A low NOx swirl burner suitable for multi-mode operation

Abstract

The present application relates to a kind of low NOx swirl burner suitable for multi-mode operation, the low NOx swirl burner includes successively from inside to outside: center ammonia injection pipe, primary air pipe, inner secondary air passage and outer secondary air passage, the primary air pipe is provided with pulverized coal concentration separator near outlet section, the burner outlet is provided with separation ring, separation ring is located at the outlet end of pulverized coal concentration separator, by adjustable fuel and air volume distribution, multi-stage ammonia injection and strengthen stable combustion structure, realize the efficient, stable combustion of pure coal, ammonia coal mixed combustion and pure ammonia three modes, and by the active intervention to reaction path, all modes are realized in ultra-low NOx emission.

Description

Technical Field

[0001] This invention relates to the field of combustion equipment technology, and in particular to a low-NOx swirl burner suitable for multi-mode operation. Background Technology

[0002] As a major energy supply device, coal-fired boilers face the dual pressure of carbon emission reduction and coordinated control of pollutants. The traditional pure coal combustion mode can no longer meet the increasingly stringent environmental protection and emission reduction standards, and there is an urgent need to develop low-carbon and efficient alternative combustion technologies.

[0003] Ammonia, as a highly promising hydrocarbon-free carrier fuel, possesses significant advantages such as low transportation and storage costs, high safety, and zero carbon emissions during combustion. Its co-combustion with coal in existing boilers or direct pure ammonia combustion is widely recognized as a feasible technological path for rapidly reducing carbon emissions. Currently, stable operation tests with a maximum ammonia blending ratio of 35% have been successfully completed on a 300 MW coal-fired unit, verifying the engineering feasibility of ammonia-coal co-combustion technology. However, ammonia-coal co-combustion and pure ammonia combustion technologies face core technological challenges: on the one hand, the addition of ammonia fuel significantly increases the formation potential of nitrogen oxides (NOx), exacerbating the difficulty of pollutant emission control; on the other hand, ammonia itself has inherent characteristics such as low laminar combustion velocity, high ignition energy requirements, and poor combustion stability, leading to a significant reduction in the stability of the combustion system when co-combusted with coal or burned purely with ammonia.

[0004] Low NOx emissions are a key indicator for the environmental compliance of coal-fired boilers. Existing low-NOx pulverized coal burners are all optimized for pure coal combustion. When applied to ammonia-coal co-fired or pure ammonia combustion scenarios, there are obvious inapplicability issues. Specifically, firstly, they cannot effectively utilize the chemical properties of ammonia to suppress NOx generation during its own combustion process. Related studies have confirmed that the premixed combustion of ammonia and coal is not conducive to NOx control. Secondly, the existing burners have unreasonable designs for the mixing of ammonia and pulverized coal, which can easily lead to decreased flame stability or uncontrolled NOx emissions, making it difficult to adapt to the special requirements of ammonia-coal co-fired and pure ammonia combustion.

[0005] In summary, existing low-NOx pulverized coal burners cannot meet the technical requirements of ammonia-coal co-firing and pure ammonia combustion, and have key defects such as poor fuel adaptability, insufficient NOx control capability, and poor combustion stability. Developing a new type of burner with efficient and stable combustion and ultra-low NOx emissions has become a core technical problem that urgently needs to be solved in the field of carbon emission reduction and pollutant synergistic control of coal-fired boilers. Summary of the Invention

[0006] To address the aforementioned technical issues, this invention utilizes a multi-layer channel structure, adds a coal powder concentration separation and angle-adjustable separation ring assembly, and matches parameter control strategies under multiple combustion modes. This enables adaptation to pure coal, ammonia-coal co-combustion, and high-proportion ammonia modes. It not only solves the core defects of traditional burners, such as limited fuel adaptability, insufficient NOx control capabilities, and mismatched combustion stabilization methods, but also achieves the dual goals of efficient and stable combustion and ultra-low NOx emissions under various modes.

[0007] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a low-NOx swirl burner suitable for multi-mode operation. The low-NOx swirl burner, from the inside out, comprises: a central ammonia injection pipe, a primary air duct, an inner secondary air channel, and an outer secondary air channel. A pulverized coal concentration separator is installed near the outlet section of the primary air duct. A separation ring is installed at the outlet of the low-NOx swirl burner. The separation ring, located at the outlet end of the pulverized coal concentration separator, is composed of multiple angle-adjustable wedge-shaped blades arranged in a circular array around the central axis of the separation ring. The central ammonia injection pipe is used to transport any one or a combination of ammonia and central air. The primary air duct is used to transport any one or a combination of pulverized coal and primary air. The inner and outer secondary air channels are used to transport distribution air. This invention utilizes a central ammonia injection pipe and a layered channel structure to transport ammonia and pulverized coal through different channels, avoiding the problem of increased NOx generation caused by traditional premixing methods. Furthermore, the angle of the separation ring at the burner outlet is adjustable, allowing for further optimization of the mixing path between pulverized coal and ammonia under different operating conditions, thus preventing flame disturbance. This invention solves the problems of unreasonable ammonia and pulverized coal mixing and insufficient NOx control mechanisms in traditional burners, achieving improved orderliness in multi-fuel delivery and enhanced combustion stability.

[0008] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0009] As a preferred technical solution of the present invention, the pulverized coal concentration separator is an annular structure that is attached and fixed to the inner wall of the primary air duct, and both ends of the annular structure are provided with inclined transition slopes.

[0010] Preferably, the inner diameter of the annular structure is 1 / 2 to 4 / 5 of the inner diameter of the primary air duct, for example, it can be 1 / 2, 2 / 3, 3 / 4 or 4 / 5, etc.

[0011] Preferably, the inclination angle of the inclined transition slope is 30°~60°, for example, it can be 30°, 35°, 40°, 45°, 50° or 60°.

[0012] This invention designs the pulverized coal concentration separator as a ring-shaped structure with an inclined transition slope. On the one hand, the inclined transition slope reduces the accumulation of pulverized coal on the separator surface, preventing blockage. On the other hand, the ring-shaped structure enables the pulverized coal airflow in the primary air duct to form a uniform concentration zone, rather than local accumulation, ensuring a stable reducing atmosphere in the concentrated pulverized coal zone, further enhancing the NOx suppression effect, while ensuring the smooth flow of pulverized coal. This solves the problems of easy pulverization and uneven concentration zone in the separator, and improves the reliability of burner operation.

[0013] As a preferred technical solution of the present invention, the separation ring is provided with a root hinge, and all wedge blades rotate synchronously around the root hinge to form an adjustable conical flare. The root hinge is fixedly or detachably connected to the inner wall of the outlet of the primary air duct.

[0014] The connection between the wedge-shaped blade and the root hinge of the present invention can be achieved through a structure commonly used in the art. For example, the wedge-shaped blade can be fitted with a hole at the root and fitted onto the root hinge, and a circumferential limit can be provided so that the wedge-shaped blade can only rotate around the root hinge.

[0015] The fixed or detachable connection between the root hinge and the outlet inner wall of the primary air duct described in this invention includes, but is not limited to, connecting rods, connecting chains, or connecting brackets, and is not further limited herein.

[0016] As a preferred technical solution of the present invention, the angle between the wedge-shaped blade of the separation ring and the central axis is set to different angles depending on the different operating conditions. The angle is 0~30°, for example, it can be 0°, 5°, 10°, 15°, 20°, 25° or 30°.

[0017] This invention designs the separation ring as an adjustable wedge-shaped blade structure, which can flexibly adjust the blade angle according to the needs of different combustion modes. Under different fuel ratios, by changing the size and angle of the conical flare, the mixing speed and mixing area of ​​the primary air pulverized coal and the ammonia or central air injected from the central ammonia injection pipe can be precisely controlled, avoiding NOx surges caused by excessively fast mixing or incomplete combustion caused by excessively slow mixing. At the same time, the circumferential array design of the wedge-shaped blades can make the airflow evenly distributed, avoiding flame instability caused by local eddies. This solves the problem of fixed structure of traditional burners and inability to adapt to multi-mode mixing requirements, and improves the flexibility and stability of the burner.

[0018] As a preferred technical solution of the present invention, the multi-mode operation includes pure coal mode, ammonia-coal co-fired mode and high-proportion ammonia mode.

[0019] As a preferred embodiment of the present invention, in the pure coal mode operation, the angle between the wedge-shaped blades of the separation ring and the central axis is a first angle, which is 10~20°, for example, 10°, 12°, 15°, 18°, or 20°. Within this angle range, the wedge structure generates a moderate centrifugal effect, which can moderately confine most of the dense-phase coal powder in the central region, forming an effective reducing atmosphere to suppress fuel-type NOx. At the same time, it allows a sufficient amount of light-phase coal powder to mix with the internal secondary air in a timely manner on the outside of the flare, facilitating stable ignition.

[0020] As a preferred embodiment of the present invention, in the ammonia-coal co-combustion mode, the angle between the wedge-shaped blades of the separation ring and the central axis is a second angle, which is greater than or equal to the first angle. This second angle is 20-30°, for example, 20°, 22°, 25°, 28°, or 30°. At this point, the guiding and separating effects of the flared end are most intense. Centrifugal force tightly concentrates and confines the dense-phase coal powder within the narrow channel at the center of the burner, creating a high-temperature, extremely high-fuel-concentration, and extremely oxygen-deficient enhanced reducing atmosphere region. This structure ensures that the ammonia gas injected from the central ammonia injection channel is completely enveloped within this enhanced reducing zone, maximizing its pyrolysis rather than oxidation, and providing sufficient reaction time for NOx reduction. The intense separation also delays premature mixing with peripheral air, protecting the reducing atmosphere in the core area.

[0021] As a preferred embodiment of the present invention, in the high-proportion ammonia mode operation, the angle between the wedge-shaped blades of the separation ring and the central axis is a third angle, which is less than or equal to the first angle, and the third angle is 0~10°, for example, 0°, 2°, 5°, 8°, or 10°. At this angle, the separation effect of the separation ring on the rich and lean gas flow is weakened. At a small angle, the physical shielding area of ​​the separation ring is maximized, and it acts as a blunt body, generating a large and highly stable recirculation zone behind it. This recirculation zone can effectively entrain a large amount of high-temperature flue gas, providing a stable ignition point for the low-reactivity ammonia flame and preventing flameout. A small amount of pulverized coal and primary air can ignite rapidly under this structure, providing a stable high-temperature ignition source for the entire combustion process.

[0022] In the pure coal mode of this invention, a small amount of central air is introduced through the central ammonia injection pipe, and pulverized coal and primary air are transported through the primary air duct. The inner and outer secondary air channels are supplied with distribution air as needed. In the ammonia-coal co-combustion mode, the mass ratio of coal flow rate to ammonia flow rate is 1:1 to 1:2. Ammonia is injected through the central ammonia injection pipe, pulverized coal is transported through the primary air duct, and distribution air is supplied through the inner and outer secondary air channels. In the high-proportion ammonia mode, the mass ratio of coal flow rate to ammonia flow rate is 1:2 to 1:4. The central ammonia injection pipe serves as the main fuel channel, injecting most of the ammonia. The primary air duct is not closed, but a very small amount of pulverized coal is transported. Distribution air is supplied through the inner and outer secondary air channels.

[0023] This invention achieves precise adaptation across multiple modes by setting specific angle ranges for the separation ring blades and fuel delivery strategies for different combustion modes. It solves the problems of mismatched parameters and difficulty in balancing stable combustion and NOx control during multi-mode operation of traditional burners, ensuring efficient and stable combustion in all modes.

[0024] As a preferred technical solution of the present invention, the outlet of the external secondary air duct is provided with an axial vortex.

[0025] Preferably, the axial cyclone includes adjustable cyclone blades.

[0026] As a preferred technical solution of the present invention, the swirl angle of the adjustable swirl blades during pure coal mode operation is 0~90°, for example, it can be 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° or 90°, which can be adaptively adjusted according to the coal fuel flow rate and combustion conditions.

[0027] Preferably, when the ammonia-coal co-combustion mode is running, the swirl angle of the adjustable swirl blade is a first swirl angle, which is 20~40°, for example, it can be 20°, 22°, 24°, 26°, 28°, 30°, 35° or 40°, etc.

[0028] Preferably, the swirl angle of the adjustable swirl blade during high-proportion ammonia mode operation is a second swirl angle, which is greater than or equal to the first swirl angle. The second swirl angle is 40~60°, for example, it can be 40°, 42°, 44°, 46°, 48°, 50°, 55° or 60°, etc.

[0029] The smaller the swirl angle of the swirl blades in this invention, the greater the intensity of the secondary air swirl, which is beneficial to pulverized coal combustion and inhibits the formation of thermal NOx. Therefore, a smaller opening is selected for pure coal operation to obtain high-intensity swirl and promote complete combustion; while for ammonia-coal co-fired operation, the swirl intensity needs to be appropriately reduced, but a certain intensity of swirl is still needed to aid the combustion of pulverized coal to maintain a high temperature and promote ammonia pyrolysis; for high-proportion ammonia operation, high-intensity swirl is not required, so a larger blade opening is selected to make the secondary air approach a jet and maintain stable combustion.

[0030] The swirl angle described in this invention is the angle between the chord length of the adjustable swirl blade and the channel axis. The adjustable swirl blade in the axial swirler can be connected to the fixed assembly via a bearing assembly, and the angle can be adjusted by a drive gear or similar material commonly used in the art. No further limitations are made here.

[0031] This invention, by setting an axial swirler with adjustable swirling blades at the outlet of the external secondary air duct, can adjust the swirling intensity in combination with different combustion modes, and form a synergy with the angle control of the separation ring, further optimizing the combustion atmosphere in multiple modes. It solves the problem that the swirling intensity of traditional burners is fixed and cannot adapt to the combustion characteristics of different fuels, and improves the overall control capability of the combustion system.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Compared with the traditional burner design for a single fuel, the present invention combines a switchable central nozzle with a continuously operating primary air duct, enabling a single burner to adapt to pure coal, a wide range of ammonia-coal co-firing and high ammonia conditions, providing boiler units with operational flexibility to cope with different fuel supply and environmental protection policies. (2) This invention is based on reaction path control of NOx. Compared with the traditional technology that mainly relies on air stage to reduce oxygen concentration, when ammonia and coal are co-fired, the ammonia gas is accurately delivered to the high temperature and oxygen-deficient zone created by dense phase coal powder through the synergistic effect of the central ammonia injection pipe and the adjustable separation ring. This guides the ammonia gas to preferentially undergo pyrolysis and generate reducing intermediate products, thereby achieving effective intervention in the fuel nitrogen conversion process and in-situ reduction of NOx in the early stage of combustion, providing a more promising low-NOx emission path. (3) The present invention enhances the flame stability under high proportion of ammonia: In view of the characteristics of slow flame propagation speed and easy flameout of ammonia fuel, the adjustable separation ring acts as a flame stabilizer under high proportion of ammonia. Its structure helps to form a stable recirculation zone. The trace amount of coal powder in the primary air duct provides a stable ignition source for the ammonia flame, which together ensures the robustness of the combustion process. (4) The present invention forms an integrated collaborative control system that integrates coal powder concentration separation, airflow physical separation and adjustable swirl technology. By adjusting the angle of the separation ring and the intensity of the swirl, the flow field and combustion state under different operating modes can be optimized in a targeted manner, showing good working condition adaptability and control potential. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of a low-NOx swirl burner operating in multiple modes provided in some embodiments of the present invention; Wherein: 1-Central ammonia injection pipe, 2-Primary air duct, 3-Inner secondary air channel, 4-Outer secondary air channel, 5-Pulverized coal concentration separator, 6-Axial cyclone separator, 7-Separation ring; Figure 2 This is a front view of the separation ring in a low NOx swirl burner operating in multiple modes, provided in some embodiments of the present invention; Figure 3This is a side view of the separation ring in a low NOx swirl burner operating in multiple modes, as provided in some embodiments of the present invention. Detailed Implementation

[0034] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0035] Example 1 This embodiment provides a low-NOx swirl burner suitable for multi-mode operation, such as... Figure 1 As shown, the low-NOx swirl burner includes, from the inside out: a central ammonia injection pipe 1, a primary air duct 2, an inner secondary air channel 3, and an outer secondary air channel 4. A pulverized coal concentration separator 5 is installed near the outlet section of the primary air duct. A separation ring 7 is installed at the burner outlet, located at the outlet end of the pulverized coal concentration separator 5. The pulverized coal concentration separator 5 is an annular structure fixed to the inner wall of the primary air duct 2. Both axial ends of the annular structure have inclined transition slopes. The inner diameter of the annular structure is half the inner diameter of the primary air duct, and the inclination angle of the inclined transition slopes is 60°. Figure 2 and Figure 3 The separation ring shown is composed of multiple wedge-shaped blades arranged in a circular array around a central axis. The separation ring is equipped with a root hinge, and all the wedge-shaped blades rotate synchronously around the root hinge axis to form an adjustable conical flare. The angle between the wedge-shaped blades and the axis of the separation ring is 25°. It operates in ammonia-coal co-combustion mode and a high-proportion ammonia mode, with a coal flow rate to ammonia flow rate mass ratio of 1:1.5. Ammonia gas is injected through the central ammonia injection pipe, pulverized coal is transported through the primary air duct, and air distribution is introduced through the inner and outer secondary air channels. An axial vortex 6 is provided at the outlet of the outer secondary air channel. The axial vortex 6 includes adjustable vortex blades with a vortex angle of 30°. The adjustable vortex blades can be connected to the fixed component through a bearing assembly, and the angle can be adjusted by driving a gear.

[0036] Example 2 This embodiment provides a low-NOx swirl burner suitable for multi-mode operation, such as... Figure 1 As shown, the low-NOx cyclone burner includes, from the inside out: a central ammonia injection pipe 1, a primary air duct 2, an inner secondary air channel 3, and an outer secondary air channel 4. A pulverized coal concentration separator 5 is installed near the outlet section of the primary air duct. A separation ring 7 is installed at the burner outlet, located at the outlet end of the pulverized coal concentration separator 5. The pulverized coal concentration separator 5 is an annular structure fixed to the inner wall of the primary air duct 2. Both axial ends of the annular structure have inclined transition slopes. The inner diameter of the annular structure is 4 / 5 of the inner diameter of the primary air duct, and the inclination angle of the inclined transition slopes is 30°. Figure 2 and Figure 3 The separation ring shown is composed of multiple wedge-shaped blades arranged in a circular array around a central axis. The separation ring is equipped with a root hinge, and all wedge-shaped blades rotate synchronously around the root hinge axis, forming an adjustable conical flare. The angle between the wedge-shaped blades and the axis of the separation ring is 15°. In pure coal mode operation, the central ammonia injection pipe switches to supplying a small amount of central air, and the primary air duct transports pulverized coal and primary air. The inner and outer secondary air channels supply air as needed. The outlet of the outer secondary air channel is equipped with an axial cyclone separator 6, which includes adjustable cyclone blades with a swirl angle of 20°. The adjustable cyclone blades can be connected to a fixed assembly via a bearing assembly, and the angle can be adjusted by a drive gear.

[0037] Example 3 This embodiment provides a low-NOx swirl burner suitable for multi-mode operation, such as... Figure 1 As shown, the low-NOx cyclone burner includes, from the inside out: a central ammonia injection pipe 1, a primary air duct 2, an inner secondary air channel 3, and an outer secondary air channel 4. A pulverized coal concentration separator 5 is installed near the outlet section of the primary air duct. A separation ring 7 is installed at the burner outlet, located at the outlet end of the pulverized coal concentration separator 5. The pulverized coal concentration separator 5 is an annular structure fixed to the inner wall of the primary air duct 2. Both axial ends of the annular structure have inclined transition slopes. The inner diameter of the annular structure is 3 / 4 of the inner diameter of the primary air duct, and the inclination angle of the inclined transition slopes is 50°. Figure 2 and Figure 3 The separation ring shown consists of multiple wedge-shaped blades arranged in a circular array around a central axis. The separation ring is equipped with a root hinge, and all wedge-shaped blades rotate synchronously around the root hinge axis, forming an adjustable conical flare. The angle between the wedge-shaped blades and the axis of the separation ring is 5°. In high-proportion ammonia mode operation, the central ammonia injection pipe serves as the main fuel channel, injecting most of the ammonia gas. The primary air duct is not closed, but it conveys a very small amount of pulverized coal. Internal and external secondary air ducts supply distribution air; the outlet of the external secondary air duct is equipped with an axial cyclone separator 6, which includes adjustable cyclone blades with a swirl angle of 60°. The adjustable cyclone blades can be connected to a fixed assembly via a bearing assembly, and the angle can be adjusted by driving gears.

[0038] In summary, this invention achieves multiple technical effects, including multi-mode adaptability, ultra-low NOx emissions, high combustion efficiency, and high stability, through the synergistic design of structural innovation and parameter optimization. It effectively solves the core technical pain points of ammonia substitution combustion in coal-fired boilers and provides a reliable technical solution for carbon emission reduction and pollutant synergistic control in coal-fired units.

[0039] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A low-NOx swirl burner suitable for multi-mode operation, characterized in that, The low-NOx cyclone burner comprises, from the inside out: a central ammonia injection pipe, a primary air duct, an inner secondary air channel, and an outer secondary air channel. A pulverized coal concentration separator is installed near the outlet section of the primary air duct. A separation ring is installed at the outlet of the low-NOx cyclone burner. The separation ring, located at the outlet end of the pulverized coal concentration separator, is composed of multiple angle-adjustable wedge-shaped blades arranged in a circular array around the central axis of the separation ring. The central ammonia injection pipe is used to transport either ammonia or a combination of both, as well as central air. The primary air duct is used to transport either pulverized coal or a combination of both, as well as primary air. The inner and outer secondary air channels are used for air distribution.

2. The low-NOx swirl burner according to claim 1, characterized in that, The pulverized coal concentration separator is an annular structure that is attached and fixed to the inner wall of the primary air duct. Both ends of the annular structure are provided with inclined transition slopes.

3. The low-NOx swirl burner according to claim 1 or 2, characterized in that, The separation ring is equipped with a root hinge, and all wedge blades rotate synchronously around the root hinge to form an adjustable conical flare. The root hinge is fixedly or detachably connected to the inner wall of the primary air duct outlet.

4. The low-NOx swirl burner according to claim 3, characterized in that, The angle between the wedge-shaped blades of the separation ring and the central axis is set to different angles depending on the operating conditions.

5. The low-NOx swirl burner according to any one of claims 1 to 4, characterized in that, The multi-mode operation includes pure coal mode, ammonia-coal co-fired mode, and high-proportion ammonia mode.

6. The low-NOx swirl burner according to claim 5, characterized in that, When the pure coal mode is running, the angle between the wedge-shaped blades of the separation ring and the central axis is the first angle.

7. The low-NOx swirl burner according to claim 5, characterized in that, When the ammonia-coal co-fired mode is running, the angle between the wedge-shaped blades of the separation ring and the central axis is a second angle, which is greater than or equal to the first angle.

8. The low-NOx swirl burner according to claim 5, characterized in that, When the high-proportion ammonia mode is running, the angle between the wedge-shaped blades of the separation ring and the central axis is a third angle, which is less than or equal to the first angle.

9. The low-NOx swirl burner according to any one of claims 1 to 8, characterized in that, The outlet of the external secondary air duct is equipped with an axial vortex. Preferably, the axial cyclone includes adjustable cyclone blades.

10. The low-NOx swirl burner according to claim 9, characterized in that, The swirl angle of the adjustable swirl blades during pure coal mode operation is 0~90°; Preferably, the swirl angle of the adjustable swirl blades during the operation of the ammonia-coal co-combustion mode is the first swirl angle; Preferably, when the high-proportion ammonia mode is running, the swirl angle of the adjustable swirl blade is a second swirl angle, which is greater than or equal to the first swirl angle.

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