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EP-4577729-B1 - TURBINE ASSEMBLY OF AN AXIAL-FLOW TURBINE AND AXIAL-FLOW TURBINE

EP4577729B1EP 4577729 B1EP4577729 B1EP 4577729B1EP-4577729-B1

Inventors

  • SIMKA, Zdenek
  • PINKAS, Jan
  • Bílý, Miloslav

Dates

Publication Date
20260506
Application Date
20230824

Claims (20)

  1. Turbine assembly of an axial-flow turbine, consisting of a stator wheel and a rotor wheel arranged in the direction of a working medium flow downstream, or turbine stage, - wherein the stator wheel consists of airfoils of blades (1s) arranged side by side around the circumference of the stator wheel to form a stator blade cascade, and a fixing part (2s) fixing the blades (1s) to the stator and also sealing the blade cascade at the outer circumference, wherein the blade cascade is sealed to the rotor at the inner circumference by a shroud (3s) or a stator disc (13s) with a non-contact seal (4s), and - the rotor wheel consists of airfoils of blades (1r) placed side by side around the circumference of the rotor wheel to form a rotor blade cascade, a fixing part (2r) fixing the blades (1r) to the rotor or rotor disc (13r) and which also seals the blade cascade on the inner circumference, wherein on the outer circumference the blade cascade is sealed against the stator by a shroud (3r) with a non-contact seal (4r), characterized in that passages (7r) are formed in the fixing part (2r) of the rotor wheel at least between some adjacent blades (1r) for draining the working medium which has leaked through the non-contact seal (4s), from the axial gap (6s) into the primary flow path, wherein - the inlet of the passage (7r) is located on the side of the fixing part (2r) facing the non-contact seal (4s) of the preceding stator wheel radially between - a virtual circle with the centre on the axis of the turbine assembly and with a radius of R 8 s in − 0.6 * Ar - and a virtual circle with the centre on the axis of the turbine assembly and a radius of R 8 s out + 0.6 * Ar where R8s in is the inner radius of the radial gap (8s) at the last fin of the non-contact seal (4s), R8s out is the outer radius of the radial gap (8s) at the last fin of the non-contact seal (4s), and Ar is the axial distance between the last fin of the non-contact seal (4s) and the side of the fixing part (2r) of the next rotor wheel facing the non-contact seal (4s) of the preceding stator wheel in operation, - the outlet of the passage (7r) exits into the primary flow passage between the blades (1r) at an axial distance of at least 1/5*Br from the leading edge of the blades (1r), where Br is the total axial width of the rotor blade cascade at the point of its connection to the fixing part (2r).
  2. The turbine assembly according to claim 1, characterized in that the passages (7r) are formed between each two adjacent blades (1r) of the rotor wheel.
  3. The turbine assembly according to claim 1, characterized in that the inlet of the passage (7r) is located on the side of the fixing part (2r) facing the non-contact seal (4s) of the preceding stator wheel radially at the level of the gap (8s) at the last fin of the non-contact seal (4s).
  4. The turbine assembly according to claim 1, characterized in that the inlet of the passage (7r) extends in a circumferential direction across the entire width of the blade passage in a circumferential direction between adjacent blades (1r) of the rotor wheel.
  5. The turbine assembly according to claim 1, characterized in that the radial height of the passage (7r) at the inlet exceeds or equals the radial size of the gap (8s) at the last fin of the non-contact seal (4s) (R8s out - R8s in ), preferably is between (R8s out - R8s in ) and 4*(R8s out -R8s in ).
  6. The turbine assembly according to claim 1, characterized in that the passage (7r) outlet cross-section has an area ranging from 20% to 120%, preferably 85%, of the area Fs seal of the gap (8s) at the last fin of the non-contact seal (4s) attributable to one rotor blade.
  7. The turbine assembly according to claim 1, characterized in that the outlet of the passage (7r) exits into the primary flow passage between the blades (1r) at an angle βr, measured in the meridian plane from the blade passage end wall surface at the outlet of the passage (7r), of less than 45°, wherein preferably the angle βr has a magnitude of less than 26°.
  8. The turbine assembly according to claim 1, characterized in that at least another additional fin (10s) of the non-contact seal (4s) is formed on the shroud (3s) of the stator wheel or on the stator disc (13s), and at least one cylindrical surface (11r) is formed on the fixing part (2r) or directly on the rotor or on the rotor disc (13r), forming together with this additional fin the last radial gap (8s) of the non-contact seal (4s) and connecting radially the inner side of this last radial gap (8s) of the non-contact seal (4s) with radially inner side of the inlet of the passage (7r).
  9. Turbine assembly of an axial-flow turbine, consisting of a rotor wheel and a stator wheel arranged in the direction of a working medium flow downstream, - wherein the rotor wheel consists of airfoils of blades ( 1r) arranged side by side around the circumference of the rotor wheel to form a rotor blade cascade, a fixing part ( 2r) fixing the blades ( 1r) to the rotor or rotor disk (13r) and that seals the blade cascade on the inner circumference, wherein the blade cascade being sealed against the stator on the outer circumference with a shroud (3r) with a non-contact seal (4r), and - the stator wheel consists of airfoils of blades (1s) placed side by side around the circumference of the stator wheel to form a stator blade cascade, a fixing part (2s) fixing the blades (1s) to the stator and which also seals the blade cascade on the outer circumference, wherein on the inner circumference the blade cascade is sealed against the rotor by a shroud (3s) or a stator disc (13s) with a non-contact seal (4s), characterized in that at least between some adjacent blades (1s), passages (7s) are formed in the fixing part (2s) of the stator wheel for draining the working medium that has escaped the non-contact seal (4r) from the axial gap (6r) into the primary flow path, wherein - the inlet of the passage (7s) is located on the side of the fixing part (2s) facing the non-contact seal (4r) of the preceding rotor wheel radially between - a virtual circle with the centre on the axis of the turbine assembly and with a radius of R 8 r in − 0 . 6 * As - and a virtual circle with the centre on the axis of the turbine assembly and a radius of R 8 r out + 0 . 6 * As where R8r in is the inner radius of the radial gap (8r) at the last fin of the non-contact seal (4r), R8r out is the outer radius of the radial gap (8r) at the last fin of the non-contact seal (4r), and As is the axial distance between the last fin of the non-contact seal (4r) and the side of the fixing part (2s) of the following stator wheel facing the non-contact seal (4r) of the preceding rotor wheel in operation, - the outlet of the passage (7s) exits into the primary flow passage between the blades (1s) at an axial distance of at least 1/5*Bs from the leading edge of the blades (1s), where Bs is the total axial width of the stator blade cascade at the point of its connection to the fixing part (2s).
  10. The turbine assembly according to claim 9, characterized in that passages (7s) are formed between each two adjacent blades (1s) of the stator wheel.
  11. The turbine assembly according to claim 9, characterized in that the inlet of the passage (7s) is located on the side of the fixing part (2s) facing the non-contact seal (4r) of the preceding rotor wheel radially at the level of the gap (8r) at the last fin of the non-contact seal (4r).
  12. The turbine assembly according to claim 9, characterized in that the inlet of the passage (7s) extends in a circumferential direction across the entire width of the blade passage in a circumferential direction between adjacent blades (1s) of the stator wheel.
  13. The turbine assembly according to claim 9, characterized in that the radial height of the passage (7s) at the inlet exceeds or equals the radial size of the gap (8r) at the last fin of the non-contact seal (4r) (R8r out - R8r in ), preferably is between (R8r out - R8r in ) and 4*(R8r out -R8r in ).
  14. The turbine assembly according to claim 9, characterized in that the outlet of the passage (7s) extends in a circumferential direction across the entire width of the blade passage in a circumferential direction between adjacent blades (1s) of the stator wheel.
  15. The turbine assembly according to claim 14, characterized in that the radial height of the passage (7s) at the outlet to the primary blade passage is 0.25 to 1.1 times its radial height at the inlet, preferably 70% of its radial height at the inlet.
  16. The turbine assembly according to claim 9, characterized in that the outlet of the passage (7s) exits into the primary flow passage between the blades (1s) at an axial distance of at least 1/2*Bs from the leading edge of the blades (1s), preferably between 0.64*Bs and 0.86*Bs from the leading edge of the blades (1s), where Bs is the total axial width of the stator blade cascade at the point of its connection to the fixing part (2s).
  17. The turbine assembly according to claim 9, characterized in that the outlet cross-section of the passage (7s) has an area ranging from 20% to 120%, preferably 85%, of the area Fr seal of the gap (8r) at the last fin of the non-contact seal (4r) attributable to one stator blade.
  18. The turbine assembly according to claim 9, characterized in that the outlet of the passage (7s) exits into the primary flow passage between the blades (1s) at an angle βs, measured in the meridian plane from the blade passage end wall surface at the outlet of the passage (7s), of less than 45°, wherein preferably the angle βs has a magnitude of less than 26°.
  19. The turbine assembly according to claim 9, characterized in that at least another additional fin (10r) of the non-contact seal (4r) is formed on the shroud (3r) of the rotor wheel, and a cylindrical surface (11s) is formed on the fixing part (2s) or directly on the stator, forming together with this additional fin the last radial gap (8r) of the non-contact seal (4r) and connecting radially the outer side of this last radial gap (8r) of the non-contact seal (4r) with radially outer side of the inlet of the passage (7s).
  20. Axial-flow turbine, characterized in that it comprises at least one turbine assembly according to claim 1 and/or at least one turbine assembly according to claim 9.

Description

TECHNICAL FIELD The present invention concerns all types of axial-flow turbines in general, both steam turbines (where the working medium is steam) and gas turbines in general (where the medium may also be flue gas, gas, air, etc.), in all variants thereof, and it particularly concerns a turbine assembly of an axial-flow turbine and an axial-flow turbine. The flow path of the axial-flow turbine consists of individual axial stages. The stages are formed alternately by consecutive wheels of stator and rotor. The stator wheel consists mainly of a blade cascade which consists of individual airfoils placed side by side around the circumference of the stator wheel. On the outer circumference, the airfoils are fixed to the stator with the fixing part(s). The fixing part can either be integral (the ring in the assembled stator wheels) or each blade can have its own partial fixing part (in milled blades). On the inner diameter, the stator blade cascade is sealed against the rotor using a shroud or a disc with a non-contact seal. The stator wheel shroud can be either integral for up to half of the cascade or (for milled blades) it can be integral for each blade separately. The rotor wheel consists mainly of a blade cascade which consists of individual airfoils placed side by side around the circumference of the rotor wheel. On the inner circumference, the airfoils are firmly fixed by fixing parts to the rotor or rotor disc. On the outer diameter, the rotor blade cascade is sealed against the rotor using rotor shroud with a non-contact seal. The rotor wheel shroud can be either common for several blades or integral for each blade separately in the case of milled blades. The stator blades are designed to accelerate the flow of the working medium and direct it in the circumferential direction, the rotor blades are designed to capture the spinning flow and transfer the forces caused by flowing around to the rotor. The blade passages of the stator and rotor blade cascade together with the axial gaps between the blade cascades form the primary flow path. The mounting arrangement of the rotor blades affects the stage design. The stage can be either of the drum type, where the blades forming the rotor wheel are attached directly to the rotor body, or it can be of the wheel or disc type, where the disc is formed on the rotor and then the blades attached to it. Drum-type stages are usually used for higher reaction stages, whereas wheel-type stages are usually used for low reaction stages. The rotor must be allowed to rotate relatively with respect to the stator and possibly also have some axial movement, e.g. due to different deformations caused by thermal expansion. Due to the requirements for long durability, non-contact seals are usually used for this purpose which must have a certain gap or clearance. The gap/clearance is to be as minimal as possible, but cannot be closed completely. Therefore, manufacturers try to reduce the flow coefficient of the non-contact seal as much as possible. Typical representatives of such non-contact seals are labyrinths of various types - staggered labyrinth, look through labyrinth, fin-fin type seals. Non-contact seals also include honeycomb seals which work on a similar principle and can, therefore, be also considered as labyrinth seals, only the labyrinth fins have a more complicated shape. The non-contact seal together with the axial gaps in front and behind it, which connects them to the primary flow path, form the secondary flow path. Thus, a small amount of working medium, called secondary flow, flows through the non-contact seal (as opposed to the primary flow passing through the blades). Secondary flows are a source of losses. The losses are caused by the leak itself - the medium bypassing the stator blades through seal does not accelerate to the required velocity, the medium bypassing the rotor blades cannot exert force on them and thus drive the rotor. Further losses occur at the point where the secondary flow of media leaked through the seal reenters into the primary flow. This is because there is a mixing of flows that have different direction and velocity. In addition, there is an unfavourable interaction of the two flows in the sensitive region upstream of the following blade cascade. This is where secondary vortexes are formed that can be reinforced by this interaction. All these losses depend on the amount of medium flowing through the secondary flows. Therefore, one of the ways to reduce these losses is to reduce the flow rate through non-contact seals. However, this reduction has its limits due to the need for reliable operation throughout the operating range of the machine. STATE OF THE ART In the standard design of the stage, the non-contact seal usually exits into the axial gap (the "cavity") between the shroud or disc and the blade fixing part in the direction of the main flow of the next wheel. The secondary flow exits the non-contact seal at a relatively high velocity