Patent Publication Number: US-2004045295-A1

Title: Flame-holding, single-mode nozzle assembly with tip cooling

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates generally to the field of fuel nozzles and, more particularly, to a single-mode flame holding, tip-cooled combustion engine fuel nozzle.  
       BACKGROUND OF THE INVENTION  
       [0002] Combustion engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to this energy conversion process. In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor. The rotor produces shaft horsepower or torque; this output shaft may, in turn, be linked to devices such as an electric generator to produce electricity.  
       [0003] As the need for electricity rises, so to do the performance demands made upon industrial turbine combustion engines. Increasingly, these engines are expected to operate at increased levels of efficiency, while producing only minimal amounts of unwanted emissions. Various approaches have been undertaken to help achieve these results.  
       [0004] One approach has been to utilize multiple single-mode nozzles arranged in discrete groups to form a so-called “dry, low-NO x ” (DLN) combustor. DLN combustors typically provide lowered amounts of unwanted emissions by lowering the burning temperature and by pre-mixing the fuel and air and by providing independent flows of fuel to two or more discrete groups or “stages” of nozzles, with each stage contributing in a different manner to the overall combustion process. Two common gaseous fuel stages found in DLN arrangements are the “pilot” and “main” stages. Quite often, the pilot stage is a fuel-rich “diffusion” nozzle capable of holding a flame. Diffusion-type nozzles are quite stable, but they unfortunately provide a source of combustion hot spots that lead to the formation of NO x  emissions. To keep these unwanted emissions at a minimum, typically only one diffusion nozzle is used in a given combustor. The main stage nozzles, therefore, typically operate in a “premix” mode, producing a mixture of fuel and air that burns through interaction with other flames, such as the fuel-rich flame produced by the pilot stage. Although this arrangement produces relatively-low levels of NO x  emissions when compared to diffusion-only combustors, the presence of only one flame-holding nozzle reduces operational flexibility. This limitation, combined with the NO x  emissions produced by the pilot nozzle diffusion flame, make traditional DLN combustors unsuitable for many settings.  
       [0005] In an attempt to reduce NO x  emissions even further and to provide increased operational flexibility, combustors that employ flame-holding nozzles capable of operating in a premix mode have been developed. Typically, these combustors employ at least one pilot nozzle capable of providing a diffusion flame to initiate startup combustion. Multiple flame-stable nozzles capable of operating in a premix mode are included to support combustion during the majority of remaining operating conditions. While the use of flame-holding premix nozzles advantageously reduces NO x  emissions levels and may provide increased operational flexibility, efforts to produce such a nozzle have met with difficulty. This type of nozzle must not only produce a controlled stream of mixed fuel and air, it must also provide tip cooling to avoid melting as combustion temperatures rise to meet increased demands for power output. Flame-holding diffusion nozzles also face tip cooling and fuel dispersion requirements and present similar difficulties. Nozzles attempting to provide these characteristics have succeeded to varying degrees. For a variety of reasons, however, the practical difficulties imposed by meeting these requirements simultaneously has resulted in nozzles that are prone to leaks, are not reliable, and which may actually reduce efficiency due to losses generated by a large number of components.  
       [0006] Accordingly, there exists a need for a flame-stable nozzle that provides tip cooling and controlled fuel dispersion in a simplified manner. The nozzle should transmit cooling air in a passive manner through a dedicated passage that eliminates the need for complex valve arrangements, thereby reducing costs and increasing reliability. The nozzle should also include discrete fluid-guiding regions that are sealed in a leak-resistant manner without the reliance upon bellows or slip fits.  
       SUMMARY OF THE INVENTION  
       [0007] The instant invention is a single-mode, flame-holding nozzle for a gas turbine combustion engine that provides passive tip cooling and controlled fuel dispersion. The nozzle includes several elongated sleeves that cooperatively form discrete passageways adapted to transmit fluids through the nozzle. The nozzle includes conduits that allow fuel and cooling air to reach designated fuel and cooling passageways without mixing. This arrangement advantageously ensures that air used to cool the nozzle does not become flammable, thereby reducing the chances of unwanted flashback occurrences. Portions of the nozzle sleeves are also strategically arranged to transmit fluids in a manner that provides substantially-uniform thermal expansion, thereby reducing the need for sliding joints or bellows arrangements.  
       [0008] Accordingly, it is an object of the present invention to provide a single-mode combustor nozzle having tip cooling and controlled flame-holding capabilities.  
       [0009] It is another object of the present invention to provide a single-mode combustor nozzle that includes a dedicated cooling fluid passageway that eliminates the need for complex valve and manifold arrangements.  
       [0010] It is another object of the present invention to provide a single-mode combustor nozzle that includes discrete fluid-guiding regions that are sealed without the need for sliding joints or bellows arrangements.  
       [0011] Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0012]FIG. 1 is a side elevation of a combustion engine employing the nozzle of the present invention;  
     [0013]FIG. 2 is a side sectional view of the nozzle of the present invention;  
     [0014]FIG. 3 is an end view of the mounting flange shown in FIG. 2, taken along cutting line III-III′;  
     [0015]FIG. 4 is a side sectional view of the nozzle shown in FIG. 2, having an alternate cooling fluid transfer arrangement;  
     [0016]FIG. 5 is a side sectional view of the nozzle shown in FIG. 2 having alternate flow conditioning elements; and  
     [0017]FIG. 6 is a side sectional view of an alternate embodiment of the nozzle shown in FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0018] Reference is now made in general to the Figures, wherein the nozzle  10  of the present invention is shown. As shown in FIG. 1, the nozzle  10  of the present invention is especially suited for use in a combustion system  36  using nozzles that operate in a single-mode, but could have application as a dual-mode nozzle, as well. By way of overview, and with additional reference to FIG. 2, the nozzle  10  resembles an elongated cylinder having several substantially-concentric tubes  12 ,  14 ,  16 ,  18  that cooperatively form a collection of annular chambers  20 ,  22 ,  24 ,  26  which facilitate controlled flow of fluids through the nozzle. The nozzle  10  is characterized by a first end  40  and an opposite second end  42 , with fluids flowing generally from the first end to the second end during operation. The nozzle  10  also includes conduit groups  28 ,  30  that advantageously allow fuel  32  and tip cooling air  34  to reach designated passageways within the nozzle. More particularly, the first conduit group  28  allows fuel  32  to move from the second passageway  22  into the first passageway  20 , to interact with air  52  located therein. The second conduit group  30  beneficially allows cooling air  34  to reach the third passageway  24  from a location radially outward of the fuel-containing second passageway  22 , without allowing fuel  32  to contaminate the cooling air. Third passageway exits  60  allow cooling air  34  to leave the third passageway exits  60  and cool the nozzle second end  42 . The conditions within an associated combustor  46  at the nozzle second end  42  ensure the flame is self-stable. As is understood in the art, this generally means that the fuel/air mixture in passage  20  has sufficient velocity to prevent ignition upstream of the tip, and has an adequate fuel/air ratio to provide stable combustion in the lower velocity flame region immediately downstream of the tip. The nozzle  10  will now be described in further detail.  
     [0019] In one embodiment, the nozzle  10  of the present invention is especially suited for use as a flame-holding main nozzle in a premix mode, where premix fuel  32  travels from a source of fuel (not shown) through apertures  50  at the upstream end  40  of the nozzle  10  and enters a nozzle second passageway  22 . The fuel  32  flows through the second passageway  22  and travels into the first passageway  20 , where it forms a flammable mixture with air  52  located therein. The flammable mixture flows toward the nozzle second end  42 ; combustion may be initiated by an igniter  76  that is positioned in a nozzle inner passageway  26  or located remotely. Other components, including a diffusion nozzle (as seen in FIG. 6) may also be used to initiate combustion, if desired. If the inner passageway  26  is not used to hold an igniter  76 , the inner passageway may be plugged or adapted to transmit a fluid to the nozzle tip  42 . Tip cooling air  34  passes through the third passageway and prevents tip melting, as described below.  
     [0020] With particular reference to FIGS. 2 and 3, the nozzle  10  includes a mounting flange  44  that helps secure the nozzle within a combustor  46  of a selected gas turbine combustion system  36 . The mounting flange  44  includes two groups of apertures  48 ,  50  that allow premix air  52  and premix fuel  32 , respectively, to pass through the flange and enter corresponding passageways, or chambers, formed by the nozzle sleeves  14 , 16 , 18 . More particularly, the first set of apertures  48  facilitates entry of premix air  52  into the nozzle first passageway  20 . Similarly, the second set of apertures  50  allows premix fuel  32  to enter the nozzle second passageway  22 .  
     [0021] With continued reference to FIGS. 2 and 3, conduits  28 , 30  beneficially allow premix fuel  32  and cooling air  34 , respectively, to flow between portions of the nozzle  10  without becoming commingled. The first group of conduits  28  includes fuel injection members  54  that are each characterized by an entrance  56  in fluid communication with the second passageway  22  and an exit  58  in fluid communication with the first passageway  20 . With continued reference to FIG. 2, the fuel injection members  54  are hollow and include a group of exit holes  58 . With this arrangement, the fuel injection members  54  transmit premix fuel  32  into the first passageway  20 , where it mixes with premix air  52  and creates a flammable mixture of fuel and air. The fuel injection members  54  may be adapted condition flow within the first passageway  20  by, for example, having a substantially-airfoil-shaped cross-section. As seen in FIGS. 5 and 6, other flow conditioning elements, such as discrete swirler vanes  78 , or other suitable components, may also be provided as desired. The flow conditioning elements  78  may be connected to either or both of the nozzle first sleeve  14  and/or to a nozzle outer wall  12 .  
     [0022] It is noted that the first set of conduits  28  need not include fuel injection members  54 , and may take a variety of forms that permit fuel to travel from the second passageway  22  to the first passageway  20 . For example, as shown in FIG. 5, simple exit apertures  72  disposed within the first sleeve  14  may be used. It is further noted that the fuel  32  may exit the second passageway  22  from a variety of axially-different locations. It is also noted that the outer wall  12  is not required for operation; the first passageway  20  may be bounded by the first sleeve  14  and a supplemental sleeve or partition, such as the combustor wall  82  or other suitable boundary, as seen in FIG. 1.  
     [0023] As noted above, the second group of conduits  30  provide dedicated paths through which air  34  reaches the third passageway  24 . As will be described in more detail below, the air  34  in the third passage acts as cooling air, flowing downstream and through third passageway exits  60  to cool the nozzle tip or second end  42 .  
     [0024] Each of the conduits  30  in the second conduit group includes an entrance  62  in fluid communication with a source of cooling air (such as a compressor  80  coupled with the associated combustion turbine engine  38 , seen in FIG. 1) and an opposite exit  64  in fluid communication with the third passageway  24 . In one embodiment, the second conduit entrances  62  are in fluid communication with compressor discharge air  66 , and the second group of conduits  30  directs a portion of the compressor discharge air into the third passageway  24  to, as noted above, cool the nozzle second end  42 .  
     [0025] With particular reference to FIG. 3, each of the cooling air conduits  30  is oriented radially within the mounting flange  44 . With continued reference to FIG. 3, the cooling fluid conduits  30  lie between the premix air and fuel apertures  48 ,  50 , which extend longitudinally through the mounting flange  44 . In keeping with the objects of the invention, this arrangement advantageously allows the entrances  62  of the cooling fluid conduits  30  to be located radially-outboard of the fuel  32  and the cooling fluid conduit exits  64  to be located radially-inboard of the premix fuel. As a result, the cooling fluid conduit entrances  62  are located upstream of the locations where fuel  32  joins the compressor discharge air  66 . This arrangement advantageously allows one source of air  66  to provide air for several purposes, while safely ensuring that the air  34  used for cooling is fuel-free and not flammable.  
     [0026] As seen in FIG. 2, sliding interface  59  permits relative motion at the second end of the nozzle  42 , thereby accommodating thermal growth differences during operation. With this arrangement, air, and not fuel, flows within passageway  34 . This advantageously ensures that fluid which may emanate from the interface  59  is not flammable.  
     [0027] It is noted that the cooling fluid conduits  30  need not be radially arranged; any suitable orientation that allows the cooling air  34  to enter the third passageway  24  from a location upstream of the premix fuel  32  would suffice. Radial arrangement of the cooling fluid conduits  30  does, however, provide enhanced manufacturability. It is also noted that the cooling fluid conduits  30  need not be located in a mounting flange  44 ; other locations may be used as desired. For example, as shown in FIG. 4, the second group of conduits  30  may extend through a component that does not support the nozzle  10 , such as a fluid supply ring or hub  70 . It is also noted that compressor discharge air  66  substantially surrounds the nozzle first end  40 , and that such air may enter the first passageway by travelling around the nozzle first end and flowing between the outer wall  12  and first sleeve  14 , thereby eliminating the need for the first group of apertures  48 .  
     [0028] With continued reference to FIG. 2, the cooling fluid passageway exits  60  are in fluid communication with the first passageway  20 , and a pressure drop across the first passageway helps move the flow of cooling air  34  through the third passageway  24 /exit  60 . The pressure drop in the first passageway  20  may be increased through, among other methods, increasing turbulence and/or velocity in the first passageway  20 . With this arrangement, the nozzle  10  of the present invention provides a passive tip cooling system that employs a dedicated, air-only cooling fluid which eliminates the need for flows of purge fluid or fuel-blocking members.  
     [0029] Although the nozzle  10  of the present invention has been described as especially suited for use in a premix mode, the nozzle could also be used in a diffusion mode, wherein fuel  32  would be released through fuel exit apertures  72  located adjacent the nozzle second end  42 . An example of such an arrangement is shown in FIG. 6.  
     [0030] It is noted that while the nozzle  10  of the present invention has been described as diverting a portion of the compressor discharge air  66  into the third passageway  24  to provide cooling air  34 , other arrangements may be used. For example, the entrances  62  of the cooling fluid conduits  30  may be in fluid connection with other sources of cooling air, including a cooling air manifold (not shown). It is also noted that cooling air  34  may be motivated through the third passageway  24  by a pump (not shown) or other suitable flow-inducing components.  
     [0031] During operation, the first and second sleeves  14 , 16  are each exposed to compressor discharge air  66  and premix fuel  32 . As a result, the thermal expansion exhibited by the first sleeve  14  is substantially, if not identically, the same as the thermal expansion exhibited by the second sleeve  16 . With this arrangement, the first sleeve  14  may advantageously be connected to the second sleeve  16  in a rigid manner, thus eliminating the need for flexible connections, such as bellows, or slip-fit arrangements. This advantageously makes the nozzle  10  more reliable, increases the nozzle life span, and makes the nozzle less likely to leak.  
     [0032] It is to be understood that while certain forms of the invention have been illustrated and described, it is not to be limited to the specific forms or arrangement of parts herein described and shown. It will be apparent to those skilled in the art that various, including modifications, rearrangements and substitutions, may be made without departing from the scope of this invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification. The scope if the invention is defined by the claims appended hereto.