THE EFFECT OF LIMING CONDITIONS IN JUICE CLARIFICATION

The juice clarification process used in the Australian cane sugar industry is best described as simple defecation. However, there are many variants of this simple process used throughout the cane sugar industry. Milk of lime is often used instead of lime saccharate solutions, lime addition may be batch-wise rather than continuous, and the point of lime addition may be to cold juice (35–40oC), to intermediate juice (72–76oC) or to hot juice (100oC). Despite a wealth of practical experience, the impact that the various liming conditions have on the physical chemistry of clarification is not well known. This study reports some recent laboratory work to quantify the effects of liming techniques on clarified juice quality and floc settling behaviour. The results indicate that liming with lime saccharate gives lower turbidity but higher mud levels and slower settling flocs than liming with milk of lime. However, the clarified juice obtained with saccharate has a higher calcium level but a lower phosphate level than milk of lime clarified juice. The higher calcium level in the clarified juice obtained with saccharate may result in an increase in scale formation in the evaporators. The underlying physical chemistry of the clarification process is used to explain the observed differences in the performance of the various liming techniques.