Search

• Multi-field modeling on simultaneously removing mercury and particulate matter. • The mass transfer module shows relatively higher accuracy than previous models. • Sorbent particle size predominates over simultaneous removal efficiency. • The influences of other typical operating parameters are carefully discussed. • EHD conditions have complex effects on capture of mercury and particulate matter. A computational fluid dynamics (CFD) model coupled with gas-particle mass transfer, electrohydrodynamic (EHD) effect, electric field, particle motion and particle charging is established to advance the understanding of combined particulate matter precipitation and mercury capture within industrial electrostatic precipitators (ESPs). The comparisons between experimental data and numerical results demonstrate that this model can reasonably predict the mercury removal efficiency by powdered sorbent injection (PSI). The mechanism of simultaneous removal of mercury and particulate matter is then discussed in detail by considering the complex interactions among multi-physics. The influences of particle size, mercury concentration, particle injection rate and the EHD effect are investigated. The simulation results indicate that the mercury removal process is primarily controlled by the sorbent particle residence time, surface area and mass transfer rate. Accordingly, reducing the size of sorbent particles (activated carbon) can promote mercury removal efficiency while decreasing the particle collection efficiency. Increasing the initial mercury concentration and adsorbent mass loading also benefit mercury adsorption by influencing the mass transfer rate and the surface area. The EHD effect plays important roles in mercury removal and particle collection by means of altering the flow patterns and particle migration. The two mechanisms of in-flight and wall-bounded mercury adsorption affected by ionic wind are also evaluated and some interesting phenomena are observed. [ABSTRACT FROM AUTHOR]

Electrostatic precipitators (ESPs) separate particles from flue gas by corona discharge and accompany by the generation of ionic wind. In this work, a Computational Fluid Dynamics model was presented to investigate the effects of ionic wind on flow field and particle precipitation in a honeycomb ESP in terms of the coupled processes among corona discharge, gas flow, particle charging and transport. Results indicated that the electric field and ion charge density around the needle tips were highest and respectively reach 2.5 × 106 V/m and 0.164 C/m3 in the gas without suspended particles, which played a key role in corona-electrostatic field. The maximum velocity of ionic wind could reach 13.81, 11.74 and 9.42 m/s under the applied voltage of 27, 21 and 15 kV, and ionic wind velocity sharply decreased away from the needle tip. Meanwhile, the flow field could be divided into three regions (ionic wind affected region, vortex and back flow region) according to the direction of gas flow velocity. When the electrically neutral particles with a spherical shape were injected into ESP at the entrance, the charged particles were transported by drag force and electric force, and inhomogeneous distribution of the deposited particle has occurred because of ionic wind. More intense vortices were formed with the increase in applied voltage, and promoting the particle precipitation process. Moreover, higher applied voltage enhanced the aggregation of particles in the upstream, and reduced the dead zone of deposited particles in the downstream. The ionic wind generated by corona discharge strongly disturbed the flow field and particle precipitation process. Image 1 • A 3D spike-honeycomb ESP model was established to study the role of ionic wind. • The distributed pattern of the electric field and ion charge were investigated. • High velocity ionic wind was generated near the tips and could reach 13.81 m/s. • The flow field of gas phase was divided into three regions because of ionic wind. • The correlation between the ionic wind and particle precipitation were analyzed. [ABSTRACT FROM AUTHOR]