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

This paper presents a study on the hydrodynamic behaviour of a fluidiz ed bed dryer containing two kinds of solids (corn kernels and sand par ticles) 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 cu rve of the system shows four regions, corresponding respectively to fi xed bed, fully segregated, partially segregated and completely fluidiz ed beds. This result is confirmed by the measure of the axial concentr ation profiles of corn in the bed. Transitions between the states occu r for three characteristic velocities which have been identified: the initial fluidization velocity (U(fi)), the apparent fluidization veloc ity (U(fa)) and the complete fluidization velocity (U(fc)) of the bina ry system. U(fi) is practically independent of the corn-to-sand weight ratio, while U(fa) and U(fc) increase monotonically with this paramet er. Correlations have been proposed for these velocities.