MATERIAL HANDLING IN MINING – LOS PELAMBRES
When by the end of 1999 the Los Pelambres overland
conveyor system starts its operation, a new benchmark in belt conveyor
technology will be set. This presentation gives an introduction into the design
of this record breaking conveyor system and will elaborate on some of its
innovative features.
Introduction The Los Pelambres copper mine is located approximately 200 km
north of Santiago, Chile,
high in the Andean mountains next to the border to Argentina. When the owner decided
to proceed with a major expansion, it became necessary to find an efficient way
to transport the coarse ore from the mine to the new concentrator facility at a
rate of 8,700 metric tons per hour, over a distance of some 13 kilometers and
dropping over 1300 meters in elevation. To handle this task, a belt conveyor
system consisting of three individual conveyors has been selected. To protect
the conveyor from the rock slides and avalanches prevalent in this area, most
of the conveyor runs inside tunnels which have been driven through the mountain
side.
Conveyor Layout
In July of 1997, a contract was awarded to Krupp Canada to
design and supply the entire coarse ore conveyor system. At the time of this
presentation, the installation of the conveyor system is nearing completion.
The commissioning of the system is expected to take place in the last quarter
of 1999. Conveyor Layout Copper ore is transported by large mine haultrucks to
the primary crushing plant located at the outside perimeter of the mine. A
gyratory crusher reduces the run-of-mine material to belt-conveyor acceptable
particle sizes of 300 mm and less. The crushed material is collected in a surge
bin underneath the crusher, then reclaimed by the crusher discharge conveyor
and stacked onto the
Crusher Discharge Conveyor and Mine Stockpile
Material Handling in Mining – A Case Study
Technical Seminar 1999
mine ore stockpile. With a belt width of 3,000 mm at a belt speed of 3 meters
per second, the crusher discharge conveyor is designed to convey 14,000 tons
per hour. The material is reclaimed from the mine stockpile by four belt
feeders and loaded onto the first of the three coarse ore overland conveyors.
At the end of the coarse ore conveyor system, the copper ore is discharged onto
the concentrator stockpile. The discharge end of the last coarse ore overland
conveyor can shuttle back and forth over a distance of 62 meters, stacking the
material onto the longitudinal stockpile.
Head End Conveyor Cv-007 with Concentrator Stockpile location
The overall conveying distance of 12.7 kilometers is
divided into three individual conveyors of 6.0 km (CV-005), 5.3 km (CV-006),
and 1.4 km (CV-007) lengths. The conveyors follow a downhill slope of
approximately 10 % with a short 25% slope at the end of the tunnel at conveyor
CV-007. Drive System Due to their similar length and vertical drop, conveyors
CV-005 and CV-006 arelargely identical with regard to their drive
configuration. Both conveyors are equipped each with four 2,500 kW drives.
Conveyor CV-007 is equipped with two 2,500 kW drives, bringing the total
installed drive power to 25 MW. The conveyor system will operate in motoric
mode at low capacities, and will change to generative operation at a belt
loading of 20% or more. In this condition, the drives will feed electrical energy
back into the power grid. The electric motors are regulated by adjustable
frequency drives (AFD). When started, the conveyors are accelerated in 40
seconds following a S-shaped speed curve. Stopping is
performed in Drive Station Conveyor CV-005 sequence based on predetermined
stopping ramps ranging in length from 76 to 80 seconds. Operational parameters,
such as belt speed, belt tension, belt loading, motor torque, etc. are
continuously monitored and processed by the drive control system to adjust the
speed and to detect any possible failure. Since loss of control can lead to
catastrophic consequences for a downhill conveyor of this magnitude, utmost
attention was given to the control system. Depending on the diagnosed
conditions, the conveyor system can be brought to a complete stop in several
different ways: In fully functional conditions, the drives will be decelerated
by the AFD to their full stop, by feeding the electric energy into the power
network. In case of power failure (network not available), the electric energy
is diverted into externalresistors, allowing stopping the conveyors
electrically without external power. As a next level of safety, a large
mechanical brake system is installed, consisting of a total of 13 disc brakes,
with a diameter of 2500 mm each. The mechanical brake system can either operate
fully PLC controlled, following a determined deceleration ramp, or in case of
PLC failure or hydraulic failure, engage mechanically (fail safe).
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Material Handling in Mining – A Case Study
Technical Seminar 1999
Great effort was made to develop a suitable mechanical brake system. The
temperatures generated by the mechanical brakes during an emergency stop create
a challenge regarding the selection of the brake lining material and the brake
disc Conveyor Belt ST-7800 design. Also, in the interest of safety, almost all
brake control components are fully redundant. Conveyor Belt
Brake Caliper Assembly
Conveyors CV-005 and CV-006 are equipped with steel cable belting rated at
ST-7800. This marks a new world record for conveyor belting, assuming the
distinctions of the world’s strongest conveyor belt from the
Prosper-Haniel mine in Germany, which carried the record for the last 14 years.
Belt forces will reach 250 tons during running, and can peak at 320 tons during
emergency braking. Special attention was given to the splice as the weakest
link of the belt. Testing performed at the University of
Hanover, Germany showed that the fatigue strength of the splice exceeds 50% of
the ultimate brakingstrength of the belt. As a safeguard, a splice failure
detection system has been provided for the first time. This system is designed
to detect splice elongation resulting from impending splice failure, and to
safely stop the conveyor before the damage occurs. Reducers The 2500 kW
two-stage helical bevel reducers are the largest reducers ever employed for
conveyor drives. At a unit weight of 26 tons, the reducers are fully
self-cooling and do not rely on auxiliary devices for temperature regulation.
Several studies were made by Universities and scientific institutes to validate
the reducer design, such as a heat dissipation study, a finite element analysis
of the housing, and a bearing smear study.
2500 kW Conveyor Drive
Reducers during Testing
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Material Handling in Mining – A Case Study
Technical Seminar 1999
Pulleys As another new record, the drive pulleys supplied for the Los Pelambres
overland conveyors are the largest conveyor pulleys built to date. The pulleys
have a shell diameter of 2,500 mm. The pulley shaft measures 630 mm in
diameter. The bearings have an inside diameter of 560 mm. The total assembly
weight is 37 tons per pulley. Conclusion The Los
Pelambres overland conveyor system sets a new standard for many aspects of belt
conveyor design. While it is technically possible to build yet larger systems,
it can be assumed that the limits of practicality and economy will not allow
pushing the envelope much further.
Conveyor Drive Pulley
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