1,093,449. Vacuum and freeze drying. PENNSALT CHEMICALS CORPORATION. May 12, 1965 [May 13, 1964], No. 20049/65. Heading F4G. In apparatus for vacuum or freeze drying material, the material, which may be frozen, is fed through a vacuum lock 62 having a slide valve 88 into a hopper 34 in an evacuated drying chamber 12 for passage therethrough in separate streams formed by upstanding ribs of two inclined and superposed conveyers 36, 38 which are vibrated by vibrators 110, 112, the material passing radiant heater 126 before discharge from a hopper 108 through a second vacuum lock 164 with a slide valve 160. The conveyers are of a heat-conducting metal except for their discharge ends which are of electrically non-conductive material and which pass between electrodes 134 ... 140 connected to a H.F. microwave generator for final removal of moisture from the material. A refrigeration chamber 76 is mounted in the lock 62 to retain pre-frozen material in a frozen condition prior to its insertion into the chamber 12 when the pressures in chamber 12 and the lock are equalized. Capacitance plates 142 . . . 148 adjacent the discharge end form a moisture sensing device connected in a control circuit whereby the vibrators and/or heaters are controlled automatically in accordance with the residual moisture content of the material.
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