Environmental Engineering Reference
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In order to model the residence time more accurately, a set of mixing tanks in se-
ries can be considered. Thus, the total residence time can be obtained by connecting
several models in series. In other words, the discharge of one mill will be fed to the
next mill. The volume hold-up of each model
V
can be used to adjust the residence
time of each sub-model.
5.4.2 SAG Mill
The modeling of SAG mills has been addressed by different researchers [6, 12-14].
In this simulator, the model developed by Amestica [13] was implemented. The
main input and output variables are defined in Figure 5.6.
feed
f
q
f
f
γ
f
Flowrate
Water flowrate
Size distribution
Hardness
product
Flowrate
Water flowrate
Size distribution
Hardness
p
q
p
p
γ
Figure 5.6
A SAG mill
This model is based on a dynamic balance equation for ore and water mill con-
tents, as well as several sub-models for grinding, classification, mass transport and
power draw in terms of hold-up, pulp solid percentage inside the mill, and volumet-
ric filling fraction.
The grinding phenomena inside the mill is modeled by the block diagram de-
picted in Figure 5.7, where the process is decomposed into two steps.
The first block represents the grinding itself. The second block represents the
classification of ore flow emerging from the grinding chamber and considers the
effect of grate and pulp lifters. Thus, the mass balance of ore content in the grinding
chamber can be determined by the following equation:
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