FI67029C - ANORDNING FOER TVAETTNING AV MASS - Google Patents

Description

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Patent · och registrerttyreiMn '' AmHm uthgi och utUkrHfn pubttcand 20.09.84 (32) (33) (31) Pyydetty etuoilceuj —Begird prloritet (71) Rauma-Repola Oy, Helsinki, FI; Porin Tehtaat, PO Box 96, 28101 Pori 10, Finland-Finland (Fl) (72) Esko Jääskelä, Pori, Paul Widqvist, Pori, Finland-Fin1and (FI) (7 * 0 Ruska & Co Oy (5 * 0 Pulp washing device The present invention relates to an apparatus for washing pulp, the apparatus comprising a basin and shaft-mounted filter discs rotating in the basin, and washing liquid dispensing means arranged between the filter discs in the vicinity of each filter surface of each filter disc.

Pulp washing in the following means the displacement of either chemicals or heat by means of a washing liquid. For example, clean water can be used for washing, which displaces chemicals, or cold water, which displaces the heat in the pulp.

It is previously known to use drum filters for washing pulps, in which the washing liquid is passed over separate nozzles or overflow thresholds in a thin layer on the fibrous web at the top of the drum and the washing liquid is transferred to the web under vacuum or overpressure (suction or pressure washers). However, the space required by the drum filters is relatively large and the drum filter is not suitable for handling highly ground, low-density pulp.

The device according to the present invention is characterized in that the washing liquid distributor is formed by a wall 67029 arranged in the vicinity of the filter surface, which together with the pulp layer on the filter surface forms a substantially horizontal trough and through which the Desuvesi can be led to the pulp layer.

Disc filters are known per se and are described, for example, in Finnish patents 5 ^ 060 and 56628 and in Finnish patent application no. 803100 filed simultaneously with this application.

In a disc filter, the pulp web rises from the liquid surface of the bath to the surface of the disc, which is always in an almost vertical position. In the drum filter, on the other hand, the pulp web is supported by the filter surface of the drum during the washing operation. Due to the location of the pulp web on the disc filter, the washing liquid must be guided in an even layer against the pulp web on the surface of the disc so that the washing liquid cannot flow along the pulp web, thus allowing the pulp web to peel off the disc surface.

The device according to the present invention is particularly well suited to e.g. for washing groundwood, pulp, TMP (thermo-mechanical pulp) and CTMPrn (Chemo-thermo-mechanical pulp), i.e. various highly ground, low-density pulps with a feed density of 0.3 ~ 2%. The use of a disc filter increases the filter surface by about 2-3 times compared to drum filters, which is advantageous for highly ground pulps with poor permeability. Washing can be used to lower the temperature of, for example, the hot pressure grit before storing it or feeding it to the dryer.

The invention and its applications will be described in more detail below with reference to the accompanying schematic drawings, in which Figure 1 shows a cross-section of a disc filter according to the invention, Figure 2 shows a larger detail of the disc filter, seen from the side of the filter and cut and Figure 3 shows a disc filter without a hood.

Reference numeral 1 denotes a bath to which the pulp is led from the feed point 9. The dashed line 2 indicates the height of the pulp surface. The discs 3 formed by the sectors are attached to the shaft. Each disc has two water-permeable opposite filter surfaces 5 · There is a hood 6 above the bath 1.

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Between the discs, on the other side of the filter, there are vertical tubes 7 as discharge chutes, into which the filtered mass is collected from the surface of the discs. The lower ends of the vertical tubes 7 merge into a horizontal trough with a screw conveyor 8 for conveying the mass away.

For conducting the washing liquid, the pipe 10 extends over the entire length of the filter and branches against both surfaces of each disc against the washing liquid distribution member 11, which is arranged above the liquid surface 2 of the bath.

Figure 2 shows two alternative embodiments of the distributor 11. The figure shows on the left a trough 15 fixed to the upper edge of the wall of the drop chute 7, one side of which is open and provided with a seal 12. The right side of Figure 2 shows an alternative with a trough tube 13 in the trough.

When the disc filter is operating, it rotates in the direction indicated by arrow A in Figure 1. Due to the suction inside the discs, the mass accumulates on the surface of the discs as they rotate partially immersed in the mass. The vacuum absorbs the filtrate from the pulp inside the discs, from where the filtrate is led inside the shaft and further away.

The pipe 10 is used to supply the washing liquid to the dispensers 11 (arrow B). By means of the washing liquid distributor, the washing liquid is further fed to the pulp web before the pulp is removed, which occurs when the disc sector enters at l1 *.

In the alternative shown on the left side of Fig. 2, washing liquid is introduced into the trough 15, for example through one or more pipes connected to the top of the trough (not shown). Because the other side of the trough is open, the washing liquid can freely "lean" on the pulp web and the suction Excess washing liquid flows over the chute wall and can be recirculated.The height of the chute allows the amount of washing water to be adjusted.

In the alternative on the right-hand side of Figure 2, the washing liquid is sprayed by means of a spray nozzle 13 as a mist against the pulp mat, where it forms a thin film and further seeps through the mat into the disc. In addition to the shower pipe, a trough 15 can be used, into which the excess water drains.