The right compressor for your business

Compressor technology has come a long way in recent times. But choosing the right machine isn’t a one size fits all game and it pays to choose wisely. Matt McDonald reports.

Compressed air is something a lot of manufacturing operations can’t do without. But the thing is, it uses a lot of energy and therefore costs a lot. So it makes sense for manufacturers to seek out the latest and best products.

So what are the latest products?

One is the KHE series ‘2 Stage’ rotary screw air compressor from Southern Cross Compressors.

“It’s a two–stage compressor as opposed to a typical compressor used in industry which is a single stage compressor,” Mark Ferguson, CEO of Southern Cross Compressors told Manufacturers’ Monthly.

“A single stage compressor takes air at its atmospheric pressure, boosts it to its final discharge pressure which means you have a very high overall compression ratio.”

In contrast, 2 Stage technology works by dividing the overall compression ratio between two distinct screw air ends, rather than one; and cooling the air in between the stages.

“That means that the compression ratio over each of those stages is significantly reduced (less than half) which has the effect of significantly improving the efficiency of the machine,” added Ferguson.

“So what you’re getting is a lot more compressed air from the unit for the given power than you’re putting into it. And that’s typically around 15-20 per cent at full load.”

To put this in perspective, a 15% power saving based on replacing a conventional 200kW compressor with a 2 Stage unit could realise annual energy savings of around $40,000.

2 Stage technology is not new but the significant thing about the KHE Series is its wide range. Southern Cross Compressors have extended their range to cover capacities from 17.4m³/min (75kW) up to 70m³/min (355kW) and with pressures ranging up to 13 barg.

Ferguson said that, by incorporating a variable speed drive into the system, potential savings are even greater.

“We’re getting almost linear reduction in power with demand. In a plant where the demand varies considerably, throughout the day, the night, what have you, these machines will actually respond proportionally to give the required amount of air for the plant at any given time with proportional absorbed power,” he said.

“These start at 75kW which covers medium to large manufacturing organisations, chemical plants, the oil and gas industry, mining applications, really anywhere a customer needs a high volume of reliable compressed air.”

Asked what the next compressor developments will be, Ferguson said he expected to see an expansion of permanent magnet motor technology and different methods of control.

But he added, “We aren’t seeing a new mouse trap out there yet.”

Making the right choice

He stressed the importance of manufacturers choosing the right compressors for their businesses. He said that, by finding the right machine, you can maximise efficiency and keep costs as low as possible.

“There’s not a one size fits all approach because every application is different,” he said.

He added that a lot of this comes down to the skill of the people that are making recommendations. They need to interpret what a customer’s usage looks like and make a recommendation based on that.

“I’ve seen plenty of applications where customers have bought a variable speed drive compressor for applications where they use air constantly. There’ just no benefit and in fact there’s a penalty to be paid because of the cost of running the variable speed drive,” he said.

According to Jim Rohner, Managing Director of Boge Compressors (Australia), cost savings can also come down to your purchasing behaviour.

“All major manufacturers do oil-injected screw compressors. Some of them do oil-free screw compressors and most do a variation of sorts of a piston compressor,” he told Manufacturers’ Monthly.

“Boge is a little bit different to that. We do all of those products then we also do oil-free piston compressors – very small ones which are suitable for hospital applications. We do nitrogen generators, oxygen generators, the BC converter…”

He explained that Boge aims to provide a total solution. Instead of going to one supplier to buy a compressor, then another to buy another component, then a third supplier to buy drying equipment (such as desiccant dryers and carbon absorbers), you can purchase everything from Boge.

“We supply everything,” he said. “When it’s a total package it’s more cost efficient you’re only dealing with one person. Which saves time.”

The company’s list of specialised products includes a Nitrogen Generator, which has applications in the food sector. For example, it can be used to prolong the life of fruit such as apples and plums.

As Rohner explained, if such fruit is left in an oxygen-rich atmosphere it goes off. But, by pumping nitrogen into the refrigerator or holding bay, you can preserve it.

“We have nitrogen generators where you can regulate the purity, you can measure the flow,” he said. “And your ability to produce nitrogen can continue to grow just by adding modules.”

There is no need to replace the whole system. You can just add to it.

Boge also recently released a catalytic converter called the BC Converter (pictured below). When positioned after any brand of compressor, this product takes all of the contaminants that are drawn into the compressor and leaves you with class 0 oil-free air.

The BC Converter is suitable for applications within the food and pharmaceutical sectors, as well as in other areas such as CD manufacturing.

Rohner explained that, within these sectors, there are two disadvantages associated with using an oil-free compressor.

“It still takes in whatever is in the ambient air and that comes back at the other end. So if there are contaminants in the air like silicon you will get those same contaminants coming out the other end, he said.

And the second disadvantage is the fact that oil-free screw compressors are so expensive.

“It’s a false economy to make them too small so generally speaking they start at around 60 horse power and they’re well over $100,000,” Rohner said.

So instead of buying an oil-free screw compressor you can purchase a BC Converter at a fraction of the cost.

He cited the example of Melbourne-based yoghurt maker, five:am. Though a successful business, it didn’t have the budget for an oil-free screw compressor. It simply wouldn’t have been able to make enough yoghurt to make it pay.

“They’re a typical example of a plant that would have had to spend $150,000 to buy an oil-free screw compressor.”

Instead, he said, they bought two Boge model C30s and a BC converter at about 25% of the capital outlay.