GB2178672A

GB2178672A - Continuous screw centrifuge

Info

Publication number: GB2178672A
Application number: GB08614931A
Authority: GB
Inventors: Wilfried Flory
Original assignee: HEINKEL IND ZENTRIFUGEN
Current assignee: HEINKEL IND ZENTRIFUGEN
Priority date: 1985-06-27
Filing date: 1986-06-19
Publication date: 1987-02-18
Also published as: DD246047A5; DE3522970A1; JPS6223462A; IT8620952A0; IT8620952A1; GB8614931D0; IT1191825B

Abstract

A continuous screw centrifuge has a rotating solid-walled drum 5 and a filter 1 which extends generally transversely across the drum to filter the liquid discharging therefrom. The filter may be an annular disc mounted either on the drum or on the differentially-rotating screw 4. Apertures 10 may allow liquid to bypass a clogged filter, and baffles 11, 12 separate the filtrate from the bypass liquid. The filter may be cleaned continuously by an arm 9 rotating with the screw or the drum. <IMAGE>

Description

SPECIFICATION Apparatus for clarifying the centrifugated matter of a continuously impinged solidjacket screw centrifuge The invention relates to an apparatus for clarifying the centrifugated matter of a continuously impinged solid-jacket screw centrifuge.

This type of centrifuge is often used in the separation of solid and liquid matter, in particular when large amounts of suspension are to be treated and these contain greater amounts of solid matter. It is also designated as a decanting centrifuge or decanter. The essential feature of this centrifuge is a screw for discharging the solid matter; this screw corotates in the interior of the drum at a slightly different rotational speed.

Although very small particles are also deposited as sediment on the drum floor in the centrifugal field, in particular when flocculation means are used, small solid particles do remain in the centrifugated matter for various reasons.

In many cases, the centrifugated matter is desired to be as free of solids as possible, for example during recovery of valuable solvents.

Moreover, the use of flocculation means is very costly and often disadvantage because subsequent chemical processes may be affected thereby.

A discontinuously operated centrifuge, in which the centrifugated matter is clarified, is already known (Swiss patent specification CH-PS 076). The mode of operation of this centrifuge is based on the fact that, in the solid-jacket drum impinged by suspension, the liquid phase flows through a filter in axial direction whereas the solids are deposited on the drum floor. After a certain filling time, the supply of suspension ceases, the suspension is centrifugally dried and the dehydrated solids discharged.

Due to its discontinuous discharge of solids, this centrifuge is suitable only for suspensions having a low solids content as, otherwise, the apparatus has to be emptied too often. Moreover, the supply of suspension has to be interrupted to allow solids to be discharged and this is undesirable in a number of processes.

Proceeding on the basis of this state of the art, the object is to construct a continuously operated solid-jacket screw centrifuge such that the centrifugated matter hereby obtained is as free of solids as possible.

This object is accomplished by the invention in that a filtering device is provided in the region of the centrifuge outlet for the centrifugated matter.

The filtering medium, through which the centrifugated matter automatically flows, sepa rates off the solid particles which results in centrifugated matter free of solids. Since most of the solid particles in the suspension are deposited as sediment on the drum floor and transported away by the screw, the liquid to be filtered has only a minimal solids content.

This means that any filtering media which are utilized for clarifying filtration may be used in this case.

In a particularly advantageous embodiment of the invention, a filter is secured either to the screw or to the drum at tight angles to the axis of rotation. This filter consists of a filter frame, over which a filtering medium is stretched which is suitable for the specific separation problem involved. If the filter is secured to the screw, a seal or gap must be provided between the drum casing and the filter rim. This prevents the passage of any unclarified liquid. If the filter is secured to the drum there is no necessity for a seal between filter rim and screw as the level of liquid is not located in this region.

According to an alternative embodiment of the invention, a filter body is provided on the rear wall of the drum and positively penetrates the drum rear wall of a customary centrifuge.

The filter body projects into the rear wall of the drum to such a depth that the overflow openings are covered by a suitable filtering medium, which is secured to the filter body, in the region of the inner side of the drum.

This embodiment is eminently suitable when available decanting centrifuges are to be subsequently equipped with such an apparatus.

In an advantageous embodiment of the invention, the overflow openings in the rear wall of the drum are substantially enlarged in comparison with conventional centrifuges. The overflow openings can hereby extend a considerable distance over the periphery or the radius of this rear wall. In this case, as weli, a positively adapted filter body is secured directly on the rear wall of the drum. The filtering medium is again secured to the filter body in the region of the inner side of the drum. In this embodiment, the surface available for filtering is substantiaily increased in size and so the throughput can also be considerably increased.

In a further embodiment of the invention, the rear wall of the drum is designed such that it can be used itself as a filter frame. In this case, as well, a filtering medium suitable for the specified separating problem to be encountered is mounted in the region of the inner side of the drum. An additional filter body is superfluous in this embodiment and this can save on energy.

Under average, operating conditions it may be assumed that the filtered solid particles agglomerate on the filtering medium and are removed by centrifugal and shearing forces, due to the difference in the speed of rotation between screw and drum.

For special separating problems it may be advantageous to provide a cleaning device.

This may consist of a cleaning arm which ro tates at a different speed to the filtering medium and wipes off solid particles adhering thereto.

If the filtering medium becomes clogged, despite these measures, it is advantageous to provide auxiliary overflow openings which prevent the centrifuge becoming blocked or obstructed.

The clarified liquid is prevented from mixing with the auxiliary overflow liquid by a dividing means. This may, for example, consist of a guide baffle or gutter and a collecting baffle or gutter. The auxiliary overflow liquid is transported away separately in the collector housing and fed to the suspension supply.

It should be mentioned that use of the invention apparatus is particularly recommended in those cases where agitator elements are mounted on the screw for the purpose of reducing residual moisture.

As it is possible, in this case, for particularly small particles which have already been sedimented out to be whirled about and mix with the centrifugated matter, the filtration of this centrifugated matter can eliminate this disadvantage.

The invention is described in the following, by way of example, on the basis of the drawings, in which Figure 1 is a schematic longitudinal section of one embodiment of a solid-jacket screw centrifuge, Figure 2 is a schematic longitudinal section of another embodiment, Figure 3 is a plan view of the drum rear wall of a further embodiment.

In the embodiment illustrated in Fig. 1, the disc-shaped filter 1 is mounted on the screw 4 at right angles to its axis of rotation. The screw rotates at a different speed to the drum 5. The filter 1 comprises a filter frame 3 and a filtering medium 2 which is suitable for the respective separation problem involved and is secured to the filter frame. A seal 6 is provided between the circumference of the filter and the drum casing to prevent the passage of any unclarified liquid. A cleaning arm 9 is attached to the drum 5. This arm rotates at a different speed to the filtering medium 2 and can wipe off any solid particles adhering thereto.

If the filter 1 does become clogged, despite these measures, auxiliary overflow openings 10 are provided in the filter frame 3 and in the rear wall 7 of the drum. These prevent the centrifuge becoming blocked or ob structed. The clarified liquid is prevented from mixing with the unclarified auxiliary overflow liquid in the hollow space between filter 1 and the rear wall 7 of the drum by means of a guide baffle 11 and a collecting baffle 12.

The collector housing is subdivided in a cor responding manner. The auxiliary overflow liquid is carried away separately and fed to the supply of suspension. The return means required for this preferably consists of a conduit system and a suspension pump.

A further embodiment of the invention is illustrated in Fig. 2. A filter body 15 is mounted directly at the overflow openings in the drum rear wall 7 of a conventional solidjacket screw centrifuge. This filter body protrudes into the overflow openings 14 to such a depth that the filtering medium 2 which is attached to the filter body 15 covers the overflow openings 14 in the region of the inner side of the drum.

If necessary, a cleaning arm 9 and auxiliary overflow openings 10 can again be provided.

A collector housing 13 subdivided by a guide baffle 11 and a collecting baffle 12 prevents mixing of the streams of liquid.

An advantageous development of the invention is illustrated in Fig. 3. Enlarged overflow openings 8 are provided in the rear wall 7 of the drum and extend a considerable distance over the circumference and radius of the wall.

In this embodiment, the surface available for filtering is greatly increased and so the throughput can also be increased.

In this embodiment as well, a positively adapted filter body is mounted in the rear wall of the drum.

Claims

1. An apparatus for clarifying the centrifugated matter of a continuously impinged solidjacket screw centrifuge, characterized in that a filtering device is provided in the region of the outlet for the centrifugated matter.

2. Apparatus as defined in claim 1, characterized in that a filter (1) comprising a filter frame (3) and a suitable filtering medium (2) is arranged on the screw (4) or the drum (5) at right angles to the axis of rotation, a seal (6) or a gap being provided if necessary between drum casing and filter rim.

3. Apparatus as defined in claim 1, characterized in that a filter body (15) is provided on the rear wall (7) of the drum and positively penetrates the overflow openings in said rear wall.

4. Apparatus as defined in claim 3, characterized in that round or specially designed overflow openings (14, 8) are provided and extend partially over the periphery and the radius of the drum rear wall (7).

5. Apparatus as defined in claims 3 and 4, characterized in that the overflow openings are covered by a suitable filtering medium (2) secured to the filter body (15).

6. Apparatus as defined in claim 1, characterized in that the drum rear wall is designed as a filter frame covered on the inner side of the drum by a suitable filtering medium.

7. Apparatus as defined in any of claims 2 to 6, characterized in that for cleaning the filtering medium (2) a cleaning device, preferably a cleaning arm (9), is disposed on the screw (4) or the drum (5) such that it moves relative to the filtering medium.

8. Apparatus as defined in any of claims 2 to 6, characterized in that auxiliary overflow openings (10) are provided in the filter frame (3), the filter body (5) and the drum rear wall (7).

9. Apparatus as defined in claim 8, characterized in that a dividing means consisting of a guide baffle (11) arranged on the filter frame (3) and a collecting baffle (12) arranged on the drum rear wall (7) is associated with the auxiliary overflow openings (10).

10. Apparatus as defined in claim 8, characterized in that the collected housing (13) is subdivided by a guide baffle (11) and a collecting baffle (12).

11. Apparatus as defined in claim 10, characterized in that the divided collector housing (13) is connected to the supply of suspension via a return means such that the auxiliary overflow liquid collected may be treated again.

12. Apparatus as defined in claim 11, characterized in that the return means preferably comprises a conduit system and a suspension pump.