Implementation of a first-mill cane-feeding control strategy based on a cane-harvest system

Abstract

The analysis of the extraction performance of three Colombian sugarcane factories revealed large variations in milling operations. Because more than 70% of the extraction occurs in the first mill, the chute level behavior was evaluated, and the coefficient of variation (CV) values were greater than 55%. This was mainly caused by the control strategy not being capable of mitigating the effect of processing different densities of sugarcane. This variability resulted from the frequent change between manual and mechanically harvested sugarcane. An in-line indicator was designed to determine the type of sugarcane; this was based on the electric current drawn by the cane leveller. In collaboration with factory A, a control strategy was designed that changes the velocity relationship of the conveyor belts depending on the sugarcane harvest type. The control strategy was also applied in the second factory (B), with only a 1.5 m high first-mill chute, which affects feeding stability, but dynamic current protection was added. This was based on PID controllers that manipulate conveyor velocity proportionally, reducing the chance that it would come to a halt, protecting the cane knives and shredder from electrical overload, and providing a more constant mill feed. The evaluation of the new control strategy was compared with the old control loops, increasing the overall extraction of 0.40 and 0.68% for factories A and B, respectively. Better stability was achieved in the first mill chute with a CV of approximately 30%, which was also reflected in the chute levels of the following mills. The new control strategy used the instruments and actuators already installed without any additional investments and can greatly improve the milling performance and, as a result, profitability.