Analysis of pressure fluctuations in fluidized beds

Pressure fluctuations were measured in a fluidized bed and evaluated in the frequency domain. The objective of this research was to determine the effect of bed parameters on the power spectra from the corresponding pressure fluctuations. The motivation for this work is to develop pressure fluctuations as a diagnostic tool for fluidized-bed reactors and combustors. Pressure fluctuation data for a range of bed heights, fluidization velocities, particle sizes, particle densities, and bed temperatures were taken to determine the effect of these parameters on the power spectrum. The dominant frequency was a function of the height of the fluidized bed. Secondary peaks were not influenced by the height of the bed, although they did depend on the position of the probe in the bed. Peaks in power spectra were observed to shift in frequency as the gas superficial velocity through the bed was changed. Powders of different classification had distinctive power spectra. Group A powders behaved like first-order linear systems; group B powders showed similarities to second-order linear systems; and group D powders exhibited harmonic behavior in their power spectra. When pressure fluctuations were measured over a temperature range from ambient to above 500 degreesC, power spectra varied little when the ratio of the superficial velocity to the minimum fluidization velocity was held relatively constant.