Compressed Air - The 4th Utility
Compressed air is a safe and reliable power source that is widely used throughout
industry. Approximately 90% of all companies use compressed air in some aspect
of their operations, however unlike gas, water and electricity; compressed air
is generated on-site, giving the user responsibility for air quality and operational
costs.
The problem with compressed air
Compressed air is not without its problems, with all systems suffering from
performance and reliability issues. Almost all of these can be directly attributed
to contamination. After generation, compressed air can typically have up to
ten different contaminants present as it enters the distribution system and
as modern production facilities become more complex and the applications for
compressed air become more critical, the purification of the compressed air
before use is essential.
The four sources of compressed air contamination
Atmospheric Air
Air compressors draw in huge amounts of atmospheric air, which continuously
fills the compressed air system with contaminants such as water vapour, micro-organisms,
atmospheric dirt & oil vapour.
The Air Compressor
In addition to the contaminants drawn in through the compressor intake, the
compressor also adds contamination in the form of liquid oil, oil aerosols (lubricated
compressors) and wear particles. The compressor after-cooler will also condense
water vapour, introducing it into the compressed air in both a liquid and aerosol
form.
Compressed air storage devices and distribution systems
As the air leaves the compressor it now contains eight different contaminants.
The air receiver (storage device) and the system piping that distribute the
compressed air around the facility can store large amounts of this contamination.
Additionally, they cool the warm, saturated compressed air which causes condensation
on a large scale adding more liquid and aerosol water into the system, promoting
corrosion and microbiological growth.
The ten major contaminants found in compressed air
To many compressed air users, the realisation that there are ten main contaminants
in a compressed air system is somewhat of a surprise. Many only think of water
and oil as these contaminants are visual and are regularly seen to be causing
problems.
The 10 contaminants are:
- Water Vapour
- Atmospheric Dirt
- Liquid Oil
- Micro-organisms
- Condensed Water
- Rust
- Oil Aerosols
- Water Aerosols
- Pipescale
- Oil Vapour
The largest quantity of contamination introduced into the compressed air system
originates from the atmospheric air drawn into the compressor and not as often
believed, introduced by the compressor itself. The most prolific and problematic
of the contaminants is water which accounts for 99.9% of the total liquid contamination
found in a compressed air system.
Contaminant removal
Failure to remove this contamination can cause numerous problems in the compressed
air system, such as:
- Corrosion within storage vessels and the distribution system
- Blocked or frozen valves, cylinders, air motors and tools
- Damaged production equipment
- Premature unplanned desiccant changes for adsorption dryers
In addition to problems associated with the compressed air system itself,
allowing contamination such as water, particulate, oil and micro-organisms to
exhaust from valves, cylinders, air motors and tools, can lead to an unhealthy
working environment with the potential for personal injury, staff absences and
financial compensation claims. Compressed air contamination will ultimately
lead to:
- Inefficient production processes
- Spoiled, damaged or reworked products
- Reduced production efficiency
- Increase manufacturing costs
The table below highlights each of the purification technologies required to
remove the different contaminants present in the compressed air system.
