Effective methods for dealing with fouling in heat exchangers

Let’s first look at why heat exchangers get scaled. The reason is quite simple: firstly, the environment in which the heat exchanger operates is a major factor contributing to scaling. For example, some heat exchangers are installed in workshops where there is a lot of dust; over time, this dust forms scale. Other heat exchangers are placed in water, and over time, the suspended particles in that water can also lead to scaling. Various such situations can result in scaling. Let’s take a look at the common types of scale: 1) Particle scale: Solid particles suspended in the fluid that accumulate on the surface of the heat exchange area. This type of fouling also includes a sediment layer formed on the horizontal heat exchange surface due to gravity, consisting of larger solid particles – namely so-called sedimentary fouling – as well as the deposition of other colloidal particles. 2) Crystalline fouling: Deposits formed when inorganic salts dissolved in the fluid crystallize on the heat exchange surface, usually occurring under conditions of supersaturation or during cooling. Typical fouls include calcium carbonate, calcium sulfate, and silica scaling layers on the cooling water side. 3) Chemical reaction fouling: Fouling that results from chemical reactions occurring on the heat transfer surface; the material of the heat transfer surface does not participate in the reaction, but it can act as a catalyst for such reactions. 4) Corrosive fouling: Fouling resulting from the corrosion of heat exchange surfaces by corrosive fluids or corrosive impurities present in such fluids. Generally, the degree of corrosion depends on the components in the fluid, temperature, and the pH value of the fluid being treated. 5) Biological fouling: Except for seawater cooling systems, biological fouling generally refers to microbial fouling. It may produce sludge, which in turn creates conditions for the growth of biological fouling; this fouling is sensitive to temperature, and under suitable temperature conditions, it can form a layer of fouling of considerable thickness. 6) Solidified fouling: Fouling formed when fluid solidifies on subcooled heat exchange surfaces. For example, when the water is below freezing point and freezes into ice on the heat exchange surface. The uniformity of the temperature distribution has a significant impact on this type of fouling. Techniques to prevent scaling should take the following points into account: 1) Preventing the formation of scale ； 2) Prevent adhesion between substances after scaling and their deposition on the heat transfer surface ； 3) Remove deposits from the heat transfer surface. Measures to prevent scaling include the following aspects: 1. Measures to be taken during the design phase. During the design of plate heat exchangers, when considering potential fouling, the following 6 aspects should be taken into account: 1) The heat exchanger should be easy to clean and maintain (such as plate heat exchangers) ； 2) After the heat exchange equipment is installed, it can be cleaned on-site without having to remove it, allowing dirt to be removed directly at the location where it is in use ； 3) The minimum dead zone and low flow velocity area should be adopted ； 4) The flow velocity distribution within the heat exchanger should be uniform in order to avoid large velocity gradients and ensure a uniform temperature distribution (such as in the baffle area) ； 5) Increasing the flow rate helps reduce fouling, provided that a reasonable pressure drop is maintained and corrosion is avoided ； 6) The effect of the heat exchange surface temperature on fouling formation should be considered. 2 Control of fouling during operation 1) Maintaining design conditions: Since an excess heat exchange area was used in the design of the heat exchanger, operational conditions must be adjusted in terms of flow rate and temperature to meet process requirements, resulting in differences from the design conditions. However, the design conditions (flow rate and temperature) should be maintained as much as possible through a bypass system in order to extend operational time and delay the occurrence of fouling. 2) Operating parameter control: During the operation of the heat exchanger, the conditions of the incoming material may change; therefore, it is necessary to regularly test the concentration of scaling substances in the fluid, the particle size, and the pH value of the liquid. 3) Good maintenance practices: Welds and scratches that occur during the maintenance of heat exchange equipment can accelerate the formation of scale; uneven flow rates can speed up corrosion. Fluid leakage into the cooling water provides nutrients for microorganisms. The lack of measures to remove dust from the air surrounding the air coolers can accelerate particle deposition as well as the chemical reactions that lead to scale formation in the heat exchangers. Conducting hydrostatic tests with unclean water can accelerate the formation of corrosive scale. 4) Use of additives: Depending on the different types of scaling mechanisms, various additives can be used to reduce or eliminate the formation of scale. Such as biocides and inhibitors, crystal modifiers, dispersants, flocculants, corrosion inhibitors, chemical reaction inhibitors, and additives suitable for preventing scaling in combustion systems. 5) Reducing the concentration of scaling substances in the fluid. Generally, scaling increases as the concentration of scaling substances in the fluid rises; particulate contaminants can be removed through filtration, coagulation, and sedimentation ； For scarring substances, they can be removed through ion exchange or chemical treatment ； Ultraviolet light, ultrasound, magnetic fields, electric fields, and radiation treatment – ultraviolet light is very effective at killing bacteria, while high-intensity ultrasound can effectively suppress biological fouling. Current research also involves magnetic fields, electric fields, and radiation treatment devices, though further studies are needed to draw definitive conclusions. 3 Chemical or mechanical cleaning techniques. Chemical cleaning is a widely used method; cleaning can sometimes be carried out while the equipment is in operation. However, its main drawback is that the chemical cleaning agents are unstable and can cause corrosion in heat exchangers and connection pipes. Mechanical cleaning techniques are commonly used to remove dirt from the shell side. First, the tube bundle is taken out and immersed in different liquids to soften and loosen the dirt, after which the scale layer is removed by mechanical means. 4 Mechanical online descaling technology 1) Use of abrasive particles: Solid particles are added to the fluid to scrub the surface of the heat exchanger and remove dirt, but this can cause corrosion on the heat exchanger surface. 2) The continuous descaling using sponge rubber balls is primarily used to remove fouling on the cooling water side of power plant condensers. These sponge rubber balls are circulated within the heat exchanger tubes by a pump; they are slightly larger in diameter than the tubes, and as they move through the tubes, they gently press against the tube walls, thereby removing any deposits that have accumulated there. 3) Automatic cleaning: The cleaning device for the heat exchanger tubes consists of 2 covers and 1 nylon brush; the covers are installed at both ends of each tube, and by changing the direction of the water flow, the brush can move back and forth along the tube to perform cleaning. Changing the direction of the water flow allows the brush to be pushed forward along the pipe for cleaning. The reversal of water flow is achieved by compressed air, which controls a four-way valve connected to the pipeline on a timed basis.

I just saw a copper-based scale remover today; I’m not sure how effective it is； Additionally, the circulating water needs to be treated to ensure its water quality

Chemical or mechanical cleaning techniques: Chemical cleaning is a widely used method; cleaning can sometimes be carried out while the equipment is in operation. However, its main drawback is that the chemical cleaning agents are unstable and can cause corrosion in heat exchangers and connecting pipes. Mechanical cleaning techniques are commonly used to remove dirt from the shell side. First, the tube bundle is taken out and immersed in different liquids to soften and loosen the dirt, after which the scale layer is removed by mechanical means.

Select a few heat exchange tubes at intervals and use a three-nozzle spray gun to perform high-pressure cleaning on those tubes; the results are good

The first step in dealing with the problem of scale is not to remove it, but to prevent its formation!

If it cannot be stopped, high-pressure cleaning is a good option

If scaling occurs on the heat exchangers in a circulating water system, it is recommended to install an LT3F descaling and anti-scaling device for online descaling; it operates without electricity or magnetism and requires no chemicals, making it energy-efficient and environmentally friendly.

The key is to exercise control at the source; preventing the formation of scale is of utmost importance.