A low cost automatic mill load level control strategy

Abstract

A low cost control strategy has been developed, which can maintain a mill production near optimum, with little operator intervention. The mill load control strategy is based on the use of classic sensors such as mill sound and recirculating bucket elevator power plus the not-so-often used mill motor power. The heart of the strategy consists of a standard PID algorithm for control: therefore, it is not rule-based or considered an expert system. Because of this, there is no requirement for special hardware or additional computers. The control strategy is integrated into the plant's existing control system which provides training and maintenance benefits. The strategy uses the traditional signals such as mill sound and recirculating bucket elevator power as well as the mill power to determine the mill load level. The load level is defined as the total of the grinding charge and material in the mill. The control strategy attempts to keep this load level as constant as possible. The setpoint for the master controller is derived from the mill motor power. The strategy automatically takes into account changes in material grindability, grinding charge, material retention time and different product types. Maintaining a mill load level is accomplished by balancing the mill load level against the power-derived setpoint.