SRDC final report project BS177S - Proving a natural gamma ray soil monitor in sugar mill application
Soil in sugarcane supplied to mills is a major industry concern, causing wear on milling trains and in boilers, increased difficulty in clarification and additional costs and sugar losses in handling mud solids. Sugar quality is also at risk. Visual assessment of soil in cane has been used but this method is inaccurate. Development of a method for measuring soil in cane based on the natural gamma radiation from soil commenced at Tully Mill in 1992 in conjunction with BSES and CSIRO (Minerals Division). A prototype instrument was obtained from CSIRO for the work. Success with this experimental monitor up to and including 1996 resulted in support from SRDC to purchase and evaluate a commercial instrument from Mineral Control Instrumentation Ltd (now Scantech Ltd). A CANESCAN 1500, based on a model successfully applied to the coal industry, was installed at Tully Mill for the beginning of the 1997 season. The new instrument was required to provide improved reliability and availability of technical backup compared with the experimental monitor. It also provided greater precision for counts per second (cps) data, enabling the use of separate values for each of the potassium (K), uranium (U) and thorium (Th) channels in addition to total cps in prediction equations. Although the work with the CSIRO instrument showed that soil in cane could be measured, several phenomena needed to be resolved. It had been observed that soil predictions tended to be overestimated during dry weather periods and to be underestimated in wet weather. A distinctive diurnal cycle had been observed for the predicted soil in cane. Also, large peaks in gamma radiation occurred prior to the arrival of a storm.