Boliden has developed an optimizing grinding control strategy that is used on all five autogenous grinding lines in the Boliden Aitik concentrator (mill capacity 18 Mtpy). The control strategy maximizes throughput subject to two operational constraints in the mills, motor power and mill filling (i.e. pulp level). Mill filling is measured with strain gauge sensors mounted inside lifters in the mills, and transferred to the control system via radio. Neither constraint can be exceeded due to risk of damages to the machinery. Excessive motor power is detrimental for gearboxes and motors, and excessive mill filling/pulp level may be detrimental for mill bearings as back spillage of pulp flows over the bearings. Excessive mill filling may also in extreme cases lead to overfilling of the mills causing expensive losses in production. The ore properties determine which limitation that is critical at a given time. Coarse feed size and/or hard ore results in control towards the power limit, while fine feed size and/or soft ore results in control towards critical pulp level/mill filling. Power is the most common constraint. This grinding control strategy has, in combination with operator education programs and structured improvement exercises, lead to significantly increased utilization of the installed power in the mills and a corresponding increase of production.
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