Numerical simulation of sorbent injection for mercury removal within an electrostatic precipitator: In-flight plus wall-bounded mechanism

Abstract

Powder sorbent injection upstream of an electrostatic precipitator (ESP) is of great potential for mercury removal from coal-fired power plants. Nevertheless, the migration and transformation of mercury and sorbents within an ESP remains poorly understand ascribing to internal inaccessibility of an operating ESP for direct measurement. A multi-field model was established to simulate mercury removal by sorbent injection within an ESP. The particle diameter, sorbent concentration, equilibrium constant (K), and operation voltage were key factors for affecting mercury removal. When the particle diameter increased from 20 to 80 μm, the in-flight (EIn-flight) and wall-bounded (EWall-bounded) adsorption efficiency decreased from 48.1% and 5.0% to 3.3% and 2.2%, respectively, indicating that decreasing the particle diameter would benefit mercury removal. Besides, EIn-flight and EWall-bounded climbed to 91.9% and 5.3% when increasing the sorbent concentration by four folds (i.e., from 2 to 8 g/m3), suggesting a promotional effect of higher sorbent concentration. The K value exhibited a similar influential trend as sorbent concentration, i.e., changing the K value from 300 to 60000 m3/kg enhanced EIn-flight and EWall-bounded to 48.3% and 5.1%, respectively. The electrohydrodynamic (EHD) flow played dual roles under various voltages. When the voltage was lower than 20 kV, the EHD flow slightly promoted mercury removal. However, an obvious decline of EIn-flight and EWall-bounded was observed when the voltage climbed from 20 to 35 kV. Such results adequately clarified key factors for affecting mercury removal performance, which provides the fundamental to elucidate the behaviors of particulate matter precipitation and mercury capture within ESPs.