Nowadays, there is the possibility to combine solar evaporation with modern
salt crystallization for improving salt quality.
Beside normal FC-types there is installed one fluidized-bed crystallizer for
producing a coarse quality as well. The plant is operated as multiple-effect
evaporation unit in sequence. The Oslo-type crystallizer is set as the first
effect ensuring best conditions for crystal growth at the highest temperature.
The plant is fed with concentrated liquor from the solar pond into tank B, from
where the Oslo-type crystallizer gets fed. This tank is operated undersaturated
ensuring crystal-freeness in the feed to the Oslo-type crystallizer, otherwise
the production of coarse crystals is getting endangered. Solution not used for
the Oslo-type overflows into tank C, from where the FC-type crystallizers get
fed. The slurry withdrawal from the FC-type crystallizers is taken from stage
to stage and from the last effect to tank A.
From there the separation station is served which consists of a
hydrocyclone, a washing-thickener and a centrifuge. In the washing thickener,
the highly impure mother liquor is exchanged against the fresh feed liquor,
before the suspension is given to the centrifuge, finally. On the centrifuge
the salt is washed with water, then dried and packed. The separation of the
grain-size product is effected by a special pusher-type centrifuge, ensuring a
soft treatment of this sensitive product.
A plant of this type was erected for the treatment of 60t/h concentrated
liquor from a solar pond on the coast of the Mediterranean Sea. It is producing
2.5t/h grain-size salt of <=2mm mean crystal size and 6.5 t/h of normal
vacuum salt. Per hour it consumes 11t of steam and evaporates 34t of water. By
harvesting the concentrated liquor in special tanks over the summer period, the
plant is able to be operated the entire year.