I recently worked on a metal forming site which had significant compressed air use (baseload consumption of »200kW). The areas highlighted below were identified as potential modifications to the existing compressed air system, which could be implemented in order to achieve compressed air efficiency improvements and cost reduction. Compressed air on the site was used for driving pneumatic machinery, fluid agitation, powering hand tools and CNC machining. It is envisaged that the majority of these modifications would be applicable across multiple sectors.
Isolation of high pressure users
Any items of machinery which have a requirement for air at a higher pressure (e.g. pneumatic hammers) should, if possible, be isolated by a valve from the rest of the system and have an independent secondary supply. This, then allows the remainder of the site to operate at a lower air pressure, thus using less energy. Generally, reducing the pressure in the system by 1 bar will lead to a 7% saving on annual energy consumption.
Key items of machinery which require higher pressure can be isolated from the main air ring to ensure that they are not affected if there are any issues with the primary air supply, therefore minimising disruptions in production.
On demand pressure increase
If isolating the items of machinery with their own ring/ supply is cost prohibitive, then a control system can be utilised. This can ramp up the pressure in the system (triggered by the operator) when the machinery is being utilised. The higher pressure air is supplied for a finite period of time before the control system reverts back to the standard system pressure. This would ensure that higher pressure air is not being generated for long periods unnecessarily.
Automatic air supply cut off linked to machine operation
The control system described above can also be further evolved and fully automated. In addition to the above, it could then also cut off the air supply to the machinery (via electric solenoids) if the machinery is inactive for a length of time or has been switched off. This would ensure that air isn’t being wasted.
Isolate different business areas
Different business areas within a site which all utilise compressed air, can have different operating times and hours of operation. As such, areas which have shorter operating hours should have a dedicated compressor or have the ability to be isolated from the rest of the system. This would ensure air isn’t being supplied to an area where it isn’t required, therefore minimising losses through air leaks.
Shift generation time of compressed air
One way to reduce the cost of producing compressed air, is to shift the generation of compressed air to a time period when electricity costs are lower (i.e. through the night). The air can be liquefied and stored in receivers as an energy reserve to be used when it’s required throughout the day. The cost savings could be significant, particularly if the period of generation is outside of potential Triad periods.
Minimise compressed air applications
Where possible, alternatives to compressed air should be explored. These include the replacement of hand tools and blowers with suitable electric alternatives.
At the metal forming site I referenced above, compressed air agitation of the fluid vats/ tanks will be systematically replaced with high efficiency pump motors (subject to the successful completion of a trial). The pumps will circulate the fluid around the tank to achieve the same net effect of air agitation but using significantly less energy. The replacement of air also has additional benefits; where tanks/vats are heated, cold air isn’t being introduced to the tank and increasing the heating load.
In addition to the modifications listed above, if the compressed air system is antiquated the following should also be considered in order to optimise it:
- Legacy redundant lengths of pipe (which are blind/ dead at one end)should be removed or isolated.
- A continuous program of air leak detection and maintenance should be implemented.
- Compressors approaching the end of their useful lifetime, should be replaced with correctly sized modern high efficiency compressors equipped with Variable Speed Drives(VSDs) If appropriate.
- Ensure ancillary equipment (dryers, oil separators, etc.) are in good working order.
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