Selection of heat exchanger type and scaling treatment methods

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Selection of heat exchanger types and scaling treatment methods 1. When the temperature difference is large, floating head heat exchangers, U-shaped tube heat exchangers, stuffing box heat exchangers and sliding tube plate heat exchangers can be used. When the shell side is frequently mechanically cleaned, a structure with extractable tube bundles can be selected. At high temperatures and high pressures, U-shaped tube heat exchangers can be used. When the shell-side medium is flammable, explosive, toxic or volatile, or when the operating pressure and temperature are high, it is not appropriate to use a packed function heat exchanger. When the tube-side medium and the shell-side medium are not allowed to mix, a heat exchanger with a double tube sheet structure can be used. 2. Types and selection principles of tube and tube heat exchangers (1) Tube and tube heat exchangers can be divided into the following main types:: ① The tube plates at both ends of the tube bundle of the tube heat exchanger are integrated with the shell. The structure is simple, but it is only suitable for heat exchange operations when the temperature difference between hot and cold fluids is not large, and the shell side does not require mechanical cleaning. When the temperature difference is slightly larger and the shell side pressure is not too high, an elastic compensation ring can be installed on the shell to reduce thermal stress. ② The tube plate at one end of the tube bundle of the floating head heat exchanger can float freely, completely eliminating thermal stress, and the entire tube bundle can be extracted from the shell, making it easy for mechanical cleaning and maintenance. Floating head heat exchangers are widely used, but their structures are complex and their costs are high. ③ Each heat exchange tube of the tube-and-tube heat exchanger is bent into a U shape, and its two ends are respectively fixed on the same tube plate in the upper and lower areas. It is divided into two chambers, the inlet and outlet, with the help of partitions in the tube box. This type of heat exchanger completely eliminates thermal stress and has a simpler structure than the floating head type, but the tube side is not easy to clean. For heat exchange of highly corrosive fluids in chemical production, non-metallic materials such as ceramics, glass, polytetrafluoroethylene, and graphite need to be used to make shell-and-tube heat exchangers. This type of heat exchanger has poor heat transfer performance and is only used in situations with low pressure, small vibration, and low temperature. (2) For the hot and cold fluids to be used for heat exchange, flow channels should be selected according to the following principles: ① Fluids that are unclean and prone to scaling should be routed through the pipe because it is easier to clean inside the pipe. ② Corrosive fluids should be routed along the pipe side to prevent the pipe bundle and shell from being corroded at the same time. ③ Fluids with high pressure should be routed through the pipe to prevent the shell from bearing pressure. ④ Saturated steam should be transported to the shell side because the steam condensation heat transfer coefficient has nothing to do with the flow rate and the condensate is easily discharged. 3. Precautions and working principles of fixed tube plate heat exchangers. Things that should be paid attention to during the operation of fixed tube plate heat exchangers are:: (1) The heat exchanger must be pressure tested before being used after new installation or maintenance. (2) When the heat exchanger is started, the cold flow must be passed first and then the hot flow. When the heat exchanger is shut down, the hot flow must be stopped first and then the cold flow. To prevent leakage or damage caused by uneven thermal expansion and contraction. (3) Fixed tube plate heat exchangers are not allowed to receive heat in one direction, and floating heat exchangers are not allowed to have excessive temperature differences on both sides of the tube and shell. (4) During the start-up process, the exhaust valve should be kept open to discharge all air, and should be closed after the start-up is completed. (5) If hydrocarbons are used, use inert gas to purge the air in the heat exchanger before loading hydrocarbons to avoid explosion. (6) When shutting down for purging, the condensed water must be drained before steam introduction, and ventilation must be carried out slowly to prevent water hammer. When venting one side of the heat exchanger, the vent valve on the other side must be opened to avoid pressure damage. When closing the heat exchanger, the exhaust valve and drain valve should be opened to prevent vacuum damage caused by cooling. (7) When using the air cooler, pay attention to the uniform flow of parts to ensure the cooling effect. (8) Always monitor to prevent leakage. Working principle of fixed tube plate heat exchanger: The picture shows the structure of a fixed tube plate heat exchanger. Fluid A flows into the housing from nozzle 1 and flows out from nozzle 2 through the space between the tubes. B fluid flows in from the nozzle 3 and flows out from the nozzle 4 through the pipe. If the temperature of fluid A is higher than that of fluid B, heat will be transferred from fluid A to fluid B through the pipe wall. ； On the contrary, fluid B is transferred to fluid A through the pipe wall. The area inside the shell and outside the pipes and pipe boxes is called the shell side, and the fluid passing through the shell side is called shell side fluid (A fluid). The area within the pipe and pipe box is called the pipe pass, and the fluid passing through the pipe pass is called the pipe pass fluid (B fluid). Shell and tube heat exchangers are mainly composed of tube boxes, tube sheets, tubes, shells and baffles. Usually the shell is cylindrical and the tube is straight or U-shaped. In order to improve the heat transfer efficiency of the heat exchanger, threaded tubes, fin tubes, etc. can also be used. The layout of pipes can be in many forms, such as equilateral triangles, squares, squares turned at an angle of 45°, and concentric circles. The first three are the most common. When arranged in a triangle, more tubes can be arranged in a shell of the same diameter to increase the heat transfer area, but it is difficult to clean the tubes mechanically and the fluid resistance is also large. The collection of tubesheets and tubes is called a tube bundle. There are two types of connections between the pipe end and the tube sheet: welding and expansion. Some baffles are installed transversely in the tube bundle to guide the shell-side fluid to change its flow direction multiple times to effectively flush the tubes to improve heat transfer efficiency and at the same time support the tubes. The shapes of baffles include arcuate, circular and rectangular. In order to reduce the flow cross-section of the shell-side and tube-side fluids, speed up the flow rate, and improve the heat transfer efficiency, split-pass partitions can be installed longitudinally in the tube box and shell to divide the shell side into 2 passes and the tube pass into 2 passes, 4 passes, 6 passes, and 8 passes. 4. Types and connection methods of floating head heat exchangers. One end of the tube sheets at both ends of the floating head heat exchanger is not connected to the shell, and this end is called a floating head. When the tubes are heated, the tube bundle together with the floating head can freely expand and contract along the axial direction, completely eliminating the temperature difference stress. The tube sheet at one end of the floating head heat exchanger is fixed to the shell, while the tube sheet at the other end can float freely in the shell. The shell and tube bundle are free to thermal expansion, so when the temperature difference between the two media is large, there will be no temperature difference stress between the tube bundle and the shell. The floating head end is designed with a detachable structure so that the tube bundle can be easily inserted or withdrawn, which provides convenience for maintenance and cleaning. This form of heat exchanger is particularly suitable for working conditions where the temperature difference stress between the shell and the heat exchange tube is large, and both the shell and tube sides are required to be cleaned. (1) Advantages of floating head heat exchanger: a The tube bundle can be extracted to facilitate cleaning of the tube and shell side. bThe temperature difference between media is not limited. c. It can work under high temperature and high pressure. Generally, the temperature is less than or equal to 450 degrees, and the pressure is less than or equal to MPa. d can be used in situations where scaling is severe. e can be used in situations where pipes are prone to corrosion. (2) Disadvantages of floating head heat exchanger: aSmall floating head is prone to internal leakage. b Metal material consumption is large and the cost is 20% higher. c has a complex structure. (3) Selection requirements for floating head heat exchanger component materials: (4) Connection method between heat exchange tube and tube sheet: The connection methods between heat exchange tubes and tube sheets include expansion joints, welding, and a combination of expansion welding. a Expansion joint The formation of expansion joint can be divided into stick expansion and strength expansion according to the degree of expansion. Sticking expansion refers to the slight expansion joint to eliminate the gap between the heat exchange tube and the tube sheet. Strength expansion refers to the expansion joint to ensure the sealing performance and pull-off strength of the connection between the heat exchange tube and the tube sheet. b The welded connection between the heat exchange tube and the tube plate is divided into two types: strength welding and sealing welding. Strength welding refers to the welding that ensures the sealing performance and pull-off strength of the connection between the heat exchange tube and the tube plate. Sealing welding refers to the welding that ensures the sealing performance of the connection between the heat exchange tube and the tube sheet. The welding of heat exchange tubes and tube sheets generally uses manual arc welding, manual sub-arc welding and automatic rotating argon arc welding. c Combined use of expansion welding From the perspective of the process of expansion welding connection, it can be divided into two processes: expansion first and then welding, and welding first and then expansion. The combined use of expansion welding is suitable for occasions with high sealing performance requirements. ； Where subjected to vibration or fatigue loads ； Where there is crevice corrosion ； Where composite tube sheets are used. (5) Selection of the connection type between the heat pipe and the tube plate. The applicable scope of the strength expansion joint specified in GB150 "Pressure Vessel" is:: Design pressure is less than or equal to 4MPa ； Design temperature is less than or equal to 300°C ； There is no severe vibration, no excessive temperature changes and no obvious stress corrosion during operation. The applicable scope of strength welding is: It can be used for the design pressure specified in this standard, but it is not suitable for occasions with large vibration and gap corrosion. The combined use of expansion welding is suitable for occasions with high sealing performance requirements. ； Where subjected to vibration or fatigue loads ； Where there is crevice corrosion ； Where composite tube sheets are used. 5. Reasonable selection of heat exchange media and preliminary treatment methods generally add scale inhibitors and algaecides, and if necessary, add sulfuric acid to adjust the pH value. Pay attention to the hardness and pH value of circulating water, and adjust the dosage of scale inhibitors and sulfuric acid in a timely manner. The algaecide generally adopts the impact addition method. Pay attention to sewage discharge within 1-2 days after adding the algaecide. If conditions permit, a soft water treatment system can be used, but algaecide must be added. Even so, some biological slime will adhere to the heat exchanger. You can consider using high-pressure water for cleaning. The chemicals added in the circulating water system are mainly bactericidal algaecide and corrosion and scale inhibitors. Their purpose It is to improve the quality of circulating water, slow down the corrosion of equipment and pipelines, prevent scaling in the heat exchanger, and increase the thermal resistance of fouling. In the actual production process, we must strictly control the relevant process parameters, and at the same time hang coupons at different points in the circulating water system, and make appropriate adjustments to the chemicals according to the corrosion of the coupons. 6. Reduce and eliminate scaling from the process control of heat exchanger operation. The process conditions of the heat exchanger include heat transfer, thermodynamic parameters of the fluid (temperature, pressure, flow, phase state, etc.) and physical and chemical properties (density, viscosity, corrosiveness, etc.). While ensuring heat transfer efficiency, minimize the conditions for scaling formation. ； The operation must be carried out strictly in accordance with the specifications. The general practice is: (1) Increase the heat transfer coefficient. Under the premise of comprehensive consideration of fluid resistance and the absence of fluid-induced vibration, try to select a high flow rate. (2) Increase the average temperature difference. For fluids without phase change, try to use a heat transfer method close to countercurrent. Because this not only increases the average temperature difference, but also helps reduce the temperature difference stress in the structure. When conditions permit, the inlet temperature of the hot fluid can be increased or the inlet temperature of the cold fluid can be reduced. (3) Properly arrange the heat transfer surface. For example, heat exchangers, cold plates, etc., using appropriate tube spacing or arrangement can not only increase the heat transfer area per unit space, but also improve the flow characteristics of the fluid. The heat transfer method of staggered tube bundles is better than that of parallel tube bundles. (4) Cleaning methods for scale that has formed ① Chemical method Chemical method uses chemical reaction to remove scale or uses chemical reaction to loosen scale, and then uses external force to remove it. Of course, for chemical cleaning, it is best to hire an experienced professional company. The cost of cleaning by yourself is low. Before cleaning, you should analyze the ingredients of scaling and formulate a detailed construction plan. When cleaning, ensure that the heat exchange tubes and process pipelines are not corroded by the chemical liquid. ② Mechanical method (a) High pressure water jet cleaning: Generally, a pressure of 1-5MPa is used to form a powerful jet through the spray gun nozzle, with a water volume of 80-120 L/min, to break and flush the scale layer to achieve the purpose of cleaning. At present, manual hand-held flexible or rigid spray guns are basically used to flush the inside of the heat transfer tubes one by one, and the outside of the tube bundle is rotated section by section to flush from multiple directions. In order to improve efficiency and reduce labor intensity, different spray equipment should be used according to the scale situation, such as improved nozzles (nozzle size, shape, number and angle) for cleaning. For some refractory scales and blockages, special cleaning methods should be used, such as high-pressure water jet drills or >70 MPa ultra-high-pressure water jet cleaning. Combined cleaning with chemicals or heat is also possible. (b) Clean by hand or with mechanical pipe cleaning brushes: Use manual cleaning or a mechanical pipe cleaning brush to clean the inner wall of the pipe. This method has good adaptability and can be cleaned multiple times, but care must be taken not to cause damage to the pipe wall. ③ In order to eliminate scaling during the operation of the heat exchanger, regular cleaning can temporarily increase the flow rate or perform countercurrent operation, which can effectively eliminate light attachments on the inner wall of the tube, but a backwash pipeline must be preset on the equipment. You can also use glue balls for cleaning. Appropriate chemicals can also be injected according to the type of fluid to remove dirt. It is best to clean it in time every time you stop for maintenance. ④ Cleaning of heat exchangers during shutdown. Different methods should be used for parking cleaning of heat exchangers according to different types of heat exchangers and scaling conditions. They mainly include high-pressure water jet cleaning, chemical cleaning and mechanical cleaning. Mechanical cleaning involves manually pulling out strips or rotating electric drills to descale and clean the heat transfer tubes one by one. If the compression oil cooler is inspected, it should be cleaned in time. It is not easy to clean if it is left for a long time. It is labor-intensive and can easily damage the inner wall of the steel tube. Selection of heat exchanger types and scaling treatment methods 1. When the temperature difference is large, floating head heat exchangers, U-shaped tube heat exchangers, stuffing box heat exchangers and sliding tube plate heat exchangers can be used. When the shell side is frequently mechanically cleaned, a structure with extractable tube bundles can be selected. At high temperatures and high pressures, U-shaped tube heat exchangers can be used. When the shell-side medium is flammable, explosive, toxic or volatile, or when the operating pressure and temperature are high, it is not appropriate to use a packed function heat exchanger. When the tube-side medium and the shell-side medium are not allowed to mix, a heat exchanger with a double tube sheet structure can be used. 2. Types and selection principles of tube and tube heat exchangers (1) Tube and tube heat exchangers can be divided into the following main types:: ① The tube plates at both ends of the tube bundle of the tube heat exchanger are integrated with the shell. The structure is simple, but it is only suitable for heat exchange operations when the temperature difference between hot and cold fluids is not large, and the shell side does not require mechanical cleaning. When the temperature difference is slightly larger and the shell side pressure is not too high, an elastic compensation ring can be installed on the shell to reduce thermal stress. ② The tube plate at one end of the tube bundle of the floating head heat exchanger can float freely, completely eliminating thermal stress, and the entire tube bundle can be extracted from the shell, making it easy for mechanical cleaning and maintenance. Floating head heat exchangers are widely used, but their structures are complex and their costs are high. ③ Each heat exchange tube of the tube-and-tube heat exchanger is bent into a U shape, and its two ends are respectively fixed on the same tube plate in the upper and lower areas. It is divided into two chambers, the inlet and outlet, with the help of partitions in the tube box. This type of heat exchanger completely eliminates thermal stress and has a simpler structure than the floating head type, but the tube side is not easy to clean. For heat exchange of highly corrosive fluids in chemical production, non-metallic materials such as ceramics, glass, polytetrafluoroethylene, and graphite need to be used to make shell-and-tube heat exchangers. This type of heat exchanger has poor heat transfer performance and is only used in situations with low pressure, small vibration, and low temperature. (2) For the hot and cold fluids to be used for heat exchange, flow channels should be selected according to the following principles: ① Fluids that are unclean and prone to scaling should be routed through the pipe because it is easier to clean inside the pipe. ② Corrosive fluids should be routed along the pipe side to prevent the pipe bundle and shell from being corroded at the same time. ③ Fluids with high pressure should be routed through the pipe to prevent the shell from bearing pressure. ④ Saturated steam should be transported to the shell side because the steam condensation heat transfer coefficient has nothing to do with the flow rate and the condensate is easily discharged. 3. Precautions and working principles of fixed tube plate heat exchangers. Things that should be paid attention to during the operation of fixed tube plate heat exchangers are:: (1) The heat exchanger must be pressure tested before being used after new installation or maintenance. (2) When the heat exchanger is started, the cold flow must be passed first and then the hot flow. When the heat exchanger is shut down, the hot flow must be stopped first and then the cold flow. To prevent leakage or damage caused by uneven thermal expansion and contraction. (3) Fixed tube plate heat exchangers are not allowed to receive heat in one direction, and floating heat exchangers are not allowed to have excessive temperature differences on both sides of the tube and shell. (4) During the start-up process, the exhaust valve should be kept open to discharge all air, and should be closed after the start-up is completed. (5) If hydrocarbons are used, use inert gas to purge the air in the heat exchanger before loading hydrocarbons to avoid explosion. (6) When shutting down for purging, the condensed water must be drained before steam introduction, and ventilation must be carried out slowly to prevent water hammer. When venting one side of the heat exchanger, the vent valve on the other side must be opened to avoid pressure damage. When closing the heat exchanger, the exhaust valve and drain valve should be opened to prevent vacuum damage caused by cooling. (7) When using the air cooler, pay attention to the uniform flow of parts to ensure the cooling effect. (8) Always monitor to prevent leakage. Working principle of fixed tube plate heat exchanger: The picture shows the structure of a fixed tube plate heat exchanger. Fluid A flows into the housing from nozzle 1 and flows out from nozzle 2 through the space between the tubes. B fluid flows in from the nozzle 3 and flows out from the nozzle 4 through the pipe. If the temperature of fluid A is higher than that of fluid B, heat will be transferred from fluid A to fluid B through the pipe wall. ； On the contrary, fluid B is transferred to fluid A through the pipe wall. The area inside the shell and outside the pipes and pipe boxes is called the shell side, and the fluid passing through the shell side is called shell side fluid (A fluid). The area within the pipe and pipe box is called the pipe pass, and the fluid passing through the pipe pass is called the pipe pass fluid (B fluid). Shell and tube heat exchangers are mainly composed of tube boxes, tube sheets, tubes, shells and baffles. Usually the shell is cylindrical and the tube is straight or U-shaped. In order to improve the heat transfer efficiency of the heat exchanger, threaded tubes, fin tubes, etc. can also be used. The layout of pipes can be in many forms, such as equilateral triangles, squares, squares turned at an angle of 45°, and concentric circles. The first three are the most common. When arranged in a triangle, more tubes can be arranged in a shell of the same diameter to increase the heat transfer area, but it is difficult to clean the tubes mechanically and the fluid resistance is also large. The collection of tubesheets and tubes is called a tube bundle. There are two types of connections between the pipe end and the tube sheet: welding and expansion. Some baffles are installed transversely in the tube bundle to guide the shell-side fluid to change its flow direction multiple times to effectively flush the tubes to improve heat transfer efficiency and at the same time support the tubes. The shapes of baffles include arcuate, circular and rectangular. In order to reduce the flow cross-section of the shell-side and tube-side fluids, speed up the flow rate, and improve the heat transfer efficiency, split-pass partitions can be installed longitudinally in the tube box and shell to divide the shell side into 2 passes and the tube pass into 2 passes, 4 passes, 6 passes, and 8 passes. 4. Types and connection methods of floating head heat exchangers. One end of the tube sheets at both ends of the floating head heat exchanger is not connected to the shell, and this end is called a floating head. When the tubes are heated, the tube bundle together with the floating head can freely expand and contract along the axial direction, completely eliminating the temperature difference stress. The tube sheet at one end of the floating head heat exchanger is fixed to the shell, while the tube sheet at the other end can float freely in the shell. The shell and tube bundle are free to thermal expansion, so when the temperature difference between the two media is large, there will be no temperature difference stress between the tube bundle and the shell. The floating head end is designed with a detachable structure so that the tube bundle can be easily inserted or withdrawn, which provides convenience for maintenance and cleaning. This form of heat exchanger is particularly suitable for working conditions where the temperature difference stress between the shell and the heat exchange tube is large, and both the shell and tube sides are required to be cleaned. (1) Advantages of floating head heat exchanger: a The tube bundle can be extracted to facilitate cleaning of the tube and shell side. bThe temperature difference between media is not limited. c. It can work under high temperature and high pressure. Generally, the temperature is less than or equal to 450 degrees, and the pressure is less than or equal to MPa. d can be used in situations where scaling is severe. e can be used in situations where pipes are prone to corrosion. (2) Disadvantages of floating head heat exchanger: aSmall floating head is prone to internal leakage. b Metal material consumption is large and the cost is 20% higher. c has a complex structure. (3) Selection requirements for floating head heat exchanger component materials: (4) Connection method between heat exchange tube and tube sheet: The connection methods between heat exchange tubes and tube sheets include expansion joints, welding, and a combination of expansion welding. a Expansion joint The formation of expansion joint can be divided into stick expansion and strength expansion according to the degree of expansion. Sticking expansion refers to the slight expansion joint to eliminate the gap between the heat exchange tube and the tube sheet. Strength expansion refers to the expansion joint to ensure the sealing performance and pull-off strength of the connection between the heat exchange tube and the tube sheet. b The welded connection between the heat exchange tube and the tube plate is divided into two types: strength welding and sealing welding. Strength welding refers to the welding that ensures the sealing performance and pull-off strength of the connection between the heat exchange tube and the tube plate. Sealing welding refers to the welding that ensures the sealing performance of the connection between the heat exchange tube and the tube sheet. The welding of heat exchange tubes and tube sheets generally uses manual arc welding, manual sub-arc welding and automatic rotating argon arc welding. c Combined use of expansion welding From the perspective of the process of expansion welding connection, it can be divided into two processes: expansion first and then welding, and welding first and then expansion. The combined use of expansion welding is suitable for occasions with high sealing performance requirements. ； Where subjected to vibration or fatigue loads ； Where there is crevice corrosion ； Where composite tube sheets are used. (5) Selection of the connection type between the heat pipe and the tube plate. The applicable scope of the strength expansion joint specified in GB150 "Pressure Vessel" is:: Design pressure is less than or equal to 4MPa ； Design temperature is less than or equal to 300°C ； There is no severe vibration, no excessive temperature changes and no obvious stress corrosion during operation. The applicable scope of strength welding is: It can be used for the design pressure specified in this standard, but it is not suitable for occasions with large vibration and gap corrosion. The combined use of expansion welding is suitable for occasions with high sealing performance requirements. ； Where subjected to vibration or fatigue loads ； Where there is crevice corrosion ； Where composite tube sheets are used. 5. Reasonable selection of heat exchange media and preliminary treatment methods generally add scale inhibitors and algaecides, and if necessary, add sulfuric acid to adjust the pH value. Pay attention to the hardness and pH value of circulating water, and adjust the dosage of scale inhibitors and sulfuric acid in a timely manner. The algaecide generally adopts the impact addition method. Pay attention to sewage discharge within 1-2 days after adding the algaecide. If conditions permit, a soft water treatment system can be used, but algaecide must be added. Even so, some biological slime will adhere to the heat exchanger. You can consider using high-pressure water for cleaning. The chemicals added in the circulating water system are mainly bactericidal algaecide and corrosion and scale inhibitors. Their purpose It is to improve the quality of circulating water, slow down the corrosion of equipment and pipelines, prevent scaling in the heat exchanger, and increase the thermal resistance of fouling. In the actual production process, we must strictly control the relevant process parameters, and at the same time hang coupons at different points in the circulating water system, and make appropriate adjustments to the chemicals according to the corrosion of the coupons. 6. Reduce and eliminate scaling from the process control of heat exchanger operation. The process conditions of the heat exchanger include heat transfer, thermodynamic parameters of the fluid (temperature, pressure, flow, phase state, etc.) and physical and chemical properties (density, viscosity, corrosiveness, etc.). While ensuring heat transfer efficiency, minimize the conditions for scaling formation. ； The operation must be carried out strictly in accordance with the specifications. The general practice is: (1) Increase the heat transfer coefficient. Under the premise of comprehensive consideration of fluid resistance and the absence of fluid-induced vibration, try to select a high flow rate. (2) Increase the average temperature difference. For fluids without phase change, try to use a heat transfer method close to countercurrent. Because this not only increases the average temperature difference, but also helps reduce the temperature difference stress in the structure. When conditions permit, the inlet temperature of the hot fluid can be increased or the inlet temperature of the cold fluid can be reduced. (3) Properly arrange the heat transfer surface. For example, heat exchangers, cold plates, etc., using appropriate tube spacing or arrangement can not only increase the heat transfer area per unit space, but also improve the flow characteristics of the fluid. The heat transfer method of staggered tube bundles is better than that of parallel tube bundles. (4) Cleaning methods for scale that has formed ① Chemical method Chemical method uses chemical reaction to remove scale or uses chemical reaction to loosen scale, and then uses external force to remove it. Of course, for chemical cleaning, it is best to hire an experienced professional company. The cost of cleaning by yourself is low. Before cleaning, you should analyze the ingredients of scaling and formulate a detailed construction plan. When cleaning, ensure that the heat exchange tubes and process pipelines are not corroded by the chemical liquid. ② Mechanical method (a) High pressure water jet cleaning: Generally, a pressure of 1-5MPa is used to form a powerful jet through the spray gun nozzle, with a water volume of 80-120 L/min, to break and flush the scale layer to achieve the purpose of cleaning. At present, manual hand-held flexible or rigid spray guns are basically used to flush the inside of the heat transfer tubes one by one, and the outside of the tube bundle is rotated section by section to flush from multiple directions. In order to improve efficiency and reduce labor intensity, different spray equipment should be used according to the scale situation, such as improved nozzles (nozzle size, shape, number and angle) for cleaning. For some refractory scales and blockages, special cleaning methods should be used, such as high-pressure water jet drills or >70 MPa ultra-high-pressure water jet cleaning. Combined cleaning with chemicals or heat is also possible. (b) Clean by hand or with mechanical pipe cleaning brushes: Use manual cleaning or a mechanical pipe cleaning brush to clean the inner wall of the pipe. This method has good adaptability and can be cleaned multiple times, but care must be taken not to cause damage to the pipe wall. ③ In order to eliminate scaling during the operation of the heat exchanger, regular cleaning can temporarily increase the flow rate or perform countercurrent operation, which can effectively eliminate light attachments on the inner wall of the tube, but a backwash pipeline must be preset on the equipment. You can also use glue balls for cleaning. Appropriate chemicals can also be injected according to the type of fluid to remove dirt. It is best to clean it in time every time you stop for maintenance. ④ Cleaning of heat exchangers during shutdown. Different methods should be used for parking cleaning of heat exchangers according to different types of heat exchangers and scaling conditions. They mainly include high-pressure water jet cleaning, chemical cleaning and mechanical cleaning. Mechanical cleaning involves manually pulling out strips or rotating electric drills to descale and clean the heat transfer tubes one by one. If the compression oil cooler is inspected, it should be cleaned in time. It is not easy to clean if it is left for a long time. It is labor-intensive and can easily damage the inner wall of the steel tube.