(255e) Characterization of Gas-Solid Fluidization for Fine Powders - A New Characteristic Fluidization Gas Velocity

Fluidization of over 100 Geldart group C and A/C powder samples with various flow properties were studied by measuring pressure drops and bed expansion ratios with respect to gas velocities. It was found that bed expansion ratio associates closely with the fluidization of fine powders. As a result, a new characteristic velocity, breakthrough fluidization gas velocity (Ubf), was proposed to demarcate the transition between poor and smooth fluidization. Ubf was defined as the gas velocity at which the bed expansion ratio has the highest rate of increase. Therefore Ubf can be identified through locating the inflection point on the plot of bed expansion ratio with respect to superficial gas velocity. Ubf is different from other characteristic gas velocities because it is developed from bed expansion while others are based on pressure drop measurement and/or force balance. Ubf is able to characterize the fluidizability of Geldart group C and A/C powders well, but not necessarily for groups A, B and D powders. The validity has been confirmed by comparing it with angle of repose. Based on Ubf, it is promising to develop a practical and applicable powder characterization technique, which is desirable for applications where the fluidization of fine powders is required.