2024-03-11

How to remove pollutants from compressed air?


If the compressed air is contaminated and comes into contact with the final products, the quality of these products may be affected. In this article, we will explain how to easily remove these pollutants from the compressor system.
 
Use a filter to remove oil from compressed air
 
Modern fiber filters are very effective in removing oil. However, because factors such as temperature have a significant impact on the separation process, it is difficult to accurately control the amount of oil remaining in the air after filtration. The efficiency of the filter is also affected by the concentration of oil in the compressed air and the amount of free water. The data stated in the filter specifications always apply to a specific air temperature, usually 21°C. This corresponds to the approximate air temperature after the air-cooled compressor is operated at an ambient temperature of 10°C. However, climate and seasonal changes may cause temperature changes, which in turn affects the separation capacity of the filter.
 
The air should be as dry as possible for best results. If there is free water in the air, oil, activated carbon and sterile filters are all less effective (in this case, the filter specifications are not applicable). The fiber filter can only remove oil in the form of oil droplets or aerosols. Oil vapors must be removed using a filter with activated carbon. A properly installed fiber filter and a suitable pre-filter can reduce the amount of oil in compressed air to about 0.01 mg/m3. A filter with activated carbon can reduce the amount of oil to 0.003 mg/m3.
 
Activated carbon is specifically used to cover a wide range of internal surfaces. Activated carbon is capable of absorbing 10-20% of its own weight in oil. Therefore, a filter coated with activated carbon powder contains only a small amount of carbon powder. This limits its service life, and its use is limited to 20°C. The bulk activated carbon bead filter contains a large amount of activated carbon. This makes it more suitable for many applications (even at higher temperatures) and extends the service life of the filter.
 
The lifetime is affected by the air temperature. As the temperature increases, the amount of oil vapor increases exponentially. Activated carbon filters should contain the right amount of carbon and be sized to minimize pressure drop. Filters with activated carbon can only remove air pollution in the form of steam and should be done before other suitable filters. For best results, the filter should also be placed as close as possible to the relevant application. In addition, they must be checked regularly and replaced frequently.
 
Oil-free compressors do not require oil filters. This means that the compressor can work at a lower discharge pressure, thereby reducing energy consumption. From an economic point of view and from an air quality point of view, oil-free compressors are the best solution in many cases.
 
Reduce water content with aftercooler
 
 
The compressed air from the compressor is very hot after compression, usually at a temperature between 70-200°C. The use of an aftercooler reduces this temperature and, in turn, the water content. Today, this equipment is often included as standard equipment for compressor installations. The aftercooler should always be placed directly after the compressor. The heat exchanger cools the hot air and then delivers most of the condensed water, otherwise the condensed water will flow into the system as soon as possible. The aftercooler can be water-cooled or air-cooled, and is usually equipped with an automatic water separator.
 
Separation of condensed water and compressed air using a water separator
 
 
Most compressor plants are equipped with aftercoolers and water separators to separate as much condensate as possible from the compressed air. By correctly selecting and sizing the water separator, 80-90% efficiency can be achieved. The remaining water flows into the air receiver together with the compressed air as a water mist.
 
 
oil-water separation
 
 
The oil in the form of droplets is partially separated in the aftercooler, condensate separator or condensate tap, and flows through the system together with the condensate. From an environmental point of view, this oil/water emulsion is classified as waste oil and must not be discharged into the sewage system or directly into nature.
 
With regard to the treatment of environmentally hazardous waste, new and stricter laws are constantly being introduced. Condensate drainage and its collection is complex and expensive. A simple and cost-effective solution to this problem includes installing an oil/water separator, for example, using a membrane filter to produce a clean drain and drain the oil into a dedicated receiver.
 
 
Purifying medical air
 
 
In addition to the conventional air purity requirements, there are special applications that require a higher degree of air treatment purification. High-quality air is essential for many industries, but in the medical field, it is unparalleled. 100 per cent must be guaranteed to ensure medical air purity for hospital patients. However, the air extracted from our environment to produce air for medical use, especially in cities or industrial areas, is rarely of sufficient quality.
 
 
Medical air filtration includes several purification stages for processing compressed air, so the result is very clean. By using a water separator and two coalescing filters, contaminants (such as water, particles and oil droplets) can be removed from the air before entering the cold regenerative adsorption dryer. The dryer reduces the dew point to -40°C, which is a temperature that meets medical requirements.
 
 
After passing through the adsorption dryer, the air passes through an additional filtration stage, the function of which is twofold. The activated carbon reduces hydrocarbons (such as oil vapors) and odors to harmless levels, and the catalyst converts excess concentrations of carbon dioxide into carbon dioxide. In this filtration stage, the contamination of sulfur oxides and nitrogen oxides is also reduced to an absolute minimum. In the final stage, the particle filter eliminates dust particles that may be introduced into the air by the dryer or additional filter units. The requirements for the healthcare market vary from country to country and are governed by local regulations.

Removal, filter, air, activated carbon, temperature, compressor, compressed air, condensate, separator, cooler