Nesans fitch series thickeners consists of the following sub-assemblies

1. Feed-well
2. Rakes
3. Weir launder
4. Thickener tank
5. Underflow removal pump
6. Floc dosing unit
7. Integrated sensors and Automation

The overflow from a Hydrocyclone or a sand washing equipment is introduced into the inlet of the fitch series thickener where optional dilution is done before the slurry stream is taken into the feed well. The flocculant is added here.

The  involute design of the feed-well allows for a laminar flow of the feed slurry so that the flocs are not broken, reducing its efficiency. The dewatering cones attached to the feed-well allows for the even mixing of the feed around the circumference of the feed-well.

Heavier particles formed by the action of flocculating agents enters the transition zone after which they will eventually end up in the compression zone. Water, clear of suspended particles moves upward through the zone of free settling into the clarifier zone.

The weir discharge launder given around the inner edge of the thickener tank at a predetermined height allows the overflowing clear water to exit the thickener.

Solids settled in the bottom cone of the thickener are removed by the movement of the rakes which propels them towards the underflow exit. 

Sensor Integration and Automation

Bed Pressure Sensor:

Turbidity sensor :

The quality of the overflow is monitored with a turbidity sensor which will further increase or decrease the loading rate of the flocculating agent.

Flow meter :

The input slurry flow rate is monitored to keep the handling capacity of the thickener under check and to avoid over loading of the thickener. The underflow flow rate is also monitored to keep the mass-balance of the thickener.

Rake torque Sensor :

The Rake arm of the thickener is suspended from above the feedwell of the thickener. Temporary plant shut-downs or power failure will allow free solids to settle and undergo compaction when the thickener is started again. There is a chance the rakes may fail due to overload. In order to avoid a possible scenario, the torque of the rake drive gearbox is monitored closely. Should the torque increases above the pre-determined limit, the entire rake assembly is raised up to avoid failure of the gearbox. Once the torque is restored, the rakes are again lowered back.

Underflow density :

The underflow density is monitored to make sure the compressed solids have reached their required density. The retention time inside the thickener is selected based on the underflow density of the solids.