Patent Publication Number: US-8967951-B2

Title: Turbine assembly and method for supporting turbine components

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to turbines. More particularly, the subject matter relates to an assembly of turbine static structures. 
     In turbine engines, such as steam or gas turbine engines, static or non-rotating structures may have certain clearances when placed adjacent to one another. The clearances between adjacent structures allow for movement caused by temperature changes or pressure changes. For instance, in a gas turbine engine, a combustor converts chemical energy of a fuel or an air-fuel mixture into thermal energy. The thermal energy is conveyed by a fluid, often air from a compressor, to a turbine where the thermal energy is converted to mechanical energy. High combustion temperatures and/or pressures in selected locations, such as the combustor and turbine nozzle areas, may enable improved combustion efficiency and power production. In some cases, high temperatures and/or pressures in certain turbine structures may cause relative movement of adjacent structures, which can cause contact and friction that lead to stress and wear of the structures. For example, stator structures, such as rings or casing, are circumferentially joined about the turbine case and are exposed to high temperatures and pressure as the hot gas flows along the stator. 
     It is desirable to improve turbine performance by reducing turbine clearances. In some cases reducing clearances requires accounting for eccentricity, out of roundness and part variation. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a turbine assembly includes a first static structure and a second static structure radially outward of the first static structure. The assembly also includes a support member placed in a recess of the second static structure, wherein the support member includes first and second curved surfaces to contact the first and second static structures, respectively, and wherein the support member includes a biasing structure to retain the support member in the recess. 
     According to another aspect of the invention, a method for supporting turbine components includes positioning an inner turbine shell substantially concentric with a rotor and surrounding the inner turbine shell with an outer turbine shell. The method also includes supporting the inner turbine shell with respect to the outer turbine shell with a support member, wherein the support member includes a biasing structure configured to maintain a position of the support member when the support member is not in contact with one of the inner or outer turbine shell. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is partial cross-section of an exemplary turbine; 
         FIG. 2  is a simplified axial cross-section of the turbine shown in  FIG. 1 ; and 
         FIG. 3  is a detailed sectional view of a turbine assembly. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention include a clearance control system that adjusts the position of an inner turbine shell with respect to a rotor and/or an outer turbine shell. In doing so, the system addresses several parameters to reduce operating clearance between rotating and stationary components in the turbine to improve performance in a cost-effective manner. The key parameters include friction, eccentricity, out of roundness, muscle, cost, and ease-of-use. They system may further include clearance control structures and methods to control the temperature, and thus the expansion and contraction, of the inner turbine shell. Although various embodiments of the present invention may be described and illustrated in the context of a turbine, one of ordinary skill in the art will understand that the principles and teachings of the present application apply equally to type of turbine having rotating and stationary components in close proximity. 
       FIG. 1  provides a simplified partial cross-section of a turbine  10  according to one embodiment of the present invention. As shown, the turbine  10  generally includes a rotor  12 , one or more inner turbine shells  14 , and an outer turbine shell  16 . The rotor  12  includes a plurality of turbine wheels  18  separated by spacers  20  along the length of the rotor  12 . A bolt  22  extends through the turbine wheels  18  and spacers  20  to hold them in place and collectively form a portion of the rotor  12 . Circumferentially spaced turbine buckets  24  connect to and extend radially outward from each turbine wheel  18  to form a stage in the turbine  10 . For example, the turbine  10  shown in  FIG. 1  includes three stages of turbine buckets  24 , although the present invention is not limited to the number of stages included in the turbine  10 . 
     The inner turbine shells  14  completely surround at least a portion of the rotor  12 . As shown in  FIG. 1 , for example, a separate inner turbine shell  14  completely surrounds the outer perimeter of each stage of turbine buckets  24 . In this manner, the inner turbine shells  14  and the outer periphery of the turbine buckets  24  reduce the flow of hot gases that bypass a turbine stage. The outer turbine shell  16  generally surrounds the rotor  12  and the inner turbine shell  14 . Circumferentially spaced nozzles  28  connect to the outer turbine shell  16  and extend radially inward toward the spacers  20 . For example, as shown in  FIG. 1 , the first stage nozzle  28  at the far left connects to the outer turbine shell  16  so that the flow of the gases over the first stage nozzle  28  exerts a pressure against the outer turbine shell  16  in the downstream direction. 
     As shown in  FIG. 1 , the inner turbine shell  14  may include on or more internal passages  30 . These passages  30  allow for the flow of a medium to heat or cool the inner turbine shell  14 , as desired. For example, airflow from a compressor or combustor may be diverted form the hot gas path and metered through the passages  30  in the inner turbine shell  14 . In this manner, the inner turbine shell  14  may be heated or cooled to allow it to expand or contract radially in a controlled manner to achieve a designed clearance between the inner turbine shell  14  and the outer periphery of the turbine buckets  24 . For example, during turbine  10  startup, heated air may be circulated through the various passages  30  of the inner turbine shell  14  to radially expand the inner turbine shell  14  outwardly form the outer periphery of the turbine buckets  24 . Since the inner turbine shell  14  heats up faster than the rotor  12 , this ensure adequate clearance between the inner turbine shell  14  and the outer periphery of the turbine buckets  24  during startup. During steady-state operations, the temperature of the air supplied to the inner turbine shell  14  may be adjusted to contract and expand the inner turbine shell  14  relative to the outer periphery of the turbine buckets  24 , thereby producing the desired clearance between the inner turbine shell  14  and the outer periphery of the turbine buckets  24  to enhance the efficiency of the turbine  10  operation. Similarly, during turbine  10  shutdown, the temperature of the air supplied to the inner turbine shell  14  may be adjusted to endure the inner turbine shell  14  contracts slower than the turbine buckets  24  to avoid excessive contact between the outer periphery of the turbine buckets  24  and the inner turbine shell  14 . To that end, the temperature of the medium may be adjusted to maintain a desired clearance during the shutdown. 
     As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of working fluid through the turbine. As such, the term “downstream” refers to a direction that generally corresponds to the direction of the flow of working fluid, and the term “upstream” generally refers to the direction that is opposite of the direction of flow of working fluid. The term “radial” refers to movement or position perpendicular to an axis or center line. It may be useful to describe parts that are at differing radial positions with regard to an axis. In this case, if a first component resides closer to the axis than a second component, it may be stated herein that the first component is “radially inward” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. Although the following discussion primarily focuses on turbines, the concepts discussed are not limited to turbines and may apply to any rotating machinery. 
       FIG. 2  shows a simplified axial cross-section of the turbine  10  shown in  FIG. 1  taken along line A-A. In this view, the rotor  12  is in the center with the turbine buckets  24  extending radially therefrom. The inner turbine shell  14  completely surrounds the turbine buckets  24  and at least a portion of the rotor  12 , providing a clearance  32  between the inner turbine shell  14  and the outer periphery of the turbine buckets  24 . In an embodiment, the inner turbine shell  14  comprises a single-piece construction that completely surrounds a portion of the rotor  12 . The single-piece design reduces eccentricities and out of roundness that may occur in multi-piece designs. Other embodiments may include an inner turbine shell  14  comprising multiple pieces that completely surround a portion of the rotor  12 . A block, key or other detent  34  between the bottom of the inner turbine shell  14  and the bottom of the outer turbine shell  16  may be used to fix the inner turbine shell  14  laterally in place and restrict the inner turbine shell  14  from rotational movement with respect to the rotor  12  and/or the outer turbine shell  16 . 
     As shown in  FIG. 2 , a gap  36  or space exists between the inner turbine shell  14  and outer turbine shell  16 . As a result, the inner turbine shell  14  is physically isolated form the outer turbine shell  16 , preventing any distortion, contraction, or expansion of the outer turbine shell  16  from being transmitted to the inner turbine shell  14 . For example, eccentricities or out of roundness created by thermal gradients of the hot gas path in the outer turbine shell  16  will not be transmitted to the inner turbine shell  14  and will therefore not affect the design clearance  32  between the inner turbine shell  14  and outer periphery of the turbine buckets  24 . 
     A support member assembly  38  provides support between the inner turbine shell  14  and the outer turbine shell  16 . In the case of an inner turbine shell  14  comprising a single-piece construction, the assembly  38  may be located between the inner turbine shell  14  and the outer turbine shell  16  on opposite sides at approximately the vertical midpoint (i.e., approximately half of the distance between the top and bottom of the inner turbine shell  14 ) of the inner turbine shell  14 . In other embodiments having multi-piece inner turbine shell  14 , the system may include multiple support member assemblies  38  evenly spaced around the periphery of the inner turbine shell  14 . In an embodiment, the outer turbine shell  14  includes shelf members  70  configured to contact the support member assembly  38 . 
     The depicted embodiment of the support member assembly  38  reduces the friction between two independent static turbine structures, such as the inner turbine shell  14  and outer turbine shell  16 . As shown in  FIG. 3 , the support member assembly  38  includes a support member  40 , such as a rolling block, that reduces friction during relative movement of the structures. In addition, the exemplary assembly and support member  40  has fewer parts than other embodiments of the turbine assembly. The support member is also configured to retain the member&#39;s orientation and position when not in contact with at least one of the shell structures  14 ,  16 . As depicted, the support member  40  is in contact with support surfaces  44  and  46  of the inner turbine shell  14  and outer turbine shell  16 , respectively. Further, a recess  42  in the outer shell structure  16  receives the support member  40 . 
     The exemplary support member  40  comprises a substantially square block with round edges. The support member  40  is a stiff structure that is able to roll or rotationally move  58  as the inner and outer shell structures  14  and  16  move relative to each other. The support member  40  includes biasing members  48  and  52  to support the block. In an embodiment, the biasing members  48  and  52  are springs positioned proximate corners of the support member  40 . Specifically, the biasing members  48  are positioned in the recess  42  and contact support surface  46  and lateral surfaces  50  to retain the support member  40  when the member is not in contact with the support surface  44 . In an example, by retaining the support member  40  within the recess  42 , the position and orientation of the support member  40  is maintained. Further, the biasing members  48  are configured to have a selected stiffness to allow the rotational movement  58  of the support member  40  during relative movement of the shell structures  14 ,  16 . The biasing members  52  provide support and enable the support member  40  to maintain the desired orientation when forces, such as gravity, cause the curved surface  54  to contact the support surface  44 . 
     Relative movement of the shell structures  14 ,  16  causes the support member  40  to roll and rotate a small angle  60 . For example, a relative movement between the inner shell structure  14  and outer shell structure  16  of about 0.200 inches may result in a rotation of about 4 degrees for the small angle  60 . In addition, curved surfaces  54  and  56  contact support surfaces  44  and  46 , respectively, to allow rotational movement  58  with reduced friction. The exemplary curved surfaces  54 ,  56  comprise a high strength material, such as high strength stainless steel or high nickel alloy. In embodiments, the entire support member  40  may comprise the high strength material or may have the block portion comprise a different material, such as carbon steel or other suitable stainless steel. Reduced friction provided by the support member assembly  38  enables reduced clearances between adjacent turbine parts, such as shell structures  14 ,  16 , to improve performance and efficiency. Further, the reduced friction provided by the support member  40  reduces eccentricity and out of roundness for components while reducing costs. 
     In an embodiment, two or more support members are placed at each support member assembly  38  location (as shown in  FIG. 2 ), wherein the second and “opposite” support member is substantially a mirror image of the member in  FIG. 3  taken across a vertical midpoint of the inner shell structure  14 . The opposite support member is adjacent to the support member  40  and across a line running through the vertical midpoint. Accordingly, the opposite support member is positioned to contact a surface of inner shell structure  14  that is substantially parallel to support surface  44 . 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.