Industrial Utility Efficiency    

Air Compressors

As an end user, have you ever heard the message to put in the biggest VFD air compressor, and the system will always be reliable and efficient.  Why do an audit?  Just add up the compressors on site and put one VFD for that size or larger.  Why have the complexity of multiple compressors, storage, sequencing, etc?  Even better, put in two of them, one for the whole system, and one for back-up.  If you could wave a wand, wouldn’t that be what every system should look like?  Perfect peace and efficiency, with 100% confidence of reliability.
Northwest Pump & Equipment was founded in 1959 - opening three branches on the same day in Portland, Seattle and Spokane. The business focus was to distribute petroleum equipment for the oil and gas market – primarily to service stations and oil jobbers. In-ground fuel tanks, hoists, lubrication equipment, lighting, farm pumps, air compressors and other gas pumping equipment were our primary product lines back when there were “Full-Service Gas Stations”. Over the years, this successful business model was expanded so the Company did business in California, Hawaii, Washington, Alaska, Arizona, Nevada, Idaho, and Montana.
This is a corn mill processing cornstarch, sugar, and other byproducts. Ambient air is contaminated with extremely high levels of dust due to the manufacturing processes and material handling. Average electric rates at the plant are $0.04 / kWh. The actual plant electric cost for compressed air production is $553,630 per year.
This glass bottle production plant had a complete compressed air audit in 2001 and 2002 at which time many successful projects reduced and stabilized the demand at 3,148 scfm at 95 psig for the high pressure system air and 9,300-9,500 scfm at 58 psig for the low pressure system. Successful application of an oversized 7,200-scfm rated cycling refrigerated dryer completely dried up the high-pressure air, allowing the removal of several non-performing desiccant dryers and savings in direct kW and purge air.
Not long ago most air compressors were controlled with mechanical pressures switches, relays and gauges. The setup of these units, especially when attempting to coordinate multiple compressors could be a frustrating and fruitless experience because often, no sooner than the controls were correctly adjusted, some sort of mechanical gremlin would throw something out of adjustment again.
Energy conservation measures (ECM) associated with compressed air have received a significant amount of attention over the years, mostly due to a reasonably short financial return compared with other energy consuming equipment. Over time many of the corrective actions put forward to reduce compressed air energy consumption have been simplified with the goal of encouraging action. Although this is done with the best of intentions, sometimes simplifications and generalizations do not necessarily lead to positive results. One of the most common energy conservation measures for compressed air that leverages best practice calculations involves reducing system pressure. It is the objective of this series of articles to highlight some of the more common issues associated with estimating energy conservation resulting from changing system pressure.
The rise in energy prices is an unwelcome reality in today’s manufacturing and business environment. And while the rate of price increases for natural gas, heating oil and electricity may vary from year to year, the upward trajectory is clear. Energy cost reduction strategies are vital to staying competitive. Compressed Air Best Practices® Magazine recently discussed heat recovery, from industrial compressed air systems, with the Compressed Air and Gas Institute’s (CAGI) Technical Director, Rick Stasyshan and with CAGI member – Werner Rauer of Kaeser Compressor. Their inputs should provide you with some insight in energy-saving technology.
When compressed air is generated, heat is inevitably produced as a by-product. Anyone looking to enhance efficiency can use this heat and increase the efficiency of compressors to about 95 percent as a result. To achieve this, there are easy-fit heat exchangers which can be fitted to existing air compressor stations. This investment often pays for itself within less than a year.  
Compressed Air Best Practices® Magazine recently discussed variable speed drive (VSD) air compressors with the Compressed Air and Gas Institute’s Technical Director, Rick Stasyshan and with CAGI member – Bob Baker of Atlas Copco. Their inputs should provide you with some insight to this energy-saving technology.
It is common to see energy assessment specialists treat centrifugal compressors like positive displacement compressors when attempting to reduce compressed air system energy consumption. Unfortunately, centrifugal compressors are normally much larger, and miscalculations can easily represent hundreds of thousands of dollars in overestimated energy savings. These errors are not malicious; they result from oversimplified best practices perpetuated by individuals with limited centrifugal compressor knowledge. This type of knowledge is not readily available and most energy assessment specialists do not have access to engineering teams responsible for the technical development and design of centrifugal compressors.
Grand Manufacturing, a small community owned Canadian agricultural products manufacturer, has upgraded their compressed air system as a result of a production expansion, yet increased the compressed air energy efficiency 61% by consolidating their system and implementing an innovative dual pressure control strategy.