EP2055902A1

EP2055902A1 - Turbine for a thermal power plant comprising a rotor bucket and a guide bucket

Info

Publication number: EP2055902A1
Application number: EP07021317A
Authority: EP
Inventors: Budimir Rosic; Armin Dr. De Lazzer
Original assignee: Siemens AG; Siemens Corp
Current assignee: Siemens AG; Siemens Corp
Priority date: 2007-10-31
Filing date: 2007-10-31
Publication date: 2009-05-06

Abstract

A turbine (10) for a thermal power plant is provided. The turbine (10) comprises a rotor shaft (12) having a rotational axis (14), a rotor bucket (20) and a guide bucket (22), wherein each bucket (20, 22) is mounted in the turbine (10) and comprises a respective blade section (26, 36) providing a working surface for a propulsion fluid powering the turbine (10), each of the blade sections (26, 36) comprises an edge (30, 40; 32, 39) extending radially with respect to the rotational axis (14), the edges (30, 40; 32, 39) being separated from each other by a gap (41; 241) between the respective blade sections (26, 36), which gap (41) has a given axial extension (d, d'), a first one (20; 22) of the buckets (20, 22) comprises a shroud (28; 28), which is arranged on a radial end portion (27; 37) of its blade section (26; 36) and is configured for delimiting the flow of said propulsion fluid in a radial direction. According to the invention the shroud (28; 38) has a protrusion (42, 142; 242) protruding with respect to the edge (30; 39) of the first bucket (20; 22) by a distance of at least 10% of the given axial extension (d, d') of the gap (41; 241).

Description

Field of the invention

This invention relates to a turbine for a thermal power plant, e.g. a gas turbine or a steam turbine, comprising a rotor shaft having a rotational axis, a rotor bucket and a guide bucket, wherein each bucket is mounted in the turbine and comprises a respective blade section providing a working surface for a propulsion fluid powering the turbine, each of the blade sections comprises an edge extending radially with respect to the rotational axis, the edges being separated from each other by a gap between the respective blade sections, which gap has a given axial extension, and a first one of said buckets comprises a shroud, which is arranged on a radial end portion of its blade section and is configured for delimiting the flow of the propulsion fluid in a radial direction.
Further, the present invention relates to a guide bucket for a turbine of a thermal power plant comprising a foot section and a blade section, wherein the foot section is configured for mounting the guide bucket to a housing of the turbine surrounding a rotor shaft of the turbine having a rotational axis, the blade section provides a working surface for a propulsion fluid powering the turbine and comprises an edge extending radially with respect to the rotational axis, and the foot section has an exposed portion, which is exposed to the propulsion fluid during the operation of the turbine.

Background of the invention

In a turbine for a thermal power plant a propulsion fluid or working fluid, usually in the form of steam or air, is expected to follow a predefined path, the so-called flow-path within the main flow channel of the turbine.
For a typical turbine configuration the propulsion fluid alternately passes stationary rings of guide buckets and rings of rotor buckets, which rotor buckets are mounted on a rotor shaft of the turbine. The propulsion fluid interacts with the blade sections of the buckets and thereby rotates the rotor buckets to propel the rotor shaft. The rotor shaft typically is connected to a generator, which converts the mechanical energy of the rotor shaft into electrical energy. In such a turbine the rotating components, like the rotor shaft and the rotor buckets, are sealed against stationary components, like the housing and the guide buckets. The sealing is required to prohibit the propulsion fluid to bypass the blade sections of the turbine buckets.
The sealing technology typically used is configured such that under all possible boundary conditions of operation contact between the rotating components and the stationary components is avoided to protect the turbine from mechanical damage. Due to comparatively large axial and radial movements of the stationary components and the rotating components relative to one another during operation of the turbine the sealing designs usually are of the so-called non-contacting sealing type. In this sealing type there is no sealing device contacting both components. Instead, residual axial and radial clearances are remaining.
On the other hand, the existence of clearances between the stationary parts and the rotating parts is a source of losses with respect to the possible amount of work that can be extracted from the propulsion fluid, since part of the propulsion fluid is diverted from the main flow channel and can therefore bypass the desired flow path. Conventional sealing designs therefore provide so-called sealing fins on surfaces facing in a radial direction with respect to the rotor shaft, for example on the surface of a shroud of a rotor bucket facing towards the housing of the turbine. Such fins have a throttling effect and therefore limit the amount of leakage fluid being diverted from the main flow channel of the propulsion fluid.

Summary of the invention

It is an object of the present invention to provide a turbine for a thermal power plant of the above mentioned type, which provides an improved power output during operation. Put in different words, it is an object of the invention to increase the amount of work which can be extracted during operation of the turbine from a propulsion fluid having a given pressure and temperature.
The above object is achieved according to the present invention by providing a turbine according to claim 1, a turbine according to claim 13 and a guide bucket according to claim 22. Advantageous embodiments of the invention are described in the dependent claims.
According to the present invention a turbine of the afore mentioned kind is provided, in which the shroud has a protrusion protruding with respect to the edge of the first bucket by a distance of at least 10% of the given axial extension of the gap. The first bucket can be the rotor bucket or the guide bucket of the turbine.
Put in different words, the guide bucket and the rotor bucket are arranged at different locations along the rotational axis of the rotor shaft such that there is a gap between them, which gap has a given axial extension. Typically, the rotor bucket is mounted in a turbine by moving the rotor bucket in an axial direction from an assembly position into a mounted position. The gap referred to above is the gap between the respective blade sections in the mounted position of the rotor bucket. In case the axial extension of the gap varies along the blade sections the given axial extension is preferably determined in the area of a radially outer end of the blade sections. The rotor bucket can be rotated into a position, in which the edge of its blade section facing towards the guide bucket is arranged directly opposite of the neighbouring edge of the guide bucket. In this arrangement the distance between the two neighbouring edges corresponds to the axial extension of the gap.
According to the invention in particular a shroud arranged on a radially outer end of the blade section of the rotor bucket and typically used for connecting several rotor buckets to each other has a protrusion. This protrusion protrudes with respect to the afore mentioned edge of the rotor bucket by a distance of at least 10% of the given axial extension of the gap. Therefore, the protrusion protrudes towards the guide bucket, advantageously towards a foot section of the guide bucket.
The inventive protrusion influences the fluid flow of propulsion fluid entering into a non-contacting seal between the shroud and a housing of the turbine or a non-contacting seal between the shroud and the rotor shaft in case of said protrusion being on a shroud of said guide bucket. The non-contacting seal comprises a so-called sealing cavity extending in a radial direction with respect to the rotational axis between the shroud e.g. and the housing of the turbine. The portion of the propulsion fluid diverted off the main fluid flow and headed for entering into the sealing cavity is referred to as leakage fluid. The leakage fluid is diverted off the main flow of propulsion fluid flowing in the direction of the rotational axis in a main flow channel of the turbine, in which the blade sections of the buckets are arranged.
By providing the protrusion according to the invention mixing effects between the main fluid flow and the leakage fluid are reduced. A vortex typically forming on the inlet side of the fluid cavity is reduced in its momentum or avoided completely by the inventive protrusion. Therefore, a retardation effect of such a vortex on the fluid flow in the main flow channel is reduced. That means, a loss of momentum of the main fluid flow due to the leakage fluid being diverted into the non-contacting seal between the rotor shroud and the housing is reduced. In general, due to the inventive protrusion the flow guidance of fluid entering into the non-contacting seal is improved, which reduces a loss of momentum of the propulsion fluid. Therefore, the overall power output of the turbine is improved.
Further, the above object is achieved according to the present invention by providing a turbine for a thermal power plant comprising a rotor shaft having a rotational axis, and a bucket, which bucket comprises a foot section and a blade section, wherein the blade section provides a working surface for a propulsion fluid powering the turbine and comprises an edge extending radially with respect to the rotational axis, and the foot section has an exposed portion, which is during the operation of the turbine exposed to the propulsion fluid, wherein the exposed portion of the foot section has a recess being recessed with respect to the edge of the guide bucket. The bucket can be a guide bucket or a rotor bucket.
Additionally, the above object is achieved according to the present invention by providing a guide bucket of the afore mentioned kind in which the exposed portion of the foot section has a recess being recessed with respect to the edge of the guide bucket.
In case of the above mentioned bucket being a guide bucket, the foot section is used for mounting the guide bucket to the housing of the turbine. In the mounted state a main portion of the foot section, also referred to as inserted portion, is generally inserted into the housing and therewith not exposed to the propulsion fluid. A generally smaller portion of the foot section adjacent to the blade section sticks out of the housing and is exposed to the propulsion fluid, mostly the leakage fluid, during the operation of the turbine. The above applies correspondingly to the foot section of a rotor bucket, which is used for mounting the bucket in a rotor shaft.
The exposed portion of the foot section has a recess or a depression being recessed with respect to the respective edge of the bucket. The depression therefore receeds behind a line formed by an extension of the edge of the bucket into the area of the foot section. The inventive recess in the exposed portion of the foot section influences the fluid dynamics of the propulsion fluid entering into a sealing cavity forming a non-contacting seal, e.g. between a shroud of a rotor bucket arranged next to the guide bucket and a housing of the turbine. This fluid is referred to as leakage fluid.
The recess has the effect that the leakage fluid diverted from the main stream of propulsion fluid in the turbine gets oriented in a direction in which it can pass into the sealing cavity without additional turning or turbulences. Therefore, mixing effects between the leakage fluid and the propulsion fluid in the main flow channel of the turbine are reduced. Therefore, possible losses in the momentum of the propulsion fluid in the main flow channel are reduced and the power output of the turbine is improved.
Advantageously, the before mentioned inventive turbine having a protrusion in the shroud of the first bucket, like the rotor bucket, comprises an other bucket, like a guide bucket, having the recess described before. The protrusion and the recess in combination have the effect to minimize the mixing effect between the leakage fluid flow and the main fluid to a particularly large extent. A possible vortex developing in the leakage fluid before entering the sealing cavity can thus be minimized in its extent or prevented completely. Further, the provision of the recess in the other bucket reduces the risk of damaging the protrusion of the first bucket during assembly of the turbine. During assembly of the turbine the rotor bucket is axially shifted towards the guide bucket.
In an advantageous embodiment of the turbine according to the invention the protrusion protrudes with respect to the edge of the rotor bucket by a distance of at least 20%, preferably at least 30% of the given axial extension of the gap. Preferably, the protrusion protrudes by a distance of about 50% of the given axial extension of the gap. With the protrusion being dimensioned as mentioned, the mixing effects between leakage fluid entering into the sealing cavity and the propulsion fluid continuing in the main flow channel can be contained particularly well.
It is further advantageous, if the other one of the buckets, in particular the guide bucket comprises a foot section, which is mounted to a housing of the turbine, and the turbine comprises an inlet cavity extending in an axial direction between the shroud and the foot section and being configured for accepting a flow of leakage fluid from the propulsion fluid, which leakage fluid is ducted through a non-contacting seal between the shroud and the housing or the rotor shaft, depending on the type of the other bucket, wherein the protrusion extends into the inlet cavity. Therewith, the flow path of the propulsion fluid diverted from the main flow channel, also referred to as leakage fluid passes through a well defined area of the inlet cavity and is therewith guided such that an interaction with the propulsion fluid in the main flow channel is prevented to a large extent.
It is further advantageous, if the protrusion protrudes in an axial direction of the rotor shaft of the turbine towards the other one of the buckets, in particular the guide bucket, in particular towards a foot section of the other bucket. This way, the leakage fluid diverted from the main fluid flow for entering into the sealing cavity is prevented from interacting with the fluid in the main flow channel in a particularly effective manner.
Is further preferable, if the turbine is configured for being powered with the propulsion fluid flowing in a given flow direction along the longitudinal axis, and if the edge of the first bucket, in particular the rotor bucket, is an upstream edge facing opposite to the flow direction. In particular, the protrusion is protruding with respect to the upstream edge of the rotor bucket in a direction opposite to the flow direction. This way, the leakage fluid diverted from the main fluid flow is redirected in its flow direction basically two times before entering the sealing cavity. Therefore, the path of the diverted leakage fluid follows an s-shape, which reduces the amount of leakage fluid entering into the sealing cavity. This way, less leakage fluid is diverted from the main flow channel of the turbine, which further increases the power output of the turbine.
It is further advantageous, if the protrusion protrudes with respect to the edge of the first bucket, in particular the rotor bucket, by a distance of at least 5%, preferably 15% of an extension of the shroud in the axial direction. Such a protrusion reduces the amount of leakage fluid entering the sealing cavity as well as mixing effects between the diverted leakage fluid and the main fluid flow.
Further it is preferable, if the protrusion is tapered in a direction facing away from the edge of the first bucket, in particular the rotor bucket. Preferably, the extension of the protrusion in a radial direction of the turbine is reduced in a direction facing away from the edge of the first bucket. The taper in the protrusion improves the guidance of the leakage fluid diverted from the main fluid flow and detrimental turbulences in the propulsion fluid are suppressed even more.
In a further advantageous embodiment the protrusion has a surface, which is tilted with respect to the longitudinal axis of the rotor shaft, in particular such that the surface includes an obtuse angle with the edge of the first bucket. The provision of such a tilt improves the flow guidance of the fluid in the main flow channel of the turbine. The fluid is therefore prevented from loosing a considerable amount of momentum due to the diversion of the leakage fluid into the sealing cavity.
It is further advantageous, if the protrusion has a flat surface, which faces in an axial direction and extends parallel to the edge of the first bucket. The flat surface in particular extends perpendicular to the rotational axis. It faces upstream with regards to the flow direction of the propulsion fluid in the main flow channel. Providing the protrusion with such a shape the shroud of the first bucket can be manufactured more cost efficiently.
In a further advantageous embodiment, the shroud comprises a sealing surface, which faces in a radial direction and is configuard to form a non-contacting seal with a housing of the turbine or the rotor shaft, depending on the type of the first bucket, wherein the sealing surface has a stepped profile and/or at least one recess. By providing the stepped profile and/or the at least one recess in the sealing surface, the amount of leakage fluid passing through the non-contacting seal is reduced and therefore the power loss of the turbine is minimized.
It is further advantageous, if the turbine is configured for being powered with the propulsion fluid flowing in a given flow direction in the main flow channel along the rotational axis and the edge of the other bucket, in particular the guide bucket is a downstream edge facing in the flow direction of the propulsion fluid. There-with the recess in the foot section is recessed with respect to the edge in a direction opposite to the flow direction. The leakage fluid diverted from the main fluid flow is therefore essentially redirected twice before entering the sealing cavity. This reduces the amount of leakage fluid being diverted as well as possible mixing effects between the leakage fluid and the fluid in the main flow channel.
It is further advantageous, if the protrusion of the shroud of the other bucket, in particular the rotor bucket, faces towards the recess in the foot section of the neighbouring bucket. This way, between the recess and the protrusion a defined channel for guiding the diverted leakage fluid is formed. Mixing effects between the diverted leakage fluid and the fluid in the main flow channel can thereby be reduced to a large extent.
Further it is preferable, if the recess is recessed with respect to the edge of the first bucket, in particular the guide bucket by a distance of at least 10%, preferably at least 30% of the given axial extension of the gap. With a recess having such dimensions the above mentioned effects on the fluid flow are increased even further.
In a further advantageous embodiment the protrusion of the shroud protrudes with respect to the edge of the first bucket, in particular the rotor bucket, by at least the distance, by which the recess is recessed with respect to the edge of the other bucket, in particular the guide bucket. That means the protrusions sticks out relative to the edge of the blade section of the first bucket to the same extent or more than the recess in the foot section of the other bucket receeds with respect to the edge of the other bucket. This way, the channel formed between the recess and the protrusion becomes relatively narrow, which reduces the amount of leakage fluid being diverted.
It is further preferable, if the recess portion has a rounded shape, in particular a profile in the form of a segment of a circle. With such a shape the fluid is guided particularly smoothly along the recess and possible turbulences affecting the main fluid flow are avoided.

Brief description of the drawings

A detailed description of the present invention is provided herein below with reference to the following diagrammatic drawings, in which:

Fig. 1 is a partial sectional view of a first embodiment of a turbine according to the present invention having a rotor bucket arranged in a mounted position;
Fig. 2 is a partial sectional view of the turbine according to Fig. 1 having the rotor bucket arranged in an assembly position;
Fig. 3 is a partial sectional view of a second embodiment of a turbine according to the present invention; and
Fig. 4 is a partial sectional view of a third embodiment of a turbine according to the present invention.

Description of preferred embodiments

Fig. 1 shows a portion of a turbine 10 in a first embodiment according to the invention. The turbine 10 comprises a rotor shaft 12 having a rotational axis 14. The turbine 10 further includes by a housing 16 surrounding the rotor shaft 12 at a radial distance therefrom. Between the rotor shaft 12 and the housing 16 a main flow channel 18 for ducting a propulsion fluid is provided. The propulsion fluid flows in a given flow direction 19 parallel to the rotational axis 14. The turbine 10 further contains a rotor bucket 20 and a guide bucket 22. The rotor bucket 20 is mounted via a foot section 24 to the rotor shaft 12. The rotor bucket 20 is a single rotor bucket 20 within a row of rotor buckets 20. The row of rotor buckets 20 contains a number of rotor buckets 20 arranged around the circumference of the rotor shaft 12 in a given axial position, wherein each rotor bucket 20 extends radially with respect to the rotor shaft 12. Such a row of rotor buckets 20 extends in a plane perpendicular to the rotational axis 14. Therefore, only one rotor bucket 20 is shown in the drawing of fig. 1.
In an axially shifted position next to the rotor bucket 20 a guide bucket 22 is arranged. The guide bucket 22 also comprises a foot section 34, which is mounted in the housing 16. The guide bucket 22 is also part of a row of guide buckets 22 arranged at the inside of circumference of the housing 16 at one axial position. Each guide bucket 22 extends radially with respect to the rotational axis 14. In the turbine 10 several rows of guide buckets 22 and rotor buckets 20 are arranged in an alternating sequence.
The rotor bucket 20 further comprises a blade section 26 and a shroud 28. The shroud 28 is arranged on the radially outer end of the blade section 26. The shroud 28 connects this end 27 of the blade section 26 with ends 27 of other blade sections within the row of rotor buckets 20 and therefore extends circumferentially with respect to the rotor shaft 12. Also the guide bucket 22 comprises a blade section 36 and a shroud 38, which in this case is arranged at a radially inner end 37 of the blade section 36. During the operation of the turbine 10 the propulsion fluid flowing in the main flow channel 18 in the flow direction 19 interacts with the blade sections 26 and 36 and thereby drives the rotor bucket 20 together with the rotor shaft 12 to rotate around the rotational axis 14.
The blade sections 26 and 36 of the rotor bucket 20 and the guide bucket 22 respectively, each have an upstream edge 30 and 39, respectively, extending radially with respect to the rotational axis 14 and facing oppositely to the flow direction 19 of the propulsion fluid. Correspondingly, each of the blade sections 26 and 36 have downstream edges 32 and 40, respectively, also extending radially and facing in the flow direction 19. The downstream edge 40 of the guide bucket 22 and the upstream edge 30 of the rotor bucket 20 are separated from each other by a gap 41. The gap 41 has an axial extension d being the distance between the respective edges 40 and 30 in the state, in which the rotor bucket 20 is arranged in the mounted position shown in fig. 1.
Further, the shroud 28 of the rotor bucket 20 and the housing 16 are separated from each other by a so-called non-contacting seal. That means the shroud 28 and the housing 16 are separated by a sealing cavity 48. During operation of the turbine 10 part of the propulsion fluid flowing in the main flow channel 18 is diverted into the sealing cavity 48. The portion of the propulsion fluid diverted into the sealing cavity 48 is subsequently referred to as leakage fluid. The leakage fluid splits off the main fluid flow in an area between the foot section 34 of the guide bucket 22 and the shroud 28 of the rotor bucket 20. This area is referred to as inlet cavity 46. From the inlet cavity 46 the leakage fluid enters the sealing cavity 48, wherein a labyrinth-like duct structure is provided. The labyrinth-like duct structure is in part formed by a stepped profile of a sealing surface 50 of the shroud 28 facing towards the inside the sealing cavity 48.
The shroud 28 has a protrusion 42 protruding with respect to the upstream edge 30 of the rotor bucket 20 in an axial direction of the rotor shaft 12 and facing towards the foot section 34 of the guide bucket 22. The protrusion 42 thereby extends about 50% of the axial extension d of the gap 41 with respect to the upstream edge 30. The protrusion 42 has a surface 43, which faces towards the rotor shaft 12 and is tilted with respect to the rotational axis 14 such that the distance between the surface 43 and the rotor shaft 12 narrows in the flow direction 19 of the propulsion fluid. The surface 43 therefore includes an obtuse angle α with the upstream edge 30 of the rotor bucket 20.
The foot section 34 of the guide bucket 22 comprises an inserted portion 34, which is inserted into the housing 16 and is therefore not exposed to the propulsion fluid during operation. Further, the foot section 34 has an exposed portion 35, which sticks out of the housing 16 in a radially inward direction and is therefore exposed to the propulsion fluid during operation of the turbine 10. The exposed portion 35 has a recess 44, which is located on the downstream side of the foot section 34. The recess 44 is recessed with respect to the downstream edge 40 of the guide bucket 22 by a distance of about 30% of the axial extension d of the gap 41. The protrusion 42 faces towards the recess 44 and forms together with the recess 44 a channel for redirecting the leakage fluid after its diversion off the main fluid flow. The recess 44 has a profile in the form of a segment of a circle in a section along a longitudinal plane of the turbine 10, as shown in fig. 1. The recess 44 therefore guides the leakage fluid together with the protrusion 42 smoothly into the sealing cavity 48. The provision of the recess 44 and the protrusion 42 prevents the formation of a vortex, which would cause some of the leakage fluid to re-enter the main flow channel 18 and therefore cause an undesired interaction of the leakage fluid with the main fluid flow slowing the momentum of the propulsion fluid in the main flow channel 18.
While according to Fig. 1 the rotor bucket 20 is arranged in a mounted position, fig. 2 depicts the portion of the turbine 10 shown in fig. 1 with the rotor bucket 20 being arranged in an assembly position. In this position the rotor bucket 20 is shifted in the axial direction toward the guide bucket 22. It can be seen from fig. 2 that the provision of the recess 44 reduces the risk of damaging the protrusion 42 during the assembly process as it provides a dent in the foot section 34 of the guide bucket 22 corresponding to the protrusion 42. At this point it is noted that depending on the operation of the turbine 10 the clearances between the guide bucket 22 and the rotor bucket 20 can also change in reverse when moving the rotor bucket 20 from the mounted position into the assembly position.
Fig. 3 depicts a portion of a second embodiment of a turbine 10 according to the invention corresponding to the upper half of fig. 1. Corresponding parts in the embodiments of figs. 1 and 2 are referred to with the same reference numerals. The embodiment according to fig. 3 differs from the embodiment according to fig. 1 only in the shape the protrusion 42, which in fig. 3 is referred to by reference numerous 142. The protrusion 142 has a flat surface 144, which faces in an axial direction with respect to the rotational axis 14 and extends parallel to the edge 30 of the rotor bucket 20. Further, the foot section 34 in the embodiment according to fig. 3 differs from the foot section 34 in the embodiment according to fig. 1 in that no recess 44 is provided in the embodiment according to fig. 3.
Fig. 4 depicts a portion of a third embodiment of a turbine 10 according to the invention in an area around the rotor shaft 12. Parts corresponding to respective parts in the embodiments of fig. 1 and 2 are referred to with the same reference numbers wherever feasible. The embodiment according to fig. 4 differs form the embodiment according to fig. 1 in that the protrusion 42, which in the embodiment according to fig. 1 is part of the shroud 28 of the rotor bucket 20, according to fig. 4 is referred to as protrusion 242 and is part of the shroud 38 of the guide bucket 22.
Correspondingly, a recess 244 is contained in an exposed portion 225 of the foot section 24 of the rotor bucket 20. The recess is located on the side of the downstream edge 32 of the blade section 26 of the rotor bucket 20. Correspondingly, the protrusion 242 is located on the side of the upstream edge 39 of the blade section 36 of the guide bucket 22. The upstream edge 39 and the downstream edge 32 are separated from each other by a gap 241. The gap 241 has an axial extension d' being the distance between the respective edges 39 and 32 in the state, in which the rotor bucket 20 is arranged in a mounted position.
The protrusion 242 extends about 50 % of the axial extension d' of the gap 241 with respect to the upstream edge 39. The protrusion 242 has a surface 243, which faces away from the rotor shaft 12 and is tilted with respect to the rotational axis 14 such that the distance between the surface 243 and the rotor shaft widens in the flow direction 19 of the propulsion fluid. The surface 243 therefore includes an obtuse angle α with the upstream edge 39 of the guide bucket 22.
The shroud 38 of the guide bucket 22 and the rotor shaft 12 are separated from each other by a so called non-contacting seal. That means, the shroud 38 and the rotor shaft 12 are separated by a sealing cavity 248. During operation of the turbine 10 part of the propulsion fluid flowing in a main flow channel 18 is diverted into the sealing cavity 248. The portion of the propulsion fluid diverted into the sealing cavity 248 is referred to as leakage fluid. The leakage fluid splits off the main fluid flow in an area between the foot section 24 of the rotor bucket 20 and the shroud 38 of the guide bucket 22. This area is referred to as inlet cavity 246. From the inlet cavity 246 the leakage fluid enters the sealing cavity 248, wherein a labyrinth - like duct structure is provided. The labyrinth - like duct structure is in part formed by a stepped profile of a sealing surface 250 of the shroud 38 facing towards the inside of the sealing cavity 248.
It is further noted, that a guide bucket 22 having a foot section 33 according to fig. 1 can be configured with a shroud 38 according to fig. 4. The same applies analogously to the rotor bucket 20 of fig. 1.

Claims

Turbine (10) for a thermal power plant comprising a rotor shaft (12) having a rotational axis (14), a rotor bucket (20) and a guide bucket (22),
wherein each bucket (20, 22) is mounted in said turbine (10) and comprises a respective blade section (26, 36) providing a working surface for a propulsion fluid powering said turbine (10), each of said blade sections (26, 36) comprises an edge (30, 40; 32, 39) extending radially with respect to said rotational axis (14), said edges (30, 40; 32, 39) being separated from each other by a gap (41; 241) between the respective blade sections (26, 36),
which gap (41) has a given axial extension (d; d'), a first one (20; 22) of said buckets (20, 22) comprises a shroud (28; 38),
which is arranged on a radial end (27; 37) of its blade section (26; 36) and is configured for delimiting the flow of said propulsion fluid in a radial direction,
characterized in that said shroud (28; 38) has a protrusion (42; 142; 242) protruding with respect to said edge (30; 39) of said first bucket (20; 22) by a distance of at least 10% of said given axial extension (d; d') of said gap (41; 241).
Turbine according to claim 1,
characterized in that first bucket is said rotor bucket (20) and said shroud (28) is arranged on a radially outer end (27) of its blade section (26).
Turbine according to claim 1,
characterized in that said first bucket is said guide bucket (22) and said shroud (38) is arranged on a radially inner end of its blade section (36).
Turbine according to any one of the preceding claims,
characterized in that said protrusion (42; 142; 242) protrudes with respect to said edge (30; 39) of said first bucket (20; 22) by a distance of at least 20%, preferably at least 30%, of said given axial extension (d, d') of said gap (41; 241).
Turbine according to any one of the preceding claims,
characterized in that said other one (22; 20) of said buckets (20, 22) comprises a foot section (34; 24), which is mounted to a further element (16; 12) of said turbine (10) and said turbine (10), and comprises an inlet cavity (46; 246) extending in an axial direction between said shroud (28; 38) and said foot section (34; 24) and being configured for accepting a flow of leakage fluid from said propulsion fluid, which leakage fluid is ducted through a non-contacting seal between said shroud (28; 38) and said other element (16; 12),
wherein said protrusion (42, 142; 242) extends into said inlet cavity (46; 246).
Turbine according to any one of the preceding claims,
characterized in that said protrusion (42; 142; 242) protrudes in an axial direction towards the other one (22; 20) of said buckets (20; 22), in particular towards a foot section (34) of said other bucket (22; 20).
Turbine according to any one of the preceding claims,
characterized in that said turbine (10) is configured for being powered with said propulsion fluid flowing in a given flow direction (19) along said rotational axis (14), and said edge (30; 39) of said first bucket (20; 22) is an upstream edge (30) facing opposite to said flow direction (19).
Turbine according to any one of the preceding claims,
characterized in that said protrusion (42; 142; 242) protrudes with respect to said edge (30; 39) of said first bucket (20; 22) by a distance of at least 5%,
preferably 15% of an extension of said shroud (28; 38) in the axial direction.
Turbine according to any one of the preceding claims,
characterized in that said protrusion (42; 242) is tapered in a direction facing away from said edge (30; 39) of said first bucket (20; 22).
Turbine according to any one of the preceding claims,
characterized in that said protrusion (42; 242) has a surface (43; 243),
which is tilted with respect to said rotational axis (14), in particular such that said surface (43) includes an obtuse angle (α) with said edge (30; 39) of said first bucket (20; 22).
Turbine according to any one of the preceding claims,
characterized in that said protrusion (142) has a flat surface (144), which faces in an axial direction and extends parallel to said edge (30; 39) of said first bucket (20; 22), and in particular extends perpendicular to said rotational axis (14).
Turbine according to any one of the preceding claims,
characterized in that said shroud (28; 38) comprises a sealing surface (50; 250), which faces in a radial direction and is configured to form a non-contacting seal with a housing (16) and said rotor shaft (12), respectively of said turbine (10),
wherein said sealing surface (50) has a stepped profile and/or at least one recess.
Turbine (10) for a thermal power plant, in particular according to any one of the preceding claims, comprising a rotor shaft (12) having a rotational axis (14), and a bucket (22; 20), which bucket (22; 20) comprises a foot section (34; 24) and a blade section (36; 26), wherein said blade section (36; 26) provides a working surface for a propulsion fluid powering said turbine (10) and comprises an edge (40; 32) extending radially with respect to said rotational axis (14), and said foot section (34; 24) has an exposed portion (35; 225), which is during the operation of said turbine (10) exposed to said propulsion fluid, characterized in that said exposed portion (35; 225) of said foot section (34; 24) has a recess (44; 244) being recessed with respect to said edge (40; 32) of said bucket (22; 20).
Turbine according to claim 13,
characterized in that said bucket is a guide bucket (22) and said foot section (34) is mounted to a housing (16) of said turbine (10), which housing (16) surrounds said rotor shaft (12).
Turbine according to claim 13,
characterized in that said bucket is a rotor bucket (20) and said foot section (24) is mounted to said rotor shaft (12).
Turbine according to any one of claims 13 to 15,
characterized in that said turbine (10) is configured for being powered with said propulsion fluid flowing in a given flow direction (19) along said rotational axis (14) and said edge (40; 32) of said bucket (22; 20) is a downstream edge facing in said flow direction (19).
Turbine according to any one of claims 13 to 16,
characterized in that said recess (44) has a rounded shape, in particular a profile in the form of a segment of a circle.
Turbine according to any one of claims 13 to 17,
characterized in that said turbine (10) is the turbine according to any one of claims 1 to 12 and said bucket (22; 20) is the other one (22; 20) of said buckets (22, 20) according to any one of claims 1 to 12.
Turbine according to claim 18,
characterized in that said protrusion (42; 142; 242) of said shroud (28; 38) of said first bucket (20; 22) faces towards said recess (44; 244).
Turbine according to claim 18 or 19,
characterized in that said recess (44; 244) is recessed with respect to said edge (40; 32) of said other bucket (22; 20) by a distance of at least 10%, preferably at least 30%, of said given axial extension (d, d') of said gap (41).
Turbine according to any one of claims 18 to 20,
characterized in that said protrusion (42; 142; 242) of said shroud (28; 38) protrudes with respect to said edge (30; 39) of said first bucket (20; 22) by at least the distance, by which said recess (44; 244) is recessed with respect to said edge (40; 30) of said other bucket (22; 20).
Guide bucket (22) for a turbine (10) of a thermal power plant comprising a foot section (34) and a blade section (36),
wherein said foot section (34) is configured for mounting said guide bucket (22) to a housing (16) of said turbine (10) surrounding a rotor shaft (12) of said turbine (10) having a rotational axis (14), said blade section (26) provides a working surface for a propulsion fluid powering said turbine (10) and comprises an edge (40) extending radially with respect to said rotational axis (14), and said foot section (34) has an exposed portion (35), which is exposed to said propulsion fluid during the operation of said turbine (10),
characterized in that said exposed portion (35) of said foot section (34) has a recess (44) being recessed with respect to said edge (40) of said guide bucket (22).
Guide bucket according to claim 22,
characterized in that said edge (40) of said guide bucket (22) is a downstream edge (40),
which extends in the mounted state radially with respect to said rotor shaft (12) and faces in a flow direction of said propulsion fluid (19).
Guide bucket according to claim 22 or 23,
characterized in that said recess (44) has a rounded shape, in particular a circular profile.