JP7803201B2 - Burner - Google Patents

Description

The present invention relates to a burner.

Conventionally, there have been gas burners using a premixed combustion method, which have an inner air passage surrounded by an outer air passage, and inject fuel into the outer air passage (for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2015-212599

However, with conventional gas burners, when the flow rate of the combustion gas flowing through the combustion chamber becomes slow, for example during low combustion, a flame stabilization section for stable combustion cannot be formed in the outer air flow path, which can increase the frequency of oscillating combustion and can make it difficult to suppress the generation of carbon monoxide (CO). While it may be possible to stabilize the flame by controlling the flame temperature to a high temperature, this will increase the amount of nitrogen oxides (NOx) generated, making it impossible to achieve low NOx emissions.

The present invention was conceived in light of this situation, and aims to provide a burner that can stabilize the flame regardless of the combustion state.

In order to achieve the above-mentioned object, a burner according to one aspect of the present invention comprises 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, and 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, wherein the outlet of the fuel gas pipe is located upstream of the outlet of the air nozzle, and a through hole is provided in the fuel gas pipe until it reaches the outlet of the fuel gas pipe.

According to the above configuration, since the outlet of the fuel gas pipe is located upstream of the outlet of the air nozzle, a circulating flow entraining the air-fuel mixture can be generated at the tip of the fuel gas pipe. Furthermore, a circulating flow entraining 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, the generation of carbon monoxide (CO), and the generation of nitrogen oxides (NOx). Furthermore, since the combustion air and fuel gas can be premixed upstream of the fuel gas pipe, mixing efficiency can be improved, resulting in a more stable flame.

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 located opposite the inner surface of the air nozzle.

With the above configuration, the gas flow velocity increases on the inner surface of the air nozzle, which has a small cross-sectional area, further improving the mixing efficiency of the combustion air and fuel gas and making the flame more stable.

FIG. 2 is a diagram illustrating a cross section of a boiler equipped with a burner. FIG. 2 is an enlarged cross-sectional view for explaining a cross section of a burner. FIG. 2 is a bottom view of the burner seen from below. FIG. 10 is a diagram showing an example of a location where a circulating flow occurs.

Embodiments of the present invention will be described below with reference to the drawings. The schematic configuration of a boiler 1 according to this embodiment will be described with reference to Figure 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.

Figure 1 shows the boiler body 3, one of the components of the boiler 1, which burns fuel to generate steam. The boiler body 3 is formed in a roughly 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 around the circumferential direction of the boiler body 3, and outer water tubes 4b that are erected at predetermined intervals around 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, leaving a gap at the upper end to close the gap. This forms a combustion chamber 8 and combustion gas passage 9 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.

The gas burner 2 is located 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 volume of the boiler 1 is adjusted continuously or in stages by a control device that controls the operation and behavior of the boiler 1, controlling the blower and flow control valve in a manner corresponding to the combustion state (combustion volume). For example, when the combustion state is high combustion, the opening of the flow control valve is controlled to 100%, and when the combustion state is low combustion, where the combustion volume is lower than that of the high combustion state, the opening of the flow control valve is controlled to 50%.

The lower header 5 is located 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 located 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 located 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, which is supplied from the upper header 6 via a steam supply pipe 62 to various devices that use steam.

In the boiler 1 of this embodiment, a combustible air-fuel mixture supplied from the gas burner 2 is first 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. The combustion gas then 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.

Next, the gas burner 2 will be described. As shown in Figures 2 and 3, the gas burner 2 comprises a pilot burner 11, a cylindrical first tube portion 10 arranged to cover the outside of the pilot burner 11, a cylindrical second tube portion 20 (also shown by dotted lines in Figure 3 for ease of explanation) arranged outside the first tube portion 10 (with a larger diameter than the first tube portion 10), a cylindrical third tube portion 30 arranged outside the second tube portion 20 (with a larger diameter than the second tube portion 20), a first lid portion 12 located below the pilot burner 11 and covering part of the inside of the first tube portion 10, and a second lid portion 22 covering the area from the tip of the first tube portion 10 to the tip of the second tube portion 20 and covering part of the area from the tip of the second tube portion 20 to the tip of the third tube portion 30.

The area within the first cylindrical section 10, excluding the pilot burner 11, forms the first air flow path 51, to which the pilot burner 11 and combustion air used for primary combustion, described below, are supplied. The area outside the first cylindrical section 10 and inside the second cylindrical section 20 forms the 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 the second air flow path 52, to which combustion air, used for secondary combustion, described below, is supplied. Therefore, the second air flow path 52 can be said to be a flow path that supplies combustion air surrounding 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.

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 tubular 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 circumferentially around 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 mix in the combustion chamber 8 below the opening 13 to generate a combustible mixture.

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 Figure 1, and is positioned so that its tip is close to the opening 13 of the first lid portion 12. The pilot burner 11 ignites the combustible mixture generated below the opening 13, initiating combustion (hereinafter also referred to as primary combustion) in the combustion chamber 8.

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 flow path 52 into the combustion chamber 8. As shown in FIG. 3, multiple air nozzles 31 are formed at equal intervals circumferentially on the second lid portion 22. Each of the multiple air nozzles 31 is a cylindrical member with a diameter 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 multiple air nozzles 31 is narrowed down to be smaller than the portion of the second air flow path 52 leading up to the air nozzle 31.

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

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. The wall 42 is made of a material with 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.

Furthermore, through holes (hereinafter also referred to as second through holes) 41 are formed in the multiple fuel gas pipes 40 on their way to the second nozzles 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, multiple second through holes 41 are formed at equal intervals around the circumference of the fuel gas pipe 40.

This allows fuel gas supplied from the fuel gas flow path 53 to 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 from the second outlets 43 located slightly upstream of the nozzle outlets 33 of the air nozzle 31. As a result, in the combustion chamber 8 below the air nozzle 31, combustion air and fuel gas are mixed to generate a combustible mixture, which is ignited by the primary combustion gas (flame) generated by the primary combustion below the opening 13, initiating combustion (hereinafter also referred to as secondary combustion). Note that the ratio of the amount of combustion generated on the secondary combustion side to the amount of combustion generated on the primary combustion side is greater than that of primary combustion, for example, a ratio of 1:9, and the numbers and opening areas of the second outlets 43 and second through-holes 41 and the first through-holes 21 are adjusted.

In the gas burner 2 of this embodiment, combustion air supplied to the air nozzle 31 via the second air flow path 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, because the cross-sectional area of the air nozzle 31 is narrowed to be smaller than the portion of the second air flow path 52 leading to the air nozzle 31, the flow velocity of the combustion air is faster within the air nozzle 31 than within the second air flow path 52. By mixing the combustion air and fuel gas in this way at the point within the air nozzle 31 where the flow velocity of the combustion air is faster, mixing efficiency can be further improved.

Further downstream within the air nozzle 31, the 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 allows a circulating flow involving the mixture to be generated at the tip of the fuel gas pipe 40 between the fuel gas ejected downward from the second outlet 43 and the mixture supplied downward from between the tip of the fuel gas pipe 40 and the air nozzle 31 (see the dotted-line area shown as circulating flow A in Figure 4). This promotes mixing of the combustion air and combustion gas at the tip of the fuel gas pipe 40 before supplying them into the combustion chamber 8, improving flame stability and suppressing the generation of carbon monoxide (CO) and nitrogen oxides (NOx). In this embodiment, a wall portion 42 is formed to surround the second nozzle 43, which increases 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. As a result, a larger circulating flow can be generated, further improving mixing efficiency.

In addition, in the combustion chamber 8, the combustible mixture for primary combustion supplied below the first lid portion 12 and the combustible mixture for secondary combustion ejected from the second nozzle 43 each flow as shown by the dotted arrows in Figure 4. This allows a large circulating flow involving the combustible mixture to be generated between the combustible mixture for primary combustion supplied below the first lid portion 12 and the combustible mixture for secondary combustion ejected from the second nozzle 43, i.e., between the downstream side of the first lid portion 12 and the downstream side of the air nozzle 31 (see the dotted-line area shown as circulating flow B in Figure 4). This further promotes mixing of the combustion air and combustion gas within the combustion chamber 8, further improving flame stability within 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.

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, allowing a circulating flow that entrains the air-fuel mixture to 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 path 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 for efficient mixing even when the flow rate of the combustion gas is slow, such as during low combustion, further improving flame stability.

In addition, the cross-sectional area of the air nozzle 31 is narrowed down to be smaller than the portion of the second air flow path 52 leading up to the air nozzle 31, and a second through-hole 41 is provided in the fuel gas pipe 40 at a position opposite the inner surface of the air nozzle 31. This allows the combustion air and fuel gas to be mixed in advance even upstream of the fuel gas pipe 40. This further improves mixing efficiency and stabilizes the flame, further reducing the generation of carbon monoxide.

The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. Below, we will explain modifications of the above-described embodiment that can be applied to the present invention.

In the above embodiment, an example was 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. However, the position of the second outlet 43 of the fuel gas pipe 40 may be within the air nozzle 31, and may be, for example, at 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), thereby improving mixing efficiency.

In the above embodiment, an example was described in which a wall portion 42 is formed to surround the second nozzle 43, but a wall portion 42 may not be formed. Even in this case, a gap equal to the thickness of the fuel gas pipe 40 is created 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, making it possible to generate a circulating flow within the air nozzle 31.

In the above embodiment, the boiler 1 has been described as using gas (gaseous fuel) as fuel. This gaseous fuel is not limited to this, and can be any gasified fuel, such as natural gas, hydrogen gas, or coal gas. Furthermore, the fuel used in the boiler 1 is not limited to gaseous fuel, and may also be liquid fuel.

In the boiler 1 in the above embodiment, an example was 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. However, 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 provided corresponding to each flow path.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications that are equivalent in meaning to and within the scope of the claims.

REFERENCE SIGNS LIST 1 Boiler 2 Gas burner 3 Boiler body 4 Water tube 4a Inner water tube 4b Outer water tube 4a' Inner vertical fin 4b' Outer vertical fin 5 Lower header 6 Upper header 7 Exhaust passage 8 Combustion chamber 9 Combustion gas passage 10 First cylindrical portion 11 Pilot burner 12 First lid portion
13 Opening 14 Perforation 20 Second cylindrical portion 21 Through hole 22 Second cover portion 30 Third cylindrical portion 31 Air nozzle 32 Communication hole 33 First outlet 40 Fuel gas pipe 41 Second through hole 42 Wall portion 43 Second outlet 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 (2)

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 . 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.