Modeling the pre-breakdown V-I characteristics of an electrostaticprecipitator

A novel mathematical model for determining the electrical characteristics in a dc energized duct type electrostatic precipitator is described. The method is a quasi-analytical one, based on solving the current continuity equation by finite-difference method and Poisson's equation by variational principle with the help of Rvachev functions (R-functions). The methodology described represents a valuable design tool for simulating and comparing the voltage-current characteristics of different wire-plate precipitator configurations before optimizing the geometric parameters namely shape of the corona wire, shape of the collection electrodes, wire cross-section, wire-wire and wire-plate spacing. The proposed method will be useful in trying innovative ideas in the design aspect of a wire-duct precipitator. Other significant features of this method are reduced problem domain, less memory space, and faster convergence. The proposed method has been validated with published experimental results and the agreement is excellent. A comparison of electrical characteristics has been made for different sizes and shapes of corona wire and also for various configurations of the wire-plate precipitators     

Semipilot plant pulse energized cold-precharger electrostaticprecipitator tests for collection of moderately high resistivity flyashparticles

The performance of an electrostatic precipitator (ESP) to collect moderately high resistivity flyash has been tested under pulse/precharger energization using the semipilot scale integrated electrostatics combustion flue gas (IECFG) cleaning system at Ontario Hydro's 640 MJ/h Combustion Research Facility Center. The pulse energization enhanced the performance of the existing de-energized wire-plate electrostatic precipitator in collecting moderately high resistivity (ρ~10¹⁰ Ω·cm) flyash. A 26% improvement in particle collection efficiency and 30% energy saving were obtained with pulse energization, with moderately high resistivity flyash generated by burning high-sulfur (3.7%) Nova Scotia coal with limestone conditioning. The cold precharger specially designed to suit the three-stage wire-plate ESP has also been tested for its ability to improve the performance of ESP in reducing the back corona. With an additional 30% of energy supplied to the precharger it was possible to obtain up to 40% enhancement in collection efficiency. In general an enhancement factor of 1.8-2.8 was obtained with dust loading ~2 g/m³. A thyratron switched pulse power supply was used for the ESP     

The Effect of Back Corona in a Laboratory Scale Electrostatic Precipitator

The results are presented of a study on the influence of back corona on the performance of a laboratory scale wire-plate precipitator, with the plate to plate spacing as a parameter. Back corona is introduced into the precipitator by increasing the ash resistivity, attained by increasing the ash-laden gas temperature from 21 ° C (a no back discharge condition) to 104 ° C. Performance is evaluated in terms of the Deutsch migration velocity and using the particle concentration measurements made at the inlet and outlet of the precipitator with an optical counter. Results for the four different plate spacings with no back discharge show a time-independent migration velocity and current density, with higher migration velocities for the wider plate spacings. Results with back discharge show an initially rapid decrease in migration velocity with time, accompanied by a rapid increase in the current density, with greater decreases for the wider plate spacings. The behavior of the precipitator with and without back discharge is consistent with the space charge model interpretation of the wide-plate spacing precipitator.     

Numerical modeling of near corona wire electrohydrodynamic flow in a wire-plate electrostatic precipitator

Numerical modelling of the flow velocity fields for the near corona wire electrohydrodynamic (EHD) flow was conducted. Solutions of the steady, two-dimensional momentum equations have been computed for a wire-plate type electrostatic precipitator (ESP). The equations were solved in the conservative finite-difference form on a fine uniform rectilinear grid of sufficient resolution to accurately capture the momentum boundary layers. The numerical procedure for the differential equations was used by SIMPLEST algorithm. The CFD code coupled with Poisson's electric field, ion transport equations and the momentum equation with electric body force, was used for the numerical simulation with the Chen-Kim k-epsiv turbulent model. The numerical results show that EHD secondary flow was clearly visible in the downstream regions of the corona wire despite the low Reynolds number for the electrode (Re _cw=12.4). Secondary flow vortices caused by the EHD increases with increasing discharge current or EHD number, hence pressure drop of ESP increases     

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.     

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     

Ozone generation in DC-energized electrostatic precipitators

Ozone emissions from a short wire-plate precipitator and three commercial electronic air cleaners were measured. Ozone generation was most strongly affected by the corona current and polarity of the discharge electrode. To a lesser extent, the type of corona (i.e. whether tuft or glow) was also important. Water vapor seems to reduce the ozone emission rate for negative corona, but ozone emissions from positive coronas are relatively unaffected. Ozone emission rate was also affected by the radius of the discharge electrode     

Flow visualization inside a wire-plate electrostatic precipitator

A flow visualization study was performed in a wire-plate precipitator with a plate-plate spacing of 20.32 cm and wire-wire spacing of 20.32 cm. Smoke was used as the flow tracer, where injection and illumination were accomplished by two different techniques. In one method smoke was released from a single heated probe and illuminated by electronic flash. The other method employed a uniform smoke flow made visible by a laser sheet. The latter technique proved to be superior, providing well-defined views of the flow in both streamwise and spanwise planes over a wide range of velocities (0.2-2 m/s) and current densities (0-0.5 mA/m). The illuminated flow patterns were recorded by still 35 mm photography and color video taping. Of particular interest was the interaction between the precipitator gas flow and the corona-generated electric wind for both polarities of discharge. Results showed that positive corona discharge produces a stable two-dimensional smoke flow with negligible turbulent dispersion for precipitator velocities greater than 0.7 m/s. Lower velocities allowed the electric wind to dominate producing unstable, recirculating flow with widespread turbulence. Negative discharges were inherently unsteady and three-dimensional at all operating conditions but displayed extreme instability and recirculation (similar to positive polarity) for precipitator velocities less than 0.7 m/s     

Application of different types of high-voltage supplies on industrial electrostatic precipitators

Investigations of the requirements for high-voltage (HV) power supplies for zones within an electrostatic precipitator (ESP) were conducted with regard to the properties of different technologies for HV generation. The zones of an ESP show different electrical behavior and efficiency. This is a result of: 1) the different dust loads of the zones; 2) the particle size and properties; and 3) the possibility of charging the particles in the entire zone using suitable technology. An overview of common and new topologies of HV supplies and their typical properties is given. It is shown how these properties can be used to match the requirements of the different zones of an ESP regarding the actual operating conditions. Large particles and high dust loads can be addressed effectively using high-frequency dc power supplies. Fine particles, however, can be separated even more efficiently by pulsed power supplies. Additionally, the power consumption of different HV sources has been investigated in relation to the separation efficiency. Experimental results were obtained on an industrial ESP containing 3 zones in a sinter plant and on a large scale precipitator in a fossil power plant, containing 30 zones. It was shown that a high frequency IGBT inverter combined with a microsecond-pulsed power supply significantly improved the overall performance of the precipitator.     

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     

All-Solid-State Power Modulator for Pulsed Corona Plasma Reactors

Atmospheric pressure pulsed corona plasma (PCP) reactors of wire-plate design offer novel solutions to environmental issues and to a number of industrial processes. Emerging applications include indoor air sterilization and odor removal in air conditioning systems, chemical synthesis in non-thermal plasmas, and plasma reforming of gaseous fuels. We previously reported on experimental investigations of a laboratory size, wire-plate plasma reactor for pulsed corona treatment of gas flows. Operation with gas flow, at pulse repetition frequencies of between 10 pps and 200 pps, has been achieved at pulse voltage amplitudes of between 10 and >30 kV, at pulse durations of around 0.3 mus (FWHM). High efficiencies of up to 70 g/kWh have been reported using an all-solid-state pulse generator. In this work, we report on the development of all-solid-state power modulators for use with nonlinear loads like pulse corona plasmas. The pulse generators are based on a fast thyristor switch discharging pulse capacitors, a pulse step-up transformer, and one or two stages of magnetic pulse compression. At pulse repetition rates of up to 200 pps, amplitudes of > 30 kV into a resistive-capacitive load (1 kOmega200 pF) have been achieved, at risetimes of about 80 ns and a pulse width of 0.3 mus. The pulse generator is insensitive to load variations, in particular to sparking in the reactor. An advanced generator version uses two magnetic pulse compression stages resulting in even shorter rise times. The modulator and its performance concerning experimental results will be described in detail when driving a pulsed corona reactor.     

脉冲等离子体反应器放电特性研究

脉冲放电等离子体被广泛用于气态污染物处理的研究,放电参数直接影响反应器内等离子体状态,进而影响污染物的去除效果,研究不同条件下的放电特性可为脉冲等离子体技术的应用提供参考.本文利用线板式脉冲等离子体反应器, BPFN型高压脉冲电源供电, 研究了电源电容、极板间距及介质阻挡对放电特性的影响.结果表明:增大电源电容可以有效地提高电源能量效率;增大极板间距,峰值电压VP增大,峰值电流IP减小,脉宽减小,波形更加理想;陶瓷板阻挡放电可解决间隙火花放电,使脉冲电晕放电空间分布均匀,在大范围内提高电源能量效率.     

空间电荷对SF_6气体正雷电冲击击穿的作用

利用两种实验方法对比测试了预注入单极性空间电荷时,SF_6气体极不均匀场间隙正雷电冲击击穿特性。分析表明;直流叠加冲击电压法不适用于观察空间电荷的作用,而切换直流/冲击电压法能有效地反映空间电荷对冲击击穿的作用。     

临界脉冲电源在静电除尘器上的应用

简要介绍了电除尘技术发展,并针对静电除尘电源新技术——临界脉冲电源技术特点进行了详细阐述,同时根据临界脉冲电源应用于300MW火力发电机组上的相关运行数据进行了分析,从而为临界脉冲电源在静电除尘器上的应用提供了科学依据。     

基于Kerr电光效应的变压器油中直流电场测量系统

在直流电场下油纸绝缘系统中,空间电荷的存在会对系统的绝缘性能造成影响。通过实时测量得到绝缘系统中的电场分布和电荷分布具有重要意义。Kerr电光效应法因不会对绝缘系统中电场分布造成影响而得到很多研究者的关注。由于实验系统中包含较复杂的光学器件及微弱信号检测单元,其实现具有一定的难度。文章采用光电二极管作为光接收器件,采用一种交流电压调制方法,结合锁相放大器实现了对微弱信号的检测;通过检测输出光强中直流和所施加的交流信号分量,计算得到了待测直流电场的数值。试验结果表明该系统具有较好的线性度。     

Quasi-static and dynamical computation of V-I characteristics of adust-loaded pulse-energized electrostatic precipitator

This paper describes an accurate model and a new procedure for the numerical computation of the electric field, current and charge density, in a pulse energized electrostatic duct-type precipitator, in presence of dust. The proposed model is compared to the classical steady-state model used in the past. The old model shows nonphysical bumps and discontinuity whereas the new approach predicts the natural transient behavior of electrical quantities. The partial differential equations governing the transient phenomena are solved by means of an implicit-explicit finite-difference time-domain method, which ensures a fast computation. The obtained results, compared with experimental values, show a good accuracy of the presented method     

基于磁脉冲压缩技术的电除尘器供电电源

阐述了脉冲供电电源对比其他种类电源的优点及其应用,提出了基于磁脉冲压缩技术的电除尘用脉冲供电电源,利用磁材料的B-H曲线和伏秒积特性解释了磁开关即可饱和电感的实质及其工作原理,在分析一阶磁压缩网络的基础上,给出了基于二阶磁脉冲压缩供电电源的电除尘器的仿真实例,通过仿真结果证实了磁脉冲压缩理论运用在电除尘领域的可行性。指出减小磁芯体积可有效降低损耗,并推导了构成磁开关的两个重要参数-磁芯体积和电感量的计算公式。     

风力发电用双PWM变频器仿真研究

本文针对无刷双馈风力发电机,采用了一种新的三相电压源型双PWM变频器控制方案,网侧采用d-q模型的空间矢量脉冲宽度调制(SVPWM),较好地实现了电压的跟踪和单位功率控制,转子侧采用电流滞环控制。仿真表明,该双PWM变频器网侧能够获得单位功率因数的正弦输入电流,稳定的直流输出电压,转子侧电流具有快速的动态响应;变频器能够实现能量的双向流动,仿真验证了控制策略的正确性和有效性。     

脉冲放电能量传输的实验研究

针对脉冲电压Up沿放电线传播发生流光电晕放电,脉冲能量注入反应器内产生活性自由基进行烟气脱硫脱硝过程中,沿线Up波形的变形及脉冲能量的衰减会影响活性自由基产生的问题,为给设计工业应用反应器的几何尺寸提供依据,研究了Up及脉冲能量沿放电线变形、衰减的特性,且研究了电压、脉冲成形电容Cp、线径d及线长l等因素对能量传输、衰减的影响。实验结果表明脉冲电压沿放电线传输时,电压波形发生衰减,随着传输距离的增大,电压波形变形严重;电压、Cp、d和l对能量衰减有一定的影响,增大电压、Cp和d,沿线脉冲能量的衰减速度增大;l越短,能量衰减越快。实验得出最佳l≤10 m。     

线—板式脉冲电晕放电系统研究

线—板式电晕放电系统被广泛应用于大型除尘器及烟气脱硫反应器上。通过改变收集极板间距、放电极邻距及脉冲成形电容值,研究这些参数变化对高压ｎｓ级脉冲波形的影响,为设计脉冲电晕脱硫反映器内部电极结构提供了实用性实验依据。