A method for reducing the durchlaessigkeit and capability for attacks of the walls of a an aggressive flue signal containing from gefa as a function of the refractory material, preferably for the production of aluminum by fused salt electrolytic reduction and apparatus for carrying out this method

摘要

871,114. Crucibles. MONTECATINI SOC. GENERALE PER L'INDUSTRIA MINERARIA E CHIMICA, and DE VARDA, G. Dec. 30, 1957 [Jan. 5, 1957], No. 40349/57. Class 82(1) [Also in Groups V and XXXVI] The permeability of the inner walls of a vessel containing a corrosive liquid metal and composed of porous refractory material e.g. magnesia as used in electrolytic furnaces for the production of aluminium, is reduced by injecting an inert gas e.g. nitrogen, 'carbon monoxide, carbon dioxide, helium or the gas evolved during treatment of the corrosive liquid in the vessel, through the walls of the vessel towards the liquid therein at a pressure sufficient to ensure the formation of gas bubbles on the wall surface contacting the corrosive liquid. The gas pressure, which is preferably of from 1.05 to 3 atmospheres, may be sufficient to cause the gas bubbles to leave the pores at the wall surface and form a gaseous layer between liquid and wall. The pores are preferably pre-treated by impregnation with pitch which is subsequently cokefied, thus regularizing pore size. As shown, fused salt 1 is contained in a heat-insulated vat 2 made of refractory bricks e.g. magnesia of uniform porosity not greater than 15%. Small holes or channels 5 which do not extend to either inside or outside faces of the vat communicate with a tube 8 through which inert gas is passed. Bubbles of gas 13 form at the pores in the wall surface. Vat surfaces 6 and 9 not in contact with corrosive liquid are preferably sealed and insulated e.g. by metal coatings or, where vats are constructed of magnesia for use at temperatures below 950‹C. by potassium metaborate, calcium and potassium sulphates, and potassium metasilicate or disilicate. Evolved gas leaves by a pipe 14. The process may be applied to a multi-cell electrolytic furnace such as that described in Specification 800,092.