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Adsorption
Adsorption is a process by which molecules adhere to a surface, creating a thin film. The surface that traps the molecules does not chemically change form, meaning it can be regenerated.
Many air compressor drying systems use the principle of adsorption to remove water molecules from the air. These adsorption or desiccant dryers create exceptionally dry air, making them useful in industries that require high air quality. The adsorption process also prevents corrosion in pipelines and malfunction of air compressor equipment.
FAQs
In adsorption, a molecule, such as water, adheres to the surface of a desiccant. In absorption, the molecule permeates the desiccant and the desiccant changes form. The adsorption process is a surface-level change and is much easier to reverse.
Air compressors often have desiccant dryers with two chambers filled with a desiccant, typically aluminum oxide, silica gel or a combination of the two. These chambers collect water from the compressed air in the following stages:
- Drying: Compressed air passes through one chamber, and the moisture is adsorbed, reducing the pressure dew point.
- Regenerating: While air passes through the first chamber in one direction, a small portion of the already dry compressed air passes through the other chamber in the opposite direction, picking up moisture from the desiccant before returning to the environment. This process enables the desiccant to pick up more moisture.
- Switching: Once the desiccant in the first chamber collects all the water it can, the two chambers switch functions. The second dries while the first regenerates. This switching creates reliable air quality.
Adsorption dryers come in four varieties:
- Heatless: These compressed air dryers use only the dried compressed air to regenerate the desiccant. Heated dryers use heat to reduce the compressed air needed for regeneration.
- Heated purge: An electric air heater within these dryers warms the purge air, enabling the system to use less energy and less compressed air during regeneration.
- Blower regenerated: Instead of using compressed air, these systems blow ambient air over an electric heater before passing it over the desiccant. The compressed air is preserved, lowering energy consumption.
- Heat of compression (HOC): These dryers use heat generated by the air compressor, saving energy while creating a lower pressure dew point.
Desiccant air dryers provide the highest effectiveness and air quality compared to other compressor air drying methods. Different drying methods, like absorption and refrigerated dryers, are beneficial for cost-effective drying in applications where air quality is less essential.
Industries like food and beverage, pharmaceuticals and electronics often use desiccant dryers because they rely on the highest-quality air to prevent product contamination. These and other industries may need to meet strict air quality standards like Standard 8573-1 from the International Organization for Standardization (ISO). Adsorption dryers are also helpful in creating the driest air, where pressure dew points as low as -40°C or even lower are critical.
Desiccant dryers also work well in low ambient temperatures, preventing corrosion and freezing in air lines. They can serve in outdoor, cold environments where refrigerated dryers can’t function effectively. Solid adsorbents in these dryers also prevent the introduction of chemicals into the air stream, which could create contamination risks.