CN1997794B - A method and an arrangement at a paper machine - Google Patents

Abstract

The present invention relates to a method for reducing the spreading of additional agent(s) which is/are introduced into the process at a papermaking machine. A flowable paper pulp including fibres and a process liquid and having a consistency of not more than 10% is conducted towards the paper machine's headbox (5). Prior to the introduction (14) of said additional agent the consistency of the pulp is increased to a value higher than 10% by removing (8) process liquid and conducting (11) it in the upstream direction, while compensating process liquid is introduced (13) downstream. The present invention also relates to an arrangement at a paper machine, where separating means (8) are arranged in the process direction before means (14) for introducing additional agent (s). The arrangement further includes means (11) for conveying process liquid separated from the process in an upstream direction in the process, as well as means (13) for a downstream introduction of process liquid from a short circulation in order to compensate for the separated process liquid.

Description

Method and device for use in a paper machine

technical field

The invention relates to a method in a paper machine for reducing the dispersion of additives added to the process in a continuous process for preparing pulp in a paper machine, whereby a flowable pulp comprising fibers and process liquid and having a viscosity of not more than 10% is guided into the bin of the paper machine. the

The invention also relates to an arrangement in the pulp preparation of a paper machine in order to limit the dispersion of additives in the further process, which comprises a possible An inlet for the flowing pulp, also relates to a closed circulation system comprising a headbox for the paper machine, and means for adding said additives. the

In this patent application, a paper machine is defined as a machine for making a continuous paper web (or web). The expression pulp preparation as used in this patent application denotes a process starting from a pulp (or pulp-like substance) comprising fibers, usually a cellulosic material, and having a more or less stable consistency, pulp is prepared under blending conditions for further delivery to a headbox, and the pulp comprises no more than 10% fibrous material, usually at least 1%, suitably 2 to 7%, and usually 3 to 5%, and The added process liquid is usually water. Typically, such pulp preparation involves a so-called pulper in which fibrous material is broken down from a cellulosic process in a disintegration and agitation process and mixed with process water. the

Background technique

Traditional papermaking involves a process in which pulp comprising essentially fibrous material and process liquid is directed into a headbox for dewatering on a filament (wire). Numerous subsequent steps and devices are associated with the process, including vessels for slurry, typically 3 to 5% in viscosity, to direct most of the excess liquid back into the process in an upstream direction. the

In the production of special qualities of paper such as decorative paper, colored paper or other grades of paper, expensive, perhaps process-sensitive additives such as titanium dioxide (TiO ₂ ), pigments or similar often expensive components are added to the In the process, a problem thus arises that the retention of these additives in the process is poor, so that so-called white water may typically contain up to 1% or more of such additives. For the recovery of these additives, the conventional process consists of recovery by means of flotation, for example in a recovery plant, after which the clean water from the flotation is reused in the pulp preparation.

In order to obtain sufficient mixing and contact time with the actual papermaking pulp when making paper of this special quality, the additives are usually added to the process already during the pulp preparation. In practice, this means that the entire process will actually be completely dyed. Therefore, when changing paper grades, the process must initially reach an equilibrium, which requires a long time to establish equilibrium, while color changes require extensive cleaning of the system and cause a large loss of material. Even so, colored paper, including white paper colored with pigments, is difficult to produce, and determining the correct color, especially for decorative paper, is difficult. In addition, there is the fact that a web break under these conditions will cause instability. the

Since, for example, the decorative paper will be impregnated in a further finishing process, its optical properties will also change. The refractive index of the fiber and the impregnating agent are approximately the same, therefore, factors such as the concentration, distribution and optical properties of the pigment are decisive for the quality of the product. For this reason, it is often necessary to carry out a test multilayer product before starting actual production, and this takes about half an hour, during which period the pulp flows in one cycle of the machine. the

Therefore, this can be achieved partly more efficiently by means of the devices disclosed in the Applicant's International Patent Applications No. PCT/FI93/00214, PCT/FI94/00578, PCT/FI96/00052 and PCT/F101/00365. The process, however, still presents certain problems, although the device makes it possible to select the appropriate white water for each particular use. However, in a typical conventional process, approximately 20 to 30 kg of the additive titanium dioxide ( _TiO2 ) will be passed through the fiber recovery unit for every 100 kg of paper (see also Table I below). In conventional fiber recycling plants using flotation technology, chemical products will cause clumping, which will reduce the optical effect of the pigment. As a result, the titanium dioxide will lose its optical effect and some will be lost, for example in the form of deposits in the system. In addition, there are of course disadvantages related to fiber recovery, investment and operating costs due to separate units, and costs depending on the contamination and cleaning of the system, and more complex processes are required for the recovery units associated with the prior art Chemical disadvantages.

Contents of the invention

It is therefore an object of the present invention to avoid the disadvantages hitherto associated with the use of pigments, in particular with paper grade changes.

The present invention is based on the surprising realization that, by increasing the viscosity of the pulp at an early stage of the process, it is possible in practice to cut off what in traditional papermaking is known as a long cycle, i.e. A circulation system in which white water, according to conventional arrangements, can flow upstream in the system from the filament (wire) depressions of the paper machine up to the point where the pulp is added, eg to the pulp machine. By interrupting this cycle, it is possible to prevent the upstream flow of valuable additives, such as titanium dioxide and other pigments, which would otherwise be partially lost and possibly partially pollute the entire process chain. the

The characteristics of the invention are disclosed in the individual characterizing parts of the appended independent claims, while the dependent claims disclose advantageous embodiments of the invention. Therefore, the method according to the invention is characterized in that the viscosity of the pulp is increased to a value greater than 10% by removal of process liquid before introducing said additive, suitably in a separate process stage, wherein, in the process These process liquids are conveyed upstream in the process direction, while make-up process liquids, which may suitably contain additives, are added downstream in the process direction. the

Correspondingly, the process according to the invention is characterized in that, viewed in the direction of the process, separating means are arranged before the means for introducing the additive, but after said inlet, whereby these separating means are arranged such that the process liquid is separated from the The flowable pulp separates so that the viscosity of the pulp will increase to a value greater than 10%, in some cases even advantageously up to 50%. The apparatus of the present invention further comprises a means for transferring process liquid which has been separated from the pulp upstream into the process and a means for introducing downstream process liquid from said circulation in order to supplement the separated process liquid. Such process liquids may contain more or less additives. the

Description of drawings

The present invention will be described in more detail below with reference to some advantageous embodiments and accompanying drawing, in accompanying drawing:

Fig. 1 has shown device (or arrangement) according to an embodiment of the present invention as a schematic diagram; And

Figure 2 generally shows a paper machine arrangement according to a particularly advantageous embodiment. the

Detailed ways

According to Figure 1, a paper machine typically includes an inlet for fibrous material, i.e. cellulose, which is usually supplied in the form of dry flakes, or in so-called integrated chemical plants directly from a cellulose plant containing The fiber process is available in liquid form. If the incoming material is in the form of flakes, the process (or processing) begins with pulp preparation involving a so-called pulper 2 where the flakes are disintegrated and mixed with process liquid, e.g. raw materials or pulp for papermaking. The pulp passes through different process (or processing) stages 4a, 4b, 4c, 4d, 4e... etc., which are basically irrelevant to the invention in this context, and at the end, through the headbox of the paper machine 5 The pulp is spread onto a filament (mesh) 6 . The filament (wire) passes through a machine 7, where a large part of the process liquid is drained by suction in the form of so-called white water, while the pulp, which remains moist, is gradually made by means of a pressurizing device 9 and drying. into paper. the

White water contains, in addition to water, chemicals to some extent that will remain in the paper. The process water carries these chemical products, which are used for some parts in so-called short cycles for the purpose of dilution in some process stages, for example, for which the chemical products are required, or which are described in these process stages Chemical products cause only very little damage in any case. The white water used for other purposes is cleaned in different processes and cleaning stages, on the one hand to recover chemical products and on the other hand to obtain clean water that can be used in other parts of the process. However, each such cleaning process is somewhat incomplete and additionally requires energy, time and equipment. the

Especially for special papers such as decorative papers and other colored papers, relatively small quantities are produced. This makes the production of these grades rather unprofitable in integrated paper mills, and for this reason special grades are often produced in mills that receive fibrous material essentially in dry sheet form, which will The process liquid is already required from the beginning of the process. In known processes, such process liquids are generally extracted from clean white water in the long circulation described. In practice, however, such clean process liquids also contain more or less parts of impurities, ie mainly materials belonging to some other part of the process. For colored papers, some of these impurities consist among others of pigments such as titanium dioxide, which are often added already in the pulp machine 1 in order to mix well, so that the system will practically be completely pigmented . This situation in combination with these expensive components deposited as deposits on different parts (or components) of the system, for example for colored paper, will actually cause this when changing, for example, to a different color In this case, the entire system must be cleaned before subsequent grades of paper can be made. the

The system according to the invention differs substantially from the known art described above. Additional separation of process liquids 8, 8a is achieved by temporarily increasing the viscosity of the pulp by introducing a separation device at least in one part of the process, which interrupts the reverse long-distance flow of these process liquids containing valuable additives in the system . Earlier separations were employed only to prevent the downstream flow of chemical products interfering with subsequent processes, and the idea that expensive additives can also be prevented from contaminating upstream in a corresponding manner is rather novel. the

The rationale behind the invention is given in Table I by means of pulp sticking data for a typical process (T) according to the prior art on the one hand and a process (U) according to an embodiment of the invention on the other hand. Consistency (expressed in % (percentage)), volume ("X" is the number of liters of liquid per kilogram of pulp) and dry matter (expressed in kilograms) shows the balance of material in different parts of the system, where A indicates in Values of the pulp according to the initial stages 1...4a of the process of the prior art, A ₁ represents the value of the pulp after the separation 8 according to the invention, B represents the situation in the headbox 5, C represents when the paper leaves the press In the case of device 9, D denotes the "remaining water" that must be cleaned before the water can be used again, while E denotes the situation in short cycles:

Table I

From Table I above, it is evident that about 20 to 30 kg of TiO per 100 kg of paper passes through the fiber recovery unit 10, and when the viscosity of the pulp is temporarily increased according to the present invention _{, the} remainder containing TiO The volume of water and the dry matter allocated to it will be greatly reduced.

In practice, the separation of the removal process liquids can advantageously be achieved by means of concentration techniques already known per se from, for example, cellulose production, bleaching and decolorization. Such devices are often able to increase the viscosity of pulp containing fibres, from an initial value of 2% to 10%, in present cases typically of the order of about 4% to 6%, even up to 50% last value of , and possibly even higher. the

According to an advantageous embodiment, the separation is effected by means of a pressurization device, such pressurization preferably taking place before the beating 4c. The pressurization at the stage of concentration can advantageously be carried out in a screw press or a belt press 8a of a type known per se, so that after pressurization the pulp has a dry matter content greater than 10% in the form of a slime, Especially in the range of 20% to 50%, suitably 25% to 40%, preferably at least 30%. the

The process liquid which is separated off during the pressurization is conveniently returned to the pulp machine 2 while being conveyed back 11 in the upstream direction to the process. It is expedient to replace the liquid 13 which has been separated from the process in a spreading device 12 with a substantially corresponding amount of liquid withdrawn from the circulation of the paper machine. This is preferably carried out in a device according to the Applicant's International Patent Application No PCT/FI99/00143, or alternatively by means of a screw device or some other type of mixing device. In order to achieve optimum intermixing, the spreading device 12 is preferably arranged in the process direction, essentially directly after the separating device 8, 8a. the

According to an advantageous embodiment of the invention, the main introduction 14 of important additives such as very expensive pigments and colorants is carried out in conjunction with adding the liquid to the spreading device 12 (see FIG. An effective intermixing of the additives is achieved at an early stage. Figure 2 shows that the additives 14, 14b can also be introduced at a later stage in the process. Since the introduction of at least a part of the additive is advantageously carried out simultaneously with the introduction of the replacement liquid 13, little will result if the replacement liquid is taken from that part of the process where the remaining content of additive may be even higher. the

In practice, the devices discussed above where the viscosity of the pulp will increase will create a situation where the removal and return of process liquid is to "make room" for the introduction of such additive materials, one wishes to prevent the upstream direction Decentralization, in which this removal and return functionally belongs to an earlier process stage in a certain sense. Thereby, the subsequent additive material and thus for example the colored part of the process can be limited to the short cycle of the paper machine, while the long cycle is kept free of valuable and/or polluting material, making it possible to reach lines which may require such (or loop) degree. the

Since the system is essentially self-cleaning in the particularly advantageous embodiment according to Fig. 2, it is possible in practice to provide white water of different composition very well, and to provide a relatively clean residual liquid, to the extent that these The level of liquid required. Thus, the correct degree of cleaning can be selected for these needs, which further reduces the loss of valuable additive materials. The small amount of residual water that still remains can be treated in a fine filter, spray water etc. provided, so that the filter cake is returned to the spreading unit. the

Figure 2 therefore shows a particularly advantageous arrangement in which the water extracted by the system is redirected at a point where the concentration of material is as low as possible. According to this embodiment, it is possible to reduce this concentration by arranging a suction box 15 under the filaments (web) at a location where the fiber roll has been formed so that the fiber roll acts as a filter. This suction box 15 is operated with a moderate vacuum so that careful filtration is achieved and very clean white water is obtained. This filtering process reduces the amount of material such that this white water can be normally directed 16 to overflow 17 without any additional recovery means. the

With the aid of the device according to the invention, a near 100% retention of valuable additives can be achieved, while at the same time, e.g. Time to build new colors. the

Some advantageous embodiments of the invention have been disclosed above, but it is clear to a person skilled in the art that the invention can also be implemented in many other ways within the scope of the appended claims .

Claims (17)

1. A method for reducing the dispersion of additives introduced into a continuous process in a paper machine when preparing pulp from a flowable pulp as raw stock pulp, which will include fibers and process liquid and have a consistency not greater than 10% flowable pulp is transferred to the headbox (5) of the paper machine, characterized by removing (8, 8a) the process liquid before introducing said additive (14) and conveying upstream where the process liquid is removed (11) This removed process liquid is used to increase the consistency of the pulp to values greater than 10%, while additional process liquid (13) is added downstream of where the additive is added. 2. The method according to claim 1, characterized in that by separating the process liquid from the pulp, the consistency of the pulp is increased by means of a pressurizing device (8, 8a) so that the pulp Corresponding to a dry matter content of 20% to 50% therein, the process liquid is simultaneously sent (11) upstream back into the process. 3. The method according to claim 1 or 2, characterized in that, before transferring the pulp to the headbox (5), a short circuit of the paper machine is added a Supplementary Liquids (13). 4. The method according to claim 1, characterized in that in conjunction with the dispersion (12) of the pulp whose consistency has been increased, the introduction of additives and, proportionately, the additional process liquid. 5. The method of claim 1, wherein the additive comprises a pigment or other colorant. 6. An apparatus in a paper machine for the preparation of pulp from a flowable pulp as raw stock pulp to limit the dispersion of additives upstream in a further process, wherein said process includes for a consistency of not more than 10%, and comprising inlets (1, 2) for flowable pulp of fibrous material and process liquid, a closed circulation system comprising a head box (5) for the fine wire of said paper machine and for introducing said additives (14 ), characterized in that a separating device (8, 8a) is arranged in the direction of the process before the device for introducing the additive, but after said inlet (1, 2), said separating device (8, 8a ) is arranged to separate the process liquid from the flowable pulp such that the consistency of the pulp is increased to more than 10%, the means for sending the process liquid (11) upstream is used to separate the process liquid (11) which has been separated from the pulp The process liquid is conveyed upstream into the process, and means for adding make-up process liquid (13) is used to introduce downstream the process liquid from the closed circulation system in order to make up the The process liquid separated. 7. The device according to claim 6, characterized in that the separating device is capable of increasing the consistency of the fiber-containing pulp from an initial value of 2% to 10% to 20% by means of a pressurizing device (8, 8a). % to 50% of the final value. 8. The device according to claim 6 or 7, characterized in that the means for adding supplementary process liquid (13) are arranged in connection with said inlet for additives or added after said inlet ( 14) Make-up water from the short circulation system of the paper machine. 9. The device according to claim 6, characterized in that the dispersing device (12) is arranged to redisperse the pulp that has separated excess liquid, whereby the device for introducing the additive (14) is arranged in conjunction with The dispersing device (12) is associated substantially immediately after the separating device (8, 8a) in the direction of the process. 10. The device according to claim 6, characterized in that a separate suction box (15) is provided at a part of the fine wire mesh (6), which has a function that facilitates careful filtering and very Clean white water, low magnitude vacuum, in that part of the fine wire mesh has formed a fiber roll, and the means (16) for conveying the water are arranged to draw the water from such a separate suction The tank (15) is conveyed upwards in the system towards a separate overflow pipe (17). 11. The method according to claim 2, characterized in that the consistency of the pulp is increased so that the pulp corresponds to a dry matter content of 25% to 40%. 12. The method according to claim 2, characterized in that the consistency of the pulp is increased such that the pulp corresponds to a dry matter content of at least 30%. 13. The method according to claim 2, characterized in that the consistency of the pulp is increased by separating the process liquid from the pulp by means of a pressurizing device. 14. The device according to claim 7, characterized in that the separating device (8, 8a) is able to increase the consistency of the fiber-containing pulp from an initial value of 4 to 6% to 20% by means of a pressurizing device to 50% of the final value. 15. The device according to claim 7, characterized in that the separating device (8, 8a) is capable of increasing the consistency of the fiber-containing pulp from 4% to 6% to a final value of 25% to 40%. 16. Device according to any one of claims 7, 14, 15, characterized in that the separation device (8, 8a) is capable of increasing the consistency of the fiber-containing pulp to a final value of at least 30%. 17. The device according to claim 6, characterized in that the dispersing device (12) is arranged to redisperse the pulp that has separated the excess liquid after adding supplementary process liquid (13), thereby being used to introduce the The means of said additive (14) is arranged in connection with said dispersing means (12), so that said dispersing means (12) is arranged in the direction of said process, substantially next to said separating means (8, 8a )after.

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