Patent Application
20080213091
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.
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
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.
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.
The invention is to be subsequently explained in more detail based on exemplary embodiments in conjunction with the drawing. In the drawing:
In
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 00349/07 | Mar 2007 | CH | national |
