Multi-fuel burner

Abstract

To provide a mixed combustion burner capable of suppressing increase in a generation amount of nitrogen oxide (NOx) when reducing an oxidizer ratio such as an air ratio.SOLUTION: A mixed combustion burner includes a first injection hole for injecting first fuel into a furnace, and a second injection hole second fuel which is different in a flame propagation speed from the first fuel, into the furnace so as to cause local mixed combustion with the first fuel, the first injection holes being plurally formed at predetermined spaces in a peripheral face part of a cylindrical body coaxially provided at an end of a first fuel supply pipe, the second injection holes being formed at ends of second supply pipes plurally arranged annularly at predetermined spaces around the first fuel supply pipe and the cylindrical body. More oxidizer is supplied into a region deviating from a mixed combustion region for the first fuel and the second fuel where the first fuel is only injected, than into the mixed combustion region.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a multi-fuel burner. [Background technology]

[0002] The following Patent Document 1 discloses a forced once-through burner that aims to provide a forced once-through boiler that can suppress the generation of NOx without reducing thermal efficiency. As described in claim 1 of Patent Document 1, this forced once-through burner is an asymmetric combustion burner that injects air-rich combustion gas and fuel-rich combustion gas in parallel in a forced once-through boiler in which the furnace wall is composed of evaporation tubes arranged vertically in an inner and outer double cylinder and a burner is provided in the upper center of the furnace chamber, and is attached so that a flame caused by the air-rich combustion gas is formed on the side of the slit that introduces the combustion gas between the inner and outer double evaporation tubes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-60302 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, although the above-mentioned background art can suppress the generation of NOx in the combustion gas without reducing the thermal efficiency of the forced once-through boiler, there is a tendency for the amount of NOx generated to increase as the ratio of the theoretical air volume to the amount of supplied air (air ratio) decreases. When attempting to operate a boiler in a combustion region with a relatively low air ratio, the tendency for the amount of NOx generated to increase in opposition to the reduction in the air ratio is an important technical issue that must be resolved.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a multi-fuel burner that can suppress the increase in the amount of nitrogen oxides (NOx) generated when the oxidizer ratio, such as the air ratio, is reduced. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention employs, as a first solution relating to a co-combustion burner, a means including a first injection hole for injecting a first fuel into a furnace, and a second injection hole for injecting a second fuel, the second fuel having a flame propagation speed different from that of the first fuel, into the furnace so as to be locally co-combusted with the first fuel, and supplying more oxidizer to a region outside the co-combustion region of the first fuel and the second fuel than to the co-combustion region.

[0007] The present invention employs, as a second solution related to a multi-fuel burner, a solution according to the first solution, in which the first injection hole and the second injection hole inject the first fuel and the second fuel into the furnace so that they locally intersect.

[0008] The present invention employs, as a third solution for a multi-fuel burner, the second solution described above, in which the first injection holes are provided in a plurality of positions at predetermined intervals in the circumferential direction of the cylindrical surface, and the second injection holes are provided in a plurality of positions at predetermined intervals in the circumferential direction in a flame stabilizing ring provided on the outer periphery of the cylindrical surface in an orientation perpendicular to the cylindrical surface.

[0009] The present invention employs, as a fourth solution for a multi-fuel burner, the third solution described above, in which a notch is formed in the flame stabilizing ring within a predetermined angular range around a center, and the notch is located on the exhaust side of the combustion gas in the furnace.

[0010] The present invention employs, as a fifth solution related to a multi-fuel burner, any one of the first to fourth solutions described above, where the first fuel is fossil fuel gas and the second fuel is hydrogen gas.

[0011] In the present invention, as a solution relating to a boiler, a solution is adopted in which the multi-fuel burner relating to the above-mentioned fifth solution is mounted on a furnace. Effect of the Invention

[0012] According to the present invention, it is possible to provide a multi-fuel burner capable of suppressing an increase in the amount of nitrogen oxides (NOx) generated when the oxidizer ratio, such as the air ratio, is reduced. [Brief description of the drawings]

[0013] [Figure 1] 1A and 1B are a side view and a front view showing the configuration of a once-through boiler A according to one embodiment of the present invention. [Diagram 2] 1A, 1B, and 1C are a front view, a bottom view, and a partially enlarged view, respectively, showing the configuration of a multi-fuel burner 2 according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a cross-sectional view showing the internal configuration of a boiler body (furnace) in one embodiment of the present invention. [Figure 4] FIG. 2 is a characteristic diagram showing the performance of the multi-fuel burner 2 according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, the once-through boiler A according to this embodiment at least comprises a boiler body 1, a multi-fuel burner 2, and a fuel gas receiving section 3. The boiler body 1 is a hollow cylindrical body with a bottom, and is fixed onto a base with its central axis oriented vertically. The multi-fuel burner 2 is attached to the top of the boiler body 1, and the fuel gas receiving section 3 is provided on the side of the boiler body 1.

[0015] Such a boiler body 1 corresponds to the furnace in the once-through boiler A. In other words, the approximately cylindrical and vertical inner space of this boiler body 1 is the combustion chamber of the once-through boiler A. In the inner space (combustion chamber) of the boiler body 1, as shown in Fig. 3, a plurality of water tubes 1a, 1b are arranged in an approximately annular shape near the side wall and extend vertically.

[0016] 3, the water tubes 1a, 1b are arranged in a double configuration around the central axis of the boiler body 1. That is, the water tubes 1a arranged in an annular shape are inner water tubes provided closer to the central axis of the boiler body 1 than the water tubes 1b also arranged in an annular shape. In contrast, the water tubes 1b arranged in an annular shape are outer water tubes provided farther from the central axis of the boiler body 1 than the water tubes 1a also arranged in an annular shape.

[0017] As shown in the figure, the multiple inner water tubes 1a and the multiple outer water tubes 1b are connected to each other when they are adjacent in the circumferential direction. In addition, the multiple inner water tubes 1a connected in the circumferential direction have slits S formed at specific locations in the circumferential direction. These slits S are locations where the circumferentially adjacent inner water tubes 1a are not connected to each other, and form an exhaust flow path for the combustion gas generated in the inner space (combustion chamber) of the boiler body 1.

[0018] Furthermore, the multiple outer water tubes 1b connected in the circumferential direction have a boiler outlet E formed at a specific location in the circumferential direction. This boiler outlet E is a portion where adjacent inner water tubes 1a in the circumferential direction are not connected to each other, and is an exhaust port for combustion gas in the boiler body 1. Furthermore, this boiler outlet E is provided at a position different from the slit portion S in the circumferential direction, for example, at a position offset by an angle of 180 degrees from the slit portion S as shown in the figure.

[0019] In such a boiler body 1, fuel injected from the multi-fuel burner 2 is burned inside the multiple water tubes 1a, 1b to generate combustion gas. This combustion gas passes through the slits S and flows around the outside of the multiple inner water tubes 1a, that is, the inside of the multiple outer water tubes 1b, and is then exhausted to the outside through the boiler outlet E. That is, the combustion gas passes through the inside and outside of all of the inner water tubes 1a and the inside of all of the outer water tubes 1b before being exhausted to the outside.

[0020] Here, as shown in the figure, the once-through boiler A according to this embodiment takes in and burns two different fuels, i.e., fossil fuel gas and mixed-fuel gas, from the outside. That is, this once-through boiler A generates high-temperature combustion gas by injecting the fossil fuel gas and mixed-fuel gas into a combustion chamber from a mixed-fuel burner 2, and vaporizes water flowing through a plurality of water tubes 1a, 1b using the combustion gas as a heat source. The water vapor generated by the vaporization of water is the final product of the once-through boiler A.

[0021] Of the fossil fuel gas and the mixed fuel gas, the fossil fuel gas is the first fuel in the present invention, for example, city gas. The mixed fuel gas is the second fuel in the present invention, for example, hydrogen gas. These two different fuels have the characteristic that they have different flame propagation speeds during combustion.

[0022] That is, the fossil fuel gas and the co-fired fuel gas in this embodiment are selected as examples of fuels with different flame propagation speeds. Therefore, fuels other than the fossil fuel gas and the co-fired fuel gas may be selected as long as they have different flame propagation speeds. Note that it is well known, as described in various documents, that the flame propagation speed of the fossil fuel gas and the flame propagation speed of the co-fired fuel gas are relatively significantly different.

[0023] The mixed-fuel burner 2 is the most characteristic mechanical component of the once-through boiler A, and is attached to the central axis at the top of the boiler body 1. That is, the tip of the mixed-fuel burner 2, which injects fuel into the inner space (combustion chamber) of the boiler body 1, is located a predetermined distance below the top of the boiler body 1.

[0024] The mixed combustion burner 2 is additionally provided with a mixed combustion fuel receiving port 2a that opens to the outside, and is connected to one end of a fuel gas receiving section 3. The mixed combustion burner 2 injects the fossil fuel gas G1 supplied from the fuel gas receiving section 3 and the mixed combustion fuel gas G2 supplied to the mixed combustion fuel receiving port 2a into the combustion chamber, and also injects air (combustion air X) that functions as an oxidizer for the fossil fuel gas G1 and the mixed combustion fuel gas G2 into the combustion chamber, thereby combusting them.

[0025] Such a multi-fuel burner 2 has a detailed structure as shown in Fig. 2. That is, in addition to the above-mentioned multi-fuel receiving port 2a, the multi-fuel burner 2 has a housing 2b, a fossil fuel supply pipe 2c, a cylindrical body 2d, a plurality of multi-fuel supply pipes 2e, and a flame stabilizing ring 2f.

[0026] The housing 2b is a metal member that supports the mixed fuel receiving port 2a, the fossil fuel supply pipe 2c, and the mixed fuel supply pipe 2e, and is fixed to an upper opening formed on the upper part of the boiler body 1. The mixed fuel receiving port 2a is fixed to the outside of the housing 2b, and the fossil fuel supply pipe 2c and the mixed fuel supply pipe 2e are fixed in a vertical position from the outside to the inside.

[0027] The fossil fuel supply pipe 2c is a straight pipe made of metal that extends vertically as shown in the figure. The fuel gas receiving section 3 is connected to the upper end (rear end) of the fossil fuel supply pipe 2c. That is, the fossil fuel supply pipe 2c allows the fossil fuel gas G1 supplied from the fossil fuel supply pipe 2c to flow toward the lower end.

[0028] The cylinder 2d is a hollow metal part provided at the lower end of the fossil fuel supply pipe 2c. The cylinder 2d is formed in a cylindrical shape with a bottom and is provided at the lower end of the fossil fuel supply pipe 2c with its central axis in the vertical direction. The upper end of the cylinder 2d is connected to the fossil fuel supply pipe 2c, and the fossil fuel gas G1 flows from the fossil fuel supply pipe 2c into the internal space.

[0029] The cylindrical body 2d has a disk-shaped lower end closed, and a plurality of fossil fuel gas nozzles 2g are formed at predetermined intervals in the circumferential direction of the annular peripheral surface as shown in the figure. These fossil fuel gas nozzles 2g inject the fossil fuel gas G1 approximately evenly in the circumferential direction of the cylindrical body 2d. Such fossil fuel gas nozzles 2g are the first injection holes in the present invention.

[0030] That is, the multiple fossil fuel gas nozzles 2g inject the fossil fuel gas G1, which is the first fuel, into the furnace, i.e., into the inner space (combustion chamber) of the boiler body 1. The fossil fuel gas G1 flowing from the fossil fuel supply pipe 2c into the upper end of the cylindrical body 2d is injected into the inner space (combustion chamber) of the boiler body 1 through the multiple fossil fuel gas nozzles 2g formed on the circumferential surface of the cylindrical body 2d.

[0031] The multiple mixed fuel supply pipes 2e are straight metal pipes provided at predetermined intervals around the fossil fuel supply pipe 2c and the cylindrical body 2d. The multiple mixed fuel supply pipes 2e each have an upper end (rear end) connected to the mixed fuel receiving port 2a. The multiple mixed fuel supply pipes 2e are also set to have the same vertical position at the tip. The multiple mixed fuel supply pipes 2e allow the mixed fuel gas supplied from the mixed fuel receiving port 2a to flow toward the lower end.

[0032] The flame stabilizing ring 2f is a generally ring-shaped metal member provided to close the lower end of the mixed fuel supply pipe 2e. One side (upper side) of the flame stabilizing ring 2f is connected to the lower end of the mixed fuel supply pipe 2e in a position perpendicular to the mixed fuel supply pipes 2e, and the center is, for example, concentric with the central axis of the boiler body 1. The flame stabilizing ring 2f is provided with mixed fuel gas nozzles 2h at positions that correspond to the tips of the mixed fuel supply pipes 2e.

[0033] These multiple mixed-fuel gas nozzles 2h are openings for injecting the mixed-fuel gas G2 into the combustion chamber, and are second injection holes in the present invention. That is, the multiple mixed-fuel gas nozzles 2h inject the mixed-fuel gas G2 (second fuel) having a flame propagation speed different from that of the fossil fuel gas G1 (first fuel) into the furnace, i.e., into the inner space (combustion chamber) of the boiler body 1, so as to locally mix the mixed-fuel gas G2 with the fossil fuel gas G1 (first fuel).

[0034] The mixed fuel gas G2 received from the outside flows into the upper ends of the multiple mixed fuel supply pipes 2e from the mixed fuel receiving port 2a, and is supplied to the flame stabilizing ring 2f through the insides of the multiple mixed fuel supply pipes 2e. This mixed fuel gas G2 is injected into the combustion chamber from multiple mixed gas nozzles 2h formed in the flame stabilizing ring 2f.

[0035] Further, the generally ring-shaped flame stabilizing ring 2f is formed with a notch K. This notch K is an arc-shaped portion where the base material is missing within a predetermined angular range in the circumferential direction of the flame stabilizing ring 2f, and is positioned so as to face the slit portion S of the boiler body 1 as shown in Fig. 3. The lower end of the multi-fuel supply pipe 2e is not connected to this notch K, and naturally, a multi-fuel gas nozzle 2h is not provided therein.

[0036] In other words, the multiple mixed-fuel gas nozzles 2h are formed in a flame stabilizing ring 2f having a cutout portion K, and are injected into the combustion chamber so that the mixed-fuel gas G2 intersects with the fossil fuel gas G1 only in a localized area of ​​the combustion chamber, in other words, so that the mixed-fuel gas G2 mixes with the fossil fuel gas G1 only in a localized area of ​​the combustion chamber.

[0037] The localized region is the central axis of the boiler body 1, i.e., the central axis of the cylinder 2d, and is also an area in which the flame stabilizing ring 2f exists over a predetermined angle range around the center point of the flame stabilizing ring 2f, as shown in Figures 2(b) and 3. In this area, the mixed-combustion fuel gas G2 is not injected at the notch K of the flame stabilizing ring 2f, and only the fossil fuel gas G1 is injected from the fossil fuel gas nozzle 2g.

[0038] As shown in Figures 2(b) and 3, the notch K is provided in an angular range of 180° or less around the center point of the flame stabilizing ring 2f. The angular range of the notch K is appropriately set in consideration of the amount of nitrogen oxide (Nox) generated, which will be described later. In other words, the angular range of the notch K may be wider or narrower than the angular range shown in Figures 2(b) and 3.

[0039] In Fig. 2, the reference symbol 2i indicates an ignition device. The ignition device 2i is a device for igniting the fossil fuel gas G1 and the mixed-fuel gas G2 injected into the combustion chamber, and is supported by the housing 2b and extends vertically inside the housing 2b. The ignition device 2i ignites the fossil fuel gas G1 and the mixed-fuel gas G2 by generating a spark from a lower end (tip) exposed inside the combustion chamber.

[0040] 1(a), the fuel gas receiving section 3 is provided on the side of the boiler body 1. The fuel gas receiving section 3 has a fossil fuel receiving port 3a at its lower end, and its upper end is connected to the upper end of the fossil fuel supply pipe 2c in the mixed-fuel burner 2. The fuel gas receiving section 3 has a piping structure that supplies the fossil fuel gas G1 received at the fossil fuel receiving port 3a to the mixed-fuel burner 2.

[0041] In addition, in this multi-fuel burner 2, as shown in Fig. 2(a), air, which is an oxidizer, mainly flows into the combustion chamber through the notch K of the flame stabilizing ring 2f. That is, the notch K of the flame stabilizing ring 2f forms an air flow path for supplying more air (oxidizer) to the combustion chamber. Therefore, the amount of air in the region where the flame stabilizing ring 2f is present, i.e., the local region (mixed combustion region) where the fossil fuel gas G1 and the mixed combustion fuel gas G2 are mixed, is less than the amount of air in the region of the notch K of the flame stabilizing ring 2f, i.e., the region where only the fossil fuel gas G1 is injected.

[0042] For example, the amount of air in the mixed combustion region is set to a first amount that is less than the theoretical amount of air for completely combusting the fossil fuel gas G1 and the mixed combustion fuel gas G2, whereas the amount of air in the region of the notch K of the flame stabilizing ring 2f is set to an amount of air that is greater than the first amount.

[0043] Next, the operation, function, and effect of the once-through boiler A and the multi-fuel burner 2 according to the first embodiment will be described with reference to FIG.

[0044] In this once-through boiler A, fossil fuel gas G1 is injected into the combustion chamber from a fossil fuel gas nozzle 2g provided on the multi-fuel burner 2, and multi-fuel gas G2 is injected into the combustion chamber from a nozzle 2h. In this once-through boiler A, combustion air X is mainly supplied to the region of the notch K of the flame stabilization ring 2f. In the combustion chamber, in the region (local region) where the flame stabilization ring 2f exists around the central axis, the fossil fuel gas G1 and the multi-fuel gas G2 cross each other and are mixed and burned, and in the region of the notch K in the flame stabilization ring 2f, only the fossil fuel gas G1 is burned.

[0045] Since the amount of air supplied to the localized region is less than the amount of air supplied to the region of the notch K of the flame stabilizing ring 2f, an excess fuel flame F1 and an excess air flame F2 are formed in the combustion chamber as shown in Fig. 2(a). That is, the excess fuel flame F1 is a flame formed by co-firing the fossil fuel gas G1 and the co-firing fuel gas G2. The excess air flame F2 is a flame formed by burning the fossil fuel gas G1 under excess air.

[0046] Figure 4 is a graph showing the combustion characteristics of such a once-through boiler A. Figure 4(a) shows the amount of nitrogen oxides (Nox) generated depending on the air ratio during combustion, i.e., the oxygen concentration (O2%) contained in the combustion gas. Figure 4(b) also shows the fuel characteristics (density, explosion range, flame temperature, and flame propagation speed) of the mixed-fuel gas G2 (hydrogen gas) and the fossil fuel gas G1 (methane, the main component of city gas) for reference.

[0047] Fig. 4(a) shows the change characteristics of the amount of nitrogen oxides Nox generated when the ratio of fossil fuel gas G1 and co-fired fuel gas G2 is set to 80%:20% in once-through boiler A. Fig. 4(a) also shows, as a reference example, the change characteristics of the amount of nitrogen oxides Nox generated when the forced once-through boiler of Patent Document 1 is used, that is, when only fossil fuel gas G1 is burned.

[0048] 4(a), in the once-through boiler A according to this embodiment, the amount of nitrogen oxides (Nox) generated hardly changes even when the air ratio changes within the range of 1.17 to 1.75. In contrast, in the forced once-through boiler of Patent Document 1, the amount of nitrogen oxides (Nox) generated increases as the oxygen concentration decreases within the air ratio range of 1.17 to 1.75.

[0049] Such a change characteristic of elemental oxides Nox in this embodiment is presumed to be due to the difference in flame propagation speed between the fossil fuel gas G1 and the co-fuel gas G2. That is, when two types of fuels with different flame propagation speeds are burned, the co-fuel gas G2 with the faster flame propagation speed burns first, so that the oxygen supplied to the fossil fuel gas G1 with the slower flame propagation speed is reduced.

[0050] At the same time, sufficient oxygen is not supplied to the mixed fuel gas G2, which has a faster flame propagation speed, and the combustion reaction of the mixed fuel gas G2 is delayed. This suppresses the rise in temperature of the fuel-rich flame F1 as a whole, and reduces the amount of nitrogen oxides (Nox) generated in the combustion gas.

[0051] In addition, since the excess air flame F2 is formed by burning the fossil fuel gas G1 in excess air, the flame temperature is relatively low, and therefore the amount of nitrogen oxides (Nox) generated in the combustion gas is low.

[0052] According to this embodiment, the fossil fuel gas nozzle 2g (first injection hole) injects the fossil fuel gas G1 (first fuel) into the boiler body 1 (furnace), and the mixed-fuel gas nozzle 2h (second injection hole) injects the mixed-fuel gas G2 (second fuel) having a flame propagation speed different from that of the fossil fuel gas G1 (first fuel) into the boiler body 1 (furnace) so as to locally mix with the fossil fuel gas G1 (first fuel). Since the combustion air X (oxidizer) is supplied to a region outside the mixed-fuel region of the fossil fuel gas G1 (first fuel) and the mixed-fuel gas G2 (second fuel) in a larger amount than the mixed-fuel region, it is possible to provide a mixed-fuel burner 2 and a once-through boiler A that can suppress an increase in the amount of nitrogen oxides NOx generated when the air ratio (oxidizer ratio) is reduced.

[0053] In addition, according to this embodiment, the fossil fuel gas nozzle 2g (first injection hole) and the mixed-fuel gas nozzle 2h (second injection hole) inject the fossil fuel gas G1 (first fuel) and the mixed-fuel gas G2 (second fuel) into the boiler body 1 (furnace) so that the fossil fuel gas G1 (first fuel) and the mixed-fuel gas G2 (second fuel) intersect locally, so that the fossil fuel gas G1 (first fuel) and the mixed-fuel gas G2 (second fuel) can be effectively mixed and burned.

[0054] In addition, according to this embodiment, the fossil fuel gas nozzles 2g (first injection holes) are provided in multiple places at predetermined intervals in the circumferential direction of the peripheral surface (cylindrical surface) of the cylindrical body 2d, and the mixed-fuel gas nozzles 2h (second injection holes) are provided in multiple places at predetermined intervals in the circumferential direction in a flame stabilizing ring 2f provided on the outer periphery of the peripheral surface (cylindrical surface) of the cylindrical body 2d in an orientation perpendicular to the peripheral surface (cylindrical surface) of the cylindrical body 2d, so that the fossil fuel gas G1 (first fuel) and the mixed-fuel gas G2 (second fuel) can be effectively mixed and burned.

[0055] Furthermore, according to this embodiment, the flame stabilizing ring 2f has a notch K formed in a predetermined angular range around the center, and this notch K is located on the combustion gas discharge side of the boiler body 1 (furnace), so that the water flowing through the multiple water tubes 1a, 1b can be effectively heated. In other words, according to this embodiment, it is possible to provide a once-through boiler A with excellent thermal efficiency in generating steam.

[0056] The present invention is not limited to the above-described embodiments, and the following modifications are possible. (1) In the above embodiments, the fossil fuel gas G1 (first fuel) and the co-fuel gas G2 (second fuel) having a flame propagation speed faster than that of the fossil fuel gas G1 (first fuel) are used as the two fuels having different flame propagation speeds, but the present invention is not limited to this. For example, a fuel having a flame propagation speed slower than that of the first fuel may be used as the second fuel.

[0057] (2) In the above embodiments, the present invention has been described as being applied to the once-through boiler A, but the present invention is not limited thereto. The multi-fuel burner according to the present invention can also be applied to boilers of types other than the once-through type.

[0058] (3) In each of the above embodiments, the fossil fuel gas G1 (first fuel) and the mixed-fuel gas G2 (second fuel) are mixed by being injected in a direction perpendicular to each other, but the present invention is not limited to this. That is, the relationship between the injection direction of the fossil fuel gas G1 (first fuel) and the injection direction of the mixed-fuel gas G2 (second fuel) is not limited to being perpendicular to each other as long as they intersect at least.

[0059] (4) In each of the above embodiments, the air flow path of the combustion air X for forming the excess air flame F2 is formed by the notch K of the flame stabilizing ring 2f, but the present invention is not limited to this. For example, without providing the notch K, a plurality of injection holes may be provided as the air flow path at a portion of the flame stabilizing ring 2f corresponding to the notch K. In this case, a gas in which the fossil fuel gas G1 (first fuel) and the combustion air X are mixed in an excess air state is injected from the plurality of injection holes into the combustion chamber to form the excess air flame F2. [Explanation of symbols]

[0060] A Once-through boiler E Boiler outlet F1 Fuel Excess Flame F2 Excess air flame G1 Fossil fuel gas (first fuel) G2 Co-fuel gas (second fuel) K Notch S slit section X Combustion air (oxidizer) 1 Boiler body 1a, 1b water pipe 2. Dual-fuel burner 2a Mixed combustion fuel inlet 2b Case 2c Fossil fuel supply pipe 2d cylinder 2e Mixed combustion fuel supply pipe 2f Flame holding ring 2g fossil fuel gas nozzle (first nozzle) 2h Mixed combustion gas nozzle (second nozzle) 3. Fuel gas receiving section

Claims

[Claim 1] a first injection hole for injecting a first fuel into the furnace; a second injection hole that injects a second fuel having a flame propagation speed different from that of the first fuel into the furnace so as to locally mix and burn the second fuel with the first fuel; The first injection holes are formed at a predetermined interval on a peripheral surface of a cylinder provided coaxially at an end of the first fuel supply pipe, the second injection holes are formed at ends of a plurality of second supply pipes arranged annularly at predetermined intervals around the first fuel supply pipe and the cylindrical body; A multi-fuel burner that supplies an oxidizer to a region outside a multi-fuel combustion region of the first fuel and the second fuel and into which only the first fuel is injected, in a larger amount than in the multi-fuel combustion region.

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