Patent GB-1421121-A (GB)
Title: Furnaces
IPC: F27D99/00
Filed: 1972-04-05
Abstract: 1421121 Glass furnace NATIONAL RESEARCH DEVELOPMENT CO 4 Dec 1972 [29 March 1971 5 April 1971] 56324/71 and 15682/72 Heading C1M [Also in Divisions C7 F4 and H3-H5] Material to be melted is introduced into a furnace having a refractory lining 8 with a smoothly contoured inner surface which is rotated about a substantially vertical axis so that the molten material forms a liquid wall 9 of paraboloid shape and the molten product is withdrawn through a permanently open orifice 13 in the bottom. As shown, the furnace has a metal shell 1 provided with a ceramic lining 8 and is rotated in bearings 3 by means of a variable speed motor and a pulley 4. Water sprays 7 are directed on to shell 1 for cooling. In use, during heating, material introduced via ports 14 in the furnace roof melts on the furnace lining to form a molten layer 9 on the lining 8 which can be withdrawn through orifice 13 intermittently by slowing the rotation of the furnace or continuously by adding fresh material continuously. The furnace may be heated by a plasma torch 10 operating in a transferred mode to a carbon (graphite) electrode 12, by an arc between consumable carbon or non-consumable metal electrodes, (Figs. 4 and 5, not shown), by a single D.C. plasma torch (Fig. 3, not shown), by a pair of plasma torches connected in series (Fig. 5, not shown) or by an induction coil (Fig. 6, not shown). Arc current may flow through the material to be heated. When consumable carbon electrodes are used an inert gas, e.g. ArN 2  may be fed down electrode sheaths whilst oxygen is fed to the furnace. The furnace may be used for melting manufacturing bubble free glass since the liquid nature of the glass and the centrifugal forces enable the ready escape of gas bubbles. It is preferred that the lining has a similar composition to the melt. A water cooled collector in the form of a cylindrical passage (Figs. 7 and 8, not shown) or a trough (Fig. 9, not shown) may be provided to prevent product particles being flung out of the orifice 13 by centrifugal action. Melting alumina.-An alumina lining is formed to the shell 1 by ramming or casting whilst the furnace is spinning and then heated to form a molten inner surface layer to which powdered alumina is added. Molten alumina droplets emerge from orifice 13. Melting a mixture of refractory components, e.g. glass.-A slurry of silica alumina and baria is cast on the inner surface of the shell 1 spun dried and heated in a plasma to form a lining. The lining is then heated by a plasma to form a molten inner surface layer to which a powdered mixture of the same composition is fed. A A transparent fully reacted glass emerges from the orifice 13 in the form of droplets, if the furnace is fed continuously, or large slabs may be produced if the furnace rotation is periodically reduced. Metallurgical fuming.-A furnace lining of ground tin containing slag and organosilicate binder was formed and heated to provide a molten inner surface which was then fed with ground tin containing slag in a neutral atmosphere. Volatile tin species emerge with the gas stream and are cooled by air jets. The tin species are converted to a fine particle fume of tin oxide which is collected by cyclones, bag filters, electrostatic precipitators or other means. The fume may be exhausted through a roof chimney or collected at the exit orifice 13 with the slag. Lead and zinc slags may also be treated to recover oxides. The process may be speeded by carrying out the reaction in the presence of sulphides or chlorides. Metallurgical smelting.-A furnace with a refracting lining of alumina, magnesite etc. is strongly heated under a natural gas reducing atmosphere. Iron oxide supplied is rapidly reduced to molten iron which runs down the lining to leave via orifice 13. Slag forming agents may be added in which case, the less dense slag forms an innermost molten layer resting on the molten iron layer. The two liquids flow out of the furnace and are separated by settling.