CMD Gears – perfecting thickening and clarification

CLARIFICATION AND THICKENING

CMD Gears – perfecting thickening and clarification

CMD Gears is the French market leader in mechanical power transmission. In the phosphate industry, the company enjoys an excellent reputation for its drive heads used in thickeners and clarifiers. These provide the main rotational and translational movement for the mixing rake in large settling tanks several tens of meters in diameter. CMD’s durable and reliable drive heads are based on DURAND® gearboxes, featuring classic ‘Archimedes’ worm drive geometry (ZA profile), and are particularly suitable for low-speed operation. Robustness and precision are essential for the proper functioning of these installations.

Sedimentation – a natural phenomenon

Settling is a liquid-solid separation technique based on sedimentation. This phenomenon allows suspended particles to settle from a liquid under gravitation.

During settling by gravity, suspended matter sinks to the bottom of tanks where it forms a sludge. This is then collected by pumping it from the bottom of the (usually conical shaped) tank. The exact process used differs depending on whether the aim is to increase the concentration of solids (thickening) or to obtain a clear liquid from a diluted suspension (clarification).

Recovering solids and clarified water

Phosphate rock sourced from a variety of deposits is used in the manufacture of fertilizers. Globally, major producers specialise in phosphate extraction, processing and sales.

Phosphate fertilizer production consumes large quantities of water, exactly how much depending on the ore type and processing operations such as froth flotation. To address this problem and avoid excessive consumption, increasing emphasis is being placed on water recycling during settling.

Typically, smaller particles (fines) and flotation rejects are sent to the settlers during beneficiation – these unts being used to thicken the sludge and recover the clarified water. As already stated, recovery is based on particle sedimentation, with the falling speed of particles varying according to their density.

Over time, particles move to the bottom of the settler and the clear liquid rises to the surface. The settling operations is improved by adding a flocculent to the feed to speed up the sedimentation process. Decantation then provides both clear liquid flows and a solids-rich sludge.

Once processed, the phosphate rock concentrate is then delivered to the chemical plant to be transformed into phosphoric acid (merchant-grade or purified) and finished fertilizers.

CMD Gears – the go-to company for drive heads

CMD Gears has been designing and manufacturing drive heads for the phosphate industry for over thirty years. Nearly two hundred systems have already been installed, mainly in North Africa and Asia.

CMD’s drive head systems (Figure 1) are installed above settling tanks and are used to rotate and move a rake (a shaft fitted with blades) up and down, thereby agitating the slurry stored within the tank. Incorporating worm gear reducers based on the DURAND® ZA profile, CMD’s drive heads combine maximum load capacity with an exceptionally long service life.