WO2008000308A1

WO2008000308A1 - Method of loading a pulp suspension with filler

Info

Publication number: WO2008000308A1
Application number: PCT/EP2007/002535
Authority: WO
Inventors: Klaus Doelle; Joachim Henssler
Original assignee: Voith Patent Gmbh
Priority date: 2006-06-28
Filing date: 2007-03-22
Publication date: 2008-01-03
Also published as: JP2009541604A; EP2038477A1; US20090056888A1; CN101479427A; CA2636454A1; KR20090031848A; DE102006029642B3; BRPI0712858A2

Abstract

The method serves for loading a pulp suspension S with a filler, more particularly with calcium carbonate (fibre loading). In accordance with the invention the loaded pulp suspension S' is divided into at least two fractions, a light fraction (1) and a heavy fraction (2), for which one advantageous embodiment uses hydrocyclones (13). The different fractions have different degrees of loading; in other words, the amount of precipitated fillers adhering to the fibres is different in each case. The possibility exists of recycling the fibres loaded to a lesser extent back into the loading operation, in order to achieve a further increase in the degree of loading of that fraction.

Description

Method for loading a pulp suspension with filler

The invention relates to a method for loading a pulp suspension according to the preamble of claim 1.

Several methods of fiber loading technology for loading pulp fibers with calcium carbonate are already known. US 5,223,090 discloses a process employing fibrous material having elongated fibers with a cell wall surrounding a cavity, the fibers having a humidity sufficient to form a dewatered pulp slurry. The fibers have a moisture content corresponding to a proportion of 40 to 50% of the weight of the fibers. The water is essentially present inside the fibers and inside the fiber walls. Subsequently, alternatively calcium oxide or calcium hydroxide is added to the pulp so that at least part of the incorporated calcium oxide or calcium hydroxide is associated with the water present in the pulp. Subsequently, the fibrous cellulosic material is contacted with carbon dioxide while simultaneously subjected to a shear mixing process to produce a fibrous material having a substantial amount of calcium carbonate in the hollow interior and within the fibrous walls of the cellulosic fibers by precipitation.

From DE 102 04 254 A1 a further method for loading a pulp suspension is known. The process comprises the following steps: introduction of calcium hydroxide in liquid or dry form or of calcium oxide into the pulp suspension, introduction of gaseous carbon dioxide into the pulp suspension, precipitation of calcium carbonate by the carbon dioxide.

It is the object of the invention to provide a method for loading a

To provide pulp suspension in which the advantages of the loading process can be increased, possibly also a significantly higher loading effect can be achieved. According to the invention this object is achieved by the measures mentioned in claim 1.

By this method it is possible to produce fiber loaded with calcium carbonate (FLPCC = fiber loaded precipitate calcium carbonate), in particular for the production of pulp or for pulp use in papermaking. The fiber stock to be loaded is made, for example, from recycled paper, DIP (= deinked paper), secondary pulp, bleached or unbleached pulp, wood pulp of any kind, any paper pulp, bleached or unbleached sulphate pulp, finished pulp, linen, cotton and / or hemp fibers (used primarily for cigarette paper) and / or any other paper stock used in a paper machine. The process can be used independently of the fiber raw material to be loaded.

The field of application of the invention extends to paper and pulp production and process technology, including the filler produced, and includes applications of all paper grades, including packaging paper grades and production-related rejects, having a filler content between 1% and 60%, and / or a white topcoat having a filler content between 1% and 60%. Preferably, the filler content may be between 5% and 50%.

Treating a pulp suspension in papermaking with fiber-loading technology results in a completely new product that has new and improved properties over the products known in the market. Such a process allows, directly in the stock preparation in one

Papierfabrik filler (calcium carbonate), which is uniformly distributed and deposited exclusively on and in the pulp, in particular the paper fiber.

In the process according to the invention, the fractionation may conveniently be carried out with hydrocyclones which produce a high centrifugal field, eg 200 times the gravitational field of the earth.

Another possibility lies in the use of pressure sorters, especially if they are designed as fiber fractionators, ie provided with fine screen openings. Of course, multi-stage separation systems and / or combinations of different separation principles are conceivable.

The inventive method is carried out with particular advantage so that the different effect of loading the pulp suspension is either used or compensated by appropriate measures partially or completely. In a loading method embodying this invention, e.g. a pulp suspension composed of different fibers is formed. Due to the different properties, it is possible that the loading is not the same for all participating fibers. In addition, a statistical influence is conceivable such that, due to parameter variations during the precipitation process, whether temporal or local, precipitation is not uniform. The different degree of loading, that is to say the amount of precipitated crystals adhering to the fibers, makes it possible to carry out a fractionation subsequent to the loading process in which at least two fractions having different degrees of loading are formed. Since heavier loaded fibers are expected to be heavier than less heavily loaded fibers, the terms heavier fraction for higher load fiber and light fraction for lower load fiber are used herein.

Depending on the requirements of the process, two options are conceivable in order to further treat the different fractions.

The first possibility is to recycle the light fraction into a plant part which is before loading, to perform the loading process again, which is e.g. is particularly advantageous if they are guided in the light fraction

Fibers by a re-loading a significantly higher degree of loading reachable. The cause may be that, due to the fiber properties, a longer loading time or a higher concentration of the chemicals would be more favorable. In such cases it is more economical not to tune the process to the "most difficult fibers", but to optimize the overall economy.

The second possibility is to selectively use the fractions formed in paper or board production. As is well known, different quality requirements are placed on paper production for the individual grades and possibly also layers on the paper machine. It is therefore possible to improve the overall process of paper production through fractionation.

Compared to conventional processes for producing a pulp suspension can be achieved energiegünstig by loading a higher freeness; e.g. can be saved up to 50% of the grinding energy. This particularly affects all types of paper that undergo a milling process in their manufacture, and especially those that have a high or very high freeness, such as FL (Fiber Loading) papers, FL-B & P papers, FL sack kraft papers and FL filter paper. For these papers, which do not require fillers, free filler that is not deposited on or in the fibers may be removed after the milling process or prior to introduction of the pulp suspension into the headbox or prior to feeding to the paper machine. However, the fibers themselves are externally and / or internally and externally provided with filler, so that the positive effects of the fiber-loading technology remain.

The loading has a positive effect on the production of all types of paper, since by process-related mechanical stresses in the various sections of the paper machine, as in the press section, the dryer section or in the area in which the paper web is rolled, the intermediate product produced and the end product to be produced is mechanically stressed by the use of reeling, winding, reeling and converting machines.

Another advantage of using the technology of the invention in the above listed paper types is that they can be further processed in a calender. By using fiber-loading technology, fiber-loading particles are deposited in, around and on the fibers, thus avoiding blackening, ie black satin coating.

The following is a typical example of loading a pulp suspension:

The starting material used is aqueous fibrous material, in particular aqueous paper stock, of from 0.1 to 20% consistency, preferably between 2 and 8%. Calcium hydroxide in aqueous or in dry form or calcium oxide is mixed in a range between 0.01 and 60% of the existing solids content in the aqueous paper pulp. For the mixing process, a static mixer, a receiver chest or a material dissolving system is used; In this case, a pH in the range between 7 and 12, preferably between 9 and 12, is used. The reactivity of the calcium hydroxide is between 0.01 and 10 minutes, preferably between 1 second and 3 minutes. Dilution water is mixed in according to given reaction parameters.

Carbon dioxide is mixed in accordance with the reaction parameters in a moist pulp dimension. Calcium carbonate precipitates in the carbon dioxide atmosphere.

Preferably, the process temperature is between -15 ° C and 120 ° C, in particular between 20 ° and 90 ° C. Preferably rhombohedral, scalenohedral and spherical crystals are produced, wherein the crystals dimensions between 0.05 and 5 .mu.m, in particular between 0.3 and 2.5 μm.

Static and / or mobile, in particular rotating, mixing elements are used to produce a fibrous suspension laden with calcium carbonate. The process is preferably carried out in a pressure range between 0 and 15 bar, in particular between 0 and 6 bar. Likewise, the process is advantageously carried out at a pH of between 6 and 10, in particular between 6.5 and 9.5. Here, the reaction time is between 0.03 seconds and 1 minute, in particular between 0.05 and 10 seconds.

For example, precipitate product particles of a rhombohedral shape having a respective cube size in a range of about 0.05 to about 2 μm can be produced. In certain cases, it is also advantageous to produce precipitate product particles of a scalenohedral shape having a respective length in a range of about 0.05 to about 2 μm and a respective diameter in a range of about 0.01 to about 0.05 μm ,

According to a preferred embodiment of the method according to the invention, the solids concentration of the pulp suspension provided for precipitation is selected in a range from about 0.1 to about 60% and preferably in a range from about 15 to 35%.

According to an expedient practical embodiment of the loading method, the carbon dioxide is added to the pulp suspension at a temperature in a range of about -15 to about 120 ° C and preferably in a range of about 20 to about 9O ⁰ C.

The invention and its advantages will be explained with reference to drawings. Showing:

Fig. 1 system diagram to illustrate an example of the invention

process;

Fig. 2 shows a variant of the method.

FIG. 1 shows by way of example a system with the most important method steps and devices. In this plant, the pulp P, for example, pulp or deinked waste paper, entered together with water W in a pulper 10. This Stoffiöser 10 may be conventionally built, ie in its bottom area containing a pulper screen 11 and a pulper rotor 12, which provides for the Umtrieb in the pulper and the pulper screen 11 keeps free of blockages. In the example shown here, the pulp thus dissolved is supplied to a plurality of cleaning devices, which are symbolically represented as a fabric cleaner 14 and a fabric sorter 15. It then follows a screw press 16 to raise the consistency of the pulp suspension S again. The press filtrate 18 of the screw press 16 can be recycled for dissolution in the pulper 10. The thickened pulp 19 then passes into a crystallizer 20, which serves to initiate the desired precipitation of calcium carbonate in the form of finely divided filler with the aid of supplied carbon dioxide gas 24. The carbon dioxide gas is provided by a carbon dioxide supply 21 and can be brought in a heat exchanger 22 by means of a cooling or heating means 23 to the desired temperature. But there are other possibilities for temperature control, for example, the direct addition of steam, if an increase in temperature is appropriate. In a Vorratsbütte 26, the loaded pulp suspension is collected, possibly diluted with dilution water 27.

It then follows directly or after an intermediate treatment, such as grinding, a fractionation of the loaded pulp suspension S ^' . For this purpose, a cleaner system with highly effective hydrocyclones 13 is used here by way of example and with advantage. These form a heavy fraction 2 and a light fraction 1. Fibers that are more heavily loaded with adhesive fillers are specifically heavier than less heavily loaded fibers. They can also be stiffer. The fractionation carried out according to the invention, in particular when using sedimentation or centrifugal forces, makes use of these differences. It is therefore to be assumed that the heavy fraction 2 contains fibers loaded with fillers more strongly than the light fraction 1.

The light fraction 1 is recirculated here in the loading process, ie guided into the inlet of the screw press 16. The heavy fraction 2 stands as Pulp suspension 28 eg a - not shown - paper machine available.

The plant part shown in Fig. 1 for loading with fillers, in particular calcium carbonate, is to be regarded only as a simplified example. In many cases, a bleach can be integrated. More details on the implementation of the load can be seen from the publications mentioned above. The loading process is advantageously operated as an online process in the paper mill.

As already mentioned, the fractionation of the loaded pulp can also be used to produce different material qualities or to provide different qualities in paper production. For this procedure, Figure 2 shows a plant scheme as an example, in which, however, the resolution and the pre-cleaning of the pulp suspension are no longer shown. This can correspond to that of FIG. 1 or comparable plant components known per se. By means of the method according to the invention it is e.g. possible, the light fraction 1, so with the less loaded fibers, from the

Heavy fraction 2 to lead the headbox 32 of a paper or board machine separately. In this case, as a rule, the addition of further components 30, 31

(Fibers or aggregates) to be made. It is also possible (not shown here) to process the fractions differently, e.g. to grind.

The headbox 32 forms three layers in this example. Advantageously, the light fraction 1 is guided into the inner layer and the heavy fraction 2 into the outer layers, in particular if the higher strength and / or the better retention of the higher-loaded fibers are to be utilized. Several layers can also be formed with the help of several headboxes.

The constant part of the paper machine is not shown here.

Claims

claims

1. A method for loading a pulp suspension (S) with a filler, in particular with calcium carbonate, wherein calcium hydroxide is introduced in liquid or dry form into the pulp suspension (S) and precipitated by a chemical reaction of the filler in the pulp suspension, characterized in that the loaded pulp suspension in (S ^' ) is fractionated at least two fractions with different loading levels and that these fractions are treated differently.

2. The method according to claim 1, characterized in that the fractionation is carried out by application of centrifugal forces.

3. The method according to claim 2, characterized in that the fractionation in hydrocyclones (13) is performed.

4. The method according to claim 3, characterized in that the hydrocyclones (13) generate a centrifugal field which is at least as large as 200 times gravitational acceleration.

5. The method according to any one of the preceding claims, characterized in that at least one light fraction (1) is formed with a lower degree of loading and at least one heavy fraction (2) with a higher degree of loading.

6. The method according to claim 5, characterized in that the light fraction (1) is loaded again.

7. The method according to claim 6, characterized in that the light fraction (1) is recirculated in the same loading process in which it has already been loaded.

8. The method according to claim 6, characterized in that the light fraction (1) is loaded in another loading process.

9. The method according to any one of claims 5 to 8, characterized in that light fraction (1) and heavy fraction (2) are ground in different ways.

10. The method according to any one of claims 5 to 9, characterized in that light fraction (1) and heavy fraction (2) are used for different paper or cardboard products.

11. The method according to any one of claims 5 to 10, characterized in that light fraction (1) and heavy fraction (2) are used in different layers in the paper or board production.

12. The method according to any one of the preceding claims, characterized in that as starting material aqueous pulp material, in particular aqueous paper pulp, from 0.1 to 20% consistency, preferably between 2 and 8%, is used.

13. The method according to any one of the preceding claims, characterized in that the process temperature in the precipitation between - 15 ° C and 120 ° C, in particular between 20 ° and 90 ° C, is.

14. The method according to any one of the preceding claims, characterized in that the chemical precipitation of the fillers is carried out by gaseous carbon dioxide.

15. The method according to any one of the preceding claims, characterized in that rhombohedral, scalenohedral and spherical crystals are produced.

16. The method according to claim 15, characterized in that the crystals have dimensions between 0.05 and 5 microns, in particular between 0.3 and 2.5 microns.

17. The method according to any one of the preceding claims, characterized in that the loading in a pressure range between 0 and 15 bar, in particular between 0 and 6 bar, is performed.

18. The method according to any one of the preceding claims, characterized in that the loading at a pH between 6 and 10, in particular between 6.5 and 9.5, is performed.

19. The method according to any one of the preceding claims, characterized that the loading is carried out at a dry content of between 0.1% and 60%, preferably 15% to 35%.

20. The method according to any one of the preceding claims, characterized in that the reaction time of the precipitation is between 0.03 seconds and 1 minute, in particular between 0.05 and 10 seconds.