Your heat exchanger works hard to keep your boiler or cooling tower performing effectively. But at some point, even a high-quality heat exchanger will likely become fouled because of minerals or other small particles in your water.
How do you get rid of fouling in heat exchangers? Minimizing fouling is quick and easy, and in the guide below, we’ll show you how.
What Is Fouling?
What is fouling in a heat exchanger? Fouling occurs when deposits of undesirable materials like bacteria, minerals or other contaminants form on heat transfer surfaces. This accumulation of materials increases heat transfer resistance and can lead to poor performance.
Fouling in a heat exchanger can take several forms:
Scaling, also known as crystallization fouling, is particularly common, especially in systems involving water. Scaling occurs when minerals in the water precipitate and collect on the heat exchanger’s surfaces as crystals, forming a whitish buildup.
2. Particulate Fouling
Particulate fouling occurs when small particles of matter collect on the heat exchanger’s surfaces. The particulates are sometimes tiny, less than a nanometer in diameter, though they may be larger. Particulate fouling may occur in both gas and liquid systems.
3. Corrosion Fouling
Corrosion fouling occurs when impurities in the water change the composition of the heat exchanger’s metal surfaces, degrading the metal and often making it structurally unsound. Corrosion occurs because although refined metals like steel are strong and sturdy, they are not as chemically stable as other substances. Chemical reactions between the metals and the surrounding environment slowly turn the surfaces of these metals into more chemically stable, if weaker, forms, including oxides and sulfides.
4. Biological Fouling
Biological fouling is common in wastewater treatment applications, but it can occur in many operations that involve water. Biological fouling occurs when microbes settle and form a biofilm or sludge on equipment surfaces. It is a particular concern in food processing applications where safe, sanitary products are essential and the potential for biological contamination is high.
5. Chemical Fouling
Chemical fouling occurs when a chemical reaction takes place near the surface of a heat exchanger. If chemicals are present in the water, the heat of the process water as it passes through the heat exchanger can speed up the reactions and leave unwanted surface deposits.
6. Freezing Fouling
Freezing fouling most often takes place with chilling operations. It occurs when a liquid freezes at a surface and the frozen layer impedes heat transfer.
The Impact of Fouling
Fouling reduces the amount of heat exchange that can take place. This reduced heat exchange leads to a host of other issues, including reduced efficiency, diminished product quality, local hot spots, equipment breakdowns, safety concerns and increased frequency of maintenance and repairs.
Fouling also causes issues with water flow. Because fouling tends to be much rougher than the smooth surfaces of pipes and metal components, it often impedes the movement of water. Blocked water flow can cause inefficiencies and pressure drops and diminish the heat exchanger’s performance overall.
One of the main commercial consequences of fouling is dramatically increased maintenance costs. Because buildup on your heat exchanger’s surfaces tends to accelerate the rate of degradation, the heat exchanger will likely require more frequent cleanings and more extensive and costly repairs.
Fouling can also increase expenses by making your heat exchanger less efficient. When your heat exchanger works less efficiently, it consumes much more power to do the same amount of heating, so you’ll likely see an increase in your utility bills if your heat exchanger becomes fouled.
Why Does Fouling Occur?
What are the common causes of fouling in a heat exchanger? Fouling often occurs because of the composition of the water in the system. Here’s a more detailed look at what can cause heat exchanger fouling:
- Mineral impurities: Scaling occurs because the water flowing through the heat exchanger contains mineral impurities such as calcium carbonate, magnesium, chloride or iron. Hard water, which contains excessive amounts of calcium and magnesium, is particularly prone to causing scaling. The impurities tend to precipitate out of the water and form a scum on the heat exchanger’s surfaces.
- Operating conditions: Certain operating conditions in a heat exchanger are conducive to corrosion and other forms of fouling. These characteristics include high heat, high levels of dissolved oxygen, low pH and high-velocity flow.
- Contaminants: Fouling also sometimes occurs because the water contains airborne pollutants as well as mineral impurities. These contaminants can build up on the heat exchanger surfaces over time.
- Microbes: The water in a heat exchanger may contain microorganisms like bacteria, viruses, fungi or algae. As they congregate on surfaces, they may form a slick film.
How to Detect Heat Exchanger Fouling
How do you detect fouling in a heat exchanger? If you want to monitor the level of fouling on your heat exchanger, you have a few different options:
- Pressure drop measurements: Because it’s so common for fouling to cause pressure drops, facilities often try to check for fouling by computing a sliding average value for pressure drops over time. Though this method is indirect, it can achieve reliable results, especially when the pressure drop is significant.
- Deposit analysis: Deposit analysis involves taking a sample from the heat exchanger’s surface and then analyzing its composition. The presence of mineral salts or other contaminants likely indicates fouling.
- Metal detectors: When the contaminants in your feedwater include metal salts like iron or mercury, you may be able to use metal detectors to locate them. Metal detectors on a feed stream can detect individual metals even at minimal concentrations.
- Mathematical modeling: If your facility is technologically and mathematically savvy, you may be able to use advanced techniques to detect fouling. Detection methods such as calculating heat transfer data and mapping its slope or using a cumulative sum control chart may be effective.
Research on fouling often involves experimental studies or simulators. More direct research on fouling samples and different types of heat exchangers is likely necessary.
Tips for Reducing Fouling in Heat Exchangers
Keeping your heat exchanger free from fouling is essential for its longevity, efficiency, cost-effectiveness and overall performance. Below are a few tips for how to reduce fouling in heat exchangers:
1. Increase Energy Consumption
Though increasing your energy consumption isn’t always in your facility’s best environmental or budgetary interests, it can help reduce fouling in your heat exchanger. If you increase your energy consumption so that your heat exchanger operates at peak intensity, the increased turbulence may mean the contaminants in the feedwater do not have a chance to settle. However, this method of fouling reduction is expensive and wasteful, and it’s not always effective.
2. Control Materials Causing Buildup
If you have a choice in the water you use in your heat exchanger, you can try to choose softer water that contains fewer impurities. You can also try to filter out impurities, including microbiological contaminants. Even though systems like boiler systems are so hot they rarely provide ideal breeding grounds for bacteria, microbes may be a significant concern in some heat exchanger applications like cooling towers.
However, filtration and purification systems are expensive. They are sometimes feasible on smaller scales, but they are rarely practical for large-scale commercial and industrial applications.
3. Select Durable Materials
Selecting resistant materials for your heat exchanger can help reduce fouling. Generally, when you have the option, you’ll want to choose materials that are hygienic, durable and long-lasting and exhibit the thermal characteristics you need for effective heat transfer.
For example, even though carbon steel is cheaper and easier to work with than stainless steel, it is also brittler and much more susceptible to corrosion. Choosing stainless steel for your applications can help your heat exchanger resist fouling, maintain its optimal performance and last much longer.
Using scraped-surface or corrugated-tube heat exchangers can also decrease fouling. Because of their rough surfaces, these designs increase turbulence in the water, and the turbulence prevents solids from settling.
However, when you choose materials for their fouling resistance, this can have a few drawbacks. Certain materials can deter fouling, but they are not always 100% effective. They are also likely to be more expensive than traditional options.
4. Apply Coatings
Applying protective coatings to your heat exchanger surfaces can prevent foulant adhesion and adsorption and reduce fouling. Inert coatings are useful because they prevent the base metal from interacting with substances in the water that cause fouling. Synthetic fluoropolymers like polytetrafluoroethylene (PTFE) and perfluoropolyether (PFPE) are common coating materials because of their hydrophobic and nonstick properties, high thermal stability and chemical inertness.
Protective fouling-resistant coatings are flexible and effective. If you already have plans to upgrade your equipment, purchasing a new heat exchanger that features these coatings is an excellent strategy. However, if you’re happy with your current heat exchanger and merely want to reduce fouling in an existing system, retrofitting the surfaces with coatings may not be practical logistically. Certain coatings also cannot stand up to high temperatures or extreme abrasion and will wear down under these conditions.
5. Perform Regular Cleanings
Cleaning heat exchangers can remove fouling and keep the equipment operating efficiently. Cleaning scale from a heat exchanger, in particular, removes mineral deposits to improve performance and decrease operational costs.
To clean scale from a heat exchanger, you can follow a series of simple steps:
- Isolate the chiller: Isolate the chiller by closing the valves. You’ll need to take your heat exchanger offline in this way because the acid you use for cleaning needs substantial contact time to dissolve the scale buildup.
- Estimate volume: The next step is to estimate the capacity of your heat exchanger and the relevant section of pipe. You’ll need a cleaning solution tank with at least double the volume of your heat exchanger.
- Set up the feed pump: Position the chemical feed pump so that the return line to the cleaning solution tank comes off the top of the heat exchanger.
- Add water: Add water to the cleaning solution tank and start circulating it with the circulation pump. Keep the pump operating until water begins to flow back into the cleaning solution tank.
- Add anti-foaming agent: While the pump is running, add CTA-800 or a similar anti-foaming product.
- Add the cleaning solution: After adding the anti-foaming agent, add a gallon of the recommended cleaning product to the cleaning solution tank.
- Measure pH: Test the pH of the resulting solution by dipping a testing strip into the tank. Keep adding more of the cleaning product until the pH of the solution is sufficiently acidic, usually between 2 and 3.
- Let the solution circulate: Allow the cleaning solution to flow through the heat exchanger. Add more of the cleaning product if the pH rises to about 5. You’ll know the heat exchanger is clean when the cleaning solution’s pH has remained between 2 and 3 for at least half an hour.
- Neutralize the cleaning solution: Add BD-6 or a similar product to raise the cleaning solution’s pH to 5 or more.
- Drain the solution: Drain the heat exchanger and tank to an approved sanitary sewer.
- Add more water: Add fresh water to the tank and use the pump to circulate it through the heat exchanger until the pH reaches 6 or 7.
- Passivate surfaces: Make your heat exchanger’s raw metal surfaces inert and scale-resistant by adding a product like Tube Bright for a final 15-minute rinse.
- Check for debris: Remove the end bells and inspect the bells, tubes and tube sheets for contamination. If necessary, flush these areas with water or repeat the steps outlined above.
One of the most effective products for scale removal is called Scalzo. Scalzo contains hydrochloric acid to dissolve mineral deposits. It also contains special corrosion inhibitors and dispersants to help a heat exchanger’s surfaces resist fouling even after cleaning is complete.
However, because it is so caustic, hydrochloric acid is not suitable for use with stainless steel. It causes pitting, a more severe and localized form of corrosion that leaves large depressions in the metal. For stainless steel heat exchanger components, you’ll want to use a product like CA-100, which contains citric acid instead of hydrochloric acid. It is gentler on stainless steel while still providing effective scale cleaning.
6. Set up a Treatment System
One of the most effective steps you can take to reduce fouling in your heat exchanger is to set up a regular treatment plan. Partner with a reliable water treatment company like Chardon Labs for quality chemical treatment. When you work with a professional company for industrial water treatment services, you’ll save valuable time and gain peace of mind of knowing your heat exchanger is in expert hands.
Chardon Labs can deliver the chemicals, treat your water and dispose of these substances for you, so you can continue focusing on your facility’s most pressing needs.
Contact Chardon Laboratories for Help With Reducing Heat Exchanger Fouling
Fouling reduces efficiency, impedes performance and increases the frequency of expensive, time-consuming maintenance and repairs. Fortunately, working with water treatment professionals to prevent fouling can help your equipment last longer and perform better. You’ll diminish your utility bills and make your operations more cost-effective overall.
At Chardon Labs, we can provide you with essential chemical treatments at a fixed price that works for your budget. We are also happy to work with you on a custom treatment plan that fits your facility’s unique needs.
Contact us today to learn more.