Gas burners and boilers

Abstract

The gas burner (1) according to one aspect of the present invention comprises: a fuel supply pipe (10) that extends in a predetermined combustion air jet direction and is supplied with fuel gas; an air jet outlet (40) that is disposed on the periphery of the fuel supply pipe (10) and blows combustion air in the combustion air jet direction; and a plurality of outflow nozzles (70) that are located downstream of the air jet outlet (40) in the combustion air jet direction and extend from the fuel supply pipe (10), and from the tips of which the fuel gas flows out.

Description

Technical Field

[0001] The present invention relates to a gas burner and a boiler. This application claims priority based on Japanese Patent Application No. 2021-15590 filed in Japan on February 3, 2021, the content of which is incorporated herein by reference.

Background Art

[0002] For example, in a boiler or the like, a gas burner that mixes fuel gas with combustion air and burns it is widely used. In a gas burner, the combustion temperature may become high, and the generation of nitrogen oxides (NOx) may become a problem. In order to reduce nitrogen oxides, a self-recirculation type burner is known in which high-speed combustion air is ejected into the furnace to attract the exhaust gas in the furnace. Since the ejected combustion air contacts the flame while entraining the exhaust gas in the furnace with a low oxygen concentration, the combustion becomes slow, the flame temperature decreases, and the generation of nitrogen oxides can be reduced.

[0003] As such a self-recirculation type burner, a gas burner is known in which a fuel nozzle extending in the ejection direction of the combustion air is disposed in the jet of the combustion air, and fuel gas is ejected into the flow of the combustion air (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the gas burner described in Patent Document 1, the generation of nitrogen oxides may not be sufficiently reduced in some cases. For example, when using a fuel gas with a high combustion rate such as hydrogen, the amount of nitrogen oxides generated may increase.

[0006] Therefore, the present invention aims to provide a gas burner and boiler that can suppress the generation of nitrogen oxides. [Means for solving the problem]

[0007] A gas burner according to one aspect of the present invention comprises a fuel supply pipe extending in a predetermined combustion air ejection direction and supplied with fuel gas; an air outlet arranged around the fuel supply pipe and ejecting combustion air in the combustion air ejection direction; and a plurality of outlet nozzles extending from the fuel supply pipe downstream of the air outlet in the combustion air ejection direction and discharging the fuel gas from their tips.

[0008] In the gas burner described above, the outlet nozzle may extend from the fuel supply pipe to beyond the outermost edge of the air outlet when viewed in the direction of combustion air ejection.

[0009] The gas burner described above further comprises an inner wall pipe positioned inside the fuel supply pipe and restricting the cross-sectional area of ​​the fuel gas flow path to an annular shape, and the inner wall pipe may have an enlarged portion that widens in diameter upstream of the outlet nozzle to reduce the cross-sectional area of ​​the fuel gas flow path.

[0010] The gas burner described above is positioned inside the fuel supply pipe and further comprises an inner wall pipe that restricts the cross-sectional area of ​​the fuel gas flow path to an annular shape, and an annular sealing plate located in the middle of the fuel supply pipe that seals the gap between the fuel supply pipe and the inner wall pipe, wherein the outlet nozzle extends from the sealing plate through the fuel supply pipe and does not need to be directly fixed to the fuel supply pipe.

[0011] The gas burner described above further comprises a pilot fuel pipe positioned inside the inner wall pipe and supplied with pilot fuel, and pilot combustion air may be supplied to the gap between the inner wall pipe and the pilot fuel pipe.

[0012] The gas burner described above may further include a pilot burner positioned inside the inner wall tube, and cooling air may be supplied to the gap between the inner wall tube and the pilot burner.

[0013] In the gas burner described above, the air outlet may be the gap between a limiting member positioned on the outer circumference of the fuel supply pipe and an air supply pipe positioned outside the fuel supply pipe and the limiting member, but not fixed to the limiting member.

[0014] In the gas burner described above, it is preferable that the diameter of the virtual circumscribed circle of the air outlet is less than twice the outer diameter of the fuel supply pipe.

[0015] A boiler according to one aspect of the present invention comprises the above-described gas burner and a boiler body arranged to surround the gas burner and having a plurality of water tubes extending in the direction of combustion air ejection, defining a flow path for the combustion exhaust gas of the gas burner to flow in the axial direction of the plurality of water tubes.

[0016] In the boiler described above, it is preferable that the diameter of the virtual circle connecting the centers of the air outlets is greater than 0.15 times the diameter of the inner space of the boiler body and less than 0.7 times. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a gas burner and a boiler that can suppress the generation of nitrogen oxides. [Brief explanation of the drawing]

[0018] [Figure 1] This is a cross-sectional view of a boiler according to the first embodiment of the present invention. [Figure 2] This is a cross-sectional view showing the configuration of the gas burner in the boiler shown in Figure 1. [Figure 3] Figure 2 shows the gas burner viewed from the downstream side in the direction of combustion air ejection. [Figure 4] This is a cross-sectional view showing the configuration of a gas burner according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of a boiler 100 including a gas burner 1 according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing the configuration of the gas burner 1. FIG. 3 is a view of the gas burner 1 as seen from the downstream side in the combustion air ejection direction.

[0020] The boiler 100 includes a gas burner 1 that forms a flame extending in a predetermined combustion air ejection direction (in this embodiment, the vertical direction), and a can body 110 that is heated by the combustion exhaust gas of the gas burner 1. The boiler 100 is itself an embodiment of a boiler according to the present invention.

[0021] The can body 110 is arranged to surround the gas burner 1, and has a plurality of water pipes 111 extending in the combustion air ejection direction (vertical direction), a lower header 112 connecting the lower ends of the plurality of water pipes 111, and an upper header 113 connecting the upper ends of the plurality of water pipes 111. The can body 110 defines a flow path through which the combustion exhaust gas of the gas burner 1 flows in the axial direction of the plurality of water pipes 111.

[0022] In the can body 110, the plurality of water pipes 111 are arranged in a double annular shape when viewed in the injection direction of the gas burner 1. Except for the end of the inner water pipe 111 on the side opposite to the gas burner 1, the adjacent water pipes 111 in the circumferential direction are connected directly or by a strip-shaped member so that the combustion exhaust gas cannot pass through. As a result, the combustion exhaust gas of the gas burner 1 passes through the space inside the inner water pipe 111, passes through the gap between the water pipes 111 at the end opposite to the gas burner 1, passes through the space between the inner water pipe 11 and the outer water pipe 111 in the reverse direction, and is then discharged to the outside.

[0023] The gas burner 1 includes a fuel supply pipe 10 extending in the direction of combustion air ejection, a wind box 20 positioned to surround the upstream portion of the fuel supply pipe 10, an air supply pipe 30 extending from the wind box 20 positioned outside the fuel supply pipe 10, a plurality of air outlets 40 provided at the end of the air supply pipe 30 positioned around the fuel supply pipe 10, an inner wall pipe 50 positioned inside the fuel supply pipe 10, an annular sealing plate 60 sealing the gap between the fuel supply pipe 10 and the inner wall pipe 50 at the end of the fuel supply pipe 10, a plurality of outlet nozzles 70 extending from the fuel supply pipe 10 downstream of the air outlets 40 in the direction of combustion air ejection, and a pilot burner 80 positioned inside the inner wall pipe 50.

[0024] The fuel supply pipe 10 defines a flow path through which fuel gas is supplied and guided to the outlet nozzle 70. Examples of fuel gases used in the gas burner 1 include hydrogen gas, methane gas, propane gas, and hydrogen-containing gases. The present invention is particularly effective in reducing nitrogen oxides when using hydrogen gas or hydrogen-containing gases, which have a high combustion rate.

[0025] The wind box 20 is supplied with combustion air, and the supplied combustion air is distributed so as not to vary depending on its angular position relative to the fuel supply pipe 10, and then introduced into the air supply pipe 30.

[0026] The air supply pipe 30 guides the combustion air along the fuel supply pipe 10 in the direction of combustion air ejection to the air outlet 40.

[0027] The air outlet 40 ejects combustion air in the direction of combustion air ejection (downward in Figures 1 and 2). In the illustrated example, the air outlet 40 is defined by a short pipe 42 provided on the end plate 41 that seals the end of the air supply pipe 30. Multiple air outlets 40 are arranged in an annular pattern surrounding the fuel supply pipe 10 so as to form a flow of combustion air along the fuel supply pipe 10 over the entire circumference of the fuel supply pipe 10.

[0028] The air nozzle 40 is preferably provided at a radial distance from the fuel supply pipe 10. By providing the air nozzle 40 at a certain distance from the fuel supply pipe 10, the flow of combustion air along the fuel supply pipe 10 can be efficiently formed.

[0029] The jet of combustion air ejected from the air outlet 40 creates a low-pressure region near the jet, and the combustion exhaust gas in the furnace is continuously drawn into the combustion air from the circumferential direction along the flow of the jet toward the fuel gas supply section, thereby effectively reducing the oxygen concentration of the combustion air.

[0030] The diameter of the virtual circumscribed circle of the air outlet 40 (shown as a dashed line in Figure 3) is preferably less than twice the outer diameter of the fuel supply pipe 10, and more preferably less than 1.65 times. By not making the diameter of the virtual circumscribed circle of the air outlet 40 unnecessarily large relative to the outer diameter of the fuel supply pipe 10, the thickness of the combustion air jet becomes thinner, and the specific surface area per unit volume increases, so that the combustion gases in the furnace can be efficiently drawn into the combustion air jet.

[0031] The diameter of the virtual circle connecting the centers of the air outlets 40 (shown as a dashed line in Figure 3) is preferably greater than 0.15 times and less than 0.7 times the diameter D of the inner space of the boiler body 110 (the diameter of the pitch circle of the inner water tubes 111, see Figure 1). This ensures that the combustion air jet entrains the combustion exhaust gas, secures the space necessary for combustion, and allows the combustion exhaust gas to be efficiently entrained in the combustion air jet while simultaneously preventing incomplete combustion.

[0032] The inner wall tube 50 is positioned inside the fuel supply pipe 10 and restricts the cross-sectional area of ​​the fuel gas flow path to an annular shape. The inner wall tube 50 has an enlarged diameter section 51 that widens its diameter upstream of the outlet nozzle 70 to reduce the cross-sectional area of ​​the fuel gas flow path. Because the inner wall tube 50 has an enlarged diameter section 51, the flow velocity of the fuel gas inside the tip of the fuel supply pipe 10 increases, so the tip of the fuel supply pipe 10, which tends to get hot due to combustion, can be cooled by the fuel gas, improving the durability of the gas burner 1. In particular, since fuel gas has a higher thermal conductivity than air, the increase in the cooling effect of the fuel supply pipe 10 due to the increased flow velocity of the fuel gas is significant. In particular, when hydrogen gas is used as the fuel gas, the thermal conductivity of hydrogen gas is 0.257 W / mk at 200°C, which is nearly seven times that of air at 200°C (0.038 W / mk), so the increase in the cooling effect of the fuel supply pipe 10 due to the enlarged diameter section 51 is remarkable.

[0033] The sealing plate 60 terminates the gap between the fuel supply pipe 10, which is the flow path for the fuel gas, and the inner wall pipe 50. As a result, the fuel gas flows out only from the outlet nozzle 70.

[0034] The discharge nozzle 70 discharges fuel gas from its tip. In other words, the tip of the discharge nozzle 70 constitutes a fuel discharge opening 71 from which the fuel gas discharges. In this embodiment, the discharge nozzle 70 is arranged to discharge fuel gas in the radial direction of the fuel supply pipe 10, but the fuel gas may also be discharged in a direction inclined from the radial direction toward the injection direction.

[0035] The position and direction of fuel gas discharge can be controlled by the arrangement of the discharge nozzles 70. Furthermore, by discharging fuel gas from multiple discharge nozzles 70, the uneven distribution of fuel around the gas burner 1 can be reduced. In addition, by providing discharge nozzles 70, the diffusion of combustion exhaust gas or purge air from inside the furnace into the fuel supply pipe 10 can be suppressed when combustion stops.

[0036] The outlet nozzle 70 is positioned downstream of the air outlet 40 and at a certain distance from the air outlet 40. By positioning the air outlet 40 at a certain distance from the fuel supply pipe 10, the combustion exhaust gas from the furnace is mixed into the combustion air jet before the fuel gas is mixed in. As a result, the oxygen concentration of the combustion air at the time of mixing with the fuel gas decreases, which reduces the combustion temperature and suppresses the generation of nitrogen oxides.

[0037] Furthermore, in the gas burner 1, the fuel outlet opening 71 of the outlet nozzle 70 is positioned in the low-pressure region formed by the air jet, allowing the required amount of fuel gas to be discharged even with a lower supply pressure than conventional systems. For this reason, the gas burner 1 can be used with fuel gases that have a low supply pressure, such as by-product hydrogen or low-pressure supplied city gas, without pressurizing them.

[0038] The distance L from the air outlet 40 to the outlet nozzle 70 (center of the fuel outlet opening 71) in the direction of combustion air ejection is preferably 3 to 15 times the equivalent diameter of the air outlet 40, and more preferably 6 to 12 times. By setting the distance L from the air outlet 40 to the outlet nozzle 70 to be above the lower limit, the fuel gas can be mixed with combustion air that has an oxygen concentration capable of effectively suppressing the generation of nitrogen oxides. Furthermore, by setting the distance L from the air outlet 40 to the outlet nozzle 70 to be below the upper limit, the oxygen concentration of the combustion air cannot be reduced too much, resulting in incomplete combustion, and the flow velocity of the combustion air can be reduced, suppressing the generation of nitrogen oxides due to localized temperature increases.

[0039] The discharge nozzle 70 extends from the fuel supply pipe 10 to beyond the outermost edge of the air outlet 40 when viewed in the direction of combustion air ejection. In other words, the fuel discharge opening 71 at the tip of the discharge nozzle 70 opens outside the virtual circumscribed circle of the multiple air outlets 40. As a result, the fuel gas is discharged into a region where the oxygen concentration is sufficiently reduced due to the entrainment of combustion exhaust gas outside the combustion air jet, thus reducing the combustion speed. Therefore, the gas burner 1 can reduce the combustion temperature and suppress the generation of nitrogen oxides. In this way, by using the discharge nozzle 70 extending from the fuel supply pipe 10 to discharge fuel into a region outside the combustion air jet where the influence of combustion exhaust gas is significant, the effect of suppressing nitrogen oxides by reducing the oxygen concentration of the combustion air can be improved.

[0040] Furthermore, since the gas burner 1 forms the flame on the outside away from the center by the outlet nozzle 70, the surface area of ​​the flame can be increased. In addition, since the gas burner 1 discharges the fuel gas into a low-pressure region near the outside of the combustion air jet, the required amount of fuel gas can be supplied even if the fuel gas supply pressure is low. Moreover, since the fuel gas is supplied towards the air jet from multiple fuel outlet openings 71 near the outside of the combustion air jet, there is no uneven distribution of fuel gas, and the formation of localized high-temperature areas can be suppressed.

[0041] The number and angular position of the outflow nozzles 70 can be set arbitrarily without being limited by the number and angular position of the air outlets 40. However, in the illustrated example, multiple outflow nozzles 70, the same number as the air outlets 40, are arranged alternately with the air outlets 40 in the circumferential direction.

[0042] The pilot burner 80 includes a pilot air pipe 81 to which pilot combustion air is supplied, and a pilot fuel pipe 82 located inside the pilot air pipe 81 to which pilot fuel is supplied. The pilot burner 80 mixes the pilot fuel and pilot combustion air at the tip of the pilot air pipe 81 to form a pilot flame.

[0043] Cooling air may be supplied to the gap between the pilot burner 80 and the inner wall pipe 50. This allows the fuel gas and, consequently, the fuel supply pipe 10 to be cooled through the inner wall pipe 50 by the cooling air, thereby improving the durability of the gas burner 1. The cooling air can be a portion of the combustion air, the flow rate of which is set according to the flow rate of the fuel gas supplied to the fuel supply pipe 10.

[0044] As described above, the gas burner 1 burns the fuel gas downstream of the air outlet 40 using combustion air mixed with combustion exhaust gas from the furnace, which has a reduced oxygen concentration. This lowers the combustion temperature and suppresses the generation of nitrogen oxides. In particular, the gas burner 1 uses the outlet nozzle 70 to discharge the fuel gas into an area outside the combustion air jet where the reduction in oxygen concentration due to combustion exhaust gas is significant, thus more reliably suppressing the generation of nitrogen oxides.

[0045] In boiler 100, the gas burner 1 is arranged in a space enclosed by multiple water tubes 111, preventing bias in the flow of combustion air in the circumferential direction. As a result, a uniform low-pressure region is formed outside the jet of combustion air in the circumferential direction, and the combustion exhaust gas in the furnace is drawn into the combustion air, effectively suppressing the generation of nitrogen oxides. Therefore, boiler 100 can efficiently generate steam while suppressing the generation of nitrogen oxides. Furthermore, by employing a boiler body 110 that defines a flow path for the combustion exhaust gas of the gas burner 1 to flow axially through multiple water tubes 111, boiler 100 not only prevents bias in axial flow velocity and suppresses the formation of localized high-temperature areas due to combustion, but also reduces pressure loss in the boiler body 110, resulting in reduced energy consumption for the blower and also reducing the fuel gas supply pressure.

[0046] Next, a gas burner 1A according to a second embodiment of the present invention will be described. Figure 4 is a cross-sectional view showing the configuration of the gas burner 1A. In the following description, components similar to those described in the previously described embodiment will be denoted by the same reference numerals, and redundant descriptions may be omitted. This gas burner 1A can be used in place of the gas burner 1 in the boiler 100 of Figure 1.

[0047] The gas burner 1A of this embodiment includes a fuel supply pipe 10 extending in a predetermined direction for combustion air ejection, a wind box 20 positioned to surround the upstream portion of the fuel supply pipe 10, an air supply pipe 30 extending from the wind box 20 to be positioned outside the fuel supply pipe 10, a single air outlet 40A provided at the end of the air supply pipe 30 to be positioned around the fuel supply pipe 10, an inner wall pipe 50A positioned inside the fuel supply pipe 10, an annular sealing plate 60A sealing the gap between the fuel supply pipe 10 and the inner wall pipe 50A at the end of the fuel supply pipe 10, a plurality of outlet nozzles 70A extending from the fuel supply pipe 10 downstream of the air outlet 40 in the direction for combustion air ejection, and a pilot fuel pipe 82 positioned inside the inner wall pipe 50A.

[0048] The air outlet 40A is the gap between the air supply pipe 30 and a restricting member 43, which is disposed on the outer circumference of the fuel supply pipe 10 and restricts the flow path of combustion air. The restricting member 43 may be configured to have an annular flange portion 44 attached to the fuel supply pipe 10, and a cylindrical guide tube portion 45 that extends from the outer edge of the flange portion 44 parallel to the air supply pipe 30 to the same combustion air ejection direction position as the tip of the air supply pipe 30. Therefore, the air outlet 40A is an annular opening in the combustion air ejection direction at the tip of the gap between the air supply pipe 30 and the guide tube portion 45.

[0049] It is preferable that the limiting member 43 is not fixed to the air supply pipe 30, and more specifically, that the guide cylinder portion 45 and the air supply pipe are not connected by a spacer or the like. With this configuration, when the flow rate of fuel gas and combustion air is increased under high load, the area of ​​the air outlet 40 increases due to the thermal expansion of the air supply pipe 30 as the temperature rises, thereby reducing the pressure loss of combustion air and suppressing the increase in energy consumption of the blower.

[0050] The inner wall pipe 50A has no enlarged section and extends to the end with the same diameter. In the gas burner 1A, pilot combustion air is supplied between the inner wall pipe 50A and the pilot fuel pipe 82. In other words, in this embodiment, the inner wall pipe 50A defines the flow path for the pilot combustion air. For this reason, the gas burner 1A indirectly cools the fuel supply pipe 10 by cooling the fuel gas through the inner wall pipe with the pilot combustion air. For this reason, it is preferable to supply pilot combustion air in the gas burner 1A even when a pilot flame is not being formed. In this case, the flow rate of combustion air ejected from the air outlet 40A may be reduced by the flow rate of the pilot air.

[0051] The sealing plate 60A terminates the gap between the fuel supply pipe 10, which is the flow path for the fuel gas, and the inner wall pipe 50A upstream of the point where the outlet nozzle 70A extends from the fuel supply pipe 10. The outlet nozzle 70A is connected to the sealing plate 60A, and an opening is formed in the connected outlet nozzle 70A for the fuel gas to flow out.

[0052] The outlet nozzle 70A is connected to the sealing plate 60A inside the fuel supply pipe 10, extends from the sealing plate 60A in the direction of combustion air ejection, bends radially outward inside the fuel supply pipe 10, and extends through the fuel supply pipe 10. The outlet nozzle 70A passes through an opening formed in the fuel supply pipe 10 and is not directly fixed to the fuel supply pipe. In other words, the outlet nozzle 70A is fixed to the sealing plate 60A, which is not exposed to the flame, and is not fixed to the tip portion of the fuel supply pipe 10, which is exposed to the flame and becomes hot. Therefore, since there is no connection point between the fuel supply pipe 10 and the outlet nozzle 70A where thermal stress can concentrate, the gas burner 1A has excellent durability.

[0053] Although preferred embodiments of the heat supply system according to the present invention have been described above, the present invention is not limited to the embodiments described above and can be modified as appropriate.

[0054] In a configuration where the outlet nozzle is connected to a sealing plate that seals the gap between the fuel supply pipe and the inner wall pipe, in particular, when a pilot burner having a pilot air pipe and a pilot fuel pipe inside the inner wall pipe is provided, the inner wall pipe may be terminated upstream of the fuel supply pipe. [Explanation of symbols]

[0055] 1.1A gas burner 10 Fuel supply pipe 20 Window Boxes 30 Air supply pipe 40, 40A Air outlet 41 Termination plate 42 Short tube 43 Restricting member 44 Flange section 45 Guide tube section 50,50A inner wall pipe 51 Expanded diameter part 60,60A sealing plate 70, 70A Outlet Nozzle 71 Fuel outflow opening 80 Pilot Burner 81 Pilot air pipe 82 Pilot fuel pipe 100 boilers 110 Can body 111 Water pipe

Claims

1. A fuel supply pipe extending in a predetermined direction of combustion air injection, through which fuel gas is supplied, An air outlet is provided around the fuel supply pipe and ejects combustion air in the direction of combustion air ejection, A plurality of outlet nozzles extend from the fuel supply pipe downstream of the air outlet in the combustion air ejection direction, and discharge the fuel gas from their tips, Equipped with, The discharge nozzle is a gas burner that extends from the fuel supply pipe to beyond the outermost edge of the air outlet when viewed in the direction of combustion air ejection.

2. A fuel supply pipe extending in a predetermined direction of combustion air injection, through which fuel gas is supplied, An air outlet is provided around the fuel supply pipe and ejects combustion air in the direction of combustion air ejection, A plurality of outlet nozzles extend from the fuel supply pipe downstream of the air outlet in the combustion air ejection direction, and discharge the fuel gas from their tips, An inner wall pipe is positioned inside the fuel supply pipe and restricts the cross-sectional area of ​​the fuel gas flow path to an annular shape, Equipped with, A gas burner in which the inner wall tube has an enlarged diameter portion that enlarges upstream of the outlet nozzle to reduce the cross-sectional area of ​​the flow path for the fuel gas.

3. A fuel supply pipe extending in a predetermined direction of combustion air injection, through which fuel gas is supplied, An air outlet is provided around the fuel supply pipe and ejects combustion air in the direction of combustion air ejection, A plurality of outlet nozzles extend from the fuel supply pipe downstream of the air outlet in the combustion air ejection direction, and discharge the fuel gas from their tips, An inner wall pipe is positioned inside the fuel supply pipe and restricts the cross-sectional area of ​​the fuel gas flow path to an annular shape, An annular sealing plate is provided in the middle of the fuel supply pipe to seal the gap between the fuel supply pipe and the inner wall pipe, Equipped with, The discharge nozzle extends from the sealing plate through the fuel supply pipe and is not directly fixed to the fuel supply pipe, in a gas burner.

4. The system further comprises a pilot fuel pipe located inside the inner wall pipe and supplied with pilot fuel, The gas burner according to claim 2 or 3, wherein pilot combustion air is supplied to the gap between the inner wall tube and the pilot fuel tube.

5. The system further comprises a pilot burner positioned inside the inner wall tube, The gas burner according to claim 2 or 3, wherein cooling air is supplied to the gap between the inner wall tube and the pilot burner.

6. The gas burner according to any one of claims 1 to 5, wherein the air outlet is the gap between a limiting member disposed on the outer circumference of the fuel supply pipe and an air supply pipe disposed outside the fuel supply pipe and the limiting member, but not fixed to the limiting member.

7. The gas burner according to any one of claims 1 to 6, wherein the diameter of the virtual circumscribed circle of the air outlet is less than twice the outer diameter of the fuel supply pipe.

8. A gas burner according to any one of claims 1 to 7, A boiler body is arranged to surround the gas burner and has a plurality of water pipes extending in the direction of the combustion air ejection, defining a flow path for the combustion exhaust gas of the gas burner to flow in the axial direction of the plurality of water pipes, A boiler equipped with the following features.

9. The boiler according to claim 8, wherein the diameter of the virtual circle connecting the centers of the air outlets is greater than 0.15 times and less than 0.7 times the diameter of the inner space of the boiler body.

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