Companies are yet to realise how signifi- cant the costs of air leaks in compressor systems can be; hence, the surprise at the costliness of having high leak rates, which could have been avoided, says condition assess- ment and monitoring company Martec.

Air compressor systems consistently experience up to 30% loss of energy and air, business unit manager for ultrasonic detection services Mark Shepherd tells Engineering News.

“Recently, we assessed a tyre manufacturer’s compressed-air system, which runs constantly and has four 250 kW compressor units draw- ing 1 MW of energy. At industrial rates of between 50c/kWh and 60c/kWh for State-owned power utility Eskom, it costs this facility about R14 400 a day and about R5.26-million a year to run the system. Considering the company’s energy losses of 36%, owing to air leaks, it was losing close to R2-million a year,” says Shepherd.

Martec was commissioned by the tyre manu- facturer to perform an ultrasonic air-loss survey because, despite having installed a new compressor system that should have been generating enough compressed air for the facility, the company was constantly experiencing pressure drops and an insufficient compressed-air supply to carry out operations efficiently.

“It was found that the problems at the tyre manufacturer’s facility were caused by air leaks,” he says.

Pressure drops, owing to leaks in a compressed-air system, result in unreliable equipment that does not perform properly; therefore, leaks also impact on the efficiency of a production process, Shepherd explains.

“Once the air leaks at the tyre manufacturer’s facility are repaired, at least one of the compressors will not need to come on line and will, in effect, be a standby unit, allowing for service rotation of the four compressors,” he elaborates.

This will stabilise the tyre manufacturer’s system and allow operations to proceed without the associated production loss and product rejects.

There are many places where leaks can occur in a compressed-air system, highlights Shepherd, noting that these leaks often occur because of the deterioration of old systems, insufficient maintenance and inappropriate use.

However, the unnecessary cost associated with compressed air is not only limited to leaks in a compressed-air system, he adds.

“The energy output of a compressor is only 10% of the total input. This energy loss occurs because heat is generated when air is compressed and this heat energy is lost.”

There are systems that can be put in place to recover the heat energy, such as using water-cooling systems on the compressor, Shepherd notes. However, he suggests that factories using older systems and equipment should replace inefficient compressed-air systems with high-efficiency compressors, dryers and filters and use blowers where high volume but low pressure is required.

The air quality required for processes is another factor and includes specifications such as cleanliness or dryness and the constant pressure and temperature of the air, which are required to operate critical pneumatic actuators and equipment. Producing the correct air quality for any application or process usually requires equipment such as filters, dryers, heaters and coolers.

“Costs are also involved in cleaning and replacing the filters, buying desiccants for drying the air and maintaining the compressors. This all adds up to a costly unit, without even taking into account the running costs,” explains Shepherd.

Further, regular maintenance of a compressor system has proved to reduce energy losses, he says, highlighting that a recent survey reports that companies in Europe using compressed-air systems carry out maintenance every four months. Maintenance in South Africa is not carried out as regularly and he attributes this to a lack of training in identifying system leaks.

However, Shepherd says most South African companies using a compressed-air system have their own maintenance departments capable of servicing the system and replacing any faulty equipment.

In terms of the inappropriate use of the compressed-air system, he cites the example of using three-quarter-inch pipe to cool a bearing with compressed air, which is uneconomical owing to the high costs associated with compressed air. “There are reasons for that bearing overheating. The cause needs to be investigated and a less costly solution needs to be implemented,” says Shepherd.

Leak Detection

Martec provides solutions for air leaks in a compressed-air system by looking at the system as a whole, notes Shepherd.

“If leaks are detected anywhere within a system, we can quantify the extent of those leaks and, using this information, we can establish the approximate energy loss of that system and the costs attendant on that loss.

“Air leaks make a noise and are often loud enough to cause discomfort. The problem is that people do not realise that the noise is an air leak, or cannot hear it in a high noise environment” he explains.

For an air leak that is not as obvious, Martec uses a range of ultrasonic detectors to pinpoint its location. The ultrasonic detectors calculate specific losses from the noise level – measured in decibel microvolts – of the leak.

“The ultrasonic detectors provide a reasonably accurate indication of the amount of air a system is losing. Based on the compressor system being used, its output and the amount of kilowatts consumed, the energy and financial loss of the system are calculated,” says Shepherd.

He adds that, although the readings are not 100% accurate, accuracy does improve when there are a large number of leaks in a system.

Martec’s services have been used by several industries, including the tyre, steel and food and beverage packaging manufacturing industries. Its services have also been used by companies in Mozambique, Botswana, Zimbabwe and Zambia.

“We recently completed a substantial project involving a steel plant in the Western Cape, where a substantial energy loss was detected in the compressor system being used,” says Shepherd.

Currently, Martec is registered with Eskom as an Energy Saving Company and is working to improve the energy efficiency of glass bottle manufacturer Bottle-Man. The project entails improving energy efficiency throughout the facility.