In the manufacturing process of compressed air, the temperature often decreases gradually. At the beginning, the humidity in the air keeps vaporizing because of the high temperature of heat generated by air compression. When flowing in the pipeline, heat exchange occurs in the surrounding environment, which will slow down the cooling of compressed air. The lower the temperature (ambient air temperature), the more condensation of water vapor in compressed air will occur. When the compressed air is discharged from the outlet in use, the pressure drops suddenly, the volume expands and the temperature drops, which will cause the water vapor in the compressed air to condense further into water.
The harm caused by water content in compressed air is mainly manifested in the fact that condensate water will take away lubricating oil on pneumatic equipment, resulting in the reduction of equipment efficiency and even damage. Condensate also accelerates the wear of valves in the pipeline, resulting in failure or misoperation of pneumatic control equipment; corrosion of pipelines and equipment; if water freezing occurs at the low point of the pipeline, the pipeline is also in danger of bursting. If there is water mist in the compressed air used for spraying, it will affect the adhesion of paint on the workpiece and lead to the failure of painting.
Compressed air with water can be caused by many reasons, including unreasonable process design and improper operation, as well as the structure of the equipment itself, as well as the technical level of equipment and control elements.
The excessive moisture content of compressed air directly affects the air pipeline and equipment using compressed air. How can the moisture content of compressed air produced by air compressor reach a minimum? As we all know, the atmosphere we breathe contains water, but this water content will change due to weather and environmental reasons. The moisture content in the dry environment is much lower than that in the compressed air in the high humidity air, where the environment is a factor. Air compressor's own storage tank and external storage tank as compressed air storage devices, most of the stored compressed air, but compressed air will contain a small amount of water and lubricants and other substances. Therefore, one of the reasons for the high water content of compressed air is how long it takes to discharge the water in the storage tank. If there is no discharge for a long time, there will be too much water in the storage tank, and the water content of compressed air will increase accordingly.
Compressed air moisture content is too high also has one of the most important reasons, after-treatment equipment, precision oil mist filter, freeze dryer, adsorption dryer, drainage and other faults. The main function of these equipments is to filter moisture and oil in compressed air, so that compressed air becomes pure and impurity-free.
For example, pharmaceutical factories, toy factories and other manufacturers which require high compressed air requirements, or even need to deodorize and disinfect compressed air in order to use. Returning to the air compressor post-processing equipment, the difference between installation and no installation of these equipment is that the moisture content of compressed air without post-processing equipment is about 20% - 30% at room temperature, while the moisture content of compressed air after installation of these post-processing equipment will be reduced to about 0.01% - 1%. With good quality equipment, water content will be reduced to lower or reach high standard compressed air without water. If the requirement for compressed air is not high, the compressor is used for an average of 10 hours a day. It is suggested that the water in the storage tank and precision oil mist filter should be discharged once every 3 days on average, which will reduce the moisture content of compressed air. If it is used 24 hours a day, it is recommended to discharge water once a day. It is also possible to install drains and other equipment to discharge water automatically. Regular maintenance of air compressors can also reduce water content!
Causes and solutions of excessive moisture in compressed air:
The screw air compressor itself has a dewatering device. Generally, at the outlet of the machine, a part of the moisture can be removed initially. The dewatering, deoiling and dedusting filters entering the post-treatment equipment can remove a part of the moisture, but most of the moisture can be removed mainly by the dryer of the drying equipment, so that the compressed air through it can be dried and cleaned. To the gas pipeline. Many enterprise users adopt micro-thermal regeneration double-tower adsorption dryer, but the use of this dryer can not guarantee that compressed air no longer has water to separate out. Below, combined with some actual situations, the reasons and solutions for incomplete dewatering of compressed air after dryer are analyzed.
(1) The cooling fin of air compressor is blocked by dust, the cooling of compressed air is not good, and the dew point of pressure is increased, which will make the water removal of post-treatment equipment more difficult. Especially in spring, the cooler of air compressor is often blocked by willow catkins.
Solution: Install filter sponge on the window of air compressor station, and often blow ash on the cooler to ensure good cooling of compressed air and normal dewatering.
(2) The malfunction of steam-water separator of screw air compressor. If all air compressors use cyclone separators, a spiral baffle is added inside the cyclone separator to enhance the separation effect (and also increase the pressure drop). The disadvantage of this kind of separator is that its separation efficiency is higher at its rated capacity. Once it deviates from its separation efficiency, it will be worse, leading to the rise of dew point.
Solution: Check the gas-water separator regularly and deal with the blockage in time. If the gas-water separator is not drained in summer when the air humidity is high, it should be checked immediately.
(3) The large amount of compressed air used in the process exceeds the design scope. The large pressure difference between the compressed air at the air compressor station and the user end results in high air velocity, short contact time between the compressed air and the adsorbent, and uneven distribution in the dryer. The centralized flow in the middle makes the adsorbent in the middle part saturate too quickly and adsorb after saturation. The agent can not effectively adsorb the moisture in the compressed air, and compressed air carries a large amount of water through the center, which produces a "tunnel effect", resulting in a large amount of liquid water at the gas end. In addition, compressed air in the transport process to the low-pressure end expansion adsorption drying dissipation is too fast, its pressure rapidly reduces, while the temperature decreases greatly, lower than its pressure dew point, water vapor precipitation in the supersaturated state, in winter will quickly solidify and hang ice on the inner wall of the pipeline, hanging ice is getting thicker and thicker, and eventually the pipeline may be blocked.
Solution: Increase the flow of compressed air. The excess instrument air can be added to the process air. The instrument air can be connected to the front end of the process air dryer and controlled by a valve. The problem of insufficient supply of compressed air for the process can be solved. At the same time, the problem of "tunnel effect" of compressed air in the adsorption tower of the dryer can also be solved.
(4) Activated alumina is the adsorbent material used in the adsorptive dryer, and its filling is not compact, which will lead to friction and collision with each other under the impact of strong compressed air, which will make the adsorbent void larger and larger. A large number of compressed air passing through the void has not been effectively treated, and ultimately lead to the failure of the dryer. The problem is that there is a large amount of liquid water and slurry in the filter.
Solution: When filling active alumina, fill it as closely as possible and check and supplement it after using for a period of time.
(5) The oil in compressed air will lead to the poisoning and failure of activated alumina oil. The super coolant used in screw air compressor has high thermal conductivity, which is used to cool compressed air. However, the incomplete separation of super coolant from compressed air will bring oil into compressed air. The oil in compressed air will attach to the surface of activated alumina ceramic ball, plug the capillary of activated alumina, and make activated alumina lose its absorption. Oil poisoning occurs due to adsorptive capacity, thus losing the function of adsorbing water.
Solution: Replace oil separator core and post-oil removal filter core on time to ensure complete oil-gas separation of air compressor and good oil removal of post-oil removal filter. In addition, the super coolant in the unit should not exceed the limit.
(6) The air humidity changes greatly, the drainage frequency and time of each timing drain valve are not adjusted in time, which can make more and more water accumulated in each filter, and these water accumulated can be brought into compressed air again.
The drainage frequency and time of timing drainage valve can be set according to air humidity and experience. When the air humidity is high, the frequency of drainage should be increased, and the time of drainage should be increased. The standard should be adjusted to observe that the accumulated water can be drained out without discharging compressed air at each time of drainage. In addition, heat preservation and steam tracing are added to the pipeline, and drainage valves are added at low points to check and drain regularly. Through this measure, freezing pipes in winter can be prevented, and part of moisture in compressed air can be removed, so as to reduce the influence of water carried by compressed air on users. By analyzing the causes of water entrainment in compressed air, the above measures are taken to solve the problem.
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