GB1268263A - Method for vacuum dehydration and apparatus therefor - Google Patents

Abstract

1,268,263. Drying apparatus. I.F.C. CORP. 24 March, 1969, No. 15382/69. Heading F4G. A method of vacuum dehydration comprises the steps of, placing the material to be treated in a carrier between electrically conductive plates; sealing the loaded carrier in a chamber of dielectric material; reducing the pressure therein; heating the plates by induction heating. In the preferred embodiment the carrier is a series of vertical, spaced aluminium plates (35), the floor of the carrier being formed by spacers (38), Fig. 5, not shown. The plates may be either square with the corners removed (Fig. 7, not shown) to receive cakes of solid material, e.g. fish, meat, or round with a segment removed at the top (Fig. 6, not shown) to receive pre-frozen liquid or powdered material, e.g. coffee. Such material is loaded into the carrier by rams (52), Fig. 9, not shown, whereas the cakes of solid matter are inserted individually between the plates. The carriers are then loaded into tubes of glass or other insulating material which are then sealed by cover-plates 55. The tubes 10, which may be lined with P.T.F.E. have a single, or two parallel induction windings of insulated copper or aluminium wire or tubing 14 wound thereon. Valve 23 is then opened establishing a vacuum in the tubes 10, shock to the material is prevented by bleeder line and valve 56. The induction heating is then switched on, the apparatus may be operated either at high frequency or mains frequency. For H.F. operation tubing is used for the windings 14 and cooling water is circulated therethrough. The temperature of the material is sensed by thermocouples 17 which control the power supply via switch 19 for H.F. operation or via toroidal voltage regulators for mains frequency operation. During heating the water vapour evolved is drawn off through the vacuum manifold 24 into the condenser 26 where it freezes on the condenser plates. There may be two condensers 26 one of which is in operation while the other is defrosted. At the completion of the predetermined drying cycle valve 23 is closed and valve 25 opened introducing nitrogen or another relatively inert gas at atmospheric pressure into the tubes 10. The cover-plates 55 are removed and the carriers which may be coated with P.T.F.E. are emptied.