NZ200028A

NZ200028A - Screening suspension using oscillating screen

Info

Publication number: NZ200028A
Application number: NZ200028A
Authority: NZ
Inventors: F V Sundman
Original assignee: Ahlstroem Oy
Priority date: 1981-04-28
Filing date: 1982-03-16
Publication date: 1985-02-28
Also published as: FR2504405A1; FI63076C; BR8202410A; FI811319L; JPS5814918A; DE3208387A1; SE8201511L; AU8151782A; FI63076B; AU530608B2; NO821377L

Description

200028 Priority Ds;®(s): . P?? • ^ .... -3.2& P.O. Journal, No: .... JP&7- N.Z. No.

NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION "METHOD AND APPARATUS FOR CLEANING OR SCREENING MATERIAL SUSPENSIONS." We, A. AHLSTROM OSAKEYHTIO, a Finnish body corporate, of ^ 29600 NOORMARKKU, Finland do hereby declare the invention, for which we pray that a Patent may be granted to usy and the method by which it is to be performed, to be particularly described in and by the following statement:- 1 - (Followed by 1A.) 200028 Method and apparatus for cleaning or screening material suspensions The present invention is related to a method and an apparatus for treating stock suspensions or slurries by means of a moving screen surface which is intended especially for screen-ing of fibre suspensions.

The conventional screening method, e.g. in the paper industry, is to cause a screen plate to vibrate perpendicularly to the plane of the screen plate in order to prevent clogging of the screen plate. This kind of an apparatus causes both thickening of the stock to be screened and the dilution of the accepted stock due to the motion of the screen plate and the required pressure difference over the screen plate. Owing to the thickening of the stock, liquid has to be added, which further dilutes the accepted fraction. Moreover, the specific capacity of the apparatus is low and the power consumption high.

It is an object of the invention to provide a method and an apparatus which eliminate the above mentioned drawbacks. According to the invention, this is achieved by setting the screen plate into an alternating motion in the material suspension in a direction which does not substantially differ from the plane of the screen plate.

The movement of the screen plate causes fluidization of the stock layers in its immediate vicinity on its both sides.

Owing to this the liquid in the stock layer and those fibres or particles having a cross-section smaller than the apertures of the screen plate and which thus can pass through the screen plate, pass through it simultaneously. Since the stock layer is fl*uidized, a big pressure difference over the screen plate is not required for providing the desired flow through the screen plate. Additionally, the capacity of the apparatus based on the surface atea of the screen plate is big. 2 2 0002 8 The treating of the material can be carried out under pressure in a closed housing or in an open channel. Yet the method requires that the screen plate moves in the material to be treated in such a manner that it is on both sides surrounded— by the material suspension.

The screening of the material' suspension is preferably carried out so that those particles which are bigger than the apertures of the screen plate and which thus cannot pass through the screen plate can fall down towards the bottom of the apparatus.

The method according to the invention is suitable for cleaning, washing and screening of stock suspensions and slurries. In addition to the treating of the fibre suspensions of the paper industry, the method is suitable also for e.g. separating colloidal substances from peat.

The apparatus according, to the invention comprises a closed housing or an open channel having a perforated screen plate which divides the housing or the channel into a feeding chamber and an accept chamber positioned on the opposite side of the screen plate, an inlet pipe for the material to be treated as well as an outlet pipes for the accept and reject. It is characterized in that it is provided with means for setting the screen plate in an alternating motion in a direction which does not essentially differ from the plane of the screen surface.

The invention is described in more detail with reference to the accompanying drawings which schematically show the principle of the invention.

Fig. 1 is a vertical sectional elevational view of an embodiment according to the invention, Fig. 2 is a sectional view as taken on line A-A of Fig. 1; Fig. 3 is a sectional view as taken on' line B-B of Fig. 1; 3 200028 i Figs. 4 and 5 show the details C and D of Fig. 1 in a bigger scale; Fig. 6 shows the detail E of Fig. 3 in a bigger scale; Fig. 7 is a vertical sectional elevational view of another embodiment of the invention; Fig. 8 is a vertical sectional elevational view of a third embodiment of the invention; Fig. 9 is a vertical sectional elevational view of a fourth embodiment of the invention.; Fig. 10 is a cross-sectional view of a fifth embodiment of the invention; Fig. 11 is a sectional view as taken on line F-F of Fig. 10; Fig. 12 is a cross-sectional view of a sixth embodiment of the invention; and Fig. 13 is a sectional view as taken on line G-G of Fig. 12.

In the apparatus illustrated in Figs. 1-6 the reference number 1 is a closed housing which is provided with an inlet, pipe 2 for the material to be treated, an outlet pipe 3 for the accepted fraction (accept) and an outlet pipe 4 for the rejected fraction (reject). In the housing there is disposed a screen plate 5 which divides the housing into a feeding chamber 6 under the screen plate and an accept chamber 7 above it. The screen plate is mounted between guide rails 8 positioned on the sides of the housing. In the other end of the screen plate there is positioned a bar 9 connected to an eccentric device which in a manner known per se sets the screen plate into a fast alternating motion in the direction of the plane of the screen surface,. A rear wall 11 of the housing through which the bar 9 passes is provided with a stuffing box 12 in which seal rings 13 are disposed so that liquid cannot leak from the housing through the opening in it. In both ends of the housing there is a sealing ledge 14 which prevents communication between the feeding chamber 6 and the accept chamber 7 past the screen plate. If required, liquid can be supplied to the feeding chamber through an inlet pipe 15. 0 4 200028 » The apparatus illustrated in Figs. 1 to 6 operates in the following way. The material to be treated, e.g. a fibre suspension to be screened, is fed into the feeding chamber 6 through the inlet pipe 2. Due to the tO-an-fro motion of the screen plate the fibre suspension layers adjacent on both sides of the plate are fluidized and the fibers, the size of which allows it, flow together with liquid through the apertures of the screen plate to the accept chamber 7 and are removed through the outlet pipe 3. The particles whiqh are bigger than the apertures of the screen plate and which remain in the feeding chamber move towards the reject outlet 4 and are removed through it continuously or periodically.

Example Stock of a consistency of 3 % was screened in an apparatus according to Fig. 1. The apertures of the screen plate had a diameter of 4 mm and the open screen area was 10 %. The length of the movement of the screen plate ranged from 1 to 30 mm and its frequency from 500 to 3000 /min. When the frequency was 500 "'"/min, the screen plate became clogged. When the frequency was 750 /min, the screen plate remained open and the pressure loss over the screen plate was 150 to 250 mm H_0. When the 1 frequency was 1500 /min, the pressure loss was 90 to 150 mm H„0 and when the frequency was 2400 ^/min, it was 40 to 10 0 mm . 2 H2O. The capacity of the screen was 130 t/m 24 h based on the dry matter of the stock.

By way of comparison it can be mentioned that the capacity of a corresponding open screen in which the screen plate vibrates in a direction perpendicular to the plane of the screen plate 2 ranges from 30 to 50 t/m 24 h. The pressure loss of a pressurized screen is 3 to 8 m 1^0.

In the alternative embodiment of the invention shown schematically in Fig. 7 profile bars 16 are positioned adjacent the screen surface 5. When the screen plate moves, these bars cause pressure changes which detach the fibres eventually 0 2 00028 » fastened in the apertures of the screen plate and thus prevent the clogging of the screen plate.

In Fig. 8 a bar 17 which can~be moved back and forth is con—~ nected to the screen plate 5 in its reject end. By means of this bar the screen plate can be set into a continuous or periodical motion perpendicular to the screen plate surface. The amplitude of this movement is zero in the inlet end of the screen plate and at its highest in the reject end of the screen plate. This movement is simultaneous with the alternating motion of the screen plate in the plane of the screen surface.

In the embodiment illustrated in Fig. 9 the screen plate consists of two parts. One part 18 of it is immersed in the .fibre suspension and set into an alternating motion the direction of which does not substantially differ from the plane of the screen surface. The material to be treated is introduced to the feeding chamber 6,above the screen plate 5 and the accept flows downwards through the screen surface. The other part 19 of the screen surface adjacent the outlet is set in a motion, the direction of which deflects about 30° from the-plane of the screen plate for moving the stock onwards.

In the apparatus illustrated in Figs. 10 to 11 the material to be treated is fed to a space 21 inside a screen drum 20 through an inlet pipe 2 of a cylindrical housing 22. The reject is discharged from the lower end of the screen drum through a discharge opening 4. The accept fraction which has passed through the screen drum flows to a space 23 encompassing the screen drum. The screen drum is set into an alternating motion in the direction of its longitudinal axis.

The apparatus illustrated in Figs. 12 and 13 is similar to the preceding ones, but the motion of the screen drum 20 is an alternating rotational motion around its center axis. 0 2 0002 8 6 # The liquid feeding pipe 15 shown in Fig. 1 is for flushing the material in the reject end of the apparatus in order to separate the eventual fine particles from the reject. The apparatus -can, however, be provided with several liquid feeding pipes, some of which can be located in the inlet end of the apparatus so that considerable amounts of liquid can be introduced there for washing the material to be treated. <3 / / „ - - 7 - 200022

Claims

WHAT WE CLAIM IS:

1. A method for cleaning or screening of a material suspension by means of a moving screen surface, characterized in that the screen surface is set into an oscillating motion in the material to be treated, the direction of which motion does not substantially differ from the plane of the screen surface.

2. A method according to claim 1, wherein the screen surface is set into a translatory rotational motion.

3. An apparatus for carrying out the method according to claim 1, comprising a closed chamber or an open channel, a perforated screen plate which divides the closed chamber or the channel into a feeding chamber and an accept chamber on the opposite sides of the screen plate; an inlet pipe and outlet pipe for the feeding chamber and an outlet pipe for the accept chamber characterized in that the apparatus is provided with means for setting the screen plate in an oscillating motion in a direction which does not substantially differ from the plane of the screen surface.

4. An apparatus according to claim 3, wherein the screen plate is planar.

5. An apparatus according to claim 3, wherein the screen plate is cylindrical.

6. An apparatus according to claim 4, wherein the feed chamber is disposed under the screen plate.

7. An apparatus according to claim 5, wherein the feed chamber is disposed inside the cylindrical screen plate.

8. An apparatus according to claim 5, further including - 8 - o n r- . <_ 'L O means for setting the cylindrical screen plate into an oscillating rotational motion around its centre axis.

9. An apparatus according to claim 5, further including means for setting the cylindrical screen plate into an Oscillating motion in the direction of its longitudinal axis.

10. The method according to claim 1, substantially as herein described.

11. The apparatus according to claim 3, substantially as herein described and with reference to the accompanying drawings. A AHLSTROM OSAKEYHTIO By Their Attorneys HENRY HUGHES/LIMITED