Hydrocyclones are among the easiest pieces of mineral processing equipment, often operating without needing maintenance or attention from anyone in operation.Cyclones remain highly effective separation tools despite their intricate fluid mechanisms and structural configurations that affect separation performance. This article will give an overview of their operation as well as possible troubleshooting steps when they don’t perform as designed.
They Separate Coarse Particles
Hydrocyclones’ main purpose is the separation of coarse from fine particles. Centrifugal force applied to its inner structure ensures this separation; heavier particles tend to move downward into its swirling flow while finer ones move more towards its edge, with coarse particles eventually discharging through a bottom spigot liner or apex while finer ones move toward an overflow and into an upper overflow chamber.
Movement characteristics within a hydrocyclone determine its separation effect, and researchers have explored this aspect to increase it. Researchers, led by Zhang, conducted extensive tests to understand particle movement behavior so as to improve this cyclone’s separation effect. Zhang discovered that under high-concentration feeding conditions, fine and medium particles with small densities could easily enter the overflow while large-density fine and coarse particles could enter through interior swirling flows and be discharged through its outlet as overflow.
An air core forms in the center of a cyclone when liquid is introduced tangentially into its cylindrical chamber, producing an intense swirling vortex. A cyclone has an axial bottom outlet with restricted access that restricts all but a portion of its liquid from flowing out. Once inside, its flow countercurrently towards its top outlet gives rise to an air core at the core.
Hydrocyclones secondary-cylindrical section sizes have a significant influence on particle circulation flow region and separation performance, with perfection values decreasing monotonically as the diameter of this section grows. Due to more coarse particles circulating within the swirling flow of a cyclone, misplacement of these particles occurs, leading to their dispersal across a larger area. Encompassing more coarse particles reduces separation performance and inhibits formation of an effective circular-flow pattern inside of the cyclone, and hampers its separation capabilities. The separation performance achieved is satisfactory; however, perfection values do not meet expectations due to rotational resistance and viscosity of cyclone liquid influencing particle velocity distribution and movement trajectory.
They Separate Fine Particles
Hydrocyclones use centrifugal force and differential fluid flow to effectively separate fine from coarse particles. Centrifugal force is created by directing inlet fluid tangentially toward the wall of the cylinder, creating circular movement within its liquid that causes heavy particles to move outward and aggregate before lighter ones spiral down its wall and out the top overflow opening of the hydrocyclone.
Hydrocyclone separation efficiency depends heavily on its structure design, including the dimensions of its vortex finder, overflow and underflow openings and size of cyclone. Furthermore, larger diameters generally yield better separation performance.
Hydrocyclones are often utilized in mineral applications, like producing C-33 concrete sand, to control what size material exits the comminution circuit. Different ore types have differing liberation sizes which must be monitored closely in order to create an economically feasible product.
Pressure drop, the amount of energy it takes for particles to move through a hydrocyclone, is an integral component of its control. Varying its inlet pressure can dramatically change separation efficiency – for instance if pressure is set lower than target more fines will report to underflow leading to coarser cut points; conversely if pressure exceeds target more fines will report into overflow leading to reduced d50 values and finer separation.
Density of feed material can have an enormous effect on Hydrocyclone separations. A higher density can result in coarser cuts while lower densities produce finer cuts; to select an optimum density feed solution it is therefore essential that one understands their application’s objective and choose a feed density according to this.
Adjusting the spigot diameter allows for adjustment in bypass fines sent directly to the overflow, increasing or decreasing their flow directly towards it and decreasing what goes back into cyclone for further processing.
They Separate Liquids
Hydrocyclones separate liquids from fine particles by creating a whirling action that throws heavier material against the inner wall of a cylinder while lighter material moves outward and downward. This separation method works best when solids have diameters greater than 10 microns and are spherical in shape; however, their efficiency varies with conditions; for instance, as concentration of slurry increases so too does resistance against centrifugal forces from particles increasing their size and number.
Fluid entering the cyclone from a pump must overcome resistance; this causes pressure drops and an increase in radial pressure gradient, ultimately resulting in interference sedimentation states between particles and fluid. Therefore, using low viscosity drilling fluid is important – this allows particles of different sizes to settle at their own rates without becoming trapped between fluid and particles.
Feed density is another critical element to consider in hydrocyclone performance. To meet target cut sizes, feed density must coincide with target cut size, which can be accomplished either through changing density of feed or altering pressure at inlet – lower pressure sends more fines into overflow, creating coarser cut size; higher pressure sends fines into underflow for finer cuts.
Hydrocyclones are widely utilized to control what size material exits comminution circuits for hard rock and precious metal applications. When applied in these contexts, instantaneous fluid inflow to a hydrocyclone equals total instantaneous light particle flow plus heavy particle flow; heavy particles will move more rapidly than light ones and accumulate at the top overflow of the hydrocyclone.
Heavy materials can then be removed from the system. Any remaining fluid mixture in the cyclone will then be pumped out through its bottom outlet, known as an Apex, via a vortex finder pipe.
They Separate Oils
Hydrocyclones have become an innovative solution to the challenge of separating oily particles from coarse material. A special form of the equipment has been designed that utilizes shear force to separate droplets of oil from liquid medium. This technology can be applied in metal working to separate lubricants from cooling water or drilling operations to remove sand and clay from mud.
Hydrocyclones differ from other mineral processing equipment in that they feature few moving parts and depend on geometry and fluid pressure to perform separation processes. They’re designed to be simple yet reliable pieces of machinery that often operate for years without much in terms of maintenance costs – yet many users don’t know how to troubleshoot a hydrocyclone when something doesn’t go as expected.
One of the key challenges associated with hydrocyclones is entrainment. When coarse material is separated from fines, some heavier materials will be carried into the overflow while others remain caught underflow due to the complex internal flow field of a hydrocyclone. Connecting multiple cyclones together may help solve this issue but requires additional pumps, pipelines and investment costs as well.
As such, it is vitally important that one understands how a hydrocyclone operates and its separating mechanism works. For a particle to exit through its overflow and be discharged into its underflow, they must migrate towards positions where centrifugal force exceeds drag force – these three areas can be identified on radial velocity contours within the hydrocyclone itself; first near its sidewall where axial velocity is negative so liquid flows downward towards its underflow.
The second area lies at the middle of the conical section, where axial velocity is positive and liquid moves upward into an overflow. Here is where most separating takes place. Finally, at the apex of the cone there is negative axial velocity discharged back out and shear effects help concentrate heavy phases to be released through it.