Cleaning of heat exchangers

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A heat exchanger is a compact and efficient heat exchange device, serving as an excellent tool for applications such as heating, cooling, heat recovery, and rapid sterilization. However, due to the long-term operation of the heat exchanger, as well as differences in the purity of the fluids used for cooling or heating and the inherent properties of the process media, scaling of the heat exchanger becomes inevitable. This reduces the heat exchange efficiency of the heat exchanger, thereby affecting the normal progress of production and the safety of the equipment. Therefore, heat exchangers should be cleaned regularly to remove dirt, thereby ensuring their efficient heat transfer and the normal operation of production. Causes, types, and hazards of fouling in heat exchangers. The three main causes of fouling in heat exchangers are as follows: (1) Since most common heat exchangers operate using water as the heat transfer medium, certain salts precipitate out of the water when the temperature rises and the concentration increases; these deposits adhere to the surface of the heat exchange tubes, forming scale. Over time, as usage continues and the frequency of operation increases, this scale layer becomes thicker and harder, adhering tightly to the surface of the heat exchange tubes. (2) Similar to scale, the fluid on the other side of the heat exchanger may also produce non-scale solid deposits due to the properties of the substances present. If these deposits are not removed over time, they will accumulate more and more on the surface of the heat exchange tubes. (3) When the fluid contains a large amount of mechanical impurities and organic matter, and the flow rate of the fluid is low, some of these impurities or organic substances can deposit within the heat exchanger, resulting in loose, porous, or gel-like contaminants. Six main scaling processes in heat exchangers – for commonly used heat exchangers. Based on the mechanisms of scaling, we generally classify scaling into the following categories: (1) Crystallization-induced scaling: In water cooling systems, supersaturated calcium and magnesium salts in the water crystallize and deposit on the surface of heat exchangers due to changes in temperature, pH, etc., thus forming scale; (2) Particle scaling: The accumulation of suspended solid particles in the fluid on the heat exchange surface; (3) Chemical reaction-induced scaling: Deposition of solids resulting from chemical reactions; (4) Corrosion-induced scaling: The corrosion of the heat exchange surface by the medium in use leads to the deposition of corrosion products on that surface, forming fouling; (5) Biological scaling: In common cooling water systems, industrial water often contains microorganisms along with the nutrients they require. These microorganisms multiply, and they along with their excretions form biological scale on the heat exchange surface; (6) Deposition-induced scaling: On subcooled heat exchange surfaces, highly soluble components of pure liquids or multi-component solutions deposit as a result of deposition processes. The above classifications merely indicate that a certain process is a key factor in the formation of that type of dirt. Scaling is often the result of multiple processes acting together; therefore, the actual fouling on the heat exchange surface is typically a mixture of various types of fouling. Dangers of not cleaning scale buildup: (1) Scale buildup significantly reduces the heat exchange efficiency of equipment, leads to increased energy consumption, and raises production costs ； (2) Scaling deteriorates the heat transfer conditions in heat exchange equipment, causing the heat transfer surfaces to overheat, which leads to safety incidents such as bulging, cracks, and tube failures ； (3) Scaling can cause corrosion beneath the scale, leading to equipment perforation and leakage as well as reducing the equipment’s service life. It can also disrupt the production process, affect product quality, and trigger quality issues. To ensure product quality and production safety, it is necessary to regularly descale and clean heat exchangers. Selection of heat exchanger cleaning methods: Depending on the cleaning approach, the main methods are physical cleaning and chemical cleaning. Chemical cleaning: Chemical cleaning involves using chemical cleaners to initiate a chemical reaction that causes the scale and other deposits on the surface of the heat exchanger’s heat transfer tubes to dissolve, fall off, or be removed. Chemical cleaning does not require disassembling the heat exchanger, which simplifies the cleaning process and reduces the labor involved. Its drawback is that if the chemical cleaning solution is not selected properly, it can corrode and damage the substrate being cleaned, resulting in losses. Chemical cleaning methods ◉ Circulation method: A pump is used to force the cleaning solution to circulate for cleaning. ◉ Immersion method: Fill the equipment with cleaning solution and let it stand for a certain period of time. ◉ Surge method: Fill the device with cleaning solution, then periodically remove a portion of the solution from the bottom and pour the removed liquid back into the device to achieve thorough mixing and cleaning. Chemical circulation cleaning steps: (1) Isolate the equipment and drain all the water from the heat exchanger. (2) Clean the pipes of impurities using high-pressure water and seal the system. (3) A ball valve is installed between the isolation valve and the exchanger; a transfer pump and pipes are connected, with the cleaning agent being pumped in from the bottom of the heat exchanger and flowing out from the top. (4) Add the required cleaning agent and perform repeated circulation cleaning. (5) Release gas at any time and inject appropriate water.   (6) Use a pH test strip to determine the effectiveness of the cleaner. (7) Recover the cleaning solution and rinse it repeatedly with clean water until the pH becomes neutral. Physical cleaning: Physical cleaning involves using various mechanical forces and energies to crush, separate, and detach dirt from the surface of an object, thereby achieving the effect of cleaning. Physical cleaning methods all share one common feature: they are efficient, non-corrosive, safe, and environmentally friendly. Its drawback is that when cleaning the interior of devices with complex structures, its force sometimes cannot reach all areas evenly, resulting in \"dead zones\". Common methods include ultrasonic scale removal, PIG pipeline cleaning technology, electric field scale removal technology, etc. High-pressure water jet cleaning