Abstract:
A gas turbine membrane seal is disclosed. The gas turbine membrane seal includes a membrane, the membrane configured and arranged to extend from a first gas turbine component to a second gas turbine component and to separate two volumes, and an anti-fretting part configured and arranged to be attached to the first gas turbine component. A face of the anti-fretting part is adjacent to the membrane, and the face of the anti-fretting part is convex. Further embodiments of the gas turbine membrane seal are also described, along with a gas turbine having the gas turbine membrane seal and a retrofitting method.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to gas turbine membrane seals, and particularly to gas turbine membrane seals with a membrane and an anti-fretting part. 
       BACKGROUND OF THE INVENTION 
       [0002]    Modern gas turbines are extremely complex and include a large number of seals to reduce leakage through various cavities and gaps, helping to control flow of the various fluids around the gas turbine. One such type of seal is the membrane seal, and U.S. Pat. No. 6,857,849, a granted patent assigned to the current applicant, shows an example of a known membrane seal. Known membrane seals such as that described in U.S. Pat. No. 6,857,849 can provide an effective seal, but tend to have a relatively short lifetime and can often require replacing due to wear. The replacement frequency is greater when the sliding distance and pressure difference at the side of membrane is relatively high. It has therefore been appreciated that the existing designs can be further improved. 
       SUMMARY OF THE INVENTION 
       [0003]    The invention is defined in the appended independent claims to which reference should now be made. Advantageous features of the invention are set forth in the dependent claims. 
         [0004]    A first aspect provides a gas turbine membrane seal comprising a membrane configured and arranged to extend from a first gas turbine component to a second gas turbine component and to separate two volumes, and an anti-fretting part configured and arranged to be attached to said first gas turbine component, wherein a face of the anti-fretting part is adjacent to the membrane, and wherein the face of the anti-fretting part is convex. 
         [0005]    In a membrane seal where the curved surface is on the membrane and the flat surface is on the adjacent gas turbine component, the curved surface of the membrane is always in contact with the adjacent gas turbine component, and will therefore always be in a position to wear. In other words, the curved surface of the membrane is subjected to a higher contact sliding distance during operation compared to the flat contact surface on the anti-fretting part (fretting ring) and thus is more prone to fretting wear. As a result, membrane seals can require frequent replacement during use due to high rates of wear, while the anti-fretting part, which is generally cheaper, remains unworn. 
         [0006]    In contrast, a membrane seal as described above provides the curved surface (convex surface) on an anti-fretting ring on the gas turbine component, and therefore it is the anti-fretting part that is always in contact with the membrane and liable to wear. This can reduce the membrane replacement frequency, and can provide good membrane lifetime despite high contact pressure and large relative gas turbine component displacement. This can reduce maintenance costs as it is generally cheaper to replace an anti-fretting ring than to replace a membrane. 
         [0007]    The sealing efficiency of contact surfaces between the membrane and the anti-fretting ring normally depends on the surface condition, and it is therefore generally preferable to minimise wear and thereby minimise leakage. The present design can provide reduced wear and therefore reduced leakage, which can improve engine efficiency and power. 
         [0008]    Preferably, the face of the anti-fretting part has a plurality of separate convex portions. The second convex portion can provide a backup contact seal in case of wear of the first convex portion. 
         [0009]    Preferably, the membrane is planar. This provides a flat surface for the anti-fretting part to contact. Preferably, the anti-fretting part is a first anti-fretting part and the membrane has a first face adjacent to the first anti-fretting part and a second face facing away from the first anti-fretting part, and wherein the gas turbine membrane seal comprises a second anti-fretting part adjacent to the second face of the membrane. 
         [0010]    Preferably, at least the face of the anti-fretting part is made of a softer material than the membrane. This can reduce membrane wear, as the anti-fretting part has lower wear resistance and will wear more than the membrane. 
         [0011]    A second aspect provides a gas turbine comprising a first gas turbine component, a second gas turbine component and a gas turbine membrane seal as described above. 
         [0012]    Preferably, the first gas turbine component is a turbine vane carrier and the second gas turbine component is a turbine housing or a combustor liner carrier, or the first gas turbine component is a turbine housing or a combustor liner carrier and the second gas turbine component is a turbine housing. 
         [0013]    A third aspect provides a method of retrofit for a gas turbine, comprising the steps of removing an existing membrane seal and inserting a gas turbine membrane seal as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: 
           [0015]      FIG. 1  shows a cross section of a membrane seal; 
           [0016]      FIG. 2  shows a cross section of another example of a membrane seal; 
           [0017]      FIG. 3  shows a cross section of the membrane seal of  FIG. 2  after wear of part of the anti-fretting ring; 
           [0018]      FIG. 4  shows a cross section of a membrane seal with two anti-fretting rings; 
           [0019]      FIG. 5  shows a cross section of another membrane seal with two anti-fretting rings; 
           [0020]      FIG. 6  shows a perspective view of the anti-fretting ring extending in the circumferential direction; 
           [0021]      FIG. 7  shows a cross section of a gas turbine showing possible locations for a membrane seal; and 
           [0022]      FIG. 8  shows a cross section of a gas turbine showing further possible locations for a membrane seal. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]      FIG. 1  shows a membrane seal  10  (also known as a cavity splitter or a large cavity splitter) comprising a membrane  20  and an anti-fretting part  30 , such as an anti-fretting ring or an anti-fretting ring section. The membrane  20  adjacent to a face  32  of the anti-fretting ring  30 ; the face  32  is convex. The anti-fretting ring is attached to a first gas turbine component  40 . 
         [0024]      FIG. 2  shows a membrane seal  10  with a different anti-fretting ring  30 . The face  32  of the anti-fretting ring shown in  FIG. 1  is convex with a single convex portion; the membrane seal of  FIG. 2  has a first convex portion  34  and a second convex portion  36 . The first convex portion  34  is in contact with the membrane  20 , and the second convex portion  36  is spaced apart from the membrane  20 . 
         [0025]    When in use, the first convex portion  34  may become worn as shown in  FIG. 3 . After a certain amount of wear of the first convex portion  34 , the second convex portion  36  is also in contact with the membrane. 
         [0026]      FIG. 4  shows a membrane seal in which the membrane  20  has two anti-fretting rings  30 , one arranged adjacent to a first face  22  of the membrane and the other adjacent to a second face  24  of the membrane. The first face  22  faces in the opposite direction to the second face  24 . Both anti-fretting rings are attached to the first gas turbine component  40 . 
         [0027]      FIG. 5  shows a membrane seal in which the membrane has two anti-fretting rings on the same face, arranged at opposite ends (first end  26  and second end  28 ) of the membrane in a radial direction  42  relative to a longitudinal gas turbine axis (which extends in an axial direction  44 ). The first anti-fretting ring  30  is attached to a first gas turbine component  40 , and the second anti-fretting ring  31  is attached to a second gas turbine component  41 . 
         [0028]      FIG. 6  shows a perspective view of part of a membrane, showing the curvature of the anti-fretting ring  30  and the first gas turbine component in the circumferential direction  46 . 
         [0029]      FIG. 7  shows a turbine housing  50  and a turbine vane carrier  52 . Two membranes  20  extend between the turbine housing  50  and the turbine vane carrier  52 . In total, there are eight places on  FIG. 7  where an anti-fretting ring could be arranged between a membrane and an adjacent gas turbine component (turbine housing or turbine vane carrier); these are indicated with the reference numeral  56 . 
         [0030]      FIG. 8  shows a turbine vane carrier  52  and a combustor liner carrier  54 . A membrane  20  extends between the turbine vane carrier  52  and the combustor liner carrier  54 . As in  FIG. 7 , the places where an anti-fretting ring could be arranged between the membrane and an adjacent gas turbine component (turbine housing or combustor liner carrier) are indicated with the reference numeral  56 . 
         [0031]    A more detailed example of where a membrane seal is located is given with reference to  FIG. 7 . A cavity is divided into three parts  60 ,  62 ,  64  by the two membrane seals  10 . When in use, the first part  60  is at a higher pressure from the second part  62 , and the second part is at a higher pressure than the third part  64 . This means that the membrane seal between the second part and the third part, for example, is pushed towards the third cavity  64  by the pressure in the second cavity  62 . As a result, it could be useful to put anti-fretting rings  30  at the two locations  56  between the membrane  20  and the two adjacent gas turbine components (turbine vane carrier, turbine housing) on the side of the membrane facing the third cavity  64  (the right-hand side in  FIG. 7 ), to help reduce rubbing and wear. This would give a membrane seal similar to the one shown in  FIG. 5 . 
         [0032]    Planar cross sections are shown in most of the Figures, extending in the radial direction  42  and the axial direction  44 . Generally, the parts described in this application also extend in a circumferential direction  46  relative to a central axis, which would normally be the longitudinal gas turbine axis (extending in the axial direction  44 ) around which the rotating parts of the gas turbine rotate. For example, the membranes and the anti-fretting rings normally extend in a circumferential direction  46 , and each can either be a full ring or ring segments. 
         [0033]    The membrane  20  may be a flat plate. That is, the membrane may be planar, normally extending in the radial direction  42  and the circumferential direction  46 . The membrane separates two volumes and extends from a first gas turbine component to a second gas turbine component. 
         [0034]    The anti-fretting part  30  may be a ring or a ring section or any other appropriate shape. In the examples shown in  FIGS. 7 and 8 , the anti-fretting part would normally be a ring or a ring section. 
         [0035]    The anti-fretting rings  30  described herein are attached to gas turbine components, and are shown in cavities within the gas turbine components. Variations in this design are possible; for example, an anti-fretting ring may alternatively be attached directly to the surface of a gas turbine component rather than in a cavity. 
         [0036]    In some cases, only a single anti-fretting ring is necessary, for example in a location where there is a particular problem with rubbing. In some cases, it may be preferable to put anti-fretting rings on both sides, as shown in  FIG. 4 . In some case, it may be preferable to put anti-fretting rings at both ends on one side, as shown in  FIG. 5 . This may be the case, for example, where the pressure difference between the two faces  22 ,  24  of the membrane means that most of the rubbing occurs only on one face of the membrane. Any combination is also possible, with anti-fretting rings at one or both sides and/or one or both ends  26 ,  28  (in the radial direction  42 ) of the membrane. 
         [0037]    The second anti-fretting ring  31  and the face  33  of the second anti-fretting ring are equivalent to the anti-fretting ring  30  and the face  32  of the anti-fretting ring  30  as described in this application, and may have the same designs and design variations. 
         [0038]    The face  32  of the anti-fretting ring is adjacent to a face of the membrane, and is preferably in contact with the face of the membrane. 
         [0039]    The face  32  of the anti-fretting rings described herein is convex. This effectively means that the face is not planar, and that it bulges outwards from the body of the anti-fretting ring. As a result, only a portion of the face  32 ,  33  can be in contact with the adjacent membrane when the anti-fretting ring is newly installed. 
         [0040]    The convex face of the anti-fretting ring will normally be curved in the radial direction  42  so that when the gas turbine is in use and the gas turbine components are moving relative to one another the membrane moves relative to the face. This typically means that the face of the anti-fretting ring is convex when viewed in cross section in a plane containing the radial direction  41  and the axial direction  44 . In the circumferential direction  46 , the shape of the face of the anti-fretting ring normally remains constant, as shown in  FIG. 6 . 
         [0041]    The anti-fretting ring is preferably made of a softer material than the membrane. As an example, an anti-fretting ring and the membrane may be made of different types of steel, such as an anti-fretting ring made of low alloy steel (content other than iron and carbon: 4% or less by weight) and a membrane made of high alloy steel (content other than iron and carbon: higher than 4% by weight). The entire anti-fretting ring can be made of a softer material than the membrane. Alternatively, just the face of the anti-fretting ring can be made of a softer material than the membrane, with the rest of the anti-fretting ring being made of a different material. Alternatively, when the membrane is made of low alloy steels, the contact surface of the membrane can be nitrated/carburized to present a relative higher strength on the face of the membrane than on than anti-fretting ring. The Mohs Scale, for example, may be used to measure the relative hardness of the materials. 
         [0042]    Where a plurality of separate convex portions are provided, for example a first convex portion and a second convex portion (see  FIG. 2 ), the first and second convex portions are generally at different points in the radial direction  42  (so at different distances from the gas turbine axis), and can also be adjacent in the radial direction  42 . In  FIG. 2 , the convex portion  34  closest to the end of the membrane (furthest from the gas turbine axis) is the portion closest to the membrane, but the other convex portion  32  could alternatively be the portion closest to the membrane. Examples with one or two convex portions are shown above, but three or more convex portions may also be provided. When newly installed, the second convex portion is normally further from the membrane than the first convex portion. When more than two convex portions are provided, the convex portions would normally all be at a different distance from the membrane than each other. Each convex portion effectively has a peak, and once the peak of one convex portion has worn down then the peak of the next convex portion can come into contact with the membrane. 
         [0043]    In the example shown in  FIG. 4 , both anti-fretting rings are normally attached to the same gas turbine component (first gas turbine component  40 ). 
         [0044]    The membrane seals described in this application can be used in various places in a gas turbine, including those shown in  FIGS. 7 and 8  and also elsewhere, for example between other inner casings and outer casings in a gas turbine. The membrane seals can be fitted into a new gas turbine or retrofitted into an existing gas turbine by removing an existing membrane seal and inserting a membrane seal as described herein. 
         [0045]    Membrane seals can be used to separate various cavities, such as those with different pressures, temperatures or contents (e.g. two different gases). The cavities being separated are normally between two components that may move relative to one another; the relative movement means that a seal is required that allows relative movement of the two components. As a result, the first gas turbine component  40  and second gas turbine component  41  can be various components, including those shown in  FIGS. 7 and 8  (turbine housing  50 , turbine vane carrier  52 , combustor liner carrier  54 ), and the first and second gas turbine components can normally move relative to one another during use of a gas turbine. A gas turbine comprises a compressor, a combustor and a turbine, and may also comprise various other parts, such as a turbine housing, a turbine vane carrier and a combustor liner carrier. 
         [0046]    The combustor liner carrier  54  may be an outer liner carrier for a sequential environmental (SEV) combustor. 
         [0047]    Various modifications to the embodiments described are possible and will occur to those skilled in the art without departing from the invention which is defined by the following claims. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 REFERENCE NUMERALS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 membrane seal 
               
               
                 20 
                 membrane 
               
               
                 22 
                 first face of the membrane 
               
               
                 24 
                 second face of the membrane 
               
               
                 26 
                 first end of the membrane 
               
               
                 28 
                 second end of the membrane 
               
               
                 30 
                 anti-fretting ring 
               
               
                 31 
                 second anti-fretting ring 
               
               
                 32 
                 face of the anti-fretting ring 
               
               
                 33 
                 face of the second anti-fretting ring 
               
               
                 34 
                 first convex portion 
               
               
                 36 
                 second convex portion 
               
               
                 40 
                 first gas turbine component 
               
               
                 41 
                 second gas turbine component 
               
               
                 42 
                 radial direction 
               
               
                 44 
                 axial direction 
               
               
                 46 
                 circumferential direction 
               
               
                 50 
                 turbine housing 
               
               
                 52 
                 turbine vane carrier 
               
               
                 54 
                 combustor liner carrier 
               
               
                 56 
                 anti-fretting ring location 
               
               
                 60 
                 first part of the cavity 
               
               
                 62 
                 second part of the cavity 
               
               
                 64 
                 third part of the cavity