Miniaturized draft tube baffle crystallizer for continuous cooling crystallization

Abstract

Industrial draft tube baffle (DTB) crystallizers are well known and can be found in many applications; however, DTBs are rarely investigated on the laboratory scale. A miniaturized DTB for continuous cooling crystallization with integrated fine-grain dissolution was designed, set up, and characterized. A typical DTB from the m³-scale was scaled down to 2 L filling volume to enable lab-scale investigations concerning process development. The fluid dynamic behavior was determined with suspension performance and residence time of the liquid and solid phase. Five different start-up variations were investigated for cooling crystallization of l-alanine dissolved in water. Hurdles with the periphery were identified, different start-up variations were tested, and the promising ones were determined. It was found that the residence time of the solid phase is shorter than the liquid phase due to the classifying behavior of the DTB, i.e., the crystal residence time could be shortened by decreasing the stirrer speed. The investigations show the potential of the miniaturized DTB for the process development of continuous procedure and small-scale production.