September 1, 2008
Tilcon’s Mount Hope Quarry achieves significant savings through air classification.
In this era of outrageous oil prices, any time a producer can create a saleable product from waste material and reduce fuel costs at the same time — without sacrificing production or quality in any stage of the process — it’s like putting money in the bank.
By changing the way it processes asphalt sand, Tilcon New York, Inc.’s Mount Hope Quarry, located in Wharton, N.J., found that it has significantly reduced downstream fuel costs associated with its on-site asphalt plants from 10 to 20 percent, depending on product and type of fuel used.
The Mount Hope facility has enjoyed a mining history that dates back to the mid-1700s. The 560-acre quarry site surrounds the historic Mount Hope Mine, which was the last iron mine to operate in New Jersey — mining iron ore until the mid-1970s, when it turned to producing crushed stone. Located about 40 miles west of New York City, Mount Hope became part of the Tilcon New York family of operations, a division of Washington, D.C.-based Oldcastle Materials Inc., in 2001.
The Mount Hope Quarry has become legendary over the years as one of the nation’s largest producers of quality crushed granite and the highest-volume, single-location producer of hot-mix asphalt. With more than 300 million tons of permitted reserves, the site operates 24 hours a day and produces more than 4 million tons per year. Many of its crushed stone products are used in the facility’s three on-site asphalt plants — including manufactured sand that meets Superpave specifications.
Until two years ago, the Mount Hope facility could only produce an asphalt sand via a wet process — pulling out the minus-200 material in order to use the remaining manufactured sand product as specification sand for asphalt mixes. But the company had excess screenings that it could not efficiently process with the washing plant.
Then in 2006, Tilcon New York acquired the nearby Bedrock Quarry Materials location, which was in the process of installing an air classification system manufactured by the Lebanon, Pa.-based Buell Division of Fisher-Klosterman, Inc. The company quickly decided that the system, made up of two 75-ton-per-hour Buell GI-108 gravitational inertial classifiers, would find a better fit at the Mount Hope facility.
Clif Morris, quarry manager at the Mount Hope facility, says the team decided to move the classifiers based on several factors. “One was the foreseeable life of the Bedrock quarry; it didn’t have a long-term plan. Also, Mount Hope is a much larger operation, with asphalt plants on site and a bigger need for the manufactured sand that would feed the plant. Bedrock was using it to make a clean grit product, for which there wasn’t a real need in the area. And we had to do something with the excess screenings at Mount Hope. We knew the Buell system could answer that need.”
The answer’s in the air
Air classification is similar to wet classification in that it uses gravity and inertia as two forces exerted on the material to split the sand and remove fines. Unlike water classifiers, however, air classifiers use airflow and directional changes in addition to gravity and inertia to cut the material — and they provide a dry product at the end of the process.
The screenings and primary air enter the top of the unit. Both travel downward until the air makes a 120-degree change in direction — moving upward again. The air exits through vanes, carrying the fine particles (-200 material) with it into a fabric filter, which collects the fines. The coarse particles are too heavy to turn with the air, and fall to the bottom, passing through a second air stream before being discharged. Any fines that might have remained in the material stream are caught in the eddy of the second air stream and are pulled back up to follow the air flow out the vanes. This secondary airflow also serves to provide scrubbing action for the material — creating a cleaner manufactured sand product in the end.
Tilcon worked with the manufacturer to move the system to the Mount Hope facility, contracting with G/S/M Industrial, Inc., based in Lancaster, Pa., to handle the fabrication needs. “Buell looked at our feed gradation and recommended we set up the classifiers in a parallel configuration at Mount Hope,” Morris explains. “At Bedrock, they had been in a series configuration. Here, they decided it would be better to feed in a single step. In this configuration, we’re getting 150 tons per hour.”
Once the system was in place, Mount Hope was able to choose the amount of feed for the air classifications system based on its material needs. “We haven’t eliminated the washing plant because we wash material other than the screenings,” Morris says. He adds that while the site makes washed concrete sand, the air classification system enabled it to make manufactured sand for its asphalt plant. The mix of screenings that go to the air classification system and wash plant is currently evenly split.
From waste product to saleable material
The benefit of processing excess material for the quarry was immediate. “It’s definitely been a win for us,” Morris says. “We’ve turned a non-usable product into a sellable product. Also, we can grab the material and process it to make a finished product before it reaches the wash plant — as part of the plant flow. Before, we had to pick up the screenings and haul them to the wash plant. So the in-stream process has helped us save money — and make money.”
In addition, the dry classification has helped reduce manpower and equipment needed to dredge wet pond fines, because it has reduced the amount of washing needed for the site’s screenings.
But the bigger benefit for Tilcon has been the fuel savings that the air classification has indirectly provided downstream at the company’s on-site asphalt plants. According to Rebecca Guardino, quality manager at Mount Hope, the manufactured sand that feeds the asphalt plants now has much lower moisture content than it previously did.
“We’ve seen a big difference in fuel savings at the asphalt plant now that we have drier sand going into the mix,” she says. “Previously, feeding the asphalt plant with washed sand, we were looking at a moisture content of 5 percent.” By using the air classification system, however, the moisture content dropped to between 1 to 1/2 percent.
With drier material going into the asphalt drum, Tilcon uses less fuel to process the asphalt material, while also increasing throughput. “Depending on the type of fuel we’re using in the plants, we have seen between 10 and 20 percent savings in fuel costs at the asphalt plant,” says Jiries (Jerry) Saba, electrician supervisor at Mount Hope, explaining that the Mount Hope asphalt plant uses natural gas, and he’s seen a 10-percent decrease in fuel costs at that site. “Other locations use spec’d oil, and they’ve seen a 15- to 20-percent decrease in fuel costs,” he adds.
While 10 to 20 percent fuel savings might not seem large at first glance, an example of actual dollars saved better drives the point home. Saba offers a savings scenario: “Say the fuel you’re using is currently $4 per gallon, and it takes 1-1/2 gallons to process a ton of material. You look at how many gallons of fuel you’re using per hour.” Using these parameters, a 350-ton-per-hour asphalt plant would require 525 gallons of fuel each hour, at a cost of $2,100. An eight-hour shift alone would use $16,800 in fuel to process the asphalt. And even a modest 10 percent savings of $1,680 per shift is significant. With fuel costs continuing to soar, the savings are even more important.
In addition, because it weighs less, dry sand is less costly to haul to other asphalt plant locations — providing additional fuel savings.
Between its impact on rising energy costs and its ability to improve efficiencies at the asphalt plant, Guardino notes that the classifier has become more and more of a valued piece of equipment at the site.
Hard wearing despite hard rock
Morris says while other Tilcon New York sites had installed air classification systems successfully, the ones at Mount Hope were his first experience with air classification. And he had some initial concerns about wear within the system. “The granite gneiss here is very abrasive and hard on our equipment. But we lined the classifiers with ceramic and that has given us a longer wear life. And because we’re familiar with how the material flows through the units, we can easily patch the ceramic where it tends to wear. But overall, because it has only a few moving parts, the units require very little maintenance,” he says.
“From a quarry perspective, having the Buell system on site has allowed us to take an excess of product that we couldn’t use and turn it into something usable,” Morris says, adding that the real return for Tilcon is seen at the asphalt plant. “If we were just relying on it to make a premium product that we could sell for a couple dollars more, it might not have been the best answer for us,” he says. “But with the asphalt plant on site, the money is coming back to us in energy savings and throughput downstream.”
Moving the air classification system from the Bedrock site to Mount Hope was “a slam-dunk,” Guardino says. “With the volume of stone we process, the amount of sales we have here and the asphalt plants on site, this is the best location for us to have the air classification system. The energy savings we’re seeing at the asphalt plant is the big benefit in our eyes. It’s been a successful endeavor for us.”
Article courtesy of the Buell division of Fisher-Klosterman, Inc.