FREQUENCY-ANALYSIS OF PRESSURE FLUCTUATION IN FLUIDIZED-BED PLENUM

Pressure fluctuations in the plenum chamber of a solid-gas fluidized bed were measured and analyzed in order to develop a method for the diagnosis of fluidization conditions. Power spectral density functions obtained by FFT analysis of the pressure fluctuation data had three principal frequencies. These frequencies were compared with the bubble eruption frequency observed at the bed surface and the bubble generation frequency, which was obtained by an optic fiber probe installed above the distributor opening, and two of the three frequencies were found to agree well respectively with the obtained frequencies of bubble generation and of eruption. The third principal frequency was judged to be a natural frequency of the fluidized bed, since the frequency depended on the particle content in the fluidized bed and on the plenum volume. The frequency corresponding to bubble generation was observed to be influenced significantly by the natural frequency of the fluidized bed when the natural frequency had a low value.