Patent Publication Number: US-2012027582-A1

Title: Floating packing ring assembly

Description:
BACKGROUND OF THE INVENTION 
     The disclosure relates generally to rotary turbomachines, and more particularly, to a floating packing ring assembly for use in a turbomachine to avoid transient rubs. 
     In rotary machines such as turbines, seals are provided between rotating and stationary components. For example, in steam turbines, it is customary to provide a plurality of arcuate packing ring segments to form an annular labyrinth seal between the stationary and rotating components. Typically, the arcuate packing ring segments (typically, four to six per annular seal) are disposed in an annular groove in the stationary component concentric to the axis of rotation of the machine and hence concentric to the sealing surface of the rotating component. Each arcuate seal segment carries an arcuate seal face in opposition to the sealing surface of the rotating component. In labyrinth type seals, the seal faces carry a radially directed array of axially spaced teeth, which teeth are radially spaced from an array of axially spaced annular teeth forming the sealing surface of the rotating component. The sealing function is achieved by creating turbulent or flow restriction of an operative fluid, for example, steam, as it passes through the relatively tight clearances within the labyrinth defined by the seal face teeth and the opposing surface of the rotating component. 
     The ability to maintain proper clearances without physical contact between the rotating equipment and stationary components allows for the formation of an effective seal. If this radial clearance between the seal faces of the segments and the opposing seal surfaces of the rotating component becomes too large, less restriction is produced and the sealing action is compromised. Conversely, if the clearance is too tight, the sealing teeth may contact the rotating element, with the result that the teeth lose their sharp profile and tight clearance and thereafter create less restriction, likewise compromising the sealing action. 
     In order to create and maintain a desired seal and to avoid damage to the rotor and packing ring during transient conditions, positive pressure, variable clearance packing rings may be used, for example, a packing ring as disclosed in U.S. Pat. No. 7,384,235 in which a spring assembly is provided which retracts the packing rings radially in and out of the rotor to maintain clearances. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A packing ring assembly for use between a rotating and a stationary component in a turbomachine is disclosed, the assembly including an arcuate packing ring casing, an arcuate packing ring segment positioned at least partially within the packing ring casing, and a resistance component configured to allow movement of the packing ring segment in an axial direction, relative to the rotating component, between a first and second position in response to a pressure condition. In one embodiment, the resistance component allows movement when the pressure condition comprises approximately 30% of the turbomachine load. Also disclosed is an altered surface topography of the rotating component to accommodate variable length teeth extending from the packing ring segment, such that when the packing ring segment is in the first position, a clearance between the packing ring segment and the rotating component is larger than when the packing ring segment is in the second position. 
     A first aspect of the disclosure provides a packing ring assembly for use between a rotating and a stationary component in a turbomachine, the assembly comprising: an arcuate packing ring casing having an annular groove; an arcuate packing ring segment having a mounting portion and a sealing portion, wherein the mounting portion is positioned at least partially within the annular groove and the sealing portion is proximate to the rotating component; and a resistance component configured to allow movement of the packing ring segment in an axial direction, relative to the rotating component, between a first and second position in response to a pressure condition. 
     A second aspect of the disclosure provides a turbomachine comprising: a substantially cylindrical rotating component; and a stationary component including a packing ring assembly, the packing ring assembly comprising: an arcuate packing ring casing having an annular groove; an arcuate packing ring segment having a mounting portion and a sealing portion, wherein the mounting portion is positioned at least partially within the annular groove and the sealing portion is proximate to the rotating component; and a resistance component configured to allow movement of the packing ring segment in an axial direction, relative to the rotating component, between a first and second position in response to a pressure condition. 
     The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which: 
         FIG. 1  is a partial cross-sectional view of an illustrative turbomachine as known in the art. 
         FIG. 2  is a cross-sectional view of a packing ring assembly for use between rotating and stationary components of a turbomachine as known in the art. 
         FIGS. 3-5  show cross-sectional views of a packing ring assembly for use between a rotating and stationary component of a turbomachine according to embodiments of this invention. 
     
    
    
     It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning to  FIG. 1 , a portion of a turbomachine  5 , as known in the art, is shown. Turbomachine  5  includes a plurality of arcuate packing ring assemblies  10  to provide a seal between a rotating component  12  and a stationary component  14 . One such packing ring assembly  10 , as known in the art, is shown in  FIG. 2 . Assembly  10 , as shown in  FIG. 2 , includes at least one arcuate packing ring casing  16 , at least partially positioned within stationary component  14 . Packing ring casing  16  has an annular groove  18 . At least one arcuate packing ring segment  20  is also provided, positioned at least partially within annular groove  18 . Assembly  10  further includes a spring  22  for moving packing ring segment  20 . Spring  22  is positioned within annular groove  18 , between packing ring casing  16  and packing ring segment  20 , on a side of packing ring segment  20  that is radially opposite rotating component  12 . Spring  22  is configured such that it allows packing ring segment  20  to move in a radial direction, i.e., to and from rotating component  12 , as indicated by the arrows in  FIG. 2 . 
     Packing ring segment  20 , shown in  FIG. 2 , further includes a plurality of teeth  24  that extend radially from packing ring segment  20  towards rotating component  12 . As spring  22  moves ring segment  20  to and from rotating component  12 , teeth  24  move to and from rotating component  12 . Rotating component  12  can also include a plurality of protrusions  26  extending from the surface of rotating component  12 . This arrangement is generally referred to as a labyrinth seal, because when packing ring segment  20  is moved closer to rotating component  12 , teeth  24  move closer to protrusions  26 , thereby providing non-contact sealing action between rotating component  12  and packing ring segment  20 , by effectively forcing operative fluid of the turbomachine to travel a tortuous path between teeth  24  and protrusions  26 . 
     Turning to  FIG. 3 , a packing ring assembly  100  according to an embodiment of this invention is disclosed. Packing ring assembly  100  is used between a substantially cylindrical rotating component  102  (partially shown) and a stationary component  104  in a turbomachine (such as turbomachine  5  partially shown in  FIG. 1 ). Stationary component  104  includes at least one arcuate packing ring casing  106  having an annular groove  108 . As shown in  FIG. 3 , packing ring casing  106  has an upstream axial face  122  and a downstream axial face  124 . Annular groove  108  also has an upstream inside axial face  126  (axially opposite upstream axial face  122 ) and a downstream inside axial face  128  (axially opposite downstream axial face  124 ). Packing ring assembly  100  further includes at least one arcuate packing ring segment  110  having a mounting portion  112  and a sealing portion  114 , wherein mounting portion  112  is positioned at least partially within annular groove  108  and sealing portion  114  is proximate to rotating component  102 . 
     Sealing portion  114  can further include at least one sealing member  117  that extends in a radial direction from packing ring segment  110  towards rotating component  102 .  FIG. 3  shows the at least one sealing member  117  as a plurality of teeth  116   a ,  116   b  that extend in a radial direction towards rotating component  102 , but any known sealing means can also be utilized with embodiments of this invention. For example, sealing member  117  can be a leaf seal, a brush seal, a labyrinth seal (including Hi-Lo, straight/smooth, slant/smooth, Hi-Lo/smooth types of labyrinth seals), a finger seal, a compliant plate seal, a shingle seal, a honeycomb seal, an abradable seal, or any other now known or later discovered sealing means between rotating and stationary components. It is also understood that the embodiments of this invention can be applied to various regions of a turbomachine that require sealing, such as root sealing, tip sealing, end packing and mid packing regions of turbomachines. 
     Packing ring assembly  100  further includes a resistance component  118  for allowing movement of packing ring segment  110  in an axial direction, relative to rotating component  102 . In one embodiment, resistance component  118  is positioned in annular groove  108 , between mounting portion  112  of packing ring segment  110  and downstream inside axial face  128  of annular groove  108 . Resistance component  118  may be positioned within annular groove  108  by coupling it to either mounting portion  112  or packing ring casing  106 , or both. As such, resistance component  118  can at least partially support packing ring segment  110  because as a portion of resistance component  118  is attached to packing ring casing  106 , and a portion of resistance component  118  is attached to mounting portion  112 , mounting portion  112  will be suspended, i.e., floated, within annular groove  108 . Packing ring assembly  100  is referred to as a “floating” seal arrangement because packing ring  110  can be positioned, i.e., ‘floated’, in an axial direction in packing ring casing  106  due to a pressure of the operating fluid flowing through the turbomachine and a stiffness of resistance component  118 . Any known means of attaching resistance component  118  can be used, including welding, brazing, adhesive bonding, diffusion bonding, mechanical joining including but not limited to dovetail joints, mortise and tendon joints, flexible and sliding joints, threaded holes, screws or nuts or bolts. 
     Resistance component  118  can comprise any known means that can be configured to allow packing ring segment  110  to move axially between a first and second position, relative to rotating component  112 . Suitable means can include a hydraulic, pneumatic or electromagnetic resistance component that is configured to compress, or move, in response to a pressure condition, to allow packing ring segment  110  to move in an axial direction. For example, as discussed in more detail herein,  FIG. 3  shows a spring  118 , positioned in annular groove  108 , configured such that spring  118  maintains packing ring segment  110  in its first position ( FIG. 3 ) and then, in response to a pressure condition in annular groove  108 , spring  118  allows packing ring segment  110  to move in an axial direction into its second position ( FIG. 4 ). In one example, spring  118  may have a stiffness such that it requires an operative force of approximately 30% of the turbomachine load to compress and allow movement, therefore, the pressure condition could comprise a pressure in annular groove  108  of approximately 30% of the turbomachine load. Another example of a resistance component  118  that could be used is a configuration similar to this embodiment is a bellows, which would compress and decompress similar to a spring. While the use of one resistance component  118  is discussed herein and shown in  FIGS. 3-5 , it is understood that one or more suitable means could be used. Resistance component  118  can be compressive or tensile as mounted. 
     As discussed herein, resistance component  118  can be configured such that, in response to a pressure condition in annular groove  108 , resistance component  118  allows packing ring segment  110  to move in an axial direction. In one embodiment, this pressure condition can be passively controlled. For example, packing ring casing  106  can further include at least one opening  120  extending from upstream axial face  122  of packing ring casing  106  to upstream inside axial face  126  of annular groove  108 , wherein opening  120  is configured to allow operating fluid, OF, of the turbomachine to travel through opening  120  into annular groove  108  to contact mounting portion  112  of packing ring segment  110 . Opening  120  can comprise an opening or hole of any desired shape or configuration and can be positioned in packing ring casing  106  as desired.  FIG. 3  shows one configuration where opening  120  extends substantially axially from upstream face  122  of packing ring casing  106  to upstream inside axial face  126  of annular groove  108 , and resistance component  118  is positioned between mounting portion  112  and downstream inside axial face  128  of packing ring casing  106 , axially opposite opening  120 . While one opening  120  is shown in  FIG. 3 , it is understood that multiple openings  120  can be included in packing ring casing  106  in keeping with this embodiment of the invention. In addition, it is understood that openings  120  can be oriented at different angles than substantially axially (as shown in  FIG. 3 ) through packing ring casing  106 . Also, the location of openings  120  and resistance component  118  can be interchanged based on design needs. 
     As operative fluid (OF) of the turbomachine travels through opening  120  (illustrated by arrow “OF” in  FIG. 3 ) and enters annular groove  108 , a pressure condition within annular groove  108  may change. In response to this pressure condition, resistance component  118  allows packing ring segment  110  to move in an axial direction. For example, resistance component  118  may require a force of approximately 30% of the turbomachine load to allow movement, that is, when the pressure condition comprises a force of the operating fluid of approximately 30% of a load of the turbomachine, resistance component  118  allows movement (for example, by being compressed or decompressed when in the form of a spring or bellows), and packing ring segment  110  can move axially from a first position to a second position ( FIG. 3  to  FIG. 4 ). In other words, when the pressure within annular groove  108  is below approximately 30% of the turbomachine load, resistance component  118  does not allow movement and packing ring segment  110  remains in its first position ( FIG. 3 ). Once the pressure within annular groove  108  reaches approximately 30% of the turbomachine load, resistance component  118  allows movement and packing ring segment  110  moves to its second position ( FIG. 4 ). 
     Turning to  FIG. 4 , packing ring assembly  100  is shown when resistance component  118  has allowed movement and packing ring segment  110  is in its second position. In other words, packing ring segment  110  has moved in an axial direction relative to rotating component  102 . This axial movement of packing ring segment  110  is illustrated in  FIGS. 3 and 4  by the double arrows. When packing ring segment  110  is in the first position ( FIG. 3 ) a clearance, C 1 , between sealing member  117  of packing ring segment  110  and rotating component  102  is larger than the clearance, C 2 , between sealing member  117  of packing ring segment  110  and rotating component  102  when packing ring segment  110  is in the second position ( FIG. 4 ). Therefore, sealing member  117  is closer to rotating component  102  when packing ring segment  110  is in the second position. 
     Turning back to  FIG. 3 , the configuration of sealing member  117  and rotating component  102  can also be modified from existing labyrinth seal configurations according to embodiments of this invention. For example, sealing member  117  can comprise a plurality of teeth  116   a ,  116   b  of variable lengths, and a surface of rotating component  102  can be modified to include a plurality of valleys and peaks to accommodate the varying lengths of teeth  116   a ,  116   b . In other words, as shown in  FIG. 3 , teeth  116  can include a first set of teeth  116   a  having a first length and a second set of teeth  116   b  having a second length, wherein the first length is longer than the second length. The first set of teeth  116   a  (the longer teeth) can alternate with the second set of teeth  116   b  (the shorter teeth) as shown in  FIG. 3 , or can be arranged in any desired pattern. In addition, a surface topography of rotating component  102  can be altered to include at least three different radii, R 1 , R 2  and R 3 , wherein radius R 1  is larger than radius R 2  and radius R 2  is larger than radius R 3 , as illustrated in  FIGS. 3 and 4 . 
     The movement of packing ring segment  110  in an axial direction as discussed herein allows variable length teeth  116   a ,  116   b  and rotating component  102  with a variable surface topography to interact in a way that provides a sealing arrangement between packing ring segment  110  and rotating component  102 . As shown in  FIG. 3 , when packing ring segment  110  is in the first position, first set of teeth  116   a  are proximate to a surface of rotating component  102  having the R 3  radius and second set of teeth  116   b  are proximate to a surface of rotating component  102  having the R 2  radius. As shown in  FIG. 4 , when packing ring segment  110  is moved axially into the second position, first set of teeth  116   a  are proximate to a surface of rotating component  102  having the R 2  radius and second set of teeth  116   b  are proximate to a surface of rotating component  102  having the R 1  radius. Therefore, and as shown in  FIGS. 3 and 4 , when packing ring segment  110  is in the second position ( FIG. 4 ), clearance C 2  between teeth  116   a ,  116   b  is smaller than clearance C 1  between teeth  116   a ,  116   b  when packing ring segment  110  is in the first position ( FIG. 3 ). When describing teeth  116   a ,  116   b  as being “proximate” to a particular surface of rotating component  102 , it is understood that “proximate” in this context means that teeth  116   a ,  116   b  are near, or close to, that particular surface of rotating component  102 , or are substantially radially aligned with that particular surface of rotating component  102 . 
     This movement of the packing ring segment  110  axially between a first position as shown in  FIG. 3  and second position as shown in  FIG. 4  helps in avoiding rubs and severe damage to packing ring segment  110 . This, in turn, helps in reducing the degradation of the turbomachinery section efficiencies under steady state operations. In particular, during turbomachine transient conditions such as start-up, shut-down, speed ramp-up, load ramp-up, forward-flow/reverse flow, trip, turning gear operation and at low loads when the vibration levels are higher, resistance component  118  will maintain packing seal segment  110  in the first position ( FIG. 3 ) to maintain a larger clearance C 1  between packing seal segment  110  and rotating component  102 . Once the turbomachine is in normal operational mode, for example, when the operative fluid moving through the turbomachine reaches a certain pressure, resistance component  118  will allow movement of packing seal segment  110  into the second position ( FIG. 4 ) to create smaller clearance C 2  between packing seal segment  110  and rotating component  102 . 
     In another embodiment, the pressure condition within annular groove  108  can be actively controlled to move packing ring segment  110 . In other words, the pressure condition can be manipulated to be a certain pressure, rather than relying on the natural flow of the operating fluid through opening(s)  120  to create the pressure condition. For example, as shown in  FIG. 5 , a fluid bypass system  129  can be used to direct operating fluid of the turbomachine around packing ring segment  110  in order to control the pressure condition within annular groove  108 . Again, as with the passively controlled system disclosed herein, fluid bypass system  129  can be used to control the pressure condition within annular groove  108  such that once the pressure within annular groove  108  reaches a certain pressure, e.g., approximately 30% of the turbomachine load, resistance component  118  is compressed and allows packing ring segment  110  to move to its second position. 
     Fluid bypass system  129  can comprise a series of pipes or conduits configured to direct the operating fluid of the turbomachine around packing ring segment  110 . For example, as shown in  FIG. 5 , fluid bypass system  129  can include at least one conduit or pipe  130  extending from an inlet  132  at a location in stationary component  104  upstream of packing ring segment  110  to an outlet  134  at a location in stationary component  104  downstream of packing ring segment  110 . Inlet  132  is configured to redirect operating fluid that normally travels through the turbomachine between packing ring segment  110  and rotating component  102 , through fluid bypass system  129 , and around packing ring segment  110 . 
     At least one bypass control valve  136  is located between inlet  132  and outlet  134  for controlling flow through fluid bypass system  129 . Valve  136  may be operated manually or automatically. Automatic operation can be either direct or in conjunction with a machine controller. When valve  136  is open, fluid bypass system  129  offers significantly less resistance to flow as compared to the leakage between sealing members  117  and rotating component  102 . This results in a significant reduction in pressure drop across packing ring segment  110 . An example of an actively activated fluid bypass system is disclosed in U.S. Pat. Pub. No. 2008/0169616. 
     A labyrinth seal is shown in the figures herein to illustrate embodiments of this invention, but as one of skill in the art would understand, packing ring assembly  100  disclosed herein can be used on any type of seal used between rotating and stationary components in a turbomachine, including but not limited to brush seals, leaf seals, finger seals, compliant plate seals, shingle seals, honeycomb seals and abradable seals. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.