Monitoring of Fluidized Bed Dryers and Granulators Using Pressure Fluctuation Signals

Monitoring of fluidized bed dryers and granulators using pressure fluctuation signals

Lilian de Martín and 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.