Patent GB-819165-A (GB)
Title: Improvements in method and apparatus for producing silicon dioxide
IPC: C01B33/18
Filed: 1955-10-11
Abstract: Particulate, amorphous silicon dioxide is prepared by oxidizing silicon monoxide in a gas-mixing device comprising a container partitioned into two chambers, the first chamber being in heat-exchange relation with the second and having an inlet and outlet for circulation of coolant therethrough, and the second chamber having a gas inlet, and annular baffle to ensure gas distribution throughout the chamber and a cylindrical passageway through the chamber, and a circumferential outlet connecting the second chamber and the passageway through the wall of the passageway, and directed to converge at a point adjacent the end of the <PICT:0819165/III/1> <PICT:0819165/III/2> <PICT:0819165/III/3> passageway, whereby gas from the second chamber is mixed with gas passing through the passageway without creating positive or negative pressure on the gas entering the passageway.  The SiO is obtained by reducing silicon-containing material in a furnace and is oxidized by an oxidizing gas.  Oxidizing gas may be air, oxygen, steam, carbon dioxide, or mixtures thereof, which may be heated, but preferred is air at room temperature. Silicon-containing material, e.g. sand, quartz, or mineral silicate may be reacted with anthracite, coke, carbon black, silicon, or silicon carbide.  A 1 : 1 molar ratio charge of sand and carbon is contained in reaction chamber 4 of carbon, graphite, or "Alundum" (Registered Trade Mark), enclosed in circular steel shell 2 with intermediate packing 3 of sand or refractory.  An arc is struck between carbon electrodes 5, 5, mounted with insulating sleeves and washers 6, 7, and provided with water-cooling glands 8, 8.  Silicon monoxide and carbon monoxide are vaporized from the charge and leaving crater 61, pass through port 9 in cover 11, and then through gas mixer ring 15, which is of smaller diameter than port 9, with increasing velocity.  Air is injected into the furnace vapours in ring 15, and the resulting mixture of silica and carbon dioxide passes through conduit 16 which may be cooled by water spray from ring 18 collected in trough 19 and conduit 17 to a bag filter or screen for collection. The gas mixer ring 15 (Fig 4), has two annular chambers in the walls, chamber 41 being for circulation of cooling water, and chamber 42 for air.  Chamber 42 has circular baffle plate 46 to distribute the air evenly, and the air flows out of ports 48, inclined at about 45 degrees to the axis of the ring at 50-600 cu.ft./lb. product.  Wear ring 49 having bevelled surfaces 50, 51 may be provided to prevent distortion of the ring 15. Reciprocable, rotatable scraper 52 on shaft 53 is provided to remove silica deposits from the mixer ring 15.  Alternatively, the ports may be drilled at the desired angle, e.g. greater than 2 degrees but less than 90 degrees in a ring having straight walls instead of inclined wall 47, or a narrow slit may be used in place of the ports.  At 90 degrees to the electrodes, feed channel 20 (Fig. 2) is provided, and sand and carbon charge mixture from hopper 21 is pressed into reaction chamber 4 by continuously, or intermittently operated hydraulic ram 22, having return spring 31, so that the hottest material is forced up to the arc and the crater 61 is shaped as required.  Plate 34 on ram 22 acts as a gate to close hopper 21. Other feed channels and hoppers 35, 36, may be provided.  The process may be continuously operated by continuous supply of sand and carbon mixture and of electrodes, and by the use of a series of bag filters. The silica product is of average particle size 5-50 mm  and of average surface area 80-350 sq. m./grm.  It is stated that a resistance furnace and screw conveyer feeds may be used as alternatives, and that lime may be used as a flux.