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"Membrane has a higher up-front cost with higher operating costs," Jenson said. "But, if the cake needs to be drier that's the best technology commercially avail- able. If a recessed chamber dries to 75% solids, the membrane might dewater to 78%-79% solids; it's typically only three or four points better, but if that's what a mine needs to meet specifications as far as compaction, then that's the determin- ing factor," he said. Cloth selection is also important. "Different cloths have different surface tensions depending on the material it contacts," Jenson said. "One cloth may have less friction or be less electrically attractive. Different weaves have differ- ent properties. There are a number of ways to improve cake release, but we nev- er had to use paddles at Bishop." McLanahan has made some improve- ments based on the performance at Bishop. "The main changes were switch- ing from four hydraulic cylinders to one main hydraulic cylinder," Jenson said. "It reduced the horsepower and reduced the number of valves. For automation, we no longer have to synchronize the cylinders. We kept four tensioned shafts. We kept the advantages of the old design, simplified it and used less parts and horsepower." The latest design has reduced the horsepower by one-third. "All of the tor- sional valves balancing the flow between the four cylinders require a lot of head and horsepower," Jenson said. "By going with a single cylinder we cut out all of those valves and we no longer have to worry about synchronizing it and main- taining alignment. We were able to sim- plify everything, use less horsepower. Of course, we have a couple of new pump vendors as well." Operating the System at Bishop At the time Forge was commissioning the filter press at Bishop, a freak accident occurred with a filter press at Patriot Coal's Blue Creek prep plant. During February 2013, an engineer was killed at the facility when he was struck by one of the hydraulic cylinders on a plate-type filter press from another vendor. A hydraulic cylinder catas- trophically failed while the press was in operation, according to the Mine Safety and Health Administration (MSHA). The victim was positioned near the hydraulic cylinders, troubleshooting the operation of the filter press, when the accident occurred. A second employee received non-life threatening injuries. "Obviously, this raised some serious concerns and we looked at what hap- pened," said Borreggine. "Blue Creek was also operating two plate-and-frame presses. For whatever reason, they chose to put the operator controls between the two units. The operators panels at Bishop are on the outside of the units, and they are perpendicular to the hydraulic cylin- ders that operate the presses." Borreggine said the key to keeping the machines running is keeping the cake off of the cloth or the panels, and they did not encounter any issues with the cake sticking. A sticking cake can cause issues with cloth tearing or possibly cracking the plates. "The McLanahan machine performed as it was supposed to," Borreggine said. "It performed very well." The Blue Creek prep plant purchased the plate-and-frame press and Taggart installed it. "With this installation, we were involved with the purchasing and we were able to select the plate-and- frame press we wanted to install," Borreggine said. "We have a great rela- tionship with McLanahan and felt that they, from a technical and service stand- point, had the best plate-and-frame press." During startup, there was not much of a learning curve, Borreggine explained. Maintenance, he added, is also fairly sim- ple. "One thing we did not have to deal with at Bishop was clay," Borreggine said. "If we would have high-clay application, you would need a blow-back system or an automated spray wash system. We did not have those because this is what we call a 'clean' refuse dewatering system because it did not have a lot of clays." From the time Taggart (Forge) commis- sioned and operated the system, it has been nothing but standard maintenance — no issues, Borreggine explained. The Southern Coal team took over and it has been smooth sailing so far. In the future, Borreggine thinks more prep plants will adopt this technique. "They would have to do some due dili- gence," Borreggine said. "What are they doing as far as tonnage and coal quality. It is good to minimize chemical con- sumption. As they become more popular, I think McLanahan will make these units better, more user-friendly, and more cost –effective." Forge is looking at installing another facility considering plate-and-frame presses in U.S. coal. They currently oper- ate belt presses. Because conditions are changing and they need more capacity, they are going to add a plate-and-frame press. d e w a t e r i n g f i n e s c o n t i n u e d 40 www.coalage.com March 2014 The system produces 20 tons of filter cake per cycle or 100 to 120 tph with both presses. CA_pg38-41_V3_CA_pg46-47 3/11/14 2:46 PM Page 40