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How to reduce the cost of compressed air

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With electricity costs at an all time high, there are a number of areas manufacturers can focus on to reduce their spiralling compressed air generating costs. Alan Johnson reports.

Advanced ultrasonic flow meters can be connected to the outside of a pipe, offering zero pressure drops, no process interruption, high accuracy, resistance to dust and humidity, and reduced installation time. 

A data log graph from data using a flow meter. 

Using an ultrasonic detector to identify air leaks. 

While many manufacturers get fixated with the capital cost of an air compressor, if they looked a little deeper they would see that the largest cost related to producing compressed air is in energy usage. 

And in a manufacturing plant, this typically represents the highest energy usage. It is an area which businesses should address as a priority to achieve substantial savings. 

According to Rod Peirce, Southern Cross Compressors' General Manager, the approach to lower cost compressed air should include sound technical advice; selection of the right unit for the application; the appropriate control system, air quality and set pressure; adequate ventilation and a clean environment; appropriate servicing and a preventative maintenance program.  

"A correctly sized and designed downstream reticulation system free from leaks is also vitally important," Peirce said. 

Air audits 

Experts estimate that up to 50% of energy used in producing compressed air is wasted, so an air audit of a manufacturing plant makes good business sense. 

The experts also estimate that around 10% of the world's energy is used to generate compressed air, and with energy costs rising at an alarming rate, even the smallest improvement in efficiency can result in significant power cost savings. 

According to Peirce, the initial purchase price of an air compressor typically represents between 5% and 10% of the lifetime cost of owning and running a compressed air system, when calculated over a ten year period. 

While 20 years ago air compressors were big, heavy and cumbersome with a long life expectancy there was little consideration to energy efficiency. Compressors today are cheaper, lighter, energy efficient and have components designed to provide value for money over a shorter period of operational life - usually ten years. 

Peirce says the initial equipment selection is therefore a key element and a full audit prior to capital investment in this plant will take in a broad study of the compressed air requirements rather than just the compressor.  

"It looks into areas such as the air demand on each shift, load profile, the operating environment, air quality and the pressure required. Plus it looks at the company's installation and servicing requirements; the air service lines or reticulation system; life expectancy; reliability; future plans and safety issues; and more. 

"With many apparently cheap compressors on the market, key features to look for are a direct drive (no gears) air end; high efficiency (MEPS2 compliant) known brand motors and high quality electrics; a laminar flow intake controller; large 'single pass' coolers; 316SS control lines; and solid piping or stainless braided hoses," he said. 

A simple start, says Peirce, is to take an inventory of the current equipment; and to understand the production requirements and how compressed air impacts on this.  

"Of particular importance is a comprehensive check of the air reticulation lines, because if you can hear a leak it's already costing you around $360 - $400 per year. 

"Other areas include the development of a leak management program using ultrasonic leak detection, eliminating any improper uses of air through bad work practices, shutting down the compressor when air is not required and setting the air line pressure to meet the production line requirements. All these areas will save money. For example, a reduction in pressure of just 50kPa can represent savings in the order of 4% per year," he said. 

"Compressed air is expensive and does not end with the initial purchase and commissioning of the compressor," said Peirce.  

"For example, a 37kW motor operating for 4,000 hours with a power consumption of $0.12c/kWhr at 95% efficiency operating at 100% loading is calculated to cost almost $19,000 per annum to run and that is serious money for any company," he said. 

Hidden efficiency opportunities 

While compressed air is one of the most expensive energy sources used in industry, Peirce says due to inefficiencies in most compressed air systems, 20-30% of the generated power is lost before it even reaches its end use.  

"Another 10% is lost to artificial demand caused by higher than required operating pressures and a further 10% is lost due to end use equipment using air when production is turned off. 

"These facts are surprising to most people but they highlight how inefficient a compressed air system can be, particularly with rising electricity costs, as the more inefficient the system the more power is consumed," explained Peirce. 

"This builds a strong case for every compressed air user to define a flow profile to identify peak demands, low points and variability which occurs throughout different shifts.  

"For example, if a plant is closed overnight with no production and the compressors are not shut down, a flow meter may show that there is still some air being leaked representing inefficiencies in the system that can be addressed. Equally it will identify if the right compressor is being used for the application," he said. 

"In the past flow meters have been intrusive, requiring the cutting of pipes to install into the air system. Today we can take advantage of the latest technology in advanced ultrasonic flow meters connecting to the outside of a pipe only, resulting in benefits such as: zero pressure drops, no process interruption, high accuracy, resistance to dust and humidity, and reduced installation time. 

"Ultrasonic flow meter technology used to build an accurate flow profile creates opportunities to reduce a company's energy costs significantly. By creating a baseline profile it can be compared to future profiles to see how air demand changes over time, enabling the company to make informed decisions on equipment and system design," Peirce said. 

Detecting air leaks 

Air leaks can have a drastic effect on compressed air system performance. Each air leak leads to wasted output, ultimately increasing compressor demand, energy usage and energy costs. 

They can also have a significant affect on production by causing system pressure drop, impacting plant and equipment efficiencies, shortening the life of equipment through more frequent cycling, increases in running time leading to additional maintenance, and added unnecessary compressor demand. 

"Air leaks can come from any part of the compressed air system including sources such as couplings, hoses, tubes and fittings, pressure regulators, open condensate drains and shut-off valves, pipe joints, disconnects and thread sealants." 

With most air leaks inaudible to the human ear, Peirce recommends companies use ultrasonic detectors to identify air leaks.  

"An air leak as small as 1.6 mm in diameter is not only inaudible to the human ear it can cost around $450 per year in wasted energy," he said. 

Cost savings 

A comprehensive compressed air audit recently undertaken at Godfrey Hirst's Victorian carpet manufacturing plants identified cost savings of up to 50% on its compressed air energy costs plus many environmental benefits. 

Peirce said the brief was to identify opportunities for improvements in efficiency, reduce operating costs and at the same time further improve the company's environmental footprint and sustainability. 

"The review included a complete compressed air audit and analysis of both the supply and demand side at sites within Victoria.  

"On the supply side this involved reviewing the size of the compressors, their installation, filters, dryers and receivers, supply pipe dimensions, pressure settings and the method of control. Critical ventilation and maintenance programs were also studied to allow recommendations to be made," he said. 

"The demand side audit reviewed piping to point of use, identifying air leaks, incorrect pressure settings, pressure drops and inappropriate uses." 

Using ultrasonic flow meters, technicians were able to determine the exact air flow and usage profile on each line for each shift on all sites studied.  

With dramatically varying loads, profiles were then established to identify more suitable, cost effective equipment to ultimately achieve maximum efficiency. 

Peirce explained that the air leaks on the demand side were identified with every leak tagged, photographed and detailed in a report providing information on leak volumes, corresponding kW's wasted and annualised energy costs. 

"As a result of the audit, air leaks alone were identified as costing the company thousands of dollars per annum in wasted power and with energy costs escalating, this would only increase.  

Overall, the air supply side audit identified additional savings through the use of more efficient modern compressors, common issue opportunities, oversized compressors in use, inefficient or non-existing sequencing between multiple compressors, flow imbalance between main air lines, incorrect pipe sizing causing pressure drop, incorrect pressure settings and undersized air receivers.

Southern Cross Compressors 1300 372 056 southerncrossaircompressors.com.au 

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