Reducing the energy footprint of grinding circuits: the process control paradigm

The grinding process in ball mills is notoriously known to be highly inefficient: only 1 to 2% of the inputted electrical energy serves for creating new surfaces. There is therefore obvious room for improvement, even considering that the dominant impact mechanism in tumbling mills is a fundamental liability limiting the efficiency. Moreover, the Coalition for Energy Efficient Comminution estimates that on average, 53% of the energy consumed on a mine site is for comminution processes. This represents a tremendous leverage to generate economical and environmental benefits. This paper analyses how properly designed control systems allow a better usage of the capacity of grinding circuits, and a reduction of the specific energy consumption even without modifying the product size target. Three different control systems are compared: (1) typical basic regulatory, (2) regulatory control of the product size attribute, and (3) model-based predictive control. Simulation results show that controlling the product size distribution attribute ensures not only meeting downstream requirements and avoiding overgrinding, but also allows processing higher throughput in some instances, hence decreasing the specific energy. The discussion highlights the pros and cons of all three scenarios.