METHOD FOR DETERMINING AT LEAST ONE CHARACTERISTIC VARIABLE OF A PARTICLE SIZE DISTRIBUTION AND A DEVICE COMPRISING A MEASURING APPARATUS

Abstract

A method for determining at least one characteristic variable of a particle size distribution in a moving flow of particles includes structuring at least one microwave resonator to determine at least two measured values for the moving flow of particles. At least one quantile of the particle size distribution is further determined from the at least two measured values. Moreover, a device for generating a moving flow of particles includes a measuring apparatus having at least one microwave resonator that determines at least two measured values for the flow of particles. The measuring apparatus evaluates at least one quantile of a particle size distribution from the at least two measured values of the microwave resonator.

Claims

1-17. (canceled)

18. A method for determining at least one characteristic variable of a particle size distribution in a moving flow of particles, comprising: structuring at least one microwave resonator to determine at least two measured values for the moving flow of particles; and determining at least one quantile of the particle size distribution from the at least two measured values.

19. The method according to claim 18, wherein the at least two measured values of the microwave resonator correspond to a resonance frequency shift (A) and a broadening of a resonance curve (B).

20. The method according to claim 18, further comprising evaluating at least one temperature of the moving flow of particles.

21. The method according to claim 18, wherein the moving flow of particles is present in a fluidized bed.

22. The method according to claim 21, further comprising evaluating at least one of: (i) an amount of air supplied to the fluidized bed; and (ii) a fill level of the fluidized bed.

23. The method according to claim 18, further comprising determining at least one of: (i) a fineness characteristic; and (ii) a quantile, is linearly approximated using the at least two measured variables.

24. The method according to claim 23, wherein the quantile relates to one of a number distribution sum, a length distribution sum, an area distribution sum, a volume distribution sum, or a mass distribution sum.

25. The method according to claim 23, wherein multiple quantiles are recorded over time.

26. A device for generating a moving flow of particles, comprising: a measuring apparatus comprising at least one microwave resonator configured to determine at least two measured values for the flow of particles, wherein the measuring apparatus is configured to evaluate at least one quantile of a particle size distribution from the at least two measured values of the microwave resonator.

27. The device according to claim 26, wherein the measuring apparatus is further configured to measure a temperature of the flow of particles.

28. The device according to claim 26, wherein the at least two measured values are measured in a fluidized bed.

29. The device according to claim 28, wherein the measuring apparatus is configured to evaluate at least one of: (i) an amount of air supplied to the fluidized bed; and (ii) a fill level of the fluidized bed.

30. The device according to claim 29, wherein the measuring apparatus is configured to linearly approximate the quantile using: (i) the amount of air supplied to the fluidized bed; and (ii) the fill level of the fluidized bed.

31. The method according to claim 26, wherein the measuring apparatus is configured to determine the quantile for one of: a number distribution sum, a length distribution sum, an area distribution sum, a volume distribution sum, or a mass distribution sum.

32. The method according to claim 26, wherein the measuring apparatus is configured to record multiple quantiles over time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above invention will be explained in more detail below with the aid of some measured values. In the drawings:

[0019] FIG. 1 graphically illustrates an embodiment of the temporal development of three fineness characteristics relating to the number distribution sum;

[0020] FIG. 2 graphically illustrates an embodiment of three fineness characteristics relating to the volume distribution sum; and

[0021] FIG. 3 graphically illustrates an embodiment of a temporal development for a mean diameter of the particles.

DETAILED DESCRIPTION OF THE INVENTION

[0022] Fluidized bed processes are used in many different technical fields. One important field of application is the pharmaceutical production process, in the manufacture of discrete active ingredient units that can, for example, be pressed into tablets or filled into capsules. In this case, a granulation process with a subsequent fluidized bed drying process is used. During the granulation process, the present pharmaceutical powder mixture is processed into granules with a defined particle size while an, often aqueous, solution is sprayed in. In the subsequent fluidized bed drying process, the granules are dried to a defined target moisture content. Both processes can take place in separate systems, but it is also possible to perform them in a combined manner in one system. In addition to the moisture content, an important parameter for characterizing the quality of the substrate produced is the mean particle size of the granules. In addition to process and end product monitoring, measuring the particle size distribution also makes it possible to identify operational malfunctions, for example at the spray nozzles. It is important to bear in mind here that not only is a mean particle diameter crucial, but rather knowledge of the overall particle size distribution is helpful for assessing the process. If, for example, large particles are present, i.e. so-called “oversize”, this does not necessarily lead an associated increase in the average particle diameter, but it is nevertheless prejudicial to further processing processes. Likewise, a high fine content can occur, for example due to mechanical stress with insufficient stability of the granules, and also poses difficulties for subsequent further processing. The properties of the granules with their particle size distribution have a direct influence on the subsequent processing and also on the properties, for example, of the finished tablet with regard to the dissolution kinetics thereof as well as uniform release of the active ingredient content.

[0023] Currently, the measurement of the particle size directly during the fluidized bed process is mainly done using a laser method, as described, for example, in DE 10 111 833 C1. The disadvantage of the optical method is that it is extremely sensitive to contamination and, additionally, is only suitable for optically measuring the particle size and not for simultaneously measuring the moisture content.

[0024] When measuring in a flow of particles, a distinction can be made between the particle (disperse phase) and its surrounding medium (continuous phase). In the fluidized bed, the drying granules constitute the particles, whereas the surrounding air constitutes the continuous medium. It is typical to decide grains, drops, or bubbles based on an equivalent diameter to be measured and to classify them into selected classes according to their size. In order to represent a particle size distribution, the proportions of the respective particle classes in the disperse phase are determined.

[0025] Different types of quantity are known. If the particles are counted, then the quantity is the number. However, if they are weighed, it is the mass or rather, in the case of a homogeneous density, the volume. Other types of quantity are derived from length, projection area, and surface area. In general, the following can be distinguished:

TABLE-US-00001 Type of quantity Index R Number 0 Length 1 Area 2 Volume (mass) 3

[0026] It is typical to use a standardized quantitative measure for graphical representation, such that the dependency of the proportions on the total quantity used are eliminated. When using the above-mentioned indices, a number distribution sum Q0 and, for example, a volume distribution sum Q3 are obtained. If X denotes a particle size as an equivalent diameter, in the usual notation this produces, for example, X10,0 for the fineness characteristic at which the distribution sum Q0 assumes the value 10%. In other words, the 10% quantile of the distribution function is at the value X10,0, which means that 10% of all particles have this or a lesser diameter.

[0027] In FIG. 1, the measurement results of the method according to the invention are plotted by means of the solid line. The upper curve X90,0 is shown for a process duration of 20-80 minutes. The y-axis shows the diameter of the particles. A value of approximately 400 μm in the curve X90,0, as occurs, for example, shortly before 50 minutes and shortly after 50 minutes of process duration means that 90% of the particles have a diameter of less than or equal to 400 μm. The curve X50,0 indicates the equivalent diameter that 50% relative to the number have, for example a diameter of less than 150 μm. The fineness characteristic X10,0 indicates the maximum diameter of the 10% smallest particles. The temporal development of these three fineness characteristics gives a good indication of the grain size distribution. If, for example, the value for X10,0 is too small, it can be deduced that 10% of the particles relative to the number are smaller than this value and are thus possibly too small. Equally, an excessively large value for X90,0 can be an indication that isolated large grains are oversized.

[0028] FIG. 2 shows the fineness characteristic in μm in relation to the volume distribution sum. The curve X.sub.90,3 indicates the quantiles for the volume distribution sum. This means that X.sub.90,3 denotes, for example, the largest diameter of the particles, which make up 90% of the total volume.

[0029] FIG. 3 shows how the mean diameter of the particles develops over time. The mean particle diameter increases constantly during granulation and decreases during the drying phase due to the constant collision of the particles. The transition between granulation and the drying phase takes place at approximately 52 to 55 min.

[0030] FIG. 1-3 each show parallel optical measurements, which are referred to as laser measurement. A comparison shows that values can also be reliably obtained using a microwave resonator here.

[0031] The following approaches have proven successful for the evaluation of the measured values:

Xa,0=a.sub.1.Math.A+a.sub.2.Math.B+a.sub.3.Math.L+a.sub.4.Math.T+a.sub.5.Math.F+a.sub.0

Xa,3=b.sub.1.Math.A+b.sub.2.Math.B+b.sub.3.Math.L+b.sub.4.Math.T+b.sub.5.Math.F+b.sub.0

wherein, here, X.sub.a,0 denotes the fineness characteristics to the quantiles a of the number distribution sum in μm and X.sub.a,3 denotes the fineness characteristics to the quantiles a of the volume distribution sum in μm and a.sub.i and b.sub.i each denote the calibration coefficients. The measured variables 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, L the amount of air supplied to the fluidized bed in m.sup.3/h, T the product temperature in degrees Celsius, and F the fill level of the fluidized bed system in kg.