Hydrocyclones For Efficient Liquid Solid Separation

Hydrocyclones are designed to enhance separation performance while simultaneously lowering energy consumption by altering fluid flow within the device.

Primary separation takes place in the cylindrical section of a cyclone before particles enter the conical section for additional separation processes that depend upon feed density.

Cyclone Geometry

A cyclone is a circular piece of equipment that uses centrifugal force to separate larger particles or droplets from a medium. When its centrifugal force exceeds drag force of fluids, larger or denser particles leave through an upper outlet at the top, while finer or rejected particles exit via lower reject outlets at the base.

Tangential inlet designs promote strong vortex formation, increasing separation efficiency. Furthermore, the design prevents short circuit flow which occurs when high velocity gas enters the separator.

For maximum separation efficiency, the body/barrel of a cyclone should be appropriately sized to ensure optimal separation efficiency. To determine this, look for a slight fanning spray as material exits the apex of the cyclone; this indicates it has been properly sized. If instead material leaks out from below your separator instead, either increase feed pressure/flow or decrease cut size (i.e. coarsen it up).

Overflow Slits

Design of overflow slits has an enormous influence on hydrocyclone separation efficiency and split ratio. In general, performance increases with increasing overflow slit width and decreasing underflow slit width.

When fed into a cyclone, slurry rotates within its cylindrical walls creating centrifugal force to sort materials by density. Heavy particles collide against the wall and are pulled down through an outflow pipe called vortex finder before exiting through an underflow outlet pipe; heavy ones remain trapped against it and thus accumulate there until being overflown via vortex finder or the vortex finder outflow pipe.

For optimal efficiency of a hydrocyclone, an optimal ratio between axial and tangential velocity must be attained in order to minimize turbulence intensity and energy losses within its walls as well as enable light particles to access sufficient centrifugal force to reach their overflow outlet.

Orifice Angles

When fed tangentially into a cyclone cylinder, its spinning action converts liquid velocity into centrifugal force that pulls heavier particles toward the wall while lighter finer particles agglomerate and spiral upward to exit through its top overflow outlet; heavier coarser particles then fall backward into its bottom reject outlet with some liquid through an extension tube (called vortex finder).

Hydrocyclone separation can be made more effective using non-shear flow patterns that minimize shear forces; shear-free designs may offer other advantages over traditional media filtration such as increased coolant life. When designing the system, however, shear must also be considered.

Axial Velocity Distribution

When centrifugal force can surpass friction forces experienced by fluid, heavy particles are separated from liquid and exit through an axial bottom outlet (underflow) while lighter liquids enter through a top outlet of a hydrocyclone (overflow).

A cyclone features two outlets on its axial axis; one on the bottom known as “reject side,” and another larger outlet at the top known as “overflow side.” Tangential injection into its cylindrical chamber creates a swirling flow pattern; discharge from overflow side goes through an axial pipe projecting out from apex of cyclone.

However, inherent fluid flow characteristics lead to imperfect separation and energy loss regardless of geometry. Aiming at optimal design, various fluid flow enhancement designs have been proposed and tested – such as inserting a center body9, inner cone11, double overflow pipes12-13, slit cone14 and overflow cap15 for example; all have shown to reduce air core diameter while increasing particle size classification performance.