Abstract: A thermal treatment system and method characterized by an outer drum mounted on the base for rotation about a rotational axis; an inner drum mounted coaxially within the outer drum closer to a heater end thereof than an inlet end of the outer drum, the inner and outer drums forming therebetween an annular flow passage surrounding the inner drum; a passage at a heater end of the inner drum for allowing material to drop from the inner drum into the outer drum for flow through the annular flow passage from its inlet end to its outer end; material conveying structure for conveying material within a feed tube from the inlet end of the outer drum to the inner drum for deposit within the interior of the inner drum at its inlet end, the feed tube being mounted coaxially within the outer drum and being spaced radially inwardly from the annular wall of the outer drum to form an annular flow passage surrounding the feed tube that has an inlet end connected to the outlet end of the annular passage surrounding the inner d