Abstract:
A fluid flow machine, in particular a steam turbine, is provided having a piston-equalizing line which conducts a vapour from a fresh vapour region of a second flow duct to a thrust-equalizing piston, wherein the surface of the piston-equalizing line is enlarged, and wherein the inner surface of the piston-equalizing line is enlarged.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2012/065103 filed Aug. 2, 2012, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP11179311 filed Aug. 30, 2011. 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 mounted rotatably about an axis of rotation, an inner housing arranged about the rotor and an outer housing arranged about the inner housing, wherein a first flow region and a second flow region, formed in the opposite flow direction to the first flow region, are arranged between the rotor and the inner housing, wherein the rotor has a thrust-equalizing piston, wherein a piston-equalizing line is formed for introducing steam between the inner housing and the thrust-equalizing piston. 
       BACKGROUND OF INVENTION 
       [0003]    In turbomachines, such as steam turbines, hot fresh steam with comparatively high thermal energy is converted into rotational energy of a rotor. This occurs in a flow duct formed by guide vanes and rotor blades. Modern steam turbines have steam temperatures of over 600° C. Such high temperatures place increased demands on the materials to be used. A steam turbine comprises, substantially, a rotatably mounted rotor, an inner housing arranged about the rotor and an outer housing arranged about the inner housing. The temperature distribution over these three components is very different. Thus, the fresh steam inflow region is subject to particularly high thermal loading, whereas those regions in which the thermal energy of the steam has already been largely converted into rotational energy, and thus the temperature has dropped, are subject to less loading. 
         [0004]    Embodiments of steam turbines which have only one flow duct between the rotor and the inner housing are known. Such steam turbines are usually referred to as single-flow steam turbines. Embodiments of steam turbines which have two flow ducts in one outer housing are known. As a rule, such steam turbines are embodied with one inner housing. The flow directions of the flow ducts can in that case be made to be in opposite directions (reverse flow) or in the same direction (straight flow). 
         [0005]    In operation, as a consequence of the steam pressure, the rotor experiences thrust in one direction. This thrust force must be counteracted, which is done by providing a thrust-equalizing piston upon which steam acts at a predetermined point and which thus exerts a force acting opposite to the thrust force. 
         [0006]    It is known that the steam from the inflow region of the second flow duct is bled via a piston-equalizing line and is introduced into the region of the thrust-equalizing piston. However, this entails that the hot steam from the second flow region is guided in part over the thrust-equalizing piston and thus impinges on the outer housing. The outer housing is thus subject to high thermal loading at this point. It would not be possible to use a standard material for the outer housing at this point. Therefore, more expensive materials, for example GGGSIMO, would have to be used at this point. Such materials are generally comparatively expensive and, moreover, are not easily cast, leading to material defects. 
       SUMMARY OF INVENTION 
       [0007]    It is therefore an object of the invention to prevent this. 
         [0008]    This object is achieved by a turbomachine comprising a rotor mounted rotatably about an axis of rotation, an inner housing arranged about the rotor and an outer housing arranged about the inner housing, wherein a first flow region and a second flow region, formed in the opposite flow direction to the first flow region, are arranged between the rotor and the inner housing, wherein the rotor has a thrust-equalizing piston, wherein a piston-equalizing line is formed for introducing steam between the inner housing and the thrust-equalizing piston, wherein the piston-equalizing line outer surface is embodied enlarged with respect to a pipe outer surface and/or the piston-equalizing line inner surface is embodied enlarged with respect to a pipe inner surface. 
         [0009]    A substantial consideration of the invention is thus to extract energy from the hot steam which issues from the second flow duct and is guided via the piston-equalizing line. This occurs, according to the invention, such that the piston-equalizing line outer surface is embodied enlarged with respect to a pipe of identical diameter. This means that, by virtue of the enlarged surface area of the piston-equalizing line, improved heat exchange with the surroundings is possible, as a result of which the temperature of the steam in the piston-equalizing line can drop. Equally, the piston-equalizing line inner surface of the piston-equalizing line is embodied such that it is enlarged with respect to a conventional pipe inner surface which is embodied smooth, as is known. By virtue of this enlarged surface area, improved thermal interaction between the steam in the piston-equalizing line and the piston-equalizing line occurs here, too. 
         [0010]    In a first advantageous development, outer cooling ribs are arranged on the piston-equalizing line outer surface. The embodiment with cooling ribs, wherein as many cooling ribs should be used as possible, makes excellent thermal equalization possible. In this context, it is also to be considered that the larger the surface area of these outer cooling ribs, the better the thermal interaction. 
         [0011]    In a further advantageous development, the outer cooling ribs are arranged in series in the direction of the piston-equalizing line. It is also the case here that the more outer cooling ribs there are, the better the thermal interaction. Advantageously, the outer cooling ribs are formed as annular disks extending in the radial direction with respect to the direction of the piston-equalizing line. Annular disks are characterized by two surfaces arranged parallel to each other and are thus simple to produce. In an advantageous development, the annular disks are arranged at regular intervals. 
         [0012]    Thermal equalization thus takes place in a homogeneous fashion and, in addition, such a piston-equalizing line can have a simpler and less expensive design. 
         [0013]    In a further advantageous development, inner cooling ribs are arranged on the piston-equalizing line inner surface. These inner cooling ribs are arranged in series in the inner circumferential direction and are embodied in such a manner that they do not markedly influence the flow properties of the steam flowing in the piston-equalizing line. For this reason, these inner cooling ribs are embodied as plates, projections or disks in the longitudinal direction or twisted about the longitudinal direction, arranged at regular intervals in an inner circumferential direction. In this case, too, it is important to consider that the greater the surface area achieved by means of the inner cooling ribs, the better the thermal equalization between the steam flowing in the piston-equalizing line and the piston-equalizing line itself. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will now be explained in greater detail with reference to an exemplary embodiment. Identical reference signs have substantially the same function. 
           [0015]      FIG. 1  shows the cross-sectional view of a steam turbine, 
           [0016]      FIG. 2  shows a perspective view of a piston-equalizing line. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0017]      FIG. 1  shows a steam turbine  1  as an embodiment of a turbomachine. The steam turbine  1  comprises, substantially, a rotor  2  rotatably mounted about an axis of rotation  3 . An inner housing  4  is arranged about the rotor  2 , with a first flow duct  5 , which can also be designated as the high-pressure flow region, being formed between the inner housing  4  and the rotor  2 . The flow direction of the first flow duct  5  is to the left as shown in the representation according to  FIG. 1 . In operation, steam flows, via a HP fresh steam region  6 , through the inner housing  4  into the first flow duct  5 . The steam flowing into the first flow duct  5  via the high-pressure fresh steam region  6  cools down in the flow direction, emerges from the steam turbine  1  via a HP outflow region  7  and, after an intermediate superheater stage, is reintroduced, via an IP inflow region  8  into the steam turbine, to a second flow duct  9 . Finally, the steam flows out of the steam turbine  1  via the intermediate-pressure outflow region  10 . An outer housing  11  is arranged about the inner housing  4 . 
         [0018]    The rotor  2  is formed with a thrust-equalizing piston  12  at the end of the first flow duct  5 . 
         [0019]    In operation, a fluidic connection is established, via a piston-equalizing line  13 , between the IP inflow region  8  and the region of the thrust-equalizing piston  12 . This steam issuing from the second inflow region  8  is comparatively hot steam and is guided between the thrust-equalizing piston  12  and the inner housing  4 . However, in this context some of this comparatively hot steam flows between the thrust-equalizing piston  12  and the inner housing  4  and flows against the outer housing  11  at that point. The outer housing  11  is thus subject to a particularly high thermal load at that point. 
         [0020]    The piston-equalizing line  13  is therefore formed, according to the invention, as shown in  FIG. 2 . Fundamentally, the piston-equalizing line  13  is embodied such that the piston-equalizing line outer surface  14  is embodied enlarged with respect to a pipe outer surface. To that end, as represented in  FIG. 2 , a pipe outer surface  15  is formed with outer cooling ribs  16  (in  FIG. 2 , only the first outer cooling rib is provided with a reference sign). The outer cooling ribs  16  are in this case embodied as annular disks which extend in a radial direction  17 . The radial direction  17  is in this context substantially perpendicular to the direction  18  of the piston-equalizing line. The outer cooling ribs  16  are in this context arranged in series in the direction  18  of the piston-equalizing line. Particularly advantageously, outer cooling ribs  16  are arranged at regular intervals in the direction of the piston-equalizing line. In this context, the outer cooling ribs  16  are embodied such that the largest possible surface area results on the piston-equalizing line outer surface  19 . 
         [0021]    In this context, the piston-equalizing line inner surface  20  is embodied enlarged with respect to a pipe inner surface  21 . To that end, the piston-equalizing line inner surface is formed with inner cooling ribs  22  which are embodied at regular intervals in an inner circumferential direction. The inner cooling ribs  22  are formed as projections extending in a radial direction  17 , which are embodied, so to speak, as disks or longitudinal ribs or as ribs which are twisted about the flow direction  18 . In  FIG. 2 , only one cooling rib  22  is provided with a reference sign. The inner cooling ribs  22  thus extend in the direction  18  of the piston-equalizing line and thus establish good thermal contact between the steam in the piston-equalizing line  13  and the piston-equalizing line  13  itself. 
         [0022]    By virtue of this configuration, according to the invention, of the piston-equalizing line  13 , it is possible to reduce the temperature of the steam in the piston-equalizing line  13 .