Examples of Realized Continuous Crystallization Processes

A crystallization process has to be designed to meet a number of requirements, for example, particle properties such as particle size and purity. As concerns the purification, a continuously operated crystallization has to deal with the accumulation of impurities in the mother liquor. The drain point for these impurities has to be carefully chosen. It is one of the most underestimated aspect of the process design activity and the source of many errors. Moreover, the process yield is strongly connected with the planning of the process drain points, as is the specific energy consumption and, thus, the success of the process. However, die separation attribute of the unit operation crystallization may not be the best available and one should remain open for competing alternatives. That could be recommendable, for example, in cases of solid solutions, especially with distribution coefficients close to 1, which are not feasible to separate by crystallization at all. 

In most of the cases, lab tests are already sufficient to balance the process design ideas against each other, and besides this function these tests are used to provide all the substance properties needed for the mass and heat balance and the dimensioning of the plant. Only in more complicated processes, additional piloting work may be required. 

Such a strategy is particularly suitable for the isolation of products from fermentation broths. Those processes are called crop processes. There are two crops at least the first crop provides the desired product quality and the second 

Crystallization Basic Concepts and Industrial Applications, First Edition. Edited by Wolfgang Beckmann. 

There are many possibilities to optimize this crop concept for the respective case. For instance, the crystallization in the second crop - if the phase system and the frame conditions allow - can be executed at a lower temperature to minimize the product losses (to be balanced against energy costs). In some of the cases, however, the concentration of impurities or the viscosity may already be too high to still realize the desired product purity within the first crop. In such cases, one can regard the 

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I 76 Examples of Realized Continuous Crystallization Processes Typical situation ... 

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