Spiral-flow type pure ammonia burner capable of promoting mixing based on high-frequency oscillation

Abstract

The invention relates to a spiral-flow type pure ammonia burner capable of promoting mixing based on high-frequency oscillation, and belongs to the technical field of ammonia burners. The fuel injection system is arranged around the periphery of the central air pipe and comprises a plurality of ammonia fuel pipes and correspondingly arranged high-frequency oscillation cavities, and the high-frequency oscillation cavities are coaxially arranged right in front of outlets of the corresponding ammonia fuel pipes and used for exciting high-frequency oscillation under the impact of high-speed ammonia gas jet. According to the spiral-flow type pure ammonia burner capable of promoting mixing based on high-frequency oscillation, the high-frequency oscillation cavity coaxially aligned with the ammonia fuel nozzle is introduced, controllable high-frequency oscillation is excited through high-speed fuel jet flow, and therefore rapid and uniform premixing of ammonia fuel and distributed air is achieved through enhanced entrainment and shear mixing; the ignition and stable combustion performance is enhanced, the load adjusting range is widened, and the method is suitable for pure ammonia combustion scenes such as boilers and industrial furnaces.

Description

Technical Field

[0001] This invention relates to the field of ammonia burner technology, specifically to a swirling pure ammonia burner based on high-frequency oscillation to promote mixing. Background Technology

[0002] Ammonia, as a carbon-free chemical energy storage and fuel carrier, possesses advantages such as diverse sources, large-scale storage and transportation capabilities, and compatibility with existing combustion systems. Against the backdrop of dual-carbon goals and fuel structure transformation, pure ammonia or high-ammonia blending is considered a key candidate pathway for gas turbines, industrial boilers, kilns, and distributed energy. If stable, efficient, and low-emission operation can be achieved in pure ammonia combustion, it can significantly reduce carbon dioxide emissions during combustion and support renewable energy consumption and inter-seasonal energy storage. Therefore, developing high-performance burners suitable for pure ammonia has urgent engineering needs and broad application prospects.

[0003] However, pure ammonia combustion faces significant bottlenecks in engineering applications. Ammonia exhibits relatively slow chemical reaction kinetics, resulting in a low laminar combustion rate, making ignition and stable combustion difficult, and leading to problems such as flame detachment, narrow flashback boundaries, and instability under low loads. The nitrogen content of ammonia molecules results in a high potential for nitrogen oxide formation during combustion, especially under localized high-temperature and oxygen-rich conditions, which facilitates the formation of both thermal and fuel-type nitrogen oxides, significantly increasing the difficulty of emission control. Simultaneously, ammonia combustion may also be accompanied by the risk of unburned ammonia escape and the formation of byproducts such as nitrous oxide, imposing stricter constraints on the environment and equipment operation. To achieve both high efficiency and low emissions under a wide range of operating conditions, the key lies in promoting rapid and uniform mixing of fuel and air, suppressing localized oxygen-rich hotspots and high-temperature peaks, and improving the flame structure's adaptability to disturbances.

[0004] Existing pure ammonia combustion organization methods mainly include premixing, diffusion, and partial premixing schemes, often combined with swirl flame stabilization, staged air supply, recirculation zone enhancement, and micro-orifice injection to expand the stable combustion range. Swirl burners, by inducing a central recirculation zone through swirl blades, can enhance mixing and improve combustion stability to some extent. However, under pure ammonia conditions, insufficient mixing rate may still lead to local equivalence ratio fluctuations, resulting in flame oscillations and emission fluctuations. To enhance mixing, engineering practices also employ measures such as incorporating shear layers and recirculation structures within the burner. However, these methods often struggle to balance mixing intensity, pressure drop loss, and backfire safety under low load or rapid adjustment conditions. Furthermore, they may introduce higher flow resistance and more complex acoustic coupling, increasing the risk of combustion instability.

[0005] In recent years, research on using acoustic or ultrasonic perturbations to promote mixing and combustion has attracted attention. High-frequency vibrations can enhance shear and entrainment on a small scale, promote jet breakup and interface renewal, and accelerate the diffusion and reaction of ammonia and air, thus potentially improving ignition and stable combustion, and suppressing nitrogen oxide formation by reducing local high-temperature oxygen-rich zones. However, existing acoustic enhancement methods mostly focus on external excitation or applying perturbations to the entire combustion chamber, resulting in complex system integration and room for improvement in reliability and adaptability. How to achieve structured, controllable, and engineerable coupling of high-frequency oscillations in the near-field of fuel injection, while simultaneously synergizing with swirl-staged air supply, to achieve rapid mixing, wide-condition stability, and low nitrogen oxide emissions within a small volume and with a reasonable pressure drop, remains a key technical challenge in the design of pure ammonia burners. Summary of the Invention

[0006] The purpose of this invention is to provide a swirling pure ammonia burner based on high-frequency oscillation to promote mixing, which can solve the technical problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a swirl-type pure ammonia burner based on high-frequency oscillation to promote mixing, comprising a central air distribution system and a fuel injection system. The central air distribution system includes a central air duct. The fuel injection system is arranged around the outer periphery of the central air duct and includes multiple ammonia fuel pipes and correspondingly arranged high-frequency oscillation chambers. The high-frequency oscillation chambers are coaxially arranged in front of the outlet of the corresponding ammonia fuel pipes and are used to excite high-frequency oscillations under the impact of high-speed ammonia jets.

[0008] In a preferred embodiment, the central air distribution system further includes a central perforated plate fixedly connected to the outlet end of the central air duct, the central perforated plate having a plurality of evenly distributed through holes.

[0009] In a preferred embodiment, the high-frequency oscillation cavity is fixedly connected to the ammonia fuel pipe or other burner fixing structure via a support rod.

[0010] In a preferred embodiment, the high-frequency oscillation cavity is a resonant cavity.

[0011] In a preferred embodiment, the outlet end of the ammonia fuel pipe is connected to an ammonia fuel nozzle, which is configured as a constricted structure with a flow channel cross-section that narrows along the flow direction.

[0012] In a preferred embodiment, the cavity depth H of the high-frequency oscillation cavity satisfies the relationship with the target oscillation frequency f: H=C / (4f), where C is the speed of sound of ammonia gas under the actual working temperature and pressure conditions of the burner, and the target oscillation frequency f is not less than 5kHz.

[0013] In a preferred embodiment, the cavity diameter D of the high-frequency oscillation cavity satisfies the relationship between the nozzle inner diameter d of the ammonia fuel nozzle: D = 1.2~1.6d.

[0014] In a preferred embodiment, the axial distance S between the nozzle end face of the ammonia fuel nozzle and the inlet end face of the high-frequency oscillation cavity satisfies the relationship between the cavity depth H and the distance S = 0.2~0.4H.

[0015] In a preferred embodiment, the pure ammonia burner further includes a secondary air system surrounding the fuel injection system, the secondary air system comprising at least two layers of secondary air ducts arranged in a concentric ring.

[0016] In a preferred embodiment, the secondary air system includes an inner secondary air duct and an outer secondary air duct, and a cyclone separator is provided at the inlet of each secondary air duct.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a swirling ammonia burner based on high-frequency oscillation-promoted mixing. By introducing a high-frequency oscillation chamber coaxially aligned with the ammonia fuel nozzle, the high-speed fuel jet generated by the nozzle excites controllable high-frequency oscillations, thereby enhancing entrainment and shear mixing to achieve rapid and uniform premixing of ammonia fuel and distribution air. Furthermore, two stages of secondary air, passing through a swirling device, form a strong swirling and recirculation zone, further achieving staged air supply and flame stabilization, suppressing localized high-temperature oxygen-rich zones, thus reducing NOx formation and minimizing unburned ammonia escape. The burner provided by this invention improves ignition and combustion stability, broadens the load adjustment range, and is suitable for pure ammonia combustion scenarios such as boilers and industrial furnaces. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of the swirl-type pure ammonia burner based on high-frequency oscillation to promote mixing in an embodiment of the present invention; Figure 2 for Figure 1 The right view; Figure 3 This is a schematic diagram of the mating structure of the ammonia fuel pipe and the high-frequency oscillation cavity in an embodiment of the present invention; Figure 4 This is a dimensioned diagram showing the fit between the ammonia fuel nozzle and the high-frequency oscillation chamber in an embodiment of the present invention.

[0019] The meanings of the labels in the diagram are as follows: 1. Central air duct; 2. Ammonia fuel pipe; 3. Inner secondary air duct; 4. Outer secondary air duct; 5. Inner secondary air cyclone separator; 6. Outer secondary air cyclone separator; 7. Ammonia fuel nozzle; 8. High-frequency oscillation chamber; 9. Central air perforated plate; 10. Through hole; 11. Support rod. Detailed Implementation

[0020] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. 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. Therefore, they should not be construed as limitations on this invention.

[0022] See Figures 1-2 This embodiment discloses a swirl-type pure ammonia burner based on high-frequency oscillation to promote mixing, including an axially arranged central air distribution system, a fuel injection system circumferentially distributed around the central air distribution system, and a secondary air system surrounding the outside.

[0023] The central air distribution system constitutes the innermost primary air supply channel of the burner, used to supply the air required for primary combustion to the burner head region. Specifically, it includes a central air duct 1 arranged along the burner axis and a central air perforated plate 9 fixedly connected to the outlet end of the central air duct 1. The central air duct 1 serves as the main primary air delivery channel, used to deliver air to the front end of the burner; the central air perforated plate 9 is constructed as a plate-like structure with multiple through holes 10, which are evenly distributed on the perforated plate to distribute the overall airflow from the central air duct 1 into multiple fine jets. These fine jets are ejected from the front of the perforated plate and enter the burner head region at a higher flow rate, thereby improving the uniformity of air distribution and enhancing the mixing effect with the fuel jet.

[0024] The fuel injection system is arranged around the periphery of the central air distribution system. This system includes several independent ammonia fuel pipes 2 evenly distributed around the periphery of the central air duct 1, and several high-frequency oscillation chambers 8 corresponding to each ammonia fuel pipe 2. The high-frequency oscillation chambers 8 are located directly in front of the outlet of the corresponding ammonia fuel pipe 2. The number of ammonia fuel pipes 2 can be adaptively configured according to the burner's design heat load, typically 6 to 10, to ensure uniform fuel supply in the circumferential direction. Each ammonia fuel pipe 2 has an ammonia fuel nozzle 7 integrally connected to its outlet end. The ammonia fuel nozzle 7 is constructed with a tapered flow channel structure, its cross-section gradually narrowing along the flow direction. This design can accelerate the fluid by reducing the cross-sectional area without significantly increasing the upstream gas supply pressure, thereby greatly increasing the ammonia gas velocity ejected from the nozzle to provide the kinetic energy for oscillation. The nozzle inner diameter d of the ammonia fuel nozzle 7 needs to be determined based on the design ammonia volumetric flow rate Q and the target outlet velocity V (d=(4Q / πV)). 1 / 2 This ensures that the ammonia gas velocity V at the nozzle of the ammonia fuel nozzle 7 reaches Mach 0.2 to 0.4, thereby providing sufficient kinetic energy.

[0025] See Figure 3 The axis of the high-frequency oscillation cavity 8 is coaxially aligned with the injection axis of the corresponding ammonia fuel nozzle 7, allowing the high-speed ammonia jet ejected from the ammonia fuel nozzle 7 to directly and completely act on the inlet region of the high-frequency oscillation cavity 8, and to excite the flow-sound coupling vibration effect, thereby achieving high-frequency disturbance and mixing enhancement in the near field of the jet. To ensure the stability of the coaxial alignment between the high-frequency oscillation cavity 8 and the ammonia fuel nozzle 7, in this embodiment, the high-frequency oscillation cavity 8 is connected and fixed to the ammonia fuel pipe 2 or other burner fixing structure by one or more rigid support rods 11. This fixed connection structure ensures that the relative position of the high-frequency oscillation cavity 8 and the ammonia fuel nozzle 7 remains constant under vibration conditions.

[0026] In this embodiment, the high-frequency oscillation cavity 8 is a resonant cavity. When a high-speed ammonia jet is ejected from the ammonia fuel nozzle 7 and directly impacts the inlet of the high-frequency oscillation cavity 8, the stable jet will be subjected to periodic disturbances in the cavity structure, exciting strong oscillations of the gas inside the cavity. This oscillation frequency is determined by the geometric dimensions of the high-frequency oscillation cavity 8. Combined with... Figure 4Specifically, the target oscillation frequency f mainly depends on the cavity depth H of the high-frequency oscillation cavity 8, and the two satisfy the relationship: H=C / (4f), where C is the speed of sound of ammonia gas under the actual working temperature and pressure conditions of the burner. In this embodiment, the target frequency f is preferably set at 5kHz or higher. The generation of high-frequency oscillation modulates the smooth high-speed ammonia jet ejected from the ammonia fuel nozzle 7 into a pulsating jet carrying high-intensity, high-frequency longitudinal vibration. This high-frequency pulsation transforms the mixing process of ammonia gas and primary air from the traditional, relatively slow molecular diffusion to a rapid mixing mode driven by both strong convection and pulsating diffusion. This enables sufficient premixing of ammonia gas and primary air over a very short distance and time, laying the foundation for subsequent stable combustion.

[0027] Furthermore, to ensure that the high-frequency oscillation cavity 8 can be effectively excited by the high-speed jet and generate sufficiently strong oscillations, the geometric matching relationship between it and the ammonia fuel nozzle 7 is designed as follows: the cavity diameter D of the high-frequency oscillation cavity 8 and the nozzle inner diameter d of the ammonia fuel nozzle 7 must satisfy D = 1.2 ~ 1.6d. This ratio range ensures the jet oscillation effect on a radial scale. Specifically, this ratio range ensures that the impact area of ​​the high-speed jet on the cavity opening of the high-frequency oscillation cavity 8 is moderate, which can input sufficient energy into the cavity to excite strong pressure oscillations, while avoiding excessive dispersion of jet kinetic energy due to an excessively large impact area, thus weakening the excitation efficiency. If the cavity diameter of the high-frequency oscillation cavity 8 is too small, the impact area of ​​the jet on the cavity opening will be insufficient, resulting in low excitation efficiency; if the cavity diameter is too large, the jet energy will be too dispersed, making it difficult to form concentrated and strong pressure oscillations within the cavity, which will also weaken the disturbance effect. Furthermore, the axial distance S between the nozzle end face of the ammonia fuel nozzle 7 and the inlet end face of the high-frequency oscillation cavity 8 is preferably set to S = 0.2~0.4H. This setting ensures the jet oscillation effect from the axial arrangement. This distance range guarantees that when the high-speed jet develops to a stage with a stable structure and sufficient kinetic energy, it interacts precisely with the high-frequency oscillation cavity 8, thereby obtaining the optimal flow-sound coupling and mixing disturbance effect. If the axial distance is set too close, the jet has not yet fully developed, its impact state is unstable, and the coverage of the inlet of the high-frequency oscillation cavity 8 is uneven; if the distance is set too far, the mixing of the jet and air has reached a certain extent, the velocity core decays, and the impact energy weakens, which is also not conducive to the efficient excitation of high-frequency oscillation. This embodiment, through the above-mentioned synergistic optimization design of the radial and axial angles, jointly ensures the reliability and efficiency of the high-frequency oscillation effect.

[0028] The secondary air system is distributed around the ammonia fuel pipe 2 and includes at least two layers of concentric ring-shaped secondary air channels. Specifically, the secondary air system includes an inner secondary air duct, an outer secondary air duct, and a burner shell, which are coaxially arranged from the inside to the outside. An annular inner secondary air channel 3 is formed between the inner secondary air duct and the outer perimeter of the central air duct 1. The outer secondary air duct is fitted outside the inner secondary air duct, forming an annular outer secondary air channel 4 between them. The burner shell is fitted on the outermost side. The inner secondary air channel 3 has an independent inner secondary air inlet; the outer secondary air channel 4 has an independent outer secondary air inlet. The inner and outer secondary air come from different air sources or different branches of the same air source, thus achieving independent adjustment of air volume and ratio. An inner secondary air cyclone separator 5 is installed at the inner secondary air inlet, and an outer secondary air cyclone separator 6 is installed at the outer secondary air inlet. The two cyclone separators cause the two stages of secondary air to form swirling airflows and induce a recirculation flame stabilization structure near the burner outlet, achieving staged air supply and flame stabilization enhancement. Simultaneously, the inner secondary airflow forms an annular envelope airflow. This envelope airflow and the oscillating jet create a strong shear layer at the contact interface. This shear layer, under high-frequency disturbances, is more prone to Kelvin-Helmholtz instability, promoting faster mixing of ammonia and air in the near field of the ammonia fuel nozzle 7. The inner secondary air cyclone separator 5 and the outer secondary air cyclone separator 6 can be configured to rotate in the same direction to enhance the overall swirling intensity, or they can be configured to rotate in opposite directions to generate stronger shear turbulence at the interface between the two swirling airflows, further promoting mixing. The specific swirling direction must be determined based on the comprehensive requirements for flame stability and mixing intensity in the actual application.

[0029] The working process of this embodiment is as follows: When the burner is running, the central air enters through the central air duct 1 and is distributed through the central air perforated plate 9 to form multiple air jets; ammonia gas is accelerated into a high-speed jet through several circumferentially distributed ammonia fuel pipes 2 and ejected as an ammonia fuel nozzle 7. This high-speed jet directly impacts the high-frequency oscillation cavity 8 located directly in front of the ammonia fuel nozzle 7 along the injection axis, generating high-frequency oscillations under the effect of flow-sound coupling, enhancing jet entrainment, shear layer disturbance, and micro-scale mixing, thereby achieving rapid and uniform premixing of ammonia gas and central air distribution. Subsequently, the inner and outer secondary air are respectively acted upon by the inner secondary air cyclone separator 5 and the outer secondary air cyclone separator 6 to form a strong swirling flow and induce a recirculation zone, so that the mixed gas is stably ignited at the burner outlet and the swirling flame shape is maintained. This staged mixing and swirling flame stabilization design is beneficial to promoting complete combustion of fuel, reducing local high temperature and oxygen-rich areas in the combustion chamber, thereby effectively suppressing the formation of thermal NOx and minimizing the escape of unburned ammonia.

[0030] This embodiment enhances entrainment and mixing by coupling a fuel-constricted high-speed jet with high-frequency oscillation, achieving rapid and uniform mixing of ammonia and distribution air and improving ignition and combustion stability. Meanwhile, the two-stage swirl secondary air can form a stable recirculation zone and achieve staged air supply, broadening the load adjustment range, reducing flame fluctuation and detachment risks, improving the local equivalence ratio distribution, suppressing high-temperature oxygen-rich hot spots, reducing the generation of fuel-type and thermal NOx, and reducing the escape of unburned ammonia.

[0031] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A swirling pure ammonia burner based on high-frequency oscillation to promote mixing, characterized in that, include: The central air distribution system includes a central air duct (1); The fuel injection system is arranged around the outer periphery of the central air duct (1), including multiple ammonia fuel pipes (2) and corresponding high-frequency oscillation chambers (8). The high-frequency oscillation chambers (8) are coaxially arranged in front of the outlet of the corresponding ammonia fuel pipe (2) and are used to generate high-frequency oscillations under the impact of high-speed ammonia jet.

2. The swirl-type pure ammonia burner according to claim 1, characterized in that, The central air distribution system also includes a central perforated plate (9) fixedly connected to the outlet end of the central air duct (1), and the central perforated plate (9) is provided with a plurality of uniformly distributed through holes (10).

3. The swirl-type pure ammonia burner according to claim 1, characterized in that, The high-frequency oscillation cavity (8) is fixedly connected to the ammonia fuel pipe (2) or other burner fixing structure via a support rod (11).

4. The swirl-type pure ammonia burner according to claim 1, characterized in that, The high-frequency oscillation cavity (8) is a resonance cavity.

5. The swirl-type pure ammonia burner according to claim 4, characterized in that, The outlet end of the ammonia fuel pipe (2) is connected to an ammonia fuel nozzle (7), which is constructed as a constricted structure with the flow channel cross section narrowing along the flow direction.

6. The swirl-type pure ammonia burner according to claim 5, characterized in that, The cavity depth H of the high-frequency oscillation cavity (8) satisfies the following relationship with the target oscillation frequency f: H=C / (4f), where C is the speed of sound of ammonia gas under the actual working temperature and pressure conditions of the burner, and the target oscillation frequency f is not less than 5kHz.

7. The swirl-type pure ammonia burner according to claim 5, characterized in that, The cavity diameter D of the high-frequency oscillation cavity (8) and the nozzle inner diameter d of the ammonia fuel nozzle (7) satisfy the following relationship: D = 1.2~1.6d.

8. The swirl-type pure ammonia burner according to claim 6, characterized in that, The axial distance S between the nozzle end face of the ammonia fuel nozzle (7) and the inlet end face of the high-frequency oscillation cavity (8) satisfies the relationship between the cavity depth H and the distance S = 0.2~0.4H.

9. The swirl-type pure ammonia burner according to any one of claims 1 to 8, characterized in that, The pure ammonia burner also includes a secondary air system surrounding the fuel injection system, the secondary air system comprising at least two layers of secondary air channels arranged in a concentric ring.

10. The swirl-type pure ammonia burner according to claim 9, characterized in that, The secondary air system includes an inner secondary air channel (3) and an outer secondary air channel (4), and a vortex generator is installed at the entrance of each secondary air channel.

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