Abstract:
A turbomachine is disclosed that has a main fluid flowpath extending axially along the turbomachine with a rotating shaft partly enclosed in a casing, wherein the rotating shaft and casing are moveable relative to each other and define a clearance opening about the rotating shaft, whereby the main fluid flowpath fluidly communicates with an outside region, and an annular seal body defining a fluid passage having a primary fluid inlet configured to receive a pressurized fluid, a fluid outlet disposed proximate to the clearance opening, and a convergent chamber interposed therebetween, wherein the convergent chamber is configured to accelerate the pressurized fluid out of the fluid outlet so as to create a local reduced pressure at the clearance opening.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT International Patent Application No. PCT/US10/21218, which was filed on Jan. 15, 2010 and which claims priority to U.S. Patent Application Ser. No. 61/144,902 filed Jan. 15, 2009. These priority applications are hereby incorporated by reference in their entirety into the present application. 
     
    
     BACKGROUND 
       [0002]    Sealing assemblies for turbomachines are generally located on both ends of a rotating shaft that is journalled with bearings. The sealing assemblies are used to prevent leakage into the atmosphere of process gas from a defined flow path through clearance openings formed between the rotating shaft and the turbomachine housing. Effectively sealing the process gas not only increases turbomachine efficiency, but in certain operations involving toxic or explosive gas under pressure, it also prevents dangerous gases from reaching the surrounding area and thereby causing volatile and possibly dangerous situations. 
         [0003]    A typical sealing assembly may consist of a series of labyrinth seals and gas/oil seals axially spaced along the rotating shaft. Since each seal consumes a portion of axial shaft length, the centerline distance between the bearings is predictably increased, thus resulting in a longer and a heavier rotating shaft. Although all shafts deflect during rotation, an unnecessary increase in shaft length and weight can adversely affect shaft rotordynamics. For example, an increase in shaft length may lower the natural frequency of a shaft, thus resulting in higher potential amplitudes. Moreover, lower natural frequencies generally result in reduced critical speeds, and thus a less effective turbomachine. 
       SUMMARY 
       [0004]    Embodiments of the disclosure may provide a sealing device configured to form a seal between a rotating shaft and a casing of a turbomachine. The sealing device may include a seal body disposed within the casing and defining a fluid passage having a primary fluid inlet configured to receive a pressurized fluid, and a fluid outlet defined by the seal body and communicably coupled to the fluid passage and in fluid communication with an inner-region of the casing. The seal device may also include a convergent chamber interposed between the primary fluid inlet and the fluid outlet, wherein the convergent chamber is configured to accelerate the pressurized fluid out of the fluid outlet so as to create a local reduced pressure within the inner-region of the casing. 
         [0005]    Embodiments of the disclosure may further provide a turbomachine. The turbo machine may include a main fluid flowpath extending axially along the turbomachine, and a rotating shaft partly enclosed in a casing, wherein the rotating shaft and casing are moveable relative to each other and define a clearance opening about the rotating shaft. The turbomachine may also include a fluid passage defined in the casing and having a primary fluid inlet configured to receive a pressurized fluid, and also having a fluid outlet disposed proximate the clearance opening, and a convergent chamber interposed between the primary fluid inlet and the fluid outlet, the convergent chamber being configured to accelerate the pressurized fluid out the fluid outlet so as to create a local reduced pressure in the main fluid flowpath adjacent the clearance opening. 
         [0006]    Embodiments of the disclosure may further provide a method of sealing a rotating shaft partly disposed in a casing, wherein the rotating shaft and the casing define a clearance opening that fluidly communicates an inner-region of the casing to an outside region. The method may include injecting a pressurized fluid into a seal body defining a fluid passage, receiving the pressurized fluid in a primary fluid inlet defined by the seal body, and accelerating the pressurized fluid in a convergent chamber fluidly coupled to the primary fluid inlet. The method may also include discharging the pressurized fluid out a fluid outlet fluidly coupled to the convergent chamber, wherein the fluid outlet is disposed proximate to the clearance opening, generating a local reduced pressure within the inner-region of the casing, and entraining a secondary fluid flow through the clearance opening from the outside region. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present disclosure is best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
           [0008]      FIG. 1  is a schematic view an exemplary turbomachine according to one or more aspects of the present disclosure. 
           [0009]      FIG. 2  is a schematic cross-section view through a portion of an exemplary turbomachine according to one or more aspects of the present disclosure. 
           [0010]      FIG. 3  is an enlarged scale detail view of the dashed area “FIG.  3 ” from  FIG. 2  and illustrating a convergent nozzle according to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure, however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure. 
         [0012]    Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Further, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. 
         [0013]    The present disclosure generally relates to a shaft seal, in particular, a non-contacting convergent nozzle seal configured to reduce the number of labyrinth and gas/oil seals necessary to seal a turbomachine shaft. With a decrease in labyrinth and gas/oil seals, the shaft length may be shortened, resulting in a lighter and more rigid shaft. A shorter and more rigid shaft may increase the critical speed of the shaft and make the shaft less prone to rotor instability, including shaft vibration. Such increases may result in an overall increased speed and discharge pressure, thus an increase in turbomachine efficiency. Furthermore, as it is used in the claims or specification, the term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein. 
         [0014]    Referring now to the drawings in detail, wherein like numbers are used to indicate like elements throughout, there is shown in  FIG. 1  an exemplary turbomachine  102  according to one or more aspects of the present disclosure. In an exemplary embodiment, the turbomachine  102  may include a high-pressure turbo-compressor having a casing  104  with a low-pressure gas entry side  102   a  and a high-pressure gas exit side  102   b.  The casing  104  may include any stationary structure configured to house or encase the inner-workings of the turbomachine  102 . The turbomachine  102  may also include a rotating shaft  106  configured to extend through the turbomachine  102  and exit both ends of the casing  104  where it may be journalled at each end with suitable bearings  108  as known in the art. 
         [0015]    Referring to  FIG. 2 , illustrated is a side-view schematic of the turbomachine  102 , according to one or more aspects of the present disclosure. As described above, the rotating shaft  106  may pass through and extend out each end of the casing  104 , and be appropriately journalled at each end by one or more bearings  108 . The casing  104  may also include a discharge nozzle  200 . The rotating shaft  106  may be operably coupled to a plurality of impellers  202  configured to sequentially compress a process gas in the direction of the main fluid flowpath  204 . In exemplary operation, the process gas enters the main fluid flowpath  204  through the low-pressure gas entry side  102   a  and is thereafter compressed through the plurality impellers  202  before being discharged from the casing  104  as a pressurized process gas via the discharge nozzle  200 . 
         [0016]    As illustrated, a clearance opening  206  may be defined between the casing  104  and the rotating shaft  106 . The opening  206  may be configured to allow the shaft  106  to rotate during normal operation. As shown, the clearance  206  may provide fluid communication between the main fluid flowpath  204  and an outside region  208 . In an exemplary embodiment, the outside region  208  may include the atmosphere, but may in other embodiments include a separate, inner-stage of the turbomachine  102 . Unless effectively sealed, the clearance opening  206  will allow pressurized process gas to escape from the main fluid flowpath  204  to the outside region  208 , thereby resulting in a loss of operating efficiency. 
         [0017]    In one embodiment, the pressurized process gas may be sealed into the main fluid flowpath  204  by at least two convergent nozzles  210   a,    210   b.  Briefly, a convergent nozzle, also known as an ejector, can be designed to entrain fluids in a high velocity jet of propelling fluid. In operation, the convergent nozzle may be capable of converting a high-pressure, low-velocity fluid flow into a low-pressure, high-velocity fluid flow capable of entraining a secondary fluid flow. As can be appreciated, the higher the velocity of the jet from the nozzle, the greater the vacuum created and pressure against which the nozzle can exhaust. 
         [0018]    In the illustrated embodiment, the convergent nozzles  210   a,    210   b  may be operably coupled to each end of the casing  104 , and may circumferentially extend around the shaft  106 . In other embodiments, the convergent nozzles  210   a,    210   b  may be cast or integrally-formed into the casing  104  itself. In operation, the convergent nozzles  210   a,    210   b  may be configured to prevent the pressurized process gas from escaping the main fluid flowpath  204  through the clearance openings  206 , and thereby leaking into the outside region  208 . 
         [0019]    Referring now to  FIG. 3 , an exemplary convergent nozzle  210   b  is shown according to one or more aspects of the present disclosure. As can be appreciated, the following description may correspond and be equally applied to the opposing convergent nozzle  210   a.  The convergent nozzle  210   b  may include a body  302  having a primary fluid passage  304  configured to receive, channel, and discharge a primary fluid. In at least one embodiment, the primary fluid may include a pressurized fluid. The body  302  may include a primary fluid inlet  306 , a fluid outlet  308 , and a convergent chamber  310  interposed between the inlet  306  and the outlet  308 . The fluid outlet  308  may extend circumferentially around the rotating shaft  106  so as to be substantially adjacent the clearance opening  206 . 
         [0020]    During operation, a pressurized primary fluid entering the primary fluid inlet  306  may be accelerated through the convergent chamber  310  and discharged at a high velocity through the outlet  308  and into an adjacent inner-region  312 . Accelerating the primary fluid may generate a local reduced pressure, or vacuum effect, in the inner-region  312 , thereby entraining or drawing-in a flow of secondary fluid from the outside region  208  through the clearance opening  206 . Accordingly, the interaction at the inner-region  312  of the high-velocity, low pressure primary fluid with an influx of a secondary fluid from the outside region  208  may generate a non-contacting, continuous sealing effect at the clearance opening  206 . This sealing effect may, therefore, prevent process gas leakage from the main fluid flowpath  204  into the outside region  208 . 
         [0021]    In one or more embodiments, at least one adjustable valve or restrictor (not shown) may be used to adjust the mass-flow rate of the primary fluid through the convergent nozzles  210   a,    210   b.  By adjusting the mass-flow rate of the primary fluid, the influx of secondary fluid into the inner-region  312  may be regulated even to a point of achieving pressure equilibrium where no fluid enters or leaves the casing  104 . Therefore, a continuous fluid seal may be created and optimized for operation. 
         [0022]    In one or more embodiments, a control system (not shown) may be communicably coupled to the adjustable valve or restrictor and configured to automate the regulation of the mass-flow rate of the primary fluid entering the converging nozzles  210   a,    210   b.  The control system may be communicably coupled to at least one sensor arranged in the inner-region  312 . The sensor may be capable of detecting environmental conditions therein and relaying such conditions back to the control system for processing. For example, a higher pressure detected in the main fluid flowpath  204  may result in a command to the control system to adjust the valve in order to increase the mass-flow rate of the primary fluid. Likewise, a lower pressure detected in the main fluid flow path  204  may result in a command to the control system to adjust the valve in order to decrease the mass-flow rate of the primary fluid. As can be appreciated, adjusting the mass-flow rate of the primary fluid may be used to establish a point of pressure equilibrium where no fluid enters or leaves the casing  104  through the clearance openings  206 . 
         [0023]    Referring again to  FIG. 2 , in an exemplary embodiment, the primary fluid channeled into the convergent nozzles  210   a,    210   b  may originate, at least in part, from the discharge nozzle  200 . As illustrated, one or more supply pipes  212  may fluidly communicate the discharge nozzle  200  to the convergent nozzles  210   a ,  210   b,  thereby exploiting the exiting high pressure process gas. In another embodiment, the primary fluid flow may originate from an alternative source, for example, an intermediate compressor stage of the machine  102  or an upstream turbine stage. In yet other embodiments, especially relevant during turbomachine  102  startup when process gas pressures tend to be low, the primary fluid may originate from a secondary or booster compressor (not shown). The booster compressor may be configured to either maintain the required pressure throughout turbomachine  102  operation, or discontinue after the turbomachine  102  reaches pressures sufficient to independently supply the primary fluid to the nozzles  210   a ,  210   b.    
         [0024]    In at least one embodiment, the present disclosure may provide a convergent nozzle seal applied to a turbomachine  102  and configured to seal the fluid flowing in a main fluid flowpath  204 , thus preventing any leakage from such main fluid flowpath  204 . Employing the convergent nozzle seal may render labyrinth and gas/oil seals unnecessary along the shaft  106  of the turbomachine  102 . By eliminating these excess seals, the shaft  106  length and weight may be reduced, thereby increasing the critical speed of the shaft  106  and allowing the turbomachine  102  to deliver higher pressures more efficiently. Moreover, another possible improvement resulting from the present disclosure may include the ability to maintain larger clearances between the rotating and stationary members of a turbomachine. 
         [0025]    In another embodiment, the present disclosure may be applied to a turbomachine with a back-to-back configuration. The dominant component affecting rotordynamics in a back-to-back configuration is a damper seal, typically located at the division wall between the two sections where shaft deflection is the greatest. In light of the length and weight of the rotating shaft in back-to-back turbomachines, the damper seal is generally configured to improve rotordynamic stability, particularly shaft vibration, and reduce section-to-section process gas leakage. According to embodiments of the disclosure, the shaft in a back-to-back configuration turbomachine may be significantly shortened by using at least one convergent nozzle seal at the shaft ends, as described above. Furthermore, in at least one embodiment, a convergent nozzle seal as generally described above may be used to replace the damper seal at the middle of the shaft. Each convergent nozzle seal in the back-to-back configuration may be regulated by an adjustable valve or restrictor controlled either directly or remotely by a control system, as described above. 
         [0026]    In another exemplary embodiment, the present disclosure may be used in conjunction with a steam turbine turbomachine. In particular, at least one convergent nozzle seal may be implemented at the steam inlet end and the steam exhaust end of an exemplary steam turbine. Use of the at least one exemplary convergent nozzle seal may potentially supplement or replace labyrinth seals normally used to seal the process gas at the shaft ends. By replacing these seals with a convergent nozzle configuration, the shaft length may be decreased, thereby increasing the potential speed and efficiency of the machine. 
         [0027]    In another exemplary embodiment the convergent nozzle seals of the present disclosure may be used in conjunction with an axial flow compressor, or a power turbine. In particular, at least one exemplary convergent nozzle seal may serve to replace the typical balance piston seal located near the shaft end of the axial flow compressor or the power turbine. Furthermore, at least one exemplary convergent nozzle seal may supplement or completely replace the shaft-end seals used on axial flow compressors and power turbines. 
         [0028]    As can be appreciated by those skilled in the art, the present disclosure may be employed in numerous other applications not particularly disclosed herein. For example, convergent nozzle seals may be used to seal rotating shafts in a variety of turbomachine applications, including, steam turbines, gas turbines, compressors, separators, and expanders, each of which employ any number of shaft seals. Furthermore, the present disclosure may be employed on the overhang-type turbomachine that will typically employ only one convergent nozzle. 
         [0029]    The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.