Vacuum Tray Dryer By Ravi Industries

Vacuum Tray Dryer

Vacuum Tray Dryer is used mainly for drying of high grade,
temperature and oxygen sensitive products. Vacuum Tray Dryer is highly
suitable for drying hygroscopic substances, which are dried to very low
residual moisture, content level. Frequently vacuum drying cabinets are
the sole possibility for drying lumpy, glutinous products or products
of low pomposity.
Capacity
Standard models range from 4 trays to 48 trays.






Vacuum
Tray dryer is the most commonly used batch dryer. They are box-shaped
and loaded and unloaded via a door. Inside are several heating plates
mounted one above the other on which the product is placed in trays. 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. To
avoid retrograde condensation the cabinet walls are indirectly
preheated by the heating plates. Next, the product is introduced 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 in
order that the drying curve and the foaming of the product is 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.
Depending on product and surface load, drying takes from a few hours to
1 to 2 days. For some products the vacuum and
temperature profiles are automatically controlled in order to prevent a
pass over of the critical product temperature. The
dimensioning of the vacuum system is an important factor in the design
of drying cabinet systems. If for example vigorous foaming of the
product is desired, evacuation to the operational vacuum level must
take place very quickly. Vapours produced during
drying are taken out direct, or via a steam jet compressor to a surface
condenser in which the vapours condensate. The non-condensable vapours
are extracted by the vacuum system. On completion of the drying, the product can be cooled by circulating of cooling water through the heating plates. Often
vacuum drying cabinets are supplied to new, small production operations
in newly opened markets. Following successful development of the
market, it could be worthwhile to replace the cabinets through
continuous vacuum belt type dryers.