Putting the pressure on compressed air costs.

Do you want to reduce the operating cost of your compressed air utility by 25 to 40% and improve the air quality to a clean, dry, constant pressure state for all operating conditions? If so, consider a thorough audit of the entire compressed air system. The compressed air utility is usually the least carefully designed and managed of all mill utilities. It represents a great opportunity to reduce operating cost, which improves the bottom line. Maintaining an efficient compressed air system is vital, since the only readily available solution to system problems is to increase the pressure and power--which increases operating costs and lowers system efficiency.

COMPRESSED AIR IS NOT FREE

Few mills have any idea of the cost of compressed air. In fact, many operating personnel think that compressed air is free. Also, mills typically do not know how much air is compressed, how much is used appropriately, and how much is wasted through artificial demand, drainage, blow off, open blowing, leaks, or poor applications. For example, if a new process is proposed that will use 550-scfm, what will be the utility cost of the compressed air and how can it be cost justified? Most mills do not know. Also, compressed air costs vary widely in every mill.

Recently, two identical plants (built by the same contractor from the same drawings making the same products) were audited. The cost of air and the solution varied by more than 100%--which is a fairly typical situation. We see variations in compressed air cost from US$ 0.51 to US$ 2.03 per 100-scfm per hour with an energy cost of US$ 0.05-kWh. Another problem is that contamination is common in most systems, which shortens the life of components, creates off quality and downtime, and increases operating costs.

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In most cases, a systemwide analysis is needed to design an efficient supply. When systems are poorly designed and operated, the cause is typically inadequate understanding of demand. Most mills design supply with no idea of compressed air demand, believing that the system is supply-driven or can be controlled by supply. The exact opposite is true. One cannot design an efficient supply without a thorough analysis of the dynamics of demand--including coincidental events and peak usage.

A retrofit, guided by an audit, can produce a contamination-free compressed air system that operates at a constant pressure for all conditions, at reduced cost. Frequently, operating savings will return the retrofit's investment within two years. Every piece of air-consuming equipment in the plant will function more reliably, consistently, and repeatably--reducing off quality and downtime.

A compressed air audit consists of a thorough analysis of the supply side of the system to determine power consumed, volume compressed, drainage wasted, blow off, and pressure fluctuations. System efficiency is calculated and expressed as standard cubic feet per brake horsepower (scf/bhp) for the existing system. The demand side is also analyzed for waste, leaks, and good and bad applications. The audit should also include specific and detailed corrective recommendations.

Typically, between 40 and 60% of the improvement opportunities will be on the demand side. Drawings are provided for existing and proposed system arrangement (supply and demand) as well as any details needed for demand side application solutions. All electronic data recorded (pressure and compressor motor amperage) are provided with the report, as well as spreadsheets for financials, volume, power, and both existing and proposed artificial demand. Return on investment is also calculated.

Nearly all existing compressed air systems can be improved, even if they were audited a few years ago, because of new technology and system dynamics. Almost all systems have cost and performance improvement opportunities.

ABOUT THE AUTHOR:

Robert B. Laine II is president of Compressed Air Auditing, a division of Southern Corporation of South Carolina, Augusta, Georgia. He has been providing audits of compressed air systems for more than 10 years and is independent of any compressed air equipment manufacturer. Laine has completed more than 300 audits worldwide, including assignments in pulp and paper and many other industries. Prior to forming his compressed air consulting group, he owned and managed a manufacturer's agency for 30 years, selling to the chemical process industries. Contact him by phone at [phone], fax [phone], email at [e-mail], or on the Web at www.compressedairauditing.com.

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