FI70803C - ANORDING WITH ROTARY FILTER - Google Patents

Description

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(51) Kv.ik. '/ int.ci. * B 01 D 33/36, 33/06 FINLAND —FINLAND (21) Patent application - Patentansdkning 793233 (22) Application date - Ansökningsdag 1 8.1 0.79 (EN) (23) Starting date - Giltighetsdag 18. 10.79 (41) Become Public - Blivit offentlig 07-05.80

National Board of Patents and Registration Date of publication and hearing. -

Patent and registration authorities '' Ansökan utlagd och utl.skriften publicerad 18.07.86 (86) Kv. application - Int. ansökan (32) (33) (31) Privilege claimed - Begärd priority 06.11.78

Sweden i -Sver ige (SE) 7811 ^ * 31 ~ 1 Proven-Styrkt (71) Sunds Defibrator Aktiebolag, Fack, 851 01 Sundsvall, Sweden-Sverige (SE) (72) Kjell Felix Forslund, Sundbruk, Sweden-Sverige (SE) ) (7 * 0 Berggren Oy Ab (51+) Rotating filter device - Anordning vid roterande filter The present invention relates to a filter with a rotating filter drum for removing water from materials in the form of liquid mixtures, such as cellulose pulp fiber suspensions, and such filters can be advantageously used to wash the material. More specifically, the invention relates to a scraper device for removing a web of material from a filter drum of a filter.

A filter with a filter drum designed to rotate partially immersed in the suspension is used to remove water from the fibrous suspensions of the cellulosic pulp. Such a filter drum consists of a jacket with screen openings on which a filter cloth is placed. Usually, there is also an inner sheath that does not have such openings. Between these two casings there are mainly straight partitions in the longitudinal direction of the drum, which divide the space between the casings by the so-called suction kennoiksi. In the so-called self-priming filter, the suction cells are connected to the suction or discharge channels bent backwards in the direction of rotation of the drum, to which a vacuum develops as the drum rotates. In so-called vertical tube filters, the suction cells are connected to a fixed suction or vertical tube by one or more valves. The vacuum of the cells causes the water in the fiber suspension to drain into the cells, leaving the fibrous material on the outer surface of the filter drum, so that a web of material is formed. Due to said vacuum, more water is removed from the pulp web when it is taken up from the suspension as the drum rotates. The pulp web is removed from the filter cloth at a point usually located some distance above the surface of the suspension on the downward side of the drum. This is possible by replacing the vacuum in the cells at this point with atmospheric pressure.

The invention can also be applied to the so-called dewaterers in which the pulp web is formed due to the fact that the level of the suspension outside the drum is substantially higher than the level of the filter inside the drum.

Various devices such as grooved or smooth discharge rollers can be used for pulp removal. The simplest removal device is a scraper fitted with a small clearance of approx. 2-7 mm to the filter cloth. Removal is usually facilitated by spraying air, steam or liquid into the space between the scraper and the filter cloth. To prevent the scraper from bending down, it must rest with a form-retaining holder mounted at its ends.

In recent years, filters have been built for even larger production volumes that require long drums, so that the extent of the scrapers in the direction of the drum axis is often up to 6 meters. In very long filter drums, 10-12 meters, the holder is made in two parts, so that the parts are likewise mounted at their ends. Due to the small clearance between the edge of the scraper and the filter cloth, it is very important that the load-bearing holder does not change shape, as the scraper can otherwise damage the filter cloth.

Even if the holder is made very rigid, thermal stresses can still cause deformations. Before starting the filter, e.g. in black liquor washes, it is often circulated in hot air at about 90 ° C and at the same time the filter cloth is cleaned with a lye having essentially the same temperature or with a gas such as air or steam. In bleach filters, the lye is replaced by warm water, suitably circulating water. The filter drum then heats up strongly, and the heat is primarily distributed below the holder 3 70803, i.e. on the side facing the filter drum. The lower side then expands more than the upper side. As a result, the scraper becomes curved, i.e. the distance to the drum at the center of the scraper is smaller than at the ends of the scraper. In order to prevent the scraper and the filter drum from sticking, the distance must be increased too much, which in turn leads to insufficient removal of the pulp web at the ends of the scraper during use. Thermal stresses in scrapers and their holders have often caused detachments of filter fabrics, and these fabrics are very expensive.

It is an object of the present invention to obviate these disadvantages by feeding a gas or liquid injected into the gap between the scraper and the filter drum and a liquid or gas to clean the filter drum through the scraper holder so that different parts of the holder are kept substantially at the same temperature. At the same time, the filter cloth can be effectively cleaned. Further features of the invention will become apparent from the claims.

The invention will now be described with reference to a filter used for dewatering a pulp suspension and with reference to the drawings, in which Figure 1 shows a filter with a scraper according to the invention and Figure 2 shows a section along the line II-II in Figure 1.

The filter comprises a rotating filter drum 1 partially immersed in a trough 2 containing a fiber suspension. A scraper 4 is arranged next to the drum to remove the pulp web which is absorbed by the filter drum 1 and which accompanies it. The scraper 4 is attached to a holder 5 which is hollow and bounded by the upper and lower walls 6 and 7 and the ends.

At the front of the holder, i.e. in the part closest to the pulp web discharge point, spray nozzles 8 for air are arranged. These nozzles 8 are attached to the holder 5 and connected to a front chamber 9 located at the front of the holder. At the ends of the holder, the front chamber 9 communicates with supply lines 10 for pressurized air, the pressure of which is suitably 0.1-3 kp / cm, preferably about 0.3 kp / cm.

At the rear of the holder there are spray nozzles 11 for liquids, i.e. 4 70303 days for lye. These nozzles 11 communicate with the rear chamber 12, which fills a relatively large part of the holder cavity. This chamber 12 communicates with the liquid supply lines 13.

In the embodiment shown, the scraper holder is pivotable about an axis of rotation which coincides with the axis of the wires 10,13. This allows the nozzles 8 to be easily cleaned if necessary. Alternatively, the lines may be flexible hoses connected adjacent to the pivot axis. The gap between the scraper 4 and the drum 1 is adjustable by bolts 14 or the like cooperating with fixed response members 15.

Before starting the filter, the filter drum is circulated in hot air at approx. 90 ° C. At the same time, the same temperature of liquor is passed through the lines 13 to the rear chamber 12 in the scraper holder 5, whereby the liquor is sprayed towards the filter drum through the nozzles 11 for cleaning the drum. In this way, the upper and lower walls 6, 7 of the scraper holder heat up equally, and the holder and the scraper 4 retain their straight shape.

When the filter is then deactivated, the filter cloth can be constantly rinsed clean, as this is often necessary. Otherwise, the feed of the liquor can be well stopped, because the exiting pulp web during use is passed over the upper wall of the scraper holder, whereby the web keeps the wall at approximately the same temperature as the lower wall.

The removal of the pulp web is facilitated by spraying air through the nozzles 8 into the gap between the scraper 4 and the drum 1.

Of course, the invention is not limited to the embodiment shown and described, but can be modified within the scope of the idea of the invention.

Claims (2)

5 -Oo07 Claims' ^ ^ o A scraper device for removing a web of material from a filter filter drum (1) for removing water from liquid material mixtures, such as cellulose pulp fiber suspensions, the device comprising a holder (5) running along the filter drum (1) and a scraper (4) attached to the filter drum (1). adjacent, and front nozzles (8) for spraying gas or liquid towards the gap between the scraper (4) and the filter drum (1), characterized in that the holder (5) is hollow and includes a front chamber (9) located closest to the scraper (4) and communicating with the front nozzles (8) and extending the full length of the holder (5), a rear chamber (12) filling a relatively large portion of the holder (5) and communicating with rear nozzles (11) attached to the holder to spray gas or liquid towards the drum (1) for its cleaning, lines (10) for supplying gas or liquid to the front chamber (9) and lines (13) for supplying gas or liquid of substantially constant temperature into the rear chamber (12). Scraper device according to Claim 1, characterized in that the scraper holder (5) is rotatably mounted at its ends so that it can be lifted up from the filter drum (1).