Compressed air refrigeration dryer

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A compressed air refrigeration dryer removes the condensing moisture from the air compressed by a compressor .

Mode of action

The air sucked in and compressed by a compressor contains water vapor , which is described by the relative humidity . The water absorption capacity of the air depends mainly on the temperature. If the air temperature rises, then the ability to absorb the water vapor also increases. If the sucked-in air is compressed by a compressor, the proportion of water vapor in the compressed compressed air increases , which then condenses when the temperature drops and appears as liquid water. The condensate is particularly harmful in compressed air systems and the many applications. Corrosion is promoted, system components are damaged, workplaces and processed products or even food can be polluted. For this reason, the condensate must be removed from the compressed air.

In a compressed air station, the compressed air refrigeration dryer can be installed directly after the compressor (variant 1) or, viewed in the direction of flow, after a compressed air tank (variant 2). With variant 2, the good pre-cooling via the compressed air tank can be used, which reduces the inlet temperature of the compressed air in the compressed air refrigeration dryer. A constant compressed air consumption without strong pressure fluctuations is to be aimed for so that a consistently good pressure dew point can be maintained. In the event of pressure fluctuations, it can be advantageous to install the compressed air refrigeration dryer after the compressor (variant 1), as the pressure vessel stores the dried compressed air and can thus compensate for the pressure fluctuations. The disadvantage is the higher inlet temperature (the outlet temperature of the compressor is decisive here) in the compressed air refrigeration dryer, which must be taken into account when designing the compressed air refrigeration dryer.

Functional principle of refrigeration dryer

The function of the refrigeration dryer is based on water vapor condensation in the heat exchange process. Every refrigeration dryer has at least one air-refrigerant heat exchanger and, from an energetic point of view, should always have an air-air heat exchanger. The warm and moist compressed air from the compressor first flows through the air-to-air heat exchanger. There it is pre-cooled by the already dried, cold compressed air using the counterflow principle . The dried and cold compressed air absorbs the thermal energy and then flows out of the compressed air refrigeration dryer in a heated state. The compressed air pre-cooled in the air-to-air heat exchanger flows into the air-to-refrigerant heat exchanger. Here, the pre-cooled compressed air is further cooled by a liquid refrigerant that absorbs the thermal energy of the compressed air. As a result, the compressed air continues to lose its ability to hold moisture. The resulting condensate is separated from the compressed air by a condensate separator and discharged from the system via a condensate drain. Plate heat exchangers, tube bundle heat exchangers and lamellar heat exchangers are preferably used for refrigerant heat exchangers.

Lamellar heat exchanger

Lamellar heat exchangers are much larger in design than plate heat exchangers. It is advantageous that this lamellar heat exchanger for an optimized use of the cooling energy, in a bed of z. B. quartz sand, or a brine bath can be inserted. This storage medium serves as a cold store for the energy given off by the refrigerant. When the storage medium has been sufficiently cooled by the refrigerant, the circuit switches off and the thermal energy of the compressed air is now absorbed by the quartz sand . As soon as the quartz sand can no longer extract enough heat energy from the compressed air, the refrigerant circuit switches on again. Systems with lamellar heat exchangers and storage media can work very energy-efficiently. However, since the generation of cold is regulated as a function of the temperature in the storage medium, a fluctuation in the cooling temperature reached cannot be prevented.

Plate heat exchanger

Plate heat exchangers are very compact in their design. However, in order to generate a constant output, they must also be in continuous operation, as they do not have a storage medium for absorbing the thermal energy. This means that they can cause a higher power consumption than fin heat exchangers with the same service life.

Areas of application for refrigeration dryers

Water vapor condensation with a refrigeration dryer is the most frequently used method for compressed air drying. These refrigeration dryers can be used in many areas of application in trade, workshops, businesses and industry and ensure greater operational and functional reliability of the complete compressed air system, the pipeline components, the compressed air tools and the pneumatic controls.

Other types of compressed air drying

Individual evidence

  1. ↑ Information sheet for compressed air preparation at energieschweiz.ch, Federal Office of Energy (PDF, 702 kB).