Patent Publication Number: US-2013236293-A1

Title: Systems and methods for an improved stator

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to casings for use in various types of rotary systems such as compressors and gas turbines. 
     Rotary systems, such as compressors and turbines, may generally include a rotor portion that rotates about an axis during the operation of the system as well as a stator portion (e.g., casing, shroud, etc.) that remains substantially immobile during system operation. For example, in a compressor, the rotor portion may include a number of blades disposed about a shaft. During operation of the compressor, this shaft may rotate, causing the attached blades to rotate within a stationary casing (i.e., the stator) surrounding the rotor. However, since the temperature present within the compressor may be high (e.g., in excess of 1000° C.), portions of the rotor and/or casing of the compressor may warm and expand during operation. This expansion may change the clearance between these portions of the rotor and/or casing during operation of the compressor, which may affect the ability of the compressor to properly function and/or operate efficiently. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
     In an embodiment, a system includes a rotary machine. The rotary machine includes a rotor having a plurality of blades and a segmented stator having a plurality of stator segments arranged circumferentially about the plurality of blades. Each adjacent pair of first and second segments of the plurality of stator segments includes a recess extending circumferentially across an intermediate joint between the first and second segments. Furthermore, each recess includes at least one eccentricity control insert configured to mitigate eccentricity of an inner circumference of the segmented stator due to thermal expansion or thermal contraction of the segmented stator. 
     In another embodiment, a system includes an eccentricity control insert configured to mount in a recess at an intermediate joint between an adjacent pair of first and second segments of a segmented stator of a rotary machine. Furthermore, the eccentricity control insert is configured to mitigate eccentricity of an inner circumference of the segmented stator due to thermal expansion or thermal contraction of the segmented stator. 
     In another embodiment, a system includes a segmented stator including a plurality of stator segments arranged circumferentially about a rotational axis of a rotary machine. Each adjacent pair of first and second segments of the plurality of stator segments includes a recess extending circumferentially across an intermediate joint between the first and second segments. Furthermore, each recess includes at least one eccentricity control insert configured to mitigate eccentricity of an inner circumference of the segmented stator due to thermal expansion or thermal contraction of the segmented stator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a block diagram of an embodiment of a rotary machine, e.g., a turbine system, having an eccentricity control system for a segmented stator (e.g., segmented casing); 
         FIG. 2  is a schematic cross-section of an embodiment of a rotary machine, e.g., a compressor, having an eccentricity control system with an eccentricity control insert disposed in a recess in a segmented stator; 
         FIG. 3  is a schematic cross-section of the segmented stator of  FIG. 2 , taken along line  3 - 3 , illustrating an embodiment of the recess and the eccentricity control insert disposed across an intermediate joint between adjacent stator segments; 
         FIG. 4  is a partial schematic cross-sectional view of the segmented stator of  FIG. 3 , taken within line  4 - 4 , illustrating an arcuate shaped configuration, a variable radial thickness, an arc length, and other characteristics of the recess and the eccentricity control insert; and 
         FIG. 5  is a partial perspective view of one segment of the segmented stator of  FIGS. 1-4 , illustrating a T-shaped joint that couples the eccentricity control insert to the recess. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     As set forth above, the temperature of the gases present within a rotary system (e.g., a compressor, turbine of a gas turbine system, steam turbine, pump, or similar rotary system) may be relatively high and/or fluctuate during certain points during the operation of the system. These elevated and fluctuating temperatures in the rotary system may cause portions the casing (i.e., stator) encircling the rotor to warm and expand or cool and contract during system operation. Additionally, since a casing of a rotary system may include a number of coupled segments, then the expansion/contraction of the casing at or near the joints may not be the same as the expansion in the middle of the casing segments. This may generally result in the casing (e.g., the inner circumference of the casing) becoming less round (e.g., more eccentric) as a result of the thermal expansion. As such, if, for example, the casing of a rotary system (e.g., a compressor or turbine) expands and/or contracts in a certain manner during operation, then portions of rotor and casing may contact one another, resulting in premature wear, vibration, and/or cracking in the rotary system. If, by further example, the casing of the rotary system expands and/or contracts in another manner during operation, then clearance between the rotor and the casing may be too great, resulting in reduced efficiency of the rotary system. Accordingly, it may be generally desirable to improve the casing (i.e., stator) design to control the clearance between the rotor and the casing by mitigating the eccentricity of the casing at it warms and/or cools during operation of the rotary system. The disclosed embodiments employ inserts in recesses along each joint between casing segments, thereby helping to maintain roundness of the casing (e.g., an inner surface of the casing) despite thermal expansion or contraction. 
     With the foregoing in mind,  FIG. 1  is a block diagram of an embodiment of a turbine system  10  that includes two rotary systems (i.e., a compressor and a gas turbine) having an eccentricity control system in accordance with aspects of the present technique. That is, as discussed in detail below, the casings of the rotary systems of the turbine system  10  have been modified to include an eccentricity control insert to help maintain the roundness of the casings despite thermal expansion or contraction. The illustrated turbine system  10  includes a gas turbine engine  12  coupled to a load  14 , such as an electrical generator. The gas turbine engine  12  includes a compressor  16 , a plurality of combustors  18  each having at least one fuel nozzle  20 , a turbine  22 , and an exhaust section  24 . As illustrated, one or more shafts  26  connect the load  14 , compressor  16 , and turbine  22 . The compressor  16  and the turbine  22  each include a rotor with blades, which rotate about a rotational axis  28  within a stator (i.e., casing) that has been modified to mitigate eccentricity during thermal expansion, as discussed in detail below. During operation, the compressor  16  receives air  30  and delivers compressed air  32  to the combustors  18  and/or fuel nozzles  20 , which then injects fuel  34  (or an air-fuel mixture) into a combustion region in the combustors  18 . In turn, the air-fuel mixture combusts in the combustors  18  to produce hot combustion gases  36 , which drive blades within the turbine  18 . As the turbine is driven to rotate the shaft  26 , the compressor  16  is driven to compress the air  16  into the combustors  18  and/or fuel nozzles  20 . For purposes of discussion, reference may be made to an axial direction or axis  38 , a radial direction or axis  40 , and a circumferential direction or axis  42 . The axial direction  38  is generally oriented along the rotational axis  28 . 
     As mentioned, the illustrated compressor  16  and turbine  22  include casings (i.e., stators or shrouds) that have been modified in order to reduce the potential of the casings to expand or contract out of roundness (e.g., become eccentric) during operation of the system  10 . In particular, disclosed embodiments generally have portions of each of the segments of the case absent or removed near the joints (e.g., removed portions where the individual segments of the case meet). For example, in certain embodiments, the removed portions of the segments near the joints may take the form of a recess, a groove, or a slot. Furthermore, the disclosed embodiments utilize an insert that may be disposed within the groove or recess to generally control the clearance between the blades of the rotor and the casing of the rotary machine (e.g., compressor  16  or turbine  22 ). While the various aspects of the modified casing embodiments are described below with respect to the compressor  16 , it should be appreciated that the presently disclosed casing embodiments are applicable to the gas turbine  22  or any rotary system where uniform and/or minimized clearance between the rotor and stator are desirable. 
     Accordingly,  FIG. 2  illustrates a cross-section of an embodiment of the compressor  16  having the modified casing in accordance with aspects of the present technique. The illustrated compressor  16  includes a rotor  50  having a number of blades  52  disposed about a shaft  54 . Furthermore, the blade  52  of the rotor  50  are configured to rotate (i.e., about the rotational axis  28 ) within the stator or compressor casing  56 . Generally speaking, it is desirable for the casing  56  of the compressor  16  to provide a uniform, minimal clearance  58  between the blades  52  of the rotor  50  and the casing  56 . That is, it is generally desirable for the blades  52  of the rotor  50  to come as close as possible to the casing  56  without actually contacting the casing  56  during the operation of the compressor  16 . It should be also appreciated if the clearance  58  between the blades  52  of the rotor  50  and the casing  56  is too large, then the efficiency of the compressor  16  may be significantly reduced. For example, for certain compressors, a clearance  58  that is 10 mils larger than a desired clearance may result in roughly 1 MW loss in efficiency of the compressor  16 . Furthermore, by providing a uniform clearance between the rotor and casing over the inner circumference of the casing may generally enable the rotary system to have more uniform performance (e.g., fewer fluctuations in power output). 
     Accordingly, the casing  56  of the compressor  16  has at least one recess  60  that supports at least one insert  62  in accordance with aspects of the present technique. Generally speaking, the recess  60  extends into the interior surface of the casing  56  in the radial direction  40  (i.e., having a radial depth  51  into the wall of the casing  56 ). In certain embodiments, the recess  60  may be formed by grinding or turning down a portion of the casing  56  after manufacturing. In other embodiments, the recess  60  may be formed during the manufacturing of the casing  56  (e.g., as an element defined by the mold used to cast the casing  56 ). Regardless, the recess  60  is an area of the casing in which a portion of the casing material (e.g., steel or other suitable metal or alloy) is absent or has been removed (e.g., via grinding or turning). For example, in certain embodiments, the recess  60  may be in the form of a groove, a slot, a channel, or other similar recess  60 . Additionally, as discussed below with respect to  FIGS. 3 and 4 , the recess  60  may be present in the casing  56  of the compressor  16  at portions where the various segments of the casing  56  meet (i.e., at or near casing segment joints). Furthermore, as discussed below with respect to  FIG. 5 , the recess  60  may have a particular shape (e.g., a V-shape, a rectangular shape, a rounded shape, or other suitable shape). 
     Additionally, in the illustrated compressor  16 , an insert  62  is disposed within the recess  60 . As illustrated, the insert  62  may slightly protrude radially  40  from the recess  60  into the clearance space  58 . For example, the insert  62  may extend between approximately 20 mm and 60 mm beyond the inner surface  53  of the casing  56 . The illustrated insert  62  also includes at least two layers: a substrate layer  64  and an abradable surface coating  66 . In certain embodiments, the substrate layer  64  of the insert  62  may be manufactured from the same material (e.g., metal or alloy) as the casing  56 . For example, in certain embodiments, the insert  62  and the casing  56  may both be manufactured from steel. In other embodiments, the substrate layer  64  of the insert  62  may be manufactured from a different material (e.g., metal or alloy) than the casing  56 . For example, in certain embodiments, the substrate layer  64  of the insert  62  may be a different type of steel (e.g., higher carbon steel) than the casing  56 . Furthermore, the material used for the substrate layer  64  of the insert  62  may be selected based on the thermal expansion properties of the material. That is, the substrate layer  64  of the insert  62  may have slightly different thermal expansion properties from the casing  56  such that the insert  62  and the casing  56  may not expand or contract at the same rate as they are heated and cooled (e.g., during operation of the compressor  16 ). 
     Moreover, the insert  62  is disposed within the recess  60  such that the abradable surface coating  66  is facing the blades  52  of the rotor  54 . The abradable surface coating  66  may be any surface coating that may be preferentially removed upon contact with the blades  52  of the rotor  54 , rather than remove material from the rotor blades  52  or the casing  56 . That is, while the blades  52  of the rotor  54  are generally configured not to contact the casing  56 , the aforementioned thermal expansion of the casing  56  during operation of the compressor may cause the blades  52  of the rotor  54  to temporarily contact the abradable surface coating  66  of the insert  62  (e.g., rather than the substrate  64  of the insert  62  or the casing  56 ). Therefore, the abradable surface coating  66  may generally allow for tighter clearance  58  while protecting the tips of the blades  52 . Additionally, the abradable surface coating  66  may generally be considered a self-adjusting coating as it may be slightly by the tips of the blades  52  until the desired clearance  58  is achieved. In certain embodiments, the abradable surface coatings  66  may be an alumina, silica, titania, chrome carbines, or other suitable abradable surface coating  66 . In general, materials for the abradable surface coating  66  may be selected according to a relative hardness of the abradable surface coating  66  compared to the casing  56  and the blades  52  of the rotor  54 . For example, in certain embodiments, the abradable surface coating  66  may be manufactured from a material that is 10%, 20% 50%, 75%, or 95% softer than the material used to manufacture the casing  56  and/or the blades  52 . Additionally, as set forth below with respect to  FIGS. 4 and 5 , the abradable surface coating  66  may either have either a uniform thickness or a variable thickness across the insert  62 . 
       FIG. 3  illustrates a cross-section of the embodiment of the compressor  16  illustrated in  FIG. 2  taken within line  3 - 3  (i.e., without the rotor  54  and blades  52 ). Accordingly,  FIG. 3  illustrates the location of the recesses  60  in the casing  56  of the compressor  16  relative to the locations of intermediate joints  70  and  72  (i.e., where the first segment  74  and the adjacent second segment  76  meet). While the illustrated embodiment of the casing  56  includes two 180° segments (e.g., segments  74  and  76 ), in other embodiments the casing  56  may include any number of segments (e.g., 3, 4, 5, 6 or more). Furthermore, the illustrated casing  56  includes recesses  60  that are generally deeper  59  near the joints  70  and  72  and become generally shallower  61  moving away from the joints in a circumferential direction  42 . Additionally, the recesses  60  may occupy a portion of the casing  56  measured as an angle  71  from the point  73  at the center of the casing (e.g., the axis of rotation  38 ). For example, the illustrated angle  71  is approximately 60°. In certain embodiments, the angle  71  may be between approximately 10° and 60°, between approximately 20° and 50°, or between approximately 30° and 45°. 
     Accordingly, the inserts  62  disposed within each of the recesses  60  similarly are thicker in the portions that are disposed near the joints  70  and  72  and thinner in portions that are disposed away from the joints. Furthermore, in certain embodiments, a one-piece or integral insert  62  may be disposed in the each of the recesses  60 , and each of these inserts  62  may occupy the entire recess  60  that extends circumferentially  38  into both segments  74  and  76  of the compressor casing  56 . In the illustrated embodiment, recesses  60  include a recess portion  63  and a recess portion  65  that are each loaded with an insert  62 . That is, each recess  60  of the illustrated casing  56  includes a first insert  62  (e.g., disposed within the recess portion  63  of the recess  60  in segment  74 ) and a second insert  62  (e.g., disposed within the recess portion  65  of the recess  60  in segment  76 ). 
     Additionally, the illustrated casing  56  of the compressor  16  is substantially round (i.e., circular). Furthermore, it should be appreciated that, as the casing  56  warms or cools during operation of the compressor  16 , the portions of the segments  74  and  76  near the joints  70  and  72  may not expands or contract as much as the portions of the segments  74  and  76  away from the joints  70  and  72 . That is, since the casing  56  may generally have more freedom to move near the joints  70  and  72 , the casing  56  generally push outwardly  67  or pull inwardly  69  (e.g., center  73  of the casing  56 ), deforming at the joints  70  and  72  (e.g., shift out of roundness and/or become eccentric). Moreover, the illustrated casing  56  has the recesses  60  with the inserts  62  disposed within. Accordingly, as the casing  56  begins to thermally expand, the recesses  60  and the inserts  62  enable the casing  56  of the compressor to thermally expand without becoming substantially eccentric. That is, the recesses  60  and the inserts  62  generally enable the clearance  58  between the blades  52  of the rotor  54  to remain substantially uniform throughout the operation of the compressor  16 . For example, in certain embodiments, the recesses  60  and inserts  62  may cooperate to provide a uniform clearance  58  (e.g., circumferentially  38  between the rotor blades  52  and the casing  56  and insert  62 ) of between 1 mm and 50 mm, between 5 mm and 30 mm, between 8 mm and 20 mm, or approximately 10 mm at the joints  70  and  72 . 
       FIG. 4  illustrates an enlarged view of the joint  70  of the casing embodiment illustrated in  FIG. 3 . Accordingly,  FIG. 4  illustrates the recess  60  in the segments  74  and  76  of the casing  56 . Moreover, the illustrated recess  60  is substantially deeper  59  near the joint  70  and substantially shallower  61  away from the joint  70 . Furthermore, the insert  62 , including the substrate  64  and the abradable coating  66 , is disposed within the illustrated recess  60 . Like the illustrated recess  60 , the insert  62  is substantially thicker  75  at the portion disposed near the joint  70  and substantially thinner  77  at the portion disposed away from the joint  70 . In other embodiments, the recess  60  and the insert  62  may both have a substantially uniform radial  40  depth and thickness, respectively. Furthermore, the abradable coating  66  of the illustrated insert  62  is substantially thicker  79  near the joint  70  and substantially thinner  81  moving away from the joint  70  circumferentially  42 . Accordingly, in certain embodiments, the recess  60 , the insert  62 , and/or the abradable coating  66  may generally be described as having a generally arcuate shape. In other embodiments, the abradable coating  66  may have a substantially uniform thickness over the length of the insert  62 . 
       FIG. 5  is a partial perspective view of one segment of the segmented stator of  FIGS. 1-4 , illustrating a T-shaped joint  83  that couples the eccentricity control insert  62  to the recess  60 . That is,  FIG. 5  illustrates the insert  62  disposed within the recess  60  of segment  76  of the casing  56 . In particular, the illustrated recess  60  includes the T-shaped joint  83  and, accordingly, the insert  62  is a T-shaped insert  62 . Additionally, in certain embodiments, the recess  60  and the insert  62  may have a dove-tail shape, a rounded shape, a “V” shape, a triangular shape, a semicircular shape, or other suitable shape. Furthermore, the T-shaped joint  83  includes ridge portions  85  that may generally serve to hold the insert  62  in place within the T-shaped joint  83 . The illustrated T-shaped insert  62  includes a neck portion  89  and a mounting base portion  91  that extend in a lengthwise direction along the eccentricity control insert  62 , and the mounting base portion  91  is wider than the neck portion  89  in a crosswise direction relative to the lengthwise direction. In certain embodiments, the abradable coating  66  of the insert  62  extends beyond the neck portions  85  such that, during operation, the tips blades  52  of the rotor  54  most proximate to the abradable coating  66  of the insert  62 . Additionally, the insert  62  may be introduced into the T-shaped joint  83  from the top portion  85  of the joint  83 , and seated in a downward motion  87  such that the insert  62  is circumferentially loaded or mounted into the segment  76  of the casing  56 . 
     Furthermore, the illustrated insert  62  is substantially thicker  75  near the joint  70 . That is, both the substrate  64  and the abradable coating  66  of the illustrated insert  62  are substantially thicker  75  near the joint  70  and gradually taper along the segment  76  (i.e., moving away from the joint  70  circumferentially  42 ), where the substrate  64  and the abradable coating  66  of the illustrated insert  62  are thinner  77 . Accordingly, when the blades  52  of the rotor  54  are rotating during operation of the compressor  16 , the groove  60  and the insert  62  may provide a uniform circumferential clearance  58  such that the compressor  16  may efficiently function. 
     Technical effects of the present embodiments include mitigating the eccentricity of stators in rotor/stator system (e.g., casings for compressors, gas turbines, steam turbines, pumps, or other rotary machines) in order to control the clearance between the rotor and the stator as the system expands and/or contracts during heating and/or cooling. By controlling the clearance between the rotor and the casing of the compressor or gas turbine, present embodiments enable the compressor or gas turbine to continue to properly and efficiently function, even as the casing expands and contracts during operation. Accordingly, present embodiments may reduce maintenance costs by reducing the likelihood of contact between the rotor blades in the casing and by providing an abradable coating that may be preferentially removed to preserve the integrity of the rotor blades and/or casing in case of contact. Furthermore, present embodiments enable the compressor or gas turbine to maintain efficiency during operation, limiting energy costs and waste. 
     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 have 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 language of the claims.