WO1995030046A1

WO1995030046A1 - Method of treating a liquid-containing fibre material and apparatus for carrying out the method

Info

Publication number: WO1995030046A1
Application number: PCT/SE1995/000432
Authority: WO
Inventors: Sture Eriksson; Ann-Sofi JÖNSSON; Bengt Jönsson
Original assignee: Kvaerner Pulping Technologies Ab
Priority date: 1994-05-03
Filing date: 1995-04-21
Publication date: 1995-11-09
Also published as: AU2458095A; SE502815C2; SE9401514D0; SE9401514L

Abstract

A method and an apparatus for treating pulp with a treatment agent for simultaneous displacement and thickening, in which the pulp is fed into a space (6) in order to form a layer on the perforated casing (5) of a rotating drum (3). According to the invention, the treatment agent is also fed into the space (6) in order to form a continuous layer (22) of treatment agent up against the mobile pulp layer (20). The displacement and thickening are carried out continuously at a mechanical pressure on the pulp layer (20) which is less than 100 kPa, and for the most part using the treatment agent. The quantity of liquid which is displaced through the casing (5) per unit of time exceeds the quantity of treatment agent which is supplied. A distribution channel for the treatment agent is designed and arranged in association with the space (6) in such a way that the layer of treatment agent is formed and maintained in free contact with the pulp layer.

Description

Method of treating a liquid-containing fibre material and apparatus for carrying out the method

The present invention relates to a method of treating a liquid-containing fibre material with a treatment agent in order to displace liquid out of the fibre material and simultaneously thicken the fibre material, which fibre material is fed into a continuous material space which is delimited by an endless, mobile filter member and a stationary wall element, in order to form a continuous layer of fibre material which is in contact with, and moves with the same speed as, the filter member. The invention also relates to an apparatus for carrying out a treatment of this nature, which apparatus comprises an endless, mobile filter member; a housing which is arranged at a distance from the filter member; a wall element which is arranged at a distance from the filter member so that they enclose a material space between themselves; a gap-shaped inlet for fibre material which is to be treated in the material space; a gap-shaped outlet from the material space for treated fibre material; feeding-in members for feeding in fibre material via the said inlet so that a continuous layer of fibre material is formed on the filter member; feeding-out members for feeding out treated fibre material via the said outlet; one or more distribution members for treatment agent; and feeding- in members for feeding in treatment agent via the said distribution member(s) .

The washing results which are achieved in washing apparatus which is equipped with pressure devices are conditioned by the final dry substance content of the pulp, and depend on the final compression which iε achieved in the nip between the pressure device and the filter drum. The filter drum, as well as the pressure device, must be designed so that their strength is adequate to withstand the compression which is envisaged. The costs of filter drums depend on the compression which they can withstand and constitute a major portion of the total cost of the apparatus. Within the chemical pulp industry, several washing operations take place for the purpose of removing liquid, by displacement, from the fibre material in order to recover chemicals and purify the fibre material while using the least possible quantity of displacement liquid and taking into account economic and environmental aspects. These washing operations are carried out using different types of apparatus such as cylinder filters, flat filters, radial washers, pressure washers, etc. Such apparatus operates on the displacement principle, which involves the liquid phase which is initially present in the fibre suspension or fibre web being displaced by, and replaced by, a suitable washing liquid with the proportion of liquid in the pulp web being maintained. When the process proceeds optimally, a part of the displacement liquid is not mixed with the original liquid. In practice, however, the displacement liquid mixes both longitudi¬ nally and axially with the original liquid during a normal, conventional displacement operation, as a result of which increased quantities of displacement liquid are required in order to achieve the desired washing effect.

In order to obtain a washing result which is good for the process, the ratio between the washing liquid which iε supplied per unit of width and the liquid in the fibre web must be kept conεtant per unit of width of the fibre web. This situation can only be achieved by the washing liquid being supplied uniformly at each unit of width, with a first prerequisite being that the quantity of washing liquid supplied over the whole of the width of the web is constant, and a second prerequisite being that the consistency over the whole of the width of the web is constant, i.e. that the dry substance iε constant for each unit of width. While the first prerequisite is relatively easy to satisfy, the second prerequisite is technically difficult to meet, as a result of which concentration deviations of +10% are to be expected during practical operation when the concentration of the formed fibre layer is relatively high; as a result, the washing liquid flows trans¬ versely through the fibre layer to those parts in which the concentration is lower. The object of the present invention is to eliminate the abovementioned disadvantages and provide an improved method and an improved arrangement for treating the liquid-containing fibre material.

The method according to the invention is characterized in that the treatment agent is fed into the material space in order to form a continuous layer of treatment agent up against the mobile layer of fibre material, and in that the displacement and thickening are carried out continuously at a mechanical pressure on the fibre material layer which is less than 100 kPa, and principally using the treatment agent, with the quantity of liquid which is displaced through the filter member per unit of time exceeding the quantity of treatment agent which is supplied. The apparatuε according to the invention is characterized in that the distribution member is designed and arranged in association with the material εpace in such a way that a continuous layer of treat¬ ment agent is formed and maintained in free contact with the fibre material layer along the whole, or a substantial part, of the latter between the said inlet and outlet.

The present invention provides an improved method for treating liquid-containing fibre material, which method can be carried out using a filter surface which is only a fraction of the filter surface which is required in conventional methods, calculated on the basis of the same washing losses. The invention implies that the investment and operational costs for high- quality washing can be reduced to such a low level that all environmental requirements can be satisfied. The invention provides an improved method for displacing the original liquid from the pulp web and simultaneously compressing the pulp web such that the original liquid departs at a speed which is greater than the speed at which the displacement liquid is supplied, as a result of which axial mixing is eliminated and the degree of displacement is improved, with the course of the displacement approaching that which is optimal. In order to ensure that this process functions in accordance with the abovementioned description, the mechanical pressure must not exceed 100 kPa, while the hydrostatic pressure should be at least 50 kPa, and preferably at least 100 kPa, in accordance with deductions which can be made from a computer calculation which is based on several equations in two articles in AICHE Journal, September 1992, vol. 38, no. 9, pp. 1340 and 1349. The method according to the invention involves so-called dynamic displacement. Accordingly, in the method and apparatus according to the invention, the fibre layer is compressed, and liquid is displaced, while the fibre concentration is rising, with the quantity of liquid which is being removed from the fibre layer through the fibre drum exceeding the quantity of washing liquid which is being supplied, calculated per unit of time.

The invention is described in more detail below with reference to the drawings. Figure 1 is a cross-sectional view of a first embodiment of an apparatus for treating pulp in accordance with the invention.

Figure 2 is a cross-sectional view along line II-II in Figure 1. Figure 3 is a cross-sectional view of a second embodiment of an apparatus for treating pulp in accordance with the invention.

Figure 4 is a cross-sectional view of parts of a third embodiment of an apparatus in accordance with the invention.

Figure 5 is a cross-sectional view along line V-V in Figure 4.

Figure 1 is a diagrammatic representation of an apparatus in accordance with the present invention for treating a water-containing and cellulose-containing fibre material, for example a pulp. Washing filters, displacement presses, flat wire washers and radial washers are examples of apparatus of this nature within the chemical pulp and paper industry. The apparatus comprises a stand 1, a curved, rigid housing 2 and a drum 3, which is rotatably mounted on the stand by means of a horizontal axle. The housing 2, which consists of a plate, is sealed at the two opposite ends by means of side walls 23, 24 such that a vessel is formed in which the drum 3 rotates in the direction indicated by an arrow. The drum 3 has a cylindrical, liquid-permeable casing 5 which forms an endless filter member, which is thus mobile in relation to the housing 2, which is stationary during operation. The casing 5 comprises a perforated, rigid plate and at least one wire (not shown) which encircles the plate. The housing 2 extends at a predetermined distance from the casing 5 of the drum. In the embodiment shown in Figures 1 and 2, the housing 2 itself forms a wall element 4 which, between itself and the casing 5, delimits a continuous, arciform treatment space 6 which expediently tapers in the direction of rotation of the drum 3, as shown.

The apparatus additionally comprises a helicoid feeding-in member 7 for feeding pulp into the material space 6 and a helicoid feeding-out member 8 for feeding out the treated pulp. The screws 7, 8 are parallel to the axis of rotation of the drum 3 and arranged along one long side of the apparatus where the drum 3 is exposed by means of the housing 2 extending in a limited manner around the drum while encircling a predetermined major part of the latter. The feeding-in screw 7 communicates with the material space 6 via a horizontal channel 11 which extends axially and thus has a rectangular cross section. The feeding-out screw 8 communicates with the material space 6 via an oblique channel 12 which extends axially and thus has a rectangular cross section. A scraper 13 is arranged in the channel 12 so that it bears against the casing 5 of the drum .

Reference number 14 designates a pressure member which is arranged in association with the outlet section of the material space 6 for the purpose of imparting a final compression to the pulp web. The pressure member 14 can consist of a pressure shoe, as shown, or of a pressure roller. Having a pressure shoe 14 in association with the outlet section is advanta¬ geous when used in combination with the concentration gradient which is obtained in the apparatus described. The pulp web 20 becomes detached from the filter casing 5 directly after the outlet 10 as a result of the influence of two different forces, one of which arises as a consequence of the concentration gradient, since the concentration increases in the direction of the filter casing 5, while the other arises as a conse¬ quence of the friction-generating contact of the pulp web with the inside of the wall plate 4 in association with the pressure shoe 14, so that the pulp web 20 is subjected to a braking effect on its side directed towards pressure shoe 14 while the opposite side of the pulp web is still entrained by the filter casing 5. The result of these two forces is that the pulp web is deflected outwards from the filter casing as soon as it leaves the outlet 10 and iε fed onwards into the outlet channel 12. This eliminates the requirement for a conventional arrangement for removing the pulp layer from the filter caεing 5.

An outlet 10, through which the treated pulp web passes, is present at the outlet section of the material space 6, which outlet 10 has a rectangular shape having a width which corresponds to the width of the material space 6, i.e. the length of the filter drum, and having a predetermined height. The apparatus shown in Figures 1 and 2 includes a distribution member 16 for treatment agent, for example washing liquid, which member has the form of a channel which iε delimited by the housing 2 and an internal partition wall 17 which extends in the material space 6 in parallel or concentrically with, and at a predetermined distance from, the housing 2. The distribution channel 16 for washing liquid forms, with its orifice, an inlet 18 to the material space 6, which inlet is situated at a predetermined distance from, and downstream of, the point at which the pulp strikes the filter casing 5. An inner channel is formed between the partition wall 17 and the filter caεing 5, which channel can be regarded as constituting an extension of the channel 11 for pulp, which thereby, with its orifice, forms an inlet 19 to the material space 6, which inlet is consequently situated immediately inside, in a radial direction, the inlet 18 for washing liquid. The two specified inlets 18 and 19 have rectangular shapes with a width which corresponds to the width of the material space 6, i.e. the length of the filter drum 5, and with predetermined heights which vary as a function of the operational circum¬ stances in question. The height H₆ of the material space 6 at the inlets 18 and 19, and the height H₁₆ of the distribution channel 16 at the inlet 18, can be calculated as follows on the basis of normal operating conditions:

Proportion of liquid (Lpi) in the incoming pulp at the inlet 19 10-30 1/kg

Grammage (6) of the incoming pulp 4-10 kg/

Proportion of liquid (Lpo) in the outgoing pulp at the outlet 10. 1.5-5 1/kg Dilution factor (DF) 0-4 1/kg with the following correlations applying: H₆ = (Lpi + 0.6) • G H₁₆ = (Lpo + DF) • G

The lowest height H₁₆ of the distribution channel 16 at the inlet 18, and consequently the minimum thickness of the liquid layer 22 in association with the inlet 18, is thus 6 mm (H₁₆ = (1.5 + 0) x 4) .

In the embodiment shown in Figures 1 and 2, the apparatuε also includes a multiplicity of strips 25 made of, for example, sheet metal, which are firmly welded onto the inside of the housing 2 and extend into the distribution channel 16 such that the latter is subdivided into compartments 26. The strips 25 are parallel to each other and to the gables 23, 24 of the apparatus. The strips 25 consequently extend in the direction of movement of the pulp layer and out of the distribution channel 16 for a substantial distance in order to enclose a sector angle of approximately 90°, as shown, or more, for example up to 270° if so desired. It is suitable for each strip 25 to have a radial dimension such that it extends for a short distance into the pulp layer, expediently 1-3 cm. The strips 25 function as partition walls and prevent washing liquid from being conducted laterally towards areas of the pulp layer where there is less resistance to liquid penetrating radially through the pulp layer towards the filter casing 5 due to the consistency being less within these areas than in adjacent areas. Instead, the washing liquid comes to be pressed directly forwards through each compartment 26 of the distribution channel and to be guided in a forward direction between two guide strips 25 or between an outer guide strip 25 and an outer wall 23 or 24, respectively.

The washing liquid is fed into the material space 6 by means of a feeding-in member 15 which comprises a pump (not shown) and a collecting pipe 29 which is connected to the diεtribution channel 16 via a conduit 28 to each compartment 26 of the distribution channel 16. The collecting pipe 29 is expediently conical in the direction of flow, as is shown in Figure 2. Each conduit 28 is provided with a valve and control component 30 for adjusting the flow of liquid to the diεtribution compartment 26 such that there iε a uniform flow of liquid to all the diεtribution compart- mentε 26. The washing liquid is pumped from a store

(not shown) to the collecting pipe 29 at high pressure, for example 5 bar .

During operation, the pulp is in contact with the filter casing 3, and forms a layer 20 which passes through the inlet 19. Consequently, the pulp layer 20 is supported by, and moves at the same speed as, the filter casing 5. Due to the fact that the distribution channel 16 for washing liquid extends along the inside of the housing 2 and along the filter casing 5, and opens out directly forwards in the same direction as the direction of movement of the pulp layer 20, the washing liquid which is pumped under predetermined pressure through the distribution channel 16 will be imparted this forward direction, such that a distinct liquid layer 22, which flows along the inside of the housing 2, is formed downstream of the inlet 16. The washing liquid is fed into the material space 6 at a speed which corresponds to, or in the main corresponds to, the speed of the pulp layer 20. The liquid layer 22 is continuous and can be maintained right up to the pressure cone 14, aε iε evident from Figure 1. An almost distinct boundary 27 is formed between the two different material layers 20, 22, which move as one unit without displacements appearing between them, as seen in the direction of movement, if the said speeds are the same.

Figure 3 iε a diagrammatic representation of a second embodiment of an apparatus according to the invention, which embodiment differs from that of Figure 1 only with regard to the fact that it has been complemented by a second distribution channel 31 for treatment agent of the same design aε the distribution channel 16, with the second distribution channel 31 being arranged approximately 170° downstream of the first distribution channel 16, which, in this case aε well, iε located at the inlet section of the material space 6. The housing is extended in order to provide room for the second distribution channel 31 and the additional quantity of treatment agent which is fed in in order to repeat the displacement procesε and to continue the compression of the pulp layer 20. Accordingly, the washing liquid is fed into the material space 6 at two locations by means of two feeding-in members 15, 35, each of which includes a pump 32 (the drawing only shows the pump for feeding-in member 15) . The second feeding-in member 35 also includes a collecting pipe 33, which is connected to the distribution channel 31 via conduits 34 to each compartment in the distribution channel 31, with each conduit 34 having a valve and control component 37 in the same way as the firεt feeding-in member 15. The arrangement makes it possible to wash the pulp with washing liquid of differing quality. Thus, the second feeding-in member 35 feeds in pure washing liquid which displaces liquid through the filter casing 5, which liquid is collected in a trough 36, from which the liquid which has been collected in this way iε pumped by means of the pump 32, via a conduit 38, to the collecting pipe 29. Figures 4 and 5 provide a diagrammatic repre¬ sentation of a third embodiment of an apparatus according to the invention for treating pulp, for example, with washing liquid, for example. Figure 4 showε only a longitudinal section of the apparatus, which includeε an endless filter member 40 in the form of a perforated band which runs around two rollers or liquid-permeable drums (not shown) in the direction indicated by an arrow. A housing 41 of plate metal encircles a major part of, and extends at a predeter- mined distance from, the filter band 40, which distance can be constant around the whole of the extent of the housing. The side walls, which, together with the housing 41, form a vessel, have, like the feeding-in and feeding-out screws and the pressure member, not been drawn in. A plane wall element 42 extends between the housing 41 and the filter band 40, which element iε located at a predetermined distance from the filter band 40 such that, between them, there is delimited a continuous treatment space 46. The pulp is fed into the material space 46 via a channel 43 which extends axially and thus has a rectangular cross section. A distribution member 44 for treatment agent has the form of a channel which is delimited by the housing 41 and the inner wall element 42. The inner wall element 42, which is encircled by the distribution channel 44, forms a εcreen member, and can consist of a rigid screen plate or screen cloth which is supported by several parallel strips 47 (only shown in Figure 5) , which stripε are fixed to the inside of the housing 41 and extend in the direction of rotation of the filter band 40. The screen member 42 is sufficiently resistant to flexion and strong to withstand the stresses from the washing liquid. In addition, it exhibits a very high degree of permeability for the washing liquid such that the latter flows instantaneously through the screen member into the material space 46. The width of the strips 47 can be increased such that they now possess internal sections 48 (only shown in Figure 5) which extend into the material space 46, thereby giving the strips the same function as the stripε 25 in the firεt embodiment described. The stripε 47, and their internal sections 48, delimit compartments 49 which can be likened to the first compartments 26 described. The channel 43 for feeding in the pulp extends through the housing 41 into the material space 46, where an inlet 50 iε formed which determines the initial thickness of the pulp layer 54.

The washing liquid is pressed into the material space 46 by means of a number of feeding-in members 55 which are arranged at suitable distances, one after the other, as seen in the direction of rotation of the filter band 40. Figure 4 shows parts of two of the feeding-in members 55. Each feeding-in member 55 comprises a pump (not shown) and a collecting pipe 51 which is connected to the diεtribution channel 44 via a conduit 52 to each compartment 49 of the diεtribution channel 44. Each conduit 52 iε provided with a valve and control component 53 aε described in conjunction with the firεt embodiment. Arranging several feeding-in members 55 of the type described at suitable distances one after the other ensures that, during operation, the whole of the distribution channel 44 iε filled with washing liquid and that a continuous layer 56 of washing liquid of the desired thickness is maintained, by way of the screen plate 42 or the like, in the material space 46, which layer presses against the pulp layer 54 as it passes by in such a way that liquid in the pulp layer is diεplaced by the waεhing water at the same time as the pulp layer 54 iε compressed, with liquid departing through the filter band 40 in a quantity per unit of time which iε greater than the quantity of washing liquid which is εupplied during the same unit of time.

The simultaneous occurrence of displacement and concentration (compression) , in accordance with the invention, resultε in a halving of the total time which is required for the two operationε to take place separately in accordance with the conventional tech¬ nique. Carrying out compression and displacement at a high hydroεtatic pressure and a low mechanical pressure, in accordance with the present invention, leads to substantially higher production. These unique operating conditions give rise to a steep concentration gradient which reεultε in a low level of friction againεt the stationary plate sweep, implying in turn that the power required to rotate the filter drum is lesε. The pulp web becomes detached from the filter casing aε a reεult of the combination of the described concentration gradient and the influence of the frictional and shearing forces on the pulp web in asεociation with the pressure cone upstream of the outlet. As a consequence, conventional, expensive detachment devices, such aε air and steam scrapers, toothed rollers, blowing fans, etc., can be eliminated.

Claims

PATENT CLAIMS

1. Method of treating a liquid-containing fibre material with a treatment agent in order to displace liquid out of the fibre material and simultaneously thicken the fibre material, which fibre material is fed into a continuous material space (6; 46) which is delimited by an endless, mobile filter member (5; 40) and a stationary wall element (4; 42) in order to form a continuouε layer (20; 54) of fibre material which is in contact with, and moves at the same speed as, the filter member (5; 40), c h a r a c t e r i z e d in that the treatment agent is fed into the material space (6; 46) in order to form a continuous layer (22; 56) of treatment agent up against the mobile layer (20; 54) of fibre material, and in that the displacement and thickening are carried out continuously at a mechanical pressure on the fibre material layer (20; 54) which is less than 100 kPa, and principally using the treatment agent, with the quantity of liquid which iε diεplaced through the filter member (5; 40) per unit of time exceeding the quantity of treatment agent which is supplied.

2. Method according to Claim 1, c h a r a c t e r i z e d in that the hydrostatic pressure of the treatment agent iε at least 50 kPa, preferably at least 100 kPa.

3. Method according to Claim 1 or 2, c h a r a c t e r i z e d in that the gradient of the concentration profile of the liquid in the fibre material is altered by altering the hydrostatic presεure.

4. Method according to Claim 1 or 2, c h a r a c t e r i z e d in that the treatment agent iε a liquid for waεhing the fibre material.

5. Method according to any one of Claims 1 - 3, c h a r a c t e r i z e d in that the treatment agent iε a liquid which containε chemicalε εuch aε bleaching agents, chelating agents and the like.

6. Method according to any one of Claims 1 - 3, c h a r a c t e r i z e d in that the treatment agent is an inert or reactive gas.

7. Method according to any one of Claims 1 - 3, c h a r a c t e r i z e d in that the treatment agent is a mixture of liquid and inert or reactive gas.

8. Method according to any one of Claims 1 - 7, c h a r a c t e r i z e d in that the thicknesε of the layer of treatment agent in aεεociation with the inlet (18) iε at leaεt approximately 6 mm.

9. Apparatuε for treating a liquid-containing, celluloεe-containing fibre material with a treatment agent by means of displacing liquid out of the fibre material and simultaneously thickening the fibre material, comprising an endlesε mobile filter member

(5; 40); a houεing (2; 41), which iε arranged at a diεtance from the filter member (5; 40) ; a wall element (4; 42) , which iε arranged at a diεtance from the filter member (5; 40) εuch that they enclose a material space (6; 46) between themselves; a gap-shaped inlet (19; 50) for fibre material which is to be treated in the material space (6; 46); a gap-shaped outlet (10) from the material εpace (6; 46) for treated fibre material; a feeding-in member (7) for feeding in fibre material via the εaid inlet (19; 50) in such a way that a continuous layer (20; 54) of fibre material is formed on the filter member (5; 40); a feeding-out member (8) for feeding out treated fibre material via the said outlet (10); one or more distribution members (16, 31; 44) for treatment agent; and also feeding-in members (15; 55) for feeding in treatment agent via the said distribution members (16, 31; 44) , c h a r a c t e r i z e d in that the distribution member (16, 31; 44) is designed and arranged in connection with the material space (6) in such a way that a continuous layer (22; 56) of treatment agent is formed and maintained in free contact with the fibre material layer (20; 54) along the whole, or a substantial part, of the latter between the said inlet and outlet (19; 50, 10) .

10. Apparatus according to Claim 9, c h a r a c t e r i z e d in that the wall element (4) is formed by the said housing (2) ; and in that the distribution member has the form of a distribution channel (16) which forms a horizontal, gap-shaped inlet

(18) which has the same width as the filter member (5) and which is directed forwards in the direction of movement of the filter member (5) and is also located in the material space (6) directly up against the wall element (4) , and which distribution channel (16) is aligned with the wall element (4) and arranged to emit treatment agent in such a way that a continuous, distinct layer (22) of treatment agent is formed, which layer is in direct contact with the wall element (4) and is located up against, and moves with the εame, or principally the same, speed as, the fibre material layer (20), which is likewise distinct.

11. Apparatuε according to Claim 10, c h a r a c t e r i z e d in that a number of parallel strips (25) are arranged in the distribution channel (16) and subdivide the latter into compartments (26) .

12. Apparatus according to Claim 11, c h a r a c t e r i z e d in that the εtripε (25) protrude out from the diεtribution channel (16) through its inlet (18) and extend for a predetermined distance into the treatment space (6) in order to form guide members (25) for the treatment agent.

13. Apparatus according to Claim 10, c h a r a c t e r i z e d in that the wall element (42) is arranged between the houεing (41) and the filter member (40) and forms a screen member; in that the distribution member (44) forms a channel which is delimited by the housing (41) and the screen member

(42) in order to encircle the treatment space (46) , with the screen member (42) being arranged to allow treatment agent to pass through from the distribution channel (44) into the inner treatment space (46) in such a way that a continuous, distinct layer (56) of treatment agent iε formed and maintained in free contact with the fibre material layer (54) .

14. Apparatus according to Claim 13, c h a r a c t e r i z e d in that the screen member is supported by a number of parallel strips (47) which are firmly connected to the inside of the housing (41) and extend in the direction of rotation of the filter member (40) , which strips (47) delimit, between themselves, compartments (49) for receiving and distributing treatment agent.

15. Apparatus according to any one of Claims 11, 12 and 14, c h a r a c t e r i z e d in that each feeding-in member (15; 55) for treatment agent comprises a number of conduits (28; 52) each of which is connected to its own compartment of the said compartments (26; 49) , and in that each conduit (28;

52) is provided with a valve and control component (30;

53) for individually discontinuing the flow of treatment agent to each compartment (26; 49) .

16. Apparatuε according to any one of Claimε 9 -

15. c h a r a c t e r i z e d in that it includes a presεure member (14) for finally compressing the fibre material layer (20) directly upstream of the outlet

(10) , which pressure member is arranged to form an extended nip between the wall element (4) and the filter member (5) .