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Presents a study that examined the plasma-assisted decomposition of dilute concentrations of methanol and trichloroethylene in atmospheric pressure air steams by electrical discharge processing. Background on nonthermal plasma processing; Use of electron-beam method and Fourier transform infrared spectrometer; Types of electrical discharges.

Electron beam treatment technologies should be versatile in the removal of chlorofluorocarbons (CFCs) owing to their exceptional cross sections for the thermal electrons generated in the radiolysis of air. Humidity, dose rates, O2 concentration, and CFC concentration influence the efficiency of the destruction process under electron beam treatment. Computer simulations have been used to theoretically demonstrate the destruction of chlorotrifluoromethane (CF3Cl), dichlorodifluoromethane (CF2Cl2), and trichlorofluoromethane (CFCl3) in the air (N2 + O2: 80% + 20%) in room temperature up to a dose of 13 kGy. Under these conditions, it is predicted that the removal efficiency is in the order CF3Cl (0.1%) < CF2Cl2 (7%) < CFCl3 (34%), which shows the dependence of the process on the number of substituted Cl atoms. Dissociative electron attachment with the release of Cl– is the primary process initiating the destruction of CFCs from the air stream. Reactions with the first excited state of oxygen, namely, O(1D), and charge-transfer reactions further promote the degradation process. The degradation products can be further degraded to CO2, Cl2, and F2 by prolonged radiation treatment. Other predicted products can also be removed through chemical processes. [ABSTRACT FROM AUTHOR]

This paper studies the degradation effect of high-concentration toluene in dielectric barrier discharge (DBD) plasma under different operating conditions. The degradation efficiency and energy yield (EY) were comprehensively evaluated by a response surface method under different operating parameters (discharge powers, gas flow rate, and initial concentrations) in the DBD plasma system. The results showed that the EY and degradation efficiency could reach 22.17 g kWh−1 and 72.3% when discharge power, initial concentration, and gas flow rate were 5.49 W, 1374.5 ppm, and 529.5 ml min−1, respectively. Furthermore, a mineralization effect was also analyzed related to different operating parameters. When the gas flow rate was 600 ml min−1 and the initial concentration was 2500 ppm, the CO x selectivity could reach 98.5%. Through analysis of the effect of oxygen content in the background gas on high-concentration toluene degradation, it was found that oxygen content had a significant effect on the formation of oxygen-containing active substances. Emission spectra showed that normal air discharge occurred in the discharge space of the DBD plasma, and nitrogen-containing active substances were generated. Therefore, active substances containing oxygen and nitrogen played an important role in DBD plasma degradation of high-concentration toluene. [ABSTRACT FROM AUTHOR]

Green and efficient NOx removal at low temperature is still desired. NOx removal via non-thermal plasma (NTP) reduction is one of such technique. This work presents the experimental and theoretical study on the NOx removal via NTP reduction (NTPRD) in dielectric barrier discharge reactor (DBD). The effect of O2 molar fraction on NOx species in the outlet of DBD, and effects of NH3/NO molar ratio and discharge power of DBD on NOx removal efficiency are investigated. Results indicate that anaerobic condition and higher discharge power is beneficial to direct removal of NOx, and the NOx removal efficiency can be up to 98.5% under the optimal operating conditions. It is also found that adding NH3 is favorable for the reduction of NOx to N2 at lower discharge power. In addition, the NOx removal mechanism and energy consumption analysis for the NTPRD process are also studied. It is found that the reduced active species (N*, N−, N+, N2*, NH2+, etc.) generated in the NTPRD process play important roles for the reduction of NOx to N2. Our work paves a novel pathway for NOx removal from anaerobic gas in industrial application. [ABSTRACT FROM AUTHOR]

This work presents a femtosecond two-photon absorption laser-induced fluorescence (fs-TALIF) diagnostic for measuring ground-state atomic nitrogen in nanosecond repetitively pulsed (NRP) discharges. Absolute atom density is obtained from the TALIF signal via a novel calibration technique based on one-photon direct absorption measurements performed in a low-pressure DC discharge. The Vacuum Ultraviolet (VUV) measurements were done at the Soleil synchrotron facility using the high-resolution Fourier-transform spectrometer (minimum linewidth Î" ν ~ = 0.08 cmâˆ'1). The main goal of this work was to develop a quench-free diagnostic technique, which would allow measurements at elevated pressures with high spatial and temporal resolution. Here fs-TALIF measurements of N(4S) are demonstrated in the NRP post-discharge between 1â€"500 ÎĽ s after the nanosecond high-voltage pulse. A maximum number density of N-atoms of 5 Ă— 1016 cmâˆ'3 was measured at 1 ÎĽ s after the pulse when the discharge was operated at 1 bar in pure nitrogen. This corresponds to a dissociation fraction of ∼0.1%. The fs-TALIF technique at high laser intensity regime (>1 TW cmâˆ'2) calibrated using VUV absorption was compared with the fs-TALIF at low laser intensity regime (<100 MW cmâˆ'2) calibrated via the well-established non-saturated TALIF technique using krypton as an etalon gas. It was found that the two measurements of N(4S) in the NRP post-discharge agree within a factor of 3. Importantly, the limit of detection of the fs-TALIF at high laser intensity regime was determined to be n N ( S 4 ) ∼ 1 0 12 c m âˆ' 3 . This is approximately one order of magnitude better than previously reported by ns-TALIF in low-pressure discharges. [ABSTRACT FROM AUTHOR]

The state-of-art of studies of processes involving small fractions of particles formed as a result of chemical transformations of the source gas or appearing from the outside as an impurity is discussed. Various high-sensitivity methods for measuring the low concentrations of particles are considered. The main focus is on spectral methods, both classical and laser ones. The main modern fields of the application of non-equilibrium plasma, features, and achievements of the diagnostic tools used in them are highlighted. The emphasis is on spectroscopic studies of plasma purity in the low-temperature near-wall layers of thermonuclear reactors. In this case, the issue of the penetration of water molecules into the plasma chamber from the cooling circuits is of particular importance. In view of the limited accessibility to the reactors, new remote versions of spectral emission methods are being developed that are focused on the diagnostics of the ITER near-wall plasma. A new method of multispectral optical actinometry is discussed, in which intermediate chemically unstable particles can play the role of actinometers. This broadens the range of possibilities for quantitative measurements of concentrations of particles of different kinds, and increases the sensitivity. Effective actinometric pairs were found for the objects under consideration, e.g., hydrogen and deuterium atoms. The schemes are worked out on laboratory facilities, and kinetic models of plasma-chemical processes are developed. Scaling of the results of model experiments makes it possible to predict the measurement of the impurity flows at the level (10–9–10–13) Pa m3 s–1 with the localization of sources determined by the spatial resolution of the optical system. [ABSTRACT FROM AUTHOR]

A microwave plasma torch operated at atmospheric pressure (APMPT) is used for abating CF4 gas diluted by nitrogen. The variation of destruction and removal efficiency (DRE) of CF4 by measuring Fourier transformation infrared spectra is investigated with respect to the microwave power, CF4 concentration, total gas flow and the length and material of discharge tube in reaction chamber respectively. The partition into annular free-discharge and central plasma regions in the cross section of discharge tube, influenced by the flow rate and microwave power, plays an important role in determining DRE value, and the measurement of vibrational temperature by means of OES along the axis in afterglow presents a minimum value on the transiting point between near and far afterglow. Meanwhile, the explanations are delivered in good agreement with the experimental observations with respect to variation of DRE for decomposing CF4 by APMPT. [ABSTRACT FROM AUTHOR]

Nanosecond pulsed streamer discharge has unique characteristics that differentiate it from longer discharges. The very fast voltage rise time, peak voltage plateau, short pulse duration, and fast fall time enable a large volume of uniform nonthermal plasma generation at atmospheric pressure. This review explains the physics of nanosecond discharge plasma through experimental and simulated studies for plasma processing techniques. The following are discussed and compared between sub-microsecond and nanosecond discharge plasma: discharge phase transition, discharge propagation, production of chemically active species, temperature change of gas during plasma propagation, electrode geometry, effect of voltage rise rate, voltage polarities, and N2/O2 gas composition ratio in air seeding gas. Nanosecond pulse discharge plasma is characterized by a considerably faster streamer head propagation velocity and reduced gas heating, resulting in a higher energy efficiency for plasma processing. Ozone generation, nitric oxide treatment and volatile organic compound treatment results are given as examples of plasma processing. [ABSTRACT FROM AUTHOR]

Non thermal plasma (NTP) reactors packed with non-catalytic or catalytic packing material have been widely used for the abatement of volatile organic compounds such as toluene, benzene, etc. Packed bed reactors are single stage reactors where the packing material is placed directly in the plasma discharge region. The presence of packing material can alter the physical (such as discharge characteristics, power consumption, etc.) and chemical characteristics (oxidation and destruction pathway, formation of by-products, etc.) of the reactor. Thus, packed bed reactors can overcome the disadvantages of NTP reactors for abatement of volatile organic compounds (VOCs) such as lower energy efficiency and formation of unwanted toxic by-products. This paper aims at reviewing the effect of different packing materials on the abatement of different aliphatic, aromatic and chlorinated volatile organic compounds. [ABSTRACT FROM AUTHOR]

Gliding discharge plasma in a large scale reactor was used for decomposition of tetrachloromethane. The new power supply system based on a power inverter was used. The conversion of CCl4 was investigated in air at normal pressure. The reactor was made of a quartz-glass tube 60 mm in diameter and contained three converging electrodes 140 mm long. Effects of the initial CCl4 concentration, gas flow rate and discharge power on CCl4 conversion have been studied. The conversion of CCl4 was high in all cases reaching a maximum of 90%. The conversion of tetrachloromethane decreased with increasing initial concentration of CCl4 in the reaction mixture. Changing the gas flow rate from 1000 Nl h-1 to 1400 Nl h-1 decreased the conversion of tetrachloromethane. [ABSTRACT FROM AUTHOR]

The decomposition of CCl4 in air was investigated at atmospheric pressure in two discharges. Reactors used to generate electrical discharges were powered by the same electric power supply. In both reactors, nearly 90% conversion of CCl4 was obtained. All chlorine was in the form of Cl2 in the process carried out in the barrier discharge, while in the spark discharge, COCl2 was formed. The conversion of CCl4 to COCl2 ranged from 2 to 12%. NO was formed in both discharges but the NO content in the gas leaving the reactors was 1.7-2.7% for the spark discharge and 0.045-0.06% for the barrier discharge. O3 was produced only in the barrier discharge and its content ranged from 0.1 to 0.2%. [ABSTRACT FROM AUTHOR]

A method to design the composite insulation structures in pulsed power systems is proposed in this paper. The theoretical bases for this method include the Weibull statistical distribution and the empirical insulation formula. A uniform formula to describe the reliability (R) for different insulation media such as solid, liquid, gas, vacuum, and vacuum surface is derived. The dependence curves of the normalized applied field on R are also obtained. These curves show that the normalized applied field decreases rapidly as R increases but the declining rates corresponding to different insulation media are different. In addition, if R is required to be higher than a given level, the normalized applied field should be smaller than a certain value. In practical design, the common range of the applied fields for different insulation media should be chosen to meet a global reliability requirement. In the end, the proposed method is demonstrated with a specific coaxial high-voltage vacuum insulator. [ABSTRACT FROM PUBLISHER]