电除尘技术发展与应用

Development and Application of Electrostatic Precipitation Technology

电除尘技术是目前主要的颗粒物分离和捕集技术之一,为此,根据目前的研究热点和难点,对现代电除尘技术的现有进展与应用进行了综述。研究结果表明:1)在比电阻与电除尘方面,面对细颗粒物控制的需求,需要通过燃煤特性、高压电源、电除尘器(ESP)本体选型等多方面优化来实现超低排放目的;颗粒物特性如形状、粒径和比电阻等都会影响电收尘过程,其中比电阻影响最为显著;比电阻随温度增加而呈先增后降的趋势,中国煤种粉煤灰的比电阻可以采用Yan&Li模型通过锂、钠、铁的质量分数、湿度和电场强度来进行预测。2)在电除尘器中的PM2.5与PM10方面,电除尘器出口粒径低于2.5μm的颗粒物(PM2.5)与粒径低于10μm的颗粒物(PM10)的质量浓度比值一般在6%~40%范围内;而其后端脱硫塔在捕集PM10的同时还会产生次生颗粒物,因此其出口PM2.5与PM10质量浓度比值在28%~60%范围内;电除尘器出口PM2.5还与振打形式相关,断电振打时出口质量浓度可比带电振打约高6 mg/m3。3)在电除尘器收尘效率预测方法方面,为了预测分级效率和提供设计依据,以平均电场强度、峰值电场强度和比收尘面积的乘积作为电除尘指数;电除尘器出口质量浓度限值低于10mg/m3时,该指数值应大于1 300。4)在电除尘器供电形式方面,电除尘指数要求较高的运行电场强度,不仅三相电源的平均工作电压可以接近单相电源的峰值电压,而且三相电源的收尘效率也可以比单向电源提高10%以上。5)在电除尘技术路线和本体选型方面,电除尘器本体则应采取小分区差异供电,前端应对高粉尘负荷,后端应对细颗粒物二次扬尘;同时运行温度应控制在130℃以下以提高收尘效率并满足能量回收要求。6)在离子风、电凝并及粉煤灰高值化方面,电晕放电产生的离子风及次生湍流、电凝并器引起的颗粒荷电和凝并都对细颗粒物控制有益;为降低电除尘器运行成本,粉煤灰还可以进行高值化应用,用于废气废水处理、矿物聚合物合成等用途。这些研究结果的总结和梳理可以对电除尘技术的发展有所裨益。

Electrostatic precipitation technology is one of the major particle separating and collecting methods. Based on the most active research problems, we have reviewed the recent development and application of electrostatic precipitation technology. 1） The characteristics of coal, high-voltage power supply, and electrostatic precipitation（ESP） sizing should all be optimized for ultra-low emission. The characteristics of particle, such as its shape, diameter, and resistivity, can af- fect dust collection. Resistivity of particle has a marked effect on collection, and it shows inverted U-shaped relationship with temperature. By calculating contents of lithium, sodium, and iron ,humidity and electrical strength as well as the re- sistivity of fly ash released by combustion of Chinese coal can be predicted using Yan＆ Li model. 2） The ratio of PM2.5 and PM 10 at the outlet of ESP is normally in the range of 6%-40%. This ratio can increase to 28%-60% at the outlet of downstream desulfurization devices for generation of secondary aerosols and collection of PM 10. The PM2.5 emission at the ESP outlet is also related with rapping, and its concentration can be 6 mg/m3 higher during outage rapping than power-on rapping.3） The so-called ESP index, products of average, peak electrical strength, and specific collecting area, can predict the grade collecting efficiency and help ESP design. The value of ESP index should be higher than 1 300 for controlling the outlet emission under 10 mg/m3. 4） ESP index also indicates the higher electrical strength is, the better ESP performs. Therefore, the three-phase hig-voltage power supply can collect 10% more particle than single-phase one and keep its operating voltage near the peak voltage of single-phase power supply. 5） The front side of ESP should be available to cope with high dust load and the end of ESP should focus on preventing re-entrainment based on multi-sectionalization and differentiated power supply. Meanwhile, the operating temperature should be controlled under 130℃ for lowering dust resistivity and recovering heat. 6） For fine particle capture, the ionic wind produced by corona discharge, charging and agglomeration inside the pre-charger should both be considered. To lower the operating capital of ESP, fly ash can also be widely applied for high value application, such as waste gas and water treatment or mineral geopolymer synthesis. The discussions and results are expected to indicate some trends of electrostatic precipitation technology development and contribute to this area.