EP0421188B1 - Pusher centrifuge - Google Patents

Description

The invention relates to a pusher centrifuge with at least two rotating sieve drums in a housing, in the interior of which centrifugal material can be fed at one end, and with at least one annular thrust ring at the edge of one of the sieve drums, which has an oscillating movement in the axial direction of the sieve drums for feeding the partially dewatered centrifuged material on the inside of each subsequent drum towards a solids outlet.

Such pusher centrifuges are known from DE-C-38 10 565 and are used for the continuous dewatering of centrifuged material, which is fed to the inner end of a centrifugal space via a feed pipe and is successively dewatered on the inside of the sieve drums. During this process, the centrifuged material by the axially oscillating movement of one or more thrust rings between adjacent sieve drums gradually advanced towards a solids outlet, and at the same time non-dewatered centrifugal material is refilled in the vicinity of the thrust floor. Such a pusher centrifuge has a plurality of sieve drums, two adjacent sieve drums each oscillating in the axial direction relative to one another and the edge of the inner sieve drum acting as a push ring. For example, in a two-stage centrifuge, the drum, in a three-stage centrifuge, the moving floor and the second drum, and in a four-stage centrifuge, the first and third drums can oscillate in the axial direction.

Such a pusher centrifuge enables continuous dewatering of a centrifugal material, which is gradually dewatered in the centrifugal field from the centrifugal material inlet to the solids outlet during the feed on the inside of the sieve drums and reaches the solids outlet in a largely dewatered state, while the filtrate reaches the outside through the sieve drums penetrates and is discharged there. Especially with high centrifugal material throughputs and fine grain, a cake layering is formed on such push centrifuges on the sieve drums, which does not change significantly during feed until ejection. The solid cake formed becomes increasingly compact and therefore impermeable, so that the degree of dewatering and the residual moisture of the discharged solid contribute certain centrifugal goods is not yet optimal and requires an extension of the dewatering time and an increased speed and a high energy consumption.

To improve the drainage, it has been proposed to loosen the solid cake formed during the drainage process when the thrust ring is pushed forward in the axial direction by inclined surface elements on the thrust rings and thus to accelerate the drainage. For many centrifugal goods, this measure leads to an improvement in dehumidification without increasing the speed of the sieve drums and the residence time of the centrifuged material. In the case of particularly sensitive centrifugal goods, however, there is a risk of grain breakage and abrasion if such thrust elements move abruptly.

A single-stage pusher centrifuge is known from DE-B-1 060 795, in which the pusher floor is additionally rotated relative to the screen drum during the forward stroke. A shear movement is only exerted on the freshly supplied, still largely liquid suspension, which, however, does not improve the dewatering of the already partially dewatered filter cake.

The invention has for its object to avoid the aforementioned disadvantages of the prior art and to create a pusher centrifuge with an increased degree of dewatering and lower residual moisture of the discharged solid, which also Drainage of particularly sensitive centrifugal material without grain breakage and abrasion is suitable.

According to the invention, this object is achieved in that a rotating device is provided, by means of which the thrust ring simultaneously executes a rotary movement about the axis direction of the sieve drums during the feed, the thrust ring having a rough surface structure.

Due to this additional rotary movement of the thrust ring during the feed process, the solid cake is very gently carried along and loosened by the lateral movement in the circumferential direction, so that the dewatering performance is improved. By suitable adjustment of the angle of rotation at each feed phase, this loosening can be carried out so gently that grain breakage is largely avoided. The rough surface of the push ring ensures that the cake is carried particularly gently, e.g. depending on the material due to micro-roughness or radial grooves on the surface.

With particular advantage, the rotary movement can also take place in an oscillating manner, so that turning back and loosening also take place when withdrawing, which can be effected in a simple manner with a screw guide of the corresponding sieve drum shafts against one another. However, it is also possible to provide the rotary movement only during the feed phase, while the pulling ring is retracted by a movement in the axial direction or in another direction.

The relative rotary movement of the thrust ring can moreover be directed in the direction of rotation of the sieve drums, which can be advantageous in the case of fragile crystals, or else opposite to this direction of rotation. The latter can be important for mixtures that are difficult to filter or low solids concentrations in the centrifuged material.

Fig. 1

eine teilweise aufgeschnittene Schubzentrifuge in perspektivischer Ansicht,

Fig. 2

diese Zentrifuge im Schnitt entlang einer die Rotationsachse enthaltenden Schnittebene, und

Fig. 3

a-d verschiedene Ausführungen der Oberfläche des Schubringes.

The invention is explained in more detail with reference to the exemplary embodiments shown in the figures. Show it:

Fig. 1

a partially cut open centrifuge in perspective view,

Fig. 2

this centrifuge in section along a section plane containing the axis of rotation, and

Fig. 3

ad different designs of the surface of the thrust ring.

The pusher centrifuge shown in FIGS. 1 and 2 in perspective and in section has a centrifugal unit consisting of two rotatable sieve drums 1 and 2, a stationary centrifuge housing 3 surrounding it, a solid space 4 adjacent to the centrifugal unit at the outlet, and one close to the inner end of the centrifugal unit a moving floor 8 with a centrifugal material inlet 9 leading supply line 5 for the centrifuged material to be dewatered, a solids outlet 6, and a liquid space 7 for the ejected liquid.

The inner screening drum 1 is mounted on a shaft 10, by means of which it can be set in rotation at a certain speed. At the same time, the shaft 10 can be displaced in the axial direction A and, in addition to its rotation, can also perform an oscillating movement in the axial direction with a certain amplitude. The outer screening drum 2 is fastened to a hollow shaft 11, with which it can also be set in rotation, but without an oscillating movement in the axial direction.

The shaft 10 of the inner sieve drum is connected to the hollow shaft 11 of the outer sieve drum by means of a screw guide 12. In the example shown, this consists of a number of helically shaped grooves 13 on the outside of the shaft 10, in which a number of cams 14 engage on the inside of the hollow shaft 11. This has the effect that when the two screening drums 1 and 2 are displaced relative to one another in the axial direction or when the inner shaft 10 moves relative to the hollow shaft 11, the inner screening drum 1 and especially its edge acting as a thrust ring 1 'also undergo a rotary movement in addition to the feed movement executes a certain angle. Conversely, the grooves can also be provided on the outside of the shaft and the cams on the inside of the hollow shaft.

The push centrifuge described is operated as follows: through the feed pipe 5, the centrifugal material to be dewatered is fed into the interior of the innermost Screen drum 1 is then introduced directly into the sliding floor 8 and flows there radially outward onto the screen drum 1, where the dewatering process begins. The partially dewatered centrifugal material is advanced through the oscillating sieve drum 1 in the direction of the adjoining outer sieve drum 2 and is further dewatered in the process. Additional centrifugal material to be dewatered is now continuously supplied through the feed line 5. When the partially dewatered centrifugal material reaches the end of the inner sieve drum 1, it is transported from the edge thereof, which acts as a thrust ring 1 ', to the outer sieve drum 2 and is further dewatered there. Finally, the completely dewatered centrifuged material is transported through the relative oscillation of the two sieve drums 1 and 2 to the solids space 4, which it leaves via the solids outlet 6.

Due to the relative rotary movement of the thrust ring 1 'about the axis A in the circumferential direction with respect to the outer sieve drum 2, the cake, which has already been partially dewatered, is taken along a little by the thrust ring and loosened gently, so that the still bound coarse capillary and gusset liquid of the partially dewatered cake is exposed without provoking a grain break, so that the drainage is significantly improved. In addition, the movement along a helix has a greater drainage effect because of the somewhat longer length. The washing effect of loosened cakes is also significantly improved. In addition, the formation of unbalance in the centrifuge is avoided because the cake is reshaped with every turning stroke and is thus balanced.

The degree of twisting in the circumferential direction with a full stroke of the thrust ring must be matched to the centrifuged material to be processed and selected in accordance with the need for protection and the risk of grain breakage when loosening the partially dewatered cake. In an example of a two-stage pusher centrifuge with a 630 mm largest drum diameter for dewatering, for example, NaHCO₃, a rotation of approximately 8 ° was chosen at a speed of 1400 revolutions / minute and 75 strokes of the thrust ring per minute of 60 mm amplitude for each stroke. Here, the degree of drainage of the NaHCO₃ at the solids outlet was improved from approximately 13% to approximately 12% without increasing the speed, without disturbing grain breakage occurring. This means a reduction in the liquid content of almost 8%.

While the subject matter of the invention has been described above with reference to an embodiment with a screw guide and twisting when feeding and turning back when the thrust ring is withdrawn, other embodiments with an analogous effect are also possible.

The additional rotary movement of the thrust ring can be carried out in the same direction as the rotation of the sieve drums, which generally results in a gentler treatment of the centrifuged material, which is particularly advantageous in the case of fragile, for example needle-shaped, crystals. With less sensitive centrifugal material, however, the additional rotary movement of the thrust ring can also be provided counter to the drum rotation.

The thrust ring 1 'could indeed be designed with a relatively smooth surface, as shown in FIG. 3a, the shear movement of the centrifuged material being effected solely by the sliding friction occurring during the additional rotary movement. The treatment of the centrifuged material would be particularly gentle here, but it is often not sufficient to take it with you. For better entrainment of the centrifugal material by the thrust ring in the circumferential direction, however, this is provided with a certain micro-roughness 17 on its surface, as shown schematically in FIG. 3b. An even better entrainment results if the thrust ring 1 'has a rough surface structure deviating from a smooth circular ring surface, e.g. by providing radially extending grooves 15, 16 on the thrust ring, as shown in Fig. 3c or 3d.

Analogous relationships apply to more than two-stage pusher centrifuges. In the case of a three-stage centrifuge, the push floor and the second sieve drum can oscillate synchronously in the axial direction and at the same time perform a rotary movement, in the case of four-stage centrifuges, however, the first and third drums.

Claims (7)

1. A pusher centrifuge having at least two straining drums (1, 2) which rotate in a housing (3) and into the interior of which material to be centrifuged can be fed at one end, and having at least one annular pusher ring (1') at the edge of one of the straining drums (1, 2) which carries out a movement, oscillating in the axial direction of the straining drums, for the advance of the partially drained material to be centrifuged on the inside of the respectively following straining drum (2) in the direction of a solids outlet (6), characterised in that a rotating mechanism (12, 13, 14) is provided, by means of which the pusher ring (1') during the advance at the same time carries out a rotary movement about the axial direction (A) of the straining drums (1, 2), the pusher ring (1') having a rough surface structure.
2. A pusher centrifuge according to claim 1, characterised in that the pusher ring (1') has a microroughness (17) on its annular surface.
3. A pusher centrifuge according to claim 1, characterised in that the pusher ring (1') has radial grooves (15, 16) on its annular surface.
4. A pusher centrifuge according to any one of claims 1 to 3, characterised in that the rotating mechanism (12, 13, 14) is arranged to carry out a mutual return rotation of the straining drums (1, 2) during the pull-back of the pusher ring (1').
5. A pusher centrifuge according to claim 4, characterised in that the rotating mechanism has a screw guide (13, 14) for the shaft (10) of the straining drum (1) carrying the pusher ring (1').
6. A pusher centrifuge according to claim 5, characterised in that the screw guide (12) is provided between the shaft (10) of the one straining drum (1) and the shaft (11) of the following straining drum (2) and has helically fashioned grooves (13) on the one shaft (10) and bosses (14) on the other shaft (11).
7. A pusher centrifuge according to claim 6, characterised in that the helically fashioned grooves (13) are provided on the outside of the shaft (10) of the straining drum (1) carrying the pusher ring (1') and the bosses (14) are provided on the inside of the shaft, designed as a hollow shaft (11), of the following straining drum (2).

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