Burners and combustion furnaces

Abstract

To propose a structure which enables improvement of combustion efficiency of a gas fuel while inhibiting disturbance of a circular vortex and deterioration of combustion reaction in the circular vortex at a burner using the gas fuel as a supplementary fuel.SOLUTION: A burner includes a multi-walled pipe including an inner pipe and multiple outer pipes disposed at the outer side of the inner pipe, which are coaxially arranged centered on a burner axis. The multi-walled pipe has: a fuel jetting port which is disposed at a downstream end of the inner pipe and jets air-fuel mixture of a main fuel and primary combustion air which are supplied to the inner pipe; a secondary air outlet which is disposed at an outer periphery of the fuel jetting port and blows secondary combustion air supplied to a space between the multiple outer pipes; and an annular gas fuel outlet which is disposed between the fuel jetting port and the secondary air outlet and blows a gas fuel serving as a supplementary fuel and supplied to a space between the inner pipe and the multiple outer pipes to a border portion between the air-fuel mixture and flow of the secondary combustion air.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a burner that uses gas fuel as an auxiliary fuel and a combustion furnace equipped with the burner. [Background technology]

[0002] In response to the trend toward reducing carbon dioxide (CO2), there is a demand for the use of CO2-free fuels that do not generate carbon dioxide in thermal boilers. Examples of such fuels include hydrogen (H2) and ammonia (NH3), which are hydrogen-rich gas fuels. For example, Patent Document 1 discloses a burner that can co-fire solid fuel and ammonia.

[0003] The burner in Patent Document 1 includes a fuel supply nozzle that sprays a mixture of a solid fuel such as pulverized coal and a carrier gas for the solid fuel, an air nozzle that is disposed outside the fuel supply nozzle and sprays combustion air radially outward from the mixture, and an ammonia supply nozzle that sprays ammonia gas from downstream of the outlet of the fuel supply nozzle. The ammonia supply nozzle supplies ammonia gas toward a reduction zone (primary combustion 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-203631 Summary of the Invention [Problem to be solved by the invention]

[0005] In the burner structure disclosed in Patent Document 1, the strongest high-temperature reduction zone is formed forward between the outlet of the fuel supply nozzle and the outlet of the air nozzle. Here, a circulating vortex is formed by the air-fuel mixture and the secondary and tertiary air flows surrounding it. Because combustible components and heat are stored within this circulating vortex, favorable combustion conditions are maintained, serving as the starting point for ignition, and a high-temperature reduction zone is formed within and downstream of the circulating vortex. Therefore, injecting a gaseous fuel such as ammonia toward the circulating vortex is considered more advantageous for improving combustion efficiency than injecting ammonia toward the primary combustion zone, as in Patent Document 1. However, when injecting gaseous fuel toward the circulating vortex, there are concerns that an increase in the flow velocity of the gaseous fuel may disrupt the flow of the circulating vortex due to the gaseous fuel jet, or that the temperature of the circulating vortex may be reduced by the inflow of unreacted gaseous fuel, thereby suppressing the combustion reaction within the circulating vortex.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to propose a structure in a burner that uses gas fuel as auxiliary fuel, which can increase the combustion efficiency of gas fuel while suppressing disruption of the circulating vortex or a reduction in the combustion reaction within the circulating vortex. [Means for solving the problem]

[0007] In order to solve the above problem, a burner according to one aspect of the present disclosure includes: The burner has a multi-tube structure including an inner tube coaxially arranged around a burner axis and a plurality of outer tubes arranged outside the inner tube, The multiple pipes have a fuel outlet disposed at the downstream end of the inner pipe for injecting a mixture of main fuel and primary combustion air supplied to the inner pipe, a secondary air outlet disposed on the outer periphery of the fuel outlet for injecting secondary combustion air supplied between the plurality of outer pipes, and an annular gas fuel outlet disposed between the fuel outlet and the secondary air outlet for injecting gas fuel as auxiliary fuel supplied between the inner pipe and the plurality of outer pipes toward a boundary portion of the flow of the mixture and the flow of the secondary combustion air. death, a gas fuel guide that guides the gas fuel blown out from the gas fuel outlet toward a circulating vortex generated at a boundary between the flow of the air-fuel mixture and the flow of the secondary combustion air, It is characterized by the fact that A burner according to another aspect of the present disclosure includes: The burner has a multi-tube structure including an inner tube coaxially arranged around a burner axis and a plurality of outer tubes arranged outside the inner tube, the multiple tubes have a fuel outlet disposed at the downstream end of the inner tube and for ejecting a mixture of main fuel and primary combustion air supplied to the inner tube, a secondary air outlet disposed on the outer periphery of the fuel outlet and for ejecting secondary combustion air supplied between the plurality of outer tubes, and an annular gas fuel outlet disposed between the fuel outlet and the secondary air outlet and for ejecting gas fuel as auxiliary fuel supplied between the inner tube and the plurality of outer tubes toward a boundary portion between the flow of the mixture and the flow of the secondary combustion air, The gas fuel outlet is characterized in that it can be switched so as to blow out combustion air instead of the gas fuel.

[0008] Furthermore, a combustion furnace according to an aspect of the present disclosure includes: a high-temperature reduction zone in a reducing atmosphere, provided with at least one of the burners; The combustion gas generated in the high-temperature reduction zone flows into a low-temperature oxidation zone, which has a lower temperature than the high-temperature reduction zone and an oxidizing atmosphere. [Effects of the Invention]

[0009] According to one aspect of the present disclosure described above, in a burner that uses gas fuel as auxiliary fuel, a structure can be proposed that can increase the combustion efficiency of the gas fuel while suppressing disruption of the circulating vortex or a reduction in the combustion reaction within the circulating vortex. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a boiler equipped with a burner according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view of a burner according to the present disclosure. [Figure 3] FIG. 3 is a partially enlarged view of the burner shown in FIG. [Figure 4] FIG. 4 is a view of the burner shown in FIG. 2 as viewed from the axial direction of the burner. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment 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 an embodiment of the present disclosure will be described.

[0012] [General configuration of boiler 10] FIG. 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 and a superheater 42 that generate steam using the combustion heat. The boiler 10 is a pulverized coal-fired thermal boiler that uses a powdered or granular fossil fuel (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.

[0013] A vertical combustion chamber 20 is formed inside the combustion furnace 2. 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. Alternatively, the combustion furnace 2 to which the burner 5 according to the present disclosure is applied may be a combustion furnace of a type other than a vertical furnace.

[0014] The portion of the inner wall of the combustion furnace 2 that forms the high-temperature reduction zone 21 is covered with refractory material 25. A plurality of burners 5 that blow fuel and air for first-stage combustion into the high-temperature reduction zone 21 are provided on the lower furnace wall of the combustion furnace 2. A mixture of fuel and air is blown from each burner 5 into the combustion chamber 20, generating a flame. A plurality of burners 5 are provided on each of a pair of opposing furnace walls. Each furnace wall is provided with at least one burner stage in the vertical direction, and each burner stage is formed by a plurality of burners 5 lined up horizontally. The plurality of burners 5 arranged opposite each other in this manner are arranged in a staggered pattern so that the burner axes of each burner 5 do not intersect.

[0015] The outlet of the high-temperature reduction zone 21 is connected to the inlet of the low-temperature oxidation zone 22 via a constricted portion 23. The smallest horizontal cross-sectional area of ​​the constricted portion 23 is about 20 to 50% of the horizontal cross-sectional area of ​​the high-temperature reduction zone 21.

[0016] A plurality of air nozzles 26 are provided on the furnace wall at the top of the combustion furnace 2. Air for second-stage combustion is blown from each air nozzle 26 into the low-temperature oxidation zone 22. In this embodiment, a plurality of air nozzle stages are provided in the vertical direction, and each air nozzle stage is formed by a plurality of air nozzles 26 lined up in the horizontal direction. 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. The furnace wall of the cooling section 24 is a water-cooled wall in which water pipes (not shown) of the boiler body 40 are laid out.

[0017] An outlet 11 of the low-temperature oxidation zone 22 is connected to an inlet of a flue 28. A heat transfer tube 43 of a boiler body 40 is provided in the flue 28. An exhaust gas treatment system 30 is connected to the outlet of the flue 28.

[0018] In the boiler 10 configured as described above, the air ratio of the fuel supplied to the high-temperature reduction zone 21 to 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 temperature of approximately 1500°C (an air-deficient atmosphere in which the amount of air is lower than the theoretical air amount), and fuel gasification is promoted in the high-temperature reduction zone 21.

[0019] In the high-temperature reduction zone 21, the fuel is gasified to generate combustion gas. The generated combustion gas flows into the low-temperature oxidation zone 22 through the constricted section 23. The air ratio in the low-temperature oxidation zone 22 is maintained at 1 or more (for example, about 1.1) by the air for second-stage combustion supplied to the low-temperature oxidation zone 22 from the air nozzle 26. This creates an oxidizing atmosphere in the low-temperature oxidation zone 22, which promotes combustion of the combustion gas in the low-temperature oxidation zone 22.

[0020] In the low-temperature oxidation zone 22, combustion of unburned fuel in the combustion gas is completed. 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.

[0021] [Burner 5] The burner 5 provided in the boiler 10 configured as described above is a dual-fuel burner that uses a solid fuel as the main fuel and a gas fuel containing hydrogen as the auxiliary fuel. The solid fuel is a powdered or granular fossil fuel, such as pulverized coal. In this embodiment, ammonia gas containing hydrogen and nitrogen is used as the gas fuel. However, hydrogen gas or a by-product gas generated in a plant may also be used as the gas fuel.

[0022] 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 a fuel outlet 71a of the burner 5 in Fig. 2. Fig. 4 is a view of the burner 5 shown in Fig. 2 as viewed from the burner axial direction X. As shown in Figs. 2, 3, and 4, the burner 5 is equipped with a multi-tube 7 consisting of multiple tubes arranged coaxially around a predetermined burner axis 70. The extension direction of this burner axis 70 is referred to as the "burner axial direction X." The multi-tube 7 includes an inner tube 71 extending in the burner axial direction X and multiple outer tubes (a first outer tube 91, a second outer tube 72, and a third outer tube 73) arranged outside the inner tube 71.

[0023] Powdered solid fuel and carrier air for transporting the solid fuel are supplied to the inner pipe 71. The carrier air serves as primary air (primary combustion air). A first flame stabilizing plate 77 is provided at the downstream end of the inner pipe 71, continuing in the circumferential direction. The first flame stabilizing plate 77 expands in diameter in a trumpet shape as it progresses toward the downstream end of the inner pipe 71. A fuel outlet 71a is formed at the downstream end of the inner pipe 71 by the first flame stabilizing plate 77. A mixture 51 consisting of solid fuel and carrier air is ejected from the fuel outlet 71a.

[0024] A swirl adjustment plate 711 is provided inside the downstream end of the inner pipe 71 and on the upstream side of the first flame stabilizing plate 77. A dispersion vane 713 is provided inside the inner pipe 71 and on the upstream side of the swirl adjustment plate 711.

[0025] A heavy oil burner 79, through which a burner axis 70 passes, is inserted into the axial center of the inner pipe 71. The downstream end of the heavy oil burner 79 is located near the downstream end of the inner pipe 71. Therefore, the flow path cross section at the downstream end of the inner pipe 71 is annular (donut-shaped) with the burner axis 70 as the center.

[0026] A first outer pipe 91 is provided on the outer periphery of the inner pipe 71. A first flow passage 91f having an annular flow passage cross section is formed between the inner pipe 71 and the first outer pipe 91. Gas fuel 90 is supplied to the first flow passage 91f from a gas fuel source. The gas supplied to the first flow passage 91f may be selectively switched between the gas fuel 90 and combustion air.

[0027] The gas fuel outlet 91a, which is the downstream end of the first flow path 91f, is an annular opening located on the outer circumferential side of the fuel ejection port 71a of the inner pipe 71, in other words, an opening that is continuous in the circumferential direction. On the outer circumferential side of the air-fuel mixture 51 ejected from the inner pipe 71, gas fuel 90 is ejected from the gas fuel outlet 91a.

[0028] A gas fuel guide 91b whose diameter increases in a trumpet shape as it proceeds downstream is provided at the downstream end of the first outer pipe 91. The downstream end of the gas fuel guide 91b may be located upstream or downstream of the downstream end of the first flame stabilizing plate 77. The downstream end of the gas fuel guide 91b faces more inward than the burner axial direction X, so that the gas fuel 90 ejected from the gas fuel outlet 91a is guided to approach the air-fuel mixture 51 ejected from the inner pipe 71, in other words, toward the radially inward direction.

[0029] A second outer pipe 72 is provided on the outer periphery of the first outer pipe 91. A second flow passage 72f having an annular flow passage cross section is formed between the second outer pipe 72 and the first outer pipe 91. Secondary air 52 (secondary combustion air) is supplied to the second flow passage 72f. A secondary air outlet 72a, which is the downstream end of the second flow passage 72f, is located on the outer periphery side of the gas fuel outlet 91a, and blows out the secondary air 52 on the outer periphery side of the gas fuel 90 blown out from the gas fuel outlet 91a.

[0030] A third outer pipe 73 is provided on the outer periphery of the second outer pipe 72. A third flow path 73f having an annular flow path cross section is formed between the third outer pipe 73 and the second outer pipe 72. In this way, in the burner 5, a triple flow path is formed on the outer periphery of the inner pipe 71 by the multiple pipes 7. Tertiary air 53 (air for tertiary combustion) is supplied to the third flow path 73f from the wind box. A tertiary air outlet 73a, which is the downstream end of the third flow path 73f, is located on the outer periphery side of the secondary air outlet 72a, and blows out the tertiary air 53 on the outer periphery side of the secondary air 52 ejected from the secondary air outlet 72a.

[0031] The downstream end of the second outer pipe 72 is provided with a second flame stabilizer 72b, the diameter of which increases in a trumpet-like manner as it advances downstream. The downstream end of the gas fuel guide 91b may be located upstream or downstream of the downstream end of the second flame stabilizer 72b. Furthermore, the opening edge of the downstream end of the third outer pipe 73 is provided with an outer guide 73b, the diameter of which increases in a trumpet-like manner as it advances downstream. The first flame stabilizer 77 and the second flame stabilizer 72b guide the secondary air 52 ejected from the secondary air outlet 72a radially outward from the air-fuel mixture 51 ejected from the inner pipe 71. The second flame stabilizer 72b and the outer guide 73b also guide the tertiary air 53 ejected from the third outer pipe 73 radially outward from the secondary air 52 ejected from the second outer pipe 72.

[0032] In the burner 5 configured as described above, a mixture 51 of solid fuel and primary air supplied to the inner tube 71 is ejected as a swirling flow from the fuel outlet 71a due to the action of the dispersion vane 713 and the swirl adjustment plate 711. Moreover, on the outer circumferential side of the 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. Due to the action of the gas fuel guide 91b and the second flame stabilizer 72b, the secondary air 52 is ejected so as to spread radially outward around the burner axis 70. Similarly, due to the action of the second flame stabilizer 72b and the outer guide 73b, the tertiary air 53 is ejected so as to spread radially outward.

[0033] A pressure drop creates a circulation vortex 55 at the boundary between the flow of the air-fuel mixture 51 and the flow of the secondary air 52. High-temperature combustion gas accumulates within the circulation vortex 55. In this embodiment, as shown in FIG. 3 , an outer circulation vortex 55a and an inner circulation vortex 55b are formed, which are radially inward of the outer circulation vortex 55a. Each of the outer circulation vortex 55a and the inner circulation vortex 55b consists of a forward flow toward the downstream side and a reverse flow returning to the upstream side. The swirling of the tertiary air 53 creates a circulation region 50 radially inward of the circulation vortex 55. In the circulation region 50, a circulation flow is created that returns the ejected flow of the air-fuel mixture 51 from the fuel ejection port 71a toward the fuel ejection port 71a, and high-temperature combustion gas is constantly exchanged with unburned circulation gas. As a result, the volatile components of the solid fuel in the mixture 51 quickly combust, generating a peripheral ignition flame in the circulation vortex 55. Furthermore, combustion occurs as the combustion air and the mixture 51 are mixed in stages in the order of secondary air 52 and tertiary air 53.

[0034] The burner 5 can switch between single-fuel combustion of solid fuel and mixed-fuel combustion of solid fuel and gas fuel. When single-fuel combustion of solid fuel is performed, combustion air is supplied to the first flow path 91f, or the supply of gas fuel to the first flow path 91f is stopped. When mixed-fuel combustion of solid fuel and gas fuel is performed, gas fuel 90 is supplied to the first flow path 91f, and the gas fuel 90 is blown out from the gas fuel outlet 91a. The burner 5 can switch between single-fuel combustion and mixed-fuel combustion without stopping the operation of the boiler 10.

[0035] The flow of gaseous fuel 90 blown out from the gaseous fuel outlet 91a merges with the outermost flow of the circulating vortex 55, i.e., the forward flow toward the downstream side, due to the action of the gaseous fuel guide 91b. As a result, the gaseous fuel 90 is taken into the circulating vortex 55, which is the starting point of ignition, and the gaseous fuel 90 can be burned efficiently.

[0036] [Summary] As described above, the burner 5 according to one embodiment of the present disclosure has the following features: The burner includes a multi-tube assembly including an inner tube arranged coaxially around a burner axis and a plurality of outer tubes arranged outside the inner tube. And the multi-tube 7 is a fuel outlet 71a disposed at the downstream end of the inner pipe 71 and for injecting a mixture 51 of the main fuel and primary combustion air supplied to the inner pipe 71; a secondary air outlet 72a disposed on the outer periphery of the fuel outlet 71a and for blowing out the secondary combustion air 52 supplied between the outer tubes 91 and 72; The combustion chamber is characterized by having an annular gas fuel outlet 91a arranged between the fuel injection port 71a and the secondary air outlet 72a, which blows out gas fuel 90 as auxiliary fuel supplied between the inner tube 71 and the plurality of outer tubes 91, 72, 73 toward the boundary between the flow of the mixture 51 and the flow of the secondary combustion air 52.

[0037] According to the burner 5 having the above configuration, the gaseous fuel 90 discharged from the gaseous fuel outlet 91a disposed between the fuel nozzle 71a and the secondary air outlet 72a flows toward the circulating vortex 55 generated at the boundary between the flow of the air-fuel mixture 51 and the flow of the secondary air 52, and merges with the flow of the circulating vortex 55. Because the gaseous fuel outlet 91a is an annular opening surrounding the fuel nozzle 71a, the blowout speed of the gaseous fuel 90 can be reduced when the same amount of gaseous fuel 90 is supplied, compared to when the gaseous fuel outlet is one or more small-diameter nozzles. This makes it possible to prevent the circulating vortex 55 from being disturbed by the merging of the gaseous fuel 90, and to prevent the combustion reaction in the circulating vortex 55 from being slowed down due to a drop in the temperature of the circulating vortex 55.

[0038] The burner 5 may include a gas fuel guide 91b that guides the gas fuel 90 ejected from the gas fuel outlet 91a toward a circulating vortex 55 that occurs at the boundary between the flow of the air-fuel mixture 51 and the secondary air 52. Here, it is more desirable that the gas fuel guide 91b guides the gas fuel 90 so that it abuts against a forward flow flowing toward the downstream side of the circulating vortex 55.

[0039] If the gaseous fuel 90 is blown out so as to come into contact with the reverse flow flowing toward the upstream side of the circulating vortex 55, the flow of the gaseous fuel 90 may disturb the circulating vortex 55. In contrast, in the burner 5 according to the present disclosure, the gaseous fuel guide 91b guides the flow of the gaseous fuel 90 so as to come into contact with the forward flow flowing toward the downstream side of the circulating vortex 55, so that the gaseous fuel 90 is taken into the circulating vortex 55 without disturbing the flow of the circulating vortex 55.

[0040] In the burner 5 described above, the gas fuel outlet 91a may be switchable so as to blow out combustion air instead of the gas fuel 90.

[0041] According to the burner 5 having the above configuration, the burner 5 can be switched between burning only the main fuel and burning the main fuel and auxiliary fuel. In the above embodiment, a solid fuel is used as the main fuel, but the main fuel may be a gas fuel or a liquid fuel. Also, the main fuel and the auxiliary fuel may be the same type of fuel. Alternatively, in the burner 5 having the above configuration, the gas fuel 90 may be ammonia gas.

[0042] The combustion furnace 2 according to the present disclosure also includes a high-temperature reduction zone 21 having a reducing atmosphere and equipped with at least one of the burners 5 described above, and a low-temperature oxidation zone 22 having a lower temperature than the high-temperature reduction zone 21 and an oxidizing atmosphere, into which the combustion gas generated in the high-temperature reduction zone 21 flows.

[0043] In the combustion furnace 2 configured as described above, solid fuel and gas fuel containing a large amount of nitrogen are mixed and burned in the high-temperature reduction zone 21, whereby NOx generated from the nitrogen contained in the solid fuel and gas fuel is denitrified in the furnace, thereby suppressing NOx emissions. Furthermore, a water-gasification reaction occurs in which water generated from the hydrogen contained in the solid fuel and / or gas fuel is converted into an activated gas, thereby improving combustion efficiency. Here, if the gas fuel is ammonia gas, a large amount of water is generated in the water-gasification reaction, further improving combustion efficiency.

[0044] The foregoing description 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. However, multiple features included in the present disclosure can be combined into alternative embodiments, configurations, or aspects other than those discussed above. [Explanation of symbols]

[0045] 2: Combustion furnace 5: Burner 7:Multiple pipes 21: High temperature reduction zone 22: Low temperature oxidation zone 51: Mixture (mixture of main fuel and primary combustion air) 52: Secondary air (air for secondary combustion) 53: Tertiary air (air for tertiary combustion) 55: Circulating vortex 70: Burner axis 71: Inner tube 71a:Fuel spout 72:Second outer tube 72a: Secondary air outlet 72b:Second flame holding plate 72f: Second flow path 73:Third outer tube 73:Outer tube 73a: Tertiary air outlet 73f: Third flow path 77: 1st flame holding plate 90: Gas fuel 91: 1st outer tube 91a: Gas fuel outlet 91b: Gas Fuel Guide 91f: First flow path

Claims

1. The burner has a multi-tube structure including an inner tube coaxially arranged around a burner axis and a plurality of outer tubes arranged outside the inner tube, The multi-tube a fuel ejection port disposed at a downstream end of the inner pipe and ejecting a mixture of main fuel and primary combustion air supplied to the inner pipe; a secondary air outlet disposed on an outer periphery of the fuel outlet and configured to blow out secondary combustion air supplied between the outer tubes; an annular gas fuel outlet disposed between the fuel injection port and the secondary air outlet, for blowing out gas fuel as auxiliary fuel supplied between the inner tube and the plurality of outer tubes toward a boundary portion between the flow of the air-fuel mixture and the flow of the secondary combustion air; The combustion chamber further includes a gas fuel guide that guides the gas fuel blown out from the gas fuel outlet toward a circulating vortex generated at a boundary between the flow of the air-fuel mixture and the flow of the secondary combustion air. Burner.

2. the gas fuel guide guides the gas fuel so that the gas fuel comes into contact with a forward flow of the circulating vortex toward a downstream side, 2. The burner of claim 1.

3. A multi-tube system including an inner tube coaxially arranged around a burner axis and a plurality of outer tubes arranged outside the inner tube, The multi-tube a fuel ejection port disposed at a downstream end of the inner pipe and ejecting a mixture of main fuel and primary combustion air supplied to the inner pipe; a secondary air outlet disposed on an outer periphery of the fuel outlet and configured to blow out secondary combustion air supplied between the outer tubes; an annular gas fuel outlet disposed between the fuel injection port and the secondary air outlet, for blowing out gas fuel as auxiliary fuel supplied between the inner tube and the plurality of outer tubes toward a boundary portion between the flow of the air-fuel mixture and the flow of the secondary combustion air; The gas fuel outlet is switchable to blow out combustion air instead of the gas fuel. Burner.

4. The gas fuel is ammonia gas. A burner according to any one of claims 1 to 3.

5. a high-temperature reduction zone in a reducing atmosphere provided with at least one burner according to any one of claims 1 to 4; a low-temperature oxidation zone into which combustion gas generated in the high-temperature reduction zone flows and which has a lower temperature than the high-temperature reduction zone and an oxidizing atmosphere; Combustion furnace.

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