The Control of pH and Oxidation Reduction Potential (ORP) in Cooling Tower Applications

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Courtesy of Walchem, Iwaki America Inc.

The importance of keeping cooling tower water in proper chemical balance is becoming clearer. Cooling tower treatment control systems can limit scale formation to improve efficiency, limit corrosion to increase the service life of the cooling water system, and maintain a residual halogen level to reduce liability associated with biological growth, particularly Legionellae.  
The use of automatic control equipment rather than manual measurement and adjustment has increased dramatically in the past several years, motivated in part by the loss of on-site personnel to perform the task, in part by the safety aspects of chemical handling, and in part by efforts to conserve water.  
Environmental concerns have also driven the increased use of pH and oxidation-reduction potential (ORP) controllers in cooling water systems. After the use of heavy metals was banned, the simple treatment method to control chromate passivation could not be used to protect the cooling systems. The newer, alternative methods can be more sensitive to pH fluctuations. For example, alkaline orthophosphate treatments can result in corrosion if the pH drops, and in calcium phosphate scaling if the pH rises. The use of automatic pH control minimizes this problem.  
Similarly, the combination of pH control and ORP control can maintain chlorine and/or bromine residuals at the levels required to inhibit survival of bacterium and the biofilm that supports them. Maintaining a constant low-level halogen residual also minimizes the amount of chemical that is discharged into the environment.  
Installation of automatic control equipment is also a great way for water treatment chemical providers to differentiate themselves from the competition by increasing their level of service to the owner of the cooling towers.

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