Compressed air is one of the most important and versatile energy carriers in production plants. But the losses, such as from leaks in piping or incorrectly dimensioned pipes, are high and yet all too often ignored. To this day, a standard 10 percent loss is still factored in when calculating compressed air generation requirements. The energy savings potential here is enormous and promises attractive cost benefits: As a rule of thumb, investments in cost-reducing measures pay for themselves in one or two years . At the ComVac event at HANNOVER MESSE the topic of energy efficiency is high on the agenda. The world's premier manufacturers are showcasing their products here.
A thousand compressed air solutions for billions of kilowatt hours
A compressed air system is a complex configuration of generators and consumers with long distances in between. In line with this, there are many ways to reduce energy consumption.
The first place to start is with the compressor itself. High-efficiency electric motors have advanced by leaps and bounds in recent years. Frequency converters, for instance, adjust the speed of the compressor drive to meet the actual load. This means that only the required amount of compressed air is generated at a particular point of time. Jürgen Wisse, Business Line Manager for Industrial Compressed Air at Atlas Copco Kompressoren und Drucklufttechnik GmbH in Essen, explains, "In our view, the use of variable speed compressors is a clear must if you want to generate compressed air as energy-efficiently as possible."
Equally important is the means of power transmission used, since gearboxes and belt drives translate into transmission losses. This is avoided in modern direct drive systems, where the drive motor and compressor block are directly connected, as in the latest compressor generation from BRENNER.
In addition to the compressor itself, efficiency also depends on the internal control setup. Modern systems use a variety of control options and can precisely adjust the capacity of the compressor to match the varying demand for compressed air.
Even compressed air treatment plays a not insignificant role in determining the energy efficiency of compressed air supply systems. This is primarily dictated by the drying process. The new generation of refrigerated compressed air and adsorption dryers starts up only when treated compressed air is needed. This makes energy-guzzling bypass control systems redundant. This in turn saves energy – depending on the type of dryer and operating conditions, up to 60 percent. Manufacturers such as Beko, Kaeser, Boge and Ultrafilter have taken the lead in this area.
Simply optimizing individual system components is not enough
To maximize the efficiency of the overall compressed air system, innovative companies are optimizing the integration of each component. Computer-aided demand analyses aka "compressed air audits" are valuable tools here. Without any intervention in the piping, data loggers quickly determine how air demand varies over time, how economically a station is operating and whether it can be operated more efficiently or made more fail-proof. Such an audit is highly recommended before investing in a new compressed air system. In fact such audits are an integral part of the offerings from many manufacturers, including Festo and Atlas Copco.
Savings can even be made in the controlling and regulating systems of compressed air stations. Modern cross-machine control and regulation systems can reduce energy consumption dramatically. According to Harald Härter from Gardner Denver Industrial, "The efficiency of compressed air stations with up to twelve compressors including downstream devices can be maximized using the higher level SmartAir Master control system."
But the front-runner in the efficiency stakes may likely be heat recovery.
In a hot water recovery system, up to 72% of the compressor power can be recovered as heat, whereas in a pure air cooling system, recovery is as high as 90%.
The applications for recovered heat range from space heaters and hot air curtains to the heating of process water or the pre-heating of burner air.
Probably the easiest way to obtain big savings is in the area of leakage. The energy losses from leaks in a compressed air piping network typically range from 10 to 25 percent. With advanced detection equipment, leaks can now be easily located and fixed.
More than the sum of its parts – systematic energy conservation
There are many small steps to making compressed air systems more energy-efficient. But to optimize savings means taking a holistic approach – from the generation, treatment and distribution of compressed air to the applications for it. That is the only way to exploit the potential of energy savings to the full. And that's massive.
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