Electrostatic classifier in mechano-chemical activation

Abstract

The present invention relates to a device for mechano-chemical activation, the device comprising a mill 10, the mill 10 having a material inlet 12 and a material outlet 14, the device comprising a first separation device 20 downstream of the mill 10 in the material flow, the device comprising a product outlet 30 downstream of the first separation device 20 in the material flow, characterized in that the first separation device 20 is an electrostatic classifier, the electrostatic classifier having a first outlet 22 for charged particles and a second outlet 24 for discharged particles, the first outlet 22 being connected to the product outlet 30, the second outlet 24 being connected to a return line 40, the return line 40 being connected to the material inlet 12 of the mill 10.

Description

The invention relates to the use of an electrostatic separator in mechanochemical activation for the separation of the activated fraction.Activated clays have become established as an additive, particularly in the field of the cement industry. The currently customary way is drying and calcining of the clays, i.e. thermal activation. In this case, on the one hand, energy is required for the heating, and on the other hand, the high temperature can also bring about further material changes, which are possibly undesirable. Furthermore, the thermal process frequently requires flue gas cleaning, for example for the separation of the nitrogen oxide and sulfur oxide emissions formed. In addition, the thermal process requires the use of methods for separating out and optionally purifying the carbon dioxide generated or released in the future.Cement aggregates are nowadays used to save clinkers and thus carbon dioxide emissions. According to DIN EN 450-1, the activity index describes the ratio (in %) of the compressive strengths of standardized mortar prisms tested at the same age, which comprise a proportion by mass of 75% test cement and a proportion by mass of 25% cement aggregate, and standardized mortar prisms produced exclusively with test cement. The test cement used is a Portland cement (type CEM I) of the strength class 42.5 or higher. The cement additive (SCM) to be evaluated can be less efficient or more efficient than the test cement. An SCM to be considered inert, such as limestone, leads to an activity index of 75%, i.e. the SCM makes no contribution to strength development. However, performance SMCs such as granulated blast furnace slags can also achieve activity values of more than 100 up to about 120. If the activity index is more than 100, this means that the clinker content in the binder can be reduced even further, namely exactly by the amount necessary to obtain an activity index of 100 again. The clinker content is usually replaced by an inert, finely ground filler such as limestone, which is considerably more advantageous in production than clinker.Therefore, the so-called mechanochemical activation by intensive milling is increasingly discussed. The mechanochemical activation process can be used to produce cement aggregates with which other secondary cementitious materials, i.e. SCMs, can optionally be replaced. SCMs ideally have pozzolanic, latent hydraulic or even hydraulic properties, so that these materials contribute to the development of strength when making the finished binder with water. Inert substances such as limestone do not exhibit this additional development of strength when made with water.In mechanochemical activation, water bound in crystalline form beforehand is retained in the mineral material, for example, as inner layer water (Xerox gels). This differentiation into thermally activated materials is an essential quality feature of mechano-chemically activated substances when used as a cement aggregate, since this results in improved binder properties, in particular a low water requirement. This has an improving effect on, for example, strength development and processing of the binder-containing mortar or concrete without the need to use expensive cement additives such as superplasticizers.From post-published DE 10 2023 106 210 a method for grinding and pozzolanic activation in an agitator ball mill is known.From post-published DE 10 2023 106 217, a method for grinding and pozzolanic activation is known in two separate stages of an agitator ball mill.The combination of mechanochemical and thermal activation in at least one stirred ball mill is known from post-published DE 10 2023 106 221.The color optimization in the mechanochemical activation of clays is known from post-published DE 10 2023 106 222.From post-published DE 10 2023 123 525 a cement additive made of old concrete is known.An advantage of mechanochemical activation is that clays with a lower kaolin content can also be mechanochemically activated, which are not suitable for thermal activation. This broadens the available raw material base.Since clays are a complex system (especially as compared to limestone firing), different activation methods result in different products (activated clays) with different properties. Also, the diversity of clays that can be used results in not every method being usable for each clay.Mechanochemical activation is fundamentally different from thermal activation as far as understanding of the operations is concerned. While thermal activation is primarily determined by temperature and time, mechanochemical activation in a mill appears to be substantially more complex and dependent on substantially more parameters. Furthermore, a large part of the introduced grinding energy is converted into heat.In order to operate the activation efficiently, the challenge is thus presented of separating activated particles from particles that have not yet been activated, in order to be able to return particles that have not yet been activated as much as possible. In mechano-cmemic activation, the primary particles are first comminuted in a preceding step until virtually no grinding progress occurs any longer (Rittinger stage). This is followed by activation, in which changes in the crystal structure occur up to amorphization of the (clay) minerals. Moreover, agglomeration and aggregation effects of the particles can be observed, which is reflected in a decrease in the specific surface area. The usual concept, the separation of fine product particles and coarse grit, cannot therefore be used here. The concept according to the invention therefore provides for the largest particles to be regarded as activated and to be separated off, the finest particles to be regarded as non-activated and to be recirculated.It is an object of the invention to provide a reliable separation of already activated and not yet activated particles during mechanochemical activation.This object is achieved by the device having the features specified in claim 1, by the use having the features specified in claim 5 and by the method having the features specified in claim 6. Advantageous refinements emerge from the dependent claims, the following description and the drawings.The device according to the invention serves for mechanochemical activation. Conventionally, the activation is carried out thermally, wherein the mineral material is heated to 900° C. to 1000° C., for example. The aim of activation is achieved in mechanochemical activation by very intensive grinding, wherein substantially more energy is introduced than is required for comminution. In this region of mechanical activation, particle growth can rather be detected by grinding. The apparatus comprises a mill. Preferably, the mill is an agitator ball mill. Such devices are known, for example, from DE 10 2023 106 210, DE 10 2023 106 217, DE 10 2023 106 221, DE 10 2023 106 222 or DE 10 2023 123 525. These devices known per se are developed to improve them. The apparatus comprises a mill. Preferably, the mill is an agitator ball mill. The mill has a material inlet and a material outlet. The device has a first separating device downstream of the mill in the material stream. The device has a product outlet downstream of the first separating device in the material stream.Size-selective separating devices are usually used as the first separating device. Since the mill is operated here in a region in which particle growth can be detected by the energy input, the coarse fraction is the activated fraction and the fine fraction is the not yet activated fraction.According to the invention, the first separating device is an electrostatic classifier. The electrostatic classifier has a first output for charged particles and a second output for discharged particles. In the context of the invention, discharging is used to be uncharged or noncharged. An outlet is connected to the product outlet and the second outlet is connected to a return line. The recirculation line is connected to the material inlet of the mill.It has surprisingly been found that the separation used in an electrostatic classifier is able to separate substantially better activated and not yet activated particles. The fraction which comprises the charged particles has proven to be more reactive and thus to be the fraction which already comprises activated particles. This separation thus avoids a significant problem. In the size-selective separation, it is precisely not possible to distinguish between coarse particles which have not yet been completely ground (i.e. from the first stage of the grinding with an approximately linear relationship between grinding energy) and the already activated and therefore already re-grown or agglomerated particles (i.e. from the third stage, increase in the particle size with further introduction of grinding energy). Therefore, just the worst fraction remained in the product fraction. This drawback can be overcome by the use of an electrostatic classifier.In a further embodiment of the invention, the device has a second separating device. The second separating device is a size-selective separating device. Examples of a size-selective separating device are a normal classifier, a cyclone or also a sieve. Such a size selective separation device serves to separate a material stream into a coarse fraction (for example, on top of the screen) and a fine fraction (under the screen). In this case, each size-selective separating device has a different separating size and separating sharpness, so that although it is fundamentally not possible to say what is coarse or fine, in a specific case on a specific size-selective separating device this is, however, clear and immediately clear. The second separating device has a fine outlet and a coarse outlet. The fine outlet serves for discharging the fine fraction and the coarse outlet serves for discharging the coarse fraction.In a further embodiment of the invention, in a first alternative, the second separating device is arranged downstream of the first separating device in the material stream. The first output of the first separating device is connected to the second separating device. Therefore, only the charged particles and thus the activated particles are fed to the second separating device. The coarse outlet is connected to the product outlet. Thus, only the largest activated particles are dispensed as product, since they have the highest activity. The fine outlet is connected to the material inlet of the mill. This material is thus not yet adequately activated.In a further embodiment of the invention, in a second alternative, the second separating device is arranged upstream of the first separating device in the material stream. Thus, the entire material coming from the mill is first size-selective and only then electrostatically separated. The material outlet of the mill is therefore connected to the second separating device. The coarse outlet is connected to the first separating device in order to separate the non-activated, hardly comminuted particles from the activated and re-grown particles. The fine outlet is connected to the material inlet of the mill.In a further aspect, the invention relates to the use of an electrostatic separator for separating activated particles and non-activated particles after mechanochemical activation in a mill. As already stated, this has surprisingly proved to be a very suitable separation method which can avoid, in particular, the undesired discharge of coarse starting material as product.In a further aspect, the invention relates to a method for mechanochemical activation. The method comprises the steps of: a) mechanochemical activation in a mill, b) transferring the activated material into an electrostatic classifier, c) separating the material in the electrostatic classifier into a charged fraction and a discharged fraction, d) transferring the charged fraction to the product outlet, e) recycling the discharged fraction for re mechanochemical activation.Steps d) and e) are logically parallel.The separation in an electrostatic classifier is essential, and not in a size-selective separation device as before. As a result, the different charge behavior of the activated and the non-activated particles can be utilized to separate them and thus obtain a pure activated fraction.In a further embodiment of the invention, in a first alternative, size-selective separation is carried out between step a) and step b) in a second separating device. The coarse fraction of the size selective separation is then transferred in step b) to the electrostatic classifier. The fine fraction of the size selective separation is again fed to step a). Thus, a size selective separation as before is performed first and then the electrostatic separation is performed subsequently.In a further embodiment of the invention, in a second alternative, between step c) and step d) a size-selective separation of the charged fraction is carried out in a second separation device. Only the coarse fraction of the size selective separation containing the most activated particles is fed to the product outlet in step d). The fine fraction is fed back to the size-selective separation step a). Thus, the electrostatic separation is carried out first and then, in a second step, the small, least activated particles are separated off by the size-selective separation and are returned for further activation.Overall, the activity of the product can thus be increased and thus the usability as a cement additive can be increased and thus the need for clinker can be reduced and thus the total amount of CO 2 produced for the production of cement can be reduced.The device according to the invention is explained in more detail below with reference to exemplary embodiments shown in the drawings. FIG. 1 basic shape FIG. 2 shows a first alternative FIG. 3 shows a second alternativeThe basic shape is shown in FIG. 1. The material to be activated is introduced into the mill 10 via the material inlet 12 and is intensively ground there such that mechanochemical activation occurs, for example at an energy input of 600 kWh / t. The activated material leaves the mill 10 via the material outlet 14 and is transferred into the first separating device 20, an electrostatic classifier. Here, separation into charged and uncharged particles takes place. The charged particles leave the first separating device via the first outlet and are fed as a finished activated product to the product outlet 30, which can be, for example, a silo, a filling station or the transfer point to a further installation. The uncharged, not yet activated particles leave the first separating device 20 through the second outlet 24 and are guided again via the return line 40 to the material inlet 12 of the mill 12.FIGS. 2 and 3 show the combination of a first separating device 20 in the form of an electrostatic separator with a second separating device 50 in the form of a size-selective separating device, for example a cyclone. For simplification, only the differences from the basic form are discussed below.FIG. 2 shows the first alternative in which the second separating device 50 is arranged behind the first separating device 20. Thus, the charged particles from the first separation device are transferred from the first outlet 22 into the second separation device 50 and are separated there in a size-selective manner into a coarse fraction and a fine fraction. The coarse fraction is fed via the coarse outlet 54 to the product outlet 30 and the fine fraction via the fine outlet 52 and is fed again to the material inlet 12 of the mill 10, for example via the return line 40.In Fig. 3 the second alternative is shown, in which the second separating device 50 is arranged between the mill 10 and the first separating device 20. Thus, the activated material from the mill 10 is transferred through the material outlet 14 into the second separating device 50 and separated there into a coarse fraction and a fine fraction. The fine fraction is fed again to the material inlet 12 of the mill 10 via the fine outlet 52 and, for example, the return line 40. The coarse fraction is fed through the coarse outlet 54 to the first separating device 20.Reference numerals denote reference numerals10 Mill 12 Material inlet 14 Material outlet 20 First separator 22 First outlet 24 Second outlet 30 Product outlet 40 Return line 50 Second separator 52 Fine outlet 54 Coarse outletReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2023 106 210 [0006, 0017]DE 10 2023 106 217 [0007, 0017]DE 10 2023 106 221 [0008, 0017]DE 10 2023 106 222 [0009, 0017]DE 10 2023 123 525 [0010, 0017]Cited Non-Patent LiteratureDIN EN 450-1

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Claims

A mechanochemical activation device, the device comprising a mill (10), the mill (10) comprising a material inlet (12) and a material outlet (14), the device comprising a first separation device (20) downstream of the mill (10) in the material stream, the device comprising a product outlet (30) downstream of the first separation device (20) in the material stream, characterized in that the first separation device (20) is an electrostatic classifier, the electrostatic classifier comprising a first charged particle outlet (22) and a second discharged particle outlet (24), the first outlet (22) being connected to the product outlet (30), the second outlet (24) being connected to a recirculation line (40), wherein the recirculation line (40) is connected to the material inlet (12) of the mill (10).The device according to claim 1, characterized in that the device comprises a second separating device (50), wherein the second separating device (50) is a size selective separating device, wherein the second separating device (50) comprises a fine outlet (52) and a coarse outlet (54).Device according to claim 2, characterised in that the second separating device (50) is arranged downstream of the first separating device (20) in the material stream, the first outlet (22) of the first separating device (20) being connected to the second separating device (50), the coarse outlet (54) being connected to the product outlet (30), the fine outlet (52) being connected to the material inlet (12) of the mill (10).Device according to claim 2, characterised in that the second separating device (50) is arranged upstream of the first separating device (20) in the material flow, wherein the material outlet (14) of the mill (10) is connected to the second separating device (50), wherein the coarse outlet (54) is connected to the first separating device (20), wherein the fine outlet (52) is connected to the material inlet (12) of the mill (10).Use of an electrostatic separator for separating activated particles and non-activated particles after mechanochemical activation in a mill (10).A method of mechanochemical activation, the method comprising the steps of: a) mechanochemical activation in a mill (10), b) transferring the activated material into an electrostatic classifier, c) separating the material in the electrostatic classifier into a charged fraction and a discharged fraction, d) transferring the charged fraction to the product outlet (30), e) recycling the discharged fraction for mechanochemical activation again.Method according to claim 6, characterised in that between step a) and step b) a size-selective separation is carried out in a second separation device (50), wherein the coarse fraction of the size-selective separation is transferred in step b) into the electrostatic classifier, wherein the fine fraction of the size-selective separation is fed back to step a).Method according to claim 6, characterised in that between step c) and step d) a size selective separation of the charged fraction is carried out in a second separation device (50), wherein the coarse fraction of the size selective separation is fed in step d) to the product outlet (30), wherein the fine fraction of the size selective separation is fed again to step a).

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