A CENTRIFUGAL SEPARATOR FOR CLEANING GAS

Abstract

A centrifugal separator for cleaning gas containing contaminants includes a stationary casing, a gas inlet, a rotating member including a plurality of separation members, a gas outlet, a drainage outlet arranged in the lower portion of the stationary casing and a drive member for rotating the rotating member. The axial inner side surface of the stationary casing incudes at least one straight recess extending in the axial direction for accumulating oil that has been separated in the plurality of separation members. The at least one recess includes a first radial recess surface extending from the axial inner side surface of the stationary casing. The at least one recess extends axially on the inner side surface at least along the axial length of the radially outermost portion of the separation members.

Claims

1. A centrifugal separator for cleaning gas containing contaminants comprising: a stationary casing, enclosing a separation space through which a gas flow is permitted; a gas inlet extending through the stationary casing and permitting supply of the gas to be cleaned; a rotating member comprising a plurality of separation members arranged in said separation space and being arranged to rotate around an axis of rotation, a gas outlet arranged in an upper portion of the stationary casing and configured to permit discharge of cleaned gas and comprising an outlet opening through a wall of the stationary casing; a drainage outlet arranged in a lower portion of the stationary casing and configured to permit discharge of liquid contaminants separated from the gas to be cleaned; and a drive member for rotating the rotating member, wherein an axial inner side surface of the stationary casing comprises at least one straight recess extending in an axial direction for accumulating oil that has been separated in said plurality of separation members, wherein said at least one recess comprises a first radial recess surface extending from the axial inner side surface of the stationary casing, and wherein said at least one recess extends axially on the inner side surface at least along an axial length of a radially outermost portion of said separation plurality of members.

2. The centrifugal separator according to claim 1, wherein the axial inner side surface comprises at least one rib extending axially alongside said at least one recess.

3. The centrifugal separator according to claim 2, wherein said at least one rib extends axially adjacent to said first radial recess surface.

4. The centrifugal separator according to claim 3, wherein the first radial recess surface also forms a portion of the at least one rib.

5. The centrifugal separator according to claim 1, wherein an inner area of the at least one recess is less than half of an area of a total axial inner side surface of the stationary casing.

6. The centrifugal separator according to claim 1, wherein the axial inner side surface of the stationary casing comprises at least three recesses.

7. The centrifugal separator according to claim 1, wherein said at least one recess extends axially down to a bottom of the stationary casing.

8. The centrifugal separator according to claim 1, wherein the plurality of separation members is a stack of separation discs.

9. The centrifugal separator according to claim 1, wherein the at least one recess extends along a whole axial length of the axial inner side surface.

10. The centrifugal separator according to claim 1, wherein said at least one recess has a tip-shaped cross-section as seen in a radial plane such that the cross-section of the recess tapers from a radial inner position to a radial outer position.

11. The centrifugal separator according to claim 10, wherein said tip-shaped cross-section of the recess is formed by said first radial recess surface extending from the axial inner side surface of the stationary casing and a second recess surface forming an angle with a radial direction.

12. The centrifugal separator according to claim 3, wherein said at least one rib and an adjacent of said at least one recess form a Z-shaped cross-section in a radial plane.

13. The centrifugal separator according to claim 1, wherein the gas inlet is arranged at the upper portion of the stationary casing.

14. The centrifugal separator according to claim 13, wherein the plurality of separation members is a stack of separation discs, and wherein the gas inlet is arranged to guide the gas into a central space of the stack of separation discs axially from above, and wherein said centrifugal separator comprises a guiding member for guiding the gas, liquid oil and larger aerosols from the central space of the disc stack to interspaces between the discs of the disc stack at an axial entry position that is below an uppermost axial position of the disc stack.

15. The centrifugal separator according to claim 14, wherein the guiding member is arranged to guide the gas at an axial entry position that is below an upper 25% of a total axial length of the disc stack.

16. The centrifugal separator according to claim 14, wherein the guiding member is in the form of a cylindrical collar arranged in the central space of the disc stack for bringing the gas axially downwards in the central space of the disc stack.

17. The centrifugal separator according to claim 16, wherein said disc stack is arranged axially under a top disc and said collar extends axially down from an inner radius of said top disc.

18. The centrifugal separator according to claim 1, wherein the axial inner side surface of the stationary casing comprises at least five recesses.

19. The centrifugal separator according to claim 2, wherein an inner area of the at least one recess is less than half of an area of a total axial inner side surface of the stationary casing.

20. The centrifugal separator according to claim 3, wherein an inner area of the at least one recess is less than half of an area of a total axial inner side surface of the stationary casing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.

[0092] FIG. 1 shows a schematic drawing of a centrifugal separator for cleaning gas.

[0093] FIG. 2 shows a schematic drawing of the cross-section in the radial plane of the stationary casing.

[0094] FIG. 3a shows a close-up view of the cross-section of a single recess.

[0095] FIG. 3b shows a close-up view of the cross-section of a single recess with an adjacent rib.

[0096] FIG. 3c shows a further close-up view of the cross-section of a single recess with an adjacent rib.

[0097] FIG. 3d shows a schematic drawing of a portion of the inner side surface 4a.

[0098] FIG. 4 shows a close-up view of a portion of the centrifugal separator of FIG. 1.

DETAILED DESCRIPTION

[0099] The centrifugal separator according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.

[0100] FIG. 1 shows a section of a centrifugal separator 1 according to the present disclosure. The centrifugal separator 1 comprises a stationary casing 2, which is configured to be mounted to a combustion engine (not disclosed), especially a diesel engine, at a suitable position, such as on top of the combustion engine or at the side of the combustion engine.

[0101] It is to be noted that the centrifugal separator 1 is also suitable for cleaning gases from other sources than combustion engines, for instance the environment of machine tools which frequently contains large amounts of liquid contaminants in the form of oil droplets or oil mist.

[0102] The stationary casing 2 encloses a separation space 3 through which a gas flow is permitted. The stationary casing 2 comprises, or is formed by, a surrounding side wall 4, an upper end wall 5 and a lower end wall 6

[0103] The centrifugal separator comprises a rotating member 7, which is arranged to rotate around an axis (X) of rotation. It should be noted that the stationary casing 2 is stationary in relation to the rotating member 7, and preferably in relation to the combustion engine to which it may be mounted.

[0104] The stationary casing 2 has a radius from the axis (X) of rotation to the surrounding side wall 4 that is constant at least with respect to a major part of the circumference of the surrounding side wall 4. The surrounding side wall 4 thus has a circular, or substantially, circular cross-section.

[0105] The rotating member 7 comprises a spindle 8 and a stack of separation discs 9 attached to the spindle 8. All the separation discs of the stack 9 are provided between a top disc 10 and a lower end plate 11.

[0106] The spindle 8, and thus the rotating member 7, is rotatably supported in the stationary casing 2 by means of an upper bearing 12 and a lower bearing 13, the bearings being arranged one on each side of the stack of separation discs 9. The upper bearing 12 is supported by a cap 19 which by a cylindrical part surrounds an upper end portion of the centrifugal rotor shaft, i.e. the spindle 8, the upper end portion being situated axially above the upper bearing 12. The gas inlet 20 is formed by through holes between the cap 19 and stationary inlet conduit 21, through which the inlet conduit 18 communicates with the central space 15.

[0107] The separation discs of the disc stack 9 are frusto-conical and extend outwardly and downwardly from the spindle 8. The separation discs thus comprise a flat portion 9a, which extend perpendicularly to the axis of rotation (X), and a conical portion 9b, that extend outwardly and downwardly from the flat portion 9a.

[0108] It should be noted that the separation discs also could extend outwardly and upwardly, or even radially.

[0109] The separation discs of the stack 9 are provided at a distance from each other by means of distance members (not disclosed) in order to form interspaces 14 between adjacent separation discs 9, i.e. an interspace 14 between each pair of adjacent separation discs 9. The axial thickness of each interspace 14 may e.g. be in the order of 1-2 mm.

[0110] The separation discs of the stack 9 may be made of plastic or metal. The number of separation discs in the stack 9 is normally higher than indicated in FIG. 1 and may be for instance 50 to 100 separation discs 9 depending on the size of the centrifugal separator.

[0111] The centrifugal separator 1 comprises an oil nozzle 21 arranged for being connected to an engine oil circuit of an internal combustion engine. During running of the internal combustion engine, oil is pumped through the oil nozzle 21 onto a wheel 22 connected to the spindle 8 to thereby rotate the rotating member 7 and thus the stack of separation discs 9.

[0112] As an alternative, the centrifugal separator 1 may comprise an electric motor arranged to rotate the spindle 8 and rotating member 7. As a further alternative, the centrifugal separator 3 may comprise a turbine wheel connected to the spindle 8, where the turbine wheel is arranged to be driven by exhaust gases from the internal combustion engine to rotate the spindle 8 and the rotating member 7. The rotating member 7 may also be arranged for being rotated by a mechanical drive unit. Thus, the centrifugal separator may comprise a mechanical drive unit for rotating the rotating member.

[0113] The rotating member 7 defines a central space 15. The central space 15 is formed by a through hole in each of the separation discs 9. In the embodiments of FIG. 1, the central space 15 is formed by a plurality of through holes, each extending through the top disc 10 and through each of the separation discs 9, but not through the lower end plate 11. The through holes are arranged in the flat portions 9a of the separation discs.

[0114] The gas inlet 20 is for the supply of the gas to be cleaned. The gas inlet 20 extends through the stationary casing 2, and more precisely through upper end wall 5. The gas inlet 20 communicates with the central space 15 so that the gas to be cleaned is conveyed from the inlet 20 via the central space 15 to the interspaces 14 of the stack of separation discs 9. The gas inlet 20 is configured to communicate with the crankcase of the combustion engine, or any other source, via an inlet conduit 18 permitting the supply of crankcase gas from the crankcase to the gas inlet 20 and further to the central space 15 and the interspaces 14 as explained above.

[0115] The centrifugal separator 1 comprises a drainage outlet 29 arranged in the lower portion 26 of the stationary casing 2 and configured to permit discharge of liquid contaminants separated from the gas The drainage outlet 29 is in this embodiment in the form of through holes arranged in the lower end wall 6 so that separated liquid contaminants flow through the second bearing 13 as they are drained from the separation space 3. The separated oil, and other particles and/or substances, is led to an oil outlet 24 of the centrifugal separator 1, which together with oil from the oil nozzle 21 used to drive the wheel 22, may be led back to the engine oil circuit of an internal combustion engine.

[0116] The gas outlet 28 of the centrifugal separator 1 is arranged in the upper portion 27 of the stationary casing 2 and is configured to permit discharge of cleaned gas. The gas outlet 28 comprises an outlet opening through a wall of the stationary casing 2. The gas outlet 28 is in this embodiment arranged in the upper portion of the surrounding side wall 4, but the gas outlet 28 could also be arranged e.g. in the upper end wall 5.

[0117] In the centrifugal separator of FIG. 1, the axial inner side surface 4a of the stationary casing 2, i.e. the inner side surface 4a of surrounding wall 4, comprises at a plurality of recesses 30 extending in the axial direction for accumulating oil that has been separated in the stack of separation discs 9. The recesses 30 are shown in more detail in FIG. 2 and in FIGS. 3a and 3b.

[0118] The recesses 30 extend axially down to the bottom of the surrounding side wall 4a. In this embodiment, the plurality of recesses extend on the inner side surface 4a from an upper axial position X1 to a lower axial position X2. The upper axial position is above the upper axial position Y1 of the radial outermost portion of the disc stack 9 whereas the lower axial position X2 is below the lowest axial position Y2 of the radial outermost portion of the disc stack 9. In this example, the axial positions X1 and X2 are such that the recesses extend throughout the whole axial length of the surrounding side wall 4, i.e. the recesses extend axially from the top to the bottom of the axial inner side surface 4a.

[0119] During operation of the centrifugal separator as shown in FIG. 1, the rotating member 17 is kept in rotation by the oil nozzle supplying oil against the wheel 22. As an example, the rotational speed may be in the range of 7.500-12.000 rpm.

[0120] Contaminated gas, e.g. crankcase gas from the crankcase of an internal combustion engine, is supplied to the gas inlet 20 via conduit 18. This gas is conducted further into the central space 15 and from there into and through the interspaces 14 between the separation discs of the stack 9. As a consequence of the rotation of the rotating member 7 the gas is brought to rotate, whereby it is pumped further on radially outwardly through gaps or interspaces 14.

[0121] During the rotation of the gas in the interspaces 14, solid or liquid particles such as oil suspended in the gas are separated therefrom. The particles settle on the insides of the conical portions 9b of the separation discs and slide or run after that radially outwardly thereon. When the particles and/or liquid drops have reached out to the radial outer edges of the separation discs 9, they are thrown away from the rotating member 7 and hit the inner surface 4a of the surrounding side wall 4. Separated oil particles may form a film on the surrounding inner surface 4a due to the rotating flow of gas, and some reach the recesses 30 of the inner wall 14a.

[0122] From there, oil may be pulled by gravity downwardly within the recesses 30 to bottom end wall 6 and then and leave the separation space 3 through the drainage outlet 29. For this, the inner wall of the bottom end wall may be tilted radially inwards, so that oil leaving the recesses may be pulled by gravity towards drainage outlet 29. The path of the contaminants in the gas is schematically illustrated by arrows D in FIG. 1.

[0123] Cleaned gas freed from particles and exiting from the stack of separation discs 9 leaves the stationary casing 2 through the gas outlet 28. The path of the gas through the centrifugal separator 1 is schematically shown by arrows C in FIG. 1. The gas is more evenly distributed in the stack of separation discs 9 as compared to the contaminants. This is further discussed in relation to FIG. 4 below.

[0124] FIG. 2 shows the cross-section in the radial plane of the stationary casing 2 along line A in FIG. 1. Thus, FIG. 2 shows the cross-section of the surrounding wall 4 of the stationary casing 2. As illustrated in FIG. 2, the plurality of recesses 30 are distributed evenly on the inner side surface 4a around the inner side wall 4. In this embodiment, there are eight recesses in the inner wall 4a, and each recess 30 has a rectangular cross section as seen in the radial. Thus, the hole made by the actual recess 30 is in the form of a rectangular prism extending in the vertical direction. The total inner area of the recesses is much lower than the total inner area of the inner side surface 4a. As an example, the inner area of the plurality of recesses 30 may be less than half of the area, such as less than 25%, such as less than 10% of the total axial inner side surface 4a of the stationary casing 2.

[0125] As also illustrated in FIG. 2, the axial inner surface 4a of the stationary casing 2 may be substantially flat apart from the at least one recess.

[0126] FIG. 3a shows an alternative embodiment of the shape of a recess 30 in which the cross-section has a triangular shape in the radial plane. The recess 30 has a tip-shaped cross-section such that the cross-section tapers from a radial inner position to a radial outer position. Thus, the tip 31 as seen in the radial plane is arranged at a radial outermost position of the triangular cross-section. The tip 31 is shifted from the center of the cross-section. Thus, the recess 30 is formed by a first radial recess surface 30a extending from the inner side surface 4a of the stationary casing 2 and a second recess surface 30b forming an angle with the radial direction. The tip 31 of the triangular cross section is thus where these first and second recess surfaces meet at the radially innermost position of the cross-section.

[0127] The inner side surface 4a may also comprise axial ribs 35 extending axially alongside the recesses 30. The rib 35 forms a protrusion of the inner side surface 4a and there may be one rib 35 for each recess 30 extending along an axial side of the recess 30. An example of a rib 35 and recess is illustrated in FIG. 3b, which shows the cross-section in the radial plane of a rib 35 and a recess 30. In this example, the rib 35 has its rib peak 35a shifted against the direction of the recess 30. The rib 35 and recess 30 forms a Z-shaped cross-section in the radial plane. This is due to the radial recess surface 30a also forming part of the surface forming the rib or protrusion 35. Thus, as seen in the radial cross-section, the radial recess surface extends from the tip 31 of the recess to the peak 35a of the rib.

[0128] Thus, the first radial recess surface 30a extends out from the axial inner side surface 4a and form a portion of the rib 35 that is arranged alongside the at least one recess 30.

[0129] As illustrated in FIG. 3b, the second recess surface 30b forms an angle with the radial direction R. This angle may for example be between 0-75 degrees. Further, angle may be constant for all recesses 30 on the inner surface 4a. However, the angle may also vary between recesses 30 on the inner surface 4a.

[0130] In analogy, the rib surface 35b may form an angle with the radial direction R. This angle may for example be between 0-75 degrees. Further, angle may be constant for all ribs 35 on the inner surface 4a. However, the angle may also vary between ribs 35a on the inner surface 4a.

[0131] The centrifugal separator 1 may comprise recesses 30 and/or recesses 30 with corresponding ribs 35 of different axial length. This is illustrated in FIG. 3d, which shows a schematic illustration of a part of the axial inner side surface 4a of the stationary casing 2. The

[0132] In embodiments, the angle is substantially equal to angle for all ribs 35 and adjacent recesses 30 on the inner surface 4a of the stationary casing 4. The inner side surface 4a comprises a first set 30a of recesses 30 extending only in the axial lower portion 26 of the axial inner surface 4a of the stationary casing 2 as well as a second set 30b of recesses 30 extending in both an axial lower portion 26 and an axial upper portion 27 of the stationary casing 2. This may be an advantage if e.g. more contaminants such as oil is separated out to the lower portion 26 of the axial inner surface 4a.

[0133] Apart from the above-described ribs 35 and the recesses 30, the inner side surface 4a may be substantially flat.

[0134] FIG. 4 shows a close-up view of on side of the centrifugal separator 1 of FIG. 1 and how gas to be cleaned is led into the central space 15, as indicated by arrows C (gas) and D (contaminants including liquid oil and/or larger aerosols). The centrifugal separator 1 also comprises a guiding member 40 in the form of a cylindrical collar that is attached to the top disc 10. This collar 40 is arranged for guiding gas, as well as liquid oil and larger aerosols, from the central portion 15 of the disc stack 9 to the interspaces 14 between the discs of the disc stack 9 at an axial entry position Z3 that is below the uppermost axial position Z2 of the disc stack 9. Thus, the central space 15 may extend from the inner circumference 41 of the uppermost disc at an axial position Z1 down to the inner circumference 41 of the lowermost disc at an axial position Z1. By the use of the cylindrical collar 40 extending down into central space 15, the axial entry position is provided somewhere between Z1 and Z2, depending on the axial length of collar 40. Asan example, the axial length of the collar 40 may be such that the axial entry position is below the upper 25% of the total axial length, i.e. the axial length between Z1 and Z2, of the disc stack. Such mid-stack entry of the gas aids in preventing separated liquid from re-entering cleaned gas at the gas outlet 28 arranged in the upper portion 27 of the casing 2, since fewer liquid contaminants is separated and thrown against the inner side wall 4a from the upper portions of the disc stack 9.

[0135] As illustrated in FIG. 4, the gas, as indicated by arrows C are more evenly distributed axially throughout the stack of separation discs 9 even with the presence of the collar 40, whereas liquid oil is guided in a middle and lower axial portion of the stack of separation discs 90 by the use of the collar 40, as indicated by arrows D. This may thus facilitate for separated oil to hit a lower axial portion of the inner wall 4a of the stationary casing 2, and thereby reduce the risk of separated oil to re-enter the clean gas that is discharged through the gas outlet 28 at an axial upper portion of the stationary casing 2.

[0136] 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 orientation of the axis of rotation (X) disclosed in the figures. The term centrifugal separator also comprises centrifugal separators with a substantially horizontally oriented axis of rotation. In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.