Pulsed Corona Plasma Research Articles

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.

Enhanced degradation of complex organic compounds in wastewater using different novel continuous flow non – Thermal pulsed corona plasma discharge reactors

The presence of pharmaceutically active compounds (PhAcs) in water bodies is a major concern due to their persistence, biological activity, and detrimental environmental effects. The present study focuses on the application of pulsed corona plasma technology to degrade such compounds. Three different plasma reactors, namely, sequential flow plasma reactor (SFR), continuous flow top discharge plasma reactor (TDPR) and continuous flow side discharge plasma reactor (SDPR), are designed and fabricated for their performance evaluation with respect to PhAC degradation. In all the reactors, wastewater was discharged as fine droplets for better interaction between the reactive oxidizing species (ROS) generated in the system and the pollutants. Enhanced degradation of the selected pharmaceutical compounds, i.e., diclofenac (DCF) and verapamil hydrochloride (VPL), is achieved with decreased treatment time and lower energy consumption. In SFR reactor water was recycled, whereas in continuous flow reactors hydraulic retention times (HRTs) were varied. The degradation efficiency of DCF (1 mg/L) and VPL (1 mg/L) was 99 % in SDPR, at HRTs of 9 and 12 min, respectively. Deposited energies (SFR- 71 W, TDPR - 92 W, SDPR- 51 W) varied due to the difference in reactor geometries. In the SDPR reactor, 99 % degradation of mixed pollutants with an initial concentration of 10 mg/L was achieved, at a HRT of 21 min. With an input power of 51 W, good energy efficiency (EEO) of 3.8 kWh/m3 and high yield (G) of 256.2 mg/kWh were obtained. . Nitrate formation was reduced by 73.2 % in TDPR and 85.0% in SDPR (32.1–8.6 mg/L) as compared to SFR (32.1 mg/L). The operating cost estimated was 0.71 $/m3, 0.80 $/m3 and 0.67 $/m3 for SFR, TDPR and SDPR, respectively. The results clearly indicate that the continuous flow reactor with side discharge is a viable alternative to traditional plasma reactors.

Energizing a Long Nanosecond Pulsed Corona Reactor: Electrical Characterization

Industrial application of nanosecond pulsed corona technology for air purification requires high volume, high power plasma reactors. Cylinder-wire type reactors require multiple cylinders or very long reactors to meet these demands. In this article, we focus on the characterization of a pulsed corona plasma in a long (4.5 m) plasma reactor. The reactor cylinder acts as a coaxial transmission line wherein high-voltage pulses propagate with close to the speed of light. Interactions between plasma generation and reflection behavior inside the reactor are expected and therefore investigated. A 4.5-m-long corona reactor is constructed and equipped with voltage and current sensors at multiple positions along the reactor length. A lumped element SPICE model is developed to simulate the reflection behavior. Strong reflections at the end of the reactor are observed for pulse rise times which are shorter than the transient time of the reactor. Plasma generation and energy distribution in the reactor, as well as impedance matching between source and reactor, are affected by these reflections. We investigate the role of the input voltage and rise time and analyze the electrical characterization, impedance characterization, and reactor efficiency.

Boosting the Energy Efficiency of a Nanosecond Pulsed Corona Plasma System With a Multiple-Wire Plasma Reactor

Transient plasma generated by high-voltage nanosecond pulses in a pulsed corona configuration has proven to be an efficient medium for e.g., air purification applications. In this article, we present a study on boosting the energy efficiency of such a system by using a special type of plasma reactor: the multiple-wire plasma reactor. The basic principle of such a reactor is that it has a lower transmission-line impedance than a normal wire-cylinder reactor while at the same time still producing the required high electric fields necessary for plasma generation. The lower impedance of the reactor results in a smaller impedance mismatch between the high-voltage pulse source and the reactor, thereby minimizing pulse reflections on the source-reactor interface, increasing the energy efficiency of the system. We calculate the impedance of the multiple-wire reactor and assess both the electrical energy efficiency as well as the chemical efficiency of the plasma by measuring electrical energies and ozone concentrations generated by the plasma when energized by a fast solid-state nanosecond pulse source (with 7-ns rise time pulses of up to 20kV) for a range of multiple-wire plasma reactor parameters. We show that with the multiple-wire reactor we can almost double the energy efficiency of the reactor (from 45% to 85%), reduce the voltage stress in the system by 29%–31% and increase the system efficiency by 95%–98% when using a multiple-wire electrode geometry (as compared to a single-wire system).

Remediation of perfluorooctanoic acid (PFOA) polluted soil using pulsed corona discharge plasma

Perfluorooctanoic acid (PFOA) from contaminated soil accumulates in higher organisms, and causes health risks to humans. In this research, 71 % of the PFOA was degraded, of which 51 % was decomposed into short chain by-products, 19 % mineralized, and 1 % volatilized with 30 kV of voltage, 50 Hz of discharge frequency, 1 % of soil moisture, 300 ppm of PFOA concentration and 6.3 of soil pH using pulsed positive discharge plasma. From a series of experiments, electrons were identified as the dominant active means of PFOA degradation. The decomposition by-products were analyzed by LC–MS. The results indicated that PFOA was decomposed into small by-products including perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluoropentanoic acid (PFPeA), perfluorobutyric acid (PFBA), pentafluoropropionic acid (PFPrA) and trifluoroacetic acid (TFA). Moreover, in plasma treated soil, the concentration of ammonia nitrogen increased from less than 10 ppm–462 ppm, and the average dry weight of lettuce was 1.6 mg higher than that in natural soil. Additionally, Planctomycetes and Nitrospirae increased after treatment, indicating that plasma technology promotes the process of nitrogen cycle. Thus, PFOA polluted soil could be remediated using this pulse corona plasma technology, and simultaneously improve the fertility of soil without chemical injections.

Degradation and intermediates of diclofenac as instructive example for decomposition of recalcitrant pharmaceuticals by hydroxyl radicals generated with pulsed corona plasma in water

Seven recalcitrant pharmaceutical residues (diclofenac, 17α-ethinylestradiol, carbamazepine, ibuprofen, trimethoprim, diazepam, diatrizoate) were decomposed by pulsed corona plasma generated directly in water. The detailed degradation pathway was investigated for diclofenac and 21 intermediates could be identified in the degradation cascade. Hydroxyl radicals have been found primarily responsible for decomposition steps. By spin trap enhanced electron paramagnetic resonance spectroscopy (EPR), OH-adducts and superoxide anion radical adducts were detected and could be distinguished applying BMPO as a spin trap. The increase of concentrations of adducts follows qualitatively the increase of hydrogen peroxide concentrations. Hydrogen peroxide is eventually consumed in Fenton-like processes but the concentration is continuously increasing to about 2mM for a plasma treatment of 70min. Degradation of diclofenac is inversely following hydrogen peroxide concentrations. No qualitative differences between byproducts formed during plasma treatment or due to degradation via Fenton-induced processes were observed. Findings on degradation kinetics of diclofenac provide an instructive understanding of decomposition rates for recalcitrant pharmaceuticals with respect to their chemical structure. Accordingly, conclusions can be drawn for further development and a first risk assessment of the method which can also be applied towards other AOPs that rely on the generation of hydroxyl radicals.

Fenton chemistry promoted by sub-microsecond pulsed corona plasmas for organic micropollutant degradation in water

Differences in the liquid chemistry due to different ground electrode materials (titanium, stainless steel) were compared for corona discharges in water. The plasma was generated by applying positive high voltage pulses that are characterized by short rise times of about 20 ns, a peak voltage of 80kV and pulse lengths of about 150–160ns (FWHM). Phenol was admixed to the water for quantification of the bulk reaction chemistry, such as phenol decomposition and H2O2-formation. Optical emission spectroscopy was conducted to relate chemistry to plasma processes. Possible electrode corrosion was determined by atomic absorption spectroscopy (AAS).The post-discharge chemistry strongly depends on ground electrode material. With stainless steel electrodes, decomposition efficiency of phenol increased by about three quarters (74.9 %) when compared with titanium electrodes. This result can be explained by dissolved metal ions corroded from the ground electrode, which catalytically decomposed the H2O2 that had been formed into hydroxyl radicals again. Ground electrodes were corroded due to electrochemical processes. Corrosion rates and overall reaction chemistries cannot readily be described similar to conventional DC electrochemical processes at low voltages. The repetitive application of sub-microsecond high voltage pulses has to be taken into account explicitly. Altogether, electrode materials, ground electrode corrosion and associated catalytic processes are more important for plasma processes in aqueous solutions than was recognized so far. Therefore, the effects need to be taken into account in the analysis of laboratory results as well as the development of respective novel water treatment technologies.

Comparison of pulsed corona plasma and pulsed electric fields for the decontamination of water containing Legionella pneumophila as model organism

Pulsed corona plasma and pulsed electric fields were assessed for their capacity to kill Legionella pneumophila in water. Electrical parameters such as in particular dissipated energy were equal for both treatments. This was accomplished by changing the polarity of the applied high voltage pulses in a coaxial electrode geometry resulting in the generation of corona plasma or an electric field. For corona plasma, generated by high voltage pulses with peak voltages of +80kV, Legionella were completely killed, corresponding to a log-reduction of 5.4 (CFU/ml) after a treatment time of 12.5min. For the application of pulsed electric fields from peak voltages of −80kV a survival of log 2.54 (CFU/ml) was still detectable after this treatment time. Scanning electron microscopy images of L. pneumophila showed rupture of cells after plasma treatment. In contrast, the morphology of bacteria seems to be intact after application of pulsed electric fields. The more efficient killing for the same energy input observed for pulsed corona plasma is likely due to induced chemical processes and the generation of reactive species as indicated by the evolution of hydrogen peroxide. This suggests that the higher efficacy and efficiency of pulsed corona plasma is primarily associated with the combined effect of the applied electric fields and the promoted reaction chemistry.

Decontamination of 2-Chloroethyl Ethyl Sulfide by Pulsed Corona Plasma

Decontamination of 2-chloroethyl ethyl sulfide (2-CEES, CH3CH2SCH2CH2Cl) by pulsed corona plasma was investigated. The results show that 212.6 mg/m3 of 2-CEES, with the gas flow rate of 2 m3/h, can be decontaminated to 0.09 mg/m3. According to the variation of the inlet and outlet concentration of 2-CEES vapor with retention time, it is found that the reaction of 2-CEES in a pulsed corona plasma system follows the first order reaction, with the reaction rate constant of 0.463 s−1. The decontamination mechanism is discussed based on an analysis of the dissociation energy of chemical bonds and decontamination products. The C–S bond adjacent to the Cl atom will be destroyed firstly to form CH3CH2S· and ·CH2CH2Cl radicals. CH3CH2S· can be decomposed to ·C2H5 and ·S. ·S can be oxidized to SO2, while ·C2H5 can be finally oxidized to CO2 and H2O. The C–Cl bond in the ·CH2CH2Cl radical can be destroyed to form ·CH2CH2. and ·Cl, which can be mineralized to CO2, H2O and HCl. The H atom in the ·CH2CH2Cl radical can also be substituted by ·Cl to form CHCl2–CHCl2.

Analysis of reactivity and energy efficiency of methane conversion through non thermal plasmas

The non oxidative conversion of natural gas by non thermal plasmas offers a promising route to produce higher value products, such as hydrogen and C2 hydrocarbons, at a low energetic cost. In this work we present the results of a theoretical research aimed to study the reactivity of methane treated with atmospheric plasmas. The effects of various process parameters on energy efficiency, conversion, and selectivity to acetylene, ethylene, and ethane have been investigated for different reactor configurations. For this purpose two different models were used. The first consists of a detailed kinetic model and a simplified reactor description, based on the assumption that the plasma volume is homogeneous and adiabatic. It is apt to describe stationary discharges such as microwave and radio frequency plasmas. The second is a time dependent micro-discharge model based on similar assumptions that is suitable to study pulsed discharges. The results evidence a strong dependence between the energy efficiency of the discharge and the specific energy supplied. A kinetic analysis was performed in order to understand the main reaction paths activated by the plasma discharge. One of the main findings of this study is that the temperature evolution in the plasma volume plays a key role in determining the system reactivity, in particular in the case of atmospheric pulsed discharges. In fact, though such plasmas are often considered non-thermal, our calculations show that in the few milliseconds that follow a pulsed discharge the local temperature rapidly rises up to the point where endothermic reactions, such as homolytic scissions, get activated. Our simulations show that the inception of these reactions is accompanied by an increase of the process energy efficiency. Furthermore, since in micro-discharges transport phenomena can be important, fluid dynamic simulations of pulsed corona plasmas have been performed using a simplified kinetic scheme. Such computations have been useful to understand the main physical features of micro-discharges. Among the conclusions of this study are reported a set of guidelines that may be useful to improve the energy efficiency of plasma methane conversion processes.

Studies on a non-thermal pulsed corona plasma between two parallel-plate electrodes in water

A non-thermal plasma generated between two parallel-plate electrodes submerged in water was studied in this work. The surface of one of the stainless-steel electrodes (the cathode) was coated with a ceramic layer of Al2O3. This reactor cell was connected to a water cycle and the discharge was carried out in a closed loop and therefore an equilibrium was established during discharge. The dependence of hydrogen peroxide formation as an indicator for the generation of most important oxidative species OH radicals on the pulse repetition rate, the solution conductivity and the pH of the solution was investigated. The highest yield of H2O2 (3.5 mg L−1) was obtained at 20 pps in a NaCl solution with a conductivity of 400 µS cm−1 and pH 7 in 90 min. The maximum energy efficiency of ∼0.1 g kWh−1 H2O2 was obtained. The surface of the coated electrodes, before and after applying of electrical discharges, was analysed by scanning electron microscopy. During the discharge process, the coating was destroyed and the formation of H2O2 decreased to 10% after discharging of nearly 35 h.

Effect of Flue Gas Humidity on Toxic Gaseous Pollutants Conversion by Pulse Corona Plasma

Effect of Flue Gas Humidity on Toxic Gaseous Pollutants Conversion by Pulse Corona Plasma

Pulsed corona plasma source characterization for film deposition on the inner surface of tubes

A microplasma jet has been constructed for chemical vapour deposition on the inner surface of narrow long tubes and is tested on a quartz tube with the inner diameter of 6 mm and the outer diameter of 8 mm. A long plasma filament (>100 mm) is generated inside the tube in argon with methane admixture. Depending on the quantity of admixture in argon, the negative as well as the positive corona discharges are ignited. Both modes of plasma are characterized using optical emission spectroscopy. For this purpose, nitrogen is admixed with argon and its emission is used for the determination of gas temperature, electron velocity distribution function and electron density at various places along the axis of the tube. The formation of active species, such as C, C2 and CH during the dissociation of methane, is observed through their characteristic emission. The rate of methane dissociation is determined at various places along the axis of the tube during both modes of discharge. Since the chemical kinetics of the film growth process is different, different kinds of films are obtained during different modes of discharge.

All-Solid-State Power Modulator for Pulsed Corona Plasma Reactors

Atmospheric pressure pulsed corona plasma (PCP) reactors of wire-plate design offer novel solutions to environmental issues and to a number of industrial processes. Emerging applications include indoor air sterilization and odor removal in air conditioning systems, chemical synthesis in non-thermal plasmas, and plasma reforming of gaseous fuels. We previously reported on experimental investigations of a laboratory size, wire-plate plasma reactor for pulsed corona treatment of gas flows. Operation with gas flow, at pulse repetition frequencies of between 10 pps and 200 pps, has been achieved at pulse voltage amplitudes of between 10 and >30 kV, at pulse durations of around 0.3 mus (FWHM). High efficiencies of up to 70 g/kWh have been reported using an all-solid-state pulse generator. In this work, we report on the development of all-solid-state power modulators for use with nonlinear loads like pulse corona plasmas. The pulse generators are based on a fast thyristor switch discharging pulse capacitors, a pulse step-up transformer, and one or two stages of magnetic pulse compression. At pulse repetition rates of up to 200 pps, amplitudes of > 30 kV into a resistive-capacitive load (1 kOmega200 pF) have been achieved, at risetimes of about 80 ns and a pulse width of 0.3 mus. The pulse generator is insensitive to load variations, in particular to sparking in the reactor. An advanced generator version uses two magnetic pulse compression stages resulting in even shorter rise times. The modulator and its performance concerning experimental results will be described in detail when driving a pulsed corona reactor.

Characterization of pulsed discharge plasma at atmospheric pressure

The production of hydrogen and carbon nanotubes (CNTs) by the decomposition of methane inside the reactor using pulsed discharge plasma under conditions of room temperature and atmospheric pressure was investigated and characterized. The development of dissociation of methane with corona discharge under several conditions had been observed. We have noticed that the key radicals such as CH 3 and H produced by pulse corona plasma from source gas, will undergo chain reaction leading to efficient formation of hydrogen gas as well. We have found the external diameter and resistivity of CNTs around 50 nm and 0.15 Ω cm respectively. The main results obtained from the present experiments could be quite useful for the production of hydrogen, CNTs, and future industrial applications.

An Industrial Streamer Corona Plasma System for Gas Cleaning

For pulsed corona plasma applications, it becomes important to develop pilot systems with large average power and high-energy conversion efficiency. Since the beginning of 2000, we have been working on an industrial corona plasma system with tasks of 10-30 kW in average power and higher than 90% of total energy conversion efficiency. The pulsed-power source should have the following specifications: rise time of 10-25 ns, pulsewidth of 50-150 ns, pulse repetition rate of up to 1000 pulses per second, peak voltage pulse of 70 kV, peak current of 3.5 kA, dc bias voltage of 10-35 kV, and energy per pulse of up to 30 J. Sixteen parallel wire cylinder reactors are used to match the source. Gas and reactor temperatures can be controlled individually with water flow around the outside of those cylinders. The system is designed for gaseous oxidation and electrostatic dust precipitation. The system has been used for up to 17 kW in average power. This paper reports the system in detail, discusses issues related to the matching between the source and the reactor, and presents an example of industrial demonstrations on odor abatement at 1000 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /h. Finally, this paper also gives a general guideline for design of corona plasma systems

Water vapor desorption and adsorbent regeneration for air conditioning unit using pulsed corona plasma

The dehumidifying action of a dehumidifier or air conditioner was employed to achieve a comfortable and desirable indoor comfort. Water vapor adsorbed on an adsorbent substance needs to be regenerated when the water vapor exceeds the adsorption capacity. The conventional process for adsorbent regeneration or moisture desorption uses the heat by means of the electric heater. In the present study, the water vapor desorption from the adsorbent material was investigated using a pulsed corona plasma for possible replacement of the electric heater. The water vapor desorption for a given power (defined as desorption efficiency) using the pulsed corona plasma was found to be superior over conventional thermal desorption. The gradient of desorption (desorption rate) was found to be significantly higher for plasma desorption, so that faster desorption can be achieved without excessive gas heating. In addition, the plasma desorption was not affected by the initial moisture content in an indoor environment, which leads to more economical, controllable, and flexible air conditioning system.

Removal Characteristics of Gaseous Sulfur-Containing Compounds by Pulsed Corona Plasma

Pulsed corona plasma was employed to treat the gases containing hydrogen sulfide, methyl mercaptan (MM), and dimethyl sulfide (DMS), respectively. For the plasma oxidation only, the removal efficiencies of hydrogen sulfide, MM, and DMS were approximated to be 90%, 69%, and 52% when the discharge power was 5.6 W. But all the removal efficiencies were over 98% when an activated carbon fiber (ACF) filter was used downstream from the plasma reactor. In addition, the decomposition reaction mechanism was discussed and a competitive reaction kinetics model was proposed to describe the plasma decomposition reaction kinetics. The ACF filter appeared to be co-beneficial in the improvement of removal efficiency, reduction of energy consumption, and the abatement of ozone or other byproducts. The energy consumption was about 3 W·h/m3 for hydrogen sulfide to obtain about 90% of the removal efficiency by plasma oxidation only, but it can be reduced below 1.2 W·h/m3 in the present of the ACF filter.

Diesel Engine Emission Control Using Pulsed Corona Plasma-Wet Chemical Hybrid Process

The plasma-wet chemical hybrid process for NOx removal from the flue gas emissions is extremely effective and economical in comparison with the conventional selective catalytic reduction system. A series of experiments using the plasma-wet chemical hybrid system are performed to control NOx from the diesel engine emission. The operation characteristics and optimum operation for plasma and chemical reactors are investigated in regard to reaction products such as N2O, CO, CO2, HNO3 and NO3- as well as NOx removal efficiency using the pulsed corona and barrier type packed-bed plasma reactors. The oxidation from NO to NO2 without reducing NOx concentration (i.e., minimum reaction byproducts) and with least power consumption is the key for the optimum reactor design. The produced NO2 is totally converted to N2 and Na2SO4 with Na2SO3 scrubbing. The hybrid reactors followed by the chemical reactor achieved extremely low operating cost and around 90% NOx removal efficiency with small amount of byproducts.

Comparative Analysis of Experiment Treating Benzene and CEES by Pulse Corona Plasma

Based on an experiment treating benzene and 2-chloroethyl ethyl sulfide (CEES) by pulse corona induced-plasma, the similarities and differences found in the experimental data and analytical results are analyzed in a comparative manner in this paper. The theory applied is also discussed.