Two-stage grinding of material for the production of a binder, especially a cement

Description

[0001] The invention relates to a method for two-stage grinding and for the production of a binder, in particular a cement, wherein the second stage of grinding with high energy input makes it possible to increase reactivity.

[0002] From DE 10 2017 114 831 A1 a process for the processing of fly ash as well as a plant and a process for the production of cement are known.

[0003] From DE 10 2017 115 994 A1 a two-stage grinding cycle and a method for producing a ground product by means of a two-stage grinding process are known.

[0004] From DE 10 2017 117 985 A1 a process and a plant for the production of cement are known.

[0005] A process for processing fly ash is known from DE 10 2019 008 945 B4.

[0006] From DE 19 501 616 A1 a grinding process and a plant for the comminution of grinding material are known.

[0007] Furthermore, methods for mechanical activation are known.

[0008] From WO 2017 / 008 863 A1 a process and a plant arrangement for processing and activating a raw material are known.

[0009] From EP 3 909 682 A1 a method and a roller mill for the thermomechanical activation of a clay mixture are known.

[0010] From DE 10 2015 106 109 A1 a process for the tribochemical activation of binders and additives is known.

[0011] From DE 10 2017 114 831 A1 a process for the processing of fly ash and a process for the production of cement is known.

[0012] The mechanical activation of clays is known from the subsequently published DE 10 2023 106 210.

[0013] The mechanical activation of clays is known from the subsequently published DE 10 2023 106 217.

[0014] The combined mechanical and thermal activation of clays is known from the subsequently published DE 10 2023 106 221.

[0015] The color optimization during the mechanical activation of tones is known from the subsequently published DE 10 2023 106 222.

[0016] A method for increasing the efficiency of grinding ores, minerals and concentrates is known from CN 101 282 790 B.

[0017] The object of the invention is to provide a grinding process for a binder which enables optimized product quality.

[0018] This problem is solved by the method with the features specified in claim 1. Advantageous further developments are described in the dependent claims, the following description, and the drawing.

[0019] An apparatus for carrying out the process according to the invention serves to grind a mineral material, in particular for the production of cement. Examples of such mineral materials are clinker, gypsum, activated clays, sand, recycled cement paste, slag, and the like. The apparatus comprises a first grinding device and a second grinding device downstream of the first. The mineral material to be ground thus passes first through the first grinding device and then through the second grinding device. The first grinding device is designed to achieve a fineness of 2500 to 5000 cm² / g according to Blaine. This corresponds to a fineness that is approximately equivalent to the fineness of the individual components in conventional cements. Thus, the first grinding device is simply a normal grinding device and is not designed to achieve mechanochemical activation.This allows the first grinding device to be significantly simpler than the second. The second grinding device has an energy input of at least 100 kW / m³. This corresponds to a comparatively high energy input for a fine mill and exceeds the usual amount of energy input. The aim is to achieve a particularly advantageous property of the binder, which in turn makes it possible to increase the proportion of substitutes and thus conserve valuable primary raw materials. The second grinding device is therefore considerably more complex than the first. The combination allows the initial comminution to take place in the first grinding device, approximately to the limit of fineness, i.e., the fineness achievable through grinding.This can be done in a simpler first grinding device; only then does the mechano-chemical activation take place in the second grinding device, which is considerably more complex and expensive. However, since the comminution is no longer necessary in the second device, it can be smaller, as it only needs to perform the mechano-chemical activation.

[0020] Of course, the first and second grinding devices can also be designed identically. This allows for limited redundancy, since mechano-chemical activation can still be carried out in reduced quantities on the remaining grinding device even after the failure of one grinding device, without the inventive method and its advantages.

[0021] In a further embodiment of the invention, the second grinding device is a stirred ball mill. The stirred ball mill is particularly preferably operated continuously. This makes the high energy inputs technically easy to implement, and also allows for the simple realization of the throughput and series connection with a continuous first grinding device.

[0022] In a further embodiment of the invention, the second grinding device has an energy input of at least 200 kW / m³. This further enhances the effect, which in particular enables an increase in the substitute content.

[0023] In a further embodiment of the invention, the first grinding device is a vertical roller mill or a bed roller mill. These types have proven effective in grinding intermediate products into finished cement.

[0024] In a further embodiment of the invention, the first grinding device comprises a grinding circuit with a size separation device. This means that the coarse material is ground in the first grinding device and then transferred to the size separation device. There, the material is separated into a coarse fraction and a fine fraction. The coarse fraction is fed back to the first grinding device for further grinding, and the fine fraction is conveyed to the second grinding device. This makes it easier to achieve a higher degree of fineness in the first grinding device. Preferably, the size separation device is a classifier. The classifier can also be integrated directly into a housing containing the first grinding device.

[0025] In a further embodiment of the invention, the device comprises two secondary grinding devices connected in parallel. This allows, on the one hand, the throughput to be increased, and on the other hand, the two parallel secondary grinding devices can be used to produce two different product qualities. For example, and preferably, the two parallel secondary grinding devices are stirred ball mills and are filled with different types of balls.

[0026] In a further embodiment of the invention, the ratio of the grinding energy input between the first grinding device and the second grinding device is at most 2:1. For example, the first grinding device can input a grinding energy of 2 MW, and the second grinding device 1 MW, which corresponds to a ratio of 2:1. Likewise, with the same total energy, the first grinding device and the second grinding device could each input 1.5 MW, which then corresponds to a ratio of 1:1. Since the first stage in the first grinding device already produces a comminution to an approximately suitable fineness, a large portion of the energy input in the second grinding device is used for product optimization, which in turn makes it possible to increase the substitute content.

[0027] In a further embodiment of the invention, a feedstock feeder is arranged between the first and second grinding devices. This allows additional material to be fed to the mineral material ground in the first grinding device, particularly if it already possesses the necessary fineness. This additional material could, for example, be one of the precursors selected from the group comprising fly ash, calcined clay, clay, blast furnace slag, limestone, natural and naturally tempered pozzolan-fired slate, and silicate dust. If the first grinding device includes a size separator, the additional material can also be applied, for example, and preferably, to the size separator.

[0028] The invention relates to a method for producing a binder from at least one first precursor by milling. Typically, the individual components of a cement are mixed and milled together before grinding, resulting in intimate blending. The material is first milled in a first milling device to produce a first product with a fineness of 2500 to 5000 cm² / g according to Blaine, i.e., in a range where normal milling occurs but close to the limiting fineness, i.e., the size at which further input of milling energy no longer leads to particle size reduction. The first product is then fed into a second milling device. In the second milling device, the material is milled to produce a second product with an energy input of at least 100 kW / m³.The very intensive grinding process in the second step of an already relatively fine material has a positive effect, namely mechano-chemical activation, thus improving its binding properties. This makes it possible, for example, to increase the substitute content in cement and thus conserve valuable primary raw materials. The second step in the second grinding device therefore takes place in the range where the additional grinding energy no longer leads to a reduction in particle size, but rather results in renewed particle growth during grinding. A portion of the additional grinding energy is converted into mechano-chemical activation; that is, the chemical bonding relationships are specifically altered, making the product a significantly better binder.The two-stage process allows the first stage of comminution to be carried out in a simpler first grinding device, while the mechano-chemical activation is carried out in the second grinding device, which can therefore be smaller.

[0029] The mechanochemical activation consists of three phases or stages: In the first stage, the particle size decreases (more or less linearly) with increasing energy input (Rittinger zone). Put simply, the more the material is ground, the finer the product becomes. According to the invention, this should occur, to a first approximation, in the first grinding device. However, there is a limit to this, a particle size that can hardly be reduced further. From this point onward, a second stage begins, in which the particle size cannot be changed further with additional energy input (activation and aggregation zone). In this stage, crystallographic structures are destroyed by the breaking of atomic bonds; individual atoms or entire groups of atoms are replaced by other atoms or groups of other atoms.Particularly on the particle surfaces, the initial crystal structure, as well as the bond type and oxidation states of atoms, are altered due to high energy transfer and subsequent chemical reactions. For economic reasons, the transition from the first to the second stage, which is necessary for mechanochemical activation, is avoided in normal milling, where only surface creation is expected. If the energy input is increased even further, a third stage can be reached in which the particle size increases again due to the agglomeration of nanoparticles (agglomeration zone), which has a positive effect on the workability of activated clay cement concrete. This zone is therefore avoided even more during milling, as a better result in terms of particle size distribution can be achieved with less effort.According to the invention, the second and third stages are carried out in the second grinding device.

[0030] However, it has been found that high energy inputs, i.e., in the second stage, lead to changes in the material itself. In the case of clays, for example, this results in activation, i.e., a reactivity that enables their use as binders (and thus as clinker substitutes), just as with thermal activation. Therefore, subsequent thermal treatment can be omitted at such high energy inputs.

[0031] However, it has been found that the energy requirement for purely mechano-chemical activation can be higher than for thermal activation. Therefore, the inventive method initially appears to be at a disadvantage compared to conventional thermal activation. However, it has been shown that, despite the comparatively likely high energy requirement, particularly electrical, the inventive method is advantageous, especially for the activation of clays that are difficult to activate thermally. Particularly with complex starting materials, such as clays, thermal activation regularly leads to several negative effects. For one, it is known that, for example, substances can escape from clays in gaseous form at elevated temperatures, requiring more complex exhaust gas purification. This can be avoided by foregoing higher temperatures.On the other hand, elevated thermal activation temperatures often lead to the oxidation of color-imparting components, such as iron compounds, which, in the case of clays with a high iron content, results in an undesirable red coloration of the product. To avoid this, either a protective gas atmosphere or subsequent reduction is necessary, both of which are technically complex. Thus, while the energy requirement for the actual activation step is increased in the process according to the invention, the exhaust gas treatment is simplified and subsequent reduction can be avoided. Furthermore, carbon dioxide is still released during the thermal activation process, originating from fossil fuels or waste fuels, but also from the deacidification of carbonate minerals during calcination, which ultimately necessitates a carbon capture process.The process according to the invention requires only electrical energy, and it has been shown that the carbonate minerals are not decomposed in the mechano-chemical activation process but are retained as amorphous and reactive material in the activated clay product. Thus, the entire activation process for producing a marketable binder can be efficiently simplified and decarbonized. Furthermore, different clay minerals exhibit different optimal activation temperatures. For example, minerals of the kaolin and chlorite groups are activated at significantly lower temperatures than, for example, minerals of the mica group (muscovite, illite, and others). If the optimal activation temperature of kaolinite is selected for the thermal activation of clays containing minerals of these groups, minerals such as muscovite and illite will not yet be activated.If, however, the significantly higher activation temperature of muscovite and illite is chosen for thermal activation, the formation of new mineral phases, especially spinels, leads to overheating of the kaolinite, resulting in deactivation. This differentiation of clay minerals with respect to the optimal activation temperature does not occur with mechanochemical activation.

[0032] In a further embodiment of the invention, a second intermediate product is added to the first milled material. The second intermediate product is preferably selected from the group comprising fly ash, calcined clay, clay, blast furnace slag, limestone, natural and naturally tempered pozzolan, burnt shale, and silicate dust.

[0033] In a further embodiment of the invention, the second material is ground to a fineness of 5000 to 15000 cm² / g according to Blaine. Preferably, the second material is ground to a fineness of 7000 to 15000 cm² / g according to Blaine. Particularly preferably, the second material is ground to a fineness of 7500 to 15000 cm² / g according to Blaine.

[0034] In a further embodiment of the invention, the pre-product or pre-products are selected from the group comprising clinker, gypsum, activated clays, slag, for example blast furnace slag, sand, recycled cement brick.

[0035] In a further embodiment of the invention, the material is ground in the second grinding device with an energy input of at least 200 kW / m 3< to produce a second product.

[0036] The device according to the invention is explained in more detail below with reference to an embodiment shown in the drawing.

[0037] Fig. 1 exemplary embodiment

[0038] In Fig. 1 An exemplary embodiment of a device 10 according to the invention is shown. A first pre-product 51, for example clinker, is fed to a first grinding device 20, for example a vertical roller mill, and ground to a fineness of, for example, 4000 cm² / g. The ground material is fed to a size separator 40. The coarse fraction is fed back to the first grinding device 20. The fine fraction is combined with a second pre-product 52, for example activated clay, and fed to a second grinding device 30. There, the material is ground to a fineness of 10000 cm² / g with an energy input of 300 kW / m³, thus obtaining the finished product, a binder. Reference sign

[0039] 10 Device 20 First grinding device 30 Second grinding device 40 Size separating device 51 First intermediate product 52 Second intermediate product

Claims

1. A process for producing a binder from at least one first precursor (51) by grinding, wherein the material is first ground in a first grinding apparatus (20) to obtain a first regrind having a Blaine fineness of 2500 to 5000 cm2 / g, wherein the first regrind is introduced into a second grinding apparatus (30), wherein the material in the second grinding apparatus (30) is ground with an input of energy of at least 100 kW / m3 to obtain a second regrind.

2. The process as claimed in claim 1, characterized in that a second precursor (51) is supplied to the first regrind.

3. The process as claimed in either of claims 1 and 2, characterized in that the second regrind is ground to a Blaine fineness of 5000 to 15 000 cm2 / g.

4. The process as claimed in claim 3, characterized in that the second regrind is ground to a Blaine fineness of 7000 to 15 000 cm2 / g.

5. The process as claimed in any of claims 1 to 4, characterized in that the precursor(s) (51, 52) is / are selected from the group comprising clinker, plaster, activated clays, slags, for example ground granulated blast-furnace slag, sand, and old cementstone.

6. The process as claimed in any of claims 1 to 5, characterized in that the material is ground in the second grinding apparatus (30) with an input of energy of at least 200 kW / m3 to obtain a second regrind.