INDA 2017

Best of Germany 2014 - Mining Equipment and Mining Technology

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Page 18 of 51

VDMA 17 2017 • VDMA MINING SUPPLEMENT rial coming from the surface miner needs to be crushed, as opposed to more than 26% when processing ripped coal. Another trial location was a sedimentary ore deposit that is mined using surface miners vs. a conventional drill-and-blast method. There, the surface miner continually produced feed materi- al with 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 degrada- tion occurring during the mining process. Simulating the rehandling of material, Wirtgen conducted a study to establish the amount of material degradation that does occur. For simulation purposes, 80 mt of material were loaded by a wheel loader and run through a screen- ing plant several times. With every throughput, the amount of fine material increased significantly. During five test cycles for coal, the amount of minus 4-mm coal increased from 19% to 26%, represent- ing 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 stockpiling results in an even higher increase of the fine fractions. Keeping in mind that even this kind of "soft" re-handling caus- es significant material degradation and that a lot of re-handling steps occur all along the mining process, it is important to mini- mize the number of re-handling steps. What is more, every re-han- dling step itself results in additional costs. This is where Wirtgen surface miners offer a twofold advantage: Material mined with a surface miner has not been blasted, but cut out of the ground by the rotating cutting 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 min- er 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, mining operators can overcome the mechanical limits of conven- tional drive systems, and benefit from economies of scale — as demonstrated in several projects in South America. A direct conveyor drive system comprises a low-speed syn- chronous motor, a cycloconverter or voltage source converter, drive control, power distribution, an E-House and a cooling system. Elim- inating 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 confirmed 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, each with a power rating of 3,800 kW, and the associated Sinam- ics SL150 cycloconverters, E-House cooling system and convertor transformers. In 2015, Siemens commissioned direct conveyor drive systems for two additional copper mines. One was for one of the largest cop- per mines in the world, which is located in Chile (5 x 5,000 kW). For the overland conveyor supplied by thyssenkrupp with a length of more than 10 km, Siemens supplied five direct-drive systems (for a total of four conveyors) with the largest conveyor motors pres- ently in operation. The overland conveyors at Las Bambas copper mine in Peru were designed and supplied by thyssenkrupp and have been in Wirtgen surface miners — here the 4200 SM — cut and crush the rock with a special cutting drum and load it onto dumpers in a single pass via conveyor system. Wirtgen is the only manufacturer that can offer a performance range up to 3,000 t/h with direct loading by conveyor belt.

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