The influence of NH3 on NO2 conversion in a dc corona discharge in N2:O2:CO2:NO2:NH3 mixture

The aim of this paper is to investigate the influence of NH₃ additive (540–1470 ppm) on the conversion of NO₂ and the creation of NO and N₂O in a mixture of N₂:O₂:CO₂: NO₂:NH₃ subjected to the so-called direct current (dc) corona discharge. The dc corona discharge was generated in a needle-to-plate reactor. Seven positively polarized needles were used as one electrode and a stainless steel plate as the other. The time-averaged discharge current was varied from 0 to 7 mA. It was found that the dc corona discharge decomposed NO₂ and produced NO and N₂O. The reduction of NO₂ was higher without NH₃ additive if the residence time of the operating gas was relatively short. However, in a longer corona discharge processing the NH₃ additive may be useful for reduction of NO₂.Supports from the Research and Development Commitee (KBN) under Programme KBN 0889/P4/93/04 and the Polish Academy of Sciences within IMP 3.1 project are gratefully acknowledged.     

Removal of NOx from NO2∶NO∶N2 mixture by a pulsed and dc streamer corona in a needle-to-plate reactor

The results of laboratory experiments on reduction of NO _x in the oxygen free gas mixture NO₂NON₂ simulating exhaust gas, by means of pulsed and dc streamer corona discharges generated in a needle-to-plate reactor have been presented. The results show that the dc corona discharge is more efficient in De-NO _x process than the pulsed corona discharge. This is in contrast to the results obtained in the wire-to-cylinder reactors where the pulsed corona discharge removes NO _x more efficiently. The results also lead to the conclusion that in the dc streamer corona discharge the short pulses and long interelectrode distances are recommended in order to increase the NO _x conversion rate.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was financially supported by the Polish Academy of Sciences (projects IMP 3.1 and 3.3) and by the Polish Committee for Scientific Research (KBN Grant No. P40103304).     

Conversion of nitrogen oxides in N2:O2:CO2 and N2:O2:CO2:NO2 mixtures subjected to a dc corona discharge

This paper concerns the influence of a direct current (dc) corona discharge on production and reduction of NO, NO₂ and N₂O in N₂:O₂:CO₂ and N₂:O₂:CO₂:NO₂ mixtures. The corona discharge was generated in a needle-to-plate reactor. The positively polarized electrode consisted of 7 needles. The grounded electrode was a stainless steel plate. The gas flow rate through the reactor was varied from 28 to 110 cm³/s. The time-averaged discharge current ranged from 0 to 6 mA. It was found that in the N₂:O₂:CO₂ mixture the corona discharge produced NO, NO₂ and N₂O. In the N₂:O₂:CO₂:NO₂ mixture the reduction of NO₂ was between 6–56%, depending on the concentration of O₂, gas flow rate and corona discharge current. The NO₂ reduction was accompanied by production of NO and N₂O. The results show that efficient reduction of nitrogen oxides by a corona discharge cannot be expected in the mixtures containing N₂ and O₂ if reducing additives are not employed.     

Influence of temperature and humidity on NO x removal by corona discharge

The object of this experimental investigation was the influence of temperature and humidity on the efficiency of removal of NO _x by a pulsed corona discharge from a mixture N₂ : O₂ : CO₂ : H₂O : NO simulating a combustion flue gas. The pulsed corona discharge was generated in a wire-to-cylinder reactor. It was found that removal of NO _x was most efficient when H₂O concentration corresponded with the saturated vapour pressure. In the case of the operating gas containing constant H₂O concentration removal of NO _x decreased with increasing temperature of the operating gas. Dedicated to Prof. Jan Janča on the occasion of his 60^th birthday. This work is devoted to the 60^th birthday of Professor Jan Janca, our good colleague, merited teacher, researcher and famous physicist, discussion with whom stimulated this and other our work during years.     

DC corona discharge influence on chemical composition in mixtures of natural gas with air and its combustion exhaust with air

Experiments in dc supplied corona discharge in natural gas + air mixture and in combustion exhaust of natural gas + air mixture were realized. The influence of discharge on CO, CO₂, NO _x and other minority components was studied using IR absorption spectrometry. Production of NCO radicals in gas and consequent formation of NCO containing surface layers on a plate electrode was detected. In natural gas + air mixture after about 1 min oxygen poor combustion exhaust was produced due to slow combustion by corona discharge. Occurrence of various pulses in discharge current was typical.     

Characterization of LaMnAl11O19 by FT-IR spectroscopy of adsorbed NO and NO/O2

The nature of the NO_x species produced during the adsorption of NO at room temperature and during its coadsorption with oxygen on LaMnAl₁₁O₁₉ sample with magnetoplumbite structure obtained by a sol-gel process has been investigated by means of in situ FT-IR spectroscopy. The adsorption of NO leads to formation of anionic nitrosyls and/or cis-hyponitrite ions and reveals the presence of coordinatively unsaturated Mn³⁺ ions. Upon NO/O₂ adsorption at room temperature various nitro-nitrato structures are observed. The nitro-nitrato species produced with the participation of electrophilic oxygen species decompose at 350 °C directly to N₂ and O₂. No NO decomposition is observed in absence of molecular oxygen. The adsorbed nitro-nitrato species are inert towards the interaction with methane and block the active sites (Mn³⁺ ions) for its oxidation. Noticeable oxidation of the methane on the NOx⁻-precovered sample is observed at temperatures higher than 350 °C due to the liberation of the active sites as a result of decomposition of the surface nitro-nitrato species. Mechanism explaining the promoting effect of the molecular oxygen in the NO decomposition is proposed.     

Comparison of different electrode arrangements for gas decomposition efficiency using experimental method

The environmental pollution is a central issue in the present industrial societies. Within that the air pollution and the removal of hazardous components of flue and exhaust gases are very much important.In this paper the target is to decrease of the NO_x emission by means of a technology similar to that is used in the electrostatic precipitators. In most of the papers dealing with this technique cylindrical precipitator is used as a discharge chemical reactor, and fast rising electric discharges are applied for energizing the reactor. In the industry the over helming majority of the electrostatic precipitators are plate type one.In the cylindrical precipitator the discharge electrode is parallel with the gas flow, and the corona discharge filament is perpendicular to both of them. In the case of plate type industrial electrostatic precipitator the discharge electrodes are positioned vertically, and the flow of the flue gas is horizontal. Consequently, the discharge filaments are mainly perpendicular to both the flow and the discharge electrode.In cylindrical precipitator the decomposition of NO_x is done in one filament very soon, but there is no chance to modify the byproducts with a new pulse, because the energization is the same for the whole length of the discharge electrode.In the present paper a cylindrical precipitator, a plate type precipitator with horizontal electrode, and a plate type precipitator with vertical electrode were tested. The total length of the discharge electrodes of all of the precipitators was the same.The results of the NO_x decomposition were experimentally determined, and the differences between the precipitators were investigated. The cylindrical and the plate type precipitators with vertical electrodes had shown basically similar decomposition rate, while the plate type one with horizontal discharge electrode had proven inferior to the others.     

The Conversion of NOx in a Corona Discharge with an Electrode Material Variation

The spatial and surface chemical products and effectiveness of NO_x removal (abbreviated deNO_x) under the corona discharge action at atmospheric pressure were investigated. The influence of high-voltage electrode material on a discharge character and the heterogeneous influence of the electrode surface are also reported in the article. The qualitative analysis was performed using infrared absorption spectrometry. Special attention was paid to NO and NO₂ calibration measurements.     

Optical emission spectroscopy of point-plane corona and back-corona discharges in air

Results of spectroscopic investigations and current-voltage characteristics of corona discharge and back discharge on fly-ash layer, generated in point-plane electrode geometry in air at atmospheric pressure are presented in the paper. The characteristics of both discharges are similar but differ in the current and voltage ranges of all the discharge forms distinguished during the experiments. Three forms of back discharge, for positive and negative polarity, were investigated: glow, streamer and low-current back-arc. In order to characterize ionisation and excitation processes in back discharge, the emission spectra were measured and compared with those obtained for normal corona discharge generated in the same electrode configuration but with fly ash layer removed. The emission spectra were measured in two discharge zones: near the tip of needle electrode and near the plate. Visual forms of the discharge were recorded with digital camera and referred to current-voltage characteristics and emission spectra. The measurements have shown that spectral lines emitted by back discharge depend on the form of discharge and the discharge current. From the comparison of the spectral lines of back and normal discharges an effect of fly ash layer on the discharge morphology can be determined. The recorded emission spectra formed by ionised gas and plasma near the needle electrode and fly ash layer are different. It should be noted that in back arc emission, spectral lines of fly ash layer components can be distinguished. On the other hand, in needle zone, the emission of high intensity N₂ second positive system and NO _γ lines can be noticed. Regardless of these gaseous lines, also atomic lines of dust layer were present in the spectrum. The differences in spectra of back discharge for positive and negative polarities of the needle electrode have been explained by considering the kind of ions generated in the crater in fly ash layer. The aim of these studies is to better understand the discharge processes encountered in electrostatic precipitators.     

Pulsed cavity ring-down spectroscopy of NO and NO2 in the exhaust of a diesel engine

The application of pulsed cavity ring-down spectroscopy has been demonstrated for the in situ quantitative determination of NO and NO₂ in the exhaust of a diesel engine. NO absorption has been monitored at the transition from the Χ²Π ground state to the A²Σ⁺ state at 226 nm. For NO₂, absorption bands in the spectral region from 438 nm to 450 nm were used. At the selected engine conditions, concentrations of 212±22 ppm and 29±4 ppm have been measured for NO and NO₂, respectively, in good agreement with separate chemical exhaust gas analysis. The method is sensitive enough to meet the European Euro V standard directive on NO_x emissions. This communication discusses the relatively simple setup needed for this type of measurement, the problems encountered, as well as the prospects for single-stroke, simultaneous measurements of both NO and NO₂ at the sub-ppm level. Received: 30 November 2001 / Revised version: 18 February 2002 / Published online: 14 March 2002     

Influences of water vapor and fly ash addition on NO and SO2 gas conversion efficiencies enhanced by pulsed corona discharge

The NO and SO₂ gas conversion processes in a pulsed corona discharge field have been studied. The experiments were conducted to investigate the influences of water vapor and fly ash addition on the conversion efficiencies of NO and SO₂. Experimental results show that positive pulsed corona discharge can facilitate NO and SO₂ conversion processes, and the conversion efficiencies of NO and SO₂ are primarily dependent on the radicals OH, O and the active species O₃, HO₂, H₂O₂, etc. With water vapor addition, SO₂ conversion efficiency is improved, but NO conversion process is restrained. Low fly ash concentration helps to enhance the conversion of NO and SO₂; however, the conversion efficiencies of NO and SO₂ are drastically degraded by high fly ash concentration addition. The synergistic effects of water vapor and fly ash addition strengthen the chemical adsorption ability of the fly ash surface, which results in a considerable improvement in the conversion of NO and SO₂. Furthermore, the specific input energy plays an important role in NO and SO₂ conversion efficiencies. Measured conversion efficiencies of NO and SO₂ reach about 60% and 90%, respectively, under the conditions tested.     

Non-thermal plasma generation by using back corona discharge on catalyst

This paper discusses a novel plasma catalysis generation method based on back-corona discharge along porous catalyst bed reactor. The reactor consists of a high-voltage needle electrode, one floated mesh electrode, one catalyst bed and one grounded mesh electrode. Typical plasma current density is 11.88 μA/cm². It can be used for ozone generation and volatile organic compounds decomposition. By using a home-made AgMnOx/Al₂O₃-1 catalyst, 90% of toluene is removed at the specific plasma energy density of 123 J/L. At the same time, aerosol byproducts are collected and then decomposed on the catalyst bed. Moreover, the catalyst is regenerated because of the back-corona discharge.     

Boron and nitrogen co-doped graphene nanosheets for NO and NO2 gas sensing

Using dispersion-corrected density functional theory calculations, the adsorption behavior of NO and NO₂ molecules is studied over B-doped and BN co-doped graphene sheets (BC_mN_n-Gr; $m,n=0,1,2,3$ and $m+n=3$). To examine practical gas sensing application and selectivity, the adsorption of H₂O, CO and CO₂ molecules is also studied on the BC_mN_n-Gr surfaces. It is found that the preferred adsorption site for the adsorption of these molecules is above the B atom due to accumulation of a local positive charge. Meanwhile, the incorporation of nitrogen atoms in BC_mN_n-Gr makes a substantial increase in the adsorption energies of NO and NO₂, mainly due to the shift in the Fermi energy and electron (donor) concentration states of these surfaces. According to our results, the electronic structure of BC₃-Gr, BC₂N-Gr and BCN₂-Gr is sensitive to NO and NO₂ as evidenced by relatively large variation of the electronic structure as well as charge-transfer values. To address the curvature effect of BC_mN_n-Gr nanosheets on the adsorption and sensing properties of NO and NO₂, the adsorption of these molecules is also investigated over B-doped and BN-codoped ($6,6$) carbon nanotubes. The calculations also indicate that BN co-doped graphene sheets can be used as an efficient and promising gas sensing material for detecting NO and NO₂ molecules in the presence of H₂O, CO and CO₂.     

Opto-galvanic spectroscopy of some molecules in discharges: NH2, NO2, H2 and N2

The change of the discharge voltage when laser light crossing the discharge is tuned to a molecular transition has been measured. Experiments have been performed in the wavelength region between 570 nm and 620 nm with discharges in NH₃, NO₂, H₂, N₂, O₂ and argon. Transitions from the ground states of NH₂ and NO₂ and transitions from metastable states of N₂ and H₂ have been detected. The spacial dependence of the opto galvanic in a low pressure dc-discharge of H₂ and N₂ has been studied.     

B-, N-doped and BN codoped C60 heterofullerenes for environmental monitoring of NO and NO2: a DFT study

ABSTRACT

Using density functional theory calculations, we investigate the gas sensing performance of B-, N-doped and BN-codoped C₆₀ fullerenes towards NO and NO₂ molecules. The calculated adsorption energies and net charge-transfer values indicate that NO and NO₂ molecules have a stronger interaction with the BN-codoped fullerenes compared to the B- or N-doped ones. It is also found that the electronic properties of the BN-codoped C₆₀ exhibit a larger sensitivity towards NO and NO₂ molecules. An increase in the concentration of doped/co-doped B and N atoms tends to weaken the gas sensing ability of these systems.     

Fundamental investigation of NOx formation during oxy-fuel combustion of pulverized coal

NO_x formation was measured during combustion of pulverized coals and pulverized coal char in N₂ and CO₂ environments under isothermal and nearly constant oxygen conditions (i.e. using dilute coal loading). Three different oxygen concentrations (12% O₂, 24% O₂, and 36% O₂) and two representative US coals were investigated, at a gas temperature of 1050 °C. To investigate the importance of NO reburn reactions, experiments were also performed with an elevated concentration (550 ppm) of NO in the gases into which the coal was introduced. For low levels of background NO, the fractional fuel-nitrogen conversion to NO_x increases dramatically with increasing bath gas oxygen content, for both N₂ and CO₂ environments, though the fuel conversion is generally lower in CO₂ environments. Char N conversion is lower than volatile N conversion, especially for elevated O₂ concentrations. These results highlight the importance of the volatile flame and char combustion temperatures on NO_x formation. For the high background NO_x condition, net NO_x production is only observed in the 36% O₂ environment. Under these dilute loading conditions, NO reburn is found to be between 20% and 40%, depending on the type of coal, the use of N₂ or CO₂ diluent, the bulk O₂ concentration, and whether or not one considers reburn of volatile-NO_x. This dataset provides a unique opportunity to understand and differentiate the different sources and sinks of NO_x under oxy-fuel combustion conditions.     

Corona discharge in electrospraying

The paper presents investigations of current–voltage and light emission characteristics of electrospraying of various liquids in atmospheric air. The spectroscopic measurements have shown that the onset of corona discharge coincides with the onset of electrospraying, with the voltage increasing. The emission intensity in selected spectral lines during electrospraying depends on spraying mode, discharge power and a kind of liquid. In the specific experimental conditions in air, mainly the N₂ second positive system, which is visible as violet faint light, has been recorded. The emission intensity of other gaseous species, which could be product of electrosprayed molecules decomposition or dissociation, was at very low level for the voltages applied, i.e., for glow or onset streamer discharges. From the measured light emission spectra of discharges from capillary nozzle and liquid jet, the dependence of the amplitude of selected spectral lines on capillary-nozzle voltage has been determined and it was found that this relation can be approximated by a third-degree polynomial function. This approximation has been supported by theoretical considerations. The presented results support the hypothesis that faint electrical discharges (glow, onset streamers) usually occur during and are inherent to electrospraying.     

Study of shock waves interacting with Ar and N<Subscript>2</Subscript> low pressure dc discharges

Acoustical shock waves (Mach number <2) generated in situ by spark gap are propagated in weakly ionized dc discharges working at low pressure (399 Pa) and containing either Ar or N₂ gas. The electrical characterization and the laser deflection technique are used to measure the characteristics of dc discharge (such as voltage, resistance and power of discharge) and the structure and velocity of shock wave, respectively. The results stress the importance of atomic and molecular nature of the gases in affecting the power deposition and the shock wave properties.     

Impulse breakdown characteristics of the plane-to-plane electrode system with a needle-shaped protrusion in SF6

This paper presents the impulse pre-breakdown and breakdown characteristics of the plane-to-plane electrode system with a needle-shaped protrusion in SF₆ gas. The breakdown voltage–time (V–t) characteristics and the breakdown voltage–gas pressure (V–p) characteristics of a highly non-uniform SF₆ gas gap under positive and negative lightning impulse voltages are investigated in the pressure range between 0.1 and 0.5 MPa. The pre-breakdown developments are examined by the corona current and light emission measurements with high time resolution. As a result, the dielectric strengths versus time-to-breakdown of SF₆ gas gap under positive lightning impulse voltages were nearly independent of the gas pressure. The first streamer corona was initiated at the tip of the needle electrode, and the streamer corona pulses developed with a stepwise propagation. The discharge paths were zigzag, and the branches of the discharge channel for positive polarity were created. On the other hand, the leader channel in the negative polarity was thicker and brighter than that in the positive polarity.     

Spectroscopic investigation of the plasma of the capillary discharge of a waveguide CO2 laser

The temperature conditions and the chemical composition of the gas in the plasma of a capillary discharge of a waveguide CO₂ laser are investigated It is shown that in helium-rich CO₂–N₂–He mixtures the gas temperature is independent, in a wide range of its variation, of the discharge-tube diameter and of the working-mixture pressure. It is established by the optical actinometry method that capillary discharges are characterized by a stronger decomposition of the working CO₂ molecules and by a higher density of the reaction products than in reduced-pressure discharges in wide tubes.Translated from FIAN Preprint No. 119, Lebedev Physics Institute, Moscow, 1990.