Application of chaos analysis to pressure fluctuation data from a fluidized bed dryer containing pharmaceutical granule

The S-statistic, a statistical test between chaotic attractors for fluidized systems introduced by van Ommen et al. [J.R. van Ommen, Monitoring fluidized bed hydrodynamics, PhD thesis, Technical University of Delft (2001).; AIChe J., 46 (11) (2000), 2183] has been applied to pressure fluctuations collected in a conical fluidized bed of dry pharmaceutical granule as well as a fluidized bed of wet granule as it progresses to the dry state. In a dry bed, the S-statistic has been found sensitive to the particle size distribution (PSD). Changes in bed hydrodynamics arising from PSD have been found to be most easily resolved at low gas velocities, indicating segregation at superficial velocities less than 2 m/s. In a drying bed, two stable states have been identified. These states correspond to visual observations of the presence of a centralized core of bubbles in a bed of high moisture content and more uniform fluidization throughout the bed cross-section toward the end of the drying process. The effect of moisture has been found to dominate the hydrodynamic changes taking place within the bed in the drying process identified with the S-statistic. The hydrodynamic changes identified by the S-statistic are not discerned by frequency and amplitude analysis techniques. Response of the S-statistic to the hydrodynamic changes associated with drying indicates the potential application of this technique to the quantification of fluidized bed hydrodynamic behavior. (C) 2004 Elsevier B.V. All rights reserved.