Dewatering Screens and Screws: Dry Idea
California producer eliminates the need for settling ponds and captures water for reuse.
Any time an aggregates producer can provide sound environmental practices while improving its own profitability, it is on the winning side of the production equation. Sustainability in the aggregates industry is a business approach that has gained considerable attention in the past several years. The BoDean Co., Inc, of Santa Rosa, Calif., however, has applied a sustainable approach to its business practices almost from day one.
Dean and Belinda (Bo) Soiland opened BoDean Co. in 1989 with the purchase of the Mark West Quarry in the northern Napa Valley. The quarry has been in operation since 1910, and the Soilands put plans in place not only to reclaim mined-out land but also to begin using a benching method as they continued to mine. Over the past 20 years, this system of benches has improved safety and operational costs, remediated stormwater runoff, and helped to better manage the mine plan in general. BoDean Co. has since applied the same practice to its newer Blue Rock Quarry in Forestville, Calif.
Both the Mark West Quarry and the Blue Rock Quarry supply aggregate material for customers in the surrounding area, as well as to BoDean Co.’s vertical asphalt operation in Santa Rosa. In 2006, in order to combat the cost of purchasing sand for its asphalt plant, BoDean installed a washing plant at the Mark West Quarry and began to produce its own sand. The wash plant includes a blademill, washing screen, cyclone, and dewatering screen. At the same time, BoDean opted to install a Phoenix HiFlo circular thickening plant and an overhead beam Diemme GHT 1500 P13 recessed-plate-frame filter press at the end of the washing stage to capture and reclaim as much water as possible.
According to Robb Folmar, site manager for the Mark West Quarry, “We don’t have space for settling ponds, and water is hard to come by here with just a pond above the plant and a creek below.” In addition, the footprint shared by the processing plant and loadout area within the quarry is very tight. Because of this, he says, the wash plant operates in a closed circuit with fresh water coming off the thickener over a weir through gravity overflow to a fresh water tank, pumping back to the wash circuit. The underflow thickens from about 4-percent solids by weight to about 50-percent solids. This mud slurry feeds the filter press, which removes the remainder of the water and produces hard cakes of filtered fines that are up to 90-percent dry.
The use of belt presses to claim moisture from fines is not unusual in North American aggregate operations. The application of plate presses for aggregates dewatering, however, is new in the United States. BoDean Co.’s plate press, manufactured by Diemme S.p.A. of Italy (now represented in the United States by Louisville, Ky.-based Phoenix Process Equipment Co.), operates by compacting mud slurry between 140 vertical plates that are each about 5-foot square, until the end product is a dry cake that drops beneath the press for loadout.
“Dean had seen Diemme presses used in mining in Europe, and he thought the method would work well for us,” says Folmar. “He is really good at looking forward to the bigger picture and applying his ideas to the company.”
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