A rotary kiln is a “pyroprocessing” device used to heat materials to a high temperature continuously. It is typically a long, cylindrical vessel, inclined slightly horizontally (typically a 4-5 degree inclination), and is rotated slowly about its long axis.

The material to be processed is fed into the upper or raised end of the cylinder and as it rotates, this material gradually moves down towards the lower end to a discharge collector or output port.