Electron Beam Irradiation for Mercury Oxidation and Mercury Emissions Control

A variety of air pollution control strategies have been investigated to reduce mercury emissions from coal-fired sources. The most developed and deployed technologies are based on adsorption of mercury onto powdered activated carbon followed by carbon collection. Mercury oxidation over selective catalytic reduction catalysts followed by wet scrubbing is another potential technique, and tests suggest that emissions reductions of 20–80% are possible, but test results are variable and ultrahigh removal (95%+) is unusual. The objective of this study was to investigate the effectiveness of electron beam irradiation to oxidize mercury vapor, to improve mercury removal with wet scrubbers or wet electrostatic precipitators (ESPs). Metallic mercury vapor samples in air and other atmospheres were prepared at concentrations of approximately 16 μg/m3. Samples were electron irradiated at energy levels of 2.5–10 kGy, equivalent to 3.1–12.4 kJ/m3 stack gas. Results show that mercury oxidation rate was dependent on both the gaseous atmosphere composition and the irradiation energy level. At medium energy levels, approximately 98% of gaseous mercury vapor was readily oxidized. Electron beam irradiation demonstrated high levels of mercury oxidation at the bench scale, and the technology might help improve mercury removal in wet scrubbers or wet ESPs when employed as a primary or secondary mercury oxidation technique.