It is very common to see pipes — or pipe plugs with holes drilled in them — fashioned into a blowing device in industrial plants. These are quick to build, and easy to install, but come at a price on the energy bill, due to the high energy intensity of producing compressed air. These applications can often be retrofitted with specialty designed air knives that can save compressed air flow and reduce sound pollution. However, these conversions need to be done carefully to ensure there are actually savings gained.
The photograph shows a rotating cleaning basket where cutting parts are cleaned and dried after they are sharpened. This application previously used six homemade nozzles each with 3/32-in. drilled hole (they are still installed at the top of the picture). Each of these nozzles consumes 15 cfm at 100 psi line pressure, for a total of 90 cfm flow during operation.
The device was fitted with designed compressed air knives totaling 24-in. in length. The flow rating of these knives is 3.5 cfm per inch at 100 psi for a total of 84 cfm. Comparing the consumption of the two conditions we can see that there in not significant savings in compressed air consumption if the new nozzles operate at higher pressure.
However, the sharp and consistent blow pattern produced by the arranged air knives is far superior to that of the homemade nozzles. By experimenting, the operators of the cleaner were able to turn down the pressure fed to the new knives to about 60 psi for a total new consumption of 55 cfm. This cut the compressed air flow by about 40%. Further to this, the cleaning operation time was shortened by 50%, providing even more savings, and increasing operation throughput. The operators found that the cleaning operation with the new nozzles also cut the sound pollution in the sharpening shop, since the new setup produced 22 db less noise.
Overall the conversion was a success and saved significant peak demand and energy. Key to this conversion is the necessity to reduce blowing pressure, something that is often forgotten in converting compressed air blowing to more efficient devices.
The main points in converting compressed air blowing:
- The first question to ask is if compressed air blowing is really required at all, and could it be done using low pressure blowers or heated air for drying applications?
- It is best to measure the original blowing to determine the consumption? Nozzle flow can differ greatly from published orifice tables.
- Carefully calculate the new blowing demand to ensure will actually be less.
- Ensure blowing pressure is adjusted to as low as possible to gain savings.
- Reduce the time of the blow to as short as possible.
- Control the blowing, stop the blowing electrically if there is nothing to blow.