When the particle size you need to separate is too fine to screen, air classification systems present significant advantages in terms of dry processing, for granular coarse product with very little fines and dust through to fines discharge with very little coarse material.
As the Australian representative for Sturtevant, Brolton Group supplies solutions for dry processing utilising air classification systems that eliminate the need for water and settling ponds, and with the excessive time, equipment and water required with wet wash systems, air classification systems provide a more environmentally friendly solution that reduces capital costs, maintenance costs, overhead expenses, resource use and land requirements.
Air classifiers can separate powders as superfine as five micron through to as coarse as 150 micron. The effectiveness of air classification systems in producing fine products relates to the precise balance between the quantity of rejector blades, the speed at which the rejector blades operate, the velocity of the air flow and the rate of material feed. Even with fragile powders, air classifiers rarely fracture or degrade particles, as they do not operate at pulveriser speeds, and most of the product never makes contact with the rotating parts.
Air classifiers balance the physical principles of centrifugal force, drag force, collision and gravity to generate a high precision method of classifying particles according to size and density, eliminating the blinding and breaking issues associated with screens.
An example of this process is Sturtevant’s Whirlwind air classifier, which processes up to 1200 tonnes per hour (tph) using internal air currents to separate heavy and fine particles, with heavier and larger particles settling into the coarse cone.
Finer particles are swept up by the air flow, where selector blades generate further classification. During this secondary separation, oversized particles are spun out of the air flow and drop down into the coarse cone. The selected fines then continue through the circulating fan and into the fines cone. This process increases product consistency.
The Whirlwind air classifier does not require auxiliary equipment such as cyclones, process dust collectors, air locks and system fans, making it a very cost-effective solution from a capital cost perspective, as well as reducing ongoing maintenance and parts expenses.
MOBILE AIR CLASSIFICATION PLANT
{{image2-a:r-w:300}}Sturtevant has developed a self-contained, 100 per cent mobile air classifying plant with integral collapsible conveyors, enabling parking to processing in one hour or less at the push of a button. The Whirlwind air classifier and conveyors hydraulically unfold for set-up and fold away for breakdown and transport, with no cranes, boom trucks, front-end loaders or special crew needed for any part of the operation. Dual hydraulic cylinders provide smooth, steady raising and lowering of the Whirlwind air classifier and the integral, collapsible feed and dual discharge conveyors. The mobile Whirlwind air classifier is identical to the model successfully used in stationary applications worldwide for more than 90 years.
“Many aggregate and sand producers own multiple quarries,” Joe Muscolino, Sturtevant’s senior project manager, said. “A portable air classifier eliminates the cost of owning and maintaining multiple stationary classifiers. And for major paving projects it is more economical to move the air classifier to a quarry nearer to the job site or to the job site itself than to haul the de-dusted manufactured sand.
“Also, many asphalt companies own or lease portable asphalt plants that normally require adjoining portable equipment for crushing, screening and fines handling. A portable air classifier negates the need for a wash plant where water is not readily available or where waste water disposal is a problem.”
The plant is mounted on a rugged chassis frame with tri-axle suspension for stable travel on highways or back roads. It is designed and constructed for vibration-free operation and long service life with low maintenance. The compact design features a low transport height (4.1m), short trailer transport length (18.8m) and trim transport width (3.8m) for easy manoeuvring on roadways and at job sites. Feed capacity is 30 to 90 tph, with a 37kW variable frequency motor for low energy consumption.
{{image3-a:r-w:300}}“Producers tell us they want a portable unit large enough for high feed rates but compact and completely mobile to keep transportation costs reasonable,” Muscolino said. “We estimate that our ample tph range and compact, totally self-contained design will keep transportation costs 40 per cent to 50 per cent lower than if we had designed a larger plant with unattached conveyors that require assembly.”
Other features requested by aggregate and asphalt producers include a long, high discharge conveyor for greater stockpile heights of de-dusted manufactured sand, and a feed conveyor intake hopper that is low to the ground and can be fed by a front-end loader, eliminating the need for an intermediate conveyor. Also, the feed hopper is located behind the trailer rear wheels to prevent spillage of feed material onto the chassis, where it could cause damage and requires clean-up. The smaller side conveyor is for by-product fines.
For safety and nuisance dust control, all three belt conveyors are covered and can be easily vented. In addition, the gravity feed inlet at the top of the classifier is under a slight vacuum to prevent airborne nuisance dust during material transfer.
The conveyor covers also help reduce moisture during rain to ensure efficient performance. The air classifier is designed for dry operation. Material moisture preferably should not exceed two to three per cent, with four to five per cent as maximum for most materials.
An internal fan lifts minus 75 micron fines out of the feed, and removable selector blades within the housing control the amount of fines to be removed, so the process can be adjusted to nearly any material or spec requirement. Any additional fine tuning and quick adjustments are made with easy to use speed controls. The product fineness can be adjusted to minus 45, 75 and 150 fines.
APPLICATIONS
Air classifiers are useful for a range of applications, including:
- De-dusting fines in aggregates and crushed stone such as limestone, granite, trap rock, sandstone, basalt, diabase rock, gabbro, sand and gravel.
- Reducing the fines load on a water floatation system for extracting precious metals, including iron, gold, phosphate or ilmenite ores.
- Increasing the fineness of milled limestone, silica, feldspar, refractory slag, fused glass, kyanite, zirconia, alumina, lithium carbonate, copper oxide and others.
- Removing undesirable contaminates in flyash, coal, kaolin, hydrated lime, diatomaceous earth and mica.
SUPPLIER AND DISTRIBUTOR
Brolton Group is a leading Australian multi-disciplined engineering solution provider, with an enviable project delivery track record. The company has worked on projects for multiple industries across a broad spectrum, ranging from conceptual studies through to major turnkey processing facilities.
All projects are managed by Brolton Group’s in-house team of highly skilled professionals, providing the highest standards of leadership, supervision and project management. Brolton Group’s core capabilities include turnkey materials handling projects, mechanical, electrical, civil and construction engineering, automation control systems, general engineering, welding and fabrication, emergency breakdown support, preventative maintenance, equipment, plant and factory fit-out, relocation or decommissioning, design and construction of building, and comprehensive technical support.
Brolton also holds a portfolio of key agencies, enabling the provision of powerful internationally backed solutions with in-depth knowledge in their areas of expertise. These brands include fine milling and air classification equipment from
Sturtevant, Ventilex drying solutions, bulk handling systems from Claudius Peters, and Coperion K-Tron materials handling applications, including high quality feeders, pneumatic conveying systems and related equipment for the handling of bulk solids.
Sturtevant is a family-owned manufacturer of material processing equipment, including three types of high performance air classifiers that separate fine and coarse particles with precision and accuracy. Sturtevant has sold more than 5000 air classifiers and has designed and manufactured a wide range of material processing equipment since 1883, including three generations of air classifiers: the Whirlwind, Sidedraft and Superfine classifiers.
Source: Brolton Group/Sturtevant
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