Reduction of NO x /SO2 by Wire-plate Type Pulsed Discharge Reactor with Pulsed Corona Radical Shower

Pulsed discharge deNO _x /deSO₂ process has been studied for over 20 years, but how to achieve higher removal rate at lower cost remains one of the crucial issues for realization of its industrial application. This paper presents a novel deNO _x /deSO₂ process that combines a wire-plate type pulsed discharge reactor and a corona radical shower. Our aim is to increase the deNO _x /deSO₂ rate of wire-plate type reactor by enhancing the generation of radicals with pulsed corona radical shower. Effect of a nozzle electrode on the production of OH radical was studied by emissive spectrum, and deNO _x /deSO₂ experiments using a wire-plate reactor with pulsed corona radical shower were conducted. The experimental results demonstrated that corona radical shower could enhance the production of radicals and the deNO _x /SO₂ performance of a wire-plate reactor. This study will play a positive role in the industrial application of wire-plate pulsed discharge deNO _x /deSO₂ reactor.     

Evaluation of Energy Utilization Efficiencies for SO2 and NO Removal by Pulsed Corona Discharge Process

Pulsed corona discharge process was applied to the removal of sulfur dioxide and nitrogen oxides from simulated flue gas. The energy transfer efficiency of the pulse generation circuit and the energy utilization efficiencies for SO ₂ and NO removal are evaluated and discussed. When the pulse-forming capacitance was five times larger than the geometric capacitance of the reactor, the energy utilization efficiency was maximized, and the energy requirements for NO and SO ₂ removal could be lowered. With regard to radical utilization efficiency, producing small amounts of radicals frequently was found to be more advantageous than producing large amounts of radicals less frequently. Removal efficiency of SO ₂ increased with the applied peak voltage, but the energy utilization efficiency was nearly independent of the peak voltage when the peak field intensity was high enough to induce corona discharge (above 10 kV cm ^–1 in this system).     

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.     

Effects of Process Variables on NOx Conversion by Pulsed Corona Discharge Process

We investigated the effects of several process variables (initial concentrations of NO, NH₃, and H₂O and electron concentration) on NOx conversion by the pulsed corona discharge process (PCDP). In the PCDP, most of the NO is converted into NO₂ and, later, into HNO₃ which reacts with NH₃ to form NH₄NO₃ particles. We solved the model equations of chemical species in the PCDP considering 23 chemical species and 54 chemical reactions. As the initial NO concentration increases or electron concentration decreases, it takes a longer reactor length to remove the NO_x by the PCDP. As the initial H₂O, it takes a shorter reactor length to remove the NO_x. As the initial NO and H₂O and electron concentration decreases, or as the initial NH3 concentration increases, it takes a longer reactor length to consume the NH₃ by the particle formation reactions. The information on the effects of several process variables on the plasma chemistry in NO_x conversion can be the basis guideline to develop a more efficient PCDP and this study can be extended to obtain the information on particle characteristics of ammonium salts.     

Density distribution of high energy electrons in pulsed corona discharge of NO+N2 mixture

Emission spectroscopy of the high-voltage pulsed positive corona discharge in a line-cylinder reactor is used to investigate the high-energy electron density distribution in the discharge gap. The relative overall emission intensity spatial distribution profile of the A2Sigma+ --> X2Pi transition of NO is successfully recorded against a severe electromagnetic pulse interference coming from the corona discharge at one atmosphere. The spectroscopic investigation shows that the high-energy electron density in the discharge has a nonlinearly decline in the radial distribution. When varying the discharge voltage, the absolute emission intensity of NO is different but the radial distribution profile is similar. If an oxygen flow was introduced into the discharge reactor, the emission intensity of NO decreases tremendously and, therefore, the high-energy electron density decreases reasonably.     

Study on Reduction of Energy Consumption in Pulsed Corona Discharge Process for NOx Removal

We investigated the reduction of electrical energy consumption in thepulsed corona discharge process for the removal of nitrogenoxides. Hydrocarbon chemical additives used in the laboratory-scaleexperiment are responsible for the enhancement of the NO conversionthrough the chain reactions of free radicals, such as, R, RCO, RO,and others. Electrical energy consumption per converted NO moleculehas a minimum value of 17 eV when pentanol is injected. When ethyleneand propylene are injected, 30 and 22 eV of electrical energy consumptionare required for the conversion of a NO molecule, respectively. The ratioof the pulse-forming capacitance (C_e) to the reactor capacitance (C_R)plays an important role in the energy transfer efficiency to thereactor. The maximum energy transfer efficiency of approximately 72%could be obtained by the pulse-forming capacitance, which is 3.4 timeslarger than the reactor capacitance; the maximum NO conversionefficiency was also observed with the same condition.     

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.     

Oxidation and Reduction Processes During NO x Removal with Corona-Induced Nonthermal Plasma

In this paper, the NO-to-NO ₂ conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO _x removal experiments in N ₂ +NO _x and N ₂ +O ₂ +NO _x gaseous mixtures, it is supposed that the reverse reaction NO ₂ +ONO+O ₂ may not only limit NO ₂ production in N ₂ +NO _x mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NON ₂ +O, induce negligible NO removal provided the O ₂ concentration is larger than 3.6%. With adding H ₂ O into the reactor, the produced NO ₂ per unit removed NO can be significantly reduced due to NO ₂ oxidation. NH ₃ injection could also significantly decrease the produced NO ₂ via NH and NH ₂ - related reduction reactions. Almost 100% of NO ₂ can be removed in gaseous mixtures of N ₂ +O ₂ +H ₂ O+NO ₂ with negligible NO production.     

Evaluation of Multiple Corona Reactor Modes and the Application in Odor Removal

Effects of multiple corona reactor modes on pulse characteristics, energy transfer efficiency, and odor (H₂S and NH₃) removal were investigated experimentally by the wire-plate corona reactor(s). The removal efficiency of H₂S was only 91% and the energy consumption was 16.1 Wh m⁻³ by the single mode with a gas-flow rate of 23 m³ h⁻¹ and an initial concentration of 200 mg m⁻³. At the same experimental conditions, almost 100% removal efficiency was achieved and the energy consumption was only 12.8 and 14.9 Wh m⁻³ by the series and parallel modes. In the case of 50 mg m⁻³ NH₃ removal at the same gas-flow rate, the removal efficiencies with the single mode, the series and parallel modes were 64, 92 and 70%, respectively. The energy requirement did not increase at the same residence time under the experimental conditions of the single mode with a gas-flow rate of 11.5 m³ h⁻¹ and the series or parallel mode with a gas-flow rate of 23.0 m³ h⁻¹. The experimental results indicate that the series and parallel modes are effective in saving energy consumption, improving removal ability and efficiency, especially for the series mode.     

Coupling of methane under pulse corona plasma (I)

At normal temperature and pressure, pulse corona plasma was used as a new method for the dehydrogenative coupling of methane in the absence of oxygen. The effects of voltage polarity and input energy on the dehydrogenative coupling of methane were investigated. The parameter “energy efficiency” was introduced to examine the coupling of the input energy and the dehydrogenative coupling of methane. The experimental results show that positive corona gives higher energy efficiency than negative corona. When the positive corona was chosen, C₂ yield per pass was 31.6% and acetylene yield per pass was 30.1% with 44.6% methane conversion at an input energy density of 1788kJ/mol and a pulse repetition frequency of 66Hz. The function of input energy density towards methane conversion may be expressed as a formula of-In(1-X) =k (PIF). In the range of input energy employed, C₂ yield is proportional to input energy density, but energy efficiency drops off with increasing input energy density.     

An Analysis of Exhaust Emission of the Internal Combustion Engine Treated by the Non-Thermal Plasma

Industries’ air pollution causes serious challenges to modern society, among them exhaust gases from internal combustion engines, which are currently one of the main sources. This study proposes a non-thermal plasma (NTP) system for placement in the exhaust system of internal combustion engines to reduce the toxic contaminants (HC, CO, and NO_x) of exhaust gases. This NTP system generates a high-voltage discharge that not only responds to the ion chemical reaction to eliminate NO_x and CO, but that also generates a combustion reaction at the local high temperature of plasma to reduce HC. The NTP system was designed on both the front and rear of the exhaust pipe to analyze the difference of different exhaust flow rates under the specified frequency. The results indicate that the NTP system can greatly reduce toxic contaminants. The NTP reactor placed in the front of exhaust pipe gave HC and CO removal efficiency of about 34.5% and 16.0%, respectively, while the NTP reactor placed in the rear of exhaust pipe gave NO_x removal efficiency of about 41.3%. In addition, the voltage and material directly affect the exhaust gases obviously. In conclusion, the proposed NTP system installed in the exhaust system can significantly reduce air pollutants. These results suggest that applying NTP to the combustion engine should be a useful tool to simultaneously reduce both emissions of NO_x and CO.     

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.     

Methanol and Dimethyl Sulfide Removal by Pulsed Corona Part I: Experiment

Methanol and dimethyl sulfide are volatile organic compound (VOC) air pollutants that are subject of severe environmental regulations due to their toxicity, environmental persistence and odor. Traditional technologies are often inefficient for their removal, especially in the case of the dilute industrial streams. Non-thermal plasma methods, typically characterized by high removal efficiency, energy yields and good economy, offer possible alternative solutions. The present research employs pulsed corona discharge known for its high selectivity and low energy costs of emission control. This paper provides experimental (Part I) and in a later issue numerical (Part II) data on removal of methanol and dimethyl sulfide from dry and humid air streams. The removal efficiency and the specific energy input are evaluated along with the energy costs required for the removal process. Particular attention is given to the formation of unwanted byproducts such as NO _x , CO, and SO₂.     

Total Diesel Emission Control Technology Using Ozone Injection and Plasma Desorption

An innovative total diesel emission control system for diesel particulate and NOx simultaneous reduction is proposed. In this system, the plasma reactor is located outside the emission exhaust pipe and activated gas induced from ozone activated by the plasma is injected into the exhaust pipe. On the other hand, the NOx reduction is achieved using oxygen-poor nonthermal plasma desorption. The concentration of oxygen can be changed either by controlling the incineration state of the engine or by injecting oxygen-poor gas. Experiments are carried out for the emission of small diesel engine generator and high performance is demonstrated. The effective or apparent required plasma energy can be decreased further using this system because of the periodic or intermittent application of the plasma. In the present study, the excellent reduction energy efficiencies of 6.6 g/kWh for PM and 16 g (NO₂)/kWh for NOx are achieved.     

脉冲电晕环境中13X分子筛对NO分解作用的研究

在常温、常压下，利用脉冲电晕放电产生冷等离子体，使一氧化氮发生分解，直接生成氮气和氧气，用四极杆质谱仪在线测量反应过程中反应物和生成物的变化。在自行研制的实验台上，考察了13X分子筛在不同的脉冲电晕放电条件下，表现出来的不同特性及其对反应转化率的影响。在30 ℃～430 ℃、流量375 mL/min～1 333 mL/min，分析了该反应过程中13X分子筛对转化率的促进作用。在同一脉冲放电条件下，控制13X分子筛的温度为200 ℃，转化率从30 ℃时的1.2%上升到19.7%；转化率最高可以达到35.9%。并对反应过程中13X分子筛的吸附特性做了初步探讨。     

By-Products NOx Control and Performance Improvement of a Packed-Bed Nonthermal Plasma Reactor

NO_x are main toxic by-products in the effluent gas whendecomposing volatile organic compounds in air by a packed-bed plasmareactor. Several types of materials such as 13X zeolite, BaTiO₃and Pd/Pt catalysts have been selected to be packed in the reactor, andmethane decomposition and NOx by-products in discharged gases areinvestigated at different range of reaction temperature and dischargeenergy density at atmospheric pressure. The ratios of methane decompositionpercentage/NO_x concentration are used to assess these packed bedmaterials and reaction conditions. The results show that usingPd/-Al₂O₃ with lower percentage Pd as packedbed, and discharging with lower discharge density at higher reactiontemperature can reduce NO_x output effectively and greatly improveperformance of the reactor.     

PFAS Degradation in Ultrapure and Groundwater Using Non-Thermal Plasma

Perfluoroalkyl substances (PFAS) represent one of the most recalcitrant class of compounds of emerging concern and their removal from water is a challenging goal. In this study, we investigated the removal efficiency of three selected PFAS from water, namely, perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and pefluorooctanesulfonic acid (PFOS) using a custom-built non-thermal plasma generator. A modified full factorial design (with 2 levels, 3 variables and the central point in which both quadratic terms and interactions between couple of variables were considered) was used to investigate the effect of plasma discharge frequency, distance between the electrodes and water conductivity on treatment efficiency. Then, the plasma treatment running on optimized conditions was used to degrade PFAS at ppb level both individually and in mixture, in ultrapure and groundwater matrices. PFOS 1 ppb exhibited the best degradation reaching complete removal after 30 min of treatment in both water matrices (first order rate constant 0.107 min⁻¹ in ultrapure water and 0.0633 min⁻¹ in groundwater), while the degradation rate of PFOA and PFHxA was slower of around 65% and 83%, respectively. During plasma treatment, the production of reactive species in the liquid phase (hydroxyl radical, hydrogen peroxide) and in the gas phase (ozone, NO_x) was investigated. Particular attention was dedicated to the nitrogen balance in solution where, following to NO_x hydrolysis, total nitrogen (TN) was accumulated at the rate of up to 40 mg^N L⁻¹ h⁻¹.     

Energy efficiency of NO removal by pulsed corona discharges

Pulsed positive corona discharges are used to remove NO from the flue gas of a methane burner. At low power input this leads to an increase in NO₂, which shows that the process is oxidative. Removal efficiency is greatest when discharges are produced with high-voltage pulses, which are shorter in duration than the time required by the primary streamers to cross the discharge gap, in combination with a dc bias. Other important parameters are input power density and residence time. The best result obtained so far is an energy consumption of 20 eV per NO molecule removed, at 50% deNOx i.e., a removal of 150 ppm NO_x, using a residence time of 15 s and an input power density, of 3.5 Wh/Nm³. [Wh/Nm³ stands for watt-hour per normal cubic meter, i.e., at normal conditions (273 K and 1 bar). This implies that 1 Nm³ contains 2.505 10²⁵ molecules.] There appears to be room for improvement by the addition of gaseous and particulate chemicals or the use of multiple corona treatment. It is argued front comparison between results from models and experiments that the direct production of OH by the discharge is only the initiation of the cleaning process.     

Efficient Energy Delivery Condition from Pulse Generation Circuit to Corona Discharge Reactor

The energy transfer efficiency from pulse generation circuit to corona discharge reactor was investigated. To find the optimum energy transfer condition, we varied the value of the pulse-forming capacitor in pulse generation circuit. Maximum energy transfer from pulse generation circuit to corona discharge reactor was achieved when the ratio of the pulse-forming capacitance to the geometric capacitance of the reactor was around 3.0. From the analyses of the voltage and current waveforms, we found that the capacitance of the reactor increases about three times, due to the corona development. This increase is the reason why the maximum energy transfer occurs when the pulse-forming capacitance is three times larger than the initial capacitance of the reactor. The energy consumption for removal of nitric oxide was also minimized at this capacitance ratio.     

Hydrocarbon Effects on the Promotion of Non-Thermal Plasma NO–NO2 Conversion

Kinetic modeling of non-thermal plasma chemistry is conducted to investigate hydrocarbon (CH₄, C₂H₄, C₃H₆, and C₃H₈) effects on the promotion of NO–NO₂ conversion. A reduced plasma chemistry model, in which radical reactions are selectively involved, is validated with experimental data. The higher reactivity of hydrocarbon additive with O radicals, which produces initial radicals, is requisite to initiate hydrocarbon decomposition, thus providing NO–NO₂ conversion. Initial radicals by plasma discharge induce continual hydrocarbon decomposition and this self-preserved reaction mechanism greatly contributes to the promotion of energy efficient NO–NO₂ conversion. Increase in the conversion extent by ethylene and propylene additives is substantial because of their stronger affinity with O radical. The primary routes of NO–NO₂ conversion process differed by hydrocarbon additives are presented and discussed with the assistance of sensitivity analysis.