Solid Bowl Centrifuge

Abstract

The invention relates to a solid bowl centrifuge with a horizontal elongated, hollow, rotatable, solid-wall bowl (2) with an inlet and an outlet and a rotatable screw conveyor with a shaft (6) and helical screw (7) rotatable mounted inside said bowl and extending substantially the full length thereof. It is mainly characterized in that on the shaft there are mounted a number of truncated conical discs (24), whereby the discs are directly surrounded by the helical screw. With such design the decanter capacity can be increased and the polymer consumption reduced. Further power consumption can be reduced by obtaining the same performances as the traditional decanter at lower rotational speed (lower g-force).

Claims

1.-9. (canceled)

10. Solid bowl centrifuge including: a horizontal elongated, hollow, rotatable, solid-wall bowl (2) with an inlet (11), an outlet (18) for solids, and an outlet (19) for liquids, a rotatable screw conveyor (5) with a shaft (6) having a length and helical screw (7) rotatably mounted inside said bowl (2) and extending substantially the full length of the bowl, and on the shaft (5) there are mounted a plurality of truncated conical discs (24), wherein the improvement comprises that the discs (24) are directly surrounded by the helical screw (7) with a gap between the discs and the screw and without any separating wall in between.

11. Solid bowl centrifuge according to claim 10, wherein discs (24) are mounted along only a part of the length of the shaft (6).

12. Solid bowl centrifuge according to claim 10 wherein each disc has a diameter and the diameter of the discs (24) varies along the length of the shaft (6).

13. Solid bowl centrifuge according to claim 10, wherein the discs (24) are spaced apart longitudinally at a distance and the distance between the discs (24) varies along the length of the shaft (6).

14. Solid bowl centrifuge according to claim 10, wherein the solids outlet (18) and liquid outlet (19) are at opposite ends of the bowl, each disc has a diameter, the discs (24) are spaced apart longitudinally at a distance, and the diameter of the discs (24) increases and the distance between the discs (24) decreases progressively closer to the liquid outlet (19).

15. Solid bowl centrifuge according to claim 10, wherein at least some of the discs (24) have longitudinal through openings (26).

16. Solid bowl centrifuge according to claim 15, wherein the openings (26) have different shapes.

17. Solid bowl centrifuge according to claim 15 wherein the openings (26) have a uniform distribution.

18. Solid bowl centrifuge according to claim 15 wherein the openings (26) have a non-uniform distribution.

19. Solid bowl centrifuge according to claim 10, wherein the gap varies along the length of the screw (7).

20. Solid bowl centrifuge according to claim 11, wherein the discs (24) are spaced apart longitudinally at a distance and the distance between the discs (24) varies along the length of the shaft (6).

21. Solid bowl centrifuge according to claim 12, wherein the discs (24) are spaced apart longitudinally at a distance and the distance between the discs (24) varies along the length of the shaft (6).

22. Solid bowl centrifuge according to claim 12, wherein at least some of the discs (24) have longitudinal through openings (26).

23. Solid bowl centrifuge according to claim 13, wherein at least some of the discs (24) have longitudinal through openings (26).

24. Solid bowl centrifuge according to claim 14, wherein at least some of the discs (24) have longitudinal through openings (26).

Description

[0008] The invention is now explained by example in the following figures, where

[0009] FIG. 1 shows a decanter centrifuge from the state of the art

[0010] FIG. 2 shows an embodiment of the solid bowl centrifuge according to the invention

[0011] FIG. 3 shows a part of the scroll with a different distance between the discs,

[0012] FIG. 4 shows an embodiment of the invention with different gaps and different diameters,

[0013] FIG. 5 shows an embodiment of the invention with a uniform distribution of holes in the discs,

[0014] FIG. 6 shows an embodiment of the invention with a non-uniform distribution of holes in the discs.

[0015] The decanter centrifuge 1 in FIG. 1 according to the state of the art consists of a horizontal, axially symmetrical bowl 2 with a cylindrical section 3 and a conical section 4. The bowl 2 includes an elongated conveyor screw 5 with a central body portion or shaft 6 and surrounded by a continuous screw flight 7. The bowl 2 is at its ends rotatable supported in bearings 8 and 9, respectively, and is driven via a gear 10 ensuring in a known manner that bowl 2 and conveyor 5 in operation rotate relative to each other.

[0016] The suspension to be separated is supplied through an inlet 11 in the form of an inlet tube 12 and extending coaxially with the axis of rotation of the centrifuge through a central passage 13 provided in the shaft 6. The tube 12 ends in a transverse, radial passage 14 discharging into the separating space 15 of the centrifuge. The liquid level in operation is illustrated in dotted lines 16 and solid lines 17. After separation in space 15 solids are discharged through apertures 18 while liquid is discharged through the holes 19 at the end of the bowl.

[0017] Conveyor 5 is constructed as a hollow body with closed cavities 20 and 21. Further a radial support bearing 22 is provided with the radial external surface being adapted to cooperate with the radial internal surface of s circular collar 23 on the shaft 6.

[0018] In FIG. 2 a solid bowl centrifuge 1 according to the invention is shown. Similar parts have the same reference numeral as in FIG. 1. It has as well a bowl 2 with a cylindrical section 3 and a conical section 4. There is also a screw flight 7 (with co-current design), however this flight 7 more or less scratches at the inner surface of the cylindrical section 3 of bowl 2. Directly mounted on the shaft 6 are a number of discs 24, which here are shown as conical discs. These discs are directly surrounded by screw flight 7 without any separating wall inbetween. To allow the liquid (in most cases water) to be separated and discharged a central passage 13 is provided. At the outer radial passage 14 the mixture of liquid and solid particles is transported in direction to the conical section 4 where the separated solids are discharged. The solid particles due to gravity are transported to the outer diameter of the bowl 2 while the liquid phase is recovered due to overflow in the center of the bowl. With the high number of disks 24 in a conical design the surface will be inclined to the axis of the bowl 2. Therefore liquid is flowing only through a small layer of particles. Further the sedimentation speed of the particles is increased, which leads to a shorter clarification time. So the decanter capacity can be increased and the necessary polymer consumption reduced. Another option would be to save energy by running the decanter centrifuge at a lower bowl speed but keeping the same performances compared with traditional decanters at high bowl speed.

[0019] FIG. 3 shows a section of the shaft 6. This part rotates around the axis of rotation 25 of the whole bowl. At the outside of the shaft 6 there is the central passage 13 while on the distance from the shaft 6 there is the radial passage 14 where the liquid solid mixture is introduced and after the separation mainly by gravity the solids are transported by the screw flights 7 to the conical section. On the shaft there are mounted a number of discs 24 between which the separation of liquid and solids takes place.

[0020] In FIG. 4 a design with different disc diameters and different gaps between the discs 24 (with a scroll in counter-current design) is shown. Here the number and diameters of the discs 24 are increasing progressively close to the liquid outlet. With such design an intermediate and high load can be managed with the decanter.

[0021] FIG. 5 shows another embodiment of the invention. Here the discs 24 have holes 26, where the distribution is uniform, i.e. the holes 26 are on the same axis. With such holes the flows between the discs 24 can be improved especially for thickening applications. Instead of holes also openings in the form of windows with different shapes may be used. Also there will be less turbulence for the liquid, which will reduce the re-suspension of the solids inside the decanter.

[0022] FIG. 6 shows a different arrangement of the holes 26 in the discs 24. Here there is a non-uniform distribution of the holes 26. By this measure the flowing time between the discs will be extended and thus a better sedimentation is achieved.