In a vacuum crystallizer, super-saturation is obtained by adiabatic evaporative cooling. When the warm saturated solution is introduced into the crystallizer, due to high vacuum the solution undergoes flashing. A part of the solvent gets evaporated, thereby causing the cooling of the solution. From the resulting super-saturation, crystals are produced.
It is a cylindrical vessel, attached with a condenser and high vacuum is created using a vacuum system (Steam/Power). The vacuum so created must correspond to the boiling point of the solution, but lower than the feed temperature. A hot saturated solution is fed into the crystallizer; solution undergoes flashing, which results in evaporation of the solvent. This process is allowed adiabatically so that the crystallizer body is cooled. The resultant cooling causes super-saturation and crystallization. The evaporation of the solvent enhances the yield. Flashing of the solution in the crystallizer leads to ebullition, which keeps the crystals in suspension until they become large enough to fall into the discharge pipe, the product is collected and sent to settler followed by centrifuge to obtain crystals. The filtrate returns to the feed.