METHOD AND DEVICE FOR THE MANUFACTURE OF CRUSHED SAND OR ARTIFICIALLY GROWN SAND BY THERMAL TREATMENT WITH THE USE OF FINE SAND AND / OR ROLLED SAND AS STARTING MATERIAL

Description

[0001] The invention relates to a method and a device for producing artificial crushed sand or squashed sand by thermal treatment using sand in the form of fine sand (fS / FSa) and / or rounded sand as a starting material.

[0002] The term "sand" is defined as all unconsolidated rock sediments composed of individual mineral grains with a grain size of 0.063 to 2 mm. According to DIN 4022, different types of sand are distinguished based on their grain size, surface texture, and shape. Depending on the grain size distribution, sand is categorized as fine sand (fS / FSa), medium sand (mS / MSa), or coarse sand (gS / CSa). Sands are further subdivided into "rounded sands" and "angular sands." Rounded sands consist primarily of rounded components. They are mainly found in desert regions and predominantly fall within the grain size range of fine sands (fS / FSa). Angular sands are further subdivided into naturally occurring crushed sands and artificially produced crushed sands, also known as squashed sands. Natural crushed sands are primarily extracted from seabeds and riverbeds.

[0003] The enormous and steadily growing demand for concrete is also driving a sharp increase in the need for sand. Concrete consists of approximately 70% aggregate and the remaining 30% water and cement. The aggregate in concrete, also known as aggregates, comprises gravel and sand with grain sizes ranging from 0.025 to 16 or 32 mm, depending on the grading curve. On average, these aggregates contain around 30% fine particles, meaning grains smaller than 2 mm. Therefore, concrete consists of approximately 21% sand. The proportion of fine particles in concrete varies depending on its application: The aforementioned grading curve of the concrete provides information about the precise composition of the aggregates. Experts refer to the fine particles in the aggregate as "crushed aggregate." The use of crushed sands as fine-grained aggregates is of central importance for the strength of the concrete, because only these grains allow mutual interlocking, thus supporting the concrete from within.

[0004] It is known that the mineralogical composition of desert sand and coastal sand differs fundamentally in two aspects. While the average coastal sand grain is generally classified as medium sand (mS / MSa) to coarse sand (gS / CSa) and exhibits an angular shape and rough surface, desert sand grains are typically fine sand (fS / FSa) with a predominantly rounded geometry and smooth surface. These differences between coastal and desert sand grains can be easily explained by the significantly more severe weathering of desert sand grains, which are constantly worn down by wind and rolling motions, becoming progressively smaller, rounder, and smoother.

[0005] It is also known that these seemingly insignificant differences pose major problems, particularly for the construction industry, because desert sand, due to its unfavorable grain properties, is unsuitable for land reclamation in the sea and also unsuitable as a fine aggregate in concrete and cement production (see DELESTRAC, D. (Director) (2013). Sand - The New Environmental Time Bomb. [Documentary]. France: ARTE). So far, only small proportions of fine aggregates are replaced by desert sand – simply using desert sand instead of coastal sand is technically impossible.

[0006] Since the sources of naturally occurring crushed sand on land are largely exhausted, and the sand in the vast deserts—which are also constantly expanding—is unsuitable for concrete production, the only remaining option is to pump sand from the seabed. This process severely damages vegetation. At the same time, the risk of natural disasters increases, posing a particular threat to coastal communities. Furthermore, the saline sea sand must undergo extensive purification before it can be used as an aggregate in concrete production, as an excessively high salt content dramatically accelerates corrosion (especially in reinforced concrete).

[0007] The aim is to develop an environmentally friendly and mass-producible process for producing crushed sand in order to cover the shortage of natural crushed sand and to stop the ongoing pollution of coastal areas.

[0008] The following methods are currently employed to address the rapidly increasing shortage of crushed sand, particularly angular medium sand (mS / MSa). Attempts are underway to curb the extraction of coastal and marine sand through legal measures, which tends to drive up sand prices and simultaneously promote illegal mining activities. A major sector is the production of crushed sand, i.e., artificial crushed sand, through the crushing of gravel and boulders in very large crushers. While this process artificially produces crushed sand, it requires the crushing of large rock sediments, thus accelerating desertification. At the same time, the price of crushed sand is significantly higher than that of natural crushed sand (coastal sand) due to the enormous energy expenditure required to operate the expensive, high-performance crushing machines.In contrast, recycling waste glass represents a significantly more effective solution, as crushing and breaking down glass waste can produce artificial crushed sand, which is suitable, among other things, for concrete production. However, for logistical reasons, this method is not capable of supplying the required quantities of sand needed for concrete production worldwide. Furthermore, research teams are increasingly searching for methods to accelerate the natural weathering process. One approach involves bombarding rock fragments with high-voltage lightning to achieve the end product, sand (JÜNGLING, T. (2014). The vital hunt for more sand [online]. Available at: http: / / www.welt.de / wirtschaft / webwelt / article127216019 / Dielebensnotwendige-Jagd-nach-mehr-Sand.html [01.05.2014]). This method, if it is a viable solution at all, is only a medium-term one, as it also accelerates desertification.One day, this method will lead to a shortage of rock for bombardment – ​​just as with the production of crushed sand from gravel and rubble. The considerable amounts of energy required to generate high-voltage lightning completely rule out this method. The last important area of ​​research lies in construction chemistry, primarily to find synthetic substitutes for sand and suitable binders. Researchers are attempting to develop and find suitable materials for concrete production by modifying the cement paste, such as desert sand or other synthetic substances.

[0009] None of the aforementioned methods offers a mass-market, environmentally friendly solution for meeting the demand for sand. Furthermore, none of the methods addresses the problem in the way it is now presented in the invention. A process must be developed to make the vast sand deposits in the deserts usable for both concrete production and land reclamation.

[0010] Based on this prior art, a method and an apparatus for producing artificial crushed sand or smeared sand by thermal treatment using sand in the form of fine sand (fS / FSa) and / or rounded sand as a starting material, and correspondingly produced crushed sand or smeared sand with the features of the independent patent claims, are proposed. Desert sand – which, due to its aforementioned properties, can also be described as fine sand (fS / FSa) and rounded sand – is first melted to form an intermediate product. The resulting conglomerate is then broken up again, so that crushed sand or smeared sand, in particular angular medium sand (mS / MSa), is obtained as the final product.

[0011] From DE 3248537 C2, a process is known in which sintered bodies are produced from quartz sand that exhibit low density and simultaneously high strength. According to the process, quartz sand is first filled into specific molds. In a preferred embodiment, these molds are electrically conductive so that a high-voltage electric field can be applied within the molds, which must be maintained until the sintering process. Due to the influence of the electric field, the individual sand grains in the sintering mold assume a specific spatial arrangement with relatively high porosity. This high porosity is subsequently decisive for the low density of the sintered body. In the final sintering process, the quartz sand is sintered within the mold at temperatures significantly below its melting point.In DE 19516867 A1, the parameters of the process from DE 3248537 C2, for producing low-density sintered bodies, are revised, and some incorrect assumptions are corrected. The temperature range of the sintering process is therefore not the originally assumed 1400–1650 °C, but significantly lower at 1250–1350 °C. The composition of the starting material has also been defined more precisely and limited to compositions between 50–75% SiO₂ and 50–25% Al₂O₃. The sintered bodies obtained in this way can be used in a variety of applications, such as tiles, bricks, and other building materials, but they do not replace the fine aggregates in concrete. Even if these sintered bodies were crushed to fractions of less than 2 mm—which is not the aim of either patent—the desired angular medium sand (mS / MSa) would not be obtained.The reason for this lies in the sintering process, because at temperatures of up to 1600 °C (maximum value from DE 3248537 C2), the temperature is significantly below the melting point of sand (1713 °C). The sand grains do not melt completely, but only bond together through the partial melting of their surfaces. This is called agglutination. This agglutination prevents the formation of new grain boundaries. Subsequent crushing would therefore not yield the desired "broken grain," but merely the original product, as the conglomerate would break apart at its bonding points. A transformation of the desert sand does not occur here, especially at the aforementioned temperatures. The melting of the sand and the formation of new grain boundaries are not the aim of any of the patent specifications and must, in fact, be strictly avoided with regard to a successful end product, namely sintered bodies with low density and high strength.Melting the individual grains and thus creating new grain boundaries would destroy the voids directly related to the low density, resulting in a high-density end product, as the porosity painstakingly created by the electric field would not be maintained. Further disadvantages include the indispensable use of (complex graphite) molds, the filling and emptying of which represent a discontinuous step in an otherwise automatable process. This method is less suitable for mass production, and even rather unsuitable for the quantities of sand required. Ultimately, the process is very costly and energy-intensive due to the generation and maintenance of a high-voltage electric field, the operation of continuous tunnel kilns, and the generally complex design and manufacture of the molds.Sand produced using such a process would therefore have no prospect of profitable distribution.

[0012] A more economical method for sintering sand grains is known in the prior art. In Markus Kayser's "Solar Sinter Project," sand is sintered using solar energy to create aesthetic shapes (see KAYSER, M. (2011). Solar Sinter [online]. Available at: http: / / www.markuskayser.com / work / solarsinter / [01.05.2014]). In this project, sunlight is concentrated in a lens and focused onto a layer of sand, allowing three-dimensional structures to be produced from the powdered material—similar to known 3D printing processes. This process constitutes a sub-process of the invention described in claim 1, with the fundamental difference that the invention according to claim 1 produces molten bodies rather than sintered bodies. Sintered bodies have the same disadvantages as described above in relation to DE 3248537 C2.Furthermore, the process in the Solar Sinter Project does not envisage the production of angular medium sand (mS / MSa) or crushed sand, but is limited to the production of sintered molded bodies, primarily for aesthetic design.

[0013] CN 101 987 discloses a process for treating desert sand wherein the starting material is heated to a melting temperature by focusing sunlight and the intermediate product thus formed is then cooled.

[0014] None of the sintering processes mentioned offer a method for converting desert sand, i.e., rounded sand or fine sand (fS / FSa), into angular medium sand (mS / MSa).

[0015] The present invention provides a fully-fledged replacement for the finite resource of natural crushed sand and an economically viable and, in particular, environmentally friendly process for producing this artificial substitute. This substitute, hereinafter referred to as crushed sand or smothered sand, especially as angular medium sand (mS / MSa), represents a good alternative to the use of coastal and marine sand, i.e., natural crushed sand, particularly in the field of concrete production and as bulk material for land reclamation.

[0016] Preferably, the initially round, smooth mineral grains of fine sand (fS / FSa) (desert sand) change their state of matter during the melting process and form a common bond in the liquid phase, resulting in the formation of new grain boundaries. When these mineral grain aggregates are crushed into fragments smaller than 2 mm, sand is obtained whose mineral grains exhibit a geometry and surface texture clearly distinguishable from the original material. Suitable crushing machines include, for example, a shredder, a conical mill, or a rotor impact mill, as used in waste and glass recycling. The mineral grain aggregate, a three-dimensional structure, breaks randomly, forming fragments with an angular geometry. This angular shape later allows the grains to interlock with each other in the construction material (concrete as well as bulk material for land reclamation).The second important property, the increased surface roughness, is achieved through the thermal forming process. The solidification of the three-dimensional sand grain composite after the melting process is comparable to known forming processes. When forming granules into metals, it is observed that the surface finish after solidification from the melt usually does not meet the high requirements (in engineering terms: smooth surfaces). These surfaces almost always require post-processing in grinding processes. In the invention, this principle is applied in reverse. Due to natural grinding processes, the starting material has a surface that is too smooth for use in concrete. This surface finish is created by the continuous abrasion of the sand grains against each other, which is attributable to wind dispersal and the resulting rolling motion.Thermal forming of the raw material degrades its surface. In other words, the surface roughness increases. However, in this case, this is beneficial to the application. The increased roughness prevents individual grains from sliding against each other and thus also contributes to the stabilization of the building material.

[0017] The fundamental replacement of conventional coastal and marine sand with crushed sand produced using the aforementioned manufacturing process is thus guaranteed.

[0018] The advantages of the described process lie primarily in its extremely environmentally friendly operation, which can rely entirely on renewable energy. In one variant of the invention, even photovoltaic fields, i.e., expensive semiconductor technology, are not required. The immediate location of the raw material, sand, in areas of highest solar irradiance offers advantages in terms of transport and storage, as well as the high technical efficiency of the process. This invention makes it possible to tap into the vast sand deposits in desert regions for the construction sector and land reclamation while protecting marine vegetation. The increased risk of natural disasters in coastal areas caused by sand extraction can thus be drastically reduced. At the same time, the increasing spread of deserts is slowed.

[0019] Advantageously, the starting material is heated at least to the point where new grain boundaries form. This prevents and eliminates the decomposition back to the original product during the comminution process. It has been shown that under typical ambient conditions (pressure = 1 bar, temperature = 23°C), a temperature of at least 1700°C is sufficient to produce the necessary three-dimensional structure and ensure the formation of new grain boundaries. However, in some experiments, the desired result was only achieved at temperatures significantly above the melting point, from approximately 1810°C. Methods for generating the melting point by focusing sunlight allow for very high temperatures, exceeding 2000°C, and cannot be precisely controlled anyway.Setting the desired melting temperature is therefore only relevant when using conventional melting devices and should be precisely determined in a preliminary series of tests, taking into account the exact composition of the sand and the ambient parameters. It should be noted here that the subsequent strength of the concrete or the reclaimed land depends heavily on the proportion of crushed aggregate in the sand used. While a sand mixture of crushed and uncrushed aggregate is conceivable, it should be avoided during the production process by ensuring the correct melting temperature.

[0020] According to an advantageous embodiment of the process, the three-dimensional structure is cooled after the melting process to such an extent that brittle fractures occur during comminution. It has been found that the structure should preferably be cooled to at least 600 °C to exhibit brittle behavior. A suitable assessment of this brittle behavior can be made using the scratch hardness scale (Mohs hardness). Quartz, the main component of the starting material, has a scratch hardness of 7 under normal conditions. Above a value of 6, plastic deformation is prevented before the material fractures. It is therefore advantageous to cool the intermediate product until a scratch hardness of 6 or higher is reached. The change of the state of matter from liquid (melt) to solid (glassy, ​​three-dimensional structure) does not occur abruptly, but rather proceeds through several phases.At temperatures above 1600 °C, the material is liquid to viscous. Up to a temperature of 1200 °C, it has a slurry-like consistency, which would cause clogging in some grinding machines. Between 600 °C and 1200 °C, the material appears solid, but successful grinding is not guaranteed. Most successful results were achieved by cooling below 600 °C. To be on the safe side, complete cooling to ambient temperature is recommended.

[0021] According to a preferred embodiment, the melting temperature is generated by focusing solar rays using at least one converging lens and / or at least one mirror. Both systems follow a similar principle, capturing and focusing solar rays. The highest temperatures are reached at the focal point, i.e., the intersection of the focused solar rays. Temperatures exceeding 2000 °C can easily be generated at this focal point using either a converging lens or the mirror(s).

[0022] In a preferred embodiment, the mirror(s) are configured as at least one parabolic mirror or as an arrangement of at least two mirrors with different angles of inclination to concentrate sunlight onto a common point or cutting area. The use of many smaller mirrors, e.g., 100 mirrors with a surface area of ​​0.4 square meters, is advantageous for concentrating power levels of up to 1000 watts per square meter onto the processing area for the thermal treatment of the raw material. The sum of the differently inclined mirrors is referred to by those skilled in the art as a concentrator.

[0023] A further development of the invention involves the use of reflective plane mirrors, which are aligned, particularly automatically, with the position of the sun and thus focus the light onto the mirror(s) and / or the converging lenses. This increases the efficiency of the system, as the actual firing device does not need to be movable to follow the sun's position. Consequently, the focal point also does not wander along the processing surface, allowing the high temperature to be generated precisely at a fixed point. Those skilled in the art refer to these plane mirrors as heliostat arrays. The combination of a heliostat array and a parabolic mirror is used, for example, in solar melting furnaces. "Centre du Four Solaire Felix Trombe" in French Odeillo application.

[0024] According to an advantageous further development, the starting material is first heated to a preheating temperature, either in variant C by focusing solar radiation and / or, as shown in variant D, by using a conventional heating device that obtains its energy supply from converted or stored solar power. The preheating temperature is below the melting temperature, and the heating to the preheating temperature is carried out separately from the heating to the melting temperature. By heating the starting material to a preheating temperature of, for example, 1000 °C before the actual melting process, the duration of the process can be approximately halved while maintaining a constant mass of the starting material. It is therefore advantageous to heat the starting material in a first thermal treatment either via a tunnel furnace or a device for focusing solar radiation.In the latter variant, it is recommended to position the feedstock above the focal point, as this allows for a larger effective area and the maximum power output achievable at the focal point is usually not required during preheating. Due to their superior distribution and overlap possibilities, converging mirrors can be more advantageous than converging lenses with regard to the effective areas. Effective areas are preferably defined as those located above the focal point in the direction of the device used to focus the sunlight. The closer the actual effective area is to the focusing device, the larger the effective area and the lower the power output per unit area.

[0025] This design is optimized for mass production and energy efficiency and, based on initial assessment, represents the most economical of the alternatives mentioned. It is proposed that the starting material be fused into thin sheets.

[0026] According to a preferred embodiment, the melting temperature is generated conventionally using a laser and / or a tunnel furnace, with the limitation that these melting devices obtain their energy from photovoltaic fields. One possible embodiment thus includes at least one photovoltaic field, whereby the energy for the conventional melting device is derived from solar power. The system operates completely autonomously and is not dependent on any other energy sources. The limitation to the combination of a conventional melting device and photovoltaic fields is based on two reasons. Firstly, it is technically advantageous to locate the device in the desert, since the raw material is found there and there is very high solar irradiance. Secondly, the energy requirements of the system are thus covered by inexpensive solar energy, so that the produced crushed sand can also be sold at a lower price.The solar energy converted by photovoltaic systems can be efficiently stored in various intermediate storage devices until it is actually needed by consumers. These intermediate storage devices can include, for example, electrical batteries, mechanical flywheels, as well as hydraulic and pneumatic storage systems.

[0027] Another advantageous embodiment involves piling the raw material onto a base, particularly a conveyor belt, melting it, cooling it, and then transferring it directly to the crushing process to produce the crushed pieces. The conveyor belt is advantageous for the mass production of angular medium sand (mS / MSa) or crushed sand, as it ensures a continuous process. The cooling section can also be implemented using the conveyor belt by adjusting its speed and / or length to maintain the required cooling time between the melting and crushing processes. Active cooling devices, such as a blower or an electric cooling system, are also conceivable and can accelerate the process, but these consume significant energy and are not strictly necessary.The optimal length and speed of the conveyor belt should be determined through testing, as they depend primarily on the ambient temperature and the actual melting temperature achieved. It should also be noted that the energy required to operate the conveyor belt can be supplied by photovoltaic panels.

[0028] The substrate is subjected to significant thermal stress due to the very high melting temperatures, which is why special, heat-resistant coatings (e.g., ceramic alloys) can be used. Preferably, the starting material is layered to a sufficient height so that it melts only in an upper section, e.g., ¾, 2 / 3, or ½, while simultaneously creating an insulating layer between the substrate and the molten, three-dimensional structure in a lower section, corresponding to ¼, 1 / 3, or ½. This also prevents the three-dimensional structure from adhering to the substrate after the melting process. The layering should generally be chosen to prevent the material from melting onto the substrate while simultaneously creating the smallest possible insulating layer, as this layer must be dissipated.The insulating layer, which usually consists of sintered or partially melted sand grains, is expediently separated from the composite plate before the comminution process by, for example, a sieving or short grinding process, in order not to reduce the purity of the final product.

[0029] It is advisable to use a sieve upstream of the melting device to remove coarser foreign particles from the feedstock and to limit the particle size range. Experience has shown that limiting the particle size range produces a more homogeneous material and ensures a slight acceleration of the melting process. However, since this time saving is not crucial, the primary purpose of the sieving process is to remove foreign particles, such as coarse rock or organic residues, from the feedstock.

[0030] It is proposed to start the conveyor belt directly at the sieving process, guide it through the melting unit, and continue it into the comminution process. This fully automates the process and ensures a high production rate.

[0031] It is also recommended to upgrade the conveyor belt with a scraper plate and / or a vibrating belt, as these components allow for the creation of a thin, uniform layer of sand, the thickness of which can be finely adjusted, particularly with an adjustable scraper plate. Adjusting the layer height is especially advantageous for creating the described insulating layer.

[0032] After the crushing process, the sand is transported, for example, into appropriate collection containers and can then be prepared for transport or storage.

[0033] According to the invention, the described method can also be used with an autonomous system in the form of a desert vehicle, for example, a tracked vehicle, which has a melting device as defined in the invention. This device focuses sunlight, for example, through a central opening in the vehicle, onto the layer of sand located beneath the vehicle. The central melting device could be implemented in the form of a tower structure and is ideally designed to rotate 360°. A movable heliostat array can capture the sun at any possible angle and reflect it to the movable melting device. Alternatively, a movable device for focusing sunlight, such as a tilting and swiveling Fresnel lens, can be used. This results in the formation of molten intermediate products directly beneath the vehicle, which can then be collected, for example, by a rake in the rear of the vehicle or in another, e.g.,The sand is then transported to a following vehicle for crushing. This process produces sand grains whose shape and surface roughness have been improved or made suitable for use in concrete. The angular, concrete-compatible sand can either be collected directly in the vehicle or ejected and collected separately.

[0034] The continuous weathering of mountains, buildings, and all other rock sediments, which ultimately disintegrate into the finest dust particles (Saharan dust), makes desertification a natural and currently unavoidable process. In the future, our method will ensure the cost-effective and permanent stabilization of desert edges (near populated areas) through the use of autonomous machines.

[0035] The invention will now be explained using exemplary embodiments and the enclosed schematic figures.

[0036] They show: Fig. 1- a first preferred embodiment of a device according to the invention for producing concrete-grade sand Fig. 2 - a second preferred embodiment of a device according to the invention for producing concrete-grade sand Fig. 3 - a third preferred embodiment of a device according to the invention for producing concrete-grade sand Fig. 4 - a preferred embodiment of a vehicle according to the invention for producing concrete-grade sand

[0037] The schematic Figure 1Figure 1 shows a possible setup for carrying out a preferred embodiment of a method according to the invention. Desert sand, as the starting material 1, is fed from a storage container 6 (e.g., funnel-shaped) onto a sieve 7, thereby removing the coarsest impurities from the starting material 1. After the sieving process, the sieved starting material 1 is conveyed directly onto a suitable conveyor belt 8 as a base. This conveyor belt is equipped with a scraper plate 9, which produces a uniform layer with an adjustable thickness. Optionally, the flatness of the layer can be improved using a vibrating conveyor belt. The uniform layer of sand then travels via the conveyor belt 8 to the thermal treatment area by passing through the immediate vicinity of the focal point 10 of a device 5 for focusing sunlight (e.g., a plano-convex converging lens), causing the starting material 1 to melt.The larger the surface area of ​​the device 5 for concentrating sunlight, the more sunlight 13 is captured and focused onto the focal point 10, and consequently, the greater the system's output. Preferably, during the thermal treatment, not the entire stacked raw material 1 melts, but only an upper portion, e.g., the top two-thirds, in order to form an insulating layer 11 for the underlying conveyor belt 8 with the bottom third. An advantageous layer thickness is between 5 and 50 mm, depending on the system's output. The required exposure time for thermal melting can be regulated by the speed of the conveyor belt 8, so that a composite panel 2 is formed as an intermediate product in a continuous melting process. This composite panel has, for example, dimensions of 500 x 500 x 20 mm (L x W x H) and, after sufficient cooling on the conveyor belt 8, is fed directly into a comminution machine 4, e.g.,a shredder, which reduces the composite panel 2 to the end product 3, the crushed sand or smeared sand, in particular angular medium sand (mS / MSa). The end product 3 is collected and stored in a suitable container 12 for transport.

[0038] In Figure 2 Another preferred embodiment of a device according to the invention is shown. This embodiment is analogous to the Figure 1At this point, the pre-sifted, leveled, and stacked raw material 14 is conveyed via conveyor belt 8 into a tunnel kiln 15, which is operated, for example, at 1000 °C. Heat sources 16 are preferably located above the base, the conveyor belt 8. This allows the prepared raw material 14 to pass under the heat sources 16. The pre-heated raw material 14 is thus heated to a preheating temperature, e.g., 1000 °C, thereby accelerating the overall process. The tunnel kiln 15 is supplied with the necessary energy via photovoltaic arrays 17, so no additional power sources are required. The preheated raw material 18 then proceeds to the melting device, preferably a parabolic mirror 21, for concentrating reflected sunlight 20. This light is reflected by one or more plane mirrors 19 to the concentrator, the parabolic mirror 21.The planar mirrors 19 are designed so that they can preferably be automatically aligned with the position of the sun. The preheated starting material 18 melts at the focal point 10 of the concentrator 21, and it is advantageous to use the lower third of the stacked material 18 to form an insulating layer 11 for the base, the conveyor belt 8. The molten intermediate product 2 then enters a crushing machine 4, which reduces the composite panel to the final product 3, crushed sand or smeared sand, in particular angular medium sand (mS / MSa). The smeared sand 3 produced in this process can be used both for land reclamation in the sea and for the production of concrete, since its now angular geometry causes it to wedge itself together, thus providing the necessary stabilization in the building material.

[0039] In Figure 3A process is described in which the starting material 1, e.g., fine sand (fS / FSa) or rounded sand, preferably desert sand, is first melted so that new grain boundaries form. The resulting three-dimensional structure, as intermediate product 2, is then cooled and crushed into fragments smaller than 2 mm in a crushing machine 4. The resulting sand grains of the final product 3 correspond in particular to the category of medium sand (mS / MSa) and are referred to as crushed sand or squashed sand. The high melting temperatures can be achieved, as shown in this schematic figure, by focusing sunlight in a concentrator 22, e.g., an arrangement of mirrors. In a preferred embodiment, the individual mirrors 23 are inclined at different angles so that the reflected sunlight 20 is focused onto an effective area 10.The sunlight 13 is preferably focused onto the concentrator 22 via a plane mirror 19, referred to by those skilled in the art as a heliostat array. This process offers a long-term solution for meeting the demand for crushed sand and makes desert sand available to the construction industry. The crushed sand (artificial crushed sand) produced in this process can be used for the production of concrete and for land reclamation in the sea, thus conserving the finite resources of natural crushed sand from coastal areas, oceans, and rivers.

[0040] The schematic Figure 4Figure 1 shows a possible vehicle for carrying out a preferred embodiment of a method according to the invention. The vehicle, designed as a tracked vehicle 24, moves over the starting material 1 under direct sunlight 13. It is preferably controlled via a control console 27 in the front area of ​​the vehicle, or via sensors that enable autonomous driving with respect to the ground and the position of the sun. The housing of the control console 27 can advantageously be covered with photovoltaic panels 17, so that no further energy sources are required to operate the vehicle. A device 5 for focusing sunlight, e.g., a Fresnel lens, generates the necessary melting temperature at the focal point 10 to convert the starting material 1 into the intermediate product 2, a composite panel. The Fresnel lens 5 is mounted in a tower structure above the vehicle for this purpose.Simultaneously, a sufficiently wide shaft in the center of the vehicle, or directly beneath the Fresnel lens 5, ensures that the focused light is not interrupted before reaching the ground. The intermediate product 2 is separated from the ground by a rake 25 in the rear of the vehicle and deflected towards the crushing machine 4. There, the final product 3, the crushed sand, is produced, analogous to the embodiments described above. The final product 3 can be collected by a collection container 26, which is pulled by the tracked vehicle 24 like a sled, and temporarily stored, for example, for further transport. Reference symbol list:

[0041] 1 Raw material (desert sand, fine sand, rounded sand) 2 Intermediate product (three-dimensional structure, composite panel) 3 End product (crushed sand, crushed sand, angular medium sand (mS / MSa)) 4 Crushing machine (e.g., shredder) 5 Device for focusing sunlight (e.g., collecting or Fresnel lens) 6 Storage container (e.g., hopper) 7 Screen 8 Conveyor belt 9 Scraper plate (e.g., height-adjustable) 10 Focal point (or effective area) 11 Insulation layer (e.g., consisting of the raw material) 12 Collection container (e.g., container) 13 Sunlight 14 Stacked raw material (screened and leveled) 15 Tunnel kiln 16 Heat source (e.g., heating coil) 17 Photovoltaic fields (e.g., with direct power supply) 18 Preheated starting material (e.g., 1000 °C) 19 Planar mirror (e.g., heliostat array) 20 Reflected sunlight (from planar mirror to concentrator) 21 Parabolic mirror 22 Concentrator (e.g., arrangement of several mirrors) 23 Mirror (e.g., all inclined at different angles) 24 Tracked vehicle 25 Rake 26 Collection container (e.g.,Sled) 27 Control console (e.g. driver's cab).

Claims

1. A method for producing artificial broken sand or crushed sand by means of thermal treatment using desert sand in the form of fine sand and / or round sand as the starting material (1), wherein the starting material (1) is heated A) through the bundling of solar rays, and / or B) through the use of a conventional melting device which achieves its energy supply using converted or stored solar power, to a melting temperature, whereby a plurality of sand grains is melted together in each case to form a three-dimensional intermediate product (2), wherein the resulting intermediate product (2) is cooled, and finally comminuted to a particle size of less than 2 mm, wherein an end product is produced which differs from the starting material (1) with respect to the shape and surface roughness.

2. The method according to claim 1, wherein the starting material (1) is heated up to or beyond the formation of new grain boundaries and / or wherein the starting material (1) is initially heated C) through the bundling of solar rays and / or D) through the use of a conventional heating device, which obtains its energy supply via converted or stored solar power, to a pre-heating temperature, wherein the pre-heating temperature is disposed below the melting temperature, and the heating to the pre-heating temperature is implemented with spatial separation from the heating to the melting temperature, and / or wherein impurities are first removed from the starting material (1) before the thermal treatment via an appropriate riddle (7), and / or the grain size range of the starting material (1) is accordingly limited for the further processing.

3. The method according to claim 1 or 2, wherein the intermediate product (2) is cooled down until it comprises a brittle behaviour in the comminution process.

4. The method according to any one of claims 1 to 3, wherein the melting temperature in variant A is achieved through the bundling of solar rays by means of at least one converging lens (5) and / or at least one mirror, which is constituted as a parabolic mirror (21), and / or an arrangement (22) of at least two mirrors with different angles of inclination (23) to concentrate the solar light onto a common focal point or respectively active region.

5. The method according to claim 4, wherein the efficiency of the at least one converging lenses (5) and / or of the at least one mirror for the concentration of the solar light is improved through the use of reflecting mirrors (19), which are orientated according to the position of the sun and guide the solar light towards the converging lenses (5) or the at least one mirror for the concentration.

6. The method according to any one of claims 1 to 3, wherein the melting temperature in variant B is achieved through the use of a tunnel furnace (15) and / or a laser which draws its energy supply from solar collectors (17).

7. The method according to any one of claims 1 to 6, wherein the starting material (1) is deposited on a support surface and melted to form the intermediate product (2), wherein the support surface is especially a conveyor belt (8) or a crucible.

8. The method according to claim 7, wherein the support surface is especially a conveyor belt (8) and the intermediate product (2) is supplied on the conveyor belt (8) directly to the comminution process for the production of the end product (3), and / or wherein the starting material (1) is placed onto the conveyor belt (8) as a thin layer with uniform layer thickness, by means of which it is guided at least directly to the position for the thermal treatment or through the latter, wherein the acting time of the thermal energy is controlled via the speed of the conveyor belt (8).

9. The method according to claim 7, wherein a processing surface of the conveyor belt (8), on which the starting material (1) is disposed and conveyed comprises a material or a coating resistant to melting up to at least 2000°C, which further guarantees an easy detachment of the thermally treated starting material (1).

10. The method according to claim 9, wherein, as the three-dimensional intermediate product (2), a flat intermediate product (2) is produced, in that either a) the focal point (10) of a lens (5) is focused on a processing area of the conveyor belt (8) on which the starting material (1) is disposed, and the starting material (1) is caused to melt in this manner through the introduction of solar power, so that a plurality of sand grains is melted thermally together in each case to form the flat intermediate product (2), and / or b) the starting material (1) is caused to melt via a laser, which obtains its energy supply using converted and / or stored solar power.

11. The method according to claim 10, wherein the intermediate product (2) is then cooled to below 500°C and finally comminuted in one or more steps in a comminution process to a grain size between 0.0125 and 2.0 mm, wherein the end product (3) is produced.

12. The method according to any one of claims 7 to 11, wherein the starting material (1) is melted only in an upper region, so that a lower region represents an insulation layer (11) between the intermediate product (2) and the support surface.

13. An artificial broken or crushed sand obtained through a method according to any one of claims 1 to 12.

14. A device for the production of artificial broken or crushed sand using thermal treatment with the use of desert sand in the form of fine sand and / or round sand as the starting material (1), with - a melting device for heating the starting material to melting temperature, wherein the melting device comprises a device for the bundling of solar rays or a tunnel furnace (15) and / or a laser, which draw their energy supply from solar collectors (17), - with a cooling track disposed downstream of the melting device - with a comminution machine (4) disposed downstream of the cooling track.

15. The device according to claim 14, wherein the cooling track comprises an active cooling device, and / or which is constituted as a vehicle, and / or which is set up to implement a method according to any one of claims 1 to 12.