CLASSIFICATION OF CONCENTRATED SUSPENSIONS USING INCLINED SETTLERS

Sedimentation vessels with parallel inclined walls are able to clarify or classify particle suspensions more rapidly than conventional settl ers due to their increased surface area and decreased settling distanc es. The use of continuous inclined settlers to classify or separate pa rticles by size and/or density from concentrated suspensions is consid ered. Mass balances are applied to each particle species in order to p redict its concentration in the settler overflow (fine fraction) and s ettler underflow (coarse fraction), given the settler geometry, operat ing conditions, fluid and particle properties, and the particle concen tration and size distribution in the feed. A hindered settling functio n with no adjustable parameters is employed for bidisperse and polydis perse suspensions. Unlike many processes, it is shown that the efficie ncy of the classification process increases with increasing particle c oncentration in the feed, as measured by an increasing fraction of sma ller or slower-settling particles partitioning to the fine fraction ra ther than contaminating the coarse fraction. This is a direct result o f hindered settling, which reduces the settling rate and increases the relative concentration of slower-settling particles in the upper port ion of the vessel. Experimental data are presented for bidisperse susp ensions of glass and acrylic beads and of coal particles and yeast cel ls, and for polydisperse suspensions of polystyrene latex beads. The r esults are in good agreement with the model predictions. Copyright (C) 1996 Elsevier Science Ltd.