Water loop: Closed-circuit clarifier at wash plant operation
January 1, 2008 By: Carol Wasson Pit & QuarryAportable wash plant operation is only as efficient as its water resource management, and, when water is tight, production may often come to a halt. "If you don't have the water, you're not going to get the job done," said Larry Peak, owner of Sandpoint, Idaho-based Peak Sand & Gravel Inc., an operation with three portable plants and one stationary location. The company is constantly on the move, working seven local sites, and completing custom crushing and washing projects for customers located within Idaho's panhandle and across its borders into Montana and Washington.
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In past years, its portable washing projects had been limited by water availability at certain sites. "We had to schedule most of our jobs in the spring because we had the highest water table, but in the end we would always run out of water and by June we would have to stop as we didn't even have enough recharge water to fill a well," Peak said.
"Sometimes we were even taking the water out of the well, putting it in the pond, sucking it out of there, and running it through the plant. Then we would run dirty water through mud tanks, pump the mud out, and put the clean water back in the pond. We were going through nearly 300-gallons-per-minute of steady makeup water alone," he added.
Upon the award of a 100,000-ton portable washing project in Haugen, Mont., Peak decided to upgrade his processes with the purchase of a portable, closed-circuit water clarifier manufactured by Clearwater Industries. "The new clarifier allows us to recycle and reuse water, while keeping our makeup water to a minimum. This opens many new opportunities for us – sites where there is little-to-no water and no place for a settling pond," said Peak, who worked closely with Bob Gralton, president of Clearwater Industries, to create a customized solution.
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Gralton explained that traditional closed-loop systems typically require ponds for water discharge and for feed water to the plant. Alternatively, Peak's unit has a clean water tank placed right on the clarifier. From this tank, the water is pumped directly to the wash plant. Then the clarifier takes the dirty water stream and produces clean water immediately, concentrating the fines or solids to a thick state.
The totally self-contained unit includes a dry polymer feed system, hydraulic package, control panels, mud discharge pump and clean water return pump to supply the wash plant. With this very tight closed-circuit operation, at least 90 percent of the water is reclaimed, and the need for a pond is eliminated.
Problematic ponds
Long familiar with the downside of pond use, Peak said that doing portable washing the old way has always involved trucking in large volumes of water. "You fill the ponds and then they evaporate or leak into the ground. We've even had ponds that we've shotcreted or paved, and they've still leaked. With the new clarifier, we bypass the clean water pond altogether," he said.
 All water and mud pumps on the Clearwater Model 2000 portable water clarifier are variable speed in operation. |
Peak also stressed that, previously, his wash plant operation was outfitted with fabricated "mud tanks" taken from a hot mix plant. They had drag chains in them that would periodically scrape up mud that would settle on the bottom of the tanks. "The mud tanks worked but they consumed too much water, much of which would go out with the mud. And, our situation is how much water do we have available to us, and how much room do we have to store the mud? With the new equipment, we can thicken the solids easily, while circulating and recycling the water efficiently," he said.
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