| Electrostatic precipitator（ESP）, widely used for dust removal in coal-fired power plant, achieving a collection efficiency of more than 99.5% for bulk ash particles, becomes difficulty to meet the more strict standards of 20mg/m3 due to its deficiency for capturing fine particulate(e.g. PM2.5). Recently, the extra cold-side ESP, reducing flue-gas operational temperature to improve dust removal performance, has been used gradually in engineering applications for the capture of these fine particles. However, the fundmental studies on the mechanisms of performance improvement and coal applicability of extra cold-side ESP are still absent. In the paper, the field tests of ESP are firstly carried out to evaluate its dust removal performance. Then, the interaction model of SO3 and particles is established to analyze their synergetic control as well as the coal applicability. The effect of temperature on charging distribution and removal efficiency of dust particles is studied by a lab-scale experiment.Tests of particle size distributions are carried out at the inlet and outlet of industrial ESP by using electrical low pressure impactor（ELPI）. The data of both number concentration and mass concentration indicate that the collection efficiencies of PM2.5 and PM10 are continuously increased with the decreasing gas temperature from 130℃, to 93℃ and eventually to 84℃. The on-line tests of dust resistivity shows a decrease from 6.09×1011 to 2.46×1011 and 1.60×1011Ω?cm, corresponding to temperatures of 130℃, 93℃ and 84℃, respectively. The particle charging distributions under different temperatures testify the improvement of charging characteristic with lower temperature.Based on the existence form of SO3 under different flue gas conditions, the formation process of sulfuric acid from SO3 is analyzed. The interaction of sulfuric acid and dust particles is studied by using a population balance model of coagulation process. It is found that that the sulfuric acid tend to collide with large particles and deposite on them. The results show that the deposition rate of sulfuric acid on particles increases as the mass ratio of dust to SO3（D/S） increases. The deposition rate could not reach 40% even with the D/S of 200 when SO3 content is 5ppm, while the deposition rate could exceed 80% with SO3 content of 40 ppm and D/S of 100. This reveals that both the SO3 content and D/S influence the deposition rate. It indicates these two parameters should play an important role in optimizing the performance of extra cold-side ESP equipped in coal power plants.The effects of temperature on discharge characteristics, dust removal efficiency and dust charging characteristics are examind by using a lab-scale extra Colder-side ESP setup. The corona current decreases and the breakdown voltage increases with the decreasing temperature. The minimum of size-dependent removal efficiencies always appear in the particle diameter range of 0.1-1μm in different opration voltage at 90℃ and 130℃. The distinction is that the minimum appears in the size of about 0.7μm under 130℃, meanwhile it would be about 0.3μm under 90℃. In contrast to ESP operated at 130℃, the ESP operated at 90℃ shows a remarkable improvement of dust charging distribution, especially for more residence time of particles in electric field. |
