Electrostatic precipitation

Electrostatic precipitators have been used widely in industry, and play an important role in environmental protection. An electrostatic precipitator (ESP) can be operated with a high collection efficiency and a low pressure drop. Recently, an ESP also has been used for cleaning indoor air. In this review, principles of electrostatic precipitation, such as particle charging, migration velocity of charged particles and collection efficiency, are described. The performance of the ESP deteriorates by abnormal phenomena, including back corona for treating high resistivity dust, abnormal re-entrainment for low resistivity dust, and corona quenching for fine dusts. To cope with these phenomena, new technologies have been developed. Pulsed energization is a technique which copes with high resistivity dusts, and this results in lower power consumption. Using pulsed energization, non-thermal plasma can be generated and chemical reactions can be promoted for treating gaseous pollutants such as NO and volatile organic compounds. Wet ESP can also remove dusts and gaseous pollutants simultaneously. These new advancements will widen the field of application of electrostatic precipitation. Some novel applications of ESP, such as removal of dioxin from incinerators, are also included in this review     

The effect of high-voltage waveforms on ESP current densitydistributions

The efficiency of an electrostatic precipitator (ESP) collecting high resistivity dust is degraded by maldistribution of corona current in the interelectrode space. The current distribution can be improved by applying novel high-voltage waveforms to the discharge electrodes. Online measurements are presented of collecting plate current density distributions in a precipitator collecting fly ash from a coal-fired electric generating plant. The precipitator was operated with both round-wire and barbed-strip discharge electrodes. The current density distributions are compared for three high-voltage waveforms: conventional, pulse, and intermittent energization. A direct relationship is established between the ability of the waveforms to distribute useful values of corona current and the collection efficiency of the ESP     

Fundamental Behavior of Direct-Coupled Submicrosecond Pulse Energization in Electrostatic Precipitators

The fundamental characteristics of the direct-coupled pulse energization in electrostatic precipitators (EP's) are investigated in a test rig comprised of a coal pulverizing facility, a furnace, a gas cooling system, and an EP. The EP consisted of a corona electrode with barbed wires and a collection electrode with 300-mm duct spacing. This simulates the type of EP normally used in a coal-fired power station. The pulse-energized collection field shows a very high collection performance of more than 99 percent collection efficiency and the performance enhancement compared to the conventional dc energization, causing very severe back corona, becomes as large as H = 2.50.H is the enhancement factor in terms of the Deutsch migration velocity in the case of the very high resistivity dust of rd = 2 x 1013 ?cm at the gas temperature of Tg = 150°C. Even at the lower level of the dust resistivity at Tg = 110°C, where no back corona occurs in the dc-energized collection field, the performance enhancement is as large as H = 1.21. The mechanism of such great performance enhancement is likely to be the result of the very uniform and very intense formation of corona plasmas on the wires as a result of the very fast rise in the pulse voltage applied and a special sawtooth waveform of the operating voltage between the corona and collection electrodes.     

Modeling of prebreakdown VI characteristics of a wire-plateelectrostatic precipitator operating under combined dc-pulseenergization

With the advent of pulse energization in electrostatic precipitators, the need for developing a model to simulate the physical processes in the prebreakdown region, at which the precipitator normally operates, is also increasing. The development of such a model helps in predicting the VI characteristics of a precipitator, which will be important to diagnose the electrical problems associated with the precipitator during its operation. The paper reports the details of a proposed model to predict the VI characteristics of a wire-plate precipitator operating under the influeuce of repetitive pulses superposed on a dc bias. The model begins with the calculation of space charge density near the HV electrode during the pulse-on period and then proceeds with the drift of space charges in the pulse-off period aided by the dc bias. The pulse duration was ~250 ns. The pulse repetition rate was 50 Hz. The predicted results were validated against the experimental results conducted on a laboratory model of a wire-plate precipitator. The studies were conducted for dust free conditions     

低低温电除尘器对粉尘特性和SO3脱除效果影响分析

分析了低低温除尘技术对粉尘特性和SO₃脱除效果的影响,说明低低温除尘器通过降低粉尘比电阻来改善粉尘的荷电能力,有效地提高了除尘效果;同时增大粉尘平均粒径,有利于提高脱硫系统协同除尘效果;另外湿法脱硫系统本身不具备较高的SO₃去除率,低低温电除尘器和湿式电除尘器对SO₃的去除率可达到80%左右,因此,低低温电除尘器和湿式电除尘器可作为控制SO₃的有效技术手段。     

Mercury and other trace elements removal characteristics of DC andpulse-energized electrostatic precipitator

Removal of zinc-rich ash and mercury from a gas stream using prototype electrostatic precipitators (ESPs) has been investigated. Dust particles collected from the thermal plasma ash volume reduction system of the Matsuyama, Japan, municipal incineration plant were used to study the performance of an ESP to collect zinc-rich ash. The ash was analyzed by neutron activation analysis using the nuclear reactor at McMaster University, Hamilton, ON, Canada. Collection efficiency as high as 99.9% was obtained in the removal of Zn from the flue gas with DC energization of the ESP. The mercury concentration was measured using a cold vapor atomic absorption spectrometer after sampling (OSHA-140 method) from the flue-gas stream. As a function of concentration, the mercury collection efficiency was higher at a higher concentration of mercury. Higher collection efficiency was obtained under negative DC energization compared to other modes of energization of the ESP; however, power consumption under the pulse application was much smaller compared to DC energization     

Modeling of the electrical parameters of a wire-cylinderelectrostatic precipitator under pulse energization

Modeling of the electrical parameters of an electrostatic precipitator (ESP) with dust loading under pulse energization is difficult, and little progress has been made in the past. A method for modeling a wire-cylinder ESP under pulse energization based on the characteristics of Trichel pulses, and a means of dealing with the particle charging under such conditions are presented. The quantitative studies of the interactions between ion space charge and particle charging and their influence on the electric potential and field distributions have been numerically obtained under nanosecond pulse energization. The results show that the time-averaged current increased with applied peak voltage, pulsewidth, and pulse frequency and decreased with increased dust loading as expected. The space-charge density distribution was significantly influenced by the dust loading under pulse energization conditions. The proposed model is valid as long as the width of the applied voltage is less than 1 μs     

紧凑型混合颗粒收集器的数值模拟

单独的静电除尘器(electrostatic precipitator,ESP)和布袋除尘器均对于0.1~1 mm的亚微米颗粒具有较低的除尘效率。采用复合外加条件,即ESP和布袋除尘器串联的紧凑型混合颗粒收集器(compact hybrid particulate collector,COHPC),有望提高可吸入颗粒物的除尘效率。针对一典型300 MW机组的ESP,讨论了2种对其进行改造的技术方案,即对ESP本体进行改造和采用COHPAC,对改造前后ESP的除尘过程进行了颗粒群平衡模拟,并对电增强布袋除尘器的非稳态除尘过程进行了数值模拟,从而定量描述可吸入颗粒物在多种外加条件下的非线性和微尺度动力学演变规律。数值模拟结果表明,COHPAC比本体改造前后ESP具有更高的可吸入颗粒物(particulate matter,PM)除尘效率,整体质量和整体数目除尘效率可以达到99%以上。     

Bipolar Structure of a Back-Discharge Field in an Electrostatic Precipitator

The current densities of positive and negative ions i+ and i- in the back-discharge field of an electrostatic precipitator (ESP) are measured with a bipolar current probe. The ratio i+/i- rises with increasing total current density i (= i+ + i-) in the streamer-mode back discharge, but it remains almost constant (10-20 percent) in the glow-mode back discharge. The probe-measured values of the back-discharge-starting current density are slightly higher in pulse charging than in dc charging. In addition, the pulse charging does not cause back discharge at a resistivity below 1013 ?cm. However, beyond 1014 ?cm the back discharge can hardly be avoided, even by pulse charging. The probe diagnosis of i+/i- in an ESP enables an approximate estimation of the charge-to-mass ratio of dust and the collection performance when i+/i-, averaged in space, is used.     

New Trends in Electrostatic Precipitation: Wide Duct Spacing, Precharging, Pulse Energization

Increased research in electrostatic precipitation has resulted in the emergence of promising new technologies. In a new design concept already widely used in Japan, the precipitator duct spacing is increased from the traditional 200-300 mm up to 400-600 mm, and the precipitator voltage is raised correspondingly, with precipitator performance remaining almost unchanged for the same precipitator volume and the same gas flow. For suitable applications, this design results in reduced installation costs and easier maintenance. Various devices for precharging of high resistivity dust now under development improve particle charging and thereby enhance precipitator performance. Pulse energization improves the performance of precipitators collecting high resistivity dust by improving particle charging and current distribution and allowing regulation of the precipitator current independent of precipitator voltage.     

PM2.5分布指数对线管式电除尘器除尘效率的影响

为了确定线管式静电除尘器（ESP）捕集PM_2.5性能的改善途径，需探明PM_2.5分布指数（分布指数）对ESP脱除细微颗粒PM_2.5效率的影响规律。为此，建立了多场耦合作用下的理论模型和简化模型，分别从分级效率和综合效率的角度描述了离子风、磁约束作用下EPS对PM_2.5的脱除性能。结果表明：随着颗粒粒径的减小、分布指数的降低，PM_2.5分级脱除效率会显著升高；离子风的存在提高了PM_2.5的脱除效率，但削弱了由降低分布指数给PM_2.5脱除效率带来的提升幅度；磁场有效地提升了线管式ESP对PM_2.5的捕集性能，且强化了减小分布指数对脱除PM_2.5性能的促进效果。     

电除尘器用高频高压脉冲数控电源

脉冲或间歇供电模式可以大幅度降低电除尘器能耗和提高除尘效率。为了实现电除尘器的脉冲供电,减少脉冲电源的成本和体积,在IGBT高性能器件基础上,综合利用串联谐振逆变技术和倍压整流技术,搭建了一高频高压脉冲数控电源,并用PSpice软件对此电源进行了仿真,分析了倍压器所用电容和负载电阻对倍加器输出电压的影响。最后给出基于LabVIEW环境的倍加器型高频高压电源实验,其输出电压峰值达到了30kV,频率为70kHz。实验的结果验证了频率、输出的可控性及仿真的正确性,仿真和实验结果可用于数控闭环系统的设计和构建。鉴于目前国内火电脱硫主流模式是化学湿法,产生大量无经济利用价值的低品位石膏,脉冲或间歇供电模式在火电领域推广可以大幅度提高除尘效率,从而使石膏变白并提高石膏品位,变废为宝,达到节能减排目的。     

Automatic control and management of electrostatic precipitator

The efficient operation of an electrostatic precipitator (ESP) in practice depends upon many variables, such as charging method, particle size, gas flow, temperature, dust resistivity, etc. With air pollution control requirements becoming increasingly stringent, it is essential to closely monitor and accurately control the key parameters of an ESP control system. The efficient functioning of an ESP normally means minimizing power consumption and maximizing dust collection. Several control strategies can be adopted to meet this broad requirement. In this paper, a distributed control technique of an ESP, which uses the actual dust emission and boiler load as feedback inputs has been explained. The electrostatic precipitator management system, which is a system designed by Bharat Heavy Electricals Ltd., Hyderabad, India, to meet the above control strategies using the distributed architecture to achieve efficient ESP operation is also described     

单区静电除尘器捕集烟尘过程的数值模拟

通过得到烟尘的颗粒尺度谱(PSD)演变过程的详细信息来定量描述静电除尘器(ESP)对烟尘的捕集过程,此时需要同时考虑静电力、流体对颗粒的水平输运力和颗粒横向湍流和布朗扩散作用等烟尘捕集机制。发展事件驱动常体积法来求解考虑烟尘捕集的通用动力学方程以得到颗粒尺度谱的演变过程。对于典型的火电厂单区ESP进行的数值模拟结果表明：ESP对直径大于10mm的烟尘具有良好的捕集效果,也能有效脱除直径小于0.02mm 的烟尘,但是对粒径范围在0.02~10mm的烟尘的除尘效率相对较低;这种"U"型分级除尘效率主要是由于颗粒自身惯性力与静电力之间的相互竞争的结果;布朗扩散机制对任何尺度颗粒的捕集效果影响很小;减小气流输运速度和增加电场强度有利于任何粒径的烟尘颗粒的脱除。     

Agglomeration of particles by ac corona discharge

Improving the collection efficiency for particles smaller than 1 μm on every precipitator is important. We sought to improve the collection of these particles on an ESP due to particle agglomeration. Particles are charged by ac corona discharge in a precharger and agglomerated by a dc electric field in an agglomerator downstream of the precharger. Diesel exhaust particles were used as particulate matter for the experiments. The distribution of particle size was measured using a particle counter and a scanning electron microscope. By these methods, particles as small as 0.01 μm could be counted. Results showed the agglomeration between particles at ac corona discharge operating mode. The concentration of particles smaller than approximately 0.35 μm decreases, and that of particles larger than approximately 0.35 μm increases in the agglomerator. The agglomeration rate increases with increasing applied voltage, then saturates. These results may be due to the size distribution and to decrease of concentration by agglomeration. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 30–37, 2000     

Capture of fine particles on charged moving spheres: a newelectrostatic precipitator

It was verified experimentally that electrostatic cleanup of fly ash dust is possible using the scrubbing action of charged copper particles with diameters 10-100 times the size of the dust particles. Results show that target efficiencies in excess of unity (up to 1.8) are possible as a result of the induced charge on the target particles. Power consumption to the precipitator was confirmed to be very small (~5×10^-4 W). Values of the total collection efficiency of 0.65 (65%) were obtained for a precipitator zone length of 1.2 cm (in the direction of air flow) at air velocities of about 3 cm/s. This value decreased with increasing air flow rate. Collection efficiencies up to 0.99 (99%) are projected with a longer test section of at least 5.3 cm in length for low air velocities of about 3 cm/s, an electric field strength of 10.91 kV/cm, and 114.5 μm copper particles     

Experiments with Pulsing Energization on an Industrial ESP

A single electric field of an electrostatic precipitator installed for collecting fly ash from a 320-MWb boiler burning low-sulphur coal was energized with a pulse generator of original design. The tests showed a good performance of the pulse generator, a statistically significant decrease of dust emission in comparison to the conventional energization, and a lower power consumption.     

“低低温+移动电极”电除尘技术研究与应用

“低低温+移动电极”是新的电除尘组合技术。低低温电除尘技术有二次扬尘的缺陷,需结合移动电极来保证高除尘效率,为此研究了“低低温+移动电极”的技术特点和结构原理,并对国外碧南电厂和华能河北某电厂等典型案例进行了介绍和分析。实践经验表明,“低低温+移动电极”电除尘技术是实现超低排放的较佳电除尘组合技术之一,其可实现燃煤电厂电除尘器出口粉尘质量浓度达到15 mg/m³以下,配合脱硫系统可满足10 mg/m³以下甚至5 mg/m³以下的烟尘超低排放要求。     

燃煤电厂污染控制设备脱汞效果及汞排放特性试验

为了解燃煤电厂汞的排放规律以及现有的污染控制设备对烟气中汞的协同脱除效果,采用安大略法对江西省内4台机组进行汞排放及控制试验研究,得到现阶段燃煤电厂配置条件下汞的排放特性。研究结果表明：未投入汞氧化剂的机组污染控制设备协同脱汞效率在69.01%~75.63%,投入汞氧化剂的机组脱汞效率可达89.69%;SCR脱硝装置对烟气总汞的减排效果不明显,但能促使Hg⁰成为易于脱除的Hg²⁺和颗粒态汞,机组投入汞氧化剂后可大幅提高Hg⁰氧化为Hg²⁺的比率;除尘器可以脱除全部的颗粒态汞,其协同脱汞效率平均值为24.37%;湿式脱硫系统对Hg²⁺的脱除效率为88.39%;烟气经过脱硝、除尘、湿式脱硫装置后,最终排放气体中汞的质量浓度在3.91~8.89 μg/m³,远小于国家排放标准限值。