Investigation into the cause of turbidity at Malelane mill 2013

摘要

The Malelane mill experienced major turbidity events during early spring 2005 and again in 2013. The 2005 events were investigated by a team of consultants, with the outcomes being inconclusive. With the 2013 event, a collaborative effort between the RCL Foods Sugar Agricultural division and factory teams led to the conclusion that the turbidity could be traced back to sources of cane supplied during the event. The methodology included tracing every load of cane delivered to the mill over an extended period and then linking the load sources to subsequent turbidity events in the mill. The sequence and source of loads in the period prior to the events were analysed and it was found that deliveries from certain farms always occurred prior to turbidity events. By using a co-variance analyses derivative a strong correlation between specific deliveries and turbidity events, as well as severity of turbidity, was determined. From these results a simple model was developed which was used for the balance of the season to develop a turbidity prediction system for the mill. The prediction system enabled the mill to pay attention to procedures during risk periods and thereby avoided further major disruptions in manufacturing. The turbidity events were linked to deliveries from cane fields on very sandy soils. Where the deliveries from such farms were concentrated in time or as a series of extended sequential deliveries, turbidity events were triggered. The actual turbidity was linked to the formation of amorphous silica. Once the rainy season started the turbidity no longer occurred although some deliveries should have sparked events.