English: Edwards reverberatory furnace, used to roast ore. The burden is stired by a succession of rabbles.
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The Edwards Roasting Furnace. —
This is a single-hearth reverberatory furnace with hearth dimensions 57 ft. long by 6 ft. wide. Fig. 74, in plan, shows a portion at the firebox end, the feeding mechanism and the cooling floor in section. The elevation shows the side, constructed like a plate-iron beam, the stirring mechanism and the conveyor for transferring the roasted ore to the cooling-pit. Fig. 75 is a transverse section of the hearth showing the details of the stirring mechanism. The slope of the furnace can be changed a httle by tilting. This regulates the rate of travel of the
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ore through the furnace; but for a given kind of ore, this slope, once determined, is not again changed. The furnace has a slope of i in. per foot toward the discharge or firebox end. The stirring and propulsion of the charge are effected by means of rabbles fixed to vertical shafts, as shown in the elevation of Fig. 75, and in the plan of Fig. 74. These rabble-shafts make one revolution in sixty to ninety seconds. The rabbles at the firebox end are water-cooled, and this is foimd especially necessary where a high finishing heat is needed. The blades or plows of the rabbles can be easily replaced through the doors adjacent to them. The figure indicates the hearth as broken away, at the discharge end, to show two of the rabbles in plan. The last rabble sweeps the roasted ore into the discharge shoot, and the push-conveyor then moves the ore to the coolingpit. The bottom of the conveyor trough is fmnished with sUdes, by means of which the ore can be dropped at any desired point on the cooling-floor. The ore is fed to the furnace from the feed-hopper, by an endless-screw conveyor which discharges into a feed-opening in the roof of the furnace. The smoke is carried off by a flue. The furnace takes 1 H.P. to operate, and has a daily capacity of 25 tons on sulphide ore of 30 to 35 per cent sulphur. The roasted ore contains 3 to 8 per cent of sulphur. The moving parts are durable, and the furnace has proved efficient in practice. Large installations, of the duplex type with a double instead of a single row of rabbles, and of hearth-dimensions 120 by 12 ft., have been built for a daily capacity of 60 tons. These furnaces do not have the tilting hearth.