METHOD FOR PROVIDING A REACTIVE CEMENT COMPONENT OR CONCRETE ADDITIVE

Description

[0001] The present invention relates to a method for the production of cement or concrete.

[0002] Global trends such as population growth, increasing urbanization, and economic progress are driving up the demand for new buildings and infrastructure, and consequently, for concrete. Even today, concrete is the second most widely used material by humans, after water, in terms of mass. Although concrete has low specific CO₂ emissions of less than 150 kg CO₂eq / t of concrete, its sheer volume accounts for 5-8% of human-caused CO₂ emissions.

[0003] The majority of concrete emissions originate from the production of cement clinker, the main component of cement. Cement clinker is produced by grinding a mixture of calcareous rock and clay, which is then burned. During this process, the lime contained in the raw meal releases carbon dioxide (CO₂) and is converted into quicklime (CaO). In the further course of the burning process, the raw meal, now deacidified by the CO₂ release, is sintered into various calcium silicate phases, as well as calcium aluminate and calcium aluminate ferrite. A correspondingly complex and energy-intensive plant for the production of cement clinker, along with a related process, is described, for example, in German patent DE 10 2013 006 236.

[0004] Today, cement is produced in modern cement plants using a continuous, dry process from predominantly natural raw materials. The raw materials (limestone, clay, and possibly sand and iron ore) are typically extracted from quarries, pre-crushed in crushers, and transported to the cement plant. In pipe mills or other fine mills, the raw materials are ground together and simultaneously dried, producing so-called raw meal. This meal is then fired in a rotary kiln at temperatures of approximately 1450 °C to produce clinker, which is subsequently cooled in a cooler to a temperature below 200 °C. The resulting grayish-brown granules are then ground together with gypsum or anhydrite in ball mills or other fine mills to create the finished product: cement.By adding different additives such as granulated blast furnace slag, pozzolan, fly ash and limestone, cements with different chemical and physical properties can be produced.

[0005] Cement is a so-called hydraulic binder. Substances are described as hydraulic if they harden and are resistant to both air and water. Cement reacts with water to form insoluble, stable compounds. These compounds, calcium silicate hydrates, form fine, needle-shaped crystals that interlock, resulting in the high strength of cement stone. These properties make cement a binder that meets the demanding requirements of the construction industry.

[0006] The cement industry must drastically reduce its associated emissions while simultaneously meeting the increasing cement demand of the global economy.

[0007] US 7 481 878 B1 discloses the provision of activated clay obtained from an oil-containing waste material.

[0008] Therefore, the object of the present invention is to at least partially solve the problems mentioned with reference to the prior art. In particular, a method for the environmentally friendly and / or resource-efficient production of another main component for cement is to be proposed. Furthermore, a material for use as a concrete additive in concrete production is to be proposed, with which the cement content of the concrete can be reduced. Specifically, a method for the production and provision of binder-compatible components for the manufacture of cement or concrete is to be specified.

[0009] These problems are solved by a method or use according to one of the independent claims. Advantageous embodiments are specified in the dependent claims. It should be noted that the features listed in the claims can be combined with one another in any technologically meaningful way and that further embodiments are given. The description, particularly in conjunction with the figures, explains the invention and names further advantageous embodiments of the invention.

[0010] This is facilitated by a process for providing a reactive cement component or concrete additive, which includes at least the following steps: a) Removing a carbonaceous spoil heap containing at least coal and clayey rock; b) Extracting at least calcined rock; c) Producing fine-grained calcined rock; d) Providing fine-grained calcined rock for use as a cement component or concrete additive.

[0011] The clay-bearing rock includes calcined rock. This calcined rock comprises autogenously calcined clay, which originated from coal combustion.

[0012] The steps mentioned above can be carried out in the specified order, but this is not mandatory. In particular, it is possible that the steps overlap at least partially, are carried out at different locations with a time difference, and / or are repeated a different number of times.

[0013] According to step a), a carbonaceous spoil heap is being dismantled. The spoil heap comprises at least coal and clay-bearing rock, the rock containing at least autogenously calcined clay. The coal is specifically bituminous coal. Rock, in this context, is understood to be a (solid) natural material consisting predominantly or even at least essentially of mineral components. The rock contains a substantial proportion of clay. Most preferably, the spoil heap is an accumulation of excavated material from a bituminous coal mine. "Dismantling" in this context includes, in particular, the at least partial removal, sorting, redistribution, relocation, and / or relocation of coal, rock, and / or foreign materials from the spoil heap, especially after the spoil heap has existed for a long period (without dismantling). The coal and / or rock in the spoil heap may have a grain size of up to 100 mm [millimeters].

[0014] This process is particularly applicable to spoil heaps containing bituminous coal, calcined clay, and non-calcined clay. The average proportion of bituminous coal can be up to 15%. The calcined clay is "autogenously" calcined clay, formed by the combustion of the coal. This usually occurs, or rather primarily occurs, through spontaneous combustion of the coal within the spoil heap under appropriate environmental conditions. Due to potentially multiple and localized spontaneous combustion events over time, dry conditions and temperatures in the range of 350–800°C can develop in sections of the spoil heap for extended periods, resulting in the calcination of rock, especially clay.

[0015] Due to the sometimes coarse grain size, it may be useful to pre-crush at least some of the components of the stockpile, for example to a grain size of approximately 30 to 40 mm. Such a process can be carried out before and / or during step b).

[0016] According to step b), at least some of the calcined rock contained in the spoil heap is removed. It is possible that only the calcined rocks are selectively removed from the heap. However, it is usually standard practice to remove a section containing all components of the spoil heap and subsequently identify and separate the calcined rocks from it. In particular, measures and / or equipment are planned or used that (independently and / or automatically) identify and remove the calcined rocks from the components of the spoil heap.

[0017] For the subsequent addition of the calcined rock to cement, the fineness of the calcined rock is adjusted according to step c). In particular, the fine particles of the calcined rock, especially clay, are produced and / or separated (with or without grinding steps). This may already take place during conditioning or immediately after removal from the stockpile, but alternatively or cumulatively, the calcined rock removed from the stockpile may first be processed (e.g., dried and / or ground) before step c) is carried out. In this context, "fine-grained" means, in particular, that the particle size of the calcined rock is less than 5 mm [millimeters], especially less than 2 mm or even less than 1 mm. It is possible that the calcined rock with a grain size of less than 200 µm [micrometers] or even less than 125 µm is provided as a binder component in the cement.

[0018] In accordance with step d), fine-grained calcined rock is prepared for use as a cement component or concrete additive. This can mean that this calcined rock is fed directly into a cement manufacturing process. In many cases, however, cement production takes place at a different location, so the extracted calcined rock is transported there and processed at a later date.

[0019] During the calcination of clay, it loses surface and structural water. One consequence of this water loss is the potential formation of X-ray amorphous meta-clay minerals. Upon further heating (500–1250°C), the melting of these meta-clay minerals leads to the formation of either aluminosilicate glasses or, potentially, mullite or cristobalite. High concentrations of mullite and cristobalite are undesirable in this case. These properties can be utilized for the (selective) extraction of calcined clay from the fuel pile.

[0020] Step b) can include at least one of the following processes: Gravimetric sorting Sensory sorting

[0021] The processes mentioned above can be used, in particular, to separate or select the components of the stockpile. For this purpose, it can be advantageous to provide the components with a grain size suitable for the process, i.e., to crush them beforehand so that the grain size is a maximum of 50 mm.

[0022] Gravimetric sorting, or density sorting, includes in particular the determination of the mass of components in the stockpile, for example by means of a so-called weighing system. Specifically, this can include the sensory determination of the specific gravity of heavy and light materials and the separation of these components using the sensor signal.

[0023] Sensory sorting is preferably performed using an image and / or video-generating sensor, in particular a camera. This may be an optical sensor. A near-infrared sensor can also be used.

[0024] Step b) and / or step c) may include at least one of the following processes: Electrostatic deposition Magnetic deposition

[0025] The processes mentioned above can be used, in particular, to separate or select the components of the spoil heap or the extracted calcined rock. For this purpose, it can be advantageous to provide the components with a grain size suitable for the process, i.e., to crush and / or grind them beforehand so that the grain size is a maximum of 5 mm.

[0026] For electrostatic separation, a particle size of no more than 2 mm is preferred. A separator can be used that includes a high-voltage system, spray and collecting electrodes, and a cleaning system. An airflow laden with particles or containing the components / foreign matter can be ionized by spray electrodes to which a high negative voltage is applied. The particles become negatively charged and adhere to positively charged collecting electrodes. The separated particles can then be removed from the separator by the cleaning system.

[0027] When using magnetic separation, the iron content of the rock to be separated should be greater than 1.5 wt.% and the grain size a maximum of 5 mm. In the simplest case, the material is conveyed on a conveyor belt under a magnet. The magnetic rocks, especially the calcined clay with the specified iron content, are then attracted to the magnet and thus separated from non-magnetic materials.

[0028] After step b), at least part of the rock can be conditioned, whereby it is at least partially crushed or dried.

[0029] In this context, "conditioned" means, in particular, that the (calcined) rock is adjusted in terms of its properties so that at least the subsequent process or process step can be carried out as efficiently as possible. This can include adjusting a predetermined grain size, for example by crushing, grinding, etc., and / or adjusting a temperature and / or adjusting a density or distribution within a volume or over a surface, and / or adjusting a moisture content. This may involve temperature treatment up to approximately 120 °C.

[0030] The fine-grained or powdery fraction of the calcined rock can be mixed with other fractions of a cement composition. In the case of calcined clay, the clinker and / or fly ash fraction of conventional cement compositions can be at least partially replaced. Alternatively, it can be used as a concrete additive. The properties of the calcined rock have been specifically tailored for these substitute applications using the method proposed here.

[0031] It is assumed here that the use of calcined clay as a reactive additive for cement and / or concrete production is becoming increasingly important. This is because the calcination of clay occurs at significantly lower temperatures than the clinkering of limestone. In this specific case, the calcination has already taken place, resulting in a considerably more favorable CO₂ balance than with artificially calcined clays.

[0032] With the ongoing dismantling of coal-fired power plants, the continued abandonment of new coal-fired power plants, and the declining demand for pig iron, the availability of suitable fly ash and blast furnace slag will decrease.

[0033] Since coal is separated into a low-ash (fuel) and a high-ash product (waste rock), an ash-rich fraction is produced, which is usually used to fill in abandoned mines or deposited in spoil heaps. Many waste rock heaps have spontaneously combusted due to the residual coal content within them and are burning, or have burned, uncontrollably. The thermal process within the heaps clinkers or calcines the contained waste rock, so that significant quantities of such a heap consist of burnt clays. These calcined clays are mineralogically and chemically very similar to the additives used in Portland cement clinker. Furthermore, these calcined rocks are more CO₂-neutral compared to limestone and the Portland cement clinker produced from it, because the thermal treatment is practically complete.

[0034] As part of remediation measures, an increasing number of waste rock dumps are being secured, relocated, and renaturalized. The process described here allows a large proportion of the material (>50%) to be recycled in an environmentally sound, sustainable, and economically viable manner. Material destined for landfill is transformed into a marketable raw material. This reduces the amount of material that needs to be landfilled, lowers the land requirement, reduces transport costs, and also lowers the CO₂ emissions generated during transport.

[0035] Furthermore, it is also possible to use the described method to sort out unburned residual coal in addition to the calcined rocks and to use it as fossil fuel.

[0036] Similarly, the remaining non-calcined components or rocks can be sorted out using the described method and further processed. For example, these rocks can be used as road construction material or recycled building material.

[0037] The fired clays obtained from coal deposits or washing spoil heaps using the proposed method can therefore make a significant contribution to the production of cement substitute materials (SCMs). supplementary cementitious materials ) because these clays are already clinker-faced and no heat treatment is required.

[0038] It has been demonstrated that selectively processed "autogenously" calcined coal washes, after fine crushing to cement fineness (>5000 Blaine), are of a quality equivalent to, or even surpass, that of industrially calcined clays or currently used fly ash from hard coal. The composite cement thus obtained therefore has excellent potential for widespread use in the binder industry.

[0039] The solution proposed here significantly reduces CO2 emissions during cement production and lowers the required energy input. Furthermore, many emerging economies with high cement demand lack high-quality raw materials for the production of binders. The cement substitute produced using this process can make a valuable contribution to raw material supply in these countries. It is known from China and India that numerous tailings piles are burning, and even coal deposits have spontaneously combusted. This presents significant potential for the application of this process.

[0040] Another aspect proposes the use of calcined clay obtained from a carbonaceous spoil heap to adjust the hydraulic properties of a cement or concrete mix. This calcined clay is "autogenously" calcined, resulting from the combustion of coal.

[0041] Preferably, the calcined clay is used as a substitute for cement clinker and / or fly ash and / or other artificial pozzolans or natural pozzolanic additives.

[0042] Furthermore, the use of calcined clay obtained from a carbonaceous spoil heap is proposed for the emission-reduced or energy-reduced production of a cement or concrete mix. This calcined clay is "autogenously" calcined clay, produced by the combustion of coal.

[0043] It is possible to use calcined clay with a fraction of up to 25% or even up to 40% of the cement composition without having to accept significant disadvantages in terms of the strength of the concrete - compared to a cement composition made of pure clinker.

[0044] Therefore, the energy-rich "autogenous" calcined clay can comprehensively replace the expensive and energy-intensive clinker produced in conventional cement compositions.

[0045] The invention and its technical context are explained below with reference to figures that disclose particularly preferred embodiments, to which the invention is not limited. These figures schematically depict Fig. 1: an overview of a spoil heap remediation with an integrated process for providing a reactive cement component or concrete additive, and Fig. 2: an overview of a treatment of spoil heap components for providing a reactive cement component or concrete additive.

[0046] Fig. 1 The diagram above shows a spoil heap, which serves as the starting point for the process. Below, a possible process sequence is depicted. Starting with the spoil heap, which contains coal, rock, and potentially foreign materials, the first step, according to step a), is dismantling. This results in three distinct components: contaminated components, which must be disposed of in a landfill, and (calcined and non-calcined) waste rocks, which can be further processed. In particular, the calcined components or rocks are extracted (step b)). These waste rocks are then further classified, sorted, and extracted or further diversified according to step c). As a result, a portion of the calcined rock is then removed as a binder component (step d)). Additionally, components unsuitable for use in cement / concrete can be used as road construction material, and selected coal can be used as a fossil fuel.

[0047] Fig. 2 A differentiated approach to steps b) and c) can be derived from Fig. 1This illustrates how the waste rock can be (re)sorted for foreign materials, removing any material destined for landfill. The remaining portion can then be gently crushed (possibly several times), heat-treated, and / or dried, and subsequently (repeatedly) classified to determine / approve the suitability of the current properties of the components or rocks for downstream processes and, if necessary, further adjust them. Fine-grained or dust-like components can, for example, be identified, sorted, and assigned to their intended use using electrostatic and / or magnetic separation. Further fine particles can, for example, be identified, sorted, and assigned to their intended use using density sorting. Coarser-grained components can also be evaluated using density sorting, if necessary.using sensory sorting, before these are also recognized, sorted and assigned to their intended purpose.

Claims

1. Method for providing a reactive cement component or concrete additive, comprising at least the following steps: a) taking down a carbonaceous heap containing at least coal and clayey rock, wherein the clayey rock includes calcined rock with autogenously calcined clay produced by burning out the coal; b) removing at least calcined rock; c) producing fine-grained calcined rock; d) providing fine-grained calcined rock for use as a cement component or concrete additive.

2. Method according to claim 1, wherein step b) comprises at least one of the following processes: - gravimetric sorting - sensory sorting3. Method according to one of the preceding claims, wherein at least step b) or step c) comprises at least one of the following processes: - electrostatic separation - magnetic separation4. Method according to one of the preceding claims, wherein after step b) at least part of the rock is conditioned, whereby it is at least partially crushed or dried.

5. Method according to one of the preceding claims, wherein the separated portion of the calcined rock in step d) is mixed with further fractions of a cement composition.

6. Use of autogenously calcined clay, which has been produced by burning out the carbon from a carbon-containing heap and has been extracted from the carbon-containing heap, for adjusting a hydraulic property of a cement composition or concrete composition.

7. Use according to claim 6, wherein the calcined clay is used as a substitute for cement clinker, fly ash or other artificial pozzolans or natural pozzolanic additives.

8. Use of autogenously calcined clay, which has been produced by burning coal from a carbon-containing heap and extracted from the carbon-containing heap, for the emission-reduced production of a cement composition or concrete composition.