Enhanced mercury control but increased bromine and sulfur trioxides emissions after using bromine injection technology based on full-scale experiment
Abstract Controlling mercury emissions has been a global and national goal with the implementation of the Minamata Convention on Mercury. Bromine injection technology could be used to reduce mercury emissions from coal-fired power plants. In this study, the final emitted Hg concentrations from the tested plant that combusts bituminous coal continuously decreased as the Br injection amount increased. Bromine injection could control the mercury concentrations below 1 µg/Nm3 at an injection rate of 30 mg/kg (bromine/coal). The presence of bromine improved mercury adsorption and oxidation in the selective catalytic oxidation system (SCR) and promoted synergic mercury removal in the fabric filter (FF) and wet flue gas desulfurization system (WFGD). However, we observed increased bromine escape as the bromine injection rate increased, although the increases in the emitted bromine concentrations were not fully proportional to the amount of bromine injected. Additionally, the emitted concentration of sulfur trioxides simultaneously increased from 0.43 mg/Nm3 at baseline to 0.73 mg/Nm3 at an injection rate of 30 mg/kg. The increased emissions of sulfur trioxides could be attributed to the combined effects of accelerated sulfur dioxide oxidation in FF and WFGD, and decelerated sulfur trioxide reaction on the surface of the fly ash. This study aimed to draw attention to the extensive strong oxidation properties of bromine and the potential environmental risk of using bromine injection technology.