Abstract:
The invention relates to a mounting and sealing arrangement for a guide vane of a gas turbine, which includes a vane carrier for carrying said vanes in a ring-like arrangement, whereby the vanes each comprise an airfoil and an outer diameter platform. The thermal stress is reduced and lifetime improved by providing a separate intermediate mounting element between the vane carrier and the outer diameter platform of each of the vanes, and mounting the intermediate mounting element with an outer side on the vane carrier, whereby the intermediate mounting element abuts with an inner side on the outer diameter platform in a sealing fashion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to EP Application No. 14184727.7 filed Sep. 15, 2014, the contents of which are hereby incorporated in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to the technology of gas turbines. It refers to a mounting and sealing arrangement for a guide vane of a gas turbine according to the preamble of claim  1 . 
       BACKGROUND 
       [0003]    In a gas turbine the hot gas coming from the combustor flows through a turbine section, where alternating rings of running blades mounted on a rotor and guide vanes mounted on a vane carrier at the inner casing of the turbine are arranged. There are various possibilities of mounting the vanes on said vane carrier. 
         [0004]    Cantilever design vanes are attached to the casing via outer radii platform formed as a box (see for example document U.S. Pat. No. 8,292,580 B2). Such design leads to inducing of high temperature gradient over the platform box and hence, to high thermal stresses. In its turn it leads to part cyclic life shortage. 
         [0005]    Additionally, the circumferentially machined casing-vane platform surfaces are difficult to fit to each other due to relatively high shape tolerances causing the platform-casing gaps opening. 
       SUMMARY 
       [0006]    It is an object of the present invention to avoid the difficulties of prior art vane attachments. 
         [0007]    It is another object of the invention to reduce thermal gradients in turbine guide vanes (also called vane), thereby increasing part life time and reduce cooling air leakage and finally improve gas turbine performance. 
         [0008]    These and other objects are obtained by a vane mounting and sealing arrangement according to claim  1 . 
         [0009]    Various embodiments of the invention are claimed in the dependent Claims. 
         [0010]    The mounting and sealing arrangement according to the invention for a vane of a gas turbine, which gas turbine comprises a vane carrier for carrying a plurality of said vanes in a ring-like arrangement, whereby said vanes each comprise an airfoil and an outer diameter platform, is characterized in that a separate intermediate mounting element is provided between said vane carrier and said outer diameter platform of each of said vanes, and that said intermediate mounting element is mounted with an outer side on said vane carrier and abuts with an inner side on said outer diameter platform in a sealing fashion. 
         [0011]    The mounting element abuts with the inner side on said outer diameter platform in a sealing fashion to reduce or avoid any loss of cooling air between the two elements. 
         [0012]    An embodiment of the mounting and sealing arrangement according to the invention is characterized in that said vanes are attached to said intermediate mounting element. 
         [0013]    Specifically, said vanes are attached by a fixation means provided on the outer side of said outer diameter platform. The fixation means may for example be in the form of two ears arranged on one side of and projecting from the outer diameter platform one behind the other in circumferential direction, or in the form of a fir-tree. 
         [0014]    Another embodiment of the mounting and sealing arrangement according to the invention is characterized in that said intermediate mounting element is part of a ring or a ring segment, that said outer side of said intermediate mounting element is curved in accordance with the ring structure, and that said inner side comprises a flat section for each of said vanes such that said abutment between said inner side and said outer diameter platform takes place in a plane. In effect, the inner side has a polygonal form. 
         [0015]    A further embodiment of the mounting and sealing arrangement according to the invention is characterized in that said intermediate mounting element encloses a cavity, which receives cooling air supplied from the vane carrier side. 
         [0016]    Specifically, said cooling air is supplied through a bore in said vane carrier. 
         [0017]    Another embodiment of the mounting and sealing arrangement according to the invention is characterized in that said intermediate mounting element is provided on its inner side with a circumferential sealing groove, which receives a circumferential seal for sealing said intermediate mounting element against a sealing surface on said outer diameter platform. 
         [0018]    A further embodiment of the mounting and sealing arrangement according to the invention is characterized in that said circumferential seal has the form of a corrugated metal strip. 
         [0019]    Alternatively, said circumferential seal may have the form of a C-shaped metal strip. 
         [0020]    Another embodiment of the mounting and sealing arrangement according to the invention is characterized in that said intermediate mounting element is made of a single material. Especially, said intermediate mounting element may be a moulded component. 
         [0021]    Just another embodiment of the mounting and sealing arrangement according to the invention is characterized in that said intermediate mounting element is made of at least two different materials. This allows an optimization of the component with regard to its thermal loading. 
         [0022]    Specifically, said intermediate mounting element comprises two separate parallel annular and circumferential or segmented sidewalls made of a first material suitable for a first operating temperature, which are connected by equidistant transverse webs made of a second material suitable for a second operating temperature higher than said first operating temperature, such that each of said vanes is mounted between two adjacent webs. 
         [0023]    A further embodiment of the mounting and sealing arrangement according to the invention is characterized in that an impingement plate is provided for each of said vanes just above said outer diameter platform for impingement cooling of said outer diameter platform. 
         [0024]    Another embodiment of the mounting and sealing arrangement according to the invention is characterized in that said intermediate mounting elements are each provided with hooks for mounting said intermediate mounting elements on said vane carrier. 
         [0025]    Another embodiment provides a gas turbine comprising a mounting and sealing element as described above, a vane carrier and a plurality of vanes carried on the vane carrier in a ring-like arrangement, whereby said vanes each comprise an airfoil and an outer diameter platform. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings. 
           [0027]      FIG. 1  shows an arrangement of a gas turbine vane with an intermediate mounting element according to an embodiment of the invention; 
           [0028]      FIG. 2  shows various forms of seals used in an arrangement according to  FIG. 1 ; 
           [0029]      FIG. 3  shows in a perspective view the upper part with outer diameter platform and fixing elements of the vane mounted in  FIG. 1 ; 
           [0030]      FIG. 4  shows in a perspective view an embodiment of an intermediate mounting element according to the invention moulded in one piece and provided with separate cavities for each vane to be mounted; 
           [0031]      FIG. 5  shows in a perspective view another embodiment of an intermediate mounting element according to the invention, which comprises two different materials for sidewalls and transverse webs; 
           [0032]      FIG. 6  shows in perspective views seals similar to  FIG. 2 ; 
           [0033]      FIG. 7  shows in a perspective view the upper part with outer diameter platform and fixing elements of a vane similar to  FIG. 3  with an open airfoil; 
           [0034]      FIG. 8  shows in a perspective view the upper part with outer diameter platform and a fir-tree fixation of another kind of vane, which may be used with the invention; 
           [0035]      FIG. 9  shows an intermediate mounting element suitable for the vane of  FIG. 8 ; 
           [0036]      FIG. 10  shows an arrangement of a gas turbine vane with an intermediate mounting element and adjacent heat shield according to another embodiment of the invention, where the intermediate mounting element is open at the outside; 
           [0037]      FIG. 11  shows a possible form of an intermediate ring with circular outer side and polygonal inner side; and 
           [0038]      FIG. 12  shows in a perspective view the upper part with outer diameter platform and fixing elements of the vane according to  FIG. 3  equipped with an impingement plate for impingement cooling of the outer diameter platform. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    A basic idea behind the invention is to reduce thermal stresses and reduce cooling air leakage in gas turbine guide vanes by means of implementation of:
       1) A ‘flat’ outer diameter guide vane platform attached to suitable intermediate segments, which are mounted into the turbine casing (vane carrier);   2) Specific (especially E-type or W-type) seals in between the outer diameter vane platform and said intermediate mounting segments.       
 
         [0042]    Currently used guide vanes, on the other hand, are often equipped with boxes placed at outer diameter platforms forming the hot gas flow path and providing the vane attachment to the turbine casing (vane carrier). 
         [0043]    Temperature gradients, which are high for the prior art box design, are supposed to be reduced by introduction of the ‘flat’ outer diameter platform. 
         [0044]    A first embodiment of the configuration according to the invention is presented in  FIG. 1 , which gives a detailed view of one ring of gas turbine vanes  12  crossing the path of hot gas  39  within said gas turbine  10 . The single vane  12  projects with an airfoil  13  in a radial direction into said hot gas path  39 . The airfoil  13  is bordered at an outer diameter (or radius) by means of an outer diameter platform  14 , which at the same time is part of the outer wall of the hot gas path  39 . 
         [0045]    Vane  12  is fixed to an intermediate mounting element  15 , which itself is mounted on a vane carrier  11  by means of two hooks  15   a  and  15   b . Intermediate mounting element  15  has a cavity  16 , which is open to but sealed against the vane platform side (outer diameter platform  14 ) by means of a sealing arrangement  22  (see  FIG. 2 ). Intermediate mounting element  15  further has an opening  17  at the upper side, through which cooling air  19 , which is supplied through bore  18  in vane carrier  11 , can enter the cavity  16 . Fixation of vane  12  to intermediate mounting element  15  is done by two fixing elements  20  on the outer side of outer diameter platform  14  (see details in  FIG. 3 ) with bolts extending through respective holes  20   a  in said fixing elements  20 . An alternative fixation means is shown in  FIG. 8  (fixation  35  rather than fixing element  20 ). 
         [0046]    For sealing the intermediate mounting element  15  (and the cavity  16 ) against the outer diameter platform  14  of vane  12  a circumferential sealing groove  23  ( FIG. 2 ) is provided at said intermediate mounting element  15  in the plane facing outer diameter platform  14 . According to  FIG. 2 , sealing groove  23  receives a seal, which may have the form (profile) of a corrugated metal strip (seal  24   a  in  FIG. 2(   a )) or a C-shape (seal  24   b    FIG. 2(   b ). Especially, the seal  24  may be in the form of a closed (rectangular) ring, as shown in  FIG. 2(   c ). 
         [0047]      FIG. 3  shows in a perspective view the upper part with outer diameter platform  14  and fixing elements  20  of the vane  12  mounted in  FIG. 1 . It can be seen that outer diameter platform  14  has on its outer side a plane circumferential sealing surface  57 , which closes sealing groove  23  in the adjacent intermediate mounting element  15 . 
         [0048]    According to  FIG. 4 , the intermediate mounting element  15  may have the form of a moulded one-piece half-ring or ring segment receiving a plurality of vanes  12 . In this case (see  FIG. 11 ), the intermediate mounting element is part of an intermediate ring  53  or ring segment, whereby the outer side  54  of said intermediate mounting element or ring  53  is curved in accordance with the ring structure of the ring or ring segment, and the inner side  55  is of polygonal shape and comprises a flat section  56  for each of said vanes  12 , such that the abutment between said inner side  55  and the outer diameter platform  14  of vane  12  takes place in a plane. As shown in  FIG. 4 , the cavities  16  in intermediate mounting element or ring  15  may be separated by separating walls  15   c.    
         [0049]      FIG. 5  shows another embodiment of the intermediate mounting element or segment according to the invention. The intermediate mounting element or segment  25  of  FIG. 5  has a segment design with incorporated impingement plate  30  to provide cooling of outer diameter vane platform  14  and airfoil  13  in case of a vane  12 ′ ( FIG. 7 ), where an opening  31  to the interior of airfoil  13  is provided in the outer diameter platform  14 . 
         [0050]    In the case of  FIG. 5 , the intermediate mounting element  25  is made of at least two different materials. It comprises two separate parallel annular and circumferential or segmented sidewalls  26 ,  27  made of a first material suitable for a first operating temperature, which sidewalls  26 ,  27  are connected by equidistant transverse webs  28  made of a second material suitable for a second operating temperature higher than said first operating temperature. The second material, which is in contact with the gas, may be a Hastelloy® X material, while the first material may be a cheaper material. The webs  28  are so arranged that adjacent webs define a cavity  29  and receive an impingement plate  30  for each vane  12 ,  12 ′, which is mounted between two adjacent webs  28 . The seals  24 ,  24   a  ( FIG. 6 ) may be the same as for the embodiment of  FIG. 1 . 
         [0051]      FIG. 8  is presenting a different kind of vane attachment of a vane  32  with airfoil  33  and outer diameter platform  34  and a (fir-tree) fixation  35  to an intermediate mounting element or segment  36  with suitable hooks  36   a  and  36   b  according to  FIG. 9 . There is the same idea behind this configuration, i.e. to split the “hot” part of the vane  32  (leading edge and trailing edge of the airfoil  33 ) from the “cold” attachment part, and thus reduce the thermal stresses in those parts of the airfoil  33  most prone to LCF cracking. Again, a sealing arrangement  38  of the kind already described is used between intermediate mounting element  36  and outer diameter platform  34 . Furthermore, an opening  37  in the intermediate mounting element  36  gives access to the interior for cooling air. 
         [0052]      FIG. 10  shows a variant of a possible turbine stage layout of a gas turbine  40  including a blade  51  and stator heat shield  52 . The vane  45  with its airfoil  46  and outer diameter platform  47  is attached to intermediate mounting element  43  with a sealing arrangement  50  of the kind already shown. Vane  45  is fixed to intermediate mounting element  43  by means of bolts  49  and fixing elements  48  as explained before. Intermediate mounting element  43 , which is in this case open to the other side, has suitable hooks  43   a  and  43   b  and encloses a cavity  44 , which can be cooled through bore  42  in the vane carrier  41 . 
         [0053]    Finally,  FIG. 12  makes clear that an impingement plate  58  may be directly arranged on the upper side of outer diameter platform  14  of vane  12 . 
         [0054]    In summary
       a central idea here is to split all “hot” from all “cold” walls by means of separate “boxes”, especially in form of intermediate rings/segments; and   only “cold” part of the “hot” vanes is fixation part; this cold part could be fixed either on the “boxes” or directly to the casing/or other carrier.       
 
         [0057]    The main advantages are:
       improved leakage control (“2D” sealing)   reduced thermal stress   simplified assembly.       
 
         [0061]    A gas turbine normally comprises a compressor, a combustor and a turbine. The turbine section contains at least one set (stage) of vanes supported on a vane carrier.