(67b) Monitoring of Fluidized Bed Dryers and Granulators Using Pressure Fluctuation Signals

Monitoring of fluidized bed dryers and granulators
using pressure fluctuation signals

Lilian de
Martínand J. Ruud van Ommen

Delft University of Technology, Department of Chemical Engineering,
Product & Process Engineering, Julianalaan 136, 2628 BL Delft, The
Netherlands

The
monitoring of the particle moisture content and the particle size is of great
importance in fluidized bed drying and granulation. Due to the implementation
of the Process Analytical Technology initiative in the pharmaceutical industry
[1], there is an increasing interest to apply on-line monitoring tools for
process control. In spite of the amount of the existing techniques developed to
monitor the beds, there are only a few techniques available to do monitor
granule properties on-line. Near infrared microscopy and microwave absorption
are the most used. Nevertheless, these techniques present several drawbacks
that compromise their applicability. Consequently, the challenge of developing
a suitable technique for the on-line monitoring of fluidized bed dryers and
granulators is still open.

Given the
advantages of the pressure fluctuation measurement over other techniques (e.g.
low cost and easy implementation), three signal processing approaches (dominant
frequency, standard deviation of a narrow frequency band and attractor
comparison [2]) have been applied to pressure data to get information about the
particle moisture and the granule size inside a fluidized bed dryer/granulator.

The
analysis of the pressure signals show that some frequency bands of these
signals are more sensitive to the changes in the bed dynamic related with the
particle moisture and the granule size than others. By processing the signal
properly it is possible to have clear relationships between the particle
moisture or granule size and the standard deviation of the pretreated signal.
Moreover, in the case of the granulator, the relationship between the granule
size and the standard deviation is linear. The results show that the pressure
fluctuation measurements are a promising tool to monitor on-line the fluidized
bed drying and granulation process.

[1] Guidance
for Industry PAT ? A Framework for Innovative Pharmaceutical Development,
Manufacturing and Quality Assurance, U.S. department of health and human
services. Food and Drug Administration, 2004.

[2] J. R. van
Ommen, M.-O. Coppens, C. M. van den Bleek, J. C. Schouten, Early warning of
agglomeration in fluidized beds by attractor comparison, AIChE J. 46 (2000)
2183 ? 2197.