Abstract:
A transition piece seal assembly includes a transition piece seal support having a first flange for supporting a transition piece seal, and a second flange adapted for mounting in an adjacent nozzle; and at least one spring seal element having a mounting flange adapted to engage the second flange of the transition piece seal support, and a flex portion having a free edge adapted to engage a forward face of the nozzle.

Description:
[0001]    This invention relates to seals for turbine applications and particularly to seals between combustor transition pieces and stage one turbine nozzles.  
         BACKGROUND OF THE INVENTION  
         [0002]    Sealing is oftentimes essential in rotary machines, especially when there are two relatively movable mechanical members in close proximity to one another. For example, sealing is required to prevent or at least minimize leakage of combustion gases at the interface between combustor transition pieces and stage one nozzles of gas turbines.  
           [0003]    In can-annular combustor arrangements typically found in gas turbines manufactured by the assignee, a plurality of combustors are disposed in an annular array about the axis of the turbine. Hot combustion gases flow from each combustor through a respective transition piece into the first stage nozzle. In addition to relative movement (due, e.g., to dynamic pulsing) between these components, the transition pieces and first stage nozzle are formed of different materials and are thus subjected to different temperatures during operation, thereby experiencing different degrees of thermal growth. Thus, both the transition pieces and the first stage nozzle and/or nozzle support elements may move radially, circumferentially and axially relative to one another. This “mismatch” at the interface of the transition pieces and the first stage nozzle and/or nozzle support elements requires an effective seal to contain the combustion products and the pressure differential across that interface, and to prevent compressor discharge air from bypassing the combustor.  
           [0004]    It is known to employ a dual stiffness cloth brush seal for sealing between combustor transition pieces and first stage nozzles or nozzle supports. Specifically, the layers of cloth material are disposed in a frame and suitably secured thereto, for example, by clamping to the frame, welding the material to the frame, or the like. The free edge of the layers are engaged within a U-shaped channel extending about the periphery of the downstream end of each transition piece, while a seal support is mounted within a groove or slot formed in the first stage nozzle or nozzle support. A cloth brush seal of this type is disclosed in commonly owned U.S. Pat. No. 6,042,119. This seal is not completely effective, however. For example, the inner and outer side walls of the stage one nozzle are unevenly heated, due to varied velocities on the pressure and suction sides of the nozzle. This causes the groove or slot where the seal support is secured to unevenly distort. This distortion, in effect, lifts the transition piece seal off its pressure sealing surface in the groove or slot, causing compressor discharge air to bypass the combustor, thereby increasing the levels of NOx emitted to atmosphere.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    This invention seeks to minimize leakage by combining the transition piece seal with flexible spring sealing elements that provide better leakage control at the interface of the transition piece and the stage one nozzle or nozzle support. For purposes of this disclosure, it matters not whether the spring sealing element engages the nozzle itself or a nozzle support element. Thus, reference will be made herein simply to the first stage nozzle.  
           [0006]    Specifically, each flexible spring seal element includes a generally horizontal mounting flange that enables the spring seal element to be secured within the slot formed in the first stage nozzle, along with the transition piece seal support. The remainder of the spring seal element has a sideways S or Z shape, with a flexible free end of the seal element adapted to engage the forward face of the first stage nozzle. The spring element is formed with a plurality of laterally spaced, axially oriented slots extending from the free sealing edge substantially to the horizontal mounting flange so that the spring seal element can differentially adapt or conform to the forward face of the first stage nozzle. To prevent leakage through the slots, a second substantially identical spring seal element is layered over the first spring seal element, but laterally offset in a shingled arrangement, thereby closing the slots in the respective spring elements. When the spring seal elements are mounted in the groove or slot in the first stage nozzle, along with the transition piece seal support, the free ends of the spring seal elements are resiliently compressed or biased against the forward face of the stage one nozzle, creating a first sealing location. At the same time, axial compression of the sealing elements also results in a downward force on the mounting flange, pushing the transition piece seal support against the lower surface of the groove or slot in the first stage nozzle, creating a second seal location.  
           [0007]    Accordingly, in its broader aspects, the present invention relates to a transition piece seal assembly comprising a transition piece seal support having a first flange for supporting a transition piece seal, and a second flange adapted for mounting in an adjacent nozzle; and at least one spring seal element having a mounting flange adapted to engage the second flange of the transition piece seal support, and a flex portion having a free edge adapted to engage a forward face of the nozzle.  
           [0008]    In another aspect, the invention relates to a gas turbine comprising an annular array of combustors, each having a transition piece extending between the combustor and a first stage turbine nozzle, and wherein a transition piece seal assembly is interposed at the interface of each transition piece and the first stage turbine nozzle, each transition piece seal assembly comprising a transition piece seal support having a first flange for supporting a transition piece seal, and a second flange secured in the first stage turbine nozzle; and at least one spring seal element having a mounting flange seated on the second flange of the transition piece seal support, and a flex portion having a free edge compressively engaged with a forward face of the nozzle.  
           [0009]    In still another aspect, the invention relates to a method of reducing leakage at an interface of a transition piece and a first stage turbine nozzle comprising: a) providing a seal assembly between the transition piece and the first stage turbine nozzle wherein the transition piece seal assembly is supported on a forward face of the first stage turbine nozzle and includes a seal support supporting sealing media engaged in a peripheral slot or channel on the transition piece; and b) providing at least one additional sealing element supported at one end in the forward face of the first stage turbine nozzle and having a free edge remote from the one end engaged with the forward face of the first stage turbine nozzle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is an enlarged fragmentary perspective view of a known transition piece cloth brush seal, employed between a transition piece and a first stage nozzle;  
         [0011]    [0011]FIG. 2 is an enlarged fragmentary cross sectional view of the transition piece seal of FIG. 1;  
         [0012]    [0012]FIG. 3 is a cross sectional view of a combination transition piece seal and flexible spring seal element in accordance with this invention;  
         [0013]    [0013]FIG. 4 is a cross sectional view of the transition piece seal and flexible spring seal element shown in FIG. 3, but mounted at the interface of a transition piece and first stage nozzle;  
         [0014]    [0014]FIG. 5 is an enlarged fragmentary perspective view of the combined transition piece seal and flexible spring seal element shown in FIG. 3;  
         [0015]    [0015]FIG. 6 is a rear elevation view of a pair of layered spring seal elements in accordance with the invention; and  
         [0016]    [0016]FIG. 7 is a front elevation of a single spring seal element in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Referring to FIGS. 1 and 2, there is illustrated a known transition piece seal  10  interposed between a forward end of a transition piece  12  and a first stage nozzle  14 . It will be appreciated that the transition piece  12  and the first stage nozzle or nozzle support  14  are movable radially, circumferentially and axially relative to one another due to vibratory or pulsing dynamics and also due to differential thermal growth.  
         [0018]    The transition piece  12  includes an upstanding groove  20  or channel formed by a pair of flanges  16  and  18 . The seal  10  includes a support  22  including a mounting flange  24  at one end, and an inverted J-shaped support channel  26  at an opposite end. The mounting flange  24  is secured within a groove or slot  28  in the first stage nozzle, with the aid of one or more shims  30 . The brush or cloth seal surfaces per se of the seal  10  comprise multiple layers  32  of woven material superposed directly one over the other. Marginal edges of the layers are suitably secured within the channel  26 , for example, by welding, clamping or the like. The layers  32  extend freely from the margin secured to the channel  26 , into the peripheral slot  20 . This seal may be of the type disclosed in commonly owned U.S. Pat. No. 6,042,119, but other transition piece seal arrangements may be utilized in conjunction with this invention.  
         [0019]    With reference now to FIGS.  3 - 7 , the new transition piece seal  34  is generally similar to seal  10  and includes a seal support member  36  with a horizontal mounting flange  38 , a vertical extension  40 , and an offset, substantially vertical seal flange  42  that provides a support for sealing media, which, in the exemplary embodiment, comprises the cloth seal  44 . The cloth seal  44  in the illustrated embodiment may be comprised of 0.027 inch thick Dutch twill weave, 30×250 mesh cloth of alloy L605. The cloth is wrapped about a pair of overlapped (in the lengthwise direction of the seal) shims  48  and pressed to flatten the woven mesh against the shims. The mesh layers are then spot welded to the shims along the side and top edges thereof as shown in FIG. 5. The seal is supported between seal flange  42  on one side, and an elongated backing bar  46  on the other, with the ends of the mesh cloth and shims clamped (or welded) therebetween.  
         [0020]    In accordance with this invention, flexible spring sealing elements  49  are added to interface between the transition piece seal  34  and the vertical forward face  50  of the stage  1  nozzle  51 .  
         [0021]    Each flexible spring element  49  includes a horizontal mounting flange  52  and a substantially sideways S or Z-shaped section including compressive flex portions  54 ,  56  and  58 , the latter terminating at a free sealing edge  60 , remote from the flange  52 . As best seen in FIGS.  5 - 7 , each spring element  49  is slotted at spaced locations along its length, each slot  62  extending from the free sealing edge  60 , through the compressive flex portions  54 ,  56  and  58  to, but not into, the mounting flange  52 . It is contemplated that the transition piece seal as well as the spring elements, will be formed in two or more lengthwise segments to extend about the periphery of the transition piece aft end. Moreover, each segment will include a pair of spring elements  49 , layered together but laterally offset, or shingled, so that the individual slots of one are closed by the solid flex portions between the slots of the other, as best seen in FIGS. 5 and 6.  
         [0022]    For example, if the slots  62  are spaced 1 inch apart, the cooperating spring elements would be laterally offset by about ½ inch. Thus, it will be understood that each spring element has a 1 inch flex portion at one end and a ½ inch flex portion at its opposite end (see FIG. 7) to enable the shingling arrangement at adjacent spring segment interfaces.  
         [0023]    The spring seal elements  49  provide two separate sealing interfaces with the forward face  50  of the stage  1  nozzle  51 . With reference to FIG. 4, with the mounting flanges  38  and  52  secured in the slot  66  with the aid of elongated shim  68 , it can be seen that a first seal is established between the sealing edges  60  and the vertical forward face  50  of the stage  1  nozzle  51 , and a second seal is established at the base  64  of the nozzle slot  66  as a result of downward pressure exerted on the transition piece seal mounting flange by the mounting flange  52  resulting from the compression of the spring seal elements against the forward face  50  of the nozzle  51 .  
         [0024]    The above arrangement further reduces combustion system leakage at the transition piece/nozzle interface.  
         [0025]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.