2024-03-11

What contaminants are found in compressed air?

 
 
It is essential for the user that the quality of the compressed air is correct. If air containing contaminants comes into contact with the final product, the cost of waste quickly becomes unacceptably high. In this article, we will introduce the most common pollutants in compressed air?
 
Water vapor in compressed air
 
Atmospheric air always contains moisture in the form of water vapor. Compressed air contains some water vapor and may cause problems. Examples include: higher maintenance costs, shortened service life and impaired tool performance, high scrap rates through paint and plastic injection, increased leakage, failure of control systems and instruments, shortened service life of piping systems due to corrosion, and higher prices for installation. The following accessories can be used to separate water: aftercooler, condensate separator, refrigerant dryer and adsorption dryer. A compressor operating at 7 bar(e) overpressure will compress air to 7/8 of its volume. This also reduces the air's ability to hold water vapor by 7/8. The amount of water released is large. For example, a 100 kW compressor sucking in air at 20°C and 60% relative humidity will release about 85 liters of water in an 8-hour shift. Therefore, the amount of water to be separated depends on the application area of the compressed air. This, in turn, determines which combination of cooler and dryer is suitable.
 
Oil in compressed air
 
The amount of oil in compressed air depends on several factors, including the type, design, age and condition of the machine. In this regard, there are two main types of compressor design: compressors that use a lubricant in the compression chamber and compressors that do not use a lubricant. In a lubricated compressor, the oil participates in the compression process and is also contained in (all or part of) the compressed air. However, in modern lubricated piston compressors and screw compressors, the amount of oil is very limited. For example, in an oil-injected screw compressor, the oil content in the air is less than 3 mg / m3 at 20°C. By using a multi-stage filter, the oil content can be further reduced. If you choose this solution, you must consider quality limitations, risks and energy costs.
 
Microorganisms in compressed air
 
More than 80% of the particles that pollute the compressed air are less than 2 µm in size, so they can easily pass through the inlet filter of the compressor. Since then, the particles have spread throughout the pipeline system and mixed with water and oil residues and pipeline deposits. This can lead to the growth of microorganisms. A filter placed next to the compressor can eliminate these risks.
 
However, to obtain pure compressed air, the bacterial growth behind the filter must be completely controlled. The situation becomes more complicated because even after passing through multiple filters, gases and aerosols can be concentrated into droplets (by concentration or charging). The microorganisms can germinate through the filter wall and are therefore present in the same concentration on the inlet and outlet sides of the filter.
 
Microorganisms are very small and include bacteria, viruses and phages. Generally, the size of bacteria can be from 0.2 µm to 4 µm, and the size of viruses can be from 0.3 µm to 0.04 µm. Pollutants with a diameter of less than 1 µm, so microorganisms can easily pass through the compressor inlet filter. Despite their size, these microorganisms are a serious problem in many industries because, as "living" organisms, they are able to reproduce freely under the right conditions. Studies have shown that microorganisms systems thrive in compressed air systems with high humidity (100 percent) non-dry air.
 
Oil and other pollutants act as nutrients that allow microbes to thrive. The most effective treatment method is to dry the air to a relative humidity of less than 40% (which can be achieved by using any type of dryer), and then install a sterile filter in the system. The sterile filter must be installed in the filter housing for in-situ steam sterilization or easy opening. Sterilization must be carried out frequently to maintain good air quality.

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