EP1065314A1 - Process for making paper products - Google Patents

Abstract

During the prodn. stages for a paper material, using a fraction of recycled paper pulp, the acidification stage uses an injection of carbon dioxide into the pulp suspension at a point where the fractions are in the process circuit between the outlet of the pulper (15) for the used paper fraction and the mixing point where the pulp is mixed with fresh pulp. The second stage dilutes the pulp in at least two phases, using clean water which has been injected with carbon dioxide. The clean water is recovered from the papermaking machine or from an external supply such as from the pulp preparation stage and/or cleaned water recovered from other stages. The carbon dioxide is injected pref. at two points in the fraction treatment circuit, on leaving the pulper for the fractions and the end point of the treatment process. The second fraction processing stage has at least one phase where lumps are broken down and/or at least one complementary cleaning phase for the pulp delivered by the pulper (15). The first injection of carbon dioxide is to set the pH at an intermediate level for the grinding and/or cleaning phases. The second injection gives the diluted pulp a pH compatible with the pH level in force during the mixing stage (2). The diluted pulp has a pH value of 5.5-8.5 from the fraction treatment, and the intermediate pH value of the pulp during grinding and/or cleaning is 7.5-9.0 and pref. 8.0-8.5. The carbon dioxide is injected into one and/or more of the points of: Into the clean water used to dilute the fractions (18); into the clean water (20) for dilution at the outlet of the fraction pulper (15); into the clean water for final dilution of the fraction mixed with fresh pulp; into the pulp fraction on leaving the pulper (15) and before the following stages; or into the pulp fraction at the end of the processing but before mixing with fresh pulp. The carbon dioxide is fed by an initial dilution water feed on leaving the pulper to give a pH value of 7.5-9.0 and pref. 8.0-8.5 to the level at the grinder, and by a second dilution water feed between the grinder and the final stage to give a pH value for the diluted pulp equal to the level in force at the pulp mixing stage, where the fraction is mixed with the remainder of the cellulose pulp. The carbon dioxide is fed as a gas or a liquid, or partially a gas and partially a liquid.

Description

The present invention relates to an improvement to the methods of manufacture of paper products with a view to incorporating waste into these products stationers requiring basic treatment, including broken ones.

The papermaking process consists of two successive, distinct parts. The first part is the preparation of the pulp; in this part, we makes pulp from various fibrous materials containing cellulose (wood and / or annual plants) using chemical agents and / or actions mechanical.

The second part is making paper. The term paper actually designates a paper product, it can be for example, and not restrictive, paper for graphic use, wrapping paper, household paper, miscellaneous special papers, as well as cardboard and the like. Both terms will indifferently used in the rest of the text. The starting product of this papermaking is pulp, that is, a suspension of fibers in the water. In order to obtain the paper, the fibers must be dispersed in water and then worked to obtain the desired paper characteristics for the final product, in particular, they must be refined, tangled, dried. During drying, the fibers have the property to adhere naturally to each other. We can also fix on fibers various non-fibrous materials, such as fillers, dyes, starches and other auxiliary products.

This incorporation can be done by adding to the fibrous mat or by deposition on the surface of the sheet of paper; its purpose is to confer on the end product with specific properties specific to its use.

The present invention relates to the second part of the manufacture of the paper, i.e. the process of obtaining the paper product from the pulp to paper.

As indicated above, the paper pulp is obtained from various fibrous cellulosic materials.

When it is obtained from raw materials (wood, plants various) this dough is commonly called "virgin dough", it can be of the type chemical, mechanical, chemical mechanical, chemical thermal ... or other, in depending on the nature of the plants and the mechanical or chemical means used work for its obtaining. It has characteristics linked to its process manufacturing (pH, presence of additives ...).

Virgin pulp may have been made in the factory (integrated factory), it then takes the form of a suspension essentially consisting of cellulosic fibers in water, at a concentration of the order of 4 to 30% by weight.

If the factory does not make the dough, or if it is stored in a way intermediate, this may be in the form of bullets to dryness in general close to 90%. The first papermaking operation will be then put the cellulose fibers in suspension in water. This operation, called disintegration, aims to obtain individual fibers, it is facilitated by the affinity of the fiber for water, affinity due to the numerous OH groups of cellulose.

The pulp used for papermaking can also be a pulp recycled, i.e. pulp from the recycling of old paper, old papers undergoing treatment schematically comprising all or part (in depending on the use for which the recycled pulp is intended) of the pulping steps, coarse purification, deinking, bleaching and other treatments complementary ...

The pulp used in the production of paper comes from very mostly from either of these two origins, or a mixture of pasta of these two origins can include different virgin pasta of nature various and different recycled pasta of various kinds. The term new paste, used by the applicant in the rest of the text, means a mixture of pasta including 0-100% virgin pasta and 0-100% pasta recycled.

In some manufacturing processes, it happens that the types of pasta previously mentioned we add a third type of dough from reincorporation into the paper waste process, notably from the formation of the sheet of paper. This paper waste is called broken; they come in particular from broken leaves, trimmed edges leaves, you can also find papers from various sources, among which, coated papers, uncoated papers, from one or more several paper machines, as well as paper waste from various origins.

In order to be reincorporated into the papermaking process, these paper or broken waste must undergo treatment, which treatment will be named in the following description of the treatment of broken items.

The main steps in making paper from pulp paper are now briefly explained with reference to Figure 1 on which we have schematized the essential operations of the process.

The process described in this figure is presented by way of example not limiting, the steps described do not necessarily always succeed in this order and are not always present in the process; similarly, processes papermakers use steps not described here.

The method according to the invention as will be described later applies broadly to the different papermaking processes in which the pulp passes through a so-called "short circuit" before entering the paper machine.

We can schematically separate the process into two parts: a first part concerns the treatment of the dough, it is mainly carried out in the short circuit or primary circuit in which the dough from the mixing vat is found diluted and purified before entering the paper machine.

The second part of the process is the formation of the leaf, it is made in the paper machine. The paste from the short circuit is injected into the paper machine at the machine head.

More specifically, with reference to Figure 1, the dough previously refined in a refiner 1 is introduced into a mixing tank 2 in which are introduced, in 3, different additional materials including broken, dough manufacturing aids including starch, bonding agents and fillers.

The dough prepared in the mixing tank 2 is then introduced via 4 in the dough castle 5 where it is stored before being introduced into the circuit called short or primary dough preparation circuit.

• des dispositifs d'épuration cyclonique 6, généralement de type hydrocyclone,
• facultativement, des dispositifs destinés à éliminer le gaz contenu dans la pâte diluée pour améliorer l'homogénéité de la pâte introduite dans la caisse de tête de la machine à papier, de façon à ne pas perturber la formation de la feuille. Ces dispositifs sont désignés ci-après par dispositif de type désaérateur 7,
• un dispositif 8 destiné à réaliser une dernière étape d'épuration en vue d'éliminer les dernières particules. Ce dispositif est généralement désigné par "classeur".

This short circuit conventionally includes, but not necessarily a purification step using all or part of the following devices or equivalent devices:

• cyclonic purification devices 6, generally of hydrocyclone type,
• optionally, devices intended to eliminate the gas contained in the diluted pulp in order to improve the homogeneity of the pulp introduced into the headbox of the paper machine, so as not to disturb the formation of the sheet. These devices are referred to below as a deaerator type device 7,
• a device 8 intended to carry out a final purification step in order to eliminate the last particles. This device is generally designated by "filing cabinet".

These three types of device form with the line 9 supplying the aqueous paste dilution vehicle, essential elements of what is conventionally called in the field the short circuit for processing the dough, circuit in which the dough previously prepared and possibly stored in the pulp castle is both purified and diluted properly before introduction into the paper machine 10. Said aqueous vehicle is in particular formed from white water, recovery water from the machine paper 10 and from the drainage of the pulp in the wet section 11 of said machine 10 which typically represent at least 80% and preferably at minus 90% of said vehicle; the balance being made up in particular of process and / or fresh water. In the following specifications, the terms water white, white water and aqueous vehicle will be used indifferently for designate the aqueous vehicle previously described.

The head element 11 of the paper machine 10, also called cash box head, delivers an identical fibrous suspension jet across its width.

The sheet of paper is then formed by depositing the fibers on a canvas; free water is evacuated through the canvas by gravity and possibly using vacuum pumps. This water from the drainage of the dough constitutes what is calls the white waters, mentioned above, and is used in particular in dilution operations of the dough during its circulation in the circuit short previously defined.

This so-called white water contains various fine and varied elements. She contains, in particular, a small proportion of cellulosic fibers which have no were fixed on the sheet during its formation.

When leaving the headbox, the sheet previously formed in said headbox enters section 12 of the paper machine, said section presses where the leaf is wrung out to a dryness of around 40%.

This section of the paper machine consisting of the headbox and the section of the presses constitutes the wet part of the paper machine.

The sheet of paper then enters the dryer section 13 of the paper machine where the remaining water is removed by evaporation to reach a dryness greater than 90%, preferably of the order of 95% or more.

The roughness of the sheet surface is then eventually found corrected in the following sections of the machine.

Thus, the surface roughness of the sheet can be corrected according to the needs by smoothing or calendering, generally achieved by crushing the sheet between cast iron rollers.

Then, in order to improve the state of the surface of the sheet, we deposit furthermore, on its surface, elements, in particular fine pigments and adhesives contained in a composition called coating sauce. Of course, this coating operation is only carried out for certain paper applications, for example for the production of papers intended for writing or printing.

In FIG. 1, sections 13 and 14 show the sections intended for carrying out the coating and finishing of the sheet.

It is obvious that the coating operation is not necessarily performed on the paper machine itself. It may be carried out outside the machine after smoothing the product leaving the paper machine.

As previously stated, it is not uncommon to recover paper waste, generally called broken, from in particular the section of paper machine presses and process them so that they are reintegrated into the papermaking process. Such treatment which in fact depends on the composition of broken and the degree of purification required is not detailed on the diagram of the figure where these broken are recovered in 15 to undergo a treatment intended for allow their re-injection in the form of a properly diluted and refined paste, preferably at the level of the mixing tank 2. This treatment consisting when it exists to recover the broken ones and to make them undergo a treatment intended for them reincorporate as a mixture with the new paste initially introduced into the vat mixture is simply represented by a dotted line on the diagram of the figure 1.

When the simple crushing of this waste in water is not enough to ensure sufficient defibration to allow after proper dilution of reinject the dough obtained directly into the mixing vat, we proceed generally to a preliminary treatment in an alkaline medium carried out in a device conventionally called "pulper" in which the fiber is disintegrated in the presence of a alkaline medium which makes it possible to swell and weaken the fibers which soften, thus making it possible to dissociate the fibers under the action of mechanical agitation.

It is not uncommon, however, and this is particularly the case when treated waste contains ink pellets that need to be forwarded the preliminary treatment in an alkaline medium of a so-called de-tableting treatment allowing to dissociate the ink pellets, so as to reduce their size thus that possibly different purification operations carried out before and / or after the de-tableting operation.

It is indeed well known that paper undergoes on the machine surface treatments intended to give excellent resistance to water and oil treated paper and cardboard. The cohesion of the paper is obtained by formation during drying of low energy hydrogen bonds, but very numerous between fibers.

Rewetting the paper with stirring is generally sufficient to separate the fibers during recycling. This operation called "defibration" or "crushing" is preferably carried out in a low pulper (5%) or medium (15%) concentration and poses no standard problem for untreated papers (newsprint, for example).

Difficulties appear as soon as the paper has been treated with "bonding" type with products intended to limit the penetration of water or resins creating covalent and water-resistant bonds between the fibers.

In the latter cases, it will be necessary to extend the duration of defibration or to use chemical agents intended to destroy bonds covalent between the fibers as well as to materials (de-pastillers) fragmenting by impacts non-disintegrated pieces of paper (tablets).

If the papers are too strong, defibration will not be possible and the fragments of paper not or badly defibrated will then be equivalent to contaminants that will need to be removed from the dough, helping to reduce the material yield.

Defibration is also inevitably accompanied by fragmentation of certain contaminants, which will reduce the effectiveness of their elimination. The evolution of technologies, mainly towards pulpers medium concentration (15%), in the area of deinking meets the objectives to reduce the fragmentation of contaminants, to save energy and increasing the reactivity of the chemicals used.

Figure 2 shows, in more detail, an example of operation made on broken pieces before their reintroduction into the dough. It is given as non-limiting illustration.

In the example given in FIG. 2, the treatment of broken parts consists in a prior treatment with soda as well as in various other treatments which are detailed with reference to Figure 2. The broken ones are then introduced according to the treatment they underwent, either directly in the mixing tank 2, either in the mixing tank after having undergone an operation Complementary refining in the refiner 1.

With reference to this figure, we see that the broken ones coming from the section presses 12 of the paper machine 10 are introduced into the broken pulper 15 by line 16. In this pulper are also introduced soda by the line 17 and a fraction of the white water recovered from the pulp discussed in the head section. This introduction is done through lines 18 and 19 in such a way that one obtains inside the pulper a broken fiber concentration of the order of 15%.

At the outlet of the broken pulper 15, the suspension is then diluted by a new introduction of white water through line 20, so as to bring its concentration to a value of the order of 8%.

This suspension is then subjected to a purification operation 21, then to a de-tableting operation 22 and, finally, to a more fine 23. It should be noted, however, that not all of these successive operations not always necessary, as will emerge from the following description.

Finally, the fiber suspension is again diluted by a new introduction of white water through line 24 to bring it to a concentration generally of the order of 3 to 4% before introducing it either into the mixing tank 2, either in refiner 1 to undergo an operation additional refining before introduction into the mixing tank 2.

In practice, the different successive operations described previously purified and / or de-pelletizing complementary to the pulp produced treatment in a basic environment of broken pieces is not always essential. In fact, the treatment depends on the nature of the broken pieces treated and the degree of purity required for the dough to be treated in the full process.

However, the dough from the broken pieces thus obtained having undergone, or not, all or part of the purification and / or de-tableting treatments is mixed with new to new dough in a mixing vat. Before being added to the dough new, it is diluted to bring its concentration to a value close to that of the new dough in which it is incorporated, for example a value of around 3%.

Because of these dilutions by water with pH often higher than 7 and of the possible addition of chemicals such as soda -whose role is especially to hydrate and swell the fiber, thus destroying the bonds, which allows reduce the subsequent mechanical crushing which damages the fibers, the pH rises at values higher than those of new dough.

The papermakers neutralize this pulp from time to time before trituration in a broken storage tank 25, this neutralization is traditionally done using sulfuric acid, SO ₂ or Al ₂ (SO ₄ ) ₃ with all the problems, in particular of corrosion, of imperfect control of the pH, of sulphate contributions that this entails (the sulphates weaken, for example, the cellulose fiber).

The present invention relates specifically to methods production of paper products in which part of the cellulose pulp used comes from the recovery of paper waste such as broken or assimilated, resulting from the process implemented, or from another type process stationer.

The present invention provides a solution to all of the problems linked to traditional acidification processes for broken wines, especially those exposed previously, and proposes to regulate the pH at the level of the treatment of broken by introduction of carbon dioxide at at least one point of said broken circuit.

• le brevet EP 0 281 273 proposant un procédé d'amélioration de la défibrillation d'une pâte cellulosique alcaline produite par délignification d'une matière cellulosique par ajout de CO₂.
• le brevet EP 0 572 304 décrivant un procédé de collage du papier par le dimère d'alkylcétène ,catalysé par des ions bicarbonates générés par ajout de CO₂.
• la demande internationale WO 98/56988 combinant un hydroxyde de métal alcalin et le dioxyde de carbone pour tamponner une suspension de fibres et produire un papier à partir de la pâte stabilisée.
• la demande de brevet EP 0 884416 décrivant un procédé dans lequel un ajout de CO₂ est effectué pour minimiser l'apport de composés d'aluminium.

We already know a number of improvements to paper manufacturing processes using carbon dioxide, including:

• EP 0 281 273 proposing a process for improving the defibrillation of an alkaline cellulosic pulp produced by delignification of a cellulosic material by adding CO ₂ .
• Patent EP 0 572 304 describing a process for bonding paper with the alkyl ketene dimer, catalyzed by bicarbonate ions generated by adding CO ₂ .
• international application WO 98/56988 combining an alkali metal hydroxide and carbon dioxide to buffer a suspension of fibers and produce a paper from the stabilized pulp.
• patent application EP 0 884416 describing a process in which an addition of CO ₂ is carried out to minimize the supply of aluminum compounds.

However, these methods do not propose the use of anhydride carbon dioxide as a pH regulator in the broken circuit, and does not in no way suggest this use.

• non-dissociation des charges présentes dans les cassés ou bordures sur des papiers couchés ou collés provoqués par des chocs de pH dus à de l'acide fort. Il y a diminution des pertes de charges et donc diminution des charges rajoutées en machine, avec notamment
• absence de sulfates donc de corrosion éventuelle,
• régulation fine du pH (le CO₂ est un acide faible),
• souplesse de mise en oeuvre (pas de pompes doseuses ni de bacs de rétention).

The addition of carbon dioxide as a pH regulator in the treatment of broken products, according to the invention has numerous advantages over sulfuric acid, including:

• non-dissociation of the charges present in the broken or edged on coated or glued papers caused by pH shocks due to strong acid. There is a reduction in pressure losses and therefore a reduction in the charges added to the machine, in particular
• absence of sulphates, therefore possible corrosion,
• fine pH regulation (CO ₂ is a weak acid),
• flexibility of implementation (no dosing pumps or retention tanks).

Patent application EP 0 911 443 describes a process for treating broken pieces of the discontinuous type in which the broken pieces undergo a basic treatment at high temperature in a pulper, then are acidified in one step and diluted in said pulper before being reincorporated. in a papermaking process. It does not provide any solution to the problem which arises for a person skilled in the art who wishes to carry out a fine, flexible pH regulation, adapted to the constraints of the different stages of the treatment of broken products, easy to implement, both during treatments in continuous broken only discontinuously, and whatever the temperature in the pulper 15. In addition, this addition of carbon dioxide at the level of the pulp in the pulper affects the precision of the regulation.
It is to these problems also that the method according to the invention provides solutions.

Thus in particular, and as it appears in the following of the description, the preferred variant of the invention which consists in injecting quantities carbon dioxide directly in the white water of the process used for the dilution of the paste resulting from the preliminary treatment of the broken allows obtain all the advantages listed above with, in addition, increased efficiency, simplicity and flexibility of implementation also increased, which constitutes an additional advantage of the present invention over the art anterior. It allows in particular, from different points of introduction of white water in the circuit, jointly ensuring a consistency of dough and a pH that is best suited for each stage of processing broken pieces, and this so for continuous treatments than for discontinuous treatments, whatever or the temperature in the pulper 15.

The rest of the description will be given with reference to FIGS. 1 and 2 which relate to examples of production of paper products according to art earlier as well as with reference to FIG. 3 which gives a particular example, but not limiting of a preferred embodiment of the invention.

• une première étape consistant en une remise en solution sous agitation et en milieu alcalin des fibres cellulosiques contenues dans les dits cassés, ladite étape étant réalisée dans un pulpeur dit pulpeur à cassés 15,
• puis une deuxième étape, destinée à amener la pâte issue dudit pulpeur 15 à une concentration et à un pH voisin de ceux de la pâte neuve contenue dans le cuvier de mélange 2, ladite deuxième étape comprenant au moins une étape de dilution par des eaux blanches du procédé et au moins une étape d'acidification,

caractérisé en ce que ladite étape d'acidification est réalisée par injection de dioxyde de carbone en au moins un point du circuit de traitement des cassés situé entre la sortie du pulpeur à cassés 15 et le mélange de la pâte issue du traitement des cassés avec la pâte neuve.According to one of its essential characteristics, the invention relates to a process for manufacturing a paper product from cellulosic pulp, part of which comes from the processing of broken products, said broken products having undergone a treatment known as treatment of broken products comprising:

• a first step consisting in re-solution with stirring and in an alkaline medium of the cellulosic fibers contained in the so-called broken pulp, said step being carried out in a pulper known as a broken pulper 15,
• then a second step, intended to bring the pulp from said pulper 15 to a concentration and to a pH close to that of the new pulp contained in the mixing tank 2, said second step comprising at least one step of dilution with white water the process and at least one acidification step,

characterized in that said acidification step is carried out by injecting carbon dioxide at at least one point in the broken processing circuit located between the outlet of the broken pulper 15 and the mixture of the pulp resulting from the broken processing with the new dough.

The first step in dealing with broken items is trituration of these broken, preferably in the presence of white water from different process steps and in an alkaline medium at a pH generally between 8.5 and 13. This trituration step is carried out in what is conventionally called a pulper to broken 15.

As previously explained, the dough from this pulper has broken preferably has a concentration of around 15%. This dough should therefore be diluted to bring it to a suitable concentration, generally 3 at 4% in the mixing tank 2 where the cellulosic paste intended to enter is prepared in the short circuit of the cellulosic pulp preparation process. The mixture dough from broken pieces and new dough used in the process preferably, but not necessarily at this stage of the process.

The pulp from the broken pulper 15 must therefore be diluted. Of a in general, this dilution is carried out by introducing white water from the proceeded in at least one step. This dilution is often carried out in two steps as shown in Figure 2. A greater number of steps dilution can be envisaged without departing from the process of the invention.

In the prior art, an acid such as sulfuric acid, preferably immediately after leaving the pulper broken. This introduction presents the drawbacks exposed above.

Patent application EP 0 911 443, for its part, recommends the introduction of carbon dioxide into the pulper 15 at the end of the mixing step. Proposed in the case of a high temperature treatment, discontinuously, broken in a pulper with broken, acidification with carbon dioxide as described this invention is carried out in the pulper at the end of the middle crushing step alkaline. Carried out under these conditions, it does not however allow a mixture satisfactory carbon dioxide in the medium to be treated. It turns out consumes time and carbon dioxide for a poor result. Of more, limited to batch processing of broken pieces, it does not provide satisfactory solution to the problem posed.

The invention therefore proposes to advantageously replace the modes acidification of the prior art by the introduction of carbon dioxide into the minus one point in the broken circuit after leaving the pulper at broken 15, and this, so as to regulate the pH of the dough during the successive stages of the treatment of broken pieces, until bringing it to a desired pH in the vat of mixture, preferably close to that of the new dough contained in said vat where the said paste will be introduced at the end of the processing of the broken pieces. This pH is generally between 5.5 and 8.5.

The introduction of CO ₂ into the broken-down treatment circuit will take into account the well-known effect of pH on cellulosic fibers. Indeed, it proves to be particularly advantageous to carry out the operations of de-tableting and / or mechanical disintegration before having lowered the pH too considerably, so as not to weaken too much the fiber made more fragile by a more acidic medium. . In fact, in a more acidic environment, the fibers become harder and more fragile. Refining in a more acidic medium leads to an excess of brittle fibers, resulting from shorter fibers and generates many fines. However, the energy required for de-tableting decreases proportionally with the drop in pH.

Furthermore, refining at too high pH levels can lead to yellowing and reversion of the brightness of bleached fibers.

It will therefore be necessary to find the best compromise by achieving, if possible, a progressive acidification allowing precise control of the pH by CO ₂ with if necessary (pH too high) a first regulation after the pulper with broken containing the basic agent and a regulation final at the desired pH for the mixture in the mixing tank 2 so as not to create pH disturbances on the line.

This is why, advantageously, said second step comprises at least two stages of dilution by white water.

According to a particularly advantageous embodiment, the dioxide of carbon is injected into the white water used to dilute the paste obtained broken ones.

Preferably, the white waters used to dilute the dough after the broken include white water recovered from the machine paper and possibly white waters of other origins, especially waters white from the preparation of the dough and / or clarified water from different stages of the process.

Advantageously, the introduction of carbon dioxide is carried out at at least two points in the broken circuit, partly at the outlet of the pulper to broken and partly at the end of treatment of broken.

If the introduction of carbon dioxide can be carried out at any point between the outlet of the pulp for basic processing of broken products and the step of mixing the pulp resulting from broken products with the rest of the cellulose pulp, it is particularly advantageous to carry out this injection of carbon dioxide into the dilution water of the pulp from the broken ones. Indeed, it is well known to those skilled in the art that the introduction of carbon dioxide into a relatively concentrated suspension of fibers requires the use of a specific material of the porous candle type or static mixer intended to obtain the dispersion and dissolving gaseous CO ₂ within this dispersion of fibers. The recommended injection of carbon dioxide directly into the white water used to dilute the paste and, because of the very low solid content of the white water, can be done without using specific injection equipment.

The direct introduction of CO ₂ , into the dilution and purification circuit of the pulp from the broken pieces at two points in the circuit, one located immediately after the exit of the broken pulp and the other at the end of treatment of the broken presents an increased interest in the case where the second step of the treatment of broken includes an additional step of disintegration and / or de-pastillage since it allows to carry out this step at a relatively high pH, with the advantages explained beforehand. which concerns the resistance of the fibers to said treatment.

According to a particular case of the invention, the second stage of processing broken pieces includes at least one step of de-pastillage and / or at least one step additional purification of the pulp from the treatment carried out in the pulper 15.

Advantageously, the carbon dioxide is introduced in at least two points, at a first point so as to obtain a suitable intermediate pH during stages of de-pastillage 22 and / or of purification 21, 23 of said paste and in a second point located after said steps and before the end of the broken circuit of so as to have a pH of the diluted pulp resulting from the treatment of broken pieces substantially compatible with the pH maintained in the mixing tank 2.

In particular, the pH of the diluted paste resulting from the treatment of broken pieces is between 5.5 and 8.5.

According to an advantageous embodiment of the invention, the pH intermediate of the dough during the de-pelletizing step 22 and / or during the steps treatment 21.23 is between 7.5 and 9, and preferably between 8 and 8.5.

• dans les eaux blanches destinées à la dilution des cassés 18,
• dans les eaux blanches 20 pour dilution en sortie du pulpeur à cassés 15,
• dans les eaux blanches 24 pour dilution en fin de traitement des cassés, avant mélange avec la pâte neuve,
• dans la pâte des cassés, en sortie de pulpeur 15 et avant les étapes 21 et/ou 22 et/ou 23,
• dans la pâte des cassés, en fin de traitement des cassés, et avant mélange avec la pâte neuve.

In a judicious manner, carbon dioxide is injected in one and / or in several of the following points:

• in white waters intended for the dilution of broken 18,
• in white water 20 for dilution at the outlet of the pulper to break 15,
• in white water 24 for dilution at the end of the treatment of the broken pieces, before mixing with the new paste,
• in the broken pasta, at the outlet of the pulper 15 and before steps 21 and / or 22 and / or 23,
• in the broken dough, at the end of the broken treatment, and before mixing with the new dough.

In particular, carbon dioxide is advantageously introduced by through a first supply of dilution water after leaving the pulper broken so as to obtain a pH between 7.5 and 9, and preferably 8 and 8.5 at the complementary de-pastillage device for said dough, and by via a second dilution water inlet located between the outlet of this device and the end of the broken circuit so as to have a diluted dough pH resulting from the treatment of broken pieces substantially equal to the pH maintained in the vat of mixing the pulp from the broken with the rest of the cellulosic pulp.

Carbon dioxide can take many forms. It can be essentially in gaseous form. It can be basically under liquid form. It can be partially in gaseous form and partially in liquid form.

The diagram given in Figure 3 presents a special case particularly advantageous of the complete process according to the preparation invention of a paper product into which carbon dioxide is introduced by the white water of the process. The following description is made opposite this figure 3 where the reference numbers indicated correspond to those used for the description of the devices of the prior art according to FIGS. 1 and 2 previous ones.

In this FIG. 3, the steps of treatment of broken pieces from their introduction into the broken pulper 15 up to their re-injection into the mixing tank 2, without trying to represent on this figure all the stages of paper preparation from the pulp prepared in the mixing tank 2.

Broken pieces from the processing stage in the press section 11 from the paper machine are recovered and introduced into the broken pulper 15 where they are treated in an alkaline medium in the presence of white water from different process steps. In this broken pulper 15, the broken pieces from the section of presses 11 and possibly waste of other origins but also requiring treatment in an alkaline medium at a pH between 9 and 13, in the presence of white water from the process. We thus prepare in this pulper to broken a paste generally having a concentration of cellulosic fibers of the order of 15% by weight. This paste then undergoes a first dilution by white water from the process in which we have previously introduced carbon dioxide to bring said paste to a pH generally of the order of 8 to 8.5, then this dough thus diluted is subjected to different stages of complementary treatments shown schematically by block 26. These additional steps may include, in particular, steps such as described with reference to FIG. 2 of primary treatment 21, de-pastillage 22 and of finer purification 23, the cascade of complementary treatments depending on made of the state of the pulp from the broken pieces after the treatment in the broken pulper and the degree of purity sought.

The dough thus treated is then subjected to a second dilution by white water from the process containing carbon dioxide. This white water is introduced into the circuit through line 24.

In the diagram shown in FIG. 3, the CO ₂ is advantageously introduced upstream of the point of separation of the supply of white water intended to carry out the two dilution stages, which makes it possible to proceed with only one CO ₂ injection.

The supply of white water intended for the dilution of the paste obtained of the preliminary treatment of broken parts includes in the case shown in Figure 3 on the one hand, white water from the first stage of preparation of the paper in the headbox 11 of the paper machine. This water is introduced by line 18. It also contains other water from other stages of the process introduced respectively by pipes 27 and 28. These are, by example, other white waters from the thickening step of the dough during washing to remove the various impurities and which leads to the recovery of diluted water.

At the end of the second dilution step, the dough is brought to a pH on the order of that which one seeks to impose in the mixing vat, by for example a pH of 8.0 and a degree of dilution generally of the order of 3 to 4%, dilution which is also that which is carried out in the mixing tank 2.

The following application examples provide a better illustration the invention:

In these examples, the broken ones are of the REH type (wet strength) (it was not carried out during the tests reported here to injections of dioxide of carbon in white waters).

Object of the tests:

This is to compare locations of carbon dioxide injections in the broken circuit and to evaluate the interest of the substitution of the acid sulfuric with carbon dioxide according to the process of the invention.

In this particular case, the processing of the broken presents, at the level of the de-pastillage stage, a loop circuit in which the broken parts are pumped in tank 25 and reinjected between 21 and 22 until the finished product is obtained satisfactory; they are then evacuated to 2 in accordance with FIG. 2.

Implementation :

Test n ° 1 = Point of introduction of CO ₂ to the discharge of the pulper drain pump 15.

Test n ° 2 = Point of introduction of CO ₂ at the delivery of the pump from tank 25 into the loop circuit;

Test # 3 = CO ₂ introduction point at the suction of the pulper drain pump 15.

Results:

Test No. 1 : initial pH of paste of 9.6 (in 15) - Dosed addition of 6 kg of CO2 for 4 minutes (drain time = 2'30) - for a final pH of paste after stabilization of 7.3 (at the outlet of the broken circuit).

Test n ° 2 : initial pH of dough of 10.9 (in 15) - Dosed addition of 8.5 kg of CO2 in 10 min - re-circulation of the dough in the decastor circuit - final pH after stabilization = 7.02 (at the outlet of the broken circuit).

Test # 3 : initial pH of paste of 10.8 (in 15) - Addition of 9 kg of CO2 in 2'30 - final pH after stabilization = 7.45 (at the outlet of the broken circuit)

Results analysis : Location of the injection

Test # 3 is a good compromise between industrial use and good dissolution yield.

A) consommation de H₂SO₄ par pulpeur = 200 litres dilués 12 fois (correspondant à 30kg de H₂SO₄ pur).

B) consommation de CO2 par pulpeur = 9 kg.

Comparison with sulfuric acid : For 106 liters of NaOH at 375 g / l in a 2-ton pulper:

A) consumption of H ₂ SO ₄ per pulper = 200 liters diluted 12 times (corresponding to 30kg of pure H ₂ SO ₄ ).

B) CO2 consumption per pulper = 9 kg.

A saving of 10 kg of acid per tonne of pulp from broken WER.

For a treatment estimated at 10,000 tonnes per year, an saving around 100 T of acid.

These tests illustrate the advantage of the process according to the invention which allows in particular, with an easy implementation and requiring no investment particular, substantial acid savings compared to processes traditionally implemented, (saving 10 kg of acid per tonne of broken REH), with a further decrease in the amount of sulfates in the circuits.

Claims (14)

Process for manufacturing a paper product from cellulosic pulp, part of which comes from broken pieces, said broken pieces having undergone a treatment called treatment of broken pieces comprising: a first step consisting in re-solution with stirring and in an alkaline medium of the cellulosic fibers contained in the so-called broken pulp, said step being carried out in a pulper known as a broken pulper (15), then a second step, intended to bring the pulp from said pulper (15) to a concentration and to a pH close to that of the new pulp contained in the mixing vat (2), said second step comprising at least one dilution step with white water from the process and at least one acidification step, characterized in that said acidification step is carried out by injecting carbon dioxide at at least one point in the broken processing circuit located between the outlet of the broken pulper (15) and the mixture of the pulp resulting from the broken processing with the new dough. Method according to claim 1, characterized in that said second stage comprises at least two stages of dilution by white water. Method according to one of claims 1 or 2, characterized in that carbon dioxide is injected into the white water used to dilute the paste resulting from the treatment of broken. Method according to one of claims 1 to 3, characterized in that said white water used for diluting the pulp from the broken includes white water recovered from the paper machine and possibly white waters of other origins, in particular white waters from the preparation of the paste and / or clarified water from different stages of the process. Method according to one of claims 1 to 4, characterized in that carbon dioxide is introduced at at least two points in the circuit treatment of broken parts, partly at the outlet of the pulper to be broken and partly at the end of treatment of broken Method according to one of claims 1 to 5, characterized in that the second stage of processing broken pieces includes at least one stage of de-pastillage and / or at least one additional purification step for the pulp from the treatment carried out in the pulper (15). Process according to claim 6, characterized in that the dioxide of carbon is introduced at at least two points, at a first point so as to obtain an appropriate intermediate pH during the de-tableting steps (22) and / or purification (21,23) of said paste and at a second point located after said stages and before the end of the broken circuit so as to have a pH of the diluted dough resulting from the treatment of broken pieces that are substantially compatible with the pH maintained in the mixing tank (2). Method according to one of claims 1 to 7, characterized in that the pH of the diluted paste resulting from the treatment of broken pieces is between 5.5 and 8.5. Method according to one of claims 1 to 8 characterized in that the Intermediate pH of the dough during the de-tableting step (22) and / or during purification steps (21,23) is between 7.5 and 9, and preferably between 8 and 8.5. Method according to one of Claims 1 to 9, characterized in that the carbon dioxide is injected at one and / or more of the following points: in white water intended for the dilution of broken (18), in white water (20) for dilution at the outlet of the broken pulper (15), in white water (24) for dilution at the end of the treatment of broken pieces, before mixing with the new paste, in the broken dough, at the outlet of the pulper (15) and before the steps (21 and / or 22 and / or 23), in the broken dough, at the end of the broken treatment, and before mixing with the new dough. Method according to one of Claims 1 to 10, characterized in that that carbon dioxide is introduced via a first arrival dilution water after leaving the pulp of broken pieces so as to obtain a pH between 7.5 and 9, and preferably 8 and 8.5 at the de-tableting device complementary to said dough, and through a second dilution water inlet located between the outlet of this device and the end of the broken so as to have a pH of the diluted pulp resulting from the treatment of broken substantially equal to the pH maintained in the mixing tank of the dough from broken with the rest of the cellulose pulp. Method according to one of claims 1 to 11, characterized in that that carbon dioxide is essentially in gaseous form. Method according to one of claims 1 to 11, characterized in that that carbon dioxide is essentially in liquid form. Method according to one of claims 1 to 11, characterized in that that carbon dioxide is partially in gaseous form and partially in liquid form.

Images