Cooling Tower Acid Injection

Published on by in Academic

Cooling Tower Acid Injection
What is the proper way to inject acid to a cooling tower system for pH control?

Media

Taxonomy

7 Answers

  2. Sulfuric acid, being less expensive than other industrial acids, is usually preferred, I have seen it fed through a drizzle line fed by gravity directly into the basin (this is the least preferred means), pumped into a mixing trough (preferred by me due to the low pressure involved), pumped into a header under controlled pressure (below 20 psig is better) with static mixer in line.  The only time sulfuric acid treatment could be considered to be a problem is when the calcium levels in the make-up water are high at the start, not lowered by softening, and high cycles of concentration of the water is attempted.  The real problem there could be Calcium Sulfate scale (not so easily reversed). Use of an eductor with chemical feed is only allowed when positive cutoff of the chemical is available automatically, otherwise a likely over feed could result, although if a small enough restriction valve is utilized, and steady flow is preferred, this can be done with reasonable control.

    CO2 injection can not really lower the total alkalinity of cooling water, but it can shift the pH to slightly lower values.  

    Hydrochloric acid is not my preferred choice to add to any system (other than possibly upstream treatment of RO feed water) due to the corrosion issues from fugitive vapor.

  3. I think dosing a solution of dilute hydrochloric acid into the feed water before the cooling tower is a good way to reduce the bicarbonate ion content. This will increase the amount of carbon dioxide in the water. Carbon dioxide will be removed with evaporated water in the cooling tower.

    With the effective operation of the cooling tower, the pH of the water will always be at least 8.3 if there is a bicarbonate ion in the source water. Thus, in order to avoid the formation of deposits of solid calcium carbonate, it is necessary to keep the amount of bicarbonate ion in the water of the cooling tower not more than 0.5-0.7 mmol/l. Although it also still depends on the hardness of the source water.

    It is important not to reduce the concentration of bicarbonate ion in the source water after dosing the acid below 0.1-0.3 mmol/l (depending on how effectively the cooling tower removes carbon dioxide with the evaporated water).

    If the concentration of the bicarbonate ion in the source water is lower, the pH of the water in the cooling tower will be low, which means that corrosion processes are activated.

    In any case, it is necessary to control not only the pH of the water in the cooling tower, but also the alkalinity with hardness and salt concentration of water.

  4. As many of the replies have already mentioned, it is best to have the acid diluted and added into the cooling tower basin.  I have preferred to do this by having a 2" water line run to the rear of the basin. This line then becomes a source of water for a corrosion coupon rack and then it powers an eductor (hastalloy or kynar). The pH control signal then opens and closes the water supply to the eductor. This does several things all of which provide safety features.

    1) acid will only be fed when the circulator header is pressurized (water running)

    2) The acid is never under pressure to spray onto anyone or anything

    3) acid is diluted in the eductor and you do not have a pump that will fail.

    4) the acid is well diluted as it moves across the tower basin this avoids large spikes in pH

  5. Tower basin would be best location as much as close to the make up water addition. If concentrated acid is used then care should be taken such that it is diluted or dosed into the center of the tower. ON/OFF or proportional control will suffice for a cooling tower. However PID control will be more accurate and optimal. Above all periodic maintenance is essential ensuring safety and reliability.

  6. Dear Mr. McDonald,

        There is a huge mistake in modern tower water coolers and it is related to the used packing, a weird packing is now becoming worldwide accepted. if you have inside your tower water cooler a kind of packing which does not allow free downfall of water, then this packing is most probably the reason for troubles. The appropriate packing is Raschig Rings or any similar packing which is normally used in mass transfer towers and recommended by chemical engineering textbooks.

     

  7. Meter it in with a pump through a dilution trough in the basin of the tower.  Have the pump cycle on/off based on pH limits or use 4-20mA signal for more precise control.