Decanter centrifuge and a screw conveyer

Abstract

A decanter centrifuge for separating a supplied material in a light phase and a heavy phase comprising an elongate bowl arranged for rotation about its longitudinal axis, the bowl having a separation chamber with a circumferential wall, a screw conveyor being provided in the separation chamber and being coaxial with the bowl, the screw conveyor comprising a conveyor hub. The conveyor hub comprises a longitudinal tubular steel body part and a helical steel conveyor flight attached to the tubular steel body part. The conveyor hub further comprises an inner longitudinal body extending coaxially relative the longitudinal tubular steel body part. The inner longitudinal body is extending through at least a part of the tubular steel body and is made of a first material, such as carbon fiber reinforced epoxy, whose specific modulus is larger than specific modulus of the steel material of the tubular steel body part.

Claims

1. A decanter centrifuge for separating a supplied material in a light phase and a heavy phase, comprising: an elongate bowl arranged for rotation about its longitudinal axis, said bowl having a separation chamber with a circumferential wall, a screw conveyor being provided in the separation chamber and being substantially coaxial with the bowl, said screw conveyor comprising a conveyor hub, said conveyor hub comprising a longitudinal tubular steel body part, and a helical steel conveyor flight attached to said longitudinal tubular steel body part, said conveyor hub further comprising an inner longitudinal body extending substantially coaxially relative to said longitudinal tubular steel body part, said inner longitudinal body extending through at least a part of the longitudinal tubular steel body part and being made of a first material whose specific modulus is larger than a specific modulus of the steel material of the longitudinal tubular steel body part; wherein said inner longitudinal body comprises a first section having at least one fiber along a longitudinal axis of said inner longitudinal body at an angle relative to said longitudinal axis, and a second section adjoining the first section, the second section having at least one second fiber arranged circumferentially to the longitudinal axis.

2. A decanter centrifuge according to claim 1, wherein an adhesive layer is applied between at least a portion of an inner surface of the longitudinal tubular steel body part and an outer surface of the inner longitudinal body.

3. A decanter centrifuge according to claim 1, wherein said first material is a fiber reinforced polymer.

4. A decanter centrifuge according to claim 3, wherein said polymer is epoxy.

5. A decanter centrifuge according to claim 3, wherein said fibers comprise carbon fibers.

6. A decanter centrifuge according to claim 1, wherein said at least one fiber of said first section runs at an angle below 20? to said longitudinal axis of the inner longitudinal body to maximize bending strength.

7. A decanter centrifuge according to claim 1, wherein said at least one fiber of said first section runs at an angle below 15? to said longitudinal axis of the inner longitudinal body to maximize bending strength.

8. A decanter centrifuge according to claim 1, wherein said at least one fiber of said first section runs at an angle below 10? to said longitudinal axis of the inner longitudinal body to maximize bending strength.

9. A decanter centrifuge according to claim 1, wherein at least one second fiber is arranged circumferentially relative to said longitudinal axis for every 5-20 substantially longitudinal windings.

10. A decanter centrifuge according to claim 1, wherein said inner longitudinal body is tubular and has a wall thickness that is at least equal to a wall thickness of said longitudinal tubular steel body part.

11. A decanter centrifuge according to claim 1, wherein said inner longitudinal body, over at least a part of its length, radially extends to a center of the conveyor hub.

12. A decanter centrifuge for separating a supplied material in a light phase and a heavy phase, comprising: an elongate bowl arranged for rotation about its longitudinal axis, said bowl having a separation chamber with a circumferential wall, a screw conveyor being provided in the separation chamber and being substantially coaxial with the bowl, said screw conveyor comprising a conveyor hub, said conveyor hub comprising a longitudinal tubular steel body part, and a helical steel conveyor flight attached to said longitudinal tubular steel body part and spaced apart from an inner circumferential wall of the bowl to prevent contact between said helical steel conveyor flight and said inner circumferential wall, said conveyor hub further comprising an inner longitudinal body extending substantially coaxially relative to said longitudinal tubular steel body part, said inner longitudinal body extending through at least a part of the longitudinal tubular steel body part and being made of a first material whose specific modulus is larger than a specific modulus of the steel material of the longitudinal tubular steel body part; wherein said inner longitudinal body comprises a first section having at least one first carbon fiber running at an angle below 20? to a longitudinal axis of the inner longitudinal body to maximize bending strength and a second section adjoining the first section, said second section having at least one second carbon fiber arranged circumferentially to the longitudinal axis.

13. A decanter centrifuge according to claim 12, wherein an adhesive layer is applied between at least a portion of an inner surface of the longitudinal tubular steel body part and an outer surface of the inner longitudinal body.

14. A decanter centrifuge according to claim 12, wherein said first material is a fiber reinforced polymer.

15. A decanter centrifuge according to claim 14, wherein said polymer is epoxy.

16. A decanter centrifuge according to claim 12, wherein said at least one fiber of said first section runs at an angle below 15? to said longitudinal axis of the inner longitudinal body to maximize bending strength.

17. A decanter centrifuge according to claim 12, wherein said at least one fiber of said first section runs at an angle below 10? to said longitudinal axis of the inner longitudinal body to maximize bending strength.

18. A decanter centrifuge according to claim 12, wherein at least one second fiber is arranged circumferentially relative to said longitudinal axis for every 5-20 substantially longitudinal windings.

19. A decanter centrifuge according to claim 12, wherein said inner longitudinal body is tubular and has a wall thickness that is at least equal to a wall thickness of said longitudinal tubular steel body part.

20. A decanter centrifuge according to claim 12, wherein said inner longitudinal body, over at least a part of its length, radially extends to a center of the conveyor hub.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

(2) FIG. 1 shows schematically a decanter centrifuge 1;

(3) FIG. 2a is a front view of a conveyor hub according to a first embodiment of the present invention;

(4) FIG. 2b is a cross-sectional view of the conveyor hub along the line b-b of FIG. 2a;

(5) FIG. 2c is a cross-sectional view corresponding to FIG. 2b, but showing a variant of the conveyor hub; and

(6) FIG. 3 shows an inner longitudinal body with fibre strands according to an embodiment of the present invention.

DETAILED DESCRIPTION

(7) The decanter centrifuge 1 shown in FIG. 1 comprises a bowl 2 and a screw conveyor 3 which are mounted on a shaft 4 such that they in use can be brought to rotate around an axis 5 of rotation, the axis 5 of rotation extending in a longitudinal direction of the bowl 2. Further, the decanter centrifuge 1 has a radial direction 5a extending perpendicularly to the longitudinal direction.

(8) For the sake of simplicity directions up and down are used herein as referring to a radial direction towards the axis 5 of rotation and away from the axis 5 of rotation, respectively.

(9) The bowl 2 comprises a base plate 6 provided at one longitudinal end of the bowl 2, which base plate 6 has an internal side 7 and an external side 8. The base plate 6 is provided with a number of liquid phase outlet openings 9. Furthermore the bowl 2 is at an end opposite to the base plate 6 provided with solid phase discharge openings 10.

(10) In addition, the screw conveyor 3 comprises inlet openings 11 for supplying a material e.g. a slurry to the decanter centrifuge 1, the slurry comprising a light or liquid phase 12 and a heavy or solid phase 13. During rotation of the decanter centrifuge 1 as previously described, separation of the liquid 12 and solid 13 phases is obtained in a separation chamber 26 delimited by a circumferential wall of the bowl 2. The liquid phase 12 is discharged through the liquid phase outlet openings 9 in the base plate 6, while the screw conveyor 3 transports the solid phase 13 towards the solid phase discharge openings 10 through which the solid phase 13 eventually is discharged. As it may be seen, play 21, which is typically 1-2 mm, is provided between the screw conveyor 3 and the circumferential wall of the bowl 2. The play 21 ensures that contact between the flights and the circumferential wall of the bowl 2 is avoided, thus preventing wear on the flights as well as on the circumferential wall of the bowl 2.

(11) FIG. 2a is a front view of a screw conveyor 3 in another embodiment while FIG. 2b is a cross-sectional view of said screw conveyor 3 along the line b-b of FIG. 2a. The screw conveyor 3 comprises the conveyor hub 14 and a helical conveyor flight 15 attached to its outer surface, both provided in steel material. The conveyor hub 14 comprises a cylindrical section 16 having an outer radius (R), a substantially frusto-conical section 17 and a feed inlet section 25 positioned between the cylindrical section 16 and the frusto-conical section 17. A longitudinal tubular steel body part 18 constitutes the outermost portion of said cylindrical section 16. By providing the outermost portion of said cylindrical section 16 in steel material it is ensured that the conveyor hub 14 may withstand the potentially damaging effect of the supplied material. The feed inlet section 25 is provided with inlet openings 11 for supplying the slurry into the interior of the bowl 2, i.e. the separation chamber 26.

(12) The cylindrical section 16 further comprises an inner longitudinal body 19 that may be tubular and that extends coaxially relative said longitudinal tubular steel body part 18 and through the cavity defined by the longitudinal tubular steel body part 18. In a variant embodiment, an inner longitudinal body 19 may, over at least a part of its length, radially extend to the centre of the conveyor hub 14, as shown in FIG. 2c. The inner longitudinal body 19 is made of a material whose specific modulus is larger than specific modulus of the steel material of the longitudinal tubular steel body part 18. The inner longitudinal body 19 and the longitudinal tubular body part 18 are made from a suitable material, such as but not limited to, steel. The specific modulus or stiffness-to-weight ratio is defined as the ratio of elastic modulus and mass density of a material. The material of the inner longitudinal body 19 is, thus, rigid and lightweight. In the preferred embodiment, an epoxy matrix reinforced with carbon fibres, more thoroughly described in conjunction with FIG. 3, is used. A plurality of other materials may be envisaged, provided that their specific modulus is larger than specific modulus of the steel material of the longitudinal tubular steel body part 18. Other polymers as well as non-polymer materials, are equally conceivable. By way of example, carbon fibres may be substituted with kevlar or glass fibres. By combining the longitudinal tubular steel body part 18 and the therein enclosed, inner longitudinal body 19 in rigid and lightweight material, it is achieved that the conveyor hub 14 and, inferentially, decanter centrifuge 1 are capable of withstanding high speed operating conditions while the diameter of the conveyor hub 14 is reduced. The longitudinal tubular steel body part 18 may be constructed with a decreased wall thickness compared to conventional decanter centrifuges. In some embodiments, inner longitudinal body 19 has a greater thickness (T1) than the thickness of longitudinal tubular steel body part 18 (T2). However the wall thickness should be sufficient to provide the necessary strength for carrying the helical conveyor flight 15, which is usually welded onto the hub 14.

(13) As it may be seen in FIG. 2b, an adhesive layer 20 is applied at the interface between the longitudinal tubular steel body part 18 and the inner longitudinal body 19. By applying said adhesive layer 20, said longitudinal tubular steel body part 18 and said inner longitudinal body 19 are fixedly engaged to each other. A suitable adhesive is, for instance, epoxy.

(14) FIG. 3 shows an inner longitudinal body 19 with fibre strands 22 according to an embodiment of the present invention. The fibre strands 22 are wound into a tube and worked into the polymer matrix in a manner well known to the person skilled in the art. In order to achieve a strong and rigid material, carbon fibres are used. In some embodiments, inner longitudinal body 19 includes a first section having at least one fiber, e.g., at least one of fibre strands 22, along a longitudinal axis 23 at an angle (?) relative to the longitudinal axis of the inner longitudinal body, and a second section adjoining the first section, the second section having at least one second fiber, e.g., at least one of fibre strands 24, arranged circumferentially to the longitudinal axis. Said angle (?) is preferably inferior to 20? corresponding to a single winding extending from one end to the other of the tube. This provides for maximum bending strength of the tube. In addition, the at least one winding or layer of fibre strands 24 is arranged substantially circumferentially relative said longitudinal axis for every 5-20 substantially longitudinal windings 22. In this way, an increased structural strength of the inner longitudinal body 19 may be achieved. As an advantage, the risk of crack formation in the inner longitudinal body 19 may be greatly reduced.

(15) The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.