Plant Services - May 2008 - (Page 36) cfm Compressed air systems EFFICIENCY Trim with a VSD Energy consumption comparison 100 Shaft power % curve 6000 8000 10000 12000 flow rate (gal/min) Savings 30-35% Energy savings: VSD vs on/off control VSD vs modulation control Modulation control On/off control VSD control 0 0 50 Full load/off load ratio % 100 50 Figure 1. Compared to on/off or modulation controls, a variable-speed drive (VSD) compressor generally uses considerably less energy at partial loads, but at high load ratios the difference can be insignificant. to 100 psi or 125 psi or even 150 psi.” motor speed or by altering the airend,” On the design of screw impellers, Censays Heinonen. “Most compressors in ters says, “We’re continually working on the U.S. are optimized for 125 psi; it’s Energy cost equip- improving profiles. The geometry is pretty 110-115 psi elsewhere. And mostsavings through reduction complex, and also ment needs only 75-80 psi.” of differential pressure the machining.” Screw rotors traditionally were made There’s more at stake than efficiency. $2,500 in uniquely timed, matched sets. Mov“When manufacturers match the airend Example: 600 scfm, ing from milling and hobbing to grindto the horsepower, more options are re3.0 psi marginality,” quired$2,000 to avoid overkill and lesspressure loss, ing the finished profile has allowed $1,452 savings per year. tighter tolerances that increase efficiensays Bill Kennedy, rotary screw product 4.5 psi less dp $1,500 cy while allowing drop-in replacement manager, FS-Curtis (www.curtistoledo. of individual parts. “Improvements in com). “A marginal system raised from 100 $1,000 manufacturing have lead to tighter tolpsi to 125 psi or higher usually requires a 3.0 psi less dp erances and better volumetric efficienhigher-service-factor motor.” $500 cies,” says Heinonen. As they approach more closely the 1.5 psi commented on the Several experts less dp optimum size and RPM for each aptrend to smaller airends. North Ameriplication,$0 engineers are gaining incre50 100 150 200 250 300 can designs 500 550 600 650 mental improvements by improving 350 400 450 have typically been larger Flow Rate in scfm operated at lower rpm than and have rotor profiles and housing designs using European models, but that’s no longer computational fluid dynamics. the case. Smaller, higher-speed airends “A lot of work has been done using can hold tighter tolerance, making them computer simulation on the inlet valves, at least as efficient and durable as larger etc. to reduce pressure drops throughout models with lower initial cost. the machine,” says Fasano. “It’s ideal to Engineers have worked on packhave a first-stage compressor with a rotor age design, eliminating pressure drops wrap optimized for the interstage presthrough tubing, fittings, coolers, etc. A sure – 40 psi to 60 psi – then take that up 36 Annual Energy Cost Savings www.PLANTSERVICES.com May 2008 http://www.curtistoledo.com http://www.curtistoledo.com http://www.timken.com/conditionmonitoring http://www.timken.com http://www.PLANTSERVICES.com
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.