Hydrocyclones – Effective Separation for Enhanced Processing

Hydrocyclones use liquid velocity to convert into rotary motion, with heavier or denser particles spiralling around the inner wall until exiting through a restricted axial bottom outlet as underflow, while finer particles exit via an axial top outlet as overflow.

Separation efficiency in cyclones depends on several key design and operating variables, which will be discussed herein as factors impacting grade separation efficiency (GSE).

Size and Density

Hydrocyclones use size and density to distinguish materials. Heavier particles become trapped against the walls, then exit through an underflow outlet at the bottom. Lighter finer particles remain suspended near the top and are discharged via overflow outlets (also called spigots) at varying heights depending on downstream application needs.

Separation performance in cyclones depends upon its internal flow field, which can be adjusted through optimizing its structure or changing operating parameters. Feed flow rate and pressure difference across the cyclone have particular influence over centrifugal force generated.

Consistency between inlet pressure and feed flow rate helps minimize particle residence time in a cyclone, and selecting one with a large apex diameter helps minimize risk of roping which occurs when material enters both overflow and underflow outlets simultaneously.

Pressure Drop

Hydrocyclones can become blocked with solid contaminants, creating serious operational and equipment issues like feed pumps. Regular inspection of their liners for signs of wear is key in helping decrease this risk.

To achieve an efficient separation process, the diameter of a cyclone must be carefully selected according to its application. Furthermore, changing flow rates or tons per hour (tph) may alter its cut point and thus affect efficiency levels.

As soon as slurry enters a cyclone, it is propelled into rotation by centrifugal force and begins forming a vortex inside its cylindrical chamber. Heavier particles fall down the barrel section to exit through its apex while lighter materials are drawn into the center of the vortex by inward fluid motion and transported towards its overflow outlet.

Slurry Concentration

Hydrocyclone separation requires a certain amount of internal pressure that must be created within the cyclone to achieve success. Slurry’s density, volume fed into it and size all play an integral role in creating this centrifugal force – pushing heavier particles towards the center rather than toward its apex and out the overflow outlet.

Low feed concentration can result in coarser separation while high feed pressure produces finer results. Furthermore, inlet size can have a great impact on separation outcomes; larger inlets increase capacity.

Yang et al. conducted research to evaluate the separation performance of hydrocyclones with various main diameters by employing both simulation and experiment methods. Their results demonstrated that when used to separate slurry into smaller Dc hydrocyclones at overflow outlet concentration gradually increases while it decreases at farther areas away from cyclone apex, suggesting these hydrocyclones achieve improved separation efficiency.

Vortex Finder

Feed material is introduced tangentially into the cyclone and spun to generate centrifugal force which separates heavier particles from lighter ones, with lighter ones exiting through an overflow outlet while coarser, heavier particles exit via an underflow outlet.

Particle cut size in a hydrocyclone is affected by many variables, such as its inlet velocity, short-circuit flow rate ratios and separation efficiency. To assess these influences on particle cut size in hydrocyclones, a model using Reynolds Stress analysis and Volume of Fluid was utilized to predict its separation process.

Results indicated that inlet velocity and Vortex Finder length have the greatest effect on particle cut size. A longer Vortex Finder could reduce pressure drop and axial/tangential/radial velocities but would increase fluctuations of AVWZ; thicker walls could still help reduce these factors, yet have less of an effect on circulation flow in pre-separation spaces.