Patent Publication Number: US-6668557-B2

Title: Pilot nozzle of gas turbine combustor

Description:
FIELD OF THE INVENTION 
     This invention relates to the pilot nozzle of the gas turbine combustor intended to improve flame stabilization. The invention further relates to the pilot nozzle of the gas turbine combustor that improves flame stabilization by using the circulation of the combustion gas arising from combustion in the gas turbine combustor. 
     BACKGROUND OF THE INVENTION 
     FIG. 8 shows a cross section of a pilot nozzle  83  of a conventional gas turbine combustor. The pilot nozzle  83  is a dual type that injects two types of fuels, namely, fuel oil  81  and fuel gas  82 . The fuel oil  81  flows along the longitudinal axis (“oil-flow channel”) of the pilot nozzle  83  and is diffusion-injected from the tip of the pilot nozzle  83 . On the other hand, the fuel gas  82  flows through a plurality of fuel-flow channels  84  and is diffusion-injected obliquely forward relative to the pilot nozzle  83 . The fuel-flow channels  84  are laid longitudinally at, say, eight locations along the outer circumferential periphery of the pilot nozzle  83 . Peripherally to the pilot nozzle  83  flows in spirals the pilot air that has passed through the pilot swirler  85 , the swirling air then in a mixture with the fuel gas producing a spurt of pilot flame. 
     The conventional pilot nozzle  83  has a drawback that the fuel consumption is rather high, and there is a demand for curbing the fuel consumption. The combustion of fuel oil from the main nozzle constitutes the main combustion in the combustion chamber, because of which the curbing of the use of fuel oil injected from the main nozzle is in no sense appropriate. On the other hand, the flame of fuel gas  82  injected from the pilot nozzle  83  is functionally meant to just aid in the ignition of fuel oil injected from the main nozzle. It is this very function of fuel gas  82  that renders it possible for fuel consumption to be curbed without impairing the role of the pilot nozzle  83 , if and only if flame stabilization can be improved nonetheless. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a pilot nozzle of the gas turbine combustor that utilizes circulation of the combustion gas arising from the combustion taking place in the combustor and improves flame stabilization. 
     The pilot nozzle of a gas turbine combustor according to one aspect of the present invention comprises a first structure, near a main nozzle of a combustor that injects fuel oil, having a flow channel for a fuel gas and an outlet for the fuel gas, the first structure diffusion-injecting the fuel gas obliquely forward through the outlet to maintain a flame and to aid ignition of the fuel oil injected from the main nozzle, and a second structure which circulates in whirls a combustion gas generated due to the combustion of the fuel gas. 
     The pilot nozzle of the gas turbine combustor according to another aspect of the present invention comprises a central axis, a flow channel for a fuel gas, the flow channel being parallel to the central axis, and an outlet for injecting the fuel gas and aiding ignition of the fuel oil injected from the main nozzle. A portion of the flow channel in the vicinity of the outlet is bent towards the central axis. 
     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 A through FIG. 1D are cross-sections of a portion of a pilot nozzle according to the first embodiment of the present invention, 
     FIG.  2 A and FIG. 2B are cross-sections of a portion of a pilot nozzle according to the second embodiment of the present invention, 
     FIG.  3 A and FIG. 3B are cross-sections of a portion of a pilot nozzle according to the third embodiment of the present invention, 
     FIG.  4 A and FIG. 4B are cross-sections of a portion of a pilot nozzle according to the fourth embodiment of the present invention, 
     FIG.  5 A and FIG. 5B are cross-sections of a portion of a pilot nozzle according to the fifth embodiment of the present invention, 
     FIG. 6 is a cross-section of a portion of a pilot nozzle according to the sixth embodiment of the present invention, 
     FIG. 7 is a cross-section of a portion of a pilot nozzle according to the seventh embodiment of the present invention, 
     FIG. 8 is a cross-section of a pilot nozzle of a conventional gas turbine combustor. 
    
    
     DETAILED DESCRIPTIONS 
     Embodiments of the gas turbine combustor and of the pilot nozzle according to this invention will be explained in detail below with reference made to the accompanying drawings. 
     FIG.  1 A and FIG. 1C show cross-sections of a portion of a tip of the pilot nozzle of the gas turbine combustor according to a first embodiment of this invention. FIG. 1A shows a cylindrical flow dividing body  5  as it is set at the injecting port outlet, the portion corresponding to the flame root. FIG. 1C shows a disk (circular plate)  7  as it is set central to the injection port outlet. In FIG. 1A, pilot air flows downstream surrounding a pilot nozzle  1 . A fuel-flow channel  2  is disposed inside the pilot nozzle  1 . The fuel-flow channel  2  is parallel to the axis of the pilot nozzle  1  and bent outward at the tip  3 . 
     The pilot nozzle  1  diffusion-injects fuel gas-obliquely forward to form flame  4 . FIG. 1B shows a view from the direction of an arrow A. As is clear from FIG. 1B, the fuel gas injection port outlet has the cylindrical flow dividing body  5  installed in the center. The combustion gas that accompanies the combustion of fuel gas circulates in whirls in the direction of the arrows  6  at the outlet of the fuel gas injection port, the circulation being induced by the flow of fuel gas that jets out as if to avoid the flow dividing body  5 . This stabilizes the flame  4  at the root of the flame and prevents the flame being blown off in a swift flow of air from upstream. 
     FIG. 1C shows a case in which instead of the cylindrical flow dividing body  5  a flow dividing body  7  having a disk shape at the center is fitted to the outlet of the fuel gas injection port. FIG. 1D shows a view from the direction of an arrow B. As is clear from FIG. 1D, the disk in the center of the flow dividing body  7  is supported on four sides by a ring fitted to the fuel gas injection port outlet. Because of this, fuel gas flows as if to avoid the centrally set disk and the combustion gas that accompanies a fuel gas combustion at the injection port outlet begins to circulate in the direction of the arrows  8 . The flow dividing body  7  may well come in an elliptically cylindrical or prismatic shape also. Provision of the flow dividing body  7  in any shape thus improves the stability of the flame that occurs at the pilot nozzle. The flame stability thus improved is a substantial contribution to fuel economy. 
     According to the first embodiment, the fuel gas injected from the pilot nozzle reacts with air to form a flame, around which then forms combustion gas accompanying the combustion. As this combustion gas circulates around the fuel injection port outlet, namely the portion where the root of pilot flame occurs, the pilot flame gets stabilized since the flame is protected by the circulating gas from being blown off in a rapid stream of pilot air from upstream. 
     FIG. 2A shows a cross-section of a portion of a pilot nozzle  11  of the gas turbine combustor according to a second embodiment of this invention. The pilot air that surrounds the pilot nozzle  11  and a fuel-flow channel  12  are the same as the pilot nozzle  1  and the fuel-flow channel  2  in the first embodiment, so they are not explained but omitted. The pilot nozzle  11  has a cavity  14  provided on the downstream side of the fuel gas injection port  13 , a downstream side, that is, relative to the flow of pilot air. FIG. 2B shows a view from the direction of an arrow C. As is clear from FIG. 2B, the cavity  14  is formed of a hollow partly provided on the downstream side of the fuel gas injection port  13 . 
     Combustion gas arises around a flame at the pilot nozzle. In the presence of the cavity  14  near the root of the flame, the combustion gas flows into, and circulates in, the cavity  14  in the direction of the arrow  15 . The whirls that the circulation produces stabilize the root of the flame and help prevent the flame from being blown off in a stream of air from upstream. The cavity  14  is easily worked by cutting or by electric discharge machining. The cavity, therefore, may not necessarily limit itself to the shape, size, or depth illustrated but may well choose any forms or dimensions that may facilitate the circulation of combustion gas. As the flame stability is improved, so also is fuel economy since the combustion of fuel oil from the main nozzle can be aided with a smaller input of fuel gas than in the conventional practices. 
     FIG. 3A shows a cross-section of a portion of a pilot nozzle  21  of the gas turbine combustor according to a third embodiment of this invention. FIG. 3B shows a view from the direction of an arrow D. The pilot nozzle  21  is characterized such that the bore Dm of a fuel-flow channel  22 , at the fuel gas injection port outlet  23 , has been expanded in a counter boring fashion. When the fuel-flow channel bore is drastically expanded at the injection port outlet  23 , the combustion gas that accompanies the combustion of fuel gas circulates in the directions of the arrows  24 . The whirls that the circulation produces surround the flame root and prevent the flame from being blown off in a stream of air from upstream. In expanding the channel bore, a choice is made of sizes or depths suitable enough to facilitate the circulation of combustion gas. 
     Such a structure related to the fuel-flow channel bore not only facilitates the working or machining involved. It also makes easy the formation of whirls in which combustion gas circulates. The structure further precludes the chance of pilot air blowing direct onto the root of the flame. This improves the flame stability of a diffusive flame  25  arising at the pilot nozzle  21 . As the flame stability improves, so also does fuel oil economy. 
     FIG. 4A shows a cross-section of a portion of a pilot nozzle  31  of the gas turbine combustor according to a fourth embodiment of this invention. FIG. 4B shows a view from the direction of an arrow E. The pilot nozzle  31  according to the fourth embodiment is characterized in that it has a U-shaped wall  32  provided in a way such that an injection port  33  is thereby surrounded to head off the pilot air blowing from upstream. The U-shaped wall  32  not simply heads off the air current from upstream of the pilot nozzle  31 , it also helps whirls to arise inside the wall as combustion gas circulates in the direction of the arrow  34 . Thus structured, the pilot nozzle mounted with the U-shaped wall also forms whirls of combustion gas and improves the flame stability of the diffusive flame arising at the pilot nozzle  31 . As the flame stability improves, so also does fuel oil economy. 
     FIG. 5A shows a cross-section of a portion of a pilot nozzle  41  of the gas turbine combustor according to a fifth embodiment of this invention. FIG. 5B shows a view from the direction of an arrow F. The pilot nozzle  41  according to the fifth embodiment is characterized in that a cylindrical body  43  that protrudes so as to surround an injection port  42  is provided. This cylindrical body  43  heads off the pilot air that flows from upstream of the pilot nozzle  41  and forms whirls  44  of combustion gas inside the cylindrical body. That end of the cylindrical body  43  which is spaced afar downstream from the outlet of an injection port  42  may selectively be turned back inward in the shape  45 . The purpose is to allow whirls to circulate more stably and to evade the impacts of entrained air. The cylindrical body  43  may also be installed on its flank with an air inlet  46  to supply air in a suitable amount and in a suitable direction. 
     In the same manner as the first through fourth embodiments of this invention, it is possible in the fifth embodiment to form whirls of combustion gas and to improve the flame stability of the diffusive flame that arises at the pilot nozzle. As the flame stability improves, so also does fuel oil economy. 
     FIG. 6 shows a cross-section of a portion of a pilot nozzle  51  of the gas turbine combustor according to a sixth embodiment of this invention. The pilot nozzle  51  according to the sixth embodiment is shaped so that a mixture of air and the combustion gas that accompanies fuel gas combustion does circulate. This pilot nozzle has an inclined plane  53  provided to hold off from the outlet of an injection port  52  the air flowing from upstream of the outlet of the injection port  52 , relative to the flow of pilot air. At the outlet of the injection port  52 , the pilot nozzle  51  has a pocket  54  provided, internal to the inclined plane  53 , to allow the combustion gas to circulate. 
     Pilot air flows in the direction of from the rear end to the leading end of the pilot nozzle  51 . When, relative to the flow of pilot air, there exists the inclined plane  53  extending from upstream of the outlet of the injection port  52  down to the outlet of the injection port  52 , the air flows in the direction increasingly away from the outlet of the injection port  52 . This precludes the chance of the pilot air blowing off the flame that forms at the outlet of the injection port  52 . 
     A provision of the pocket  54  at the outlet of the injection port  52 , internal to the inclined plane  53 , makes a combustion gas at the injection port outlet circulate in the pocket in the direction of the arrow  55  to stabilize the flame. The inclined plane  53  may not necessarily be flat but may moderately be curved. Desirably, the angle of inclination “a” of the inclined curve  53  and the angle of formation “b” of the pocket may be suitably chosen so as to allow combustion gas to circulate efficiently. 
     In the same manner as the first through fifth embodiments of this invention, it is possible in the sixth embodiment to form whirls of combustion gas and to improve the flame stability of the diffusive flame that arises at the pilot nozzle. As the flame stability improves, so also does fuel oil economy. 
     FIG. 7 shows a cross-dimension of a portion of a pilot nozzle  61  of the gas turbine combustor according to a seventh embodiment of this invention. The pilot nozzle  61  according to the seventh embodiment is characterized in that it internally comprises a fuel-flow channel  62  that runs from a fuel gas supply source down in parallel with the axis of the pilot nozzle. The fuel-flow channel  62  is bent inward at the leading end, in the direction of the axial center of the pilot nozzle. 
     The fuel-flow channel  62  that runs parallel to the pilot nozzle axis  63  is bent inward at the leading end, fuel gas is accordingly injected inward in the direction of the axial center  63  of the pilot nozzle to produce a flame  64 . The high temperature gas that the flame  64 -induced combustion produces circulates (see  65 ) outward from inside the combustor. When the flame  64  is built to match the flow direction of the high temperature circulating gas, then the flame can be stabilized that much easier. 
     Desirably, the fuel-flow channel  62  should be directed not only inward in the direction of the pilot nozzle&#39;s axial center  63  but also outward in the direction of the pilot nozzle circumference, in order that the direction of fuel gas injection relative to the circulating gas be optimized. An inward angle α and outward angle θ should be set appropriately. The leading end of the fuel-flow channel  62  may not necessarily be inflected as illustrated but may well be turned inward at an optimum curvature. 
     In the same manner as the first through sixth embodiments of this invention, this inward directed structure of the leading end of the fuel-flow channel according to the seventh embodiment improves the flame stability of the diffusive flame arising from the pilot nozzle, the rate of improvement being substantially higher than in the case of injecting fuel gas on the circumferential side of the pilot nozzle, the side where the temperature is relatively low. This also improves flame stability and as the flame stability improves, so also does fuel oil economy. 
     According to the seventh embodiment, the flow channel, up to and including the leading end, is laid in parallel with the pilot nozzle axis, the flow channel is bent inward at the leading end in the direction of the axial center of the pilot nozzle. Because of this, fuel gas is injected in the direction of the axial center of the pilot nozzle to produce a pilot flame. Near this flame, a high temperature gas produced consequent upon the combustion triggered by a flame from the main nozzle circulates outwardly from inside the combustor. When, considering this, a pilot flame is produced not so much on the pilot nozzle&#39;s circumferential side where temperature is relatively low as in the direction of the circulating gas flow induced by the flame from the main nozzle, where temperature is relatively high, it becomes easy for the pilot flame to get stabilized. Desirably, as well as directing the flow channel inward perpendicularly in the direction of the axial center of the nozzle axis, the same channel may well be directed outward in the direction of the nozzle circumference so as to optimize the direction of gas injection relative to the circulating gas flowing outward. 
     According to the pilot nozzle of the gas turbine combustor of this invention, it becomes possible to improve the flame stability of the flame that arises at the pilot nozzle. As the flame stability improves, so also does fuel oil economy. 
     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.