Rotary drum dryer having internal flights

Claim 1

A rotary drum dryer adapted for heating and drying stone aggregate useful in the production of asphalt paving composition or the like, and comprising an elongate hollow drum having a cylindrical wall which defines a central axis, means mounting said drum for rotation about said central axis and with said central axis being inclined with respect to the horizontal so as to define an upper end and a lower end of said drum, aggregate inlet means positioned adjacent said upper end of said drum for introducing aggregate into the interior of said drum, and aggregate outlet means positioned adjacent said lower end of said drum for withdrawing the aggregate from the interior of said drum, and so as to define a downstream direction from the inlet means toward the outlet means and an opposite upstream direction, means for rotating said drum about said central axis so as to cause the aggregate which is introduced at said inlet means to move through the interior of said drum in the downstream direction to said outlet means, heating means comprising a burner positioned adjacent one of said ends of said drum for introducing air and a high temperature flame into the interior of said drum, and so as to define a combustion zone in said drum which surrounds said flame, exhaust duct means positioned adjacent the other of said ends of said drum for exhausting the heated gas therefrom and so that the heated gas flows through said drum, a dam coaxially encircling the inside surface of said wall of said drum and located adjacent the downstream end of said combustion zone, with said dam defining an inside circumferential edge which is spaced from said wall of said drum, a plurality of longitudinally extending flights mounted to the inside surface of said wall of said drum and extending upstream from said dam along at least a substantial portion of the length of said combustion zone, with each of said flights, when viewed in transverse cross section, comprising a medial portion which is generally parallel to the adjacent portion of said inside circumferential edge of said dam, and a trailing edge portion which is inclined away from the wall of said drum, whereby the dam is adapted to retain and raise the level of the aggregate flowing through the combustion zone of the rotating drum so that the flights pass through the aggregate in the bottom of the drum, and the flights collect a portion of the aggregate on their top surfaces and carry the collected aggregate to an elevated discharge point.