Mercury is a regulated hazardous air pollutant. Power plants, cement kilns, waste incinerators, and industrial boilers all emit mercury in flue gas — and most jurisdictions now require treatment before discharge.
Activated carbon is the dominant technology for mercury capture from flue gas. Two approaches exist: powdered activated carbon (PAC) injection directly into the flue gas duct, and fixed-bed granular/pellet activated carbon adsorbers downstream of particulate control. This guide covers both methods, the carbon specifications that determine performance, and how to select the right product for your plant.
| Regulation | Scope | Mercury Limit | Status |
|---|---|---|---|
| U.S. EPA MATS (2012) | Coal- and oil-fired EGUs >25 MW | 1.2 lb/TBtu
(existing coal units) |
In effect; 2024 amendments
repealed Feb 2026 |
| EU Industrial Emissions
Directive (IED) / BREF |
Large combustion plants,
waste incineration |
1–10 μg/Nm³
(varies by sector) |
In effect; BAT-AELs
under periodic review |
| Minamata Convention
on Mercury |
All signatory
countries (140+) |
BAT/BEP for new sources;
national plans for existing |
In force since 2017;
phase-down obligations tightening |
| China GB 13223-2011 | Thermal power plants | 0.03 mg/Nm³ | In effect; ultralow emission
standard even stricter in some provinces |
Even in jurisdictions where enforcement has relaxed — for example, the U.S. EPA repealed the 2024 MATS amendments in February 2026 — the original 2012 MATS rule remains in effect. Most coal-fired plants that already installed mercury control equipment continue operating it. And internationally, the trend is toward stricter limits, not looser ones: the EU's BAT-AELs and China's ultralow emission standards both push mercury limits below what MATS requires.
Mercury in flue gas takes three forms, and the form determines which removal technology works best:
| Mercury Form | Symbol | Characteristics | Removal Method |
|---|---|---|---|
| Elemental mercury | Hg⁰ | Gaseous, insoluble in water,
not captured by scrubbers or ESPs |
Activated carbon adsorption (PAC
or fixed bed) |
| Oxidized mercury | Hg²⁺ | Water-soluble, captured by
wet scrubbers and ESPs |
Wet FGD scrubbers,
ESPs, or activated carbon |
| Particulate mercury | Hg(p) | Bound to fly ash particles | Particulate control
(ESP, baghouse) |
Elemental mercury (Hg⁰) is the hardest to capture — it passes through conventional pollution control equipment (scrubbers, ESPs) without being removed. This is exactly where activated carbon becomes essential. Activated carbon adsorbs Hg⁰ from the gas stream, either through physical adsorption or chemical reaction on the carbon surface.
The ratio of Hg⁰ to Hg²⁺ in flue gas varies by fuel type: bituminous coal produces more Hg²⁺ (easier to capture with existing equipment), while subbituminous and lignite coals produce more Hg⁰ (requires activated carbon injection for compliance).
Powdered activated carbon injection is the most widely deployed mercury control technology for coal-fired power plants. The process is straightforward:
| Parameter | Typical Range | Notes |
|---|---|---|
| PAC injection rate | 1–10 lb/MMacf | Higher rates for Hg⁰-dominant
flue gas (subbituminous/lignite) |
| Particle size (d₅₀) | 10–25 μm | Finer particles = faster adsorption
kinetics but more ESP penetration risk |
| Injection point | Upstream of ESP or baghouse | Baghouse provides longer contact
time and better performance |
| Flue gas temperature | 250–400°F (120–200°C) | Lower temperatures favor adsorption;
above 400°F performance drops sharply |
| SO₃ concentration | <5 ppm preferred | High SO₃ competes for adsorption
sites and degrades performance |
PAC injection with a downstream baghouse consistently delivers >90% mercury removal. With an ESP only, removal rates are typically 50–80%, because the shorter gas-carbon contact time (seconds vs. minutes in a baghouse filter cake) limits adsorption.
Standard (untreated) PAC works well for Hg²⁺ capture and for flue gas from bituminous coal, which naturally produces more oxidized mercury. For subbituminous and lignite coals — where elemental mercury (Hg⁰) dominates — brominated PAC is often needed.
Brominated PAC contains bromine compounds that oxidize Hg⁰ to Hg²⁺ on the carbon surface, making it adsorbable. This allows injection rates 40–60% lower than standard PAC for the same removal efficiency. The tradeoff: brominated PAC costs more per ton, and the bromine content can affect fly ash quality for concrete recycling.
For waste incinerators, cement kilns, and industrial boilers, fixed-bed activated carbon adsorbers offer an alternative to PAC injection. These systems use granular (GAC) or pelletized activated carbon in a packed bed or moving bed configuration.
Advantages over PAC injection:
Disadvantages:
Fixed-bed systems are standard practice in European waste incineration plants, where they're often combined with lime/calcium reagent injection to also capture acid gases (HCl, SO₂).
Standard activated carbon specifications (iodine number, BET surface area) do not directly predict mercury removal performance. The critical factors are:
For elemental mercury (Hg⁰) capture, impregnated activated carbons significantly outperform unimpregnated carbon. Common impregnants:
| Impregnant | Mechanism | Best Application |
|---|---|---|
| Sulfur (S) | Hg⁰ reacts with S to form
HgS (cinnabar) — stable, non-leachable |
Natural gas processing,
LNG, industrial flue gas |
| Bromine (Br) | Oxidizes Hg⁰ to Hg²⁺ for
enhanced adsorption |
Coal-fired power
plants (PAC injection) |
| KI (Potassium Iodide) | Hg⁰ reacts with KI
to form HgI₂ |
Waste incinerators,
low-temperature gas streams |
| Chloride (HCl, CaCl₂) | Promotes Hg⁰ oxidation
on the carbon surface |
Enhanced performance
in low-chloride coals |
Sulfur-impregnated carbon is the most widely used for fixed-bed mercury removal because HgS is thermally stable and passes TCLP leaching tests. For PAC injection in coal plants, brominated carbon dominates because of its lower injection rate requirement.
Both coal-based and coconut shell-based carbons are used for mercury applications. Coal-based pelletized carbon is more common in fixed-bed flue gas systems because of its broader pore size distribution (better for large Hg-impregnant complexes) and higher mechanical strength at the larger pellet diameters needed for low pressure drop.
Mercury adsorption on activated carbon is strongly temperature-dependent. Below 300°F (150°C), adsorption capacity is highest. Above 400°F (200°C), physical adsorption weakens, and even chemisorption (with impregnants) becomes less efficient. If your flue gas is above 350°F, consider gas cooling before the carbon treatment stage.
Waste incinerators and some industrial boilers must control both mercury and dioxins/furans (PCDD/F). Activated carbon is effective for both pollutants, and a single fixed-bed system can handle both simultaneously.
Dioxins adsorb onto activated carbon through a similar mechanism to mercury — surface adsorption driven by van der Waals forces. The key difference: dioxin adsorption favors carbons with high mesopore volume (pores 2–50 nm), because dioxin molecules are large and need accessible pore structures.
For combined mercury + dioxin removal:
European waste incineration BAT/BREF guidelines typically specify activated carbon injection rates or fixed-bed contact times sufficient for both mercury and dioxin compliance in a single treatment step.
Huamei manufactures pelletized activated carbon and powdered activated carbon for gas-phase applications. For mercury removal from flue gas:
We supply activated carbon to power plants, cement kilns, and waste incinerators in more than 40 countries. If you're planning a mercury control upgrade or building a new treatment system, send us your flue gas composition data — temperature, Hg speciation (if available), SO₂/SO₃ levels, particulate loading — and we'll recommend the appropriate carbon grade and estimate consumption rates.
For PAC injection in coal-fired power plants, brominated powdered activated carbon delivers the best performance at the lowest injection rate, especially for subbituminous and lignite coals with high elemental mercury (Hg⁰). For fixed-bed systems in waste incinerators and industrial applications, sulfur-impregnated pelletized activated carbon is the standard choice because it forms stable HgS that passes leaching tests.
PAC injection with a downstream baghouse typically achieves >90% mercury removal. PAC injection with an ESP only achieves 50–80%. Fixed-bed activated carbon adsorbers can exceed 95% removal when properly designed with adequate contact time and appropriate impregnation chemistry.
Yes. Activated carbon adsorbs both mercury and dioxins/furans (PCDD/F) from flue gas. A single fixed-bed activated carbon system can be designed to handle both pollutants simultaneously, which is standard practice in European waste incineration plants. The carbon should have sufficient mesopore development to accommodate the large dioxin molecules.
Standard PAC relies on physical adsorption to capture mercury. Brominated PAC contains bromine compounds that chemically oxidize elemental mercury (Hg⁰) to oxidized mercury (Hg²⁺) on the carbon surface, making it much easier to adsorb. Brominated PAC typically requires 40–60% lower injection rates than standard PAC for the same mercury removal efficiency, especially in flue gas from subbituminous and lignite coals.
It depends on the mercury concentration and local regulations. In the U.S., spent mercury-laden carbon must pass the TCLP (Toxicity Characteristic Leaching Procedure) test. Sulfur-impregnated carbons form HgS (cinnabar), which is highly stable and typically passes TCLP, allowing disposal as non-hazardous waste. Untreated spent carbon with high mercury loading may fail TCLP and require hazardous waste management. Always test spent carbon before disposal and follow local environmental regulations.
Planning a mercury control system? Send us your flue gas data and compliance targets. We'll recommend the right activated carbon — PAC, pelletized, or impregnated — and provide samples for testing.
