Centrifugal separator having an intermittent discharge system with hydraulically operated sliding bowl bottom

Abstract

A centrifugal separator for separation of at least two components of a fluid mixture of different densities includes a centrifuge rotor with a sliding bowl bottom movable between a closed position, in which the peripheral ports are closed, and an open position, in which the peripheral ports are open, an inlet channel for supplying hydraulic fluid to a closing chamber between the sliding bowl bottom and the rotor casing in order to hold the sliding bowl bottom in the closed position. The centrifugal separator includes at least one hermetic seal at a second end, other than the first end, of a hollow spindle and the inlet channel for supplying hydraulic fluid to the closing chamber extends through the hollow spindle and is arranged such that the hydraulic fluid is in thermal contact with the at least one hermetic seal when the hydraulic fluid is supplied to the closing chamber.

Claims

1. A centrifugal separator for separation of at least two components of a fluid mixture which are of different densities, said centrifugal separator comprising: a frame; a hollow spindle rotatably supported by the frame; a centrifuge rotor mounted to a first end of the hollow spindle to rotate together with the hollow spindle around an axis of rotation, wherein the centrifuge rotor comprises a rotor casing enclosing a separation space in which a stack of separation discs is arranged; a duct arranged to be through-flown by process medium during operation of the centrifugal separator and extending through said hollow spindle and in fluid contact with said separation space; at least one liquid outlet for discharging a separated liquid phase from said separation space; and a plurality of peripheral ports extending from the separation space through the rotor casing to a surrounding space for discharging a phase from the periphery of said separation space, wherein said centrifuge rotor comprises: a sliding bowl bottom movable between a closed position, in which the peripheral ports are closed, and an open position, in which the peripheral ports are open; and an inlet channel for supplying hydraulic fluid to a closing chamber between the sliding bowl bottom and the rotor casing in order to hold the sliding bowl bottom in the closed position, wherein the centrifugal separator further comprises at least one hermetic seal at a second end, other than the first end, of the hollow spindle, and wherein said inlet channel for supplying hydraulic fluid to said closing chamber extends through the hollow spindle and is further arranged such that said hydraulic fluid is in thermal contact with said at least one hermetic seal when said hydraulic fluid is being supplied to said closing chamber.

2. The centrifugal separator according to claim 1, wherein said at least one hermetic seal is a mechanical seal.

3. The centrifugal separator according to claim 2, wherein the mechanical seal comprises: a stationary part arranged to be fitted onto a non-rotating member; and a rotating part arranged on the hollow spindle, wherein the inlet channel for supplying hydraulic fluid to the closing chamber is arranged such that said hydraulic fluid is in thermal contact with the interface between the stationary part and the rotating part of the mechanical seal when said hydraulic fluid is being supplied to said closing chamber.

4. The centrifugal separator according to claim 2, wherein said at least one hermetic seal is a seal that seals against said duct arranged to be through-flown by process medium during operation of the centrifugal separator.

5. The centrifugal separator according to claim 1, wherein said at least one hermetic seal is a seal that seals against said duct arranged to be through-flown by process medium during operation of the centrifugal separator.

6. The centrifugal separator according to claim 5, wherein the mechanical seal comprises: a stationary part arranged to be fitted onto a non-rotating member; and a rotating part arranged on the hollow spindle, wherein the inlet channel for supplying hydraulic fluid to the closing chamber is arranged such that said hydraulic fluid is in thermal contact with the interface between the stationary part and the rotating part of the mechanical seal when said hydraulic fluid is being supplied to said closing chamber.

7. The centrifugal separator according to claim 1, wherein the separator comprises: a first hermetic seal at said second end of the spindle, the first hermetic seal being arranged for sealing against a first stationary pipe that is in fluid contact with said duct of the hollow spindle that is arranged to be through-flown by process medium during operation; and a second seal for sealing against a second stationary pipe arranged for supplying said hydraulic fluid to said inlet channel of the hollow spindle.

8. The centrifugal separator according to claim 7, wherein the second seal is a second hermetic seal.

9. The centrifugal separator according to claim 8, wherein said inlet channel for supplying hydraulic fluid to said closing chamber is arranged such that said hydraulic fluid is in thermal contact with said first hermetic seal and said second hermetic seal when said hydraulic fluid is being supplied to said closing chamber.

10. The centrifugal separator according to claim 1, wherein the inlet channel for supplying hydraulic fluid is arranged in the hollow spindle as an annular space surrounding said duct arranged to be through-flown by process medium during operation of the centrifugal separator.

11. The centrifugal separator according to claim 1, wherein the inlet channel for supplying hydraulic fluid is arranged in the hollow spindle as a pipe extending in said duct arranged to be through-flown by process medium during operation of the centrifugal separator for feeding the fluid mixture into said separation space.

12. The centrifugal separator according to claim 1, further comprising a pressure generator arranged for supplying said hydraulic fluid under a pressure that is higher than atmospheric pressure.

13. The centrifugal separator according to claim 1, wherein said duct arranged to be through-flown by process medium during operation of the centrifugal separator is a duct for the fluid mixture that is to be separated.

14. The centrifugal separator according to claim 1, wherein said duct arranged to be through-flown by process medium during operation of the centrifugal separator is a duct for a separated liquid phase.

15. The centrifugal separator according to claim 1, further comprising a duct through the rotor casing for supply of liquid to open at least one outlet passage through which the hydraulic fluid of the closing chamber is drained, thereby initiating moving of the sliding bowl bottom to the open position.

16. The centrifugal separator according to claim 1, further comprising means that facilitates a continuous consumption of the hydraulic fluid or a circulation of the hydraulic fluid to a heat exchange unit.

17. A method for separation of at least two components of a fluid mixture which are of different densities, said method comprising the steps of: providing the centrifugal separator according to claim 1; supplying hydraulic fluid into the inlet channel to the closing chamber between the sliding bowl bottom and the rotor casing in order to hold the sliding bowl bottom in the closed position; and feeding the fluid mixture to be separated to the separation space of the centrifuge rotor via the duct arranged to be through-flown by process medium during operation of the centrifugal separator.

18. The method according to claim 17, wherein the hydraulic fluid is water.

19. The method according to claim 17, wherein the hydraulic fluid is supplied under pressure via the second end of the spindle.

20. The centrifugal separator according to claim 1, wherein the centrifuge rotor is mounted on a top of the hollow spindle and the duct extends from a bottom of the hollow spindle through the hollow spindle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a shows a schematic drawing of a section of an embodiment of a centrifugal separator of the present disclosure.

(2) FIG. 1b shows a section of the hollow spindle of the centrifugal separator of FIG. 1a.

(3) FIG. 2a shows a schematic drawing of a section of an embodiment of a centrifugal separator of the present disclosure.

(4) FIG. 2b shows a section of the hollow spindle of the centrifugal separator of FIG. 2a.

(5) FIG. 3 shows a schematic drawing of a close-up view of the lower end of the spindle of the separator of FIG. 1a.

(6) FIG. 4 shows a schematic drawing of a close-up view of the lower end of the spindle of the separator of FIG. 2.

(7) FIG. 5 shows a schematic drawing of a close-up view of the lower end of the spindle of an embodiment of a separator in which a separated liquid phase is discharged via the spindle.

(8) FIG. 6 shows a schematic drawing of a close-up view of the lower end of the spindle of another embodiment of a separator in which a separated liquid phase is discharged via the spindle.

DETAILED DESCRIPTION

(9) 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.

(10) FIG. 1a shows a centrifugal separator 1 for separating a liquid mixture. The separator comprises a frame 2, a hollow spindle 3, which is rotatably supported by the frame 2 in a bottom bearing 23 and a top bearing 15, and a centrifuge rotor 4 mounted to a top of the hollow spindle 3. The centrifuge rotor 4 is adjoined to the upper end 3a of the spindle 3 to rotate together with the spindle 3 around an axis (X) of rotation. The centrifuge rotor 4 comprises a rotor casing 5 enclosing a separation space 6 in which a stack 7 of separation discs is arranged in order to achieve effective separation of the liquid mixture that is separated. The separation discs of the stack 7 have a frustoconical shape and are examples of surface-enlarging inserts. The stack 7 is fitted centrally and coaxially with the rotor and the discs of the stack 7 may comprise through holes (not shown) which form channels for axial flow of liquid when the separation discs are fitted in the centrifugal separator 1. In FIG. 1a, only a few discs are shown. The stack 7 may for example contain above 100 discs, such as above 200 discs.

(11) The rotor 3 has extending from it a liquid light phase outlet 12 for a lower density component separated from the liquid mixture, and a liquid heavy phase outlet 11 for a higher density component, or heavy phase, separated from the liquid mixture. The outlets 11 and 12 extend through the frame 2. In certain applications, the separator 1 only contains a single liquid outlet, such as only liquid outlet 12. This depends on the liquid material that is to be processed. The rotor 4 is further provided with a plurality of peripheral ports 8 that extend from the separation space 6 through the rotor casing 5 to a surrounding space 9 outside the centrifuge rotor 4. The peripheral ports 8 may be intermittently openable during a short time period, e.g. in the order of milliseconds, and permit total or partial discharge of sludge from the separation space as will be explained below.

(12) The centrifugal separator 1 is further provided with a drive motor 16. This motor 16 may for example comprise a stationary element and a rotatable element, which rotatable element surrounds and is connected to the spindle 3 such that it transmits driving torque to the spindle 3 and hence to the rotor 4 during operation. The drive motor 16 may be an electric motor. Furthermore, the drive motor 16 may be connected to the spindle 3 by transmission means. The transmission means may be in the form of a worm gear which comprises a pinion and an element connected to the spindle 3 in order to receive driving torque. The transmission means may alternatively take the form of a propeller shaft, drive belts or the like, and the drive motor may alternatively be connected directly to the spindle.

(13) A central duct 13 extends from a bottom of the hollow spindle 3 through the hollow spindle 3, which takes the form of a hollow, tubular member. The central duct 13 forms in this embodiment an inlet duct for supplying the liquid mixture for centrifugal separation to the separation space 6 via the inlet 10 of the rotor 4. Introducing the liquid material from the bottom provides a gentle acceleration of the liquid material. The spindle 3 is further connected to a stationary inlet pipe 17 at the bottom end 3b of the separator 1, such that liquid material to be separated may be transported to the central duct 13, e.g. by means of a pump.

(14) A first mechanical hermetic seal 18 is arranged at the bottom end 3b to seal the hollow spindle 3 to the stationary inlet pipe 17. The hermetic seal 18 is an annular seal that surrounds the bottom end 3b of the spindle 3 and the stationary pipe 17. There is also a second mechanical hermetic seal 29 that seals the bottom end 3b of the spindle to a stationary pipe 20 for supply of hydraulic fluid, such as water, to the annular inlet channel 14 of the spindle 3. The hermetic seals of FIG. 1a are shown in more detail in FIG. 3 and are further described below.

(15) During operation of the separator in FIG. 1a, the rotor 4 is caused to rotate by torque transmitted from the drive motor 16 to the spindle 3. Via the central duct 13 of the spindle 3, liquid material to be separated is brought into the separation space 6 via inlet 10. In the hermetic type of inlet 10, the acceleration of the liquid material is initiated at a small radius and is gradually increased while the liquid leaves the inlet and enters the separation space 6. Further, the separator 1 may also have a hermetic outlet and the separation space 6 may be intended to be completely filled with liquid during operation. In principle, this means that preferably no air or free liquid surfaces is meant to be present within the rotor 4. However, liquid may also be introduced when the rotor is already running at its operational speed. Liquid material may thus be continuously introduced into the rotor 4.

(16) The path of the liquid material to be separated through the spindle 3 to the separation space 6 is illustrated by arrows “A” in FIG. 1a.

(17) Depending on the density, different phases in the liquid is separated between the separation discs of the stack 7 fitted in the separation space 6. Heavier components in the liquid move radially outwards between the separation discs, whereas the phase of lowest density moves radially inwards between the separation discs and is forced through outlet 12 arranged at the radial innermost level in the separator. The liquid of higher density is instead forced out through outlet 11 that is at a radial distance that is larger than the radial level of outlet 12. Thus, during separation, an interphase between the liquid of lower density and the liquid of higher density is formed in the separation space 6. Solids, or sludge, accumulate at the periphery of the separation space 6 and may be emptied intermittently from the separation space by opening of sludge outlets, i.e. the peripheral ports 8, whereupon sludge and a certain amount of liquid is discharged from the separation space by means of centrifugal force.

(18) The opening and closing of the peripheral ports 8 is controlled by means of a sliding bowl bottom 21 which is movable between a closed position, shown in FIG. 1a, in which the peripheral ports 8 are closed, and an open position, in which the peripheral ports 8 are open. The sliding bowl bottom 21 is movable between the open and closed position along a direction parallel to the axis of rotation. The sliding bowl bottom 21 may be of a rigid type that is movable as a whole between the open position and the closed position along the direction parallel to the axis of rotation. Such a sliding bowl bottom is for example disclosed in U.S. Pat. No. 4,514,183. However, the sliding bowl bottom 21 may also be of a flexible kind, wherein an inner end of the sliding bowl bottom is fixedly attached to the rotor casing and the outer end of the sliding bowl bottom 21 is moveable. Such a sliding bowl bottom 21 is for example disclosed in U.S. Pat. No. 5,792,037.

(19) A closing chamber 22 is provided between the sliding bowl bottom 21 and the rotor casing 5. During operation, the closing chamber 22 may contain the hydraulic fluid, such as water, acting on the sliding bowl bottom 21. An inlet channel 14 extends through the hollow spindle 3 as an annular channel surrounding the central duct 13 and is configured for supplying the hydraulic fluid to the closing chamber 22 in order to hold the sliding bowl bottom 21 in the closed position. The hydraulic fluid is supplied under pressure to the inlet channel 14 from tank 19 via pipe 20 by means of pump 30. When passing the first hermetic seal 18 and the second hermetic seal 29, the hydraulic fluid is in thermal contact with the seals. Thus, the first and second hermetic seals 18, 29 are cooled as hydraulic fluid is supplied via the inlet channel 14 to the closing chamber 22. This is further shown in FIG. 3.

(20) An outlet passage 27 comprising drainage nozzles 24 for draining the hydraulic fluid from the closing chamber 22 is provided in order to move the sliding bowl bottom 21 to the open position, thereby permitting discharge of the sludge. The draining of the hydraulic fluid from closing chamber 22 is initiated by introducing liquid, such as water, to a duct 25 through the casing for opening at least one outlet passage 27. Such water is hereinafter called “opening water”. The duct 25 terminates in an opening channel 28 located axially below the closing chamber. The opening channel 28 may comprise an annular operating slide (not shown) extending around the axis of rotation and being movable from a first position to a second position upon supply of opening water to the opening channel 28. The annular operating slide may be located in the opening channel 28 axially below the closing chamber 22. Moving the operating slide to the second position may initiate opening of drainage nozzles 24 located in the outlet passages 27, thereby starting the drainage of the hydraulic fluid from the closing chamber 22. This will in turn cause the sliding bowl bottom 21 to move to its lower position so that sludge is discharged through peripheral ports 8.

(21) When the hydraulic fluid has been drained from the closing chamber 22, the annular operating slide moves to its first position, thereby closing drainage nozzles 24, and the sliding bowl bottom 21 is raised to its closed position upon further supply of hydraulic fluid to the closing chamber 22.

(22) The hydraulic fluid to the closing chamber 22 may be supplied at a high pressure, e.g. higher as compared to the supply of liquid to the opening channel 21, so that the sliding bowl bottom 21 may move to its closed position quickly after discharge of the sludge through peripheral ports 8.

(23) In the embodiment shown in FIG. 1a, the liquid to the opening channel 28 is provided from the same tank 19 as the liquid to the closing chamber 22. However, liquid to the opening channel 28 is provided from the tank 19 using a pipe 26 that extends through the casing 5 to the opening channel 28. This pipe 26 is other than the pipe 20 which is for supplying hydraulic liquid to the inlet channel 14.

(24) In the embodiment of FIG. 1a, the material to be separated is introduced via the central duct 13 of the spindle 3. However, the central duct 13 may also be used for withdrawing e.g. the liquid light phase and/or the liquid heavy phase. Thus, in embodiments, the central duct 13 comprises at least one additional duct, i.e. at least three ducts. In this way, the liquid mixture to be separated may be introduced to the rotor 4 via the central duct 13, and concurrently, the liquid light phase and/or the liquid heavy phase may be withdrawn through such an additional duct extending in the central duct 13.

(25) FIG. 1a is a schematic drawing and is thus not drawn into scale. FIG. 1b is a cross-section of the spindle 3 of FIG. 1a along line Y. The total diameter D1 of the spindle may be 5-300 mm, such as 10-200 mm, and the central inner duct may have a diameter D2 such that D2 has a length that is more than half of D1, such as more than 75% of the length of D1. Thus, the cross-sectional area A1 of the inlet channel for the hydraulic fluid 14 is considerably less than the cross-sectional area A2 of the inlet duct for the feed 13.

(26) FIG. 2a shows a schematic drawing of centrifugal separator according to another embodiment of the invention. The separator 1 is almost identical to the separator as shown in FIG. 1a, but with the difference that the inlet channel 14 for hydraulic fluid extends in the hollow spindle 3 as a central pipe, whereas the inlet duct 13 for liquid mixture to be separated extends as an annular chamber surrounding the inlet channel 14. Thus, the hollow spindle 3 is similar to the spindle 3 as shown in FIG. 1a, i.e. it is in the form of two concentric pipes, but the hydraulic fluid is, after having cooled the hermetic seal 18, instead led through the inner pipe and the feed is led through the outer pipe.

(27) FIG. 2a is a schematic drawing and is thus not drawn into scale. FIG. 2b is a cross-section of the spindle 3 of FIG. 2a along line Y. The cross-sectional area A1 of the inlet channel for the hydraulic fluid 14 is considerably less than the cross-sectional area A2 of the inlet duct for the feed 13, in analogy with the embodiments shown in FIGS. 1a and 1b. The diameter D1 of the whole spindle 3 in FIGS. 2a and 2b may be 5-300 mm, such as 10-200 mm.

(28) FIG. 3 shows a close-up view of the lower end 3b of the spindle 3 of the centrifugal separator as shown in FIG. 1a. As seen in FIG. 3, there is a first mechanical hermetic seal 18 that seals the lower part of the hollow spindle 3b to stationary pipe 17 that supplies the liquid mixture to be separated, indicated by arrows “A”, to the duct 13 of the spindle. The first hermetic seal 18 comprises a rotating part 18a attached on the lower end of the spindle 3b, and a stationary part 18b attached to the stationary pipe 17. There is also a second mechanical hermetic seal 29 that seals the lower part of the hollow spindle 3b to stationary pipe 20 that supplies the hydraulic fluid to inlet channel 14 (indicated by arrows “B”). The second hermetic seal 29 comprises a rotating part 29a attached on the lower end of the spindle 3b, and a stationary part 29b attached to the stationary pipe 20. Thus, during operation and rotation of the centrifuge rotor, the lower end 3b of the spindle and the rotating parts 29a and 18a of the hermetic seals 29 and 18 rotate, whereas inlet pipes 17 and 20, as well as the stationary parts 29b and 18b of the hermetic seals 29 and 18 stand still. Upon supply of hydraulic fluid to the closing chamber 20 of the centrifugal separator via inlet channel 14 of the spindle, both the interface 18c between the rotating part 18a and the stationary part 18b of the first hermetic seal and the interface 29c between the rotating part 29a and the stationary part 29b of the second hermetic seal are cooled.

(29) FIG. 4 shows a close-up view of the lower end 3b of the spindle 3 of the centrifugal separator as shown in FIG. 2a. As described in relation to FIG. 2a, the liquid mixture that is to be separated, indicated by arrows “A”, is supplied via the radially outermost channel whereas the hydraulic fluid, indicated by arrows “B”, is supplied via the central channel. In other words, the duct 13 is arranged radially outside the inlet channel 14. The first mechanical hermetic seal 18 seals the spindle against stationary pipe 20, whereas the second mechanical hermetic seal 29 seals the spindle against stationary pipe 17. Upon supply of hydraulic fluid to the closing chamber 20 of the centrifugal separator via inlet channel 14 of the spindle, the interface 18c between the rotating part 18a and the stationary part 18b of the first hermetic seal is cooled.

(30) FIG. 5 shows a close-up view of the lower end 3b of the spindle 3 of a centrifugal separator in which a separated liquid phase, indicated by arrows “C” is discharged via the duct 13 of the spindle. The duct 13 is in this embodiment arranged as a central duct in the spindle and the inlet channel 14 for supply of hydraulic fluid is arranged as annular space surrounding the duct 13. As in the embodiment shown in FIG. 3, both the interface 18c between the rotating part 18a and the stationary part 18b of the first hermetic seal and the interface 29c between the rotating part 29a and the stationary part 29b of the second hermetic seal are cooled upon supply of hydraulic fluid to the closing chamber 20 of the centrifugal separator via inlet channel 14 of the spindle.

(31) FIG. 6 shows a close-up view of the lower end 3b of the spindle 3 of a centrifugal separator in which a separated liquid phase, indicated by arrows “C” is discharged via the duct 13 of the spindle. The duct 13 is in this embodiment arranged as an annular space surrounding the inlet channel 14 for supply of hydraulic fluid. The inlet channel 14 thus forms a central duct of the spindle. As in the embodiment shown in FIG. 4, the interface 18c between the rotating part 18a and the stationary part 18b of the first hermetic seal is cooled upon supply of hydraulic fluid to the closing chamber 20 of the centrifugal separator via inlet channel 14 of the spindle.

(32) 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.