5
As highlighted above, a drop in crusher availability
(i.e., 75 to 65%) incurs significant project costs, resulting
in an increased footprint for the coarse ore stockpile and
an increased number of dump trucks to maintain crusher
throughput. Installing coarse ore stockpiles below 15 m
in diameter is not cost-effective. Due to the high primary
crusher availability, incorporating a COS in the flowsheet
can be avoided with a direct feed option for the grinding
circuit.
DUTY STANDBY VS DUTY ONLY
PROCESS EQUIPMENT
In comminution flowsheet design, the selection of duty-
only vs. duty-standby equipment is primarily driven by the
maturity of the maintenance team managing the equip-
ment and the allowance in the design to manage quick
replacement of the spare parts. Figures 4 and 5 illustrate
examples of duty-standby and duty-only pebble-crushing
facilities and cyclone feed pumps. Table 5 presents sum-
mary comparisons between the two circuit types. The main
Figure 4. Duty-standby vs duty only pebble crushing facility
Figure 5. Duty-standby vs duty only cyclone feed pump
Table 5. Advantages and disadvantages of duty standby and
duty-only pebble crushers
Duty Only Duty Standby
Advantages Lower capital cost
Smaller footprint
requirement
Low steel and
concrete quantities
Lower requirement
of spares
High availability of
the facility
Lower impact on the
process (i.e., no need
to bias uncrushed
pebbles to SAG mill)
Flexible to operate at
higher throughput
rates—can switch to
duty-duty mode
Disadvantages Not flexible to
operate at higher
feedrates
Will impact the
process during an
offline period—i.e.,
uncrushed pebbles
sent to the SAG mill
Larger footprint
(more concrete and
steel)
More equipment
to maintain in the
flowsheet