The formation of a suspension bed on dual flow distributors

The formation of suspension beds on a dual flow distributor was studied using mono-sized particles (group D, Geldart, 1973). Three stages are experienced during the formation of a suspension bed: The induced, the growing and the final stage. The discharge mechanisms are raining, weeping, dumping (I) and dumping (II). The operating variables of a suspension bed are the opening ratio of the distributor (m), the solids feeding rate (F), the normalised air velocity through the hole (U_o/U_t, where U_t is the terminal velocity of a single sphere in the air), the ratio of the diameter of the hole of the perforated plate to the size of the particle (d_o/d_p), and the density of the particles (ρ_p). Their influences on the formation of a suspension bed were examined. Five different types of beds were formed depending on the combination of the operating variables; these can be catagorised as dilute beds, oscillating shallow beds, bubbling beds, slugging beds and flooding beds. The ranges for stable operating conditions using 2-mm polystyrene spheres are mapped, which have the following ranges: 0.31≤m≤0.52; 0.082 kg/s·m²≤F≤0.455 kg/s·m² and 0.8≤U_o/U_t≤1.25. A model was developed to simulate the growth of the bed in terms of the net pressure drop across the bed. There is a good qualitative agreement between the experimental pressure drop and model predictions.