FI67892B - FOERFARANDE OCH ANORDNING FOER TVAETTNING AV CELLULOSAMASSA - Google Patents

Description

1 67892

The present invention relates to a method for washing pulp on a flat wire machine in two or more steps as the pulp web passes over the wire, whereby the liquid contained in the pulp-5 web is displaced by the washing liquid.

The invention also relates to an apparatus for applying the method, the apparatus comprising an endless wire and means for conveying it and a device for guiding the pulp to the wire.

In the previously known flat wire washers, in order to displace the track-10 liquid with the washing liquid, either overpressure air above the wire, suction (air) below the wire or a combination thereof is used in the actual washing step.

These previously known scrubbers have the following disadvantages: - Devices that consume energy are required to achieve air pressure or suction.

- When mixed with the pulp stock, the air causes foaming in the temporal liquids, which in turn 20 reduces the displacement of the washing liquids.

- When using suction, washing cannot be performed at boiling point (100 ° C).

- Difficulties in sealing the device, especially when recycling sulfur-containing gases (eg sulphite process).

The object of the present invention is to eliminate the above-mentioned drawbacks. The method according to the invention is mainly characterized in that the pulp web and the wire pass during immersion immersed in the washing liquid as the washing liquid flows through the pulp web and the wire. The apparatus according to the invention is characterized in that the apparatus has two or more successive bottomless wash basins above the wire and devices for conducting wash water to the basins, and below the wire there are other basins for collecting wash water from the basins above the wire and means for washing the wash water.

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In the method according to the invention, the pulp web runs completely inside the liquid on the wire cloth so that there is liquid both above and below the pulp web.

The liquid in the track is displaced by the washing liquid 5 by means of the flow of the liquid. The liquid is evenly displaced throughout the washing step, allowing a slow flow rate of washing liquid.

Liquid washing can be achieved in two different applications: either with a single-wire machine, in which case the flow of liquid through the wire always takes place from top to bottom, or with a double-wire machine, in which case the flow of liquid back and forth is also possible.

The method according to the invention has at least the following advantages: - low need for pumping liquids and electrical energy - washing operation in an airless space - no need for separate filtrate tanks - enables washing at boiling point - low stress on the wire due to submersibility - very simple instrumentation - reliable operation, no blockage

The invention and its details will be described in more detail below with reference to the accompanying drawings, in which Fig. 1a schematically shows a side sectional view of a single wire washer applying the method of the invention, Fig. Ib schematically shows a side sectional view of an alternative solution of the invention with a single wire washer, Fig. 2a schematically shows a side section Fig. 2b schematically shows in side section 35 an alternative solution for applying the invention with a two-wire washer and Fig. 3 67892 Fig. 3 schematically shows in side section another solution for applying the invention with a single wire washer.

The apparatus according to Fig. 1a has an endless wire 3. At the beginning of the wire there is a so-called headbox 2 and at the end 5 an outlet screw 4. Above the wire there are several successive, bottomless wash basins 6, 6 ', 6 "and 6'.” The vertical walls between the basins can be sealed against the pulp web running on the wire 3, e.g. basins 10, 10 ', 10 "and 10'". After the last 10 wash basins, there is an overpressurized space 8 above the wire. The apparatus has an outlet 5 for conducting wash water to the last wash water basin and an outlet 7 for conducting wash water from the first bottom basin 10 to the evaporator. 15 for conducting wash water from each of the basins 10 to the basin 6 above the previous washing step. Furthermore, the apparatus has the necessary pumps and flow regulators.

The formation of the shark is achieved by the design of the inlet box, whereby the liquid washing starts immediately after the 20 inlet boxes.

The pulp 1, which is introduced at a pumping consistency (about 3%) into the headbox 2, precipitates at the pumping pressure under the lip of the headbox on an endless wire 3 passing through the entire scrubber with the wire and finally leaving the discharge screw 4.

The washing water 5 is led to the last washing step 6 '"in the washing zone 6, where it displaces the track liquid left in the pulp web in the previous step. By means of the level control, the basins 10 and 6 are kept filled with liquid at all times, whereby the wire and the pulp web run inside the liquid at all times.

The concentrated liquid eventually leaves the evaporator 7.

35; If it is desired to increase the consistency of the pulp web after the oes zone, the last stage of the scrubber T— - - · 4 67892 can be used e.g. overpressurized space 8, where the precipitated liquid is led from the pool 10 "'

The application shown in Fig. Ib is otherwise similar to the embodiment of Fig. 1a, but after the headbox there is an overpressure space 9 in the apparatus before the first washing step. The track formation and thickening takes place by means of overpressure air at point 9 before the start of the actual washing zone.

In the embodiment according to Figure 2a, there is in addition a second endless wire 11 above the wire 3. The pulp 1 is introduced at a pumping consistency (about 3%) into the headbox 2, from where it is passed between two wires 3 and 11. The precipitation takes place partly due to the pumping pressure, partly due to the narrowing of the space between the wires and the flow of the washing liquid.

The wires are guided by means of rollers 12 and rollers 13 at the initial end.

The pulp passes between the wires 3 and 11, eventually leaving the discharge screw 4.

The washing water 5 is led to the last stage 10 "'of the washing zone, from where it passes countercurrently through the pulp path alternately upwards, alternately downwards, finally leaving the concentrator 7 in a concentrated state.

After the washing zone 8, e.g. pressurized air is used to increase the consistency 25 of the pulp. The precipitated liquid is introduced into the washing liquid into a basin 10 "'.

The application shown in Fig. 2b is otherwise similar to the embodiment of Fig. 2a, but before the first washing step the apparatus has an overpressure space 9. The thickening of the pulp web 30 takes place before the actual washing step, e.g. by means of overpressure air.

In the embodiment of Figure 3, the wire supporting the pulp web runs back to the beginning of the scrubber at the top of the basins. In this case, it is considerably easier to support the entire equipment than when the wire passes under the basins.

A hood 14 is arranged above the basins 6, which communicates with the outside air.

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After washing in the liquid phase between the basins 6 "and 10", the final washing step in the gas phase takes place in the embodiment of Figure 3. In the last basin 10 "'the liquid surface is kept so low that there is a gas space 15 in the top of the basin. The fan blows part of the space 15 from the sucked gas under the hood and part elsewhere. There is a constant slight vacuum under the hood. In this case, no harmful gases are released into the outside air.

10! The part of the wire supporting the pulp web is in an inclined position so that it rises towards the end of the washer.

Above the gas space 15, a washing liquid is sprayed onto the wire and passes through the wire by the suction in the space 15 to the basin 10 ". This effectively removes the liquid from the last washing-15 stage. Since the pulp has already passed through several washing stages, is carried out in the gas phase.

In the solution according to Fig. 20 3, the lower ends of the partitions 17 between the basins 6 are not sealed against the wire, but are arranged at a distance from the wire and the pulp web thereon. The lower end of the partitions 17 is provided with a plate 18 projecting in the direction of travel of the wire, which is located at a distance between the wire and the pulp web. In the solution 25 according to Figures 1 and 2, the rollers 12 may press the pulp web against the wire so that the wire becomes clogged. When there is a gap between the vertical walls and the wire, there is no risk of clogging. In this case, there is also no friction against the wire. Preferably, the gap between the plate 18 and the wire should be aligned. The liquid flows, which are maintained by means of pumps 30, cause the distribution point between liquids of different concentrations between two adjacent basins 6 to be located below the plate 13, so that the liquids contained in the basins do not mix despite the gap.

Claims (10)

A method for washing the pulp (1) on a flat wire machine in two or more steps (6, 10; 6 ', 10'; 6 ", 10"; 6 '", 10f") with the pulp web passing over the wire (3) covered with washing liquid, wherein the liquid contained in the pulp web is displaced by the washing liquid as the washing liquid flows through the pulp web and the wire, characterized in that the pulp web and the wire (3) run completely inside the washing liquid during washing so that there are also liquids below the pulp web. A method according to claim 1, characterized in that after the washing step (6 ", 10") inside the washing liquid, the washing is performed as the pulp web and the wire pass through the gas space. Method according to Claim 1 or 2, characterized in that the formation or thickening of the pulp web takes place before the first washing step (6, 10) by means of pressurized air (9). Method according to one of Claims 1 to 3, characterized in that after the last washing step (6 '1, 10 *') the pulp web passes the overpressure space (8). Method according to one of Claims 1 to 4, characterized in that the pulp web passes between two wires (3, 11). Method according to Claim 5, characterized in that the washing water flows countercurrently through the pulp track alternately upwards and alternately downwards. Apparatus for applying the method according to claim 1, wherein the apparatus comprises an endless wire 30 (3) and means for conveying it and a device for guiding the pulp (1) to the wire, the apparatus having two or more successive bottomless washbasins (6) above the wire (3). 6 ', 6 ", 6'") and devices for conducting wash water to the basins, characterized in that in the repetition of iait-35 there are second basins (10, 10 ', 1 ·' ", 13 '") below the wire (3) for collecting the wash water in the wire. from the above basins ι * 5, 6 ', ό ", 6; and devices for draining the wash water 67892 away from the basins below the wire and level controls to keep the basins (10, 10', 10”, 10 '") below the wire constantly filled with liquid. Apparatus according to claim 7, characterized in that the part of the wire supporting the mass path of the wire (3) circulating above the basins back to the beginning of the apparatus is arranged in a tilted position so as to rise towards the end of the apparatus. Apparatus according to claim 7 or 8, characterized in that the lower ends of the vertical partitions (17) between the wash water basins (6, 6 ', 6 ”) above the wire (3) are spaced apart from the wire and the pulp path passing therethrough. Apparatus according to claim 9, characterized in that the lower ends of the vertical partitions (17) between the wash basins (6, 6 ', 6 ”) above the wire (3) are provided with an extension (18) projecting in the direction of travel of the wire, which located at a distance from the wire and the pulp path passing through it. ____ - τ ~ ____ '67892