German Lab Relies upon Water-injected Oil-free Air Compressor
Rotary screw air compressor that makes its own lubricant from the surrounding air delivers oil-free compressed air to an environmental laboratory in Stuttgart, Germany
Many sensitive sectors of industry require oil-free compressed air. However, meeting this demand is often not as simple as it sounds. One way is to use oil-injected air compressors with downstream air treatment to meet the demand. A second option is oil-free air compressors, which operate without lubricants. Both versions have their own advantages as well as risks. Another alternative is to use rotary screw air compressors that use water as a lubricant. In an environmental laboratory in Stuttgart, Germany, this has been proven to be a clean and sustainable solution.
At a major construction site ‘Stuttgart 21’, 30 trucks full of earth are waiting for the results of a representative soil sample. At another location, a mineral water factory, a batch of sparkling water cannot be delivered because of suspicions that the water is contaminated. In both cases, fast and reliable laboratory results are required. This is the bread and butter of SUI Synlab Umweltinstitut GmbH in Stuttgart. “We are one of the largest service providers in Germany for the analysis of soil, water, air and food,” explains the Technical Director of the environmental laboratory, Michael Tokarsky. And the samples come not only from Germany, but also from France, the Netherlands, the Czech Republic, Hungary, Bulgaria and now also the United Arab Emirates.
Nitrogen Generation Requires Oil-free Compressed Air
Where does the compressed air come in? The laboratory uses spectrometers for the analysis of the environmental samples. These require nitrogen to operate, which is filtered out of compressed air using the membrane method by nitrogen generators at Synlab. The problem here is that even the slightest amount of oil could cause severe damage to the generator. This is why the environmental laboratory needs absolutely oil-free compressed air – and in enormous quantities: it takes 1000 liters of compressed air to produce 100 liters of nitrogen.
“We used to do this with dry rotors,” reports Michael Tokarsky. With dry-running, i.e. unlubricated air compressors, the high operating temperatures impose high loads on the material. “There were equipment failures,” continues the Technical Director. “Every morning I was expecting the call saying we have no compressed air. That means we have no nitrogen and cannot do our work. So I looked around for an alternative.” Oil-injected air compressors cover a wide performance range. The fact that the oil is subsequently separated using filters or catalytic converters means there is a certain residual oil content, and the risk that something could go wrong and oil could get into the system anyway.
An Environmentally Sound Solution
“Water-injected air compressors seemed to me to be a practical solution,” says Tokarsky. “However, there are not many suppliers in the market, most of them cover a higher performance range than we require and do no offer output-controlled machines. Then I discovered the company Aqua Air during my internet research.”
The company was founded in 2011, and supplies oil-free screw compressors, either as an OEM kit or as an operationally ready system from 4 to 22 kW and 75 to 110 kW. The basis for this is the special Aqua Air technology, the focus of which is on rotors manufactured from polymer materials. The compressors use water for lubrication, sealing and cooling, and thus operate entirely without oil. Not even the slide bearings have so much as a drop of grease. The special feature here, is that the air compressor collects the water directly and exclusively from the ambient air.
Aqua Air technology is a self-contained design generating the necessary coolant directly and exclusively from ambient air – by using the water from the atmosphere. In this manner, the air compressor produces no waste oil. Maintenance costs are also reduced as purchasing, filtering, and disposing of oil-based lubricants is not necessary. The key system components are water-free floating bearings, a condensate separator system with no mechanical components, a leak-free water filtration system, the self-healing proprietary polymer material air end , and inlet air control valve with a three-stage heavy duty inlet filter.
The Sullivan-Palatek Aqua Air unit is being introduced with 5-15 hp models at pressure between 72-145 psi (5-10 bar).
This was precisely what Michael Tokarsky was looking for. Nevertheless, at first he had some reservations. “As Technical Director, I have a responsibility to secure reliable partners, whose manufacturing facility is not in some backyard garage. Innovative is well and good, but if one machine works and another does not, that is a problem. So I drove out to visit Aqua Air in Augsburg, to get an idea of the company for myself.” And what Tokarsky saw there convinced him. “For one thing, there was a very tidy production hall, and on the other I met the director, co-developer, and head of the company Marco Lodni, who is deeply involved in the subject matter. He is really passionately involved, and knows exactly what he can expect his machine to do.”
Because they had no reference customers yet in Germany from the field of environmental analysis, we decided together to perform a trial run at the environmental laboratory of Synlab in Stuttgart. Compressor type LTWA 11-8 was selected. It has a 11 kW drive motor and delivers 8 bar pressure at a volume flow rate of 1.71 m3/h. When it was delivered in the middle of October, a further advantage of the machine became apparent: its design is compact, about half the size of comparable devices. “This paid off with our poor infrastructure, because there is no lift down to the basement. Three of us were able to carry the system down easily,” reports Michael Tokarsky. A further positive aspect is that the compressor does not need a water connection in the way water-lubricated compressors from other manufacturers do.
“I’m not really a fan of maintenance contracts,” says Michael Tokarsky. “I want to understand the machine myself before I have to call someone and say, ‘Please come!’ But the point is simple, we need operational reliability.” For this reason, the maintenance was part of the inquiry from the start, and it is also covered. “We arrange this through contracted partners based locally,” explains Reinhard Wundsam, Sales and Marketing Manager of Aqua Air, continuing, “They handle the sale of machinery on the one hand, and the services and maintenance on the other.”
Overall Michael Tokarsky was more than satisfied with the trial run. “I was very sceptical when I went into this. I would have had no problem saying, ‘No, that won’t work’. But seeing the product at work simply convinced me. The machine has now been running for almost six months in what is essentially the toughest environment.” It has been operating without stopping, 24 hours a day, 7 days a week. “And the system produces just barely more air than we can use,” explains Tokarsky.
So the system is continuously switching back and forth between standby and operating mode. Switching the compressor on and off would generate a higher load current and apply greater loads to the motor and V-belt. “In principle, we’re torturing the machine,” says the Technical Director of the laboratory. “This is not economical or resource-friendly, which is why we want to control this in future using a frequency converter.”
The environmental laboratory will soon be relocating to new and larger premises. There they will have two Aqua Air compressors, as a redundant system with a corresponding control system. “We have between six and eight production sites where compressed air is used. Thanks to our good experience, a colleague in the field of human diagnostics has already expressed interest in the Aqua Air compressors.”
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