the water is not blown down but rather it circulates.

 

They have a side filtration tank in order to keep the water soft, they also feed the chemicals in timely manner to control the water quality. 

 

Does this mean that the cooling water system is overly designed to keep the COC much less than the optimum level?

 

How can we make this cooling tower run close to 3.67 ?

 

I am not an expert in this field, so please let me know if i am missing something here?

 

Thank You 

 

[PingPong]

Every open cooling tower has drift losses: small liquid water droplets that leave the cooling tower together with the air due to entrainment.

 

It could be that your cooling tower has a high drift loss because its drift eliminators do not work properly, have been removed in the past, or were never installed in the first place. Inspect next time the tower is out of operation.

 

Another possibility is that cooling water is bled due to use for flushing or quenching or whatever. Ask the operators.

[prashamjain]

I have already talked about this with an operator.

They do have a drift eliminators installed in the cooling tower and at last inspection it was in good condition.

They also have side louvers to avoid the loss by wind-age.

 

According to my research, there is a significant amount of loss due to evaporation and blowdown.

 

Currently i am keeping a track of the make up water and depending upon the use of cooling tower the average addition is coming out to be 4000 gallons/day ?

 

So, with zero blowdown is it possible that the only loss is due to the evaporation ? Because i don't feel that the tower can loose 4000 gallons just by evaporation. (ignoring the loss by drift and wind-age) 

 

Please share your thoughts on this too.

Thank You 

[PingPong]

Even with drift eliminators installed the drift is not going to be zero.

 

Evaporation loss is proportional to the duty that the cooling tower has to remove.

 

To determine the duty you need to know:

- what is the flowrate of the circulating cooling water,

- what is the cooling tower inlet temperature,

- what is the cooling tower outlet temperature.

[prashamjain]

Thank you so much for the valuable response to my query. 

 

I have talked to the operator about this too, But unfortunately they don't keep the track of these parameters.

 

They only keep the track of Cooling tower outlet temperature which is approx 72F.

 

But i went through the operation manual of the cooling tower and while going through the specs. I found the values for the circulating Flow-rate to be 15000 GPM, Inlet temperature = 105F and outlet temperature = 80F  

 

Even the evaporation loss (at Design) is given as 322.35 gpm.

 

So, now how can this information help me ?

 

Also, for Zero Blowdown tower, does the COC level have any significance ?

 

If yes, what is the significance in that case ?

 

They don't keep track of the outlet temperature as the water that enters the cooling tower is mixed water from several manifolds, therefore making it difficult to know the actual efficiency of the tower.

 

Using the values from specs. the efficiency of cooling tower is coming out to be 75%.

 

I have read that increasing COC will increase the efficiency of the tower.

 

I feel that the low COC level is causing the tower to be inefficient but, again i don't have any valid evidence to prove that point.

 

Kindly share your thoughts on this too ?  
 

[PingPong]

But i went through the operation manual of the cooling tower and while going through the specs. I found the values for the circulating Flow-rate to be 15000 GPM, Inlet temperature = 105F and outlet temperature = 80F  

 

Even the evaporation loss (at Design) is given as 322.35 gpm.

Does that manual also give the design Wet Bulb Temperature of the air?

I have read that increasing COC will increase the efficiency of the tower.

Where did you read that?

[prashamjain]

The design wet bulb is given as 71.5 F

 

Below is the link where i read about the tower efficiency. 

 

https://watertechnol...-concentration/

 

"In a study performed by the California Utilities Statewide Codes and Standards Team (October 2011) and adopted in the 2013 California Building Energy Efficiency Standards, they conclude that “most towers are not operated in such a manner as to maximize cycles of concentration and minimize water losses.” They further conclude that because of the diversity and complexity of water treatment technology most cooling tower operations adopt an “overly conservative approach to tower bleed frequency.”

That said, it is well accepted that cooling tower efficiency can be improved by increasing the cycles of concentration

[PingPong]

When somebody talks about efficiency it is always important to understand what they really mean.

That study seems to refer to water efficiency.

 

According to the design data of the cooling tower that you mentioned,

the design thermal efficiency is (105 - 80) / (105 - 71.5) = 75 %.

 

I am not a cooling tower expert but I don't see why a high COC would increase the thermal efficiency.

 

The mentioned design evaporation loss of 322 GPM seems in the right order of magnitude, although I would estimate roughly 360 GPM.

Currently i am keeping a track of the make up water and depending upon the use of cooling tower the average addition is coming out to be 4000 gallons/day

4000 gallons/day is not even 3 GPM so something must be wrong with your 4000 number.

 

 

To determine whether the cooling tower actually performs as designed you need to measure tower inlet- and outlet temperatures as well as air WBT and do the same thermal efficiency calculation.

Without actual operating data this whole discussion will not lead anywhere.

[prashamjain]

Well that is what i was trying to find, the cooling tower efficiency.

 

As they don't keep track of the tower inlet temperature i am not able to find the efficiency.

 

And that is why it is becoming very hard to conclude anything.

 

And about the 4000 number, is it possible that the makeup meter reading is showing inaccurate numbers.

 

I was told by an operator that the meter has not been calibrated since years.

[PingPong]

Anything is possible, but even if you would know the actual make-up water flowrate it would not mean much without also  knowing the total cooling water flowrate and its inlet and outlet temperatures.

[breizh]

Hi ,

Consider reading these resources to support your work

 

Breizh