By design, recirculating aerated water cascades through cooling towers to extract unwanted heat to the atmosphere. When foaming occurs, it can have negative impacts on both the cooling tower system and the surrounding environment. Foaming can not only confuse sensors and damage nearby equipment and car paint, it can also serve as a carrier for Legionella bacteria. Cooling water can foam due to a multitude of reasons. In some cases, it is even the result of a combination of factors. Some reasons cooling tower foaming may occur include:
- Chemical overfeed
- Surfactants
- Process contamination
- Over cycling
- Excessive alkalinity
- Microbiological growth
Chemical Overfeed
Sometimes water treatment chemicals and biocides are overfed. Depending upon the level of overfeed and the type of chemical, foaming may be seen. Decreasing the chemical feed, blowing the cooling tower down, and possibly adding a small amount of antifoam/defoamer can assist in foam reduction or elimination. It is important to add only a small amount of antifoam/defoamer, as too much can cause foaming as well.
Surfactants
Cooling tower sumps are often located below the facility floor. When the floors are washed with detergent, they can drain into the sump, causing foaming. In commercial or college environments, pouring a bottle of soap into the system may be the cause. Removing the surfactant, blowing down the cooling tower, and using antifoam/defoamer will assist in foam reduction.
Process Contamination
Contaminants like oil can cause cooling tower foam. Stopping the contamination, blowing down the cooling tower, and using an antifoam/defoamer if needed can stop or reduce foaming.
Over Cycling
Foaming may be seen in an over cycled cooling tower system, meaning the conductivity is above set point. Blowing down the system within the control parameters may help eliminate or decrease foaming.
Excessive Alkalinity
The source of foaming in cooling tower water can be excessive alkalinity. This is a common cause when softened, non-degasified reverse osmosis concentrate is used as makeup to the cooling tower. Reverse osmosis concentrate can be soft water, which may allow operation at higher alkalinity levels. However, the increased alkalinity can also cause foaming. Reassessment of control parameters and increasing blowdown may help.
Microbiological Growth
The waste and decomposition of microbiological growth can cause foam in the cooling tower, especially when a high dose of oxidizing biocide is added to help bring a problem system under control. Foam may also appear when the treatment program uses intermittent biocide feed. Reassess the biocide program and use an antifoam/defoamer if needed.
Conclusions
Cooling tower foam can be the result of many factors, each of which needs to be addressed. Prioritizing the following to meet your unique circumstances may help when handling a foaming cooling tower:
- Return the cooling tower to normal operating parameters
- Eliminate the foam source
- Blowdown the system to remove contaminants
- Apply antifoams/defoamers when necessary
Your water treatment consultant can help evaluate the causes and corrective actions for cooling tower foaming. As a knowledgeable water treatment partner, Chem-Aqua provides value that goes far beyond the chemical program costs. Contact us today!
Written by: James McDonald