Double-circulation fuel grading low-nitrogen combustor

Abstract

The invention relates to the technical field of industrial combustors, and particularly discloses a double-circulation fuel staged low-nitrogen combustor which comprises a shell, a first fuel system and a second fuel system are coaxially arranged in the shell, the first fuel system is arranged in the middle of the shell, and the second fuel system is arranged in the middle of the shell. The first fuel system comprises a first combustion channel, a rotational flow combustion stabilizer and a first-stage fuel nozzle which are sequentially communicated from inside to outside, the rotational flow combustion stabilizer is fixedly installed in the first combustion channel, and the first-stage fuel nozzle is installed at the outlet end of the first combustion channel and used for spraying out first-stage main fuel; the second-stage spray guns are evenly distributed in the circumferential direction of the shell and located on the periphery of the first combustion channel. The second-stage spray gun is used for spraying out second-stage graded fuel. According to the invention, the stability of flames and the continuous low value of nitrogen oxide emission can be ensured.

Description

Technical Field

[0001] This application relates to the technical field of industrial burners, and in particular to a dual-cycle fuel staged low-NOx burner. Background Technology

[0002] A burner is a general term for devices that mix and burn fuel and air in a specific manner. Low-NOx burners are environmentally friendly devices that provide heat energy to industrial oil or gas boilers. They reduce nitrogen oxide (NOx) emissions and improve combustion efficiency by optimizing the combustion structure. Their core principles include staged combustion, flue gas recirculation (FGR), and premixed combustion technologies. By controlling the fuel-air mixing ratio and reducing combustion temperature, NOx formation is suppressed, with emissions generally below 30 mg / m³. They are suitable for heating boilers, industrial furnaces, and commercial applications.

[0003] Traditional fuel grading systems exhibit large fluctuations in NOx emissions (>50%) when the load changes, and are prone to flameout under low load conditions, resulting in poor stability. Secondly, external FGR systems require additional fans and ductwork, leading to an increase in system energy consumption of approximately 12-15%, and may cause condensation corrosion problems due to flue gas temperatures falling below the dew point. Summary of the Invention

[0004] To address the issue of poor stability in existing combustion grading systems, this application provides a dual-cycle fuel grading low-NOx burner.

[0005] This application provides a dual-cycle fuel staged low-NOx burner, which adopts the following technical solution: A dual-cycle fuel staged low-NOx burner includes: case; A first fuel system is coaxially disposed within the housing. The first fuel system is located in the middle of the housing. The first fuel system includes a first combustion channel, a swirling flame stabilizer, and a primary fuel nozzle. The swirling flame stabilizer is disposed within the first combustion channel, and the primary fuel nozzle is disposed at the outlet end of the first combustion channel. A second fuel system, coaxially disposed within the housing, includes multiple sets of secondary spray nozzles arranged circumferentially along the housing, with the secondary spray nozzles positioned around the outer periphery of the first combustion channel; and The primary flue gas passage connects the furnace and the secondary spray gun inlet, and is used to guide the flue gas from the high-temperature zone of the furnace to the secondary spray gun inlet. A secondary flue gas passage is connected in series with the primary flue gas passage. The secondary flue gas passage connects the outlet of the secondary spray gun to the main combustion zone and is located in the system for injecting flue gas into the first fuel system.

[0006] By adopting the above technical solution and constructing built-in primary and secondary flue gas channels, a built-in dual-cycle flue gas recirculation system is achieved without the need for an external high-power FGR fan. The high-temperature primary flue gas is premixed with the secondary fuel, creating a highly reducing atmosphere and efficiently reducing NOx; the low-temperature secondary flue gas dilutes the main combustion zone, reducing oxygen concentration and flame temperature. The primary and secondary flue gas channels work in deep synergy with the first and second fuel systems, enabling the burner to achieve deep low-NOx combustion (NOx < 30 mg / m³) without the need for complex external systems. Furthermore, the system boasts low energy consumption, a compact structure, and avoids the corrosion risks associated with external FGR fans. In some embodiments, the swirl flame stabilizer includes a central shaft and a plurality of blades disposed on the central shaft, the blades having an inclination angle of 30°-60°. In some embodiments, the primary fuel nozzle is provided with a plurality of small holes, the diameter of which is ≥20mm, and the small holes are arranged in a circumferential array to form a recirculation zone with a size of 1.2-1.8 times the diameter of the primary fuel nozzle behind the primary fuel nozzle.

[0007] In some embodiments, the number N of the secondary nozzles of the second fuel system satisfies the following relationship: N ≥ 6 + 0.02 × (D - 200), where D is the diameter of the housing in mm.

[0008] In some embodiments, the outlet velocity of the secondary spray gun is 150-290 m / s, and the angle between the axis of the secondary spray gun and the main axis of the housing is 15°-45°.

[0009] In some embodiments, the burner head is also integrated with a waste acid atomizing spray gun, wherein the atomizing medium of the waste acid atomizing spray gun is compressed air, with a working pressure ≥0.5 MPa and an atomized particle size ≤50μm.

[0010] In some embodiments, two ultraviolet flame detectors are symmetrically arranged on both sides of the burner housing. The detection wavelength of the ultraviolet flame detectors is 185-260 nm, and they are connected to a flameout protection shut-off valve.

[0011] In some embodiments, the blades of the swirl stabilizer are coated with a high-temperature resistant coating; and / or, the primary fuel nozzle is made of a high-temperature resistant ceramic material.

[0012] In some embodiments, the fuel supply to the burner is configured such that primary fuel accounts for 40-50% of the total fuel mass, and secondary fuel accounts for 50-60% of the total fuel mass.

[0013] In some embodiments, the side wall of the housing is provided with an external circulation flue gas interface, the external circulation interface is located in the middle section of the housing, the external circulation interface is 300-500 mm away from the outlet of the first-stage nozzle, and the interface diameter is 50-80 mm.

[0014] Compared with the prior art, this application includes at least one of the following beneficial technical effects: 1. The primary flue gas passage creates a highly reducing atmosphere, which efficiently reduces NOx. The secondary flue gas passage dilutes the main combustion zone, reducing the oxygen concentration and flame temperature. This allows the burner to achieve deep low-NOx combustion (NOx < 30 mg / m³) without the need for a complex external system. The system also has low energy consumption and a compact structure. 2. The swirling flame stabilizer can generate a rotating jet of moderate intensity. This swirling intensity can ensure that a sufficiently large and strong internal recirculation zone is formed behind the primary fuel nozzle to effectively entrain high-temperature flue gas to continuously ignite fresh fuel and ensure flame stability. It also avoids problems such as excessive resistance, short flame, or easy flameout caused by excessive swirling. 3. The number of secondary spray guns ensures that the injection point density of secondary fuel is scientifically matched with the size (power) of the burner. For burners with larger diameters, more secondary spray guns can ensure that the staged fuel is more evenly covered on the cross-section of the furnace, avoiding the phenomenon that there is insufficient reducing atmosphere in some areas due to insufficient fuel, or incomplete combustion due to excessive fuel in some areas. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of an embodiment of this application.

[0016] Figure 2 yes Figure 1 Sectional view along line AA.

[0017] Figure 3 This is a schematic diagram of the swirl flame stabilizer in the embodiments of this application.

[0018] Figure 4 This is a schematic diagram of the external flue gas recirculation structure in an embodiment of this application.

[0019] In the picture: 1. Shell; 2. First fuel system; 21. First combustion channel; 22. Swirl flame stabilizer; 221. Central shaft; 222. Blade; 23. First-stage fuel nozzle; 3. Second fuel system; 31. Second-stage spray gun. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the term "and / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Furthermore, the character " / " in this document, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0022] Reference Figure 1 and Figure 2 This application provides a dual-cycle fuel-stage low-NOx burner, comprising a housing 1, within which a first fuel system 2 and a second fuel system 3 are coaxially arranged. The first fuel system 2 is located in the middle of the housing 1 and includes a first combustion channel 21, a swirl stabilizer 22, and a primary fuel nozzle 23. The swirl stabilizer 22 is fixedly installed within the first combustion channel 21. The primary fuel nozzle 23 is installed at the outlet end of the first combustion channel 21 and is used to spray 40-50% of the total primary fuel (such as natural gas or light oil). The second fuel system 3 includes multiple sets (e.g., 6 sets) of secondary spray guns 31, which are evenly arranged circumferentially along the housing 1 and located around the periphery of the first combustion channel 21. The secondary spray guns 31 are used to spray 50-60% of the total secondary staged fuel.

[0023] Furthermore, the dual-cycle fuel-stage low-NOx burner provided in this application also includes a primary flue gas passage and a secondary flue gas passage. The primary and secondary flue gas passages are connected in series. The inlet of the primary flue gas passage extends to the high-temperature zone of the furnace (above approximately 1200°C), and the outlet connects to the fuel / air inlet of each secondary spray gun 31. Under the negative pressure of the furnace or the action of the ejector, the high-temperature flue gas is directly introduced into the secondary spray gun 31 and pre-mixed with the secondary fuel. The inlet of the secondary flue gas passage can connect to the medium-temperature flue gas in the furnace, and the outlet leads to the first fuel system 2, for example, opening in the area behind the swirl stabilizer 22, introducing the lower-temperature flue gas (approximately 200-400°C) into the main combustion zone. By constructing built-in primary (high-temperature) and secondary (low-temperature) flue gas passages, built-in dual-cycle flue gas recirculation without the need for an external high-power fan is achieved. The primary high-temperature flue gas is premixed with the secondary fuel to create a strong reducing atmosphere, which efficiently reduces NOx. The secondary low-temperature flue gas dilutes the main combustion zone, reducing the oxygen concentration and flame temperature. This allows the burner to achieve deep low-NOx combustion (NOx < 30 mg / m³) without the need for a complex external system, and the system has low energy consumption and a compact structure.

[0024] Reference Figure 3 In this embodiment, the swirl burner 22 includes a central shaft 221 extending axially, and multiple (e.g., eight) helical blades 222 welded to the central shaft 221. The installation angle of these blades 222 (the angle between the blade plane and the axis of the central shaft) is 30°-60°, preferably 45° in this embodiment. The 45° angled blades can generate a rotating jet of moderate intensity. The rotating jet can ensure that a sufficiently large and strong internal recirculation zone is formed behind the primary fuel nozzle 23, effectively entraining high-temperature flue gas to continuously ignite fresh fuel and ensure flame stability; while avoiding the problems of excessive resistance, short flame, or easy flameout caused by excessive swirl. This makes the burner have excellent flame stabilization performance over a wide load range, especially under low load.

[0025] The primary fuel nozzle 23 has multiple small holes with a diameter ≥20mm, arranged in a circumferential array. These holes are used to form a recirculation zone 1.2-1.8 times the diameter of the primary fuel nozzle 23 behind it. In conjunction with the swirl stabilizer 22, the primary fuel nozzle 23 forms a high-temperature flue gas recirculation zone with stable dimensions and concentrated vorticity. This provides a continuous and stable ignition source and residence space for the core flame, greatly enhancing its combustion resistance and further reducing the risk of flameout during rapid load changes or fuel quality fluctuations.

[0026] Furthermore, the number N of the secondary spray guns 31 in the second fuel system 3 satisfies the following formula: N ≥ 6 + 0.02 × (D - 200), where D is the diameter of the shell in mm. For example, for a medium-sized burner with a shell diameter D = 400 mm, the number of secondary spray guns N ≥ 6 + 0.02 × (400 - 200) = 10. This formula ensures that the injection point density of the secondary fuel is scientifically matched with the burner's size (power). For burners with larger diameters, more secondary spray guns 31 ensure a more uniform coverage of the staged fuel across the furnace cross-section, avoiding insufficient reducing atmosphere in some areas due to insufficient fuel, or incomplete combustion due to excessive fuel in some areas.

[0027] Specifically, the outlet velocity of the secondary spray gun 31 is 150-290 m / s, preferably 220 m / s in this embodiment. The angle between the axis of the secondary spray gun 31 and the main axis of the housing 1 is 15°-45°, preferably 30°. The velocity of 220 m / s provides sufficient kinetic energy for the secondary fuel jet, enabling it to penetrate any stagnant flue gas zones within the furnace and deeply and rapidly mix with the high-temperature flue gas introduced from the primary flue gas channel. The 30° injection angle allows the secondary fuel jet to cut into an appropriate position downstream of the main flame with a suitable trajectory, preventing premature mixing with the main flame and weakening the staged combustion effect, while also avoiding excessive distance that could lead to temperature drops and incomplete reduction reactions. This optimizes the spatial organization of staged combustion and improves the overall NOx reduction efficiency.

[0028] In some embodiments, the burner head also integrates a waste acid atomizing spray gun (not shown in the figure). The atomizing medium of the waste acid atomizing spray gun is compressed air, with an operating pressure ≥0.5 MPa and an atomized particle size ≤50 μm. The waste acid atomizing spray gun uses compressed air from the factory pipeline network as the atomizing medium, with an operating pressure set at 0.7 MPa. Through high-pressure air atomization, waste acid (such as dilute sulfuric acid) can be atomized into fine droplets with a median particle size of no more than 40 μm. The high-pressure air of 0.7 MPa ensures excellent atomization effect, producing ultra-fine droplets. These fine droplets rapidly evaporate and pyrolyze upon being injected into the high-temperature (>850°C) furnace, and the acidic components are ultimately converted into corresponding metal oxides and sulfur dioxide, which can be removed in the subsequent flue gas treatment system.

[0029] In some embodiments, two ultraviolet flame detectors (not shown in the figure) are symmetrically arranged on both sides of the burner housing 1. The detection wavelength of the ultraviolet flame detectors is 185-260 nm, and they are connected to a flameout protection shut-off valve. The ultraviolet flame detectors detect the characteristic ultraviolet spectrum generated by hydrocarbon flames during combustion, and their sensitive wavelength is 200-250 nm. The signals from the two ultraviolet flame detectors are jointly input to the combustion controller and interlocked with the emergency flameout protection shut-off valve (not shown in the figure) on the fuel main. The use of ultraviolet band detection effectively avoids background interference such as furnace wall radiation light, significantly reducing the false alarm rate of flame signals. The dual ultraviolet flame detectors constitute a highly reliable safety monitoring system: only when both detectors detect a flame simultaneously is it considered normal; if either detector detects flameout and after a brief confirmation, the controller will trigger the rapid shut-off valve to cut off the fuel supply in a very short time (e.g., 0.08 seconds). This dual protection greatly improves the intrinsic safety level of the burner and prevents serious accidents such as deflagration.

[0030] The blades 222 of the swirl burner 22 are coated with a high-temperature resistant coating; and / or, the primary fuel nozzle 23 is made of a high-temperature resistant ceramic material. The high-temperature resistant coating provides the metal blades with an excellent barrier against oxidation and thermal corrosion, significantly slowing down the oxidation and embrittlement process of the material in high-temperature flue gas environments. The ceramic nozzle, on the other hand, has extremely high thermal shock resistance, high-temperature strength, and chemical inertness, and is virtually unaffected by combustion products. These two measures significantly extend the service life of the most vulnerable components of the burner head, reduce the frequency of downtime for maintenance and replacement of spare parts, and lower the total life-cycle operating cost of the equipment.

[0031] Reference Figure 4 In some embodiments, to increase system flexibility, an external recirculation flue gas interface is provided on the side wall of the housing 1. This interface is located in the middle section of the axial length of the housing 1, with its central axis 300-500 mm away from the outlet plane of the primary fuel nozzle 23. The external recirculation flue gas interface is connected to the housing 1 via a flange, and the diameter of the external recirculation flue gas interface is 50-80 mm.

[0032] The implementation principle of this application embodiment is as follows: the primary flue gas channel directly injects high-temperature flue gas from deep within the furnace to the inlet of the circumferentially arranged secondary fuel injectors, allowing the secondary fuel to pre-mix with the high-temperature flue gas, forming a strongly reducing atmosphere within the furnace, thereby deeply reducing the generated nitrogen oxides; the secondary flue gas channel then introduces lower-temperature flue gas into the central primary fuel system 2, diluting the oxygen concentration in the main combustion zone and reducing the peak flame temperature, thus suppressing the generation of nitrogen oxides from the source. The main fuel achieves stable, low-temperature combustion through the swirl stabilizer 22 and the primary fuel nozzle 23 in the primary fuel system 2, while the staged fuel achieves spatial staged reduction through the synergistic effect of high-speed, multi-angle injectors and high-temperature flue gas circulation.

[0033] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A dual-cycle fuel staged low-NOx burner, characterized in that, include: Shell (1); A first fuel system (2) is coaxially disposed within the housing (1). The first fuel system (2) is disposed in the middle of the housing (1). The first fuel system (2) includes a first combustion channel (21), a swirling flame stabilizer (22), and a primary fuel nozzle (23). The swirling flame stabilizer (22) is disposed within the first combustion channel (21), and the primary fuel nozzle (23) is disposed at the outlet end of the first combustion channel (21). The second fuel system (3) is coaxially disposed inside the housing (1). The second fuel system (3) includes multiple sets of secondary spray guns (31). The multiple sets of secondary spray guns (31) are arranged circumferentially along the housing (1). The secondary spray guns (31) are disposed on the outer periphery of the first combustion channel (21). as well as The primary flue gas passage connects the furnace and the inlet of the secondary spray gun (31), and is used to guide the flue gas in the high-temperature zone of the furnace to the inlet of the secondary spray gun (31); A secondary flue gas passage is connected in series with the primary flue gas passage. The secondary flue gas passage connects the outlet of the secondary spray gun (31) to the main combustion zone and is used to inject flue gas into the first fuel system (2).

2. The dual-cycle fuel staged low-NOx burner according to claim 1, characterized in that: The swirl flame stabilizer (22) includes a central shaft (221) and a plurality of blades (222) disposed on the central shaft (221), wherein the blades (222) have an inclination angle of 30°-60°.

3. The dual-cycle fuel staged low-NOx burner according to claim 1, characterized in that: The primary fuel nozzle (23) is provided with a plurality of small holes, the diameter of which is ≥20mm and the small holes are arranged in a circumferential array to form a recirculation zone behind the primary fuel nozzle (23) with a size of 1.2-1.8 times the diameter of the primary fuel nozzle (23).

4. The dual-cycle fuel staged low-NOx burner according to claim 1, characterized in that: The number N of the secondary spray guns (31) of the second fuel system (3) satisfies the following relationship: N ≥ 6 + 0.02×(D - 200), where D is the diameter of the housing (1) in mm.

5. A dual-cycle fuel staged low-NOx burner according to claim 1, characterized in that: The outlet velocity of the secondary spray gun (31) is 150-290 m / s, and the angle between the axis of the secondary spray gun (31) and the main axis of the housing (1) is 15°-45°.

6. A dual-cycle fuel staged low-NOx burner according to claim 1, characterized in that: The burner head also integrates a waste acid atomizing spray gun, the atomizing medium of which is compressed air, with a working pressure ≥0.5MPa and an atomized particle size ≤50μm.

7. A dual-cycle fuel staged low-NOx burner according to claim 1, characterized in that: Two ultraviolet flame detectors are symmetrically arranged on both sides of the burner housing (1). The detection wavelength of the ultraviolet flame detector is 185-260nm, and it is connected to a flameout protection shut-off valve.

8. A dual-cycle fuel staged low-NOx burner according to claim 2, characterized in that: The blades (222) of the swirl stabilizer (22) are coated with a high-temperature resistant coating; and / or the primary fuel nozzle (23) is made of a high-temperature resistant ceramic material.

9. A dual-cycle fuel staged low-NOx burner according to claim 1, characterized in that: The fuel supply to the burner is configured such that primary fuel accounts for 40-50% of the total fuel mass, and secondary fuel accounts for 50-60% of the total fuel mass.

10. A dual-cycle fuel staged low-NOx burner according to claim 1, characterized in that: The side wall of the housing (1) is provided with an external circulation flue gas interface. The external circulation interface is located in the middle section of the housing (1). The external circulation interface is 300-500 mm away from the outlet of the first-stage nozzle and has a diameter of 50-80 mm.

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