压缩空气的吸附干燥以物理吸附为主。当干燥的压缩空气与吸附剂接触时，空气中的水分子扩散到吸附剂上并因范德华引力而被吸附。与此同时，被吸附的水分子因本身的热运动及外界气态分子碰撞，有一部分离开吸附剂表面返回气相，即发生脱附。当单位时间内水分子的吸附量与脱附量相等时，就达到了一个动态吸附平衡，虽然吸附与脱附过程均在进行但速度相等。此时，单位质量吸附剂所吸附的水蒸气量称为吸附剂的“静态吸附量”，常用g(水)/kg(吸附剂)、或%表示。
吸干机一般采用硅胶、活性氧化铝、分子筛作为干燥剂。硅胶：较易受水分潮解。通常用于压力露点为-20℃；活性氧化铝：吸附性能强、稳定，遇到水分不潮解，具有高抗碎强度和抗磨蚀性，适用范围较广，通常压力露点为-40℃；分子筛：由于在相对湿度20%以下有较好的干燥性能，常常作为深度干燥的干燥剂，通常用于压力露点为-70℃。
The so-called adsorption is the phenomenon that the concentration of matter changes automatically on the two phase interface. When the gas molecules move to the surface of the solid, the gas molecules will temporarily stay on the solid surface due to the interaction between the gas molecules and the solid molecules, forming the increase of the concentration of the gas molecules on the solid surface, that is, the gas molecules are adsorbed on the solid surface. The study shows that the adsorption phenomenon occurs not only at the solid gas interface, but also on the liquid gas interface and the solid liquid surface. The system that can have obvious adsorption phenomena is called "adsorption system", and the material with certain adsorption capacity is called "adsorbent", and the adsorbed substance is called "adsorbate".
In the process of adsorption and dehydration of compressed air, the commonly used adsorbents are silica gel, active alumina and molecular sieve, and the water vapor, which is evenly mixed in the compressed air, is the adsorbate. In the adsorbent regenerative dryer, the active alumina and other solid adsorbents together with the water vapor in the compressed air constitute an adsorption system. The dry air in the compressed air plays the task of carrying the adsorbate in the adsorption system, and it does not take part in the adsorption process itself. The reverse process of adsorption operation is "desorption" or "desorption" process. We usually call it "regeneration".
According to the nature of the interaction between solid surface and gas molecule, adsorption can be divided into two types: physical adsorption and chemical adsorption. The former is also known as Fan Dehua adsorption, which is caused by intermolecular forces and electrostatic forces, and the latter is caused by chemical bonds. Chemisorption is stronger than physical adsorption, and selectivity is high.
The adsorption drying of compressed air is mainly physical adsorption. When the dry compressed air is in contact with the adsorbent, the water molecules in the air diffuse to the adsorbent and are adsorbed by Fan Dehua attraction. At the same time, the adsorbed water molecules are separated from the surface of the adsorbent and return to the gas phase because of their thermal movement and the impact of the external gaseous molecules. When the adsorption amount of water molecules is equal to the amount of desorption in the unit time, a dynamic adsorption equilibrium is achieved, although the adsorption and desorption processes are all at the same speed. At this point, the amount of water vapor adsorbed by the unit mass adsorbent is known as the "static adsorption capacity" of the adsorbent, commonly expressed as G (water) /kg (adsorbent) or%.
The adsorption dryer generally uses silica gel, activated alumina and molecular sieve as desiccant. Silica gel: more vulnerable to moisture deliquescence. Usually used for pressure dew point of -20 C; active alumina: strong and stable adsorption properties, no moisture deliquescence, high crushing strength and abrasion resistance, wide application range, and usually pressure dew point at -40 C; molecular sieve: because of better drying performance under relative humidity of less than 20%, it is often used as dry drying. The agent is usually used for the pressure dew point at -70 C.
