Hydrocyclonen – Improving Efficiency in Material Classification and Separation

Hydrocyclones are used to separate materials through centrifugal force. Light phases with lower densities travel spirally toward the overflow outlet while heavy phases with higher densities move toward the center and are discharged through underflow outlets.

Average OC value curves at overflow outlet illustrate changing trends as Dc increases.

Flow Rate

Feed material is fed tangentially into the hydrocyclone under pressure and causes centrifugal forces to move upward and downward along its conical wall, pushing heavier phases upward and downward in response. With each decrease in diameter comes an increase in speed for maximum separation; concentrated solids exit at the apex.

An appropriate flow rate must be established in order to produce the desired concentration of material in an overflow. Variations in velocity can alter particle trajectories within both inner and outer vortex flows, ultimately altering split ratio.

Bicalho et al have reported that increasing feed flow rates within certain parameters could strengthen centrifugal force fields and increase overall separation efficiency, but exceeding these parameters may reduce effective retention time of particles and drop split ratio. Daarom, proper record keeping must be maintained to identify performance deviations or degradation and assess whether maintenance action must be taken to restore optimal performance.

Pressure

Slurry is introduced tangentially into a cyclone’s cylindrical zone at high velocity and then accelerated by its geometry and pressure to produce an intense centrifugal force, creating separation between light and heavy components of slurry, with heavy particles exiting via overflow from its apex exit while lighter components continue to fall to the base of the cylinder where they are collected.

Increased feed pressure has the effect of increasing separation efficiency and underflow concentration by altering both inner and outer vortex flows, thus producing a higher split ratio.

Excessive turbulence can create erosion within a hydrocyclone that leaves behind wear spirals in its liner and may cause ropeing in its underflow, so regular evaluation of each hydrocyclone’s performance must take place and compared against maintenance records or manufacturer specifications to identify deviations or degradation. Record-keeping helps identify any recurring issues quickly so maintenance staff can plan accordingly.

Cyclone Length

Cyclone length is an essential factor when it comes to improving material classification and separation efficiency, as it determines how much centrifugal force will be applied to particles within it. Generally speaking, the longer its length is, the more complete its separation process becomes.

Large particles are temporarily retarded before entering a cyclone, while smaller ones are accelerated at high speed – leading to low inlet velocity for larger particles, which helps minimize erosion and extend cyclone lifespan.

The ideal length for material separation depends on its desired cut size. When applied to mineral applications, for example, this usually means selecting a cut size in which most solids report to the overflow stream and only some to the underflow stream; typically this target cut size determines which cyclone diameter to use in each application.

Vortex Finder

Vortex finders are an integral component of efficient cyclone separation. They act as the interface between Team Centrifugal force and Team Drag force – similar to tug-of-war between two flags tied at either end of a rope. As Team Centrifugal pulls particles closer towards the shell of the cyclone while Team Drag pushes away.

This explains why inlet section design and cone angle have an effect on classification sharpness. For instance, an arc inlet creates stronger radial acceleration and preclassification effects which assist with maintaining Cc (Figure 17).

Pumps that feed cyclones also play an integral part in its capacity and cutpoint, as their speed alters flow rate and pressure feeding the Cyclone, ultimately altering its separation characteristics; bijvoorbeeld, decreasing pump speed results in coarser cut, while increasing it can produce finer ones; capacity is determined by size of its apex as well.