Pulsed Corona Discharge Research Articles

Interaction between NO and SO2 removal processes in a pulsed corona discharge plasma (PCDP) reactor and the mechanism

The interaction between De-NO and De-SO2 from flue gas in a pulsed corona discharge plasma (PCDP) reactor was studied experimentally. A mechanism and kinetic scheme of De-NO and De-SO2 inside the PCDP reactor has been proposed and verified by comparison of the simulated and experimental results. The dominant radicals and elementary reactions are confirmed through sensitivity analysis. It has been found that there is significant interaction between the De-NO and De-SO2 processes in a PCDP reactor, and that the De-NO reactions prevail over the De-SO2 ones. The interaction consists of competitive reactions between NO and SO2 involving oxidative radicals, as well as interaction reactions between NO, SO2 and their derivatives. Through sensitivity analysis it has been found that the most effective elemental reaction to De-NO is NO + HO2 <=> OH + NO2 and that the most helpful radical is HO2. The most effective reaction for De-SO2 is SO2 + O <=> SO3 and the most helpful radical is atomic O. The study reveals the interaction mechanism between De-NO and De-SO2 in PCDP and provides a theoretical basis to improve the performance of simultaneous NO and SO2 abatement in a PCDP reactor.

Corona-stabilized gas spark gap switch for a double forming line with 300 kV working voltage

A high-current self-breakdown gas switch stabilized by corona preionization was developed for closing of 300 kV repetitively operated at 10 pps water insulated double-forming line (Blumlein) of a nanosecond electron accelerator. The switch is installed at the end of the Blumlein and is used for closing of outer of two coaxial lines. High stability of the self-breakdown voltage (within ±1%) at fast charging of Blumlein (during ≈1.4 μs) is achieved by gas preionization in the spark-gap by additional pulsed corona discharge. The spark-gap electrode system includes two main toroidal electrodes and an additional corona needle that is located in the cavity of one of them (negative during the operation). It combines two parallel gas discharge gaps – the main spark gap and an additional corona discharge gap. Separating the functions of the spark and corona gaps makes it possible to optimize the geometry of the electrodes of each gap and provide both the ability to switch high currents and high dynamic characteristics for a long operating time. Dried air is used as a working gas at pressure of 3-4 atm (abs.). Gas blowing system includes 4 gas inlets located at outer flange supporting the high voltage insulator (water-gas interface) and one outlet in the cavity of the grounded main electrode. This scheme of gas flow protects the insulator from deposition of electrode erosion products and minimizes gas flow (≈20 l/min) for stable operation of the switch by removing of the hot gas throw the cavity of the grounded electrode.The design of the switch together with the main results of the working tests will be presented and discussed.

Characteristics of high pressure nanosecond discharge in methane-containing gas mixtures

A nanosecond discharge of voltage up to 240 kV and pulse length of 10÷25 ns in mixtures of CH4 and CO2 at gas pressures up to 6 bar was investigated. For a pulse corona discharge and diffuse discharge from pointed cathodes, the dependences of the energy input in the gas on pressure, gas composition, and electrode geometry were obtained. It is demonstrated that the pulse energy of the diffuse discharge far exceeds the pulse energy of the corona discharge. The maximum specific energy input per pulse for the diffuse discharge was 0.5 J/cm3. The data obtained are necessary to determine the specific energy consumption for methane reforming and correct assessment of the efficiency of discharge technologies for processing natural gas.

Applicability of pulsed corona discharge treatment for the degradation of chloroform

Degradation of chloroform was investigated using plasma corona discharge by a needle-plate reactor. Chloroform concentration of 200 mg/L was completely degraded in 10 min of treatment. Almost complete dechlorination happened in 10 min and 91% total organic carbon (TOC) removal occurred in 12 min of treatment. Several important parameters such as input voltage, initial concentration, pH, conductivity, alkalinity, presence of OH radical and aqueous electron scavengers were evaluated to understand their effect on rate of chloroform degradation. The degradation rate of chloroform increased with increase in pH, conductivity and alkalinity of the solution. The maximum concentrations of OH radical, H2O2 and superoxide produced after 10 min of corona discharge were estimated to be 0.260 mM, 0.353 mM and 0.046 mM respectively. Various intermediates such as dichloromethane, dichloroethane, trichloroethane, trichloroethylene (TCE), tetrachloroethylene (PCE), trichloronitromethane and acetaldehyde were identified using GC-MS purge and trap technique. Based on the identified intermediates, reductive and oxidative degradation pathway of chloroform is proposed.

Investigation of Spatially Resolved Spectrum of N2 (C3&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\Pi_{\rm{u}} \rightarrow$ &lt;/tex-math&gt; &lt;/inline-formula&gt; B3&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\Pi_{\rm{g}}$ &lt;/tex-math&gt; &lt;/inline-formula&gt;) in Positive Nanosecond Pulsed Streamer Corona Discharge

In this paper, the spatially resolved spectrum of the nitrogen second positive system ( $\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ ) has been measured in a nanosecond pulsed streamer corona N2 discharge with a wire-plate electrode structure. The spatial distributions of emission intensity of N2 ( $\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) at different pulse peak voltages, pulse repetition rates, and gas components are used to explore the distribution and variation of the high electron density (higher than 11.03 eV) with the reaction radiation rate analysis. It is found that the high electron density increases with increasing both the peak voltage and pulsed repetition rate but decreases with increasing the oxygen contents. The spatial distribution of the emission intensity of N2 ( $\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) is normalized to the value of the emission intensity at the wire electrode at different experimental conditions. The results show that the normalized distribution of the spatially resolved spectral intensity of N2 ( $\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) is independent of pulsed peak voltage, pulsed repetition rate, and gas component, which indicate that the normalized distributions of the high-energy electron density in the gap space at different experimental conditions are similar. These experimental results are significant to understand the discharge characters of pulsed streamer corona discharge and establish the molecule reaction dynamics model of pulsed streamer corona discharge.

Continuous flow pulse corona discharge reactor for the tertiary treatment of drinking water: Insights on disinfection and emerging contaminants removal

The widespread occurrence of emerging contaminants (ECs) and pathogens in potable water sources has led to the need of an efficient alternative method for water treatment. Three pharmaceuticals and two pesticides were selected for the ECs degradation study in a continuous flow pulse corona discharge reactor. For a power dissipation of 58.67 W, ECs were completely removed from lake water with a flow rate of 10 mL/min. Whereas, 91–100% ECs degradation was achieved in river water after a hydraulic retention time (HRT) of 24 min. Initial bacterial concentrations were determined in lake and river water samples and subsequently, disinfection studies were carried out. With the same power input, complete disinfection (3 log reduction in river water) was achieved within HRT of 10 min. The toxicities of the ECs were completely eliminated after the plasma treatment. Several other water quality parameters were also monitored and an increase in nitrate concentration and decrease in pH value was observed after treatment. The problem of increased nitrate concentrations in the plasma treated water was tackled, thus making the plasma treated water suitable for drinking purpose. Using oxygen as a feed gas instead of atmospheric air, nitrate concentration was brought down significantly. Energy efficiency of the reactor was also compared in terms of electrical energy per order (EEO) and G value. Depending on the nature of the ECs, the EEO values ranged between 20 and 86 kWh/m3 and G-value between 8.4 and 36.8 mg/kWh in different potable water sources. The operating cost for treating ECs from contaminated water was found to be as low as 4.3 $/m3.

Behaviour of aqueous sulfamethizole solution and temperature effects in cold plasma oxidation treatment

The increase in volume and variety of pharmaceuticals found in natural water bodies has become an increasingly serious environmental problem. The implementation of cold plasma technology, specifically gas-phase pulsed corona discharge (PCD), for sulfamethizole abatement was studied in the present work. It was observed that sulfamethizole is easily oxidized by PCD. The flow rate and pH of the solution have no significant effect on the oxidation. Treatment at low pulse repetition frequency is preferable from the energy efficiency point of view but is more time-consuming. The maximum energy efficiency was around 120 g/kWh at half-life and around 50 g/kWh at the end of the treatment. Increasing the solution temperature from room temperature to 50 °C led to a significant reaction retardation of the process and decrease in energy efficiency. The pseudo-first order reaction rate constant (k1) grows with increase in pulse repetition frequency and does not depend on pH. By contrast, decreasing frequency leads to a reduction of the second order reaction rate constant (k2). At elevated temperature of 50 °C, the k1, k2 values decrease 2 and 2.9 times at 50 pps and 500 pps respectively. Lower temperature of 10 °C had no effect on oxidation efficiency compared with room temperature.

Estimation of Qualitative and Quantitative Parameters of Air Cleaning by a Pulsed Corona Discharge Using Multicomponent Standard Mixtures

The efficiency of removal of volatile organic impurities in air by a pulsed corona discharge is investigated using model mixtures. Based on the method of competing reactions, an approach to estimating the qualitative and quantitative parameters of the employed electrophysical technique is proposed. The concept of the “toluene coefficient” characterizing the relative reactivity of a component as compared to toluene is introduced. It is proposed that the energy efficiency of the electrophysical method be estimated using the concept of diversified yield of the removal process. Such an approach makes it possible to substantially intensify the determination of energy parameters of removal of impurities and can also serve as a criterion for estimating the effectiveness of various methods in which a nonequilibrium plasma is used for air cleaning from volatile impurities.

Design and Analysis of Nano-Pulse Generator for Industrial Wastewater Application

Recently, the application of a pulsed power system is being extended to environmental and industrial fields. The non-dissolution wastewater pollutants from industrial plants can be processed by applying high-voltage pulses with a fast rising time (a few nanoseconds) and short duration (nano to microseconds) in a pulsed corona discharge reactor. The high-voltage nano-pulse generator with a magnetic switch has been developed. It can be used for a spray type water treatment facility. Its corona current in load can be adjusted by pulse width and repetition rate. We investigated the performance of the nano-pulse generator by using the dummy load that is composed of resistor and capacitor equivalent to the actual reactor. In this paper, the results of design, construction and characterization of a high-voltage nano-pulse generator for an industrial wastewater treatment are reported. Consequently, a pulse width of 1.1 μs at the repetition rate of 200 pps, a peak voltage of 41 kV for the nano-pulse generator were achieved across a 640 Ω load. The simulation results on magnetic switch show reasonable agreement with experimental ones.

Effect of pulse width on streamer propagation of underwater corona discharge

The propagation of pulsed negative corona discharges in water as a function of electrical pulse width ranging from 100 ns to 100 μs has been studied experimentally. Using point‐to‐plane electrodes, it is demonstrated that the propagation of streamers exhibits different behavior under excitations with different pulse width. For pulses with width shorter than 1 µs, the average velocity stays relatively constant at about 1000 m s−1. For pulses with width longer than 1 µs, the average velocity decreases dramatically with increasing pulse width. Numerical fitting shows that the relationship between the velocity and pulse width follows u ∝ τ−0.72. Two different mechanisms are proposed to explain the different discharge characteristics observed at different time scales. At the initial stage before the generation of any significant heat, we show that the electrostatic force may play a major role in supplying the driving force. As the pulse width increases, the gas temperature rises, and the pressure caused by evaporation may become the dominant force to push the head of the filament to propagate. The transition time between two modes was estimated to be in the order of microseconds. Our quantitative predictions are in reasonable agreement with experimental results.

Hospital Wastewater Treatment with Pilot-Scale Pulsed Corona Discharge for Removal of Pharmaceutical Residues

Hospital Wastewater Treatment with Pilot-Scale Pulsed Corona Discharge for Removal of Pharmaceutical Residues

Removal of tetracycline antibiotics from wastewater by pulsed corona discharge plasma coupled with natural soil particles

In this study, pulsed corona discharge plasma coupled with natural soil particles (PCDP/SPs) were used to remove tetracycline hydrochloride (TCH) from wastewater. The differences among three typical and natural soil particles (SPs, black soil (BS) of Jilin, loess soil (LS) of Shaanxi, and red soil (RS) of Hunan in China) for TCH removal were compared by the PCDP/SPs system. The energy yields upon TCH removal and synergistic effects between the pulsed corona discharge plasma (PCDP) and SPs were analyzed. The effects of various factors on removal efficiency of TCH were investigated. The results indicated that the removal efficiency of TCH and the energy yield of PCDP were obviously improved in the PCDP/SPs system. Different SPs types had significant effects on the TCH removal. The removal efficiencies of TCH in the PCDP/SPs system with LS and BS were higher than that in the PCDP/SPs system with RS. The removal efficiency of TCH increased with an increase in the pulsed peak voltage, pulsed frequency, and SPs weight and a decrease in the SPs size. The removal efficiency of TCH decreased upon increasing the initial concentration of TCH and solution conductivity. The recycling experiment showed that the removal efficiency of TCH still maintained a high level after four cycles in the PCDP/LS system; however, a decrease in the removal efficiency of TCH was also observed. The consumption of active species in solution demonstrated that OH and O3 play key roles in TCH degradation. Intermediates in the process of TCH degradation for the PCDP/SPs system with LS were identified by GC–MS, and a possible degradation pathway was also proposed.

Non-thermal gas-phase pulsed corona discharge for lignin modification

Lignin has the potential to become a significant resource of renewable aromatics for the chemical industry. The current work studies pulsed corona discharge (PCD) as an alternative method for lignin modification. The effect of initial lignin concentration and gas phase composition on aldehydes formation was studied experimentally. Kraft lignin was used as a test compound. It was concluded in the work, that treatment in low oxygen content atmosphere and high initial lignin concentration leads to higher lignin conversion to aldehydes. Despite the proven aldehydes formation, the precise nature of the changes in the lignin structure during oxidation with PCD remained unclear. To address this question, a number of advanced analytical techniques were implemented: NMR, GPC, HSQC, HPSEC, and GCMS. The effect of PCD treatment on lignin structure was studied for two types of lignin: kraft lignin, purchased from Sigma Aldrich, and birch lignin acquired from a pressurized hot water extraction and soda pulped biorefinery process (BLN lignin). Changes in solubility, molecular weight and proportion of phenolic and aliphatic OH groups, as well as lignin repolymerization were detected. The findings are of value to efforts to make lignin modification tunable to the production of desired products.

Hospital wastewater treatment with pilot-scale pulsed corona discharge for removal of pharmaceutical residues

In recent years, accumulation of pharmaceutical compounds in the environment has been an issue of growing concern. Conventional wastewater treatment has limited effectiveness with many pharmaceuticals at concentrations of ppb or ppt scale. An intuitive solution would be to treat the pharmaceuticals-contaminated wastewaters at the source sites before dilution in sewer networks. Health institutions with concentrated drug consumption provide logical point sources for pharmaceuticals entering the sewage. This paper describes the pilot-scale removal of a wide range of pharmaceuticals from real wastewaters via gas-phase pulsed corona discharge oxidation. The process was studied for raw sewage from a public hospital and for biologically treated wastewater of a health-care institute. The non-selective oxidation of the observed pharmaceuticals (32 compounds) was effective at reasonable energy cost: 87-% reduction in residual pharmaceuticals (excluding biodegradable caffeine) from raw sewage was attained with 1 kWh m−3 from the raw sewage and 100% removal was achieved for biologically treated wastewater at only 0.5 kWh m−3. The impact for affected aquatic environments upon the present solution would be a dramatically reduced load of pharmaceutical accumulation.

High efficiency plasma treatment of water contaminated with organic compounds. Study of the degradation of ibuprofen

The degradation of ibuprofen in water by nonthermal plasma is studied using a pulsed corona discharge above liquid, generated in oxygen. The influence of pulse duration (50–430 ns FWHM) on removal efficiency and on mineralization was investigated. Complete removal of the target compound was achieved within 15–20 min plasma treatment and the mineralization degree reached 76% after 60 min. The energy efficiency was greatly enhanced by reducing pulse length: 20.2 g kWh−1 was obtained for 50 ns pulses at 90% IBP removal, more than one order of magnitude higher than the value for the longest pulses. Higher initial concentration of the target compound led to further improvement of the energy yield, but required more time to complete the degradation process.

Effect of recycling overhead gases on pollutants degradation efficiency in gas-phase pulsed corona discharge treatment

In the present study, pollutant degradation efficiency was investigated by recycling of overhead gases from gaseous phase to aqueous phase in gas-liquid interface pulsed corona discharge reactor. Methylene blue (MB) was used as a model pollutant and its degradation was compared by recycling and non-recycling of oxygen, air and argon gases. The degradation rate constants of MB were 0.28 and 0.23 min−1 in recycled condition which was decreased to 0.22 and 0.21 min−1 in non-recycled condition in oxygen and argon gas, respectively. On contrary, in air medium, comparatively higher MB degradation rate (0.21 min−1) was achieved in non-recycled condition compared to recycled condition (0.11 min−1). The long-lived reactive oxygen species (ROS) such as hydrogen peroxide and ozone were quantified in both conditions. We observed that the concentration of ozone present in the aqueous solution was slightly higher in recycling conditions as compared to that of non-recycled condition in all the gases. Moreover, higher hydrogen peroxide concentration was detected in recycled condition (185 and 168 mg/L) compared to non-recycled condition (112 and 40 mg/L) in the presence of oxygen and argon, respectively, and vice-versa in air medium. The economic comparison revealed that up to 33% of electrical energy could be saved by recycling overhead oxygen gas.

Effect of electronegative additives on physical properties and chemical activity of gas discharge plasma

Effect of electronegative additives (oxygen O2, sulfur dioxide SO2, carbon disulfide CS2, and carbon tetrachloride CCl4) on physical properties and chemical activity of plasma formed by pulsed corona discharge and by non-self-sustained discharge supported by pulsed electron beam in atmospheric pressure gas mixtures was investigated. It is shown that a decrease in discharge current depends on a sort of the additive and on its concentration. The reason is the difference in rate constants of electron attachment processes for the above molecules. In experiments on volatile organic compounds (VOCs) conversion in air by streamer corona it is obtained that an addition of CCl4 both decreases the discharge current amplitude and increases the VOCs conversion degree. An installation for investigation of electron attachment processes and for study of toxic impurities conversion in plasma formed by non-self-sustained discharge initiated by pulsed nanosecond electron beam is created.

Analysis of electroionization processes while applying pulse corona discharge to charge finely dispersed aerosol phas

The paper considers problems of electroionization processes while applying pulse corona discharge; in addition, a system of corona producing devices of “point-net” type has been proposed. A dependence of concentration of air ions from distance to ionizer has been determined. The dependence makes it possible to identify the preset ionic composition to accumulate maximum possible charge value within fine-dispersed particles, but the airflow velocity is limited by technological parameters and its values are determined depending on conditions (technological equipment, etc.), and the magnitude of the impulse voltage is limited by the parameters of the charger at which the "breakdown" is excluded. Also on the basis of the studies carried out, a device for generating a high voltage voltage pulse is proposed, which makes it possible to intensify the ionization of the medium in the interelectrode space and at the moments of a pause between the voltage pulses, to ensure the outflow of the ions formed beyond the discharge gap by the moving dust and gas environment.

The Catalytic Effect of Electronegative Additives on Removal of Perchloroethylene Vapor from Air by Pulsed Corona Discharge

It is established that electronegative additives (CCl4, freon-113) produce a catalytic effect on the conversion of volatile organic compounds (VOCs) under the action of atmospheric-pressure nonequilibrium plasma generated in pulsed corona discharge. At concentrations below 0.1%, these additives significantly decrease the discharge current, but the energy efficiency of the process of VOC removal from air increases. The catalytic effect of electronegative additives on the VOC conversion in air and nitrogen is quantitatively demonstrated in the case of perchloroethylene C2Cl4 (PCE) vapor removal. The addition of 0.085% CCl4 to air reduces the energy consumption for PCE removal at initial concentration of 0.09% by half (from 12 to 6 eV per molecule) at a 63% degree of cleaning. Mechanisms explaining the active inf luence of electronegative additives on the discharge current and the process of impurity removal are suggested.

Pulsed Corona Discharge Induced Hydroxyl Radical Transfer Through the Gas-Liquid Interface

The highly energetic electrons in non-thermal plasma generated by gas phase pulsed corona discharge (PCD) produce hydroxyl (OH) radicals via collision reactions with water molecules. Previous work has established that OH radicals are formed at the plasma-liquid interface, making it an important location for the oxidation of aqueous pollutants. Here, by contacting water as aerosol with PCD plasma, it is shown that OH radicals are produced on the gas side of the interface, and not in the liquid phase. It is also demonstrated that the gas-liquid interfacial boundary poses a barrier for the OH radicals, one they need to cross for reactive affinity with dissolved components, and that this process requires a gaseous atomic H scavenger. For gaseous oxidation, a scavenger, oxygen in common cases, is an advantage but not a requirement. OH radical efficiency in liquid phase reactions is strongly temperature dependent as radical termination reaction rates increase with temperature.