The high cost of air

?Not many process operations really understand or appreciate how much it costs to operate a compressed air system, and so fail to take even basic steps to improve the efficiency of their systems.

This shortcoming is despite there being many sources of advice available on how process companies can avoid spending large sums of money on wasted energy and - perhaps more significantly - on equipment that doesn’t really match their requirements.

Figures from the Carbon Trust, suggest that UK businesses could make annual savings of over £630 million simply by using more efficient electric motors and variable speed drives - and that 10% of all electricity used in industry is linked to compressed air applications.

As a recent example, steel components maker Astrum, cut its compressed-air energy costs by over 50% after installing two variable-speed compressors at its County Durham foundry - helped by an interest-free loan from the Carbon Trust to fund the project.

Paul Clark, business line manager, industrial air division at Atlas Copco Compressors, estimates that his company’s UK customers alone will save 16.5 million kWh of energy in 2012 as a result of using its VSD compressor technology.

“It is difficult to believe,” commented Clark, “but [one] reason why some UK businesses are not taking advantage of VSD compressor technology is a lack of knowledge; in some cases people are not even aware that energy savings can be made.

“A detailed energy audit of a compressed air system, however, can identify potential savings and energy monitoring services are now being offered by many compressed air manufacturers and distributors.”

Larger companies, generally, have a good awareness of the cost of waste and bad practice, but many smaller companies are still not clued up, reports a Beko spokeswoman. Customers, she said, tend to believe the figures in brochures whereas many of the claims would not stand up to measurement of key parameters, such as dew point, flow, pressure loss and oil content.

A particular problem here is that many regard sales people from the compressed air industry in the same way as commodity sales people, the Beko representative noted.

“Most staff selling compressed air products are qualified technical people who will provide solutions if only they could get access. Too many companies are unwilling to talk to ‘sales people’ about improvements

Another issue, she said, is that new technology is not being properly promoted:?“For example, water-injected, oil-free compressors “should be taking over their market segment but because of ‘cash-cow products’ they are not pushed.

“[It is a] similar story with catalytic converters being the only way to provide oil-free air, regardless of inlet conditions.”  

According to Chris Hall, sales director, Gardner Denver (CompAir), the economic climate has led many businesses to reflect carefully on their capital expenditure.

“Some of our customers have deferred their normal timescales for replacing equipment and, instead, have focused their efforts on improving the energy efficiency and performance of their existing compressor installation.

“The cost of ownership of a compressor during its lifetime is also now a key purchasing factor, with the unit’s parts and maintenance costs often considered as critical as the initial purchase price.”

While variable-speed drives are high on the list of priorities for UK companies, Hall notes that there is still a lot of fixed-speed compressors in use.
A compressor, he said, with a greater range of volume output is generally more cost-efficient to operate, as the machine will automatically adjust, or ‘turndown’ its flow rate to the most economic level.

“With a compressor that has a limited flow range, the machine will typically go in to off-load mode when it reaches its minimum flow,” said Hall.

“This is both inefficient and costly as the compressor continues to run, thereby consuming energy, with no output.
“In addition, the motor will be forced to stop and restart, putting additional wear on components and increasing overall cost of ownership through increased maintenance and energy consumption.”

For his part, Andy Jones, general manager at Mattei points to the widespread use of pressure settings that are higher than needed - noting that just a 1-bar reduction in pressure will reduce energy consumption by about 7%.

Another issue, he said, is the use of a higher air quality than is actually needed, which again adds cost to compressed air production.

There is often a legitimate reason to use ‘oil-free’ compressors to produce ‘oil-free’ compressed air, said Jones. But, he said, before investing in costly equipment, purchasers should thoroughly assess the actual purity of air required and specify it using ISO 8573-1:2010 to see if ‘oil-free’ air is needed.

Even where ‘oil-free’ air is found to be necessary, companies still need to assess if class 1 rather than class zero would be sufficient.

“The more stringent the purity, the higher the cost is to achieve it - so it’s important to consider whether or not the entire system requires the highest purity or just a particular area, which could then be served by point-of-use air treatment or a dedicated smaller compressor,” explained Jones.

Suppliers commonly see compressed air systems with sections added or removed without any thought for checking whether it is still running efficiently.

Mattei, said Jones, recently changed a 75kW compressor for a 45kW compressor at one company without reducing production capacity and saving the customer over £10,000 per annum.

Compressed air systems, meanwhile, are estimated to lose an average of around 30% of the air they produce through leaks in the system.
“In some cases, we have found leakage levels as high as 67%,” said Jones.

“We often see compressed air systems with around 150 to 300 leaks, and a company using 50m3 of compressed air per minute could potentially save around £63,000 if they were to have them repaired.

“Leaks are simple to identify and rectify, and it’s cost-effective; the average cost of a Mattei leak detection survey is less than 10% of the overall leakage costs. Typically an 800% return on investment is delivered, and customers will generally see a payback within three to six months.”

But even when presented with the facts and figures about the significant cost savings that can be achieved, there is often unwillingness among process companies to act on the data.

“We have offered solutions where the payback is just a few months, but many companies still don’t take the opportunity to improve their systems,” said Jones.

“Not enough managing, financial or engineering directors are really aware of the potential savings that can be achieved by improving the efficiency of a compressed air system - therefore perhaps not realising it is a golden opportunity for their business to reduce energy usage, carbon emissions and costs.”

As around 75% of the five-year cost of ownership - including the capital purchase price - comes from electrical consumption, much more consideration should be given to the running cost of a compressor, rather than just the initial purchase price.

“It is important to remember that while investing in a new compressor can significantly reduce energy use, any savings could be completely negated if the new machine is added to an inefficient air treatment and pipework distribution system with numerous leaks,” concluded Jones.

“Even the most energy-efficient compressor will not make a system like this energy-efficient.”