Thickeners

The separation of solids from a liquid by gravity sedimentation has traces to the early days of civilization. The normal practice at those times was to use jars or pits mainly for the clarification of extracted liquids such as wine or olive oil from contaminating insoluble matter. These batch processes required four separate steps:

• Filling the vessel with slurry.

• Leaving the slurry for a predetermined time until the solid matter has settled to the bottom of the vessel.

• Decanting the clarified supernatant from the upper part of the vessel.

• Removing the settled underflow that has accumulated at the bottom of the vessel.

This cycle, depending on solid and liquid properties that effect settling rate, may require long detention times so often several vessels are incorporated in the layout to operate in sequential steps.

The method of operating on a batch process is still practiced in small flow industries but its shortcomings are obvious so once the plants grew larger the need for continuous operation become inevitable. The trend in this direction started at the late 19^th century when heavy duty application such as iron ore taconites, hematite, coal, aluminum hydrate, copper pyrite, phosphates and other beneficiation processes have grown rapidly. The high time for thickeners was in the 60's when the metallurgical industries were booming and sizes of up to 150 m diameter were constructed. Such jumbo thickeners, when centrally driven, require for most demanding application extra heavy duty drive heads some of which reach a continuous operating torque of 3.300.000 Nm.

ВАРІАНТ III