gas burner

Abstract

To obtain a gas nozzle capable of executing rating combustion even when a combustion gas is fed under a low pressure.SOLUTION: A gas burner 11 comprises: a fuel feed pipe 22 for a gas fuel 37 arranged at the inside of a blast tube 18; a rear plate 31 for clogging an opening end of a blast tube 18; a front plate 33 arranged in a posture of facing the rear plate 31; a fuel jet port 36 formed at the part of the fuel feed pipe 22 in a space between the rear plate 31 and the front plate 33; and an air jet port 44 for jetting the air in the blast tube 18 from the position of the rear plate 31 to the side of the front plate 33. The respective shapes and the mutual positions of the rear plate 31 and the front plate 33 are adjusted so that an air flow 48 jetted from the air jet port 44 forms an air vortex.SELECTED DRAWING: Figure 3

Description

Technical Field

[0006] , , , , ,

[0001] The present invention relates to a gas burner.

Background Art

[0002] A gas burner is known that includes a blast tube that forms an air passage and can also be called a funnel, an inner tube for fuel supply provided inside the blast tube, a disk-shaped rear plate that is arranged to close the open end of the blast tube and has an air outlet, a disk-shaped front plate that is arranged to close the opening of the inner tube at a position spaced apart from the rear plate, and a fuel outlet provided in a portion of the inner tube between the rear plate and the front plate (Patent Document 1).

[0003] With such a gas burner, combustion stabilization and low NOx can be achieved.

Prior Art Documents

Patent Documents

[0004] The present invention aims to further improve the above-described conventional gas burner to obtain a gas burner capable of performing rated combustion even when fuel gas is supplied at a low pressure.

Means for Solving the Problems

[0006] To achieve this object, the gas burner of the present invention includes a blast tube for supplying air, a fuel supply pipe for gaseous fuel disposed inside the blast tube,​​​​​​​​​​​​​​ A rear plate positioned to close the open end of the blast tube, A front plate is positioned at a location further from the opening end of the blast tube than the rear plate, facing the rear plate, and configured to block the fuel supply pipe protruding from the rear plate. A fuel nozzle formed in the portion of the fuel supply pipe between the rear plate and the front plate, It has an air outlet for ejecting air from the position of the rear plate towards the front plate, The rear plate has alternating recessed portions that are radially recessed inward from the inner circumferential surface of the blast tube to form an air outlet, and protruding portions that project radially outward from the recessed portions, along the circumferential direction. The front plate has alternating small-diameter portions facing the protruding portions of the rear plate and large-diameter portions that are larger in diameter than the small-diameter portions and facing the recessed portions of the rear plate, along the circumferential direction, so that the airflow ejected from the air outlet forms an air vortex in the gap between the front plate and the rear plate. It is characterized by being such.

[0008] According to the gas burner of the present invention, the shape of the annular flame downstream of the front plate is such that the flame has varying intensity along the circumferential direction, compared to the case where the front plate is a disc shape without these small and large diameter portions, and the front plate is The small diameter portion without the large diameter portion It is preferable that the flame lengthen along the circumferential direction of the front plate compared to when it is in the form of a disc.

[0009] According to the gas burner of the present invention, it is preferable that the airflow ejected from the air outlet forms an air vortex due to at least one of the Coanda effect on the airflow ejected from the air outlet and a vortex generated downstream of the rear plate of the airflow.

[0010] According to the gas burner of the present invention, it is preferable that a portion of the flame is held in place by the front plate and another portion of the flame is held in place by the rear plate, thereby preventing localized flame stagnation.

[0011] According to the gas burner of the present invention, it is preferable that the front plate has a recirculation vortex region along the surface opposite to the rear plate. [Effects of the Invention]

[0012] According to the gas burner of the present invention, since the shapes of the front plate and the rear plate and their mutual positions are adjusted so that the air flow ejected from the air ejection port forms an air vortex, the fuel ejected from the fuel ejection port can be drawn in by the air flow ejected from the air ejection port. Therefore, even when the fuel gas is supplied at a low pressure, rated combustion can be performed.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram showing the structure of the gas burner of the embodiment of the present invention. [Figure 2] It is an enlarged view taken along arrow A in FIG. 1. [Figure 3] It is a diagram showing in detail the structure of the main part in FIG. 1. [Figure 4] It is a diagram showing three-dimensionally the part shown in FIG. 3. [Figure 5] It is a diagram showing the dimensional relationship of the part shown in FIGS. 3 and 4. [Figure 6] It is a diagram showing the dimensional relationship of the front plate in the part shown in FIGS. 3 and 4. [Figure 7] It is a diagram showing the flow state of air, fuel, and flame (combustion gas) in the main part of FIG. 1. [Figure 8] It is a cross-sectional view taken along line B-B in FIG. 7. [Figure 9] It is a diagram showing the measurement results of the exhaust gas NOx concentration in the gas burner of the embodiment of the present invention and the gas burner described in Patent Document 1. [Figure 10] It is a diagram showing more clearly the shape of the rear plate shown in FIG. 1. [Figure 11] It is a diagram showing the details of the shape of another example of the rear plate.

Embodiments for Carrying Out the Invention

[0014] The gas burner 11 shown in Fig. 1 is installed in a combustion chamber 12 such as a boiler, and has a wind box 15 that receives air sent from a blower 14 equipped with a motor 13. An air damper 17 whose opening degree is adjusted by a motor 16 is provided between the blower 14 and the wind box 15, and the air damper 17 enables the flow rate of the air supplied to the wind box 15 to be adjusted. The base end portion 19 of a horizontal cylindrical blast tube 18 is connected to the wind box 15, and an opening 20 is formed at the tip of the blast tube 18.

[0015] A fuel supply pipe 22 penetrating the wind box 15 and the blast tube 18 in the vertical direction is provided. This fuel supply pipe 22 is installed horizontally in the same manner as the blast tube 18 and is arranged at the center of the blast tube 18. That is, the fuel supply pipe 22 is arranged concentrically with the blast tube 18 at the center of the blast tube 18. The fuel supply pipe 22 has a protruding portion 23 that protrudes in a direction away from the blast tube 18 from the wind box 15, and a fuel supply path 24 from outside the system is connected to this protruding portion 23.

[0016] A pilot burner 25 is provided inside the fuel supply pipe 22. The pilot burner 25 is arranged in the same direction as the fuel supply pipe 22 at the center of the fuel supply pipe 22. The pilot burner 25 has a base end portion 26 that further protrudes from the protruding portion 23 of the fuel supply pipe 22, and a pilot fuel supply path 27 and a pilot air supply path 28 are respectively connected to this base end portion 26. Figure A rear plate 31 is provided at the position of the opening 20 of the blast tube 18. The fuel supply pipe 22 is arranged in a state of penetrating the rear plate 31 and has a combustion chamber side protruding portion 32 that protrudes toward the combustion chamber 12 side from the rear plate 31. A front plate 33 is provided at the tip of the combustion chamber side protruding portion 32. The tip of the fuel supply pipe 22 is blocked by the front plate, and the pilot burner 25 communicates with the inside of the combustion chamber 12 through an opening 34 formed in the front plate 33.

[0018] As shown in Figures 1 to 3, the rear plate 31 and the front plate 33 are both made of flat plates and are arranged perpendicular to the axis of the blast tube 18 and the fuel supply pipe 22, i.e., in a vertical direction. A gap 35 is formed between the rear plate 31 and the front plate 33, corresponding to the protruding length of the combustion chamber side projection 32 of the fuel supply pipe 22.

[0019] Fuel nozzles 36 are formed through the combustion chamber side projection 32 of the fuel supply pipe 22 at multiple positions along the circumferential direction. The fuel nozzles 36 are configured to eject gaseous fuel 37 that has reached the combustion chamber side projection 32 from the fuel supply passage 24 through the fuel supply pipe 22 outwards along the radial direction of the blast tube 18 and the fuel supply pipe 22, as shown in Figure 3. As a result, the gaseous fuel 37 is injected into the gap 35 in a radially dispersed state along the circumferential direction of the fuel supply pipe 22, as shown in Figure 2.

[0020] As shown in Figure 2, the rear plate 31 has a shape that can be described as star-shaped, flower-shaped, or multi-winged. In detail, the rear plate 31 has a plurality of protrusions 38 and recesses 39 alternating along the circumferential direction. The protrusions 38 have an outer peripheral edge 42 that is close to or in contact with the inner circumferential surface 41 of the cylindrical blast tube 18, and this outer peripheral edge 42 is formed in an arc shape along the inner circumferential surface 41 of the cylindrical blast tube 18. The recesses 39 are formed in a V-shape, cut radially inward from the outer peripheral edge 42 of the protrusions 38, and the bottom 43 of the V shape is formed in an arc shape rather than being an acute angle.

[0021] The rear plate 31, configured in this way, is positioned to close the opening 20 of the blast tube 18. In this configuration, the space formed by the recessed portion 39 connects the inside and outside of the blast tube 18 in the axial direction of the blast tube 18, and constitutes an air outlet 44. As shown in Figures 1 and 2, when the protrusion 38 is close to the inner circumferential surface 41 of the blast tube 18 without contacting it, a gap 45 is formed between the outer circumferential edge 42 of the protrusion 38 and the inner circumferential surface 41 of the blast tube 18, and this gap 45 also functions as an air outlet.

[0022] As shown in Figure 2, the front plate 33 is formed in a roughly circular shape, and the portion facing the recessed portion 39 of the rear plate 31 is configured as a large-diameter portion 49, each having radially outward-facing protrusions 46. The protrusions 46 are formed in a rectangular shape so as to cover the recessed portion 39 when viewed in the axial direction. The space between adjacent protrusions 46, 46 in the circumferential direction is a small-diameter portion 50, and the small-diameter portion 50 has an arc-shaped outer edge 47. The large-diameter portions 49 and small-diameter portions 50 are formed alternately along the circumferential direction.

[0023] The combustion conditions in a gas burner with this configuration will be explained.

[0024] Conventional NOx-suppressing burner combustion methods include multi-stage air combustion, multi-stage fuel combustion, self-exhaust gas circulation, split / thin film combustion, rich / lean combustion, and premixed / lean combustion, including the one described in Patent Document 1 above. Burners exhibiting low NOx values ​​are provided by combining these methods.

[0025] The combustion method described in Patent Document 1 above fixes the flame to a rear plate, which can also be called a flame-holding plate. In other words, the gaseous fuel is burned at the rear plate. However, in such a system, if the flame-holding properties of the rear plate are too strong, the flame may concentrate locally, making it difficult to achieve segmented, thin-film combustion for NOx suppression. While strong flame-holding properties result in a stable and good combustion state, they also lead to higher NOx levels. Therefore, from the viewpoint of NOx suppression, it is actually possible to achieve a better combustion state by weakening the flame-holding properties to some extent by forming a thin-film flame.

[0026] When considering the pressure of the gaseous fuel supplied to a gas burner, if the gaseous fuel pressure is at a medium pressure of around 0.1 to 0.3 MPa, a thin flame is easily formed due to the high injection pressure of the gaseous fuel. However, if the supplied gaseous fuel pressure is low, for example, 2 kPa or less, a thin flame is less likely to form due to the low gas injection pressure, and therefore NOx levels tend to be high. For this reason, when gaseous fuel is supplied at low pressure, rated combustion becomes difficult in burners with high combustion rates.

[0027] In contrast, the gas burner of the present invention described above can perform rated combustion even when the pressure of the supplied gaseous fuel is low. This point will be explained in detail below based on the gas burner of the embodiment of the present invention described above.

[0028] According to the gas burner of the embodiment of the present invention described above, as shown in Figure 3, the shapes of the rear plate 31 and the front plate 33, and their positional relationship, etc., cause the airflow 48 from the air outlet 44 to form an air vortex in at least the portion of the gap 35 between the rear plate 31 and the front plate 33 where the fuel outlet 36 is provided. As a result, the gaseous fuel 37 ejected from the fuel outlet 36 is drawn into the airflow 48, and this makes it possible to perform rated combustion even when the pressure of the gaseous fuel 37 supplied to the fuel supply pipe 22 is low.

[0029] The above phenomenon will be explained in more detail. In the gas burner of the illustrated embodiment, an air outlet 44 is formed by a recess 39 in the rear plate 31, and the radially inner portion of this air outlet 44 is covered by a front plate 33 and, in particular, its protruding portion 46, which is provided at a predetermined distance from the rear plate 31. As a result, as shown in Figures 3 and 4, the airflow 48 forms an air vortex due to the Coanda effect occurring in the airflow 48 and the effect of vortices 51 generated downstream of the rear plate 31. This causes the gaseous fuel 37 to be drawn into the airflow 48 as described above, and for this reason, rated combustion can be performed even when the pressure of the gaseous fuel 37 supplied to the fuel supply pipe 22 is low.

[0030] In order to generate an airflow 48 with such characteristics, it is necessary to appropriately set the shape and dimensions of each part. Conversely, by appropriately setting the shape and dimensions of each part, it is possible to appropriately generate an airflow 48 that forms an air vortex.

[0031] The appropriate dimensions when adopting the illustrated shape will be explained below with reference to Figures 5 and 6. In the configurations shown in Figures 5 and 6, the outer diameter Da of the fuel supply pipe 22 and the hole diameter φG of the fuel injection port 36 are used as the reference dimensions. In this case, it is appropriate for the dimensions of each part to be within the following ranges. Specifically, the number N of fuel injectors 36 is preferably 3 to 18, the inner diameter Db of the blast tube 18 is preferably 1.5 to 3.5 Da, the diameter Dc of the part of the front plate 33 other than the protrusion 46 is preferably 1.2 to 1.8 Da, the diameter Dd of the part of the front plate 33 where the protrusion 46 is preferably 1.1 to 1.5 Dc, the width W of the protrusion 46 on the front plate 33 is preferably 1.5 to 4φG, the length La of the downstream surface 52 of the rear plate 31 extending from the tip of the blast tube 18 into the interior of the blast tube 18 is preferably 0 to 6φG, the distance Lb from the downstream surface 52 of the rear plate 31 to the center of the fuel injector 36 is preferably 0.5 to 8φG, and the distance Lc from the upstream surface 53 of the front plate 33 to the center of the fuel injector 36 is preferably 0.5 to 10φG. Those skilled in the art can easily derive the optimal values ​​from the preferred ranges of each of the above-described parts, either from a hydrodynamic perspective or through experimental methods, so that the gaseous fuel 37 ejected from the fuel nozzle 36 is drawn into the airflow 48.

[0032] In the illustrated embodiment, in particular, when a protrusion 46 was provided on the front plate 33, a flame retaining pattern was observed that covered the edge of the protrusion 46 during combustion experiments. This meant that the flame was less likely to concentrate locally in the central part of the front plate 33. In other words, it meant that a good segmented, thin-film flame capable of reducing NOx was formed.

[0033] In this case, by providing the protrusion 46 on the front plate 33, the length of the front plate 33 along the circumferential direction, i.e., the outer circumference, becomes longer, and as a result the length of the part that fixes the flame becomes longer, it was possible to promote the thinning of the flame.

[0034] Figure 7 shows the flow of airflow 48, gaseous fuel 37, and flame, or combustion gas, flow 55 in the vicinity of the rear plate 31 and the front plate 33 of the main part of Figure 1, represented by streamlines. Figure 8 is a cross-sectional view along line BB in Figure 7.

[0035] The air supplied to the inside of the blast tube 18 flows downstream as an airflow 48 from the air outlet 44 formed by the recess 39 of the rear plate 31. Meanwhile, the gaseous fuel 37 supplied to the inside of the fuel supply pipe 22 is ejected from the fuel outlet 36, mixed with the airflow 48 between the rear plate 31 and the front plate 33, and ignited and combusted by the flame of the pilot burner 25 that reaches the combustion chamber 12 through the opening 34 of the front plate 33, thereby generating a flame, or combustion gas flow 55.

[0036] In this configuration, because the rear plate 31 and its vicinity, and the front plate 33 and its vicinity have the above-described configuration, downstream of the front plate 33, the flame, i.e., the flow of combustion gas 55, becomes a cylindrical thin-film flame. Also, a portion of the flame is fixed to the rear plate 31, and the majority of the flame is held in place by the front plate 33. The shape of the flame becomes rectangular, and localization or stagnation of the flame is effectively prevented.

[0037] As shown in Figure 7, a recirculation vortex region 56 is formed on the downstream surface 54 of the front plate 33, extending from the outer periphery towards the center. This recirculation vortex region 56 is under lower pressure than other areas. As a result, combustion exhaust gas flows into the recirculation vortex region 56, providing a NOx reduction effect through self-circulation.

[0038] Figure 8 shows schematic examples of a strong flame retainer 57 formed on the edge of the front plate 33, a strong flame 58 formed corresponding to the protruding portion 46 of the front plate 33, and a weak flame 59 formed corresponding to the outer peripheral edge 47 of the front plate 33.

[0039] With this configuration, in addition to being able to perform rated combustion even when the fuel gas is supplied at low pressure as described above, NOx emissions can be reduced even further than those of the gas burner described in Patent Document 1.

[0040] By setting the dimensions of the protruding portion 46 in the front plate 33 within the above-mentioned preferred range, the combustion state can be made less susceptible to the influence of the pressure inside the wind box 15 and the pressure inside the combustion chamber 12.

[0041] By providing the protrusion 46 on the front plate 33, the outer diameter of the portion other than the protrusion 46, i.e., the portion where the outer peripheral edge 47 is formed, can be made smaller than in the case of Patent Document 1. This makes it possible to reduce the air differential pressure in the front plate 33, and therefore reduce the air pressure inside the wind box 15. As a result, it becomes possible to handle low-pressure gases.

[0042] Furthermore, by narrowing the diameter of the fuel nozzle 36 of the fuel supply pipe 22, the injection force (pressure and flow velocity) of the gaseous fuel 37 from the fuel nozzle 36 can be increased, thereby providing a cooling effect from the gaseous fuel 37. This cooling effect can also be used to lower the flame temperature, thereby reducing NOx emissions.

[0043] Based on these NOx reduction effects, the gas burner shown in the figure was able to further reduce NOx compared to the gas burner described in Patent Document 1. The results are shown in Figure 9. In Figure 9, the horizontal axis represents the load factor of the gas burner, and the vertical axis represents the NOx concentration of the exhaust gas.

[0044] Figure 10 shows the rear plate 31 shown in Figure 1 and other figures more clearly. For reference, the front plate 33 is drawn with dashed lines. However, the shape of the rear plate 31 shown is illustrative, and the rear plate 31 can be modified in various ways as long as it achieves the effects of the present invention. For example, Figure 11 shows an example in which the air outlet 44 formed by the recessed portion 39 is wider and shallower than that shown in Figure 10 and other figures. In Figure 11, the recessed portion 39 is formed in a trapezoidal shape. Alternatively, the air outlet 44 of the rear plate 31 can be in the form of a through hole formed in the rear plate 31 instead of being formed by the recessed portion 39 shown.

[0045] Furthermore, according to the present invention, the rear plate 31 and the front plate 33 are not limited to the shapes shown. For example, any configuration is possible as long as the airflow 48 ejected from the air outlet 44 forms an air vortex, and this airflow 48 can draw in the gaseous fuel 37 ejected from the fuel outlet 36, thereby enabling rated combustion even when the gaseous fuel 37 is supplied at low pressure. Such a configuration can be realized without difficulty by those skilled in the art, based on fluid dynamics and experimental viewpoints. [Explanation of Symbols]

[0046] 18 blast tubes 20 aperture 22 Fuel supply pipe 31 Rear Plate 33 Front plate 36 Fuel outlet 37. Gaseous fuels 38 Protrusion 39 Recessed area 44 Air outlets 48 Airflow 49 Large diameter section 50 Small diameter section 56 Recirculating vortex region

Claims

1. A blast tube for supplying air, A fuel supply pipe for gaseous fuel is arranged inside the blast tube, A rear plate positioned to close the open end of the blast tube, A front plate is positioned at a location further from the opening end of the blast tube than the rear plate, facing the rear plate, and configured to block the fuel supply pipe protruding from the rear plate. A fuel nozzle formed in the portion of the fuel supply pipe between the rear plate and the front plate, It has an air outlet for ejecting air from the position of the rear plate towards the front plate, A gas burner characterized in that the rear plate has alternating recessed portions that are radially recessed inward from the inner circumferential surface of the blast tube to form an air outlet, and protruding portions that project radially outward from the recessed portions, along the circumferential direction, and the front plate has alternating small-diameter portions that face the protruding portions of the rear plate and large-diameter portions that face the recessed portions of the rear plate and are formed to be larger in diameter than the small-diameter portions, along the circumferential direction, so that the airflow ejected from the air outlet forms an air vortex in the gap between the front plate and the rear plate.

2. The gas burner according to claim 1, characterized in that the shape of the annular flame downstream of the front plate is such that the flame has varying intensity along its circumferential direction, compared to when the front plate is a disc without these small and large diameter portions, and the flame is longer along its circumferential direction, compared to when the front plate is a disc with only the small diameter portion and no large diameter portion.

3. The gas burner according to claim 1 or 2, characterized in that the airflow ejected from the air outlet forms an air vortex due to at least one of the Coanda effect on the airflow ejected from the air outlet and a vortex generated downstream of the rear plate of the airflow.

4. A gas burner according to any one of claims 1 to 3, characterized in that a portion of the flame is held on the front plate and another portion of the flame is held on the rear plate, thereby preventing localized flame stagnation.

5. A gas burner according to any one of claims 1 to 4, characterized in that it has a recirculation vortex region along the surface of the front plate opposite to the rear plate.

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