Coating processes – Measuring – testing – or indicating
Reexamination Certificate
1999-09-24
2002-05-07
Parker, Fred J. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S185000, C427S459000, C023S3130FB, C034S474000
Reexamination Certificate
active
06383553
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method and a device for monitoring and/or controlling and regulating a granulation, agglomeration, instantization, coating and/or drying process in a fluidized bed or a moving bulk by determining the product moisture.
In the prior art indirect methods are known for determining the product moisture, for example using a balancing of the inlet and outlet streams from which the product moisture is determined. The inlet and exhaust air conditions (temperature and humidity) are measured, as well as the volume flow of the inlet and exhaust air and the spray rate. From many different measuring positions (a minimum of seven measurement quantities), a correspondingly large number of measurement errors results and thereby a product moisture that is not exactly specified. Problems occur especially for processes which require a fast regulation, for example the detection of the shut-off point for spraying during granulation. An indirect measurement of the humidity of the product environment can be performed by a capacitive measuring sensor which is positioned directly in the fluidized bed. Generally, the actual measurement sensor is surrounded by a water vapor-permeable protection cap, through which the water vapor must diffuse, which is then correspondingly detected by the sensor.
It is problematic therein that this involves a slow measuring method. During granulation, an air atmosphere always appears in the product environment which is almost completely saturated with water, which can lead to condensation on the sensor (so-called over-moistening of the sensor). The condensed water requires a considerably longer time until it is released again to the outside via the protection cap. During this time, the measurement signal always lies at about 100% air humidity. Furthermore, contamination of the sensor can lead to considerable measurement error. In addition, as a result of the partly strong abrasive forces by the fluidized product, the sensor only has a short service life.
Using NIR-spectroscopy, only the surface moisture can be measured. Usually, a very high calibration expense and an expensive mathematical evaluation and averaging of the measurement signal are necessary for this. The IR-sensor can be integrated in the fluidized layer only via a window that is flush with the wall, so that problems result from glazing of the window, because this leads to the immediate reflection of radiation. A measurement is then ruled out. Furthermore, due to the short wavelengths and the high reflection of the radiation thus present, there is no penetration depth into the fluidized layer or the product. Thus, only the surface moisture can be recorded. Finally, the dependence of the measurement signal on the grain size and on the bulk density, and the dependence of the measurement signal on the color change and the thereby resulting high calibration expense, are disadvantageous.
A measurement of the moisture can also be performed via an impedance measurement with two electrodes on an electrically insulating substrate (PTFE), which are connected together to be electrically conducting via a moisture-sensitive layer of an electrolytic solid (water vapor permeable). An equilibrium humidity is measured, which appears in the product environment. The direct product moisture is not measured. The service life of the sensor in the fluidized layer is very unsatisfactory.
Furthermore, it is known to record the levels of inlet and exhaust air temperature, volume flow, inlet and exhaust air humidity, and the spray rate. From these quantities, however, generally only indirect information can be derived about the actual product or the water content appearing in the product. Exact readings are generally only possible with off-line measurement methods, such as dry weight determination, vacuum drying chamber, desiccator method, infrared scales, or by the Karl-Fischer titration. These methods are, however, very time consuming and require a time expenditure of 10 minutes to half a day for a moisture measurement, so that these methods permit no real-time or current information for the process.
A further possibility for detecting the result or the progression of a granulation process is represented by the possibility of directly determining or measuring the particle size or the grain size distribution during the process. The processes known for this, such as ultrasound measurement or laser diffraction spectroscopy, are characterized by a very high cost of devices and by extremely complicated mathematical and statistical evaluation procedures. For the measurement, defined measurement sections, for example a defined bypass for the product, are usually necessary, such that an insertion directly into the fluidized layer is not possible. A reproducibility of the method is generally achieved only under certain conditions.
With all of the above-mentioned known processes for controlling or regulating the processes, it is disadvantageous that they are either too slow and/or too susceptible to disturbances and/or not accurate enough, and therefore a limited practical suitability is available only for certain products.
SUMMARY OF THE INVENTION
An object of the present invention is to create a method of the type mentioned at the beginning, as well as a device, whereby under the more difficult conditions that are prevalent with these processes, in particular with respect to the accessibility of the product, the contamination and the service life of the sensor, etc., the product moisture can be measured reliably with higher measurement accuracy, and this measurement quantity can be used for the control or the regulation of the process. In particular, this moisture measurement should provide a result that can be used directly as a measure for certain product characteristics. Moreover, the measurement should also be applicable for different products without costly adaptation and calibration.
In order to achieve this object, it is proposed that, at least during one segment of the process, the total product moisture is measured substantially continuously at least over a period of seconds, in a contact-free manner using electromagnetic radiation in the high frequency or microwave range, by evaluation of the attenuation as a measure of this total product moisture, and taking into consideration the product temperature, the total product moisture is held in a pre-determined range via a control circuit by changing the spray rate and/or the gas temperature and/or the volume flow.
The invention is based upon the discovery that the total product moisture, and consequently both the surface moisture as well as the moisture present within the product in the capillaries or the cavities of a granulate grain, is a key piece of information, by which an exact influence of the respective process is possible.
From European published patent application EP-A-0 403 820 a process for drying a bulk is indeed known, in which an electromagnetic radiation is used in order to dry the bulk and to measure its moisture. The electromagnetic radiation is used therein for drying the bulk, wherein the microwave device functions as an active drying device, while the reflected output is only measured in order to determine the end of the drying process. However, no indication is contained therein that the electromagnetic radiation is used only for measurement and that this measurement is used to control the total product moisture by adjustment of the spray rate.
The method according to the invention and the corresponding measurement device constitute an improvement of a conventional process, in which the drying is not influenced by the microwave radiation, so that measurement data are available about the actual, directly present total product moisture, which can thus be used directly, i.e., “online”, as process-accompanying measurement quantities for the control of the directly on-going process. The device according to the invention makes it possible to measure the product moisture within very narrow limits, exactly and reprod
Luy Bernhard
Prasch Armin
Tondar Mathias
Akin Gump Strauss Hauer & Feld L.L.P.
Glatt GmbH
Parker Fred J.
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