A method and system for efficient use of energy cascade of an air preheater

Abstract

This invention discloses a method and system for efficient energy cascade utilization of an air preheater. The method involves dividing the outlet flue into a high-energy irregular-shaped flue gas channel and a low-energy irregular-shaped flue gas channel; extending the high-energy and low-energy irregular-shaped flue gas channels to form parallel high-energy rectangular flue gas outlet channels and low-energy rectangular flue gas outlet channels; the flue gas temperature in the high-energy irregular-shaped flue gas channel is higher than that in the low-energy irregular-shaped flue gas channel; the cross-section of the high-energy irregular-shaped flue gas channel is 3%-12% larger than that of the low-energy irregular-shaped flue gas channel; the high-energy rectangular flue gas outlet channel is adjacent to the inlet of the cold secondary air duct; the two ends of a heat pipe heat exchanger are respectively arranged in the cold secondary air inlet channel and the high-energy rectangular flue gas outlet channel, recovering the heat from the flue gas in the high-energy flue gas outlet channel and heating the cold secondary air, preventing blockage, improving the utilization efficiency of waste heat from the flue gas, and requiring no external heat exchange medium, making it simple and efficient.

Description

Technical Field

[0001] This invention relates to a method and system for efficient energy utilization in an air preheater, belonging to the technical field of air preheater ash blockage treatment and boiler tail flue gas waste heat utilization. Background Technology

[0002] A rotary air preheater (hereinafter referred to as "air preheater") is a heat exchange device used in large power plant boilers. It utilizes the heat of boiler flue gas to heat the air required for combustion, thereby improving boiler efficiency. Key issues concerning air preheaters include ash blockage, high air leakage rate, low heat transfer efficiency, and severe low-temperature corrosion. These problems have long affected the safe and economical operation of air preheaters and the entire boiler system.

[0003] The aforementioned problems have existed for a long time and are mutually reinforcing and influential. In recent years, with the widespread operation of denitrification systems, the operating environment of air preheaters has changed, making the aforementioned ash blockage problem particularly prominent, and difficult and complex to manage.

[0004] Currently, the flue gas denitrification facilities added to coal-fired power plants mainly utilize selective catalytic reduction (SCR) technology. After adopting SCR denitrification, some SO2 in the flue gas is oxidized to SO3 by the denitrification catalyst, increasing the volume concentration of SO3 in the flue gas. Coupled with the unavoidable ammonia escape, this leads to the large-scale generation of byproducts such as ammonium bisulfate (NH4HSO4), and also raises the flue gas acid dew point temperature, resulting in accelerated low-temperature corrosion and exacerbating ash accumulation and blockage problems in the air preheater. To alleviate the air preheater ash blockage problem, many coal-fired power plants have adopted various modification measures to reduce heat transfer efficiency in order to increase the exhaust gas temperature, resulting in a significant decrease in furnace efficiency.

[0005] To address the issues of ash accumulation and blockage in air preheaters, Chinese patents 202111005642.7 and 202111005676.6 have disclosed methods for removing ammonium bisulfate, sulfuric acid, and fly ash adhering to the surface of the heat storage elements in air preheaters through periodic ring-by-ring heating and dry burning. In practice, these methods have proven effective in resolving the ash accumulation and blockage problems in air preheaters.

[0006] Due to the rotating structure of the air preheater, the exhaust gas temperature at the flue gas outlet of the actual air preheater is extremely uneven, which to some extent results in a low heat transfer efficiency of the air preheater and is not conducive to fully tapping the energy-saving potential of the air preheater. Summary of the Invention

[0007] To address the corrosion and blockage issues of the low-temperature economizer downstream of the air preheater outlet in existing technologies, and to improve the operational safety and reduce costs of the boiler tail heating surface, this invention provides a method and system for efficient energy cascade utilization of air preheaters. Applicable to the efficient energy cascade utilization of reverse-rotation air preheaters, this invention combines the structure and principle of ring-type temperature rise and blockage prevention in air preheaters with the rotation and heat exchange characteristics of rotary air preheaters. The flue gas outlet duct on the flue gas side is irregularly divided, converging the high-temperature flue gas from the air preheater outlet into a high-efficiency flue gas channel, while the remaining relatively lower-temperature flue gas converges into a low-efficiency flue gas channel. Heat pipe heat exchangers are installed in the high-efficiency outlet flue gas duct and the cold secondary air channel to achieve efficient energy recovery and utilization. Furthermore, the system can dynamically adjust the flue gas temperature at the inlet of the heat pipe heat exchanger through the ring-type blockage prevention function, which not only improves heat exchange efficiency but also prevents corrosion and blockage of the heat pipe heat exchanger.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for efficient energy cascade utilization of an air preheater involves dividing the outlet flue into two irregularly shaped flue gas channels—a high-energy irregularly shaped flue gas channel and a low-energy irregularly shaped flue gas channel—through a flue gas circumferential partition plate and a flue gas radial partition plate. The high-energy irregularly shaped flue gas channel and the low-energy irregularly shaped flue gas channel extend downward through an intermediate flue transition partition plate, forming a parallel arrangement of a high-energy rectangular flue gas outlet channel and a low-energy rectangular flue gas outlet channel. The flue gas temperature in high-energy irregular flue gas channels is higher than that in low-energy irregular flue gas channels; the cross-section of high-energy irregular flue gas channels is 3%-12% larger than that of low-energy irregular flue gas channels; The high-energy flue gas rectangular outlet channel is adjacent to the cold secondary air inlet. The two ends of the heat pipe heat exchanger are respectively arranged in the cold secondary air inlet channel and the high-energy flue rectangular outlet channel. The heat of the flue gas in the high-energy flue gas outlet channel is recovered and heated to heat the cold secondary air, preventing blockage and improving the utilization efficiency of flue gas waste heat. No external heat exchange medium is required.

[0009] The above methods can ensure the safe and normal operation of the tail flue equipment and can, to a certain extent, replace the low-temperature economizer.

[0010] To further improve heat utilization, one end of the heat pipe heat exchanger is arranged in the cold secondary air inlet channel, and the other end is arranged in the high-energy flue rectangular outlet channel. The end of the heat pipe heat exchanger in the cold secondary air inlet channel is higher than the end in the high-energy flue rectangular outlet channel. The heat pipe heat exchanger forms an angle of 3-10° with the horizontal plane, thereby improving energy utilization and efficiency.

[0011] A system for efficient energy cascade utilization of an air preheater includes an air preheater. In the outlet flue gas passage at the bottom of the cold end of the air preheater rotor, a flue gas circumferential partition plate and a flue gas radial partition plate are installed to divide the outlet flue gas passage into two irregularly shaped flue gas passages: a high-energy irregularly shaped flue gas passage and a low-energy irregularly shaped flue gas passage. The two sides of the outlet flue gas passage in the circumferential direction are defined as the upstream flue gas side and the downstream flue gas side, respectively, with the direction from the upstream flue gas side to the downstream flue gas side consistent with the rotor's rotation direction. Part or all of the flue gas passages inside the flue gas circumferential partition plate and the flue gas passages on the downstream side of the flue gas radial partition plate are merged to form the high-energy irregularly shaped flue gas passage. The remaining flue gas passages are merged to form the low-energy irregularly shaped flue gas passage. The high-energy irregular flue gas channel and the low-energy irregular flue gas channel extend downward through the intermediate flue transition partition plate, forming a parallel arrangement of high-energy flue gas rectangular outlet channel and low-energy flue gas rectangular outlet channel. It also includes a heat pipe heat exchanger, and the high-energy flue gas rectangular outlet channel is adjacent to the cold secondary air inlet. The two ends of the heat pipe heat exchanger are respectively arranged in the cold secondary air inlet channel and the high-energy flue rectangular outlet channel; one end of the heat pipe heat exchanger is arranged in the cold secondary air inlet channel and the other end is arranged in the high-energy flue rectangular outlet channel, and the end of the heat pipe heat exchanger in the cold secondary air inlet channel is higher than the end in the high-energy flue rectangular outlet channel. The upper edge of the flue gas radial partition plate is provided with a radial sealing structure; The cross-section of high-energy irregular flue gas channels is 3%-12% larger than that of low-energy irregular flue gas channels.

[0012] The cross-section of the aforementioned high-energy irregular flue gas channel is 3%-12% larger than that of the low-energy irregular flue gas channel, which can balance the flue gas volume on both sides and achieve self-balancing. This ensures balanced heat exchange, avoids localized low-temperature corrosion and ash blockage, reduces uneven wear of air preheater components, and simultaneously guarantees the stability and safety of downstream equipment operation.

[0013] The aforementioned inclined arrangement of heat pipes in the cold secondary air inlet channel and the rectangular outlet channel of the high-energy flue allows the medium within the heat pipes to flow downwards after condensation and upwards after heating, thus fully utilizing the heat of the high-energy flue gas. This method is simple, convenient, requires no external medium, and is low-cost. Simultaneously, a radial sealing structure is installed at the top of the flue gas radial partition plate to reduce or avoid energy flow losses, further improving energy utilization.

[0014] The aforementioned air preheater is a rotary air preheater.

[0015] Further optimization shows that the cross-section of the high-energy irregular flue gas channel is 6%-9% larger than that of the low-energy irregular flue gas channel.

[0016] To further improve the utilization rate of thermal energy, the heat pipe heat exchanger is at an angle of 3-10° to the horizontal plane.

[0017] In order to further ensure the effectiveness of the ring-type blockage control function, the bottom of the cold end of the air preheater rotor is divided into three concentric ring structures with equal area by one or more rotor circumferential separation seals. In the cold secondary air inlet duct at the bottom of the cold end of the air preheater rotor, a cold secondary air circumferential partition plate is installed, which is opposite to the circumferential separation seal of each rotor, dividing the cold secondary air inlet duct into three concentric rings. In the cold secondary air inlet duct, each ring gradually transitions downwards to a rectangular inlet of equal area. Each rectangular inlet is equipped with a cold secondary air volume regulating damper. By periodically circulating and reducing or isolating the air volume of each ring, the heat storage element in the corresponding ring is prevented from clogging. One end of the heat pipe heat exchanger is located in the cold secondary air inlet channel below the cold secondary air volume regulating valve.

[0018] In order to reduce energy loss and improve the blockage relief effect, circumferential sealing structures are respectively provided on the upper edge of the flue gas circumferential partition plate and the cold secondary air circumferential partition plate. The innermost rotor circumferential separator seal is the rotor inner ring separator seal; The rotor inner ring separator seal and the circumferential seal structure on the flue gas circumferential separator plate are opposite each other but not connected together; instead, they form a dynamic sealing pair. Each rotor's circumferential partition seal is positioned vertically opposite to the circumferential sealing structure of each cold secondary air circumferential partition plate, but they are not connected together; instead, they form a dynamic sealing pair. This scheme combines all the flue gas passages of the innermost ring and some flue gas passages in other rings downstream of the rotor's rotation direction into a high-energy irregular-shaped flue gas passage; the remaining flue gas passages are combined into a low-energy irregular-shaped flue gas passage.

[0019] As a specific implementation scheme, the flue gas radial partition plate is set radially along the outside of the inner ring partition seal on the cold end face of the rotor, and the included angle between the flue gas radial partition plate and the downstream flue gas side is 35~45°.

[0020] One end of the flue gas circumferential partition plate starts from the upstream flue gas side, and the other end connects to the flue gas radial partition plate. After the flue gas circumferential partition plate and the flue gas radial partition plate are connected, a dividing boundary is formed, which divides the outlet flue into a high-energy irregular flue gas channel and a low-energy irregular flue gas channel. The high-energy irregular flue gas channel and the low-energy irregular flue gas channel gradually transition from top to bottom, forming a parallel arrangement of a high-energy flue gas rectangular outlet channel and a low-energy flue gas rectangular outlet channel. The high-energy irregular flue gas channel is formed by splicing together a flue gas annular partition plate, a flue gas radial partition plate, and an outlet flue gas channel on the downstream flue gas side. The low-energy irregular flue gas channel is formed by splicing together a flue gas annular partition plate, a flue gas radial partition plate, and an outlet flue gas channel on the upstream flue gas side.

[0021] To improve sealing performance and energy efficiency, the cross-section of the radial sealing structure is fan-shaped or trapezoidal.

[0022] To ensure the stability and safety of downstream equipment operation, the cross-sections of the high-energy flue gas rectangular outlet channel and the low-energy flue gas rectangular outlet channel are equal.

[0023] Unless otherwise specified, the term "section" in this application generally refers to the cross section.

[0024] To further improve heat utilization and anti-clogging effect, the heating end of the heat pipe heat exchanger is arranged along the entire cross-section of the rectangular outlet channel of the high-energy flue, and the condensing end of the heat pipe heat exchanger is arranged along the entire cross-section of the cold secondary air inlet channel.

[0025] The directional terms used in this application, such as up and down, left and right, top and bottom, inside and outside, are based on the relative positions shown in the attached drawings and are used for ease of description and understanding. They should not be construed as limitations on this application.

[0026] This invention relates to a method and system for efficient energy cascade utilization of a reversible air preheater. Combining the structure and principle of the air preheater's ring-type anti-clogging mechanism, and the rotation and heat exchange characteristics of a rotary air preheater, the flue gas outlet duct of the air preheater is irregularly divided. The high-temperature flue gas from the air preheater outlet is gathered into a high-efficiency flue gas channel, and heat pipe heat exchangers are installed in both the high-energy flue gas channel and the cold secondary air inlet channel to further utilize the waste heat of the high-energy flue gas. The remaining relatively low-temperature flue gas is gathered into a low-efficiency flue gas channel, without waste heat utilization, and directly flows to the dust collector. To balance the resistance and flow rate of the high-temperature and low-temperature flue gas channels, the cross-sectional area of ​​the high-energy irregularly shaped flue gas channel is preferably slightly larger than that of the low-energy irregularly shaped flue gas channel. The system can also increase the inlet flue gas temperature of the dynamic heat pipe heat exchanger by approximately 50°C through the operation of the ring-type anti-clogging function, simultaneously meeting the requirements of centralized heat exchange to improve energy utilization efficiency and tail-end heat exchange to prevent low-temperature corrosion and clogging.

[0027] Any techniques not mentioned in this invention are based on existing technologies.

[0028] This invention relates to a method and system for efficient energy cascade utilization of air preheaters. It classifies and rationally utilizes the waste heat from the flue gas at the air preheater outlet. By adding a heat pipe heat exchanger, it recovers the heat from the high-energy flue gas outlet channel and heats the cold secondary air. This not only improves the utilization efficiency of waste heat and ensures the safe and normal operation of the tail flue equipment, but also, to a certain extent, can replace the low-temperature economizer, saving initial investment and maintenance costs. Furthermore, it also features an online loop-based anti-clogging function for the air preheater. The structure is compact, the modification is simple, and through flexible control, it can adapt to any operating condition. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the air preheater system for efficient energy cascade utilization according to the present invention.

[0030] Figure 2 This is a front view cross-sectional view of the system for efficient energy cascade utilization of the air preheater according to the present invention.

[0031] Figure 3 This is a schematic diagram of the structure of the air preheater rotor cold secondary air inlet duct ring and flue gas outlet irregularly shaped partition channel in Example 1.

[0032] Figure 4 This is a three-dimensional structural diagram of the circumferential sealing surface of the cold secondary air inlet channel, the circumferential sealing surface of the flue gas outlet channel, and the radial sealing surface of the flue gas outlet channel in Example 1.

[0033] Figure 5 This is a three-dimensional structural diagram of the rectangular flue gas outlet channels at the cold end of the air preheater in Example 1, representing the high-energy and low-energy levels.

[0034] Figure 6 This is a top view of the rectangular flue gas outlet channels at the cold end of the air preheater in Example 1, representing the high-energy and low-energy levels.

[0035] Figure 7 This is a schematic diagram of the circumferentially separated sealing structure of the cold end face of the air preheater rotor in Example 1.

[0036] Figure 8 This is a front structural cross-sectional view of the circumferential sealing surface of the cold secondary air inlet channel and the circumferential sealing surface of the flue gas outlet channel in Example 1.

[0037] Figure 9 This is a partial enlarged view of the structure of the circumferential separation sealing surface of the cold secondary air inlet channel and the circumferential separation sealing surface of the flue gas outlet channel in Example 1.

[0038] Figure 10This is a schematic diagram of the circumferential sealing surface of the cold secondary air inlet channel, the circumferential sealing surface of the flue gas outlet channel, and the radial sealing surface of the flue gas outlet channel in Example 5.

[0039] In the diagram, 1 is the air preheater rotor, 2 is the cold secondary air circumferential partition plate, 3 is the rotor circumferential partition seal, 4 is the flue gas circumferential partition plate, 5 is the flue gas radial partition plate, 6 is the intermediate transition partition plate, 7 is the high-energy irregular flue gas channel, 8 is the low-energy irregular flue gas channel, 9 is the high-energy flue gas rectangular outlet channel, 10 is the low-energy flue gas rectangular outlet channel, 11 is the heat pipe heat exchanger, 12 is the cold secondary air volume regulating valve, 13 is the ash hopper, 14 is the circumferential sealing structure, and 15 is the radial sealing structure. Detailed Implementation

[0040] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0041] The directional terms used in this application, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," are based on the orientation or positional relationship shown in the accompanying drawings or in the usage state, and are only for the convenience of describing this application. They are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application.

[0042] Example 1

[0043] like Figure 1-2 As shown, a system for efficient energy cascade utilization of an air preheater includes a rotary three-compartment air preheater. In the outlet flue gas passage at the bottom of the cold end of the air preheater rotor, a flue gas circumferential partition plate and a flue gas radial partition plate are installed, dividing the outlet flue gas passage into two irregularly shaped flue gas passages: a high-energy irregularly shaped flue gas passage and a low-energy irregularly shaped flue gas passage. The two sides of the outlet flue gas passage in the circumferential direction are defined as the upstream flue gas side and the downstream flue gas side, respectively, with the direction from the upstream flue gas side to the downstream flue gas side consistent with the rotor's rotation direction. Part or all of the flue gas passages inside the flue gas circumferential partition plate and the flue gas passages on the downstream side of the flue gas radial partition plate are merged to form the high-energy irregularly shaped flue gas passage. The remaining flue gas passages are merged to form the low-energy irregularly shaped flue gas passage. The flue gas temperature in the high-energy irregularly shaped flue gas passage is higher than the flue gas temperature in the low-energy irregularly shaped flue gas passage. The high-energy irregular flue gas channel and the low-energy irregular flue gas channel extend downward through the intermediate flue transition partition plate, forming a parallel arrangement of high-energy flue gas rectangular outlet channel and low-energy flue gas rectangular outlet channel. It also includes a heat pipe heat exchanger, and the high-energy flue gas rectangular outlet channel is adjacent to the cold secondary air inlet. The heat pipe heat exchanger is positioned at both ends in the cold secondary air inlet channel and the high-energy flue rectangular outlet channel, respectively. One end of the heat pipe heat exchanger is positioned in the cold secondary air inlet channel, and the other end is positioned in the high-energy flue rectangular outlet channel, with the end of the heat pipe heat exchanger in the cold secondary air inlet channel being higher than the end in the high-energy flue gas rectangular outlet channel. Through the heat pipe heat exchanger, the heat of the flue gas in the high-energy flue gas outlet channel is recovered and used to heat the cold secondary air, preventing blockage and improving the utilization efficiency of waste heat from the flue gas, without the need for an external heat exchange medium. This ensures the safe and normal operation of the tail flue equipment and can, to some extent, replace the low-temperature economizer. The upper edge of the flue gas radial partition plate is provided with a radial sealing structure; The cross-section of the high-energy irregular flue gas channel is 8% larger than that of the low-energy irregular flue gas channel (it can also be set to 6%, 9%, etc. as needed) to balance the flue gas volume on both sides and achieve self-balancing. This ensures balanced heat exchange, avoids local low-temperature corrosion and ash blockage, reduces uneven wear of air preheater components, and guarantees the stability and safety of downstream equipment operation.

[0044] The aforementioned inclined arrangement of heat pipes in the cold secondary air inlet channel and the rectangular outlet channel of the high-energy flue allows the medium within the heat pipes to flow downwards after condensation and upwards after heating, thus fully utilizing the heat of the high-energy flue gas. This method is simple, convenient, requires no external medium, and is low-cost. Simultaneously, a radial sealing structure is installed at the top of the flue gas radial partition plate to reduce or avoid energy flow losses, further improving energy utilization.

[0045] Example 2

[0046] Based on Example 1, the following improvements were made: In order to further improve the utilization rate of thermal energy, the heat pipe heat exchanger is at an 8° angle to the horizontal plane.

[0047] Example 3

[0048] Based on Example 2, the following improvements were made: Figure 2-9 As shown, in order to further take into account the effect of the ring-type blockage control function, the bottom of the cold end of the air preheater rotor is divided into three concentric rings with equal area by two rotor circumferential separation seals. In the cold secondary air inlet duct at the bottom of the cold end of the air preheater rotor, a cold secondary air circumferential partition plate is installed, which is opposite to the circumferential separation seal of each rotor, dividing the cold secondary air inlet duct into three concentric rings. In the cold secondary air inlet duct, each ring gradually transitions downwards to a rectangular inlet of equal area. Each rectangular inlet is equipped with a cold secondary air volume regulating damper. By periodically circulating and reducing or isolating the air volume of each ring, the heat storage element in the corresponding ring is prevented from clogging. One end of the heat pipe heat exchanger is arranged in the cold secondary air inlet channel below the cold secondary air volume regulating valve, and the other end is arranged in the high-energy flue rectangular outlet channel. The heating end of the heat pipe heat exchanger is arranged along the entire cross-section of the high-energy flue rectangular outlet channel, and the condensing end of the heat pipe heat exchanger is arranged along the entire cross-section of the cold secondary air inlet channel.

[0049] Example 4

[0050] Based on Example 3, the following improvements were further made: Figure 8-9 As shown, in order to reduce energy loss and improve the blockage relief effect, circumferential sealing structures are respectively provided on the upper edge of the flue gas circumferential partition plate and the cold secondary air circumferential partition plate. The innermost rotor circumferential separation seal is the rotor inner ring separation seal; the rotor inner ring separation seal and the circumferential sealing structure on the flue gas circumferential separation plate are opposite each other but not connected together, but form a dynamic sealing pair. Each rotor's circumferential partition seal is positioned vertically opposite to the circumferential sealing structure of each cold secondary air circumferential partition plate, but they are not connected together; instead, they form a dynamic sealing pair. This scheme combines all the flue gas passages of the innermost ring and some flue gas passages in other rings downstream of the rotor's rotation direction into a high-energy irregular-shaped flue gas passage; the remaining flue gas passages are combined into a low-energy irregular-shaped flue gas passage.

[0051] Example 5

[0052] Based on Example 4, the following improvements were made: Figure 3-4 As shown, the flue gas radial partition plate is arranged radially along the rotor outside the inner ring partition seal on the cold end face of the rotor, and the included angle between the flue gas radial partition plate and the downstream flue gas side is 45°.

[0053] One end of the flue gas circumferential partition plate starts from the upstream flue gas side, and the other end connects to the flue gas radial partition plate. After the flue gas circumferential partition plate and the flue gas radial partition plate are connected, a dividing boundary is formed, which divides the outlet flue into a high-energy irregular flue gas channel and a low-energy irregular flue gas channel. The high-energy irregular flue gas channel and the low-energy irregular flue gas channel gradually transition from top to bottom, forming a parallel arrangement of a high-energy flue gas rectangular outlet channel and a low-energy flue gas rectangular outlet channel. The high-energy irregular flue gas channel is formed by splicing together a flue gas annular partition plate, a flue gas radial partition plate, and an outlet flue gas channel on the downstream flue gas side. The low-energy irregular flue gas channel is formed by splicing together a flue gas annular partition plate, a flue gas radial partition plate, and an outlet flue gas channel on the upstream flue gas side.

[0054] To improve sealing performance and energy efficiency, the cross-section of the radial sealing structure is fan-shaped or trapezoidal, such as... Figure 10 As shown, in this example, it is a trapezoid.

[0055] To ensure the stability and safety of downstream equipment operation, the cross-sections of the high-energy flue gas rectangular outlet channel and the low-energy flue gas rectangular outlet channel are equal.

[0056] This solution, applied to two air preheaters in a 660MW coal-fired unit, utilizes heat pipe heat exchangers to recover heat from the high-energy flue gas outlet channel and reheat the cold secondary air. The temperature difference between the hot and cold ends of the air preheater (the temperature difference between the hot flue gas and the hot secondary air) is reduced from 32℃ to 16℃, lowering coal consumption for power generation by approximately 1.8g / kWh. This patented solution not only improves the utilization efficiency of waste heat from the flue gas and ensures the safe and normal operation of the tail flue equipment, but also, to a certain extent, can replace low-temperature economizers, saving initial investment and maintenance costs. Simultaneously, it reduces corrosion and ash blockage, improves boiler thermal efficiency, and reduces fuel consumption. Furthermore, it also features online loop-based anti-blockage functionality for the air preheater; its compact structure and simple modification allow for flexible adjustment to adapt to any operating condition.

Claims

1. A method for efficient energy cascade utilization of an air preheater, wherein the outlet flue is divided into two irregularly shaped flue gas channels, namely a high-energy irregularly shaped flue gas channel and a low-energy irregularly shaped flue gas channel, by means of a flue gas circumferential partition plate and a flue gas radial partition plate; the high-energy irregularly shaped flue gas channel and the low-energy irregularly shaped flue gas channel extend downward through an intermediate flue transition partition plate, and form a high-energy flue gas rectangular outlet channel and a low-energy flue gas rectangular outlet channel arranged in parallel; Its features are: The flue gas temperature in high-energy irregular flue gas channels is higher than that in low-energy irregular flue gas channels; the cross-section of high-energy irregular flue gas channels is 3%-12% larger than that of low-energy irregular flue gas channels; The high-energy flue gas rectangular outlet channel is adjacent to the cold secondary air inlet. The two ends of the heat pipe heat exchanger are respectively arranged in the cold secondary air inlet channel and the high-energy flue rectangular outlet channel. The heat of the flue gas in the high-energy flue gas outlet channel is recovered and heated to heat the cold secondary air, preventing blockage and improving the utilization efficiency of flue gas waste heat. No external heat exchange medium is required.

2. The method for efficient energy cascade utilization of an air preheater according to claim 1, characterized in that: One end of the heat pipe heat exchanger is arranged in the cold secondary air inlet channel, and the other end is arranged in the high-energy flue rectangular outlet channel. The end of the heat pipe heat exchanger in the cold secondary air inlet channel is higher than the end in the high-energy flue rectangular outlet channel and forms an angle of 3-10° with the horizontal plane, thereby improving energy utilization efficiency.

3. A system for efficient energy cascade utilization of an air preheater, comprising an air preheater, wherein a flue gas circumferential partition plate and a flue gas radial partition plate are provided in the outlet flue gas passage at the bottom of the cold end of the air preheater rotor to divide the outlet flue gas passage into two irregularly shaped flue gas passages, namely a high-energy irregularly shaped flue gas passage and a low-energy irregularly shaped flue gas passage; wherein, The two sides of the circumferential direction of the outlet flue gas passage are defined as the upstream flue gas side and the downstream flue gas side, respectively. The direction from the upstream flue gas side to the downstream flue gas side is consistent with the rotation direction of the rotor. Part or all of the flue gas passages inside the flue gas circumferential partition plate and the flue gas passages on the side of the flue gas radial partition plate facing the downstream flue gas side are merged to form a high-energy irregular flue gas passage. The flue gas passages in the remaining area are merged to form a low-energy irregular flue gas passage. The high-energy irregular flue gas channel and the low-energy irregular flue gas channel extend downward through the intermediate flue transition partition plate, forming a parallel arrangement of high-energy flue gas rectangular outlet channel and low-energy flue gas rectangular outlet channel. Its features include: a heat pipe heat exchanger, with a high-energy flue gas rectangular outlet channel adjacent to the cold secondary air duct inlet. The two ends of the heat pipe heat exchanger are respectively arranged in the cold secondary air inlet channel and the high-energy flue rectangular outlet channel; One end of the heat pipe heat exchanger is arranged in the cold secondary air inlet channel, and the other end is arranged in the high-energy flue rectangular outlet channel, with the end of the heat pipe heat exchanger in the cold secondary air inlet channel being higher than the end in the high-energy flue rectangular outlet channel. The upper edge of the flue gas radial partition plate is provided with a radial sealing structure; The cross-section of high-energy irregular flue gas channels is 3%-12% larger than that of low-energy irregular flue gas channels.

4. The system for efficient energy cascade utilization of an air preheater according to claim 3, characterized in that: The cross-section of high-energy irregular flue gas channels is 6%-9% larger than that of low-energy irregular flue gas channels.

5. The system for efficient energy cascade utilization of an air preheater according to claim 3 or 4, characterized in that: The heat pipe heat exchanger is at an angle of 3-10° to the horizontal plane.

6. The system for efficient energy cascade utilization of an air preheater according to claim 3 or 4, characterized in that: The bottom of the cold end of the air preheater rotor is divided into three concentric rings of equal area by one or more rotor circumferential separation seals. In the cold secondary air inlet duct at the bottom of the cold end of the air preheater rotor, a cold secondary air circumferential partition plate is installed, which is opposite to the circumferential separation seal of each rotor, dividing the cold secondary air inlet duct into three concentric rings. In the cold secondary air inlet duct, each ring gradually transitions downwards into a rectangular inlet of equal area, and each rectangular inlet is equipped with a cold secondary air volume regulating damper. One end of the heat pipe heat exchanger is located in the cold secondary air inlet channel below the cold secondary air volume regulating valve.

7. The system for efficient energy cascade utilization of an air preheater according to claim 6, characterized in that: The upper edges of the flue gas circumferential partition plate and the cold secondary air circumferential partition plate are respectively provided with circumferential sealing structures; The innermost rotor circumferential separator seal is the rotor inner ring separator seal; The rotor inner ring separator seal and the circumferential seal structure on the flue gas circumferential separator plate are positioned opposite each other to form a dynamic sealing pair; Each rotor's circumferential separator seal is positioned vertically opposite to the circumferential seal structure of each cold secondary air circumferential separator plate, forming a dynamic sealing pair.

8. The system for efficient energy cascade utilization of an air preheater according to claim 7, characterized in that: The flue gas radial partition plate is set radially along the outside of the rotor inner ring partition seal on the cold end face of the rotor, and the included angle between the flue gas radial partition plate and the downstream flue gas side is 35~45°. One end of the flue gas circumferential partition plate starts from the upstream flue gas side, and the other end connects to the flue gas radial partition plate. After the flue gas circumferential partition plate and the flue gas radial partition plate are connected, a dividing boundary is formed, which divides the outlet flue into a high-energy irregular flue gas channel and a low-energy irregular flue gas channel. The high-energy irregular flue gas channel and the low-energy irregular flue gas channel gradually transition from top to bottom, forming a parallel arrangement of a high-energy flue gas rectangular outlet channel and a low-energy flue gas rectangular outlet channel. The high-energy irregular flue gas channel is formed by splicing together a flue gas annular partition plate, a flue gas radial partition plate, and an outlet flue gas channel on the downstream flue gas side. The low-energy irregular flue gas channel is formed by splicing together a flue gas annular partition plate, a flue gas radial partition plate, and an outlet flue gas channel on the upstream flue gas side.

9. The system for efficient energy cascade utilization of an air preheater according to claim 3 or 4, characterized in that: The cross-section of the radial sealing structure is fan-shaped or trapezoidal.

10. The system for efficient energy cascade utilization of an air preheater according to claim 3 or 4, characterized in that: The cross-sections of the high-energy flue gas rectangular outlet channel and the low-energy flue gas rectangular outlet channel are equal; the heating end of the heat pipe heat exchanger is arranged along the entire cross-section of the high-energy flue gas rectangular outlet channel, and the condensing end of the heat pipe heat exchanger is arranged along the entire cross-section of the cold secondary air inlet channel.

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