Numerical simulation of homogeneous elemental mercury oxidation within an electrostatic precipitator

Abstract

The corona discharge in electrostatic precipitator (ESP) can contribute to homogenous Hg⁰ oxidation, thus favoring the simultaneous removal of mercury by the existing air pollution control devices in coal-fired power plant. A multi-field model consisting of reaction kinetics and dynamics was established to simulate the Hg⁰ oxidation performance in ESPs. The HCl dissociation products (i.e., Cl and Cl₂) were responsible for the oxidation of Hg⁰ to HgCl₂ and HgCl, in which the Hg⁰ oxidation efficiency (E_Hg) was increased from 13.3 % to 52.6 % with the increase of HCl concentration from 1 to 4 ppm. The increase of O₂ concentration from 2 % to 8 % resulted in 2.1 % reduction of E_Hg, which was primary attributed to the inhibition of HCl dissociation process to form Cl-containing species. As the H₂O content increased from 3 % to 12 %, E_Hg rose from 25.9 % to 29.1 %, due to H₂O dissociation products (i.e., H and OH) enhancing the formation of Cl-containing species from HCl dissociation. The voltage fluctuations demonstrated dual effects on E_Hg: increasing from 35 kV to 40 kV reduced efficiency from 27.3 % to 26.4 %, attributed to diminished Cl-containing species, whereas further increasing to 50 kV enhanced efficiency to 32.1 % due to increased production of O-containing substances. A higher flow rate facilitated the escape of reactive chemical species from ESPs. The E_Hg decreased from 36.3 % to 17.5 % when the flow velocity increased from 0.1 to 0.25 m/s. These results clarified the key factors for affecting Hg⁰ oxidation within an ESP, which provides the fundamental to simultaneously control Hg⁰ emission from coal-fired power plants.