Superposed effect of UV rays on ozone generation by electrical discharge

Generally, ozone is generated by using silent discharge or surface discharge; however, the energy efficiency of ozone generation by using only one kind of discharge is about 200 g/kWh. The energy efficiency of ozone generation is about one-fifth of the theoretical energy efficiency. Ozone decomposition occurs at high concentrations, high temperatures, and so on. In order to increase ozone generation efficiency, many studies of ozone generation methods have been carried out to date. Experiments on ozone generation by using surface discharge and UV rays were carried out. In an experiment on superposing surface discharge and UV rays in the same space, the ozone yield by the superposing mode is lower than either the ozone yield by surface discharge or by UV rays at the same power. It appears that noticeable ozone dissociation by UV rays occurs because a high ozone concentration is achieved by the superposing mode. In cascade connection of a surface discharge reactor and UV lamp reactor, the ozone yield of the cascade mode (from the UV lamp reactor to the surface discharge reactor) is higher than that of the superposing mode at the same power. It is confirmed that cumulative disassociation is an effective reaction of ozone generation. © 1998 Scripta Technica, Electr Eng Jpn, 123(4): 8–14, 1998     

Improvement in ozone yield using discharge superposition method

The efficiency of ozonizers using silent discharge is very low compared with the theoretical value. Although many studies have attempted to improve the efficiency of ozonizers, we cannot expect to do so without changing the process of ozone generation. In this study, two high voltages are applied to an ozonizer which has three electrodes (central, surface, and outer electrodes) arranged coaxially, and the phase difference between applied voltages can be changed. The silent and surface discharges are superposed in the same space of the ozonizer. This paper considers the optimum experimental conditions leading to improved efficiency of an ozonizer using the discharge superposition method. It is found that when two kinds of discharges are superposed while using the central electrode as a common‐ground electrode, the maximum ozone yield efficiency is obtained, especially at a phase difference of about 180°. However, when using the surface electrode as a common‐ground electrode, the ozone efficiency is higher at phase differences of about 90° or 270° than at other angles. © 1998 Scripta Technica, Electr Eng Jpn, 126(1): 1–6, 1999     

Power supply based on a multi-stage-shunt class E amplifier applied to ozone generation with high efficiency

In this paper, the analysis, design, and implementation of a power supply based on a multi-stage-shunt class E amplifier applied to ozone generation are presented. The proposed topology operates with pulsating waveforms and allows unidirectional energy flow from the power supply to the load with no energy return. Furthermore, due to the multi-stage operation, it presents a lower stress in the switches compared with other similar topologies. To validate the proposed topology, a prototype was designed to feed a set of ozone generating cells in a power range of 0 to 500 W. This prototype provides an efficiency of 95% with an ozone production of 10.5 g/h and efficacy of 22.89 g/kWh. The proposed power supply is an alternative to feed any other type of dielectric barrier discharge load while keeping the efficiency of the power supply above 90%.     

Improvement of the energy efficiency in the decomposition of dilute trichloroethylene by the barrier discharge plasma process

In order to improve the energy efficiency in the dilute trichloroethylene (TCE) removal by the nonthermal plasma process, the barrier discharge reactor was studied experimentally. It is investigated by combining it with catalyst of manganese dioxide at the downstream of the barrier discharge reactor. Decomposition efficiency by the barrier discharge reactor was about 83% at the gas flow rate 2 L/min, where the dilute TCE concentration is 250 ppm. Decomposition efficiency with passing through manganese dioxide was improved about 99% at the specific energy of 40 J/L. However, other by-products including ozone and oxidation by-products such as DCAC and TCAA were detected by the gas chromatograph mass spectrometry or the Fourier transform infrared spectroscope measurement. DCAC is generated at the plasma reactor, but TCAA is generated at catalyst during ozone decomposition. CO/sub x/ yield increased about twice with passing through catalyst in the Direct Process. Nitric oxides such as NO, NO/sub 2/, and N/sub 2/O did not generate so much in this barrier discharge process. The dielectric barrier discharge process combined with manganese dioxide is considered as a very desirable way to improve the energy efficiency.     

双极性窄脉冲介质阻挡放电合成臭氧的研究

利用火花隙开关的双极性陡前沿窄脉冲高压电源 ,产生双极性陡前沿窄脉冲 ,在放电反应器中引发介质阻挡放电。试验结果表明 :该种形式的放电兼有短脉冲电晕放电和介质阻挡放电的优点 ,合成臭氧产率高 :进气为露点 <-40℃的干燥空气 ,臭氧质量浓度在 4～ 8g/ m3时 ,产率为 90～ 12 0 g/ (k Wh) ;进气为工业瓶装氧气 ,臭氧质量浓度在 3～18g/ m3时 ,对应产率为 30 0～ 390 g/ (k Wh) ,对比普通的介质阻挡放电提高产率幅度 >30 %。     

结构及供电电源对沿面介质阻挡放电装置放电特性及臭氧生成的影响

沿面介质阻挡放电(SDBD)等离子体能够高效生成反应活性物质,在生物医学、环保等应用领域得到广泛研究。SDBD装置的结构和供电电源参数是影响其放电特性及反应活性物质生成的主要因素,为此,以具有螺环线形高压电极的管状沿面放电装置为对象,研究了装置结构及供电电源对其放电特性及臭氧生成的影响。结果表明:在相同的供电电压下,螺环线形高压电极的螺距、介质厚度影响电极间的电场强度和分布、放电功率和臭氧生成量,但螺环线形高压电极的线径对放电功率和臭氧生成量几乎没有影响;螺环线形高压电极的螺距存在一个优化值,在螺距低于25mm时,放电功率和臭氧产生量随着螺距的增加而增加,当螺距大于25mm时,放电功率和臭氧产生量基本不再变化;当绝缘介质管厚度由3mm减小到1.6mm时,放电功率提高约2倍,臭氧产生量提高约3倍。同采用50Hz交流电源供电相比,SDBD装置采用9.6k Hz高频电源供电时,在较低的电压下即可获得较大的放电功率及臭氧产量,且臭氧生成的能量效率提高约25%。     

Ozone production using pulsed dielectric barrier discharge inoxygen

The production of ozone was investigated using a dielectric barrier discharge in oxygen, and employing short-duration pulsed power. The dependence of the ozone concentration (parts per million, ppm) and ozone production yield (g(O₃)/kWh) on the peak pulsed voltage (17.5 to 57.9 kV) and the pulse repetition rate (25 to 400 pulses/s, pps) were investigated. In the present study, the following parameters were kept constant: a pressure of 1.01×10⁵ Pa, a temperature of 26±4°C a gas flow rate of 3.0 1/min and a gaseous gap length of 11 mm. A concentric coaxial cylindrical reactor was used. A spiral copper wire (1 mm in diameter) was wound on a polyvinylchloride (PVC) cylindrical configuration (26 mm in diameter) and placed centrally in a concentric coaxial electrode system with 4 mm thick PVC dielectric layer adjacent to a copper outer electrode of 58 mm in internal diameter. HV and current pulses were provided by a magnetic pulse compressor power source     

SPWM电源频率对DBD臭氧产生影响的试验研究

介质阻挡放电产生臭氧与工作频率关系密切,臭氧的产量、浓度与产率指标往往相互背离,研究工作频率对臭氧指标的综合影响有重要意义。SPWM电源与臭氧发生器负载的等效电路及仿真结果表明SPWM输出方波的基波为正弦波,幅值10%~95%可调,频率50~2 000 Hz可调,可方便地用于测试频率对臭氧产生性能的影响。搭建由145根放电单元组成的工业应用级臭氧发生器,设计单相三阶SPWM臭氧电源,试验结果表明：谐振频率点随调制度的改变、运行电压的高低会有些变化,当工作频率略低于谐振频率时,发生器性能指标较好,当工作频率大于谐振频率时,臭氧浓度、产率等性能指标出现较大幅度下降。该装置SPWM电源在三种不同的试验路径下,均可优选出合适的工作频率,其中一个优选工作频率为810 Hz,此时臭氧产量为2 095 g/h,臭氧浓度为150.7 g/m³,产率为135.1 g/（kW·h）。     

Diesel engine exhaust treatment with a pulsed streamer coronareactor equipped with reticulated vitreous carbon electrodes

Reticulated vitreous carbon (RVC) has been shown to be useful for high-voltage and ground electrodes in gas-phase pulsed streamer corona reactors. RVC disks with large macroscopic porosity are placed perpendicular to the gas flow and the main axis of a cylindrical corona reactor. This electrode geometry produces streamers that propagate in the direction of the gas flow and are uniformly distributed in the cross section of the reactor. This highly electrically conductive material has large macroscopic porosity, thus allowing for gas flow through the electrodes with low pressure drop. Previous work has considered the effects of RVC electrodes on NO/NO_x removal from various test gases containing air, water vapor, and ethylene. The present studies show removal of NO/NO_x from the exhaust of a 5 kW diesel engine. Under cold reactor operating conditions (12°C) 81% NO and 53% NO_x could be removed at an energy yield of 4.8 g/kWh (based on NO). Furthermore, experiments with the combination of TiO₂ or γ-Al₂O₃ catalyst particles placed in the region between the high-voltage and ground electrode disks gave NO removal at energy yields of 29 g/kWh and 9 g/kWh, respectively, at about 100°C, and significant fractions of the nitrogen were recovered as NO₃^- deposited on the catalyst surface. The RVC electrode system without catalysts was found to lead to efficient ozone production (55-70 g/kWh) in dry air at room temperature     

Structural and electrochemical properties of LiNi0.7Co0.15Mn0.15O2 thin film prepared by high frequency hybrid direct current and radio frequency magnetron sputtering

A LiNi_0.7Co_0.15Mn_0.15O₂ thin film cathode has been successfully prepared by hybrid direct current - radio frequency magnetron sputtering onto glass substrate from the LiNi_0.7Co_0.15Mn_0.15O₂ target and post-annealed by the rapid thermal annealing process. Its structure and morphology were characterized by X-ray diffraction, and scanning electron microscopy while its chemical compositions were confirmed with the inductively coupled plasma atomic absorption spectrophotometer, Raman spectroscopy, Auger electron spectroscopy, and glow discharge spectrometer. Its electrochemical properties were measured by galvanostatic charge - discharge test and cyclic voltammetry. First discharge capacity of 73 μAh?cm^?2?μm^?1 was obtained from a half cell with the LiNi_0.7Co_0.15Mn_0.15O₂ thin film cathode and lithium metal anode in the potential range of 4.3?~?2.5 V at 30 μA and its coulombic efficiency was more than 99 %.     

Initiation of a discharge channel in water by means of electrical explosion of aluminum foil

This paper reports the results of an experimental investigation into initiation of the electric discharge in service water by means of explosion of aluminum foil having various mass and dimensions. The electric discharge was formed in a chamber with a movable wall (the piston). As an electric energy storage, the capacitor bank having the capacity C = 200–600 μF with charging voltage U ₀ = 2–5 kV (stored energy Q ₀ = 0.4–7.5 kJ) and the rate of rise of the discharging current dI/dt = (3–4) × 10⁹ A/s. The results of experiments showed that destruction (loss of conductivity) of foil occurs at the value of the integral of the current density h _j = (0.3–0.65) × 10⁹ (A²/cm⁴)/s. The stage of the repeated breakdown in the electric discharge occurs when the value of the intensity of the electric field along the discharge channel is of E _rb ≥ 50 V/mm. Geometric dimensions and mass of the initiating conductor that provide the maximum efficiency of conversion of the value of Q ₀ into kinetic energy of the piston have been determined.     

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     

Change of characteristics of desulfurization and denitrification by combustion flue gas composition and electrode configuration under pulsed corona discharge

Laboratory-scale and parametric experiments of SO₂ and NO_x removal from the simulated combustion gas by pulsed corona discharge have been performed by changing the combustion gas composition and temperature, the electrode configuration of plasma reactor, and the polarity of high-voltage electrode. The following results are obtained: 1) the higher the concentration of H₂O and O₂, the higher the efficiency of desulfurization and denitrification at the same specific input; 2) the pulsed corona discharge with a voltage pulsewidth as short as 200 ns of negative polarity shows the possibility to attain almost 90 percent deSO_x and deNO_x efficiency at the specific discharge input of 20 J/g, which is almost the same as the specific input in the electron-beam process; 3) the deNO_x characteristics show a little temperature dependence in the range of 70 to 130°C, but the deSO_x efficiency increases rapidly in the temperature region below 100°C suggesting the thermochemical dependence of deSO_x reaction; 4) when desulfurization and denitrification proceed, the white dendritic powder deposits on the plasma reactor whose composition is identified to be 49 mol% (NH₄)₂SO₄ and 47 mol% of 2NH₄NO₃ · (NH₄)₂SO₄, and the ratio of SO₂, NO and NH₃ of the deposit is almost equal to that of supplied gas.     

A ceramic-based ozonizer using high-frequency discharge

A thin ceramic layer, either cylindrical or planar in form, is sandwiched by a number of parallel strip-like discharge electrodes and a film-like induction electrode. An AC exciting voltage of frequency 10 kHz and 10 kV peak-to-peak (p-p) is applied between the electrodes to produce a stable high-frequency surface glow discharge for generation of ozone. As a result of its high frequency, low exciting voltage, and small size, a great reduction in cost is achieved in both the ozonizer and its power supply. The presented ozonizer can easily produce a very high ozone concentration (5000-15000 volume p.p.m. for air; 50-100000 volume p.p.m. for oxygen) without using a special enrichment means. Its power efficiency can be made very high (170 gO/kWh for air) by proper selection of operating parameters     

Synthesis of anatase TiO2 film by reactive vacuum arc deposition method

TiO₂ in anatase crystalline structure has strong photocatalysis. In this paper, TiO₂ films are deposited on soda‐glass substrate using a Ti cathode vacuum arc with O₂ flow. Experimental conditions are as follows: arc current, 50 A; pressure, 0.3 and 1.0 Pa; O₂ flow rate, 20 ml/min; cathode–substrate distance, 250 mm; bias dc voltage to the substrate, none and –300 V. As‐deposited films are annealed for 60 min under atmosphere and vacuum. The following results were obtained. (1) Deposition rate is 0.07 μm/min. (2) As‐deposited films are amorphous. (3) Films annealed at 250 to 500 °C have an anatase crystalline structure. These results are independent of pressure, bias, and annealing environment. In another process, the films are deposited for 30 min when the substrate holding table is connected to the anode chamber. Experimental conditions are as follows: arc current, 50 A; pressure, 1.0 Pa; O₂ flow rate, 20 ml/min; cathode–substrate distance, 250 mm. Almost 30% of the arc current was observed to flow through the substrate table, and the surface temperature of the table increased up to 450 °C. The reason for this is considered to be that Joule heating occurs when the current flows through the film deposited on the table. The film deposited in this process is dominantly anatase. The above experiments show that anatase TiO₂ film can be deposited on soda‐glass by the reactive vacuum arc method. © 1999 Scripta Technica, Electr Eng Jpn, 126(4): 12–20, 1999     

A new type of ozone generator using Taylor cones on water surfaces

Ozone has been found to be effective in many forms of water treatment. As concerns about the safety of alternate methods of water treatment increase (in particular, chlorination), ozone, which is already extensively used in Europe, offers an effective option. This paper describes a new method of ozone generation particularly suited for use in water purification. Most current industrial ozone production is based on “silent” electrical discharges in a gap between concentric electrodes separated by a glass or ceramic dielectric barrier. The authors present experimental results obtained using a parallel-plate discharge geometry. The lower electrode consists of a grounded “pool” of still water separated by a discharge gap from an upper insulated planar electrode. When the electrode is energized by an AC high voltage, a multitude of “Taylor cones” forms on the water surface. The Taylor cones form and collapse randomly and continuously, depending on the electric field. The tips of the cones provide points for electrical discharge pulses which initiate ozone generation. This method generates ozone in close proximity to the water surface. Laboratory experiments show efficiencies for gaseous ozone production as high as 110 g/kWh     

Influence of voltage rise time on oxidation treatment of NO in simulated exhaust gas by polarity‐reversed pulse discharge

This paper describes an experimental study of NO removal from a simulated exhaust gas by repetitive surface discharge on a glass barrier subjected to polarity‐reversed voltage pulses. The very fast polarity‐reversal with a rise time of 20 ns is caused by direct grounding of a charged coaxial cable 10 m in length. The influence of the voltage rise time on energy efficiency for NO removal is studied. The results of NO removal using a barrier‐type plasma reactor with a screw‐plane electrode system indicate that the energy efficiency of very fast polarity reversal caused by direct grounding is higher than that of slower polarity reversal caused by grounding through an inductor at the cable end. The energy efficiency of direct grounding is approximately 80 g/kWh for a 50% NO removal ratio and approximately 60 g/kWh for a 100% NO removal ratio. Very intense discharge light is observed at an initial time of 10 ns for fast polarity reversal, whereas the intensity of the initial discharge light for slower polarity reversal is relatively small. To confirm the effectiveness of the polarity‐reversed pulse application, a comparison of the energy efficiency of polarity‐reversed voltage pulses and an AC 60‐Hz voltage is presented. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(4): 32–38, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21215     

Pulsed power production of ozone in O2/N2 ina coaxial reactor without dielectric layer

Very short duration pulsed streamer discharges have been used to produce ozone in a gas mixture of nitrogen and oxygen at atmospheric pressure. The ratio of nitrogen to oxygen in the mixture was varied in the range from 2.5/0.5 to 0.5/2.5, while maintaining a total flow rate of 3 l/min. The production of ozone was found to be higher for a specific mixture ratio of N₂/O₂ than that in oxygen or in dry air. The production of ozone in O₂ was higher than that in dry air. The production yield of ozone (g/kWh) increased with decreasing nitrogen in the O₂/N₂ mixture. It has been found that the peak of the streamer discharge current decreased with time after application of the pulsed power. This decrease in the current corresponded with the increase in the ozone production and is attributed to the loss of electrons in the discharge current due to their attachment to ozone to form negative ions     

Destruction of volatile organic compounds used in a semiconductorindustry by a capillary tube discharge reactor

Nonthermal plasma technologies offer an innovative approach to the problem of decomposing various volatile organic compounds (VOCs). The authors focused on DC capillary tube discharge plasma reactors to study the decomposition/destruction efficiency for toluene, EGM, trichloroethane and trichloroethylene at 50-2300 ppm levels in dry air. The effects of gas flow rate, VOC concentration and reactor operating conditions on decomposition and analysis of reactant conversion for each VOC were investigated. The results show that VOC destruction efficiency as high as 90% can be achieved, even under a short residence time (3.8 ms) with a destruction energy efficiency of up to 95 g (VOC)/kWh. Laboratory-scale plasma technology was successfully demonstrated for its potential application for VOC control in the semiconductor clean-room environment     

Fabrication and performance of a ScMnSZ/LaSrCuFe cell with GDC interlayer for solid oxide fuel cells

Strontium- and copper-doped lanthanum ferrite (LaSrCuFe) was used as new cathode material for solid oxide fuel cells (SOFCs) with scandia-stabilized zirconia electrolyte at intermediate temperatures. The performance of an anode-supported single cell prepared using a Ni/YSZ anode, ScMnSZ ((ZrO₂)_0.89(Sc₂O₃)_0.1(MnO₂)_0.01) electrolyte, and a LaSrCuFe cathode was evaluated. The effects on the cell performance of the GDC (GD_0.1Ce_0.9O_1.95) interlayer between the electrolyte and cathode were also investigated. The microstructure and chemical composition of the cell were analyzed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS). AC impedance spectroscopy was used to measure the polarization resistance of a single cell. The results highlight the promising combination of ScMnSZ electrolyte and LaSrCuFe cathode material in terms of chemical compatibility and electrical performance.