Pilot-Scale Experiment for Simultaneous Dioxin and NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Removal from Garbage Incinerator Emissions Using the Pulse Corona Induced Plasma Chemical Process

A pilot-scale pulse corona induced plasma chemical process (PPCP) reactor for controlling gas-phase dioxins and NO _x simultaneously is installed in a garbage incineration plant. The flow rate of the sampled flue gas is 5,000 Nm³/h (N: standard state) in maximum at the PPCP reactor, which consists of 22 wire-cylinder electrodes and is energized by a 50 kW nanosecond pulse high voltage generator. With an applied plasma energy density of 2.9–6.1 Wh/Nm³, the decomposition efficiency for dioxins is 75–84% based on TEQ (toxic equivalents); the conversion efficiency of NO to NO₂ is ~93% at maximum. The flue gas treated by the PPCP reactor is introduced at a rate of 50 Nm³/h to a wet-type chemical reactor, which uses an aqueous solution of sodium sulfite (Na₂SO₃). More than 90% of NO _x is reduced to nitrogen, with negligible byproducts such as NO₂ ⁻ or NO₃ ⁻ ions left in the solution.     

An NO+ reactant ion source for ion mobility spectrometry

The major reactant ion in conventional ion mobility spectrometry (IMS) is the hydronium ion, H₃O⁺ which is produced in the usual ionization sources such as corona discharge or radioactive sources. Using the hydronium reactant ion, mostly the analytes with proton affinity higher than that of water are ionized. A broader range of compounds can be detected by IMS if other alternative ionization channels, such as charge transfer from NO⁺, are employed. In this work we introduce a simple and novel method for producing NO⁺ as the major reactant ion in IMS. This was achieved by adding neutral NO to the corona discharge ionization source. The neutral NO was prepared via an additional discharge in an air stream, flowing into the corona discharge source. A curtain plate was mounted in front of the corona discharge to prevent the influence of the analyte on the production of NO⁺. Using this technique, the reactant ion could easily and quickly switch between the H₃O⁺ and NO⁺. The performance of the new source was evaluated by recording ion mobility spectra of test compounds with both H₃O⁺ and NO⁺ reactant ions.     

Kinetic Modelling of Atmospheric Pressure Corona Discharges in Humid Air

Corona discharge is a self-sustained discharge of gaseous medium in inhomogeneous electric fields, which often occurs on transmission lines and has some adverse effect on the power transmission system. In this paper, a kinetic model of corona discharges is presented to simulate the evolution process of charged particles and neutral species in humid air. To investigate the effect of humidity, our model consists of 69 species and 393 chemical reactions which consider important reactions containing H₂O molecules and hydrates. In addition, CO₂ molecules are also included to improve the integrity of reaction database. A temporal evolution of reduced electric field strengths E/N, which are typical experimental values of corona discharges, is used as input. The simulation results show that H₃O⁺ is one of the dominant positive ions which is in qualitative agreement with previous experimental results. The effect of humidity and pulse width on the plasma chemistry is also discussed. It is found that the humidity affects the maximum density and life time of the specific species. Meanwhile, the plasma chemistry could be affected by different pulse widths of the input electric field.

     

Design and Operating Characteristics of a Simple and Reliable DBD Reactor for Use with Atmospheric Air

The paper reports on the construction and operating characteristics of a planar dielectric barrier discharge (DBD) plasma generator. The generator was powered from a commercial frequency inverter at 400 Hz through a high voltage transformer. It could be operated up to a specific energy density (power per gas flow) of 20 Wh/m³. The corresponding power density was about 0.5 W per cubic centimeter of discharge volume. Special emphasis was given to a simple and reliable construction, which was easy to assemble and is based on a new, nonexpensive barrier material with excellent electrical, mechanical, and thermal properties. The modular reactor design allows simple plasma power scale-up. The reactor works with undried ambient air without additional cooling. In the range up to 10 Wh/m³ the ozone generation from ambient air was directly proportional to the energy density at a rate of 60 g O₃ per kWh or 30 ppm/Wh/m³. Thus the generator can serve as an effective source for chemically active radicals in plasma gas cleaning applications.     

Controllable Synthesis of NiCo LDH Nanosheets for Fabrication of High‐Performance Supercapacitor Electrodes

A unipolar pulse electrodeposition method was employed to controllably synthesize nanosheet type NiCo LDH. The effect of concentration rate of Ni(NO₃)₂/Co(NO₃)₂ preparation solution on crystalline structure, morphology and supercapacitive performance was investigated systematically. Experimental found that the morphology and composition of NiCo LDH was highly depend on the Ni²⁺/Co²⁺ molar ratios of preparation solution; and the obtained Ni_0.76Co_0.24 LDH materials showed small nanosheet size and uniform distribution on carbon fiber electrode. Ni_0.76Co_0.24 LDH electrode was evaluated for supercapacitor application, which revealed a high specific capacitances of 2189.8 and 1908.8 F g⁻¹ at the current density of 1 and 30 A g⁻¹ respectively and a good cycle stability, retaining 70.3 % of the initial capacitance after 20000 charge and discharge cycles at 50 A g⁻¹. Moreover, the Ni_0.76Co_0.24 LDH electrode exhibits a high energy density of 76 Wh Kg⁻¹ at a power density of 250 W Kg⁻¹ and a high power density of 7500 W Kg⁻¹ at energy density of 66 Wh Kg⁻¹. The as‐prepared Ni_0.76Co_0.24 LDH as positive electrode for asymmetric supercapacitor exhibits excellent energy density of 4.1 Wh Kg^‐1 at a power density of 4000 W Kg^‐1     

Concentrations of active species in a bulk barrier discharge in a plasmochemical reactor

The results of theoretical and experimental studies of the chemical composition of the ensemble of active species formed in a plasmochemical reactor that consists of a multicell bulk-barrier-discharge generator of active species and a working chamber are presented. To calculate the composition of the neutral species in the barrier discharge, an approach based on the averaging of the power input over the entire volume of the discharge gap was proposed. One advantage of this approach is that it involves no adjustable parameters, such as the sizes of the microdischarges, their surface density, and frequency of breakdowns. The calculations and measurements were performed using dry air (with a relative humidity of 20%) as the plasma-forming medium. The concentrations of O₃, HNO₃, HNO₂, N₂O₅, and NO₃ in the discharge gap and working chamber were measured at a mean residence time of the species in the discharge gap of τ = 0.3 s and a specific power input of 1.5 W/cm³. The best agreement between the calculation results and the experimental data was obtained when the temperature of the gas mixture in the discharge was set equal to 400–425 K, a value that coincided with the measured rotational temperature of molecular nitrogen. Generally, the calculated and measured concentrations of O₃, HNO₃, HNO₂, N₂O₅, and NO₃ in both the bulk barrier discharge and the working chamber were found to be in close agreement.     

Generation of Antimicrobial NO<Subscript>x</Subscript> by Atmospheric Air Transient Spark Discharge

Atmospheric pressure air plasma discharges generate potential antimicrobial agents, such as nitrogen oxides and ozone. Generation of nitrogen oxides was studied in a DC-driven self-pulsing (1–10 kHz) transient spark (TS) discharge. The precursors of NO_x production and the TS characteristics were studied by nanosecond time-resolved optical diagnostics: a photomultiplier module and a spectrometer coupled with fast intensified camera. Thanks to the short (~10–100 ns) high current (>1 A) spark current pulses, highly reactive non-equilibrium plasma is generated. Ozone was not detectable in the TS, probably due to higher gas temperature after the short spark current pulses, but the NO_x production rate of ~7 × 10¹⁶ molecules/J was achieved. The NO₂/NO ratio decreased with increasing TS repetition frequency, which is related to the complex frequency-dependent discharge properties and thus changing NO₂/NO generating mechanisms. Further optimization of NO₂ and NO production to improve the biomedical and antimicrobial effects is possible by modifying the electric circuit generating the TS discharge.     

Atmospheric pressure chemical ionization of explosives using alternating current corona discharge ion source

The high‐sensitive detection of explosives is of great importance for social security and safety. In this work, the ion source for atmospheric pressure chemical ionization/mass spectrometry using alternating current corona discharge was newly designed for the analysis of explosives. An electromolded fine capillary with 115 µm inner diameter and 12 mm long was used for the inlet of the mass spectrometer. The flow rate of air through this capillary was 41 ml/min. Stable corona discharge could be maintained with the position of the discharge needle tip as close as 1 mm to the inlet capillary without causing the arc discharge. Explosives dissolved in 0.5 µl methanol were injected to the ion source. The limits of detection for five explosives with 50 pg or lower were achieved. In the ion/molecule reactions of trinitrotoluene (TNT), the discharge products of NO_x^? (x = 2,3), O₃ and HNO₃ originating from plasma‐excited air were suggested to contribute to the formation of [TNT ? H]^? (m/z 226), [TNT ? NO]^? (m/z 197) and [TNT ? NO + HNO₃]^? (m/z 260), respectively. Formation processes of these ions were traced by density functional theory calculations. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of Plasma Regimes and Catalysts on Ethanethiol Oxidation

Plasma oxidation of ethanethiol in air was investigated using three plasma regimes: surface dielectric pulsed corona discharge, surface dielectric barrier discharge and pulsed corona discharge (PCD) in the plasma reactor. Catalytic plasma degradation of ethanethiol was also performed on the singular or binary metals doped ?èCAl₂O₃. The ethanethiol removal rate increased with increasing energy density but energy efficiency was first increased and then decreased with increasing energy density under three various types of discharges. PCD plasma required the lowest energy density at the similar ethanethiol removal performance compared with the other two plasma discharges. The main intermediate by-products of ethanethiol oxidation by plasma are CH₃CHO, HCHO, CO and CO₂. The sum of these intermediate products selectivities is 19?C43?%, implying that some other intermediates containing carbon were undetermined. When using PCD plasma combined with catalysts, ethanethiol removal rate and energy efficiency were all evidently improved. The maximum energy efficiency was achieved about 200?g kWh^?1 using Fe?CMn/?èCAl₂O₃ assisted PCD plasma, which was about 4.4 times when using PCD plasma alone. The mechanism of ethanethiol oxidation is also discussed.     

Simultaneous Removal of Nitrogen Oxides and Particulate Matters from Diesel Engine Exhaust using Dielectric Barrier Discharge and Catalysis Hybrid System

Dielectric barrier discharge (DBD) and catalysis hybrid process was used to remove nitrogen oxides and particulate matters from diesel engine exhaust. The DBD reactor converts a part of NO into NO₂, and then the exhaust gas containing the mixture of NO and NO₂ enters the catalytic reactor where both NO and NO₂ are reduced to N₂. The effect of energy density (power input divided by gas flow rate) and reaction temperature on the removal of nitrogen oxides was investigated with a stationary diesel engine. The hybrid process was able to remove about 80% of the initial nitrogen oxides at an energy density of 25 J/L and 150°C. The removal of particulate matters did not largely depend on the electrode structure, but it was a strong function of the energy density. On the basis of 80% removal efficiency, the energy yield for nitrogen oxides was 40 eV/molecule while that for particulate matters was 83 kJ/mg. The present study suggests that this kind of hybrid process can be applied to simultaneous removal of nitrogen oxides and particulate matters from diesel engine exhausts.     

Oxidation of Acetylene in Atmospheric Pressure Pulsed Corona Discharge Cell Working in the Nanosecond Regime

Combined experimental and modeling studies of acetylene oxidation in pulsed corona discharges working in the nanosecond regime are presented. The corona cell was characterized in term of power deposition to provide input data for the model. The concentrations of ozone, CO, CO₂ and residual acetylene were systematically measured for model validation purposes. The model used allows describing the detailed chemistry in the discharge and the mass transfer between the microdischarges and the discharge free regions in the corona cell. Results showed that the model allows a satisfactory prediction of the acetylene residual fraction, CO and CO₂ yields and O₃ concentration for a wide range of conditions. They enabled a precise identification of the product distribution and confirmed the central role of O-atom in the oxidation process. They also revealed that ketene, H₂CCO, plays an important role in the oxidation mechanism and allowed drawing some conclusions on the optimization of the oxidation process.     

Scaling of Shielded Sliding Discharges for Environmental Applications

Shielded sliding discharges are nanosecond streamer discharges which develop along a dielectric between metal foil electrodes, with one of the foils extended over the entire rear of the dielectric layer. The electrode configuration not only allowed rearranging discharges in parallel due to the decoupling effect of the metal layer, but also to modify the electric field distribution in such a way that components normal to the surface are enhanced, leading to an increased energy density in the discharge plasma. By varying the electrode gap, the applied voltage, and the repetition rate, it is shown that by keeping the average electric field constant, the discharge voltage can be reduced from tens of kV to values on the order of a few kV, but only at the expense of a reduced energy density of the plasma. Varying the repetition rate from 20 to 500 Hz resulted in a slightly reduced energy per pulse, likely caused by residual charges on the dielectric surface. Measurements of the NO conversion to NO₂ and ozone synthesis in dry air showed that the conversion is only dependent on the energy density of the discharge plasma. Although reducing the pulse voltage from the tens of kV range to that of few kV, and possibly even lower, causes a reduction in energy density, this loss can be compensated for by increasing the electrode gap area. This and the possibility to form discharge arrays allows generating large volume discharge reactors for environmental applications, at modest pulsed voltages.     

Point and Multipoint to Plane Barrier Discharge Process for Removal of NOx from Engine Exhaust Gases: Understanding of the Reactional Mechanism by Isotopic Labeling

An experimental study on the removal of NO_x in a simulated vehicle exhaust gas has been carried out using point to plane and multipoint to plane DBD corona reactors. Hydrocarbon (C₃H₆) and NO_x by-products were systematically investigated with a Gas Chromatography coupled to a Mass Spectrometry (GC/MS). NO_x (NO and NO₂) and CO output were also monitored with a gas analyzer in order to complete the mass balance. ¹⁸O tracer technique analyzes is applied to investigate the mechanism of propylene decomposition. From the plasma chemical reaction pathway proposed, it is apparent that the oxygen activation is one of the important steps for initiating the oxidation processes and the R-NO_x formation. We present data for the reaction of the (N₂/O₂/C₃H₆/CO₂NO/H₂O system in the corona discharge reactors mentioned above. This system has been shown to generate a significant amount of aldehyde. CH₃NO₂ and CH₃ONO₂ are the main R-NO_x compounds produced. Reactant composition and discharge energy densities (controlled by a numerical oscilloscope) were the operating parameters under study in wet and dry air mixture. Water vapors played an important role in NO_x removal (especially in NO₂ removal) via the reaction forming HNO₃. Therefore, in wet-gas mixture supplied reactors the highest removal rates of NO_x were as high as 30%, while in dry-gas only 15%. Different dielectric materials such as Al₂O₃/SiO₂ and TiO₂ on Al₂O₃/SiO₂ support have been used.     

Nitric Oxide Conversion and Ozone Synthesis in a Shielded Sliding Discharge Reactor with Positive and Negative Streamers

Positive and negative streamer discharges in atmospheric pressure air were generated in a shielded sliding discharge reactor at operating voltages as low as 5 kV for a gap length of 1.6 cm. In this reactor, electrodes are placed on top of a dielectric layer and one of the electrodes, generally the one on ground potential, is connected to a conductive layer on the opposite side of the dielectric. The energy per pulse, at the same applied voltage, was more than a factor of seven higher than that of pulsed corona discharges, and more than a factor of two higher than that of sliding discharges without a shield. It is explained on the basis of enhanced electric fields, particularly at the plasma emitting electrode. Specific input energy required for 50 % removal from ~1,000 ppm initial NO could be reduced to ~18 eV/molecule when ozone in the exhaust of negative streamers was utilized. For sliding discharges and pulsed corona discharges this value was ~25 eV/molecule and it was 35 eV/molecule for positive shielded sliding discharges. Also, the ozone energy yield from dry air was up to ~130 g/kW h and highest for negative streamer discharges in shielded sliding discharge reactors. The high energy density in negative streamer discharges in the shielded discharge reactor at the relatively low applied voltages might not only allow expansion of basic studies on negative streamers, but also open the path to industrial applications, which have so far been focused on positive streamer discharges.     

Cleaning of Air Streams from Organic Pollutants by Plasma–Catalytic Oxidation

Oxidative removal of a mixture of chlorinated ethylenes and aromaticcompounds in air in a pulse corona discharge reactor combined with metaloxide catalyst downstream was investigated in a field experiment. Dischargewas initiated by high-voltage pulses of 70–75 kV peak voltage and200 ns risetime. A flow of 60 m³/h was treated at11–12 Wh/m³ with catalyst held at 110°C at a spacevelocity of 6000 h^–1. Removal rates of 70–90% havebeen found with input concentrations in the parts per million and thesubparts per million range. No partially oxidized hydrocarbons could bedetected in cleaned air. A closed carbon balance was confirmed underlaboratory test conditions.     

Effect Of Propene, <Emphasis Type="Italic">n</Emphasis>-Decane,and Toluene Plasma Kinetics on NO Conversion in Homogeneous Oxygen-Rich Dry Mixtures at Ambient Temperature

A photo-triggered discharge is used to study the influence of three hydrocarbons (HCs), propene (C₃H₆), n-decane (C₁₀H₂₂), and toluene (C₆H₅CH₃) on NO conversion in N₂/O₂/NO/HC mixtures, with 18.5% O₂ concentration, 700 ppm of NO, and an hydrocarbon concentration ranging between 190 ppm and 2,700 ppm. The electrical system generates a transient homogeneous plasma, working under 400 mbar total pressure, with a 50 ns short current pulse at a repetition frequency up to a few Hz. The NO concentration at the exit of the reactor is quantified using absolute FTIR spectroscopy measurements, as a function of the specific deposited energy in the discharge and the mixture composition. Owing to the plasma homogeneity, the experimental results can be compared to predictions of a self-consistent 0-D discharge and kinetic model based on available data in the literature about reactions and their rate constants. It is shown that the addition of either propene (as for DBD or corona discharges) or n-decane to N₂/O₂/NO leads to an improvement of the NO removal as compared to the mixture without hydrocarbon molecules. The adopted kinetic schemes explain this effect for the two mixture types. On the other hand, both the experiments and model predictions emphasize that the addition of toluene does not lead to the improvement of NO conversion. Moreover, compounds that are useful for NO _x reduction catalysis, such as aldehydes, are less produced in the mixture with toluene.     

Mechanisms for negative reactant ion formation in an atmospheric pressure corona discharge

In an effort to better understand the formation of negative reactant ions in air produced by an atmospheric pressure corona discharge source, the neutral vapors generated by the corona were introduced in varying amounts into the ionization region of an ion mobility spectrometer/mass spectrometer containing a ⁶³Ni ionization source. With no discharge gas the predominant ions were O₂ ⁻, however, upon the introduction of low levels of discharge gas the NO₂ ⁻ ion quickly became the dominant species. As the amount of discharge gas increased the appearance of CO₃ ⁻ was observed followed by the appearance of NO₃ ⁻. At very high levels, NO₃ ⁻ species became effectively the only ion present and appeared as two peaks in the IMS spectrum, NO₃ ⁻ and the NO₃ ⁻·HNO₃ adduct, with separate mobilities. Since explosive compounds typically ionize in the presence of negative reactant ions, the ionization of an explosive, RDX, was examined in order to investigate the ionization properties with these three primary ions. It was found that RDX forms a strong adduct with both NO₂ ⁻ and NO₃ ⁻ with reduced mobility values of 1.49 and 1.44 cm²V⁻¹ s⁻¹, respectively. No adduct was observed for RDX with CO₃ ⁻ although this adduct has been observed with a corona discharge mass spectrometer. It is believed that this adduct, although formed, does not have a sufficiently long lifetime (greater than 10 ms) to be observed in an ion mobility spectrometer.     

Pilot-plant for NOx, SO2 and HC removal from flue-gas of municipal waste incinerator by electron beam irradiation

According to the basic research performed using a small size reactor at TRCRE of JAERI, the electron beam irradiation process was proved to be very effective for NO_x, SO₂ and HC removals from flue-gas of municipal waste incinerators. Based on this result, a pilot-plant was constructed for the demonstration of NO_x, SO₂ and HC removal performance using electron accelerator of maximum energy 0.95 MeV and maximum power 15kW.The pilot-plant was constructed at Matsudo City waste Disposal Center. The flue-gas of 1,000 Nm³/hr is guided from the waste incinerator flue-gas line of 30,000Nm³/hr to the pilot-plant to be processed by spraying Ca(OH)₂ slurry or powder and irradiation with high-energy electron beam of the accelerator. NO_x, SO₂ and HC are removed simultaneously from the flue-gas by the enhanced reaction with Ca (OH)₂ under irradiation.A brief explanation of the pilot-plant and preliminary results of the experiments are introduced in this paper.     

Decomposition of Cyanogen Chloride by Using a Packed Bed Plasma Reactor at Dry and Wet Air in Atmospheric Pressure

The decomposition rate of CNCl in a BaTiO₃-filled Packed Bed Plasma Reactor was studied as a function of AC input power, power frequency, residence time in the reactor, and inlet flow rate. The decomposition rate was compared with those of CH₃CN and CCl₂CHCl. Under the condition of 6.7 Wh/m³ specific energy den- sity, the decomposition rate of CNCl was found to be 50%, which is lower than those of CH₃CN and CCl₂CHCl at the same or similar conditions. At a higher frequency of the power input system, the decomposition rate of inlet gas becomes lower due to a decrease in field strength for the same level of power. And, under the same level of input power, a higher decomposition rate was obtained at an increased residence time. The relation between gas decomposition rates stemmed from the electron–molecule collision and bounding energy within the molecule. The decomposition ratio of CNCl was lower than those of CCl₂CHCl and CH₃CN because the bond strength of the weakest bond in the molecule is higher. In order to test the decomposition efficiency of CNCl with catalytic packing material in a plasma reactor, the catalyst of γ-Al₂O₃ and Pt/γ-Al₂O₃ was packed in the packed bed plasma reactor. Although byproducts were formed, the plasma-catalyst hybrid reactor containing Pt/γ-Al₂O₃ showed a higher efficiency in CNCl decomposition as shown in the decomposition rate of above 99% in 0.3 kWh/m³.     

High‐Performance Chemically Regenerative Redox Fuel Cells Using a NO3−/NO Regeneration Reaction

In this study, we proposed high‐performance chemically regenerative redox fuel cells (CRRFCs) using NO₃⁻/NO with a nitrogen‐doped carbon‐felt electrode and a chemical regeneration reaction of NO to NO₃⁻ via O₂. The electrochemical cell using the nitrate reduction to NO at the cathode on the carbon felt and oxidation of H₂ as a fuel at the anode showed a maximal power density of 730 mW cm⁻² at 80 °C and twofold higher power density of 512 mW cm⁻² at 0.8 V, than the target power density of 250 mW cm⁻² at 0.8 V in the H₂/O₂ proton exchange membrane fuel cells (PEMFCs). During the operation of the CRRFCs with the chemical regeneration reactor for 30 days, the CRRFCs maintained 60 % of the initial performance with a regeneration efficiency of about 92.9 % and immediately returned to the initial value when supplied with fresh HNO₃.