|Minimize Compressed Air Leaks|
|Written by USDOE Office of Industrial Technologies|
|Wednesday, 09 June 2010 11:28|
Minimize Compressed Air Leaks
Leaks are a significant source of wasted energy in a compressed air system, often wasting as much as 20%-30% of the compressor’s output. Compressed air leaks can also contribute to problems with system operations, including:
Although leaks can occur in any part of the system, the most common problem areas are couplings, hoses, tubes, fittings, pipe joints, quick disconnects, FRLs (filter, regulator, and lubricator), condensate traps, valves, flanges, packings, thread sealants, and point-of-use devices. Leakage rates are a function of the supply pressure in an uncontrolled system and increase with higher system pressures. Leakage rates identified in cubic feet per minute (cfm) are also proportional to the square of the orifice diameter. See table below.
a For well-rounded orifices, values should be multiplied by 0.97 and by 0.61 for sharp ones.
b Used with permission from Fundamentals of Compressed Air Systems Training offered by the Compressed Air Challenge®.
The best way to detect leaks is to use an ultrasonic acoustic detector, which can recognize high frequency hissing sounds associated with air leaks. These portable units are very easy to use. Costs and sensitivities vary, so test before you buy. A simpler method is to apply soapy water with a paintbrush to suspect areas. Although reliable, this method can be time consuming and messy.
A chemical plant undertook a leak-prevention program following a compressed air audit at their facility. Leaks, approximately equivalent to different orifice sizes, were found as follows: 100 leaks of 1/32” at 90 pounds per square inch gauge (psig), 50 leaks of 1/16” at 90 psig, and 10 leaks of 1/4” at 100 psig. Calculate the annual cost savings if these leaks were eliminated. Assume 7,000 annual operating hours, an aggregate electric rate of $0.05 kilowatt-hour (kWh), and compressed air generation requirement of approximately 18 kilowatts (kW)/100 cfm.
Cost savings = # of leaks x leakage rate (cfm) x kW/cfm x # of hours x $/kWh Using values of the leakage rates from the above table and assuming sharp-edged orifices:
Cost savings from 1/32” leaks = 100 x 1.46 x 0.61 x 0.18 x 7,000 x 0.05 = $5,611
Cost savings from 1/16” leaks = 50 x 5.72 x 0.61 x 0.18 x 7,000 x 0.05 = $10,991
Cost savings from 1/4” leaks = 10 x 100.9 x 0.61 x 0.18 x 7,000 x 0.05 = $38,776
Total cost savings from eliminating these leaks = $57,069
Note that the savings from the elimination of just 10 leaks of 1/4” account for almost 70% of the overall savings. As leaks are identified, it is important to prioritize them and fix the largest ones first.
FOR ADDITIONAL INFORMATION, PLEASE CONTACT:
EERE Information Center 1-877-EERE-INF (1-877-337-3463) www.eere.energy.gov
Industrial Technologies Program Energy Efficiency and Renewable Energy U.S. Department of Energy
Washington, DC 20585-0121 www.eere.energy.gov/industry