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DC and sub-microsecond impulse energisation of electrodes in electrostatic precipitation

Mermigkas, Athanasios and Timoshkin, Igor and Macgregor, Scott and Wang, Tao and Wilson, Mark and Given, M (2011) DC and sub-microsecond impulse energisation of electrodes in electrostatic precipitation. In: 8th Technological Plasma Workshop, 2011-01-06 - 2011-01-07. (Unpublished)

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Abstract

Airborne fine particles generated by internal combustion engines, power plants and other industrial and domestic sources pose a potential health risk, and this risk is exacerbated by the increasing use of nano-particle based technologies. Particles of size less than two-and-a-half micrometers (PM2.5) have recently started to attract attention as they can be carried long distances, can stay airborne for long periods of time and can penetrate deep into the lungs. As a result, manufacturers of air cleaning systems for domestic and commercial use are continuously looking for more effective methods to reduce the concentration of PM2.5 airborne particulate matter. The present paper discusses the development of the scientific and engineering basis for the impulsive micro-electrostatic precipitation technology, which will use superposition of sub-microsecond high field pulses and DC electric field. Such short HV impulses allow application of significantly higher voltages to the active ionisation electrodes of the precipitation system without the initiation of spark breakdown. The breakdown properties of atmospheric air show that the reduction of the impulse duration from 2 µs to 200 ns results in a 2-fold increase in the breakdown voltage. Higher levels of electric field will help to generate higher ionic concentrations, resulting in efficient charging of the airborne particles and improved removal efficiency. This paper reports initial results on the development of the micro-ESP system and analysis of its efficiency. A coaxial micro-ESP precipitation chamber composed of plasma-generation and particle-collection electrodes has been designed. The transmission-line based impulse energising system is able to generate square sub-microsecond impulses with frequency up to 100 Hz and magnitude of a few tens of kV. The efficiency of precipitation of dust micron and sub-micron sized particles has been investigated using different voltage levels and frequencies in order to establish optimal electrode topologies and energisation modes. At the present stage the precipitation efficiency has been evaluated by weighting of the collected particles; in future it is planned to use a portable particle spectrometer. Positive and negative DC and impulse energisation of the ionizing electrode has been used. It has been shown that the polarity of the high voltage stress and energisation mode has significant influence on the precipitation efficiency.