Patent Publication Number: US-8117845-B2

Title: Systems to facilitate reducing flashback/flame holding in combustion systems

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &amp; DEVELOPMENT 
     This invention was made with Government support under DE-FC26-05NT42643 awarded by the Department of Energy (“DOE”). The Government has certain rights in this invention 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to combustion systems and more particularly, to methods and systems to facilitate reducing flashback/flame holding in combustion systems. 
     During the combustion of natural gas and liquid fuels, known lean-premixed combustors generally experience flame holding or flashback in which a pilot flame that is intended to be confined within the combustion liner travels upstream towards the injection locations of fuel and air into the combustion liner. Generally, uniform lean fuel-air mixtures, lower flame temperatures, and/or shorter residence burning time are known to reduce formation of local near stoichiometric zones and lower flow velocity regions in which flashback may occur. At least some known gas turbine combustion systems include premixing injectors that premix fuel and compressed airflow in attempts to channel uniform lean fuel-air premixtures to a combustion liner. 
     Generally, at least some known premixing injectors include an inlet flow conditioner that conditions compressed airflow in attempts to obtain a substantially uniform airflow to mix with fuel. Such known injectors also generally include a burner tube that channels a fuel-air mixture to a combustor. Non-uniform fuel-air concentrations within the burner tube may enable flame holding or flashback conditions such that a pilot flame that is intended to be confined within the combustion liner travels into the premixing injector. As a result, such injectors may be damaged and/or the operability of the combustor may be compromised. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A method for assembling a premixing injector is provided. The method includes providing a centerbody including a center axis and a radially outer surface, and providing an inlet flow conditioner. The inlet flow conditioner includes a radially outer wall, a radially inner wall, and an end wall coupled substantially perpendicularly between the outer wall and the inner wall. Each of the outer wall and the end wall include a plurality of openings defined therein. The outer wall, the inner wall, and the end wall define a first passage therebetween. The method also includes coupling the inlet flow conditioner to the centerbody such that the inlet flow conditioner substantially circumscribes the centerbody, such that the inner wall is substantially parallel to the centerbody outer surface, and such that a second passage is defined between the centerbody outer surface and the inner wall. 
     A premixing injector is provided. The premixing injector includes a centerbody including a center axis and a radially outer surface. The premixing injector also includes an inlet flow conditioner coupled to the centerbody such that the inlet flow conditioner substantially circumscribes the centerbody. The inlet flow conditioner includes a radially outer wall including a plurality of openings defined therein. The outer wall is oriented substantially parallel to the center axis. The inlet flow conditioner also includes a radially inner wall extending substantially parallel to the outer wall. The inner wall is spaced from the outer wall such that a first passage is defined therebetween. The inner wall is spaced from the centerbody outer surface such that a second passage is defined therebetween. The inlet flow conditioner further includes an end wall extending substantially perpendicularly between the outer and inner walls. The end wall includes a plurality of openings defined therein. 
     A gas turbine combustor system is provided. The gas turbine system includes a combustion liner and at least one premixing injector coupled to the combustion liner. The at least one premixing injector includes a centerbody including a center axis and a radially outer surface. The at least one premixing injector also includes an inlet flow conditioner coupled to the centerbody such that the inlet flow conditioner substantially circumscribes the centerbody. The inlet flow conditioner includes a radially outer wall including a plurality of openings defined therein. The outer wall is substantially parallel to the center axis. The inlet flow conditioner also includes a radially inner wall extending substantially parallel to the outer wall. The inner wall is spaced from the outer wall such that a first passage is defined therebetween. The inner wall is also spaced from the centerbody outer surface such that a second passage is defined therebetween. The inlet flow conditioner further includes an end wall extending substantially perpendicularly between the outer and inner walls. The end wall includes a plurality of openings defined therein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an exemplary turbine engine assembly including a combustion section; 
         FIG. 2  is a schematic illustration of a cross-sectional view of an exemplary known lean-premixed combustor that may be used with the combustion section shown in  FIG. 1 ; 
         FIG. 3  is an enlarged cross-sectional view of the premixing injector shown in  FIG. 2  and taken along area  3 ; 
         FIG. 4  is an enlarged cross-sectional view of an exemplary premixing injector that may be used with the gas turbine system shown in  FIG. 1 ; 
         FIG. 5  is an end view of an exemplary premixing injector that may be used with the gas turbine system shown in  FIG. 1 ; and 
         FIG. 6  is a top view of the exemplary premixing injector shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The exemplary methods and systems described herein overcome the structural disadvantages of known inlet flow conditioners (“IFC”) by redesigning an IFC to direct compressed airflow towards local areas of low velocity flow within a burner tube. It should be appreciated that the terms “axial” and “axially” are used throughout this application to refer to directions and orientations extending substantially parallel to a center longitudinal axis of a centerbody of a premixing injector. It should also be appreciated that the terms “radial” and “radially” are used throughout this application to refer to directions and orientations extending substantially perpendicular to a center longitudinal axis of the centerbody. It should also be appreciated that the terms “upstream” and “downstream” are used throughout this application to refer to directions and orientations located in an overall axial fuel flow direction with respect to the center longitudinal axis of the centerbody and/or a combustor case. 
       FIG. 1  is a schematic illustration of an exemplary gas turbine system  10  including an intake section  12 , a compressor section  14  downstream from the intake section  12 , a combustor section  16  coupled downstream from the intake section  12 , a turbine section  18  coupled downstream from the combustor section  16 , and an exhaust section  20 . Turbine section  18  is rotatably coupled to compressor section  14  and to a load  22  such as, but not limited to, an electrical generator and a mechanical drive application. 
     During operation, intake section  12  channels air towards compressor section  14 . The inlet air is compressed to higher pressures and temperatures. The compressed air is discharged towards combustor section  16  wherein it is mixed with fuel and ignited to generate combustion gases that flow to turbine section  18 , which drives compressor section  14  and/or load  22 . Exhaust gases exit turbine section  18  and flow through exhaust section  20  to ambient atmosphere. 
       FIG. 2  is a cross-sectional view of an exemplary known lean-premixed combustor  24  that includes a plurality of premixing injectors  26 , a combustion liner  28  having a center axis A-A, and a transition piece  30 . Premixing injectors  26  are typically coupled to an end cap  40  of combustor  24  or near a first end  42  of combustion liner  28 . Liner first end  42  is coupled to end cap  40  such that combustion liner  28  may receive a fuel-air premixture injected from premixing injectors  26  and burn the mixture in local flame zones  44  defined within combustion chamber  28   b  defined by combustion liner  28 . A second end  46  of combustion liner  28  is coupled to a first end  48  of transition piece  30 . Transition piece  30  channels the combustion gases to a turbine section, such as turbine section  18  (shown in  FIG. 1 ). 
     Each premixing injector  26  generally includes an annular inlet flow conditioner (“IFC”)  32 , an annular swizzle/swirler  34  coupled to IFC  32 , and an annular burner tube  36  coupled to swirler  34 . Each premixing injector  26  also includes an annular fuel centerbody  38  that is coupled within and coaxial with IFC  32 , swirler  34 , and burner tube  36 . During operation, compressed air enters premixing injectors  26  through IFC  32 , which channels the compressed air towards swirler  34 . Centerbody  38  channels fuel towards swirler  34 . Swirler  34  then premixes the air and fuel, and channels the fuel-air premixture to burner tube  36 . Burner tube  36  subsequently channels the fuel-air premixture to combustion liner  28 . 
       FIG. 3  is an enlarged cross-sectional view of a portion of known premixing injector  26  taken along area  3 . In the exemplary embodiment, known IFC  32  includes a outer wall  50  that defines a plurality of openings  52  between a radially inner surface  50   a  and a radially outer surface  50   b  that are each substantially parallel to a center axis CA of centerbody  38 . 
     IFC  32  also includes an upstream end wall  54  that defines a plurality of openings  56  between a radially inner surface  54   a  and a radially outer surface  54   b  that are each substantially perpendicular to center axis CA. End wall  54  is also coupled between outer wall inner surface  50   a  of and centerbody outer surface  38   a . Outer wall  50 , end wall  54 , and centerbody  38  define an annular IFC passage  60  therebetween. IFC  32  further includes an arcuate turning vane  58  that is coupled to inner surface  50   a  within IFC passage  60 . Although swirl-based premixing injectors  26  is illustrated as including turning vane  58 , it should be appreciated that IFC  32  may include other fuel injection/nozzle concepts. 
     During operation, compressor  14  channels compressed air  62  towards IFC  32 . Compressed air  62  enters IFC  32  through outer wall openings  52  and end wall openings  56 . Subsequently, IFC  32  channels air towards swirler  34  to mix with fuel. The fuel-air premixture is then channeled towards burner tube  36 . 
     Because of the orientation and location of openings  52  and  56 , airflow distribution within IFC passage  60  is non-uniform. As a result of the non-uniform airflow distribution, air and fuel channeled to swirler  34  do not uniformly mix. The non-uniform fuel-air premixture is channeled towards burner tube  36  in an uneven distribution. Due to boundary layer formation along surfaces, burner local areas of low velocity flow are known to be defined within an annular burner tube passage  66  along burner tube inner surface  36   a , centerbody outer surface  38   a  and surfaces of vane  58  during operation. The burner local areas of low velocity may define local flame zones  64  where flameholding/flashback may occur. Inadvertent ignition within burner tube  36  could result in flameholding along burner tube inner surface  36   a  where the velocity is low. Alternatively, during operation, a swirling fuel-air mixture is channeled from burner tube  36  towards a larger combustion liner  28 . 
     At the entry into the combustion liner  28 , the swirling mixture is known to radially expand in combustion liner  28 . The axial velocity at the center of liner  28  is reduced. Such combustor local areas of low turbulent velocity may be below the flame speed for a given fuel-air mixture such as, but not limited to, areas within premixing injectors  26 . As such, pilot flames in such areas may flashback towards areas of desirable fuel-air concentrations as far upstream as the low turbulent velocity zone will allow, such as, but not limited to, areas within premixing injectors  26 . As a result of such flashback, premixing injectors  26  and/or other combustor components may be damaged and/or operability of combustor  24  may be compromised. 
       FIG. 4  is an enlarged cross-sectional view of an exemplary premixing injector  68  that may be used with gas turbine system  10  (shown in  FIG. 1 ). Premixing injector  68  includes components that are substantially similar to components of known premixing injector  26  (shown in  FIGS. 2 and 3 ), and components in  FIG. 4  that are identical to components of  FIGS. 2 and 3 , are identified in  FIG. 4  using the same reference numerals used in  FIGS. 2 and 3 . 
     In the exemplary embodiment, IFC  70  includes an annular outer wall  72  that defines a plurality of openings  74  between a radially inner surface  72   a  and a radially outer surface  72   b  that are each substantially parallel to center axis CA of centerbody  38 . 
     IFC  70  also includes a radially inner wall  76  that is substantially parallel to outer wall  72 . Inner wall  76  includes a radially inner surface  76   a  and a radially outer surface  76   b  that are each substantially parallel to center axis CA. IFC  70  further includes an upstream end wall  78  that defines a plurality of openings  80  between a radially inner surface  78   a  and a radially outer surface  78   b  that are each substantially perpendicular to center axis CA. End wall  78  is also coupled between outer wall inner surface  72   a  and inner wall inner surface  76   a . Outer wall  72 , inner wall  76 , and end wall  78  define an annular IFC passage  82  therebetween. IFC  70  further includes turning vanes  84  and  85  that are coupled to inner surface  72   a  within IFC passage  82 . 
     When fully assembled, in the exemplary embodiment, IFC  70  is coupled to swirler  34  such that IFC inner wall  76  is radially spaced a distance from centerbody outer surface  38   a . As such, in addition to IFC passage  82 , IFC  70  and centerbody  38  define an annular IFC passage  86  therebetween. 
     During operation, compressor  14  channels compressed air  62  towards IFC  70 . Compressed air  62  enters IFC  70  through outer wall openings  74  and end wall openings  80 . Compressed air  62  also enters IFC  70  through IFC passage  86 . Because of the orientation and location of turning vane  85  and/or openings  98 , airflow within IFC passage  82  is more concentrated and directed along swirler and burner tube inner surfaces  34   a  and  36   a  as compared to the flow directed at the center of the burner tube  36  between inner wall  76  and turning vane  84  and between vanes  84  and turning vane  85 . As a result, IFC  70  facilitates distributing more air along inner surface  36   a  of burner tube  36  such that a fuel-air premixture portion  88  is leaner and higher in velocity along inner surfaces  34   a  and  36   a  as compared to known IFCs. As such, IFC  70  facilitates reducing the formation of known local flame zones  64  (shown in  FIG. 3 ) within burner tube  36 . IFC  70  also facilitates containing pilot flames  90  within combustion liner  28 . It should be appreciated that openings and/or passageways of different shapes and/or locations other than illustrated may be used to facilitate similar directed airflow concentrations as discussed above. 
     Because of the orientation and location of inner wall  76 , airflow within IFC passage  86  is also more concentrated and directed along outer surface  38   a  of centerbody  38  as compared to the flow directed at the center of burner tube  36  between inner wall  76  and turning vane  84  and between vanes  84  and  85 . As a result, IFC  70  facilitates distributing more air along outer surface  38   a  of centerbody  38  such that a fuel-air premixture portion  92  is leaner and higher in velocity along outer surface  38   a  as compared to known IFCs. As such, IFC  70  facilitates reducing the formation of known local flame zones  64  (shown in  FIG. 3 ) within burner tube  36 . IFC  70  also facilitates containing pilot flames  90  within combustion liner  28 . In other words, the inlet air flow turbulence intensity is minimized to facilitate reducing the turbulent flame speed near burner tube surfaces. It should be appreciated that openings and/or passageways of different shapes and/or locations other than illustrated may be used to facilitate similar directed airflow concentrations as discussed above. 
       FIG. 5  is an end view of an exemplary premixing injector  102  that may be used with gas turbine system  10  (shown in  FIG. 1 ).  FIG. 6  is a top view of premixing injector  102  shown in  FIG. 5 . Premixing injector  102  includes components that are substantially similar to components of known premixing injector  26  (shown in  FIGS. 2 and 3 ), and components in  FIGS. 5 and 6  that are identical to components of  FIGS. 2 and 3 , are identified in  FIGS. 5 and 6  using the same reference numerals used in  FIGS. 2 and 3 . 
     In the exemplary embodiment, premixing injector  102  includes IFC  104  having an annular outer wall  106  and an upstream end wall  108 . End wall  108  defines a plurality of openings  110  and slots  112 . IFC  104  further includes four vanes  114  coupled between outer surface  38   a  of centerbody  38  and coupled within IFC passage  116 . During operation, compressor  14  channels compressed air  62  towards IFC  102 . Compressed air  62  enters IFC  102  through end wall openings  110  and slots  112 . 
     Because of the larger size and orientation of slots  112  along outer surface  38   a , airflow within IFC passage  116  is more concentrated and directed along surfaces  114   a  of vanes  114  as compared to outer wall inner surface  106   a . As a result, IFC  104  facilitates distributing more air along vane surfaces  114   a  such that a fuel-air premixture is leaner and/or higher in velocity along vane surfaces  114   a  as compared to known IFCs. As such, IFC  104  facilitates reducing the formation of known local flame zones  64  (shown in  FIG. 3 ) within burner tube  36 . IFC  104  also facilitates containing pilot flames  90  within combustion liner  28 . It should be appreciated that openings, slots and/or passageways of different shapes and/or locations other than illustrated may be used to facilitate similar directed airflow concentrations as discussed above. 
     A method for assembling premixing injector  68  is provided. The method includes providing centerbody  38  including center axis CA and radially outer surface  38   a . The method also includes providing IFC  70 . IFC  70  includes radially outer wall  36 , radially inner wall  76 , and end wall  78  coupled substantially perpendicularly between outer wall  36  and inner wall  76 . Each of outer wall  38  and end wall  78  include a plurality of openings  74  and  80  defined therein. Outer wall  38 , inner wall  76 , and end wall  78  define first passage  82  therebetween. The method also includes coupling IFC  70  to centerbody  38  such that IFC  70  substantially circumscribes centerbody  38 , such that inner wall  76  is substantially parallel to centerbody outer surface  38   a , and such that second passage  86  is defined between centerbody outer surface  38   a  and inner wall  76 . 
     In each exemplary embodiment, IFCs are oriented and configured to direct compressed airflow along surface of burner tubes and centerbodies of premixing injectors. As a result, higher velocity and leaner fuel-air mixture portions are directed towards known local areas of lower velocity that facilitate formation of local flame zones during operation. The enhanced distribution of airflow facilitates reducing turbulence fluctuations, reducing flashback, reducing component damage, and increasing operability. Although components of the exemplary IFCs have been described as substantially annular, it should be appreciated that the exemplary IFCs may have any shape that enables the exemplary IFCs to function as described above. 
     Exemplary embodiments of premixing injectors are described in detail above. The premixing injectors are not limited to use with the specified combustors and gas turbine systems described herein, but rather, the premixing injectors can be utilized independently and separately from other combustor and/or gas turbine system components described herein. Moreover, the invention is not limited to the embodiments of the combustors described in detail above. Rather, other variations of injector embodiments may be utilized within the spirit and scope of the claims. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.