Industrial Utility Efficiency    

Compressor Controls

Quite often the typical variability in compressed air flow demand does not proportionately translate into power reductions at the air compressors. This can be a result of numerous problems with the compressed air supply system. It is important to understand the supply-side’s ability to respond to the demand-side of the compressed air system. If the air compressors, on the supply-side, are not able to translate flow reductions into energy savings, implementation of demand reduction projects should be re-evaluated.  
A recently completed energy efficiency improvement programme at the Britvic Beckton bottling plant has resulted in substantial energy savings and a positive impact on the company’s carbon emissions allocation.
A large multi-service public utility provider was faced with an ongoing problem. The utility, which services 93,000 retail and wholesale customers, employed five oil-free compressors at one power generation facility, but, if they needed to take down Unit 2 at the facility, it almost always pulled Unit 1 down with it, overloading the system’s capacity and causing service interruptions.  
This building products factory spent an estimated $240,000 annually on energy to operate the compressed air system at their Midwestern facility. This figure will increase as electric rates rise from their current average of 7.8 cents per kWh. The set of projects recommended, by the system assessment, reduced these energy costs by an estimated $104,336 or 43% of current use. Project costs totalled $73,000, representing a simple payback period of 8 months.
“I don’t understand. I attended the Compressed Air Challenge® Fundamentals and Advanced courses. I read every article and book I could find on improving the efficiency of compressed air systems. I developed great ideas about how to reduce my compressed air consumption. We fixed leaks, “right-sized” filters to reduce pressure drop, changed piping, moved some processes to shifts that used less compressed air, bought low consumption nozzles and educated our entire workforce. We did all of this work and I still have six out of six compressors running. Reducing my air consumption does not appear to have reduced my air production!”  
Air Demand Increase of 43% Results in Only a 5% Energy Cost Increase Compressed air is an expensive medium; yet, many compressed air systems are wastefully managed with minimal system transparency. Capturing essential system performance data and monitoring critical air quality data is not only eye opening, it enables future investments in compressed air systems to be fact-based and traceable.
The Trinity Mirror Group print works on Oldham is one of the UK’s largest newspaper printers. The nine presses in the facility produce around 1million papers every day, including the Independent, the Daily Mirror and a range of local, regional and sports titles. Printing on this scale does not come cheap in energy terms, however. The plant’s annual electricity bill is in the order of £1.5millon. With energy prices on the rise, and a strong desire to improve environmental performance and reduce its carbon footprint, the plant’s management has recently embarked on a project to cut energy use substantially.
It has been my experience that more than 50% of industrial air users don’t control their air compressor resources effectively. As a result, a tremendous amount of energy is wasted. When my firm does audits of plant energy consumption, it’s not unusual for us to encounter installations with large numbers of independently-controlled compressors that are all running at different pressure settings and different loads.
Treating compressed air as a true utility and outsourcing the entire process is a growing trend in the industry. If a plant does not generate their own power, provide their own water or deliver their own natural gas, then why not treat compressed air requirements in the same manner? This article will use a recent project as a case study to show the benefits one factory received by making the decision to outsource compressed air like a utility.
The U.S. Department of Energy estimates that air compressors use as much as 10% of all electricity generated in the United States. Further, the DOE calculates that as much as 50% of this energy is wasted. Compressed air leaks alone account for 25-30% of compressed air use.
While control storage was originally an integral component of a reciprocating air compressor installation, this article will only briefly explore that application. The content of this article will focus instead on rotary screw installations since the rotary screw air compressor has essentially replaced the reciprocating as the compressor of choice in industrial applications. It should also be noted that in compressed air systems where reciprocating and rotary screw air compressors are operating together, control storage should always be utilized.