Method for providing a reactive cement component or concrete additive

Abstract

The invention relates to a method for providing a reactive cement component or a concrete additive, comprising the following steps: a) treating a pile of carbon-containing material containing at least coal and clay rock; b) removing at least calcined rock; c) producing fine-grained calcined rock; and d) providing fine-grained calcined rock for use as a cement component or concrete additive.

Description

Method for providing a reactive cement component or concrete additive The present invention relates to a method for manufacturing cement or concrete. The global trend of population growth, increasing urbanization, and economic progress is driving up the demand for new buildings and infrastructure, and consequently, for concrete. Currently, concrete is, in terms of mass, the second most used material by humans after water. Although concrete has low specific CO2 emissions, less than 150 kg CO2 eq / t of concrete, due to the sheer volume used, it is responsible for 5-8% of anthropogenic CO2 emissions. Most emissions from concrete come from the production of cement clinker, the main component of cement. To manufacture cement clinker, a mixture of limestone and clay is ground and then heated. During this process, the lime contained in the raw meal releases carbon dioxide (CO2) and is transformed into quicklime (CaO). As the calcination process progresses, the raw meal, deacidified by the removal of CO2, is sintered to form various phases of calcium silicate, as well as calcium aluminate and calcium aluminum ferrite. For example, a complex and energy-intensive plant for the manufacture of cement clinker, as well as the corresponding method, is described in publication DE 102013006236. Today, cement is manufactured in modern cement plants using a continuous process from primarily natural raw materials, employing a dry method. The raw materials (limestone, clay, and, where applicable, sand and iron ore) are typically extracted from quarries, pre-crushed, and transported to the cement plant. In tube mills or, alternatively, fine mills, the raw materials are ground together and dried simultaneously, resulting in what is known as raw meal. This meal is then calcined in a rotary kiln at temperatures of approximately 1450 °C to become clinker, which is subsequently cooled in a cooler to a temperature below 200 °C. The resulting grayish-brown granules are then ground in ball mills or, alternatively, in other fine mills, along with gypsum or anhydrite, to obtain the final product: cement.By adding various additives, such as ground granulated blast furnace slag, pozzolan, pulverized fuel ash, and limestone, cements with different chemical and physical properties can be manufactured. Cement is what is known as a hydraulic binder. Hydraulic binders are materials that harden and consolidate both in air and underwater. Cement reacts with water to form insoluble and stable compounds. These compounds, calcium silicate hydrates, form fine, needle-like crystals that interlock with each other, giving cement stone its high strength. These properties make cement a binder that meets the demanding requirements of the construction industry. The cement industry must drastically reduce the emissions it generates and, at the same time, meet the growing demand for cement from the global economy. Document US 7481878 B1 discloses the supply of activated clay obtained from a waste material containing oil. Therefore, the objective of the present invention is to solve, at least in part, the aforementioned problems in relation to the prior art. In particular, a method is proposed for obtaining, in a more environmentally and / or resource-friendly manner, another major component of cement. Furthermore, a material is proposed as a concrete additive for concrete production that allows for a reduction in the cement content of the concrete. Specifically, a method is described for obtaining and supplying binding components for the manufacture of cement or concrete. These objectives are achieved by a method or use conforming to one of the independent claims of the patent. Advantageous variations are indicated in the dependent claims. It should be noted that the features listed in the patent claims can be combined with each other in any technologically reasonable manner and constitute further embodiments. The description, particularly with regard to the figures, explains the invention and lists other advantageous embodiments thereof. A method for providing a reactive cement component or concrete admixture, comprising at least the following steps, contributes to this explanation: a) dismantling of a coal waste dump containing at least coal and clay rock; b) extraction of at least calcined rock; c) production of fine-grained calcined rock; d) supply of fine-grained calcined rock for use as a cement component or concrete additive. Clay rock comprises calcined rock. Calcined rock comprises autogenously calcined clay, resulting from the combustion of coal. The stages mentioned above can be carried out in the order indicated, although this is not mandatory. In particular, it is possible for the stages to overlap with each other, at least partially, in time, to take place in different locations with a time lag, and / or to be repeated with varying frequency. According to stage (a), a coal waste dump is being dismantled. The dump contains at least coal and clay rock, and the clay rock contains at least autogenously calcined clay. Specifically, the coal referred to is bituminous coal. In this context, "rock" means a natural (solid) material composed mainly, or at least mostly, of mineral components. The rock contains a considerable proportion of clay. Specifically, the dump is a deposit of waste extracted from a coal mine. In this context, "dismantling" includes, in particular, the removal, at least partial, sorting, relocation, transfer, and / or displacement of the coal, rocks, and / or extraneous materials from the dump, especially when it has remained standing for a long period of time (without dismantling).In the spoil heap, the coal and / or rock may have a grain size of up to 100 mm. Specifically, the method applies to spoil heaps containing bituminous coal, calcined clay, and uncalcined clay. The average percentage of bituminous coal can reach up to 15%. The calcined clay is "autogenous" calcined clay, resulting from coal combustion. This usually occurs primarily through spontaneous combustion of the coal in the spoil heap under certain environmental conditions. Due to the potential for multiple, localized instances of spontaneous combustion over time, some areas of the spoil heap may experience prolonged periods of dryness and temperatures between 350 and 800 °C, leading to the calcination of the rock, particularly the clay. Since the grain size is partly coarse, it may be advisable to pre-crush at least some of the spoil heap components, for example, to obtain granules of approximately 30 to 40 mm. This process can be carried out before and / or during step b). According to step b), at least some of the calcined rock from the spoil heap is removed. It is possible that, in fact, only the calcined rocks are selectively removed from the spoil heap. However, the usual practice is to extract a sample containing all the components from the spoil heap and then identify and separate the calcined rocks. In particular, measures and / or equipment are provided or used to identify and extract (autonomously and / or automatically) the calcined rocks from among the spoil heap components. For the subsequent mixing of the calcined rock with the cement, the fineness of the calcined rock is adjusted according to step c). In particular, fine particles of the calcined rock, especially clay, are generated and / or separated (with or without grinding stages). This may take place during conditioning or immediately after extraction from the spoil heap; however, it may also be provided, either alternatively or cumulatively, that the calcined rock extracted from the spoil heap is processed first (e.g., dried and / or ground) before carrying out step c). In this context, fine grain size means, in particular, that the grain size of the calcined rock is less than 5 mm [millimeters], specifically less than 2 mm or even less than 1 mm. It is possible that calcined rock, with a grain size of less than 200 µm [micrometers] or even less than 125 µm, may be used as a binding component in cement. According to step d), fine-grained calcined rock is prepared for use as a cement component or concrete additive. This may mean that this calcined rock is used directly in a cement manufacturing process. However, in many cases, cement production takes place elsewhere, so the extracted calcined rock is transported there and processed later. During clay calcination, clay loses primarily surface and structural water. One consequence of this water loss can be the formation of amorphous metatonic minerals as seen by X-ray diffraction. If heating continues (500–1250 °C), the melting of these metatonic minerals leads to the formation of aluminosilicate glasses or, in some cases, mullite or cristobalite, although high mullite and cristobalite contents are undesirable in this case. These properties can be exploited for the (selective) extraction of calcined clay from the fuel waste dump. Stage b) may include at least one of the following processes: Gravimetric classification Classification using sensors The processes mentioned above can be used, in particular, to separate or select the components of the spoil heap. For this purpose, it may be advisable to prepare the components with a suitable particle size for the process, i.e., to crush them beforehand so that the particle size does not exceed 50 mm. Gravimetric sorting, or density sorting, involves determining the mass of the spoil heap's components, for example, through weighing. Specifically, this may include determining the specific gravity of heavy and light materials using sensors, and then separating these components based on the sensor signals. Sensor-based classification is preferably carried out using a sensor capable of generating images and / or videos, particularly a camera. This may be an optical sensor. A sensor operating in the near-infrared range can also be used. Stage b) and / or stage c) may include at least one of the following processes: Electrostatic separation Magnetic separation The processes mentioned above can be used, in particular, to separate or select the components of the waste rock or the extracted calcined rock. For this purpose, it may be advantageous to prepare the components with a grain size suitable for the process, i.e., to crush and / or grind them beforehand so that the grain size does not exceed 5 mm. In electrostatic separation, it is recommended that the particle size of the components not exceed 2 mm. This can be achieved using a separator equipped with a high-voltage system, spray and precipitation electrodes, and a cleaning system. An air stream laden with particles or containing components or foreign matter can be ionized within the separator by applying a high negative voltage to the spray electrodes. The particles become negatively charged and deposit onto the positively charged precipitation electrodes. The particles separated in this way can then be removed from the separator by the cleaning system. When magnetic separation is used, the iron content of the rock to be separated must be greater than 1.5% by weight, and the grain size must not exceed 5 mm. In the simplest case, the material is conveyed by a conveyor belt that passes under a magnet. Magnetic rocks, particularly calcined clay with the specified iron content, are attracted to the magnet and thus separated from the non-magnetic materials. After step b), at least some of the rock may be treated, either by crushing or drying it, at least partially. In this context, "conditioned" means, in particular, that the (calcined) rock is treated in such a way that its properties allow the subsequent process or processing stage to be carried out as efficiently as possible. This may include adjusting the grain size to a predetermined size, for example, by crushing, grinding, etc.and / or the adjustment of a temperature, and / or the adjustment of a density or distribution in a volume or on a surface, and / or the adjustment of humidity. For this purpose, a heat treatment of up to approximately 120 °C may be included. The fine-grained or powdered fraction of calcined rock can be mixed, in particular, with other fractions of a cement composition. In the case of calcined clay, it is possible to replace, at least partially, the clinker and / or pulverized fuel ash fraction of a conventional cement composition. It can also be used as a concrete admixture. In particular, the properties of the calcined rock for these replacement purposes have been adjusted using the method proposed herein. In this context, it is assumed that the use of calcined clay as a reactive additive for the production of cement and / or concrete is becoming increasingly important. This is because clay calcination is carried out at considerably lower temperatures than limestone calcination. In this specific case, calcination has already taken place, resulting in a significantly more favorable CO2 balance than with artificially calcined clays. As decommissioning progresses, opposition to new coal-fired power plants continues, and demand for pig iron declines, the availability of suitable pulverized fuel ash and blast furnace slag will decrease. Once coal is separated into a low-ash product (fuel) and a high-ash product (wash tailings), an ash-rich fraction is generated, which is generally used to backfill old mines or deposited in waste dumps. Numerous waste tailings dumps have spontaneously combusted due to the residual coal they contain and have burned or are currently burning uncontrollably. The thermal process that takes place inside the dumps calcines the rock components they contain, so a considerable portion of these dumps is composed of calcined clays. These calcined clays are very similar, both mineralogically and chemically, to the additives used in Portland cement clinker. Furthermore, these calcined rocks are more carbon-neutral than limestone and the Portland cement clinker made from it, as the heat treatment is virtually complete. As part of rehabilitation measures, an increasing number of tailings piles are being protected, relocated, and restored to a more natural state. Thanks to the method described herein, it is possible to recycle a large portion of the material (>50%) in an environmentally sound, sustainable, and economically viable manner. A marketable raw material is obtained from material destined for landfill. This reduces the amount of waste that must be disposed of in landfills, decreases the required land area, lowers transportation costs, and also reduces CO2 emissions generated during transport. Furthermore, with the method described it is also possible to separate, in addition to the calcined rocks, the unburned residual coal and use it as a fossil fuel. Similarly, the remaining uncalcined components or rocks can be separated using the described method and sent for further processing. In this way, it is possible, for example, to use these rocks as road construction material or as recycled building material. Calcined clays obtained by the proposed method from coal deposits or waste rock dumps can therefore contribute significantly to obtaining cement substitutes (SCM, supplementary cementitious materials), since these clays are already calcined and do not need to be subjected to any heat treatment. It has been demonstrated that "autogenous" calcined washing waste, selectively treated using this method, after fine grinding to a cement-like fineness (>5000 Blaine), is of equivalent quality to, or even surpasses, that of industrially calcined washing waste or even the pulverized coal fuel ash currently in use. Therefore, the composite cement obtained in this way has excellent potential for widespread use in the binder industry. The solution proposed in this document significantly reduces CO2 emissions in cement production and decreases the necessary energy consumption. Furthermore, many emerging countries with high cement demand continue to face shortages of high-quality raw materials for binder production. The cement substitute obtained through this method can make a valuable contribution to raw material supply. Numerous waste rock dumps are known to burn in China and India, and some coal deposits have even spontaneously combusted. This area offers significant potential for the application of this method. According to another approach, the use of calcined clay obtained from a coal waste dump is proposed to adjust the hydraulic properties of a cement or concrete mix. The calcined clay is "autogenous" calcined clay, resulting from coal combustion. It is preferred to use calcined clay in such a way that it is used as a substitute for cement clinker and / or pulverized fuel ash and / or other artificial pozzolans or natural pozzolanic additives. Furthermore, the use of calcined clay obtained from a coal waste dump is proposed for the production of cement or concrete mixes with lower emissions or energy consumption. The calcined clay is "autogenous" calcined clay, resulting from coal combustion. It is possible to use calcined clay in a fraction of up to 25%, or even up to 40%, of the cement mix without significantly compromising the concrete's strength compared to a pure clinker-based cement mix. Therefore, high-energy "autogenous" calcined clay can completely replace the clinker in conventional cement compositions, which is costly and energy-intensive to produce. The invention and its technical context are described below by means of figures showing particularly preferred embodiments, without the invention being limited to them. A schematic representation is shown. Figure 1: an overview of a spoil heap rehabilitation process with an integrated method for providing a reactive cement component or concrete additive, and Figure 2: An overview of the treatment of spoil heap components to provide a reactive cement component or concrete additive. Figure 1 shows, firstly, a spoil heap, which constitutes the starting point of the method. A possible development of the method is then shown. Starting with the spoil heap, which contains coal, rock, and possibly extraneous materials, dismantling is carried out first, according to step a). As a result, three parts can be defined: the contaminated waste that must be taken to a landfill and the washing waste (calcined and uncalcined) that can be subjected to further treatment; in particular, the calcined components or rocks (extracted in step b). These washing wastes are then sorted, separated, and removed, or further diversified, following step c). As a result, a portion of the calcined rock is separated for use as a binding component (step d).In addition, components that are not suitable for use in cement or concrete can be used as road construction material, and the selected coal can be used as a fossil fuel. Figure 2 may represent a detailed method for steps b) and c) of Figure 1. Therefore, with regard to the washing waste, a (further) classification of extraneous materials can be carried out, separating the materials destined for landfill. The remainder can be crushed (where applicable, in several stages) in a controlled manner, subjected to heat treatment and / or drying, and, if necessary, subsequently classified (repeatedly) to determine whether the current properties of the components or rocks are suitable for further processing, authorize them, and, where appropriate, adjust them. Fine-grained or powdered particles can, for example, be detected and classified by electrostatic or magnetic separation and allocated to their intended use. The finest particles can, for example, be (further) detected by density classification, separated, and allocated to their intended use.Coarser grain particles can also be assessed by density classification, using sensor classification where appropriate, before they are identified, classified and allocated to their intended use.

Claims

1. A method for providing a reactive cement component or a concrete admixture, comprising at least the following steps: a) dismantling a coal waste dump containing at least coal and clay rock, wherein the clay rock contains calcined rock with autogenously calcined clay resulting from coal combustion; b) extracting at least calcined rock; c) producing fine-grained calcined rock; d) supplying fine-grained calcined rock for use as a cement component or concrete admixture.

2. A method according to claim 1, wherein step b) comprises at least one of the following processes: - gravimetric classification - sensor-based classification.

3. A method according to any of the preceding claims, wherein at least step b) or step c) comprises at least one of the following processes: - electrostatic separation - magnetic separation. 4.A method according to any one of the preceding claims, wherein, after step b), at least a portion of the rock is treated by crushing or drying it, at least partially.

5. A method according to any one of the preceding claims, wherein the portion separated from the calcined rock in step d) is mixed with other fractions of a cement composition.

6. Use of autogenously calcined clay, obtained by burning coal from a coal waste dump and extracted from said dump, to adjust a hydraulic property of a cement composition or a concrete composition.

7. Use according to claim 6, wherein the calcined clay is used as a substitute for cement clinker, pulverized fuel ash, or other artificial pozzolans or natural pozzolanic additives. 8.Use of autogenously calcined clay, obtained by burning coal from a coal waste dump and extracted from said dump, for the low-emission production of a cement composition or a concrete composition.

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