Basic Concept and Processing Modes of Crystallization

Crystallization is a thermal, phase-forming separation process from an amorphous phase, at least one solid crystalline phase is formed by phase transformation or by crystallization from a solution, which has one or more solids molecularly dispersed in a solvent, or by crystallization from a melt, or by desublimation out of a vapor phase. A crystalline product is produced from an initial amorphous phase, liquid or gas, with one or more components, for the purpose of forming, cleaning or mixture separation. 

The produced crystals usually have to be cleaned and require aftertreatment as shown schematically in Fig. 7-1. The crystal size distribution and crystal form mainly depend on the operating conditions such as pressure, temperature, degree of supersaturation and concentration of separating agents influencing the yield. 

Crystallization from a solution is a thermal separation process. A solution of one or more solids molecularly dispersed in a solvent is usually concentrated by multistage evaporation of the solvent. Since the concentrated solution becomes supersaturated by cooling ( cooling crystallization ), evaporation of solvent ( evaporation crystallization ) or flash evaporation ( vacuum crystallization a combination of cooling and evaporation) causes crystals to form and grow. To reduce the degree of supersaturation, the surplus forms a solid which 

Representation according to Mannesmaim Engineering AG, Messo-Chemietechnik. 

Crude solution throughput Amount of crystals Water evaporated Steam consumption Temperature levels 

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