Rotary Hearth furnaces are used when it is convenient for the charge and discharge
positions of the furnace to be near to each other, as in a seamless tube piercing
mill. These furnaces consist of a turn-table on which the product travels while
moving under the stationary furnace walls. For example, steel blooms can be set
on the turning hearth by a manipulator and indexed through temperature controlled
furnace. Once heated to the desired temperature, they are removed by the same manipulator
and sent to the mill for piercing. These furnaces are up to 120 mtph and 35 m in
diameter.
Rotary Hearths are also useful when handling bulk goods for calcining or direct
reduction. The charge for Direct Reduced Iron (DRI) furnaces is generally self-reducing
pellets or briquettes consisting of iron ore, coal fines, and a binder. The charge
is placed on the hearth by a conveyor and passes through the furnace for heating.
As the pellets heat, the carbon from the coal reduces the iron oxide to metallic
iron. Once reduced, a discharge screw mechanism sweeps the DRI from the hearth and
onto a discharge conveyor or into a retort. DRI rotary hearth furnaces are up to
60 m diameter and can provide an annual production of 600,000 mtpy.