Abstract:

The MnO_x modified activated carbon (MnO_x/AC) was prepared by impregnation method to simulate the removal of elemental mercury in coal combustion flue gas. The effects of Mn loading on sorbent, sorption temperature and flue gas composition on removal performance of elemental mercury in simulated flue gas were investigated. Mechanism of SO₂ inhibition on mercury removal was revealed. The average Hg⁰ removal efficiency on MnO_x/AC is 97.0% at 150℃ in 3 hours when Mn loading is 14% (mass) with 5% (vol) O₂ in simulated flue gas. A small amount of O₂ and trace amounts of HCl and NO promoted the removal of mercury in gas phase, while trace amount of SO₂ inhibited it. TG/DTG, XPS and Hg-TPD analyses of spent MnO_x modified activated carbon indicated that the inhibition of SO₂ on Hg⁰ removal of modified activated carbon is due to the consumption of lattice oxygen in MnO_x by formation of sulfate that occupies active sites on the surface of 14Mn/AC. This inhibition of SO₂ on removal of elemental mercury could be effectively reduced by adding trace amount of NO.

Key words: activated carbon, sorption, flue gas, elemental mercury, MnO_x, SO₂

摘要：

采用浸渍法制备了MnO_x改性活性炭（MnO_x/AC），用于模拟煤燃烧烟气中的元素态汞的脱除。实验研究了吸附剂的Mn负载量、吸附温度和烟气组分对所制备的改性活性炭的脱汞性能的影响，以及SO₂对活性炭脱汞的抑制作用机理。研究结果表明，当模拟烟气中含有5%（体积）O₂，Mn负载量为14%（质量），吸附温度为150℃时，改性活性炭的平均脱汞效率为97.0%（3 h）。模拟烟气中少量的O₂和微量的HCl、NO均对汞的脱除起促进作用，而微量的SO₂则对汞的脱除有抑制作用。通过吸附后的MnO_x改性活性炭的TG/DTG、XPS和Hg-TPD分析，推测SO₂对改性活性炭脱汞的抑制作用是由于其消耗MnO_x中的晶格氧，形成的硫酸盐占据了14Mn/AC表面上的活性位点所致。模拟烟气中微量的NO可以有效降低SO₂对脱汞的抑制作用。

关键词: 活性炭, 吸附, 烟道气, 元素汞, MnO_x, SO₂