Compressed Air Best Practices - May 2008 - (Page 26)

| 05/08 Compressed Air Industry AUTOMOTIVE ASSEMBLY | G U I D E L I N E S F O R S TA R T I N G A I R F O R CENTRIFUGAL COMPRESSORS I. Introduction: Centrifugal compressors, when shut off, often need a source of “instrument” quality compressed air volume (scfm) and pressure (psig) in order to restart. If the machine is off but the system is “pressured up” with other compressors on, this is not a problem and the “starting air” is available from the main air system supply. On such occasions when the total air system is off and at no pressure — such as during a power failure — a separate source of the proper volume and proper pressure must be available to start most centrifugal compressors. Sometimes this can come from other non-centrifugal compressors (positive displacement), which are part of the air supply, but other times only centrifugals are available in a powerhouse. What size compressors at what pressure is needed? What dictates this requirement in most commercial centrifugal air compressors? How is the best way to supply the air so it will be of proper quality and volume, “always available”, when needed? The economic cost of not being able to start the air system in a major plant (centrifugals are often the compressor of choice — 1,000 hp and up) can generate very significant dollars very quickly. Centrifugals are usually on larger air systems — i.e. plants with high fixed costs — unscheduled loss of production is to be avoided. II. Various methods and equipment used for centrifugal start up air — basis 1,000 hp compressor, nominal 5,000 scfm @ 100 psig Different sized air compressor packages from 10 hp to 75 hp or more. Packages installed with air receivers, dryers, filters, etc., to deliver instrument quality air. Different types of air compressors: lubricated, oil free, and non-lubricated have all been used somewhere. p Lubricated compressors: oil is in the compression chamber and must be removed. Oil-free – no oil in the compression chamber but there is oil in the drive train. The most common type would be a reciprocating single or double acting cross head design with “distance piece” to stop the oil from migrating up the piston rod into the compression area. Non-lubricated — there is no oil in the compression chamber or anywhere else in the unit. p p 26 www.airbestpractices.com http://www.airbestpractices.com

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Compressed Air Best Practices - May 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month Pneumatics Real World Best Practices Delta Industries: Doing What is Right for Customers Delta Industries: Six Truths You Need to Know about Really Putting the Customer First Power Supply Industries Resources for Energy Engineers Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - May 2008

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