Separation disc for a centrifugal separator having spacing members with a triangular shape

Abstract

A separation disc for a centrifugal separator is adapted to be included in a stack of separation discs inside a centrifugal rotor for separating a fluid mixture. The separation disc has a truncated conical shape with an inner surface and an outer surface and a plurality of spot-formed spacing members extending from at least one of the inner surface and the outer surface. The spot-formed spacing members are for providing interspaces between mutually adjacent separation discs in a stack of separation discs, and the plurality of spot-formed spacing members are tip-shaped and taper from a base at the surface of the separation disc towards a tip extending a height from the surface. A stack of separation discs, a centrifugal separator and a method for separating at least two components of a fluid mixture are also disclosed.

Claims

1. A separation disc for a centrifugal separator, said disc being adapted to be included in a stack of separation discs inside a centrifugal rotor for separating a fluid mixture, wherein the separation disc comprises: a body having a truncated conical shape with an inner surface and an outer surface, a circumferential direction and a longitudinal direction; and a plurality of spot-formed spacing members extending a height from at least one of the inner surface and the outer surface, the plurality of spot-formed spacing members spaced from each other in the circumferential direction and the longitudinal direction, wherein said plurality of spot-formed spacing members are for providing interspaces between mutually adjacent separation discs in a stack of separation discs, wherein said plurality of spot-formed spacing members have a generally triangular cross-section that tapers from a base at said at least one of the inner surface and the outer surface of the separation disc towards an apex at said height from said at least one of the inner surface and the outer surface, wherein the base of the spot-formed spacing members extend to a width which is less than 5 mm along the surface of the separation disc, and wherein the width is a largest dimension of the spot-formed spacing members.

2. The separation disc according to claim 1, wherein at least one of said inner surface and said outer surface is free of spacing members other than said spot-formed spacing members.

3. The separation disc according to claim 1, wherein the plurality of spot-formed spacing members is integrally formed in one piece with the material of the separation disc.

4. The separation disc according to claim 1, wherein the separation disc has a thickness that is less than 0.5 mm.

5. The separation disc according to claim 1, wherein the separation disc comprises more than 300 of said plurality of spot-formed spacing members.

6. The separation disc according to claim 1, wherein the inner or outer surface has a surface density of said plurality of spot-formed spacing members that is above 25 spacing members/dm2.

7. A stack of separation discs adapted to be comprised inside a centrifugal rotor for separating a liquid mixture, comprising axially aligned separation discs having a truncated conical shape with an inner surface and an outer surface, and wherein said axially aligned separation discs comprise a plurality of discs having spot-formed spacing members according to claim 1.

8. The stack of separation discs according to claim 7, wherein said discs having spot-formed spacing members are arranged so that a majority of said spot-formed spacing members of one of said discs are axially aligned with the spot-formed spacing members of an adjacent disc.

9. A centrifugal separator for separation of at least two components of a fluid mixture which are of different densities, which centrifugal separator comprises: a stationary frame; a spindle rotatably supported by the frame; a centrifuge rotor mounted to a first end of the spindle to rotate together with the spindle around an axis of rotation, wherein the centrifuge rotor comprises a rotor casing enclosing a separation space in which a stack of separation discs is arranged to rotate coaxially with the centrifuge rotor; a separator inlet extending into said separation space for supply of the fluid mixture to be separated; a first separator outlet for discharging a first separated phase from said separation space; and a second separator outlet for discharging a second separated phase from said separation space, wherein the stack of separation discs is as according to claim 7.

10. A method for separating at least two components of a fluid mixture which are of different densities comprising the steps of: providing the centrifugal separator according to claim 9; supplying said fluid mixture which are of different densities via said separator inlet to said separation space; discharging a first separated phase from said separation space via said first separator outlet; and discharging a second separated phase from said separation space via said second separator outlet.

11. The separation disc according to claim 1, wherein a line between an apex of the spacing member and a center of the base is in substantially the axial direction of the truncated conical shape of said separation disc.

12. The separation disc according to claim 1, wherein the generally triangular cross-section is formed by a first side wall extending from the body to a point and a second sidewall extending from the body to the point.

13. A separation disc for a centrifugal separator, said disc being adapted to be included in a stack of separation discs inside a centrifugal rotor for separating a fluid mixture, wherein the separation disc comprises: a body having a truncated conical shape with an inner surface and an outer surface, a circumferential direction and a longitudinal direction; and a plurality of spot-formed spacing members extending a height from at least one of the inner surface and the outer surface, the plurality of spot-formed spacing members spaced from each other in the circumferential direction and the longitudinal direction, wherein said plurality of spot-formed spacing members are for providing interspaces between mutually adjacent separation discs in a stack of separation discs, wherein said plurality of spot-formed spacing members have a generally triangular cross-section that tapers from a base at said at least one of the inner surface and the outer surface of the separation disc towards an apex at said height from said at least one of the inner surface and the outer surface, wherein the base of the spot-formed spacing members extend to a width which is less than 5 mm along the surface of the separation disc, and wherein a base of each of the plurality of spacing members is a circle, an ellipse or a square.

14. A separation disc for a centrifugal separator, said disc being adapted to be included in a stack of separation discs inside a centrifugal rotor for separating a fluid mixture, wherein the separation disc comprises: a body having a truncated conical shape with an inner surface and an outer surface, a circumferential direction and a longitudinal direction; and a plurality of spot-formed spacing members extending a height from at least one of the inner surface and the outer surface, the plurality of spot-formed spacing members spaced from each other in the circumferential direction and the longitudinal direction, wherein said plurality of spot-formed spacing members are for providing interspaces between mutually adjacent separation discs in a stack of separation discs, wherein said plurality of spot-formed spacing members have a generally triangular cross-section that tapers from a base at said at least one of the inner surface and the outer surface of the separation disc towards an apex at said height from said at least one of the inner surface and the outer surface, wherein the base of the spot-formed spacing members extend to a width which is less than 5 mm along the surface of the separation disc, and wherein the tip of said plurality of spot-formed spacing members has a tip radius in a cross-section which is less than the height to which said spot-formed spacing members extend from the surface.

15. A stack of separation discs adapted to be comprised inside a centrifugal rotor for separating a liquid mixture, comprising axially aligned separation discs having a truncated conical shape with an inner surface and an outer surface, and wherein said axially aligned separation discs comprise a plurality of discs having spot-formed spacing members, wherein each of the plurality of disc comprises: a body having a truncated conical shape with an inner surface and an outer surface, a circumferential direction and a longitudinal direction; and a plurality of spot-formed spacing members extending a height from at least one of the inner surface and the outer surface, the plurality of spot-formed spacing members spaced from each other in the circumferential direction and the longitudinal direction, wherein said plurality of spot-formed spacing members are for providing interspaces between mutually adjacent separation discs in a stack of separation discs, wherein said plurality of spot-formed spacing members have a generally triangular cross-section that tapers from a base at said at least one of the inner surface and the outer surface of the separation disc towards an apex at said height from said at least one of the inner surface and the outer surface, wherein the base of the spot-formed spacing members extend to a width which is less than 5 mm along the surface of the separation disc, and wherein said plurality of discs having spot-formed spacing members are arranged so that a majority of said spot-formed spacing members of one of said discs are displaced compared to the spot-formed spacing members of an adjacent disc.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a-c shows an embodiment of a separation disc. FIG. 1a is a perspective view, FIG. 1b is a view from the bottom, i.e. showing the inner surface of the separation disc, and FIG. 1c is a close-up view of the outer periphery of the inner surface.

(2) FIG. 2a-f shows embodiments of different tip-shaped and spot-formed spacing members.

(3) FIG. 3 shows an embodiment of a disc stack.

(4) FIG. 4a-c shows an embodiment of a disc stack in which the spot-formed spacing members of a separation disc are displaced in relation to the spot-formed spacing members of an adjacent disc. FIG. 4a is a perspective view, FIG. 4b is a radial section and FIG. 4c is a close up-view of the inner surface.

(5) FIGS. 5a and b shows an embodiment of a disc stack in which the spot-formed spacing members of a separation disc are axially aligned with the spot-formed spacing members of an adjacent disc. FIG. 5a is a radial section and FIG. 5b is a close up-view of the inner surface.

(6) FIG. 6 shows a cross-section through a centrifugal separator.

(7) FIG. 7 illustrates a method for separating at least two components of a fluid mixture.

DETAILED DESCRIPTION

(8) The separation disc, stack of separation discs and centrifugal separator according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.

(9) FIGS. 1a-c show schematic drawings of an embodiment of a separation disc. FIG. 1a is a perspective view of a separation disc 1 according to an embodiment of the present disclosure. The separation disc 1 has a truncated conical shape, i.e. a frusto-conical shape, along conical axis X1. Axis X1 is thus the direction of the axis passing through the apex of the corresponding conical shape. The conical surface forms cone angle α with conical axis X1. The separation disc has an inner surface 2 and an outer surface 3, extending radially from an inner periphery 6 to an outer periphery 5. In this embodiment, the separation disc is also provided with a number of through holes 7, located at a radial distance from both the inner and outer peripheries. When forming a stack with other separation discs of the same kind, through holes 7 may thus, form axial distribution channels for e.g. liquid mixture to be separated that facilitates even distribution of the liquid mixture throughout a stack of separation discs. The separation disc further comprises a plurality of spot-formed spacing members 4 extending above the inner surface of the separation disc 1. These spacing members 4 provide interspaces between mutually adjacent separation discs in a stack of separation discs. The spot-formed spacing members are tip-shaped and are shown in more detail in FIGS. 2a-2f. As seen in FIG. 1a, only the inner surface 2 is provided with spot-formed spacing members 4, whereas outer surface 3 is free of spot-formed spacing members 4 and also free of other spacing members. Inner surface 2 is also free of other spacing members than the spot-formed spacing members 4. Thus, in a stack of separation discs 1 of the same kind, spot-formed spacing members 4 are the only spacing members, i.e. the only members that form the interspaces and axial distances between discs in the stack. The spot-formed spacing members are thus the only load-bearing element on the disc 1 when discs are axially stacked on top of each other. This is thus a difference from a conventional separation disc, in which a few elongated, radially extending spacing members on each disc form the interspaces and bear the compression forces in a disc stack.

(10) However, as an alternative, it is to be understood that outer surface 3 could be provided with the spot-formed spacing members 4 whereas inner surface 2 could be free of spot-formed spacing members 4 and also free of other spacing members.

(11) FIG. 1b shows the inner surface 2 of the separation disc 1. The diameter D of the disc is in this embodiment about 530 mm, and the spot-formed spacing members 4 extends from a base at the inner surface 2 that has a width that is less than 1.5 mm along the inner surface 2 of the separation disc 1. Furthermore, the mutual distance d1 between the spot-formed spacing members 4 is about 10 mm, and the whole inner surface 2 comprises more than 4000 spot-formed spacing members 4.

(12) There are also a number of cut-outs 13 at the inner periphery 6 of the separation disc 1 in order to facilitate stacking on e.g. a distributor.

(13) FIG. 1c shows a close-up view of the outer periphery 5 of the inner surface 2 of the separation disc 1. In this embodiment, the density of spot-formed spacing members 4 is higher at the outer periphery than on the rest of the disc. This is achieved by having more spot-formed spacing members arranged in an outer peripheral zone P, so that the distance d2 between the radially outermost spacing members 4 within the outer peripheral zone P is less than the distance d1 between spacing members 4 outside this zone. Distance d2 may for example be around 5 mm, if d1 is about 10 mm. The peripheral zone P may for example extend 10 mm radially from the outer periphery 5. A higher density of spacing members at the outermost periphery is advantageous in that it decreases the risk for mutually adjacent discs in a disc stack touching each other at the outermost periphery where the compression and centrifugal forces are high. Mutually adjacent discs touching each other will block the interspace and thus lead to a decreased efficiency of the disc stack.

(14) FIGS. 2a-2f show embodiments of different tip-shaped and spot-formed spacing members. FIG. 2a shows a section of a part of a separation disc 1 in which the spot-formed spacing members 4 are arranged in a line extending in the radial direction on the inner surface 2 of the disc 1. Outer surface 3 is free of any kind of spacing member. The spacing members 4 are integrally formed in the separation disc 1, i.e. formed in one piece with the material of the separation disc itself. The spacing members 4 are tip-shaped and taper from the surface to a tip that extends a certain distance or height from the inner surface 2.

(15) FIG. 2b shows a close-up view of an embodiment of a tip-shaped spacing member 4. The tip-shaped spacing member 4 extends from a base 8 on the inner surface 2. This base 8 extends to a width that is less than 1.5 mm along the inner surface 2 of the separation disc 1. The tip-shaped spacing member tapers from the base 8 to a tip 9 located a distance z2 from the base. Thus, the height of the tip-shaped spacing member is distance z2, which in this case is between 0.15 and 0.30 mm, whereas the thickness of the separation disc, as illustrated by distance z1 in FIG. 2b, is between 0.30 and 0.40 mm. In the example of FIG. 2a, the tip-shaped spacing member 4 extends from base 8 in the direction y1 that is substantially perpendicular to the inner surface 2. Direction y1 is thus parallel to the normal N of the inner surface 2.

(16) FIG. 2c shows an example of a tip-shaped spacing member 4 that extends from the surface of the separation disc in a direction that forms an angle with the surface which is less than 90 degrees. The spacing member 4 of FIG. 2c is the same as the spacing member shown in FIG. 2b, but with the difference that it extends in a direction y2 that forms an angle with the normal N of the inner surface. In this case, the tip-shaped spacing member 4 extends in a direction y2 that forms angle β1 with the inner surface 2, and angle β1 is less than 90 degrees. Thus, tip 9 extends from base 8 in direction γ2 that forms an angle with the surface that is about 60-70°.

(17) FIG. 2d shows a further example of a tip-shaped spacing member 4 that extends from the surface of the separation disc in a direction that forms an angle with the surface which is less than 90 degrees. The spacing member 4 of FIG. 2d is the same as the spacing member shown in FIG. 2c, but with the difference that it extends in a direction γ3 that forms an angle β2 with the inner surface 2 that is less that angle β1 in FIG. 2c. In this example, angle β2 is substantially the same as the alpha angle α of the separation disc 1, i.e. half of the opening angle of the corresponding conical shape of the separation disc. Angle α is thus the angle of the conical portion with conical axis X1 of the separation disc 1. Angle α may be about 35°. In other words, the tip-shaped spacing member 4 extend from the inner surface 2 of the separation disc 1 in substantially the axial direction of the truncated conical shape of the separation disc 1. Thus, in a formed stack of separation discs, a tip extending substantially axially may better adhere to an adjacent disc in the stack, thereby further decreasing the risk for unevenly sized interspaces between the discs as the stack is compressed.

(18) It is to be understood that a majority or all spot-formed and tip-shaped spacing members 4 on a separation disc may extend in the same direction, i.e. a majority or all spot-formed and tip-shaped spacing members 4 on a separation disc may extend in a direction that is substantially perpendicular to the surface, like the example shown in FIG. 2b, or a majority or all spot-formed and tip-shaped spacing members 4 on a separation disc may extend in a direction that forms an angle with the surface, i.e. like the examples shown in FIGS. 2c and 2d. However, the spacing members on a surface may also extend in different directions.

(19) Furthermore, the tip 9 of a tip-shaped and spot-formed spacing member has a tip radius R.sub.tip, and is further shown in more detail in FIG. 2e. This tip radius R.sub.tip is small in order to get as sharp tip as possible. As an example, tip radius R.sub.tip may be less than the height z2 to which the spot-formed spacing member 4 extend from the inner surface 2. Further, tip radius R.sub.tip may be less than half the height z2, such as less than a tenth of the height z2.

(20) FIG. 2f shows an example of a spot-formed spacing member 4 that is tip-shaped in at least one cross-section and has a longitudinal extension in one direction. The spacing member 4 thus forms a ridge on the surface of the separation disc that extends in a direction indicated by arrow A along the surface. The direction A may be the radial direction of the separation disc. The direction A may be along the direction of the flow on the separation disc when used in a centrifugal separator. The tip 9 of the spot-formed spacing member 4 may have a longitudinal extension along the direction A of substantially the same length as the base 8 of the spot-formed spacing member 4 arranged on the surface (not shown) of the separation disc. Alternatively, the tip 9 of the spot-formed spacing member 4 may have a longitudinal extension along the direction A, which is shorter than the length of the base 8 of the spot-formed spacing member 4 arranged on the surface (not shown) of the separation disc.

(21) The dimensions as discussed above related to the width of the base 8 of the spot-formed spacing member 4, also apply to the width of the spot-formed spacing member 4 along the direction A in the embodiments of FIG. 2f. The width along direction A may be the same as, or differ from the distance across direction A. Thus, according to embodiments the width of the base 8 may be less than 5 mm along the surface of the separation disc. As an example, the base 8 of the spot-formed spacing member may extend to a width 8 which is less than 2 mm along the surface of the separation disc, such as to a width which is less than 1.5 mm along the surface of the separation disc, such as to a width which is about or less than 1 mm along the surface of the disc.

(22) FIG. 3 shows an embodiment of a disc stack 10 according to the present disclosure. The disc stack 10 comprises separation discs 1 provided on a distributor 11. For clarity, FIG. 3 only shows a few separation discs 1, but it is to be understood that the disc stack 10 may comprise more than 100 separation discs 1, such as more than 300 separation discs. Due to the tip-shaped and spot-formed spacing members, interspaces 28 are formed between stacked separation discs 1, i.e. interspaces 28 is formed between a separation disc 1a and the adjacent separation discs 1b and 1c located below and above separation disc 1a, respectively. Through holes in the separation discs form axial rising channels 7a extending throughout the stack. Furthermore, the disc stack 10 may comprise a top disc (not shown), i.e. a disc arranged at the very top of the stack that is not provided with any through holes. Such a top disc is known in the art. The top disc may have a diameter that is larger than the other separation discs 1 in the disc stack in order to aid in guiding a separated phase out of a centrifugal separator. A top disc may further have a larger thickness as compared to the rest of the separation discs 1 of the disc stack 10. The separation discs 1 may be provided on the distributor 11 using cut outs 13 at the inner periphery 6 of the separation discs 10 that are fitted in corresponding wings 12 of the distributor.

(23) FIGS. 4a-c show an embodiment in which the separation discs 1 are axially arranged in the stack 10 so that a majority of the spot-formed and tip-shaped spacing members 4a of a disc 1a are displaced compared to the spot-formed and tip-shaped spacing members 4b of an adjacent disc 1b. In this embodiment, this is performed by a small rotation in the circumferential direction of disc 1a as compared to adjacent disc 1b, as illustrated by arrow “A” in FIGS. 4a and 4c. Thus, as seen in FIG. 4a, adjacent separation discs 1a and 1b are axially aligned along rotational axis X2, which is the same direction as conical axis X1 as seen in FIGS. 1 and 2, but due to the arrangement of the spot-formed and tip-shaped spacing members, a spot-formed and tip-shaped spacing member 4a of separation disc 1a is not axially aligned over corresponding spot-formed and tip-shaped spacing member 4b of separation disc 1b. As an example, the discs 1a and 1b are arranged so that a spot-formed and tip-shaped spacing member 4a of disc 1a is displaced a circumferential distance z3 in relation to corresponding spot-formed and tip-shaped spacing member 4b of disc 1b. Distance z3 may be about half the distance of the mutual distance between spot-formed and tip-shaped spacing members on a disc, such as between 2-10 mm.

(24) In other words, the separation discs of the disc stack 1 are arranged so that a spot-formed and tip-shaped spacing member 4a of a separation disc 1a does not abut adjacent disc 1b at a position where the adjacent disc 1b has spot-formed and tip-shaped spacing member 4b. This is also illustrated in FIG. 4b, which shows a section of adjacent discs 1a and 1b. The spot-formed and tip-shaped spacing members 4a of disc 1a and the spot-formed and tip-shaped spacing members 4b of disc 1b may be provided at the same radial distance, but are shifted in the circumferential direction. Furthermore, FIG. 4c shows a close-up view of the outer periphery 5 of disc 1b. The spot-formed and tip-shaped spacing members 4a of adjacent disc 1a abut separation disc 1b at positions indicated by crosses in FIG. 4c, which are positions that are shifted in the circumferential direction as compared to the positions of the spot-formed and tip-shaped spacing members 4b, as illustrated by arrow “A”.

(25) However, the separation discs 1 of the disc stack 10 may be provided on the distributor 11 so that a majority of the spot-formed and tip-shaped spacing members of a disc are axially aligned with the spot-formed and tip-shaped spacing members of an adjacent disc, as in a conventional disc stack having elongated radial spacing members. This is illustrated in FIGS. 5a and 5b, in which adjacent separation discs 1a and 1b are provided so that the spot-formed and tip-shaped spacing members 4a of disc 1a are aligned with the spot-formed and tip-shaped spacing members 4b of disc 1b. FIG. 5a, shows a section of adjacent discs 1a and 1b in which spacing members 4a and 4b are aligned, whereas FIG. 5b shows a close-up view of the outer periphery 5 of disc 1b. In contrast to the embodiment illustrated in FIG. 4c, the spot-formed and tip-shaped spacing members 4a of adjacent disc 1a actually abut separation disc 1b at the positions of the spot-formed and tip-shaped spacing members 4b of discs 1b, as indicated by the crosses in FIG. 5b.

(26) FIG. 6 shows a schematic example of a centrifugal separator 14 according to an embodiment of the present disclosure, arranged to separate a liquid mixture into at least 2 phases.

(27) The centrifugal separator 14 comprises a rotating part arranged for rotation about an axis of rotation (X2) and comprises rotor 17 and spindle 16. The spindle 16 is supported in a stationary frame 15 of the centrifugal separator 14 in a bottom bearing 24 and a top bearing 23. The stationary frame 15 surrounds rotor 17.

(28) The rotor 17 forms within itself a separation chamber 18 in which centrifugal separation of e.g. a liquid mixture takes place during operation. The separation chamber 18 may also be referred to as a separation space 18.

(29) The separation chamber 18 is provided with a stack 10 of frusto-conical separation discs 1 in order to achieve effective separation of the fluid to be separated. The stack 10 of truncated conical separation discs 1 are examples of surface-enlarging inserts. These discs 1 are fitted centrally and coaxially with the rotor 17 and also comprise through holes which form axial channels 25 for axial flow of liquid when the separation discs 9 are fitted in the centrifugal separator 1. The separation discs 1 and stack 10 are as discussed in relation to any embodiment shown in FIGS. 1-4 above. In FIG. 6, only a few discs 1 are illustrated in the stack 10, and the stack may comprise more than 100 separation discs 1, such as more than 200 separation discs, such as more than 300 separation discs.

(30) The centrifugal separator 14 is in this case fed from the top via stationary inlet pipe 19, which thus forms an inlet channel for introducing e.g. a liquid mixture for centrifugal separation to the separation space 18 of the centrifugal separator. The inlet channel may also be referred to as a separator inlet. Liquid material to be separated may be transported to a central duct in the distributor 11, e.g. by means of a pump (not shown). Such a pump may be arranged to supply liquid material to be separated with a flow rate of above 60 m.sup.3/hour, such as above 70 m.sup.3/hour to the inlet pipe 19 of the centrifugal separator 14.

(31) The rotor 17 has extending from it a liquid light phase outlet 20 for a lower density component separated from the liquid, and a liquid heavy phase outlet 21 for a higher density component, or heavy phase, separated from the liquid. The outlets 20 and 21 extend through the frame 15. The outlets 20, 21 may also be referred to as separator outlets 20, 21. Further, centripetal pumps, such as paring discs, may be arranged at outlets 20 and 21 to aid in transporting separated phases out from the separator.

(32) However, the centrifugal separator 14 may also be of a so-called hermetic type with a closed separation space 18, i.e. the separation space 18 may be intended to be completely filled with liquid during operation. In principle, this means that preferably no air or free liquid surfaces is meant to be present within the rotor 17. This means that also the inlet 19 and the outlets 20 and 21 may be mechanically hermetically sealed to reduce the risk of oxygen or air getting into the separation space and contact the liquid to be separated.

(33) The rotor 17 is further provided at its outer periphery with a set of radially sludge outlets 22 in the form of intermittently openable outlets for discharge of higher density component such as sludge or other solids in the liquid. This material is thus discharged from a radially outer portion of the separation chamber 18 to the space around the rotor 17.

(34) The centrifugal separator 14 is further provided with a drive motor 25. This motor 25 may for example comprise a stationary element 26 and a rotatable element 27, which rotatable element 27 surrounds and is so connected to the spindle 16 that during operation it transmits driving torque to the spindle 16 and hence to the rotor 17. The drive motor 25 may thus be an electric motor. Furthermore, the drive motor 25 may be connected to the spindle 16 by transmission means. The transmission means may be in the form of a worm gear which comprises a pinion and an element connected to the spindle 16 in order to receive driving torque. The transmission means may alternatively take the form of a propeller shaft, drive belts or the like, and the drive motor may alternatively be connected directly to the spindle.

(35) During operation of the separator in FIG. 6, the rotor 17 is caused to rotate by torque transmitted from the drive motor 25 to the spindle 16. Via the stationary inlet pipe 19, liquid mixture to be separated is brought into the separation space 18. The liquid mixture to be separated, i.e. the feed, may be introduced when the rotor is already running at its operational speed. Liquid material may thus be continuously introduced into the rotor 17.

(36) Depending on the density, different phases in the liquid is separated in the interspaces 28 between the separation discs 1 of the stack 10 fitted in the separation space 18. Heavier components in the liquid move radially outwards between the separation discs, whereas the phase of lowest density moves radially inwards between the separation discs and is forced through outlet 20 arranged at the radial innermost level in the separator. The liquid of higher density is instead forced out through outlet 21 that is at a radial distance that is larger than the radial level of outlet 20. Thus, during separation, an interphase between the liquid of lower density and the liquid of higher density is formed in the separation space 18. Solids, or sludge, accumulate at the periphery of the separation chamber 18 and is emptied intermittently from the separation space by the sludge outlets 22 being opened, whereupon sludge and a certain amount of fluid is discharged from the separation space by means of centrifugal force. However, the discharge of sludge may alternatively take place continuously, in which case the sludge outlets 22 take the form of open nozzles and a certain flow of sludge and/or heavy phase is discharged continuously by means of centrifugal force.

(37) In certain applications, the separator 14 only contains a single liquid outlet, such as only liquid outlet 20, and the sludge outlets 22. This depends on the liquid material that is to be processed.

(38) In the embodiment of FIG. 6, the liquid mixture to be separated is introduced from above via a stationary pipe 19. However, the liquid mixture to be separated may as an alternative be introduced from below via a central duct arranged in spindle 16. However, such a hollow spindle may also be used for withdrawing e.g. the liquid light phase and/or the liquid heavy phase. As an example, the spindle 16 may be hollow and comprise a central duct and at least one additional duct. In this way, the liquid mixture to be separated may be introduced to the rotor 17 via a central duct arranged in the spindle 16, and concurrently the liquid light phase and/or the liquid heavy phase may be withdrawn through the additional duct in the spindle 16.

(39) The centrifugal separator 14 may be arranged to separate milk into cream and skimmed milk.

(40) FIG. 7 illustrates a method 100 for separating at least two components of a fluid mixture which are of different densities comprising the steps of: providing 102 a centrifugal separator 14 according to any of aspects and/or embodiments discussed herein, supplying 104 the fluid mixture which are of different densities via the separator inlet 19 to the separation space 18; discharging 106 a first separated phase from the separation space 18 via the first separator outlet 20; and discharging 108 a second separated phase from the separation space via the second separator outlet 21.

(41) The invention is not limited to the embodiment disclosed but may be varied and modified within the scope of the claims set out below. The invention is not limited to the type of separator as shown in the Figures. The term “centrifugal separator” also comprises centrifugal separators with a substantially horizontally oriented axis of rotation and separator having a single liquid outlet.