Method of controlling at least one mill in cement production via the reactivity of the cement produced

Abstract

The present invention relates to a method of producing cement, comprising the following steps: a) defining a cement type and cement quality to be produced, b) providing the reactants, where the reactants selected are at least clinker, a sulfate carrier and a clinker substitute, c) defining a ratio of the reactants and a grinding fineness of the cement, d) combining the reactants according to the defined ratio of the reactants, e) grinding at least one reactant in at least one mill to the defined grinding fineness, f) removing the finished cement, g) analysing the finished cement, where the analysis includes the following component steps: h) mixing the sample with water and continuously detecting the heat generated by the reaction that proceeds, i) determining the detected heat generated in the time window from 45 s to 60 min after mixing of the sample with the water, j) comparing the heat release determined from the hydrating cement with a heat associated with the defined cement quality and distinguishing between the following three cases: in the first case that the heat determined is less than the defined amount of heat, in the second case that the heat determined is equal to the defined amount of heat, and in the third case that the heat determined is greater than the defined amount of heat, characterized in that k) an energy cost, a CO2 cost and costs for the reactants are determined or defined, l) the defined grinding fineness and the energy cost are used to determine grinding costs, the CO2 cost and the CO2 load, especially of the clinker, are used to determine CO2 costs, and the costs for the reactants and the ratio of the reactants are used to determine material costs, where the sum total of grinding costs plus CO2 costs plus material costs is the total cost, m) where a closed-loop control method for minimizing total costs according to step I) is run in parallel with an optimization of the heat determined in step j) in order to achieve the second case in step j), where, in the first case in step j), the ratio of the reactants in step c) is altered by increasing the proportion of clinker and / or adjusted by increasing the grinding fineness defined in step c), where, in the third case in step j), the ratio of the reactants in step c) is altered by reducing the proportion of clinker and / or adjusted by reducing the grinding fineness defined in step c).

Description

[0001] Method for controlling at least one mill in cement production by means of the reactivity of the cement produced

[0002] The invention relates to a method which enables a very rapid measurement of the reactivity of cement and thus makes it possible for the first time to control the grinding of the components to produce the finished cement depending on a previously selected reactivity.

[0003] The reactivity of a cement is based on the hydration reactions of the clinker with the mineralogical components C3S, C3A, C2S, C4AF and others, the reaction behavior of the composite materials, the addition and adjustment of sulfate carriers and the degree of grinding, i.e. the fineness.

[0004] The tricalcium aluminate (C3A) content of clinker reacts very quickly with water. However, excessive hydration of the C3A leads to excessively rapid setting (spoon binder). To prevent this rapid setting, a sulfate carrier, typically calcium sulfate, is added to adjust the stiffening and setting behavior according to requirements. The development of the compressive strength of the building materials mortar and concrete is determined by the hydration of the C3S and its hydration product, calcium silicate hydrate. C2S and C4AF hydrate with a time delay and, like the composite materials, contribute in particular to the final strength. Finally, the strength development can be adjusted by the degree of grinding of the cement; higher fineness accelerates the reaction.

[0005] In the absence of other methods, the reactivity of a cement is determined using mortars. The mortars are usually prepared in a physical laboratory from a daily average sample according to recipes specified in standards (e.g., ASTM, EN196), poured into molds, and aged for specified periods in a climate chamber and later in a water tank. After periods also specified in the standards, specifically 1 day, 2 days, 3 days, 7 days, and 28 days, the test specimens are removed from the molds and tested for compressive strength. The reactivity of a sample is assessed relative to other samples based on the strength development over time and the measured values ​​achieved. This method is widely used, and regular use is usually required.

[0006] However, due to the duration of strength development, determining compressive strength is time-consuming and therefore cannot be used for true process control. Although the first compressive strength measurements from a daily average sample are only available after at least one day, production is carried out continuously. To avoid quality losses due to process-related eventualities, such as material fluctuations or machine damage, production must have sufficient safety margins to meet product requirements. This, in turn, leads to a tendency for too much clinker to be added or ground too finely. Thus, these safety margins have a negative impact on the process's carbon footprint.

[0007] A cement production process is known from WO 2020 / 091 821 A1.

[0008] From CN 111551698 A a method for online detection of cement production quality is known.

[0009] From CN 104965532 A a control system for cement raw materials and a method therefor are known.

[0010] From the subsequently published DE 10 2023 107 837, a regulation for the addition of the sulfate carrier for cement is known.

[0011] There is a desire to produce cements with the required reactivity as precisely as possible, since both an unnecessarily high clinker addition and excessively fine grinding ultimately have a negative impact on the CO2 balance. The object of the invention is to provide a process that produces cement with the required reactivity in the most resource-efficient way possible.

[0012] 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 drawing.

[0013] The inventive cement production process optimizes cement production according to the resulting costs and CCh emissions. The production process refers to the final step of the industrial cement process, which includes mixing and grinding the components to produce commercially available cement. The process comprises the following steps: a) determining the type and quality of cement to be produced; b) providing the reactants, with at least one clinker, a sulfate carrier, and a clinker substitute being selected as reactants; c) specifying a quantitative ratio of the reactants and a grinding fineness of the cement; d) combining the reactants according to the specified quantitative ratio of the reactants; e) grinding at least one reactant in at least one mill to the specified grinding fineness; steps d) and e) can be performed in any order.

[0014] 0 taking out the finished cement, g) analyzing the finished cement, the analysis comprising the following sub-steps: h) mixing the sample with water and continuously recording the heat generated by the ongoing reaction, i) determining the recorded heat generated, in particular as cumulative heat release at specified times or the maximum heat release at a time in the time window from 45 to 60 minutes after mixing the sample with the water, j) comparing the determined heat release from the hydrating cement with a heat assigned to the specified cement quality and distinguishing between three cases, where in the first case the determined heat is less than the specified amount of heat, where in the second case the determined heat is equal to the specified amount of heat, where in the third case the determined heat is greater than the specified amount of heat.

[0015] In step a), a cement type is selected. This usually corresponds to the compositions specified in EN 197-1, for example, Portland cement. This composition is defined within a range for the individual components. Furthermore, a cement quality is selected, for example, compressive strength, but also setting behavior. This is the specification of the product to be sold.

[0016] The starting materials or components of the cement are provided in step b). Typically, in addition to clinker and sulfate carriers, such as gypsum, anhydrite or hemihydrate, or mixtures thereof, and composite materials, these can include artificial pozzolans, activated clays, granulated blast furnace slag or other slags, limestone or old cement brick, and the like.

[0017] In step c), the proportions of the reactants are specified. These proportions are within the specifications specified in the standards for the cement type selected in step a). A grinding fineness is also specified as the target for production. These specifications can (and are, according to the invention) adjusted over time within the limits set by step a).

[0018] Steps d), e) and e) correspond to the usual production of cement and can be carried out in all known variations. For example, grinding can take place in one step or in two sub-steps, for example a first coarse grinding followed by a fine grinding. For example, the reactants can be introduced into a mill together and ground together, mixing them thoroughly. Alternatively, the reactants can also be ground individually (or in groups), which allows different finenesses for different reactants. Likewise, different reactants can also be ground using different mill types. This allows different physical properties of the reactants, such as hardness, to be taken into account. If the reactants or one or some of the reactants are first ground, they can then be brought together in step d), for example in a mixer.

[0019] In steps g) and h), the reactivity is then determined using a sample. Water includes all aqueous solutions, including, for example, aqueous alkalis.

[0020] It is essential that in step i), as in DE 10 2023 107 837, only the first peak is considered, i.e., only the heat release from the first hydration. Typically, this peak is ignored, and only the heat release over a period longer than 30 to 60 minutes, up to several days, is considered. However, it has surprisingly been shown that the first peak in particular is proportional to the overall reactivity and can therefore be used as a quick measure of the intensity of the hydration reaction as a basis for strength formation. The rapid availability of a reactivity determination of the newly produced cement can actually be used as a control variable in the grinding process to optimize the process for producing a binder with specific reactivity. Therefore, three cases are distinguished in step j). In other words, a distinction is made between whether the cement either meets the specifications,higher or lower quality. While previously a higher quality had to be aimed for on average in order to always produce at least sufficient quality over a long period without a current measured value, even with production fluctuations, the reactivity determination within the first 60 minutes now opens up the possibility of optimising the process control, for example, and in particular, the CO2 footprint. Therefore, the process further comprises the following steps: k) an energy price, a CO2 price and prices for the reactants are determined or specified, l) from the specified grinding fineness and the resulting current energy consumption of the mill, the current grinding costs are determined using the current energy price, from the CCh price and the CCh load, especially of the clinker,determined and a weighted price of the milled product (specific variable costs) is determined from the prices for the reactants (in particular purchase prices or specific production costs) and the quantity ratio of the reactants, whereby the sum of milling costs plus CCh costs plus material costs is the current total costs, m) whereby a control to minimize the total costs according to step I) takes place in parallel with an optimization of the heat determined in step j) to achieve the second case in step j), whereby in the first case in step j) the quantity ratio of the reactants is changed in step c) by increasing the clinker content and / or is adjusted by increasing the grinding fineness specified in step c), whereby in the third case in step j) the quantity ratio of the reactants is changed in step c) by reducing the clinker content and / or is adjusted by reducing the grinding fineness specified in step c).

[0021] In step k), the energy price and / or the CO2 price can be determined at current levels, as these can fluctuate significantly on the trading markets.

[0022] The goal is to factor in both the costs for, for example, clinker and the electricity for grinding. The simplest approach is therefore to consider the total costs of the milled product and to directly consider the CO2 costs. If the overall optimization is to be achieved, for example when renewable electricity is highly available (and therefore cheap), it may make sense to grind more finely, thus consuming more energy, but reducing the proportion of clinker and replacing it with composite material such as limestone, fly ash, granulated blast furnace slag or calcined clay. This is only possible because the analysis specified in step i) ensures that the information required for such a control is available in a timely manner. Therefore, different cases must be considered in step m).The third case is particularly relevant, whereby in the third case, in step j), the quantitative ratio of the reactants in step c) is changed by reducing the clinker content and / or the specified grinding fineness is adjusted by reducing it in step c). Therefore, if a higher reactivity is currently being produced than required by the customer, the clinker content (direct CCh savings) or the grinding energy (indirect CCh savings) is reduced, thus delivering the required product in a more environmentally friendly manner. Of course, in such a case, for example, due to quality fluctuations in the reactants, the first case could also result in the reactivity not being sufficiently high. In this case, the clinker content and / or the grinding energy must be increased to achieve a higher fineness.Overall, however, production safety can be reduced due to the rapid availability of meaningful measurement results, thus making production more cost-effective and sustainable.

[0023] In the second case, the simplest approach is to keep the proportions and grinding fineness constant in step c). Alternatively, if CO2 prices rise more sharply than energy prices, the clinker content is reduced and the grinding fineness, and thus the energy consumption for grinding, is increased in step e). Since energy prices reflect the CO2 price on the one hand and are influenced by the proportion of available renewable energy on the other, a simple optimization can be achieved by considering costs.

[0024] In a further embodiment of the invention, the predetermined grinding fineness in step e) is adjusted by the rotational speed of a classifier integrated into the grinding unit or downstream of the grinding unit. This makes it comparatively easy to adjust the fineness by adjusting the proportion of particles returned to the grinding unit accordingly.

[0025] In a further embodiment of the invention, in step m), the variation in the proportions of the reactants occurs only within the specified limits for the cement quality determined in step a). This ensures that the normatively specified cement type continues to be produced and is therefore also marketable as this cement type.

[0026] In a further embodiment of the invention, the grinding in step e) is carried out using two grinding devices arranged one behind the other. For example, one grinding device is used for coarse grinding and a downstream grinding device is used for fine grinding.

[0027] It is well known that when different grinding units are available, such as a ball mill, a vertical roller mill, or a high-pressure roller press, even with the same fineness and composition, different qualities cannot be produced due to different particle size distributions in the respective ground products. With the new method, it is now possible to use reactivity measurement as a readily available metric to compare product quality, for example, the ground product from a ball mill and a vertical roller mill, or from a ball mill and a high-pressure roller press. The goal is to always provide the market with a product of the same quality, but produced on multiple grinding units.

[0028] In a further embodiment of the invention, the method is computer-implemented. For example, and in particular, the method can be carried out using an AI system. The advantage is the ability to recognize patterns. This is only possible because the very short analysis times, in the range of one hour, provide measured values ​​that enable such evaluation.

[0029] The analysis procedure of steps h) and i) is further explained below.

[0030] The analysis procedure includes the following steps:

[0031] D) Mixing the sample with water to form a paste and recording the heat generated by the reaction,

[0032] E) Analysis of the recorded heat generated in the time window from 45 s to 60 min after mixing the sample with the water, and distinguish between Case I, Case II, and Case III. In Case I, the observed cumulative heat after a period of time or maximum heat at a time is below the target value. In Case II, the corresponding measured values ​​are within the desired interval, and in Case III, they are above the desired interval. In Cases I and III, manipulated variables are then changed by adjusting either the clinker content and / or the fineness so that the observed reactivity values ​​in the subsequent analyses again correspond to Case II.

[0033] In step D) or before step D), mortar or concrete can also be produced by adding sand and other aggregates. This allows the hydration reaction to be simulated, similar to the tests performed in a mortar or concrete laboratory.

[0034] In step D), water is then added and mixed. This is preferably done quickly to allow for the earliest possible start of the measurement. The heat generated by the ongoing reaction can be recorded in various ways. For example, it can be done isothermally in a heat flow calorimeter, or using differential scanning calorimetry (DSC), or semi-adiabatic by temperature measurement, or adiabatically, for example using differential thermal analysis (DTA). The measurement is preferably carried out in an isothermal heat flow calorimeter, into which the (usually paste-like) mixture of water and the sample is introduced and the heat flow is recorded under thermal insulation. The exact recording method is less important here, since in step E) absolute values, concrete energies, or the like are evaluated and compared.

[0035] In step E), the heat generated by the ongoing reaction, recorded in step D), is analyzed over time. The measured values ​​can be read out cumulatively after the end of a period, or intensities at a specific time, for example, the maximum heat release. In case I, all calorimetric measured values ​​will be below those of case II, and by increasing, for example, the classifier speed, the target reactivity can be achieved again. The rapid sequence of measured data - for example, hourly - allows for rapid determination of the ideal classifier setting. If the measured values ​​are above the value in case II, control is achieved by reducing the classifier speed until the measured values ​​again correspond to case I.A particular advantage of the new process is that reactivity can be adjusted not only by the classifier or other parameters at the mill, but also, analogous to the cases described above, by changing the clinker content or replacing a different raw material. The rapid availability of reactivity values ​​thus opens up various ways to adjust the quality of the milled product to a target reactivity with minimal safety and cost.

[0036] Furthermore, isothermal heat flow calorimetry can detect early on if the sulfate addition is insufficient for the given C3A grinding process. In the case of insufficient sulfate carrier addition, the C3A reaction is initially noticeably delayed. However, as soon as the insufficient amount of sulfate is consumed, the heat released increases again after 10 to 30 minutes due to an uncontrolled C3A reaction. If this undesired second C3A reaction is observed calorimetrically, this effect can be corrected by adding more sulfate to the mill.

[0037] In a further embodiment of the analysis method, the analysis in step E) is limited to the time window 5 min to 40 min.

[0038] In a further embodiment of the analysis method, the analysis in step E) is limited to the time window 10 min to 40 min.

[0039] In a further embodiment of the analysis method, the analysis in step E) is limited to the time window 20 min to 40 min.

[0040] In a further embodiment of the analysis method, the analysis in step E) is limited to determining the gradient exclusively at two points in time, for example, 20 minutes and 40 minutes. An estimate can be made extremely simply from the ratio of the two gradients. In a further embodiment of the analysis method, the heat generated is recorded in step D) in the form of the sample temperature. Since the evaluation is comparatively robust, the measurement does not have to be carried out isothermally or adiabatically, as is the case with DTA or DSC, for example. It is therefore sufficient to measure the sample temperature in a thermally somewhat insulated measuring area in which the sample is located.Without an exothermic or endothermic reaction, the imperfect insulation leads to an exponential temperature adaptation to the ambient level, from which exothermic reactions then stand out as temperature increases, which are the two reactions considered here (initial peak, hydration of CaO and hydration of C3A). This enables a comparatively simple measurement setup, which in turn enables a large number of samples to be collected cost-effectively and thus simplifies applicability for controlling the manufacturing process.

[0041] In another embodiment of the analytical method, the sample is ground before step D). It has been found that the observed effect is more pronounced the finer the material, as this also increases the surface area. Therefore, the sample is ground, for example, using a vibrating disc mill for 2 to 5 minutes.

[0042] The method according to the invention is explained in more detail below using an embodiment shown in the drawing.

[0043] Fig. 1 Flowchart

[0044] The process is roughly illustrated in Fig. 1 using a flow diagram. In step a, a cement type, for example Portland cement, and a cement quality are specified. This usually arises from the customer requirements. From this specification, bands, for example from EN 197-1, follow in which the composition can be selected. Within this specification, the exact proportions of the components and the grinding fineness are then specified in c. The reactants are provided in b, brought together in d according to the proportions, ground to the specified grinding fineness in e and removed in f. Steps b, d, e and f run continuously during production. Samples are taken from the product stream at regular intervals and analyzed in g. For this purpose, the sample is mixed with water in h and the heat released by the reaction is recorded for a maximum period of 60 min.In j, the heat recorded in this way is compared with a heat defined from the specification in a. Three cases are distinguished here. In the first case, the recorded heat is too low, the reactivity and thus the quality is insufficient. In the second case, this specification is met. In the third case, more heat is released, the reactivity and thus the quality is higher than the specification. In order to decide how to proceed in the first and third cases in particular, the CO2 price, the reactant price and the energy price are also specified in k. This means that the total costs in I can now be determined. And this leads, via m, to an adjustment of the c) specification of the quantity ratio of the reactants and the grinding fineness of the cement. This will be explained using the third case as an example. The quality of the cement produced is therefore above the required standard.Two options are now available: reducing the amount of clinker and replacing it with lime, for example, thus directly saving CO2, or reducing the energy input during milling and thus achieving an indirect CO2 reduction effect through energy savings. While CO2 prices tend to be constant, energy prices, in particular, can fluctuate significantly due to the availability of renewable energy. Therefore, in cases of a shortage of corresponding electricity (represented by a high price), energy savings during the milling process may be more sensible.

Claims

Patent claims 1. A method for cement production, comprising the following steps: a) determining a cement type and cement quality to be produced, b) providing the reactants, wherein at least clinker, a sulfate carrier, and a clinker substitute are selected as reactants, c) specifying a quantitative ratio of the reactants and a grinding fineness of the cement, d) combining the reactants according to the specified quantitative ratio of the reactants, e) grinding at least one reactant in at least one mill to the specified grinding fineness, wherein steps d) and e) can be carried out in any order, f) removing the finished cement, g) analyzing the finished cement, wherein the analysis comprises the following sub-steps: h) mixing the sample with water and continuously recording the heat generated by the ongoing reaction, i) determining the recorded heat generated in the time window of 45 s to 60 min after mixing the sample with the water,j) comparing the determined heat release from the hydrating cement with a heat assigned to the specified cement quality and distinguishing between three cases, wherein in the first case the determined heat is less than the specified heat quantity, wherein in the second case the determined heat is equal to the specified heat quantity, wherein in the third case the determined heat is greater than the specified heat quantity, characterized in that k) an energy price, a CCh price and prices for the reactants are determined or specified, l) grinding costs are determined from the specified grinding fineness and the energy price, CCh costs are determined from the CCh price and the CCh load, in particular of the clinker, and material costs are determined from the prices for the reactants and the quantity ratio of the reactants, whereby the sum of grinding costs plus CCh costs plus material costs is the total costs, m) whereby a control to minimize the total costs according to step I) takes place in parallel with an optimization of the heat determined in step j) to achieve the second case in step j), whereby in the first case in step j) the quantity ratio of the reactants is changed in step c) by increasing the clinker content and / or is adjusted by increasing the grinding fineness specified in step c),wherein in the third case in step j) the quantitative ratio of the reactants in step c) is changed by reducing the clinker content and / or by reducing the grinding fineness specified in step c) is adjusted.

2. Method according to claim 1, characterized in that the predetermined grinding fineness in step e) is set by the rotational speed of a classifier integrated into the grinding unit or connected downstream of the grinding unit.

3. Process according to one of the preceding claims, characterized in that in step m) the variation of the quantitative ratio of the reactants takes place only within the predetermined limits for the cement quality determined in step a).

4. Method according to one of the preceding claims, characterized in that the grinding in step e) is carried out with two grinding devices arranged one behind the other.

5. Method according to one of the preceding claims, characterized in that the method is carried out in a computer-implemented manner.

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