WO1997013918A1

WO1997013918A1 - Screening arrangement

Info

Publication number: WO1997013918A1
Application number: PCT/SE1996/001203
Authority: WO
Inventors: Tauno Laakso
Original assignee: Sunds Defibrator Industries Ab
Priority date: 1995-10-10
Filing date: 1996-09-26
Publication date: 1997-04-17
Also published as: SE507932C2; AU7348796A; SE9503536D0; SE9503536L

Abstract

An arrangement for screening pulp suspensions, comprising a casing (1) with inlet (6) for inject and outlets (10, 11) for accept and reject. Between a rotor (3) in the casing a screening zone (4) is formed. The inject inlet (6), reject outlet (11) and a scrap outlet (8) for coarse and heavy impurities are connected in the same horizontal plane to the lower portion of the casing (1). The connections are offset in relation to each other and defined from each other by walls (15-17).

Description

Screening arrangement

This invention relates to an arrangement for screening pulp suspens¬ ions in order to separate impurities and other pulp fractions not desired to be included in the final product, such as coarse part¬ icles, undefibered material and poorly worked fibers.

At the making of fiber suspensions, undesired coarse particles, for example undefibered material, bark, knots etc, are obtained in the suspension as a result of incomplete manufacturing processes. Also other heavy impurities, such as sand and scrap etc., can be found in the suspension. These impurities can cause interruptions in the screening process. It is, therefore, desired to separate them at an early stage of the screening. For eliminating the coarse im¬ purities or reduce them in size, special devices, for example knot screens or refiners, can be arranged before the screen. It is also possible to separate the coarse impurities by a first screening step in the screening arrangement or to separate scrap and heavy particles when the suspension enters the screen, and other impur¬ ities at the fine screening. In the lastmentioned case, the screen¬ ing process can be disturbed by the impurities, as mentioned above.

When the coarse impurities in the form of scrap and heavy particles are to be separated at a first screening step in the screening arrangement, special spaces are required in the screening εrrange- meπr. This implies increased dimensions of the screening arrangement and thereby a greater space demand for the installation.

The present invention solves this problem in such a way that the dimensions of the screening arrangement can be limited while the efficiency and capacity of the screening are maintained.

The characterizing features of the invention become apparent from the attached claims. 4

The pulp to be screened is supplied tangentially through the inlet 6, from where the pulp via the openings 13 flows upward through the rotor 3 at the same time as coarse and heavy impurities are collected in the scrap outlet 8 due to the effect of centrifugal force. The pulp flows from the top of rotor 3 downward through the screening zone 4 where it is screened and split into accept and reject. This splitting is promoted by the pulsation means 7, which produce press¬ ure and speed variations in the pulp suspension which are favourable for the screening. The outgoing reject concentration can be controlled by supplying dilution liquid at the end of the screening.

The reject is moved from the screening zone 4 down into the reject chamber 14, from where it is removed through the reject outlet 11. The accept is taken out via the space 9 through the accept outlet 10.

The invention is not restricted to the embodiments shown and described, but can be varied within the scope of the invention idea.

A space 9 for collecting the accept is located outside of the screen¬ ing member 2, from which space the accept is discharged through an outlet 10. The reject passing through the screening zone 4 past the screening member 2 is discharged through an outlet 11.

The inject inlet 6, scrap outlet 8 and reject outlet 11 are all connected to the casing 1 in the same horizontal plane. The conn¬ ections are offset in the circumferential direction in relation to each other. It is thereby possible to reduce the height of the screening arrangement. The screen design can thereby be compact without affecting negatively the screening process.

The preferably tangential inject inlet 6 is connected to an inject chamber 12 extending through about 90 to 270 of the casing 1 all the way to the scrap outlet 8. The inject chamber 12 is defined in the circumferential direction by a first wall 15 and a second wall 16. The inject chamber 12 communicates with the interior of the rotor via openings 13 radially inward from the chamber 12.

A reject chamber 14 is located in the circumferential direction after the scrap outlet 8 and defined therefrom by the second wall 16. The reject chamber 14 extends from the second wall 16 to a third wall 17 through about 60 to 120 of the casing 1 and terminates with the preferably tangential reject outlet 11. The reject chamber 14 communicates upwardly with the screening zone 4 along its entire length.

An inlet 18 for dilution liquid is connected to the casing 1 of the screening arrangement. This inlet can communicate with a dilution chamber 19 located between the first wall 15 and the third wall 17 in the same horizontal plane as the aforementioned connections 6,8 and 11. This dilution chamber 19 communicates with a space 20 in the rotor 3, which space is formed with openings 21 in the rotor for the supply of dilution liquid to the screening zone 4, prefer¬ ably in the lower portion of the screening zone. The supply can take place through the means 7.

Claims

1. An arrangement for screening pulp suspensions, comprising a casing (1) with inlet (6) for inject and outlets (10,11) for accept and reject, a screening member (2) located stationary in the casing (1), and a rotor (3) located within the screening member, whereby a screening zone (4) is formed between the rotor and screening member, c h a r a c t e r i z e d i n that the inject inlet (6), reject outlet (11) and a scrap outlet (8) for coarse and heavy impurities are connected in the same horizontal plane to the lower portion of the casing (1) , and the connections are offset in relation to each other and defined from each other by walls (15-17).

2. An arrangement as defined in claim 1, c h a r a c t e r i z e d i n that the inject inlet (6) is connected tangentially to an inject chamber (12) , which extends through 90-270 in the circum¬ ferential direction of the casing (1) and is defined in the cir¬ cumferential direction by a first wall (15) and a second wall (16) .

3. An arrangement as defined in claim 2, c ha r a c t e r i z e d i n that the inject chamber (12) via radially inward directed openings (13) communicates with the interior of the rotor (3) for the supply of the pulp suspension through the rotor (3) to the screening zone (4) .

4. An arrangement a s defined in claim 1 or 2, c h a r a c t ¬ e r i z e d i n that the scrap outlet (8) is located at the end of the inject chamber (12) at the second wall (16).

5. An arrangement as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the reject outlet (11) is connected to a reject chamber (14) , which communicates with the screening zone (4) and extends through 60-120 in the circumferent¬ ial direction of the casing (1) and is defined in the circumfer¬ ential direction by walls (16,17).