GB881220A - Method and apparatus for drying and classifying aspirin and like material - Google Patents

Abstract

881,220. Drying apparatus. MONSANTO CHEMICALS (AUSTRALIA) Ltd. July 10, 1959 [July 14, 1958], No. 23787/59. Class 34(2) A method and apparatus for drying and classifying aspirin and like crystalline material comprises supplying the wet aspirin through a feeder 11, Fig. 1, into a primary fluidized bed of the material which is partially dried to a moisture content below which it is possible to maintain the bed in a fluidized state, displacing the upper surface portion of the bed through a spillway 16 down to a stand-pipe 17 into a lower secondary fluidized bed 3 having a lower fluid velocity than the primary bed whereby drying of the material is completed and the dried material is classified by stratifying into different masses of crystal-size ranges which are discharged through outlets 18, 19 at different strata levels in the bed. The beds are supplied with heated air from a blower 7 through a controlled inlet 9, which air enters through perforated screens 5, 6 supporting the beds, the cross-sectional area of the secondary bed being greater than that of the primary to lower the fluid velocity therethrough. The air is exhausted through a conduit 20 to a cyclone separator 21 wherein the crystalline fires are collected and a control 12 regulates the intake of wet material through the feeder 11 in accordance with the humidity of the exhausted air. Large agglomerates of the material which settle to the bottom of the primary bed flow across the bed to an outlet 15. In a modification the beds 1, 3, Fig. 2, are arranged side-by-side in chambers 2, 4 with the partially-dried material from the primary bed flowing over a spillway 16 which separates the beds into the secondary bed and each chamber has a controlled supply of heated air from a common blower 7 and an air outlet to a cyclone separator 21.