The DTB evaporative crystallizer is a slurry circulation crystallizer, also known as a guide tube crystallizer due to the presence of an internal guide tube in the crystallizer. It is widely used in crystallization operations in industries such as chemical, pharmaceutical, and pesticide. The lower part of the DTB evaporative crystallizer is connected to an elution column, which is equipped with a guide tube and a cylindrical baffle. During operation, the hot saturated liquid is continuously added to the lower part of the circulation tube, mixed with the mother liquor containing small crystals in the circulation tube, and pumped to the heater. The heated solution flows into the crystallizer near the bottom of the guide tube and is transported to the liquid level along the guide tube by a slowly rotating propeller. The solution evaporates and cools at the liquid surface, reaching a supersaturated state, where some solutes deposit on the surface of suspended particles, causing crystal growth. There is also a settling zone around the annular baffle, where large particles settle while small particles enter the circulation pipe with the mother liquid and dissolve under heat. The crystal enters the elution column at the bottom of the crystallizer. In order to make the particle size of the crystallized product as uniform as possible, a portion of the mother liquor from the settling zone is added to the bottom of the elution column, and the hydraulic classification is used to allow small particles to return to the crystallizer with the liquid flow, while the crystallized product is discharged from the lower part of the elution column.

DTB evaporative crystallizer process flow:

The material liquid to be processed is added by the feed pump through the circulation pipeline, and then sent to the DTB crystallizer. The suspension is pushed by the propeller and circulation pump, rises to the boiling liquid surface through the guide tube, and then flows along the annular channel between the guide tube and the baffle to the bottom of the crystallizer. It is then sucked into the lower end of the guide tube again, forming an internal circulation channel. It circulates repeatedly at a high speed to fully mix the material liquid, ensuring that the supersaturation is relatively uniform and the undercooling is low throughout the crystallizer, greatly enhancing the production capacity of the crystallizer. The cylindrical baffle separates the crystallizer into a crystal growth zone and a clarification zone. The annular gap between the baffle and the wall is the clarification zone. After the overflow clarified mother liquor exchanges heat, it is returned to the crystallizer through the circulation pump, which enhances the mixing effect of the crystallizer and minimizes the occurrence of scarring. The crystal slurry is discharged from the discharge pump at the bottom of the crystallizer, and after centrifugal separation, the crystal products are dried and used as products. The mother liquor can be returned to the crystallizer or directly discharged to the next process after impurity removal, concentration enhancement, or system circulation. The DTB evaporative crystallizer adopts an external tube heat exchanger for heating, with a vacuum set at the top to remove moisture and heat to generate supersaturation, which is then pumped into the bottom of the crystallizer through a circulation pump to form an external circulation channel.