Dynamic Simulation and Model-based Control System Design for Comminution Circuits - Advanced Control and Supervision of Mineral Processing Plants - page 241

32

30

28

26

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 5.17 Level and power draw for a change in the ore hardness with a 1200 ton/h ore feedrate

Outputs are:

1. power draw ( y 1 );
2. pebbles flowrate ( y 2 );
3. sump level ( y 3 );
4. pulp density of sump output flowrate ( y 4 );
5. level filling ( y 5 );
and disturbances:

1. hardness ( d 1 );
2. feed particle size distribution ( d 2 ).
In this application, all output variables are not required to reach a set-point. Some
of them, for example the flow rate of pebbles, are only required to stay within a
certain range.
In the first level, four control loops are implemented: inlet pressure in the hy-
drocyclones is controlled by the number of hydrocyclones in operation. (Therefore,
this variable is considered as constant in this simulation.) Sump level is controlled
by pump speed, considering a model in terms of pump speed, water flowrate and
fresh ore feedrate. Density is controlled by the water feedrate and also considers ore
feed rate as a measurable disturbance. Filling level is controlled by the ore feedrate
and mill speed is subject to constraints in the pebble flowrate. The controller consid-
ers a model including mill speed, fresh ore feedrate and the pebble flowrate, which
is modeled in terms of mill speed and fresh ore feedrate.
The stabilizing strategy was simulated by considering a constant particle size
distribution and a ratio between water flowrate and ore feedrate of 76% as well as a
change of 30% in ore hardness at time 250 minutes. Figure 5.18 shows the response