In compressed air dryers, activated alumina is the most used adsorbent because of its many excellent application characteristics. Activated alumina is generally artificially synthesized, usually by heating and dehydrating the water compound of aluminum twice. The nature of the activated substance is closely related to the structure and morphology of the primary raw material hydroxide. The activated alumina in the form of Y is used for compressed air adsorption and drying, and its activation temperature is lower than 600°C.
Activated alumina has a strong affinity for water. Under certain operating conditions, its drying effect can reach a dew point below -60℃. Its regeneration temperature is lower than that of molecular sieves. Activated alumina has high surface hardness and compressive strength. , The point crushing strength can reach ~100N/particle (commodity), the wear rate is less than 0.04, it is not easy to break under the action of static pressure, and it is not easy to wear off under the action of variable pressure. Due to the large adsorption capacity (static adsorption capacity: 15-20%), the adsorption-regeneration cycle can be longer than other adsorbents in the drying process of high-temperature gas, thus avoiding frequent switching regeneration operations.
Silica gel is a commonly used dehydrating adsorbent, which can be divided into natural and synthetic. The natural porous SiO₂ is usually called diatomaceous earth, and the synthetic one is called silica gel.
Silica gel (mSiO2·nH2O) is a colloid formed by polycondensation of silicic acid. It can be made into products with various pore sizes. Type A has a pore size of 2-3nm, and Type B has a pore size of 0.7nm and a specific surface area of 100-1000m³/ g around. Silica gel has a strong adsorption effect on water, so it is widely used for dehydration and drying of substances. Type A silica gel can be used in various dry occasions, while Type B silica gel is only used in occasions where the humidity is greater than 50%.
The silica gel used for gas separation is artificially synthesized. They have high chemical stability, heat resistance and abrasion resistance. The performance of silica gel is hydrophilic, its pore size distribution is single and narrow, and the adsorption capacity for water is large. In an air flow with a humidity of 20°C and a relative humidity of 60%, the moisture content of the microporous silica gel is 24% of its own mass. Adsorption and drying of air with high moisture content.