The ‘Star Spot’ award for June 2022 went to a consultant who spotted completely avoidable waste of compressed air in a factory. Compressed-air systems are both costly to run and prone to hidden losses, so it pays to do what our reader did, namely a walk-round check with his client while the factory was shut for the weekend. They suspected a serious problem because outside working hours there were enough leaks to keep one compressor running almost continuously. As they walked around they found the odd poor joint but when they went outside there was quite a significant hissing from one of the factory’s dust collectors.In this installation the life of the filter bags was prolonged by timed short pulses of compressed air inside the individual bag in order to blow or knock the dust off of the outside of the filter. Unfortunately one of the air lines had become detached upstream of the solenoid valve and was continuously discharging compressed air. With this fixed, the load on the duty air compressor dropped dramatically.
Remember also that all the time the air line was disconnected, the filter bag wasn’t ever being back-flushed: another perfect example of how energy waste often goes hand in hand with loss of service.
Incidentally, it would have been possible to improvise a measurement of the compressed-air savings quite simply. During a period of no demand, you can shut off the compressors and time how long it takes the pressure of the stored air to drop by one bar. Knowing the volume of receivers on the system allows you to compute the rate of air loss. When the pressure drops by one bar, you have lost the receivers’ volume of free air. So for example if you have a 690-litre receiver and it drops from 7 to 6 bar in 30 minutes, the air loss rate is 690/30 litres per minute or the equivalent of over 12,000 cubic metres per year on a continuously-running system. As an efficient compressor takes about 0.1 kWh per m3 of air compressed, that would be wasting 1,200 kWh per year. Repeating the test after attending to leaks would show you how much you had saved; repeating it periodically allows you to monitor for deterioration.