Method for optimizing the operation of a mill for mechanochemical activation

Abstract

The invention relates to a method for a mechanochemical activation in a mill, said method having at least two operating states, wherein in a first operating state, a first quantity of energy is input per mass of milling material and a first product is produced, and in a second operating state, a second quantity of energy is input per mass of milling material and a second product is produced. The first energy input is greater than the second energy input, and the first product is activated with a higher intensity than the second product. The first operating state is selected when electric energy is cheaper or more available than the long-term average, and the second operating state is selected when electric energy is more expensive or less available than the long-term average.

Description

[0001] Method for optimized operation of a mill for mechano-chemical activation

[0002] The invention relates to a method for mechano-chemical activation taking into account optimal energy utilization.

[0003] Activated clays have established themselves as an additive, 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, potentially undesirable, changes in the material. Furthermore, the thermal process requires flue gas purification to capture the resulting nitrogen oxide and sulfur oxide emissions. Furthermore, the thermal process will require the use of processes to capture and, if necessary, purify the carbon dioxide produced or released.

[0004] Cement aggregates are now used to reduce clinker 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 contain a mass fraction of 75% test cement and a mass fraction of 25% cement aggregate, and standardized mortar prisms produced exclusively with test cement. The test cement used is a Portland cement (type CEM I) with a strength class of 42.5 or higher. The cement aggregate to be evaluated (supplementary cementitious material, SCM) can be less or more effective than the test cement. An SCM considered inert, 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 about 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 restore an activity index of 100. The clinker content is usually replaced by an inert, finely ground filler such as limestone, which is considerably cheaper to produce than clinker. Therefore, so-called mechano-chemical activation through intensive grinding is increasingly being discussed. The process of mechano-chemical 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, so that these materials 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.

[0005] During mechanochemical activation, previously crystalline water remains in the mineral material, for example, as inner-layer water (xerogels). This differentiation from thermally activated materials is an essential quality feature of mechanochemically activated materials when used as cement aggregates, as it results in improved binding properties, particularly low water requirements. This has an improved effect on, for example, the strength development and processing of the binder-containing mortar or concrete, without the need for expensive cement additives such as superplasticizers.

[0006] From the subsequently published DE 10 2023 106 210 a process for grinding and pozzolanic activation in a stirred ball mill is known.

[0007] 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.

[0008] 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.

[0009] The subsequently published DE 10 2023 106 222 describes color optimization through the mechanochemical activation of clays. The subsequently published DE 10 2023 123 525 describes a cement additive made from old concrete.

[0010] From US 2013 / 0 153 694 A1 a method for controlling a mill system with at least one mill is known.

[0011] One advantage of mechanochemical activation is that even clays with a lower kaolin content, which are not suitable for thermal activation, can be mechanochemically activated. This broadens the available raw material base.

[0012] Because clays are a complex system (especially compared to the firing of limestone), different activation processes result in different products (activated clays) with different properties. Likewise, the diversity of the clays that can be used means that not every process is suitable for every clay.

[0013] 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.

[0014] A key difference from conventional thermal activation is that the required energy does not come from a fuel introduced into the reactor, but rather as drive power to the mill and is therefore preferably provided as electrical energy. However, the process is subject to fluctuations in the electrical energy supply, whether in terms of price via a utility grid or due to the availability of electricity from renewable sources, such as wind power or photovoltaics. The object of the invention is to adapt the mechano-chemical activation process to fluctuations in the electrical energy supply.

[0015] This object is achieved by the method having the features specified in claim 1. Advantageous further developments emerge from the subclaims, the following description, and the drawings.

[0016] The method according to the invention serves for mechanochemical activation in a mill. Conventionally, activation is carried out thermally, whereby the mineral material is heated, for example, to 900°C to 1000°C. The objective of activation is achieved in mechanical activation through very intensive grinding, whereby significantly more energy is input than is required for comminution. In this range of mechanical activation, particle growth is detectable through grinding. Specifically, this means that, despite further energy absorption by the particles, a coarsening of the grain size range is detected using conventional analytical methods. The device comprises a mill. The mill is preferably an agitated 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 known processes are being further developed in order to improve them. The process according to the invention has at least two operating states. In a first operating state, a first energy input per mass of ground material takes place and a first product is thus produced; in a second operating state, a second energy input per mass of ground material takes place and a second product is produced. The first energy input is higher than the second energy input. The first product is therefore more highly activated than the second product. This means that in the first operating state, greater activation of the ground material is achieved, i.e. a higher activity index is achieved. The first operating state is selected when electrical energy is cheaper or more widely available than the long-term average. The second operating state is selected when electrical energy is more expensive or less available than the long-term average.

[0017] When grinding a material, three stages can be observed depending on the energy input. In the first stage, the particle size decreases (more or less linearly) with the energy input (Rittinger zone). Put simply, the more you grind, the finer the product becomes. However, there is a limit to this, a particle size that can hardly be exceeded. From this point on, a second stage follows, in which the particle size cannot be changed any further with further energy input (aggregation zone). For economic reasons, the transition from the first to the second stage is avoided during grinding, as there is no further comminution effect for the additional effort. If the energy input is increased even further, a third stage can be reached, in which a further increase in particle size can be observed (agglomeration zone).This area is therefore much more likely to be avoided during grinding, as a better result in terms of particle size distribution can be achieved with less effort.

[0018] However, it has been shown that high energy inputs, i.e., in the third stage, lead to changes in the material itself. In clays, for example, just like thermal activation, this leads to activation, i.e., to a reactivity that enables its use as a binder (and thus as a clinker substitute). This third stage is therefore mechanochemical activation and differs from the grinding, which is carried out in the first stage. Thus, according to the state of the art, grinding is not mechanochemical activation.

[0019] If, for example, electrical energy generated from renewable sources is used for activation, the availability of the electrical energy is subject to fluctuations. If the electrical energy is provided by photovoltaics, the well-known day-night rhythm arises with a pattern throughout the day (neglecting cloud cover). With wind power, the situation is more complex. Typically, attempts are made to minimize these effects by combining wind and solar energy, for example, to achieve a more consistent energy supply. In addition, energy storage systems such as batteries are commonly used to achieve uniformity. However, the generation volume remains dependent. These cycles also lead to corresponding price developments on the electricity market, which today are largely attributable to this variable generation volume.The simplest and easiest way to illustrate this is with the example of photovoltaics and its daily rhythm. At night, there is no electricity, and the mill stands still. At midday, the maximum amount of electricity is available (more in summer, less in winter). At this time, the mill can produce the maximum amount with the best quality. In the period immediately after sunrise and before sunset, the available electrical energy is too low, making it unprofitable to operate the mill. Now, with constant quality, the amount of material fed in can be scaled with the available amount of electricity, yielding a constant result. The disadvantage is that energy is no longer sufficient relatively early in the day; for example, if the mass flow through the mill is below 50%, it is no longer viable to operate the mill. As already explained, this more complex situation also applies to other (fluctuating) electricity sources, be it in terms of availability or (therefore) in price.

[0020] Therefore, at least a second operating mode is introduced, which still produces activated product even at lower availability, but with a lower activation. In the simplest case, the "good" and "bad" fractions can then be mixed, thus achieving medium activity with a higher production volume. Alternatively, the higher-value product can also be sold at a higher price. The crucial point is that the two operating modes produce two different products based on the activity index, thus achieving better overall utilization of the mill.

[0021] Of course, multiple operating states are also possible, for example three operating states. This can make sense, for example, if the fluctuation consists solely of price fluctuations, but electricity from the grid is always available. In this case, for example, an operating state for an average mean electricity price can be selected for medium activation, an operating state for maximum activation at a low electricity price, and low activation at a high electricity price. This achieves optimal utilization of the mill. Furthermore, the different products can be stored more effectively than electricity can be buffered. The goal is therefore to advantageously convert the electricity fluctuation into controlled quality levels and thus achieve an optimum. There can also be a very large number of operating states to enable particularly good dynamic adaptation.In a further embodiment of the invention, the mechanochemical activation increases the R3 value (7d) according to ASTM C1897-20 by at least 100 J / g, preferably by at least 200 J / g. The activation is thus sufficiently high to use the activated materials as cement substitutes (supplementary cementitious materials, SCMs). The ASTM C1897-20 standard is the standard commonly used in the cement industry for investigating reactivity and setting behavior. Preferably, the first product exhibits an activation that is at least 50 J / g, preferably at least 100 J / g, higher than the second product.

[0022] In a further embodiment of the invention, the first energy input is selected to be greater than 500 kWh / t, and the second energy input is selected to be less than 500 kWh / t. For example, in the case of three operating modes, the energy inputs are selected from the ranges of 200 to 400 kWh / t, 400 to 500 kWh / t, and greater than 500 kWh / t.

[0023] In a further embodiment of the invention, the first energy input and the second energy input have a difference of at least 50 kWh / t, preferably at least 100 kWh / t.

[0024] In a further embodiment of the invention, the long-term average is considered a forecasting average for 1 to 10 days. This optimally reflects price predictability on the spot market.

[0025] In a further embodiment of the invention, the long-term average is considered to be an annual average. For renewable energy, a long-term average of 5 to 30 years is preferably used.

[0026] In a further embodiment of the invention, in the second operating state, the product already activated in the mill is fed to the mill for further activation. This reduces the product quantity, but increases the activation and thus the product quality. In a further embodiment of the invention, a forecast is made for the availability of electrical energy. This enables early planning of the operating states and also of the required product quantities. Preferably, renewed activation by returning to the mill in the second operating state can also be taken into account. Again using photovoltaics as an example, more electricity is available in summer, so the amount of high-quality product from the first operating state will be higher. In winter, the second operating state will predominate. In order to obtain a sufficiently high-quality product, a sufficient proportion is reactivated and thus refined.With a forecast, it can therefore be decided, for example, in the second operating state whether a simple product or a higher-quality product is produced by reactivation in order to ultimately achieve the desired mixture of both qualities.

[0027] In a further embodiment of the invention, in the first operating state the maximum material flow is driven through the mill and in the second operating state 50% of the maximum material flow is driven through the mill.

[0028] In a further embodiment of the invention, in the first operating state, the ground material is activated to an activity index of 100 to 120, preferably 110 to 120, and in the second operating state, the ground material is activated to an activity index of 80 to 100, preferably 80 to 90. The activity index is defined according to DIN EN 450-1.

[0029] In a further embodiment of the invention, the process is carried out in a mill having an internal volume of at least 1 m 3 carried out.

[0030] In a further embodiment of the invention, the process is carried out in a mill with an energy density of at least 200 kW / m 3 carried out.

[0031] In a further embodiment of the invention, the process is carried out in a mill with a length of at least 2 m, preferably 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 at least 0.75 m 2 , on.

[0032] In a further embodiment of the invention, the process is carried out in a mill having a length to diameter ratio of at least 3, preferably of at least 3.5.

[0033] In a further embodiment of the invention, the mill is operated with a residence time of the material to be ground in the mill of at least 5 minutes, preferably at least 10 minutes, particularly preferably at least 20 minutes.

[0034] The method according to the invention is explained in more detail below using an embodiment shown in the drawings.

[0035] Fig. 1 Summer

[0036] Fig. 2 Winter

[0037] The figures show an example of photovoltaic power generation in a highly simplified and schematic form. The power generation is shown at the top (highly simplified). The activity index is shown at the bottom. An example shows a first operating state that achieves an activation index A of 120, and a second operating state that achieves an activation index A of 80.

[0038] Fig. 1 shows the summer condition, and Fig. 2 the winter condition. In addition to the shorter sunshine duration, a lower maximum intensity is indicated in winter. Compared to the summer condition in Fig. 1, it is also evident that the ratio of well-activated material to less-activated material changes significantly in winter in Fig. 2. Therefore, it can be advantageous, especially in winter, to activate material a second time in the second operating condition in order to achieve a better ratio.

Claims

Patent claims 1. A method for mechano-chemical activation in a mill, the method having at least two operating states, wherein in a first operating state a first energy input per mass of ground material takes place and a first product is produced, wherein in a second operating state a second energy input per mass of ground material takes place and a second product is produced, wherein the first energy input is higher than the second energy input, wherein the first product is more strongly activated than the second product, wherein the first operating state is selected when electrical energy is cheaper or more available than in the long-term average, wherein the second operating state is selected when electrical energy is more expensive or less available than in the long-term average.

2. Method according to claim 1, characterized in that the first energy input is selected with more than 500 kWh / t and the second energy input is selected with less than 500 kWh / t.

3. Method according to one of the preceding claims, characterized in that the first energy input and the second energy input have a difference of at least 50 kWh / t, preferably at least 100 kWh / t.

4. Method according to one of the preceding claims, characterized in that the long-term average is considered as a forecasting agent for 1 to 10 days.

5. Method according to one of claims 1 to 3, characterized in that the long-term average is considered as an annual average.

6. Method according to one of the preceding claims, characterized in that in the second operating state, the second product already activated in the mill is fed back to the mill for further activation and a third product is produced, the third product being more highly activated than the second product.

7. Method according to one of the preceding claims, characterized in that a forecast for the availability of electrical energy is made.

8. Method according to one of the preceding claims, characterized in that in the first operating state the maximum material flow is driven through the mill, wherein in the second operating state 50% of the maximum material flow is driven through the mill.

9. Method according to one of the preceding claims, characterized in that in the first operating state the ground material is activated to an activity index of 100 to 120, preferably 110 to 120, wherein in the second operating state the ground material is activated to an activity index of 80 to 100, preferably 80 to 90.

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