Cooling Tower operation at a lower load? 1

[Techcitizen]

If I run a Natural Draft Cooling Tower at a heat load lower than its capability, keeping the hot water inlet temperature same for given ambient conditions, what will be the effect on the water outlet temperature?

 

[MortenA]

Assuming that by "hot water" you mean your process inlet - The process outlet temperature will at a lower flow rate depend on the dT between ambient and process outlet. If this is large initially then you may expect colder outlet temperature if flow rate is reduced - if the dT is small at the design flow rate then the outlet temperature will not change much i would assume.

Best regards

Morten

 

[stanlsimon]

In cold climate conditions you may need to provide a heater to keep the sump from freezing up. One design scheme is to use a dry cooler for light loads, the open tower for heavy loads.

 

[Techcitizen]

Thanks friends for your thoughts, let me expand/explain the matter a little more in detail. Let us assume that the ambient conditions remain constant and freezing is not an issue. The NDCT (hyperbolic) is running with a certain fix ciculation flow rate which is basically governed by the pumps which feed a steam turbine condenser and is less than the rated flow rate of the NDCT. Now, if I add another circuit, increasing the circulation flow rate by 1.5% and remaining within the rated flow rate of the NDCT, by putting pps feeding to a heat exchanger and return the water at the same temp as condenser return water, what effect will it have on the cold water temp?
Hope I am able to make the problem clear!

 

[MortenA]

Its clear and then again - as i said: I think the possible temp change will depend on your initial situation: If your dT (process out and air out) is large then there is room for some additional colling - if not then increasing the flow rate may cause the process out temp to go up and decreasing the flow rate may not cause a significant change.

Try it or get a consultant to work out the numbers.

Best regards

Morten

 

[rmw]

You need to consult with your NDCT sales person or a sales person for his competitor. The NDCT works on the principle draft induced by temperature. It may be that you have enough capacity left such that the increased heat load will induce enough more draft to help the duty across the whole range. I'd have to look at a capacity curve for a NDCT, but I don't have any handy at this moment.

rmw

 

[katmar]

This is a bit confusing because in your initial post you spoke of lowering the heat load, but in your second post you asked about an increased heat load.

Anyway, I agree with Morten - in principle the cold water temperature will decrease when you lower the heat load and increase when you raise the heat load, but the magnitude of the changes will depend on the details. One of the critical factors is the "approach", i.e. how close is the cold water temperature to the wet bulb temperature. No matter how much you decrease the load, the cold water temperature will never go below the wet bulb temperature. But, as stanlsimon pointed out, in cold dry conditions the wet bulb temperature can go below freezing, and then your tower can freeze up.

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