GB682356A - - Google Patents

Abstract

682,356. Glass manufacture. METALLGES. AKT.-GES. Sept. 26, 1950 [Oct. 31, 1949; Oct. 31, 1949], No. 23601/50. Class 56. Mixtures of initial materials for use in the production of glass are prepared by mixing the constituents consisting substantially of quartz, soda, and lime with waste glass material and solid fuel, granulating and sintering the granulated mixture disposed in a layer on a gaspermeable grate by passing air through the layer in accordance with the suction draught sintering process to form a separate intermediate product adapted to be subsequently melted in a glass melting furnace. Alternatively the constituents and waste glass without fuel may be mixed, granulated, and sintered, whilst disposed on the gas-permeable base of a sintering apparatus, by the passage therethrough of hot gases, for example the hot waste gases of glass furnaces. Advantageously calcium carbonate is replaced by quicklime or calcium hydrate, and the coke fuel is moistened and powdered with calcium oxide before being mixed with the granulated constituents. The permeability of the charge to gas during the sintering process is further ensured by adding 1-4 per cent, preferably 2 per cent, of wood flour, which burns at a low temperature leaving cavities. Additions such as arsenic, ZnO, CeO 2 , CaSO 4 e.g. as gypsum or anhydrite, or other alkaline earth sulphates may also be made, such additions may be made during sintering and are not too finely ground. Sodium sulphate or alkali chlorides may be used instead of soda. The fuels preferably have low ash and iron contents, and the SiO 2 , CaO, Al 2 O 3 , and MgO in the coke ash may be taken into account in compounding the mixture. Burnt limestone may be used as a quicklime, or lime sludge or calcined dolomite may be used. 10-50 per cent by weight of glass waste, cullet, or glass fragments disintegrated to particles below 5 mms. may be used as waste or return material to be added to the initial constituents. The grate of the sintering apparatus is advantageously first covered with a layer of presintered material. Granular quartz of maximum particle size of 1 to 2 mms. is a suitable source of SiO 2 . A short intermediate furnace, e.g. a rotary tube furnace traversed by part of the incandescent gases of the tank furnace with air added to maintain the oxidising condition of the gases, may be interposed between the sintering apparatus and the melting tank to preheat the sinter, re-oxidise any reduced iron oxide, and to burn out the final carbon residues. Advantageously hot gases having a low sulphur content are used for the sintering, and care is taken e.g. by adding sufficient air to the hot combustion gases to ensure the complete combustion of any sulphur obtained as sulphide during the reaction of the components.