Abstract:
A three-shell steam turbine is provided. The three-shell steam turbine includes an outer housing, an outer inner housing and an inner inner housing, wherein the outer inner housing is arranged around the inner inner housing, in such a way that a cooling steam chamber is formed in between and a flow duct is formed between the outer inner housing and the rotor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2009/064492, filed Nov. 3, 2009 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 08019820.3 EP filed Nov. 13, 2008. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a turbomachine, comprising a rotor which is mounted such that it can rotate about a rotation axis, an inner inner housing and an outer inner housing which are arranged around the rotor, and an outer housing which is arranged around the inner and the outer inner housings, wherein the outer inner housing is arranged around the inner inner housing along the rotation axis, wherein the outer inner housing is arranged around the inner inner housing along the rotation axis, wherein a first flow area for a flow medium to flow in a flow direction is formed between the inner inner housing and the rotor, and wherein a second flow area is formed between the outer inner housing and the rotor downstream from the first flow area, seen in the flow direction. 
       BACKGROUND OF INVENTION 
       [0003]    By way of example, a turbomachine means a steam turbine. A steam turbine normally has a rotor, which is mounted such that it can rotate, and a housing which is arranged around the rotor. A flow channel is formed between the rotor and the inner housing. The housing in a steam turbine has to be able to carry out a number of functions. On the one hand, the stator blades in the flow channel are arranged on the housing and, on the other hand, the inner housing must withstand the pressures and the temperatures of the flow medium for all load and special operating situations. In the case of a steam turbine, the flow medium is steam. Furthellnore, the housing must be designed such that inputs and outputs, which are also referred to as bleeds, are possible. A further function which a housing must carry out is the capability to allow a shaft end to pass through the housing. 
         [0004]    With the high stresses, pressures and temperatures which occur during operation, it is necessary for the materials to be suitably chosen and for the design to be chosen such that the mechanical integrity and functionality are made possible. For this purpose, it is necessary to use high-quality materials, in particular in the area of the inlet flow and the first stator blade grooves. 
         [0005]    Nickel-based alloys are suitable for applications with fresh steam temperatures of more than 650° C., for example 700° C., since they withstand the loads which occur at high temperatures. However, the use of a nickel-based alloy such as this is associated with new requirements. For example, the costs of nickel-based alloys are comparatively high and, furthermore, the capability to manufacture nickel-based alloys is restricted, for example because the casting capability is restricted. This means that the use of nickel-based materials must be minimized. Furthermore, nickel-based materials are poor heat conductors. The temperature gradients across the wall thickness are therefore so great that thermal stresses are comparatively high. Furthermore, it should be noted that the temperature difference between the inlet and outlet of the steam turbine rises when using nickel-based materials. 
         [0006]    Various concepts are currently being pursued in order to produce a steam turbine which is suitable for high temperatures and for high pressures. For example, it is known for an inner housing structure, which comprises a plurality of parts, to be incorporated into an outer housing structure according to the article by Y. Tanaka et al. 
         [0007]    “Advanced Design of Mitsubishi Large Steam Turbines”, Mitsubishi Heavy Industries, Power Gen Europe, 2003, Dusseldorf, May 6-8, 2003. 
         [0008]    It is likewise known for an inner housing to be formed from two parts, according to DE 10 2006 027 237 A1. 
         [0009]    DE 342 1067 likewise discloses a multi-component inner housing structure, as does DE 103 53 451 A1. 
         [0010]    The object of the invention is to offer a further possible way to design an inner housing such that it is suitable for high temperatures and pressures. 
       SUMMARY OF INVENTION 
       [0011]    This object is achieved by the features of the claims. Advantageous developments are specified in the dependent claims. 
         [0012]    A major idea of the invention is to design a triple-casing steam turbine. The inner housing is in this case fondled into an inner inner housing and an outer inner housing. The inner inner housing is arranged in the area of the inlet-flow area, and must therefore withstand the high temperatures and the high pressures. The inner inner housing is therefore formed from a suitable material, for example from a nickel-based alloy. The flow channel is formed between the inner inner housing and the rotor. The inner inner housing therefore has apparatuses such as grooves, in order to allow stator blades to be fitted therein. An outer inner housing is arranged around the inner inner housing. The essential feature in this case is that a cooling steam area is created between the inner inner housing and the outer inner housing, and cooling medium is applied to this area. The outer inner housing is in this case designed such that it is adjacent to the inner inner housing, seen in the flow direction, and represents a boundary of the flow channel, in which case apparatuses such as grooves are also provided in the outer inner housing, in order to allow stator blades to be fitted. 
         [0013]    A steam which is at a lower temperature and a lower pressure is applied to the outer inner housing, as a result of which the material of the outer inner housing may be less resistant to heat than the material of the inner inner housing. In particular, it is sufficient for the outer inner housing to be formed from a less high-quality material. An outer housing is arranged around the inner inner housing and the outer inner housing. 
         [0014]    In one advantageous development, a flow connection is provided between the inner inner housing and the outer inner housing, and makes it possible to feed a cooling medium from the flow channel into the cooling steam area. This cooling steam is therefore taken from the flow channel, thus allowing the primary stresses and the secondary stresses in the inner inner housing to be kept low. Primary stresses are mechanical stresses which occur as a result of external loads, for example steam pressures, weight forces etc. In contrast, secondary stresses, which are also referred to as theimal stresses, are mechanical stresses which occur as a result of temperature fields which cannot be equalized, or changes in thermal expansions. 
         [0015]    The cooling steam which is located in the cooling steam area can at the same time be used as insulation from the outer inner housing. Furthermore, a water extraction line is provided, which dissipates condensed water which occurs when stationary. In a further advantageous development, the steam turbine is in the form of a twin-flow steam turbine, thus allowing stresses and forces to be optimally matched to one another, for symmetry reasons. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Exemplary embodiments of the invention will be described in the following text with reference to the drawings. These drawings are intended to illustrate the exemplary embodiments, but not to scale, and in fact the drawing, where used for explanatory purposes, is in a schematic and/or slightly distorted form. With respect to additions to the teachings which can be identified directly from the drawing, reference is made here to the relevant prior art. 
           [0017]    In detail, in the drawing: 
           [0018]      FIG. 1  shows a section illustration through a twin-flow steam turbine; 
           [0019]      FIG. 2  shows a partial section illustration through a steam turbine, seen in the flow direction. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0020]    The section illustration shown in  FIG. 1  through the turbomachine  1  essentially comprises an outer housing  2 , an outer inner housing  3 , which is arranged within the outer housing  2 , and an inner inner housing  4 , which is arranged within the outer inner housing  3 . 
         [0021]    A rotor  5  is mounted between the outer inner housing  3  and the inner inner housing  4  such that it can rotate about a rotation axis  6 . A flow channel  7  is formed between the outer inner housing  3  and the rotor  5 , as well as between the inner inner housing  4  and the rotor  5 . For the sake of clarity, individual rotor blades and stator blades are not illustrated in any more detail. The stator blades are arranged on the inner inner housing  4  and on the outer inner housing  3 . The rotor blades are arranged on the rotor  5  such that the thermal energy of fresh steam can be converted to rotation energy in the flow channel  7 . Fresh steam flows via a fresh-steam inlet area, which is not illustrated in any more detail, first of all into a first flow area  8 , which is arranged between the inner inner housing  4  and the rotor  5 . 
         [0022]    The inner inner housing  4  is formed from a nickel-based material. The outer inner housing  3  can be formed from a material which is less resistant to high temperatures. In one alternative embodiment, the inner inner housing  4  is faulted from a steel with a high chromium content, which comprises 9-10% by weight of chromium, wherein the outer inner housing  3  is formed from a material of less high quality than the inner inner housing  4 . 
         [0023]    The steam flowing in the first flow area  8  flows along the flow channel  7  in a flow direction  9 . The steam turbine  1  illustrated in  FIG. 1  is a twin-flow machine, that is to say the steam flows both along a first path and along a second path in the first inlet-flow area  8 . The outer inner housing  3  is adjacent to the inner inner housing  4 . A second flow area  10  is formed between the outer inner housing  3  and the flow channel  7 . The outer inner housing  3  comprises apparatuses, for example grooves, for holding the stator blades. The inner inner housing  4  is suspended in the outer inner housing  3  in a manner which is not illustrated in any more detail. The outer inner housing is formed around the inner inner housing  4  in the area of the first flow area  8 . The outer inner housing  3  is in this case formed around the inner inner housing  4 , with respect to the rotation axis  6 . Outside the first flow area  8 , the outer inner housing  3  is not arranged around the inner inner housing  4  with respect to the rotation axis  6 . The first flow area  8  comprises the flow channel as far as the point at which the inner inner housing  4  ends. A flow connection  11  is arranged between the inner inner housing  4  and the outer inner housing  3  at the junction area between the first flow area  8  and the second flow area  10 . Steam which has been expanded from the flow channel  7  can thus flow via the flow connection  11  into a cooling steam area  12 , which is located between the inner inner housing  4  and the outer inner housing  3 . The location of the flow connection  11  must therefore be appropriately chosen to ensure that a cooling medium at an appropriate temperature and an appropriate pressure flows into the cooling steam area  12  via the flow connection  11 . This cooling medium which flows in the cooling steam area  12  insulates the inner inner housing  4  from the outer inner housing  3 . The outer inner housing  3  essentially comprises a first outer inner housing upper part and a second lower outer inner housing part. The outer inner housing  3  essentially comprises three sections, which are shaped differently. In a first section, the inner housing is therefore designed to be essentially parallel to the flow channel  9 . This first area is designed to be more or less symmetrical, both in the one path and in the other path. In a junction area, which is arranged in the vicinity of the flow connection  11 , the second central area of the outer inner housing  3  is adjacent. This central area is characterized by an alignment which is first of all radial, in order to allow a cooling steam area  12  to be formed between the inner inner housing  4  and the outer inner housing  3 . 
         [0024]    A water extraction line, which is not illustrated in any detail but dissipates condensed water which occurs when the steam turbine is stationary, is provided, inter alia, in the cooling steam area  12 , in order to protect the steam turbine.  FIG. 2  shows an illustration of the steam turbine  1  in the flow direction. The section illustrated in  FIG. 2  is approximately in the center  13  of the steam turbine  1 . The cooling steam which is located in the cooling steam area  12  is passed out of the cooling steam area via a cooling steam outlet line. In this case, the cooling steam outlet line is formed by means of a hole in the outer inner housing  3 . The cooling steam outlet line  14  is, in particular, arranged in the upper part of the outer inner housing  3 . 
         [0025]    In an alternative embodiment, the cooling steam outlet line  14  can likewise be arranged in the lower part of the outer inner housing  3 . This alternative cooling steam outlet line  14  design can likewise be seen underneath the joint  15  in  FIG. 2 .