Patent Application
20130181408
The invention relates to rotary machine seals and, specifically, to seals between stationary and rotating turbine components.
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.
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.
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.
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.
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.
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.
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.
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.
The invention will now be described in connection with the drawings identified below.
With reference to
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
