Annular gap expander

A method and apparatus in the context of a rotating conveying screw situated within a cylindrical housing which has an inlet port on one end of the cylinder and a discharge opening on the other end of the cylinder. A resistance plate is mounted transversely to the conveying screw near the discharge opening for corotation with the screw. The plate is mounted to define a discharge gap between the opening and the plate. A sleeve on the housing is employed to adjust the size of the gap between the plate and the opening. A process controller positions the sleeve by means of a pair of screw jacks. The controller adjusts the discharge gap width to maintain feed material temperature within a predetermined band. Alternatively the controller adjusts the discharge gap width and feed screw speed to maintain a predetermined specific energy input into the feed material. The helical screw is preferably supported at both ends by a bearing means. Breaker bars are mounted on the transverse plate and extend over the gap between the discharge opening and the plate. Breaker bars may also be mounted to the cylindrical sleeve and extend over the gap between the sleeve and the plate.