Abstract:
A gas turbine including a plurality of rotor blades assembled into rotor blade rows and arranged on a turbine shaft and including a plurality of guide vanes assembled into guide van rows and mounted on a turbine housing by means of a guide van carrier is provided. The guide vane carrier includes a plurality of cooling air holes, and has a particularly high efficiency, while maintaining maximum operating reliability. Therefore, a cooling insert is introduced into a cooling air hole.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2009/061461, filed Sep. 4, 2009 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 08018754.5 EP filed Oct. 27, 2008. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention refers to a gas turbine with a number of rotor blades which in each case are assembled to form rotor blade rows and arranged on a turbine shaft, and with a number of stator blades which in each case are assembled to form stator blade rows and fastened on a turbine casing by means of a stator blade carrier, wherein the stator blade carrier has a number of cooling air holes. 
       BACKGROUND OF INVENTION 
       [0003]    Gas turbines are used in many fields for driving generators or driven machines. In this case, the energy content of a fuel is used for producing a rotational movement of a turbine shaft. For this, the fuel is combusted in a combustion chamber, wherein compressed air is fed from an air compressor. The operating medium, under high pressure and under high temperature, which is produced in the combustion chamber as a result of combusting the fuel is directed in this case through a turbine unit, which is connected downstream of the combustion chamber, where it expands, performing work. 
         [0004]    For producing the rotational movement of the turbine shaft, in this case a number of rotor blades, which customarily are assembled into blade groups or blade rows and drive the turbine shaft via an impulse transfer from the operating medium, are arranged on this turbine shaft. For flow guiding of the operating medium in the turbine unit, moreover, stator blades, which are connected to the turbine casing and assembled to form stator blade rows, are customarily arranged between adjacent rotor blade rows. 
         [0005]    The combustion chamber of the gas turbine can be constructed as a so-called annular combustion chamber, in which a multiplicity of burners, which are arranged around the turbine shaft in the circumferential direction, lead into a common combustion chamber space which is enclosed by a high temperature-resistant surrounding wall. For this, the combustion chamber in its entirety is designed as an annular structure. In addition to a single combustion chamber, provision may also be made for a multiplicity of combustion chambers. 
         [0006]    A first stator blade row of a turbine unit as a rule directly adjoins the combustion chamber and together with the directly following rotor blade row, as seen in the flow direction of the operating medium, forms a first turbine stage of the turbine unit to which further turbine stages are customarily connected. 
         [0007]    The stator blades in this case are fixed in each case on a stator blade carrier of the turbine unit via a blade root which is also referred to as a platform. In this case, the stator blade carrier can comprise an insulating segment for fastening the platforms of the stator blades. Between the platforms—which are arranged in a spaced apart manner in the axial direction of the gas turbine—of the stator blades of two adjacent stator blade rows, a guide ring is arranged in each case on the stator blade carrier of the turbine unit. Such a guide ring, by means of a radial gap, is at a distance from the blade tips of the rotor blades of the associated rotor blade row which are fixed on the turbine shaft at the same axial position. As a result, the platforms of the stator blades and the guide rings, which in their turn are possibly of a segmented construction in the circumferential direction of the gas turbine, form a number of wall elements of the turbine unit, constituting the outer limit of a flow passage for the operating medium. 
         [0008]    The aforesaid guide rings, as known from U.S. Pat. No. 3,864,056, for example, in this case can be of a cooled design. According to U.S. Pat. No. 3,864,056, the guide ring segments are hooked to the stator blade carrier. In its wall, provision is made for a feed of cooling air to the guide rings in the form of a through-opening. A pretensioned sleeve, which presses the guide ring segment against the hooks, is screwed in the through-opening, wherein the cooling air which flows inside the sleeve can transfer via openings into the cold gas-side rear space of the guide ring segment and is further used there for cooling the guide ring segment. GB 1 524 956 shows a fastening and cooling of guide ring segments which is alternative to this. 
         [0009]    Furthermore, provision can also be made in the stator blade carrier for holes through which are guided measuring lances with which the radial gap between guide ring segment and rotor blade tip is recorded. A cooled measuring lance is known from US 2006/0140754 A1 in this case. 
         [0010]    In the design of such gas turbines, in addition to the achievable output, a particularly high efficiency is customarily a design aim. An increase of the efficiency in this case can be achieved, for thermodynamic reasons, basically by increasing the exit temperature at which the operating medium flows out of the combustion chamber and flows into the turbine unit. Therefore, temperatures of about 1200° C. to 1500° C. are aimed at and also achieved for such gas turbines. 
         [0011]    With such high temperatures of the operating medium, however, the components and parts which are exposed to this are subjected to high thermal loads. Therefore, particularly the stator blade carrier of the gas turbine is customarily produced from cast steel since this is suitable for withstanding the high temperatures inside the gas turbine. Furthermore, provision is customarily made in the stator blade carrier for cooling air holes through which cooling air from the outer regions of the gas turbine flow into the interior and cool the stator blade carrier in the process. In this case, a plurality of cooling air reservoirs at different temperatures and pressures are customarily provided between turbine casing and stator blade carrier. 
         [0012]    Adequate cooling of the stator blade carrier inter alia is therefore required since excessively high temperatures and consequently excessively high temperature differences in different operating states result in thermal deformations of the stator blade carrier which have to be taken into consideration in the construction of the gas turbine. In this case, the gap dimensions especially of the radial gaps between rotor blade tips and inner wall must be correspondingly large in their selection in order to compensate for variances which are created as a result of deformation of the stator blade carrier and so to prevent damage to the gas turbine. Enlarging the gaps, however, results in a lowering of the efficiency of the gas turbine. Consequently, adequate cooling should always be ensured for reducing deformation of the stator blade carrier. 
         [0013]    On the other hand, intense cooling of the stator blade carrier also means high consumption of cooling air which then flows into the interior of the gas turbine. This lowers the temperature inside the gas turbine and can therefore also lower the efficiency of the gas turbine. 
       SUMMARY OF INVENTION 
       [0014]    The invention is therefore based on the object of disclosing a gas turbine which has particularly high efficiency while maintaining the best possible operational reliability. 
         [0015]    This object is achieved according to the invention by a cooling insert being introduced into at least one cooling air hole for its wall cooling. 
         [0016]    The invention in this case starts from the consideration that particularly high efficiency can be achieved by increasing the temperature inside the gas turbine. This can be effected by reducing the cooling air consumption, i.e. by reducing the amount of cooling air which is introduced into the interior of the gas turbine. A reduction of the amount of cooling air, however, results in an increase of the temperature of the stator blade carrier since less air then flows through its cooling air holes and consequently less heat is transported away from the stator blade carrier. This, however, can result in deformation of the stator blade carrier which would then have to be taken into consideration in the construction of the gas turbine. Therefore, the available cooling air should be used particularly effectively for cooling, i.e. a largest possible amount of heat should be transported away with a smallest possible amount of cooling air. Based on the knowledge that a turbulent flow enables a better heat transfer than a laminar flow, it is therefore advisable to create a flow vortex in the cooling air holes for more efficient wall cooling. This can be achieved by a cooling insert being introduced into the cooling air holes. The more efficient wall cooling compensates for the reduced stator blade carrier cooling which would occur in the cooling air holes on account of the reduced cooling air flow rate. 
         [0017]    The cooling insert is of tubular design and equipped with window-like wall openings arranged in its tube wall. As a result of this, it is possible that the cooling air which flows through the cooling insert can furthermore come into contact with the wall of the cooling air holes of the stator blade carrier in order to extract the heat energy from these. 
         [0018]    According to an especially preferred embodiment, the wall openings are separated from each other over a large area and by means of ribs, as a result of which the cooling air can come into contact with the wall of the cooling air hole over a large area. 
         [0019]    In an advantageous embodiment, the respective cooling insert comprises at least one turbulator. Turbulators are small projections, i.e. generally applied surface interruptions which allow a laminar flow to be converted into a turbulent flow. These can be formed by the ribs, for example, or in the form of raised wires, sheet metal corners or the like. Even if the flow in the cooling air hole is already turbulent, these turbulators ensure an even better heat transfer and therefore overall ensure better cooling of the stator blade carrier with reduced cooling air consumption. 
         [0020]    The cooling insert can advantageously also be formed as an impingement cooling insert, for example when the wall openings are formed as impingement cooling holes which are distributed in a grid-like manner. The cooling air which flows through the cooling insert can discharge through the impingement cooling holes in a radial manner and in so doing impinge transversely upon the cooling air hole walls of the stator blade carrier. As a result of this, particularly efficient cooling of the stator blade carrier is achieved. 
         [0021]    The respective cooling insert advantageously comprises a screw thread-like structure. As a result of a screw thread-like structure, a swirl can be imposed upon the flow inside the cooling air hole, which on the one hand ensures a flow vorticity, and on the other hand results in longer residence of the cooling air in the cooling air hole. As a result, a better heat transfer from the material of the stator blade carrier to the cooling air flowing through is also ensured. 
         [0022]    The respective cooling insert is advantageously produced from the same material as the stator blade carrier. As a result, possible complications on account of different material selection of the cooling insert and of the stator blade carrier, such as a different thermal expansion, can be avoided and overall a comparatively simpler construction is possible. 
         [0023]    By introducing cooling inserts into the cooling air holes of the stator blade carrier, the cooling characteristics of these cooling air holes are altered. For achieving the same cooling effect, a smaller amount of cooling air which is introduced is necessary. Consequently, the cooling air feed to the cooling air holes should advantageously be adapted to the cooling characteristics of the respective cooling insert. This means that temperature and pressure of the cooling air which is introduced are optimized to the new, altered characteristics with regard to cooling by means of the cooling inserts. 
         [0024]    Such a gas turbine is advantageously used in a gas and steam turbine plant. 
         [0025]    The advantages which are associated with the invention are especially that by introducing cooling inserts into the cooling air holes of the stator blade carrier an altogether better efficiency of the gas turbine is achieved as a result of the improved cooling with reduced amount of cooling air at the same time. Furthermore, such inserts can be introduced particularly simply and can also be applied correspondingly relatively simply in the manner of a retrofit in the case of older gas turbines. The cooling inserts can also be flexibly adapted to the respective requirements with regard to cooling and cooling air consumption. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    An exemplary embodiment of the invention is explained in more detail with reference to a drawing. In the drawing: 
           [0027]      FIG. 1  shows a half section through a gas turbine, 
           [0028]      FIG. 2  shows a half section through the lower half of a cooling insert, and 
           [0029]      FIG. 3  shows a plan view of a cooling insert. 
       
    
    
       [0030]    Like parts are provided with the same designations in all the figures. 
       DETAILED DESCRIPTION OF INVENTION 
       [0031]    The gas turbine  1  according to  FIG. 1  has a compressor  2  for combustion air, a combustion chamber  4  and also a turbine unit  6  for driving the compressor  2 , and a generator or a driven machine, which is not shown. In addition, the turbine unit  6  and the compressor  2  are arranged on a common turbine shaft  8  which is also referred to as a turbine rotor to which the generator or the driven machine is also connected, and which is rotatably mounted around its center axis  9 . The combustion chamber  4  which is constructed in the style of an annular combustion chamber is equipped with a number of burners  10  for combusting a liquid or gaseous fuel. 
         [0032]    The turbine unit  6  has a number of rotatable rotor blades  12  which are connected to the turbine shaft  8 . The rotor blades  12  are arranged on the turbine shaft  8  in a ring-like manner and therefore form a number of rotor blade rows. Furthermore, the turbine unit  6  comprises a number of fixed stator blades  14  which are also fastened in a ring-like manner on a stator blade carrier  16  of the turbine unit  6 , forming stator blade rows. The rotor blades  12  in this case serve for driving the turbine shaft  8  as a result of impulse transfer from the operating medium M which flows through the turbine unit  6 . The stator blades  14  on the other hand serve for flow guiding of the operating medium M between two consecutive rotor blade rows or rotor blade rings in each case, as seen in the flow direction of the operating medium M. A consecutive pair, consisting of a ring of stator blades  14  or a stator blade row and a ring of rotor blades  12  or a rotor blade row, in this case is also referred to as a turbine stage. 
         [0033]    Each stator blade  14  has a platform  18  which, for fixing of the respective stator blade  14  on a stator blade carrier  16  of the turbine unit  6 , is arranged as a wall element. The platform  18  in this case is a thermally comparatively heavily loaded component which forms the outer limit of a hot gas passage for the operating medium M which flows through the turbine unit  6 . Each rotor blade  12  is fastened in a similar way on the turbine shaft  8  via a platform  19  which is also referred to as a blade root. 
         [0034]    Between the platforms  18 —which are arranged in a spaced apart manner—of the stator blades  14  of two adjacent stator blade rows, a guide ring  21  is arranged in each case on a stator blade carrier  16  of the turbine unit  6 . The outer surface of each guide ring  21  in this case is also exposed to the hot operating medium. M which flows through the turbine unit  6  and in the radial direction, as a result of a gap, is at a distance from the outer end of the rotor blades  12  which lie opposite it. The guide rings  21  which are arranged between adjacent stator blade rows in this case especially serve as cover elements which protect the inner casing  16  in the stator blade carrier or other installed components of the casing against thermal overstress as a result of the hot operating medium M which flows through the turbine  6 . 
         [0035]    The combustion chamber  4  in the exemplary embodiment is designed as a so-called annular combustion chamber in which a multiplicity of burners  10 , which are arranged around the turbine shaft  8  in the circumferential direction, lead into a common combustion chamber space. For this, the combustion chamber  4  in its entirety is designed as an annular structure which is positioned around the turbine shaft  8 . 
         [0036]    Since the stator blade carrier  16  is also heated up as a result of the high temperatures of the operating medium M, cooling air holes are introduced into the stator blade carrier  16  through which cooling air of different temperature and different pressure is guided from different chambers outside the region of the stator blade carrier  16  through the stator blade carrier  16  into the interior of the gas turbine  1 . This cooling air ensures cooling of the stator blade carrier  16  so that thermal deformations of the stator blade carrier  16  are reduced. 
         [0037]    Since a large amount of cooling air, however, reduces the temperature inside the gas turbine  1  and therefore lowers the efficiency, the amount of cooling air which is used is to be minimized as far as possible. In order to ensure adequate cooling of the stator blade carrier  16 , however, cooling inserts  22  are inserted into the cooling air holes. If the cooling insert  22  is formed as an impingement cooling insert, its outside diameter is slightly smaller than the diameter of the cooling air hole. 
         [0038]    A cross section through a half of such a cooling insert  22  is shown in  FIG. 2 . The cooling insert  22  has an essentially cylindrical shape in order to be able to be inserted into the existing cooling air holes. In this way, existing gas turbines can also be retrofitted with such a cooling insert  22 . Moreover, it is of a tubular form, that is to say it can be exposed to throughflow along its axial extent. On one side, the cooling insert  22  in this case comprises a flange  23  for fixing. 
         [0039]    The cooling insert  22  on its tube wall, which is circular in cross section, has a plurality of window-like wall openings  25  which can be distributed both along its axial extent and on the circumference. The wall openings are of comparatively large area and are separated from each other by means of ribs  26 . Such a cooling insert  22 , in contrast to the impingement cooling insert, then has an outside diameter which corresponds to the diameter of the cooling air hole. 
         [0040]    The ribs  26  which extend in the circumferential direction of the cooling insert  22  are designed as turbulators  24  on which the air flow breaks up and the laminar flow is converted into a turbulent flow. Other shapes and arrangements of turbulators are also possible in this case. The turbulent flow comes into contact with the wall of the cooling air hole of the stator blade carrier in the region of the wall openings  25  for cooling of the wall and of the stator blade carrier. As a result, a better heat transfer from the material of the stator blade carrier  16  to the cooling air is ensured. The ribs  26  and/or the turbulators  24  can also be arranged in the style of a screw thread so that an additional swirl is imparted to the cooling air so that the residence time and the vorticity in the cooling air hole become greater. 
         [0041]      FIG. 3  once more shows the cooling air insert  22  in plan view. The flanges  23  for fixing in the cooling air holes of the stator blade carrier  16  are again evident here. Since as a result of the cooling insert  22  the heat transfer from the material of the stator blade carrier  16  to the cooling air in the cooling air holes is improved, the cooling air feed into the stator blade carrier  16  should furthermore still be adapted to the new cooling air characteristics. As a result, a comparatively better and more effective cooling of the stator blade carrier  16  is ensured with lower cooling air consumption at the same time. Consequently, the efficiency of the gas turbine  1  can be increased overall.