Characterization of fluidization regimes by analysis of pressure fluctuations in gas-solid fluidized beds.
Date
2017
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Abstract
Fluidized beds are ranked as the top contacting method with the best overall benefits, and have
been used over many years in several industrial applications. Literature indicates that pressure
fluctuations are influenced by variables related to fluidization regimes in a fluidized bed; such
as the bubble size, bubbling rising velocity and the motion of the bed surface (Fan et al., 1981).
Hence several researchers have employed pressure fluctuations to aid in the understanding of
fluidized bed system hydrodynamics.
This study was focused on gas-solid fluidized beds, during aggregative fluidization represented
by the bubbling, slugging and turbulent regimes. Geldart (1973) materials from the
classification were studied in this research; Group A (spent Fluid Cracking Catalyst), Group B
(sand) and Group D (plastic beads). The experimental equipment was composed of an existing
laboratory-scale gas-solid fluidized bed and data acquisition system. Three transparent fluidized
bed columns were investigated; fluidized bed 1 (I.D 5 cm), fluidized bed 2 (I.D 11 cm) and
fluidized bed 3 (I.D 29 cm). The time-series analysis of pressure fluctuation signals were
investigated using the time and frequency domain methods. The pressure fluctuation signal was
converted into the frequency domain by use of the Fast Fourier Transform (FFT).
For increased bed heights the power spectrum was narrower, higher in amplitude, had more
distinct peaks and the dominant frequency was lower, when compared to the lower bed height
for the same material and fluidization regime. Also decreasing dominant frequencies and large
increases in the amplitude of the pressure fluctuation were observed for each increasing
fluidization regime; from the bubbling to slugging and to the turbulent regimes. The research
contribution from this study was realized, as a range of dominant frequencies were successfully
identified for each specific fluidization regime at its respective velocities. The identification of
the transition phase was accomplished with low accuracy from the research contribution. It was
recommended to employ differential pressure measurements for larger columns to increase the
accuracy of data achieved; thereby permitting the comparison of useable power spectra results
for scale-up.
Description
Masters Degree (Chemical Engineering). University of KwaZulu-Natal. Durban, 2018.