| 摘要 |
A continuous process of making inert, stable, anhydrous alumina, principally of alpha alumina, from hydrated alumina, comprises feeding the hydrated alumina to a first and endothermic stage, supplying to the alumina in the first stage sufficient heat to effect a rapid preliminary substantially complete dehydration of the alumina without allowing any substantial change in the physical structure of the dehydrated alumina, continuously passing the dehydrated alumina from the first stage to a second and exothermic stage, maintaining the dehydrated alumina in the second and exothermic stage at a higher temperature and for a longer period of time than in the first stage to ensure complete dehydration of the alumina and to effect substantially complete recrystallization of the dehydrated alumina, and collecting the dehydrated recrystallized alumina at the end of the second stage, the vapour driven off the alumina being separately extracted from each stage. The first stage may be carried out for up to 60 seconds at a temperature of 300 DEG -600 DEG C., and the second stage for 10 to 120 minutes at 900 DEG -1200 DEG C. The heating for the first stage may be accomplished by flowing hot gases counter-current to the alumina hydrate. In the described apparatus, the first stage is carried out in a series of cyclone heat exchangers, and the second stage in either a fluidized bed or a rotary furnace. Since the second stage is exothermic it is sufficient to initially heat the second stage apparatus to the required temperature, no further heating then being necessary. |
