Abstract:
A thermal machine is provided, in particular a gas turbine, which includes an annular combustion chamber which is bounded on the outside by an outer shell and an inner shell. The outer shell and the inner shell are each split on a separating plane into an upper half and a lower half, which are mechanically interlocked by welding one to the other on the separating plane. Increased mechanical robustness and a longer life of the combustion chamber are achieved in that an additional mechanical interlock is provided on the separating planes in order to absorb tensile and shear forces acting on the separating planes.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of International Application No. PCT/EP2009/051644 filed Feb. 12, 2009, which claims priority to Swiss Patent Application No. 00245/08, filed Feb. 20, 2008, the entire contents of all of which are incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to the field of thermal machines, and in particular to a thermal machine, as well as a method for assembling such a thermal machine. 
       BACKGROUND 
       [0003]    Modern industrial gas turbines (IGT) are generally designed with annular combustion chambers. Most relatively small IGTs are in the form of so-called “can-annular combustors”. In the case of an IGT with an annular combustion chamber, the combustion area is bounded by the side walls and the inlet and outlet plane of the hot gas. One such gas turbine is illustrated in  FIGS. 1 and 2 . The gas turbine  10 , a detail of which is illustrated in  FIGS. 1 and 2 , has a turbine housing  11  in which a rotor  12 , which rotates about an axis  27 , is accommodated. On the right-hand side, a compressor  17  is formed on the rotor  12  in order to compress combustion air and cooling air, and a turbine  13  is arranged on the left-hand side. The compressor  17  compresses air which flows into a plenum chamber  14 . An annular combustion chamber  15  is arranged concentrically with respect to the axis  27  in the plenum chamber, is closed on the inlet side by a front plate  19  which is cooled by front plate cooling air  20 , and is connected on the outlet side via a hot-gas channel  25  to the inlet of the turbine  13 . 
         [0004]    Burners  16  are arranged in a ring in the front plate  19 , are, for example, in the form of premixing burners, such as those preferably disclosed in EP-A1-321 809 or EP-A1-704 657 and inject a fuel-air mixture into the combustion chamber  15 . The cited documents and the further developments derived from them form an integrating component of this application. The hot-air flow  26  which is created during combustion of the mixture is passed through the hot-gas channel  25  into the turbine  13 , where it is expanded, creating work. The combustion chamber  15  together with the hot-gas channel  25  is surrounded on the outside at a distance by an outer and an inner cooling jacket  21  and  31 , respectively, which are attached to the combustion chamber  15 ,  25  by means of attachment elements  24  and in each case form an outer and an inner cooling channel  22  and  32 , respectively, between themselves and the combustion chamber  15 ,  25 . Cooling air flows in the cooling channels  22 ,  32  in the opposite direction to the hot-gas flow  26 , along the walls of the combustion chambers  15 ,  25  along a combustion chamber shroud  18 , and flows from there into the burners  16 , and front plate cooling air  20  flows directly into the combustion chamber  15 . 
         [0005]    The side walls of the combustion chambers  15 ,  25  are in this case either in the form of shell elements or complete shells (outer shell  23 , inner shell  33 ). When using complete shells, it is necessary for assembly purposes to provide a separating plane ( 29  in  FIG. 4  et seq) which allows an upper half of the shell  23 ,  33  (the upper part) to be removed in order, for example, to fit or to remove the gas turbine rotor  12 . The separating plane  29  correspondingly has two separating plane weld beads which, based on the example of the gas turbine designed by the applicant, are located at the same height as the machine axis  27 . 
         [0006]    Access is possible both from the hot-gas side and from the cooling-air side in order to weld the separating planes  29  on the outer shell  23 . Access is ensured only from the hot-gas side for welding the separating planes on the inner shell  33  (access via a manhole in the turbine housing  11 ). The separation of a shell into an upper half and a lower half (upper part and lower part) and the welding after fitting of the rotor  12  are known from the prior art, and are normal practice. 
         [0007]    Because the material characteristics of the weld bead are not as good as those of the basic material, and because of the lack of a thermal barrier coating (TBC) on and in the immediate vicinity of the weld beads, the side walls are less strong and have a shorter life in the area of the separating planes  29 . The very severely thermally loaded outer and inner shells  23  and  33 , respectively, result in high compression and tensile stresses being applied to the four separating planes ( 29  and so on). The required operating life of outer and inner shells  23  and  33 , respectively, is typically two so-called service intervals (service cycles). A service interval describes the time between the (re)commission of the combustion chamber and the reconditioning of the components. Both shells, the outer and inner shells  23 ,  33 , often start to tear in at the start and end of the separating plane weld beads during operation. 
       SUMMARY 
       [0008]    The present disclosure is directed to a thermal machine including an annular combustion chamber, which is bounded on the outside by an outer shell and an inner shell. The outer shell and the inner shell are each split on a separating plane into an upper half and a lower half, which are mechanically interlocked by welding one to the other on the separating plane. An additional mechanical interlock is provided on the separating planes in order to absorb tensile and shear forces acting on the separating planes. 
         [0009]    The present disclosure is also directed to a method for assembling the above thermal machine. The method includes inserting a connecting element into the upper half of the respective shell, which is separated into an upper half and a lower half and placing the two halves one on top of the other. The method also includes driving the connecting element into the lower half of the respective shell and connecting the connecting element to the two halves in a final position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention will be explained in more detail in the following text with reference to exemplary embodiments and in conjunction with the drawing. All of the elements which are not required for immediate understanding of the invention have been omitted. Identical elements are provided with the same reference symbols in the various figures. The flow direction of the media is indicated by arrows. In the figures: 
           [0011]      FIG. 1  shows a longitudinal section through a cooled annular combustion chamber of a gas turbine according to the prior art; 
           [0012]      FIG. 2  shows, in detail, the annular combustion chamber from  FIG. 1  with the cooling jackets attached on the outside; 
           [0013]      FIG. 3  shows a longitudinal section through the turbine-side end of the outer shell of the combustion chamber from  FIG. 1  with the attached flange; 
           [0014]      FIG. 4  shows, in the form of a detail, the halves of the outer shell, which abut against one another on the separating plane, with a screwed bridge arranged on the flange, according to one preferred exemplary embodiment of the invention; 
           [0015]      FIG. 5  shows the detail from  FIG. 4 , viewed from a different direction; 
           [0016]      FIG. 6  shows a first sub-step during the fitting of the bridge as shown in  FIG. 4 ; 
           [0017]      FIG. 7  shows, in various sub-figures (a), (b) and (c), various views of a bridge as shown in  FIG. 4 ; 
           [0018]      FIG. 8  shows, in the form of a detail, the halves of the outer shell, which abut against one another on the separating plane, with a screwed bridge arranged on the flange, according to another preferred exemplary embodiment of the invention; 
           [0019]      FIG. 9  shows the detail from  FIG. 8 , viewed from a different direction; 
           [0020]      FIG. 10  shows, in various sub-figures (a), (b) and (c), various views of a bridge as shown in  FIG. 8 , and 
           [0021]      FIG. 11  shows, in two sub-figures (a) and (b), different views of a bridge provided with additional cooling means, in a similar manner to  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Introduction to the Embodiments 
       [0022]    The object of the invention is to provide a thermal machine, in particular a gas turbine, which avoids the abovementioned disadvantages of known machines and in particular prevents the combustion chamber shells from tearing in on the weld beads which connect the shell halves, and to specify a method for its assembly. 
         [0023]    The object is achieved by the totality of the features of claims  1  and  16 . It is essential for the invention that an additional mechanical interlock is provided on the separating planes in order to absorb tensile and shear forces acting on the separating planes. 
         [0024]    In one preferred refinement of the invention, a connecting element which extends over the separating plane and is in the form of a bridge is in each case provided as the additional mechanical interlock, the outer shell and the inner shell have a flange at the inlet and/or outlet of the combustion chamber, the connecting elements are arranged on the outside of the flange, the flange has a circumferential groove on the outside, and the connecting elements are inserted into the groove. 
         [0025]    The strength deficit which exists in the prior art can be compensated for by the retrospective incorporation of (cooled) screwed and/or welded integral bridges in the grooves of the (two) flanges at the location of the separating plane weld beads. The structure bridges in this case absorb the tensile and shear forces which occur at the start and end. 
         [0026]    The connecting elements in this case may be detachably connected to the two halves of the outer shell and inner shell. In particular, the connecting elements are then detachably connected to the two halves of the outer shell and inner shell by screws or bolts. 
         [0027]    However, the connecting elements may also be integrally connected, in particular welded, to the two halves of the outer shell and inner shell. 
         [0028]    Another refinement of the invention is distinguished in that the groove and the connecting elements are designed such that the connecting elements are held in the groove by an interlock. 
         [0029]    According to a further refinement, the connecting elements have first means in order to improve the mechanical integrity, wherein notches in the form of fillets are preferably provided at the ends as means in order to improve the mechanical integrity. 
         [0030]    In another refinement, the connecting elements have second means in order to improve the assembly capability, with a stud preferably being provided on the upper face as means in order to improve the assembly capability. 
         [0031]    A further refinement is distinguished in that the connecting elements have third means in order to improve the cooling of the connecting elements. 
         [0032]    According to another refinement of the invention, the connecting elements have fourth means in order to form cooling channels between the connecting element and the flange, with a corrugated base surface preferably being provided on the lower face as means in order to form cooling channels. 
         [0033]    In one refinement of the method according to the invention, in the first step, the connecting element is inserted loosely into the upper half, and is welded to the two halves in the final position. 
         [0034]    In another refinement, in the first step, the connecting element is inserted into the upper half at its final position, and is secured by screws or bolts, and, in the third step, the upper half is positioned while the connecting element is driven in on the lower half at the same time. 
       DETAILED DESCRIPTION 
       [0035]    One major feature of the inventive idea is an additional mechanical interlock of the separating plane weld beads between the half-shells of the outer shell and/or inner shell of an annular combustion chamber (note: all the following explanatory notes and descriptions relate to the outer shell, but also apply in a corresponding manner to an inner shell). In this case, a bridge is used as an additional connecting element on both sides of the separating plane, preferably in a flange which is in each case already provided. This bridge may, but need not be, designed such that it still allows or makes possible cooling of the flange part. 
         [0036]    The design implementation is in general subject to the following principles:
       the bridges are designed to be virtually interlocking. As a result, they fit precisely into the respective flange geometry and are clamped in an interlocking manner during operation by the thermal deformation of the shells and of the flange.   the bridges should be located as close as possible to the “cold” shell outer wall in order that no further, unnecessarily high, lever-action forces occur.   the bridges can be welded, clamped in an interlocking manner, or screwed.   cooling air can be used in order to cool the lower face of the bridges in the immediate vicinity of the thermally loaded shell structure, in order to use the bridge to transmit stresses to a greater extent away from the separating plane weld bead.       
 
         [0041]    In one practical embodiment of the inventive idea, the bridge is inserted into a flange groove on one side, in the upper part of the outer shell. The two shells are placed one above the other in the gas turbine (GT) and the bridge is pushed or knocked into its position (a stud or a tab on the external diameter of the bridge can in this case be used as a point of contact for a mandrel or hammer). As soon as the bridge is located in position above the separating plane, its upper face is welded to the flange. The geometrical configuration of the flange and of the bridge itself in this case preferably allows the cooling air to flow through the flange under the bridge—thus ensuring the preconditions for convection cooling. 
         [0042]    Instead of the integral welded joint between the bridge and the flange, it is, however, also possible to use a detachable connection: the bridge is then inserted into the flange groove on one side, in the upper part (in the upper half) of the outer shell, and is positioned at its attachment point by one or more bolt. The two half-shells are placed one on top of the other in the gas turbine, and the bridge is driven into the lower half-shell. As soon as the two half-shells are located exactly one on top of the other, the bridge can also be secured in the lower half-shell (by bolts and/or screws). In order to improve the accessibility during welding of the separating plane, the bridge may also be removed and reinserted again at any time. 
         [0043]    The two abovementioned alternatives (welded or screwed bridge) will be explained in the following text using the exemplary embodiments in  FIGS. 4 to 11 . The shells  23 ,  33  of the annular combustion chambers  15 ,  25  are preferably provided at the burner-side end and at the turbine-side end with flanges which are used for the connection between the combustion chamber and adjacent components. As an example,  FIG. 3  shows, in the form of a longitudinal section, the turbine-side end of the outer shell  23  of the combustion chambers  15 ,  25  from  FIG. 1  with the attached flange  28 . On the outside, the flange  28  has a groove  34  which holds the bridges which are provided in order to reduce the mechanical load on the separating plane weld beads. 
         [0044]      FIGS. 4 and 5  show a detail—viewed from different viewing angles—of the halves  23   a ,  23   b , which abut against one another on the separating plane  29 , of the outer shell  23 , with a screwed bridge  30 , arranged on the flange  34 , according to one preferred exemplary embodiment of the invention. The bridge  30  itself is illustrated in various views in  FIGS. 7   a  to  7   c . The bridge  30  is in the form of an elongated flat strip with the rectangular cross section, which has the slightly curved shape of a circular arc segment. The length of the bridge  30  is chosen such that two attachment holes  36  can in each case be incorporated, at an adequate distance from one another, on both sides of the separating plane  29 , and are used to screw/bolt the bridge  30  to the two welded half-shells  23   a ,  23   b . If the bridge  30  is screwed, appropriate screws  35  are used, as shown in  FIGS. 4 and 5 . During assembly, the bridge—as already mentioned above—is first of all screwed to the upper half  23   a  of the outer shell, as shown in  FIG. 6 , before the half-shells  23   a ,  23   b  are then joined together. A corresponding procedure also applies to the inner shell  33 . 
         [0045]    A connecting element  40  as shown in  FIG. 8-10  or  11  is preferably used as a load-reducing arrangement with a welded bridge. The cross-sectional contour of the bridge  40  ( FIG. 10   b ) is matched to the cross-sectional contour of the flange groove  34  such that the bridge  40  can be inserted into the groove  34  in an interlocking manner and, at the same time, engages with a foot strip  37  in an undercut in the groove  34 . A stud  39  which projects laterally is provided in the center on the upper face of the bridge  40 , to which stud  39  a striking tool can be applied when the bridge  40  is being knocked into the groove  34 . A corrugated base surface  38  is formed ( FIG. 10   b ) on the lower face of the bridge  40 , creating a cooling channel, which runs in the circumferential direction of the flange  28 , between the bridge  40  and the groove base. Notches  41 ,  42  in the form of fillets are advantageously arranged at the ends of the bridge  40  and are introduced partially on one side ( FIG. 10   c ) or as a cruciform ( FIG. 11 ). The radii of curvature of the notches may in this case vary. 
         [0046]    Overall, the novel, interlocking connecting elements, which act as structure bridges for the combustion chamber shell separating plane, significantly ensure better force transmission at the ends of the separating plane. 
         [0047]    In this case, various deviations and variants on a basic embodiment are possible within the scope of the invention:
       the bridges ( 40 ) may have notches ( 41 ,  42 ) in the form of fillets at their ends in order to improve the mechanical integrity—better power flow transmission, breaking of the force peaks;   the notches in the bridge can be incorporated partially on one side or as a cruciform;   the radii of the notches illustrated in  FIG. 10  may vary;   the wall thicknesses of the two illustrated bridges ( 30 ,  40 ) may vary;   the bridges may have turbulence ribs added to them on the cooling-air side in order to increase the cooling effectiveness;   the bridges could be cooled with impact cooling air on the cooling-air side, in order to improve the cooling effectiveness;   in order to make it easier to fit them to the upper face, the bridges may have a stud ( 39 ) in order to allow them to be moved more easily by striking them with a hammer; and   any type of adequate welding process may be used in the workshop for welding the bridges to the flange.       
 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
         
           
               10  Gas turbine 
               11  Turbine housing 
               12  Rotor 
               13  Turbine 
               14  Plenum chamber 
               15  Combustion chamber 
               16  Burner (double-cone or EV burner) 
               17  Compressor 
               18  Combustion chamber shroud 
               19  Front plate 
               20  Front plate cooling air 
               21  Outer cooling jacket 
               22  Outer cooling channel 
               23  Outer shell 
               23   a  Upper half of the outer shell 
               23   b  Lower half of the outer shell 
               24  Attachment element 
               25  Hot-gas channel 
               26  Hot-gas flow 
               27  Axis 
               28  Flange 
               29  Separating plane 
               30 ,  40  Connecting element (bridge) 
               31  Inner cooling jacket 
               32  Inner cooling channel 
               33  Inner shell 
               34  Groove 
               35  Screw 
               36  Attachment hole 
               37  Foot strip 
               38  Base surface (corrugated) 
               39  Stud 
               41 ,  42  Notch (in the form of a fillet)