09-04-2 Topic — Questions regarding the operation of plate heat exchangers (prizes for participation)

　Operation of Plate Heat Exchangers I. Startup Procedures and Precautions 1. When using it in new process pipelines, it is necessary to remove any debris from within the pipelines to prevent blockages in the heat exchanger. 　　2. If wastewater is used as the cooling medium, or if the waste heat from the wastewater is to be recovered, or if the medium contains particulate solids, a filter or dirt remover should be installed at the inlet of the heat exchanger to prevent it from getting clogged. 　　3. When the temperature of the cooling water (after being heated) exceeds 40°C, softening treatment should be carried out as much as possible to prevent scaling in the heat exchanger, which could affect heat transfer efficiency. 　　4. Check whether the pipeline connections are correct to prevent the mixing of the two media, which could lead to adverse consequences. 　　5. Before starting the machine, carefully check whether the inlet valves for the cold and hot media are closed and whether the outlet valves are open. 　　6. The device can be turned on only after the above tasks are completed. When starting the vehicle, first activate the pumps for the cold and hot media. Slowly open the inlet valve for the cold medium, and then open the inlet valve for the hot medium, allowing the media to flow into the heat exchanger gradually to prevent excessive temperatures. 　　7. Check all sealing surfaces and all welds for any abnormalities such as leaks. 　　8. Raise the temperature slowly, while simultaneously measuring and calculating whether the process requirements are met. Once satisfied, normal operation can be resumed. 　　II. Normal Operation and Inspection 　　1. Regularly inspect all sealing surfaces and welds of the heat exchanger to check for any signs of leakage or other abnormal conditions. If a leak is detected, it should be marked promptly at the location of the leak, and addressed after the machine is shut down. 　　2. Regularly check the pressure gauge and thermometer to observe for any abnormal conditions. 　　3. When stopping the machine, first slowly close the inlet valves for the hot and cold media, and then close the outlet valves for both media. During startup, the process is reversed: first open the outlet valve, and then slowly open the inlet valve. 　　4. Regular tests should be conducted on the medium on the low-voltage side to prevent contamination by medium from the high-voltage side. If contamination occurs, it indicates an internal leak, and the machine should be shut down for repair. 　　III. Shutdown Procedures and Precautions 　　1. Before shutting down, the pump must be stopped first, and the power supply must be disconnected. 　　2. After stopping the pump, first slowly close the hot medium inlet valve, and then close the cold medium inlet valve. Finally, close the outlet valves of the two media. 　　3. If there is a vent valve on the pipeline, it should be opened. 　　4. For media with high temperatures or corrosive properties, the equipment should be emptied as much as possible to prevent burns to people and corrosion of the equipment when it is opened.

The information on the second floor is already quite comprehensive; here are some additional details: 1. Before using the equipment, check whether the tightening screws are loose and whether the tightening degree meets the specifications stated in the manual. If not, tighten the bolts evenly until they reach the specified degree. II. When the equipment is not in use for an extended period, a hydrostatic test must be conducted on it before use. Tests should be carried out on both the cold and hot sides, with the test pressure being 1.25 times the operating pressure; the pressure should be maintained for 30 minutes. The equipment can be put into use only if there are no leaks at any of the sealing points. III. When the equipment is used in the food industry or pharmaceutical industry, where high hygiene standards are required, it should be cleaned and disinfected before use to remove any oil residues and debris from within it. IV. The inlet and outlet connections for hot and cold media should be made in accordance with the markings on the equipment’s compression plate; otherwise, it will affect the equipment’s operational performance. V. When operating the equipment, liquid should be slowly injected into the low-pressure side first, and then into the high-pressure side ； When stopping the machine, the fluid on the high-pressure side should be shut off slowly first, followed by the fluid on the low-pressure side. VI. After the equipment has been in operation for a long time, varying degrees of scale or deposits will form on the surface of the plates, which reduces heat transfer efficiency and increases flow resistance. Therefore, the equipment should be inspected regularly to remove such dirt. When cleaning the plates, do not use metal brushes to avoid scratching them and reducing their corrosion resistance. VII. Damaged plates should be replaced promptly. If there are no spare plates, it is possible to remove two adjacent plates during operation (note: the plates removed should not be direction-changing plates, but rather plates with four holes), while simultaneously reducing the compression amount accordingly.

I. Power-on and Precautions 1. Before operating the equipment, check whether all the clamping bolts are loose; if they are loose, tighten them evenly, making sure that the two pressing plates remain parallel during the tightening process. 2. Open the outlet valves for each medium at the device connection point ； Slowly open the inlet valve on the cold side when both flow rate and pressure are below normal operating levels ； When abnormalities are detected in the equipment, adjust the various inlet and outlet valves so that the flow rate and pressure meet the process requirements, thereby restoring normal operation. 3. When the heat exchanger is in operation, to prevent overpressure on one side, the inlet valves for the cold and hot fluids entering the heat exchanger should be opened simultaneously; or else, the fluid from the low-pressure side should be introduced slowly first, followed by the introduction of the high-pressure fluid slowly. 4. Before using equipment in the food industry, the heat exchangers must be thoroughly cleaned and disinfected. For cleaning, steam disinfection can be carried out using hot water to remove oil and debris from the equipment. 5. An air release valve should be installed in the piping system; after the system is started up, the air inside the equipment must be removed to prevent it from remaining there and reducing the heat transfer efficiency. 6. Hot and cold media containing large particles of sediment or other impurities should be filtered first. It is prohibited to use sewage for pressure testing and operation, to prevent damage to the equipment’s lifespan. II. Normal Operation and Inspection 　　1. Regularly check whether there are any leaks in the heat exchanger. If a leak is detected, it should be marked immediately at the location of the leak. In the case of a minor leak, it can be addressed after the machine is shut down; if the leak is severe, the machine should be stopped right away to deal with it. (Removable plate heat exchangers tend to have leaks at the double seals; in such cases, it is sufficient to check the signal holes. For brazed heat exchangers, it is necessary to examine the welds.) 2. It is necessary to record the readings of the pressure gauge and thermometer at regular intervals, in order to check whether there are any abnormalities in the pressure difference or temperature difference (which serve as the main indicators to determine whether the heat exchanger is blocked). 　　3. When stopping the machine, first slowly close the inlet valves for the hot and cold media, and then close the outlet valves for both media. 　　 4. Regular tests should be conducted on the medium on the low-voltage side to prevent contamination by medium from the high-voltage side. If contamination occurs, it indicates an internal leak, and the machine should be stopped. If the pressures on both sides are the same, it is possible to determine whether there is an internal leak by observing temperature changes. III. Shutdown Procedures and Precautions 　　1. Before shutting down, slowly close the hot medium inlet valve first, then stop the pump and cut off the power supply. Then close the inlet valve for the cold medium. Finally, close the outlet valves of the two media. 　　2. If there is a vent valve on the pipeline, it should be opened. 　　3. For media with high temperatures or corrosive properties, the equipment should be emptied as much as possible to prevent burns to people and corrosion of the equipment when it is opened.

Plate heat exchangers need to be cleaned regularly. When cleaning, attention should be paid to the order of the plates; generally, the first and last plates are different from each other, while the middle plates are identical. It is important to protect the plates, and chemical cleaning or high-pressure water flushing can be used for this purpose. The gaskets should also be inspected or replaced. In case of leaks, the plates can be colored for inspection to determine whether there are any cracks in them.

One more point: Diagnosis and handling of common operational faults 1. Operating conditions not meeting process requirements: If a newly installed plate heat exchanger does not meet the process requirements, it is necessary to carefully check whether the original design parameters, design calculations, and assembly processes are correct. Based on this, a decision can be made as to whether it is necessary to increase or decrease the heat exchange area, or to modify the process layout. If the plate heat exchanger starts operating normally, but deviations from the process requirements occur after it has been running for some time, such as an increase or decrease in pressure drop ； The medium outlet temperature rises or falls. The method to handle this type of fault is: A. Check whether the inlet parameters of the cold and hot media match the original design values. If it does not match, efforts should be made to adjust it back to the original value. If the inlet parameters have changed and it is not possible to adjust them to the original design values, then redesign calculations must be carried out to determine whether to increase or decrease the heat exchange area or to modify the process configuration. B. If the inlet parameters of the cold and hot media match the original design values, but the outlet parameters do not meet the design values, the system should be shut down; the plates should be removed to check for any blockages or scaling, and such issues should be addressed promptly. 　　2. Leakage in the heat exchanger: Due to the long sealing perimeters of plate heat exchangers and the thinness of the plates, leakage may occur during use. Leakage can be divided into two types: internal leakage and external leakage. A. External leakage of plate heat exchangers: This refers to the leakage of the fluid inside the heat exchange equipment into the external environment. This kind of leakage is generally easy to detect. The main causes of this leakage are aged gaskets, corrosion, or deformation of the plates. When such a leak occurs, the leak site should be marked promptly, and the equipment should be opened to replace the gasket or plate. B. Internal leakage in plate heat exchangers: This refers to the situation where, for some reason, the medium on the high-pressure side leaks into the low-pressure side within the heat exchange equipment. This kind of leakage is generally not easy to detect in a timely manner. The main causes of this leakage are plate perforations, cracks, and corrosion. The method to detect such leaks is to regularly test the medium on the low-pressure side and make a judgment based on changes in its composition. The method for conducting a shutdown inspection due to such leakage is as follows: a. Disassemble the plate heat exchanger, remove the dirt from the surface of the plates, dry them, and then reassemble the heat exchanger. A hydraulic test at a pressure of 0.2–0.3 Mpa is conducted on one side. Once water flows out from the other side, the test is stopped; the heat exchanger is opened, and the side of the plates that has not been pressure-tested is carefully inspected – the plates that are wet are those with holes or cracks. b. At the site, transparent and colored inspection methods can also be used to identify defective sheets. Any defective sheets and gaskets identified during inspection must be replaced, and the assembly must be reassembled before use. 　　3. Misalignment of the plates in plate heat exchangers: In plate heat exchangers that experience large fluctuations in fluid flow rate and pressure, are designed with multiple pass configurations, and are used for extended periods of time, misalignment of the plates is a common phenomenon. After the plate is misaligned, leakage can sometimes occur quite quickly ； Some may not result in immediate leakage, but they represent a risk of seepage, so they must all be dealt with promptly. The main reasons for misalignment are: deformation of the heat exchanger plates ； The gasket of the plate heat exchanger has slipped out of its groove. To address this misalignment issue, the deformed plates and gaskets that have slipped out of their grooves should be replaced promptly. 　　4. Simple methods for dealing with plate heat exchangers when maintenance equipment is unavailable on site. During use, plate heat exchangers require timely replacement in cases where the plates become deformed, cracked, or perforated, or where the gaskets age or break. In the event that there are not enough spare parts on site, and the heat exchange equipment has no backup unit nor can it be shut down, simple on-site repairs should be carried out. A simple on-site solution is to remove the damaged plates and those with leaks in pairs (Plate A + Plate B). If the number of such plates is not large, and consequently the number of reduced flow channels is also small, they can be used again after assembly, with little impact on production.

I don’t know much about plate heat exchangers, so I can only offer my humble opinions and learn from everyone else!*learn!*