Staged combustor capable of reducing NOx emission through water vapor and combustor adjusting method

Abstract

The invention provides a staged combustor for reducing NOx emission by using water vapor and a combustor adjusting method. The burner comprises an air inlet shell, a steam coil pipe, a secondary air shell, a fire protection barrel, a gas gun and a displacement driving mechanism. The steam coil pipe comprises a water inlet pipe, a heated coil pipe and a steam spraying ring pipe which are sequentially connected. Water enters from a water inlet pipe of the steam coil pipe to cool primary flame combusted in the fire protection barrel, local high temperature is prevented, NOx emission of a primary combustion area is reduced, meanwhile, steam generated by heating is sprayed out from a steam outlet hole of the steam spraying ring pipe, and the steam and secondary air participate in secondary combustion after being mixed in a secondary air shell. OH and H groups generated by decomposition of the water vapor can be subjected to chain reaction with CO generated by primary combustion, the reducing atmosphere is enhanced, NO in-phase reduction reaction is facilitated, meanwhile, H and OH free radicals generated by dissociation of the water vapor can inhibit oxidation of HCN to NO, and the generation amount of NO is reduced under the combined action of the H and OH free radicals and the CO free radicals.

Description

Technical Field

[0001] The invention relates to the technical field of burners, in particular to a staged burner which utilizes water vapor to reduce NOx emission. Background Art

[0002] With the improvement of environmental awareness, reducing NOx emissions generated by burners has always been a topic of continuous concern in this field. In the prior art, there are records of research on the mechanism of water vapor in NOx control technology, but there is no research on the application of water vapor to reduce NOx emissions in burners. Therefore, it is urgent to propose a technical solution for reducing NOx using water vapor for burners. Summary of the invention

[0003] In order to overcome the above-mentioned deficiencies of the prior art, the object of the present invention is to provide a staged burner and a burner adjustment method for reducing NOx emissions by using water vapor.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present invention to solve the technical problem is: a staged burner for reducing NOx emissions by using water vapor, comprising an air inlet housing, a steam coil, a secondary air housing, a flame protection tube, a gas gun and a shift drive mechanism;

[0005] The air inlet shell is provided with a first air inlet for inputting combustion-supporting gas, the tail of the fire protection tube is provided with a second air inlet, the secondary air shell is installed at the front end of the air inlet shell, the fire protection tube is installed inside the secondary air shell, a part of the combustion-supporting gas inputted from the first air inlet enters into the space between the secondary air shell and the fire protection tube, and the other part enters into the inner cavity of the fire protection tube through the second air inlet;

[0006] The gas gun is provided with a gas inlet for inputting gas, a gas nozzle is provided at the front end of the gas gun, and a spark plug for ignition is also provided on the gas gun. The gas gun is movably mounted on the fixed sleeve of the air inlet housing, and the front end of the gas gun is located in the inner cavity of the fire protection tube. The displacement drive mechanism is used to drive the gas gun to move forward and backward along the axis direction of the fire protection tube;

[0007] The steam coil comprises a water inlet pipe, a heating coil and a steam ejection ring pipe which are connected in sequence. The heating coil is located in the inner cavity of the fire protection tube. The steam ejection ring pipe is located between the secondary air shell and the fire protection tube. The steam ejection ring pipe is provided with a plurality of steam outlet holes facing forward.

[0008] According to the technical solution of the present invention, water enters from the water inlet pipe of the steam coil to cool the primary flame burning in the fire protection tube, prevent local high temperature, and reduce the NOx emission in the primary combustion area. At the same time, the water vapor generated by the heat is ejected from the steam outlet hole of the steam ejection ring tube. The water vapor and the secondary air are mixed in the secondary air shell to participate in the secondary combustion. The OH and H groups generated by the decomposition of the water vapor can start a chain reaction with the CO generated by the primary combustion, enhance the reducing atmosphere, and facilitate the occurrence of the same-phase reduction reaction of NO. At the same time, the H and OH free radicals generated by the dissociation of water vapor can inhibit the oxidation of HCN to NO, and their combined effect reduces the amount of NO generated. The shift drive mechanism can drive the gas gun to move forward and backward axially to control the flame position to adapt to different combustion powers. At low power, the gas gun can be moved backward to increase the heat exchange area to ensure that the water in the steam coil is fully heated to be converted into superheated steam; at high power, the gas gun can be moved forward to prevent the primary flame from being insufficiently cooled and the coil from being damaged due to overheating of the steam coil.

[0009] Furthermore, a flow regulating valve is provided on the water inlet pipe of the steam coil.

[0010] The above preferred solution is adopted to adjust the amount of water vapor produced according to the changes in combustion power and air-fuel ratio. The water flow rate is increased at high power to suppress the appearance of high temperature areas, while keeping the amount of water vapor and the total amount of smoke produced by combustion in a reasonable ratio to enhance the effect of reducing NOx emissions.

[0011] Furthermore, the volume of water vapor generated by the steam coil accounts for 5%-8% of the total volume of smoke generated by combustion.

[0012] The above preferred solution and reasonable ratio range are adopted to achieve better effect in reducing NOx emission.

[0013] Furthermore, it also includes a detector for detecting the temperature of the heating coil.

[0014] By adopting the above preferred solution, the temperature of the heating coil can be conveniently monitored to prevent the heating coil from being overheated, resulting in insufficient primary flame cooling and damage to the heating coil.

[0015] Furthermore, a flow equalizing orifice plate is provided in the fire protection tube behind the gas nozzle.

[0016] By adopting the above preferred solution, the uniformity of the combustion-supporting gas entering the gas nozzle is improved, and the stability of flame establishment is improved.

[0017] Furthermore, the flow rate of the combustion-supporting gas entering into the inner cavity of the fire protection tube through the second air inlet accounts for 40%-45% of the total flow rate of the combustion-supporting gas input from the first air inlet.

[0018] The above preferred solution is adopted to improve the staged combustion effect, reduce the flame temperature and reduce NOx emissions.

[0019] Furthermore, the heating coil of the steam coil comprises an outer spiral coil and an inner spiral coil connected to each other, and the inner circle contour diameter of the outer spiral coil is larger than the outer circle contour diameter of the inner spiral coil.

[0020] The above preferred solution is adopted to improve the heating effect and the uniformity of primary flame cooling.

[0021] Furthermore, the outer ring profile diameter of the outer spiral coil is 75%-90% of the inner diameter of the fire protection tube, the inner ring profile diameter of the inner spiral coil is 45%-55% of the inner diameter of the fire protection tube, and the spacing between the inner ring of the outer spiral coil and the outer ring of the inner spiral coil is greater than 5mm.

[0022] By adopting the above preferred solution, both flame stability and flame cooling effect are maintained in a better state.

[0023] Furthermore, the plurality of steam outlet holes on the steam ejection ring pipe are distributed in a circular pattern.

[0024] The above preferred solution is adopted to improve the uniformity of water vapor spraying.

[0025] Furthermore, assuming that the diameter of the circle where the centers of the multiple steam outlet holes are located is D1, the outer diameter of the fire protection tube is D2, and the inner diameter of the secondary air shell is D3, then (D2+D3) / 2≤D1≤1.1*(D2+D3) / 2.

[0026] Furthermore, if the outer diameter of the steam ejection ring pipe is d, then (D3-D2) / 6≤d≤(D3-D2) / 3.

[0027] Furthermore, the front end of the fire protection tube is provided with a retracted portion that shrinks forward, the angle between the retracted portion and the axial direction is 30°-45°, and the length of the retracted portion in the axial direction is 10% D2-20% D2.

[0028] Furthermore, a retracting stop ring which retracts forward is provided on the inner wall of the secondary air housing at a position corresponding to the retracted portion, and the angle between the retracting stop ring and the axial direction is 30°-45°. Taking the inner diameter of the small opening at the front end of the retracting stop ring as D4, 0.95*(D2+D3) / 2≤D4≤1.05*(D2+D3) / 2.

[0029] By adopting the above-mentioned preferred scheme, the steam ejection ring pipe provides a certain resistance in the secondary air duct to achieve the rectification effect on the secondary air, and cooperates with the retracted part of the fire protection tube and the retracted baffle ring of the secondary air shell to ensure the mixing effect of water vapor and secondary air without generating excessive resistance to the secondary air, thereby further improving the effect of using water vapor to reduce NOx emissions.

[0030] Furthermore, the gas nozzle includes a plurality of first gas holes facing forward in the axial direction, a plurality of second gas holes arranged at 45° to the axial direction, and a plurality of third gas holes arranged at 90° to the axial direction.

[0031] Furthermore, the total opening area of ​​the first gas holes accounts for 40%-50% of the opening area of ​​all gas holes.

[0032] Furthermore, the total opening area of ​​the second gas holes is 0.8-1.2 times the total opening area of ​​the third gas holes.

[0033] By adopting the above preferred solution, the gas holes in three directions of the gas nozzle cooperate with the double-layer heating coil to ensure a uniform temperature field.

[0034] Furthermore, the displacement drive mechanism includes a screw motor connected to the fixed sleeve, an ear plate with a threaded hole is fixedly connected to the gun body of the gas gun, and a screw of the screw motor is connected to the threaded hole of the ear plate.

[0035] The above preferred solution has a compact structure and can quickly adjust the front and rear positions of the gas gun.

[0036] The burner adjustment method comprises the following steps:

[0037] Step 1, according to the gas volume and combustion-supporting gas volume of the burner, calculate the total flue gas volume generated by combustion, and adjust the flow control valve of the water inlet pipe of the steam coil so that the volume of water vapor generated by the steam coil accounts for 5%-8% of the total flue gas volume generated by combustion;

[0038] Step 2, detect the temperature of the heating coil through the detector. When the temperature of the heating coil exceeds the set range, the gas gun is moved forward through the shift drive mechanism; when the temperature of the heating coil is lower than the set range, the gas gun is moved backward through the shift drive mechanism until the temperature of the heating coil is within the set range.

[0039] By adopting the above burner adjustment method, the amount of water vapor and the total amount of flue gas generated by combustion are kept in a reasonable ratio range, which has a better effect on reducing NOx emissions. The shift drive mechanism can drive the gas gun to move forward and backward axially to control the flame position to adapt to different combustion powers. At low power, the gas gun can be moved backward to increase the heat exchange area to ensure that the water in the steam coil is fully heated to be converted into superheated steam; at high power, the gas gun can be moved forward to prevent the steam coil from overheating and causing insufficient primary flame cooling and damage to the coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 It is a schematic structural diagram of the burner of the present invention.

[0042] Figure 2 It is one of the cross-sectional views of the burner of the present invention.

[0043] Figure 3 It is the second cross-sectional view of the burner of the present invention.

[0044] Figure 4 It is a schematic diagram of the structure of the steam coil.

[0045] Figure 5 It is a structural schematic diagram of a gas gun and a shift drive mechanism.

[0046] The numbers and letters in the figure represent the names of the corresponding parts:

[0047] 10-air entering the shell; 11-first air inlet; 12-fixed sleeve; 20-secondary air shell; 21-retracted baffle ring; 30-fire protection tube; 31-second air inlet; 32-flow-equalizing orifice plate; 33-retracted part; 40-steam coil; 41-water inlet pipe; 42-heating coil; 421-outer spiral coil; 422-inner spiral coil; 43-steam ejection ring pipe; 431-steam outlet hole; 44-flow regulating valve; 50-gas gun; 51-gas inlet; 52-gas nozzle; 521-first gas hole; 522-second gas hole; 523-third gas hole; 53-spark plug; 60-shift drive mechanism; 61-screw motor; 62-screw; 63-ear plate. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] In order to facilitate the description of technical features, the directional descriptions of "front" and "rear" in the present invention are based on the direction in which the flame of the ignition gun is ejected as the front.

[0050] like Figure 1-5 As shown, one embodiment of the present invention is: a staged burner for reducing NOx emissions by using water vapor, comprising an air inlet housing 10, a steam coil 40, a secondary air housing 20, a flame protection tube 30, a gas gun 50 and a shift drive mechanism 60;

[0051] The air inlet housing 10 is provided with a first air inlet 11 for inputting combustion-supporting gas, and the tail of the fire protection tube 30 is provided with a second air inlet 31. The secondary air housing 20 is installed at the front end of the air inlet housing 10, and the fire protection tube 30 is installed inside the secondary air housing 20. A part of the combustion-supporting gas inputted from the first air inlet 11 enters into the space between the secondary air housing 20 and the fire protection tube 30, and the other part enters into the inner cavity of the fire protection tube 30 through the second air inlet 31.

[0052] The gas gun 50 is provided with a gas inlet 51 for inputting gas, a gas nozzle 52 is provided at the front end of the gas gun 50, and a spark plug 53 for ignition is also provided on the gas gun 50. The gas gun 50 is movably mounted on the fixed sleeve 12 of the air inlet housing 10, and the front end of the gas gun 50 is located in the inner cavity of the fire protection tube 30. The displacement driving mechanism 60 is used to drive the gas gun 50 to move forward and backward along the axis direction of the fire protection tube 30;

[0053] The steam coil 40 includes a water inlet pipe 41, a heating coil 42 and a steam ejection ring pipe 43 which are connected in sequence. The heating coil 42 is located in the inner cavity of the fire protection tube 30, and the steam ejection ring pipe 43 is located between the secondary air shell 20 and the fire protection tube 30. The steam ejection ring pipe 43 is provided with a plurality of steam outlet holes 431 facing forward.

[0054] The beneficial effects of the above technical solution are: water enters from the water inlet pipe of the steam coil to cool the primary flame burning in the fire protection tube, prevent local high temperature, and reduce NOx emissions in the primary combustion area. At the same time, the water vapor generated by the heat is ejected from the steam outlet hole of the steam ejection ring tube. The water vapor and the secondary air are mixed in the secondary air shell to participate in the secondary combustion. The OH and H groups generated by the decomposition of the water vapor can start a chain reaction with the CO generated by the primary combustion: H+O2→OH+O, O+H2→OH+H, enhance the reducing atmosphere, which is conducive to the occurrence of the NO homogeneous reduction reaction. At the same time, the H and OH free radicals generated by the dissociation of water vapor can inhibit the oxidation of HCN to NO. Their combined effect reduces the amount of NO generated. The shift drive mechanism can drive the gas gun to move forward and backward axially to control the flame position to adapt to different combustion powers. At low power, the gas gun can be moved backward to increase the heat exchange area to ensure that the water in the steam coil is fully heated to be converted into superheated steam; at high power, the gas gun can be moved forward to prevent the steam coil from overheating and causing insufficient primary flame cooling and damage to the coil.

[0055] like Figure 2 , 4 As shown, in other embodiments of the present invention, a flow regulating valve 44 is provided on the water inlet pipe 41 of the steam coil 40. The beneficial effect of adopting the above technical solution is that it is convenient to adjust the amount of water vapor generated according to the changes in combustion power and air-fuel ratio. The water flow rate is increased at high power to suppress the appearance of high temperature areas, and at the same time, the amount of water vapor and the total amount of smoke generated by combustion are kept in a reasonable proportion to enhance the effect of reducing NOx emissions.

[0056] In other embodiments of the present invention, the volume of water vapor generated by the steam coil 40 accounts for 5%-8% of the total volume of flue gas generated by combustion. The beneficial effect of adopting the above technical solution is: a reasonable ratio range has a better effect on reducing NOx emissions.

[0057] In other embodiments of the present invention, a detector is further included for detecting the temperature of the heating coil 42. The beneficial effect of adopting the above technical solution is: conveniently monitoring the temperature of the heating coil, preventing the heating coil from overheating and causing insufficient primary flame cooling and damage to the heating coil.

[0058] like Figure 2 As shown, in other embodiments of the present invention, a flow equalizing orifice plate 32 is provided in the flame protection tube 30 behind the gas nozzle 52. The beneficial effects of the above technical solution are: improving the uniformity of the combustion-supporting gas entering the gas nozzle and improving the stability of flame establishment.

[0059] In other embodiments of the present invention, the flow rate of the combustion-supporting gas entering the inner cavity of the flame protection tube 30 through the second air inlet 31 accounts for 40%-45% of the total flow rate of the combustion-supporting gas input from the first air inlet 11. The beneficial effects of adopting the above technical solution are: improving the staged combustion effect, reducing the flame temperature, and reducing NOx emissions.

[0060] like Figure 3 , 4As shown, in other embodiments of the present invention, the heating coil 42 of the steam coil comprises an outer spiral coil 421 and an inner spiral coil 422 connected to each other, and the inner circle profile diameter of the outer spiral coil 421 is larger than the outer circle profile diameter of the inner spiral coil 422. The beneficial effects of adopting the above technical solution are: improving the heating effect and the uniformity of the primary flame cooling.

[0061] In other embodiments of the present invention, the outer circle profile diameter of the outer spiral coil 421 is 75%-90% of the inner diameter of the fire protection tube 30, the inner circle profile diameter of the inner spiral coil 422 is 45%-55% of the inner diameter of the fire protection tube 30, and the spacing between the inner circle of the outer spiral coil 421 and the outer circle of the inner spiral coil 422 is greater than 5mm. The beneficial effect of adopting the above technical solution is: taking into account the flame stability and the flame cooling effect to maintain a better state.

[0062] like Figure 4 As shown, in some other embodiments of the present invention, the plurality of steam outlet holes 431 on the steam ejection ring pipe 43 are distributed in a circle. The beneficial effect of adopting the above technical solution is: improving the uniformity of steam ejection.

[0063] like Figure 2 , 3 As shown, in some other embodiments of the present invention, the front end of the fire protection tube 30 is provided with a retracted portion 33 that tapers forward.

[0064] like Figure 2 , 3 As shown, in some other embodiments of the present invention, an inward-retracting retaining ring 21 that retracts forward is provided at a position of the inner wall of the secondary air housing 20 corresponding to the inward-retracting portion 33 .

[0065] like Figure 3As shown, in other embodiments of the present invention, the diameter of the circle where the center of the multiple steam outlet holes 431 is located is D1, the outer diameter of the fire protection tube 30 is D2, and the inner diameter of the secondary air housing 20 is D3, then (D2+D3) / 2≤D1≤1.1*(D2+D3) / 2. The outer diameter of the steam ejection ring tube 43 is d, then (D3-D2) / 6≤d≤(D3-D2) / 3. The angle between the conical surface of the retracted portion 33 and the axial direction is 30°-45°, and the length of the retracted portion 33 in the axial direction is 10% D2-20% D2. The angle between the conical surface of the retracted retaining ring 21 and the axial direction is 30°-45°, and the inner diameter of the small opening at the front end of the retracted retaining ring 21 is D4, then 0.95*(D2+D3) / 2≤D4≤1.05*(D2+D3) / 2. The beneficial effect of adopting the above technical scheme is: the steam ejection ring pipe provides a certain resistance in the secondary air duct to achieve the rectification effect on the secondary air, and cooperates with the retracted part of the fire protection tube and the retracted baffle ring of the secondary air shell to ensure the mixing effect of water vapor and secondary air without generating excessive resistance to the secondary air, thereby further improving the effect of using water vapor to reduce NOx emissions.

[0066] like Figure 5 As shown, in other embodiments of the present invention, the gas nozzle 52 includes a plurality of first gas holes 521 facing forward along the axial direction, a plurality of second gas holes 522 arranged at 45° to the axial direction, and a plurality of third gas holes 523 arranged at 90° to the axial direction. The beneficial effect of adopting the above technical solution is that the gas holes in three directions of the gas nozzle cooperate with the double-layer heating coil to ensure a uniform temperature field.

[0067] In some other embodiments of the present invention, the total opening area of ​​the first gas holes 521 accounts for 40%-50% of the opening area of ​​all gas holes.

[0068] In some other embodiments of the present invention, the total opening area of ​​the second gas holes 522 is 0.8-1.2 times the total opening area of ​​the third gas holes 523 .

[0069] like Figure 5 As shown, in other embodiments of the present invention, the displacement driving mechanism 60 includes a screw motor 61 connected to the fixed sleeve 12, an ear plate 63 with a threaded hole is fixedly connected to the gun body of the gas gun 50, and a screw 62 of the screw motor is connected to the threaded hole of the ear plate 63. The beneficial effects of adopting the above technical solution are: the structure is compact, and the front and rear positions of the gas gun can be quickly adjusted.

[0070] The burner adjustment method comprises the following steps:

[0071] Step 1, according to the gas volume and combustion-supporting gas volume of the burner, calculate the total flue gas volume generated by combustion, and adjust the flow control valve of the water inlet pipe of the steam coil so that the volume of water vapor generated by the steam coil accounts for 5%-8% of the total flue gas volume generated by combustion;

[0072] Step 2, detect the temperature of the heating coil through the detector. When the temperature of the heating coil exceeds the set range, the gas gun is moved forward through the shift drive mechanism; when the temperature of the heating coil is lower than the set range, the gas gun is moved backward through the shift drive mechanism until the temperature of the heating coil is within the set range.

[0073] By adopting the above burner adjustment method, the amount of water vapor and the total amount of flue gas generated by combustion are kept in a reasonable ratio range, which has a better effect on reducing NOx emissions. The shift drive mechanism can drive the gas gun to move forward and backward axially to control the flame position to adapt to different combustion powers. At low power, the gas gun can be moved backward to increase the heat exchange area to ensure that the water in the steam coil is fully heated to be converted into superheated steam; at high power, the gas gun can be moved forward to prevent the steam coil from overheating and causing insufficient primary flame cooling and damage to the coil.

[0074] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A staged burner for reducing NOx emissions using water vapor, characterized in that: It includes air inlet housing, steam coil, secondary air housing, flame shield, gas gun and shift drive mechanism; The air inlet shell is provided with a first air inlet for inputting combustion-supporting gas, the tail of the fire protection tube is provided with a second air inlet, the secondary air shell is installed at the front end of the air inlet shell, the fire protection tube is installed inside the secondary air shell, a part of the combustion-supporting gas inputted from the first air inlet enters into the space between the secondary air shell and the fire protection tube, and the other part enters into the inner cavity of the fire protection tube through the second air inlet; The gas gun is provided with a gas inlet for inputting gas, a gas nozzle is provided at the front end of the gas gun, and a spark plug for ignition is also provided on the gas gun. The gas gun is movably mounted on the fixed sleeve of the air inlet housing, and the front end of the gas gun is located in the inner cavity of the fire protection tube. The displacement drive mechanism is used to drive the gas gun to move forward and backward along the axis direction of the fire protection tube; The steam coil comprises a water inlet pipe, a heating coil and a steam ejection ring pipe which are connected in sequence. The heating coil is located in the inner cavity of the fire protection tube. The steam ejection ring pipe is located between the secondary air shell and the fire protection tube. The steam ejection ring pipe is provided with a plurality of steam outlet holes facing forward.

2. The staged burner for reducing NOx emissions by using water vapor according to claim 1, characterized in that: A flow regulating valve is arranged on the water inlet pipe of the steam coil, and the volume of water vapor generated by the steam coil accounts for 5%-8% of the total volume of smoke generated by combustion.

3. The staged burner for reducing NOx emissions by using water vapor according to claim 2, characterized in that: Also included are probes for detecting the temperature of the heated coils.

4. The staged burner for reducing NOx emissions by using water vapor according to claim 1, characterized in that: A flow equalizing orifice plate is arranged in the fire protection tube behind the gas nozzle.

5. The staged burner for reducing NOx emissions by using water vapor according to claim 1, characterized in that: The flow rate of the combustion-supporting gas entering into the inner cavity of the fire protection tube through the second air inlet accounts for 40%-45% of the total flow rate of the combustion-supporting gas input from the first air inlet.

6. The staged burner for reducing NOx emissions by using water vapor according to claim 1, characterized in that: The heated coil of the steam coil comprises an outer spiral coil and an inner spiral coil connected to each other, and the inner circle contour diameter of the outer spiral coil is larger than the outer circle contour diameter of the inner spiral coil.

7. The staged burner for reducing NOx emissions by using water vapor according to claim 6, characterized in that: The outer ring profile diameter of the outer spiral coil is 75%-90% of the inner diameter of the fire protection tube, the inner ring profile diameter of the inner spiral coil is 45%-55% of the inner diameter of the fire protection tube, and the spacing between the inner ring of the outer spiral coil and the outer ring of the inner spiral coil is greater than 5mm.

8. The staged burner for reducing NOx emissions by using water vapor according to claim 1, characterized in that: The multiple steam outlet holes on the steam ejection ring pipe are distributed in a circle, the diameter of the circle where the centers of the multiple steam outlet holes are located is D1, the outer diameter of the fire protection tube is D2, and the inner diameter of the secondary air housing is D3, then (D2+D3) / 2≤D1≤1.1*(D2+D3) / 2; The outer diameter of the steam ejection ring pipe is d, then (D3-D2) / 6≤d≤(D3-D2) / 3; The front end of the fire protection tube is provided with a retracted portion that shrinks forward, the angle between the retracted portion and the axial direction is 30°-45°, and the length of the retracted portion in the axial direction is 10%D2-20%D2; A forward-retracting retaining ring is provided on the inner wall of the secondary air housing at a position corresponding to the retracted portion, and the included angle between the retracted retaining ring and the axial direction is 30°-45°. The inner diameter of the front end small opening of the retracted retaining ring is D4, then 0.95*(D2+D3) / 2≤D4≤1.05*(D2+D3) / 2.

9. The staged burner for reducing NOx emissions by using water vapor according to claim 1, characterized in that: The gas nozzle comprises a plurality of first gas holes facing forward in the axial direction, a plurality of second gas holes arranged at 45° to the axial direction, and a plurality of third gas holes arranged at 90° to the axial direction, wherein the total opening area of ​​the first gas holes accounts for 40%-50% of the opening area of ​​all gas holes, and the total opening area of ​​the second gas holes is 0.8-1.2 times the total opening area of ​​the third gas holes.

10. A burner adjustment method, characterized in that: The staged burner for reducing NOx emissions by using water vapor as claimed in claim 3 comprises the following steps: Step 1, according to the gas volume and combustion-supporting gas volume of the burner, calculate the total flue gas volume generated by combustion, and adjust the flow control valve of the water inlet pipe of the steam coil so that the volume of water vapor generated by the steam coil accounts for 5%-8% of the total flue gas volume generated by combustion; Step 2, detect the temperature of the heating coil through the detector. When the temperature of the heating coil exceeds the set range, the gas gun is moved forward through the shift drive mechanism; when the temperature of the heating coil is lower than the set range, the gas gun is moved backward through the shift drive mechanism until the temperature of the heating coil is within the set range.

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