16 September 2010
Is compressed air destined to be consigned to the role of utility of last resort – when alternatives are too dangerous, dirty or inconvenient? Not so, says Brian Wall
Clean, dry compressed air is essential for pneumatic systems to run efficiently. In fact, compressed air is often called the fourth utility – clean, reliable and critical to manufacturing. According to the British Compressed Air Society, around 70% of all companies use compressed air for some aspect of their operations.
"There can be little doubt that compressed air is widely accepted by industry, often as the energy source of choice, says Colin Mander, managing director, CompAir UK. "This is especially the case in applications where the alternatives could pose a problem – such as in extremes of temperature, where there is a risk of explosion or in areas where no other power source is available."
However, compressed air is also regarded as expensive and environmentally unfriendly. Indeed, it is charged with sucking up one tenth of all electricity used by European industry – whether that be for cooling, drying, removal of scrap product, removal of contamination or vacuum generation. In some cases, it is said to be up to 30% of total energy usage, making the process even more wasteful.
But the worst accusation is that, of the total energy supplied to a compressor, as little as 8-10% may be converted into useful energy. Leaks, poor maintenance, misapplication and poor control are all cited. So what's to be done? For one thing, compressed air audits by specialist suppliers can help manufacturers to identify the true extent of any shortcomings and seriously improve energy efficiency – removing leaks, using less energy to create the same amount of air, providing practical advice and ensuring compressed air is used resourcefully.
Then there is the matter of exerting tight control over the filtration processes in place. In many factories, the compressor provider will supply filtration systems as part of their contract to deal with contamination in the generation process. It's a different story, however, at usage stage. As compressed air enters into the factory via the ring main, it picks up particles of contaminants from the pipework. As it passes over ovens and furnaces, it heats up, but, on cooling, water droplets form which, if not removed before usage, will mix with the oil and form an emulsion which potentially slows down the valve and cylinder action, and can impact greatly on production efficiency.
Appropriate filtration at this juncture is therefore key to maximising machine efficiency (and so avoiding penalties for missed delivery times); compliance with customer standards; and reducing energy costs. "Consulting a specialist supplier can help ensure appropriate levels of filtration – whether this be installing a finer filter into the filter, regulator and lubricator (FRL) already on the machine or alternatively fitting a membrane or small refrigerant dryer – and guarantee optimal compressed air quality," according to MRO products and services distributor Brammer (see box text).
Moreover, by using the latest ultrasound technology, which detects and reads the sound pitch of air leaks, potential cost savings can now be fully quantified – by machine, department, area or even factory. These data can be presented in a dynamic document which, as leaks are fixed, is updated accordingly. Ongoing monitoring can also be provided by fitting an air flow meter to the equipment – ensuring a lasting solution and a proactive approach to dealing with future leaks.
All of which makes the often tarnished image of compressed air seem less than fair – a point that is readily taken up by Sean Fairest, divisional manager industrial air, Atlas Copco Compressors. "Anyone who still thinks of an air compressor installation as being a noisy, oily machine banging away in a factory shed, would not recognise today's compressed air solutions, which are light years ahead by comparison."
Unlike gas, electricity and water, compressed air is generated on site giving users greater control over its use and cost. "While it is regularly claimed that compressed air accounts for 10% of all electricity used by European industry, that figure must be up for challenge, as increasingly it is offset by more energy-efficient compressors, in combination with sophisticated monitoring, management and control systems," he argues. "In fact, of all the 'utilities', compressed air represents the largest opportunity for immediate energy and carbon savings on any site."
Extensive and continuous investment in the research and development of compressed air systems has resulted in the availability of a host of innovative compressor products and techniques that have revolutionised the workplace, industrial productivity and energy efficiency, Fairest insists. "The Specific Energy Requirement (SER) measures just how much electrical energy a compressor will use and the latest designs in compact compressors show an SER improvement of up to 13%."
Any trace of the 'fuel guzzling image of the past is eliminated, he adds, with today's well recognised compressor technology. By way of example, he singles out the integration of energy recovery systems as a major achievement for water-cooled, oil-free compressors, "where 100% of the electrical power input can be recovered in the form of hot water. This 'Carbon Zero' technology, where hot water can be used directly for process operations or as pre-heated boiler feed, has enormous potential for energy efficiency and consumption reduction in a great range of applications."
Returning to FRL (filter, regulator and lubricator) assemblies, the accurate specification of FRL units in particular can achieve significant energy savings, while also reducing unplanned maintenance and downtime, comments John Hill, marketing services manager for Parker Hannifin's pneumatics division. "For example, Parker's Moduflex Extras coalescing and absorption filters have been developed using computational fluid dynamic software to calculate ideal flow paths through inlet and outlet ports, and across filter media under a diverse range of operating conditions to improve internal flow geometries," he states.
Additionally, the design of the filter element will affect energy efficiency. "Indeed, modern deep pleated filter elements have been designed to reduce the velocity of the air as it passes through, giving excellent filtration, high dirt holding capacity and low pressure drop. Ultimately, this translates to dramatic energy savings of almost 5,000kW per annum or some 2,100kg of C02, by comparison with their traditional filter equivalent."
This technology also offers further benefits, as improved oil atomisation allows lubricating oil mist to travel much farther – around 40m – along air lines, as opposed to the more normal 15m in competitive units. "Moreover, size for size, these products can be up to 45% lighter and smaller than conventional units, while maintaining higher flow rates," Hill continues, "enabling engineers to replace older devices with smaller, more cost effective units."
Clearly, there are many areas where improvements can be made to lower operating costs and step up the energy efficiency of compressed air. CompAir UK's Colin Manders singles out three areas:
Buying new. Operators can consider replacing an existing compressor for a newer, more energy-efficient model that is correctly sized for the application.
Improving control. Capital investment is fine, but for companies unable to make such a purchase, installing a modern sequencer will enable much tighter control, bringing compressors on and off stream to match varying plant demand, helping to maintain a set pressure within tight tolerances and reducing off load running to a minimum.
Better maintenance. An independent test on more than 300 typical compressors in the UK market showed that energy savings of 10% were achievable by implementing a regular maintenance programme, with predictive maintenance one of the fastest growth areas.
So, far from living up to its 'dirty' tag, compressed air – with much indebtedness to the technology that delivers it – seems to be transforming its image to the point where its status and environmental credentials are rapidly on the rise. The final word goes to Atlas Copco Compressors' Sean Fairest: "While there has been much written about compressed air being the fourth utility, for many industrial applications it is, in fact, the primary utility." Higher praise could not be lavished on what has often been a much maligned technology.
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