COMBUSTION BURNER AND COMBUSTION DEVICE PROVIDED WITH SAME

Abstract: A combustion burner includes a mixture nozzle, a gas supply nozzle, and guide means. The mixture nozzle extends toward an interior of a furnace, and defines a mixture passage through which a mixture containing powdered solid fuel and gas for transferring the solid fuel flows. A distal end portion of the mixture nozzle is flared so that a flow passage area of the mixture passage increases progressively in a direction of flow of the mixture. The gas supply nozzle radially surrounds the mixture nozzle to define between the gas supply nozzle and the mixture nozzle a gas passage through which a combustion oxygen-containing gas flows toward the furnace. The guide means is provided within the mixture nozzle at a position upstream of the flared portion of the mixture nozzle with respect to a flow of the mixture so as to make the mixture flow straightly along an inner peripheral surface of the flared portion of the mixture nozzle.

Description: This invention relates to a combustion burner comprising the features of the first part of claim 1, as disclosed in the EP 0 489 928 A. In a pulverized coal burner disclosed in the JP-63-87508 A an impeller for swirling an air-fuel mixture is provided within a mixture nozzle. The swirled mixture from an outlet of the mixture nozzle is rapidly diffused within a furnace, and is mixed with secondary air and tertiary air, supplied from a gas supply nozzle, in the vicinity of the outlet of the mixture nozzle. Therefore, a reduction area is not sufficiently formed, and a flame does not spread in the furnace. As a result, a part of fine pulverized coal remains unburned, and the production of NOx can not be suppressed. In a pulverized coal burner disclosed in the JP-60-200008 A, a throat portion is provided within a mixture nozzle, and an outlet of the mixture nozzle is flared. In this burner, as in the above-mentioned burner, an air-fuel mixture from an outlet of the mixture nozzle is rapidly diffused within a furnace, and is mixed with secondary air and tertiary air, supplied from a gas supply nozzle, in the vicinity of the outlet of the mixture nozzle. As a result, a part of fine pulverized coal remains unburned, and the production of NOx can not be suppressed. The known combustion burner shown in Fig. 10 of the cited EP 0 489 928 A comprises a mixture tube or nozzle for supplying pulverized coal mixed with primary air into a furnace. At the distal end of that mixture nozzle there is provided a radially outwardly flared flame holding ring. For preventing burning and slag depositing on that flame holding ring a projecting body is extended beyond the flame holding ring in the furance. Guiding means formed as a separation rod are disposed centrally inside the mixture nozzle for heightening the concentration of the mixture. The separation rod has a flared upstream portion, a cylindrical middle portion and a conical downstream portion. The mixture nozzle has a constant outer diameter and no flared end portion. In EP 0 315 802 A there is disclosed a coal dust burner comprising a mixture tube for supplying the mixture of pulverized coal and primary air into a furnace. Coaxially inside of the mixture tube there is disposed an ignition tube having a conical end portion. The mixture tube has a flared end portion which forms, together with the conical end portion of the ignition tube, a funnel-shaped ring nozzle. It is an object of this invention to provide a combustion burner which solves these problems, and can achieve low-NOx combustion. To this end, according to one aspect of the present invention, there is provided a combustion burner comprising: a mixture nozzle which extends toward an interior of a furnace, and defines a mixture passage through which a mixture containing powdered solid fuel and gas for transferring the solid fuel flows, and a distal end portion of which mixture nozzle is flared so that a flow passage area of the mixture passage increases progressively in a direction of flow of the mixture; a gas supply nozzle radially surrounding the mixture nozzle and defining between the gas supply nozzle and the mixture nozzle a gas passage through which combustion oxygen-containing gas flows towards the furnac e; and guide means provided within the mixture nozzle at a position upstream of the flared portion of the mixture nozzle with respect to a flow of the mixture so as to make the mixture flow straightly along an inner peripheral surface of the flared portion of the mixture nozzle. According to another aspect of the present invention, there is provided a combustion burner comprising: a mixture nozzle extending towards an interior of a furnace, and defining a mixture passage through which a mixture containing powdered solid fuel and gas for transferring the solid fuel flows, and a distal end portion of which mixture nozzle is flared so that a flow passage area of the mixture passage increases progressively in a direction of flow of the mixture; a gas supply nozzle radially surrounding the mixture nozzle, and defining between the gas supply nozzle and the mixture nozzle a gas passage, through which combustion oxygen-containing gas flows towards the furnace, and a gas jet nozzle through which gas is injected radial inwardly towards the mixture flowed into the furnace from the distal end of the mixture nozzle. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of an embodiment of a burner of the present invention; Fig. 2 is a cross-sectional view of a furnace of a boiler using the burners of Fig. 1, showing a condition of a flame in the furnace; Fig. 3 is a cross-sectional view taken along the line III-III of Fig. 2; Fig. 4 is a cross-sectional view showing the condition of the flame in the furnace; Fig. 5 is a cross-sectional view showing a flow of a mixture and a flow of combustion air in the burner; Fig. 6 is a cross-sectional view showing a condition of a flame in a furnace using a conventional burner; Fig. 7 is a cross-sectional view of the furnace of a boiler using the conventional burners, showing the condition of the flame in the furnace; Fig. 8 is a cross-sectional view taken along the line VIII-VIII of Fig. 7; Fig. 9 is a cross-sectional view showing another embodiment of a burner; Fig. 10 is a cross-sectional view taken along the line X-X of Fig. 9; Figs. 11 to 13 are cross-sectional views showing further embodiments of burners, respectively; Fig. 14 is a cross-sectional view showing a further embodiment of a burner; Fig. 15 is a cross-sectional view taken along the line XV-XV of Fig. 14; Figs. 15A to 15D are front-elevational views respectively showing modified air injection nozzle constructions of a burner of Fig. 14; Fig. 16 is a fragmentary, cross-sectional view showing a condition of flow of a mixture and a condition of flow of combustion gas in the vicinity of an outlet of the burner shown in Fig. 14; Fig. 17 is a cross-sectional view taken along the line XVII-XVII of Fig. 16; Fig. 18 is a cross-sectional view showing another embodiment of a burner; Fig. 19 is a cross-sectional view taken along the line XIX-XIX of Fig. 18; and Fig. 20 is a cross-sectional view showing a further embodiment of a burner. BEST MODE FOR CARRYING OUT THE INVENTION A combustion burner 1 according to one embodiment of the present invention shown in Fig. 1, which is used in a boiler, comprises a mixture nozzle 10 through which a mixture 12 containing fine pulverized coal as solid fuel and primary air for transferring purposes flows. In this embodiment, as shown in Figs. 2 and 3, twelve combustion burners 1 are arranged in an opposed manner in a common horizontal plane at a furnace 3, and also the combustion burners are arranged in three stages in a vertical direction. However, the number of the burners 1 as well as the number of stage is not limited to this arrangement. The mixture 12 is supplied via the nozzle 10 into the furnace 3 through an opening 30 formed in the furnace 3. A gas supply nozzle 20 is provided around the nozzle 10. A secondary air passage 21 is defined between the nozzle 10 and the nozzle 20, and a tertiary air passage 31 is defined between the nozzle 20 and the opening 30 of the furnace 3. A swirl-producing device 23 is provided in the secondary air passage 21 so as to swirl the secondary air 22 from a wind box 4. A swirl-producing device 33 is provided in the tertiary air passage 31 so as to swirl the tertiary air 32 from the wind box 4. A ring-shaped flame stabilizer 13 is provided at a distal end of the nozzle 10, which has a peripheral edge portion of an L-shaped cross-section. A distal end portion 14 of the nozzle 10 is flared so that its flow passage area increases progressively along the flow of the mixture 12. A guide 51 is disposed in the nozzle 10 so that the mixture 12 can flow radially outwardly along the flared distal end portion 14. The guide 51 is provided at a distal end of an oil burner 52. The oil burner 52 is used when activating the boiler and in a low-load condition. In the case where no oil burner is needed, the guide 51 is placed by a suitable support. The guide 51 has a first guide portion 511, a second guide portion 512 and a third guide portion 513 along the flow of the mixture 12. The outside dimension of the first guide portion 511 increases progressively in the direction of flow of the mixture 12, and the outside dimension of the third guide portion 513 decreases progressively in the direction of flow of the mixture 12. Both are interconnected by the second guide portion 512 having a constant outside dimension. The guide 51 is located upstream side of the flared distal end portion 14 with respect to the flow of the mixture 12. In the burner 1 of this construction, a flame 5 is spread outwardly as shown in Fig. 4. As a result, unavailable areas NA of the furnace are reduced as shown in Figs. 2 and 3. Air supply ports 6 are provided downstream of the burners 1, and additional air 62 is supplied into the furnace 3 through these air supply ports. In reduction areas RA delimited by the flames 5 from the most downstream burners 1 and the additional air flows 62 from the air ports 6, the combustion gas stays for a longer time period. Therefore, the NOx concentration in the combustion gas is reduced, so that the combustion efficiency is enhanced. The unburned pulverized coal is completely burned by the air 62 from the air ports 6. The momentum of the pulverized coal is greater than that of the primary air, and therefore the pulverized coal is condensed at a region close to the peripheral wall of the flared distal end portion 14 of the nozzle 10, as shown in Fig. 5. Therefore, the combustion efficiency in the vicinity of the outlet of the burner is enhanced, so that the flame 5 is thermally expanded to be more spread. In this embodiment, the nozzle 20 is provided at a distal end thereof with a flared, annular deflection guide tube 24. Accordingly, the primary air 22 and the tertiary air 23, which are swirled respectively by the swirl-producing devices, flow forwardly and radially outwardly. As shown in the drawings, if the annular deflection guide tube 24 is so designed that the angle  1 between the annular deflection guide tube 24 and the axis of the mixture nozzle 10 is equal to or larger than the angle  2 between the flared distal end portion 14 and the axis of the mixture nozzle 10, the secondary air and the tertiary air are more spread radially outwardly. As a result, an air-insufficient area, that is, a fuel-excessive area is formed in a central portion of the flame, thereby enabling the low NOx combustion. On the other hand, in a conventional burner shown in Fig. 6, a mixture nozzle 10 does not have the flared distal end portion 14, and the guide 51 is not provided within the mixture nozzle. Therefore, a flame does not spread, but behaves as a free jet. As a result, as shown in Figs. 7 and 8, the area in a furnace 3 where flames are not present, that is, the unavailable area NA in the furnace become larger as compared with the furnace of Figs. 2 and 3. Further, the time period of stay of the pulverized coal in reduction areas RA becomes shorter, and then the NOx concentration in the combustion gas can not be lowered. As compared with the burner of Fig. 1, a burner 1 of Fig. 9, which is another embodiment, further comprises a swirl-producing device 53 for swirling the mixture 12, and flow-rectifying plates 54. Hereinafter, the parts which are identical in construction or correspond in effect to those of the above embodiment will be designated by the same reference numerals, respectively, and explanation thereof will be omitted. The swirl-producing device 53 is placed upstream of the guide 51. Accordingly, a larger amount of pulverized coal in the mixture flows along the inner peripheral surface of the flared distal end portion 14, thereby enabling the flame 5 to be further spread. However, if the mixture is supplied in the form of a swirling flow into a furnace 3, such mixture is immediately mixed with the secondary air or the tertiary air in the vicinity of the burner 1, so that the low NOx combustion is not effected. Therefore, the plurality of flow-rectifying plates 54 are provided on the inner peripheral surface of the flared distal end portion 14 disposed downstream of the swirl-producing device 53 (Fig. 10). With this construction, a circumferential velocity component of the mixture 12 is suppressed while a forward velocity component thereof is increased, and then the mixture is mixed with the secondary air and the tertiary air at a location far from the burner 1. As a result, the reduction areas are increased, so that the low NOx combustion is possible. As compared with the embodiment of Fig. 9, a burner 1 of Fig. 11, which is another embodiment, further comprises a Venturi tube 54 provided upstream of the swirl-producing device 53. A throat portion of the Venturi tube 54 once converges the pulverized coal in an air-fuel mixture toward a radially-central portion of the mixture nozzle 10, and directs it toward the swirl-producing device 53. With this construction, the pulverized coal in the mixture can flow more efficiently along the inner peripheral surface of the flared distal end portion 14. Therefore, the generation of NOx can be more suppressed. As compared with the embodiment of Fig. 11, a burner 1 of Fig. 12, which is a further embodiment, has an annular spacer 25 instead of the annular deflection guide tube 24, the spacer 25 being provided at a distal end of the gas supply nozzle 20. An inner peripheral surface of the spacer 25 is so flared that its diameter increases progressively along the flow of mixture, and an outer peripheral surface of the spacer 25 is parallel to an axis of the mixture nozzle 10. An end of the inner peripheral surface of the spacer 25 and an end of the outer peripheral surface thereof are interconnected by an end wall disposed perpendicular to the axis of the mixture nozzle 10. With this construction, the secondary air 22 flows along the flared inner peripheral surface of the spacer 25, and is spread into a furnace 3 as in the above embodiment. The tertiary air 23 flows along the outer peripheral surface of the spacer 25, and is supplied into the furnace 3 from a radially-outward position, and therefore is mixed with the flame 5 with a delay at a position far from the burner 1. As a result, the reduction areas are formed in the vicinity of the burner 1, and the generation of NOx can be suppressed. As compared with the embodiment of Fig. 1, a burner 1 of Fig. 13, which is a further embodiment, includes the mixture nozzle 10 whose distal end portion is not flared. The venturi tube 54 having a throat portion is provided inside the distal end portion of the mixture nozzle 10 in opposed to the guide 51. In this embodiment, the mixture 12 out from the throat portion flows along a flared inner peripheral surface of the Venturi tube 54 by means of the guide 51, and is spread into the furnace 3. If the guide 51 is disposed downstream of the throat portion of the Venturi tube as shown in the drawings, a larger amount of the pulverized coal flows along the inner peripheral surface of the Venturi tube 54, and can be supplied into the furnace 3 in an outwardly-spread manner. As compared with the embodiment of Fig. 1, a burner 1 of Fig. 14, which is a further embodiment, further comprises air injection nozzles 61. Four air injection nozzles 61 (though the number of nozzles is not significant) are circumferentially equiangulary spaced from each other (Fig. 15). As shown in Figs. 15A to 15C, the number of the nozzles 61 may be 1 to 3, or may be 5 or more. Further, as shown in Fig. 15D, there may be used an arrangement in which injected air jets 62 are slightly deviated from an axis of the mixture nozzle. Further, as shown in Fig. 15A, the nozzles 61 may not be arranged equiangulary. The air injection nozzles 61 are provided immediately downstream of the flame stabilizer 13, and disposed between the mixture nozzle 10 and the gas nozzle 20. The air injection nozzles 61 are interconnected by pipes, and communicate with an external air compressor means. The pre-warmed air 62 from the air compressor means is injected through the nozzle 61 toward the mixture flow in a direction substantially perpendicular to the axis of the mixture nozzle. As a result, as shown in Figs. 16 and 17, a stagnation point is formed in the flow of the mixture 12 due to the injected air 62, and a relatively-negative pressure area NP is formed downstream of the injected air 62 with respect to the flow of the mixture 12. High-temperature combustion gas is carried by the injected air 62 into the negative pressure area NP, thereby promoting the ignition of pulverized coal in the mixture. As a result, the combustion in reduction areas is promoted, and also the flame temperature rises in the vicinity of the burner 1, thereby promoting the expansion of the flame. The air injection nozzles 61 may be movable in the direction of the axis of the mixture nozzle so as to effect the optimum air injection in accordance with combustion properties of the pulverized coal as solid fuel, a burner load, combusting conditions and so on. Further, an air injection nozzle may be so arranged that it can swing in a plane perpendicular to the axis of the mixture nozzle. If the injection nozzles 61 are directed slightly toward the upstream side of the mixture 12, an ignition area can be increased. Accordingly, high-fuel ratio coal and coarse pulverized coal whose ignition properties are not good can be used as solid fuel. A burner 1 shown in Figs. 18 and 19 differs from the burner of Fig. 14 in the positions of mounting of air injection nozzles. As shown in Fig. 19, the air injection nozzles 61 are disposed immediately downstream of the flame stabilizer 13, and are provided on the annular deflection guide tube 24 of the gas nozzle 20. Air 62 is injected from the air injection nozzle 61 toward a flow of the mixture. In order to inject the air 62 in such a manner that it can pass through the secondary air and the mixture, a greater energy is needed as compared with the burner of Fig. 14. However, a larger amount of high-temperature combustion gas is carried by the injected air 62 and flowed into the negative pressure area NP. Therefore, this is suitable for burning high-fuel ratio pulverized coal (having a smaller amount of volatile components). A burner 1, shown in Fig. 20, is a combination of the constructions of Figs. 11 and 14. The above-mentioned operations and effects can be enjoyed in a combined manner. CAPABILITY OF EXPLOITATION IN INDUSTRY The present invention can be used as a combustion apparatus, for example a coal-burning boiler.

Claims: Combustion burner comprising a mixture nozzle (10) for supplying a mixture of a solid fuel and primary air into a furnace (3), a flame stabilizer ring (13) of an L-shaped cross-section disposed at the distal end of the mixture nozzle (10), a secondary air nozzle (20) radially surrounding the mixture nozzle and provided at its distal end with a flared annular deflection guide tube (24), guide means (51) provided within said mixture nozzle (10), comprising an upstream portion (511) of progressively increasing outside dimensions, a middle portion (512) of constant outside dimensions and a downstream portion (513) of progressively decreasing outside dimensions, characterized in that the mixture nozzle (10) has a flared distal end portion (14) disposed in the flow direction between the middle portion (512) of the guide means (51) and the deflection guide tube (24) of the secondary air nozzle (20), which progressively increases the mixture flow passage and the guide means (51) is disposed in the mixture nozzle (10) at a position corresponding to an interconnecting portion between the flared distal end portion (14) of the mixture nozzle (10) and the upstream portion thereof. Combustion burner according to claim 1, characterized in that gas jet nozzles (61) are provided at a position downstream of the flared distal end portion (14) of the mixture nozzle (10) through which gas is injected radially inwardly toward said mixture flowed into said furnace (3) from a distal end of said mixture nozzle (10). Combustion burner according to claim 2, characterized in that a plurality of gas jet nozzles (61) are circumferentially equiangularly provided. Combustion burner according to claim 3, characterized in that said gas jet nozzles (61) are provided at the distal end of said mixture nozzle (10). Combustion burner according to claim 3, characterized in that said gas jet nozzles (61) are provided on said gas supply nozzle (20). Combustion burner according to any one of claims 1 to 5, characterized in that a swirl portion (53) is provided on said guide means (51) so as to swirl said mixture, and a rectifier (54) is provided on an inner peripheral surface of said flared portion (14) of said mixture nozzle (10) so as to rectify the swirled mixture. Combustion burner according to any one of claims 1 to 6, characterized in that a throat portion (54a) for reducing the flow passage area of said mixture passage is formed on the inner peripheral surface of said mixture nozzle (10) and is disposed upstream of said guide means (51). Combustion burner according to any one of claims 1 to 7, characterized by separation means for radially separating the flow of said mixture flowing from the distal end of said mixture nozzle (10) into said furnace (3) from the secondary air flow flowing from said air supply nozzle (20) into said furnace (3). Combustion burner according to any one of claims 1 to 8, characterized in that the angle between said flared distal end portion (24) of said air supply nozzle (20) and the length axis of the air supply nozzle (20) is substantially equal to or larger than an angle between the flared distal end portion (14) of said mixture nozzle (10) and the length axis of said mixture nozzle. Combustion apparatus comprising at least one combustion burner as defined in any one of claims 1 to 9. Combustion apparatus according to claim 10, in which said combustion apparatus is a boiler.

Inventors: JIMBO TADASHI, KIYAMA KENJI, KURAMASHI KOUJI, MORI MIKI, MORITA SHIGEKI, TSUMURA TOSHIKAZU, JIMBO, TADASHI, KIYAMA, KENJI, KURAMASHI, KOUJI, MORI, MIKI, MORITA, SHIGEKI, TSUMURA, TOSHIKAZU, KIYAMA, Kenji, 6-6, Yakeyamahonjo 3-chome, MORITA, Shigeki, 9-32, Yanohigashi 3-chome, TSUMURA, Toshikazu, 14-17, Nigatahonmachi 1-chome
Applicants: BABCOCK HITACHI KK, BABCOCK-HITACHI KABUSHIKI KAISHA
Application year: 1997
Main classification: F23D1
IPC codes: F23D1