Flue gas recirculation low-nitrogen turbulent burner for burning pulverized coal

Abstract

The invention relates to the field of boiler combustion devices, and discloses a flue gas recirculation low-nitrogen turbulent burner for burning pulverized coal, which comprises a central air channel, a primary air channel, a flue gas channel, an inner secondary air channel and an outer secondary air channel which are coaxially arranged step by step from inside to outside, an inner fixed rotational flow blade is annularly arranged at the outlet end of the inner secondary air channel, an outer fixed blade and an outer adjustable rotational flow blade are arranged in the outer secondary air channel, a spindle pulverized coal concentrator is arranged in the primary air channel, and a separation ring is arranged at the outlet of the primary air channel. The inner secondary air channel and the outer secondary air channel are both used for introducing air; and the flue gas channel is used for introducing recycled flue gas. The invention provides an economical and environment-friendly transformation technical route for reducing the emission concentration of nitrogen oxide for the rotational flow pulverized coal burner, and safe and stable operation of the burner and a boiler can be realized while the environment-friendly standard requirement is met.

Description

Technical Field

[0001] The present invention relates to the field of boiler combustion devices, and particularly to a flue gas recirculation low-nitrogen swirl burner for burning pulverized coal. Background Art

[0002] Nitrogen oxides are one of the main air pollutants, which can cause ecological environmental pollution and affect human health. The nitrogen oxides emitted by thermal power plants during combustion each year account for a relatively high proportion in the global nitrogen oxides emissions. And the generation amount of nitrogen oxides is closely related to the structure of the burners in thermal power plants. At present, the national requirements for nitrogen oxides emissions are further tightened, and low-nitrogen swirl burners are increasingly widely used in large-scale power station boilers.

[0003] Chinese Utility Model Patent CN214840783U discloses a concentrated double-tuning air swirl low-nitrogen burner provided with central air. The burner has good coal type adaptability, high combustion efficiency, good flame stability, good low-nitrogen effect, and good anti-coking property, achieving a win-win situation in environmental and economic benefits.

[0004] Chinese Invention Patent CNCN109028051A discloses a three-swirl low-CO high-efficiency pulverized coal burner. The invention has the advantages of sufficient mixing of pulverized coal and air, complete combustion, high efficiency, etc., effectively reducing the generation of CO in the flue gas, reducing the heat loss of incomplete combustion in the boiler, and improving the combustion efficiency of the boiler. The adjustable guide vanes in the inner secondary air duct can adjust the air volume and air direction of the inner secondary air according to different coal types, thereby improving the coal type adaptability of the burner.

[0005] Chinese Utility Model Patent CN219473640U discloses a pulverized coal swirl burner assembly. Through the setting of the deflector plate, the pulverized coal forms a concentrated and lean separation state under the action of the deflector plate, realizing the full combustion of the pulverized coal, making the temperature distribution in the burner more uniform, thereby meeting the NOx emission requirements while improving the combustion efficiency of the boiler.

[0006] Chinese Invention Patent CN115751300A discloses a low-nitrogen burner in the form of flue gas internal circulation for a coal-fired boiler. It can greatly reduce the generation amount of NOx in the main combustion zone, is beneficial to the volatilization and ignition combustion of pulverized coal, solves the problem of poor pulverized coal adaptability of the swirl burner, and at the same time enhances the low-load flame stability performance of the burner, ensuring stable combustion and ultra-low NOx emission under different operating conditions of the boiler.

[0007] At present, the pollutants in coal-fired industrial boilers seriously exceed the standards, the overall operating efficiency is low, the combustion process is unstable, and the operating cost is high. The existing low-nitrogen swirl combustion technology has limited inhibitory effect on the formation of nitrogen oxides. Therefore, to solve the instability problem during coal combustion and reduce the nitrogen oxide emissions while achieving economic combustion, it is urgent to develop a flue gas recirculation swirl burner for pulverized coal that combines low-nitrogen swirl combustion technology and air staging technology. Summary of the Invention

[0008] The purpose of the present invention is to solve the deficiencies of the prior art and provide a flue gas recirculation low-nitrogen swirl burner for burning pulverized coal.

[0009] The present invention is realized through the following technical solutions:

[0010] A flue gas recirculation low-nitrogen swirl burner for burning pulverized coal includes a central air passage, a primary air passage, a flue gas passage, an inner secondary air passage, and an outer secondary air passage that are coaxially arranged step by step from the inside out. There are also inner fixed swirl vanes annularly arranged at the outlet end of the inner secondary air passage, and outer fixed vanes and outer adjustable swirl vanes are respectively arranged inside the outer secondary air passage. A spindle-shaped pulverized coal concentrator is arranged inside the primary air passage, and a separation ring is arranged at the outlet of the primary air passage. Among them, both the inner secondary air passage and the outer secondary air passage are used to introduce air; the flue gas passage is used to introduce recirculated flue gas.

[0011] The central air passage introduces central air through the central air passage interface. When a large amount of recirculated flue gas needs to be introduced, the roots blower can be connected to the central air pipeline, and the flue gas can be pumped from the tail passage to the central air passage interface and sprayed into the furnace to dilute the oxygen concentration in the central area of the burner, effectively reducing the temperature in the main combustion zone, thereby playing a role in reducing the emission of nitrogen oxides. The proportion of the introduced flue gas can be adjusted according to the actual combustion situation.

[0012] The primary air passage is connected to the outlet pipeline of the coal mill through the primary air passage interface and is used to introduce the pulverized coal-air mixture. The coal powder is sent into the burner by air and ignited. The ammonia channel interface 18 is connected to the primary air passage, and ammonia can be introduced into it when ammonia needs to be co-fired. A spindle-shaped pulverized coal concentrator is arranged inside the primary air passage to guide the air-powder mixture. After passing through this structure, the pulverized coal particles with larger particle sizes have greater inertia, so they gather on the outside of the primary air passage, while the air and the pulverized coal particles with smaller particle sizes gather towards the inside of the primary air. The separation ring strengthens the concentration-dilution separation of the burner, making the pulverized coal into two airflows of concentrated pulverized coal and lean pulverized coal. At the same time, the structure of the separation ring 8 is conducive to forming a recirculation zone behind it and ensuring the stable combustion of the pulverized coal.

[0013] The inboard secondary air passage and the inlet of the outboard secondary air passage are connected to the secondary air interface for introducing hot air to ensure the ignition and combustion of pulverized coal. The other ends of the inboard secondary air passage and the outboard secondary air passage are respectively connected to the outboard secondary air conical flare and the inboard secondary air conical flare. The conical flare plays a role in guiding the air, which is beneficial to forming a larger recirculation zone at the burner nozzle, entraining high-temperature flue gas back to the combustion zone, and reducing nitrogen oxides formed in the initial stage of combustion.

[0014] The flue gas passage is used to introduce recirculated flue gas suctioned from the boiler tail. The flue gas passage interface is connected to a Roots blower to draw the flue gas from the tail passage into the flue gas passage and spray it into the furnace. This can delay the mixing of pulverized coal in the primary air and secondary air, strengthen air staging, thereby reducing the occurrence of local high-temperature areas and reducing the generation of NOx. The thickness of the annular air flow passage of the flue gas interlayer is 10 - 20 mm, thus ensuring the stability of combustion.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The present invention applies the flue gas recirculation technology to address the problem of a relatively high generation amount of nitrogen oxides during the pulverized coal combustion process. Compared with the existing swirl burners, it can reduce the generation amount of nitrogen oxides. In the prior art, for burners applying the flue gas recirculation technology, the air and flue gas are mostly mixed and then introduced, and there is no flue gas interlayer structure between the secondary air inlet and the primary air inlet. By combining the flue gas interlayer passage with the pulverized coal concentrator structure in the present invention, the pulverized coal forms a distribution of thick outside and thin inside. By setting the flue gas interlayer, it plays a role in delaying the mixing of the hot secondary air and the primary air. At the same time, it enables the flue gas to enter the high-concentration pulverized coal area more deeply, strengthening the anoxic reduction atmosphere in the combustion zone, further reducing the oxygen concentration in this area, thereby reducing the emission of nitrogen oxides, reducing the conversion of intermediate bodies HCN / NH3 of N element to NOx, and thus reducing the emission of nitrogen oxides during the combustion process.

[0017] 2. By setting the separation ring structure, this swirl burner further strengthens the separation of thick and thin pulverized coal, splitting the pulverized coal air flow into two streams. At the same time, the structure of the separation ring can form a local recirculation zone behind it, which can, to a certain extent, reduce the content of nitrogen oxides generated during combustion while ensuring the stability of combustion.

[0018] 3. The present invention provides an economical and environmentally friendly retrofit technical route for reducing the emission concentration of nitrogen oxides in swirl pulverized coal burners, which can achieve the safe and stable operation of the burner and the boiler while meeting the requirements of environmental protection standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural cross-sectional view of the swirl burner of the present invention.

[0020] Label description: 1. Inner secondary air channel, 2. Outer secondary air channel, 3. Outer fixed vane, 4. Outer adjustable air vane, 5. Inner fixed vane, 6. Outer secondary air conical flare, 7. Inner secondary air conical flare, 8. Separation ring, 9. Primary air channel, 10. Central air channel, 11. Spindle coal powder concentrator, 12. Secondary air interface, 13. Flue gas channel, 14. Flue gas channel interface, 15. Primary air interface, 16. Coal powder distributor, 17. Central air channel interface. 18. Ammonia channel interface Specific implementation mode

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] Please refer to Figure 1 , the present invention provides a technical solution:

[0023] The present invention includes a central air channel 10, a primary air channel 9, a flue gas channel 13, an inner secondary air channel 1 and an outer secondary air channel 2 which are coaxially arranged step by step from the inside to the outside. An inner fixed swirl vane 5 is also annularly arranged at the outlet end of the inner secondary air channel 1. An outer fixed vane 3 and an outer adjustable swirl vane 4 are respectively arranged inside the outer secondary air channel 2. A spindle coal powder concentrator 11 is arranged inside the primary air channel, and a separation ring 8 is arranged at the outlet of the primary air channel. Among them, both the inner secondary air channel 1 and the outer secondary air channel 2 are used to introduce air; the flue gas channel 13 is used to introduce recirculated flue gas.

[0024] The central air channel 10 introduces central air through the central air channel interface 17. When a large amount of recirculated flue gas needs to be introduced, the roots blower can be connected to the central air pipeline, and the flue gas can be pumped from the tail channel to the central air channel interface 17 and sprayed into the furnace to dilute the oxygen concentration in the central area of the burner, effectively reducing the temperature in the main combustion area, thereby playing a role in reducing the emission of nitrogen oxides. The proportion of the introduced flue gas can be adjusted according to the actual combustion situation.

[0025] The primary air passage 9 is connected to the pulverizer outlet pipe through the primary air passage interface 15 and is used to introduce the pulverized coal-air mixture. The pulverized coal is sent into the burner by air for ignition. A spindle-shaped pulverized coal concentrator 11 is arranged in the primary air passage to guide the air-powder mixture. After passing through this structure, the pulverized coal particles with larger particle sizes have greater inertia, so they gather on the outer side of the primary air passage, while the air and the pulverized coal particles with smaller particle sizes gather towards the inner side of the primary air. The separation ring 8 strengthens the separation of rich and lean in the burner, causing the pulverized coal to be divided into two airflows of rich pulverized coal and lean pulverized coal. At the same time, the structure of the separation ring 8 is conducive to forming a recirculation zone behind it, while ensuring the stable combustion of the pulverized coal.

[0026] The inlets of the inner secondary air passage 1 and the outer secondary air passage 2 are connected to the secondary air interface 12 and are used to introduce hot air to ensure the ignition and combustion of the pulverized coal. The other ends of the inner secondary air passage 1 and the outer secondary air passage 2 are respectively connected to the outer secondary air conical flare 6 and the inner secondary air conical flare 7. The conical flare plays a role in guiding the air, which is conducive to forming a larger recirculation zone at the burner nozzle, entraining high-temperature flue gas back to the combustion area, and reducing the nitrogen oxides formed in the initial stage of combustion.

[0027] The flue gas passage 13 is used to introduce the recirculated flue gas sucked from the boiler tail. The flue gas passage interface 14 is connected to the Roots blower, and the flue gas is pumped from the tail passage to the flue gas passage 13 and sprayed into the furnace. It can play a role in delaying the mixing of the pulverized coal in the primary air and the secondary air, strengthening air staging, thereby reducing the occurrence of local high-temperature areas and reducing the generation of NOx. The thickness of the annular air flow passage of the flue gas interlayer 4 is 10 - 20 mm, thus ensuring the stability of combustion.

[0028] The ammonia passage interface 18 can be used to introduce ammonia, so that the ammonia is fully mixed with the primary air carrying the pulverized coal and then enters the furnace for combustion, playing a role in replacing part of the pulverized coal combustion. At the same time, since ammonia contains a large amount of N element, more NOx may be generated during the combustion process. It can cooperate with the flue gas interlayer 4 to reduce the NOx generated during the combustion process.

[0029] The hot air entering the burner is divided into two parts: inner secondary air and outer secondary air, and enters the furnace through the inner secondary air passage 1 and the outer secondary air passage 2 respectively. Their ratio is self-distributed according to the structural resistance, and the excess air coefficient is 1.05 - 1.1 to meet the needs of fuel combustion. Inner fixed vanes 5 are arranged at the position near the nozzle of the inner secondary air passage 1, and outer fixed vanes 3 are arranged at the position near the inlet of the outer secondary air passage 2 to evenly distribute and guide the air flow, so that the air is evenly distributed circumferentially. Outer adjustable vanes 4 are arranged at the position near the nozzle of the outer secondary air passage 2, and the blade angle can be adjusted according to the operation needs, forming an annular outer swirling air region in the outer secondary air passage 2, strengthening the mixing of air and gaseous fuel, enhancing the combustion stability, and playing a role in stabilizing combustion.

[0030] Operation steps: Step 1, the pulverized coal-air mixture is sent into the burner through the primary air duct 9 and ignited. After passing through the pulverized coal distributor 16, it is evenly distributed along the primary air duct. The spindle-shaped pulverized coal concentrator 11 and the separation ring 8 perform concentration and dilution separation on the pulverized coal mixture, dividing the pulverized coal into two airflows of concentrated pulverized coal and diluted pulverized coal;

[0031] Step 2: The hot secondary air is divided into two parts, the inner secondary air and the outer secondary air, and is introduced into the furnace through the inner secondary air duct 1 and the outer secondary air duct 2 respectively. The generation of some nitrogen oxides is inhibited through air staging technology, and its ratio is self-distributed according to the structural resistance, with the excess air coefficient being 1.05 - 1.1;

[0032] Step 3: The burner has a double swirl structure. Inner fixed vanes 5 are arranged near the nozzle of the inner secondary air duct 1, and outer fixed vanes 3 are arranged near the inlet of the outer secondary air duct 2, which play a role in evenly distributing and guiding the air flow. Outer adjustable vanes 4 are arranged near the nozzle of the outer secondary air duct 2, and the vane angles are adjusted according to the operation needs, forming an annular outer swirl air region in the outer secondary air duct 2;

[0033] Step 4: The high-temperature flue gas at the tail of the furnace is entrained back into the combustion area through the outer secondary air conical flare 6 and the inner secondary air conical flare 7. The recirculated flue gas is introduced into the furnace through the flue gas duct 13, and the oxygen concentration in the central area of the burner is diluted by the low-temperature and low-oxygen flue gas, reducing the temperature in the main combustion area.

[0034] Step 5: In the case of ammonia injection combustion required, ammonia can be introduced through the ammonia channel interface 18, so that the ammonia is fully mixed with the primary air carrying the pulverized coal and then enters the furnace for combustion, playing a role in replacing part of the pulverized coal combustion, thereby reducing the carbon dioxide generated by combustion while ensuring combustion stability.

[0035] This specific embodiment is only an explanation of the present invention and not a limitation to it. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as it is within the scope of the claims of the present invention, it is protected by the patent law.

Claims

1. A flue gas recirculation low-nitrogen swirl burner for burning pulverized coal, comprising a central air passage (10), a primary air passage (9), a flue gas passage (13), an inner secondary air passage (1) and an outer secondary air passage (2) which are coaxially arranged step by step from the inside to the outside, and is characterized in that: The outlet end of the inner secondary air passage (1) is annularly arranged with inner fixed swirl vanes (5), and the inner part of the outer secondary air passage (2) is respectively arranged with outer fixed vanes (3) and outer adjustable swirl vanes (4). A spindle-shaped pulverized coal concentrator (11) is arranged in the primary air passage, and a separation ring (8) is arranged at the outlet of the primary air passage; wherein, the inner secondary air passage (1) and the outer secondary air passage (2) are used for introducing air, and the flue gas passage (13) is used for introducing recirculated flue gas. The following steps are further included: Step 1: The pulverized coal-air mixture is sent into the burner through the primary air passage (9) and ignited. After passing through the pulverized coal distributor (16), it is evenly distributed along the primary air duct. The spindle-shaped pulverized coal concentrator (11) and the separation ring (8) perform lean-rich separation on the pulverized coal mixture, so that the pulverized coal is divided into two airflows of rich pulverized coal and lean pulverized coal; Step 2: The hot secondary air is divided into two parts, namely inner secondary air and outer secondary air, and is respectively introduced into the furnace through the inner secondary air passage (1) and the outer secondary air passage (2). The generation of some nitrogen oxides is inhibited through air staging technology, and its proportion is self-distributed according to the structural resistance. The excess air coefficient is 1.05 - 1.1; Step 3: The burner has a double swirl structure. Inner fixed vanes (5) are arranged near the nozzle of the inner secondary air passage (1), and outer fixed vanes (3) are arranged near the inlet of the outer secondary air passage (2), which play a role in evenly distributing and guiding the air flow. Outer adjustable air vanes (4) are arranged near the nozzle of the outer secondary air passage (2), and the blade angle is adjusted according to the operation needs, forming an annular outer swirl air region in the outer secondary air passage (2); Step 4: The high-temperature flue gas at the tail of the furnace is entrained back to the combustion area through the outer secondary air conical flare (6) and the inner secondary air conical flare (7). The recirculated flue gas is introduced into the flue gas passage (13) and sprayed into the furnace, and the oxygen concentration in the central area of the burner is diluted by the low-temperature and low-oxygen flue gas, reducing the temperature of the main combustion zone. Step 5: In the case of ammonia injection combustion required, ammonia can be introduced into the primary air passage (9) through the ammonia channel interface (18), so that the ammonia is fully mixed with the primary air carrying pulverized coal and then enters the furnace for combustion, playing a role in replacing part of the pulverized coal combustion, thereby reducing the carbon dioxide generated by combustion while ensuring combustion stability.

2. A flue gas recirculation low-nitrogen swirl burner for burning pulverized coal according to claim 1, characterized in that: The central air passage (10) introduces central air through the central air passage interface (17). When the amount of recirculated flue gas to be introduced is relatively large, the roots blower is connected to the central air pipeline, and the flue gas is pumped from the tail passage to the central air passage interface (17) and sprayed into the furnace. The proportion of the introduced flue gas is adjusted according to the actual combustion situation.

3. A flue gas recirculation low-nitrogen swirl burner for burning pulverized coal according to claim 1, characterized in that: The primary air passage (9) is connected to the outlet pipeline of the coal mill through the primary air passage interface (15) and is used for introducing the pulverized coal-air mixture.

4. A flue gas recirculation low-NOx swirl burner for burning pulverized coal according to claim 1, characterized in that: The inlets of the inner secondary air passage (1) and the outer secondary air passage (2) are connected to the secondary air interface (12), and the other ends are respectively connected to the outer secondary air conical flare (6) and the inner secondary air conical flare (7).

5. A flue gas recirculation low-nitrogen swirl burner for burning pulverized coal according to claim 1, characterized in that: The flue gas channel interface (14) of the flue gas channel (13) is connected to a Roots blower, and the flue gas is pumped from the tail channel into the flue gas channel (13) and sprayed into the furnace. The thickness of the annular air flow channel of the flue gas channel (13) is 10 - 20 mm.

6. A flue gas recirculation low-nitrogen swirl burner burning pulverized coal according to claim 1, characterized in that: The ammonia channel interface (18) is connected to the primary air channel (9) and is used to introduce ammonia for co - firing of ammonia and coal.

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