CN109931605B - Multistage air distribution radial outer thick and inner thin cyclone burner - Google Patents

Abstract

The invention discloses a multistage air distribution radial outer thick inner thin cyclone burner, which relates to a burner and aims to solve the problems that the existing burner is unfavorable for reduction of NOx and stability of combustion due to low concentration rate of a pulverized coal concentrator, has poor stability of a backflow area of the burner and cannot be well suitable for combustion of various coals. The invention comprises a central pipe, a primary air pipe, an inner secondary air pipe, a middle secondary air pipe, an outer secondary air pipe, a coal dust concentrator and a spoiler; the central pipe, the primary air pipe, the inner secondary air pipe, the middle secondary air pipe and the outer secondary air pipe are sleeved together from inside to outside in sequence, and the outlet ends of the central pipe, the primary air pipe, the inner secondary air pipe, the middle secondary air pipe and the outer secondary air pipe are sequentially provided with primary air flaring, inner secondary air flaring, middle secondary air flaring and outer secondary air flaring; the primary air pipe is internally provided with a pulverized coal concentrator and a flow equalizing ring. The invention reduces nitrogen oxides, improves the ignition capability of the burner and improves the stable combustion effect of the burner. The invention is suitable for boilers.

Description

A radial outer-dense inner-dilute swirl burner with multi-stage air distribution

Technical Field

The invention relates to a burner, in particular to a radial outer-concentrated and inner-dilute swirl burner with multi-stage air distribution.

Background technique

Traditional boiler swirl pulverized coal burners are prone to form oxygen-rich combustion zones due to strong airflow disturbances at the initial stage of combustion and rapid mixing of secondary air, and the flame is short, the heat release is concentrated, and the flame temperature is high, so the NOx emissions are very high. Therefore, many low-NOx swirl burners have emerged, which divide the secondary air into multiple levels, send pulverized coal into the furnace through the primary air, and extend the combustion time of pulverized coal through graded combustion of multi-level air. The air classification is to achieve the purpose of delaying mixing and controlling the combustion process. Only the amount of air required to maintain stable ignition and volatile combustion is sent into the primary combustion zone to form a dense core flame and reduce the peak flame temperature; due to the delay in the mixing of secondary air, a reduction zone is formed, which can not only reduce the amount of NOx generated but also reduce part of _NOx .

The current low-NOx outer-concentrated and inner-lean swirl burner, since the coal powder concentrator mostly adopts a Venturi coal powder concentrator, the primary air coal powder is concentrated by the concentrator and is distributed radially in a concentrated outer-lean inner pattern, that is, the coal powder concentration is high in the inner wall area of the primary air duct, and low in the outer wall area of the central air duct, thereby realizing staged combustion of the fuel, which can effectively reduce the formation of nitrogen oxides and improve the ignition stability of coal powder. The concentration rate of this type of concentrator is relatively low, generally between 60% and 75%, which is not conducive to the reduction of NOx and the stability of combustion. The stability of the burner recirculation zone is poor, so it can only adapt to bituminous coal and lignite with high volatile content, and incomplete combustion will occur for other types of coal.

Summary of the invention

In order to solve the problems that the existing swirl burner has a low concentration rate of the coal powder concentrator, which is not conducive to the reduction of NOx and the stability of combustion, the stability of the burner recirculation zone is poor, and it can only adapt to the combustion of coal with high volatility but cannot adapt well to the combustion of various types of coal, the present invention provides a radial outer-concentrated and inner-dilute swirl burner with multi-stage air distribution.

The technical solution adopted by the present invention to solve the above technical problems is:

Solution 1: A radial outer-concentrated inner-dilute swirl burner with multi-stage air distribution includes a central tube, a primary air duct, an inner secondary air duct, a middle secondary air duct, an outer secondary air duct, an inner swirl device, an outer swirl device, a secondary air bellows, a spoiler, a pulverized coal concentrator and a flow equalizing ring;

The central tube, the primary air duct, the inner secondary air duct, the middle secondary air duct and the outer secondary air duct are sequentially mounted together from the inside to the outside, and the primary air channel, the inner secondary air channel, the middle secondary air channel and the outer secondary air channel are sequentially formed between the adjacent two from the inside to the outside. The outlet ends of the primary air duct, the inner secondary air duct, the middle secondary air duct and the outer secondary air duct are respectively provided with a primary air expansion port, an inner secondary air expansion port, a middle secondary air expansion port and an outer secondary air expansion port. The spoiler is arranged on the inner wall of the outlet end of the primary air duct, the inner cyclone is arranged in the middle secondary air channel, and the outer cyclone is arranged in the outer secondary air channel.

The pulverized coal concentrator comprises a support plate and N concentrating rings, where N is an integer of 2-5;

The diameters of the N concentrating rings increase in sequence along the flow direction of the primary air pulverized coal, and a certain distance is provided between two adjacent concentrating rings. The N concentrating rings are fixed together by a support plate, and the support plate is fixed to the outer wall of the central tube. The N concentrating rings are provided on one side adjacent to the outlet of the central tube;

The flow balancing ring is arranged on the inner wall of the primary air duct, and is arranged adjacent to a side of a concentrating ring with a larger diameter.

Furthermore, the spoiler is composed of M trapezoidal plates whose plate surfaces are in the same plane, M is an integer of 8-16, the M trapezoidal plates are evenly arranged at the outlet end of the inner wall of the primary air duct, and two adjacent trapezoidal plates are set with a certain gap, and the length of each trapezoidal plate is 0.1 to 0.4 times the distance from the outer wall of the central tube to the inner wall of the primary air duct.

Solution 2: A radial outer-concentrated inner-dilute swirl burner with multi-stage air distribution includes a central tube, a primary air duct, an inner secondary air duct, an outer secondary air duct, an inner swirl device, an outer swirl device, a secondary air bellows, a spoiler, a pulverized coal concentrator, a flow equalizer and a spacer tube;

The central tube, the primary air duct, the spacing tube, the inner secondary air duct and the outer secondary air duct are sequentially mounted together from the inside to the outside, a primary air channel is formed between the central tube and the primary air duct, the spacing tube, the inner secondary air duct and the outer secondary air duct are adjacent to each other and sequentially form an inner secondary air channel and an outer secondary air channel from the inside to the outside, both ends of the spacing tube are respectively fixedly connected to the primary air duct through an annular plate to form a closed space, the outlet ends of the primary air duct, the inner secondary air duct and the outer secondary air duct are respectively provided with a primary air expansion port, an inner secondary air expansion port and an outer secondary air expansion port, a spoiler is arranged on the inner wall of the outlet end of the primary air duct, an inner cyclone is arranged in the inner secondary air channel, and an outer cyclone is arranged in the outer secondary air channel;

The pulverized coal concentrator comprises a support plate and N concentrating rings, where N is an integer of 2-5;

The diameters of the N concentrating rings increase in sequence along the flow direction of the primary air pulverized coal, and there is a certain distance between two adjacent concentrating rings. The N concentrating rings are fixed together by a support plate, and the support plate is fixed to the outer wall of the central tube. The N concentrating rings are arranged on one side adjacent to the outlet of the central tube;

The flow balancing ring is arranged on the inner wall of the primary air duct, and is arranged adjacent to a side of a concentrating ring with a larger diameter.

Compared with the prior art, the present invention has the following beneficial effects:

1. The burner system of the present invention has low resistance, and the total secondary air resistance does not exceed 800Pa, which saves fan power consumption. Moreover, the present invention can well maintain combustion stability under all loads, and no coking occurs at the nozzle.

2. Compared with the prior art, the present invention realizes the separation of primary air pulverized coal into thick and thin parts through a new type of pulverized coal concentrator and flow equalizing ring, and its separation efficiency can reach 90%, that is, the fuel staged combustion of primary air pulverized coal is realized, and the primary air velocity near the primary air duct wall can be well reduced, effectively reducing the scouring of the primary air pulverized coal mixture on the primary air duct wall, and extending the service life of the equipment. The primary air of the present invention carries pulverized coal into the primary air channel, as shown in Figures 12 and 14. Under the concentration effect of the pulverized coal concentration device, the primary air pulverized coal is divided into thick and thin parts, a thick pulverized coal area is formed near the primary air inner duct wall area, and a thin pulverized coal area is formed near the outer surface of the central air duct. The pulverized coal concentration ratio is between 75-90%, and the primary air pulverized coal distribution form of thick outside and thin inside along the radial direction of the primary air duct is realized. A large amount of pulverized coal is concentrated near the inner surface of the primary air duct and sprayed into the furnace, realizing the staged combustion of pulverized coal, increasing the amount of pulverized coal in the middle high-temperature reflux zone, so that the reducing atmosphere in the central reflux zone is strengthened, the residence time of pulverized coal in the reflux zone is prolonged, and the generation of fuel-type nitrogen oxides is suppressed.

3. The present invention divides the main combustion air into three levels of inner secondary air, middle secondary air and outer secondary air to increase the degree of air classification. As shown in the velocity distribution cloud diagram of the burner outlet in FIG12 , while a stable central recirculation zone is formed at the burner outlet, there is a low-speed zone between the primary air and the secondary air, which delays the mixing of the primary air and the secondary air. This is because the inner secondary air is a direct current secondary air with a small air volume and a low wind speed, so its penetration ability and ability to entrain the primary air are weak, and the primary air will not be entrained too early, which increases the distance between the primary air and the peripheral mainstream secondary air, delays the mixing of the primary air and the swirl secondary air, strengthens the reducing atmosphere in the central recirculation zone, and inhibits the formation of nitrogen oxides. At the same time, the middle secondary air and the outer secondary air are formed into swirl winds after passing through the inner swirler and the outer swirler and are injected into the furnace at a relatively high speed. Their function is to complete the combustion of unburned carbon away from the burner outlet area and to ensure the formation of a stable recirculation zone near the combustion area.

Fourth, the present invention divides the main combustion air into inner secondary air and outer secondary air for staged combustion, and at the same time, a spacing tube is set between the primary air duct and the inner secondary air duct, as shown in Figure 12, a stable central recirculation zone is formed at the outlet of the present invention, and at the same time, there is a low-speed zone between the primary air and the secondary air, which delays the mixing of the primary air and the secondary air. This is because a spacing tube is set between the primary air and the inner secondary air, so that the primary air mixture at the outlet of the present invention and the secondary air are sprayed in at intervals, increasing the distance between the primary air and the peripheral mainstream secondary air, delaying the mixing of the primary air and the swirl secondary air, strengthening the reducing atmosphere in the central recirculation zone, and inhibiting the formation of nitrogen oxides. At the same time, both the inner secondary air and the outer secondary air pass through the inner swirler and the outer swirler to form a swirling wind that is injected into the furnace, with a relatively high speed, which is used to complete the combustion of unburned carbon away from the outlet area of the present invention and ensure that a stable recirculation zone is formed in the near-combustion zone.

5. The present invention provides a spoiler on the inner surface of the outlet end of the primary air duct. The spoiler is composed of M trapezoidal plates and is evenly arranged on the circumference of the primary air duct, where M is an integer of 8-16; the length of the spoiler is 0.1 to 0.4 times the distance between the central air duct and the primary air duct. Under the combined effect of the spoiler, it can be seen from the primary air coal powder concentration distribution schematic diagram in Figure 12 that the primary air concentrated coal powder is distributed in a concentrated and light distribution mode in the circumferential direction under the effect of the spoiler, which increases the local coal powder concentration of the primary air outlet section and strengthens the graded combustion of the coal powder, which is particularly beneficial to improving the stable combustion performance of the burner and reducing the generation of nitrogen oxides. At the same time, due to the existence of the spoiler, when the coal powder airflow flows around the spoiler, a small vortex circle is formed on its circumference, attached to the root of the high-temperature recirculation zone, and in the small vortex zone, the coal powder is easy to ignite, strengthening the coal powder ignition characteristics, and ensuring the stable combustion characteristics of the burner.

6. The present invention arranges expansions in the middle secondary air and the outer secondary air to strengthen the swirl intensity of the inner swirl and the outer swirl secondary air, and at the same time delays the mixing of the middle secondary air and the outer secondary air with the primary air powder, thereby prolonging the residence time of the coal powder in the central reflux zone of the reducing atmosphere, so as to form an oxygen-deficient environment in the area near the burner, which is beneficial to NOx reduction and reduces the formation of nitrogen oxides.

7. Under the combined effect of the unique coal powder concentration device, expansion structure and unique air volume distribution of the present invention, as shown in Figures 10 to 14, the primary air powder jet area at the burner outlet forms a stable central recirculation zone, which can suck the primary air that is thick on the outside and thin on the inside into the recirculation zone, bring the high-temperature flue gas back to the area near the burner, heat the primary air powder, promote the ignition of coal powder, ensure the stability of the flame, and achieve stable combustion under different loads. The high-temperature flue gas brought back has a low oxygen content, so that the recirculation zone is in an oxygen-deficient environment, thereby inhibiting the formation of nitrogen oxides.

8. The concentration rate of the coal powder concentration device of the present invention is above 90%, which further improves the reduction of NOx and the stability of combustion. The unique coal powder concentration device of the present invention and the use of a specific expansion combination structure can better adapt to the combustion of different types of coal and make the combustion more stable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an overall structural diagram of a first embodiment of the present invention;

FIG2 is a partial enlarged view of location I in FIG1 , in which the arrow direction indicates the direction of coal powder conveying;

FIG3 is a schematic diagram of a spoiler 7;

FIG4 is a partial enlarged view of point II of FIG1 ;

FIG5 is a partial schematic diagram of the first solution at the outlet of FIG1;

FIG6 is a partial schematic diagram of the second solution at the outlet in FIG1 ;

FIG7 is an overall structural diagram of solution 2 of the present invention;

FIG8 is a partial schematic diagram of the first solution at the outlet of FIG7;

FIG9 is a partial schematic diagram of the second solution at the outlet in FIG7;

10 is a schematic diagram of the recirculation area and expansion angle of the outlet cold flow field of the present invention;

FIG11 is a numerical simulation distribution diagram of the outlet velocity vector of the present invention;

FIG12 is a numerical simulation cloud diagram of the outlet velocity distribution of the present invention;

FIG13 is a cloud diagram of the distribution of coal powder concentration in the primary air duct of the present invention;

FIG14 is a cloud diagram of the distribution of pulverized coal concentration at the primary air outlet of the present invention;

The arrow in the primary air duct 2 in FIG. 1 and FIG. 7 indicates the direction of coal powder conveying, and the arrows at the inner secondary air duct 3, the middle secondary air duct 4 and the outer secondary air duct 5 indicate the direction of air inlet.

Detailed ways

Specific implementation method 1: This implementation method is described in conjunction with Figures 1 to 4. In this implementation method, a radial outer-concentrated inner-dilute swirl burner with multi-stage air distribution includes a central tube 1, a primary air duct 2, an inner secondary air duct 3, a middle secondary air duct 4, an outer secondary air duct 5, an inner swirler 13, an outer swirler 14, a secondary air box 15, a spoiler 7, a coal powder concentrator 6 and a flow equalizing ring 8;

The central tube 1, the primary air duct 2, the inner secondary air duct 3, the middle secondary air duct 4 and the outer secondary air duct 5 are sequentially mounted together from the inside to the outside, and the primary air channel, the inner secondary air channel, the middle secondary air channel and the outer secondary air channel are sequentially formed between the adjacent two from the inside to the outside. The outlet ends of the primary air duct 2, the inner secondary air duct 3, the middle secondary air duct 4 and the outer secondary air duct 5 are respectively provided with a primary air expansion opening 9, an inner secondary air expansion opening 10, a middle secondary air expansion opening 11 and an outer secondary air expansion opening 12. The spoiler 7 is arranged on the inner wall of the outlet end of the primary air duct 2, the inner cyclone 13 is arranged in the middle secondary air channel, and the outer cyclone 14 is arranged in the outer secondary air channel.

The pulverized coal concentrator 6 comprises a support plate 6-1 and N concentrating rings 6-2, where N is an integer of 2-5;

The diameters of the N concentrating rings 6-2 increase in sequence along the flow direction of the primary air pulverized coal. Two adjacent concentrating rings 6-2 are arranged at a certain distance. The N concentrating rings 6-2 are fixed together by a support plate 6-1. The support plate 6-1 is fixed to the outer wall of the central tube 1. The N concentrating rings 6-2 are arranged on one side adjacent to the outlet of the central tube 1.

The flow balancing ring 8 is arranged on the inner wall of the primary air duct 2, and the flow balancing ring 8 is arranged adjacent to one side of the concentrating ring 6-2 with a larger diameter.

Preferably, the outer cyclone 14 is installed in the secondary air box 15 , and the horizontal section of the primary air duct 2 and the horizontal section of the outer secondary air duct 5 are respectively welded to the secondary air box 15 .

The pulverized coal concentrator 6 comprises a support plate 6-1 and N concentrating rings 6-2, where N is an integer of 2-5;

The diameters of the N concentrating rings 6-2 increase successively along the flow direction of the primary air pulverized coal, and there is a certain distance between two adjacent concentrating rings 6-2. The N concentrating rings 6-2 are fixed together by a support plate 6-1, and the support plate 6-1 is fixed to the outer wall of the central pipe 1. The N concentrating rings 6-2 are arranged on one side adjacent to the outlet of the central pipe 1.

Preferably, a stainless steel outer shell and a wear-resistant ceramic structure are used in the concentrating ring 6-2 to improve the wear resistance of the concentrating ring and increase the service life of the concentrating ring.

Adjustable dampers are provided at the entrances of the inner secondary air duct 3, the middle secondary air duct 4 and the outer secondary air duct 5. By adjusting the size of each damper, the size and strength of the central recirculation zone can be adjusted to meet the requirements of different coal types, air volumes and loads, thereby increasing the coal type adaptability of the burner.

As shown in Figure 13, the primary air-powder mixture in this embodiment is gradually concentrated under the action of the coal powder concentrator 6, and the coal powder airflow is divided into two parts, a thick coal powder area close to the inner wall of the primary air duct, and a thin coal powder area close to the outer surface of the central air duct. The coal powder concentration distribution in the radial direction is thick on the outside and thin on the inside, thereby realizing the staged combustion of coal powder, increasing the amount of coal powder in the middle high-temperature reflux zone, reducing the ignition heat of coal powder and prolonging the residence time of coal powder in the reflux zone, enhancing the reducing atmosphere in the central reflux zone, and inhibiting the formation of nitrogen oxides.

The present invention divides the secondary air into inner secondary air, middle secondary air and outer secondary air, thereby increasing the radial air classification degree of the present invention, and the inner secondary air is a direct current air with a small air volume. At the same time, an inner secondary air expansion port is added, as shown in the burner outlet velocity cloud map distribution diagram in FIG12 . Since this secondary air is a direct current air with a small air volume and a low wind speed, its penetration ability and entrainment ability are weak, and it will not entrain the primary air prematurely, thereby increasing the distance between the primary air and the swirl secondary air, delaying the mixing of the primary air coal powder mixture and the peripheral swirl secondary air, strengthening the reducing atmosphere in the central reflux zone, and inhibiting the formation of nitrogen oxides in the early stage of combustion.

As shown in Figures 10 to 14, the burner cold-state modeling experiment and numerical simulation calculations show that a stable central recirculation zone is formed in the outlet area of the present invention. This recirculation zone is stable and has a good recirculation effect. It can draw the primary air that is thick outside and thin inside into the recirculation zone, and draw the high-temperature flue gas on the outside back to the vicinity of the burner outlet, heat the primary air pulverized coal, promote ignition of the pulverized coal, and maintain flame stability. At the same time, due to the low oxygen content of the drawn high-temperature flue gas, the central recirculation zone in the primary air outlet area is in an oxygen-deficient state, forming a reducing atmosphere and reducing the generation of nitrogen oxides.

Specific implementation method 2: This implementation method is described in conjunction with Figure 2. In this implementation method, N concentrating rings 6-2 are all conical rings, and the tapers of the N concentrating rings 6-2 are equal. The angle δ between the generatrix of each concentrating ring 6-2 and the center line of the central tube 1 is 20° to 40°.

Other components and connection relationships are the same as those in the first specific implementation mode.

Specific implementation method three: This implementation method is explained in combination with Figures 1, 5 and 6. In this implementation method, the flow equalizing ring 8 is arranged on the inner tube wall of the primary air duct 2 between the primary air expansion port 9 and the coal powder concentrator 6. The distance Ls from the end of the flow equalizing ring 8 adjacent to the primary air expansion port 9 to the end of the primary air expansion port 9 is 4 to 8 times the distance S1 from the outer wall of the central tube 1 to the inner wall of the primary air duct 2. The thickness Hs of the flow equalizing ring 8 is 0.04 to 0.1 times the distance S1 from the outer wall of the central tube 1 to the inner wall of the primary air duct 2.

Other components and connection methods are the same as those in the second specific implementation method.

Specific implementation mode four: This implementation mode is illustrated in conjunction with Figure 3. The spoiler 7 described in this implementation mode is composed of M trapezoidal plates whose plate surfaces are in the same plane, M is an integer of 8-16, and the M trapezoidal plates are evenly arranged at the outlet end of the inner wall of the primary air duct 2, and two adjacent trapezoidal plates are set with a certain gap. The height S of each trapezoidal plate is 0.1 to 0.4 times the distance S1 from the outer wall of the central tube 1 to the inner wall of the primary air duct 2.

As shown in Figure 13, numerical calculation analysis shows that after adding the spoiler 7, the primary air pulverized coal is distributed in a thick and thin distribution pattern in the circumferential direction under the action of the spoiler 7, which increases the local pulverized coal concentration in the primary air outlet section and strengthens the graded combustion of pulverized coal, which is particularly beneficial to improving the stable combustion performance of the burner and reducing the generation of nitrogen oxides. At the same time, due to the existence of the spoiler 7, when the pulverized coal airflow flows around the spoiler 7, a small vortex circle is formed on its circumference, attached to the root of the high-temperature recirculation zone, and in the small vortex zone, the pulverized coal is easy to ignite, strengthening the ignition characteristics of the pulverized coal, and ensuring the stable combustion characteristics of the burner.

Other components and connection relationships are the same as those of the third specific implementation method.

Specific implementation mode five: This implementation mode is illustrated in conjunction with Figure 5. In this implementation mode, the expansion angle β of the primary air expansion port 9 is in the range of 15° to 25°, the expansion angle γ of the middle secondary air expansion port 11 is in the range of 20° to 25°, the expansion angle θ of the outer secondary air expansion port 12 is in the range of 20° to 25°, and the expansion angle υ of the inner secondary air expansion port 10 is in the range of 20° to 25°.

As shown in Figures 10-12, numerical calculations and burner cold state modeling experiments show that the above expansion combinations of different angles can form a stable recirculation zone in the burner outlet area. The present invention can select different expansion angle combinations according to different types of coal and different furnace forms to achieve the best combustion effect, reduce the generation of nitrogen oxides, and reduce high-temperature corrosion of the water-cooled wall. If each expansion angle is too large, the airflow expansion angle will increase, forming an open recirculation zone, resulting in unstable combustion and coking of the water-cooled wall. If the expansion angle is too small, the primary air and the secondary air will mix too early, and the recirculation zone will be too small, which is not conducive to the stable combustion of coal powder.

In this embodiment, the secondary air expansion opening 11 and the primary air expansion opening 9 delay the mixing of the primary air powder and the secondary air, prolong the residence time of the coal powder in the reducing atmosphere, and reduce the generation of nitrogen oxides.

Other components and connection relationships are the same as those of the fourth specific implementation method.

Specific implementation method six: This implementation method is described in conjunction with Figure 5. In this implementation method, the end of the inner secondary air expansion port 10, the end of the middle secondary air expansion port 11 and the end of the primary air expansion port 9 are arranged flush.

The other components and connection relationships are the same as those of the fifth specific implementation method.

Specific implementation method seven: This implementation method is illustrated in conjunction with Figure 5. In this implementation method, the length L4 of the primary air expansion port 9, the length L3 of the inner secondary air expansion port 10 and the length L2 of the middle secondary air expansion port 11 are equal; the length L4 of the primary air expansion port 9 is 0.4 to 0.7 times the length L1 of the outer secondary air expansion port 12.

The primary air-powder mixture coming out of the primary air nozzle is first premixed with the central air flow, then enters the outer secondary air expansion port to be premixed with the inner direct air, and then is sprayed into the furnace together with the middle secondary air and outer secondary air flows. By adding two premixing sections, it is helpful to form a stable central recirculation zone in the burner outlet area, prolong the residence time of the primary air pulverized coal in the central recirculation zone, so that the pulverized coal can burn stably and effectively inhibit the formation of nitrogen oxides.

The other components and connection relationships are the same as those of the sixth specific implementation method.

Specific implementation eight: This implementation is illustrated in conjunction with Figure 6. In this implementation, the length L3 of the inner secondary air expansion port 10 is equal to the length L2 of the middle secondary air expansion port 11; the length L3 of the inner secondary air expansion port 10 is 0.6 to 0.8 times the length L1 of the outer secondary air expansion port 12; the length L4 of the primary air expansion port 9 is 0.5 to 0.7 times the length L3 of the inner secondary air expansion port 10.

This embodiment further delays the mixing of the primary air-powder mixture and the secondary air by adding three premixing sections, enhances the swirl intensity of the secondary air, and realizes graded combustion of coal powder through three-stage premixing. It is also helpful to form a stable central recirculation zone in the burner outlet area, prolong the residence time of primary air coal powder in the central recirculation zone, so that the coal powder can be stably burned and the formation of nitrogen oxides can be effectively suppressed. It is suitable for sub-bituminous coal, lean coal and anthracite.

Other components and connection relationships are the same as those of the sixth specific implementation method.

Specific embodiment nine: This embodiment is described in conjunction with Figure 7. In this embodiment, a radial outer-concentrated inner-dilute swirl burner with multi-stage air distribution includes a central tube 1, a primary air duct 2, an inner secondary air duct 3, an outer secondary air duct 5, an inner swirler 13, an outer swirler 14, a secondary air box 15, a spoiler 7, a pulverized coal concentrator 6, a flow equalizer ring 8 and a spacer tube 16;

The central tube 1, the primary air duct 2, the spacer tube 16, the inner secondary air duct 3 and the outer secondary air duct 5 are sequentially mounted together from the inside to the outside, a primary air channel is formed between the central tube 1 and the primary air duct 2, the spacer tube 16, the inner secondary air duct 3 and the outer secondary air duct 5 are adjacent to each other and sequentially form an inner secondary air channel and an outer secondary air channel from the inside to the outside, both ends of the spacer tube 16 are respectively fixedly connected to the primary air duct 2 through an annular plate to form a closed space, the outlet ends of the primary air duct 2, the inner secondary air duct 3 and the outer secondary air duct 5 are respectively provided with a primary air expansion port 9, an inner secondary air expansion port 10 and an outer secondary air expansion port 12, the spoiler 7 is arranged on the inner wall of the outlet end of the primary air duct 2, the inner cyclone 13 is arranged in the inner secondary air channel, and the outer cyclone 14 is arranged in the outer secondary air channel;

The pulverized coal concentrator 6 comprises a support plate 6-1 and N concentrating rings 6-2, where N is an integer of 2-5;

The diameters of the N concentrating rings 6-2 increase in sequence along the flow direction of the primary air pulverized coal. Two adjacent concentrating rings 6-2 are arranged at a certain distance. The N concentrating rings 6-2 are fixed together by a support plate 6-1. The support plate 6-1 is fixed to the outer wall of the central tube 1. The N concentrating rings 6-2 are arranged on one side adjacent to the outlet of the central tube 1.

The flow balancing ring 8 is arranged on the inner wall of the primary air duct 2, and the flow balancing ring 8 is arranged adjacent to one side of the concentrating ring 6-2 with a larger diameter.

Preferably, the outer cyclone 14 is installed in the secondary air box 15 , and the horizontal section of the primary air duct 2 and the horizontal section of the outer secondary air duct 5 are respectively welded to the secondary air box 15 .

The other components and connection relationships are the same as those of the second, third or fourth specific implementation modes.

Specific implementation method ten: This implementation method is described in conjunction with FIG. 7 . In this implementation method, the thickness of the spacer tube 16 is 0.05-0.4 times the distance S1 from the outer wall of the central tube 1 to the inner wall of the primary air duct 2 .

Other components and connection relationships are the same as those of the ninth embodiment.

Specific embodiment eleven: This embodiment is illustrated in conjunction with Figure 7. In this embodiment, the expansion angle β of the primary air expansion port 9 is in the range of 10° to 20°, the expansion angle θ of the external secondary air expansion port 12 is in the range of 20° to 25°, and the expansion angle υ of the internal secondary air expansion port 10 is in the range of 20° to 25°.

Other components and connection relationships are the same as those of the ninth embodiment.

Specific embodiment 12: This embodiment is described in conjunction with FIG. 8 . In this embodiment, the end of the inner secondary air expansion opening 10 and the end of the primary air expansion opening 9 are arranged flush.

The other components and connection relationships are the same as those of the ninth embodiment.

Specific implementation method thirteen: This implementation method is described in conjunction with Figure 8. In this implementation method, the length L4 of the primary air expansion port 9 is equal to the length L3 of the inner secondary air expansion port 10; the length L4 of the primary air expansion port 9 is 0.4 to 0.7 times the length L1 of the outer secondary air expansion port 12.

The other components and connection relationships are the same as those in the twelfth specific implementation manner.

Specific embodiment 14: This embodiment is described in conjunction with Figure 9. In this embodiment, the length L3 of the inner secondary air expansion port 10 is 0.6 to 0.8 times the length L1 of the outer secondary air expansion port 12; the length L4 of the primary air expansion port 9 is 0.5 to 0.7 times the length L3 of the inner secondary air expansion port 10.

The other components and connection relationships are the same as those of the ninth, tenth or eleventh specific embodiments.

The two types of burners of the present invention are applied to the HG-1913/25.4-PM8 boiler: When the coal is burned, the nitrogen oxide emissions are as follows:

1. When burning bituminous coal, Vdaf = 26.35%, Aar = 22.65%, Mt = 10.23%, Qnet,ar = 21.18Mj/kg (where Vdaf is the volatile matter on a dry ash-free basis, Aar is the ash parameter on an as-received basis, Mt is the total moisture parameter, and Qnet,ar is the low calorific value on an as-received basis). After all 24 burners adopt the new burner of the present invention, the emission of nitrogen oxides at the tail of the boiler is less than 210mg/ ^m3 .

2. When burning a mixture of 50% lean coal and 50% bituminous coal: the chemical analysis of the lean coal is as follows: Vdaf = 19.9%, Aar = 32.65%, Mt = 7.2%, Qnet,ar = 19.13Mj/kg, and the chemical analysis of the bituminous coal is as follows: Vdaf = 26.35%, Aar = 22.65%, Mt = 10.23%, Qnet,ar = 21.18Mj/kg. After all 24 burners adopt the new burners of the present invention, the emission of nitrogen oxides at the tail of the boiler is less than 270mg/m3.

The above experimental data show that the present invention can ensure that nitrogen oxides meet the standards when burning different coal qualities, and the emission of nitrogen oxides after combustion meets the relevant regulations and standards, and can be applied to the combustion of more types of coal.

The working principle of scheme one of the present invention is: the primary air-powder mixture enters the primary air duct 2 through the powder delivery pipe, and a coal powder concentrator 6 is arranged in the primary air duct of the burner. The diameter of the concentrating ring 6-2 of the coal powder concentrator 6 increases successively along the flow direction of the primary air. The primary air-powder mixture is divided into two parts after passing through the coal powder concentrator 6. A thick coal powder area is formed near the inner wall area of the primary air duct 2, and a thin coal powder area is formed near the outer surface area of the central air duct 1. At the same time, due to the presence of the flow equalizing ring 8, the wind speed in the inner wall area of the primary air duct 2 is reduced, which effectively reduces the erosion of the primary air-coal powder mixture on the primary air duct 2 and extends the service life of the equipment. At the same time, due to the presence of the flow equalizing ring and the spoiler 7, the primary air coal powder is distributed in a thick and thin pattern in the circumferential direction at the outlet end of the primary air duct 2. The pulverized coal fuel is burnt radially and circumferentially, the amount of fuel in the central recirculation zone is increased, the generation of nitrogen oxides is reduced, the stable combustion ability of the burner is improved, and a small vortex circle is formed around the spoiler, attached to the root of the high-temperature recirculation zone. In the small vortex zone, the pulverized coal is easy to ignite, the ignition characteristics of the pulverized coal are enhanced, and the stable combustion characteristics of the present invention are guaranteed. The secondary air enters the inner secondary air duct 3, the middle secondary air duct 4 and the outer secondary air duct 5 respectively through the secondary air wind box 15. The middle secondary air is a direct current wind with a small amount of wind and a low wind speed. Its penetration ability and ability to entrain the primary air are weak, and the primary air will not be entrained too early, increasing the distance between the primary air and the peripheral mainstream secondary air, delaying the mixing of the primary air and the secondary air. The middle secondary air duct 4 is provided with an inner swirler 13, and the outer secondary air duct 5 is provided with an outer swirler 14, so that the middle and outer secondary air generate rotation, and the rotation direction is consistent. It is sprayed into the furnace through the middle and outer secondary air nozzles, and a suitable central recirculation zone is formed in the burner area to make the pulverized coal burn stably and reduce the generation of nitrogen oxides.

The working principle of the second scheme of the present invention is: the primary air-powder mixture enters the primary air duct 2 through the powder delivery pipe, and a coal powder concentrator 6 is arranged in the primary air duct 2. The diameter of the concentrating ring 6-2 of the coal powder concentrator 6 increases successively along the flow direction of the primary air coal powder. After passing through the coal powder concentrator 6, the primary air-powder mixture is divided into two parts. The inner wall area close to the primary air duct 2 forms a coal powder area, and the area close to the outer surface of the central tube 1 forms a light coal powder area. Due to the effect of the spoiler 7, the primary air coal powder is distributed in a thick and light interval in the circumferential direction of the outlet end of the primary air duct 2, so as to realize the graded combustion of coal powder fuel in the radial and circumferential directions, increase the fuel amount in the central recirculation area, reduce the generation of nitrogen oxides, and improve the stable combustion ability of the present invention. At the same time, a small vortex circle is formed around the spoiler 7, attached to the root of the high-temperature recirculation area. In the small vortex area, the coal powder is easy to ignite and strengthen the ignition characteristics of the coal powder, ensuring the stable combustion characteristics of the present invention. The secondary air passes through the secondary air box 15 and enters the inner secondary air duct 3 and the outer secondary air duct 5 respectively, and a spacing tube 16 is arranged between the primary air duct 2 and the inner secondary air duct 3, so that the primary air pulverized coal mixture and the secondary air at the outlet end of the present invention are sprayed in at intervals, which increases the distance between the primary air and the peripheral mainstream secondary air, and delays the mixing of the primary air and the secondary air. The inner swirler 13 is arranged in the inner secondary air channel, and the outer swirler 14 is arranged in the outer secondary air channel, so that the inner and outer secondary air rotate with the same rotation direction, and are sprayed into the furnace through the inner and outer secondary air nozzles, forming a suitable central recirculation zone in the present invention to stabilize the combustion of pulverized coal and reduce the generation of nitrogen oxides.

Claims (2)

1. The utility model provides a multistage air distribution's radial outside dense interior light cyclone burner which characterized in that: the device comprises a central tube (1), a primary air pipe (2), an inner secondary air pipe (3), an outer secondary air pipe (5), an inner cyclone (13), an outer cyclone (14), a secondary air box (15), a spoiler (7), a coal dust concentrator (6), a flow equalizing ring (8) and a spacing cylinder (16);

The central tube (1), the primary air tube (2), the interval cylinder (16), the inner secondary air tube (3) and the outer secondary air tube (5) are sequentially sleeved together from inside to outside, a primary air channel is formed between the central tube (1) and the primary air tube (2), the interval cylinder (16), the inner secondary air tube (3) and the outer secondary air tube (5) are adjacent to each other and sequentially form an inner secondary air channel and an outer secondary air channel from inside to outside, two ends of the interval cylinder (16) are fixedly connected with the primary air tube (2) through annular plates respectively to form a closed space, primary air flares (9), inner secondary air flares (10) and outer secondary air flares (12) are correspondingly arranged at the outlet ends of the primary air tube (2), the spoiler (7) is arranged on the inner wall of the outlet end of the primary air tube (2), the inner cyclone (13) is arranged in the inner secondary air channel, and the outer cyclone (14) is arranged in the outer secondary air channel;

The pulverized coal concentrator (6) comprises a supporting plate (6-1) and N concentrating rings (6-2), wherein N is an integer of 2-5;

The diameters of N concentration rings (6-2) are sequentially increased along the flowing direction of primary air pulverized coal, a certain distance is formed between every two adjacent concentration rings (6-2), the N concentration rings (6-2) are fixedly connected together through a supporting plate (6-1), the supporting plate (6-1) is fixedly connected to the outer wall of the central tube (1), and one side, adjacent to the outlet of the central tube (1), of the N concentration rings (6-2);

The flow equalizing ring (8) is arranged on the inner wall of the primary air pipe (2), and the flow equalizing ring (8) is arranged adjacent to one side of the concentration ring (6-2) with larger diameter.

2. A multi-stage air-distribution radially outer rich and inner lean swirl burner according to claim 1, characterized in that: the N concentration rings (6-2) are conical rings, the conicity of the N concentration rings (6-2) is equal, and the included angle (delta) between the bus of each concentration ring (6-2) and the central line of the central tube (1) is 20-40 degrees.