GB2102308A

GB2102308A - A flotation device for processing waste-paper

Info

Publication number: GB2102308A
Application number: GB08218457A
Authority: GB
Inventors: Pfalzer Lothar; Werner Cechovsky; Jurgen Mittag
Original assignee: JM Voith GmbH
Current assignee: JM Voith GmbH
Priority date: 1981-07-10
Filing date: 1982-06-25
Publication date: 1983-02-02
Also published as: JPS5817854A; AT378015B; FR2509337B3; SE451676B; IT8222186A0; FR2509337A1; IT1153105B; SE8203594L; DE3127290C2; DE3127290A1; GB2102308B; ATA200982A

Abstract

In a flotation device for processing waste-paper, the flotation tank (1) is substantially in the form of an upright cylinder and the waste- paper suspension, mixed with air, is supplied to the flotation tank substantially tangentially and with a horizontal in-flow direction through a single supply line (6, 6') connected in the vicinity of the floor of the flotation tank (1) and having a diffuser widening portion (6) therein. The extraction line (3) for the cleaned suspension is provided near to the connection opening (2) of the supply line in the flotation tank (1), also in the region of the floor thereof. <IMAGE>

Description

SPECIFICATION A flotation device for processing waste-paper The invention relates to a flotation device for processing waste-paper of the kind in which a flotation tank is substantially in the form of an upright cylinder and in which the suspension, mixed with air, can be supplied to the flotation tank via injectors provided at the circumference of the cylinder substantially tangentially and with a horizontal in-flow direction.

Such a device is known from German Patent Specification No. 29 14 393. The device according to this German Specification is yet another of the many attempts to provide flotation devices wherein the suspension, mixed with air, is supplied via injectors to a substantially circular cylindrical flotation tank in order to increase the flotation efficiency. With this device the suspension is also drawn off in the immediate vicinity of the floor of the flotation tank. However, the supply of the suspension is effected firstly, with unprocessed suspension, through a plurality of injectors dsitributed around the circumference approximately half way up the flotation tank, and then again for a second time at a lower level in the flotation tank, when suspension which has already been processed is introduced into the container once more by means of injectors.This arrangement with the supply of the suspension at two levels and through a plurality of injectors makes the whole device extremely complicated and not very easy to operate. in addition, supervision in this case also requires particular care, or a relatively high factor of unreliability would be entailed.

An object of the invention is to provide a flotation device which has a simple design and functions satisfactorily i.e. which, with low energy consumption and a high level of efficiency, effects the best possible removal of soil, which means that air bubbles should be present in great numbers, distributed as widely as possible throughout the suspension in the flotation tank.

According to the invention, a device of the kind referred to in the introduction is mainly characterised by the features set out in the characterising clause of the appended Patent Claim 1.

A favourable development of the invention is set out in Patent Claim 2.

A particularly favourable development is set out in Patent Claim 3. Particularly good introduction ol air into the suspension is achieved by the arrangement of an injector with a free jet. In this case, arranging the inlet hole of the mixing tube at a height which lies above the fluid level in the flotation tank makes it possible in a simple way to prevent the suspension from overflowing. The further embodiment of the injector with a plurality of parallel supply tubes is then also advantageous, since this further improves the introduction of air.

Due to the flow ratios in the flotation tank it is also possible to draw off the froth out of the flotation container centrally through the inner cylinder without further means, via a froth extraction opening with an overfall type of design.

In order that the invention will be readily understood, embodiment examples will now be described with reference to the accompanying drawing in which: Figures 1 a and 1 b show two alternative embodiments according to the invention with a diffuser, where the flotation tank is only indicated with broken lines, and, Figure 2 shows another embodiment according to the invention with an injector simiiar to a water jet pump.

The embodiments shown in Figures 1 a and 1 b quite simply use a diffuser 10 for distributing the air. The air is blown into the suspension at a position upstream of the diffuser via line 1 4. In the case of Figure 1 b, where the lines 4 and 1 4 extend substantially horizontally, it must be possible to shut these off in order to prevent the suspension from running out when the plant is stopped.

The embodiment shown in Figure 2 with an injector works very similarly.

The suspension is first supplied to the mixing pipe 6 via the collecting pipe 4 and the individual supply pipes 5 leading off from the collecting pipe.

In this case the mixing pipe 6 and the supply pipes 5 virtually form the injector. Here, a plurality of supply pipes are connected in before the mixing pipe 6, but it would also be possible to continue the collecting pipe 4 directly to the mixing pipe 6 alone. The air is sucked in the vicinity of the inlet funnel 7 which is mounted on the mixing pipe 6.

The inlet opening 9 of the funnel 7 and the outlet hole 8 of the supply pipes 5 extend here substantially horizontally, and the suspension enters the mixing pipe in a substantially perpendicular direction. Naturally, instead of the injector shown it would also be possible to use a closed injector which works on the venturi principle, at the narrowest point of which the air is introduced through an air supply pipe. The embodiment example shown in Figure 2 has the advantage, however, that firstly a very simple construction is achieved and secondly the introduction of air into the suspension is good. The inlet hole 9 in the funnel 7 lies here at a level above the level 20 of the liquid in the flotation tank 1 which is sufficiently far above it to ensure that it is not possible for the suspension to escape when the plant is stopped. Supervision is therefore not essential at this point.This results in a further simplification of the plant.

The flotation tank is constructed substantially as an upright cylinder with another inner cylinder 1 5 located centrally in its axis. In this way an annular chamber is formed between the circumferential wall of the flotation tank and the inner cylinder. The supply of the suspension is effected after the injector through the supply pipe 6' which is made with a flat rectangular crosssection, with the long sides lying horizontally. This means that the suspension is actually supplied to the flotation tank 1 in a widely splayed jet from the connection opening 2 of the supply pipe 6', substantially tangentially, but also spread across the entire width of the annular chamber.Since the suspension with air mixed through it is lighter than the suspension which has already been de-gassed which is present in the vicinity of the drawing-off pipe 3 which is also disposed closely adjacent to the supply pipe 6' in the region of the floor of the flotation tank 1, it flows first in a rotary movement obliquely upwards. During this process the particles of dirt adhere to the bubbles of gas and float to the surface of the suspension. The froth thus formed is then drawn off through the froth extraction opening 22, which is actually formed by the overflow of the inner cylinder 1 5. This process can be enhanced if air is blown onto the surface of the suspension, thereby producing a head of the froth. Very little energy is needed for this, however.

Naturally, it would also be possible instead to use the device provided for this purpose with the blow funnel 11 and the air blast pipe 12 reversed, and to suck the froth away.

In order to avoid a short circuit between the inlet and the outlet by the suspension in the flotation tank a dividing wall 1 6 is inserted between them which can extend upwards approximately a third to a half of the way towards the surface of the liquid in the flotation tank 1.

Supply of the supension is naturally substantially tangential only if considered as a whole. Deviations from the horizontal direction are equally also possible, within a narrow range.

If required, in order to increase the degree of purity of the suspension which has been subjected to flotation, correspondingly more flotation tanks may be superimposed on each other. A very space-saving arrangement is obtained in this way.

The level of the suspension in the flotation tank expediently amounts here to between 70 and 120 cm, and preferably between 75 and 100 cm.

Usable diameters for the flotation tanks 1 and inner cylinders 15 amount to around 300 cm and 100 cm respectively, for example, so that the annular intermediate space between them has a width of approximately 100 cm.

This is a difference between the arrangement according to the invention and that according to German Laid-open Patent Specification No.

29 04 619, in which the suspension level should be only approximately 40 cm high and in which the pulp stock is supplied firstly only at the outer edge, and secondly not substantially horizontally, and the suspension leaves through a central shaft.

For drawing off the froth in the Laid-open Specification there is really only one suction device, which is also described therein.

Claims

1. A flotation device for processing wastepaper of the kind in which a flotation tank is substantially in the form of an upright cylinder and in which the suspension, mixed with air, can be supplied to the flotation tank via injectors provided at the circumference of the cylinder, substantially tangentially and with a horizontal in-flow direction, characterised in that a single supply line is provided for the supply of suspension and is connected to the circumference of the container, in that said supply line has a diffuser-type widening therein, and in that an air line is connected into said supply line upstream of said widening for flow-wise supply of flotation air.

2. A device according to Claim 1, characterised in that the diffuser-type widening is a component part of the nozzle of an injector which works like a water jet pump.

3. A device according to Claim 2, characterised in that the injector is provided with a free suction jet formed by the whole of the suspension conducted through the injector and drawing in environmental air, where the suspension can be supplied via at least one supply pipe with a substantially vertical outlet to a horizontal inlet opening arranged substantially directly opposite the emerging jet of suspension, in a mixing pipe.

4. A device according to Claims 1 to 3, characterised in that the inlet opening in the mixing pipe lies above the level of the fluid in the flotation tank.

5. A device according to any one of Claims 1 to 4, characterised in that a plurality of parallel supply pipes is provided for the suspension.

6. A device according to any one of Claims 3 or 5, characterised in that the mixing pipe widens out in the form of a funnel at the inlet end for the supply pipes, and in that the supply pipes dip into the funnel-shaped wider section.

7. A device according to any one of Claims 1 to 6, characterised in that there is a central inner cylinder in the flotation tank, having the same axis as the flotation tank and projecting above the level of the fluid in the flotation tank.

8. A device according to Claim 7, characterised in that the inner cylinder has a froth extraction opening constructed as an overflow, which connects the surface of the suspension with the inner chamber of the inner cylinder.

9. A device according to any one of Claims 1 to 8, characterised in that between the connection opening of the suspension supply pipe connected to the mixing pipe and the suspension extraction pipe there is a dividing wall extending upwards between the circumferential wall of the tank and the inner cylinder from the floor of the fluid tank approximately a third to a half of the way up to the surface of the fluid.

10. A device according to any one of Claims 1 to 9, characterised in that the froth extraction opening lies at a height in the flotation tank such that a suspension depth of between 0.7 and 1.2 m, and preferably between 0.75 and 0.1 m, prevails.

1 A flotation device for processing waste paper constructed, arranged and adapted for use substantially as hereinbefore described, and as shown in, the accompanying drawings.