EP4760149A1

EP4760149A1 - Burner and combustion furnace

Info

Publication number: EP4760149A1
Application number: EP24851598.3A
Authority: EP
Inventors: Atsunori KATO; Suguru YABARA; Taishin YAMAGUCHI; Takafumi KOMINE
Original assignee: Kawasaki Heavy Industries Ltd; Kawasaki Jukogyo KK
Current assignee: Kawasaki Heavy Industries Ltd; Kawasaki Motors Ltd
Priority date: 2023-08-07
Filing date: 2024-07-23
Publication date: 2026-06-17
Also published as: CN121464299A; WO2025033170A1; JP2025024428A

Abstract

A burner includes: a first nozzle shaped as a tube having a burner axis as a central axis, the first nozzle including a main fuel outlet from which the first nozzle ejects a fluid mixture of a main fuel and primary air; a flame-holding plate shaped as a truncated circular cone with a diameter that increases downstream, the flame-holding plate being located at a tip of the first nozzle and around a periphery of the main fuel outlet to generate a flame-holding eddy downstream of the flame-holding plate; a second nozzle including a secondary air outlet that surrounds the main fuel outlet and from which the second nozzle ejects secondary air; and an auxiliary fuel nozzle located in a second flow path that is defined between the first nozzle and the second nozzle and through which the secondary air flows, the auxiliary fuel nozzle including an auxiliary fuel outlet from which the auxiliary fuel nozzle ejects a gaseous fuel containing a nitrogen component along an outer surface of the flame-holding plate or an outer surface of the first nozzle. The flame-holding plate includes a protrusion located downstream of the auxiliary fuel outlet, the protrusion being circumferentially continuous on the outer surface of the flame-holding plate.

Description

Technical Field

The present disclosure relates to a burner that burns a gaseous fuel containing a high proportion of a nitrogen component such as ammonia, and also relates to a combustion furnace including the burner.

Background Art

With increasing awareness of the need to reduce carbon dioxide (CO₂) emissions, ammonia (NH₃) has attracted attention as a fuel that does not emit carbon dioxide upon combustion. The use of ammonia as a fuel involves various challenges. For example, ammonia has a slower combustion rate and a lower flame temperature than methane which is a main component of city gas, thus being poorly flammable and difficult to combust stably. In addition, since ammonia contains a high proportion of nitrogen, its combustion tends to generate a large amount of NO_x emissions. In view of these issues, a technology for reducing NO_x emissions in a burner using ammonia as a fuel has been developed as disclosed in Patent Literature 1.
The burner of Patent Literature 1 includes: a fuel supply nozzle that ejects a fluid mixture composed of a solid fuel such as pulverized coal and a carrier gas for conveying the solid fuel; an air nozzle that is located outside the fuel supply nozzle and ejects combustion air such that the ejected air flows radially outside, and separately from, the fluid mixture; and an ammonia supply nozzle that ejects ammonia gas from a point downstream of the outlet of the fuel supply nozzle. The ammonia supply nozzle extends within the air nozzle and has an ammonia outlet located at the air outlet of the air nozzle. The ammonia supply nozzle supplies ammonia gas toward a high-temperature reduction zone which is located immediately downstream of the outlet of the fuel supply nozzle and where oxygen concentration is low due to oxygen consumption associated with fuel combustion. Since ammonia undergoes combustion in the high-temperature reduction zone, the generated NO_x is reduced to nitrogen through a reduction reaction, and consequently NO_x emissions are kept low.

Citation List

Patent Literature

PTL 1: Japanese Laid-Open Patent Application Publication No. 2019-203631

Summary of Invention

Technical Problem

In the burner of Patent Literature 1, a flame-holding eddy is generated in a region located downstream of a flame-holding plate and between the flow of the fluid mixture and the flow of the combustion air. In the case of combustion of ammonia, where flame stabilization is difficult, maintenance of the flame-holding eddy is important for sustaining the flame. In the burner of Patent Literature 1, the flow of ammonia gas ejected from the ammonia supply nozzle moves toward the high-temperature reduction zone through the flame-holding eddy and the flow of the fluid mixture. Accordingly, when the flow rate of ammonia gas is low, the flow of ammonia gas might be blocked by the flame-holding eddy or the flow of the fluid mixture, failing to reach the high-temperature reduction zone. Conversely, when the flow rate of ammonia gas is excessively high, the flow of ammonia gas might disturb the flame-holding eddy or the circulating stream, resulting in failure of flame holding and unstable combustion.
The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a technology that enables a burner for burning a gaseous fuel containing a nitrogen component such as ammonia to achieve both stable combustion and reduced NO_x emissions.

Solution to Problem

To solve the above problem, a burner according to one aspect of the present disclosure includes:

a first nozzle shaped as a tube having a burner axis as a central axis, the first nozzle including a main fuel outlet from which the first nozzle ejects a fluid mixture of a main fuel and primary air;
a flame-holding plate shaped as a truncated circular cone with a diameter that increases downstream, the flame-holding plate being located at a tip of the first nozzle and around a periphery of the main fuel outlet to generate a flame-holding eddy downstream of the flame-holding plate;
a second nozzle including a secondary air outlet that surrounds the main fuel outlet and from which the second nozzle ejects secondary air; and
an auxiliary fuel nozzle located in a second flow path that is defined between the first nozzle and the second nozzle and through which the secondary air flows, the auxiliary fuel nozzle including an auxiliary fuel outlet from which the auxiliary fuel nozzle ejects a gaseous fuel containing a nitrogen component along an outer surface of the flame-holding plate or an outer surface of the first nozzle, wherein
the flame-holding plate includes a protrusion located downstream of the auxiliary fuel outlet, the protrusion being circumferentially continuous on the outer surface of the flame-holding plate.

Advantageous Effects of Invention

The present disclosure can provide a technology that enables a burner for burning a gaseous fuel containing a nitrogen component such as ammonia to achieve both stable combustion and reduced NO_x emissions.

Brief Description of Drawings

FIG. 1 shows a schematic configuration of a boiler including a burner according to one embodiment of the present disclosure.
FIG. 2 is a schematic view of a cross-section of the burner according to the present disclosure, the cross-section including a burner axis of the burner.
FIG. 3 is an enlarged view of of the outlet of the burner of FIG. 2 in a cross-section including the burner axis.
FIG. 4 is an enlarged view of a flame-holding plate in a cross-section including the burner axis.
FIG. 5 is an enlarged view of the flame-holding plate in a cross-section including the burner axis.
FIG. 6 is an enlarged view of the flame-holding plate in a cross-section including the burner axis.

Description of Embodiments

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. First, a schematic configuration of a boiler 10 including a burner 5 according to one embodiment of the present disclosure will be described.

<<Schematic configuration of boiler 10>>

FIG. 1 shows a schematic configuration of the boiler 10 including the burner 5 according to one embodiment of the present disclosure. The boiler 10 shown in FIG. 1 includes a combustion furnace 2 that combusts a fuel and a boiler body 40 that produces steam using combustion heat from the combustion furnace 2. The boiler 10 is a pulverized coal-fired thermal boiler that uses a powdery or particulate fossil fuel (i.e., a solid fuel) as a main fuel. The boilers to which the burner 5 according to the present disclosure is applicable are not limited to pulverized coal-fired boilers, and the burner 5 may be used in other types of boilers such as a co-fired boiler that uses both pulverized coal and biomass as main fuels and a petroleum residue-fired boiler that uses petroleum residue as a main fuel.
The combustion furnace 2 includes an internal vertical combustion chamber 20. The combustion furnace 2 according to the present embodiment is an inverted-type vertical furnace. A high-temperature reduction zone 21 is defined in an upper portion of the combustion chamber 20, and a low-temperature oxidation zone 22 is defined in a lower portion of the combustion chamber 20. A throat 23 is located between the high-temperature reduction zone 21 and the low-temperature oxidation zone 22. Alternatively, the combustion furnace 2 may be a vertical furnace in which the high-temperature reduction zone 21 is defined in a lower portion of the combustion chamber 20 and the low-temperature oxidation zone 22 is defined in an upper portion of the combustion chamber 20.
The high-temperature reduction zone 21 is defined by a region of the inner wall of the combustion furnace 2, and this region is covered with a refractory material 25. On the furnace wall of the high-temperature reduction zone 21 of the combustion furnace 2, one or more burner rows are arranged vertically adjacent to each other. Each burner row includes horizontally arranged burners 5. Each burner 5 ejects the fuel and first-stage combustion air 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 the throat 23.
Air nozzles 26 are located on the furnace wall of the low-temperature oxidation zone 22 of the combustion furnace 2. Each air nozzle 26 ejects second-stage combustion air into the low-temperature oxidation zone 22. In the low-temperature oxidation zone 22, the space extending vertically between the throat 23 and the air nozzles 26 functions as a cooling region 24, and the furnace wall of the cooling region 24 is a water-cooling wall over which water pipes of the boiler body 40 are laid out. 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 body 40 are located in the flue 28. An exhaust gas treatment line 30 is connected to the outlet of the flue 28.
In the boiler 10 configured as described above, the air-to-fuel ratio of the fuel and first-stage combustion air supplied to the high-temperature reduction zone 21 is kept below 1 (for example, maintained at approximately 0.7). In addition, in the high-temperature reduction zone 21 covered with the refractory material 25, the internal furnace temperature is less likely to decrease than in the rest of the furnace. Accordingly, the high-temperature reduction zone 21 maintains a high-temperature reducing atmosphere (i.e., an air-lean atmosphere in which the amount of air is smaller than the theoretical amount of air) with an average temperature of about 1500°C, thereby facilitating gasification of the fuel.
In the high-temperature reduction zone 21, gasified fuel is generated through thermal decomposition of the supplied fuel. The gasified fuel flows into the low-temperature oxidation zone 22 through the throat 23. Second-stage combustion air is supplied from the air nozzles 26 into the low-temperature oxidation zone 22, so that the air-to-fuel ratio is maintained at 1 or more (for example, approximately 1.1) in the low-temperature oxidation zone 22. Accordingly, the low-temperature oxidation zone 22 has an oxidizing atmosphere, thereby facilitating combustion of the gasified fuel.
Combustion of the fuel is completed in the low-temperature oxidation zone 22. Combustion exhaust gas from the low-temperature oxidation zone 22 is discharged into the exhaust gas treatment line 30 through the flue 28. The heat of the combustion exhaust gas is recovered by the flue 28 and by the heat transfer tubes 43 located on the furnace wall, and steam is produced by the boiler body 40. The produced steam is used, for example, in a steam turbine of power generation equipment.

<<Configuration of burner 5>>

The following describes the configuration of each burner 5 included in the boiler 10 configured as described above. The burner 5 is a co-fired burner that uses a solid fuel as a main fuel and further uses, as an auxiliary fuel, a gaseous fuel 90 containing a high proportion of a nitrogen component such as ammonia. The solid fuel according to the present embodiment is, for example, a powdery or particulate fossil fuel such as pulverized coal. The main fuel of the burner 5 is not limited to such a fossil fuel, and may be biomass or petroleum residue. The gaseous fuel 90 according to the present embodiment is a flammable gas containing 50 vol% or more of ammonia. The gaseous fuel 90 is not limited to ammonium gas and may be any nitrogen-containing gas. The gaseous fuel 90 may be a gas containing 50 vol% or more of a flammable nitrogen compound (such as hydrogen cyanide, methylamine, or hydrazine). The gaseous fuel 90 may be a gas mixture of a flammable gas such as methane or propane and a gas containing a nitrogen component such as nitrogen or a nitrogen compound.
FIG. 2 is a schematic cross-sectional view of the burner 5 according to the present disclosure, and FIG. 3 is an enlarged view of the outlet and its vicinity in the burner 5 of FIG. 2. As shown in FIGS. 2 and 3, the burner 5 includes a multiple nozzle including first, second, and third nozzles 71, 72, and 73 that are coaxial about a burner axis 70. The direction in which the burner axis 70 extends will be referred to as the "burner axis direction X".
The first nozzle 71 includes a first flow path 71f extending through its interior in the burner axis direction X. The first nozzle 71 further includes, at its tip, a main fuel outlet 71a, which is the downstream end of the first flow path 71f. A flame-holding plate 77 is located around the main fuel outlet 71a. The flame-holding plate 77 is shaped as a truncated circular cone with a diameter that increases downstream. A swirling control plate 711 is located in the first flow path 71f. In the first flow path 71f, a dispersing impeller 713 is located upstream of the swirling control plate 711.
A heavy oil burner 79 aligned with the burner axis 70 extends through an axially extending portion of the first nozzle 71. The outlet of the heavy oil burner 79 is located substantially at the center of the main fuel outlet 71a. The heavy oil burner 79 is mainly used for ignition.
The solid fuel and primary air are supplied into the first flow path 71f. The primary air is air for fuel combustion and also serves as a carrier gas for the solid fuel. A fluid mixture 51, which is composed of the solid fuel and the primary air, swirls under the effect of the dispersing impeller 713. The swirling is then reduced by the effect of the swirling control plate 711, after which the fluid mixture 51 is ejected from the main fuel outlet 71a in the burner axis direction X.
The second nozzle 72 is located around the outer circumference of the first nozzle 71. A second flow path 72f having an annular cross-section is defined 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 circumference of the main fuel outlet 71a. An air cone 72b with a diameter that increases downstream is located along the periphery of the secondary air outlet 72a. Secondary air 52 is supplied from a wind box into the second flow path 72f. The secondary air 52 blows out from the secondary air outlet 72a toward the outer circumference of the flow of the fluid mixture 51. The secondary air 52 blowing out from the secondary air outlet 72a is guided by the flame-holding plate 77 and the air cone 72b outward away from the fluid mixture 51 ejected from the first nozzle 71.
The third nozzle 73 is located around the outer circumference of the second nozzle 72. A third flow path 73f having an annular cross-section is defined 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 circumference of the secondary air outlet 72a. An air cone 73b with a diameter that increases downstream is located along the periphery of the tertiary air outlet 73a. A swirling vane 731 is located in the third flow path 73f. Tertiary air 53 is supplied from a wind box into the third flow path 73f. The tertiary air 53 swirls under the effect of the swirling vane 731, and the swirling tertiary air 53 blows out from the tertiary air outlet 73a toward the outer circumference of the flow of the secondary air 52. The tertiary air 53 blowing out from the third nozzle 73 is guided by the air cones 72b and 73b outward away from the secondary air 52 blowing out from the second nozzle 72.
The burner 5 includes auxiliary fuel nozzles 91 that eject the gaseous fuel 90 as an auxiliary fuel. The auxiliary fuel nozzles 91 are circumferentially arranged on the outer surface of the first nozzle 71. Each auxiliary fuel nozzle 91 includes an auxiliary fuel flow path 91f in its interior and includes, at its tip, an auxiliary fuel outlet 91a which is the downstream end of the auxiliary fuel flow path 91f. The gaseous fuel 90 is supplied from a gaseous fuel source into the auxiliary fuel flow paths 91f of the auxiliary fuel nozzles 91, and is ejected from the auxiliary fuel outlets 91a.
The auxiliary fuel outlets 91a are located within the secondary air outlet 72a and circumferentially arranged along the outer surface of the first nozzle 71 or the flame-holding plate 77. The surface of the flame-holding plate 77 that faces the first flow path 71f will be referred to as the inner surface, and the opposite surface of the flame-holding plate 77 that faces the second flow path 72f will be referred to as the outer surface. On the outer surface of the flame-holding plate 77, there is a protrusion 75 that is circumferentially continuous. The protrusion 75 may be formed integrally with the flame-holding plate 77 or may be fixedly attached to the flame-holding plate 77. The auxiliary fuel outlets 91a are located upstream of the protrusion 75, and the protrusion 75 acts as an obstacle to the flow of the gaseous fuel 90 ejected from the auxiliary fuel outlets 91a.

<<Burning mechanism of burner 5>>

The following describes the burning mechanism of the burner 5 configured as described above. As shown in FIGS. 2 and 3, in the burner 5, the fluid mixture 51 composed of the solid fuel and primary air supplied to the first nozzle 71 swirls under the effect of the dispersing impeller 713, and the swirling is then reduced by the effect of the swirling control plate 711, after which the fluid mixture 51 is ejected as a swirling flow from the main fuel outlet 71a. Outside the outer circumference of the main fuel outlet 71a, the secondary air 52 blows out from the secondary air outlet 72a, and the tertiary air 53 blows out from the tertiary air outlet 73a. The secondary air 52 is guided by the flame-holding plate 77 and the air cone 72b and blows out so as to spread radially outward with respect to the burner axis 70. Likewise, the tertiary air 53 is guided by the air cones 72b and 73b and blows out so as to spread radially outward while swirling.
The solid fuel contained in the fluid mixture 51 ejected from the main fuel outlet 71a is gasified through thermal decomposition, and the resulting gasified fuel is combusted in the presence of the primary air. A circulation zone 49 having a high-temperature reducing atmosphere due to oxygen consumption associated with combustion is generated immediately downstream of the main fuel outlet 71a. Immediately downstream of the flame-holding plate 77, a flame-holding eddy 55 is generated by the effect of the flame-holding plate 77. The fluid forming the flame-holding eddy 55 contains burnt gas generated by combustion and having a relatively high temperature.
In the circulation zone 49 that is radially inside the flame-holding eddy 55, the swirling flow of the tertiary air 53 generates a circulating stream 50 by which the fluid having flowed downstream along the inner edge of the flame-holding eddy 55 is returned toward the main fuel outlet 71a along the burner axis 70. The circulating stream 50 includes: a forward flow portion in which the fluid flows away from the main fuel outlet 71a along the inner edge of the flame-holding eddy 55; and a reverse flow portion in which the fluid flows toward the main fuel outlet 71a along the burner axis 70. The fluid forming the circulating stream 50 contains burnt gas having a relatively high temperature. The flame-holding eddy 55 and the circulating stream 50 enable continuous heat exchange among the air-fuel mixture composed of the gasified fuel and primary air, the unburnt gas, and the high-temperature burnt gas, thereby facilitating combustion and stabilizing the flame. Furthermore, the secondary air 52 and the tertiary air 53, serving as combustion air, are sequentially mixed with the fuel to sustain combustion.
The gaseous fuel 90 ejected from each auxiliary fuel nozzle 91 flows out of the auxiliary fuel outlet 91a, which is located in the second flow path 72f, along the outer surface of the first nozzle 71. A portion of the flow of the gaseous fuel 90, in particular, a portion including a boundary layer flowing along the outer surface of the first nozzle 71, comes into contact with the protrusion 75. As a result, the flow of the gaseous fuel 90 separates from the outer surface of the first nozzle 71, and a separation eddy 92 is generated behind the protrusion 75. The region where the separation eddy 92 is generated extends from a point upstream of the downstream end of the flame-holding plate 77 to a point downstream of the secondary air outlet 72a in the burner axis direction X. In the separation eddy 92, a fluid flow that turns inward and backward is generated by the effect of the gaseous fuel 90 and the secondary air 52 which flow outside the separation eddy 92. In the flame-holding eddy 55 generated downstream of the flame-holding plate 77, a fluid flow that turns outward and backward is formed by the effect of the flow of the fluid mixture 51. The flow of the separation eddy 92 and the flow of the flame-holding eddy 55 form an eddy zone of a certain extent, and the flame-holding eddy 55 is substantially expanded radially outward.
The flows of the gaseous fuel 90 and the secondary air 52 passing outside the separation eddy 92 spread outward along the outer edge of the separation eddy 92 so as to circumvent the separation eddy 92. After passing through the region where the separation eddy 92 is generated, the flows of the gaseous fuel 90 and the secondary air 52 are forcibly turned inward by the pressure distribution of the separation eddy 92, and are directed toward the flame-holding eddy 55. The flow of the gaseous fuel 90 is taken into the flame-holding eddy 55, and the gaseous fuel 90 is combusted in an environment with a low oxygen concentration. As a result, the NO_x emissions caused by combustion are kept low. In addition, the combustion of the gaseous fuel 90 taken into the flame-holding eddy 55 stabilizes the flame within the flame-holding eddy 55, thereby contributing to stable combustion. Furthermore, since the flow of the gaseous fuel 90 turns inward after circumventing the separation eddy 92, the amount of the gaseous fuel 90 that passes outside the flame-holding eddy 55 and collides with the tertiary air 53 can be reduced. This prevents the gaseous fuel 90 from being rapidly mixed with the tertiary air 53 and combusted in an oxygen-rich environment. Consequently, a large amount of NO_x emissions can be avoided.
The following describes a preferred aspect of the protrusion 75 on the flame-holding plate 77. As shown in FIG. 4, a coordinate axis extending in the burner axis direction X and parallel to the burner axis 70 is defined. The coordinate of the upstream end of the flame-holding plate 77 on the coordinate axis in the burner axis direction X is defined as [-L], and the coordinate of the downstream end of the flame-holding plate 77 is defined as [0]. The coordinate value on the coordinate axis in the burner axis direction X increases downstream in the direction in which the fluid mixture 51 containing the main fuel flows. The coordinate P of the protrusion 75 on the coordinate axis in the burner axis direction X is preferably from [-L/2] to less than 0. In other words, the protrusion 75 is preferably located between the downstream end of the flame-holding plate 77 and a point corresponding to 1/2 of the length L of the flame-holding plate 77 in the burner axis direction X. In this case, the coordinate of the auxiliary fuel outlet 91a is smaller than [-L/2]. The coordinate of the auxiliary fuel outlet 91a on the coordinate axis in the burner axis direction X may be from [-L] to less than [-L/2], and the auxiliary fuel outlet 91a may be located along the outer surface of the flame-holding plate 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-holding plate 77. With the protrusion 75 located in this manner, the region where the separation eddy 92 is generated due to separation of the flow of the gaseous fuel 90 extends to a point downstream of the back end of the air cone 72b, that is, downstream of the secondary air outlet 72a. This enables the flame-holding eddy 55 generated by the flame-holding plate 77 and the separation eddy 92 to reliably interact with each other.
The surface of the protrusion 75 with which the flow of the gaseous fuel 90 collides is referred to as the front surface, and the opposite surface of the protrusion 75 is referred to as the back 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-holding plate 77 is preferably from 90° to 135°. With the angle θ set in this manner, the flow of the gaseous fuel 90 colliding with the protrusion 75 spreads radially outward to a greater extent, and accordingly the separation eddy 92 is expanded. As a result, the interaction between the separation eddy 92 and the flame-holding eddy 55 can be enhanced.
As shown in FIG. 6, in a cross-section including the burner axis 70, the angle α between a straight line drawn from the radially outer end of the front surface of the protrusion 75 to the downstream end of the flame-holding plate 77 and the outer surface of the flame-holding plate 77 is preferably from 5° to 20°. The height of the protrusion 75 from the outer surface of the flame-holding plate 77 is designed such that a portion of the flow of the gaseous fuel 90 ejected from the auxiliary fuel outlet 91a collides with the protrusion 75, while the rest of the flow of the gaseous fuel 90 flows downstream without colliding with the protrusion 75. If the angle α is less than 5° under conditions where the flow velocity of the secondary air is from 20 m/s to 40 m/s on average over the flow path and the flow velocity of the auxiliary fuel gas is from 50 m/s to 100 m/s on average over the flow path, the separation eddy 92 does not reach beyond the downstream end of the flame-holding plate 77, and the interaction between the separation eddy 92 and the flame-holding eddy 55 is less likely to occur. If the angle α is greater than 20° under the same conditions, the separation eddy 92 is expanded radially outward to an excessive extent, pressing the secondary air flow path 72f. When the secondary air flow path 72f is excessively pressed, the flow velocity of the secondary air becomes too high, with the result that the balance between the flow velocity of the secondary air and the flow velocity of the tertiary air is disturbed.

[Overview]

A burner 5 according to a first item of the present disclosure includes:

a first nozzle 71 shaped as a tube having a burner axis 70 as a central axis, the first nozzle 71 including a main fuel outlet 71a from which the first nozzle 77 ejects a fluid mixture 51 of a main fuel and primary air;
a flame-holding plate 77 shaped as a truncated circular cone with a diameter that increases downstream, the flame-holding plate 77 being located at a tip of the first nozzle 71 and around a periphery of the main fuel outlet 71a to generate a flame-holding eddy 55 downstream of the flame-holding plate 77;
a second nozzle 72 including a secondary air outlet 72a that surrounds the main fuel outlet 71a and from which the second nozzle 72 ejects secondary air 52; and
an auxiliary fuel nozzle 91 located in a second flow path 72f that is defined between the first nozzle 71 and the second nozzle 72 and through which the secondary air 52 flows, the auxiliary fuel nozzle 91 including an auxiliary fuel outlet 91a from which the auxiliary fuel nozzle 91 ejects a gaseous fuel 90 containing a nitrogen component along an outer surface of the flame-holding plate 77 or an outer surface of the first nozzle 71, wherein
the flame-holding plate 77 includes a protrusion 75 located downstream of the auxiliary fuel outlet 91a, the protrusion 75 being circumferentially continuous on the outer surface of the flame-holding plate 77.

In the burner 5 configured as described above, the flame-holding eddy 55 is generated downstream of the flame-holding plate 77 upon the start of combustion. A portion of the flow of the ejected gaseous fuel 90 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 and, as a result, a separation eddy 92 is generated downstream of the protrusion 75. The flow of the separation eddy 92 is taken into the flow of the flame-holding eddy 55, thereby forming an eddy region including the flame-holding eddy 55 that has been expanded outward. After passing through the region where the separation eddy 92 is generated, the flows of the gaseous fuel 90 and the secondary air 52 along the outer edge of the separation eddy 92 are forcibly turned inward by the pressure distribution of the separation eddy 92, and are directed toward the flame-holding eddy 55. Thus, the flow of the gaseous fuel 90 is taken into the flame-holding eddy 55, and the gaseous fuel 90 is combusted in an environment with a low oxygen concentration. As a result, NO_x emissions caused by combustion are kept low, and the flame is stabilized by the combustion of the gaseous fuel 90 in the flame-holding eddy 55. Furthermore, since the flow of the gaseous fuel 90 turns inward after circumventing the separation eddy 92, the amount of the gaseous fuel 90 that passes outside the flame-holding eddy 55 and collides with the tertiary air 53 can be reduced. This also reduces the NO_x emissions caused by combustion.
A burner 5 according to a second item includes the features of the burner 5 according to the first item, wherein a coordinate of an upstream end of the flame-holding plate 77 on a coordinate axis parallel to the burner axis 70 is -L, a coordinate of a downstream end of the flame-holding plate 77 on the coordinate axis is 0, and a coordinate of the protrusion 75 on the coordinate axis is from -L/2 to less than 0.
In the burner 5 configured as described above, where the protrusion 75 is located in the manner described above, the separation eddy 92 generated downstream of the protrusion 75 reaches the flame-holding eddy 55 downstream of the secondary air outlet 72a of the second nozzle 72, and thus the separation eddy 92 can be taken into the flame-holding eddy 55.
A burner 5 according to a third item includes the features of the burner 5 according to the first or second item, wherein in a cross-section including the burner axis 70, an angle θ between a front surface of the protrusion 75 and the outer surface of the flame-holding plate 77 is from 90° to 135°.
In this configuration, the flow of the gaseous fuel 90 ejected from the auxiliary fuel outlet 91a collides with the protrusion 75 and spreads radially outward to a greater extent, and accordingly the separation eddy 92 is expanded. As a result, the interaction between the separation eddy 92 and the flame-holding eddy 55 can be enhanced.
A burner 5 according to a fourth item includes the features of the burner 5 according to any one of the first to third items, wherein in a cross-section including the burner axis 70, an angle α between a straight line drawn from a radially outer end of a front surface of the protrusion 75 to the downstream end of the flame-holding plate 77 and the outer surface of the flame-holding plate is from 5° to 20°.
This configuration enables the separation eddy 92 to interact with the flame-holding eddy 55 while maintaining the balance between the flow velocity of the secondary air and the flow velocity of tertiary air.
A combustion furnace 2 according to a fifth item of the present disclosure includes: a combustion chamber 20; and the burner 5 according to any one of the first to fourth items, the burner 5 being located on a wall of the combustion chamber 20.
The burner 5 configured as described above is suitable for use as a burner 5 in the combustion furnace 2.
The foregoing discussion on the present disclosure is merely illustrative and explanatory, and is not intended to limit the present disclosure to the modes described herein. For example, although the foregoing detailed description presents various features of the present disclosure together in a single embodiment in order to streamline the disclosure, only some of the described features may be combined. The features disclosed herein may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Claims

A burner comprising:
a first nozzle shaped as a tube having a burner axis as a central axis, the first nozzle including a main fuel outlet from which the first nozzle ejects a fluid mixture of a main fuel and primary air;

a flame-holding plate shaped as a truncated circular cone with a diameter that increases downstream, the flame-holding plate being located at a tip of the first nozzle and around a periphery of the main fuel outlet to generate a flame-holding eddy downstream of the flame-holding plate;

a second nozzle including a secondary air outlet that surrounds the main fuel outlet and from which the second nozzle ejects secondary air; and

an auxiliary fuel nozzle located in a second flow path that is defined between the first nozzle and the second nozzle and through which the secondary air flows, the auxiliary fuel nozzle including an auxiliary fuel outlet from which the auxiliary fuel nozzle ejects a gaseous fuel containing a nitrogen component along an outer surface of the flame-holding plate or an outer surface of the first nozzle, wherein

the flame-holding plate includes a protrusion located downstream of the auxiliary fuel outlet, the protrusion being circumferentially continuous on the outer surface of the flame-holding plate.
The burner according to claim 1, wherein
a coordinate of an upstream end of the flame-holding plate on a coordinate axis parallel to the burner axis is -L,

a coordinate of a downstream end of the flame-holding plate on the coordinate axis is 0, and

a coordinate of the protrusion on the coordinate axis is from -L/2 to less than 0.
The burner according to claim 1, wherein in a cross-section including the burner axis, an angle between a front surface of the protrusion and the outer surface of the flame-holding plate is from 90° to 135°.
The burner according to claim 2, wherein in a cross-section including the burner axis, an angle between a straight line drawn from a radially outer end of a front surface of the protrusion to the downstream end of the flame-holding plate and the outer surface of the flame-holding plate is from 5° to 20°.
A combustion furnace comprising:
a combustion chamber; and

the burner according to any one of claims 1 to 4, the burner being located on a wall of the combustion chamber.