Method and Device for the Thermal Treatment of Sand

Abstract

The invention relates to a method and an apparatus for sintering sand. An object of the invention consists in using energy-saving sintering to make it possible to use round-grain sand with evenly distributed grain fractions as a building material, and particularly as an aggregate.

The object is achieved by providing a focusing device (3) for thermal energy-rich radiation (2) for generating at least one focal point (5) on the surface of a bulk sand (10) and a positioning device (6) for continuous relative movement between the focal point (5) and the sand (10).

The object is further achieved by using desert sand as an aggregate for a construction element (12), characterized in that grain agglomerates (11) of desert sand (10) obtained by sintering are introduced as an aggregate into a matrix material (13).

Claims

1. A method for the thermal treatment of sand, characterized in that a radiation (4) focused to at least one focal point (5), through which heat is created when meeting a surface, is directed onto a surface of a bulk sand (10), that the local temperature of the sand (10) is increased such that the crystal lattice structure of the SiO.sub.2 compounds changes, and/or deformations and/or grain agglomerates (11) are created when a sintering temperature is reached.

2. The method according to claim 1, wherein the change in the crystal lattice structure is followed by at least one further method stage of sintering.

3. The method according to claim 1, wherein free sintering, in which the focal point (5) is directed onto the surface of the bulk of the sand (10) in an appropriate manner, results in grain agglomerates (11) having the intended dimensions.

4. The method according to claim 1, wherein mold sintering, in which the focal point (5) is directed in an appropriate manner onto the bulk of the sand (10) introduced into a temperature resistant sintering mold which is open towards the top, results in grain agglomerates (11) having the intended dimensions, so that a molded part is formed.

5. The method according to claim 1, wherein a selective and timed reduction of the temperature is provided after the sintering, so that the crystal lattice structure of the SiO.sub.2 compounds is selectively influenced further.

6. The method according to claim 1, wherein the local temperature is increased or decreased stepwise or constantly by means of multiple focusing devices (3) successively supplying focused radiation (4) to the surface of the sand (10).

7. The method according to claim 1, wherein a device for utilization of solar energy provides thermal energy obtained through focused solar radiation (2), and a lens system acting as a focusing device (3) focuses the solar radiation (2) in a controlled manner, so that the usable amount of energy and the temperature at the focal point (5) of the lens system are continuously adjustable.

8. The method according to claim 7, wherein control is achieved through a continuously acting lamellar aperture or through application of a shutter technology in which the duration of exposure is changed by fully allowing and obstructing passage of the beam in alternating, sequential intervals at a predetermined frequency.

9. An apparatus for the thermal treatment of sand, wherein a focusing device (3) for a radiation (2), through which heat is created when meeting a surface, is provided for generating at least one focal point (5) on the surface of a bulk sand (10), wherein a device for utilization of solar energy comprising a lens or a lens system (3) is provided, characterized in that the device for utilization of solar energy focuses the solar radiation in a controlled manner such that the temperature at the focal point (5) of the lens or the lens system (3) is continuously and variably adjustable.

10. The apparatus according to claim 9, wherein a positioning device (6) is provided for continuous or discontinuous relative movement between the focal point (5) and the sand (10).

11. The device according to claim 10, wherein multiple lens systems (3) are provided and are arranged in such a manner that the temperature of the sand (10) can be changed stepwise or constantly during the continuous relative movement between the focal point (5) and the sand (10).

12. A reinforcement material for the construction industry, consisting of round-grain sand grains as the source material, characterized in that the sand grains (10) are agglomerated by sintering to form grain agglomerates (11) having a predetermined size distribution.

13. The reinforcement material according to claim 12, wherein grain agglomerates (11) shaped in a load and/or geometry dependent manner are provided.

14. The reinforcement material according to claim 12, wherein three-dimensional bodies or hollow bodies designed as a single- or multi-layer lattice or space lattice with variable lattice parameters are provided as the grain agglomerates (11).

15. Use of desert sand as an aggregate for a construction element (12), characterized in that coarse grain agglomerates (11) of desert sand (10) obtained by surface modification through thermal treatment according to claim 1 and/or by sintering are introduced as an aggregate into a matrix material (13).

16. The use according to claim 15, wherein sintered, freely shaped grain agglomerates (11) are incorporated in the matrix material (13) in a directionally oriented manner, so that the grain agglomerates (11) are present in the construction element according to load and required dimensions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further details, features and advantages of the invention become apparent from the following description of embodiments under reference to the associated drawings. In the schematic drawings:

[0045] FIG. 1 is a schematic perspective view of an embodiment of a sintering apparatus according to the invention;

[0046] FIG. 2 is a schematic side view of an embodiment of a dual sintering apparatus according to the invention; and

[0047] FIG. 3 is a schematic cross-sectional side view of an embodiment of a construction element according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] FIG. 1 shows the operating principle of an embodiment of a sintering apparatus 1 according to the invention. Sunlight 2 is collimated via a lens system 3, which in the shown embodiment is a Fresnel lens, and is focused at the focal point 5. The intensity of the collimated sun rays 4 can be adapted depending on the set position of an aperture 8, whereby the temperature to be reached at the focal point 5 can be adjusted variably.

[0049] Via a metering device, the sand 10, i.e., raw sand as the source material, is supplied to a temperature resistant conveyor device 16 made of or coated with a ceramic material and moving in the conveying direction 16. The sintering process takes place at the focal point 5 of the lens system 3 (and under pressure where needed).

[0050] As the conveyor device 16 proceeds further, the sintered sand 10, which has formed a grain agglomerate 11, cools down or, alternatively or additionally, is actively cooled down by a cooling device 7, which is not described and shown in more detail here.

[0051] FIG. 2 shows a schematic side view of a dual sintering apparatus according to the invention and particularly also the metering and conveying process of a multi-stage, in this case two-stage method. Areas I. and II. designate the two process stages. The sintering (see focused radiation 4) and cooling processes here systematically alternate in order to combine and sinter several layers of sand 10 successively supplied from the metering devices 9 with one another and with the grain agglomerates 11 of the previous stage, respectively, to form grain fractions, i.e., grain agglomerates 11, which grow larger with every process stage.

[0052] A conveyor device 6 moves the sand 10 relative to the focused radiation 4.

[0053] The waste heat released during the cooling can be returned, for example via energy recovery processes, to the transport system or the facility technology such that the entire system can be operated in a self-sufficient manner. Solar energy, which is used anyway, may also be used here, i.e., the entire facility technology may be designed to use solar energy.

[0054] FIG. 3 is a schematic cross-sectional side view of an embodiment of a construction element 12 according to the invention. The construction element 12 comprises a matrix material 13. Said matrix material consists of hydrated cement and an aggregate directionally oriented according to need or required dimensions. According to the invention, the introduced aggregate consists in grain agglomerates 11 oriented in the direction 15 of tension of the construction element 12 to be formed.

[0055] A particularly advantageous variant provides grain agglomerates 11 which have a higher tensile strength than the matrix material 13 and thus have an effect similar to that of a fiber reinforcement. Together with the directionally oriented introduction into the matrix material 13, this results in a considerable increase in tensile strength of the construction element 12 in the direction 15 of tension.

LIST OF REFERENCE NUMERALS

[0056] 1 sintering apparatus

[0057] 2 radiation, solar radiation, sun rays, sunlight

[0058] 3 focusing device, lens system, Fresnel lens

[0059] 4 focused radiation

[0060] 5 focal point

[0061] 6 conveyor device, positioning device

[0062] 7 cooling device

[0063] 8 aperture

[0064] 9 metering device

[0065] 10 sand, sand grain, desert sand

[0066] 11, 11 grain agglomerate

[0067] 12 construction element

[0068] 13 matrix material

[0069] 14 direction of compression

[0070] 15 direction of tension

[0071] 16 conveying direction