Horizontal scroll screen centrifuge

Information

  • Patent Grant
  • 6736968
  • Patent Number
    6,736,968
  • Date Filed
    Tuesday, June 25, 2002
    22 years ago
  • Date Issued
    Tuesday, May 18, 2004
    20 years ago
Abstract
A horizontal centrifuge has a basket rotatably mounted within a housing. The basket has a plurality of rings disposed between open and closed ends of the basket and a plurality of guide rails circumferentially spaced with respect to the rings. The guide rails have respective lengths extending between the open and the closed ends of the basket and provide a plurality of respective bearing surfaces. A tubular screen is supported in the basket by the plurality of bearing surfaces of the guide rails. A scroll with helical screw flights is also rotatably mounted within the basket. In various aspects of the invention, the tubular screen is made from six arcuate screen segments; the bearing surfaces of the guide rods and the peripheral edges of the helical screw flights are machined surfaces; and the scroll is fabricated.
Description




FIELD OF THE INVENTION




The present invention relates generally to the area of fluid handling and solid/liquid separation and, more particularly, to a horizontal scroll and screen centrifuge.




BACKGROUND OF THE INVENTION




It is well known to use a scroll and screen centrifuge to separate a crystalline, a granular or a fibrous product from a liquid in which the crystalline, granular or fibrous product is carried. Scroll and screen centrifuges are typically used with a continuous process in which a combined liquid and solid material is continuously fed into and continuously discharged from the centrifuge. The continuous process is distinguished from a batch process in which a batch of the liquid and solid material is fed into the centrifuge; and the liquid and solid materials are separated. The centrifuge is stopped, and the separated materials are removed before another batch is loaded into the centrifuge. Both the continuous and batch separation processes are also considered to dry the solid material. The separation process is used in a wide range of applications including the production of soap powders, coal, gypsum, plastic granules, potash, salt, etc.




In a typical horizontal scroll and screen centrifuge, a scroll and basket assembly is frustoconical, that is, shaped like a frustum, and is mounted for rotation within a housing with respect to a generally horizontal axis of rotation. A frustoconical scroll has a tubular side wall with outwardly projecting helical screw flights and rotates within an independently rotating frustoconical screen and basket assembly. The scroll rotates at a slightly different angular velocity from the screen and basket assembly, so that the helical screw flights on the scroll pass close to an inner directed surface of the screen. The helical length of the screw flights varies in a range of from about a fraction of a revolution to several revolutions around the scroll member. A liquid containing solids to be separated therefrom is fed into a closed rearward portion of the scroll and the rotations of the scroll and the screen and basket assembly produce a centrifugal force causing the liquid to pass through openings in the screen thereby separating the liquid from the solids. The rotational velocity difference between the scroll and the screen and basket assembly causes the screw flights to push the solid material across the screen from the smaller, closed, rear end of the scroll flights to the larger open, forward end of the scroll from which the solid material is discharged. The processing time or retention time of the material in the centrifuge is controlled by the pitch of the helical screw flights on the scroll and the difference in angular velocities between the scroll and the screen and basket assembly. Retention time can also be influenced by the design of the feed openings in the scroll. The solid particles pass from the centrifuge to another processing station, a conveyor or a collection unit.




Using a centrifuge to separate a liquid from a solid material in oil mud presents numerous challenges. First, the centrifuge must often be located on an oil derrick platform at sea. As will be appreciated, it is very important that the centrifuge be as small as possible to minimize its footprint and consume the least possible area on the platform.




Second, the solid material separated from the oil mud must be removed from the oil rig platform for proper disposal, either by hauling it inland or, if properly processed and reduced to a low enough moisture level, disposed of at sea. Therefore, it is desirable that the centrifuge be very efficient in order to minimize the quantity of liquid in the solid material.




Third, a centrifuge mounted on an oil rig platform is exposed to the elements, and therefore, the design of a centrifuge intended for use on an oil rig platform must be rugged to withstand extended exposure to the elements.




Fourth, unlike many other environments in which a centrifuge is located, an oil rig platform does not have a crane readily available to lift various components, for example, the scroll, when the centrifuge is being serviced or the screen is being changed. Therefore, it must be possible to perform all of the routine maintenance and service on the centrifuge without the need of an independent and separate crane.




Fifth, a centrifuge separating oil mud on an oil rig platform is subjected to long periods of continuing use and therefore, must operate very reliably between scheduled down times. Further, such a centrifuge must be price competitive with other liquid/solid separation equipment.




Thus, there is a need for a centrifuge that provides an improved performance and is particularly suitable for separating liquid and solids in oil mud on an oil rig platform.




SUMMARY OF THE INVENTION




The present invention provides a horizontal centrifuge having a relatively small footprint and very efficient in operation. Further, the horizontal centrifuge of the present invention includes a self-contained scroll removal tool and is especially useful for separating oil mud on an oil rig platform.




According to the principles of the present invention and in accordance with the described embodiments, the invention provides a horizontal centrifuge for separating oil mud into a liquid and a solid material. The centrifuge has a basket rotatably mounted within a housing. The basket has a plurality of rings disposed between open and closed ends of the basket and a plurality of guide rails are circumferentially spaced with respect to the rings. The guide rails have respective lengths extending between the open and the closed ends of the basket, and the guide rails provide a plurality of respective bearing surfaces. A tubular screen is supported in the basket by the plurality of bearing surfaces of the guide rails. A scroll is mounted within the basket to rotate about the axis of rotation relative to the basket. The scroll has a tubular side wall and a plurality of helical screw flights extending outwardly from the tubular side wall between outer and inner ends of the scroll. Each of the plurality of screw flights has an edge moving in close proximity and relative to an inner surface of the screen. The scroll further has a feed opening proximate the rear end of the tubular side wall, and an infeed tube with an outlet extending into the outer end of the scroll. The infeed tube directs oil mud into the rotating scroll and through the feed opening. The helical screw flights of the scroll carry solid material to a solid material exit while liquid passes through the rotating screen and basket to a liquid exit.




In one aspect of this invention the tubular screen is made from six arcuate screen segments joined together. Using six arcuate segments provides the screen with greater circularity and allows the screen to better conform to the bearing surfaces on the guide rails, thereby making the screen more concentric with the basket and the scroll. A retaining ring or clamp ring urges the screen against the bearing surfaces, which helps maintain the roundness of the screen. The greater concentricity permits the edges of the helical screw flights to be positioned more closely to the inner surface of the screen. The net result is that the centrifuge is more effective at separating the liquid from the solid material, thereby resulting in lesser volume of solid material that must be transported for proper disposal. In another aspect of this invention, the bearing surfaces of the guide rods and the peripheral edges of the helical screw flights are machined surfaces to provide even greater concentricity between the scroll and the screen, thereby further improving the performance of the centrifuge.




In another embodiment of the invention, a horizontal scroll screen centrifuge of the type generally described above has a fabricated scroll. The fabricated scroll has a tubular side wall with outer and inner ends adjacent respective open and closed ends of the basket. The fabricated scroll further has a plurality of helical screw flights attached to and extending outwardly from the tubular side wall. Each of the plurality of screw flights has an edge moving in close proximity and relative to an inner surface of the screen. An end plate is attached at the inner end of the tubular side wall to form a generally closed scroll end, and an infeed plate is attached circumferentially inside the tubular side wall intermediate the inner and outer ends. A fabricated scroll is used instead of the known cast scrolls; and further, machining the edges of the screw flights as described above permits the fabricated scroll to achieve a superior performance than centrifuges using known cast scrolls. In addition, the fabricated scroll weighs less and is easier to handle during a scroll changing process.




In a further embodiment of the invention, a horizontal scroll screen centrifuge of the type generally described above further has a scroll changing tool mounted to the housing to support the scroll during a screen changing process. The scroll changing tool has a base mounted to an upper side of a centrifuge housing, and an overarm support mounted on the base and extending forward of the housing. In one aspect of the invention, the overarm support is pivotally mounted in the base. Thus, the scroll can be removed from the centrifuge, the screen replaced and the scroll reinstalled in the centrifuge without the need for a crane or other device separate from the centrifuge.











These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein.




BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a partial cross-sectional view of a horizontal scroll screen centrifuge in accordance with the principles of the present invention.





FIG. 2

is an end view of a screen used in the horizontal scroll screen centrifuge of FIG.


1


.





FIG. 3

is an end view of a basket used in the horizontal scroll screen centrifuge of FIG.


1


.





FIG. 4

is a cross-sectional view taken along line


4





4


of

FIG. 3

of the basket used in the horizontal scroll screen centrifuge of FIG.


1


.





FIG. 5

is an enlarged view of the encircled portion


5


illustrating how the screen is secured in the horizontal scroll screen centrifuge of FIG.


1


.





FIG. 5A

is an enlarged view of the encircled portion


5


A illustrating how the screen is secured in the horizontal scroll screen centrifuge of FIG.


1


.





FIG. 6

is a plan view of the retaining ring used to secure the screen in the basket of the horizontal scroll screen centrifuge of FIG.


1


.





FIG. 6A

is a cross-sectional view taken along line


6


A—


6


A of

FIG. 6

of the retaining ring used to secure the screen in the basket of the horizontal scroll screen centrifuge of FIG.


1


.





FIG. 7

is a centerline cross-sectional view of a scroll used in the horizontal scroll screen centrifuge of FIG.


1


.





FIG. 8

is a cross-sectional view illustrating an attachment of a helical screw flight to the scroll of FIG.


7


.











DETAILED DESCRIPTION OF THE INVENTION




Referring to

FIG. 1

, a horizontal centrifuge


20


has a discharge housing


22


that is mounted to a drive housing


24


. The discharge housing


22


has a front wall


26


that includes a cover


28


that permits access to the interior of the centrifuge


20


. Further, the drive housing


24


has an interior surface


30


bounding the contained volume of the discharge housing


22


. A basket and scroll assembly


32


is rotatably mounted within the discharge housing


22


. The basket and scroll assembly


32


is comprised of a basket


34


having a frustoconical shape, that is, the shape of a frustum or a truncated cone, and a plurality of slots


36


. An inner, closed end


37


of the basket


34


has a hub


38


that is mechanically connected to the outer drive shaft


40


. A peripheral screen


42


has a similar frustum shape that has slots or perforations


44


(

FIG. 2

) and is secured inside the basket


34


. Thus, the assembly of the basket


34


and screen


42


is mounted to rotate within the discharge housing


22


about a generally horizontal axis of rotation


46


.




An inner, closed end


48


of a scroll


50


has a hub


52


that is centrally located within the scroll


50


and is mechanically connected to an inner drive


54


; and thus, the scroll


50


is also mounted to rotate within the discharge housing


22


about the axis of rotation


46


. The scroll


50


also has a frustum shape and has an outer open end


56


adjacent an outer open end


58


of the basket


34


. A plurality of screw flights


60


extend in a generally radial direction outwardly from the scroll


50


, and the screw flights


60


extend helically relative to the axis of rotation


46


between the respective closed and open ends


48


,


56


of the scroll


50


. The screw flights


60


have respective peripheral edges


62


, which, upon rotation of the scroll


50


, move in close proximity to and relative to an inner surface


64


of the screen


42


.




The centrifuge


20


is powered by a motor (not shown) that is mechanically coupled by a belt (not shown) to an input shaft


66


in a known manner. The input shaft


66


is connected via internal gearing to the inner and outer drive shafts


54


,


40


to provide first and second rotary drives to the basket


34


and scroll


50


, respectively, in a known manner. Thus, the outer and inner drive shafts


54


,


40


rotate the scroll


50


and basket


34


, respectively, at different angular velocities.




The effectiveness of the centrifuge


20


is determined in part by how much liquid is left in the solid material after the centrifuging process. The less liquid in the solid material, the more effective the centrifuge


20


. A factor that controls the effectiveness of the separation process is the gap or space between the inner surface


64


of the screen


42


and the outer edges


62


of the helical screw flights


60


. Further, that gap varies because the screen is often noncircular and less circular than the boundary defined by the screw flight outer edges


62


. The noncircularity of the screen is caused in part by how the screen


42


is manufactured. Known screens are made by welding or otherwise connecting four screen segments, wherein each of the screen segments represents an axial or longitudinal quarter segment of the screen. The screen is fabricated by welding the four screen segments together, thereby producing four axially extending joints. The welding or joining process often changes the radius of the screen segment near the joints, and therefore, those nonconstant, different radii cause the screen to lose circularity at the joints between the four segments. The net result is that the gap between the screen and the screw flight peripheral edges changes near the screen segment joints. To address that problem, referring to

FIG. 2

, the screen


42


is fabricated from six screen segments that are joined together to form the frustum shape of the screen. While there is still a loss of circularity at the welded joints between the six screen segments, the loss of circularity is substantially less than with the four segment screen. Therefore, with a six segment screen, the gap between the screen inner surface


64


and the screw flight peripheral edges


62


is less variable and more constant than with a four segment screen.




There are other factors that effect the circularity of the screen


42


and concentricity between the screen


42


and the screw flight peripheral edges


62


. For example, known screens have a mounting flange that extends radially outward from the outer open end of the screen. That flange is mounted to the outer open end of the basket. Any irregularities in the squareness or other geometry of the screen flange or the outer ends of the basket or screen can result in the circularity of the screen and its concentricity with the basket being adversely affected in the process of mounting the screen to the basket with the flange. Therefore, the screen


42


is mounted differently than known screens.




Referring to

FIGS. 3 and 4

, the basket


34


is comprised of a plurality of annular plates or rings


70


that form the slots


36


therebetween. The rings


70


have notches (not shown) formed on respective outer circumferences


72


that are sized and shaped to receive axial rods


74


, for example, lengths of circular bar stock. Outer rings


76


,


78


of the rings


70


and inner rings


80


,


82


of the rings


70


have peripheral through holes that are sized to receive the support rods


74


that extend therethrough. About 16 support rods


74


are substantially equally distributed about the outer circumferences


72


of respective rings


70


. Inner circumferences


84


of respective rings


70


are notched to receive axially or longitudinally extending guide rails


86


. About 8 guide rails


86


are substantially equally spaced about the inner circumferences


84


of respective rings


70


and connected thereto, for example, by welding.




The guide rails


86


have respective inner surfaces


88


that project outward from the inner circumferences


84


of the annular rings


72


. Further, the bearing surfaces


88


are machined so that, first, they provide a locus of surfaces that form a frustum substantially identical to the frustum of the screen


42


, and second, at any axial position, they form a locus of surfaces that is circular with respect to an axial centerline


90


of the basket


34


. As the screen


42


is slid into the basket


34


, the bearing surfaces


88


help guide the screen


42


into a concentric relationship with the basket


34


. In addition, the application of an axial force against the outer end of the screen


42


, for example, by a clamp ring or the retaining ring


92


, helps to move the screen


42


into a contacting relationship with the bearing surfaces


88


, thereby further contributing to the concentricity of the screen


42


with the basket


34


.




Referring back to

FIG. 1

, the basket


34


is first placed in the discharge housing


22


; and its hub


38


connected to the outer drive shaft


40


. Thereafter, the screen


42


is slid inside the basket


34


. The bearing surfaces


88


(

FIG. 3

) facilitate a concentric disposition of the screen


42


within the basket


34


. Thereafter, referring to

FIG. 5

, a retaining ring


92


, as detailed in

FIGS. 6 and 6A

, is attached to an outer end of the basket


34


by fasteners


94


extending through clearance holes


96


of the retaining ring


92


and engaging the outer end of the basket


34


. The retaining ring


92


further has a radially directed inner lip


98


(

FIGS. 5

,


6


A) with a bearing surface


100


in contact with the outer end


102


of the screen


42


. Therefore, as the fasteners


94


are tightened, the retaining ring pushes axially against the screen outer end


102


to dispose the outer surface


104


of the screen firmly against the guide rail bearing surfaces


88


, which maintains the roundness of the screen. Thus, the screen


42


has the greatest possible concentricity with respect to the basket


34


. Thus, the tightening of the fasteners


94


is governed by the screen


42


contacting the bearing surfaces


88


, and the retaining ring


92


is not tightened against the end of the basket


34


. Normally, the retaining ring


92


is separated from the front of the basket by a gap


105


.




It is also desirable that the screen


42


be as concentric as possible with the helical flight edges


62


. Therefore, as will be further described later, the helical flight edges


62


are also machined such that they represent a locus of surfaces of a frustum that is substantially identical to the frustum formed by the locus bearing surfaces


88


of the basket


34


.




As shown in

FIG. 1

, four equally spaced paddles or wipers


106


are mounted to the outer end of the basket


34


, so that they have an accurate and predictable position with respect to a raceway


142


adjacent the outer end of the basket


34


. However, as earlier described, the retaining ring


92


is not tightened against the end of the basket


34


but its position is determined by the screen


42


contacting the bearing surfaces


88


. Therefore, the paddles


106


must be mounted independent of the retaining ring


92


. Referring to

FIG. 5A

, to facilitate that mounting, the retaining ring


92


has a plurality of clearance holes


108


(FIG.


6


). Each paddle


106


is mounted on a pair of bushings


110


that extend through the clearance holes


108


of the retaining ring


92


. A fastener


112


extends through holes in each of the paddles


106


, through the pair of bushings


110


and into threaded holes


114


(

FIG. 3

) in the outer end of the basket


34


. Therefore, the paddles


106


maintain the desired position with respect to the end of the basket


34


independent of the relationship of the retaining ring


92


to the basket


34


.




The centrifuge


20


differs from known centrifuges in that the scroll


50


of the centrifuge


20


is a fabricated part versus being a die cast part that is used with known centrifuges. Referring to

FIG. 7

, the scroll


50


has a tubular body


120


that has a frustum shape similar to the frustum shape of the basket


34


. An end plate


122


is attached, for example, by welding, to one end of the tubular side wall


120


, thereby forming a closed end


48


of the scroll


50


. An infeed plate


124


is attached circumferentially, for example, by welding, to an inner surface


126


of the tubular side wall


120


. The infeed plate


124


has an infeed opening


128


sized to receive a feed tube


130


(FIG.


1


). Referring to

FIG. 8

, a plurality of helical screw flights


60


are attached, for example, by welding, to an outer surface


132


of the tubular side wall


120


. There are eight helical screw flights


60


substantially equally spaced around the tubular side wall


120


, and the helical screw flights


60


have a helical flight angle of about 60°. In other words, referring to

FIG. 1

, a radial inner edge


134


intersecting the axial centerline


46


is separated from a radial outer edge


136


by an angle of about 60°. The screw flight outer edges


62


are machined to have a size and shape such that they sweep through a frustum that is substantially identical in size and shape to the frustum formed by the guide rod bearing surfaces


88


(FIG.


3


).




The post drilling oil mud is fed into the centrifuge


20


through a feed tube


130


to a wet end, or inner end,


48


of the scroll


50


. Rotation of the scroll


50


moves oil mud through scroll feed openings


140


into a space between the helical screw flights


60


. Centrifugal forces caused by the rotations of the scroll


50


and basket


34


push the oil mud against the screen


42


and the high degree of concentricity of the helical screw flights


60


relative to the screen


42


results in more liquid being moved through the screen


42


than if the helical screw flights


60


and screen


42


were less concentric. The liquid passes through the scroll


34


and is discharged from the housing


22


in a known manner. The solid material in the oil mud is carried by the helical screw flights


60


to the outer, open end


58


of the basket


34


and is discharged into an annular raceway


142


. The raceway is lined with a ceramic tile in a known manner. Paddles


106


rotating with the basket


34


scrap the solid material off of the walls of the raceway


142


and into a solid material discharge chute


144


.




The continuous operation of the centrifuge


20


results in wear on the screen


42


, and it is expected that the screen must be periodically replaced. Changing the screen


42


requires removal of the scroll


50


, which process normally uses a crane or overhead lifting device to support the scroll while the screen is being changed. However, as mentioned, on an oil rig platform, cranes are not available at the centrifuge location; and therefore, the scroll


50


must be supportable by other structure. Referring to

FIG. 1

, after the cover


28


has been removed, a mandrel and end support


150


(shown in phantom) are used to support the scroll


50


after it has been removed from the centrifuge


20


. A scroll removal tool


152


is then used to support the scroll


50


during the remainder of the screen replacement process.




The scroll removal tool


152


has a base


154


that is bolted to the top of the housing


22


. The base


154


supports a bushing


156


and a lower support


158


, and an overarm


160


is rotatably mounted in the bushing


156


and lower support


158


. The bushing


156


is laterally supported by two turnbuckles


162


that have respective upper ends connected to opposite sides of the bushing


156


and respective lower ends connected to the housing


22


. After the scroll is pulled onto the mandrel


150


, it is supported by a known lift device


164


, for example, a “come-along”, block and tackle, etc.; and the overarm


160


is rotated to provide access to the front of the centrifuge


20


. The screen


42


is changed; and the above process is executed in reverse order to place the centrifuge back in service.




Thus, the horizontal screen scroll centrifuge


20


is suitable for use on a platform of an oil rig because of its relatively small footprint and very efficient in operation. Several structural improvements combine to provide greater concentricity between the scroll outer flights


62


and the screen


42


, thereby improving the performance of the centrifuge


20


. More specifically, the six segment screen


42


provides the screen with greater circularity and allows the screen to better conform to the bearing surfaces


88


on the guide rails


86


, thereby making the screen


42


more concentric with the scroll outer edges


62


. Further, the guide rod bearing surfaces


88


and the scroll outer edges


62


are machined surfaces to provide even greater concentricity between the scroll outer edges


62


and the screen


42


. With the above, it is possible to fabricate the scroll


50


, thereby providing a substantial reduction in cost over known cast scrolls. The above features provide a horizontal scroll screen centrifuge that is effective at separating the liquid from the solid material in an oil mud, thereby resulting in lesser volume of solid material that must be transported from the oil rig for proper disposal.




The horizontal screen scroll centrifuge


20


is further suitable for use on a platform of an oil rig because the centrifuge has a self-contained scroll changing tool


152


mounted to the housing


22


, which is capable of supporting the scroll


50


during a screen changing process. Thus, the scroll


50


can be removed from the centrifuge


20


, the screen


42


replaced and the scroll


50


reinstalled in the centrifuge


20


without the need for a crane or other device separate from the centrifuge.




While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, the horizontal scroll screen centrifuge


20


is described as being particularly well suited for use on a platform of an oil rig to separate liquid from solid material in oil mud. As will be appreciated, depending on the application, the various improvements discussed herein, for example, a six segment screen


42


, guide rod bearing surfaces


88


, machined guide rod bearing surfaces


88


and scroll helical flight edges


62


, a fabricated scroll


50


, etc., can be used together or in different combinations.




Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.



Claims
  • 1. A horizontal centrifuge comprising:a housing; a basket having an outer open end and an inner closed end and mounted within the housing to rotate about an axis of rotation; a plurality of rings disposed between the open and closed ends of the basket; a plurality of guide rails circumferentially spaced with respect to the rings and having respective lengths extending between the open and the closed ends of the basket, the guide rails providing a plurality of bearing surfaces; a tubular screen having inner and outer surfaces terminating with opposed open ends, the tubular screen being supported inside the basket by the plurality of bearing surfaces; a scroll mounted within the basket to rotate about the axis of rotation, the scroll having open and closed ends adjacent the respective open and closed ends of the basket; and an infeed tube having an outlet extending into the outer end of the scroll.
  • 2. The horizontal centrifuge of claim 1 wherein the basket further comprises:a ring mounted to the basket to force the screen against the bearing surfaces to maintain the roundness of the screen.
  • 3. The horizontal centrifuge of claim 1 wherein the plurality of bearing surfaces are machined surfaces equally spaced from an axial centerline of the basket.
  • 4. The horizontal centrifuge of claim 3 wherein the scroll further comprises a plurality of helical screw flights having respective machined end surfaces equally spaced from an axial centerline of the scroll and moving in close proximity and relative to the inner surface of the screen.
  • 5. A horizontal centrifuge comprising:a housing; a basket having an open outer end and an inner closed end and mounted within the housing to rotate about an axis of rotation; a tubular screen having inner and outer surfaces terminating with opposed inner and outer ends, the tubular screen being mounted inside the basket with the outer surface adjacent the basket; a retaining ring mounted to the outer end of the basket, the retaining ring contacting the outer end of the tubular screen to retain the tubular screen inside the basket; a scroll mounted within the basket to rotate about the axis of rotation, the scroll having open and closed ends adjacent the respective open and closed ends of the basket; and an infeed tube having an outlet extending into the outer end of the scroll.
  • 6. The horizontal centrifuge of claim 5 wherein the retaining ring comprises an annular retaining flange extending radially inward and contacting the outer end of the tubular screen.
  • 7. The horizontal centrifuge of claim 5 wherein the outer end of the tubular screen comprises a flangeless edge.
  • 8. The horizontal centrifuge of claim 5 further comprising:a hole in the retaining ring; a bushing having one end extending through the hole in the retaining ring and bearing against an outer end of the basket; and a paddle disposed adjacent the bushing and extending outward from the basket into the housing, the paddle being mounted to the outer end of the basket with the bushing.
  • 9. The horizontal centrifuge of claim 5 further comprisinga plurality of holes in the retaining ring; a plurality of bushings, each of the plurality of bushings having an inner end extending through a different hole in the retaining ring; and a plurality of paddles, each of the plurality of paddles being disposed adjacent a different bushing and extending outward from the basket into the housing and each of the paddles being mounted to the outer end of the basket with a respective bushing.
  • 10. The horizontal centrifuge of claim 9 wherein the plurality of holes, the plurality of bushings and the plurality of paddles is substantially equally spaced around the outer end of the basket.
  • 11. The horizontal centrifuge of claim 10 wherein there are four paddles.
  • 12. The horizontal centrifuge of claim 11 further comprising two fasteners for connecting each of the four paddles to the outer end of the basket, each of the two fasteners extending through a respective bushing that, in turn, extends through a respective hole in the ring, each of the two fasteners being attached to the outer end of the basket.
  • 13. A horizontal centrifuge comprising:a housing; a basket having an outer open end and an inner closed end and mounted within the housing to rotate about an axis of rotation; a tubular screen having inner and outer surfaces terminating with opposed open ends, the tubular screen being mounted inside the basket with the outer surface adjacent the basket, the tubular screen comprising six arcuate screen segments joined together; a scroll mounted within the basket to rotate about the axis of rotation, the scroll having open and closed ends adjacent the respective open and closed ends of the basket; and an infeed tube having an outlet extending into the outer end of the scroll.
  • 14. A horizontal centrifuge comprising:a housing; a basket having an open outer end and an inner closed end and mounted within the housing to rotate about an axis of rotation; a tubular screen having inner and outer surfaces terminating with opposed ends, the tubular screen being mounted inside the basket with the outer surface adjacent the basket; a fabricated scroll mounted within the basket to rotate about the axis of rotation relative to the basket, the scroll comprising a tubular side wall with outer and inner ends adjacent the respective open and closed ends of the basket, the tubular side wall having a plurality of feed openings proximate the rear end, a plurality of helical screw flights attached to and extending outwardly from the tubular side wall between the outer and inner ends of the scroll, each of the plurality of screw flights having respective machined end surfaces equally spaced from an axial centerline of the scroll and moving in close proximity and relative to the inner surface of the screen, an end plate attached at the inner end of the tubular side wall to form a generally closed scroll end adjacent the closed end of the basket, and an infeed plate attached circumferentially inside the tubular side wall intermediate the front end and the rear end; and an infeed tube having an outlet extending through the infeed plate.
  • 15. The horizontal centrifuge of claim 14 wherein the plurality of helical screw flights comprises eight helical screw flights.
  • 16. The horizontal centrifuge of claim 15 wherein each of the helical screw flights has a flight angle of about 60°.
  • 17. The horizontal centrifuge of claim 16 wherein the eight flights are substantially equally spaced about the tubular side wall.
  • 18. The horizontal centrifuge of claim 14 wherein the basket, tubular screen and tubular side wall have a frustum shape.
  • 19. A horizontal centrifuge comprising:a housing; a basket having an open outer end and an inner closed end and mounted within the housing to rotate about an axis of rotation, a tubular screen having inner and outer surfaces terminating with opposed ends, the tubular screen being mounted inside the basket with the outer surface adjacent the basket; a scroll mounted within the basket to rotate about the axis of rotation, the scroll having open and closed ends adjacent the respective open and closed ends of the basket; an infeed tube having an outlet extending into the outer end of the scroll; and a scroll changing tool mounted to the housing and supporting the scroll during a process of inserting and removing the scroll from the housing.
  • 20. The horizontal centrifuge of claim 19 wherein the scroll changing tool comprises:a base mounted to an upper side of the housing; and an overarm support mounted on the base and extending forward of the housing.
  • 21. The horizontal centrifuge of claim 20 wherein the overarm support is rotatably mounted on the base to pivot with respect to a substantially vertical axis of rotation.
  • 22. A horizontal centrifuge comprising:a housing; a basket having an outer open end and an inner closed end and mounted within the housing to rotate about an axis of rotation, the basket further comprising a plurality of bearing surfaces; a tubular screen comprising six arcuate screen segments joined together and having inner and outer surfaces terminating with opposed open ends, the tubular screen being supported inside the basket by the plurality of bearing surfaces; a retaining ring mounted to the outer end of the basket, the retaining ring contacting the outer end of the tubular screen to retain the tubular screen inside the basket; a scroll mounted within the basket to rotate about the axis of rotation, the scroll having open and closed ends adjacent the respective open and closed ends of the basket; and an infeed tube having an outlet extending into the outer end of the scroll.
  • 23. The horizontal centrifuge of claim 22 wherein the plurality of bearing surfaces are machined surfaces equally spaced from an axial centerline of the basket.
  • 24. The horizontal centrifuge of claim 23 wherein the scroll further comprises a plurality of helical screw flights having respective machined end surfaces equally spaced from an axial centerline of the scroll and moving in close proximity and relative to the inner surface of the screen.
  • 25. The horizontal centrifuge of claim 24 further comprising a scroll changing tool mounted to the housing and supporting the scroll during a process of inserting and removing the scroll from the housing.
  • 26. The horizontal centrifuge of claim 25 wherein the retainer ring is mounted to urge the screen against the bearing surfaces to maintain the roundness of the screen.
US Referenced Citations (10)
Number Name Date Kind
1478660 Barnes et al. Dec 1923 A
3419148 Niwa et al. Dec 1968 A
3980563 Greutert et al. Sep 1976 A
4193874 Gerteis Mar 1980 A
5091084 Krettek Feb 1992 A
5378364 Welling Jan 1995 A
5380434 Paschedag Jan 1995 A
5397471 Rodebush et al. Mar 1995 A
5433849 Zittel Jul 1995 A
5468389 Keller Nov 1995 A
Foreign Referenced Citations (1)
Number Date Country
0845296 Jun 1998 EP
Non-Patent Literature Citations (1)
Entry
TEMA Systems, Inc., Coal Centrifuges, Product Brochure, 1993.