| 摘要 |
1,143,880. Alumina from aluminium hydroxide. METALLGESELLSCHAFT A.G. and VEREINIGTE ALUMINIUM WERKE A.G. 18 Dec., 1967 [16 June, 1967], No. 57423/67. Heading C1A. Anhydrous alumina is made from aluminium hydroxide in a fluidized bed process. Aluminium hydroxide from 1 is charged into a Venturitype drier 3 where it is dewatered and partially dehydrated by the hot exhaust gases from a fluidized bed furnace 9, and is carried by the gas to cyclone separators 4 and 5, whence moist air is discharged, and the alumina then passes to Venturi drier 6, where it is entrained by dustbearing exit gas from the furnace, and carried to cyclone 7, whence the alumina passes to furnace 9. The furnace is at a temperature of 600 to 1200‹ C, and solids entrained in its exhaust gas are part recycled to the fluidized bed by recirculating cyclone 8, and part cycled to fluidizing cooler 16, and cooled by a bank of cooling tubes 21 and also by direct cooling by passage of fluidizing air, prior to discharge as product at 25. The heated air from cooling tubes 21 is used as fluidizing gas for the fluidized bed in 9, and the heated fluidizing gas from cooler 16 is fed into furnace 9, after removal of entrained solids in recirculating cyclone 23 as secondary air, at an inlet height above the grate of 0À3 to 1À5 times the height of the water gauge in mm. corresponding to the pressure drop to which the fluidized bed in the furnace is adjusted, the ratio fluidizing gas : secondary air being 1: 2 to 4: 1. Heating of the furnace is effected by a supply of residue-free fuel into the zone between the grate and the secondary air inlet. |
