Use of CO2 as Water Demand Reducer in Gypsum Stucco Rehydration Mortars

Abstract

The present application concerns a method for the production of a gypsum article, which includes introducing a measured quantity of carbon dioxide into the process water and mixing the stucco with the thus treated water. The CO.sub.2-enriched water has the advantage of providing compositions with sufficient processing properties at considerably lower water contents, thus allowing for significant energy savings. The invention also concerns slurries prepared according to this method as well as an apparatus which is adapted to implement this method.

Claims

1. A method for producing a gypsum article, wherein the method comprises introducing a measured quantity of carbon dioxide into a process water and mixing stucco with the thus treated process water to form a slurry, wherein the addition of carbon dioxide to the process water results in a reduction of the amount of process water necessary to achieve a given fluidity of the slurry.

2. The method according to claim 1, wherein the amount of carbon dioxide introduced into the process water provides a concentration of dissolved/dispersed carbon dioxide of at least 1 g/L, preferably at least 1.5 g/L or at least 1.8 g/L but no more than 15 g/L, preferably no more than 10 g/L or no more than 8 g/L.

3. The method according to claim 1, wherein the process water having the carbon dioxide introduced therein exhibits a pH of 8.0 or less.

4. The method according to claim 1, wherein the stucco is mixed with the process water having the carbon dioxide introduced therein to provide a water/stucco ratio in the range of about 0.5 to 1.2, preferably about 0.6 to 1.0, more preferably about 0.65 to 0.8.

5. The method according to claim 1, wherein prior to the mixing of the stucco with the carbon dioxide containing process-water paper pulp or additives are fed into the carbon dioxide containing water.

6. The method according to claim 1, wherein a foam is mixed with the slurry, and wherein the addition of carbon dioxide to the process water results in a reduction of the amount of foaming agent necessary to achieve a given density of the slurry.

7. The method according to claim 1, wherein the mixture containing stucco and carbon dioxide containing process water is formed to an article, preferably a building board, especially a plasterboard.

8. The method according to claim 7, further comprising a step of drying the article or plasterboard.

9. A slurry prepared from a water/stucco mixture prepared according to the method of claim 1.

10. An apparatus for preparing a slurry comprising a mixture of at least stucco and process water, wherein means are provided upstream of a mixer in which the stucco is mixed with the process water, wherein the means 1 allow for the directed introduction of carbon dioxide into the process water.

11. The apparatus according to claim 10, wherein the means, by which the carbon dioxide is introduced into the process water, comprises a sparger.

12. The apparatus according to claim 10, further comprising a mixer to mix the carbon dioxide enriched water with the stucco and preferably a means to feed a foam into the mixer or into a line, by which the slurry fed to the conveyor.

13. The apparatus according to claim 10, further comprising a forming means, by which the water/stucco mixture produced in mixer is formed into a desired shape.

14. The apparatus according to claim 10, wherein the forming means comprises a dispenser which applies a continuous layer of the slurry onto a liner.

15. The apparatus according to claim 13, further comprising a dryer downstream of the forming means.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0025] FIG. 1 illustrates an apparatus for preparing an article, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention concerns an apparatus for preparing a slurry comprising stucco and process water, wherein means 1, allowing the directed introduction of carbon dioxide into the process water, is provided upstream of a mixer, in which the process water is mixed with the stucco.

[0027] The means 1 above is preferably fitted with an appropriate device to finely disperse the carbon dioxide in the process water and which provides a contact surface as large as possible for the carbon dioxide with the water into which the carbon dioxide is introduced. Preferably, the means comprises a sparger 2 to introduce the carbon dioxide into the water.

[0028] The mixer 4 allows for the blending of carbon dioxide enriched process water and the stucco. In addition, the inventive apparatus preferably has means 6 to feed a foam stream into the mixer 4 or into a line 10, by which the slurry is fed to the conveyor 12.

[0029] With respect to the distance between the means 1 and the mixer 4, the distance should regularly be such that the dissolution or “dispersion” of the carbon dioxide into the process water is stably formed to avoid or reduce devolatilization and loss of the carbon dioxide during the process water/stucco mixing process. Evidently, this distance depends on the process parameters (i.e. how much carbon dioxide is incorporated, the temperature, the speed by which the water moves in the lines, etc.), but the positioning of the mixer 4 at an appropriate distance will not confront the skilled practitioner with particular difficulties.

[0030] If the apparatus is constructed with inlets (7a, 7b, etc.) for additives or strengthening materials such as paper fibers, these inlets are preferably added to the line 5 at a position, where the carbon dioxide has already been introduced into the water, i.e. downstream of the means 1. Therefore, the apparatus may have inlets (7a, 7b, etc.) by which fibrous materials and additives are introduced into the line 5. It is further preferred that the inlets (7a, 7b, etc.) for fibrous materials and additives are at positions sufficiently far removed from the carbon dioxide introduction site of means 1 into the process water so as to ensure a sufficiently stable gas/liquid dispersion at the point in time, where the fibrous materials and/or additives are introduced.

[0031] In addition, it is preferred that the inventive apparatus comprises a forming means by which the process water/stucco mixture produced in mixer 4 is formed into the desired shape. The forming means may be a continuous forming means such as a moving conveyor equipped with a forming station or a discontinuous forming means such as a mould into which a respective quantity of process water/stucco mixture is introduced.

[0032] As indicated above, preferred products of the present invention are plasterboards. Therefore, in a preferred aspect of the present application, the apparatus comprises a dispensing means 9 which is shaped to dispense a continuous layer of the slurry onto a liner, for example a cellulose based fibrous material 11a or a fiber mat. The slurry layer thus applied to the liner will be covered by second liner 11b. The apparatus preferably in addition has a conveyor 12 to convey the layers of liner material concurrent with the dispense of the slurry there between. The layers of liner materials are preferably paper or paper-board layers or woven or non-woven mat comprising glass or mineral or polymer fibers or a mixture thereof.

[0033] Furthermore, it is preferred in the context of the present application that the apparatus comprises a dryer 13 downstream of the forming means.

[0034] Referring to FIG. 1, an apparatus is depicted, wherein process water is fed via line 3 to a carbon dioxide introduction means 1 which is fitted with a sparger 2. After the carbon dioxide has been introduced into the process water, the process water is passed through line 5 which has inlets for additives 7a and for fibrous materials 7b. Further an inlet for foam 6 can be provided. Via line 5, the process water is transferred into a mixer 4 which has an inlet 8 for the addition of stucco and may optionally also have an inlet for foam 6. Once the stucco and the process water have been thoroughly mixed in the mixer, they are passed to a dispensing means 9 via line 10 by which the mixture is dispensed onto a liner 11b and subsequently covered by an additional liner 11a. These layers are continuously conveyed in the direction depicted by the arrow by means of the conveyor 12. After the stucco process water mixture has been dispensed onto the first liner and covered by the second liner, the structure thus formed is passed through a forming station, cut to size and dried in a dryer 13 to drive off the excess water still contained in the board.

[0035] The invention will be further described by way of examples, which are, however, only to be understood as an illustration of the invention and not in any way as limiting.

Example 1

[0036] Different amounts of gaseous CO.sub.2 were introduced into water prior to mixing with a stucco powder. The amount of water in each case was adjusted such that substantially identical processing properties such as fluidity/viscosity were obtained. The fluidity of a slurry was determined according the dispersal method as described prEN 1379-2:2014 was kept a constant. The amount of water necessary to achieve the given fluidity was recorded. The results of this test are provided in the following Table 1.

TABLE-US-00001 TABLE 1 CO.sub.2 incorporated Ratio of water added Water reduction potential [g/L] [g/g] [%] 0 0.725 1.2 0.701 3.3 1.8 0.694 4.3 5.1 0.675 6.9

[0037] Table 1 lists the concentration of CO.sub.2 added to the water, the amount of water with reference to the applied amount of stucco necessary to reach a given fluidity and the achieved water reduction with respect to the reference. It shows that with increasing amounts of a carbon dioxide, a significant reduction in the water necessary for the preparation of the slurry was possible although the fluidity was maintained on the same level. The highest water reduction of about 7% was obtained with about 5 g/L CO.sub.2. At about 5 g/L CO.sub.2 addition a moderate retarding of the slurry stiffening is observed. Thus, taking the retarding effect into account no more than 15 g/L CO.sub.2, preferably no more than 8 g/L CO.sub.2 should be incorporated into the slurry.

[0038] A water reduction of 3.3 and 4.3% in a regular processing line translates into energy savings of about 0.8 and 0.12 kWh/m.sup.2, respectively. For the 5% CO.sub.2-containing water, the energy savings would be about 0.2 kWh per square meter of produced boards.

[0039] Furthermore, it was observed that the board prepared at a concentration of 1.8 g/L CO.sub.2 allowed for a reduction of 3% of the foaming agent and to provide nevertheless about the same characteristics as the composition prepared with water containing no carbon dioxide.

[0040] Taking into consideration the fact that plasterboard plants usually produce several million of m.sup.2 of plasterboards per year the possible savings in energy and foaming agent add up to substantial amounts.