The final induration is accomplished in a rotary kiln, wherein the principal heat transfer mechanism is radiation from the system's main burner.
The process system is designed so that material transfer from the grate to the kiln occurs when the material on the grate is sufficiently preheated to have the requisite indurate strength for subsequent processing in the rotary kiln.
A rotary kiln is a steal round shell with refractory lining that rotates. This shell is rotated by a drive gear and electric or hydraulic drive system. The shell is supported on large bearings.
See Rotary Kiln Technologies for more info