Crystallizers are used to concentrate feed into solid crystals and clean water. Crystallization is a solid-liquid separation technique in which solid crystals are formed from a liquid solution. Crystallizers can eliminate liquid wastes to create zero liquid discharge (ZLD). Crystallization is divided into two stages: primary nucleation and secondary nucleation. Primary nucleation involves the growth of new crystals. Secondary nucleation grows crystals and is the main stage that causes the mass production of crystals. There are evaporative crystallization processes and cooling crystallization processes.
Selecting crystallizers requires an analysis of application requirements. For example, a salt crystallizer processes brine and produces both solid salt crystals and clean water. A continuous cooling crystallizer (CCC) is used to crystallize other types of salts.
Crystallizers can either stand alone or be combined with other technologies, such as evaporators. Steam-driven evaporators remove water from a solution. During evaporation, a product is concentrated by boiling the solvent, generally water. A wastewater concentrator is a specific type of evaporator used to turn waste-saturated industrial wastewater into distilled water for reuse. A typical brine concentrator can recover 95 to 99% of wastewater for reuse.
Crystallizers are suitable for recovering salts from wastewater that can then be used or sold. In this way, a crystallizer maximizes waste stream usage and helps plants meet zero liquid discharge (ZLD) requirements.
Crystallizers are used in manufacturing, chemical processing, mining, power stations, and many other applications.
We possess the know-how and expertise for all types of crystallization equipment: with total or partial classification, involving the recirculation of the magma, with or without settling zones.
Forced circulation crystallizers can be either single or multiple effects and the vapor recompression concept (either thermal or mechanical) is often applied. Usually, they operate from low vacuum to atmosphere pressure. In general, these units are used when crystal size is not of the utmost importance or if crystal grows at a fair rate. Almost any material of construction can be considered for the fabrication of these crystallizers, depending on the application.
Typical products are:
When the problem of scaling impedes the process of concentration, a design similar to the one described above is proposed. This applies to CaSO4 saturated solutions, like fertilizer-grade phosphoric acid, demineralization effluents, and vinasses.
Oslo type crystallizer also called classified-suspension crystallizer is the oldest design developed for the production of large, coarse crystals.
The basic design criteria are twofold:
The classifying crystallization chamber is the lower part of the unit. The upper part is the liquor-vapor separation area where supersaturation is developed by the removal of the solvent (water for most applications). The slightly supersaturated liquor flows down through a central pipe and the supersaturation is relieved by contact with the fluidized bed of crystals. The desupersaturation occurs progressively as the circulating mother liquor moves upwards through the classifying bed before being collected in the top part of the chamber. Then it leaves via the circulating pipe and after the addition of the fresh feed, it passes through the heat exchanger where heat make-up is provided. It is then recycled to the upper part.
Additional devices, such as those described for the forced circulation crystallizer, are of course available.
It is worth bearing in mind that the operating costs of the Oslo-type crystallizer unit are much lower than with any other type when both large and coarse crystals are required. Since crystals are not in contact with any agitation device, the amount of fines to be destroyed is lower and so is the corresponding energy requirement.
This Oslo-type crystallizer (classified – a suspension crystallizer) allows long cycles of production between washing periods.
Typical products are:
• (NH4)2SO4
• Na2SO4
• AgNO3
• Mono ammonium phosphate (MAP)
