Patent GB-176025-A (GB)
Title: Improvements in apparatus for conducting furnacing operations
IPC: C01D5/02
Filed: 1920-09-04
Abstract: 176,025. Skinner, L. B. Sept. 4, 1920. Chemical manufactures, furnaces for; roasting- furnaces; charging; charges, agitating; hearths; roofs.-In a furnace for heating more or less viscous materials, the charge is fed to a mixing- pan and is thence advanced along an elongated rectangular hearth by a series of overlapping rabbling devices, the necessary heat being supplied mainly from above through a roof of heatconducting material. As shown in connection with a furnace for the manufacture of salt cake and hydrochloric acid, the salt and sulphuric acid are fed by a screw conveyer 40 and a spout 15 respectively to a mixing-pan 12, the bottom of which slopes upwards to join a long, preferably inclined, main hearth 10, built of fire-clay tiles. The furnace has a double-arched roof, and the space between the two arches is in communication at one end with a fire-place 19, and at the other with dampered downcast flues 24, 25 at the two sides of the furnace, by which the heating- gases can be passed either directly to the stack 23, or indirectly thereto through, passages beneath the mixing-pan. Longitudinal flues 35, 36, Fig. 7, are also provided beneath the main hearth, and by temporarily bricking up the ports beneath the downcast flues 25 and the stack. The heating gases may be directed through these longitudinal flues to supply heat to the under-surface of the main hearth. The inner arch 16 is made of carborundum, silica brick, or metal, and in the last case the part near the fire-place may be protected by a covering of fire-brick. To prevent leakage of acid from the muffle into the arch flue, the heating-gases in the latter may be kept under slight pressure. The acid is normally fed to the mixing-pan by means of a mechanically-driven pocketed plug valve 43, and a valve-controlled bvpass 46 is provided for use instead of, or in addition to, the normal supply. The rabbling-mechanism comprises a series of shafts 48 mounted in bearings 53, 54 in an overhead framework and passing through seals in the furnace roof formed by upstanding and depending rims 51, 50, a gland member 52, and a plate 52<a> resting on the rim 51. The space between the member 52 and the rim 50 may be filled with sand. The shafts are driven by bevel gearing 56, 57 so arranged that adjacent shafts rotate in opposite directions, and the shaft for the mixing-pan is set at right angles to the surface over which it operates. Each rabble shaft consists of upper and lower sections coupled together, the lower section having a transverse tapering socket for the correspondingly-formed end of the rabble arm 49, which is locked therein by means of a wedge-shaped key extending through a slot in the arm and a groove in the socket, so that rotation of the arm in the socket is prevented. The rabble teeth 71 are strung on the arm with alternating spacer members 97, and are supported thereon by engagement of the hooked portions 93, Fig. 12, with ribs 70 on the arm. Each tooth comprises a yoke-shaped portion 92, an offset arm 94 strengthened by a web 95, and a plough portion 96 of rectangular or triangular cross-section. The spacer members may have tongues to fit corresponding recesses in the teeth. The shaft and arm are hollow, and each is partitioned by a diametral web to form flow and return passages for cooling air, which is supplied from a main through a stuffing-box connection 87. In the double arm construction of rabble shown in Fig. 25, a tapered boss 104 at the middle of the length of the arm member 103 fits into a tapered socket on the shaft, and the arm is locked against movement by forcing the teeth on the arm extending from the smaller end of the boss against the socket on the shaft, by driving a wedge into a keyway 116 in the outer end of the arm. In a modified construction of furnace, the main hearth is stepped along its length, or the same effect may be obtained with a plane inclined hearth by allowing the material to cake in steps beneath the horizontally-disposed rabble arms.