Abstract:
Undue flexing and cracking of an internal exhaust shield of a turbine is eliminated by isolating thermally-induced movement in the shield from that of strut apparatus passing therethrough to a surrounding outer exhaust casing. Methods and apparatus are disclosed.

Description:
PRIORITY CLAIM 
       [0001]    Applicant claims the benefit of the filing date of Feb. 11, 2011 of U.S. provisional patent application Ser. No. 61/448,876, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to jet turbines, more particularly to land-based turbines used, for example in Combined Cycle Power Generation facilities and even more particularly to the exhaust structures of such turbines and the inherent problems therein of cracking due to differentials in thermal generated expansion and contraction of the respective exhaust components. 
       BACKGROUND OF THE INVENTION 
       [0003]    Typically, such turbines include an exhaust structure which comprises an outer exhaust casing in the form of an annulus, and an inner exhaust tunnel defined by an annular exhaust cylinder or shield with an annular dead air space defined between the outer casing and the inner shield. Simply stated, an outer casing or cylinder surrounds an inner shield or cylinder in the exhaust area of a turbine. 
         [0004]    The turbine typically includes a cylindrical bearing housing disposed around a central axis of a turbine and located and centered there, preferably by two sets or arrays of radially-extending struts. The respective struts in each array, at about 120 degrees apart, are encased in strut housings, extending radially inwardly to the bearing housing from the outer exhaust casing and through the inner shield to the bearing housing. The strut housings are welded to the inner shield, where they pass outwardly therethrough to the outer casing and inwardly therethrough to the bearing housing. Typically the struts, strut housings and inner shield are made from high heat-resistant materials or alloys, including, for example, an alloy known in the industry as “hastalloy”. 
         [0005]    It is in the area of the welded joinery between the strut housings and the inner shield which suffer the principal consequences of differential thermal-caused material expansion and contraction. 
         [0006]    As the turbine is operated, it can produce exhaust gases of high temperatures such as 1000 to 1300 degrees Fahrenheit or more. This heat, applied to the strut housing and to the inner shield causes them to expand or move in respective directions in response to this heating. Thus, the strut housing may expand longitudinally (in a radial direction from the bearing housing) while the inner shield moves or expands in other directions, or at least at different rates, all in response to the exhaust heat. Thus, there is a differential of material movement and destructive force at the welded joint between the strut housing and the inner shield. This differential causes the inner shield to flex, then crack or break apart at the intersection area at and around the welded joint to the strut housing. The dead air space between the inner shield and outer casing is thus opened to direct exhaust gas. 
         [0007]    In the past, this material failure is cured only by shutting down the turbine, accessing the cracked area, removing the affected parts of the inner shield and welding replacement and reinforcing plates in the shield and to the strut housing. This work is expensive, requires periods of turbine shutdown, is difficult to access, is subject eventually to repeat of the continuing problem and is, for these and other reasons, very problematical. 
         [0008]    Such turbines generally experience these adverse thermally-caused movement and force differentials on startup from inoperative conditions. Those cycles occur periodically on even a daily basis or multiple times per day. Thus, every time the turbine is started, the thermal expansion produces the described stress and flexes the inner shield eventually to failure. 
         [0009]    Accordingly, it has been one objective of this invention to provide an improved exhaust structure for turbines which is not subject to the failure of materials due to differential thermal expansion and/or contraction. 
         [0010]    A further objective of the invention has been to provide an improved exhaust structure for a turbine extending the life and maintenance requirements of such turbines in the exhaust components. 
         [0011]    A further objective of the invention has been to provide an improved method for handling turbine exhaust. 
       SUMMARY OF THE INVENTION 
       [0012]    In summary, a preferred embodiment of the invention contemplates the isolation of thermally-caused expansion in the strut apparatus from thermally caused expansion in the shield. By isolating these respective forces, one from the other, undesirable flexing and cracking of the shield caused by these prior interfering differential forces is eliminated. 
         [0013]    This method and result is obtained by passing the strut apparatus through the shield such that both these components are slidable or moveable with respect to each other so that the relative movement of one dose not stress or adversely affect the other. A combination of mounting plates, on the shield and stops of the strut apparatus are useful in attaining these results. 
         [0014]    These and other objectives will be readily apparent from the following written description and from the drawings in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a diagrammatic illustration of the invention and turbine environment in which it is used; 
           [0016]      FIG. 1A  is an enlarged diagrammatic detail of the encircled area  1 A of  FIG. 1 ; 
           [0017]      FIGS. 2A-2E  are diagrammatic sketches of the invention of  FIG. 1 , shown in exploded view illustrating the progressive construction of the invention components for clarity with various components in the FIGS. not shown for clarity and with some components or portions shown in phantom for clarity; 
           [0018]      FIG. 2A  is an exploded view showing the strut housing inner shield and outer exhaust casing and illustrating positioning of a first pair of complementary mounting plates interiorly of the shield; 
           [0019]      FIG. 2B  is an exploded view showing the first pair of mounting plates in position and illustrating insertion of a pair of elongated angle plates; 
           [0020]      FIG. 2C  is an exploded view showing the first pair of mounting plates and the angled filler plates in position and a second pair of complementary mounting plates for mounting interiorly of the first pair of mounting plates and thereon; 
           [0021]      FIG. 2D  is an exploded view showing the mounting plate pairs and angled filler plates in position and the respective stop pairs for mounting on the strut housing; 
           [0022]      FIG. 2E  is an exploded view illustrating the mounting plates and angle fillers and the top members, all in position in the finished construction; 
           [0023]      FIG. 3  is a cross-sectional view taken along lines  3 - 3  of  FIG. 2E ; 
           [0024]      FIG. 4  is a cross-sectional view taken along lines  4 - 4  of  FIG. 2E , with the inner shield positioned with respect to the radially inward elongated stops on the strut housing; and spaced from the radially outward stops; 
           [0025]      FIG. 5  is a cross-sectional view taken from the same perspective of  FIG. 3 , but showing the inner shield positioned on the radially outer angle stops on the strut housing spaced from the interior stops; 
           [0026]      FIG. 6  is a cross-sectional view from the same perspective as  FIG. 4  but further showing the position of the inner shield position on the outer angle stops, spaced from the radially inward stops; and 
           [0027]      FIG. 7  is an elevational view in partial cross-section similar to  FIGS. 3 and 4  but shows an alternate embodiment of the invention showing the inner shield in an intermediate position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Turning now to the drawings,  FIG. 1  diagrammatically illustrates the invention and its use. A turbine  10  is oriented about a major axis  11 . A bearing housing  14  extends rearwardly from the turbine about axis  11  and provides support for a rotary turbine shaft (not shown). An outer exhaust casing  20  in the form of an annulus or cylinder and defining an outer exhaust cylinder extends rearwardly from turbine  10 . An inner shield  30  in the form of an annulus or a cylinder and defining an exhaust tunnel also extends rearwardly from turbine  10 , radially inward from outer casing  20 . The outer casing  20  outwardly surrounds inner shield  30  such that there is an annular dead space  40  between casing  20  and shield  30 . Exhaust from turbine T flows in the direction of arrows E. 
         [0029]    A series of radially-extending struts  50  extends from outer casing  20  to bearing housing  14 , through shield  30  at intersection  35 . Struts  50  are encased in strut housing  60  as shown. Struts  50  and housings  60  are attached, as by welding, to the bearing housing  14  and to outer casing  20  where strut housing end  60   a  is attached as by welding to casing  20 . However, according to the invention and advantageously, neither the housings  60  or the struts  50  are welded to inner shield  30 . The intersection  35  or joint area between strut housing  60  and inner shield  30  are shown in more detail in Detail A of  FIG. 1  and in the other Figures. 
         [0030]    More specifically, and according to the invention, the intersection of strut housing  60  to inner shield  30  is defined as a sliding, relatively moveable or extensible intersection  35  which alleviates any undesirable interconnection between these components. In other words, and in accordance with the invention, any thermal differential expansion, between inner shield  30  on one hand and the housing  60  and struts  50 , are accommodated by the relative movement between and at the intersection of the shield  30  and housing  60 . These parts are thus free to move responsive to thermal variations without exerting structural impact or force on the other component. As a result, thermal expansions of these components are accommodated without creation of stress on the other component. Cracking due to the differentiation of respective thermal expansion/contraction is thus eliminated, significantly reducing structural failure, maintenance schedules, downtime and expense previously associated with the exhaust structures of turbines. 
         [0031]    More particularly, the FIGS.  1 A and  2 A- 6  illustrate the construction steps and final configuration of the interface components of the moving intersection between each strut  50 ,  60  and the inner shield  30 . 
         [0032]    Preferably, the shield  30  is provided with an opening  70 , larger than but preferably complementary to the elongated, oval-like cross-sectional shape of the strut housing  60 . Accordingly, there is a clearance (at  71 ) between the strut housing  60  and the shield  30 . Two pairs of complementary mounting plates  72 ,  73  and  74 ,  75  are arranged about the housing  60  and welded to the shield  30  with a small clearance  74 A between the formed apertures in plates  72 ,  73  and the opposed faces of plates  74 ,  75  with housing  60 . Plates  74 ,  75  are welded along the plates  72 ,  73 . Two elongated angle filler plates  76 ,  77  are inserted between plates  72 ,  73  and housing  60  and are welded to plates  72 ,  73  but not to housing  60 . These elongated filler plates  76 ,  77  extend between ends of plates  74 ,  75 . Accordingly, the housing  60  is not attached to, but extends slidably through shield  30  at intersection  35  so the housing  60  can elongate in thermal response to exhaust heat, but without transferring any of that elongation force to shield  30 . Likewise, shield  30  can move in response to thermal stimulus without resulting in undue stress from attachment to the strut apparatus. Housing  60  is thus slidable with respect to filler plates  76 ,  77 . 
         [0033]    A pair of stops  78 ,  79  in the form of elongated bars are welded to housing  60  as shown radially inwardly with respect to shield  30  and angle plates  76 ,  77 . 
         [0034]    Likewise, a pair of two, relatively shorter angle-shaped stops  80 ,  81  are welded to strut housing  60  radially outwardly with respect to shield  30  for non-attached engagement with outer surfaces of shield  30 . The distance between the relative shield-facing stop surfaces of stops  78 ,  79  and  80 ,  81 , respectively are at least slightly greater than the combined thicknesses of shield  30  and the respective plates  72 - 75 , such that there can be relative motion between strut housing  60  and shield  30  in at least a radial direction along strut  60  (and preferably some at least slight motion normal to the radial extension of strut housing  60 ). 
         [0035]    Thus, it will be appreciated that the relative radial position of shield  30  on strut housing  60  is variable between interior stops  78 ,  79  and outer stops  80 ,  81 . 
         [0036]    In another aspect of the invention, an alternative embodiment of the invention is illustrated in  FIG. 7 . This embodiment provides similar function of the preceding embodiment but with a modified structure. 
         [0037]    Referring to  FIG. 7 , it should be noted that stops  78 ,  79  of  FIGS. 1-6  have been omitted. Also, the angled filler plates  76 ,  77  are omitted. Components of  FIG. 7  which are like those in  FIGS. 1-6  bear the same numbers. New components with specific new numbers are described below. 
         [0038]    In the embodiment of  FIG. 7 , a collar  90  is provided about the strut housing  60 , and is slidable thereon. Collar  90  is welded to shield  30  at an end  91  of collar  90  (or to mounting plates such as plates  72 - 75 , if used in this embodiment). 
         [0039]    In place of stops  78 ,  79  of  FIGS. 1-6 , there are welded angle stops  92 ,  93  along the sides of strut housing  60 . 
         [0040]    Collar  90  is provided with two opposed slots  94 ,  95  on opposite sides of the collar  90 . 
         [0041]    Pins  96 ,  97  are attached to strut housing  60  by welding or any suitable expedient, on opposite sides thereof in a position such that each extends through a respective slot  94 ,  95 , respectively. 
         [0042]    Washers  98 ,  99  of larger extend than slots  94 ,  95  are secured to pints  96 ,  97  respectively, so collar  90  is captured thereby on housing  60 . 
         [0043]    The length of slots  94 ,  95  is long enough to accommodate translation or movement of collar  90  along strut housing  60  between stops  92 ,  93  radially inward of shield  30 , and stops  80  on housing  60 , radially outward of shield  30 . 
         [0044]    It will be appreciated that collar  90  extends much further along strut housing  60  than did filler plates  76 ,  77 , thereby providing a more efficient sliding contact between the collar  90  and housing  60  than did filler plates  76 ,  77 . 
         [0045]    Also, the interaction of pins  96 ,  97  and slots  94 ,  95  can define relative parameters of motion of collar  90  on strut  60  as desired. 
         [0046]    Accordingly, the actual thermal responsive movement of shield  30  and strut housing  60  in both embodiments do not adversely transfer between these components. Material flex and failure due to thermal expansion or contraction is eliminated, and the exhaust structure for turbine  10  is vastly improved. 
         [0047]    Other structures may be used to produce the same or similar isolation of thermal caused movement, reducing and eliminating cracking or damage. 
         [0048]    These and other modifications and advantages will become readily apparent to those of ordinary skill in the art to which this invention pertains, without departing from the scope of the invention, and applicant intends to be bound only by the claims appended hereto.