Studies on Nitrogen Oxides Removal Using Plasma Assisted Catalytic Reactor

An electric discharge plasma reactor combined with a catalytic reactor was studied for removing nitrogen oxides. To understand the combined process thoroughly, discharge plasma and catalytic process were separately studied first, and then the two processes were combined for the study. The plasma reactor was able to oxidize NO to NO2 well although the oxidation rate decreased with temperature. The plasma reactor alone did not reduce the NOx (NO NO2) level effectively, but the increase in the ratio of NO2 to NO as a result of plasma discharge led to the enhancement of NOx removal efficiency even at lower temperatures over the catalyst surface (V2O5-WO3/TiO2). At a gas temperature of 100℃, the NOx removal efficiency obtained using the combined plasma catalytic process was 88% for an energy input of 36 eV/molecule or 30 J/L     

DeNOx Study in Diesel Engine Exhaust Using Barrier DischargeCorona Assisted by V2O5／TiO2 Catalyst

A plasma-assisted catalytic reactor was used to remove nitrogen oxides (NOx) from diesel engine exhaust operated under different load conditions. Initial studies were focused on plasma reactor (a dielectric barrier discharge reactor) treatment of diesel exhaust at various temperatures. The nitric oxide (NO) removal efficiency was lowered when high temperature exhaustwas treated using plasma reactor. Also, NO removal efficiency decreased when 45% load exhaust was treated. Studies were then made with plasma reactor combined with a catalytic reactor consisting of a selective catalytic reduction (SCR) catalyst, V2O5/TiO2. Ammonia was used as a reducing agent for SCR process in a ratio of 1:1 to NOx. The studies were focused on temperatures of the SCR catalytic reactor below 200℃. The plasma-assisted catalytic reactor was operated well to remove NOx under no-load and load conditions. For an energy input of 96 J/1, the NOx removal efficiencies obtained under no-load and load conditions were 90% and 72% respectively at an exhaust temperature of 100℃.     

Removal of NO and SO2 in Corona Discharge Plasma Reactor with Water Film

In this paper, a novel type of a corona discharge plasma reactor was designed, which consists of needle-plate-combined electrodes, in which a series of needle electrodes are placed in a glass container filled with flue gas, and a plate electrode is immersed in the water. Based on this model, the removal of NO and SO2 was tested experimentally. In addition, the effect of streamer polarity on the reduction of SO2 and NO was investigated in detail. The experimental results show that the corona wind formed between the high-voltage needle electrode and the water by corona discharge enhances the cleaning efficiency of the flue gas because of the presence of water, and the cleaning efficiency will increase with the increase of applied dc voltage within a definite range. The removal efficiency of SO2 up to 98%, and about 85% of NO~ removal under suitable conditions is obtained in our experiments.     

Study of Humidity Effect on Benzene Decomposition by the Dielectric Barrier Discharge Nonthermal Plasma Reactor

The humidity effects on the benzene decomposition process were investigated by the dielectric barrier discharge(DBD) plasma reactor.The results showed that the water vapor played an important role in the benzene oxidation process.It was found that there was an optimum humidity value for the benzene removal efficiency,and at around 60% relative humidity(RH),the optimum benzene removal efficiency was achieved.At a SIE of 378 J/L,the removal efficiency was 66% at 0% RH,while the removal efficiency reached 75.3% at 60% RH and dropped to 69% at 80% RH.Furthermore,the addition of water inhibited the formation of ozone and NO_2 remarkably.Both of the concentrations of ozone and NO_2 decreased with increasing of the RH at the same specific input energy.At a SIE of 256 J/L,the concentrations of ozone and NO_2 were 5.4 mg/L and 1791 ppm under dry conditions,whereas they were only 3.4 mg/L and 1119 ppm at 63.5%RH,respectively.Finally,the outlet gas after benzene degradation was qualitatively analyzed by FT-IR and GC-MS to determine possible intermediate byproducts.The results suggested that the byproducts in decomposition of benzene primarily consisted of phenol and substitutions of phenol.Based on these byproducts a benzene degradation mechanism was proposed.     

High-efficiency removal of NO_x using dielectric barrier discharge nonthermal plasma with water as an outer electrode

With the rapid increase in the number of cars and the development of industry, nitrogen oxide(NO_x)emissions have become a serious and pressing problem. This work reports on the development of a water-cooled dielectric barrier discharge reactor for gaseous NOxremoval at low temperature. The characteristics of the reactor are evaluated with and without packing of the reaction tube with 2 mm diameter dielectric beads composed of glass, ZnO, MnO_2, ZrO_2, or Fe_2O_3. It is found that the use of a water-cooled tube reduces the temperature, which stabilizes the reaction, and provides a much greater NO conversion efficiency(28.8%) than that obtained using quartz tube(14.1%) at a frequency of 8 k Hz with an input voltage of 6.8 k V. Furthermore,under equivalent conditions, packing the reactor tube with glass beads greatly increases the NO conversion efficiency to 95.85%. This is because the dielectric beads alter the distribution of the electric field due to the influence of polarization at the glass bead surfaces, which ultimately enhances the plasma discharge intensity. The presence of the dielectric beads increases the gas residence time within the reactor. Experimental verification and a theoretical basis are provided for the industrial application of the proposed plasma NO removal process employing dielectric bead packing.     

Application of dielectric barrier discharge (DBD) plasma packed with glass and ceramic pellets for SO2 removal at ambient temperature: optimization and modeling using response surface methodology

Air pollution is a major health problem in developing countries and has adverse effects on human health and the environment. Non-thermal plasma is an effective air pollution treatment technology. In this research, the performance of a dielectric barrier discharge (DBD) plasma reactor packed with glass and ceramic pellets was evaluated in the removal of SO₂ as a major air pollutant from air in ambient temperature. The response surface methodology was used to evaluate the effect of three key parameters (concentration of gas, gas flow rate, and voltage) as well as their simultaneous effects and interactions on the SO₂ removal process. Reduced cubic models were derived to predict the SO₂ removal efficiency (RE) and energy yield (EY). Analysis of variance results showed that the packed-bed reactors (PBRs) studied were more energy efficient and had a high SO₂ RE which was at least four times more than that of the non-packed reactor. Moreover, the results showed that the performance of ceramic pellets was better than that of glass pellets in PBRs. This may be due to the porous surface of ceramic pellets which allows the formation of microdischarges in the fine cavities of a porous surface when placed in a plasma discharge zone. The maximum SO₂ RE and EY were obtained at 94% and 0.81 g kWh⁻¹, respectively under the optimal conditions of a concentration of gas of 750 ppm, a gas flow rate of 2 l min⁻¹, and a voltage of 18 kV, which were achieved by the DBD plasma packed with ceramic pellets. Finally, the results of the model's predictions and the experiments showed good agreement.     

Synthesis of thorium sol for fabricating fuel kernels

To fabricate thorium-based fuel kernel for solid fuel molten salt reactor,a component of tri-structural isotropic fuel particles is mostly based on sol-gel method.The preparation of thorium sol is an important step for fabrication of thorium-based fuel kernels,such as thorium carbide and thorium oxide.The gel quality affects the gel particle dispersion and the final products.In this work,thorium sols were prepared using Th(NO_3)_4 and NH_3·H_2O by sol-gel method.The effects of thorium concentration,mole ratio of NH_4~+/NO_3~- and reaction temperature on the pH,viscosity,turbidity,particle size and the thorium sol distribution were investigated.The results show that the viscosity and turbidity increased with the NH_4~+/NO_3~- ratio;the turbidity and colloidal particle size increased with the reaction temperature,which affected little the sol viscosity;the sol viscosity increased with the thorium concentration,which virtually did not change the turbidity;and the particle size decreased and the size distribution narrowed with increasing thorium concentration.The sol could be stored at room temperature for one day without significant property changes.Thorium gel spheres of good quality were prepared at 60℃ with the NH_4~+/NO_3~- ratio of 75-85% and the thorium concentration of 1.2-1.4 mol/L.     

The Influence of Iron on Ammonium Ion Generation from Nitrate Ion in Liquid Phase

Flue gas cleaning in discharge plasma process has been Studied intensively and we have tried to remove the NOx and S02 using the wet-type plasma reactor. In this system, NO is oxidized to NO2 and absorbed as NO3^-, and SO2 is absorbed as SO3^2- and oxidized in the liquid to SO4^2-. But the concentration of NO3^- was saturated and the absorption of NOx and SO2 was inhibited. Then, the reduction of NO3^- in the liquid is required. We examined the reductive reaction of NO3^- to NH4^ using discharge above the liquid surface then the pH value of the liquid was changed to alkaline slightly. When the Fe plate was used as a ground electrode in the liquid, NH4^ was generated. Then, the relation between the generation of NH4^ and Fe ions (Fe^2 and Fe^3 ) was studied. When Fe^2 was presented in the liquid, NH4^ was generated and Fe^2 was oxidized to Fe^3 . Fe^2 is required to generate NH4^ from NO3^-. When NH4^ was generated from NO3^-, both the calculated pH value from NH4^ concentration and the measured pH value indicated a similar value. From these results, the discharge above the liquid surface was effective to convert NO3^- to NH4^ and the reductive reaction leads to more absorption of NO3^-. These results showed that the wet-type plasma reactor is effective for NOx and SO2 removal system.     

Bromate removal by gamma irradiation in aqueous solutions

Bromate(BrO_3) is a disinfection by-product in drinking water, and its removal is very difficult especially at low levels.60 Co gamma rays were used to remove BrO_3in aqueous solution in this study. The effects of absorbed doses, BrO_3initial concentration, gas saturation, p H value and coexisting anions(Cl, NO 3, SO2 4and HCO 3=CO_3~(2 -))on BrO_3reduction were evaluated. After 4.0-k Gy irradiation of air-equilibrated solution of 30.7 lg/L BrO_3, the residual BrO_3was 8.3 lg/L, which is below the maximum contaminant level of drinking water. The BrO_3reduction rate increased with the dose, in the order of N2[ air [ O_2[ N_2O atmosphere under similar conditions. The results also show that high p H favored the BrO_3removal. According to the experimental results, it can be concluded that the efficiency of decomposing BrO_3by reactive species followed the order of e aq[ H [ HO_2 [ O_2. Coexisting Cl, HCO 3=CO_3~(2 -)and SO2 4ions have little effect on BrO_3removal, whereas NO_3can inhibit its removal as a result of competition with BrO_3for e aq.     

超声波+四价铈去污技术研究

针对核设施退役过程中产生的不锈钢废物,开展了超声波+四价铈去污技术研究。利用失重法,设计正交实验,研究了硝酸浓度、硝酸铈铵浓度、温度和超声时间对不锈钢的平均腐蚀速率及去污因子的影响。条件实验结果表明:温度、硝酸铈铵浓度为主要影响因素;当硝酸铈铵的浓度为0.15 mol/L,温度为85 ℃,硝酸浓度为0.1 mol/L时,不锈钢的平均腐蚀速率最高,达到8.07 μm/h,引入超声波后将极大提高四价铈去污技术的效率。扫描电镜观测结果表明: 去污后的不锈钢表面大部分区域出现了很多蚀孔,表明空化效应强化Ce(IV)去污技术具有强烈的空蚀作用;对乏燃料冷却套管开展了验证去污实验,去污因子达到158.8。     

Unfiltered Diesel Engine Exhaust Treatment by Discharge Plasma：Effect of Soot Oxidation

A cascaded system of electrical discharges (Non-thermal plasma), catalyst and adsorption process was investigated for the removal of oxides of nitrogen (NOx) and carbon monoxide (CO) from a Diesel engine raw exhaust. The three processes were separately studied first, and then the cascaded processes, namely plasma-catalyst and plasma-adsorbent, were investigated. In this paper main emphasis was laid on the effect of carbonaceous soot oxidation on the plasma treatment process. While the cascaded plasma-catalyst process exhibits a higher CO removal,the cascaded plasma-adsorbent process exhibits a higher NOx removal. The experiments were conducted under no-load. The plasma and adsorbent reactors were kept at room temperature throughout the experiment while the catalyst reactor was kept at 200℃ / 300℃.     

Regulation characteristics of oxide generation and formaldehyde removal by using volume DBD reactor

Discharge plasmas in air can be accompanied by ultraviolet(UV) radiation and electron impact,which can produce large numbers of reactive species such as hydroxyl radical(OH·),oxygen radical(O·),ozone(O3),and nitrogen oxides(NOx),etc.The composition and dosage of reactive species usually play an important role in the case of volatile organic compounds(VOCs) treatment with the discharge plasmas.In this paper,we propose a volume discharge setup used to purify formaldehyde in air,which is configured by a plate-to-plate dielectric barrier discharge(DBD) channel and excited by an AC high voltage source.The results show that the relative spectral-intensity from DBD cell without formaldehyde is stronger than the case with formaldehyde.The energy efficiency ratios(EERs) of both oxides yield and formaldehyde removal can be regulated by the gas flow velocity in DBD channel,and the most desirable processing effect is the gas flow velocity within the range from2.50 to 3.33 m s-1.Moreover,the EERs of both the generated dosages of oxides(O3 and NO2) and the amount of removed formaldehyde can also be regulated by both of the applied voltage and power density loaded on the DBD cell.Additionally,the EERs of both oxides generation and formaldehyde removal present as a function of normal distribution with increasing the applied power density,and the peak of the function is appeared in the range from 273.5 to 400.0 W l-1.This work clearly demonstrates the regulation characteristic of both the formaldehyde removal and oxides yield by using volume DBD,and it is helpful in the applications of VOCs removal by using discharge plasma.     

Investigation of NO removal using a pulse-assisted RF discharge

In this paper,removal of nitrogen oxide (NO) is investigated in capacitive atmospheric pressure discharges driven by both radio-frequency (RF) and trapezoidal pulsed power with a onedimensional self-consistent fluid model.The results show that the number density of NO could be reduced significantly once a short pulse of low duty ratio is additionally applied to the RF power.It is found that the process of NO removal by the pulse-modulated RF discharge could be divided into three stages:the quick reaction stage,the NO removal stage,and the sustaining stage.Furthermore,the temporal evolution of particle densities is analyzed,and the key reactions in each stage are discovered.Finally,the influence on the removal efficiency of the voltage amplitude of the pulse and the RF voltage amplitude is investigated.     

Experiment and Analysis on the Treatment of Gaseous Benzene Using Pulsed Corona Discharge Plasma

An experiment and analysis on removal of gaseous benzene by pulse corona inducedplasma is presented in this article. Important parameters effecting removal efficiency have been investigated, such as pulse peak voltage, pulse frequency, gas inlet concentration, gas flow rate and reactor temperature. The result shows that the removal efficiency increases with the increase in pulse peak voltage, pulse frequency and reactor temperature, but decreases in the rise of gas inlet concentration and gas flow rate. On the condition of Vp = 36 kV, f = 80 Hz, C = 1440 mg/m^3 and Q = 640 ml/min, the largest removal efficiency is 98%. Finally, the reacted products are qualitatively analysed and the reaction processes are deduced in combination with plasma-chemistry theory.     

Time-resolved measurements of NO2 concentration in pulsed discharges by high-sensitivity cavity ring-down spectroscopy

To describe the complex kinetics of formation and destruction mechanism of nitrogen dioxide(NO_2), there is an increasing demand for real-time and in situ analysis of NO_2 in the discharge region. Pulsed cavity ring-down spectroscopy(CRDS) provides an excellent diagnostic approach. In the present paper, CRDS has been applied in situ for time evolution measurement of NO_2 concentration which is rarely investigated in gas discharges. In pulsed direct current discharge of NO_2/Ar mixture at a pressure of 500 Pa, a peak voltage of -1300 V and a frequency of 30 Hz, for higher initial NO_2 concentration(3.05?×?10~(14)cm~(-3), 8.88?×?10~(13)cm~(-3)),the NO_2 concentration sharply decreases at the beginning of the discharge afterglow and then becomes almost constant, and the pace of decline increases with pulse duration; however, for lower initial NO_2 concentration of 1.69?×?10~(13)cm~(-3), the NO_2 concentration also decreases at the beginning of the discharge afterglow for 200 ns and 1 μs pulse durations, while it slightly increases and then declines for 2 μs pulse duration. Thus, the removal of low-level NO_2 could not be promoted by a higher mean energy input.     

Evaluation on a double-chamber gas-liquid phase discharge reactor for benzene degradation

A double-chamber gas-liquid phase DBD reactor (GLDR), consisting of a gas-phase discharge chamber and a gas-liquid discharge chamber in series, was designed to enhance the degradation of benzene and the emission of NOx. The performance of the GLDR on discharge characteristics, reactive species production and benzene degradation was compared to that of the single-chamber gas phase DBD reactor (GPDR). The effects of discharge gap, applied voltage, initial benzene concentration, gas flow rate and solution conductivity on the degradation and energy yield of benzene in the GLDR were investigated. The GLDR presents a higher discharge power, higher benzene degradation and higher energy yield than that of the GPDR. NO₂ emission was remarkably inhibited in the GLDR, possibly due to the dissolution of NO₂ in water. The benzene degradation efficiency increased with the applied voltage, but decreased with the initial concentration, gas flow rate, and gas discharge gap, while the solution conductivity presented less influence on benzene degradation. The benzene degradation efficiency and the energy yield reached 61.11% and 1.45 g kWh^–1 at 4 mm total gas discharge gap, 15 kV applied voltage, 200 ppm benzene concentration, 0.2 L min⁻¹ gas flow rate and 721 μS cm⁻¹ water conductivity. The intermediates and byproducts during benzene degradation were detected by FT-IR, GC-MS and LC-MS primarily, and phenols, CO_x, and other aromatic substitutes, O₃, NO_x, etc, were determined as the main intermediates. According to these detected byproducts, a possible benzene degradation mechanism was proposed.     

Degradation of tiamulin by a packed bed dielectric barrier plasma combined with TiO2 catalyst

Recently, a plasma catalyst was employed to efficiently degrade antibiotic residues in the environment. In this study, the plasma generated in a packed bed dielectric barrier reactor combined with TiO2 catalyst is used to degrade the antibiotic tiamulin (TIA) loaded on the surface of simulated soil particles. The effects of applied voltage, composition of the working gas, gas flow rate and presence or absence of catalyst on the degradation effect were studied. It was found that plasma and catalyst can produce a synergistic effect under optimal conditions (applied voltage 25 kV, oxygen ratio 1%, gas flow rate 0.6 l min−1, treatment time 5 min). The degradation efficiency of the plasma combined with catalyst can reach 78.6%, which is 18.4% higher than that of plasma without catalyst. When the applied voltage is 30 kV, the gas flow rate is 1 l min−1, the oxygen ratio is 1% and the plasma combined with TiO2 catalyst treats the sample for 5 min the degradation efficiency of TIA reached 97%. It can be concluded that a higher applied voltage and longer processing times not only lead to more degradation but also result in a lower energy efficiency. Decreasing the oxygen ratio and gas flow rate could improve the degradation efficiency. The relative distribution and identity of the major TIA degradation product generated was determined by high-performance liquid chromatography–mass spectrometry analysis. The mechanism of TIA removal by plasma and TiO2 catalyst was analyzed, and the possible degradation path is discussed.     

The Degradation of Organic Pollutants by Bubble Discharge in Water

Organic pollutants could be degraded by using bubble discharge in water with gas aeration in the discharge reactor and more plasma can be generated in the discharge process.When pulsed high voltage was applied between electrodes with gas aerated into the reactor,it showed that bubbles were broken,which meant that breakdown took place.It could also be observed that the removal rate of phenol increased with increasing discharge voltage or pulse frequency,and with reducing initial phenol concentration or solution electric conductivity.It could remove more amount of phenol by oxygen aeration.With increasing oxygen flow rate,the removal rate increased.There was little difference with air or nitrogen aeration for phenol removal.The solution temperature after discharge increased to a great extent.However,this part of energy consumption did not contribute to the reaction,which led to a reduction in the energy utilization efficiency.     

Removal of Nitrogen Oxides in Diesel Engine Exhaust by Plasma Assisted Molecular Sieves

This paper reports the studies conducted on removal of oxides of nitrogen (NOx) from diesel engine exhaust using electrical discharge plasma combined with adsorbing materials such as molecular sieves. This study is being reported for the first time. The exhaust is taken from a diesel engine of 6 kW under no load conditions. The characteristic behavior of a pulse energized dielectric barrier discharge reactor in the diesel exhaust treatment is reported. The NOx removal was not significant (36%) when the reactor without any packing was used. However, when the reactor was packed with molecular sieves (MS -3A, -4A & -13X), the NOx removal efficiency was increased to 78% particularly at a temperature of 200℃ . The studies were conducted at different temperatures and the results were discussed.     

Experiments on Reactivity Balance as Malfunction Detector for Research Reactor

An amalgamation method is described for the determination of both hydroxide and non-hydroxide hydrogen in sodium. Using a mercury ejector pump and a Toepler pump, hydrogen (non-hydroxide hydrogen) liberated from sodium amalgam at 200°C under vacuum is collected and determined by gas chromatography. Then, the vessel containing the remaining sodium amalgam is filled with argon to a pressure of 600 mmHg and heated at 400°C under argon stream. The hydrogen (hydroxide hydrogen) collected is in the gas phase of a cold trap maintained at liquid nitrogen temperature, which condenses the argon but not hydrogen. The hydrogen thus collected is determined by gas chromatography. The detection limits for non-hydroxide and hydroxide hydrogen possible with this proposed method are 0.05 and 0.1 ppm in sodium, respectively.