Enhanced removal of benzene in nonthermal plasma with ozonation,flow recycling,and flow recirculation

A double stage AC/DC sequential high voltage reactor has been developed to study the decomposition of benzene in the air stream at atmospheric pressure. The removal efficiency was measured as a function of ozonation, flow recycling, and flow recirculation. Ozonation in the inlet, and recycling of the exhaust stream increased the removal of benzene, also with increasing of specific input energy (J l⁻¹) the effect of inlet flow ozonation on benzene decomposition was enhanced. The highest removal efficiency was obtained up to >99% in recirculation six times, while CO₂ selectivity reached 99.9% and energy efficiency was 0.59 g kWh⁻¹. O₃ production/ decomposition > production of OH radicals > electronic and ionic collisions were indicated as the main mechanisms influencing benzene abatement in this research.     

Influence of gas atmosphere on synergistic control of mercury and dioxin by nonthermal plasma

In this paper, narrow-pulse power discharge is used to study the synergistic control of mercury and dioxins, in which 1,2,4-trichlorobenzene (TCB) was used as a dioxin analog, by using a self- designed experimental system. The competitive effects of NO, SO₂ and HCl on the TCB removal by non-thermal plasma are discussed. The influence of acid gas on TCB degradation is reflected in the competitive effect. NO has the greatest influence on TCB degradation efficiency. The oxidation efficiency of Hg⁰ decreased by about 10% in all three acidic gas atmospheres, and the effect of each gas component on Hg⁰ oxidation is complex. In the flue gas atmosphere of ‘acid gas+Hg⁰ +TCB’, the mechanism of the synergistic control of Hg⁰ and TCB by the non- thermal plasma is different, which has competition and promotion relationship between each other. The contribution of various flue gas components to the results was complicated, but the overall experimental results show that the synergistic control effect of the system can continue to improve. According to the generated product backstepping, ·OH plays an important role in the synergistic control of the degradation of Hg⁰ and TCB. Through this study, we hope to provide basic research data for the collaborative control of flue gas in the incineration industry.     

Design of a MT-DBD reactor for H_2S control

This study aimed to discuss the removal of hydrogen sulfide(H_2S)with non-thermal plasma produced by a multilayer tubular dielectric barrier discharge reactor,which is useful in the field of plasma environmental applications.We explored the influence of various factors upon H_2S removal efficiency(η_(H_2S))and energy yield(Ey),such as specific energy density(SED),initial concentration,gas flow velocity and the reactor configuration.The study showed that we can achieveη_(H_2S)of 91%and the best Ey of 3100 mg kWh~(-1)when we set the SED,gas flow velocity,initial H_2S concentration and layers of quartz tubes at 33.2 J 1~(-1),8.0 m s~(-1),30 mg m~(-3)and five layers,correspondingly.The average rate constant for the decomposition of hydrogen sulfide was 0.206 gm~(-3)s~(-1).In addition,we also presented the optimized working conditions,byproduct analysis and decomposition mechanism.     

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.     

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.     

Decomposition of a gas mixture of four n-alkanes using a DBD reactor

This study investigates the decomposition of a gas mixture of four n-alkanes (n-heptane, n-octane, n-nonane, and n-decane) using a dielectric barrier discharge reactor. We show that the conversion of n-alkanes increased from 7.2% (C₇H₁₆), 9.7% (C₈H₁₈), 8.4% (C₉H₂₀), and 10.5% (C₁₀H₂₂) to 23.8% (C₇H₁₆), 25.0% (C₈H₁₈), 27.9% (C₉H₂₀), and 32.1% (C₁₀H₂₂) when the energy density increased from 84 J l⁻¹ to 324 J l⁻¹. The conversion of n-alkanes when using the gas mixture is close to that found when using a single n-alkane. The influences of reaction temperature and O₂ concentration are also investigated, and the activation energies for the decomposition of each alkane are given.     

Activated persulfate by DBD plasma and activated carbon for the degradation of acid orange Ⅱ

In this study, the effect of activated peroxydisulfate(PDS) by dielectric barrier discharge(DBD) plasma and activated carbon(HGAC) on the removal of acid orange Ⅱ(AOⅡ) was investigated. The effects of applied voltage, PDS dosage, HGAC dosage, initial pH value, and inorganic anions on the removal rate of AOⅡ were discussed. The main free radicals degrading azo dyes during the experiment were also studied. Experimental results show that the removal rate of AOⅡ in DBD/HGAC/PDS synergistic system is much higher than that in the single system. With the applied voltage of 16 kV, HGAC dosage of 1 g l-1, PDS and AOⅡ molar ratio of 200:1, initial pH value of 5.4 and concentration of AOⅡ solution of 20 mg l-1, the removal rate of AOⅡ reached 97.6% in DBD/HGAC/PDS process after 28 min of reaction.Acidic and neutral conditions are beneficial for AOⅡ removal. Sulfate and hydroxyl radicals play an important role in the removal of AOⅡ. Inorganic anions are not conducive to the removal of AOⅡ.     

Kinetic analysis of soil contained pyrene oxidation by a pulsed discharge plasma process

A pulsed discharge plasma (PDP) reactor with net anode and net cathode was established for investigating the pyrene degradation in soil under different pulse peak voltage, air flow rate, pyrene content in soil, initial pH value and initial water content of the soil. Pyrene oxidation within the 60 min discharge time was fitting according to the pseudo-first order equation and the corresponding reaction kinetics constants (k values) were calculated. The obtained results show that pyrene oxidation under all the different reaction conditions obeyed the pseudo-first order equation well. Higher pulsed peak voltage and appropriate air flow rate were in favor of the increase of reaction rate of pyrene oxidation. A higher k value could be achieved in the lower initial pyrene content (the value was 100 mg kg⁻¹). The k value of pyrene oxidation in the case of pH=4 was 11.2 times higher than the value obtained under the condition of pH=9, while the initial water content of the soil also has a large effect on the oxidation rate of pyrene due to the effect of PDP.     

层状金属硫化物硫化锡钾的制备及其对Sr2+的吸附性能研究

本文用水热法合成了硫化锡钾（KSnS）,利用扫描电镜（SEM）、X射线衍射（XRD）仪等对KSnS的形貌和组成进行了表征分析,并通过静态吸附实验分别研究了pH值、接触时间、共存离子和Sr²⁺初始浓度对KSnS吸附Sr²⁺的影响。结果表明,在40 ℃、pH=7.25、Sr²⁺初始浓度为5.5 mg/L的条件下,KSnS对Sr²⁺的吸附平衡时间约为35 min,Sr²⁺去除率为99.62%。吸附反应可操作pH值范围较宽,52+去除率保持在80%以上。溶液中含有K⁺、Na⁺、Ca²⁺和Mg²⁺等共存离子时,二价离子的干扰大于一价离子。KSnS对Sr²⁺的吸附动力学行为可用准二级动力学方程描述,吸附过程属于化学吸附。通过Weber-Morris模型和Boyd模型分析可知,液膜扩散是主导吸附速率的步骤。     

Performance of a 4 cm iodine-fueled radio frequency ion thruster

The performance of an iodine radio ion thruster with a 4 cm diameter(IRIT4) was studied experimentally in this paper. Regulation of the mass flow rates of the iodine propellant is achieved by using a temperature control method of the iodine reservoir. Performance of the thruster using iodine as propellants is obtained at different total thruster powers of 40.6–128.8 W,different grid voltages of 1000–1800 V and the iodine flow rate of 100 μgs~(-1). Results show that thrust and specific impulse increase approximately linearly with the increasing total thruster power and the screen grid voltage. The thrust of 2.32 mN and the specific impulse of 2361 s are obtained at the nominal total thruster power of 95.8 W and the screen grid voltage of 1800 V. It is also indicated that performance of the iodine propellant is comparable to that of the xenon propellant; and a difference between them is that the iodine thrust is slightly higher than xenon when the total thruster power is more than 62 W. At the nominal 95.8 W total thruster power, the thrust values of them are 2.32 m N and 2.15 mN respectively, and the thrust-to-power ratios of them are 24.2 mN kW~(-1) and 23.5 mN kW~(-1), respectively.     

Measurement of radial temperature distributions of the blown CO_2 arcs under different conditions

In this paper, the radial temperature distributions of the blown CO_2 arcs in a model gas circuit breaker were investigated by optical emission spectroscopy methods. The CO_2 flows with different flow rates(50, 100 and 150 1 min~(-1)) were created to axially blow the arcs burning in a polymethyl methacrylate(PMMA) nozzle. Discharges with different arc currents(200 and 400A) were conducted in the experiment. The absolute intensity method was applied for a carbon ionic line of 657.8 nm to obtain the radial temperature profiles of the arc columns at a cross-section 1 mm above the nozzle. The calibration for the intensity of the CⅡ 657.8 nm line was achieved by the Fowler–Milne method with the help of an oxygen atomic line of 777.2 nm.The highest temperature obtained in the arc center was up to 19 900 K when the arc current was 400 A and the CO_2 flow rate was 50 1 min~(-1), while the lowest temperature in the arc center was about 15 900 K when the arc current was 200 A and the CO_2 flow rate was 150 1min~(-1). The results indicate that as the arc current increases, the temperature in the arc center would also increase apparently, and a larger gas flow rate would lead to a lower central temperature in general. It can also be found that the influence of the CO_2 flow rate on the arc temperature was much less than that of the arc current under the present experimental conditions. In addition,higher temperature in the arc center would cause a sharper temperature decrease from the central region towards the edge.     

Enhancing toluene removal in a plasma photocatalytic system through a black TiO_2 photocatalyst

An efficient toluene removal in air using a plasma photocatalytic system(PPS) not only needs favorable surface reactions over photocatalysts under the action of plasma,but also requires the photocatalysts to efficiently absorb light emitted from the discharge for driving the photocatalytic reactions. We report here that the PPS constructed by integrating a black titania(B-TiO_2)photocatalyst with a dielectric barrier discharge(DBD) can effectively remove toluene with above 70% CO_2 selectivity and remarkably reduced the concentration of secondary pollutants of ozone and nitrogen oxides at a specific energy input of 1500 J·l~(-1),while exhibiting good stability. Photocatalyst characterizations suggest that the B-TiO_2 provides a high concentration of oxygen vacancies for the surface oxidation of toluene in DBD,and efficiently absorbs ultraviolet–visible light emitted from the discharge to induce plasma photocatalytic oxidation of toluene. The presence of B-TiO_2 in the plasma region also results in a high discharge efficiency,facilitating the generation of large numbers of reactive species and thus the oxidation of toluene towards CO_2. The greatly enhanced performance of the PPS integrated with B-TiO_2 in toluene removal offers a promising approach to efficiently remove refractory volatile organic compounds from air at low temperatures.     

废磷酸三异戊酯有机溶剂的间接电化学氧化分解行为研究

银媒介间接电化学氧化(Ag/MEO)技术是一种有机溶剂分解破坏的有效方法。本文采用小型氧化电解池和新鲜磷酸三异戊酯（TiAP）有机溶剂模拟研究了在含Ag+的HNO₃溶液体系中氧化分解TiAP,包括电解氧化过程中阳极室HNO₃浓度、操作温度等条件对Ag²⁺产生量的影响,以及影响Ag²⁺氧化分解TiAP有机溶剂的相关因素。研究结果表明,溶液中Ag⁺和HNO₃浓度的提高有利于Ag²⁺的生成;操作温度的升高,不利于Ag²⁺的生成。最佳条件为：温度,40 ℃;HNO₃浓度,8 mol/L;电流密度,0.5 A/cm²。在此条件下,8 h可将99.9%的TiAP氧化分解。     

Comparison of Reynolds average Navier-Stokes turbulence models in numerical simulations of the DC arc plasma torch

Five turbulence models of Reynolds average Navier-Stokes(RANS),including the standard k-ω model,the RNG k-e model taking into account the low Reynolds number effect,the realizable k-ω model,the SST k-ω model,and the Reynolds stress model(RSM),are employed in the numerical simulations of direct current(DC)arc plasma torches in the range of arc current from 80 A to 240 A and air gas flow rate from 10 m^3 h^-1 to 50 m^3 h^-1.The calculated voltage,electric field intensity,and the heat loss in the arc chamber are compared with the experiments.The results indicate that the arc voltage,the electric field,and the heat loss in the arc chamber calculated by using the standard k-ω model,the RNG k-ωmodel taking into account the low Reynolds number effect,and the realizable k-ω model are much larger than those in the experiments.The RSM predicts relatively close results to the experiments,but fails in the trend of heat loss varying with the gas flow rate.The calculated results of the SST k-ω model are in the best agreement with the experiments,which may be attributed to the reasonable predictions of the turbulence as well as its distribution.     

Microchannel cooling technique for dissipating high heat flux on W/Cu flat-type mock-up for EAST divertor

As an important component of tokamaks, the divertor is mainly responsible for extracting heat and helium ash, and the targets of the divertor need to withstand high heat flux of 10 MW m⁻² for steady-state operation. In this study, we proposed a new strategy, using microchannel cooling technology to remove high heat load on the targets of the divertor. The results demonstrated that the microchannel-based W/Cu flat-type mock-up successfully withstood the thermal fatigue test of 1000 cycles at 10 MW m⁻² with cooling water of 26 l min⁻¹, 30 °C (inlet), 0.8 MPa (inlet), 15 s power on and 15 s dwell time; the maximum temperature on the heat-loaded surface (W surface) of the mock-up was 493 °C, which is much lower than the recrystallization temperature of W (1200 °C). Moreover, no occurrence of macrocrack and 'hot spot' at the W surface, as well as no detachment of W/Cu tiles were observed during the thermal fatigue testing. These results indicate that microchannel cooling technology is an efficient method for removing the heat load of the divertor at a low flow rate. The present study offers a promising solution to replace the monoblock design for the EAST divertor     

Influence of high-voltage pulse parameters on the propagation of a plasma synthetic jet

In this work, a typical pin-to-pin plasma synthetic jet in static air is excited by a pulsed DC power supply. The influences of the pulse rising time, the amplitude and the repetition frequency of the pulse voltage on the jet flow have been investigated. First, using a high-speed Schlieren imaging technique, the induced shock waves and the fast jet flow generated by the plasma synthetic jet are characterized. With a deposited energy of 44 mJ per pulse, the velocity of the shock wave and the maximum velocity of the jet flow reach 320 m s⁻¹ and 100 m s⁻¹, respectively. Second, when the applied voltage increases from 12.8 kV to 16 kV, the maximum jet velocity increases from 66 m s⁻¹ to 93 m s⁻¹. On the other hand, as the pulse rising time varies from 50 ns to 500 ns, or the pulse repetition frequency increases from 5 Hz to 40 Hz, the jet velocity induced by the plasma synthetic jet is weakly dependent. In addition, a comparative study of the plasma synthetic jets using three commercial pulsed power supplies (XJ-15, NPG- 18, and PG-30) is implemented. It reveals that the maximum jet velocity of 120 m s⁻¹ is obtained in the case of PG-30, with the longest pulse rising time and the lowest breakdown voltage, while the maximum velocity of 33 m s⁻¹ is detected in the case of NPG-18, even though it has the shortest pulse rising time and the highest breakdown voltage.     

硝酸体系中Pt催化肼的分解

研究了肼的初始浓度、硝酸浓度、催化剂的量(S/V)、温度、β放射性对Pt催化肼分解反应速率的影响,获得了其动力学方程。结果表明:增大肼的初始浓度、温度、催化剂的量和降低硝酸浓度,肼的分解速率加快;β放射性对Pt催化体系中肼的分解速率有显著的提高作用,其分解表观速率常数比单独Pt催化提高了19.3倍,比单独β辐解提高了1.35倍,β放射性辐照位置不同肼的分解速率也不同。Pt催化硝酸体系中肼分解的动力学速率方程为:-dc(N₂H⁺₅)/dt=kc(N₂H⁺₅)c^-0.39(HNO₃),296 K时,速率常数k=(5.90±0.35)×10^-3 mol/(L·min),活化能E_a=(333.3±2.9) J/mol。     

Study on purification technology of polyacrylamide wastewater by non-thermal plasma

In this work, non-thermal plasma has been applied to treat polyacrylamide (PAM) wastewater. We have investigated the influence of the rule of PAM wastewater initial pH, solution concentration and discharge time, discharge voltage on chemical oxygen demand (COD) degradation rate. At the same time, the effect of pH and discharge time on the viscosity removal rate of PAM solution was also studied. Then, the effect of pH on the viscosity removal rate of 1.0 gl ⁻¹ PAM solution was studied separately. Through orthogonal test, the factors affecting the COD degradation rate of PAM wastewater were determined as follows: discharge time>discharge voltage>solution concentration>wastewater initial pH. The COD highest removal rate of PAM wastewater reached 85.74%, when the optimal conditions are as follows: discharge voltage 40 kV, discharge time 5 h, solution concentration 1.0 gl ⁻¹, pH 1.5. This research provides some basic data and new theoretical basis for PAM wastewater purification.     

DBD coupled with MnOx/γ-Al2O3 catalysts for the degradation of chlorobenzene

This paper investigates the degradation of chlorobenzene by dielectric barrier discharge(DBD)coupled with MnOx/γ-Al2O3 catalysts.MnOx/γ-Al2O3 catalysts were prepared using the impregnation method and were characterized in detail by N2 adsorption/desorption,x-ray diffraction and x-ray photoelectron spectroscopy.Compared with the single DBD reactor,the coupled reactor has a better performance on the removal rate of chlorobenzene,the selectivity of COx,and the inhibition of ozone production,especially at low discharge voltages.The degradation rate of chlorobenzene and selectivity of COx can reach 96.3%and 53.0%,respectively,at the specific energy density of 1350 J l-1.Moreover,the ozone concentration produced by the discharge is significantly reduced because the MnOx/Al2O3 catalysts contribute to the decomposition of ozone to form oxygen atoms for the oxidation of chlorobenzene.In addition,based on analysis of the byproducts,the decomposition mechanism of chlorobenzene in the coupled reactor is also discussed.     

Characteristics of GaAs buffered FET logic (BFL) MESFETs andinverters exposed to high-energy neutrons

A systematic investigation of the effects of high-energy neutrons on GaAs metal-semiconductor field-effect transistors (MESFETs) and buffered FET logic (BFL) gates has been carried out. Discrete transistors, inverters, and ring oscillators were characterized and modeled as a function of neutron fluence. Measurements were made of the threshold voltage shifts, the transconductance degradation, and saturation current degradation of GaAs depletion mode MESFETs, which comprise the BFL logic gates, irradiated with neutron fluences ranging from 5×10¹³ n/cm² to 2×10¹⁵ n/cm² (for particle energies above 10 keV). The threshold voltage was found to shift positively by 0.45 V, the transconductance decreased to 3%, and the saturation current to 1% of their unirradiated values at the highest neutron fluence (2×10¹⁵ n/cm²). The BFL inverter characteristics were measured and successfully simulated with SPICE using device parameters extracted from the neutron-damaged FETs. Ring oscillator measurements were made to determine the effects of high-energy neutrons on the frequency performance of BFL circuits. The ring oscillator frequency decreased to 9% of its unirradiated value at the highest neutron fluence