A novel low grade heat driven process to re-concentrate process liquor in alumina refineries

Evaporation is an essential process in alumina refineries both to produce water for such applications as residue washing processes, and re-concentrating process liquor back to the main process circuit for further digestion. This article reports on the application of a re-concentration process driven by low grade heat. It couples flash and falling film evaporation, fed by a low-grade heat source, to recover heat and concentrate process liquor. Process condensate is the stream used for this evaluation. The condenser of the re-concentration process is cooled barometrically by water from the recovery lake. The freshwater generated is either discharged or sent to the freshwater lake so as to manage the water balance of a refinery. For 200 m3/h process condensate simulated at two fixed temperatures of 75 °C and 85 °C, the process generates up to 36% more re-concentrated process liquor, and about 10% less specific capital cost compared to the conventional multi effect falling film evaporation system.