Compressed Air Best Practices - June 2008 - (Page 30)

| 06–07/08 Focus Industry PHARMACEUTICALS | REAL WORLD BEST PRACTICES EVALUATION GUIDELINES FOR TWO-STAGE, LUBRICANT-FREE ROTARY SCREW AND MULTI-STAGE (3) CENTRIFUGAL AIR COMPRESSORS This clearly shows the net effect of many normal operating variables resulting in BHP ranges from 573 Bhp to 680 Bhp. Full-load capacity ranges from 2,422 scfm to 3,224 scfm and turn down from 29% to 47%. Comments to Chart 1 1. Specific Power — The referenced 4.5% better specific power for a three-stage centrifugal is for the 500 hp class, 2,400 cfm units. As the sizes increase, this number will get a little better in favor of the three-stage centrifugal. As the sizes decrease, the two will be about even at 300–350 hp class and the two-stage, oil-free rotary screw will be more efficient down to 100 hp. (The smaller centrifugals are mostly two-stage.) Effects of Hot and Cold Temperatures — The Centrifugal is a dynamic compressor, or a “mass flow” compressor and therefore its ability to deliver air and its input power is significantly altered by ambient conditions — particularly temperature. At colder temperatures, the unit delivers more air volume but also requires commensurate more horsepower. The positive displacement oil-free rotary screw will react as all positive displacement units to ambient temperatures changes — with slight increases or decreases in scfm flow and negligible changes in horsepower. The magnitude of these movements depends on several conditions but overall doesn’t result potential in extra air and extra horsepower of the centrifugal. III. Comparing the Basic Performance Characteristics of Oil-Free Rotary Screw and Three-Stage Centrifugal Compressors CHART 1: PROS AND CONS 2-STAGE ROTARY SCREW 3-STAGE CENTRIFUGAL Type Continuous Duty Specific Power (Approx. 2,500 cfm/500 hp) Effect of cold temperature scfm volume and bhp Effect of hot temperature scfm volume and bhp Modulate On-line/Off-line Variable Speed Drive Blow down idle Effective storage required for idle Interface with networking or master control system Multi-year warranty programs available Type Main Bearings Drive Gears Seals pressure Effects of Higher Pressure: Flow BHP (1⁄2% 1 psig) Effects of Lower Pressure: Flow BHP Efficiency General: New (depending on size and model) Part Load 100%/70%/60% Below 70–60% without blow down idle Below 70–60% with blow down and idle Loss due to normal wear over time Positive Displacement Yes 6.47 cfm/kW Slight increase Slight decrease No Yes Yes Yes (20%–25%) Yes Yes Yes Anti-friction Part of air end Part of air end Load/No Load Band Dynamic Yes 6.77 cfm/kW Significant increase 2. Significant decrease 30% (+) IGV No No Yes (25%–35%) Yes Yes Yes Oil Film/Journal Field replaceable Field replaceable/constant pressure Slight decrease Significantly higher BHP Stays about same Significant decrease Slight increase Significantly lower BHP Significant increase Stays about same About equal within Less efficient More efficient N/A Some About equal for this unit More efficient w/IGV Less efficient Somewhat less efficient with proper storage Some 30 www.airbestpractices.com http://www.airbestpractices.com

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

Compressed Air Best Practices - June 2008 Contents From the Editor Utility-Air News A Pharmaceutical Compressed Air System Audit Talking Dew Point Puerto Rico, Pharmaceuticals and Airequipo Inc. Oil-Free Rotary and Oil-Free Centrifugal Compressor Comparison SMC: Managing Energy and Dew Point in Pneumatic Systems Utility Grade Compressed Air Systems Training Calendar & Product Picks Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - June 2008

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