SE502815C2 - Method and apparatus for treating a liquid fibrous material - Google Patents

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

15 20 25 30 35 CD BJ CO U1 In the cellulose industry, there are a number of washing operations in order to by displacement remove liquid from the fibrous material in order to recover chemicals and purify the fibrous material using the least possible amount of displacement liquid while taking into account economic and environmental aspects. These washing operations are performed by means of devices of different types such as cylinder filters, flat filters, radial washers, press washers, etc. Such devices operate according to the narrowing principle, which means that the liquid phase present in the fiber suspension or fiber web is initially displaced by and replaced by a suitable washing liquid with maintained liquid ratio in the pulp web. The optimal course is that no part of the displacement liquid is mixed with the original liquid. In practice, however, in a normal conventional displacement operation, a longitudinal and axial mixing of displacement fluid in the original fluid takes place, which means increased amounts of displacement fluid in order to achieve the desired washing effect.

In order to obtain a good washing result in terms of process, the ratio between the supplied washing liquid per unit width and the liquid in the fibrous web must be kept constant per unit width of the fibrous web. This ratio can only be achieved by applying the washing liquid uniformly to each width unit, a first condition being that the amount of washing liquid applied over the entire web width is constant and a second condition that the consistency over the entire web width is constant, ie. that the dry matter is constant for each width unit. The first condition is relatively easy to fulfill, while the second condition is technically difficult to solve, so at higher concentrations on the formed fiber layer in practical operation one must expect concentration deviations of: 10%, which means that the washing liquid flows in transverse 10 15 20 25 30 35 01 * ID in the direction of the fibrous layer to the parts where the concentration is lower. The object of the present invention is to eliminate the above-mentioned disadvantages and to provide an improved method and an improved device for treating the liquid-containing fibrous material.

The method according to the invention is characterized in that the treatment agent is fed into the material space to form a continuous layer of treatment agent next to the movable layer of fibrous material, and that the constriction and thickening are carried out continuously at a mechanical pressure on the fibrous material layer of less than 100 kPa. of the treatment agent, the amount of liquid displaced by the filter means per unit time exceeding the amount of treatment agent added.

The apparatus according to the invention is characterized in that the distribution means is designed and arranged in connection with the material space in such a way that a continuous layer of treatment means is formed and maintained in free contact with the fibrous material layer along all or a substantial part thereof between said inlet and outlet.

The present invention provides an improved method of treating liquid fibrous material which can be carried out using a filter surface, which is only a fraction of conventional methods, of the filter surface required at calculated at the same washing losses.

The invention means that the investment and operating costs for high-grade washing can be reduced so low that all environmental requirements can be met. The invention provides an improved way of displacing the original liquid from the pulp web and at the same time compressing the pulp web so that the original liquid departs at a higher velocity than the velocity of the supplied displacement liquid, thereby eliminating the axial mixing and the degree of displacement. improved and the narrowing process approaches the optimum. For this process to work as described above, the mechanical pressure must not exceed 100 kPa and the hydrostatic pressure must be at least 50 kPa and preferably at least 100 kPa as can be deduced from a data calculation, based on a number of equations in two articles in the AICHE Journal, September 1992 Vol. 38, no. 9, p. 1340, 1349. The method according to the invention involves a so-called dynamic constriction. In the method and apparatus according to the invention, the compression of the fibrous layer and the narrowing of liquid thus takes place under increasing fiber concentration, the amount of liquid removed through the fibrous drum from the fibrous layer exceeding the amount of washing liquid supplied, per unit of time.

The invention is described in more detail in the following with reference to the drawings.

Figure 1 is a sectional view of a first embodiment of an apparatus for treating pulp according to the invention.

Figure 2 is a sectional view along the line II-II in Figure 1.

Figure 3 is a sectional view of a second embodiment of an apparatus for treating pulp according to the invention.

Figure 4 is a sectional view of parts of a third embodiment of an apparatus according to the invention.

Figure 5 is a sectional view taken along the line V-V in Figure 4. Figure 152 schematically shows an apparatus according to the present invention for treating an aqueous, cellulosic fibrous material, e.g. a lot. Examples of such devices in the cellulose and paper industry are washing filters, narrowing presses, flat wire washers and radial washers. The apparatus comprises a stand 1, a curved, stable housing 2 and a drum 3, which with a horizontal axis is rotatably mounted to the stand. The housing 2, which consists of a plate, is closed at the two facing ends by means of side walls 23, 24 so 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 jacket 5, which forms an endless filter means, which is thus movable relative to the stationary housing 2 during operation. The jacket 5 comprises a perforated stable plate and at least one wire (not shown) enclosing 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 casing 2 itself forms a wall element 4, which delimits between itself and the casing 5 a continuous arcuate treatment space 6, which suitably tapers in the direction of rotation of the drum 3 such as ViSâS.

The apparatus further comprises a helical feed means 7 for feeding pulp to the material space 6 and a helical discharge means 8 for discharging the treated pulp. The screws 7, 8 are parallel to the axis of rotation of the drum 3 and are arranged along one long side of the apparatus, where the drum 3 is exposed in that the housing 2 has a limited extension around the drum to enclose a predetermined larger part thereof. The feed screw 7 communicates with the material space 6 via a horizontal channel 11, which has an axial extent and thus a rectangular cross-section. The discharge screw 8 communicates with the material space 6 via an inclined channel 502 815 10 15 20 25 30 35 12 12, which has an axial extent and thus a rectangular cross-section. A doctor blade 13 is arranged in the channel 12 for abutment against the jacket 5 of the drum.

The reference numeral 14 denotes a pressing member which is arranged in connection with the outlet portion of the material space 6 in order to effect a final compression of the pulp web. The pressing member 14 may be a press shoe, as shown, or a press roll. A press shoe 14 at the outlet portion is advantageous in combination with the concentration gradient obtained with the described apparatus.

The pulp web 20 detaches from the filter jacket 5 immediately after the outlet 10 by being actuated by two different forces, one of which arises as a result of the concentration gradient in that the concentration increases in the direction of the filter jacket 5, and the other arises as a result of the friction-forming contact of the pulp web with the inside of the wall plate 4 adjacent to the press cone 14 so that the pulp web 20 is subjected to a braking effect on its side facing the press cone 14, while the opposite side of the pulp web is still drawn by the filter jacket 5. The result of these two forces, the pulp web is bent out of the filter jacket as soon as it leaves the outlet 10 and is fed further into the outlet channel 12. Thus, a conventional device for removing the pulp layer from the filter jacket 5 is eliminated.

At the outlet portion of the material space 6 there is an outlet 10, through which the treated pulp web passes, which outlet 10 has a rectangular shape with a width corresponding to the width of the material space 6, i.e. the length of the filter drum, and with a predetermined height.

The apparatus shown in Figures 1 and 2 comprises a distribution means 16 for treatment means, e.g. washing liquid, which is in the form of a channel delimited by the casing 2 and an inner partition wall 17, which extends in the material space 6 parallel or concentrically with and at a predetermined distance from the casing 2. The distribution channel 16 for washing liquid forms with its mouth an inlet 18 to the material space 6 which is located at a predetermined distance from and downstream of the point where the mass hits the filter jacket 5. Between the partition wall 17 and the filter jacket 5 a inner channel which can be considered to be an extension of the channel 11 for pulp which thereby with its mouth forms an inlet 19 to the material space 6, which is thus located immediately radially inside the inlet 18 for washing liquid. The two mentioned inlets 18, 19 have rectangular shapes with a width corresponding to the width of the material space 6, i.e. the length of the filter drum 5, and with predetermined heights that vary depending on the actual operating condition. The height H6 of the material space 6 at the inlets 18, 19 and the height H16 of the distribution channel 16 at the inlet 18, can be calculated on the basis of normal operating conditions as follows: Liquid ratio (Lpi) of the constituent mass in the inlet 19 ...... ................... 10-30 1 / kg Surface weight (YV) of constituent mass .............. 4-10 kg / m2 Liquid ratio (Lpo) of outgoing mass in the outlet 10 .......................... 1.5-5 l / kg Dilution factor (UF) ............ . . . . . . . . . . ..O-4 l / kg whereby the following relationship applies: H6 = (Lpi + 0.6) -YV H16 = (Lpo + UF) -YV The minimum height H16 of the distribution channel 16 at the inlet 18 and thus the minimum thickness of the liquid layer 22 in connection with the inlet 18 thus becomes 6 mm (H16 = (1.5 + 0) x4).

In the embodiment shown in Figures 1 and 2, the apparatus further comprises a plurality of strips 25 of e.g. 502 815 10 15 20 25 30 35 35, which are welded to the inside of the housing 2 and extend into the distribution channel 16 so that it is divided into compartments 26. The strips 25 are parallel to each other and to the ends 23, 24 of the apparatus. Thus extends in the direction of movement of the pulp layer and out of the distribution channel 16 a substantial distance to enclose a sector angle of about 90 °, as shown, or more, e.g. up to 270 ° if desired. It is suitable that each strip 25 has such a radial dimension that they extend into the pulp layer a small piece, suitably 1-3 cm. The strips 25 act as partitions and prevent washing liquid from being guided laterally towards portions of the pulp layer where the resistance is less for liquid to penetrate radially through the pulp layer against the filter jacket 5 because the consistency is less within these portions than adjacent portions. Instead, the washing liquid will be pressed straight forward through each compartment 26 of the distribution channel and guided in the forward direction between two guide strips 25 or between an outer guide strip 25 and an outer wall 23 and 24, respectively.

The washing liquid is fed into the material space 6 by means of an inlet means 15, which comprises a pump (not shown) and a manifold 29, which communicates with the distribution channel 16 via a line 28 to each compartment 26 of the distribution channel 16. The collecting tube 29 is suitably conical in the direction of flow as shown in Figure 2.

Each line 28 is provided with a valve and control device 30 for adjusting the liquid flow to the distribution compartment 26 so that the liquid flow becomes uniform to all distribution compartments 26. The washing liquid is pumped from a supply (not shown) to the manifold 29 with a high pressure, t. ex. 5 bar.

During operation, the mass is in contact with the filter jacket 3 and forms a layer 20 which passes through the inlet 19.

The pulp layer 20 is supported by and thus moves at the same speed as the filter jacket 5. In that the distribution channel 16 for washing liquid extends along the casing 2 on its inside and along the filter jacket 5 and opens straight forward in the same direction as the direction of movement of the pulp layer 20, the washing liquid pumped under predetermined pressure through the distribution channel 16 will have this direction forward so that downstream of the inlet 16 a distinct liquid layer 22 is formed, which flows along the inside of the casing 2. The washing liquid is fed into the material space 6 at a speed corresponding to or substantially corresponding to the speed of the pulp layer 20. The liquid layer 22 is continuous and can be maintained all the way to the press cone 14 as shown in Figure 1. An almost distinct boundary 27 is formed between the two different material layers 20, 22, which move as a unit without displacements occurring between them seen in the direction of movement, if said speeds are equal.

Figure 3 schematically shows a second embodiment of an apparatus according to the invention which differs from that according to Figure 1 only in that it has been supplemented with a second distribution channel 31 for treatment means of the same design as the distribution channel 16, where at the second distribution channel 31 is arranged downstream about 170 ° after the first distribution channel 16, which also in this case is located at the inlet portion of the material space 6. The casing is enlarged to make room for the second distribution channel 31 and the additional amount of action means fed to repeat the displacement process and continue the compression of the pulp layer 20. The washing liquid is thus fed into the material space 6 at two places by means of two feed means 15, 35, each of which comprises a pump 32 (only the pump of the feed means 15 is drawn ). The second feed means 35 also comprises a manifold 33, which communicates with the distribution channel 31 via lines 34 to each compartment of the distribution channel 31, each line 34 having a valve and control device 37 in accordance with the first the feeding means 15. The arrangement allows washing of the mass with washing liquid of different qualities. Thus, the second inlet means 35 feeds pure washing liquid, which displaces liquid through the filter jacket 5 to be collected in a trough 36, from which the liquid thus collected is pumped with the pump 32 via a line 38 to the manifold 29.

Figures 4 and 5 schematically show a third embodiment of an apparatus according to the invention for treating e.g. mass with e.g. washing liquid. Figure 4 shows only a longitudinal section of the apparatus, which comprises 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 cover 41 of sheet metal encloses a larger portion of and extends at a predetermined distance from the filter belt 40, which distance may be constant around the entire length of the cover. The side walls together with the housing 41 have not been drawn out, nor have the feed-in and discharge screws and the pressing member. Extending between the housing 41 and the filter belt 40 is a flat wall element 42, which is located at a predetermined distance from the filter belt 40 so that it delimits a continuous treatment space 46 therebetween. The mass is fed into the material space 46 via a channel 43, which has an axial extent and thus rectangular cross-section. A treatment means distribution member 44 is in the form of a channel defined by the housing 41 and the inner wall member 42. The inner wall member 42, which is enclosed by the distribution channel 44, forms a screen member, and may consist of a stable screen plate or screen cloth. , which is supported by a plurality of parallel strips 47 (shown only in Figure 5), which are fixedly arranged on the inside of the housing 41 and extend in the direction of rotation of the filter belt 40. The screen member 42 is sufficiently flexurally rigid and strong to withstand the stresses of the washing liquid. In addition, it has a very high permeability of the washing liquid so that it momentarily flows through the screen means into the material space 46. The strips 47 can have an increased width so that they have inner portions 48 (shown only in Figure 5), which extend into the material space 46 for thereby obtaining the same function as the strips 25 of the first described embodiment.

The strips 47 and their inner portions 48 define compartments 49, which can be compared to the first described compartments 26. The channel 43 for feeding the pulp extends through the casing 41 into the material space 46, where an inlet 50 is formed, which determines the initial thickness of the pulp layer 54. .

The washing liquid is forced into the material space 46 by means of a plurality of feed means 55, which are arranged at suitable distances one after the other seen in the direction of rotation of the filter belt 40. Figure 4 shows parts of two of the input means 55. Each input means 55 comprises a pump (not shown) and a manifold 51, which communicates with the distribution channel 44 via a line 52 to each compartment 49 of the distribution channel 44. Each line 52 is provided with a valve and control device 53 as described in connection with the first embodiment. By arranging a plurality of feed means 55 of the type described at a suitable distance one after the other, it is ensured that the entire distribution channel 44 is filled with washing liquid during operation and that a continuous layer 56 of washing liquid of the desired thickness is maintained via the screen plate 42 or the like in the material space 46. pressing against the passing pulp layer 54 so that liquid in the pulp layer is displaced by washing water while the pulp layer 54 is compressed as liquid passes through the filter belt 40 in an amount per unit time which is greater than the amount of wash liquid supplied per same time unit.

The simultaneous constriction and concentration (compression) according to the invention results in a halving of the sum of the time required for both operations separately according to conventional technology. Performing compression and compression at high hydrostatic pressure and low mechanical pressure according to the present invention results in a considerably higher production.

These unique operating conditions result in a large concentration gradient, which provides low friction against the stationary sheet metal sweep, which in turn means that the filter drum requires lower rotational power. Through the combination of the described concentration gradient and the effect of the friction and shear forces on the pulp web in connection with the press cone before the outlet, the pulp web will become detached from the filter jacket. Thereby, conventional, expensive removal devices, such as air and steam fans, etc., can be eliminated. scrapers, bag rollers,

Claims (14)

10 15 20 25 30 35 m c: w 13 P A T E N T K R A V A method of treating a liquid-containing fibrous material with a treatment means for displacing liquid from the fibrous material and simultaneously thickening the fibrous material, which fibrous material is fed into a continuous material space (6:46), which is delimited by an endless, movable filter means (5:40) and a stationary wall element (4:42), for forming a continuous layer (20: 54) of fibrous material, and moving at the same speed as the filter means (5:40), that the treatment agent is fed into the material space (6 : 46) to form a continuous layer (22: 56) of treatment agent adjacent to the movable layer (20: 54) of fibrous material, and that the narrowing and thickening is carried out continuously at a mechanical pressure on the fibrous material layer (20: 54) of less than 100 kPa and mainly by means of the treatment agent, the amount of liquid being displaced through the filter means (5:40) per unit time exceeding the amount of treatment agent supplied. which is in contact with characterized by Method according to claim 1, characterized in that the treatment agent has a hydrostatic pressure of at least 50 kPa, preferably at least 100 kPa. Method according to Claim 2 or 2, characterized in that the inclination of the concentration profile of the liquid in the fibrous material is changed by changing the hydrostatic pressure. 4. A method according to claim 2 or 2, characterized in that the treatment agent is a liquid for washing the fibrous material. 502 815 10 15 20 25 30 35 14 A method according to any one of claims 1-3, characterized in that the treatment agent is a liquid which contains chemicals such as bleaching agents, chelates and the like. 6. A method according to any one of claims 1-3, characterized in that the treatment agent is an inert or reactive gas. 7. A method according to any one of claims 1-3, characterized in that the treatment agent is a mixture of liquid and inert or reactive gas. Method according to one of Claims 1 to 7, characterized in that the layer thickness of the treatment agent in connection with the inlet (18) is at least about 6 mm. An apparatus for treating a liquid, cellulosic fibrous material with a treatment agent by displacing liquid from the fibrous material and simultaneously thickening the fibrous material, comprising an endless movable filter means (5:40); a housing (2:41) arranged at a distance from the filter means (5:40); a wall element (4:42) arranged at a distance from the filter means (5:40) so that they enclose a material space (6:46) between them: a slit-shaped inlet (19:50) for fibrous material to be treated in the material space ( 6:46); a slit-shaped outlet (10) from the material space (6: 46) for treated fibrous material; feeding means (7) for feeding fibrous material via said inlet (19:50) so that a continuous layer (20: 54) of fibrous material is formed on the filter means (5:40); discharge means (8) for discharging treated fibrous material via said outlet (10): one or more distribution means (16, 31; 44) for treatment means; and input means (15: 55) for inputting treatment means via said distribution means (16, 31; 44), characterized in that the distribution means 10 (15, 31; 44) is designed and arranged in connection to 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 fibrous material layer (20: 54) along all or a substantial part thereof between said inlet and outlet ( 19:50, 10). Apparatus according to claim 9, characterized in that the wall element (4) is formed by said housing (2): and that the distribution means is in the form of a distribution channel (16) which forms a horizontal, slit-shaped inlet (18) having the same width as the filter means ( 5) and facing forward in the direction of movement of the filter member (5) and is located in the material space (6) immediately adjacent to the wall element (4), and which distribution channel (16) is aligned with the wall element (4) and arranged to deliver treatment. the means so as to form a continuous distinct layer (22) of treatment agent, which is in direct contact with the wall element (4) and is located adjacent to and moves at the same or substantially the same speed as the likewise distinct fibrous material layer (20). 11. ll. Apparatus according to claim 10, characterized in that a plurality of parallel strips (25) are arranged in the distribution channel (16) and divide it into compartments (26). Apparatus according to claim 11, characterized in that the strips (25) are extended out of the distribution channel (16) through its inlet (18) and extend a predetermined distance in the treatment space (6) to form guide elements (25) for the treatment means. . Apparatus according to claim 10, characterized in that the wall element (42) is arranged between the housing (41) and the filter means (40) and forms a screen means; the distributing means (44) forming a channel defined by the housing (41) and the screening means (42) for enclosing the treatment space (46), the screening means (42) being arranged to pass through treatment agent from the distribution channel (44) to the inner treatment space (46) so that a continuous distinct layer (56) of treatment agent is formed and maintained in free contact with the fibrous material layer (54). Apparatus according to claim 13, characterized in that the screen means is supported by a plurality of parallel strips (47), which are fixedly connected to the inside of the housing (41) and extend in the direction of rotation of the filter means (40), which strips (47) define between them compartment (49) for receiving and distributing the treatment agent. characterized in (157 55) for treatment means comprises a plurality of lines (28; 52) connected to each of said compartments (26: 49), and that each line (28: 52) is provided with a valve and control device (30:53) for setting the Apparatus according to any one of claims 11, 12 and 14, in that each input means the flow of treatment agent individually to the respective compartment (26:49). 160 drawn for final compression of the fibrous material layer (20) immediately. Apparatus according to any one of claims 9-15, characterized in that it comprises a pressing means (14) just before the outlet (10), which pressing means is arranged to form an extended nip between the wall element (4) and the filter means (5).