Clear Juice Turbidity Monitoring for Sugar Quality

A considerable amount of South African raw sugar is sold to export markets. Consistently good filterability of this sugar is important for satisfying the requirements of customers. To the refiner, the filterability of raw melt is important as this affects refinery throughput. Analysis of filtrationimpeding impurities in raw sugar has shown that, among other things, poor juice clarification could be related to poor filtering sugars. To this end, a South African Sugar Association sponsored investigation into sources of high turbidity in clarified juices and their relation to poor filtering sugars was begun. Results from the 2002 season show that both process variables and cane quality were causes of high juice turbidities. In particular, flow disturbances, poor pH control, and poor and frequent start-up and shutdown incidents were major process variable contributors to poor turbidities. Some of the worst start-up and shutdown incidents would have resulted in carryover. Poor cane quality consistently resulted in high juice turbidity. While cane quality is largely a field issue, evidence suggests that slowing down of the factory does improve juice turbidity. This strategy would be particularly beneficial when employed to minimise the frequency of the shutdown and start-up often associated with poor cane supply. It is planned to correlate juice turbidity to sugar filterability and to relate these to various aspects of cane quality. Filterability of raw sugar is generally only measured at the Sugar Terminal and then only on composited samples. More frequent measurements are needed for process monitoring and, to this end, filterability test equipment is being manufactured for use at mills.