The compressed air quality for normal pneumatic applications can be provided by a refrigeration air dryer. This style of dryer is the most common and the least expensive purchase and is the simplest method of drying compressed air.
What does an Air Dryer Do The function of the dryer is to remove the water and oils generated by an air compressor.
How do water and oil get into compressed air? Water is contained in our atmosphere. The air compressor draws in this moist atmospheric air and compresses the air to 7 bar. In this process, some oils escape from the air compressor and are introduced into the airline.
The energy used in the compression process heats the compressed air. Most compressors contain an aftercooler. An aftercooler is a radiator that contains compressed air with an electric fan that draws in ambient air to cool the hot compressed air. It cools the compressed air from 100 °C (average compression temperature) to 40 °C. This cooling process condenses the water vapor into a liquid. This liquid condensate can be drained from the compressed air by a mechanical or timed automatic drain. The use of an aftercooler is important as refrigerated air dryers cannot tolerate a compressed air temperature above 60 °C. This is the first phase of air treatment.
How Does a Dryer Work? The dryer takes in the warm compressed air typically at 40° from the aftercooler and cools it in an air-to-air heat exchanger. The air leaves this exchanger at +/- 20 °C. The compressed air is then cooled again by an air-to-freon exchanger. The compressed air temperature drops to 3°, at this point, the remainder of the water that was in vapor form is now condensed into a liquid. The condensate is captured and drained to waste by a mechanical or timed automatic drain. The compressed air is now dry to a dew point of 3 °C at the working pressure of 7 bar G.
The cold compressed air is now reheated by the warm air coming into the dryer in air to air heat exchanger. The air leaving the dryer will be approximately 5° cooler than the incoming compressed air. The compressed air is now practically moisture free as some 97% of the water content has been removed in this process. Once the compressed air is dried it remains dry, unless the air line temperature drops below 3 °C.
Coalescing FIlters. Artic Driers recommends that the dryer is fitted with an E series coalescing pre filter and after-filter filters. The oil used for cooling and lubrication in the compression process is not totally recovered by the compressor system when the air leaves the compressor package. If this residual oil is not removed it will be a “sticky” viscous film of thick oil in your airline. This is not a grade/viscosityIt’sIt’s that can be used in pneumatics. Its too thick and will create valve and actuator problems. Its best removed by the E series coalescing filters. Filtration also ensures that your air dryer drain functions without constant attention.
Are All Air Dryers the Same? In general they have the same number of heat exchangers in the same layout as described. However, many low-cost dryers have a shell and tube design using mild steel casings with copper tubes and aluminum baffles. The difference in materials can lead to internall corrosion. These heat exchangers were originally designed for R12 or R22 freon gases that were single component gases. With the newer eco-friendly single-component internal gases these exchangers are not the ideal solution as they struggle to achieve a consistent dew point. The modern gases do not react the same as the older gas versions. Dry air is what you are buying, spend a little more and get a real result.
Artic Driers favours the Aluminum Plate and Bar exchangers or the stainless Plate to Plate exchangers for compressed air drying. Shell and tube exchangers have a greater chance of leaking due to the number of internal brazed joints.
Dew Point Monitors. Artic markets the brand of SUTO iTEC dew point meters. These are low-cost dew point monitors that measure the actual water content in the compressed air, not the temperature. No refrigeration air dryer marketed in South Africa has a dew point probe built-in. It would escalate the price too much!
The dryers control panel will tell you a physical temperature inside the dryer cabinet, and this is an acceptable practice. But the fact to remember is that a dryer may give a temperature readout of 3 deg C BUT if the dryer has a drain malfunction the dryer becomes a water generator not a water removal system.
To monitor your compressed air quality a dew point monitor such as the S305 is a far better option, it reads air dew point, has alarm set points, and can transmit the information to a SCADA system while still giving local display. This kind of system takes the onus of monitoring the dryer operator and place the results into an automating monitoring system.
Artic Driers International is a family-owned 31-year-old automated place and operated 31 year old business that has the widest range of compressed air products.