Catalytic oxidation of Hg⁰ by bromide over Ce-modified regenerated V-Mo/Ti catalyst: a field study conducted in a 600 MW power plant unit

Abstract

Mercury (Hg) is largely emitted from coal-fired power plants. For Hg purification, the oxidation of elemental Hg (Hg⁰) to Hg²⁺ in the flue gas over selective catalytic reduction (SCR) catalysts with halogen involvement is the most important step. Based on laboratory tests of Hg⁰ oxidation over cerium (Ce)-modified regenerated V₂O₅-MoO₃/TiO₂ (V-Mo/Ti) SCR catalysts in the presence of HBr, it is necessary to investigate how the Ce-modified catalysts perform in real power plants for further industrial application. Therefore, a 1-year field verification was conducted in a 600 MW power plant unit. The results showed that with increased CaBr₂ addition to coal, the rate-determining factor for Hg⁰ oxidation shifted from the intrinsic catalytic properties of SCR catalysts to bromide concentrations. Meanwhile, owing to the decomposition of CaBr₂, bromide could participate in Hg⁰ oxidation via adsorptive, homogeneous, and heterogeneous chemical processes. For NO_x, its removal efficiency decreased from 96.22% to 61.10% over the Ce-modified catalyst after 1 year of operation, with little effect exerted by CaBr₂, compared with a decrease from 95.79% to 43.92% over the unmodified catalysts. For SO₃, only 41.78 mg/m³ of SO₃ was generated from 6174.27 mg/m³ of SO₂ over the Ce-modified catalysts after 1 year of operation compared with 97.29 mg/m³ of SO₃ over the unmodified catalysts. This study verifies the long-term commercial applicability of Ce-modified regenerated V-Mo/Ti SCR catalysts in power plants.

Graphical abstract

Keywords

Regenerated V-Mo/Ti catalyst / Ce modification / Field verification / Hg⁰ oxidation / NO_x removal / SO₃ generation

Highlight

	● High-concentration bromide has bigger effects on Hg0 oxidation than Ce modification.
	● Bromides of HBr, Br and Br2 enhance Hg0 oxidation via three chemical processes.
	● Ce modification lowers decrease level of Hg0 oxidation efficiencies as SCR proceeds.
	● Ce modification contributes to higher NO x removal efficiency and anti-deactivation.
	● Small loadings of Ce limits SO2 oxidation to SO3 over the modified SCR catalysts.

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