(201e) Vibration Propagation in a Gas Fluidized Bed of Fine Aeratable Fcc Powder

Fluidization behaviour of a fine aeratable FCC powder assisted by vibration was studied in a 85 mm ID transparent perspex column. The parameters of vibration which have been investigated are the peak acceleration value and the frequency. Three different acceleration levels (0.5, 1 and 2 g) were tested . Frequency was varied in the range between 7 and 200 Hz. Four different bed mass values between 0.3 and 1.2 kg, corresponding to 4 different bed heights were tested. Fluidization experiments show significantly different behaviours with the change of the bed height especially under fluidized conditions. The most significant variations regard the maximum bed expansion, the intensity of the deviation between the bed weight pressure drop and the measured pressure drop that are typical of vibrated fluidization, the onset of bubbling conditions. At fixed bed height, local pressure drops may change along the column. All these phenomena may indirectly be explained by vibration attenuation phenomena along the bed. In this work a direct observation of these attenuation phenomena has been pursued by direct observation of oscillation of the bed surface at different bed heights. Time series of the position of the oscillating column wall and those of the oscillating bed height were obtained by means of a cross correlation technique applied to sequences of digitised images of the bed taken with the help of a high speed video camera. These time series were compared to characterize the dynamic response of the bed as a function of bed height and vibration intensity.