PdM applications to improve compressed air efficiency

Compressed air systems comprise some of the most necessary and the most expensive equipment in an industrial plant. It just makes sense to monitor their condition with predictive-maintenance (PdM) technology to ensure operation is optimized. While no system is 100% perfect (http://www.plantservices.com/articles/2013/04-perfect-compressed-air-system/), getting as close to perfect as possible can be a big money saver.

Detecting air leaks is a given. That hiss is the sound of profits escaping and floating off. Lubrication and pump issues also are prime candidates for monitoring in a PdM program. But there might be a few applications of PdM technology that you hadn’t considered for making your compressed-air system more efficient.

“On the electrical side, infrared cameras can detect electrical issues, such as loose or corroded connections revealed by temperature differences seen by a thermal camera,” says Joe LiPetri, communications manager, Flir Commercial Systems (www.flir.com). “Technicians often perform quick hotspot scans of systems such as primary switchboards, distribution boards, control panels, fuse boxes, electrical cabinets, and motor control systems.”

Thermal cameras are most effective in company cultures that embrace preventive practices engineered to increase uptime, as opposed to reactive programs designed to respond only when something goes wrong, explains LiPetri. “Evaluating equipment on a periodic basis provides more insight by establishing a baseline reference of equipment operating under normal conditions, which enables technicians to see right away when systems are not running properly,” he says. “PdM professionals who use thermal cameras often use them in conjunction with test equipment to monitor power quality and electrical factors, such as current loads. Combining temperature data from a thermal camera with electrical readings from a clamp meter, for example, can provide more insightful troubleshooting and reporting so that repairs are made correctly and quickly. The combination of thermal imaging and test and measurement enables PdM professionals to detect emerging issues and keep systems operational, according to their schedules. This organized approach to PdM can significantly reduce and prevent premature and unexpected equipment failures of air compressor systems, thus maintaining production levels, reducing unplanned failures, extending equipment life, and ensuring worker safety.”

All of the standard PdM technologies apply to the motor side, says Scott Dow, senior instructor, Mobius Institute (www.mobiusinstitute.com). “Infrared can also be useful in finding hotspots on the high-pressure piping side and other areas,” he explains. In those cases, you won’t necessarily know what you’re looking for until you find it.”

Analysis of performance indicators, such as pressure drops in an area of the system, helps predict problems and reveals where production can be optimized to increase efficiency and save energy, advises Brian Blum, CTS optimization marketing/Department of Energy - Airmaster+, Atlas Copco Compressors (www.atlascopco.us). “If knowledge is power, knowing exactly how the compressed air system is performing at any time gives facility managers the power to identify ways to improve the system quickly and easily,” he says. “A 24/7 real-time monitoring system provides the information needed to accurately assess system performance and determine a course of action to improve system usage and efficiency while minimizing downtime.”

Applying condition monitoring to compressed air systems ensures on-demand availability and eliminates the hidden costs that occur when these systems are not correctly maintained, explains Trent Phillips, condition monitoring manager, Ludeca (www.ludeca.com). “Several condition monitoring technologies can be utilized to ensure the availability and manage the costs associated with compressed air systems,” he says.

Regularly checking condensate drains and pressure drop across filters are also simple examples of predictive maintenance, suggests Waheed Chaudhry, engineering manager, Kaeser Compressors (us.kaeser.com). “If you notice that the condensate drains need to be drained more frequently, this could be indicative of problems with an aftercooler, or that the compressor is not coming up to a high enough operating temperature,” he advises. “Likewise, pressure drop across filters can indicate that the filter cartridge needs to be changed. If you are changing filters more often than normal, you should consider looking for the cause of the extra contaminates — perhaps piping is corroded or a receiver tank is rusted. Pressure drop often creates production issues, such as poorly operating equipment and high scrap rates.”

Most compressor air systems are driven by ac induction motors, notes Daniel J. Hogan, vibration/oil analyst, Azima DLI (www.azimadli.com). “Motor current analysis (MCA) can be an effective, powerful, and complementary tool to monitor the motor end of a compressor system when used with vibration analysis,” he explains. “Motor current analysis can be used to confirm and accurately qualify the severity of cracked rotor bar condition with ease. Together, MCA and vibration analysis can help justify the removal and overhaul before a failure, avoiding the possible complete destruction of the motor end.”

Ron Marshall, member of the project development committee, Compressed Air Challenge (www.compressedairchallenge.org), reminds us of the importance of ensuring compressor controls are fully functional. “Mr. Fixit resides in every plant,” he explains. “He can easily screw up the operation of the simplest compressed air system control by pushing the buttons with his curious fingers or tweaking the controls with his handy-dandy pocket screwdriver. Monitoring compressor power and flow over time and calculating the compressor ‘gas mileage’ or specific power can be an excellent indicator of problems due to misadjustment or control failure.”

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