| In recent years, China has suffered from heavy air pollution and haze weather, and the control of PM2.5(Particulate matter with diameter less than2.5micrometer) has evolved from a scientific research problem to a public issue. Viewing from a national scope, the air compound pollution is the main type of air pollution in China, and the particulate matter (PM) control of coal-fired flue gas is an important measure in controlling haze phenomenon. Therefore, the strictest emission standards of thermal power plant flue gas abatement in the world have been published. The standards require that the particle concentration in flue gas from the power plant should below30mg/Nm3for all, and below20mg/Nm3for the special regions. The major dust removal equipment in our country is dry electrostatic precipitator (DESP). However, due to back corona and re-entrainment, the removal efficiency of fine particles in dry ESP cannot meet the new standard. Wet electrostatic precipitator (WESP), by using a water film cleaning dust cake instead of rapping, can effectively control the fine particulate matter after the wet desulfurization tower and achieve ultra-low emissions of fine particulate matter, even to the gas turbine standard (5mg/Nm3). This paper focuses on the research of uniformity of water film and enhancement of fine particulate removal in WESP.Firstly, focusing on uniformity of water film, this paper studied the atomization characteristics during the process of single nozzle atomization, double nozzle spray impingement and spray wall-impingement with the Phase Droplet Particle Analyzer (PDA) applied to a pilot-scale experiment system. The results showed that the Sauter average particle diameter (SMD) and Weber number became more stable when the atomization angle and distance from the atomization axes increase. Wetted capability of different materials were tested subsequently, and pickled304stainless steel was chosen as the collection electrode. Based on the previous researches, a water film uniformity experiment platform was built. The effects of nozzle type, arrangement position and height were studied by water accumulated from independent region and the method to get uniform water film was found.Secondly, a wire-plate bench scale wet electrostatic precipitator (WESP) with single channel was designed to study the enhancement of fine particle removal efficiency. The influences of flue gas characteristics, spray nozzle parameters and discharge electrode geometry on discharge characteristics as well as particle collection efficiency were studied in this paper. The results showed that since electrons are easy to attach to SO2, the current density and removal efficiency all decreased as the concentration of SO2in precipitator increased. The current density decreased with the increase of dust concentration while the removal efficiency increased. Water spray had a profound influence on Ⅴ-Ⅰ characteristics. In order to get different number of droplets in precipitator, this study used different nozzles and spray rates. The results showed that the current and removal efficiency all increased with the increase of the numbers of droplets and the efficiency reached98.26%. The discharge electrode matching form is also key design parameters for WESP, the study compared three different discharge electrodes including wire, spiked band and barbed tube electrodes. The results showed that among the three types of discharge electrode, barbed tube electrode performed the best collection efficiency.Lastly, in order to simulate the real WESP operation condition, a pilot experimental platform was built after desulfurizing tower, Ⅴ-Ⅰ characteristics and removal efficiencies were studied and the results proved that WESP can effectively reduced the PM emission to3.4mg/m3, realizing the ultra-low emission target. |
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