Do you really understand adsorption dryers

Do you really understand adsorption dryers

All atmospheric air contains water vapor: higher in high temperature, lower in low temperature. When air is compressed, the density of water vapor also increases. In order to avoid the interference of condensate in the pipes and connected equipment, the compressed air must be dry. "Pressure dew point" (PDP) refers to the temperature at which water vapor begins to condense into water under the current working pressure. A low PDP value means that the water vapor content in compressed air is low.

　　 All atmospheric air contains water vapor: the content is higher at high temperature and smaller at low temperature. When air is compressed, the density of water vapor also increases. For example, a compressor with a working pressure of 7bar and a flow rate of 200l/s can release 10l/h of water on the compressed air line with air with a relative humidity of 80% at 20°C. In order to avoid the interference of condensate in the pipes and connected equipment, the compressed air must be dry. The drying process is realized in the aftercooler and drying equipment.

　　 The term "pressure dew point" (PDP) is used to describe the water content of compressed air. It refers to the temperature at which water vapor begins to condense into water under the current working pressure. A low PDP value means that the compressed air contains less water vapor.

　　It should be remembered that when comparing different dryers, the atmospheric dew point should not be confused with the pressure dew point. For example, the pressure dew point at 7 bar and +2°C is equal to the normal pressure dew point at -23°C. Using a filter to remove moisture (lower the dew point) will not work. This is because further cooling will cause the water vapor to continue to condense. You can choose the type of drying equipment based on the pressure dew point. When considering the cost, the lower the dew point requirement, the higher the input and operating costs of air drying. There are five technologies for removing moisture from compressed air: cooling plus separation, overcompression, membrane, absorption and adsorption drying. Here we will focus on adsorption drying.

The general working principle of adsorption dryer is very simple: moist air flows through the hygroscopic material (usually silica gel, molecular sieve, activated alumina), where it is dried. Water vapor is transferred from the humid compressed air to the hygroscopic material or "adsorbent". This process makes the adsorbent gradually saturated with water. Therefore, the adsorbent must be regenerated regularly to restore its drying capacity. Therefore, adsorption dryers usually have two drying containers: the first container is drying the incoming air, while the second is being regenerated. When one of the containers ("tower") is completed, the regeneration of the other is completely completed. The achievable PDP is generally -40°C. These dryers can provide enough dry air for more stringent applications.