A comprehensive collection of heat exchanger descaling methods

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Introduction Heat exchangers are widely used in industrial processes such as petroleum, chemicals, light industry, pharmaceuticals, and energy production. However, over time, dirt accumulates inside these heat exchangers. This accumulation reduces the cross-sectional area of the internal channels or even causes them to become blocked, resulting in insufficient flow of cooling water and a drop in pressure. This can lead to shutdowns and interruptions in production; it may also cause safety incidents such as bulging, cracks, and pipe ruptures. 　　Before and after operation of the heat exchanger Causes of fouling 1. Deposition fouling Most heat exchangers are heat transfer systems that use water as the heat carrier; when the temperature rises or the concentration is high, Ca(HCO3)2 and Mg(HCO3)2, which were originally dissolved in water, precipitate to form CaCO3 and MgCO3, which are slightly soluble in water. The precipitated salts adhere to the surface of the heat exchange tubes, forming scale that sticks tightly to those surfaces. 　　2. Particulate dirt: Solid particles suspended in fluid systems, such as sand grains, dust, and carbon black, which accumulate on the heat exchange surfaces to form dirt. 　　3 Chemical reaction fouling: The formation of deposits between the heated surface and the fluid, resulting from autoxidation and polymerization reactions, that is, chemical reactions. 　　4 Corrosive fouling: The heat exchange surface is corroded due to the corrosive nature of the fluid or the presence of corrosive impurities, resulting in the deposition of corrosion products on the surface and the formation of fouling. 　　5 Biological fouling refers to the adhesive deposits that form on the walls of heat exchange tubes as a result of microorganism colonies and their excretions, along with chemical pollutants and mud-like substances; this type of fouling is known as biological fouling. 　　6 Solidified fouling: Fouling that forms on subcooled heat exchange surfaces as a result of the solidification and deposition of highly soluble components in the cleaning liquid or multi-component solution. 　　Common cleaning methods for heat exchangers Chemical cleaning Chemical cleaning involves using chemical cleaners to induce certain chemical reactions, thereby dissolving, removing, or stripping the scale and other deposits from the surface of the heat exchanger’s heat transfer tubes. 　　Chemical cleaning does not require disassembling the heat exchanger, which simplifies the cleaning process and reduces the labor effort involved. Its drawback is that if the chemical cleaning solution is not chosen properly, it can corrode and damage the substrate being cleaned, resulting in losses. 　　Common chemical cleaners ● Cleaners that remove dirt through dissolution (including water and organic solvents); ● Surfactant-based cleaners that remove dirt by utilizing surfactant properties (such as cationic, anionic, non-ionic, and amphoteric surfactants); ● Chemical cleaners that remove dirt through chemical reactions (such as acids, bases, salts, oxidizers, etc.). 　　Common methods for chemical cleaning ● Circulation method: A pump is used to force the cleaning solution to circulate, thereby carrying out the cleaning process. 　　●Impregnation method: Fill the equipment with the cleaning solution and let it sit for a certain period of time. 　　●Surge method: Fill the equipment with cleaning solution, then periodically remove a portion of the solution from the bottom and pour it back into the equipment to achieve thorough mixing and cleaning. 　　Chemical circulation cleaning process for heat exchangers: 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. Inject the required cleaning agent and perform repeated cyclic 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 reaches neutrality. 　　Physical cleaning: Physical cleaning involves using various mechanical forces and energies to break down dirt, separate it from the surface of an object, and remove it, thereby achieving a cleaning effect. 　　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 descaling, PIG pigging technology, and electric field descaling technology. 　　High-pressure water jet cleaning: High-pressure water generated by a piston pump is ejected at the scale layer through special nozzles, enabling thorough scale removal with high efficiency; however, it requires large storage containers and consumes a lot of water. 　　Ultrasonic descaling involves using an ultrasonic sound field to treat fluids; under the action of this sound field, the scaling substances present in the fluid undergo a series of changes in their physical structure and chemical properties, which causes them to disperse, break down, and become less likely to adhere to the pipe walls and form scale. The scale-inhibiting mechanisms of ultrasonic waves mainly include: A. cavitation effect; B. activation effect; C. shear effect; D. inhibition effect. 　　Removal of scale using mobile descaling equipment inside pipes: The new type of mobile descaling equipment for use inside pipes is highly efficient and of good quality; it is suitable for removing scale from oil and gas transmission pipelines, as well as from pipelines used for transporting chemical liquids and water. 　　Based on the driving mechanism, this classification does not hold; typical mobile descaling equipment used in pipelines falls into the following categories: A. Electrically driven mobile descaling equipment; B. Hydraulically driven mobile descaling equipment; C. Compressed air-driven mobile descaling equipment. 　　Mechanical cleaning: It relies on mechanical action to exert a force greater than the adhesion force of the dirt, thereby removing the dirt from the heat exchange surface. This method can remove carbonized dirt and hard deposits that cannot be removed by chemical methods, but to thoroughly clean the deposits inside the pipes, it is generally necessary to