AdsorptionAdsorption Drying of Compressed Air
The article describes adsorption compressed air drying systems and types of adsorbents used in drying filters. The most important features of each of them are presented and the purity classes of compressed air are described in accordance with the ISO 8573-1 standard
Adsorption Drying of Compressed Air
Adsorption drying is a chemical process in which water vapor is bound to the adsorption material as a result of the intermolecular interaction of the adsorbent surface and adsorbate molecules. The general principle of operation of adsorption dehumidification systems is simple: moist air flows through a column filled with a hygroscopic material, on the surface of which water is adsorbed. The dried air leaves the column and is directed to consumption. Drying the air causes the adsorption material to gradually become saturated until it is full. In typical industrial setups, the saturated bed column is transferred to another tank, and the saturated bed is regenerated to restore desiccant capacity. Regeneration can be carried out in the PSA (pressure swing adsorption) or TSA (temperature swing adsorption) cycle. The main parameter determining the degree of air drying is the pressure dew point, while the purity of compressed air is classified into 6 classes (according to the ISO 8573 standard).
Pressure dew point
The pressure dew point is a parameter in degrees Celsius used to determine the temperature at which condensation occurs. Reaching the pressure dew point means that the relative humidity has reached 100% and the process of condensation (condensation) of water vapor begins.
Compressed air purity classes
The purity classes of compressed air are specified in the ISO 8573 standard. The standard distinguishes 6 air classes, which classify the air from the cleanest (class 1) to the lowest quality air (class 6).
Degree of air purity | ||||
| ISO 8573-1 cleanliness class | Max size of solid elements [µm] | Max concentration of solid elements[mg/m3] | Pressure dew point [°C] | Maximum oil concentration [mg/m3] |
1 | 0,1 | 0,1 | -70 | 0,01 |
2 | 1 | 1 | -40 | 0,1 |
3 | 5 | 5 | -20 | 1 |
4 | 15 | 8 | +3 | 5 |
5 | 40 | 10 | +7 | 25 |
6 | – | – | +10 | – |
Compressed air adsorption drying systems
Adsorption compressed air drying systems are divided into:
- heat regenerated adsorption dryers (e.g. BEKO EVERDRY, L&W , PNEUDRI DH, KSI – Filtertechnik ECOTROC, PARKER) – External heat regenerated systems,
- cold regenerated adsorption dryers (e.g. OMEGA AIR A-DRY, FST DPS, ATLAS Copco CD) – Cold regenerated heatless systems.
Adsorbents for drying filters
Adsorption dryers use drying adsorbents of various characteristics and efficiency. The most commonly used adsorbents are silica gel (silica gel, colloquially also silica gel), active alumina Al2O3 (activated aluminum) and molecular sieves 3A, 4A, 13X. There are many manufacturers of dedicated drying adsorbents, e.g. BASF Sorbead® Air (modified aluminosilicates), KC-Trockenperlen.
Parametr | Active alumina | Dilica gel | Molecular sieve |
| Description | Dehumidification systems | An amorphous form of silicon dioxide with a high water vapor adsorption capacity | Synthetic zeolites with regular pore shape and shape. The main types of molecular sieves used are 3A, 4A, 5A and 13X |
| Pressure dew point [°C] | -40 | -60 | -70 (up to -100) |
| Dehumidification systems | PSA, TSA | TSA | PSA, TSA |
What desiccant material should I choose?
The selection of a desiccant is influenced by many factors, the main of which are the achievable degree of drying of compressed air (expressed by pressure dew point), the method of regeneration (PSA, TSA) and the cost of the material. If you need a new adsorption air dehumidification system, contact us and our experts will offer you the right solution. If you have an existing system and would like to reduce the cost associated with the delivery of a new drying filling, we are also able to help you. We supply desiccant adsorbents for most adsorption dehumidifiers available on the market!
You can also find more information on our website dedicated to adsorption technology!
