Plate heat exchanger cleaning processes and case studies

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【Abstract】Plate heat exchangers suffer from easy blockage due to their small flow cross-section after scaling, which leads to a decrease in heat exchange efficiency and directly affects the safe operation of the equipment as well as the normal production of enterprises. This article introduces two cleaning methods for plate heat exchangers using cleaning agents, namely closed-loop online circulation cleaning and disassembly immersion cleaning processes, as well as the precautions during the cleaning process, to ensure the safe descaling of plate heat exchangers. 【Keywords】Plate heat exchanger ； cleaning ； Plate exchanger cleaning ； Foshitek Cleaning Agent ； 1. Introduction to plate heat exchangers: A plate heat exchanger is a type of heat exchanger in which thin metal sheets (usually stainless steel) are pressed into plates with specific wave patterns, sealed with gaskets, and then stacked together (see Figure 1). It is mainly composed of components such as plates, sealing gaskets, clamping bolts, pressing plates, and the overall frame of the machine. The hot and cold media flow through their respective channels via adjacent heat exchange plates, with heat exchange taking place between them through a thin layer of heat exchange plates. As a result, it features high efficiency and energy savings, a high heat transfer coefficient, safety and reliability in operation, a compact structure, small volume, low space requirement, flexible configuration, and ease of adjustment and maintenance. 2. Preparation work for cleaning plate heat exchangers 2.1 Analysis of scaling in plate heat exchangers Plate heat exchangers can generally be divided into two types: water-to-water heat exchange and steam-to-water heat exchange. In the water-water exchange method, both the cold and hot media are water; the temperature difference between them is generally between 70-90°C, and the degree of scaling on both sides is essentially the same ； In the steam-water exchange method, the heat medium is water vapor, and scaling generally does not occur. The cold medium is water, at a temperature of about 90°C, and it tends to form scale. Its scale can be roughly divided into water scale and dirt, with water scale being the predominant type. Scale is primarily formed when various salts dissolved in water undergo thermal decomposition, resulting in a decrease in their solubility and subsequent crystallization and deposition on the heat transfer surfaces. It usually consists of carbonates, phosphates, sulfates, and silicates; such scale crystals are relatively hard and difficult to remove. Dirt generally consists of fine-grained sediment, dust, insoluble salt deposits, gelatinous hydroxides, various debris, corrosion products, oil stains, algae, etc. This type of dirt is large in volume and loose, making it easy to remove. 2.2 Selection of cleaning processes: The cleaning methods for plate heat exchangers include closed-loop circulation cleaning and disassembly immersion cleaning. Before cleaning, it is possible to analyze the scale sample based on the quality of the circulating water, and then select the appropriate cleaning process using the table below. 2.3 Selection of cleaning agents: The following are descriptions of the cleaning agents used in this article; they prove to be effective for cleaning plate heat exchangers. Please discuss them rationally, and those who have objections may skip this section. Fushitek’s high-efficiency, environmentally friendly series of cleaning agents are safe, efficient, and eco-friendly. Their innovative technology involves adding wetting agents, penetrants, dispersants, and stripping agents to the formula, which enables effective dissolution and removal of deposits. It is a series of fully synthetic, high-tech liquid descaling agents specifically designed to remove all types of scale, lime, sludge, rust, and other dirt deposits that form within water treatment equipment systems. Foshitek’s high-efficiency, environmentally friendly cleaning agents are mainly divided into the Foshitek universal type, the F2 type specifically for stainless steel, the FCS type designed for use with sulfates, the FB2 bio-based cleaning agent, the F16 sulfur-suppressing cleaning agent, and the FN neutral rust remover. Foshitek F2, a cleaning agent specifically designed for stainless steel, is a chloride-free specialized cleaning product developed for cleaning heat exchange equipment made of stainless steel, aluminum, and aluminum alloys. In particular, some important stainless steel equipment has strict restrictions against chloride ions; for such equipment, cleaning with a single type of stainless steel material can achieve zero-corrosion cleaning. For the cleaning of single-aluminum and aluminum alloy equipment, Fostek’s F2 stainless steel-specific cleaner also performs very well. It exhibits a lower corrosion rate compared to Fostek’s universal cleaners (see Table 1), but it cannot be used for cleaning in combination with carbon steel, copper and copper alloys, or other materials other than stainless steel. For such applications, Fostek’s multi-metal additives are provided, and they must be added in strict accordance with the proportions specified in the product instructions. In short, the Fostek F2 cleaning agent specifically designed for stainless steel is a high-quality cleaning product tailored for stainless steel, aluminum, and their alloys, offering a corrosion rate that is low or even zero for these materials. The plate material of plate heat exchangers is generally austenitic stainless steel, with models including A ISI, 304, 304L, A IsI, 316, 316L, and 316Ti ； The gasket materials are generally NBR 130-140, R0B 140, and ERDM 150; all of these materials can resist corrosion by acids, alkalis, alcohols, and other solutions. Based on this, it is appropriate to use the Fostek F2 cleaning agent, an efficient and environmentally friendly cleaning solution, for cleaning. 3. Online cyclic cleaning process 3.1 Check whether the inlet and outlet valves of the object to be cleaned are tightly sealed, to ensure that closed-loop cyclic cleaning can be carried out; add blind flanges if necessary ； 3.2 First, determine the amount of pure cleaning agent required based on the heat exchange area of the heat exchanger and the thickness of the scale buildup ； 3.3 Based on the volume of the pipeline, prepare a container for the cleaning agent; the inner surface of the container must be clean and free of oxidation layers, or a container made of non-metallic material should be used ； 3.4 Prepare the industrial centrifugal pump for circulation, and prepare the connection pipelines between the pump, the heat exchanger, and the containers (see Figure 2); flange connections shall be made if necessary ； 3.5 Determine whether it is necessary to dilute the concentrated cleaning agent based on the conditions on site; the dilution ratio can range from 1:1 to 1:5 depending on the circumstances ； 3.6 Pour an adequate amount of cleaning agent into the container, connect the pipelines properly, and turn on the switch to perform a closed-loop cleaning of the heat exchange equipment ； 3.7 During the cyclic cleaning process, due to the chemical reaction between the cleaning agent and the scale deposits, visible dissolved scale impurities and foam can be found in the solution tank ； 3.8 Test the solution using a pH test strip; if the result is above around 4–5, add the pure cleaning agent to the solution in order to increase its concentration ； 3.9 After cleaning for a period of time, swap the inlet and outlet of the circulation pipeline to perform reverse circulation cleaning ； 3.10 During the cleaning process, the solution should be tested continuously to maintain its concentration within the effective range, until no changes in the concentration are observed for an extended period of time ； 3.11 Fill the container with clean water to carry out cyclic cleaning and flushing, in order to wash away the scale and other impurities that have remained inside the equipment; during this cleaning process, it is also necessary to switch the inlet and outlet pipes to perform repeated flushing. 4. Disassemble and soak for cleaning 4.1 Disassemble the plate exchangers and arrange them in order, keeping a record of it ； 4.2 Manufacturing the cleaning tank ； 4.3 Pour the cleaning agent into the cleaning tank and add an appropriate amount of water to dilute it until the heat transfer fins are completely submerged. 4.4 Start the soaking and cleaning process; check the concentration of the cleaning agent as well as the pH value in the cleaning tank every hour, ensuring that the concentration of the cleaning agent remains within a safe and effective range and that the pH value stays between 1 and 3. Add more cleaning agent based on the measurement results. 4.5 Cleaning is considered complete when the concentration of the cleaning agent and its pH remain unchanged or change only slightly over a period of 2 consecutive hours, and it is observed that the scale on the surface of the plates has significantly decreased and can be removed easily with a plastic brush. 4.6 After cleaning is complete, rinse each plate thoroughly with water. 5. Application example: Cleaning was carried out on the plate heat exchangers in the lubricating oil station of a thermal power plant. The water used was reclaimed water, and the scale present consisted mainly of sediment. Fostek F2 cleaner was employed for closed-loop cleaning; the cleaning process involved back-and-forth circulation for 4 hours, followed by two hours of back-and-forth flushing with clean water. After the cleaning process was completed, the plate heat exchanger was disassembled to verify the cleaning effectiveness, and it was found that the cleaning had been successful – a 100% removal rate of scale was achieved after rinsing with clean water. 6. Conclusion: Due to their small flow cross-section, flow channels tend to become blocked after scaling occurs, which reduces heat exchange efficiency and directly affects the safe operation of the equipment as well as the normal production processes of enterprises. Through years of practical application, it has been found that using these two cleaning methods in combination with Foshitek’s high-efficiency, environmentally friendly cleaning agents yields good results in removing scale from plate heat exchangers. The scaling removal rate reaches 95% with the disassembly and soaking cleaning method, while it reaches 100% after brushing the surface following soaking and rinsing it with water. The closed-loop cleaning process also achieves very good descaling results through the tracking and monitoring of the operating temperature of the plate exchanger at later stages.