Compressed Air Best Practices - November 2008 - (Page 12) | 11–12/08 Focus Industry STEEL & METALS | COMPRESSED AIR AUDIT OF THE MONTH Steel Processing The five pre-selected points were: p Location #1 — 10" line before the Roll Shop in Hot Strip Mill. Located between the Bar Mill and the Roll Mill. Measured air flow to Hot Strip Mill was 4,000 scfm Location #2 — 8" line near Column 31. Before air take off to Slab Yard. Measured air flow to Slab Yard was 1,200 scfm Location #3 — 10" line outside Lube Shop to Green Coat — 2" ball valve now in place. Measured air flow to Green Coil, Pickler and Cold Mill was 4,000 scfm Location #4 — 10" line from Coil Distribution building. Measured air flow to Annealing was 4,750. Note #3 flow is included in #4 Location #5 — 10" line from Compressor Room to Electric Galvanizing and Shipping. Measured air flow to Electric Galvanizing and Shipping was 5,300 scfm Total measured flow was 15,250 scfm p p p p p Annual plant electric and diesel fuel costs for air production were $1,686,863 per year. This does not include engine oil changes, rental or fuel cost. If the total system was serviced by only electric compressors, along with today’s equipment, the total cost would be $1,515,068 per year. Neither cost estimate includes the cost of operating the dryers, which totals $115,070 per year. It is expected that the current air dryers (blower purge and refrigerated) will be able to efficiently purify the reduced air loads after the audit. Table 1. Key Air System Characteristics — Current System* ELECTRIC MEASURE NORMAL FLOW CONDITIONS AVERAGE SYSTEM FLOW LOW FLOW CONDITION NORMAL FLOW CONDITION DIESEL (1 UNIT ON) ADDITIONAL DE-SCALE OPERATION EXTRA FLOW TOTAL 18,500 scfm (17,165 scfm) 95 psig 3,541 kW 7,008 hrs 4.85 cfm/kW $67.82/scfm year $1,116,670/year 15,500 scfm 95 psig 3,277 kW 1,752 hrs 4.73 cfm/kW $16.66/scfm year $258,359/year 18,500 scfm (17,165 scfm) 95 psig 18 gph 7,008 hrs/yr 126,144 gallons/yr $160.63/scfm year $214,445/year 1,905 scfm 95 psig 90.7 kW 18 gph 2,808 hrs 4.58 scfm/kW $27.58/scfm year $11,461/year (electric) $85,925/yr (diesel) $48,269/year $1,383,490 (electric) $300,373 (diesel) $1,686,863 total $1,515,068 AVERAGE COMPRESSOR DISCHARGE PRESSURE INPUT ELECTRIC POWER OPERATING HOURS OF AIR SYSTEM SPECIFIC POWER ENERGY COST FOR AIR — PER UNIT OF FLOW ANNUAL ENERGY COST FOR COMPRESSED AIR ANNUAL ELECTRIC COST WITH DIESEL CONVERSION TO COMPARABLE ELECTRIC UNITS $1,116,670/year $258,359/year $91,770/year * Based on a blended electric rate of $0.045 per kWh, 8,760 hours/year. Diesel fuel cost — $1.70/gallon. 12 www.airbestpractices.com http://www.airbestpractices.com
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