Four common problems and solutions for non-dismantling cleaning of plate heat exchangers and chemical cleaning of plate heat exchangers

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Four Common Problems and Solutions Regarding Non-Dismantling Cleaning of Plate Heat Exchangers and Chemical Cleaning of Plate Heat Exchangers. Abstract: The cleaning of plate heat exchangers is usually carried out either by dismantling them for cleaning or by using a circulating cleaning method without dismantling. The key lies in the selection and preparation of the cleaning agents; these agents affect both the speed and effectiveness of the cleaning process. This article discusses four common problems related to the selection and preparation of cleaning agents for non-dismantling cleaning of plate heat exchangers and chemical cleaning of such devices, along with corresponding solutions. Keywords: plate heat exchanger cleaning ； Cleaning of plate heat exchangers without disassembly ； Plate heat exchanger cleaning ； Removal-free cleaning of plate heat exchangers ； Plate heat exchanger chemical cleaning ； Plate heat exchanger cleaning without disassembly – Circulating cleaning. I. Reasons and purposes for cleaning plate heat exchangers: The plate heat exchangers in the heat supply station of thermal power companies are important devices for heat exchange between the primary and secondary networks in centralized heating systems. When these plate heat exchangers become scaled, the heat transfer rate decreases, thermal efficiency drops, and the pressure difference increases. This severely affects the efficiency of heat transfer, leads to increased energy consumption for heating, and results in a lower quality of heating. Moreover, corrosion caused by scale on the plate heat exchangers can also reduce their service life. To increase the heating temperature and ensure the quality of heat supply, finding a cost-effective way to clean plate heat exchangers is an important aspect for heating companies to achieve energy savings, reduce consumption, and improve efficiency. The cleaning of plate heat exchangers is usually carried out in two ways: disassembly cleaning and circulation cleaning. Both disassembly cleaning of plate heat exchangers and circulation cleaning without disassembly have their own advantages and disadvantages. Figure 1 above: Disassembly and cleaning of stainless steel heat exchange fins in a plate heat exchanger. II. Advantages and disadvantages of disassembling and cleaning plate heat exchangers. 1. Advantages of disassembling and cleaning plate heat exchangers: ① Intuitive. The scaling and corrosion conditions of plate heat exchangers, plate elements, etc. can be seen clearly; the amount of scaling on the plate elements, the thickness of the scale layer, the composition of the scale, and its color can all be observed directly ； The corrosion distribution, the size of pitting, the depth of corrosion pits, and whether there is perforation and leakage can also be observed directly. 2. Disadvantages of disassembling and cleaning plate heat exchangers: ① The disassembly process for plate heat exchangers is labor-intensive and requires a lot of work. There are numerous plates in such exchangers, and tasks such as disassembly, soaking, cleaning, and reassembly demand great patience and responsibility from the workers ； Due to objective constraints, the sites of heat exchange stations operated by heating companies are usually filled with numerous internal pipelines and have limited space; workers must carry out tasks that may seem simple but require great patience and responsibility in a hot, humid, and cramped environment. ②When disassembling and cleaning plate heat exchangers, leakage can occur. Over time, the sealing strips used in these heat exchangers lose their elasticity, become aged, deformed, and harden, making them prone to breaking and becoming unusable; therefore, careful disassembly and installation are necessary ； The installation of the sealing strips for plate heat exchanger plates must be precise and proper; any leakage that leads to the need for rework must be avoided. This requires not only great patience and a strong sense of responsibility but also a high level of technical skill from the workers. In Figure 2 above, it shows the process of removing and cleaning the stainless steel heat exchange plates of a plate heat exchanger, followed by the installation of sealing strips. ③ The process of disassembling and cleaning a plate heat exchanger involves multiple steps and takes a long time; these steps include removing the heat exchange plates, soaking them, cleaning them, and reassembling them, as well as removing, placing, and installing the sealing strips for those plates. In cases where scaling is severe, it may take several hours just for the plates to be soaked in acid solution at elevated temperatures. ④ Disassembling and cleaning plate heat exchangers requires a large number of workers and equipment. Given the substantial volume of work involved, it is necessary to have a sufficient number of skilled workers to complete the cleaning process within a limited time frame ； Disassembling and cleaning plate heat exchangers also requires investing in specialized cleaning equipment such as soaking and heating tanks, high-pressure water guns, etc. The advantage of disassembling and cleaning plate heat exchangers is that the results are immediately visible. The disadvantages, however, include a large amount of work, the need for many skilled workers, lengthy processing time, and a risk of water leakage; consequently, the economic efficiency is poor. In Figure 3 above, it shows iron oxide mixed scale on the stainless steel heat exchange plates of a plate heat exchanger. III. Advantages and disadvantages of cyclic cleaning of plate heat exchangers without disassembly: Cyclic cleaning of plate heat exchangers without disassembly involves using a pressure-driven circulation pump to inject the prepared cleaning solution into the plate heat exchanger, thereby carrying out a cyclic flushing process that dissolves, reacts with, and removes the scale from the heat exchanger; the cleaned substances are then carried out of the heat exchanger via the circulation of the cleaning solution. 1. Disadvantages of cyclic cleaning of plate heat exchangers without disassembly: ① Lack of visibility – Since cyclic cleaning of plate heat exchangers without disassembly does not allow direct observation of the amount and distribution of scale inside the heat exchanger, it is necessary for skilled workers with practical experience to determine when this cleaning process should be terminated. 2. Advantages of cyclic cleaning of plate heat exchangers without disassembly: Compared to the disassembly-based cleaning method, cyclic cleaning of plate heat exchangers without disassembly offers the following advantages. First, it requires less effort and work volume – there is no need to remove, soak, clean, or reassemble numerous plate elements, nor is there any need to remove and install sealing gaskets on these elements, tasks that demand a high level of patience and responsibility. ② With plate heat exchangers that can be cleaned through a cycle process without disassembly, there is no need to remove or install the sealing gaskets of the plate elements; as a result, leaks caused by aging or improper installation of these gaskets do not occur. ③ Plate heat exchangers require few cleaning procedures and little time without disassembly; it only takes a few hours to clean one set of plate heat exchangers in this way, and usually 2-3 sets can be cleaned simultaneously, increasing efficiency by 5-6 times. ④ Plate heat exchangers can be cleaned without disassembly, requiring fewer workers and less equipment. Only 3-4 workers are needed to clean 2-3 sets of plate heat exchangers simultaneously using 2-3 pressure circulation pumps; no specialized equipment such as immersion heating tanks is required. In summary, the disadvantage of cyclic cleaning of plate heat exchangers without disassembly is that the results are not immediately apparent; the advantages, on the other hand, include reduced workload, fewer skilled workers required, faster processing times, no risk of water leakage, and good economic benefits. Colleagues and peers, how often is the plate heat exchanger in your facility cleaned? For plate heat exchangers, should disassembly and cleaning be used or a non-disassembly cyclic cleaning method? What cleaning agents are used, and what is the efficiency of such cleaning? How often does your unit clean its boilers? Is the boiler scaling removed when the boiler is shut down or while it’s in operation? What is the effectiveness of such cleaning? What is the boiler’s blowdown rate, and is its energy consumption high? Regarding issues such as boiler corrosion, scaling, and tube failure; excessive iron content in steam condensate; red color of boiler water; yellow color of steam condensate; online descaling techniques that allow continued operation of the boiler without shutdown; cleaning techniques for plate heat exchangers; and online cleaning and descaling methods for condensers that enable continued operation without interruption, Yan Hui from Beijing University of Chemical Technology at I86OO475З86 is always ready to welcome colleagues to share their experiences in the management and use of boiler equipment. He also welcomes discussions and exchanges of insights regarding various practical problems related to boilers, so that everyone can learn from one another. Four common problems and their solutions regarding non-disassembly cleaning of plate heat exchangers and chemical cleaning of plate heat exchangers. IV. Four common problems in non-disassembly cleaning of plate heat exchangers and chemical cleaning of plate heat exchangers. For these two methods of cleaning—non-disassembly cleaning of plate heat exchangers and chemical cleaning of plate heat exchangers—the most crucial factor is the selection and preparation of the cleaning agents. The cleaning agents determine both the speed of cleaning and its effectiveness. Four common problems related to the selection and preparation of cleaning agents for non-disassembly cleaning of plate heat exchangers and chemical cleaning of plate heat exchangers: 1. For non-disassembly cleaning of plate heat exchangers and chemical cleaning of plate heat exchangers, a cleaning agent prepared from hydrochloric acid and a corrosion inhibitor is often used. This type of cleaning agent is commonly employed for cleaning boiler equipment, and it is highly effective in removing iron oxide scale as well as calcium and magnesium scales from such equipment. However, today’s heat exchange fins in plate heat exchangers are usually made of stainless steel. Cleaning stainless steel with hydrochloric acid can cause chloride-induced corrosion, leading to stress corrosion cracking, intergranular corrosion, and surface damage, especially posing a significant threat to austenitic stainless steels such as 304 and 316. It is mainly manifested in the following 4 aspects: The image above shows a self-made plate heat exchanger cleaning device that allows for cycle cleaning without disassembly. ① The passivation film on the surface of the stainless steel heat exchange plates in plate heat exchangers is damaged; the corrosion resistance of these plates relies on the Cr₂O₃ passivation film on their surface. Chloride ions Cl⁻ in hydrochloric acid can penetrate this passivation film and react with it to form soluble chlorides (such as CrCl₃), thereby exposing the metal substrate. ② Intergranular corrosion of stainless steel heat exchange fins in plate heat exchangers: Chloride ions Cl⁻ in hydrochloric acid adsorb onto the chromium-deficient regions at the grain boundaries of these stainless steel heat exchange fins (Cr content