LOAD & HAUL
TITANSTEXAS IN
Erik Zimmermann explains how two surface miners are bringing light to South Texas and Northern Mexico
Corporation in Eagle Pass, Texas, USA – right on the border with Piedras Negas, Coahuila, Mexico. T e extracted coal is then transported over the border by train to a multi-unit power plant in Coahuila. Meanwhile, at another open cast mine
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in Texas, another 4200 SM is extracting lignite, just as economically. T e two surface miners – the largest
models in Wirtgen’s product range – went into operation in the past two years and are extracting coal with a low sulphur content, operating 24/7. T e 4200 SM is 6.53m high and has an operating weight of 204,300kg. It is
ne 4200 Wirtgen Surface Miner (SM) is extracting sub-bituminous coal at an open cast mine owned by the North American Coal
powered by a highly effi cient diesel engine with 1,521hp. When cutting soft material such as coal, limestone or gypsum, the 4200 SM cuts down to a depth of 830mm using a 4,200mm-wide milling drum and operating in an up-cut direction.
NEW MINE, NEW EXTRACTION METHOD Eagle Pass Mine is located in an area that has been worked for coal since as early as the late 19th century. At the mine, a 2,550-ha area is available for coal extraction, off ering suffi cient deposits for eight years of mining work. One special
The loading conveyor of the 4200 SM can be slewed 90° to either side
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feature of this location is the fact that the seams are very thin, some of them only 15cm thick. “And this is precisely where the Wirtgen surface miner proves invaluable. We use it to selectively extract coal from the rock. T is enables us to achieve a high material quality,” explains John C. Duff ey, chief engineer of Camino Real Fuels. T e four seams lie beneath an 18.3m
layer of top soil and overburden, in a series of layers around 6m thick. “Barely 1.65 to 2m of this is coal,” says Duff ey. “We conduct preliminary examinations in an attempt to fi nd out exactly how much coal there is under the surface, but we are often surprised. T e thin seams can be mined precisely with the 4200 SM, which also saves us a great deal of money for processing. We don’t need a primary crusher at the trans- shipment centre anymore, because the 4200 SM crushes the coal directly during loading.” T e surface miner crushes the coal to a maximum size of 10cm while minimising fi nes. As coal fi nes tend to block the loading conveyors at the transfer points when there is a high moisture content, a low proportion of fi nes is a great advantage. “Blasting, excavating and loosening – the 4200 SM does away with all this,” explains Duff ey. “We don’t have a permit for blasting and we don’t blast coal or surrounding rock. Almost 95% of our coal is crushed and loaded by the 4200 SM.”
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