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 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. The separation disc further includes at least one elongated rib extending from the inner surface to a height (h) that is less than the height (H) to which the plurality of spacing members extend. Further, at least one elongated rib extends from first position on the inner surface to a second position on the inner surface. The second position is at a radial distance that is larger than the radial distance of the first position, and the relation between the height of the elongated ribs (h) and the spacing members (H) are h/H>0.7.
Claims
1. A separation disc for a centrifugal separator, said disc being adapted to be comprised in a stack of separation discs inside a centrifugal rotor for separating a fluid mixture, wherein the separation disc has a truncated conical shape with an inner surface and an outer surface and a plurality of spacing members extending a first height (H) from at least one of the inner surface and the outer surface, wherein said plurality of spacing members are for providing interspaces between mutually adjacent separation discs in the stack of separation discs, wherein said separation disc further comprises at least one elongated rib extending from the inner surface to a second height (h) that is less than the first height (H) to which said plurality of spacing members extend, wherein said at least one elongated rib extends from a first position on the inner surface to a second position on the inner surface, wherein the second position is at a radial distance that is larger than a radial distance of the first position, and wherein a relation between the second height of the elongated ribs (h) and the first height of the spacing members (H) is h/H≥0.7.
2. The separation disc according to claim 1, wherein the relation between the second height of the elongated ribs (h) and the first height of the spacing members (H) is 0.75≤h/H≤0.95.
3. The separation disc according to claim 1, wherein said spacing members extend from the inner surface.
4. The separation disc according to claim 1, wherein said separation disc comprises at least four elongated ribs.
5. The separation disc according to claim 1, wherein said at least one elongated rib is straight and extends in the radial direction.
6. The separation disc according to claim 1, wherein said at least one elongated rib is curved.
7. The separation disc according to claim 1, wherein said at least one elongated rib extends a length that is more than 50% of the radial extension of the inner surface of the disc.
8. The separation disc according to claim 7, wherein said at least one elongated rib extends radially along substantially an entire radial extension of the inner surface of the disc.
9. The separation disc according to claim 1, wherein said at least one elongated rib has a width at the inner surface of the separation disc that is below 2 mm.
10. The separation disc according to claim 1, wherein said spacing members and said at least one elongated rib are integrally formed in one piece with the material of the separation disc.
11. The separation disc according to claim 1, wherein said at least one elongated rib is wider at the inner surface of the separation disc than at a portion at the second height (h) to which the elongated rib extends, when viewed in a cross-section that is perpendicular to the direction in which the elongated rib extends on the inner surface.
12. The separation disc according to claim 1, wherein said plurality of spacing members comprises a plurality of spot-formed spacing members.
13. The separation disc according to claim 12, wherein said spot-formed spacing members have a tip-shaped cross-section.
14. 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, wherein said axially aligned separation discs comprise a plurality of discs having the spacing members and the at least one elongated rib according to claim 1 arranged so that said elongated rib on a separation disc is not in contact with an adjacent separation disc.
15. A centrifugal separator for separation of at least two components of a fluid mixture having different densities, said centrifugal separator comprising: 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 (X) 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 the stack of separation discs according to claim 14.
16. The separation disc according to claim 2, wherein said spacing members extend from the inner surface.
17. The separation disc according to claim 2, wherein said separation disc comprises at least four elongated ribs.
18. The separation disc according to claim 1, wherein the relation between the second height of the elongated ribs (h) and the first height of the spacing members (H) is 0.80≤h/H≤0.90.
19. The separation disc according to claim 1, wherein the elongated ribs are spaced from the spacing members in a circumferential direction.
20. The separation disc according to claim 1, wherein the second height of the elongated ribs is less than the first height of the spacing members.
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-d shows further embodiments of separation discs having elongated ribs.
(3) FIG. 3a-c show embodiments of different shapes of elongated ribs.
(4) FIG. 4a-f shows embodiments of different tip-shaped and spot-formed spacing members.
(5) FIG. 5 shows the relation between spacing members and elongated ribs.
(6) FIG. 6a-d shows different spot-formed and tip-shaped spacing members.
(7) FIG. 7 shows an embodiment of a disc stack.
(8) FIG. 8a-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. 8a is a perspective view, FIG. 8b is a radial section and FIG. 8c is a close up-view of the inner surface.
(9) FIGS. 9a 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. 9a is a radial section and FIG. 9b is a close up-view of the inner surface.
(10) FIG. 10 shows a section of a centrifugal separator.
DETAILED DESCRIPTION
(11) Examples of separation discs, stacks of separation discs as well as a centrifugal separator according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.
(12) FIGS. 1a-c shows a schematic drawing 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. Examples of spot-formed spacing members are shown in more detail in FIGS. 4a-4f. 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.
(13) 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.
(14) FIG. 1b shows the inner surface 2 of the separation disc 1. 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 about 100 spacing members/dm.sup.2. The inner surface 2 further comprises six elongated ribs that extend radially from the inner periphery out to the outer periphery of the separation disc. Thus, the inner periphery represents a first position and the outer periphery represents a second position at a radial distance that is larger than the radial distance of the first position. The elongated ribs 36 are lesser in height than the spot-formed spacing members and thus do not contribute in forming the interspaces in a stack of separation discs.
(15) 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.
(16) 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. 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.
(17) FIG. 2a-d show different variations of the disc as seen in FIG. 1a-c. In FIG. 2a, the elongated ribs are of lesser length and extend on the inner surface all the way to the outer periphery but start at a radial position so that a radial inner portion 41 of the separation disc 1 is free of elongated ribs. In FIG. 2b, the elongated ribs 36 are curved. FIG. 2c shows an example of a disc having 12 elongated ribs arranged on the inner surface, each extending straight in the radial direction. However, as discussed above, the ribs may be straight but extend in a direction that forms an angle to the radial direction. FIG. 2d shows an embodiment of a separation disc 1 having shorter ribs, i.e. ribs that extend a shorter distance in the radial direction, than the previous examples. The ribs 36 extend from a first position 39 being other than the inner periphery and at to a second position 40 that is radially inward compared to the outer periphery.
(18) FIGS. 3a-c shows different examples on the shape of the ribs 36. The ribs 36 in FIGS. 3a-c are not drawn to scale, but merely represents a schematic drawing of the shape. The rib 36 of FIG. 3a extends a distance L along the surface of the separation disc. L may be about 50-250 mm. The rib 36 extends a height h from the surface and has further width w at the surface. The width w is thus the width at the base portion 37 of the rib 36. The width w may for example be less than 20 mm, such as about or less than 10 mm. The height h may for example be between 0.20-0.40 mm. The width w at the surface is wider than the width at the outermost portion 38 of the rib 36, i.e. at height h from the surface. Thus, the elongated rib tapers from the surface outwards to the outermost portion 38. In FIG. 3a, the cross-section perpendicular to the direction in which the rib 36 is extends is tip-shaped with a sharp tip. In FIG. 3b, the rib also tapers from the base portion 37 to the outermost portion 38, but the outermost portion is flat with a surface substantially parallel to the base portion 37, i.e. parallel to the surface of the disc. In FIG. 3c, the rib 36 also tapers from the surface but the cross-section perpendicular to the direction in which the rib 36 is extends is tip-shaped with a more smooth, rounded tip than the cross-section of the rib 36 of FIG. 3a.
(19) FIGS. 4a-f show embodiments of different types of spot-formed spacing members that may be used as spacing members on the separation disc of the present disclosure. FIG. 4a 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. FIG. 4b shows a similar section as the disc of FIG. 4a, but in this example the tip-shaped and spot-formed spacing members are only provided on the outer surface 3, whereas inner surface 2 is free of spot-formed spacing members.
(20) FIG. 4c also shows a section of a part of another example 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 whereas outer surface 3 is free of any kind of spacing member. The spacing members 4 are in this example shaped as half-spheres that protrude from the inner surface 2. FIG. 4d shows a similar section as the disc of FIG. 4c, but in this example the half-spherical and spot-formed spacing members are only provided on the outer surface 3, whereas inner surface 2 is free of spot-formed spacing members.
(21) FIG. 4e also shows a section of a part of another example 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 whereas outer surface 3 is free of any kind of spacing member. The spacing members 4 are in this example shaped as cylinders that protrude from the inner surface 2. FIG. 4f shows a similar section as the disc of FIG. 4e, but in this example the cylindrical and spot-formed spacing members are only provided on the outer surface 3, whereas inner surface 2 is free of spot-formed spacing members.
(22) FIG. 5 shows the relation in height between an elongated rib 36 and the spacing members 4. The disc as seen in FIG. 5 is a similar to the disc in FIG. 4a, having spot-formed and tip-shaped spacing members 4 that extend a height H from the inner surface 2. Also drawn in FIG. 5 is the size of an elongated rib 36 that extends height h from the surface. The relation between h and H is that H is larger than h and h/H>0.7, i.e. the elongated ribs 36 do not bear any weight in a compressed stack of separation discs 1.
(23) FIGS. 6a-d show embodiments of different tip-shaped and spot-formed spacing members that may be used on the separation disc of the present disclosure, FIG. 6a 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 H from the base. Thus, the height of the tip-shaped spacing member is distance H, which in this case is between 0.15 and 0.30 mm, whereas the thickness of the separation disc, as illustrated by distance z in FIG. 6b, is between 0.30 and 0.40 mm. In the example of FIG. 6a, 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.
(24) FIG. 6b 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. 6b is the same as the spacing member shown in FIG. 6a, 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 y2 that forms an angle with the surface that is about 60-70°.
(25) FIG. 6c 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. 6c is the same as the spacing member shown in FIG. 6b, but with the difference that it extends in a direction y3 that forms an angle β2 with the inner surface that is less than angle β1 in FIG. 6b. 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 extends 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 spot-formed spacing member 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.
(26) It is to be understood that a majority or all spot-formed spacing members 4 on a separation disc may extend in the same direction, i.e. a majority or all spot-formed spacing members 4 on a separation disc may extend in a direction that is substantially perpendicular to the surface 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. 6b and 6c.
(27) 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. 6d. 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 H 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 H, such as less than a tenth of the height H.
(28) FIG. 7 shows an embodiment of a disc stack 10 comprising separation discs 1 according to the present disclosure. The disc stack 10 comprises separation discs 1 provided on a distributor 11. For clarity, FIG. 7 only shows a few separation discs 1, but it is to be understood that the disc stack 10 may comprise more than 200 separation discs 1, such as more than 300 separation discs. Due to the spacing members, interspaces 28 are formed between stacked separation discs 1, i.e. interspace 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 5 of the separation discs 10 that are fitted in corresponding wings 12 of the distributor.
(29) FIGS. 8a-c shows an embodiment in which the separation discs 1 comprises spot formed spacing members. The separation discs 1 are axially arranged in the stack 10 so that a majority of the spot-formed spacing members 4a of a disc 1a are displaced compared to the spot-formed and 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. 8a-c. Thus, as seen in FIG. 8a, 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 spacing members, a spot-formed spacing member 4a of separation disc 1a is not axially aligned over corresponding spot-formed spacing member 4b of separation disc 1b. As an example, the discs 1a and 1b are arranged so that a spot-formed spacing member 4a of disc 1a is displaced a circumferential distance z3 in relation to corresponding spot-formed spacing member 4b of disc 1b. Distance z3 may be about half the distance of the mutual distance between spot-formed spacing members on a disc, such as between 2-10 mm.
(30) In other words, the separation discs of the disc stack 1 are arranged so that a spot-formed and 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 spacing member 4b. This is also illustrated in FIG. 8b, which shows a section of adjacent discs 1a and 1b. The spot-formed spacing members 4a of disc 1a and the spot-formed spacing members 4b of disc 1b may be provided at the same radial distance, but are shifted in the circumferential direction. Furthermore, FIG. 8c shows a close-up view of the outer periphery 5 of disc 1b. The spot-formed members 4a of adjacent disc 1a abut separation disc 1b at positions indicated by crosses in FIG. 8c, which are positions that are shifted in the circumferential direction as compared to the positions of the spot-formed spacing members 4b, as illustrated by arrow “A”.
(31) However, the separation discs 1 of the disc stack 10 may be provided on the distributor 11 so that a majority of the spacing members of a disc are axially aligned with the 8 spacing members of an adjacent disc. This is illustrated in FIGS. 9a and 9b, in which adjacent separation discs 1a and 1b are arranged so that spot-formed spacing members 4a of disc 1a are aligned with the spot-formed spacing members 4b of disc 1b. FIG. 9a shows a section of adjacent discs 1a and 1b in which spacing members 4a and 4b are aligned, whereas FIG. 9b shows a close-up view of the outer periphery 5 of disc 1b. In contrast to the embodiment illustrated in FIG. 8c, the spot-formed spacing members 4a of adjacent disc 1a actually abut separation disc 1b at the positions of the spot-formed spacing members 4b of discs 1b, as indicated by the crosses in FIG. 9b.
(32) FIG. 10 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 two phases. Further, it is to be understood that FIG. 10 is a schematic drawing and is thus not drawn into scale.
(33) 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.
(34) The rotor 17 forms within itself a separation chamber 18 in which centrifugal separation of e.g. a liquid mixture to takes place during operation. The separation chamber 18 may also be referred to as a separation space 18.
(35) 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 in the interspaces 28 between the discs 1. 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 1 are fitted in the centrifugal separator 14. The separation discs 1 are as discussed in the examples above and comprises both spot-formed spacing members and elongated ribs integrally formed on the inner surface of each disc.
(36) In FIG. 10, only a few discs 1 are illustrated in the stack 10, and the stack comprises in this case more than 200 separation discs having spot-formed spacing members.
(37) The rotor 17 has extending from it a liquid light phase outlet 33 for a lower density component separated from the liquid mixture, and a liquid heavy phase outlet 34 for a higher density component, or heavy phase, separated from the liquid mixture. The outlets 33 and 34 extend through the frame 15. The outlets 33, 34 may also be referred to as separator outlets 33, 34. In certain applications, the separator 14 only contains a single liquid outlet, such as only liquid outlet 33. This depends on the liquid material that is to be processed. The rotor 15 is further provided with a third outlet for discharge of sludge that has accumulated at the periphery of the separation chamber 18. The sludge outlet is in the form of a plurality of peripheral ports 19 that extend from the separation chamber 18 through the rotor casing to a surrounding space 20 outside the centrifuge rotor 17. The peripheral ports 19 may be intermittently openable during a short time period, e.g. in the order of milliseconds, and permit total or partial discharge of sludge from the separation space, using a conventional intermittent discharge system as known in the art.
(38) The centrifugal separator 1 is further provided with a drive motor 21. This motor 21 may for example comprise a stationary element 22 and a rotatable element 26, which rotatable element surrounds and is connected to the spindle 16 such that it transmits driving torque to the spindle 16 and hence to the rotor 17 during operation. The drive motor 21 may be an electric motor. Furthermore, the drive motor 21 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.
(39) A central duct 27 extends through the spindle 16, which takes the form of a hollow, tubular member. The central duct 27 forms in this embodiment an inlet duct for supplying the liquid mixture for centrifugal separation to the separation space 18 via the inlet 29 of the rotor 17. The inlet duct may also be referred to as a separator inlet. Introducing the liquid material from the bottom provides a gentle acceleration of the liquid material. The spindle 16 is further connected to a stationary inlet pipe 30 at the bottom end of the spindle 16 such that liquid material to be separated may be transported to the central duct 27 by transporting means.
(40) A first mechanical hermetic seal 32 is arranged at the bottom end of the spindle 16 to seal the hollow spindle 16 to the stationary inlet pipe 30. The hermetic seal 32 is an annular seal that surrounds the bottom end of the spindle 16 and the stationary pipe 30. Further, also the liquid light phase outlet 33 and the liquid heavy phase outlet 34 may be hermetically mechanically sealed. As an alternative, centripetal pumps, such as paring discs, may be arranged at outlets 33 and 34 to aid in transporting separated phases out from the separator.
(41) During operation of the separator in FIG. 10, the rotor 17 is caused to rotate by torque transmitted from the drive motor 21 to the spindle 16. Via the central duct 27 of the spindle 16, liquid material to be separated, such as milk, is brought into the disc stack 10 via inlet 29 and axial rising channels 25. In the hermetic type of inlet 29, the acceleration of the liquid material is initiated at a small radius and is gradually increased while the liquid leaves the inlet and enters the separation chamber 18 and disc stack 10. Further, as discussed above, the separator 14 may also have hermetic outlets and the separation chamber 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. However, liquid may also be introduced when the rotor is already running at its operational speed. Liquid material may thus be continuously introduced into the rotor 17.
(42) The path of the liquid material to be separated through the spindle 16 to the separation space 18 is illustrated by arrows “B” in FIG. 10.
(43) Depending on the density, different phases in the liquid is separated in the interspaces 28 between the separation discs 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 33 arranged at the radial innermost level in the separator. The liquid of higher density is instead forced out through outlet 34 that is at a radial distance that is larger than the radial level of outlet 33. 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 space 18 and may be emptied intermittently from the separation space by opening of sludge outlets, i.e. the peripheral ports 19, whereupon sludge and a certain amount of liquid is discharged from the separation space by means of centrifugal force. The opening and closing of the peripheral ports 19 are controlled by means of a sliding bowl bottom 35 which is movable between an open and closed position along a direction parallel to the axis of rotation (X2).
(44) In the embodiment of FIG. 10, the material to be separated is introduced via the central duct 27 of the spindle 16. However, the central duct 27 may also be used for withdrawing e.g. the liquid light phase and/or the liquid heavy phase. Thus, in embodiments, the central duct 27 comprises at least one additional duct, i.e. at least two ducts. In this way, the liquid mixture to be separated may be introduced to the rotor 17 via a central duct 27, and concurrently, the liquid light phase and/or the liquid heavy phase may be withdrawn through such an additional duct extending e.g. within the central duct 27 or surrounding central duct 27.
(45) The invention is not limited to the embodiments 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.
