Drying method and apparatus

A drier for particulate matter, said drier comprising:

• An enclosed vessel having an upper section with a vertically oriented, substantially cylindrical sidewall, and a coaxially aligned lower section with a downwardly and inwardly tapered frustoconical sidewall, the bottom edge of said upper section being substantially coextensive with the top edge of said lower section;
• A rotatable shaft coaxially disposed within said vessel and extending substantially the entire interior length of said vessel;
• Means for rotating said shaft within said vessel;
• A plurality of axially spaced arrays of circumferentially spaced, radially extending, downwardly inclined stirring arms connected to said shaft in fixed relation to said shaft and in substantially fixed relation to each other;
• Inlet means near the top of said vessel for introducing particulate matter to be dried into said vessel;
• Outlet means at the bottom of said vessel for discharging dried particulate matter from said vessel;
• Means for introducing a heated gas into the lower section of said vessel;
• and
• At least two perforated substantially frustoconical separator means coaxially disposed within said vessel in fixed relation to each other and to the sidewalls of said vessel:
• said first separator means tapering inwardly in the downward direction and having a top edge substantially coextensive with the sidewall of said vessel and a bottom edge terminating near the bottom of said vessel, said first separator means comprising a first inwardly and upwardly facing surface and a second downwardly and outwardly facing surface, said second surface further cooperating with the sidewall of said vessel to define an annular plenum within the lower section of said vessel, said plenum being adapted to receive said heated gas introduced into the lower section of said vessel and to distribute said heated gas upwardly through said vessel, the perforations in said first separator means being adapted to permit the passage of heated gas upwardly therethrough and not being substantially larger than the average particle size of said particulate matter;
• said second separator means being inverted relative to said first separator means and having a top edge closely adjacent to but spaced apart from said shaft, and a bottom edge disposed inwardly of and below the top edge of said first separator means but spaced sufficiently above the interiorly facing surface of said first separator means to permit the passage of particulate matter therebetween, at least some of the perforations in said second separator means being sufficiently large to permit the passage of particulate matter therethrough.