oa South African Journal of Chemical Engineering - Time-series analysis of pressure fluctuations in gas-solid fluidized beds
Fluidization regime is dependent on factors such as particle size, particle density, particle geometry, column geometry, gas density, gas viscosity together with gas velocity. A significant amount of research has been dedicated to the measurement and analysis of pressure fluctuations in a fluidized bed. Identification of each regime could be achieved through time-series analysis of the pressure fluctuation in the time domain, frequency domain as well as state space domain.
The purpose of this work was to focus on the time-series analysis for the characterisation of the different fluidization regimes (particulate, bubbling, slugging and turbulent) in a gas-solid fluidized bed through the use of spectral analysis. The mathematical tool known as the Fast Fourier Transform (FFT) was used to analyse and interpret the pressure fluctuation in the fluidized bed. Experimental measurements were conducted in a single transparent glass column with a column height and diameter of 128 cm and 11 cm respectively. Two different kinds of solids were used: sand particles (particle size: 0.30 mm) and glass beads (particle size: 2.28 mm). The sampling frequency used for pressure measurements in this work was fixed at 500 Hz with a sampling time of 30 minutes.
Results indicated that factors such as bed height, choice of material as well as gas velocity had a strong influence on fluidization regimes. The dominant frequency characteristics were much more evident for the slugging and turbulent regime respectively. It was further observed that a higher bed height led to more pronounced frequency peaks which allowed for easy differentiation between the various fluidization regimes.
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