Dynamic Simulation and Model-based Control System Design for Comminution Circuits - Advanced Control and Supervision of Mineral Processing Plants - page 240

The next two simulations illustrate the effects of a 30% increase in hardness on
two ore feedrates. Level and power draw for an ore feedrate of 1095 ton/h is depicted
in Figure 5.16, where the change occurs at 200 minutes. Only after 50 minutes is
there a variation in level and power draw, reaching a stable, steady-state.

29

28

27

26

25

24

1000 1500 2000 2500 3000 3500 4000

1.074 x 10 4

1.072

1.07

1.068

1.066

1.064

1000 1500 2000 2500 3000 3500 4000

Samples (k)

Figure 5.16 Level and power draw for a change in the ore hardness with a 1095 ton/h ore feedrate

However, if the ore flowrate is 1200 ton/h, the SAG mill enters a region where
level and power draw do not follow the same tendencies. As level increases, power
draw decreases, stabilizing at 30

. 5% and 10 . 71MW respectively, as seen in Figure

5.17.

5.6.2.2 A Two-level Optimizing Strategy

The goal of an optimizing strategy is to maximize feedrate without violating opera-
tional constraints. To reach this objective, a two-level strategy is proposed. The first
level considers the stabilization of main operating variables. The second level sets a
desired filling level so that the mill can operate near this optimal point.
The design of the control strategy considers a system composed of a SAG mill
and a sump as a MIMO system with four inputs, five outputs and two unmeasurable
disturbances as listed below.
The inputs are:

1. water addition to the sump box ( u 1 );
2. fresh ore feedrate ( u 2 );
3. pump speed ( u 3 );
4. mill speed ( u 4 ).