Air preheater for increasing temperature of side wall at air inlet
Patent Information
- Application Number
- CN202522474798.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-21
- Publication Date
- 2026-11-03
- Estimated Expiration
- 2035-11-21
AI Technical Summary
Dust accumulation at the junction of the flue gas outlet area and the cold air inlet area of the air heat exchanger causes wear, corrosion and blockage, affecting heat exchange efficiency and equipment life.
A heat insulation element is installed at the air inlet of the air channel. By gradually increasing the size and thickness of the element, the heat exchange efficiency between the flue gas and the cold air is reduced, and the temperature at the junction is kept above the liquefaction point of ammonium bisulfate to prevent ash accumulation.
It effectively prevents ammonium bisulfate from liquefying and adhering, reduces ash accumulation, improves heat exchange efficiency, extends equipment service life, and ensures safe and stable operation.
Smart Images
Figure CN224932774U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the technical field of flue gas treatment equipment, and in particular to an air preheater that increases the temperature of the air inlet sidewall. Background Technology
[0002] Air heat exchangers, as key equipment for preheating air in power plants, face serious ash accumulation problems in actual operation. Ammonium bisulfate, formed by the reaction of ammonia escaping from the denitrification system with sulfur trioxide and water vapor in the flue gas, liquefies and becomes viscous within a temperature range of 150-200℃. This viscous substance readily adheres to the surface of the heat exchanger's heat storage fins, thereby capturing fly ash particles from the flue gas and forming a stubborn ash layer. Ash accumulation not only significantly reduces heat exchange efficiency but also triggers a series of operational safety hazards.
[0003] The thermal resistance of ash deposits is much higher than that of metallic materials, and their presence significantly reduces the heat transfer performance of heat exchangers. More seriously, ash accumulation reduces the flow area of flue gas passages, causing localized increases in flow velocity and exacerbating wear and corrosion of heated surfaces. Simultaneously, ash accumulation increases flue gas flow resistance, leading to higher exhaust gas temperatures and directly impacting the safe and stable operation of the boiler system.
[0004] In traditional heat exchangers, flue gas and cold air flow in a vertical, cross-flow pattern. This arrangement results in the lowest temperature at the junction of the flue gas outlet and the cold air inlet, which falls precisely within the critical temperature range for ammonium bisulfate liquefaction. This area therefore becomes the most prone to ash accumulation, leading to channel blockage after prolonged operation and severely impacting the equipment's heat exchange performance and lifespan. Utility Model Content
[0005] The purpose of this invention is to provide an air preheater that increases the temperature of the air inlet side wall, thereby solving the problem of wear, corrosion, and blockage of the heat exchanger's heating surface caused by ash accumulation at the junction of the flue gas outlet area and the cold air inlet area. This effectively prevents the liquefaction and deposition of ammonium bisulfate, reduces ash accumulation, and improves heat exchange efficiency and service life.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: an air preheater for increasing the temperature of the air inlet sidewall, comprising a heat exchanger, the heat exchanger comprising multiple heat exchange plates arranged sequentially at intervals, each heat exchange plate comprising a first thin plate and a second thin plate, the opposite sides of the first and second thin plates being welded and sealed, the middle of the first and second thin plates being welded through multiple welding columns, the unwelded parts of the first and second thin plates being far apart from each other to form an air channel for airflow, the two ends of the first and second thin plates between adjacent air channels being sealed and connected, a flue gas channel being formed between adjacent heat exchange plates, and a heat insulation element for reducing the heat exchange between the heat exchange plate and the air in the air channel being provided on the side of the first and second thin plates in contact with the air channel, the heat insulation element being located at the air inlet end of the air channel.
[0007] Furthermore, the dimensions of the heat insulation element in the direction of cold air intake gradually increase along the direction of flue gas flow.
[0008] Furthermore, the thickness of the heat insulation element gradually increases along the flue gas flow direction.
[0009] Furthermore, the heat insulation element includes a first heat insulation plate and a second heat insulation plate. The first heat insulation plate is attached to a first thin plate to increase the thickness of the first thin plate and reduce the amount of heat exchange between the heat exchange plate and the air in the air channel. The second heat insulation plate is attached to a second thin plate to increase the thickness of the second thin plate and reduce the amount of heat exchange between the heat exchange plate and the air in the air channel. The middle portion of the first heat insulation plate and the second heat insulation plate protrudes in a direction away from each other to form an auxiliary air intake channel.
[0010] Furthermore, the inner end of the first heat insulation plate is provided with auxiliary heat insulation teeth, which are attached to the inner sidewall of the first thin plate. An avoidance opening is formed between two adjacent auxiliary heat insulation teeth, and the welding column between the first thin plate and the second thin plate is located in the avoidance opening.
[0011] Furthermore, the heat insulation element includes a first heat insulation plate and a second heat insulation plate, with a gap between the first heat insulation plate and the first thin plate, and a gap between the second heat insulation plate and the second thin plate, and through holes provided on the first heat insulation plate and the second heat insulation plate.
[0012] Furthermore, the inner diameter of the through hole increases along the direction of cold air flow.
[0013] Furthermore, the air inlet end of the first heat insulation plate is integrally formed with the air inlet end of the first thin plate, and the air inlet end of the second heat insulation plate is integrally formed with the air inlet end of the second thin plate.
[0014] Furthermore, the air inlet end of the first heat insulation plate is provided with a first folded edge, and the air inlet end of the second heat insulation plate is provided with a second folded edge. The first folded edge is welded to the air inlet end of the first thin plate, and the second folded edge is welded to the air inlet end of the second thin plate.
[0015] Furthermore, the heat insulation element is an enamel coating, which is attached to the air inlet end of the first and second thin plates, and the enamel coating is located in the air channel to reduce the amount of heat exchange between the heat exchange plate and the air in the air channel.
[0016] As can be seen from the above, the air preheater provided by this utility model for increasing the temperature of the air inlet side wall is achieved by setting a heat insulation element with an auxiliary air inlet channel at the air inlet end of the air channel, thereby reducing the heat exchange efficiency between the flue gas and cold air at the junction of the flue gas outlet area and the cold air inlet area, thus increasing the temperature at the junction of the flue gas outlet area and the cold air inlet area, avoiding the liquefaction and adhesion of ammonium bisulfate, effectively preventing the formation of ash at the junction of the flue gas outlet area and the cold air inlet area of the heat exchanger, improving heat exchange efficiency and operational safety. Attached Figure Description
[0017] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a partial schematic diagram of an air preheater for increasing the temperature of the air inlet sidewall according to the present invention; Figure 2 This is a schematic diagram of the heat exchange plate in this utility model; Figure 3 This is a schematic diagram of the first thin plate and the second thin plate in this utility model; Figure 4 This is a schematic diagram of the heat insulation element in this utility model; Figure 5 This is a schematic diagram of the structure of the first heat insulation plate and the second heat insulation plate in this utility model; Figure 6 This is a schematic diagram showing the thickness of the heat insulation plate in this utility model; Figure 7 This is a schematic diagram of the through hole in this utility model; Figure 8 This is a schematic diagram of the first and second folded edges in this utility model. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.
[0019] The terms "first," "second," etc. (if present) in the specification and claims of this utility model are used to distinguish similar objects, not to describe a specific order or sequence. Even if "second" is used before a technical feature for distinction, it does not necessarily imply the presence of "first." It should be understood that in this utility model, "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. It should be understood that in this utility model, "multiple" refers to two or more. "And / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, X and / or Y can represent: X alone, X and Y simultaneously, and Y alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "Containing X, Y, and Z," "Containing X, Y, and Z" means that all three X, Y, and Z are included; "Containing X, Y, or Z" means that one of X, Y, and Z is included; "Containing X, Y, and / or Z" means that any one, two, or three of X, Y, and Z are included.
[0020] The technical solution of this utility model will be described in detail below with specific embodiments. The following specific embodiments can be selected to be combined or substituted with each other according to the actual situation, and the same or similar concepts or processes may not be described again in some embodiments.
[0021] like Figure 1 , Figure 2 and Figure 3As shown, this utility model provides an air preheater for increasing the temperature of the air inlet sidewall, including a heat exchanger. The heat exchanger includes multiple heat exchange plates 1 arranged in sequence. Each heat exchange plate 1 includes a first thin plate 11 and a second thin plate 12. The opposite sides of the first thin plate 11 and the second thin plate 12 are sealed together. The middle parts of the first thin plate 11 and the second thin plate 12 are welded together by welding columns 13. The unwelded parts on the first thin plate 11 and the second thin plate 12 are far apart to form an air channel 3 for airflow. The two ends of the first thin plate 11 and the second thin plate 12 between two adjacent air channels 3 are sealed together. A flue gas channel 2 is formed between two adjacent heat exchange plates 1. The air channel 3 and the flue gas channel 2 are perpendicular to each other. A heat insulation element 4 is provided in the air channel 3. The heat insulation element 4 is located at... At the air inlet of air channel 3, by placing the heat insulation element 4 at the air inlet of air channel 3, the heat exchange efficiency between flue gas and cold air at the air inlet of air channel 3 is reduced, thereby increasing the temperature of flue gas at the air inlet of air channel 3. This effectively reduces the possibility of ammonium bisulfate being in a liquid state at the air inlet of air channel 3 and adsorbing fly ash particles in the flue gas, thereby reducing the possibility of ash accumulation on the heat exchange plate 1 at the air inlet of air channel 3, leading to wear, corrosion, and blockage. Specifically, the heat insulation element 4 has an auxiliary air inlet channel 43, which connects air channel 3 with the cold air inlet pipe. After the heat insulation element 4 is installed, the auxiliary air inlet channel 43 ensures that flue gas can enter air channel 3 from the air inlet of air channel 3, ensuring the normal operation of the heat exchanger.
[0022] In this embodiment, as Figure 1 and Figure 2 As shown, the heat exchange plate 1 is a plate structure formed by a first thin plate 11 and a second thin plate 12 through side sealing. Specifically, it can be achieved by welding a stamped corrugated plate, with a gas flow space formed by the central protrusion. The end seals between adjacent heat exchange plates 1 form a continuous passage for the flue gas channel 2, ensuring that the flue gas and air are positively circulated in the flue gas channel 2 and the air channel 3, respectively. The heat insulation element 4 is embedded in the air inlet of the air channel 3, which reduces the efficiency of heat exchange between the initial section of cold air and flue gas through physical isolation, keeping the temperature of the flue gas at the air inlet of the air channel 3 above the liquefaction point of ammonium bisulfate. The positive flow channel layout maintains the overall counter-current heat exchange efficiency, and the heat insulation element 4 precisely controls the temperature field distribution at the air inlet of the air channel 3, thereby reducing the possibility of dust accumulation and blockage on the heat exchanger surface.
[0023] To further increase the temperature of the flue gas at the outlet area of flue gas passage 2 and the inlet area of air passage 3, such as Figure 4As shown, the dimensions of the heat insulation element 4 gradually increase along the flow direction of the flue gas in the direction of cold air intake. Specifically, the dimensions of the heat insulation element 4 refer to its length along the cold air flow path. The length of this structure is smaller at the flue gas inlet end. As the flue gas flows in the flue gas channel 2, the length of the heat insulation element 4 gradually increases along the flow direction of the flue gas. When cold air enters the air channel 3 from the inlet end, the coverage area of the heat insulation element 4 near the inlet end of the flue gas channel 2 is smaller, and the temperature of the flue gas at the inlet part of the flue gas channel 2 is relatively high. After the flue gas enters the flue gas channel 2, the temperature of the flue gas gradually decreases. By gradually increasing the length of the heat insulation element 4, the flue gas gradually flows along the flue gas channel 2 at the inlet end of the air channel 3, and the coverage area of the heat insulation element 4 gradually increases, forming a progressive heat insulation barrier. This reduces the heat exchange efficiency of the subsequent area, thereby effectively preventing the temperature of the flue gas at the junction of the flue gas outlet area and the air inlet area from being lower than the liquefaction temperature of ammonium bisulfate, reducing the deposition of viscous substances, thereby reducing the risk of corrosion and blockage on the surface of the heat exchange plate and extending the continuous operation cycle of the heat exchanger.
[0024] In another embodiment, such as Figure 5 As shown, the thickness of the heat insulation element 4 gradually increases along the flue gas flow direction. Specifically, the heat insulation element 4 can be made of metal or ceramic materials to reduce the heat exchange efficiency between cold air and flue gas. The thickness of the heat insulation element 4 gradually increases along the flue gas flow direction. When cold air flows at the inlet end, the flue gas outlet area is more susceptible to low temperature effects due to its proximity to the flue gas channel 2 outlet. Increasing the thickness of the heat insulation element 4 at the flue gas outlet channel enhances the insulation effect in this area, suppressing heat loss from the flue gas. Since the initial temperature of the cold air is low in the flue gas inlet area, appropriately reducing the insulation thickness can balance the overall heat exchange efficiency. This gradual design matches the heat exchange requirements of different height areas, maintaining the flue gas temperature above the liquefaction point of ammonium bisulfate at the junction of the flue gas outlet area and the air inlet area. This reduces the liquefaction and adhesion of ammonium bisulfate in this area, lowering the risk of wear, corrosion, and blockage on the heat exchanger's heated surfaces caused by ash accumulation.
[0025] To ensure that cold air can enter the air passage 3 from the auxiliary air intake passage 43, such as Figure 4 and Figure 5As shown, the heat insulation element 4 includes a first heat insulation plate 41 and a second heat insulation plate 42. The first heat insulation plate 41 is attached to the first thin plate 11 to increase the thickness of the first thin plate 11 and reduce the amount of heat exchange between the heat exchange plate 1 and the air in the air channel 2. The second heat insulation plate 42 is attached to the second thin plate 12 to increase the thickness of the second thin plate 12 and reduce the amount of heat exchange between the heat exchange plate 1 and the air in the air channel 2. The middle portion of the first heat insulation plate 41 and the second heat insulation plate 42 protrudes in a direction away from each other to form an auxiliary air intake channel 43. Specifically, the first heat insulation plate 41 and the second heat insulation plate 42... The hot plates 42 are all thin metal plates, which can be formed by stamping. Their edge areas are in planar contact with the first thin plate 11 and the second thin plate 12. When the cold air flows in the auxiliary air intake channel 43, its contact with the heat exchange plate is blocked by the first heat insulation plate 41 and the second heat insulation plate 42, which reduces the heat exchange efficiency and the heat loss of the flue gas. This effectively reduces the heat exchange efficiency of the area where the cold air intake end meets the flue gas, keeping the flue gas temperature in this area above the liquefaction critical point of ammonium bisulfate and reducing the heat loss in the low temperature area.
[0026] In this embodiment, as Figure 2 and Figure 6 As shown, the inner end of the first heat insulation plate 41 is provided with auxiliary heat insulation teeth 411. The auxiliary heat insulation teeth 411 are attached to the inner sidewall of the first thin plate 11, and a clearance opening 412 is formed between two adjacent auxiliary heat insulation teeth 411. The welding column 13 between the first thin plate 11 and the second thin plate 12 is located in the clearance opening 412. The auxiliary heat insulation teeth 411 refer to the protruding structures extending from the edge of the heat insulation plate. Specifically, they can be achieved by stamping or welding attachments. Their function is to increase the contact range with the inner wall of the heat exchange plate through the toothed structure, and enhance the connection between the heat insulation element 4 and the first thin plate 11 and the second thin plate 12. The heat conduction barrier effect; the clearance opening 412 provides physical accommodation space for the welding column 13, avoiding positional interference between the welding column 13 and the heat insulation element 4; the size of the clearance opening 412 can be adjusted according to the diameter of the welding column 13. For example, the width of the clearance opening 412 can be set to be 0.5 to 1 mm larger than the outer diameter of the welding column 13. During the assembly process, the welding column 13 is precisely positioned inside the clearance opening 412, which not only retains the sealing function of the welding connection point, but also allows the heat insulation plate to cover a larger area of the air inlet end area of the inner wall of the heat exchange plate, thus enhancing the heat barrier effect between the heat insulation element 4 and the heat exchange plate.
[0027] In another embodiment, such as Figure 2 and Figure 7As shown, the heat insulation element 4 includes a first heat insulation plate 41 and a second heat insulation plate 42. The first heat insulation plate 41 is spaced apart from the first thin plate 11, and the second heat insulation plate 42 is spaced apart from the second thin plate 12. Through holes 413 are provided on both the first and second heat insulation plates 41 and 42. The gap arrangement refers to maintaining a gap between the first heat insulation plate 41 and the first thin plate 11. This gap can be achieved using a spaced support structure or positioning protrusions. This gap forms a heat insulation buffer area to reduce heat conduction from direct contact between cold air and the heat exchange plate, thus slowing down the rapid heat transfer of cold air to the heat exchange plate. Cooling is used to prevent a sudden drop in temperature in the area from causing ammonium bisulfate to liquefy. The through-hole 413 forms a controllable airflow channel on the heat insulation plate. Part of the cold air enters the air channel 3 through the through-hole 413, while the other part flows along the inner sidewalls of the first heat insulation plate 41 and the second heat insulation plate 42. By adjusting the position and aperture ratio of the through-hole 413, the cold air forms a stratified flow at the air inlet. This ensures the heat exchange effect of the heat exchanger while reducing the flue gas temperature below the liquefaction threshold of ammonium bisulfate, which would cause the ammonium bisulfate to liquefy and adsorb fly ash particles in the flue gas.
[0028] To further ensure the heat exchange efficiency of the heat exchanger, such as Figure 7 As shown, the inner diameter of the through hole 413 increases along the flow direction of the cold air. When the cold air enters the auxiliary air intake channel 43, the air enters the gap between the first heat insulation plate 41 and the second heat insulation plate 42 and the first thin plate 11 and the second thin plate 12 through the through hole 413. While the first heat insulation plate 41 and the second heat insulation plate 42 reduce the heat exchange efficiency of the heat exchanger at the air intake end of the air channel 3, the through hole 413 allows some cold air to contact the heat exchange plate 1, ensuring that the flue gas temperature is higher than the liquefaction critical point of ammonium bisulfate while ensuring the heat exchange efficiency of the heat exchanger. By increasing the inner diameter of the through hole 413 along the flow direction of the cold air, as the air gradually penetrates deeper into the air channel 3, the air temperature rises, and the corresponding flue gas temperature is also higher than that at the air intake end of the air channel 3. At this time, the contact between the air and the heat exchange plate 1 is increased, thereby improving the heat exchange efficiency of the heat exchanger.
[0029] To ensure the stability of the first heat insulation plate 41 and the second heat insulation plate 42 within the air channel 3, the air inlet end of the first heat insulation plate 41 is connected to the air inlet end of the first thin plate 11 by an integral molding method, and the air inlet end of the second heat insulation plate 42 is connected to the air inlet end of the second thin plate 12 by an integral molding method. The integral molding method eliminates the assembly gaps caused by traditional welding or bolt connections, completely blocking the heat conduction path at the cold air inlet end, achieving a seamless transition between the heat insulation element 4 and the heat exchange plate, and avoiding cracking at the connection due to differences in the coefficients of material expansion. In another embodiment, the integral structure will not undergo relative displacement when subjected to mechanical vibration, ensuring that the fit between the auxiliary heat insulation tooth 411 and the inner wall of the heat exchange plate remains stable, thereby ensuring the precise positioning of the clearance opening 412 on the welding column 13.
[0030] In another embodiment, such as Figure 2 and Figure 8 As shown, the air inlet end of the first heat insulation plate 41 is provided with a first folded edge 414, and the air inlet end of the second heat insulation plate 42 is provided with a second folded edge 421. The first folded edge 414 is welded to the air inlet end of the first thin plate 11, and the second folded edge 421 is welded to the air inlet end of the second thin plate 12. The first folded edge 414 and the second folded edge 421 refer to the bending structures respectively set on the edges of the air inlet ends of the first heat insulation plate 41 and the second heat insulation plate 42. Specifically, they can be formed by folding the edges of the plates outward using a stamping process. By increasing the welding contact area, the connection strength between the heat insulation plate and the heat exchange plate is improved, thereby improving the stability of the first heat insulation plate 41 and the second heat insulation plate 42.
[0031] In another embodiment, the heat insulation element 4 is an enamel coating, which is attached to the air inlet ends of the first thin plate 11 and the second thin plate 12, and is located within the air channel 3. The enamel coating is an inorganic glassy material layer formed on the surface of a metal substrate by a high-temperature sintering process, possessing low thermal conductivity and high chemical stability. The low thermal conductivity of the enamel coating reduces the initial heat exchange rate between the cold air and the heat exchange plate when the cold air enters the channel, thus delaying the heating process of the cold air. This delaying effect maintains the temperature of the flue gas in the cold air inlet junction area above the critical temperature for the liquefaction of ammonium bisulfate, preventing the formation of liquid ammonium bisulfate.
[0032] In addition to the preferred embodiments described above, there are other embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection claimed by this utility model.
Claims
1. An air preheater for increasing the temperature of the air inlet sidewall, comprising a heat exchanger, the heat exchanger comprising a plurality of heat exchange plates arranged at intervals in sequence, each heat exchange plate comprising a first thin plate and a second thin plate, the opposite sides of the first and second thin plates being welded and sealed, the middle portions of the first and second thin plates being welded together by a plurality of welding pillars, the unwelded portions of the first and second thin plates being spaced apart to form air channels for airflow, the ends of the first and second thin plates between adjacent air channels being sealed and connected, and a flue gas channel being formed between adjacent heat exchange plates, characterized in that… The first and second thin plates are provided with heat insulation elements on the side that contacts the air channel to reduce the amount of heat exchange between the heat exchange plate and the air in the air channel. The heat insulation elements are located at the air inlet end of the air channel.
2. The air preheater for increasing the air inlet sidewall temperature according to claim 1, characterized in that, The dimensions of the heat insulation element gradually increase along the direction of flue gas flow in the direction of cold air intake.
3. The air preheater for increasing the air inlet sidewall temperature according to claim 1, characterized in that, The thickness of the heat insulation element gradually increases along the direction of flue gas flow.
4. The air preheater for increasing the air inlet sidewall temperature according to claim 1, characterized in that, The heat insulation element includes a first heat insulation plate and a second heat insulation plate. The first heat insulation plate is attached to a first thin plate to increase the thickness of the first thin plate and reduce the amount of heat exchange between the heat exchange plate and the air in the air channel. The second heat insulation plate is attached to a second thin plate to increase the thickness of the second thin plate and reduce the amount of heat exchange between the heat exchange plate and the air in the air channel. The middle part of the first heat insulation plate and the second heat insulation plate protrudes in a direction away from each other to form an auxiliary air intake channel.
5. The air preheater for increasing the air inlet sidewall temperature according to claim 4, characterized in that, The inner end of the first heat insulation plate is provided with auxiliary heat insulation teeth, which are attached to the inner sidewall of the first thin plate. An avoidance opening is formed between two adjacent auxiliary heat insulation teeth, and the welding column between the first thin plate and the second thin plate is located in the avoidance opening.
6. The air preheater for increasing the air inlet sidewall temperature according to claim 1, characterized in that, The heat insulation element includes a first heat insulation plate and a second heat insulation plate. The first heat insulation plate is separated from the first thin plate, and the second heat insulation plate is separated from the second thin plate. Through holes are provided on the first heat insulation plate and the second heat insulation plate.
7. The air preheater for increasing the air inlet sidewall temperature according to claim 6, characterized in that, The inner diameter of the through hole increases along the direction of cold air flow.
8. The air preheater for increasing the air inlet sidewall temperature according to claim 4 or 6, characterized in that, The air inlet end of the first heat insulation plate is integrally formed with the air inlet end of the first thin plate, and the air inlet end of the second heat insulation plate is integrally formed with the air inlet end of the second thin plate.
9. The air preheater for increasing the air inlet sidewall temperature according to claim 4 or 6, characterized in that, The first heat insulation plate has a first folded edge at its air inlet end, and the second heat insulation plate has a second folded edge at its air inlet end. The first folded edge is welded to the air inlet end of the first thin plate, and the second folded edge is welded to the air inlet end of the second thin plate.
10. The air preheater for increasing the air inlet sidewall temperature according to claim 1, characterized in that, The heat insulation element is an enamel coating, which is attached to the air inlet end of the first and second thin plates, and the enamel coating is located in the air channel to reduce the amount of heat exchange between the heat exchange plate and the air in the air channel.