Abstract: The invention relates to a device for thermally treating or post-treating synthetic material, especially polyester material such as polyethylene terephthalate (PET). The gassing of the granulate (8) primarily takes place in the conical discharge area (5) of the shaft reactor. To this end, a middle cylindrical partial area (5b) is situated in the conical discharge area (5) between an upper conical partial area (5a) and a lower conical partial area (5c). Said middle cylindrical partial area has a cylinder jacket-shaped slotted hole screen (10) whose slots run parallel to the axis of the discharge area (5) in a vertical manner. The invention is characterized in that the bulk of the granulate (8) located in the discharge area (5) is gassed. In addition, the friction between the downwardly moving granulate (8) and the gassing area (7) formed by the slotted hole screen (10) is minimized.