Rotary Kiln is usually working as following : The kiln is a cylindrical vessel, inclined slightly to the horizontal, which is rotated slowly about its axis. The raw material to be processed is fed into the upper end of the cylinder. While the kiln rotates, material gradually goes down towards the lower bottom, and may undergo a certain amount of stirring and mixing. Hot gas pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gas may be generated in an external furnace, or may be generated by a flame inside the kiln. Such a flame is projected from a burner-pipe (or “firing pipe”) which acts like a large bunsen burner. The fuel for this may be gas, oil or pulverized coal.