Important Advantages.—Of the marked advantages of this type of furnace, the following are perhaps the most striking and important:—
(1) There is a great saving of floor space by having the six hearths one above the other.
(2) The use of a central common spindle carrying the arms and ploughs simplifies the mechanism.
(3) The form is convenient for the compact arrangement of a roasting plant of many units for feeding, discharge, and supervision.
(4) Very little heat is lost by radiation, as the heat passes mostly from one hearth to another.
(5) Very little fuel is required, none with heavy sulphides (except for starting), as the heat of oxidation of the iron and sulphur usually yields a high enough temperature to keep the operation going. The fuel costs are lower than in other types of roaster.
(6) Thorough rabbling, greater uniformity and better mixing of product, continuous and regular feed and discharge are obtained.
(7) The roasting is thorough, and perfect control of the degree of oxidation is ensured by adjusting the rate of passage of the ore through the furnace, which is regulated by varying the ore feed and the speed of rotation of the rabbles.
(8) Great saving in labour costs and difficulties. The labour in roasting plants is extremely arduous, on account of the high temperature of the material, and is dangerous on account of the atmosphere.
The Evans-Klepetko-MacDougal Roasting Furnace Plant at Anaconda.—The roasting plant at Anaconda formerly consisted of 56 Brückner cylinders, which were eventually all scrapped and replaced by new plant of the MacDougal type, subsequently greatly modified and improved as one difficulty after another had to be overcome.