A CONCENTRATING METHOD AND MEANS THEREFOR

Abstract: A liquid suspension of solid particles is concentrated by screening. An endless, movable screening web (1) is folded at a first station (8) into a tube-like configuration and is unfolded at a second station (12), wherein the tube thus formed extends between the first and the second stations (8, 12). Suspension is introduced into the tube formed by the screening web (1) at the first station (8), and liquid is allowed to run through the liquid-permeable tube walls to form a concentrate. The concentrate accompanies the movable screening web (1) to the second station (12), where the concentrate (17) is removed. An apparatus for concentrating liquid-solid suspensions includes an endless screening web (1), means (2-7) for guiding the web continuously or intermittently in an endless path, a web-folding device (6) located at a first station (8) along the web path, a web-unfolding device (7) located at a second station (12) along the web path, means (16) for introducing suspension into a tube-shaped web section at the first station (8), and means (7) for conducting away concentrate at the second station (12).

Description: A Concentrating Method and Means Therefor The present invention relates to a method and to an apparatus for concentrating a liquid suspension of solid particles, particularly fibres, by screening the suspension. It has earlier been suggested to concentrate liquid- particle suspensions, for instance to de-water highly diluted paper pulp suspensions, by passing the suspen¬ sions through stationary, perforated screening cylin¬ ders that are comprised of a relatively soft, flexible and perforated material. The liquid present in the suspension departs through the walls of the screening cylinders while the concentrate exits or is discharged through one end of respective screening cylinders. In the case of concentrates of high dry solids content, significant frictional forces may be generated between the cylinder wall and the concentrate, making it difficult to discharge the concentrate. The object of the present invention is to provide a novel method and a novel apparatus with which the aforesaid difficulties are avoided. To this end, it is proposed in accordance with the invention that a method and an apparatus of the kind defined in the introduction are also given the charac¬ teristic features set forth in the respective charac- terizing clauses of Claim 1 and Claim 9. This will ensure, in a rational manner, that friction occurring between concentrate and screening cloth webs will have no influence on the discharge of concentrate. Other advantageous features of the invention are set forth in the dependent Claims 2-8 and 10-16. The invention will now be described in more detail with reference to the accompanying drawing, in which Figure 1 illustrates schematically and in perspective an exemplifying embodiment of an inventive concentrat¬ ing apparatus; and Figure 2 illustrates highly schematically and in side view a modified inventive concentrating apparatus. The illustrated apparatus includes an endless rela¬ tively soft and flexible screening web, for instance a wire web which is preferably comprised of a plastic material. The screening web 1 is guided in an endless path around guide rollers 2-5 and around web-folding and web-unfolding devices 6 and 7 respectively. The apparatus also includes a pair of motor-driven rolls (not shown) by means of which the screening web 1 is moved continuously or intermittently in the direction indicated by arrows in the drawing. Longitudinal edge parts 9, 10 of the web 1 are folded over a centre web part 11 at a first station 8 along the path travelled by the web by means of the web-folding device 6, so as to form a screening tube which is closed by the web. The web 1 is then unfolded into a flat shape by means of the web-unfolding device 7 at a second station 12 along the web-path, so that the web will pass around the guide rollers 2-5 back to the first station 8 in an unfolded state. In the section between the first and the second stations 8, 12, in which the web-path slopes downwards in the direction of web movememt, the folded tubular-shaped web 1 is encircled by a perfo¬ rated supportive tube or cylinder 13. A liquid-collec- ting tray 14 having an outlet 15 for removing liquid from this section of the web path extends beneath the tubular web and the supportive cylinder 13. The reference numeral 16 identifies the end of a conduit through which fibre suspension to be concen¬ trated is delivered to the apparatus, and the refer¬ ence numeral 17 identifies the resultant concentrate. A further web 19 comprised of highly liquid-permeable material is wound on a storage roller 18. The further web 19 is guided around the guide roller 2 together with the screening web 1 and is folded at 8 to form a second tube which is located within the first tube formed by folding the screening web 1. The further web 19 can be unfolded at 12 and wound onto another stor¬ age roller or alternatively may be retained around the concentrate 17 and discharged from the apparatus at station 12 as a casing which encases and accompanies the concentrate. When using the suspension concentrating apparatus illustrated in the drawings, the suspension to be concentrated is introduced into the apparatus at station 8 through the conduit 16, to the tube formed . by the screening web 1, wherewith liquid leaves through the tube walls and through the perforated supportive cylinder 13 surrounded by said tube. The liquid runs down into the collecting tray 14 and departs therefrom through the outlet 15. Formed con- centrate is collected in the tube and forms a concen¬ trate plug 17 in the lower end of said tube, this plug being discharged from the tube at station 12 by driv¬ ing the screening web 1 in the direction of the arrows shown, either intermittently or continuously. The concentrating apparatus may be used advantageously in the pulp and paper industry for concentrating pulp suspensions or for recovering fibre rests, etc., from white water for instance. In those instances when the concentrate plug 17 is formed from very small particles, a further web 19 of smaller mesh size can be used. Similarly, when it is desirable to hold together the concentrate plug 17 formed in the apparatus, there may be used a further web 19 which is allowed to remain around the plug 17 to form a plug holding casing. The further web 19 may advantageously consist of an essentially autogenous material, for instance paper, when concentrating suspensions that contain cellulose fibres intended for recycling purposes, so as to enable the fibres in the web to be recovered together with the fibres embraced by said web. The illustrated web-folding device 6 is of a known kind and includes a first folding edge which extends transversely to the direction of web movement and over which the centre part 11 of the web 1 is folded. Located at a respective end of the first web-folding edge are folding edges which extend obliquely forwards and outwards and obliquely forwards and inwards as seen in the direction of web movement, over which the longitudinal edge parts 9, 10 of the web 1 are first folded in over the centre part of the web 1 and then again folded so as to again extend parallel with the centre part 11. In their folded state, the edges of the web overlap one another, so that the web forms a closed tube. The web-unfolding device 7 has the same configuration as the device 6 but in the reverse sense, so that the web is guided in an opposite direc¬ tion therethrough. Figure 2 illustrates an endless screening web 1 which is shaped in a web-folding device 6 to form a tube at a first station 8, and is unfolded in a web-unfolding device 7 at a second station 12, in the manner descri¬ bed with reference to Figure 1. Suspension to be concentrated, for instance a paper pulp suspension to be de-watered, is passed through a conduit 16 and into the tube-shaped web, wherewith a large part of the suspension liquid departs as the tube-shaped web is led through a downwardly sloping or possibly vertical perforated supportive tube or cylinder 13. The tube- shaped web 1 is then led into frictional contact with a large roller or drum 20, which is driven in the direction of arrow 21 by means of a motor (not shown) and drives the web 1 around the endless web path. The web 1 extends around a large part of the periphery of the roller 20 and the periphery of said roller may be provided with a shallow web-guiding recess. The tube- shaped web 1 containing partially concentrated or partially dewatered suspension is pressed against the periphery of the driven roller 20 by pressure rollers 21, as indicated by arrows 23, so as to further con¬ centrate or de-water the suspension. The apparatus illustrated in Figure 2 also comprises a guide plate 24 which functions to guide the concen- trate plug 17, while guide rollers 25 serve to guide the web 1 unfolded at station 12 to the web-folding device 6. The web-folding and unfolding devices 6 and 7 may conveniently be orientated such as to lay the mutually overlapping web edges of the tube-shaped. eb 1 adjacent the periphery of the roller 20. It will be understood that the web l may move in a path different to that illustrated. It will also be understood that the invention is not restricted to the described and illustrated embodiment thereof and that the invention can be realized in any desired manner within the scope of the inventive concept as defined in the following Claims.

Claims: Claims 1. A method for concentrating a liquid suspension of solid particles, particularly fibres, by screening, characterized by folding longitudinally extending edge parts (9, 10) of an endless suspension screening web (1) , which is moved continuously or intermittently in an endless path, over a centre part (11) of the web at a first station (8) along said path and unfolding said web at a second station (12) along said path, so as to form a tube between said first and said second sta¬ tions (8, 12); introducing suspension to be concen¬ tration into the tube formed by the screening web (1) at said first station (8) , wherein liquid is allowed to run from the suspension through the liquid-perme¬ able tube walls, and wherein the concentrate formed is carried by the screening web (1) to said second sta¬ tion (12) at which the concentrate (17) is removed from the screening web (1) . 2. A method according to Claim 1, characterized by passing the tube-shaped screening web (1) through a tube-embracing perforated supportive tube (13) down¬ stream of the first station (8) . 3. A method according to Claim 1, characterized by passing that section of the endless screening web (1) that has been folded to a tube-like configuration around a driven roller (20) whose diameter is large in relation to the diameter of said tube, so as to drive the endless web (1) around said path. 4. A method according to Claims 1-3, characterized by passing the tube-shaped screening web (1) first through a tube-embracing perforated supportive cylin¬ der (13) and then around a driven roller (20) whose diameter is large in relation to the diameter of said tube. 5. A method according to Claim 3 or 4, characterized by pressing the tube-shaped screening web (1) against the periphery of the driven roller (20) by means of at least one pressure roller. 6. A method according to any one of Claims 1-5, characterized by folding a further web (19) of good liquid-permeability to form a second tube which is located within the tube formed by folding the screen- ing web (1) , and permitting this second tube to depart at said second station (12) as a casing which accompa¬ nies and embraces the concentrate (17) . 7. A method according to any one of Claims 1-6, characterized in that when concentrating a fibre suspension the further web (9) is built-up of fibres similar to the fibres contained in the suspension. 8. A method according to any one of Claims 1-7, characterized by forming the tube or tubes extending between said first and said second stations (8, 12) in a downwardly inclined section of the endless path as seen in the direction of web movement. 9. Apparatus for concentrating a liquid suspension of solid particles, particularly fibres, by screening, characterized in that the apparatus includes an end¬ less screening web (1) , means (2-7) for guiding the web continuously or intermittently in an endless path; a web-folding device (6) which is located at a first station (8) in said path and which functions to fold longitudinally extending edge parts (9, 10) of the screening web in over a centre part (11) of the web (1) ; a web-unfolding device (7) which is located at a second station (12) in said path and which functions to unfold the edge parts (9, 10) of the screening web, the arrangement being such as to obtain a tube having liquid-permeable walls between said first and said second stations (8, 12), and means (16) for introduc- ing suspension to be concentrated into the tube formed by the screening web (1) at said first station (8) , and means (7) for discharging from the screening web (1) concentrate that has been obtained as a result of liquid draining through the tube walls from the sus¬ pension delivered to the tube, at said second station (12). 10. Apparatus according to Claim 9, characterized in that the path section downstream of said first station (8) slopes downwardly as seen in the direction of web movement. 11. Apparatus according to Claim 9 or 10, character- ized by a perforated outer supportive tube (13) which is located downstream of said first station (8) and which functions to support the tube-shaped screening web (1) . 12. Apparatus according to any one of Claims 9-11, characterized in that the endless screening web (1) is driven by a driven roller (20) , wherein the tube- shaped screening web moves in contact with the peri¬ phery of said driven roller, and wherein the diameter of said driven roller (20) is large in relation to the diameter of the tube. 13. Apparatus according to Claim 11 and 12, charac¬ terized in that the tube-shaped screening web (1) extends first through the perforated supportive tube (13) and thereafter in contact with the driven roller (20) over at least a part of the periphery thereof. 14. Apparatus according to Claim 12 or 13, character- ized by at least one pressure roller (22) which func¬ tions to press the tube-shaped screening web (1) against the periphery of the driven roller (20) . 15. Apparatus according to any one of Claims 9-14, characterized by means (2, 18) for delivering to the web-folding device located at said first station a further, liquid-permeable web (19) which is intended to be folded together with said screening web (1) so as to cover the inner surface of a tube-shaped screen¬ ing web in the region between said first and second stations (8, 12) . 16. Apparatus according to any one of Claims 9-15, characterized by a liquid-collecting tray (14) placed beneath the folded web in the region between said first and second stations (8, 12) and having a draina¬ ge outlet (15) for conducting liquid away from the web path region.

Inventors: HODEN EBBE, HODEN, EBBE
Applicants: HODEN EBBE, SUNDS DEFIBRATOR IND AB, HODEN, EBBE, SUNDS DEFIBRATOR INDUSTRIES AB
Application year: 1993
Main classification: B01D33
IPC codes: B01D29, B01D33, D21F1