Method for determining at least one characteristic parameter of a particle size distribution and a device with a measuring instrument

Abstract

Method for determining at least one characteristic parameter of a particle size distribution in a moving particle stream using at least one microwave resonator which provides at least two measured values ​​for the particle stream, characterized in that at least one quantile of the particle size distribution is determined from the measured values.

Description

[0001] The present invention relates to a method for determining at least one characteristic parameter of a particle size distribution in a moving particle stream. The invention also relates to a device for generating a moving particle stream with a measuring device for determining at least one characteristic parameter of a particle size distribution in the moving particle stream.

[0002] From WO 2009 / 030314, a method for measuring the moisture content of dielectric materials using at least one resonator is known. In this method, a shift in the resonance frequency is evaluated for at least two resonance modes with different resonance frequencies, and a density-independent moisture content is calculated from the measured shift. The particular advantage of this method is that it no longer requires relying on a damping value as a measure of moisture content. Instead, a density-independent moisture content is calculated with high reliability from at least two shifts in the resonance frequency occurring at different resonance frequencies. By using the frequency shift at two resonance frequencies, a particle size D can be calculated without relying on damping characteristics.In practice, it has been found that determining a particle size D in a moving particle stream is only possible with a high degree of unreliability.

[0003] German patent DE 101 11 833 C1 discloses a measuring probe for the in-line determination of the size of moving particles in transparent media. The measuring probe has a tubular probe body into which individual moving particles enter and are optically measured. For this purpose, the particles are separated using a dispersing medium.

[0004] From DE 3 241 544 A1, a method for monitoring and / or controlling drying, granulating, instantiation, coating, and film-coating processes is known. In the known method, the humidity of the exhaust air and the humidity of the supply air are measured, and the resulting humidity difference is used to control the work process.

[0005] From JP 4 230 058 B2 it is known to determine a quantile value using a neural network, wherein the measurement of the material is carried out optically and the neural network is trained with a particle size distribution.

[0006] The invention is based on the objective of reliably measuring at least one characteristic parameter of a particle size distribution in a moving particle stream. The invention is also based on the objective of providing such a measuring device for a device for generating a moving particle stream.

[0007] According to the invention, the problem is solved by a method with the features of claim 1 and a device with the features of claim 9. Advantageous embodiments are the subject matter of the dependent claims.

[0008] The method according to the invention is designed to determine at least one characteristic parameter of a particle size distribution in a moving particle stream. For this determination, at least one microwave resonator is used, which provides at least two measurement values ​​for the particle stream. An important feature is that the characteristic parameter determines a quantile of the particle size distribution. Unlike in the prior art, where, for example, a mean particle size or another mean parameter was determined, the invention uses the quantile to determine a proportion of a gradient. That is, the number, mass, or other parameter is evaluated to determine the proportion of particles that are less than or equal to the value of the quantile. Thus, the focus is not on a specific size value itself, but rather on the proportion up to that size value.The quantile defines a threshold value at which a certain proportion of the values ​​are smaller than the quantile, while the remainder are larger. For example, the 25% quantile denotes the value for which 25% of all values ​​are smaller and 75% are larger. A particular step in evaluating particle size distributions using a microwave resonator according to the invention involves not focusing on specific values ​​or averages, but rather evaluating the measured quantities in such a way that the contributions of all moving particles smaller than the quantile under investigation are always taken into account. In addition to using multiple microwave resonators, it is also possible to use microwave resonators that have two or more resonance modes. For each resonance mode, two measurements of the particle flux can then be provided.

[0009] In a preferred embodiment, it has proven particularly advantageous to base the two measured values ​​of the microwave resonator on a resonance frequency shift and a resonance curve broadening. The resonance frequency shift and the resonance curve broadening (B) as measured values ​​are fundamentally density-dependent quantities, while the quotient of the two measured values ​​yields a mass- or density-independent quantity. In particular, by focusing on the quantile, the use of both measured values ​​of the microwave resonator—resonance frequency shift and resonance curve broadening—is especially advantageous. Instead of the resonance curve broadening, other measured values ​​of the microwave resonator can also be used that provide information about the damping of the resonance.

[0010] In a preferred embodiment of the method, at least one temperature of the particle stream is evaluated. The temperature of the particle stream results from the temperature of the supplied air and the heat of vaporization. Therefore, due to the greater evaporation rate, the temperature of a moist particle stream is lower than that of a dry particle stream (with constant filling and supply air volume) at a constant supply air temperature.

[0011] For a moving particle stream in a fluidized bed, at least one of the following parameters is preferably evaluated as additional measured variables: supply air volume and fluidized bed fill volume. The supply air volume is set on fluidized bed dryers depending on the specific process and is usually also varied during the processes. It can, for example, be specified as the air volume in cubic meters per hour [m³ / h]. The fill volume in a fluidized bed system indicates, for example, how many kilograms [kg] of material are present in the system.

[0012] It has been found that at least one quantile can be determined very accurately by a linear approximation of the evaluated measurements. This means that the measured quantities are combined as a simple linear combination with a constant term to determine the quantile. This linear approximation also makes it clear that for microwave measurements, the quantile is the appropriate parameter for the particle size distribution. Of course, other parameters such as mean particle weight or mean particle diameter can be determined from these parameters. However, the primary focus is on determining the quantile.

[0013] It is preferable to consider different particle size distributions. One can focus on a number distribution sum, a length distribution sum, an area distribution sum, or a volume / mass distribution sum. Determining several parameters simultaneously is particularly important for a good understanding of particle size distributions. For example, using the same measurements but different coefficients for the linear combination of number distribution sum and volume distribution sum, one could consider both. It is also possible to determine multiple quantiles of a distribution sum.

[0014] The problem according to the invention is also solved by a device for generating a moving particle stream with the features of claim 10. The device has a measuring device for determining at least one characteristic parameter of a particle size distribution in the moving particle stream. The measuring device has at least one microwave resonator, which provides at least two measured values ​​for the particle stream. The at least two measured values ​​are preferably the resonance frequency shift and a resonance curve broadening. Furthermore, the measuring device is configured to evaluate at least one quantile of the particle size distribution from the two measured values ​​of the microwave resonator. The measuring device, to which the measured values ​​of the at least one microwave resonator are applied, can be arranged spatially together with the microwave resonator or separately from it.The microwave resonator can be designed to generate two or more resonance modes, in each of which at least two measured values ​​can be recorded.

[0015] Preferably, the measuring device is also configured to evaluate the temperature of the particle stream.

[0016] Preferably, the measuring device is arranged such that the measured quantities are measured in a fluidized bed. Particularly when used in a fluidized bed, the measuring device is configured to evaluate at least one of the following parameters: the supply air and the fill volume of the fluidized bed. The supply air and the fill volume strongly influence the microwave measurement and are therefore preferably taken into account for determining the quantile of a particle stream.

[0017] The measuring device is preferably configured to determine the quantile for a number distribution sum, a length distribution sum, an area distribution sum, a volume distribution sum, and / or a mass distribution sum. It is important that the measuring device can also determine several quantiles simultaneously.

[0018] By recording several quantiles over time, a reliable determination of the processes taking place in the advertising layer can be obtained.

[0019] The above invention is explained in more detail below with the help of some measured values. These show: Fig. 1. The temporal development of three fineness characteristics relating to the number distribution sum, Fig. 2 three fineness characteristics that relate to the volume distribution sum and Fig. 3 the temporal evolution for a mean diameter of the particles.

[0020] Fluidized bed processes are used in numerous different technical fields. One important application is in pharmaceutical production, specifically in the manufacture of discrete active ingredient units, which are then compressed into tablets or filled into capsules. This process employs a granulation process followed by fluidized bed drying. During granulation, the pharmaceutical powder mixture is sprayed with an often aqueous solution to form granules with a defined particle size. The subsequent fluidized bed drying process dries the granules to a defined target moisture content. Both processes can be carried out in separate systems, or they can be combined in a single system. Besides the moisture content, the average particle size of the granules is an important parameter for characterizing the quality of the manufactured substrate.Besides monitoring the process and its end product, measuring the particle size distribution also allows for the detection of operational malfunctions, for example, in the spray nozzles. It is important to remember that not only the average particle diameter is decisive, but knowledge of the entire particle size distribution is helpful for evaluating the process. For example, the presence of large particles, so-called "oversize," does not necessarily lead to a significant increase in the average particle diameter, but is nevertheless detrimental to further processing. Similarly, mechanical stress, combined with insufficient granule stability, can result in a high proportion of fines, which also poses problems for subsequent processing.The properties of the granules, including their particle size distribution, have a direct influence on subsequent processing and also on the properties of, for example, the finished tablet, with regard to its dissolution kinetics and a uniform release of the active ingredient content.

[0021] Currently, particle size measurement directly within the fluidized bed process is primarily performed using a laser method, as described, for example, in DE 10 111 833 C1. A disadvantage of this optical method is its extreme sensitivity to contamination and its suitability only for optical particle size measurement, not for simultaneously measuring moisture content.

[0022] When measuring particles in a particle stream, a distinction can be made between the particle (dispersed phase) and its surrounding medium (continuous phase). In a fluidized bed, the drying granules constitute the particles, while the surrounding air forms the continuous medium. It is common practice to distinguish between grains, droplets, and bubbles using a measured equivalent diameter and to classify them into selected categories according to their size. To represent a particle size distribution, the proportions of each particle class in the dispersed phase are determined.

[0023] Different types of quantity are known: When particles are counted, the quantity is the number. In the case of weighing, it is mass, or, in the case of homogeneous density, volume. Other types of quantity are derived from length, projection, and surface area. In general, the following can be distinguished: Quantity type Index R Number 0 length 1 Area 2 Volume (mass) 3

[0024] It is common practice to use a standardized quantity unit for graphical representation, thus eliminating the dependence of the quantity proportions on the total quantity used. Using the indices mentioned above, we obtain a number distribution sum Q0 and, for example, a volume distribution sum Q3. If we denote a particle size as the equivalent diameter by X, then in the usual notation, we obtain, for example, X 10,0 for the fineness characteristic at which the distribution sum Q0 takes the value 10%. In other words, the 10% quantile of the distribution function lies at the value X. 10,0 This means that 10% of all particles have this or a smaller diameter.

[0025] If one considers Fig. 1. The measurement results of the method according to the invention are plotted there with the solid line. The upper curve X 90,0The graph shows the process duration of 20-80 minutes. The ordinate represents the particle diameter. A value of approximately 400 µm, as occurs, for example, shortly before and after 50 minutes of process duration, is shown in curve X. 90,0 This means that 90% of the particles have a diameter less than or equal to 400 µm. The curve X 50,0 This indicates the equivalent diameter, meaning that 50% of the sample have a diameter of, for example, less than 150 µm. The fineness characteristic X 10,0 This indicates the maximum diameter of the 10% smallest particles. The temporal development of these three fineness characteristics provides good information about the grain size distribution. For example, is the value for X 10,0 If X is too small, it can be deduced that 10% of the particles, relative to their number, are smaller than this value and therefore potentially too small. Similarly, a value that is too large for X could also be... 90,0This could indicate that the grain is oversized with isolated large grains.

[0026] Fig. Figure 2 shows the fineness characteristic in µm relative to the volume distribution sum. The curve X 90,3 This gives the quantiles for the volume distribution sum. This means X 90,3 For example, it refers to the largest diameter of the particles that make up 90% of the total volume.

[0027] Fig. Figure 3 shows how the mean diameter of the particles develops over time. The mean particle diameter increases steadily during granulation and decreases again during the drying phase due to the constant collision of the particles. The transition between granulation and the drying phase occurs at approximately 52 to 55 minutes.

[0028] Fig.Figures 1-3 show parallel optical measurements, referred to as laser measurements. The comparison shows that reliable values ​​can also be obtained using a microwave resonator.

[0029] The following approaches have proven effective for evaluating the measured values. Xa,0=a1⋅A+a2⋅B+a3⋅L+a4⋅T+a5⋅F+a0 Xa,3=b1⋅A+b2⋅B+b3⋅L+b4⋅T+b5⋅F+b0 where X a,0 the fineness characteristics for the quantiles a of the number distribution sum in µm and X a,3 The fineness characteristics for the quantiles a of the volume distribution sum in µm are designated and a i and b i The calibration coefficients are used in each case. The measured quantities to be evaluated are A for the resonance frequency shift of a resonance mode in MHz, B a broadening of the resonance curve of the same resonance mode in MHz, and L the supply air volume to the fluidized bed in m³. 3 / h, T is the product temperature in degrees Celsius and F is the filling quantity of the fluidized bed system in kg.

Claims

[1] Method for determining at least one characteristic of a particle size distribution in a moving particle stream using at least one microwave resonator, each of which provides at least two measured values ​​for the particle stream, characterized by that at least one quantile of the particle size distribution is determined from the measured values. [2] Method according to claim 1, characterized by that the at least two measured values ​​of the microwave resonator relate to a resonance frequency shift (A) and a resonance curve broadening (B). [3] Method according to claim 1 or 2, characterized by that the at least one microwave resonator has two or more resonance modes, each of which provides two measured values ​​for the particle stream. [4] Method according to one of claims 1 to 3, characterized by that at least one temperature of the particle stream is additionally evaluated. [5] Method according to one of claims 1 to 4, characterized by that the moving particle stream is present in a fluidized bed. [6] Method according to claim 5, characterized by that at least one of the following variables is evaluated as an additional measured variable: supply air quantity and filling quantity of the fluidized bed. [7] Method according to one of claims 1 to 6, characterized by that the quantile is linearly approximated by the evaluated measured variables. [8] Method according to one of claims 1 to 7, characterized by that the quantile refers to a number distribution sum, a length distribution sum, an area distribution sum, a volume distribution sum, or a mass distribution sum. [9] Method according to one of claims 1 to 8, characterized by that several quantiles are recorded over time. [10] Device for generating a moving particle stream with a measuring device for determining at least one characteristic of a particle size distribution in the moving particle stream, which has at least one microwave resonator which provides at least two measured values ​​for the particle stream, characterized by that the measuring device is designed to evaluate at least one quantile of the particle size distribution from the at least two measured values ​​of the microwave resonator. [11] Device according to claim 10, characterized by that the at least one microwave resonator is designed to provide two measurement values ​​for the particle stream using two or more resonance modes. [12] Device according to claim 10 or 11, characterized by that the measuring device is arranged in such a way that a temperature of the particle stream is also measured. [13] Device according to one of claims 10 to 12, characterized bythat the measuring device is arranged in such a way that the parameters are measured in a fluidized bed. [14] Device according to claim 13, characterized by that the measuring device is set up to evaluate at least one of the following variables such as supply air quantity and filling quantity of the fluidized bed. [15] Device according to claim 13 or 14, characterized by that the measuring device is set up to linearly approximate the quantile using the evaluated measured variables. [16] Device according to one of claims 10 to 15, characterized by that the measuring device is set up to determine the quantile for a number distribution sum, a length distribution sum, an area distribution sum or a volume distribution sum or a mass distribution sum. [17] Device according to one of claims 10 to 16, characterized by that the measuring device is designed to record several quantiles over time.

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