Patent Publication Number: US-2017363294-A1

Title: Pilot premix nozzle and fuel nozzle assembly

Description:
FIELD OF THE INVENTION 
     The present invention generally involves a fuel nozzle assembly for a gas turbine combustor. More specifically, the invention relates to a pilot premix nozzle for a fuel nozzle assembly. 
     BACKGROUND OF THE INVENTION 
     As requirements for gas turbine emissions have become more stringent, one approach to meeting such requirements is to move from diffusion flame combustors to combustors utilizing lean fuel and air mixtures using a fully premixed operations mode to reduce emissions of, for example, NOx and CO. These combustors are generally known in the art as Dry Low NOx (DLN), Dry Low Emissions (DLE) or Lean Pre Mixed (LPM) combustion systems. 
     Certain DLN type combustors include a plurality of primary fuel nozzles which are annularly arranged about a secondary or center fuel nozzle. The fuel nozzles are circumferentially surrounded by an annular combustion liner. The combustion liner defines an upstream combustion chamber and a downstream combustion chamber of the combustor. The upstream combustion chamber and the downstream combustion chamber may be separated by a throat portion of the combustion liner. 
     During operation of the combustor, the primary fuel nozzles may provide fuel to the upstream combustion chamber. Depending on the operational mode, the fuel from the primary fuel nozzles may be burned in the upstream combustion chamber or may be premixed with compressed air within the upstream combustion chamber for ignition in the downstream combustion chamber. The secondary fuel nozzle serves several functions in the combustor including supplying fuel and air mixture to the downstream combustion chamber for premixed mode operation, supplying fuel and air for a pilot flame supporting primary nozzle operation and providing transfer fuel for utilization during changes between operation modes. 
     In certain combustors, the secondary fuel nozzle may include a diffusion pilot nozzle disposed at a downstream end of the secondary fuel nozzle. The diffusion pilot nozzle provides a stream of fuel and air to the second combustion chamber and is employed for anchoring a secondary flame. However, in order to comply with various emissions requirements the fuel flow to the pilot fuel circuit may be reduced. As a result, the reduced fuel flow to the pilot fuel circuit may impact combustion dynamics and/or lean blow out limits. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     One embodiment of the present invention is a pilot premix nozzle. The pilot premix nozzle includes a nozzle body. The nozzle body comprises a forward wall that is axially spaced from an aft wall and an outer band that extends axially between the forward wall and the aft wall. The aft wall includes an inner surface that is axially spaced from an outer surface. An air tube extends coaxially within the nozzle body and terminates at the inner surface of the aft wall. The air tube at least partially defines a cooling air plenum within the nozzle body. A fuel tube extends coaxially within the nozzle body and at least partially circumferentially surrounds the air tube. The fuel tube and the air tube define a fuel inlet plenum therebetween. A fuel distribution plenum is defined within the nozzle body and is in fluid communication with the fuel inlet plenum. The nozzle body also includes a plurality of premix tubes. Each premix tube of the plurality of premix tubes defines a respective premix passage through the nozzle body and includes an inlet defined along the forward wall and an outlet defined along the aft wall of the nozzle body. Each respective premix tube extends helically around the fuel tube within the fuel distribution plenum. One or more of the premix tubes of the plurality of premix tubes is in fluid communication with the fuel distribution plenum. 
     Another embodiment of the present disclosure is a fuel nozzle assembly. The fuel nozzle assembly includes an outer tube, an inner tube that extends coaxially within the outer tube, an intermediate tube that extends coaxially within the outer tube and that circumferentially surrounds and is radially spaced from the inner tube, and a premix pilot nozzle that is coupled to a downstream end of the outer tube via a nozzle ring. The premix pilot nozzle comprises a nozzle body. The nozzle body includes a forward wall that is axially spaced from an aft wall and an outer band that extends axially between the forward wall and the aft wall. The aft wall includes an inner surface that is axially spaced from an outer surface. An air tube is coupled at one end to the inner tube and extends coaxially within the nozzle body. The air tube terminates at the inner surface of the aft wall and at least partially defines a cooling air plenum within the nozzle body. A fuel tube is coupled at one end to the intermediate tube. The fuel tube extends coaxially within the nozzle body and circumferentially surrounds at least a portion of the air tube. The fuel tube and the air tube define a fuel inlet plenum therebetween. A fuel distribution plenum is defined within the nozzle body and is in fluid communication with the fuel inlet plenum. The nozzle body also includes a plurality of premix tubes. Each premix tube defines a premix passage through the nozzle body and includes a respective inlet that is defined along the forward wall and a respective outlet that is defined along the aft wall. Each premix tube extends helically around the fuel tube within the fuel distribution plenum. One or more of the premix tubes of the plurality of premix tubes is in fluid communication with the fuel distribution plenum. 
     Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
         FIG. 1  illustrates a schematic depiction of an embodiment of a gas turbine; 
         FIG. 2  illustrates a simplified cross-section of an exemplary combustor known in the art and which may incorporate one or more embodiments of the present disclosure; 
         FIG. 3  is a cross sectional side view of an exemplary fuel nozzle or fuel nozzle assembly as may be used in the combustor as shown in  FIG. 2 , according to at least one embodiment of the present disclosure; 
         FIG. 4  is a perspective view of a premix pilot nozzle of the fuel nozzle assembly as shown in  FIG. 3 , according to at least one embodiment of the present disclosure; 
         FIG. 5  is a perspective cross sectional view of the premix pilot nozzle as shown in  FIG. 4 , according to at least one embodiment of the present disclosure; 
         FIG. 6  is a cross sectioned perspective view of a portion of the tip portion of the premix pilot nozzle as taken along section lines A-A as shown in  FIG. 4 , according to at least one embodiment of the present disclosure: 
         FIG. 7  is a cross sectioned perspective view of a portion of the premix pilot nozzle as taken along section lines B-B as shown in  FIG. 4 , according to at least one embodiment of the present disclosure; and 
         FIG. 8  is a perspective view of a premix pilot nozzle of the fuel nozzle assembly as shown in  FIG. 4 , according to at least one embodiment of the present disclosure; and 
         FIG. 9  is an upstream view of the premix pilot nozzle as shown in  FIG. 4 , according to at least one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to present embodiments of the disclosure, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the disclosure. 
     As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. The terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example, “upstream” refers to the direction from which the fluid flows, and “downstream” refers to the direction to which the fluid flows. The term “radially” refers to the relative direction that is substantially perpendicular to an axial centerline of a particular component, and the term “axially” refers to the relative direction that is substantially parallel and/or coaxially aligned to an axial centerline of a particular component. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Each example is provided by way of explanation, not limitation. In fact, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents. Although exemplary embodiments of the present disclosure will be described generally in the context of a fuel nozzle assembly for a land based power generating gas turbine combustor for purposes of illustration, one of ordinary skill in the art will readily appreciate that embodiments of the present disclosure may be applied to any style or type of combustor for a turbomachine and are not limited to combustors or combustion systems for land based power generating gas turbines unless specifically recited in the claims. 
     Referring to the drawings,  FIG. 1  illustrates a schematic depiction of an embodiment of a gas turbine  10 . The gas turbine  10  includes a compressor section  12 , a combustion section  14 , and a turbine section  16 . The compressor section  12  and turbine section  16  may be coupled by a shaft  18 . The shaft  18  may be a single shaft or a plurality of shaft segments coupled together to form the shaft  18 . During operation, the compressor section  12  supplies compressed air to the combustion section  14 . The compressed air is mixed with fuel and burned within the combustion section  14  to produce hot gases of combustion which flow from the combustion section  14  to the turbine section  16 , wherein energy is extracted from the hot gases to produce work. 
     The combustion section  14  may include a plurality of combustors  20  (one of which is illustrated in  FIG. 2 ) positioned in an annular array about a center axis of the gas turbine  10 .  FIG. 2  provides a simplified cross-section of an exemplary combustor  20  known in the art and which may incorporate one or more embodiments of the present disclosure. As shown in  FIG. 2 , a casing  22  surrounds the combustor  20  to contain compressed air  24  flowing from the compressor section  12  ( FIG. 1 ). Multiple fuel nozzles are arranged across an end cover  26 . For example, in particular embodiments, a plurality of primary fuel nozzles  28  is circumferentially spaced radially outwardly from a secondary fuel nozzle  30 . A liner  32  extends downstream from the fuel nozzles  28 ,  30  and defines an upstream or forward combustion chamber  34  and a downstream or aft combustion chamber  36  which are separated by a throat or converging/diverging portion  38  of the liner  32 . 
     During operation of the combustor  20 , the primary fuel nozzles  28  may provide fuel to the upstream combustion chamber  34 . Depending on the operational mode of the combustor  20 , the fuel from the primary fuel nozzles  28  may be burned in the upstream combustion chamber  34  or may be premixed with the compressed air  24  within the upstream combustion chamber  34  for ignition in the downstream combustion chamber  36 . The secondary fuel nozzle  30  serves several functions in the combustor  20  including supplying a fuel and air mixture to the downstream combustion chamber  36  for premixed mode operation, supplying fuel and air for a pilot flame which supports primary nozzle operation and providing transfer fuel for utilization during changes between operation modes. 
       FIG. 3  provides a cross sectional side view of an exemplary fuel nozzle or fuel nozzle assembly  100  as may be incorporated into the combustor  20  as shown in  FIG. 2  as the secondary fuel nozzle  30 , according to at least one embodiment of the present disclosure. The fuel nozzle  100  may be connected to the end cover  26  or may be breach loaded through an opening  40  defined in the end cover  26 . 
     In various embodiments, as shown in  FIG. 3 , the fuel nozzle  100  includes an outer tube  102  having an upstream end portion  104  that is axially spaced from a downstream end portion  106  with respect to an axial centerline of the fuel nozzle  100 . An inner tube  108  extends axially within the outer tube  102  and may be coaxially aligned with the outer tube  102  with respect to the axial centerline of the fuel nozzle  100 . In particular embodiments, the inner tube  108  may be in fluid communication with an external compressed air supply (not shown). An intermediate tube  110  extends axially within the outer tube  102  and circumferentially surrounds the inner tube  108 . The intermediate tube  110  may be coaxially aligned with the outer tube  102  and/or the inner tube  108  with respect to the axial centerline of the fuel nozzle  100 . The intermediate tube  110  is radially spaced from the inner tube  108  so as to define a pilot fuel passage  112  therebetween. In particular embodiments, the intermediate tube  110  may be in fluid communication with an external fuel supply (not shown). The outer tube  102  is radially spaced from the intermediate tube  110  so as to define an annular air passage  114  therebetween. The annular air passage  114  may be in fluid communication with an external compressed air supply (not shown). 
     In particular embodiments, the fuel nozzle  100  may include a secondary intermediate tube  116  that extends axially within the outer tube  102  with respect to the axial centerline of the fuel nozzle  100 . The secondary intermediate tube  116  circumferentially surrounds at least a portion of the intermediate tube  110  and defines a secondary fuel passage  118  within the outer tube  102 . A plurality of fuel pegs  120  may be circumferentially spaced about the outer tube  102 . Each fuel peg  120  may extend radially outwardly from the outer tube  102  with respect to the axial centerline of the fuel nozzle  100 . One or more of the fuel pegs  120  may include one or more fuel injection orifices  122  which are in fluid communication with the secondary fuel passage  118 . 
     In various embodiments, the fuel nozzle  100  includes a premix pilot nozzle  124 . The premix pilot nozzle  124  includes a nozzle body  126  that extends axially through a nozzle ring  128 . The nozzle ring  128  may be coupled to the downstream end portion  106  of the outer tube  102 . In particular embodiments, the nozzle ring  128  may be formed as a singular or unitary component with the nozzle body  126 . 
       FIG. 4  provides a perspective view of the premix pilot nozzle  124  including the nozzle body  126  extending through the nozzle ring  128  according to at least one embodiment of the present disclosure.  FIG. 5  provides a perspective cross sectional view of the premix pilot nozzle  124  including the nozzle ring  128  as shown in  FIG. 3 . As shown collectively in  FIGS. 4 and 5 , the nozzle body  126  includes a forward wall  130  that is axially spaced from an aft wall  132  with respect to an axial centerline of the nozzle body  126 . As shown in  FIG. 5 , an outer band  134  extends axially between and circumferentially around the forward wall  130  and the aft wall  132  with respect to an axial centerline of the nozzle body  126 . The outer band  134  may define a radially outer perimeter of the nozzle body  126 . As shown in  FIG. 5 , the nozzle body  126  includes a tip portion  136 . The tip portion  136  extends downstream from the nozzle ring  128  and terminates at the aft wall  132 . In particular embodiments, the tip portion  136  of the nozzle body  126  may be cylindrical but is not limited to any particular shape unless otherwise recited in the claims. 
     In various embodiments, as shown in  FIG. 5 , the nozzle body  126  includes a first tube or air tube  138  that extends coaxially within the nozzle body  126  with respect to the axial centerline of the nozzle body  126 . The air tube  138  terminates within the nozzle body  126  at or proximate to an inner surface  140  of the aft wall  132 . A downstream portion of the air tube  138  may flare or diverge radially outwardly from the centerline of the nozzle body  126  at and/or proximate to the inner surface  140  of the aft wall  132 . The air tube  138  and a portion of the inner surface  140  of the aft wall  132  define a cooling air plenum  142  within the nozzle body  126 . 
     In at least one embodiment, the aft wall  132  defines a plurality of exhaust ports  144 . Each exhaust port  144  includes a respective inlet  146  that is defined within or surrounded by the air tube  138  and a respective outlet  148  defined along an outer surface  150  of the aft wall  132 . Each exhaust port  144  is in fluid communication with the cooling air plenum  142 . As shown in  FIG. 3 , an upstream end portion  152  of the air tube  138  may be coupled to the inner tube  108  of the fuel nozzle  100  and may be in fluid communication with the external compressed air supply (not shown) via inner tube  108 . 
     In various embodiments, as shown in  FIG. 5 , the nozzle body  126  includes a fuel tube  154 . The fuel tube  154  extends coaxially within the nozzle body  126  with respect to the axial centerline of the nozzle body  126 . The fuel tube  154  circumferentially surrounds at least a portion of the air tube  138  and is radially spaced from the air tube  138  so as to define a fuel inlet plenum  156  therebetween within the nozzle body  126 . In at least one embodiment, a baffle or orifice plate  158  may extend radially between the air tube  138  and the fuel tube  154 . The orifice plate may include a plurality of holes or metering holes  160  which may be sized and/or shaped to control flow of fuel into the fuel inlet plenum  156 . As shown in  FIG. 3 , an upstream end portion  162  of the fuel tube  154  may be coupled to the intermediate tube  110  of the fuel nozzle  100  and may in fluid communication with the external fuel supply (not shown) so as to provide fuel to the fuel inlet plenum  156 . 
     As shown in  FIG. 5 , the nozzle body  126  further includes or defines a fuel distribution plenum or void  164  which is defined inside or within the nozzle body  126 . The fuel distribution plenum  164  is defined within the nozzle body  126  radially outwardly from the fuel tube  154  and as such radially outwardly from the fuel inlet plenum  156 . The fuel distribution plenum  164  is separated from the fuel inlet plenum  156  via the fuel tube  154 . 
       FIG. 6  provides a cross sectioned perspective view of a portion of the tip portion  136  of the premix pilot nozzle  124  as taken along section lines A-A as shown in  FIG. 4 .  FIG. 7  provides a cross sectioned perspective view of a portion of the premix pilot nozzle  124  as taken along section lines B-B as shown in  FIG. 4 . As shown most clearly in  FIG. 6 , the fuel inlet plenum  156  is in fluid communication with the fuel distribution plenum  164  via a plurality of orifices or openings  166  which are circumferentially spaced about the axial centerline of the nozzle body  126 . The openings  166  are defined proximate to or adjacent to a portion of the inner surface  140  of the aft wall  132 . 
     In various embodiments, as shown in  FIG. 5 , the nozzle body  126  includes a plurality of premix tubes  168  disposed radially outwardly from the fuel tube  154  and/or from the fuel inlet plenum  156 . Each premix tube  168  defines a respective premix passage  170  through and/or within the nozzle body  126 . As shown collectively in  FIGS. 5 and 7 , the plurality of premix tubes  168  and as such to the respective premix passages  170  extend helically or wrap around the fuel tube  154  and/or the fuel inlet plenum  156  within the fuel distribution plenum  164  with respect to the axial centerline of the nozzle body  126 . 
     As shown in  FIGS. 4 and 5  collectively, each premix tube  168  and as such each premix passage  170  includes a respective inlet  172  ( FIG. 5 ) defined along the forward wall  130  and a respective outlet  174  ( FIG. 4 ) defined along the aft wall  132  of the tip portion  136 . As shown in  FIG. 4 , the respective inlets  172  are circumferentially spaced along the forward wall  130  and annularly arranged about the axial centerline of the nozzle body  126 . As shown in  FIG. 4 , the respective outlets  174  are circumferentially spaced along the aft wall  132  and annularly arranged about the axial centerline of the nozzle body  126 . As shown in  FIG. 5 , each premix tube  168  and as such each premix passage  170  may be in fluid communication with the fuel distribution plenum  164  via one or more fuel ports  176  defined along each respective premix tube  168 . 
     In various embodiments, as shown in  FIG. 5 , the nozzle ring  128  includes an upstream wall  178 , a downstream wall  180  axially spaced from the upstream wall  178 , an outer sleeve  182  that circumferentially surrounds the upstream and downstream walls  178 ,  180  and a plurality of thru-holes  184  that extend through the upstream and the downstream walls  178 ,  180 . The plurality of thru-holes  184  is annularly arranged around and disposed radially outwardly from the outer band  134  of the nozzle body  126  and defined radially inwardly from the outer sleeve  182  of the nozzle ring  128 . As shown in  FIG. 3 , the outer sleeve  182  may be coupled to the outer tube  102  of the fuel nozzle  100 . In various embodiments, the plurality of thru-holes  184  is in fluid communication with the annular air passage  114 . 
       FIG. 8  provides a perspective view of the tip portion of the nozzle body  126  and the nozzle ring  128  according to at least one embodiment of the present disclosure.  FIG. 9  provides an upstream view of the nozzle body  126  according to at least one embodiment of the present disclosure. In particular embodiments, as shown collectively in  FIGS. 8 and 9 , a portion of the aft wall  132  of the tip portion  136  which is defined radially inwardly from the respective outlets  174  of the premix passages  170  with respect to the centerline of the nozzle body  126  is dimpled, cupped or concaved axially inwardly along the axial centerline of the nozzle body  126  back towards the forward wall  130  or the nozzle ring  128 . In particular embodiments as shown in  FIG. 8 , a radially outer surface  186  of the tip portion  136  of the nozzle body  126  may include a plurality of grooves  188  that extend helically along the outer surface  186  about the axial centerline of the nozzle body  126 . 
     In at least one embodiment, as shown in  FIGS. 8 and 9 , one or more of the outlets  148  of the of the exhaust ports  144  ( FIG. 5 ) is disposed within the dimpled or cupped portion of the aft wall  132 . In at least one embodiment, as show collectively in  FIGS. 8 and 9 , one or more of the outlets  170  of the premix passages  170  is partially surrounded by a respective boss or collar  190  that extends axially downstream from the outer surface  150  of the aft wall  132 . In particular embodiments, each of the outlets  174  of the premix passages  170  is partially surrounded by a respective boss or collar  190  that extends axially downstream from the outer surface  150  of the aft wall  132 . 
     In at least one embodiment, the nozzle body  126  is formed as a singular body. In other words, the forward wall  130 , the aft wall  132 , the outer band  134 , the air tube  138 , the fuel tube  154  and the premix tubes  168  may all be formed from or as a singular body. In at least one embodiment, the nozzle body  126  and the nozzle ring  128  are formed from a singular body. For example, in particular embodiments, the nozzle body  126  with or without the nozzle ring  128  may be formed via an additive manufacturing process. The terms additive manufacturing or additively manufactured as used herein refers to any process which results in a useful, three-dimensional object and includes a step of sequentially forming the shape of the object one layer at a time. Additive manufacturing processes may include three-dimensional printing (3DP) processes, laser-net-shape manufacturing, direct metal laser sintering (DMLS), direct metal laser melting (DMLM), plasma transferred arc, freeform fabrication, etc. 
     During operation of the premix pilot nozzle  124 , as shown collectively in  FIGS. 3 through 9 , air flows from the annular air passage  114  defined between the intermediate tube  110  and the outer tube  102 , through the plurality of thru-holes  184  and through the respective premix passages  170 . Fuel flows through the pilot fuel passage  112  and into the fuel inlet plenum  156  via the inner tube  108  and the fuel tube  154 . The fuel flows into the fuel distribution plenum  164  via the plurality of orifices  166 . The relatively cool fuel may provide cooling to a portion of the aft wall  132 , thereby enhancing the mechanical life of the premix pilot nozzle  124 . The fuel then flows from the fuel distribution plenum  164  and into the respective premix passages  170  via the respective fuel ports  176 . The fuel and air mix within the respective premix passages  170  before being injected into the downstream combustion chamber  36  for combustion. The helical premix tubes  168  may impart angular swirl to the premixed fuel and air as it exits the respective outlets  174  of the premix passages  170 , thereby encouraging further mixing of the fuel and air upstream from the downstream combustion chamber  36 . 
     Compressed air may be routed through the inner tube  108  and into the cooling air plenum  142  defined within the air tube  138  of the nozzle body  126 . The compressed air may then flow out of the cooling air plenum  142  via the plurality of exhaust ports  144 . The exhaust ports  144  may be formed or angled so as to create a film of the compressed air across the outer surface  150  of the aft wall  132 , thereby cooling the and/or providing a protective film across the outer surface  150  of the aft wall  132 . The bosses  190  may prevent or block the cooling air from mixing with or otherwise interacting with the flow of premixed fuel and air as it exits the respective outlets  174  of the premix passages  170 . 
     The premix pilot nozzle  124  as shown and described herein, may replace known high temperature and high Emissions diffusion type pilot nozzles which stabilize the flame in the downstream combustion chamber  36  at high temperature but at the expense of emissions. The premix pilot nozzle  124  as shown and described herein may replace known diffusion type premix pilot nozzles with a swirl stabilized premixed pilot nozzle. The premixed pilot nozzle  124  may result in more desirable emissions levels with the same flame stability provided by known diffusion type pilot nozzles while also providing improved dynamics and/or lean blow out limits. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.