A combined air preheater system

Abstract

The application discloses a composite air preheater system, belongs to the technical field of boiler tail heat exchange equipment of coal-fired power plant, and solves the problems of abrasion, corrosion and blockage of heating surface caused by adhesion and deposition of liquid ammonium bisulfate of heat exchange plate, and the technical scheme for solving the problems mainly comprises a rotary air preheater, a heat exchanger, a flue gas pipeline and an air pipeline, the heat exchanger comprises heat exchange plates and a third flue gas passage, the heat exchange plate comprises two thin plates and an air passage between the two thin plates, the flue gas pipeline comprises a first flue gas passage and a second flue gas passage, an auxiliary flue gas passage is arranged between the first flue gas passage and the second flue gas passage, the second flue gas passage is provided with a first guide plate, and the first guide plate is arranged in an inclined mode, so that the flue gas amount entering the air inlet end of the heat exchanger of the third flue gas passage is increased. The application mainly prevents liquefaction, adhesion and deposition of ammonium bisulfate, reduces the possibility of ash deposition, blockage, corrosion and abrasion of the heating surface of the heat exchange plate, and further improves the heat exchange efficiency and service life.

Description

Technical Field

[0001] This invention relates to the technical field of heat exchange equipment at the tail end of coal-fired power plant boilers, and in particular to a composite air preheater system. Background Technology

[0002] As a crucial heat exchange device at the tail end of a coal-fired power plant boiler, the air preheater's operating condition directly impacts the unit's economy and safety. While existing technologies combining rotary air preheaters and tubular heat exchangers can improve heat exchange efficiency, they still face a serious problem of ammonium bisulfate ash accumulation. This issue primarily stems from the reaction of ammonia escaping during selective catalytic reduction (SCR) denitrification with flue gas components to form ammonium bisulfate. This substance forms a viscous liquid state at temperatures between 150-200°C, readily adhering to the heated surfaces of heat exchange elements and forming an ash layer.

[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 cold air inlet areas, 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. Particularly in the inlet section of the heat exchange plates, the largest temperature difference upon initial contact with the cold air makes it easier for localized low-temperature zones to form, exacerbating the problem of ammonium bisulfate liquefaction and deposition. Summary of the Invention

[0005] The objective of this invention is to provide a composite air preheater system that solves the problem of wear, corrosion, and blockage of the heat exchange plate's heating surface caused by the adhesion and accumulation of ash from liquid ammonium bisulfate at the junction of the flue gas outlet area and the cold air inlet area. This effectively prevents the liquefaction, adhesion, and deposition of ammonium bisulfate, reduces ash accumulation, and thus lowers the possibility of blockage, corrosion, and wear on the heat exchange plate's heating surface, thereby improving heat exchange efficiency and service life.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a composite air preheater system, comprising a rotary air preheater, a heat exchanger, a flue gas duct, and an air duct. The heat exchanger includes multiple heat exchange plates arranged side by side, with adjacent heat exchange plates spaced apart. Each heat exchange plate includes two thin plates welded together side by side, the welding position of the two thin plates forming a welded column, and the unwelded portions forming an air passage away from each other. The flue gas duct includes a first flue gas passage communicating with the flue gas inlet of the rotary air preheater and a second flue gas passage for conveying flue gas from the rotary air preheater to the heat exchanger. A passage for conveying the first flue gas is provided between the first flue gas passage and the second flue gas passage. High-temperature flue gas in the channel is introduced into the auxiliary flue gas channel in the second flue gas channel. Two adjacent thin plates are welded together at both ends of the air channel between two adjacent heat exchange plates to form a third flue gas channel between the two adjacent heat exchange plates. The second flue gas channel is provided with a first guide plate that divides the second flue gas channel into multiple sub-channels at the end away from the heat exchanger. The first guide plate is inclined relative to the axial direction of the second flue gas channel to guide part of the flue gas in the second flue gas channel to the area near the air inlet end of the heat exchanger, so that the amount of flue gas entering the area at the air inlet end of the heat exchanger is greater than the amount of flue gas entering the rear end of the connection between the third flue gas channel and the heat exchanger.

[0007] Using the aforementioned technical solution, after the high-temperature flue gas enters the rotary air preheater through the first flue gas channel, it exchanges heat with the air inside the rotary air preheater, causing the flue gas temperature to drop. The relatively high-temperature flue gas then enters the heat exchanger through the second flue gas channel to exchange heat with the cooler air, thus performing secondary heat exchange on the flue gas, transferring as much heat as possible from the flue gas and improving the heat exchange efficiency of the composite air preheater system. During the process of the flue gas entering the second flue gas channel from the rotary air preheater, the flue gas, under the action of the second guide plate, enters different sub-channels. The sub-channel with a larger inlet receives a relatively larger amount of flue gas. Under the guidance of the second guide plate, a larger amount of flue gas is guided towards the air inlet area of ​​the heat exchanger, resulting in more flue gas entering the air inlet of the heat exchanger. By increasing the amount of flue gas at the air inlet of the heat exchanger, the temperature drop after heat exchange between the flue gas and air is reduced. This ensures that the temperature of the flue gas at the air inlet after heat exchange is higher than the liquefaction temperature of ammonium bisulfate, thus preventing ammonium bisulfate from liquefying and adhering to the heated surface of the air inlet of the heat exchanger, which could cause blockage of the flue gas passage, corrosion, and wear of the heated surface. If the air inlet of the heat exchanger is blocked, the high-temperature flue gas in the first passage is directly introduced into the second flue gas passage through an auxiliary flue gas passage, and then flows into the third flue gas passage through the second flue gas passage. This increases the temperature in the third flue gas passage, cleaning the ammonium bisulfate adhering to the heated surface of the heat exchanger, and preventing the third flue gas passage from being blocked, which would affect the heat exchange between the flue gas and air.

[0008] Furthermore, the connection between the auxiliary flue gas passage and the second flue gas passage is located below the tail end of the first guide plate and on the side of the second flue gas passage facing the air inlet end of the air passage.

[0009] Furthermore, the auxiliary flue gas passage is equipped with a control switch for controlling the opening and closing of the auxiliary flue gas passage.

[0010] Furthermore, the exhaust port of the auxiliary flue gas channel is provided with a second guide plate, which extends inclined toward the heat exchanger.

[0011] Furthermore, the heat exchange plate has an air inlet section that first contacts the air, and the air inlet section is provided with heat-insulating elements to reduce the heat transfer efficiency of the air inlet section.

[0012] Furthermore, the heat-insulating element includes two heat-insulating components, which are correspondingly arranged with the two thin walls.

[0013] Furthermore, the heat-insulating component includes a heat-insulating plate, which is welded and fixed to the thin plate.

[0014] Furthermore, the length of the heat-insulating element in the airflow path direction gradually increases along the flue gas flow path direction.

[0015] As can be seen from the above, the composite air preheater system provided by the present invention optimizes the flue gas distribution and introduces high-temperature flue gas to regulate the temperature field by setting a second flue gas channel with an inclined first guide plate and an auxiliary flue gas channel. This effectively avoids the formation of a low-temperature zone at the junction of the cold air inlet area and the flue gas outlet, thereby inhibiting the liquefaction and deposition of ammonium bisulfate. It has the advantages of reducing the risk of ash accumulation, improving heat exchange efficiency and equipment operation stability. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a composite air preheater system according to the present invention; Figure 2 This is a schematic diagram of the heat exchanger in this invention; Figure 3 This is a schematic diagram of the heat exchange plate in this invention; Figure 4 This is a schematic diagram of the installation of the first guide plate in this invention; Figure 5 This is a schematic diagram of multiple first guide vanes in this invention; Figure 6 This is a schematic diagram of the heat-resistant element in this invention; Figure 7 This is a schematic diagram of the installation of the heat-resistant element in this invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0018] The terms "first," "second," etc. (if present) in the specification and claims of this invention 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 invention, "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. It should be understood that in this invention, "a plurality of" 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.

[0019] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The following specific embodiments may 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.

[0020] like Figure 1 As shown, the present invention provides a composite air preheater system, including a rotary air preheater 1, a heat exchanger 2, a flue gas duct 3, and an air duct 4. Figure 2 As shown, the heat exchanger 2 includes multiple heat exchange plates 21 arranged side by side, with adjacent heat exchange plates 21 spaced apart. Figure 2 and Figure 3As shown, the heat exchange plate 21 is composed of two thin plates 212 welded side by side. The welding position forms a welded column, which is a supporting structure formed after the two thin plates 212 are welded. Specifically, it can be formed by spot welding or continuous welding process. It is used to maintain the spacing of the air channel 213 and enhance the structural strength. The unwelded parts of the two thin plates 212 are far apart to form the air channel 213. Specifically, a high-pressure medium is passed between the two thin plates 212. Due to the lack of support, the unwelded parts of the two thin plates 212 are far apart to form a cavity under the pressure of the high-pressure medium. The cavity and the two ports on the two thin plates 212 that are connected to the cavity form the air channel 213. The air channel 213 is connected to the air pipe 4. Two adjacent thin plates 212 of two adjacent heat exchange plates 21 are welded together at both ends of the air channel 213 to form a third flue gas channel 211 between the two adjacent heat exchange plates 21. Specifically, the two adjacent thin plates 212 between the two adjacent heat exchange plates 21 are welded and fixed at both ends in the air flow direction within the air channel 213, so that a third flue gas channel 211 perpendicular to the air channel 213 is formed between the two adjacent heat exchange plates 21. The third flue gas channel 211 is connected to the flue gas pipe 3. During the heat exchange process, air enters the air channel 213 from the front end of the air pipe 4, and flue gas enters the third flue gas channel 211 from the flue gas pipe 3. The flue gas and air flow independently between the two thin plates 212. During the flow, heat exchange occurs under the heat conduction of the thin plates 212, causing the air temperature to rise and the flue gas temperature to fall. This transfers the heat in the flue gas to the air for storage and use, reduces the heat loss in the flue gas, and improves the heat utilization rate after coal combustion.

[0021] In this embodiment, as Figure 1 and Figure 4As shown, the flue gas duct 3 includes a first flue gas passage 31 connected to the flue gas inlet of the rotary air preheater 1 and a second flue gas passage 32 that supplies flue gas from the rotary air preheater 1 to the heat exchanger 2. The high-temperature flue gas first enters the rotary air preheater 1 through the first flue gas passage 31 and exchanges heat with the air in the rotary air preheater 1. After heat exchange in the rotary air preheater 1, the flue gas enters the heat exchanger 2 through the second flue gas passage 32 and exchanges heat with the air in the heat exchanger 2 again. This two-stage heat exchange improves heat recovery in the flue gas and further reduces heat loss. Specifically, the end of the second flue gas passage 32 furthest from the heat exchanger 2 is equipped with... A first guide plate 321 divides the inlet end of the second flue gas passage 32 into multiple sub-passages. The first guide plate 321 is inclined relative to the axial direction of the second flue gas passage 32. Specifically, in this embodiment, there is only one first guide plate 321. The first guide plate 321 divides the inlet end of the second flue gas passage 32 into a first sub-passage 3211 and a second sub-passage 3212 distributed along the air flow path direction in the air passage 213. The first sub-passage 3211 is close to the colder section of the heat exchanger 2. The first guide plate 321 is inclined relative to the axial direction of the second flue gas passage 32 to divide the second flue gas passage 32 into multiple sub-passages. The flue gas inside the air passage 32 is guided towards the area near the air inlet of the heat exchanger 2, so that the amount of flue gas entering the area near the air inlet of the heat exchanger 2 is greater than the amount of flue gas entering the rear end of the connection between the third flue gas passage 211 and the heat exchanger 2; specifically, the first sub-passage 3211 is arranged in a shape with a large inlet and a small outlet in the flue gas flow direction, and the inlet of the first sub-passage 3211 is larger than the inlet of the second sub-passage 3212; when the flue gas enters the second flue gas passage 32 from the outlet of the rotary air preheater 1, the flue gas is divided into two parts under the action of the first guide plate 321, due to the first sub-passage 3211 The inlet is larger, and more flue gas enters the first sub-channel 3211 than the second sub-channel 3212. Under the guidance of the first guide plate 321 towards the air inlet of the heat exchanger 2, a larger portion of the flue gas in the first sub-channel 3211 enters the air inlet of the heat exchanger 2. More flue gas exchanges heat with the air in the air inlet. Under the same heat loss, the flue gas temperature at the air inlet of the air channel 213 drops less, thus ensuring that the temperature of the flue gas at the colder end of the heat exchanger 2 is not lower than the liquefaction temperature of ammonium bisulfate, thereby reducing the accumulation of ash on the heated surface of the colder end of the heat exchanger 2. Specifically, the first guide plate 321 can be made of a steel plate at an acute angle to the axis of the second flue gas channel 32. The tilt angle of the second guide plate 332 is used to change the cross-sectional change rate of the sub-channel, thereby adjusting the amount of flue gas entering the air inlet of the air channel 213, and further ensuring that the temperature of the flue gas exchanging heat with the air inlet of the air channel 213 is higher than the liquefaction temperature of ammonium bisulfate after heat exchange.

[0022] In the above embodiments, further, such as Figure 1 and Figure 5As shown, multiple first guide plates 321 are provided, which divide the air inlet of the second flue gas passage 32 into multiple sub-channels. The width of the flue gas inlet of the multiple sub-channels gradually decreases along the air flow path in the air passage 213. Specifically, there are three first guide plates 321, namely a first plate 3201, a second plate 3202, and a third plate 3203 distributed along the air flow direction in the air passage 213. The three first guide plates 321 divide the air inlet of the second flue gas passage 32 into a first sub-channel 3211, a second sub-channel 3212, a third sub-channel 3213, and a fourth sub-channel. Channel 3214, the first sub-channel 3211, the second sub-channel 3212, the third sub-channel 3213 and the fourth sub-channel 3214 are distributed along the air flow direction in the air channel 213, and the width of the first sub-channel 3211, the second sub-channel 3212, the third sub-channel 3213 and the fourth sub-channel 3214 gradually decreases in the air flow path; wherein, the first plate 3201 is inclined, so that the first sub-channel 3211 has a large inlet and a small outlet, and guides the flue gas in the first sub-channel 3211 to the air inlet area of ​​the heat exchanger 2, ensuring that more flue gas enters the colder end of the heat exchanger 2.

[0023] To further prevent dust accumulation on the heating surface of the colder end of heat exchanger 2, which could cause blockage, corrosion, and wear, such as... Figure 1 and Figure 5 As shown, an auxiliary flue gas channel 33 is provided between the first flue gas channel 31 and the second flue gas channel 32 to introduce the high-temperature flue gas in the first flue gas channel 31 into the second flue gas channel 32. Specifically, one end of the auxiliary flue gas channel 33 is connected to the first flue gas channel 31 and the other end is connected to the second flue gas channel 32. When ash accumulates on the heating surface of the colder end of the heat exchanger 2, to the point of blockage or wear, the high-temperature flue gas in the first flue gas channel 31 is directly introduced into the second flue gas channel 32 through the auxiliary flue gas channel 33. This allows the high-temperature flue gas in the first flue gas channel 31 to directly enter the heat exchanger 2 through the auxiliary flue gas channel 33 and the second flue gas channel 32 without heat exchange. The liquefied ammonium bisulfate turns into a gaseous state under the action of the high-temperature flue gas and leaves the heating surface of the heat exchanger 2 with the flow of flue gas, thus removing the ash accumulation on the heating surface of the heat exchanger 2 and effectively preventing blockage, wear and corrosion of the colder end of the heat exchanger 2 due to ash accumulation.

[0024] In this embodiment, as Figure 5As shown, the connection between the auxiliary flue gas passage 33 and the second flue gas passage 32 is located below the tail end of the first guide plate 321 and on the side of the second flue gas passage 32 facing the air inlet end of the air passage 213. "Below the tail end of the first guide plate 321" refers to the area downstream of the end of the first guide plate 321 in the flue gas flow direction. This position prevents the high-temperature flue gas entering the second flue gas passage 32 from impacting the first guide plate 321. "The side of the second flue gas passage 32 facing the air inlet end of the air passage 213" refers to the side wall area of ​​the second flue gas passage 32 near the cold air inlet direction. This can be achieved by opening a connection port on the side wall of the second flue gas passage 32. This position ensures that the high-temperature flue gas preferentially covers the low-temperature area at the inlet end of the air passage 213. This, in turn, ensures that the ash layer adhering to the heated surface of the colder end of the heat exchanger 2 can be treated. Specifically, when the high-temperature flue gas from the auxiliary flue gas passage 33 enters the second flue gas passage 32 through the connection, because the connection is located below the tail end of the first guide plate 321, the high-temperature flue gas is guided by the flow field formed by the inclination of the first guide plate 321 to the low-temperature convergence area near the air inlet end of the air passage 213. At the same time, the fact that the connection is located on the side of the air inlet end of the air passage 213 allows the high-temperature flue gas to diffuse along the side wall of the second flue gas passage 32 towards the cold air inlet, thereby expanding the coverage of the low-temperature area. This allows the high-temperature flue gas to accurately raise the temperature of the easily liquefied area of ​​ammonium bisulfate above the liquefaction critical point, preventing liquid ammonium bisulfate from adhering to the surface of the heat exchange plate 21.

[0025] To facilitate control of the auxiliary flue gas passage 33, such as Figure 5 As shown, to ensure that high-temperature flue gas only enters the heat exchanger 2 when needed, a control switch 331 is provided on the auxiliary flue gas channel 33 to control the opening and closing of the auxiliary flue gas channel 33. By setting the control switch 331, when a layer of ash accumulates on the heated surface of the colder end of the heat exchanger 2, the control switch 331 on the auxiliary flue gas channel 33 is opened, allowing the high-temperature flue gas in the first flue gas channel 31 to directly enter the second flue gas channel 32 from the auxiliary flue gas channel 33, and then enter the colder end of the heat exchanger 2, causing the ammonium bisulfate adhering to the heated surface to change from liquid to gaseous, and to detach from the heated surface of the heat exchanger 2 with the flow of flue gas. The setting of the control switch 331 also reduces the possibility of high-temperature flue gas continuously entering the heat exchanger 2 and increasing heat loss.

[0026] In another embodiment, such as Figure 5As shown, to ensure that the high-temperature flue gas in the auxiliary flue gas passage 33 can cover more of the colder end of the heat exchanger 2, a second guide plate 332 is provided at the outlet of the auxiliary flue gas passage 33. The second guide plate 332 extends inclined towards the heat exchanger 2. Specifically, the second guide plate 332 can be made of high-temperature resistant alloy steel plate, and its inclination angle can be adjusted according to the flue gas flow rate and the internal flow field distribution of the heat exchanger 2. The second guide plate 332 is used to constrain the flow direction of the high-temperature flue gas. The inclination of the second guide plate 332 towards the heat exchanger 2 means that the second guide plate 332 forms a non-perpendicular angle with the outlet axis of the auxiliary flue gas passage 33. Specifically, it can be installed at an inclination angle of 30° to 60°, so that the high-temperature flue gas enters the second flue gas passage 32 along a predetermined path and then enters the colder end of the heat exchanger 2, thereby increasing the overall temperature level of the colder end of the heat exchanger 2. This keeps the temperature of the area where the colder end of the heat exchanger 2 meets the flue gas outlet above the critical temperature for the liquefaction of ammonium bisulfate, significantly reducing the formation of viscous deposits.

[0027] In this embodiment, as Figure 5 As shown, multiple second guide plates 332 are spaced apart, and all of them are inclined. The inclination angle of the multiple second guide plates 332 gradually increases as they approach the heat exchanger 2. By setting multiple second guide plates 332 with different inclination angles, the flue gas flow direction in the sub-auxiliary channel formed between adjacent second guide plates 332 is deviated to a certain extent, which increases the distribution range of high-temperature flue gas in the air channel 213, so as to clean the ash layer on the heat exchanger 2 heating surface over a larger area.

[0028] To further reduce the possibility of dust accumulation on the heating surface of heat exchanger 2, such as Figure 2 and Figure 6As shown, the heat exchange plate 21 has an air inlet section that first contacts the air. A heat-insulating element 22 is provided on the air inlet section to reduce its heat transfer efficiency. Specifically, the air inlet section refers to the initial area of ​​the heat exchange plate 21 where it first contacts the cold air. This area is located at the front end of the heat exchange plate 21 in the airflow path direction. This can be achieved by dividing the first 10% to 30% of the length of the heat exchange plate 21 into an air inlet section. The heat-insulating element 22 is a component that reduces heat conduction efficiency through material or structural design. Specifically, it can be implemented using a heat-insulating plate, a heat-insulating coating, or a low thermal conductivity composite material. The heat-insulating element 22 is disposed on the thin plate 212 of the air inlet section to reduce heat transfer in this area and prevent a rapid drop in the metal surface temperature. When cold air enters the heat exchange plate 21 from the air duct 4, it first flows through the air inlet section. Due to the presence of the heat-insulating element 22, heat transfer in this area is suppressed, reducing the heat absorbed by the cold air and preventing the metal surface temperature of the air inlet section from dropping below the critical temperature for ammonium bisulfate liquefaction due to rapid heat absorption by the cold air. By adjusting the thermal conductivity of the heat-insulating element 22, the temperature of the intake section can be maintained above 150°C, thereby preventing ammonium bisulfate from liquefying and adhering in this area.

[0029] In this embodiment, the heat-insulating element 22 includes two heat-insulating components, which are correspondingly arranged with the two thin plates 212. In the initial contact section of the airflow path, cold air simultaneously contacts both thin plates 212. The arrangement of the heat-insulating components on both sides makes the temperature drop rate of the two thin plates 212 tend to be consistent, avoiding local low-temperature areas caused by a sudden drop in temperature on one side. Furthermore, the heat-insulating component includes a heat-insulating plate, which is welded and fixed to the thin plate 212. The heat-insulating plate can be made of a high-temperature resistant alloy material to increase the thermal resistance between the flue gas and the air. The heat-insulating plate and the thin plate 212 are connected by welding, which can be achieved by laser welding or arc welding processes. A continuous connection interface is formed through metallurgical bonding, eliminating contact thermal resistance.

[0030] In another embodiment, such as Figure 7 As shown, the length of the heat-insulating element 22 in the airflow path direction gradually increases along the flue gas flow path direction. When the flue gas flows in the third flue gas channel 211, the temperature of the flue gas gradually decreases as the flue gas exchanges heat with the air. The temperature of the air that exchanges heat with the flue gas at the tail end of the third flue gas channel 211 is also lower than that at the inlet of the third flue gas channel 211. Therefore, the temperature of the flue gas decreases significantly as the flue gas flows. By setting the size of the airflow path of the heat-insulating element 22 in the air channel 213 to gradually increase along the direction of the third flue gas channel 211, the heat exchange efficiency of the flue gas at the tail end of the third flue gas channel 211 is reduced, thereby avoiding the formation of a dust accumulation layer on the heated surface of the heat exchanger 2 at the tail end of the third flue gas channel 211.

[0031] In addition to the preferred embodiments described above, the present invention has other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection claimed by the present invention.

Claims

1. A composite air preheater system, comprising a rotary air preheater, a heat exchanger, a flue gas duct, and an air duct, wherein the heat exchanger comprises a plurality of heat exchange plates arranged side by side, with adjacent heat exchange plates spaced apart, each heat exchange plate comprising two thin plates welded together side by side, the welded portion of the two thin plates forming a welded column, and the unwelded portions forming an air passage away from each other; the flue gas duct comprises a first flue gas passage communicating with the flue gas inlet of the rotary air preheater and a second flue gas passage for conveying flue gas from the rotary air preheater to the heat exchanger; an auxiliary flue gas passage is provided between the first and second flue gas passages to introduce high-temperature flue gas from the first flue gas passage into the second flue gas passage; adjacent thin plates of adjacent heat exchange plates are welded together at both ends of the air passage to form a third flue gas passage between adjacent heat exchange plates, characterized in that... The second flue gas passage is provided with a first guide plate at the end away from the heat exchanger, which divides the second flue gas passage into multiple sub-passes. The first guide plate is inclined relative to the axial direction of the second flue gas passage to guide part of the flue gas in the second flue gas passage toward the area near the air inlet end of the heat exchanger, so that the amount of flue gas entering the area at the air inlet end of the heat exchanger is greater than the amount of flue gas entering the rear end of the connection between the third flue gas passage and the heat exchanger. The auxiliary flue gas passage is provided with a second guide plate at the flue gas outlet, which extends inclinedly toward the heat exchanger; multiple second guide plates are spaced apart, and all of them are inclined, with the inclination angle of the multiple second guide plates gradually increasing as they approach the heat exchanger; the heat exchange plate has an air inlet section that first contacts the air, and the air inlet section is provided with heat-insulating elements to reduce the heat transfer efficiency of the air inlet section.

2. The composite air preheater system according to claim 1, characterized in that, The connection between the auxiliary flue gas passage and the second flue gas passage is located below the tail end of the first guide plate and on the side of the second flue gas passage facing the air inlet end of the air passage.

3. The composite air preheater system according to claim 1, characterized in that, The auxiliary flue gas passage is equipped with a control switch to control the opening and closing of the auxiliary flue gas passage.

4. The composite air preheater system according to claim 1, characterized in that, The heat-resistant element includes two heat-resistant components, which are correspondingly arranged with two thin plates.

5. The composite air preheater system according to claim 4, characterized in that, The heat-insulating component includes a heat-insulating plate, which is welded and fixed to a thin plate.

6. The composite air preheater system according to claim 1, characterized in that, The length of the heat-insulating element gradually increases along the airflow path.

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