Patent Publication Number: US-2011072640-A1

Title: Methods for modifying sealing systems for rotary machines

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application to U.S. patent application Ser. No. 12/135379, entitled “SEALING SYSTEMS FOR ROTARY MACHINES AND METHODS FOR MODIFICATION”, filed Jun. 9, 2008, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The invention relates generally to rotary machines and more particularly to sealing systems and methods for modifying inner oil deflectors in hydrogen-cooled generators. 
     In turbo-machinery such as gas turbines, steam turbines, compressors, and turbo-pumps, seals are used at different locations for minimizing leakage flows. For example, seals may be provided between sealing surfaces which are both movable relative to one another or between components in which one component moves relative to another component, e.g., a housing wall and a rotating shaft. 
     In an example including a hydrogen-cooled generator, a housing or casing surrounds a rotor, and seals are interposed between the housing wall and the rotor to seal between a hydrogen atmosphere on one side of the housing wall and oil (or oil mist) and air on the opposite side of the housing wall in a bearing cavity. Various approaches have been designed to maintain hydrogen purity and reduce hydrogen consumption. 
     In one example, a bolted, babbitted seal ring design has been used to lower the oil flow required of the shaft seals configured for sealing hydrogen gas in the end cavity from ambient air. This embodiment requires a re-design of the end shield structure of the generator. 
     In another example, hydrogen purity is improved by vacuum treating the seal oil to remove entrained impurities prior to pumping the seal oil into the hydrogen shaft seals. This embodiment results in pure hydrogen in the end cavities and thus eliminates the need for a diffusion barrier. Vacuum treatment systems are expensive and require additional power plant equipment and controls. 
     There is a need for a less complex system and method for maintaining hydrogen purity and reducing hydrogen consumption. There is a need to have non-sparking sealing materials in hydrogen-cooled generators, at locations where combustible mixtures of hydrogen and air could be present. 
     BRIEF DESCRIPTION 
     In accordance with one exemplary embodiment of the present invention, a rotary machine includes a sealing device disposed between a rotor and a stator. The sealing device is configured for at least partially segregating a first fluid cavity on one side of the sealing device and a second cavity on an opposite side of the sealing device. The sealing device includes a non-contacting seal. The sealing device further includes a contacting seal including an aluminum body coupled to the non-contacting seal and a plurality of non-metallic bristles projecting from the aluminum body with tips of the bristles engaging the rotor of the rotary machine. 
     In accordance with another exemplary embodiment of the present invention, a hydrogen-cooled generator includes a sealing device disposed between a rotor and a stator. The sealing device is configured for at least partially segregating hydrogen atmosphere on one side of the sealing device and a cavity on an opposite side of the sealing device. The sealing device includes a non-contacting seal. The sealing device further includes a contacting seal including an aluminum body coupled to the non-contacting seal and a plurality of non-metallic bristles projecting from the aluminum body with tips of the bristles engaging the rotor of the generator. 
     In accordance with another exemplary embodiment of the present invention, a method for modifying a hydrogen-cooled generator is disclosed. The method includes coupling to a sealing device, a contacting seal including a plurality of non-metallic bristles projecting from an aluminum body with tips of the bristles engaging a rotor of the hydrogen-cooled generator. 
     In accordance with another exemplary embodiment of the present invention, a method for modifying a hydrogen-cooled generator is disclosed. The method includes removing at least a portion of a non-contacting seal and replacing the removed portion with an aluminum body and a plurality of non-metallic bristles projecting from the aluminum body to form a replacement sealing device. The method further includes inserting the replacement sealing device such that tips of the bristles contact a rotor so as to prevent flow or diffusion of one or more contaminants from the cavity to the hydrogen chamber. 
     In accordance with another exemplary embodiment of the present invention, a method for modifying a hydrogen-cooled generator is disclosed. The method includes removing an original sealing device from the hydrogen-cooled generator. The method also includes providing a replacement sealing device including an aluminum body and a plurality of non-metallic bristles projecting from the aluminum body. The method further includes inserting the replacement sealing device into the hydrogen-cooled generator such that tips of the bristles contact a rotor of the hydrogen-cooled generator so as to prevent flow or diffusion of one or more contaminants from the cavity to the hydrogen chamber. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a diagrammatical view of a hydrogen-cooled generator having a sealing device in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a conventional sealing device provided in a hydrogen-cooled generator; 
         FIG. 3  is a diagrammatical view of a sealing device in accordance with the aspects illustrated in  FIG. 1 ; 
         FIG. 4  is a diagrammatical view of a brush seal of the sealing device in accordance with an exemplary embodiment of the present invention; 
         FIG. 5  is a diagrammatical view of a sealing device having a plurality of brush seals in accordance with an exemplary embodiment of the present invention; and 
         FIG. 6  is a diagrammatical view of a sealing device disposed in a hydrogen-cooled generator in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As discussed in detail below, embodiments of the present invention provide a rotary machine having a sealing device disposed between a rotor and a stator. In one exemplary embodiment, the rotary machine includes a hydrogen-cooled generator having a sealing device disposed between a rotor and a stator. The sealing device is configured for at least partially segregating a hydrogen atmosphere on one side of the sealing device and a cavity on an opposite side of the sealing device. The exemplary sealing device includes a non-contacting seal and a contacting seal including an aluminum body coupled to the non-contacting seal and a plurality of non-metallic bristles projecting from the aluminum body with tips of the bristles engaging the rotor of the hydrogen-cooled generator. In accordance with certain embodiments of the present invention, a method for modifying a hydrogen-cooled generator including a sealing device is disclosed. In one embodiment, a brush seal is coupled to an existing inner oil deflector of the hydrogen-cooled generator. In another embodiment, a portion of the inner oil deflector is replaced by a brush seal. In yet another embodiment, the entire inner oil deflector is replaced by a new sealing device that includes a brush seal. The exemplary brush seal may comprise a plurality of non-metallic bristles, e.g. aramid filaments. The brush seal provides an effective molecular diffusion barrier between a generator winding cavity containing pure hydrogen and an end cavity containing hydrogen contaminated with oil mist and air. The barrier is helpful to maintain higher hydrogen purity in the winding cavity and results in less hydrogen being scavenged. As a result, hydrogen consumption is reduced and power efficiency of the generator is improved. As used herein, “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. 
     Referring now to the drawings, particularly to  FIG. 1 , a hydrogen-cooled generator  10  having a rotor  12 , a housing wall or stator  14 , and a portion of an end shield  16  is illustrated. Also illustrated is a rotor shaft bearing  18  having an inner and outer bearing ring  20  and  22 , respectively, disposed in a bearing cavity  24  containing oil, oil mist, and air. A bearing cap  26  and an end oil deflector  28  are provided at an outer side to close the bearing cavity  24 . 
     Along an inner surface of the end shield  16  (to the left of shield  16  in  FIG. 1 ) and along inner surface of housing wall  14 , a hydrogen atmosphere (generator cavity) designated by reference numeral  30  is provided for cooling the generator. A low flow fluid film seal, designated by reference numeral  32 , is provided between the rotor  12  and the housing wall or stator  14 . The end shield  16  and stator  14  is configured to maintain the hydrogen atmosphere (first fluid cavity)  30  segregated from the fluid in bearing cavity (second fluid cavity)  24 . A seal casing  34  is interposed between the end shield  16  and rotor  12 . The seal casing  34  includes an annular plate or ring secured to an insulation  36  along its radially outer diameter by bolts passing through the insulation  36 . As illustrated, the seal casing  34  includes an annular chamber  38  opening radially inwardly towards the rotor  12  and defined between a pair of axially spaced flanges  40  and  42 . A pair of low clearance seal rings  44  and  46  are provided within the annular chamber  38 . An annular garter spring  48  engages against inclined surfaces (not shown) along radial outermost portions of the seal rings  44  and  46 , respectively. The spring  48  biases the seal rings  44  and  46  along axial and radial directions. It will be appreciated that the chamber  38  is provided with oil under pressure to provide a thin film of oil along the surface of rotor  12 . 
     An inner oil deflector (sealing device)  50  is disposed between the end shield  16  and rotor  12  inboard of the seal casing  34  defining a seal cavity  52  therebetween. As a result, the seal cavity  52  contains a significantly lesser purity of hydrogen than the hydrogen atmosphere  30 . The exemplary inner oil deflector  50  includes a non-contacting seal support element  54 , such as a labyrinth seal, and a contacting seal  56 , such as a brush seal. The inner oil deflector prevents diffusion and mass transfer of one or more contaminants from the seal cavity  52  to the hydrogen atmosphere  30 . The details of the inner oil deflector are explained in greater detail with reference to subsequent figures. It should be noted herein that the brush seal  56  may be provided at any location in the generator where combustible mixtures of hydrogen and air could be present. 
     It should be noted herein that the exemplary sealing device is also applicable to other rotary machines where the sealing device is configured to segregate one gaseous fluid from another gaseous fluid or a gaseous medium from a liquid medium with a lower pressure differential across the seal. 
     Referring now to  FIG. 2 , a conventional inner oil deflector  58  provided in a hydrogen-cooled generator is illustrated. The inner oil deflector  58  includes a plurality of non-contacting seals situated on seal support elements  60 ,  62 , and  64  and disposed facing a rotor  66 . The non-contacting seals may include a plurality of labyrinth teeth  68 ,  70 , and  72  respectively protruding towards the rotor  66 . It should be noted herein that in the conventional system, a gap  74  exists between the labyrinth- teeth  68 ,  70 , and  72  and the rotor  66 . The inner oil deflector  58  is configured to at least partially segregate a hydrogen atmosphere  76  on one side of the inner oil deflector  58  from a seal cavity  78  on an opposite side of the inner oil deflector  58 . 
     In the conventional system, an end shield structure of the generator may be too flexible and thus may deflect to such an extent that lower oil flow, bolted hydrogen seal rings cannot be used. Rather, higher oil flow, unbolted hydrogen seal rings are typically used. As a consequence of the higher oil flow, an increased level of dissolved air is released from the seal oil, which migrates from the seal cavity  78  to the cavity with hydrogen atmosphere  76  through the gap  74 . The gap  74  is a pathway for impurities  75  (air molecules) to diffuse across into the cavity of hydrogen atmosphere  76  resulting in contamination of hydrogen and subsequent lowering of generator efficiency. One option to control diffusion of impurities is to increase hydrogen scavenging rates. Scavenging refers to extracting impure hydrogen at a controlled flow rate from seal cavity  78  and replenishing it with an equal volume of pure hydrogen from the cavity with the hydrogen atmosphere  76  across the gap  74 ; thus removing impurities and inhibiting the flow of impurities from the seal cavity  78  to the cavity with the hydrogen atmosphere  76 . However, these scavenging flow rates must be small so as to consume no more than a predefined economical volume of hydrogen. These predefined flow rates are too small to adequately prevent diffusion and mass transfer from the seal cavity  78  to the cavity with hydrogen atmosphere  76 . Likewise, increasing scavenging rates may exceed predefined hydrogen consumption limits and often have little effect to improve purity of hydrogen. 
     Referring now to  FIG. 3 , an inner oil deflector  50  in accordance with the aspects of  FIG. 1  is illustrated. In the illustrated embodiment, the exemplary inner oil deflector  50  includes the non-contacting seal support element  54  and the contacting seal  56 . The inner oil deflector  50  prevents diffusions of one or more contaminants from the seal cavity  52  to the hydrogen atmosphere  30 . In the illustrated embodiment, the non-contacting seal support element  54  includes a plurality of seal support elements  80 ,  82 , and  84  disposed facing the rotor  12 . The seal support elements  80 ,  82 , and  84  may include, for example, a plurality of labyrinth-teeth  86 ,  88 , and  90  respectively protruding towards the rotor  12 . In one embodiment the seal support elements  86 ,  88 , and  90  comprise an aluminum material. In a more specific embodiment, the seal support elements  80 ,  82 , and  84  and teeth  86 ,  88 , and  90  are fabricated from cast aluminum. If desired, the seal support element  84  itself may comprise the aluminum body into which brush seal bristles are inserted. Alternatively, an aluminum body element may hold the brush seal bristles and be connected to the seal support element. 
     It should be noted herein that in the exemplary system, the brush seal  56  is coupled to seal support element  84 , which also includes labyrinth teeth  90 . The brush seal  56  extends across a gap  92  between the labyrinth-teeth  86 ,  88 , and  90  and the rotor  12  and engages the rotor  12 . The inner oil deflector  50  is configured to at least partially segregate a hydrogen atmosphere  30  on one side of the inner oil deflector  50  from the seal cavity  52  on an opposite side of the inner oil deflector  50 . The brush seal  56  is configured to prevent diffusion of contaminants  85  such as gaseous impurities, and oil mist from the seal cavity  52  to the cavity with hydrogen atmosphere  30 . The exemplary brush seal  56  helps the inner oil deflector  50  to act as a contacting seal and thus close the gap  92  that impurities diffuse across from the seal cavity  52  to the cavity with hydrogen atmosphere  30 . 
     Referring to  FIG. 4 , a detailed view of an exemplary brush seal  56  is illustrated. The brush seal  56  in accordance with certain aspects of the present invention includes a plurality of non-metallic fibers  94  configured to contact the rotor  12  to reduce diffusion of contaminants such as air molecules and oil from the seal cavity to the cavity with hydrogen atmosphere. 
     In one embodiment, the brush seal  56  includes a holding device  96 , which is coupled to a respective seal support element. The holding device  96  includes a first plate (front plate)  98  and a second plate (back plate)  100 . The plurality of non-metallic fibers  94  are disposed between the first plate  98  and the second plate  100  of the holding device  96 . Typically, the fibers  94  may be canted at a predetermined angle. As known to those skilled in the art, the canting of fibers  94  improves the compliance of the seal with the rotor  12 . Such radial deflection of the fibers  94  advantageously ensures “gentle ride” over the contact surfaces to prevent structural deformation of the fibers. The cant angle depends on trade-off relationship between factors such as, for example, structural stability of the fibers and ease of assembling the fibers  94  with the plates  98 ,  100 . The fibers  94  sandwiched between the plates  98  and  100  are packed densely enough to prevent diffusion of contaminants such as air molecules and oil mist. The packing density of the fibers is maintained within predetermined limits in such a way so as to enhance sealing effectiveness and avoid any significant increase of frictional force arising due to frictional contact between the fibers and contact surfaces. 
     Each fiber  94  includes a first end  102  coupled to the holding device  96  and a second end  104  configured to contact the rotor  12 . The coupling may be accomplished through any conventional brush seal methodology with one example including first and second plates  98  and  100  and either an affixing material  106  such as an epoxy or a mechanical fastener such as a clamp (not shown). In certain exemplary embodiments, holding device  96  comprises an aluminum material. It should be noted herein that aluminum has the advantages that it does not spark and would not score the rotor in the event of contact. Aluminum is much easier to work with compared to other materials known to those skilled in the art. The first end  102  of each fiber  94  is coupled to the holding device  96  and the second end  104  protrudes from the holding device  96  towards the rotor  12 . 
     In the exemplary embodiment, the non-metallic fibers may include aramid filaments such as Kevlar fibers. It should be noted herein that other non-metallic fibers are also envisaged. Fiber materials and diameters are chosen depending on trade-off relationships among properties such as stiffness, creep resistance, wear resistance, and chemical inertness against oil, for example. Fiber diameters are chosen to ensure structural stability against aerodynamic forces applied thereupon by the working fluid while considering trade-off factors such as structural stability and desired compliance. For example, smaller diameters (i.e. diameters less than 0.002 inches including Kevlar aramid fibers at 0.0005 inches and carbon fiber at 0.00025 inches) of non-metallic fibers result in lower effective clearance at the seal-rotary component interface and also lower stiffness resulting in lower heat generation. In the illustrated exemplary embodiment, Kevlar fibers are capable of withstanding the high surface speeds of generator rotor. As a result, higher hydrogen purity can be maintained in the cavity with hydrogen atmosphere by using the fibers  94  to close the gap between the non-rotating plates  98 ,  100  and the rotor  12 . 
     Referring to  FIG. 5 , an inner oil deflector  50  in accordance with another exemplary embodiment of the present invention is illustrated. In the illustrated embodiment, exemplary inner oil deflector  50  includes the seal support element  54  and the contacting seals (brush seals)  56 ,  57 . In the illustrated embodiment, the brush seals  56 ,  57  act as replacement seals. In the illustrated embodiment, the seal support element  54  includes a plurality of seal support elements  80 ,  82 , and  84  disposed facing the rotor  12 . The seal support elements  80 ,  82 , and  84  include a plurality of labyrinth teeth  86 ,  88 , and  90  respectively protruding towards the rotor  12 . 
     In the exemplary embodiment, some the labyrinth-teeth  88 ,  90  are removed from the seal support elements  82  and  84  respectively. The removed portions are replaced by a plurality of brush seals  57 ,  56 . It should be noted herein that in the exemplary system, the brush seals  56 ,  57  are coupled to the seal support elements  84 ,  82  respectively. The brush seals  56 ,  57  extend across a gap  92  between the labyrinth-teeth  80 ,  82 , and  84  and the rotor  12  and engage the rotor  12 . In the illustrated embodiment, the brush seal  57  includes bristles directly coupled to the seal support element  82 . In other words, the seal support element  82  itself acts as an aluminum body for holding the bristles. The inner oil deflector  50  is configured to segregate or at least partially segregate a hydrogen atmosphere  30  on one side of the inner oil deflector  50  from the seal cavity  52  on an opposite side of the inner oil deflector  50 . The brush seals  56 ,  57  are configured to prevent diffusion of contaminants  85  such as gaseous impurities, oil mist, and oil from the seal cavity  52  to the cavity with hydrogen atmosphere  30 . The exemplary brush seals  56 ,  57  facilitate the inner oil deflector  50  to act as a contacting seal and thus, close the gap  92  that impurities easily diffuse across from the seal cavity  52  to the cavity with hydrogen atmosphere  30 . 
     It should be noted herein even though two brush seals are illustrated; in certain other embodiments a single brush seal may be inserted or more than two brush seals may be provided. In one embodiment, each of the seal support elements  80 ,  82 , and  84  may be provided with one or more brush seals. In certain other embodiments, the number of brush seals provided to the seal support elements  80 ,  82 , and  84  may vary among each other. All such permutations and combinations are envisaged. In one embodiment, the brush seals may be bolted to the seal support elements. In another embodiment, grooves may be formed in the seal support elements and the brush seals may be coupled to the grooves in the seal support elements. Each brush seal serves as both an oil barrier and as a diffusion barrier. The bristles engage the rotor directly, unlike non-contacting labyrinth teeth, and, as a result, the seal has superb oil leakage prevention and diffusion reducing characteristics. The brush seal can be adapted to fit into existing inner oil deflector designs on generators, thus making provision of brush seals an interchangeable and efficient solution. The labyrinth teeth serve as a sturdy back up seal in the event the brush seal were severely damaged or worn, allowing the generator to continue operation. 
     Referring now to  FIG. 6 , a hydrogen-cooled generator  10  in accordance with an exemplary embodiment of the present invention is illustrated. The generator  10  is structurally similar to the embodiment illustrated in  FIG. 1 , except that an inner oil deflector (original sealing device)  50  disposed between the end shield  16  and rotor  12  inboard of the seal casing  34  is removed. In the illustrated embodiment, the inner oil deflector  50  is replaced by a replacement sealing device, in one embodiment, the brush seal  56 . The efficient oil leakage and diffusion prevention traits of the fiber brush seal would enable the rotor length to be shortened by eliminating the need for multiple tooth labyrinth, non-contacting seals. Reduced diffusion of impurities across the gap between the seal and the rotor enables higher hydrogen purity to be maintained in the cavity of hydrogen atmosphere resulting in higher power efficiency of the generator. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.