Centrifugal air classifying apparatus

A centrifugal air classifying apparatus for use with a cyclone type centrifugal separator and a fan for drawing air from the cyclone separator and returning the same at superatmospheric pressure to the centrifugal classifying apparatus, comprising a main classifying rejector chamber having a rotary particle rejector in its upper portion supported for rotation about a vertical axis, means forming an expansion chamber below and communicating with the rejector chamber, means for supplying superatmospheric air from the fan to the expansion chamber to develop a rising and rotating column of air in the expansion chamber and in the rejector chamber outwardly surrounding the rotary particle rejector, the material to be classified being introduced directly into the air column in the zone of the rejector chamber outwardly surrounding the rotary particle rejector by feed conduit means, the rotary particle rejector being generally in the configuration of a cylindrical fan having a large number of vertically aligned blades about its circumference whereby air from the rising and rotating column of air in the rejector chamber outwardly surrounding the rejector flows through the spaces between the blades to a discharge chamber located inside the rejector carrying with it particles of material being thrown off the blades, means communicating with the discharge chamber for transfer of the separated fine particles from the discharge chamber to the cyclone collector, a first primary annular sealing ring inwardly adjacent the tops of the blades at the top of the rejector chamber providing a primary seal zone, and a secondary annular sealing ring extending from a boundary portion of said discharge chamber to a location closely adjacent the inner edges of the rejector blades at an intermediate location between the upper and lower ends of the blades providing a secondary seal zone.