Blowing off inefficient compressor systems

Waste not, want not: new design technologies are helping manufacturers eliminate excessive air usage in compressed air systems, with some remarkable results. Katherine Crichton reports.

Waste not, want not: new design technologies are helping manufacturers eliminate excessive air usage in compressed air systems, with some remarkable results. Katherine Crichton reports.

DESPITE the fact approximately 10% of power consumption in Australia is used for compressing air, eliminating excess air usage has only recently become a top priority for governments and industry.

Driven by the threat of climate change, diminishing natural resources and increases in fuel and energy prices, air compressor systems manufacturers are constantly looking for ways to increase energy efficiency and reduce costs.

While variable speed drive (VSD) technology is not a new concept, continuous development of power electronics has meant that VSD technology is becoming more accepted in the market place.

According to Nick Iser, product manager — oil free air division with Atlas Copco, using speed control to regulate the capacity of a compressor enables more precise delivery of the required amount of air for a system. “This can lead to average savings of 20%,” Iser told Manufacturers Monthly.

“Traditional systems need to unload or blow off air as there is only a limited choice of how much air they can deliver, while VSD air technology can match the exact system requirements and therefore minimise wastage in power consumption.

“Additional compression stages can increase the theoretical efficiency of a compressor, however we need to look beyond the screw element and look at the efficiency of the package as a whole and take into account the additional pressure drops and frictional losses.

“The overall efficiency of a compressor package is commonly published as the electrical power required to operate the compressor package divided by the FAD flowrate.

“This is the equivalent of a car’s fuel consumption figure (L/100km) and provides a comparison between compressors.

“In addition to the increased capital cost of adding compression stages, increased maintenance costs such as overhauls need to be factored in to the Life Cycle Costs (LCC).”

Iser advises that VSD technology can come at an initial capital price premium compared to traditional fixed speed systems, but says ROI can be within 12 months depending on the application.

“The capital cost of the system is far outweighed by the benefits.

“Customers only pay for what they use and VSD technology can minimise wastage, air leaks, pressure drops and blow offs, with around 80% of the LCC of compressors calculated by energy consumption.

“Other flow on effects include low starting currents, reduced mechanical shocks during starting and lower average speeds of the bearings.

“It is important to ensure the technology is implemented to improve reliability and efficiency and not just for the sake of putting in the technology.”

Iser says VSD technology can also be used with significant benefits in other areas of compressor operation.

“While VSD technology has been traditionally used to vary the speed of the compressor drive motor, recent developments have led us to also include variable speed cooling air fans in some of our compressor models.

Iser believes as the price of energy increases VSD technology will be more widely used.

“Certainly anywhere the price of energy is very high, such in Europe and the Pacific Islands where they generate their own power, the ratio of VSD compressors to non-VSD compressors is relatively high.

Getting air

One of the biggest inefficiencies in any air compression system is air leakage, which David Green, GM – sales & marketing at CAPS Australia says was once totally underestimated by industry.

“A 5mm hole in a pipe, with a system running at 7 bar and 100psi results in significant air loss, Green explained.

“Anything up to 30% of air leakage comes from the pipe system. This could equate to a compressor running fully loaded just to accommodate pipe leaks.”

Green says regular air audits are vital for any company wanting to reduce their energy consumption.

“Air audits are not so much devices used to save energy, but rather a means to measure inefficiencies in pre-existing systems.

“What a full air audit can achieve is a thorough assessment of system efficiency. Even with a brand new system you should allow for 5% air consumption through the pipe system and this figure increases as the compressor gets older,” he said.

Green says there is a distinct trend towards incorporating air audits in any companies’ regular maintenance routine, irrespective of size.

“The industry has gone from having basic air audits only performed in large companies 5-10 years ago, to an increasing number of businesses investing in complete air system audits.”

Green largely attributes this trend to customer demand — not only motivated by a need to save money, but to also reduce their impact on the environment.

“The type of companies performing air audits is also changing.

“Traditionally only carried out by independent bodies, advances in air testing equipment is not only allowing a more accurate assessment of the compressor system but this now can be done by the manufacturer of the equipment,” Green told Manufacturers Monthly.

“Users can now get a comprehensive audit of air quality produced in the system showing what it should be producing. You can get a full energy consumption profile, simulate what the energy consumption will be with an alternative compressed air system and also get an extremely good view of actual air quality.”

The ability to be able to simulate air compressor efficiency in particular applications is a valuable tool in the quest towards eliminating excessive air usage as Green explains.

“We recently evaluated an existing compressed air system which was running three shifts, 24 hours a day. After examining the results we decided to implement a two stage compressor with a purchase price in the region of $80,000 to replace the existing single stage compressor, which was still working quite well, and the customer is looking at savings of around $30,000 a year with an immediate payback in three years.

“There was nothing wrong with the initial system but there were many benefits of changing it to a two stage compressed air system,” Green said.

“For plants that have an old inefficient system the savings could be significantly larger,” he added.

“A complete air audit can give companies a visual representation of what’s happening with their compressed air system.

Green says to get the best results, an air audit should occur over one to two weeks rather than just one day, “so compressor users can get a full picture of their system performance and have all the information they need to gain maximum energy efficiency in their compressor”.

Atlas Copco 1800 023 469.

CAPS Australia 1800 800 878.

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