A coal powder cyclone combustor based on gap type oxygen increasing and combustion stabilization

Abstract

The utility model discloses a kind of coal powder cyclone combustor based on gap type oxygen-increasing stable combustion, belong to coal powder combustion technical field, including by inside to outside sequentially coaxially arranged central tube, primary air pipe, oxygen-increasing air pipe and secondary air pipe, the setting of gap type oxygen-increasing airflow channel between oxygen-increasing air pipe and primary air pipe, so that oxygen-increasing airflow for stable combustion can be evenly transported to the ignition area root of primary air coal powder airflow, realize the stable flame combustion of coal powder under the low load state of combustor.The coal powder cyclone combustor in the utility model, its structure is simple, control is convenient, can realize the uniform delivery of oxygen to the ignition area root under the low load operating state of coal powder cyclone combustor, ensure the uniformity and stability of oxygen supply, avoid the flame deflection or pulsation caused by uneven oxygen supply, greatly strengthen the chemical reaction intensity of initial ignition stage, improve the stable combustion performance of combustor under low load operating condition, with good practical value.

Description

Technical Field

[0001] This utility model belongs to the field of pulverized coal combustion technology, specifically relating to a pulverized coal swirl burner based on slit-type oxygen-enriched stable combustion. Background Technology

[0002] For coal-fired power units, how to achieve deep peak shaving is a key technical issue that operators are concerned about. The core challenge in deep peak shaving is usually stable combustion control under low load conditions.

[0003] Currently, most traditional swirl burners rely on high-temperature flue gas recirculation to heat pulverized coal. However, under low load conditions, the furnace temperature is low and the recirculated flue gas temperature is insufficient, leading to delayed ignition or even flameout of the pulverized coal, which affects the normal operation of coal-fired units.

[0004] In existing technologies, oxygen-enrichment technology is typically used to add extra oxygen to adapt to low-load combustion in coal-fired units, addressing control under low-load conditions. However, due to the high concentration and high velocity of pulverized coal in the primary air duct, it is difficult to uniformly introduce oxygen. Therefore, most existing oxygen-enrichment technologies mix oxygen into the secondary air or deliver it into the furnace through discrete spray guns. While these methods can increase the oxygen concentration in the combustion gases to some extent, they fail to directly and uniformly transport oxygen to the critical area requiring the most ignition enhancement: the root of the ignition zone in the primary air-pulverized coal flow. This results in uneven mixing of oxygen and pulverized coal, low oxygen utilization, and the potential for localized high temperatures and increased NOx emissions. Utility Model Content

[0005] In response to one or more of the above-mentioned defects or improvement needs of the existing technology, this utility model provides a pulverized coal swirl burner based on slit-type oxygen-enriched combustion, which can directly deploy oxygen in a uniform and controllable manner at the root of the pulverized coal airflow, thereby maximizing the ignition stability of the pulverized coal swirl burner under low-load operation.

[0006] To achieve the above objectives, this utility model provides a pulverized coal swirl burner based on slit-type oxygen-enriched stable combustion, comprising a central tube, a primary air duct, and a secondary air duct arranged coaxially from the inside out; and An oxygenation duct is also provided between the primary air duct and the secondary air duct; The oxygen-enriching duct is coaxially sleeved around the outer periphery of the primary air duct, and a slit-type oxygen-enriching flow channel is formed between the oxygen-enriching duct and the primary air duct, so that the oxygen-enriching flow used for stable combustion can be transported to the root of the ignition zone of the primary air pulverized coal flow through the slit-type oxygen-enriching flow channel.

[0007] As a further improvement of this utility model, the secondary air duct includes an inner secondary air duct and an outer secondary air duct that are coaxially sleeved from the inside to the outside of the oxygenation air duct, and an inner secondary air flow channel is formed between the inner secondary air duct and the oxygenation air duct, and an outer secondary air flow channel is formed between the inner secondary air duct and the outer secondary air duct.

[0008] As a further improvement of this utility model, a swirling device is respectively provided in the slit-type oxygen-enriching airflow channel, the inner secondary airflow channel, and the outer secondary airflow channel.

[0009] As a further improvement of this utility model, the outlet of the slit-type oxygen-enhancing flow channel is an annular slit-type oxygen-enhancing flow outlet, and the slit width of the slit-type oxygen-enhancing flow outlet is 5mm~20mm.

[0010] As a further improvement of this utility model, the airflow injection direction of the slit-type oxygen-enhancing airflow outlet forms an angle of 10° to 30° with the axis of the central tube.

[0011] As a further improvement of this utility model, the gas introduced into the slit-type oxygen-enriching flow channel is oxygen-enriching gas, and the oxygen concentration of the oxygen-enriching gas is 21%~40%.

[0012] As a further improvement of this utility model, the oxygen-enhancing gas is a mixture of air and oxygen; or, the oxygen-enhancing gas is a mixture of oxygen and circulating flue gas.

[0013] As a further improvement of this utility model, the outer periphery of the central pipe is provided with a duct convergence section, a pulverized coal concentration ring and a combustion stabilizing ring in sequence along the axial direction, and the combustion stabilizing ring is disposed on the outer periphery of the central air outlet of the central pipe.

[0014] As a further improvement of this utility model, it also includes a control system and an oxygen supply subsystem; The control system is connected to the gas supply device of each pipeline of the pulverized coal cyclone burner, and is used to adjust the gas flow rate of the corresponding gas supply device according to the operating status of the burner; the oxygen supply subsystem is connected to the gas supply device of the oxygen-enhancing stream and the control system respectively, and is used to adjust the oxygen concentration in the oxygen-enhancing stream according to the control command of the control system.

[0015] As a further improvement of this utility model, the pipe outlets located on the outer side protrude forward from the pipe outlets located on the inner side. and / or The outlets of the primary air duct, the oxygenation air duct, the inner secondary air duct, and the outer secondary air duct are respectively designed as flared mouths with increased outer diameters, so that the airflow in each duct is ejected outward at an upward angle.

[0016] The aforementioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0017] In summary, the beneficial effects of the above-described technical solutions conceived by this utility model compared with the prior art include: This utility model relates to a pulverized coal swirl burner based on slit-type oxygen-enriched combustion stabilization. It includes a central pipe, a primary air pipe, an oxygen-enriched air pipe, and a secondary air pipe arranged coaxially from the inside out. The slit-type oxygen-enriched flow channel between the oxygen-enriched air pipe and the primary air pipe allows the oxygen-enriched flow for combustion stabilization to be evenly delivered to the root of the ignition zone of the primary air-pulverized coal flow. This achieves stable flame combustion of pulverized coal under low-load conditions, avoids ignition delay under low-load conditions, improves the combustion stabilization performance and combustion efficiency of the pulverized coal swirl burner, and effectively suppresses the formation of nitrogen oxides.

[0018] The pulverized coal swirl burner based on slit-type oxygen-enriched combustion in this invention has a simple structure and is easy to control. It can achieve uniform oxygen delivery to the root of the ignition zone under low-load operation of the pulverized coal swirl burner, ensuring the uniformity and stability of oxygen supply, avoiding flame deflection or pulsation caused by uneven oxygen supply, greatly enhancing the chemical reaction intensity in the initial ignition stage, and improving the stable combustion performance of the burner under low-load operation conditions. It has good practical value. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of the pulverized coal cyclone burner based on slit-type oxygen-enriched stable combustion in this utility model embodiment; Figure 2 This is a schematic diagram of the airflow and root ignition ring of the pulverized coal cyclone burner in this embodiment of the present invention; In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1. Central duct; 2. Primary air duct; 3. Oxygen-enriched air duct; 4. Inner secondary air duct; 5. Outer secondary air duct; 6. Swirl device; 7. Root ignition ring; 8. Central recirculation zone; 101. Central air inlet; 102. Central air outlet; 201. Primary air inlet; 202. Duct convergence section; 203. Pulverized coal concentration ring; 204. Combustion stabilization ring; 205. Primary air outlet; 301. Oxygen-enriched air inlet; 302. Slotted oxygen-enriched air outlet; 401. Internal secondary air inlet; 402. Internal secondary air outlet; 501. External secondary air inlet; 502. External secondary air outlet. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present utility model and are not intended to limit the present utility model. Furthermore, the technical features involved in the various embodiments of the present utility model described below can be combined with each other as long as they do not conflict with each other.

[0022] In the description of this utility model, it should be understood that, unless otherwise explicitly specified and limited, the terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this utility model 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. Therefore, they should not be construed as limitations on this utility model.

[0023] Furthermore, unless otherwise expressly defined, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly and specifically defined.

[0024] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0025] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0026] Below, for reference Figure 1 , Figure 2 This invention describes a pulverized coal cyclone burner based on a slit-type oxygen-enriched combustion system according to a preferred embodiment of the present invention.

[0027] like Figure 1 As shown, in the preferred embodiment, the pulverized coal swirl burner based on slit-type oxygen-enriched stable combustion includes a central tube 1, a primary air duct 2, and a secondary air duct arranged coaxially from the inside to the outside.

[0028] More importantly, an oxygen-enriching duct 3 is installed between the primary air duct 2 and the secondary air duct. The oxygen-enriching duct 3 is coaxially sleeved around the outer periphery of the primary air duct 2, and a longitudinally continuous and annular slit-type oxygen-enriching flow channel is formed between the oxygen-enriching duct 3 and the primary air duct 2, so that the oxygen-enriching flow used for stable combustion can be delivered to the root of the ignition zone of the primary air pulverized coal flow through the slit-type oxygen-enriching flow channel.

[0029] By utilizing the oxygen-enriched air duct 3, oxygen-enriched gas (i.e., oxygen-enriched flow) can be precisely delivered to the root of the ignition zone (i.e., the front end area of ​​the outlet of primary air duct 2) of the primary air pulverized coal airflow (i.e., the material conveyed by primary air duct 2) through a slotted oxygen-enriched flow channel when the pulverized coal swirl burner is operating at low load. This ensures that the increased oxygen can be uniformly and controllably deployed directly to the root of the pulverized coal airflow, acting synchronously with the high-temperature return flue gas on the pulverized coal particles, maximizing the ignition stability of the pulverized coal, thereby enhancing the stable combustion performance of the burner under low load operation.

[0030] Furthermore, by using the oxygen-enriching duct 3 coaxially sleeved around the primary air duct 2, the oxygen-enriching flow is uniformly and coaxially mixed with the primary air and pulverized coal flow at the root of the ignition zone in a 360° circumferential direction, forming a root ignition ring 7. This achieves uniform and synchronous ignition in the circumferential direction, effectively avoiding flame deflection or pulsation caused by uneven oxygen supply in the circumferential direction, and fully ensuring the stability and reliability of oxygen-enriched combustion. Moreover, the method of using the oxygen-enriching duct 3 to form a slotted oxygen-enriching flow channel is a static mechanical structure with no moving parts, resulting in high stability. Since the oxygen-enriching duct 3 is located outside the primary air duct 2, it can be continuously cooled by the primary air, resulting in a relatively low operating temperature and avoiding the risk of burn-off and coking, thus fully ensuring the stability of the oxygen-enriching duct 3 installation.

[0031] Specifically, in the preferred embodiment, the central tube 1 is located at the center of the burner, with one end being the central air inlet 101 and the other end being the central air outlet 102. The central tube 1 is mainly used to create a low-pressure zone at the burner outlet by introducing high-speed central air (which can also be part of the primary air), entraining high-temperature flue gas to form an internal recirculation zone, and bringing unburned coal powder and high-temperature flue gas back to the root of the flame, providing continuous heat and active groups, and significantly improving ignition stability.

[0032] Meanwhile, in the preferred embodiment, the primary air duct 2 has a primary air inlet 201 and a primary air outlet 205. In the preferred embodiment, the primary air inlet 201 and the primary air outlet 205 are preferably orthogonally arranged. At this time, the central pipe 1 passes through the pipe wall of the primary air duct 2 and extends into the inner cavity of the primary air duct 2, forming an annular cavity in the inner cavity of the primary air duct 2 to transport the primary air pulverized coal airflow.

[0033] Furthermore, in the preferred embodiment, the secondary air duct includes an inner secondary air duct 4 and an outer secondary air duct 5 coaxially sleeved from the inside to the outside of the oxygenation air duct 3, forming an inner secondary airflow channel between the inner secondary air duct 4 and the oxygenation air duct 3, and forming an outer secondary airflow channel between the inner secondary air duct 4 and the outer secondary air duct 5.

[0034] More specifically, the internal secondary air duct 4 includes an internal secondary air inlet 401 and an internal secondary air outlet 402, and the external secondary air duct 5 includes an external secondary air inlet 501 and an external secondary air outlet 502. The two secondary air inlets are respectively connected to the corresponding gas supply devices, and can continuously introduce secondary air into the burner.

[0035] To ensure the stability and controllability of the oxygen-enhancing flow and secondary air swirl transport, in the preferred embodiment, swirl devices 6 are respectively installed in the slit-type oxygen-enhancing flow channel, the inner secondary airflow channel, and the outer secondary airflow channel, such as... Figure 1 As shown in the image.

[0036] In actual installation, the outlet of the slit-type oxygen-enhancing flow channel is an annular slit-type oxygen-enhancing flow outlet 302, with a slit width of 5mm to 20mm. The slit-type design of the oxygen-enhancing flow channel ensures sufficient penetration and velocity of the oxygen-enhancing flow while preventing backflow of pulverized coal.

[0037] More preferably, in an optional example, the slit width at the outlet of the slit-type oxygen-enhancing flow channel decreases sequentially from the side near the middle of the airflow channel to the outlet end side, thereby ensuring the concentration and stabilization effect of the slit-type oxygen-enhancing flow channel on the oxygen-enhancing flow and ensuring the stability of the oxygen-enhancing flow delivery.

[0038] Furthermore, in actual installation, the airflow injection direction of the slit-type oxygen enrichment outlet 302 is preferably at an angle of 10° to 30° with the axis of the central pipe 1. That is, the outlets of the primary air pipe 2 and the oxygen enrichment air pipe 3 are respectively set as flared mouths with enlarged inner diameters, thereby forming an outwardly slit-type oxygen enrichment outlet 302, so that the oxygen enrichment flow from the oxygen enrichment inlet 301 can be injected at an upward angle to the ignition root of the burner, ensuring the reliability of oxygen enrichment flow delivery.

[0039] In a preferred embodiment, the gas introduced into the slit-type oxygen-enriching flow channel is oxygen-enriching gas, and the oxygen concentration of the oxygen-enriching gas is 21% to 40%.

[0040] More specifically, the oxygen-enhancing gas is a mixture of air and oxygen; or, the oxygen-enhancing gas is a mixture of oxygen and circulating flue gas. Depending on actual needs and operating conditions, the aforementioned combination of oxygen-enhancing gas flow can be adjusted accordingly, which will not be elaborated upon here.

[0041] Furthermore, in actual installation, it is preferable to sequentially install a duct convergence section 202, a pulverized coal concentration ring 203, and a combustion stabilizing ring 204 along the axial direction on the outer periphery of the central pipe 1. The combustion stabilizing ring 204 is located on the outer periphery of the central air outlet 102 of the central pipe 1, and the duct convergence section 202 is located on the side of the pulverized coal concentration ring 203 opposite to the combustion stabilizing ring 204. Figure 1 Therefore.

[0042] By utilizing the combination of the duct convergence section 202, the pulverized coal concentration ring 203, and the combustion stabilization ring 204, the convergence and acceleration of the primary airflow can be fully realized, as well as the uniform concentration and stable delivery of the pulverized coal carried by the primary airflow.

[0043] More specifically, the burner in the preferred embodiment further preferably includes a control system and an oxygen supply subsystem (not shown in the figure). The control system is connected to the gas supply devices of each pipe of the pulverized coal swirl burner, and is used to adjust the gas flow rate of the corresponding gas supply device according to the burner's operating status, thereby adjusting the supply status of the central air, primary air, and secondary air. Simultaneously, the oxygen supply subsystem is connected to both the oxygen-enhancing flow supply device and the control system, and is used to adjust the oxygen concentration in the oxygen-enhancing flow according to the control commands of the control system, thereby improving the control flexibility and adjustment versatility of the burner's oxygen-enhanced combustion stability design.

[0044] More preferably, the outlets of the outer pipes protrude forward from the outlets of the inner pipes, that is, the outlet of the primary air duct 2 protrudes from the outlet of the central pipe 1, the outlet of the oxygenation air duct 3 protrudes from the outlet of the primary air duct 2, the outlet of the inner secondary air duct 4 protrudes from the outlet of the oxygenation air duct 3, and the outlet of the outer secondary air duct 5 protrudes from the outlet of the inner secondary air duct 4.

[0045] Furthermore, the outlets of primary air duct 2, oxygenation air duct 3, inner secondary air duct 4, and outer secondary air duct 5 are respectively designed as flared mouths with increased outer diameters, so that the airflow in each duct is ejected outward at an upward angle, forming a... Figure 2 The airflow jet trajectory shown in the middle (dashed line) forms a central recirculation zone 8 at the front end of the burner nozzle and a root ignition ring 7 of pulverized coal in front of the outlet of the oxygen-enriching duct 3.

[0046] For the pulverized coal cyclone burner in the preferred embodiment, its operation under low load conditions is preferably as follows: (1) When the boiler load is lower than the stable combustion threshold, oxygen supply is provided to the slit-type oxygen supply channel; (2) The oxygen-enriched flow forms an annular gas jet through the annular nozzle gap (slot-type oxygen-enriched flow outlet 302), and the jet is injected into the furnace close to the outer surface of the primary air pulverized coal flow. (3) The annular oxygen-enriched flow and the high-temperature flue gas returning from the central return zone 8 work together at the outlet edge of the primary air pulverized coal flow to form a stable root ignition ring 7 that surrounds the pulverized coal flow. (4) The root ignition ring 7 ignites the entire primary air pulverized coal flow, achieving stable combustion under ultra-low load.

[0047] In actual control, the ignition position of pulverized coal can be controlled by independently adjusting the swirl intensity of the oxygen-enriching flow in the slit-type oxygen-enriching flow channel; by independently adjusting the swirl intensity of the internal and external secondary air, while ensuring stable ignition at the root, the entire combustion process can be controlled to achieve air staging, thereby reducing nitrogen oxide emissions.

[0048] The pulverized coal swirl burner based on slit-type oxygen-enriched combustion in this invention has a simple structure and is easy to control. It can achieve uniform oxygen delivery to the root of the ignition zone under low-load operation of the pulverized coal swirl burner, ensuring the uniformity and stability of oxygen supply, avoiding flame deflection or pulsation caused by uneven oxygen supply, greatly enhancing the chemical reaction intensity in the initial ignition stage, and improving the stable combustion performance of the burner under low-load operation conditions. It has good practical value.

[0049] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion, characterized in that, It includes a central duct, a primary air duct, and a secondary air duct, arranged coaxially from the inside out; and An oxygenation duct is also provided between the primary air duct and the secondary air duct; The oxygen-enriching duct is coaxially sleeved around the outer periphery of the primary air duct, and a slit-type oxygen-enriching flow channel is formed between the oxygen-enriching duct and the primary air duct, so that the oxygen-enriching flow used for stable combustion can be transported to the root of the ignition zone of the primary air pulverized coal flow through the slit-type oxygen-enriching flow channel.

2. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to claim 1, characterized in that, The secondary air duct includes an inner secondary air duct and an outer secondary air duct that are coaxially sleeved from the inside to the outside of the oxygenation air duct. An inner secondary air flow channel is formed between the inner secondary air duct and the oxygenation air duct, and an outer secondary air flow channel is formed between the inner secondary air duct and the outer secondary air duct.

3. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to claim 2, characterized in that, Swirling devices are respectively installed in the slit-type oxygen-enriching airflow channel, the inner secondary airflow channel, and the outer secondary airflow channel.

4. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to any one of claims 1 to 3, characterized in that, The outlet of the slit-type oxygen-enhancing flow channel is an annular slit-type oxygen-enhancing flow outlet, and the slit width of the slit-type oxygen-enhancing flow outlet is 5mm~20mm.

5. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to claim 4, characterized in that, The airflow injection direction of the slit-type oxygen-enhancing airflow outlet forms an angle of 10° to 30° with the axis of the central tube.

6. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to any one of claims 1 to 3 and 5, characterized in that, The gas introduced into the slit-type oxygen-enriching flow channel is oxygen-enriching gas, and the oxygen concentration of the oxygen-enriching gas is 21%~40%.

7. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to claim 6, characterized in that, The oxygen-enhancing gas is a mixture of air and oxygen; or, the oxygen-enhancing gas is a mixture of oxygen and circulating flue gas.

8. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to any one of claims 1 to 3, 5, and 7, characterized in that, The outer periphery of the central pipe is provided with a duct convergence section, a pulverized coal concentration ring and a combustion stabilization ring in sequence along the axial direction. The combustion stabilization ring is located on the outer periphery of the central air outlet of the central pipe.

9. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to any one of claims 1 to 3, 5, and 7, characterized in that, It also includes the control system and the oxygen supply subsystem; The control system is connected to the gas supply device of each pipeline of the pulverized coal cyclone burner, and is used to adjust the gas flow rate of the corresponding gas supply device according to the operating status of the burner; the oxygen supply subsystem is connected to the gas supply device of the oxygen-enhancing stream and the control system respectively, and is used to adjust the oxygen concentration in the oxygen-enhancing stream according to the control command of the control system.

10. The pulverized coal cyclone burner based on slotted oxygen-enriched stable combustion according to claim 2 or 3, characterized in that, The pipe outlets located on the outer side protrude forward from the pipe outlets located on the inner side; and / or The outlets of the primary air duct, the oxygenation air duct, the inner secondary air duct, and the outer secondary air duct are respectively designed as flared mouths with increased outer diameters, so that the airflow in each duct is ejected outward at an upward angle.

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