FC crystallizer

Working Principle

1. Circulation and Evaporation: 

The raw material solution enters the crystallizer through the inlet, mixes with the circulating mother liquor, and is then pumped to the heater (e.g., a shell-and-tube heat exchanger) by an external circulation pump.

The heated solution enters the evaporation chamber, where it flashes under reduced or normal pressure. Part of the solvent evaporates, creating a supersaturated state, and the solute begins to crystallize.

The supersaturated solution contacts the suspended crystals in the evaporation chamber, and the solute deposits on the crystal surface, promoting crystal growth while maintaining a stable supersaturation.

2. Crystal Classification and Discharge:

The crystal slurry settles at the bottom of the evaporation chamber. Large crystals are separated by a separation device (e.g., a classifier) and discharged continuously or intermittently from the bottom discharge port.

Fine crystals enter the circulation pipe with the mother liquor. Some are returned to the heater to dissolve, while others continue to grow in the evaporation chamber. The crystal particle size distribution is maintained by controlling the circulation flow rate.

3. Supersaturation Control: 

By adjusting the heating temperature, evaporation chamber pressure, or feed flow rate, the supersaturation of the solution is precisely controlled to prevent spontaneous nucleation and promote the growth of existing crystals.

Core Structure and Components

1. Evaporation Chamber: The main unit, containing a separation space for gas-liquid separation and crystal growth. It is often equipped with an anti-foaming device to prevent foam overflow.

2. Circulation Pump: Forces high-speed circulation of the solution, ensuring crystal suspension and efficient heat transfer.

3. Heater: Typically a shell-and-tube heat exchanger, providing heat to evaporate and concentrate the solution.

4. Classification Device: Such as a classifier leg or hydrocyclone, using fluid dynamics principles to separate crystals of different particle sizes.

5. Fine Crystal Removal System: By controlling the bypass flow rate in the circulation loop, some fine crystals are dissolved or returned to the growth zone, optimizing particle size distribution.

6. Control System: Integrates temperature, pressure, and level sensors, as well as automatic regulating valves, to achieve closed-loop parameter control.

Significant Advantages and Limitations

Advantages:

1. High Evaporation Efficiency: The forced external circulation design shortens the heat transfer path, making it suitable for high-viscosity materials and reducing heat transfer resistance.

2. Controllable Crystal Quality: Particle size is classified through a grading device, resulting in uniform and high-purity crystals.

3. High Operational Flexibility: Parameters such as circulation flow rate and heating temperature can be adjusted to adapt to different material characteristics.

4. Strong Adaptability: Compatible with both evaporation crystallization and cooling crystallization modes; multi-functional operation can be achieved by changing the heat exchanger.

5. Convenient Maintenance: Circulation pipelines and heating components are easy to clean, reducing the impact of scaling.

Limitations:

1. High Energy Consumption: Forced circulation requires significant pump power, especially in large-scale production.

2. Complex Structure: The external circulation system increases equipment footprint and pipeline costs.

3. Material Sensitivity: Highly corrosive or easily crystallized and clogged materials require special materials or anti-clogging designs.

Application Areas

1. Wastewater Treatment: Treating high-salinity wastewater (such as wastewater containing sodium chloride and sodium sulfate) and recovering crystalline salt resources.

2. Chemical Industry: Production of inorganic salts (such as potassium chloride and ammonium sulfate) and organic acids (such as oxalic acid).

3. Pharmaceuticals and Food: Crystallization separation of active ingredients and food additives (such as glucose and lactose).

4. New Energy Materials: Purification and crystallization of battery-grade lithium salts, nickel-cobalt salts, and other materials.

Key Operating Points and Optimizations

1. Circulation Rate Control: Maintain an appropriate flow rate to ensure crystal suspension and avoid sedimentation or excessive wear.

2. Evaporation Chamber Pressure and Temperature Matching: Adjust the vacuum level according to the material's boiling point to optimize the evaporation rate.

3. Seed Management: Add seed crystals as needed to control the nucleation rate and stabilize crystal growth.

4. Anti-scaling Measures: Clean the heating element regularly or apply an anti-scaling coating, and monitor heat transfer efficiency.

FC crystallizers, with their high-efficiency circulation, flexible operation, and controllable crystal quality, have become important equipment for processing the crystallization of complex materials. They perform particularly well in scenarios requiring high evaporation efficiency or strict control of crystal particle size. However, a balance must be struck between energy consumption and equipment cost, and economical operation can be achieved through process optimization.