Foaming refers to the formation and accumulation of bubbles on the surface of circulating water within an industrial cooling system. Excessive foaming can have major impacts on cooling tower performance. Expertly managing and controlling foaming is key for maintaining peak cooling tower operation, water conservation, and infrastructure longevity. This article will provide an in-depth exploration of foaming in industrial cooling towers and potential solutions.

Understanding Foaming in Cooling Towers

Cooling tower foam appears as a thick blanket of white foam that can expand to large volumes given the right conditions. This foam often overflows basins, clogs distribution systems, and causes other operating issues.

Causes of Foaming

There are several root causes leading to foaming in cooling towers:

• Water chemistry imbalances: High pH, alkalinity, hardness, and dissolved solids create conditions ideal for bubble formation and foam stability.
• Contaminants: Organic matter like oil and grease, detergents, and other substances act as foaming agents.
• Process leaks and spills: Leaked process fluids contain surfactants, hydrocarbons, and other chemicals that induce foaming.
• Mechanical issues: Damaged spray nozzles increase air entrainment while clogged nozzles concentrate fluids, both of which can create foam.

Types of Foaming

The stability and persistence of foam is dependent on the specific substances present:

• Stable foam is difficult to dissipate due to the presence of surfactants and soluble organics.
• Unstable foam tends to break down more rapidly when caused by suspended solids or temporary imbalances.

Careful analysis is needed to characterize cooling tower foam and derive appropriate solutions. This requires a multi-pronged approach.

Impact of Foaming on Cooling Tower Performance

Foaming can significantly hinder cooling tower thermal performance and water conservation efforts. Persistent foam insulation leads to a cascade of operational issues.

• Reduced heat transfer efficiency: Foam acts as a thermal barrier between water and air, decreasing evaporation rates and heat rejection. This raises cold water temperatures.
• Increased water loss: Foam is easily carried out by wind and drift. This bleed-off creates more makeup water usage.
• Corrosion and scaling: Foam provides surface area for biofouling and corrosion to occur on tower internals that can lead to scale formation.
• Microbiological growth and fouling: Bacteria, algae, and other microorganisms prosper in stable foam environments can lead to biological fouling issues.
• Safety hazards: Slippery foam on walkways and landing creates falling and other risks for operators.

If foaming persists, these factors compound over time, degrading tower capacity. Proper monitoring and treatment are required to avoid significant efficiency and water usage losses.

Diagnosing Foaming Issues

Properly diagnosing the root cause of foaming is critical for selecting appropriate mitigation strategies. A systematic investigation should be conducted utilizing visual inspection, water analysis, and performance monitoring. Contact EAI Water to schedule a free on-site audit.

Visual Inspection

Conducting a thorough visual inspection of the cooling tower and associated equipment is the first step toward diagnosing foaming causes. Observe foam directly in multiple locations to characterize color, density, stability, volume, and growth tendencies. Bright white and extremely persistent foam points to surfactants as the cause, while grayish brown foam indicates solids and organic matter. Check basin and ladder walls for foam accumulation and overflow patterns. Also, inspect tower internals like fill and drift eliminators if safely accessible.

Additionally, visually survey the tower cold water basin, pump suction basins, pipe galleries, and process equipment in the vicinity for evidence of leaks, spills, or contamination ingress. Common signs include oil sheens, soap residue, and unexpected wet areas. Inspect the tower fan and casing for dead insects, dirt buildup, bird nests, and other debris that could wash into the cold water flow. Examine the condition of water distribution system components like spray nozzles. Malfunctioning nozzles can lead to uneven flow, excessive splashing, and concentrated chemical treatments which encourage foaming.

Water Analysis

Water testing provides vital insights into the water chemistry and contaminants that cause cooling tower foaming. Full lab analysis includes several important parameters:

• pH/Alkalinity: Higher pH and alkalinity promote stable foam. Target ranges exist.
• Hardness/TDS: Solids provide nucleation sites for bubble formation and foam stability.
• Microbiological: Bacteria and their metabolic byproducts enhance foaming tendency.
• Surfactants/Tensioactives: Detect specific foaming agents from process leaks or contamination.
• Hydrocarbons: Oil and grease are notorious cooling tower foamers, even in small amounts.
• Specific Conductivity: Changes can indicate pollution ingress or performance issues.

Trend key water parameters that influence foaming over time. Comparing historical data against new outlier results can indicate the onset of contamination issues.

Performance Monitoring

Online monitoring and trending of cooling tower operational parameters provide tangible data on efficiency loss and water usage increases associated with foaming events. Log approach temperatures, heat rejection rates, condenser pressure changes, and flow rates through the tower over time. Abnormal acceleration in these metrics indicates impaired thermal performance, likely due to insulating foam buildup.

Also, record tower blowdown, evaporation, drift, and makeup water flow rates to quantify additional water usage. Check chemical treatment feed rates for evidence of increased biocide and anti-foam product usage corresponding to foam-related issues. Evaluate data during and after foaming episodes to correlate operational impacts. Integrate information from all available plant monitoring systems, especially the plant SCADA system, to piece together a timeline of circumstances around each foaming incident.

Utilizing all three diagnostic methods—visual, water analytical, and operational data—provides the comprehensive ground-truth information needed to troubleshoot the root causes of cooling tower foaming and prioritize corrective actions.

Prevention and Treatment of Foaming

Once the underlying causes of foaming have been uncovered through methodical diagnosis, targeted preventative measures and treatment options can be deployed. Anti-foaming strategies fall into three main categories—water chemistry control, operational practices, and advanced technologies.

Water Chemistry Control Strategies

Properly controlling water chemistry is the foundation of most cooling tower treatment programs, including foaming prevention. Key chemical parameters to monitor and maintain within guideline ranges are:

pH/Alkalinity

The ideal pH range is 6.5 to 7.5. Lower pH water has less foaming tendency. High alkalinity water provides more buffering capacity for surfactants to destabilize and foam. Carbon dioxide addition is an effective pH/alkalinity control method compatible with many towers.

Hardness and TDS Control

Cycles of concentration must balance heat transfer efficiency versus solubility limits. Elevated concentrations of calcium, magnesium, silica, and other salts lead to more stable, persistent foam and strategically timed blowdowns remove excess dissolved solids.

Chemical Defogging

Specialty surfactants reverse the effects of foaming surfactants, speeding the drainage of lamella walls. Silicone-based antifoams spread rapidly and are long-lasting. Several products can be applied depending on the contaminants present in order to mitigate these foaming issues over time.

Sidestream Treatment

Portable clarifiers, media filters, and oil water separators polish a slipstream of water to remove contaminants that cause foaming, although this is solely a mitigation as opposed to preventative solution.

Operational Practices

In parallel with water treatment, operational practices that eliminate root causes of foaming should be implemented:

Prevent External Contamination

Institute strict housekeeping procedures, install oil and chemical storage containment and fix process leaks that allow entry of foaming agents into cooling water. Locking out-of-service tower cells whenever major nearby work occurs is a vital SOP for all operators.

Distribution System Maintenance

Flush debris from clogged spray nozzles causing uneven flow and stagnation and replace damaged or worn nozzle components.

Air Flow & Water Balancing

Proper air inlet modulation, variable speed drives, and basin level controls optimize contact and minimize turbulence between air and water flows. Stable, uniform contact prevents air ingestion and foam formation.

Advanced Defoaming Technologies

For severe foaming from surfactants and organic matter, supplemental technologies provide chemical-free treatment:

Ultrasonic Defoamers

High-frequency sound waves collapse foam bubbles through pressure differentials. Useful for immediate foam knockdown during a crisis although this is a costly solution as compared to alternatives.

Membrane Filtration

Ultrafiltration membranes provide a physical barrier removing particles, oils, surfactants, and even biological contaminants. While a strong solution, UF membrane systems oftentimes need to be custom designed and manufactured, making them a less than suitable option for the typical foaming outbreak.

A total systems approach utilizing multiple prevention layers tailored to address the diagnosed foaming cause will provide reliable, long-term control with flexibility to handle upsets. Ongoing vigilance and corrective actions are key to managing cooling tower foaming and maintaining efficiency.

Consider working with an experienced water treatment vendor if you are running into foaming issues. EAI Water offers on-site audits to help you diagnose and then solve your cooling tower foaming concerns.