Role of SO₂ for elemental mercury removal from coal combustion flue gas by activated carbon

In order to clarify the role of SO₂ in the removal of mercury from coal combustion flue gas by activated carbon, the removal of Hg⁰ vapor from simulated coal combustion flue gas containing SO₂ by a commercial activated carbon (AC) was studied. The Hg⁰ removal experiments were carried out in a conventional flow type packed bed reactor system with simulated flue gases having a composition of Hg⁰ (4.9 ppb), SO₂ (0 or 500 ppm), CO₂ (10%), H₂O (0 or 15%), O₂ (0 or 5%), and N₂ (balance gas) at a space velocity (SV) of 6.0 × 10⁴ h^-1 in a temperature rang 60-100 °C. It was found that, for SO₂ containing flue gas, the presence of both O₂ and H₂O was necessary for the removal of Hg⁰ and the Hg⁰ removal was favored by lowering the reaction temperature in the order of 60 > 80 > 100 °C. The presence of SO₂ in the flue was essential for the removal of Hg⁰ by untreated activated carbon. The activated carbons pretreated with SO₂ or H₂SO₄ prior to the Hg⁰ removal also showed Hg⁰ removal activities even in the absence of SO₂; however, the presence of SO₂ also suppressed the Hg⁰ removal of the SO₂-pretreated AC or H₂SO₄ preadded AC.