Cut the Cost of Compressed Air

Chemical makers, just like other manufacturers, are suffering from today’s economic conditions. To help trim costs and keep operations profitable, many have reduced production levels, cut hours, imposed wage and hiring freezes and, in worst cases, resorted to layoffs and even plant closings.

However, despite the push for savings, plant technical staff often overlook a number of steps that can trim costs without sacrificing productivity or manpower. Indeed, in many instances, these moves actually can increase productivity and efficiency.

One area that demands attention is energy use. While energy costs have escalated in recent years, technological advances have helped facilities increase productivity and do more with less. Many energy- and money-saving tips are really quite easy and straightforward — maintaining infrastructure, coupled with sound decision-making and sensible operating practices, quickly can add up and save most facilities revenue that otherwise would be squandered through simple laziness and improper equipment use.

Compressed Air Efficiency Measurement

Figure 1. Free compressed-air-system health checks can pinpoint improvement opportunities.

Water, electricity and fuels such as natural gas are critical components for plant operation and their basic costs are out of your control. However, you can control the cost of the often forgotten fourth utility, compressed air, which is just as critical to production.

Some estimates indicate that poorly designed and maintained compressed air systems in the U.S. waste up to $3.2 billion in energy every year. A careful review of your compressed air system likely will reveal multiple opportunities to reduce energy draw and, thus, dramatically lower operating costs.

As one of the Top 100 global sustainable companies, Atlas Copco knows firsthand how to maximize production and lower energy usage during manufacturing. The company shares this knowledge in various ways. Our service team provides free compressed-air-system health checks that can help a plant’s technical staff recognize areas where improvements are possible (Figure 1). We also offer a free 156-p. “Compressed Air Best Practices Guide.” (For a copy e-mail paul.humphreys@us.atlascopco.com. Put “Manual — Chemical Processing” in the subject line and include your mailing address in the body of the e-mail.)

Opportunities for Savings
For plants that operate 24/7, several money-saving options can improve efficiency and provide a quick return on investment. For example, variable speed drive (VSD) air compressors continually and automatically adjust compressed air production to match actual plant requirements (Figure 2); analysis shows that VSDs suit more than 90% of compressor services. Compared to a fixed speed drive, a VSD sized for the same end applications requires about 35% less power, which translates into a comparable cut in energy costs.

The cost of energy is significant for compressors. Consider a plant running a 200-hp air compressor 24 hours a day. Five years ago, electricity might have cost 3¢/kWh. Today, electricity costs 8¢/kWh or more. So, the annual tab for electricity to operate that compressor has risen from around $41,000 (at 3¢/kWh) to about $110,000 (at 8¢/kWh). Switching to a VSD compressor could save almost $39,000 annually.

Better Option

Figure 2. A variable speed drive can replace a fixed drive and save energy for most compressor applications.

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.