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     

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.     

Basic characteristics of Ar/N2 atmospheric pressure nonequilibrium microwave discharge plasma jets

To understand the mechanism of surface processing by atmospheric pressure nonequilibrium microwave discharge plasma jets of coaxial type without a resonator, we measured the vibrational and rotational temperatures in plasmas using optical emission spectroscopy. The plasma was excited by a microwave power supply, using a gas mixture of Ar and N₂ as the plasma gas, and changing the flow rate of N₂ gas. We also measured the change in the contact angle of a PET film before and after the plasma processing. It decreased as the plasma rotational temperature increased, indicating that the hydrophilicity of the PET surface was improved as the plasma rotational temperature became higher. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Discussion on population kinetics and number densities of excited species of low‐pressure discharge nitrogen plasma

A numerical model is constructed to calculate the number densities of some excited species of nitrogen in low‐pressure discharge nitrogen plasma, together with simultaneous solution of the self‐consistent electron energy distribution function and N₂‐vibration distribution function. We consider species N₂(X), N₂(A), N₂(B), N₂(C), N₂(a), N₂(a′), N2+, N4+, N(⁴S) ande⁻. In addition to electron collisional reactions, diffusion losses and molecular relations are included. It is found that the ratio of number densities of N₂(B) and N₂(C) states can be a good measure of the electron kinetic temperature. The N₂(C) state is found to be almost in a corona equilibrium, whereas the N₂(B) state becomes mainly populated by N₂(X,v≥6) + N₂(A) reaction and depopulated by collisional relaxation by the ground‐state N₂(X) molecule. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Preparation of SnO2 whiskers via the decomposition of tin oxalate

A new method for preparing SnO₂ whiskers by the decomposition of SnC₂O₄ is suggested. A Whisker-like morphology of a SnC₂O₄ precipitate was attained via the gradual addition of an oxalic acid solution to a hot SnCl₂ aqueous solution (T > 50^∘C). In comparison, when the solution temperature was either lower than 50^∘C or when ethanol was used as the solvent, the SnC₂O₄ precipitate showed an angular and relatively isotropic morphology. The morphology of the SnC₂O₄ precipitate remained even after its thermal decomposition into SnO₂ at 400^∘C indicating that SnC₂O₄ precipitation is a key step in preparing the whiskers. The formation mechanism of SnO₂ whiskers was explained by the supersaturation during the precipitation of SnC₂O₄.     

Water treatment with pulsed discharges generated inside bubbles

The parallel operation of pulsed discharges generated inside bubbles is successfully demonstrated by applying a fast rising voltage to a multielectrode system immersed in treated water. A 10 ppm solution of acetic acid, which cannot be decomposed by ozone, was used as a persistent material and the acetic acid decomposition efficiency was evaluated by measuring the total organic carbon (TOC) values of the solution. The electric conductivity of the solution affected decomposition efficiency because the solution resistance, which was inversely proportional to the conductivity, limited the magnitude of the discharge current flowing along the surface of the bubbles generated by the feeding of oxygen or argon gas. With a nine‐hole electrode system, the discharge power deposited in one discharge was lower, and the acetic acid decomposition efficiency was higher, than the values obtained with a single‐hole electrode system. Lower discharge power seemed to minimize the self‐quenching of OH radicals, and resulted in the efficient decomposition of acetic acid. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 1–7, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20918     

Structure and electrochemical performance of LiFexNi1-xO2 (0.00 ≤ x ≤ 0.20) cathode materials for rechargeable lithium-ion batteries

LiFe_xNi_1-xO₂ (0.00?≤?x?≤?0.20) nanoparticles were synthesized by sol–gel method using aqueous solution of metal nitrate precursor at 600 °C for 10 h. Structure and physical properties were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscope (TEM) and X-ray photoelectron microscopy (XPS) analysis. XRD studies revealed a well defined layer structure and a linear variation of lattice parameters with the substitution of Fe confirms phase pure compounds in a rhombohedral structure for all the materials. The surface morphology and particle size changes brought about by the substitution of Fe in LiFe_0.15Ni_0.85O₂ using SEM and TEM analysis. Electrochemical properties of the as prepared LiFe_xNi_1-xO₂/Li/LiPF₆ in assembled cells were studied by charge/discharge, cyclic performance and different discharge rates. LiFe_0.15Ni_0.85O₂ shows better electrochemical properties than LiNiO₂ with the highest charge/discharge capacity (214/191 mAh/g) discharge rate of 0.5-C among LiFe_xNi_1-xO₂ (0.00?≤?x?≤?0.20). LiFe_0.15Ni_0.85O₂ was superior electrochemical properties, such as high charge/discharge capacity, high coulombic efficiency and low irreversible capacity.     

Aqueous Phenol Decomposition by Pulsed Discharges on the Water Surface

Decomposition of environmental contaminants such as phenol contained in water was investigated using a pulsed high-voltage gas-phase discharge on the water surface (water surface plasma). The discharge consists of streamer channels that spread out over the water surface. Discharge characteristics were dependent upon the distance between the needle-tip electrode and the water surface, the shape of the submerged ground electrode, and the composition of the gas enveloping the electrode. When the electrode–water distance was decreased, the discharge mode changed from corona to streamer, and then, finally, to a water surface discharge when the distance was small. Argon gas was the most effective enveloping gas for decomposing phenol in water (compared to oxygen or air). When the gas flow rate was increased to carry away the active species formed in the gas phase; the decomposition rate did not change in argon, but decreased in oxygen. The shape of the submerged ground electrode influenced the discharge state and the phenol decomposition rate. A ring-shaped ground electrode was more effective for decomposition of phenol than straight or semicircular shapes. Experiments were performed to identify the mechanism(s) responsible for the decomposition of organic materials in water.      

Decomposition Characteristics of an Artificial Biogas in a Low‐Pressure DC Glow Discharge

The decomposition characteristics of an artificial biogas, which is a mixture of CH ₄, CO ₂, and H ₂ S, using a low‐pressure DC glow discharge have been investigated. It is found that H ₂, CO, C ₂ H ₂, H ₂ O, CS ₂, and COS are produced from the artificial biogas in the glow discharge. About 65% of the hydrogen atoms in CH ₄ are converted into H ₂ at an input energy of 800 J, at which CH ₄ is completely decomposed, and the decomposition characteristics of the artificial biogas are minimally dependent on the H ₂ S additive. Further, H ₂ S has a tendency to be decomposed earlier than the other components of the artificial biogas. When the glow discharge is generated in the artificial biogas with H ₂ S, some of the carbon atoms are found to deposit on the electrodes and the wall of the discharge chamber. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 26–33, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22304     

Voltage-current characteristics of high-current pulsed discharges in SF

A high-current pulsed discharge in SF₆ has been used as a closing switch for a pulsed power generator. The characteristics of a high-current pulsed discharge are not clear, since it is difficult to measure the time-dependent arc voltage accurately. In the present paper, the voltage-current characteristics and the time-dependent arc resistance of the high-current pulsed discharge in SF₆ are obtained accurately from the arc current and the breakdown voltage by solving the circuit equation. The electrode separation and the pressure are changed from 0.1 to 1 cm and from 200 to 760 torr, respectively. The current rise time is about 380 ns. The minimum arc resistance occurs at the maximum arc current, and is from 0.04 to 0.1 Ω under the experimental conditions. The voltage-current characteristics in SF₆, which are characterized by five phases, are similar to the characteristics in air but not in Ar.     

A study on condition assessment method of gas‐insulated switchgear. part II. influence of moisture in the SF6, detection of a partial discharge on a spacer,repetition discharge and overheating by incomplete contact

Rationalization of the maintenance of gas‐insulated equipment under operation and lifetime extension based on the results of appropriate diagnosis are necessary to reduce the cost of gas‐insulated equipment. Therefore, condition‐based maintenance (CBM) is required and accurate methods for observing the inside of equipment are important. In this report, we describe a diagnosis method that can be used for actual gas‐insulated equipment, such as to assess the deterioration of the spacers made of epoxy resin and to detect loose connections in the central conductor. The principal results are summarized as follows: (1) The quantity of decomposition gases depends on the moisture and magnitude of the partial discharge. However, decomposition gases were detected even if SF₆ had low moisture content (less than 100 ppm) similar to that used in actual equipment. This means that our method can be applied to actual equipment. (2) It became clear that CF₄ is a typical gas generated by partial discharge on the spacer surface. Therefore, it is possible to diagnose spacer deterioration by monitoring CF₄. (3) Decomposition gases (SF₄, SO₂, SO₄, SO₂F₂) were generated by impulse breakdown, which was assumed to be due to repetition discharge caused by insulation failure and loose connections. (4) SF₆ gas was assumed to be exposed to a loose connection and was heated from room temperature to 800 °C, and the generated decomposition gases were analyzed by FTIR in real time. As a result, the decomposition gases were generated at temperatures above approximately 500 °C in a heating time of 1.5 minutes. Therefore, a loose connection can be detected by analyzing the decomposition gas. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(2): 22–30, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21108     

Effect of etch gases on iridium etching using a hard mask

Abstract

The dry etching of iridium(Ir) and iridium oxide(IrO₂) using a hard mask has been studied in a high density Inductively Coupled Plasma (ICP). The etch rate and etch selectivity have been obtained in terms of gas chemistry including CI₂/O₂/Ar, HBr/O₂/Ar, and C₂F₆/O₂/Ar gases. The etch profile and the etch mechanism have been examined for various etch gases by using field emission scanning electron microscopy (FESEM) and field emission auger electron spectroscopy (FEAES). In addition, the electrical properties of the etched ferroelectric capacitors were measured for each etching gas.     

NOx Sensing Properties of Varistor-Type Gas Sensors Consisting of Micro p-n Junctions

NO _x sensing properties of SnO₂-xCr₂O₃ as a varistor-type gas sensor have been investigated in the temperature range of 200–600°C. The breakdown voltage of SnO₂ shifted to a higher electric field upon exposure to NO₂ at 300–500°C, and the largest breakdown voltage shift, i.e. the highest NO₂ sensitivity was observed at 400°C. In contrast, the direction of the breakdown voltage shift in NO varied with temperature: the breakdown voltage shifted to a lower electric field at 300°C, but to a higher electric field at 500°C, and remained almost unchanged at 400°C. The NO₂ sensitivity of SnO₂ was superior to the NO sensitivity at every temperature, and then the SnO₂ exhibited good selectivity to NO₂ at 400°C. The breakdown voltage of Cr₂O₃ shifted in the reverse direction upon exposure to NO and NO₂, in comparison with those observed with SnO₂, owing to its p-type semiconductivity. Thus, Cr₂O₃ also exhibited certain sensitivity to both NO and NO₂ at 200°C, being more sensitive to NO₂, though the sensitivities decreased drastically at temperatures higher than 300°C. The addition of 5.0 wt% Cr₂O₃ to SnO₂ resulted in a significant improvement of NO and NO₂ sensitivities at 600°C, being accompanied by an increase in the breakdown voltage in air. Especially, the NO sensitivity was superior to the NO₂ sensitivity in the concentration range of 20–100 ppm, and then SnO₂ mixed with 5.0 wt% Cr₂O₃ was found to be the most suitable candidate for a NO sensor among the sensors tested. The increase in the breakdown voltage in air induced by the Cr₂O₃ addition was confirmed to arise from both the decrease in the particle size of SnO₂ and the formation of micro p-n junctions at grain boundaries. The decrease in the particle size was also responsible for the increased NO and NO₂ sensitivities, but the p-n junctions were suggested to play a more important role in promoting and stabilizing the chemisorption of NO at higher temperatures.     

Surface evaluation of LiNbO3 and LiTaO3 crystals etched using fluorine system gas plasma reactive ion etching

The etching characteristics of LiNbO₃ and LiTaO₃ single crystals have been investigated by performing plasma reactive ion etching (RIE) with CF₄/Ar, CF₄/H₂, and CF₂/Ar/H₂ gas mixtures. The etched surface was evaluated by atomic force microscopy and X‐ray diffraction. The in situ surface temperature of the sample was measured during RIE. F atoms exist in the contamination layer on the surface etched using mixtures of CF₄, Ar, and H₂ gases. The etch rate was dependent on the crystal orientation. The etch rate of LiTaO₃ was less than that of LiNbO₃. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(2): 18–24, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10365     

Effects of oxidants on the deposition and dielectric properties of the SrTiO3 thin films prepared by liquid source metal-organic chemical vapor deposition (MOCVD)

Abstract

SrTiO₃ thin films are deposited by a liquid source metal-organic chemical vapor deposition (MOCVD). The effects of oxidants on the deposition characteristics and dielectric properties of the films are mainly tested. O₂, N₂O and O₂ + N₂O gases are used as the oxidants and the films with Ti-rich and Sr-rich compositions are obtained when O₂ and N₂O is used, respectively. Deposition of thin initial layer under O₂ atmosphere is very effective to obtain large dielectric constant of the SrTiO₃ thin film when the main layer is deposited under O₂ + N₂O atmosphere. The dielectric constants of 40 nm thick SrTiO₃ films with thin O₂, N₂O initial layers and without the initial layers are 235, 145 and 210, respectively.     

Effects of Ar post-annealing on the electrical properties of Pt/YMnO3/p-Si and Pt/YMnO3/Y2O3/p-Si

Abstract

YMnO₃ thin films were prepared on p-Si(111) and Y₂O₃/p-Si(111) substrates by chemical solution deposition and annealed at 800°C for 1 hour under the oxygen pressure of 2 Torr. The YMnO₃ thin films showed good crystallinity and c-axis preferred orientation. Effects of Ar post-annealing on electrical properties were examined in Pt/YMnO₃/p-Si and Pt/YMnO₃/Y₂O₃/p-Si structures. Leakage current densities decreased considerably by Ar post-annealing. The Pt/YMnO₃/p-Si and Pt/YMnO₃/Y₂O₃/p-Si showed clockwise C-V hysteresis induced by ferroelectric polarization after Ar post-annealing and memory windows of MFS and MFIS structure were 1.1V and 0.6V, respectively.     

A numerical simulation tool for nanoscale ion‐sensitive field‐effect transistor

In this work, a self‐contained numerical simulation tool for nanoscale Ion‐Sensitive Field‐Effect Transistor (ISFET) is developed. The tool is based on merging nanoscale ballistic MOSFET analytical equations with the Gouy–Chapman–Stern model equations of ISFET to form a system of nonlinear equations that can be solved iteratively to yield ISFET output current. The numerical solution is accomplished using Newton–Raphson method with efficient trust‐region‐dogleg algorithm using MATLAB software coding. The tool is used to optimize the sensitivity and linearity of nanoscale ISFETs, and to study their dependence on reference voltage, drain current level, and gate‐insulator thickness. Moreover, a comparison between three types of insulators, SiO₂, Si₃N₄, and Al₂O₃, has been made. The tool is given the name: NIST (Nanoscale ISFET Simulation Tool). It can be used as a guide for design and optimization of nanoscale ISFETs and can be applied for both single‐gate and double‐gate structures. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of the O2/Ar gas flow ratio on the electrical and transmittance properties of ZnO:Al films deposited by RF magnetron sputtering

ZnO:Al thin films for transparent conductors were deposited on sapphire (0001) substrates by using an RF magnetron sputtering technique. Effects of the O₂/Ar flow ratio in the sputtering process on the crystallinity, carrier concentration, carrier mobility, and transmittance of the films were investigated. The FWHM of the (002) XRD intensity peak is minimal at the O₂/Ar flow ratio of 0.5. According to the Hall measurement results the carrier concentration and mobility of the film decrease and thus the resistivity increases as the O₂/Ar flow ratio increases. The transmittance of the ZnO:Al film deposited on the glass substrate is characteristic of standing wave. The transmittance increases as the O₂/Ar flow ratio in-RF magnetron sputtering increases up to 0.5. Considering the effects of the the O₂/Ar flow ratio on the electrical resistivity and transmittance of the ZnO:Al film the optimum O₂/Ar flow ratio is 0.5 in the RF magnetron sputter deposition of the ZnO:Al film.     

线板脉冲放电对罗丹明B脱色的实验研究

为了提高脉冲放电对罗丹明B染料废水的脱色率η,采用线-板式脉冲放电反应器实验研究了脉冲电压Up、脉冲频率f、线板间距d、线线间距s、曝气量Q等对η的影响。研究表明,当Up为35kV、f为60Hz、d为8mm、s为5mm、Q为15L/h时,处理50min后,η达99.43%,溶液中总有机碳质量浓度ρ(TOC)由70mg/L降到17.3mg/L。最佳实验条件下,在放电反应器中投放Fenton试剂对罗丹明B废水进行联合处理,研究Fenton的投放量在放电过程中的作用及对脱色的影响,结果表明投放Fe2+的量为0.05mmol和H2O2的量为88.2mmol时能有效地发挥Fenton和脉冲放电低温等离子体的协同作用,提高了η,处理30min时η达99.87%。     

Development of a catalytic decomposition system for chlorofluorocarbons

It is becoming increasingly important to decompose chlorofluorocarbons (CFC), which destroy the ozone layer. The purpose of this study is to investigate the CFC decomposition activities of a catalyst and a decomposition system. CFC decomposition with H₂O by KI‐100 catalyst, a TiO₂‐based catalyst which we have developed, was investigated. KI‐100 catalyst showed high activity for CFC11, CFC12, and CFC113 decomposition. However, the conversion rate CFC113 decreased with time and was 70% after 1000 h. In order to determine the cause, the KI‐100 catalyst was analyzed. From the results of quantitative analyses, it was found that the weight of TiO₂ in the catalyst decreased from 11.42 g to 1.09 g (–90.5 wt%) and TiO₂ changed to TiOF₂. To prevent the formation of TiOF₂, another component, which was less reactive with CFC than TiO₂, was applied to the catalyst surface. The improved catalyst, KI‐1000, showed long durability for CFC12 decomposition and the conversion rate was above 99.99% over 2000 h. Based on these results, we have commercialized Catalytic Decomposition Equipment for CFCs. © 2000 Scripta Technica, Electr Eng Jpn, 132(1): 57–63, 2000