Mechanical Technology July 2016

⎪ On the cover ⎪ range to better meet client needs

and allowing the trapped gas to discharge to atmosphere.” he explains. For foundry use and for laser cutting applications, for example, the compres- sors, nitrogen or oxygen generators, tanks and pressure boosters can be assembled onto a common skid. “So we can deliver a plug-and-play gas solution to foundries and fabricators – and by using a pressure booster, we can typically provide nitrogen to a laser cutter at 25 bar and up to 40 bar, if needed,” he adds. Specialised solutions Atlas Copco also offers specialised compressor ranges for key industries. “We have a railway range, for example, which will be very useful for the new rail rejuvenation projects currently be- ing implemented in South Africa. Our GAR railway compressors are used for operating brakes, doors and toilets on train locomotives and coaches all over the world and will be ideal for use on the 600 Alstom X’Trapolis Mega passenger trains being built in South Africa by the Gibela Rail consortium for PRASA or by Bombardier for the new Transnet Freight Rail fleet currently under construction,” Ackerman says. A full medical range, which conforms to the SANS 7396 standards for medical gases is also on offer for hospital qual- ity air – for breathing and for powering surgical instruments. “These expansions are enabling us to be competitive in a much wider range of applications,” continues Van Wyk. “And while Atlas Copco has deliberately cho- sen to operate in the premium segment of the market with a broadening product range, increasingly, customers are un- fairly comparing our full-featured quality products to lower cost brands,” he says. “So we have also launched Atlas Copco ranges that maintain our qual- ity standards but do not have all of the functionality and class-leading energy efficiency associated with our flagships. These are simpler, less expensive ver- sions that preserve the quality and reliability associated with Atlas Copco branded compressors and air treatment products. “Along with all of our other range ex- pansions, these further enhance our pre- ferred supplier status.” he concludes. q

99,999% purity. Pressure swing adsorp- tion, on the other hand, can achieve that purity with a 4:1 ratio,” Ackerman explains. “But for lower purities, membrane technology becomes more efficient, with a purity of 98% being the break-even point between the two. So for nitrogen purities between 95 and 98%, we recom- mend using membrane technology, while for higher purities, our NGP swing ad- sorption solution is better,” he suggests. Typical uses of lower purity nitrogen include inflating car tyres (95% purity) and fire suppression. “For food preserva- tion applications, such as filling potato crisp packets with nitrogen before sealing them, or for preserving maturing wine, 99.5% is required. And we have recently supplied high-purity units in Cape Town for packaging biltong,” Ackerman says. Van Wyk adds: “Food and beverage industries are less affected by the down- turn, so we are experiencing strong sales growth for all of our products at food, chocolate, soft drink and beer manufac- turing plants.” Membrane technology separates nitrogen in compressed air from oxygen and water vapour. The compressed air is passed into the cores of bundled semi- permeable membrane fibres. The larger nitrogen molecules travel directly up the cores to the outlet, but the smaller oxygen and H 2 O molecules permeate under pres- sure through the membrane walls and are discharged to atmosphere. “The technology can produce rela- tively high volumes and since water vapour also permeates, the nitrogen is inherently dry,” Ackerman says. PSA adsorption, on the other hand, relies on molecular sieves, which work in a similar way to desiccant dryers. If producing nitrogen, the sieves trap and isolate oxygen and water vapour molecules, allowing the nitrogen to pass through. The principle can also be used to produce high purity oxygen, however. In this case, the sieve material isolates the nitrogen molecules and the oxygen passes through. Once the molecular sieve material in a vessel is saturated, the unit ‘swings’ over to a new adsorption vessel, while the saturated one is regenerated. “This is done simply by releasing the pressure

he reveals. “The centrifugal ZB range was previously limited to 132 kW, but we can now go up to 250 kW, with VSD options available for most compressors in the range,” he says, adding, “we can also cater for larger flows and sizes with our multistage centrifugal (ZM) range. “In the municipal space, we have had visibility problems. Wastewater plant op- erators seldom know about the difference between screw and centrifugal technolo- gies. All they know about is the common roots-type blower, which is not always the most effective or efficient option. “Going forward, we can now offer best-fit solutions for almost any applica- tion requiring low pressure compressed air,” he explains, before suggesting that “the different technology options and their advantages really need to be prop- erly introduced to the market”. Nitrogen and oxygen generators Another key product for Atlas Copco Compressor Technique is its range of nitrogen and oxygen generators. “Com- pared to the on-demand ordering of gas bottles or tanks, on-site production of nitrogen or oxygen offers cost savings, flexibility and continuous delivery advan- tages,” says Ackerman. For nitrogen production, two technolo- gies are available: membrane separation and pressure swing adsorption. “Purities of up to 99.999% can be achieved with either technology but the membrane technology is less efficient for producing high purity nitrogen, requiring an air to nitrogen ratio of about 7:1 to produce a

Mechanical Technology — July 2016

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