LU505652B1 - Electrostatic classifier in mechano-chemical activation - Google Patents

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

Electrostatic classifier in mechano-chemical activation

The invention relates to the use of an electrostatic classifier in mechanochemical activation for separating the activated fraction.

Activated clays have become established as additives, particularly in the cement industry. The current method is drying and calcining the clays, i.e., thermal activation. This requires energy for heating, and the high temperature can also cause further material changes that may be undesirable. Furthermore, the thermal process often requires

Flue gas cleaning, e.g. for the separation of the resulting nitrogen oxide and sulphur oxide

emissions. In addition, the thermal process will require the use of

Process for the capture and, if necessary, purification of the carbon dioxide produced or released.

In order to save clinker and thus carbon dioxide emissions,

Cement aggregates are used. According to DIN EN 450-1, the activity index describes the ratio (in %) of the compressive strengths of standardized aggregates tested at the same age

Mortar prisms containing a mass fraction of 75% test cement and a mass fraction of 25% cement aggregate, and standardized mortar prisms made exclusively with test cement. The test cement used is Portland cement (type

CEM |) of strength class 42.5 or higher. The cement aggregate to be evaluated (Supplementary Cementitious Material, SCM) may be less or more efficient than the test cement. A cement considered to be inert

SCM, such as limestone, results in an activity index of 75%, meaning the SCM makes no contribution to strength development. However, high-performance SMCs such as granulated blast furnace slag can also achieve activity values of more than 100 up to approximately 120. If the activity index is above 100, this means that the clinker content in the binder can be further reduced, namely by exactly the amount necessary to achieve an activity index of 100.

The clinker portion is usually made from an inert, finely ground

Fillers such as limestone are replaced, which are considerably cheaper to produce than clinker.

Therefore, so-called mechanochemical activation through intensive grinding is increasingly being discussed. The process of mechanochemical activation can be used to produce cement aggregates that can optionally replace other secondary cementitious materials, i.e., SCMs. Ideally, SCMs possess pozzolanic, latent hydraulic, or even hydraulic properties, allowing these materials to contribute to the strength development when the finished binder is mixed with water. Inert materials such as limestone do not exhibit this additional strength development when mixed with water.

During the mechano-chemical activation, previously crystalline bound water remains for

For example, preserved as inner-layer water in mineral material (xerogels).

This differentiation from thermally activated materials is an essential

Quality feature of mechano-chemically activated materials when used as

Cement aggregate, as this results in improved binding properties, in particular a low water requirement. This has an improving effect on

Example: Strength development and processing of the binder-containing mortar or concrete without the need to use expensive cement additives such as superplasticizers.

From the subsequently published DE 10 2023 106 210 a process for grinding and pozzolanic activation in a stirred ball mill is known.

From the subsequently published DE 10 2023 106 217 a process for grinding and pozzolanic activation in two separate stages of a stirred ball mill is known.

From the subsequently published DE 10 2023 106 221, the combination of mechanochemical and thermal activation in at least one agitator ball mill is known.

The color optimization in the mechano-chemical activation of clays is known from the subsequently published DE 102023 106 222.

A cement additive made from old concrete is known from the subsequently published DE 10 2023 123 525.

An advantage of mechano-chemical activation is that even clays with a lower kaolin content, which are not suitable for thermal activation, can be mechano-chemically activated. This broadens the available

Raw material base.

Since clay is a complex system (especially compared to

Burning of limestone), different activation processes lead to different products (activated clays) with different properties.

Likewise, the diversity of the clays that can be used means that not every

The procedure can be used for any tone.

Mechanochemical activation differs fundamentally from thermal activation in terms of the understanding of the processes involved. While thermal activation is primarily determined by temperature and time, mechanochemical activation in a mill appears to be considerably more complex and dependent on many more parameters. Furthermore, a large portion of the input grinding energy is converted into heat.

In order to operate the activation efficiently, the challenge is to separate activated particles from those that are not yet activated in order to

In the mechano-chemical activation, the primary particles are first crushed in a preliminary step until practically no

Milling progress no longer occurs (Rittinger stage). This is followed by activation, which leads to changes in the crystal structure up to the amorphization of the (clay) minerals. Furthermore, agglomeration and aggregation effects of the particles can be observed, which is reflected in a decrease in the specific surface area. The usual concept of separating fine product particles and coarse grit cannot therefore be applied here. The inventive concept therefore proposes to consider the largest particles as activated and to separate them, while the finest

Particles are to be regarded as non-activated and returned.

The object of the invention is to provide a reliable separation of already activated and not yet activated particles during mechano-chemical activation.

This object is achieved by the device with the features specified in claim 1

Features, by the use with the features specified in claim 5 and by the method with the features specified in claim 6. Advantageous

Further developments arise from the subclaims, the following

Description and drawings.

The device according to the invention serves for mechano-chemical activation.

Traditionally, activation is carried out thermally, whereby the mineral material is heated to temperatures of, for example, 900 °C to 1000 °C. In mechano-chemical activation, the objective of activation is achieved through very intensive grinding, whereby considerably more energy is input than is required for comminution. In this area of mechanical activation, grinding rather

Particle growth can be detected. The device comprises a mill. Preferably, the

Mill a stirred ball mill. Such devices are known, for example, from

DE 10 2023 106 210, DE 102023 106217, DE 102023 106221, the

DE 10 2023 106 222 or DE 10 2023 123 525. These known

Devices are being further developed to improve them. The device has a

The mill is preferably a stirred ball mill. The mill has a

The device has a material inlet and a material outlet.

A first separation device is arranged downstream of the material flow. The device has a product outlet arranged downstream of the first separation device in the material flow.

Usually, size-selective separators are used as the first separator. Since the mill is operated in an area where the

Energy input a particle growth is detectable, the coarse fraction is the activated

Fraction and the fine fraction the fraction that has not yet been activated.

According to the invention, the first separation device is an electrostatic separator. The electrostatic separator has a first outlet for charged particles and a second outlet for discharged particles. Discharge, in the sense of the invention, refers to uncharged or non-charged particles. One outlet is connected to the product outlet, and the second outlet is connected to a return line.

Return line is connected to the material inlet of the mill.

Surprisingly, it has been found that the separation used in an electrostatic classifier is significantly better at separating activated and non-activated particles. The fraction containing the charged particles has been found to be more reactive and therefore more sensitive than the fraction containing the already activated particles. This separation thus circumvents a significant problem. With size-selective separation, it is not possible to distinguish between coarse particles that are not even completely ground (i.e., from the first stage of grinding with a roughly linear relationship between grinding energy) and the already activated and therefore already regrown or agglomerated particles (i.e., from the third stage,

Increase in particle size with further input of grinding energy).

Therefore, the worst fraction remained in the product fraction. This disadvantage can be overcome by using an electrostatic classifier.

In a further embodiment of the invention, the device has a second

The second separation device is a size-selective

Separation device. Examples of a size-selective separation device are a normal

A sifter, a cyclone or even a sieve. Such a size-selective separation device serves to separate a material flow into a coarse fraction (for example, on top of the sieve) and a fine fraction (below the sieve). Each size-selective

Separation device has a different separation size and selectivity, so that although it is generally impossible to say what is coarse or fine, in a specific case with a specific size-selective separation device this is unambiguously and immediately clear. The second separation device has a fine outlet and a coarse outlet.

The fine outlet is used to discharge the fine fraction and the coarse outlet is used to discharge the

Coarse fraction.

In a further embodiment of the invention, in a first alternative, the second

Separation device downstream of the first separation device in the material flow. The first

The output of the first separator is connected to the second separator. Therefore, only the charged particles and thus the activated particles of the second

The coarse outlet is connected to the product outlet. Therefore, only the largest activated particles are discharged as product, as these have the highest activity. The fine outlet is connected to the mill's material inlet. This material is therefore returned as insufficiently activated.

In a further embodiment of the invention, in a second alternative, the second

Separation device is located upstream of the first separation device in the material flow. Therefore, all material coming from the mill is first separated by size and only then electrostatically. The material outlet of the mill is therefore connected to the second separation device. The coarse outlet is connected to the first

A separator is connected to separate the non-activated, barely crushed particles from the activated and regrown particles. The fines outlet is connected to the mill's material inlet.

In a further aspect, the invention relates to the use of an electrostatic

A classifier for separating activated and non-activated particles after mechanochemical activation in a mill. As already mentioned, this has surprisingly proven to be a very suitable separation method, which can, in particular, prevent the unwanted discharge of coarse starting material as a product.

In a further aspect, the invention relates to a method for mechano-chemical

Activation. The process comprises the following steps: a) Mechano-chemical activation in a mill, b) Transfer of the activated material to an electrostatic classifier, c) Separation of the material in the electrostatic classifier into a charged fraction and a discharged fraction, d) Transfer of the charged fraction to the product outlet, e) Return of the discharged fraction for further mechano-chemical

Activation.

Steps d) and e) logically run in parallel.

The separation in an electrostatic separator is essential and not, as previously, in a size-selective separator.

The charge behavior of the activated and non-activated particles can be used to separate them and thus obtain a pure activated fraction.

In a further embodiment of the invention in a first alternative, between

In step a) and step b), a size-selective separation is carried out in a second separation device. The coarse fraction of the size-selective separation is then transferred to the electrostatic classifier in step b). The fine fraction of the size-selective separation is returned to step a). Thus, first, a size-selective

Separation is carried out as before and then the electrostatic separation.

In a further embodiment of the invention, in a second alternative, a size-selective separation of the charged fraction is carried out in a second separation device between step c) and step d). Only the coarse fraction of the size-selective separation, which contains the best activated particles, is

Step d) is fed to the product outlet. The fine fraction is subjected to size-selective

separation is returned to step a). Therefore, first the electrostatic

separation and then in a second step by the size-selective

Separation the small, least activated particles are separated and sent for further

activation returned.

Overall, the activity of the product can be increased and thus the

Increase its usability as a cement additive and thus reduce the demand for clinker and thus reduce the total amount of CO2 generated in the production of cement.

The device according to the invention is explained in more detail below with reference to embodiments shown in the drawings.

Fig. 1 Basic form

Fig. 2 first alternative

Fig. 3 second alternative

The basic form is shown in Fig. 1. The material to be activated is

Material inlet 12 is introduced into the mill 10 and ground there so intensively that a mechano-chemical activation occurs, for example in a

Energy input of 600 kWh/t. The activated material leaves mill 10 via the

Material outlet 14 and is fed into the first separating device 20, an electrostatic

Here, a separation into charged and uncharged particles takes place. The charged particles leave the first separation 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 another

The uncharged, not yet activated particles leave the first

Separating device 20 through the second output 24 and are

Return line 40 is led back to the material inlet 12 of the mill 12.

Fig. 2 and Fig. 3 show the combination of a first separation device 20 in the form of an electrostatic separator with a second separation device 50 in the form of a size-selective separation device, for example, a cyclone. For simplicity, only the differences from the basic design will be discussed below.

Fig. 2 shows the first alternative, in which the second separating device 50 is located behind the first

separating device 20. Thus, the charged particles from the first

Separation device from the first outlet 22 into the second separation device 50 and there separated into a coarse fraction and a fine fraction according to size. 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, for example, via the return line 40 to the

Material inlet 12 of the mill 10 is fed back.

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 back to the material inlet 12 of the mill 10 via the fine outlet 52 and, for example, the return line. The coarse fraction is fed to the first separation device 20 through the coarse outlet 54.

Reference number 10 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 outlet

Claims (8)

Patent claims 1. 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). 2. Device according to claim 1, characterized in that the device has a second separation device (50), wherein the second separation device (50) is a size-selective separation device, wherein the second separation device (50) has a fine outlet (52) and a coarse outlet (54). 3. Device according to claim 2, characterized in that the second separating device (50) is arranged downstream of the first separating device (20) in the material flow, 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). 4. Device according to claim 2, characterized in that the second separating device (50) is arranged upstream of the first separating device (20) in the material flow, the material outlet (14) of the mill (10) being connected to the second separating device (50), the coarse outlet (54) being connected to the first separating device (20), the fine outlet (52) being connected to the material inlet (12) of the mill (10). 5. Use of an electrostatic classifier to separate activated particles from non-activated particles after mechano-chemical activation in a mill (10). 6. A process for mechano-chemical activation, the process comprising the following steps: a) mechano-chemical activation in a mill (10), b) transferring the activated material to 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) returning the discharged fraction for renewed mechano-chemical activation. 7. The method according to claim 6, characterized in that between step a) and step b) a size-selective separation is carried out in a second separation device (50), the coarse fraction of the size-selective separation in step b) being transferred to the electrostatic classifier, the fine fraction of the size-selective separation being fed back to step a). 8. The method according to claim 6, characterized 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 in step d) is fed to the product outlet (30), wherein the fine fraction of the size-selective separation is fed back to step a).