Gas burners and boilers

Abstract

A gas burner (1) according to an aspect of the present invention includes: a fuel supply pipe (10) that extends in a predetermined combustion-air ejection direction and through which a fuel gas is supplied; air ejection ports (40) that are disposed around the fuel supply pipe (10) and that eject combustion air in the combustion-air ejection direction; and a plurality of effusion nozzles (70) that extend from the fuel supply pipe (10) so as not to protrude outward farther than the air ejection ports (40) and so as to be inclined at an acute angle with respect to the combustion-air ejection direction, and distal ends of which form fuel flow-out ports (71) from which the fuel gas is made to flow 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. 2021-15591, filed in Japan on February 3, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] For example, gas burners that burn fuel gas mixed with combustion air are widely used in boilers. The combustion temperature of gas burners becomes high, and the generation of nitrogen oxides (NOx) can become a problem. To reduce nitrogen oxides, a self-recirculating burner is known that injects high-speed combustion air into the furnace to attract exhaust gas from the furnace. The injected combustion air comes into contact with the flame while entraining the exhaust gas from the furnace, which has a low oxygen concentration, so the combustion slows down, the flame temperature drops, and the generation of nitrogen oxides can be reduced.

[0003] One such self-recirculating burner known in the art is a gas burner in which a fuel nozzle extending in the direction of the combustion air jet is disposed in the combustion air jet, and fuel gas is sprayed into the combustion air flow (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-173506 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the gas burner described in Patent Document 1 may not be able to sufficiently reduce the generation of nitrogen oxides. For example, when using a fuel gas with a high combustion speed, such as hydrogen, the amount of nitrogen oxides generated may be large. In addition, since there is a trade-off between the generation of nitrogen oxides and the increase in unburned matter in the combustion exhaust gas, it is necessary to suppress the generation of nitrogen oxides and reduce the generation of unburned matter.

[0006] Therefore, an object of the present invention is to provide a gas burner and a boiler that can suppress the generation of nitrogen oxides and reduce the amount of unburned matter remaining in the combustion exhaust gas. [Means for solving the problem]

[0007] A gas burner according to one embodiment of the present invention comprises a fuel supply pipe extending in a predetermined combustion air ejection direction and through which fuel gas is supplied, an air ejection port 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 so as not to protrude outward beyond the air ejection port and at an acute angle relative to the combustion air ejection direction, the tips of which constitute fuel outlets through which the fuel gas flows out.

[0008] In the above-described gas burner, the air outlet and the fuel outlet may overlap when viewed in the combustion air outlet direction.

[0009] The above-mentioned gas burner may further include an inner wall tube arranged inside the fuel supply pipe and restricting the flow path cross-section of the fuel gas into an annular shape, and the inner wall tube may have an expansion portion that expands in diameter so as to reduce the flow path cross-sectional area of ​​the fuel gas upstream of the outlet nozzle.

[0010] The above-mentioned gas burner further comprises an inner wall pipe arranged inside the fuel supply pipe and restricting the flow path cross-section of the fuel gas into an annular shape, and an annular sealing plate midway through the fuel supply pipe and sealing the gap between the fuel supply pipe and the inner wall pipe, and the outflow nozzle extends from the sealing plate through the fuel supply pipe and does not have to be directly fixed to the fuel supply pipe.

[0011] In the above-mentioned gas burner, it is preferable that the diameter of an imaginary circumscribing circle of the air nozzle is less than twice the outer diameter of the fuel supply pipe.

[0012] A gas burner according to one embodiment of the present invention comprises the above-mentioned gas burner, and a can body arranged to surround the gas burner, having a plurality of water tubes extending in the direction of the combustion air ejection, and defining a flow path for flowing the combustion exhaust gas from the gas burner in the axial direction of the plurality of water tubes.

[0013] In the above boiler, it is preferable that the diameter of an imaginary 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. Effect of the Invention

[0014] According to the present invention, it is possible to provide a gas burner and a boiler that can suppress the generation of nitrogen oxides and reduce the amount of unburned matter remaining in the combustion exhaust gas. [Brief description of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of a boiler according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing the configuration of a gas burner of the boiler of FIG. [Diagram 3] 3 is a view of the gas burner in FIG. 2 as viewed from the downstream side in the direction of combustion air ejection. [Figure 4] FIG. 4 is a cross-sectional view showing the configuration of a gas burner according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment 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 equipped with 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 viewed from the downstream side in the combustion air ejection direction.

[0017] The boiler 100 includes a gas burner 1 that forms a flame extending in a predetermined combustion air ejection direction (vertical direction in this embodiment), and a boiler body 110 that is heated by combustion exhaust gas from the gas burner 1. The boiler 100 itself is one embodiment of the boiler according to the present invention.

[0018] The can body 110 is disposed so as to surround the gas burner 1, and has a plurality of water tubes 111 extending in the combustion air ejection direction (vertical direction), a lower header 112 connecting the lower ends of the plurality of water tubes 111, and an upper header 113 connecting the upper ends of the plurality of water tubes 111. The can body 110 defines a flow path through which the combustion exhaust gas from the gas burner 1 flows in the axial direction of the plurality of water tubes 111.

[0019] In the can body 110, the multiple water tubes 111 are arranged in a double ring shape when viewed from the injection direction of the gas burner 1. Except for the end of the inner water tube 111 opposite the gas burner 1, the water tubes 111 adjacent in the circumferential direction are connected to each other directly or by a band-shaped member and are arranged so that the combustion exhaust gas cannot pass through. As a result, the combustion exhaust gas from the gas burner 1 passes through the space inside the inner water tube 111, passes through the gaps between the water tubes 111 at the end opposite the gas burner 1, and passes through the space between the inner water tube 111 and the outer water tube 111 in the reverse direction before being discharged to the outside.

[0020] The gas burner 1 comprises a fuel supply pipe 10 extending in the direction of combustion air ejection, a wind box 20 arranged to surround the upstream portion of the fuel supply pipe 10, an air supply pipe 30 extending from the wind box 20 so as to be positioned outside the fuel supply pipe 10, a plurality of air ejection ports 40 provided at the tip of the air supply pipe 30 so as to be positioned around the fuel supply pipe 10, an inner wall pipe 50 arranged inside the fuel supply pipe 10, a ring-shaped sealing plate 60 that seals the gap between the fuel supply pipe 10 and the inner wall pipe 50 at the tip of the fuel supply pipe 10, a plurality of outlet nozzles 70 extending from the fuel supply pipe 10 downstream of the air ejection port 40 in the combustion air ejection direction, and a pilot burner 80 arranged inside the inner wall pipe 50.

[0021] The fuel supply pipe 10 defines a flow path through which the fuel gas is supplied and which guides the fuel gas to the outflow nozzle 70. The fuel gas used in the gas burner 1 may be, for example, hydrogen gas, methane gas, propane gas, or a gas containing hydrogen, and the effect of reducing nitrogen oxides according to the present invention is particularly noticeable when hydrogen gas or a gas containing hydrogen, which has a high combustion speed, is used.

[0022] The wind box 20 is supplied with combustion air, distributes the supplied combustion air so as not to vary depending on the angular position relative to the fuel supply pipe 10, and introduces the air into the air supply pipe 30.

[0023] The air supply pipe 30 guides the combustion air along the fuel supply pipe 10 to the air outlet 40 in the combustion air ejection direction.

[0024] The air outlet 40 ejects the combustion air in a combustion air ejection direction (downward in Figs. 1 and 2). In the example shown, the air outlet 40 is defined by a short pipe 42 disposed on an end plate 41 that seals the tip of the air supply pipe 30. The multiple air outlets 40 are arranged in an annular shape 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.

[0025] The air outlet 40 is preferably provided radially away from the fuel supply pipe 10. By providing the air outlet 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.

[0026] The jet of combustion air ejected from the air outlet 40 creates a low-pressure region in the vicinity of the jet, and the combustion exhaust gas in the furnace is continuously entrained in the combustion air from the circumferential direction along the flow of the jet toward the fuel gas supply section, effectively reducing the oxygen concentration of the combustion air.

[0027] The diameter of the imaginary circumscribing circle of the air nozzle 40 (shown by a two-dot chain line in FIG. 3) is preferably less than twice, and more preferably less than 1.65 times, the outer diameter of the fuel supply pipe 10. By not making the diameter of the imaginary circumscribing circle of the air nozzle 40 larger than necessary relative to the outer diameter of the fuel supply pipe 10, the thickness of the combustion air jet becomes thin and the specific surface area per volume becomes large, so that the combustion gas in the furnace can be efficiently entrained in the combustion air jet.

[0028] The diameter of an imaginary circle connecting the centers of the air outlets 40 (shown by a dashed line in FIG. 3) is preferably greater than 0.15 and less than 0.7 times the diameter D of the inner space of the can body 110 (the pitch circle diameter of the inner water tube 111, see FIG. 1). This ensures an area in which the jet of combustion air can entrain the combustion exhaust gas, as well as the space necessary for combustion, allowing the combustion exhaust gas to be efficiently entrained in the jet of combustion air while preventing incomplete combustion.

[0029] The inner wall pipe 50 is disposed inside the fuel supply pipe 10 and restricts the cross section of the fuel gas flow path to an annular shape. The inner wall pipe 50 has an expanded diameter portion 51 that expands in diameter to reduce the cross section of the fuel gas flow path upstream of the outflow nozzle 70. Since the inner wall pipe 50 has the expanded diameter portion 51, the flow rate of the fuel gas inside the tip of the fuel supply pipe 10, which is likely to become hot due to combustion, can be cooled by the fuel gas, and the durability of the gas burner 1 can be improved. In particular, since the thermal conductivity of the fuel gas is higher than that of air, the increase in the cooling effect of the fuel supply pipe 10 due to the increase in the flow rate of the fuel gas is not small. 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 the thermal conductivity 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 expanded diameter portion 51 is significant.

[0030] The sealing plate 60 terminates the gap between the fuel supply pipe 10 and the inner wall pipe 50, which serves as a flow path for the fuel gas. This allows the fuel gas to flow out only from the outflow nozzle .

[0031] The outflow nozzle 70 extends so as not to protrude outward beyond the air outlet 40 and so as to form an acute inclination angle α with respect to the combustion air outlet direction. The outflow nozzle 70 causes the fuel gas to flow out from its tip. In other words, the tip of the outflow nozzle 70 constitutes a fuel outlet 71 through which the fuel gas flows out.

[0032] The position and direction of the fuel gas outflow can be controlled by arranging the outflow nozzles 70. In addition, by discharging the fuel gas from a plurality of outflow nozzles 70, it is possible to reduce the bias of the fuel distribution in the circumferential direction of the gas burner 1. Furthermore, by providing the outflow nozzles 70, it is possible to suppress the diffusion of the combustion exhaust gas or purge air in the furnace into the inside of the fuel supply pipe 10 when the combustion is stopped.

[0033] The outflow nozzle 70 is disposed downstream of the air outlet 40 at a fixed distance from the air outlet 40. By providing the air outlet 40 at a fixed distance from the fuel supply pipe 10, the combustion exhaust gas in the furnace is mixed into the combustion air jet before the fuel gas is mixed in. This reduces the oxygen concentration in the combustion air at the time the fuel gas is mixed in, thereby reducing the combustion temperature and suppressing the generation of nitrogen oxides.

[0034] In addition, in the gas burner 1, the fuel outlet 71 of the outlet nozzle 70 is disposed in the low pressure region formed by the air jet, so that even if the fuel gas has a lower supply pressure than before, a necessary amount can be discharged. Therefore, the gas burner 1 can use fuel gas with a low supply pressure, such as by-product hydrogen or low-pressure city gas, without pressurizing it.

[0035] The distance L of the outflow nozzle 70 (the center of the fuel outlet 71) from the air outlet 40 in the combustion air ejection direction is preferably 3 to 15 times, more preferably 6 to 12 times, the equivalent diameter of the air outlet 40. By setting the distance L of the outflow nozzle 70 from the air outlet 40 to the lower limit or more, the fuel gas can be mixed with the combustion air having an oxygen concentration that can effectively suppress the generation of nitrogen oxides, so that the generation of nitrogen oxides can be effectively suppressed. In addition, by setting the distance L of the outflow nozzle 70 from the air outlet 40 to the upper limit or less, it is possible to suppress the generation of nitrogen oxides due to a local temperature rise caused by a too low oxygen concentration in the combustion air, and the generation of nitrogen oxides due to a local temperature rise caused by a decrease in the flow rate of the combustion air.

[0036] The outflow nozzle 70 is disposed so as not to protrude from the outermost part of the outer edge of the air outlet 40 when viewed from the fuel supply pipe 10 in the combustion air ejection direction. In other words, the fuel outlet 71 at the tip of the outflow nozzle 70 opens inside the imaginary circumscribing circle of the multiple air outlets 40 in the figure. This causes the fuel gas to flow out into a low-pressure region that is locally formed on the back side of the fuel supply pipe 10 by the jet of combustion air ejected from the air outlet 40, making it possible to further reduce the outflow pressure of the fuel gas.

[0037] Since the outflow nozzle 70 is inclined, the fuel gas flows out of the fuel outlet 71 with a velocity component in the combustion air ejection direction. This allows the fuel gas to move quickly downstream in the combustion air ejection direction, making it easier to ensure a mixing area and mixing time for the combustion air and the combustion exhaust gas, and suppressing the emission of unburned materials (unburned fuel gas and incompletely combusted materials such as carbon monoxide). In addition, since the outflow nozzle 70 ejects the fuel gas in a direction at an acute angle to the combustion air ejection direction, the fuel gas is less likely to come into contact with the water tube 111 compared to the case where the fuel gas is ejected in the radial direction, and therefore the emission of unburned materials (unburned fuel gas and incompletely combusted materials such as carbon monoxide) can be more reliably suppressed.

[0038] The lower limit of the inclination angle α of the outflow nozzle 70 with respect to the combustion air ejection direction is preferably 15°, more preferably 30°, while the upper limit of the inclination angle α of the outflow nozzle 70 is preferably 75°, more preferably 60°. By setting the inclination angle α of the outflow nozzle 70 to the lower limit or more, the opening of the fuel supply pipe 10 is not too large in the combustion air ejection direction, making it easier to attach the outflow nozzle 70 and ensuring strength against thermal stress. Furthermore, by setting the inclination angle α of the outflow nozzle 70 to the upper limit or less, the generation of nitrogen oxides can be appropriately suppressed.

[0039] It is preferable that the air outlet 40 and the fuel outlet 71 partially overlap when viewed from the combustion air ejection direction. By overlapping the air outlet 40 and the fuel outlet 71, mixing of the combustion air jet and the fuel gas is promoted, so that unburned materials can be reduced. In addition, by optimizing the degree of overlap, it is possible to highly simultaneously suppress the generation of nitrogen oxides due to a decrease in the oxygen concentration of the combustion air caused by the influence of the combustion exhaust gas, and reduce unburned materials by promoting mixing of the fuel gas with the combustion air.

[0040] The number of the outflow nozzles 70 and their angular positions around the fuel supply pipe 10 are not limited by the number and angular positions of the air outlets 40 and can be set arbitrarily.

[0041] The pilot burner 80 has a pilot air pipe 81 to which pilot combustion air is supplied, and a pilot fuel pipe 82 that is arranged inside the pilot air pipe 81 and to which pilot fuel is supplied. The pilot burner 80 mixes the pilot fuel and the pilot combustion air at the tip of the pilot air pipe 81 to form a pilot flame.

[0042] Cooling air may be supplied to the gap between the pilot burner 80 and the inner wall tube 50. This allows the fuel gas and thus the fuel supply pipe 10 to be cooled via the inner wall tube 50 by the cooling air, improving the durability of the gas burner 1. The cooling air can utilize 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.

[0043] As described above, the gas burner 1 burns the fuel gas with combustion air in which the oxygen concentration has been reduced by mixing with the combustion exhaust gas from the furnace downstream of the air outlet 40, and therefore can lower the combustion temperature and suppress the generation of nitrogen oxides. In particular, the gas burner 1 discharges the fuel gas from the outlet nozzle 70 in a state in which the fuel gas has a velocity component in the combustion air ejection direction, so that the fuel gas moves quickly downstream in the combustion air ejection direction. Therefore, the gas burner 1 can easily ensure the mixing area and mixing time of the combustion air and the combustion exhaust gas, and can reduce the amount of unburned material remaining.

[0044] In the boiler 100, the gas burner 1 is disposed in a space surrounded by a plurality of water tubes 111, so that the flow of the combustion air is not biased in the circumferential direction. Therefore, a uniform low-pressure area is formed in the circumferential direction outside the jet of the combustion air, and the combustion exhaust gas in the furnace is entrained in the combustion air, so that the generation of nitrogen oxides can be reliably suppressed while the generation of unburned matter can be suppressed. In addition, the boiler 100 employs a boiler body 110 that defines a flow path for flowing the combustion exhaust gas of the gas burner 1 in the axial direction of the plurality of water tubes 111, so that the flow rate in the axial direction is not biased and the formation of local high-temperature parts due to combustion can be suppressed, and the pressure loss in the boiler body 110 can be reduced, which has the effect of suppressing the energy of the blower and also has the effect of reducing the supply pressure of the fuel gas. Therefore, the boiler 100 can efficiently generate steam while suppressing the generation of nitrogen oxides.

[0045] Next, a gas burner 1A according to a second embodiment of the present invention will be described. Fig. 4 is a cross-sectional view showing the configuration of the gas burner 1A. In the following description, the same components as those in the previously described embodiment are given the same reference numerals, and duplicated descriptions may be omitted. This gas burner 1A can be used in place of the gas burner 1 in the boiler 100 of Fig. 1.

[0046] The gas burner 1A of this embodiment comprises a fuel supply pipe 10 extending in a predetermined combustion air ejection direction, a wind box 20 arranged to surround the upstream portion of the fuel supply pipe 10, an air supply pipe 30 extending from the wind box 20 so as to be positioned outside the fuel supply pipe 10, a single air ejection port 40A provided at the tip of the air supply pipe 30 so as to be positioned around the fuel supply pipe 10, an inner wall pipe 50A arranged inside the fuel supply pipe 10, an annular sealing plate 60A that seals the gap between the fuel supply pipe 10 and the inner wall pipe 50A at the tip of the fuel supply pipe 10, a plurality of outflow nozzles 70A extending from the fuel supply pipe 10 downstream of the air ejection port 40 in the combustion air ejection direction, and a pilot fuel pipe 82 arranged inside the inner wall pipe 50A.

[0047] The air outlet 40A is disposed on the outer periphery of the fuel supply pipe 10, and is a gap between the air supply pipe 30 and a restricting member 43 that restricts the flow path of the combustion air. The restricting member 43 may have a configuration including 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 in parallel with the air supply pipe 30 to the same position in the combustion air outlet direction as the tip of the air supply pipe 30. Therefore, the air outlet 40A is an annular opening in the combustion air outlet direction at the tip of the gap between the air supply pipe 30 and the guide tube portion 45.

[0048] It is preferable that the restricting member 43 is not fixed to the air supply pipe 30, more specifically, that the guide tube portion 45 and the air supply pipe are not connected by a spacer or the like. With this configuration, when the flow rates of the fuel gas and combustion air are increased during high load, the area of ​​the air outlet 40 increases due to thermal expansion of the air supply pipe 30 as the temperature rises, so that the pressure loss of the combustion air can be reduced and the increase in energy consumption of the blower can be suppressed.

[0049] The inner wall tube 50A does not have an expanded diameter portion and extends to the end with the same diameter. In the gas burner 1A, pilot combustion air is supplied between the inner wall tube 50A and the pilot fuel tube 82. That is, the inner wall tube 50A in this embodiment defines a flow path for the pilot combustion air. Therefore, in the gas burner 1A, the fuel supply tube 10 is indirectly cooled by cooling the fuel gas through the inner wall tube with the pilot combustion air. Therefore, in the gas burner 1A, it is preferable to supply pilot combustion air even when the pilot flame is not formed. In this case, the flow rate of the combustion air to be ejected from the air ejection port 40A may be reduced by the flow rate of the pilot air.

[0050] The sealing plate 60A terminates the gap between the fuel supply pipe 10 and the inner wall pipe 50A, which serves as a flow path for the fuel gas, upstream of the position where the outflow nozzle 70A extends from the fuel supply pipe 10 in the middle of the fuel supply pipe 10. The outflow nozzle 70A is connected to the sealing plate 60A, and an opening for outflowing the fuel gas is formed in the connected outflow nozzle 70A.

[0051] The outflow nozzle 70A is connected to the sealing plate 60A inside the fuel supply pipe 10, extends from the sealing plate 60A in the combustion air ejection direction, bends radially outward inside the fuel supply pipe 10, and extends through the fuel supply pipe 10. The outflow nozzle 70A penetrates an opening formed in the fuel supply pipe 10 and is not directly fixed to the fuel supply pipe. In other words, the outflow nozzle 70A is fixed to the sealing plate 60A that is not exposed to flames, and is not fixed to the tip portion of the fuel supply pipe 10 that is exposed to flames and becomes hot. For this reason, there is no connection between the fuel supply pipe 10 and the outflow nozzle 70A where thermal stress can concentrate, and therefore the gas burner 1A has excellent durability.

[0052] Although the preferred embodiment of the heat supply system according to the present invention has been described above, the present invention is not limited to the above-described embodiment and can be modified as appropriate.

[0053] In the case of a configuration in which the outflow nozzle is connected to a sealing plate that seals the gap between the fuel supply pipe and the inner wall pipe, particularly when a pilot burner having a pilot air pipe and a pilot fuel pipe is provided inside the inner wall pipe, the inner wall pipe may terminate upstream of the fuel supply pipe. [Explanation of symbols]

[0054] 1,1A gas burner 10 Fuel supply pipe 20 Wind Box 30 Air supply pipe 40,40A Air outlet 41 Termination plate 42 Short tube 43 Restriction member 44 Flange part 45 Guide tube part 50,50A inner wall pipe 51 Expanded diameter part 60,60A sealing plate 70,70A Outlet nozzle 71 Fuel outlet 80 Pilot Burner 81 Pilot air pipe 82 Pilot fuel line 100 Boiler 110 Can body 111 Water pipe

Claims

1. a fuel supply pipe extending in a predetermined combustion air ejection direction and through which a fuel gas is supplied; an air outlet that is disposed around the fuel supply pipe and that ejects combustion air in the combustion air ejection direction; a plurality of outlet nozzles extending from the fuel supply pipe so as not to protrude beyond the air outlet and at an acute angle with respect to the combustion air outlet direction, the tips of the outlet nozzles constituting fuel outlets through which the fuel gas flows out; Equipped with A gas burner, wherein a distance in a combustion air ejection direction from the air ejection port to a center of the fuel outlet is 3 to 15 times the equivalent diameter of the air ejection port.

2. a fuel supply pipe extending in a predetermined combustion air ejection direction and through which a fuel gas is supplied; an air outlet that is disposed around the fuel supply pipe and that ejects combustion air in the combustion air ejection direction; a plurality of outlet nozzles extending from the fuel supply pipe so as not to protrude beyond the air outlet and at an acute angle with respect to the combustion air outlet direction, the tips of the outlet nozzles constituting fuel outlets through which the fuel gas flows out; an inner wall pipe disposed inside the fuel supply pipe and limiting a cross section of the fuel gas flow path to an annular shape; Equipped with The inner wall pipe has a diameter expansion portion that expands in diameter so as to reduce a flow passage cross-sectional area of ​​the fuel gas upstream of the outlet nozzle.

3. a fuel supply pipe extending in a predetermined combustion air ejection direction and through which a fuel gas is supplied; an air outlet that is disposed around the fuel supply pipe and that ejects combustion air in the combustion air ejection direction; a plurality of outlet nozzles extending from the fuel supply pipe so as not to protrude beyond the air outlet and at an acute angle with respect to the combustion air outlet direction, the tips of the outlet nozzles constituting fuel outlets through which the fuel gas flows out; an inner wall pipe disposed inside the fuel supply pipe and limiting a cross section of the fuel gas flow path to an annular shape; a ring-shaped sealing plate disposed midway in the fuel supply pipe for sealing a gap between the fuel supply pipe and the inner wall pipe; Equipped with A gas burner, wherein the outlet nozzle extends from the sealing plate through the fuel supply pipe and is not directly fixed to the fuel supply pipe.

4. 4. The gas burner according to claim 1, wherein the fuel outlet is disposed within an outermost portion of an outer edge of the air outlet from the fuel supply pipe when viewed in the combustion air outlet direction.

5. 5. The gas burner according to claim 1, wherein a diameter of an imaginary circumscribing circle of said air nozzle is less than twice an outer diameter of said fuel supply pipe.

6. A gas burner according to any one of claims 1 to 5; a can body that is disposed so as to surround the gas burner, has a plurality of water tubes that extend in the direction of ejection of the combustion air, and defines a flow path through which the combustion exhaust gas from the gas burner flows in the axial direction of the plurality of water tubes; A boiler equipped with

7. The boiler according to claim 6 , wherein a diameter of an imaginary circle connecting centers of the air jets is greater than 0.15 times and less than 0.7 times a diameter of the inner space of the boiler body.

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