Title:
Steam Turbine
Kind Code:
A1


Abstract:
A steam turbine (10), especially in the form of a double-flow low-pressure steam turbine, includes a rotor (11) which is rotatably mounted around an axis (21) and which is concentrically enclosed with a spacing by an inner casing (13), forming annular steam passages (28, 29), and which has a multiplicity of rotor blades (12) which project into the steam passages (28, 29), wherein the inner casing (13) supports a multiplicity of stator blades (12) which project into the steam passages (28, 29) and which, for feeding steam to the steam passages (28, 29), has an inlet duct (15) which is directed around the axis (21) and tapers in the flow cross section. With such a steam turbine, the production is simplified by the inner casing (13) being formed as a welded construction, in which blade carriers (14), which delimit the steam passages (28, 29) and are produced as cast parts, are welded to additional forged or rolled steel elements (20) for fastening the stator blades (12′).



Inventors:
Lageder, Heinrich (Baden, CH)
Lukasik, Lucjan (Turgi, CH)
Greim, Ralf (Birmenstorf, CH)
Schreier, Thomas (Neuenhof, CH)
Fischer, Michael (Gippingen, CH)
Application Number:
12/033091
Publication Date:
09/04/2008
Filing Date:
02/19/2008
Primary Class:
International Classes:
F01D25/24; F01D9/00
View Patent Images:



Other References:
BLAIR, M., and MONROE, R. Cast or Forgings? A Realistic Evaluation. Steel Founders' Society of America[online], Engineered Casting Solutions, Spring 2000 [Retrieved on 2012-08-10]. Retrieved from the internet:
Primary Examiner:
BEEBE, JOSHUA R
Attorney, Agent or Firm:
Cermak Nakajima & McGowan LLP (Alexandria, VA, US)
Claims:
What is claimed is:

1. A steam turbine comprising: a rotor rotatably mounted around an axis; an inner casing which concentrically encloses the rotor with a spacing, the spacing forming annular steam passages; a multiplicity of rotor blades projecting into the steam passages; and a multiplicity of stator blades supported by the inner casing and projecting into the steam passages; wherein the inner casing includes an inlet duct for feeding steam to the steam passages directed around the axis and tapers in the flow cross section; wherein the inner casing is a welded construction and comprises cast blade carriers which delimit the steam passages, and additional forged or rolled steel elements supporting the blade carriers, for fastening the stator blades.

2. The steam turbine as claimed in claim 1, wherein the inlet duct, which tapers in the flow cross section, comprises an inlet scroll.

3. The steam turbine as claimed in claim 1, further comprising: a plurality of steam extraction chambers formed in the inner casing, and wherein the steam extraction chambers are formed or delimited by the blade carriers and the steel elements which are connected to them.

4. The steam turbine as claimed in claim 1, further comprising: support rings arranged concentrically to the axis with axial spacing and supporting the blade carriers on their rear side, the support rings stiffening the inner casing; tie rods between the support rings configured and arranged to absorb transverse forces; and wherein the steel elements are welded to the support rings.

5. The steam turbine as claimed in claim 4, wherein the tie rods are welded or screwed to the support rings.

6. The steam turbine as claimed in claim 1, further comprising: at least one radial guide vane arranged in the inlet duct.

7. The steam turbine as claimed in claim 1, wherein the blade carriers are formed of nodular cast iron or cast steel.

8. The steam turbine as claimed in claim 1, wherein the steam turbine is a double-flow low-pressure steam turbine.

Description:

This application claims priority under 35 U.S.C. § 119 to Swiss application No. 00349/07, filed 2 Mar. 2007, the entirety of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of thermal machines, and more particularly to a steam turbine.

2. Brief Description of the Related Art

With large steam turbosets, as are described, for example, in the article by L. Busse et al., “World's highest capacity steam turbosets for the lignite-fired Lippendorf power station”, ABB review 6/1997, p. 13-22 (1997), and are shown in FIG. 2 there, double-flow low-pressure steam turbines are used, in which the steam is fed radially via a central scroll-shaped inlet duct, and then flows out in both directions through the steam passages which are formed between the rotor and the concentric inner casing, and, expanding on the rotor blades of the rotor, performs work. The inlet scroll is integrated into the inner casing, as well as a plurality of steam extraction chambers into which steam, at a specified pressure, can flow from the steam passages through openings in the inner casing, and be extracted. Furthermore, the inner casing, on the sides which delimit the steam passages, serves as a carrier for a multiplicity of fixed stator blades which project into the steam passages.

With the known low-pressure steam turbines, the inner casing, with the inlet scroll and the steam extraction chambers, is divided along a horizontal parting plane into an upper half and a lower half. The two halves are produced in each case as one-piece cast parts, preferably from nodular cast iron. This technique allows the production of large castings with complicated shape (with inlet scroll, steam extraction chambers and exhaust diffuser) at low cost. The stator blade carriers in this case are integrated into the inner casing.

With this solution, it is disadvantageous that such casings are very difficult to produce. The number of manufacturers, therefore, is limited and problems frequently occur. Also, it is difficult to repair such castings if problems occur during casting or during the subsequent machining.

In the past, it has already been proposed (U.S. Pat. No. 1,483,995) to assemble a separate scroll casing for a turbine or pump from one or more central cast parts, which form a central stator blade ring, and plate-like steel elements, which, connected in an overlapping manner, form the scroll casing with the inlet opening. The parts of the device (the rotor) which are equipped with rotor blades, are not enclosed by this casing. In particular, is it also not apparent how the associated stator blades are to be fastened on a casing which encloses the rotor.

A low-pressure turbine section, which is designed in a multi-shell, entirely welded construction, is known from U.S. Pat. No. 3,594,095. A scroll-shaped inlet duct in this case is not provided.

SUMMARY

One of numerous aspects of the invention, therefore, includes creating a steam turbine which addresses the disadvantages of known steam turbines and which, in particular, includes an inner casing which can be more easily and more cost-effectively produced.

According to another, particularly advantageous aspect of the invention, the inner casing is formed as a welded construction, in which the blade carriers, for fastening the stator blades, which blade carriers delimit the steam passages and are produced as castings, are supported by additional forged or rolled steel elements. Since the cast parts with this solution are limited to the blade carriers and, therefore, are formed in a smaller and less complicated manner, fewer fabrication and repair problems result. At the same time, radial and axial deformations of the blade carriers are less than with an integrated cast casing, so that narrower gaps at the blade tips, and therefore higher efficiency of the turbine, are possible.

According to another aspect of the invention, the inlet duct, which tapers in the flow cross section, is formed as an inlet scroll.

Another aspect includes a plurality of steam extraction chambers formed in the inner casing, and the steam extraction chambers are formed or delimited by the blade carriers and the steel elements which are welded to them.

A further aspect of the invention includes that support rings, which are arranged concentrically to the axis with axial spacing and which support the blade carriers on their rear side, are provided for stiffening the inner casing, tie rods are provided between the support rings for absorbing transverse forces, and the steel elements are welded to the support rings.

The tie rods can especially be welded or screwed to the support rings.

Furthermore, it is conceivable and advantageous that at least one radial guide vane is arranged in the inlet duct.

According to yet another aspect, the blade carriers consist of nodular cast iron or cast steel.

BRIEF DESCRIPTION OF THE FIGURES

The invention is to be subsequently explained in more detail based on exemplary embodiments in conjunction with the drawing. In the drawing:

FIG. 1 shows, in longitudinal section, a double-flow low-pressure steam turbine with its inner casing according to an exemplary embodiment of the invention, and

FIG. 2 shows the section along the center plane II-II in FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In FIG. 1, a double-flow low-pressure steam turbine, with its inner casing according to an exemplary embodiment of the invention, is represented in longitudinal section. FIG. 2 shows the section of this turbine in the center plane (plane II-II in FIG. 1). The steam turbine 10 is constructed with its two flows mirror-symmetrical to a vertical center plane 30. It includes a rotor 11, which is rotatable around a horizontal axis 21 and concentrically enclosed with a spacing by an inner casing 13. Outwards widening annular steam passages 28, 29 are formed between the rotor and the inner boundary wall of the inner casing, through which the steam, which is fed radially in the center, flows outwards and, expanding on the rotor blades 12 which are fastened on the rotor 11, performs work.

Rows of fixed stator blades 12′, which are fastened on blade carriers 14 on the root side, alternate with the rows of rotor blades 12. The blade carriers 14 are cast parts and preferably are formed of nodular cast iron or cast steel. They are a part of the inner casing 13 and form the boundary walls for the steam passages 28, 29. The inner casing 13 is altogether formed as a welded construction, in which the blade carriers 14 are supported on the outside in an axially movable manner by forged or rolled steel elements 20, and are sealed by sealing elements. The welded plate-form steel elements 20 not only form a scroll-shaped inlet duct or an inlet scroll 15 in the central section of the steam turbine, but also form a plurality of steam extraction chambers 16 on the two sides of the center plane 30.

The steel elements 20 do not bear directly on the blade carriers 14, but bear via support rings 18, which are arranged concentrically to the axis 21 with axial spacing for stiffening the inner casing 13. Tie rods 17, which by their ends are fastened on the support rings 18, especially screwed or welded, are provided between the support rings 18 for absorbing transverse forces.

The scroll-shaped inlet duct 15 is delimited on the outside by a scroll casing 24 which (on account of the splitting of the inner casing 13 in the parting plane 25) is constructed from simple steel plates. At least one radial guide vane 19, which serves for deflection of the steam which flows in through the steam inlet 23, is arranged in the inlet duct 15.

The inner casing 13 is split in the horizontal parting plane 25. As well as the outer casing 26, it is supported by a support construction 27 which lies beneath it and which in turn bears upon the outer casing 22.

By the combination according to the invention of cast blade carriers and forged or rolled steel plates or steel elements which are welded to them for forming the inner casing, which is provided with an integrated inlet scroll and with integrated steam extraction chambers, significant simplifications and facilitations result during production of the casing, without the mechanical and thermal characteristics being disadvantageously altered.

LIST OF DESIGNATIONS

    • 10 Steam turbine (low-pressure, double-flow)
    • 11 Rotor
    • 12 Rotor blade
    • 12′ Stator blade
    • 13 Inner casing
    • 14 Blade carrier
    • 15 Inlet scroll (inlet duct)
    • 16 Steam extraction chamber
    • 17 Tie rod
    • 18 Support ring
    • 19 Radial guide vane
    • 20 Steel element (forged or rolled)
    • 21 Axis
    • 22 Outer casing
    • 23 Steam inlet
    • 24 Scroll casing
    • 25 Parting plane
    • 26 Outer casing
    • 27 Support construction
    • 28, 29 Steam passage
    • 30 Center plane

While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. The entirety of each of the aforementioned documents is incorporated by reference herein.