Study On The Electrostatic Precipitatability And Escape Mechanism Of The Fine Particulate From Electrostatic Precipitator Of Coal-fired Boilers

The main collection way of the fly ash is electrostatic precipitator (ESP) in coal-fired power plants in China because of its higher collection efficiency and lower secondary pollution. With the development of economy, the requisition for environmental quality will be improved constantly, the air pollution will be more noticeable, and the emission standard of particles in power plants is increasingly strict, so the concentration of fly ash escaped from ESP could not meet the demand of emission standard. The fine fly ash can not be disposed effectively, it is one of the main factors that influenced the efficiency improvement of ESP. In this paper, the formation mechanisms of fly ash during coal combustion, the particle size distribution, resistivity and element composition, the charging mechanism and mechanical behaviors of fly ash in ESP and escaped from ESP have been studied, and the escape mechanism of fine fly ash has been analysed. The effective methods of collecting the fly ash escaped from ESP have been put forward and demonstrated. The mostly harvest and innovation are as follows.(1) The fragment model of coarse particle and the vaporization-condensation model of submicron fly ash have been established and calculated, and the size distributions of fly ash sampled from ESP of four power plants have been experimented by Bacho. The results indicate that the curve of the model calculation tallies with the experiment. The size distributions of fly ash display two peaks around 10μm and 0.1μm respectively.(2) Under the operating mode, the charged particles can cause the electric field change in ESP, such as ion electric current weakening, original electric field distorting and voltage of dust layer influence particle charging, etc. The charging model of particle group has been established and the current decay coefficient has been calculated. The results show as follows.①Regarding 0-10μm particle, it is too remarkable to be neglect that the ion diffusion influences the current decay coefficient.②The particle is finer, the decay current caused by ions diffusion is more obvious.(3) The element compostion, resistivity and size distribution of fly ash have been experimented. The results show that the surface free energy is connected with the fusing characteristic of fly ash, and the surface free energy is enough high that solid can form fine particle.So the element composition is different with different size of fly ash. The content of SiO2, TFeO decrease and Al2O3, CaO, MgO increase gradually with the diminishing of grain-sizes of fly ash. Before resistivity is peak value, the coarse particle has higher resistivity than the fine particle, while the law is contrary after resistivity peak. The reasons are that the resistivity is influenced by surface and volume conductivity, the fine particle has bigger porosity, and the content of SiO2 and TFeO contributed to decline resisitivity is lower in the fine fly ash than coarse ash, while the content of Al2O3, CaO and MgO contributed to...