EP1434655A1

EP1434655A1 - Wet classification device

Info

Publication number: EP1434655A1
Application number: EP01274580A
Authority: EP
Inventors: Guntram Krettek
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-10-06
Filing date: 2001-10-06
Publication date: 2004-07-07
Anticipated expiration: 2021-10-06
Also published as: DE10196972D2; JP4188240B2; CN1308089C; CN1578703A; WO2003035267A1; EP1434655B1; JP2005506192A; US7033311B2; DE50109652D1; US20040259711A1

Abstract

Disclosed is a wet classification device in the form of a centrifuge provided with a stationary outer housing (1), a centrifugal drum (2) arranged in the outer housing, a device (13) for cleaning sediment deposited on the wall of the centrifugal drum, and inlets and outlets. The cleaning device comprises a shaft which extends into the centrifugal drum and has cutting devices (21, 22) arranged on the periphery thereof, in addition to a device for introducing a dispersing fluid in the centrifugal drum. The cutting devices are configured and arranged in such a way that turbulence can be created in the infed dispersing fluid, thereby resulting in a wash-out effect with respect to the sediment cake and facilitating the removal thereof.

Description

wet classification device

The present invention relates to a wet classifying device in the form of a centrifuge with a stationary outer housing, a centrifugal drum arranged in the outer housing, a cleaning device for the sediment deposited on the wall of the centrifugal drum and inlets and outlets.

Such a wet classification device is known. It is used, for example, to remove the large proportion of powders such as titanium dioxide. Today, more and more ultrafine materials with a particle size between 0.1-5 μm are used. Such particle sizes can be achieved by finely grinding raw materials, but this is associated with relatively high operating costs, since this requires a great deal of energy, cooling systems are required, there is a relatively high level of pollution of the environment and a large proportion of undersized particles are produced, etc. Such problems do not occur with wet class centrifuges. Here, the solid (powder) is mixed with a liquid (usually water) in a premix tank in order to obtain a suspension. If necessary, the suspension is diluted in a subsequent dilution tank and then introduced into the wet classifier designed as a centrifuge. Within In the rotating centrifugal drum, the heavier and coarser particles are guided radially outwards against the drum wall faster than the lighter and finer ones in the suspension, where they settle as sediment. The sediment is detached from the drum wall in the cleaning phases of the wet classification device, with cleaning liquids, mechanical cleaning devices such as knives etc. being used for this, depending on the embodiment. The sediment redispersed in the cleaning liquid is finally removed from the centrifugal drum and, for example, fed to a separately arranged ball mill, in which the bulk of the redispersed suspension is ground. The prepared suspension can then be reintroduced into the system, for example fed to the premix tank.

The classified suspension is continuously withdrawn from the wet classification device during the classification process and used for further use.

When centrifuging ultrafine materials, high centrifuging factors are required in addition to an optimal rotor design in a large number of applications for a high separation effect. Due to these high centrifugation factors, a very stable and very hard sediment cake is formed with the appropriate centrifugation time. To make matters worse, in a large number of applications hard materials with a Mohs hardness of between 3 to 10 must be centrifuged suspended in liquid. The devices known for emptying centrifuges generally fail here, ie they cannot peel or discharge the sediment cake. This has been confirmed in the past by worn knives, broken peeling devices and bent or broken knife shafts. Because of the high cutting forces to brake the main drive motor to a standstill.

The object of the invention is to create a wet classifying device of the type specified at the outset with which the sediment cake can be removed or discharged in a particularly problem-free manner.

This object is achieved according to the invention in a wet classification device of the type specified in that

the cleaning device comprises a shaft which can be pivoted or moved linearly in the centrifugal drum, on the circumference of which at least two strip-shaped cutting devices are arranged, and a device for introducing a shaft

Has dispersing liquid in the centrifugal chamber and

the two cutting devices are set against each other, form a space widening between them in the direction of movement of the shaft and have a gap between them at their adjacent ends.

With the solution designed according to the invention, the problems outlined above are avoided. It is thus possible to easily peel or remove the sediment cake without causing damage to the cutting devices and the shafts carrying them. In other words, the wear on the cutting devices and the shafts carrying them is reduced, and lower forces occur than in the prior art, so that breaks, bending etc. of the cutting devices and shafts are largely eliminated. The problems with a negative influence (braking) of the main drive motor, which are caused by the high cutting forces in the prior art, are also avoided. As stated above, this is achieved by a special configuration of the cleaning device of the wet classification device. The cleaning device uses a combination of mechanical features with the addition of a dispersing liquid. The design of the mechanical features, ie the special arrangement and design of the cutting devices, results in a swirling of the dispersing liquid supplied, which has a positive effect on the peeling and removal of the sediment cake.

In particular, the mutually opposed cutting devices, which form a space which narrows against the direction of movement of the shaft and which opens into a gap, mean that no linear flow conditions of the dispersing liquid form, but instead generate turbulence by repeatedly pushing the liquid back towards the sediment that lead to an intensive swirling of the dispersion liquid, which results in an intensive washout on the sediment surface. As a result, the cake can be detached more easily and better by the cutting devices penetrating it, i.e. lower forces are required for detachment than in the prior art. The above-described hydrodynamic effects are achieved by the narrowing of two adjacent cutting devices, which results in the mentioned gap, which must be present in order to allow the dispersion liquid to pass through, albeit slightly.

The dispersing liquid is preferably added via the cutting and return movement phase of the cleaning device. The liquid still present in the centrifugal drum from the classification process is usually not sufficient to achieve the hydrodynamic effect described above (swirling in the area of the sediment cake surface).

The narrowing or widening space ensures that the additional dispersion liquid (dilution liquid) supplied during the cleaning process is led to the largest drum diameter and thus also to the largest sediment mass. This results in the aforementioned intensive swirling, which also has a certain cake washing effect. There is therefore no concrete mechanical contact between the sediment cake and the tips of the cutting devices. Rather, the sediment cake is liquefied and discharged gently.

As far as the introduction of the dispersing liquid into the centrifugal drum is concerned, the device for introducing the dispersing liquid in the head region of the cutting devices preferably opens into the drum chamber. As a result, the dispersing liquid is led directly into the vicinity of the sediment cake surface, so that the desired swirling effect can be achieved well. In this solution, the dispersing liquid supplied does not have to be introduced into the liquid column (classification liquid) located in the centrifugal drum, but the dispersing liquid is introduced directly inside the liquid column, which has a number of advantages.

Investigations have shown that the strip-shaped cutting devices should preferably be arranged at an angle of 15-45 ° to a plane perpendicular to the shaft axis in order to achieve the best results with regard to problem-free peeling. The gap between the adjacent ends of the cutting devices can expediently be set as a function of the solids content and the viscosity of the suspension or of further parameters. In this way, optimal conditions can be achieved for the respective application. It goes without saying that the size of the widening or narrowing space (the distance between the employed cutting devices) is also adjusted by the gap adjustment mentioned. Of course, the cutting devices can also be adjusted so that their angle of attack is changed.

In a particularly preferred embodiment of the invention, the gap additionally widens in the direction from the shaft to the head of the cutting devices. This results in a preferably double-conical design, which further promotes the effects mentioned above. This creates double turbulence that further promotes detachment. In this embodiment, the space between the two cutting devices thus narrows in addition to the smallest radius.

In a further development of the invention, the cutting devices or their heads have structured surfaces. These surfaces can be formed, for example, by the arrangement of grooves, ridges, etc. All surfaces of the cutting devices or only a part of these surfaces can be structured. As a result, an additional vortex generation is achieved in the dispersion liquid supplied.

The cutting devices can be detachably arranged on the shaft, so they can be replaced depending on the application. The device for introducing the dispersing liquid preferably has a channel extending through the shaft, from which channels running through the cutting devices branch off. As a result, the dispersing liquid can be guided up to the tips of the cutting devices and can exit into the centrifugal chamber at a point adjacent to the sediment cake.

The shaft can perform a linear movement or a pivoting movement in order to move into the sediment cake. When performing a swiveling movement, the shaft preferably moves by 80-120 ° to penetrate the sediment. In this case, the shaft performs a step movement (back and forth) over the desired angle, which movement can preferably be adjusted depending on the respective product.

The device for introducing the dispersing liquid expediently introduces this during the cutting and return movement phase of the shaft.

As far as the formation of the strip-shaped cutting devices is concerned, the invention has no restrictions here. Known strip-shaped cutting devices (knives) can be used. The strip-shaped cutting devices preferably consist of flat steel profiles clad with high-strength material.

In the embodiment in which the dispersing liquid is passed through channels running through the cutting devices, these channels preferably open at the end faces of the cutting devices, so that the dispersing liquid exits from the end faces of the cutting devices into the drum chamber. The introduced dispersing liquid can be under pressure in order to further support the washout effect described above. In addition to the pure dispersing function, it can also have other functions, for example

Washing functions, solid concentration adjustment functions etc.

The invention leads to particularly good results if the centrifugal drum has chambers separated from one another by partitions. These partitions preferably extend horizontally and form rings which are connected to the outer wall of the drum. The arrangement of such partitions is known in principle.

The present invention is used in particular in wet classifying devices in which the slenderness ratio of the centrifugal drum is L / D> 1.2, where L is the length or height of the classifying surface available in the centrifugal drum and D is the inside diameter of the

Centrifugal drum is. Such a wet classification device is described in DE 199 25 082 AI. The disclosure of this publication is incorporated by reference into the present disclosure.

The invention is also particularly well suited to a wet classifier that is provided with an integrated grinder. Such a wet classification device is described for example in DE 199 14 089 AI. The disclosure of this publication is also incorporated by reference into the present disclosure.

Finally, the invention is particularly suitable for a wet classifying device which is at the same time designed as a dispersing device. Such a device is described for example in DE 199 14 086 AI. The disclosure of this publication is also incorporated by reference into the present disclosure.

The invention is described in detail below using an exemplary embodiment in conjunction with the drawing. Show it:

1 shows a longitudinal section through a wet classification device, the provided on the shaft

Cutting devices are not shown;

FIG. 2 shows an enlarged partial view of the shaft with cutting devices arranged thereon;

FIG. 3 shows a detail from FIG. 2 with cutting devices shown in detail; and

FIG. 4 shows a section along line A-B in FIG. 3

The wet classifying device shown in FIG. 1 in the form of a centrifuge has a stationary housing 1 with a cover 15 arranged thereon. The stationary housing 1 is mounted on a storage rack by means of suitable vibration damping devices. A centrifugal drum 2 with a vertical axis is arranged within the stationary housing 1 and is rotated by a vertical shaft 8. The vertical shaft 8 extends into the centrifugal drum 2 from below. It is surrounded by a bearing housing 11 which contains an upper main bearing 9 and a lower second bearing 10 for supporting the shaft 8. The bearing housing 11 is fastened to a plate 17, which in turn is fastened to the stationary housing 1. The shaft 8 extends through the bearing housing 11 and the plate 17 downwards via a suitable coupling device. device 18 to a direct drive forming electric motor 12. The speed of the shaft 8 is adjustable.

The centrifugal drum 2 has a suitable feed (not shown) for the suspension to be classified, which extends, for example in the form of a tube, through the centrifugal drum open at the top into the lower end region thereof and has an outlet opening there. The classified suspension is drawn off from the upper end of the centrifugal drum 2 via a draw-off tube 16. A discharge pipe 14 at the lower end of the centrifugal drum serves to remove the sediment.

As can also be seen in FIG. 1, the centrifugal drum is thus circular in its lower region and circular in its upper region. Horizontal dividing walls 4 divide the inside of the centrifugal drum into six classification chambers 3 arranged one above the other, in the radial end regions of which the sediment is deposited. From there, this is shown schematically at 13

Cleaning device removed.

The centrifugal drum 2 described here is as slim as possible, and the main bearing 9 of the shaft is as central as possible, i.e. in the area of the focus of the

Centrifugal drum, arranged. It can be seen that the main bearing 9 is arranged so deep in the centrifugal drum that the vertical center of the main bearing 9 of the shaft 8 is arranged at a height h, measured from the inner lower end of the centrifugal drum, which is approximately 40% of the

Length or height L of the classification area available in the centrifugal drum 2. Furthermore, the slenderness ratio L / D of the centrifugal drum has, ie the ratio between the length or height of the classification area available in the centrifugal drum and that Inside diameter of the centrifugal drum, a value of about 1.24. It is understood that the values given above are purely exemplary. In this embodiment, there are six classification chambers 3 arranged one above the other in the centrifugal drum 2.

As mentioned, an upper main bearing 9 and a lower second bearing 10 for the shaft 8 are arranged in the bearing housing 11. This results in stable storage. The shaft 8 extends from the top of the bearing housing 11 and ends in a section with a reduced diameter. At this section, the central hub 6 of the centrifugal drum is fixed, which is formed in the axial extension of the cylindrical inner wall 5 of the centrifugal drum. The fixation is realized via friction contact (at 7). At the upper end, the hub 6 is closed by a cover.

The mode of operation of such a wet classifying device is known and need no longer be explained in detail at this point. It is essential that the high slenderness ratio selected results in a large distance between the intake and removal and thus a reduction in the risk of short-circuit currents, which ultimately leads to better separation. Furthermore, a high spin factor (it can be driven at high speeds) and a large classification area are achieved by a large number of chambers arranged one above the other.

It goes without saying that, on the basis of these conditions, particularly high demands must be placed on the functionality of the cleaning device 13, since a correspondingly stable and very hard sediment cake is formed. These requirements are met with the cleaning device described below. The cleaning device 13 has a shaft 20 projecting into the centrifugal drum from above, which carries out a step movement (pivoting movement by an angular dimension of approximately 80-120 °) into the sediment cake formed on the drum wall and back into the starting position. During the cutting as well as during the return movement phase of the shaft 20, a dispersing liquid is introduced into the centrifugal drum for cleaning. Details of this will be described later.

Figure 2 shows an enlarged view of a portion of the shaft 20 of the cleaning device 13. This shaft is driven by a suitable stepper motor. A plurality of strip-shaped cutting devices 21, 22 are arranged one above the other on their circumference, two adjacent cutting devices 21, 22 being positioned against one another and forming between them a space 26 widening in the direction of movement of the shaft 20 and having a gap X between them at their adjacent ends , The strip-shaped cutting devices 21, 22 (knives) are structured over their entire surfaces, i.e. provided with grooves, as shown schematically at 25 on a cutting device 22.

Figures 3 and 4 show the more precise structure of the

Cutters 21, 22. It can be seen that the cutters are set up so that they are arranged at an angle (o./2) of 15-45 ° to a plane perpendicular to the shaft axis. The main plane of the cutting devices 21, 22 extends in the embodiment shown here perpendicular to the axis of the shaft 20, but can also run obliquely to the latter, so that the gap X and the space 26 also widen in the radial direction towards a larger diameter. The horizontal sectional view of FIG. 4 shows the lower one in FIG. 3 Cutting device 21 with its cutting head 27 and cutting bar 28. The cutting device consists of a flat steel profile, which is armored.

FIG. 2 shows that a feed channel 23 for the dispersing liquid (cleaning liquid) is arranged in the shaft 20 and extends parallel to the shaft axis. Two channels 24 extend from the channel 23 through the respective strip-shaped cutting devices 21, 22 which open at the end faces (heads) of the cutting devices.

The gap X formed between the adjacent cutting devices and thus the space 26 extending therefrom is adjustable.

The cleaning device works in such a way that the stepper motor (not shown) moves the shaft 20 counterclockwise by approximately 80-120 ° into the sediment cake formed in the chambers 3. During this movement phase, dispersing liquid is supplied via the channels 23 and 24 and discharged into the drum chamber at the tips (heads) of the cutting devices. The dispersing liquid escaping is repeatedly pressed towards the sediment cake by the arrangement of the cutting devices and thereby swirled. In this way, a corresponding washout process is achieved on the surface of the sediment cake, so that the cutting devices no longer have to come into direct contact with the sediment cake. Rather, it is liquefied and thus peeled off gently by the cutting devices. When the shaft moves backwards, dispersing liquid is also supplied so that a good and complete removal of the sediment cake can be achieved.

Claims

claims

1. Wet classifying device in the form of a centrifuge with a stationary outer housing (1), a centrifugal drum (2) arranged in the outer housing (1), a cleaning device (13) for the sediment deposited on the wall of the centrifugal drum and inlets and outlets (14, 16 ) , in which

the cleaning device (13) has a shaft (20) which can be pivoted or moved linearly in the centrifugal drum (2) and on the periphery of which at least two strip-shaped cutting devices (21, 22) are arranged, and a device for introducing a dispersing liquid into the centrifugal drum (2 ) and

the two cutting devices (21, 22) are set against each other, form a space (26) which widens in the direction of movement of the shaft (20) and have a gap (X) between them at their adjacent ends.

2. Wet classifying device according to claim 1, characterized in that the device for introducing dispersing liquid in the head region of the cutting devices (21, 22) opens into the drum chamber.

3. Wet classification device according to claim 1 or 2, characterized in that the strip-shaped cutting devices (21, 22) are arranged at an angle of 15-45 ° to a plane perpendicular to the shaft axis intersecting.

4. Wet classification device according to one of the preceding claims, characterized in that the gap (X) between the adjacent ends of the cutting devices (21, 22) is adjustable.

5. Wet classification device according to one of the preceding claims, characterized in that the gap (X) additionally widens in the direction from the shaft (20) to the head (27) of the cutting devices (21, 22).

6. Wet classification device according to one of the preceding claims, characterized in that the cutting devices (21, 22) or their heads (27) have structured surfaces (25).

7. Wet classification device according to one of the preceding claims, characterized in that the cutting devices (21, 22) are detachably arranged on the shaft (20).

8. Wet classification device according to one of the preceding claims, characterized in that the device for introducing the dispersing liquid has a channel (23) extending through the shaft (20), from which through the cutting devices (21, 22) branch channels (24) ,

9. Wet classification device according to one of the preceding Claims, characterized in that the shaft (20) carries out a pivoting movement of 80-120 ° into the sediment.

10. Wet classification device according to one of the preceding

Claims, characterized in that the device for introducing the dispersing liquid introduces it during the cutting and return movement phase of the shaft (20).

11. Wet classification device according to one of the preceding claims, characterized in that the strip-shaped cutting devices (21, 22) consist of flat steel profiles clad with high-strength material.

12. Wet classification device according to one of claims 2 to 11, characterized in that the device for introducing dispersing liquid from the end faces of the cutting devices (21, 22) opens into the drum combs.

13. Wet classification device according to one of the preceding claims, characterized in that the introduced dispersing liquid is pressurized.

14. Wet classifying device according to one of the preceding claims, characterized in that the dispersing liquid has further functions, for example washing functions, solids concentration setting functions, etc.

15. Wet classification device according to one of the preceding claims, characterized in that the centrifugal drum (2) separated from one another by partitions (4) Has chambers (3).

16. Wet classification device according to one of the preceding claims, characterized in that the slenderness ratio of the centrifugal drum (2) is L / D> 1.2, where L is the length or height of the classifying surface available in the centrifugal drum (2) and D is the inside diameter of the centrifugal drum (2).

17. Wet classification device according to one of the preceding claims, characterized in that it is provided with an integrated grinder.

18. Wet classification device according to one of the preceding claims, characterized in that it is simultaneously designed as a dispersing device.