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Feeders, Tramp Metal Detectors an Important Part of the Load-Out Process at Virginia’s Carmeuse Lime & Stone.

By Mark S. Kuhar

Many East Coast Power Plants can’t wait to get their hands on crushed limestone that comes from the Middletown, Va., operation of Carmeuse Lime & Stone. Why are they so hot to obtain this product? The answer is flue gas desulfurization (FGD).

FGD is a technology used for removing sulfur dioxide from the exhaust flue gasses of fossil fuel plants, those that burn coal or oil to produce steam for the turbines that drive their electricity generators.

To reduce sulfur dioxide – which is responsible for acid rain formation – electric utilities rely on a wet-scrubbing technique using slurry from limestone to scrub the gases. For a typical coal-fired power plant, FGD will remove 95 percent of the sulfur dioxide in the flue gases.

The limestone to create this important slurry typically comes from Carmeuse. Kemper Equipment, located in Honey Brook, Pa., worked with the company to design, engineer and supply a 3,500 tph rail load-out system to keep material flowing smoothly from the Middletown site. The system includes a scalping screen, cone crusher, Kemper conveyors and Eriez mechanical feeders, suspended magnet and metal detector. Kemper has sourced Eriez equipment on various projects for more than 20 years.

“Power plants will take the crushed limestone, grind it real fine and use that for the scrubbing agent,” said Andy Wright, project manager. “The power plants get ¾ in. minus limestone that has been crushed into particles. The limestone goes through several crushers and has tramp metal removed in the process before being loaded onto the train cars. Through a series of conveyor belts, we have the capability to load 100 cars in six hours.”

Big-Time Production
Carmeuse is one of the largest producers of lime and limestone products in North America, manufacturing and distributing up to 7 million tpy of finished product (see sidebar). The company also produces another 25 million tons of high-purity chemical limestone and aggregates and 2 million tons of high-grade silica sand products. More than 32 manufacturing facilities supply and serve 33 states and provinces in the eastern United States and Canada.

The lime, limestone and industrial sands are not only used for flue gas desulfurization, but also for road construction, water treatment, paper and glass production, masonry, mortars and other building materials. The company has a corporate history that dates back almost 150 years.

Removing Tramp Metal
During the initial phase of production, rocks are fed through a primary crusher, achieving reduction to approximately 8 in. in diameter, according to Wright.  The crushed rocks then pass under an Eriez Model SP-6548 Suspended Manual Clean Permanent Magnet to remove any large pieces of tramp metal imbedded in the rocks during the mining process.

“The SP magnet removes any stray metal from the rocks before they proceed along the conveyor line to the cone crusher, which is more sensitive to metal particles; anything metal is bad for that cone crusher,” Wright says. “Metal can come from a lot of places, but a lot of times it's from a tooth off a loading bucket. We don’t want any teeth to enter the crusher.”

The Eriez SP magnet in use at the Carmeuse Middletown operation automatically removes large amounts of ferrous materials conveyed in heavy burden depths on almost any type of conveyor or chute. It is ideal for separation applications on wet or dry, fine or coarse materials, large or small tonnages.

The Erium–powered magnetic circuit of the SP magnet is long and flat, providing a greater area of magnetic coverage with a maximum depth of field and with less head room required than an electromagnet.

The possibility of accidental shutdown and shutdown due to power failure is eliminated and its strength never varies. The unit operates at peak efficiency at all times since no heat is generated by the magnet.

“You get a lot of bang for the buck with this Eriez magnet,” says Wright.”It's a big heavy-duty magnet that is reasonably priced, robust and well-built.”

Another Safety Checkpoint
After the 8-in. diameter rocks pass through the SP magnet, they pass through an Eriez Metalarm MA3600 Hawk Metal Detector that detects any nonferrous tramp metal.  

“The SP Magnet picks up any large piece of ferrous tramp metal, but should any ferrous, nonferrous or stainless steel metal pass by it, the metal detector detects it and stops the conveyor.  Sometimes, the SP magnet can't pull a piece of metal that is really imbedded in the rock. That's why we have the Eriez metal detector on the other side before the rocks proceed to the cone crusher,” Wright says.

The Metalarm MA3600 uses pulse-induction technology that offers balance coil detection sensitivity and performance, resulting in a superior Metal Detector ideally suited for quarry operations.

Higher detection sensitivity ensures that even the smallest problematic tramp metal can be detected; thus providing better protection for crushers, screens and conveyor belts.  Adequate protection saves time and money with less equipment downtime.

High belt speeds often pose a problem for metal detectors, but not for the MA3600 where the high level of sensitivity is maintained. The Hawk model can be used with steel corded belts and highly conductive products such as gold and
copper ore, giving the operator far more flexibility and protection.

Effectively Moving Limestone
The cone crusher at the Middletown mine takes the 8-in. diameter rock and reduces it to a ¾-in. minus product before final transport to awaiting railcars. Eight Eriez Model HVF 36-in. wide x 60-in. long mechanical feeders take the ¾-in. limestone and deposit it onto a series of conveyor belts, which load up the railcars.

The eight feeders convey 500 tph of product, for a total load out of 4,000 tph, according to Wright.

"These feeders are very low maintenance and fit into a compact footprint, which is ideal for a mining site," he says. "Their low profile allows us to put them into a smaller work area and because they have a variable frequency drive for control, it makes for a simpler, cleaner installation."

Carmeuse Lime & Stone enjoys higher productivity and maximum benefit from the Eriez products. And the power plants and utility companies stay happy as well.