A compressed air dryer is equipment designed to separate water vapor or moisture (dehumidify) from industrial process air. In the typical system, a compressor draws in moist air and compresses it, which raises the air temperature and then cools the air that condenses the water vapor in the unit. These air dryers work by pushing air through membrane tubes that collect and retain water vapor. After this, a small amount of dry air is used to sweep moisture away from the membranes and restore them.
Membrane air dryers can lower the dew point of compressed air down to -40°C, although they do not reduce the temperature of the air itself. Compressed air dryers are special types of filter systems designed specifically to remove water inherent in compressed air. The air compression process raises its temperature and concentrates air pollutants, mainly water vapor. Consequently, compressed air is generally at an elevated temperature and at 100% relative humidity.
As the compressed air cools, water vapor condenses in the tank (s), pipes, hoses, and tools downstream of the compressor. Water vapor is removed from compressed air to prevent condensation and to prevent moisture from interfering with sensitive industrial processes. The purpose of air dryers is to suppress the dew point of compressed air by removing water from it. Compressed air may contain moisture, which, under the right conditions, can reach dew point temperature and condense into a harmful liquid.
This can be a big problem, as it can contaminate your products or equipment, cause pipes to freeze, cause corrosion, and cause other problems. To maintain the concentration gradient across the fiber walls, part of the dry air discharge is directed to the other side of the membrane wall. This type of air dryer uses two towers: one containing a desiccant that removes moisture from the air stream coming from the compressor, while the other regenerates the used desiccant after the pressure has dropped to atmospheric conditions. Water can develop scale inside these devices, which decreases the power delivered by the air motor.
They remove water from the air stream by cooling the air to approximately 3 °C (38 °F) and effectively condensing moisture in a controlled environment. Oil and water vapors in compressed air must have cooled to their dew point (converted to aerosols) before the coalescing filter can operate effectively. The compressors used in this type of dryer are usually of the hermetic type and the most commonly used gas is R-134a and R-410a for smaller air dryers up to 100 cfm. At this temperature, water vapor in the air begins to condense and precipitate on the surfaces of objects, such as the walls of a pipe, the interior of a tank, or the surfaces of dry goods.
The purpose of having two heat exchangers is for the outgoing cold air to cool the incoming hot air and reduce the required compressor size. If the incoming air has an inlet dew point of only 0 °C (32 °F), the outlet dew point will be slightly lower. This is because water droplets from the condensation of the water vapor and the brine solution from the liquefaction of the deliquescent substance can travel along with the discharge air stream. Compressed air temperatures above 38°C (100°F) are very common in southern climates, mining operations, steel mills, onboard, etc.
Water droplets entrained in the air stream represent a greater problem for downstream equipment than the presence of water vapor; therefore, the need for dryers coalescing. The hot and humid air directly from the compressor is at a high temperature due to the heat of compression. They can also produce high-quality dry air due to their inherent efficiency in removing moisture along with other contaminants. Diffusion is the ability of submicroscopic particles or aerosols to move randomly and independently of the bulk air stream.
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