A METHOD OF SEPARATING A LIQUID MIXTURE IN A CENTRIFUGAL SEPARATOR

Abstract

In a method of separating a liquid mixture in a centrifugal separator, the centrifugal separator includes a centrifuge bowl arranged to rotate around an axis of rotation and in which the separation of a liquid mixture takes place; a frame which delimits a surrounding space that is sealed relative the surroundings of the frame and in which the centrifuge bowl is arranged; a drive member configured to rotate the centrifuge bowl in relation to the frame around the axis of rotation, wherein the centrifuge bowl further comprises an inlet for receiving the liquid mixture to be separated, at least one liquid outlet for discharging a separated liquid phase and a sludge outlet for discharging a separated sludge phase to the surrounding space and a vessel connected to the surrounding space and arranged for collecting the separated sludge phase discharged from the centrifuge bowl. The method includes supplying a liquid feed mixture to be separated to the inlet of the centrifuge bowl; separating the liquid feed mixture into at least one separated liquid phase and a separated sludge phase; removing gas from the surrounding space to obtain a sub-atmospheric pressure in the surrounding space; discharging a separated sludge phase to the surrounding space; collecting the sludge phase in the vessel; removing the sludge phase from the vessel; and spraying liquid into the vessel after removing the sludge phase from the vessel to reduce the level of foam present in the vessel.

Claims

1. A method of separating a liquid mixture in a centrifugal separator, wherein the centrifugal separator comprises: a centrifuge bowl arranged to rotate around an axis of rotation and in which the separation of a liquid mixture takes place; a frame delimiting a surrounding space that is sealed relative to surroundings of the frame and in which said centrifuge bowl is arranged; a drive member configured to rotate the centrifuge bowl in relation to the frame around the axis of rotation, wherein the centrifuge bowl further comprises an inlet for receiving the liquid mixture to be separated, at least one liquid outlet for discharging a separated liquid phase and a sludge outlet for discharging a separated sludge phase to the surrounding space; and a vessel connected to the surrounding space and arranged for collecting the separated sludge phase discharged from the centrifuge bowl, wherein the method comprises the steps of: a) supplying a liquid feed mixture to be separated to the inlet of the centrifuge bowl; b) separating the liquid feed mixture into at least one separated liquid phase and a separated sludge phase; c) removing gas from the surrounding space to obtain a sub-atmospheric pressure in the surrounding space; d) discharging a separated sludge phase to said surrounding space; e) collecting said sludge phase in said vessel; f) removing said sludge phase from said vessel; and g) spraying liquid into said vessel after step f) to reduce a level of foam present in said vessel.

2. The method according to claim 1, wherein step g) comprises spraying said liquid into the vessel from a top of the vessel.

3. The method according to claim 1, wherein step g) comprises spraying said liquid with spray droplets that are larger than a mist.

4. The method according to claim 1, wherein the vessel is a cyclone.

5. The method according to claim 1, wherein the liquid feed mixture comprises a dissolved gas.

6. The method according to claim 5, wherein the liquid mixture is a liquid mixture in the processing of beer.

7. The method according to claim 1, wherein step g) comprises receiving information that that there is still matter present in said vessel after step f) has been performed.

8. The method according to claim 7, wherein said information is received from a level switch arranged in said vessel.

9. The method according to claim 1, wherein step g) is performed before initiating a further discharge of a separated sludge phase.

10. The method according to claim 1, wherein step d) comprises spraying liquid to said vessel before said discharge of a separated sludge phase

11. The method according to claim 1, wherein step e) comprises spraying liquid to said vessel after collecting said sludge phase to wet said sludge phase.

12. The method according to claim 1, wherein step c) also involves removing gas to obtain a sub-atmospheric pressure in said vessel.

13. The method according to claim 1, wherein step f) is performed using a sludge pump.

14. A centrifugal separator for separating at least one liquid phase and a sludge phase from a liquid feed mixture, comprising: a centrifuge bowl arranged to rotate around an axis of rotation and in which the separation of the liquid mixture takes place; a frame delimiting a surrounding space that is sealed relative the surroundings of the frame and in which said centrifuge bowl is arranged; a drive member configured to rotate the centrifuge bowl in relation to the frame around the axis of rotation, wherein the centrifuge bowl further comprises an inlet for receiving the liquid mixture to be separated, at least one liquid outlet for discharging a separated liquid phase and a sludge outlet for discharging a separated sludge phase to the surrounding space; a vessel connected to the surrounding space and arranged for collecting the separated sludge phase discharged from the centrifuge bowl; a pump device arranged for removing gas to obtain sub-atmospheric pressure in said surrounding space; a spray device for spraying liquid into said vessel; a sludge pump for removing sludge from said vessel; and controller configured to initiate spraying of liquid into said vessel after sludge has been removed from said vessel to reduce a level of foam present in said vessel.

15. The centrifugal separator according to claim 14, further comprising a level switch arranged in said vessel, and wherein the controller is configured to receive input from said level switch after sludge has been removed from said vessel and to initiate spraying of liquid into said vessel if said input from the level switch indicates that there is still matter present in said vessel.

16. The method according to claim 5, wherein the dissolved gas is CO.sub.2.

17. The method according to claim 2, wherein step g) comprises spraying said liquid with spray droplets that are larger than a mist.

18. The method according to claim 2, wherein the vessel is a cyclone.

19. The method according to claim 3, wherein the vessel is a cyclone.

20. The method according to claim 2, wherein the liquid feed mixture comprises a dissolved gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] 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.

[0080] FIG. 1 shows a schematic drawing of a centrifugal separator according to an embodiment of the present invention.

[0081] FIG. 2 shows a flow chart of a method of separating a liquid mixture in a centrifugal separator.

DETAILED DESCRIPTION

[0082] The method and the centrifugal separator according to the present disclosure will be further illustrated by the following description with reference to the accompanying drawings.

[0083] FIG. 1 show a cross-section of an embodiment of a centrifugal separator 1 arranged to separate a sludge phase, a liquid heavy phase and a liquid light phase from a liquid feed mixture.

[0084] The centrifugal separator 1 comprises a centrifuge bowl 10 which is arranged to rotate around an axis of rotation (X) by means of a spindle 7. The spindle 7 is supported in the centrifugal separator's frame 2 in a bottom bearing 5 and a top bearing 6. The centrifuge bowl 10 forms within itself a separation chamber in which centrifugal separation of the liquid feed mixture takes place during operation. The separation space within the centrifuge bowl 10 is provided with a stack of frustoconical separation discs in order to achieve effective separation of the liquid feed mixture.

[0085] The spindle 7 is in this example a hollow spindle for introducing the liquid feed mixture to the inlet 11 of the centrifuge bowl 10. The centrifuge bowl 10 further comprises a liquid outlet 12 for discharging a separated liquid light phase and a liquid outlet 13 for discharging a liquid heavy phase. The liquid light phase outlet 12 is arranged at a smaller radius than the liquid heavy phase outlet 13. There is further a stationary outlet pipe 12a connected to the liquid light phase outlet 12 for receiving the separated liquid light phase, and a stationary outlet pipe 13a connected to the liquid heavy phase outlet 13 for receiving the separated liquid heavy phase.

[0086] The centrifuge bowl 10 further comprises a sludge outlet 14 for discharging a separated sludge phase to the surrounding space 3, which is sealed relative the surroundings of the frame 2 and in which the centrifuge bowl 10 is arranged. The sludge outlet 14 takes the form of a set of intermittently openable sludge outlets arranged at the outer periphery of the centrifuge bowl 10, for discharge of sludge from a radially outer portion of the separation space to the surrounding space 3. Such intermittent discharge may be performed by an axially movable operating slide arranged within the centrifuge bowl 10, as known in the art.

[0087] The centrifugal separator 1 further comprises a drive motor 4 configured to rotate the centrifuge bowl 10 in relation to the frame 2 around the axis of rotation (X). The drive motor 4 is connected directly to the spindle 7. However, the drive motor may also be connected to the spindle 7 via a transmission means in the form of a worm gear which comprises a pinion and an element connected to the spindle in order to receive driving torque. The transmission means may alternatively take the form of a propeller shaft, drive belts or the like.

[0088] The surrounding space 3 is sealed relative the surroundings of the frame by means of an upper seal 15 and a lower seal 16. The frame 3 thus delimits a space 3 which contains the centrifuge bowl 10 and which is air-tightly sealed relative to the surroundings of the frame. The upper seal 15 may be an outlet seal that seals the liquid outlets from the surroundings. If the centrifugal separator is arranged with a stationery inlet pie extending into the centrifuge bowl from the top, the upper seal 15 could also be the seal that seal the inlet from the surroundings.

[0089] The upper seal 15 could for example be a mechanical seal or a liquid seal. Further, the upper seal 15 may be a gas seal, a liquid seal, a labyrinth seal or combinations thereof. Also the lower seal 16 could be a mechanical seal or a liquid seal. Further, the lower seal 16 may be a gas seal, a liquid seal, a labyrinth seal or combinations thereof.

[0090] One or both of the upper 15 and lower seal 16 could be a hermetic seal.

[0091] The centrifugal separator is further provided with a pump device 26 for removal of gas from the surrounding space 3, which pump device 26 takes the form of a water-filled liquid ring pump or, as an alternative, a lamella pump. The pump device is in this example connected directly to the frame 3 but could as an example also be connected to the vessel 20 discussed below.

[0092] The centrifugal separator further comprises a vessel 20 connected to the surrounding space 3. The vessel 20 is in the form of a cyclone and arranged for collecting the separated sludge phase discharged from the centrifuge bowl 10. The vessel 20 is further connected to a discharge device 25 in the form of a sludge pump for discharge of sludge and liquid present in the vessel 20. The sludge pump is provided with a check valve function which prevents flow into the vessel 20 via the sludge pump.

[0093] The vessel 20 further comprises a spray device in the form of spray nozzles 21a, 21b for spraying liquid, such as water, into the vessel 20. As an example, the vessel may comprise at least two, such as at least three, spray nozzles. The spray nozzles 21a, 21b, are in the form of spray nozzles having rotary spray heads and are configured to spray liquid droplets larger than a mist into the vessel 20.

[0094] Spraying liquid into the vessel 20 is controlled by control unit 30, as indicated by arrow 31. The control unit 30 is configured for initiating spraying with the nozzles 21a 21b after sludge has been removed from the vessel 20 to reduce the level of foam present in the vessel 20. However, the control unit may also be configured to spray liquid into the vessel before discharge of a sludge phase and after discharge of a sludge phase, to both wet the inner surfaces of the vessel 20 and to wet the discharged sludge.

[0095] There is further a level switch 22 arranged in the vessel 20. This level switch 22 may for example comprise one or several sensors for indicating the level of sludge or matter in the vessel 20. The control unit 30 is further configured to receive input from the level switch 22 continuously or e.g. after sludge has been removed from the vessel (20). Based on this input, the control unit 30 is configured to initiate spraying of liquid into the vessel 20 if the input from the level switch 22 indicates that there is still matter present in the vessel 20 after the sludge pump 25 has removed sludge.

[0096] Thus, the control unit 30 may for example comprise a calculation unit which may take the form of substantially any suitable type of programmable logical circuit, processor circuit, or microcomputer, e.g. a circuit for digital signal processing (digital signal processor, DSP), a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The calculation unit may represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The control unit 30 may further comprise a memory unit which provides the calculation unit with, for example, stored program code and/or stored data which the calculation unit needs to enable it to do calculations. The calculation unit may also be adapted to storing partial or final results of calculations in the memory unit. The memory unit may comprise a physical device utilised to store data or programs, i.e., sequences of instructions, on a temporary or permanent basis.

[0097] The method of the present invention is further illustrated by the flow chart in FIG. 2. During operation of the separator in FIG. 1, the centrifuge bowl 10 is caused to rotate by torque transmitted from the drive motor 4 to the spindle. Gas is pumped out of the surrounding space 3 outside the centrifuge bowl 10 by the vacuum pump 26, thereby maintaining in the surrounding space 3 a pressure of e.g. 1-50 kPa, such as 2-10 kPa. Since vessel 20 is in connection with the surrounding space 3, the pump also maintains a sub-atmospheric pressure in the vessel 20. Via the inlet 11, a liquid mixture to be separated is brought into the separation space within the centrifuge bowl 10 and between the conical separation discs fitted in the separation space. The liquid mixture is a liquid mixture comprising dissolved gas, such as dissolved CO.sub.2.

[0098] Heavier components in the liquid mixture, e.g. sludge particles and/or heavy phase, move radially outwards between the separation discs and accumulate within the sludge phase outlets 14. Sludge is emptied intermittently from the separation space by the sludge outlets 14 being opened, whereupon sludge and a certain amount of fluid is discharged from the separation space by means of centrifugal force. The discharge of sludge may also take place continuously, in which case the sludge outlets 14 take the form of open nozzles and a certain flow of sludge and/or heavy phase is discharged continuously by means of centrifugal force. Sludge which is discharged from the separation space via the sludge outlets 14 is conveyed from the surrounding space 3 to the vessel 20 connected thereto, in which the sludge accumulates and from which it is pumped out by the sludge pump 25. A separated liquid light phase moves radially inwards between the separation discs and is discharged via the liquid light phase outlet 12 to the stationary outlet pipe 12a, whereas separated liquid heavy phase is discharged via the liquid heavy phase outlet 13 to the stationary outlet pipe 13a. Thus, as illustrated in FIG. 2, the method comprises the steps of [0099] a) supplying 101 a liquid feed mixture to be separated to the inlet 11 of the centrifuge bowl 10, [0100] b) separating 102 the liquid feed mixture into at least one separated liquid phase and a separated sludge phase, [0101] c) removing 103 gas from the surrounding space 3 to obtain a sub-atmospheric pressure in the surrounding space 3 and a sub-atmospheric pressure in said vessel 20 [0102] d) discharging 104 a separated sludge phase to the surrounding space 3 and discharging 111 a separated liquid phase, [0103] e) collecting 105 the sludge phase in the vessel 20, and [0104] f) removing 106 the sludge phase from the vessel 20,

[0105] The discharge of step d) may be preceded by spraying liquid into the vessel 20 by the spray nozzles 21a, 21b to wet the inner surfaces of the vessel 20. Further when sludge has been collected in the vessel 20, an additional spray of liquid may be performed by the spray nozzles 21a, 21 b. Thus, the method 100 may comprise spraying 109 liquid to said vessel 20 before the discharge of a separated sludge phase and spraying 110 liquid to the vessel 20 after collecting sludge phase. Consequently, the method may comprise a discharge spray sequence at discharge which comprises spraying liquid just before and/or during discharge of the sludge phase and spraying liquid to the vessel 20 when sludge has been collected. Such a spray sequence may be initiated by the control unit 30, which may thus be connected to or form part of the control system of the whole centrifugal separator 1.

[0106] The sub-atmospheric pressure in the vessel 20 may give rise to foaming in the vessel 20 due to the creation of bubbles from the released carbon-dioxide (CO.sub.2) that has been discharged in the sludge phase. This is because the solubility of CO.sub.2 is a function of temperature and pressure of the liquid and from the amount of dissolved CO.sub.2. Foam in the vessel 20 may activate the high-level switch 22 and as a response to this, the method comprises an additional step g) of spraying 107 liquid into the vessel 20 after step f) has been performed. This additional spraying of liquid, which is thus outside the discharge spray sequence, is to reduce the level of foam present in said vessel 20. Such a step g) is thus performed initiating a further discharge of a separated sludge phase, i.e. before initiating a further discharge spray sequence.

[0107] The additional spraying of step g) may also be activated by the control unit based on input from the level switch 22. Thus, step g) comprises receiving 108 information that that there is still matter (foam) present in the vessel 20 after step f) has been performed, and then spraying 107 liquid into the vessel 20 after step f) to reduce the level of foam present in the vessel 20.

[0108] Thus, the control unit 30 is configured to [0109] initiate spraying of liquid via the spray nozzles 21a, 21b into the vessel 20 before discharge [0110] initiate spraying of liquid via the spray nozzles 21a, 21b into the vessel 20 when sludge has been collected in the vessel [0111] receive input from level switch 20 that there is still matter present in the vessel after sludge has been removed from the vessel, and [0112] initiate an additional spraying of liquid via the spray nozzles 21a, 21b based on the received input from the level switch 22 to reduce foam in the vessel 20.

[0113] The control unit 30 may further be configured to control the discharge of the sludge phase from the centrifuge bowl 10. The discharge may be controlled via an operating water module OWM (not shown) as known in the art. Consequently, the control unit 30 may be further configured to [0114] initiate discharge of a sludge phase from centrifuge bowl 10.

[0115] 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.