Compressed Air, also known as the fourth utility, is utilized as energy by more than 90% of all manufacturing processes worldwide. The process of compressing air as a form of energy presents two major challenges. The first challenge is the removal and management of water, also known as “Air Compressor Condensate”, the second challenge is the removal of “Contaminants” such as Dirt, Bacteria, Viruses, Fungi, Spores, Oil, Rust, Scale and Trace Gases. These two removal processes are known as “Compressed Air Treatment and Purification” and unlike other utilities, it is the responsibility of the owner to treat and dispose of the contaminated condensate responsibly while respecting local environmental regulations.
Compressed Air Treatment & Purification
Clean compressed air is essential to the safe and efficient operation of tools, machinery and production processes such as paint spraying, sandblasting, food and drug processing and industrial production. There are 10 major contaminants that need to be removed and contolled from compressed air systems, they are: 1. Water in the form of liquids, aerosols and vapours, 2. Dirt Particles, 3. Microorganisms such Bacteria, 4. Viruses, 5. Fungi, 6. Spores, 7. Hydrocarbons such as Oil in the form of liquids, aerosols and vapours, 8. Rust, 9. Scale and 10. Trace Gases such as carbon monoxide, carbon dioxide and other trace gases.
Air Compressor Condensate (Contaminated Oily Water)
A 25 horsepower (100 cfm) air compressor operating 24 hours / seven days per week will generate an average of 2,500 gallons (10,000 litres) of air compressor condensate annually. The condensate that is produced by the air compressor is caused by the action of compressing the ambient air which contains water in the form of vapour or humidity. The warmer the temperature of the air, the more water vapour it can hold until it becomes fully saturated and condenses in the form of liquid water. 100 cubic feet of atmospheric air at 100% RH and 77℉ (25℃) contains 2.5 ounces of water vapour.
Ambient air containing water vapour, dirt particles and microorganisms enter through the compressor intake filter into the compression chamber in average conditions at normal atmospheric pressure of 14.5 psi, normal temperatures of 68℉ (20℃) and normal relative humidity of 68% RH depending on the season and the geographical location. Most air compressors have an intake filter with an efficiency rating between 10 to 25 microns so, dirt particles larger than these micron sizes are retained by the intake filter. Once the air is compressed, the conditions increase to an average pressure of 115 psi, a temperature 250℉ and a relative humidity of 100% RH. As the air exits the air compressor and continues towards the process it cools and the water vapour condenses into “contaminated liquid compressor condensate”. The compressor outlet is where the compressed air must be treated and purified before it reaches the manufacturing process, tools, machinery and work stations.
Dirt Particles in the ambient atmosphere number in the 4 million particles per cubic foot range of which 80% are below 2 microns in size. Microorganisms (bacteria, viruses, fungi and spores) are also present in the mix which number in the 3 million particles per cubic foot. Imagine how toxic and acidic the contaminated liquid condensate becomes once everything is mixed with water from the atmosphere and oil from the compressor lubrication system at a temperature of 250℉.
Compressed Air Treatment and Purification consists of after-coolers, condensate separators, coalescing filters, air dryers, condensate drains and condensate oil/water separators.
Rotary Screw Compressor
Reciprocating Piston Compressor
The After-Cooler and Condensate Separator
The compressed air after-cooler, which is usually built into the compressor, reduces the air temperature from 250℉ down to 100℉. This cooling process condenses 60% of the water vapour into liquid and is drained through a centrifugal condensate separator and condensate drain into the oil water separator.
The remaining 40% of the water vapour is removed by coalescing filters and air dryers. The filters and dryers also drain any remaining compressor condensate through drainage lines and into the oil water separator.
Coalescing filters remove dirt particles, contaminated water and oil aerosols larger than 1 micron in size and water and oil vapours larger than .01 micron in size. The process of coalescing, accumulates the aerosol and vapour molecules and turns them into liquid droplets where the filter is designed to allow the droplets to roll off into the filter bowl and drain through to the oil water separator. Only clean compressed air can exit the filter and enter the process. ISO 8573.1 is a recognized international standard of performance that most manufacturers of compressed air coalescing filters conform to. Look for the ISO 8573.1 designation when choosing your filter.
Compressed Air Dryer
Refrigerated air dryers remove the remaining water vapour by lowering the temperature of the compressed air to near freezing temperatures 37℉ to 39℉ but never below freezing. Lowering the air temperature allows for the remaining water vapour to condense into liquid form and drain off into the oil water separator for safe disposal. The compressed air temperature is then raised back to approximately 70℉ and continues on to the process. The refrigerated type air dryer which provides a pressure dew point suppression of 37℉ to 39℉ is the most common type of air dryer and most cost effective to operate. Desiccant Adsorption and Membrane type dryers provide much lower dew point suppressions in the range of -70℉ to 37℉ for critical applications such as food and drug processing to paint spraying and sandblasting operations. The term dew point suppression means that the compressed air will not condense into liquid until the pressure dew point falls below the pressure dew point rating of the dryer in use.
Compressed Air Condensate Drains are responsible for taking away the accumulation of air compressor condensate from after-coolers, condensate separators, air receivers, air filters and refrigerated air dryers. Without a properly functioning condensate drain the air treatment system will fail and condensate separators will back up, filter elements will become saturated with wet condensate, evaporators in refrigerated dryers will fill with condensate, in the case of a desiccant dryer, the desiccant media will become saturated with humidity and contaminated air compressor condensate will find it’s way to machines, tools and production processes. These outcomes are costly and can result in thousands of dollars of clean up, repairs, parts replacement and production down time.
There are four basic types of condensate drains, manual ball valves, timed electronic ball valve, automatic float drains and electronic level controlled no air loss drains. The simplest, least costly to purchase and install but the most expensive to operate is the manual ball valve condensate drain. It requires operator attention to manually drain the condensate but the air loss during condensate evacuation can be costly. Compressed air is the most expensive form of energy there is and air loss due to poorly selected components and air leaks throughout the piping network connections are very expensive. For example a 1/16″ inch air leak will cost $860.00 per year or $0.10 cents per hour (based on a power cost $0.08 cents per KW Hour). The cost might be minimal to a small commercial workshop or home handyman who may only use a compressor between 50 and 100 hours per year but for operations that run compressed air between 2,000 and 8,000 hours per year and have large networks with a potential of hundreds or thousands of poorly selected components or air leaks, the figure can reach the ten’s of thousands of dollars per year. The best choice of drain would be the no air loss type automatic float drains or electronic level no air loss drain.