The use of conductivity measurements in the control of grinding mills

CIM Bulletin, Vol. 80, No. 907, 1987

M.H. MOYS, Department of Chemical Engineering, and A. MONTINI, Department of Electrical Engineering University of Witwatersrand Johannesburg, South Africa

A conductivity probe mounted in the shell of the mill has been used to measure the behaviour of the load in the mill as a function of operating variables. It was found that certain properties of the conductivity signal correlate strongly with the per cent solids of the slurry passing through the mill; in particular the angular location 6D of the shoulder of the load is an increasing function of the per cent solids. A method for measuring the viscosity of the pulp discharging from the mill has also been developed. The use of the measurements in mill control is illustrated by simulating various control strategies for open circuit milling. It is shown that the use of 6D allows very tight but imprecise control of the slurry rheology in the mill, while the use of viscosity is subject to severe limitations in speed of response. A cascade control system involving both measurements provides adequate control of slurry rheology within the mill. Applications to closed circuit milling are discussed.

Keywords: Mineral processing, Grinding mills, Mill operation, Slurry rheology, Milling circuits, Computer control.