Patent GB-349625-A (GB)
Title: Improved method of and apparatus for producing molten and refined metals from their crude ores
IPC: C21B13/12
Filed: 1930-03-01
Abstract: 349,625. Extracting and purifying iron. WHITE, A. E., 5, Quality Court, Chancery Lane, London.-(Doherty Research Co.; 60, Wall Street, New York, U.S.A.) March 1, 1930, No. 6840. [Class 72.] Metal charge reduced from crude ore is fed upwardly in the vertical column to a furnace hearth, the top of the charge column being used as an electrode from which to cast an arc to an electrode in the furnace, the temperature of the top of the column being controlled by varying the rate of feed of the column. In the embodiment, the crude ore is fed from a hopper 10, Fig. 4, through a pulverizer and mixer 12 and a shoot 14, to a feed hopper 16 of a sloping low temperature reduction furnace 18 which is rotatably mounted on supports 20 and formed with longitudinal shelves 22 so as to produce a showering effect of charge material when the furnace 18 is revolved by a motor 156 through gearing. Hot gases from a main supply 30 circulate in a helical flue 24 round the outside of the furnace 18. The charge material passes from the furnace 18 through a stationary chamber 36 and a magnetic or air separator 44, from which the purified charge passes through a shoot 50 into the lower end of a feed barrel 52 of an underfeed electric furnace 54. The furnace 54 comprises a dome roof 56 of refractory material, preferably bonded zircon, which rests on a hearth 58 of similar material, the parts having a tight joint 60. A sump 62 in the hearth floor is formed with tap holes 64, 66 for slag and refined metal respectively. A circular feed aperture 70 in a central boss 68 of the furnace floor connects with the feed barrel 52. The barrel 52 is an upright hollow cylinder closed at its lower end by a gear box 72 in which is journalled a hollow drive shaft 74 of a screw feed mechanism 76. A central aperture 78 in the shaft 74 connects the interior of the barrel 52 with a pipe 80 through which hot gases may be passed into the barrel charge. Short ring sections 82 of the barrel 52 are preferably formed of material which is electrically conductant and of low heat conductance, and the sections 82 are insulated from each other to serve as contacts through which electric current may enter the barrel charge from a movable contact 84 electrically connected through a transformer 87 with a generator 88, Fig. 4. The return lead of the generator 88 is connected through the transformer 87 to an annular insulated conductor 92 built in the boss 68. Spaced electrodes 94, preferably of graphite, are embedded in the boss 68 and alternate with radial drains 96 adapted to take the flow of molten metal without shortcircuiting arcs cast from the electrodes 94 to the top of the charge column. The conductor 92 is preferably hollow and water-cooled. A pipe connection 98 leads through the furnace roof to lead off hot gases and fumes to the gas main 30. A valved byepass 100 connects the main 30 with an annular chamber 102 in the feed barrel wall, the chamber 102 communicating with the interior of the feed barrel through a perforated cylindrical screw 104. The furnace roof is water-cooled. A starting electrode 134 is movably mounted over the furnace hearth and may be placed in the main generator circuit by a connection 136 controlled by a switch 138, the power supply to the conductor 92 being preferably cut off by a switch 140 when quick heats are developed by casting an arc from the electrode 134 to the top of the charge column. To control the rate of charge feed to the furnace hearth, variable speed motors 130, 132 are geared to actuate respectively feed screws 76, 142, the screw 76 being mounted in the barrel 52, and the screw 142 in the feed shoot 50. Fig. 1 shows the furnace operating as a resistance furnace, the current passing through the charge from an adjustable contact 84 and segment 82 to electrodes 94, conductor 92 and back to the generator 88. In Fig. 2, the furnace is shown operating as an arc furnace, the arc being thrown from the top of the charge column to the electrodes 94. In operation, a pulverized charge of iron ore and coal or coke breeze is fed from the mixer 12 to the furnace 18 and is heated from the flue 24. Further heating of the charge mixture may be effected by passing hot gases from the furnace 54 into the furnace 18 through a valved connection 158. The temperature of the charge is preferably maintained slightly below 1000‹ C. If a magnetic separator 44 is used, the charge is cooled in the chamber 36 to restore magnetic properties. After separation of the gangue, the sponge iron, mixed with a little carbonaceous material, is fed to the base of the feed barrel 52. Refining fluxes, such as lime, haematite or fluor spar, may be mixed with the sponge iron at the top of the shoot 50. The rate of upward of the charge in the feed barrel 52 is controlled by the feed screw 76, and to assist in preheating the lower portion of the charge column, steam and hot gases may be introduced through the aperture 78 in the feed screw shaft. The gases, broken down to hydrogen and carbon monoxide, may pass out through the chamber 102 and the byepass 100, or may be supplemented by hot gas introduced through the byepass 100 and chamber 102, the gases then passing off through the main take-off 30. An electric contact is made between the column of sponge iron and a section 82 of the feed barrel wall so that the charge column forms one electrode of the furnace. The movable contact 84 is adjustable by a rack and pinion device 160 so that the degree of preheating due to the electric resistance of the charge column may be controlled. According to the rate of feed of the charge, the furnace 64 is adapted to operate as a resistance furnace, or an arc furnace or as a combination of the two. When the rate of charge allows material to drop over on to the carbon-electrodes 94 so that a closed circuit is formed through the charge, the furnace is stated to operate as a resistance furnace. At a slower feed rate, the heating is stated to take place partly by resistance and partly by arcing and at a still lower rate of feed, only by arcing. It is stated that the electric resistance of the charge column may be varied by varying the amount of refining fluxes added through the shoot 50, and refining fluxes may also be added through a normally sealed door 161 in the hearth of the furnace 54. The gases in the furnace 54 are removed through the take-off 30, and after passing through a dust and fuel precipitator (not shown) are preferably led to the heating flues 24, thence through a steam generator whence the cool gas is passed to a scrubber. The gas is then stored, or may be passed to a power unit, e.g. an internalcombustion engine 122, or steam boiler and engine set, adapted to drive the generator 88. A thermocouple 148 may be fitted over the hearth of the furnace 54 and may actuate automatic control devices to operate relays (not shown) to change the speed of the feed screw 76, and thus vary the rate of feed.