Pollution control of actual flue gas using pulsed power at a thermal power plant

There are several important environmental problems in the world. One of them is acid rain caused by combustion flue gases from thermal power plants, factories, and automobiles. Different kinds of gas discharges, such as surface discharge, dc and ac corona discharge, silent discharge, and electron beam controlled discharge, have been studied for the removal of NO_x and SO₂ from flue gases. The recent development of repetitive pulsed power generators gives the pulsed steamer corona discharges a chance of success in the removal of NO_x and SO₂. In this paper, the experimental results of NO_x and SO₂ removal by a repetitive pulse power generator are described. The actual flue gas at a thermal power plant was used. It is shown that about 90% of the NO was removed at a flow rate of 0.8 liters/min and a repetition rate of 7 pps. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 28–35, 2001     

脉冲放电烟气脱硫脱硝与除尘相结合工艺研究

提出了一种脉冲放电烟气脱硫脱硝与除尘相结合工艺,除尘和脱硫脱硝过程在采用脉冲+直流供电的同一装置内完成,脱硫脱硝产物用直流电除尘回收。与现有脉冲放电烟气净化工艺相比,省去了专门的除尘装置,可降低投资,减少占地面积,且能保证回收产物的经济价值。     

Pulsed discharge purification of water containing nondegradable hazardous substances

We investigate the decomposition characteristics of phenol in an aqueous solution under exposure to pulsed discharge plasma. The investigation is carried out with different electrode configurations, applied voltages, and humidity levels and compositions of the background gas. It is possible that in the case of all gases, OH radicals are responsible for the decomposition of phenol in the solution. In pure O₂, the decomposition rate of phenol increases due to the generation of O and O₃. In pure N₂, OH radicals produced by N₂, which is excited in the metastable state, contribute to phenol decomposition. In N₂‐O₂, the decomposition rate of phenol remains low, and the NO_x produced by the pulsed plasma in a N₂‐O₂ mixture destroys O₃, and the production of the NO_x inhibits O₃ production. In Ar‐O₂, the decomposition rate of phenol increases with an increase in the concentration of Ar in the mixture. It is possible that excited Ar atoms are responsible for the decomposition of phenol in the solution at higher concentrations of Ar in Ar‐O₂. Further, it is found that the decomposition rate of phenol in aqueous solution exposed to a pulsed discharge is almost the same as that of phenol in aqueous solution exposed to a DC corona discharge. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 1–8, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.20937     

Effects of a barrier on creeping discharge characteristics in SF6 and N2 gases under pulse voltages

This paper describes the effect of a barrier on creeping discharge characteristics in SF₆, N₂, and their mixtures. The barrier height effect on the discharge voltage was investigated under a positive pulse voltage. The discharge voltage increased with increasing barrier height in SF₆ gas. On the other hand, the discharge voltage hardly changed with the barrier height in N₂ gas. In order to clarify the mechanism of the initial creeping corona, it was observed by optical techniques, including an ultra-high-speed electronic imaging system (IMACON 468). The creeping corona path revealed differences in images at various barrier heights. The accumulated charge induced on the barrier by the initial corona in SF₆ gas was able to suppress the development of the later creeping corona, in contrast with N₂ gas. © 1998 Scripta Technica, Electr Eng Jpn, 125(4): 1–8, 1998     

Treatment of exhaust gas from vehicles by discharge plasma reactors

The exhaust gas from diesel engines is one of the major causes of air pollution. As one method for pollution control, the authors have been developing plasma reactors. The authors' reactor is a concentric cylinder type which has a glass tube barrier between electrodes. Connecting two of these reactors in series, the NO_x (NO + NO₂) component from diesel engine exhaust gas is decomposed up to 93%. This reactor was mounted on a 3-liter diesel engine and received six-mode load testing at an authorized public facility (JARI, Tsukuba City) and cleared the legal critical value of 350 ppm of NO_x. By this success, the effectiveness of discharge plasma treatment of diesel exhaust gas and its practical evaluation have been confirmed. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(2): 1–7, 1997     

High Selective deNO x Electrochemical Cell with Self-Assembled Electro-Catalytic Electrode

A new family of electrochemical cells for decomposition of NO gas in the presence of excess O₂, in which the cathode was covered with mixed oxide layer of NiO and YSZ (electro-catalytic electrode) were designed and investigated. The deNO_x properties were increased by microstructural and compositional control of the electro-catalytic electrode. Nano-size Ni grains were self-assembled at NiO/YSZ interfaces by oxidation-reduction reaction of the NiO during the cell operation. In order to use the reduced Ni for NO decomposition reaction effectively, the authors investigated multilayering of the electro-catalytic electrode. Through this process, the adsorption of coexisting O₂ was prevented and the deNO_x properties of the electrochemical cell were improved.     

放电电场对SO2气相传质过程的影响

研究了SO2在放电电场中的气相传质过程。通过模拟试验，研究了外加电压、放电区长度、放电空间大小等与放电电场相关的参数对SO2电迁移和脱硫效率的影响。试验结果表明：放电电场对SO2传质过程具有促进作用，这种促进作用和系统脱硫效率随电压升高、放电区长度和单位能耗增加、放电空间减小而增加。放电电场之后的辅助匀强电场有助于改善SO2的电迁移效果。系统脱硫效率可达95%以上，由放电电场促进SO2传质而引起的脱硫效率增量接近50%。     

Characteristics of N2/SF6 mixture gas in creeping discharge developing in narrow gap with backside electrode

The flashover voltage with a backside electrode was found to be lower than that without the backside electrode. Under microsecond pulse voltage application, we describe the characteristics of a creeping discharge developed in the narrow gap with the backside electrode. Using a CCD camera and ultrahigh‐speed camera, we observed the corona extension processes. The lowest flashover voltage was found to be obtained at positive polarity with a SF₆ content D = 3%. In the corona extension obtained using an ultrahigh‐speed camera, peculiar differences were observed in the corona extension process. The corona extension increased, and rapid flashover was observed at D = 3%. Using a CCD camera, small coronas were detected from the backside electrode. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 31–38, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20431     

Formation Characteristics of SF6 Decomposition under Partial Discharge Induced by Metal Protrusions with Varying Degrees of Severity

Due to its excellent insulating and arc-suppression properties, sulfur hexafluoride (SF₆) is widely used in gas-insulated switchgear. In the presence of partial discharge, SF₆ decomposes into various by-products according to discharge scenarios. These by-products are often used to detect and identify partial discharge. In this article, formation characteristics of SF₆ decomposition under partial discharge induced by metal protrusions with varying degrees of severity are investigated. The varying degrees of severity of partial discharge were assessed by partial discharge applied voltage and partial discharge inception voltage. Partial discharge applied voltage and partial discharge inception voltage are related to magnitude of partial discharge and varying degrees of the non-uniform electric field distribution distortion, respectively. The results show that the production rates of SO₂F₂ and SOF₂+SO₂ decrease with increasing partial discharge inception voltage, while increasing proportionally to partial discharge applied voltage. The ratio of SO₂F₂ to (SOF₂+SO₂) exhibits a similar trend. As partial discharge applied voltage increases, the production rates of CO₂ and CF₄ increase, but the ratio of CO₂ to CF₄ decreases. Based on the experiments, the formation mechanisms of SF₆ decomposition by-products under varying degrees of severity of partial discharge are analyzed.     

等离子体资源化模拟烟气脱硫的实验研究

针对目前传统烟气脱硫方法不能完全满足需要的情况,采用强电离放电的方法产生非平衡等离子体,进行了不外加吸收剂和催化剂的SO2脱除实验研究,该法在密闭的等离子体反应器中将SO2直接氧化为H2SO4,实现资源化脱硫且无二次污染。实验分别研究烟气的φ(H2O)、初始φ(SO2)、外加电压U、停留时间tr等因素对脱硫效率η的影响。结果表明,U=3.5 kV、气体流量Q=0.16 m3/h、φ(H2O)=2.1%t、r=0.85 s时,η可达80%。     

Laser‐induced burst corona and streamer corona for a positive DC nonuniform field gap in N2/NO mixtures

The characteristic of sparkover in a DC nonuniform field gap is closely related to the discharge mode at the onset time of corona. In order to investigate the transition mechanism from burst corona to glow corona or streamer corona, a discharge experiment which is controlled by a pulsed laser in N₂/NO mixture has been performed. From highly sensitive observation of discharge luminescence which corresponds to the discharge current wave, the transition from burst corona to streamer corona is identified by the electron avalanche, which is formed initially at the tip of the rod electrode with the highest electric field, and the effect of secondary ionization. Moreover, it is verified that the measured electron burst drift time with laser irradiation in the discharge gap is determined by the electric field of the discharge gap. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(2): 10–17, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10007     

电子束法脱NO_x的能耗分析与脉冲电子束实验

成都电厂200MW机组锅炉30万Nm3/h烟气电子束脱硫硝示范工程是目前世界上已投入运行的处理烟气量最大的电子束脱硫装置,其脱硫率及脱硝率均分别>80%及10%的设计值。为了衡量该法的经济效益,以其实际运行数据为依据,分析计算了该法脱硫硝工艺过程各主要部分能耗所占的份额,得出脱除每个NOx和SO2分子的能耗分别为12.39eV和0.563eV,两者有协同脱除效应;将运行能耗点折算成常用的单位体积能耗后,列入国际上基于高电压技术发展的两类主要技术-电子束法和脉冲电晕法的能耗比对图的结果表明,电子束法在能耗方面优于脉冲电晕法,后者能耗约是前者的3倍。为发展此类高电压、高效率环保装备,给出了近期2.6A强流脉冲电子束最新实验。     

超低排放改造前后SCR脱硝装置性能评价分析

选取2台燃煤机组进行实测,分析了超低排放改造前后选择性催化还原技术(selective catalytic reduction,SCR)脱硝装置出口NOx浓度、氨逃逸率以及烟气在线监测系统所测SCR脱硝出口与烟囱入口NOx浓度;同时,分析了超低排放改造机组的催化剂、空预器垢样。结果表明,机组排放超低改造后存在NOx浓度分布均匀性变差和逃逸氨浓度急剧增加问题,并由此造成空预器硫酸氢铵堵塞严重,催化剂活性成分流失较为严重,硫酸盐和碱土金属元素含量上升明显。为解决上述问题,文中提出多点监测、喷氨优化、催化剂定期测试和空预器冷端更换镀搪瓷元件等措施。     

等离子体作用下甲烷和氮氧化物活化转化研究

比较了不同的放电方式,即单纯脉冲火花放电、脉冲流光放电(针-板式、线-筒式)、介质阻挡放电(正脉冲、交流)对NO和CH4的活化转化能力。其中脉冲火花放电和针-板式脉冲流光放电对CH4的活化能力较强,CH4的最大转化率分别为100%和36%,但是在N2+O2体系中NOx的合成加剧。如在针-板式脉冲流光放电中,在O2体积分数为9.8%时,NO的体积分数为449μL/L。线-筒式脉冲流光放电中,即使在输入功率为14.4W时,CH4的最大转化率小于3%,而NO的最大转化率为25%。正脉冲介质阻挡放电中,在21.6kV、输入功率6.4W时,NO和CH4的转化率分别为31%和4.4%,在交流介质阻挡放电中,在低温下有利于NO的转化,在100℃、输入功率为6W时,NO转化率为34.5%,但是对CH4的活化能力较弱。     

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。     

Positive Creeping Discharge along Aerial Insulated Wire Generated by Lightning Stroke

There are two causes, inductive lightning surge and direct lightning stroke, as the aerial insulated wire accidents accompanying lightning in a power distribution system. When the overvoltage due to the inductive lightning surge invades to the wire core, the creeping discharge can develop along the wire surface from the free end of the binding wire just after a flashover of the post insulator at the wire supporting point. This creeping discharge may give rise to the accidents such as a melting or snapping of the wire. The creeping discharge along the wire surface has the positive or negative polarity. Positive creeping discharge is restricted to the area where a positive lightning generates. Only a few examples have been reported on the positive creeping discharge, and its characteristic has many unsolved points. In the previous studies, we have observed the positive creeping discharges along the wire surface under the negative inductive lightning surge with the peak values in the range |V_m| ≤80 kV. In this study, the positive creeping discharges are examined newly in the range |V_m| > 80 kV. It is reported that the positive creeping discharges are greatly affected by the negative corona discharges generating from the wire surface in |V_m| ≥ 95 kV.     

Impulse insulation characteristics of a composite insulation system having a wedge gap in SF6 gas

Impulse insulation characteristics were investigated in a composite insulation system having a wedge gap in SF₆ gas. The partial discharge inception voltages of wedge gaps with various types of film were measured and compared with the calculated breakdown voltages estimated from Paschen's curve of SF₆ gas. Also discussed is how the charge accumulated on the film surface due to a partial discharge had an effect on the creepage breakdown voltage. Partial discharge inception voltages in wedge gaps were higher with higher SF₆ gas pressures and with lower film permittivities. Creepage breakdown voltages depended little on gas pressures or on creepage distances. The dependency of breakdown voltages on gas pressures and the effect of polarity on the breakdown voltage differed with the types of film. This may be partly because the charge on the film due to partial discharge had an effect on the discharge propagation, and that charging of the film differed with the types of film.     

水界面电晕放电脱硫脱氮的等离子化学反应研究

以控制大气污染为目的,对锅炉排烟进行脱硫、脱氮和除尘。依据气水界面电晕放电机理,提出了一种气-水协同电晕放电净化法。为了实现除尘与脱硫脱硝一体化,设计了烟气净化模型和它的实验系统,并进行了脱硫实验模拟和等离子化学分析。     

Economic and environmental dispatch of power/CHP production systems

The paper describes a method for complying with emission quotas for a power producing or CHP producing system in an economically rational and optimal way. The method is based on extended use of a simulation model (SIVAEL) and a pre-processor which optimises the environmental aspects of each system unit. SIVAEL is a unit commitment/load dispatching model, which solves the problem of optimal scheduling of CHP production. On a weekly basis, the scheduling of power producing units, heat producing units and units with-CHP production is laid down. The pre-processor, PRESIVAEL, calculates the environmental parameters of each system unit. When handling the SO₂ quota, for instance the pre-processor optimises the operation of each coal-fired (or oil-fired) unit, including possible deSO_x plants. The application of the method is illustrated by examples.     

新型复合静电除尘器脱硝性能研究

NO是燃烧产生的重要气体污染物之一。脉冲放电与直流放电相结合的新型除尘方式在有效提高对粒径小于 2.5 mm的颗粒物(PM2.5)脱除效率的同时,还具有氧化NO的能力。高压脉冲放电产生的高能电子可以产生强氧化性的自由基,对NO进行氧化,同时还可以直接打断N-O键,游离态的N原子大部分生成了N2分子。线筒式放电结构氧化NO的能力明显优于线板式放电,与除尘能力具有一致性。氧化效率随着电压的升高而升高,由于一定电压下对NO的处理量趋于定值,氧化效率与NO的初始浓度具有重要的关系,同时也受NO2浓度的影响。在该文讨论的反应器中,当脉冲峰值电压达到50kV,NO初始体积分数低于10-4时,NO的氧化率可以达到90%以上。氧化产物NO2可以在湿法脱硫设备中脱除。