Patent Publication Number: US-10760582-B2

Title: Stabilizing arrangement for a rotating vertical shaft of a machine, machine and stabilizing method

Description:
BACKGROUND 
     Embodiments of the subject matter disclosed herein correspond to stabilizing arrangements for a rotating vertical shaft, machines with a stabilizing arrangement and stabilizing methods. 
     In particular, the machines concerned are those commonly used in the field of “Oil &amp; Gas”, mainly subsea single phase or multi phase pumps or compressors; sea water injection is also a possible application of the present invention. 
     Rotating vertical shafts of machines, especially when shafts are long, are typically subject to radial movements (for example random vibrations) due to lateral asymmetrical actions. 
     In the field of “Oil &amp; Gas”, vertical shafts are used in turbomachines, such as subsea pumps and compressors, and are typically maintained in position by plain cylindrical or tilting-pad journal bearings. These machines tend to suffer from instability phenomena due to inherent lightly-loaded condition and the vertical orientation of their shafts inside the bearings. Such instability phenomena cause radial vibrations and may lead to damages to the rotor and even its failure. 
     From the article “Practical use of rotordynamic analysis to correct a vertical long shaft pump&#39;s whirl problem” by Mark A. Corbo and Robert A. Leishear in “Proceedings of the 19th International pump users symposium” pages 107-120, “tilting-pad bearings” with a geometric preload are used on a rotating long vertical shaft of a pump to solve the problem of high level of vibrations and “rotordynamic instability”. According to the known operation of “tilting-pad bearings”, one or more of the pads slightly rotate about a vertical axis and thus the rotating shaft remains substantially vertical. 
     Tilting-pad bearings do not really solve the problem of the instability phenomena due to lightly-loaded and vertical shafts. 
     Use of bearings eccentrically mounted about the vertical shaft is also known in order to generate a radial load to solve such instability problem. 
     SUMMARY 
     In the field of “Oil &amp; Gas”, there is a general need for improved solutions to the problem of stability of rotating vertical shafts, in particular the long ones; typically, such shafts suffer from instability due to lightly-loaded and vertical shafts. 
     An important idea is to apply at least a lateral loading or action to the rotating shaft of the machine. In particular, this is obtained through a pulling or pushing pressure acting on the rotating shaft. In particular, this is generated directly or indirectly by a fluid under pressure in the machine, in particular a working fluid of the machine. 
     Embodiments of the subject matter disclosed herein relate to a stabilizing arrangement for a rotating shaft. 
     Such arrangement comprises: a shaft being arranged substantially vertically in a machine so as to rotate during machine operation; first pressure delivery system for delivering a fluid pressure, in particular of a fluid circulating inside the machine, at a first location of the machine; said first location is close to the shaft and part of said first pressure delivery system is arranged at said first location so as to exert a lateral pulling or pushing action on the shaft. 
     Embodiments of the subject matter disclosed herein relate to a machine with a stabilizing arrangement for at least one of its rotating shafts. 
     Embodiments of the subject matter disclosed herein relate to a method for stabilizing a rotating shaft of a machine. 
     According to such method, the rotating shaft of the machine is arranged substantially vertically, and a lateral pulling or pushing action is applied to the rotating shaft at least at a first position close to the shaft. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate exemplary embodiments of the present invention and, together with the detailed description, explain these embodiments. In the drawings: 
         FIG. 1  shows a longitudinal cross-section of an embodiment of a machine comprising a stabilizing arrangement, 
         FIG. 2  shows perspective views of a detail of the embodiment of  FIG. 1 , specifically a sealing device, 
         FIG. 3  shows a front and a lateral view of the detail of  FIG. 2  in a working position, 
         FIG. 4  shows two cross-section views, according to lines A-A and B-B in  FIG. 3 , of the detail of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description of exemplary embodiments refers to the accompanying drawings. 
     The following description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
     One embodiment of a machine comprising the stabilizing arrangement will be described in the following with reference to  FIG. 1 ,  FIG. 2 ,  FIG. 3  and  FIG. 4   
     The showed machine, indicated as  10  in its whole, is a centrifugal pump, in particular a subsea pump for processing oil or natural gas or sea water. It comprises a stabilizing arrangement for a rotating shaft  12 , which comprises: a shaft  12 , which is arranged vertical inside the machine  10  so as to rotate during machine operation, first pressure delivery system for delivering a fluid pressure of a fluid circulating inside the machine  10  at a first location  1  of the machine  10 , the first location  1  being close to the shaft  12 , second pressure delivery system for delivering a fluid pressure of a fluid circulating inside the machine  10  at a second location  2  of the machine  10 , the second location  2  being close to the shaft  12 . 
     The shaft  12  is arranged inside a pump case  11  of the pump  10  by means of two journal bearings  13  located next to ends of the shaft  12 , the upper one being located between a coupling  14 , to be fastened to a motor unit, for rotating the shaft  12 , and a mechanical seal  15 . Down the seal  15 , a balancing chamber  16  and a balancing drum  17  follow along the shaft  12 , just up a pump body  18  in the pump case  11 . The pump case  11  is provided with a pump suction flange  19 , wherein a suction pressure is present during the pump operation, and a pump discharge flange  20 , where a discharge pressure is present during pump operation. Down to the pump body  18 , second mechanical seal  15  and second journal bearing  13  are provided at the shaft  12  lower end. 
     The first pressure delivery system comprises: a first line  21  (corresponding to a balancing line that may be considered a first bleeding means), which connects the suction flange  19  to the balancing chamber  16 , and which is connected to a first pressure conduit  22 , a first pressure delivery opening  23  provided at a final end of the first pressure conduit  22 , the opening  23  being located at the first location  1  close to the shaft  12 ; a first sealing device  30 , close to the shaft  12  at the first location  1 , surrounding the delivery opening  23  and arranged so as to convey a fluid first pressure to the shaft  12  through a first area  31  (see  FIG. 4 ) on which the first pressure is exerted. 
     The second pressure delivery system comprises: a first line  26  (that may be considered a second bleeding means), which connects the discharge flange  20  to a second pressure conduit  24 , a second pressure delivery opening  25  provided at a final end of the second pressure conduit  24 , the opening  24  being located at the second location  2  close to the shaft  12 ; a second sealing device  30 , close to the shaft  12  at the second location  2 , surrounding the delivery opening  25  and arranged so as to convey a fluid second pressure to the shaft  12  through a first area  32  on which the second pressure is exerted. 
     From the above, it is apparent that the first and the second pressure delivery systems comprise bleeding systems  21  and  26  of a working fluid of the machine  10 , the bleeding systems being in fluid connection to the pressure delivery openings  23 ,  25 . Between them, pressure conduits  22 ,  24  are realized out for example by simply drilling bodies  11  and  18  of the machine  10 . So the stabilizing arrangement comprising such bleeding systems is simple and cheap to be arranged and carried out. 
     The following is the operation of the above described stabilizing arrangement when the pump  10  is operated, for instance by means of a motor shaft which is coupled to the coupling  14 . 
     A first pressure of a fluid operated in the pump  10 , which is a suction pressure, is delivered via the above described first pressure delivery system working as bleeding means, which are the balancing line  21 , the derived first pressure conduit  22  and the first pressure delivery opening  23 , to the first area  31  facing to a lateral portion of the shaft  12  at the first location  1 . By defining the surface extension of the first area  31  surrounded by the sealing device  30 , is possible do precisely determine the lateral pulling load acting on the shaft  12  at the first location  1  in order to stabilize the same shaft  12 . 
     A second pressure of the fluid operated, which is a discharge pressure, is delivered via the above described second pressure delivery system working as bleeding means, which are the second pressure conduit  24  and the second pressure delivery opening  25 , to the second area  32  facing to a lateral portion of the shaft  12  at the second location  2 . By the means of defining the surface extension of the second area  32  surrounded by the sealing device  30 , is possible do precisely determine the lateral pushing load acting on the shaft  12  at the second location  2  in order to stabilize the same shaft  12 . 
     It follows that the stabilizing arrangement disclosed herein allows to determine the precise needed lateral loading at certain locations on the shaft, so granting to fully stabilize the same shaft. 
     In  FIG. 2 ,  FIG. 3  and  FIG. 4  the sealing device  30  is of a labyrinth type. It comprises a pad  30  with a lower concentric labyrinth type seal configured with an empty central portion  33  having e.g. the lower area  31  defined by means of an external lip of the labyrinth tread of the seal. This kind of sealing device allows a perfect adherence to the shaft  12  with an optimum sealing to the fluid pressure as conveyed through the central portion  33  to the area  31 . As said before, the possibility of varying surfaces extensions of the area  31  allows a perfect calibration of local loading to be exerted on the shaft  12 , so fully stabilizing the same. 
     In other embodiments, the sealing device may be of a honeycomb type or of a abradable type. 
     Moreover, first location  1  and second location  2  inside the machine  10  and close to the shaft  12  are remote from each other, in particular being substantially located next to opposite ends of the shaft  12 . This displacement allows a better and wide possibility of exerting an efficient lateral loading onto the shaft in order to fully stabilize it. Furthermore, through such arrangement of parts, it is easier and simpler to configure the pressure delivery system and concerned bleeding means (e.g. system or systems). 
     According to the above description, an embodiment of the subject matter disclosed herein relates to a method for stabilizing a rotating shaft  12  of a machine, the shaft being substantially arranged vertical. It provides a lateral loading which is applied to the rotating shaft  12  at least at a first position  1  close to the shaft  12 . 
     Moreover, lateral loading is applied to the rotating shaft  12  at a first position  1  and at a second position  2 , in particular said first position  1  and second position  2  being remote from each other. 
     The working fluid is bled from one or more points, the first and second pressure delivery openings  23 ,  25  being at different fluid pressures inside the machine  10 , more in detail at the pump suction and discharge or delivery pressure. 
     In another embodiment, each lateral loading of the shaft is due to one or more pulling or pushing pressures of a working fluid acting on the rotating shaft. 
     In one embodiment, the lateral loading may be generated by one or more working fluids under pressure, where the fluids may be delivered from working fluids inside or outside the machine. 
     Another embodiment of a stabilizing arrangement may comprise first and/or second pressure delivery system or systems which are fixed to or integrated in a journal bearing of the machine in order to fit the final configuration of the machine in a more practical way. 
     In another embodiment of a stabilizing arrangement, first and/or second pressure delivery system or systems are fixed to or integrated in a balancing drum of the machine in order to simplify the final configuration of the machine. 
     This written description uses examples to disclose the invention, including the preferred embodiments, 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.