Draft Tube Baffle Type (DTB) Crystallizers are suitable for processes with vacuum cooling and moderate evaporation rates. Due to the low additional heat requirement during the process stage, they have a positive effect on operating costs.
(DTB) Crystallizers are commonly used in the chemical and fertilizer industries for producing crystalline products such as ammonium sulfate, potassium chloride, and monoammonium phosphate.
DTB Crystallizers sometimes operate at low supersaturation, which can be a limitation for crystal growth; very large crystals can be produced only by dissolving fine particles. In processes where the dissolution of fine crystals is not required or desired, the internal circulation rate in the crystallizer is adjusted to have minimal nucleation effect on the suspension.
For effective crystallization process control, it is important to control retention time and crystal mass to achieve optimal conditions in terms of specific crystal surface area and the fastest possible growth. Removing crystal slurry by gravity settling and managing mass flow around the crystallizer is necessary to obtain a dense crystal slurry.
DTB Crystallizers feature an internal or external circulator that pushes the solution upward through a draft tube, with a circular settling area located outside the crystallizer. The solution inside the crystallizer moves upward at a very low velocity. This allows large crystals to return to the main circulation through the draft tube, while only fine crystals below a certain size are redissolved with heat, thus additionally creating a point of supersaturation.
