Circulating fluidized bed boiler

Abstract

This invention provides a circulating fluidized bed boiler, relating to the field of combustion components in circulating fluidized bed boilers. The aim is to improve the combustion efficiency of the boiler. The circulating fluidized bed boiler includes a furnace body and secondary air nozzles; the secondary air nozzles are conical tubes, having a large end and a small end positioned opposite each other. The secondary air nozzles are mounted on the furnace body, with the small end extending into the furnace body; the secondary air nozzles include a first nozzle located at a corner of the furnace body; the centerline of the first nozzle forms an angle with the centerline of the furnace chamber. The conical structure of the secondary air nozzles increases the kinetic energy of the secondary air; the first nozzle is inclined towards the centerline of the furnace chamber, preventing wear of the water-cooled wall tubes by the secondary air, while minimizing the impact of the secondary air on the downward flow along the wall, ensuring material mixing, improving boiler thermal efficiency, thereby reducing the carbon content of fly ash, reducing boiler heat loss, and lowering operating costs.

Description

Technical Field

[0001] This invention relates to the field of combustion components for circulating fluidized bed boilers, and more specifically, to a circulating fluidized bed boiler. Background Technology

[0002] In response to the national call for energy conservation and emission reduction, many power plants have adopted circulating fluidized bed (CFB) boilers with low-NOx combustion technology. These boilers have a relatively high material concentration within the furnace, which meets NOx emission control requirements. However, the increased material concentration leads to a higher back pressure in the furnace, hindering the effective delivery of secondary air to the furnace center for oxygen replenishment. This results in fly ash being carried out of the furnace before complete combustion, causing heat loss in the CFB boiler. Fly ash accounts for approximately 70% of the bottom ash and fly ash after combustion in CFB boilers. Excessive carbon content in fly ash increases fuel consumption for power plants. Therefore, reducing the carbon content of fly ash to lower operating costs and improve economic and social benefits is crucial. Summary of the Invention

[0003] The object of the present invention includes, for example, providing a circulating fluidized bed boiler that can improve the combustion efficiency of the boiler.

[0004] The embodiments of the present invention can be implemented as follows:

[0005] An embodiment of the present invention provides a circulating fluidized bed boiler, comprising:

[0006] Furnace body and secondary air nozzles;

[0007] The secondary air nozzle is a conical tube with a large end and a small end that are positioned opposite each other. The secondary air nozzle is disposed on the furnace body, and the small end of the secondary air nozzle extends into the furnace body.

[0008] The secondary air nozzle includes a first nozzle located at a corner of the furnace body; the centerline of the first nozzle is set at an angle to the centerline of the furnace chamber of the furnace body.

[0009] Optionally, the secondary air nozzles are arranged in a single layer.

[0010] Optionally, the furnace body includes a front wall;

[0011] The circulating fluidized bed boiler also includes an air box installed on the front wall and multiple secondary air ducts; one end of each of the multiple secondary air ducts is connected to the air box, and the other end of each of the multiple secondary air ducts is connected to the secondary air nozzles respectively.

[0012] The cross-sectional area of ​​the air box on the front wall is 2.1 to 2.3 times the sum of the cross-sectional areas of the plurality of secondary air ducts on the front wall.

[0013] Optionally, the air velocity in the bellows ranges from 15 to 20 m / s, and the air velocity in the secondary air duct is 20 m / s to 25 m / s.

[0014] Optionally, the secondary air nozzle further includes a second nozzle disposed between two adjacent corners of the furnace body; the diameter of the small end of the second nozzle is larger than the diameter of the small end of the first nozzle.

[0015] Optionally, the length of the secondary air nozzle is in the range of 640-660 mm.

[0016] Optionally, the circulating fluidized bed boiler further includes an air distribution plate; the distance between the secondary air nozzle and the air distribution plate ranges from 3450 to 3950 mm.

[0017] Optionally, the angle between the centerline of the first nozzle and the centerline of the furnace chamber of the furnace body is in the range of 10°-20°.

[0018] Optionally, when the volatile matter Vdaf in the fuel is 20%-30%, the secondary air volume accounts for 50% of the total primary and secondary air volume; when the volatile matter Vdaf in the fuel is 31%-40%, the secondary air volume accounts for 55%-60% of the total primary and secondary air volume.

[0019] Optionally, the circulating fluidized bed boiler further includes swirl vanes; the swirl vanes are disposed on the inner wall of the secondary air nozzle, and the swirl vanes are spirally arranged around the axis of the secondary air nozzle; the swirl vanes are used to cause the air in the secondary air nozzle to gradually converge in the direction from the large end to the small end.

[0020] The beneficial effects of the circulating fluidized bed boiler in this embodiment of the invention include, for example:

[0021] A circulating fluidized bed boiler includes a furnace body and secondary air nozzles. The secondary air nozzles are conical tubes with opposite large and small ends. They are mounted on the furnace body, with the small end extending into the furnace. The secondary air nozzles include a first nozzle positioned at a corner of the furnace body. The centerline of the first nozzle forms an angle with the centerline of the furnace chamber. The conical structure of the secondary air nozzles increases the kinetic energy of the secondary air. The first nozzle's inclined orientation towards the furnace centerline prevents wear on the water-cooled wall tubes of the sidewalls and minimizes the impact of the secondary air on the downward flow along the wall, ensuring effective material mixing. This allows for more thorough mixing of the secondary air with the circulating materials within the furnace, improving boiler thermal efficiency, reducing CO values ​​and fly ash carbon content, and effectively increasing boiler utilization even at low bed temperatures. It overcomes the problem of high fly ash carbon content at low bed temperatures, reduces operating costs, and improves economic and social benefits. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a structural schematic diagram of a circulating fluidized bed boiler from a frontal view, provided in an embodiment of the present invention.

[0024] Figure 2 A top-view structural schematic diagram of a circulating fluidized bed boiler provided in an embodiment of the present invention;

[0025] Figure 3 This is a structural schematic diagram of the front wall of a circulating fluidized bed boiler provided in an embodiment of the present invention;

[0026] Figure 4 A schematic diagram of the structure of a circulating fluidized bed boiler from the rear wall perspective, provided in an embodiment of the present invention;

[0027] Figure 5 This is a first-view structural schematic diagram of a secondary air duct provided in an embodiment of the present invention;

[0028] Figure 6 This is a structural schematic diagram of a secondary air duct from a second perspective, provided in an embodiment of the present invention.

[0029] Figure 7 This is a structural schematic diagram of a secondary air duct from a third perspective, provided in an embodiment of the present invention.

[0030] Icons: 10-Circulating fluidized bed boiler; 100-Wind box; 200-Secondary air duct; 300-Expansion joint; 400-Air damper; 500-Secondary air nozzle; 510-Swirl vane; 501-First nozzle; 502-Second nozzle; 600-Sealing cover; 700-Furnace body; 710-Front wall; 720-Rear wall. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0033] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0034] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not 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 a limitation of this invention.

[0035] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0036] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0037] Due to the high concentration of circulating material in the furnace and the large back pressure at the secondary air nozzle, the secondary air cannot fully penetrate into the center of the furnace to mix with the oxygen-deficient circulating material in the middle. As a result, the fly ash is carried out of the furnace before it is completely burned, causing heat loss in the circulating fluidized bed boiler.

[0038] The following is combined with Figures 1 to 7 The circulating fluidized bed boiler 10 provided in this embodiment will be described in detail.

[0039] Please refer to Figure 1 as well as Figure 2 An embodiment of the present invention provides a circulating fluidized bed boiler 10, including a boiler body 700 and a secondary air nozzle 500; the secondary air nozzle 500 is a conical tube, and the secondary air nozzle 500 has a large end and a small end that are positioned opposite each other. The secondary air nozzle 500 is disposed on the boiler body 700, and the small end of the secondary air nozzle 500 extends into the boiler body 700; the secondary air nozzle 500 includes a first nozzle 501 disposed at a corner of the boiler body 700; the center line of the first nozzle 501 is set at an angle to the center line of the furnace chamber of the boiler body 700.

[0040] The size and arrangement of the secondary air nozzles (500mm) will vary depending on the size of the boiler. This embodiment of the invention uses a 75t / h to 280t / h boiler as an example for illustration.

[0041] Reference Figure 1 The circulating fluidized bed boiler 10 also includes a wind box 100, a secondary air duct 200, an expansion joint 300, an air damper 400, and a sealing cover 600, all mounted on the boiler body 700. The wind box 100, secondary air duct 200, expansion joint 300, and secondary air nozzles 500 are connected sequentially. The smaller end of the secondary air nozzle 500 extends into the boiler body 700 through the sealing cover 600, and the air damper 400 is mounted on the secondary air duct 200. This allows for air supply to the boiler body 700. The larger end of the secondary air nozzle 500 is connected to the wind box 100, and the smaller end extends into the boiler body 700. It should be noted that the larger end of the secondary air nozzle 500 refers to the end with the larger diameter, and the smaller end refers to the end with the smaller diameter; specifically, the diameter of the larger end of the secondary air nozzle 500 is larger than the diameter of the smaller end.

[0042] In this embodiment, the air box 100, the secondary air duct 200, and the secondary air nozzle 500 are connected in sequence; the air velocity in the air box 100 is 15-20 m / s, and the air velocity in the secondary air duct 200 is 20 m / s-25 m / s. The air velocity is highest at the secondary air nozzle 500.

[0043] In this embodiment, the secondary air nozzle 500 adopts a tapered tube, which can reduce frictional resistance and enable the secondary air to have greater kinetic energy.

[0044] Reference Figure 2 The furnace body 700 includes four corners, and each of the four corners is equipped with a first nozzle 501. (See reference...) Figure 1 The centerline of the furnace is the line indicated by label A. (Refer to...) Figure 2 The center line of the furnace is the point indicated by label B.

[0045] Because the flow is upward in the center of the furnace and downward around the perimeter, the secondary air nozzle (i.e., the smaller end of the secondary air nozzle 500) has a relatively high height from the furnace outlet flue, allowing sufficient time for the secondary air to mix and burn with the circulating material inside the furnace. Secondary air located in corners, being close to the downward flow, has a shorter distance to the sidewalls. Excessive secondary airflow can disrupt the downward flow direction, easily causing wear on the water-cooled wall tubes, requiring frequent anti-wear treatment or replacement. Therefore, each first nozzle 501 is inclined towards the furnace centerline to prevent wear on the sidewall water-cooled wall tubes by the secondary air, while minimizing the impact of the secondary air on the downward flow along the wall, ensuring effective material mixing.

[0046] Continue to refer to Figure 2 In this embodiment, the centerline of the first nozzle 501 is coplanar with the centerline of the furnace chamber of the furnace body 700. That is, the first nozzle 501 is inclined towards the center of the furnace body 700. Because the secondary air is offset towards the center during arrangement, the secondary air is injected into the upward flow in the middle, increasing the mixing time between the secondary air and the circulating material in the furnace, allowing for more efficient utilization of the secondary air. This satisfies the oxygen demand in the middle of the furnace while preventing excessive secondary air volume on the sides from causing wear on the water-cooled wall tubes.

[0047] In this embodiment, the angle between the centerline of the first nozzle 501 and the centerline of the furnace chamber of the furnace body 700 is in the range of 10°-20°.

[0048] The angle between the centerline of the first nozzle 501 and the centerline of the furnace chamber of the furnace body 700 is related to the length of the first nozzle 501 extending into the furnace body 700. The shorter the length, the larger the angle; the longer the length, the smaller the angle.

[0049] In this embodiment, the secondary air nozzles are arranged in a single layer (500). This helps reduce the frictional resistance between the secondary air preheater and the secondary air nozzles, improves the effective utilization rate of the secondary air fan, and reduces fan power consumption. The secondary air arrangement is changed from the original double-layer arrangement to a single-layer arrangement, eliminating the lower layer and only arranging the upper layer. The height of the upper secondary air inlet point is selected based on the furnace size: 3000–4000 mm for furnaces below 200 t / h, and 4000–5000 mm for furnaces between 200 and 400 t / h. The location is selected based on the back pressure within the furnace, ensuring sufficient depth and velocity of the secondary air after it enters the furnace.

[0050] Furthermore, the circulating fluidized bed boiler furnace is not oxygen-deficient around the perimeter, but is oxygen-deficient in the center. In this embodiment, based on the oxygen distribution pattern within the circulating fluidized bed boiler furnace, different secondary air arrangements are required for oxygen supplementation in different areas. Large-diameter secondary air nozzles are used in the center of the furnace to provide a large air volume, while small-diameter nozzles are used in the corners to provide only a smaller air volume.

[0051] Specifically, the secondary air nozzle 500 also includes a second nozzle 502 disposed between two adjacent corners of the furnace body 700; the diameter of the small end of the second nozzle 502 is larger than the diameter of the small end of the first nozzle 501.

[0052] This means that the small end of the 500 secondary air nozzle is arranged with unequal diameter, and the air is distributed in the furnace according to the needs of different areas.

[0053] For example, the diameter of the small end of the second nozzle 502 is 220 mm. The diameter of the small end of the first nozzle 501 is 200 mm. The diameter of the large end of both the second nozzle 502 and the first nozzle 501 is 377 mm.

[0054] Reference Figure 5 In this embodiment, the inclination angle between the large end and the small end of the first nozzle 501 is 6°-7°; the inclination angle between the large end and the small end of the second nozzle 502 is also 6°-7°. The inclination angle between the large end and the small end of the first nozzle 501 refers to the acute angle between the generatrix of the conical surface of the first nozzle 501 and its centerline. Figure 5 The angle indicated by the symbol W. Similarly, the inclination angle from the large end to the small end of the second nozzle 502 refers to the acute angle between the generatrix of the conical surface of the second nozzle 502 and the center line. For example, the inclination angle from the large end to the small end of the first nozzle 501 is 7°. The inclination angle from the large end to the small end of the second nozzle 502 is 6°. The inclination angle from the large end to the small end of the first nozzle 501 is greater than the inclination angle from the large end to the small end of the second nozzle 502.

[0055] The secondary air nozzle 500 uses a tapered tube, which helps reduce frictional resistance and allows the secondary air to have greater kinetic energy. The tilt angles of the first nozzle 501 and the second nozzle 502 are 6°-7°. By controlling the angle difference, the resistance of the secondary air nozzle 500 is reduced, and the resistance is controlled only at the end of the furnace on the fire side, giving it stronger kinetic energy. This ensures that the adjusted large and small ends have a flow velocity of ≥90m / s under hot air conditions. The secondary air nozzle 500 has a large orifice diameter and a large secondary air volume, resulting in more uniform mixing.

[0056] In this embodiment, the length of the secondary air nozzle 500 ranges from 640 to 660 mm. Specifically, the length of the secondary air nozzle 500 is 650 mm. The purpose of this longer length is to ensure that the secondary air has a high acceleration within the cone, and then the velocity at the nozzle is set according to the depth dimension of the furnace. For example, the velocity at the nozzle is designed to reach 75–100 m / s based on the depth dimension of the furnace, resulting in high kinetic energy.

[0057] Refer again Figure 2 , combined Figure 3 as well as Figure 4In this embodiment, the furnace body 700 includes a front wall 710; the circulating fluidized bed boiler also includes a wind box 100 and a plurality of secondary air ducts 200 disposed on the front wall 710; one end of each of the plurality of secondary air ducts 200 is connected to the wind box 100, and the other end of each of the plurality of secondary air ducts 200 is connected to a secondary air nozzle 500; the cross-sectional area of ​​the wind box 100 on the front wall 710 is 2.1 to 2.3 times the sum of the cross-sectional areas of the plurality of secondary air ducts 200 on the front wall 710.

[0058] Reference Figure 3 as well as Figure 4 The furnace body 700 includes a front wall 710 and a rear wall 720. Multiple secondary air ducts 200 and multiple secondary air nozzles 500 are respectively installed on the front wall 710 and the rear wall 720. The cross-sectional area of ​​the bellows 100 installed on the front wall 710 is equal to 2.1 to 2.3 times the sum of the cross-sectional areas of the multiple secondary air ducts 200 installed on the front wall 710. Similarly, the cross-sectional area of ​​the bellows 100 installed on the rear wall 720 is equal to 2.1 to 2.3 times the sum of the cross-sectional areas of the secondary air ducts 200 installed on the rear wall 720.

[0059] Specifically, the cross-sectional area of ​​the bellows 100 on the front wall 710 is equal to 2.2 times the sum of the cross-sectional areas of the multiple secondary air ducts 200 on the front wall 710.

[0060] After the secondary air exits the air preheater, a larger air box 100 is needed to deliver the secondary air to the secondary air nozzle 500. The larger cross-sectional area of ​​the air box 100 reduces the frictional resistance between the secondary air preheater and the secondary air nozzle 500, improving the effective utilization rate of the secondary air fan and reducing fan power consumption. The air preheater is essentially an air preheater. An air preheater transfers the heat carried by the flue gas discharged from the boiler's tail flue through heat dissipation pipes to the air entering the boiler, preheating the air to a certain temperature. It is a device used to improve the boiler's heat exchange performance and reduce energy consumption.

[0061] In this embodiment, the circulating fluidized bed boiler also includes an air distribution plate; the distance between the secondary air nozzle 500 and the air distribution plate ranges from 3450 to 3950 mm. Early circulating fluidized bed boilers had a secondary air nozzle height distance from the air distribution plate ranging from 2500 to 2800 mm; this invention proposes designing the distance between the nozzle center and the air distribution plate to be 3450-3950 mm.

[0062] In this embodiment, the secondary air volume accounts for 50%-60% of the total air volume. This embodiment optimizes the primary and secondary air ratio, reducing the primary air proportion to ensure a reducing atmosphere in the bottom region. In early circulating fluidized bed boilers, regardless of the fuel, the primary and secondary air ratio was generally 60%:40%. This embodiment proposes that the primary and secondary air ratio should be set according to the volatile matter content of the fuel; when the volatile matter content (Vdaf) in the fuel is 20%-30%, the secondary air volume accounts for 50% of the total primary and secondary air volume; when the volatile matter content (Vdaf) in the fuel is 31%-40%, the secondary air volume accounts for 55%-60% of the total primary and secondary air volume. Using the above design can effectively reduce NOx generation and primary air fan power consumption.

[0063] Reference Figure 6 as well as Figure 7 In this embodiment, a swirl vane 510 is provided inside the secondary air nozzle 500. The hot air inside the secondary air nozzle 500 rotates after entering the furnace. During this rotation, it can draw in oxygen-deficient materials from the surrounding area into the vortex formed by the secondary air, resulting in more uniform disturbance and mixing of the circulating materials within the furnace. Because the shape formed by the rotating secondary air resembles a drill bit, it penetrates deeper and mixes more evenly, giving the airflow greater kinetic energy. This allows for more thorough mixing of the secondary air with the circulating materials within the furnace, increasing the disturbance to the circulating materials. Therefore, the conical tube with the swirl vane 510 allows the secondary air to be more concentrated, effectively blowing it into the center of the furnace for oxygen replenishment, further increasing the disturbance to the circulating materials within the furnace, improving combustion efficiency, and thus reducing the carbon content of the fly ash.

[0064] Reference Figure 6 as well as Figure 7 In this embodiment, there are multiple swirl vanes 510; the multiple swirl vanes 510 are arranged at intervals along the circumference of the secondary air nozzle 500, and each swirl vane 510 is spirally arranged around the axis of the secondary air nozzle 500.

[0065] Specifically, in this embodiment, there are three swirl vanes 510, which are evenly distributed around the secondary air nozzle 500. This helps to improve the converging effect of the swirl vanes 510.

[0066] In this embodiment, the helix angle of the swirl vane 510 ranges from 16° to 20°. Specifically, the helix angle of the swirl vane 510 is 18°. This ensures that the swirl vane 510 has a better wind-gathering effect. The width of the swirl vane 510 is 30 mm.

[0067] It should be noted that "helix angle" refers to the acute angle between the tangent to the cylindrical helix on the cylindrical surface and the straight generatrix of the cylindrical surface passing through the point of tangency. In this embodiment, it refers to the acute angle between the tangent to the swirl vane 510 and the straight generatrix of the conical surface passing through the point of tangency.

[0068] It should be noted that the first nozzle 501 and the second nozzle 502 are identical except for the differences mentioned in the text. For example, both the first nozzle 501 and the second nozzle 502 are tapered tubes and have swirl vanes 510 inside.

[0069] The circulating fluidized bed boiler 10 provided in this embodiment has at least the following advantages:

[0070] The secondary air nozzle 500 uses a tapered tube, which reduces frictional resistance and allows the secondary air to have greater kinetic energy, thereby improving the boiler's combustion efficiency.

[0071] The first nozzle 501 is inclined toward the center line of the furnace, which can prevent the secondary air from wearing the water-cooled wall tubes on the side wall, and at the same time minimize the impact of the secondary air on the downward flow along the wall.

[0072] The small ends of the secondary air nozzles 500 are arranged with unequal diameters. Based on the oxygen distribution pattern within the furnace, different secondary air arrangements are made to meet the oxygen supplementation needs of different areas. The diameter of the small end of the second nozzle 502 is set to be larger than the diameter of the small end of the first nozzle 501. This further prevents wear on the water-cooled sidewalls from the secondary air nozzles, minimizing the impact of the secondary air on the downward flow along the wall.

[0073] The secondary air nozzle 500 is equipped with a swirl vane 510. The hot air inside the secondary air nozzle 500 is in a rotating state after entering the furnace. The shape formed during the rotation is similar to a drill bit, which blows into the furnace to a greater depth, has greater kinetic energy, and mixes more evenly.

[0074] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A circulating fluidized bed boiler, characterized in that, include: Furnace body (700), secondary air nozzle (500) and swirl vane (510); The secondary air nozzle (500) is a tapered tube, and the secondary air nozzle (500) has a large end and a small end that are positioned opposite each other. The secondary air nozzle (500) is disposed on the furnace body (700). The circulating fluidized bed boiler also includes a wind box (100), a secondary air duct (200), an expansion joint (300), and a sealing cover (600) disposed on the furnace body (700); the wind box (100), the secondary air duct (200), the expansion joint (300), and the secondary air nozzle (500) are connected in sequence, and the small end of the secondary air nozzle (500) extends into the furnace body (700) through the sealing cover (600). The secondary air nozzle (500) includes a first nozzle (501) disposed at a corner of the furnace body (700) and a second nozzle (502) disposed between two adjacent corners of the furnace body (700); the centerline of the first nozzle (501) is set at an angle to the centerline of the furnace chamber of the furnace body (700); the diameter of the small end of the second nozzle (502) is larger than the diameter of the small end of the first nozzle (501); The swirl vane (510) is disposed on the inner wall of the secondary air nozzle (500), and the swirl vane (510) is spirally arranged around the axis of the secondary air nozzle (500); the swirl vane (510) is used to make the air in the secondary air nozzle (500) gradually converge along the direction from the large end to the small end.

2. The circulating fluidized bed boiler according to claim 1, characterized in that: The secondary air nozzles (500) are arranged in a single layer.

3. The circulating fluidized bed boiler according to claim 1, characterized in that: The furnace body (700) includes a front wall (710); The circulating fluidized bed boiler also includes a wind box (100) and a plurality of secondary air ducts (200) disposed on the front wall (710); one end of each of the plurality of secondary air ducts (200) is connected to the wind box (100), and the other end of each of the plurality of secondary air ducts (200) is connected to the secondary air nozzles (500); The cross-sectional area of ​​the air box (100) on the front wall (710) is 2.1 to 2.3 times the sum of the cross-sectional areas of the plurality of secondary air ducts (200) on the front wall (710).

4. The circulating fluidized bed boiler according to claim 3, characterized in that: The air velocity in the bellows (100) is 15-20 m / s, and the air velocity in the secondary air duct (200) is 20 m / s-25 m / s.

5. The circulating fluidized bed boiler according to any one of claims 1-4, characterized in that: The length of the secondary air nozzle (500) ranges from 640 to 660 mm.

6. The circulating fluidized bed boiler according to any one of claims 1-4, characterized in that: The circulating fluidized bed boiler also includes an air distribution plate; the distance between the secondary air nozzle (500) and the air distribution plate is 3450-3950mm.

7. The circulating fluidized bed boiler according to any one of claims 1-4, characterized in that: The angle between the centerline of the first nozzle (501) and the centerline of the furnace chamber of the furnace body (700) is in the range of 10°-20°.

8. The circulating fluidized bed boiler according to any one of claims 1-4, characterized in that: When the volatile matter content (Vdaf) in the fuel is 20%-30%, the secondary air volume accounts for 50% of the total primary and secondary air volume. When the volatile matter content (Vdaf) in the fuel is 31%-40%, the secondary air volume accounts for 55%-60% of the total primary and secondary air volume.

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