(62g) Numerical Simulation of Electro-Hydrodynamically Influenced Gas-Particle Flows Affecting the Capture of Particles and Toxic Metals within Electrostatic Precipitators

The U.S. EPA’s Mercury and Air Toxics Standard (MATS) mandates reductions in emissions of toxic metals from electric utilities and industrial boilers.  Coal combustion is the primary source of toxic metal emissions and electrostatic precipitators (ESPs) are the most common particulate control device in use at large-scale power generation and industrial processing facilities. Numerous full-scale demonstration tests over the past decade have shown that cadmium and antimony partition largely to the particulate phase and are substantially collected along with particulate matter (PM) in the PM control device.  The partitioning of mercury, and to a lesser extent selenium, is much more susceptible to gas conditions, potentially leading to the release to the atmosphere of substantial fractions of the metals initially present in the fuel.  For all of these toxic metals, understanding the coupled fluid dynamic and electric fields that exist within ESPs, specifically as they relate to gas-particle mass transfer and adsorption of trace species, is a prerequisite for those facilities seeking to achieve the maximum removal efficiency of toxic metals within their existing pollution control equipment before investing in additional equipment to meet the MATS emissions caps.   The present study presents numerical simulation results of the internal gas-particle dynamics of ESPs that govern simultaneous PM collection and toxic metal adsorption.   Using a multi-physics computational software suite to solve the coupled set of fluid dynamic and electric field equations that underlie electro-hydrodynamic (EHD) fluid-particle phenomena, the computational results provide valuable insight into an environment whose extreme conditions preclude direct experimental measurement.  The results reveal the separate contributions to the total trace metals removal efficiency of in-flight adsorption by the suspended PM and wall-bounded adsorption by the collected PM retained on the ESP collection electrodes.   The secondary fluid flow features driven by the flow of ions between the discharge and collection electrodes are shown influence both in-flight and wall-bounded particle collection depending on the strength of the electric field and the inlet gas velocity.