Two- and Three-dimensional Simulation of Ball and Rock Charge Motion in Large Tumbling Mills

摘要

The mining industry routinely uses ball mills and semi-autogenous mills for processing ore bodies. A typical mine site processes 80,000 tons/day of ore employing two semi-autogenous mills and four-ball mills. Since the energy consumption is 2-5 kWh/ton of ore for grinding rock particles to sieve mesh sizes, a substantial portion of the cost of ore processing is expended in tumbling mills. The energy efficiency of tumbling mills can be examined by directly looking at the motion of rocks and steel balls inside the mill. The make-up of the charge and the lifter bars attached to the inside of the mill shell can be designed particularly to maximize the mass of ore fractured per unit of energy spent on the mill. At the same time, the unnecessary collisions of steel balls against the mill shell can be reduced. Furthermore, the cascading charge flow can be altered in such away as to maximize grinding efficiency. The emergence of the discrete element method (DEM) allowed simulation of charge motion in tumbling mill. In the last eight years, the DEM for simulation of tumbling mills has advanced sufficiently that it has become a very practical tool in the mining industry. This manuscript gives an overview of the DEM as applied to the tumbling mill problem. Both the two- and three-dimensional (2-d and 3-d, respectively) models as well as the parallelization of the 3-d code are described, followed by validation against plant size mill data.