A crystallizer is a specialize equipment use in wastewater treatment to concentrate dissolve solids in a liquid stream by inducing the crystallization of these solids. It is employ in various industrial processes, including zero liquid discharge (ZLD) systems, to reduce the volume of liquid waste and recover valuable materials.

Process Description

The crystallization process involves cooling or evaporation of the liquid solution, causing the solutes to form solid crystals. The crystallizer provides the necessary conditions, such as temperature control and nucleation surfaces, to facilitate the crystallization process. The resulting solid crystals can then be separate and collected for further processing or disposal.

Types of Crystallizers

Forced Circulation Crystallizer : In this type, the liquid solution is circulate through a heat exchanger or evaporator to remove water and concentrate the dissolve solids. The circulation is achieve using pumps or agitators, ensuring efficient heat transfer and nucleation.
Batch Crystallizer: A batch crystallizer operates by periodically introducing a liquid solution into a vessel, where crystallization occurs under controll conditions. The vessel may be agitate to enhance the mass transfer and crystallization process.
Continuous Crystallizer: In a continuous crystallizer, the liquid solution is continuously fed into the crystallization vessel, while the concentrate solution and solid crystals are continuously removed. 
Cooling Crystallizer: A cooling crystallizer relies on the cooling of the liquid solution to induce crystallization. By reducing the temperature of the solution, the solubility of the dissolve solids decreases, leading to the formation of crystals.

System Objectives

Concentration of dissolve solids: Crystallizers enable the removal of water from the liquid solution, resulting in a concentrated stream with higher solids content.
Recovery of valuable materials: By selectively crystallizing specific compounds, crystallizers can facilitate the recovery of valuable materials from wastewater, such as salts or metals.
Volume reduction: Crystallization allows for the reduction in the volume of liquid waste, facilitating efficient storage, disposal, or further treatment.
The specific design and operation of a crystallizer depend on factors such as the composition of the wastewater, desired crystal size and purity, and process requirements.

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