Abstract: Single or multi-screw indirect-heating screw conveyor desorbers having a heating gas guide enclosed by the screw shaft wall (single-wall screw shafts) or located between a screw shaft wall and an internal chamber wall (double-walled screw shafts). Predetermined amounts of cooling and diluting fluid may be added to a heating gas stream to control the maximum temperature thereof. Screw shaft support bearings and rotary drive components may be cooled, and conveyor wall and/or screw shaft surfaces (e.g.. screw flights and interflight surfaces) may be automatically cleaned during screw shaft rotation by hardened bits and/or breaker devices. Cleaning operations may also involve the interaction of two counter-rotating conveyor screw shafts having mutually interleaved and opposite-handed external flights.