DTB crystallizer

Working Principle

1. Circulation Process: 

• Hot saturated feed solution is added from the bottom of the circulation pipe, mixing with the mother liquor containing small crystals. This mixture is then pumped to the heater (or cooler, depending on the crystallization method).

  The mixed solution enters the crystallizer from the bottom of the guide tube, and is transported upwards to the liquid surface by a slowly rotating propeller (or agitator).

• The solution evaporates and cools at the liquid surface (or cools naturally), reaching a supersaturated state. The solute deposits on the surface of the suspended crystals, promoting crystal growth.

• The crystal slurry descends along the annular gap between the guide tube and the crystallizer body. Large crystal particles settle to the bottom, while small particles enter the settling zone with the mother liquor.

2. Fine Crystal Control: 

A fine crystal removal device (such as a sifting column) is installed outside the settling zone. Through hydraulic classification, small particles are returned to the crystallization zone with the mother liquor to continue growth, or excess fine crystal nuclei are dissolved, ensuring uniform crystal particle size.

3. Supersaturation management: 

Maintain a stable supersaturation by controlling the evaporation rate (vacuum flash evaporation) or cooling temperature to avoid spontaneous nucleation and promote crystal growth rather than the generation of new nuclei.

Core Structure and Components

1. Flow Guide: Center-mounted, typically with a variable diameter design (narrower at the bottom and wider at the top), guides the crystal slurry circulation, creating a stable hydrodynamic environment and reducing splashing and surface crystallization.

2. Baffle: Separates the crystallization zone from the settling zone, controls fluid velocity, and promotes crystal classification.

3. Stirring System: Built-in propeller-type agitator operates at low speed to prevent crystal deposition while driving circulation.

4. Separation Column: Located at the bottom of the crystallizer, utilizes density differences for hydraulic classification, separating particles of different sizes.

5. Heat Exchanger: Can be integrated with a cooler or evaporator to achieve cooling crystallization or evaporative crystallization.

6. Fine Crystal Removal Device: Such as a settling zone and circulation pipe design, dissolves or recirculates fine crystals, optimizing particle size distribution.

Key Advantages:

1. High-efficiency heat and mass transfer: The internal circulation design shortens the heat transfer path, rapidly removing heat and solute.

2. High crystal quality: Uniform supersaturation zone and fine crystal control mechanism ensure uniform particle size and high purity.

3. Low energy consumption: Built-in agitator with low resistance and low circulation drive power; non-contact heat exchanger (e.g., vacuum flash evaporation) reduces scaling and maintenance.

4. Continuous automation: The PLC control system automatically adjusts parameters such as temperature, speed, and liquid level, simplifying operation.

5. Strong adaptability: Suitable for different crystallization systems (e.g., cooling crystallization, evaporation crystallization), offering high capacity flexibility, small footprint, and outdoor installation capability.

6. Safety: Sealed design prevents leakage of harmful substances, ensuring a stable production environment.

Applications

1. Typical Products: 

Potassium nitrate, ammonium chloride, sodium phosphate, boric acid, amino acids (such as aspartic acid), magnesium sulfate, anhydrous sodium sulfate, etc.

2. Industry Sectors:

• Chemicals: Production of high-purity inorganic salts and organic acid salts.

• Pharmaceuticals: Crystallization and separation of active ingredients to ensure drug purity.

• Food: Such as sugar crystallization and food additive production.

• Pesticides: Crystallization of pesticide intermediates.

Key Technical Points

1. Operating Parameter Control: Evaporation intensity, crystallization temperature, stirring speed, and circulation rate need precise adjustment to avoid supersaturation fluctuations.

2. Equipment Design Optimization: The size of the guide tube and the position of the baffles directly affect fluid distribution and need to be customized according to material characteristics.

3. Fine Crystal Management: The design of the settling zone and the separation column must match the density difference between the crystals and the mother liquor to ensure classification efficiency.

The DTB crystallizer, with its unique guide tube and baffle structure, efficient circulation system, and fine crystal control mechanism, has significant advantages in the field of continuous crystallization. Its low energy consumption, high automation, and product uniformity make it a core piece of equipment in crystallization processes in industries such as chemical and pharmaceutical, and it is especially suitable for scenarios with strict requirements on crystal particle size and purity.