Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/513927
AGGREGATES MANAGER Voices of Experience Bryan Pfohl Cory Jenson Jason Voss A North Carolina company re- cently installed a Matec filter press at one of its quarries that mines trap rock. "Trap rock fines are more difficult to work with be- cause they have a completely differ- ent nature in the settling pond envi- ronment," says Bryan Pfohl, president and chairman of Carolina Sunrock LLC and Sunrock Group Holdings Corp. "Where most rock types will settle easily on their own, trap rock requires flocculants to get the fines to settle, and if you disturb them, they re-sus- pend themselves and won't settle." Pfohl says they tried a variety of solutions at the 31-year-old quarry. The conventional wet settling ponds were messy and difficult to clean out. The dry collection system that sepa- rated the fines during the manufac- turing process was only moderately successful. He knew he had to find a better way. "We studied the filter press system and elected to go with it for a variety of reasons," Pfohl says. "It offered more of a batch-type nature, had the resiliency to give us some flexibility of growth in our system, and we felt it was easier to operate for our person- nel, by its nature." Pfohl says where most operations allow the filter press to drop the dried cakes of material on the ground, his operation installed it over a set of bins. When the cakes fall out of the filter press, they go right into a series of hoppers. A dump truck can drive beneath the bins, load up, and carry the material away to a disposal area or use it for other industrial purposes. "The filter press was a large capital investment, so the capital payback is slower," Pfohl says. "Now that we've operated it for a while, we've been quite satisfied with it, but people have to make a personal judgement based on their personnel and their material to determine what's best for them." F ilter presses have only recently found a place in the aggregates industry in the United States, according to Cory Jenson, general manager – Environmental Division, McLanahan Corp. "There's now a pretty wide acceptance of the technology," he says. "When we first introduced it here, the early adopters were ready to jump on board, but a lot of other companies wanted to wait and see how it went. Now, people are a lot more comfortable with it." Jenson says there are several factors that make filter presses of interest to aggregate producers. Some operations are running out of space for settling ponds. In some cases, it may be too ex- pensive for the operation to put in and maintain a pond. At first glance, it may seem cheap to dump processing water into a settling pond, but cleaning it out can be very expensive. Environmental regulations can be an- other factor, as well as the lack of water in some areas of the country. "We're putting in filter press systems where people can't get a permit for a new settling pond or are uncertain of getting a permit," Jenson explains, adding that some prefer the closed-loop filter press system so they don't need complicated permits. "Where water is a constraint or costly, it's definitely an advantage to recycle as much water as possible. If they do it right, they can use it for good public relations. They can show that they're trying to do everything in the most environmentally friendly way possible." Safety is another reason some aggre- gate operations are looking to replace settling ponds with filter presses, according to Jenson. Most operations are concerned about the possibility of a child or someone else falling into a settling pond full of mud. Equipment operators have died in the past when the equipment they were driving broke through a berm or toppled over into a settling pond. A small family-owned quarry in California has been using a McLanahan filter press, along with a deep cone thicken- er, for two and a half years. "We pretty much operate on the side of a mountain, so we don't have a lot of real estate," says Jason Voss, quarry operations manager at Stevens Creek Quarry. By installing a filter press on site, the company was able to put a concrete pad where the settling pond was and turn it into a stockpile area for finished product. Voss says he wasn't sorry to see the settling pond go. Cleaning it out was very expensive and time con- suming, and the material had to be handled several times. The material that comes out of the filter press is a much drier product than they were ever able to get from the settling pond, and it's much easier to handle. "Now, we handle the material once when we load it right out from underneath the filter press and put it into the truck," he says. "Then we haul it up to the reclamated fill to compact it in, and we never have to touch it again." The lack of space to have more than one settling pond created another problem for the quarry. "We had to build up a large inventory and then shut the plant down for a week to clean the settling pond," Voss says, explaining that this caused a big fluctuation in inventory. "Now we're able to keep a steady inven- tory and press mud while we're operating, so there's no downtime." The fact that the filter press offered automation was also a big deal for the quarry. "We wanted to make sure that a certain part of the filter press was automated so we wouldn't have to put more manpower in the plant," Voss explains. "The same operator who runs the processing plant is able to run the filter press."