Different Types of Classifier Equipment Based on Working Principle

Posted on 10 April, 2021 by Chanderpur Group

Air classifiers are widely popular in mineral processing, cement manufacturing, solid waste gasification etc. to separate finer sized particles which is not possible using screens. Several kinds of classifier equipment are available that varies in principle and operation.

Gravitational Air Classifiers

These classifiers use gravitational force to separate coarser particles of size up to 150 microns which are collected at the bottom in response to gravity. A stream of air throws finer sized particles out, thereby, accomplishing separation.

Fluidized Beds Air Classifiers

The particle separation can be narrowed down to a smaller size using fluidized bed classifiers. The particles are separated based their settling velocities. The heavier particles would settle down first and lighter particles remain suspended for long time creating a gradient of varying sized particles. An upward water stream is injected to separate some particles allowing others to settle down.

Inertial Air Classifier

The setup for this kind of classifier consists of an inlet pipe inclined at 45˚ on an outlet pipe. When the air-particle mixture passes to the outlet, the fine particles stay in the air due to abrupt change in the angle while coarse ones fall straight down towards the discharge pipe. A series of separations occur inside the chamber causing varying sized particles to separate due to secondary air flow. A separation in the range of 40-100 microns can be achieved.

Centrifugal Air Classifiers

This method employs tangential pipes or rotating blades to create a stable centrifugal motion which results in particle separation. The particles up to size 50-1000 micron may be separated using this technique.

Cyclone Air Classifiers

A conventional cyclone design aims to segregate as much particles as possible from the air using a descending vortex. Another design of this classifier equipment, however, uses cyclone design to separate ultrafine particles in the range of 10-50 microns. An ascending vortex in addition to descending vortex is introduced for separating particles in the finer range.

Gyrotor Air Classifier

This design is used in combination with a grinding mill and helps in customizing the product as well as increasing efficiency. A multi-vaned rotor mounted on a vertical shaft is used to move the discharge form the mill to the bottom of the classifier. The use of centrifugal force removes the coarse particles while the fine particles remain there for collection. A final size of 35 micron or smaller may be obtained.