Impure crystals rising in twin-worm tower - exchange material with descending pure melt from separate upper container

Impure crystal mixt. enters laterally (6) pref. projected by an extruder worm above the floor of a vertical purifcn. column (1) which the drive shafts (3,5) rotate. Each shaft carries a continuous helical fin (4,4') of opposite pitch to its neighbour and partly overlapping while driven in opposite rotary directions by an upper motor. Crystals taken upwards by the fins exchange material with descending molten crystals and emerge in purifed state from an upper lateral outlet (7). Part of the purified crystals are taken to a jacketed melter (8) producing the melt to descend the column. An apertured sieve floor (5) separates liq. from solids, to be pumped (11) away for further treatment. USE - Suitable e.g. for purifying paradichlorobenzene or paraxylene contg. ethyl benzene.