Abstract:
A method for assembling a turbine engine including an exhaust diffuser extending aftward from exhaust casing, wherein the method includes coupling a relief diaphragm to the exhaust diffuser and coupling a guide system to the exhaust diffuser such that the guide system is radially inward from the relief diaphragm and defines at least a portion of the exhaust flow path through the exhaust diffuser.

Description:
BACKGROUND OF INVENTION 
   This invention relates generally to rotary machines and, more particularly, to a method and a system for reducing internal exhaust turbulence from rotary machines. 
   Steam and gas turbines are used, among other purposes, to power electric generators. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Some known steam turbines are coupled to a condenser. Under normal operating conditions, an engine casing channels exhaust flow axially through the engine to an exhaust diffuser and then the condenser condenses the exhaust. Know casings include cut away ducts which include relief diaphragms. Under abnormal operating conditions, the condenser can fail and cause a rapid pressure increase in the exhaust diffuser. Under this condition, the relief diaphragm is designed to rupture and release steam outside and facilitate preventing damage to the turbine. 
   An operating efficiency of the turbine depends at least in part on flow dynamics within the turbine, and as such, engine efficiency may be limited by the geometry of aerodynamic components. More specifically, changing the geometric shape of certain aerodynamic components, such as exhaust diffusers, may facilitate reducing flow variations and increasing engine efficiency. However, because relief diaphragms are adjacent the exhaust flow, the cut away ducts may induce turbulence into the exhaust flow path. Such turbulence may cause flow losses which may decrease turbine efficiency. 
   SUMMARY OF INVENTION 
   In one aspect, a method is provided for assembling a turbine engine including an exhaust diffuser extending aftward from exhaust casing, wherein the method includes coupling a relief diaphragm to the exhaust diffuser and coupling a guide system to the exhaust diffuser such that the guide system is radially inward from the relief diaphragm and defines at least a portion of the exhaust flow path through the exhaust diffuser. 
   In another aspect, a turbine engine is provided, wherein the engine includes an exhaust casing defining a portion of an exhaust flow path therethrough, an exhaust diffuser coupled to the exhaust casing, a relief diaphragm coupled to the exhaust diffuser, and a guide system coupled to the exhaust diffuser such that the guide system is radially inward from the relief diaphragm and between the relief diaphragm and the exhaust flow path. 
   In further aspect, a turbine engine is provided including an exhaust casing, an exhaust diffuser, a relief diaphragm, wherein the relief diaphragm includes a cut away duct extending from the casing and configured to rupture during engine overpressurization conditions, and a guide system coupled within the engine between the diaphragm and an exhaust flow path extending through said exhaust casing. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a cross-sectional view of an exemplary turbine engine. 
       FIG. 2  is a cross-sectional schematic end view of a known exhaust diffuser that may be used with the turbine shown in FIG.  1 . 
       FIG. 3  is a partial cross-sectional schematic side view of an exemplary guide system that may be used with the exhaust diffuser shown in FIG.  1 . 
       FIG. 4  is a cross-sectional schematic end view of the guide system shown in FIG.  3 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a partial cross-sectional of an exemplary steam turbine engine  10  including a rotor assembly  12 , a stator assembly  14 , and a casing  16 . Rotor assembly  12  includes a shaft  18  and a plurality of bucket assemblies  20 . Each bucket assembly  20  includes a plurality of buckets  22  arranged in rows that extend circumferentially around shaft  18 . 
   Stator assembly  14  includes a stator  24  and a plurality of nozzle assemblies  26 . Nozzle assemblies  26  include a plurality of nozzles  28  arranged in rows that extend radially inwardly and circumferentially around stator  24 . Nozzles  28  cooperate with buckets  22  to form a turbine stage and to define a portion of a steam flow path through turbine  10 . 
   In operation, steam  30  enters an inlet  32  of turbine  10  and is channeled through nozzles  28 . Nozzles  28  direct steam  30  downstream against buckets  22 . Steam  30  passing through the turbine stages imparts a force on buckets  22  causing shaft  18  to rotate. Steam  30  exits turbine  10  through an exhaust casing  34  and an exhaust diffuser  36 . An atmospheric relief diaphragm  38 , an aperture  44 , and a cut away duct  50  are positioned on diffuser  36 . In the event of an exhaust overpressure condition, diaphragm  38  is configured to rupture and exhaust gases are channeled outside the turbine  10  through aperture  44 , duct  50 , and diaphragm  38 . 
   At least one end of turbine  10  may extend axially away from shaft  18  and may be attached to a load or machinery (not shown), such as, but not limited to, a generator, and/or another turbine. Accordingly, a large steam turbine unit may actually include several turbines that are all co-axially coupled to the same shaft  18 . Such a unit may, for example, include a high-pressure turbine coupled to an intermediate-pressure turbine, which is coupled to a low-pressure turbine. In one embodiment, steam turbine  10  is commercially available from General Electric Power Systems, Schenectady, N.Y. 
     FIG. 2  is a cross-sectional schematic end view of a known exhaust diffuser  36  that may be used with turbine engine  10 . Diffuser  36  includes a first side  40  and a second side  42  that is positioned opposite from first side  40  such that an aperture  44  is defined therebetween. A ledge  46  extends substantially circumferentially into aperture  44  from an inner surface  48  of diffuser  36 . An atmospheric relief diaphragm  38  is coupled to diffuser  36  such that diaphragm  38  is in flow communication with the exhaust flow path. Diaphragm  38  is known in the art, and is coupled to a cut away duct  50  extending radially outwardly from diffuser  36 . 
   During normal operation, diaphragm  38  remains sealed and diffuser  36  channels exhaust gases axially outward from turbine engine  10 . The geometry and orientation of sides  40  and  42 , ledge  46 , and cut away duct  50  may induce turbulence in the exhaust flow path, thereby reducing the turbine efficiency. In the event of an exhaust overpressure condition, diaphragm  38  is configured to rupture and to discharge exhaust gases through aperture  44  and from turbine  10  to facilitate reducing the peak abnormal operating pressure within diffuser  36  to an acceptable peak operating pressure. 
     FIG. 3  is a partial cross-sectional schematic side view of exemplary guide system  70  that may be used with the upper half exhaust diffuser  36 .  FIG. 4  is a cross-sectional schematic end view of guide system  70 . Guide system  70  includes a first guide member shell  72  and a second guide member shell  74 . Member shell  74  is positioned opposite member shell  72  and each shell  72  and  74  is pivotably coupled to diffuser  36 . More specifically, shells  72  and  74  are pivotably coupled to diffuser  36  by a pair of hinges  76  such that each shell  72  and  74  is rotatable from a closed position  85  to an open position  102 . In an alternate embodiment, shells  72  and  74  are pivotably coupled to diffuser  36  using at least one of a spring-loaded latch, a detent mechanism, and a cable. In the exemplary embodiment, hinges  76  are mounted against diffuser ledge  46 . 
   Member shell  72  includes a radially outer edge  80 , a radially inner edge  82 , and an arcuate body  84  extending therebetween. In the exemplary embodiment, shell  74  is identical to shell  72  and includes a radially inner edge  86  and a radially outer edge  88 , and an arcuate body  90  extending therebetween. In an alternative embodiment, bodies  84  and  90  are substantially planar. 
   Guide system  70  also includes a support ledge  94  and at least one shear pin  96 . Ledge  94  extends across aperture  44  between a forward diffuser ledge  78  and an aft diffuser ledge  92  such that member shells  72  and  74  are restricted from pivoting inward towards a diffuser cavity  98 . In the exemplary embodiment, ledge  94  extends perpendicular to the vertical center axis  100 . Member shell  72  and member shell  74  are secured in the closed position against ledge  94  by at least one shear pin  96 . In the exemplary embodiment, inner edges  82  and  86  form a contact line with ledge  94  in the closed position. Cavity  98  is positioned between bodies  84  and  90  and relief diaphragm  38  in flow communication with exhaust diffuser  36  by at least one cutout  87  in bodies  84  and  90 . In one embodiment, cutout  87  is substantially centered within in bodies  84  and  90 . Cutout  87  is sized to permit rapid transmission of abnormal pressure to relief diaphragm  38  such that relief diaphragm  38  may rupture. 
   During normal operation, diaphragm  38  remains sealed, guide system  70  remains closed  85  and isolates diaphragm  38  from exhaust path flow, and diffuser  36  channels exhaust path flow axially outward from the turbine engine  10 . The geometry and orientation of guide system  70  facilitates a reduced turbulent flow  52 . More specifically, the geometry of first guide member shell  72  and second guide member shell  74  substantially compliment the geometry and orientation of diffuser  36  and form a continuous flow surface across aperture  44 . 
   In the event of an exhaust overpressure condition, diaphragm  38  ruptures, pins  96  shear, and guide system  70  moves to an open position  102  such that exhaust gases from engine turbine  10  are discharged through aperture  44  and diaphragm  38  to facilitate reducing the operating pressure within diffuser  36 . More specifically, during overpressure condition shear pins  96  break and first guide member shell  72  and second member shell  74  rotate into open position  102 . Guide system  70  is sized to allow unimpeded flow through ruptured diaphragm  38 . In the exemplary embodiment, diaphragm  38  is configured to rupture when the pressure inside the exhaust casing exceeds approximately 15 psig. In the another embodiment, diaphragm  38  is configured to rupture when the pressure inside the exhaust casing exceeds approximately 1 psig. 
   The above-described guide system is performance enhancing and efficient. The guide system increases the aerodynamic qualities of the exhaust diffuser by reducing the flow variations and losses induced by the cut away ducts, thus facilitating the reduction of exhaust flow turbulence and increasing engine efficiency. As a result, the guide system significantly improves the performance of the turbine and increases operating efficiency in a cost-effective manner. 
   Exemplary embodiments of the guide system are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of the guide system may be utilized independently and separately from other components described herein. Each guide system component can also be used in combination with other guide system and turbine components. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.