WO1993006299A1

WO1993006299A1 - An arrangement and a method for concentrating a suspension

Info

Publication number: WO1993006299A1
Application number: PCT/SE1992/000676
Authority: WO
Inventors: Ebbe HODÉN
Original assignee: Sunds Defibrator Industries Ab
Priority date: 1991-09-26
Filing date: 1992-09-28
Publication date: 1993-04-01
Also published as: AU2669192A; CA2120010A1

Abstract

An arrangement for concentrating or thickening a liquid suspension of solid particles by screening the suspension comprises stationary, elongated screening conduits (10; 10A, 10B). Each conduit (10; 10A, 10B) is comprised of a relatively soft and flexible wire cloth, particularly a plastic wire cloth, which has the form of a vertical tube. The invention also includes the use of essentially vertical screening conduits (10; 10A, 10B) constructed from such wire cloth, for the purpose of concentrating a suspension. When concentrating a suspension by means of such an arrangement, liquid departs through the screening conduit wall. The suspension is introduced through the upper end of the conduit (10; 10A, 10B) while blocking the lower end of the conduit at the same time. The lower end of the conduit is then opened, so that concentrate is able to depart.

Description

An arrangement and a method for concentrating a suspen¬ sion-

The present invention relates to a method and to an arrangement of the kind defined in the preamble of

Claim l and the preamble of Claim 13 respectively. The invention also relates to the use of wire-cloth screen¬ ing conduits.

The invention is primarily conceived for use in concen¬ trating or thickening suspensions of fibers in liquid, and in particular for dewatering paper pulp suspensions of low dry solids content, e.g. 0.5 % by weight, to a much higher dry solids content, e.g. 6 % by weight or higher.

Fiber suspensions have earlier been dewatered with the aid of different types of suction filter. Apparatus of the kind defined in the preamble of Claim 1 have also been proposed (see for instance EP-A-0 274 690), al¬ though in this case the screening conduit is comprised at least partially of perforated rubber cloth or the like which is deformed in a manner to form a constric¬ tion for the suspension flowing in the direction of the longitudinal axis of the screening conduit. Irrespective of whether the perforating holes are formed in metal sheet or in rubber cloth, the holes afford only a relatively small dewatering capacity, which can only be improved by expensive subsequent machining of the holes.

Consequently, it is an object of the present invention to provide a novel and improved suspension concentrating apparatus which has a high liquid removal capacity and which can be constructed in a relatively simple and inexpensive manner. Another object of the invention is to provide a novel and improved suspension concentrating method which can be carried out with relatively simple apparatus while obtaining, at the same time, a high liquid removal capacity.

The aforesaid objects are achieved with an apparatus and a method that are characterized by the features set forth in Claim 1 and Claim 13 respectively. The suspen¬ sion can be caused to flow through the screening conduit upwardly or downwardly. When the suspension flows down- wardly, the force of gravity acting on the suspension and its components in the screening conduit reduce the energy required to effect concentration. The flow through the screening conduit can be controlled by adapting the flows of suspension to and the flow of concentrated suspension from a respective first and second end of the screening conduit. The use of screen¬ ing conduits that are made of a flexible wire cloth, e.g. plastic, will mean that only a slight frictional force will act on a concentrate coating on the conduit wall and on a concentrate plug formed at the outlet end of the conduit, thereby benefiting concentration of the suspension. In practice, there are preferably used a plurality of mutually parallel screening conduits. The invention also relates to the use of wire-cloth screen- ing conduits according to Claim 12. other features characteristic of the invention are set forth in the dependent claims.

The invention will now be described in more detail with reference to a number of exemplifying embodiments of the invention illustrated in the accompanying schematic drawings.

Figures 1 and 2 are partial vertical section views of a first and a second embodiment of the invention respec¬ tively. Figure 3 illustrates a lower part of a third embodiment of the invention.

Figure 4 is a cross-sectional view of one variant of a screening conduit. Figures 5 and 6 are respectively a partial vertical section view and a sectional view taken on the line VI- VI in Figure 5 of a fourth embodiment of the invention. Figures 7-9 illustrate a favourable alternative con¬ struction of side-by-side screening conduits which are comprised of double-laid wire cloth.

Figures 10-12 are sectional views of a fifth embodiment of the invention, these views being taken on the lines X-X in Figure 11 and lines XI-XI and XII-XII in Figure 10.

Figure 1 illustrates an arrangement for concentrating or thickening solid-particle/liquid suspensions, particu¬ larly fiber/liquid suspensions, by screening. The refer¬ ence numeral 10 identifies two essentially vertical screening conduits which are comprised of liquid-perme¬ able woven material, more specifically a relatively soft and flexible wire cloth, particularly a plastic cloth. The upper ends of the conduits are fitted onto tubular connectors 11 which extend down from a vessel 12 which is common to all conduits and which is intended to accommodate a suspension to be concentrated. The refer¬ ence numeral 13 identifies clamping bands by means of which the upper ends of the conduits 10 are secured to the tubular connectors 11. The lower ends of respective conduits 10 are connected to the upper ends of tubular members 14 which extend through the bottom of a further vessel 15 which is intended to collect liquid that has passed through the walls of the conduits. The vessel 15 is provided with a liquid outlet 16. The tubular members 14 extend down into tubular connectors 17 which extend up from a screw housing 18. The screw housing 18 houses a screw feeder 19 having an axle 20 which is driven by a motor, not shown. The reference numeral 21 identifies an opening provided in the bottom of the screw housing 18 for the discharge of concentrate that has passed down into the screw housing from the screening conduit 10, shown to the left of the Figure. It will be understood that each screening conduit may be assigned an individu¬ al bottom opening 21. The openings may open into a collecting vessel (not shown), from which concentrate is removed by means of one single concentrate transporting line, for instance a thick-pulp pump when the suspension concentrated is a paper pulp suspension.

When using the arrangement shown in Figure 1 , suspension is delivered to the vessel 12 and runs down therefrom to fill the conduits 10. Part of the suspension liquid will exit through the liquid-permeable walls of the conduits and pass along the outer surface of the conduits 10 down into the vessel 15, from which liquid is led away through the outlet 16. The suspension is thus concen¬ trated or thickened successively as it passes down through the conduits 10, wherein the flow through the conduits is adapted so that there is obtained in the lower ends of the conduits concentrate-plugs which move downwards from the conduits 10 and into the screw hous¬ ing 18, from which the plugs, the pulp, is transported to and out through the bottom openings 21, by means of the screw feeder 19, 20. By adapting the supply of suspension and the discharge of concentrate in relation to the liquid permeability of the conduits 10 and also to the tendency of the suspension to give up liquid therefrom, it is possible to achieve an equilibrium such that a concentrate having the desired dry-solids content will depart from each screening conduits, for instance in the form of a plug flow. Because the screening conduits are soft and pliable, further regulating and control means can be provided for setting and influencing the suspension concentrating process. Accordingly, the illustrated arrangement in- eludes devices 22 which are located adjacent the lower ends of the conduits 10 and which can be urged against the outer surface of said conduits, so as to enable the conduits to be clamped together more or less completely. The devices 22 of the illustrated embodiment are comprised of rollers which are journalled in bearings that can be moved, by means of a roller adjusting device, not shown, towards and away from one another in guides provided in holders 23 at mutually opposite ends of the rollers 22. The roller adjusting devices may be controlled auto atic- ally in accordance with the dry-solids content of the concentrate, with the aid of control signals delivered by a concentration meter which measures the dry-solids content of the concentrate departing from the lower end of an associated screeing conduit 10.

With the intention of assisting the dewatering process, the arrangement may include a number of devices which move reciprocatingly along the conduits so as to par¬ tially compress the same. In the illustrated embodiment, these devices are comprised of roller pairs 24, 25, which are journalled for movement towards and away from each other in holders 26, 27, which, in turn, can be raised and lowered along an associated screening conduit with the aid of drive means, not shown. The screening conduits 10 may widen downwardly towards their concen¬ trate outlet ends, in the manner shown, so as to facili¬ tate the flow of suspension therethrough.

Figure 2 illustrates an inventive arrangement in which the suspension flows upwardly through the screening conduit 10. The suspension is introduced through respec¬ tive tubular connectors 11 by means of a pump, not shown. The suspension is concentrated successively as it passes up through the conduit 10, and liquid that has passed through the conduit wall is collected in the vessel 15 and discharged through the outlet 16. The concentrate, comprising solid material and residual liquid, departs through the tubular member 14 and the tubular connector 17 to the screw housing 18 and is transported to and out of the screw housing 18 through the opening 21. Pressure applying devices 22, 23 are provided at the upper end of the screening conduit and function to more or less totally compress or squeeze the conduit 10 together. Similar to the arrangement illus- trated in Figure 1, the Figure 2 embodiment includes devices 24-27 which move reciprocatingly along the conduit so as to partially compress or squeeze the conduit. The holders 27 include arms 28 which carry spray nozzles 29 for spraying the external surface of the conduit with gas or liquid when required, so as to remove material which blocks or clogs the meshes of the wire cloth. The screening conduit 10 is shown to widen upwardly towards its outlet end, so as to facilitate the flow of concentrate up through the conduit.

Figure 3 illustrates an exemplifying embodiment of the invention which is similar to the Figure 1 arrangement in all essentials. The Figure 3 arrangement, however, lacks the screw housing of the Figure 1 arrangement and, instead, a pair of driven rollers 30 are mounted in the vicinity of the concentrate outlet of the conduit 10. These rollers 30 can be brought under pressure against a concentrate plug passing between the rolls, so as to compress the plug and further thicken the concentrate. At least one of the rollers 30 is in the form of a suction roll. Figure 4 illustrates a screening conduit 10 which is comprised of a relatively soft, flexible or pliable wire cloth and embraced by a rigid, coarse mesh support net 31 or the like of rectangular cross-section. The net 31 imparts to the conduit a corresponding rectangular cross-sectional shape, which may be beneficial since it reduces the smallest cross-section dimension of the suction-conduit cross-section and therewith the distance through which the liquid contained by the suspension is forced to pass in order to reach the wall of the suc¬ tion-conduit 10 during the suspension concentrating process.

Figures 5 and 6 illustrate yet another arrangement for concentrating or thickening a solid particle/liquid suspension, particularly a fiber/liquid suspension, by screening. Reference signs 10A and 10B identify a plu¬ rality of vertical screening conduits which are con¬ structed from wire cloth, e.g. plastic wire cloth. The upper and lower ends of the conduits 10A, 10B are con¬ nected to tubular connectors 11, 17, e.g. fitted over said connectors, and are secured detachably thereto by means of clamping bands 13, in the illustrated manner. In the case of the illustrated embodiment, the upper tubular connectors 11 extend down from a horizontal, upper plate 35 which supports a movable slide 37 having holes 38. The slide is moved with the aid of a piston-cylinder device 38 and the holes provided in the slide can be caused to coincide with each alternate upper-end of respective tubular connectors 11.

The reference numeral 39 identifies a deflecting plate by means of which concentrate exiting from the upper connectors 11 is passed to a^' collecting chute 40 which is common to all screening conduits 10A, 10B. The col¬ lecting chute accommodates a screw transporter 42 which is driven by a motor 41 and which functions to feed collected concentrate to a concentrate-receiving sta¬ tion, not shown.

The lower tubular connectors 17 have a closed lower end and each connector is provided with an inlet 43 for suspension to be concentrated. The tubular connectors 17 extend up through the bottom of a vessel 15 which col¬ lects liquid that has passed through the walls of res- pective conduits 10A, 10B. The vessel 15 is provided with a liquid outlet 16.

In the case of the illustrated embodiment, the vertical conduits 10A, 10B are disposed in a row, in side-by-side relationship. The conduits are divided into two groups, wherein each alternate conduit 10A forms part of a first group and the remaining conduits 10B form part of a second group. The suspension is pumped, by a pump 46, into a line 47 which branches to form two branch lines 48, 49, each of which is provided with a respective valve 50. Each alternate inlet 43 is connected to the branch line 48, while the remaining inlets 43 are con¬ nected to the branch line 49.

Each conduit 10A, 10B surrounds a screw transporter 51 whose axle 52 extends out through one of the tubular connectors, in the illustrated case the lower connec¬ tors. The external diameter of the screw transporters 51 is smaller than the internal diameter of the conduits 10A, 10B, and the transporters are driven by a motor 53 through the intermediary of a shaft 54 and a gear means 55, wherewith each of the screw axles 52 per se may be held selectively connected to the drive shaft 53.

When using the arrangement illustrated in Figures 5 and 6, suspension is introduced through the inlets 43 and rises in the conduits 10A, 10B while liquid departs successively through the conduit walls and runs down along the outer surface of said walls and into the vessel 15, from where the liquid departs through the outlet 16. The suspension is concentrated or thickened successively as it moves up through the conduits 10A, 10B, the screw transporters 51 of which therewith rotate in a direction for upward transportation of the suspen¬ sion. The thus concentrated suspension is finally dis- charged from the upper ends of the conduits 10A, 10B as a finished concentrate.

The extent to which the suspension is concentrated can be adjusted to desired values by one or more of the following procedures: Controlling the delivery pressure and/or delivery flow of the suspension, controlling the speed at which the screw rotates and holding the outlet end of respective conduits 10A, 10B closed during a smaller or larger part of a suspension concentrating operation. In order to eliminate the risk of liquid in the suspension from breaking through the above-located concentrate in the^"conduits 10A, 10B and departing from the conduits through the upper ends thereof, the suspension may, advantageously, be delivered to the screening conduits at a moderate overpressure which is lower than the counterpressure that is exerted against such liquid breakthrough by the content of the conduits 10A, 10B above the suspension inlet 43.

In the case of the embodiment illustrated in Figures 5 and 6, the conduits 10A, 10B are arranged in packs or blocks, with the conduits 10A forming a first pack or block and the conduits 10B forming a second pack or block. In Figure 5, the suspension is concentrated in the second conduit block formed by the conduits 10B, wherein the upper ends of the conduits 10B are held closed by means of the slide 37, at the same time as suspension is introduced into the lower ends of the con¬ duits 10B and the screw transporters 51 of said conduits 10B feed concentrate in a direction towards the closed upper ends of the conduits. As the suspension is concen¬ trated in the conduits 10B, concentrate is discharged from the first conduit block comprised of the conduits 10A, with the aid of the screw transporters 51. The suspension inlets 43 of the screening conduits 10A are therewith closed, whereas their upper ends coincide with the openings 38 in the slide 37 and are thus open. When concentration of the suspension in the conduits 10B is completed and the conduits 10A have been emptied, the slide 37 is moved so that the openings 38 will coincide with the upper ends of the conduits 10B, wherewith suspension is delivered to the conduits 10A and the supply of suspension to conduits 10B is stopped. In this way, suspension is concentrated in the conduits 10A while concentrate is discharged from the conduits 10B. By using soft, flexible or pliable wire-cloth conduits 10A, 10B whose internal diameters are greater than the external diameter of the screw 51 (e.g. a clearance of 3-9 mm between the inner surface of the conduit and the outer periphery of the screw) , low friction losses are achieved, because the conduit wall is able to yield slightly to permit the passage of lumps of concentrate, and a high degree of concentration can be achieved, e.g. 10-12% dry solids content, when dewatering cellulose pulp. As a result of this clearance between screw and conduit, a filtering fiber-layer is built-up on the inner surface of the conduits, thereby enabling the meshes of the screening conduits to be relatively large. As will be seen from Figure 6, the illustrated embodi¬ ment includes holders 56 which are movable along the length of the conduits and which carry spray nozzles 57 by means of which the external surfaces of the conduits 10A, 10B can be sprayed, as required, with gas or liquid with the intention of unblocking those meshes of the conduits 10A, 10B which have become excessively blocked with material particles.

According to one embodiment of the invention, the screw axle 52 may be hollow and provided with openings, indi¬ cated at 44 in Figure 5, through which, e.g. a washing or treatment liquid can be delivered to the fiber sus- pension being concentrated.

At higher suspension consistencies, the friction acting between the deflecting plate 39 and the discharged concentrate may become significant. It may therewith be beneficial to construct the upper plate 35 so that it slopes to one side, downwardly towards the collecting chute 40, and therewith minimize contact of the concen¬ trate with the deflecting plate 39, or so that no such contact will take place at all.

When the screening conduits 10A, 10B are comprised of a soft, flexible material, such as a plastic wire cloth, it may be suitable, and at times necessary, to provide devices which will prevent those parts of the screening conduit that are located between the conduit ends from rotating about the longitudinal axes of said conduits. For example, the conduits may be attached to a station¬ ary support at locations between the ends of said con¬ duits, for instance to stationary rods which extend along the conduits 10A, 10B.

Figures 7-9 illustrate a favourable alternative con¬ struction of, e.g., the screening conduits 10A, 10B, in which the conduits are prevented automatically from rotating together with the screw transporters. The screening conduits 10A, 10B are formed (Figure 7) by two screening cloths 58, 59 which are laid one upon the other and which are held pressed against one another at intervals which correspond to one half the circumference of the screening conduit, by profiled sections 60, 61 which are held pressed against mutually opposite sides of the double-laid screening cloths by means of fastener means 62. These pressure exerting, or clamping means formed by the devices 60-62 extend vertically in the assembled plant and along mutually separate and neigh- bouring conduits 10A, 10B. For the purpose of forming the screening conduits 10A, 10B, the clamping means 60- 62 are moved towards one another, in accordance with Figure 8, so as to be spaced mutually apart at a dis¬ tance which corresponds to the diameter of a screening conduit, whereafter those screening-cloth parts that are located between the clamping means at the ends of the screening conduit are brought together with and pressed against the tubular connectors 11, 17, as illustrated for the lower conduit ends in Figure 9. As illustrated in Figure 9, the ends of the screening conduits are clamped by means of horizontally disposed elongated devices 63, 64, whose mutually facing sides have gener¬ ally semi-circular recesses which connect with the outer surface of the ends of the conduits 10A, 10B fitted onto the tubular connectors 17 and are pressed against said ends with the aid of penetrating fastener means 65.

Figures 10-12 illustrate another suspension concentrat¬ ing arrangement. This arrangement includes a number of pairs of associated screening conduits 10A, 10B com¬ prised of a relatively soft and flexible wire cloth, preferably a plastic wire cloth. The illustrated screen¬ ing conduits are comprised of two wire cloths 58, 59 which are held pressed against one another, at interval distances corresponding to the diameter of a screening conduit, by means of vertical, clamping means 60, 61; 70, 71 which act together in pairs. These pairs of clamping means 60, 61, 70, 71 extend along the conduits, wherein the clamping means in each pair of means act on and are preferably connected with the surfaces of the cloths 58, 59 that face away from each other. The wire- cloth width between neighbouring pairs of clamping means is at least generally equal to half the conduit circum¬ ference. These latter clamping means normally hold the wire-cloth parts located between the pairs of clamping devices 60, 61, 70, 71 together with and pressed against the upper tubular connectors 11 and against lower stop¬ per means 72 which have a cylindrical cross-section which corresponds essentially to the diameter of the conduits 10A, 10B. In the embodiment illustrated in Figures 10-12, each alternate pair of clamping means 60, 61 are stationary, similar to the embodiment illustrated in Figures 7-9, while the remaining alternate pairs are movable outwardly from their clamping positions and from one another respectively, so that the screening conduits 10A, 10B which are normally separated from one another by clamping means 70, 71 will form a unified single conduit whose cross-sectional area is essentially great¬ er than the combined cross-sectional area of the afore¬ said mutually separate screening conduits 10A, 10B. These unified conduits can be best seen at 73 in Figure 10.

In the embodiment illustrated in Figures 10-12, the tubular connectors 11 are supported stationarily in a manner not shown. The stopper means 72 are also station¬ ary and are carried by a horizontal supporting surface 74, through the intermediary of arms 75. The supporting surface 74 is provided with holes 76 which are located opposite the unified conduits 73 and which are equally as large as or lager than the conduit orifices. The areas of the holes also extend beyond the peripheries of the stopper means 72.

When concentrating suspension in the arrangement accord¬ ing to Figures 10-12, suspension is delivered to the screening conduits through their respective inlet con¬ nectors 11, wherein liquid departs through the walls of the conduits and flows down along said walls and through the openings 76. Columns of concentrate are formed within the conduits 10A, 10B. These columns are caused to depart from the conduits, by separating the normally combined clamping means 70, 71 to the position shown by broken lines in Figure 10, wherewith the concentrate columns will slide down through the resultant unified conduits 73 and out through the openings 76. As shown in Figure 12, the arrangement includes a plate 77 which is hinged on the undersurface of the carrier surface 74 adjacent the opening 76, this plate functioning to guide the concentrate to a removal chute 79 equipped with a screw transporter 78. The plate 77 can be swung, by means of a piston-cylinder device 80, between its effec¬ tive position and an ineffective position, shown in broken lines, wherein liquid pressed from the suspension during a suspension concentrating process is allowed to pass freely downwards to an appropriate liquid receiving device, not shown. In order to facilitate removal of the concentrate, the stopper means 72 have sloping upper surfaces 81, which also preferably slope to one side in relation to one another, as shown in the Figure 11 illustration and indicated by arrows 82 in Figure 10.

The movable clamping means 70, 71 are moved by means of a number of toggle devices which are formed by pairs of links 83, 84 which are pivotally connected together at respective one ends thereof and the opposite ends of which are connected pivotally to a movable clamping means 70, 71 and to a fixed frame part 85 respectively. When the arrangement is in its active clamping state, the links suitably extend horizontally in a straight line with one another and at right angles to associated clamping means 70, 71, whereby the pressure force origi- nating from the concentrate in the screening conduits and endeavouring to move the clamping means apart can be transferred effectively to and taken-up by said frame parts 85. The toggle tools are manouvered by drive devices, in the illustrated case piston-cylinder devices 86. As will best be seen from Figure 12, all toggle tools used to move a clamping means 70 or 71 can be driven by one and the same drive device 86. To this end, the mutually facing ends of the links 83, 84 are also connected pivotally to a common pull-and-push rod 87, which is pivotally connected at one end to an associated piston-cylinder device 86. This latter device is pivot¬ ally mounted on a frame part, not shown. When the rods 87 move upwards, the associated clamping means 70 or 71 is moved away from its clamping position and carries with it the wire-cloth part connected to the clamping means, as illustrated to the right of Figure 12. The clamping means 70, 71 are carried by rods which extend between the frame parts 85 and are movable axi lly in relation to said rods. One such rod, referenced 88, is shown in Figure 12 and is provided with adjustable abutment screws 89, which enable adjustments to be made to the outer position of the movable clamping means 70, 71.

It will be understood that the invention is not restric¬ ted to the illustrated and aforedescribed exemplifying embodiments thereof, and that modifications can be made within the scope of the inventive concept defined in the following claims.

Claims

1. An arrangement for concentrating a liquid suspension of solid particles, particularly fibers, by screening the suspension, said arrangement including at least one, stationary elongated screening conduit (10; 10A, 10B) which is comprised of a material which is permeable essentially only to liquid; devices (11, 12, 17, 43) for introducing suspension to and removing concentrated suspension from said screening conduit; and devices (15, 16, 76) for collecting and discharging liquid that has passed through the wall of said conduit; c h a r a c ¬ t e r i z e d in that said at least one screening conduit (10; 10A, 10B) is comprised of a relatively soft and flexible wire cloth, particularly a plastic wire cloth, shaped into an essentially vertical tubular configuration.

2. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d by a plurality of screening conduits (10; 10A, 10B) disposed in mutually parallel relationship.

3. An arrangement according to Claim 1 and 2, c h a r a c t e r i z e d in that a plurality of mutu¬ ally neighbouring screening conduits (10A, 10B) are formed from two wire cloths (58, 59), which are held pressed against one another at intervals corresponding to the diameter of a screening conduit by means of pairs of vertically arranged clamping means (60, 61, 70, 71) which extend along said conduits and which have pairs of surfaces which act respectively on conduit surfaces which face away from one another, wherein the width of the wire cloth located between adjacent pairs of clamp¬ ing means is equal to half the circumference of the conduit.

4. An arrangement according to Claim 3, c h a r a c ¬ t e r i z e d in that the wire-cloth parts located between pairs of clamping menas (60, 61, 70, 71) at the upper and the lower ends are combined with and held pressed against tubular connector members (11,17) or stopper means (72) having at least a generally cylindri¬ cal cross-section and a diameter corresponding essen¬ tially to the diameter of the screening conduit (10; 10A, 10B).

5. An arrangement according to Claim 3 or 4, c h a r a c t e r i z e d in that at least one clamping means (70 or 71) in one or more clamping-means pairs (70, 71) located between two screening conduits (10A, 10B) is movable away from the other clamping means (71 or 70) in said pair, so that the wire-cloth parts form¬ ing these screening conduits enable a common unified conduit (73) to be formed whose cross-sectional area is substantially greater than the combined cross-sectional area of the aforesaid screening conduits _(1QA,_10B).

6. An arrangement according to Claim 5, c h a r a c ¬ t e r i z e d in that those wire-cloth parts which are located between the pairs of movable clamping means (70, 71) are connected to respective clamping means.

7. An arrangement according to Claim 5 or 6, c h a r a c t e r i z e d in that those screening-cloth parts which are located between said pairs of movable clamping means (70, 71) are intended to be brought together at the lower ends and held pressed against stopper means (72) which normally close the lower ends of the screening conduits (10A, 10B) and which have downwardly sloping upper surfaces (81).

8. An arrangement according to Claim 7, c h a r a c ¬ t e r i z e d in that the upper surfaces of respective stopper means (81) slope downwardly and to one side in relation to one another.

9. An arrangement according to any one of Claims 5-8, c h a r a c t e r i z e d in that a number of toggle tools (83, 84, 86, 87) extend between at least one clamping means in each pair of clamping means (70, 71) and a fixed frame part (85), in that each toggle tool includes two links (83, 84), which are pivotally con¬ nected at opposite ends to said clamping means (70, 71) and said frame part (85) respectively and which are connected pivotally together at their mutually facing ends.

10. An arrangement according to Claim 9, c h a r a c ¬ t e r i z e d in that the two links (83, 84) forming part of each toggle tool (83, 84, 86, 87) are disposed generally in line with one another when the associated clamping means (70, 71) is in its clamping state.

11. An arrangement according to Claim 9 or 10, c h a r a c t e r i z e d in that for the purpose of enabling a plurality of toggle tools (83, 84, 86, 87) to be manouvered simultaneously, the arrangement includes a reciprocatingly movable pull-and-push rod (87) which is driven by a drive device (86) and which is connected to a respective toggle tool at its pivotal connection with mutually facing ends of the links (83, 84).

12. The use of essentially vertical wire-cloth screening conduits (10; 10A, 10B), particularly plastic wire cloths, for concentrating a liquid suspension of solid particles, particularly fibers, by screening the suspen¬ sion.

13. A method for concentrating a liquid suspension of solid particles, particularly fibers, by screening the suspension, wherein the suspension is introduced into at least one stationary, essentially vertical, elongated screening conduit (10; 10A, 10B), which is comprised of a flexible wire cloth, particularly a plastic wire cloth, and wherein the suspension is concentrated by the departure of liquid which exits through the wall of the screening conduit, c h a r a c t e r i z e d by intro- ducing the suspension through the upper end of the screening conduit (10; 10A, 10B) while blocking the lower end of the conduit at the same time, and by then opening the lower end of the conduit so as to discharge concentrate, optionally while interrupting the supply of suspension at the same time.