Abstract:
A hybrid seal carrier for establishing a seal between a rotating component and a stationary component substantially surrounding the rotating component includes a first seal element held between forward and aft end plates and adapted to be seated within a first slot formed in the stationary component. A second seal element is seated within a second slot formed in one of the forward or aft end plate; wherein said first seal element comprises a plurality of bristles forming a brush seal; and said second seal element comprises at least one honeycomb seal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to rotary machine seals and, specifically, to seals between stationary and rotating turbine components. 
         [0002]    Rotary machines, such as steam and gas turbines, used for power generation and mechanical drive applications are generally large machines consisting of multiple turbine stages. In rotary machines, seals between the stationary and rotating components are used to control leakage between regions of high and low pressures. The efficiency of the rotary machine is directly dependent on the ability of the seals to minimize leakage, e.g., between the rotor and stator. 
         [0003]    Traditionally, rigid labyrinth seals of either a hi-lo, stepped, or straight shaft design are used. These types of seals are employed at virtually all rotor machine locations where leakage between rotating and stationary components must be controlled. In a turbine, for example, this includes interstage shaft seals, rotary end seals, and bucket (or blade) tip seals. Steam turbines of both impulse and reaction designs typically employ rigid, sharp teeth for rotor/stator sealing. While labyrinth seals have proved to be quite reliable, their performance degrades over time as a result of transient events in which the stationary and rotating components interfere, rubbing the labyrinth teeth into a “mushroom” profile and/or abrading the stator surfaces, thus opening the seal clearance. 
         [0004]    Another type of seal used in many environments, including rotary machines, is a brush seal. Brush seals are generally more resistant to leakage than labyrinth seals. A brush seal can also accommodate relative radial movement between fixed and rotational components, for example, between a rotor and a stator, because of the flexibility of the seal bristles. Brush seals also generally conform better to surface non-uniformities. The result of using brush seals is better sustained rotary machine performance than is generally possible with labyrinth seals. 
         [0005]    Abradable honeycomb seal lands are also sometimes employed with labyrinth seals to seal the radial gap between stationary and rotary components in turbines. In addition, brush seals have been combined with honeycomb/labyrinth seals in a hybrid arrangement described in, for example, U.S. Pat. No. 6,827,350. 
         [0006]    There remains a need, however, for effective hybrid seals with a more compact design and that can enable tighter cold gaps between the stationary and rotary turbine components, and that facilitate assembly and/or replacement of the seal components. 
       BRIEF DESCRIPTION 
       [0007]    Accordingly, in a first exemplary but nonlimiting embodiment, the present invention provides a hybrid seal carrier for establishing a seal between a rotating component and a stationary component substantially surrounding the rotating component, the hybrid seal carrier comprising a first seal element held between forward and aft end plates and adapted to be held within a first slot formed in the stationary component; and a second seal element seated within a second slot formed in one of the forward and aft end plates. 
         [0008]    In another aspect, the present invention provides a hybrid seal carrier mounted between a rotating component and a stationary component substantially surrounding the rotating component, the hybrid seal carrier comprising a brush seal held between forward and aft end plates seated within a first substantially T-shaped slot formed in the stationary component; a seal carrier extension portion integrally formed with at least one of the forward and aft end plates and extending in an axial direction, the seal carrier extension portion seated in an axial extension of the first substantially T-shaped slot formed in the stationary component; and at least one additional seal seated within a second substantially T-shaped slot formed in the seal carrier extension portion. 
         [0009]    In still another exemplary but nonlimiting embodiment, the invention provides a hybrid seal carrier assembly for establishing a seal between a rotating component and a stationary component substantially surrounding the rotating component comprising a first seal element held between forward and aft end plates and adapted to be held within a first slot formed in the stationary component; a seal carrier extension portion integrally formed with one of the forward and aft end plates and extending in an axial direction, the seal carrier extension portion adapted to be seated in an axial extension of the first slot formed in the stationary component; and a second seal element seated at least partially within a second slot formed in the seal carrier extension portion; wherein the first seal element comprises a brush seal, and the second seal element comprises at least one honeycomb seal. 
         [0010]    The invention will now be described in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic side elevation of a combined brush/honeycomb seal for use between a turbine stator and a turbine rotor in accordance with an exemplary but nonlimiting embodiment of the invention; 
           [0012]      FIG. 2  is a schematic side elevation of a combined brush/honeycomb seal in accordance with another exemplary embodiment; and 
           [0013]      FIG. 3  is a schematic side elevation of a combined brush/honeycomb seal in accordance with still another exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    With reference to  FIG. 1 , a rotor/stator configuration  10  is partially shown, and includes a rotatable turbine rotor  12  and a surrounding, stator component  14 . 
         [0015]    The rotor  12  is formed to include at least one radially-projecting seal tooth  16  that interacts with the hybrid seal assembly  18  described below. 
         [0016]    The seal carrier assembly (or simply, seal carrier)  18  includes a brush seal component  20  including a radially-oriented front plate  22  and a substantially parallel back plate  24  sandwiched about a plurality of bristles (or bristle pack)  26  (also referred to as a first seal element). It will be appreciated that the seal carrier  18  is made up of arcuate segments which, when installed in the stator  14 , form an annular seal surrounding the rotor  12 . The radially outer portions of the front and back plates  22 ,  24 , are formed to include enlargements or flanges  28 ,  30  that impart an overall T-shape to the brush seal component  20 . This configuration allows the seal carrier  18  to be received within a corresponding substantially T-shaped, annular slot, (or first slot)  32  formed in the stator  14 . 
         [0017]    The front plate  22  engages the radially outer end of the bristle pack  26  along a radially-oriented surface portion  34 , and is offset at  36 , establishing a radial gap  38  along the remainder of the radial length of the bristle pack  26 , thus permitting the bristle pack to flex during operation of the turbine. 
         [0018]    In accordance with one exemplary but nonlimiting embodiment, the seal carrier  18  is formed with an axially-extending side plate  40  (or axial extension), projecting axially from the back plate  24 , and formed with its own radially-oriented T-shaped slot (or second slot)  42 . The T-shaped slot  42  receives a honeycomb seal component  44 . The honeycomb seal component  44  includes a mounting plate or backing  46  that supports the honeycomb seal element (or second seal element)  48 . The honeycomb seal land element  48  is located so as to interact with the rotor seal tooth  16 . Like the overall seal assembly  18 , the honeycomb seal component  44  is also made up of arcuate segments, each seal segment  18  supporting an arcuate honeycomb seal segment. 
         [0019]    In the exemplary embodiment, the tip  27  of the plurality of bristles  26  project radially to the same position, higher position or lower position relative to the radially inward projection of the second seal element  48 . 
         [0020]    In order to accommodate the axially-extending side plate  40 , a groove  50  is formed in the stator to one side of, or adjacent the first T-shaped slot  32 . The stem portion of the second T-shaped slot  50  is formed to include oppositely tapered entry surfaces  52 ,  54 , extending from a narrow neck portion  51  with surface  52  extending further in the radial inward direction so as to enable the back plate  24  to provide extended support for the bristle pack  26 . 
         [0021]      FIG. 2  illustrates an alternative but nonlimiting embodiment of a combined brush/honeycomb seal. For convenience, various of the reference numerals (but with the prefix “1” added) are used to designate corresponding components. In this alternative arrangement the axially-extending side portion or plate  140  is formed such that the second slot  142  is open-ended on one side such that the mounting or backing plate  146  of the honeycomb seal  148  can be bolted directly to the side plate  140  by means of a radial flange  147  that abuts an axial edge  149  of the side plate  140 . The bolt  151  extends through the flange  147  directly into the side plate  140  to thereby secure the honeycomb seal  148  to directly to the seal carrier  118 . Note also that in this arrangement, the brush seal  126  interacts with a raised seal land  113  on the turbine rotor  112  and that the aft plate  130 , rather than having a tapered surface  52  as in the  FIG. 1  embodiment, is now formed with a radial surface  153  which provides full backing for the honeycomb seal  148 . 
         [0022]      FIG. 3  represents further exemplary but nonlimiting embodiment that is similar to the embodiment described above in connection with  FIG. 2  particularly with respect to the modified honeycomb seal backing plate  246 , radial flange  247 , axial edge  249  and bolt  251 . In this embodiment, however, the rotor configuration is more similar to that shown in  FIG. 1  except that the radially-extending tooth  16  has a significantly greater radial height than the tooth  16  in  FIG. 1 . In this arrangement, the aft plate  224  of the brush seal  226  is similar to the aft plate  30  in  FIG. 1  but surface portion  252  is extended and also includes an extended radial surface  253  which provides full backing support for the honeycomb seal  248 . 
         [0023]    In other exemplary embodiments, the axially-extending side plates  40 ,  140  and/or  240  may extend in the opposite axial direction from the front plates  22 ,  122  and/or  222 . 
         [0024]    In still another exemplary embodiment, axially-extending side plates, or axial extensions  40 ,  140  and/or  240 , may extend in opposite directions from both the front plates  22 ,  122  and/or  222  and the back plates  24 ,  124  and/or  224  each axial extension supporting one or more honeycomb seals. 
         [0025]    It will also be appreciated that the axially-extending side plate(s) may support two or more side-by-side seal elements, depending on the number of opposed rotor teeth. 
         [0026]    It will also be appreciated that the axially-extended side plate(s) may support other seals, such as abradable-coating seals as substitutes for, or in addition to, honeycomb seals. 
         [0027]    The seal elements may also be arranged at an angle to the rotor, i.e., with a slant in either axial direction, relative to the rotor. 
         [0028]    The invention described herein provides a compact design which makes possible tighter cold gaps, and provides flow resistance in series which increases the resistance to flow which, in turn, improves performance. The honeycomb or other seal element carried by the seal carrier also acts as a reliable back-up to the adjacent brush seal, and enables easy maintenance and/or replacement of the seals. 
         [0029]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.