| 摘要 |
Non-magnetic, iron oxide ores are converted to magnetic magnetite for concentration by magnetic separation by introducing the ground ore into a reaction zone with a reducing gas under sufficient pressure to blow fine ore particles directly through the reaction zone to effect magnetic conversion by flash roasting thereof whilst the remaining coarse particles pass through at a slower rate to effect magnetic conversion by roasting. The ore may be haematite and may be ground to minus 65 mesh. The reducing gas may be produced by combustion of a hydrocarbon gas, e.g. methane, or a solid fuel reformed gas, e.g. producer gas within the reaction zone. The spent reducing gases may be separated from the converted ore and used as an aid in heating the reaction zone and to preheat the ore, and a portion may be cooled and used to cool the converted are particles. In the Fig. ground ore is fed into and dried in countercurrent cyclone 15 by contact with hot spent reducing gases from conduit 22. The dried ore is further heated by hot, spent reducing gases in cyclone 18 and fed into the interior tube 11 of a concentric double tube kiln rotated by motor 14. A mixture of air preheated hydrocarbon gas or solid fuel reformed gas and spent reducing gas through pipe 38 is admitted into tube 11 so that ore particles of minus 200 mesh are blown rapidly through tube 11. The magnetite is separated from hot, spent reducing gases in dust collector 23 and fed into cyclone 25 where the waste heat is recovered in prehating fresh reducing gas admitted through valve 35 and spent reducing gas from cyclone 23 which has been cooled by heat exchange with air in heat exchanger 28 and scrubbed in scrubbing tower 33 to remove entrained fines. The preheated gas mixture is conveyed through pipe 36, mixed with air from blower 39 and fed into the tube 11 wherein partial combustion produces the hot, reducing gases. The minor portion of the hot, spent reducing gases from cyclone 23 and the hot air from heat exchanger 28 are passed into annulus 13 of the kiln through pipes 30 and 31 respectively, which serves to insulate the reaction zone and maintain the temperature of the kiln by further burning of the spent reducing gases. From annulus 13, the hot gas mixture passes through pipe 21 to cyclones 18 and 15 to dry and preheat the ore. |
