Hi Friends,
As per the chemistry of Bayer's process, no evaporation unit is required in Alumina refinery. But it is not practically feasible to achieve ideal operational conditions to avoid ingress of external dilution to various process streams because of presence of impurities with bauxite and other process requirement.
Evaporation units are installed in Alumina refinery for meeting two process requirements as listed below-
- Evaporation of extraneous dilution for management of plant volume and
- Salting out carbonates for controlling impurities in Bayer liquor.
In addition to these two objectives, it also meets the supply of good quality hot water as condensate to co-generation plant resulting in negligible requirement of make up water to boilers. No direct heating of any process stream is done by injection of steam as ingress of water to process stream is considered as poison as it badly affects the process efficiency figures.
Overall water balance for Alumina refinery clearly reveals that specific evaporation requirement in efficient plant ranges from 2.10 to 2.20 tonnes per tonne of alumina production. This figure may be used as a guideline to compare the same with any operative Alumina refinery to have an idea about dilution control as well as volume management in Alumina refinery.
Trust, you will agree with my personal views. Kindly put your views / suggestions / remarks / comments, if any.
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Thanks and regards.
Kunwar Rajendra
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