Method and device for loading fibers contained in a fibrous suspension with calcium carbonate

Abstract

In a method and device for loading the fibers that are contained in a fiber stock suspension with calcium carbonate by way of a chemical precipitation reaction, calcium oxide and/or calcium hydroxide are added to the fiber stock suspension. In order to trigger the precipitation reaction at least partially liquid carbon dioxide is injected into the reactor thereby ensuring the transformation of the starting substance calcium dioxide or calcium hydroxide into the reaction products calcium carbonate and water. The carbon dioxide can be added in an exclusively liquid state or partially in a liquid state and partially in a gaseous state.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation of prior PCT application No. PCT/EP02/01603, entitled “METHOD AND DEVICE FOR CHARGING FIBERS CONTAINED IN A FIBROUS SUSPENSION WITH CALCIUM CARBONATE”, filed Feb. 15, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method and to a device for loading of fibers that are contained in a fibrous suspension, with calcium carbonate by way of a chemical precipitation reaction.

[0004] 2. Description of the Related Art

[0005] Loading with an additive, for example a filler, can occur through a chemical precipitation reaction, especially through a so-called “Fiber Loading™” process, as described in addition to other publications, in U.S. Pat. No. 5,223,090. In this type of “Fiber Loading™” process an additive, especially a filler, is deposited onto the moistened fiber surfaces of the fibrous material. The fibers can for example be loaded with calcium carbonate. Moreover, calcium oxide and/or calcium hydroxide are added to the moist, disintegrated fibrous material so that at least a part of this associates itself with the water that is contained in the fibrous material. The so treated fibrous material is subsequently treated with carbon dioxide.

[0006] Hitherto gaseous carbon dioxide was always exclusively added to the pulp in order to trigger the chemical precipitation reaction.

SUMMARY OF THE INVENTION

[0007] The present invention provides an improved method as well as an improved device for loading of fibers that are continued in a fibrous suspension, with calcium carbonate by way of a chemical precipitation reaction, which especially facilitates better control of the reaction temperature.

[0008] The present invention comprises a method for loading the fibers that are contained in a fiber stock suspension with calcium carbonate by way of a chemical precipitation reaction, whereby calcium oxide and/or calcium hydroxide are added to the fiber stock suspension. In order to trigger the precipitation reaction at least partially liquid carbon dioxide is injected into the reactor thereby ensuring the transformation of the starting substance calcium dioxide or calcium hydroxide into the reaction products calcium carbonate and water.

[0009] When adding the medium that contains the calcium oxide and/or the calcium hydroxide to the fiber stock suspension, a chemical reaction with exothermal characteristic occurs, whereby the calcium hydroxide is added preferably in liquid form (milk of lime). The water that is possibly embedded in or deposited on the fibers which are contained in the fibrous stock suspension is not absolutely necessary for the start and conclusion of the chemical reaction.

[0010] Based on this configuration, the reaction temperature can be controlled as desired by adding liquid carbon dioxide. The injected liquid carbon dioxide is transformed in part into a gaseous medium and in part into a solid medium, dry ice. The solid medium consists of very small particles (particle mist) that have a diameter smaller than 3 mm and evaporate very quickly and transition from the solid state into the gaseous state. This is an exothermal process. Since dry ice, that is solid carbon dioxide possesses the ability to transition directly from a solid state into a gaseous state without going through a liquid phase, no energy expenditure is necessary in order to vaporize the liquid carbon dioxide. The excess reaction energy can be utilized to convert carbon dioxide from its solid state into the gaseous state. Not only is a new method for the production of calcium carbonate found, but especially also an optimum sequence for the loading of fibers is achieved.

[0011] The carbon dioxide can be added exclusively in liquid form, or partially in liquid form and partially in a gaseous form. If the carbon dioxide is added partially in liquid form and partially in a gaseous form, then the reaction temperature and thereby the crystalline form is adjusted preferably through the ratio of the volume of the liquid carbon dioxide component to the volume of the gaseous carbon dioxide component.

[0012] In accordance with an additional advantageous embodiment of the present invention the reaction temperature is regulated via the differential pressure P&Dgr;=PCO2−PR between the liquid carbon dioxide and the reaction space where PR is the pressure in the reaction space. The differential pressure P&Dgr; is selected preferably so that it is within a range of 0<P&Dgr;<100 bar and preferably in a range of 1<P&Dgr;<50 bar.

[0013] If the reaction temperature is lower than or equal to 45° C. then a rhombohedral crystallite form of the precipitated calcium carbonate emerges. However, if this reaction temperature is higher than 45° C. then a scalenohedron crystallite form of the precipitated calcium carbonate emerges. One or the other crystallite form can be achieved, depending upon in which range the reaction temperature is maintained.

[0014] The total requirement of added carbon dioxide that includes, for example of a liquid and a gaseous component, results from a stoichiometric consideration of the balance reaction:

Ca(OH)2+Ca2CaCO3+H2O

CaO+H2O+CO2CaCO3+H2O

[0015] Liquid carbon dioxide in pressure vessels, for example bottles, is normally under high pressure to approximately 300 bar. Advantageously, the carbon dioxide can now be relieved into the reactor chamber so that it cools down and in part becomes solid, in other words, transitions from the liquid state into the solid state of aggregation and ices up. This causes a cooling action whereby the temperature of the exothermic balance reaction is influenced accordingly.

[0016] The greater the gaseous carbon dioxide content (CO2), as well as the calcium hydroxide (Ca(OH)2) content, are the greater the reaction temperature can be, or vice versa. As already mentioned, the temperature, or in other words the cooling action of the liquid carbon dioxide can be regulated as desired through the ratio between the volume of the liquid carbon dioxide content and the volume of the gaseous content, as well as through the differential pressure between the liquid carbon dioxide and the reaction space. The larger the differential pressure, the greater the cooling effect, as long as equal volumes of carbon dioxide are considered. The liquid or gaseous carbon dioxide respectively is injected into the reactor advantageously through a valve.

[0017] When loading the fibers with calcium carbonate (CaCO3) it is deposited on the moistened fiber surfaces by adding calcium oxide (CaO) and/or calcium hydroxide (Ca(OH)2) to the moist fiber material, whereby at least a part of which can associate itself with the water of the fibrous stock volume. The thereby processed fiber material is then treated with carbon dioxide (CO2). The term “moistened fiber surfaces” may encompass all moistened surfaces of the individual fibers. This specifically also includes the scenario where the fibers are loaded with calcium carbonate or any other desired precipitation product on their outside surfaces as well as on their inside (Lumen).

[0018] Accordingly the fibers are loaded with the filler calcium carbonate, whereby the loading onto the moistened fiber surfaces occurs through a so-called “Fiber Loading™” process, as described in U.S. Pat. No. 5,223,090. In this “Fiber Loading™” process the carbon dioxide with the calcium hydroxide reacts to water and calcium carbonate.

[0019] The present inventive device for loading of fibers that are contained in a fiber stock suspension with calcium carbonate by way of a chemical precipitation reaction accordingly includes elements through which calcium oxide and/or calcium hydroxide can be added to the fiber stock suspension. It further includes a reactor and elements through which at least partially liquid carbon dioxide can be injected into the reactor in order to trigger the precipitation reaction, thereby ensuring a transformation of the starting substances calcium oxide or calcium hydroxide into the reaction products calcium carbonate and water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing, which is a schematic view of an embodiment of the present invention. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring now to the drawing, there is shown a purely schematic illustration of device 10 for loading of fibers 12 that are contained in a fiber stock suspension with calcium carbonate, by way of a chemical precipitation reaction.

[0022] Device 10 includes element 14 through which calcium oxide CaO and/or calcium hydroxide Ca(OH)2 can be added to the fiber stock suspension. Device 10 further includes a “Fiber Loading™” reactor 16, as well as valve 18, through which the liquid carbon dioxide CO2 can be injected into reactor 16.

[0023] The carbon dioxide can be added exclusively in a liquid state or in part in a liquid state, and in part in a gaseous state. In the second scenario an additional valve 20 is provided, through which gaseous carbon dioxide CO2 can be supplied to reactor 16.

[0024] Device 10 can include controller 22 for the adjustment of reaction temperature TR and ratio control 24 by way of which the ratio (Volliquid/Volgaseous) of the volume Volliquid of the liquid carbon dioxide component and the volume Volgaseous of the gaseous carbon dioxide component is appropriately variable for a corresponding adjustment of reaction temperature TR. A ratio controller 26 can be provided that is actuated by ratio control 24 and that determines the ratio of the flows through the two valves 18, 20 and compares them with the desired value that was predetermined by ratio control 24 in order to then adjust this ratio accordingly. Controller 22 receives the actual value of, for example, reaction temperature TR via a corresponding measuring device 28. This actual value is compared with a desired value 30 in the controller 22. Then ratio control 24 is accordingly supplied in order to deliver an appropriate desired ratio value to ratio controller 26.

[0025] The reaction temperature is adjustable also through differential pressure P&Dgr;=PCO2−PR between the liquid carbon dioxide and the reaction space in addition to being adjustable through the volume ratio of the liquid and the gaseous carbon dioxide components. Reactor 16 then supplies fiber stock 32 that is loaded with, for example, calcium carbonate CaCO3.

[0026] Calcium oxide and/or calcium hydroxide (slaked lime) is added to the fiber material in such a way that at least a portion of this can associate itself with the water that is contained in the fiber material, i.e. between the fibers, in the hollow fibers and in their walls, thus creating the following chemical reaction: 1

[0027] The fiber material is then treated with carbon dioxide (CO2) in the relevant reactor, so that calcium carbonate (CaCO3) is extensively deposited onto the moistened fiber surfaces. This results in the following chemical reaction: 2

[0028] While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Component Identification

[0029] 10 Device

[0030] 12 Fibers

[0031] 14 Means for adding calcium oxide and/or calcium hydroxide

[0032] 16 Reactor

[0033] 18 Valve

[0034] 20 Valve

[0035] 22 Controller

[0036] 24 Ratio control

[0037] 26 Ratio controller

[0038] 28 Measuring device

[0039] 30 Desired value

[0040] 32 Loaded fiber stock

[0041] PR Pressure in the reaction space

[0042] TR Reaction temperature

Claims

1. A method for loading fibers in a fiber stock suspension with calcium carbonate by way of a chemical precipitation reaction, comprising the steps of:

adding at least one of a calcium oxide and a calcium hydroxide to the fiber stock suspension;

injecting an at least partially liquid carbon dioxide into a reactor; and

transforimig said at least one of calcium oxide and calcium hydroxide into a plurality of reaction products including calcium carbonate and water.

2. The method of claim 1, wherein said at least partially liquid carbon dioxide is exclusively liquid carbon dioxide.

3. The method of claim 1, wherein said at least partially liquid carbon dioxide includes a gaseous liquid carbon dioxide.

4. The method of claim 3, further including the step of adjusting both a reaction temperature in said reactor and a crystalline form of the calcium carbonate through a ratio of a volume of said liquid carbon dioxide to a volume of said gaseous carbon dioxide.

5. The method of claim 1, further including the step of regulating a reaction temperature in said reactor via a differential pressure P&Dgr;=PCO2−PR between said liquid carbon dioxide and a reaction space in said reactor.

6. The method of claim 5, wherein said differential pressure P&Dgr; is approximately between 0 bar and 100 bar.

7. The method of claim 5, wherein said differential pressure P&Dgr; is approximately between 1 bar and 50 bar.

8. The method of claim 1, further including the step of achieving a rhombohedral crystallite form of the calcium carbonate by keeping a reaction temperature in said reactor no greater than 45° C.

9. The method of claim 1, further including the step of achieving a scalenohedron crystallite form of the calcium carbonate by keeping a reaction temperature in said reactor greater than 45° C.

10. The method of claim 1, further including the step of cooling down said carbon dioxide by relieving said carbon dioxide into said reactor thereby creating an at least partially solid carbon dioxide.

11. The method of claim 1, wherein said at least partially liquid carbon dioxide is injected into said reactor through a valve.

12. A device for loading a plurality of fibers that are contained in a fiber stock suspension with calcium carbonate by way of a chemical precipitation reaction, comprising:

at least one first adding element through which at least one of calcium oxide and calcium hydroxide are added to the fiber stock suspension;

a reactor connected to said at least one first adding element; and

at least one second adding element connected to said reactor; said at least one second adding element through which at least partially liquid carbon dioxide is injected into said reactor in order to trigger a precipitation reaction, thereby transforming said at least one of calcium oxide and calcium hydroxide into a plurality of reaction products including a calcium carbonate and water.

13. The device of claim 12, wherein said at least partially liquid carbon dioxide is exclusively liquid carbon dioxide.

14. The device of claim 12, wherein said at least partially liquid carbon dioxide includes a gaseous liquid carbon dioxide.

15. The device of claim 14, wherein both a reaction temperature in said reactor and a crystalline form of the calcium carbonate are adjusted through a ratio of a volume of said liquid carbon dioxide to a volume of said gaseous carbon dioxide.

16. The device of claim 12, wherein a reaction temperature in said reactor is regulated via a differential pressure P&Dgr;=PCO2−PR between said liquid carbon dioxide and a reaction space in said reactor.

17. The device of claim 16, wherein said differential pressure P&Dgr; is approximately between 0 bar and 100 bar.

18. The device of claim 16, wherein said differential pressure P&Dgr; is approximately between 1 bar and 50 bar.

19. The device of claim 12, wherein a rhombohedral crystallite form of the calcium carbonate is achieved by keeping a reaction temperature in said reactor no greater than 45° C.

20. The device of claim 12, wherein a scalenohedron crystallite form of the calcium carbonate is achieved by keeping a reaction temperature in said reactor greater than 45° C.

21. The device of claim 12, wherein said carbon dioxide is relieved into said reactor cooling said carbon dioxide thereby creating an at least partially solid carbon dioxide.

22. The device of claim 12, wherein said at least partially liquid carbon dioxide is injected into said reactor through a valve.