Question of the Day: Cooling Tower Drift Losses

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Question of the Day: Cooling Tower Drift Losses
How much water is typically lost from the system through cooling tower drift?

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7 Answers

  1. Drift = (Drift factor) * (recirculation rate)

    recirculation rate  ~= 3 * system tonnage

    Drift can be a wide range 0.001-0.15%

  2. Dramatic improvements in drift eliminator technology since 2000

    üOlder designs up to 0.02% of recirculation rate

    Drift rates reduced by an order of magnitude to as low as 0.001% for counterflow towers

    üCross-Flow 0.005% of recirculation rate

  3. It also depends on the design of the cooling tower.  If the tower water cascades from the top and the fan is a forced draught, there will be a lower level of water droplets generated when compared to a tower, which sprays the water at the top of the tower.  Most modern drift eliminators are effective.  If there is no lip at the edge of the unit then water droplets can pass between the eliminators.  Ill fitting drift eliminators will also reduce their effectiveness.  The temperature of the water can also impact the eliminators.  High water temperatures can cause the eliminators to warp and become ineffective if they are the incorrect type.  This is why they should be regularly inspected.

  4. First  what is drif:  Water droplets suspended  in air and  discharged from the cooling tower is called drift. Drift is the byproduct  of the evaporating cooling process taking place in the C.T. Drift escapes  the system as mist or vapour  and that means loss of  cooling tower  and that means high make up water                                CALCULATION OF DRIFT LOSS:        With blow down blocked in , determine the con , of (CrO4-) at a measured intervals until the cycle of concentration returns to normal. So DRIFT LOSS (D) = (V/t)ln[Ci / Cf] where  V=VOL  capacity of the C.T. t = time in hour ,Cf = final con of CrO4- and Ci is that initial con.and using this formula at two definite time intervals  D1/D2 are calculated and then D = 1/2 (D1+D2)               source :Boiler Operation Engineering by P. Chottopadhyay .

  5. 0.1 - 0.2% RR old CT

    0.01 - 0.03% RR average CT

    0.001 - 0.005% RR new and well-maintained CT

  6. Yes, I agree with Tom that it is calculated as a percentage of circulation rate in the cooling system.

    0.005% I agree also to be a useful number.  I would also point out that ultimately the particulate emission of a cooling tower is a function of drift, and the TDS of the drifted water droplets.  Please note that at really high TDS (say 50,000 mg/L and up), It becomes virtually impossible to make a 10 micrometer dry particle, since that would require drifted droplets  so tiny they would be out of the statistical distribution by a lot of standard deviations from average.