(54k) Numerical Simulation of Wire-Plate Electrostatic Precipitator - Effect of Particle Concentration

Electrostatic Precipitators (ESP) have been widely used to separate fine particles from large scale industrial exhaust gases, such as coal fired power generation plants. Design optimization is critical to meeting the increasingly strict flue gas discharging standard. Due to the complex nature in the interaction among electric field, gas-particle flow and particle charging, there are a number of phenomena that have not been well understood. In the present work, the model developed earlier (“Numerical modelling of electrostatic precipitation: effect of gas temperature”, J. Aerosol Science, 77, 2014, 102-115) is improved from one-way to two-way coupling. Coupled electric field, gas-particle flow and particle charging processes are simulated using Eulerian-Lagrangian method in Computational Fluid Dynamics (CFD), for an electrostatic precipitator with four-wire electrodes. For other dimensions, wire diameter is 3.5 mm, wire-to-wire spacing 0.24m, wire-to-plate 0.2m. The effect of particle charging on the electric field distribution, IV characteristics and particle collection efficiency are investigated, as the entry particle loading/concentration varies from 0 up to 30 g/Nm³ for a particle size of 2.5mm under gas velocity of 1 Nm/s and fixed voltage Va=60 kV.

The simulation results show that the electric field can be distorted significantly by the secondary electric field generated by the space charges on the floating particles, which mostly reduces particle collection efficiency, except at low loading up to 5 g/m3. Under fixed voltage the corona current decreases as particle loading increases. As particle loading increases to some point, the corona current from the downstream wires can be extinguished completely. At high particle loadings, corona ion charges may not be able to reach the plate due to the absorption of passing particles. So-called “electrical shield” phenomenon arises when solid loading increases above 10 g/Nm³, i.e., the electric streamlines in a small zone around the last wire reverse direction locally. A charged particle, once falls accidently within the zone, could be trapped and be attracted to the same wire. Thus this wire is subject to heavier dust deposition.