Cooling water systems tend to become more alkaline as water "cycles". As alkalinity (pH) increases, cooling water becomes more scale-forming in nature. Acid is frequently added to cooling water to destroy alkalinity; thus, depressing pH and scale-forming tendencies. However, the addition of acid to control pH also increases the corrosiveness of cooling water. Additional amounts of corrosion inhibiting chemicals are usually required in pH controlled systems to keep corrosion rates down.

In the past, cooling water programs were predominantly pH control programs. The addition of acid to control pH was necessary to control scale and because chlorine and hypochlorite biocidal programs required depressed pH to be effective. Chlorine dissociation into non-effective hypochlorite ions increases with system pH. At a pH of 8, only 25% of the chlorine added is hypochlorous acid, while over 75% dissociates into the hypochlorite ion.

The desire to create a more efficient and environmentally friendly treatment regiment led Applied Specialties to develop a cooling water treatment program which operates in an alkaline pH using bromine or chlorine dioxide.

Bromine

Bromine is also recognized as being less environmentally harmful than chlorine. Brominated organics are much less persistent in the environment than the THMs and dioxin formed by the reaction of chlorine with organics.

Bromine is basically unaffected by the presence of ammonia-- unlike chlorine which reacts with ammonia and becomes unavailable to perform the desired functions.

Chlorine Dioxide

Chlorine dioxide has roughly 2 and ½ times the oxidizing power of chlorine. The selectivity of chlorine dioxide makes it more efficient than chlorine. Chlorine dioxide has a microbiological toxicity of greater than 2.5 times that of chlorine because it reacts preferentially with the biological component of water. Like bromine, chlorine dioxide demands in a system do not increase with the presence of ammonia or other nitrogenous compounds.

Chlorine dioxide is also more compatible with cooling system components than chlorine. Yellow metal corrosion is accelerated by chlorine. The most common yellow metal corrosion inhibitor, tolyltriazole, is readily destroyed and stripped away from yellow metal surfaces by chlorine. Not only is chlorine dioxide less corrosive than chlorine, it is also much more compatible with tolyltriazole. Switching from chlorine to chlorine dioxide lowers yellow metal corrosion rates and reduces the amount of yellow metal corrosion inhibitor required.

A long-standing problem in cooling towers with chlorination has been wood delignification. Delignification of wood is a serious problem in towers with wooden supports. Years of chlorination can make wood brittle and possibly cause a collapse of cooling tower internals. Chlorine dioxide does not cause wood delignification.

Environmentally, chlorine dioxide is quite superior to chlorine. No chlorinated organics are produced by reaction of chlorine dioxide with organic material. Neither THMs or dioxin are formed. Chlorine dioxide does not react to form chlorine. Total residual oxidant limits are easily met because chlorine dioxide is fed at a fraction of the chlorine feed rate and reacts very quickly. Complete biological control is usually maintained without ever carrying a residual in the blowdown.

Interested in seeing if bromine and chlorine dioxide can work for you? Contact techservices@appliedspecialties.com for a FREE no cost survey of your cooling water system. At ASI, we produce results!