Dynamic Simulation and Model-based Control System Design for Comminution Circuits - Advanced Control and Supervision of Mineral Processing Plants - page 243

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Figure 5.20 Stabilizing controller: percentage of solids and water flow rate

The supervisory level (second level) calculates a set-point for filling level so that
the SAG mill always operates at a point near its maximum possible power draw.
Power draw level is modeled as a quadratic function of mill filling level [37]. The
strategy tries to maximize power draw while keeping all variables within defined
constraints. If no constraint is active, then optimal operation will be obtained when
the gradient of this quadratic function is zero.

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Figure 5.21 Optimizing controller: filling level, fresh flowrate, mill speed, gradient

Figure 5.21 shows how the supervisory level changes the set-point every 50 min-
utes so that ore feedrate is maximized. Gradient values near zero provide an indica-
tion of being at an optimal value. At time 250 minutes, ore hardness increases and