Burner plate for flat flame burners

Abstract

Burner plate (1) for a flat flame burner (21), wherein the burner plate (1) has several burner openings (29) into which premixed gas of fuel and air is supplied, wherein the burner plate (1) has a front surface which faces a combustion zone (B), wherein the burner plate (1) has: a combustion area (31) in which the several burner openings (29) are formed; and a separating area (33) which surrounds the combustion area (31) and has no burner opening, wherein the separating area (33) is formed as an area which has a distance which is greater than a distance between adjacent burner openings (29) in the combustion area (31), and wherein, with respect to a combustion zone-side front surface of the separating area (33), a combustion zone-side front surface of the combustion area (31) is recessed in the direction of a supply zone (S) of premixed gas,wherein the combustion region (31) comprises several first combustion regions (31A) and several second combustion regions (31B), each second combustion region (31B) forming a region having a smaller area than the first combustion region (31A), each of the first combustion regions (31A) and the second combustion regions (31B) forming a rhombus-shaped region in plan view, and the combustion zone-side front surface of the combustion region is recessed rearward relative to the combustion zone-side front surface of the separation region (33) such that it has a pyramid shape, the several first combustion regions (31A) being arranged at predetermined intervals such that the sides of the rhombuses are opposite each other, and the several second combustion regions (31B) being arranged between respective corners of two first combustion regions (31A).

Description

Cross-Reference to the Related ApplicationThe present application is based on and claims priority from Japanese Patent Application No. 2015-256327 filed on Dec. 28, 2015, the disclosure of which is incorporated herein in its entirety by reference.BACKGROUND OF THE INVENTION(Field of Invention)The present invention relates to a structure of a burner plate used for a flat flame burner.(Description of Prior Art)The flat flame burner is used, for example, for a regenerator of an air conditioner such as a cold and hot water absorption machine. The flat flame burner has the advantage that the installation space for the burner can be reduced by its use.[Prior Art Document][Patent Document][Patent Document 1] Japanese Patent Publication JP2004-239483AOverview of the InventionGenerally, however, premixed gas having a low fuel concentration is burned in a flat flame burner. In the flat flame burner in which flames are held in a plurality of burner ports, combustion vibrations sometimes occur due to unstable combustion by flames, particularly when the combustion load is low.For example, in order to prevent the occurrence of combustion vibration, Patent Document 1 contemplates modifying the structure of an exhaust passage in a regenerator using a flat flame burner. However, changing the structure of an apparatus in which the flat flame burner is installed is undesirable because such a change may result in an increase in size and an increase in cost. U.S. Pat. No. 4,569,657 A discloses a burner plate in which burner openings are arranged in a uniformly distributed manner and some burner openings are arranged in depressions. In order to avoid heat losses due to heat conduction, the amount of material in the region between the depressions should be minimized. JP S60-53710 A discloses a burner plate having uniformly distributed burner openings, the burner plate forming elevations and depressions. According to JP S60-53710 A, this leads to an irregular radiation distribution of infrared radiation formed by the heated plate. DE 1 526 037 A discloses a burner plate with uniformly distributed burner openings, wherein the burner plate forms depressions. As a result, a flame of one burner opening is intended to serve for stabilizing the flame of an adjacent burner opening. EP 0 751 344 B1 discloses another burner plate having a plurality of burner openings, wherein the burner plate has a front surface facing a combustion zone, wherein the burner plate has a combustion region in which the plurality of burner openings are formed and a separation region surrounding the combustion region and having no burner opening, wherein the separation region is formed as a region having a distance greater than a distance between adjacent burner openings in the combustion region, and wherein, with respect to a combustion zone-side front surface of the separation region, a combustion zone-side front surface of the combustion region protrudes toward the combustion zone or is recessed toward a premixed gas supply zone.In order to solve the above-described problem, it is an object of the present invention to provide a burner plate for a flat flame burner which enables combustion vibration to be prevented from occurring without changing the dimensions of a peripheral device.To achieve the above object, a burner plate for a flat flame burner according to the present invention is a burner plate having a plurality of burner ports into which premixed gas of fuel and air is supplied, the burner plate being used for a flat flame burner and having a front surface facing a combustion zone. The burner plate includes: a combustion region in which the plurality of burner openings are formed; and a partition region surrounding the combustion region and having no burner opening, wherein the partition region is formed as a region having a distance larger than a distance between adjacent burner openings in the combustion region, and wherein, with respect to a combustion zone-side front surface of the partition region, a combustion zone-side front surface of the combustion region protrudes toward the combustion zone or is recessed toward a premixed gas supply zone.According to this configuration, since the depression or protrusion is formed in the front surface of the burner plate, the height of the flames to be held by the plurality of burner openings is not uniform, thereby preventing the occurrence of combustion fluctuations.According to an embodiment of the present invention, the combustion zone-side front surface of the combustion region may be recessed to have a pyramid or an elliptic cone shape with respect to the combustion zone-side front surface of the partition region. According to this configuration, unevenness of flame lengths is ensured by a zone which is formed in front of the combustion region and in which the density of a vibration transmission medium is high, thereby preventing occurrence of combustion vibrations.According to an embodiment of the present invention, the combustion zone-side front surface of the combustion region may be stepped recessed with respect to the combustion zone-side front surface of the partition region. According to this configuration, the convergence of flames to a central portion of the combustion portion is facilitated and the flame lengths become uneven, thereby preventing the occurrence of combustion vibrations.According to an embodiment of the present invention, the combustion zone-side front surface of the combustion region may protrude to have a pyramid or an elliptic cone shape with respect to the combustion zone-side front surface of the partition region. In this configuration, since the combustion region is formed to project toward the center region, an uneven flow rate field is formed on the combustion region and the flame lengths become uneven, thereby preventing combustion vibration from occurring.Any combination of at least two constructions disclosed in the appended claims and / or the specification and / or the accompanying drawings should be considered to fall within the scope of the present invention. In particular, any combination of two or more of the appended claims should equally be considered to fall within the scope of the present invention.Brief Description of the DrawingsA better understanding of the present invention will in any case be obtained from the following description of preferred embodiments thereof in conjunction with the accompanying drawings. The embodiments and drawings are, however, given for purposes of illustration and explanation only and should not be considered as limiting the scope of the invention in any way which is defined by the appended claims. In the accompanying drawings, like reference numerals designate like parts throughout the several views, and: FIG. 1 is a block diagram showing an example of an apparatus in which a burner plate according to the present invention is used; FIG. 2 is a cross-sectional view schematically illustrating a schematic configuration of a flat flame burner in which the burner plate according to the present invention is used; FIG. 3 is a plan view showing a burner plate according to a first embodiment of the present invention; FIG. 4 is a perspective view of the burner plate according to the first embodiment of the present invention; FIG. 5 is a schematic view for explaining a function of the burner plate illustrated in FIG. 4 ; FIG. 6 is a perspective view illustrating a burner plate according to a second embodiment of the present invention; FIG. 7 is diagrams for explaining a function of the burner plate shown in FIG. 6, wherein the diagram (a) is a heat generation contour diagram according to a conventional example and the diagram (b) is a heat generation contour diagram according to an example of the second embodiment; FIG. 8 is a perspective view illustrating a burner plate according to a third embodiment of the present invention; and FIG. 9 is diagrams for explaining a function of the burner plate shown in FIG. 8, wherein the diagram (a) is a generated heat contour diagram according to a conventional example and the diagram (b) is a generated heat contour diagram according to an example of the third embodiment.DESCRIPTION OF EMBODIMENTSHereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to this embodiment.FIG. 1 shows a schematic configuration of an absorption chiller R which is an example of an apparatus in which a burner plate for a flat flame burner (hereinafter, simply referred to as "burner plate") 1 according to a first embodiment of the present invention is installed. In the absorption chiller R, water is evaporated in an evaporator 3, so that water W 1, which is a cooling object flowing through a cold water pipe 5, is cooled by the latent heat of evaporation. Water W2 is supplied to the evaporator 3 and is obtained by condensing water vapor in a condenser 7. The water vapor W 3 generated in the evaporator 3 is absorbed by a moisture absorption medium (for example, an aqueous lithium bromide solution) in an absorber 9. A low-concentration moisture absorption medium M1 that has absorbed the water vapor W3 in the absorber 9 is supplied to a regenerator 11 and heated in the regenerator 11 to be separated into water vapor W4 and a high-concentration moisture absorption medium M2. The water vapor W4 produced in the regenerator 11 is supplied to the condenser 7, and the high-concentration moisture absorption medium M2 is returned to the absorber 9.In the absorption chiller R, a flat flame burner 21 is provided in the regenerator 11 as a device for heating the low-concentration absorption medium M1. As illustrated in FIG. 2, the regenerator 11 includes: a regenerator body 23 that accommodates a tube to be heated (not illustrated), through which the low-concentration moisture absorption medium M 1 (FIG. 1 ), which is an object to be heated, flows; and the flat flame burner 24 disposed adjacent to the regenerator body 23. In the flat flame burner 21, a fuel F and air A supplied at a predetermined ratio are mixed together in a premixing chamber 25, and the resultant premixed gas P generated in the premixing chamber 25 is supplied to the burner plate 1. The burner plate 1 is generally a substantially plate-shaped member made of a heat resistant material such as ceramic. A plurality of burner openings 29 are formed in the burner plate 1 in such a way that they pass through the burner plate 1 from its front side to the rear side. The premixed gas P is supplied to each of the burner ports 29 of the burner plate 1 and is ignited by an unillustrated igniter.In the following description, in the burner plate 1, a side facing the combustion zone B on which flames are to be held may be referred to as a "front side", and a side facing the zone S (the premixed chamber 25 in the illustrated example) to which the premixed gas P is supplied may be referred to as a "rear side". In the example of FIG. 1, the inside of a casing of the regenerator body 23 is the combustion zone B for the flat flame burner 21, and in the burner plate 1, a surface facing the combustion zone B is simply referred to as a "front surface", and a surface facing the premixed gas supply zone S is simply referred to as a "rear surface".As shown in FIG. 3, the burner plate 1 has: a combustion region 31 having a plurality of burner openings 29 formed therein; and a partition region 33 surrounding the combustion region and having no burner opening 29. The "partition portion" is different from gap portions between the burner openings 29 in the combustion portions 31 in that the "partition portion" is formed as a portion having a distance larger than a distance between the adjacent burner openings 29, 29 in the combustion portion 31 to separate the combustion portions 31 from each other.The burner plate 1 includes: a plurality of first combustion regions 31A each forming a substantially diamond-shaped region in plan view; and a plurality of second combustion regions 31B each similarly substantially diamond-shaped in plan view and forming a region having a smaller area than the first combustion region 31A. The plurality of combustion regions 31A are arranged at predetermined intervals such that the sides of the diamonds are opposed to each other. The plurality of second combustion regions 31B are respectively disposed between respective corners of two first combustion regions 31A. Regions between the plurality of first combustion regions 31A form the partition region 33 surrounding each of the combustion regions 31 and having no burner opening 29. The partition portion 33 is formed such that the entire front surface thereof is planar and parallel to the rear surface of the burner plate 1. In the following description, the first combustion regions 31A and the second combustion regions 31B may be collectively referred to as a "combustion region 31" when describing aspects that do not need to be distinguished from each other.In the illustrated example, in each first combustion region 31A, thirty-six burner openings 29 in total are arranged at equal intervals in a layout of 6 rows x 6 columns. In each second combustion region 31B, four burner ports 29 are arranged at equal intervals in a layout of 2 rows x 2 columns. However, the number and layout of the burner openings 29 in the combustion area 31 are not limited to this example.As illustrated in FIG. 4, in the burner plate 1, the front surface of the first combustion region 31A and the front surface of the second combustion region 31B are each formed to be recessed rearward from the partition region 33 to have the shape of a pyramid (quadrilateral pyramid in this case). Thus, the front surface of each combustion region 31 is formed by a plurality (four in this example) of triangular sides defined by: an apex located at the center of the combustion region 31 in plan view; and sides each forming the boundary between the combustion region 31 and the separation region 33. As shown in FIG. 2, the back surface of the burner plate 1 is formed as a flat surface having no recess or protrusion.Effects of the thus-formed burner plate 1 will be described with reference to FIG. 5, which schematically illustrates a flow field of a vibration transmission medium in the combustion zone B. As shown in FIG. 5, in the combustion zone B, a flow of the vibration transmission medium (pressure wave) PW moving toward the burner plate 1 is generated as a result of reflection by the inner wall surface of a casing constituting the combustion zone B (the casing of the regenerator body 23 in this example). The pressure wave PW is reflected from a front surface 31 aof the combustion region 31 which is pyramidally recessed, that is, inclined rearward toward a center region of the combustion region 31, thereby forming a region H in which the density of the medium is locally high on a front side of the center region of the combustion region 31. In the zone H where the density of the medium is high, the acoustic impedance (which is reproduced as the product of the density of the medium and the speed of sound in the medium) becomes high, and the propagation of the pressure wave PW is decelerated. In this way, in the combustion region B in which flame lengths are nonuniform as a result of the nonuniform arrangement of the burner openings 29, interference of the pressure wave PW by the local increase in the density of the medium is further prevented, and ex-PW by the local increase in the density of the medium is prevented, and expansion or contraction of the flames is less likely, thereby maintaining the nonuniformity of the flame lengths. Accordingly, in the burner plate 1 according to the present embodiment, occurrence of combustion vibration is prevented.The shapes and / or the arrangements of the combustion portion 31 and the partition portion 33 of the burner plate 1 are not limited to the example illustrated in FIGS. 3 and 4. For example, the combustion region 31 may be formed as a region having an elliptical shape (including a circular shape. In this case, the combustion chamber 31 is formed to be recessed from the partition portion 33 to have an elliptical conical shape (including a conical shape). Moreover, in the present embodiment, an example has been shown in which two kinds of combustion regions, i.e., the first combustion regions 31A and the second combustion regions 31B, having respective sizes different between the two types are provided as the combustion regions 31 in the burner plate 1. However, a plurality of combustion regions each having the same size as each other may be provided, or three or more types of combustion regions 31 each having different sizes may be provided.FIG. 6 shows a burner plate 1 according to a second exemplary embodiment of the present invention. The burner plate 1 according to the second embodiment is different in structure from the burner plate 1 described as the first embodiment only in that the front surface of the combustion region 31 is formed to be stepped recessed from the front surface of the partition region 33. In the following description, only the differences in structure and function from the first embodiment will be described.Specifically, the first combustion region 31A, which is the combustion region 31 of the burner plate 1 according to the first embodiment, is formed such that the entire front surface thereof is parallel to the front surface of the separation region 33 and is formed to be steppedly recessed toward the premixed gas supply zone S side. Thus, at a boundary portion between the first combustion portion 31A and the partition portion 33, a wall surface 41 as a step-forming surface is formed to be perpendicular to the front surface of the first combustion portion 31A of the burner plate 1.Effects of the thus formed burner plate 1 will be described with reference to FIG. 7 illustrating heat generation contour diagrams obtained in combustion. In FIG. 7, the contour diagram (a) is a heat generation contour diagram obtained when combustion is performed using a burner plate 1 in which the combustion region 31 and the separation region 33 are formed to be in one plane (Comparative Example 1), and the contour diagram (b) is a heat generation contour diagram obtained when combustion is performed using a burner plate 1 according to Example 1 of the present embodiment.As is clear from the drawing, in the burner plate according to the comparative example, the flame lengths held by the respective burner openings 29 are substantially uniform in the combustion region 31, while in the burner plate 1 according to the example 1, the flame lengths increase from an end portion of the combustion region 31 which is stepped toward the region around the center portion. In other words, in the burner plate 1 according to Example 1, the flame lengths are non-uniform over the combustion region 31. It is considered that this phenomenon is caused due to the convergence of the flames to the central portion of the combustion portion 31, being facilitated by the wall surface 41 shown in FIG. 6 which constitutes the step between the combustion portions 31 and the separation portion 33. In other words, by flames subjected to the influence of friction caused on the wall surface, the flow rate decreases at and near the wall surface 41, thereby facilitating the convergence of flames toward the central portion of the combustion portion 31. Therefore, the flame lengths in the combustion region 31 become uneven, and as a result, the occurrence of combustion vibration is avoided in the burner plate according to the present embodiment.In the present embodiment, only the first combustion region 31A among the combustion regions 31 is recessed in a stepped shape. However, the second combustion portion 31B may be recessed in a stepped shape.FIG. 8 shows a burner plate 1 according to a third exemplary embodiment of the present invention. The burner plate 1 according to the third embodiment is different in structure from the burner plate 1 described as the first embodiment only in that the combustion region 31 protrudes from the partition region 33 to have a pyramid shape. In the following description, only the differences in structure and function from the first embodiment will be described.As described above, in the burner plate 1 according to the present embodiment, the front surfaces of the combustion regions 31 (the first combustion regions 31A and the second combustion regions 31B) are formed to project forward from the partition region 33 in a pyramid shape (quadrilateral pyramid in this example). Thus, the front surface of each combustion region 31 is formed by a plurality of (in this example, four) triangular sides defined by: an apex located at the center of the combustion region 31 when viewed in plan view; and sides each forming the boundary between the combustion region 31 and the separation region 33.Effects of the thus-formed burner plate 1 will be described with reference to FIG. 9, which shows flow rate contour charts obtained in the combustion. In the drawing, the contour diagram (a) is a flow rate contour diagram obtained when combustion is performed using a burner plate 1 (Comparative Example 2) in which the combustion region 31 and the separation region 33 are formed to be in a plane, and the contour diagram (b) is a flow rate contour diagram obtained when combustion is performed using a burner plate 1 according to Example 2 of the present embodiment.As is apparent from the drawing, in the burner plate according to Comparative Example 2, a substantially uniform flow rate field is formed in the combustion region 31, while in the burner plate 1 according to Example 2, as the amount of protrusion of the combustion region 31 from an end portion of the combustion region 31 that is stepped toward a region around the center portion increases, the flow rate also increases. In other words, in the burner plate 1 according to Example 2, an uneven flow rate field is formed in the combustion region 31, and as a result, the flame lengths also become uneven. Therefore, the flame lengths in the combustion region 31 become uneven, and as a result, the occurrence of combustion vibration is avoided in the burner plate according to the present embodiment.As described above, in each of the embodiments, the combustion region 31 of the burner plate 1 is formed such that the front surface thereof protrudes or is recessed with respect to the partition region 33, so that the flame lengths to be held by the plurality of burner openings 29 become uneven, thereby preventing the occurrence of combustion vibration. Further, the provision of the depression or protrusion on the front surface of the burner plate 1 does not result in any significant change in the dimensions of the burner plate 1, and thus combustion vibration can be prevented without changing the dimensions of the flat flame burner 21 using the burner plate 1 and the dimensions of an apparatus in which the flat flame burner 21 is installed.The burner plate 1 is not limited to the examples described as the first to third embodiments. Combustion vibrations are avoided as long as the front surface of the combustion portion 31 is shaped to protrude toward the combustion zone B side or recessed toward the premixed gas supply zone S side with respect to the separation portion 33, so that the flame lengths to be held by the burner openings 29 become uneven due to this shape. As an intermediate embodiment between the first embodiment and the second embodiment, for example, the combustion region 31 may be recessed to have the shape of a truncated pyramid or the shape of an ellipsoidal truncated cone with respect to the separation region 33.Although the present invention has been described above in connection with the preferred embodiments thereof with reference to the accompanying drawings, various additions, modifications or omissions may be made without departing from the scope of the present invention. Such additions, modifications or omissions are thus considered to fall within the scope of the present invention.[Reference Numeral]1 Flat flame burner plate 21 Flat flame burner 29 Burner opening 31 Combustion region 33 Separation region B Combustion zone P Premixed gas S Premixed gas supply zone

Claims

A burner plate (1) for a flat flame burner (21), the burner plate (1) having a plurality of burner openings (29) into which premixed gas of fuel and air is supplied, the burner plate (1) having a front surface facing a combustion zone (B), the burner plate (1) having: a combustion region (31) in which the plurality of burner openings (29) are formed; and a partition region (33) surrounding the combustion region (31) and having no burner opening, wherein the partition region (33) is formed as a region having a distance larger than a distance between adjacent burner openings (29) in the combustion region (31), and wherein, with respect to a combustion zone-side front surface of the partition region (33), the partition region (33) is formed, a combustion zone side front surface of the combustion portion (31) is recessed toward a premixed gas supply zone (S), the combustion portion (31) includes a plurality of first combustion portions (31A) and a plurality of second combustion portions (31B), each second combustion portion (31B) forming a portion having a smaller area than the first combustion portion (31A), each of the first combustion portions (31A) and the second combustion portions (31B) forming a diamond-shaped portion in plan view, and the combustion zone side front surface of the combustion portion is recessed rearward relative to the combustion zone side front surface of the partition portion (33) to have a pyramid shape, the plurality of first combustion portions (31A) being arranged at predetermined intervals such that sides of the diamonds are opposed to each other, and wherein the plurality of second combustion regions (31B) are each disposed between respective corners of two first combustion regions (31A).A burner plate (1) for a flat flame burner (21), the burner plate (1) having a plurality of burner openings (29) into which premixed gas of fuel and air is supplied, the burner plate (1) having a front surface facing a combustion zone (B), the burner plate (1) having: a combustion region (31) in which the plurality of burner openings (29) are formed; and a partition portion (33) surrounding the combustion portion (31) and having no burner opening, wherein the partition portion (33) is formed as a portion having a distance larger than a distance between adjacent burner openings (29) in the combustion portion (31), and wherein, with respect to the combustion zone side front surface of the partition portion (33), the combustion zone side front surface of the combustion portion (31) protrudes toward the combustion zone (b), and wherein the combustion zone side front surface of the combustion portion (31) protrudes to have a shape of a pyramid or an elliptic cone with respect to the combustion zone side front surface of the partition portion (33).

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