Minimum fluidization velocity and defluidization behavior of binary-solid liquid-fluidized beds

The minimum fluidization behavior of five different binary-solid systems with a wide range of composition is experimentally investigated by carrying out slow defluidization of an initially fluidized bed. The size ratios of these binaries vary from 4 to 10 while their buoyed-density ratios vary from 0.22 to 0.52 such that their larger components are lighter and smaller ones are denser. The difference in the physical properties of the two constituent solid phases of the fluidized bed is found to strongly influence the evolution of the packing structure, and consequently the minimum fluidization velocity during the slow defluidization process. For binaries with the same size ratio, segregation increases with the decrease in their buoyed-density ratios. On the other hand, even for binaries with large difference in their densities, increasing the size ratio enhances the mixing. Depending upon the composition of the bed, a completely mixed defluidized structure sometimes develops for high size-ratio binaries. Finally, a simple correlation is proposed that can better describe the present minimum fluidization velocity data than other existing correlations. (C) 2002 Elsevier Science B.V. All rights reserved.