Burner and combustion furnace

Abstract

This burner comprises: a first nozzle that has a cylindrical shape centered on a burner axis, and that has a main fuel outlet for ejecting a mixed fluid of main fuel and primary air; a flame stabilizing plate that has a truncated conical shape that expands diametrically toward the downstream side, is disposed at the peripheral edge of the main fuel outlet at the tip end of the first nozzle, and generates a flame stabilizing vortex downstream; a second nozzle that has a secondary air outlet surrounding the main fuel outlet, and that blows out secondary air from the secondary air outlet; and an auxiliary fuel nozzle that is disposed in a second flow passage through which the secondary air flows, between the first nozzle and the second nozzle, and that has an auxiliary fuel outlet for ejecting a gas fuel containing an N component along the outer surface of the flame stabilizing plate or the outer surface of the first nozzle. The flame stabilizing plate is disposed downstream of the auxiliary fuel outlet and has protrusions that are continuous in the circumferential direction on the outer surface of the flame stabilizing plate.

Description

Burners and combustion furnaces

[0001] The present disclosure relates to a burner that burns a gas fuel containing a large amount of nitrogen, such as ammonia, and a combustion furnace equipped with the burner.

[0002] Carbon dioxide (CO ２ In line with the trend toward reducing carbon dioxide emissions, ammonia (NH ３ ) has been attracting attention. Issues with using ammonia as fuel include its slower combustion speed and lower flame temperature compared to methane, the main component of city gas, making it difficult to burn stably and difficult to burn stably, and its high nitrogen content, which tends to increase NOx emissions. Therefore, as disclosed in Patent Document 1, technology is being developed to suppress NOx emissions in burners that use ammonia as fuel.

[0003] The burner in Patent Document 1 includes a fuel supply nozzle that sprays a mixed fluid of a solid fuel such as pulverized coal and a carrier gas for the solid fuel, an air nozzle disposed outside the fuel supply nozzle that separates combustion air from the mixed fluid and sprays it toward the outer periphery, and an ammonia supply nozzle that sprays ammonia gas from downstream of the outlet of the fuel supply nozzle. The ammonia supply nozzle is passed through the air nozzle, and an ammonia outlet is disposed at the air outlet of the air nozzle. The ammonia supply nozzle supplies ammonia gas toward a high-temperature reduction zone immediately downstream of the outlet of the fuel supply nozzle, where oxygen has been consumed by fuel combustion and the oxygen concentration has become low. By burning ammonia in the high-temperature reduction zone, NOx produced by combustion is converted into nitrogen through a reduction reaction, thereby suppressing NOx emissions.

[0004] Japanese Patent Application Laid-Open No. 2019-203631

[0005] In the burner of Patent Document 1, a flame-holding vortex is generated downstream of the flame-holding plate, at a position sandwiched between the flow of the mixed fluid and the flow of the combustion air. In ammonia combustion, where flame stabilization is difficult, protection of the flame-holding vortex is important for flame stabilization. In the burner of Patent Document 1, the flow of ammonia gas emitted from the ammonia supply nozzle passes through the flame-holding vortex and the flow of the mixed fluid toward the high-temperature reduction region. Therefore, if the flow rate of ammonia gas is low, there is a concern that the ammonia gas will be blocked by the flame-holding vortex or the flow of the mixed fluid and will not be able to reach the mixed reduction region. Furthermore, if the flow rate of ammonia gas is high, there is a concern that the flame-holding vortex and the circulating flow will be disturbed, making flame stabilization impossible and resulting in unstable combustion.

[0006] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a technology that achieves both stable combustion and suppression of NOx emissions in a burner that burns gas fuel containing N, such as ammonia.

[0007] In order to solve the above problems, a burner according to one aspect of the present disclosure comprises: a first nozzle having a cylindrical shape centered on the burner axis and having a main fuel outlet for ejecting a mixed fluid of main fuel and primary air; a flame stabilizing plate having a truncated cone shape expanding in diameter downstream, arranged on the periphery of the main fuel outlet at the tip of the first nozzle and generating a flame stabilizing vortex downstream; a second nozzle having a secondary air outlet surrounding the main fuel outlet and ejecting secondary air from the secondary air outlet; and an auxiliary fuel nozzle arranged in a second flow path through which the secondary air flows between the first nozzle and the second nozzle and having an auxiliary fuel outlet for ejecting gas fuel containing an N component along the outer surface of the flame stabilizing plate or the outer surface of the first nozzle, wherein the flame stabilizing plate is arranged downstream of the auxiliary fuel outlet and has protrusions that are continuous in the circumferential direction on the outer surface of the flame stabilizing plate.

[0008] According to the present disclosure, it is possible to provide a technology that achieves both stable combustion and suppression of NOx emissions in a burner that burns gas fuel containing nitrogen, such as ammonia.

[0009] Fig. 1 is a diagram showing a schematic configuration of a boiler including a burner according to an embodiment of the present disclosure. Fig. 2 is a schematic diagram of a cross section including the burner axis of a burner according to the present disclosure. Fig. 3 is an enlarged view of a cross section including the burner axis of an outlet of the burner shown in Fig. 2. Fig. 4 is an enlarged view of a cross section including the burner axis of a flame stabilizer. Fig. 5 is an enlarged view of a cross section including the burner axis of a flame stabilizer. Fig. 6 is an enlarged view of a cross section including the burner axis of a flame stabilizer.

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a schematic configuration of a boiler 10 including a burner 5 according to an embodiment of the present disclosure will be described.

[0011] 1 is a diagram showing a schematic configuration of a boiler 10 including a burner 5 according to an embodiment of the present disclosure. The boiler 10 shown in FIG. 1 includes a combustion furnace 2 that burns fuel and a boiler body 40 that generates steam by utilizing the combustion heat of the combustion furnace 2. The boiler 10 is a pulverized coal-fired thermal boiler that uses a powdered or granular fossil fuel (i.e., a solid fuel) as its primary fuel. However, the boiler to which the burner 5 according to the present disclosure is applied is not limited to pulverized coal-fired boilers, and may also be a multi-fuel boiler that uses pulverized coal and biomass as its primary fuels, a petroleum residue-fired boiler that uses petroleum residue as its primary fuel, or the like.

[0012] The combustion furnace 2 has a vertical combustion chamber 20 therein. The combustion furnace 2 according to this embodiment is an inverted vertical furnace, in which a high-temperature reduction zone 21 is formed in the upper part of the combustion chamber 20 and a low-temperature oxidation zone 22 is formed in the lower part of the combustion chamber 20, with a throttle section 23 provided between the high-temperature reduction zone 21 and the low-temperature oxidation zone 22. However, the combustion furnace 2 may also be a vertical furnace in which the high-temperature reduction zone 21 is formed in the lower part of the combustion chamber 20 and the low-temperature oxidation zone 22 is formed in the upper part of the combustion chamber 20.

[0013] The 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 by a plurality of burners 5 arranged horizontally. Each burner 5 blows fuel and air for first-stage combustion into the high-temperature reduction zone 21 to generate a flame. The outlet of the high-temperature reduction zone 21 is connected to the inlet of the low-temperature oxidation zone 22 via a throttle section 23.

[0014] A plurality of air nozzles 26 are provided on the furnace wall of the low-temperature oxidation zone 22 of the combustion furnace 2. Air for second-stage combustion is blown from each air nozzle 26 into the low-temperature oxidation zone 22. The cooling section 24 is located above and below the throttle section 23 and the plurality of air nozzles 26 in the low-temperature oxidation zone 22, and the furnace wall of the cooling section 24 is a water-cooled wall with water pipes of the boiler body 40 running throughout. The outlet 11 of the low-temperature oxidation zone 22 is connected to the inlet of the flue 28. The flue 28 is provided with a heat transfer tube 43 of the boiler body 40. The outlet of the flue 28 is connected to the exhaust gas treatment system 30.

[0015] In the boiler 10 configured as described above, the air / fuel ratio between the fuel supplied to the high-temperature reduction zone 21 and the air for first-stage combustion is maintained at less than 1 (for example, about 0.7). Furthermore, the temperature inside the high-temperature reduction zone 21, which is covered with the refractory material 25, is less likely to drop than in other parts of the furnace. As a result, the high-temperature reduction zone 21 is in a high-temperature reducing atmosphere with an average air volume of approximately 1500°C (i.e., an air-deficient atmosphere in which the amount of air is lower than the theoretical air volume), and fuel gasification is promoted in the high-temperature reduction zone 21.

[0016] In the high-temperature reduction zone 21, gasified fuel is generated by thermal decomposition of the fuel. The gasified fuel flows into the low-temperature oxidation zone 22 through a throttle section 23. The air ratio in the low-temperature oxidation zone 22 is maintained at 1 or more (for example, approximately 1.1) by air for second-stage combustion supplied to the low-temperature oxidation zone 22 from an air nozzle 26. This creates an oxidizing atmosphere in the low-temperature oxidation zone 22, promoting combustion of the gasified fuel in the low-temperature oxidation zone 22.

[0017] The combustion of the fuel is completed in the low-temperature oxidation zone 22. The combustion exhaust gas from the low-temperature oxidation zone 22 flows into the exhaust gas treatment system 30 through the flue 28. The heat of the combustion exhaust gas is recovered by the heat transfer tubes 43 installed in the flue 28 and the furnace wall, and steam is generated in the boiler body 40. The generated steam is used, for example, in a steam turbine of a power generation facility.

[0018] <Configuration of Burner 5> The configuration of the burner 5 included in the boiler 10 configured as described above will now be described. The burner 5 is a dual-fuel burner that uses a solid fuel as the primary fuel and a gas fuel 90 containing a high nitrogen content, such as ammonia, as the auxiliary fuel. The solid fuel according to this embodiment is a powdered or granular fossil fuel, such as pulverized coal. However, the primary fuel of the burner 5 is not limited to fossil fuels and may be biomass or petroleum residue. Furthermore, the gas fuel 90 according to this embodiment is a combustible gas containing 50% or more of ammonia by volume. However, the gas fuel 90 is not limited to ammonia gas as long as it contains nitrogen. The gas fuel 90 may also be a gas containing 50% or more by volume of a combustible nitrogen compound (e.g., hydrogen cyanide, methylamine, hydrazine, etc.). The gas fuel 90 may also be a mixed gas of a combustible gas, such as methane or propane, and a gas containing nitrogen, such as nitrogen or a nitrogen compound.

[0019] Fig. 2 is a schematic cross-sectional view of a burner 5 according to the present disclosure, and Fig. 3 is an enlarged view of the vicinity of the outlet of the burner 5 in Fig. 2. As shown in Fig. 2 and Fig. 3, the burner 5 is equipped with a multiple nozzle consisting of a first nozzle 71, a second nozzle 72, and a third nozzle 73 that are arranged coaxially around a burner axis 70. The extension direction of the burner axis 70 is referred to as the "burner axis direction X."

[0020] The first nozzle 71 has a first flow passage 71f extending in the burner axial direction X therein and a main fuel outlet 71a at its tip, which is the downstream end of the first flow passage 71f. A flame stabilizing plate 77 is provided around the main fuel outlet 71a. The flame stabilizing plate 77 has a frusto-conical shape that widens in diameter downstream. A swirl suppression plate 711 is provided in the first flow passage 71f. Furthermore, a dispersion vane 713 is provided upstream of the swirl suppression plate 711 in the first flow passage 71f.

[0021] A heavy oil burner 79 is inserted into the axial center of the first nozzle 71, and is arranged so as to overlap with the burner axis 70. The outlet of the heavy oil burner 79 is arranged approximately in the center of the main fuel outlet 71a. The heavy oil burner 79 is mainly used for ignition.

[0022] The first flow path 71f is supplied with solid fuel and primary air. The primary air is used for combustion of the fuel and also serves as a carrier gas for the solid fuel. The mixed fluid 51 consisting of the solid fuel and primary air is swirled by the action of the dispersion vanes 713, and the swirling force is weakened by the action of the swirl suppression plate 711, and the mixed fluid 51 is ejected from the main fuel outlet 71a in the burner axial direction X.

[0023] A second nozzle 72 is provided on the outer periphery of the first nozzle 71. A second flow passage 72f having an annular flow passage 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 passage 72f, surrounds the outer periphery of the main fuel outlet 71a. An air cone 72b, whose diameter increases downstream, is provided on the periphery of the secondary air outlet 72a. Secondary air 52 is supplied to the second flow passage 72f from the wind box. 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. The flame stabilizer 77 and the air cone 72b guide the secondary air 52 blown out from the secondary air outlet 72a so as to move away from the mixed fluid 51 blown out from the first nozzle 71.

[0024] A third nozzle 73 is provided on the outer periphery of the second nozzle 72. A third flow path 73f having 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, whose diameter increases downstream, is provided on the periphery of the tertiary air outlet 73a. A swirl vane 731 is disposed in the third flow path 73f. Tertiary air 53 is supplied to the third flow path 73f from the wind box. The tertiary air 53 swirls due to the action of the swirl vane 731 and is blown out from the tertiary air outlet 73a toward the outer periphery of the secondary air 52. The air cone 72b and the air cone 73b guide the tertiary air 53 blown out from the third nozzle 73 away from the secondary air 52 blown out from the second nozzle 72.

[0025] The burner 5 is equipped with auxiliary fuel nozzles 91 that spray gaseous fuel 90 as auxiliary fuel. The multiple auxiliary fuel nozzles 91 are arranged in a line in the circumferential direction on the outer surface of the first nozzle 71. Each auxiliary fuel nozzle 91 has an auxiliary fuel flow passage 91f therein and an auxiliary fuel outlet 91a at its tip, which is the downstream end of the auxiliary fuel flow passage 91f. Gaseous fuel 90 is supplied to the auxiliary fuel flow passage 91f of the auxiliary fuel nozzle 91 from a gaseous fuel source, and the gaseous fuel 90 is sprayed from the auxiliary fuel outlet 91a.

[0026] The multiple auxiliary fuel outlets 91a are arranged in the secondary air outlet 72a and are aligned in the circumferential direction along the outer surface of the first nozzle 71 or the flame stabilizer 77. The surface of the flame stabilizer 77 facing the first flow passage 71f is referred to as the inner surface, and the surface of the flame stabilizer 77 facing the second flow passage 72f is referred to as the outer surface. A circumferentially continuous protrusion 75 is provided on the outer surface of the flame stabilizer 77. The protrusion 75 may be formed integrally with the flame stabilizer 77 or may be fixed to the flame stabilizer 77. The multiple auxiliary fuel outlets 91a are arranged upstream of the protrusion 75, which acts as an obstacle to the jet of gas fuel 90 emitted from the auxiliary fuel outlet 91a.

[0027] <Combustion Method of Burner 5> Next, a combustion method of the burner 5 configured as described above will be described. As shown in Figures 2 and 3, in the burner 5, a mixed fluid 51 of solid fuel and primary air supplied to the first nozzle 71 swirls due to the action of the dispersion vanes 713, and the swirl force is weakened by the action of the swirl suppression plate 711, causing the mixed fluid 51 to be ejected as a swirling flow from the main fuel outlet 71a. Furthermore, on the outer periphery of the main fuel outlet 71a, secondary air 52 is ejected from the secondary air outlet 72a, and tertiary air 53 is ejected from the tertiary air outlet 73a. The secondary air 52 is guided by the flame stabilizing plate 77 and the air cone 72b, and is ejected so as to spread outward from the burner axis 70 as a center. Similarly, the tertiary air 53 is guided by the air cones 72b and 73b, and is ejected so as to spread outward from the outer periphery while swirling.

[0028] The solid fuel in the mixed fluid 51 ejected from the main fuel outlet 71a is pyrolyzed and gasified, and this gasified fuel is combusted by the primary air. Immediately downstream of the main fuel outlet 71a, a circulation region 49 is created where oxygen is consumed by combustion and a high-temperature reducing atmosphere is created. Immediately downstream of the flame stabilizer 77, a flame stabilizer vortex 55 is created by the action of the flame stabilizer 77. The fluid that forms the flame stabilizer vortex 55 contains burned gases at a relatively high temperature produced by combustion.

[0029] In the circulation region 49 on the inner periphery of the flame-holding vortex 55, the swirling flow of the tertiary air 53 generates a circulation flow 50 that returns the fluid flowing downstream along the inner edge of the flame-holding vortex 55 to the main fuel outlet 71a along the burner axis 70. The circulation flow 50 includes a forward flow portion in which the fluid flows along the inner edge of the flame-holding vortex 55 away from the main fuel outlet 71a and a reverse flow portion in which the fluid flows along the burner axis 70 toward the main fuel outlet 71a. The fluid forming the circulation flow 50 includes relatively high-temperature burned gas. The flame-holding vortex 55 and the circulation flow 50 continuously exchange heat between the gasification fuel and primary air mixture and between unburned gas and high-temperature burned gas, promoting combustion and stabilizing the flame. Furthermore, combustion air and fuel are mixed in stages, in the order of secondary air 52 and tertiary air 53, to generate combustion.

[0030] The gaseous fuel 90 ejected from the auxiliary fuel nozzle 91 flows out along the outer surface of the first nozzle 71 from the auxiliary fuel outlet 91a arranged in the second flow path 72f. A portion of the flow of the gaseous fuel 90, particularly a portion including the boundary layer flowing along the outer surface of the first nozzle 71, contacts the protrusion 75. This causes the flow of the gaseous fuel 90 to separate from the outer surface of the first nozzle 71, generating a separation vortex 92 behind the protrusion 75. The region in which the separation vortex 92 occurs extends from upstream of the tip of the flame stabilizer 77 to downstream of the secondary air outlet 72a in the burner axial direction X. In the separation vortex 92, an inward-swirling fluid flow is generated by the action of the gaseous fuel 90 and secondary air 52 flowing outside. Meanwhile, in the flame stabilizer vortex 55 generated downstream of the flame stabilizer 77, an outward-swirling fluid flow is generated by the action of the flow of the mixed fluid 51. The flow of the separation vortex 92 and the flow of the flame stabilizer vortex 55 form a vortex region, and the flame stabilizer vortex 55 is substantially expanded toward the outer periphery.

[0031] The flow of gaseous fuel 90 and secondary air 52 passing outside the separation vortex 92 expands outward along the outer edge of the separation vortex 92 to bypass the separation vortex 92. However, once they pass through the region of the separation vortex 92, the pressure distribution of the separation vortex 92 forces them to change direction inward and head toward the flame-holding vortex 55. The flow of gaseous fuel 90 is caught in the flame-holding vortex 55, and the gaseous fuel 90 burns in an environment with a low oxygen concentration. As a result, NOx emissions after combustion are suppressed. In addition, the combustion of the gaseous fuel 90 caught in the flame-holding vortex 55 stabilizes the flame in the flame-holding vortex 55, contributing to stable combustion. Furthermore, by the flow of gaseous fuel 90 turning inward after avoiding the separation vortex 92, the flow of gaseous fuel 90 passing by the flame-holding vortex 55 and colliding with the tertiary air 53 can be suppressed. This prevents the gaseous fuel 90 from rapidly mixing with the tertiary air 53 and burning in an oxygen-rich environment, which would result in the emission of large amounts of NOx.

[0032] A preferred embodiment of the protrusion 75 provided on the flame stabilizer 77 will be described below. As shown in FIG. 4 , a coordinate axis in the burner axial direction X parallel to the burner axis 70 is defined, and the coordinate of the base end of the flame stabilizer 77 on the coordinate axis in the burner axial direction X is defined as [−L], and the coordinate of the tip of the flame stabilizer 77 on the coordinate axis in the burner axial direction X is defined as [0]. The value of this coordinate axis in the burner axial direction X increases toward the downstream side of the flow of the mixed fluid 51 containing the main fuel. On the coordinate axis in the burner axial direction X, the coordinate P of the protrusion 75 is preferably equal to or greater than [−L / 2] and less than 0. In other words, the protrusion 75 is preferably disposed between the tip of the flame stabilizer 77 and ½ of the length L of the flame stabilizer 77 in the burner axial direction X. In this case, the coordinate of the auxiliary fuel outlet 91a is smaller than [−L / 2]. On the coordinate axis in the burner axial direction X, the coordinate of the auxiliary fuel outlet 91a may be equal to or greater than [-L] and less than [-L / 2], and the auxiliary fuel outlet 91a may be provided along the outer surface of the flame stabilizer 77. Alternatively, the coordinate of the auxiliary fuel outlet 91a may be smaller than [-L] and the auxiliary fuel outlet 91a may be located upstream of the flame stabilizer 77. With the protrusions 75 positioned in this manner, the region in which separation vortex 92 occurs when the flow of gas fuel 90 separates extends to the rear end of the air cone 72b, that is, downstream of the secondary air outlet 72a. This ensures that the flame stabilizer vortex 55 generated by the flame stabilizer 77 and the separation vortex 92 interfere with each other.

[0033] The surface of the protrusion 75 against which the flow of gaseous fuel 90 collides is referred to as the front surface, and the opposite surface is referred to as the rear surface. As shown in Fig. 5, in a 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 stabilizing plate 77 is preferably 90 degrees or more and 135 degrees or less. By setting the angle θ in this manner, the flow of gaseous fuel 90 that collides with the protrusion 75 expands more radially outward, and the separation vortex 92 is expanded in reaction, thereby strengthening the interference between the separation vortex 92 and the flame stabilizing vortex 55.

[0034] 6 , in a cross section including the burner axis 70, the angle α formed by a line connecting the protruding end of the front of the projection 75 and the tip of the flame stabilizer 77 with the outer surface of the flame stabilizer 77 is preferably 5 degrees or more and 20 degrees or less. However, the protruding height of the projection 75 from the outer surface of the flame stabilizer 77 is designed so that a portion of the flow of gas fuel 90 ejected from the auxiliary fuel outlet 91 a collides with the projection 75 and the remainder flows downstream without colliding with the projection 75. Under conditions where the flow path average secondary air flow velocity is 20 m / s or more and 40 m / s or less 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 separation vortex 92 does not reach the downstream end of the flame stabilizer 77, and interference between the separation vortex 92 and the flame stabilizer 55 is unlikely to occur. Furthermore, under the same conditions, if the angle α exceeds 20 degrees, the separation vortex 92 expands excessively radially outward, compressing the secondary air flow path 72f. Note that if the secondary air flow path 72f is compressed excessively, the secondary air flow velocity becomes excessive, and the balance between the tertiary air flow velocity and the secondary air flow velocity is lost.

[0035] [Summary] The burner 5 according to the first item of the present disclosure comprises: a first nozzle 71 having a cylindrical shape centered on a burner axis 70 and having a main fuel outlet 71a for ejecting a mixed fluid 51 of main fuel and primary air; a flame stabilizing plate 77 having a frusto-conical shape expanding in diameter downstream, arranged on the periphery of the main fuel outlet 71a at the tip of the first nozzle 71, and generating a flame stabilizing vortex 55 downstream; a second nozzle 72 having a secondary air outlet 72a surrounding the main fuel outlet 71a, and ejecting secondary air 52 from the secondary air outlet 72a; and an auxiliary fuel nozzle 91 arranged in a second flow path 72f through which the secondary air 52 flows between the first nozzle 71 and the second nozzle 72, and having an auxiliary fuel outlet 91a for ejecting gas fuel 90 containing an N component along the outer surface of the flame stabilizing plate 77 or the outer surface of the first nozzle 71. The flame stabilizing plate 77 is disposed downstream of the auxiliary fuel outlet 91 a and has a projection 75 that is continuous in the circumferential direction on the outer surface of the flame stabilizing plate 77 .

[0036] In the burner 5 configured as described above, when combustion begins, a flame-holding vortex 55 is generated downstream of the flame-holding plate 77. Furthermore, a portion of the ejected flow of gaseous fuel 90 flowing along the outer surface of the flame-holding plate 77 collides with the protrusion 75 and separates from the outer surface of the flame-holding plate 77, generating a separation vortex 92 downstream of the protrusion 75. The flow of the separation vortex 92 is entrained in the flow of the flame-holding vortex 55, creating a vortex region in which the flame-holding vortex 55 expands outward. The flows of gaseous fuel 90 and secondary air 52 flowing along the outer edge of the separation vortex 92 are forced to change direction inward due to the pressure distribution of the separation vortex 92 after passing through the region of the separation vortex 92, and then head toward the flame-holding vortex 55. In this way, the flow of gaseous fuel 90 is entrained in the flame-holding vortex 55, and the gaseous fuel 90 burns in an environment with a low oxygen concentration. As a result, NOx emissions after combustion are suppressed, and the flame is stabilized by the combustion of the gaseous fuel 90 in the flame-holding vortex 55. In addition, by the flow of gas fuel 90 avoiding the separation vortex 92 and then turning inward, the flow of gas fuel 90 passing by the flame-holding vortex 55 and colliding with the tertiary air 53 is suppressed, thereby suppressing the emission of NOx after combustion.

[0037] The burner 5 according to the second item is the burner 5 according to the first item, in which a coordinate axis parallel to the burner axis 70 is defined, and when the coordinate of the base end of the flame stabilizing plate 77 on the coordinate axis is defined as -L and the coordinate of the tip end of the flame stabilizing plate 77 is defined as 0, the coordinate of the protrusion 75 is not less than -L / 2 and less than 0.

[0038] In the burner 5 having the above configuration, by arranging the protrusions 75 as described above, the region of the separation vortex 92 generated downstream of the protrusions 75 reaches the region of the flame-holding vortex 55 downstream of the secondary air outlet 72a of the second nozzle 72, and the separation vortex 92 can be drawn into the flame-holding vortex 55.

[0039] The burner 5 according to the third item is the burner 5 according to the first or second item, wherein the angle θ formed between the front surface of the protrusion 75 and the outer surface of the flame stabilizing plate 77 in a cross section including the burner axis 70 is 90 degrees or more and 135 degrees or less.

[0040] As a result, the ejection flow of gas fuel 90 coming out of the auxiliary fuel outlet 91a collides with the protrusion 75 and expands radially outward, and the resulting reaction expands the separation vortex 92, thereby strengthening the interference between the separation vortex 92 and the flame-holding vortex 55.

[0041] The burner 5 according to the fourth item is a burner 5 according to any one of the first to third items, wherein in a cross section including the burner axis 70, the angle α formed by the straight line connecting the protruding end on the front side of the protrusion 75 and the tip of the flame stabilizing plate 77 and the outer surface of the flame stabilizing plate 77 is greater than or equal to 5 degrees and less than 20 degrees.

[0042] This allows the separation vortex 92 to interfere with the flame-holding vortex 55 while maintaining a balance between the secondary air flow velocity and the tertiary air flow velocity.

[0043] A combustion furnace 2 according to a fifth aspect of the present disclosure includes a combustion chamber 20 and a burner 5 according to any one of the first to fourth aspects arranged on a wall of the combustion chamber 20 .

[0044] The burner 5 having the above configuration is suitable as the burner 5 to be provided in the combustion furnace 2.

[0045] The foregoing discussion of the present disclosure has been presented for purposes of illustration and description and is not intended to limit the present disclosure to the form disclosed herein. For example, in the foregoing detailed description, various features of the present disclosure are grouped together in a single embodiment for the purpose of streamlining the disclosure, but some of the features may also be combined. Furthermore, the features included in the present disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Claims

1. A burner comprising: a first nozzle having a cylindrical shape centered on the burner axis and having a main fuel outlet for spraying a mixed fluid of main fuel and primary air; a flame stabilizing plate having a truncated cone shape expanding in the downstream direction, arranged on the periphery of the main fuel outlet at the tip of the first nozzle and generating a flame stabilizing vortex downstream; a second nozzle having a secondary air outlet surrounding the main fuel outlet and blowing out secondary air from the secondary air outlet; and an auxiliary fuel nozzle arranged in a second flow path through which the secondary air flows between the first nozzle and the second nozzle, having an auxiliary fuel outlet for spraying gas fuel containing an N component along the outer surface of the flame stabilizing plate or the outer surface of the first nozzle, wherein the flame stabilizing plate is arranged downstream of the auxiliary fuel outlet and has protrusions that continue in the circumferential direction on the outer surface of the flame stabilizing plate.

2. A burner as described in claim 1, wherein when a coordinate axis parallel to the burner axis is defined, and the coordinate of the base end of the flame stabilizing plate on said coordinate axis is defined as -L and the coordinate of the tip end of the flame stabilizing plate on said coordinate axis is defined as 0, the coordinate of the protrusion is greater than or equal to -L / 2 and less than 0.

3. A burner as claimed in claim 1, wherein in a cross section including the burner axis, an angle formed between a front surface of said projection and an outer surface of said flame stabilizing plate is between 90 degrees and 135 degrees.

4. A burner as described in claim 2, wherein in a cross section including the burner axis, an angle between a straight line connecting the protruding end of the front surface of said projection and the tip of said flame stabilizing plate and the outer surface of said flame stabilizing plate is between 5 degrees and 20 degrees.

5. A combustion furnace comprising: a combustion chamber; and a burner according to any one of claims 1 to 4 arranged on a wall of the combustion chamber.

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