EP1172478A1 - Process for loading fibers with calcium carbonate - Google Patents

Abstract

To the fibrous suspension (26), a medium containing calcium oxide (quicklime) and/or calcium hydroxide (slaked lime) is added. The treated suspension is reacted with pure carbon dioxide or a medium containing carbon dioxide, in reactors (12). During chemical reaction, to complete lime and carbon dioxide conversion into calcium carbonate and water, the pH of the fibrous suspension is suitably controlled.

Description

The invention relates to a method for loading in a fiber suspension contained fibers with calcium carbonate through a chemical reaction.

Fibrous suspensions of the type mentioned serve in particular the Paper and / or cardboard manufacturing. The particularly from economic and ecological reasons necessary careful handling of raw material resources manifests itself in paper making in increasingly lower basis weights the paper web and in the partial replacement of the fibrous material with fillers. If cheaper raw materials are used, the paper quality should at least be maintained. Here, among other things, the strength that optical properties and the processability of the end product are crucial Role.

The aim of the invention is in particular the method of the type mentioned with regard to the highest possible economy and the highest possible To further optimize the quality of the fiber suspension.

According to the invention, this object is achieved by the fiber suspension a medium containing calcium oxide and / or calcium hydroxide is added, that the fibrous suspension treated in this way in particular in at least one Reactor with another, pure carbon dioxide or containing carbon dioxide Medium is applied and that in the course of the chemical reaction for a at least essentially complete conversion of the starting materials mentioned Calcium oxide or calcium hydroxide and carbon dioxide in the reaction products Calcium carbonate and water are taken care of by the pH of the pulp suspension is regulated accordingly. Thereby the measurement of the pH value at one or more points in the process flow. The fiber suspension (Pulp) has a consistency of greater than 5%, preferably between 15% to about 40%, which also in this area is adjustable.

If calcium oxide and / or calcium hydroxide are added Medium to the fiber suspension runs a chemical reaction exothermic property, the calcium hydroxide preferably in liquid Form (milk of lime) is added. This means that not necessarily that possibly in or on the fibers of the fiber suspension Accumulated water is necessary for the start and completion of the chemical reaction is.

Due to this training, a significantly higher economy and a achieved higher quality of the fiber suspension.

When the fibers are loaded, calcium carbonate is deposited on the wetted fiber surfaces by adding calcium oxide and / or calcium hydroxide to the moist fiber material, at least some of which can be associated with the water of the fiber amount. The fiber material treated in this way is then charged with the pure carbon dioxide or with the medium containing carbon dioxide. In addition, the resulting CaCO ₃ can form a suspension around the fibers.

The term "wetted fiber surfaces" can mean all wetted surfaces of the individual fibers. In particular, this also includes the case where the fibers both on their outer surface and inside (lumen) be loaded with calcium carbonate.

Accordingly, the fibers are loaded with the filler calcium carbonate, the attachment to the wetted fiber surfaces being carried out by a so-called "Fiber Loading ™" process as described as such in US Pat. No. 5,223,090. In this "Fiber Loading ™" process, the CO ₂ reacts with the calcium hydroxide to form water and calcium carbonate.

• Verweilzeit der Faserstoffsuspension im Reaktor;
• Zuflußgeschwindigkeit der Faserstoffsuspension;
• Druck des Kohlendioxids;
• Temperatur der Faserstoffsuspension und/oder des Calciumhydroxids;
• Druck im Reaktor;
• Temperatur des CO₂;
• Druck des CO₂;
• Konzentration des CO₂ im Medium;
• Konzentration des CaO, des Ca(OH)₂ und der Fasern;
• spezifische Faseroberfläche.

In a preferred embodiment of the method according to the invention, the respective actual pH value is compared with a correspondingly predeterminable target value and the control deviation is reduced or eliminated via at least one of the following process control variables:

• Residence time of the fiber suspension in the reactor;
• Flow rate of the pulp suspension;
• Pressure of carbon dioxide;
• Temperature of the fiber suspension and / or calcium hydroxide;
• Pressure in the reactor;
• Temperature of CO ₂ ;
• Pressure of CO ₂ ;
• Concentration of CO ₂ in the medium;
• Concentration of CaO, Ca (OH) ₂ and fibers;
• specific fiber surface.

The pH of the fiber suspension is advantageously in a range of adjustable from about 5.5 to about 10.5.

It is also advantageous if the ash content of the fiber suspension is in one Range is adjustable from about 1% to about 70%.

The carbon dioxide is preferably supplied in gaseous form.

The temperature of the supplied carbon dioxide can range from about - 10 ° to about 250 ° C adjustable or adjustable.

In certain cases it is advantageous if additional optical properties, for example whiteness, brightness, opacity, color locus, light scattering coefficient, used as an indicator of the course of the chemical reaction become.

• mindestens vor/nach Reaktion;
• auch während der Reaktion;
• ggf. mehrere Messungen.

The pH measuring location is preferably selected at least one of the following steps:

• at least before / after reaction;
• also during the reaction;
• possibly several measurements.

The pH is preferably at the end of the chemical reaction or after enlarging the specific surface by means of at least one Fluffers measured.

According to the invention, pressure regulation is in the range from approximately 0.1 to approximately 20 bar intended.

Furthermore, the fiber suspension becomes shear, preferably in at least a fluffer, exposed to to enlarge their specific surface.

Otherwise, in particular when loading the fibers with calcium carbonate proceed as described in US-A-5,223,090. The content this document is hereby incorporated by reference into the present application recorded with.

Figur 1:

in schematischer Darstellung eine mögliche Ausführungsform einer Vorrichtung zum Beladen von in einer Faserstoffsuspension enthaltenen Fasern mit Calciumcarbonat;

Figuren 1a - 1c:

verschiedene pH-Wert-Verläufe über der Reaktionszeit; und

Figur 2:

eine schematische Darstellung einer weiteren Ausführungsform zum Beladen von Fasern.

Further features and advantages of the invention will become apparent from the following description of exemplary embodiments, in which reference is made to the drawing; in this show:

Figure 1:

a schematic representation of a possible embodiment of a device for loading fibers contained in a fiber suspension with calcium carbonate;

Figures 1a - 1c:

different pH values over the reaction time; and

Figure 2:

is a schematic representation of another embodiment for loading fibers.

FIG. 1 shows a schematic representation of a purely exemplary embodiment of a device 10 for loading fibers contained in a fiber suspension with calcium carbonate (CaCO ₃ ). Accordingly, this device 10 is used to store calcium carbonate on the wetted fiber surfaces of the fiber material. In principle, this loading of the fibers can take place in particular in accordance with the "Fiber Loading ™" process mentioned above.

The device 10 can comprise one or more reactors R _i , in which the fibrous suspension mixed with calcium oxide (CaO) and / or calcium hydroxide (Ca (OH) ₂ ) contains pure carbon dioxide (CO ₂ ) or a medium containing carbon dioxide (CO ₂ ) is acted upon.

• mindestens vor/nach Reaktion;
• auch während der Reaktion;
• ggf. mehrere Messungen.

pH-measuring location:

• at least before / after reaction;
• also during the reaction;
• possibly several measurements.

A fluffer 14 can be provided before and / or after and / or in the reactor (s) R _i , in which the fiber material of the fiber suspension is split with the aim of increasing the specific surface area of the fiber material in such a way that the accessibility for the Educts to the fiber material surface is optimized. This results in a further improvement of the homogenization and the "Fiber Loading ™" process is optimized accordingly.
This can be done by subjecting the fiber suspension to shear forces, for example in a fluffer. The pH value measurement is preferably carried out at the end of the reaction, after the increase in the specific surface.
In the present exemplary embodiment, the first fluffer 14 is provided between a refiner 16 and the reactor or reactors 12 _i . Alternatively or additionally, it is also possible, for example, to provide such a fluffer 14 between the at least one reactor 12 _i and a tank 18. In the present exemplary embodiment, a refiner 20 follows the tank 18, after which it goes to the paper machine PM.

The further details still contained in FIG. 1 are also purely exemplary and can be used individually or in any combination.

By means of this device 10, for example, calcium carbonate can be deposited on the wetted fiber surfaces of the fiber material, this loading of the fibers, in principle, again correspondingly the aforementioned "Fiber Loading ™" process can be done.

The medium containing calcium oxide and / or calcium hydroxide (slaked lime) can be added to the fiber material in such a way that at least some of it can associate with the water present in the fiber material, ie between the fibers, in the hollow fibers and in their walls. the following chemical reaction occurs:

In a respective reactor, carbon dioxide (CO ₂ ) is then applied to the fiber material in such a way that calcium carbonate (CaCO ₃ ) is largely deposited on the wetted fiber surfaces. The following chemical reaction occurs: "Fiber Loading": Ca (OH) ₂ + CO ₂ ⇒ CaCO ₃ + H ₂ O
(Calcium carbonate + water)

For example, by means of the device described above, the "Fiber Loading "process is now preferably carried out so that the fiber suspension a medium containing calcium oxide and / or calcium hydroxide is added is that the fiber suspension treated in this way in particular in at least a reactor with another, pure carbon dioxide or containing carbon dioxide Medium is applied and that in the course of the chemical reaction for an at least substantially complete implementation of the above Starting materials calcium oxide or calcium hydroxide and carbon dioxide in the reaction products Calcium carbonate and water is taken care of by the pH of the Fibrous suspension is regulated accordingly.

• Verweilzeit der Faserstoffsuspension im Reaktor;
• Zuflußgeschwindigkeit der Faserstoffsuspension;
• Druck des Kohlendioxids;
• Temperatur der Faserstoffsuspension und/oder des Calciumhydroxids;
• Druck im Reaktor;
• Temperatur des CO₂;
• Druck des CO₂;
• Konzentration des CO₂ im Medium;
• Konzentration des CaO, des Ca(OH)₂ und der Fasern;
• spezifische Faseroberfläche.

It is advantageous if the respective actual pH value is compared with a correspondingly specifiable setpoint and the control deviation is reduced or eliminated using at least one of the following process control variables:

• Residence time of the fiber suspension in the reactor;
• Flow rate of the pulp suspension;
• Pressure of carbon dioxide;
• Temperature of the fiber suspension and / or calcium hydroxide;
• Pressure in the reactor;
• Temperature of CO ₂ ;
• Pressure of CO ₂ ;
• Concentration of CO ₂ in the medium;
• Concentration of CaO, Ca (OH) ₂ and fibers;
• specific fiber surface.

FIGS. 1a-c each show the pH for different exemplary embodiments displayed over the respective reaction time.

Such a pH control is, for example, also the one shown in FIG. 2 Embodiment possible.

According to this FIG. 2, the present fibrous raw material 22 in a pulper 24 processed into a fiber material 26, in which the fibers are then at least essentially already isolated, i.e. are separated from each other. The Fiber material 26 at least partially contains water. This can be both between the fibers as well as in the interior (lumens) and in the walls of the hollow fibers are present. The fiber material 26 can, for example, in Form of a so-called "dewatered crump pulp" (see. US-A-5,223,090) provided his.

The fiber material 26 is then fed to a collecting container 28 or the like, in which an agent 30 containing calcium oxide and / or calcium hydroxide (slaked lime) is added in such a way that at least a part thereof coincides with that in the fiber material, ie between the fibers, in the hollow fibers and associated in their walls, existing water. The following chemical reaction occurs, as already mentioned above:

The dry content of the fiber material can then be increased, for example, by feeding to a press 32, the press water 34 again is returned to the cycle. In this example, by two fluffers 14 completed reactor 36, the fiber material 26 with the pure carbon dioxide or carbon dioxide-containing medium, which in the figure 2 is indicated by the arrow pointing into the reactor 36.

By applying the pure carbon dioxide or carbon dioxide to the already pretreated fiber material in the manner described, the following chemical reaction occurs, which has also been mentioned previously: "Fiber Loading ™": Ca (OH) ₂ + CO ₂ ⇒ CaCO ₃ + H ₂ O
(Calcium carbonate + water)

Regardless of the particular type of device used are regarding a further optimization of the "Fiber Loading ™" process individually or in any Combination also the following measures or features are advantageous:

The pH of the fiber suspension can be measured to monitor and / or regulate the chemical reaction. The pH is preferably adjustable in a range from about 5.5 to about 10.5.
The ash content of the fiber suspension can be regulated, for example, in a range from about 1% to about 70%.

The carbon dioxide can in particular be supplied in gaseous form. The temperature of the carbon dioxide supplied is advantageously in a range of adjustable from about -10 ° to about 250 ° C.

As indicators for regulating the chemical reaction, for example optical properties, for example whiteness, brightness, opacity, Color locus, light scattering coefficient can be used.

In principle, it is also possible to use the pH, the ash content and / or the calcium carbonate (CaCO ₃ ) content as a controlled variable when regulating the chemical reaction.

A dilution (H ₂ O) is also possible in the areas designated "VD" in FIG. 1.

Zufuhr von Pulp:

• Volumen und Massenstrom regelbar;
• Temperatur regelbar in einem Bereich von etwa 5°C bis etwa 95°C;
• Stoffdichte regelbar in einem Bereich von etwa 15% bis etwa 40%; vorzugsweise von etwa 20 % bis etwa 25 %;
• pH-Wert regelbar von etwa 10 bis etwa 13.

Calciumcarbonat (CaCO) im Reaktor:

• Kristalltypen: rhomboedrisch, skalenoedrisch, rosettenartig, sphärisch, nadelförmig, prismenförmig, aragonitisch, plättförmig, GCC und ähnliche;
• Reaktion unter etwa 0,1 bis etwa 20 bar;
• Temperatur von etwa -10° bis etwa 200°C;
• Verweilzeit von etwa 1 Minute bis etwa 1 Stunde.

Fluffing:

• dient der Vergrößerung der spezifischen Oberfläche;
• einsetzbar vor und/oder nach und/oder in einem jeweiligen Reaktor bzw. den Reaktoren;
• Spaltweite von etwa 0,1 bis etwa 100 mm, vorzugsweise einstellbar;
• Energieeintrag in einen Bereich von etwa 5 kWh/t bis etwa 200 kWh/t.

Refining:

• vor und/oder nach und/oder in einem jeweiligen Reaktor bzw. den Reaktoren bzw. dem "Fiber Loading™"-Prozeß.

Druckbehälter oder Reaktor (*) / Verweilpulper nach Reaktor (**):

• (*) Kristalltypen: romboedrisch, skalenoedrisch, rosettenartig, sphärisch, nadelförmig, prismenförmig, aragonitisch, plättförmig, GCC und ähnliche;
• (*) Reaktion unter etwa 0,1 bis etwa 20 bar;
• (**) Temperatur in einem Bereich von etwa -10° bis etwa 250°C;
• (*) pH-Wert von etwa 5,5 bis etwa 10,5 regelbar;
• (**) Stoffdichte etwa 0,1% bis etwa 15%;
• (**) CO₂-Zugabe;
• (**) Verweilzeit.

CaCO₃-Anteil am Pulp:

• Bei einem zugrundeliegenden Massenanteil von etwa 1 % bis etwa 70 % des Füllstoffs, etwa 1 % bis etwa 60 % an den Fasern angelagerter Füllstoff, der Rest freies FLPCC™ (Fiber Loaded Precipiated Calcium Carbonate) in der Suspension.

The measures or features mentioned below can also be used, individually or in any combination, to further optimize the fiber loading process:

Intake of pulp:

• Volume and mass flow adjustable;
• Temperature adjustable in a range from about 5 ° C to about 95 ° C;
• Consistency adjustable in a range from about 15% to about 40%; preferably from about 20% to about 25%;
• pH adjustable from about 10 to about 13.

Calcium carbonate (CaCO) in the reactor:

• Crystal types: rhombohedral, scalenohedral, rosette-like, spherical, needle-shaped, prism-shaped, aragonitic, plate-shaped, GCC and the like;
• Reaction under about 0.1 to about 20 bar;
• Temperature from about -10 ° to about 200 ° C;
• Residence time from about 1 minute to about 1 hour.

fluffing:

• serves to enlarge the specific surface;
• can be used before and / or after and / or in a respective reactor or reactors;
• Gap width from about 0.1 to about 100 mm, preferably adjustable;
• Energy input in a range from about 5 kWh / t to about 200 kWh / t.

Refining:

• before and / or after and / or in a respective reactor or the reactors or the "Fiber Loading ™" process.

Pressure vessel or reactor (*) / indwelling pulper after reactor (**):

• (*) Crystal types: rhombohedral, scalenohedral, rosette-like, spherical, needle-shaped, prism-shaped, aragonitic, plate-shaped, GCC and the like;
• (*) Reaction under about 0.1 to about 20 bar;
• (**) temperature in a range from about -10 ° to about 250 ° C;
• (*) pH adjustable from about 5.5 to about 10.5;
• (**) consistency from about 0.1% to about 15%;
• (**) CO ₂ addition;
• (**) dwell time.

CaCO ₃ content in the pulp:

• With an underlying mass fraction of about 1% to about 70% of the filler, about 1% to about 60% of the filler attached to the fibers, the rest free FLPCC ™ (Fiber Loaded Precipiated Calcium Carbonate) in the suspension.

LIST OF REFERENCE NUMBERS

10

Device for loading fibers

12 _i

reactor

14

Fluffer

16

refiner

18

tank

20

refiner

22

starting material

24

pulper

26

fiber material

28

Clippings

30

Containing calcium oxide and / or calcium hydroxide reactant

32

Press

34

press water

36

reactor

38

Valve

40

paper machine

VD

Dilution (H ₂ O)

Claims (12)

Method for loading fibers contained in a fiber suspension (26) with calcium carbonate by a chemical reaction,
characterized, that a fiber (30) containing calcium oxide and / or calcium hydroxide is added to the fiber suspension (26), so that the fiber suspension (26) treated in this way is treated in particular in at least one reactor (12, 36) with a further medium containing pure carbon dioxide or carbon dioxide and that, in the course of the chemical reaction, an at least substantially complete conversion of the starting materials mentioned calcium oxide or calcium hydroxide and carbon dioxide into the reaction products calcium carbonate and water is ensured by regulating the pH value of the fiber suspension (26) accordingly. Method according to claim 1,
characterized in that the respective actual pH value is compared with a correspondingly predeterminable target value and the control deviation is reduced or eliminated via at least one of the following process control variables: Residence time of the fiber suspension (26) in the reactor (12, 36) Flow rate of the fiber suspension (26) Pressure of carbon dioxide Temperature of the fiber suspension (26) and / or calcium hydroxide Pressure in the reactor Temperature of CO ₂ CO ₂ pressure Concentration of CO ₂ in the medium Concentration of CaO, Ca (OH) ₂ and fibers specific fiber surface. The method of claim 1 or 2,
characterized in that the pH of the fibrous stock suspension (26) can be regulated in a range from about 5.5 to about 10.5. Method according to one of the preceding claims,
characterized in that the ash content of the fiber suspension (26) can be regulated in a range from approximately 1% to approximately 70%. Method according to one of the preceding claims,
characterized in that the carbon dioxide is supplied in gaseous form. Method according to one of the preceding claims,
characterized in that the temperature of the supplied carbon dioxide is adjustable or controllable in a range from approximately -10 ° to approximately 250 ° C. Method according to one of the preceding claims,
characterized in that additional optical properties, for example whiteness, brightness, opacity, color locus, light scattering coefficient, are used as indicators for the course of the chemical reaction. Method according to one of the preceding claims,
characterized in that at least one of the following steps is selected with regard to the pH measuring location: at least before / after reaction; also during the reaction; possibly several measurements. Method according to one of the preceding claims,
characterized in that the pH is preferably measured at the end of the chemical reaction. Method according to one of claims 1 to 8,
characterized in that the pH is preferably measured after increasing the specific surface by means of at least one fluff. Method according to one of the preceding claims,
characterized in that a pressure control in the range of about 0.1 to about 20 bar is provided. Method according to one of the preceding claims,
characterized in that the fiber suspension (26) is subjected to shear forces, preferably in at least one fluffer.

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