Kayasand sees a future where quarries can turn the water off on aggregate washing by replacing their water-based washing systems with much cleaner and more precise dry washing systems, such as found in the RCAS system.
When Japanese company Kemco first launched their innovative V7 sand manufacturing technology 20 years ago, they set out to revolutionise the way quarries produce concrete sand. They developed a new high-throughput, precision dry screening system that they called RCAS. This quad-deck dry screen combines the processing rate of air-classifiers, with higher accuracy than conventional screens and no dust emissions. It’s ideal for screening materials with high fines content or where accurate cuts of fine fractions are required. Kayasand has brought this same innovative technology to Australia, New Zealand, and the pacific islands.
How it works
The novel RCAS screening process uses a unique combination of high-volume air flow and mesh screen decks. It can accurately separate aggregates from 40 millimetres (mm) down to 75 micrometres (µm), and uses air to wash the aggregate rather than water. A blower creates an air-knife that raw material must pass through as it falls into the screening chamber. This blower spreads the raw material across a vibrating four-deck screen to maximise screen area utilisation.
At the same time, a powerful dust collector sucks out ultra-fines from the coarse material before it even hits the screen deck. This, as Bram Smith, Kayasand’s general manager explained, results in cleaner aggregates passing through the screen and avoids blinding of screen decks caused by buildup of ultra-fines on the mesh.
“What you end up with is the throughput benefits of an air separation system, with the accuracy of a mesh screen system,” Smith told Quarry.
The action of the blower pushes the finer particles away from the feeder. This means the lightest particles travel further on the screen, and spread more evenly, while the heavier particles drop down below the feeder. As material passes through the screen, a powerful counter current of air is sucked up through the decks and into the dust collector. It’s this reverse movement of ultra-fines in air through the screen decks that reduces the risk of blockage even further.
The combination of dust collector, skimmer and four screen decks, means the RCAS system can produce up to seven different precisely fractioned and de-dusted products from the feed. It’s ideal for a range of materials including quarry aggregates, limestone, recycled glass, recycled concrete, sand, quicklime and more.
According to Smith, there are many advantages offered by the novel screening approach. As well as higher throughput, which is typically double or more than that of conventional screens, it is also incredibly accurate. Installations in Japan achieve less than one per cent passing 0.075mm in the coarse aggregate fractions, while at the same time reducing the ultra-fines in the manufactured sand so it doesn’t need washing for use in concrete.
Moving away from water
Perhaps the most exciting feature of the RCAS is the ability to eliminate water from the product screening process. As the ultra-fines material gets extracted by the RCAS dust collector, there’s no need to wash the aggregate or the sand. Quarries can do without a wash plant and wash screens for final screening, and avoid the heavy costs of tailings management and waste minimization.
“In a quarry, you typically use water for three main purposes: wash down of plant and equipment, wash screens for coarse aggregate, and wash plants for manufactured sand. The latter two being the biggest contributors to tailings,” said Smith. “If you remove those two elements and make them a dry process, you can have significant reduction in maintenance required for your silting ponds. Plus, the ultra-fines you extract using dry extraction can be used for other products.”
Smith said Kayasand’s goal is to help quarries slash their water demand by precisely screening sand without using water. This principle is embedded in Kayasand’s flagship V7 crushing and screening plant. It is designed to produce accurately graded concrete sand from any type of aggregate material. “We [at Kayasand] see a future where quarries can turn off the water on their aggregate washing process and replace it with dry systems that transform waste into products and by-products for use in all sorts of applications,” said Smith. “By removing the need for tailing control and the reliance on water, quarries can reduce costs and increased throughput.”
The value in versatility
According to Kayasand’s Sales Manager, Frank Grech, the versatility of RCAS is a big benefit for quarries too.
“With products like limestone and recycled glass, accurately graded fractions find applications in a variety of markets. So, quarries can create a real value stream by tapping into those markets with their by-products,” he said.
“Similarly, having a screen that de-dusts the coarse aggregate and crusher dust at the same time provides sand that is perfect for cement, concrete and asphalt production. By producing accurately cut fractions, the RCAS improves the consistency of those outputs.”
Versatility also finds another meaning when it comes to re-configuring the screening process.
“The RCAS screen is designed so that the screening decks are extremely easy to remove and replace. As such, a quarry can process one type of feed in one round and then change the configuration to produce other fractions or process a different material, with minimal delays.”
Reduced wear and tear
Reduced wear on the screen decks is another advantage in the RCAS. Although the use of an air blower and a dust collector, along with linear motion vibrating screens, can create turbulence inside the chamber, the elimination of water, and by extension cyclone systems, means less wear on screening surfaces.
“With RCAS, it’s the air flow that guides the material around, instead of it being dumped onto a screen. The screen area is used to greater effect, accuracy is preserved and there’s not the same wear and tear on the mesh system. It’s air with less wear,” Grech said.
Dust reduction is another side benefit of the RCAS screening plant. With the process taking place in an enclosed chamber and under negative pressure, any dust concern at the tertiary screening stage is eliminated.
“The dust collector is sucking the air at about twice the rate that the blower is blowing air. You can open the screen chamber while it’s working and see the process in action. In most other plants, there’s too much dust to even get close to the screen.” The combination of high throughput, accurate screening and high efficiency in dry filler collection, makes the RCAS an ideal final screen for a variety of applications, according to Grech.
“If you need to screen products with fine screen mesh, or deal with materials that have excessive amounts of fines, then this screening solution offers significant advantages,” he said. “Using the RCAS, you have a screening system that’s highly effective in cutting down to your desired fractions, controlling filler levels in the product, and producing a dry filler by-product, with no water, no dust and a lot of flexibility.” •