Activated Carbon Adsorbers

Activated Carbon Adsorber as a Final Filtration Stage in Compressed-Air Treatment

An activated carbon adsorber is used in situations where standard particle and coalescing filtration alone is insufficient. While filters primarily remove solid particles and liquid aerosols, activated carbon specifically binds gaseous hydrocarbon and oil vapors as well as odorous substances. This makes it a downstream fine-cleaning stage for applications with increased requirements regarding residual oil content and low odor levels in compressed air.

The current product range includes activated carbon adsorbers for flow rates from 0.5 to 6 m³/min and operating pressures up to 16 bar. The sizes range from compact units with a G 1/2-inch connection to larger models with a G 1 1/2-inch connection. Under the specified reference conditions, a residual oil content of ≤ 0.003 mg/m³ is specified.

Why “absolutely oil-free” would be too general from a technical standpoint

The achievable compressed-air quality does not depend solely on the activated carbon adsorber itself. Other decisive factors include the contamination level of the incoming air, the upstream filtration, the pressure dew point, the temperature, the actual flow rate, and the condition of the activated carbon. For this reason, a specific residual oil specification under defined conditions is technically more meaningful than the general term “absolutely oil-free.”

The specified value of ≤ 0.003 mg/m³ describes the performance of the current adsorbers under the intended operating conditions. Whether this value is achieved on a sustained basis in a specific complete system depends on the correct design and maintenance of all upstream treatment stages.

Pre-filtration protects the activated carbon

Activated carbon is particularly effective for gaseous residues. Larger quantities of liquid oil, oil mist, water, or particles should be removed beforehand. Appropriate coalescence and fine filtration reduce this load and prevent the adsorption capacity from being exhausted unnecessarily quickly.

This clearly distinguishes the activated carbon adsorber from a compressed-air filter: it complements filtration but does not replace it. Similarly, it does not replace a cyclone separator when large amounts of liquid condensate are produced.

Pre-drying and Pressure Dew Point

The moisture content of the compressed air also affects service life. On the large internal surface area of the activated carbon, water competes with the substances that are actually supposed to be adsorbed. Therefore, the compressed air should be sufficiently dried before entering the activated carbon adsorber. For the current system, pretreatment with a pressure dew point of approximately +3 °C or lower is recommended.

A refrigerated air dryer can provide exactly this range for many standard applications. If significantly lower pressure dew points are required—for example, for cold outdoor lines or particularly demanding processes—a desiccant air dryer may instead be the appropriate upstream drying stage.

Post-filter behind the activated carbon

The current system features an integrated afterfilter. This serves to trap the finest particles or any activated carbon dust downstream of the adsorption stage. This functionally completes the treatment chain. However, the actual removal of gaseous hydrocarbons is performed by the activated carbon and not by this afterfilter.

Correctly sizing 0.5 to 6 m³/min

The available sizes cover nominal volume flows ranging from 0.5 through 0.7, 1.0, 1.5, 2.0, 3.0, and 4.5 up to 6.0 m³/min. The selection should be based on the actual maximum flow rate. If an adsorber is operated continuously above its intended range, the contact time between air and activated carbon is reduced, and the desired purification performance cannot be reliably guaranteed.

Temperature also plays a role: adsorption works better at favorable, lower temperatures than with very warm compressed air. Therefore, the entire treatment system should be designed so that the inlet conditions remain within the specified operating limits.

Buy activated carbon adsorbers

Anyone looking to purchase an activated carbon adsorber should first determine the actual residual oil content or compressed-air quality required. Next, the flow rate, pressure, temperature, pre-filtration, and pressure dew point should be evaluated. When used correctly, the activated carbon adsorber serves as a targeted fine-cleaning stage for compressed air with particularly low oil and odor levels—but it should always be part of a coordinated treatment chain.