DE1926516A1 - Method and device for washing cellulose - Google Patents

Description

“IPX.-IITO. KLAUS BEHN DIFL-FHTS. ROBERT MÜNZHUBER l

»MUNICH3β

WItMNMAYEBSTH. B.

^{A192 / 19369} May 23, 1969

Company AKTIEBOLAGET KARLSTADS MEKANISKA WERKSTAD Karlstad / Sweden

Method and device for washing cellulose

The invention relates to a method for washing a continuously conveyed web obtained from a suspension of cellulose fibers, in which process the web is subjected to such an effective pressure in a caustic discharge zone that the one exiting the caustic discharge zone Bahn has a comparatively high solids content is brought, whereupon the displacement of the suspension liquid enclosed in the web by the supply of Washing liquid follows under an overpressure in a washing zone which immediately follows in the conveying direction of the web and is connected to the caustic discharge zone. The invention also relates to a device for washing after the above-described method of a continuously conveyed web consisting of a suspension of cellulose fibers which device has a rotatable drum with a permeable jacket as well as a perforated pressing member concave to the jacket, which is arranged at a distance from the outside of the jacket is and together with this delimits a caustic discharge zone »

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extending along part of the circumference of the drum from one inlet and vertex housing to the beginning of a subsequent one Washing zone extends along which part the radial distance; between the pressing member and the drum shell, in the direction of rotation seen of the drum, which subsequent washing zone extends along a further part of the circumference of the drum and through the drum shell and at least one rigid, perforated pressing member which is concave to the jacket and which is arranged outside the drum jacket, is limited, with a * sieve for movement in the direction of rotation | the drum through the lye disposal zone and the washing zone is arranged along the pressing members.

In the chemical treatment of wood or other cellulosic material to release and recover cellulose, a liquid suspension is usually obtained by boiling in a pulp digester which contains organic and inorganic substances in addition to cellulose. The cellulose in the form of fibers must then be separated from the suspension as effectively as possible. The recovery of the liquid remaining after the cellulose has been separated is necessary both for economic reasons and for reasons of nature conservation. Certain chemicals present in the liquid w can preferably be returned to the process, while the organics can be used as fuel. This recovery of chemicals and organics usually takes place by evaporating the liquid. In order to avoid that excessive amounts of dilute liquid are obtained for evaporation, it is desirable that the amount of washing liquid supplied is as small as possible in the so-called washing process.

With the well-known so-called filter washing, the fiber * - suspension first diluted to a suitable consistency and fed to a trough in which a partially immersed

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Filter drum is driven to rotate. As a result of the hydrostatic If there is a difference in pressure between the inside of the drum and the trough, lye can be drained off the fiber suspension takes place and a fiber web is formed on the drum. After the fiber web is out of suspension has come out due to the rotation of the drum, washing liquid is sprayed on. After deriving, the Fiber web. Removed from the filter. From the through the drum separated liquid is withdrawn an amount of liquid that is equal to the sprayed washing liquid, while the remainder is returned to the aforementioned dilution of the fiber suspension upstream of the filter.

The main disadvantage of filter washing is its necessity large amounts of circulating liquid to form the fiber web, which means that systems that require a large amount of space and high costs, with difficult foaming problems often occurring. Except for these disadvantages it should be mentioned that the displacement takes place at the low solids content of the fiber web, so that both cavity liquid- (lumen liquid) as well as stagnant volumes, which are present in the path, are not affected by this displacement take part. Movements in the fiber web are caused at every point along it where a washing liquid supply takes place, whereby the washing effect is reduced.

Another known method for washing cellulose is what is known as press washing. When press washing is the Washing liquid supplied to the fiber material to be washed, whereupon the pressing usually takes place in screw presses. When the washing liquid is the fiber material at high solids content is supplied, the cavity liquid also takes part in the process and large amounts of liquid can be avoided. The disadvantage of ablution with help of pressing is that several stages are required since this process is only a mixing process. The presses become mechanically sensitive and complicated when they

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be adapted to the optimal cellulose plant production flows.

The object of the invention is on the one hand to create a effective method for washing eircr conveyed continuous Cellulose fiber web in that the suspension liquid enclosed in the web by means of washing liquid is repressed, and on the other hand in the creation of a reliable device for performing this method while avoiding the known methods mentioned and Disadvantages inherent in devices "

Some of the conditions that must be present in order to achieve the aforementioned goals are:

a) a homogeneous structure of the fiber web in which the Displacement should take place,

b) in a uniform thickness of the fiber web,

c) the displacement must take place under a high pressure, i.e. under a high pressure difference between the sides the fiber web to which the washing liquid is added and the other side on which the liquid displaced from the fiber web is to be carried away,

d) a high solids content of the fiber web during the whole process of repression,

e) the washing liquid must not move between the Cause fibers in the fiber web.

In a device according to the invention, the under a), b) and c) specified conditions in a known manner e.g. fulfilled insofar as the fiber suspension is used for lye » discharge zone in uniform distribution and with an essentially constant pressure through an inlet opening

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obtained, which extends the full length of the drum, and that the wash liquor of high pressure to one side the fiber web can arrive evenly distributed over its full width, while the other side of the Faaa? Exposed to outside air or negative pressure

Make the conditions specified above under d) and e) Present problems which are solved by the invention.

A method according to the invention is characterized in that that the fiber web is prevented by pressing at the end of the caustic removal zone and in the entire washing zone, to expand.

A device according to the invention for performing the The method described above differs essentially in that one or more perforated pressing members are provided throughout the washing zone to exert a compressive force on the wire loop in the direction of the drum shell to generate and to let washing liquid access to the fiber web under an overpressure.

As a result of the fact that the fiber web in its formation in the caustic discharge zone between the perforated shell of the drum and the sieve loop an effective, progressive one is subjected to increasing pressure by pressing members which are arranged so that the radial distance between the Wire loop and the drum shell decreases continuously in the conveying direction of the fiber web, becomes a considerable Part of the suspension liquid is squeezed out and carried away, so that the fiber web opens at the end of the Laugenablitzzone a solids content of at least 18%, preferably 33%, is brought. When the web is subjected to such an effective pressure it becomes that the solids content in the web reaches 18%, become stagnant volumes and sometimes also cavity fluid (lumen liquid) squeezed

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content in the web of 33%, the entire hollow rubbing liquid is squeezed out so that it takes part in the displacement process.This high solids content is maintained during the entire subsequent washing process by pressing elements that are arranged along the washing zone and connect the pressing elements along the caustic discharge zone, thereby preventing the web from expanding. The washing efficiency of the displacement process is a function of the ratio of the volume of washing liquor supplied and the volume of suspension liquid trapped in the web · L · The higher the solids content in the fibrous web, the smaller the volume of washing liquor required to achieve a certain washing efficiency The method and a device according to the invention therefore require a comparatively small volume of washing liquid cext.

As a result of the fact that the fiber web is kept under pressure during the entire washing process and washing liquid is admitted through perforations in the pressing members, movements between the fibers in the fiber web are prevented.

r The pressing elements, which are placed on the wire loop in the caustic discharge zone, or «should work in the washing zone, can lead to a single rigid unit can be assembled, however it is it is often advantageous to use several individual units that are articulated to one another at their ends . Such an arrangement makes it possible to reduce the pressing forces along the various zones in the conveying direction of the fiber web within to further limits and with maintained continuity.

As a result of the fact that the arranged along the washing zone pressing member is provided with a housing that a Has connector, it is achieved that washing liquid with an overpressure evenly on the perforations in the

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Press member can be distributed. In certain cases it may be expedient that the space between the pressing member and its housing by partition walls in the axial Direction of the drum are arranged, divided into sections is each of which with separate fittings is provided so that the displacement with washing liquid texts of different qualities within the different Zones along the fiber web can happen in their conveying direction. In the last-mentioned case, it is appropriate that the displaced suspension liquid mixed with washing liquid is collected in separate troughs built into the drum, one for each washing section.

To derive the _? To facilitate fiber suspension in the caustic discharge zone and to produce a homogeneous structure in the formed fiber web, it is advisable that the pressing members in the caustic discharge zone are provided with perforations so that the squeezed suspension liquid can escape on both sides of the fiber web.

In a device according to the invention, the fiber web are pressed in a press nip which is formed by a press roll and the drum immediately following the washing zone and is operated with a high linear pressure. The fiber web can to a very high solids content of about 50% solids to be brought.

The invention is described below in connection with the accompanying Drawings described in more detail, namely show:

Fig. 1 in a schematic representation a. Sectional view a device according to the invention, seen in the axial direction of the drum;

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Fig. 2 in a schematic representation a sectional view as in Fig. 1, but the washing zone is arranged for washing in three stages.

The device shown in FIG. 1 has a drum 3 which is rotatable about a shaft 1 and is provided with a perforated jacket 5. A sieve loop 7 is arranged for movement at a short distance from the drum shell 5 in such a way that a space exists between the drum shell 5 and the sieve loop 7. Two perforated pressing members 9 and 11 are arranged along the wire loop 7 and in contact with it. That part of the space delimited between the drum shell 5 and the wire loop 7, along which the pressing element 9 extends, forms a lye discharge zone 13, while another part of this space, along which the pressing element 11 extends, forms a washing zone 15 9 is provided with a housing 19 which has an outlet 21. The pressing member 11 is provided with a housing 25 which has one or more connecting pieces 27 on vast. The pressing members 9 and 11 are articulated to one another by a member 29 and supported by pressing devices 31. From the end of the washing zone 15 to the beginning of the lye discharge zone 13, viewed in the direction of rotation of the drum 3 ^, the wire loop is guided away from the drum 3 and passed over a press roller 37, guide rollers 39 and a tensioning roller Hl and then returned to the drum 3. Between the press roller 37 and the beginning of the caustic discharge zone 13 within the sieve loop 7, an inlet and distribution housing 43 is provided with a slot arrangement which extends over the full axial length of the drum 3. This slot arrangement is equipped with flexible sealing strips 45 which are in contact with the sieve loop 7 and with the drum shell 5. Furthermore, within the same part of the sieve die 7, a screw conveyor 47 is provided for a sliver

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49 lead away. Inside the drum 3 is a discharge 51 provided * The drum 3 and the pressing members 9 and 11 are between two end walls (not shown in the drawing) installed and sealed by this.

The device is provided with a pulse instrument 53, which is used to continuously measure the thickness of the fiber web 49. This instrument is via an impulse line 55 with connected to a controller 57, which it actuates, which in turn has a control valve 59 which can be actuated by a servomotor controls to regulate the flow of the fiber suspension to the device. If necessary, the controller 57 can be used to to regulate the speed of rotation of the drum 3.

A device of the type shown in FIG. 1 operates in such a way that a fiber suspension is fed under overpressure to the caustic discharge zone 13 via the inlet and distribution housing 43, the drum 3 being driven to rotate. As a result of the difference in the pressures that prevail in the fiber suspension and within the drum 3 and within the space between the press member 9 and the housing 19, liquid flows partly through the jacket 5 into the drum 3, partly through the wire loop 7 and the press member 9 into the space between 9 and the housing 19, while the cellulose fibers are collected between the jacket 5 and the wire loop 7, so that a sliver 49 is formed in the caustic discharge zone 13. As a result of the friction between the jacket 5, the sliver 49 and the wire loop 7, the latter is carried along. By appropriate pressing by means of the pressing member 9 in the direction of the Trosamel 3 with the help of the pressing devices 31, the fiber balra 49 is brought to a successively increasing solids content and when the "fiber web 49 comes to the washing zone 15 _s the solid material is resounding: to a comparatively high one B © z> t brought _o washing liquid- is ranter ¹ eiae® h © h © a ÜöeBär-uck

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via the connection piece 27 the space between the housing and fed to the pressing member 11. The washing liquid is through the perforations of the pressing member 11 and through the Sieve loop 7 is pressed into the fiber web 49 and at the same time the pressing member 11 is joined by the pressing devices 31 pressed a constant pressure towards the shell 5, so that the solids content of the fibrous web 49 during their Along the washing zone. 15 is kept constant. Washing liquid, pressed into the pressurized fibrous web 49 displaces an equal amount of in the web Enclosed suspensxons fluid, which has the consequence, that this flows into the drum 3, from which it flows through the Drain 51 together with separated in the caustic discharge zone 13 Liquid is carried away.

After passing through the washing zone 15, the fiber web 49, passed through a press nip between the shell 5 of the drum 3 and the press roller 37, which means of a high linear pressure washing liquid trapped in the fibrous web C49) and about "remaining existing suspension liquid squeezes,) so that the The solids content of the fiber web 49 is further improved, "" e.g. to about 50%. Following the press nip is the fiber web 49 of the screw conveyor 47 which feeds the fiber web comminuted and the fiber material out of the »device.

Is similar to th Figure 2 shows an apparatus in Fig diedfer _e 1 shown, but with the following differences.:

The space between the pressing element II and the <S @ liäus © 25 is divided by two partition walls - 61 iß three Sections ® S.3, each of which with a connecting rod 2? ₃ @S uzsd 67 vex »=» you can see that for the supply of toe l-Jasehliquidkei-fe di © irt _o Inside the drum are two Tx "Sg @ Si ₉ 11 ₀ which have the task of» assessed © Saspeasionsflfesiglceit "

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and used washing liquid from those parts of Collect washing zone 15, which is along the last two Sections 63, seen in the direction of rotation of the drum, are located. The trough 69 is provided with an outlet 73 and the trough 71 with an outlet 75.

A device according to Fig. 2 operates in the same way like a device of the type shown in Figure 1, however exist, the following differences:

Through the connector 67 receives pure washing liquid, usually Water, under an overpressure access to the last Section 63, seen in the direction of rotation of the drum 3. The Pure washing liquid is pressed through the perforations in the pressing member 11 into the fiber web 49 and displaced suspension liquid remaining in the latter and washing liquid supplied earlier, so that they are in the Drum 3 flows through the jacket 5. These liquids are collected in trough 71 and carried away through drain 75. This liquid is then under an overpressure over the Arischlußstück 65 to the middle section 63 for the supply pumped to the fiber web. The displacement of the fiber web 49 below the middle section 63 enclosed liquid takes place in the same way as previously described, and the displaced liquid is in the Collected trough 69. The liquid is over from the trough 69 the outlet 73 wegführung'und then under an overpressure to first section 63 at the beginning of the washing zone 15 over the Anachlußstüek 27 for the supply to the fiber web 49 is pumped. Displaced from the fiber web 49 below the first section 63 Liquid is collected in the lower part of the drum 3, where it is mixed with the suspension liquid separated in the Laügen disposal zone 13 and carried away through the drain 51 will.

The above description is only given as an example

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and are various within the scope of the invention Changes possible.

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Claims (1)

P a te η- ta n Proverbs 1.) Method of washing a continuously conveyed Web obtained from a suspension of cellulosic fibers at which such an effective pressure is exercised on the web in a Laugenableitzone that the web when leaving the Laugenableitzone comparatively high solids content is brought, whereupon a displacement of suspension liquid trapped in the web by supplying washing liquid follows under an overpressure in a washing zone, which in the conveying direction of the web immediately following the Lye discharge zone and is arranged connected to it, characterized in that the track (49) at one extension in the washing zone (15) by a continuous, mechanically exerted pressure over the entire washing zone (15) is prevented, which pressure is the pressure of the supplied Washing liquid exceeds. 2 · Apparatus for washing according to the method of claim 1 of a continuously conveyed web obtained from a suspension of cellulose fibers a rotatable drum which is provided with a permeable jacket, at least one concave to the jacket perforated pressing member which is arranged at a distance outside the shell and together with the latter defines a caustic discharge zone extending along part of the perimeter of the drum from an inlet and distribution housing to the beginning of a subsequent washing zone extends along which part the radial distance between the pressing member and the drum shell, seen in the rotary 9098 8 1/0937 direction of the drum, which continuously decreases subsequent washing zone extends along a further part of the circumference of the drum and through the drum shell and at least one rigid one that is concave to the jacket perforated press member is limited, which latter is arranged outside the drum shell, a sieve for movement in the direction of rotation of the drum through the Laugenablitzone and the washing zone is arranged along the pressing members, characterized in that the pressing member (11) in the washing zone (15) is used to apply pressure to the wire loop (7) in the direction of the jacket (5) to exercise over the entire washing zone (15) by means of gold plating (31), which the latter serve to Adjust the pressing member (11) so that the radial distance between the pressing member (11) and the jacket (5) not the radial distance between the jacket (5) and the Pressing member (9) at the end of the Laugenableitzone (13) exceeds, and the pressing member (11) for the supply of Washing liquid under an overpressure to the web Ct9) serves. 3 »Device according to claim 2, characterized in that that the pressing members C9, 11), which are arranged along the caustic discharge zone C13) and the washing zoneCl5), are hinged together. Device according to claim 2, characterized in that that the space between the pressing member ClI) and the housing C25) by one or more partition walls C61) arranged in the axial direction of the drum C3), in sections C63) for the distribution of washing liquid on the perforations of the pressing organ ClI) of several 90988 1/0937 Connection pieces 027, 65, 67) is divided from. 5. Apparatus according to claim 2, characterized in that one or more troughs (69, 71) within the
Shell CS) of the drum (3) are arranged along the washing zone (15) in order to collect and carry away liquid. 30988 17093 7