Air compressors tend to be one of the most overlooked pieces of equipment in industrial facilities. This may not sound too surprising — air can seem inconsequential and cheap to come by. It is, after all, air. However, air compressors are extremely inefficient (as in 10 percent efficient). Leaks make up a large portion of their load, and most of the energy they consume ends up as waste heat. Therefore, learning about air compressors and how to use them efficiently and effectively is crucial for saving energy and money.
Compressed air has been used in industrial settings for a long time and has applications in many processes. Air compressors are popular because they are a quick medium for energy transfer and are inherently safe in potential explosive environments.
Different types of air compressors exist, including reciprocating, scroll, screw and centrifugal. The most popular are lubricated screw compressors, though oil-free screw compressors are available if very clean compressed air is required. Each type uses a different mechanism to compress air and has its own advantages and disadvantages. For example, reciprocating compressors have many moving parts and require significant maintenance. Screw and centrifugal compressors have fewer moving parts and do not cost as much to maintain, but they have poorer performance at part-load, which is when the unit is not running at full capacity.
Because air compressors consume a large amount of energy yet are frequently ignored, they are a point of focus for Advanced Energy’s commercial and industrial team. Every facility is different, but our engineers have identified a number of common concerns during energy assessments and have developed recommendations to address them.
Install a master controller to optimize compressor use. Many plants have multiple air compressors; however, they are not always managed effectively and may be run independently and without supervision. In such a scenario, a facility could be producing more compressed air than is necessary, especially considering demand often fluctuates throughout the day.
To address this issue, a facility can install a master controller that helps decide when to operate certain compressors, helping increase efficiency. Master controllers dispatch air compressors intelligently based on existing load and avoid the need for constant manual operation. Typically, one compressor will be run in “full mode,” while others are in “trim mode.” This means that one is running at full power, but the others are not. (An air compressor’s power is measured in kilowatts [kW] and it produces compressed air in cubic feet per minute [CFM] to meet compressed air demand.)
Reduce air leaks. Air leaks are a major contributor to compressed air consumption and waste – in fact, they typically add up to about 30 percent of a facility’s compressed air demand. Leak management programs can go a long way toward identifying and addressing these leaks. They have been found to reduce leaks by 50 percent, helping save compressed air capacity, conserve energy and lower costs.
Most air leaks occur at quick connects, hoses, actuators and tubing on equipment, and once identified, they should be noted and cataloged. This record keeping helps facilities determine where and how often leak assessments are needed. Leaks that are noted should be tagged and repaired immediately. It is also important to recognize that not all leaks can be heard; loud machinery and background noise make it difficult to hear and locate leaks during plant operation. Therefore, many plants perform air leak checks only during scheduled downtime, which may occur just a few days per year. Large air leaks can then go undetected for long periods of time, wasting significant amounts of energy. An ultrasonic leak detector can help locate leaks even when machinery is operating.
Increase compressed air storage. When additional compressed air is needed to meet rising demand, a frequent remedy is to add more units or increase the pressure on existing units. However, this approach can have unintended, and unnecessary, consequences, such as excessive costs, and other solutions are available.
One of these solutions is to increase the amount of compressed air storage. Stored compressed air can quickly react to changes in a facility’s demand and help reduce short cycling of the air compressors. To get the most out of compressed air storage, make sure the storage tanks are located effectively (they should be close to points of use) and that you have the appropriate amount of storage (screw compressors, for example, should have 10 gallons of storage for every CFM).
Managing compressed air systems can greatly improve a facility’s energy use and reduce costs. Implementing proper controls, sticking to a leak management strategy and investing in storage tanks are three ways to start making a difference.