Abstract:
To provide a burner structure that is capable of efficiently cooling a nozzle main body with a small amount of air, and takes an efficient countermeasure against a falling clinker or radiation heat. The burner structure includes: a pulverized coal-air mixture path provided in a burner central portion and supplying a mixture of a fuel and a primary air; a secondary air path provided around the pulverized coal-air mixture path and supplying a secondary air; a cooling air path provided around or above and below the secondary air path and supplying a cooling air; a nozzle main body attached to furnace-side end portions of the pulverized coal-air mixture path and the secondary air path in a tiltable form and provided with a flame holder at its tip end; and a cooling air nozzle attached to a furnace-side end portion of the cooling air path in a tiltable form.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a burner structure applicable to various types of combustion apparatuses such as a pulverized coal boiler.  
         [0003]     This application is based on Japanese Patent Application No. 2006-303780, the content of which is incorporated herein by reference.  
         [0004]     2. Description of Related Art  
         [0005]     Hitherto, boilers fired with a fuel powder, for example, pulverized coal or petroleum coke have been used.  
         [0006]     To describe a burner structure employed in a pulverized coal boiler that is fired with pulverized coal, a burner is composed of a pulverized coal-air mixture system provided in the burner center and containing pulverized coal and a primary air, a secondary air system provided around the pulverized coal-air mixture system, and cooling air (tertiary air) systems optionally provided around or above and below the secondary air system.  
         [0007]      FIG. 5  is a sectional view showing a pulverized coal burner structure of the related art.  
         [0008]     A burner  10  of  FIG. 5  is structured such that a secondary air path  12  as a secondary air system is provided around a pulverized coal-air mixture path  11  as a pulverized coal-air mixture system. In addition, a cooling air path  13  as a cooling air (tertiary air) system is provided above the secondary air path  12 .  
         [0009]     Provided at furnace-side ends of the pulverized coal-air mixture  11  and the secondary air path  12  is a nozzle main body  17  that integrates a pulverized coal nozzle  14  and a secondary air nozzle  15  with a flame holder  16  provided at their tip ends. Further, a cooling air nozzle  18  is attached at the furnace-side end of the cooling air path  13 . The cooling air nozzle  18  functions to prevent a falling clinker from the upper part in the furnace from colliding against the burner  10  and to shield a flame radiation heat. In  FIG. 5 , reference numeral  19  denotes a wind box.  
         [0010]     In the thus-structured burner  10 , the following combustion method is employed. That is, a fuel and an air are supplied while the total amount of the primary air, the secondary air, and the tertiary air is set smaller than an ideal air amount relative to an amount of pulverized coal loaded to fire the burner as required by the regulations on nitrogen oxides (NOx). In this way, a main combustion zone is kept under a reducing atmosphere. Then, NOx generated upon burning the pulverized coal is reduced, after which an additional air is supplied from an additional air nozzle (not shown) provided on the downstream side of the main combustion zone for oxidation combustion. In this way, combustion is completed. Thus, enough air is supplied around a pulverized coal flow in the main combustion zone.  
         [0011]     Further, in the burner  10  of the related art, the nozzle main body  17  is tiltable for controlling a steam temperature or an amount of NOx at the outlet as shown in  FIG. 6 , but the cooling air nozzle  18  is fixed.  
         [0012]     In addition, there is reported another structure that the entire nozzle inclusive of an air flow path corresponding to the above cooling air nozzle  18  is tiltable (see the Publication of the U.S. Pat. No. 6,260,491, for instance).  
         [0013]     Recently, an ignition performance has been enhanced year by year along with improvements in the flame holder  16 . As a result, materials for the burner  10  are exposed to higher temperatures. On the other hand, if a flow rate of the cooling air supplied to the cooling air nozzle  18  is increased to increase a cooling ability, a combustion temperature lowers and causes an increase in unburned components. Thus, exhaust gas characteristics are deteriorated, so it is necessary to efficiently cool the nozzle main body  17  with a small amount of air.  
         [0014]     Moreover, in the burner  10  of the related art, the nozzle main body  17  is only tiltable and the cooling air nozzle  18  is fixed, which causes a problem in that the tilted nozzle main body  17  is exposed to radiation heat.  
         [0015]     On the other hand, in the structure where the entire nozzle is tiltable as disclosed in the Publication of U.S. Pat. No. 6,260,491, an air flow rate is determined in accordance with an air-flow-path area ratio, resulting in a problem in that an air flow rate cannot be adjusted during operation.  
         [0016]     Further, the part corresponding to the cooling air nozzle  18  does not have a function of protecting the nozzle main body from a falling clinker or radiation heat, which situation might occurs in the case where a fuel powder such as pulverized coal is used. Therefore, this structure is disadvantageous from the viewpoint of ensuring a long component life.  
         [0017]     In view of such circumstances, there is an increasing demand for a burner structure that is capable of adjusting an air flow rate and efficiently cooling a nozzle main body with a small amount of air, and takes an efficient countermeasure against a falling clinker or radiation heat.  
       BRIEF SUMMARY OF THE INVENTION  
       [0018]     The present invention has been accomplished in view of the above circumstances, and it is an object of the present invention to provide a burner structure that is capable of adjusting an air flow rate and efficiently cooling a nozzle main body with a small amount of air, and takes an efficient countermeasure against a falling clinker or radiation heat.  
         [0019]     The present invention adopts the following solutions with a view to attaining the above object.  
         [0020]     A burner structure according to the present invention includes: a fuel-air mixture system provided in a burner central portion and supplying a mixture of a fuel and a primary air; a secondary air system provided around the fuel-air mixture system and supplying a secondary air; a cooling air system provided around or above and below the secondary air system and supplying a cooling air; a nozzle main body attached to furnace-side end portions of the fuel-air mixture system and the secondary air system in a tiltable form and provided with a flame holder at its tip end; and a cooling air nozzle attached to a furnace-side end portion of the cooling air system in a tiltable form.  
         [0021]     According to the above burner structure, since the burner structure includes a nozzle main body attached to furnace-side end portions of the fuel-air mixture system and the secondary air system in a tiltable form and provided with a flame holder at its tip end, and a cooling air nozzle attached to a furnace-side end portion of the cooling air system in a tiltable form, the secondary air and the cooling air are independently supplied from different air supply systems. Hence, an air flow rate can be adjusted and controlled in each air supply system.  
         [0022]     In the burner structure, it is preferred that a tip end position of the cooling air nozzle be substantially the same as a tip end position of the flame holder in a tiltable range of the nozzle main body and the cooling air nozzle because an influence of a falling clinker or radiation heat on the nozzle main body can be eradicated or suppressed.  
         [0023]     In the burner structure, it is preferred that the cooling air nozzle include a canopy-like member for partitioning an inner portion of a tubular member, and a tip end of the canopy-like member be adjusted to substantially the same position as a tip end of the flame holder in a tiltable range of the nozzle main body and the cooling air nozzle because the cooling air nozzle can be made lightweight, and an influence of a falling clinker or radiation heat on the nozzle main body can be eradicated or suppressed.  
         [0024]     In the burner structure, it is preferred that the cooling air nozzle be provided with a cooling fin because a cooling efficiency is improved.  
         [0025]     Further, in the burner structure according to the present invention, it is preferred that axes of tilt of the nozzle main body and the cooling air nozzle coincide with each other because a tilting mechanism can be simplified.  
         [0026]     In the burner structure, it is preferred that the cooling air nozzle be detachably attached to the nozzle main body because the cooling air nozzle can be replaced alone.  
         [0027]     In this case, a flow rate of an air supplied to the cooling air and the secondary air is determined in accordance with a sectional area ratio, so a wind box structure can be simplified.  
         [0028]     According to the burner structure of the present invention, it is possible to adjust an air flow rate and more efficiently cool a nozzle main body with a small amount of air, and protect a nozzle main body from a falling clinker or radiation heat. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0029]      FIG. 1  is a sectional view of a burner structure according to a first embodiment of the present invention;  
         [0030]      FIG. 2A  is a sectional view of a burner structure according to a second embodiment of the present invention;  
         [0031]      FIG. 2B  shows the burner structure of the second embodiment and a cooling air nozzle as viewed from the front on the outlet side;  
         [0032]      FIG. 3A  is a sectional view of a burner structure according to a third embodiment of the present invention;  
         [0033]      FIG. 3B  shows the burner structure of the third embodiment and a burner as viewed from the front on the outlet side;  
         [0034]      FIG. 4  is a sectional view of a modified example of the third embodiment of  FIGS. 3A and 3B ;  
         [0035]      FIG. 5  is a sectional view of a burner structure of the related art; and  
         [0036]      FIG. 6  is a sectional view of the burner structure of the related art in a tilted form. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]     Hereinafter, embodiments of a burner structure according to the present invention will be described with reference to the accompanying drawings.  
       First Embodiment  
       [0038]     A burner structure according to a first embodiment of the present invention as shown in  FIG. 1  is a pulverized coal burner used for a pulverized coal boiler fired with pulverized coal as a fuel.  
         [0039]     This burner  10 A includes a pulverized coal-air mixture path  11  that is provided in the burner center as a fuel-air mixture system for supplying a pulverized coal-air mixture containing pulverized coal as a fuel and a combustion primary air. A secondary air path  12  as a secondary air system for supplying a combustion secondary air is provided around the pulverized coal-air mixture path  11 . In addition, a cooling air path  13  as a cooling air system for supplying a cooling tertiary air (hereinafter referred to as “cooling air”) is provided above the secondary air path  12 .  
         [0040]     To take an example of the case where pulverized coal is used as a fuel, a pulverized coal-air mixture is set to about 80° C. and supplied to the pulverized coal-air mixture path  11  in the burner center. Moreover, a secondary air and a cooling air are set to about 300° C. to 350° C. and supplied to the secondary air path  12  and the cooling air path.  
         [0041]     A nozzle main body  17  is attached to furnace-side end portions of the pulverized coal-air mixture path  11  and the secondary air path  12 , and a tilting mechanism (not shown) is provided, so the nozzle can be tilted to change a blowoff angle from a horizontal angle to a desired one. The nozzle main body  17  is completed by combining a pulverized coal nozzle  14  that ejects a pulverized coal-air mixture and a secondary air nozzle  15  that ejects a secondary air, and integrally attaching a flame holder  16  to tip ends of both the nozzles.  
         [0042]     To describe the structure of the nozzle main body  17  in detail, the pulverized coal nozzle  14  has a tapered tube-like form, and the secondary air nozzle  15  similarly has a tapered tube-like form with a large diameter and is integrally provided around the pulverized coal nozzle  14 . The pulverized coal nozzle  14  and the secondary air nozzle  15  constitute a double-walled tube-like structure with a large diameter. Then, the flame holder  16  that has similarly a double-walled tube-like structure and increases its diameter toward an outlet at the tip end is integrally attached to tip ends of the pulverized coal nozzle  14  and the secondary air nozzle  15 .  
         [0043]     A cooling air nozzle  18  is provided at a furnace-side end portion of the cooling air path  13  independently of the nozzle main body  17 . The cooling air nozzle  18  is provided with a tilting mechanism (not shown) similar to the nozzle main body  17  and thus can be tilted to change a blowoff angle from a horizontal angle to a desired one. The cooling air nozzle  18  has a tube-like shape, and it is preferred that its tip end position on the outlet side be substantially the same as that of the flame holder  16  in a tiltable range of the nozzle main body  17  and the cooling air nozzle  18 .  
         [0044]     In the thus-structured burner  10 A, the cooling air path  13  for supplying a cooling air to the cooling air nozzle  18  is independent of the pulverized coal-air mixture path  11  and the secondary air path  12 , so a flow rate of the cooling air can be adjusted and controlled solely. To be specific, a flow rate of the cooling air can be controlled independently of a pulverized coal-air mixture or a secondary air by providing the cooling air path  13  with a flow rate adjusting part such as a damper.  
         [0045]     As a result, a flow rate of the cooling air can be adjusted and controlled more precisely and finely than a conventional structure that determines an air flow rate in accordance with a path sectional area ratio. Hence, if a flow rate of the cooling air is optimized in accordance with operation conditions, the nozzle main body  17  can be efficiently cooled. In addition, the cooling air nozzle  18  is independent of the nozzle main body  17 , so if the cooling air nozzle needs to be replaced as a result of periodical checkup or the like, only the nozzle can be replaced.  
         [0046]     Further, also in the case where the cooling air nozzle  18  is tilted to thereby tilt the nozzle main body  17 , if the cooling air nozzle  18  is tilted to the best position, a falling clinker adheres to the cooling air nozzle  18  first. Hence, it is possible to shield radiation heat with the cooling air nozzle as well as to prevent the clinker from adhering to the nozzle main body  17 , so the nozzle main body  17  is not directly exposed to radiation heat.  
         [0047]     If the outlet-side tip end position of the cooling air nozzle  18  is substantially the same as a tip end position of the flame holder  16  in a tiltable range of the nozzle main body  17  and the cooling air nozzle  18 , the nozzle main body  17  can be protected from a clinker or radiation heat with higher reliability.  
         [0048]     Incidentally, in the case of tilting the cooling air nozzle  18  to protect the nozzle main body  17  from a clinker or radiation heat, if axes of tilt of the cooling air nozzle  18  and the nozzle main body  17  coincide with each other, the structure can be simplified, for example, the tilting mechanism is shared. Here, the cooling air nozzle  18  and the nozzle main body  17  may be integrally formed so that both nozzles are always tilted to the same direction at the same time.  
       Second Embodiment  
       [0049]     Referring next to  FIGS. 2A and 2B , a burner structure according to a second embodiment of the present invention will be described. Here, the same components as those of the above embodiment are denoted by identical reference numerals, and detailed description thereof is omitted.  
         [0050]     A burner  10 B of this embodiment includes cooling fins  20  provided inside a tube-like cooling air nozzle  18 A. The cooling fins  20  alternately protrude from an upper surface and a lower surface of the inner portion of the tube-like nozzle as shown in  FIG. 2B , but the present invention is not limited to this structure. If the cooling air nozzle  18 A is provided with the cooling fins  20  in this way, a contact area with a cooling air is increased to improve a cooling efficiency. Incidentally, the cooling air nozzle  18 A is tiltable as in the above cooling air nozzle  18 .  
       Third Embodiment  
       [0051]     Referring next to  FIGS. 3A and 3B , a burner structure according to a third embodiment of the present invention will be described. Here, the same components as those of the above embodiments are denoted by identical reference numerals, and detailed description thereof is omitted.  
         [0052]     A burner  10 C ( 10 D) of this embodiment includes a canopy-like member  21  of a plate shape, which partitions an inner portion of a tube-like cooling air nozzle  18 B, and is tiltable as in the cooling air nozzle  18 . The canopy-like member  21  is provided to partition the inner portion of the cooling air nozzle  18 B obtained by cutting a tube main body  18   a  into upper and lower portions. A tip end position of the canopy-like member  21  is substantially the same as the tip end position of the flame holder  16  in a tiltable range of the nozzle main body  17  and the cooling air nozzle  18 .  
         [0053]     If the cooling fins  20  are optionally attached to, for example, an upper surface of the canopy-like member  21 , a cooling efficiency can be improved. In the illustrated example, the fins alternately protrude from a lower surface of the canopy-like member  21  and an upper surface of the nozzle main body  17 , but the present invention is not limited to this structure.  
         [0054]     In the thus-structured cooling air nozzle  18 B, the tube main body  18   a  is shortened and thus, the nozzle itself can be made lightweight. Further, the canopy-like member  21  can shield radiation heat as well as prevent a clinker from adhering to the nozzle main body  17 , so the nozzle main body  17  is not directly exposed to radiation heat.  
         [0055]     Moreover, if the canopy-like member  21  is detachably attached to the tube main body  18   a  by means of bolts or the like, in the case where the canopy-like member  21  needs to be replaced as a result of periodical checkup or the like, only the member can be replaced.  
         [0056]     Further, air flow rates of a secondary air and a cooling air may be determined in accordance with a sectional area ratio instead of using the member that partitions a wind box  19  into the secondary air path  12  and the he cooling air path  13  as in a modified example of  FIG. 4 . According to this structure, the wind box structure can be made simple and lightweight.  
         [0057]     Further, if the cooling air nozzle  18 B is detachably attached to the nozzle main body  17  by means of bolts or the like and integrated with the nozzle main body, the cooling air nozzle  18 B and the nozzle main body  17  can be tilted at the same time, and the cooling air nozzle  18 B can be replaced alone.  
         [0058]     As set forth above, the burner structure according to the present invention can adjust an air flow rate and thus efficiently cool the nozzle main body  17  with a small amount of air, and can protect the nozzle main body  17  from a falling clinker or radiation heat.  
         [0059]     The present invention is not limited to the above-described embodiments and might be modified as appropriate without departing from the scope of the present invention. For example, a fuel is not limited to pulverized coal, and petroleum coke, fuel oil, or fuel gas can be used instead.