Air separator generates more saleable product

Many quarries have investigated the value of ?dry? processing fines. Where a ?dry? fines processing system has been implemented, aggregate producers have reduced the amount of sludge they produce. Some applications have also eliminated the need for a traditional wash plant and silt ponds.

One such dry processing application is an air separator from US-based Fisher Industries. The air separator has been designed to remove unwanted fines without the need for sandwashing. There is no baghouse required or external air source. The air is generated by the rotor fan spinning counter-clockwise and creating a ?tornado? effect within the two inner cones. The air re-enters the unit through a set of louvers halfway down the outer cone, and is then lifted up through auction and passes through the material as it is centrifugally thrown out into the separation zone. The air traps the finer particles and distributes them in the outer cone and the heavier particles fall down through the inner cone. The faster the fan is, the more air that is moved around in the unit and the more particles that are removed from the feed.

Fisher Industries manufactures one size of unit, with a four metre diameter. While stationary products are available, the air separator has been designed mainly for the mobile contractor and is offered in a portable or stationary configuration. The portable unit comes with the separator, feed conveyor, two discharge conveyors, a hydraulic system for set-up and tear down, a removable electrical panel stand with controls and a 50m power cord and a triple axle assembly with brakes and suspension on a heavy beam chassis frame. The separator is operated by a 56kW electric motor with a Cutler Hammer AC inverter to control speed. It also incorporates an automated grease system to get the proper amount of grease to the main bearing and seals. A Martin vibrator also keeps the inner cones free of material build-up.

The three covered conveyors are all powered by 5.6kW motorised head pulleys and rubber boots and clamps seal the separator to the two discharge conveyors. The unit?s operating capacity is up to 150tphand no larger than 10mm material (-5mm material is considered the best feed material for producing manufactured sand). A 125kW generator or 150amp breaker online is required to power and operate the portable unit.

In the United States, the air separator has been used to crush abrasive and non-abrasive applications and separate unwanted fines in limestone, granite, trap rock, basalt, silica, sand and gravel operations. There are 50 air separators being used in quarries throughout the United States and around the world, including Sweden, Dubai and Asia. Dry fines from limestone, granite, sand and gravel applications have been sold in niche markets as aglime, mineral fillers for fertiliser, concretefiller and for use in composite shingles.

Fisher Industries? first air separator in Australia is on-site at a dolomite quarry of Southern Quarries Direct Mix Group, 50km from Adelaide.
Southern Quarries operates the quarry at Sellicks Hill, supplying concrete, aggregate and road base materials to the building and construction industry. The affiliated Direct Mix Concrete runs several concrete plants in Adelaide and the surrounding area.

Before acquiring the air separator, Southern Quarries Direct Mix Group did not manufacture sand, but it had processed crushed fines through a rod mill to produce an agricultural lime.

?The rod mill was crushing our fine materials from a -5mm dust to 0.75mm, and we were marketing that as an agricultural lime,? explained Brett Brown, the chief executive officer of Southern Quarries Direct Mix Group. ?However, the power bill was expensive (447kW) and the quality of the lime was inconsistent. When one of the rods got tangled, we?d have to strip it out and install a new set of rods. It was an inefficient way of producing agricultural lime.?

Given these problems, Southern Quarries explored alternatives. When the Group identified that a dry classification system would be ideal for producing the agricultural lime, it also realised it could use the system to manufacture sand as well.

?It gave us two options,? said Brett. ?A graded specified product and then reject fines in an agricultural lime.?

Southern Quarries did not consider a wet classification system because it was not perceived as ?sustainable?, due to the large volume of water used to wash the sand and the environmental issues that surround building new slimes or silt dams.

?If you have an existing silt dam, then the  South Australian Department of Primary Industries and Resources is more tolerant of a wet classification system,? Brett explained,? but the problem in the future is that they just don?t know what to do with those sites because they can be an environmental liability. So that?s one reason why we opted for the dry classification system. The other issue was water. The amount of mains water required would have been phenomenal, so it really wasn?t an option.?

Brett said the dry processing system was ?more environmentally responsible?, as water was not used. He added that dry classification also promised a 100 per cent dry product, compared to washed sand with up to 10 per cent moisture.

?When we?re talking to customers,? said Brett, ?we?re talking about moisture content, product versus water, so with dry classification, you?re obviously getting more product and better value for money.

?The moisture content of the material plays a major role in the efficiency of the air separator. We have been successful in separating material direct from the crushing operation with moisture content up to four per cent. Material that is stockpiled or natural fines are more difficult to separate because moisture content is higher.

?The key issue is the environmental issues that come with slimes and silt dams. If you don?t have a slime or silt dam, you?re talking about a $1 million investment in a press to extract the water and have the material and you still have all the handling issues with the slimes afterwards.?

Southern Quarries evaluated numerous  suppliers, but it was Fisher Industries? dry classification system that most impressed the Group. In 2008, Southern Quarries staff visited three quarry sites in California to view two stationary versions and one mobile version of the air separator. They also visited Fisher Industries? manufacturing facility in Dickenson, North Dakota to view the air separators at the assembly and production stages.

?We were kindly provided with test results from other limestone quarries that were using the air separator as reference data before we went over,? Brett explained. ?The material and moisture content of the product that they were using in some of the Californian quarries was very similar to what we would process in our quarry. We were able to see first hand their results, the feed materials and the grading from those sites, so we knew an air separator would work for us.

?I suppose what sealed it for us was seeing the Fisher Industries facility. The build quality of the air separator was exceptional. Fisher was also committed to performing the commissioning and training – in effect, the after sales service. Once we saw the build quality in the manufacturing facility, and we had a commitment for after sales service, we were convinced that this was the right plant for our circumstances.?

When the unit arrived at Sellicks Hill quarry in November 2008, Fisher personnel flew out to Australia to assist with the commissioning, set up and training of Southern Quarries? key personnel.

?The great thing for us was that all the wiring was done in the US to Australian standards prior to installation,? Brett added. ?We didn?t have to worry about the fact that it might come here wired up to American standards.?

While Southern Quarries? air separator is a stationary unit, Brett said that it could be disassembled, moved and reassembled.
?Basically the difference between the stationary unit and the mobile unit is obviously the chassis. If we want to pick up ours and drop it on the back of a truck and ship it to the other end of the quarry or to another quarry altogether, it?s a simple matter of undoing the hold-down bolt from the concrete slab, taking the two discharge conveyors up, moving it down the other end and putting the new conveyors in, putting it on a new pad and you?re off and running again. On the whole, hooking it up is very simple,? Brett explained. ?If we have to move it around, we can, but if you want something that?s fully portable, then the mobile unit is better for you.?

Brett Brown explained that Southern Quarries was using the air separator to blend manufactured sand with natural sand to create ?a perfect construction sand?. The current throughput is up to 150 tph of blended sand through the machine. ?We currently run between 120 and 130 tph on average,? Brett said. ?We believe that we could produce and use a 100 per cent manufactured sand in the future.?

Southern Quarries has an agreement with Fisher Industries to distribute the air separator in Australia. Brett Brown said that interested customers in Australia considering a dry fines processing system could visit Southern Quarries? operations and view the air separator working first hand. ?When a unit is sold and commissioned on-site, the key personnel from that site are given full training on plant maintenance. We also offer critical spare parts for local distribution in Australia.?

Brett added that several operators who had visited the Sellicks site came away believing that the air separator was exactly what they are looking for. ?They need to get the fines down as low as possible, and we?re getting it down to about seven per cent, so they were really impressed,? he said.

Brett said that he recommended interested parties visit the Fisher Industries website to look at the literature and video demonstration of the air separator. ?If you like what you see, we would be more than happy to show you our unit operating at our quarry in Adelaide,? he offered.

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