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.”