Plant Services - July 2008 - (Page 37)

efficiency Compressors • Compressors can use the so-called “new impeller design” with good efficiency well below the first critical speed. Most conventional units go carefully past the first critical speed and try to operate below the second or between the second and third. • Capacity control is achieved with a microprocessor-controlled variable-speed drive. When the demand for air falls and the pressure starts to rise, the drive speed reduces proportionally down to about 25% (or the calculated actual turndown range). If the pressure continues to rise and crosses the adjustable maximum pressure point (usually 10 psid), the unit then goes to no load. The speed falls to idle and the energy draw falls to 2.5% (compared to 25% to 35% or more for conventional units). When the pressure falls to the preset “load in pressure,” the compressor immediately goes to full flow. Every time the unit goes through this cycle, it calculates the actual surge point and adjusts the control accordingly to optimize the turndown capability. Unlimited starts and stops each hour allows significant operating efficiencies. Obtaining the full benefits of this capacity-control system, like every other, requires a minimum volume of effective storage. Depending on the size of the dead band, average flow and piping configuration, this probably will range between 3 gal. and 5 gal. of effective storage per cfm of flow. Effective storage includes all air receivers, equipment and piping inside the dead band range (unload pressure/load pressure). Unlike a positive displacement compressor, there’s no extra energy required to produce the dead band. Running the centrifugal compressor at a higher pressure means lower flow at about the same horsepower. Obviously, if we’re unloading, we don’t need the extra flow. As presented, this new technology promises a two-stage, oil-free compressor with overall full-load efficiencies equal to most similarly sized three-stage centrifugals and is somewhat better than many two-stage, oilfree rotary screw compressors. The controls allow an effective load/no-load (two-step) operation with a low idle input power of 2.5%. The electronic microprocessor continues to recalculate the actual turndown capability and use it appropriately. There’s a lot going on in the centrifugal air compressor world. Product and performance improvements are constant. Take a good look at your existing units. A full review or compressed air audit might identify real opportunities for improvement. Hank van Ormer is owner of AirPower USA, Pickerington, Ohio. Contact him at HankvanOrmer@aol.com and (740) 862-4112. SLUDGE. SLIME. ALGAE. BACTERIA. IT’S A JUNGLE IN THERE. With Goodway’s new, portable CTV-1500 TowerVac®, cooling tower debris is easily removed without shutting down the unit. An optional filter allows wastewater to be filtered and recycled back into the tower. That means no system downtime and a significant operational cost savings. So lose the hassle, time and environmental mess associated with cleaning your cooling tower — clean it the good way. To find out more, call Goodway today at 800-333-7467, or visit us online at www.goodway.com. ® Innovative Maintenance Solutions www.goodway.com Keep an eye on all your equipment with LEM split core current transducers Integrated transducers combine the most advanced sensing technologies with signal conditioning electronics in very compact cases. Easy to install high quality current transducers are ideal for designing cost-effective, accurate and reliable solutions for condition monitoring, process control and automation. · DC and AC (True) RMS current measurement · Measuring ranges from 2 to 2000A · Self-powered, loop-powered or +24-48V power supply · Isolated standard outputs, e.g. 4-20mA, 0-5/10VDC, switch or relay More resources at www.PlantServices.com Capacity controls – “Compressor capacity controls” Speed-regulated drives – “Drive down the cost of compressed air” Proper line sizes – “The secret is in the pipe” Compressor controls – “The rise and fall of modulation” For more, search www.PlantServices.com using the keywords centrifugal, control and piping. July 2008 www.lem.com Energy & Automation www.PLANTSERVICES.com 37 http://www.goodway.com http://www.goodway.com http://www.goodway.com http://www.lem.com http://www.PlantServices.com http://www.lem.com http://www.PlantServices.com http://www.PLANTSERVICES.com

Table of Contents Feed for the Digital Edition of Plant Services - July 2008

Plant Services - July 2008 Contents From the Editor Letters The PS Files Up and Running Crisis Corner Asset Manager Technology Toolbox Cover Story Compressors Power Transmission Flooring Web Hunter In the Trenches Product Picks Classifieds Energy Expert

Plant Services - July 2008

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