By Ron Marshall for the Compressed Air Challenge
A highway coach manufacturer had a large compressed air system feeding their growing plant. Over the years, the plant had expanded three times—and each time, new air compressors were installed. There wasn’t room to install all the compressors in one location so new compressor rooms were built with each expansion.
Plant maintenance staff knew that all their air compressors didn’t need to run (especially during evenings and weekends), but it was too difficult to coordinate the pressure settings between rooms. Filters and air dryers in each location all had different pressure differentials, which made pressure setting coordination very confusing. The operating mode they settled on was inlet modulation, which proved very easy to maintain over multiple locations, but can be very inefficient.
The plant personnel attended some compressed air training where they learned that they needed to improve their system efficiency. They tried to improve, but switching the compressors to more efficient load/unload mode was impossible because there wasn’t any system receiver capacity, other than that existing in system piping. The lack of storage caused the compressors to cycle rapidly between loaded and unloaded—placing the compressors in danger of failing.
An innovative employee came up with the idea to place electric mechanical timers on each air compressor to turn off selected compressors on a schedule. This worked for a while, reducing the hours the compressors would run, and system efficiency, but after a year or so, the plant started to have pressure problems. An auditor was called in to assess the situation. The auditor found that the timers had lost their coordination due to various maintenance power outages and nobody was maintaining the settings. The staff member who designed the system had left the company and had not left any documentation … so nobody knew how the system was to be set up correctly. As a result, the compressors were turning off at the wrong time of the day, sometimes during peak demands, with disastrous affect on system pressure!
The auditor informed the company that straight timer control of compressed air systems is a poor way to maintain adequate system pressure under all conditions. The company then installed a proper system master controller to coordinate all the compressor rooms from one location. The controller did have a timer schedule to select compressor priority, but the primary control strategy is pressure based, much more acceptable for a compressed air system. A large storage receiver was purchased to allow the compressor s to run in more efficient load/unload mode. Energy savings were measured at 68% and—most important of all—the pressure issues were eliminated.
Learn more about compressor control in our next Compressed Air Challenge seminar in your area. Visit www.compressedairchallenge.org for more information.
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