HYDRODYNAMICS OF A FLUIDIZED-BED FLOTATION DRYER - DETERMINATION OF THE CHARACTERISTIC FLUIDIZATION RATES OF CORN AND SAND MIXTURES

This paper presents a study on the hydrodynamic behaviour of a fluidized bed dryer containing two kinds of solids (corn kernels and sand particles) with a size ratio of 25 and density ratio about 0.45. For corn-to-sand weight ratio above 0.14, the pressure drop vs gaz velocity curve of the system shows four regions, corresponding respectively to fixed bed, fully segregated, partially segregated and completely fluidized beds. This result is confirmed by the measure of the axial concentration profiles of corn in the bed. Transitions between the states occur for three characteristic velocities which have been identified: the initial fluidization velocity (U(fi)), the apparent fluidization velocity (U(fa)) and the complete fluidization velocity (U(fc)) of the binary system. U(fi) is practically independent of the corn-to-sand weight ratio, while U(fa) and U(fc) increase monotonically with this parameter. Correlations have been proposed for these velocities.