Gas-phase activated carbon is used wherever an air stream carries organic vapours or odorous compounds that must be captured before discharge or recirculation. The same adsorption mechanism applies as in water, but the grades, the pore structure and the way performance is measured all differ.
Applications run from commercial HVAC filtration through solvent recovery to industrial emission control and odour abatement at wastewater and waste handling facilities.
Where gas-phase carbon is used
The common thread is a contaminant present at low concentration in a large volume of air, where adsorption is more practical than combustion or scrubbing.
- Volatile organic compounds
- Solvent vapours from coating, printing and chemical handling operations, captured either for emission compliance or for recovery and reuse.
- Odour control
- Hydrogen sulphide, mercaptans and amines at wastewater plants, pump stations, composting sites and rendering operations.
- HVAC and indoor air
- Removal of outdoor pollutants and indoor-generated organics in commercial buildings, often in combination with particulate filtration.
- Process and exhaust streams
- Industrial emission control where a stack must meet a discharge limit.
How gas-phase performance is measured
Gas-phase carbon is specified against different parameters from water-grade carbon. Buying a water grade for an air application, or the reverse, is a common and expensive mistake.
- Carbon tetrachloride (CTC) activity
- The conventional measure of gas-phase adsorption capacity, reported as a percentage by weight.
- Butane activity and butane working capacity
- Used where the carbon will be regenerated in service, since working capacity reflects what is usable across repeated cycles rather than total capacity.
- Hardness and particle size
- Determine pressure drop across the bed and resistance to attrition in high-velocity streams.
Granular, pelletized and impregnated grades
Pelletized carbon offers a uniform shape and lower pressure drop, which matters when a fan has to push large volumes through a deep bed continuously. Granular grades are common in lighter-duty and filter-frame applications.
Some compounds — hydrogen sulphide and certain acid gases among them — are handled far better by carbons impregnated with a reactive agent than by plain carbon, because the contaminant is chemically converted rather than simply held. Where an odour problem is dominated by one known compound, it is worth identifying it before selecting a grade.
Humidity and service life
Gas-phase beds are sensitive to relative humidity in a way water-phase beds obviously are not. Above roughly 50% relative humidity, water vapour begins to compete for pore volume and capacity for the target compound falls. Where a stream is close to saturation, conditioning the air or selecting a grade tolerant of moisture makes a substantial difference to bed life.
Common questions
Can water treatment carbon be used for air purification?
It is not advisable. Gas-phase and liquid-phase carbons are specified against different parameters — CTC or butane activity for air, iodine number for water — and are optimised for different pore structures and particle sizes. A water grade in an air application typically delivers poor capacity and excessive pressure drop.
How does humidity affect activated carbon in air service?
Water vapour competes with the target compound for pore volume. Above roughly 50% relative humidity, capacity begins to fall, and in near-saturated streams the reduction can be severe. Conditioning the air or selecting a moisture-tolerant grade helps preserve bed life.
What removes hydrogen sulphide odour?
Hydrogen sulphide is usually handled with an impregnated carbon, which converts the compound chemically rather than relying on physical adsorption alone. Plain carbon has comparatively limited capacity for it, so identifying the dominant compound before selecting a grade matters.
What shape of carbon gives the lowest pressure drop?
Pelletized carbon, because of its uniform shape and packing, generally produces a lower pressure drop than granular material of comparable size. That becomes important in deep beds and high-volume continuous systems where fan energy is a running cost.
Tell us what you are treating and we will match the grade before quoting.
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