Understand the threats of carryover and foaming in boilers, which reduce efficiency and damage equipment. Learn about the causes of high TDS and alkalinity, as well as effective solutions with blowdown and chemical antifoam to maintain the performance of your boiler system.

The Threats of Carryover and Foaming in Boilers and Effective Solutions to Overcome Them

Boilers are the heart of many industrial operations, producing steam that is vital for production processes, power generation, or heating. However, optimal boiler performance is often threatened by two very damaging ‘silent’ problems: carryover and foaming.

These two problems not only significantly reduce energy efficiency, but can also cause costly equipment damage and disrupt production. This article will thoroughly explore what carryover and foaming are, their main causes, and practical solutions to prevent them.

What Are Carryover and Foaming? Understanding the ‘Enemies’ in Boilers

Before discussing the solutions, it is important to understand the definitions of these two problems.

1. Carryover

2. Carryover is the phenomenon of boiler water droplets (along with their solid content and impurities) being carried along with the steam produced. Ideally, the steam coming out of the boiler should be dry and pure. However, when carryover occurs, the steam becomes ‘wet’ and contaminated.

3. Foaming

4. Foaming is a condition in which the water surface inside the boiler is covered by a layer of stable foam or bubbles. Imagine it like the foam on a glass of beer, but occurring under high pressure and temperature. This foam acts as a ‘bridge’ for water to be carried into the steam system, causing carryover.

Relationship: Foaming is the main cause of carryover. When foam forms, the boundary between the water surface and the steam becomes unclear, allowing the steam to easily sweep up water droplets and carry them out.

Main Causes: High TDS and Excessive Alkalinity

The root cause of carryover and foaming lies in the quality of the boiler water. The two key factors that are most often to blame are:

1. Excessively High Total Dissolved Solids (TDS)

• What is TDS? TDS is a measure of the total amount of all inorganic and organic solids dissolved in boiler water, such as calcium, magnesium, chloride, silica, and others.

• Why is it dangerous? When water evaporates, these dissolved substances do not evaporate and remain in the boiler. Their concentration will continue to accumulate. At a certain concentration level, high TDS will:
  

  • Increase the surface tension of the water, making it easier to form bubbles.

  • Stabilise these bubbles so that they do not break easily, leading to foaming.

2. Excessive Alkalinity

• What is Alkalinity? Alkalinity is the ability of water to neutralise acids, which is generally caused by the presence of bicarbonates, carbonates, and hydroxides.

• Why is it Dangerous? High alkalinity, especially under boiler temperature and pressure conditions, can cause two things:
  

  • Soda Brittle Embrittlement: A very dangerous phenomenon of metal cracking.

  • Increased Foaming Conditions: Similar to TDS, high alkalinity contributes to foam stability within the boiler.

In addition to the two main factors above, contaminants such as oil, grease, organic matter, or high silica levels can also trigger foaming by acting as natural surfactants that reduce the surface tension of water.

Impact of Damage Caused: More Than Just Wet Steam

Ignoring carryover and foaming is a costly mistake. Here are some of the negative impacts that can occur:

• Damage to Turbines and Rotating Equipment: Water droplets carried by steam can erode and damage turbine blades rotating at very high speeds, causing imbalance and operational failure.

• Fouling and Scaling in Piping & Steam Equipment: Carried solids will settle (form scale) in pipes, heat exchangers, and steam traps. Scale acts as an insulator, reducing heat transfer efficiency and obstructing flow.

• Product Contamination: In the food, pharmaceutical, or chemical industries, contaminated steam can contaminate the final product, leading to rejected production batches and significant financial losses.

• Corrosion in Steam Systems: Carried contaminants such as chlorides can cause pitting corrosion in pipes and equipment, shortening their service life.

• Decreased Energy Efficiency: Scale deposits inhibit heat transfer, forcing boilers to work harder to produce the same output, which means higher fuel consumption.

Effective Solution: A Combination of Mechanical and Chemical

Fortunately, carryover and foaming can be controlled with proper boiler water management. Two complementary solutions are:

1. Blowdown: Controlling TDS Concentration

Blowdown is the process of removing a portion of the water from the boiler to control the concentration of TDS and other impurities. This process is the most crucial first mechanical defence.

• Working Principle: By removing concentrated water and replacing it with cleaner feed water, the TDS concentration is maintained at a safe level.

• Types of Blowdown:
  

  • Bottom Blowdown: Removes sludge and suspended solids that settle at the bottom of the boiler.

  • Surface/Skimmer Blowdown: Removes the most concentrated water at the surface, just below the foam level, to effectively control TDS.

• Key to Success: Blowdown must be performed regularly and in a controlled manner based on TDS measurements. Performing too little blowdown causes TDS to accumulate, while excessive blowdown wastes energy and water. The use of a Continuous Blowdown System with heat recovery is often the best option for efficiency.

2. Antifoam: The Last Line of Defence Against Foam

Antifoam (or defoamer) is a special chemical designed to prevent and break down foam. It is a fast-acting chemical solution.

• Working Principle: Antifoam works by reducing the surface tension of foam bubbles. Insoluble antifoam particles infiltrate the bubble walls, making them unstable and eventually causing them to burst.

• Advantages: Antifoam is highly effective in overcoming foaming caused not only by high TDS, but also by contaminants such as oil or organic matter. It acts as additional ‘insurance’ when boiler conditions approach critical limits.

• Usage: Antifoam should be used in accordance with the dosage recommended by the supplier. Overdosing is not only wasteful, but can also cause new problems.

Synergy: Blowdown and antifoam are not alternatives, but complementary partners. Blowdown keeps conditions from reaching critical points, while antifoam is ready to protect in the event of fluctuations or emergencies that trigger foaming.

Conclusion: Prevention is Better than Cure

Carryover and foaming are real threats that impact the safety, efficiency, and reliability of your boiler system. Managing these two issues is essentially about proactive boiler water quality control.

By doing the following:

• Routine monitoring of TDS, alkalinity, and other water parameters.

• Implementation of measured and disciplined blowdown.

• Using chemical treatment (such as antifoam and other water conditioners) appropriately,

you can prevent foam formation, avoid carryover, and ensure your boiler operates efficiently, safely, and has a long service life. Consult with a water treatment expert to design an optimal boiler water management programme tailored to your plant's specific conditions.