Managing a compressed air system is just one of many responsibilities for most industrial facility maintenance teams. Along with the boilers, chillers, cooling towers, wastewater treatment system, the compressed air system is another item that is essential to operations, requiring significant capital and maintenance investments, and commitment of resources to ensure trouble-free operation.
On top of simply keeping the compressed air system running reliably, there is increasing pressure to reduce and manage demand while making the system more efficient. The compressed air demand and efficiency discussions nearly always include the topic of leaks.
Identification and remediation of compressed air system leaks should be an ongoing focus in any production facility that uses compressed air. In the August 2017 edition of Plant Engineering, Bob Vavra states that 50 percent of compressed air generated is wasted. Of this wasted 50 percent, 33 percent is attributed directly to leaks, with another 8 percent wasted due to elevating the system pressure to compensate for leaks.
Leaks and inappropriate uses of compressed air have real and significant impacts. If an industrial user has 200 HP online (approximately 1,000 acfm capacity), the leaks and inappropriate uses of compressed air consume a significant quantity of electrical power, needlessly add to the cost of electrical power for the plant and contribute to carbon emissions.
|Leaks and Artificial Demand||kWh/year||$/year||US (short) tons CO2/year|
Impact of leaks and inappropriate uses of compressed air for an industrial user with system specific power of 20kW/100 cfm, paying $0.0771/kW-hr operating 8,000 hours/year. Tons of CO2/year based on coal-fired utility.
Leaks and inappropriate uses of compressed air are discussed jointly in this article because the leak identification and remediation process (leak audit) nearly always results in the identification of inappropriate uses of compressed air, yielding even greater opportunities to realize cost and energy consumption reductions.
The leak audit process is not complicated, but the sheer size of a production facility can make the task seem daunting. By segmenting a facility so that each part is included in a leak identification/remediation maintenance work order regularly, the audit process does not become overly burdensome.
Leak detection and remediation is also not a one-time or every five-year kind of event. In a well-maintained compressed air system, leak detection and remediation are continuing efforts. One approach to managing leaks is to segment the plant into 10-12 relatively equal areas, based on the distribution of production equipment using pneumatic power. Assign one segment per month for a leak audit, and audit the entire plant every year.
It is recommended that the individual performing the leak audit utilize an ultrasonic leak detector. The audible frequency range of hearing for the human ear is 20 Hz to 17kHz. Ultrasonic sound begins at 20kHz. The suggested setting of an ultrasonic leak detector being used for compressed gas leaks is 40 kHz., so the frequency range of most leaks is higher than what can be heard by the human ear. Many users find that most leaks are small, and only located by using an ultrasonic leak detector.
The table below correlates system pressure, observed leak sound power level (dB) (at 15” from the source), and estimated leak volume.
|Measured dB @ 15” from source||System Pressure|
|100 psig||75 psig|
|10 dB||0.5 cfm||0.3 cfm|
|20 dB||0.8 cfm||0.9 cfm|
|30 dB||1.4 cfm||1.1 cfm|
|40 dB||1.7 cfm||1.4 cfm|
|50 dB||3.0 cfm||2.8 cfm|
|60 dB||3.6 cfm||3.0 cfm|
|70 dB||5.2 cfm||4.9 cfm|
|80 dB||7.7 cfm||6.8 cfm|
|90 dB||8.4 cfm||7.7 cfm|
|100 dB||10.6 cfm||10.0 cfm|
Leak table adapted from UE Systems “Guesstimator Chart”.
A best practice is to document each leak when it is identified. Many ultrasonic leak detectors include cameras so that the leak can be photographed, associated with its intensity (dB) while allowing the user to include a description such as the location in the plant or a specific piece of production equipment. Using this technology, downloading the leak audit information into a useable report is very easy.
Along with documenting the leak information, attaching a two-part tag to the leak makes locating the leak for repair easy for the maintenance team. Using a two-part tag allows one part to be attached to a work order for the purposes of tracking and confirming repair status.
Associating leak intensity and the estimated power cost of the leak, allows the maintenance team to determine if a leak is worth fixing. For example, the packing gland and seat in a valve are found to be leaking, but the leak cannot be repaired without replacing the valve. The cost of the valve, plus the labor associated with the repair, could cause the repair to be considered financially unwise.
Very often, particularly with equipment that has pneumatically operated moving parts, leaks are found where compression fittings and ferrules compress tubing. The repeated motion at the fitting, along with chemical action from the carried over lubricant, causes the tubing to fail. Often a pattern of failure is found (time, location, component) that allows for predictive repair – eliminating the potential for leak as part of a routine maintenance procedure.
An added benefit of a thorough leak audit is that the detailed inspection of the compressed air system will typically uncover other issues with the compressed air system. Often, point of use issues such as leaking or failed filter-lubricator-regulators (FRL’s) and hose reels are identified. Hose barbs, secured with worm gear clamps, will often cause hose to wear from the inside out, creating significant leaks at the joint.
Other cost-effective improvements are unearthed during a leak audit. A common example is replacement of V-notch valves or timer valves with no-loss drains for condensate removal.
Often, improvised production solutions involve the use of compressed air to assist with product conveying, address a sticking issue, or provide cooling. These improvisations will register as large leaks on the ultrasonic leak detector. And, to a degree, they are leaks. These improvised solutions addressed a manufacturing issue that allowed production to continue, and in the short term, do no harm. However, properly resolving the production issue (use low pressure blower for cooling) or correctly applying compressed air (engineered nozzle or air knife) can provide significant energy savings as compared to an unregulated, open blow nozzle.
Looking at each leak or inappropriate use of compressed air individually can help with the ROI and economic justification of a repair or upgrade. Collectively, however, the demand created by leaks and inappropriate uses can have a significant impact on the total cost of ownership associated with the compressed air system.
What if, by reducing the leak load and addressing inappropriate uses of compressed air, a compressor could be taken off-line? Not only are the power savings significant, but now reductions in maintenance costs may be realized. Perhaps, by reducing demand, the plant can enjoy the benefit of back-up compressors without the capital investment associated with purchasing equipment. Possibly, an expected compressor purchase to meet increased demand can be deferred or avoided.
Without a doubt, reducing demand is a positive step for every production facility. An unintended and often unexpected result is that system pressure rises because demand is reduced as the supply side of the compressed air system is better able to meet demand. An increase in system pressure typically results in an increase in usage in unregulated users, off-setting some of the potential savings associated with leak remediation.
Maintaining plant pressure at the lowest acceptable pressure is the best way to manage demand. Controlled storage, a combination of appropriately sized dry storage and an intermediate (flow) controller provides the means to maintain plant pressure at its lowest acceptable point, maximize the benefits associated with leak remediation and optimize the operation of the compressed air system.
At the end of the day, a leak identification and remediation program provides many benefits to a user and should be implemented. To realize the full potential of a leak identification and remediation program, it should be part of an overall compressed air system management initiative. Combining compressor sequencing, controlled storage, and addressing inappropriate uses of compressed air will provide the optimum operating conditions while minimizing energy consumption.
Collectively, these recommendations may seem overwhelming. For a production facility maintenance or engineering manager, tasked with many other initiatives, the compressed air system may be relegated to a lower priority. It doesn’t have to be that way.
Contact a qualified industrial compressed air solutions provider. Allow an expert to develop the plan, recommend equipment and define the value proposition that will be needed to persuade leadership to make the investments needed. In fact, leak audits, and in some cases, repairs, are part of maintenance programs offered by many distributors.
Don’t delay – act now. Every day that passes represents unrealized and unrecoverable savings.
About the author:
Brian Mann ME, PE is the Air Systems Manager for Sullair. Since joining Sullair in 2019, Brian has collaborated with Sullair channel partners and customers to maximize compressed air system energy efficiency. He holds a Master of Engineering in mechanical engineering degree from the University of Louisville and is a CAGI Certified Compressed Air System Specialist.
Typical leak rate in industrial compressed air system:
A fresh approach to compressed air savings – Take a systematic approach to uncovering and fixing waste.
By Bob Vavra, Content Manager, Plant Engineering - August 10, 2017
US Electrical Power Cost:
Tons of CO2 per kWh:
Human hearing and compressed air leakage frequency references