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Desiccant dryer (adsorption dryer) its working principle is to use the adsorbent adsorption characteristics of water to reduce the moisture content in compressed air, generally speaking, the pressure dew point of the desiccant dryer outlet gas reaches -20 ℃ ~ -70 ℃. The common adsorbents of adsorption dryers are activated alumina, molecular sieve, etc. When the adsorption dryer is to obtain extremely dry compressed air (dew point below -60℃), molecular sieve is the only choice.

Activated alumina, also known as activated alumina, the English name is Activated Alumina or Reactive alumina, it is a porous, high dispersion of solid materials, has a large surface area, its microporous surface has the characteristics required for catalysis, such as adsorption properties, surface activity, excellent thermal stability, etc., so it is widely used as a chemical reaction catalysts and catalyst carriers. Activated alumina has the ability to selectively adsorb water from gases, water vapor and some liquids. After saturated with adsorption, it can be revived by removing water by heating at about 175-315℃. Adsorption and revival can be performed several times. Activated alumina in the air separation industry variable pressure adsorption dew point can reach -55 degrees.

Molecular sieve is a class of substances with uniform micropores, the pore size of which is comparable to the general molecular size. Molecular sieve has a wide range of applications, and can be used as efficient desiccant, selective adsorbent, catalyst, ion exchange agent, etc. Compared with other adsorbent materials, the most important feature of molecular sieve is that it has a uniform diameter microporous structure, so it can selectively adsorb gaseous molecules with a diameter smaller than its pore size. Molecular sieve is generally synthetic, in the air drying (separation) process to get more molecular sieve is zeolite-type silica aluminate of polyhydric compound crystals. Its thermal and chemical stability is very high, but also has the sieving performance, ion exchange performance, selective single and good adsorption performance, etc., usually used in adsorption dryer adsorption cavity.

Theoretically alumina can reach the pressure dew point of -50, in fact it can be completely guaranteed to -40, while molecular sieve can reach the pressure dew point of -70. In terms of drying performance, it is much stronger than alumina, but the replacement cost is high and the lifetime is not as long as alumina. Therefore, before choosing which adsorbent to use, you must first understand the user's requirements or expectations of the dew point, so as to choose the best solution that can meet the user's requirements for performance and also reduce the user's cost of use.

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