Crystallizers are machines used to convert wastewater 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 perpetuates growth and is the main stage that causes the mass production of crystals.
Types of Crystallizers
There are three types of crystallization processes:
- cooling (under vacuum or with a heat exchanger)
- reaction or equilibrium displacement
Selecting crystallizers requires an analysis of application requirements. For example, a salt crystallizer processes wastewater and produces both solid salt crystals and clean water. A resin crystallizer allows for the crystallization of flake or amorphous resin pellets. A vertical continuous cooling crystallizer (VCCC) is used to crystallize highly viscous and extremely slowly crystallizing fill masses. Other application-specific crystallizers are also available.
Crystallizers can either stand alone or be combined with other technologies, such as a brine concentrator or evaporator. Steam-driven evaporators remove water from a solution or slurry, but the discharge is still in liquid and not crystal form. During evaporation, a product is concentrated by boiling the solvent, generally water. A brine 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. Evaporators and crystallizers often replace steam hosts when a plant’s original host is lost.
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, petrochemical refining, and electric component fabrication applications.
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