Working Principle of Closed-Loop Spray Dryers

Closed-loop centrifugal spray dryers are specialised equipment for drying organic solvent slurries. This unit employs nitrogen (or other inert gases) as the drying circulation gas, thereby preventing oxidation of the material during the drying process. Simultaneously, the organic solvent can be recovered. Closed-loop spray dryers are typically used for drying powders prepared from organic solvent slurries such as ethanol, propylene, and hexane. The equipment incorporates explosion-proof design, ensuring a safe and environmentally sound drying process.

The closed-loop centrifugal spray drying system operates within a sealed environment, employing an inert gas (typically nitrogen) as the drying medium. It is suitable for drying materials containing toxic vapours, organic solvents, or substances prone to oxidation during processing. The inert gas circulation provides protective effects on the material, undergoing cycles of moisture loading and removal, allowing the medium to be reused. Nitrogen is heated via a heater before entering the drying tower. Liquid material is conveyed by a screw pump to the centrifugal nozzle, where it is atomised by a high-speed circulating atomiser, forming droplets that undergo heat and mass transfer within the drying tower. The dried powdered material discharges from the tower base. Evaporated organic solvent vapour, under fan-generated negative pressure, carries entrained dust through a cyclone separator and spray tower for dust removal. The saturated organic solvent vapour condenses into liquid within the condenser and discharges. The inert gas medium is continuously reheated and recirculated within the system as the drying carrier. Conventional centrifugal spray drying achieves moisture removal through continuous air supply and exhaust. This constitutes a significant distinction between explosion-proof closed-loop centrifugal spray drying equipment and standard centrifugal spray dryers: the drying system employs nitrogen as the drying medium, operating under positive pressure with a maintained set point. Should internal pressure decrease, a pressure transmitter automatically regulates nitrogen feed to ensure system pressure equilibrium.