Sectional type combustion low-nitrogen combustion head

Abstract

The utility model discloses a sectional type combustion low-nitrogen combustion head which comprises a center combustion head, a flame tube and a secondary gas nozzle, and the flame tube is arranged on the periphery of the center combustion head in a sleeved mode. The central combustion head comprises a central gas distributor, a plurality of premixing nozzles and a central gas connecting pipe; an annular gap is formed between the wall of the flame tube and the outer wall of the central gas distributor, combustion-supporting air is introduced into the flame tube, one part of the combustion-supporting air and the gas meet and are mixed in the straight tube of the premixing nozzle, the combustion-supporting air is ignited when flowing out of the straight tube, a plurality of independent combustion flames are formed, and the other part of the combustion-supporting air flows out through the annular gap. Combustion is controlled in a segmented mode, oxygen-enriched lean combustion is adopted in the initial stage to control generation of nitric oxide, smoke and heat generated by combustion in the initial stage are utilized in the secondary stage, combustion in the secondary stage is diffused to a larger space, combustion is carried out in a flameless combustion mode, combustion is more uniform, local high temperature is avoided, and overall low-nitrogen combustion is achieved.

Description

Technical Field

[0001] The utility model belongs to the technical field of burners and related air-gas-smoke mixing devices, and specifically relates to a staged combustion, graded premixed oxygen-rich and lean combustion low-nitrogen burner head. The utility model relates to related industrial burners, including burner heads installed on combustion chambers, fueled by natural gas, and used in systems without external flue gas circulation. Background Art

[0002] As we all know, nitrogen oxides (NOx) are toxic and harmful gases, among which thermal nitrogen oxides are the main type produced during the combustion process. Their characteristic is that as the temperature of the flame and the combustion area increases, the emission of pollutant nitrogen oxides also increases exponentially. How to control and lower the flame temperature of combustion has become the main technical means to reduce thermal nitrogen oxides.

[0003] Flue gas circulation technology is a low-nitrogen combustion technology that is widely used in boiler systems. Flue gas circulation technology uses the flue gas generated by combustion, the main components of which are carbon dioxide, water vapor and nitrogen, and transports the non-combustible flue gas back to the combustion area in a circulating manner, so that during the chemical reaction of combustion, the combustibles and oxidants are diluted by the flue gas before burning, so as to reduce the intensity of the combustion reaction and the flame temperature. At the same time, the temperature of the combustion area is also reduced, effectively weakening the conditions for oxygen and nitrogen to generate thermal nitrogen oxides, thereby reducing the generation of nitrogen oxides.

[0004] Flue gas circulation technology is basically divided into two types: external flue gas circulation and internal flue gas circulation. External flue gas circulation is achieved by extracting a portion of flue gas at the flue gas outlet at the rear of the boiler, sending the flue gas into the combustion air, mixing with the combustion air, and then entering the combustion area together; internal flue gas circulation is achieved by forming a swirling airflow inside the combustion chamber of the boiler, and directly circulating the flue gas inside the combustion chamber and sending it into the combustion area. The difference between internal and external flue gas circulation refers to whether the circulation of flue gas occurs inside or outside the combustion chamber. In many cases, internal and external circulation are used in combination. The internal circulation technology of NOx≤80mg / m3 is relatively mature, and combined with external circulation, NOx≤30mg / m3 can be achieved.

[0005] The most widely used model in the market is the diffusion burner with additional flue gas external circulation technology to reduce the emission of nitrogen oxides. The combustion head structure of this type of burner is relatively simple and the operation is more reliable. Since its working principle is to use a fan to circulate the flue gas for combustion, it is necessary to increase the power of the blower or use a flue gas circulation fan, which increases the investment cost.

[0006] In addition, most of the flue gas return pipes installed on site are connected to the air inlet side of the burner blower. The flue gas temperature is high and the combustion air temperature is low. When the two meet, the water vapor in the flue gas will condense into water when it is cooled, causing corrosion at the intersection. In severe cases, condensed water enters the burner, causing the flame detector sensing components and ignition elements to malfunction, creating safety hazards. In addition, condensed water enters the burner casing, causing erosion on the blower impeller, internal parts of the burner, and the casing itself, affecting the service life of the burner.

[0007] In order to achieve the effect of reducing nitrogen oxides, the flue gas internal circulation models used in the market usually require the diameter of the boiler combustion chamber to be large enough and the internal circulation reflow space to be sufficient to ensure the internal circulation effect of sufficient flue gas volume. Increasing the size of the combustion chamber has caused a significant increase in boiler costs.

[0008] These flue gas recirculation burners, by circulating the flue gas into the combustion area, achieve the goal of reducing nitrogen oxides. However, in pursuit of lower emission targets, the amount of flue gas circulation must be increased, which further reduces the intensity of the combustion flame. These practices will cause a decrease in combustion stability, making combustion pulsation and flame instability more likely to occur, and the failure rate of the burner operation will increase.

[0009] Patent document DE 3811477 A1 states that for a gas burner, gas and air are mixed at the inlet of the combustion chamber, and the gas enters through a number of mixing pipes. The gas is directly fed into the inlet of the combustion chamber through the mixing pipe and its nozzle, and mixed with the combustion-supporting air to enter the combustion chamber. The gas pipe outlets are distributed in different sections in the mixing chamber of the burner according to the divergent direction.

[0010] Patent document DE 195 09 219 describes a method and a combustion head of a burner thereof, wherein combustion air is supplied while fuel gas is burning, and inactive gas is used to reduce nitrogen oxides, wherein the fuel gas is divided into two stages, one stage is superimposed behind the other stage, and is blown in from the root of the flame in the flow direction of the combustion air, a mixture of combustion air and fuel gas exceeding the chemical reaction ratio in the first stage flows toward the flame, supplementary fuel gas is added at the second stage section, where the recycled flue gas is added to the second stage as an inactive gas, a portion of the combustion gas is injected into the second stage to form a mixed gas with a lower chemical reaction ratio with the circulating flue gas, and the gas is mixed before reaching the flame.

[0011] Patent EP 0 635 676 records a method for a low NOx combustion device for liquid fuel or gas fuel, wherein the burner used extends into the combustion chamber of the boiler, and its burner flame tube has at least one fuel nozzle for supplying fuel and is adjacent to the flame stabilizing disk. This method sends a large amount of fuel gas from the flame stabilizing disk to the inner wall area of ​​the flame tube. The rapid airflow flowing through the gap between the flame tube and the flame stabilizing disk will generate negative pressure at the leading edge of the flame tube. The smoke generated in the combustion chamber is sent to the negative pressure area through internal circulation. There are multiple guide corners on the flame tube that penetrate into the negative pressure area.

[0012] Chinese patent CN112178626B records an internal circulation low-nitrogen gas burner, in which a cyclone is sleeved at one end of a first gas pipe, an annular gas head is sleeved on the outside of the cyclone and is in clearance with the cyclone, a second gas pipe delivers gas to the annular gas head, a diverter is sleeved on the outside of the annular gas head, a flow partition is sleeved on the outside of the diverter, and a flue gas channel is formed with the diverter. Multiple groups of inner ring gas components are located in the flue gas channel, and multiple groups of outer ring gas components are installed on the peripheral side of the flow partition. The diverter is used to divert air to form air for mixed smoke and air for mixed combustion. When the air for mixed smoke flows through the flue gas channel, negative pressure is generated at the smoke inlet, thereby sucking in the flue gas in the combustion chamber and re-participating in combustion. Due to the use of vacuum to directly recover the flue gas, not only the flue gas channel is omitted, the safety hazard is eliminated, but also the use cost is reduced.

[0013] Chinese patent CN107120652 records a graded gas low-nitrogen burner, which relates to the field of burner technology. The graded gas low-nitrogen burner includes a distributor, a guide plate, an ignition electrode, an ignition fuel pipe and a combustion cylinder. The distributor is used to provide a flow path for gas and air, including a body, a plurality of gas nozzles, a gas distribution ring and a plurality of air distribution pipes. The body is a cylinder with a first interlayer, and the gas enters the gas pipe through the body and is ejected by the gas distribution ring. The air flows through the hollow part of the body, the air distribution pipe and the outside of the distributor to form an air flow path, providing combustion-supporting gas to the gas. The thickness of the distribution ring of CN107120652 is relatively thin, and as shown in the figure, it is not greater than 4 times the diameter of the gas distribution hole. It only distributes the gas as an inner and outer ring, and does not have the function of separating the air. The guide plate of CN107120652 guides the air introduced by multiple air distribution pipes to form a rotating air flow. The main body is air, and no gas distribution device is provided.

[0014] The above-mentioned known patented methods and structures are not enough to meet the increasing demand for reducing pollutant emissions from combustion equipment, especially when the legal requirements for nitrogen oxide emission targets are further reduced. These methods and structures are limited and still have problems of excessive nitrogen oxides or unstable combustion, making it difficult to meet the requirements of environmental emission standards.

[0015] The utility model utilizes the concept of staged combustion to control combustion in sections. The initial stage adopts the principle of oxygen-rich and lean combustion to control the generation of nitrogen oxides. The secondary stage utilizes the smoke and heat generated by the initial stage combustion to create a secondary stage combustion environment that satisfies the conditions that the combustion-supporting air required for the secondary combustion is diluted and preheated, and the fuel is also diluted and preheated, so that the secondary stage combustion diffuses to a larger space in a manner similar to flameless combustion. After such diffusion, the combustion is more uniform, local high temperature is avoided, and the generation of nitrogen oxides is suppressed, thereby achieving overall low-nitrogen combustion.

[0016] The most important and different thing about the utility model is that the utility model has innovated a central multi-stage premixing combustion head, which utilizes the even distribution of multiple premixing nozzles to divide the combustion flame into multiple independent flames, giving full play to the nitrogen reduction effect of oxygen-rich and lean combustion. At the same time, since the air and gas are mixed in each premixing nozzle, the risk of flashback and deflagration that may occur in most premixing burners, which need to be premixed first and then distributed for combustion, is avoided. Utility Model Content

[0017] The utility model is developed to solve the above-mentioned problems, and aims to provide a stable, safe, compact, efficient and environmentally friendly staged combustion low-nitrogen gas burner.

[0018] The technical solution of the utility model is a staged combustion low-nitrogen burner, which includes a primary combustion using a multi-stage premixing structure in the initial stage, combined with the principle of rich oxygen, lean burn and low nitrogen, and a secondary combustion using the principle of internal circulation of flue gas and low nitrogen, in which the flue gas from the initial stage is mixed with the remaining air and fuel gas for combustion.

[0019] The utility model discloses a low-nitrogen burner head for staged combustion, which comprises a central burner head, a flame tube and secondary gas nozzles distributed around the flame tube, wherein the flame tube is coaxially sleeved on the periphery of the central burner head; wherein the central burner head comprises a central gas distributor, a plurality of premixing nozzles and a central gas connecting pipe, wherein the central gas distributor is a hollow cylinder, the central gas connecting pipe is connected to the interior of the central gas distributor, each of the premixing nozzles is a straight pipe running through the interior of the central gas distributor, and a gas hole is opened on the inner wall of each straight pipe, through which the central gas distributor is connected to the central gas distributor. Inside the distributor, multiple straight tube-shaped premixing nozzles are evenly distributed on the central gas distributor, and the gas introduced by the central gas connecting pipe passes through the interior of the central gas distributor and then passes through the gas hole into the premixing nozzle; an annular gap is provided between the flame tube wall and the outer wall of the central gas distributor, and combustion air is introduced into the flame tube, and a part of the combustion air meets and mixes with the gas inside the straight tube of the premixing nozzle and is ignited when flowing out of the straight tube, forming multiple independent combustion flames on the central gas distributor on one side of the combustion chamber, and another part of the combustion air flows out through the gap between the flame tube and the central gas distributor.

[0020] Furthermore, the hollow cylindrical central gas distributor is composed of a cylindrical body and two front and rear end covers, which enclose a hollow cylindrical space with the cylindrical body. The front and rear end covers are provided with through holes corresponding to the positions, and the straight tube premixing nozzles are embedded in and penetrate the through holes of the front and rear end covers. The gas outlet end of the central gas connecting pipe is connected to the front end cover, and the straight tube of the premixing nozzle extends and protrudes from the rear end cover. There is a gap between each straight tube premixing nozzle. During combustion, independent flames are formed at the root of each premixing nozzle, thereby forming a primary combustion graded flame with the same number as the premixing nozzles.

[0021] Furthermore, the flame tube is a conical closing structure, and the distance of the central gas distributor relative to the conical opening of the flame tube can be adjusted in the axial direction, thereby being able to change the size of the annular gap between the flame tube and the central gas distributor.

[0022] Furthermore, the gas inlet end of the central gas connecting pipe is connected to the main gas pipe via a central gas regulating valve, so that the central gas regulating valve can adjust the gas volume of the central gas distributor.

[0023] Furthermore, a secondary gas distributor is connected to the other end opposite to the conical closing end of the flame tube, and the secondary gas distributor is a cylindrical annular cavity, the diameter of which is larger than the diameter of the flame tube, and a plurality of connected secondary gas nozzles are evenly arranged on the end surface of the annular cavity facing the combustion chamber.

[0024] Furthermore, the connecting end of the annular cavity and the flame tube has a connecting flange for connecting to the front wall of the boiler, and the other end has a connecting flange connected to the blower. The flame tube is installed on the connecting flange surface on one side of the annular cavity boiler, and a plurality of gas nozzle connecting holes are arranged on this flange surface for connecting the secondary gas nozzle.

[0025] Furthermore, the secondary gas nozzle is a straight tube, and the length of the straight tube of the secondary gas nozzle extends beyond the air outlet of the flame tube and extends into the combustion chamber.

[0026] Furthermore, the radial thickness of the inner cavity of the annular cavity is greater than the diameter of the secondary gas nozzle, and the secondary gas nozzle is connected with the interior of the annular cavity through the nozzle hole.

[0027] Furthermore, a hole is opened on the outer wall of the annular cavity, a connecting flange is arranged at the opening, a secondary gas regulating valve is connected through the connecting flange, the secondary gas regulating valve is connected to the main gas pipe, and the secondary gas regulating valve is used to adjust the secondary stage gas volume.

[0028] Furthermore, the inner cylinder of the secondary gas distributor is hollow, and the central combustion head is installed and fixed in the inner cylinder of the gas distributor through a bracket arranged in the inner cylinder space. The blower transports the combustion air from the inner cylinder of the secondary gas distributor into the flame tube, and then enters the combustion chamber through the premixing nozzle on the central gas distributor and the annular gap between the central gas distributor and the flame tube.

[0029] In summary, the beneficial effects of the present invention are:

[0030] The utility model discloses a low-nitrogen burner head for staged combustion, including a primary combustion component that utilizes the oxygen-rich, lean-burn and low-nitrogen principle in the initial stage, and a secondary gas distribution component that utilizes the flue gas circulation low-nitrogen principle in the secondary stage, and mixes the surplus air other than the air required for the initial stage combustion with the primary combustion flue gas, and then mixes the secondary gas with the reflux flue gas, and then burns them together. The utility model discloses a low-nitrogen burner head for oxygen-rich, lean-burn combustion in the initial stage, and the air and gas flowing out of the premixing nozzle of the central gas distributor are set to an air-fuel ratio with a high excess air coefficient according to the oxygen-rich, lean-burn and low-nitrogen. The surplus air other than the air required for the initial stage combustion flows out of the burner head through the annular gap formed by the central gas distributor and the flame tube, and this part of the surplus air surrounds the multi-stage flame at the primary center, and flows coaxially with the multi-stage combustion flame in the initial stage in a laminar manner, like an annular sleeve, and diffuses and mixes with the exhaust gas of the initial stage combustion in the middle and rear stages of the initial stage combustion. Multiple secondary gas nozzles are evenly arranged around the flame tube. The outlet of the secondary gas nozzle exceeds the air outlet end of the flame tube and extends into the combustion chamber. There is a gap between the secondary gas nozzle and the outlet of the flame tube in the axial direction. The direction of gas injection is the same as the direction of the central main airflow. Usually, the return flue gas is distributed in the gap. This part of the secondary gas will not immediately contact the excess air flow after being ejected, so it will not burn immediately. Instead, it will diffuse and mix with the return flue gas and excess air along with the accompanying vortex formed in the middle and rear sections of the central main airflow, and then burn. The initial stage combustion output power needs to meet the requirements that the heat and flue gas volume generated are large enough to heat and dilute the excess air. After the excess air is mixed with the initial stage flue gas, the temperature is not lower than the auto-ignition temperature of the gas. The excess air is diluted by the mixed flue gas, and the gas molecules and oxygen molecules diffuse into a larger space. The secondary stage of combustion is a chemical reaction that occurs in an environment that meets the temperature above the auto-ignition temperature of the gas, and there is no obvious stagnation flame phenomenon.

[0031] The utility model realizes low-nitrogen combustion in the initial stage through the multi-stage premixing structure and the ratio of rich oxygen and lean fuel in the initial stage, and creates conditions for the secondary stage, so that the combustion-supporting air and fuel gas are mixed and burned after being mixed with flue gas and preheated, so that the secondary stage combustion occurs in a fully diffused space, avoiding local high temperature and limiting the generation of nitrogen oxides. This staged combustion technology can meet the requirements of achieving low nitrogen oxide emissions when the combustion chamber diameter is small. Since the secondary stage combustion occurs when the fuel gas and air are fully diffused, the temperature in the entire furnace is uniform, which improves the heat exchange efficiency of the boiler and makes the heat-using equipment more efficient and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a structural cross-sectional view of a segmented combustion low-nitrogen burner head installed in a combustion chamber according to the utility model.

[0033] Figure 2The utility model is a schematic diagram of the flow direction of fuel gas, combustion-supporting air and smoke in a combustion chamber of a segmented combustion low-nitrogen burner.

[0034] Figure 3 It is a structural schematic diagram of a central combustion head of a segmented combustion low-nitrogen combustion head of the utility model.

[0035] Figure 4 This is a sectional view of the structure of a segmented combustion low-nitrogen burner head of the utility model.

[0036] Figure numerals: 1. combustion chamber; 2. combustion head; 3. central combustion head; 4. secondary gas distributor; 5. main gas pipe; 11. combustion chamber front wall; 12. combustion chamber furnace wall; 13. heat medium; 21. flame tube; 31. central gas distributor; 32. premixing nozzle; 33. gas hole; 34. central gas connecting pipe; 35. central gas regulating valve; 36. central regulating valve actuator; 41. annular cavity; 42. boiler connecting flange; 43. blower connecting flange; 44. secondary gas nozzle; 45. secondary gas connecting pipe; 46. secondary gas regulating valve; 47. secondary regulating valve actuator; 48. central combustion head fixing bracket; A. combustion air; B1. central gas; B2. secondary gas; C. flue gas; C1. initial stage combustion flue gas; C2. reflux flue gas; D. associated vortex; C3. circulating flue gas; F. flame. DETAILED DESCRIPTION

[0037] In order to make the technical means, technical features, objectives and technical effects achieved by the present invention easier to understand, the present invention is described in detail below in conjunction with embodiments and drawings.

[0038] like Figures 1 to 4 As shown, it shows the specific principle and specific structure of the segmented combustion low-nitrogen burner head of the utility model.

[0039] like Figure 1 As shown, a segmented combustion low-nitrogen burner head 2 of the utility model comprises a central burner head 3, a flame tube 21, and secondary gas nozzles 44 distributed around the flame tube 21, and the flame tube 21 is coaxially sleeved on the periphery of the central burner head 3. The burner head 2 is installed on the combustion chamber front wall 11 of the combustion chamber 1 through the boiler connection flange 42 of the secondary gas distributor 4, and the outer side of the combustion chamber furnace wall 12 is the heat medium 13. The central burner head 3 of the burner head 2, the flame tube 21, and the secondary gas nozzles 44 evenly arranged around the flame tube all exceed the combustion chamber front wall plane 11 and extend into the combustion chamber 1; at the same time, the burner head 2 is connected to the burner blower through the blower connection flange 43 of the secondary gas distributor 4.

[0040] like Figures 1 to 4As shown, the combustion head of the utility model includes a central combustion head 3 located at the center of the combustion head 2 and adopting a multi-stage premixed combustion method. The central combustion head 3 includes a central gas distributor 31, a plurality of premixed nozzles 32 and a central gas connecting pipe 34. The central gas distributor 31 is a hollow cylinder, and a hollow cylindrical space is surrounded by a cylindrical body and front and rear disc-shaped end covers. The central gas connecting pipe 34 is connected to the front end cover and connected to the internal space of the cylindrical body. A plurality of through holes are evenly arranged at corresponding positions on the front end cover and the rear end cover, and the positions and sizes of the through holes of the front and rear end covers are the same. The premixed nozzle 32 is a straight tube structure, which is embedded in and passes through the through holes on the front end cover and the rear end cover, and the straight tube of the premixed nozzle 32 extends and protrudes from the rear end cover. The length of the straight tube meets the requirement for uniform mixing of gas and air. There is a gap between each straight tube premixing nozzle 32, and a gas hole 33 is opened on each straight tube of the premixing nozzle 32, and the gas hole 33 is connected to the inner and outer walls of the straight tube, that is, connected to the inside of the central gas distributor 31. During operation, combustion air is introduced into the flame tube 21, and a part of the combustion air passes through the inner wall of the straight tube of the premixing nozzle 32 and the disk surface of the gas distributor 31 to enter the combustion chamber 1. The gas enters the central gas distributor 31 through the central gas connecting pipe 34, and then enters the straight tube of the premixing nozzle 32 through the gas holes 33 on these straight tubes. The combustion air and the gas meet and mix inside the straight tube of the premixing nozzle 32, and are ignited when flowing out of the straight tube. On the disk surface of the central gas distributor 31 located on one side of the combustion chamber 1, each premixing nozzle forms independent flames at the root during combustion, thereby forming a primary combustion graded flame with the same number as the premixing nozzles.

[0041] During combustion operation, the combustion-supporting air required for the initial stage of combustion flows out from the premixing nozzle 32 on the central gas distributor 31, and the remaining surplus air flows out of the combustion head through the annular gap formed by the central gas distributor 31 and the flame tube 21. A plurality of secondary gas nozzles 44 are evenly arranged around the flame tube 21. The length of the secondary gas nozzle 44 is longer than that of the flame tube 21, so the outlet of the secondary gas nozzle 44 exceeds the air outlet end of the flame tube 21 and extends into the combustion chamber 1. The secondary gas nozzle 44 and the air outlet of the flame tube 21 have an axial spacing space that is not less than the conical closing, and the gas injection direction is the same direction as the central main airflow.

[0042] like Figure 2, showing a schematic diagram of the flow direction of the fuel gas, combustion-supporting air and flue gas of the utility model, wherein after the combustion-supporting air A enters the burner head 2, the combustion-supporting air of the initial stage central combustion passes through the straight pipe of the premixing nozzle 32 on the end cover of the central gas distributor 31, and enters the space behind the disk of the central gas distributor 31 of the combustion chamber 1, and the surplus air other than the air required for the initial stage central combustion enters the combustion chamber 1 through the annular gap formed between the central gas distributor 31 and the flame tube 21, and the central gas B1 enters the internal space of the central gas distributor 31 through the central gas connecting pipe 34, and then enters the interior of the straight pipe of the premixing nozzle 32 through the gas hole 33 on the premixing nozzle 32, and after mixing with the initial stage combustion air, it is ignited when it flows out of the premixing nozzle 32, forming a multi-stage independent combustion flame F, and entering the combustion chamber 1; the secondary gas B2 enters the annular cavity 41 of the secondary gas distributor 4 through the secondary gas connecting pipe 45, and enters the combustion chamber 1 through the secondary nozzle 44 arranged and connected around the flame tube. The central gas flow rate can be controlled by the central gas regulating valve 35 to achieve low-nitrogen combustion with an oxygen-rich and fuel-lean air-fuel ratio of the initial multi-stage flame. The surplus air beyond the air required for the initial central combustion flows out of the combustion head through the annular gap between the central gas distributor 31 and the flame tube 21. This surplus air surrounds the primary central multi-stage flame, like an annular sleeve, and flows coaxially with the multi-stage flame of the initial stage combustion in a laminar flow manner. In the middle and rear sections of the initial stage combustion, it diffuses and mixes with the initial stage combustion flue gas C1. The air flowing out from the center of the premixing nozzle, the surplus air, and the flue gas generated by the central multi-stage flame combustion have the same axial flow direction, and are mixed into a combined airflow in the middle and rear stages of the initial combustion. Usually, this airflow will generate an associated vortex D, especially when the flame tube 21 adopts a conical closing structure, the air will be accelerated when it flows out, and a negative pressure area will be formed at the air outlet of the flame tube 21 around the outer edge of the conical closing. The existence of negative pressure will guide the return flue gas C2 of the associated vortex D to flow back to the negative pressure of the combustion head. The pressure zone position forms an internal circulation of the flue gas. The secondary gas nozzle 44 and the air outlet of the flame tube 21 have a radial spacing space that is not less than the conical closing end. The gas injection direction is the same flow direction as the central airflow. The circulating flue gas C3 is normally distributed in the spacing space. This part of the secondary gas will not immediately contact the excess air flow after being ejected, so it will not burn immediately. Instead, it will diffuse and mix with the circulating flue gas C3, excess air and the initial combustion flue gas C1 along with the accompanying vortex D formed in the middle and rear sections of the central airflow, and then burn.The output power of the initial stage combustion is adjustable, and after adjustment, it can meet the heating and dilution of the surplus air. After the surplus air is mixed with the initial flue gas, the temperature is not lower than the auto-ignition temperature of the gas. The surplus air is diluted by the mixed flue gas, and the gas molecules and oxygen molecules diffuse into a larger space. The secondary stage of combustion is a chemical reaction that occurs in an environment that meets the temperature above the auto-ignition temperature of the gas. The reaction area is expanded, there is no obvious stagnation flame phenomenon, the temperature is average, and the generation of nitrogen oxides is limited. At the same time, the secondary stage of combustion consumes the surplus air in the initial stage to prevent the occurrence of a high excess air coefficient and low combustion efficiency.

[0043] like Figure 1 and Figure 4 As shown, the utility model shows a segmented combustion low-nitrogen burner head, wherein the flame tube 21 is a conical closing structure, and the size of the annular gap can be changed by adjusting the distance position between the central gas distributor 31 and the cone of the flame tube 21 in the axial direction, so that the air volume ratio of the initial stage combustion and the secondary stage combustion, as well as the total power of the combustion output can be changed. When the gap is reduced, the wind pressure increases, the total air volume decreases, and the total power decreases. The central primary air volume increases due to the increase in wind pressure, and the initial stage combustion power also increases together. Increasing the gap has the opposite effect.

[0044] On the other hand, when the air flows through the outlet rapidly, due to the effect of the tapered closing, a negative pressure area is formed on one side of the combustion chamber around the outer edge of the air outlet of the flame tube 21. The suction force of the negative pressure guides the flue gas inside the combustion chamber to flow back, forming an internal circulation effect of the flue gas. The refluxed flue gas effectively isolates the secondary fuel gas from the surplus air flow in the initial section after it is ejected. At the same time, this part of the refluxed flue gas effectively heats and dilutes the secondary fuel gas.

[0045] like Figure 4 As shown, the utility model shows a segmented combustion low-nitrogen burner head, wherein the central gas distributor 31 is connected and communicated with the main gas pipe 5 through the central gas connecting pipe 34 via the central gas regulating valve 35, and the central gas regulating valve 35 is adjusted by the central regulating valve actuator 36, so as to adjust the amount of gas introduced into the central burner head in the initial stage of combustion.

[0046] like Figure 1 and Figure 4As shown, the utility model shows a segmented combustion low-nitrogen burner head, with a secondary gas distributor 4 connected to the other end opposite to the conical closing end of the flame tube 21. The secondary gas distributor 4 is a cylindrical annular cavity, the diameter of which is larger than the diameter of the flame tube 21, and a plurality of interconnected secondary gas nozzles 44 are evenly arranged on the end surface of the annular cavity facing the combustion chamber, and the plurality of secondary gas nozzles 44 are evenly arranged around the flame tube 21. The connection end of the annular cavity and the flame tube 21 has a boiler connection flange 42 for connecting to the front wall of the boiler, and the other end has a blower connection flange 43 connected to the blower. The flame tube 21 is connected and installed on the boiler connection flange surface of the annular cavity close to the boiler side, and a plurality of gas nozzle connection holes are arranged on this flange surface for connecting the secondary gas nozzles 44. The secondary gas nozzle 44 is a straight pipe structure, and the straight pipe length of the secondary gas nozzle 44 extends beyond the air outlet of the flame tube 21 and extends into the combustion chamber 1. The radial thickness of the inner cavity of the annular cavity is greater than the diameter of the secondary gas nozzle 44 , and the secondary gas nozzle 44 is connected to the inside of the annular cavity through the nozzle hole.

[0047] A hole is opened on the outer wall of the annular cavity, and a connecting flange is arranged at the hole, which is connected to the main gas pipe 5 via a secondary gas regulating valve 46. The secondary gas regulating valve 46 is adjusted by a secondary regulating valve actuator 47 to adjust the gas volume of the secondary stage combustion.

[0048] like Figure 1 and Figure 4 As shown, the inner cylinder of the secondary gas distributor 4 is hollow and transparent, and the central combustion head 3 is installed and fixed in the inner cylinder of the secondary gas distributor 4 through a bracket 48 arranged in the inner cylinder space. The blower conveys the combustion air from the inner cylinder of the secondary gas distributor 4 into the flame tube 21, and then enters the combustion chamber through the premixing nozzle 32 on the central gas distributor 31 and the annular gap with the flame tube 21.

[0049] The utility model discloses a staged combustion low-nitrogen burner head, which adopts a primary combustion that uses a multi-stage premixing structure in the initial stage and combines the oxygen-rich, lean-burn and low-nitrogen principle, and a secondary combustion that uses the flue gas of the primary combustion to mix with the remaining air and fuel gas before combustion and the flue gas internal circulation low-nitrogen principle. The structure of the burner head includes a primary central burner head located at the center of the burner head and using a multi-stage premixing combustion method, as well as a flame tube and a secondary gas nozzle surrounding the flame tube. Among them, the central combustion head is composed of a central gas distributor, multiple premixing nozzles and a gas connecting pipe. The premixing nozzle is a straight pipe structure, embedded in the disk of the gas distributor. The combustion-supporting air required for the initial stage of combustion passes through the inner wall of the straight pipe of the premixing nozzle through the disk of the central gas distributor and enters the combustion chamber. There are multiple small holes on the straight pipe of the premixing nozzle, connecting the inner and outer walls of the straight pipe. After the gas enters the central gas distributor through the gas connecting pipe, it enters the straight pipe through these small holes. The combustion-supporting air and the gas meet and mix inside the straight pipe of the premixing nozzle and are ignited when flowing out of the straight pipe. Finally, multiple independent combustion air are formed on the disk of the gas distributor on one side of the combustion chamber. The combustion flame achieves the premixed, oxygen-rich, lean-burn low-nitrogen combustion effect in the initial stage by adjusting the air-fuel ratio and utilizing the cooling effect of excess air on the flame. Usually, the primary combustion volume does not exceed 50% of the gas consumption, but 100% of the combustion-supporting air can be utilized. Under the initial stage combustion condition that meets the oxygen-rich and lean-burn ratio, the surplus air flows out of the combustion head through the annular gap formed by the central gas distributor and the flame tube. This part of the surplus air surrounds the multi-stage flame in the primary center, and flows coaxially with the primary combustion in a laminar manner, like an annular sleeve. In the middle and rear stages of the initial combustion, the surplus air and the initial combustion flue gas diffuse and mix with each other. Secondary gas nozzles are evenly arranged around the flame tube, and the gas nozzle outlet exceeds the air outlet end of the flame tube and extends into the combustion chamber. There is a gap between the secondary gas nozzle and the surplus air flow of the central combustion in the axial direction, and the gas injection direction is also laminar. Since the return flue gas is distributed in the gap, this part of the secondary gas will not contact the air immediately after being ejected, so it will not burn immediately, but will diffuse and mix with the accompanying vortex formed in the middle and rear sections of the main airflow. Since the initial combustion power is large enough, the temperature of the surplus air after mixing with the initial flue gas is not lower than the auto-ignition temperature of the gas. Since the surplus air is diluted by the mixed flue gas, the secondary gas is also diluted by the surrounding return flue gas, and the secondary stage of combustion diffuses to a larger space. In an environment that meets the temperature above the auto-ignition temperature of the gas, the gas molecules and oxygen molecules meet and react at any time, there is no obvious stagnation flame, no local violent combustion occurs, the temperature is average, there is no high temperature area, and the formation of nitrogen oxides is suppressed, thereby achieving overall low-nitrogen combustion.

Claims

1. A low-nitrogen burner head with staged combustion, characterized in that: The invention comprises a central combustion head, a flame tube and secondary gas nozzles distributed around the flame tube, wherein the flame tube is coaxially sleeved on the periphery of the central combustion head; wherein the central combustion head comprises a central gas distributor, a plurality of premixing nozzles and a central gas connecting pipe, wherein the central gas distributor is a hollow cylinder, the central gas connecting pipe is connected to the interior of the central gas distributor, each of the premixing nozzles is a straight pipe running through the interior of the central gas distributor, a gas hole is opened on the inner wall of each straight pipe, and the interior of the central gas distributor is connected through the gas hole, and a plurality of straight tube-shaped The premixing nozzles are evenly distributed on the central gas distributor, and the gas introduced through the central gas connecting pipe passes through the interior of the central gas distributor and then through the gas hole into the premixing nozzle; an annular gap is provided between the flame tube wall and the outer wall of the central gas distributor, and combustion air is introduced into the flame tube, and a part of the combustion air meets and mixes with the gas inside the straight pipe of the premixing nozzle, and is ignited when flowing out of the straight pipe, forming a plurality of independent combustion flames on one side of the combustion chamber of the central gas distributor, and another part of the combustion air flows out through the gap between the flame tube and the central gas distributor.

2. A staged combustion low nitrogen burner according to claim 1, characterized in that: The hollow cylindrical central gas distributor is composed of a cylindrical body and two front and rear end covers. The front and rear end covers and the cylindrical body form a hollow cylindrical space. The front and rear end covers are provided with through holes corresponding to the positions. The straight tube premixing nozzles are embedded in and penetrate the through holes of the front and rear end covers. The gas outlet end of the central gas connecting pipe is connected to the front end cover, and the straight tube of the premixing nozzle extends and protrudes from the rear end cover. There is a gap between each straight tube premixing nozzle. During combustion, independent flames are formed at the root of each premixing nozzle, thereby forming a primary combustion graded flame with the same number as the premixing nozzles.

3. A staged combustion low nitrogen burner according to claim 1, characterized in that: The flame tube is a conical closing structure, and the distance between the central gas distributor and the flame tube cone can be adjusted in the axial direction, so that the size of the annular gap between the flame tube and the central gas distributor can be changed.

4. A staged combustion low nitrogen burner according to claim 1, characterized in that: The gas inlet end of the central gas connecting pipe is connected to the main gas pipe via a central gas regulating valve, so that the central gas regulating valve can adjust the gas amount of the central gas distributor.

5. A staged combustion low nitrogen burner according to claim 1, characterized in that: A secondary gas distributor is connected to the other end opposite to the conical closing end of the flame tube. The secondary gas distributor is a cylindrical annular cavity with a diameter larger than the diameter of the flame tube, and a plurality of interconnected secondary gas nozzles are evenly arranged on the end surface of the annular cavity facing one end of the combustion chamber.

6. A staged combustion low nitrogen burner according to claim 5, characterized in that: The connecting end of the annular cavity and the flame tube has a boiler connecting flange for connecting to the front wall of the boiler, and the other end has a blower connecting flange connected to the blower. The flame tube is installed on the flange surface on one side of the annular cavity boiler, and a plurality of gas nozzle connecting holes are arranged on this flange surface for connecting the secondary gas nozzle.

7. A staged combustion low nitrogen burner according to claim 6, characterized in that: The secondary gas nozzle is a straight pipe, and the length of the straight pipe of the secondary gas nozzle extends beyond the air outlet of the flame tube and extends into the combustion chamber.

8. A staged combustion low nitrogen burner according to claim 7, characterized in that: The radial thickness of the inner cavity of the annular cavity is greater than the diameter of the secondary gas nozzle, and the secondary gas nozzle is connected with the inside of the annular cavity through the nozzle hole.

9. A staged combustion low nitrogen burner according to claim 8, characterized in that: A hole is opened on the outer wall of the annular cavity, a connecting flange is arranged at the hole, a secondary gas regulating valve is connected via the connecting flange, the secondary gas regulating valve is connected to the main gas pipe, and the secondary gas regulating valve is used to adjust the secondary stage gas volume.

10. A staged combustion low nitrogen burner according to claim 7, characterized in that: The inner cylinder of the secondary gas distributor is hollow, and the central combustion head is installed and fixed in the inner cylinder of the gas distributor through a bracket arranged in the inner cylinder space. The blower transports the combustion air from the inner cylinder of the secondary gas distributor into the flame tube, and then enters the combustion chamber through the premixing nozzle on the central gas distributor and the annular gap between the central gas distributor and the flame tube.

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