Compressed air is the second largest power source after electricity, and it is also a multi-purpose process gas source. Its application scope covers petroleum, chemical industry, metallurgy, electric power, machinery, light industry, textile, automobile manufacturing, electronics, food, medicine, biochemistry, national defense, scientific research and other industries and departments. It is not ideal for compressed air to contain a considerable amount of impurities, mainly including: solid particles-in a typical big city environment, there are about 65.438+40 billion particles per cubic meter of air, of which about 80% particles are smaller than 2μm, and the air compressor suction filter is unable to eliminate them. In addition, the air compressor system will continue to produce wear debris, rust residue and oil carbide, which will accelerate the wear of gas equipment and lead to seal failure; Moisture-The relative humidity in the atmosphere is usually as high as 65% or higher. After compression and condensation, it becomes moist saturated air with a lot of liquid water droplets, which is the root cause of corrosion of equipment, pipelines and valves. Ice in winter will also block the small hole passage of pneumatic system. It is worth noting that even if it is separated from pure saturated air, there will still be condensed water with the decrease of temperature. Every time 10℃ is lowered, its saturated water content will be reduced by 50%, that is, half of the water vapor will be converted into liquid water droplets (see table 1). Therefore, it is necessary to adopt multi-stage separation and filtration device in compressed air system or pretreat compressed air into dry air with certain relative humidity. Oil-Lubricating oil used in high-speed and high-temperature air compressors can play the role of lubrication, sealing and cooling, but it pollutes the compressed air. Oil-free, semi-oil-free and oil-free machines developed with self-lubricating materials have reduced the oil content in compressed air, but they have also produced some side effects, such as shortening the life of wearing parts, corrosion of internal parts and pipeline systems of the machine, and increasing the oil content of air compressors during running-in period, wear period and load reduction period. This is undoubtedly a threat to the automatic production line that pursues high reliability. In addition, it should be emphasized that the oil brought into the system from the air compressor is not good under any circumstances. Because after many times of high-temperature oxidation and condensation emulsification, the performance of the oil has been greatly reduced, showing acidity, which not only can not lubricate the subsequent equipment, but will destroy the normal lubrication; Microbes-In the process of pharmacy, bioengineering, food manufacturing and packaging, the pollution of bacteria and bacteriophages can not be ignored.