Coal Age

MAY 2017

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28 www.coalage.com May 2017 moving overburden continued rarely reach 90% of their fill factor and most shovels rarely load at 6,000 tons per hour (tph) when they should be loading at 10,000 tph because they are waiting on trucks." About 12 years ago, MMD worked with a mine in Colombia to develop an apron feeder for loading trucks with a dragline. The mine couldn't buy a shovel because of long lead times, so they developed an alternative system. "The trucks drive un- der a hydraulically powered feeder, which can be started and stopped immediately," Pitchford said. "We could load trucks three times faster. What we also found was that we could load trucks accurately [98% fill factor]. The system also eliminated the time consumed in reversing the trucks into their loading position. The trucks fall in line and it takes about 75 seconds to load them precisely." MMD also built an IPSC installation in China where a shovel loads rock into it continuously and it sizes the material and places it on a conveyor. Pitchford said he spent four hours on the machine one day and the shovel operator never quit load- ing the IPSC. "The shovel operator never needs to stop until he repositions the ma- chine," Pitchford said. "For the first time, a shovel operator is continuously loading 10,000 tph to 12,000 tph." At that point, Pitchford knew MMD could connect trucks and shovels with a continuous loading system. The IPSC system in China feeds a conveyor system, but he knew mines with large truck-shovel fleets would not replace their equipment with conveyors after making that invest- ment, plus they would have to redesign the pits. Combining the experience in Co- lombia and China with the feeder and the IPSC concepts, MMD developed the Surge Feeder for loading trucks. To crack the nut, MMD needed to build a piece of kit that would sit next to the shovel, and make it mobile to move along with the shovel, so the mine can use the shovel to its maximum capacity, Pitch- ford reasoned. The Surge Feeder is positioned be- tween the shovel and the truck. The feeder is continuously processing the rock that the shovel dumps into it as the trucks queue. They never reverse into position. The processing capacity of the surge feed- er is greater than the cycle time of the shovel so the operator is not able to over- whelm the feeder. If the rock fits in the dip- per, the feeder can load it. The system can load trucks with one operator accurately. The truck can sense the load and signal the feeder to stop at full payload. The shovel never waits. The dump area for the Surge Feeder is the same shape as a 350-ton truck. The shov- el swing passes remain in the 90° to 120° range and it can run all day long. By the time the shovel cycles, the operators can easily dump another load. To prove his thesis, Pitchford used a production modeling system to compare the Surge Feeder loading process with conventional techniques. "We talked to miners to get as much input as we could and develop software to determine actu- al production run rates," Pitchford said. "The software [Arena] told us exactly what would happen. Using all of the informa- tion, it generated animation of trucks loaded in a traditional fashion and com- pared it to trucks being loaded using the Surge Feeder and we saw that the arrange- ment with Surge Feeder immediately out- paces the tradition loading method. The processing capacity of the Surge Feeder is greater than the cycle time of the shovel so the operator is unable to overwhelm it. The dump area is the same shape as a 350-ton truck. If the rock fits in the dipper, the feeder will crush it.

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