When air is compressed, both the temperature of the air and the water vapor present in the air increase. Before the air can be used in its intended process, the air needs to be cooled and dried. Two weeks ago, we began a short dryer series to explore the topic of drying compressed air. If you missed the first blog post on the five techniques for removing moisture from air, you can catch up here.
In adsorption drying, moist air flows over a hygroscopic material or “desiccant” such as silica gel, molecular sieves and activated alumina which adsorbs the water. The desiccant eventually becomes saturated and has to be regenerated to maintain its drying capacity.
Adsorption dryers typically feature two drying towers that switch back and forth from drying to regenerating. There are four methods of regenerating the desiccant and the method used determines the type of adsorption dryer needed.
1) Purge regenerated adsorption dryers or “heatless-type dryers” use expanded or “purged” compressed air in the regeneration process. These dryers use the most energy and are best suited for smaller air flow rates.
2) Heated purge regenerated dryers heat the expanded air during the regeneration process and as a result, use 25% less energy than heatless-type dryers.
3) Blower regenerated dryers do not use compressed air in the process, but rather blow ambient air over an electric heater to regenerate the saturated desiccant. This type of dryer uses 40% less energy than heatless-type dryers.
4) Instead of evacuating the compressed air heat in an after-cooler, heat of compression dryers make use of the heat from the compressor to regenerate the desiccant. These dryers can provide a pressure dew point of -20°C without using additional energy.
Typical pressure dew points reached with adsorption dryers is -40°C, making adsorption dryers suitable for critical applications that require very dry air.
Want to learn more? Contact us to discuss your specific dryer needs.
