Compressed Air Best Practices - June 2008 - (Page 31)

Focus Industry PHARMACEUTICALS | 06–07/08 | 3. Control System — Oil-free two-stage rotary screws are standard with a full load/no load two-step capacity control system. Modulation (which matches supply to demand by throttling the inlet) is not used due to (1) putting a higher percentage load in the second stage and (2) having to keep the total compression ratio at a maximum of about 11:1 or 12:1. Variable speed drive is also used, but with a much less favorable performance curve than on the lubricant cooled rotary screw. Often in a given frame size, extra turndown has to be offset with lower specific power by utilizing different impellers/diffusers with different aerodynamic characteristics. For example, following are the operating performances of a two-step, 500-hp class, 50-psig centrifugal: TWO-STAGE WITH 3 COMPRESSION ELEMENT OPTIONS Predictive Maintenance Compression Module: Two-Stage Lubricant-Free Rotary Screw Most two-stage oil-free rotary screw compressors are machined to a critical tapered .064 metal-to-metal clearance, which is then effectively reduced to 0 with a coating application. Over the course of operation the 0 clearance widens, through erosion, deteriorating performance and ultimately requiring a compressor “air end” rebuilds. Various manufactures have specific recommendations but generally replacement occurs with normal use at about 45–55,000 hours or five to seven years. This time frame is optimized with proper inlet filtration. (Continued on pg. 42) Option 1 Option 2 Option 3 Full Load — 3,319 scfm — 506 bhp — 397 kW — 8.36 scfm/kW Turndown — 2,589 scfm — 22% Full Load — 2,914 scfm — 448 bhp — 352 kW — 8.28 scfm/kW Turndown — 2,239 scfm — 24% Full Load — 2,900 scfm — 464 bhp — 362 kW — 8.01 scfm/kW Turndown — 1,829 scfm — 37% two-step controls are operated by “sensed” system maximum and minimum preset pressures. It is very power efficient when applied with adequate piping and storage to avoid “short cycling” . 4. Three-Stage Centrifugals — Use a modulation or turn down capacity control, which reacts instantly by opening and closing the inlet to the compressor to match supply to “sensed” demand. Newer units offer a very power efficient turndown with Inlet Guide vanes from 100% to 70% load or better. If the centrifugal has to run any significant amount of time at loads lower than this, there is a full idle position available (similar to rotary screw), which also requires proper effective piping and storage. Normally, the full idle power draw will be between 25–35% of full load power. In all cases, centrifugal and rotary screw units will interface well with an effective networking or master control system. Air Composition Monitor FOR COMPRESSED AIR APPLICATIONS ■ Monitors up to 4 Gas Conditions at the Same Time ■ Continuous, Real-Time Hydrocarbon Monitor ■ User-Programmable Alarm Relays for Control Functions ■ Available for VOCs, Dew Point, O2 and Toxic Gas in One Monitor ■ Meets NFPA-99 Requirements ■ Classified to UL 60601-1, IEC 60601-1 CSA 22.2, No. 601.1 ProAir 2200 ProAir 2200 is available for a wide range of toxic gases, including ETO, NH3, NO, NO2, Cl2 HCl, CO, etc. www.enmet.com info@enmet.com Phone: 734-761-1270 Fax: 734-761-3220 Ann Arbor, Michigan www.airbestpractices.com 31 http://www.enmet.com http://www.enmet.com http://www.airbestpractices.com

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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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