Mechanical Technology July 2016

Mechanical Technology — July 2016

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On the cover

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range

to better meet client needs

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

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

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

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.