FI60895C - ANORDNING FOER SILNING AV FIBERSUSPENSIONER - Google Patents

Description

RjSSrTl γβ! «« Advertisement publication $ 0895 JMsTa IBJ utläggningsskrift w C (45) Patent granted 13 04 1932 Patent meddelat v (51) Kv.ik.3 / int.ci.3 D 21 D 5/06 FINLAND —FINLAND (21) Patanttlhakamu * - PatantansMutinf 802650 (22) Hakemlspllvt - AntSknlngadag 22.08.80 (23) AlkupUvi — GlMghatsdag 06.06.78 (41) Tullut JulklMk *! - Bllvlt offamllg 22.08.80

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Patent- och registerstyreisen Anaökan utlagd och Utl. * Kriftan publkarad OJ- (32) (33) (31) Requested front - Bagird prlorltat (71) A. Ahlström Osakeyhtiö, Noormarkku, Finland-Finland (FI) (72) Johan Gullichsen, Siuntio, Finland-Finland (FI) (51 *) Apparatus for screening fiber suspensions - Anordning för silning av fibersuspensioner (62) Separated from application 792655 (patent 59276) -Avdelad frän ansökan 792655 (patent 59276)

The present invention relates to an apparatus for screening high-density fiber suspensions, in particular in connection with the production of cellulosic pulps.

Screening of fiber suspensions in the cellulose industry is usually performed at 0.5 to 5% blindness. Since other pulping processes take place at higher blindness, e.g. 8-12%, this means that the pulp must first be diluted for processing and then re-thickened. This requires a lot of power and requires supportive equipment. Nevertheless, treatment can lead to an inhomogeneous result.

The object of the invention is to provide a device by means of which a fiber suspension with a blindness of 5 to 25% can be screened. It is also an object of the invention to provide devices which are reliable and simple in construction and which have a low power requirement. This is achieved

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2,60895 by causing the fiber suspension to flow between surfaces where it is subjected to repetitive, opposite direction changes and shear forces greater than the forces cohesive to the fiber network so that it fluidizes, removes the substance and removes the fiber suspension from the screening zone.

The invention is based on the fact that when the fiber suspension is subjected to sufficiently high shear forces, it fluidizes, i.e. it changes easily into a fluid form, whereby the fibers in it move relative to each other. In this case, for example, particles of different weights or sizes can be easily separated and the flow resistance of the fiber mixture is small. Since the treatment can be performed when the fiber suspension is very thick, the power requirement calculated for the fibrous material is small. There are protrusions and / or recesses on both surfaces between which the fiber suspension flows. As a result, the fiber suspension stream can be fluidized without having to use large velocity differences between surfaces. By properly dimensioning and shaping the protrusions and recesses of the surfaces, directionally changing flows deviating from the main flow direction of the fiber suspension are obtained such that the entire fiber suspension stream fluidizes even if the distance between the surfaces is large.

Fluidization-based devices have previously been proposed for use in screening fiber suspensions. Swedish patent application 7513434-6 discloses a screening device with which large particles can be separated from a high-density fiber suspension. In it, the fluidization of the fiber suspension is effected in the gap between two rotating walls, which move relative to each other as the device rotates, transferring energy to the fiber suspension through rotating parts and vanes fitted thereto. Because the gap between the walls is small, in order to increase the capacity, the device must be equipped with several slots, which complicates the structure.

The screening devices have previously used flow channels formed by a movable and a fixed surface, in which the movable surface is provided with protrusions and recesses. As an example of such a solution, reference may be made to U.S. Pat. No. 3,586,172, which relates to a screening device comprising a screening drum and a rotating drum arranged inside it, between which the fiber suspension to be treated is fed. The outer surface of the rotating drum has pressure-boosting bumps and recesses. However, such screening devices operate only at relatively low blindness, i. less than 3%.

The device according to the invention is characterized in that it comprises members attached to the outer surface of the screen drum, guiding the fiber suspension outwards from the screen drum surface and an inner surface surrounding the screen drum, which with.

The invention will now be described in more detail with reference to the accompanying drawing, in which Figure 1 shows a device for screening a fiber suspension in vertical section along the line G-G in Figure 2, Figure 2 shows a section in Figure 1 along the line H-H.

The screening device shown in Figures 1 and 2 comprises a rotating screening drum 50 consisting of a plurality of adjacent rings 51 of rectangular cross-section, between which gaps 52 are formed. The screen drum is connected to the drive shaft 55 by ribs 54. Inside the screen drum there is a triangular rotor 56, the corners 90 of which form projections towards the screen drum and which is also connected to the drive shaft, so that the parts 51-56 rotate together. Arranged inside the screen drum near the surface of the screen drum are substantially triangular rods 57, the lower and upper ends of which are connected to each other by rings 58 and 59. The upper ring 59 is attached to the screen attachment so that the rods 57 remain in place. Knives 60 are attached to the rods to prevent clogging of the slots in the screen-drum. The screen detergent washer 61 surrounds the screen drum and has a triangular axial protrusion 62 on its inner surface.

The fibrous suspension to be screened is fed through the inlet 63 to the fluidizing zone 66 inside the screen drum delimited by the inwardly directed side surfaces 91 of the screen drum 57 and rods 57 and the outer surface 69 of the rotor 69. and towards and away from the rotor surfaces and fluidizes. The approved fiber fraction enters through the slots of the screen drum into a space 67 outside the screen drum, which forms a second fluidization zone and where it is repeatedly moved towards and away from said surfaces of the screen drum and the stationary surface of the screen and from it through the outlet 64. The wreckage fraction is removed through an outlet 65 at the lower end of the screening device.

Experiments have shown that the fluidization zone should be 10 to 150 mm high, the most suitable height being 30 to 60 mm. The height of the protrusions should be 0.1 to 0.3 parts of the height of the channel. The distance between the protrusions in the flow direction should be 2-50 times greater than their height, preferably 5-20 times. The speed of the moving surface should be 5-30 m / s, preferably greater than 10 m / sj the most suitable speed is about 20 m / s.

The power consumption of the screening device according to Figures 1 and 2 is about 3 kWh / t at 100% mass with a blindness of 12%. The power consumption of a conventional device is 6-7 kWh / t with a blindness of 1.5-2%.

The invention is not limited to the embodiment shown, but numerous modifications may be made therein without departing from the scope of the claims. The shape of the surfaces of the fluidization zones may differ from that shown in the figures by way of example.

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Claims (2)

5,60895 Patent Claims 1. Apparatus for screening high density fiber suspensions, comprising a rotating screen drum and a housing surrounding the screen drum having an inlet for the fiber suspension to be screened, outlets for an approved fraction and a waste fraction, a fluidizing zone within the screen drum bounded by the outer surface of the protruding rotor inside the screen drum, in which the fiber suspension is subjected to repeated, opposite changes of direction and which communicates with the fiber suspension inlet and the scrap fraction outlet, characterized in that it comprises a screen drum outwardly guiding members (53) and an inner surface surrounding the screen drum with predominantly axial projections (62) inside the housing (61); which, together with the outer surface of the screen drum, form a fluidization zone (67) outside the screen drum which communicates with an approved river outlet (64). Screen device according to Claim 1, characterized in that triangular rods (53) are attached to the outer surface of the screen drum.