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 novel low grade heat driven reconcentration process. It consists of both flashing and falling film techniques, and is meant to couple to one of the available waste streams in the evaporation unit as a heat source and thereby reconcentrating the process liquor. The heat source has been identified as the process condensate stream. The condenser of the reconcentration process is cooled by barometric water from the recovery lake. The generated freshwater is either discharged or sent to the freshwater lake so as to manage the water balance of a refinery. For 200 m3/hr process condensate simulated at two fixed temperatures of 75°C and 85°C, the novel process generates up to 34% more reconcentrated process liquor (which translates to 9 m3/hr and 17 m3/hr of reconcentrated process liquor, respectively), and between 9% and 12% reduction in terms of specific capital cost as compared to the conventional multi effect falling film evaporation system.