Coal Age

JAN 2013

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dewatering continued Installing the Filter Press Circuit Tons Per Hour, Conn-Weld Industries and Taggart Global worked together to construct all of the necessary components around the filter presses. In addition to the two filter presses, the circuit also included one 30,000-gallon surge tank, two 6 x 4 Schurco slurry pumps, two 75-hp air compressors, one 3,000-gallon air tank, one 110-ton refuse bin, one 72- x 285-inch collecting conveyor with structure and drive, and a wash-water tank. A full cycle of the Blue Creek plate and frame press begins with the thickener underflow material being pumped with the existing underflow slurry pumps to the valve house located at the press building. Once through the valve house the slurry is directed to a 30,000 gallon surge tank. This is the feeding source for both presses. The two Schurco slurry pumps pull from the bottom of the surge tank which pumps the slurry to each press. At the beginning of each cycle, the presses hydraulically seal and send a signal for feed from each of these slurry pumps. These pumps feed the presses to a desired pressure. Once the desired pressure is reached, a PLC timer starts and the pump will continue pumping for the designed amount of time. When the timed feed function is complete, the feed pumps are turned off and the press is sealed with automatic valves, this allows the membrane squeeze cycle to start. Filled from the two 75-hp air compressors, the 3,000-gallon tank now releases the stored air into the membrane plates. This squeeze cycle allows for further dewatering of the material without the addition of more slurry. Similar to the feed cycle, the squeeze cycle is set up on a designed pressure (around 180 psi) with a PLC timer to manipulate the density of the final filter cake. As the membrane cycle ends, air is blown into the slurry feed port and the material that is not made into cake is recycled to the refuse surge tank. This segment is referred to as "core-blow." Once the core-blow cycle is complete, the hydraulic cylinder of the press will begin to retract and pull the plates open. When the press is completely open, the plate shifting mechanism, or "rabbit," is sent to open those plates that have not opened by the cylinder. This rabbit is a chain driven device that uses levers that are able to pull plates forward and backward. The rabbit will pull five plates at a time, allowing the filter cake to drop (gravity) from the plate cavity onto the collection conveyor belt beneath it. Upon completion of this plate shifting cycle, the hydraulic ram presses the plates back together and starts the feed process again. The material on the belt is conveyed into the 100-ton refuse bin. Press cycle times average 20 minutes or about three cycles per hour. In combination, the filter press circuit can make six cycles per hour. Each press delivers 20 tons per cycle at 25% moisture. With these cycle times, the plate and frame system processes the necessary 120 tph fine tailings to allow the Blue Creek prep plant January 2013 www.coalage.com 39

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