Many users don’t realise how much leaks are costing them. Neil Frater, AIRScan technical support engineer at Atlas Copco Compressors UK, outlines how to maximise the benefits of a compressed air energy audit.
Manufacturing businesses seeking to reduce production costs and improve energy efficiency may well benefit from reviewing their compressed air systems. Conservative estimates suggest that such systems account for 10% of all energy used in global industry and that 10-30% of this is wasted by leaks. Such waste can be very expensive: even a 3mm leak could cost around £2,000 a year.
Nevertheless, compressed air energy audits are not as common as they could be. Some users are simply not aware of the extent of on-site leakage, or the associated cost; others are concerned that an audit will be disruptive and time-consuming. But when done correctly, auditing can be efficient, fast and hassle-free, while highlighting opportunities for energy-saving and process improvements.
Initial steps can be taken that involve little or no technology. First, a compressor can be run without attached equipment operating, to minimise background noise. Some leaks can then be found simply by listening – although larger ones may be inaudible, or only occur at certain pressures, and others may be inaccessible.
Results can be somewhat improved by applying a soapy water solution with a spray or soft brush to potential leak points like joints, flanges and valves. Bubbling will indicate any leaks. However, this method is very time-consuming, and still relies on good access to all pipework.
The best, and most widely used, approach is to use ultrasonic detection equipment. This operates without interrupting plant operation, reaches system areas that are inaccessible, and locates all leaks.
The principle behind ultrasonic air leak detection is simple. As air moves from high pressure to low pressure through a leak, it creates a turbulent flow. The turbulence has strong ultrasonic components which are detectable. In general, the larger the leak, the greater the ultrasound level.
Ultrasonic detectors are usually unaffected by background noises in the audible range because these are filtered out. Accordingly, leaks can be detected in even the noisiest environments.
Various hand-held, battery-operated probes are available, which can be aimed at the pipework under investigation. One type electronically converts the high-frequency emissions into lower-frequency equivalents audible through a headset. Another is designed as a camera which shows images of the surveyed pipework, with leaks appearing as bright dots.
The money-saving benefits of such ultrasonic instruments are maximised when they are used as part of a monitoring strategy for the compressed air system. This should present survey results to management in a clearly understood, actionable format; the survey should be repeated at regular intervals – typically every six months or so – to catch new leaks as they appear.
Atlas Copco performs ultrasonic leak surveys as part of its AIRScan energy audit service, which checks flow, power and air quality, and assesses maintenance levels as well as leaks. Each survey report includes ID photographs where applicable, leak rates in colour-coded schedules, associated costs, and equivalent carbon dioxide emission losses.
Such surveys can have many benefits, including continuous energy cost reduction; a longer life for air compressors and treatment equipment through load reduction; productivity improvements from maintaining higher system pressures; and compliance with legislation.
A typical AIRScan can lead to 25-30% energy savings. In one recent Atlas Copco project, a leakage detection programme instigated in a UK vehicle manufacturing plant identified leaks costing £102,000 a year in lost energy. A similar programme, conducted over three days at the site of a UK-based food manufacturer, pinpointed £49,000 worth of leaks. This illustrates the benefit of conducting this type of audit.
Best of all, if the AIRScan engineers don’t find leaks to cover the cost of the survey, there’s no charge. What more could you ask for?