Compressed Air Best Practices - March 2008 - (Page 22)

| 03/08 Focus Industry FOOD PROCESSING | MANAGING ROTARY SCREW AIR COMPRESSORS AT MIDWEST BAKERY kW CO2 O Recommendation #2: Rotary Screw Compressor Sequencer Control Inappropriate Uses of Compressed Air in Bakeries Midwest Bakery was very similar to most manufacturing plants with normal leakage and some large inappropriate uses of compressed air: 1. Bakeries tend to use compressed air as a broom and production lines are often set up with air knives blowing high-pressure air continuously. This plant used air knives as air curtains on freezer openings and to blow crumbs off of lines and product. Most of these inappropriate uses were eliminated by installing centrifugal blowers that do a better job and reduce load on the high-pressure system. 2. Much of the packaging equipment for the food industry uses vacuum generators to provide vacuum to suction cups to box product. This is an inappropriate use of compressed air for which we recommend using plant vacuum instead. 3. Another big inappropriate use of compressed air is cabinet coolers that blow compressed air continuously to provide low temperature air inside a hot electrical enclosure. We recommend cabinet fans wherever possible for this application. 4. Another common problem found in food plants is air quality, and as noted in our study the plant was pushing too much air through the main compressor room dryer. We recommended an energy saving reduced purge air dryer to save energy in regeneration. The air system at Midwest Bakery needs a compressor sequencer control to maximize energy efficiency. We have included the sequencer savings in step one and this step covers in detail the functions and importance of this control. The eight compressors are currently being controlled by their own local controls. Normal operation is to run three of the eight compressors. All eight compressors are started and stopped manually. Plant pressures range, from as low as 86 psig to as high as 110 psig using the existing control methods. If a compressor were to shut down (fault) plant operators need to manually start the spare compressor after low pressure has caused production problems. Typically the plant runs excessive horsepower resulting in wasted energy consumption. High-energy cost, excessive maintenance and premature compressor failure are all attributed to poor compressed air management. All compressors are being controlled by independent compressor control receiving pressure signals from four separate pressure points. Significant improvements could be made by installing a compressor sequencer to properly match the supply compressors more efficiently. The current rotation of compressors is being done manually on an as perceived basis. Automation should be installed to properly rotate lead/lag machines. A properly applied sequencer will fill this need. The compressed air supply and demand pressures are maintained as much as 10–15 psig higher than they could be. Energy savings will be realized by keeping the pressure from rising above the 100 psig compressor’s set point, and simultaneously using an efficient compressor sequencer to turn the correct compressors off or on based on the rate of rise or decay in the dry storage receiver. The existing compressor control arrangement lacks control integrity. There is no form of automatic sequencing/interfacing or monitoring being done at this time. All of the compressors are equipped with electro pneumatic controls. Although these controls were “state of the art” at the time they were manufactured, they are inefficient and difficult to regulate when compared to what today’s technology has to offer. The existing system arrangement demonstrates excessive horsepower on-line at all times in order to accommodate worse case or heaviest demand. We recommend a microprocessor-based sequencer. The sequencer will be connected to the five compressors located in the West Compressor Room. The sequencer will: p p p Start, load, unload and stop the compressors automatically Rotate the compressors automatically Maintain +/- 2 psig control band 22 www.airbestpractices.com http://www.airbestpractices.com

Table of Contents Feed for the Digital Edition of Compressed Air Best Practices - March 2008

Compressed Air Best Practices - March 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month: Saving Energy with Blowers in Canada Do You Provide World-Class Service? Managing Rotary Screw Air Compressors at Midwest Bakery The Difference Between Acfm and Scfm for Proper Vacuum Sizing Best Practices — Multi-Module Process Air Dryers The Vacuum Formation Process in Building Compressed Air Filter Elements Solberg Manufacturing Real World Best Practices: Measuring Pressure Dewpoint in a Compressed Air System Resources for Energy Engineers: Training Calendar & Product Picks Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - March 2008

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