| Hindered-settling columns are versatile gravity concentration devices that have many possible applications. It is desirable for plant operators to have a mathematical model, which integrates all necessary parameters of the column, and predicts complex effects of inter-dependent variables. The model can assist in finding optimum design and operating conditions. For this purpose, several phenomenological models of hindered-settling columns have been developed and investigated. The models are based on the convection-diffusion equation as applied to hindered-settling conditions. Each model includes two parts: a modified form of the Concha and Almendra's hindered-settling equation to predict the settling velocities of particles within the whole range of Reynolds number, and a finite difference solution scheme to perform volume balance of solids between partitioned areas of the column as a function of time.; Simulations were carried out to evaluate column performance as a function of design and operating variables, including column height, teeter water rate, bed height, solids feed rate, solids feed location, fluid temperature, feed size distribution, and particle density. The product size distributions were also studied. The results are presented in terms of fractional recovery (partition) curves. Variations in the fractional recovery curves due to changes in design and operating conditions are quantified using the cut size, the sharpness index, and apparent bypass, which are characteristic parameters that describe the location and shape of a fractional recovery curve. For selected tests, the simulation results are compared with experimental results obtained from a laboratory hindered-settling column. |
