Cut the Cost of Compressed Air

Some easy-to-take steps can yield significant savings.

By Tim Last, Atlas Copco Compressors

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Most compressed air systems only run between 60 hours and 100 hours per week at anything near full capacity. For plants that don’t operate continuously, turning off compressors during evenings and weekends or according to shift patterns could trim energy bills by as much as 20%.

Also, consider decreasing air pressure. Each 2-psig reduction cuts energy consumption 1%. That saving initially may look inconsequential but certainly adds up over time. Using a compressor controller can greatly reduce the operational pressure band and much more effectively regulate air production.

If an existing air compressor is running at 65% or less of capacity, replacing it with a smaller more-efficient unit would provide an about-two-year payback time, on average, through lower utility payments. And those savings continue to compound in subsequent years.

When you factor leaks and inefficient flow monitoring into the equation, energy waste can become staggering. Depending upon pressure requirements and energy costs, a single ¼-in. leak in a compressed air line can cost from $2,500 to more than $8,000 per year. Air systems older than five years often lose up to 25% of their flow to leaks. Locating and fixing these leaks throughout a compressed air system will result in significant savings.

Strategically locating around the plant some compressed air storage tanks to reduce fluctuating demands and pressure drops within the system — and thus keep compressors from having to continually recharge — can provide additional energy savings.

Another way to achieve savings is to take advantage of the heat that air compression necessarily generates. In optimal conditions, 100% of the electrical power needed to run an Atlas Copco ZR 55-750 water-cooled, oil-free screw compressor can be recovered in the form of hot water for net zero energy consumption, backed by a TÜV Certification.

Pressure Profile
A great way to analyze a compressed air system is to develop a profile that shows pressure drops throughout the system. These pressure measurements provide valuable feedback for control adjustments, identify pressure drops across components, help determine system operating pressures and, as a result, point to direct and immediate cost savings.

Start by measuring and monitoring your compressed air system’s energy consumption, flow rates and operating air pressure (Figure 3). Small adjustments can reduce your operating pressure and energy costs while improving flow rates, output and productivity.

Your piping system design should optimize transfer of compressed air at the desired flow and pressure to the point of use. Because pressure drop in a pipe increases with the square of the increase in flow, opting for a larger pipe size can have a major impact. For instance, going to 3 in. diameter pipe from 2 in. can cut pressure drop by up to 50%. Air distribution piping should be large enough in diameter to minimize pressure drop. Shortening the distance air must travel can further reduce pressure drops by as much as 40%.

Check the pressures you are achieving and avoid spiking the pressure to compensate for leaks or drops in pressure due to piping problems or clogged filters. Fixing leaks also can help address a drop in pressure.

An ounce of prevention beats a pound of cure, so be proactive and look inside your piping system. A clean dry pipe means you have good quality air and shouldn’t have corrosion issues. Dust in the pipe comes from particles in your air and can quickly cause corrosion. If you see sludge, corrosion likely already has started and leaks will become larger and more abundant. Sludge also can harm end-use equipment and so requires immediate attention. If you don’t filter the air or if your filter is clogged, you'll have pressure drops and increase the risk of contaminating your product. Dried and filtered compressed air keeps piping clean and helps save money.

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