In almost all industrial enterprises where a central compressed air system is used, the pipelines of the air system are routed outside. The air passing through them has 100% humidity. In the air network, it cools, resulting in condensation. It is he who is the most common cause of corrosion of air systems and, as a consequence, defective end products. To solve this problem allows the adsorption dryer.
Each
industry has its own allowable humidity limit for compressed air. Specific indicators are described in the international standard ISO 8573-1.
How does an adsorption dryer work? The basis of it is adsorbent - a substance with high porosity, characterized by high ability to absorb moisture. When moist compressed air penetrates the adsorbent bed, it is dried. However, it should be noted that the adsorption desiccant requires periodic regeneration, because its ability to absorb moisture is limited. The essence of the regeneration process is to extract the accumulated liquid from the pores. The most popular methods for regenerating adsorption devices are:
- Cold regeneration. For these purposes, pre-dried compressed air is used. It is passed through an adsorbing layer and it, as it were, “sucks” excess moisture from it. This is the cheapest method of regeneration, however, it has a significant minus: some losses of compressed air cannot be avoided (from 15%).
- External hot regeneration. The adsorbent layer is blown under pressure above atmospheric air, previously heated in the external elements. Then it is necessary to cool it. For this purpose, already drained air is also needed, however, with this type of regeneration the losses are much lower (up to 2.5%).
- Hot regeneration under vacuum. In this case, hot air is supplied under atmospheric pressure, that is, under vacuum. Unlike the previous method, in this case, the cooling of the adsorbers can also be carried out using atmospheric air. And this means that the loss of compressed air in the system is zero.
How to choose an adsorption dryer depending on the type of regeneration? Everything is simple here. If it is necessary to supply less than 35 cubic meters per minute to the air system, from the point of view of economy, it is worth choosing dehumidifiers with a cold type of regeneration. But options with hot regeneration are appropriate when more than 35 cubic meters of air are supplied to the system per minute.
Adsorption air dryers of 4 classes are distinguished (depending on the dew point):
1. -70 degrees Celsius (for conditions of the Far North).
2. -40 degrees Celsius (for a normal continental winter).
3. -20 degrees (for winter in European countries, regions with a mild climate).
4. +3 degrees (summer version).
The class indicates the temperature limit at which there is no condensation in the system. If the incoming air is colder than the specified limit, the adsorption air dryer may simply not cope with the load.