Belt Conveying
Innovative Coarse Ore Conveyor System in Chilean Copper Mine
25.08.2009 | Deskman: Wolfgang Geisler
Located high in the Andes, Minera Los Pelambres open-pit copper mine in Chile is operating successfully since 1999. Siemens technology, combined with customized services, help to make this mining operation one of the country’s showpieces for reliability, availability, energy efficiency and resource protection.
The Los Pelambres copper mine is situated around 200 km to the north of Santiago at an altitude of 3200 meters above sea level. The concentrator is located at 1600 meters altitude to avoid stress associated with working at 3200 meters for the personnel of the concentrator as well as reduce the requirements on the equipment of the beneficiation plant and to protect it from risks of rock and snow avalanches. Therefore, a reliable and highly efficient solution was needed for the transportation to the concentrator. Due to the steep decline and the particularly challenging conditions like dust, moisture, vibration and large temperature fluctuations, all components are exposed to considerable stress, which had to be considered during the design.
The drive and automation solution designed and provided by Siemens was to install a 12,7 km long downhill conveyor belt system to connect the primary crusher with the concentrator, which even generates up to 19 MW of energy. The conveyor was designed to move a maximum of 8700 t/h of bulk material and transports the copper ore on a 1.8 m wide belt at a speed of 6 m/s. Initially, there were 8 three-phase squirrel cage motors with a rated power of 2.5 MW each, fed from Simovert® ML medium-voltage converters at the heart of the drives.
Motors used in opencast mining must operate in particularly challenging surroundings due to dust, moisture, large temperature fluctuations, and vibration. To meet these challenges, a motor design has been used for Los Pelambres that has proven itself over decades under the toughest conditions imaginable. The electrical and thermal design, as well as the actual manufacture of these machines, was done in close cooperation with the Siemens Dynamowerk in Berlin. Conveyors moving material over steep declines, such as at Los Pelambres, make significant demands on the drive system with regard to the safety of people and machines in addition to the low-stress operation of gearboxes, pulleys, and belts. An arrangement involving the redundant configuration of control and communication systems, supported by multi-stage monitoring systems in the mechanical and electrical braking equipment, ensures conveyor safety in all operating modes.
An innovative closed-loop control and drive concept ensures stress-free operation of the conveyor at all times. This feature is particularly important at the Los Pelambres mine as the local power grid is subject to irregular and unscheduled power outages. In these situations, the conveyors come to a halt while UPS equipment supplies the auxiliary drives. Even under such conditions, the equipment acts as if the shutdown took place as scheduled, meaning that, even in an unscheduled power outage situation, no additional stress arises and the mechanical brakes experience no excessive wear. These and other requirements made on a downhill conveyor can only be satisfied with AC drives, in this case, in conjunction with a Simovert® ML medium-voltage converter based on a 3-point design implemented with GTO technology.
An active front-end (AFE), combined with a chopper, enables conveyor segments to be kept well under control that would ordinarily exceed the performance limits of network-controlled converters and lead to a fault in the drive system. Together with the Transvector closed-loop control, a number of compensation and correction control loops ensure optimal operation of the conveyor. Right from the start of design engineering Los Pelambres, considerable value was attached to making commissioning as simple and effective as possible. This element also paid of in conveyor maintenance and service. In 2007, two of the three conveyor belts were fitted with an additional drive train, consisting of a motor, a converter, a transformer and medium-voltage switching devices, in order to enhance conveying capacities to match an expansion of the concentrator throughput. The belt drive output has been increased from 20 MW to 25 MW.
As a special feature the conveyor system at Los Pelambres generates energy during operation with nominal load. The 10 drive motors of the belt consume power only if the belt is carrying less than 800 mt of ore. Otherwise, they generate up to 19 MW of power. At 90 million kWh, output in 2007 represented about 15% of the mine’s power needs, reducing energy costs and cutting carbon dioxide output by more than 50,000 mt/y. In 2005, the Chilean Ministry of Economics awarded Minera Los Pelambres the National Prize for Power Efficiency for this technology.
From the beginning of this project in 1999, Siemens has provided Minera Los Pelambres with preventative and corrective maintenance services for the entire conveyor system. Los Pelambres has renewed this contract several times; the most recent one expires in 2011. Siemens is responsible for all mechanical and electrical equipment, automation systems and instrumentation, as well as for materials and spare-parts management. An on-site Siemens service team handles maintenance of the entire conveyor system, from the rollers to the belt and the motors.
A fiber optic network links all parts of the installation where sensors monitor critical status parameters on various components. This enables the installation to be monitored around the clock, irrespective of where service personnel are stationed. Faults can be detected at a very early stage and via the Internet, experts can examine the conveyor belt system and its peripheral equipment from anywhere in the world. Any faults detected can thus be analyzed and the installation can be restarted, if necessary, as well.
Payment for this maintenance service includes performance-related components: the level of success is measured in price per ton, which is trend-setting in the mining industry, and on the basis of key performance indicators such as availability, reliability and asset condition. Moreover, Siemens and Los Pelambres agree on a maintenance budget each year with Siemens taking responsibility for adherence to this budget.
Siemens AG Sector Industry IS
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