Patent Publication Number: US-2013227955-A1

Title: System and method for reducing combustion dynamics in a combustor

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 system and method for reducing combustion dynamics in 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, 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, a plurality of premixer tubes may be radially arranged in an end cap to provide fluid communication for the working fluid and fuel through the end cap and into the combustion chamber. Although effective at enabling higher operating temperatures while protecting against flashback or flame holding and controlling undesirable emissions, some fuels and operating conditions produce very high frequencies with high hydrogen fuel composition in the combustor. Increased vibrations in the combustor associated with high frequencies may reduce the useful life of one or more combustor components. Alternately, or in addition, high frequencies of combustion dynamics may produce pressure pulses inside the premixer tubes and/or combustion chamber that affect the stability of the combustion flame, reduce the design margins for flashback or flame holding, and/or increase undesirable emissions. Therefore, a system and method that reduces resonant frequencies in the combustor would be useful to enhancing the thermodynamic efficiency of the combustor, protecting the combustor from catastrophic damage, and/or reducing undesirable emissions over a wide range of combustor operating levels. 
     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 system for reducing combustion dynamics in a combustor. The system 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. A plurality of tube bundles extends from the upstream surface through the downstream surface of the end cap, wherein each tube bundle provides fluid communication through the end cap. A diluent supply in fluid communication with the end cap provides diluent flow to the end cap. A plurality of first diluent distributors are circumferentially arranged inside at least one tube bundle, wherein each first diluent distributor extends downstream from the downstream surface and provides fluid communication for the diluent flow through the downstream surface of the end cap. 
     Another embodiment of the present invention is a system for reducing combustion dynamics in 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. A plurality of tube bundles extends from the upstream surface through the downstream surface of the end cap, wherein each tube bundle provides fluid communication through the end cap. A diluent supply in fluid communication with the end cap provides diluent flow to the end cap. A plurality of diluent ports circumferentially arranged inside at least one tube bundle provides fluid communication for the diluent flow through the downstream surface of the end cap. A plurality of first diluent distributors are in fluid communication with at least some of the diluent ports, wherein each first diluent distributor extends downstream from the downstream surface. 
     The present invention may also include a method for reducing combustion dynamics in a combustor. The method includes flowing a fuel through a plurality of tube bundles that extend axially through an end cap that extends radially across at least a portion of the combustor. The method further includes flowing a diluent through a plurality of diluent distributors into a combustion chamber downstream from the end cap, wherein the plurality of diluent distributors are circumferentially arranged inside at least one tube bundle and each diluent distributor extends downstream from the end cap, and forming a diluent barrier in the combustion chamber between at least one pair of adjacent tube bundles. 
     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 simplified cross-section view of an exemplary combustor according to one embodiment of the present invention; 
         FIG. 2  is an upstream axial view of the end cap shown in  FIG. 1  according to a first embodiment of the present invention; 
         FIG. 3  is an upstream axial view of the end cap shown in  FIG. 1  according to a second embodiment of the present invention; 
         FIG. 4  is an upstream axial view of the end cap shown in  FIG. 1  according to a third embodiment of the present invention; 
         FIG. 5  is an upstream axial view of the end cap shown in  FIG. 1  according to a fourth embodiment of the present invention; 
         FIG. 6  is an enlarged cross-section view of a tube bundle shown in  FIG. 1  according to an embodiment of the present invention; 
         FIG. 7  is an enlarged cross-section view of a portion of the combustor shown in  FIGS. 1 and 4  according to an alternate embodiment of the present invention; and 
         FIG. 8  is a downstream axial view of the end cap shown in  FIG. 7 . 
     
    
    
     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. In addition, 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. 
     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 system and method for reducing combustion dynamics in a combustor. The system and method generally include a plurality of tube bundles radially arranged in an end cap. The tube bundles supply a mixture of fuel and working fluid to a combustion chamber downstream from the end cap. A diluent supply in fluid communication with the end cap provides diluent flow to the end cap. A plurality of diluent distributors circumferentially arranged inside at least one tube bundle and extending downstream from the end cap provides fluid communication for the diluent flow through the end cap. The diluent distributors thus produce a diluent barrier between at least one pair of adjacent tube bundles to decouple flame interaction between the adjacent tube bundles and thus reduce the combustion dynamics in the combustor. Although exemplary embodiments of the present invention will be described generally in the context of a combustor incorporated into a gas turbine, 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. 
       FIG. 1  shows a simplified cross-section of an exemplary combustor  10 , such as would be included in a gas turbine, according to one embodiment of the present invention. A casing  12  and end cover  14  may surround the combustor  10  to contain a working fluid  15  flowing to the combustor  10 . The working fluid  15  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  15  reaches the end cover  14 , the working fluid  15  reverses direction to flow through a plurality of tube bundles  24  into a combustion chamber  26 . 
     The tube bundles  24  are radially arranged in different shapes, numbers, and sizes in an end cap  28  upstream from the combustion chamber  26 , and  FIGS. 2-5  provide upstream views of exemplary arrangements of the tube bundles  24  in the end cap  28  within the scope of the present invention. As shown in  FIGS. 2 and 3 , for example, the tube bundles  24  may be radially arranged across the end cap  28  in circular groups of premixer tubes  30  enclosed by outer shrouds  31 , with six tube bundles  24  surrounding one tube bundle  24 . Alternately, as shown in  FIGS. 4 and 5 , the tube bundles  24  may be arranged as a circular group of premixer tubes  30  surrounded by the outer shroud  31  surrounded by a series of pie-shaped groups of premixer tubes  30 . In  FIG. 4 , alternating pie-shaped groups of premixer tubes  30  are at least partially enclosed by the outer shroud  31 . One of ordinary skill in the art will readily appreciate multiple possible combinations of shapes, numbers, and sizes of the tube bundles  24 , and the present invention is not limited to any particular arrangement of tube bundles  24  unless specifically recited in the claims. 
     In each exemplary arrangement shown in  FIGS. 2-5 , the flow of fuel and/or working fluid  15  through the premixer tubes  30  and/or tube bundles  24  may produce undesirable combustion dynamics in the combustion chamber  26 , particularly when the fuel and/or working fluid  15  flow is approximately equal between each tube bundle  24 . As a result, various embodiments of the present invention include one or more features to decouple the combustion flame interaction between the adjacent tube bundles  24  and thus reduce the combustion dynamics in the combustor  10 . The features are generally arranged inside and/or between one or more tube bundles  24  and define a structural and/or a fluid barrier between one or more pairs of adjacent tube bundles  24  that separates the adjacent tube bundles  24 . In this manner, the structural and/or fluid barrier prevents interaction between the combustion flames produced by the adjacent tube bundles  24  to reduce the undesirable combustion dynamics in the combustion chamber  26 . 
     For example, in the particular tube bundle  24  arrangements shown in  FIGS. 2-5 , a plurality of diluent distributors  32  may be circumferentially arranged inside the center tube bundle  24 . Each diluent distributor  32  may extend downstream from the end cap  28  to create a structural barrier inside or around the center tube bundle  24 . In addition, a diluent may flow through the end cap  28  and out of the diluent distributors  32  to create a fluid barrier in the combustion chamber  26  that separates the center tube bundle  24  from adjacent tube bundles radially arranged in the end cap  28 . In this manner, the diluent distributors  32  and the diluent flow through the diluent distributors  32  may sufficiently decouple any combustion flame interaction between the center tube bundle  24  and the other tube bundles  24  radially arranged in the end cap  28 . 
     Alternately, or in addition, the diluent distributors  32  may be arranged inside or between one or more of the tube bundles  24  radially arranged in the end cap  28  to provide structural and/or fluid barriers between adjacent tube bundles  24 . In the particular embodiments shown in  FIGS. 2 and 4 , the tube bundles  24  radially arranged in the end cap  28  include a plurality of diluent ports  34  circumferentially arranged inside alternating tube bundles  24 . Alternately, as shown in the particular embodiments illustrated in  FIGS. 3 and 5 , the end cap  28  may include one or more dividers  36  between the tube bundles  24  radially arranged in the end cap  28 . Each divider  36  may extend axially through the end cap  28  to separate adjacent tube bundles  24 , and diluent ports  34  may provide fluid communication for the diluent to flow out of the dividers  36  between the adjacent tube bundles  24 . In this manner, the diluent flow through the diluent ports  34  may create a fluid barrier in the combustion chamber  26  that separates the adjacent tube bundles  24  radially arranged in the end cap  28 . In addition, the diluent distributors  32  may be in fluid communication with one or more of the diluent ports  34  to create a structural barrier between the adjacent tube bundles  24  radially arranged in the end cap  28 . For example, in the particular embodiments shown in  FIGS. 2 and 3 , the diluent distributors  32  may only be coincident with the diluent ports  34  that are directly adjacent to or between the adjacent tube bundles  24 . Alternately, as shown in the particular embodiments illustrated in  FIGS. 4 and 5 , the diluent distributors  32  may be coincident with each diluent port  34  adjacent to or between the adjacent tube bundles  24 . 
       FIG. 6  provides an enlarged cross-section view of an exemplary tube bundle  24  such as is shown in  FIG. 1  and the center of  FIGS. 2-5  according to a first embodiment of the present invention. As shown, the tube bundle  24  generally includes an upstream surface  42  axially separated from a downstream surface  44 . Each premixer tube  30  includes a tube inlet  46  proximate to the upstream surface  42  and extends through the downstream surface  44  to provide fluid communication for the working fluid  15  to flow through the tube bundle  24  and into the combustion chamber  26 . Although shown as cylindrical tubes, the cross-section of the premixer tubes  30  may be any geometric shape, and the present invention is not limited to any particular cross-section unless specifically recited in the claims. The outer shroud  31  circumferentially surrounds at least a portion of the tube bundle  24  to partially define a fuel plenum  50  and a diluent plenum  52  between the upstream and downstream surfaces  42 ,  44 . A generally horizontal barrier  54  may extend radially between the upstream surface  42  and the downstream surface  44  to axially separate the fuel plenum  50  from the diluent plenum  52 . In this manner, the upstream surface  42 , outer shroud  31 , and barrier  54  enclose or define the fuel plenum  50  around the upstream portion of the premixer tubes  30 , and the downstream surface  44 , outer shroud  31 , and barrier  54  enclose or define the diluent plenum  52  around the downstream portion of the premixer tubes  30 . 
     A fuel supply  56  and a diluent supply  58  may extend through the end cover  14  and through the upstream surface  42  to provide fluid communication for fuel and diluent to flow through the end cover  14  to the respective fuel or diluent plenums  50 ,  52  in each tube bundle  24 . The fuel supplied to the tube bundle  24  may include any liquid or gaseous fuel suitable for combustion, and possible diluents supplied to the tube bundle  24  may include water, steam, fuel additives, various inert gases such as nitrogen and/or various non-flammable gases such as carbon dioxide or combustion exhaust gases. In the particular embodiment shown in  FIG. 6 , the fuel supply  56  is substantially concentric with the diluent supply  58 , although such is not a limitation of the present invention unless specifically recited in the claims. 
     One or more of the premixer tubes  30  may include a fuel port  60  that provides fluid communication from the fuel plenum  50  into the one or more premixer tubes  30 . The fuel ports  60  may be angled radially, axially, and/or azimuthally to project and/or impart swirl to the fuel flowing through the fuel ports  60  and into the premixer tubes  30 . In this manner, the working fluid  15  may flow through the tube inlets  46  and into the premixer tubes  30 , and fuel from the fuel plenum  50  may flow through the fuel ports  60  and into the premixer tubes  30  to mix with the working fluid  15 . The fuel-working fluid mixture may then flow through the premixer tubes  30  and into the combustion chamber  26 . 
     The diluent may flow from the diluent supply  58  around the premixer tubes  30  in the diluent plenum  52  to provide convective cooling to the premixer tubes  30  and/or impingement cooling to the downstream surface  44 . The diluent may then flow through the diluent ports  34  and/or diluent distributors  32  and into the combustion chamber  26 . In this manner, the diluent may form a fluid barrier between adjacent tube bundles  24  to separate the combustion flames of adjacent tube bundles  24 , thereby reducing or preventing any interaction between the combustion flames of adjacent tube bundles  24 . 
     As shown in  FIG. 6 , each diluent distributor  32  generally extends downstream from the downstream surface  44  of the end cap  28  and into the combustion chamber  26 . The diluent distributors  32  provide a physical barrier between adjacent tube bundles  24  and may include a plurality of diluent injectors  66  that project the diluent into the combustion chamber  26  between adjacent tube bundles  24 . The diluent flowing through the diluent distributors  32  provides convective and/or film cooling to the diluent distributors  32 . Alternately or in addition, a thermal barrier coating  68  on the downstream surface of the diluent distributors  32  may protect the diluent distributors  32  from excessive thermal loading and/or oxidation associated with the combustion flame. In particular embodiments, the thermal barrier coating  68  may include a plurality of layers that include at least a metallic bond coating, a thermally prepared oxide, and/or a ceramic top coating, although the particular composition and structure of the thermal barrier coating  68  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 combustor  10  shown in  FIGS. 1 and 4  according to an alternate embodiment of the present invention, and  FIG. 8  provides a downstream axial view of the end cap  28  shown in  FIG. 7 . As shown, the end cap  28  generally extends radially across at least a portion of the combustor  10  and includes the upstream and downstream surfaces  42 ,  44  previously described with respect to the tube bundle  24  shown in  FIG. 6 . As shown in  FIG. 7 , one or more tube bundles  24  extend from the upstream surface  42  through the downstream surface  44  to provide fluid communication for fuel and/or working fluid  15  through the end cap  28 . As additionally shown in  FIGS. 7 and 8 , the fuel supply  56  is in fluid communication with the tube bundles  24 , and the diluent supply  58  is in fluid communication with the diluent distributors  32 . The dividers  36  extend axially through at least a portion of the end cap  28  and through the downstream surface  44  to separate one or more pairs of adjacent tube bundles  24 . In this manner, the diluent supply  58  may supply diluent to and through the diluent distributors  32  and into the combustion chamber  26  between the adjacent tube bundles  24 . 
     The various embodiments described and illustrated with respect to  FIGS. 1-8  may also provide a method for reducing combustion dynamics in the combustor  10 . The method may include flowing the fuel through one or more tube bundles  24  that extend axially through the end cap  28  that extends radially across at least a portion of the combustor  10 . The method may further include flowing the diluent through one or more diluent distributors  32  inside and/or between one or more tube bundles  24  into the combustion chamber  26  downstream from the end cap  28 , wherein the diluent distributors  32  are circumferentially arranged inside at least one tube bundle  24  and each diluent distributor  32  extends downstream from the end cap  28 . In this manner, the method may form a diluent barrier in the combustion chamber  26  between at least one pair of adjacent tube bundles  24 . 
     In particular embodiments, the method may form the diluent barrier completely around one or more tube bundles  24  and/or between each pair of adjacent tube bundles  24 . In still further embodiments, the method may inject the diluent into the combustion chamber  26  downstream from the end cap  28  and/or flow the fuel concentrically with the diluent through at least a portion of the combustor  10 . 
     The systems and methods described herein may provide one or more of the following advantages over existing nozzles and combustors. For example, the diluent barrier created by the diluent distributors  32  and/or diluent ports  34  decouple flame interaction between the adjacent tube bundles  24  and thus reduce the combustion dynamics in the combustor  10 . The reduced combustion dynamics in the combustor  10  may extend the operating capability of the combustor  10  over a wide range of fuels without decreasing the useful life and/or maintenance intervals for various combustor  10  components. Alternately, or in addition, the reduced combustion dynamics may maintain or increase the design margin against flashback or flame holding and/or reduce undesirable emissions over a wide range of combustor  10  operating levels. 
     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 and 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.