Abstract:
The invention relates to a gas turbine. The aim of the invention is to provide an axial sealing between a vane ring and a moving blade ring, which has an excellent sealing effect, is easy to install and inexpensive to produce. For this purpose, a sealing element is used that extends across at least a fourth of the hot gas channel circumference. Preferably, said sealing element extends across approximately half the circumference and is inserted in grooves of the vane support and the vane platforms.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is the U.S. National Stage of International Application No. PCT/EP2004/007333, filed Jul. 5, 2004 and claims the benefit thereof. The International Application claims the benefits of European Patent application No. 03018240.6 EP filed Aug. 11, 2003. All of the applications are incorporated by reference herein in their entirety. 
   FIELD OF THE INVENTION 
   The invention relates to an axial gas turbine, in which guide vane rings and rotor blade rings follow one another in the axial direction in the hot-gas duct. These blade/vane rings are acted on by cooling air from various pressure levels. A sealing element is provided for forming a seal between the individual pressure levels. 
   BACKGROUND OF THE INVENTION 
   An axial gas turbine comprises a compressor, a combustion chamber and a turbine part. In the compressor, combustion air is highly compressed, and this highly compressed combustion air is then burnt with fuel in the combustion chamber. The hot gas which is formed is passed through a hot-gas duct in the turbine part. Guide vane rings and rotor blade rings follow one another alternately in the turbine part. Guide vanes and rotor blades are arranged adjacent to one another in the circumferential direction in each of these blade/vane rings. 
   The temperatures in a gas turbine of this type may reach levels which exceed the melting points of the materials that can be used and/or reduce the hot strength of the materials to an unacceptable extent. For this reason, the components in the hot-gas duct are often cooled with a cooling medium. For this purpose air is generally branched off from the compressor to act as cooling air. The demand for cooling drops along the direction of flow in the hot-gas duct. For this reason, cooling air at a lower pressure level than cooling air for front turbine stages is sufficient to cool rear turbine stages. To minimize the consumption of cooling air, since it reduces the efficiency of the gas turbine, the axially different turbine stages, i.e. the different blade/vane rings, are acted on by cooling air from different pressure levels. Blade/vane rings which lie further forward in the direction of flow are supplied with compressed air at a higher pressure than blade/vane rings lying further to the rear in the direction of flow. 
   In view of this different supply of cooling air even to blade/vane rings positioned next to one another, it is necessary to form a seal between the different pressure levels. A seal is also required in order to prevent hot gas from being mixed into the cooling air and therefore to prevent a reduced cooling action. 
   U.S. Pat. No. 5,833,244 shows a gas turbine sealing arrangement. The sealing of two adjacent blade/vane rings is in this case achieved by a labyrinth sealing system. Individual sealing elements are arranged in grooves of rotor disks. These sealing segments have tooth-like elevations which run transversely to the direction of flow, are arranged in succession in the axial direction and are arranged opposite a guide vane tip. Arranging these segments next to one another in the circumferential direction provides a labyrinth sealing system which runs all the way around the circumferential direction and is in particular also suitable for sealing in large gas turbines. 
   The sealing system located between two blade/vane rings in the axial direction is distinct from a sealing arrangement which acts in the circumferential direction between blades/vanes of a single blade/vane ring. A circumferential seal of the latter type is used to shield the hot gas flowing in the hot-gas duct from the rotor discs or guide vane carriers. Arrangements of this type are disclosed, for example, in U.S. Pat. No. 5,785,499 or U.S. Pat. No. 6,273,683. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a sealing system for forming a seal between two blade/vane rings of a gas turbine which are at different pressure levels, the sealing system having a particularly good sealing action and at the same time being simple to install and inexpensive. 
   According to the invention, this object is achieved by an axial gas turbine directed along a turbine axis and comprising a compressor, a combustion chamber and a turbine part, with guide vane rings and rotor blade rings being arranged in axial succession in a hot-gas duct in the turbine part, a hot gas flowing through the hot-gas duct in operation, and the guide vane rings and rotor blade rings being cooled by cooling air, the pressure level of which decreases in the direction of flow of the hot gas, wherein a sealing element, which seals off the different pressure levels with respect to one another and extends as a single piece around at least a quarter of a circle running perpendicularly on the turbine axis as its center point, is arranged between at least one guide vane ring and a directly adjacent rotor blade ring. 
   Therefore, the invention for the first time adopts the route of enabling a sealing element to extend over a great circumferential distance in order to form a seal in the axial direction. This considerably improves the sealing action, since sealing boundaries running in the circumferential direction are reduced. Furthermore, the reduction in the number of components facilitates installation. The reduction in the number of components also produces a less expensive design. 
   It is preferable for the sealing element to extend over half the circle. Consequently, only two sealing elements are required for each stage that is to be sealed off. In the case of a gas turbine casing which comprises two halves engaging in one another at a joint, the sealing elements are preferably arranged in such a way that in each case one sealing element extends along one of the two housing halves. This in particular also facilitates dismantling or exchange in the event of servicing being carried out on the gas turbine. 
   Preferably, the sealing element is formed as an annular metal sheet with a surface extending in the radial direction and having an outer edge and an inner edge. An annular metal sheet of this type is particularly simple to produce in manufacturing technology terms. 
   Also preferably, the outer edge is arranged in respectively corresponding platform grooves, which in the side remote from the hot-gas duct of a respective platform of guide vanes of the guide vane ring or of a guide ring located radially outside the rotor blade ring, and the outer edge is arranged in a carrier groove running within a guide vane carrier. Guide vanes have a main blade part adjoined by a platform. This platform is used to shield the guide vane carrier from the hot gas. The platform is adjoined by a securing device, by which the guide vane is secured in the guide vane carrier. A guide vane ring is axially adjoined by a rotor blade ring, which on the rotor side likewise routes the hot gas by means of platforms on the rotor blades. That surface of the hot-gas duct which is adjacent to the guide vane carrier is shielded from the hot gas by guide rings located opposite the rotating blade tips of the rotor blades. The outer edge of the annular metal sealing sheet can be guided by grooves in the guide vanes of a guide vane ring. The outer edge is guided in a carrier groove running within the guide vane carrier. 
   Therefore, to install the sealing element, it is merely necessary for it to be inserted into the abovementioned grooves or for the sealing element to be placed into the guide vane carrier groove and then the guide vanes are fitted in such a way that the sealing element comes to lie in the platform grooves. 
   Preferably, the sealing element is clamped using a screw which presses on its surface and presses the sealing element onto the opposite platform groove side wall and carrier groove side wall. This active fitting of the sealing element results in reliable sealing which is independent of the operating state. It is also preferable for the sealing element to be clamped using a multiplicity of screws, preferably one screw per blade or vane of a blade/vane ring. 
   Guide vanes generally have a hooked formation, by means of which they are hooked into the guide vane carrier. A hooked formation of this type then defines an axial fixed point by means of an axial bearing surface between the hooked formation and the guide vane carrier. It is preferable for the sealing element to be arranged in the region of the axial fixed points. This position of the sealing element is advantageous in particular with the above-described active formation of the sealing element, since thermal displacements are at a low level in the region of the axial fixed point. 
   If an active formation is not selected for the sealing element, the sealing element is preferably arranged remote from the region of the axial fixed points. On account of the considerable temperature differences when stationary and in the operational state, this results in considerable thermally induced displacements of the vane platform or guide rings with respect to the guide vane carrier. The loose insertion of the sealing element into the platform or guide vane carrier grooves results in a passive formation here specifically on account of these thermal displacements. During the thermal displacement, the sealing element is pressed onto the groove walls in such a way that a reliable sealing is not achieved. Also preferably, in addition to the groove walls, a further projection running in the circumferential direction is arranged in the guide vane carrier as an axial bearing surface for the sealing element. 
   With the active formation of the sealing element described above, it is preferable first of all to complete the guide vane ring during assembly by installing the guide vanes, and thereafter to fit the adjacent guide rings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in more detail by way of example with reference to the drawings. Identical reference designations have the same meaning throughout the various figures. 
     In the drawing, in some cases diagrammatically and not to scale: 
       FIG. 1  shows a gas turbine, 
       FIG. 2  shows a cross section through the turbine part of a gas turbine, 
       FIG. 3  shows an excerpt of a longitudinal section through the hot-gas duct of the gas turbine, 
       FIG. 4  shows an enlarged view with a sealing element from  FIG. 3 , 
       FIG. 5  shows a further excerpt from a longitudinal section through a gas turbine, and 
       FIG. 6  shows an enlarged view incorporating a sealing element from  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a gas turbine  1 . In succession along a turbine axis  10 , the gas turbine  1  has a compressor  3 , a combustion chamber  5  and a turbine part  7 . The compressor  3  and the turbine part  7  are arranged on a common shaft  9  extending along the turbine axis  10 . A hot-gas duct  12  which widens conically runs within the turbine part  7 . Guide vanes  11  and rotor blades  13  project into this hot-gas duct  12 . A multiplicity of guide vanes  11  is arranged circumferentially adjacent in a guide vane ring  14 . A multiplicity of rotor blades  13  are arranged circumferentially adjacent in a rotor blade ring  16 . Guide vane rings  14  and rotor blade rings  16  alternate with one another in the hot-gas duct  12 . 
   When the gas turbine  1  is operating, ambient air is sucked in by the compressor  3  and compressed to form compressor air  15 . The compressor air  15  is fed to the combustion chamber  5 , where it is burnt with a fuel to form a hot gas  17 . The hot gas  17  flows through the hot-gas duct  12  and therefore flows passed the guide vanes  11  and the rotor blades  13 . This sets the shaft  9  in rotation, since the rotor blades  13  take up kinetic energy from the hot gas  17  and transmit it to the shaft  9 , to which they are fixedly connected. The energy obtained from the hot gas  17  in this way can, for example, be transmitted to a generator for power generation. 
     FIG. 2  shows a cross section through the hot-gas duct  12 . Part of the rotor blade ring  16  and part of the guide vane ring  14  are illustrated. A sealing element  35 , which is designed as an annular metal sheet, extends between the guide vane ring  14  and the rotor blade ring  16  in the circumferential direction over half of a circle  41  running perpendicular to the turbine axis  10 . A sealing element  35  of the same type runs over the second half of the circle  41 , so that the two sealing elements  35  form a continuous circle. The two sealing elements  35  meet one another at a joint  42 . The joint  42  corresponds to a joint (not illustrated in more detail) dividing the gas turbine casing surrounding the hot-gas duct  12  in half. The sealing element  35  is in sheet-like form, with the figure showing a plane view onto the surface F. The surface F is delimited by an outer edge  37  and an inner edge  39  of the sealing element  35 . 
     FIG. 3  shows an excerpt from a longitudinal section through the hot-gas duct  12 . This excerpt illustrates a guide vane  11 , which is enclosed by a guide ring  51  on both sides in the axial direction. A sealing element  35  is formed in accordance with  FIG. 2 . The precise arrangement is described with reference to  FIG. 4 . Cooling air from a first pressure level is fed to the guide vane  11 . Cooling air  55  from a second pressure level is fed to the guide ring  51 . The pressure level of the cooling air  53  is higher than that of the cooling air  55 , since there is higher cooling demand for the guide vane  11  located further forward in the direction of flow of the hot gas  17  than for the guide vane  51  located further to the rear in the direction of flow. This axial graduation of the pressure level of cooling air is one reason why a seal is required between guide vane  11  and guide ring  51 . Another reason is the need to reduce mixing of hot gas into the cooling air  53 ,  55  as much as possible, in order to avoid consequent heating of the cooling air and therefore reduced cooling capacity. The sealing element illustrated here is pressed onto axial surfaces by means of an active formation, resulting in the sealing action. This is explained in more detail with reference to  FIG. 4 . 
     FIG. 4  shows an enlarged view of an excerpt from  FIG. 3  comprising the sealing element  35 . On the side remote from the hot gas, a groove  85  running in circumferential direction has been formed in a platform  87  of the guide vane  11 . A guide vane carrier  79  lies opposite the guide vane  11  on the side remote from the hot-gas duct  12 . A guide vane carrier groove  83  is also arranged running in the circumferential direction in the guide vane carrier  79 , radially opposite the platform groove  85 . The sealing element  35  is an annular sheet-metal strip designed as shown in  FIG. 2 , with its inner edge  37  engaging in the platform groove  85 . The outer edge  39  of the sealing element  35  lies in the guide vane carrier groove  83 . Furthermore, circumferential seals  91 , which seal off the gap between the guide ring  51  and the platform  87  between in each case two guide vanes  11  of a guide vane ring, have been introduced between guide vane  11  and an adjacent guide vane  51 . 
   By means of a pressure-exerting device  61 , the sealing element  35  is pressed onto the side walls of the platform groove  85  on one side and of the guide vane carrier groove  83  on the other side. For this purpose, a pressure-exerting web  65 , which is guided within a groove  67  in the pressure-exerting device  61 , is pressed onto the sealing element  35  by means of a screw  63  approximately in the radial center of the sealing element  35 . 
   The axial position of the sealing element  35  is selected to be in the region of a hooked formation  71  of the guide vane  11 . This hooked formation  71  is used to fit the guide vane  11 . This hooked formation  71  is also used to define an axial fixed point  73  by means of an axial pressure-exerting surface and a radial fixed point  75  by means of a radial stop face. Thermal expansions of the platform  87  of the guide vane  11  with respect to the guide vane carrier  79  are relatively slight in the region of the axial fixed point  73 , so that by means of the active formation of the sealing element  35 , a good sealing action is achieved irrespective of the operating state of the gas turbine. The guide ring  51  is likewise arranged in the guide vane carrier  79  by means of a hooked formation  77 . In configurations according to the prior art, i.e. without the sealing element  35 , it was often attempted to achieve axial sealing by means of the hooked formations  71  and  77 . To do this, it was necessary to maintain relatively tight tolerances in order to minimize the gaps at the hooked formations  71 ,  77  in the guide vane carrier  79 . This makes manufacture and assembly more difficult. The sealing element  35  now provides a simpler and less expensive yet reliably sealing way of forming an axial seal. 
     FIG. 5  shows a further excerpt from a longitudinal section through the hot-gas duct  12 . The figure once again illustrate a guide vane  11 , which is axially enclosed on both sides by guide rings  51 . In this case, however, the sealing element  35  is arranged well away from the axial fixed point  73 . Moreover, there is no device for pressing the sealing element  35  onto the groove walls. This is described in more detail with reference to  FIG. 6 . 
     FIG. 6  shows an excerpt encompassing the sealing element  35  from  FIG. 5 . As has already been described above, the sealing element  35  is once again arranged with its inner edge  39  in a platform groove  85  and with its outer edge  37  in a guide vane carrier groove  83 . An additional shoulder  91  is formed in the guide vane carrier  79  as axial bearing surface, in such a way that it lies approximately in the region of the radial center of the sealing element  35 . In the example shown here, the platform groove  85  is arranged in the guide ring  51 . To avoid thermal stresses, the guide ring  51  can move with respect to the guide vane carrier  79 . In operation, temperature differences lead to a displacement of the guide ring  51  with respect to the guide vane carrier  79 . As a result, the sealing element  35  is bent and pressed onto the projection  91  in the guide vane carrier  79 . This type of passive formation of the sealing element  35  leads to a good sealing action while at the same time requiring very little outlay on apparatus. 
   When assembling the gas turbine  1  or also when carrying out servicing work, the sealing element  35  is simply fitted into the guide vane carrier groove  83  and the guide vanes  11  or the guide rings  51  are mounted, depending on which of the components has the corresponding platform groove  85 . Then, in each case either the guide vanes  11  or the guide rings  51  which adjoin the previously installed components are fitted.