Computational modelling and analysis of the flow and performance in hydrocyclones

Abstract

Hydrocyclones have been widely used to separate particles by size in many industries. Their flows are complicated and involve multiple phases: liquid, gas, and particles of different sizes and densities. A two fluid model, facilitated with the mixture model, has been used to study the flow in hydrocyclones under wide range of conditions and used here to study the effects of geometrical configuration and material properties of cyclones operated at different feed solids concentrations. The variables considered include geometrical configurations such as dimensions and shape of body, cone and vortex finder as well as particle density.

The outcome shows a smaller cyclone results in an increased cut size, decreased pressure drop, sharper separation and higher water split. Both large and small spigot diameters lead to poor separation performances. Accordingly, an optimum spigot diameter can be identified depending on feed solids concentration. It is also shown that for all considered hydrocyclones, a better separation performance can be achieved by the operation at lower feed solid concentration.

Further research shows that cyclone performance is sensitive to both length and shape of conical section. A longer conical section leads to decreased inlet pressure drop, d50, and Ep, and an increased water split. When cone shape varies from concave to convex, a compromise optimum performance for the cyclone with a convex cone is observed with a minimum Ep and relatively small pressure drop and water split. A new hydrocyclone featured with a long convex cone is then proposed which can improve the performance of the conventional cyclone. The keycharacteristics of flow in a hydrocyclone are then investigated when vortex finder geometry including diameter length and shape varies. It has been shown that a compromise optimum performance can be identified with relatively small inlet pressure drop, Ep, and water split.

Discussion is then extended to flow behaviour analysis under the effect of different density fractions. The origin of flow pattern and the motion of coal particles have been predicted and discussed. The effect of coal density variation on operational conditions and performance of the large diameter hydrocyclones are also studied in this work.