WO2012017178A1 - Deinking process and installation for the implementation thereof - Google Patents

Abstract

Deinking process with a view to recycling wastepaper, consisting in mixing the wastepaper with water and, through a pulping operation (1), in disintegrating this wastepaper and obtaining a paper pulp, followed by an operation of fractionating this paper pulp into a retentate fraction (8) containing contaminants, and a filtrate fraction (9) containing free or small-sized inks and adhesives, characterized in that: - the retentate fraction (8) is subjected to an operation (3) for detachment and/or division of the contaminants; - the filtrate fraction (9) is subjected to a multistage flotation (4) for the entrainment, in at least a first stage, of one portion at least of the free or small-sized inks and adhesives by air bubbles originating from a lower flotation stage; - during this multistage flotation operation (4), at a stage lower than the first stage, the retentate fraction (8), on exiting the contaminant detachment and/or division operation (3), is mixed with the filtrate fraction (9).

Description

 METHOD OF DISENGAGING AND INSTALLATION FOR ITS IMPLEMENTATION

The invention relates to a method and an installation for implementing this method for deinking in order to recycle waste paper.

 The present invention is in the field of processing for the recovery of recovered paper.

 In particular, old paper or recovered paper can be recycled into new papers thanks to facilities to purify these old papers.

 In a usual manner, the method used by these facilities consists, first of all, in mixing these waste paper with water in a pulper, while adding suitable chemical agents. The paper is then broken down mechanically and the cellulose fibers are resuspended in water before the various operations to release it from its various contaminants take place. Thus, density gap separation principles are applied to discern the heavy components of the light components. Similarly, filtration means are frequently used to separate the particles according to their size. Thus, for example, pressurized scrubbers with slotted or hole screens or even scrubbers can be used to perform this function. Finally, dispersed air flotation cells take advantage of the distinct hydrophobic properties of the components present to ensure deinking.

 The various operations mentioned above are usually carried out behind each other on a processing line sized to treat the overall flow of paper pulp.

In the more specific case of inked paper recycling (newspaper, magazine, office paper, ...), the removal of the ink as a contaminant has priority: it is the "deinking" process. This ink is deposited on the surface of the paper when printed. If this surface of the paper is composed only of fibers, the ink will be deposited on them. On the other hand, if this surface of the paper comprises a layer of fillers (calcium carbonate, kaolin, etc.), the ink will be deposited on the latter and not directly on the fibers.

 If there are multiple printing processes (offset, helio, flexo, ...) on various paper media, both have consequences for deinking operations when recycling paper.

 Anyway, when pulping recycled paper, paper components separate by hydration and mechanical shocks. Among these components are: cellulose fibers, whether long, medium or short, fines, mainly composed of cellulose fragments too small to qualify as fiber, mineral fillers and contaminants that are, for example, plastic particles, wood sticks, inks and stickies, which are adhesive residues.

 However, the separation is rarely total. Thus, fibers can remain aggregated in the form of pellets, so that they may be evacuated during sieving steps, thus representing a loss of material. Charges can also remain agglomerated in the form of clusters or pellets and may be non-recoverable because involuntarily evacuated during the cyclone purification steps. Conversely, for adhesives that do not disperse and remain agglomerated in particles of several hundred microns, their separation of the fibers is facilitated during the sieve purification steps.

 As regards the inks, they do not fragment completely and, as the case may be, the operating mode changes.

Ink broken up into small invisible particles (<50microns) can be removed by flotation or washing. Conversely, flotation is inefficient on the ink remained in the form of large particles, called black dots. This means eliminating these black spots through cyclones or reduce them by fragmentation in a slow-acting or fast-swapper apparatus to give them the correct size for disposal by a second flotation or washing.

 Consequently, the traditional two-loop deinking process comprises, among others, a pulping step, a first flotation step, called pre-flotation step, a trituration or dispersion step to break the ink particles that are too large to float in the state, then a second flotation, called post flotation.

 In addition, the pulper and the chemistry used also have the function of detaching the ink from the fibers and / or particles of fillers composing the layer on which this ink has been deposited. However, at the output of the pulp, there is necessarily fibers with ink inked and clusters of inked charges. During the pre flotation, these inks still hooked can not be eliminated and trituration or dispersion will allow to perform this additional stall before post flotation.

 The same problem arises for the adhesive deposits on the papers. In the same way as inks, adhesives can remain attached to fibers or clusters of charges and are therefore difficult to remove by pre-flotation. Here again, trituration or dispersion is necessary to improve their subsequent elimination.

Thus this known method, often called "two-loop", completes the effect of the pulper for the stall of inks and hydrophobic adhesives of fibers and clusters of layer fillers. But it is very expensive because during the various operations of this process, the entire flow of pulp is treated systematically. Thus, it undergoes a pre-flotation after being diluted to about 12 grams of dry matter per liter of water (12g / l), operation to remove about 80% of the ink that contained this pulp initially . Then the whole of this stream is thickened to obtain a paste containing approximately 250 to 400 gram of dry matter per liter of water, (250-400g / l). It is then triturated-dispersed before being diluted again in the same proportions as before, that is to say to obtain a concentration at about 12 g / l before the post flotation for the removal of inks and adhesives which have been previously released.

 Sometimes the flotation is completed or replaced by washing whose role is also to eliminate small ink particles.

 In order to simplify this process, certain technologies have been developed to treat, in a differentiated manner, the dough fraction containing the majority of long fibers, greater than about 100 mesh, and the dough fraction composed essentially of short fibers and fine elements, such as ink particles, mineral fillers (calcium carbonate, kaolin, ...), cellulosic fines and small adhesives.

 In the usual manner, the elimination of the ink in each of these pulp fractions to be treated is obtained by a flotation step which, as recalled above, makes use of the hydrophobic properties of the ink particles by in relation to fibers and particles of pulp.

 In this regard, it is particularly known document EP-0.092.124 which discloses the principle of fractionation of pulp to obtain a so-called clean fraction composed of noble fibers and a so-called dirty fraction composed essentially of fine elements , including ink particles.

 However, prior to this fractionation, the process as described in this prior document, provides a trituration step applied to the entire flow of the pulp to be treated, this to pick up the ink of the fibers on which it remained hung, despite the initial operation of pulpage.

EP-0 261 025 also discloses a process for treating waste paper which, apart from the pulping and pre-purification operations, provides for a fractionation of the pulp into long fibers and short fibers. On this last fraction of short fiber pulp is applied a flotation step in that it contains essentially free inks, ie not hooked on fibers.

 As for the other fraction consisting mainly of long fibers, it contains a small amount of ink adhering to these fibers, adhesives, plastics, moderately bulky particles and fillers. This long fiber fraction successively undergoes a heat treatment, a fine purification and a thickening-washing. The purpose of the heat treatment is to detach the contaminants adhering to the fibers under the effect of intense friction, fiber on fiber.

 Raising a temperature favors the softening and agglomeration of certain contaminants, especially heat-fusible materials. Essentially, this heat treatment comprises a thickening phase and a trituration phase.

 In fact, the defect of the process consists in that the washing step only makes it possible to separate the inks removed from the fibers with difficulty. Also, a convincing result can only be obtained with several washing steps under high dilution.

 It is known from document US Pat. No. 4,332,638, a pulp treatment process again providing for a fractionation between long fibers and short fibers, on each of the fractions being applied a flotation operation in separate plants, the fraction long fiber further undergoing and prior to flotation a new crushing operation to pick the ink remained hung on these fibers.

 Even if this solution makes it possible to obtain good results, the flotation steps applied to each of the fractions require separate installations representing a significant investment cost.

Various techniques are currently used to remove the ink particles by flotation. At this By way of example, EP-0 674 040 discloses a process for de-inking pulp in which a stream of pulp is circulated up and down and, in the opposite direction, from bottom to top, a flow of bubbles. of air, knowing that the mass of paper pulp undergoes successive recycling steps in stages located one above the other in the same cell.

 In short, the flow of air bubbles, injected at the bottom of the cell, passes successively, in each stage, the mass of pulp, which enters, at the level of a stage, by an inlet to be taken from it. down at the level of an exit, in order to be reinjected at the height of the entry of the next stage placed immediately below.

 Possibly pumps can ensure the recovery of the pulp on each floor, knowing that at this level can also intervene a new injection of air, if necessary.

 In the upper part of the cell is recovered the foam that has formed therein entrained the ink particles.

 Such flotation cells have been found to be particularly effective and of high efficiency in comparison to facilities having, for each flotation stage, separate processing units installed side by side.

 It is still known from EP 1.798.329 to carry out a pulping operation consisting in breaking up the old paper into the fiber state. Then, beyond a washing unit, it follows a fractionation operation of this pulp in a suitable unit from which a coarse fraction and a fine fraction that can be respectively assimilated to the retentate fraction and the filtrate fraction.

If the filtrate directly joins a flotation unit, the retentate goes through a thickening step, then dispersing before being diluted again to enter a washing unit from where it leaves, again, two fractions of which one called "Guntstoff A2" and another filtrate, referenced R2 in this document. This fraction filtrate R2 joins, being mixed, the fine fraction before all is injected into the flotation unit. In a second embodiment, visible in FIG. 2, the retentate or the coarse fraction, beyond the state of thickening, then of dispersion and dilution, does not pass through the washing unit, but joins, there again, the fine fraction or filtrate before the mixture thus produced is injected into the flotation unit.

 In the embodiment corresponding to FIG. 9 of this document EP 1.798.329, it is further provided, after fractionation, to dilute the retentate in the context of a flotation operation from which there emerges a rejection, referenced R23 in this document. document, which is mixed with the fine fraction. The mixture thus obtained undergoes a new flotation operation.

 The present invention aims to rationalize waste paper deinking facilities through the implementation of an optimized treatment process.

 Thus, the treatment method provides, beyond the initial pulping step, a new step of fractionating the inks and adhesives and not fractionation of the fibers. The purpose of this operation is to separate the inks and adhesives agglomerated between them or attached to the fibers or clusters of fibers or fillers, inks or adhesives free or small.

 In this regard, the fraction retained during this fractionation operation and containing the inks and adhesives hung is called, hereinafter, the retentate, while the filtered fraction containing the free elements, is called the filtrate.

 Moreover, the retentate alone subsequently undergoes stalling and reducing the size of the inks and adhesives, while the filtrate bypasses this step.

By avoiding subjecting all the paper pulp to such a trituration or dispersion step to finally act on a reduced quantity of material still contaminated with ink hung or agglomerated, it results in improved energy efficiency. Concretely, this fractionation of inks and adhesives with creation of a retentate and a filtrate can be obtained by using a purifier equipped with a sieve with small holes or small slots or a scrubber. The setting of the apparatus will be adjusted to maximize the separation of the agglomerated inks and adhesives, whether attached or free, without presupposing the distribution of the fibrous material.

 According to the invention, it has been imagined to take advantage of a staged flotation plant, to treat the entire flow of pulp.

 It is in fact by going against the uses of a person skilled in the art preferring to treat, after fractionation, each fraction in separate deinking units, that it was thought to treat them in a single stage flotation unit. . In addition it is in the context of an inventive step that we thought to take advantage of this multi-stage flotation unit to introduce the latter to the most suitable floor. Very concretely, it has been thought to mix the retentate fraction with the filtrate fraction at a stage lower than the first stage. It is thus a filtrate fraction which is not that resulting from the initial fractionation operation, but that which has already undergone at least one flotation stage and, thus, rid of at least a part of its contaminants. .

 It follows that the invention not only allows the design of facilities with improved energy efficiency, but also a lower cost.

To this end, the invention relates to a deinking process for the recycling of waste paper, comprising mixing the old paper with water and, through a pulping operation, disintegrating the old paper into the paper. state of fibers and particles and obtain a pulp, followed by a fractionation operation of this pulp into a retentate fraction containing contaminants in the form of inks and adhesives agglomerated with each other or hung on the fibers or on the clusters fibers or fillers, and a filtrate fraction containing free or small inks and adhesives characterized by the fact that:

 the retentate fraction is subjected to an operation of stalling and / or division of the contaminants;

 the filtrate fraction is subjected to a multistage flotation operation for the entrainment, in at least a first stage, of at least a portion of the free or small inks and adhesives by air bubbles coming from a lower flotation stage;

 during this multistage flotation operation, at a stage below the first stage, the retentate fraction at the outlet of the stall and / or contaminant splitting operation is mixed with the filtrate fraction.

 The invention also relates to an installation for implementing the method comprising at least one pulverization unit, at least one fractionation unit and at least one trituration unit for subjecting, at the outlet of the fractionation unit, a retentate fraction. (8), to an ink stalling operation, said trituration unit (10) being connected to a flotation unit to which the fractionation unit is further connected for conveying, from the latter, a filtrate fraction, characterized by the fact that the flotation unit is multi-staged, the fractionation unit being connected to the inlet of a first stage of the flotation unit, while the crushing unit is connected to the inlet of the flotation unit; one of the stages following the first stage of said flotation unit.

 The invention will be better understood on reading the description which follows, referring to an exemplary embodiment and whose understanding will be facilitated by referring to the accompanying drawings.

 FIG. 1 is a schematic representation of the steps of the method according to the invention;

- Figure 2 is a schematic representation of an installation implementing this method; - Figure 3 is a similar schematic representation, illustrating the flotation cell, not in the form of a circular cell, but a substantially elongated structure.

 As shown in the diagrams of the accompanying figures, the present invention is in the field of the treatment of waste paper for recycling.

 Thus, the invention relates more particularly to a process for treating waste paper whose purpose is to deink it so that it can be reused.

 Thus, the method consists, in the usual way, of mixing the old paper with water and, through a pulping operation 1, to disintegrate this old paper in the form of fibers and particles, while staining , to a large extent, the ink and adhesives hung on this paper.

 At the end of the pulping operation 1 and in a second essential operation, the pulp 2 is fractionated so as to obtain a retentate fraction and a filtrate fraction.

 This fractionation 2, obtainable by a washing operation and / or sieving in a unit comprising a sieve, either slotted or with holes, makes it possible to distribute in the retentate inks and adhesives agglomerated or hung on particles large size material (fibers, layer pellets, ...) and in the filtrate the fraction containing small inks and adhesives, called free.

 Also, on the retentate fraction, is applied an operation of stalling ink and adhesives 3, an operation that can be conducted using various technical solutions, whether by fast-speed dispersion or trituration at slow speed, with or without whitening chemistry, with or without heating improving stall.

According to another feature of the invention, on the filtrate fraction 9 is applied a flotation operation 3, of multi-stage type, knowing that to this fraction is added the retentate fraction 8, after the operation of stall 3, beyond at least a first stage of this flotation step.

 In particular, insofar as the retentate fraction no longer contains a reduced proportion of ink inked, after trituration this fraction necessarily contains a proportion of free ink in an amount less than the filtrate fraction. Also, the amount of loose ink present in the retentate being much less than the amount of free ink in the filtrate, it is necessary to apply a more intense flotation on the filtrate than on the retentate. It is for this reason and to avoid dilution as will be explained further in the description, that this retentate fraction 8 is mixed with the filtrate fraction 9, at a lower stage of the flotation unit.

 In addition the retentate fraction containing many long fibers, it is not possible to apply a flotation action to a concentration greater than 14g / l. Beyond this, the viscosity of the paste would be such that the air bubbles could not separate from the paste and the removal efficiency of the hydrophobic particles (ink, stickies) would be very degraded. Conversely, the filtrate fraction contains very few long fibers so it is possible to float it thicker in order to reduce the size of the required installation. For example, filtrates at a concentration of 15 to 20 g / l can be injected into the first cell stage without degrading the flotation efficiency. Or one can conversely further dilute this fraction of filtrate, for example between 5 and 10 g / l, in order to maximize the effect of a bubble washing operation that can occur at the top of the cell. flotation.

The advantages resulting from the process according to the invention consist in an energy optimization insofar as only the fraction of paper pulp likely to contain inked particles or adhesives hanging, undergoes a complementary operation to pick up these particles, operation requiring, obviously, a contribution of energy to obtain the expected result. Furthermore, rather than providing two flotation facilities for the removal of the particles in each of the retentate-filtrate fractions, solution having been adopted beforehand, in the context of the present invention, it is again used to mix the fractions to remove the hydrophobic particles through a single flotation operation.

 More particularly advantageously, it again comes to optimize this flotation by executing it by floor and finally injecting into the most appropriate stage, the retentate fraction, less loaded free hydrophobic particles.

 The invention also relates to an installation for implementing the method above, according to the invention. This installation, referenced hereinafter in the description, essentially comprises a pulverizing unit 6, consisting in breaking up the old paper into water so as to form a paste of old paper contaminated with hydrophobic particles such as inks or adhesives, or even other elements.

This installation 5 further comprises a fractionation unit 7 which may be a washing and / or filtration unit intended to separate the retentate fraction 8, for example comprising inks and adhesives agglomerated or hung on long fibers, of size greater than 150. microns, a filtrate fraction 9, composed of free inks and fine elements less than 150 microns in size and containing the ink particles or adhesives that were removed during the pulpage operation 1 and, possibly, other elements still contaminating. As an indication, the fractionation unit 7 of filtration type, may comprise slotted screens or microperforated type. In the first case, the slots will preferably have a dimension of less than 0.1 mm and a smooth sieve surface or with a profile height of less than 1 mm, whereas a micro-perforated sieve will advantageously have perforations between 0 , 1 and 0.8 mm. The installation 5 further comprises a unit 10 called "trituration-dispersion" supporting the retentate fraction 8 of the pulp.

 This crushing unit 10, whatever the technical solution adopted, will aim to subject the fibers and other clusters and large particles to an action of friction or impact with the consequence of stalling inks and adhesives remained hooked or agglomerated after pulping.

 At the outlet of the crushing unit 10, this retentate fraction 8 necessarily comprises fibers and free ink particles, adhesives and other contaminants which must be evacuated.

 In this regard, the installation 5 necessarily comprises a flotation unit 11, taking advantage of the more or less hydrophobic nature of the particles in the presence to remove some of them, in this case the particles of ink and water. adhesives.

 The principle applied in such a flotation unit 11 preferably consists in passing the flow of pulp entering this flotation unit.

11 to a flow of air bubbles which, in contact with the hydrophobic particles, causes the latter.

 Advantageously this flotation unit 11 has stages 12, 12A, 12B, 12C so that the flow of air bubbles passes through several times, the flow of pulp to be treated to increase the probability of encounter between these air bubbles and particles and ensure the training of the latter.

 In FIGS. 2 and 3 of the accompanying drawings, two embodiments of this flotation unit 11 are illustrated.

Thus, according to the first embodiment shown in FIG. 2, this flotation unit 11 may be as described in document EP-0 674 040. In particular, it may be of cylindrical shape, comprising, from top to bottom , several inlet ports E _lr E ₂ , E ₃ , E ₄ , as well as several outlets. If, S ₂ , S ₃ , S ₄ . At each inlet orifice E ₁ , E ₂ , E ₃ , E ₄ , there corresponds such an outlet orifice Si, S ₂ , S ₃ , S ₄ , respectively, placed below, knowing that an outlet orifice of one stage 12, 12A, 12B is connected to the input port of the next stage 12A, 12B, 12C (Si to E ₂ , S ₂ to E ₃ , S ₃ to E ₄ ). From the outlet S ₄ of the last stage 12C flows, of course, the paper pulp freed of its hydrophobic particles.

 In the upper part, the flotation unit 11 further comprises one or more orifices M for the evacuation of the foam formed by the air bubbles having passed through the various stages 12, 12A, 12B, 12C, a foam retaining the hydrophobic particles.

 Note that at this upper part of the flotation unit 11, this foam may undergo a washing operation having the effect of retaining the pulp particles entrained by the air bubbles at the same time as the particles hydrophobic, this in order to reduce losses.

 Furthermore, at each of the connections between an outlet of a stage 12, 12A, 12B and an inlet port of the next stage 12A, 12B, 12C, a recirculation pump may be installed. Similarly, if the injection of air I is preferentially involved in the lower part of the flotation unit 11, such air injections can be made, also, at these connections, between the exit of a stage and the entrance of the next stage, or even the level of recirculation pumps between floors.

 Of course, this flotation unit can still borrow other embodiments, such as those mentioned in EP-0 674 040.

FIG. 3 further shows a flotation unit 11 in the form of a longitudinally arranged cell comprising, again, a chamber of parallelepipedal shape subdivided, vertically, in stages 12, 12A, 12B, 12C via plates Pi, P ₂ , P ₃ with slots f through which the air bubbles of a lower floor, can enter the upper storey and cross the flow of pulp flowing through it.

 Specifically, at each stage 12, 12A, 12B, the pulp flow enters an inlet port at a lateral end of the flotation unit 11 to exit at an orifice of exit at the opposite lateral end and regain, at this same lateral end and through an inlet port, the next stage 12A, 12B, 12C and so on.

 The retentate fraction 8, previously separated from the filtrate fraction 9, is, after trituration, mixed, again, with the latter at the level of the flotation unit 11.

 According to the invention, this mixing takes place beyond a first stage of the flotation unit 11, thus at the height of one of the following stages 12A, 12B, 12C, ie at a stage where the pulp already contained in the flotation unit 11 has reached a degree of purity equivalent to that contained in this retentate fraction 8.

Thus, if the fractionation unit (7) is connected to the inlet (Εχ) of the first stage (12) of the flotation unit (11), the crushing unit (10) is connected to the inlet (E ₂ ) and / or (E ₃ ) and / or (E ₄ ) of one of the stages (12A, 12B, 12C) following the first stage (12) of this flotation unit (11).

The main consequence of this procedure is that on the first stage 12 of the flotation unit 11, a pulp stream corresponding exclusively to the filtrate fraction 9 and containing the largest proportion of pulp is finally treated. free hydrophobic particles. Consequently, on this first stage, the air bubbles, coming from the lower stage (s), will retain the most important proportion of these particles, whereas at the level of the following stages the addition of the retentate fraction has not as a consequence of diluting the flow, if by dilution means the reduction of the rate of ink particles contained in the flow of dough. The injection beyond the first stage in the flotation cell of the dispersed retentate relative to the filtrate makes it possible to flotation the filtrate at a concentration different from the maximum concentration of 14 g / l of the retentate containing the majority of long fibers. If we want to maximize the washing of the bubbles we will use a more dilute filtrate than the triturated and / or dispersed retentate fraction; if we want to minimize the size of the cell we will use a thicker filtrate than the retentate fraction triturated and / or dispersed.

 It will be noted, however, that according to a preferred embodiment of the invention, the retentate fraction (8) is mixed with the filtrate fraction (9) beyond the first two stages of the flotation operation (4). In sum, the filtrate fraction (9) will have passed through two stages in the flotation cell before the retentate fraction (8) has been added to it.

 Moreover, this filtrate fraction (9) and the retentate fraction (8), once mixed, are advantageously subjected to at least two additional flotation stages.

 As can be seen from the foregoing description, the present invention brings about a clear technical progress in the field of the treatment of waste paper.

Claims

1. A process for deinking in order to recycle waste paper, comprising mixing the old paper with water and, through a pulping operation (1), disintegrating the old paper into fibers and particles and obtain a paper pulp, followed by a fractionation operation of this pulp into a retentate fraction (8) containing contaminants in the form of inks and adhesives agglomerated with each other or hung on the fibers or clusters of fibers or fillers, and a filtrate fraction (9) containing free or small inks and adhesives, characterized by the fact that:  the retentate fraction (8) is subjected to an operation (3) of stalling and / or splitting of the contaminants;  the filtrate fraction (9) is subjected to a multistage flotation operation (4) for the entrainment, in at least a first stage, of at least a portion of the inks or adhesives which are free or of small size by air from a lower flotation stage;  during this multistage flotation operation (4), at a stage below the first stage, the retentate fraction (8) at the outlet of the stall operation (3) is mixed with the filtrate fraction (9) and / or division of contaminants.  2. Process according to claim 1, characterized in that the retentate fraction (8) is mixed with the filtrate fraction (9) beyond the first two stages of the flotation operation (4).  3. Method according to claim 1 or 2, characterized in that the mixed filtrate fraction (9) and the retentate fraction (8) are subjected to at least two additional flotation stages. 4. Installation for carrying out the method according to any one of the preceding claims comprising at least one pulping unit (6), at least one unit of fractionation (7) and at least one crushing unit (10) for subjecting, at the outlet of the fractionation unit (7), a retentate fraction (8) to an ink stalling operation (3), said unit crushing unit (10) being connected to a flotation unit (11) to which the fractionation unit (7) is further connected for conveying therefrom a filtrate fraction (9), characterized in that the unit of flotation (11) is multi-stage (12, 12A, 12B, 12C), the fractionation unit (7) being connected to the inlet (Ei) of a first stage (12) of the flotation unit (11), while the crushing unit (10) is connected to the inlet (E ₂ ) and / or (E ₃ ) and / or (E ₄ ) of one of the stages (12A, 12B, 12C) following the first stage (12) of said flotation unit (11).