Furnace flue gas secondary air system

Abstract

The utility model provides an in-furnace flue gas secondary air system which comprises an in-furnace flue gas extraction opening, an in-furnace flue gas secondary air inlet, an in-furnace flue gas secondary air inlet and an in-furnace flue gas secondary air outlet. An inlet of the cyclone dust collector is connected with the in-furnace flue gas extraction opening, and the cyclone dust collector is used for filtering dust particles in the flue gas; an air inlet of the secondary fan is connected with an outlet of the cyclone dust collector; the double-flow secondary air spray gun is provided with a first connecting port, a second connecting port and a spray port, and the first connecting port is connected with the air outlet of the secondary air fan; an air inlet of the cold air fan is used for extracting air, and an air outlet of the cold air fan is connected with the second connecting port. The double-flow secondary air spray guns are installed on the front arch and the rear arch of the incinerator and used for feeding smoke and air into the incinerator. The incineration oxygen content is controlled through the flue gas in the boiler, NOx generation is controlled from the source, meanwhile, the air pipe installation cost and the comprehensive operation electric charge are reduced, the low-temperature corrosion hidden danger is eliminated, and the method is suitable for compact boiler nitrogen oxide upgrading and reconstruction projects.

Description

Technical Field

[0001] This application belongs to the field of low-nitrogen combustion control. More specifically, it relates to an in-furnace flue gas secondary air system. Background Art

[0002] Facing the in-depth development of the new round of scientific and technological revolution and industrial transformation, while the key industries such as integrated circuits and biomedicine are developing rapidly, the total emissions of major pollutants are growing rapidly. In particular, the total emissions of nitrogen oxides have been in a tight balance for a long time, and the contradiction of structural pollution problems has become increasingly prominent. Industrial production faces huge challenges. Especially for the incineration facilities that have been put into operation, problems such as the feasibility of technology application, the requirements for equipment layout space, and the compatibility of the original system will further exacerbate the difficulty of upgrading the standards.

[0003] Currently, the mainstream flue gas denitrification processes include technologies such as SNCR, SCR, and flue gas recirculation. Among them, the flue gas recirculation technology can inhibit the generation of NOx from the source, effectively reduce the initial concentration of NOx, and has low investment and operation costs. At the same time, taking into account various factors of environmental protection and economy, it is the preferred technology for upgrading the nitrogen oxide standards. The traditional flue gas recirculation technology usually extracts the flue gas at the outlet of the bag filter or the outlet of the induced draft fan, and adjusts the ratio of flue gas to air through the recirculation fan and the secondary air fan to control the oxygen content in the furnace, so as to achieve low-nitrogen combustion control. There are also two ways of flue gas inlet into the furnace: sharing the nozzle with the secondary air or separately setting the recirculation nozzles in the upper and lower layers. In addition, there are also some projects that extract flue gas through the secondary air fan and adjust the cold air ratio through the air valve.

[0004] Whether it is the outlet of the dust collector or the outlet of the induced draft fan, the length of the recirculation air duct is relatively long (at least 70 - 80 meters), and the flue gas temperature (130 - 150 °C) is close to the acid dew point, there is a risk of low-temperature corrosion; the power of the recirculation fan is equivalent to that of the secondary air fan, and the comprehensive power consumption is relatively high when used at the same time; while sharing the fan with the secondary air fan is not conducive to the adjustment of flue gas and air, and it is difficult to control NOx and CO; sharing the nozzle of the recirculation flue gas and the secondary air is prone to low-temperature corrosion, and the layered setting has high requirements for the installation space of the front and rear arches.

[0005] In summary, in order to further explore the potential of low-nitrogen combustion control and balance the operation economy and denitrification effect, it is necessary to develop a new type of secondary air system with good denitrification effect, no risk of low-temperature corrosion, low comprehensive power consumption, and compact structure with a small floor area. Summary of the Invention

[0006] The purpose of the embodiment of this application is to provide an in - furnace flue gas secondary air system to solve the problems mentioned in the background technology. Whether it is the outlet of the dust collector or the outlet of the induced draft fan, the length of the recirculation air duct is relatively long (at least 70 - 80 meters), and the flue gas temperature (130 - 150 °C) is close to the acid dew point, posing a risk of low - temperature corrosion; the power of the recirculation fan is comparable to that of the secondary fan, and the combined power consumption is relatively high when used simultaneously; sharing a fan with the secondary fan is not conducive to the adjustment of flue gas and air, and it is difficult to control NOx and CO; sharing the nozzle for recirculation flue gas and secondary air is prone to low - temperature corrosion, and the layered setting has relatively high requirements for the installation space of the front and rear arches, etc.

[0007] To achieve the above - mentioned purpose, the technical solution adopted in this application is: to provide an in - furnace flue gas secondary air system, including:

[0008] An in - furnace flue gas extraction port, which is located at the upper part of the rear arch in the burnout section of the furnace chamber;

[0009] A cyclone dust collector, the inlet of which is connected to the in - furnace flue gas extraction port and is used to filter dust particles in the flue gas;

[0010] A secondary fan, the air inlet of which is connected to the outlet of the cyclone dust collector;

[0011] A dual - flow secondary air spray gun, which is installed on the front and rear arches of the incinerator and is used to send flue gas and air into the incinerator. It has a first connection port, a second connection port, and a nozzle, and the first connection port is connected to the outlet of the secondary fan;

[0012] A cold air fan, the air inlet of which extracts air, and the air outlet of which is connected to the second connection port.

[0013] Preferably, the dual - flow secondary air spray gun is of a sleeve - type structure, including:

[0014] An inner pipe, which forms an independent flue gas flow channel, and the flue gas flow channel is communicated with the first connection port;

[0015] An outer pipe, which is sleeved outside the inner pipe, and an air flow channel is formed between the inner pipe and the outer pipe, and the air flow channel is communicated with the second connection port;

[0016] When the flue gas flow channel is out of use, the air in the air flow channel plays a role in protecting the dual - flow secondary air spray gun and preventing the dual - flow secondary air spray gun from being deformed at high temperatures.

[0017] Preferably, the air flow channel is provided with a variable diameter for the air flow channel.

[0018] Preferably, the end of the nozzle of the inner pipe is provided with an arc - shaped transition and variable diameter.

[0019] Preferably, the cyclone dust collector includes:

[0020] A cylinder body, which is a regular hexahedron. An air inlet pipe is arranged on the side surface of the cylinder body, and an exhaust pipe is arranged on the top of the cylinder body. A dust removal chamber is formed inside the cylinder body, and both the air inlet pipe and the exhaust pipe are communicated with the dust removal chamber;

[0021] A cone, which is connected to the bottom of the cylinder body and forms a dust particle separation and collection chamber that gradually narrows. The dust particle separation and collection chamber is communicated with the dust removal chamber.

[0022] Preferably, the cylinder body is in the shape of a twisted hexagonal prism, so that the dust removal chamber forms a spiral shape. When the dusty flue gas tangentially enters the dust removal chamber from the air inlet pipe, the flue gas will change from linear motion to circular motion. Most of the rotating air flow spirally moves downward along the cylinder wall from the circular cylinder body towards the cone. During the rotation process, the dust particles in the dusty flue gas are thrown towards the cylinder wall due to the action of centrifugal force. After contacting the cylinder wall, they lose the radial inertial force and fall along the wall surface by the downward momentum and downward gravity, while the purified flue gas rotates upward along the exhaust pipe and is discharged.

[0023] Preferably, a water-cooled jacket is sleeved on the cylinder body. A water-cooled chamber is formed between the water-cooled jacket and the cylinder body. Flowing cooling water is introduced into the water-cooled chamber to reduce the temperature of the flue gas extracted from the furnace.

[0024] Preferably, a bypass air duct is arranged between the air inlet pipe of the secondary air blower and the outlet of the cyclone dust collector to extract air, which is used to extract air by the secondary air blower and send it into the furnace under the condition of furnace over-temperature to reduce the furnace temperature.

[0025] Preferably, the secondary air blower is a high-temperature resistant blower, and wear-resistant linings are installed on the impeller of the secondary air blower.

[0026] Preferably, multiple flue gas extraction ports in the furnace are arranged in parallel.

[0027] The beneficial effects of a secondary air system for flue gas in the furnace provided by this application are as follows:

[0028] 1. The present utility model extracts the flue gas at the upper rear arch of the burnout section of the furnace. The length of the flue gas extraction pipeline is much shorter than that of the traditional flue gas recirculation air duct, and the investment cost of the air duct is low; at the same time, the flue gas extracted here is dust-removed and cooled by a cyclone dust collector with a water-cooled jacket, and the flue gas temperature is much higher than the acid dew point, without the hidden danger of low-temperature corrosion;

[0029] 2. The secondary air blower and the cold air blower extract flue gas and air respectively, which is beneficial to adjusting the oxygen content of the secondary air of the flue gas. The oxygen content of the flue gas at the upper part of the burnout section is relatively high compared with the flue gas at the rear of the furnace, which can reduce the load of the cold air blower;

[0030] 3. The traditional flue gas recirculation process uses a secondary air fan and a recirculation fan simultaneously. The power of the two fans is relatively large, and the comprehensive power consumption is relatively high. However, the present utility model uses a high-temperature-resistant secondary air fan and is equipped with a small-power cold air fan, with less initial investment, a significant reduction in operating electricity costs, and obvious economic advantages.

[0031] 4. The present utility model adopts a special structure of a double-flow secondary air lance and a single-layer lance design, with a compact structure, a small floor area, and a high degree of equipment centralization, which can solve the problem of insufficient installation space for the double-layer nozzles of the front and rear arches. At the same time, it can avoid the problem of low-temperature corrosion caused by the cooling of flue gas in the shared secondary air nozzles. For overloaded operating conditions, the flue gas injection volume can be reduced, and a bypass air duct is used to extract cold air. For furnace over-temperature conditions, the extraction of flue gas can be stopped, and only cold air secondary air is sprayed in as a means of controlling the furnace temperature.

[0032] 5. The present utility model replaces the traditional secondary air and flue gas recirculation processes, has an obvious NOx inhibition effect, reduces the input of combustion air at the same time, and finally the flue gas volume can be greatly reduced, and the load power consumption of the induced draft fan is also reduced accordingly, with remarkable energy-saving and consumption-reducing effects. Brief Description of the Drawings

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a schematic structural diagram of the in-furnace flue gas secondary air system provided by the embodiment of the present application;

[0035] Figure 2 It is a three-dimensional structural diagram of the cyclone dust collector provided by the embodiment of the present application;

[0036] Figure 3 It is a bottom view structural diagram of the cyclone dust collector provided by the embodiment of the present application;

[0037] Figure 4 It is a schematic structural diagram of the double-flow secondary air lance provided by the embodiment of the present application;

[0038] Figure 5 It is a schematic internal structural diagram of the double-flow secondary air lance provided by the embodiment of the present application;

[0039] Figure 6 Provided by the embodiment of the present application Figure 5 An enlarged structural diagram of A in

[0040] Among them, the reference numerals in the drawings:

[0041] 1. Furnace; 101. In-furnace flue gas extraction port;

[0042] 2. Secondary air blower;

[0043] 3. Cooling air blower;

[0044] 4. Cyclone dust collector; 401. Cylinder body; 402. Cone; 403. Inlet pipe; 404. Exhaust pipe; 405. Water-cooled jacket; 406. Water inlet; 407. Water outlet;

[0045] 5. Dual-flow secondary air lance; 501. First connection port; 502. Second connection port; 503. Outer pipe; 504. Inner pipe; 505. Flue gas flow channel; 506. Air flow channel; 507. Arc transition and diameter variation setting; 508. Air flow channel diameter variation setting. Detailed implementation manners

[0046] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer and more understandable, the following further details this application in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0047] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0048] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to this application.

[0049] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality of" means two or more, unless otherwise specifically defined.

[0050] Please refer to Figures 1 to 6 together, and now a secondary air system for in-furnace flue gas provided by the embodiments of this application is described.

[0051] Specifically, a secondary air system for flue gas in the furnace includes a flue gas extraction port 101 in the furnace. The flue gas extraction port 101 is located at the upper rear arch of the burnout section of the furnace chamber 1. Multiple flue gas extraction ports 101 can be set according to actual needs. The multiple flue gas extraction ports 101 are arranged in parallel at the upper rear arch of the burnout section of the furnace chamber 1; a cyclone dust collector 4 is connected to the flue gas extraction port 101 through a recirculation air duct. The cyclone dust collector 4 is used to filter dust particles in the flue gas to prevent dust particles from entering the secondary air blower 2 and the dual-flow secondary air spray gun 5, improving the working efficiency and service life of the secondary air blower 2 and the dual-flow secondary air spray gun 5; a secondary air blower 2 is connected to the exhaust pipe 404 of the cyclone dust collector 4 through a recirculation air duct. The secondary air blower 2 plays a crucial role in the boiler and combustion system. It supplements combustion oxygen, strengthens material mixing, adjusts the temperature field distribution, improves combustion stability, and inhibits coking in the furnace chamber 1 in various ways; a bypass air duct is provided between the suction port of the secondary air blower 2 and the cyclone dust collector 4 for introducing air into the furnace chamber 1 to adjust and control the temperature in the furnace chamber 1. The dual-flow secondary air spray gun 5 has a first connection port 501 and a second connection port 502. The first connection port 501 is connected to the secondary air blower 2. The first connection port 501 is connected to the secondary air blower 2 through a recirculation air duct. The second connection port 502 is connected to the cold air blower 3 through a recirculation air duct. The dual-flow secondary air spray gun 5 is installed at the front and rear arches of the furnace chamber 1 with a single-layer multi-spray gun parallel design. The dual-flow secondary air spray gun 5 is used to spray flue gas and air into the furnace chamber 1; a cold air blower is connected to the second connection port 502 of the dual-flow secondary air spray gun 5. The cold air blower is used to extract air and send it to the secondary air spray gun, which can achieve precise control of the temperature field in the furnace chamber 1, prevent local overheating, and thus reduce the emission of harmful substances such as NOx. The secondary air blower 2 is a high-temperature resistant blower, and wear-resistant linings are installed on the impeller of the secondary air blower. The working temperature of the blower is 250 °C. The secondary air volume is designed according to 15 - 25% of the flue gas volume, and the cold air blower volume is 30 - 50% of the secondary air volume, controlling the oxygen content in the furnace chamber between 3 - 6%.

[0052] Now, a further detailed introduction to the double-flow secondary air lance 5 is given. Specifically, the double-flow secondary air lance 5 includes: an inner pipe 504, the inner pipe 504 forms a flue gas flow channel 505, and the flue gas flow channel 505 communicates with the first connection port 501; an outer pipe 503, sleeved outside the inner pipe 504, and an air flow channel 506 is formed between the inner pipe 504 and the outer pipe 503, and the air flow channel 506 communicates with the second connection port 502; when the flue gas flow channel 505 is out of use, the air in the air flow channel 506 plays a role in protecting the double-flow secondary air lance 5, preventing the double-flow secondary air lance 5 from deforming at high temperatures, and at the same time avoiding the problem of low-temperature corrosion caused by the cooling of the flue gas in the shared secondary air nozzle, and prolonging the service life of the double-flow secondary air lance 5.

[0053] In order to further improve the injection efficiency and service life of the double-flow secondary air lance 5, the air flow channel is variably sized 508. In order to improve the rapid diffusion of the air in the air flow channel 506 after acceleration, the caliber of the air flow channel 506 gradually increases. The end of the nozzle of the inner pipe 504 is provided with a variable diameter with an arc transition 507. The design of using an arc transition for the end of the nozzle has many advantages: 1. Reducing resistance loss: The arc transition design can smoothly guide the fluid to flow out of the nozzle, reducing the eddy current and turbulence generated due to sudden cross-section changes, thereby reducing the resistance loss of the fluid during the flow process. This helps to maintain the stability of the fluid flow and improve the overall efficiency of the system. 2. Uniform velocity and pressure distribution: The arc transition variable diameter can ensure that the velocity and pressure distribution of the fluid at the end of the nozzle are more uniform, avoiding the formation of local high-pressure or low-pressure areas, and reducing the impact and wear of the fluid on the inner wall of the inner pipe 504. 3. Reducing stress concentration: The arc transition design can disperse the stress concentration phenomenon generated at the end of the nozzle due to cross-section changes, reducing the risk of rupture or leakage of the inner pipe 504 caused by excessive stress. This is of great significance for improving the safety and reliability of the pipeline system. 4. Improving wall thickness uniformity: During the variable diameter process of the inner pipe 504, by reasonably designing the transition fillet radius, the equivalent stress distribution at the end of the large-diameter area can be improved, making the wall thickness increase more uniformly, thereby improving the overall structural strength of the inner pipe 504. 5. Reducing wear and corrosion: Since the arc transition design can reduce the impact and wear of the fluid on the inner wall of the inner pipe 504, and at the same time reduce the corrosion of the eddy current and turbulence on the inner wall of the pipeline, it helps to extend the service life of the pipeline.

[0054] 6. Improving fatigue resistance: Under the action of alternating loads, the arc transition design can reduce the stress level of the pipeline, reduce the fatigue damage caused by stress cycling, and thus improve the fatigue resistance of the inner pipe 504. 7. Optimizing flow rate and flow velocity: By reasonably designing the arc transition variable diameter at the end of the nozzle, the flow rate and flow velocity in the inner pipe 504 can be controlled to keep them within the design range. This helps to ensure the efficient operation of the system, reduce energy consumption and costs.

[0055] Now, the cyclone dust collector 4 will be further introduced in detail. Specifically, the cyclone dust collector 4 includes: a cylinder body 401, which is a regular hexahedron. An air inlet pipe 403 is arranged on the side surface of the cylinder body 401, and an exhaust pipe 404 is arranged on the top of the cylinder body 401. The exhaust pipe 404 is used to discharge the purified flue gas. And a dust removal chamber is formed inside the cylinder body 401, and the inner wall of the dust removal chamber is a regular hexahedron. When the dusty flue gas tangentially enters the dust removal chamber from the air inlet pipe 403, the flue gas will change from linear motion to circular motion. Most of the rotating airflow spirally flows downward along the cylinder wall from the cylindrical body 401 towards the cone. During the rotation process, the dust particles in the dusty flue gas are thrown towards the regular hexahedron cylinder wall due to the action of centrifugal force. After contacting the cylinder wall, they lose the radial inertial force and fall along the wall surface by the downward momentum and downward gravity. And the purified flue gas rotates upward along the exhaust pipe 404 and is discharged. Both the air inlet pipe 403 and the exhaust pipe 404 are communicated with the dust removal chamber; a cone 402, which is connected to the bottom of the cylinder body 401 and forms a gradually narrowing dust particle separation chamber. The dust particle separation chamber is communicated with the dust removal chamber. The cone 402 is preferably a regular hexagonal pyramid, so that the side wall of the dust particle separation chamber forms a regular hexagonal pyramid; a dust hopper, which is located below the cone and is used to collect the dust particles separated from the airflow; a dust discharge pipe (or dust outlet), which is connected to the dust hopper and is used to regularly or continuously discharge the collected dust particles.

[0056] In order to further improve the dust removal effect of the cyclone dust collector 4, the cylinder body 401 is in the shape of a twisted hexagonal prism. When the dusty flue gas tangentially enters the dust removal chamber from the air inlet pipe 403, the flue gas will change from linear motion to circular motion. Most of the rotating airflow spirally flows downward along the cylinder wall from the cylindrical body 401 towards the cone. During the rotation process, the dust particles in the dusty flue gas are thrown towards the spiral cylinder wall due to the action of centrifugal force. After contacting the cylinder wall, they lose the radial inertial force and fall along the wall surface by the downward momentum and downward gravity. And when the purified flue gas rotates upward along the exhaust pipe 404 and is discharged, it contacts the spiral cylinder wall again, and the flue gas is dusted again, so that the dust removal effect of the cyclone dust collector 4 is further improved.

[0057] In order to reduce the flue gas temperature to 200 - 230 °C, a water-cooled jacket 405 is fixedly sleeved on the cylinder body 401. A water-cooled cavity is formed between the water-cooled jacket 405 and the cylinder body 401. Flowing cooling water is introduced into the water-cooled cavity to reduce the flue gas temperature. An inlet 406 and an outlet 407 are arranged in the water-cooled jacket 405. During use, flowing cooling water is introduced into the water-cooled cavity through the inlet 406 and the outlet 407.

[0058] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A secondary air system for flue gas in a furnace, characterized in that: include: A smoke extraction port in the furnace, wherein the smoke extraction port in the furnace is located at the upper rear arch of the combustion section of the furnace; A cyclone dust collector, the inlet of which is connected to the flue gas extraction port in the furnace and is used to filter dust particles in the flue gas; A secondary fan, wherein the air inlet of the secondary fan is connected to the outlet of the cyclone dust collector; A double-flow secondary air spray gun, which is installed on the front and rear arches of the incinerator and is used to send smoke and air into the incinerator, and has a first connection port, a second connection port and a nozzle, wherein the first connection port is connected to the secondary air fan outlet; A cold air fan, wherein an air inlet of the cold air fan draws air, and an air outlet of the cold air fan is connected to the second connecting port.

2. A secondary air system for flue gas in a furnace as claimed in claim 1, characterized in that: The double-flow secondary air spray gun is a sleeve-type structure, comprising: an inner tube, wherein the inner tube forms an independent flue gas flow passage, and the flue gas flow passage is communicated with the first connecting port; an outer tube, sleeved outside the inner tube, and an air flow channel is formed between the inner tube and the outer tube, and the air flow channel is communicated with the second connecting port; When the flue gas flow passage is deactivated, the air in the air flow passage plays a role in protecting the double-flow secondary air spray gun, thereby preventing the double-flow secondary air spray gun from being deformed due to high temperature.

3. A secondary air system for flue gas in a furnace as claimed in claim 2, characterized in that: The air flow channel is configured with a variable diameter.

4. A secondary air system for flue gas in a furnace as claimed in claim 3, characterized in that: The inner tube nozzle end has an arc transition diameter change arrangement.

5. A secondary air system for flue gas in a furnace according to any one of claims 1 to 4, characterized in that: The cyclone dust collector comprises: The cylinder is a regular hexahedron, an air inlet pipe is arranged on the side of the cylinder, an exhaust pipe is arranged on the top of the cylinder, and a dust removal chamber is formed in the cylinder, and the air inlet pipe and the exhaust pipe are both connected to the dust removal chamber; The cone is connected to the bottom of the cylinder and forms a gradually shrinking dust particle separation and collection chamber, and the dust particle separation and collection chamber is communicated with the dust removal chamber.

6. A secondary air system for flue gas in a furnace as claimed in claim 5, characterized in that: The cylinder is in the shape of a twisted hexagonal column, so that the dust removal chamber forms a spiral shape.

7. A secondary air system for flue gas in a furnace as claimed in claim 6, characterized in that: A water cooling jacket is provided on the cylinder, and a water cooling cavity is formed between the water cooling jacket and the cylinder. Flowing cooling water flows into the water cooling cavity to reduce the temperature of the flue gas extracted from the furnace.

8. A secondary air system for flue gas in a furnace as claimed in claim 7, characterized in that: A bypass air duct is provided between the air inlet duct of the secondary fan and the outlet of the cyclone dust collector to extract air, and is used for extracting air from the secondary fan and sending it into the furnace to reduce the temperature inside the furnace when the furnace is overheated.

9. A secondary air system for flue gas in a furnace as claimed in claim 8, characterized in that: The secondary fan is a high temperature resistant fan, and the impeller of the secondary fan is equipped with an anti-wear lining.

10. A secondary air system for flue gas in a furnace as claimed in claim 9, characterized in that: A plurality of smoke extraction ports are arranged in parallel in the furnace.

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