How to choose a dryer for compressed air

Why do I need dry compressed air?

Compressed air is used in various industries in the industrial sector and clean and dry compressed air is required, while air compressed by an air compressor will produce condensate, untreated compressed air containing condensate will lead to

Damage and failure of air-powered equipment;

deterioration of process quality in applications such as laser cutting and electrostatic spraying;

Decrease in the quality of the final product;

rusting of compressed air pipes, which in turn leads to compressed air leaks;

Therefore, air dryers are essential to protect the user's production systems and processes.

Theoretical basis and moisture content criteria

Relative humidity (RH) and pressure dew point (PDP) are indicators and concepts to measure the dryness of compressed air. The lower the relative humidity (RH) of compressed air, the less water vapor it contains, and the drier the compressed air is, so the lower the relative humidity (RH) of compressed air, the better. From the concept of pressure dew point (PDP), it is known that the amount of water vapor that can be accommodated in compressed air under certain temperature conditions is limited and will reach saturation. The lower the temperature, the less the maximum water vapor content in the compressed air, the use of drying equipment to reduce the pressure dew point (PDP) in the compressed air, for example, to 7 ℃, when the maximum water vapor content of compressed air is 7.732g / m3, and then the compressed air is warmed to ambient temperature, such as 25 ℃ (maximum water vapor content of 22.830g / m3), and at this time the compressed air contains only 7.732g/m3 of water vapor, compared to the maximum water vapor content of 22.830g/m3 , then the compressed air from the air compressor outlet 100% relative humidity (RH) down to 33.37%, to achieve the purpose of drying.

This is the actual application of compressed air to reduce the compressed air pressure dew point (PDP) to achieve the principle of drying and water removal, and thus, the need to develop a unified industry standard in order to measure the performance of dryer products. At present, all industries and applications follow the standard for measuring the water content of compressed air is ISO8573-1:2010, which specifies the compressed air pressure dew point (PDP) from -70 ℃ ~ 10 ℃ six levels, the lower the pressure dew point (PDP) figure, it represents the higher the quality requirements of compressed air, the drier the compressed air.

Dryers according to the different drying principles and technologies, there are usually refrigerated dryers, adsorption dryers and membrane dryers, water below 0 ℃ will be transformed from liquid to solid, that is, icing, so the refrigerated dryer can not achieve the drying effect below 0 ℃, the need for pressure dew point below 0 ℃ drying effect need to use adsorption dryers and membrane dryers.

Refrigerated dryer: cooling compressed air, reduce the pressure dew point to 3-10℃ (different brands of refrigerated dryers have different exhaust pressure dew point, the lower the exhaust pressure dew point, the better the performance of the refrigerated dryer), condensing the water vapor in the compressed air into liquid water and separating and discharging, to achieve the purpose of drying compressed air;

Adsorption dryer: when the moist compressed air flows through the adsorbent (usually silica gel, molecular sieve, activated alumina), the moisture in the air is adsorbed, so the air is dried and dry compressed air with a pressure dew point lower than 0℃ is obtained, according to ISO8753 standard, the usual product parameters are -20℃, -40℃, -70℃ three specifications.

Membrane dryer: The membrane dryer is equipped with thousands of tiny hollow polymer fiber tubes with inner coating, these fiber tubes have selective permeation function, when the compressed air flows through the inside of these tiny fiber tubes, the water vapor in the compressed air will penetrate the membrane wall, while the compressed air continues to pass inside, so as to achieve the purpose of separating and removing water, the membrane dryer can reach the pressure dew point of -20℃～3℃, and it is simple to operate and less restrictive to install. and simple operation, less installation restrictions, quiet operation, to meet the needs of some specific applications;

In the actual application, for the dryness requirement of compressed air, customers usually propose the pressure dew point index according to the corresponding level of ISO8573 standard, or we have the corresponding industry application experience to understand which type of dryer is required for the customer's application, either way, according to the following table, we can recommend the suitable dryer products to customers.

Lingyu Machinery ~ 2~10C dew point refrigerated compressed air dryer