Abstract:
A rotating assembly adapted for use in turbines and pumps is provided. The rotating assembly includes a shroud that rotates around a central axis and a disk seated in a recess in the shroud so that the disk rotates with the shroud, the disk being oriented perpendicular to the central axis. The rotating assembly also includes a stationary element in which at least one surface of the disk contacts a fluid so that when the fluid flows under pressure, the surface of the disk resists the generation of drag between the surface and the stationary element of the rotating assembly. A shroud is provided that includes a circular recess with a cavity on an outer perimeter extending away from the fixed assembly. A method of manufacturing a rotating assembly is provided.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to bearings, and more specifically, to thrust runners for hydrodynamic tilt pads and hydrostatic thrust bearings for turbines and pumps. 
       BACKGROUND 
       [0002]    Turbines and pumps are used for various purposes, and may have similar designs, with the most significant differences being the direction of flow of fluid through the device, and whether the device requires an energy input or provides an energy output. Turbines are used to convert kinetic energy of a fluid to a rotational energy in a shaft. The rotational energy may then be used to perform work, and particularly may be used to generate electricity. Pumps are used to move fluids, and in particular are used to move fluids against a back pressure. In short, pumps convert mechanical energy into hydraulic energy, while turbines convert hydraulic energy into mechanical energy. 
         [0003]    One application of a turbine is to recover energy from a natural gas processing operation. Natural gas may have significant quantities of waste gases when recovered from a well, and may need to be cleaned in order to be transported, sold, or used. One method of cleaning natural gas (also referred to as sweetening) is to combine it with water and amine in a high pressure environment. This process allows the separation of the high quality natural gas from the waste gas or gases. After this process, the natural gas may be transported to a lower pressure environment for storage or transport. 
         [0004]    Creating the high pressure environment for the cleaning of natural gas is an energy intensive process. The lean amine/water mixture is injected into the high pressure environment (also referred to as a contactor) at high pressure. The contaminant gases (specifically, CO 2  and H 2 S) are then absorbed by the amine/water mixture, and the now rich amine/water mixture flows out of the contactor where its pressure is reduced to atmosphere. Traditionally this is done using a backpressure valve. The present application proposes replacing this valve with a turbine. 
         [0005]    Natural gas recovery operations often involve natural gas having a large amount of debris in the gas. Therefore pumps and turbines used in this process must have high tolerances for debris and foreign matter, especially the bearings in pumps and turbines that are process lubricated. Process lubricating pumps and turbines use the same fluid that is flowing through the device to lubricate the pump or turbine. 
       SUMMARY OF THE INVENTION 
       [0006]    According to exemplary embodiments, the present invention provides a thermal fit thrust runner for a thrust bearing. A bearing assembly adapted for use in turbines and pumps is provided. The bearing assembly includes a shroud that rotates around a central axis and a disk seated in a recess in the shroud so that the disk rotates with the shroud, the disk being oriented perpendicular to the central axis. The bearing assembly also includes a stationary element in which at least one surface of the disk contacts a fluid so that when the disk rotates, the surface of the disk resists the generation of drag between the surface and the stationary element of the bearing assembly. 
         [0007]    In the bearing assembly, the disk may be annular and/or replaceable. The disk may be installed and secured in the recess by thermal compression. The thermal compression may be accomplished by heating the assembly to a temperature not exceeding 250 degrees Celsius, placing the disk in the recess, and allowing the assembly to cool so that the disk is secured in the recess by a radial force generated by a thermal expansion differential between the shroud and the disk. 
         [0008]    The shroud may include stainless steel. The disk may include a ceramic, graphite, and/or metallic carbide. The stationary element may include a ceramic, graphite, polyether ether ketone, and/or metallic carbide. In the bearing assembly, the recess in the shroud may include a cavity proximate to an outer diameter of the recess. The cavity may be U-shaped with parallel sides and an arcuate bottom. An interior surface of the recess between the cavity and the central axis may be substantially planar and perpendicular to the central axis, and the cavity may include parallel sides defining an angle with respect to the interior surface. The angle may be less than or equal to 90 degrees, may be more than 90 degrees, or may be substantially 95 degrees. 
         [0009]    The disk may contact the stationary element on a face opposite the recess, and a lubricant may flow between the disk and the stationary element. The lubricant may include a portion of the fluid passing through the turbine or pump. 
         [0010]    In an alternative exemplary embodiment, a rotating assembly for contacting a fixed assembly is provided. The rotating assembly is adapted to rotate around a central axis, and includes a shroud including a circular recess. The recess includes on an outer perimeter a cavity extending away from the fixed assembly. The rotating assembly also includes a disk seated in the recess and contacting an outer surface of the recess. The outer surface is substantially parallel to the central axis and compresses the disk when the shroud is at a temperature less than substantially 250 degrees Celsius. 
         [0011]    The shroud may be stainless steel, and the disk may include ceramic, graphite, and/or metallic carbide. The fixed assembly may include ceramic, graphite, polyether ether ketone, and/or metallic carbide. The cavity may be U-shaped with parallel sides and an arcuate bottom. The central axis may intersect the recess substantially centrally. 
         [0012]    An interior surface of the recess between the cavity and the central axis may be substantially planar and perpendicular to the central axis, and the cavity may include parallel sides defining an angle with respect to the interior surface. The angle may be less than 90 degrees, may be more than 90 degrees, or may be substantially 95 degrees. 
         [0013]    The shroud may be coupled to a blade or blades, and the blade or blades may contact a fluid. When the fluid flows under pressure, the blade or blades may urge the shroud to rotate around the central axis. 
         [0014]    The disk may contact the fixed assembly on a face opposite the recess, and a lubricant may flow between the disk and the fixed assembly. The lubricant may include a portion of the fluid. 
         [0015]    In an alternative exemplary embodiment, a method of manufacturing a rotating assembly is provided. The rotating assembly is used in turbines and pumps. The method includes arranging a disk in a circular recess of a shroud, and securing the disk in the shroud with a radial force between the shroud and the disk caused by thermal compression of the disk by the shroud. 
         [0016]    The shroud may include a cavity contiguous with an outer diameter of the recess. The manufacturing method may include, before the arranging operation, heating the shroud to a temperature exceeding 150 degrees Celsius. The disk may not be heated prior to arranging the disk in the recess. Alternatively, the disk may be heated prior to arranging the disk in the recess, and the radial force may be generated by a thermal expansion differential between the shroud and the disk. The thermal compression may be reversible by heating the combination of the disk and the shroud. The manufacturing method may include, before the arranging operation, cooling the disk. The thermal compression may be accomplished by allowing the assembly to warm to room temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a cross-section of an exemplary embodiment of thrust pad bearing according to the present technology. 
           [0018]      FIG. 2  is a flow chart illustrating an exemplary method according to the present technology. 
           [0019]      FIG. 3  is a perspective view of an exemplary embodiment of a shroud undergoing a stress analysis according to the present technology. 
           [0020]      FIGS. 4A and 4B  are cross-sections of an exemplary embodiment of a turbine and thrust bearing assembly according to the present technology. 
           [0021]      FIGS. 5A ,  5 B, and  5 C are various views of an exemplary embodiment of a shroud and thrust runner combination according to the present technology. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0022]    While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail several specific embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. According to exemplary embodiments, the present technology relates generally to bearings. More specifically, the present invention provides a thermal fit thrust runner for a bearing of a shroud for a blade or blades for a turbine or pump. 
         [0023]    A thrust bearing described herein may be used in a pump or turbine. In a turbine application to recover energy from high pressure natural gas or a water amine mixture after a natural gas sweetening operation, the thrust bearing provided herein may be durable and debris resistant. The thrust bearing may operate at high speeds and may be lubricated by a portion of the fluid flowing through the turbine (or pump), which is also referred to herein as a process lubricated turbine or pump. All of the surfaces in the process lubricated turbine or pump may therefore be wetted surfaces, and therefore tolerant of debris that is common in the fluids associated with a gas sweetening operation. A thrust bearing according to the disclosed technology may be used in any application requiring a debris resistant high speed bearing. 
         [0024]    The resistance to wear is provided in the described thrust bearing by a thrust runner, also referred to herein as a disk, which may be ceramic, graphite, or metallic carbide. The thrust runner may be installed in a shroud with a thermal fit that involves installing the thrust runner in the shroud during a high temperature operation. Alternatively, the installation operation may involve cooling the disk. The compression of the thermal fit may strengthen the thrust runner and improve its performance during operation. 
         [0025]      FIG. 1  is a cross-section of turbine  100 . Alternatively, element  100  may be a pump. Turbine  100  includes inlet channel  102  and diffuser  104 . Alternatively, channel  102  may be an outlet and channel  104  may be an inlet, particularly when element  100  is a pump. Turbine  100  includes a thrust pad bearing, which is a combination of fixed assembly  110  and rotating assembly  120 . 
         [0026]    Fixed assembly  110  includes tilting pad  112 , which may be made of silicon carbide or ceramic supported by stainless steel arrangement, or any other appropriate material. Fixed assembly  110  also includes tilting pad bearing base  114 , which may be made of stainless steel, or any other appropriate material, and which may be coupled to tilting pad  112  by connectors that may include spring or rocking elements. Fixed assembly  110  further includes mechanical seal  116 , which may be made of silicon carbide, tungsten carbide, polyether ether ketone (also referred to as PEEK) or ceramic, or any other appropriate material. 
         [0027]    Rotating assembly  120  includes shroud  124 , which may be made of stainless steel, or any other appropriate material, and which house blades  122 . The portions of shroud  124  that house blades  122  may also be referred to herein and generally as a turbine runner. Blades  122  may in some exemplary embodiments be a single blade, but in alternative and preferred exemplary embodiments, blades  122  are a plurality of blades arranged in a fan configuration. Rotating assembly  120  also includes thrust runner  126 , which may be made of silicon carbide or other ceramic, or any other appropriate material, and which may be seated in a recess of shroud  124  in a high temperature assembly operation such that, after cooling, shroud  124  may compress and hold thrust runner  126  in a thermal fit relationship. Shroud may also include cavity  128  adjacent and contiguous with the recess that receives thrust runner  126 , and which may remain vacant after thrust runner  126  is seated in the recess. 
         [0028]    During operation, fluid under high pressure flows into inlet channel  102  and out diffuser  104 , causing blades  122  to rotate. The rotation of blades  122  causes rotating assembly  120  to rotate, which in turn causes shaft  130  to rotate. Rotating assembly  120  may rotate at a high rate of speed due to the high pressure differential between the zone of fluid prior to entry in inlet channel  102  and the zone of fluid after exiting diffuser  104 , which may cause the fluid to flow at a high rate of speed. Rotating assembly  120  contacts fixed assembly  110 , and this area of contact may experience a high level of force due to the high pressure condition of the fluid upon entering inlet channel  102  relative to the low pressure condition of the fluid upon exiting diffuser  104 . The face of thrust runner  126  that faces tilting pad  112  may therefore experience a high level of wear due to the combination of the high pressure, and the high rate of relative rotational velocity, between these two elements. 
         [0029]    The present technology provides for convenient and easy replacement of thrust runner  126 . Thrust runner  126  may be removed by reversing the installation operation, for example by heating the combination of the thrust runner and shroud  124 . Alternatively, thrust runner  126  may be removed by impacting thrust runner  126  so that it breaks. Subsequently, a new thrust runner  126  may be installed in shroud  124  and the combination returned to turbine  100  for continued use. 
         [0030]      FIG. 2  illustrates method  200  according to the present technology. Method  200  starts at start oval  210  and proceeds to operation  220 , which indicates to heat a stainless steel shroud to a temperature in excess of 150 degrees Celsius. Alternatively, the shroud may be made of any one or more of stainless steel, a ceramic material, graphite, polyether ether ketone, and metal carbide. The shroud may be heated not in excess of 250 degrees Celsius, and the disk may be also be heated along with the shroud during operation  210 . From operation  220 , the flow proceeds to operation  230 , which indicates to arrange a ceramic or silicon carbide thrust runner into an annular recess of the shroud. The thrust runner is also referred to herein as a disk, and may alternatively include one or more of ceramic, graphite, or metallic carbide. From operation  230 , the flow proceeds to operation  240 , which indicates to cool the combination of the thrust runner and the shroud. Operation  240  further indicates to mount the combination to a fixed assembly of a thrust bearing. The fixed assembly is also referred to herein as a stationary element, and may be composed of one or more of a ceramic, graphite, polyether ether ketone, and metallic carbide. From operation  240 , the flow proceeds to end oval  250 . In still further alternatives, the disk may be cooled, while the shroud remains at room temperature or is heated, prior to operation  230 . In the case where both the shroud and the disk are heated during operation  210 , the material for the shroud has a different coefficient of thermal expansion with respect to the material of the disk. In this manner, the thermal fit between the disk and the shroud exists for a range of temperatures that includes the operating range, and the thermal fit would not exist at the manufacturing temperature. Therefore, this thermal fit is reversible by raising the temperature of the combination of the shroud and the disk to the manufacturing temperature and removing the disk from the shroud. This reversal of the manufacturing process may be very useful in situations in which the disk becomes worn and requires replacement. 
         [0031]      FIG. 3  is a perspective view of an exemplary embodiment of shroud  124  undergoing a finite element stress analysis, with different shading representing different amounts of stress. Shroud  124  includes cavity  128  along an outer perimeter of the annular recess. Face  300  of shroud  124  defines a position for a thrust runner. When a thrust runner of appropriate size to create a thermal fit (also referred to as a shrink fit) is positioned in the recess of shroud  124  and is compressed by outer face  320  of shroud  124 , stress is concentrated at line of contact  322  as well as at arcuate portion  330  of cavity  128 . Flange  310  of shroud  124  functions to support line of contact  322 , and is under a considerable amount of hoop stress. These stresses are within tolerance (below the yield stress) for the material used for shroud  124 , and create a sufficiently strong thermal fit to attach a thrust runner for use in a high speed turbine or pump. 
         [0032]      FIG. 4A  is a cross-section of an exemplary embodiment of turbine  200  including a thrust bearing having fixed assembly  210  and rotating assembly  120 . Rotating assembly  120  is coupled to shaft  130  and includes shroud  124  and thrust runner  126 . Thrust runner  126  contacts fixed assembly  210  at tilting pad  212 . 
         [0033]      FIG. 4B  is a cross-section of the exemplary embodiment of turbine  200  shown in  FIG. 4A , and additionally illustrates inlet channel  102 , diffuser  104 , and blades  122 . Fixed assembly  210  of turbine  200  illustrated in  FIG. 4B  also includes tilting pad bearing base  214 , and rotating assembly  120  includes thrust runner  126  seated in shroud  124  in a thermal fit relationship. Shroud  124  includes cavity  128 .  FIGS. 4A and 4B  are three-dimensional views of  FIG. 1 . 
         [0034]      FIG. 5A  is a front view of an exemplary embodiment of rotating assembly  120  including blades  122  arranged centrally within annular face  500  of thrust runner  126 . On outer perimeter  510  of rotating assembly  120  is flange  310  of a shroud. Cross-sectional line  520  illustrates the section used for  FIG. 5B   
         [0035]      FIG. 5B  is cross-sectional view of the exemplary embodiment of shroud  124  and thrust runner  126  of rotating assembly  120 . Thrust runner  126  includes face  500  and is seated in shroud  124 . Shroud  124  houses blades  122  occupying inlet channel  102  and is rigidly coupled to shaft  130 . Also illustrated in  FIG. 5B  is central axis  530 , about which rotating assembly  120  rotates. Shroud  124  includes perimeter zone  540  which is illustrated in more detail in  FIG. 5C . 
         [0036]      FIG. 5C  is a close-up view of perimeter zone  540  including portions of shroud  124  and thrust runner  126 . Shroud  124  includes face  300 , on which thrust runner  126  seats, and flange  310  on an outer perimeter. Shroud  124  also includes cavity  128  which is not occupied by thrust runner  126  but which is contiguous with the recess occupied by thrust runner  126 . Cavity  128  is U-shaped including inward side  552  toward a central axis, and outward side  550  away from the central axis. Arcuate portion  330  forms a bottom of cavity  128 . Outward side  550  may be parallel to inward side  552 , and may additionally be parallel to a central axis, or equivalently perpendicular to face  500  of thrust runner  126 . Alternatively, outward side  550  and inward side  552  may form an angle of varying degrees with face  500 , for example more or less than substantially 90 degrees. In particular, outward side  550  and inward side  552  may angle away from the central axis by 5 degrees, or may angle towards the central axis by 5 degrees. Outer diameter  560  of thrust runner  126  contacts outer face  320  of shroud  124 , which together represent the area of interference where the thermal fit engages. 
         [0037]    The stainless steel used in the devices and methods according to the present technology may include 2205 and 2507 stainless steels, which have a 50% higher yield strength than 316 stainless steel. 
         [0038]    The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.