Patent Publication Number: US-2018029048-A1

Title: Centrifugal separators for use in separating a mixed stream of at least two fluids

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/367,158, filed Jul. 27, 2016 for “DESIGN OF CENTRIFUGAL SEPARATOR”, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to centrifugal separation and, more specifically, to centrifugal separators having improved separation efficiency for mixtures containing at least two fluids over a wide range of concentrations. 
     Hydraulic fracturing, commonly known as fracing, is a technique used to release petroleum, natural gas, and other hydrocarbon-based substances for extraction from underground reservoir rock formations, especially for unconventional reservoirs. The technique includes drilling a wellbore into the rock formations, and pumping a treatment fluid into the wellbore, which causes fractures to form in the rock formations and allows for the release of trapped substances produced from these subterranean natural reservoirs. 
     At least some known treatment fluids are formed at least partially from water, and the water is sometimes released from the fractures and backflows into the wellbore such that a mixture of water and released hydrocarbon-based substances is formed. The water and hydrocarbon-based substances are then separated from each other such that the hydrocarbon-based substances can be recovered for subsequent refinement. However, at least some known separating devices, such as hydro-cyclones, have a high pressure drop and a narrow operating range. Moreover, separating devices that include blades or vanes may emulsify the mixture during separation, which reduces the separation efficiency of the device. 
     BRIEF DESCRIPTION 
     In one aspect, a centrifugal separator for use in separating a mixed stream of at least a first fluid and a second fluid is provided. The centrifugal separator includes a stator assembly including a housing defining a longitudinal axis of the centrifugal separator. The housing extends from a first end to a second end along the longitudinal axis, and the housing includes a first flow opening defined at the first end of the housing, a second flow opening defined at the second end of the housing, and a third flow opening defined at the second end of the housing. A rotor assembly is positioned within the housing. The rotor assembly includes a rotor shaft and a cylindrical drum coupled to the rotor shaft. The cylindrical drum includes a first open end and a second open end, and the cylindrical drum is configured to receive the mixed stream through at least one of the first open end and the second open end. The cylindrical drum further includes an interior including an outer radial portion and an inner radial portion. The outer radial portion is in flow communication with the first flow opening and the second flow opening, and the inner radial portion is in flow communication with the third flow opening. The cylindrical drum is rotatable within the housing such that the first fluid flows along the outer radial portion, and such that the second fluid flows along the inner radial portion. 
     In another aspect, a centrifugal separator for use in separating a mixed stream of at least a first fluid and a second fluid. The centrifugal separator includes a stator assembly including a housing defining a longitudinal axis of the centrifugal separator. The housing extends from a first end to a second end along the longitudinal axis, and the housing includes a first flow opening defined at the first end of the housing, a second flow opening defined at the first end of the housing, and a third flow opening defined at the second end of the housing. A rotor assembly is positioned within the housing, and the rotor assembly includes a cylindrical drum. The cylindrical drum includes a first open end configured to receive the mixed stream therethrough, a second open end, and an interior including an outer radial portion and an inner radial portion. The outer radial portion is in flow communication with the first flow opening and the third flow opening, and the inner radial portion is in flow communication with the second flow opening. The cylindrical drum is rotatable within the housing such that the first fluid flows along the outer radial portion, and such that the second fluid flows along the inner radial portion. The rotor assembly further includes a rotor shaft coupled to the cylindrical drum, wherein the rotor shaft includes a side wall defining an internal flow channel that provides flow communication between the inner radial portion of the interior and the second flow opening. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure 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 cross-sectional side view of an exemplary centrifugal separator in a first operating condition; 
         FIG. 2  is a cross-sectional side view of a first end of the centrifugal separator shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional side view of a second end of the centrifugal separator shown in  FIG. 1 ; 
         FIG. 4  is a cross-sectional side view of the centrifugal separator shown in  FIG. 1  in a second operating condition; 
         FIG. 5  is a cross-sectional side view of an alternative centrifugal separator; 
         FIG. 6  is a cross-sectional side view of a first end of the centrifugal separator shown in  FIG. 5 ; and 
         FIG. 7  is a cross-sectional side view of a second end of the centrifugal separator shown in  FIG. 5 . 
     
    
    
     Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of the disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of the disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
     DETAILED DESCRIPTION 
     In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. 
     The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged. Such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
     As used herein, the terms “axial” and “axially” refer to directions and orientations that extend substantially parallel to a longitudinal axis of the centrifugal separator. Moreover, the terms “radial” and “radially” refer to directions and orientations that extend substantially perpendicular to the longitudinal axis of the centrifugal separator. In addition, as used herein, the terms “circumferential” and “circumferentially” refer to directions and orientations that extend arcuately about the longitudinal axis of the centrifugal separator. 
     Embodiments of the present disclosure relate to centrifugal separators having improved separation efficiency for mixtures containing at least two fluids over a wide range of concentrations. More specifically, the centrifugal separators described herein include a rotor assembly including a cylindrical drum that receives a mixed stream of the at least two fluids, and that rotates to facilitate separating the mixed stream into its component parts. For example, the cylindrical drum induces rotational motion to the mixed stream as it rotates, and due to a centrifugal force induced by the rotational motion, a heavier first fluid (e.g., water) accumulates on an outer radial portion of the cylindrical drum and a lighter second fluid (e.g., oil) collects on an inner radial portion of the cylindrical drum. The centrifugal separators further include a stator assembly including a housing having flow openings positioned to discharge the separated fluid streams from the housing. 
     In general, the separation efficiency of the centrifugal separators is based on a distance that discharge outlets for the first fluid and the second fluid are positioned from a separation interface formed between the first fluid and the second fluid within the cylindrical drum. In one embodiment, such as when the centrifugal separator is used to separate a mixed stream that contains greater than about 70 percent water by volume and the remainder substantially oil, the discharge outlets are positioned at the same end of the housing while still achieving suitable separation efficiency. In a second embodiment, such as when the centrifugal separator is used to separate a mixed stream that contains greater than about 30 percent water by volume and the remainder substantially oil, the discharge outlets are positioned on opposing ends of the housing. As such, the centrifugal separators described herein facilitate separating mixtures in a space-saving and efficient manner. 
       FIGS. 1-3  are cross-sectional side views of an exemplary centrifugal separator  100 . Referring to  FIG. 1 , centrifugal separator  100  includes a stator assembly  102  and a rotor assembly  104 . Stator assembly  102  includes a housing  106  that defines a longitudinal axis  108  of centrifugal separator  100 . Housing  106  extends from a first end  110  to a second end  112  along longitudinal axis  108 . In addition, housing  106  includes a first flow opening  114  defined at first end  110  of housing  106 , a second flow opening  116  defined at second end  112  of housing  106 , and a third flow opening  118  defined at second end  112  of housing  106 . 
     In the exemplary embodiment, rotor assembly  104  includes a rotor shaft  120  and a cylindrical drum  122  coupled to rotor shaft  120 . When in use, rotor shaft  120  is coupled to a prime mover (not shown), which induces rotation of cylindrical drum  122 . Cylindrical drum  122  includes a first open end  124 , a second open end  126 , and an interior  128  including an outer radial portion  130  and an inner radial portion  132 . As will be explained in further detail below, outer radial portion  130  is in flow communication with first flow opening  114  and second flow opening  116 , and inner radial portion  132  is in flow communication with third flow opening  118 . 
     Referring to  FIG. 2 , rotor shaft  120  extends through first open end  124  of cylindrical drum  122  such that a first annular flow channel  134  is defined between rotor shaft  120  and cylindrical drum  122 . First annular flow channel  134  provides flow communication between outer radial portion  130  of interior  128  and first flow opening  114 . Rotor assembly  104  further includes a perforated coupling member  136  extending between rotor shaft  120  and cylindrical drum  122 . More specifically, in the exemplary embodiment, perforated coupling member  136  includes a plurality of vanes  138  extending radially between rotor shaft  120  and cylindrical drum  122 , and that are spaced from each other circumferentially about rotor shaft  120 . As such, perforated coupling member  136  allows fluid flow through first annular flow channel  134 . 
     As shown in  FIG. 2 , cylindrical drum  122  is spaced from housing  106  such that an annular cavity  140  is defined therebetween. In addition, cylindrical drum  122  is spaced from stator assembly  102  at both first open end  124  and second open end  126  such that fluid within housing  106  is allowed to flow into annular cavity  140 . Referring to  FIG. 2 , a first leakage flow path  142  is defined at first open end  124  of cylindrical drum  122  and, referring to  FIG. 3 , a second leakage flow path  144  is defined at second open end  126  of cylindrical drum  122 . As such, the fluid channeled into annular cavity  140  through either first leakage flow path  142  or second leakage flow path  144  provides lubrication between cylindrical drum  122  and housing  106 . 
     Moreover, cylindrical drum  122  includes an outer surface  146  having at least one balancing member  148  extending therefrom. The at least one balancing member  148  is selectively abradable from cylindrical drum  122  to modify a center of mass of cylindrical drum  122 . More specifically, balancing member  148  provides excess material that is removable from cylindrical drum  122  in the event an imbalance in cylindrical drum  122  is determined during rotation thereof. As such, the center of mass of cylindrical drum  122  is modifiable without affecting its structural integrity. 
     As noted above, rotor assembly  104  rotates relative to stator assembly  102  when centrifugal separator  100  is in operation. As such, centrifugal separator  100  includes a first bearing  150  coupled between stator assembly  102  and rotor assembly  104  and, more specifically, coupled between stator assembly  102  and rotor shaft  120 . First bearing  150  is any bearing that enables centrifugal separator  100  to function as described herein. In one embodiment, first bearing  150  is a hydrodynamic thrust bearing, or a ground face seal bearing, fabricated at least partially from tungsten carbide material. 
     Referring to  FIG. 3 , stator assembly  102  further includes an intake nozzle  152  that extends through second open end  126  of cylindrical drum  122 . Intake nozzle  152  includes a first flow channel  154  extending therethrough for providing flow communication between inner radial portion  132  of interior  128  and third flow opening  118 . In addition, intake nozzle  152  is spaced from housing  106  and cylindrical drum  122  such that a second annular flow channel  156  is defined between intake nozzle  152  and cylindrical drum  122 . Second annular flow channel  156  provides flow communication between outer radial portion of interior  128  and second flow opening  116 . As will be explained in further detail below, intake nozzle  152  is sized radially to facilitate intersecting an oil/water interface formed within interior  128  when centrifugal separator  100  is in operation. 
     In the exemplary embodiment, second flow opening  116  is oriented radially within housing  106  relative to longitudinal axis  108  (shown in  FIG. 1 ). In one embodiment, stator assembly  102  further includes a ring member  158  extending circumferentially about housing  106  and defining an annular plenum  160  therebetween. Ring member  158  is positioned relative to housing  106  such that annular plenum  160  and second flow opening  116  are in flow communication. As such, fluid discharged from second flow opening  116  is collected in annular plenum  160  and discharged from centrifugal separator  100  in a continuous and efficient manner. Alternatively, when fluid is channeled into housing  106  through second flow opening  116 , annular plenum  160  facilitates channeling the fluid into housing  106  in a continuous and efficient manner. 
     As noted above, rotor assembly  104  rotates relative to stator assembly  102  when centrifugal separator  100  is in operation. As such, centrifugal separator  100  includes a second bearing  162  coupled between stator assembly  102  and rotor assembly  104  and, more specifically, coupled between stator assembly  102  and intake nozzle  152 . Second bearing  162  is any bearing that enables centrifugal separator  100  to function as described herein. In one embodiment, second bearing  162  is a hydrodynamic thrust bearing, or a ground face seal bearing, fabricated at least partially from tungsten carbide material. 
     Referring again to  FIG. 1 , centrifugal separator  100  is shown in a first operating condition. In the exemplary embodiment, first flow opening  114  is defined as a flow inlet, and second flow opening  116  and third flow opening  118  are both defined as flow outlets. In operation, a mixed stream  164  of at least a first fluid and a second fluid is channeled through first flow opening  114  and into cylindrical drum  122  through first annular flow channel  134  (shown in  FIG. 2 ). In the exemplary embodiment, the first fluid has a greater unit weight than the second fluid. For example, in one embodiment, the first fluid is water and the second fluid is a hydrocarbon-based substance such as oil. 
     Cylindrical drum  122  is rotatable within housing  106  and induces a shearing force to mixed stream  164  received therein. More specifically, cylindrical drum  122  is rotatable within housing  106  such that the first fluid flows along outer radial portion  130  of interior  128 , and such that the second fluid flows along inner radial portion  132  of interior  128 . For example, mixed stream  164  is progressively separated into its component parts as mixed stream  164  is channeled from first end  110  towards second end  112 . As noted above, intake nozzle  152  (shown in  FIG. 3 ) is sized to facilitate intersecting an interface between the first fluid and the second fluid formed within interior  128  when centrifugal separator  100  is in operation. As such, a first stream  166  formed substantially from the first fluid is channeled through second annular flow channel  156  (shown in  FIG. 3 ) and discharged from second flow opening  116 , and a second stream  168  formed substantially from the second fluid is channeled through first flow channel  154  (shown in  FIG. 3 ) and discharged from third flow opening  118 . 
     In the first operating condition, centrifugal separator  100  facilitates separating mixed stream  164  that contains greater than about 70 percent water by volume, for example. 
       FIG. 4  is a cross-sectional side view of centrifugal separator  100  in a second operating condition. In the exemplary embodiment, first flow opening  114  is defined as a flow outlet, second flow opening  116  is defined as a flow inlet, and third flow opening  118  is defined as a flow outlet. In operation, mixed stream  164  is channeled through second flow opening  116  and into cylindrical drum  122  through second annular flow channel  156  (shown in  FIG. 3 ). Cylindrical drum  122  is rotatable within housing  106  such that the first fluid flows along outer radial portion  130  of interior  128 , and such that the second fluid flows along inner radial portion  132  of interior  128 . For example, mixed stream  164  is progressively separated into its component parts as mixed stream  164  is channeled from second end  112  towards first end  110 . 
     In the exemplary embodiment, rotor shaft  120  is a solid member that restricts the passage of fluid therethrough. As such, first stream  166  is channeled through first annular flow channel  134  (shown in  FIG. 2 ) and discharged from first flow opening  114 . Moreover, the centrifugal force created by the rotation of cylindrical drum  122  facilitates forming a high-pressure zone at outer radial portion  130  and a low-pressure zone at inner radial portion  132  proximate intake nozzle  152 . In one embodiment, the second fluid accumulates within the low-pressure zone, and a negative pressure is induced at third flow opening  118  that facilitates drawing the second fluid therethrough. As such, first stream  166  formed substantially from the first fluid is discharged from first flow opening  114 , and second stream  168  formed substantially from the second fluid is discharged from third flow opening  118 . 
     In the second operating condition, centrifugal separator  100  facilitates separating mixed stream  164  that contains greater than about 30 percent water by volume, for example. 
       FIGS. 5-7  are cross-sectional side views of an alternative centrifugal separator  170 . Referring to  FIG. 5 , housing  106  includes a first flow opening  172  defined at first end  110  of housing  106 , a second flow opening  174  defined at first end  110  of housing  106 , and a third flow opening  176  defined at second end  112  of housing  106 . 
     Referring to  FIG. 6 , rotor assembly  104  includes a rotor shaft  178  coupled to cylindrical drum  122 . Rotor shaft  178  includes a side wall  180  defining an internal flow channel  182  that provides flow communication between inner radial portion  132  of interior  128  and second flow opening  174 . In addition, rotor shaft  178  extends through first open end  124  such that first annular flow channel  134  is defined between rotor shaft  178  and cylindrical drum  122 . In one embodiment, rotor assembly  104  further includes an intake nozzle  184  coupled to rotor shaft  178 . Intake nozzle  184  extends a distance from rotor shaft  178  and is positioned within interior  128  of cylindrical drum  122 . Intake nozzle  184  facilitates collecting the second fluid that flows along inner radial portion  132 , as will be explained in further detail below. 
     In the exemplary embodiment, side wall  180  of rotor shaft  178  has a radial opening  186  defined therein. In one embodiment, radial opening  186  is in selective flow communication with second flow opening  174  as rotor shaft  178  rotates. More specifically, second flow opening  174  is at a fixed position relative to rotor assembly  104 , and radial opening  186  aligns with second flow opening  174  at a certain point in the rotation of rotor shaft  178 . Alternatively, stator assembly  102  further includes a ring member  188  extending circumferentially about rotor shaft  178  such that an annular plenum  190  is defined therebetween. Ring member  188  is positioned such that annular plenum  190  and radial opening  186  are in flow communication. Stator assembly  102  also includes a flow tube  192  extending between ring member  188  and second flow opening  174  such that flow communication is provided therebetween. As such, the second fluid may be continuously discharged from radial opening  186  and extracted through second flow opening  174 . 
     Referring to  FIG. 7 , stator assembly  102  further includes a plug member  194  extending through second open end  126  of cylindrical drum  122 . Plug member  194  is a solid member that restricts the passage of fluid therethrough. Plug member  194  is also oriented such that second annular flow channel  156  is defined between plug member  194  and cylindrical drum  122 . 
     Referring again to  FIG. 5 , first flow opening  172  is defined as a flow inlet, and second flow opening  174  and third flow opening  176  are both defined as flow outlets. In operation, mixed stream  164  is channeled through first flow opening  172  and into cylindrical drum  122  through first annular flow channel  134 . Cylindrical drum  122  is rotatable within housing  106  such that the first fluid flows along outer radial portion  130  of interior  128 , and such that the second fluid flows along inner radial portion  132  of interior  128 . For example, mixed stream  164  is progressively separated into its component parts as mixed stream  164  is channeled from first end  110  towards second end  112 . 
     As noted above, plug member  194  is a solid member that restricts the passage of fluid therethrough. As such, first stream  166  is channeled through second annular flow channel  156  (shown in  FIG. 7 ) and discharged from third flow opening  176 . Moreover, the centrifugal force created by the rotation of cylindrical drum  122  facilitates forming a high-pressure zone at outer radial portion  130  and a low-pressure zone at inner radial portion  132  proximate rotor shaft  178 . In one embodiment, the second fluid accumulates within the low-pressure zone, and a negative pressure is induced at second flow opening  174  that facilitates drawing the second fluid therethrough. As such, first stream  166  formed substantially from the first fluid is discharged from third flow opening  176 , and second stream  168  formed substantially from the second fluid is discharged from second flow opening  174 . 
     An exemplary technical effect of the devices and methods described herein includes at least one of: (a) separating a mixture including at least two fluids having different densities; (b) providing devices that are capable of separating a mixture containing at least two fluids over a wide range of concentrations; and (c) providing an enhanced separation efficiency of the mixture. 
     Exemplary embodiments of centrifugal separators and related components are described above in detail. The devices are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the configuration of components described herein may also be used in combination with other processes, and is not limited to practice with only separating a mixture of fluids received from an oil and gas well and related methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many applications where separating a mixture containing fluids having different densities is desired. 
     Although specific features of various embodiments of the present disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of embodiments of the present disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to disclose the embodiments of the present disclosure, including the best mode, and also to enable any person skilled in the art to practice embodiments of the present disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the embodiments described herein 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.