Hydrocyclones

Hydrocyclones were invented in the late 1800s and became widely used in mineral processing because they are relatively inexpensive, process high volumes, take up minimal floor space and have no moving parts.

Hydrocyclones are commonly used for desliming, dewatering and sizing -4mesh (5mm) particles. They can be used in industries such as sand, aggregates, coal, industrial minerals, hard rock mining and more. The use of Hydrocyclones in washing and stockpiling is common in the construction aggregate industry. Desliming prior to Classification Tanks and Screw Washers can significantly improve the performance of these devices in high fines situations. Separators™ provide consistent density feed to Attrition Cells in Frac Sand.

For mineral applications such as in hard rock and precious metals processing, Cyclones are the most common equipment to control what size of materials exit the comminution (ball milling) circuit. In these applications, it is the fine fraction in the overflow that is the product. Different ores have different liberation sizes, so Hydrocyclones are configured in many different ways.

Alternative linings, such as polyurethanes and ceramics, are available for different chemistries (such as where amines are present) and for handling highly abrasive materials. Hydrocyclones can also be made from cast hard metals such as ni-hard and hi-chrome. These designs are often used in processes known as heavy media for coal and iron ore, etc.

Hydrocyclones also find use in pharmaceuticals; agricultural applications, such as sand/manure separation; pulp and paper; potable water and wastewater treatment systems; degritting of spray water; etc.

In Aggregate applications, typical recovery of 2.7 specific gravity particles is +200 mesh (75µm) at 2.7 SG; in typical Fines Recovery applications, Hydrocyclones capture down to 400 mesh (38µm) at 2.7 SG; and in specialty applications, recoveries are possible down to 625 mesh (20µm) at 2.7 SG.

How Hydrocyclones Work

Slurry enters the feed inlet at a designated pressure and volume. Independent of the shape or configuration of the inlet, slurry follows the fall of the upper cylinder in a rotating action. Resultant centrifugal forces send coarser material to the outer wall to travel downward and be further accelerated in the conical sections. These coarser fractions then exit through the apex, or spigot, at the bottom of the Hydrocyclone. Finer fractions remain rotating with the fluid in the inner core and are removed upward by an air core.

The air core is formed at the spigot/apex as air is drawn in to the Hydrocyclone. The vortex finder provides a pathway for the air to exit the body of the Hydrocyclone. As the air flows through the vortex finder, the fluids and finer fractions are dragged along to perform the classification of materials. The air core is important for the proper operation of the cyclone. If the air core is not formed due to excessive solids discharge, called roping, the cyclone will not efficiently classify the slurry. The apex/spigot is sized for the expect range of solids. Significant process changes may require a resizing in the spigot/apex.

McLanahan has collected field data from hundreds of applications, allowing process engineers to make the accurate selection of size and configuration for each application using computer simulations. Performance is influenced by the size of the unit and its operating pressure, as well as the inlet area, vortex finder diameter, underflow and overflow diameters, cylindrical sections and cone angle.