Compressed Air Best Practices - October 2008 - (Page 16) | 10/08 Focus Industry AUTOMOTIVE TRANSIT | COMPRESSED AIR AUDIT OF THE MONTH Transit Bus Manufacturing capacity of the existing compressors. With the addition of a single 100 hp VSD compressor, coordination of compressor controls and some load reduction, primarily through elimination of desiccant air dryer purge, pressure reduction and reduction of blowing events, the study showed the three systems could be combined into one well-performing system with enough capacity to handle the full plant peak load with no pressure issues. Because the paint line requires higher pressure than the main plant, the supply to the line is taken from the high-pressure side of an electronically controlled intermediate controller that regulates the main plant pressure at precisely 105 psi. The base 150 hp compressors have been placed on the downstream side of this intermediate controller, reducing their discharge pressure and lowering power consumption. These units have been set to operate within a single pressure band that brackets the set point of the intermediate controller using a sequencing system internal to the compressor controls. The new system is performing well with the 200 hp of trim capacity easily and efficiently handling the average plant load. The 150 hp base units are now required only when media blasting occurs, which is about 15% of the time. With the new reduced load and the more efficient compressor operation, the system energy efficiency increased with the combined system consuming an average of 124 kW (including air dryers) while producing an average flow of 490 cfm. This calculates to a more respectable 25 kW per 100 cfm system specific power. New System To achieve the proposed savings, New Flyer consolidated their existing air system by combining all of the existing compressors into one single system. The existing 200-hp compressor was retired to standby duty with the intention to run it only on failure of one of the existing units. Once the poorly performing desiccant air dryer was eliminated and the three systems were combined, only 100 hp of extra compressor capacity was required to maintain plant pressure during peaks. This new 100 hp VSD compressor was selected to match an existing 100 hp fixed speed unit and together the two units provide 200 hp of efficient trim capacity pumping into a new 3,000-gallon storage receiver. T o Paint Booths 400 USG Main 1 200 HP Standby 115 psi 750 cfm Refrig Dryer 1000 cfm T o Paint Booths 400 USG Grit Blasting 150 HP 115 psi 650 cfm Refrig Dryer 650 cfm Mist Eliminator Filter 1600 cfm Flow Control Set to 105 psi Main 2 150 HP 115 psi 625 cfm Refrig Dryer 650 cfm 16 www.airbestpractices.com http://www.airbestpractices.com
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