Patent ID: 8486158

Claim:
Method for continuously producing a product crystallizate having a substantially constant particle size distribution by crystallization of a substance from an oversaturated solution of the substance in a solvent in a crystallization stage, wherein a suspension of oversaturated solution and crystallizate formed in the crystallization stage is circulated internally, wherein the oversaturation of the solution is produced by evaporation of the solvent in the crystallization stage and the vapour thus formed is drawn off from the crystallization stage, wherein a partial flow of a clarified solution from a clarification region of the crystallization stage having a solids proportion comprising seed crystals and fine crystals is drawn off, is heated in an external circuit and, after dissolution of the solids proportion, is then guided as a solution back into the crystallization stage and wherein the crystallization stage is continuously supplied with fresh solution and a crystal suspension, said method comprising: metering an amount of crystal suspension in dependence upon a measured value which is determined directly or indirectly in a continuous manner or at time intervals and is representative of the particle size distribution in the suspension of the crystallization stage, said measured value being representative of the relative quantity proportion of a specified segment from the particle size distribution of the suspension in a segment from a fine crystallizate region of the particle size distribution; continuously drawing off a product suspension having the proportion of product crystallizate contained therein at the desired particle size from the base region of the crystallization stage; continuously feeding the crystal suspension from a seed generation stage as a seed suspension comprising seed crystals and fine crystallizate of the substance having an average particle size of less than approximately 0.1 mm into the internally circulated suspension, generally increasing the quantity of seed suspension fed in response to a decrease in the quantity proportion of the segment from the fine crystallizate region with respect to a specified desired value, and generally reducing the quantity of seed suspension fed in response to an increase in the quantity proportion of the segment from the fine crystallizate region with respect to the specified desired value; and obtaining the seed suspension in the seed generation stage as a flash crystallization by the atomization and decompression of a heated solution of the substance with partial evaporation of the solvent and collection of seed crystals thus formed and fine crystallizate in the non-evaporated part of the injected solution.