Multiresolution Analysis of Pressure Fluctuations in a Gas-Solids Fluidized Bed: Application to Glass Beads and Polyethylene Powder Systems

ABSTRACT

Gas–solids fluidized beds are widely accepted as nonlinear and chaotic dynamic systems. Traditional methods such as statistical and spectral analyses are not sufficient to capture critical behavior in these systems. In this work, non-intrusive techniques were used to characterize the hydrodynamics in gas–solids bubbling fluidized bed using polyethylene powder and glass beads with comparable mean diameter. Pressure fluctuations and X-ray fluoroscopy measurements were performed on a pseudo two-dimensional fluidized bed. Statistical, wavelet, and chaos analyses were applied to the non-stationary pressure signal series to extract and characterize the intrinsic features of the gas–solids fluidized bed. Dominant cycle time was calculated from approximate coefficient of scale 6 decomposed from cleaned pressure fluctuation. The global bubbling behavior of the glass bead system was greatly affected by changes in the superficial gas velocity while polyethylene powder only significantly varied with the distance from the distributor. Average cycle time, dominant cycle time, Kolmogorov entropy and wavelet energy were also calculated from detail coefficients of scale 1–6 decomposed from cleaned pressure fluctuation to investigate flow dynamics at micro- and meso-scales. Similarities and difference of bubbling behavior at different scales for glass beads and polyethylene powder systems from pressure fluctuations were verified from X-ray fluoroscopy measurements. Results show that polyethylene particle systems have quite different bubble properties compared with glass beads particle systems under comparable operating conditions. The combination of statistical, chaos and wavelet analyses proved to be an effective method to characterize multi-scale flow behavior in the gas–solids fluidized bed.

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