EFFECT OF OPERATING CONDITIONS ON SUCROSE LOSSES IN EVAPORATORS IN AUSTRALIAN SUGAR FACTORIES

COMPOSITIONS OF JUICE and condensate samples collected at various locations in the Robert evaporator sets at five Australian sugar factories were determined in order to investigate the magnitude of sucrose degradation and the consequences of those degradation reactions, such as reduced pH of condensate. The factories were chosen because their different evaporator configurations allowed investigation of the impact on sucrose degradation caused indirectly by steam economy measures, such as extensive vapour bleeding (required for maximising cogeneration). Sampling was undertaken across two seasons, for different clarifier juice pH set points and while the evaporator sets were both clean and dirty. This test program examined the impacts of clarified juice pH and the presence of scale on the magnitude of the sucrose losses. The sucrose degradation results were compared with predictions using the Vukov expression (a function of juice pH, juice brix, temperature and residence time). Significant sucrose losses of over 0.5% were both measured and predicted in factories that incorporate extensive vapour bleeding and higher exhaust steam temperatures. A number of operational strategies and equipment options that can be implemented by factories were then examined and modelled to propose recommendations on ways that such large losses during juice evaporation can be reduced.