Pulsed Corona Research Articles

Study and scaling-up of multi-tip pulsed-corona air discharges for degradation of paracetamol

Abstract This study investigates the paracetamol removal efficiency by multi-tip pulsed corona discharges, highlighting the conditions avoiding mutual effects between two consecutive streamer branching discharges generated by each tip. The results show that the production of reactive oxygen and nitrogen species (RONS) in the liquid phase and the efficiency of paracetamol removal are influenced by the distance between two contiguous tips due to the mutual effects for small inter-tip distances between 4 mm and 8 mm in the case of a fixed inter-electrode distance of 5 mm (i.e. distance between the tip summit and the water surface). Beyond an inter-tip distance of 12 mm (over twice the gap distance), the mutual effects of branching discharges were no longer observed since the field lines did not overlap, making the production and absorption of liquid-phase species more efficient. Furthermore, RONS production was almost linear when moving from one to four tip electrodes: [H2O2]1tip: 0.52 mg l–1 versus [H2O2]4tips: 1.99 mg l–1, a ratio of 3.82. Optimum values were reached for an inter-tip distance of 16 mm. In this case, the enhancement factor in this reactor configuration is the surface integration between the plasma and the liquid surface to be treated. Furthermore, the results show a quasi-exponential increase in the percentage of paracetamol degradation as a function of the number of electrodes, from 4% with a mono-tip configuration to over 78% for a treatment with a four tip one.

Oxidation of Airborne m-Xylene in Pulsed Corona Discharge: Impact of Water Sprinkling

Plasma from electric discharges can be used in the abatement of volatile organic compounds (VOCs). The application of gas-phase pulsed corona discharge (PCD) in air–water mixtures provides favorable conditions for the oxidation of VOCs at unsurpassed energy efficiency. This research investigates the impact of water sprinkling on PCD performance in the oxidation of m-xylene as a model compound. Experimental research into the plasma treatment of continuous air flow was undertaken using the PCD reactor in dry and water-sprinkled modes. Water sprinkling more than doubled the m-xylene oxidation rate, which can be attributed to abundant OH-radicals produced at the plasma–water interface. Water sprinkling substantially reduced the formation of nitrous oxide, which is considered to be a secondary pollutant in the outlet air. Ozone is considered a by-product helping the subsequent photocatalytic oxidation of potential residues and photocatalyst maintenance. The use of water-sprinkled PCD is a promising approach to energy-efficient abatement of VOCs.

Air Pulsed-Corona discharges for degradation of emerging pharmaceutical pollutants in water and toxicity by-products control

The present study, based a tip-to-plane pulsed corona setup, examined the effects of tip-water distance, radius of curvature of electrode tip, and pulse voltage on the production of liquid-phase RONS used an indicator of degradation performance. Measurements of long-lived RONS species (nitrates, nitrites and H2O2) in deionized water were specifically analyzed. The optimum conditions were used for the removal of a high concentration (500 mg/L) of 4-acetaminophen (i.e. paracetamol) with study of oxidation by-products and their toxicity. The results showed that optimum RONS production in the liquid phase occurred for a short gap distance (4 mm), a tip curvature radius of 100 μm and a pulsed voltage of 10 kV and 10 kHz corresponding to an energetic corona spark regime which is characterized by optical emission spectroscopic measurements. Using these optimal corona discharge parameters, the study showed that after 30 min of exposure to the air plasma, 60 % removal efficiency was achieved at an initial paracetamol concentration of 500 mg/L based on HPLC-DAD sample analysis. GC–MS and LC-MS analysis of treated samples enabled us to identify and characterize two new by-products not previously identified in the literature: N-(4-(4-hydroxyphenylamino) phenyl) acetamide (m/z: 242) and N-(4-aminophenyl) acetamide (m/z: 150), most of which were nitrogen compounds. Further analysis of the toxicity of these by-products to the human cell line (HEK-293) demonstrated that the treated water was not toxic.Overall, these results show that the CDP system is one of the best techniques for treating highly polluted wastewater.

Pulsed corona discharge: an advanced treatment method for antibiotic-contaminated water

Water pollution is one of the most significant problems of the current century. With the increase in medicine availability and use, pharmaceutical pollutants such as antibiotics become more prevalent in natural environments with potentially negative impact. In this study, a pulsed corona discharge was investigated as a possible treatment method of water contaminated with amoxicillin (AMX). Two system configurations were used: plasma and plasma-ozonation. In order to better grasp the effect of system and water matrix on degradation, different pulse widths, solutions pH and conductivity values, as well as the nature of the dissolved salts were investigated. Decreasing the pulse width from 300 ns to 106 ns (full width at half maximum) led to almost a two-fold increase in energy yield at 50% pollutant removal, and the addition of the ozonation reactor resulted six times enhancement in efficiency. While the water matrix had little impact on AMX degradation, the buffering capacity of carbonates has proven beneficial by preventing pH decrease during treatment. Under optimum conditions, the energy yield was 57 g kWh−1 at 93% removal of AMX in tap water. A number of 26 potential degradation products have been identified, resulting from hydroxylation of the benzene ring, oxidation of the thioester and amine groups, hydrolysis, and cleavage of the benzene, β-lactam and thiazole rings, along with fragmentation of the resulting compounds. All but seven degradation intermediates are completely removed by extending treatment duration to 60 min and the persistent ones are less toxic than the parent compound.

Simulation Analysis of Corona Pulse Propagation along the Line Based on an Actual Transmission Line

Abstract In the partial discharge test of the shunt reactor of the ultra-high voltage transmission line, the corona discharge caused by high voltage interferes with the test. To further study the propagation rules of the corona pulse on the line side in the transmission line during the ultra-high voltage partial discharge test, based on the parameters of an actual transmission line, the ATP-EMTP electromagnetic simulation software was used for modeling. The propagation rules of corona pulses in the transmission line were analyzed in detail through the simulation model. As the propagation distance increases, different frequency components show different degrees of attenuation. The higher the frequency is, the faster it attenuates.

Degradation of imidazolium-based ionic liquids by UV photolysis and pulsed corona discharge: The effect of persulfates addition

Ionic liquids (ILs) are salts with exceptional properties important for future development, although potentially hazardous for humans and aquatic life due to their high aqueous solubility and toxicity. Biodegradation of ILs depends on the anion nature and cation structure: many ILs are not readily degraded during conventional wastewater treatment, thus requiring alternative cost-effective and energy-efficient solutions. In this research, the degradation of aqueous imidazolium-based ILs by pulsed corona discharge (PCD) and UV photolysis combined with persulfates was studied, using peroxymonosulfate (PMS) and peroxydisulfate (PDS) as extrinsic oxidants. 1-Ethyl-3-methylimidazolium chloride ([Emim][Cl]), 1-methyl-3-octylimidazolium chloride ([Omim][Cl]), and 1-ethyl-3-methylimidazolium bromide ([Emim][Br]) were chosen as imidazolium-based ILs with different alkyl chain lengths and anions in oxidation experiments under variable operation factors - pH, concentrations of persulfates, pulse repetition frequency in PCD. Pulsed corona discharge has previously shown high energy efficiency in the degradation of micropollutants but has not yet been applied to ionic liquids. The experimental results showed the ability of PCD, PCD/oxidant and UV/oxidant combinations to completely degrade the ILs with the degradation rates in descending order [Emim][Cl] > [Omim][Cl] > [Emim][Br], indicating an impact of both the alkyl chain length and the type of anion on the oxidation rate. The strong activation of persulfates was observed in UV/oxidant combinations, whereas PCD demonstrated the effect of persulfates addition between slight acceleration and moderate deceleration of oxidation dependent on the concentration of extrinsic oxidants. The addition of the sulfate radicals’ scavenger, however, showed the presence of those in all combinations indicating a certain replacement of PCD-generated reactive oxygen species with secondary reactants formed from persulfates. The unassisted PCD and UV/PDS combination demonstrated similar energy efficiencies of about 54 and 26 mmol kWh−1 for [Emim][Cl] and [Emim][Br] degradation, respectively, while for [Omim][Cl] the UV/PDS combination showed energy efficiency 1.42 times higher than unassisted PCD.

Ozone-assisted degradation of 2-methoxyethanol in a prototype plug flow photocatalytic reactor

Airborne volatile organic compounds (VOCs) present an increasingly relevant health hazard addressed by the EU directive 2016/2284 requiring 40-% reduction in emissions of non-methane VOCs by 2030 in comparison to 2005. Advanced oxidation processes (AOPs) provide a solution for the VOC problem in industry. Among AOPs, pulsed corona discharge (PCD) and photocatalytic oxidation (PCO) are of particular interest in their synergy complementing each other’s strengths in energy-efficient manner. In the present study, air polluted with 2-methoxyethanol (2ME) was treated by using a prototype 21.3 L photocatalytic reactor for the pollutant degradation at its variable concentrations (6–50 ppm), irradiances (65–119 W m−2) and residence times (12–77 sec). Further combination of PCO reactor with forthcoming PCD requires studies in ozone photocatalytic degradation as a standalone byproduct and in combination with 2ME. The analysis of variable conditions resulted in singling out the PCO major restrictive parameters, also demonstrating the degradation enhancement, when both 2ME and ozone were present in air. The PCO treatment combined with ozone resulted in degradation of 2ME and ozone for 40 % and 95 %, respectively.

Kinetics of Ibuprofen Degradation in Aqueous Solution by the Action of Direct-Current Glow Discharge in Air

The kinetics of decomposition of ibuprofen in its aqueous solution by the action of atmosphericpressure direct-current discharge in ambient air has been studied. The treated solution served as both the cathode and the anode of the discharge system. Degradation rates and effective degradation rate constants have been determined. Based on these data, the energy yields and degrees of destruction were calculated for various discharge powers (discharge currents). Discharges in a liquid cathode and anode differ little in the energy yields of degradation. But the rates and rate constants of degradation in the liquid cathode are higher than in the liquid anode. Therefore, the complete destruction of ibuprofen in the liquid cathode is achieved within shorter discharge times. A comparison is made of the destruction efficiencies for the cases of solution treatment using glow, dielectric barrier, and pulsed corona discharges.

Evolution of streamer groups and radical generation in high-voltage multiple-pulse-induced nonthermal plasma

Nonthermal plasmas (NTPs) induced by atmospheric nanosecond multiple-pulse corona discharge have been studied to control pollution generated by combustors, such as boilers, incinerators, and diesel engines. In high-speed short-width high-voltage pulsed corona discharge-induced plasmas, the chemical reactions that occur between multiple pulses and the characteristics of the electron density (denoted by ne) and ozone during the second pulse have not been fully clarified. In this study, we perform quasi-two-dimensional numerical analysis of nonequilibrium NTP induced by a nanosecond positive pulsed corona discharge. The continuum fluid equations for a two-temperature nonequilibrium NTP are used as governing equations. A total of 197 gas phase reactions for 25 chemical species and 21 surface reactions on the inner glass wall surface are considered in an air plasma under atmospheric pressure. We simulate streamer group behavior up to the second pulse and found that ne and the length of streamers change due to chemical reactions between pulses. In addition, we successfully simulated the phenomena of ne reduction and streamer suppression that occur primarily during the second pulse. This is caused by the decrease in potential gradient due to the space and dielectric surface charge build-up. Furthermore, it is confirmed that the ozone formation reaction mainly occurs between pulses. This simulation enables predictions of phenomena in nanosecond positive multiple-pulse plasma systems.

Assessment of lipid oxidation and microbial decontamination of sardine (Sardina pilchardus) fillets processed by plasma-activated water (PAW)

Plasma activated water (PAW) is emerging as a mild and environmentally friendly technology for microbial and chemical decontamination of food. The aim of this work was to evaluate the degree of oxidation of lipids of sardine tissue treated by PAW generated with a pulsed corona discharge. The effect of PAW on the natural microflora of the fish was also evaluated. Under the adopted experimental conditions, PAW was able to reduce the number of mesophilic aerobes and Pseudomonas spp. by 0.22 and 0.20 log units, respectively, but no increase in shelf life was observed at chilling temperatures compared to water washing. A loss of polyunsaturated fatty acids (PUFAs) and an increase in volatile oxidation products derived from the cleavage of PUFA hydroperoxides were observed at the longest treatment duration. Twelve cholesterol oxidation products (COPs) were identified in sardine lipids, but no significant differences in total COPs content were observed between PAW processed and control samples. Free radical mediated oxidation pathways led to the most abundant COPs, but a significant contribution of non-radical pathways was also observed. Further studies are needed to better understand the low efficiency of PAW in microbial decontamination of proteinaceous materials.

Characterization of DC corona discharge current pulses using high-frequency measurement techniques

This paper presents corona discharge current pulse characterization under positive and negative DC voltage excitations. Two electrode systems with three different gap spacings generated corona discharges. Different corona modes in atmospheric air were observed with voltage level changes. Commercial shunt resistors and a high-frequency current transformer (HFCT) captured corona current pulses. The appropriate resistor type and value were determined for the shunt resistor measurement. BNC terminator was proposed as a shunt resistor to detect corona discharge current pulses, and the availability of the shunt resistors and HFCTs for corona pulse detection was discussed. After gathering corona discharge pulse data, features from the pulses were extracted. The best features describing corona discharge types were specified using a recursive feature elimination method based on a decision tree estimator. The corona discharges were discriminated with an accuracy rate of 0.994.

Experimental study on positive corona discharge characteristics in plane-single/double earthed rods air gaps under negative DC voltage

In order to analyze the corona discharge characteristics at the grounding object tip under the thundercloud electric field environment, scaled simulation test has been conducted on corona discharge in the plane-single/double earthed rods air gap. Five gap configurations with three different grounding rods were built during experiments. Factors as rod tip curvature, voltage and gap configuration have been considered in detail. Corona voltage, corona current and the number of ultraviolet photons were all recorded. The grounding rod tip curvature radius can affect corona discharge processes at grounding rod tip. With increasing applied negative DC voltage, five typical corona processes of dark discharge, burst streamer corona, periodic streamer corona, glow corona and brush discharge occurred at conical and spherical grounding rod tip (r=0.75cm), but under d=5cm and d=10cm no glow corona and brush corona appeared at spherical grounding rod tip (r=1.25cm). It is much easier for grounding rod tip with smaller curvature to form glow corona phenomenon. The mean value Iav of periodic streamer corona current pulse amplitude decreases with grounding rod tip curvature radius, while the mean corona current pulse width and pulse interval increases. For grounding rod with conical tip, there is little difference of average current pulse amplitude between periodic streamer corona and brush corona; for grounding rod with spherical tip (r=0.75cm), the mean value Iav of brush corona pulse amplitude increases to 3595.8 μA which has increased by a factor of about 36. The photon number at conical grounding rod tip is larger than that at spherical grounding rod tip at low voltage but the relation reverses as the applied voltage exceeds a critical value. The shielding effect of two grounding rods in plane-double rods air gaps increased with spherical grounding rod curvature radius and decreases with the lateral gap distance between two grounding rods.

Degradation of Antibiotic Vancomycin by UV Photolysis and Pulsed Corona Discharge Combined with Extrinsic Oxidants

Antibiotics are the most frequently detected pharmaceuticals in the environment creating conditions for the development of resistant genes in bacteria. Degradation and mineralization of glycopeptide antibiotic vancomycin (VMN) were examined by UV photolysis, pulsed corona discharge (PCD), and their combinations with extrinsic oxidants, hydrogen peroxide (HP), peroxydisulfate (PDS), and peroxymonosulfate (PMS). Both combinations were effective in VMN degradation and faster at pH 11 than in acidic or neutral media. Combined with the UV photolysis, HP showed a higher oxidation rate than other oxidants, whereas PMS and PDS proved to be more efficient in combinations with PCD. In contrast to low-to-moderate mineralization of VMN in the UV/oxidant combinations, PCD and PCD/oxidant combinations appeared to be more effective, reaching up to 90% of TOC removal in acidic/neutral solutions. Application of extrinsic oxidants resulted in an energy efficiency of VMN 90% oxidation improved from 36 to 61 g kW−1 h−1 in HP-assisted photolysis, and from 195 to 250 g kW−1 h−1 in PCD with additions of HP and PDS, thus showing the promising character of the combined treatment.

Plasma energy efficiency and equivalent electrical circuit of the multi-tips pulsed corona discharge in dry air at atmospheric pressure

An electrical model equivalent multi-tips corona discharge was presented. The electrical parameters were estimated by the identification method based on the recursive least squares (RLS) algorithm.The estimated electrical parameters allow to determine the total discharge power and the power delivered by all the tips to ignite and maintain the plasma discharge and thus the energy efficiency during the discharge. This study allows to follow and control the discharge at each instant of its evolution. Thus, the operating conditions of the discharge can be optimized to increase the energy efficiency of the discharge.

Исследование относительной реакционной способности паров алкилацетатов по отношению к компонентам плазмы импульсного разряда в воздухе

A study was made of the relative reactivity of vapors of a number of acetic acid esters (alkyl acetates) with respect to plasma components of a pulsed corona discharge with a voltage of 100 kV and a duration of 40 ns. On model mixtures based on methyl-, ethyl-, propyl-, isopropyl, isobutyl-, butyl-, and vinyl acetate with a content of 250–500 ppm in air and nitrogen, the relative reactivity parameters were obtained. The reactivity of acetic acid esters increases with an increase in the hydrocarbon substituent. The high reactivity of vinyl acetate is due to the double bond reaction with ozone.

Toward a theory of ‘stepped-leaders’ in lightning

An unresolved issue in the physics of lightning is an explanation for lightning proceeding to the ground by successive luminous steps separated by ‘dark’ times of many microseconds. There is also no explanation of the structure of the dark column connecting the streamer step with the cloud that can be km in length, is electrically conducting, yet has a very low sustaining electric field. It is proposed that these two processes can be explained by the accumulation of singlet delta metastable oxygen molecules excited in the corona pulses of lightning. The step time is necessary for the excitation of large metastable densities to produce significant metastable detachment of electrons from negative ions. The detached electrons form a highly conducting step, initially luminous, that causes a redistribution of electric fields and an increase in the potential and electric fields at the end of the step to make possible a further step by ionization. These features are supported by calculations of densities of electrons, positive ions, negative ions and singlet delta metastable oxygen molecules for the first 7 μs of a discharge chosen to be initiated by a 50 cm sphere of charged hail particles. The calculated corona streamers produce metastable densities of 1017 cm−3 near the corona source. These metastables, by electron detachment, produce a conducting cylinder 10 m long with a radius of 1 cm and an electron density ∼1012 cm−3 that is attributed to being the first step and a lightning ‘leader’. These conducting regions develop within them very low electric fields. Successive steps are likely to combine to form the long conductive columns of lightning that exist before the return stroke. Electron densities in the leader and the column are an equilibrium between electron production by metastable detachment and electron loss by attachment to neutral oxygen molecules, requiring no electric field.

Experimental study on toluene removal by a two-stage plasma-biofilter system

Volatile organic compounds (VOCs) are typical pollutants that affect air quality. Discharge plasma is thought to be a potential method that can remove VOCs from flue gas. In this experiment, pulsed corona discharge plasma combined with a biological tower was carried out to remove the benzene series, and toluene was selected as the typical VOC. The results indicated that the removal efficiency of toluene by pulsed corona plasma was slightly higher than that of direct current (DC) corona plasma, while its energy efficiency was much higher than DC corona plasma. Under the optimal experimental conditions of pulse voltage 8.5 kV, initial toluene concentration 1400 mg m−3, and toluene flow rate of 12 l h−1, the toluene removal efficiency reached 77.11% by the single method of pulsed corona discharge plasma, and the energy efficiency was up to 1.515 g/(kW·h) under the pulse voltage of 4.0 kV. The trickling biofilter was constructed by using the screened and domesticated Acinetobacter baumannii, and the highest toluene removal efficiency by the pulsed corona discharge plasma combined with the trickling biofilter rose up to 97.84%. Part of the toluene was degraded into CO2, H2O, and some intermediate products such as o-diphenol under the influence of Acinetobacter baumannii. When the remaining waste gas passed through the discharge plasma reactor, the benzene ring structure could be directly destroyed by the collision between toluene and plasma. Meanwhile, O·, OH·, and some other oxidizing radicals generated by the discharge also join into the oxidative decomposition of toluene and its intermediate products, thereby further improving the removal efficiency of toluene. Therefore, the two-stage plasma-biofilter system not only showed a high toluene removal efficiency, but also had a good energy efficiency. The results of this study will provide theoretical support and technical reference for industrial VOC treatment.

Electric charge build-up and dissipation at pulsed streamer corona by EFISH and probe measurements

This work examines the dynamics of volumetric electric charge deposited by a single pin electrode streamer corona in atmospheric air at ambient conditions. Recent studies show that, at pulse-periodic operation, electric charge remains in surrounding air after the first discharge. This residual charge significantly affects the electric field distribution and morphology of discharges at subsequent pulses. In this study, the residual electrical potential/field was measured during and after dissipation of a pulsed 80 kV streamer corona of alternating polarity. This was accomplished using electrostatic probes and the electric field induced second harmonic method (EFISH generation). The residual volumetric charge of a positive pulse polarity streamer corona occupies a zone of up to 80 mm from the electrode. The subsequent application of a negative polarity pulse leads to partial neutralization of the previous charge and the generation of a region with a high-amplitude electric field. The propagation of following positive polarity pulses is limited by the residual positive volumetric charge. The EFISH method reveals the magnitude of the electric field at discharge propagation and electrostatic probes inform the polarity. Intensified imaging acquisition was used to evaluate the spatial distribution and dynamics of corona discharge during the alternating polarity waveform.

Experimental mapping of the ozone distribution in a pulsed positive corona discharge to estimate the efficiency of ozone production

The spatial and temporal evolution of the ozone density has been measured in a 1 cm electrode gap tip to plane positive pulsed corona discharge in air at atmospheric pressure with no gas flow. It was expected to observe a higher ozone density in the vicinity of the discharge gap but ozone has been found at a quasi uniform density level up to 10 cm from the electrode gap after only 30 s of ignition. Such a wide distribution of ozone in the reactor cell is attributed to strong turbulence mostly triggered by the ionic wind. The mapping of the ozone density associated to the power measurement led to the estimation of the ozone production yield in term of mass per electrical energy.

Comparison of Performance of Cold Atmospheric Plasma and Biocides on the Inactivation of Alternaria sp.

In this article, the inactivation of Alternaria sp. is investigated using cold atmospheric plasma (CAP) and the results compared with two conventional techniques: 1) sodium dichloroisocyanurate (NaDCC) and 2) quaternary ammonium compounds (QAC). CAP generated by a pulsed corona discharge device was evaluated against suspension of spore of Alternaria sp. ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times10$ </tex-math></inline-formula> 3 conidia.mL <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> ) inside a test tube. The results were compared with conventional techniques of water disinfection by NaDCC (200 and 400 ppm) or QAC (1000 ppm). Plasma treatment duration time greater than or equal to 3 min, using a voltage pulse of 20 kV, and greater than or equal to 9 min, using a voltage pulse of 10 kV, was effective in the inactivation. For conventional treatment, spores were only effectively inactivated when concentration of 400 ppm of NaDCC.