(Granulated) Vapour Phase Carbon Adsorption (GAC)
Typical Vapour-Phase Carbon Adsorption System
Process:
A remediation technology in which air pollutants are removed by physical adsorption onto activated carbon grains.
*Carbon can also be reacted with super-heated steam (steam reforming) to destroy halogenated solvents adsorbed on the activated carbon.
Limitations:
Note:
Costs range from ~$1,000-$40,000 depending on the size of unit.
It is more economical to pre-treat a VOC stream then use this vapour-phase GAC system as a finishing step.
A remediation technology in which air pollutants are removed by physical adsorption onto activated carbon grains.
- Activated Carbon is processed to create porous particles & large internal surface area.
- This enhances the adsorption of organic molecules & certain metal/inorganic molecules.
- The granular form of activated carbon is typically used in packed beds.
- The contaminated air flows until the carbon bed is saturated (contaminant concentration exceeds acceptable level).
- The vessels are connected in series or parallel & operate under atmospheric, negative, or positive pressures.
*Carbon can also be reacted with super-heated steam (steam reforming) to destroy halogenated solvents adsorbed on the activated carbon.
Limitations:
- Spent carbon may require hazardous waste handling/disposal
- Contaminants must be later destroyed (often thermal treatment).
- Reduced Carbon adsorption capacity if: relative humidity >50% or temperature > 38° C
- A high quantity adsorbed on the carbon bed reduces flow through, thus requiring periodic treatment as soon as becomes saturated.
- Some compounds (e.g. ketones) may cause carbon bed fires - high heat release upon adsorption.
Note:
- Rate of adsorption is affected by: the temperature, type and pore size of the carbon, the type and concentration of the contaminant & residence time in the bed.
- At high temperatures, the volatility of compounds increases - why their affinity for carbon reduces.
- Generally better adsorption of simple compounds at higher pH.
- If use regenerated carbon, it costs less but tends to have a lower adsorptive capacity than virgin carbon.
Costs range from ~$1,000-$40,000 depending on the size of unit.
It is more economical to pre-treat a VOC stream then use this vapour-phase GAC system as a finishing step.