Compressed air: Find the leaks, lower the pressure, and measure the results
Companies often face the challenge of identifying best practices for compressed air energy conservation by assessing the value others have realized while putting best practices into action. Without fail, every month brings an assortment of technical epiphanies, attempting to inspire the compressed air consumer with an audit expert’s secrets to success.
As an organization, Ingersoll Rand has audited thousands of systems worldwide. We routinely work with multinational companies to develop and execute strategies designed to deliver energy savings while simultaneously improving operational quality, reliability, and productivity. Leveraging this experience and associated results, we have identified what appears to be the “best” compressed air best practice of all.
For the purpose of ranking the quality or significance of any product or service, it is common to use a good, better, best segmentation. With this as a guide, some easy-to-execute energy conservation measures that may be considered good practices warrant consideration. By redefining these common practices as “good practices,” what is arguably the “best” best practice can be articulated without the redundant abuse of the word “best.”
Find the leaks
The first “good practice” is an obvious one: reduce the quantity of compressed air associated with leaks. This is an energy conservation measure that is usually executed by an organization without having to enlist the services of a specialized service provider. In theory, this should be easy because fixing a leak does not require specialized skills or capital expenditure.
Ultrasonic leak detection equipment has been readily available for years, and many organizations have purchased the tools required to easily locate compressed air leaks of all sizes during normal production periods. This technology allows an operator to hone in on the specific acoustic characteristics of a compressed air leak and filter out all surrounding production noise. This has made finding leaks easy, but unfortunately finding a leak does not impact the energy required to support a compressed air system.
No savings will be realized until the volume of air required to support leaks is reduced and a measureable reduction in compressor supply power achieved.
The leak-hunting activity is usually allocated to a member of the maintenance staff. This task is usually treated as an event driven by a corporate energy leader as part of a cost reduction goal. Even though an ultrasonic leak detector is reasonably easy to use, there is still a learning curve that can only be traversed through experience. Consequently, the time allotted to locating leaks by a technician using the tool for the first time or annually delivers marginal results.
Without a target or measureable goal, any number of identified leaks can be considered sufficient. The most significant issue associated with achieving savings can be attributed to core competency and responsibility. Maintenance teams are responsible for production equipment and subsystems required to support operations.
Because production and process goals are defined, measured, and monitored, delivering operation goals is the priority and repairing identified leaks falls to the bottom of the priority list. Without a measurable validation process, the majority of identified leaks typically remain unrepaired.
As a global organization, Ingersoll Rand has developed standard work process and tools to support a formal leak assessment program. When executing our leak assessments, it is common to find a significant volume of leaks that internal resources never identified, in addition to other leaks with old tags still in place.
In addition to identifying leaks, it is important to quantify and prioritize all leaks based on volume. A prioritized list of leaks can be used to develop leak repair objectives. A “better practice” will include a third-party validation process to measure targeted leaks and confirm they are repaired.
Lower the pressure
The second most frequently addressed “good practice” is lowering compressed air system pressure. For positive displacement compressors, like rotary screw and reciprocating compressors, reducing pressure at the discharge of the compressor will reduce the input power. It is important to note that the actual reduction in compressor power can vary depending on design and current operating pressure.
The “better practice” would measure compressor power before and after reducing pressure so the reward can be more accurately quantified before impacting a variable that influences operations. Compressor load conditions relative to time would be required to estimate savings.
For centrifugal compressors, engineering data corrected to site conditions and ambient temperatures is essential to estimate any potential savings. Depending on ambient conditions and internal components used in a given compressor, reducing pressure may have no impact on power.
Reducing system pressure can also impact compressed air demand. A common misconception estimates potential savings as a function of peak demand and system pressure. The actual influence on demand is a function of the change in pressure at the point where the gas is expanded. A better estimate will require detailed monitoring and analysis of a given system across all load conditions. Although energy savings can be realized easily by simply reducing compressor and system pressure settings, it is typically executed as an event. Sustaining results can be challenging.
For any production issue associated with compressed air, pressure is the most frequently assumed problem. Most facilities will prioritize measured production results over assumed compressor energy savings. As a result, restoring pressure settings to previous or higher settings is the typical response.
Measure the results
The “best practice” for compressed air systems requires a transition from executing random immeasurable events to a formal program with performance metrics and a team of individuals accountable for delivering monthly performance goals. When compressed air system performance goals are owned at the appropriate level within an organization, any negative variance is corrected. By focusing on delivering and sustaining reported results, compressed air system efficiency would be practiced regularly. With the appropriate level of visibility and accountability, an increase in leaks would be quantifiable, resulting in specific expectations with measurable results executed as a maintenance practice, not an isolated task.
Mark Krisa is director of Ingersoll Rand’s Global Service Solutions.