Activated Carbon for Mercury Removal
Activated carbon is used to remove mercury from gas.
Activated carbon is an effective adsorbent and is widely used to effectively remove mercury (Hg) and other pollutants (such as dioxins, heavy metals, SO₂, NOₓ, etc.) in the flue gas treatment process of coal-fired power plants, waste incineration, metal smelting and other industries.
Forms of mercury in flue gas
Mercury in flue gas mainly has the following three forms:
1. Elemental mercury (Hg⁰): gaseous elemental mercury, chemically stable and not easy to be captured.
2. Oxidized mercury (Hg²⁺): such as mercuric chloride (HgCl₂), which is easily soluble in water and can be removed by wet scrubbing.
3. Particulate mercury (HgP): mercury attached to fly ash, which can be removed by dust removal equipment.
Challenges: Elemental mercury (Hg⁰) is difficult to be captured by traditional dust removal and desulfurization equipment, so special activated carbon or catalyst treatment is required.
Technology for removing mercury from flue gas with activated carbon
1. Activated carbon injection (ACI, Activated Carbon Injection)
- Principle: Powdered activated carbon (PAC) is directly injected into the flue to make it contact and adsorb mercury in the flue gas, and then captured by a bag filter or electrostatic precipitator (ESP).
- Applicable scenarios: coal-fired power plants, waste incineration plants, non-ferrous metal smelting, etc.
- Advantages: simple process, low transformation cost, and can effectively remove 80-90% of mercury.
- Disadvantages: large consumption, which may affect the reuse of fly ash.
2. Modified activated carbon (impregnated activated carbon)
- Since pure activated carbon has a weak adsorption capacity for elemental mercury (Hg⁰), it is usually chemically modified to enhance its adsorption capacity:
- Brominated activated carbon (Br-AC): It can efficiently oxidize and adsorb Hg⁰, suitable for coal-fired power plants.
- Sulfur impregnated activated carbon (S-AC): It can form stable mercuric sulfide (HgS) with Hg to prevent secondary release, and is suitable for incineration plants.
- Iodinated activated carbon (I-AC): can improve the adsorption capacity of mercury in low-temperature flue gas.
3. Combined mercury removal technology
- Activated carbon + wet flue gas desulfurization (WFGD)**: Activated carbon first adsorbs mercury, and then the wet flue gas desulfurization system removes the remaining Hg²⁺.
- Activated carbon + SCR (selective catalytic reduction): SCR catalyst promotes the oxidation of Hg⁰, which is more easily removed by wet flue gas desulfurization after conversion to Hg²⁺.
- Activated carbon + low-temperature plasma: plasma can activate mercury and improve the adsorption efficiency of activated carbon.
The advantages of activated carbon in flue gas demercurization High efficiency in mercury removal: especially modified activated carbon can greatly improve the capture rate of Hg⁰.
Applicable to a variety of flue gas treatment processes: can be used in conjunction with desulfurization, denitrification and other technologies.
Low transformation cost: compared with more complex catalytic demercuration technology, the investment in activated carbon injection system is lower.
Strong adaptability: suitable for different fuels (coal, garbage, biomass) and process requirements.
Conclusion
Activated carbon, especially modified activated carbon, plays an important role in flue gas mercury removal, especially in coal-fired power plants, waste incineration, smelting and other industries. For different working conditions, you can choose ACI injection method, modified activated carbon or combined mercury removal technology to achieve higher mercury removal efficiency.
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