Assessment of new soft cane varieties : final report submitted to Sugar Research Australia 2015/081

In 2016, three new cane varieties, SRA1, SRA4 and QC04-1411, were either released or were proposed for release into the Bundaberg and Mackay districts. According to the pre-release fibre quality measurements undertaken by Sugar Research Australia, all three varieties were classified as a soft cane. This report documents a series of experiments undertaken to better define soft canes and to measure the effect that these three varieties had on factory operation and performance. The experiments were undertaken collaboratively by QUT, SRA and field and factory staff in the Isis, Farleigh, Millaquin and Maryborough districts. Trash has been shown to affect the fibre quality measurements, reducing the short fibre content by typically 12 units and most likely increasing the shear strength measurement by about 6 units. Comparing the cleaned stalks of cane usually used for fibre quality measurements to factory-prepared cane, it seems likely that shear strength is underestimated by about 7 units and short fibre content is underestimated by about 4 units (most likely shredder dependent). SRA1 had a low fibre content of typically 10% and an impact resistance lower than the minimum criterion considered for normal canes. The other two varieties, SRA4 and QC04-1411 had relatively normal fibre content of about 14%. While their impact resistance was low, it was still within the normal range. Shear strength is the other fibre quality parameter with a defined normal range. The shear strength of all three varieties were within the normal range, with SRA1 having the lowest values. The final fibre quality parameter, short fibre content, does not have a defined normal range. It is noted, however, that of the 35 results examined, the two highest values were for QC04-1411 and the next two highest values were for SRA1 (Q240 was the fifth highest and also had a shear strength lower than QC04-1411). The low fibre content of SRA1 is considered the biggest problem regarding the processing of the three varieties. With current major varieties having fibre contents of typically 12% to 15%, SRA1 is particularly different and will cause fuel balance issues. The fact it is different to the other varieties means that it is difficult to configure a factory to consistently achieve a fuel balance, with the likelihood that there will be periods when fuel will need to be purchased and other periods when fuel will need to be disposed of. The fact it is low means that a factory will need to be reconfigured at high capital cost to become much more energy efficient. All three varieties exhibited the soft cane characteristic of generating low mill torques. While there is some hope that mills could be re-set to achieve their torque set point when processing soft cane, the wide variation in variety characteristics between the soft canes and the other varieties in the cane supply means that a much wider control range is required to be able to achieve their torque set points across the different varieties. Associated with the inability to maintain torque set points, bagasse moisture contents from the soft canes were found to be higher than normal. This result was particularly pronounced with SRA1 where Isis and Millaquin recorded increases in final bagasse moisture content of between three and eight units. The available information from the processing of SRA4 and QC04-1411 also showed higher bagasse moisture content but the results are less conclusive, due to the limited nature of the trials of those varieties. Not all factory boilers can withstand significant increases in bagasse moisture content. The Millaquin experience processing SRA1 resulted in a rapid drop in steam pressure that only avoided a boiler shutdown because SRA1 was only processed for 15 minutes. Sustained factory operation when feeding boilers with high moisture bagasse is problematic. There was a potential concern with the processing of QC04-1411 where the bagasse caused feeding and combustion issues. It is unknown if this problem is characteristic of the variety or simply a one-off incident. Other problems such as poor mill feeding and frothing when processing the soft cane varieties were experienced but are believed to be able to be resolved with relatively small capital expenditure. While the yield of some of the soft cane supplies was measured to be quite high, those yield benefits need to be weighed up against the additional factory processing costs that will be incurred in terms of capital upgrades and stops.