Abstract:
Solutions for clutching turbine wheels are disclosed. In one embodiment, an apparatus includes: a turbine rotor shaft; a plurality of turbine wheels affixed to the turbine rotor shaft; an independent turbine wheel engagably attached to the turbine rotor shaft; and a clutch operably connected to the turbine rotor shaft, the clutch configured to couple and decouple the independent turbine wheel from the turbine rotor shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of co-pending U.S. patent application Ser. No. 12/651,744, which received a Notice of Allowance on Oct. 24, 2013, and is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to clutched turbine wheels. Specifically, the subject matter disclosed herein relates to solutions for clutching turbine wheels to improve turbine performance. 
     Turbine machines, for example, steam turbines and gas turbines, include a plurality of wheels (or stages) at different locations along a main rotor shaft. These wheels each include a plurality of turbine blades, which during operation, drive rotation of the main rotor shaft via mechanical forces caused by the flow and expansion of a working fluid across the turbine blades. During startup of these turbine machines, or in times of lower load, reduced pressure in the machine may cause one or more of the turbine wheels to function inefficiently. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Solutions for clutching turbine wheels are disclosed. In one embodiment, an apparatus includes: a turbine rotor shaft; a plurality of turbine wheels affixed to the turbine rotor shaft; an independent turbine wheel engagably attached to the turbine rotor shaft; and a clutch operably connected to the turbine rotor shaft, the clutch configured to couple and decouple the independent turbine wheel from the turbine rotor shaft. 
     A first aspect of the invention provides an apparatus comprising: a turbine rotor shaft; a plurality of turbine wheels affixed to the turbine rotor shaft; an independent turbine wheel engagably attached to the turbine rotor shaft; and a clutch operably connected to the turbine rotor shaft, the clutch configured to couple and decouple the independent turbine wheel from the turbine rotor shaft. 
     A second aspect of the invention provides an apparatus comprising: a load device; and a turbine coupled to the load device, the turbine including: a turbine rotor shaft; a plurality of turbine wheels affixed to the turbine rotor shaft; an independent turbine wheel engagably attached to the turbine rotor shaft; and a clutch operably connected to the turbine rotor shaft, the clutch configured to couple and decouple the independent turbine wheel from the turbine rotor shaft. 
     A third aspect of the invention provides a system comprising: a gas turbine operably connected to a first load device; a heat exchanger operably connected to the gas turbine; and a steam turbine operably connected to the heat exchanger; wherein at least one of the gas turbine or the steam turbine include: a turbine rotor shaft; a plurality of turbine wheels affixed to the turbine rotor shaft; an independent turbine wheel engagably attached to the turbine rotor shaft; and a clutch operably connected to the turbine rotor shaft, the clutch configured to couple and decouple the independent turbine wheel from the turbine rotor shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
         FIGS. 1-6  show schematic side views of apparatuses according to embodiments. 
         FIGS. 7-8  show schematic block diagrams illustrating portions of combined cycle power plant systems according to embodiments. 
     
    
    
     It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As indicated above, aspects of the invention provide for clutched turbine wheels. Specifically, aspects of the invention provide for coupling and decoupling an independent wheel from a turbine rotor shaft to improve turbine performance under certain operating conditions. 
     In the art of turbine power systems (including, e.g., steam turbines or gas turbines), the terms “rated power” and “rated mass flow” refer to the total power output and total mass flow, respectively, of one or more devices under certain predefined conditions. Typically, the rated power/mass flow of a turbine system is designed for a particular set of conditions, and these designed conditions are set as the 100 percent rated power/mass flow marks. When starting up a turbine system, or when operating at conditions other than design conditions (e.g., at “part load”), the power and mass flow of the turbine system drops below the 100 percent rated power/mass flow marks. This reduced mass flow of the working fluid through the turbine results in a pressure decrease inside the turbine, and reduces the pressure drop across wheels of the turbine. At lower pressure portions (larger aft stages) of the turbine, the pressure drop across a wheel may be so minimal that the mass flow does not produce a net positive force on the turbine shaft. For example, the pressure drop across a last stage bucket (LSB) may be so minimal that the turbine rotor stage must perform mechanical work to move the fluid through the stage (e.g., acting as a compressor). In these situations, lower pressure stages detract from the overall efficiency of the turbine system by causing large rotational and aerodynamic losses. 
     Turning to the figures, embodiments including an apparatus are shown, where the apparatus increases the efficiency of a turbine by using clutched turbine wheels to decouple one or more wheels from the turbine rotor shaft. Specifically, turning to  FIG. 1 , an apparatus  2  according to an embodiment is shown. Apparatus  2  may be a portion of a turbine machine, which may be, for example, a steam turbine. In another embodiment, apparatus  2  may be a portion of a gas turbine machine. In any case, apparatus  2  may include a turbine housing  3  containing a turbine rotor shaft  4  and a plurality of turbine wheels  6  affixed to turbine rotor shaft  4 . Turbine rotor shaft  4  may have a fore portion  5  and an aft portion  15 , where the fore portion  5  may be operably connected to other turbine stages (not shown) and aft portion  15  may be operably connected to, e.g., a load device  120  (shown in phantom). The plurality of turbine wheels  6  may be welded, forged or otherwise mechanically attached to turbine rotor shaft  4 . Load device  120  may be any conventional electric generator, compressor, or pump, capable of converting the mechanical energy from rotation of turbine rotor shaft  4  into electrical or other mechanical energy. Load device  120  and its relationship to apparatus  2  is further described with reference to  FIGS. 5-6 . 
     Apparatus  2  may further include an independent turbine wheel  8  engagably attached to the turbine rotor shaft  4 , and a clutch  10  operably connected to the turbine rotor shaft  4 . Clutch  10  is capable of coupling and decoupling independent turbine wheel  8  from the turbine rotor shaft  4 . In the embodiment shown in  FIG. 1  (and  FIG. 3 ), clutch  10  may be housed within independent turbine wheel  8 . However, in other embodiments (e.g., those shown and described with reference to  FIGS. 3-5 ), clutch  10  may be mounted externally of independent turbine wheel  8 . Where clutch  10  is housed within independent turbine wheel  8 , axial space on turbine rotor shaft  4  (and within turbine housing  3 ) may be saved due to independent turbine wheel  8  substantially axially containing clutch  10 . 
     Turning to  FIG. 2 , clutch  10  is shown including a clutch member  12 , an output flange  14  operably attached to turbine rotor shaft  4 , and an input flange  16  operably attached to the independent turbine wheel  8 . In this embodiment, input flange  16  is free from contact with turbine rotor shaft  4 . Where input flange  16  is free from contact with turbine rotor shaft  4 , turbine wheel  8  is free to move (or remain substantially stationary) independently of turbine rotor shaft  4  when wheel  8  is unable to contribute positive torque to shaft  4 . 
     In one embodiment, clutch  10  may include an auto-synchronous clutch configured to couple output flange  14  to input flange  16  in response to independent turbine wheel  8  and turbine rotor shaft  4  attaining a substantially similar rotational speed (e.g., revolutions per minute (RPMs) or revolutions per second). That is, the auto-synchronous clutch ensures that independent turbine wheel  8  does not couple to turbine rotor shaft  4  until independent turbine wheel  8  reaches synchronous speed with turbine rotor shaft  4 . For example, during startup, the mass flow rate of the working fluid (e.g., gas or steam) may be sufficient to force rotation of the plurality of turbine wheels  6  at higher pressure portions of apparatus  2 . However, during this same startup phase the mass flow rate of the working fluid at the independent turbine wheel  8  may be insufficient to force rotation of independent turbine wheel  8  at the same rotational speed as the plurality of turbine wheels  6 . As apparatus  2  reaches operational conditions (and mass flow rate increases), the flow of working fluid across the blades (not shown) of independent turbine wheel  8  may cause independent turbine wheel  8  to attain a substantially similar rotational speed as turbine rotor shaft  4 . When this happens, clutch  10  may couple output flange  14  to input flange  16  to allow independent turbine wheel  8  to transfer the mechanical energy from its movement to turbine rotor shaft  4 . Conversely, as the mass flow rate decreases (e.g., during reduction of the load), independent turbine wheel  8  may be decoupled from turbine rotor shaft  4  when independent turbine wheel  8  and turbine rotor shaft  4  attain different rotational speeds. In any case, clutch  10  ensures that independent turbine wheel  8  is only coupled to turbine rotor shaft  4  when independent turbine wheel  8  can provide positive mechanical energy to turbine rotor shaft  4 . 
     In another embodiment, clutch  10  may be controlled by a controller  25  (shown in phantom). Controller  25  may be mechanically and/or electrically connected to clutch  10  such that controller  25  may actuate clutch  10 . Controller  25  may instruct clutch  10  to couple/decouple independent turbine wheel  8  from turbine rotor shaft  4  in response to changes in the rotational speed of independent turbine wheel  8  and/or turbine rotor shaft  4 . Controller  25  may be a computerized, mechanical, or electro-mechanical device capable of actuating clutch  10 . In one embodiment, controller  25  may be a computerized device capable of providing operating instructions to clutch  10 . In this case, controller  10  may monitor the rotational speeds of independent turbine wheel  8  and turbine rotor shaft  4 , and provide operating instructions to clutch  10 . For example, controller  25  may send operating instructions to couple/decouple independent turbine wheel  8  from turbine rotor shaft  4  when the rotational speed of turbine rotor shaft  4  approaches a certain predetermined level. In this embodiment, clutch  10  may include electro-mechanical components, capable of receiving operating instructions (electrical signals) from controller  25  and producing mechanical motion (e.g., uncoupling of flanges). In another embodiment, controller  25  may be a mechanical device, capable of use by an operator. In this case, the operator may physically manipulate controller  25  (e.g., by pulling a lever), which may actuate clutch  10 . For example, the lever of controller  25  may be mechanically linked to clutch  10 , such that pulling the lever causes clutch  10  to fully actuate. In another embodiment, controller  25  may be an electro-mechanical device, capable of electrically monitoring (e.g., with sensors) parameters indicating that turbine rotor shaft  4  is approaching a predetermined rotational speed, and mechanically actuating clutch  10 . It is understood that controller may be a wireless or hard-wired device, and may be operated by a human operator via a user interface (e.g., a graphical user interface). 
     While  FIGS. 1 and 2  show one independent turbine wheel  8 , it is understood that a plurality of independent turbine wheels  8  may be coupled/decoupled to the turbine rotor shaft  4  by one or more clutches  10 . For example, turning to  FIG. 3 , another embodiment is illustrated in which an apparatus  32  is shown including a second independent turbine wheel  18  engagably attached to turbine rotor shaft  4 . Second independent turbine wheel  18  may be substantially similar to independent turbine wheel  8 , and may be operably attached to clutch  10  via an input flange  16  (explained in greater detail below). In one embodiment, a single clutch  10  could be configured to couple and decouple independent turbine wheel  8  and second independent turbine wheel  18  with turbine rotor shaft  4 . For example, in this embodiment, clutch  10  may be housed internally on independent turbine wheel  8 , and may be mounted external to second independent turbine wheel  18 . As shown, clutch  10  is housed internally on independent turbine wheel  8 , which is located on the aft ( 15 ) side of second independent turbine wheel  18 . However, it is understood that clutch  10  may be housed internally on second independent turbine wheel  18 , and that independent turbine wheel  8  may still be mounted on the aft ( 15 ) side of second independent turbine wheel  18 . It is also understood that that independent turbine wheel  8  and second independent turbine wheel  18  may be coupled/decoupled to turbine rotor shaft  4  by a plurality of clutches  10  (e.g., each independent turbine wheel has an internally housed clutch  10 ). 
     In one embodiment, as shown in  FIGS. 2 and 4 , the plurality of turbine wheels  6  and independent turbine wheel  8  are located on a same side of clutch  10 . In this case, clutch  10  may be located closer to the aft portion  15  of turbine rotor shaft  4  than the plurality of turbine wheels  6  and independent turbine wheel  8 . Where clutch  10  is located at the aft side of independent turbine wheel  8  and the plurality of turbine wheels  6 , clutch  10  may be accessed more readily by, e.g., an operator and/or mechanic. This access may allow for, among other things, modification and/or repair of clutch  10 . Further, location of clutch  10  as shown in  FIGS. 1-4  may require, at most, minimal modification of the aerodynamic configuration of a turbine system including apparatus  2 . That is, the mass flow pattern of the working fluid between the plurality of turbine wheels  6  and independent turbine wheel  8  may be substantially uninterrupted by clutch  10 . Additionally, because independent turbine wheel  8  is located substantially proximately to the plurality of turbine wheels  6 , the length of the turbine housing  3  holding apparatus  2  can remain substantially similar to a conventional turbine housing. 
     Turning to  FIG. 5 , an apparatus  52  is shown according to another embodiment. In this embodiment, clutch  10  is operably connected to the turbine rotor shaft  4  at a point between the plurality of turbine wheels  6  and independent turbine wheel  8 . Clutch  10  and other components included in apparatus  52  may function substantially similarly to those shown and described with reference to  FIG. 1 . However, in this embodiment, unlike the embodiment shown in  FIG. 1 , the aerodynamic configuration of a turbine system including apparatus  52  may need to be modified from its traditional arrangement. That is, the mass flow pattern of working fluid leaving the plurality of turbine wheels  6  may need to be directed toward the independent turbine wheel  8  via, e.g., flow diverters  35  (shown in phantom). Flow diverters  35  may take the form of fins (as shown) or channels allowing the working fluid to effectively flow from the plurality of turbine wheels  6  to independent turbine wheel  8 . In one embodiment, flow diverters  35  may be attached/cantilevered to walls of the turbine housing  3 . In another embodiment, flow diverters  35  may be attached to a suspension ring or other internal fixture surrounding turbine rotor shaft  4 . Further, this embodiment may require that the turbine housing  3  be lengthened in order to accommodate location of independent turbine wheel  8  at a point closer to aft portion  15 . 
     Turning to  FIG. 6 , a double-flow steam turbine apparatus  62  is shown including two portions of distinct steam turbine sections. Each distinct steam turbine section in apparatus  62  may include an apparatus  2  similar to apparatus  2  shown and described with reference to  FIG. 1 . As shown, each apparatus  2  may include a steam inlet  45  for receiving steam (not shown) from, e.g., a high-pressure or intermediate-pressure section of a turbine system. Each apparatus  2  may function substantially similarly to apparatus  2  shown and described with reference to  FIG. 1 . Both of apparatuses  2  may be mechanically coupled via a common turbine rotor shaft  4 , which may be mechanically coupled to a load device  120  (as described with reference to  FIG. 1 ). While apparatus  62  is shown and described including two apparatuses  2  shown in  FIG. 1 , it is further understood that apparatus  62  may include any combination of two apparatuses  2 ,  22 ,  32 ,  42  or  52  shown and described with reference to  FIGS. 2-5 . 
     It is understood that the embodiments shown and described herein may allow for improved performance of a turbine system including apparatus  2  and/or apparatus  22 ,  32 ,  42 ,  52 . For example, as is known in the art, turbine housings are designed to include a radial clearance surrounding turbine wheels. This radial clearance may allow for expansion (known as “thermal growth”) of the wheels and blades due to the high temperatures in the turbine. Where clutch  10  and independent turbine wheel  8  are employed, this thermal growth (correlated with higher temperatures) may be reduced via a reduction in rotational and aerodynamic losses during startup. For example, a turbine housing  3  experiencing reduced temperatures may be designed with reduced radial clearances. The resulting tighter clearances between rotating components (e.g., plurality of wheels  6 , independent turbine wheel  8 ) and stationary seals (not shown) reduces leakage of the working fluid from turbine housing  3 . This reduced leakage reduces performance losses across the entire operating range of the turbine system. In one embodiment, radial clearances can be reduced on the order of approximately 30-50% as compared to conventional rotors and turbine housings by employing apparatus  2  (or apparatus  22 ,  32 ,  42 ,  52 ). Given the decreased temperatures on the independent turbine wheels  8 ,  18 , larger (longer) buckets located on independent turbine wheel  8 ,  18  may be used without the need to upgrade materials used for those buckets (e.g., due to higher allowable stresses, associated with lower temperatures on these buckets). 
     It is additionally understood that apparatus  2  (or apparatus  22 ,  32 ,  42 ,  52 ) employing one or more independent turbine wheels  8  may experience reduced erosion on the independent turbine wheel(s)  8 . For example, during startup of a turbine system including apparatus  2  (or apparatus  22 ,  32 ,  42 ,  52 ), steam droplets flowing through the apparatus have a higher moisture content than during other times of operation. When those high-moisture steam droplets impact a moving turbine wheel (e.g., plurality of wheels  6 ), they erode portions of the moving turbine wheel. However, when those steam droplets impact a relatively stationary or slowly rotating turbine wheel (e.g., independent turbine wheel(s)  8 ), their erosive impact is significantly decreased. As such, independent turbine wheel(s)  8  will erode less quickly, and have longer life cycles, than turbine wheels which are fixed to the turbine shaft (and moving at higher speed) during startup of the turbine system. 
     Turning to  FIG. 7 , a schematic view of portions of a multi-shaft combined cycle power plant  100  is shown. Combined cycle power plant  100  may include, for example, a gas turbine  110  operably connected to a first load device  120 . Load device  120  may include, e.g., a conventional electric generator, a compressor, a pump or another conventional load device. Load device  120  and gas turbine  110  may be mechanically coupled by a shaft  175 , which may transfer energy between a drive shaft (not shown) of gas turbine  110  and load device  120 . Also shown in  FIG. 7  is a heat exchanger  130  operably connected to gas turbine  110  and a steam turbine  210 . Steam turbine  210  may include apparatus  2  (or apparatus  22 ,  32 ,  42 ,  52 , or others described herein) which may include a clutch  10  and independent turbine wheel  8 . Heat exchanger  130  may be fluidly connected to both gas turbine  110  and steam turbine  210  via conventional conduits (numbering omitted). Heat exchanger  130  may be a conventional heat recovery steam generator (HRSG), such as those used in conventional combined cycle power systems. As is known in the art of power generation, HRSG may use hot exhaust from gas turbine  110 , combined with a water supply, to create steam which is fed to steam turbine  210 . Steam turbine  210  may optionally be coupled to a second load device  220  (via a second shaft  275 ). Second load device  220  and second shaft  275  may operate substantially similarly to load device  120  and shaft  175  described above. In another embodiment, shown in  FIG. 8 , a single shaft combined cycle power plant  200  may include a single generator  120  coupled to both gas turbine and steam turbine via a single shaft  175 . 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.