OH radicals generated by DC corona discharge for improving the pulsed discharge desulfuration efficiency

Positive DC corona discharge is formed with needle-plate electrode configuration, in which the water vapor is ejected though the needle points. The purpose is to increase the numbers of the water-based radicals, ionize the water molecule and improve the desulfuration efficiency of pulsed corona reactor. The water ions were determined by four stages molecular beam mass spectrometer and diagnose the water-based radicals by emission spectrograph. A conclusion on formation of ions and radicals with DC corona discharges can be drawn.

Effects of treatment time and temperature on the DC corona pretreatment performance of waste activated sludge

In order to improve the anaerobic digestion efficiency of waste activated sludge（WAS）,a pretreatment procedure should be carried out so as to disrupt the microbial cell structure,thus releasing intracellular organic matters.In this paper,a corona discharge triggered by a DC voltage was employed to pre-treat WAS for various time periods under different temperatures.The magnitude of the DC voltage was 4 k V at both negative and positive polarities.The changes in the soluble chemical oxygen demand,phosphorus and nitrogen content,and p H value within the WAS were utilized to estimate the pretreatment performance of the DC corona.It was found that with increasing treatment time,the pretreatment efficiency tends to be reduced.With increased temperature,the pretreatment efficiency appears to be better.It is suggested that the oxidative species and the active particles generated in the corona discharge play an important role in disrupting the microbial cell structure,which is dependent upon the treatment time and the temperature.

Influence of AC Voltage on the Positive DC Corona Current Pulses in a Wire-cylinder Gap

In the development of hybrid HVDC and HVAC transmission lines,the study of radio interference is an important issue.Positive corona current pulses from high voltage transmission lines are the main source of radio interference.In this paper,the design of a wire-cylinder gap electrode system is presented to study the influence of AC voltage on the characteristics of positive corona current pulses.The study shows that the mode of the current pulses is different from that of either DC or AC corona discharge.Waveform parameters of the pulses,such as rise time,half wave time,duration time,repetition rates,average amplitude,and time intervals of secondary pulses are all statistically analyzed in this study.The empirical formulas for the repetition rates with different AC voltages are presented.A theoretical explanation based on an ion cloud model is given to reveal the mechanism behind the influence of AC voltage on positive corona discharge.The experimental results could provide some references for the prediction of radio interference from hybrid AC/DC transmission lines.

Electro-Hydrodynamics and Kinetic Modeling of Dry and Humid Air Flows Activated by Corona Discharges

The present work is devoted to the 2D simulation of a point-to-plane Atmospheric Corona Discharge Reactor （ACDR） powered by a DC high voltage supply. The corona reactor is periodically crossed by thin mono filamentary streamers with a natural repetition frequency of some tens of kHz. The study compares the results obtained in dry air and in air mixed with a small amount of water vapour （humid air）. The simulation involves the electro-dynamics~ chemical kinetics and neutral gas hydrodynamics phenomena that influence the kinetics of the chemical species transformation. Each discharge lasts about one hundred of a nanosecond while the post- discharge occurring between two successive discharges lasts one hundred of a microsecond. The ACDR is crossed by a lateral dry or humid air flow initially polluted with 400 ppm of NO. After 5 ms, the time corresponding to the occurrence of 50 successive discharge/post-discharge phases, a higher NO removal rate and a lower ozone production rate are found in humid air. This change is due to the presence of the HO2 species formed from the H primary radical in the discharge zone.

Numerical Modelling Point-to-Plane of Negative Corona Discharge in N_2 Under Non-Uniform Electric Field

The paper presents a simulation model of the negative corona discharge in N2 under various pressures. The simulated discharge is of a negative point-to-plane mass type, with an inter-electrode separation distance of 20 mm and a symmetry about the axis of discharge. This simulation investigates the behavior of the neutral density and temperature for different pressures in the range of 0.1-10.0 bar. The spatial and temporal evolution of the neutral gas is analyzed based upon the equations of continuity, momentum and energy in a two-dimensional cylindrical geometry model. For that geometry of the system, the FCT （Flux Corrected Transport） technique was adopted. The results show that the pressure plays a significant role of the neutrals dynamics.

Introduction to investigations of the negative corona and EHD flow in gaseous two-phase fluids

Research interests have recently been directed towards electrical discharges in multi-phase environments.Natural electrical discharges,such as lightning and coronas,occur in the Earth＇s atmosphere,which is actually a mixture of gaseous phase（air） and suspended solid and liquid particulate matters（PMs）.An example of an anthropogenic gaseous multi-phase environment is the flow of flue gas through electrostatic precipitators（ESPs）,which are generally regarded as a mixture of a post-combustion gas with solid PM and microdroplets suspended in it.Electrical discharges in multi-phase environments,the knowledge of which is scarce,are becoming an attractive research subject,offering a wide variety of possible discharges and multi-phase environments to be studied.This paper is an introduction to electrical discharges in multi-phase environments.It is focused on DC negative coronas and accompanying electrohydrodynamic（EHD） flows in a gaseous two-phase fluid formed by air（a gaseous phase） and solid PM（a solid phase）,run under laboratory conditions.The introduction is based on a review of the relevant literature.Two cases will be considered：the first case is of a gaseous two-phase fluid,initially motionless in a closed chamber before being subjected to a negative corona（with the needle-toplate electrode arrangement）,which afterwards induces an EHD flow in the chamber,and the second,of a gaseous two-phase fluid flowing transversely with respect to the needle-to-plate electrode axis along a chamber with a corona discharge running between the electrodes.This review-based introductory paper should be of interest to theoretical researchers and modellers in the field of negative corona discharges in single-or two-phase fluids,and for engineers who work on designing EHD devices（such as ESPs,EHD pumps,and smoke detectors）.

直流电晕放电无线电干扰随机时域计算模型研究

直流输电线路电晕放电过程中会在空间中产生随机的无线电干扰脉冲信号,目前针对电晕放电无线电干扰的测量与预测计算主要基于频域方法,并未反映出无线电干扰的时域随机脉冲特征。为此,该文在实验室搭建了直流单根导线电晕放电无线电干扰时域测量平台,采用鞭形天线实现了对正极性直流导线电晕放电无线电干扰时域特性的测量,结合无线电干扰脉冲波形特征,分析获得了脉冲波形参数(幅值、重复频率、上升时间、持续时间)的统计特性。基于统计特性,结合无线电干扰双指数函数脉冲波形建立了高压直流单根导线电晕放电无线电干扰随机时域计算模型,模型中包括随机脉冲信号产生、脉冲衰减、场强信号计算及场强信号重构,将该模型产生的无线电干扰时域波形准峰值响应值与不同测量结果进行对比,结果表明计算误差小于2dB,验证了所提模型的有效性。

超、特高压交直流输电线路可听噪声研究综述

近年来架空线路可听噪声逐渐成为限制输电线路建设的重要电磁环境问题。为此总结了交直流输电线路可听噪声研究现状,包括可听噪声的产生机理、测量以及评估,着重分析了直流线路与交流的主要区别和研究难点。结果表明目前对于可听噪声的研究已经取得了一定进展,但是交直流线路电晕效应之间存在较大差异且认识不足,造成这些差异的主要原因是直流线路离子电场的影响;分析表明未来仍然可以利用电晕笼研究直流线路的电晕效应,关键在于建立电晕笼与实际线路在合成电场上的关联。

直流电晕放电中的离子风增强带电气溶胶沉积

为解决我国水资源短缺问题和开发大气水资源的急迫需求,突破之前单电极电晕放电离子源的离子密度较低、气溶胶荷电困难的难题,开发了一套基于离子风增强带电气溶胶沉积的负直流电晕放电系统.该系统利用多个针电极与接地的网状电极,实现了大面积、阵列式的负直流电晕等离子体,可以对流经其中的气溶胶进行高效的荷电和处理.虽然单电极放电产生的开放空间中的离子密度是双电极放电的20倍,但双电极放电区域的电场约为单电极放电的15倍,放电电流也更大.强电场推动离子流进行定向运动,同时推动中性分子,使该装置可以产生速度高达2 m/s的离子风,而与之相比,单电极电晕放电的离子风速低于检测限.双电极电晕放电产生的离子风带动了云室中空气的流动,可以有效促进气溶胶的荷电、碰并以及在接地网状电极上的沉积,可以快速减少空气中的气溶胶密度,所需的时间仅为单电极放电的1/4.在水雾气溶胶的沉积实验中,其水雾的总沉积量是单电极放电的8.3倍.因此,双电极放电系统是诱导降水或消除致病生物气溶胶的潜在有效方法.

正直流电晕特性随气压和湿度变化的研究

电晕是输电线路设计和运行中面临的重要问题之一。文中通过实验测量和模拟计算,得到了不同气压湿度下的正直流电晕起始电压和电晕离子电流。计算结果和实验结果吻合较好。电晕起始电压随气压下降、湿度升高而减小,其主要原因分别为有效电离系数增大导致的电离区域的扩大和高场强区域内碰撞电离能力的增强。当直流电压和电晕起始电压的比值一定时,电晕离子电流也随气压下降、湿度升高而减小。电晕离子电流和直流电压、电晕起始电压关系式中的系数C随湿度升高而减小。当气压降低,C随湿度下降的斜率增大。湿度一定时,C和相对空气密度近似成反比。正离子迁移率是影响C变化的主要因素。

直流电晕自由基簇射治理甲苯的试验研究

利用直流电晕自由基簇射对甲苯有机废气进行试验 ,分别考察了有机污染物浓度、温度、电压、湿度和停留时间等不同因素对去除率的影响。试验结果表明 ,降低气体温度和一定的湿度能够提高脱除效率 ,电压增高可以提高脱除效率 ,停留时间长使得脱除效率升高 ,但能量效率降低。有机物的浓度增大 ,会使得脱除效率降低 ,但同时能提高能量的利用效率。本实验的目的旨在为降解烟气中的多环芳烃 (二英等 )

气压湿度对负直流电晕特性影响的研究

为得到负直流电晕特性随着气压湿度的变化规律,建立了考虑气压湿度影响的负直流电晕起始电压的物理模型,利用模拟电荷法和计算表面光电子数目的方法求解了负直流电晕起始电压。在人工气候罐中,利用棒–板电极,测量了不同气压湿度下的负直流电晕起始电压和电晕电流。计算和试验结果表明:电晕起始电压随气压下降、湿度升高而减小,主要原因分别是有效电离系数增大导致的电离区域的扩大和高场强区域内碰撞电离能力的增强。当直流电压和电晕起始电压的比值一定时,电晕电流随气压下降、湿度升高而减小;当直流电压一定时,电晕电流随气压降低而增大,随湿度升高而减小。电晕电流和直流电压、电晕起始电压关系式中的系数C随湿度增大的不同变化趋势和正负离子与水分子结合状态的差异有关。

交直流电晕对高温硫化硅橡胶性能的影响

该文使用国际大电网会议CIGRE WG D1.14推荐的多针电极系统研究了交直流电晕对高温硫化硅橡胶性能的影响。通过分析试验中的放电功率、电晕前后硅橡胶的憎水性状态、表面电阻率、拉伸强度、拉断伸长率等性能,讨论了交直流电晕、直流正负极性电晕对硅橡胶性能影响的异同。结果表明:经过电晕处理,硅橡胶的上述性能均有所下降。就硅橡胶的憎水性状态和表面电阻率而言,交流电晕对硅橡胶的影响程度大于直流电晕的影响程度,直流负极性电晕的影响程度略大于直流正极性电晕的影响程度。硅橡胶的机械强度在电晕处理后有所下降,但交直流电晕处理后的硅橡胶的机械性能差异不明显。电晕场的空间电荷效应以及硅橡胶表面的电荷积累效应是导致不同电压类型的电晕对硅橡胶性能影响不同的原因;使用傅里叶变换红外光谱(Fourier transform infrared spectroscopy,FTIR)和X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)分析方法研究了硅橡胶表面化学结构在电晕前后的变化,认为硅橡胶在电晕处理前后化学结构的变化,是造成硅橡胶性能的变化的直接原因。

空中颗粒物对直流电晕放电影响研究现状:颗粒物空间电荷效应

颗粒物捕获电子或离子以空间电荷形式对直流电晕放电产生影响。当前我国的大气污染日益严重,沙尘和霾天气频发。污染物中悬浮颗粒物荷电后带来的空间电荷效应将使高压直流输电线路周围的电磁环境复杂化,因此开展空中悬浮颗粒物对高压直流输电线路电磁环境影响的研究对指导直流输电线路的工程设计具有重要意义。该文对输电线路关于颗粒物空间电荷效应的研究历史进行回顾,并从空间电荷密度分布、颗粒物荷电量及其分布、地面合成电场和离子流密度等方面对已有研究结果进行梳理;对静电除尘、气固两相介质电晕放电和尘埃等离子体3个研究领域内关于颗粒物空间电荷效应的相关文献进行梳理,并对研究结果进行总结;指出当前对输电线路电磁环境影响的实验和理论研究中存在的问题,提出未来研究的建议。

负直流电晕流注脉冲特性随气压和湿度变化的规律

为得到负直流电晕流注脉冲特性随着气压和湿度变化的规律,建立考虑气压和湿度影响的流体模型,分别利用通量校正运移算法和分块方法求解了1维连续性方程和2维泊松方程。在人工气候罐中,利用棒–板电极,测量不同气压和湿度下的负直流电晕脉冲幅值和重复频率。计算和实验结果表明:特里切尔脉冲平均幅值及分散度随气压和湿度增大而减小。随着气压降低,电子密度增大,电导率升高,电流幅值增大。随着湿度升高,复合和附着作用增强,电子密度减小,电导率降低,电流幅值减小;同时,流注通道中包含的负离子数目减少,对阴极附近场强的影响减弱,使得阴极附近电场在负离子电荷迁移距离较短的情况下便满足新的特里切尔脉冲放电的要求,脉冲的重复频率增大。

空气温度对电晕笼中导线直流电晕特性的影响

为研究空气温度对导线直流电晕特性的影响,建立了导线直流电晕特性测试系统,定义了导线的起晕电压,在人工气候室内,测量了不同空气温度下电晕笼中导线的起晕电压、电晕电流、可听噪声水平等特征量,获得了空气温度对导线电晕特性的影响规律。试验结果表明:导线的起晕电压随空气温度的升高大致呈线性下降趋势;导线电晕电流在起晕后随空气温度的升高大致呈线性上升趋势;负极性导线电晕可听噪声水平随空气温度的升高而上升,且电压越高上升幅度越大;由于赫姆斯坦辉光过程的存在,正极性导线电晕可听噪声水平的空气温度修正系数在不同的电压时有不同的表现,并据此对我国特高压直流输电线路的工程设计提出了建议。

直流正极性下绞线电晕起始特性及影响因素分析

电晕是输电线路设计和运行中需考虑的重要问题之一。在多功能人工气候室内通过改变气压和湿度对3种不同直径钢芯铝绞线及光滑铜管进行正直流电晕试验,同时结合气体放电理论建立导线电晕起始放电模型以系统分析导线电晕起始特性影响因素。将试验数据和计算结果进行对比,两者吻合较好。电晕起始电压随相对空气密度下降、绝对湿度升高而减小,其主要原因是空气密度降低导致电离层厚度增大、湿度升高引起光子吸收系数增大及高场强区域内碰撞电离能力增强。此外,电晕起始电压随绞线半径增大和最外层股数增加而升高并呈现饱和趋势。文中还根据计算结果对绞线粗糙度系数与绞入率(绞线最外层铝线直径与绞线外径之比)的关系进行了探讨,从理论上得到表征绞线粗糙度系数的数学表达式。

气压和湿度对正直流电晕流注脉冲特性的影响

电晕是输电线路设计和运行中面临的重要问题之一。为此,测量了不同气压和湿度下的正直流电晕流注脉冲幅值和脉冲重复频率,实验结果与利用流体模型计算得到的波形随气压和湿度的变化规律一致。流注脉冲电流平均幅值Im随气压的降低和湿度的增大而减小。随着气压降低,流注头部电离减弱,使得注入流注通道的平均电子密度下降,流注通道内场强平均值E的降低是导致脉冲电流幅值下降的主要原因。随着湿度升高,流注头部电离减弱,使得注入流注通道的平均电子密度下降,流注通道内电导率λ的降低是导致脉冲电流幅值下降的主要原因。低湿度下,正直流流注电晕放电容易转化为辉光电晕,高湿度下,在较宽的电压范围内一直存在流注放电,流注脉冲平均频率随湿度升高显著增大。负离子解离产生自由电子的速率随湿度升高而减小,使得自由电子出现时,正离子已迁移到距离阳极较远的地方,是流注放电可以形成及流注脉冲重复频率随着湿度升高而增大的重要原因。

负直流下绞线电晕起始电压分析

电晕放电是输电线路设计和运行中面临的突出问题,电晕放电产生的能量损耗和无线电干扰、可听噪声干扰是线路设计和运行中需要考虑的重要因素。为求解绞线负直流电晕起始电压,采用模拟电荷法计算绞线表面电场,并利用气体放电理论建立模型。绞线表面电场比同等半径的光滑导线要高,利用绞线模型计算电场更接近于实际导线。电晕起始电压计算模型将初始电子崩能否在阴极表面产生一个自由电子触发二次电子崩的发展作为电晕起始电压的判据。利用电晕起始电压计算模型研究了负直流电晕起始电压与气压的关系,电晕起始电压随气压下降减小,主要原因是有效电离系数增大导致的电离区域的扩大。并研究了电晕起始电压与线路导线结构参数———导线半径、线路对地高度、导线分裂数、分裂间距等的关系。