Compressed Air Best Practices - February 2008 - (Page 17)

Compressed Air Industry BULK HANDLING | 02/08 | to keep them from responding to every little hiccup in the system. Experience has shown that a change of 10 psi works. In addition, if a compressor needs to be started, some time will pass before it can load and begin to support pressure. Typically, this is around 20 seconds for oilflooded rotary screw compressors of this size. So, pressure will decay to the bottom of the control range, possibly by 10 psi, and then continue decaying for a while longer. When the compressor finally does load, the increased flow through shared air treatment equipment will result in an increased loss of pressure, aggravating the situation. Because there are a number of variables at work here, the total change in pressure will vary, but we can be certain of this: it will not be stable. Therefore, adding another compressor would not have stabilized pressure. The problem was not a lack of capacity, but a lack of control. Adding another compressor would not necessarily have provided a back-up compressor either. By definition, a back-up compressor is not intended to support production on a regular basis. However, because pressure could not be supported with six machines, the seventh would have been called into service immediately and would have run almost continuously and not have solved this problem either. In fact, not only would a seventh compressor have failed to solve the original problem, it would have resulted in higher costs due to less efficient energy use. Pressure in the system would have risen, increasing the cost of every cubic foot compressed, and we would have had to compress more cubic feet because artificial demand would also have increased. It is also likely that we would have realized an increase in unloaded run hours. Furthermore, another compressor would have meant additional maintenance costs. Because good data had been collected, Brian was able to make informed decisions about the best way to provide a back-up compressor and stabilize system pressure. “Lowering . pressure is essential to reducing both power costs and artificial demand, so we kept investigating.” Cost Was this project cost effective? Let’s examine the issue by comparing the cost of implementing and operating the system with the engineered storage solution to what the costs would have been if a new compressor had been installed. While power and maintenance costs decrease when compressors are turned off, both costs would have increased if a seventh compressor had been installed. The difference is outlined below. Clearly improving efficiency has advantages — in this case, an advantage of $143,000 in just two years and $1,145,000 over ten years. Decreases in power and maintenance costs make for the big impact. To sweeten this deal, compressor discharge pressure can be lowered, and it may be possible to turn off a third compressor for about 18 hours each day. These savings are not included. BP For more information please contact Brent Ehrlich, Air Services, tel: 336-751-4904, email: Brent@AirServicesSolutions.com www.airbestpractices.com 17 http://www.airbestpractices.com

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Compressed Air Best Practices - February 2008 Contents From the Editor Utility-Air News February Audit of the Month: Dense-Phase Transport System Wreaks Havoc on Compressed Air System Real World Best Practices: Material Conveying with Pneumatic and Vacuum Systems Industrial Vacuum Cleaners Use Compressed Air in Portland Cement Manufacturing Processes The Numatics Air Preparation Group The Ins and Outs of Vacuum Generators Dekker Vacuum Technologies Do Your Meetings Sabotage Your Profits? Resources for Energy Engineers Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - February 2008

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