Burner

Abstract

To provide a burner capable of stabilizing a flame regardless of a combustion state.SOLUTION: A burner 2 includes: a first air flow passage 51 in which combustion air flows; a second air flow passage 52 in which the combustion air is supplied to surround the first air flow passage 51 and in which a plurality of air nozzles 31 are provided at a tip; a fuel gas flow passage 53 for supplying the fuel gas to a portion between the first air flow passage 51 and the second air flow passage 52; and fuel gas pipes 40 each extending from a communication part 32 between the fuel gas flow passage 53 and the second air flow passage 52 to the air nozzle 31. A jet hole 43 of the fuel gas pipe 40 is located on the upstream side of a jet hole 33 of the air nozzle.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] BACKGROUND ART Conventionally, there has been a premix combustion type gas burner that is provided with an inner air passage and an outer air passage surrounding it, and that ejects fuel into the outer air passage (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-212599 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional gas burners, when the flow rate of the combustion gas flowing through the combustion chamber becomes low, for example, during low combustion, a flame stabilization section for stable combustion cannot be formed in the outer air flow passage, which can increase the frequency of oscillating combustion and can make it difficult to suppress the generation of carbon monoxide (CO).In response to this, for example, it is possible to stabilize the flame by controlling the flame temperature to a high temperature, but in this case the amount of nitrogen oxides (NOx) generated increases, making it impossible to achieve low NOx.

[0005] The present invention has been devised in view of the above circumstances, and aims to provide a burner that can stabilize the flame regardless of the combustion state. [Means for solving the problem]

[0006] In order to achieve the above object, a burner according to one aspect of the present invention includes a first air flow passage through which combustion air flows, a second air flow passage to which combustion air is supplied so as to surround the first air flow passage and which has a plurality of air nozzles at its tip, a fuel gas flow passage through which fuel gas is supplied between the first air flow passage and the second air flow passage, and a fuel gas pipe extending from a communication portion between the fuel gas flow passage and the second air flow passage to the air nozzle, and an outlet of the fuel gas pipe is located upstream of the outlet of the air nozzle. The fuel gas pipe is provided with a through hole leading to the fuel gas outlet.

[0007] According to the above configuration, the outlet of the fuel gas pipe is located upstream of the outlet of the air nozzle, so a circulating flow that entrains the air-fuel mixture can be generated at the tip of the fuel gas pipe. Furthermore, a circulating flow that entrains the air-fuel mixture can also be generated between the downstream side of the first air flow passage and the downstream side of the air nozzle. This improves flame stability regardless of the combustion state, and suppresses the occurrence of oscillating combustion, carbon monoxide (CO), and nitrogen oxides (NOx). Furthermore, since the combustion air and the fuel gas can be mixed in advance on the upstream side of the fuel gas pipe, the mixing efficiency can be improved and the flame can be made more stable.

[0010] Preferably, the air nozzle is a portion of the second air flow path that has a smaller cross-sectional area than the portion leading to the air nozzle, and the through hole is provided in a position opposite the inner surface of the air nozzle.

[0011] According to the above configuration, the gas flow velocity increases on the inner surface of the air nozzle, which has a small cross-sectional area, thereby further improving the mixing efficiency of the combustion air and fuel gas and making the flame more stable. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram illustrating a cross section of a boiler equipped with a burner. [Figure 2] FIG. 2 is an enlarged cross-sectional view for explaining a cross section of a burner. [Figure 3] FIG. 2 is a bottom view of the burner seen from below. [Figure 4]FIG. 10 is a diagram showing an example of a location where a circulating flow occurs. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A schematic configuration of a boiler 1 according to this embodiment will be described with reference to Fig. 1. Note that the present invention is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included in the present invention.

[0014] FIG. 1 shows a boiler body 3, one of the components of a boiler 1, which burns fuel to generate steam. The boiler body 3 is formed in a substantially cylindrical shape and includes a gas burner 2 for burning fuel, multiple water tubes 4, an upper header 6, and a lower header 5. Each of the multiple water tubes 4 is connected between the upper header 6 and the lower header 5. The multiple water tubes 4 are housed inside the boiler body 3 and include inner water tubes 4a that are erected at predetermined intervals in the circumferential direction of the boiler body 3, and outer water tubes 4b that are erected at predetermined intervals in the circumferential direction of the boiler body 3 outside the inner water tubes 4a. These inner water tubes 4a and outer water tubes 4b are collectively referred to as water tubes 4. Inner vertical fins 4a' are provided in the gaps between adjacent inner water tubes 4a, leaving gaps at their lower ends, to close the gaps. For the outer water tubes 4b, outer vertical fins 4b' are provided in the gaps between adjacent water tubes 4b, leaving gaps at the upper ends so as to close the gaps. As a result, a combustion chamber 8 and a combustion gas passage 9 are formed in approximately the center of the boiler body 3. Exhaust gas sent from the combustion gas passage 9 is discharged to the outside of the boiler body 3 through the exhaust passage 7.

[0015] The gas burner 2 is provided above the combustion chamber 8. The gas burner 2 heats boiler water introduced into the multiple water tubes 4 to generate steam. The gas burner 2 is supplied with combustion air from an air supply device and fuel gas from a fuel supply device. The air supply device includes a blower, and the fuel supply device includes a flow control valve. The combustion amount of the boiler 1 is adjusted continuously or in stages by a control device that controls the operation and behavior of the boiler 1, by controlling the blower and the flow control valve in a manner according to the combustion state (combustion amount). For example, when the combustion state is a high combustion state, the opening degree of the flow control valve is controlled to 100%, and when the combustion state is a low combustion state in which the combustion amount is smaller than that of the high combustion state, the opening degree of the flow control valve is controlled to 50%.

[0016] The lower header 5 is provided at the bottom of the boiler body 3 and is connected to the lower parts of the multiple water pipes 4. The lower header 5 is connected to a water supply line 61 that supplies water to the boiler body 3. A water supply pump 63 and a check valve 64 are provided upstream of the water supply line 61. Water is supplied from the water supply pump 63 to the lower header 5 via the water supply line 61, and the supplied water is heated in the water pipes 4. The upper header 6 is provided at the top of the boiler body 3 and is connected to the upper parts of the multiple water pipes 4. The water heated inside the multiple water pipes 4 becomes steam and is supplied from the upper header 6 via a steam supply pipe 62 to various devices that use steam.

[0017] In the boiler 1 of this embodiment, first, a combustible air-fuel mixture supplied from the gas burner 2 is combusted in the combustion chamber 8. The combustion gas generated by the combustion of the combustible air-fuel mixture in the combustion chamber 8 heats the water flowing inside the multiple water tubes 4 (inner water tube 4a) arranged to surround the combustion chamber 8. Next, the combustion gas passes through a combustion gas passage 9 from a gap formed in the lower part of the combustion chamber 8, and further heats the water flowing inside the multiple water tubes (inner water tube 4a and outer water tube 4b). The combustion gas that has passed through the combustion gas passage 9 is then discharged to the outside through an exhaust passage 7 formed in the upper part of the boiler body 3.

[0018] Next, the gas burner 2 will be described. As shown in Figures 2 and 3, the gas burner 2 includes a pilot burner 11, a cylindrical first cylindrical portion 10 arranged to cover the outside of the pilot burner 11, a cylindrical second cylindrical portion 20 (also shown by a dotted line in Figure 3 for convenience of explanation) arranged outside the first cylindrical portion 10 (having a larger diameter than the first cylindrical portion 10), a cylindrical third cylindrical portion 30 arranged outside the second cylindrical portion 20 (having a larger diameter than the second cylindrical portion 20), a first lid portion 12 provided below the pilot burner 11 and closing a portion of the inside of the first cylindrical portion 10, and a second lid portion 22 that closes from the tip of the first cylindrical portion 10 to the tip of the second cylindrical portion 20 and also closes a portion from the tip of the second cylindrical portion 20 to the tip of the third cylindrical portion 30.

[0019] The area within the first cylindrical section 10 excluding the pilot burner 11 forms a first air flow path 51 to which the pilot burner 11 and combustion air used in primary combustion, which will be described later, are supplied. The area outside the first cylindrical section 10 and inside the second cylindrical section 20 forms a fuel gas flow path 53 to which fuel gas is supplied. The area outside the second cylindrical section 20 and inside the third cylindrical section 30 form a second air flow path 52 to which combustion air used in secondary combustion, which will be described later, is supplied. Therefore, the second air flow path 52 can be said to be a flow path that supplies combustion air so as to surround the first air flow path 51. Furthermore, the fuel gas flow path 53 can be said to be a flow path that supplies fuel gas between the first air flow path 51 and the second air flow path 52. The first air flow path 51 and the second air flow path 52 are each connected to an air supply device on the upstream side. The fuel gas flow path 53 is connected to a fuel supply device that supplies fuel gas on the upstream side.

[0020] The gas burner 2 also includes a through hole (hereinafter referred to as the first through hole) 21 formed in the wall surface of the first cylindrical portion 10 adjacent to the combustion chamber 8 (the wall surface downstream of the first lid portion 12), an opening 13 formed in the center of the first lid portion 12, and multiple holes 14 opened at intervals radially around the opening 13 of the first lid portion 12. A plurality of first through holes 21 are formed at intervals in the circumferential direction of the fuel gas flow path 53. Each of the multiple first through holes 21 supplies fuel gas supplied from the fuel gas flow path 53 to the combustion chamber 8 below (downstream of) the opening 13. The opening 13 and the multiple holes 14 each supply combustion air supplied from the first air flow path 51 to the combustion chamber 8. As a result, the combustion air and fuel gas are mixed in the combustion chamber 8 below the opening 13 to generate a combustible mixture.

[0021] On the other hand, the pilot burner 11 provided in the first cylindrical portion 10 extends vertically (up and down) so as to overlap with the central axis X of the can body 3 as shown in Fig. 1, and is disposed so that its tip is close to the opening 13 of the first lid portion 12. The pilot burner 11 ignites the combustible air-fuel mixture generated below the opening 13, and starts combustion in the combustion chamber 8 (hereinafter also referred to as primary combustion).

[0022] The gas burner 2 also includes air nozzles 31 that form outlets (hereinafter also referred to as first outlets) 33 that eject combustion air supplied from the second air passage 52 into the combustion chamber 8. As shown in FIG. 3, a plurality of air nozzles 31 are formed at equal intervals in the circumferential direction of the second cover portion 22. Each of the plurality of air nozzles 31 is a cylindrical member whose diameter is smaller than the width of the second air passage 52 (the distance between the second cylindrical portion 20 and the third cylindrical portion 30). Therefore, the cross-sectional area of ​​the plurality of air nozzles 31 is narrowed down to be smaller than the portion of the second air passage 52 leading to the air nozzle 31.

[0023] Furthermore, the second cylindrical portion 20 is provided with communication holes (corresponding to communication portions) 32 that communicate with the fuel gas flow path 53 at positions upstream of each of the plurality of air nozzles 31. Similar to the plurality of air nozzles 31, the communication holes 32 are formed at equal intervals in the circumferential direction. The gas burner 2 is provided with a plurality of fuel gas pipes 40 that are connected to each of the plurality of communication holes 32 and extend from each communication hole 32 toward the air nozzle 31 located downstream.

[0024] As shown in FIG. 2 , each of the fuel gas pipes 40 has a wall 42 extending from its end (most downstream side, tip) in the direction of the central axis of the fuel gas pipe 40. The wall 42 extends a predetermined length in a direction perpendicular to the pipe member (tube member) of the fuel gas pipe 40. As a result, at the end of each of the fuel gas pipes 40, a circular outlet (hereinafter also referred to as a second outlet) 43 is formed by the central end of the wall 42, as shown in FIG. 3 . Furthermore, the second outlet 43 of each of the fuel gas pipes 40 is positioned slightly upstream of the edge (dotted line) of the first outlet 33 of the air nozzle 31. Note that the wall 42 is made of a member having the same material and thickness as the pipe member (for example, by bending the tip of the pipe member), which facilitates processing of the tip of the fuel gas pipe 40.

[0025] Furthermore, through holes (hereinafter also referred to as second through holes) 41 are formed in the plurality of fuel gas pipes 40 until they reach the second outlets 43. In this embodiment, the second through holes 41 are formed at positions facing the inner surface of the air nozzle 31 and in a direction perpendicular to the inner wall of the air nozzle 31. Furthermore, the plurality of second through holes 41 are formed at equal intervals in the circumferential direction of the fuel gas pipe 40.

[0026] As a result, fuel gas supplied from the fuel gas flow path 53 can be ejected through the multiple fuel gas pipes 40 from the second through holes 41 onto the inner wall of the air nozzle 31, and can also be ejected from the second ejection ports 43 located slightly upstream of the nozzle ejection ports 33 of the air nozzle 31. As a result, in the combustion chamber 8 below the air nozzle 31, the combustion air and the fuel gas are mixed to generate a combustible mixture, which is ignited by primary combustion gas (flame) generated by primary combustion below the opening 13, thereby starting combustion (hereinafter also referred to as secondary combustion). Note that the ratio of the amount of combustion between the primary combustion and the secondary combustion is such that the amount of combustion generated on the secondary combustion side is greater than the amount of combustion in the primary combustion, for example, a ratio of 1:9, and the numbers and opening areas of the second ejection ports 43 and the second through holes 41 and the first through holes 21 are adjusted.

[0027] In the gas burner 2 of this embodiment, combustion air supplied to the air nozzle 31 via the second air passage 52 is mixed with fuel gas ejected from the second through-hole 41 in a direction perpendicular to the inner wall of the air nozzle 31. Furthermore, the cross-sectional area of ​​the air nozzle 31 is narrowed to be smaller than that of the portion of the second air passage 52 leading to the air nozzle 31, so the flow rate of the combustion air is faster inside the air nozzle 31 than inside the second air passage 52. By mixing the combustion air and fuel gas in this way at the portion inside the air nozzle 31 where the flow rate of the combustion air is faster, it is possible to further improve mixing efficiency.

[0028] Further downstream in the air nozzle 31, the air-fuel mixture mixed with the fuel gas ejected from the second through-hole 41 is further mixed with the fuel gas ejected from the second outlet 43. In this embodiment, the second outlet 43 is located upstream of the first outlet 33 of the air nozzle 31. This makes it possible to generate a circulating flow that entrains the air-fuel mixture between the fuel gas ejected downward from the second outlet 43 at the tip of the fuel gas pipe 40 and the air-fuel mixture supplied downward from between the tip of the fuel gas pipe 40 and the air nozzle 31 (see the area enclosed by dotted lines shown as circulating flow A in FIG. 4). This promotes mixing of the combustion air and the combustion gas at the tip of the fuel gas pipe 40 before supplying them into the combustion chamber 8, thereby improving flame stability and suppressing the generation of carbon monoxide (CO) and nitrogen oxides (NOx). In this embodiment, the wall portion 42 is formed to surround the second nozzle 43, so that the distance between the fuel gas ejected downward from the second nozzle 43 and the tip of the fuel gas pipe 40 and the air nozzle 31 can be increased, and as a result, a larger circulating flow can be generated, thereby further improving the mixing efficiency.

[0029] In the combustion chamber 8, the combustible mixture for primary combustion supplied below the first cover portion 12 and the combustible mixture for secondary combustion ejected from the second ejection port 43 each flow as shown by the dotted arrows in Fig. 4. This makes it possible to generate a large circulating flow that entrains the combustible mixture between the combustible mixture for primary combustion supplied below the first cover portion 12 and the combustible mixture for secondary combustion ejected from the second ejection port 43, that is, between the downstream side of the first cover portion 12 and the downstream side of the air nozzle 31 (see the area enclosed by dotted lines shown as circulating flow B in Fig. 4). This further promotes mixing of the combustion air and combustion gas in the combustion chamber 8, further improving the stability of the flame in the combustion chamber 8 and suppressing the generation of carbon monoxide (CO) and nitrogen oxides (NOx). The combustible mixture ejected from the first outlet 33 (air nozzle 31) and mixed is ignited by the primary combustion gas (flame) generated by the primary combustion downstream of the first air flow path 51, and undergoes secondary combustion.

[0030] As described above, in this embodiment, the second outlet 43 of the fuel gas pipe 40 is located upstream of the first outlet 33 of the air nozzle 31, so a circulating flow that entrains the air-fuel mixture can be generated at the tip of the fuel gas pipe 40. A circulating flow that entrains the air-fuel mixture can also be generated between the downstream side of the first air flow passage 51 and the downstream side of the air nozzle 31. This improves flame stability regardless of the combustion state (or the flow rate of the combustion gas, etc.), and suppresses the occurrence of oscillating combustion, the generation of carbon monoxide (CO), and the generation of nitrogen oxides (NOx). Furthermore, generating circulating flows at multiple locations allows efficient mixing even when the flow rate of the combustion gas is low, such as during low combustion, and further improves flame stability.

[0031] Furthermore, the cross-sectional area of ​​the air nozzle 31 is narrowed down to be smaller than that of the second air flow passage 52 up to the air nozzle 31, and the second through-hole 41 is provided in the fuel gas pipe 40 at a position facing the inner surface of the air nozzle 31, so that the combustion air and fuel gas can be mixed in advance also upstream of the fuel gas pipe 40. This further improves the mixing efficiency and stabilizes the flame, thereby further reducing the generation of carbon monoxide.

[0032] The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. Modifications of the above-described embodiment that can be applied to the present invention will be described below.

[0033] In the above embodiment, an example has been described in which the second outlet 43 of the fuel gas pipe 40 is located slightly upstream of the first outlet 33 of the air nozzle 31, but the position of the second outlet 43 of the fuel gas pipe 40 may be any position within the air nozzle 31, and may be, for example, an intermediate position in the flow direction of the air nozzle 31. If the second outlet 43 of the fuel gas pipe 40 is located within the air nozzle 31, a circulating flow can be generated at the tip of the fuel gas pipe 40 (including, for example, within the air nozzle 31), and mixing efficiency can be improved.

[0034] In the above embodiment, an example has been described in which the wall 42 is formed to surround the second outlet 43, but the wall 42 may not be formed. Even in this case, a gap corresponding to the thickness of the fuel gas pipe 40 is generated between the fuel gas ejected downward from the second outlet 43, the tip of the fuel gas pipe 40, and the air nozzle 31, so that a circulating flow can be generated within the air nozzle 31.

[0035] The boiler 1 in the above embodiment has been described as using gas (gaseous fuel) as fuel. This gaseous fuel is not limited to natural gas, hydrogen gas, coal gas, or any other gasified fuel. Furthermore, the fuel used in the boiler 1 is not limited to gaseous fuel, and may be liquid fuel.

[0036] In the boiler 1 in the above embodiment, an example has been described in which the first air flow path 51, the second air flow path 52, and the fuel gas flow path 53 are formed between three cylindrical sections (first cylindrical section 10, second cylindrical section 20, and third cylindrical section 30) of different diameters, but this is not limited to this, and the first air flow path 51, the second air flow path 52, and the fuel gas flow path 53 may be formed by dedicated pipes or ducts, etc., provided corresponding to each flow path.

[0037] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0038] 1 boiler 2 gas burners 3 Can body 4 water tube 4a Inner water tube 4b Outside water pipe 4a´ Inner longitudinal fin 4b´ Outer longitudinal fin 5 Bottom Header 6 Top Header 7 Exhaust passage 8 Combustion chamber 9 Combustion gas passage 10 First cylinder part 11 Pilot Burner 12 1st lid part 13 Opening 14 porous 20 Second cylinder part 21 Through hole 22 Second lid part 30 Third cylinder part 31 Air nozzle 32 Communication hole 33 1st spout 40 Fuel gas pipe 41 Second through hole 42 Wall 43 2nd spout 51 first air flow path 52 second air flow path 53 Fuel gas flow path 61 Water Supply Line 62 Steam supply pipe 63 Water supply pump 64 Check valve

Claims

1. a first air flow path through which combustion air flows; a second air flow path to which combustion air is supplied so as to surround the first air flow path and which has a plurality of air nozzles at its tip; a fuel gas flow path through which fuel gas is supplied between the first air flow path and the second air flow path; a fuel gas pipe extending from a communication portion between the fuel gas flow path and the second air flow path to the air nozzle, an outlet of the fuel gas pipe is located upstream of an outlet of the air nozzle; The burner, wherein the fuel gas pipe is provided with a through hole at a portion leading to the fuel gas pipe outlet.

2. the air nozzle is a portion of the second air flow path that has a smaller cross-sectional area than a portion of the second air flow path leading to the air nozzle, The burner according to claim 1 , wherein the through-hole is provided at a position facing an inner surface of the air nozzle.

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