Last updated on August 23rd, 2023 at 02:15 pm
On top of other factors that must be monitored during production, whether that’s in the food and beverage industry, pharmaceuticals, or industrial setting, we must consider fouling. It’s important to understand what it is, how it affects heat transfer in various applications, how to address it, and, ultimately, how to avoid it. Bettering our understanding of fouling will ensure the equipment used lasts longer, the materials aren’t affected, and added costs are minimized.
Fouling occurs when unwanted materials build up on a heat transfer surface. Consider a pipe used to move water. If buildup occurs inside the pipe, the water flow is reduced and the water might even become contaminated. This applies to heat transfer methods when fouling occurs. Substances, such as rust or minerals, will build on the surfaces of the heat exchanger and reduce efficiency, and affect the product and heat exchanger itself.
Fouling deposits can range from solids to liquids to gases. They can be a result of the fluid processed, the environment, or the materials that make up the heat exchanger. Some examples include scale, suspended solids, insoluble salts, and algae.
The fouling factor is the term for heat flow resistance due to buildup on the surface of the heat exchanger. The estimated fouling factor of a heat exchanger determines how often it should be cleaned.
An incorrect estimate could lead to infrequent cleaning allowing fouling to build. Liquids, such as fuel oil and seawater, have standard fouling factors that are easily implemented. However, more high-maintenance substances, such as sludge, shouldn’t be assigned a fouling factor without first analyzing how it works in the system.
This occurs when particles from the fluid in the heat exchanger attach to the surfaces and start to build a fouling layer. The most common contributors are calcium, magnesium, and dissolved salts in heated water that crystallize on the surfaces.
Scaling on the interior of a heat exchanger can cause corrosion, a shorter equipment lifespan, increased energy consumption, and decreased efficiency. Scaling can be avoided by implementing a circulation heater that helps reduce the element temperature and properly spread heat. If scaling is a concern, hot water flushing a couple of times a year will remove particles.
This type of fouling has to do with organic growth, such as bacteria, algae, and fungi. It’s most common in chemical, marine, and organic applications where these growths can thrive, but it’s especially important to manage organic fouling. Otherwise, it can severely affect industries, such as food and pharmaceuticals.
Organic growth can cause a lot of damage, and corrosion, and also affect heat transfer efficiency and lifespan. Choosing different materials when implementing a heat exchanger can help avoid organic growth. It’s also best to clean the heat transfer systems regularly.
When sediments (for example, rust, dirt, or sand) are present in a heat transfer system, they cause fouling. A small amount of sedimentation isn’t likely to cause any problems, but, as it builds, it has the same effects on production as other types of fouling.
The heat transfer tubes will erode if sedimentation increases. Eventually, the heat transfer surface will begin to leak as the tubes are worn away. Avoid this outcome by using a circulation heater for proper heat control.
Coking occurs when the temperature of the oil is too high for its stability limits, causing it to build on the surface. A small buildup quickly accumulates more until the surfaces crack and lift, causing even more coking and severe damage to the system.
In this case, choosing the right materials to avoid corrosion and damage by the fluid is key. Whatever the fluid may be, the temperature and wattage should be set accordingly. Clean and maintain the heat transfer tubes regularly; flushing or power washing are viable options.
The first effect fouling has on heat transfer is cost. This can further be broken down into four sections: avoidance cost, maintenance cost, replacement or repair cost, and profitability.
For operations trying to get ahead of fouling in inefficient ways, they rack up avoidance costs. Some applications will install larger heat exchangers and tubes to allow more liquid flow even if fouling occurs. This increases the rate at which the liquid needs to be heated and moved, and the costs of running the heat exchanger.
Maintenance costs are accrued when fouling is present and the project manager commences cleaning. As fouling occurs, maintenance is required to remove particles and buildups; otherwise, the whole system will fail.
Replacement and repair costs follow if the need for maintenance hasn’t been met. Replacement and repair can rack up the cost quickly since these operations are often large in scale and complicated.
Lastly, what we hope to avoid is shutting down the project for repairs or due to a system failure. This affects profitability since the production is paused. It’s also likely that recent production isn’t viable due to the fouling found inside the system. Shutting down an entire production plant is never what operators want, but if fouling is left unattended, it’s inevitable.
As fouling increases within the system, heat transfer becomes less and less efficient. The system has to work harder to heat and circulate the substance. Depending on the materials, fouling can also erode the piping surfaces until they begin to leak, exposing the interior to more contaminants and wasting resources.
Especially when it comes to food, beverage, and pharmaceutical production, fouling can render production useless. If the liquids being heated and transferred come into contact or chemically react with the particles that have developed on the piping surfaces, they can no longer be used. That leads to a big waste in production, the need to flush the system, and the time and money to restart after a delay.
There are four ways fouling can be cleaned depending on the type of materials and liquids being used.
Fluids traveling at higher speeds will help remove deposits as it travels. This is only helpful when there’s a small amount of fouling and when the liquid can safely be transferred this way.
Maintaining a constant flow speed also decreases the chances of deposits settling on the surface since they don’t have a chance to accumulate and stick. Deposits are more likely to settle in low-velocity areas or if there’s a pause in production.
When the temperature of a circulation heater or immersion heater increases or remains at extreme temperatures, scaling deposits and organic growth are more likely to occur. This can be avoided with lower temperatures or by spreading out the heat source with multiple circulation heaters to avoid temperature gradients.
Consider the makeup of the fluid being transferred. At certain temperatures or speeds, some substances can react or separate into multiple substances, which turn into deposits.
Not every material will work with any temperature and liquid, gas, or solid. It’s important to use materials that will complement the substance in the heat exchanger. Where corrosion is a possibility, use corrosion-resistant materials, such as stainless steel, titanium, and alloys. Next, consider the surface of the material. Rougher surfaces will accumulate fouling easier.
Wattco has all sorts of available heat transfer options depending on the project: circulation heaters, immersion heaters, flanged heaters, tubular heaters, and plenty more. On top of that, we know the ins and outs of helping businesses create operations that flow smoothly. Contact us for more information on our products and suggestions.