Patent Publication Number: US-6701713-B2

Title: Pilot burner, premixing combustor, and gas turbine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a pilot burner, a premixing combustor, and a gas turbine that generate a stable flame. 
     BACKGROUND OF THE INVENTION 
     FIG. 8 depicts a pilot burner and a main burner of a premixing combustor in a conventional gas turbine. A pilot burner  70  consists of an outer cylinder  71 , a pilot swirler  72 , a pilot nozzle  73  and a pilot cone  74 . Fuel is injected and diffused in the premixing combustor, as shown by black arrows  75 , from the pilot nozzle  73 . A plurality of premixing nozzles  76  those inject premixed gas are provided around the pilot nozzle  73 . This fuel injected from the pilot nozzle  73  is burnt in the form of a flame and this flame helps combust the premixed gas injected from the premixing nozzles  76 . 
     Pilot air is made to flow from left (“upstream”) to right (“downstream”) as shown by white arrows. The pilot swirler  72  functions to circulate the pilot air around the pilot nozzle  73  to improve the combustion efficiency. The pilot swirler  72  surrounds the pilot nozzle  73 . However, the pilot swirler  72  is not directly attached to the pilot nozzle  73  but arranged towards the side of the outer cylinder  71 . 
     The combustion of the premixed gas is conducted at a high temperature of about 1500 degree centigrade to suppress generation of toxic thermal NOx gas. However, the combustion of the fuel is conducted at relatively low temperature. As a result, thermal NOx is disadvantageously generated during the combustion of the fuel. 
     The amount of thermal Nox generated may be reduced by reducing the amount of the fuel. However, if the fuel reduced, the flame obtained by burning the fuel becomes unstable. In the worst case the flame may be extinguished because of the blow of the pilot air. Since this flame has a great influence on the combustion of the premixed gas, it is preferable that the flame is stable and does not extinguish. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a stable flame. 
     According to a pilot burner of one aspect of the present invention, a pilot nozzle diffusion-injects a fuel, a pilot swirler swirls a pilot air around the pilot nozzle, an air guide is arranged between the outer surface of the pilot nozzle and the pilot swirler. The air guide extends from the pilot swirler to a tip of the pilot nozzle. The air guide has a tip that protrudes beyond the tip of the pilot nozzle and this the tip of the air guide is bent away from a center of the pilot nozzle. 
     According to a pilot burner of one aspect of the present invention, a pilot nozzle diffusion-injects a fuel, a pilot swirler swirls a pilot air around the pilot nozzle, an air guide is arranged between the outer surface of the pilot nozzle and the pilot swirler. The air guide extends from the pilot swirler to a tip of the pilot nozzle. The air guide has a tip that protrudes beyond the tip of the pilot nozzle and this the tip of the air guide is bent radially with respect to a center of the pilot nozzle. 
     The premixing combustor according another aspect of the present invention is provided with the pilot burner according to the present invention. 
     The gas turbine according still another aspect of the present invention is provided with the pilot burner according to the present invention. 
     Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view which shows an overall gas turbine according to this embodiment, 
     FIG. 2 is a partial cross-sectional view which shows a premixing combustor according to this embodiment, 
     FIG. 3 is an enlarged outside view which shows a pilot burner according to this embodiment, 
     FIG. 4 is an enlarged outside view which shows a first modification of the pilot burner, 
     FIG. 5 is an enlarged outside view which shows a second modification of the pilot burner, 
     FIG. 6 is an enlarged outside view which shows a third modification of the pilot burner, 
     FIG. 7 is an enlarged outside view which shows a fourth modification of the pilot burner, and 
     FIG. 8 is a schematic diagram which shows a pilot burner and the like of a conventional premixing combustor. 
    
    
     DETAILED DESCRIPTIONS 
     Embodiments of the present invention will be explained hereinafter in detail with reference to the accompanying drawings. It is noted that the present invention is not limited by this embodiment. 
     FIG. 1 depicts an overall view of the gas turbine  1  according to one embodiment of the present invention. The gas turbine  1  consists of a compressor  2 , a combustor  3  and a turbine  4  among other structure. Air is introduced in the combustor  2  from an air inlet  5 . The compressor  2  compresses the air with the help of a plurality of moving blades  6  and stationary blades  7 . The compressed air is feed to the combustor  3 . In the combustor  3 , the compressed air is mixed with a fuel, the mixture of air and fuel is combust to obtain high pressure combustion gas. The combustion gas is made to pass through a tail pipe  8  and rotate the turbine. The turbine has a plurality of stages of rotors. 
     FIG. 2 depicts a premixing combustor  10  according to one embodiment of the present invention. The premixing combustor  10  includes a pilot burner  11  and a plurality of premixing nozzles  12  arranged around the pilot burner  11 . The pilot burner  11  and the premixing nozzles  12  enclosed by a cylindrical container  13 . The premixing nozzles  12  are supported by a main swirler  14  and inject and mix a fuel to and with the compressed air which is turned into a revolving flow by the main swirler  14 . The pilot burner  11  is supported by a pilot swirler  15  near its tip end and injects a pilot fuel diagonally forward from the tip end. As a result, a flame generated thereby becomes a starting flame which helps the premixing nozzles  12  combust the premixed gas. 
     The pilot swirler  15  is provided with an air induction plate  16  to be almost closely attached to the side surface of the pilot nozzle  11  toward the direction of the tip end of the pilot nozzle  11 . In addition, the end of the air induction plate which is located on the tip end of the pilot nozzle  11  is provided to be bent radially relative to the axis of the pilot nozzle  11 . This air induction plate  16  entangles the compressed air which is carried from the upstream and forms a vortex. As a result, the fuel which is injected from the pilot nozzle  11  and the air stay, making it possible to generate a stable starting flame. 
     The bent shape of the end of the air induction plate  16 , the shape of the air induction plate itself and a case in which the position of a fuel injection port is changed will be explained. FIG. 3 is an enlarged outside view which shows the pilot burner according to this embodiment. A pilot swirler  21  is provided on an outer cylinder  23  to surround a pilot nozzle  22 . An air induction plate  24  is provided to be almost closely attached to the side surface of the pilot nozzle from the pilot swirler  21  toward the direction of the tip end of the pilot nozzle  22 . The air induction plate  24  is almost closely attached to the side surface of the pilot nozzle  22  in view of processing error, assembly error, thermal expansion error. Ideally, this means that the air introduction plate  24  is closely attached to the side surface of the pilot nozzle  22 . 
     An injection port (not shown) is provided on the tip end of the pilot nozzle  22  and a fuel is spread and injected from the injection port diagonally forward as indicated by an arrow  25 . The pilot swirler  21  functions to revolve the pilot air which flows in a space which is formed between the outer cylinder  23  and the pilot nozzle  22  from the upstream and to enhance combustion efficiency. The end  27  of the air induction plate  24  is located on the tip end of the pilot nozzle  22  and bent radially outward relative to the axis of the pilot nozzle  22 . 
     If the end  27  of the air induction plate  24  is bent radially outward, the pilot air  26  turns around at the bent portion as indicated by an arrow  28  and a vortex is generated. This vortex can suppress the fuel from being blown away and prevent the fuel from being diluted by the flow of the pilot air  26 , so that flame stabilizing capability eventually enhances. If the flame stabilizing capability enhances, it is possible to operate the combustor with a reduced pilot fuel and to thereby contribute to the reduction of the thermal NOx which recently surfaces as an issue. 
     FIG. 4 depicts a first modification of the pilot burner according to this embodiment. In the first modification, an angle to which the end  31  of the air induction plate is bent is adjusted to spread and injected fuel diagonally forward from the pilot nozzle  22  as indicated by an arrow  25  directly collides against the end  31 . 
     The pilot air  26  generates a vortex on the end  31  as indicated by an arrow  32  and the pilot air  26  is fully mixed with the fuel. Besides, at a collision point at which the fuel collides against the end  31 , a fuel stagnation point appears. In this respect, similarly to the embodiment, it is possible to prevent the fuel from being diluted and to enhance flame stabilizing capability. 
     FIG. 5 depicts a second modification of the pilot burner according to this embodiment. In this second modification, the end  42  of an air induction plate  41  is bent radially inward relative to the axis. In this case, the air and the fuel are first fully mixed with each other in a clearance  43  which is formed between the end  42  of the air induction plate  41  and a fuel injection port (not shown). Thereafter, a vortex  44  which turns the mixture gas outward around the end  42  of the air induction plate  41  is generated. This can enhance the flame stabilizing capability of the pilot burner. 
     FIG. 6 depicts a third modification of the pilot burner according to this embodiment. This pilot burner is characterized in that the pilot swirler  21  which is conventionally provided on an outer cylinder  23  side is provided on the side surface  50  of the pilot nozzle  22 . A plurality of pilot swirlers  21  are provided uniformly in the peripheral direction of the pilot nozzle  22 . 
     Meanwhile, the air induction plate  51  is not always required to be connected to the pilot swirlers  21 . Further, to secure a function of inducing the pilot air  26  toward the tip end of the pilot nozzle  22 , it is necessary to provide the air induction plate  51  to be almost closely attached to the pilot nozzle side surface  52  with a certain point on the side surface  52  from the pilot swirlers  21  toward the direction of the tip end of the pilot nozzle  22  set as a starting point. The reason for almost closely attaching the air induction plate  51  to the pilot nozzle side surface  52  is the same as that explained in the embodiment. 
     In FIG. 6, the end  53  of the air induction plate  51  is bent radially outward relative to the axis of the pilot nozzle  22 . The bent shape is not limited thereto but may be radially inward or a bent angle at which the fuel spread and injected collides against the end  53  as indicated by an arrow  54  may be selected. In any case, the flame stabilizing capability enhances by the mixture of the pilot air and the fuel in the vortex and the appearance of a stagnation point similarly to the embodiment and the first to second modifications. 
     FIG. 7 depicts a fourth modification of the pilot burner according to this embodiment. This pilot burner is characterized by the injection position of a fuel spread and injected from the injection port of a pilot nozzle  61 . That is, as indicated by an arrow  62 , the fuel injection port is provided upward of the bend  64  of an air induction plate  63 . A hole is provided in the air induction plate  63  to be matched to the injection port position. By doing so, the fuel is mixed with the air before the air is entangled in the bent portion  64 . 
     As a result, the premixed gas of the air and the fuel is entangled in the bent portion  64  of the air induction plate  63 , a vortex is generated and the fuel can be prevented from being diluted. Consequently, compared with a case in which only the air is entangled, the flame stabilizing capability enhances and it is possible to stably combust the gas with reduced fuel. A saving in fuel naturally contributes to the reduction of NOx. In FIG. 7, it is explained that the air induction plate is similar to that in FIG.  3 . However, the air induction plate is not limited thereto but may be any one of the air induction plates shown in FIGS. 4 to  6 . 
     As explained so far, according to the pilot burner of a premixing combustor of the present invention, the end of the air induction plate is bent radially. In the bent portion, therefore, a vortex of the pilot air and a fuel stagnation point is generated. These phenomena can advantageously prevent the combustion gas from being diluted and enhance the flame stabilizing capability of the pilot burner. In addition, since the flame stabilizing capability enhances, it is possible to operate the pilot burner with reduced fuel and to contribute to the thermal NOx reduction. 
     Moreover, the end of the air induction plate is bent radially outward. In the bent portion, therefore, a vortex of the pilot air and a fuel stagnation point is generated. These phenomena can advantageously prevent the combustion gas from being diluted and enhance the flame stabilizing capability of the pilot burner. In addition, since the flame stabilizing capability enhances, it is possible to operate the pilot burner with reduced fuel and to contribute to the thermal NOx reduction. 
     Furthermore, the end of the air induction plate is bent radially outward and the fuel collides against the end. In the bent portion, therefore, a vortex of the pilot air and a fuel stagnation point is generated. These phenomena can advantageously prevent the combustion gas from being diluted and enhance the flame stabilizing capability of the pilot burner. In addition, since the flame stabilizing capability enhances, it is possible to operate the pilot burner with reduced fuel and to contribute to the thermal NOx reduction. 
     Moreover, the end of the air induction plate is bent radially inward. In the bent portion, therefore, the fuel is well mixed with the pilot air and a vortex outward of the end is then generated. These phenomena can advantageously prevent the combustion gas from being diluted and enhance the flame stabilizing capability of the pilot burner. In addition, since the flame stabilizing capability enhances, it is possible to operate the pilot burner with reduced fuel and to contribute to the thermal NOx reduction. 
     Furthermore, the pilot swirlers and the air induction plate are provided on the side surface of the pilot nozzle and the end of the air induction plate is bent radially. In the bent portion, therefore, the fuel is well mixed with the pilot air and a vortex outward of the end is then generated. These phenomena can advantageously prevent the combustion gas from being diluted and enhance the flame stabilizing capability of the pilot burner. In addition, since the flame stabilizing capability enhances, it is possible to operate the pilot burner with reduced fuel and to contribute to the thermal NOx reduction. 
     Moreover, the injection port is provided upward of the bent portion of the end of the air induction plate and the fuel is injected diagonally forward from the hole provided in the side surface of the air induction plate. Therefore, while the air which flows from the upstream is premixed with the fuel, the premixed gas is entangled in the bent portion. If the air thus mixed with the fuel generates a vortex on the tip end of the pilot nozzle, the combustion gas is prevented from being diluted and the flame stabilizing capability of the pilot burner is enhanced. In addition, since the flame stabilizing capability enhances, it is possible to operate the pilot burner with reduced fuel and to contribute to the thermal NOx reduction. 
     The premixing combustor of the present invention utilizes the pilot burner of a premixing combustor according to present invention. Therefore, the air mixed with the fuel generates a vortex on the tip end of the pilot nozzle and the combustion gas can be thereby prevented from being diluted. As a result, the flame stabilizing capability of the pilot burner can be enhanced. In addition, since the flame stabilizing capability enhances, it is possible to operate the pilot burner with reduced fuel and to realize a premixing combustor which can reduce the thermal NOx. 
     The gas turbine of the present invention utilizes the premixing combustor according to present invention. It is, therefore, possible to enhance the flame stabilizing capability of the pilot burner and to provide a gas turbine which can reduce the thermal NOx by the reduction of the fuel. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.