DE102006003721A1 - Loading of a fibrous material suspension for paper production, comprises dissoluting the fibrous material to form the suspension, adding liquid/dry calcium hydroxide/calcium oxide to the material/to the suspension - Google Patents

Abstract

In the loading of a fibrous material (P) suspension, a fibrous material (40-100%) is dissolved in a dissolving drum to form a suspension (S) containing cellulose fibers with calcium carbonate. The suspension is added with carbon dioxide (CO 2) for precipitating the carbonate (10-35%). A liquid/dry form of calcium hydroxide/calcium oxide is added the drum-filling region containing fibrous material. The addition of calcium hydroxide is carried out during or before the fiber dissolution (1) to form the suspension (10-20%). In the loading of a fibrous material (P) suspension, a fibrous material (40-100%) is dissolved in a dissolving drum to form a suspension (S) containing cellulose fibers with calcium carbonate. The suspension is added with carbon dioxide (24, CO 2) for precipitating the carbonate (10-35%). A liquid/dry form of calcium hydroxide/calcium oxide is added the drum-filling region containing fibrous material. The addition of calcium hydroxide is carried out during or before the fiber dissolution (1) to form the suspension (10-20%). The purified suspension is concentrated (2) before it is added with the CO 2. Filtrate (9) of the concentrated suspension is again dissolved. The suspension is converted and dispersed into fine fiber crumbs in a cutting-up step, during or after the carbonate precipitation (3). The precipitation is carried out for 0.5-10 seconds at (20-90[deg]C) using energy (0.5-4 kWh/t) and pressure (6 bar) at pH of 6.5-8.5. The dissolution of the material is carried out continuously or batch-wise, and the liquid calcium hydroxide is sprayed into the material at the beginning of dissolution. The fibrous material softens by soaking the material in water and the calcium hydroxide in a softening drum before the dissolution. The calcium hydroxide is sprayed into the material in the form of lime milk (60%) set in a dry paper pulp solid content. The calcium hydroxide reacts with the material for 3 minutes. The suspension is purified from disturbing substances.

Description

The The invention relates to a method for loading in a pulp suspension contained fibers, in particular cellulose fibers for paper or Board production.

at papermaking are fillers such as in particular felled Calcium carbonate (PCC = precipitated calcium carbonate) or crushed or ground calcium carbonate (GCC) common substances, which are used to reduce the fiber content as well as the optical Properties of the paper to improve.

at the commercial PCC or GCC fillers they are mass-produced in specialized factories is generated, which are assigned to a paper mill as a satellite system can. An online manufacturing of PCC has been or will be in the paper industry however, never considered, due to the special process properties is due which are required for the production of PCC. Instead, will PCC or GCC as bulk material or transported in the form of a suspension to the paper mills.

The loading with an additive, for example filler, can be carried out, for example, by a chemical precipitation reaction, ie in particular by a so-called "Fiber Loading ^™ " process, as described inter alia in US Pat. No. 5,223,090. In such a "Fiber Loading ^™ " process, at least one additive, in particular filler, is incorporated on the wetted fiber surfaces of the fiber material. The fibers can be loaded, for example, with calcium carbonate. For this purpose, the moist, disintegrated fiber material calcium oxide and / or calcium hydroxide is added so that at least a part of which associates with the water present in the fiber material. The fiber material treated in this way is then treated with carbon dioxide.

at Adding the calcium oxide and / or calcium hydroxide contained Medium to the pulp suspension is accompanied by a chemical reaction exothermic property, wherein the calcium hydroxide is preferably in liquid Form (milk of lime) is added. This does not mean that that may be in or on the fibers of the pulp suspension or accumulated Water is required to start and run the chemical reaction.

One Another method for loading with filler is shown in WO 03/066962. The result is e.g. through a special grinding process further improved.

For example, when loading the fibers with filler, calcium carbonate (CaCO ₃ ) may be incorporated into the wetted fiber surfaces by adding calcium oxide (CaO) and / or calcium hydroxide (Ca (OH) ₂ ) to the wet fiber material, at least part of which is itself can associate with the water of the pulp amount. The fiber material treated in this way can then be charged with carbon dioxide (CO ₂ ).

Of the Term "wetted Fiber surfaces "can all wetted surfaces of the individual fibers. In particular, the case with detected in which the fibers on both its outer surface and in its interior (Lumen) with calcium carbonate or any other precipitated product be loaded.

Accordingly, for example, the fibers can be loaded, for example, with the filler calcium carbonate, wherein the attachment to the wetted fiber surfaces by a so-called "Fiber Loading ^™ " process takes place, as it is described as such in US-A-5,223,090. In this "Fiber Loading ^™ " process, for example, the carbon dioxide reacts with the calcium hydroxide to form water and calcium carbonate.

The Calcium hydroxide can render the fibers in liquid or dry form supplied become.

aim The invention is to a method of the type mentioned above which is more economical than the known methods.

These Task is according to the invention in a in claim 1 specified by the method in the license plate mentioned features.

The method of the present invention provides the ability to add the calcium oxide (CAO) and / or calcium hydroxide (CAOH ₂ ) to the fiber material in a state where it is relatively highly consistent, eg, lyophilized or wetted. Before being introduced into the pulper and the pulp is relatively absorbent, ie the chemicals added there are easier and faster to reach the wetted surface of the fibers. Also, the penetration into the cavities of the fibers is correspondingly faster and cheaper. As in the dissolving apparatus. As a pulper or a dissolving drum, in any case liquid, especially water, is added, this process step remains simple and clear. Only a dosage of the calcium oxide or hydroxide is generally required. It is also possible to use the dissolving apparatus be designed so that in her already the precipitation of calcium carbonate can be triggered by at least a portion of the carbon dioxide is added to the apparatus. For example, it can be dissolved in the water. Or the dissolving apparatus is temporarily closed and charged with gaseous carbon dioxide. In such cases, a soaking section in front of the dissolution apparatus, in which the calcium hydroxide (lime milk) is sprayed on or added in a softening drum, should be considered.

One Another advantage of the method according to the invention is that under some circumstances a Saves machine for thickening, i. that the dissolved pulp during the dissolution process only diluted so far is that the subsequent loading can be carried out. In other cases, in particular if higher Requirements for the cleaning of the substance should be required (Waste paper) or if a separation of the fibers is not otherwise sufficiently achievable, of course, too again a thickening e.g. in the form of a screw press required be. The filtrate of such thickening would be in a short cycle directly in the dissolving apparatus can be traced back, so there for dilution serve. This has the distinct advantage that the calcium hydroxide or calcium oxide is optimally used, so that not only that Water, but also the chemicals can be recirculated.

generally known will in many cases the dissolution process not just with water, but with the addition of dissolving chemicals, especially caustic soda, carried out to a basic medium to accomplish. Again, the process has advantages, as the caustic soda can be replaced by calcium hydroxide, which for the precipitation process carried out later needed by calcium carbonate anyway becomes.

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

1 the inventive method in a schematic form;

2 a simplified illustrated system diagram for carrying out the method according to the invention.

The 1 shows that in carrying out the process, the pulp P, which may be eg waste paper or fresh pulp, in the resolution 1 is processed. This results in the addition of water W by mechanical work in a conventional manner, a pulp suspension S. The calcium hydroxide is in this example as lime 7 added at the dissolution, which for example by deleting lime in the Kalkmilcherzeugung 5 provided. Optionally, the pulp suspension S can be guided by a cleaning system, not shown here, in which, for example, heavy parts and plastic or other debris is removed. Whether this is necessary depends mainly on the quality of the raw material. Eventually, then thickening 2 done, but not always necessary and therefore was shown in dashed lines. The filtrate 9 the thickening 2 becomes dissolution 1 used. The process step of precipitation of fines, especially calcium carbonate, is triggered by the addition of gaseous carbon dioxide 8th , which consists of a carbon dioxide production 6 comes.

The thus prepared pulp suspension can then be used for paper production 4 be used, in general, a number of other processing steps not shown here are required. In paper production 4 may accumulate backwater, which is useful at the time of dissolution 1 to be used again.

In 2 exemplified is a plant with the most important process steps and devices. In this plant, the pulp P together with water W in a pulper 10 entered. This pulper 10 can be constructed conventionally, ie in its bottom area a pulper 11 included, as well as a pulper rotor 12 , which provides for the circulation in the pulper and the pulper screen 11 from blockages free. In the example shown here, the pulp thus dissolved is fed to a plurality of cleaning devices which symbolically serve as a fabric cleaner 14 and a fabric sorter 15 is shown. It then follows a screw press 16 to raise the consistency of the pulp suspension again. The press filtrate 18 the screw press 16 can with advantage to the dissolution in the pulper 10 to be led back. The thickened pulp 19 then enters a crystallizer 20 which serves, with the help of supplied carbon dioxide gas 24 to trigger the desired precipitation of calcium carbonate in the form of finely divided filler. The carbon dioxide gas is provided by a carbon dioxide supply 21 and can be in a heat exchanger 22 with the help of a cooling or heating medium 23 be brought 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. If necessary, part of the carbon dioxide gas 24 ' even after the crystallizer 20 with the help of a mixing device 25 are added to complete the loading process. In a storage chest 26 The loaded pulp suspension is collected, possibly with dilution water 27 diluted and then stands as pulp suspension 28 a paper machine 29 to Available.

The in 2 shown plant part for loading with fillers, especially calcium carbonate, is to be regarded 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.

At least one of the following devices and / or means can be used for the online process: HC cleaner, static mixer, lime luting device, press, in particular screw press or belt press, equalizing reactor, crystallizer, further static mixer, CO ₂ supply device or additional CO ₂ recovery unit, optional CO ₂ heater, optional chemical bleach additive, press water tank.

The Formation of crystalline precipitate product particles has the advantage, among other things, that, as far as necessary, for the End product higher gloss values can be achieved.

According to a practical embodiment of the method according to the invention, the press filtrate 9 at least partially in the crystallizer 20 used as dilution water.

The mixing device 25 may be a static mixer and in particular for fine adjustment of the pH of the pulp suspension, preferably in a range between 6 and 8, can be used.

Advantageously, at least a portion of the required CO _{2 is provided} by a CO ₂ recovery system. So it can be recovered, for example, from the flue gas of boilers or the flue gas of power plants.

It can for example precipitated product particles of a rhombohedral shape with a respective cube size in one Range from about 0.05 to about 2 microns be generated. In certain cases it is also advantageous Fällungsproduktteilchen of a scalenohedral form with a respective length in one Range from about 0.05 to about 2 microns and a respective diameter in a range of about 0.01 to about 0.05 μm to create.

According to one preferred practical embodiment of the method according to the invention the solids concentration of the fiber suspension provided for precipitation becomes in a range of about 5 to about 60%, and preferably in one range from about 10 to about 35%.

According to one expedient practical embodiment the loading process, the carbon dioxide of 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 90 ° C added.

The Made paper can therefore fillers in of an order of magnitude from about 0.05 to about 5 microns, whereby the optical properties of the final product are increased. At the filler it may in particular be calcium carbonate, which in the Nature e.g. as calcite or calcite, aragonite and in rarer ones Form Vaterit occurs. The filler can mainly consist of the form of calcite, of which more than 300 different crystal forms should exist. The shape of the filler particles used may be e.g. rhombohedrally with a respective cube size in one Range from about 0.05 to about 2 microns or, for example, scalenohedral with a respective length in one Range from about 0.05 to about 2 microns and a respective diameter in a range of about 0.01 to about 0.05 μm be, depending from the type of paper to be produced.

Of the filler is good at distributing to and within the fibers, which means that no agglomeration of crystals is found in bundles. The respective filler particles, namely the crystal is individually spaced or isolated on the Fiber provided. The filler particle covers the fiber by attaching to the fiber, causing the optical Properties of the final product to be improved. The particle size is therefore essential for achieving optimal opacity. A high opacity will then achieved when the color spectrum of visible light scattered well is. If the color spectrum is absorbed, the color is black. Does that fall? Size of the filler particles less than 0.2 to 0.5 μm, there is a tendency for transparency and higher gloss.

• – Feuchter oder in Auflösung befindlicher Faserstoff
• – Calciumhydroxid in Flüssig- oder Trockenform
• – CO₂
• – Gaszone
• – Rotor (Kristallisator)
• – Stator (Kristallisator)
• – Erzeugen von Kristallen in einer Gasatmosphäre ohne Einbringen von Mischenergie
• – Mischen bei geringer Scherung
• – kein Druckbehälter

For example, to achieve good loading results, the process for producing the filler crystals may be as follows and may have the following variables:

• - Wet or dissolving pulp
• - Calcium hydroxide in liquid or dry form
• - CO ₂
• - Gas zone
• - Rotor (crystallizer)
• - stator (crystallizer)
• - Generating crystals in a gas atmosphere without introducing mixing energy
• - mixing at low shear
• - no pressure vessel

The pulp suspension previously mixed with Ca (OH) ₂ becomes the crystallizer 20 For example, in a fluffer, refiner, disperser or the like at a consistency or solids concentration in a range of about 5 to about 60%, preferably in a range of about 10 to about 35%. The pulp suspension is charged with CO ₂ . The CO ₂ can z. At temperatures in the range of about -15 to about 120 ° C, and preferably at temperatures in the range of about 20 to about 90 ° C.

The pulp suspension enters the gas zone of the crystallizer 20 where each individual fiber is exposed to a gaseous atmosphere followed by the precipitation reaction which immediately yields the CaCO ₃ . The shape of the CaCO ₃ crystals can be, for example, rhombohedral, scalenohedral or spherical, with the amount of crystals in particular being dependent on the selected temperature range for the pulp suspension and on the CO ₂ and Ca (OH) ₂ contents in the pulp suspension. After the pulp suspension with the formed crystals has passed the gas zone, the formed PCC or pulp suspension with the crystals in the lumen, on the fiber and between the fibers is passed through a rotor and a stator where the distribution of the crystals in the pulp suspension with mixing is completed with low shear.

While the Fiber / crystal suspension passes the rotor, a shear distribution occurs on that a size distribution the crystals of about 0.05 to about 0.5 microns, and preferably of about 0.3 to about 2.5 microns brings with it.

The Form of the filler particles used is for example rhombohedral with a respective cube size in one Range from about 0.05 to about 2 microns or scalenohedral with a respective length in a range of about 0.05 to about 2 microns and a respective diameter in a range of about 0.01 up to about 0.5 μm, dependent of the type of paper to be produced.

The farther the pulp suspension is encountered on the rotor disk, the lower the shear, depending on the H ₂ O added for dilution. The concentration of fiber pulp passing through the rotor disk is from about 0.1 to about 50% and preferably from about 35 to about 50%. ,

In particular, the pressure applied to the CO ₂ feed line is in a range of about 0.1 to about 6 bar, and preferably in a range of about 0.5 to about 3 bar, to provide a constant CO ₂ supply to the gas ring for the desired one to ensure chemical reaction. As with the supply of water through a garden hose, the pressure is to be increased in case of high water demand in order to convey more through the hose. Since the CO ₂ is a compressible gas, the required amount can also be increased to ensure a complete reaction. The CO ₂ supply and thus the CaCO ₃ -producing precipitation reaction can be controlled and / or regulated via the pH.

For example, pH values in the range of 6.0 to about 10.0 pH, preferably in the range of about 7.0 to about 8.5, pH can be envisaged for the final reaction of the CaCO ₃ crystals. In particular, the energy used for this process may be in a range between about 0.3 and about 8 kWh / t, and preferably in a range between about 0.5 and about 4 kWh / t. Dilution water may be added and mixed with the pulp suspension to obtain a final dilution in which the resulting pulp suspension with filler has a consistency or solids concentration in a range of, for example, about 0.1 to about 16%, preferably in a range of about 2 to has about 6%. The pulp suspension is then exposed to the atmosphere in a machine, a container or the next process machine.

The Rotational speed of the rotor disk can on the outer diameter, in particular in a range of about 20 to 100 m / s and preferably in a range of about 40 to about 60 m / s.

Of the For example, the gap between the rotor and the stator is about 0.5 to about 100 mm, and preferably about 25 to about 75 mm.

Of the Diameter of the rotor and the stator can in particular in a Range from about 5 to about 2 meters.

The Reaction time is preferably in a range of about 0.001 to 1 minute, preferably in a range of about 0.1 to about 10 sec.

The process described above enables the production of individual particles equally spaced and attached to the fibers, covering the fibers in the manner required to meet the requirements for the desired high level of white or glossy paper. The particle size is preferably in a range of about 0.05 to about 5 microns, with the preferred size for the rhombohedral shape of a cube in a range of about 0.05 to about 2 microns or for a scalenohedral shape in length in a range from about 0.05 to about 2 microns and in diameter in a range of about 0.01 to about 0.5 microns. For high gloss applications, the particle size should desirably be below 0.2 to 0.5 μm.

1

resolution

2

thickening

3

precipitate

4

papermaking

5

Kalkmilcherzeugung

6

carbon dioxide production

7

lime

8th

carbon dioxide

9

filtrate

10

pulper

11

pulper

12

Pulper rotor

13

metering

14

Plastic cleaner

15

grader

16

screw Press

17

Dissolved pulp suspension

18

press filtrate

19

thickened fiber

20

Crystallizer

21

carbon dioxide supply

22

heat exchangers

23

Cooling or heating

24

Carbon dioxide gas

25

mixing device

26

storage chest

27

dilution water

28

Fibrous suspension

29

paper machine

Claims (23)

Process for loading a pulp suspension containing cellulose fibers (S) with calcium carbonate with the following process steps: introduction of calcium hydroxide in liquid or dry form or of calcium oxide into the pulp, formation of a pulp suspension (S), introduction of gaseous carbon dioxide into the pulp suspension ( S), - failures ( 3 ) of calcium carbonate by the carbon dioxide, characterized in that the calcium oxide or calcium hydroxide at or before carried out to form the pulp suspension ( 1 ) of the pulp (P) is added. Method according to claim 1, characterized in that the resolution ( 1 ) is carried out continuously. Method according to claim, characterized in that the resolution ( 1 ) is carried out discontinuously and that at the beginning of the dissolution ( 1 ) at least a portion of the calcium hydroxide is metered in liquid form. Method according to Claim 1, 2 or 3, characterized in that the resolution ( 1 ) in a pulper ( 10 ) is carried out. Method according to Claim 1, 2 or 3, characterized in that the resolution ( 1 ) is carried out in a dissolving drum. Method according to claim 5, characterized in that that the calcium oxide or calcium hydroxide in the feed area added to the dissolving drum becomes. Method according to one of the preceding claims, characterized in that the resolution ( 1 ) in a consistency range of between 3 and 30%, preferably between 10 and 20%. Method according to one of the preceding claims, characterized in that the pulp (P) before dissolution ( 1 ) is soaked with water and calcium hydroxide. Method according to claim 8, characterized in that that for used for soaking the pulp (P) a soaking drum becomes. Method according to claim 8, characterized in that that when soaking calcium hydroxide is sprayed onto the pulp (P). Method according to one of the preceding claims characterized characterized in that the calcium hydroxide is added in the form of lime milk and that the consistency of the milk of lime in the range of 0.01 to 60% of the existing solids content of the dry pulp is set. Method according to one of the preceding claims, characterized characterized in that for the reaction of the calcium hydroxide, a time between 0.01 to 10 minutes, preferably 1 second to 3 minutes, is set. Method according to one of the preceding claims, characterized in that a fibrous material (P) is used as starting material is with a consistency between 40 to 100%. Method according to one of the preceding claims, characterized in that after the resolution ( 1 ) Process steps are carried out, which serve to clean the fiber suspension of contaminants. Method according to one of the preceding claims, characterized in that the pulp suspension (S) prior to the introduction of gaseous carbon dioxide ( 24 ) is thickened again. Process according to claim 15, characterized in that during thickening ( 2 ) resulting filtrate ( 9 ) to the resolution ( 1 ) is used. Method according to one of the preceding claims, characterized in that the pulp suspension during or after the precipitation ( 3 ) is converted into fine pulp crumbs in a crushing step and dispersed. Method according to one of the preceding claims, characterized in that the failure ( 3 ) of calcium carbonate is carried out at a consistency which is between 5 and 60%, preferably between 10 and 35%. Method according to one of the preceding claims, characterized in that the energy expenditure for the precipitation ( 3 ) is between 0.3 to 8 kWh / t, preferably between 0.5 and 4 kWh / t. Method according to one of the preceding claims, characterized in that the temperature during precipitation ( 3 ) between -5 ° and 120 ° C, preferably to between 20 to 90 ° C, is set. Method according to one of the preceding claims, characterized in that the failure ( 3 ) is carried out at a pressure between 0 and 15 bar, preferably 0 and 6 bar. Method according to one of the preceding claims, characterized in that the pH at precipitation ( 3 ) between 6 and 10, preferably 6.5 to 8.5, is set. Method according to one of the preceding claims, characterized in that the reaction time of the precipitation ( 3 ) is adjusted to 0.01 to 1 minute, preferably 0.5 to 10 seconds.