Seal arrangement for a rotary machine such as a turbine

The present invention generally relates to rotary machines, such as steam and gas turbines, and, more particularly, is concerned with a seal arrangement for a rotary machine such as a turbine.

Rotary machines, such as steam and gas turbines, used for power generation and mechanical drive applications are generally large machines having multiple turbine stages. In turbines, high pressure fluid flowing through the turbine stages must pass through a series of stationary and rotary components, and seals typically are used between the stationary and rotating components to minimize leakage of the fluid. The efficiency of the turbine is dependent on the ability of the seals to prevent fluid leakage.

Traditionally, one type of seal that is used to control fluid leakage in turbines is a labyrinth seal which has sharp rigid teeth. While the labyrinth seal has proven to be quite reliable, its performance degrades over time. This occurs as a result of transient events in which the stationary and rotating components move radially relative to and thus interfere with one another causing rubbing on the teeth of the labyrinth seal so as to enlarge the clearance between the stationary and rotating components and allow increase of leakage.

Another type of seal that is used in combination with the labyrinth seal to improve leakage control is a brush seal. The brush seal is generally less prone to leakage than the labyrinth seal because the brush seal has seal bristles that can flex and thus better accommodate the relative radial movement between the stationary and rotating components. The brush seal also generally conforms better to surface non-uniformities than does the labyrinth seal. Such combination brush and labyrinth seal arrangements are disclosed in U.S. Pat. No. 5,749,584 to Skinner et al. assigned to General Electric Company, the assignee of the present invention, and U.K. Pat. Application No. 2,301,635 to Hemsley et al assigned to GEC Alsthom Limited.

In one prior art high pressure differential brush seal design shown in FIG. 1, the brush seal 10 includes a layer of bristles 12 disposed or sandwiched between an upstream plate 14 and a downstream plate 16 . The downstream plate 16 is a backing plate provided to prevent deflection of the bristles 12 under the loading from an upstream direction of the flow while an inner portion 12 a of the layer of bristles 12 project beyond the inner edge 16 a of the downstream plate 16 so as to engage the rotor R of the turbine. In order to achieve higher pressure differentials, a pressure balance design is required to relieve the net force holding the layer of bristles 12 against the downstream plate 16 . The one prior art design also includes a seal holder 18 capturing the brush seal 10 and incorporating passageways 20 for directing high pressure steam to a downstream side of the layer of bristles 12 in order to pressurize a cavity 22 present between the layer of bristles 12 and the downstream plate 16 .

A problem, however, exists with such a high pressure brush seal design. The brush seal 10 is bulky in size and thus difficult to retrofit into existing steam turbines where space is limited. Thus, a need exists for an innovation which will provide an effective solution to the aforementioned problem without introducing any new problems in place thereof

The present invention provides a seal arrangement for a rotary machine, such as a turbine, which incorporates a pressure balanced brush seal in a manner designed to satisfy the aforementioned need. In the present invention, the pressure balance element is a radial passage formed through the main seal segment (such as a labyrinth seal segment) which eliminates the need for the brush seal holder of the prior art design. As a result, the overall size of the brush seal is reduced and a more compact brush seal is achieved, permitting the installation of the brush seal in applications where space is limited.

In one embodiment of the present invention, a seal arrangement for a turbine is provided having a main seal segment and a brush seal segment. The main seal segment has an outer periphery, an inner periphery disposed radially inwardly from the outer periphery and a slot defined in the main seal segment between the outer and inner peripheries thereof and being open at the inner periphery and extending toward and terminating in a spaced relationship from the outer periphery. The brush seal segment is disposed in the slot and includes a layer of bristles having opposite outer and inner portions and upstream and downstream sides, an upstream plate having outer and inner portions and being disposed at the upstream side of the layer of bristles and a downstream plate having outer and inner portions and being disposed at the downstream side of the layer of bristles. The outer portion of the layer of bristles is secured between the outer portions of the upstream and downstream plates and the inner portion of the layer of bristles extends beyond the inner portions of the upstream and downstream plates. The downstream plate also has opposite ends, opposite sides respectively facing toward and away from the downstream side of the layer of bristles, and a cavity recessed in the one side thereof facing toward the downstream side of the layer of bristles. The cavity extends between and is terminated by the opposite ends of the downstream plate.

The seal arrangement further includes means for communicating pressure through the main seal segment to the cavity in the downstream plate of the brush seal segment from a source of pressure located exteriorly of the outer periphery of the main seal segment for providing a balance of pressure between the pressure source and the cavity of the downstream plate of the brush seal segment and thereby at the downstream side of the layer of bristles. The means for communicating pressure includes at least one elongated passage formed radially through the main seal segment between the outer periphery and the slot thereof and at least one hole formed through the downstream plate of the brush seal segment between the opposite sides of the downstream plate and communicating with the passage and opening into the cavity in the downstream plate. The hole is formed closer to the outer portion than to the inner portion of the downstream plate.

The main seal segment is arcuate-shaped for placing it end-to-end with other like main seal segments for extending about a turbine rotor. The brush seal segment is arcuate-shaped for placing it end-to-end with other like brush seal segments so as to conform to the arcuate-shaped main seal segment.

FIG. 1 is a cross-sectional view of a prior art labyrinth seal and brush seal arrangement wherein the brush seal has a layer of bristles captured in a seal holder.

FIG. 2 is a cross-sectional view of a seal arrangement of the present invention.

FIG. 3 is a top plan view of the seal arrangement as seen along line 3 — 3 of FIG. 2 .

FIG. 4 is a longitudinal sectional view of the seal arrangement taken along line 4 — 4 of FIG. 2 .

The present invention is a seal arrangement for a rotary machine. Rotary machines include, without limitation, centrifugal compressors, generators, and turbines. Turbines include, without limitation, steam turbines and gas turbines. Turbines have, without limitation, compressor sections and turbine sections. Although the invention is hereinafter described in terms of a seal arrangement for a turbine, it is understood that the invention is not so limited and applies to a seal arrangement for any rotary machine as will be appreciated by those skilled in the art. It is noted that FIG. 2 shows only a portion of a rotary machine, such portion including a housing and a rotor of a turbine.

Referring now to FIGS. 2 to 4 of the drawings, there is illustrated a seal arrangement of the present invention, generally designated 24 , provided between a turbine housing H and a turbine shaft or rotor R. The seal arrangement 24 includes an annular main seal 26 , such as a labyrinth seal, and an annular brush seal 28 . The labyrinth seal 26 has a seal ring 30 disposed about the rotor R separating high and low pressure regions P h , P l , on axially opposite sides of the seal ring 30 . It will be appreciated that while only one seal ring 30 is disclosed, typically multiple-stage labyrinth seals are provided about the rotor R. The seal arrangement 24 also has pressure communicating means 32 formed through the seal ring 30 of the labyrinth seal 26 to the annular brush seal 28 for balancing pressure between the annular brush seal 26 and a pressure source P s located exteriorly of the seal ring 30 . The annular labyrinth seal 26 is mounted in the turbine housing H and extends about the rotor R which is supported by conventional means, not shown, within the turbine housing H.

Each seal ring 30 of the labyrinth seal 26 is formed of an annular array of a plurality of like arcuate-shaped main seal segments 34 placed end-to-end in the housing H extending about the rotor R and have a plurality of radially projecting, axially spaced teeth T. The teeth T are of a hi-lo design for obtaining close clearances with radial projections or ribs P and grooves G on the rotor R. The labyrinth seal 26 functions by placing a relatively large number of barriers, i.e., the teeth T, to the flow of fluid from the high pressure region P h to the low pressure region P l on opposite sides of the brush seal 28 , with each barrier forcing the fluid to follow a tortuous path.

More particularly, each main seal segment 34 has an outer periphery 36 facing away from the rotor R, an inner periphery 38 spaced radially inwardly from the outer periphery 36 and facing toward the rotor R, and a slot 40 defined in the main seal segment 34 between the outer and inner peripheries 36 , 38 and being open at the inner periphery 38 adjacent to the rotor R. The slot 40 is, more particularly, defined by a pair of interior front and back surfaces 42 , 44 and an interior end surface 46 . The front and back surfaces 42 , 44 are spaced from one another along a longitudinal axis A of the rotor R and extend radially relative to the rotor R from the inner periphery 38 of the main seal segment 34 and terminating at outer ends 42 a, 44 a of the front and back surfaces 42 , 44 which are spaced inwardly from the outer periphery 36 of the main seal segment 34 . The interior end surface 46 extends along the longitudinal axis A of the rotor R between the outer ends 42 a, 44 a of the front and back surfaces 42 , 44 , faces toward the rotor R, and is spaced from the outer and inner peripheries 36 , 38 such that the slot 40 at an inner end 40 a is open at the inner periphery 38 of main seal segment 34 adjacent to the rotor R.

The annular brush seal 28 is formed of an annular array of a plurality of like arcuate-shaped brush seal segments 48 placed end-to-end and incorporated as a retrofit to or as original equipment in the labyrinth seal 26 . One or more teeth T of the labyrinth seal 26 are removed and replaced with the brush seal 28 . As seen in FIG. 2, a centrally-located labyrinth seal tooth is removed and the slot 40 is formed in each main seal segment 34 in its place for receiving a respective one of the brush seal segments 48 therein.

More particularly, each brush seal segment 48 is disposed in the slot 40 of one of the main seal segments 34 of the labyrinth seal 26 and includes a layer of bristles 50 and upstream and downstream plates 52 , 54 . The bristles 50 engage the rotor R about the circumference thereof. The layer of bristles 50 has opposite outer and inner portions 50 a, 50 b and upstream and downstream sides 50 c, 50 d. The upstream plate 52 has outer and inner portions 52 a, 52 b and is disposed adjacent to the upstream side 50 c of the layer of bristles 50 . The downstream plate 54 has outer and inner portions 54 a, 54 b and is disposed adjacent to the downstream side 50 d of the layer of bristles 50 . The outer portion 50 a of the layer of bristles 50 is fixedly secured between the outer portions 52 a, 54 a of the upstream and downstream plates 52 , 54 , whereas the inner portion 50 b of the layer of bristles 50 extend beyond the inner portions 52 b, 54 b of the upstream and downstream plates 52 , 54 toward the rotor R.

The downstream plate 54 also has opposite ends 54 c, opposite sides 54 d, 54 e respectively facing toward and away from the downstream side 50 d of the layer of bristles 50 , and a cavity 56 recessed in the one opposite side 54 d of the downstream plate 54 facing toward the downstream side 50 d of the layer of bristles 50 . The cavity 56 extends between and is blocked or terminated by the opposite ends 54 c of the downstream plate 54 .

The means 32 for communicating the balancing pressure from the exterior pressure source P S to the cavity 56 of the downstream plate 54 and thereby to the downstream side 50 d of the layer of bristles 50 includes one or more elongated passages 58 defined through the main seal segment 34 and one or more holes 60 defined through the downstream plate 54 . Each elongated passage 58 extends radially relative to the longitudinal axis A of the rotor R and between the outer periphery 36 of the main seal segment 34 and the interior end surface 46 of the slot 40 therein. Each elongated passage 58 also extends between the outer periphery 36 and the back surface 44 of the slot 40 of main seal segment 34 . Each hole 60 formed through the downstream plate 54 of the brush seal segment 48 between the opposite sides 54 d, 54 e of the downstream plate 54 communicates with one of the passages 58 and opens into the cavity 56 in the downstream plate 54 . Each hole 60 is formed closer to the outer portion 54 a than to the inner portion 54 b of the downstream plate 54 . The holes 60 are spaced apart with the middle hole 60 located approximately centrally between the opposite ends 54 c thereof. High pressure steam is fed through each passage 58 and hole 60 to the cavity 56 in each downstream plate 54 so as to pressurize the cavity 56 and thereby balance the pressure at the downstream side 50 d of the layer of bristles 50 with that of the pressure source P S and at the upstream side 50 c of the layer of bristles 50 . The opposite ends 54 c of the downstream plate 54 block the adjacent ends of the cavity 56 so as to prevent escape of the pressurized steam at the opposite ends 34 a of the main seal segment 34 .

It is thought that the present invention and its advantages will be understood from the foregoing description and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely preferred or exemplary embodiment thereof.