A misconception in regulatory control of secondary grinding circuits

Abstract

Control systems for secondary grinding circuits follow widely accepted guidelines in the mineral processing industry. However, some common practices appear to be built on questionable assumptions, and become detrimental to the variability of the product size distribution. Secondary grinding constitutes an intermediate unit operation reducing the diameter of ore particles to meet the requirements for downstream separation. Hence the importance of the product size distribution, which represents the only product attribute measured online directly related to actual economic performance of the overall plant. This paper demonstrates with a simulation case study how controlling the hydrocylone inlet pressure at a constant setpoint does not serve the sought purpose. It compares this base case scenario with alternative ones, aiming for a constant particle size index at the overflow. Results show that under hardness disturbances, a constant hydrocyclone inlet pressure does not lead to any benefit, and even induce additional variability to the product size index resulting from the adjustments made to the hydrocyclone feed flow rate.