FI69493C - TVAETTANORDNING FOER PAPPERSMASSA - Google Patents

Description

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v (51) Kv.lk. * / lnt.CI. * D 21 C 9/06 PIN LAND (21) Patent application - Patentansökning 782857 (22) Application date— Ansöknlngsdag 19 · 09 · 78 (F *) (23) Starting date - Glltighetsdag 19 * 09.78 (41) Has become public - Blivit offentllg 19 * 05 * 79

National Board of Patents and Registration Date of publication and publication Publication— 21 ^ 10.85

Patent- och registrstyrelsen '' Ansökan utlagd och utl.skrlften publicerad (86) Kv. application - Int. ansökan (32) (33) (31) Privilege claimed— Begird priority 18.1 1.77 USA (US) 8529Ο7 (71) Ingersol1-Rand Company, 200 Chestnut Ridge Road, Woodcliff Lake, New Jersey, USA (US) (72) Oscar Luthi , Nashua, New Hampshire, USA (7k) Berggren Oy Ab (5 ^) Pulp Washer - Tvättanordning för pappersmas This invention relates to pulp washers. More specifically, this invention relates to a novel pulp washer and pulp washing method for obtaining a low-density pulp slurry product.

The cooked pulp from the digesters is filtered and washed with water to remove black liquor that would contaminate the final product made from the pulp, and to recover as much of the cooking chemicals used as possible at the lowest possible dilutions. Most pulp washing today is done with suction washers. Normally, two to four washers are used in series, depending on the amount of pulp to be treated, to achieve the best possible washing efficiency. 98 to 99% of the chemicals used are thus washed away from the pulp.

The suction washer is a cylinder covered with a metal cloth, which rotates in a bath containing pulp slurry, so that the lower part of the cylinder is embedded in the pulp. Vacuum is applied as far as the rotating cylinder enters the pulp slurry. The black liquor flows through the metal cloth, i.e. the wire, leaving a layer of pulp on the surface of the wire, which is held in it by the vacuum inside the cylinder. The pulp layer is continuously thickened as the submerged portion of the cylinder rotates through the pulp slurry 2 69493 in the pool. As the cylinder continues to rotate, the thick layer of pulp adhering to the surface of the wire rises with the wire from the slurry. The black liquor continues to drain from the pulp due to the pressure difference between the external atmosphere and the internal vacuum of the cylinder. Nozzle tubes, i.e. on the web, are fitted with jet tubes to displace the black liquor with water as the cylinders continue to rotate. Finally, the vacuum is stopped and the washed mass is removed from the cylinder wire, just before the cycle is repeated.

It is impossible to displace all the original lye and chemicals in the wash water in the wash zone. For this reason, the pulp web leaving the first suction scrubber is reslurried in water before it is washed with the second suction filter11a. This is repeated between each filter in the scrubber set. The pulp and fresh water flow countercurrent to each other in the mildew wash to minimize black liquor dilution. Thus, fresh water is used in the scrubber of the last stage of pulp washing, and the filtrate, i.e. the water which has been absorbed through the pulp mat under the effect of a vacuum in this scrubber, is used to wash the pulp with the previous scrubber.

The slurry fed to the vacuum washing step is usually about 1% thick. Some slurry occurs at the rise of the cylinder slurry. The consistency of the outer layers of the pulp web is very low and they do not have enough strength to be lifted up from the sinks. The precipitated mass is re-diluted with the inflowing mass slurry. The consistency of the pulp web as it rises from the sinks is approximately 7-9% due to the effect of slurry and vacuum. The pulp web then passes through the washing zone and then removes more liquid from the air sucked through the web. The pulp is removed from the cylinder in a relatively thick manner, about 12-16%, by means of an removal scraper. This thick mass must be diluted to a lower consistency and resuspended before the next washing step.

One disadvantage of currently used suction filters of the type described above is that the removal of liquid by air is detrimental in many processes due to scaling and chemical reactions.

The invention relates to a pulp washer and a pulp washing method which, among other things, eliminate the removal of air from the liquid as an aid. The pulp 3 69493 is washed completely without presence. The consistency of the effluent pulp slurry is low, so that the slurry can be easily led down the pipe out of a completely enclosed basin. In order not to lose the washing efficiency, the original lye is removed in a very thick zone in the pre-washing zone before the washing zone.

Briefly, this new pulp scrubber includes a rotatable cylinder enclosed in an airtight basin. It is equipped with a device for feeding the pulp slurry to the basin. The pulp slurry is compacted to form a web of high consistency, after which the web is washed with the water contained in the washing chamber by applying a pressure difference between the different sides of the circumferential wall of the rotatable cylinder. The web is removed from the rotatable cylinder and formed into a dilute pulp slurry.

The invention and its many advantages will become more apparent from the following detailed description and the accompanying drawing, in which:

Fig. 1 is an end view, partially sectioned, of an embodiment of the invention, Fig. 2 is a sectional view on a larger scale showing the application of a jet of liquid to the formed and washed web to remove it, Fig. 3 is a partial side elevational view of on a larger scale and shows a structure which prevents the liquid in the different filter compartments of the cylinder from leaving the forming and thickening zone, mixing with the washing water, Fig. 5 is a sectional view taken substantially along line 5-5 of Fig. 4.

In these different figures, similar parts are denoted by the same reference numerals.

As shown in the drawing, and in particular in Figure 1, the substantially airtight basin 10 completely encloses the wire-coated cylinder 12 which rotates in the basin 10. The lower part of the rotating cylinder 12 is submerged in the pulp slurry chamber 13 through the pulp slurry feed opening 14.

4 69493

As the cylinder rotates on its surface, a pulp web 16 is formed. This pulp web can be embedded by a hydrodynamic baffle 18 shown in broken lines in Figure 1. A specially constructed baffle 18 mounted downstream of the inlet 14 applies a baffle force to the forming web. This force is applied by actuators 20 (one shown in Figure 1). The hydrodynamic baffle 18 is preferably of the type which seals the pulp to a high consistency, for example 15-18%, before the pulp enters the washing zone. A particularly good hydrodynamic baffle is shown and explained in Finnish patent no.

hak.no 780599). With this new device and method, additional compaction after the baffle 18 has compressed the carpet is unnecessary. During the remainder of the rotation cycle of the rotating cylinder 12, the sealed pulp web is washed by applying a pressure difference between both sides of the circumferential wall of the rotating cylinder 12. The mat is washed with a washing liquid contained in a liquid-filled washing chamber 17, the chamber of which extends at least from the web-forming and sealing zone to the dilute pulp slurry outlet 28. The washing liquid enters the washing chamber 17 from the washing liquid inlet 22 and also helps the actuators 20 to apply a blocking force to the carpet.

In the embodiment according to the drawing, the web is removed from the outside of the cylinder 12 with a liquid which is sprayed against the mat. In the web removal zone, a valve (not shown) shuts off the low pressure inside the cylinder 12. The liquid is fed to the basin 10 through the liquid supply port 24 and sprayed through the longitudinal slot 26 against the web formed to separate the web from the cylinder 12. The dilute pulp slurry thus formed is removed from the basin 10 through the outlet 28. The consistency of the removed pulp slurry may be relatively low, for example 4%. Many web removal devices other than the jet shown in the drawing can be used to remove the web, for example a wing roll.

A longitudinal shut-off type shutter 30 separates the washing chamber 17 in the web discharge area from the pulp slurry chamber 13 at the inlet 14. The pressure in the washing chamber is kept the same as in the pulp slurry chamber.

Preferably, the cylinder 12 includes an inner cylinder 32 shown in Figure 4 to which longitudinal spacers 34 are attached. Each of these longitudinal spacers 34 is generally U-shaped in cross section 69493 spaced apart support ribs 42 with holes 44 are mounted circumferentially from the dividing ribs 34.

The corrugated separator plate 46 (Figure 5) forms flow passages 48 for fluid flow through the web 16 and wire 49 and circumferentially along the flow passages 48. Each of the circumferential segments formed between the manifolds 34 and below the separator plate 46 forms a filtrate compartment.

In the radial direction of the radial portion 36 of the manifold ribs 34, the outer portion extends along the member including the radial portion 50, an integral circumferential portion 52 extending beyond the radial portion 36 of the manifold 34 and also below and in contact with the separating plate 46, and the same portion a radial portion 44 extending across one end of the separator plate 46 enclosing that end of the separator plate. The longitudinal plates 56 are attached to notches 60 made in the separating plates 46. Thus, the washing liquid flowing through the web 16 and the wire 49 also flows along the flow channels 48 in the opposite direction of rotation of the drum 12. At the end of the flow channel 48, the washing liquid flows through the opening 70, the hole 40 and the holes 44 and in the longitudinal direction up to the filtrate compartment formed between the distribution ribs 34. The filtrate in each filtrate compartment flows to the end of the drum. Thus, it can be seen that the surface of the cylinder 12 consists of a plurality of filtrate compartments that prevent or minimize mixing of the wash liquid sprayed across the web 16 into the filtrate in the filtrate compartments remaining in the filtrate compartments after the filtrate compartments leave the web forming and sealing section.

As more clearly shown in Figure 3, the filtrate flows longitudinally to the ends of the cylinder 12 and then radially down the channels 72 to the interior of the cylinder, and then out of the basin through a hollow shaft 74 mounted for rotation inside the shaft support 76. The pressure in the pulp slurry chamber 13 is maintained, as previously mentioned, at approximately the same value as the pressure in the washing chamber 17. Thus, it is only necessary to use a sealing seal 78 at the end of the cylinder.

During operation, as shown in Figure 1, a pulp having a consistency of, for example, 6 69493 about 4% is fed to a pulp washer through a pulp feed port 14 into a pulp slurry chamber 13. As the cylinder rotates, a pulp web 16 begins to form in the forming and compacting zone. The wash water, which is fed into the washing chamber 17 along the actuators 20, applies a crushing force against the formed pulp web as the pulp web passes through the crushing zone.

The pulp web is washed continuously from the time the pulp web leaves the sealing zone until the web is removed.

Due to the structure of the outer parts of the drum according to Figures 4 and 5, the original liquid fed to the chamber 13 through the feed opening 14 and compressed into the filtrate compartments 18 is kept separate from the liquid fed through the mat 12 from the washing chamber 17. The corrugated separating plates support the wire at short distances. small flow passages 48 (Figure 5) for fluid passage. The size of the flow channels is such that they are large enough for the flow requirement, especially for the inflow flow rate at the beginning of the web formation cycle, and small enough to ensure that the wash liquid flushes all of the original liquid out of the flow channels before reaching the web outlet.

Claims (3)

7 Claims 694 9 3 A pulp scrubber comprising a substantially hermetically sealed basin (10), a rotating cylinder (12) completely surrounded by the basin, means (14) for feeding pulp slurry to the basin, means (28) for removing pulp from the basin, a cylinder (12) for a pressing device (18) to compact the pulp web (16) formed on the surface in the forming zone (13) into a web of high consistency, and means for generating a pressure difference across the circumferential wall of the cylinder (12) for washing the web (16) with the washing liquid fed to the basin (10) 13) and from the pressing device (18) to the pulp removal means (28), characterized by means (24, 26) located in connection with the pulp removal means (28) for removing the web (16) from the surface of the cylinder (12) and breaking it up into a low-density pulp slurry before removal from the pool (10). Pulp scrubber according to Claim 1, characterized in that the circumference of the cylinder (12) is provided with a plurality of filtration chambers which are designed to mix the washing liquid with the liquid remaining in the filtration chambers after the forming zone (13) and the pressing device (18). minimized. A method for washing fibrous pulp, characterized in that the pulp slurry is fed into a substantially hermetically sealed basin (10) completely surrounding the rotating cylinder (12), a pulp web (16) is formed on the cylinder surface (12) by removing liquid from the pulp slurry through the cylinder openings (16) is washed with a washing liquid in the basin (10), the washed pulp web (16) is detached from the surface of the cylinder (12) and decomposed into a low-density pulp slurry and thus removed from the basin (10).