Start equipment:
Activate the heating system: Start the steam generator or electric heating device to preheat the heat exchanger tubes.
Establish vacuum (if necessary): Start the vacuum pump to pump the system to the set vacuum level.
Start the circulating pump: In forced circulation or DTB crystallizer, start the circulating pump to circulate the crystal slurry within the equipment.
Feed and evaporation:
Slow feeding: Pump the pretreated material into the evaporative crystallizer at a set flow rate to avoid equipment fluctuations caused by instantaneous shocks.
Control evaporation rate: By adjusting the pressure of heating steam or vacuum level, the evaporation rate of the solvent can be controlled, ensuring a steady increase in solution concentration.
Monitoring concentration: Monitor the solution concentration in real-time (e.g., using a densitometer or refractometer) to ensure it reaches a supersaturated state.
Crystallization and growth:
Inducing nucleation:
Natural nucleation: The solution is naturally supersaturated through slow evaporation, forming crystal nuclei.
Artificial nucleation: adding crystal seeds or inducing crystal nucleus formation through mechanical stirring or ultrasonic waves to control crystal particle size.
Control supersaturation: Maintain an appropriate supersaturation (usually by adjusting the evaporation rate or temperature) to promote crystal growth rather than secondary nucleation.
Optimize crystal granularity:
Adjusting circulation speed: In a forced circulation crystallizer, the turbulence level of the crystal slurry is controlled by changing the rotational speed of the circulation pump, which affects crystal collision and breakage.
Use baffles or draft tubes: In the DTB crystallizer, optimize the crystal slurry flow path through internal structure to reduce crystal short-circuiting and aggregation.
Separation of crystals from mother liquor:
Continuous discharge: A discharge port is set at the bottom of the crystallization chamber to continuously discharge crystal products, while replenishing fresh materials to maintain system balance.
Mother liquor circulation: Return some or all of the separated mother liquor to the evaporation chamber for further evaporation, thereby improving the utilization rate of raw materials.
Washing crystals (if necessary): Wash the discharged crystals to remove the mother liquor and impurities adsorbed on the surface, thereby improving the purity of the product.