Patent Publication Number: US-9423135-B2

Title: Combustor having mixing tube bundle with baffle arrangement for directing fuel

Description:
FEDERAL RESEARCH STATEMENT 
     This invention was made with Government support under Contract No. DE-FC26-05NT42643, awarded by the Department of Energy. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally involves a combustor and method for distributing fuel in the 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, turbomachines such as gas turbines typically include one or more combustors to generate power or thrust. A typical gas turbine includes an inlet section, a compressor section, a combustion section, a turbine section, and an exhaust section. The inlet section cleans and conditions a working fluid (e.g., air) and supplies the working fluid to the compressor section. The compressor section increases the pressure of the working fluid and supplies a compressed working fluid to the combustion section. The combustion section mixes fuel with the compressed working fluid and ignites the mixture to generate combustion gases having a high temperature and pressure. The combustion gases flow to the turbine section where they expand to produce work. For example, expansion of the combustion gases in the turbine section may rotate a shaft connected to a generator to produce electricity. 
     The combustion section may include multiple combustors annularly arranged between the compressor section and the turbine section, and various parameters influence the design and operation of the combustors. For example, higher combustion gas temperatures generally improve the thermodynamic efficiency of the combustor. However, higher combustion gas temperatures also promote flame holding conditions in which the combustion flame migrates towards the fuel being supplied by nozzles, possibly causing accelerated damage to the nozzles in a relatively short amount of time. In addition, higher combustion gas temperatures generally increase the disassociation rate of diatomic nitrogen, increasing the production of nitrogen oxides (NO X ). Conversely, a lower combustion gas temperature associated with reduced fuel flow and/or part load operation (turndown) generally reduces the chemical reaction rates of the combustion gases, increasing the production of carbon monoxide and unburned hydrocarbons. 
     In a particular combustor design, the combustor may include an end cap that extends radially across at least a portion of the combustor. A plurality of tubes may be radially arranged in one or more tube bundles across the end cap to provide fluid communication for the compressed working fluid through the end cap and into a combustion chamber. Fuel supplied to a fuel plenum inside the end cap may flow around the tubes and provide convective cooling to the tubes before flowing across a baffle and into the tubes. The fuel and compressed working fluid mix inside the tubes before flowing out of the tubes and into the combustion chamber. 
     Although effective at enabling higher operating temperatures while protecting against flame holding and controlling undesirable emissions, the fuel flowing around and into the tubes may become unevenly heated, resulting in variations in the density and therefore the flow rate of fuel flowing into each tube. In addition, the temperature of the fuel may be significantly lower than the temperature of the compressed working fluid flowing around the end cap and through the tubes, creating undesirable thermal stresses across the end cap, baffle, and/or tubes that may reduce the low cycle fatigue limits of the combustor. As a result, a combustor and method for distributing fuel in the combustor that addresses one or more of these deficiencies would be useful. 
     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 combustor that includes a tube bundle that extends radially across at least a portion of the combustor. The tube bundle includes an upstream surface axially separated from a downstream surface, and a plurality of tubes extend from the upstream surface through the downstream surface to provide fluid communication through the tube bundle. A barrier extends radially inside the tube bundle between the upstream and downstream surfaces, and a baffle extends axially inside the tube bundle between the upstream surface and the barrier. 
     Another embodiment of the present invention is a combustor that includes a tube bundle that extends radially across at least a portion of the combustor. The tube bundle includes an upstream surface, and a shroud circumferentially surrounds the upstream surface to at least partially define a fuel plenum inside the tube bundle. A plurality of tubes extend through the upstream surface of the tube bundle to provide fluid communication through the tube bundle. A barrier extends radially inside the fuel plenum downstream from the upstream surface, and the combustor further includes means for radially directing fuel inside the fuel plenum. 
     The present invention may also include a gas turbine having a compressor, a combustor downstream from the compressor, and a turbine downstream from the combustor. A tube bundle extends radially across at least a portion of the combustor. The tube bundle includes an upstream surface axially separated from a downstream surface, and a shroud circumferentially surrounds the upstream and downstream surfaces to at least partially define a fuel plenum inside the tube bundle. A plurality of tubes extend from the upstream surface through the downstream surface of the tube bundle to provide fluid communication through the tube bundle. A barrier extends radially inside the fuel plenum between the upstream and downstream surfaces, and a baffle extends axially inside the fuel plenum between the upstream surface and the barrier. 
     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  is a functional block diagram of an exemplary gas turbine within the scope of the present invention; 
         FIG. 2  is a simplified side cross-section view of an exemplary combustor according to various embodiments of the present invention; 
         FIG. 3  is a cross-section view of the end cap shown in  FIG. 2  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. 2  taken along line A-A according to an embodiment of the present invention; 
         FIG. 5  is a cross-section view of the end cap shown in  FIG. 2  taken along line A-A according to an embodiment of the present invention; 
         FIG. 6  is a partial perspective, side cross-section view of a tube bundle according to a first embodiment of the present invention; 
         FIG. 7  is a partial perspective side cross-section view of a tube bundle according to a second embodiment of the present invention; 
         FIG. 8  is a partial perspective side cross-section view of a tube bundle according to a third embodiment of the present invention; and 
         FIG. 9  is a partial perspective side cross-section view of a tube bundle according to a fourth 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. 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,” “downstream,” “radially,” and “axially” 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. Similarly, “radially” refers to the relative direction substantially perpendicular to the fluid flow, and “axially” refers to the relative direction substantially parallel to the fluid flow. 
     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 include a combustor and method for distributing fuel in the combustor. The combustor generally includes a tube bundle having a plurality of tubes that allow fuel and compressed working fluid to thoroughly mix before entering a combustion chamber. A barrier, baffle, or other means extend radially and/or axially inside the tube bundle to enhance distribution of the fuel inside the tube bundle. Although exemplary embodiments of the present invention will be described generally in the context of a combustor incorporated into a turbomachine such as 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 turbomachine combustor unless specifically recited in the claims. 
     Referring now to the drawings, wherein identical numerals indicate the same elements throughout the figures,  FIG. 1  provides a functional block diagram of an exemplary gas turbine  10  that may incorporate various embodiments of the present invention. As shown, the gas turbine  10  generally includes an inlet section  12  that may include a series of filters, cooling coils, moisture separators, and/or other devices to purify and otherwise condition a working fluid (e.g., air)  14  entering the gas turbine  10 . The working fluid  14  flows to a compressor section where a compressor  16  progressively imparts kinetic energy to the working fluid  14  to produce a compressed working fluid  18  at a highly energized state. The compressed working fluid  18  flows to a combustion section where one or more combustors  20  ignite fuel  22  with the compressed working fluid  18  to produce combustion gases  24  having a high temperature and pressure. The combustion gases  24  flow through a turbine section to produce work. For example, a turbine  26  may connect to a shaft  28  so that rotation of the turbine  26  drives the compressor  16  to produce the compressed working fluid  18 . Alternately or in addition, the shaft  28  may connect the turbine  26  to a generator  30  for producing electricity. Exhaust gases  32  from the turbine  26  flow through an exhaust section  34  that may connect the turbine  26  to an exhaust stack  36  downstream from the turbine  26 . The exhaust section  34  may include, for example, a heat recovery steam generator (not shown) for cleaning and extracting additional heat from the exhaust gases  32  prior to release to the environment. 
     The combustors  20  may be any type of combustor known in the art, and the present invention is not limited to any particular combustor design unless specifically recited in the claims.  FIG. 2  provides a simplified side cross-section view of an exemplary combustor  20  according to various embodiments of the present invention. As shown in  FIG. 2 , a casing  40  and an end cover  42  may surround the combustor  20  to contain the compressed working fluid  18  flowing to the combustor  20 . The compressed working fluid  18  may pass through flow holes  44  in an impingement sleeve  46  to flow along the outside of a transition piece  48  and liner  50  to provide convective cooling to the transition piece  48  and liner  50 . When the compressed working fluid  18  reaches the end cover  42 , the compressed working fluid  18  reverses direction to flow through a plurality of tubes  52  into a combustion chamber  54 . 
     The tubes  52  are radially arranged in an end cap  56  upstream from the combustion chamber  54 . As shown, the end cap  56  generally extends radially across at least a portion of the combustor  20  and may include an upstream surface  58  axially separated from a downstream surface  60 . A cap shield or shroud  62  may circumferentially surround the upstream and downstream surfaces  58 ,  60 . Each tube  52  may extend from the upstream surface  58  and/or through the downstream surface  60  of the end cap  56  to provide fluid communication for the compressed working fluid  18  to flow through the end cap  56  and into the combustion chamber  54 . 
     Various embodiments of the combustor  20  may include different numbers, shapes, and arrangements of tubes  52  separated into various bundles across the end cap  56 , and  FIGS. 3-5  provide upstream views of the end cap  56  according to various exemplary embodiments. Although generally illustrated as cylindrical tubes in each embodiment, the cross-section of the tubes  52  may be any geometric shape, and the present invention is not limited to any particular cross-section unless specifically recited in the claims. The tubes  52  in each bundle may be grouped in circular, triangular, square, or other geometric shapes, and the bundles may be arranged in various numbers and geometries in the end cap  56 . For example, in the embodiment shown in  FIG. 3 , the tubes  52  are radially arranged across the end cap  56  as a single tube bundle. In contrast,  FIG. 4  shows the tubes  52  arranged, for example, in six outer tube bundles  64  radially surrounding a single center tube bundle  66 . In the particular embodiment shown in  FIG. 5 , the tubes  52  are arranged in six pie-shaped tube bundles  68  that circumferentially surround a single fuel nozzle  70  aligned with an axial centerline  72  of the end cap  56 . The fuel nozzle  70  may include, for example, a shroud  74  that circumferentially surrounds a center body  76  to define an annular passage  78  between the shroud  74  and the center body  76 . One or more swirler vanes  80  may be located between the shroud  74  and the center body  76  to impart swirl to the compressed working fluid  18  flowing through the annular passage  78 . In this manner, the fuel nozzle  70  may provide fluid communication through the end cap  56  to the combustion chamber  54  separate and apart from the tubes  52 . 
       FIGS. 6-9  provide partial perspective side cross-section views of an exemplary bundle  90  according to various embodiments of the present invention. As shown in each figure, the tube bundle  90  generally extends radially across at least a portion of the end cap  56 , and the tubes  52  extend axially between the upstream and downstream surfaces  58 ,  60  to provide fluid communication for the compressed working fluid  18  to flow through the tube bundle  90  and into the combustion chamber  54 . A barrier  94  may extend radially between the upstream and downstream surfaces  58 ,  60  so that the upstream surface  58 , shroud  62 , and barrier  94  generally define a fuel plenum  92  inside the tube bundle  90 . 
     One or more conduits may provide fluid communication for fuel  22 , diluents, and/or other additives to flow into the fuel plenum  92  and/or through the end cap  56  and into the combustion chamber  54 . For example, as shown in  FIGS. 6-9 , an inner conduit  96  may extend through the upstream and downstream surfaces  58 ,  60  to supply fuel  22  directly through the end cap  56  to the combustion chamber  54 . An outer conduit  98  may surround the inner conduit  96  to define an annulus  100  between the inner and outer conduits  96 ,  98 . In this manner, fuel  22  may flow through the annulus  100  and into the fuel plenum  92  to provide convective cooling to the tubes  52  and pre-heat the fuel  22 . The fuel  22  may then flow through fuel ports  104  in one or more tubes  52  to mix with the compressed working fluid  18  inside the tubes  52  before flowing into the combustion chamber  54 . The fuel ports  104  may be angled radially, axially, and/or azimuthally to project and/or impart swirl to the fuel  22  flowing through the fuel ports  104  and into the tubes  52 . In this manner, the compressed working fluid  18  may flow into the tubes  52 , and the fuel  22  from the fuel plenum  92  may flow through the fuel ports  104  and into the tubes  52  to mix with the compressed working fluid  18 . The fuel-working fluid mixture may then flow through the tubes  52  and into the combustion chamber  54 . 
     The fuel  22  flowing around and into the tubes  52  may become unevenly heated, resulting in variations in the density of the fuel  22  flowing into the fuel ports  104 . In addition, the temperature of the fuel  22  may be significantly lower than the temperature of the compressed working fluid  18  flowing around the end cap  56  and through the tubes  52 , creating undesirable thermal stresses across the tubes  52 , upstream surface  58  and/or barrier  94  that may reduce the low cycle fatigue limits of the combustor  20 . As a result, each tube bundle  90  further includes means for radially directing the fuel  22  inside the fuel plenum  92  to more evenly distribute and heat the fuel  22  as it flows through the fuel plenum  92 . The structure associated with the means may include a baffle that extends axially inside the tube bundle  90  between the upstream surface  58  and the barrier  94 . The structure may include, for example, any combination of guides, plates, vanes, or other baffles suitable for continuous exposure in the temperatures and pressures associated with the fuel plenum  92 . In particular embodiments, the structure may further include one or more connections to the upstream surface  58 , barrier  94 , and/or outer conduit  98  to locate the means inside the fuel plenum  92 . 
       FIG. 6  provides a partial perspective side cross-section view of the exemplary tube bundle  90  according to a first embodiment of the present invention. In the particular embodiment shown in  FIG. 6 , the structure associated with the means for radially directing the fuel  22  inside the fuel plenum  92  is a cylinder  110  with perforations  112 . The cylinder  110  extends axially inside the tube bundle  90  substantially parallel to the tubes  52  between the upstream surface  58  and the barrier  94 . As shown in  FIG. 6 , the cylinder  110  connects to the upstream surface  58  and the barrier  94  to locate the cylinder  110  inside the fuel plenum  92 . In other particular embodiments, the cylinder  110  may connect to one or more of the upstream surface  58 , the barrier  94 , and/or the outer conduit  98 , as desired. As shown in  FIG. 6 , the perforations  112  in the cylinder  110  radially direct the fuel  22  flowing into the fuel plenum  92  to facilitate more even heating and flow of the fuel  22  inside the fuel plenum  92 . In particular embodiments, the perforations  112  may be non-uniform to preferentially direct fuel  22  to particular locations in the tube bundle. 
       FIG. 7  provides a partial perspective side cross-section view of the exemplary tube bundle  90  according to a second embodiment of the present invention. In the particular embodiment shown in  FIG. 7 , the structure associated with the means for radially directing the fuel  22  inside the fuel plenum  92  is a plurality of curved guides  120  that extend radially from the inner conduit  96 . The curved guides  120  are arranged axially inside the tube bundle  90  substantially parallel to the tubes  52  between the upstream surface  58  and the barrier  94 . The curvature and/or length of the curved guides  120  may be the same or different. As shown in  FIG. 7 , a wire  122  or other structure may connect the curved guides  120  to the outer conduit  98  and/or the barrier  94  to provide additional support to the curved guides  120  inside the fuel plenum  92 . In other particular embodiments, the wire  122  may connect the curved guides  120  to one or more of the upstream surface  58 , the barrier  94 , and/or the outer conduit  98 , as desired. As shown in  FIG. 7 , the curved guides  120  radially direct the fuel  22  flowing into the fuel plenum  92  to facilitate more even heating and flow of the fuel  22  inside the fuel plenum  92 . 
       FIGS. 8 and 9  provide partial perspective side cross-section views of the exemplary tube bundle  90  according to third and fourth embodiments of the present invention. In the particular embodiments shown in  FIGS. 8 and 9 , the structure associated with the means for radially directing the fuel  22  inside the fuel plenum  92  is a plurality of straight guides  130  that extend radially from the inner conduit  96 . The straight guides  130  are arranged axially inside the tube bundle  90  substantially parallel to the tubes  52  between the upstream surface  58  and the barrier  94 . The length of the straight guides  130  may be the same or different, and the angle of the straight guides  130  with respect to the upstream surface  58  may vary. For example, in the particular embodiment shown in  FIG. 8 , the straight guides  130  closer to the upstream surface  58  and/or outer conduit  100  are angled with respect to the upstream surface  58 , while the straight guides  130  closer to the barrier  94  are substantially parallel to the upstream surface  58 . As another example, in the particular embodiment shown in  FIG. 9 , the length of the straight guides  130  gradually increases from the upstream surface  58  and/or outer conduit  98  to the barrier  94 . In addition, the angle of the straight guides  130  changes from one direction, to horizontal, to the other direction as the straight guides  130  get closer to the barrier  94 . 
     As shown in  FIG. 8 , the wire  122  or other structure may connect the straight guides  130  to the barrier  94  to support the straight guides  130  inside the fuel plenum  92 . Alternately, as shown in  FIG. 9 , the wire  122  or other structure may connect the some of the straight guides  130  to the barrier  94  and other straight guides  130  to the upstream surface  58  and/or the outer conduit  98 , as desired. In each embodiment shown in  FIGS. 8 and 9 , the straight guides  130  radially direct the fuel  22  flowing into the fuel plenum  108  to facilitate more even heating and flow of the fuel  22  inside the fuel plenum  92 . 
     The various embodiments shown and described with respect to  FIGS. 1-9  may also provide a method for distributing the fuel  22  in the combustor  20 . For example, the method may include flowing the fuel  22  into the fuel plenum  92  defined at least in part by the upstream surface  58 , tubes  52 , shroud  62 , and barrier  94 . The method may further include radially directing the fuel  22  with the baffle that extends axially inside the fuel plenum  92  before flowing the fuel  22  through the fuel ports  104  and into the tubes  52 . In this manner, the fuel  22  may be distributed radially around the tubes  52  before flowing into the tubes  52  to enhance even heating of the fuel  22  inside the fuel plenum  92 . 
     The systems and methods described herein may provide one or more of the following advantages over existing nozzles and combustors. For example, the radial distribution of the fuel  22  around the tubes  52  enables the fuel  22  to flow more uniformly across all surfaces of the tubes  52 . As a result, the heat exchange between the fuel  22  and the tubes  52  increases and reduces or eliminates localized hot spots along the tubes  52  that might lead to uneven heating of the fuel  22 . The more uniform fuel  22  distribution through the fuel plenum  92  results in more even fuel  22  temperatures and flow through the fuel ports  104  and into the tubes  52 , reducing any local hot streaks or high fuel concentrations in the combustion chamber  54  that might increase undesirable emissions. 
     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 language of the claims.