Open Cycle Configuration (Open Loop)
The open-cycle configuration is the most common, simplest and consequently cheaper solution. The air is aspirated from the outside environment, filtered (possibly dehumidified) and heated before entering the drying tower. The separation of the product is made with cyclone and bag filter filter, the gas is then put back into the atmosphere. It is used when there is no risk of explosion due to the material itself or the solvent used, or in the case of environmental problems or degradation of the product if in contact with oxygen sources.
Closed Cycle Configuration (Closed Loop)
The closed loop layout instead involves the recirculation of the heating gas, which is then properly cleaned from the vapours and dusts at the process output. Dusts are removed with cyclone systems and filters, and solvent vapors are removed through a condenser. This configuration is effective to use nitrogen as process gas, instead the ambient air. So it is possible to use the spray drying process under special conditions such as:
- Treatment of toxic substances,
- Formation of potentially explosive mixtures in air,
- Use of flammable organic solvents (e.g. acetone, ethanol, dichloromethane),
- Treatment of products susceptible to oxidation in the presence of air.