Drying vacuum lock systems

Both systems A and B can be used for continuous operation with vacuum locks. In system A (Fig. 2.53), one or two carriers are be moved into a lock (4) in front of several connected tunnels (8). The lock is evacuated and the carrier(s) are moved into the tunnels. At the same time, the equal number of carriers is moved from the tunnels into an exit lock (10). Both locks can be separated from the tunnels by two large slide valves (7). In system B (Fig. 2.54), each tray (1) passes through an entrance lock (2) into a paternoster lift (3), which moves the tray to a certain level and pushes it into the drying zone. The last tray is pushed by the entering tray into the exit paternoster lift (6), which moves the tray into the exit lock (7). These plants are illustrated in Fig. 2.55 and 2.56. 

Fig. 2.82. Schematic drawing of a horizontal vibration dryerwith 10 m2 drying surface. 1, Entrance lock for the product 2, storage and dosage unit 3, heated shelves vibrated at 50 Hz 4, alternating locks for product removal 5, condensers 6, connection to the vacuum system. (Figure 7 from [2.18]).

The vacuum plate dryer is provided as part of a closed system. The vacuum dryer has a cylindrical housing and is rated for lull-vacuum operation (typical pressure range of 3 to 27 kPa absolute). The exhaust vapor is evacuated by a vacuum pump and is passed through a condenser for solvent recovery. There is no purge gas system required for operation under vacuum. Of special note in the vacuum-drying system are the vacuum feed and discharge locks, which allow for continuous operation of the plate diyer under full vacuum. 

The setup of a system for continuous vacuum drying is similar to the setup of batch systems. But in addition dosing devices and feed- and discharge locks are required for a continuous product flow into and out of the system (Figure 12.19). 

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