This optional washing-thickener is used for a counter-current wash of suspended solids settling by gravity against the solids-free liquor overflow from the salt wash tank’s settling section. By this counter-current wash a part of the particulates and a major portion of the Gypsum are removed from the NaCl slurry with the washing-thickener overflow, due to the density difference between the undesirable particles and the salt crystals (the salt is heavier). This overflow is collected in the clarification zone of the salt wash tank. The fines are then removed from the system with the solids purge as mentioned above.

The underflow of the washing-thickener, now containing a much-reduced concentration of foreign particles, or the underflow of the hydrocyclones is fed to the centrifuge. Here, the suspension is separated into crystals and centrate. The crystal cake is washed with water before it leaves the centrifuge basket. The wash water largely displaces the liquor (which contains soluble impurities) which remains on the crystal surfaces.

Pusher centrifuge for 50 mt/hr salt in a salt wash factory

The amount of wash water used corresponds to the amount of liquid that leaves as part of the system purge (the sludge from the salt wash tank). The amount of liquid purged from the system is set so as to maintain a certain maximum concentration for the impurities in the wash. The centrifuged and washed crystals are fed to the dryer and packing stations.

Read more