IMPROVING THE UNDERSTANDING OF CANE PREPARATION BY MEASURING THE PROGRESS OF POWER USAGE AND CANE SIZE REDUCTION THROUGH THE SHREDDER

MODERN shredders produce high levels of preparation (greater than 85 POC) but use considerable energy, generally 30% of steam turbine-generated power used in the factory. There is considerable interest in reducing the power consumption of the shredder. Part of the process of improving the shredder design/operation is to understand the shredding action in terms of power usage and cane preparation. This paper describes work using the SRI small-scale shredder (900 mm diameter) to obtain measurements on the progress of preparation in the shredder. The progressive power consumption and preparation through the shredder was investigated by sequentially removing components of the shredder (grid bar, anvil bar, front wall). At each stage, measurements of power consumption and preparation were recorded. For the three varieties used in the test program, the average findings were: hammers only 73 POC @ 2.63 kW.h/t; add front wall/anvil bar 81 POC @ 3.56 kW.h/t; add grid bar (0 mm) 90 POC @ 5.80 kW.h/t. The average results of power/preparation measured through the shredder were compared to typical factory shredder measurements and those from impact tests. The comparisons indicated that the front wall, anvil bar and grid bar sections were essential for the shredder to allow the shredder to achieve high levels of preparation, given the restriction of operating the shredder at 100 m/s tip speed, and that those shredder components represented a reasonably efficient method of greatly increasing the preparation which can be achieved by the shredder. The paper also details a series of trials that were conducted aimed at increasing the cane preparation in the low power consumption, hammer only configuration. The options investigated were different launch speeds of the billets into the shredder (2.5 m/s. 5.0 m/s, 8.3 m/s and 10.6 m/s), variations in billet lengths (70 mm, 220 mm and 700 mm), and recycle of a portion of the prepared cane. The various launch speeds were found to produce relatively similar preparation levels. The smaller billet lengths resulted in higher preparation, which was expected. It was noted that the energy required to cut the cane into short billets would detract from the apparent power/preparation benefits of short billets. Recycling the coarse components was found to raise the overall preparation from the 73 POC region typical of hammers only to 85 POC, but the total power usage was only slightly less than from the conventional shredder (i.e. with the front wall, anvil bar and grid bar in place).