Abstract:
A centrifuge of the type having an outer bowl and an inner rotor both of which are generally cylindrical and rotate in the same direction but at slightly different rates separates slurry fed into the interior of the rotor into solids and liquid. An auger flight on the outside surface of the rotor carries the solids along the annular channel between the outside of the rotor and the inside of the bowl. The slurry is fed into a chamber at one end of the rotor and through outlet holes in the sides of the rotor into the channel. An end plate of the chamber has a forwardly projecting domed central nose which extends into the flowing slurry. Transverse guide plates of the rotor act to engage the slurry and accelerate it into rotation with the rotor before escaping through the holes. The guide plates are shaped with curved angularly projecting ribs on the downstream side in front of the hole over which the slurry flows in a smooth path before exiting the hole.

Description:
[0001]     This invention relates to a centrifuge.  
       BACKGROUND OF THE INVENTION  
       [0002]     Centrifuges have many different types and the present invention is concerned with the two phase centrifuge type which provides high speed horizontal decanting that separate solids from liquids. Centrifuges of this type have been manufactured by United Oilfield Inc., who are assignees of the present application for a number of years and each includes three primary parts which are the base or skid, the stainless steel case mounted on the skid and the rotating assembly consisting of the bowl, auger and gearbox which assembly is mounted in the stationary steel case on the skid. The auger is mounted in the bowl so that the bowl surrounds the auger and both are mounted for coaxial rotation about a longitudinal axis. The auger comprises generally a cylindrical body coaxial to the cylindrical bowl with an auger flight on its outer surface which has an edge close to the inside surface of the cylindrical bowl.  
         [0003]     To create the desired effect, the bowl with the auger inside rotates about the axis at slightly different speeds in the same direction. The bowl speed is variable depending upon the application and operating conditions.  
         [0004]     During operation, feed slurry is fed from an axially extending stationary feed pipe at one end of the auger into a feed chamber at that end of the auger through an end wall of the bowl. The flowing slurry strikes an accelerator plate in the auger at one end of the feed chamber and is forced from the feed chamber outwardly into the bowl.  
         [0005]     Centrifugal force causes heavier solids to accumulate on the inside surface of the bowl. The auger, which is rotating with the bowl but at a slow speed relative to the bowl, acts to continuously drag them axially along the bowl. Each of the bowl and the auger includes a tapered end portion at the feed end which converges radially inwardly toward a discharge end of the bowl, which is at the same end as the feed end. The rotation of the bowl and its tapered end tends to move the heavier material axially away from the discharge end to the cylindrical section of greater diameter. Thus the auger drags the material along the tapered section toward the discharge end. The discharge end includes discharge ports surrounding the feed duct so that the heavier solid material when it reaches the discharge end is discharged outwardly by the centrifugal force into the case for collection.  
         [0006]     Finer solids are retained in the liquid traveling through the bowl away from the feed end to the remote end but are deposited on the wall of the bowl and are continuously removed as they build-up inside the bowl by the action of the auger and out the solids discharge ports.  
         [0007]     Clean fluids travel towards the remote fluid end of the bowl and exit through adjustable eccentric ports at the remote fluid discharge end of the bowl. The centrifuge is commonly but not exclusively used for mud systems in drilling where the mud is re-circulated through the drill string to extract drilling solids so that the solids can be extracted in the centrifuge and the clean fluid from the centrifuge can be recycled back into the mud system of the operation.  
         [0008]     The greatest difficulty in achieving optimal performance in a centrifuge of this type is wear caused by the combined corrosive nature of flow pressure and the abrasive solids on the steel structure of the centrifuge.  
       SUMMARY OF THE INVENTION  
       [0009]     It is one object of the invention to provide an improved centrifuge of this general type.  
         [0010]     According to one aspect of the invention there is provided a centrifuge for separation of particulates from a slurry containing the particulates in a liquid comprising:  
         [0011]     an outer bowl having a longitudinal axis and a peripheral wall surrounding the axis, the peripheral wall extending from a first end of the bowl to a second opposed end of the bowl;  
         [0012]     a first discharge arrangement at the first end of the bowl for discharge of the particulates;  
         [0013]     a second discharge arrangement at the second end of the bowl for discharge of the slurry with the particulates removed;  
         [0014]     a support assembly mounting the outer bowl for rotation about the longitudinal axis such that the particulates in the slurry within the bowl tend to move radially outwardly of the axis toward an inner surface of the peripheral wall;  
         [0015]     an inner rotor mounted coaxially within the outer bowl for rotation of an outer wall of the inner rotor about the longitudinal axis, the rotor extending along the bowl from a first end of the rotor adjacent the first end of the bowl to a second end of the rotor adjacent the second end of the bowl;  
         [0016]     a drive system for driving rotation of the outer bowl and the inner rotor for common rotation in the same direction;  
         [0017]     the drive system providing a differential in rotational speed between the outer wall of the inner rotor and the inner surface of the peripheral wall of the outer bowl such that the outer wall moves angularly relative to the inner surface of the peripheral wall;  
         [0018]     the outer wall of the rotor being spaced radially inwardly of the inner surface of the bowl so as to define a space therebetween within which the slurry is separated;  
         [0019]     a helical auger flight carried on the outer wall of the rotor having an outer edge of the auger flight which moves relative to the inner surface of the peripheral wall so as to tend to carry particulates collecting on the inner surface of the peripheral wall in a direction toward the first end of the bowl and the first discharge arrangement located at the first end;  
         [0020]     the helical auger flight having openings therein allowing movement of the slurry in the space through the openings toward the second end of the bowl;  
         [0021]     the bowl and the inner rotor each including a tapered portion such that the outer wall of the rotor and the inner surface of the bowl reduce in diameter toward the first end;  
         [0022]     the rotor having a slurry inlet opening at the first end of the rotor into a feed chamber within the rotor;  
         [0023]     a slurry inlet duct for transporting the slurry through the first end of the bowl into the inlet opening in the first end of the rotor;  
         [0024]     the rotor having at least one outlet opening in the outer wall to allow the slurry to exit through the outer wall from the feed chamber into the space;  
         [0025]     the rotor having an end accelerator plate of the feed chamber mounted on the rotor for rotation therewith;  
         [0026]     the end accelerator plate lying generally in a radial plane of the axis such that the slurry flowing generally axially into the feed chamber contacts the accelerator plate of the rotor and moves radially outwardly therefrom through the at least one outlet opening into the space;  
         [0027]     wherein the end accelerator plate includes a raised projecting member thereon extending radially therefrom toward the slurry inlet opening.  
         [0028]     Preferably the raised projecting member is dome shaped.  
         [0029]     Preferably the raised projecting member is symmetrical about the axis and converges to an apex on the axis.  
         [0030]     Preferably the raised projecting member extends to an outer edge thereof spaced inwardly of an edge of the end accelerator plate.  
         [0031]     Preferably the at least one outlet opening is located in the tapered portion.  
         [0032]     Preferably the rotor wall has a plurality of angularly spaced outlet openings each communicating with the feed chamber.  
         [0033]     Preferably the rotor wall has a plurality of angularly spaced outlet openings each communicating with the feed chamber;  
         [0034]     each outlet opening thus having a leading edge and a trailing edge when considered relative to the direction of rotation of the rotor;  
         [0035]     there is provided within the feed chamber a plurality of discharge surfaces, each discharge surface extending between the trailing edge of a respective one of the outlet openings and a leading edge of the next outlet opening so as to bridge a space therebetween;  
         [0036]     each discharge surface being shaped, relative to an imaginary plane joining the trailing edge of a respective one of the outlet openings and a leading edge of the next outlet opening, such that a portion of the discharge surface adjacent the leading edge of said next outlet defines a series of imaginary lines extending along the portion generally parallel to the axis and lying in the discharge surface, which imaginary lines are angularly retarded relative to corresponding imaginary lines lying in the imaginary plane, where each line and its corresponding line in the plane are equidistantly spaced from the axis.  
         [0037]     Preferably the portion of the discharge surface is smoothly curved in cross-section taken in a radial plane of the axis.  
         [0038]     Preferably the portion of the discharge surface has an apex which is at a maximum spacing from the imaginary plane where the apex is spaced from the leading edge and the surface tapers back toward the imaginary plane as it approaches the leading edge.  
         [0039]     Preferably the portion of the discharge surface where the surface is retarded has a width in the direction between the leading edge and the trailing edge which extends about half way across the imaginary plane.  
         [0040]     Preferably each discharge surface is shaped, relative to the imaginary plane, such that a portion of the discharge surface adjacent the trailing edge of said one of the outlets lies generally in the imaginary plane.  
         [0041]     According to a second aspect of the invention there is provided a centrifuge for separation of particulates from a slurry containing the particulates in a liquid comprising:  
         [0042]     an outer bowl having a longitudinal axis and a peripheral wall surrounding the axis, the peripheral wall extending from a first end of the bowl to a second opposed end of the bowl;  
         [0043]     a first discharge arrangement at the first end of the bowl for discharge of the particulates;  
         [0044]     a second discharge arrangement at the second end of the bowl for discharge of the slurry with the particulates removed;  
         [0045]     a support assembly mounting the outer bowl for rotation about the longitudinal axis such that the particulates in the slurry within the bowl tend to move radially outwardly of the axis toward an inner surface of the peripheral wall;  
         [0046]     an inner rotor mounted coaxially within the outer bowl for rotation of an outer wall of the inner rotor about the longitudinal axis, the rotor extending along the bowl from a first end of the rotor adjacent the first end of the bowl to a second end of the rotor adjacent the second end of the bowl;  
         [0047]     a drive system for driving rotation of the outer bowl and the inner rotor for common rotation in the same direction;  
         [0048]     the drive system providing a differential in rotational speed between the outer wall of the inner rotor and the inner surface of the peripheral wall of the outer bowl such that the outer wall moves angularly relative to the inner surface of the peripheral wall;  
         [0049]     the outer wall of the rotor being spaced radially inwardly of the inner surface of the bowl so as to define a space therebetween within which the slurry is separated;  
         [0050]     a helical auger flight carried on the outer wall of the rotor having an outer edge of the auger flight which moves relative to the inner surface of the peripheral wall so as to tend to carry particulates collecting on the inner surface of the peripheral wall in a direction toward the first end of the bowl and the first discharge arrangement located at the first end;  
         [0051]     the helical auger flight having openings therein allowing movement of the slurry in the space through the openings toward the second end of the bowl;  
         [0052]     the bowl and the inner rotor each including a tapered portion such that the outer wall of the rotor and the inner surface of the bowl reduce in diameter toward the first end;  
         [0053]     the rotor having a slurry inlet opening at the first end of the rotor into a feed chamber within the rotor;  
         [0054]     a slurry inlet duct for transporting the slurry through the first end of the bowl into the inlet opening in the first end of the rotor;  
         [0055]     the rotor having a plurality of angularly spaced outlet openings each communicating with the feed chamber to allow the slurry to exit through the outer wall from the feed chamber into the space;  
         [0056]     the rotor having an end accelerator plate of the feed chamber mounted on the rotor for rotation therewith;  
         [0057]     the end accelerator plate lying generally in a radial plane of the axis such that the slurry flowing generally axially into the feed chamber contacts the accelerator plate of the rotor and moves radially outwardly therefrom through the at least one outlet opening into the space;  
         [0058]     each outlet opening having a leading edge and a trailing edge when considered relative to the direction of rotation of the rotor;  
         [0059]     wherein there is provided within the feed chamber a plurality of discharge surfaces, each discharge surface extending between the trailing edge of a respective one of the outlet openings and a leading edge of the next outlet opening so as to bridge a space therebetween;  
         [0060]     each discharge surface being shaped, relative to an imaginary plane joining the trailing edge of a respective one of the outlet openings and a leading edge of the next outlet opening, such that a portion of the discharge surface adjacent the leading edge of said next outlet defines a series of imaginary lines extending along the portion generally parallel to the axis and lying in the discharge surface, which imaginary lines are angularly retarded relative to corresponding imaginary lines lying in the imaginary plane, where each line and its corresponding line in the plane are equidistantly spaced from the axis.  
         [0061]     Preferably the portion of the discharge surface is smoothly curved in cross-section taken in a radial plane of the axis.  
         [0062]     Preferably the portion of the discharge surface has an apex which is at a maximum spacing from the imaginary plane where the apex is spaced from the leading edge and the surface tapers back toward the imaginary plane as it approaches the leading edge.  
         [0063]     Preferably the portion of the discharge surface where the surface is retarded has a width in the direction between the leading edge and the trailing edge which extends about half way across the imaginary plane.  
         [0064]     Preferably each discharge surface is shaped, relative to the imaginary plane, such that a portion of the discharge surface adjacent the trailing edge of said one of the outlets lies generally in the imaginary plane. This forms a sharp edge at the junction with the wall of the rotor which can better engage the slurry within the rotor.  
         [0065]     Thus the accelerator plate is dominated by a “striker nose” that protrudes into the feed chamber. This adaptation can operate to eliminate splash-back, positions the flow, increases optimal performance of the auger, and minimizes wear by forcing the solids to wear onto other solids and avoid wearing on steel.  
         [0066]     In addition, the slurry passes over the base of the feed chamber which has been re-designed with a curved surface to facilitate easier movement of solids and to make the area more resistant to wear. This area has been accentuated to easier facilitate flow. By building up the height of the discharge edge or trailing of the feed chamber and giving it a slope, a path of least resistance is achieved.  
         [0067]     After passing through the feed chamber, the slurry strikes an accelerator plate and is forced into the bowl. The accelerator plate has been designed to more readily force the materials into the bowl for separation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0068]     One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:  
         [0069]      FIG. 1  is a partly schematic exploded view of a centrifuge according to the present invention.  
         [0070]      FIG. 2  is a partly schematic longitudinal cross sectional view of the centrifuge of  FIG. 1 .  
         [0071]      FIG. 3  is a cross sectional view along the lines  3 - 3  of  FIG. 2 .  
         [0072]      FIG. 4  is a cross sectional view along the lines  4 - 4  of  FIG. 3 . 
     
    
       [0073]     In the drawings like characters of reference indicate corresponding parts in the different figures.  
       DETAILED DESCRIPTION  
       [0074]     In  FIG. 1  is shown schematically a centrifuge of the type with which the present invention is concerned. Centrifuges of this type have been manufactured for a number of years by the present assignee and details of the general construction of this centrifuge is well known to one skilled in the art.  
         [0075]     The centrifuge generally comprises a base skid  10  on which is mounted on a fixed housing  11 . The housing can be opened to access the interior of the housing and the elements therein. At one end of the housing is provided a motor and gear box arrangement schematically indicated at  12  which provides drive to the components inside the housing  11 . At the other end of the housing is provided a feed duct  13  for supply of slurry from a source  14  through a duct  15 .  
         [0076]     Within the fixed housing  11  is provided an outer bowl  16  having a peripheral wall  17  with an inside surface  18 . The bowl is mounted for rotation about a longitudinal axis  19  so that the inside surface of the peripheral wall rotates around the axis providing a centrifugal force against the inside surface. The bowl is elongate along the axis  19  so as to provide a first end  20  and a second end  21 . The first end  20  is generally a feed end so that the slurry from the source  14  is fed in through the duct  13  which passes through an opening  22  in the end  20  for entry into the interior of the bowl. The second end  21  is a discharge end for the slurry and includes holes  24  through which the slurry can pass after separation of liquid from heavier particles so that the particles are generally collected within the bowl allowing the liquid component to escape through the holes  24  for collection within the housing  11 .  
         [0077]     Inside the outer bowl  16  is provided a rotor  25  which is shaped to follow generally the inside surface  18  of the bowl so that the rotor also has a first end  26  adjacent the end  22  of that bowl and a second end  27  adjacent the end  21  of the bowl. The rotor also has an outer wall  28  which follows the general shape of the inside surface  18  but is spaced radially inwardly therefrom so as to define an annular space  30  along the length of the rotor and along the length of the bowl. The space  30  defines a duct through which the slurry can pass while the centrifugal action separates the particles onto the inside surface of the bowl while the liquid component tends to move along the bowl toward the discharge end  21 .  
         [0078]     The motor and gear box  12  acts to drive the bowl through a first coupling  12 A and acts to drive the rotor through a second coupling  12 B. These are shown co-axial but this is merely schematic and suitable gear box arrangements are well known to one skilled in the art to provide this driving arrangement.  
         [0079]     In particular the motor and drive arrangement  12  acts to drive the bowl and the rotor in a common rotation direction while providing a relatively small differential between the angular velocity of the bowl and the angular velocity of the rotor. This relatively small differential causes the outside surface of the wall  28  to move relatively slowly in comparison with the common angular velocity, relative to the inside surface  18  of the peripheral wall of the bowl.  
         [0080]     The wall  17  of the bowl has a cylindrical portion  17 A extending from the end  21  to a position  17 B, from which the wall  17  tapers radially inwardly toward the end  20 . This forms a conical section  17 C which is tapered radially inwardly. It will be appreciated therefore that the rotation of the bowl provides a force on materials on the portions  17 C of the wall of the bowl tending to cause those materials to move axially toward the end  21  and away from the end  20 .  
         [0081]     The wall  28  of the rotor also includes a cylindrical portion  28 A extending to a position  28 B and includes a tapered portion  28 C matching the taper  17 C of the bowl.  
         [0082]     On the outside surface of the wall  28  is provided an auger flight  32  which is wrapped helically around the outer surface of the wall  28  from the end  21  through to the end  20  including along the tapered section  28 C. The flight is helically arranged at an angle such that the differential in angular rotation of the wall  28  relative to the bowl causes the auger flight to sweep material collecting on the inside surface  18  of the wall  16  along the wall  16  to the discharge end  20  where it can be discharged from the bowl as collected solids. It will be appreciated that the heavy solids collect on the inside surface  18  substantially immediately after the discharge into the space  30 . Lighter solids flow along the space  30  through openings  33  in the flight  32  toward the discharge end  24  but continue to accumulate on the inside surface due to the centrifugal action on the particles. Such particles whenever they collect on the inside surface are then carried by the outside edge or ribbon of the flight along the wall to the end  20  of the bowl where they are discharged into the housing for collection in a suitable launder (not shown).  
         [0083]     The duct  13  extends into the open end of the rotor at the end  26 . Thus the slurry enters into the hollow interior of the rotor and flows along the interior up to a closure plate  35  which bridges across the interior of the rotor and halts the further forward flow of the slurry. Two radially opposed holes  36 A and  36 B are provided in the outside wall of the rotor in the tapered section  28 C for discharge of the slurry radially outwardly into the space  30 .  
         [0084]     Centrifuges of the above type are previously manufactured by the present assignee and the centrifuge of this type is modified in the area of the feed chamber  37  within the hollow interior between the end  26  and the acceleration plate  35 . The feed chamber  37 , the holes  36 A and  36 B and the acceleration plate  35  are shown on an enlarged scale and in more detail in  FIGS. 3 and 4  which show the improvements of the present invention. Thus in  FIG. 3  the wall  28 C is shown which has two opposed discharge holes  36 A and  36 B which are diametrically opposed relative to a center  19 A on the axis  19 . The hole  36 A has a leading edge  38 A and a trailing edge  38 B relative to a direction of rotation R around the axis  19 . The opening  36 B has a leading edge  39 A and a trailing edge  39 B again relative to the direction of rotation. The holes  36 A and  36 B are generally rectangular so that the leading and trailing edges are generally parallel and extend along the tapered section  28 C. While the holes  36 A and  36 B are shown rectangular, they may indeed be tapered in view of the taper in the wall  28 C so that the leading and trailing edges are not exactly parallel but converge together toward the end  26 . An imaginary plane is indicated at P 1  which interconnects the leading edge  38 A with the trailing edge  39 B. Symmetrically a plane P 2  which again is imaginary interconnects the leading edge  39 A with the trailing edge  38 B. These planes are defined merely for convenience of explanation of the shape and construction of a surface  40  which extends from the leading edge  38 A through to the trailing edge  39 B. A symmetrical surface  41  extends from the leading edge  39 A to the trailing edge  38 B. These surfaces engage the material within the feed chamber  37 . It will be appreciated that the surfaces  40  and  41  are rotating with the rotor at relatively high velocity while the slurry entering through the duct  13  is moving only in the axial direction. Thus the surfaces  40  and  41  together with the acceleration plate  35  act to engage the fluid within the feed chamber  37  so as to accelerate the fluid in its rotation around the axis  19  thus causing the fluid to move outwardly through the discharge holes  36 A and  36 B.  
         [0085]     The plate  35  is generally flat and circular in plan so as to fill the interior of the rotor and define the end face of the feed chamber. The acceleration plate  35  is modified by the addition of a nose  42  which extends forwardly from the plate to an apex  43  spaced forwardly of the plate toward the end  26 . The nose  42  is mounted on the axis  19  so as to be symmetrical about the axis. The nose has a circular edge  44  at the plate surrounding the axis  19 . The nose is dome shaped so that it converges smoothly to the apex  43  with curved walls. The nose forms a wear member which projects into the flow of the fluid from the mouth  13 A of the duct  13  so that the fluid tends to engage the nose at the apex and to spread around the surface  45  of the nose onto the plate  35  and its front surface  35 A facing the fluid. The plate  35  is located at a downstream end  46  of each of the holes  36  with the holes extending with the parallel upper and lower edges to an upstream end  47  just beyond the mouth of the duct  13 . Thus the material flowing onto the accelerator plate  35  and its nose  42  is halted at that location thus causing the material to flow outwardly through the holes  36 A and  36 B. As the material begins to flow outwardly, it is engaged by the surfaces  40  and  41  as best shown in  FIG. 3 . The surfaces are symmetrical so that only one of the surfaces will be described. Thus the surface  40  includes an end  40 A commencing at the trailing edge  39 B and from that end  40 A it is flat extending to approximately a mid-point  40 C. From that mid point it is curved rearwardly toward a rearward most point  40 B. From that point  40 B, the surface  40  curves forwardly to a point  40 D after which it reaches the plane P 1 . Thus it will be noted that each of a series of lines  40 D,  40 E,  40 F are angularly retarded relative to points P 3 , P 4 , P 5  lying in the plane P 2 . It will be appreciated that all of these points or lines are purely imaginary and are used merely for explanation of the shape of the surface. Thus the point P 3  lies at a common radial distance from the center  19 A with the point  40 D with each of the further points corresponding in radial distance. It will be noted that in the whole of the area between the edge  40 A and the point  40 C, the lines in the surface are angularly retarded relative to corresponding lines within the plane P 1 . From the point  40 C to the end  40 A, the surface  40  is flat indicated at  40 G. This provides on the surface  40  a rib  40 H which is raised relative to the imaginary plane P 1 .  
         [0086]     This shape is formed by providing a part cylindrical wall  50  with one edge  51  at the edge  40 K and a second edge  52  attached to the wall  28 C at a position behind the section  41 G. Between the surface  40 G and the point  52 , the surface  41  is made up from a filler material indicated at  53 . The filler material can be weld or other materials which are resistant to the highly abrasive action of the particles within the fluid in the chamber  37 .  
         [0087]     The shaping of the surface  40  such that it is domed in an retarded direction at the trailing end  40 K assists in sweeping the material out of the opening  36 B so that it flows more smoothly over the surface and out of the opening. In addition the curvature of the surface and the smooth flowing action of the materials over the surface reduces the wear on the surface  40 . As set forth above, the surface  41  is exactly symmetrical so that it cooperates with the surface  40  as just described.  
         [0088]     Thus the portion  40 G of the surface  40  is a leading portion and rotates into the stationary or only slowly rotating slurry and acts to engage this slurry and accelerate the slurry. The slurry then moves over the surface  40  toward its end  40 K at the opening  36 B. The first part of the surface in advance of the mid point  40 C is flat and thus the slurry slides imply across this surface portion. However the second part of the surface  40  between the mid point  40 C and the end  40 K is domed as the slurry begins to accelerate and move rapidly across this portion of the surface. This domed shape which is retarded relative to the plane P 1  surprisingly allows smoother flow of the slurry with less wear on the surface caused by the highly abrasive slurry. At the end  40 K the surface curves forwardly toward the plane P 1  so that at the edge  38 A of the opening  36 B the slurry can simply slide off the surface  40  through the leading edge  38 A of the opening  36 B. It will be noted that the junction of the end  40 A of the surface  40  with the wall  28 C at the trailing edge  39 B of the opening  36 A provides a sharpened edge or nose  60  which can bite into the slurry and cause it to move away from this edge toward the end  40 K of the surface  40 .  
         [0089]     Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.