Patent Publication Number: US-2013232986-A1

Title: Combustor and method for reducing thermal stresses in a combustor

Description:
FIELD OF THE INVENTION 
     The present invention generally involves a combustor, such as may be incorporated into a gas turbine or other turbomachine, and method of reducing thermal stresses in the combustor. In particular, various embodiments of the present invention reduce thermal stresses in a combustor fuel circuit. 
     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. A typical combustor includes a casing that surrounds a combustion chamber to define an annular passage between the combustion chamber and the casing. One or more fuel nozzles may be radially arranged in an end cover at one end of the combustor. The nozzles mix fuel with a working fluid, and the mixture flows into the combustion chamber and ignites to produce combustion gases having a high temperature and pressure. 
     Combustors often utilize multiple fuel circuits to enhance thermodynamic efficiency while also reducing undesirable emissions. For example, a primary fuel circuit may supply liquid fuel to the nozzles during startup of the combustor to promote flame stability. A secondary fuel circuit may supply less expensive gaseous fuel to the nozzles during steady state operations to reduce operating costs. A tertiary fuel circuit may directly inject liquid and/or gaseous fuel into the combustion chamber downstream from the nozzles during high power operations to increase the combustor firing temperature without exceeding emissions limits. Lastly, a quaternary fuel circuit may supply liquid and/or gaseous fuel into the annular passage upstream from the nozzles to pre-mix with the working fluid before reaching the nozzles. 
     The temperature differences between the fuel and the working fluid can create substantial thermal stresses in both the fuel circuits and adjacent components. In addition, the fuel circuits often include relatively small passages or ports that may be susceptible to clogging, such as from corrosion products formed in the fuel circuit and subsequently liberated. As a result, fuel circuits often require more expensive materials that are corrosion resistant and have a high strength. In addition, the materials may often require substantial heat treatment that further increases the manufacturing cost of the fuel circuits. Therefore, an improved combustor and method of reducing thermal stresses in the combustor that reduces the material and/or manufacturing cost of the fuel circuits 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 combustion chamber and a casing that circumferentially surrounds the combustion chamber to at least partially define an annular passage between the casing and the combustion chamber. A fuel plenum extends radially through the casing to provide fluid communication through the casing to the annular passage, and the combustor includes means for shielding at least a portion of the fuel plenum from direct impingement by fuel flowing through the fuel plenum. 
     Another embodiment of the present invention is a combustor that includes a combustion chamber and a casing that circumferentially surrounds the combustion chamber to at least partially define an annular passage between the casing and the combustion chamber. A fuel plenum extends radially through the casing to provide fluid communication through the casing to the annular passage, and a liner extends inside at least a portion of the fuel plenum to prevent fuel from directly impinging upon at least a portion of the fuel plenum. 
     The present invention may also include a method of reducing thermal stresses in a combustor that includes flowing a fuel inside a fuel plenum that extends radially through a casing, shielding at least a portion of the fuel plenum from direct impingement by the fuel radially inward of the casing, and flowing the fuel from the fuel plenum into an annular passage between the casing and a combustion chamber. 
    
    
     
       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 of an exemplary gas turbine that may incorporate various embodiments of the present invention; 
         FIG. 2  is an enlarged side and partial cross-section view of the combustor shown in  FIG. 1  according to a first embodiment of the present invention; 
         FIG. 3  is an enlarged side cross-section view of a portion of the fuel plenum shown in  FIG. 2 ; and 
         FIG. 4  is an axial cross-section view of the fuel plenum shown in  FIG. 2 . 
     
    
    
     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 combustor and method of reducing thermal stresses in the combustor. The combustor generally includes a casing that circumferentially surrounds a combustion chamber to at least partially define an annular passage between the casing and the combustion chamber. One or more fuel circuits supply a liquid and/or gaseous fuel through the casing to nozzles and/or a combustion chamber. In particular embodiments, a fuel plenum supplies the fuel to the annular passage and/or circumferentially around the combustion chamber, and a liner or other means inside the fuel plenum shields at least a portion of the fuel plenum from contact with the fuel to reduce the thermal stresses created in the fuel plenum. 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 or other turbomachine unless specifically recited in the claims. 
       FIG. 1  provides a simplified cross-section of an exemplary gas turbine  10  that may incorporate various embodiments of the present invention. As shown, the gas turbine  10  may generally include a compressor  12  at the front, one or more combustors  14  radially disposed around the middle, and a turbine  16  at the rear. The compressor  12  and the turbine  16  typically share a common rotor  18  connected to a generator  20  to produce electricity. 
     The compressor  12  may be an axial flow compressor in which a working fluid  22 , such as ambient air, enters the compressor  12  and passes through alternating stages of stationary vanes  24  and rotating blades  26 . A compressor casing  28  contains the working fluid  22  as the stationary vanes  24  and rotating blades  26  accelerate and redirect the working fluid  22  to produce a continuous flow of compressed working fluid  22 . The majority of the compressed working fluid  22  flows through a compressor discharge plenum  30  to the combustor  14 . 
     The combustor  14  may be any type of combustor known in the art. For example, as shown in  FIG. 1 , a combustor casing  32  may circumferentially surround some or all of the combustor  14  to contain the compressed working fluid  22  flowing from the compressor  12 . One or more fuel nozzles  34  may be radially arranged in an end cover  36  to supply fuel to a combustion chamber  38  downstream from the fuel nozzles  34 . Possible fuels include, for example, one or more of blast furnace gas, coke oven gas, natural gas, vaporized liquefied natural gas (LNG), hydrogen, and propane. The compressed working fluid  22  may flow from the compressor discharge plenum  30  along the outside of the combustion chamber  38  before reaching the end cover  36  and reversing direction to flow through the fuel nozzles  34  to mix with the fuel. The mixture of fuel and compressed working fluid  22  flows into the combustion chamber  38  where it ignites to generate combustion gases having a high temperature and pressure. The combustion gases flow through a transition piece  40  to the turbine  16 . 
     The turbine  16  may include alternating stages of stators  42  and rotating buckets  44 . The first stage of stators  42  redirects and focuses the combustion gases onto the first stage of turbine buckets  44 . As the combustion gases pass over the first stage of turbine buckets  44 , the combustion gases expand, causing the turbine buckets  44  and rotor  18  to rotate. The combustion gases then flow to the next stage of stators  42  which redirects the combustion gases to the next stage of rotating turbine buckets  44 , and the process repeats for the following stages. 
       FIG. 2  provides an enlarged side view and partial cross-section of the combustor  14  shown in  FIG. 1  according to a first embodiment of the present invention. As shown, the combustor casing  32  and end cover  36  define a volume  50 , also referred to as the head end, inside the combustor  14 , and a liner  52  circumferentially surrounds and defines at least a portion of the combustion chamber  38 . A flow sleeve  54  may circumferentially surround at least a portion of the combustion chamber  38  to define an annular passage  56  between the flow sleeve  54  and the liner  52 . In this manner, the working fluid  22  may flow through the annular passage  56  to provide convective cooling to the liner  24 . When the working fluid  22  reaches the head end or volume  50 , the working fluid  22  reverses direction to flow through one or more fuel nozzles  34  and into the combustion chamber  38 . 
     The combustor casing  32  may include multiple annular sections that facilitate assembly and/or accommodate thermal expansion during operations. For example, as illustrated in the particular embodiment shown in  FIG. 2 , the combustor casing  32  may include a first annular casing  60  adjacent to the end cover  36  and a second annular casing  62  upstream from the first annular casing  60 . A clamp, weld bead, and/or plurality of bolts  64  may circumferentially surround the combustor  14  to provide a connection or joint  66  between the first and second annular casings  60 ,  62 . 
     In particular embodiments, a flange  70  may extend radially between the first and second annular casings  60 ,  62 , and the flange  70  may include one or more internal fluid passages that provide fluid communication through the connection  66 . For example, the flange  70  may include a fuel plenum  72  that extends radially through the casing  32  to provide fluid communication through the casing  32  to the annular passage  56 . A plurality of vanes  74  may circumferentially surround the combustion chamber  38  and extend radially in the annular passage  56  to guide the working fluid  22  flow. In particular embodiments, the vanes  74  may be angled to impart swirl to the working fluid  22  flowing through the annular passage  56 . The flange  70  may connect to one or more of the vanes  74 , and the fuel plenum  72  may extend inside one or more of the vanes  74  so fuel may flow through quaternary fuel ports  76  in the vanes  74  to mix with the working fluid  22  flowing through the annular passage  56 . Alternately, or in addition, the flange  70  may include a diluent passage  78  that provides a fluid pathway for the working fluid  22  to flow into or around the fuel nozzles  34  before flowing into the combustion chamber  38 . 
     As the working fluid  22  flows through the annular passage  56 , the difference in temperature between the working fluid  22  and the fuel may create substantial thermal gradients in the flange  70 , fuel plenum  72 , and/or vanes  74 . The thermal gradients may in turn create substantial thermal stresses that require the use of high alloy steels containing nickel, chromium, and iron and/or expensive and time consuming heat treatment during manufacture. To reduce the material and/or manufacturing costs, various embodiments of the present invention may include means for shielding at least a portion the fuel plenum  72  from direct impingement by fuel flowing through the fuel plenum  72 . As used herein, the function of the means includes preventing the fuel flowing through the fuel plenum  72  from directly impinging against at least a portion of the fuel plenum  72 . In particular embodiments, the means may further prevent the fuel flowing through the fuel plenum  72  from directly impinging with any of the fuel plenum  72  between the vanes  74  and the casing  32 . By preventing the fuel flowing through the fuel plenum  72  from directly impinging with portions of the fuel plenum  72 , the means reduces the localized cooling of the fuel plenum  72  caused by fuel that would otherwise impinge on the fuel plenum  72 . In this manner, the means acts as a shield between the fuel and the fuel plenum  72  to reduce thermal gradients in the flange  70  and/or fuel plenum  72 . Alternately or in addition, the means may also protect the fuel plenum  72  from the erosive effects of the fuel flow which may strip or otherwise liberate corrosion products from the surface of the fuel plenum  72 . As a result, the means enables the use of lower cost materials, such as carbon or low alloy steel, for portions of the fuel plenum  72  and/or eliminates or reduces the amount of heat treatment required during manufacture of portions of the fuel plenum  72 . 
       FIG. 3  provides an enlarged side cross-section view of a portion of the fuel plenum  72  shown in  FIG. 2 , and  FIG. 4  provides an axial cross-section view of the fuel plenum  72  shown in  FIG. 2  taken along line A-A. As shown in  FIGS. 3 and 4 , the structure for the means for shielding at least a portion the fuel plenum  72  from direct impingement by fuel flowing through the fuel plenum  72  may be an insert, liner  80 , or other shield made from materials having suitable corrosive and strength characteristics. For example, the liner  80  may be made from high alloy steels containing nickel, chromium, and iron, allowing use of lower cost materials, such as carbon or low alloy steel, for the fuel plenum  72 . The liner  80  may be inserted into at least a portion of the fuel plenum  72  and lightly compressed against the fuel plenum  72  to hold it tightly inside at least a portion of the fuel plenum  72  radially inward of the casing  32 . As further shown in  FIGS. 3 and 4 , the fuel plenum  72  may extend circumferentially around the combustion chamber  38 , and the same or a separate liner  80  may extend inside the fuel plenum  72  circumferentially around the combustion chamber  38 . In this manner, the liner  80  may prevent fuel flowing through the fuel plenum  72  from directly impinging with any of the fuel plenum  72  between the vanes  74  and the casing  32 . However, one of ordinary skill in the art should readily appreciate that particular embodiments of the invention do not require the liner  80  to extend continuously inside the fuel plenum  72  unless specifically recited in the claims. 
     As shown in  FIGS. 3 and 4 , the liner  80  may include multiple sections press fit or otherwise sealed together to provide a fluid boundary inside some or all of the fuel plenum  72 . In addition, one or more detents  82  inside the fuel plenum  72  may be in contact with the liner  80  to hold the liner  80  in place inside the fuel plenum  72 . The detents  82  may include any suitable structure known in the art for restraining movement between adjacent objects. For example, as shown most clearly in  FIG. 3 , the detents  82  may include rings, projections, or other surface features inside the fuel plenum  72  that provide a friction fit between the fuel plenum  72  and the liner  80  to hold the liner  80  in place. The detents  82  may also provide a seal between the fuel plenum  72  and the liner  80 . In this manner, the detents  82  may reduce or prevent fuel from flowing around the liner  80  and over areas of the fuel plenum  72  made from lower cost materials more susceptible to corrosion, thereby possibly liberating corrosion products into the fuel flow. 
     The structures described and illustrated in  FIGS. 1-4  may also provide a method of reducing thermal stresses in the combustor  14 . The method may include flowing the fuel inside the fuel plenum  72 , shielding at least a portion of the fuel from directly impinging the fuel plenum  72  between the vanes  74  and the casing  32 , and flowing the fuel from the fuel plenum  72  into the annular passage  56  between the casing  32  and the combustion chamber  38 . In particular embodiments, the method may include shielding the entire fuel plenum  72  between the vanes  74  and the casing  32  from direct impingement from the fuel. Alternately or in addition, the method may include flowing the fuel inside the fuel plenum  72  circumferentially around the combustion chamber  38  and/or shielding the fuel flowing inside the fuel plenum  72  circumferentially around the combustion chamber  38  from directly impinging the fuel plenum  72 . 
     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.