Influence of binary and ternary particle systems on the spouting stability in a three-dimensional prismatic spouted bed

Abstract

In this contribution, a three-dimensional prismatic spouted bed for coating and granulation purposes is investigated. To determine the influence of a particle size distribution on the spouting behavior, binary and ternary mixtures of different particle sizes (γ-Al2O3 particles) are used. The stability is quantified using the Fourier transforms of the pressure drop signals. The stability range of binary and ternary systems differs from the monodisperse systems. Both the lower and the upper velocity limits of stable spouting can be described by a power function dependent on the Reynolds number and the Archimedes number. A larger Archimedes number results in an increased Reynolds interval size of stable spouting, which refers to a larger size of the velocity interval. This correlation was found to be not valid for the mass equivalent mixture of three particle fractions where no stable spouting state was obtained. In addition, clustering and segregation effects were observed: Coarse particles accumulate in the spout and fine particles in the annulus region of the regarded prismatic spouted bed in case of the instable spouting regime. This is problematic for granulation and coating processes as a homogeneous droplet distribution and a proper mixing between spraying and drying zones is disabled if some particle fractions are inhibited to pass the spray zone.