Description: Vacuum Tray Dryer is mainly used for drying of high grade, temperature and oxygen sensitive products. These dryers are highly suitable for drying hygroscopic substances, which are dried to very low residual moisture, content level. These dryers are available in standard models ranging from 4 trays to 48 trays. These dryers are mostly used for batch dryer. They are box-shaped and loaded and unloaded via a door (two doors on the larger models). These dryers comprise of several heating plates mounted one above the other on which the product is placed in the tray. The bottoms of both heating plates and trays should be as smooth as possible to permit optimal heat transfer between plates and product. The medium flowing through the heating plates is water, steam or thermal oil. The distance between the heating plates is determined primarily by the surface loading and the foaming of the product. The cabinet walls are indirectly preheated by the heating plates to avoid retrograde condensation. The product is introduced latter and heated at atmospheric pressure. Only after all individual product trays reach the same temperature the cabinet is evacuated and drying can start. The preheating phase is very important, so as to have the drying curve and the foaming of the product to remain identical throughout the cabinet. During the main drying phase the vacuum is in the range of 40 to 80 mbar abs and in the final drying phase vacuums of only few mbar abs are reached. Heating temperatures are normally in the range between 800C and 1100C. It takes a few hours or 1 to 2 days for drying, depending upon the product and surface load.
