WO1988006921A1

WO1988006921A1 - Centrifuge with chamber walls

Info

Publication number: WO1988006921A1
Application number: PCT/AT1988/000011
Authority: WO
Inventors: Uwe Schaflinger
Original assignee: Uwe Schaflinger
Priority date: 1987-03-09
Filing date: 1988-03-09
Publication date: 1988-09-22
Also published as: AU1393288A

Abstract

To avoid undesirable instability and to improve separation effect, the chamber walls (3) are not disposed radially, but extend by an increasing distance along the radius in the direction of rotation (w) as the distance from the rotational axis (2) increases. A device for continuous operation involves sucking the continuous phase from the boundary layer, keeping said layer absolutely clean. Variations involve plate and bucket centrifuges.

Description

Centrifuge with chamber walls

The invention relates to centrifuges and cyclones with chamber walls. Such devices can be used to separate suspended particles from fluids, but also to enrich gas mixtures. The suspended particles can be liquid or solid, the fluid can be a gas or a liquid. The suspended particles form the discontinuous phase, the fluid the continuous phase. Which phase has the greater density depends on the particular suspension.

According to the prior art, commercially used centrifuges and cyclones are not divided into closed chambers on the inside. Existing internals in some constructions serve only for mechanical safety and do not affect the way the device is punctured. Theoretical and experimental investigations show that the separation process in centrifuges and cyclones is always influenced by the Coriolis acceleration. It causes a reduction in the peripheral speed of the heavier phase compared to the apparatus rotating at a constant angular velocity, which significantly reduces the separation performance of such devices. An increase in the speed does not lead to a corresponding increase in the settling rate.

Modern separators usually consist of several hollow, cylindrical containers that are closed with conical lids. These are intended to increase the separation performance. The mode of action is based on gravity sedimentation in containers with inclined walls.

It has recently become known from theoretical and experimental work that the container geometry of such Apparatus has little influence on the sedimentation rate. In addition, there are instabilities caused by the special shape of the container, which lead to resuspending of the already settled substance, so that the overall separation performance drops significantly below the expected values. The cause here also lies in the effect of the Coriolis acceleration on the flow of the two separating substances. As was reported at a specialist conference, the negative influence of the Ccriolis effect can be compensated for by installing radial walls which divide the annular space between the shaft and the outer wall into closed chambers. A convection flow of the continuous phase arises within each chamber, so that the azimuthal velocity of the heavier phase increases. A thin boundary layer of clear liquid forms on the front of each chamber and flows in relatively quickly (if the continuous phase is lighter than the suspended phase; in the opposite case, the clear liquid film is formed on the back of the chamber). In addition, the installation of radial walls prevents the complete, relative rotation of the two phases to be separated and the separation performance of the apparatus depends on the shape of the lid. However, the previously mentioned instabilities of the flow could not be avoided.

A centrifuge with radial walls is also known from GB-A-2 143 752, in which the walls fulfill the stated task.

From AT-P3 376 923 a conical plate of a separator is known, in which spirally shaped ribs are provided for retaining the disperse phase, the tangent of which at every point encloses an angle with the velocity vector which is greater than the 30-60 ° angle Angle of friction of the disperse phase. The instabilities mentioned are not eliminated in any of the devices.

It is an object of the invention to avoid the instabilities and to further increase the separation performance of the devices mentioned at the outset. As a result, the considerable amount of energy can be reduced or the separation can be improved with the same amount of energy.

According to the invention, this is done in that the chamber walls are not arranged radially, but rather increasingly lead the radius with increasing distance from the axis of rotation in the direction of rotation w.

In the simplest case, flat chamber walls are provided along secant sections of the circular outer wall, which is cheap and easy to manufacture. is. In a variant which makes it possible to maintain the continuous phase with the highest purity during continuous operation, this phase is suctioned off from the boundary layer.

The suction is preferably carried out through openings in the rear of the hollow chamber wall, which forms the front of the chamber.

In plate centrifuges, in accordance with the basic idea of the invention, a special plate shape is provided to support the separating effect of the chamber walls designed according to the invention: the plates should be ribbed in an approximately radial direction in order to allow the clear liquid to flow back without the formation of instabilities.

Particularly in the case of rapidly rotating disc centrifuges, the disc shape should not be conical, but should have a shape which ensures that the normal component of the speed of the phase moving away from the lid is the same for all center distances.

In cup centrifuges, there are inherently individual, but movable chambers, their equilibrium position is not optimal during centrifugation. According to the invention, stops are therefore provided, so that the cup bottoms cannot swing out as far as the equilibrium position. As a result, the inner wall of each cup in the rest position is kept steeper than the equilibrium position during centrifugation, and the centrifugal acceleration, which is dependent on the current radius and is superimposed on gravity, points away from this wall, which causes the formation of the desired boundary layer.

In one embodiment, cup centrifuges provide for the pivot axes of the individual cups to be arranged in such a way that the cup bottoms are pivoted in the direction of rotation of the centrifuge when pivoting upwards as a result of the centrifugal force. This brings the "wall" and "ceiling" of the cups closer to the positions of the walls of plate centrifuges. The cups advantageously have a square or rectangular cross section. This creates surfaces that correspond to the chamber walls.

The invention is explained in more detail with the aid of the drawings, without being restricted thereto.

Fig. 1 shows a centrifuge according to the invention with the cover removed and four chambers; 2 shows a partial view of two adjacent plates of a plate centrifuge designed according to the invention;

3 shows a comparison of the relationships between a cup centrifuge according to the invention and a cup centrifuge corresponding to the prior art

Fig. 4 shows another embodiment of a cup centrifuge according to the invention.

In a centrifuge according to the invention, the axially extending chamber walls 3 installed between the outer cylinder 1 and the drive shaft 2 face According to the invention, a positive inclination over the radius r

to use both the centrifugal acceleration and the Coriolis acceleration to form a convection flow in the plane perpendicular to the axis of rotation of the centrifuge. In the exemplary embodiment, the chamber walls 3 are curved in order to achieve a normal speed amount that is independent of the radius.

The special shape of the walls and the chamber angle θ depends on the task. Smaller angles θ - synonymous with a larger number of chambers - increase the separation performance, the minimum being given by the material properties of the suspension.

As usual, the solid can be e.g. by snails, can be removed from the apparatus. It is only important to ensure that the then unavoidable gap between the walls and sediment does not become too large to achieve an optimal separation effect.

In the chamber A of the centrifuge according to FIG. 1, a suspension 7 'with a heavier discontinuous phase is drawn in during the settling process. A layer of already sedimented material forms on the outer wall 1 under the influence of centrifugal acceleration. At the front of the chamber there is a boundary layer of the clear phase, which flows inwards in the boundary layer. The continuous phase settles along the drive shaft 2.

In the chamber B, a suspension 7 ″ is shown with a lighter discontinuous phase during settling. In this case, the clear boundary layer is created on the back of the chamber and flows outwards there. The lighter sediment is deposited along wave 2.

In plate centrifuges (separators) (Fig. 2), the design-related spacers between the plates 6 are designed as chamber walls 3. In addition, also forms on the upper chamber or - Underside a clear boundary layer. In order to ensure the backflow of the clear liquid underneath the plates (if the discontinuous phase is the easier one, the continuous phase flows outwards there), these should be ribbed, the height of the individual beads 5 again resulting from the task and should at least correspond to the boundary layer thickness. This divides the boundary layer, which corresponds to a narrower chambering.

When centrifuging a suspension with a heavier discontinuous phase, the clear boundary layer of the continuous phase flows on the underside of the chamber along the top of the plates, which is therefore to be ribbed.

The curve generating the plate 6 should only be a straight line with very slowly rotating separators. Since the radial speed of the two phases depends on the location and in order to avoid uncontrollable instabilities, the optimal curve results from the requirement that the normal component of the speed of the phase moving away from the cover is independent of the radius.

The cup centrifuge shown in section in FIG. 3 through the axis of rotation shows on the left a cup which, as is known in the prior art, swings out by the angle oc during centrifugation until it is deflected by equilibrium. Since at a given speed the particles move at different angles to the axis of rotation depending on the current distance from the axis of rotation 300 (in the case of a heavier disperse phase, the particles move within the center of gravity of the cup to the lower and outside to the upper cup wall), but the inclination of the cup walls 301 from depends on the position of the center of gravity of the cup and remains constant over the cup height no stable boundary layer formation.

Due to the stop 403 according to the invention for limiting the swivel angle α to the smaller value β (on the right in FIG. 3), the heavier phase moves reliably away from the inner cup wall 401 and towards the outer cup wall 402. A stable boundary layer of clear liquid is formed on one of the two walls, which significantly speeds up the separation process.

As shown in Fig. 4 in plan view, it is also possible to achieve this effect on the front or rear wall of a centrifuge cup if the pivot axis of the cup is not, as is known and shown on the left at 501, normal to the Connection line is the center of gravity of the axis of rotation 502-500, but has an angle ß less than 90 °. The heavier phase, which in this illustration moves approximately radially outwards and due to the Coriolis acceleration, moves reliably away from the front of the cup and thus enables the formation of a stable liquid boundary layer that accelerates the settling on one of the two sides. Even if the cups are not prismatic, but cylindrical, both measures according to the invention form a clear boundary layer in wall areas which are oriented accordingly, which favors the separation.

In the case shown in FIG. 3, the effect is similar to that of a plate centrifuge disassembled in many chambers; in the case shown in FIG. 4, it is similar to a centrifuge according to FIG.

The invention is not restricted to the examples described, but can be changed and adapted in various ways. So it is possible to vary the number of chambers and to design the shape of the chamber walls differently than specified. Aware of the Erfin It is easy for the specialist to find the cheapest solution for the respective application. With cup centrifuges it is also possible to achieve the formation of the boundary layer by changing the shape of the cups, it being necessary for at least one wall to be inclined more than the path lines of the phase of interest in its vicinity.

With continuous operation it is of course possible not only to suck off the clear continuous phase from the boundary layer, preferably on the chamber walls, but also to introduce the mixture to be separated through openings in the chamber walls where there is no clear boundary layer.

Claims

Claims:

1. Centrifuge with chamber walls between. an axis of rotation and a circular outer wall, characterized in that the chamber walls (3), with increasing distance from the axis of rotation (2) in the direction of rotation (w), increasingly lead the radius (r).

2. Centrifuge according to claim 1, characterized in that flat chamber walls are provided along secant sections of the circular outer wall (1).

3. Centrifuge for continuous operation according to one of claims 1 or 2, characterized in that the continuous phase is sucked out of the boundary layer (4).

4. Centrifuge according to claim 3, characterized in that the suction takes place through openings in the sides of the hollow chamber walls, at which a clear boundary layer (4) forms during centrifuging.

5. Centrifuge according to one of claims 1 to 3, which is designed as a plate centrifuge, characterized in that the plates (6) are ribbed in the radial direction.

6. Disc centrifuge according to claim 5, characterized in that the plates (6) have a shape by which the normal components of the speed of the phase moving away from the cover are the same for all center distances.

7. Cup centrifuge, characterized in that stops are provided which do not allow the cup bottoms to pivot as far outwards and upwards as it corresponds to the equilibrium position.

Cup centrifuge according to claim 7, characterized in that the cup bottoms are also pivoted in the direction of rotation of the centrifuge when pivoting upwards due to the centrifugal force.