Coal Age

OCT 2015

Coal Age Magazine - For more than 100 years, Coal Age has been the magazine that readers can trust for guidance and insight on this important industry.

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Page 22 of 51

sweet spot to be 2.5 rpm while reaming the shaft. Vent holes were drilled parallel to the 15-in. pilot hole for two reasons. First, since the raise bore drill cut through mul- tiple coal seams on its way to the surface, so it was important to ventilate it and flush water over the cutters to suppress sparks that could light methane gas. Water also cooled the cutters. Secondly, within 300 yards of the new drill shaft, large intake fans were sending thousands of cubic feet of air per minute to the face of the mine's workings. With the addition of the vent holes, air drawn down the holes by the intake fans increased gas ventilation. Prior to breaking through the surface, these fans were regulated down to prevent a large influx of dust. The Mine Safety and Health Admin- istration regulation was for less than 1% methane on the bit face. To dilute the potentially hazardous gas in the coal seams, air from portable compressors was used in addition to supplement the mine's ventila- tion system, sending air at 1,700 cfm down the annulus of the drill string. The Atlas Copco Robbins 123RH C raise boring machine is technically rated for making 10- to 20-ft-diameter holes. Raisebor's achievement has proven much larger holes are possible. About the Article T h i s a r t i c l e w a s p r o v i d e d c o u r t e s y of Atlas Copco; it was first published in the company's Mining & Construction magazine. October 2015 21 r a i s e b o r i n g c o n t i n u e d Using a pilot hole, the raise boring drill pulls the reamer upward letting cuttings fall to the bottom of the raise. A scoop is used to clear the cuttings below.

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