A centrifugal separator and method of separating materials

Abstract

 A centrifugal separator for and a method of separating the constituents of a fluid mixture wherein the mixture is introduced into a separating means (12), preferably a container, and the separating means is rotated about its own first (19) and simultaneously in planetary fashion about a second offset axis (28) to separate the constituents by centrifugal action, due to rotation about the second offset axis (28), the first axis (19) and the second offset axis (28) being disposed in non-parallel relationship to one another and a separated constituent being thrown out of an open end of the separating means (12) under centrifugal action due to rotation of the separating means (12) about the second offset axis (28) without removal means being required within the separating means (12). In a preferred arrangement the second offset axis (28) is substantially vertical and the first axis (19) lies at an acute angle to the vertical.

Description

[0001] This invention relates to centrifugal separators and to a method of separating materials. It relates more particularly to the separation of solids from liquids.

[0002] U.S. Patent 3 402 821 discloses a centrifugal separator for dehydrating solids contained in a slurry, wherein a series of circumferentially spaced filter baskets are arranged to revolve about their own vertically disposed axes and also to orbit about a central vertical axis, each basket including a series of filter screens which curve in involute fashion and which assume different ecliptic positions with respect to the vertical axis of revolution of the basket and to the central vertical axis so that in outside ecliptic positions the screens pass liquid to associated collector walls and in inside ecliptic positions solid particles adhering to the screens are flung free to produce a self-cleaning action. In intermediate positions between the outside and inside ecliptic positions the screens assume radial positions so that collected solids thereon slide endwise therefrom and are flung outwardly to a point of discharge.

[0003] U.S. Patent 3 627 138 discloses a similar centrifugal separator but solid wall type vanes curving in involute fashion are substituted for the filter baskets.

[0004] U.S. Patent 3 829 009 discloses a centrifugal separator comnrising a high speed bowl rotatable about a vertical axis, the separator including a series of ploughs to elevate sludge flung against the inner periphery of the bowl into the path of a series of rotatable buckets orbiting round the bowl interior to scoop up wads of sludge, centrifugal force due to orbital rotation of the buckets dislodging the wads in the buckets and causing the wads to be flung radially outwards over the rim of the bowl.

[0005] According to the invention there is provided a centrifugal separator for separating the constituents of a fluid mixture which includes at least one separating means that is rotatable about its own first axis and also about a second offset axis, characterised in that the first and second axes are disposed in non-parallel relationship to one another.

[0006] Rotation of the separating means about the second offset axis may be in a planetary manner.

[0007] The advantage offered by the invention is mainly that separated solids may be thrown out of the separating means through an open end thereof under centrifugal action due to rotation of the separating means about the second offset axis without removal means being required within the separating means.

[0008] The first and second axes may intersect one another.

[0009] In a particular arrangement the second axis may be disposed substantially vertically with the first axis disposed at an acute angle to the vertical.

[0010] The centrifugal separator may include feed means for feeding the fluid mixture into the separating means.

[0011] The separating means may comprise a container.

[0012] In one embodiment the separating means may comprise a container having a solid wall. The container may have an internal profile which is substantially circular in cross-section transversely to the first axis.

[0013] The container may have any suitable shape - it may be cylindrical, conical, frusto-conical, arcuate or the like. In a preferred form the container is frusto-conical, open at one end and closed at the other, and being narrower at its open end.

[0014] Conveniently the container may be disposed with its open end facing upwardly and away from the offset axis. More particularly the highest point of the closed end of the container may lie at or above the level of the lowest point of the open end of the container, diagonally opposed thereto.

[0015] The applicant believes that in the embodiment of a container having a solid wall and an open end, due to the rotation of the container about the second offset axis, the mixture will be subjected to a centrifugal acceleration and will be thrown from the feed means against that part of the wall of the container which is furthest from the second offset axis. With the liquid part of the mixture remaining in this region and due to rotation of the container about its own first axis, the solid constituent, which due to the centrifugal force caused by rotation about the second offset axis will settle out of the liquid on the wall of the container, will rotate together with the container to a position nearer the second offset axis. In this region the centrifugal force due to rotation about the second offset axis will become such that it tends to remove the solids from the wall and throw out the solids from the container through its open end into a collecting region. The level of the liquid in the lower region of the container will at the same time build up until it overflows from the container over the lowest region of the wall of the container and from where it is guided to an additional collecting region for such liquid. For this embodiment solids to be separated from a liquid must have a higher density than the liquid in order to settle out.

[0016] In another embodiment the separating means may comprise a foraminous container having a substantially circular transverse cross-sectional profile with respect to its axis.

[0017] The container may further have any suitable shape - it may be cylindrical, conical, frusto-conical, arcuate or the like. In a preferred form, the container may be frusto-conical, open at one end and closed at the other, and being narrower at its open end.

[0018] The applicant believes that in the embodiment of a foraminous container with an open end, due to the rotation of the container about the second offset axis, the mixture will experience centrifugal acceleration and will be thrown out against that part of the wall of the container which is furthest from the second offset axis, the liquid passing through the wall of the container and the solid constituents either being trapped by the wall or settling thereon depending on its density relative to that of the liquid. As the container rotates about its own first axis, a position will be reached where the solid constituents due to the centrifugal force caused by rotation about the second offset axis and which have been separated, will break away from the wall and be thrown out of the container through its open end. For this embodiment solids to be separated from a liquid may have a density higher or lower than that of the liquid.

[0019] In addition for each embodiment the inner surface of the container may be roughened or may have inwardly directed protrusions, i.e. protrusions projecting from the wall of the container into the container, to prevent or at least to minimize sliding of solids relative to the wall and to assist solids to rotate with the wall.

[0020] In particular the separating means may be rotatably mounted on a carrier which is rotatable about the offset axis.

[0021] The separating means may be adapted to rotate in the same sense about its own axis as it does about the offset axis. Alternatively the separating means may be adapted to rotate about its own axis in a sense opposite to that of its rotation about the offset axis.

[0022] The separating means may be adapted to rotate at a relatively slow speed about its own first axis as compared to rotation about the second offset axis. The radius and speed of rotation of the separating means about the second offset axis may be selected to produce centrifugal force of suitable magnitude to effect separation of the constituents of the fluid mixture, the separation improving and the effective capacity of the separator increasing with increasing centrifugal force.

[0023] It may be mentioned, purely by way of example without being restrictive in any way, that in a prototype separator a container having a diameter of 350mm was rotated at a speed of 10 revolutions per minute about its own first axis and was also rotated at a speed of 770 revolutions per minute about a second offset axis spaced about 900mm from a fluid mixture in the container to produce centrifugal force in the order of 300g on the fluid mixture in the container.

[0024] Furthermore the centrifugal separator may include a first rotating means for rotating the separating means about its own axis and a second rotating means for rotating the separating means about the offset axis.

[0025] The feed means may feed the fluid mixture into the closed end of the container near the lowest vertical position of said closed end.

[0026] The centrifugal separator may further include collecting means to collect separated constituents of the mixture. The collecting means may include a housing in which the separating means is housed that rotates about the offset axis with the separating means, the housing having suitable apertures through which the separated constituents may pass upon separation.

[0027] In addition the collecting means may include suitable baffles and conduits for collecting the separated constituents.

[0028] Preferably the separator may have more than one separating means at the same offset axial position and circumferentially spaced apart. Also the first and second rotating means may include suitable gears or belts and pulleys for rotating the separating means.

[0029] Further according to the invention there is provided a method of separating the constituents of a fluid mixture, which includes introducing the mixture into a separating zone and rotating the separating zone about a first axis and simultaneously in a planetary fashion about a second offset axis to separate the constituents by centrifugal action, characterised in that the first and second offset axes are disposed in non-parallel relationship to one another and a separated constituent is thrown out of the separating zone under centrifugal action.

[0030] The mixture may be introduced into a container which has solid walls and a circular internal cross-sectional profile transverse to its own axis and the container may be rotated about its own axis, which constitutes the first axis, and about the second offset axis, the first and second axes not being parallel to one another.

[0031] The first and second axes may intersect one another.

[0032] The second axis may further be vertical and the first axis may be disposed at an acute angle to the vertical.

[0033] The separating means may be rotated about the first axis in the same sense as it is rotated about the second axis. Alternatively the separating means may be rotated about the first axis in a different sense from that about the second axis.

[0034] Furthermore the method may include that the separated constituents are collected.

[0035] The invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 shows a longitudinal sectional view of part of a first embodiment of a separator in accordance with the invention;

Figure 2 shows a longitudinal sectional view of part of a second embodiment of the separator; and

Figure 3 shows a longitudinal sectional view of part of a third embodiment of the separator.

[0036] Referring first to Figure 1 the separator is designated generally by reference numeral 10. The separator is for separating water from a mixture thereof with sand.

[0037] The separator 10 has four radially and circumferentially spaced-apart separating containers 12, of which only one is shown. The containers 12 are frusto-conical, being open at their narrower ends and closed at their wider ends. Each container 12 is supported on a coaxial shaft 14 which is rotatably mounted in two members 16 and 18 to be rotatable about an axis 19. Each member 16, l8 has a planar central portion 20 which is horizontally disposed and a frusto-conical outer portion 22, the shafts 14 being mounted between the frusto-conical portions 22 to be disposed at an acute angle to the vertical. The members 16 and 18 are secured to a housing 24 which is fast with a hollow shaft 26 to be rotatable therewith. The shaft 26 is mounted for rotation about a vertical axis 28, in a support structure 30. Each container 12 further has a foraminous wall 32 having a circular internal profile in cross-section and on the inner side of which is a filter membrane 34 supported between two layers 36 of wire mesh.

[0038] Passing through shaft 26 is a further shaft 38 which at its upper end has a gear 40 which engages gears 42 fast with the containers' shafts 14. The outer shaft 26 is driven by means of a pulley 44, via a belt from a suitable drive means (not shown). The inner shaft 38 in turn is driven by the outer shaft 26 via a gearbox 46 which has a first gear 48 fast with the outer shaft 26 driving a second gear 50 which is fast with a third gear 52 which in turn drives a fourth gear 54 fast with the inner shaft 38 at its lower end. Depending on the relative ratios of the gears 48, 50, 52 and 54, the inner shaft 38 will rotate at a greater, lesser or the same speed as the outer shaft 26, but in the same direction.

[0039] The water-sand mixture is fed to the bottom of the containers 12 by means of pipes 56 and conduits 58, which rotate with the housing 24, via a feed pipe 60. Washing water is also fed into the containers 12 via pipes 62, conduits 64 and feed pipe 66.

[0040] The housing 24 has two openings 68, 70 for each container 12. The upper openings 68 are located adjacent the upper ends of the containers 12 and the lower openings 70 at the juncture between the housing 24 and the upper member 16. Surrounding the housing 24 are baffles 72 which collect the separated water and sand in discharge troughs 74, 76 respectively. Water may be supplied to the sand discharge trough 76 via a conduit 78 and feed pipe 80 to assist in removal of the sand therefrom.

[0041] In use, the outer shaft 26 is rotated via the pulley 44, causing the housing 24 and the containers 12 to rotate about the vertical axis 28. Due to the gears 48 to 54 the inner shaft 38 is also rotated. If the shafts 38 and 26 are rotating at the same speed, there will be no rotation of the gear 40 about its own axis 28 and thus no rotation of the gears 42. Consequently there will be no rotation of the containers 12. If the inner shaft 38 rotates at a faster rate than the outer shaft 26, then the containers will rotate in the opposite direction to the housing 24, and if slower in the same direction. Thus by varying the ratios of the gears 48 to 54 the containers 12 may be caused to rotate about their own axes 19, in the same or opposite direction as their rotation about the offset axis 28.

[0042] As the containers 12 are so rotating about their own axes 19 and the offset axis 28, the water-sand mixture is fed into them via the feed pipe 60, the conduits 58 and the pipes 56. The applicant believes that due to centrifugal action as a result of rotation about offset axis 23, the mixture will be thrown against the portion of the inner surface of the filter membrane 34 of each container 12 which is furthest away from the offset axis 28, some of the water passing therethrough and the sand being retained. The water that has been separated will then pass through the opening 70 to be collected in the trough 74.

[0043] The applicant further believes that as each container 12 rotates about its own axis 19 a position will be reached where due to the centrifugal action by rotation about the offset axis 28, the sand, which rotates with the container, will leave the membrane 34 and travel across the container 12 to strike and lodge against a different portion of the wall of the container. A further amount of water will then pass through the filter membranes 34.

[0044] Due to the inclination of the container's own axis 19, the portion of the container wall against which the sand now lodges will be further away from the floor of the container 12 than the initial wall portion. The procedure is repeated and in this way the sand moves up the wall of the container 12 until finally dry sand is thrown out of the mouth of the container 12 to pass through the upper openings 68 and strike the baffle 72 and be collected in the trough 76. In order to remove the sand from the trough 76 water is supplied via the pipe 80 and conduit 78.

[0045] The embodiment shown in Figure 2 is similar to that of Figure 1, except that the inner shaft 38 is stationary and the containers 12 are caused to rotate by the action of two intermediary gears 90 and 92 which are rotatably mounted to the floor of the housing 24. This embodiment is similarly referenced to that of Figure 1. Its operation is also similar to that of the embodiment of Figure 1 except that the containers 12 only rotate about the axes 19 in an opposite sense to that of the housing 24.

[0046] The embodiment shown in Figure 3 and generally indicated by the reference numeral 100 shows still a further embodiment of a separator in accordance with the invention, like parts being indicated by the same reference numerals. In this embodiment the containers 12 have solid metal walls, for example, of stainless steel, against which a liquid/solid mixture is thrown, upon being fed into the containers 12, by means of the conduit 56.

[0047] Each container 12 is frusto-conical in shape, open at its upper end and closed at its lower end, and being narrower at its upper open end. Each container 12 may have an internal profile which is substantially circular in cross-section transversely to its own axis 19.

[0048] Each container 12 is rotatable at relatively low speed about its own axis 19 which is inclined at an acute angle to the vertical and is furthermore simultaneously rotatable at relatively high speed about vertical offset axis 28 to produce centrifugal force on the mixture in the container 12. The upper open end of each container 12 faces upwardly away from offset axis 28.

[0049] The highest point of the closed lower end of each container 12 which is nearest to offset axis 28, lies above the level of the lowest point of the open upper end of the container which is furthest from offset axis 28.

[0050] A liquid/solids mixture is fed by means of conduit 56 into the closed lower end of each container 12 near the lowest vertical position of the closed end.

[0051] Upon rotation of the containers 12 about their own axes 19 and about offset axis 28, the liquid/solids mixture fed into each container 12 is thrown outwardly by centrifugal force due to rotation about offset axis 23, against a portion of the inner surface of the container wall which is remote from the offset axis 28. The applicant believes that whereas the solids will tend to stick to this portion of the wall upon rotation of the container about its own axis 19, the liquid constituent will merely collect in this region where it is fed into the container 12. Rotation of each container 12 about its own axis 19 will hence cause the solids to reach a position where the centrifugal force due to rotation about offset axis 28 tends to throw the solids away from the wall. Since the highest point of the closed lower end of each container 12 lies above the lowest point of the open upper end of the container, such solids are thus directly thrown out of the open upper end of the container 12, through the aperture 68 and into the collecting region 102.

[0052] The containers 12 are each provided with an ejection lip 104 leaving a liquid collecting region 106. As more mixture is fed into the container the liquid fills up the region 106 until it flows over the lip 104 and through the opening 70 into its own collecting region 108. The walls of the containers 12 may further have protrusions 110 directed into the container and/or may be roughened internally to enhance settling of the solids on the walls of the containers 12.

[0053] Separator 100 may include four or any other suitable number of containers 12 which are located in regular, circumferentially spaced relationship about the vertical offset axis 28.

[0054] Further collection of solids and liquids may be as described before with reference to the first and second embodiments.

[0055] With the arrangement according to the invention, separated solids may be thrown out of the separating containers under the action of centrifugal force without removal means being required within the containers.

Claims

1. A centrifugal separator including at least one separating means that is rotatable about its own first axis and also about a second offset axis, characterised in that the first and second axes are disposed in non-parallel relationship to one another.

2. A centrifugal separator as claimed in claim 1, characterised in that the first and second axes intersect one another.

3. A centrifugal separator as claimed in claim 1 or 2, characterised in that the second offset axis is disposed substantially vertically and the first axis is disposed at an acute angle to the vertical.

4. A centrifugal separator as claimed in any one of the preceding claims, characterised in that the separating means comprises a container.

5. A centrifugal separator as claimed in claim 4, characterised in that the container has an internal profile which is substantially circular in cross-section transversely to the first axis.

6. A centrifugal separator as claimed in claim 4 or 5, characterised in that the container is open at one end and closed at the opposite end, the open end facing upwardly and away from the second offset axis.

7. A centrifugal separator as claimed in claim 6, characterised in that the first axis is disposed at an acute angle to the vertical and the highest point of the closed end of the container lies at or above the level of the lowest point of the open end of the container, diagonally opposed thereto.

8. A centrifugal separator as claimed in claim 6 or 7, characterised in that the container is frusto-conical in shape and narrower at its open end.

9. A centrifugal separator as claimed in any one of claims 6 to 8, characterised by feed means adapted to introduce a fluid mixture whose constituents are to be separated, into the closed end of the container near the lowest vertical position of the closed end.

10. A centrifugal separator as claimed in any one of claims 4 to 9, characterised in that the container has solid walls.

11. A centrifugal separator as claimed in any one of claims 4 to 9, characterised in that the container is foraminous.

12. A centrifugal separator as claimed in any one of claims 4 to 11, characterised in that the inner surface of the container is roughened and/or has inwardly directed protrusions.

13. A centrifugal separator as claimed in any one of the preceding claims, characterised by collecting means to collect separated constituents of material.

14. A centrifugal separator as claimed in any one of the preceding claims, characterised by a plurality of separating means located in circumferentially spaced relationship about the second offset axis, each separating means being rotatable about the second offset axis and also about its own first axis which is disposed in non-parallel relationship to the second offset axis.

15. A method of separating the constituents of a fluid mixture, including the steps of introducing the mixture into a separating zone and rotating the separating zone about a first axis and simultaneously in planetary fashion about a second offset axis to separate the constituents by centrifugal action, characterised in that the first and second offset axes are disposed in non-parallel relationship to one another and a separated constituent is thrown out of the separating zone under centrifugal action.

16. A method as claimed in claim 15, characterised in that the first axis and the second offset axis intersect one another.

17. A method as claimed in claim 15 or 16, characterised in that the second offset axis is disposed substantially vertically and the first axis is disposed at an acute angle to the vertical.

18. A method as claimed in any one of claims 15 to 17, characterised in that the separating zone is rotated about the first axis in the same sense as it is rotated about the second σfset axis.

19. A method as claimed in any one of claims 15 to 17, characterised in that the separating zone is rotated about the first axis in a different sense from that about the second axis.

Drawing