Mechano-chemical activation with heat coupling

Abstract

The present invention relates to a device for the mechano-chemical activation of a moist starting material, the device comprising a drying device 10 and a mill 20, the drying device 10 and the mill 20 being connected for transferring the material dried in the drying device 10, the mill 20 and the drying device 10 being connected for transferring the waste heat of the mill 20 to the drying device 10.

Description

The invention relates to mechanochemical activation of moist starting material.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 requires flue gas purification 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 mechanochemical activation, only about 25% of the energy introduced is converted into chemical energy, about 75% being released as heat. This heat is at most in a range from 200° C. to 300° C., i.e. only low-value heat is used, which cannot be used efficiently for a current flow, for example. At the same time, one of the essential educts for mechanochemical activation is clay, which entails a high degree of moisture and has to be dried before activation, for which purpose thermal energy is required.It is the object of the invention to use the heat released during mechanochemical activation in an efficient manner for a preliminary drying process, for example of clays.This object is achieved by the device having the features specified in claim 1 and by the method having the features specified in claim 6. Advantageous further developments are evident from the dependent claims, the following description and the drawing.The device according to the invention serves for mechanochemical activation of a moist starting material. An example of a moist starting material is, in particular, clay. However, this can also be, for example, moist old concrete. Moist is understood to mean volatile water up to 100° C.; therefore, water of crystallization or, for example, in clays, the water incorporated between the layers, which are released only at relatively high temperatures, are not meant. The apparatus comprises a drying device and a mill. The mill is preferably a stirred ball mill. The drying device and the mill are connected for transferring the material dried in the drying device. It is essential that the mill and the drying device are connected for transferring the waste heat of the mill to the drying device. As a result, the high proportion of the energy introduced into the mill and converted only into heat can be used particularly usefully, since the temperature level in the mill is usually below 300° C. and the released heat is thus available at a low energy level, but is very well suited for drying. There are in particular two preferred options for transferring the waste heat, which can be used alternatively or preferably in combination. These will be described in detail below, one option being simply the gas stream which is passed through the mill and heated there and is suitable directly and directly for drying. The second option is to use a fluid from the cooling jacket which is integrated in the housing of the mill and / or the shaft of the mill.The advantage is that the waste heat obtained from the mill can be used to dry a starting material having an input moisture (volatile water content, not bound) of up to 20 to 30%. Thus, the heat can be utilized ideally. At the same time, therefore, even comparatively moist clays can be activated efficiently without additional drying by using, for example, conventional fuels.In a further embodiment of the invention, the mill and the drying device are connected via a mill gas line for transferring the waste heat of the mill to the drying device. Via the mill gas line, the gas flowing through the mill on the inside together with the grinding material is guided directly to the drying device. With a usual temperature of the gas stream of 200 to 250°C leaving the mill, it is also particularly suitable to be used for drying in the drying apparatus.In a further embodiment of the invention, the mill has a cooling jacket with a jacket heat exchange fluid. This is usually necessary, since the heat capacity of the gas stream passed through the mill is generally not sufficient to remove all the heat generated. In addition, a jacket heat exchange fluid particularly suitable for heat transfer can be used in the cooling jacket, in particular one with a suitably high heat capacity. Water is often preferred because of the heat capacity and availability, but this usually limits the temperature to 100° C. A thermal oil, on the other hand, can also be operated at higher temperatures. The cooling jacket is connected to the drying device for transferring the jacket heat exchange fluid heated in the cooling jacket via a jacket heat exchange fluid connection. Thus, overall, a larger amount of heat is possible, but usually at a lower temperature level, compared to the gas flow from the mill interior.In a further embodiment of the invention, the jacket heat exchange fluid connection or the drying device has a heat pump. If, for example, cooling water is used as jacket heat exchange fluid, a typical temperature level on leaving the mill is, for example, 70° C. In order to use this for the drying, it is advantageous to raise this to a higher temperature level and then transfer it to a gas stream in order to then be able to carry out the drying in the gas stream. A higher temperature level is conducive to applying the high enthalpy of vaporization of the water (the moisture of the material).In a further embodiment of the invention, the drying device is an air-flow dryer. Alternatively or upstream, a belt dryer can be used in the case of very moist material.In a further embodiment of the invention, the mill has an internal volume of at least 1 m 3.In a further embodiment of the invention, the mill has an energy density of at least 200 kW / m 3.In a further embodiment of the invention, the mill has a length of at least 2 m, preferably of at least 2.5 m.In a further embodiment of the invention, the mill has a cross-sectional area perpendicular to the longitudinal axis of at least 0.71 m 2, preferably of at least 0.75 m 2.In a further embodiment of the invention, the mill has a ratio of length to diameter of at least 3, preferably of at least 3.5.In a further aspect, the invention relates to a method for drying and mechanochemical activation of a material, preferably by means of an apparatus according to the invention. The method comprises the steps of: a) drying the material in a drying apparatus; b) transferring the dried material from the drying apparatus to a mill; and c) mechanochemical activation of the material in the mill. At least a portion of the heat generated during mechanochemical activation is transferred to at least one heat exchange fluid. The heat exchange fluid is supplied to the drying device or the heat is transferred to the drying device via a heat exchanger or a heat pump.The first alternative is usually given when the gas stream from the mill is directly fed to the drying device as a warm gas stream to be dried. The second alternative is usually provided when a jacket heat exchange fluid, for example water, is used as the heat transport medium. Preferably, it can also be a combination where the gas is transferred directly as well as indirectly the heat via a cooling liquid.In a further embodiment of the invention, the heat exchange fluid is a gas stream passed through the mill. The gas stream is fed to the drying device. This has two advantages. Firstly, the gas stream comes directly into contact with the ground material, i.e. has the highest temperature level. On the other hand, the gas stream can be used directly for drying, i.e. also for transporting away the water vapor formed during drying. A media change in a heat exchanger is not necessary. This makes this embodiment simple and efficient. The only disadvantage is that the heat capacity of the gas stream is limited and is not sufficient to transport heat completely.In a further embodiment of the invention, the heat exchange fluid or a further heat exchange fluid (if the heat exchange fluid is a gas stream as mentioned above) is a jacket heat exchange fluid conducted through a cooling jacket of the mill. It is advantageous that very large amounts of heat can be dissipated efficiently in this way and this is regularly necessary to maintain the temperature in the mill. It is disadvantageous that a lower temperature level is regularly achieved by such a cooling system, in particular if cooling water is used as (further) heat exchange fluid.In a further embodiment of the invention, water is selected as jacket heat exchange fluid. In order to raise the lower temperature level, the water is preferably passed through a heat pump. This makes it possible to raise a gas stream used for drying in the drying apparatus to a sufficiently high temperature.In a further embodiment of the invention, a thermal oil is selected as jacket heat exchange fluid. This has the advantage that significantly higher temperatures can be realized with a thermal oil than with liquid water. The thermal oil is passed through a heat exchanger for transferring the heat by a gas stream fed to the drying device. An "upgrading" of the heat in a heat pump can generally be dispensed with, which is simpler in terms of apparatus. For this purpose, thermal oil is expensive than water.In a further embodiment of the invention, the mechanochemical activation is carried out at less than 300° C., preferably at less than 250° C.In a further embodiment of the invention, the mill is operated with a residence time of the grinding material in the mill of at least 5 min, preferably at least 10 min, particularly preferably at least 20 min.The device according to the invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing. FIG. 1 shows an example of a deviceAn exemplary device is shown in FIG. 1. A moist starting material, for example clay, passes via the reactant feed 32 into the drying device 10, is transferred dried from the drying device 10 into the mill 20, is activated there and is subsequently removed via the product removal 34.The mill 20 has a cooling jacket 22, in which water is used as coolant in the example shown. The water leaves the cooling jacket 22 at, for example, 80° C. Since this temperature level is suitable for drying only to a very limited extent, the water is fed into a heat pump 50 of the drying apparatus 10, is raised there to a higher temperature level and a drying gas stream 42 is thus heated in a heat exchanger 60. The latter then dries the material and leaves the drying device 10 as a moist gas stream 44If thermal oil were used in the cooling jacket 22 instead of water, the heat pump 50 would be omitted if necessary; the cooling liquid (the thermal oil) would be passed directly from the cooling jacket 22 into the heat exchanger 60.Reference numerals denote reference numerals10 Drying device 20 Mill 22 Cooling jacket 32 Reactant feed 34 Product removal 42 Dry gas stream 44 Moist gas stream 50 Heat pump 60 Heat exchangerReferences 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] DE 10 2023 106 217

[0007] DE 10 2023 106 221

[0008] DE 10 2023 106 222

[0009] DE 10 2023 123 525

[0010]

Claims

Device for mechanochemical activation of a moist starting material, wherein the device comprises a drying device (10) and a mill (20), wherein the drying device (10) and the mill (20) are connected for transferring the material dried in the drying device (10), wherein the mill (20) and the drying device (10) are connected for transferring the waste heat of the mill (20) to the drying device (10).Device according to claim 1, characterised in that the mill (20) and the drying device (10) are connected via a mill gas line for transferring the waste heat of the mill (20) to the drying device (10).Device according to one of the preceding claims, characterized in that the mill (20) has a cooling jacket (22) with a jacket heat exchange fluid, wherein the cooling jacket (22) is connected to the drying device (10) via a jacket heat exchange fluid connection for transferring the jacket heat exchange fluid heated in the cooling jacket (22).Device according to claim 3, characterised in that the jacket heat exchange fluid connection or the drying device (10) has a heat pump (50).Device according to one of the preceding claims, characterized in that the drying device (10) is an air-flow dryer.Method for drying and mechanochemical activation of a material, wherein the method comprises the following steps: a) drying the material in a drying device (10), b) transferring the dried material from the drying device (10) into a mill (20), c) mechanochemical activation of the material in the mill (20), wherein at least a part of the heat generated during mechanochemical activation is transferred to at least one heat exchange fluid, wherein the heat exchange fluid is supplied to the drying device (10) or transfers the heat to the drying device (10) via a heat exchanger (60) or a heat pump (50).Method according to claim 6, characterized in that the heat exchange fluid is a gas stream passed through the mill (20), the gas stream being supplied to the drying device (10).Method according to one of Claims 6 to 7, characterized in that the heat exchange fluid or a further heat exchange fluid is a jacket heat exchange fluid which is guided through a cooling jacket (22) of the mill (20).Method according to claim 8, characterised in that water is selected as jacket heat exchange fluid, wherein the water is conducted through a heat pump (50).Method according to Claim 8, characterized in that a thermal oil is selected as jacket heat exchange fluid, wherein the thermal oil is guided through a heat exchanger (60) for transferring the heat by a gas stream fed to the drying apparatus (10).Method according to one of claims 6 to 10, characterised in that the mechanochemical activation is carried out at less than 300°C, preferably at less than 250°C.

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