High speed cleaning of a centrifugal separator

Abstract

A centrifugal separator for cleaning gas containing contaminants includes 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 including a plurality of separation members arranged in said separation space and being arranged to rotate around an axis of rotation, a gas outlet configured to permit discharge of cleaned gas and including an outlet opening through a wall of the stationary casing, a drainage outlet configured to permit discharge of liquid impurities separated from the gas to be cleaned, and a drive member, for rotating the rotating member. The centrifugal separator further includes a control unit configured to control the drive member to rotate the rotating member at a first speed during a separation phase and at a second speed, which is higher than the first speed, during a cleaning phase to remove clogging on or between said separation members, wherein the cleaning phase is shorter in time than the separation phase.

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 configured to permit discharge of cleaned gas and comprising an outlet opening through a wall of the stationary casing; a drainage outlet configured to permit discharge of liquid impurities separated from the gas to be cleaned; a drive member for rotating the rotating member; and a control unit configured to: control the drive member to rotate the rotating member at a first speed during a separation phase; receive a signal regarding an operation parameter of the separator or an engine connected to the separator; in response to the signal, rotate the rotating member at a second speed, which is higher than the first speed, during a cleaning phase to remove clogging on or between said separation members; and control a duration of the cleaning phase to be shorter than a duration of the separation phase.

2. The centrifugal separator according to claim 1, wherein the signal is received after a predetermined period of time.

3. The centrifugal separator according to claim 1, wherein the signal is related to a stop of the engine, and wherein the control unit is further configured to switch to the cleaning phase after a predetermined number of stops of said engine.

4. The centrifugal separator according to claim 1, wherein the signal is related to the time during which the engine has been running, and wherein the control unit is further configured to switch to the cleaning phase when said time exceeds a threshold value.

5. The centrifugal separator according to claim 1, wherein the signal is related to the gas pressure at the gas inlet; and wherein the control unit is further configured to switch to the cleaning phase when the gas pressure at the gas inlet is above a predefined threshold value.

6. The centrifugal separator according to claim 1, wherein the cleaning phase comprises rotating the rotating member during a time period that is between 30-180 s.

7. The centrifugal separator according to claim 1, wherein the cleaning phase comprises rotating the rotating member at a speed that is higher than 12,000 rpm.

8. The centrifugal separator according to claim 1, wherein the cleaning phase comprises rotating the rotating member at a speed that is more than 2000 rpm higher than the speed of the separation phase.

9. The centrifugal separator according to claim 1, wherein the drive member comprises an electrical motor.

10. The centrifugal separator according to claim 9, wherein the rotating member is journalled in the stationary casing through bearings situated at only two bearing places axially spaced from each other, and wherein the electrical motor is arranged within the stationary casing and has a stator, that is supported by the stationary casing, and a rotor, that is constituted by part of said rotating member, the rotating member being journalled relative to the stator only through said bearings.

11. The centrifugal separator according to claim 9, wherein the control unit is integrated with the electrical motor.

12. A method for removing clogging in a centrifugal separator, comprising the steps of: providing the centrifugal separator according to claim 1; running the centrifugal separator in the separation phase at said first speed; and switching to running the centrifugal separator in the cleaning phase at said second speed to remove clogging on or between said separation members.

13. The method according to claim 12, wherein switching to running the centrifugal separator in the cleaning phase is additionally initiated after a predetermined period of time.

14. The method according to claim 12, further comprising receiving a signal related to a stop of the engine to which the centrifugal separator is connected, and wherein switching to running the centrifugal separator in the cleaning phase is initiated after a predetermined number of received stops.

15. The method according to claim 12, further comprising measuring a pressure at the inlet of the separator, and wherein switching to running the centrifugal separator in the cleaning phase is initiated when the gas pressure at the gas inlet is above a predefined threshold value.

16. The centrifugal separator according to claim 2, wherein the cleaning phase comprises rotating the rotating member during a time period that is between 30-180 s.

17. The centrifugal separator according to claim 3, wherein the cleaning phase comprises rotating the rotating member during a time period that is between 30-180 s.

18. The centrifugal separator according to claim 4, wherein the cleaning phase comprises rotating the rotating member during a time period that is between 30-180 s.

19. The centrifugal separator according to claim 5, wherein the cleaning phase comprises rotating the rotating member during a time period that is between 30-180 s.

20. The centrifugal separator according to claim 2, wherein the cleaning phase comprises rotating the rotating member at a speed that is higher than 12,000 rpm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a section of an embodiment of a centrifugal separator.

(2) FIG. 2 shows a section of an embodiment of a centrifugal separator.

(3) FIG. 3a-d show different types of separation members that may be used in the centrifugal separator.

DETAILED DESCRIPTION

(4) The centrifugal separator and method according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.

(5) FIG. 1 shows a section of a centrifugal separator 1 of the separator arrangement. 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.

(6) 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 impurities in the form of oil droplets or oil mist.

(7) 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, a first end wall 5 (in the embodiments disclosed an upper end wall) and a second end wall 6 (in the embodiments disclosed a lower end wall).

(8) 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.

(9) 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.

(10) 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 first end plate 10 (in the embodiment disclosed an upper end plate) and a second end plate 11 (in the embodiment disclosed a lower end plate).

(11) The spindle 8, and thus the rotating member 7, is rotatably supported in the stationary casing 2 by means of a first bearing 12 (in the embodiment disclosed as an upper bearing) and a second bearing 13 (in the embodiments disclosed as a lower bearing), 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 cap 19 also has an annular plain portion 20, through which the cap is supported by a partition 21 in the stationary casing 2. The plain annular portion 20 of the cap 19 is provided with through holes 22, through which the inlet conduit 18 communicates with the central space 15.

(12) Axially above the upper bearing 12 the cap 19 supports on its inside, around the end portion of the spindle 8, a stator 24 belonging to an electrical motor 23. A rotor 25 belonging to this electrical motor 23 is supported by the end portion of the centrifugal rotor shaft, i.e. the spindle 8. A narrow annular slot 26 is formed between the motor stator 24 and the motor rotor 25. As can be seen, the electrical motor 23 in this embodiment has no bearings of its own, through which its rotor 25 would be rotatably journalled in its stator 24. Instead, the two bearings 12 and 13, through which the rotating member 7 is journalled in the stationary casing 2, are utilized for the journalling of the rotor 25 of the electrical motor 23.

(13) The separation discs of the stack 9 are frusto-conical and extend outwardly and upwardly 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 upwardly from the flat portion 9a.

(14) It should be noted that the separation discs also could extend outwardly and downwardly, or even radially.

(15) 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 gaps 14 between adjacent separation discs 9, i.e. a gap 14 between each pair of adjacent separation discs 9. The axial thickness of each gap 14 may e.g. be in the order of 1-2 mm.

(16) 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 of the size of the centrifugal separator.

(17) The rotating member 7 defines a central space 15. The central space 15 is formed by a 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 16, each extending through the first end plate 10 and through each of the separation discs 9, but not through the second end plate 11. The through holes are arranged in the flat portions 9a of the separation discs.

(18) The centrifugal separator 1 comprises a gas inlet 17 for the supply of the gas to be cleaned. The gas inlet 17 extends through the stationary casing 2, and more precisely through the first end wall 5. The gas inlet 17 communicates with the central space 15 so that the gas to be cleaned is conveyed from the inlet 17 via the central space 15 to the gaps 14 of the stack of separation discs 9. The gas inlet 17 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 17 and further to the central space 15 and the gaps 14 as explained above.

(19) The centrifugal separator comprises a drainage outlet 29 configured to permit discharge of liquid impurities separated from the gas and a gas outlet 30 configured to permit discharge of cleaned gas. The drainage outlet is in this embodiment arranged as a conduit in the second end wall 6, but the drainage outlet 29 may also be in the form of through holes arranged in the lower end wall 6 so that separated liquid impurities flow through the second bearing 13 as they are drained from the separation space 3. Furthermore, the gas outlet 30 is in this embodiment arranged in the second end wall 6 at a radial distance that is shorter than the radial distance to the drainage outlet 2, but the gas outlet could also be arranged e.g. in the surrounding side wall 4.

(20) By means of control unit 28, the rotational speed and thereby the cleaning efficiency of the centrifugal separator may be controlled in a suitable way so that a required cleaning of the supplied gas is obtained. This is achieved by means of connection 27, which extend into the stationary casing 1 and further through the cap 14 in to the stator 18 of the motor. This connection 27 could also be used for charging the electrical motor 23 with current. The control unit 30 includes a device for driving the electrical motor 23 at different speeds; either so that a limited number of speeds can be obtained or so that a continuous change of the motor speed can be performed. Different kinds of devices for speed regulation of motors (both direct-current and alternate-current motors) are well known. For a direct-current motor a simple device for voltage control may be used. For an alternate-current motor various kinds of frequency control equipment may be used.

(21) The control unit 28 may further comprise a communication interface 31, such as a transmitter/receiver, via which it may receive data from various sensors or the engine to which the separator is connected and further transmit data to the electrical motor 23.

(22) The received data may for instance include data on a measured pressure from a pressure sensor 32 at the gas inlet 17, as indicated by dotted arrow “A”, and/or data related to the number of stops of the engine to which the separator is connected, as indicated by dotted arrow “B”. The transmitted data may for instance include a control signal for controlling the speed of the electrical motor 23.

(23) The control unit 28 is further configured to carry out a method for controlling the electrical motor 28 according to embodiments disclosed herein. For this purpose the control unit 28 may comprise a processing unit 33, such as a central processing unit, which is configured to execute computer code instructions which for instance may be stored on a memory 34. The memory 34 may thus form a (non-transitory) computer-readable medium for storing such computer code instructions. The processing unit 33 may alternatively be in the form of a hardware component, such as an application specific integrated circuit, a field-programmable gate array or the like.

(24) In this embodiment, the control unit 28 is a separate unit from the centrifugal separator 1. However, the control unit may also be a part of the separator, such as forming a part of the electrical motor 23. Thus, the control unit with all its functions could be arranged at the electrical motor, such as being connected to the stator 24 supported by the cap 19.

(25) During operation, the rotating member 17 is kept in rotation by supply of current to the electrical motor 23 and contaminated gas, e.g. crankcase gas from the crankcase of an internal combustion engine, is supplied to the gas inlet 17 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.

(26) During the rotation of the gas in the interspaces solid or liquid particles 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 outer edges of the separation discs, they are thrown away from the rotor and hit the inner surface of the surrounding wall 4 of the stationary casing 2. The particles continue downwardly along this wall and leave the separation space 3 through the drainage outlet 29, whereas the gas freed from particles and exiting from the stack of separation discs 9 leaves the casing 1 through the gas outlet 30. The path of the gas through the centrifugal separator 1 is schematically shown by arrows “C” in FIG. 1.

(27) As discussed above, the control unit 28 controls the rotational speed of the rotating part by sending signal to the electrical motor 23. During normal operation, the rotating member is rotated at a first speed during a separation phase. This first speed may be a speed in the range of 7,500-12,000 rpm. During the separation phase, liquid impurities are separated from the gas as discussed above. The separation phase may also comprise rotating the rotating member at more than one speed. The separation phase may thus comprise a set of speed levels between which the rotating member can rotate. These shifts within the separation phase may be controlled by control unit 28, either a stepwise or continuous shift in speed.

(28) However, during time, clogging may build up between the separation discs in the stack 9. The control unit is therefore configured to shift into a cleaning phase, in which the rotating member gets a temporary increase in speed. Thus, the cleaning phase occurs during a shorter period of time compared to the separation phase. The speed during the cleaning phase, i.e. the second speed, is higher than the all speeds during the separation phase, i.e. higher than the first speed. The speed during the cleaning phase may be at least 15,000 rpm. The cleaning phase may continue for at least 30 sec, such as at least 45 sec, such as at least 60 sec. With this temporary speed increase, the centrifugal forces acting on the clogging increases, which in turn force the clogging to be released from between the discs, i.e. the separation discs are cleaned from the clogging.

(29) The control unit 28 may for example be configured to shift from the separation phase to the cleaning phase after a predetermined time period, or after receiving input from a sensor. As an example, the control unit may be configured to shift into the cleaning phase after a signal from a pressure sensor 32 at the gas inlet, which signal may be an indication of a gas pressure above a certain threshold and therefore an indication that clogging has occurred. The control unit 28 may as an alternative, or as a complement, be configured to shift to the cleaning phase after receiving an input signal from other parts of the engine to which the centrifugal separator is connected. As discussed above, the control unit may be configured to receive a signal that is related to a stop of the engine to which the centrifugal separator is connected, further configured to switch to the cleaning phase after receiving a predetermined number of stop signals of the engine, or receiving a signal with information that the engine has stopped a certain number of times.

(30) The control unit may further be configured to switch back to the separation phase after running the rotating member 7 at the speed of the cleaning phase a certain period of time. As an example, the control unit may further be configured to switch from the cleaning phase back to the separation phase after 30-180 s.

(31) An electrical motor 23 of the kind shown in FIG. 1 may alternatively be arranged around an extension of the spindle 8 below the lower bearing 13. It is also possible to arrange the motor in a space axially between the upper bearing 12 and the first end plate 10 or axially between the lower bearing 13 and the second end plate 11. An electrical motor having a disc-formed circular rotor and a stator formed so that it is situated axially on both sides of the rotor may also be used.

(32) FIG. 2 shows an example of an embodiment of a centrifugal separator in which the electrical motor 23 is arranged on an extension of the spindle 8 axially above the upper wall 5 of the stationary casing 2. As an alternative, the electrical motor 23 could also be arranged on an extension of the spindle 8 axially below the lower end wall 6 of the stationary casing 2.

(33) Thus, in the embodiment shown, the stator and the rotor of the electrical motor 23 are arranged outside the stationary casing 2. Further, the control unit 28 is arranged as a part of the electrical motor 23, but functions as discussed in relation to the embodiment shown in FIG. 1. All other functions are the same as discussed in relation to the embodiment shown in FIG. 1, i.e. the reference numerals denote the same features.

(34) In the embodiments shown in FIG. 1 and FIG. 2, the rotating member 7 for the gas cleaning is provided with a stack of conical separation discs of a conventional kind. However, the invention is not limited to a rotating member or centrifugal rotor of precisely this kind but may be used in connection with any suitable centrifugal rotor for freeing a gas from particles suspended therein.

(35) FIG. 3a-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.

(36) FIG. 3a shows an example of frustoconical discs 35 having a planar portion 9a and a frustoconical portion 9b. The planar portion 9a extends in a plane that is perpendicular to the axis of rotation (X), and the frustoconical portion 9b extends in this embodiment upwards. The planar portion 9a is closer to the rotational axis than the frustoconical portion 9b. The planar portion 9a and/or the frustoconical portion 9b may comprise through holes for gas.

(37) FIG. 3b shows an example of frustoconical discs 35 having a planar portion 9a and a frustoconical portion 9b. The planar portion 9a extends in a plane that is perpendicular to the axis of rotation (X), and the frustoconical portion 9b extends in this embodiment downwards. The planar portion 9a is closer to the rotational axis than the frustoconical portion 9b. The planar portion 9a and/or the frustoconical portion 9b may comprise through holes for gas.

(38) FIG. 3c shows an example of a disc stack in which all discs 36 are planar, i.e. all discs 36 extend in the plane that is perpendicular to the axis of rotation (X). The discs 36 may comprise through holes for gas.

(39) FIG. 3d shows an example of axial discs or plates 37. These plates 37 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). The axial discs 37 may comprise through holes for gas.

(40) 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.