For more than 100 years, compressed air has been considered a safe and reliable power source widely used in industry. Also referred to as the “fourth utility,” compressed air is used by about 90 percent of total industrial production companies at some stage of their respective operations. Unlike gas, water, and electricity, which are supplied to the site by a supplier under strict tolerances and quality specifications, compressed air is generated on-site by the user. Therefore, the quality of compressed air and the cost of producing this extraordinary utility falls on the user himself.
The problem of compressed air
By their very nature, compressed air systems present performance and reliability problems; moreover, almost all compressed air system-related problems and many of those related to production quality can be directly attributed to contaminants in compressed air.
This passage was excerpted from the whitepaper “Compressed Air Contamination.”
tablet). Download the full whitepaper here.
Sources of contamination of compressed air
Many compressed air users are unaware that a compressed air system contains a number of visible and invisible contaminants that originate from four different sources.
The four sources of compressed air contamination are:
- The ambient air
- The air compressor
- The lung
- The distribution pipes
1. Ambient air
The main source of contamination in a compressed air system is the ambient air around the compressor itself. Basically, the air compressor is a kind of big fan. During operation, it draws in large amounts of surrounding air, compresses it, and then feeds it into a pipe. In doing so, however, it acts as if it were a large vacuum cleaner, sucking up even invisible contaminants. Therefore, when ambient air is compressed, the compressor at the same time also promotes the concentration of contaminants.
Main contaminants in ambient air:
- Water vapor
- Microorganisms
- Atmospheric particulate matter
- Oil steam
Other contaminants in the ambient air:
The four contaminants highlighted are the main ones in general applications; however, there are others that can enter through the mouth of the compressor and, depending on how the air compressor is used, may require some attention. Other contaminants include:
- Sulfur dioxide (SO2)
- Nitrogen oxides (NO + NO2)
- Carbon monoxide (CO)
- Carbon dioxide (CO2)
- Vapors generated by caustic cleaning agents, bleach, etc.
2. Air compressor
During the compression and cooling process, the air compressor also changes the state of the invisible gaseous contaminants sucked in, many of which, as the state changes, become visible. In addition to changing the state of environmental contaminants, the air compressor is also responsible for the contaminants it itself introduces, effectively becoming the second source of contamination.
Contaminants introduced by the air compressor:
- Liquid oil
- Oil aerosol
- Oil vapor (from compressor oil)
- Wear particles
Environmental contaminants converted by air compressor:
- Oil steam
- Water vapor
Both gaseous contaminants cool and condense, transforming into:
- Liquid oil
- Oil aerosol
- Water in the liquid state
- Water aerosol
Therefore, as soon as air leaves the compressor aftercooler, regardless of the type of compressor used (oil-lubricated or oil-free) the compressed air will contain the following contaminants:
- Water in the liquid state
- Water aerosol
- Water vapor (100% saturated)
- Liquid oil
- Oil aerosol
- Oil steam
- Microorganisms
- Atmospheric particulate matter and compressor wear particles.
3. Lung
The third source of contamination is the lung. Installed in a compressed air system for the purpose of storing compressed air and increasing compressor efficiency and reliability, large amounts of contaminants also accumulate in the lung. These contaminants also cause chemical reactions and oxidation, which in turn cause additional contaminants introduced into the compressed air system.
Contaminants introduced from the lung:
- Rust
- Scaling
The wet lung (installed before the dryer) can reduce the compressed air temperature by as much as 5 °C. This cooling causes water vapor and oil vapor to condense further, turning into water and liquid oil. The choice of a wet lung is often dictated by this reason, since it can, in fact, provide additional cooling of compressed air where the ambient and compressed air temperatures are higher than expected. Unfortunately, however, it also promotes the formation of an ideal environment for the rapid proliferation of microorganisms, especially in compressor condensate.
4. Distribution piping
In a typical compressed air system, the final source of contamination is the distribution piping, which carries compressed air from the compressor and distributes it throughout the manufacturing plant. Similar to the lung, distribution piping not only promotes the accumulation of contaminants, but adds to the problem of contamination caused by chemical reactions and oxidation that of rust and scale introduced into the compressed air and the proliferation of microorganisms.
Contaminants introduced from distribution pipelines:
- Rust
- Fouling
Similar to the lung, the distribution piping also cools the compressed air causing further condensation of water and oil vapor, which turns into water and liquid oil generating, in turn, water and oil aerosols as the air sucks the liquid down the piping.
Summary on contaminants
To protect equipment and processes that use compressed air or products that come into contact with compressed air, either directly or indirectly, at least ten contaminants generated by four different sources of contamination must be treated.
Contaminants entering the compressed air system.
Breathing air/medical air
If compressed air is used for breathing, medical, or other critical applications, consideration must then be given to the fact that other potentially lethal contaminants may be present in the ambient air.
Hazardous contaminants for breathing air/medical air applications
- Sulfur dioxide (SO2)
- Nitrogen oxides (NO + NO2)
- Carbon monoxide (CO)
- Carbon dioxide (CO2)
Therefore, in the case of breathing air/medical air/critical applications, at least 15 contaminants must be treated.
Contaminants entering the compressed air system (breathing air):
Watch this video on compressed air and causes:
Compressed air: one more problem
There are many who believe that the amounts of contaminants in the ambient air can be considered insignificant; however, when talking about contamination of compressed air, the effect of air compression on ambient contamination, the amount of air flowing into the compressed air system, and the compressor’s operating time must also be taken into account.
The concentration effects of compression
During operation, the air compressor consistently draws in high volumes of ambient air, and as the operating pressure and/or flow rate increase, a proportionately larger volume of ambient air is required. A greater volume of ambient air corresponds to a greater amount of contaminants.
For example, wanting to make a simplification, to generate 1 cubic meter of air at a pressure of 7 bar g (8 bar A), 8 cubic meters of ambient air are required.
Legend
To be used, the accumulated compressed air is brought back to ambient pressure; some are convinced that, in this way, contamination levels return to those of ambient air and are, therefore, irrelevant. This is not the case, unfortunately.
Facts
When air is compressed, the heat of compression makes it too hot to be used; the compressed air must therefore be brought to a temperature that allows it to be used. Intercoolers and aftercoolers are installed to reduce the temperature of compressed air (either built into the compressor or installed externally). As the air is cooled, gaseous contaminants condense, turning into liquids and later into aerosols (small droplets) in the chillers; unfortunately, however, the liquid separators that come with the chillers cannot remove 100 percent of the liquids and are totally ineffective in reducing the amount of aerosols. Therefore, untreated compressed air is highly contaminated when it reaches the point of use.
The table below provides an example of what 1 cubic meter of contaminated compressed air may look like at a typical operating pressure of 7 bar g (102 psi g).
What contaminants cause most of the problems?
People are often led to believe that the oil introduced by the compressor causes most of the problems in the compressed air system. Contrary to what everyone thinks, oil is not a huge problem at all.
The most problematic contaminants are water and microorganisms. The presence of one of these two contaminants directly affects the other.
Water causes:
- The proliferation of microorganisms
- The formation of rust and encrustation
- The production of acid oil condensate in the compressor.
Oil is often considered the most prolific contaminant, as it is visible when it escapes from open drainage points and exhaust valves. Usually, what is observed is oil condensation (oil mixed with water).
What then is the extent of the problem?
The table below gives an example of how much water can be introduced into an air system every hour and over the course of a year.
The example just shown refers to a single compressor. If the compressed air system has larger compressors, operates for longer periods of time, is installed in a country with high ambient temperatures and/or relative humidity (or a combination of both), then the volume of condensate in the system increases significantly.
Summary
- There are several contaminants present in a compressed air system.
- Generally, in most compressed air applications, it is necessary to treat 10 contaminants.
- Other contaminants present can also cause problems (depending on the application).
- Contamination is caused by 4 different sources, not just the compressor.
- Air compression promotes the concentration of contaminants in the ambient air.
- It is water that is the most prolific and problematic contaminant, not oil.
- Liquid contaminants increase significantly in higher temperature and humidity environments.
This article was written by Mark White, Applications Manager for Compressed Air Processing,
Parker Gas Separation and Filtration Division EMEA
Related Content
Six Points to Consider When Applying ISO8573-1 in a Manufacturing Facility
Is Your Compressed Air Purity Validated?
How Oil Vapour in Ambient Air Affects Compressed Air Quality
Keep Employees Safe with Engineered Breathing Air Systems
For more than 100 years, compressed air has been considered a safe and reliable power source widely used in industry. Also referred to as the “fourth utility,” compressed air is used by about 90 percent of total industrial production companies at some stage of their respective operations. Unlike gas, water, and electricity, which are supplied to the site by a supplier under strict tolerances and quality specifications, compressed air is generated on-site by the user. Therefore, the quality of compressed air and the cost of producing this extraordinary utility falls on the user himself.
The problem of compressed air
By their very nature, compressed air systems present performance and reliability problems; moreover, almost all compressed air system-related problems and many of those related to production quality can be directly attributed to contaminants in compressed air.
This passage was excerpted from the whitepaper “Compressed Air Contamination.”
tablet). Download the full whitepaper here.
Sources of contamination of compressed air
Many compressed air users are unaware that a compressed air system contains a number of visible and invisible contaminants that originate from four different sources.
The four sources of compressed air contamination are:
The ambient air
The air compressor
The lung
The distribution pipes
1. Ambient air
The main source of contamination in a compressed air system is the ambient air around the compressor itself. Basically, the air compressor is a kind of big fan. During operation, it sucks in large amounts of surrounding air, compresses it, and then feeds it into a pipe. In doing so, however, it acts as if it were a large vacuum cleaner, sucking up even invisible contaminants. Therefore, when ambient air is compressed, the compressor at the same time also promotes the concentration of contaminants.
Main contaminants in ambient air:
Water vapor
Microorganisms
Atmospheric particulate matter
Oil steam
Other contaminants in the ambient air:
The four contaminants highlighted are the main ones in general applications; however, there are others that can enter through the mouth of the compressor and, depending on how the air compressor is used, may require some attention. Other contaminants include:
Sulfur dioxide (SO2)
Nitrogen oxides (NO + NO2)
Carbon monoxide (CO)
Carbon dioxide (CO2)
Vapors generated by caustic cleaning agents, bleach, etc.
2. Air compressor
During the compression and cooling process, the air compressor also changes the state of the invisible gaseous contaminants drawn in, many of which become visible as they change state. In addition to changing the state of environmental contaminants, the air compressor is also responsible for the contaminants it itself introduces, effectively becoming the second source of contamination.
Contaminants introduced by the air compressor:
Liquid oil
Oil aerosol
Oil vapor (from compressor oil)
Wear particles
Environmental contaminants converted by air compressor:
Oil steam
Water vapor
Both gaseous contaminants cool and condense, transforming into:
Liquid oil
Oil aerosol
Water in the liquid state
Water aerosol
Therefore, as soon as air leaves the compressor aftercooler, regardless of the type of compressor used (oil-lubricated or oil-free) the compressed air will contain the following contaminants:
Water in the liquid state
Water aerosol
Water vapor (100% saturated)
Liquid oil
Oil aerosol
Oil steam
Microorganisms
Atmospheric particulate matter and compressor wear particles.
3. Lung
The third source of contamination is the lung. Installed in a compressed air system for the purpose of storing compressed air and increasing compressor efficiency and reliability, large amounts of contaminants also accumulate in the lung. These contaminants also cause chemical reactions and oxidation, which in turn cause additional contaminants introduced into the compressed air system.
Contaminants introduced from the lung:
Rust
Fouling
The wet lung (installed before the dryer) can reduce the compressed air temperature by as much as 5 °C. This cooling causes water vapor and oil vapor to condense further, turning into water and liquid oil. The choice of a wet lung is often dictated by this reason, since it can, in fact, provide additional cooling of the compressed air where the ambient and compressed air temperatures are higher than expected. Unfortunately, however, it also promotes the formation of an ideal environment for the rapid proliferation of microorganisms, especially in compressor condensate.
4. Distribution piping
In a typical compressed air system, the final source of contamination is the distribution piping, which carries compressed air from the compressor and distributes it throughout the manufacturing plant. Similar to the lung, distribution piping not only promotes the accumulation of contaminants, but adds to the problem of contamination caused by chemical reactions and oxidation that of rust and scale introduced into the compressed air and the proliferation of microorganisms.
Contaminants introduced from distribution pipelines:
Rust
Fouling
Similar to the lung, the distribution piping also cools the compressed air causing further condensation of water and oil vapor, which turns into water and liquid oil generating, in turn, water and oil aerosols as the air sucks the liquid down the piping.
Summary on contaminants
To protect equipment and processes that use compressed air or products that come into contact with compressed air, either directly or indirectly, at least ten contaminants generated by four different sources of contamination must be treated.
Contaminants entering the compressed air system.
Breathing air/medical air
If compressed air is used for breathing, medical, or other critical applications, consideration must then be given to the fact that other potentially lethal contaminants may be present in the ambient air.
Hazardous contaminants for breathing air/medical air applications
Sulfur dioxide (SO2)
Nitrogen oxides (NO + NO2)
Carbon monoxide (CO)
Carbon dioxide (CO2)
Therefore, in the case of breathing air/medical air/critical applications, at least 15 contaminants must be treated.
Contaminants entering the compressed air system (breathing air):
Watch this video on compressed air and causes:
Compressed air: one more problem
There are many who believe that the amounts of contaminants in the ambient air can be considered insignificant; however, when talking about contamination of compressed air, the effect of air compression on ambient contamination, the amount of air flowing into the compressed air system, and the compressor’s operating time must also be taken into account.
The concentration effects of compression
During operation, the air compressor consistently draws in high volumes of ambient air, and as the operating pressure and/or flow rate increase, a proportionately larger volume of ambient air is required. A greater volume of ambient air corresponds to a greater amount of contaminants.
For example, wanting to make a simplification, to generate 1 cubic meter of air at a pressure of 7 bar g (8 bar A), 8 cubic meters of ambient air are required.
Legend
To be used, the accumulated compressed air is brought back to ambient pressure; some are convinced that, in this way, contamination levels return to those of ambient air and are, therefore, irrelevant. This is not the case, unfortunately.
Facts
When air is compressed, the heat of compression makes it too hot to be used; the compressed air must therefore be brought to a temperature that allows it to be used. Intercoolers and aftercoolers are installed to reduce the temperature of compressed air (either built into the compressor or installed externally). As the air is cooled, gaseous contaminants condense, turning into liquids and later into aerosols (small droplets) in the chillers; unfortunately, however, the liquid separators that come with the chillers cannot remove 100 percent of the liquids and are totally ineffective in reducing the amount of aerosols. Therefore, untreated compressed air is highly contaminated when it reaches the point of use.
The table below provides an example of what 1 cubic meter of contaminated compressed air may look like at a typical operating pressure of 7 bar g (102 psi g).
What contaminants cause most problems?
People are often led to believe that the oil introduced by the compressor causes most of the problems in the compressed air system. Contrary to what everyone thinks, oil is not a huge problem at all.
The most problematic contaminants are water and microorganisms. The presence of one of these two contaminants directly affects the other.
Water causes:
The proliferation of microorganisms
The formation of rust and encrustation
The production of acid oil condensate in the compressor.
Oil is often considered the most prolific contaminant, as it is visible when it escapes from open drainage points and exhaust valves. Usually, what is observed is oil condensation (oil mixed with water).
What then is the extent of the problem?
The table below gives an example of how much water can be introduced into an air system every hour and over the course of a year.
The example just shown refers to a single compressor. If the compressed air system has larger compressors, operates for longer periods of time, is installed in a country with high ambient temperatures and/or relative humidity (or a combination of both), then the volume of condensate in the system increases significantly.
Summary
There are several contaminants present in a compressed air system.
Generally, in most compressed air applications, it is necessary to treat 10 contaminants.
Other contaminants present can also cause problems (depending on the application).
Contamination is caused by 4 different sources, not just the compressor.
Air compression promotes the concentration of contaminants in the ambient air.
It is water that is the most prolific and problematic contaminant, not oil.
Liquid contaminants increase significantly in higher temperature and humidity environments.
The following passage was extracted from the whitepaper “Compressed Air Contamination” by Mark White. Download the full whitepaper here.
This article was written by Mark White, applications manager for compressed air processing, Parker Gas Separation and Filtration Division EMEA
Related Content
Six Points to Consider When Applying ISO8573-1 in a Manufacturing Facility
Is Your Compressed Air Purity Validated?
How Oil Vapour in Ambient Air Affects Compressed Air Quality
Keep Employees Safe with Engineered Breathing Air Systems
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