Characteristics of the mercury vapor removal from coal combustion flue gas by activated carbon using H₂S

Removal of Hg⁰ vapor from the simulated coal combustion flue gases with a commercial activated carbon was investigated using H₂S. This method is based on the reaction of H₂S and Hg over the adsorbents. The Hg⁰ removal experiments were carried out in a conventional flow type packed bed reactor system in the temperature range of 80-150 °C using simulated flue gases having the composition of Hg ⁰ (4.9 ppb), H₂S (0-20 ppm), SO₂ (0-487 ppm), CO₂ (10%), H₂O (0-15%), O₂ (0-5%), N ₂ (balance gas). The following results were obtained: in the presence of both H₂S and SO₂, Hg removal was favored at lower temperatures (80-100 °C). At 150 °C, presence of O₂ was indispensable for Hg⁰ removal from H₂S-SO₂ flue gas system. It is suggested that the partial oxidation of H₂S with O₂ to elemental sulfur (H₂S+1/2O₂=S _ad+H₂O) and the Clause reaction (SO₂+2H ₂S=3S_ad+2H₂O) may contribute to the Hg ⁰ removal over activated carbon by the following reaction: S _ad+Hg=HgS. The formation of elemental sulfur on the activated carbon was confirmed by a visual observation.