Activated Carbon in Flue Gas Treatment: Mercury, Dioxins and Trace Removal

Part of the Activated Carbon: The Complete Guide — this article is one of the detailed pages in the guide.

Direct answer: In flue gas treatment, activated carbon works as a polishing adsorbent for pollutants that exist at trace concentration but carry high toxicity — mercury, dioxins/furans and residual organic species. It is injected as powder upstream of the bag filter, or used as fixed-bed or honeycomb polishing stages, and it is consumed in service rather than regenerated in place.

What carbon captures in flue gas

Pollutant	Typical form	Carbon role
Mercury	Hg⁰ vapor	Adsorption (often with halogen impregnation)
Dioxins/furans	Trace organic species	Adsorption + surface destruction
Residual VOCs	Mixed trace organics	Final polishing
SO₂/acid gases	Acidic species	Adsorption (impregnated carbons)

Powder injection vs fixed beds

Powder injection + bag filter — carbon powder is injected into the duct and collected on the filter cake, where contact continues. Cheap per kg, no regeneration, large carbon consumption; standard for mercury and dioxin control on incineration.
Fixed/honeycomb beds — gas passes through a structured carbon stage. Higher removal per unit carbon, lower dust burden, suitable where injection would contaminate downstream product or where the species need longer contact time.
Combined — injection for the bulk, fixed bed for the guarantee.

Impregnated carbons

Trace pollutants that plain carbon captures weakly are handled by impregnation:

Sulfur-impregnated carbon for mercury (forms stable HgS).
Bromine/iodine-impregnated for oxidized mercury capture.
Alkali-impregnated for acid gases.

Impregnation changes both capacity and disposal classification — spent impregnated carbon is hazardous waste in most jurisdictions.

Design cautions

Temperature — carbon adsorption falls sharply above ~150°C; injection points are chosen downstream of cooling.
Moisture — water competes for sites; condensation on the carbon is to be avoided.
Fire risk — hot spots in a carbon bed with adsorbed organics can self-heat; temperature monitoring and inerting provisions apply.
Disposal planning — spent carbon from mercury/dioxin duty is regulated waste; the disposal route must be budgeted from day one.

Manufacturer perspective

For trace-toxic duty we specify carbon type and injection position together with the bag filter design — the filter cake is part of the adsorption system. For polishing beds we size from the target outlet concentration and expected species, with replacement cycles written into the operating budget.

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