Abstract:
An inner shell for a rotating machine including at least one segment; and at least one complementary segment in operable communication with the at least one segment, the segments forming a support structure for a shroud ring; wherein the at least one segment and the at least one complementary segment are individually moved to change a set of dimensions defined by the at least one segment and the at least one complementary segment. A method for controlling a dimension of the shroud ring in a rotating machine is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention disclosed herein relates to the field of gas turbines. In particular, the invention is used to provide control of turbine blade tip clearance. 
         [0003]    2. Description of the Related Art 
         [0004]    A gas turbine includes many parts, each of which may expand or contract as operational conditions change. A turbine interacts with hot gases emitted from a combustion chamber to turn a shaft. The shaft is generally coupled to a compressor and, in some embodiments, a device for receiving energy such as an electric generator. The turbine is generally adjacent to the combustion chamber. The turbine uses blades, sometimes referred to as “buckets,” for using energy of the hot gases to turn the shaft. 
         [0005]    The turbine blades rotate within a shroud ring. As the hot gases impinge on the turbine blades, the shaft is turned. The shroud ring is used to prevent the hot gases from escaping around the turbine blades and, therefore, not turning the shaft. 
         [0006]    The distance between the end of one turbine blade and the shroud ring is referred to as “clearance.” As the clearance increases, efficiency of the turbine decreases as hot gases escape through the clearance. Therefore, an amount of clearance can affect the overall efficiency of the gas turbine. 
         [0007]    If the amount of clearance is too small, then thermal properties of the turbine blades, the shroud ring, and other components can cause the turbine blades to rub the shroud ring. When the turbine blades rub the shroud ring, damage to the turbine blades, the shroud ring and the turbine may occur. It is important, therefore, to maintain a minimal clearance during a variety of operational conditions. 
         [0008]    Therefore, what are needed are techniques to reduce clearance between turbine blades and a shroud ring in a gas turbine. The techniques should be useful for a variety of operational conditions. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0009]    Disclosed is one embodiment of an inner shell for a rotating machine including at least one segment; and at least one complementary segment in operable communication with the at least one segment, the segments forming a support structure for a shroud ring; wherein the at least one segment and the at least one complementary segment are individually moved to change a set of dimensions defined by the at least one segment and the at least one complementary segment. 
         [0010]    Also disclosed is one embodiment of a rotating machine including a housing; a rotating component disposed at the housing; a shroud ring disposed adjacent to the rotating component; a shell comprising segments, at least one segment in operable communication with the shroud ring, wherein at least one dimension of the shroud ring is adjustable by the shell. 
         [0011]    Further disclosed is one example of a method for controlling a dimension of a shroud ring in a rotating machine, the method including receiving information from a control system; moving one or more segments of a segmented shell using the information, the shell in operable communication with the shroud ring; and deforming the shroud ring with the one or more segments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    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, wherein like elements are numbered alike, in which: 
           [0013]      FIG. 1  illustrates an exemplary embodiment of a gas turbine; 
           [0014]      FIGS. 2A and 2B , collectively referred to  FIG. 2 , illustrate an exemplary embodiment of a turbine stage and an inner turbine shell; 
           [0015]      FIGS. 3A ,  3 B, and  3 C, collectively referred to as  FIG. 3  illustrate an exemplary embodiment of a slot between adjacent segments and an inter-segment seal; 
           [0016]      FIGS. 4A and 4B , collectively referred to as  FIG. 4 , illustrate an exemplary embodiment of a segment of the inner turbine shell; 
           [0017]      FIG. 5  illustrates an exemplary embodiment of the inner turbine shell with actuators coupled to a plurality segments; 
           [0018]      FIG. 6  illustrates an exemplary embodiment of the inner turbine shell with a sleeve; 
           [0019]      FIG. 7  illustrates an exemplary embodiment of the segment with a nozzle; 
           [0020]      FIG. 8  presents an exemplary method for controlling a dimension of the shroud ring. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Various embodiments of apparatus and methods for controlling a clearance between a plurality of blades and a shroud ring in a rotating machine are disclosed herein. While the illustrated embodiments are devoted to controlling the clearance between a plurality of turbine blades and the shroud ring in a gas turbine, it is to be appreciated that the general teachings herein are applicable to other types of machines such as compressors and pumps. 
         [0022]    Specifically taught herein are apparatus and methods for controlling a dimension of the shroud ring, such as the diameter, to maintain a desired amount of clearance between the shroud ring and a set of turbine blades. In one embodiment, the desired amount of clearance is a minimum amount of clearance that avoids rubbing of the blades against the shroud ring. 
         [0023]    For convenience, certain definitions are provided. The term “rotating machine” relates to machinery that includes blades disposed circumferentially about a shaft. The shaft and blades rotate together to at least one of compress a gas, pump a fluid, convert a fluid flow to rotational work, and convert a gas flow to rotational work. The term “gas turbine” relates to a rotating machine that is a continuous combustion engine. The gas turbine generally includes a compressor, a combustion chamber and a turbine. The combustion chamber emits hot gases that are directed to the turbine. The term “turbine blade” relates to a blade included in the turbine. Each turbine blade generally has an airfoil shape for converting the hot gases impinging on the bucket into rotational work. The term “turbine stage” relates to a plurality of turbine blades disposed circumferentially about a section of a turbine shaft. The turbine blades of the turbine stage are arranged in a circular pattern about the shaft. The term “shroud ring” relates to a structure for preventing the hot gases from escaping, unimpeded, around the turbine blades of the turbine stage. The structure is disposed radially outward from the turbine stage and may be at least one of cylindrical and conical. In general, there is one shroud ring for each turbine stage. The term “clearance” relates to an amount of distance between a tip of the turbine blade and the shroud ring. The term “inner turbine shell” relates to a structure coupled to the shroud ring. The inner turbine shell surrounds the shroud ring and holds the shroud ring in place. The inner turbine shell may be coupled to several shroud rings as well as nozzles between turbine stages. The term “casing” (or “housing”) relates to a structure surrounding the inner turbine shell. The casing provides structural integrity for the entire rotating machine. The casing also provides a pressure boundary between the external pressure and the internal pressure of the gas turbine. The term “circularity” relates to a degree to which a structure is round. For example, a structure with a high degree of circularity has more roundness than a structure with low circularity. The term “perimetrically” relates to a perimeter. 
         [0024]      FIG. 1  schematically illustrates an exemplary embodiment of a gas turbine  1 . The gas turbine  1  includes a compressor  2 , a combustion chamber  3 , and a turbine  4 . The compressor  2  is coupled to the turbine  4  by a turbine shaft  5 . In the non-limiting embodiment of  FIG. 1 , the turbine shaft  5  is also coupled to an electric generator  6 . (In other embodiments, the turbine shaft  5  may be coupled to other types of machinery such as a compressor or pump.) The turbine  4  includes turbine stages  7 , respective shroud rings  8 , an inner turbine shell  10  and a casing  9 . The inner turbine shell  10  surrounds the shroud rings  8 . In general, the inner turbine shell  10  has a tapered or conical shape to conform to the sizes of the turbine stages  7 . Also depicted in  FIG. 1  is a longitudinal axis  11  in line with the shaft  5  and a radial direction  12  representative of radial directions normal to the shaft  5 . The turbine  4  is described in more detail next. 
         [0025]      FIG. 2  illustrates an exemplary embodiment of the turbine  4 .  FIG. 2A  illustrates an end view of the turbine  4 . Referring to  FIG. 2A , a clearance  20  is shown. The shroud ring  8  shown in  FIG. 2A  encloses a plurality of turbine blades  27  by about 360 degrees. In some embodiments, the shroud ring  8  is built from a plurality of shroud ring segments that include a plurality of arc segments, each arc segment less than 360 degrees. The shroud ring  8  may be made from a material that allows the shroud ring  8  to expand and contract. The arc segments of the shroud ring  8  are affixed to the inner turbine shell  10  such that, as the inner turbine shell  10  expands and contracts, the shroud ring  8  will also expand and contract. The “free” end of the inner turbine shell  10  (affixed to the shroud ring  8 ) contracts radially in accordance with an amount of force imposed radially upon the free end. By controlling the diameter of the inner turbine shell  10  and, thus, the shroud ring  8 , the clearance  20  can be minimized without an increase in a risk of rubbing. 
         [0026]      FIG. 2B  illustrates a side view of the turbine  4 . Referring to  FIG. 2B , the inner turbine shell  10  includes an assembly of sections  21 . The sections  21  are held together by a hoop  22 . The inner turbine shell  10  also includes a plurality of segments  24 . Each segment  24  can move substantially in the radial direction  12 . By moving in the radial direction  12 , each segment  24  can expand or contract the shroud ring  8 . A force imposed on one segment in the radial direction  12  will cause part the shroud ring  8  to expand or contract substantially in the radial direction  12 . A radial force imposed on all the segments in unison (or collectively) will cause the shroud ring  8  to expand or contract and maintain a degree of roundness. In general, as the number of segments  24  increase, the degree of roundness imposed upon the shroud ring  8  also increases. Each segment  24  is separated from an adjacent segment  24  by a slot  23 . The slot  23  affords free displacement between adjacent segments  24  without contact. A hole  25  is provided at one end of the slot  23  to limit stress to the inner turbine shell  10  imposed by moving the segments  24  at least one of radially inward and radially outward, either individually or in unison. 
         [0027]    Referring to  FIG. 2A , an inter-segment seal referred to as a “slot seal  26 ” is provided to seal the opening caused by each slot  23  in the inner turbine shell  10 . The slot seal  26  is disposed between two adjacent segments  24 .  FIG. 3A  illustrates a three dimensional view of the slot  23  and the hole  25 .  FIGS. 3B and 3C  illustrate a detailed view of an exemplary embodiment of the slot seal  26  that seals the slot  23  depicted in  FIG. 3A . The slot seal  26  includes a strip seal  30  welded to an inner pressure seal  31  and an outer pressure seal  32 . In general, the inner pressure seal  31  and the outer pressure seal  32  has folds to provide sealing. Because of the folds, an increase in pressure to the seals  31  and  32  results in an increase of sealing effectiveness. The inner pressure seal  31  seals against hot turbine gases  33  in the turbine  4 . The outer pressure seal  32  seals against any leakage  34  by the inner pressure seal  31 . The slot seal  26  is inserted into a sealing slot  29  in each of the adjacent segments  24  shown in  FIG. 2A  and  FIG. 3A . In the embodiments of  FIGS. 2A and 3A , the sealing slot  29  is generally perpendicular to each slot  23 . However, the sealing slot  29  may be of any angle and shape necessary to optimize sealing. 
         [0028]      FIG. 4  depicts another exemplary embodiment of one segment  24 . In the embodiment of  FIG. 4 , each segment  24  is also one section  21 . Assembling the sections  21  into a circular pattern provides the inner turbine shell  10 . Referring to  FIG. 4A , each segment  24  has a generally curved shape about the longitudinal axis  11 . The segment  24  shown in  FIG. 4  has two flat surfaces to form a flat beam  41 . The flat beam  41  provides for bending of a portion of the segment  24 . The portion that moves is coupled to the shroud rings  8  associated with two turbine stages  7  (depicted at  42  and  43  in  FIG. 4B ). As depicted in  FIG. 4 , the flat beam  41  has a reduced thickness to increase flexibility of the free end of the segment  24  affixed to the shroud ring  8 . 
         [0029]    The teachings provide that the segments  24  move in one of unison and individually. In general, when the segments  24  move individually, each segment  24  is coupled to an actuator.  FIG. 5  illustrates an exemplary embodiment of the inner turbine shell  10  in which each segment  24  is coupled to an actuator  50 . The actuator  50  may be one of an electrical actuator such as a solenoid, an electro-mechanical actuator such as an electrically operated screw, and a mechanical actuator such as a hydraulic piston. The mechanical actuator may be any actuator not including electrical actuation. In one embodiment, the actuator  50  may operate using pressure applied to a piston. In another embodiment, the actuator  50  may operate thermally using the temperature of a gas to cause movement of the actuator  50  as is known to those skilled in the art of actuators. In another embodiment, the actuator  50  may operate chemically. The actuator  50  may move in at least one of along the longitudinal axis  11  and the radial direction  12 . When the actuator  50  moves along the longitudinal axis  11 , a mechanical device is used to convert motion to the radial direction  12 . When the actuator  50  moves along the radial direction  12 , no conversion of motion is required. The actuator  50  may be one of a single acting actuator and a double acting actuator. A single-acting actuator  50  provides force in one direction. The single acting actuator  50  relies on a counteracting force provided by the turbine gases  33  or stiffness of the segments  24  to move in the other direction. A double acting actuator  50  provides force in two directions. 
         [0030]    Moving the segments  24  in unison is used to maintain roundness of the shroud ring  8 . When the segments  24  move in unison, at least one actuator  50  is used to move a device that moves the segments  24  in unison. In one embodiment the device is a ring or sleeve surrounding the segments  24  of the inner turbine shell  10 .  FIG. 6  illustrates a sleeve  60  surrounding the segments  24 . By moving the sleeve  60  along one direction of the longitudinal axis  11 , the conical shape of the inner turbine shell  10  will force the segments  24  to move in unison and contract the shroud ring  8 . By moving the sleeve  60  in the opposite direction, pressure from the turbine gases  33  or stiffness of each segment  24  will cause the segments  24  to move in unison to expand the shroud ring  8 . In one embodiment, the sleeve  60  may make contact directly with the segments  24 . In another embodiment, the sleeve  60  may use at least one of rollers, cams, linear bearings, and mechanical linkages to make contact with the segments  24 . In another embodiment, the sleeve  60  may engage circumferential threads of the inner turbine shell  10 . In this embodiment, as the sleeve  60  is rotated, the sleeve moves along the longitudinal axis  11  to one of expand and contract the shroud ring  8 . Moreover, longitudinal actuation may also be double acting wherein motion of the ring or the sleeve  60  in either direction forces the shroud ring  8  to expand or contract accordingly. 
         [0031]    The segments  24  may also be moved in unison by applying the same pressure of a gas to an outside surface of all the segments  24 . When gas pressure is used to move the segments  24 , the pressure of the turbine gases  33  or stiffness of each segment  24  is used to move the segments  24  in a direction opposing the gas pressure. Movement of the segments  24  can also be accomplished by using the pressure differential between the exterior and the interior of the inner turbine shell  10 . When the exterior pressure of the inner turbine shell  10  is greater than the interior pressure, the net effect is to move the segments  24  radially inward. Conversely, when the exterior pressure of the inner turbine shell  10  is less than the interior pressure, the net effect is to move the segments  24  radially outward. 
         [0032]    Another embodiment of the inner turbine shell  10  uses passive actuation to move the segments  24 . With passive actuation, a relative pressure drop across components internal to the inner turbine shell  10  provides a force for moving the segments  24 . One example of a component causing a pressure drop is a nozzle  70  illustrated in  FIG. 7 . Referring to  FIG. 7 , the nozzle  70  is attached to the inner turbine shell  10 . The nozzle  70  is disposed between two turbine stages  7 . The nozzle  70  redirects gas flow from one turbine stage  7  before the gas flow impinges the next turbine stage  7 . There is a pressure drop across the nozzle  70  proportional to the mass flow rate of the gas turbine  1 . During operation of the gas turbine  1 , the mass flow rate varies with the speed and output of the gas turbine  1 . The maximum pressure drop occurs at full speed and full load. In this embodiment, the maximum pressure drop across the nozzle  70  imparts a maximum bending moment  71  on each segment  24  as shown in  FIG. 7 . The maximum bending moment  71  will cause the segment  24  to move or bend inwardly reducing the diameter of the shroud ring  8 . The stiffness of each segment  24  and a reduction of the pressure drop are used move the segments  24  outwardly increasing the diameter of the shroud ring  8 . The actuator  50  may not be required with passive actuation. In other embodiments, a combination of passive and active actuation may be used. 
         [0033]    A control system known to those skilled in the art of controls may be used to actuate the actuator  50 . The control system may receive information related to the clearance  20  to control the actuator  50 . The information may be provided by a sensor and used in a feedback control loop (referred to herein as “sensor based feedback control”). The sensor may measure at least one of the clearance  20  and parameters related to the clearance  20 . The feedback control loop will control the variable measured by the sensor to maintain a setpoint. Alternatively, the information may be derived from a model of the gas turbine  1  (referred to herein as “model based control”). Generally a detailed analysis and testing are used to provide the information related to determining an amount of the clearance  20  required for different modes of operation. With model based control, sensors are not used to measure the clearance  20  as part of a feedback control loop. 
         [0034]      FIG. 8  presents an exemplary method  80  for controlling a dimension of the shroud ring  8 . The clearance  20  may be controlled by controlling the dimension, such as a diameter, of the shroud ring  8 . The method  80  calls for receiving  81  information from a control system. Further, the method  80  calls for moving  82  one or more of the segments  24  of the inner turbine shell  10  using the information. Further, the method  80  calls for deforming  83  the shroud ring  8  with the one or more of the segments  24 . 
         [0035]    The method  80  may be implemented by a computer program product included in the control system. The computer program product is generally stored on machine-readable media and includes machine executable instructions for controlling a dimension of the shroud ring  8  in the gas turbine  1 . The technical effect of the computer program product is to increase the efficiency of and prevent damage to the gas turbine  1  by controlling the clearance  20 . 
         [0036]    The use of an assembly of the sections  21  provides advantages in maintenance of the gas turbine  1 . Service and maintenance of the gas turbine  1  may include disassembling the hoop  22  and rotating the inner turbine shell  10  about the longitudinal axis  11  to gain access to any section  21 . When the top half of the casing  9  is removed, a selected section  21  may be removed and replaced individually without removing the shaft  5 . Further, service and maintenance may include removing and replacing the entire inner turbine shell  10  without removing the shaft  5  by removing and replacing the sections  21  individually. Along with removing the inner turbine shell  10 , nozzles, such as the nozzle  70 , and the shroud ring  8  may also be removed. By not removing the shaft  5 , realigning the shaft  5  and associated bearings and bearing housings can be eliminated. 
         [0037]    Gas turbines  1  are often built to be disassembled using a bolted flange at the horizontal midplane. The inclusion of the flange along with circular discontinuity associated with the flange may cause the casing  9  to become out-of-round during engine operation due to thermal gradients. In terms of Fourier coefficients, the casing  9  with two halves is termed to have N=2 out-of-roundness. By dividing the inner turbine shell  10  into the sections  21  and assembling the sections  21  by at least one hoop  22 , circularity is improved over the use of flanges. For the same thermal gradient, the out-of-roundness of the inner turbine shell  10  is decreased as the number of sections  21  used to build the inner turbine shell  10  is increased. For example, the inner turbine shell  10  with four sections  21  (N=4) has less out-of-roundness then the inner turbine shell  10  with two sections  21  (N=2). Numerous sections  21  held together with at least one hoop  22  provides a way of reducing out-of-roundness of the inner turbine shell  10 . 
         [0038]    Various components may be included and called upon for providing for aspects of the teachings herein. For example, the control system may include at least one of an analog system and a digital system. The digital system may include at least one of a processor, memory, storage, input/output interface, input/output devices, and a communication interface. In general, the computer program product stored on machine-readable media can be input to the digital system. The computer program product includes instructions that can be executed by the processor for controlling the clearance  20 . The various components may be included in support of the various aspects discussed herein or in support of other functions beyond this disclosure. 
         [0039]    It will be recognized that the various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed. 
         [0040]    While the invention has been described with reference to exemplary embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.