Coal Age

JUL-AUG 2018

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22 July/August 2018 monster wall continued 12,000 ft of development, it seems like a small bridge to gap for a significant im- provement." Mathematically, they could easily justify another 500 ft of develop- ment and an additional 500 ft of longwall mining equipment, shields, armored face conveyor (AFC) and panline. But, could it work from a technical standpoint? It Can Be Done To explain how CONSOL Energy deter- mined it could be done, Wilson discussed three hurdles that would have to be cleared: maintaining the hydraulic pres- sure on the shields, providing enough electrical power to the section, and gener- ating enough horsepower to overcome the weight of the additional steel. "At Bailey, we run Kamat four-pump systems, but we are only using three of the pumps at one time," Wilson said. "Adding 500 ft of face, we would likely lose 150 psi to 200 psi of pressure at the tailgate. One of the ways we could deal with this would be to place a ring-main at mid-face to give more flow down the face to push the shields. Or, we could also run all four pumps at one time. It would simply be a programming issue." The AFC chain would be one of the biggest concerns. "Due to the increased forces, we would likely move from a 48- to a 56-mm AFC chain," Wilson said. "Length- ening the face will add 1,600 flights and 22 tons of steel for the drives to pull. There was a time when people thought 48-mm chain would be too big." More importantly, what's going to push this chain, Wilson asked. "We would have to work with Cat on this project be- cause the CST 65 would be too small to drive that additonal 500 ft of larger AFC chain," Wilson said. "We would have to migrate to a CST 115, which is about 10 inches (in.) taller. What's another 10 in.?" Tongue in cheek, this maintenance man- ager said he couldn't understand why these production people couldn't just cut an additional 10 in. The CST 115s are also double the weight, which means the drive would have to be broken down and reas- sembled underground. The horsepower calculations, howev- er, are the proof in the pudding. "We are currently running three 1,900-hp motors on the face," Wilson said. "We would have to jump to three 2,600-hp motors. That would allow us to run from the headgate to the tailgate at 39 fpm and from tailgate to the headgate in 33 fpm. The total applied power would be 7,800 hp. At full load, with the face fully loaded running form the tail- gate to the headgate, we're looking at 7,600 hp total and the three 2,600-hp motors would give us about 5% horsepower on reserve. Variable frequency drives are be- coming more common in longwall appli- cation and they could also play a vital role in load sharing." CONSOL Energy currently runs 1.75- m shield, but 2-m shields have been prov- en in the Pittsburgh No. 8 seam at the Cumberland mine. "Weighing 28.8 tons, these shields are heavier than the ones we currently use and we would have to pur- chase more 650 scoops to move them," Wilson said." When they first started to review this project, they thought it would never work because of the increased voltage require- ment (12,470 volts) to power the extra 500 ft. "After much discussion, we decided that we could do this," Wilson said. "It would be a more advanced mining layout elec- trically for cabling systems. One side of a borehole would have to be dedicated to the longwall face. We currently run a 350 MCM cable into the section. That would have to be changed to 500 MCM cable all the way. To drive the belt, we could run a separate 350 MCM cable or a 4/0 cable to keep the amperage down. At a full load, a 500 MCM cable will provide 630 amps. For a full 2,000-ft face at full load, we would have 544 amps. So, we determined that 12,470 volts would work. We didn't think it would be possible, but it could be done." As far as ground control, rock me- chanics and pillar design, they deferred to the engineering department. After run- ning 1,500-ft faces for a while, Yackubos- key said he could see where there might be some issues. "We might have to increase the pillar sizes on development," Yacku- boskey said. "When you gain four months lead time per year, you would have time to expand the pillar size." CONSOL Energy engineers said the abutment pressures didn't differ that much going from 1,100 to 1,500. Ideal- ly, the roof should cave freely and one would think the roof behind a 2,000-ft face would cave more easily than a 1,500- ft face, he reasoned. In closing, Yackuboskey thanked the engineers at CONSOL Energy and Cat who helped him and his cohorts with these calculations. "The help they provided in answering some of these 'what-if' ques- tions could someday lead to 33% more coal, fewer longwall moves, a savings of as much as $6 million and a one-year im- provement in lead times," he said. The numbers are there and now the question is: Who will make that game- changing leap? Using a Cat CST115 would add an extra 10 inches of clearance.

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