JP7569211B2 - Premixed gas burner - Google Patents

Description

The present invention relates to a premixing device that premixes fuel gas and combustion air to form a mixture, and a premixed gas burner equipped with a premixing device.

Premix gas burners using metal knit (a porous combustion section made of a woven fabric of ultra-fine metal fibers with a fiber diameter of about 50 μm) have been known for use in boilers and the like (for example, Patent Document 1).

In this type of premixed gas burner, the premix is formed by injecting fuel gas from a gas supply pipe installed in the combustion air passage, so the mixture is mainly caused by diffusing the fuel gas into the combustion air, and the mixture of the two is insufficient. To improve the mixture, a diffuser is installed, or the fuel gas injection hole is narrowed to increase the injection speed, etc., to promote mixing. However, for example, when the pressure in the combustion air passage (the total pressure of the boiler furnace pressure and the diffuser pressure loss) exceeds 1.5 kPa, if the fuel gas supply pressure is low (2.0 kPa), the pressure loss in the gas piping such as the gas shutoff valve is about 0.5 kPa, and the fuel gas cannot be supplied.

Therefore, various mixing devices have been proposed, such as a gas supply pipe using a venturi or a gas supply pipe placed at the intake section of the blower (Patent Documents 2 to 7).

For example, Patent Document 2 discloses a venturi mixer used in a premix gas burner. When combustion air flows at high speed into the venturi throat, the static pressure of the venturi throat decreases in proportion to the square of the flow velocity, as shown by Bernoulli's equation. In response to this, fuel with a constant secondary pressure controlled by a zero governor is sucked in, making it possible to supply fuel gas at a low pressure. The combustion air and fuel gas that pass through the venturi throat are mixed. In Patent Document 2, in order to compensate for the decrease in mixing performance, a swirling flow is applied by a fuel nozzle provided at the outlet of the venturi mixer to achieve rapid mixing. However, this increases pressure loss, so in order to increase the suction force and mixing force of the fuel gas, it is necessary to increase the flow velocity of the venturi throat and increase the pressure difference of the venturi, which results in a larger blower (higher static pressure).

Therefore, in Patent Document 3, multiple fuel supply pipes are arranged to promote turbulence at the inlet of the venturi throat, but the fuel supply pipes have a complex structure and are therefore expensive.

In addition, in Patent Document 4, a gas chamber is formed between the burner duct and the venturi mixer, and the fuel injection part is placed in the vortex generation area of the venturi mixer, promoting mixing through the vortex entrainment effect and obtaining a uniform premixed air-fuel mixture. However, when customizing the fuel injection part by changing the type of fuel, etc., it is difficult to replace it because it is integrated with the burner duct.

In addition, in conventional venturi mixers such as those disclosed in Patent Documents 2 and 4, turbulence in the flow of the supplied combustion air reduces the suction force and causes uneven mixing, so it is necessary to provide some straight pipe sections before and after the venturi mixer to straighten the flow, which makes them unsuitable for compact design.

Therefore, a fan mix type fuel supply device has been proposed in which fuel gas is supplied to the suction side of the blower and the combustion air and fuel gas are mixed inside the blower (Patent Documents 5 and 6). Also, a fuel supply device that combines a fan mix type with a venturi mixer has been proposed (Patent Document 7).

However, in the fuel supply devices disclosed in Patent Documents 5 to 7, the inside of the blower is filled with flammable gas, so the blower housing must be airtight, resulting in an expensive blower dedicated to fan mix. In addition, the duct connecting the blower and burner is also filled with flammable gas, so if the supply flow rate of the mixed gas drops below the flame propagation speed due to some reason such as an operating error, the flame will propagate (backfire) inside the duct to the blower side, which is very dangerous. As a countermeasure, a backfire prevention device and a backfire safety device are installed, but these also contribute to the cost of the blower.

JP 2020-34227 A Japanese Patent Application Publication No. 1-111114 Special Publication No. 2002-534652 Patent No. 2950196 specification Japanese Patent Application Publication No. 10-318526 Japanese Patent Application Publication No. 10-89628 JP 2017-172815 A

The present invention was made in consideration of the problems in the conventional technology described above, and its main objective is to provide a premixing device and a premixed gas burner that can be made compact and low-cost while improving the mixing of fuel gas and combustion air.

To achieve the above object, the present invention provides a premixing device for a premix gas burner that mixes and burns fuel gas and combustion air, and includes a venturi-shaped main body, a gas nozzle in which fuel gas injection holes are arranged within the main body, inlet-side swirl vanes that are provided on the inlet side of the main body and swirl the combustion air supplied to the main body, and outlet-side swirl vanes that are provided on the outlet side of the main body and promote mixing of the fuel gas and the combustion air.

The gas nozzle may be provided to penetrate the inlet side swirl vane.

The inlet side swirl vane may include a central hole for the gas nozzle through which the gas nozzle passes, and a number of vanes arranged to surround the central hole for the gas nozzle.

The inlet side swirl vanes and the outlet side swirl vanes can be configured so that the swirl direction of the passing gas is the same.

The outlet swirl vane may have a central hole and a number of vanes arranged around the central hole.

The opening area of the central hole can be formed at a ratio of 5% to 80% of the cross-sectional area of the flow passage within the main body.

The main body may have a tapered portion that narrows at the tip, a cylindrical throat portion connected to the tapered portion, and a divergent portion connected to the throat portion, and the gas nozzle may be located on the axis of the main body, and the injection hole may be disposed within the throat portion.

A blower for blowing combustion air is provided alongside the main body, and the external dimensions of the main body in the axial direction of the main body can be set smaller than the external dimensions of the blower.

The device may further include a gas damper that adjusts the flow rate of fuel gas sent to the gas nozzle, an air damper that adjusts the flow rate of combustion air sent from the blower to the main body, and a control motor that controls the gas damper and the air damper.

The inlet side swirl vanes can be detachably installed.

The outlet side swirl vanes can be provided removably.

The gas nozzle can be removable.

The system further includes a wind box connected to a blower that supplies air for combustion, the wind box having a removable or openable side panel, and the gas nozzle and inlet side swirl vanes can be removably attached within the wind box.

The premix gas burner according to the present invention also includes the premixing device according to the present invention and a burner head connected to the outlet side of the premixing device.

The premixing device of the premix gas burner of the present invention provides good mixing in a compact venturi mixer by providing swirl vanes on the inlet and outlet sides of the venturi-shaped main body.

1 is a side view showing an embodiment of a premixed gas burner equipped with a premixing device according to the present invention. FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 4 is a cross-sectional view showing another embodiment of a gas nozzle. FIG. 2 is a perspective view showing a main part of the premix gas burner 2 of FIG. 1. FIG. 5 is an exploded perspective view of FIG. 4 . FIG. 5 is a partially cutaway perspective view of FIG. 4 . FIG. 13 is an explanatory diagram showing a velocity distribution. FIG. 8(a) shows a boiler equipped with a premixing burner, and FIG. 8(b) is a cross-sectional view showing an example of a boiler equipped with a premixing burner having a premixing device according to the present invention. 11 is a velocity-streamline diagram of an embodiment based on a simulation analysis. FIG. 11 is a velocity-streamline diagram of Comparative Example 1 based on a simulation analysis. FIG. 11 is a velocity-streamline diagram of Comparative Example 2 based on a simulation analysis. 13 is a velocity-vector diagram (central vertical cross section) of an embodiment according to a simulation analysis. 13 is a velocity-vector diagram (central vertical cross section) of Comparative Example 1 based on a simulation analysis. 13 is a velocity-vector diagram (central vertical cross section) of Comparative Example 2 obtained by simulation analysis. FIG. 13 is a velocity contour diagram (central vertical cross section) of an embodiment based on a simulation analysis. 1 is a velocity-contour diagram (central vertical cross section) of Comparative Example 1 based on a simulation analysis. FIG. 13 is a velocity-contour diagram (central vertical cross section) of Comparative Example 2 based on a simulation analysis. FIG. 13 is an analysis diagram of turbulent energy in an embodiment based on a simulation analysis. FIG. 11 is an analysis diagram of turbulent energy in Comparative Example 2 by simulation analysis. FIG. 11 is an analysis diagram of turbulent energy in Comparative Example 2 by simulation analysis. FIG. 13 is an analytical diagram showing density distribution in an embodiment based on a simulation analysis. FIG. 13 is an analytical diagram showing density distribution of Comparative Example 1 by simulation analysis. FIG. 13 is an analytical diagram showing density distribution of Comparative Example 2 by simulation analysis. FIG. 11 is an analytical diagram showing pressure distribution in an embodiment based on a simulation analysis. FIG. 13 is an analytical diagram showing pressure distribution in Comparative Example 1 by simulation analysis. FIG. 11 is an analytical diagram showing pressure distribution in Comparative Example 2 by simulation analysis. 1 is a graph showing the results of a combustion performance test of an example and a comparative example 2 using an actual machine. FIG. 6 is a front view of the outlet side swirl vane shown in FIG. 5 . FIG. 4 is an explanatory diagram showing a pattern of the area ratio of the center hole of the outlet side swirl vane to the flow passage cross-sectional area.

Embodiments of the present invention will be described below with reference to Figures 1 to 29. Note that the same reference numerals are used to designate the same or similar components throughout all figures and embodiments.

Figure 1 is a side view showing one embodiment of a premixed gas burner 2 equipped with a premixing device 1 according to the present invention, Figure 2 is a cross-sectional view taken along line II-II in Figure 1, Figure 3 is a cross-sectional view showing another embodiment of a gas nozzle, Figure 4 is a perspective view showing a main part of the premixed gas burner 2 in Figure 1, Figure 5 is an exploded perspective view of Figure 4, and Figure 6 is a partially cutaway perspective view of Figure 4.

The premixing device 1 comprises a venturi-shaped main body 3 with a narrowed flow path, a gas nozzle 4 with fuel gas F injection holes 4a arranged inside the main body 3, an inlet-side swirl vane 5 provided on the inlet side of the main body 3 to generate a swirling flow in the combustion air A flowing into the main body 3, and an outlet-side swirl vane 6 provided on the outlet side of the main body 3 to promote mixing of the fuel gas F and the combustion air A flowing out from the main body 3. The inlet-side swirl vane 5 and the outlet-side swirl vane 6 are formed so that the swirling direction of the gas passing through them is the same.

The main body 3 has a tapered portion 3a that narrows at the tip, a cylindrical throat portion 3b connected to the tapered portion 3a, and a divergent portion 3c connected to the throat portion 3b. In the illustrated example, the tapered portion 3a and the divergent portion 3c are formed into a truncated cone shape. In the illustrated example, the throat portion 3b is preferably formed into a cylindrical shape having a certain length in the direction of the axis X, but it can also be formed in a shape that has almost no length in the direction of the axis X (a shape in which the divergent portion is directly connected to the tapered portion).

The tapered portion 3a of the main body 3 is attached to a wind box 7 that forms part of the combustion air passage. The wind box 7 has a blower 8 connected to one side and a supply path 9 for fuel gas F connected to the other side.

An air damper 10 is provided in the passage 8a for the combustion air A supplied from the blower 8 to the wind box 7. The flow rate of the combustion air A flowing through the passage 8a is adjusted by adjusting the opening of the air damper 10. A gas damper 11 is also provided in the supply passage 9 for the fuel gas F. The flow rate of the fuel gas F flowing through the supply passage 9 is adjusted by adjusting the opening of the gas damper 11. The opening of the air damper 10 and the gas damper 11 are finely adjusted by controlling the respective openings of the air damper 10 and the gas damper 11 with a control motor CM (FIG. 8(b)). The control motor CM in the example shown in FIG. 8(b) transmits the movement of the control motor CM to the air damper 10 and the gas damper 11 via link devices L1 and L2. The opening of each of the air damper 10 and the gas damper 11 relative to the control motor CM can be set in advance by adjusting the link device.

The flow rate of the fuel gas and the combustion air can be adjusted by other known adjustment means instead of the illustrated example. For example, the air damper and the gas damper can be controlled by separate control motors. Alternatively, instead of the gas damper, the flow rate of the fuel gas can be controlled (adjusted) using an air-fuel proportional control valve that detects the pressures of the combustion air and the fuel gas and controls them proportionally. Alternatively, instead of the air damper, the flow rate of the combustion air can be controlled by inverter controlling the blower.

The gas nozzle 4 is connected to the downstream side of the supply passage 9, which has a built-in gas damper 11. The gas nozzle 4 extends from inside the wind box 7 into the main body 3 along the axis X of the main body 3, penetrating the inlet side swirl vane 5.

The gas nozzle 4 shown in FIG. 2 has an injection hole 4a that opens toward the axis X. The gas nozzle 4 may be a type in which multiple injection holes 4a are formed radially, as shown in FIG. 3.

Inside the Venturi-shaped main body 3, as the cross-sectional area of the flow path becomes smaller, i.e., as the flow path becomes narrower, the flow rate increases and the pressure decreases. The combustion air, whose flow rate increases and pressure decreases within the main body 3, draws in fuel gas from the injection hole 4a of the gas nozzle 4. As shown in FIG. 2, the injection hole 4a is preferably located in the throat portion 3b where the cross-sectional area of the flow path is the smallest.

The wind box 7 has an opening 7a1 (FIG. 5) formed in the side plate 7a to which the tapered portion 3a is connected, which communicates the inside of the wind box 7 with the inside of the main body 3. The inlet side swirl vane 5 is removably attached to the inside of the side plate 7a by a fixing means such as a screw. The inlet side swirl vane 5 in the illustrated example includes a ring-shaped outer frame 5a, a ring-shaped inner frame 5b, and a plurality of vanes 5c connected between the outer frame 5a and the inner frame 5b and arranged in a ring shape. The outer frame 5a is formed with a flange 5d for screw fastening. The inside of the inner frame 5b is a gas nozzle center hole 5e through which the gas nozzle 4 passes, and the gas nozzle 4 is inserted into the gas nozzle center hole 5e. The plurality of vanes 5c are arranged to surround the periphery of the gas nozzle center hole 5e. Instead of the illustrated example, the inlet side swirl vane 5 can also be configured to be attached to the tapered portion 3a, for example.

The gas nozzle 4 is configured to penetrate the inlet swirl vane 5, so that the combustion air A supplied to the wind box 7 passes through the inlet swirl vane 5 and flows into the main body 3, forming a swirling flow that swirls around the gas nozzle 4. The gas nozzle 4 is detachably attached to the side plate 7c of the wind box 7 by a fixing means (not shown) such as a screw.

The wind box 7 has a side plate 7b, which is opposite the side plate 7a in which the opening 7a1 is formed, attached removably by a fixing means such as a screw (not shown). By removing the side plate 7b, the gas nozzle 4 can be removed from the side plate 7c, and the inlet side swirl vane 5 can be removed from the side plate 7a. This makes it easy to replace the gas nozzle 4 or inlet side swirl vane 5 with a different one, and makes it easy to customize the inlet side swirl vane 5 and gas nozzle 4. The side plate 7b can also be configured to be openable and closable, for example, by providing a hinge or the like on one side.

The outlet side swirl vane 6 in the illustrated example is attached to the outlet side of the divergent portion 3c. The outlet side swirl vane 6 comprises a ring-shaped outer frame 6a, a ring-shaped inner frame 6b, and a number of vanes 6c connected between the outer frame 6a and the inner frame 6b and arranged in a ring shape. A central hole 6d is formed in the center of the outlet side swirl vane 6 by the inner frame 6b, and a number of vanes 6c are arranged in the circumferential direction around the central hole 6d so as to surround the central hole 6d. The outer frame 6a is formed with fixing holes 6e (Figure 28) for passing screws or the like.

The premix gas burner 2 includes a burner head 12 connected to the outlet side of the divergent portion 3c. The burner head 12 can include a known metal knit 12b in a metallic cylindrical body 12a.

The burner head 12 is removably attached to the divergent portion 3c by a fixing means such as a screw (not shown). The outlet side swirl vanes 6 are also removably attached to the divergent portion 3c by a fixing means such as a screw (not shown). This makes it easy to remove the burner head 12 from the divergent portion 3c and remove the outlet side swirl vanes 6 to replace them with other outlet side swirl vanes 6.

In the premix gas burner 2 equipped with the premixing device of the above configuration, the combustion air A supplied from the blower 8 is adjusted in volume by the air damper 10 and introduced into the wind box 7. The combustion air A introduced into the wind box 7 enters the inlet side swirl vanes 5 surrounding the gas nozzle 4, and is subjected to a swirling force about the axis X by the inlet side swirl vanes 5, leading it from the inlet side of the main body 3 through the tapered portion 3a to the throat portion 3b. As the flow velocity of the combustion air A increases in the throat portion, the static pressure in the throat portion 3b decreases in proportion to the square of the flow velocity, and as a result, the fuel gas F is sucked in through the injection holes 4a arranged in the throat portion 3b.

Because the combustion air A passes through the throat section 3b while swirling around the axis X, this swirling force increases the gas suction force compared to a normal venturi structure without swirling blades. The combustion air A that has sucked in the fuel gas F at the throat section 3b mixes with the fuel gas F at the divergent section 3c while swirling.

In the case of a premix gas burner with a normal venturi structure without swirl vanes, the velocity distribution is as shown in Figure 7 (a), and the flow near the tube wall gradually loses velocity energy due to friction with the tube wall, and the flow separates from the tube wall due to the backflow caused by the reverse pressure gradient, promoting mixing. On the other hand, when the inlet side swirl vanes are provided but the outlet side swirl vanes are not provided, the velocity distribution is as shown in Figure 7 (b), and a strong swirl flow flows near the tube wall, and a backflow occurs due to the reverse pressure gradient on the center side of the main body 3, so that the flow does not separate at the tube wall and tends to be difficult to mix. Therefore, by providing the outlet side swirl vanes 6 on the outlet side of the main body 3, the swirl flow generated near the tube wall is promoted while creating a flow toward the center of the main body 3, and the turbulent energy in the divergent part 3c can be promoted and a uniform mixed state can be obtained. The flow toward the center of the main body 3 can be further promoted by providing a center hole 6d of the outlet side swirl vanes 6.

In the case of a normal venturi structure without swirl vanes, it is necessary to provide some straight pipe sections before and after the venturi structure to straighten the combustion air, but in the case of the present invention, the performance of the venturi is hardly changed even if the air passage shape has a bend immediately upstream of the venturi-shaped main body 3 as shown in Figure 1. Since there is no need to provide straight pipe sections before and after the venturi-shaped main body 3, there is more freedom in the arrangement of the device.

The inlet side swirl vane 5 improves the suction of fuel gas from the injection hole 4a and the mixing of fuel gas and combustion air, so the venturi-shaped body 3 can be designed compactly. For example, as shown in FIG. 1, the axial length L of the venturi-shaped body 3 can be designed to be within the range of the casing dimension K of the blower 8. Therefore, FIG. 8(a) shows a boiler equipped with a premixing burner, and FIG. 8(b) shows a boiler equipped with a premixing burner equipped with the premixing device of the present invention. As shown in FIGS. 8(a) and (b), the boiler does not become larger in size compared to a premixing burner equipped with a blower 8 of the same output. The boiler shown in FIG. 8 is a so-called vacuum hot water generator, and reference numeral 13 indicates a furnace, reference numeral 14 indicates a reduced pressure steam chamber, reference numeral 15 indicates heat transfer water, reference numeral 16 indicates a water tube, reference numeral 17 indicates a smoke chamber, and reference numeral 18 indicates a heat exchange tube through which hot water W flows.

It is difficult to achieve an appropriate ratio of fuel gas and combustion air by the Venturi principle because it is necessary to fine-tune the inner diameter of the throat portion 3b and the hole diameter of the injection hole 4a. In addition, when the output of the blower 8 is changed to change the amount of combustion, it is difficult to maintain a constant mixture ratio of fuel gas and combustion air. That is, when the output of the blower is small compared to when the output of the blower is large, the effect of boundary layer separation occurring on the inner wall surface of the Venturi-shaped main body 3 becomes large, and the flow coefficient of the combustion air introduced into the Venturi-shaped main body 3 decreases. If the flow coefficient changes, the air ratio cannot be kept constant, so the supply pressure of the fuel gas must be adjusted according to the change in the flow coefficient. Therefore, by controlling the opening of the gas damper 11 and the air damper 10 with the control motor 11, it is possible to fine-tune the mixture ratio of fuel gas and combustion air.

By finely adjusting the opening of the gas damper 11 and air damper 10 using the control motor 11, it is possible to eliminate the need for a special blower (fan mix) or zero governor specifically for premixed burners, and it can be constructed using the same parts as premixed burners, making it inexpensive.

The present invention will be explained in more detail using examples and comparative examples, computational fluid dynamics (CFD) simulations, and combustion performance tests using actual equipment. However, the present invention is not limited to these examples.

The basic conditions for the examples and comparative examples were rated operation of the vacuum hot water generator (output 930 kW) shown in Figure 8 (b), with an air flow rate of 1,223 ^m3 (N)/hour (air inlet flow velocity 18.4 m/sec), a methane gas flow rate of 86.6 ^m3 (N)/hour (gas inlet flow velocity 8.2 m/sec), and a furnace pressure (burner output pressure) of 870 Pa.

The embodiment was a premixed burner with the configuration shown in Figures 1 and 2. Comparative Example 1 was a premixed burner with the configuration of the embodiment omitting the outlet swirl vanes. Comparative Example 2 was a premixed burner with the configuration of the embodiment omitting the inlet and outlet swirl vanes.

Figures 9 to 11 show velocity-streamline diagrams based on computational fluid dynamics (CFD) simulations, with Figure 9 showing the embodiment, Figure 10 showing Comparative Example 1, and Figure 11 showing Comparative Example 2. It can be seen that the embodiment in Figure 9 generates a stronger swirling flow than Comparative Example 1 in Figure 10 and Comparative Example 2 in Figure 11.

Figures 12 to 14 show velocity vector diagrams (central vertical cross section) by computational fluid dynamics (CFD) simulation, and Figures 15 to 17 show velocity contour diagrams (central vertical cross section) by computational fluid dynamics (CFD) simulation. Figures 12 and 15 show an embodiment, Figures 13 and 16 show Comparative Example 1, and Figures 14 and 17 show Comparative Example 2. In Comparative Example 2 in Figures 14 and 17, the velocity distribution is biased in the burner head 12 after passing through the venturi-shaped main body 3 due to the influence of the flow direction of the combustion air supplied to the wind box 7. Comparative Example 1 in Figures 14 and 16 does not have a large bias like Comparative Example 2 in Figures 14 and 17, but the flow near the tube wall is fast from the divergent portion 3c to the burner head 12, and the velocity distribution in the burner head 12 is non-uniform. On the other hand, in the embodiments of Figures 12 and 15, the reverse flow due to the reverse pressure gradient is completed in the divergent portion 3c of the venturi-shaped body 3 (the primary side of the outlet swirl vanes 6), and the flow near the tube wall is guided and rectified by the outlet swirl vanes 6 toward the center of the venturi-shaped body 3, so it can be seen that there is no bias in the velocity distribution in the burner head 12.

Figures 18 to 20 show the results of turbulent energy analysis by computational fluid dynamics (CFD) simulation. Figure 18 shows the Example, Figure 19 shows Comparative Example 1, and Figure 20 shows Comparative Example 2. In Comparative Example 1 (Figure 19), the turbulent energy in the venturi-shaped body 3 is clearly greater than in Comparative Example 2 (Figure 20), but since this range spans the burner head 12, it can be inferred that it takes time to complete mixing. In contrast, in the Example (Figure 18), the turbulent energy shows a large value in the divergent portion 3c of the venturi-shaped body 3 and a small value inside the burner head 12. This is inferred to be because mixing is promoted in the divergent portion 3c, and the time to complete mixing is shorter than in Comparative Example 1.

Figures 21 to 23 show density distributions based on computational fluid dynamics (CFD) simulations. In Comparative Example 2 (Figure 23), there is a bias in the velocity distribution (see Figure 14) inside the burner head 12, which shows that mixing in areas with high flow rates is poor. In Comparative Example 1 (Figure 22), the density distribution is more uniform than in Comparative Example 2, but mixing is not completed before entering the burner head 12. In the Example (Figure 21), it can be seen that mixing is almost completed before entering the burner head 12.

Figures 24 to 26 show pressure distributions based on computational fluid dynamics (CFD) simulations. In the example (Figure 24), a fast swirling flow occurs at the throat 3b, creating negative pressure inside the gas nozzle 4 and increasing the suction force of the fuel gas. In addition, compared to Comparative Example 1 (Figure 25), the example (Figure 24) has outlet swirl vanes 6, which may seem to increase pressure loss, but it can be seen that the pressure inside the wind box 7 remains almost unchanged due to the straightening action of the outlet swirl vanes 6. In actual machine testing, data was obtained showing that the pressure inside the wind box 7 is lower when the outlet swirl vanes 6 are provided. This is thought to be because the backflow caused by the reverse pressure gradient is completed on the primary side of the outlet swirl vanes 6, forming a straightened, compact circulating flow.

A combustion performance test was conducted to measure the exhaust gas components using an actual machine for the above Example and Comparative Example 2. The results of the combustion performance test are shown in the graph in Figure 27. The graph in Figure 27 shows the results of measuring the NOx concentration and CO concentration in the combustion exhaust gas. From Figure 27, it can be seen that in Comparative Example 2, the fuel gas and the combustion air are incompletely mixed, which causes the combustion to become unbalanced, resulting in an unstable combustion state and the generation of a large amount of CO, which is an indicator of incomplete combustion. On the other hand, in the Example, the fuel gas and the combustion air are well mixed, so the generation of CO is suppressed and the NOx value is also reduced, demonstrating the inherent performance of the metal knit burner. From this, it can be seen that Example 1 has better combustion than Comparative Example 2, and it is considered that good mixing of the fuel gas and the combustion air has been achieved.

Next, an experiment conducted on the outlet side swirl vane 6 will be described. Figure 28 is a front view of the outlet side swirl vane 6 shown in Figure 5. The outlet side swirl vane 6 has a central hole 6d formed at the center of the outlet side swirl vane 6, i.e., inside the inner frame 6b, and a plurality of vanes 6c are arranged in the circumferential direction around the central hole 6d. The vane 6c is connected to the outer frame 6a and the inner frame 6b at the twist origin 6f. By twisting the twist origin 6f, the vane 6c is inclined relative to the outer frame 6a and the inner frame 6b. The twist origin 6f is provided at a position biased toward one end of the vane 6c in the length direction, and the longer part of the vane 6c is formed to follow the tapered surface of the divergent portion 3c relative to the twist origin 6f.

As shown in Figure 29, the size of the central hole 6d of the outlet side swirl vane 6, i.e., the ratio of the opening area of the central hole 6d to the cross-sectional area of the flow passage (opening area ratio), was changed to multiple patterns (a) to (e). In Figure 29, the gap inside the hatching (diagonal lines) corresponds to the central hole 6d, and the numbers at the bottom of each pattern indicate the opening area ratio. As a result of the test, the generation of NOx and CO was suppressed in all patterns ((b) to (e)) where the opening area ratio was 5% or more, and good combustion performance was obtained. Furthermore, in patterns (a) to (e), the larger the opening area ratio of the central hole 6d, the better the combustion state. On the other hand, referring to the simulation results of Comparative Example 1 in Figures 13 and 16, when there is no outlet side swirl vane, there is a fast flow (15 m/s or more) near the pipe wall, and unless the outlet side swirl vane is provided in the area where this fast flow exists, the effect of the outlet side swirl vane in promoting the flow toward the center and the swirling flow is limited, so it is desirable to set the opening area ratio of the center hole 6d to 80% or less. Therefore, the outlet side swirl vane 6 can be configured so that the opening area ratio is preferably 5% to 80%.

By providing the outlet side swirl vanes 6, the pressure loss in the wind box is reduced, which creates spare capacity for the blower and expands the combustion range (upper limit of _O2 ). In addition, the CO generation rate at rated operation was almost the same in all patterns shown in Figure 29, but CO suppression was confirmed in operation at medium load (75-20%). In general, in operation at medium load, the flow rate is slow, which leads to poor mixing of the fuel gas and the combustion air, making it easier for CO to be generated, but the effect of suppressing CO generation by the outlet side swirl vanes 6 was remarkable.

The present invention should not be interpreted as being limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

Reference Signs List 1 Premixing device 2 Premixing burner 3 Body 3a Tapered section 3b Throat section 3c Divergent section 4 Gas nozzle 4a Injection hole 5 Inlet side swirl vane 5c Vanes 5e Gas nozzle central hole 6 Outlet side swirl vane 6c Vanes 6d Central hole 8 Blower 10 Air damper 11 Gas damper CM Control motor

Claims (8)

A premixing device for a premix gas burner that mixes fuel gas and combustion air and burns the mixture ;
a burner head connected to an outlet side of the premixing device ;
The premixing device comprises:
A venturi-shaped body;
a gas nozzle having a fuel gas injection hole disposed within the body;
an inlet side swirl vane provided on an inlet side of the main body for swirling the combustion air supplied into the main body;
an outlet side swirl vane provided on the outlet side of the main body for promoting mixing of the fuel gas and the combustion air;
Equipped with
The main body includes a tapered portion that narrows toward the tip, a cylindrical throat portion that is connected to the tapered portion, and a divergent portion that is connected to the throat portion,
the gas nozzle is provided to penetrate the inlet side swirl vane, is located on the axis of the main body, and the injection hole is disposed within the throat portion;
the inlet side swirl vane includes a gas nozzle central hole through which the gas nozzle passes, and a plurality of vanes arranged to surround the gas nozzle central hole,
The outlet side swirl vane includes a central hole provided at the center, and a plurality of vanes surrounding the central hole and arranged so that gas passing through the central hole swirls in the same direction as the inlet side swirl vane,
The burner head includes a metal cylinder connected to an outlet side of the divergent portion and communicating with the divergent portion, and a tubular metal knit communicating with the metal cylinder.
Premix gas burner . 2. The premix gas burner according to claim 1 , wherein an opening area of said central hole is formed at a ratio of 5% to 80% of a flow passage cross-sectional area within said body. 3. A premix gas burner as claimed in claim 1 or 2 , wherein a blower for blowing combustion air is provided in tandem with said main body, and the outer dimensions of said main body in the axial direction of said main body are set smaller than the outer dimensions of said blower . 4. The premixed gas burner according to claim 3, further comprising: a gas damper for adjusting the flow rate of fuel gas sent to the gas nozzle ; an air damper for adjusting the flow rate of combustion air sent from the blower to the main body; and a control motor for controlling the gas damper and the air damper . 5. The premix gas burner according to claim 1, wherein the inlet side swirl vane is detachably provided. 6. The premix gas burner according to claim 1, wherein the outlet side swirl vane is detachably provided. 7. The premix gas burner according to claim 1, wherein the gas nozzle is detachably provided. A wind box is further provided to which a blower for blowing combustion air is connected,
2. The premix gas burner according to claim 1, wherein the wind box has a removable or openable side plate, and the gas nozzle and the inlet side swirl vane are removably attached within the wind box.