Continuous operation or batch operation
There are two essential criteria:
- the production capacity;
- - the quantity of product.
- 1) Capacity:
In continuous operation, it is difficult to descend below 1 m3.h-1 of dry powder. Indeed, blockages become constant when the slurry extraction tube has an internal diameter less than or equal to 2 cm, which corresponds to 2 m3.h-1 of slurry at 2 m.s-1 and, if the volume fraction of crystals is 0.2 and the void fraction of dry powder 0.5, the minimum production flow of powder is:
In practice, it is wise not to descend below 1 m3.h-1 of dry powder.
The advantage of the continuous process is pronounced when the capacity increases in terms of economy, as the costs of studies and research together with monitoring are independent of the capacity. Typically, we rarely exceed 20 m3.h-1 of dry powder.
2) Product quality:
The batch method is the most flexible, and by correctly programming the temperature or the vaporization power, we can modulate granulometry. On the other hand, the product’s quality can vary from one change to another. We must also remember that seeding a vat at the beginning of the operation imposes the crystal number and avoids the uncertain process of primary nucleation.