Without treatment, it is impossible to obtain a defined quality of the compressed air, the compressor acting as a big vacuum cleaner. The impurities in the ambient air are sucked up by the compressor and returned in concentrated form to the compressed air network, regardless of the type of compressor. It is very rare that untreated compressed air can be used directly downstream of the compressor. In the quantities in which they are produced, particles, moisture and oil are generally too important for consumers. Therefore, the failure of a treatment component always has a negative effect on the functionality and lifetime of consumers. The required cleanliness of compressed air is determined first by the consumer. It can happen that in large compressed air systems, some consumers require a higher quality of compressed air than the rest of the system. For example, installations with consumers (valves, cylinders) that are in the open air and can freeze in winter may temporarily require compressed air with little moisture. Often, in such cases, it is interesting to treat the compressed air in a decentralized way to confer the required quality. It depends, however, individually on the proportion and position of these consumers in the compressed air system.
Compressed air drying Atmospheric air usually contains more water vapor at higher temperatures and less at low temperatures. When this air is compressed, the concentration of water vapor increases. A compressor (see illustration 10) with a volume flow of 200 l / s sucks in not only air but also 80 liters of water vapor in 8 hours, which it rejects in the air network. compressed (admission conditions: 20 ° C, 80% relative humidity). Filters do not remove moisture, because water vapor is contained in the air as a gas and the filters can only hold solid bodies or drops. The choice of compressed air dryer depends on the required dew point. In principle, the lower the dew point required, the higher the acquisition and operating costs of the desiccator. There are four main methods of removing moisture from compressed air: cooling, over-compression, adsorption and absorption.
In about 80% of all application cases, refrigerant dryers are sufficient for the treatment of compressed air. Their use is recommended in principle because they save expensive maintenance costs in the network of pipes and compressed air consumers. When generating a dew point between 3 and 7 ° C, refrigerating desiccators with energy-saving controls or refrigerated accumulators can save 50 to 70% of energy compared to those with a hot gas bypass system. Although relatively low dew points are required, the purchase of relatively expensive equipment can efficiently dry compressed air down to -70 ° C. Example: The combination of refrigerant and adsorption desiccators reduces the energy requirement by two-thirds compared to conventional adsorption desiccators.
