Abstract:
A combustor assembly having a transition piece and at least one orifice assembly in the transition piece, the orifice assembly comprising: a boss having an outside periphery and an inside periphery, the inside periphery including an annular seat and an upstanding flange formed with an annular, inwardly facing retaining ring groove, the boss fixed within an opening in the transition piece; an orifice plate having a bottom surface that is adapted to be received on the annular seat; and a retaining ring located in the retaining ring groove and at least partially engaged with the orifice plate.

Description:
This invention relates to gas turbine combustion technology and, more specifically, to an insert for transition piece air dilution holes that facilitates the use of changeable orifice plates for adjusting the flow of air into the transition piece. 
     BACKGROUND OF THE INVENTION 
     Current dry low NO x  combustion systems require tuning to achieve correct combustor temperatures. This is achieved in some instances by means of air dilution holes provided in the transition piece extending between the turbine and the first combustor stage. The air flowing through the holes serves as bypass and dilution air, but occasionally needs to be adjusted after turbine commissioning in the field. The current designs utilizing simple dilution holes require a lengthy and costly down time so that the transition pieces can be removed and resized. Specifically, the transition pieces must be stripped of their thermal barrier coating, patch welded, machined to add new holes, heat treated and recoated with the thermal barrier coating. In U.S. Pat. No. 6,499,993, owned by the assignee of this invention, there is provided a mechanical arrangement enabling external access to the combustion chamber which facilitates changeover of combustor dilution-hole areas to adjust the NO x  levels without disassembly of the combustors. More specifically, the assembly is provided with a boss, an orifice plate, and a retaining ring. The retaining ring is tapered, and in cooperation with a matching taper in the ring grooves, provide a wedging method for holding the orifice plate tightly in place. The boss design does not, however, have a flexible-weld distortion tolerant feature, which can lead to distortion of the undesirable distortion in the boss hole and orifice plate dimensions. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one exemplary and non-limiting aspect of this invention, there is provided a combustor assembly having a transition piece and at least one orifice assembly in the transition piece, the orifice assembly comprising: a boss having an outside periphery and an inside periphery, the inside periphery including an annular seat and an upstanding flange formed with an annular, inwardly facing retaining ring groove, the boss fixed within an opening in the transition piece; an orifice plate having a bottom surface that is adapted to be received on the annular seat; and a retaining ring located in the retaining ring groove and at least partially engaged with the orifice plate. 
     In another aspect, the invention relates to a boss and orifice plate assembly comprising an annular boss adapted to be secured in a hole formed in a combustor component, the boss formed with an annular seat supporting a replaceable orifice plate, and an annular retaining ring groove adjacent the seat, the seat extending radially inwardly of the annular retaining ring groove; and a wave spring seated in the groove and at least partially and resiliently engaged between a surface of the groove and a surface of the orifice plate. 
     In still another aspect, a method of adjusting the size of dilution air holes in a turbine combustor component comprising: (a) inserting a boss into a dilution air hole having a first diameter and welding the boss in place; (b) locating an orifice plate on an annular seat formed in the boss, the orifice plate having a center hole formed with a second diameter smaller than the first diameter; and (c) securing a retaining ring in a groove in the boss, in overlying and at least partially engaging relationship with the orifice plate, wherein the retaining ring resiliently braces the orifice plate against the seat. 
     The invention will now be described in connection with the drawings identified below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a turbine transition piece having replaceable orifice plate in accordance with a non-limiting, exemplary embodiment of the invention; 
         FIG. 2  is a perspective view of a boss employed in  FIG. 1  to hold a replaceable orifice plate; 
         FIG. 3  is a cross section through the boss in  FIG. 2 , but with an orifice plate and retaining ring installed; 
         FIG. 4  is a cross section taken through a boss in accordance with another non-limiting exemplary embodiment; 
         FIG. 5  is a cross section through a boss in accordance with yet another non-limiting exemplary embodiment; and 
         FIG. 6  is a more detailed perspective view of the boss shown in  FIG. 2  installed in a transition piece. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a gas turbine transition piece  10  is designed to connect to a turbine combustor (not shown) at an upstream end  12  and to the first turbine stage (not shown) at an opposite downstream end  14 . At various predetermined locations along the transition piece  10 , dilution flow holes are provided for flowing compressor discharge air into the combustion system in a combustor tuning process to achieve correct combustor temperatures. For purposes of this disclosure, two locations indicated by reference numerals  16  and  18 , have been designated as locations where a new orifice plate boss  20  may be welded in place to facilitate the tuning process. This is not to be interpreted, however, to mean that these are the only dilution holes present, or that the new orifice plate boss can only be used in these locations. 
       FIGS. 2 ,  3  and  6  illustrate the annular boss  20 , preferably constructed of Nimonic 263 alloy material. A base portion  22  of the boss defines an OD surface (or outside periphery)  24  and an ID surface (or inside periphery)  26  that are substantially parallel. Using  FIGS. 2 and 3  as references for orientation purposes, the surfaces  24  and  26  are substantially vertical, with surface  24  chamfered at opposite ends  28 ,  30 . Chamfer  30  connects to the lower base surface  32  that is formed in part by an upwardly tapered surface  34  that joins with the ID surface  26 . 
     The upper chamfer  28  joins to a radially inwardly tapered annular surface (or groove)  36  that, in turn, joins to an annular radiused corner  38  from which an upstanding, generally cylindrical wall or flange  40  extends upwardly, terminating at an annular flat top surface  42 . An internal wall  44  is formed with an upper chamfer  46 , an annular retaining ring groove  48 , and a radially inwardly extending shoulder or seat  50  that joins with the ID surface  26 . 
     Seat  50  is adapted to receive and support an annular and substantially planar orifice plate  52 , preformed with a center hole  54  that defines the new diameter for the dilution hole, Plate  52  may be constructed of Hastalloy X (or other suitable) material with a substantially uniform thickness in the exemplary but non-limiting embodiment of 0.125 inch. 
     The annular orifice plate  52  is held in place by an annular, undulated retaining ring  58 , i.e., the ring is formed as a wave spring, with undulations in the peripheral or circumferential direction. The groove  48  is sized, in conjunction with the selected thickness of the orifice plate  52 , such that when the retaining ring is forced into the groove  48 , it exerts a downward force on the orifice plate  52  of, for example, 35 lbs., sufficient to hold the plate in place during operation of the turbine. Note in this regard that the retaining ring  58  has a greater diameter than the orifice plate, and thus the groove  48  has a greater diameter than the seat  50 . 
     At the same time, the arrangement of the groove  48  and seat  52  in an upstanding center portion of the boss substantially isolates the groove shape and dimensions from any distortion that might otherwise be caused by welding the boss into a dilution hole, e.g., hole  16 , in the transition piece. In other words, the upstanding portion of the boss is able to flex during welding without permanent distortion, and thus, post-weld machining of the groove  48  and seat  52  is not necessary. 
     In a variation of the above boss design, the OD surface  24  may be made substantially vertical along its entire height (eliminating the chamfers  28 ,  30  similar to the OD surface  76  in  FIG. 5 ), with chamfers formed instead, on the surface defining the TP hole(s). It is understood that the chamfers on the OD surface of the boss, or alternatively, on the edges of the holes in the transition piece, facilitate the use of full penetration welds to fix the boss to the transition piece. In this case, the thickness of the base portion of the boss would exceed the thickness of the transition piece. This is helpful in that the transition piece is formed of a complex shape, and the thicker boss may be machined after welding to blend smoothly with the TP surface, leaving no “sunken” edges that could give rise to unwanted stresses. 
       FIG. 4  illustrates a boss  60  similar to boss  20 , but with a solid center portion  62 . With the retaining ring groove  64  machined into the upstanding portion  66  of the boss, the boss may be welded in place in a dilution hole in the TP. Thereafter, the solid center portion is removed along the circular dotted line  68 , leaving a seat  70  for the orifice plate. Leaving the center portion  62  in place during welding helps maintain the correct, round orientation of both the groove  64  and resulting seat  70 . 
       FIG. 5  illustrates an alternative boss design intended to even further isolate the retaining ring groove and orifice plate seat from welding stresses. In this embodiment, the boss  72  includes a base portion  74  having a substantially vertical OD surface or edge  76  that joins to top and bottom surfaces  78 ,  80 , respectively. Top surface  78  merges with an inwardly and downwardly angled surface (or groove)  82 , while lower surface  80  joins to an inwardly and upwardly angled surface  84  that joins with a horizontal bottom surface  86 . 
     A substantially inverted U-shaped loop  88  is joined to the base portion  74 . Specifically, a first outer vertical wall  90  extends upwardly from the base portion  74  and, via horizontal top surface  94 , reverses direction to form an inner vertical wall  96  that extends downwardly from the top surface  94  to a radially inwardly turned free end  98 . The radially inner side of the wall  96  is machined to incorporate the shoulder or seat  100  for supporting the orifice plate (not shown in  FIG. 5 ) as well as the retaining ring groove  102  in a manner similar to that described above in connection with  FIGS. 3 and 4 . Here, however, the inverted loop  88  serves to further isolate the snap ring groove  102  and orifice plate seat  100  from welding distortion. 
     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.