Centrifugal separator with disc stack having discs of different diameters

Abstract

A centrifugal separator includes a frame and a drive member configured to rotate a rotating part in relation to the frame around an axis of rotation. The rotating part includes a centrifuge rotor closing a separation chamber. The separation chamber includes a stack of separation discs arranged coaxially around the axis of rotation at a distance from each other such as to form passages between each two adjacent separation discs. The stack of separation discs includes a first type of separation discs having an outer diameter of A or below, and at least one separation disc of a second type having outer diameter B or above, wherein diameter B is larger than diameter A. At least one of the separation discs of the second type is arranged at a position in the disc stack that is within the upper 15% of the total number of separation discs and at least one of the first type of separation disc is arranged axially above the uppermost separation disc of the second type.

Claims

1. A centrifugal separator comprising: a frame; and a drive member configured to rotate a rotating part in relation to the frame around an axis of rotation, wherein the rotating part comprises a centrifuge rotor enclosing separation chamber, wherein the separation chamber comprises a stack of separation discs arranged coaxially around the axis of rotation at a distance from each other to form passages between each two adjacent separation discs, and wherein the stack of separation discs comprises: a first type of separation discs having an outer diameter of A or below; a plurality of first openings in each of the first type of separation discs, each opening in each of first type of separation discs being at a first radial distance from the axis of rotation; at least one separation disc of a second type having outer diameter B or above; and a plurality of second openings in each of the second type of separation discs, each opening in each of the second type of separation discs being at the first radial distance from the axis of rotation; wherein the plurality of first openings and the plurality of second openings form distribution channels in the stack of separation discs, wherein diameter B is larger than diameter A, wherein at least one of the separation discs of the second type is arranged at a position in the disc stack that is within the upper 15% of the total number of separation discs and wherein at least one of said first type of separation disc is arranged axially above the uppermost separation disc of the second type, and wherein all of the separation discs of the second type are arranged within the upper 50% of the total number of separation discs.

2. The centrifugal separator according to claim 1, wherein the discs of the second type are distributed in the stack such that more discs of the second type are arranged within the upper 15% of the total number of separation discs than arranged within the rest of the disc stack.

3. The centrifugal separator according to claim 2, wherein at least one of the separation discs of the second type is arranged at a position in the disc stack that is within the upper 10-12% of the total number of separation discs.

4. The centrifugal separator according to claim 2, wherein the diameter B is 3-15% larger than the diameter A.

5. The centrifugal separator according to claim 2, wherein the disc stack comprises a single separation disc of the second type.

6. The centrifugal separator according to claim 1, wherein at least one of the separation discs of the second type is arranged at a position in the disc stack that is within the upper 10-12% of the total number of separation discs.

7. The centrifugal separator according to claim 6, wherein the diameter B is 3-15% larger than the diameter A.

8. The centrifugal separator according to claim 1, wherein the diameter B is 3-15% larger than the diameter A.

9. The centrifugal separator according to claim 1, wherein the disc stack comprises a single separation disc of the second type.

10. The centrifugal separator according to claim 1, wherein the separation disc of the second type has a separation surface with the same inclination with respect to the radial direction that extends to the outer diameter of the separation disc.

11. The centrifugal separator according to claim 10, wherein the separation disc of the second type has a brim portion formed radially outside the diameter A, said brim portion having an inclination to the radial direction different from the inclination of the separation surface.

12. The centrifugal separator according to claim 11, wherein the angle of the brim portion to the radial direction is less than 45 degrees.

13. The centrifugal separator according to claim 1, wherein the passages between each two adjacent separation discs are formed by caulks having a thickness that is less than 0.6 mm.

14. The centrifugal separator according to claim 1, wherein the passages between each two adjacent separation discs are formed by radial caulks.

15. The centrifugal separator according to claim 1, wherein the plurality of first openings are slits arranged at the perimeter of the disc to distribute the flow of fluid to be separated through and over the disc stack.

16. A method of separating impurities from oil comprising the steps of: a) providing the centrifugal separator according to claim 1 and rotating said rotating part of said separator: b) introducing the oil into the separation chamber; and c) discharging purified oil and separated impurities as two different phases from said separator.

17. The method according to claim 16, wherein the oil is selected from heavy fuel oil and lubrication oil.

18. A centrifugal separator comprising: a frame; and a drive member configured to rotate a rotating part in relation to the frame around an axis of rotation, wherein the rotating part comprises a centrifuge rotor enclosing a separation chamber, wherein the separation chamber comprises a single stack of separation discs arranged coaxially around the axis of rotation at a distance from each other to form passages between each two adjacent separation discs, wherein the stack of separation discs comprises: a first type of separation discs having an outer diameter of A or below; a plurality of first openings in each of the first type of separation discs, each opening in each of the first type of separation discs being at a first radial distance from the axis of rotation; at least one separation disc of a second type having outer diameter B above; a plurality of second openings in each of the second type of separation discs, each opening in each of the second type of separation discs being at the first radial distance from the axis of rotation; wherein the plurality of first openings and the plurality of second openings form distribution channels in the stack of separation discs, wherein diameter B is larger than diameter A, and wherein at least 50% of the separation discs of the second type are arranged at a position in the disc stack that is within the upper 25% of the total number of separation discs and wherein at least one of said first type of separation disc is arranged axially above the uppermost separation disc of the second type.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows perspective views of embodiments of separation discs.

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

(3) FIG. 3 further shows the position of the second type of discs within the disc stack.

DETAILED DESCRIPTION

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

(5) In FIG. 1a a separation disc 1 of first type in the disc stack is shown, having a frustoconical separation portion 2 with an inner and an outer separation surface. The separation portion is provided with a plurality of distance members in the form of straight elongated caulks 3 providing distances to form passages between each two adjacent separation discs in a stack formed by a stack of separation discs. The caulks 3 in FIG. 1a form in an angle with the radius of the disc 1, but the caulks could also be straight radial caulks, i.e. caulks that do not form an angle with the radius of the disc 1. The caulks are fastened to the outer surface of the frustoconical separation portion of the disc and distributed around the circumference of the disc. The caulks may also or as an alternative be provided on the inner surface of the disc. The caulks may also be formed as an integral part of the disc.

(6) The outer diameter A of the separation disc is in this embodiment 308 mm and the inclined separation surface extend all the way out to this outer diameter. Thus the radially outer portion 4 of the separation disc is part of the inclined separation surface. The disc is provided with a plurality of cut-outs in the form of slits 5 at this radially outer portion 4 of the separation disc, which slits are open towards the outer radius of the separation disc. The number of slits 5 correspond to the number of caulks and the slits are distributed around the circumference of the disc in-between the caulks.

(7) In FIG. 1b separation disc 6a of the second type in the disc stack is shown, having a frustoconical separation portion 2 with an inner and an outer separation surface. The separation portion is provided with a plurality of distance members in the form of straight elongated caulks 3 providing distances to form passages between each two adjacent separation discs in a stack formed by a stack of separation discs. The caulks 3 in FIG. 1b form in an angle with the radius of the disc 1, but the caulks could also be straight radial caulks, i.e. caulks that do not form an angle with the radius of the disc 1. The caulks are fastened to the outer surface of the frustoconical separation portion of the disc and distributed around the circumference of the disc. As with the disc in FIG. 1a, the caulks may also or as an alternative be provided on the inner surface of the disc. The caulks may also be formed as an integral part of the disc. The separation surface extend to the diameter A and radially outside the separation surface the disc is provided with a flat brim 7 (i.e. having an angle of zero degrees to the radial direction) extending to the outer diameter of the separation disc B. The diameter B is in this embodiment 328 mm and the diameter A is in this embodiment 308 mm. The radial extension L of the brim is L=(BA)/2, i.e. 10 mm. The diameter B is thus 6.5% larger than the diameter A. The disc is provided with a plurality of cut-outs in the form of through holes 8 at the radially outer part of the separation portion, which cut-outs are closed towards the outer radius of the separation disc by means of the brim. The number of holes 8 corresponds to the number of caulks and the holes are distributed around the circumference of the disc at positions corresponding to the slits of the separation disc 1 in the first type.

(8) FIG. 1c shows a further example of a separation disc 6b of the second type. The disc 6b has a frustoconical separation portion 3 and straight elongated caulks 3 as described in relation to FIG. 1b, but in contrast to the disc in FIG. 1b, the inclined separation surface of the frustoconical separation surface 2extend all the way out to the outer diameter B. The diameter B is in this embodiment 328 mm, i.e. it extends radially a distance L of 10 mm compared to a disc having a diameter of A=308 mm. The separation disc 6b is further provided with a plurality through holes 8 that ends at a radial distance of A/2, which means when arranged above or below a separation disc 1 of the first type, the through holes 8 may be radially aligned with the slits 5 of the separation disc 1 of the first type to form distribution channels.

(9) FIG. 2 shows a portion of a centrifugal separator 9 for separation of a liquid mixture of components, the separator having a rotor 10 supported by a spindle 11 (partly shown) which is rotatably arranged in a frame 24 (partly shown in FIG. 2) around an axis of rotation (x). The rotor forms within itself a separation chamber 12 wherein a disc stack 13 is arranged. In the separation chamber 12 centrifugal separation of e.g. a liquid mixture to takes place during operation. The rotor further comprises an inlet chamber 14 formed within a distributor 15 into which a stationary inlet pipe 16 extends for supply of a liquid mixture of components to be separated. The inlet chamber communicates with the separation chamber via passages 17 formed in the rotor. The radially inner portion of the disc stack communicates with an outlet 18 for a lighter liquid component of the mixture. The outlet 18 is delimited by a top disc 19 provided at the upper axial end of the disc stack 13. The top disc 19 and the upper wall part of the rotor 10 delimits a passage for a denser liquid component of the mixture, the passage extending from the radially outer part of the separation chamber 12 to an outlet 20 for the a heavier component of the liquid mixture. The rotor is further provided with outlets 21 from the radially outer periphery of the separation chamber 12 for intermittent discharge of a sludge component of the liquid mixture comprising denser particles forming a sludge phase. The opening of the outlets 21 is controlled by means of an operating slide 22 actuated by operating water, as known in the art.

(10) The disc stack 13 comprises a first and a second type of separation discs, the first type comprising separation discs 1 of the kind shown in FIG. 1a, and the second type comprising a separation disc 6b of the kind shown in FIG. 1c. The separation discs are arranged coaxially around the axis of rotation (x) at a distance from each other by means of the caulks 3, 3, such that to form passages between each two adjacent separation discs. The passages extend from the radially outer portions of the separation discs to the radially inner portions of the separation discs. In the figure the distance between each separation disc is exaggerated and the disc stack is schematically shown to have 28 discs. A typical disc stack comprises 80-180 discs and a typical distance between the separation discs, generated by the caulks, may be below 0.75 mm, such as below 0.6 mm, such as about 0.5 mm. In embodiments, the distance between the separation discs are 0.4-0.75 mm, such as 0.4-0.6 mm, such as about 0.4-0.5 mm.

(11) The single disc 6b of the second type is arrange at a position in the disc stack 13 that is within the upper 10-12% of the total number of separation discs. In this embodiment, the rest of the disc stack contains only separation discs 1 of the first type.

(12) The cut-outs in the form of slits on the separation discs 1 of the first type and the cut-outs in the form of holes on the separation disc 6b of the second type are aligned in the disc stack to form axial distribution channels 23 for the liquid mixture.

(13) The clearance F between the radially outer end of the separation disc 6b of the second type and the interior wall of the rotor may be at least 1.5 mm and the radial extension L of the second type of separation disc 6b from the perimeter of the first type of separation disc 1 may be about 10 mm.

(14) During operation of the separator in FIG. 2, the rotor 10 is caused to rotate by torque transmitted from a drive motor (not shown) to the spindle 11. Via the inlet pipe 16, liquid material to be separated is brought into the inlet chamber and is further led via passages 17 to the separation chamber 12. Depending on the density, different phases in the liquid is separated in the disc stack 13 fitted in separation chamber 12. 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 18 arranged at the radial innermost level in the separator. The liquid of higher density is instead forced out through outlet 20 that is at a radial distance that is larger than the radial level of outlet 18. Thus, during separation, an interphase between a liquid of lower density and the liquid of higher density is formed in the separation chamber 12. Solids, or sludge, accumulate at the periphery of the separation chamber 12 and is emptied intermittently from the separation chamber by the sludge outlets 21 being opened, whereupon sludge and a certain amount of fluid is discharged from the separation chamber by means of centrifugal force. However, the discharge of sludge may also take place continuously, in which case the sludge outlets 21 take the form of open nozzles and a certain flow of sludge and/or heavy phase is discharged continuously by means of centrifugal force.

(15) FIG. 3a shows a close up of the disc stack 13 of FIG. 2 comprising a single disc 6b of the second type, whereas the rest of the discs are of the first type 1. As stated in relation to FIG. 2, the distance between each separation disc is exaggerated and the disc stack is schematically shown to have 28 discs. A typical disc stack comprises 80-180 discs. The disc stack 13 may thus comprises N number of discs, i.e. N may be 80-180, and be arranged at positions P.sub.1 to P.sub.N, wherein position 1 is the upper position closest to the top disc 19 and position P.sub.N is closest to the distributor 15. The single disc 6b is then positioned at position P.sub.n, wherein n/N0.15. As an example, if the disc stack comprises N=100 discs, then the disc 6b is positioned at position P.sub.n, wherein n15. Thus, the disc 6b is within the upper 15 discs, such as at position 10, 11, or 12.

(16) FIG. 3b shows a further embodiment of a disc stack 13 comprising a single disc 6b of the second type and the rest of the discs of the first type 1, but wherein the single disc has a brim portion, i.e. a disc as described in relation to FIG. 1b. The single disc is arranged at a position in the disc stack that is within the upper 15% of the total number of separation discs, such as within the upper 10-12% of the total number of separation discs.

(17) FIG. 3c shows an embodiment of a disc stack 13 comprising two discs 6b of the second type as described in relation to FIG. 1c and the rest of the discs of the first type 1. Both discs are arranged at positions in the disc stack that is within the upper 15% of the total number of separation discs, within the upper 10-12% of the total number of separation discs.

(18) FIG. 3d shows an embodiment of a disc stack 13 comprising two discs 6b of the second type as described in relation to FIG. 1c and the rest of the discs of the first type 1. In this example, one of the discs 6b is arranged at a position in the disc stack that is within the upper 15% of the total number of separation discs, such as within the upper 10-12% of the total number of separation discs, whereas the second of the discs 6b is arranged approximately in the middle of the disc stack 13.

(19) 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.

Experimental Example 1

(20) Material and Methods

(21) The Certified flow rate (CFR) was tested in a marine centrifugal separator suitable for separating heavy fuel oil (HFO). The CFR was tested in a test rig according to the DNV standard for certification No. 2.9 Type Approval Programme 776.60 using liquids of two different densities, 35 cSt and 55 cSt, respectively. Four different disc stack configurations were used; one reference, which was a disc stack only comprising discs of the first type, and three configurations also comprising discs of the second type. The differences in configurations are summarized in Table 1 below:

(22) TABLE-US-00001 TABLE 1 Disc stack configurations for Experimental Example 1. Disc stack configuration Total number Discs of larger diameter No of discs (N) (second type) Pn/PN Reference 160 1 160 15 discs in the middle of the stack, starting at position n = 16 from the top and arranged as every eighth disc. 2 160 Single disc at position n = 18 0.1125 from the top 3 160 Single disc at position n = 8 0.05 from the top

(23) The discs of the first type in the disc stacks of all configurations had a diameter of 308 mm and a thickness of 0.5 mm, and were spaced apart with straight radial caulks having a thickness of 0.5 mm.

(24) The discs of the second type had a larger diameter, 328 mm, and had a separation surface with the same inclination with respect to the radial direction that extended to the outer diameter of the separation disc. The discs had further a thickness of 0.5 mm and had straight radial caulks of thickness 0.5 mm.

(25) Results

(26) The CFR was tested using liquids of two different densities, 35 cSt and 55 cSt. The results are summarized in Table 2 below:

(27) TABLE-US-00002 TABLE 2 CFR values for the different disc stack configurations. Disc stack configuration CFR (m3/h) CFR (m3/h) No 55 cSt 35 cSt Reference 6.8 11.25 1 7.5 11.2 2 7.5 11.8 3 7.4 n.a

(28) The results thus shows that all Configurations performed better than the Reference disc stack, and that having a single disc in the top (Configurations 2 and 3) performed as well or better compared to when having discs of larger diameter also in the middle of the disc stack (Configuration. 1). For Configuration 2, the increase in CFR was as high as 10% with the liquid of 55 cSt. This example thus highlights the significance of having a disc of larger diameter in the top of the disc stack.