Foaming in Cooling Towers

Recirculating aerated water is directed through cooling towers to transfer excess heat to the atmosphere. Foaming within these systems can negatively affect both the cooling tower and the surrounding environment. Foam may interfere with sensors, damage nearby equipment and vehicle finishes, and act as a carrier for Legionella bacteria.

Multiple factors can contribute to cooling water foaming, and in some cases, a combination of causes is responsible.

Common causes of cooling tower foaming include:

• Chemical overfeed

• Surfactants

• Process contamination

• Over cycling

• Excessive alkalinity

• Microbiological growth

Chemical Overfeed

Overfeeding water treatment chemicals and biocides can result in foaming, depending on the dosage and chemical type. Reducing chemical feed rates, increasing blowdown, and applying a minimal amount of antifoam or defoamer can help mitigate or eliminate foam. Excessive use of antifoam or defoamer should be avoided, as it may also contribute to foaming.

Surfactants

Cooling tower sumps are frequently situated below facility floors, allowing detergents from floor washing to drain into the sump and cause foaming. In commercial or institutional settings, intentional introduction of soap into the system may also be a factor. Removing surfactants, increasing blowdown, and applying antifoam or defoamer can reduce foam formation.

Process Contamination

Contaminants such as oil can induce foaming in cooling towers. Eliminating the source of contamination, increasing blowdown, and applying antifoam or defoamer as necessary can reduce or eliminate foam.

Over Cycling

Foaming can occur in over-cycled cooling tower systems, where conductivity exceeds the designated set point. Restoring blowdown rates to maintain control parameters may help eliminate or reduce foaming.

Excessive Alkalinity

Excessive alkalinity is a frequent cause of foaming in cooling tower water, particularly when softened, non-degasified reverse osmosis concentrate is used as makeup water. While soft water from reverse osmosis concentrate permits higher alkalinity operation, elevated alkalinity levels can promote foaming. Reassessing control parameters and increasing blowdown may mitigate this issue.

Microbiological Growth

Foam in cooling towers can result from the waste and decomposition products of microbiological growth, particularly following the application of high doses of oxidizing biocide to address system issues. Intermittent biocide feed programs may also contribute to foaming. Reassessment of the biocide program and the use of antifoam or defoamer, if necessary, are recommended.

Conclusions

• Return the cooling tower to normal operating parameters.

• Eliminate the foam source.

• Blowdown the system to remove contaminants

• Apply antifoams/defoamers when necessary.

A water treatment consultant can assist in evaluating the causes of and corrective actions for cooling tower foaming. H2 Global Solutions offers expertise and value that extend beyond the provision of chemical treatment programs.