Boiler air heater system and air preheating method

Abstract

Disclosed in the present invention are a boiler air heater system and an air preheating method. The boiler air heater system comprises: a plurality of mixing and stirring structures (3) sequentially arranged in series at an air heater inlet and configured to introduce external air, wherein at least one mixing and stirring structure (3) exchanges heat with a boiler flue pipe (10), and at least one mixing and stirring structure (3) exchanges heat with a first heating assembly; an air heater (1), the inner cavity of an air heater housing being provided with a second heating assembly; and an air preheater (8) provided with an air preheater inlet and an air preheater outlet, the air preheater inlet being communicated with an air heater outlet, and the air preheater outlet being communicated with a boiler air inlet end (9).

Description

A boiler air heater system and air preheating method Technical Field

[0001] This invention relates to the field of boiler auxiliary technology, specifically to a boiler air heater system and an air preheating method. Background Technology

[0002] The primary function of a boiler air heater is to prevent low-temperature corrosion at the cold end of the air preheater. During boiler startup, low-load operation, and winter operation, the inlet air temperature of the air preheater may be low, which can easily lead to low-temperature corrosion. The boiler air heater heats the boiler intake air, increasing the inlet air temperature of the air preheater and thus preventing this corrosion. An air preheater is a heat exchanger that uses the exhaust heat from boilers and other equipment to preheat the air. Its function is to reduce the exhaust temperature of boilers and other equipment, improve thermal efficiency, facilitate fuel ignition, ensure stable combustion, and enhance combustion efficiency.

[0003] In a boiler air heater system known to the inventor, only the waste heat of the flue gas at the boiler's tail end is used to preheat the incoming air before it is introduced into the boiler. The flue gas temperature is typically low, and the quality of the waste heat is limited, resulting in a small temperature rise after the air is preheated. When the boiler load suddenly increases (e.g., during peak shaving of a generator set), the combustion system needs to draw in a large amount of air in a short period, significantly increasing the flow rate of cold air through the air heater per unit time. Since the boiler air heater system relies solely on the waste heat of the flue gas, the temperature rise of the air heated by the system will be significantly reduced if the waste heat of the flue gas remains constant. After the heated air enters the boiler, the low temperature can lead to unstable and incomplete fuel combustion, resulting in decreased combustion efficiency. Summary of the Invention

[0004] In view of this, the present invention provides a boiler air heater system and an air preheating method to solve the problem that existing boiler air heater systems only utilize the waste heat of flue gas at the boiler tail to preheat the incoming air, resulting in a low temperature of the air entering the boiler when the boiler load suddenly increases.

[0005] In a first aspect, the present invention provides a boiler air heater system, comprising: a plurality of mixing and stirring structures arranged in series at the air inlet of the air heater and through which external air is introduced, wherein at least one mixing and stirring structure exchanges heat with the boiler flue pipe, and at least one mixing and stirring structure exchanges heat with a first heating component, each of the mixing and stirring structures being used to heat the introduced external air and uniformly mix the external air before inputting it into the air heater; the air heater having an air heater shell, an air heater inlet, and an air heater outlet, wherein a second heating component is disposed in the inner cavity of the air heater shell, the air heater inlet and the air heater outlet are respectively connected to the inner cavity of the air heater shell, and the air heater inlet is connected to the mixing and stirring structure; and an air preheater having an air preheater inlet and an air preheater outlet, wherein the air preheater inlet is connected to the air heater outlet, and the air preheater outlet is connected to the boiler air inlet.

[0006] Secondly, the present invention provides an air preheating method, the method being carried out using the aforementioned boiler air heater system, comprising the following steps:

[0007] S1. External air passes through each mixing and stirring structure in sequence. Each mixing and stirring structure heats and mixes the external air. At least one mixing and stirring structure uses the waste heat of flue gas in the boiler exhaust pipe to heat the external air. At least one mixing and stirring structure uses the first heating component to heat the external air.

[0008] S2. The mixed and heated outside air enters the heater and is reheated by the second heating element inside the heater.

[0009] S3. The external air heated by the second heating component enters the air preheater and then enters the boiler through the boiler inlet. Attached Figure Description

[0010] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0011] Figure 1 is a flowchart of a boiler air heater system according to one or more embodiments;

[0012] Figure 2 is a structural diagram of the mixing and stirring structure of a boiler air heater system according to one or more embodiments.

[0013] Explanation of reference numerals in the attached drawings: 1. Heater; 2. Electric heating wire; 3. Mixing and stirring structure; 31. First mixing and stirring structure; 32. Second mixing and stirring structure; 33. Third mixing and stirring structure; 34. Cylinder; 35. Spiral groove; 4. Waste heat exchange tube; 5. Heating box; 6. Heating resistor; 7. Heating chamber; 8. Air preheater; 9. Boiler inlet; 10. Boiler exhaust pipe; 11. First temperature sensor; 12. Flue gas comprehensive analyzer; 13. Second temperature sensor; 14. Fan; 15. Solenoid valve. Detailed Implementation

[0014] 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, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] The primary function of a boiler air heater is to prevent low-temperature corrosion at the cold end of the air preheater. During boiler startup, low-load operation, and winter operation, the inlet air temperature of the air preheater may be low, which can easily lead to low-temperature corrosion. The boiler air heater prevents this corrosion by heating the boiler intake air, thereby increasing the inlet air temperature of the air preheater.

[0016] Generally, an air preheater is used to heat the air entering the furnace using the flue gas from the boiler's tail end. Although this utilizes waste heat, it also increases the heat of the boiler flue gas. Due to variations in unit load, the heat is not constant, resulting in relatively low utilization efficiency. Firstly, the air preheating temperature is unstable, leading to unstable boiler thermal efficiency. Secondly, increasing the air volume at the bottom of the boiler can improve combustion, but increasing the flow rate introduces a large amount of cold air, which lowers the temperature at the bottom of the boiler, affecting its thermal efficiency. Specifically:

[0017] 1) Affects thermal efficiency

[0018] The main function of the air preheater is to use the heat from the flue gas at the boiler tail end to heat the air needed for combustion. A low inlet temperature means less heat is brought in by the air, resulting in a relatively low temperature after the fuel and air mix during combustion. This slows down the combustion rate, leads to incomplete combustion, increases heat loss, and reduces boiler thermal efficiency.

[0019] Low air temperature will also increase the flue gas temperature, causing more heat to be discharged with the flue gas, further reducing the boiler's thermal efficiency.

[0020] 2) Leads to low-temperature corrosion

[0021] When the air preheater inlet temperature is too low, water vapor and sulfur oxides in the flue gas will condense in the low-temperature parts of the air preheater, forming corrosive substances such as sulfuric acid, which will corrode the heated surfaces of the air preheater and shorten its service life.

[0022] Long-term low-temperature corrosion can cause the metal walls of the air preheater to become thinner and perforated, leading to air leakage and affecting the normal operation of the boiler.

[0023] 3) Causes dust accumulation and blockage

[0024] Lower inlet temperatures make it easier for impurities such as fly ash in the flue gas to deposit on the heated surfaces of the air preheater, forming ash deposits. Ash deposits increase the flow resistance of air and flue gas, reduce the heat transfer efficiency of the air preheater, and degrade its performance.

[0025] Severe ash accumulation can also cause air preheater blockage, reducing the flow area of ​​air and flue gas, affecting boiler ventilation and combustion, and may even force boiler shutdown for cleaning.

[0026] 4) Affects combustion stability

[0027] A low air preheater inlet temperature will lower the temperature of the air entering the furnace, reducing the overall temperature level within the furnace and affecting fuel ignition and combustion stability. For some difficult-to-ignite fuels, this may lead to problems such as difficulty in ignition, incomplete combustion, or even flameout, affecting the normal operation of the boiler.

[0028] Therefore, in order to ensure the normal operation of the boiler air heater, this invention modifies the existing boiler air heater by adding an electric heating element as an auxiliary heat source for the air heater, which can effectively improve the inlet air temperature of the boiler air preheater and is of great significance to the stable operation of the boiler.

[0029] According to an embodiment of the present invention, in a first aspect, a boiler air heater system is provided, as shown in Figures 1 and 2, comprising a mixing and stirring structure 3, an air heater 1, and an air preheater 8.

[0030] Multiple mixing and stirring structures 3 are provided and are connected in series at the air inlet of the heater to introduce external air. At least one mixing and stirring structure 3 exchanges heat with the boiler exhaust pipe 10, and at least one mixing and stirring structure 3 exchanges heat with the first heating component. Each mixing and stirring structure 3 is used to heat the introduced external air and mix the external air evenly before inputting it into the heater 1.

[0031] The heater 1 has a heater housing, a heater inlet, and a heater outlet. A second heating element is installed inside the heater housing to further supplement heat. The heater inlet and heater outlet are connected to the inner cavity of the heater housing, and the heater inlet is connected to the mixing and stirring structure 3.

[0032] The air preheater 8 is used for air preheating and premixing. The air preheater 8 has an air preheater inlet and an air preheater outlet. The air preheater inlet is connected to the air heater outlet, and the air preheater outlet is connected to the boiler inlet 9.

[0033] The aforementioned boiler air heater system uses a segmented mixing and stirring structure 3 to sequentially mix, stir, and heat the incoming air, resulting in a larger airflow and velocity into the boiler and providing a sufficient oxygen supply. Multiple mixing and stirring structures 3 connected in series can exchange heat with the boiler exhaust pipe 10 and the first heating element, forming a dual heat source mode of "waste heat recovery + active heating." On the one hand, it effectively utilizes the waste heat of the flue gas in the boiler exhaust pipe 10; on the other hand, it avoids the problem of excessively low air temperature entering the boiler due to the limited heat of the flue gas in the boiler exhaust pipe 10. This ensures that the boiler temperature does not change significantly when the heated air enters the boiler, thus maintaining its temperature and ensuring thorough heat utilization while reducing energy loss.

[0034] When the boiler load suddenly increases and the cold air flow increases, heat is quickly replenished through the first and second heating components to prevent a temperature drop. In this embodiment, a multi-stage mixing and stirring structure 3 is used in conjunction with waste heat from the flue gas to heat the incoming air, significantly increasing the final air temperature and ensuring combustion stability.

[0035] Multiple series-connected mixing and stirring structures 3 can also mix the airflow by stirring, eliminating the problem of local wall temperature being too low due to uneven air temperature distribution in traditional systems, avoiding low-temperature corrosion of the air preheater 8, and the uniform hot air flow can improve combustion efficiency and reduce unburned fuel residue.

[0036] Furthermore, the multi-stage series mixing and stirring structure forms a "buffer-compensation" mechanism: the front stage utilizes waste heat to stabilize the base temperature rise, while the rear stage dynamically adjusts the air temperature entering the boiler through active heating components (including the first heating component and the second heating component). Under scenarios of sudden load changes such as peak shaving of generator sets, the system can quickly respond to changes in airflow and maintain a stable air temperature entering the boiler.

[0037] In some embodiments, the mixing and stirring structure 3 is provided with three structures, namely a first mixing and stirring structure 31, a second mixing and stirring structure 32, and a third mixing and stirring structure 33.

[0038] The first mixing and stirring structure 31 is surrounded by a waste heat exchange tube 4. One side of the waste heat exchange tube 4 exchanges heat with the boiler exhaust pipe 10 and can be installed inside the boiler chimney. The other side of the waste heat exchange tube 4 exchanges heat with the first mixing and stirring structure 31. After the waste heat exchange tube 4 exchanges heat with the flue gas in the boiler exhaust pipe 10, it then exchanges heat with the first mixing and stirring structure 31, thereby realizing the recovery of heat from the flue gas in the boiler exhaust pipe 10.

[0039] A heating box 5 is arranged around the second mixing and stirring structure 32. A first heat exchange medium is provided between the heating box 5 and the second mixing and stirring structure 32. The heating box 5 exchanges heat with the air inside the cavity of the second mixing and stirring structure 32 through the first heat exchange medium. The first heat exchange medium can be water or other media.

[0040] When the first heat exchange medium is water, the heating box 5 is a water bath heating box, which makes the heating more stable by heating through water bath.

[0041] A heating resistor 6 is disposed around the periphery of the third mixing and stirring structure 33, which uses electric heating as an auxiliary heat source. A heating chamber 7 is disposed around the heating resistor 6, and the heating chamber 7 is connected to the heating box 5, with both filled with a second heat exchange medium. The heating resistor 6 exchanges heat with the air inside the cavity of the third mixing and stirring structure 33, and is used to heat the heating chamber 7 and the second heat exchange medium filled in the heating box 5. The second heat exchange medium can be water or other media.

[0042] The heating box 5 and the heating resistor 6 are the first heating components. The heating resistor 6 can simultaneously heat the air inside the third mixing and stirring structure 33 and the second heat exchange medium in the heating chamber 7. The second heat exchange medium in the heating chamber 7 exchanges heat with the second heat exchange medium in the heating box 5, thereby heating the air inside the second mixing and stirring structure 32, so that the heat generated by the heating resistor 6 can be fully utilized.

[0043] The second heating element installed in the inner cavity of the heater is an electric heating wire 2. The electric heating wire 2 has high heating efficiency and stable heating performance, which can quickly heat the air inside the heater to the required temperature and maintain a constant temperature to meet the operating requirements of the boiler heater system.

[0044] In some embodiments, the first mixing and stirring structure 31, the second mixing and stirring structure 32, and the third mixing and stirring structure 33 are arranged sequentially from top to bottom. The first mixing and stirring structure 31 is in communication with the outside air, which is provided by a fan 14, driving airflow. The third mixing and stirring structure 33 is in communication with the air inlet of the heater. The heating chamber 7 is not in contact with the third mixing and stirring structure 33, and the position of the heating chamber 7 is lower than that of the heating box 5, reducing the impact of the heat absorbed by the heating chamber 7 on the third mixing and stirring structure 33. Furthermore, based on the rising characteristics of hot water, the temperature of the heating box 5 is maintained.

[0045] If the mixing and stirring structure 3 is only a straight cylinder structure, when external air is introduced into the mixing and stirring structure 3, the air near the inner wall of the cylinder is more easily heated than the air in the middle of the cylinder, which leads to the air in the outer ring of the mixing and stirring structure 3 being hotter than the air in the inner ring, and the air entering the boiler is not heated evenly.

[0046] To address the aforementioned issues, in some embodiments, the mixing and stirring structure 3 includes a cylinder 34. Two spiral grooves 35 with opposite directions of rotation are provided on the inner wall of the cylinder 34, guiding the airflow to form a bidirectional swirling flow within the cylinder. The two spiral grooves 35 are arranged opposite each other, with their inlets facing each other, and their outlets inclined towards the central axis of the cylinder 34 and arranged opposite each other. In this embodiment, after cold air enters the cylinder 34, it flows downwards along the surfaces of the two opposing spiral grooves 35, creating a vortex impact that allows for sufficient heat exchange with the wall of the cylinder 34. The air then flows out from the outlets of the spiral grooves. Since there is no limitation from the spiral grooves, and the outlets are sloped, the gas gathers towards the center, forming a vortex that opposes the flow towards the center, creating a stirring effect. This mixes the gas, ensuring that the incoming air is heated evenly and preventing the outer ring from being hotter than the inner ring.

[0047] The swirling intensity can also be controlled by adjusting the pitch of the spiral groove 35. When increased swirling intensity is needed, decreasing the pitch of the spiral groove 35 increases the number of rotations the fluid makes within the spiral groove. Conversely, when decreased swirling intensity is needed, increasing the pitch of the spiral groove 35 reduces the number of rotations the fluid makes within the spiral groove.

[0048] In some embodiments, at least one mixing and stirring structure 3 is connected to the boiler exhaust pipe 10 via a first circulation pipe, so that the flue gas in the boiler exhaust pipe 10 can circulate into the mixing and stirring structure 3 and mix with the air in the mixing and stirring structure 3. The air preheater 8 is connected to the boiler exhaust pipe 10 via a second circulation pipe, so that the flue gas in the boiler exhaust pipe 10 can circulate into the air preheater 8, allowing unburned gases in the flue gas to be recirculated and burned. Solenoid valves 15 are respectively installed on the first and second circulation pipes.

[0049] In some embodiments, the boiler air heater system further includes a first temperature sensor 11, a second temperature sensor 13, a flue gas comprehensive analyzer 12, and a controller.

[0050] The first temperature sensor 11 is installed inside the boiler exhaust pipe 10 to monitor the exhaust temperature T1, and the detected value is used as an important parameter for judging the heat utilization rate of the flue gas.

[0051] The second temperature sensor 13 is installed at the air outlet of the heater to monitor the gas outlet temperature T2 after being processed by the mixing and stirring structure 3, reflecting the mixing and heating effect and the system operating status.

[0052] The flue gas analyzer 12 has a detection end, which is located inside the boiler exhaust pipe 10. The flue gas analyzer 12 is used to detect and analyze the combustible gas content in the flue gas inside the boiler exhaust pipe 10 and feeds the detection information back to the controller. When the combustible gas concentration exceeds the standard, the controller triggers an alarm or adjusts the combustion conditions.

[0053] The outputs of the first temperature sensor 11, the second temperature sensor 13, and the flue gas analyzer 12 are respectively connected to the input of the controller. The controlled terminals of the first heating component, the second heating component, and each solenoid valve 15 are respectively connected to the output of the controller. The controller receives real-time data from the first temperature sensor 11, the second temperature sensor 13, and the flue gas analyzer 12; according to the set control strategy (such as temperature range, combustible gas concentration threshold), it adjusts the working state of the first heating component, the second heating component, and each solenoid valve 15 to achieve dynamic optimization of flue gas circulation flow and heating power.

[0054] The temperature control strategy can be as follows: if T2 is lower than the lower limit, the controller increases the power of the first heating component or opens the solenoid valve 15 of the first circulation pipeline to increase the flue gas flow rate and increase the temperature of the mixed gas.

[0055] If T2 is higher than the upper limit, the controller reduces the power of the first heating component or closes the solenoid valve 15 of the first circulation pipeline to reduce the flue gas flow rate to avoid overheating.

[0056] The combustible gas concentration control strategy can be as follows: if the combustible gas concentration exceeds the threshold, the controller controls the solenoid valve 15 on the first circulation pipeline and / or the second circulation pipeline to open, so as to realize the cyclic combustion of combustible fuel in the flue gas.

[0057] The goal of the thermal efficiency control strategy is to maximize the utilization of waste heat from boiler flue gas and reduce flue gas temperature. The thermal efficiency control strategy involves dynamically adjusting the opening of the solenoid valves in the first and second circulation pipelines based on the detected value T1 from the first temperature sensor 11. When T1 is high, the flue gas flow rate in the first circulation pipeline is increased first, utilizing the mixing and stirring structure 3 for sufficient heat exchange. When T1 is low, the flow rate in the first circulation pipeline is appropriately reduced to prevent excessive cooling of the flue gas from affecting subsequent combustion stability.

[0058] In some embodiments, a fan blade is provided at the connection between the air preheater inlet and the air heater outlet. The fan blade can rotate after receiving a control signal from the controller, thereby adjusting the airflow between the air preheater inlet and the air heater outlet. This allows for more precise control of the gas temperature and flow rate entering the air preheater, improving the overall efficiency and stability of the boiler air heater system.

[0059] According to an embodiment of the present invention, in a second aspect, an air preheating method is provided, the method utilizing a boiler air heater system, comprising the following steps:

[0060] S10. Connection: One end of the waste heat exchange tube 4 is wrapped around the outside of the first mixing and stirring structure 31, and the other end of the waste heat exchange tube 4 is installed in the boiler chimney. At the same time, the boiler exhaust pipe 10 is connected to the boiler chimney, and the remaining devices are connected in sequence.

[0061] S20. Detection: The temperature of the flue gas inside the boiler exhaust pipe 10 is detected by the first temperature sensor 11, and the composition of the flue gas inside the boiler exhaust pipe 10 is detected by the flue gas comprehensive analyzer 12.

[0062] S30. Heating: External air passes sequentially through each mixing and stirring structure 3. Each mixing and stirring structure 3 heats and mixes the external air. At least one mixing and stirring structure 3 utilizes the waste heat of flue gas in the boiler exhaust pipe 10 to heat the external air, and at least one mixing and stirring structure 3 utilizes a first heating component to heat the external air. Taking a three-stage mixing and stirring structure 3 as an example, the first mixing and stirring structure 31 performs low-temperature heating through the waste heat exchange tube 4, then the second mixing and stirring structure 32 raises the temperature to a relatively high level through water bath heating, and finally the third mixing and stirring structure 33 performs final heating.

[0063] The outside air, after being mixed and heated, enters the heater 1 and is reheated by the second heating element inside the heater 1.

[0064] The external air, heated by the second heating component, enters the air preheater 8 and then enters the boiler through the boiler inlet 9.

[0065] In the above-mentioned air preheating method, when the external air flows through each mixing and stirring structure 3, the waste heat of the flue gas is combined with the heating of the first heating component. On the one hand, it can effectively utilize the waste heat of the flue gas in the boiler exhaust pipe 10, and on the other hand, it will not cause the problem of the air temperature entering the boiler being too low due to the limited heat of the flue gas in the boiler exhaust pipe 10.

[0066] The external air passes through the mixing and stirring structure 3 (heating by waste heat from flue gas and heating by the second heating component), the air heater 1 (heating by the second heating component), and the air preheater 8 in sequence, realizing multi-stage heating of the air, ensuring that the air entering the boiler reaches the ideal temperature, and further improving combustion efficiency.

[0067] The aforementioned air preheating method further includes the following steps: detecting the combustible gas content in the flue gas inside the boiler exhaust pipe 10 using a flue gas comprehensive analyzer 12. When the detected combustible gas content in the flue gas is higher than a set threshold, at least one solenoid valve 15 is opened by a controller, allowing the flue gas from the boiler exhaust pipe 10 to be introduced into the air heater 1 and / or at least one mixing and stirring structure 3, thereby ensuring the complete combustion of the combustible gas contained in the flue gas.

[0068] The above-mentioned air preheating method also includes the following steps:

[0069] The temperature of the flue gas inside the boiler exhaust pipe 10 is detected by the first temperature sensor 11, which allows for real-time monitoring of the utilization of waste heat from the flue gas. If the flue gas temperature is too low, the controller will adjust the operating status of the solenoid valve 15 to reduce or stop the flue gas from entering the mixing and stirring structure 3, thus preventing insufficient heat from reducing the air heating effect.

[0070] The second temperature sensor 13 detects the air temperature at the outlet of the heater to ensure that the air temperature after being reheated by the heater 1 reaches the set value. If the temperature is too low, the controller can improve the heating effect by adjusting the power of the solenoid valve 15 or other heating components.

[0071] The controller controls the operation of the solenoid valve 15 based on temperature detection information from the first temperature sensor 11 and the second temperature sensor 13. For example, when the flue gas temperature is low, the flue gas flow rate is reduced; when the flue gas temperature is high, the flue gas flow rate is increased. This dynamic adjustment mechanism ensures stable system operation under different operating conditions. By monitoring the flue gas temperature and the outlet temperature of the heater in real time, the controller can rationally allocate the waste heat from the flue gas and the heat from other heating components, minimizing energy waste.

[0072] The aforementioned air preheating method also includes a temperature control step: When air is introduced, the flow rate and speed of the fan 14 are controlled based on the temperature and the flow rate of the boiler exhaust pipe 10 to achieve more precise temperature regulation. When the flue gas temperature is high and the flow rate of the boiler exhaust pipe 10 is large, the controller can instruct the fan 14 to increase the flow rate and speed to more effectively utilize the high-temperature flue gas to preheat the air. Conversely, when the flue gas temperature is low or the flow rate of the boiler exhaust pipe 10 is small, the controller will reduce the flow rate and speed of the fan 14 to prevent over-cooling of the preheated air. This temperature control step not only improves preheating efficiency but also ensures the stability and energy efficiency of the boiler air heater system under various operating conditions.

[0073] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A boiler air heater system, characterized in that, include: Multiple mixing and stirring structures (3) are sequentially connected in series at the air inlet of the heater and external air is introduced. At least one mixing and stirring structure (3) exchanges heat with the boiler exhaust pipe (10) and at least one mixing and stirring structure (3) exchanges heat with the first heating component. Each of the mixing and stirring structures (3) is used to heat the introduced external air and mix the external air evenly before inputting it into the heater (1). The heater (1) has a heater housing, a heater inlet and a heater outlet. The inner cavity of the heater housing is provided with a second heating component. The heater inlet and the heater outlet are respectively connected to the inner cavity of the heater housing. The heater inlet is connected to the mixing and stirring structure (3). The air preheater (8) has an air preheater inlet and an air preheater outlet. The air preheater inlet is connected to the air heater outlet, and the air preheater outlet is connected to the boiler inlet (9).

2. The boiler air heater system according to claim 1, characterized in that, The mixing and stirring structure (3) is provided in three parts, namely the first mixing and stirring structure (31), the second mixing and stirring structure (32) and the third mixing and stirring structure (33); The first mixing and stirring structure (31) is surrounded by a waste heat exchange tube (4). One side of the waste heat exchange tube (4) exchanges heat with the boiler exhaust pipe (10), and the other side of the waste heat exchange tube (4) exchanges heat with the first mixing and stirring structure (31). A heating box (5) is provided around the second mixing and stirring structure (32). A first heat exchange medium is provided between the heating box (5) and the second mixing and stirring structure (32). The heating box (5) exchanges heat with the air inside the cavity of the second mixing and stirring structure (32) through the first heat exchange medium. A heating resistor (6) is provided around the third mixing and stirring structure (33), and a heating cavity (7) is provided around the heating resistor (6). The heating cavity (7) is connected to the heating box (5). The heating resistor (6) exchanges heat with the air inside the third mixing and stirring structure (33) and is used to heat the heating cavity (7) and the second heat exchange medium filled in the heating box (5). The heating box (5) and the heating resistor (6) are the first heating components.

3. The boiler air heater system according to claim 2, characterized in that, The first mixing and stirring structure (31), the second mixing and stirring structure (32) and the third mixing and stirring structure (33) are arranged from top to bottom. The first mixing and stirring structure (31) is connected to the outside air, which is provided by a fan (14). The third mixing and stirring structure (33) is connected to the air inlet of the heater. The heating chamber (7) is located lower than the heating box (5).

4. The boiler air heater system according to any one of claims 1-3, characterized in that, The mixing and stirring structure (3) includes a cylinder (34). Two spiral grooves (35) with opposite directions of rotation and arranged oppositely are provided on the inner side wall of the cylinder (34). The air inlets of the two spiral grooves (35) are arranged oppositely, and the air outlets of the two spiral grooves (35) are inclined toward the central axis of the cylinder (34) and arranged oppositely.

5. The boiler air heater system according to any one of claims 1-3, characterized in that, At least one of the mixing and stirring structures (3) is connected to the boiler exhaust pipe (10) through a first circulation pipe so that the flue gas in the boiler exhaust pipe (10) can circulate into the mixing and stirring structure (3) and mix with the air in the mixing and stirring structure (3); the air preheater (8) is connected to the boiler exhaust pipe (10) through a second circulation pipe so that the flue gas in the boiler exhaust pipe (10) can circulate into the air preheater (8); Solenoid valves (15) are respectively installed on the first circulation pipeline and the second circulation pipeline.

6. The boiler air heater system according to claim 5, characterized in that, The boiler air heater system also includes: The first temperature sensor (11) is installed inside the boiler exhaust pipe (10); The second temperature sensor (13) is located at the air outlet of the heater; The flue gas analyzer (12) has a detection end. The detection end of the flue gas analyzer (12) is located inside the boiler exhaust pipe (10). The flue gas analyzer (12) is used to detect and analyze the combustible gas content in the flue gas in the boiler exhaust pipe (10) and feed the detection information back to the controller. The output terminals of the first temperature sensor (11), the second temperature sensor (13), and the flue gas analyzer (12) are respectively connected to the input terminal of the controller, and the controlled terminals of the first heating component, the second heating component, and each of the solenoid valves (15) are respectively connected to the output terminal of the controller.

7. The boiler air heater system according to any one of claims 1-3, characterized in that, A fan blade is provided at the connection between the air preheater inlet and the heater outlet. And / or, the second heating component is an electric heating wire (2).

8. An air preheating method, characterized in that, The method is carried out using the boiler air heater system according to any one of claims 1-7, and includes the following steps: S1. External air passes through each mixing and stirring structure (3) in sequence. Each mixing and stirring structure (3) heats and mixes the external air. At least one mixing and stirring structure (3) uses the waste heat of flue gas in the boiler exhaust pipe (10) to heat the external air. At least one mixing and stirring structure (3) uses the first heating component to heat the external air. S2. The outside air, after being mixed and heated, enters the heater (1) and is reheated by the second heating component inside the heater (1); S3. The external air heated by the second heating component enters the air preheater (8) and then enters the boiler through the boiler inlet (9).

9. The air preheating method according to claim 8, characterized in that, It also includes the following steps: The combustible gas content in the flue gas inside the boiler exhaust pipe (10) is detected by the flue gas comprehensive analyzer (12); when the combustible gas content in the flue gas is detected to be higher than the set threshold, at least one solenoid valve (15) is opened by the controller, so that the flue gas in the boiler exhaust pipe (10) is introduced into the air heater (1) and / or at least one mixing and stirring structure (3).

10. The air preheating method according to claim 9, characterized in that, It also includes the following steps: The temperature of the flue gas inside the boiler exhaust pipe (10) is detected by the first temperature sensor (11), and the temperature of the gas at the outlet of the heater is detected by the second temperature sensor (13). The controller controls the operating status of the solenoid valve (15) based on the temperature detection information of the first temperature sensor (11) and the second temperature sensor (13).

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