GB2057284A

GB2057284A - Rotary disc filter

Info

Publication number: GB2057284A
Application number: GB8020719A
Authority: GB
Original assignee: Voith SA Maquinas e Equipamentos
Current assignee: Voith SA Maquinas e Equipamentos
Priority date: 1979-09-03
Filing date: 1980-06-25
Publication date: 1981-04-01
Also published as: SE8001306L; IT8067846A0; IT8053257V0; FI800527A; DE2945091C2; BR5901347U; DE2945091B1; JPS56108506A; FR2464329A1

Abstract

A filter for thickening fibrous stock suspensions comprises:- a) at least two hollow shafts (4, 5) arranged parallel and adjacent to each other in a common filter trough (3), b) a row of hollow filter discs (6, 7) attached to each hollow shaft, the discs on the respective shafts intermeshing between each other, c) discharge chutes (18, 19) located beneath and extending between the discs on the respective shafts to receive filter cake therefrom. Shafts (4, 5) are connected to suction chambers (12, 15) receiving cloudy and clear filtrate from different sectors of the discs, and clear filtrate is recycled to nozzles (22--24) to spray the filter cake off the discs. <IMAGE>

Description

SPECIFICATION A filter for thickening fibrous stock suspensions The invention relates to a filter for thickening fibrous stock suspensions, with rotating disc-shaped filter elements which are surrounded by a filter trough and are constructed as pairs of filter discs attached transversely to a hollow shaft connected to a suction head, the inner space formed by each pair of filter discs being connected to the hollow shaft, with a pulp inlet, and with pulp outlets arranged between the pairs of filter discs.

Filters of this kind are generally used in the paper-making industry as so-called disc-filters for the recovery of fibrous pulp.

For this purpose a plurality of pairs of filter discs are arranged adjacent to each other on a hollow shaft in a filter trough. Due to the high pressure difference between the fibrous stock suspension in the trough and the inner space in the pairs of filter discs which is connected to a device for producing low pressure, a fleecy layer of fibrous pulp is formed on the individual discs, which layer may have up to 12% stock material on a B.D (bone dry) basis.

Normally the process for recovering the fibrous pulp in the disc filters proceeds in the following way: After the filter surfaces have been immersed in the suspension, the fibres are deposited on the surface of the filter elements, while the so-called cloudy water - water mixed with fibres - still passes through the filter surfaces (first dewatering zone). A tight fleece of fibres is formed very rapidly and serves as a supplementary filtering layer, allowing only clear water still to pass through the filter (second dewatering zone). Using water, preferably cloudy water or clear water from the first or second dewatering zone, this fibrous layer is then sprayed into pulp outlet chutes after the filter elements have been brought out of the suspension. However, it is also possible to remove the fleece from the filter elements by using suitable scrapers.

In very large plant a large number of pairs of filter discs is required on a shaft. Occasionally, it has also been necessary to arrange several disc-filters one after the other. A disadvantage in this instance was that a correspondingly greater outlay and more space were required.

An object of the present invention is to produce a filter of the kind mentioned in the introduction for thickening fibrous stock suspensions, which only requires a small amount of space and has a high throughput level.

According to the invention, such a filter is char acterised in that: a) at least two hollow shafts are arranged parallel and adjacent to each other in a common filter trough; b) the pulp outlets are arranged on either side on the longitudinal sides of the filter trough; c) the pairs of filter discs attached to the hollow shafts are arranged so that they engage meshwise with each other on the inner side which lies opposite to the pulp outlets.

A considerable saving of space is achieved with the construction of the filter according to the invention. Considerably more pairs of filter discs can be provided in a given space than was possible hitherto. In the normal way there is a pulp outlet, generally a a chute, between each to adjacently disposed pairs of filter discs. This means that a certain gap is necessary between the pairs of filter discs. By arranging the pulp outlets on either side on the longitudinal sides of the common filter trough, there is now a corresponding large free space available in the centre of the trough between each pair of filters.

This free space is now used according to the invention for arranging a further hollow shaft in the filter trough, parallel to the first shaft. With the same size diameter for all the pairs of filter discs, the second hollow shaft can be approached very close to the first hollow shaft if the pairs of filter discs are mutually arranged so that they engage meshwise in each other. The free space is expediently made good use of in this way.

In addition to the advantage of a considerable saving of space, this type of design for the filter is also more favourable financially.

If required, a common double suction head and a common drive for the hollow shafts may be provided. However, obviously separate devices are also possible. Similarly, it is possible to arrange more hollow shafts than two, parallel with each other, and also engaging meshwise with each other in the way proposed in the invention.

According to a feature of the invention, provision is also made for inlet boxes for supplying the pulp stock to be arranged on the two longitudinal sides of the filter trough. This means that all the pairs of filter discs on one side are supplied from a common pulp stock supply.

The basic principles of the invention, as applied to one embodiment of disc-filter in accordance therewith, will now be explained, together with other features of the invention, with reference to the accompanying drawing, in which: Figure 1 is a schematic illustration of the disc-filter according to the invention, in side view, and Figure 2 is a detail of a plan view of the disc-filter.

The fibrous stock suspension which is to be thickened is introduced via inlet boxes 1 and 2 which are arranged on both the longitudinal sides of a filter trough 3. In the filter trough 3 two hollow shafts 4 and 5 are disposed parallel and adjacent to each other. A plurality of pairs 6 or 7 of filter discs are arranged on the hollow shafts 4 or 5 respectively.

The inner spaces in the pairs 6 and 7 of filter discs are each in communication with the hollow shaft 4 or 5 respectively. In this way, the water extracted from the fibrous stock suspension passes via the filter elements of the pairs of filter discs into the hollow shaft 4 or 5 respectively. A suction head 8 or 9 is arranged on each hollow shaft. In each suction head a dividing wall is provided in a known way to ensure that the water passes accordingly via fall pipes 10 or 11 into a common cloudy filtrate container 12, or is conducted via lines 13 and 14 into a common clear filtrate container 15. In the first dewatering zone cloudy water is yielded in a known way, and in the second dewatering zone clear water is yielded. The necessary high level of low pressure is achieved via the lines 10,11 and 13,14.

Between each two pairs of filter discs 6 or 7 them are pulp outlet chutes 16 or 17 respectively, arranged on either side on the longitudinal sides of the filter trough. The walls of the pulp outlet chutes 16 and 17 are somewhat higher than the flow-over edge of the inlet boxes 1 and 2.

The pulp outlet chutes 16 and 17 also have a common lower part 18 or 19 respectively in which in each case a worm 20 or 21 respectively effects the removal of the thickened pulp.

The direction of rotation of the hollow shafts 4 and 5 is such that the outer sides of the pairs 6 or 7 of filter discs each run towards the top. Loosening spray nozzles 22 and 23 spray the fibres adhering to the filter elements into the outlet chutes 16 or 17.

Along the centre line of the filter trough, at the point where the pairs 6 and 7 of filter discs engage meshwise with each other, cleaning nozzles 24 are provided for each two pairs. The loosening spray nozzles 22 and 23 and the cleansing nozzles 24 are supplied with water,f,fQm the clear filtrate container 15. However, it is als#p'.ossible to use water from the cloudy filtrate container 12, or fresh water.

Claims

1. A filter for thickening fibrous stock suspensions, with rotating disc-shaped filter elements which are surrounded by a filter trough and which are constructed as pairs of filter discs attached transversely to a hollow shaft connected to a suction head, the inner space formed by each pair of filter discs being connected to the hollow shaft, with a pulp inlet, and with pulp outlets arranged between the pairs of filter discs, characterised in that a) at least two hollow shafts are arranged parallel and adjacent to each other in a common filter trough, b) the pulp outlets are arranged on either side of the longitudinal sides of the filter trough, c) the pairs of filter discs attached to the hollow shafts are arranged so that they engage meshwise with each other on the inner side which lies opposite to the pulp outlets.

2. A filter according to Claim 1, characterised in that inlet boxes for supplying the pulp are arranged on the two longitudinal sides of the filter trough.

3. A filter according to Claim 1 or 2, characterised in that the two hollow shafts may be driven from a common drive source.

4. Afilter according to Claim 1, 2 or 3, characterised in that each suction head for each hollow shaft is of a type provided with a dividing wall, in that fall pipes are connected to common sides of respective suction heads, and open out in a common cloudy filtrate container, and in that further fall pipes, are connected to the other sides of their respective suction heads and open out in a common clear filtrate container.