The sedimentation filters principle is based on gravitational separation. They can be used to clarify the liquid phase or concentrate the solid phase. In gravitational separation process, slurry enters the tank and after retention time, liquid phase will be removed from the top and concentrated solid phase will be discharged from the bottom of the tank. Retention time, tank’s dimension, inlet and outlet speed depend on the slurry properties. If the object of sedimentation filter was clarification, the system is clarifier and if the object of sedimentation filter was concentration of solid phase, the system is thickener. Sedimentation filter types are listed as follow:
High rate thickener
Separation process occur when submerging rate of solid is greater than rising rate of liquid. Clarifier diameters calculate to achieve a proper rising rate of liquid (m/s). This rate is also known as surface load. Surface load is slurry flow rate (m3/h) per 1 m2 surface of clarifier.
Thickener design is based on the required solid concentration in discharge. Thickener diameter is depending to the solid flow rate in a critical concentration. Thickener selection is based on surface (required thickener surface for 1 ton/h solid phase).
Thickener/clarifier is designed in two ways: bridge support or column support. For small thickeners with 30 to 40 meters diameter, paddle and mechanism are assembled on a bridge that moves over the tank. In the thickeners with bigger diameter than 40 meters, paddle and mechanism are assembled on central column and the bridge only uses for maintenance and holding feed well and drain pipe. In small thickeners there is no slope limit (to 45°) but for big thickeners slope limits in range of 2° to 12°.
Lamella clarifier is a conventional clarifier that rotates 55°. By the combination of short sedimentation distance and a slippery surface without friction, separation rate will increase.
Lower space requirement
Decreasing retention time
Optimization of surface proportion of surface of thickener/clarifier
Low heat loss – easy to install insulation
Low water loss (of evaporation) – easy to cover its surface
Easy to transport the unit
Appropriate to install in the plant
Fast and easy installation
When the surface load is high
Lower capital cost
Easy to manufacture special unit
When particles are heavy or large
When slurry is highly concentrated
(When the feed is scummy (like floatation of concentrate