Screening circuits optimize Maryland operation’s process flow

By |  February 6, 2017

Bluegrass Materials Co. is a fast-growing aggregate and concrete block producer with operations in Kentucky, South Carolina, Tennessee, Georgia and Maryland. One of its latest acquisitions is its North East Quarry, which serves counties surrounding North East, Maryland, a region near the headwaters of Chesapeake Bay, less than an hour’s drive from Philadelphia and Baltimore.

The 1.5-million-tpy operation features a granite and trap rock processing plant that has recently undergone significant upgrades to meet production goals.

“We needed additional crushing capacity, and we needed screening circuits that could efficiently handle the load,” says Ronnie Walker, president of the Maryland Division of Bluegrass Materials.

To meet strong market demands, the operation required a plant capable of processing about 180 tph of #8 aggregate, while balancing production demand between washed and dry screenings and providing enough versatility to produce multiple products such as ballast, #67, #7 and #467 aggregate.

“Our previous plant could process only about 80 tph of #8 aggregate and our prior screening circuits could not even handle that limited capacity. We knew we had to add crushing capacity and change out the existing screens,” Walker says.

To complete the necessary plant upgrades and design a new process flow, Walker and his team consulted with Paschal Associates LLC, a technical sales and engineering firm that supports the aggregate industry. Paschal is a representative for Deister Machine Co., a leading manufacturer of vibrating screens and feeders.

Ultimately, the site added considerable crushing capacity in the secondary and tertiary circuits and replaced the use of four vibrating screens and a wash screw with just two highly efficient Deister screens, one on the dry circuit and the other on the wash circuit.

“We’re far more efficient regarding labor, maintenance and overall productivity. We’ve been able to go to a single shift of crushing on the tertiary end, while increasing our #8 production volume up to 2.5 times,” Walker says.

Eliminate screening bottlenecks

Photo courtesy of Deister Machine Co.

The new screens at the Bluegrass Materials Co. North East Quarry are virtually maintenance free, and have not required any changes to screen settings since their shipment from the factory. Photos courtesy of Deister Machine Co.

The previous North East Quarry tertiary screening circuit presented considerable screening bottlenecks. The prior plant utilized a combination of four vibrating screens to size and separate material discharged from both a standard and a shorthead crusher. Two 6-ft. x 18-ft. high-frequency screens were set up to separate dry screenings prior to introducing material to twin three-deck wash screens.

The screens delivered inconsistent performance and were not designed to handle the larger fractions, causing a carryover problem that sent all crushed material to the twin wash screens. That meant all crushed fines were also sent to the wash screens, which would require two fine-material double screw washers to process the water and fines volume.

This extensive washing created a pond fines issue and the site has limited retention pond space. Additionally, the oversize material from the wash circuit circulated back to the tertiary surge pile creating a wet feed for the crushers. Production capacity was severely limited as the circuit was initially designed for a finer separation and could not facilitate increased load volumes.

Efficient screening circuit design

The operation installed a Deister three-deck, 10-ft. x 20-ft. screen in a new dry tower to receive material discharge from all three crushers, as well as the desired feed from a scalping screen that bypasses the secondary crusher.

This allows a dry separation that sends oversize material back to the surge pile, while removing the #10 dry screenings from the circuit prior to washing. The screen maximizes capacity, handling between 1,200 and 1,400 tph.

“We have achieved greater control as we are efficiently pulling out the fines that do not need to go to the wash tower,” Walker says. “With the old plant, we had to deal with all of the washout and the settling ponds. In the past, we were cleaning out the settling pond every week – and now we are down to only once per month.”

Also, one of the biggest benefits, adds Walker, is that “we can put all the product across the dry screen and through the crushers. In the past, we couldn’t put crusher run in the plant, as we couldn’t screen it out. Now, we can process the crusher run, which boosts our volume through the plant,” he says.

A Deister three-deck, 8-ft. x 20-ft. wash screen was installed to receive the desired material gradation from the sizing screen. Walker says both screens are virtually maintenance free, and have not required any changes to screen settings since their shipment from the factory. Alternatively, he recalls that the operation’s previous screens had failed under the loads within just days after being rebuilt.

According to Walker, results have exceeded expectations. Secondary circuit throughput averages 900 tph, which is a 33 percent increase over past performance. The key production of #8 aggregate averages between 160 and 180 tph, a more than 100 percent increase; and the operation has achieved greater control by balancing the demand between washed and dry screenings.
Walker explains that he and his team worked with Paschal to design the new process flow.

“We operated our previous plant up until the end of the year,” he says. “We were down for just two months while preparing for the installation; moving conveyors to handle multiple product stockpiles; and completing the installation and startup by March 2016.”

Bluegrass Materials Co.

Bluegrass Materials’ operations are located in Kentucky, South Carolina, Tennessee, Georgia and Maryland. The Kentucky operations are primarily located in and around the city of Bowling Green (Warren and Ohio Counties) and in rural areas close to the Kentucky-Virginia border (Lechter, Bell and Harlan Counties).

The company also operates three quarries in the Atlanta area, as well as a granite quarry near Edgefield, South Carolina, serving the Aiken, South Carolina, area; a limestone plant in Calhoun, Tennessee; and a sand plant in St. George, Georgia.

The Maryland operations are primarily located throughout the greater Baltimore and Frederick/western Maryland areas. In 2014 and 2015, the company purchased the Maryland operations of Lafarge North America and Maryland Materials Inc.

Carol Wasson is a veteran freelance writer for the aggregate and construction equipment industries.

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