Compressed Air Best Practices - March 2009 - (Page 14)

® | 03/09 | ENERGY MANAGEMENT COMPRESSED AIR AUDIT OF THE MONTH A Steel Cord Producer Manages Pressure Examining the Pressure Draw-Down Increase Pipe Size to Reduce Pressure Drop Distribution piping should be sized so that the air velocity within the pipe does not exceed 20 ft/sec. Higher velocities may cause condensate to be blown across a condensate drop leg and cause larger pressure excursions to occur. The following equation explains the sizing process: 1.) a= 144 x Q x Pa V x 60 x (Pd + Pa) The pressure profile chart has a red circle around the first big pressure draw-down. The chart below is a close-up look at this event. It was caused by the HCL pump coming on from 10:00 A.M. to 10:50 A.M. Here we can see how the compressors reacted to this event. Flow readings on the HP flow meter went from an average of 150 scfm to 300 scfm, an increase of 150. Online were compressors #1 GA55VSD, #2 ZT45, #4 ZT50VSD and the rental GA55. The rental at 85 amps was always fully loaded while #2 ZT45 at 35 amps was unloaded during the entire seven days. That leaves the two VSD’s to handle any increase in flow above what the GA55 can supply. The red line is the #1 GA55VSD, and you can see how it responded immediately and went full rpm. The problem is the green line, which is the #4 ZT50 VSD. It did not offer its full output and therefore you can see the pressure throughout the entire plant was in draw-down. This means the demand flow exceeded the supply flow. When the pump shuts down, the pressure returns to its average values. Looking back at the demand-side piping, we see that the tank farm and wastewater treatment are off the 3-inch line. Yet the entire plant experiences the draw-down of pressure due to the inability of the supply side to react to the new load. Where: a = Cross-sectional area of the pipe bore, in2 Q = Flow rate, ft3/min free air Pa = Prevailing atmospheric absolute pressure, psia Pd = Compressor discharge gauge pressure (or line pressure), psig V = Design pipe velocity, ft/sec (we will use 20) 2.) a = π x d2 4 or d= ax4 Π Where: a = Cross-sectional area of pipe bore, in2 d = Pipe bore diameter, in Here is the equation for sizing a pipe for the 450 scfm of air and keeping the velocity at 20 ft per second: a= 144 x 450 cfm x 14.5 = 7.492 sq. inches 20 x 60 x (90 + 14.5) 7.492x4 Π d= Answer is: d = 3.08 inches 14 www.airbestpractices.com http://www.airbestpractices.com

Table of Contents Feed for the Digital Edition of Compressed Air Best Practices - March 2009

Compressed Air Best Practices - March 2009 Contents From the Editor Utility-Air News Compressed Air Audit of the Month Air Standards Assessment Improves Electroplater Production and Saves Energy Demand-Side System Optimization Seven Sustainability Projects for Industrial Energy Savings Personal Productivity Resources for Energy Engineers Wall Street Watch Advertiser Index Classifieds

Compressed Air Best Practices - March 2009

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