Patent Publication Number: US-8529191-B2

Title: Method and apparatus for lubricating a thrust bearing for a rotating machine using pumpage

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/150,342 filed on Feb. 6, 2009. The disclosure of the above application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to pumps, and, more specifically, to thrust bearing lubrication for axial thrust force compensation within a fluid machine suitable for normal operation but useful also in start-up, shut down and upset conditions. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Rotating fluid machines are used in many applications for many processes. Lubrication for a rotating fluid machine is important. Various types of fluid machines use a thrust bearing that is lubricated by the pumpage. Adequate flow of pumpage should be supplied to obtain proper lubrication. Fluid machines are used under various conditions. During normal operating conditions, lubrication may be relatively easy. However, under various transient conditions, such as start-up conditions, shut-down conditions and during upset conditions, such as passage of air through the machine, lubrication may be lost and therefore damage may occur to the fluid machine. Air entrainment or debris within the pumpage may cause upset conditions. 
     Referring now to  FIG. 1 , a hydraulic pressure booster (HPB)  10  is one type of fluid machine. The hydraulic pressure booster  10  is part of an overall processing system  12  that also includes a process chamber  14 . Hydraulic pressure boosters may include a pump portion  16  and a turbine portion  18 . A common shaft  20  extends between the pump portion  16  and the turbine portion  18 . The HPB  10  may be free-running which means that it is solely energized by the turbine and will run at any speed where the equilibrium exists between a turbine output torque and the pump input torque. The rotor or shaft  20  may also be connected to an electric motor to provide a predetermined rotational rate. 
     The hydraulic pressure booster  10  is used to boost the process feed stream using energy from another process stream which is depressurized through the turbine portion  18 . 
     The pump portion  16  includes a pump impeller  22  disposed within a pump impeller chamber  23 . The pump impeller  22  is coupled to the shaft  20 . The shaft  20  is supported by a bearing  24 . The bearing  24  is supported within a casing  26 . Both the pump portion  16  and the turbine portion  18  may share the same casing structure. 
     The pump portion  16  includes a pump inlet  30  for receiving pumpage and a pump outlet  32  for discharging fluid to the process chamber  14 . Both of the pump inlet  30  and the pump outlet  32  are openings within the casing  26 . 
     The turbine portion  18  may include a turbine impeller  40  disposed within a turbine impeller chamber  41 . The turbine impeller  40  is rotatably coupled to the shaft  20 . The pump impeller  22 , the shaft  20  and the turbine impeller  40  rotate together to form a rotor  43 . Fluid flow enters the turbine portion  18  through a turbine inlet  42  through the casing  26 . Fluid flows out of the turbine portion  40  through a turbine outlet  44  also through the casing  26 . The turbine inlet  42  receives high-pressure fluid and the outlet  44  provides fluid at a pressure reduced by the turbine impeller  40 . 
     The impeller  40  is enclosed by an impeller shroud. The impeller shroud includes an inboard impeller shroud  46  and an outboard impeller shroud  48 . During operation the pump impeller  22 , the shaft  20  and the turbine impeller  44  are forced in the direction of the turbine portion  18 . In  FIG. 1 , this is in the direction of the axial arrow  50 . The impeller shroud  48  is forced in the direction of a thrust-bearing  54 . 
     The thrust bearing  54  may be lubricated by pumpage fluid provided from the pump inlet  30  to the thrust bearing  54  through an external tube  56 . A gap or layer of lubricating fluid may be disposed between the thrust bearing  54  and outboard impeller shroud which is small and is thus represented by the line  55  therebetween. A filter  58  may be provided within the tube to prevent debris from entering the thrust bearing  54 . At start-up, the pressure in the pump portion  56  is greater than the thrust bearing and thus lubricating flow will be provided to the thrust bearing  54 . During operation, the pressure within the turbine portion  18  will increase and thus fluid flow to the thrust bearing  54  may be reduced. The thrust bearing  54  may have inadequate lubricating flow during operation. Also, when the filter  58  becomes clogged, flow to the thrust bearing  54  may be interrupted. The thrust bearing  54  generates a force during normal operation in the opposite direction of arrow  50 . 
     Referring now to  FIG. 2 , another prior art hydraulic pressure booster  10 ′ is illustrated. The hydraulic pressure booster  10 ′ includes many of the same components illustrated in  FIG. 1  and thus the components of  FIG. 2  are labeled the same and are not described further. In this example, the casing  26  has an annular clearance  60  therein adjacent to the thrust bearing  54  and the outboard turbine shroud  48 . This provides a small side stream fluid flow to the thrust bearing  54  during startup. The advantage of this process is that the external tube  56  and the filter  58  are eliminated. 
     Challenges to rotating fluid machines and thrust bearings therein include a high inlet pressure in the pump that may result in a high axial thrust on the rotor in the direction of the turbine  18 . Also, during startup pumpage may be forced through the pump portion  16  by an external feed pump upstream of the high pressure booster  10  while the turbine portion  18  runs dry or nearly dry. Flow through the pump impellers may generate a torque creating rotor rotation which may damage the thrust bearing due to the lack of lubrication. Often times, the pressure in the turbine section is much lower than the pump section and thus the lubrication may be insufficient until the full rotor speed is obtained. Process equipment between the pump discharge and the turbine inlet may occasionally introduce air into the turbine. This may occur when the process chamber or system was not purged properly during startup. Consequently, intermittent lubrication to the thrust bearing may be lost. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The present disclosure provides an improved method for lubricating a rotating process machine during operation. The system provides pumpage to the thrust bearing over the entire operating range of the device. 
     In one aspect of the invention, a fluid machine comprises includes a pump portion having a pump impeller chamber, a pump inlet and a pump outlet and a turbine portion having a turbine impeller chamber, a turbine inlet and a turbine outlet. A shaft extends between the pump impeller chamber and the turbine impeller chamber. The shaft has a shaft passage therethrough. A turbine impeller is coupled to the impeller end of the shaft disposed within the impeller chamber. The turbine impeller has vanes at least one of which comprises a vane passage therethrough. A thrust bearing is in fluid communication with said vane passage. 
     In another aspect of the invention, a method for operating a fluid machine includes communicating fluid from the pump impeller chamber through a shaft passage to a thrust bearing at the inboard end of the bearing and generating an inboard axial force in response to communicating fluid. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a cross-sectional view of a first turbocharger according to the prior art. 
         FIG. 2  is a cross-sectional view of a second turbocharger according to the prior art. 
         FIG. 3  is a cross-sectional view of a first fluid machine according to the present disclosure. 
         FIG. 4  is an end view of an impeller of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a second fluid machine according to the present disclosure. 
         FIG. 6  is a cross-sectional view of a third embodiment of a turbine portion according to the present disclosure. 
         FIG. 7  is a cross-sectional view of a fourth embodiment of a turbine portion according to the present disclosure. 
         FIG. 8  is a cross-sectional view of an alternative embodiment of an impeller of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     In the following description, a hydraulic pressure booster having a turbine portion and pump portion is illustrated. However, the present disclosure applies equally to other fluid machines. The present disclosure provides a way to deliver pumpage to a thrust bearing over the operating range of the device. The rotor is used as a means to conduct pumpage to a thrust bearing surface. A high pressure is provided to the thrust bearing from startup through the shutdown process including any variable conditions. Debris entering the turbine is also reduced. 
     Referring now to  FIG. 3 , a first embodiment of a high-pressure booster  10 ″ is illustrated. In this example, the common components from  FIG. 3  are provided with the same reference numerals are not described further. In this embodiment, a hollow shaft  20 ′ is used rather than the solid shaft illustrated in  FIGS. 1 and 2 . The hollow shaft  20 ′ has a shaft passage  70  that is used for passing pumpage from the impeller chamber  23  of the pump portion  16  to the turbine portion  18 . The passage  20  may provide pumpage from the pump inlet  30 . 
     The inboard shroud  46 ′ includes radial passages  72 . The radial passages  72  are fluidically coupled to the shaft passage  70 . Although only two radial passages  72  are illustrated, multiple radial passages may be provided. 
     The impeller  40 ′ may include vanes  76 A-D as is illustrated in  FIG. 4 . The impeller  40 ′ includes axial passages  74 . The axial passages  74  may be provided through vanes  76 A and  76 C of the impeller  40 ′. The axial passages are parallel to the axis of the HPB  10 ″ and the shaft  20 ′. The axial passages  74  extend partially through the inner impeller shroud  46 ′ and entirely through the outboard impeller shroud  48 ′. The axial passages  74  terminate adjacent to the thrust bearing  54 . Again the gap between the outboard impeller shroud  48 ′ and the thrust bearing  54  is small and thus is represented by the line  55  in the Figure therebetween. The lubrication path for the thrust bearing  54  includes the shaft passage  70 , the radial passages  72  and the axial turbine impeller passages  74 . 
     In operation, at start-up pressure within the pump portion  16  is higher than the turbine portion  18 . Fluid within the pump portion travels through the shaft passage  70  to the radial passages  72  and to the axial passage  74 . When the fluid leaves the axial passage  74 , the fluid is provided to the thrust bearing  54 . More specifically, the fluid lubricates the space or gap  55  between the thrust bearing  54  and the outboard impeller shroud  48 ′. The thrust bearing  54  generates an inboard axial force in response to the lubricating fluid in the opposite direction of arrow  50 . 
     The highest pressure in the pumpage occurs in the pump inlet  30  during startup. Passages downstream of the pump inlet are at lower pressure and thus fluid from the pump portion  16  flows to the turbine portion  18 . Consequently, pumpage from the inlet is high during the startup. During shutdown of the equipment, the same factors apply due to the differential and pressure between the pump and the turbine. During normal operation, the highest pressure is no longer in the pump inlet but is at the pump outlet  32 . Due to the arrangement of the lubrication passages, the pressure increases in the pumpage due to a pressure rise occurring in the radial passage  72  due to a centrifugal force generated by the rotation of the turbine impeller  40 ′. The amount of pressure generation is determined by the radial length of the radial passages  72  and the rate of the rotor rotation. Consequently, pumpage is provided to the thrust bearing at the startup, normal operation and shutdown of the fluid machine  10 ″. 
     Referring now to  FIG. 4 , the impeller  40 ′ is illustrated having four impeller vanes  76 A- 76 D. Various numbers of vanes may be provided. The vanes extend axially relative to the axis of the shaft  20 ′. More than one impeller vane may have an axial passage  74 . The axial passage  74  extends through the vanes  76  and the inboard impeller shroud  46 ′ sufficient to intercept radial passage  72  and the outboard impeller shroud  48 ′ which are illustrated in  FIG. 3 . 
     It should be noted that the process chamber  14  is suitable for various types of processes including a reverse osmosis system. For a reverse osmosis system, the process chamber may have a membrane  90  disposed therein. A permeate output  92  may be provided within the process chamber for desalinized fluid to flow therefrom. Brine fluid may enter the turbine inlet  42 . Of course, as mentioned above, various types of process chambers may be provided for different types of processes including natural gas processing and the like. 
     Referring now to  FIG. 5 , an embodiment similar to that of  FIG. 3  is illustrated and is thus provided the same reference numerals. In this embodiment, a deflector  110  is provided within the pump inlet  30 . The deflector  110  may be coupled to the pump impeller  22  using struts  112 . The struts  112  may hold the deflector  110  away from the pump impeller so that a gap is formed therebetween that allows fluid to flow into the shaft passage  70 . 
     The deflector  110  may be cone-shaped and have an apex  114  disposed along the axis of the shaft  20 ′. The cone shape of the deflector  110  will deflect debris in the pumpage into the pump impeller  22  and thus prevent passage of debris into the shaft passage  70 . Unlike the filter  58  illustrated in  FIG. 1 , the debris is deflected away from the shaft passage  70  and thus will not clog the shaft passage  70 . 
     Referring now to  FIG. 6 , the turbine portion  18  is illustrated having another embodiment of a thrust bearing  54 ′. The thrust bearing  54 ′ may include an outer land  210  and an inner land  212 . A fluid cavity  214  is disposed between the outer land  210 , the inner land  212  and the outer shroud  48 ′. It should be noted that the thrust-bearing  54 ′ of  FIG. 6  may be included in the embodiments illustrated in  FIGS. 3 and 5 . 
     The outer land  210  is disposed adjacent to the annular clearance  60 . The inner land  212  is disposed adjacent to the turbine outlet  44 . The thrust bearing  54 ′ may be annular in shape and thus the outer land  210  and inner land  212  may also be annular in shape. 
     The cavity  214  may receive pressurized fluid from the pump portion  16  illustrated in  FIGS. 3 and 5 . That is, pumpage may be received through the shaft passage  70 , the radial passages  72  and the axial passages  74 . 
     Slight axial movements of the shaft  20  in the attached impeller shroud  48 ′ may cause variations in the axial clearance  220  between the lands  210  and  212  relative to the outer shroud  48 ′. If the axial clearances  220  increase, the pressure in the fluid cavity  214  decreases due to an increase of leakage through the clearances  220 . Conversely, if the axial gap of the clearance  220  decreases, the pressure will rise in the fluid cavity  214 . The pressure variation counteracts the variable axial thrust generated during operation and ensures that the lands  210  and  212  do not come into contact with the impeller shroud  48 ′. 
     The reduction in pressure is determined by the flow resistance in the passages  70 - 74 . The passages are sized to provide a relationship between the rate of leakage and the change in pressure in the fluid cavity  214  as a function of the axial clearance. The radial location of the channel  74  determines the amount of centrifugally generated pressure rise and is considered in ensuring an optimal leakage in addition to the diameters of the flow channel. Excessive leakage flow may impair the efficiency and insufficient fluid flow will allow clearances to be too small and allow frictional contact during operation. 
     The pressure in the fluid cavity is higher than the turbine outlet  44  and the pressure in the outer diameter of the impeller in the annular clearance  60  when the channel  74  is at the optimal radial location. Leakage will thus be out of cavity  214  to allow a desired pressure variation within the fluid cavity  214 . 
     Referring now to  FIG. 7 , an embodiment similar to that of  FIG. 6  is illustrated. The inner land  212  is replaced by a bushing  230 . The bushing  230  may form a cylindrical clearance relative to the impeller wear ring  232 . The fluid cavity  214  is thus defined between the wear ring  232 , the bushing  230  and the outer land  210 . 
     Referring now to  FIG. 8 , vane  240  of an impeller  242  having curvature in the axial plane as well as the radial plane is illustrated. The impeller  242  may be used in a mixed flow design. In this embodiment, the outer land  210 ′ and inner land  212 ′ are formed according to the shape of the impeller  242 . The fluid cavity  214 ′ may also be irregular in shape between the outer land  210 ′ and the inner land  212 ′. 
     The fluid passage  250  provides fluid directly to the fluid cavity  214 ′ in a direction at an angle to the longitudinal axis of the fluid machine and shaft  20 ′. Thus, the radial passages  72  and axial passages  74  are replaced with the diagonal passage  250 . The diagonal passage  250  may enter the fluid cavity  214 ′ at various locations including near the land  212 ′ or at another location such as near land  210 ′. Various places between panel  210 ′ and  212 ′ may also receive the diagonal passage  250 . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.