What causes high water content in compressed air, and how can these problems be solved?

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Excess moisture content in compressed air has a direct impact on air ducts as well as the equipment that uses this compressed air. How can we reduce the moisture content in the compressed air produced by air compressors to the lowest possible level? The hazards associated with high moisture levels in compressed air include: in pneumatic equipment, condensation water can carry away lubricating oil, leading to reduced efficiency or even damage to the equipment. Condensate can also accelerate the wear of valves in the pipelines, leading to malfunctions or incorrect operation of pneumatic control devices; it causes corrosion in the pipelines and equipment, and if water accumulates at the lowest points of the pipelines and freezes, there is a risk of the pipelines bursting. Analysis of the reasons for water in compressed air and solutions There are many enterprise users who employ dryers, but even with the use of such dryers, it is not possible to guarantee that no water will be present in the compressed air. Below, we analyze, based on some practical situations, the various reasons why water remains in the compressed air after passing through a dryer, as well as the corresponding solutions. 1. 90% of the moisture in compressed air is trapped by the air storage tank; refrigerated dryers and heatless regenerative dryers can only handle the small amount of moisture that remains in gaseous form. The air storage tank is the most important and essential device for drying and purifying compressed air. 2. However, a gas storage tank can only remove liquid water; water can be separated using such a tank only by cooling the compressed air below its pressure dew point at that specific pressure. Therefore, the effect of after-cooling has a significant impact on the moisture content of compressed air. 3. The pressure dew point of the cold dryer must be 10 degrees lower than the ambient temperature; however, the optimal pressure dew point for the cold dryer is 4 degrees, as at this temperature water has the highest specific gravity and can be separated most easily, without causing ice blockages. 4. A regenerative dryer without heat can, in principle, only handle gaseous moisture, that is, water vapor. An excessive amount of liquid water entering the heatless regenerative dryer can severely affect the machine’s performance. In short, aftercoolers and air tanks are the most critical water removal devices. Other drying equipment can only serve as a supplementary measure; the focus on drying compressed air should not be placed on purification equipment. Common problems and solutions for water removal devices: (1) The cooling fins get clogged with dust and other debris, which prevents effective cooling of the compressed air and raises its pressure dew point. This makes it more difficult for subsequent treatment equipment to remove water from the air. Especially in spring, the coolers of air compressors are often blocked by willow fluff. Solution: Install filtering sponges on the windows of the air compressor station, and regularly clean the coolers to ensure proper cooling of the compressed air; also ensure that the water removal system is functioning properly. (2) Fault of the water removal device in screw air compressors – air-water separator. If all air compressors use cyclone separators, spiral baffles are added inside the cyclones to improve separation efficiency (which also increases the pressure drop). The disadvantage of this separator is that its separation efficiency is high at its rated processing capacity; once it deviates from this efficiency, it becomes poor, resulting in an increase in the dew point. Solution: Regularly inspect the air-water separator, and address any issues such as blockages promptly. If the air-water separator fails to drain water during the humid summer months, it should be inspected and repaired immediately. (3) The amount of compressed air used is high, exceeding the design specifications. The pressure difference between the air compressor station and the user end is large, resulting in high airflow speeds. This leads to a short contact time between the compressed air and the adsorbent, as well as an uneven distribution of the compressed air within the dryer – with higher flow rates in the middle section. As a result, the adsorbent in that middle area becomes saturated too quickly. Once saturated, it is unable to effectively absorb the moisture present in the compressed air. A large amount of moisture-laden compressed air passes through this central area, creating a \"tunnel effect\" that results in a large quantity of liquid water at the point of use. Furthermore, during transportation, compressed air expands rapidly toward the low-pressure end in adsorption dryers, causing its pressure to drop sharply and its temperature to decrease significantly below its pressure dew point. As a result, water vapor precipitates in a supersaturated state; in winter, ice forms rapidly on the inner walls of the pipelines. This ice layer grows thicker over time, and eventually it may completely block the pipes. Solution: Increase the flow rate of compressed air. The excess instrument air can be added to the process air; by connecting the instrument air ahead of the process air dryer and controlling it with valves, the issue of insufficient compressed air supply for the process can be resolved. At the same time, this approach also eliminates the \"tunneling effect\" that occurs of compressed air within the dryer’s adsorption tower. (4) The adsorbent material used in adsorption dryers is activated alumina; if it is not packed tightly, it will rub against and collide with each other under the impact of high-pressure compressed air, resulting in pulverization. This pulverization causes the pores of the adsorbent to become larger, allowing large amounts of compressed air to pass through these pores without being effectively filtered, which ultimately leads to the failure of the dryer. This problem manifests on-site as an abundance of liquid water and slurry inside the dust removal filter. Solution: Fill the active alumina as tightly as possible, and inspect and replenish it after use for a period of time. (5) Oil in compressed air can cause oil poisoning of activated alumina, leading to its failure. The supercoolant used in screw air compressors has high thermal conductivity and is used to cool the compressed air. However, it does not separate completely from the compressed air, which results in oil being present in the air exiting the compressor. This oil adheres to the surface of the activated alumina ceramic balls, blocking their capillaries and causing the activated alumina to lose its adsorption capacity; as a result, it becomes oil-contaminated and loses its ability to absorb moisture. Solution: Replace the components on time and use a rear oil removal filter to ensure thorough separation of oil and gas in the air compressor as well as effective oil removal. Additionally, the amount of supercoolant in the unit should not be excessive. (6) Due to large fluctuations in air humidity, the drainage frequency and timing of the various timed drainage valves are not adjusted promptly, resulting in an increasing amount of water accumulating within the filters; this accumulated water can then be reintroduced into the compressed air. Solution: The frequency and duration of drainage by the timed drainage valve can be set based on air humidity and experience. When air humidity is high, the frequency of drainage should be increased, as well as the duration of each drainage session. The criterion for adjustment is to ensure that each time drainage takes place, all the accumulated water is removed without any compressed air being discharged. In addition, insulation is applied to the delivery pipelines, along with steam tracing; a drain valve is installed at the lowest point for regular inspection and drainage. These measures help prevent pipe freezing in winter and remove some of the moisture from the compressed air, thereby reducing the impact of water content in the compressed air on users. By analyzing the reasons for water in compressed air, the above corresponding measures are taken to address the issue.