ES2321990T3 - PROCEDURE FOR THE ELIMINATION OF THE TENSIANS IN THE COURSE MANUFACTURING COURSE IN MACHINE AND PAPER MACHINE USING THIS PROCEDURE. - Google Patents

Abstract

The process for fabricating a paper (2) on a machine, comprises separating surface-active agents through dispersed air (9) flotation in a wet part, and eliminating flotation foam containing the surface-active agents. The separation of the agents is carried out on all or part of filtration water from the paper formation and on all or part of clear water from a fiber recuperator. Recycled or mechanical slurry is used in the process. The flotation foam is treated with ozone and then evacuated in a purification station and a drainage table. An independent claim is included for a machine with paper.

Description

Procedure to eliminate surfactants in the course of machine paper manufacturing and paper machine that uses this procedure.

Technical field

The present invention relates to a Improved machine papermaking process, as well as to the paper machine adapted for the implementation of said process.

More precisely, the invention uses the dispersed air flotation technique, which allows the waters used in the manufacture of the role of substances surfactants

This results in a better functioning of the paper machine and a higher quality produced paper.

Prior art

It is known that the presence of substances surfactants suffers from numerous drawbacks when it has paper making place.

First, these substances tend to stabilize any air bubbles introduced in the circuits head first, particularly when the pasta is very sheared as in a classifier, a pump, .... This therefore needs to have of deaerator devices generally arranged just before the head box

On the other hand, as surfactants are also responsible for the foam observed in the circuits of head, need the use of antifoam agents, added in Almost all circuits of existing machines.

In addition to these two visible effects (air in the paste and foam), the surfactants remain in the breast of the suspension or process water and accumulate in the head circuits

Accordingly, surfactants can significantly reduce, even annihilate the effectiveness of various chemicals introduced into the machine head, such as bonding agents, retention agents and draining agents ... Thus, the publication " Influence of surface active substances on AKD sizing ", E. Zeno et al, Nordic Pulp and Paper Research Journal, Vol. 20 No. 2/2005, pp. 252-57 refers to the harmful effects of surfactants on bonding. Therefore, its presence can also have very important consequences, on the properties of paper but also on productivity.

There is therefore the obvious need to selectively and effectively remove the surfactants present in the papermaking waters.

The document DE-A-19914779 describes a papermaking process in machine comprising, in the wet part, a floating stage of the white waters as well as a paper machine that comprises, in its wet part, a white water flotation cell.

Object of the invention

First, the invention is referred to by both to a machine papermaking process that it comprises in the wet part at least one stage of separation of the surfactants present in the white waters by dispersed air flotation.

It is understood as "surfactants" chemical compounds that, introduced in a liquid, lower its surface tension, which has the effect of increasing its moisturizing properties

It can be for example fatty acids or nonionic surfactants. These substances are in particular found again in significant quantities in the waters of procedure when the paste used to manufacture the Paper is recycled pulp. Indeed, in addition to the substances added voluntarily when the deintint takes place, others Surfactants are "related" by the papers recovered (surfactants added in the formulation of the inks printing, in the formulation of the layers applied in paper surface for the manufacture of magazine papers) and also related by mechanical pulp fibers when you have place to obtain it (defibrated, refined) or its laundering.

In the present application, it appears that the surfactants have no eventual beneficial effect, even present in small quantity. The objective sought in the framework of the invention is therefore the total elimination of surfactants present in the waters that are used for papermaking in paper machine, after separation.

Within the framework of the invention, the stage of separation of the surfactants is carried out thanks to the dispersed air flotation technique.

This technique involves separating substances surfactants of the water that contains them, dragging them to the surface by insufflation, within the liquid mass, of air bubbles that have a diameter between a few hundred microns and a few millimeters. It results from it a flotation foam rich in isolated surfactants. This foam is then separated from the treated liquid, by aspiration or overflowed for example.

It has been demonstrated in the context of the invention that this technique was the most appropriate, in particular the most selective and the most effective, for the separation of surfactants from Waters intended for the preparation of paper pulp.

Another contribution of the invention has been determine the most judicious points of the manufacturing procedure  of paper in machine, in which the treatment by dispersed air flotation.

Indeed, the separation of this flow must be done minimizing material losses as much as possible in suspension and water losses, the factories being obliged to reduce your water consumption more and more.

Thus, to minimize losses of solids, the treatment is carried out on a low load flow of suspended matters. In addition, to reduce water losses, The surfactant removal procedure should concentrate as much as possible the rejection rich in surfactants.

In general, flotation treatment dispersed air is carried out in all or part of the waters white

In a first embodiment, the stage of separation of surfactants by air flotation dispersed is carried out directly on the filtration waters, that come from the fabric or paper formation table, before recirculation and recycling.

A second possibility, also more effective, it consists in carrying out this flotation by air dispersed on the fiber recovery waters, at the machine head, at the level of White water circuit of the paper machine. The recuperation of the fibers can be made or with the help of a filter of disk, or with a flotation cell by dissolved air. The outflows of this fiber recuperator are therefore impoverished in suspended matter, which allows limiting solid losses.

In practice, dispersed air flotation generates a so-called flotation foam in which substances surfactants are imprisoned in concentrated form. As already mentioned, these foams are intended to be removed after of recovery, classically by overflowing or by aspiration.

A method according to the invention provides for evacuation of this flotation foam directly to a station Debugging Advantageously, the flotation foam is previously treated with ozone, which facilitates the degradation of surfactants

Another possibility is to introduce this flow in the middle of the sludge draining table, to flow the sludge surfactants.

According to a second aspect, the invention is refers to a paper machine adapted for implementation  of the procedure described above.

A paper machine according to the invention is characterized therefore by the presence in its humid part of so least one cell adapted for flotation by dispersed air that allows the separation of the surfactants present in The white waters

In practice, said cell is designed to so that it has contact durations, between bubbles of air and water to be treated, long enough. So, all Surfactants, including slow adsorption kinetics, have time to migrate to the air / water interfaces of the bubbles of air.

The percentage of air introduced into the cell must be large enough for the adsorption surface of the surfactants is sufficient. In a way that minimizes Water losses, several stages are necessary. One of the ways to minimize water losses is also to have a cell with a foam thickness important enough to dry the foam concentrated in surfactants.

The dispersed air flotation cell, such as described above, it is advantageously positioned at white water circuit level, particularly at the level of the filtration waters that come from the formation fabric of the paper, before they are put back into circulation and recycled

Even more advantageously, the cell of flotation is located on the clarified water circuit that come from the fiber recuperator, so that they are minimized material losses.

In addition, the paper machine according to the invention It is advantageously equipped with a recovery system for foams generated by the dispersed air flotation cell. According to a first system, it is a connection between the cell of flotation and a purification station, preferably through of an ozone treatment unit. According to a second Alternatively, the flotation cell is connected to a table drained from sludge.

The present invention relates to any type of paper machines. They are more particularly planned by the present invention, paper machines or procedures that consume small amounts of fresh water, even that they work in closed circuit. It is indeed in these conditions when the waters are more loaded with surfactants

As already mentioned, the invention is also very useful and effective when the paper is formed from pastes recycled (in particular de-inked) or mechanical (pasta of wood,...).

A third application also seems particularly suitable: when the manufacturing of Coated papers from virgin pasta, the procedure can be used on thickened waters, generated when recycling of manufacturing waste that must be made be thickened

The present invention therefore presents advantages at several levels:

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the improved operation of the paper machine;

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the reduction of the flow of chemical products at the head of machine;

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the reduction of airborne defects in the paste (head of pin,...).

Execution Example

The following embodiment example, with the Support of the attached figure, aims to illustrate the invention  but it is not in any way limiting.

Figure 1 illustrates a paper machine according to the invention that allows the performance of the process of manufacture of the advantageous paper as described.

As illustrated in Figure 1, the machine for paper according to the invention it is classically equipped with a head box (1) that ensures a homogeneous distribution of the paste over the entire width of the paper formation table (2), of a Press section (3) to remove water by pressing and of a dryer (4) to remove residual water by evaporation before of the roll of the paper in reel (5).

Filtration water under the formation cloth It is recovered to be recycled and to dilute the paste in the head circuits, before hydrocyclones (6) and machine head classifiers (7) used to eliminate pollutants that have a density greater than 1 on the one hand and pollutants larger than 150-200 \ mum on the other hand.

Filtration water under the formation cloth it is either directly recycled without any treatment, or clarified by the clarifier, in the example a cell of dissolved air flotation (8).

The water flotation treatment, made with the help of an air flotation cell dispersed (9), can then be performed on the all or part of the flow of white water recovered under the formation fabric (9A), either over all or part of the flow of water free of suspended matter, at the exit of clarifier (9B).

Claims (14)

1. Papermaking procedure in machine, which comprises in the wet part at least one stage of separation of surfactants present in water white by floating by dispersed air. 2. Machine paper manufacturing process according to claim 1, characterized in that the step of separating the surfactants is carried out on all or part of the white water. 3. Machine paper manufacturing process according to one of claims 1 and 2, characterized in that the stage of separation of the surfactants is carried out on the filtration waters, exiting the paper forming stage. 4. Machine paper manufacturing process according to one of claims 1 and 2, characterized in that the step of separating the surfactants is carried out on all or part of the clarified waters, exits of a fiber recuperator. 5. Machine paper manufacturing process according to one of the preceding claims, characterized in that it uses recycled or mechanical pulp. 6. Machine paper manufacturing method according to one of the preceding claims, characterized in that it comprises a stage of removal of the flotation foam containing the separated surfactants. 7. Process papermaking machine according to claim 6, characterized in that the flotation froth is treated with ozone before being discharged to a POTW. 8. Machine paper manufacturing method according to claim 6, characterized in that the flotation foam is evacuated at the level of a sludge draining table. 9. Paper machine, which comprises wet at least one dispersed air flotation cell (9A, 9B) that allows the separation of surfactants present in white waters. 10. Paper machine according to claim 9, characterized in that the flotation cell (9A) is located at the exit of the paper formation table (2), and upstream of the white water recirculation circuit. 11. Paper machine according to claim 9, characterized in that the flotation cell (9B) is located on the clarified water circuit, at the exit of a fiber recuperator (8). 12. Paper machine according to one of claims 9 to 11, characterized in that it consumes small amounts of fresh water, even works in a closed circuit. 13. Paper machine according to one of claims 9 to 12, characterized in that the flotation cell (9A, 9B) is connected to a purification station for the evacuation of the flotation foams. 14. Paper machine according to one of claims 9 to 12, characterized in that the flotation cell (9A, 9B) is connected to a sludge draining table.