Combustion burner for boiler

Abstract

A combustion burner for a boiler includes: an inner cylinder defining a fuel supply passage for supplying fuel; an outer cylinder surrounding the inner cylinder and defining an air supply passage between the inner cylinder and the outer cylinder; and a swirler in the air supply passage, the swirler being configured to swirl air in the air supply passage. The swirler includes a plurality of blades radially disposed between the inner cylinder and the outer cylinder, the plurality of blades extending from an air-supply side toward a combustion-space side of the air supply passage, and each of the plurality of blades having, at least on an inner cylinder side of the blade, a section with a thickness varied in a burner axial direction, the thickness being smaller at an edge portion on the combustion-space side than at a maximum-thickness section of the blade.

Claims

1. A combustion burner comprising: an inner cylinder defining, at a radially-inner side, a fuel supply passage for supplying fuel; an outer cylinder surrounding the inner cylinder and defining an air supply passage between the inner cylinder and the outer cylinder; and a swirler in the air supply passage, the swirler being configured to swirl air in the air supply passage, wherein the swirler includes a plurality of blades radially disposed between the inner cylinder and the outer cylinder, the plurality of blades extending from a leading edge on an air-supply side toward a trailing edge on a combustion-space side of the air supply passage, wherein the trailing edge of each of the plurality of blades includes a cutout portion positioned at least on an inner cylinder side such that the trailing edge at the cutout portion recedes from the combustion-space side upstream in a burner axial direction, wherein each of the plurality of blades has, at least on the inner cylinder side of the blade, a section with a thickness varied in the burner axial direction, the thickness being smaller at the trailing edge on the combustion-space side including the cutout portion than at a maximum-thickness section of the blade, and wherein, for each of the plurality of blades, the cutout portion is defined such that a cutout width increases from an outer cylinder side toward a center part in a radial direction, as seen from a side surface of the blade.

2. The combustion burner for a boiler according to claim 1, wherein the side surface is a first side surface and each of the plurality of blades has a second side surface, and the first side surface or the second side surface includes an inclined portion at least on the inner cylinder side, the inclined portion being inclined so that the thickness of the blade decreases toward the trailing edge on the combustion-space side.

3. The combustion burner for a boiler according to claim 2, wherein the inclined portion is a first inclined portion, the first side surface includes the first inclined portion, the second side surface includes a second inclined portion corresponding to the first inclined portion, and the first inclined portion and the second inclined portion define the trailing edge on the combustion-space side into a tapered shape.

4. The combustion burner for a boiler according to claim 1, wherein the side surface is a first side surface and each of the plurality of blades has a second side surface, and the first side surface or the second side surface includes an inclined portion at least on the inner cylinder side, the inclined portion being inclined so that the thickness of the blade decreases toward the trailing edge on the combustion-space side, wherein each of the plurality of blades is inclined from the burner axial direction, wherein each of the plurality of blades has a bent region bent at the air-supply side so as to have a curvature center at the air-supply side, and a linear region defined linearly at the combustion-space side, and wherein the linear region includes a first portion having a constant thickness, and a second portion which is positioned on a downstream side of the first portion and at which the first side surface or the second side surface includes the inclined portion such that the thickness of the blade decreases toward the trailing edge.

5. The combustion burner for a boiler according to claim 4, wherein the inclined portion is inclined by an angle in a range of from 5 to 10 with respect to a portion of the first side surface or the second side surface other than the inclined portion, in the linear region.

6. The combustion burner for a boiler according to claim 1, wherein a first part of the trailing edge at an outer circumferential surface of the inner cylinder is positioned further upstream than a second part of the trailing edge at an inner circumferential surface of the outer cylinder.

7. The combustion burner for a boiler according to claim 6, wherein the plurality of blades is inclined in the same direction with respect to the burner axial direction and spaced from one another in a burner circumferential direction, the leading edge on the air-supply side of a first of the plurality of blades and the trailing edge on the combustion-space side of a second of the plurality of blades being overlapped in the burner axial direction to define an overlapping region, wherein the first of the plurality of blades is adjacent to the second of the plurality of blades, and wherein the cutout portion is defined such that the overlapping region remains.

8. The combustion burner for a boiler according to claim 1, wherein, for each of the plurality of blades, the leading edge extends radially as seen from the side surface of the blade.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a cross-sectional view of an overall configuration of a combustion burner according to the first embodiment.

(2) FIG. 2 is a perspective view of a swirler according to the first embodiment.

(3) FIG. 3 is an enlarged view of a blade as seen in the radial direction of a swirler.

(4) FIG. 4 is a perspective view for explaining an air flow in the vicinity of the swirler according to the first embodiment.

(5) FIG. 5 is a cross-sectional view of a swirler according to the second embodiment.

(6) FIG. 6 as a view of the swirler in FIG. 5 seen from direction A.

(7) FIG. 7 is a cross-sectional view for explaining an air flow in the vicinity of the swirler according to the second embodiment.

(8) FIG. 8 is a cross-sectional view of a swirler according to a modified example of the second embodiment.

(9) FIG. 9 is an expansion view of blades of the swirler in FIG. 8, expanded in the circumferential direction.

(10) FIG. 10 is a front view of a combustion burner, illustrating a state in which fuel is adhering to the swirler.

(11) FIG. 11 is a cross-sectional view for explaining an air flow in a conventional combustion burner.

(12) FIG. 12 is a perspective view for explaining an air flow in the vicinity of a conventional swirler.

DETAILED DESCRIPTION

(13) Embodiments of the present invention will now be described with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention unless particularly specified.

(14) (First Embodiment)

(15) FIG. 1 is a cross-sectional view of an overall configuration of a combustion burner according to the first embodiment. FIG. 2 is a perspective view of a swirler according to the first embodiment. FIG. 3 is an enlarged view of a blade as seen in the radial direction of the swirler.

(16) In an embodiment, as illustrated in FIG. 1, a combustion burner 1 includes an inner cylinder 2, an outer cylinder 4 disposed so as to surround a part of the inner cylinder 2, and a swirler 20 disposed between the inner cylinder 2 and the outer cylinder 4.

(17) A fuel supply passage 10 is formed on the inner peripheral side of the inner cylinder 2. Fuel to be supplied to the fuel supply passage 10 is, for instance, a liquid fuel, and may be a fuel containing a flame-retardant component, such as SDA pitch and vacuum residue (VR) fuel. An end portion of the inner cylinder 2 faces a combustion space 100 of a boiler furnace.

(18) A primary-air nozzle 6 is disposed on the outer peripheral side of the outer cylinder 4, and a secondary-air nozzle 8 is disposed on the outer peripheral side of the primary-air nozzle 6. A primary-air supply passage 14 to be supplied with primary air for combustion is disposed between the inner peripheral surface of the primary-air nozzle 6 and the outer peripheral surface of the inner cylinder 2. A secondary-air supply passage 16 to be supplied with the secondary air for combustion is disposed between the inner peripheral surface of the secondary-air nozzle 8 and the outer peripheral surface of the primary-air nozzle 6. A primary vane 17 and a secondary vane 18 are respectively disposed on the air-supply side of the primary-air supply passage 14 and the secondary-air supply passage 16. Air supply amounts to the respective air supply passages are adjusted by the above vanes 17, 18.

(19) The outer cylinder 4 is disposed on the combustion-space 100 side of the primary-air supply passage 14, partitioning the primary-air supply passage 14 into an inner-peripheral flow path 12 and an outer-peripheral flow path 13. A part of the primary air flowing through the primary-air supply passage 14 flows into the outer-peripheral flow path 13 to be directly discharged into the combustion space 100. Another part of the primary air flows into the inner-peripheral flow path 12 to be swirled by flowing through a swirler 20 describe below, and then discharged into the combustion space 100.

(20) The swirler 20 is disposed in the inner-peripheral flow path 12 of the primary-air supply passage 14, and swirls the primary air mainly to hold a flame. The swirler 20 extends from an air-supply side of the primary-air supply passage 14 (inner-peripheral flow path 12) toward the combustion-space 100 side. The swirler 20 may be disposed in the vicinity of an end portion of the primary-air supply passage 14 at the combustion-space 100 side. As illustrated in FIG. 2, the swirler 20 includes a plurality of blades 26 radially disposed between the inner cylinder 2 and the outer cylinder 4. As illustrated in FIG. 2, seven blades 26 are provided, for example. The swirler 20 may be an integrated piece including a swirler inner cylinder 22 corresponding to the inner cylinder 2, a swirler outer cylinder 24 corresponding to the outer cylinder 4, and blades 26 mounted between the swirler inner cylinder 22 and the swirler outer cylinder 24. In this case, the swirler 20 is fixed by being fitted between the inner cylinder 2 and the outer cylinder 4.

(21) In an embodiment, the blades 26 are inclined in the same direction from the burner axial direction O, and spaced from one another in the circumferential direction of the burner 1. As illustrated in FIG. 3, each blade 26 has a bent region 42 bent at an upstream side (the air-supply side) in the air-flow direction, and a linear region 44 formed linearly at a downstream side (the combustion-space 100 side). Further, a side surface 32 of the swirler 20 faces the combustion space 100 at an angle (see FIGS. 2 and 4). In this way, air having flowed into gaps between the blades 26 of the swirler 20 swirls due to inclination of the blades 26, thereby forming a swirl flow of air in the combustion space 100. Further, the bent region 42 is bent so as to have a curvature center at the air-supply side relative to the blades 26. Air having flowed into a gap between an adjacent two of the blades 26 has its direction changed in the bent region 42, and is rectified in the linear region 44 to be injected into the combustion space 100, which makes it possible to form a swirl flow effectively in the combustion space 100.

(22) Further, the present embodiment includes the following configuration to restrict a backflow toward the swirler 20 due to separation of the swirl flow of air.

(23) As illustrated in FIG. 3, each blade 26 of the swirler 20 has, at least on the inner-cylinder 2 (swirler inner cylinder 22) side, a section with a thickness varied in the burner axial direction O. Further, each blade 26 is formed such that, at least on the inner-cylinder 2 (swirler inner cylinder 22) side, the thickness d.sub.1 of a combustion-space side edge portion 30 is smaller than the thickness d.sub.2 of a maximum-thickness section of the blade 26. It will be understood that the above configuration may be applied not only to the inner-cylinder 2 side but also to the thickness of the blade 26 from the inner cylinder 2 to the outer cylinder 4. The maximum-thickness section of the blade 26 refers to a section with the largest thickness from an air-supply side edge portion 40 to the combustion-space side edge portion 30 of the blade 26. In FIG. 3, the thickness of the air-supply side edge portion 40 is shown as the thickness of the maximum thickness section. However, the maximum thickness section is not limited to this portion, and may be another portion such as a central portion with respect to the burner axial direction O, for instance.

(24) In an embodiment, an inclined portion 36 (or 38) may be disposed on at least one (32 or 34) of the side surfaces 32, 34 at least on the inner-cylinder 2 (swirler inner cylinder 22) side, the inclined portion 36 (or 38) being oblique so that the thickness decreases toward the combustion-space side edge portion 30.

(25) In this case, the inclined portions 36, 38 may be disposed respectively on both of the side surfaces 32, 34 of the blade 26 so that the pair of inclined portions 36, 38 forms the combustion-space side edge portion 30 into a tapered shape.

(26) As described above, according to the present embodiment, the blade 26 of the swirler 20 is formed such that, the thickness d.sub.1 of the combustion-space side edge portion 30 is smaller than the thickness d.sub.2 of the maximum-thickness section of the blade 26, which makes it possible to reduce the area of a negative-pressure region 54 formed on a combustion-space side end surface of the blade 26, as illustrated in FIG. 4. Thus, it is possible to reduce separation of a swirl flow 50 caused by the negative-pressure region 54, and to reduce generation of a backflow 52, which is a separated flow flowing toward the swirler 20. In this way, it is possible to reduce adhering of fuel to the swirler 20, which makes it possible to prevent erosion of the swirler 20 and to maintain a flame-holding function of the swirler 20 for a long time. FIG. 4 is a perspective diagram for explaining an air flow in the vicinity of the swirler according to the first embodiment.

(27) Further, since the backflow 52 of an air flow based on separation of the swirl flow 50 is generated mainly at the inner-cylinder 2 (swirler inner cylinder 22) side, it is possible to securely prevent adhering of fuel to the swirler 20 by reducing the thickness of the blade 26 at least on the inner-cylinder 2 side.

(28) Further, an adhering area is reduced by reducing the thickness of the blade 26 at the combustion-space side edge portion 30, which is likely to have fuel adhering thereto. Thus, even if there is fuel flowing backward to the blade 26 in the backflow 52 starting from separation at a blade end surface, it is possible to further reduce an adhering amount of fuel to the swirler 20.

(29) Further, in the above embodiment, as illustrated in FIG. 3, the inclined portions 36, 38 may be formed in the linear region 44 of the blade 26. As described above, with the inclined portions 36, 38 being formed in the linear region 44, it is possible to improve machining accuracy (e.g., angle) of the inclined portions 36, 38 as compared to a case in which the inclined portions 36, 38 are formed in the bent region 42.

(30) In this case, the inclined portions 36, 38 may have an obliquity angle of in a range of from 5 to 10 with respect to the side surfaces 32, 34 of the linear region 44. In this way, it is possible to prevent separation of the swirl flow and separation of an air flow at the inclined portions 36, 38.

(31) Further, the combustion-space side edge portion 30 of the blade 26 may have an end surface with the thickness d.sub.1, which secures a mechanical strength. As described above, with the combustion-space side edge portion 30 of the blade 26 being formed to have an end surface, it is possible to improve durability of the swirler 20. Further, it is more advantageous in terms of processing to have an end surface forming the combustion-space side edge portion 30 of the blade 26, and durability against erosion also improves.

(32) (Second Embodiment)

(33) With reference to FIGS. 5 and 6, a combustion burner according to the second embodiment of the present invention will be described. It is possible to extend the lifetime of a swirler even further by employing the present embodiment in combination with the first embodiment. FIG. 5 is a cross-sectional view of a swirler according to the second embodiment, and FIG. 6 is a view of the swirler in FIG. 5 seen from direction A.

(34) The present embodiment has the following configuration to reduce adhering of fuel even if there is fuel flowing backward to blades due to a backflow starting from separation at a blade end surface of the swirler 20.

(35) As illustrated in FIGS. 5 and 6, the blade 26 has a cutout portion 46 cut out in the burner axial direction O at a section facing the combustion space 100, at least on the inner-cylinder 2 (swirler inner cylinder 22) side. For instance, the cutout portion 46 has a shape such that the cutout width is the largest at the center part in the radial direction, and the cutout width decreases toward the opposite ends, as seen from a side surface of the blade 26. The shape of the cutout portion 46 is not limited to this.

(36) FIG. 7 is a cross-sectional view for explaining an air flow in the vicinity of the swirler according to the second embodiment.

(37) As described above, according to the present embodiment, with the cutout portion 46 being disposed at least on the inner-cylinder 2 (swirler inner cylinder 22) side of the blade 26, it is possible to restrict adhering of fuel to the blade 26 with the cutout portion 46, even if there is fuel flowing backward to blades due to the backflow 52 starting from separation at a blade end surface.

(38) Further, as illustrated in FIGS. 5 and 6, if the blades 26 are disposed so as to be inclined in the same direction from the burner axial direction O and spaced from one another in the circumferential direction of the burner as described above, with the air-supply side edge portion 40 of a blade and the combustion-space side edge portion 30 of an adjacent blade being overlapped in the burner axial direction O, the cutout portion 46 may be formed so as to maintain this overlapping region 60.

(39) If there is a space between two adjacent blades 26 of the swirler 20 and the space penetrates through in the axial direction O of the burner 1, the space may hamper formation of a swirl flow. Thus, with the cutout portion 46 formed so as to maintain the overlapping region 60 in which two adjacent blades 26 overlap with each other, it is possible to reduce adhering of fuel to the swirler 20 without affecting formation of a swirl flow.

(40) With reference to FIGS. 8 and 9, a modified example of the second embodiment will be described. FIG. 8 is a cross-sectional view of a swirler according to a modified example of the second embodiment, and FIG. 9 is an expansion view of blades of the swirler in FIG. 8, expanded in the circumferential direction. In the drawings, dotted lines represent an outer-shell shape of conventional blades 26.

(41) As illustrated in FIGS. 8 and 9, while the pitch of the blades 26 is maintained to be the same as that of the conventional blades 26, the length of each blade 26 in the burner axial direction O is shorter than that of the conventional blades 26, and the length of each blade 26 in the radial direction is longer. In this way, the overlapping region 60 of adjacent two of the blades 26 expands, which makes it possible to increase a region in which the cutout portion 48 can be formed. For instance, the cutout portion 48 has a shape such that the cutout width is constant from the center part in the radial direction to the swirler inner cylinder 22 side, and the cutout width decreases from the center part toward the swirler outer cylinder 24 side, as seen from a side surface of the blade 26.

(42) Embodiments of the present invention were described in detail above, but the present invention is not limited thereto, and various amendments and modifications may be implemented within a scope that does not depart from the present invention.

DESCRIPTION OF REFERENCE NUMERALS

(43) 1 Combustion burner 2 Inner cylinder 4 Outer cylinder 6 Primary-air nozzle 8 Secondary-air nozzle 10 Fuel supply passage 12 Inner-peripheral flow path 13 Outer-peripheral flow path 14 Primary-air supply passage 16 Secondary-air supply passage 17 Primary vane 18 Secondary vane 20 Swirler 22 Swirler inner cylinder 24 Swirler outer cylinder 26 Blade 30 Combustion-space side edge portion 32, 34 Side surface 36, 38 Inclined portion 40 Air-supply side edge portion 42 Bent region 46, 48 Cutout portion 50 Swirl flow 42 Backflow 54 Negative-pressure region 100 Combustion space