CYLINDRICAL FURNACES.—The Improved Bruckner Roasting-Cylinder, extensively used both for oxidizing and chloridizing roasting, consists of an iron cylinder, lined with fire-brick, and provided with two receiving and discharging doors midway in its length, which come directly under the charging hopper, and discharge directly into an iron hot-ore car placed underneath, or, if desired, into a pit. Thd cylinder revolves on four rollers, and is caused to rotate by spur gear-wheels driven by a worm-gear and pulleys. At one end of the furnace is an iron fire-box, mounted on brick foundations, and having a conical opening to match that on the cylinder, which is alike in form at both ends, the other end revolving close to the flue opening. The furnace and its conical ends (throats) are lined throughout with fire-brick. Being of smaller diameter at the ends than at the center, the ore is thrown to and fro, chang ing its position frequently, and exposing new surfaces and particles to the action of the flames which draw through from the fire-box at one end to the flue at the other. These cylinders are commonly made in two sizes, viz.: 6 ft. diameter by 12 ft. long, weighing 15,000 lbs.. which have an average capacity of 3 to 4 tons of ore; and 7 ft. diameter by 18 ft. long, weighing 2-8,000 lbs., with an average capacity of 0 to 8 tons. In the latest form of these cylinders the fire-box is really a car, running on a track at right angles to the longitudinal direction of the cylinders, and having a short flue in one side that comes exactly opposite the throat of the furnace. In this way the fire-box can be run opposite a cylinder which contains a fresh charge, and fired on until the sulphur is fairly kindled. Then the movable fire-box may be wheeled along to a neighboring cylinder, and the first one left to complete combustion of the sulphur with free access of air, and undisturbed by the reducing gases that pass up from an ordinary grate. After combustion of the sulphur it is necessary for a perfect roast to again connect the fire-box with the cylinder, and supply a little extraneous heat to complete the decomposition of the sulphates. It is estimated that two horse-power are re quired to drive a charged cylinder at an average speed. At the smelting-works of the Ana conda Mining Company, Anaconda, Mont., 150 Bruckner cylinders are in constant use,
desulphurizing ore containing about 35 per cent sulphur. The average charge is 9 tons, which in 24 hours is roasted clown to 10 per cent sulphur, or in 36 hours to 3 per cent. For each cylinder 1 ton of Rock Springs coal (much inferior to that of Pennsylvania) is required per 24 hours. Two men attend to three furnaces. Dr. Peters states that the saving in cost in Butte, Mont., by using Bruckner cylinders rather than .reverberatory furnaces amounts to 40 per cent. Mr. R. 11. Terhune states (lrans. A. I. N. E., xvi, 18) that the best results obtained with the BrUckner cylinder, 7 x 18 ft., with 4 in. brick lining, oxidizing roasting, at the Germania Smelting Works, near Salt Lake City, Utah, was the desulphurization of a charge of S tons down to 4 to 0 per cent sulphur, in 24 hours. The amount of fuel used (Pleasant Valley coal) was 20 per cent of the charge, and two men per shift of 12 hours attended to three furnaces. A cylinder 7 x 22 ft. in size was subsequently introduced at these works, and its re sults led Mr. James, the superintendent, to believe that the economic length of the Bruckner furnace had been reached at 22 ft.
Arent's Improved Bruckner Cylinder differs from the preceding in the shape of the roast ing-chamber, which is not a true cylinder, but is made in the shape of a frustrum of a cone, its base being turned toward the fireplace. In this frustrum of a cone the ore seeks the same horizontal level when revolved around its axis as in the Bruckner, and is thus forced to form a layer of graduating thickness in the chamber, with its thin end near the flue end and its thickest or deepest end toward the fireplace. The flame coming from the fireplace is, of course, hottest at that end; and there, in this furnace, it finds the most ore to heat. As the flame, in its passage through the roasting-chamber, loses in intensity, so the ore layer becomes thinner ; and there is less and less ore to heat until the flue is reached. In this manner it is claimed that the charge is "done" simultaneously at all points throughout the roasting chamber. This cylinder is usually made 18 ft. 6 in. long, 7 ft. 3 in, outside diameter at the large end, and 6 ft. 3 in. at the smaller end.