EP0579601A1

EP0579601A1 - Method and apparatus for removing ink from waste paper material

Info

Publication number: EP0579601A1
Application number: EP91918793A
Authority: EP
Inventors: Stanley Blum; Trevor William Ridgley Dean
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-10-30
Filing date: 1991-10-29
Publication date: 1994-01-26
Also published as: HU9301276D0; BR9107039A; HUT65639A; AU8748891A; FI931963A; CA2095342A1; WO1992007993A1; JPH06504327A; FI931963A0; PT99377A

Abstract

Procédé et appareil de désencrage de déchets de papier dans lesquels les matériaux sont réduits en pâte dans une cuve de réduction en pâte (1) pour former une pâte épaisse et fibreuse avec des particules d'encre en dispersion. Dans l'une des formes d'exécution, on réalise la dispersion de pâte et d'encre et on enlève ensuite les particules d'encre en dispersion dans la même cuve de réduction en pâte. On verse un mélange de déchets de papier et d'eau dans ladite cuve (1), par exemple un hydrobroyeur, où il est mélangé et agité par un rotor (2) pour former ladite pâte fibreuse épaisse (3). Pendant l'opération de réduction en pâte, les particules d'encre se dispersent dans la pâte (3), de sorte qu'on peut les en enlever soit par un dispositif d'aspiration sous vide (10, 11) soit en les faisant passer à travers les parois d'un récipient à perforations (4). Des conduits (8, 9) introduisent les flux d'air et de mélange eau/air dans la cuve (1) pour accélérer la vitesse de désencrage. Dans une autre forme d'exécution, après la réalisation de la dispersion de pâte et d'encre dans ladite cuve (1), la pâte est transférée dans une cuve de stockage (22), telle qu'un réservoir de stockage, pour enlever ensuite les particules d'encre par ledit dispositif d'aspiration sous vide (10, 11) par exemple, ou le récipient à perforations (4).Method and apparatus for deinking paper waste in which the materials are pulped in a pulping tank (1) to form a thick, fibrous pulp with dispersed ink particles. In one of the embodiments, the dispersion of paste and ink is carried out and the ink particles dispersed are then removed in the same paste reduction tank. A mixture of paper waste and water is poured into said tank (1), for example a water mill, where it is mixed and agitated by a rotor (2) to form said thick fibrous pulp (3). During the pulping operation, the ink particles disperse in the pulp (3), so that they can be removed either by a vacuum suction device (10, 11) or by making them pass through the walls of a perforated container (4). Ducts (8, 9) introduce the air and water / air mixture flows into the tank (1) to accelerate the deinking speed. In another embodiment, after completion of the dispersion of paste and ink in said tank (1), the paste is transferred to a storage tank (22), such as a storage tank, to remove then the ink particles by said vacuum suction device (10, 11) for example, or the perforation container (4).

Description

METHOD AND APPARATUS FOR REMOVING INK FROM WASTE PAPER MATERIAL

This invention relates to a method and apparatus for removing ink from waste paper material, particularly in the recycling of printed waste paper.

At recycling mills, waste paper which may carry printed matter is placed in a pulping vessel, such as a hydropulper, in which it is stirred or agitated to form a slushed fibrous stock consisting of a suspension of the disintegrated waste paper fibres in water.

Normally, after pulping, the stock is passed into a stock chest where it dwells for between 1-1 1/2 hours. It is then usually passed through a thick stock centrifugal cleaner where it is 'cleaned' as regards heavy contraries, and thence onto a vibrating screen where foil and plastics are removed. The next stage is a high speed deflaker from which it is then diluted to about 0.8% consistency from a normal low consistency pulping of about 6%, and passed into the first of a series of primary flotation cells. Flota¬ tion chemicals are added either prior to, or directly into, the first of the primary flotation cells, in which the fibrous stock is de-inked by the flotation of ink particles therefrom.

However, the conventional flotation deinking cells are expensive and take up a substantial amount of floor space, so that many smaller mills cannot use them.

It is therefore an object of the present invention to provide a method and apparatus for removing ink from the waste paper material which are particularly suitable for use in smaller mills where it is not economical to install conventional ink removal facilities which are usually complex and expensive. Accordingly, one aspect of the present invention consists in a method for removing ink from waste paper material, the method comprising pulping the waste paper material in a pulping vessel to form a slushed fibrous stock, dispersing ink particles within the fibrous stock, and removing the dispersed ink particles from the stock, characterised in that the removal of dispersed ink parti¬ cles is carried out in the pulping vessel and/or in a storage vessel to which the stock is passed from the pulp¬ ing vessel.

In one embodiment, the dispersed ink particles may be removed from the stock in the pulping vessel and/or in the storage vessel by suction using vacuum means.

In another embodiment, the dispersed ink particles may be removed by means of a container supported in the pulping vessel and/or storage vessel and having a perforat¬ ed wall structure such that when the stock is stirred or agitated, ink particles circulating therein can pass through the perforations into the container but the fibres forming the stock are substantially prevented from passing through the perforations.

In order to assist the speed of ink removal, at least one stream of air, water, or air and water may be introduced into the pulping vessel and/or storage vessel, preferably into the lower part of the vessel beneath the circulating stock.

When ink particles are removed in the pulping vessel, the waste paper material may be stirred or agitated within the pulping vessel alternately at a first speed to effect the pulping and encourage the dispersal of ink particles within the fibrous stock and at a second speed lower than the first speed to remove dispersed ink parti¬ cles. The stirring or agitating speed may be alternately increased and reduced as many times as required. Common paper making chemicals may be added into the fibrous stock in the pulping vessel and/or storage vessel. In particular, a chemical agent for dispersing ink parti¬ cles within the fibrous stock may be added, and possibly also a chemical which prevents redeposition of the ink particles onto the fibrous stock. Inorganic filler parti¬ cles to absorb any free ink particles in the vessel may also be added.

From another aspect, the present invention consists in apparatus for removing ink from waste paper material, the apparatus comprising a pulping vessel for containing the waste paper material and for pulping the waste paper material to form a slushed fibrous stock and dispersing ink particles within the stock, said apparatus including means for removing dispersed ink particles from the stock, cha¬ racterised in that said ink removal means are arranged to remove dispersed ink particles from the stock whilst it is contained in the pulping vessel and/or to remove dispersed ink particles from the stock whilst it is contained in a storage vessel to which it has passed from the pulping vessel.

In one embodiment, the ink removal means may con¬ sist of vacuum means arranged to be used in the pulping vessel and/or storage vessel. The vacuum means may comprise a vacuum device having a suction tube which is arranged to be lowered into, and lifted out of, the pulping vessel and/or storage vessel.

In another embodiment, the ink removal means com¬ prises a container supported in the pulping vessel and /or storage vessel, said container having a perforated wall structure such that ink particles circulating in the stock as it is stirred or agitated by a stirring device mounted in said vessel can pass through said perforations into said container but the fibres forming said stock are substan¬ tially prevented from passing through said perforations. The apparatus preferably includes means for lowering the container into, and raising it out of, the vessel. The apparatus may also include means for swinging the container to the side of the vessel to facilitate cleaning or mainte¬ nance. The container may be in the form of a basket, in which the perforated wall structure comprises a mesh mate¬ rial. Advantageously, the ink removal means includes a mechanism for removing the ink particles from the contain¬ er.

Preferably the vessel is circular in cross-section, and the stirring device, which may be a bladed rotor, may be mounted substantially centrally in the base of the vessel such that a central vortex is created in use of the stirring device. In practice the vessel and stirring device may be formed by the vessel and associated rotor of a pulping vessel, such as a hydropulper, or a storage vessel, such as a stock chest, already existing at the mill.

The apparatus may also include means for introduc¬ ing at least one stream of air, water, or air and water, into the pulping vessel and/or storage vessel, and prefera¬ bly into the lower part of the vessel at the bottom of the vortex formed by the stirring device. The stream assists the speed of ink removal by increasing the speed of flow of the stock in the region of the stirring device, and effects a degree of washing.

In order that the present invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 shows a schematic cross-sectional view of an apparatus according to one embodiment of the invention; Figure 2 shows a schematic cross-sectional view of another embodiment of the invention; and

Figure 3 shows a schematic cross-sectional view of a further embodiment.

Referring first to Figure 1, a pulping vessel 1, such as a hydropulper or a low consistency batch pulper, is provided with a central bladed rotor 2 which is located at the bottom of the vessel and is arranged to be driven at a variable speed.

A mixture of waste paper material and water is placed in the vessel and stirred or agitated by means of the rotor 2 to form a pulp of slushed fibrous stock 3. A container 4, in the form of a mesh basket having either a solid or mesh base, is lowerable into the centre of the vessel 1 by means of any suitable raising and lowering mechanism diagrammatically indicated by 7. A suction tube 5 extends into the basket 4 for removing ink 6 which accu¬ mulates in the basket during operation of the apparatus.

An air line 8 is located beneath the rotor 2 for introducing a stream of air into the stock, and a further air and water line is positioned for directing an air/water mixture onto the turning rotor blades also during operation of the apparatus.

In use, the basket 4 is lowered by means of the mechanism 7 into the centre of the vessel 1, in which a central vortex is created in the stock 3 by driving the rotor 2, the intensity of which can be controlled by vary¬ ing the speed of the rotor. The basket 4 and its ancillary equipment such as the suction tube 5 is constructed such that it may be raised and lowered quickly and smoothly and also swung clear to the side of the vessel 1 for cleaning or maintenance. A cleaning mechanism (not shown) such as a water spray may be provided for cleaning the basket. Air and water are added by means of the lines 8,9 to assist agitation of the stock. The water and air are introduced at the bottom of the vortex, which increases the speed of flow of the stock in that region. The air stream 8 may be of particular assistance during pulping to in¬ crease the speed of ink dispersal. The water and air stream 9 also produces a washing action which facilitates the dispersal of ink particles from the paper fibre. Such addition of water may be delayed until later in the process of pulping. Also the introduction of water can be pro¬ longed in the later stages of pulping so that the process essentially becomes a two stage treatment.

As ink particles separate from the agitated stock 3, they pass through the perforations of the mesh to col¬ lect in the basket 4, as shown at 6, while the fibre compo¬ nent is prevented from so doing by the mesh. The mesh size is chosen to suit the particular stock under treatment. To this end several baskets of different mesh size may be provided. The stock 3 circulating around the outside of the basket 4 will continually "wipe" the outer surface and minimise the build-up of fibre which can otherwise quickly block or blind the mesh. The material used in the manufac¬ ture of the mesh can be metal or plastic depending upon the size and operation of the apparatus, the constraints of the process, and the cost.

In some cases it may be desirable to construct a double-walled basket in order to minimise the blinding of the mesh and reduce fibre loss from the process. The outer mesh size may be larger than that of the inner, and again the mesh size and material of each basket wall is chosen to suit the length of fibre, under treatment and the process conditions. A rotating, flexible wiper blade can also be fitted to run between the two walls in order to encourage passage of ink to the inside of the basket while preventing fibre building up on the inner wall.

In order to effect the pulping action to form the slushed fibrous stock and to encourage the dispersal of ink particles within the stock 3, the speed of the rotor 2 may be periodically increased, and then reduced to allow the dispersed ink particles 6 to collect in the basket 4. This cycle may be operated several times for each batch of stock 3, the frequency and intensity depending upon the type of waste paper under treatment, the ink involved, and the production rate required. Accumulated ink particles 6 can be removed from the basket 4 by continuous or intermittent suction through the tube 5. Alternatively, a cleaning mechanism such as rotating scoops or paddles may be operat¬ ed, either intermittently or continuously.

Although especially suited to a batch or discontin¬ uous process, the apparatus can be easily adapted to oper¬ ate in a continuous process by ensuring that there is an adequate cleaning mechanism provided and that the process is operated for sufficient time to allow for a satisfactory level of ink dispersal from the stock.

Some water may also collect in the basket 4, and ink particles may be separated from the water fraction in a separate operation by the addition of a suitable flocculat¬ ing agent, for example papermaker's alum, or polyelectro- lytes, and any waste water may be passed back into the process. This process may be influenced by the type of ink involved and the stock conditions appertaining to each mill, for example pH, temperature, fibre type and degree of mechanical treatment of that fibre. The operation of this water recovery system may. be a major factor in the econom¬ ics of running the mill and thus the waste ink is prefera¬ bly removed as a concentrated sludge. In another embodiment shown in Figure 2, in which like features are labelled with like reference numerals with respect to Figure 1, the means for removing dispersed ink particles from the stock 3 in the pulping vessel 1 consists of a vacuum device 10 having a vacuum suction tube 11 connected to the device 10 by a flexible hose 12. The suction tube 11 is supported in a generally vertical position by a first support 13 and the flexible hose 12 is supported by a second support 14. The two supports 13 and 14 are movable in a horizontal direction by means of wheels 15 located in fixed runners 16. A pulley mechanism consisting of pulley wheels 17 and a flexible rope or chain 18 is mounted on the second support 14 and is connected to the upper end of the suction tube 11. A handle 19 is provided to operate the pulley mechanism to lower, and raise, the suction tube 11 into, and out of, the stock 3 contained within the pulping vessel 1. As the stock 3 is stirred or agitated in the pulping vessel 1 by the rotor 2 and air is introduced via the line 8, a scum 20 which consists of a mixture of ink particles and some slushed fibres blown up by the air bubbles forms in the centre of the vortex created by the stirring or agitation. In this arrangement, the scum is removed from the pulping vessel 1 by suction up through the suction tube 11, through the hose 12 and the vacuum device 10, and through an outlet 21 to an ink separator (not shown) for removing the water from the ink particles.

Figure 3 shows yet another embodiment, in which the same vacuum means is utilised as in the embodiment of Figure 2, but instead it is used for removing ink particles from the stock 3 contained in a storage vessel 22, such as a stock chest, to which the stock has been passed from a pulping vessel (not shown in Figure 3). The storage vessel 22 includes a rotor 23 for gently agitating or stirring the stock 3 and the ink particles are removed therefrom in the same manner as described above in relation to Figure 2.

In a further embodiment, the container arrangement shown in Figure 1 may be used in the storage vessel 22 shown in Figure 3 to remove the dispersed ink particles from the stock contained therein, with the rotor 23 of the storage vessel 22 agitating or stirring the stock 3.

Common papermaking chemicals may be added to the stock. In particular, a chemical agent for dispersing ink from the fibre, for example Enessco P (Trade Mark), as well as a chemical which prevents redeposition of the ink onto the fibre, for example sodium carboxy methylcellulose (SCMC) may be added.

One example of preferred operating conditions of the examples shown in Figures 1 and 2 is as follows:-

Stock temperature 10 to 80°C;

Stock consistency 2 to 10%, and preferably 4 to 8%;

0.01 - 3% addition of SCMC or similar agent for the prevention of redeposition of ink onto the fibre;

0 - 5% addition of inorganic filler particles, such as talc, china clay, whiting, to absorb any free ink in the system.

The invention is particularly suitable for removing ink from low consistency stock of, for example, 2 to 10% paper fibres in water. However, the invention could be used for high consistency stock, for example of 10-30%, which has been pulped in the hydropulper and then trans¬ ferred to the stock chest and has been diluted either prior to or in the stock chest before the ink particles are removed.

The present invention thus enables, a pulper, such as a hydropulper or low consistency batch pulper, to be used as a combined pulper/primary flotation cell, where in practice some 50-60% of the ink is separated and removed from the slushed stock at a consistency of between 4-8%. Additionally or alternatively, the present invention ena¬ bles a storage vessel, such as a stock chest, to be used as a combined stock chest/primary flotation cell. In either case, the invention is rendered particularly useful in mills where floor space is at a premium and where there is a limited budget, so that the use of conventional separate flotation cells is not possible.

Such an invention serves four main purposes:

(1) it enables more mills which are without, or unable to afford, the more expensive traditional flotation deink- ing cells, to use and recycle inky waste paper;

(2) it produces a far superior product, in terms of brightness and speck reduction, to those mills presently using inky waste paper without deinking equipment;

(3) even where mills already have the more traditional deinking equipment, deinking at the initial stages of the recycling process can prevent 50-60% of the ink going into the normally recycled backwater, giving better white water clarity by preventing the carrying of ink through the first half of the system;

(4) it provides a cleaner stock at the beginning of the recycling operation, which in paper recycling is a highly desirable objective.

Whilst various embodiments of the invention have been described, it will be appreciated that other modifica¬ tions may be made without departing from the scope of the invention, as defined in the appended claims.

Claims

CIAIMS

1. A method for removing ink from waste paper materi¬ al, the method comprising pulping the waste paper material in a pulping vessel (1) to form a slushed fibrous stock (3), dispersing ink particles within the fibrous stock (3) , and removing the dispersed ink particles from the stock (3), characterised in that the removal of dispersed ink particles is carried out in the pulping vessel (1) and/or in a storage vessel (22) to which the stock (3) is passed from the pulping vessel (1).

2. A method as claimed in claim 1, wherein the dis¬ persed ink particles are removed from the stock (3) in the pulping vessel (1) and/or the storage vessel (22) by suc¬ tion using vacuum means (10).

3. A method as claimed in claim 1, wherein the dis¬ persed ink particles are removed by means of a container (4) supported in the pulping vessel (1) and/or storage vessel (22) and having a perforated wall structure such that, when the stock (3) is stirred or agitated, ink parti¬ cles circulating in the stock (3) can pass through the perforations into the container (4) but the fibres forming the stock (3) are substantially prevented from passing through the perforations.

4. A method as claimed in claim 1, 2 or 3, wherein in order to assist the speed of ink removal, at least one stream of air, water, or air and water is introduced into the pulping vessel (1) and/or storage vessel (22).

5. A method as claimed in any preceding claim, where¬ in, when ink particles are removed in the pulping vessel (1), the waste paper material is stirred or agitated within the pulping vessel (1) and/or storage vessel (22) alternately at a first speed to effect the pulping and encourage the dispersal of ink particles within the fibrous stock (3) , and at a second speed lower than the first speed to remove dispersed ink particles.

6. A method as claimed in any preceding claim, wherein common paper making chemicals are added into the fibrous stock in the pulping vessel (1) and/or storage vessel (22).

7. A method as claimed in claim 6, wherein one or more of the following chemicals are added:- a chemical agent for dispersing ink particles within the fibrous stock; a chemi¬ cal which prevent redeposition of the ink particles onto the fibrous stock; and inorganic filter particles to absorb any free ink particles in the vessel (1;22).

8. Apparatus for removing ink from waste paper materi¬ al, the apparatus comprising a pulping vessel (1) for containing the waste paper material and for pulping the waste paper material to a slushed fibrous stock (3) and dispersing ink particles within the stock (3) , said appara¬ tus including means (4,5; 10,11) for removing dispersed ink particles from the stock (3), characterised in that said ink removal means (4,5; 10,11) are arranged to remove dispersed ink particles from the stock (3) whilst it is contained in the pulping vessel (1) and/or to remove dis¬ persed ink particles from the stock (3) whilst it is con¬ tained in a storage vessel (22) to which it has passed from the pulping vessel (1).

9. Apparatus as claimed in claim 8, wherein the in removal means (4,5; 10,11) consist of vacuum means (10,11) arranged to be used in the pulping vessel (1) and/or th storage vessel (22).

10. Apparatus as claimed in claim 9, wherein the vacuu means (10,11) comprises a vacuum device (10) having suction tube (11) which is arranged to be lowered into, an lifted out of, the pulping vessel (1) and/or storage vesse (22). 11. Apparatus as claimed in claim 8, wherein the ink removal means (4,5; 10,

11) comprises a container (4) sup¬ ported in the pulping vessel (1) and/or storage vessel (22), said container (4) having a perforated wall structure such that ink particles circulating in the stock (3) as it is stirred or agitated by a stirring device ( ) mounted in said pulping vessel (1) or storage vessel (11) can pass through said perforations into said container (4) but the fibres forming said stock (3) are substantially prevented from passing through said perforations.

12. Apparatus as claimed in claim 11, wherein the vessel (1 or 22) is substantially circular in cross-sec¬ tion, and the stirring device (2 or 23) is mounted in the base of the vessel (1 or 22) such that a central vortex is created in use of the stirring device (2 or 23) .

13. Apparatus as claimed in claim 11 or 12, wherein the perforated container (4) is supported above the stirring device (2 or 23), and the apparatus includes means (7) for lowering the container (4) into, and raising it out of, the vessel (1 or 22) .

14. Apparatus as claimed in claim 11, 12 or 13, wherein the container (4) is in the form of a basket, in which the perforated wall structure comprises a mesh material.

15. Apparatus as claimed in claim 11, 12, 13 or 14, wherein the ink removal means (4,5) includes a mechanism (5) for removing the ink particles from the container (4).

16. Apparatus as claimed in any one of claims 9 to 15, including means (8,9) for introducing at least one stream of air, water, or air and water, into the pulping vessel (1) or storage vessel (11).