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Best Practice Guide |
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Food and Beverage Growers and Processors |
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Case StudySara LeeLocation: Sacramento, California Project: Compressed air system assessment and optimization Website: http://www.saralee.com and http://www.compressedairchallenge.org/ Source: Adapted from a U.S. Department of Energy (DOE) case study
Sara Lee's Sacramento facility is a 300,000 sq. ft. industrial bakery built in 1929. With 450 full-time employees, it operates a high-speed bread and bun line, seven days a week. The onsite compressed air system supports the stacking, blowing, and cleaning operations required by bread-making machines. Compressed Air Assessment and Upgrades Sara Lee contracted Draw Professional Services, a Department of Energy (DOE) Allied Partner, to conduct a systems-level assessment of the compressed air system that included an AIRMaster+ analysis (AIRMaster+ is a free, Windows=based software tool used to analyze industrial compressed air systems; available from DOE). Sara Lee's compressed air system consisted of one 100-hp and two 150-hp rotary screw compressors. When the pressure/flow controller failed, air demand patterns began fluctuating severely, forcing workers to operate all three compressors simultaneously just so they could meet production targets. At the same time, the compressor controls were out of adjustment, causing them to respond incorrectly to different air pressures. More than one compressor would activate, for example, when only one unit was actually needed. On top of this, air leaks accounted for 15 to 20 percent of the entire system capacity. Even worse, the assessment discovered multiple uncontrolled open-blowing applications. Those two problems exacerbated the pressure fluctuations and wasted even more compressed air. Draw configured the system so that the 100-hp fixed-speed compressor is now the base unit. A 100-hp variable speed drive unit serves as the trim compressor; it comes online as needed, and can vary output to match actual demand. Sara Lee was able to retire one of the old 150-hp compressors, and stored the other one as a backup. The newly optimized system performs much better, and supplies the plant with a consistent air supply at a stable pressure. Sara Lee's compressed air project is yielding impressive energy savings while making production more reliable. Measurements indicate energy savings of 471,000 kWh and cost savings of $40,000 per year. These figures are consistent with AIRMaster+ estimates. Because two compressors can now be off-line, maintenance costs have also declined, saving another $10,000 per year, for a total annual savings of $50,000. An $11,000 rebate from the Sacramento Municipal Utility District reduced the total project costs to $27,000, for a simple payback of 6.5 months. |