The ASIA Miner - Reporting Important Issues to Mining Companies in the Asia Pacific Region
Issue link: http://asiaminer.epubxp.com/i/786114
VDMA 54 VDMA MINING SUPPLEMENT • 2017 a minus 1-mm size fraction as low as 15% to the processing plant. The normal plant feed (includes material of drill-and-blast and surface miner operation) contained 25% and more fines less than 1 mm. Re-handling contributes significantly to the material degradation occurring during the mining process. Simulating the rehandling of material, Wirtgen conducted a study to establish the amount of ma- terial degradation that does occur. For simulation purposes, 80 mt of material were loaded by a wheel loader and run through a screening plant several times. With every throughput, the amount of fine materi- al increased significantly. During five test cycles for coal, the amount of minus 4-mm coal increased from 19% to 26%, representing an increase of 34%. A similar result was found with sedimentary ore: the fine fraction increased by 24% during five test cycles. None of the steps in this re-handling simulation (loading, trans- port to the screen deck, sizing on the screen deck itself) involves the high material stress levels that would be induced, for example, by a dozer moving on stockpiled material. Nevertheless, significant material degradation was measured during the simulation. One can assume that the material degradation that takes place during stock- piling results in an even higher increase of the fine fractions. Keeping in mind that even this kind of "soft" re-handling causes significant material degradation and that a lot of re-handling steps occur all along the mining process, it is important to minimize the number of re-handling steps. What is more, every re-handling step itself results in additional costs. This is where Wirtgen surface min- ers offer a twofold advantage: Material mined with a surface miner has not been blasted, but cut out of the ground by the rotating cut- ting drum, thus the level of fines is already low. But as the material is loaded straight onto a truck, re-handling is kept to a minimum and thus the level of fines stays as low as possible. Looking at the complete mining operation, using a surface miner simplifies mining operation and reduces the number of process steps, resulting in immediate cost savings. Direct Conveyor Drives Offer High Availability Declining ore grades, leading to increased material transport and plant throughput requirements, is one of the major challenges in the current mining environment. With direct conveyor drive systems, min- ing operators can overcome the mechanical limits of conventional drive systems, and benefit from economies of scale — as demon- strated in several projects in South America. A direct conveyor drive system comprises a low-speed synchro- nous motor, a cycloconverter or voltage source converter, drive con- trol, power distribution, an E-House and a cooling system. Eliminating various components of the drive train reduces maintenance costs and spare part inventories, and allows the system to offer a uniquely high degree of availability. Even in challenging applications, direct conveyor drives can achieve a benchmark availability of more than 99% — as con- firmed by real-world data from the Antapaccay mine in Peru. There, the belt system transports approximately 5,260 metric tons per hour (mt/h) of ore from the mine to the processing plant over a distance of 6.5 km. The Siemens drive system for the belt conveyor consists of two low-speed synchronous motors, The 2.5-km overload conveyor system at the Las Bambas copper mine in Peru uses a drive system developed by Siemens that consists of two low- speed synchronous motors with a total power of 4,400 kW.