Patent Publication Number: US-8984887-B2

Title: Combustor and method for supplying fuel to a combustor

Description:
FIELD OF THE INVENTION 
     The present invention generally involves a combustor and method for supplying fuel to a combustor. 
     BACKGROUND OF THE INVENTION 
     Combustors are commonly used in industrial and power generation operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, gas turbines typically include one or more combustors to generate power or thrust. A typical gas turbine used to generate electrical power includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air may be supplied to the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or more nozzles into a combustion chamber in each combustor where the compressed working fluid mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity. 
     Various design and operating parameters influence the design and operation of combustors. For example, higher combustion gas temperatures generally improve the thermodynamic efficiency of the combustor. However, higher combustion gas temperatures also promote flashback or flame holding conditions in which the combustion flame migrates towards the fuel being supplied by the nozzles, possibly causing severe damage to the nozzles in a relatively short amount of time. In addition, localized hot streaks in the combustion chamber may increase the disassociation rate of diatomic nitrogen, increasing the production of nitrogen oxides (NO x ) at higher combustion gas temperatures. Conversely, lower combustion gas temperatures associated with reduced fuel flow and/or part load operation (turndown) generally reduce the chemical reaction rates of the combustion gases, increasing the production of carbon monoxide and unburned hydrocarbons. 
     In a particular combustor design, a plurality of tubes may be radially arranged in an end cap to provide fluid communication for the working fluid and fuel flowing through the end cap and into the combustion chamber. The tubes enhance mixing between the working fluid and fuel to reduce hot streaks that can be problematic with higher combustion gas temperatures. As a result, the tubes are effective at preventing flashback or flame holding and/or reducing NO x  production, particularly at higher operating levels. However, an improved combustor and method for supplying fuel to the tubes that allows for staged fueling or operation of the tubes at varying operational levels would be useful. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention are circuit 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 combustor that includes an end cap that extends radially across at least a portion of the combustor, wherein the end cap comprises an upstream surface axially separated from a downstream surface and a cap shield circumferentially surrounding the upstream and downstream surfaces. A first circuit of tubes extends from the upstream surface through the downstream surface, and a first fuel plenum in the end cap is in fluid communication with the first circuit of tubes. A second circuit of tubes extends from the upstream surface through the downstream surface, and a second fuel plenum in the end cap downstream from the first fuel plenum is in fluid communication with the second circuit of tubes. 
     Another embodiment of the present invention is a combustor that includes an end cap that extends radially across at least a portion of the combustor, wherein the end cap comprises an upstream surface axially separated from a downstream surface and a cap shield circumferentially surrounding the upstream and downstream surfaces. A first barrier extends radially in the end cap between the upstream and downstream surfaces. A first plenum is upstream from the first barrier, and a second plenum is downstream from the first barrier. A plurality of tubes extends from the upstream surface through the first barrier and the downstream surface to provide fluid communication through the end cap. A first conduit is in fluid communication with the first plenum, and a second conduit is in fluid communication with the second plenum. 
     The present invention may also include a method for supplying fuel to a combustor. The method includes flowing a working fluid through a plurality of tubes that extend axially through an end cap that extends radially across at least a portion of the combustor. The method further includes flowing a first fuel from a first fuel plenum in the end cap through a first circuit of the plurality of tubes and flowing a second fuel from a second fuel plenum in the end cap through a second circuit of the plurality of tubes, wherein the second fuel plenum is downstream from the first fuel 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 circuit forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
         FIG. 1  is a simplified cross-section view of an exemplary combustor within the scope of various embodiments of the present invention; 
         FIG. 2  is a cross-section view of the end cap shown in  FIG. 1  taken along line A-A according to an embodiment of the present invention; 
         FIG. 3  is a cross-section view of the end cap shown in  FIG. 1  taken along line A-A according to an embodiment of the present invention; 
         FIG. 4  is a cross-section view of the end cap shown in  FIG. 1  taken along line A-A according to an embodiment of the present invention; 
         FIG. 5  is a simplified partial perspective view of the end cap shown in  FIG. 4 ; 
         FIG. 6  is an enlarged cross-section view of a portion of the end cap shown in  FIG. 5  according to a first embodiment of the present invention; 
         FIG. 7  is an enlarged cross-section view of a portion of the end cap shown in  FIG. 5  according to a second embodiment of the present invention; and 
         FIG. 8  is an enlarged cross-section view of a portion of the end cap shown in  FIG. 5  according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to present embodiments of the invention, 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 invention. 
     Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention 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 invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Various embodiments of the present invention provide a combustor and method for supplying fuel to a combustor. In particular embodiments, a plurality of tubes arranged in an end cap enhance mixing between a working fluid, a fuel, and/or a diluent prior to combustion. The working fluid flows through the tubes, and the fuel and/or diluent may be supplied to the tubes through one or more fluid conduits. The tubes may be grouped into multiple circuits that enable flow rates of the fuel and/or the diluent to be varied between each circuit. In this manner, the combustor may be operated over a wide range of operating conditions without exceeding design margins associated with flashback, flame holding, combustion dynamics, and/or emissions limits. Although exemplary embodiments of the present invention will be described generally in the context of a combustor incorporated into a gas turbine for purposes of illustration, one of ordinary skill in the art will readily appreciate that embodiments of the present invention may be applied to any combustor and are not limited to a gas turbine combustor unless specifically recited in the claims. In addition, 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 particular structure, location, function, or importance of the individual components. 
       FIG. 1  shows a simplified cross-section view of an exemplary combustor  10 , such as would be included in a gas turbine, within the scope of various embodiments of the present invention. A casing  12  and an end cover  14  may surround the combustor  10  to contain a working fluid flowing to the combustor  10 . The working fluid may pass through flow holes  16  in an impingement sleeve  18  to flow along the outside of a transition piece  20  and liner  22  to provide convective cooling to the transition piece  20  and liner  22 . When the working fluid reaches the end cover  14 , the working fluid reverses direction to flow through a plurality of tubes  24  into a combustion chamber  26 . 
     The tubes  24  are radially arranged in an end cap  28  upstream from the combustion chamber  26 . As used herein, the terms “upstream” and “downstream” refer to the relative location of components in a fluid pathway. For example, component A is upstream from component B if a fluid flows from component A to component B. Conversely, component B is downstream from component A if component B receives a fluid flow from component A. As shown, the end cap  28  generally extends radially across at least a portion of the combustor  10  and includes an upstream surface  30  axially separated from a downstream surface  32  and a cap shield  34  that circumferentially surrounds the upstream and downstream surfaces  30 ,  32 . Each tube  24  extends from the upstream surface  30  through the downstream surface  32  of the end cap  28  to provide fluid communication for the working fluid to flow through the end cap  28  and into the combustion chamber  26 . 
     Various embodiments of the combustor  10  may include different numbers, shapes, and arrangements of tubes  24  separated into various groups across the end cap  28 . The tubes  24  in each group may be grouped in circular, triangular, square, or other geometric shapes, and the groups may be arranged in various numbers and geometries in the end cap  28 . Although generally illustrated as cylindrical tubes in each embodiment, the cross-section of the tubes  24  may be any geometric shape, and the present invention is not limited to any particular cross-section unless specifically recited in the claims.  FIG. 2  shows the tubes  24  radially arranged across the end cap  28 , and  FIG. 3  shows the tubes  24  arranged, for example, in six groups radially surrounding a single group.  FIG. 4  shows five pie-shaped groups of tubes  24  arranged around a single fuel nozzle  36  aligned with an axial centerline  38  of the end cap  28 . The fuel nozzle  36  may include a shroud  40  that circumferentially surrounds a center body  42  to define an annular passage  44  between the shroud  40  and the center body  42 . One or more swirler vanes  46  may be located between the shroud  40  and the center body  42  to impart swirl to the working fluid flowing through the annular passage  44 . In this manner, the fuel nozzle  36  may provide fluid communication through the end cap  28  to the combustion chamber  26  separate and apart from the tubes  24 . 
       FIG. 5  provides a simplified partial perspective view of the end cap  28  shown in  FIG. 4 . As shown in  FIG. 5 , a first barrier  48  may extend radially in the end cap  28  between the upstream and downstream surfaces  30 ,  32  to define a first plenum  50  upstream from the first barrier  48  and a second plenum  52  downstream from the first barrier  48 . First and second conduits  54 ,  56  may extend from the end cover  14  or casing  12  to provide fluid communication with the first and second plenums  50 ,  52 , respectively. In this manner, the first and second conduits  54 ,  56  may supply a fuel and/or a diluent to the respective first and second plenums  50 ,  52 . 
       FIG. 6  provides an enlarged cross-section view of a portion of the end cap  28  shown in  FIG. 5  according to a first embodiment of the present invention. As shown, the first barrier  48  extends radially in the end cap  28  between the upstream and downstream surfaces  30 ,  32 , and the tubes  24  extend from the upstream surface  30  through the first barrier  48  and the downstream surface  32  to provide fluid communication through the end cap  28 . As further shown, the first conduit  54  is in fluid communication with the first plenum  50 , and the second conduit  56  is in fluid communication with the second plenum  52 . 
     The tubes  24  may be arranged into multiple circuits that enable varying flow rates of the fuel and/or the diluent to each circuit. For example, as shown in  FIG. 6 , a first circuit  58  of tubes  24  may include one or more fluid passages  60  that provide fluid communication from the first plenum  50  through each tube  24  in the first circuit  58 , and a second circuit  62  of tubes  24  may include one or more fluid passages  60  that provide fluid communication from the second plenum  52  through each tube  24  in the second circuit  62 . The fluid passages  60  may be angled radially, axially, and/or azimuthally to project and/or impart swirl to the fuel and/or diluent flowing through the fluid passage  60  and into the tubes  24 . The end cap  28  may further include one or more baffles that extend radially in the first and or second plenums  50 ,  52  to distribute fluid flow in the respective plenums. For example, as shown in  FIG. 6 , a first baffle  64  may extend radially in the first plenum  50  between the upstream surface  30  and the barrier  48 , and a second baffle  66  may extend radially in the second plenum  52  between the barrier  48  and the downstream surface  32 . 
     In the particular embodiment shown in  FIG. 6 , the working fluid may flow outside the end cap  28  until it reaches the end cover  14  and reverses direction to flow through the tubes  24  in the first and second circuits  58 ,  62 . In addition, fuel and/or diluent may be supplied through the first conduit  54  to the first plenum  50 . The fuel and/or diluent may flow around the tubes  24  in the first plenum  50  to provide convective cooling to the tubes  24  before flowing across the first baffle  64  and through the fluid passages  60  in the first circuit  58  of tubes  24  to mix with the working fluid flowing through the first circuit  58  of tubes  24 . Similarly, fuel and/or diluent may be supplied through the second conduit  56  to the second plenum  52 . The fuel and/or diluent supplied through the second conduit  56  may be identical to or different from the fuel and/or diluent supplied through the first conduit  54 . The fuel and/or diluent may flow across the second baffle  66  to provide impingement cooling to the downstream surface  32  before flowing around the tubes  24  in the second plenum  52  to provide convective cooling to the tubes  24  before flowing through the fluid passages  60  in the second circuit  62  of tubes  24  to mix with the working fluid flowing through the second circuit  62  of tubes  24 . The fuel-working fluid mixture from each circuit  58 ,  62  of tubes  24  may then flow into the combustion chamber  26 . 
     The temperature of the fuel and working fluid flowing around and/or through the tubes  24  may vary considerably during combustor  10  operations. As a result, the end cap  28  may further include one or more expansion joints or bellows between the upstream and downstream surfaces  30 ,  32  to allow for thermal expansion of the tubes  24  between the upstream and downstream surfaces  30 ,  32 . For example, as shown in  FIG. 6 , an expansion joint  68  in the cap shield  34  may allow for axial displacement of the upstream and downstream surfaces  30 ,  32  as the tubes  24  expand and contract. One of ordinary skill in the art will readily appreciate that alternate locations and/or combinations of expansion joints between the upstream and downstream surfaces  30 ,  32  are within the scope of various embodiments of the present invention, and the specific location or number of expansion joints is not a limitation of the present invention unless specifically recited in the claims. 
       FIG. 7  provides an enlarged cross-section view of a portion of the end cap  28  shown in  FIG. 5  according to a second embodiment of the present invention. In this particular embodiment, a second barrier  70  extends radially in the end cap  28  between the first barrier  48  and the downstream surface  32  to at least partially define a third plenum  72  in the end cap  28  downstream from the second barrier  70 . Specifically, the second barrier  70 , downstream surface  32 , and cap shield  34  define the third plenum  72 . In addition, one or more ports  74  through the cap shield  34  provide fluid communication through the cap shield  34  to the third plenum  72 . In this manner, at least a portion of the working fluid may flow into the third plenum  72  to flow around the first and/or second circuits  58 ,  62  of tubes  24  to provide convective cooling to the tubes  24 . The working fluid may then flow through gaps  76  between the downstream surface  32  and the tubes  24  before flowing into the combustion chamber  26 . 
       FIG. 8  provides an enlarged cross-section view of a portion of the end cap  28  shown in  FIG. 5  according to a third embodiment of the present invention. In this particular embodiment, the first and second conduits  54 ,  56  are curved to more readily absorb thermal expansion and contraction in the combustor  10 . In addition, the second circuit  62  of tubes  24  includes fluid passages  60  that provide fluid communication from both the first and second plenums  50 ,  52  through one or more tubes  24  in the second circuit  62 . As a result, fuel and/or diluent supplied to the first circuit  58  of tubes  24  may also be supplied to one or more tubes  24  in the second circuit  62 . 
     The axial position, number, and size of the fluid passages  60  in each circuit  58 ,  62  may be selected to optimize the fuel flow through each tube  24  at various operating levels while also enhancing the combustion dynamics. Specifically, the fluid passages  60  upstream from the first baffle  64  allow more time for convective mixing between the fuel and working fluid compared to the fluid passages  60  downstream from the first baffle  64 , which in turn allow more time for convective mixing compared to the fuel passages  60  downstream from the first barrier  48 . Similarly, the fluid pressure in the first plenum  50  upstream from the first baffle  64  is generally greater than the fluid pressure downstream from the first baffle  64 , and the fluid pressure in the second plenum.  52  may be controlled independently from the fluid pressure in the first plenum  50 . As a result, the axial position, number, and size of the fluid passages  60  may be selected to achieve the optimum fuel flow and convective mixing for each operating level. In addition, the axial position, number, and size of the fluid passages  60  may be adjusted between the first and second circuits  58 ,  62  to reduce any harmonic interaction between individual tubes  24  to enhance the combustion dynamics produced in the combustor  10 . 
     The various embodiments shown in  FIGS. 1-8  provide multiple combinations of methods for supplying fuel to the combustor  10 . As shown in  FIGS. 6-8  for example, the method may include flowing the working fluid through the tubes  24 , flowing a first fuel from the first fuel plenum  50  through the first circuit  58  of tubes  24 , and flowing a second fuel from the second fuel plenum  52  through the second circuit  62  of tubes  24 . As previously stated, the first and second fuels and diluents may be the same or different. The method may further include flowing at least one of fuel or diluent around one or more baffles  64 ,  66  that extend radially in the first and/or second fuel plenums  50 ,  52  and/or flowing the working fluid through the third plenum  72 , as shown in the particular embodiment illustrated in  FIG. 7 . Alternately, or in addition, the method may include flowing the first fuel through the first fuel plenum  50  and the second circuit  62  of tubes  24  and/or flowing a third fuel or diluent through the nozzle  36  aligned with the axial centerline  38  of the end cap  28 . One or ordinary skill in the art can readily appreciate these and multiple other methods for staging fuel and/or diluent flow through the tubes  24  to support expanded combustor  10  operations without exceeding design margins associated with flashback, flame holding, combustion dynamics, and/or emissions 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.