Activated carbon filters for air

An activated carbon filter removes odour and volatile organic compounds (VOCs) from air. The compounds stick to the surface of the carbon; this is called adsorption. Activated carbon is by far the most widely used material for this technique. These filters are used in air handling and ventilation, and on extracted process air in industry.

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How does an activated carbon filter work?

Plain activated carbon holds compounds with weak physical forces, the Van der Waals forces. That works well for odour and VOCs. Plain carbon captures gases such as H2S, HCl, HF and SO2 to a lesser extent. For those gases the carbon is impregnated with a chemical, so the gas is also bound chemically. This is called chemisorption.

For VOCs, a filter with activated carbon or zeolite removes 90 to 99 per cent from the exhaust gas, according to the Dutch government's Informatiepunt Leefomgeving (iplo.nl). The exact figure depends on the set-up and the operating conditions.

Can a full carbon filter start to smell again?

Yes. Adsorption is reversible. Once the carbon is saturated, the filter stops working and, depending on the conditions, can start to release compounds itself. That is why every carbon filter has a service life: the time the medium works before it has to be replaced.

Which carbon for which compound

With impregnated carbon, the reaction with the gas is almost irreversible. If the air holds a mixture, one filter can combine several media. Unsure about the medium? Ask for advice.

Types of industrial activated carbon filters

• Filter cartridges and filter modules. Carbon cartridges (cylinders) and modules filled with activated carbon.
• Carbon panel filters, disposable boxes and filter plates. Carbon in panel, box or plate form, also as a disposable version.
• Bag and compact filters with carbon media. For dust and odour in one filter in the air handling unit.
• Loose activated carbon. Filter media for filling filters and drums, as pellets or granules, non-impregnated or impregnated.
• Filter installations. Deep bed scrubbers, inline odour filters, vent filters and mobile units. See Filter installations.

The largest single carbon filter in this range handles 50,000 m³/h. With several filters in parallel or in series, 100,000 m³/h is possible. Does the filter have to fit into an existing installation, with ductwork and changes? Then the installation is designed and built turnkey.

What we need for sound advice

Advice starts with the compounds and their concentration, the flow rate, the temperature and humidity, the efficiency you need and the service life. See Filter installations.

And if nobody knows what is in the air?

A gas analysis measures only one moment, and the make-up of an exhaust gas can be different the next day. A test filter on a side stream of your own air shows which medium works, how much carbon you need and how long it lasts. See Filter unit rental.

Replace or regenerate?

Saturated carbon is either destroyed or regenerated. In regeneration (desorption), the compounds are flushed out of the carbon with a gas, heated or not, or under vacuum. This can be done only a limited number of times; after that, the medium still has to be replaced.

The medium can be changed with a vacuum truck or with an exchange unit. See Media replacement.

Rent instead of buy

Mobile activated carbon filter units are available for rent and can be in use within 2 to 3 days. See Filter unit rental.

Activated carbon or another technique?

With heavy pollution, the carbon filter can sit behind another technique that removes most of the load first; the carbon then brings the emission below the limit value. A carbon filter can also be the last stage, in case an earlier stage fails. If the load is very high, with a lot of air and high concentrations, a biological filter can remove most of it first, before the carbon. That only works well with a stable, continuous airflow.

See Activated carbon or scrubber.

Where activated carbon filters are used

In industry it is often VOCs from solvents. At water treatment plants and sewage pumping stations, H2S is usually the source of the odour. For sewage pumping stations and treatment plants we have separate sites: odour at sewage pumping stations and odour at wastewater treatment plants.

Frequently asked questions

Does activated carbon also remove H2S from air?

Plain carbon does so only to a lesser extent. For H2S, carbon with an alkaline impregnation is used.

When should I replace the medium?

Before it is saturated, because a saturated filter no longer works. A test filter on a side stream gives a service life based on your own air.

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