Screw washers, dewatering screens enhancing Luck Stone sand products

Luck Stone is the largest privately-held, family-owned and -operated producer of crushed stone, sand and gravel in the U.S. Its many sites across Virginia, Maryland, Georgia and the Carolinas provide consistent, quality aggregate materials that serve as the foundation of roads, bridges and buildings.

At each new site Luck Stone develops, the company extends its core operating principles of economic development, environmentally-sound practices and values-based leadership. Luck Stone is committed to being a good neighbor and providing a positive impact on the communities in which it operates.

Challenge

In 2002, Luck Stone purchased its Bull Run Plant in Chantilly, Virginia, to serve the growing northern Virginia market.

Started in the 1950s, the quarry was a low-volume, eight- to 10-conveyor operation when Luck Stone began expansion efforts to meet market demands. Luck Stone moved a road to access more reserves, and it grew the site to about 70 conveyors that transport traprock from the quarry through the crushing and wet processing plants to stockpiles.

The expansion efforts included upgrading the asphalt sand processing plant to increase production.

“The main driver for the expansion of the sand plant here was just the demand in the market for sand products that needed to be clean,” says Craig Wiant, an assistant plant manager at Luck Stone. “At those volumes, we can’t afford to make a pile and let it decant before we sell it, so we really needed to be able to make it on the fly, ready to ship.”

The Bull Run Plant has a lot of stock turnover, so its sand needs to be ready to ship. Luck Stone wanted a solution that would put the product on the ground as dry as possible.

“It’s really critical to us to have a lot of sand-making capacity, but also to have a lot of sand on the ground that’s ready to sell,” Wiant says.

Solution

As part of the sand plant expansion, Luck Stone replaced a much smaller sand screw with two McLanahan twin 44-in. x 33-ft. fine material screw washers to more effectively remove fines from asphalt sand.

Luck Stone also wanted to include dewatering capabilities in the new wash plant – something it didn’t have in the old plant. According to McLanahan, dewatering screens have been proven to produce final products that are at least 10 percent drier than fine material screw washers. When the two are used together, they provide a greater level of dewatering.

Luck Stone followed each fine material screw washer with a VD18 dewatering screen for additional moisture removal before stockpiling.

“The screw classifiers clean the material so it’s within our customer specs and above,” Wiant says. “Then, the addition of the dewatering screens allows us to produce the product at a moisture content that’s ready to ship.”

To keep valuable solids in closed circuit, the screen throughs collect in low-profile sumps underneath the dewatering screens, and they’re pumped back to the screw feed via slurry pumps.

Results

Now, the fine material screw washers and dewatering screens help Luck Stone produce a clean, drip-free asphalt sand for its customers.
“Our customers really want to see the percent passing the 200 mesh at a 2 or less, especially for asphalt mixes,” Wiant says. “We can typically put it in the pile at about 1.5 percent passing the 200.”

Not only does the equipment help Luck Stone meet the strict specifications required of their final product, it also allows Luck Stone to produce a drier sand. The moisture content of the sand coming off the dewatering screen is as low as 7 percent, according to McLanahan.

“Depending on weather and setup, we usually see somewhere between 7 and 9 percent moisture coming off,” Wiant says. “It allows us to sell our material much quicker, so it doesn’t have to sit in the pile and decant. It’s pretty much ready for sale as it comes off the stacker.”

With the increase in infrastructure projects in northern Virginia, the fine material screw washers and dewatering screens will continue to help Luck Stone meet demand.

“Being able to provide a clean sand at low moisture to our customers allows them to build projects with the longevity to serve the surrounding community,” Wiant says.

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Information courtesy of McLanahan Corp.