CENTRIFUGAL SEPARATOR FOR CLEANING GAS

Abstract

A centrifugal separator for cleaning a gas containing liquid impurities includes a stationary casing including a surrounding sidewall, a first end wall and a second end wall which enclose a space through which a gas flow is permitted. The space includes an upper separation chamber and a lower discharge chamber. The separator further includes an inlet extending through the stationary casing and permitting supply of the gas to be cleaned to the separation chamber, a rotating member including a stack of separation discs and being arranged to rotate around an axis of rotation, wherein the stack of separation discs is arranged in the separation chamber and a drive member for rotating the rotating member. The discharge chamber is arranged axially below the stack of separation discs such that clean gas and separated liquid impurities both enter said discharge chamber after being separated in said stack of separation discs, and further, the separator includes a gas outlet configured to permit discharge of cleaned gas from said stationary casing, wherein the gas outlet includes an outlet opening through the stationary casing and a portion extending from the outlet opening into the discharge chamber. Further, there is a drainage outlet arranged in said discharge chamber and configured to permit discharge of separated liquid impurities from said stationary casing.

Claims

1. A centrifugal separator for cleaning a gas containing liquid impurities, wherein the centrifugal separator comprises: a stationary casing comprising a surrounding side wall, a first end wall and a second end wall, the surrounding side wall and the first and second end walls enclosing a space through which a gas flow is permitted, said space comprising an upper separation chamber and a lower discharge chamber; an inlet extending through the stationary casing and permitting supply of the gas to be cleaned to the separation chamber; a rotating member comprising a stack of separation discs and being arranged to rotate around an axis of rotation, wherein the stack of separation discs is arranged in the separation chamber; and a drive member for rotating the rotating member, wherein said lower discharge chamber is arranged axially below the stack of separation discs such that clean gas and separated liquid impurities both enter said lower discharge chamber after being separated in said stack of separation discs; a gas outlet configured to permit discharge of cleaned gas from said stationary casing, wherein the gas outlet comprises an outlet opening through the stationary casing and a portion extending from the outlet opening into the lower discharge chamber; and a drainage outlet arranged in said lower discharge chamber and configured to permit discharge of separated liquid impurities from said stationary casing.

2. The centrifugal separator according to claim 1, wherein the rotating member further comprises a lower flange arranged axially below said portion of the gas outlet extending from the outlet opening into the lower discharge chamber.

3. The centrifugal separator according to claim 2, wherein said lower flange is arranged axially between the drainage outlet and said portion of the gas outlet extending from the outlet opening into the lower discharge chamber.

4. The centrifugal separator according to claim 1, wherein the rotating member further comprises an upper flange arranged axially between the portion of the gas outlet extending into the lower discharge chamber and the disc stack.

5. The centrifugal separator according to claim 4, wherein the upper and lower flange are arranged in a single unit.

6. The centrifugal separator according to claim 5, wherein the single unit further comprises a frustoconical portion onto which said disc stack is arranged.

7. The centrifugal separator according to claim 1, wherein said portion of the gas outlet extending from the outlet opening into the lower discharge chamber is hollow and comprises an opening in the peripheral wall through which the cleaned gas is retrieved and directed to said outlet opening through the stationary casing.

8. The centrifugal separator according to claim 7, wherein said portion of the gas outlet extends into the stationary casing such that said opening in the peripheral wall is located on a radius from rotational axis that is less than half of the total radius of the stationary casing.

9. The centrifugal separator according to claim 7, wherein said opening in the peripheral wall faces the rotational axis.

10. The centrifugal separator according to claim 7, wherein said opening in the peripheral wall faces away from said rotational axis.

11. The centrifugal separator according to claim 10, wherein said opening in the peripheral wall is directed in a direction that is approximately 45 degrees relative the rotational axis.

12. The centrifugal separator according to claim 7, wherein said portion of the gas outlet extending from the outlet opening into the lower discharge chamber comprises a tubular part and a narrowing part, wherein said tubular part is arranged at said outlet opening through the stationary casing and said narrowing part comprises said opening in the peripheral wall and wherein said narrowing part is arranged further away from said outlet opening through the stationary casing compared to said tubular part.

13. The centrifugal separator according to claim 12, wherein said narrowing part comprises and end wall extending in a plane formed by the rotational axis and the radius from the rotational axis.

14. A method for cleaning a gas containing liquid impurities comprising the steps of: providing the centrifugal separator according to claim 1; introducing gas containing liquid impurities into the inlet of said centrifugal separator; and discharging clean gas through said gas outlet and discharging liquid impurities separated from the gas through said drainage outlet.

15. The method according to claim 14, wherein said gas containing liquid impurities is crankcase gas of a combustion engine and said liquid impurities comprises oil.

16. The centrifugal separator according to claim 2, wherein the rotating member further comprises an upper flange arranged axially between the portion of the gas outlet extending into the lower discharge chamber and the disc stack.

17. The centrifugal separator according to claim 3, wherein the rotating member further comprises an upper flange arranged axially between the portion of the gas outlet extending into the lower discharge chamber and the disc stack.

18. The centrifugal separator according to claim 2, wherein said portion of the gas outlet extending from the outlet opening into the lower discharge chamber is hollow and comprises an opening in the peripheral wall through which the cleaned gas is retrieved and directed to said outlet opening through the stationary casing.

19. The centrifugal separator according to claim 3, wherein said portion of the gas outlet extending from the outlet opening into the lower discharge chamber is hollow and comprises an opening in the peripheral wall through which the cleaned gas is retrieved and directed to said outlet opening through the stationary casing.

20. The centrifugal separator according to claim 4, wherein said portion of the gas outlet extending from the outlet opening into the lower discharge chamber is hollow and comprises an opening in the peripheral wall through which the cleaned gas is retrieved and directed to said outlet opening through the stationary casing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 shows a schematic drawing of a section of a centrifugal separator of the present disclosure.

[0073] FIG. 2 shows a side view of a rotating secondary divider according to an embodiment of the present disclosure.

[0074] FIG. 3 shows a perspective view of a secondary divider according to an embodiment of the present disclosure.

[0075] FIG. 4 shows a perspective view of a portion extending into the discharge chamber according to an embodiment of the present disclosure.

[0076] FIG. 5 shows a perspective view a portion extending into the discharge chamber arranged at a rotating secondary divider according to an embodiment of the present disclosure.

[0077] FIG. 6 shows a perspective view a portion extending into the discharge chamber arranged at a rotating secondary divider according to an embodiment of the present disclosure.

[0078] FIG. 7a-d show different types of separation discs that may be used in the centrifugal separator.

DETAILED DESCRIPTION

[0079] The centrifugal separator according to the present disclosure will be further illustrated by the following description of an embodiment with reference to the accompanying drawings.

[0080] FIG. 1 shows a schematic section view of a centrifugal separator according to an embodiment of the present disclosure. The centrifugal separator comprises a stationary casing 1, 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. The stationary casing 1 encloses a separation space 2 through which a gas flow is permitted. The stationary casing 1 comprises, or is formed by, a surrounding side wall 3, a first end wall 4 (in the embodiments disclosed an upper end wall) and a second end wall 5 (in the embodiments disclosed a lower end wall). The surrounding side wall 3 has a circular cross-section with a radius R from the axis (X) of rotation to the surrounding side wall 3, which is more or less constant at least with respect to a major part of the circumference of the surrounding side wall 3. In particular, the side wall 3 is circular cylindrical. The centrifugal separator comprises a rotating member 6 which is arranged to rotate around an axis (X) of rotation. It should be noted that the stationary casing 1 is stationary in relation to the rotating member 6, and preferably in relation to the combustion engine to which it may be mounted.

[0081] The rotating member 6 comprises a spindle 7 and a stack of separation discs 8 attached to the spindle 7. All the separation discs 8 of the stack of separation discs 8 are provided between a first end plate 9 (in the embodiments disclosed an upper end plate) and a second end plate 10 (in the embodiments disclosed a lower end plate). Each separation disc 8 may be made of plastics or metal. The number of separation discs 8 is normally higher than indicated in FIG. 1 and may be for instance 50 to 100 separation discs 8 depending on the size of the centrifugal separator.

[0082] The spindle 7, and thus the rotating member 6, is rotatably supported in the stationary casing 1 by means of a first, upper bearing (not shown) and a second bearing (not shown).

[0083] The separation discs 8 are conical and extend upwardly and outwardly from the spindle 7. It should be noted that the separation discs 8 could also extend downwardly and outwardly, or even radially. The separation discs 8 are provided at a distance from each other by means of distance members (not disclosed) in order to form gaps 13 between adjacent separation discs 8, i.e. a gap 13 between each pair of adjacent separation discs 8. The axial thickness of each gap 13 may be in the order of 1-2 mm, for instance.

[0084] The rotating member 6 defines a central space 14. The central space 14 may be formed by a hole in each of the separation discs 8. In the embodiments disclosed the central space 14 is formed by a plurality of holes each extending through the first end plate 9 and through each of the separation discs 8.

[0085] The centrifugal separator comprises an inlet 15 for the supply of the gas to be cleaned. The inlet 15 extends through the stationary casing 1, and more precisely through the first end wall 4 and into the separation chamber 11 of the stationary casing. The inlet 15 communicates with the central space 14 so that the gas to be cleaned is conveyed from the inlet 15 via the central space 14 to the gaps 13 of the stack of separation discs 8, as indicated by arrows “A” in FIG. 1.

[0086] The inlet 15 is configured to communicate with the crankcase of the combustion engine, or any other source, via an inlet conduit 16 permitting the supply of crankcase gas from the crankcase to the inlet 15 and further to the central space 14 and the gaps 13 as explained above. The inlet conduit 16 disclosed may be comprised by the centrifugal separator.

[0087] The centrifugal separator comprises a schematically disclosed drive member 17 for rotating the rotating member 6. The drive member 17 is connected to the spindle 7. The drive member 17 may comprise a turbine wheel, see WO2012/152925, rotated by means of an oil jet from the oil system of the combustion engine, or a free jet wheel comprising a blow-back disk, see WO2014/023592, wherein the free jet is provided by the oil system of the combustion engine. Alternatively, the drive member 17 may be independent of the combustion engine and comprise an electric motor, a hydraulic motor or a pneumatic motor.

[0088] The separation discs 8 are located in the upper separation chamber 11 of the space enclosed by the stationary casing and in which chamber the primary separation occurs. The liquid impurities of the gas will be separated from the gas in the gaps 13, and the cleaned gas will be conveyed out of the gaps 13 and further to the lower discharge chamber 12 of the space enclosed by the stationary casing. Separated liquid impurities, schematically drawn as small oil droplets 18, tend to flow on the inner surface of the surrounding wall down to the lower discharge chamber 12.

[0089] Cleaned gas and separated impurities are both discharged from the same volume, i.e. the lower discharge chamber 12. The centrifugal separator comprises a drainage outlet 19 configured to permit discharge of liquid impurities separated from the gas. The drainage outlet 19 is arranged in the end wall 5 and surrounding the rotational axis (X). The drainage outlet may thus be in the form of a slot or slit below the lower flange 26.

[0090] Liquid impurities discharged via the drainage outlet 19 may further be led out of the separator by a liquid outlet 29, as schematically shown by arrow “C” in FIG. 1

[0091] The centrifugal separator also comprises a gas outlet 20 configured to permit discharge of cleaned gas, as schematically shown by arrow “B” in FIG. 1.

[0092] The gas outlet 20 comprises an outlet opening 21 in the stationary casing 1, and in the embodiments disclosed in the side wall 3 of the stationary casing 1. The gas outlet 20 further comprises a portion extending into the discharge chamber 22, having an opening in the peripheral wall 23, such that the cleaned gas may be discharged via the portion extending into the discharge chamber to the outlet conduit 24 of the gas outlet. The outlet conduit 28 may advantageously recirculate the cleaned gas, for instance to the inlet side of the combustion engine.

[0093] As seen in FIG. 1, the portion extending into the discharge chamber 22 extends into the discharge chamber 12 to an extent such that the opening in the peripheral wall 23 is located close to the rotational axis X, such as extending to an extent such that the opening in the peripheral wall is arranged at a distance from the rotational axis (X) that is less than half of the radius from the rotational axis to the stationary casing 1.

[0094] FIG. 1 thus shows that both the clean gas and the liquid impurities are discharged from the same discharge chamber 12 of the space enclosed by the stationary casing. In other words, clean gas and liquid impurities does not have to be further separated by means of any walls arranged in the separation space 2 after the primary separation within the gaps 13 between the separation discs 8. The rotating member 6 further comprises a single unit 25, a “rotating secondary divider”, arranged in the discharge chamber of the separation space 2. The single unit 25 comprises a lower flange 26, which is arranged axially above drainage outlet 19, so as to prevent liquid impurities from splashing up into the clean gas that enters the opening in the peripheral wall 23. As an example, the lower flange 26 may be arranged a few millimeters above the drainage outlet 19, such as about 1-10 mm above drainage outlet 19, such as about 3-10 mm above drainage outlet 19. The single unit has further a frustoconical upper part 28, onto which the lower end plate 10 is arranged. On the frustoconical part 28, an upper flange 27 is arranged, such that the portion extending into the discharge chamber 22 of the gas outlet 20 extends into the discharge chamber 12 of the separation space 2 axially between the lower flange 26 and the upper flange 27. Both upper flange 27 and lower flange 26 are circular, but the radius of the lower flange 26 is about half of the radius of the upper flange 27. The upper flange 27 has a radius that is about the same as the radius of the separation discs 8 and further prevents separated liquid impurities from contaminating clean gas that are discharged via the portion extending into the discharge chamber 22.

[0095] FIG. 2 and FIG. 3 show the single unit 25 that is arranged to rotate with the rotating member 6 and around rotational axis (X). The single unit 25 comprises a frustoconical portion 28 that has a height in the axial direction that is more than half of the total axial height H1 of the single unit. The frustoconical portion 28 is arranged with the widest part facing upwards towards the separation discs (not shown in FIG. 2), and accordingly extend in the same direction as the separation discs, which in the embodiment shown in the Figures is upwardly and outwardly from the rotational axis (X). The single unit 25 further comprises a lower flange 26, arranged at the end surface of the single unit 25 that is not formed by the frustoconical portion, and an upper flange 27, arranged on the conical portion 28. Both flanges 26 and 27 are circular and extend in a direction perpendicular to the rotational axis (X). The radius of the lower flange 26, denoted R1 in FIG. 2, is smaller than the radius of the upper flange 27, denoted R2 in FIG. 2. As an example, R1 may be about half the distance of R2. The radius R2 may approximately be the same as the radius of the separation discs.

[0096] The frustoconical portion 28 has an inner surface 30 onto which the stack of separation discs is arranged. Thus, the lower end plate 10 of the disc stack in FIG. 1 is arranged on inner surface 30. This inner surface 30 has distance members 31, in this case in the form of spot-formed distance members, so as to create a gap also between the lower end plate 10 and the inner surface 30 of the frustoconical portion. In this way also this gap aids in the separation of liquid impurities from the gas.

[0097] FIG. 4 shows the portion extending into the discharge chamber 22 of the gas outlet. The portion extending into the discharge chamber has a hollow interior 36 and comprises a tubular portion 32 and a narrowing part 33. The narrowing part is arranged at the end of the portion extending into the discharge chamber 22 that extends furthest into the separation space 2. There is an opening in the peripheral wall 23 of the narrowing part so as to allow gas to flow from the exterior of the portion extending into the discharge chamber to the hollow interior 36. This opening in the peripheral wall 23 is oriented so that it faces away from the rotational axis (X). When arranged in the centrifugal separator, the opening in the peripheral wall 23 faces away from the rotational axis (x) upwards, i.e. away from lower end wall 5, in a direction D that forms an angle with the rotational axis (x) that is e.g. between 30 and 60 degrees, such as approximately 45 degrees, as seen in FIG. 3. The narrowing part 33 has an end wall 34 that is oriented in a plane that is formed by the rotational axis (X) and the radius from rotational axis (X). This end wall 34 has thus an area that is smaller than the area of the tubular portion 32 of the portion extending into the discharge chamber 22. The outer wall has a slight curvature 37, which means that it is slightly curved inwards when it meets with end wall 34, i.e. it is concave. This may further create a small pressure drop during operation of the separator, which in turn may decrease the risk of oil contaminating the clean gas entering the opening in the peripheral wall 23. The portion extending into the discharge chamber 22 further has a drainage hole 38, such that any oil that has entered the opening in the peripheral wall 23 may be drained from the hollow interior 36 out to the discharge chamber. The drainage hole is thus located downstream from the opening in the peripheral wall. The portion extending into the discharge chamber 22 further comprises fastening means 35 such that it may be securely fastened in the centrifugal separator, such as to the stationary casing 1 of the centrifugal separator.

[0098] FIG. 5 and FIG. 6 further show the relation between the single unit 25 and the portion extending into the discharge chamber 22 of the gas outlet when arranged in the centrifugal separator. The axial height H2 of the portion extending into the discharge chamber is less than the axial distance between the lower flange 26 and the upper flange 27. As an example, the axial height H2 may be between 50 and 95% of the axial distance between the lower flange 26 and the upper flange 27, such a about between 80 and 95% of the axial distance between the lower flange 26 and the upper flange 27. This means that the axial height of the portion extending into the discharge chamber covers most of the axial length of the discharge chamber portion 12 from which the separated liquid impurities and the clean gas is discharged. Further, FIG. 5 shows that the opening in the peripheral wall 23 faces away axially upwards from the single unit 25, and that the portion extending into the discharge chamber 22 extend with its narrowing part 33 into the stationary casing 1 such that gas may be retrieved close to the centre of the stationary casing. FIG. 6 shows that the portion extending into the discharge chamber 22 extends between the lower flange 26 and the upper flange 27, and that the upper flange 26 extend radially approximately to a distance such that is approximately equal to the radial distance to the opening in the peripheral wall 23, i.e. the upper flange 27 slightly “covers” the opening in the peripheral wall 23, thus functioning as a roof and thereby aiding in preventing liquid impurities from entering opening in the peripheral wall 23 to the interior 36 of the portion extending into the discharge chamber 22.

[0099] FIG. 7a-d shows a few examples of separation discs that may be used in a centrifugal separator of the present disclosure. For clarity reasons, only a few discs are illustrated and it is to be understood that in reality, a larger number of discs are present so that the distance between the discs is much smaller.

[0100] FIG. 7a shows an example of frustoconical discs 8a having a planar portion 8a″ and a frustoconical portion 8a′. The planar portion 8a″ extends in a plane that is perpendicular to the axis of rotation (X), and the frustoconical portion 8a′ extends in this embodiment upwards. The planar portion 8a″ is closer to the rotational axis than the frustoconical portion 8a′.

[0101] FIG. 7b shows an example of frustoconical discs 8a having a planar portion 8b″ and a frustoconical portion 8b′. The planar portion 8b″ extends in a plane that is perpendicular to the axis of rotation (X), and the frustoconical portion 8b′ extends in this embodiment downwards. The planar portion 8b″ is closer to the rotational axis than the frustoconical portion 8b′.

[0102] FIG. 7c shows an example of a disc stack in which all discs 8c are planar, i.e. all discs 8c extend in the plane that is perpendicular to the axis of rotation (X).

[0103] FIG. 7d shows an example of axial discs or plates 8d. These plates are slightly curved, i.e. they have a curved shaped as seen in a radial plane. In other words, they are curved as seen in a plane that is perpendicular to the axis of rotation (X).

[0104] 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.