Industrial Utility Efficiency    

Air Compressors

By far the most important development in the world of screw type air compressors has been the introduction of variable speed control using electronic variable frequency drives (VFD’s). Systems that run with at least one air compressor at part load can almost always operate more efficiently if a well-controlled VFD is added to the system. But what if a system has two or more VFD units? This article discusses the challenges in controlling multiple VFD air compressors with some suggested solutions.
When some people think about compressed air, they imagine the big, loud, dirty, unreliable machine in the back corner of their facility. Many businesses around the world rely on compressed air, and an unreliable air compressor can mean stopping an entire facility, costing thousands of dollars in lost productivity and repair labor. Additionally, that loud machine in the back corner is also a major energy consumer. So much so that many industry professionals refer to it as the “fourth utility.”
Compressed Air Best Practices® Magazine spoke with Mark Shedd, Head of Oil-free Air, Aggreko Rental Solutions - There are two distinct compressed air systems in a refinery or petrochemical environment: plant air and instrument air systems. Instrument air systems are almost always 100% oil-free air compressors on both the permanent and temporary systems. The demand for compressed air purity, in instrument air systems, is so high that the permanent install back-up system is usually nitrogen.
Air-operated double diaphragm (AODD) pumps are common to many manufacturing facilities. As estimated by veteran compressed air auditor Hank van Ormer of Air Power USA, approximately 85 to 90 percent of plants in the United States have AODD pumps. They are used for all kinds of liquid transfer applications, like those found in chemical manufacturing, wastewater removal, and pumping viscous food products.
Compressed Air Best Practices® Magazine and the Compressed Air and Gas Institute have been cooperating on educating readers on the design, features, and benefits of centrifugal compressor systems. As part of this series, Compressed Air Best Practices® (CABP) Magazine recently caught up with Rick Stasyshan, Compressed Air and Gas Institute’s (CAGI) Technical Consultant, and Ian MacLeod of CAGI member company, Ingersoll Rand. During our discussion, we reviewed some of the things readers should consider when installing a centrifugal compressor system.
Centrifugal compressors are dynamic, and each has a characteristic curve of rising pressure as capacity decreases. Without any control system, the compressor would operate along this natural curve. A centrifugal compressor's flow and pressure are typically controlled by a combination of an inlet control device and an unloading valve (UV).
The introduction of rotary screw air compressors controlled by variable speed drives (VSDs) is one of the best energy efficiency innovations introduced to the industry in the past few years. This style of compressor control can significantly reduce the energy wasted by compressors running in the unloaded condition. But the type of VSD control offered by various manufacturers can differ, and some of these differences can affect the efficiency of the system. This article discusses some little known tweaks to VSD compressor control, including some using hidden features that can sometimes be implemented to enhance the savings gained by the installation of this type of compressors.
Compressed Air Best Practices® Magazine recently caught up with Rick Stasyshan, the Compressed Air and Gas Institute’s (CAGI) Technical Consultant, and John Kassin of Cameron to discuss variable inlet guide vanes (IGV). The following interview describes how centrifugal compressor efficiency can be improved thanks to recent developments in IGV technology.
As the 21st century progresses, the environment is becoming very unsettling for distribution in the industrial air compressor industry. The forces of change discussed in Part 1 of this two-part series created a situation very unfamiliar to distribution. The stability experienced by the industry from 1960 to 1990 was displaced by the volatility of the last 25 years. Consolidation of manufacturers and distributors, loss of channel power, evolution of hybrid channels to market, and intense pressure on profitability are just a few of the major forces distribution has had to deal with. Distribution’s tentative reaction to these forces has resulted in both distributors and manufacturers questioning the long-term viability and relevance of distribution in the industrial air compressor industry.
Compressed Air Best Practices® (CABP) Magazine recently spoke with Rick Stasyshan, Compressed Air and Gas Institute’s (CAGI) Technical Consultant, and Mr. Neil Breedlove of CAGI's Centrifugal Compressor Section and member company, Atlas Copco Compressors, about centrifugal air compressors. Specifically, the discussion outlined how various inlet conditions can impact the performance of centrifugal air compressors.
In general, this article focuses on the operating principles of centrifugal air compressors, discussing them in simple terms to provide an understanding of application limitations and opportunities. One primary goal is to define often-confusing terminology, such as “rise to surge,” stonewall and surge,” “mass flow,” and “dynamic compression.” This article is not intended to be an engineering discussion of the various types and designs of centrifugal and other air compressors, but rather, a guideline for deciphering operating curves and understanding general performance.