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JUL-AUG 2017

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24 www.coalage.com July/August 2017 surface mining The Titans of Texas Two Wirtgen surface miners load coal and lignite in south Texas A 4200 Surface Miner (SM) extracts sub-bi- tuminous coal at North American Coal's Eagle Pass mine in Texas near the Mexican border town of Piedras Negras, in Coahui- la State. Raw coal is then transported over the border by train to a multi-unit power plant in Coahuila. Meanwhile, at another open cast mine in Texas, another 4200 SM is extracting lignite just as economically. The two surface miners — the largest models in Wirtgen's product range — went into operation in the last two years and are extracting low-sulfur coal and lignite, op- erating 24/7. The 4200 SM is 6.53 meters (m) high and has an operating weight of 204,300 kilograms (kg) (225 tons). It is powered by a 1,521-horsepower (hp) diesel engine. When cutting soft material, such as coal, limestone or gypsum, the 4200 SM cuts down to a depth of 830 millimeters (mm) using a 4,200-mm-wide milling drum and operating in an up-cut direction. New Mine, New Extraction Method The Eagle Pass mine is located in an area where coal mining dates back to the late 19 th century. Piedras Negras, the name of the town on the other side of the border, translates as "black rocks," an obvious ref- erence to the coal deposit. "Every ton we extract goes to a coal- fired power plant in Mexico," said John C. Duffey, chief engineer of Camino Real Fuels. A subsidiary of the North American Coal Corp., this company operates the mine for the owner, Dos Republicas Coal Partnership (DRCP). Eagle Pass has re- placed the depleted open-cast mine Siglo XXI (21 st century) in Mexico, on the other side of the Rio Grande — or Rio Bravo, as it is known in Mexico. At the mine, roughly 6,300 acres (2,550 hectares) are available for coal extraction, offering sufficient reserves for eight years of mining work. The total quantity of de- posits is much larger, however. One spe- cial feature of this location is the fact that the seams are very thin, some of them only 15 centimeters (cm) thick. "And this is precisely where the Wirtgen surface miner proves invaluable. We use it to selectively extract coal from the rock. This enables us to achieve a high material quality," ex- plained Duffey. The four seams lie beneath an 18.3- m layer of top soil and overburden in a series of layers around 6 m thick. "Barely 1.65 m to 2 m of this is coal," Duffey said. "We conduct preliminary examinations Cutting, crushing and loading in a single pass, the Wirtgen surface miner makes coal mining simple, economical, eco-friendly and safe. The new Eagle Pass mine began selectively mining the thin coal seams with a Wirtgen type 4200 SM surface miner in October 2015.

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