FI91291C - Screening apparatus for transferring cellulose fibers from one suspending liquid flow to another under pressure - Google Patents

Description

91291 FILTRATION DEVICE FOR TRANSFERRING CELLULOSE FIBERS FROM OVER SUSPENDING FLUID STREAM TO OVER PRESSURE - SILAP PARTS FOR ATT UNDER OVERTRYCK OVERFORA CELLULOSAFIBRER FRÅN ETT SUSPENDERAND

Filtration devices are known from the prior art (e.g. from British Patent Publication No. 618,316), in which the fiber suspension is filtered through a rotating planar or circular plate filter 10 and the fibers accumulated on the filter, e.g. , such as with a shower of clean water. Thus, the fibers transfer to another liquid and become suspended in it.

The present invention relates to a similar problem of transferring fibers from one liquid to another using a rotating planar filter plate, but the present invention solves the more difficult problem of achieving this fiber transfer by keeping the overpressure on the fibers and participating fluids substantially the same.

In principle, this is made possible by the use of a pressure vessel with a partition wall which divides the vessel into two chambers, between which an exchange takes place by means of a filter plate which moves tightly in a groove in the partition wall. The essential features of the filter device are described in more detail in the appended claims.

Some embodiments of the filtration apparatus of the present invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 shows a first embodiment of the apparatus 35 in vertical cross-section, Figure 2 shows the same horizontal cross-section in line 2 of Figure 1, and Figure 3 shows a cross-section of a filter plate belonging to the device, which cross-section is taken along the line III-III in Fig. 2. Figure 4 shows a horizontal section 5 of another embodiment of a filtration device according to the present invention.

The filtration device shown in Figures 1-3 comprises a closed pressure vessel intended to withstand a high pressure, for example of the order of 10 bar, and the casing of which is approximately flattened spherical for reasons of strength. The container consists of two, substantially identical and symmetrical halves 11, 13, which are connected horizontally together by means of opposing annular flanges 15, 17. An annular seal 19 is tightly pressed into the seam. The container is internally divided by a central partition wall consisting of an upper part 21 connected to the upper half of the container and a lower part 23 connected to the lower half half 13 of the container. taking the plane and extending diametrically across the vessel so as to be divided into two different chambers, A and B. The opposite free ends of the wall portions are connected to opposite flanges 25 and 25 27, the width of which increases as the end of the vessel passes.

These upper and lower flanges are spaced apart so that a horizontal, evenly spaced gap is formed between them. This would form a partition wall between opposite sides if the disc filter 30 29 described below were not placed therein.

The filter plate, referred to in its entirety by the number 29, consists of two equally large, horizontal, flat and parallel support plates 33 and 35 which press 35 between the dense mesh sieve cloth 31 (see Figure 3). The support plate has a number of opposing recesses 37, 39 passing through 3 91291, in which the wing fabric is free. The recesses 37 in the upper support plate form pockets, the bottom of which is formed by a sieve fabric and which are open at the top so that the fibrous material can accumulate in the pockets 5 and remain in them by means of the sieve wire. The lower support plate 35 is thinner than the upper 33 to keep the pockets as deep as possible. The center of the filter plate 29 is attached by a motor (not shown) to a rotatable vertical shaft 41 located inside the upper wall portion 21 and mounted at its lower end in a recess in the lower wall portion 23.

The filter plate extends over the entire cross-sectional area of the vessel and divides its two chambers into upper spaces 15 A, B1 and lower spaces A2, B2 · Its circular edge penetrates an annular groove between the flanges 15 and 17. In this way, the filter plate becomes guided and supported at its edge against possible bending caused by the pressure difference across its sides.

20 The thickness of the filter plate corresponds to the distance between the flanges 25 and 27 so that the gap between them fills and becomes tightly closed, but it is clear that there must be a certain amount of play so that there is no obstruction to the rotation of the plate. The chambers A and B of the filtration device belong to separate flows connected to the inlet openings 45, 49 and the outlet openings 47, 51 on the outside of the vessel. When the fiber suspension is passed in a vertical stream through the right chamber A1, A2, the fibers separate on the screen cloth at the bottom of the pockets 37 while the liquid purified from the fibers continues out through the outlet 47. Once the fiber-filled pockets are rotated to the left chamber side and the second fluid is introduced from the inlet 49, this fluid pulls the fibers out of the pockets and forms a new suspension exiting the opening 51. In both streams there may be substantially the same overpressure transfer from one fluid to another while the overpressure remains the same. Due to the pressure difference in the screen cloth, certain pressure differences may occur. In addition, in order to cause the leakage currents to flow in the desired direction, it may be advantageous to maintain a small pressure difference between the chambers.

The cavities 37, 39 in the filter plate are in the form of rain-like sectors with spherical portions 52 in between which are not pierced. The width of the outer circumference side 10 of the cavities is slightly smaller everywhere than the width of the outer circumference side of the flanges 25, 27. Thus, at the same distance from the center of the plate, no cavity or pocket can ever come into contact with both chambers at the same time. With the exception of a certain leak along the top and bottom of the plate 15, which cannot be avoided, mixing of the liquids occurs only because the hollows empty of the fibers carry the liquid through the barrier even back through the partition wall. Therefore, the pockets should be filled with fibers as well as possible so that the 20 pockets have to pass through the partitions as little as possible.

Practice experiments have shown that if the liquid to be cleaned from the fibers is lye with a fiber content of 200 ppm and 10% of the pocket filling is fiber and 90% is lye, only 0.2% of the lye to be purified is transferred.

The embodiment shown in Fig. 4 differs from the one described above in that the diameter-like partitions 21, 23 are replaced by a partition wall consisting of two planar walls 53,55 at an acute angle to each other. Other numbers refer to the same details as in Figure 1. The interior of the vessel is divided into two chambers 35 C and D extending for different lengths of circumferential periods, for example 90% and 10% of the cross-sectional area 5 91291, respectively. Thus, a larger portion of the container was used to collect more time-consuming fibers in the pockets than to empty them. If the flow rate is kept the same in both chambers, this filtering device 5 gives a 10-fold thickening, which value can be further increased if the flow rate through the lower chamber is reduced. The embodiment is particularly suitable in the case where it is desired to purify a lye with a low fiber content.

10

The flow which entrains the fiber is preferably led to a treatment tank under a slight overpressure from which the fibers are recovered. If the second chamber of the filtration device is connected to a pipe coming from a continuous cellulose jacket-15 space which brings in liquor for evaporation, the second chamber may, for example, connect to a pipe carrying liquid, e.g. washing liquid and associated fibers, from the outlet pressure diffuser or boiler 20 chip feed cycle.

Another possibility of using a filtration device is to direct the fibers from the fiber-rich outlet of the pressure diffuser to the wash water and thus back to the pulp stream.

25

The embodiments described above can, of course, be modified in detail within the scope of the invention.

The vessel may thus be cylindrical and provided with convex ends, in which case it may be necessary to install fixed supports on the inside of the cylindrical part to resist deformation in the event of large pressure differences.

Instead of the filter element being a woven metal wire mesh, the bottom of the pockets may be a perforated or grooved metal plate. The device has been described with the view that the connection has been made to a vertical liquid stream, but in certain cases it may be suitable to carry the device sideways so that the flows become horizontal or possibly oblique, in which case the pipe joints may also need to be changed. Yet the modification may consist, for example, of vertical container walls divided into four parts by vertical walls, to which the flows are connected in parallel to flow up and down alternately, their pressure effect being distributed over the circumferential area of the filter plate and mutually equalized.

Claims (11)

91291 7 CLAIMS: 1. A filtering device for separating suspended particles, by finishing cellulose fibers, from a stream of a treatment liquid, for example cooking or bleaching liquor, and transferring the particles to another liquid stream while maintaining an overpressure in the particles and streams, characterized in that a vessel (il, 13) divided in the partition wall (21, 23) into two chambers (A, B) having separate inlets (45,49) and outlets (47,51) for separate liquid streams, and having a vessel against the partitions a perpendicular circular filter plate (29) which divides these chambers (A, B) into separate spaces (A 1, A 2 and B 2, B 2, respectively), and which filter plate moves in the partition wall. in the groove, filling it substantially completely and attached to the rotatable shaft (41) so that the filter plate can be rotated between said bores so that the particles which accumulate on one side of the partition wall on the filter plate move to the other side of the partition wall. Filtration device according to claim 1, characterized in that the filter plate comprises open pockets 25 (37) with a filterable outlet, preferably for collecting fibers, etc. of the sieve cloth (31) from the flowing liquid stream when the pockets (37) are in the primary chamber. (A), and from which pockets the fibrous filling can be removed with a second, countercurrent flow of liquid when the pockets are in the second chamber (B). Filtration device according to Claim 2, characterized in that the filter plate (29) has a sieve cloth (31) fastened between two flat and parallel plates (33, 35) with opposite recesses (37, 39) so that in the 8 recesses. in the plate form pockets to hold particles that do not shovel the screen. Filter plate according to Claim 3, characterized in that the cavities (37, 39) are sector-shaped and the intact plate areas (52) in their molds are of such a width that they close to the edges of the partition wall as they pass through the partition gap and prevent the connection between the two chambers. Filtration device according to Claims 1 to 4, characterized in that both parts (21, 23) of the partition wall terminate adjacent the gap in flanges (25, 27) whose total width exceeds the width of the cavities (37, 39) so that the cavities pass through the partition wall. the lapi are never in contact with both chambers (A, B) at the same time. Filter device according to Claims 1 to 5, characterized in that the outer edge of the filter plate (29) is located in a circular or cylindrical part of the vessel wall in a curved part. Filtration device according to Claim 6, characterized in that the edge of the filter plate (29) is supported on the wall of the vessel. Filtration device according to one of the preceding claims, characterized in that the container has a separating seam (15, 17) in the middle of the filter plate (29) and in that this edge protrudes partially inside the seam. Filtration device according to Claim 1, characterized in that the partition wall consists of two planar wall sections (53.55, Fig. 4) arranged at an angle of less than 180 ° to each other, which divide the vessel into sectors, i.e. a larger particle collection chamber and a 9 91291 smaller particle outlet. . Filtration device according to Claim 1, characterized in that the shaft (41) of the filter plate is inside the casting wall (21). 5 A modification of a filtration device according to any one of claims 1 to 10, characterized in that the vessel is divided into a plurality of, for example by four, partition walls by a plurality of parallel liquid streams with alternating directions between opposite directions. 10