Patent Publication Number: US-9429325-B2

Title: Combustor and method of supplying fuel to the combustor

Description:
FIELD OF THE INVENTION 
     The present invention generally involves a combustor and method for supplying fuel to the combustor. 
     BACKGROUND OF THE INVENTION 
     Gas turbines are widely used in industrial and power generation operations. A typical gas turbine may include an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air enters the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the air to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through nozzles in the combustors where it 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. 
     It is widely known that the thermodynamic efficiency of a gas turbine increases as the operating temperature, namely the combustion gas temperature, increases. However, if the fuel and air are not evenly mixed prior to combustion, localized hot spots may form in the combustor. The localized hot spots may increase the production of undesirable NOx emissions and may increase the chance for the flame in the combustor to flash back into the nozzles and/or become attached inside the nozzles which may damage the nozzles. Although flame flash back and flame holding may occur with any fuel, they occur more readily with high reactive fuels, such as hydrogen, that have a higher burning rate and a wider flammability range. 
     A variety of techniques exist to allow higher operating temperatures while minimizing NOx emissions, flash back, and flame holding. Many of these techniques seek to reduce localized hot spots to reduce the production of NOx and/or reduce low flow zones to prevent or reduce the occurrence of flash back or flame holding. For example, continuous improvements in nozzle designs result in more uniform mixing of the fuel and air prior to combustion to reduce or prevent localized hot spots from forming in the combustor. Alternately, or in addition, nozzles have been designed to ensure a minimum flow rate of fuel and/or air through the nozzle to cool the nozzle surfaces and/or prevent the combustor flame from flashing back into the nozzle. However, the improved nozzle designs typically result in increased manufacturing costs and/or continued additional parts or components added to the combustor that increase the differential pressure across the combustor, thus detracting from the overall efficiency of the gas turbine. Therefore, improvements in combustor designs to enhance the mixing of fuel and air prior to combustion and/or cool the combustor surfaces 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 liner that defines a combustion chamber. A first pre-mix chamber is upstream of the combustion chamber, and a fuel plenum in fluid communication with the first pre-mix chamber surrounds at least a portion of the first pre-mix chamber. 
     In another embodiment of the present invention, a combustor includes a liner that defines a combustion chamber. A first pre-mix chamber is upstream of the combustion chamber, and a second pre-mix chamber circumferentially surrounds the first pre-mix chamber. An air plenum surrounds at least a portion of the second pre-mix chamber and is in fluid communication with the first pre-mix chamber. 
     The present invention also includes a method of supplying a fuel to a combustor. The method includes flowing the fuel over an outer surface of a first pre-mix chamber and into the first pre-mix chamber. 
     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 side cross-section view of a combustor according to one embodiment of the present invention; 
         FIG. 2  is an upstream perspective partial cut-away view of the pre-mix chambers shown in  FIG. 1 ; 
         FIG. 3  is downstream perspective partial cut-away view of the pre-mix chambers shown in  FIG. 1 ; 
         FIG. 4  is a simplified side cross-section view of the combustor shown in  FIG. 1  during ignition or turndown operations; 
         FIG. 5  is a simplified side cross-section view of the combustor shown in  FIG. 1  during partial load operations; and 
         FIG. 6  is a simplified side cross-section view of the combustor shown in  FIG. 1  during full load operations. 
     
    
    
     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 include a combustor design that enhances the mixing of fuel and air prior to combustion and/or reduces the combustor surface temperatures and/or peak combustion gas temperatures. In particular embodiments, the combustor may include one or more pre-mix chambers that enhance the mixing of the fuel and air prior to combustion. Alternately, or in addition, the combustor may flow fuel over or around the outside surface of the pre-mix chambers to remove heat therefrom. As a result, the combustor may be capable of extended turndown operations without exceeding emissions limits, may have enhanced safety margins in the event of a flame holding or flash back occurrence, may have longer intervals between preventative and/or corrective maintenance, and/or may be capable of operating with liquid or gaseous fuels. 
       FIG. 1  provides a simplified side cross-section view of a combustor  10  according to one embodiment of the present invention. As shown, the combustor  10  generally includes a liner  12  and first and second pre-mix chambers  14 ,  16 . The liner  12  forms a generally cylindrical or tapered cylindrical pathway through the combustor  10  to define a combustion chamber  18 . The liner  12  may be rolled and welded, forged, or cast from suitable materials capable of continuous exposure to the maximum anticipated temperatures associated with the combustion gases produced by the combustor  10 . For example, the liner  12  may be made from a steel alloy or superalloy such as Inconel or Rene. The liner  12  and/or the second pre-mix chamber  16  may include a thermal barrier coating on the internal surface to further enhance heat resistance. The first and second pre-mix chambers  14 ,  16  are located upstream from the liner  12  to provide a sufficient volume in which the fuel and air may mix before combusting. 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 of component B if a fluid flows from component A to component B. Conversely, component B is downstream of component A if component B receives a fluid flow from component A. 
       FIGS. 2 and 3  provide upstream and downstream perspective partial cut-away views of the pre-mix chambers  14 ,  16  shown in  FIG. 1 . As shown, the first pre-mix chamber  14  is generally aligned with an axial centerline  20  of the combustor  10 , and the second pre-mix chamber  16  circumferentially surrounds the first pre-mix chamber  14 . For example, the second pre-mix chamber  16  may be a toroid that surrounds the first pre-mix chamber  14 . Each pre-mix chamber  14 ,  16  generally includes an inner wall  22 ,  24  that defines a cavity and an exhaust  26 ,  28  for each respective chamber  14 ,  16 . The cavity may be curved to minimize low flow regions and promote mixing of the fuel and air in the pre-mixed chambers  14 ,  16 . Each exhaust  26 ,  28  is generally adjacent to the combustion chamber  18  so that fuel and air may more completely mix in the respective pre-mix chambers  14 ,  16  before flowing into the combustion chamber  18 . In the particular embodiment shown in  FIGS. 1, 2 , and  3 , the inner wall  24  of the second pre-mix chamber  16  curves around to form the exhaust  26  of the first pre-mix chamber  14 . 
     A compressed working fluid (e.g., air from a compressor) flows to and through the first and second pre-mix chambers  14 ,  16  through slightly different paths. Specifically, as shown most clearly in  FIGS. 2 and 3 , an outer wall  30  adjacent to or surrounding the inner wall  24  of the second pre-mix chamber  16  may define an air plenum  32  around at least a portion of the second pre-mix chamber  16 . Air ports  34  circumferentially spaced around the liner  12  allow the compressed working fluid to flow into and through the air plenum  32  to remove heat from the outer surface of the second pre-mix chamber  16  before entering the first pre-mix chamber  14 . In particular embodiments, the compressed working fluid may flow over a plurality of first swirler vanes  36  circumferentially arranged around the exhaust  26  of the first pre-mix chamber  14  before entering the first pre-mix chamber  14 . Similarly, the combustor  10  may include a plurality of second swirler vanes  38  circumferentially arranged around the exhaust  28  and/or first swirler vanes  36 , and the compressed working fluid may flow over the second swirler vanes  38  before directly entering the second pre-mix chamber  16 . The first and second swirler vanes  36 ,  38  may be curved or angled with respect to the axial centerline  20  to impart tangential velocity to the air flowing over the swirler vanes. 
     The combustor  10  may further include one or more fuel plenums that supply fuel for combustion. For example, as best shown in  FIGS. 1 and 2 , the combustor  10  may include first, second, and third fuel plenums  40 ,  42 ,  44 . The first fuel plenum  40  may comprise a supply of fuel in fluid communication with the first pre-mix chamber  14 . For example, an outer wall  46  adjacent to or surrounding the inner wall  22  of the first pre-mix chamber  14  may define a passage  48  around the inner wall  22  that connects the first fuel plenum  40  to the first pre-mix chamber  14 . In this manner, at least a portion of the first fuel plenum  40  may surround at least a portion of the first pre-mix chamber  14  so that fuel may flow over the inner wall  22  to remove heat from the outer surface of the first pre-mix chamber  14  before entering the first pre-mix chamber  14 . After entering the first pre-mix chamber  14 , the fuel from the first fuel plenum  40  mixes with the compressed working fluid flowing over the first swirler vanes  36  before exiting the first pre-mix chamber  14  through the exhaust  26  and igniting in the combustion chamber  18 . In the event that the combustion flame flashes back into the first pre-mix chamber  14 , the fuel from the first fuel plenum  40  flowing around the first pre-mix chamber  14  prevents the inner wall  22  of the first pre-mix chamber  14  from overheating. 
     The second fuel plenum  42  may comprise an annular fuel manifold surrounding the combustor  10  in fluid communication with the second pre-mix chamber  16 . Fuel from the second fuel plenum  42  may flow through metering ports in the second swirler vanes  38  directly into the second pre-mix chamber  16 . In this manner, the fuel from the second fuel plenum  42  mixes with the compressed working fluid flowing over the second swirler vanes  38 . Combustion of the fuel-air mixture in the second pre-mix chamber  16  occurs anywhere from inside the second pre-mix chamber  16  to downstream of the second pre-mix chamber  16  in the combustion chamber  18 , depending on the operating level of the particular combustor  10 . 
     The third fuel plenum  44  may similarly comprise an annular fuel manifold surrounding the combustor  10  in fluid communication with the combustion chamber  18 . Fuel from the third fuel plenum  44  may flow into a fuel injector  50  that mixes the fuel with the compressed working fluid and injects the mixture through the liner  12  and into the combustion chamber  18 . In this manner, at least a portion of the third fuel plenum  44  may surround at least a portion of the liner  12  so that fuel may flow over the liner  12  to remove heat from the outer surface of the liner  12  before entering the combustion chamber  18 . 
     The multiple pre-mix chambers  14 ,  16  and multiple fuel plenums  40 ,  42 ,  44  provide wide flexibility and multiple operating schemes for the combustor  10  without exceeding emissions limits and/or peak operating temperatures. For example,  FIG. 4  provides a simplified side cross-section view of the combustor  10  during ignition or turndown operations. In this particular operating scheme, no fuel is supplied through either the first or third fuel plenums  40 ,  44 , and fuel is only supplied from the second fuel plenum  42  to the second pre-mix chamber  16 . As a result, the fuel and air flows over the plurality of second swirler vanes  38  before entering and mixing in the second pre-mix chamber  16 . As shown in  FIG. 4 , the mass flow rate and velocity of the fuel-air mixture flowing through the exhaust  28  of the second pre-mix chamber  16  maintains a first flame  52  in the general vicinity of the exhaust  28 , with the precise location of the first flame  52  dependent on the actual power level of the combustor  10  at ignition or during turndown. 
       FIG. 5  shows the combustor  10  being operated during partial load operations. During partial load operations, the second fuel plenum  42  supplies fuel through the second swirler vanes  38  to the second pre-mix chamber  16 . In addition, the first fuel plenum  40  supplies fuel through the passage  48  to the first pre-mix chamber  14  in one or more combustors  10  included in the gas turbine, with the number of combustors  10  receiving fuel from the first fuel plenum  40  dependent on the actual power level of the gas turbine. As in  FIG. 4 , the mass flow rate and velocity of the fuel-air mixture flowing through the exhaust  28  of the second pre-mix chamber maintains the first flame  52  in the general vicinity of the exhaust  28 . In addition, the mass flow rate and velocity of the fuel-air mixture flowing through the exhaust  26  of the first pre-mix chamber  14  maintains a second flame  54  downstream of the first flame  52  in the combustion chamber  18 , with the precise location dependent on the actual power level of the combustor  10 . 
       FIG. 6  shows the combustor  10  being operated during full load operations. In this particular operating scheme, the first, second, and third fuel plenums  40 ,  42 ,  44  each supply fuel for combustion. Specifically, the first fuel plenum  40  supplies fuel through the passage  48  to the first pre-mix chamber  14 , and the second fuel plenum  42  supplies fuel through the second swirler vanes  38  to the second pre-mix chamber  16 , as previously described with respect to  FIG. 5 . In addition, the third fuel plenum  44  supplies fuel to mix with air in the fuel injector  50  before being injected through the liner  12  directly into the combustion chamber  18 , creating a third flame  56  in the combustion chamber  18 . 
     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.