Patent Publication Number: US-7722314-B2

Title: Methods and systems for assembling a turbine

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to assembling rotatable machinery and, more particularly, to methods and systems for sealing an extraction cavity in a steam turbine. 
     At least some known steam turbine designs include static nozzle segments that direct a flow of steam into blades coupled to a rotatable member in the turbine. A nozzle airfoil construction is typically called a diaphragm stage. When more than one nozzle stage is supported by an outer structure or ring, the construction is generally referred to as a nozzle carrier, a “drum construction”, or a “carrier construction” flowpath. A nozzle carrier is supported within a turbine casing such that the nozzles are substantially aligned with stages of the turbine blades. 
     In at least some known turbines, steam is extracted from the low-pressure turbine section for use in other applications. Generally, in steam turbines including a nozzle carrier, steam may only be extracted from the turbine section downstream from a last stage of the carrier. However, in some cases, this extraction location may not be the optimum stage from which steam should be extracted. For example, often a higher pressure or higher temperature steam is desired. 
     Accordingly, at least some known steam turbines utilize separate carriers within the turbine design to enable steam to be extracted from a location defined between the first and the second carriers. However, utilizing separate carriers may make alignment difficult, as both the carrier and the rotor must be removed to make necessary adjustments. Moreover, utilizing separate carriers generally adds complexity to a turbine design that the carrier is intended to improve. As such, costs and/or time associated with fabrication, assembly, and/or maintenance of the turbine may be increased. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a method for assembling a turbine is provided, wherein the method includes positioning an annular nozzle carrier radially inwardly from a casing such that a cavity is defined between the nozzle carrier and the casing. The method also includes extending a flange from at least one of a leading edge of the annular casing and a leading edge of the nozzle carrier, and extending a seal ring between the nozzle carrier and the casing such that the seal ring seals the cavity, wherein the seal ring is positioned between the flange and at least one of the nozzle carrier and the casing. 
     In another aspect, a turbine is provided, wherein the turbine includes an annular casing and an annular nozzle carrier positioned radially inwardly from the casing such that a cavity is defined therebetween. The turbine also includes a flange extending from at least one of a leading edge of the annular casing and a leading edge of the nozzle carrier, and a seal ring extending between the casing and the nozzle carrier such that the seal ring seals the cavity. The seal ring is positioned between the flange and at least one of the nozzle carrier and the casing. 
     In a further aspect, an annular component carrier assembly is provided, wherein the carrier assembly is positioned radially inwardly from an annular machine casing such that a cavity is defined therebetween. The assembly includes a flange extending from at least one of a leading edge of the casing and a leading edge of the carrier assembly, and a seal ring extending between the casing and the carrier assembly such that the seal ring seals the cavity. The seal ring is positioned between the flange and at least one of the carrier assembly and the casing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an exemplary opposed-flow steam turbine; 
         FIG. 2  is a perspective view of an exemplary nozzle carrier that may be used with the turbine shown in  FIG. 1 . 
         FIG. 3  is a schematic cross-sectional view of a portion of the turbine engine shown in  FIG. 1 . 
         FIG. 4  is an enlarged schematic cross-sectional view of the sealing assembly shown in  FIG. 3  and taken along area  4 . 
         FIG. 5  is a schematic cross-sectional view of an alternative embodiment of a portion of the turbine engine shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic illustration of an exemplary opposed-flow steam turbine  10 . Turbine  10  includes first and second low pressure (LP) sections  12  and  14 . As is known in the art, each turbine section  12  and  14  includes a plurality of stages of diaphragms (not shown in  FIG. 1 ). A rotor shaft  16  extends through sections  12  and  14 . Each LP section  12  and  14  includes a nozzle  18  and  20 . A single outer shell or casing  22  is divided along a horizontal plane and axially into upper and lower half sections  24  and  26 , respectively, and spans both LP sections  12  and  14 . A central section  28  of shell  22  includes a low pressure steam inlet  30 . Within outer shell or casing  22 , LP sections  12  and  14  are arranged in a single bearing span supported by journal bearings  32  and  34 . A flow splitter  40  extends between first and second turbine sections  12  and  14 . 
     It should be noted that although  FIG. 1  illustrates a double flow low pressure turbine, as will be appreciated by one of ordinary skill in the art, the present invention is not limited to being used with low pressure turbines and can be used with any double flow turbine including, but not limited to intermediate pressure (IP) turbines or high pressure (HP) turbines. In addition, the present invention is not limited to being used with double flow turbines, but rather may also be used with single flow steam turbines as well, for example. 
     During operation, low pressure steam inlet  30  receives low pressure/intermediate temperature steam  50  from a source, for example, an HP turbine or IP turbine through a cross-over pipe (not shown). Steam  50  is channeled through inlet  30  wherein flow splitter  40  splits the steam flow into two opposite flow paths  52  and  54 . More specifically, the steam  50  is routed through LP sections  12  and  14  wherein work is extracted from the steam to rotate rotor shaft  16 . The steam exits LP sections  12  and  14  and is routed to a condenser, for example. 
       FIG. 2  is a perspective view of an exemplary nozzle carrier assembly  210  that retains a plurality of stationary nozzles  212  of a turbine, for example, turbine  10 . In one embodiment, nozzle carrier assembly  210  is used with a low-pressure turbine section from which extractions are typically taken. In an alternative embodiment, nozzle carrier  210  is used with a high-pressure or intermediate-pressure turbine section. In the exemplary embodiment, carrier  210  includes upper and lower carrier halves  214  and  215 , respectively, which are coupled together along a horizontal joint face  216 . Nozzles  212  are arranged in an annular array at axially spaced locations along carrier  210 . Each circumferentially-spaced array of nozzles  212  includes a plurality of discrete nozzles  212  that are positioned circumferentially against each other. When a rotor (not shown) is rotatably coupled within lower carrier half  215 , and after carrier halves  214  and  215  are coupled together, nozzles  212 , together with annular arrays of airfoils or buckets extending radially outward from the rotor, form multiple stages of turbine  10 . Alternatively, each nozzle stage may also be formed from two half rings that have airfoils machined therein or fabricated into inner and outer portions of the rings to form the stage. 
       FIG. 3  is a schematic cross-sectional view of a portion of turbine engine  10 . Turbine engine  10  includes upper half casing  24  that is coupled to a lower half casing (not shown) when turbine engine  10  is fully assembled. Nozzle carrier  210  is positioned radially inwardly from casing  24  such that a cavity  300  is defined therebetween. A gusset structure  302  is positioned within cavity  300  such that a plurality of gussets  304  facilitate providing support between casing  24  and nozzle carrier  210 . Gusset structure  302  includes a radial protrusion  306  that is positioned within a notch  308  formed in casing  24  to facilitate preventing axial movement of gusset structure  302  and/or nozzle carrier  210 . Furthermore, in the exemplary embodiment, nozzle carrier  210  includes a plurality of nozzles  212  that are positioned to discharge steam from an apparatus, such as a boiler, into a turbine chamber  310 . A sealing assembly  312 , described in more detail below, is coupled to casing  24  such that sealing assembly  312  is in sealing contact with nozzle carrier  210  to facilitate sealing cavity  300  from the surrounding atmosphere. In an alternative embodiment, sealing assembly  312  is coupled to nozzle carrier  210  and is in sealing contact with casing  24  to facilitate sealing cavity  300  from the surrounding atmosphere. 
     In the exemplary embodiment, nozzle carrier  210  includes at least one aperture  314  that extends through nozzle carrier  210  from turbine chamber  310  to cavity  300 . Moreover, in the exemplary embodiment, aperture  314  is substantially aligned with a stage of rotor blades  316  that is coupled to turbine rotor  16  and is rotatable between adjacent nozzles  212 . Accordingly, in the exemplary embodiment aperture  314  extends substantially radially through nozzle carrier  210 . The alignment of aperture  314  enables steam to be extracted from rotor blade stage  316 . In one embodiment, nozzle carrier  210  includes a plurality of apertures  314  that are each substantially aligned with multiple rotor blade stages  316 , such that steam may be extracted from the various stages of rotor blades  316 . In another embodiment, nozzle carrier  210  includes a plurality of apertures  314  that are spaced circumferentially around nozzle carrier  210  and aligned with at least one rotor blade stage  316 . it should be noted that apertures  314  may be circular, slotted, or any other suitable shape which facilitates steam being extracted from turbine  10 . Moreover, in one embodiment, apertures  314  are elongated slots extending circumferentially around nozzle carrier  210 . In an alternative embodiment, apertures  314  are a combination of circular openings and other shaped openings including slotted openings. 
       FIG. 4  is an enlarged schematic cross-sectional view of sealing assembly  312 . Sealing assembly  312  extends from casing  24  to nozzle carrier  210 . Specifically, a leading edge  350  of casing  24  includes a flange  352  that extends generally radially inwardly towards nozzle carrier  210  and acts as a flow guide for the surrounding atmosphere. In the exemplary embodiment, flange  352  is coupled to leading edge  350  with a fastening mechanism  356 . In another embodiment, flange  352  is coupled to casing  24  using any other suitable coupling mechanism, such as, but not limited to welding. Moreover, in an alternative embodiment, flange  352  and casing  24  are formed together as a unitary piece. An annular sealing ring  358  is coupled between flange  352  and casing  24  and extends radially inwardly towards nozzle carrier  210 , such that a radially inner end  360  of sealing ring  358  engages a leading edge  362  of nozzle carrier  210  to facilitate sealing cavity  300 . In the exemplary embodiment nozzle carrier leading edge  362  includes a rounded protrusion  364  that is engaged by sealing ring radially inner end  360 . Rounded protrusion  364  provides a determinant sealing surface that facilitates accommodating a varying axial alignment between casing  24  and nozzle carrier  210  due to tolerances and transient conditions. In an alternative embodiment, within sealing assembly  312 , leading edge  362  is substantially planar and sealing ring radially inner end  360  engages a substantially planar portion of leading edge  362 . In the exemplary embodiment, sealing ring  358  is coupled between flange  352  and casing  24  with fastening mechanism  356 . In an alternative embodiment, sealing ring  358  is coupled between flange  352  and casing  24  using any other suitable coupling mechanism. 
     In an alternative embodiment, flange  352  is coupled to, or formed unitarily with, nozzle carrier  210 . Moreover, in the alternative embodiment, sealing ring  358  is coupled between flange  352  and nozzle carrier  210  and extends radially outward towards casing  24 , such that a radially outer end of sealing ring  358  engages leading edge  350  of casing  24 . In such an embodiment, leading edge  350  may be planar, or may include a rounded protrusion, similar to rounded protrusion  364 , to facilitate providing a determinant sealing surface that facilitates axial alignment between casing  24  and nozzle carrier  210  due to tolerances and transient conditions. Further, in the alternative embodiment, sealing ring  358  may be coupled between flange  352  and nozzle carrier  210  using any suitable coupling mechanism. In yet another alternative embodiment, turbine engine  10  includes a plurality of sealing rings  358  extending between casing  24  and nozzle carrier  210  at different axial locations. 
     In one embodiment, sealing ring  358  is formed from two semi-circular members that are coupled together. In an alternative embodiment, sealing ring  358  is formed from an annular member. Moreover, in another alternative embodiment, sealing ring  358  is formed from a plurality of arcuate members coupled together in an overlapping or leafed configuration to form either an annular member or a pair of semi-circular members. In the exemplary embodiment, the two semi-circular members are positioned such that sealing ring  358  extends substantially circumferentially around turbine  10 . In addition, in the exemplary embodiment, sealing ring  358  is fabricated from a flexible material that facilitates accommodating thermal and/or axial growth of casing  24  and/or nozzle carrier  210 . For example, in one embodiment, sealing ring  358  is fabricated from a 12Cr (410SS) material or 310SS (stainless steel). In an alternative embodiment, sealing ring  358  is fabricated from a cobalt based material to facilitate improving wear of sealing ring  358 . 
     During operation, steam is discharged from nozzles  212  into turbine chamber  310  to cause rotation of turbine rotor  16 . As steam is channeled through the turbine stages, a portion of steam is extracted from turbine  10  for use in other turbine operations or operations discrete from the turbine operation. Specifically, steam is extracted through apertures  314  and channeled into cavity  300 . Sealing assembly  312  enables steam to be retained within cavity  300  such that steam is not lost through gaps formed between casing  24  and nozzle carrier  210 . Steam within cavity  300  is channeled through ports defined in casing  24  and is used to operate machinery outside of turbine  10 . 
     Sealing assembly  312  facilitates sealing cavity  300  at the leading edges of casing  24  and nozzle carrier  210  such that leakage is substantially prevented. As such, steam can be extracted into, and retained within, cavity  300 , rather than only being extracted from a downstream end of turbine  10 , or from a juncture created between a pair of adjacent nozzle carriers. By enabling cavity  300  to receive steam, without the steam being lost through gaps defined between casing  24  and nozzle carrier  210 , steam may be extracted at any location throughout nozzle carrier  210 . Specifically, steam may be extracted at any location through apertures  314 , and apertures  314  may be positioned at any stage of turbine  10 . As such, steam at a higher pressure and/or a higher temperature may be extracted from a turbine including a unitary nozzle carrier. Moreover, using a plurality of apertures  314  enables steam to be extracted from varying stages of turbine  10  at varying temperatures and pressures. As a result, turbine assembly, maintenance, and operation costs are recovered in comparison to other turbines. In addition, by utilizing a single nozzle carrier, time and costs associated with nozzle carrier alignment are reduced in comparison to other turbines. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     Although the apparatus and methods described herein are described in the context of a nozzle carrier and seal for a steam turbine, it is understood that the apparatus and methods are not limited to nozzle carriers, seals or steam turbines. Likewise, the nozzle carrier and seal components illustrated are not limited to the specific embodiments described herein, but rather, components of the nozzle carrier and seal can be utilized independently and separately from other components described herein. For example, as will be appreciated by one of ordinary skill in the art, the present invention may be used with any suitable rotatable machine. 
     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.