Preheating and incubation of cane juice prior to liming: A comparison of intermediate and cold lime clarification

In the U.S., cold lime clarification remains the clarification process of choice in raw sugar manufacturing. A comparative study of cold vs intermediate lime clarification was undertaken at a factory that operated intermediate liming (similar to30% mixed juice (MJ) of pH 5.2 +/- 0.3 was preheated to 87-93 degreesC to help maintain clean limed juice heaters, incubated at similar to54 degreesC, and then limed) but still had the pipes to revert to cold liming (MJ incubated and limed at similar to40 degreesC) for this study. Hourly samples were collected over a 6 h sampling period across cold and intermediate clarification processes on two consecutive days, respectively, and this was repeated three times across the 1999 grinding season. A total of 1.57% less sucrose was lost to inversion reactions across intermediate rather than cold liming. In intermediate liming, which required similar to4.6% less lime, preheating of only 30% of the MJ markedly removed color (-29%), dextran (-10%), and starch (-24%) and caused large flocs to form that settled faster in the clarifiers. Faster settling led to an impressive 4.6% (season average) more turbidity removal across the clarifiers in intermediate rather than cold liming. Intermediate clarified juice (CJ) turbidity (season average 2028 ICU +/- 675) was approximately half of cold CJ turbidity (average 3952 ICU +/- 1450) with over 2-fold more CJ turbidity control. Subsequent turbidity values and control were significantly improved in the final evaporator syrup samples too. For both processes, juice incubation caused similar to10% color removal, but this was offset by color formation on liming, because of the alkaline degradation of invert; however, overall, more color was removed than formed in intermediate liming. Starch was reduced in the incubator tank, for both processes, because added filtrate reduced the acidity enabling natural diastase from the cane to degrade starch. Some dextran occasionally formed in the incubator tank, in both processes. Summed across measured parameters, intermediate liming appears to offer several advantages over cold liming.