METHOD AND PLANT FOR PROCESSING MATERIAL CONTAINING CEMENT STONE

Description

[0001] The invention relates to a method and a plant for processing material containing cement stone.

[0002] The material in question can be, in particular, a solid waste product, such as recycled concrete, generated during demolition activities. Such recycled concrete contains so-called cement paste, i.e., hardened cement slurry, which is a mixture of cement and water. Cement slurry forms the basis for concrete or mortar, to which aggregate, especially sand and / or gravel, is typically added.

[0003] Cement is produced by finely grinding cement clinker. To manufacture cement clinker, raw materials, especially limestone and clay, as well as possible corrective materials such as quartz sand and iron oxide-containing materials, are ground into raw meal, then calcined and sintered by firing in a clinker kiln. During calcination, the limestone is deacidified, releasing CO₂.

[0004] The cement paste contained in concrete, for example, is slowly recarbonated by CO2 contained in the ambient air during the use of the concrete, but only partially, usually in the range of about 25% to 30%.

[0005] The non-recarbonated portion of the cement paste exhibits significant recarbonation potential, which can be unlocked through suitable processing steps. This recarbonation potential is important because the cement paste can bind and thus immobilize CO2.

[0006] Research projects dealing with the recarbonation of cement stone are described in the following publications: Seidemann, M. et al. "CO2 sequestration in recycled concrete", (Conference paper: Papers for the Recycling R' 13 conference, 19 / 20 September 2013), Report on the study "Raw material supply and resource productivity in the German cement industry" carried out by the Wuppertal Institute for Climate, Environment and Energy GmbH, Wuppertal, completed in October 2015, Final report on a development project, funded under file number 23689 / 02 by the German Federal Environmental Foundation, entitled "Further development of the carbonation of recycled aggregates from old concrete (2nd phase: Process optimization on a laboratory scale and technology design)," dated 30 November 2015.

[0007] So far, concrete recyclates are only processed on a larger scale into lower-quality products and are used, for example, as a substitute for gravel, or they are landfilled.

[0008] One challenge regarding the higher-value use of recycled concrete lies in recovering the cement paste as cleanly as possible, since cement paste is typically present in recycled concrete only in relatively small proportions of between 15% and 20%, depending on the degree of processing. Furthermore, cement paste is usually tightly bound to other aggregates contained in the concrete. When recycled concrete is crushed for processing, this often results in non-selective fracturing, meaning that the fracture processes do not occur at the boundaries between cement paste and the other aggregates. Non-selective crushing means that the aggregates contained in the recycled concrete cannot be recovered cleanly, or only to a limited extent. Therefore, from a technological perspective, all processes that involve relatively fine grinding prior to recarbonation are less efficient.

[0009] EP 2 895 436 B1 discloses a process for the production of aggregate and calcium carbonate from concrete aggregate, comprising the following process steps: Introducing bulk material comprising concrete aggregate, which can have a grain size of 2 to 20 mm, into a reaction chamber; introducing a gas containing carbon dioxide into the reaction chamber; crushing the bulk material in the reaction chamber, which can be done particularly abrasively; allowing the concrete aggregate and the gas containing carbon dioxide to react with each other to form reaction products in the reaction chamber; removing the reaction products from the reaction chamber.

[0010] DE 197 38 471 A1 describes a concrete recycling plant for reprocessing residual concrete from unused fresh concrete residues and from residues generated during the cleaning of concrete production and transport equipment. This involves washing out solid components from the residual concrete with the addition of rinse water and classifying them in a classifying screen.

[0011] The recovery of aggregated and powdered material from demolition waste is known from WO 2014 / 154741 A1.

[0012] JP354393 discloses a method for removing aggregates from old concrete. After removing the aggregates, the cement paste is ground, mixed with water, and the mixture is carbonated.

[0013] The invention was based on the objective of demonstrating a way to process a material containing cement stone, in particular a concrete recyclate, to a high standard, whereby the cement stone is recarbonated and recovered as pure as possible from other rocks contained in the material.

[0014] This problem is solved by a method according to claim 1 and by a system suitable for carrying out such a method according to claim 14. Advantageous embodiments of the method according to the invention and preferred configurations of the system according to the invention are the subject of further claims and / or will become apparent from the following description of the invention.

[0015] According to the invention, a method for processing material containing cement paste is provided, wherein the material is (pre-)crushed in a first crushing device and subsequently fed into a reactor in which the material is mixed with an aqueous liquid and CO2 and in which a mixing motion of the material is generated, wherein the material taken from the reactor is separated by means of a classifying device into at least two fractions, a coarse fraction and a medium fraction, wherein the coarse fraction has a particle size greater than 16 mm, wherein the medium fraction has a particle size between 2 mm and 16 mm, wherein the temperature and pressure in the reactor are controlled such that an overpressure compared to atmospheric pressure and a temperature greater than 100 °C are set. characterized bythat of the at least two fractions, the coarse fraction is returned to the reactor, wherein the coarse fraction is crushed in a second crushing device before being returned to the reactor.

[0016] A system according to the invention, suitable for carrying out such a process, comprises at least a first comminution device for comminuting the material, a reactor connected to the first comminution device in a material-carrying manner and comprising a mixing device, a fluid-carrying liquid supply for an aqueous liquid connected to the reactor, a fluid-carrying gas supply for CO2 connected to the reactor, and a material-carrying classifier connected to the reactor for separating the material into at least two fractions that differ in particle size, a coarse fraction and a medium fraction, wherein the coarse fraction has a particle size greater than 16 mm and the medium fraction has a particle size between 2 mm and 16 mm, a temperature control device for influencing a temperature in the reactor, a pressure control device for influencing the pressure in the reactor, and a material return line for returning at least one of the fractions from the classifier to the reactor.a second shredding device is integrated into the material return line.

[0017] A key aspect of the process according to the invention is the mixing or contact of the pre-crushed material with the water (contained in the aqueous liquid) and the CO2 in the reactor, which enables recarbonation of the cement paste. The following reactions take place: CSH + CO2 → CaCO3 + SiO2 + H2O; CaOH + CO2 → CaCO3 + H2O.

[0018] The reaction of CaOH with CO2 appears to dominate as long as CaOH is available. Only when the availability of CaOH is limited does the decomposition of the calcium silicate hydrate phases (CSH phases) begin.

[0019] A conversion of the CaOH in the cement paste leads to a significant improvement in the properties of the aggregates when the fractions are reused; this applies, for example, if they are to be used, at least partially, in new concrete. In particular, the porosity of the cement paste decreases after carbonation of the CaOH, which essentially improves all parameters for workability.

[0020] As a result of the treatment of the material in the reactor, the strength of the cement paste also decreases. This applies particularly to treatment at temperatures above ambient temperature, whereby the temperatures to be set can also be pressure-dependent. At atmospheric pressure inside the reactor, a temperature between 50°C and 100°C can preferably be set. According to the invention, however, an overpressure (compared to atmospheric pressure) and a temperature inside the reactor greater than 100°C are set, at least temporarily. In a process according to the invention, it is therefore provided that the temperature and pressure in the reactor are controlled accordingly.An apparatus according to the invention comprises a corresponding temperature control device by means of which the temperature within the reactor can be influenced upwards or downwards, and a pressure control device with which at least an overpressure can also be generated within the reactor. The temperature in the reactor can be influenced by appropriate temperature control of the reactor itself and / or of the material and / or the aqueous liquid and / or the CO2 gas stream supplied to the reactor. Preferably, temperature control of at least the aqueous liquid can also be provided, which is advantageously feasible from a process engineering perspective.

[0021] The reduced strength of the cement paste can be exploited within another key aspect of the inventive process, namely the generation of mixing motion in the reactor, to achieve further comminution of the fragments through regular contact of the pre-crushed pieces with each other and, optionally, with the mixing elements of the mixing device of an inventive system that effect the mixing motion. As a result of the targeted reduction in the strength of the cement paste, a selective comminution of the fragments is achieved, such that the fracturing processes occur particularly at the boundaries between the cement paste and the other types of rock. In particular, the intensive contact between the fragments can produce a very fine-grained abrasion, primarily composed of cement paste.

[0022] This very fine-grained abrasion can be advantageously separated by extracting a stream of the aqueous liquid containing the abrasion in the form of suspended particles from the reactor and then separating it from the extracted stream using a suitable separation device. The extracted aqueous liquid stream can then be returned to the reactor as a recirculation stream, thereby minimizing the consumption of aqueous liquid when carrying out a process according to the invention.

[0023] According to the invention, the material is pre-crushed before being introduced into the reactor, preferably into fragments whose largest dimensions can be up to an arbitrarily defined value between 32 mm and 63 mm, which can be set by appropriately selecting and operating the (first) crushing device accordingly. Compared to crushing or pre-crushing with a lower upper limit for the respective largest permissible dimension of the fragments, a relatively coarse pre-crushing process provided for in the invention is characterized by low energy consumption.

[0024] Furthermore, according to the invention, the material is divided into at least two, preferably at least or exactly three, fractions after treatment in the reactor by means of the classification device. It is preferably provided that a coarse fraction is returned to the reactor because its particle size may be too large for recycling and / or because a sufficiently pure (coarse) fraction cannot be assumed with such a large particle size. A system according to the invention can therefore include a corresponding material return line.

[0025] The fraction, or at least one of the other fractions, which is preferably medium-sized when there are more than two fractions and is therefore hereinafter referred to as the middle fraction, can have particle sizes in a range that allows for advantageous further use and / or where a sufficiently pure fraction can be assumed. Within the framework of a process according to the invention, such a fraction can therefore be removed, i.e., no further processing of this fraction takes place within the framework of a process according to the invention. In particular, this fraction can be a finished product that is not to be further processed with the aim of modification, but can be used unchanged, for example, as an aggregate.

[0026] Preferably, it can be provided that fragments of the material with a grain size greater than 16 mm (coarse fraction) are returned to the reactor within the framework of a process according to the invention. If the fragments of the material are separated into more than two, and in particular into exactly three, fractions by means of the classifying device, it can further preferably be provided that the grain sizes of the middle fraction or one of the middle fractions are between 2 mm and 16 mm. In this case, a fine fraction with a grain size smaller than 2 mm can consequently also be separated by means of the classifying device. Such a fine fraction can also preferably be discharged, and it can be provided that the fine fraction is intended for reuse. In the processing of recycled concrete, this fine fraction can in particular be largely sorted sand, which is advantageously recyclable.If the fine fraction is unsuitable for reuse, it may be disposed of in a landfill.

[0027] It may also be the case that a fraction separated by the classifying device, in particular the aforementioned middle fraction, whose particle sizes are preferably between 2 mm and 16 mm, is not, or not always, sufficiently pure. To determine this, it may be provided that this fraction is analyzed with regard to its cement paste content. Furthermore, it may be preferably provided that this fraction is returned to the reactor if the determined cement paste content exceeds a defined limit value. The corresponding portion of this fraction can then be reprocessed within the reactor so that, after re-separation in the classifying device, the quality requirements are met. A system according to the invention may include a corresponding analysis device and a corresponding material return line.

[0028] To achieve the fastest / most complete decomposition of the calcium silicate hydrate phases (CSH phases) that give strength to the cement paste, it is preferably possible to introduce a basic additive (e.g., NaOH) into the reactor. This allows the pH value during the reaction in the reactor to be controlled. A system according to the invention can therefore include a suitable feed device for such a basic additive.

[0029] Particularly thorough mixing of the material with the aqueous liquid and the CO2 can be achieved in a process according to the invention if the material in the reactor is subjected to countercurrent flow through the aqueous liquid and the CO2. For this purpose, the reactor of a system according to the invention preferably has a first end to which a material inlet for introducing the material into the reactor, a liquid outlet for removing aqueous liquid from the reactor, and a gas outlet for removing CO2 from the reactor are assigned. Furthermore, such a reactor can preferably have a second end opposite the first end, to which a material outlet for removing the material from the reactor, a liquid inlet for introducing the aqueous liquid into the reactor, and a gas inlet for introducing the CO2 into the reactor are assigned.Preferably, the reactor can be designed as a vertical reactor, such that, with reference to the direction of gravity, it comprises the material inlet, the liquid outlet and the gas outlet at the upper, first end, and the material outlet, the liquid inlet and the gas inlet at the lower, second end.

[0030] The liquid inlet and the gas inlet can also be integrally designed, so that the aqueous liquid and the CO2 are mixed together before being introduced into the reactor. In particular, it can be provided that the CO2 is dissolved in the aqueous liquid.

[0031] In carrying out a process according to the invention, in which the material in the reactor is subjected to a countercurrent flow of aqueous liquid and CO2, it is further preferred that the CO2 be overdosed into the reactor, i.e., supplied in an amount that cannot be completely converted by the material contained in the reactor during a single pass. This ensures that sufficient CO2 is available even at the material inlet or gas outlet to guarantee the most complete possible conversion of the CO2 with the cement paste. In this case, it is advantageous to extract a gas stream of CO2 from the reactor via the gas outlet and recirculate it back to the reactor. This allows the CO2 that was not converted in the previous pass to be reused. A system according to the invention can include a corresponding gas return line for this purpose.

[0032] According to a preferred embodiment of a method according to the invention, in which a coarse fraction is recycled from the classifying device to the reactor, it can be provided that the coarse fraction is comminuted in a second comminution device before being recycled to the reactor. This increases the surface area of ​​the coarse fraction fragments that come into contact with the aqueous liquid and the CO2 in the reactor.

[0033] A technically simple approach is to discharge the material from the reactor along with a portion of the aqueous liquid. Accordingly, it can also be provided that the at least two fractions are separated from a discharge stream of aqueous liquid that was extracted from the reactor along with the material. To minimize the consumption of aqueous liquid, it is then preferable to further provide that the discharge stream of aqueous liquid, now free of the fractions, is at least partially returned to the classifying device and / or at least partially returned to the reactor.

[0034] If exactly three fractions are separated by the classifying device, it is then preferably provided that the classifying device comprises a two-stage screening device, wherein the coarse fraction is separated from the discharge stream of aqueous liquid containing the material fragments in a first screening stage and the medium fraction in a second screening stage. A separation device, which may, for example, be in the form of a hydrocyclone, can then be connected downstream of the screening device. In this separation device, the fine fraction can then be separated from the discharge stream of aqueous liquid. The discharge stream of aqueous liquid can then be largely free of the material. Optionally, a filter press can be connected downstream of the hydrocyclone, by means of which the fine fraction can be further dewatered.

[0035] The treatment in the reactor can essentially only process the mineral components of the material. Therefore, within the framework of a process according to the invention, it can be advantageous to remove non-mineral, especially metallic, components, such as those used in recycled concrete, particularly for reinforcement, from the material before it is introduced into the reactor. This can be done before and / or after pre-crushing by means of the (first) comminution device. A system according to the invention can include a corresponding removal device for this purpose.

[0036] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawings. The drawings show, in schematic representation: Fig. 1: The implementation of a method for processing material containing cement stone and the equipment used therein according to a first embodiment; Fig. 2: The implementation of a method for processing material containing cement stone and the equipment used therein according to a second embodiment; Fig. 3: The implementation of a method for processing material containing cement stone and the equipment used therein according to a third embodiment according to the invention; and Fig. 4: The implementation of a method for processing material containing cement stone and the equipment used therein according to a fourth embodiment according to the invention.

[0037] The Figs. 1 to 4 Each figure shows the execution of a process for processing material containing cement stone, as well as the equipment used in the process, whereby the processes are described in accordance with the Fig. 3 and 4According to the invention, a reactor 3 is operated at a pressure above the ambient pressure and a temperature above 100°C is set inside the reactor 3.

[0038] In carrying out such a process, a lumpy material, which may in particular be recycled concrete, is taken from a storage area 1 and fed to a first crushing device 2. The material may have been coarsely processed before being fed to the first crushing device 2. In particular, non-mineral components of the material, such as metallic reinforcements of the recycled concrete, may have been removed during this processing. Crushing may also have already taken place or become necessary during this processing, and it may be provided that the edge lengths of the resulting fragments of the material can exceed 300 mm.

[0039] In the first crushing device 2, the material is roughly pre-crushed, whereby the resulting fragments can have edge lengths or maximum dimensions of up to 63 mm.

[0040] The material pre-crushed by the first comminution device 2 is then fed to the reactor 3 of the system. This reactor is designed as a vertical reactor, which may, in particular, comprise a cylindrical reactor housing. The reactor 3 has a material inlet 4 at a first, upper end of the cylindrical reactor housing, through which the material can be introduced into the reactor interior. Sufficient tightness should be ensured in the area of ​​the material inlet 4 to prevent, as far as possible, the ingress of ambient air through the material inlet 4. At this upper end, the reactor 3 also has a liquid outlet 5 for the discharge of aqueous liquid and a gas outlet 6 (located higher than the liquid outlet 5) for the discharge of (overdosed) CO2.The aqueous liquid and the CO2 were introduced into the reactor interior via a liquid inlet 7 and a gas inlet 9 connected to a CO2 gas storage tank 8, both located at a second, lower end of the reactor 3. At this lower end, the reactor 3 also has a material outlet 10.

[0041] Material introduced into reactor 3 via material inlet 4 sinks within the reactor interior due to gravity towards material outlet 10, being subjected to countercurrent flow by the aqueous liquid and CO2 flowing from the respective inlets 7, 9 at the lower end to the respective outlets 5, 6 at the upper end of reactor 3.

[0042] Within the reactor interior, a mixing device 11 is arranged, which may, for example, have a rotating central shaft with mixing elements. However, the mixing device 11 can also be shaftless or in the form of a mixing screw. Furthermore, the mixing device 11 can also be in the form of a mill, for example a ball mill, in which case the number of grinding elements can be significantly lower compared to a conventional ball mill, which primarily serves to grind material. The mixing device 11 serves to ensure a continuous relative movement of the material fragments with respect to each other.

[0043] During its residence time within reactor 3, the material is further reduced in size due to these relative movements, continuously creating new fracture surfaces that are available for reaction with the aqueous liquid and the CO2. Furthermore, the presence of the aqueous liquid and the CO2 recarbonates the cement paste contained in the material. The process conditions are determined in particular by the residence time of the material in reactor 3 and the temperature in reactor 3 (preferably between 50°C and 100°C for the pressureless process according to the [reference to be added]). Fig. 1 and 2 ) and via the pH value in the reactor 3, which can be influenced by means of an input device 12 for introducing a basic additive (e.g. NaOH) into the reactor.

[0044] The intensive contact between the material fragments during mixing in reactor 3 also generates a very fine-grained abrasion, consisting primarily of recarbonated cement paste. This abrasion exists mainly as suspended particles within the aqueous liquid and can advantageously be discharged from reactor 3 via the liquid outlet 5 along with a withdrawal stream of the aqueous liquid. A pump 13 conveys this withdrawal stream of the aqueous liquid, containing the suspended particles, to a separation device 14, for example, a hydrocyclone. This separation device 14 separates the abrasion from the withdrawal stream of aqueous liquid and discharges it into a product storage container 15.The abrasion may still be in the form of a suspension, which may need to be dried or thickened (not shown).

[0045] Since the abrasion can essentially consist of pure cement paste that has also been recarbonated to a significant extent, it can be advantageously suited for further use. This cement paste can be chemically similar to raw meal used in the production of cement clinker and can therefore be used as a secondary raw material in such production. Because this cement paste can already be significantly finer-grained than raw meal made from natural raw materials, using it as a secondary raw material can save energy that would otherwise be required for grinding raw meal from natural raw materials. Furthermore, such raw materials would then need to be extracted to a correspondingly lesser extent.

[0046] The extracted aqueous liquid stream, now free of abrasion debris, is returned to the reactor 3 as a recirculated stream via the liquid inlet 7. This stream is first passed through a heat exchanger 16, where heat transfer to the extracted aqueous liquid stream or from this extracted aqueous liquid stream to a temperature control medium (e.g., water) circulating in a temperature control device 17 can occur. This temperature control device 17 also incorporates a heat source or heat sink 18 to either provide thermal energy (e.g., waste heat from a nearby cement plant) that can be transferred to the extracted aqueous liquid stream in the heat exchanger 16, or to dissipate thermal energy that has been transferred from the extracted aqueous liquid stream to the temperature control medium (e.g., via an ambient heat exchanger).

[0047] CO2 that has reached the upper end of reactor 3, and thus the area of ​​the gas outlet 6, and consequently has not been reacted in the reactions taking place within reactor 3, is recirculated to the gas inlet 9 by means of a conveying device 19 designed as a compressor (e.g., screw compressor) or blower (e.g., rotary lobe blower) and subsequently, if necessary mixed with fresh CO2 from the CO2 gas storage 8, is reintroduced into reactor 3. It may also be possible to introduce at least a portion of the CO2 into the aqueous liquid outlet stream downstream of heat exchanger 16 by means of, for example, an injection condenser, and thus supply it to reactor 3 (not shown). The CO2 dosage, and thus in particular the amount of CO2 added from the CO2 gas storage 8 to the recirculated CO2 gas stream, can preferably be adjusted depending on the CO2 concentration in the area of ​​the gas outlet 6.

[0048] The material treated in reactor 3 is discharged from reactor 3 together with a discharge stream of aqueous liquid via material outlet 10 and fed to a classifying device 20, which includes, among other things, a two-stage sieving device 21 and a separating device 22 downstream of the sieving device 21, which in turn is designed in the form of a hydrocyclone.

[0049] In a first screening stage of the screening device 21, a coarse fraction of the material, exhibiting particle sizes larger than 16 mm, is separated from the discharge stream. This coarse fraction is mixed into the stream of "fresh" material via a material return line 23 with an integrated second comminution device 24, which may, for example, be in the form of a high-pressure roller press, and is returned together with it to the reactor 3. If the material is in a form that allows it to be sufficiently constant and homogeneous with regard to particle size and composition even after pre-crushing in the first comminution device 2, the return of the coarse fraction can be omitted, or the proportion of the returned coarse fraction can be almost zero or extremely small.Furthermore, it is also possible to design the first comminution device 2 and the second comminution device 24 integrally, or to use the same comminution device to reduce the size of both the material supplied by the bearing 1 and the returned coarse fraction of the material.

[0050] A middle fraction of the material, exhibiting grain sizes greater than 2 mm (and less than 16 mm), is separated from the discharge stream by means of a second screening stage of the screening device 21 and conveyed to a product storage area 25. This can, in particular, consist of rocks essentially completely free of cement paste, which were intended primarily as aggregate for concrete. Due to their purity, these can also be advantageously reused directly.

[0051] A fine fraction of the material, with grain sizes smaller than 2 mm, passes through the screening device 21 together with the discharge stream of aqueous liquid and, conveyed by a pump 26, is fed to the separating device 22 of the classifying device 20 and separated from the discharge stream by this device. This fine fraction, which may consist in particular of largely sorted sand, can also be discharged into a product storage area 27 and reused.

[0052] The discharge stream of aqueous liquid, freed from the fractions, is partially returned to an inlet side of the sieve device 21, in particular also to rinse it, and partially mixed with the withdrawal or recirculation stream of aqueous liquid and returned together with it to the reactor 3.

[0053] If necessary (for example, depending on the specific material or concrete recyclate to be treated), it may be useful to analyze the middle fraction for residual cement paste content before removal, for which a system according to the Fig. 2 a corresponding analysis device 28 may be included. The plant and the procedure carried out with it otherwise correspond to that described in the Fig. 1 If the analysis device 28 detects that the middle fraction (temporarily) contains a proportion of cement paste that exceeds a defined limit value, it may be possible to return this portion of the middle fraction to reactor 3 via a further material return line. Alternatively to the embodiment according to the Fig. 2It may also be possible to route this recycled portion of the middle fraction through the second comminution device 24 in order to further comminute it before introducing it into the reactor 3.

[0054] The embodiments according to the invention of methods for processing material containing cement stone and the equipment used therein, according to the Fig. 3 and 4 differ from those according to the Fig. 1 and 2 essentially solely in that, according to the Fig. 3 and 4 The reactor 3 is intended to operate at a pressure above ambient pressure (preferably up to 500 mbar overpressure). This will, in particular, make it possible to set a temperature above 100°C within the reactor 3 without significant evaporation of the aqueous liquid.

[0055] For such pressurized operation of reactor 3, it must be temporarily isolated or pressure-wise separated, at least with regard to material supply and material removal, which is required according to the Fig. 3 and 4 This can be achieved by integrating appropriate shut-off valves 30. The introduction of material into the reactor 3 and the removal of material from the reactor 3 can either take place after pressure relief of the reactor 3, or pressure locks 31, which can also provide a relatively large intermediate storage volume for the material, can be provided in the material supply and material discharge area.

[0056] During pressurized operation of reactor 3, it should be noted that steam may escape suddenly when aqueous liquid is discharged from reactor 3 or when a pressure lock 31 is opened. Therefore, it may be advantageous to cyclically raise the temperature inside reactor 3 to more than 100°C and the pressure within it to values ​​above ambient pressure, with the pressure being released at the end of each cycle and the temperature being lowered to just below 100°C. For this purpose, cooling the discharged aqueous liquid stream by means of the heat exchanger 16 can be provided.Because reactor 3 needs to be reheated for the subsequent cycle, it could be advantageous in this case to design the heat exchanger 16 recuperatively, with the material stored in a pressure lock 31 or other intermediate storage tank serving as the storage mass for intermediate thermal energy storage. It is also possible to divide such an intermediate storage tank into individual sections and to design the walls and partitions of such a tank in such a way that they can be permeated by the temperature control medium of the temperature control device 17, in order to achieve the most efficient transfer of thermal energy. A hollow-walled design of the lower tower of the sieve device 21 could also be used as an additional control element for rapid temperature adjustments, provided that the temperature control medium could be permeated by it. Reference symbol list:

[0057] 1 Storage 2 First crushing device 3 Reactor 4 Material inlet 5 Liquid outlet 6 Gas outlet 7 Liquid inlet 8 CO2 gas storage 9 Gas inlet 10 Material outlet 11 Mixing device 12 Feeding device 13 Pump 14 Separating device 15 Product storage 16 Heat exchanger 17 Temperature control device 18 Heat source / heat sink 19 Conveying device 20 Classifying device 21 Screening device 22 Separating device 23 Material return line 24 Second crushing device 25 Product storage 26 Pump 27 Product storage 28 Analysis device 29 Material return line 30 Shut-off valve 31 Pressure lock

Claims

1. A method for processing material containing cement stone, wherein the material is crushed in a first crushing device (2) and subsequently fed to a reactor (3), in which the material is mixed with an aqueous liquid and CO2 and in which a mixing motion of the material is generated, wherein the material removed from the reactor (3) is divided by means of a classifier (20) into at least two fractions, a coarse fraction and a medium fraction, wherein the coarse fraction has a particle size greater than 16 mm, wherein the medium fraction has a particle size between 2 mm and 16 mm, wherein the temperature and pressure in the reactor (3) are controlled such that an overpressure relative to atmospheric pressure and a temperature greater than 100°C are established, characterised in that, of the at least two fractions, the coarse fraction is returned to the reactor (3), wherein the coarse fraction is comminuted in a second comminution device (24) prior to being returned to the reactor (3).

2. A method according to claim 1, characterised in that a withdrawal stream of the aqueous liquid is withdrawn from the reactor (3), wherein suspended particles of the material are separated from this withdrawal stream and discharged.

3. A method according to claim 2, characterised in that the withdrawal stream is returned to the reactor (3) as a recirculation stream after the separation of the suspended particles.

4. A method according to one of the preceding claims, characterised in that the material withdrawn from the reactor (3) is divided into at least three fractions by means of the classifier (20), of which a fine fraction and a medium fraction are discharged.

5. A method according to one of the preceding claims, characterised in that, in the case of two fractions, the smaller of the fractions, or in the case of at least three fractions, the or a medium fraction, has particle sizes between 2 mm and 16 mm.

6. A method according to one of the preceding claims, characterised in that, in the case of two fractions, the smaller of the fractions, or in the case of at least three fractions, the or a medium fraction, is analysed with regard to the content of cement stone.

7. A method according to claim 6, characterised in that the analysed fraction is returned to the reactor (3) if the determined cement stone content is greater than a threshold value.

8. A method according to one of the preceding claims, characterised in that a basic additive is introduced into the reactor (3).

9. A method according to one of the preceding claims, characterised in that the material in the reactor (3) is flowed through by the aqueous liquid and the CO2 in counter-current.

10. A method according to one of the preceding claims, characterised in that the at least two fractions are separated from a discharge stream of the aqueous liquid which was removed from the reactor (3) together with the material.

11. A method according to claim 10, characterised in that the discharge stream of the aqueous liquid, from which the fractions have been removed, is at least partially returned to the classifier (20) and / or at least partially returned to the reactor (3).

12. A method according to one of the preceding claims, characterised in that a gas stream of CO2 is withdrawn from the reactor (3) and recirculated to the reactor (3).

13. A method according to one of the preceding claims, characterised in that non-mineral constituents are removed from the material prior to introduction into the reactor (3).

14. Plant for processing material containing cement stone, comprising - a (first) comminution device (2) for comminuting the material, - a reactor (3) connected to the (first) crushing device (2) in a material-conveying manner, which comprises a mixing device (11), - a liquid supply for an aqueous liquid, connected to the reactor (3) in a fluid-conducting manner, - a gas supply for CO2 connected to the reactor (3) via a fluid conduit, - a classifier (20) connected to the reactor (3) for separating the material removed from the reactor into at least two fractions differing in particle size, a coarse fraction and a medium fraction , wherein the coarse fraction has a particle size greater than 16 mm, wherein the medium fraction has a particle size between 2 mm and 16 mm , - a temperature control device (17) for controlling a temperature in the reactor and - a pressure control device for controlling a pressure in the reactor - a material return line (23, 29) for returning at least one of the fractions from the classifier (20) to the reactor (3), wherein a second comminution device (24) is integrated into the material return line (23).

15. An apparatus according to claim 14, characterised by - an analysis device (28) for analysing the cement paste content in at least one of the fractions and / or - an introduction device (12) for introducing a basic additive into the reactor (3) and / or - a material inlet (4), a liquid outlet (5) and a gas outlet (6) associated with a first end of the reactor (3), and a material outlet (10), a liquid inlet (7) and a gas inlet (9) associated with a second end of the reactor (3) and / or - the reactor (3) designed as a vertical reactor and / or - a gas recirculation line for recirculating CO2 from one / the gas outlet (6) to one / the gas inlet (9) of the reactor (3) and / or - a separation device (14) for separating suspended particles from a discharge stream of the aqueous liquid discharged from the reactor (3) and / or - a removal device for removing non-mineral constituents of the material prior to introducing the material into the reactor (3).