Hydrocyclones – How They Separate Particles From Liquids

Hydrocyclones are one of the most frequently used pieces of mineral processing equipment. Their basic design relies on pressure from outside to produce a rotary movement in the liquid mixture inside it, causing heavy particles to congregate along its walls before discharging through its bottom outlet.

They Separate Particles

Hydrocyclones are static devices which use centrifugal acceleration to separate particles of different densities from fluid. Dense particles – whether solid or liquid – move towards the outer edge of a vortex while lighter particles migrate towards its central core, with coarser and larger particles leaving via its underflow, while fines travel further uphill before exiting via their apex through centrifugal force and out through its overflow.

Separation performance depends on several factors, including cyclone size, diameter and shape as well as fluid dynamics and particle properties in relation to liquid medium characteristics. Abrasive or dense feed material will likely not be separated effectively with hydrocyclones.

Different studies have explored the effects of particle size and shape on separation. Results have demonstrated that drag forces are proportional to maximum projected area particles along the direction of fluid flow in a hydrocyclone; Kashiwaya et al. investigated this parameter on both single and mixed separations via CFD-DEM coupling technology as well as experimental test methods.

As a measure of separation efficiency, measuring the concentration of “heavies” in the overflow is the ideal way to evaluate hydrocyclone performance. This can be accomplished on either a volumetric percentage basis or, more accurately, using weight measurements.

They Separate Coarse Particles

Hydrocyclones use tangential inlet velocity to spin a suspension inside, creating a descending external swirl flow and isolating heavy components from liquid. Heavier components agglomerate at the walls of the cyclone while lighter finer particles pass out through their top outlet.

Hydrocyclones are among the most frequently employed equipment for separating fine and coarse particles in the pulp and paper industry, thanks to their ease of design, cost effectiveness, ease of operation and long service life without needing much in terms of maintenance or input from operators. Yet even with all their advantages they may still experience performance decline over time.

When troubleshooting issues with hydrocyclones, it can be helpful to understand their operation and the factors affecting their performance. An important consideration in their separation efficiency is pressure applied at their inlet – which has an immediate influence on particle cut point depending on pressure applied, cone diameter size and material type.

Hydrocyclones come equipped with one of three inlet designs: tangential, involute or arc. Test results conducted using all three inlet designs can be seen in Figure 7 and Table 2, wherein arc inlet hydrocyclones consistently outperformed both their counterparts over a wide range of size classification conditions (SC).

They Separate Fine Particles

Hydrocyclones can be used to separate fine particles by using fluid pressure to generate a flow pattern that separates particles based on density and shape. Adjusting pressure levels in the feed line alters the separation point (also called cut point); lower pressure creates coarser cuts while higher pressure produces finer separation.

Hydrocyclones utilize their cone-shaped inner section to create a zone of low pressure, which accelerates particle settling rate. Faster-settling particles migrate toward the wall of the cyclone and exit via its apex opening as underflow, while slower settling particles that are heavier than their surrounding slurry medium are pulled downward by centrifugal force and emerge through their vortex-finder as overflow.

At 6.5 mm from the wall of a cyclone, particle phases at 6.5 mm distance from its wall are measured as the sum of pressure gradient acceleration and drag acceleration, with drag acceleration defined as relative motion between phases. Of all inlets used for classification purposes, C’s stronger drag acceleration field explains its superior classification sharpness at higher feed SCs.

They Separate Water

Hydrocyclones use fluid pressure to generate centrifugal force and flow patterns that can separate particles or droplets from liquid medium. In order for this separation to take place, their density must differ significantly from that of the fluid medium.

A typical design involves injecting feed tangentially at high speed into an upper cylindrical section that joins a conical body, creating a strong fluid movement which forces coarser materials through bottom-axial outlets known as reject sides, and finer ones through top axial tubes known as overflow sides.

Control of cut size can be accomplished by altering feed pressure into the cyclone. Pilot trials usually utilize two valves for adjustment of flow split between outlets until desired d50 value has been met; once this has been determined, one orifice can replace these valves in routine operation.

This equipment is widely utilized in mineral processing to classify particles for recirculation in grinding circuits, distinguish between economic minerals and gangue, separate oil from water in REFINERY AND OFFSHORE OIL INDUSTRIES and remove sand/silt from irrigation or potable water supplies, among many other uses. Furthermore, this equipment can also be used as incremental enrichment to decrease load on more costly separation equipment while improving overall operations economics.