Control of the reaction rate, in particular in a highly viscous system and systems with setting

Abstract

The present invention relates to a conversion device, wherein the conversion device has a mixing device (20) for mixing output components for the conversion, wherein the conversion device has a calorimeter (10) for detecting the conversion started in the mixing device (20), wherein the calorimeter (10) has at least one calorimeter cell (11) for measuring a sample, characterised in that the calorimeter cell (11) has at least one heat exchange element (40) for controlling the temperature of the calorimeter cell (11), wherein the heat exchange element (40) is thermally connected to the mixing device (20).

Description

[0001] Control of the reaction rate, especially in highly viscous systems and systems with solidification

[0002] The invention relates to a method, in particular for determining the conversion rate of highly viscous systems, for example the setting of gypsum in the production of plasterboard.

[0003] In the production of gypsum board, a slurry-like mixture is prepared, primarily consisting of gypsum, water, and additives such as retarders, accelerators, and gypsum nuclei. This mixture is applied to a first layer of paper, smoothed, and covered with a second layer. It is crucial that the mixture remains sufficiently fluid for processing but solidifies sufficiently during the manufacturing process so that the gypsum board can be cut into panels immediately afterward. Controlling the reaction rate—specifically, ensuring a sufficiently low viscosity for even distribution of the slurry-like mixture on the first paper layer and then allowing the mixture to solidify sufficiently before cutting the gypsum board panels—is therefore of paramount importance in the production of these products.The very process of manufacturing plasterboard demonstrates that the viscosity of the sample under investigation changes significantly until it is fully hardened.

[0004] However, a challenge arises from the fact that the starting materials are subject to chemical and mineralogical variations in quality, or, in the case of recycled gypsum, contain impurities. Similarly, environmental conditions, such as temperature and humidity, influence the conversion rate, for example, throughout the day or year. For manufacturing, however, it is essential that the time between mixing and solidification adheres to a predetermined value to allow, for example, subsequent cutting into sheets. A further complication is that the conversion process is not a classic chemical reaction, because the composition of the starting materials in the mixing system is unknown due to the time required for sampling and the duration of analyses using known methods, such as X-ray fluorescence analysis, X-ray diffraction analysis, and spectroscopy.The composition of the product is also unknown, since, for example, sampling requires the destruction of the plasterboard, and because the parallel chemical reaction continuously changes the ratio of reactants to products both in the mixer and in a sample. Therefore, the reaction rate cannot be determined in the usual way using the reactants and products; instead, a method is needed that essentially captures the dynamic changes of state within the system.

[0005] For example, in the cement industry, calorimetry is known to be used for reactivity analysis. However, to start a measurement immediately after adding water to the cement, it is necessary to first bring the sample precisely to the temperature of the calorimeter. This prevents an unwanted influence of a temperature difference between the sample and the calorimeter on the measurement result and allows the reaction rate to be determined as soon as possible after the reaction is initiated by measuring the temperature change. This enables reactivity control of the cement from the moment water is added to the dry powder. In the case of cement, production and application are separate, and the determination of the reaction rate can be fed back into the cement manufacturing process for product optimization.

[0006] However, this is not applicable to process control during the processing of the powder, for example, in the aforementioned gypsum board production, because the slurry-like mixture is produced in a mixer, and the residence time in the mixer is only a few seconds, as setting begins immediately. Therefore, it is not possible to take an ideally dry sample, temper it to the temperature of the calorimeter, and then trigger the reaction by adding water for analysis with a calorimeter. The reaction is already underway as soon as the water is added, and tempering the sample to counteract the simultaneous release of heat is not possible.However, an analysis of the reaction behavior under isothermal conditions would be necessary for process control in order to make decisions based on the observed reaction kinetics as to whether and which changes are needed, for example, by adding accelerators, retarders, or nucleation sites, to lengthen or shorten the reaction rate. The object of the invention is to directly monitor a comparatively fast reaction rate, such as in gypsum board production, in order to actively control the process.

[0007] This problem is solved by the conversion device with the features specified in claim 1 and by the method with the features specified in claim 5. Advantageous further developments are described in the dependent claims, the following description, and the drawings.

[0008] The invention is essential because it is only made possible by a fundamental paradigm shift. While a calorimeter is usually heated to a predetermined temperature, very often 20 °C, the invention eliminates this requirement. This means that while direct comparability between measurements is no longer possible, it allows for a precise statement about the kinetics of the mixture under investigation for each sample under the prevailing production conditions. Thus, the calorimeter measurement does not provide information about, for example, the heat of reaction under defined conditions, as is necessary for comparing different samples. Instead, it records the change in the reaction rate over time for samples that are essentially identical and taken from the same location.This conversion rate can change, for example, due to varying environmental conditions or qualitative changes in the reactants. However, the goal of process control is a constant conversion rate, independent of environmental conditions or the quality of the reactants. Therefore, if deviations from the desired conversion rate are observed during the ongoing process, this observation can be used to immediately reduce the reaction rate to the target value, for example, by changing the composition of the powder, the amount of water added, or by using additives such as retarders, accelerators, or nucleation sites. The conversion device according to the invention includes a mixing device for blending the starting components for the conversion. For example, the conversion device is part of a plant for the production of gypsum board.However, it can also be any other type of equipment. This invention is particularly advantageous in conversion devices where the conversion does not involve a readily detectable chemical reaction, but rather where a multitude of reactants influence the overall reaction behavior, as is the case, for example, in the production of gypsum plasterboard from gypsum. Further examples include the processing of gypsum waste products, the cement industry, and concrete production. The mixing device serves to initiate the conversion, for example, the mixing of plaster of Paris with water. This then results in a processing time window within the conversion device, which is usually predetermined and must be adhered to.However, fluctuations in the reactants and / or environmental conditions can lead to variable reaction durations, and the reaction process may no longer fit within the intended processing time windows, necessitating adjustments to the reactants, for example. Therefore, the reaction device and mixing device must be designed with ample capacity; this is the state-of-the-art manufacturing process that needs to be controlled.

[0009] According to the invention, the conversion device includes a calorimeter for recording the conversion process initiated in the mixing device. The calorimeter has at least one calorimeter cell for measuring a sample. For the purposes of the invention, a calorimeter cell is defined as the cell in which a single sample can be measured individually. A calorimeter often has several calorimeter cells. Since each cell can measure a sample separately from the other calorimeter cells, a plurality of calorimeter cells is advantageous for performing parallel measurements. This allows samples to be taken at shorter intervals and measured simultaneously. A key aspect of the invention is that the calorimeter cell has at least one heat exchanger element for temperature control, wherein the heat exchanger element is thermally connected to the mixing device.The calorimeter cell is therefore not heated to a prescribed temperature, for example 20 °C, as is usually the case, but rather passively brought to the temperature of the mixing device via a heat exchanger. Since a calorimeter already suffers from the problem that measuring temperature using a thermocouple yields only insufficient absolute accuracy, and therefore several thermocouples must be calibrated against each other, it is not easily possible to measure the temperature in the mixing device with sufficient accuracy and then set it in the calorimeter. Therefore, temperature control via a heat exchanger is advantageous.

[0010] The sample can be taken from the mixing device or after it; in the case of gypsum board production, this means between the mixer and the pouring onto the substrate. The sample can also be taken from the heat exchanger circuit, or a separate circuit from the mixer can be provided for sample collection. Sampling can be performed manually, semi-automatically, or automatically.

[0011] In a first embodiment of the invention, the heat exchanger element is directly connected to the mixing device. The medium from the mixing device, i.e., the actual product, directly tempers the calorimeter. This allows for particularly simple and reliable temperature control. A portion of the product is simply circulated from the mixing device through the calorimeter. However, this embodiment can be difficult or disadvantageous in certain cases. For example, in the production of gypsum board, it is necessary to safely empty and clean the relevant lines during shutdown before the gypsum hardens.

[0012] In a second alternative embodiment of the invention, the heat exchange element is indirectly connected to the mixing device. For this purpose, the mixing device has or is connected to a further heat exchange element. The heat exchange element and the further heat exchange element are connected to each other via a heat exchange fluid circuit. Although this is more complex than the first alternative, residual drainage during shutdown is not as critical, and even in the event of a failure, only the further heat exchange element, and not the calorimeter, would be affected, thus minimizing potential damage, for example, in the case of an unintended immediate shutdown. In a further embodiment of the invention, the calorimeter has a bearing area.The storage area serves to store samples or additives to be added to the samples, sample containers, mixing tools, cleaning solutions, cleaning tools, or the like, or to prepare samples in any way for introduction into a calorimeter cell, for example, by weighing them. The storage area includes a storage heat exchanger. This storage heat exchanger is thermally connected to the mixing device. This connection can be direct, as described above, or indirect, as described above. Thus, the storage area is also easily heated to the current temperature of the mixing device.

[0013] In a further embodiment of the invention, the calorimeter comprises several calorimeter cells, ideally each individually connected to a heat exchanger. The presence of multiple calorimeter cells, and thus multiple measuring stations, allows for shorter measurement intervals and therefore faster and more efficient process control, as measurements can be performed simultaneously and with a time offset. Individual temperature control is advantageous because it best ensures that a calorimeter cell into which a new sample is introduced has exactly the same temperature as the sample itself.

[0014] In another aspect, the invention relates to a method for operating a reaction device with a mixing device and a calorimeter, wherein the calorimeter comprises at least one calorimeter cell. The calorimeter cell is thermally connected to the mixing device (20) via at least one heat exchanger element and is heated to the temperature of the mixing device. As already explained, the usual practice is to heat the calorimeter to a predetermined temperature, for example, 20 °C. This makes the energy and reaction kinetics measured in the calorimeter comparable between different measurements, even on different samples, and thus forms the basis of this analytical method. However, the invention departs from this fundamental concept and instead focuses on heating the calorimeter to the variable temperature of the mixing device.This ensures that the current sample and calorimeter are at the same temperature, even without the need for temperature control. As a result, measurements can begin immediately after the sample is introduced into the calorimeter, allowing for the reliable investigation of even relatively rapid reactions lasting seconds or minutes. The focus shifts from an absolute comparison of independent samples to the recording of changes in reaction rate between successive samples in continuous or quasi-continuous processes, independent of defined standard conditions. Based on observed deviations from the desired reaction rate, decisions can be made to selectively control the reaction rate by adjusting the reactants, their mixing ratio, or the ambient conditions.Calorimetry thus also makes it possible to investigate reactions that cannot be easily tracked using other measurement methods, for example in the production of plasterboard.

[0015] The sample can be taken from the mixing device or after it; in the case of gypsum board production, this means between the mixer and the pouring onto the substrate. The sample can also be taken from the heat exchanger circuit, or a separate circuit from the mixer can be provided for sample collection. Sampling can be performed manually, semi-automatically, or automatically.

[0016] In a further embodiment of the invention, the calorimeter is temperature-controlled via a heat exchange element within the calorimeter. Here, the heat exchange element can be directly permeated by the mixture from the mixing device, as previously described, or indirectly via a further heat exchange element and a heat exchange fluid circuit. While the first direct variant is simpler, the second indirect variant is more advantageous if the mixture is hardening, as is the case, for example, with gypsum board production, since residual emptying during shutdown is only necessary in the further heat exchange element. Both the direct and the indirect methods have the advantage that precise temperature knowledge is not required due to the heat transfer; the only essential factor is that the sample from the mixing device can be introduced into the calorimeter immediately, without pre-heating, and without temperature artifacts.

[0017] In a further embodiment of the invention, the heat exchange element in the calorimeter is permeated with the contents of the mixing device. This corresponds to the direct variant. The direct variant is thermally advantageous, but complex if the mixture solidifies, since then a reliable emptying before solidification must be ensured during shutdown.

[0018] In a further embodiment of the invention, the mixing device has or is connected to a further heat exchange element. The heat exchange element and the further heat exchange element are connected to each other via a heat exchange fluid circuit, so that the calorimeter is tempered by the mixing device via the heat exchange fluid circuit. This corresponds to the indirect method and is preferred, for example, in the production of gypsum plasterboard to prevent the gypsum from solidifying in the heat exchange element of the calorimeter.

[0019] The conversion device according to the invention is explained in more detail below with reference to exemplary embodiments shown in the drawings.

[0020] Fig. 1 first example

[0021] Fig. 2 second example

[0022] Figure 1 shows a first example of gypsum board production. In a mixing device 20, for example, plaster of Paris is mixed with water and other additives and then placed between two layers of paper on a curing line 30 and cured. The additives used are primarily substances that slow down or accelerate the curing process.

[0023] To actively control this actual manufacturing process, the reaction device includes a calorimeter 10. The calorimeter measures the heat generated by the mixture from the mixing device 20, thus determining the curing time in the curing line 30. In particular, this allows for the detection of fluctuations in the setting time, which can be attributed to variations in the quality of the starting material, especially the gypsum, or to changes in environmental conditions such as temperature. Since the setting time is relatively short and the reaction is initiated within the mixing device, the sample cannot be tempered after being taken from the mixing device 20. Currently, only the starting materials are tempered, for example with water, and mixed. However, this does not reflect the setting time in the mixing device 20, but rather only provides a parameter for the gypsum quality.The usual methods used, for example in the production of plasterboard, such as the flowing compound, the cutting test or the thumb pressure, are subject to a significant subjective error and cannot be automated.

[0024] Therefore, the calorimeter 10 is heated directly above a heat exchange fluid circuit 60, thus bringing it to a common temperature level with the mixing device 20. This allows a sample taken from the mixing device 20 to be introduced directly into the calorimeter 10 and measured without further heating. The heat exchange fluid circuit 60 is connected to the heat exchange element 40 in the calorimeter and thus heats the calorimeter 10. On the other side, the heat exchange fluid circuit 60 is connected to another heat exchange element 50 in the mixing device 20 and thus assumes the temperature of the mixture in the mixing device 20.

[0025] Fig. 2 shows, in addition to the first example, a larger calorimeter 10 with one calorimeter cell 11, but it can also have multiple calorimeter cells 11 to allow for parallel measurements. The calorimeter also has a pre-chamber or storage area, which is heated to the temperature of the mixing device 20 via the storage heat exchanger element 41. This enables a more stable and simpler temperature control overall, for example, of consumables.

[0026] Reference sign

[0027] 10 calorimeters

[0028] 11 Calorimeter cell 20 Mixing device

[0029] 30 Curing line

[0030] 40 Heat exchanger element

[0031] 41 bearing heat exchanger element 50 additional heat exchanger element

[0032] 60 Heat exchange fluid circuit

Claims

Patent claims 1. Conversion device, wherein the conversion device comprises a mixing device (20) for mixing starting components for the conversion, wherein the conversion device comprises a calorimeter (10) for recording the conversion started in the mixing device (20), wherein the calorimeter (10) comprises at least one calorimeter cell (11) for measuring a sample, characterized in that the calorimeter cell (11) comprises at least one heat exchange element (40) for temperature control of the calorimeter cell (11), wherein the heat exchange element (40) is thermally connected to the mixing device (20).

2. Conversion device according to claim 1, characterized in that the heat exchange element (40) is directly connected to the mixing device (20).

3. Conversion device according to claim 1, characterized in that the heat exchange element (40) is indirectly connected to the mixing device (20), wherein the mixing device (20) has or is connected to a further heat exchange element (50), wherein the heat exchange element (40) and the further heat exchange element (50) are connected to each other via a heat exchange fluid circuit (60).

4. Conversion device according to one of the preceding claims, characterized in that the calorimeter (10) has a bearing area, wherein the bearing area has a bearing heat exchange element (41), wherein the bearing heat exchange element (41) is thermally connected to the mixing device (20).

5. Method for operating a conversion device with a mixing device (20) and a calorimeter (10), wherein the calorimeter (10) has at least one calorimeter cell (11), wherein the calorimeter cell (11) is thermally connected to the mixing device (20) with at least one heat exchange element (40) and is tempered to the temperature of the mixing device (20).

6. Method according to claim 5, characterized in that the calorimeter (10) is temperature-controlled via a heat exchange element (40) in the calorimeter (10).

7. Method according to claim 6, characterized in that the heat exchange element (40) in the calorimeter (10) is permeated with the contents of the mixing device (20).

8. The method according to claim 6, characterized in that the Mixing device (20) has or is connected to a further heat exchange element (50), wherein the heat exchange element (40) and the further heat exchange element (50) are connected to each other via a heat exchange fluid circuit (60), so that the calorimeter is tempered via the heat exchange fluid circuit (60) by the mixing device (20).

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