Charging and dynamics of fine air-borne particles in impulsive electric fields

In recent years considerable efforts have been devoted to the monitoring of concentrations of particles with diameter less than 2.5 μm in the atmosphere. These PM2.5 particles are produced by both natural and anthropogenic sources, including internal combustion engines, smelters, coal power stations and other industrial plants. Fine and ultra-fine particles can stay airborne for a very long time due to their small size, and can penetrate deep within the human respiratory system, significantly increasing the risk of heart and lung diseases and asthma. Reduction of the concentration of PM2.5 particles is an important factor in the improvement of air quality, and efficient technologies for removal of fine and ultra-fine particles from the air are in high demand. One of the approaches used for removal of fine and ultra-fine particles from air-flows is corona charging and subsequent precipitation of these particles on the grounded electrode. In order to increase the efficiency of the particle charging and air cleaning process, it was proposed to use short high-voltage impulses in combination with a DC electric field to energize corona electrodes. It was shown that such superposition or combination of DC and impulsive charging results in an increase in the efficiency of the precipitation process. The present paper is focused on analysis of the impulsive charging process of air-borne particles and their dynamics in the external electric field. Both diffusion charging and field charging effects are taken into account. The proposed model allows calculation of a particle's velocity and displacement as a function of the HV impulsive parameters to be conducted. As a result, the efficiency of the precipitation process has been obtained for particles typically emitted by coal power plants: soot particles, salt particles and Condensable Organic Compounds. The optimal energisation parameters, that is, the magnitude of the applied HV impulses, their duration and their frequency, have been established for corona treatment of flue gas. These results will be used for further development and optimisation of the impulsive electrostatic precipitation technology for the removal of fine and ultrafine particles from atmospheric air.