Industrial Utility Efficiency    

Compressor Controls

It was early summer, the air compressors were above the production floor on a mezzanine, and temperatures were heating up both outdoors and indoors. The compressed air system was comprised of three 500-horsepower centrifugal air compressors, and one 350-horsepower variable speed drive oil-free rotary screw air compressor.
Energy conservation measures (ECMs) associated with compressed air have received a significant amount of attention over the years, mostly due to a reasonably short financial return compared with other energy-consuming equipment. Over time, many of the recommended corrective actions to reduce compressed air energy consumption were simplified so much that they did not lead to positive results. One of the most common compressed air ECMs is reducing system pressure, and it leverages the best practice calculation —.5 percent power per psi — outlined in the Department of Energy’s Compressed Air Challenge. This article highlights more common issues associated with estimating energy conservation resulting from changing system pressure.
The facility generates compressed air with six (6) air compressors of various sizes located in three different compressor rooms. In recent years, the entire system converted to desiccant air dryers. Available equipment from other facilities has been utilized. The following is the layout of the facility showing the locations of the compressor rooms.
This plastic extrusion factory spent an estimated $180,711 annually on energy to operate the compressed air system at their Midwestern facility. Based on the air system operating 8,760 hours per year, the group of projects recommended below could reduce these energy costs by an estimated $116,520 or 67% of current use. Estimated costs for completing the recommended projects total $20,100. This figure represents a simple payback period of 2 months.
This facility operates one of the largest compressed air installations in industry, with 21 4000 hp process air and five 750 hp instrument air centrifugal compressors to support large-scale aerobic fermentation and related processes that require large volumes of oxygen.  
Energy management requires accurate and repeatable measurement of critical data, which is easily monitored and analyzed as required to stimulate required action. When a compressed air system assessment is implemented, the basic minimum measurement protocol to establish the baseline (pre‐measurement) and qualify and quantify the results (post‐measurement)  
This facility is part of a major corporation with dozens of manufacturing facilities where consumer good food products are processed and packaged for shipment to retail outlets. The factory was spending $210,000 annually on energy to operate their compressed air system. This system assessment detailed four (4) project areas where yearly energy savings totaling $100,855 could be found with an investment of $100,000.
A large multi-service public utility provider was faced with an ongoing problem. The utility, which services 93,000 retail and wholesale customers, employed five oil-free compressors at one power generation facility, but, if they needed to take down Unit 2 at the facility, it almost always pulled Unit 1 down with it, overloading the system’s capacity and causing service interruptions.  
This building products factory spent an estimated $240,000 annually on energy to operate the compressed air system at their Midwestern facility. This figure will increase as electric rates rise from their current average of 7.8 cents per kWh. The set of projects recommended, by the system assessment, reduced these energy costs by an estimated $104,336 or 43% of current use. Project costs totalled $73,000, representing a simple payback period of 8 months.
“I don’t understand. I attended the Compressed Air Challenge® Fundamentals and Advanced courses. I read every article and book I could find on improving the efficiency of compressed air systems. I developed great ideas about how to reduce my compressed air consumption. We fixed leaks, “right-sized” filters to reduce pressure drop, changed piping, moved some processes to shifts that used less compressed air, bought low consumption nozzles and educated our entire workforce. We did all of this work and I still have six out of six compressors running. Reducing my air consumption does not appear to have reduced my air production!”  
Air Demand Increase of 43% Results in Only a 5% Energy Cost Increase Compressed air is an expensive medium; yet, many compressed air systems are wastefully managed with minimal system transparency. Capturing essential system performance data and monitoring critical air quality data is not only eye opening, it enables future investments in compressed air systems to be fact-based and traceable.