Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/485104
AGGREGATES MANAGER April 2015 26 The electric power, which is provided by the local power company, is run out to the dredge by a power cable, which floats on styrofoam blocks to keep it out of the water. Young says a super ground fault system is necessary for the 2,300 volts of power running through the cable. The dredge operator is able to track everything from the control room inside the dredge. A couple of gauges show how much pressure is on the line and how much sand is being pumped at all times. The dredge operator can regulate the amount of vacuum to control the amount of sand being pumped up to the processing plant. Material is sucked up from the bot- tom of the lake through a 12-inch pipe and sent to a pivot point on the bank through a 10-inch discharge pipe. "We pump down so that, as we remove the deposit, the material in front of the dredge will cave in and come with it," Young says. "You want the deposit to flow to you. We pump all the way across the lake and then pump all the way back. It's what we call back pumping." Each pass the dredge makes across the lake can take three to four months. Once the dredge has pumped across the lake and back again, it is pushed out by adding a joint of pipe, and the process is repeated. Young notes that if the dredge is pushed out before pump- ing back across the lake, any sand that might have caved in after the first pass would be left on the bottom of the lake. The material pumped out of the lake flows through a pipe to the bank. "We pivot from that point on the bank," Young says, explaining that the pivot point stays in place forever. A second pump located on the bank, called a booster pump, pushes the material the rest of the way to the processing plant. The material is carried through the pipe to the top of the screen tower where a deck of gravity screens removes any rock or gravel. "Gifford-Hill got most of the gravel out of here," Young says. "What little bit of 3/8-inch pea gravel we get is generally sold before it's washed. We never have a stockpile of that." From the screens, the water and sand flow into a classifier where the sand is separated into mason and concrete sand. The finer mason sand passes through a dewatering screw and is dropped into a pile beneath the plant to dry. The concrete sand goes through a different, larger dewatering screw and is carried by conveyor belt to a radial stacker where it is stock- piled. The radial stacker has two con- trol panels, one in the control tower and one at the base of the stacker, which allows it to be controlled from the ground or the control room. A beater roller beats the fine sand off the conveyor belt as it returns to the plant, limiting carryback. Although a small supply of mason sand is available, most of the sand is used in concrete and is sold to local cus- PLANT PROFILE After gravel is screened out, the water and sand flow into a classifier where the sand is separated into mason and concrete sand. The radial stacker used to stockpile the concrete sand has two control panels, one in the control tower and one at the base of the stacker, which allows it to be controlled from the ground or the control room.