Division BAT 55
United Kingdom
In order to use energy efficiently during the production of alumina from bauxite, BAT is to use one or a combination of the techniques given below.
| Technique | Description | Applicability | |
|---|---|---|---|
| a | Plate heat exchangers | Plate heat exchangers allow a higher heat recovery from the liquor flowing to the precipitation area in comparison with other techniques such as flash cooling plants | Applicable if the energy from the cooling fluid can be reused in the process and if the condensate balance and the liquor conditions allow it |
| b | Circulating fluidised bed calciners | Circulating fluidised bed calciners have a much higher energy efficiency than rotary kilns, since the heat recovery from the alumina and the flue-gas is greater | Only applicable to smelter-grade aluminas. Not applicable to speciality/non-smelter-grade aluminas, as these require a higher level of calcination that can currently only be achieved with a rotary kiln |
| c | Single stream digestion design | The slurry is heated up in one circuit without using live steam and therefore without dilution of the slurry (in contrast to the double-stream digestion design) | Only applicable to new plants |
| d | Selection of the bauxite | Bauxite with a higher moisture content carries more water into the process, which increases the energy need for evaporation. In addition, bauxites with a high monohydrate content (boehmite and/or diaspore) require a higher pressure and temperature in the digestion process, leading to higher energy consumption | Applicable within the constraints related to the specific design of the plant, since some plants are specifically designed for a certain quality of bauxite, which limits the use of alternative bauxite sources |