(639e) Elemental Mercury Oxidation in an Electrostatic Precipitator with in-Situ Soft X-Rays

Nonthermal plasma--based techniques are considered promising for oxidizing elemental mercury (Hg⁰) in flue gas from coal combustion. In this study, we investigated Hg⁰ oxidation in a DC (direct current) corona electrostatic precipitator (ESP) coupled with in-situ soft X-rays. Soft X-rays enhanced Hg⁰ oxidation by promoting electron generation, creating a large quantity of oxidizing radicals, such as monoatomic oxygen (O) and ozone molecules (O₃). Positive corona discharges worked better in Hg⁰ oxidation than negative ones, because they generate more high energy electrons, a finding which was supported by plasma simulations of soft X-ray--coupled ESP. Reaction mechanisms were further studied in single gas environments where pure oxygen (O₂), nitrogen (N₂), or carbon dioxide (CO₂) was the carrier gas. In the CO₂ case, Hg⁰ could not be oxidized by ESP operation alone, but it could be oxidized with ESP and soft X-rays. This result indicates that soft X-ray enhancement has even greater potential for Hg⁰ oxidation by ESP when high concentrations of CO₂ are present in flue gas, such as in the oxy-combustion case. The effects of titanium dioxide (TiO₂), silicon dioxide (SiO₂), and potassium iodide (KI) particles on the oxidation processes were also studied. When the soft X-ray--coupled ESP technology is applied to mercury capture from flue gas, it still retains the co-benefit of capturing particles.