Process plants use compressed air for several different purposes including conveying, process controls and actuators, process gas compressing, etc. Interestingly, compressed air is probably the most expensive utility stream in the industry on a per unit basis. In addition, it is the most misused, mismanaged and unaccounted (wasted) utility from an overall usage perspective. So, I compared the energy used in pumping systems versus compressed air and was very surprised at the results. The chemicals sector (NAICS 325) uses a slightly higher amount of energy in producing compressed air (160 TBtu/yr) than pumping systems (151 TBtu/yr). More importantly, though, the compressed air system energy efficiency is only 11%, which means 89% of the energy supplied is wasted. No wonder compressed air is the most expensive utility in a plant!
The main subsystems of any compressed air system are generation, distribution and end use. All three subsystems work hand-in-hand to provide compressed air. A shortcoming or failure of any one of these subsystems leads to no available compressed air. Because production heavily depends upon the reliability of the system, most of us have built-in redundancies to enhance compressed air system reliability. Unfortunately, this redundancy, if not properly designed and used, can lead to significant loss in the system’s energy efficiency. Many avenues can improve energy efficiency in a compressed air system. Here, I will touch upon one of my favorites — the appropriate use of controls and storage.