The average FC crystallizer evaporates solvent, thus increasing the supersaturation in the process liquor, and causing crystallization to occur. Most conventional FC units operate under vacuum, or at slight super atmospheric pressure. Slurry from the crystallizer vessel is circulated, in plug flow fashion, through the heat exchanger, and returned to the crystallizer vessel again, where its supersaturation is relieved by deposition of material on the crystals present in the slurry. The evaporated solvent is conducted to the vacuum system, where it is condensed and removed. The FC crystallizer is used for general, simple crystallization operations, where large crystal size is not a requirement.