Experimental Study On Collection Of Low Resistivity Fly Ash In A High Temperature Electrostatic Precipitator

Along with economic and social development and the continuous improvement of people’s living standards, growing energy demand on the one hand, puts forward severe challenges on China’s energy supply, on the other hand the emissions of pollutants from the energy utilization process also caused serious air pollution problem. As the key industrial energy consumption industry in our country, the industries of chemical, metallurgy, fire power and architectural material are the main sources of pollutants. It is noticed that hot gas clean-up is one of the key techniques for the energy conservation and emission reduction of the key industrial energy consumption industry, Electrostatic precipitator (ESP) is an option with small pressure drop, operation stability, strong adaptability which has been widely used in industry. How to get high particle collection efficiency under the condition of high temperature through electrostatic interaction and realize industrial application needs to be carrying out a systematic research. The present work revolves around the high temperature electrostatic precipitation technology, mainly studies the characteristics of corona discharge and particle collection at temperatures ranging from 90℃ to 450 ℃. Systematically analyzes the particle removal efficiency through electrostatic interaction with different operating parameters and particle characteristics, and put forward the method of particle conditioning, aiming to strengthen particle removal through electrostatic interaction at high temperature.Firstly, an experimental-scale electrostatic precipitator was built to investigate the characteristics of corona discharge and particle collection at various temperatures ranging from 90℃ to 450℃. The influence of several key parameters (temperature, applied voltage, particle concentration and gas flow velocity) on particle collection efficiency were analyzed, and the results indicate that the collection efficiency can reach higher than 98%as the gas temperature increases form 90℃ to 450℃, when the specific collection area (SCA) of the ESP is 46.5m2/(m3/s) and the inlet mass concentration of particles is about 750mg/Nm3.The collection efficiency increases with the increase of applied voltage, yet the growth rate reduces gradually. At the same voltage, as the temperature increases, the corona current increases substantially, which enhances the particle charging and finally improves the collection efficiency. However, at the same corona current, the particle collection efficiency decreases because of the low electric field intensity at high temperature. The increase in gas flow velocity reduces the particle collection efficiency, and the influence of gas flow velocity on PMi.o removal is much more significant than PMio. The increase in particle concentration enhances the collisions among particles and leads to particle coagulation, which is conducive to particle removal.Secondly, the voltage-current characteristics of the system with dust layer are experimentally studied. When the plate electrode is covered with dust, corona discharge current is inversely proportional to the particle resistivity and dust layer thickness. As the particle resistivity and dust layer thickness increase, the charge release rate through the dust layer will slow down, then increase the electrical field across the dust layer and enhance the inhibition on corona discharge. When the temperature increases, the particle resistivity decreases rapidly which reduce the electrical field across the dust layer and weaken the inhibition on corona discharge.Thirdly, three different characteristics of ash samples which from the coal-fired power plant, glass furnace and coal gasification are used to investigate the characteristics of particle removal efficiency. When temperature is below 250℃, the collection efficiencies of these three kinds of fly ash can reach higher than 98%. But after reaching the high temperature of 350℃, ash from coal gasification is easily re-entrained into the gas stream owning to the low resistivity and particle adhesion, which decreases the particle removal efficiency. The removal efficiency of the ash from glass furnace also decrease because of the low resistivity and the pyrolysis at high temperature. The method of particle conditioning is proposed to improve the low removal efficiency of low resistivity fly ash (ash from coal gasification) at high temperature. Use fine calcium carbonate powder as conditioning reagent, the resistivity and particle adhesion of the original ash has been improved, the particle removal efficiency has been significantly improved from 93.5% to 99.2%. With the increase of conditioning proportion, particle removal efficiency continue to improve until to an optimal proportion. After then, the effect of conditioning proportion on the removal efficiency is not obvious.Finally, a high temperature electrostatic precipitator of glass furnace was modified to improve the performance. The method of particle conditioning was adopted, by adding ca-base compound about 30 kg/h as a conditioning reagent, the outlet particle mass concentration dramatically declined from 103mg/Nm3 to 39mg/Nm3. The performance of the ESP was improved obviously and finally meet the demands of modification.