A Singular Solution

Brooke Wisdom

February 1, 2011

A major dolomitic limestone operation creates new productivity for an old quarry and reduces energy costs at the same time.

By Carol Wasson

Several years ago, the Carmeuse Lime and Stone Quarry in Cedarville, Mich., hit a do-or-die point — “either rebuild its entire crushing facility or flounder,” says Ray LeClair, the site manager hired as the go-to guy to get a new plant up and running. The challenge was replacing equipment from the 1930s, which had been moved to the site in the 1950s, where it had operated with no upgrades other than maintenance for the next 50-plus years. Beyond that, the old primary crusher was located nearly a mile and a half from the quarry face, requiring three 150-ton trucks to haul material from the face to the primary feeder, then haul the crushed material to a secondary crusher near the edge of the quarry.

Current and future crushing capacity goals led to the selection of a robust jaw crusher at the primary. Able to process up to 1,600 tons per hour, the crushing circuit is unlikely to become a plant bottleneck.

“We had experienced numerous breakdowns with the operation of equipment that was just worn out,” LeClair says. “Upgrading was the right thing to do. We would reduce hauling, energy, and maintenance costs, all while increasing our productivity and profitability.”

Project planning began in 2007 with the major initiative being the design of a new two-stage crushing system in the pit, closer to the face. Crushed material would then travel on a newly installed 4,000-foot conveyor to an existing surge pile and rail load-out system. Material loads onto a private 14-car rail system to be transported 5 miles to an existing finishing plant and ship-loading facility where product is transported via freighter to numerous Great Lakes ports. More than 60 percent of the operation’s products supply the steel industry.

LeClair says that the project started out on the fast track and was scheduled to be online in July of 2008, but progress slowed and eventually came to a halt when then-owner Oglebay Norton sold the facility to Carmeuse North America. After some evaluation by the new owners, the project continued, and the new crushing facility was completed and started up in the spring of 2009.

Throughout changes in direction, design, and ownership, and into installation, startup, production, and current troubleshooting and diagnostics, one thing remained consistent — an atmosphere of close collaboration between LeClair and Telsmith, Inc., the company chosen to design and engineer the new crushing system and plant. According to LeClair, the manufacturer ultimately simplified a complex process by managing the project as a “singular source backed by a combination of resources.”

In-house design and engineering

After researching a number of plants and operations, LeClair says his manufacturer selection was based on its in-house design and engineering team. “From the very beginning, I worked closely with one engineer who was designated as the point person — although he did have the support of his entire staff,” he says. “We narrowed the focus to just two people — he and I. All questions would be funneled through us. This streamlined the project and made everything go very smoothly.”

The breadth and depth of Astec’s capabilities and resources eliminated confusion between different entities who might have otherwise designed various parts of the plant, he says. With the entire design under one roof, they were able to fast track the project and handle even the smallest details within the design upfront.

A modular plant concept

A modular plant concept was chosen for its two-stage crushing system. Modularity may shorten the time line for new plant development and streamline the installation process. Pre-designed modules are pre-assembled at the factory and ship in segments.

Automation allows the plant to be monitored remotely or through the control house.

LeClair says that, although modularity enabled the plant to be fast-tracked, he favors the design concept under any type of construction schedule. “No matter what the pace, I prefer the modular construction, as it creates a far better structure altogether,” he explains. “I like having these welded fabricated structures completed in a shop environment versus out in the field. You get the best penetration on the weld.”

Additionally, he explains that another incentive for the modular approach is the ability to economically relocate the primary circuit within the pit. “In about 15 years, we will move the modular primary to the face and convey to the surge pile of the secondary plant,” LeClair says.

When it came time to assemble the plant, the process was simple and straightforward. In addition to the plant and manufacturer teams, a contracting company — with no previous experience in erecting a plant — handled the assembly. Detailed drawings allowed the process to be handled seamlessly. “For the entire structure, we never had one anchor bolt out of place, which is remarkable in itself,” LeClair recalls.

Design goals

The top goals of the new crushing system design were locating both the primary and secondary circuits nearer to the face; meeting a minimum production throughput goal of 1,200 tons per hour; eliminating any bottlenecks throughout the crushing system; and minimizing fines production.

Due to the previous blasting pattern and the operation of the older gyratory crusher, the operation produced in excess of 300,000 tons of fines annually, which had no viable market at that time. Furthermore, the operator had no opportunity to remove excess fines until the material went through both processing operations and was put into the stockpiles. “So we had all the cost of processing the fines, and then had to recover them as well,” LeClair says. “Now we have the ability to remove the excess fines right at the quarry face with a two, triple-deck screen setup on the discharge side of the secondary circuit.”

The modular primary crushing station includes a 60-inch by 30-foot step-deck vibrating grizzly feeder; the largest jaw crusher currently available in the U.S. market; and a 175-ton live storage dump hopper. A 3,000-foot-pound breaker breaks up any large oversize before it hits the crusher.

The new plant has reduced monthly energy costs by more than $50,000.

“We could have gone with a smaller crusher, but to get the minimum of 1,200 tons per hour, we would have been at the top end of the capacity of that crusher — and we wanted room for growth,” LeClair says. “We would never want the first circuit, especially, to ever be a bottleneck.” He estimates that the unit can comfortably process up to 1,600 tons per hour. As such, the conveyors are sized to handle higher tonnage, and the screens are also sized for excess capacity with triple-deck versus double-deck models.

Material is conveyed from the jaw to the surge tunnel which features pan feeders to control the feed to the secondary circuit. “The tunnel was delivered to us in pre-assembled sections with lights, feeders, and conveyors actually hanging inside the tunnel. We could just lift it right off the trucks, set it on the concrete, and just bolt it up, establish all the connections, and never have to touch it again,” LeClair says. The surge feeds a modular scalping screen station with an 8-foot by 20-foot, triple-deck, inclined vibrating screen.

The modular secondary crushing station includes a 600-horsepower cone with an automated crusher control system. LeClair likes the anti-spin system on the cone, as it stops the head from spinning and reduces liner wear, while the automation program allows operators to monitor wear and allows adjustments on the fly. “We’re getting up to 1,300 tons per hour from the secondary, and that is exceeding goals,” he says.

As to the programming and PLC-controlled operation of the plant, LeClair says that the manufacturer assigned one of its in-house electrical engineers to interface with the Carmeuse electrical engineer. Either in the control house or remotely, LeClair can monitor and track every process at the facility, including transfer points, conveyors, motors, and sensors, as well as material flow and tons per hour. Diagnostics can be run on site, remotely, or by the manufacturer.

Meeting design goals resulted in significant operating cost reductions. In energy costs alone, LeClair estimates a savings of more than $50,000 monthly, in part due to the use of properly sized, high-efficiency motors throughout the plant. The operation also eliminated one 150-ton haul truck that burned more than 250 gallons of fuel in a single two-shift day and had an annual maintenance operating cost that averaged $25 per operating hour (not including labor costs).

LeClair says that Carmeuse is fortunate to have retained its seasoned employees throughout the recession, with nearly 60 being on staff today. “Through attrition, we lose some personnel, and with the new plant, we can operate without hiring replacements,” he says.

Finally, the new plant produces far less fines, and, fortunately, all current fines output is being sold to the steel market with no waste.

During its first year of seasonal operation (April to mid-November), the Cedarville plant produced nearly 2.4 million tons. “This year, we’re on pace to hit 3 million tons with the future growth capability of up to 5 million tons per year running at full capacity,” LeClair says. “That’s a great anniversary present for Carmeuse, which is celebrating its 150th year in business.” AM

Carol Wasson is an experienced writer in the construction materials market.

There are no comments

Your email address will not be published. Required fields are marked *