Batch vacuum crystallizers are used for applications with very low operating temperatures that can only be achieved by very high vacuum, applications involving relatively small amounts of materials, and applications where the material being processed must be handled on less than a continuous basis. Batch vacuum crystallizers are a convenient and economical choice for these special cases.
Cycles on batch equipment typically range from two to eight hours, not including loading and unloading time. At the conclusion of the cycle, the material is deposited in an agitated tank from which it is removed on either a batch or continuous basis for separation and drying. The entire cycle can be automated.
When the material is cooled through a very wide temperature range or to a final temperature which requires very high vacuum, a large ejector or booster compresses the vapor to a pressure high enough for condensation with available cooling water. In such cases, the batch vacuum crystallizer steam economy is approached only by multiple stage continuous equipment of five or more stages.
An added advantage of the batch vacuum type of crystallizer is its capacity for self-cleaning, which is particularly helpful when dealing with materials prone to grow on the walls of continuous crystallization equipment.