【Weekly Topic】Production Technology: Tips for Using Heat Exchangers? 2011.08.29~09.05

1. Exhausting the gas before putting it into use is necessary. 2. Venting it when it is not in use is also essential. 3. Regularly check for any leaks between the tube side and the shell side, as well as any external leaks. 4. Pay attention to the temperature and pressure of the fluids entering and leaving the heat exchanger. 5. Are there any unusual noises inside the heat exchanger?

Just check for any leaks, scaling, or blockages, that should be enough. Please forgive me if I’m wrong and offer any guidance; thank you.

1. Be careful to avoid use at excessive temperatures and pressures. 2. The water quality and steam requirements must be met. 3. Ventilate before use and pay attention to maintenance after use. 4. Regularly inspect the tubeside and shellside for testing and flaw detection. 5. Be careful to avoid large vibrations during operation. 6. Regularly check the pressure testing of the shell side and tube side. 7. Regular sewage discharge.

Maintenance and management of heat exchangers: There are many types of heat exchangers, and their operating methods are largely similar. What they all have in common is the use of a large contact area between two substances to facilitate heat exchange, thereby enabling chemical processes such as cooling, condensation, heating, and evaporation. The operating conditions of the heat exchanger, the properties of the heat transfer medium, the corrosion rate, and the operational cycle determine the contents of the heat exchanger’s maintenance and management. Taking the widely used shell-and-tube heat exchanger as an example, its maintenance and management methods are discussed. I. Startup (1) First, using the nozzles provided on the shell, completely drain all gas and condensate from the heat exchanger (in the case where the fluid is steam), to prevent water hammer from occurring. Then, fully open all vent valves. (2) First, introduce the low-temperature fluid; once the liquid fills the heat exchanger, close the vent valve. (3) Slowly introduce the high-temperature fluid to avoid thermal shock caused by a large temperature difference resulting from rapid introduction of the fluid. (4) During the temperature rise to the normal operating temperature, the external connection bolts should be retightened to prevent leakage due to improper sealing of the gasket. II. Operation and Maintenance (1) For seal points connected by flanges, the bolts expand as the temperature rises above 150°C, causing the fastening points to loosen; therefore, the bolts should be tightened again during operation. (2) For high-temperature, high-pressure, and hazardous toxic fluids, leakage must be strictly controlled, and the following points should be noted. ①From a design perspective, efforts should be made to minimize flange connections and reduce the use of gaskets. ②From an installation perspective, the fastening operation should be convenient. ③Self-tightening structural bolts are used, so there is no need to retighten them when the temperature and pressure increase. (3) After the heat exchanger has been in operation for a period of time, its heat exchange efficiency will decline; attention should be paid to the following issues. ①The heat transfer surface is severely fouled, resulting in a significant decrease in heat transfer efficiency. ②Dirt will reduce the inner diameter of the pipe, increasing the flow velocity and thus raising the pressure loss. ③It causes leaks and corrosion at the flared ends of the pipes. ④Operating conditions do not meet the design requirements, resulting in fatigue failure of the material. (4) To ensure the long-term continuous operation of the heat exchanger, regular inspections and cleaning are necessary. III. Shutdown (1) First, cut off the high-temperature fluid, and then cut off the low-temperature fluid before shutting down the device. When production requires cutting off the low-temperature fluid first, a bypass or other methods can be used to simultaneously stop the supply of high-temperature fluid. If the cold fluid is shut off too early, the equipment may be damaged due to thermal expansion. (2) After the heat exchanger is shut down, the fluid remaining inside it must be completely drained to prevent freezing, corrosion, and water hammer effects. (3) After the liquid has been drained, air can be blown in to ensure that all remaining liquid is removed. IV. Inspection and Cleaning The inspection and cleaning of the heat exchanger are carried out in two stages. 1. Inspection and cleaning during operation: Inspection and cleaning while the system is in operation is a proactive maintenance method that allows for the early detection of abnormalities and the taking of appropriate actions. It also helps to keep the surface of the tube bundles clean, thereby ensuring effective heat transfer and preventing corrosion. (1) Regularly check operation records such as flow rate, pressure, and temperature. ①If an increase in pressure loss is observed, it indicates that fouling and blockage have occurred both inside and outside the tube bundle. ②If the heat exchange temperature does not meet the requirements of the design parameters, it indicates that fouling has formed on the inner and outer walls of the tubes, resulting in a decrease in the heat transfer coefficient and a deterioration in the heat transfer rate. ③Sampling from the low-temperature fluid outlet and analyzing its color, density, and viscosity allows for the detection of damage or leaks in the tube bundle. If the viscosity of the cooling water at the outlet is high, it may be due to scale formation on the tube walls, an accelerated rate of corrosion, or leaks at the joints of the tube bundle. (2) Regularly inspect the corrosion and wear on the inner and outer surfaces of the housing; ultrasonic thickness gauges or other non-destructive thickness measurement devices are typically used to determine from the outside those areas of the housing where corrosion or thinning is likely to occur. (3) Cleaning. Cleaning during operation generally refers to the cleaning of the inside of the tubes. For fluids prone to scaling, the flow rate can be temporarily increased on a regular basis or counter-current operation can be carried out to remove the dirt from the inner walls of the tubes ； Appropriate chemicals can also be injected depending on the type of fluid to dissolve and remove the dirt. 2. Inspection and cleaning during parking (1) Check the degree of scaling on the inner and outer surfaces of the heat exchanger tubes, as well as whether there are any foreign objects causing blockages or contamination. (2) Measure the wall thickness to check for wall thinning and corrosion. (3) Check for corrosion and cracks at the welded joints. Since the welded areas are more prone to corrosion than the base material, they should be carefully inspected. Non-penetrating cracks at the weld between the tube and the tube sheet can be detected using the dye penetrant method. The inspection of the thinning wall of black and non-ferrous metal pipes, as well as pitting, prior to damage occurrence, is carried out using eddy current (electromagnetic) testing technology. The areas to be inspected include the surface of the side inlet pipe, the inlet sections at the ends of the heat exchange tubes, the contact points between the baffle plates and the heat exchange tubes, as well as the areas where the fluid turns. Internal inspection of the tube bundle can be carried out using an in-tube inspector (endoscope) or through visual inspection with light. To check for looseness at the tube bundle assembly area, a test ring can be used to conduct a leak test; based on the leakage pattern, it is possible to identify locations of pipe perforations, ruptures, and leaks at the joints between pipes and tube sheets. If a leak is detected, tube expansion or welding assembly should be performed again. (4) Washing. After the heat exchanger is taken offline, the following cleaning methods can be selected based on the shape of the heat exchanger, the type of fouling, and the available equipment at the user’s facility. ①Hydraulic cleaning involves using a high-pressure pump to spray high-pressure water in order to remove dirt from the outside of the heat exchanger tubes. ②Chemical cleaning involves circulating chemical solutions inside the heat exchanger to dissolve and remove dirt. One advantage of this method is that it allows for dirt removal without taking the heat exchanger offline, which is beneficial for descaling large-scale heat exchange equipment ； Second, it can remove dirt that is difficult to eliminate using other methods ； Third, during the cleaning process, it does not damage metal and non-ferrous metal linings. The commonly used chemical cleaning method is pickling, which involves using hydrochloric acid as the pickling solution. Since acids can corrode the steel matrix, a certain amount of corrosion inhibitor must be added to the pickling solution to prevent corrosion of the matrix; in China, \"02 Corrosion Inhibitor\" is commonly used. ③Mechanical cleaning: This method is used for cleaning the interior of pipes. A brush, drill bit, or cutting tool with an inner diameter matching that of the pipe is attached to the front end of a rod or pipe, which is then inserted into the pipe. It is rotated while being pushed forward (or downward) in order to remove dirt. This method is applicable not only to straight pipes but also to curved pipes; for stainless steel pipes, a nylon brush can be used in place of a wire brush. Existing specialized mechanical cleaning can reduce the workload on workers and improve cleaning efficiency.

Ventilation (or drainage) must be carried out before and after operation to ensure effective heat exchange； Take the opportunity to clean while parking ； Regularly analyze for internal leakage ； Before and after commissioning, ensure that changes in temperature difference and differential pressure do not occur too rapidly.

1. Venting is necessary before putting the heat exchanger into service; first, introduce the cold-side medium.
2. Depressurize the system when shutting it down to prevent negative pressure from damaging the equipment.
3. Regularly check for any leaks or external leakage between the shell and tube sides; if possible, perform cleaning periodically.
4. Monitor the temperature and pressure of the media entering and exiting the heat exchanger to ensure safe operation and prolong its service life.
5. Pay attention to any unusual noises coming from the heat exchanger; detect and address them promptly

Reply 1# sun-rock 1. Proper selection: a. Selection of heat exchanger type – There are various types of heat exchangers available, and the appropriate one should be chosen based on the specific usage conditions. b. Material selection. c. Pipe diameter selection. d. Installation method selection. e. Maintaining an appropriate inclination angle； 2. Use appropriately: a. Perform a seal check before use, and conduct regular checks after use ； b. Use a clean heat exchange medium ； c. Clean promptly and discharge waste regularly to prevent scaling ； d. Maintain normal operating temperature and pressure ； e. The medium used meets the design requirements ； f. Avoid heavy vibrations. 3. Maintenance: a. Drain the contents promptly after use to prevent freezing in winter, etc ； b. Clean up promptly after use and empty it ； c. Timely sealing inspection ； d. Detect the thickness in a timely manner ； e. Check for corrosion, etc

1. The heat exchanger must be installed vertically, and discharge ports and valves must be installed at the lowest point of all the lower connection pipes； 2. Maintain heat as much as possible as needed ； 3. Reserve space for maintenance. 4. When starting up, ensure that the outlet valves for the fluids on both sides are open. First, slowly open the valve for the cold fluid to allow it to circulate, and then slowly open the valve for the hot fluid. During this process, try to avoid large pressure fluctuations as much as possible. 5. When shutting down, first close the hot fluid inlet valve, then the cold fluid inlet valve; perform this operation slowly as well. 6. During shutdown, ensure that any remaining liquid in the channels on both sides is completely drained (open the drain valve at the bottom of the pipes), and verify that the inlet valves are tightly closed. 7. When using single-channel steam disinfection, it is necessary to ensure that the liquid in the other channel is completely drained with no residues left, and the steam valve must be opened slowly.

Reply to 1# sun-rock: The capacity and corrosion resistance of plate heat exchangers depend on whether the plate pack can be kept clean. The scale on the plates can be removed by circulating a suitable cleaning agent within the heat exchanger; there is no need to disassemble the heat exchanger for this purpose ； Or disassemble the heat exchanger and manually clean the plates. Note that the protective film on the surface of the stainless steel sheets must not be removed. The passivation film is the main barrier that protects stainless steel from corrosion. Precautions before using a plate heat exchanger: Check how to use the plate heat exchanger before starting up. (1) Verify that the pipeline connections are proper before starting, and that the compression distance between the two plates is within the specified range. (2) Whether the drain (sewage) valve is closed. 2. Operation: (1) First, slowly open the inlet and outlet valves for the cold medium, and then slowly open those for the hot medium; increase pressure and temperature gradually. To stabilize system operation, the amounts of fluid on both sides can be adjusted synchronously. (2) Exhausting air must be done with great care during filling. (3) Adjust the valve according to the inlet and outlet pressure and temperature indications to achieve the set process parameters. (4) During operation, the pressure should remain stable, avoiding sudden fluctuations. (5) To maintain the outlet temperature of the main fluid flow meter, the flow rate of the auxiliary fluid can be adjusted. (6) Carefully observe the operation of the heat exchanger, such as temperature, pressure, and external leaks. (7) During operation, if a slight leak is detected, the compression size can be reduced by 2–3 mm while under pressure relief conditions before continuing operation. (8) If the heat exchanger operates exactly as planned, then it can be put into normal use. 3. Shutdown: (1) First, close the hot medium inlet valve, and then close the cold medium inlet valve; all valve closures should be done smoothly. (2) If the operation is suspended for an extended period, the valve at the lowest point of the pipeline should be opened to drain all remaining liquid from the equipment.

Reply to 1# sun-rock: Heat exchangers are considered pressure vessels, and the primary consideration when using them is ensuring their safety; secondly, it is important to maintain and optimize their heat exchange performance. A brief analysis is provided below. Safety measures: 1. Both the tube side and shell side must be operated strictly according to the designed temperature and pressure levels; exceeding these limits is strictly prohibited. 2. Load changes during startup, shutdown, and operation should be done gradually to avoid large fluctuations. 3. Preheating (or pre-cooling) should be carried out before starting up, so that the system can reach its operating condition gradually. 4. Regular inspections should be conducted in accordance with regulatory requirements, focusing on tube wall thickness, corrosion, and stress levels ； Regular inspection of safety accessories (safety valves, rupture disks, thermometers, pressure gauges). 5. Thorough cleaning and flushing should be carried out during startup and shutdown to prevent the accumulation of toxic substances or equipment corrosion. 6. Monitoring of sensitive media is necessary, such as acids and bases; for stainless steel, monitoring of chloride levels is required, and for steam heat exchangers, monitoring of the boiler water quality is essential. Tips for ensuring performance: 1. Maintain optimal flow conditions. Heat exchangers are designed with appropriate flow patterns in mind, such as co-current, counter-current, or cross-flow; various methods such as baffle plates are used to increase fluid turbulence. If the flow pattern changes, it will have a significant impact on the heat transfer performance. Factors that cause changes in flow pattern include local scaling or blockages, damage to baffle plates leading to short circuits, and damage to process seals resulting in short circuits. Therefore, it is important to pay attention to the quality of the circulating water, as well as to monitor the temperature difference between the inlet and outlet at all times, in order to assess the internal condition of the heat exchanger based on changes in thermal efficiency ； 2. Ensure unobstructed flow channels: Solid debris in water exchange equipment, as well as condensate in steam heat exchangers, can cause obstructions in the flow channels of these heat exchangers, thereby affecting their heat exchange efficiency. The operation of the hydroscoper should be properly controlled, and dual-line drainage should be used if necessary. Water exchange equipment can be equipped with scale removal devices, etc. 3. Ensuring the heat transfer coefficient – The factor that has the greatest impact on the heat transfer coefficient is the scale layer. Therefore, for different process applications, it is necessary to have a thorough understanding of the factors that cause scaling in heat exchangers, and to implement targeted preventive measures as well as appropriate treatment plans. For example, in steam heat exchangers, the hardness of the boiler water is controlled to effectively prevent scale formation ； Circulating water heat exchangers prevent scaling by controlling turbidity, but they are prone to scaling at higher temperatures; therefore, pre-treatment devices such as ultrasonic or electrostatic scale removers can be used to reduce the formation of scale layers. Certain process media can introduce oils that form stubborn scale layers on the walls of the heat exchanger tubes. This requires controlling the source of the grease (which may be some operating equipment). 4. Ensure the heat transfer temperature difference: The temperature difference during operation is an adjustable factor to ensure effective heat transfer. If it is necessary to keep the heat exchanger operating in cases of scaling, blockage, etc., increasing the temperature difference is an optimization approach. For example, a circulating water heat exchanger can reduce the inlet water temperature and increase the water flow rate, while a steam heat exchanger can appropriately increase the steam pressure, and so on ； 5. Ensure a proper phase state of the medium. In some cases, the phase state of the medium can also have a significant impact on heat transfer efficiency ； In heat exchangers designed to use saturated steam, either a low saturation level of the steam (superheated steam) or a high saturation level (steam containing water) can have a significant impact on the heat exchange efficiency ； Certain process media require phase transformation during heat exchange, but deviations in the phase state occur due to changes in composition, temperature, pressure, etc ； In some applications, phase changes are strictly prohibited, as their occurrence can pose serious safety risks to the heat exchanger. Wait.