Decanter centrifuge

Abstract

Decanter centrifuge with a rotatable drum (10) that tapers conically towards a solids outlet (58) and forms a liquid outlet (64) at the opposite end, a stationary inlet pipe (44) arranged axially to the drum for feeding a suspension into the interior of the drum, and a screw (20) rotatably arranged in the drum and rotatably mounted at both ends in bearings (40, 42), which forms a helix (30, 32) extending radially towards the inner circumferential surface of the drum (10), characterized in that the screw (20) has at one end a projection coaxially to the inlet pipe (44) on which one of the bearings (40, 42) is arranged and which is part of a fluid pipe (38) that is tightly connected to the inlet pipe (44) outside the drum (10) via a rotary coupling (46) and extends into the interior of the drum (10) leads.

Description

[0001] The invention relates to a decanter centrifuge with a rotatably driven drum which tapers conically towards a solids outlet and forms a liquid outlet at the opposite end, a stationary inlet pipe arranged axially to the drum for feeding a suspension into the interior of the drum, and a screw rotatably arranged in the drum and rotatably mounted at both ends in bearings, which forms a helix extending radially to the inner circumferential surface of the drum.

[0002] Decanter centrifuges of this type are used to separate mixtures that typically consist of a solid and a liquid phase. However, there are also applications where two liquid phases and one solid phase are present. These mixtures are referred to here, without limitation, as "suspensions."

[0003] Examples of decanter centrifuges of this type are described in JP. Hermeler, L. Horstkötter, T. Hartmann, "New decanter generation with improved energy efficiency", F & S Filtrien und Separieren, Volume 26 (2012) No. 3 and in WO 2019 / 081177 A1. Another decanter centrifuge is known from DE3638652.

[0004] The suspension is pumped into the centrifuge via the stationary inlet pipe, where centrifugal force creates a liquid ring, a so-called "pond," on the inner circumferential wall of the drum. Internal components in the screw drive the suspension from the center outwards into the liquid ring, accelerating it to the peripheral speed of the screw and the drum. Due to centrifugal force, the heavier particles separate out on the inner wall of the drum. A slight difference in rotational speed between the screw and the drum transports the solids through the screw's helix to the solids outlet. Finally, the solids cake is pushed out of the liquid ring and discharged through outlets in the drum shell. Simultaneously, the clarified liquid flows out through the liquid outlet on the opposite side of the drum.

[0005] In conventional decanter centrifuges, the inlet pipe protrudes freely into the interior of the screw through a hub that closes off the drum on the liquid outlet side. The screw is rotatably mounted at its outlet end on a stub of a drum hub that surrounds the inlet pipe. This design can lead to the problem that, at certain screw speeds, the inlet pipe is excited to resonate vibrations, which can cause vibrations and material damage.

[0006] In practice, a centrifuge is also known in which the screw is mounted at one end on a hub of the drum and in which the inlet pipe is connected via a rotary coupling to a fluid pipe that rotates with the screw, extends freely through the interior of the screw and is supported in the hub of the drum by means of a support bearing.

[0007] The object of the invention is to create a decanter centrifuge with improved running characteristics.

[0008] This problem is solved according to the invention by the fact that the screw has at one end a projection coaxially to the inlet pipe, on which one of the bearings is arranged and which is part of a fluid pipe that is tightly connected to the inlet pipe outside the drum via a rotary coupling and leads into the interior of the drum.

[0009] This design has the advantage that the supply and distribution of the suspension inside the drum does not occur via a section of the inlet pipe projecting freely into the screw and the drum, but rather via a separate fluid pipe that forms a rigid unit with the screw. The bending stiffness of the fluid pipe is therefore increased by the overall screw design to such an extent that virtually no resonance vibrations occur within the centrifuge's regular speed range. Since the fluid pipe is rotatable relative to the inlet pipe, both pipes are connected by a rotary coupling. Part of the fluid pipe also forms an extension of the screw, on which one of the screw's bearings is mounted. This bearing can be located radially inside a hub of the drum and / or axially outside the drum, and therefore occupies only a small amount of space inside the drum.

[0010] Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0011] In one embodiment, the rotary coupling connecting the inlet pipe to the fluid pipe is located outside the hub that closes off the drum. In this case, a section of the fluid pipe adjoining the rotary coupling passes tightly through the hub and is supported outside the hub in a frame that also houses the drum bearing. This design has the advantage of reducing the radius of the liquid outlet and thus increasing the depth of the pond, since no space is required inside the drum for the screw bearing. Increasing the pond depth improves the centrifuge's process performance in many applications.

[0012] In another embodiment, the fluid tube can, for example, be supported directly in the hub of the drum by a compact needle bearing. In this case as well, no installation space inside the drum is required for the bearing.

[0013] Furthermore, the invention achieves a higher degree of design freedom in the construction of the centrifuge, since the suspension can be fed into the interior of the drum not only from the end where the liquid outlet is located, but also optionally from the conically tapered end where the solids outlet is located.

[0014] The following are examples of implementation explained in more detail with reference to the drawing.

[0015] They show: Fig. 1 shows an axial section through a decanter centrifuge according to the invention; Fig. 2 shows a section along line II-II in Fig. 1 ; and Fig. 3 shows an axial section through a decanter centrifuge according to another embodiment.

[0016] The in Fig. 1 The decanter centrifuge shown has a drum 10, which is axially divided into a cylindrical section 12 and a conical section 14 and is closed at both ends by respective hubs 16, 18. Inside the drum 10 is a screw 20, which, like the drum, is divided into a cylindrical section 22 and a conical section 24. In the conical section 24, the screw has an inner shell 26, which is closed off towards the cylindrical section 22 by an end wall 28 and carries a helical helix 30 on its outer circumference, extending to the inner surface of the conical section 14 of the drum.The cylindrical section 22 of the screw has a helical helix 32, which has a lower height than the helix 30 and is supported with its inner circumference on the axially extending outer edges of support walls 34, which extend in the axial direction of the drum and are arranged star-shaped around the axis of the drum (. Fig. 2 ).

[0017] The hub 16 of the drum is rotatably mounted in a frame 37 by means of a bearing 36. Another bearing (not shown) supports the drum 10 at the opposite end. The screw 20 forms a fluid tube 38 in its cylindrical section 22, running coaxially with the drum 10 and rigidly connected to the inner edges of the support walls 34. A section of this fluid tube forms an extension of the drum, which is led outwards through a sealed opening in the hub 16. Outside the drum 10, this extension is supported in the frame 37, in which the hub 16 is also mounted, by means of a bearing 40. At the other end of the screw, the inner shell 26 of the screw 22 forms an axial extension, which is supported in the hub 18 by means of a bearing 42. The drum 10 and the screw 20 can be driven at slightly different speeds by rotary drives (not shown).

[0018] A stationary inlet pipe 44 runs coaxially to the drum 10 outside of this drum and terminates at a distance in front of the hub 16. An outlet end of the inlet pipe 44 is connected to the fluid pipe 38 of the screw 20 via a fluid-tight rotary coupling 46.

[0019] The fluid tube 38 opens within the cylindrical section 22 of the screw into a distribution chamber 48, which is connected via radial openings to the spaces between the radial support walls 34. The support walls 34 are connected to each other by disc-shaped stiffening rings 50.

[0020] The support walls 34 are welded to the inner shell 26 of the conical section 24 of the screw as well as to the fluid tube 38 and the stiffening rings 50, so that a bending and torsionally stiff support structure for the helix 32 is formed.

[0021] In Fig. 2 The star-shaped arrangement of the load-bearing walls 34 can be seen. Furthermore, it can be seen in Fig. 2 a single turn of the helix 32, an outer part of the end wall 28 of the inner shell 26, the stiffening rings 50, and the cross-section of the fluid tube 38. In the space between the helix 32 and the end wall 28, one can see a baffle plate 52, which is arranged in the drum 10 at the transition between the cylindrical part 12 and the conical part 14 and which is interrupted in the region of the lower apex by a slot 54.

[0022] The following describes how the decanter centrifuge works.

[0023] The drum 10 and the screw 20 are driven at slightly different speeds such that the screw 20 rotates somewhat faster than the drum 10. An emulsion to be decanted is pumped into the interior of the drum 10 via the inlet pipe 44 and the fluid pipe 38 of the screw 20 and deflected radially outwards in the distribution chamber 48. The suspension is accelerated circumferentially outside the distribution chamber 48 by the radial support walls 34, so that, due to its inertia, it spreads into a thin film on the leading surface of each support wall and flows radially outwards due to centrifugal force.

[0024] The suspension collects on the inner circumferential surface of the cylindrical part 22 of the drum to form a liquid ring or "pond", the inner surface of which 56 in Fig. 1 und 2 is shown with a dashed line. Due to centrifugal force, the heavier solid phase of the suspension settles on the inner surface of the drum and is moved to the left by the helix 32 due to the differential rotation of the screw and drum. Fig. 1 driven, i.e., towards the conical end of the drum. Through the last turn of the helix 32, the solid cake is forced through the slot 54 of the baffle plate 52 into the conical section 24 of the screw under increasing compaction and then taken over by the helix 30 and transported to the tapered end of the conical section 14 of the drum, where it is discharged via a solid outlet 58 formed by radial discharge openings.

[0025] The hub 16 at the right end of the drum 10 is interrupted by openings 60, which, together with an annular weir 62, form a liquid outlet 64. The inner diameter of the weir 62 determines the position of the inner surface of the liquid ring. As the suspension is introduced, the depth of the "pond" increases, and once the level of the inner diameter of the weir 62 is reached, the clarified liquid flows in a slow, steady axial flow through the spaces between the support walls 34 to the liquid outlet 64. The flowing liquid is only slightly disturbed, allowing for very effective separation of the solid phase. Compared to conventional designs, the inner diameter of the weir 62 can be very small, since no space is required in the area of ​​the liquid outlet 64 for the bearing of the screw 20. For example, this inner diameter need not exceed 20% of the diameter of the drum 10.This allows for a greater pond depth and thus an improvement in the centrifuge's performance.

[0026] By replacing weir 62, the depth of the pond can be varied depending on the operating conditions.

[0027] The torsional stiffness of the supporting structure for the helix 32 can be increased by increasing the outer diameter of one or more of the stiffening rings 50, possibly up to the inner surface of the fluid ring or, if one accepts a small detour of the fluid via the spaces between the helix 32, also up to the inner diameter of the helix 32.

[0028] Fig. 3Figure 1 shows an embodiment that differs from the previously described embodiment in that the inlet pipe 44 and the rotary coupling 46 for the fluid pipe 38 are located at the end of the drum 10 formed by the conical section 14 and supported by a bearing 66 in the frame (not shown). Accordingly, the fluid pipe 38 passes tightly through the hub 18. In this example, the fluid pipe 38 is an integral part of the inner shell 26 and extends through the end wall 28 into the distribution chamber 48 inside the cylindrical section 12 of the drum. The support walls 34 extend coaxially from a central tube 68 of the screw. The screw is supported directly in the drum 10 by the bearing 42 and a bearing (not shown) located on the central tube 68 at the opposite end.

Claims

1. Decanter centrifuge having a rotationally drivable drum (10) which tapers conically towards a solids outlet (58) and forms a liquids outlet (64) at the opposite end, a stationary inlet tube (44) which is disposed axially to the drum for feeding a suspension into the interior of the drum, and a screw (20) which is disposed so as to be rotationally drivable in the drum and rotatably mounted by way of both ends in bearings (40, 42) and forms a helix (30, 32) which radially reaches the inner circumferential surface of the drum (10), wherein the screw (20) at one end has an appendage which projects coaxially with the inlet tube (44) and on which one of the bearings (40, 42) is disposed, wherein the appendage is part of a fluid tube (38) which is tightly connected to the inlet tube (44) outside the drum (10) by way of a rotary coupling (46) and leads into the interior of the drum (10), wherein a part of the fluid tube (38) simultaneously forms the appendage of the screw (20) and the fluid tube (38) conjointly with the screw (20) forms a rigid unit, characterized in that an internal circumference of the helix (30, 32) in a cylindrical portion of the screw (20) is supported on axially extending outer edges of radial support walls (34) which extend in the axial direction of the drum (10) and are disposed in a star shape about the axis of the drum (10), and the inner edges of which are rigidly connected to the fluid tube (38) .

2. Decanter centrifuge according to Claim 1, wherein the drum (10) is closed at one end by a hub (16, 18), and the fluid tube (38) leads in a fluid-tight manner through the hub (16; 18) and outside the drum (10) is mounted in a frame (37).

3. Decanter centrifuge according to Claim 1, wherein the drum (10) is closed off at one end by a hub (16, 18), and the fluid tube (38) is rotatably mounted in the hub (16; 18).

4. Decanter centrifuge according to one of the preceding claims, wherein the drum (10) has a cylindrical portion (12) and a conical portion (14), and the inlet tube (44) and the rotary coupling (46) are disposed at that end of the drum (10) that is formed by the cylindrical portion (12).

5. Decanter centrifuge according to one of Claims 1-3, wherein the drum (10) has a cylindrical portion (12) and a conical portion (14), and the inlet tube (44) and the rotary coupling (46) are disposed at that end of the drum (10) that is formed by the conical portion (14).

6. Decanter centrifuge according to Claim 4 or 5, wherein the fluid tube (38) opens out in the interior of the cylindrical portion (12).

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