Abstract

In the industrial processes that employ the fluidized bed technology (gasification of coal or biomasses, polymerization, etc.), solids of various kinds are simultaneously subjected to fluidization. Due to the fact that solids that differ in density and/or size differently react to the frictional force exerted by the gas stream, mixtures of two solids tend to form, when fluidized, segregated layers rich in either of their components. A peculiar case, in this frame, is that of homogeneous mixtures whose denser component is also the smaller one and achieves the fluidized state at the bottom of the column, while the other solid, bigger and lighter, forms a packed layer on top of it.With reference to this special type of binary systems, several series of experiments are presented that provide their initial and final fluidization velocities at varying composition. Following what done in a recent study on beds of two solids differing in density or size, it is shown that the theoretical equations for calculating uif and uff keep their validity even when applied to mixtures that exhibit an unusual fluidization pattern. Calculated values of the initial and final fluidization velocities are characterized by a low error level, fully comparable with that encountered with other types of binary beds.