Combustor and combustion furnace

Abstract

The burner is provided with: a first nozzle having a cylindrical shape centered on the burner axis and having a main fuel outlet for discharging a mixed fluid of main fuel and primary air; a flame holding plate which has a truncated conical shape that expands in diameter toward the downstream, is disposed at the peripheral edge of the main fuel outlet at the tip of the first nozzle, and generates a flame holding vortex at the downstream; a second nozzle that has a secondary air outlet surrounding the main fuel outlet and blows out secondary air from the secondary air outlet; and an auxiliary fuel nozzle disposed in a second flow path through which secondary air flows between the first nozzle and the second nozzle, the auxiliary fuel nozzle having an auxiliary fuel outlet through which a gaseous fuel containing an N component is discharged along the outer surface of the flame holding plate or the outer surface of the first nozzle. The flame holding plate has a protrusion disposed downstream of the auxiliary fuel outlet and continuous in the circumferential direction on the outer surface of the flame holding plate.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a combustor that combusts a gas fuel containing a large amount of ammonia or the like as an N component, and a combustion furnace having the combustor. BACKGROUND

[0002] From the trend of reducing carbon dioxide (CO2) emissions, ammonia (NH3) is attracting attention as a fuel that does not emit carbon dioxide by combustion. As problems for using ammonia as a fuel, the following two points can be cited: the combustion speed is slow and the flame temperature is low compared to methane, which is the main component of city gas, so it is difficult to ignite and difficult to stabilize combustion; and the amount of NOx emission tends to increase because a large amount of N component is contained. Therefore, as disclosed in Patent Literature 1, in a combustor that uses ammonia as a fuel, development of technology to suppress the amount of NOx emission is underway.

[0003] The combustor of Patent Literature 1 has a fuel supply nozzle that ejects a mixed fluid of a solid fuel such as coal powder and a transport gas for the solid fuel, an air nozzle that is disposed on the outer side of the fuel supply nozzle, separates and ejects combustion air from the mixed fluid to the outer peripheral side, and an ammonia supply nozzle that ejects ammonia gas from a position on the downstream side of the outlet of the fuel supply nozzle. The ammonia supply nozzle communicates with the air nozzle, and an ammonia outlet is provided at the air outlet of the air nozzle. The ammonia supply nozzle supplies ammonia gas to a high-temperature reduction region where oxygen is consumed by combustion of the fuel and thus becomes a low-oxygen concentration region, immediately downstream of the outlet of the fuel supply nozzle. By combustion of ammonia in the high-temperature reduction region, NOx generated by combustion becomes nitrogen by a reduction reaction, and thus the amount of NOx emission is suppressed.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2019-203631 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] In the combustor of Patent Literature 1, a flame-holding vortex is generated at a position downstream of the flame-holding plate and sandwiched by the flow of the mixed fluid and the flow of the combustion air. In ammonia combustion where the flame is difficult to stabilize, the protection of the flame-holding vortex becomes important for flame holding. In the combustor of Patent Literature 1, the flow of ammonia gas from the ammonia supply nozzle penetrates the flow of the mixed fluid and the flame-holding vortex and heads toward the high-temperature reduction region. Therefore, if the flow rate of ammonia gas is small, there is a concern that the ammonia gas cannot reach the mixed reduction region due to being blocked by the flow of the flame-holding vortex or the mixed fluid. In addition, if the flow rate of ammonia gas is large, there is a concern that the flame-holding vortex or the circulation flow is disturbed and the flame cannot be held, and the combustion becomes unstable.

[0009] The present disclosure was achieved in view of the above, and aims to provide a technology that balances stable combustion and suppression of NOx emission in a combustor that combusts a gas fuel containing an N component such as ammonia.

[0010] Means for solving the problem

[0011] To solve the above problem, a combustor of one embodiment of the present disclosure has a first nozzle that is cylindrical with a combustor axis as a center, has a primary fuel outlet that ejects a mixed fluid of a primary fuel and primary air, a flame holder plate that has a truncated conical shape that expands toward a downstream, is disposed at a peripheral edge of the primary fuel outlet at a front end of the first nozzle, and generates a flame holding vortex at a downstream, a second nozzle that has a secondary air outlet that surrounds the primary fuel outlet, and ejects secondary air from the secondary air outlet, and an auxiliary fuel nozzle that is disposed in a second flow path in which the secondary air flows between the first nozzle and the second nozzle, has an auxiliary fuel outlet that ejects a gas fuel containing an N component along an outer surface of the flame holder plate or an outer surface of the first nozzle, and the flame holder plate has a protrusion that is disposed at a downstream of the auxiliary fuel outlet and is continuous in a circumferential direction along an outer surface of the flame holder plate.

[0012] Effects of the invention

[0013] According to the present disclosure, in a combustor that combusts a gas fuel containing an N component such as ammonia, a technology that balances stable combustion and suppression of NOx emission can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a diagram illustrating a schematic structure of a boiler having a combustor of one embodiment of the present disclosure.

[0015] Figure 2 is a diagram illustrating a schematic structure of a boiler having a combustor of one embodiment of the present disclosure.

[0016] Figure 3 is a diagram illustrating a schematic structure of a boiler having a combustor of one embodiment of the present disclosure. Figure 2 is an enlarged view of a cross section including a combustor axis of an outlet of the combustor.

[0017] Figure 4 is an enlarged view of a cross section including a combustor axis of the flame holder plate.

[0018] Figure 5 is an enlarged view of a cross section including a combustor axis of the flame holder plate.

[0019] Figure 6 is an enlarged view of a cross section including a combustor axis of the flame holder plate. DETAILED DESCRIPTION

[0020] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. First, a schematic structure of a boiler 10 having a burner 5 of one embodiment of the present disclosure will be described.

[0021] Schematic structure of boiler 10

[0022] Figure 1 is a view showing a schematic structure of a boiler 10 having a burner 5 of one embodiment of the present disclosure. Figure 1 The illustrated boiler 10 has a combustion furnace 2 that combusts fuel and a boiler main body 40 that generates steam using combustion heat of the combustion furnace 2. The boiler 10 is a pulverized coal combustion boiler that uses a fossil fuel in a powder or granular form (i.e., a solid fuel) as a main fuel. However, a boiler to which the burner 5 of the present disclosure is applied is not limited to a pulverized coal combustion boiler, and can be a mixed combustion boiler that uses pulverized coal and biomass as a main fuel, a residual oil combustion boiler that uses residual oil as a main fuel, or the like.

[0023] The combustion furnace 2 has a vertical combustion chamber 20 inside. The combustion furnace 2 of the present embodiment is an inverted vertical furnace in which a high-temperature reduction zone 21 is formed in an upper portion of the combustion chamber 20, a low-temperature oxidation zone 22 is formed in a lower portion of the combustion chamber 20, and a throttle portion 23 is provided between the high-temperature reduction zone 21 and the low-temperature oxidation zone 22. However, the combustion furnace 2 can also be a vertical furnace in which the high-temperature reduction zone 21 is formed in the lower portion of the combustion chamber 20 and the low-temperature oxidation zone 22 is formed in the upper portion of the combustion chamber 20.

[0024] A portion of the inner wall of the combustion furnace 2 that forms the high-temperature reduction zone 21 is covered with a refractory material 25. At least one burner stage is provided in the furnace wall of the high-temperature reduction zone 21 of the combustion furnace 2 in the vertical direction, and each burner stage is formed of a plurality of burners 5 arranged in the horizontal direction. Each burner 5 blows out fuel and air for first-stage combustion into the high-temperature reduction zone 21, and generates a flame. The outlet of the high-temperature reduction zone 21 is connected to the inlet of the low-temperature oxidation zone 22 via the throttle portion 23.

[0025] A plurality of air nozzles 26 are provided in the furnace wall of the low-temperature oxidation zone 22 of the combustion furnace 2. Air for second-stage combustion is blown out from each air nozzle 26 into the low-temperature oxidation zone 22. The throttle portion 23 in the low-temperature oxidation zone 22 is between the upper and lower portions of the plurality of air nozzles 26, and a cooling portion 24 is provided therebetween. The furnace wall of the cooling portion 24 is a water-cooled wall in which water tubes of the boiler main body 40 are densely arranged. The outlet 11 of the low-temperature oxidation zone 22 is connected to the inlet of a flue 28. Heat transfer tubes 43 of the boiler main body 40 are provided in the flue 28. The outlet of the flue 28 is connected to an exhaust gas treatment system 30.

[0026] In the boiler 10 with the above-described structure, the ratio of fuel supplied to the high-temperature reduction zone 21 to air used for the first stage combustion is maintained at less than 1 (e.g., around 0.7). Furthermore, the high-temperature reduction zone 21, covered by refractory material 25, experiences less temperature drop compared to other parts of the furnace. Consequently, the high-temperature reduction zone 21 becomes a high-temperature reducing atmosphere with an average temperature of approximately 1500°C (i.e., an air-deficient atmosphere where the air volume is lower than the theoretical air volume), promoting fuel gasification within the high-temperature reduction zone 21.

[0027] In the high-temperature reduction zone 21, gasified fuel is produced through the thermal decomposition of fuel. The gasified fuel flows into the low-temperature oxidation zone 22 through the throttling section 23. The air ratio in the low-temperature oxidation zone 22 is maintained at 1 or higher (e.g., around 1.1) by the second-stage combustion air supplied to the low-temperature oxidation zone 22 from the air nozzle 26. As a result, the low-temperature oxidation zone 22 becomes an oxidizing atmosphere, promoting the combustion of the gasified fuel in the low-temperature oxidation zone 22.

[0028] In the low-temperature oxidation zone 22, fuel combustion is completed. The combustion exhaust gas from the low-temperature oxidation zone 22 flows through the flue 28 and exits into the exhaust gas treatment system 30. Heat from the combustion exhaust gas is recovered through heat transfer pipes 43 installed in the flue 28 or the furnace wall, generating steam in the boiler body 40. The generated steam is used, for example, in the steam turbine of a power generation unit.

[0029] Structure of Burner 5

[0030] Here, the structure of the burner 5 in the boiler 10 described above will be explained. The burner 5 is a co-firing burner that uses solid fuel as the main fuel and gaseous fuel 90 containing a large amount of nitrogen (N) such as ammonia as an auxiliary fuel. In this embodiment, the solid fuel is, for example, pulverized coal or other powdered or granular fossil fuels. However, the main fuel of the burner 5 is not limited to fossil fuels and can also be biomass or petroleum residues. Furthermore, the gaseous fuel 90 in this embodiment is a combustible gas containing 50% by volume or more of ammonia. However, the gaseous fuel 90 is not limited to ammonia as long as it contains nitrogen. The gaseous fuel 90 can also be a gas containing 50% by volume or more of combustible nitrogen compounds (e.g., hydrogen cyanide, methylamine, hydrazine, etc.). The gaseous fuel 90 can also be a mixture of combustible gases such as methane or propane with nitrogen, nitrogen compounds, or other gases containing nitrogen.

[0031] Figure 2 This is a schematic cross-sectional view of the burner 5 disclosed herein. Figure 3 yes Figure 2 An enlarged view of the area near the outlet of burner 5. (See image below.) Figure 2 and Figure 3As shown, the burner 5 has a multi-layer nozzle consisting of a first nozzle 71, a second nozzle 72, and a third nozzle 73 arranged coaxially with the burner axis 70 as the center. The direction of extension of the burner axis 70 is referred to as "burner axis direction X".

[0032] The first nozzle 71 has a first flow path 71f extending along the burner axis direction X internally, and a main fuel outlet 71a at its front end, which is the downstream end of the first flow path 71f. A flame retaining plate 77 is provided around the main fuel outlet 71a. The flame retaining plate 77 is a truncated cone shape with its diameter expanding downstream. A swirl suppression plate 711 is provided in the first flow path 71f. In addition, a dispersion blade 713 is provided upstream of the swirl suppression plate 711 in the first flow path 71f.

[0033] A heavy oil burner 79, which overlaps with the burner axis 70, is inserted through the axial portion of the first nozzle 71. The outlet of the heavy oil burner 79 is located approximately at the center of the main fuel outlet 71a. The heavy oil burner 79 is primarily used for ignition.

[0034] Solid fuel and primary air are supplied to the first flow path 71f. The primary air is the combustion air for the fuel and the gas for transporting the solid fuel. The mixed fluid 51, consisting of solid fuel and primary air, is swirled by the action of the dispersing blades 713, and its swirling force is weakened by the action of the swirling suppression plate 711, and it is ejected from the main fuel outlet 71a toward the burner axis direction X.

[0035] A second nozzle 72 is provided on the outer periphery of the first nozzle 71. A second flow path 72f with an annular cross-section is formed between the first nozzle 71 and the second nozzle 72. A secondary air outlet 72a, which is the downstream end of the second flow path 72f, surrounds the outer periphery of the main fuel outlet 71a. An air cone 72b with a downstream-expanding diameter is provided at the periphery of the secondary air outlet 72a. Secondary air 52 is supplied from the bellows to the second flow path 72f. The secondary air 52 is blown out from the secondary air outlet 72a toward the outer periphery of the flow of the mixed fluid 51. Through the flame retainer 77 and the air cone 72b, the secondary air 52 blown out from the secondary air outlet 72a is guided to separate from the mixed fluid 51 ejected by the first nozzle 71 to the outside.

[0036] A third nozzle 73 is provided on the outer periphery of the second nozzle 72. A third flow path 73f with an annular cross-section is formed between the third nozzle 73 and the second nozzle 72. A tertiary air outlet 73a, which is the downstream end of the third flow path 73f, surrounds the outer periphery of the secondary air outlet 72a. An air cone 73b with a downstream-expanding diameter is provided on the periphery of the tertiary air outlet 73a. A swirling vane 731 is provided on the third flow path 73f. Tertiary air 53 is supplied from the air box to the third flow path 73f. The tertiary air 53 is swirled by the action of the swirling vane 731 and blown out from the tertiary air outlet 73a toward the outer periphery of the secondary air 52. Through the air cone 72b and the air cone 73b, the tertiary air 53 blown out from the third nozzle 73 is guided to separate outward from the secondary air 52 blown out from the second nozzle 72.

[0037] The burner 5 has an auxiliary fuel nozzle 91 that sprays gaseous fuel 90 as auxiliary fuel. Multiple auxiliary fuel nozzles 91 are arranged circumferentially on the outer surface of the first nozzle 71. Each auxiliary fuel nozzle 91 has an auxiliary fuel flow path 91f inside and an auxiliary fuel outlet 91a at its front end, which is the downstream end of the auxiliary fuel flow path 91f. Gaseous fuel 90 is supplied from a gaseous fuel source to the auxiliary fuel flow path 91f of the auxiliary fuel nozzle 91, and the gaseous fuel 90 is sprayed out from the auxiliary fuel outlet 91a.

[0038] Multiple auxiliary fuel outlets 91a are disposed in the secondary air outlet 72a and arranged circumferentially along the outer surface of the first nozzle 71 or the flame retainer 77. The surface of the flame retainer 77 facing the first flow path 71f is referred to as the inner surface, and the surface of the flame retainer 77 facing the second flow path 72f is referred to as the outer surface. A continuous circumferential protrusion 75 is provided on the outer surface of the flame retainer 77. The protrusion 75 may be integrally formed with the flame retainer 77 or fixed to the flame retainer 77. The multiple auxiliary fuel outlets 91a are disposed upstream of the protrusion 75, and the protrusion 75 acts as an obstruction to the ejected flow of gaseous fuel 90 from the auxiliary fuel outlets 91a.

[0039] Combustion Method of Burner 5

[0040] Next, the combustion method of the burner 5 with the above-described structure will be explained. For example... Figure 2 and Figure 3As shown, in the burner 5, the mixture 51 of solid fuel and primary air supplied to the first nozzle 71 is swirled by the action of the dispersing blades 713, and its swirling force is weakened by the action of the swirling suppression plate 711, and it is ejected as a swirling flow from the main fuel outlet 71a. Additionally, secondary air 52 is blown out from the secondary air outlet 72a and tertiary air 53 is blown out from the tertiary air outlet 73a on the outer periphery of the main fuel outlet 71a. The secondary air 52 is guided by the flame retainer 77 and the air cone 72b, and is blown out in a manner that expands outwards from the burner axis 70. Similarly, the tertiary air 53 is guided by the air cones 72b and 73b, and is blown out in a manner that expands outwards while swirling.

[0041] Solid fuel in the mixed fluid 51 ejected from the main fuel outlet 71a undergoes thermal decomposition and vaporization, and this vaporized fuel is combusted by primary air. Immediately downstream of the main fuel outlet 71a, a circulating region 49 is created, forming a high-temperature reducing atmosphere through the consumption of oxygen during combustion. Immediately downstream of the flame retainer 77, a flame retaining vortex 55 is generated by the action of the flame retainer 77. The fluid forming the flame retaining vortex 55 contains relatively high-temperature combusted gases produced through combustion.

[0042] On the inner periphery of the flame-protecting vortex 55, in the circulation zone 49, a circulating flow 50 is generated by the swirling flow of tertiary air 53, causing the fluid flowing downstream along the inner edge of the flame-protecting vortex 55 to return along the burner axis 70 to the main fuel outlet 71a. The circulating flow 50 includes a downstream section where the fluid flows away from the main fuel outlet 71a along the inner edge of the flame-protecting vortex 55 and a counter-current section where the fluid flows towards the main fuel outlet 71a along the burner axis 70. The fluid forming the circulating flow 50 contains relatively high-temperature combusted gas. Through the flame-protecting vortex 55 and the circulating flow 50, heat exchange between the gasified fuel and the primary air mixture, and between unburned gas and high-temperature combusted gas, is continuously carried out, promoting combustion and stabilizing the flame. Furthermore, combustion is achieved by staged mixing of combustion air and fuel in the order of secondary air 52 and tertiary air 53.

[0043] Gaseous fuel 90 ejected from auxiliary fuel nozzle 91 flows out from auxiliary fuel outlet 91a, located in the second flow path 72f, along the outer surface of the first nozzle 71. A portion of the flow of gaseous fuel 90, particularly the portion containing a boundary layer flowing along the outer surface of the first nozzle 71, abuts against the protrusion 75. As a result, the flow of gaseous fuel 90 is stripped from the outer surface of the first nozzle 71, generating a stripping vortex 92 behind the protrusion 75. The region generating the stripping vortex 92 extends downstream of the secondary air outlet 72a in the burner axial direction X, from a position upstream of the front end of the flame retainer 77. In the stripping vortex 92, an inward flow of fluid is generated by the action of the outwardly flowing gaseous fuel 90 and secondary air 52. On the other hand, in the flame retaining vortex 55 generated downstream of the flame retainer 77, an outward flow of fluid is generated by the action of the flow of the mixed fluid 51. The flow of the stripping vortex 92 and the flow of the flame-preserving vortex 55 form a vortex region, and the flame-preserving vortex 55 essentially expands outward.

[0044] The flow of gaseous fuel 90 and secondary air 52 passing through the outer side of the stripping vortex 92 expands outward along the outer edge of the stripping vortex 92, bypassing it. However, when passing through the area of ​​the stripping vortex 92, it is forced to change direction inward by the pressure distribution of the stripping vortex 92, heading towards the flame-holding vortex 55. The flow of gaseous fuel 90 is entrained in the flame-holding vortex 55, where it burns in a low-oxygen environment. As a result, NOx emissions after combustion are suppressed. Furthermore, the combustion of gaseous fuel 90 entrained in the flame-holding vortex 55 stabilizes the flame, contributing to stable combustion. Moreover, the inward flow of gaseous fuel 90 after bypassing the stripping vortex 92 suppresses the flow of gaseous fuel 90 that collides with tertiary air 53 while directly passing beside the flame-holding vortex 55. Thus, the emission of large amounts of NOx due to rapid mixing of gaseous fuel 90 and tertiary air 53 and combustion in an oxygen-rich environment can be avoided.

[0045] The preferred embodiment of the protrusion 75 provided on the flame insulation plate 77 will be described below. For example... Figure 4As shown, a coordinate axis in the burner axis direction X, parallel to the burner axis 70, is defined. The coordinate of the base of the flame retainer 77 on the X-axis is defined as [-L], and the coordinate of the front end of the flame retainer 77 is defined as [0]. The value of this X-axis coordinate axis increases as it moves downstream of the flow of the mixed fluid 51 containing the main fuel. In the X-axis coordinate axis, the coordinate P of the protrusion 75 is preferably [-L / 2] or greater and less than 0. In other words, the protrusion 75 is preferably positioned between the front end of the flame retainer 77 and half the length L of the flame retainer 77 in the X-axis direction of the burner axis. In this case, the coordinate of the auxiliary fuel outlet 91a is less than [-L / 2]. In the X-axis of the burner axis, the coordinate of the auxiliary fuel outlet 91a is above [-L] and less than [-L / 2]. The auxiliary fuel outlet 91a can also be located along the outer surface of the flame retainer 77, and its coordinate can also be less than [-L]. The auxiliary fuel outlet 91a can also be positioned upstream of the flame retainer 77. With this configuration of the protrusion 75, the area where the stripping vortex 92 is generated during the flow stripping of the gaseous fuel 90 reaches the rear end of the gas cone 72b, i.e., downstream of the secondary air outlet 72a. This allows the flame retaining vortex 55 generated on the flame retainer 77 to reliably interfere with the stripping vortex 92.

[0046] In protrusion 75, the surface that collides with the flow of gaseous fuel 90 is designated as the front surface, and the surface on its opposite side is designated as the rear surface. For example... Figure 5 As shown, in the cross-section including the burner axis 70, the angle θ between the front surface of the protrusion 75 and the outer surface of the flame retainer 77 is preferably 90 degrees or more and 135 degrees or less. By setting the angle θ in this way, the flow of gaseous fuel 90 after colliding with the protrusion 75 expands more radially outward, and through its reaction, the stripping vortex 92 expands, thereby enhancing the interference between the stripping vortex 92 and the flame retainer vortex 55.

[0047] In addition, such as Figure 6As shown, in a cross-section including the burner axis 70, the angle α formed by the straight line connecting the protruding end of the front surface of the protrusion 75 and the front end of the flame retainer 77 with the outer surface of the flame retainer 77 is preferably 5 degrees or more and 20 degrees or less. However, the protrusion height of the protrusion 75 protruding from the outer surface of the flame retainer 77 is designed such that a portion of the flow of gaseous fuel 90 ejected from the auxiliary fuel outlet 91a collides with the protrusion 75, while the remaining portion flows downstream without colliding with the protrusion 75. Under the conditions that the secondary air flow velocity is 20 m / s or more and 40 m / s or less on average, and the auxiliary fuel gas flow velocity is 50 m / s or more and 100 m / s or less, if the angle α is less than 5 degrees, the stripping vortex 92 will not reach a position downstream of the downstream end of the flame retainer 77, making it difficult for the stripping vortex 92 and the flame retainer vortex 55 to interfere. Furthermore, under the same conditions, if the angle α exceeds 20 degrees, the stripping vortex 92 expands excessively radially outward, and the secondary air flow path 72f is compressed. In addition, if the secondary airflow path 72f is excessively compressed, the secondary airflow velocity becomes excessive, and the balance between the tertiary airflow velocity and the tertiary airflow velocity collapses.

[0048] 〔Summarize〕

[0049] The burner 5 of the first item of this disclosure includes: a first nozzle 71, which is cylindrical about the burner axis 70 and has a main fuel outlet 71a from which a mixture of main fuel and primary air 51 is ejected; a flame retainer 77, which has a truncated conical shape with a diameter expanding downstream, and is disposed at the front end of the first nozzle 71 around the periphery of the main fuel outlet 71a, generating a flame retainer vortex 55 downstream; a second nozzle 72, which has a secondary air outlet 72a surrounding the main fuel outlet 71a, from which secondary air 52 is blown out; and an auxiliary fuel nozzle 91, which is disposed in a second flow path 72f for secondary air 52 to flow between the first nozzle 71 and the second nozzle 72, and has an auxiliary fuel outlet 91a from which gaseous fuel 90 containing nitrogen is ejected along the outer surface of the flame retainer 77 or the outer surface of the first nozzle 71, the flame retainer 77 having a protrusion 75 disposed downstream of the auxiliary fuel outlet 91a and continuous circumferentially on the outer surface of the flame retainer 77.

[0050] In the burner 5 with the above-described structure, a flame-protecting vortex 55 is generated downstream of the flame-protecting plate 77 upon combustion. Additionally, a portion of the ejected flow of gaseous fuel 90 flowing along the outer surface of the flame-protecting plate 77 collides with the protrusion 75 and is stripped from the outer surface of the flame-protecting plate 77, generating a stripping vortex 92 downstream of the protrusion 75. The flow of the stripping vortex 92 is entrained into the flow of the flame-protecting vortex 55, creating a vortex region that expands outward from the flame-protecting vortex 55. The flow of gaseous fuel 90 and secondary air 52 flowing along the outer edge of the stripping vortex 92 is forced to change direction inward by the pressure distribution of the stripping vortex 92 as it passes through the region of the stripping vortex 92, and moves towards the flame-protecting vortex 55. Thus, the flow of gaseous fuel 90 is entrained into the flame-protecting vortex 55, and the gaseous fuel 90 burns in a low-oxygen environment. As a result, NOx emissions after combustion are suppressed, and the flame is stabilized through the combustion of gaseous fuel 90 in the flame-protecting vortex 55. In addition, the flow of gaseous fuel 90 is directed inward after avoiding the stripping vortex 92, thereby suppressing the flow of gaseous fuel 90 that directly passes next to the flame-protecting vortex 55 and collides with the three air 53, thereby suppressing the emission of NOx after combustion.

[0051] The burner 5 of the second item is based on the burner 5 of the first item, wherein, when a coordinate axis parallel to the burner axis 70 is defined and the coordinate of the base end of the flame retaining plate 77 on the coordinate axis is defined as -L and the coordinate of the front end of the flame retaining plate 77 is defined as 0, the coordinate of the protrusion 75 is greater than or equal to -L / 2 and less than 0.

[0052] In the burner 5 with the above structure, by arranging the protrusion 75 as described above, the region of the stripping vortex 92 generated downstream of the protrusion 75 reaches the region of the flame-keeping vortex 55 downstream of the secondary air outlet 72a of the second nozzle 72, and the stripping vortex 92 can be entrained into the flame-keeping vortex 55.

[0053] The burner 5 of the third item is based on the burner 5 of the first or second item, wherein, in the section including the burner axis 70, the angle θ between the front surface of the protrusion 75 and the outer surface of the flame retainer 77 is more than 90 degrees and less than 135 degrees.

[0054] As a result, the jet of gaseous fuel 90 from the auxiliary fuel outlet 91a collides with the protrusion 75 and expands radially outward, causing the stripping vortex 92 to expand through its reaction, thereby enhancing the interference between the stripping vortex 92 and the flame-preserving vortex 55.

[0055] The burner 5 of item 4 is based on the burner 5 of any of items 1 to 3, wherein, in the cross section including the burner axis 70, the angle α formed by the straight line connecting the protruding end of the front surface of the protrusion 75 and the front end of the flame retaining plate 77 with the outer surface of the flame retaining plate 77 is more than 5 degrees and less than 20 degrees.

[0056] Therefore, it is possible to make the stripping vortex 92 and the flame-preserving vortex 55 interfere while maintaining the balance between the secondary and tertiary airflow velocities.

[0057] The fifth item of this disclosure has a combustion furnace 2 having a combustion chamber 20 and a burner 5 of any one of the first to fourth items disposed on the wall of the combustion chamber 20.

[0058] The burner 5 with the above structure is suitable as a burner 5 in the combustion furnace 2.

[0059] The foregoing discussion of this disclosure is provided for illustrative purposes and is not intended to limit this disclosure to the manner disclosed herein. For example, in the detailed description above, various features of this disclosure are summarized into one embodiment for the purpose of rationalizing this disclosure, but several of the multiple features may also be combined. In addition, the multiple features included in this disclosure may also be combined with alternative embodiments, structures, or methods other than those discussed above.

Claims

1. A burner comprising: The first nozzle is cylindrical with the burner axis as its center and has a main fuel outlet that sprays a mixture of main fuel and primary air. A flame retaining plate, having a truncated conical shape with an expanding diameter towards the downstream, is disposed at the periphery of the main fuel outlet at the front end of the first nozzle, generating a flame retaining vortex downstream. The second nozzle has a secondary air outlet surrounding the main fuel outlet, from which secondary air is blown out; as well as An auxiliary fuel nozzle, configured in a second flow path for the secondary air to flow between the first nozzle and the second nozzle, has an auxiliary fuel outlet for ejecting gaseous fuel containing nitrogen along the outer surface of the flame retainer or the outer surface of the first nozzle. The flame retainer has a protrusion disposed downstream of the auxiliary fuel outlet and continuous circumferentially on the outer surface of the flame retainer.

2. The burner according to claim 1, wherein, When a coordinate axis parallel to the burner axis is defined, and the coordinate of the base of the flame retaining plate on the coordinate axis is defined as -L, and the coordinate of the front end of the flame retaining plate is defined as 0, the coordinate of the protrusion is greater than or equal to -L / 2 and less than 0.

3. The burner according to claim 1, wherein, In a cross-section including the burner axis, the angle between the front surface of the protrusion and the outer surface of the flame retainer is more than 90 degrees and less than 135 degrees.

4. The burner according to claim 2, wherein, In a cross-section including the burner axis, the angle between the straight line connecting the protruding end of the front surface of the protrusion and the front end of the flame retainer plate and the outer surface of the flame retainer plate is more than 5 degrees and less than 20 degrees.

5. A combustion furnace having a combustion chamber and a burner as described in any one of claims 1 to 4 disposed in the combustion chamber.

Images