Plasma chemical investigations for NOx andSO2 removal from flue gases

In a streamer-dominated pulsed corona the energetic electrons can interact with the background molecules and produce O, OH, and HO₂ radicals. Reactions involving these radicals are studied to analyze their effect on the removal of acidic pollutants NO, NO₂ , and SO₂ from flue gases. For the NO removal the reactions with O and HO₂ play a dominant role, whereas the OH radical is primarily responsible for the SO₂ and NO₂ removal     

脉冲放电产生螺旋流注的等离子体特性研究

通过脉冲放电方式产生三维螺旋形的等离子体放电通道,在高速摄像机拍摄下观察到放电通道中的发光电离体以流注形式沿螺旋轨迹快速传播.建立电磁模型解释螺旋放电的形成机制,对造成对称性破缺及影响其手性性质的极向电场进行分析.研究表明,螺旋放电产生的放电通道存在两种不同的手性特征,而脉冲重复频率等放电参数及边界条件对螺旋流注的传播特性存在影响.脉冲电源驱动的电磁场在介质管内所形成的波模是极向电场形成的一个重要来源,当极向电场与轴向电场强度相近时则形成螺旋流注放电.     

基于TDLAS直接检测法的柴油机NOx排放在线测试

NO_x是柴油机排放污染物中对生态环境危害最为严重的组分。随着全球环境污染问题的日益严重,柴油机NO_x排放问题受到了广泛的关注。各种排放法规相继出台,一方面对柴油机NO_x排放量提出新的要求,另一方面对测试方法也提出了更高的要求。现有测试方法多为采样分析法,采样周期较长,无法实现污染物排放的实时在线测量,柴油机污染物排放的实时在线测量不仅有利于监管,同时可为优化柴油机的燃烧过程、优化控制策略提供数据支持。光学检测技术作为一种新型的检测方法,其中的可调谐半导体激光吸收光谱技术(TDLAS)因其实验原理简单、响应速度快,在其他领域得到了广泛使用。为验证该方法在柴油机NO_x排放检测中的可行性,实验小组开展基于TDLAS的柴油机NO_x排放实时在线测量研究,针对NO_x的主要成分,利用调谐波长为5 262~5 265和6 138~6 142 nm的带间级联激光器(interband cascade lasers, ICL)分别作为检测NO、NO₂的探测光源,Thorlabs PDA10JT型热式探测器用来对信号光进行采集。采用直接探测方式在D4114B型柴油机上开展实验研究,并将测试结果与AVL排放分析仪进行对比,其测量偏差小于5%,另外,实验小组利用TDLAS技术的高时间分辨率,对柴油机的变工况过程进行NO_x瞬态排放测量,得到合理的NO_x排放变化结果。因此,采用TDLAS技术对研究柴油机瞬态排放特性具有重要的意义。     

Roles of γ-Fe2O3 in fly ash for mercury removal: Results of density functional theory study

First-principle calculations based on density function theory (DFT) are used to clarify the roles of γ-Fe₂O₃ in fly ash for removing mercury from coal-fired flue gases. In this study, the structure of key surface of γ-Fe₂O₃ is modeled and spin-polarized periodic boundary conditions with the partial relaxation of atom positions are employed. Binding energies of Hg on γ-Fe₂O₃ (0 0 1) perfect and defective surfaces are calculated for different adsorption sites and the potential adsorption sites are predicted. Additionally, electronic structure is examined to better understand the binding mechanism. It is found that mercury is preferably adsorbed on the bridge site of γ-Fe₂O₃ (0 0 1) perfect surface, with binding energy of −54.3 kJ/mol. The much stronger binding occurs at oxygen vacancy surface with binding energy of −134.6 kJ/mol. The calculations also show that the formation of hybridized orbital between Hg and Fe atom of γ-Fe₂O₃ (0 0 1) is responsible for the relatively strong interaction of mercury with the solid surface, which suggests that the presently described processes are all noncatalytic in nature. However, this is a reflection more of mercury's amalgamation ability.     

Simulation of micro discharges for the optimization of energyrequirements for removal of NOx from exhaust gases

Experimental and theoretical investigations to remove NO_x from oxygen rich engine exhaust gases using dielectric barrier discharges are conducted in our laboratory. To explain experimental results in different reactor geometries, a two-dimensional fluid model using an unstructured grid was implemented for the simulation of transient microdischarges. As an example, simulation results of simultaneously occurring microdischarges in a packed bed reactor are presented in this paper     

Preparation and characterization of Fe-doped TiO2 on fly ash cenospheres for photocatalytic application

Fe³⁺-doped TiO₂ film deposited on fly ash cenosphere (Fe-TiO₂/FAC) was successfully synthesized by the sol-gel method. These fresh photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analyses (TGA). The XRD results showed that Fe element can maintain metastable anatase phase of TiO₂, and effect of temperature showed rutile phase appears in 650 °C for 0.01% Fe-TiO₂/FAC. The SEM analysis revealed the Fe-TiO₂ films on the surface of a fly ash cenosphere with a thickness of 2 μm. The absorption threshold of Fe-TiO₂/FACs shifted to a longer wavelength compared to the photocatalyst without Fe³⁺-doping in the UV-vis absorption spectra. The photocatalytic activity and kinetics of Fe-TiO₂/FAC with varying the iron content and the calcination temperatures were investigated by measuring the photodegradation of methyl blue (MB) during visible light irradiation. Compared with TiO₂/FAC and Fe³⁺-doped TiO₂ powder (Fe-TiO₂), the degradation ratio using Fe-TiO₂/FAC increased by 33% and 30%, respectively, and the best calcined temperature was 450 °C and the optimum doping of Fe/Ti molar ratio was 0.01%. The Fe-TiO₂/FAC particles can float in water due to the low density of FAC in favor of phase separation to recover these photocatalyst after the reaction, and the recovery test shows that calcination contributes to regaining photocatalytic activity of Fe-TiO₂/FAC photocatalyst.     

Effects of substrate temperature on properties of NbNx films grown on Nb by pulsed laser deposition

NbN_x films were deposited on Nb substrate using pulsed laser deposition. The effects of substrate deposition temperature, from room temperature to 950 °C, on the preferred orientation, phase, and surface properties of NbN_x films were studied by X-ray diffraction, atomic force microscopy, and electron probe micro analyzer. We find that the substrate temperature is a critical factor in determining the phase of the NbN_x films. For a substrate temperature up to 450 °C the film showed poor crystalline quality. With temperature increase the film became textured and for a substrate temperature of 650−850 °C, mix of cubic δ-NbN and hexagonal phases (β-Nb₂N + δ′-NbN) were formed. Films with a mainly β-Nb₂N hexagonal phase were obtained at deposition temperature above 850 °C. The c/a ratio of β-Nb₂N hexagonal shows an increase with increased nitrogen content. The surface roughness of the NbN_x films increased as the temperature was raised from 450 to 850 °C.     

Influences of water vapor and fly ash addition on NO and SO2 gas conversion efficiencies enhanced by pulsed corona discharge

The NO and SO₂ gas conversion processes in a pulsed corona discharge field have been studied. The experiments were conducted to investigate the influences of water vapor and fly ash addition on the conversion efficiencies of NO and SO₂. Experimental results show that positive pulsed corona discharge can facilitate NO and SO₂ conversion processes, and the conversion efficiencies of NO and SO₂ are primarily dependent on the radicals OH, O and the active species O₃, HO₂, H₂O₂, etc. With water vapor addition, SO₂ conversion efficiency is improved, but NO conversion process is restrained. Low fly ash concentration helps to enhance the conversion of NO and SO₂; however, the conversion efficiencies of NO and SO₂ are drastically degraded by high fly ash concentration addition. The synergistic effects of water vapor and fly ash addition strengthen the chemical adsorption ability of the fly ash surface, which results in a considerable improvement in the conversion of NO and SO₂. Furthermore, the specific input energy plays an important role in NO and SO₂ conversion efficiencies. Measured conversion efficiencies of NO and SO₂ reach about 60% and 90%, respectively, under the conditions tested.     

Sonocatalytic removal of ibuprofen and sulfamethoxazole in the presence of different fly ash sources

We examined the feasibility of using two types of fly ash (an industrial waste from thermal power plants) as a low-cost catalyst to enhance the ultrasonic (US) degradation of ibuprofen (IBP) and sulfamethoxazole (SMX). Two fly ashes, Belews Creek fly ash (BFA), from a power station in North Carolina, and Wateree Station fly ash (WFA), from a power station in South Carolina, were used. The results showed that >99% removal of IBP and SMX was achieved within 30 and 60 min of sonication, respectively, at 580 kHz and pH 3.5. Furthermore, the removal of IBP and SMX achieved, in terms of frequency, was in the order 580 kHz > 1000 kHz > 28 kHz, and in terms of pH, was in the order of pH 3.5 > pH 7 > pH 9.5. WFA showed significant enhancement in the removal of IBP and SMX, which reached >99% removal within 20 and 50 min, respectively, at 580 kHz and pH 3.5. This was presumably because WFA contains more silicon dioxide than BFA, which can enhance the formation of OH radicals during sonication. Additionally, WFA has finer particles than BFA, which can increase the adsorption capacity in removing IBP and SMX. The sonocatalytic degradation of IBP and SMX fitted pseudo first-order rate kinetics and the synergistic indices of all the reactions were determined to compare the efficiency of the fly ashes. Overall, the findings have showed that WFA combined with US has potential for treating organic pollutants, such as IBP and SMX, in water and wastewater.     

Soot elimination and NOx and SOx reduction indiesel-engine exhaust by a combination of discharge plasma and oildynamics

The soot in the exhaust gas from a 2-L diesel-engine car has been eliminated almost completely, independent of the load and cruising speed, by a plasma reactor mounted downstream of the engine exhaust and a novel technique using a combination of discharge plasma and oil dynamics. The NO_x (NO₂+NO) and SO_x components have also been reduced by about 70% at a rotational speed of 1200 rpm and a load of 7 kg-m, corresponding to about 60% of maximum torque (about 11.4 kg-m at 1200 rpm). The reduction rate of NO_x in this investigation is about 20% more efficient than ordinary treatment using a discharge plasma only     

Multipoint barrier discharge process for removal of NOxfrom diesel engine exhaust

We investigated the application of the dielectric barrier discharge process to the removal of NO_x from exhaust gas of a 20-kVA diesel engine generator. A multipoint-to-plane geometry was used as an electrode for low-voltage operation. A pyrex glass plate with a 2-mm thickness was put on the plane electrode as the dielectric barrier. The reactor consists of six discharge cells, with each cell consisting of five stacked multipoint-to-plane electrodes where the exhaust gas flows with a high flow rate. The exhaust gas was successfully treated at a flow rate of 1.2 m³/min, In order to produce repetitive high-voltage pulse, we made two switching electronic devices, an insulated gate bipolar transistor (IGBT), and a pulse transformer. This pulse modulator supplied the voltage with peak value of 10 kV and repetition rate of 2.5 kp/s (pulses per second) to the reactor. The energy transfer efficiency of the pulse modulator is 65% at 300 W of the power consumed in the reactor, The NO_x (NO+NO₂) in the exhaust gas was reduced by 35 ppm with an electrical efficiency of 32 g/kWh     

应用光声效应检测粉煤灰中的碳含量

以光声效应的基本原理为理论基础,介绍了应用光场效应检测粉煤灰中碳含量的研究及仪器的结构设计。该仪器以计算机为操作平台,通过一数据采集卡将光声池中产生的光声信号采集进计算机,经计算机数据处理,给出所测样品的碳含量。检测实验数据说明,该方法是一种简便、低廉、精确的检测方法。     

微波辐照活性炭床同时脱除SO2和NOx实验研究

论文进行了微波辐照活性炭同时脱硫脱硝实验,研究了烟气中不同组分对脱硫脱硝效率的影响。结果表明,高浓度SO₂对脱硝有轻微抑制。NO对脱硫有一定程度的促进;烟气中O₂的加入对脱硫脱硝均有促进作用;而含湿量的增加首先会使脱硫脱硝效果提高,当含湿量增至9.1%时,脱硫脱硝效率均有下降趋势;烟气中加入CO₂后,脱硫脱硝效率均下降,在氧含量为10%时,脱硫效率下降6%,脱硝效率下降7%。BET测试表明,微波辐照活性炭后其表面积与基炭相比有少量下降。     

The lifetime of positive streamers in a pulsed point-to-plane gap in atmospheric air

A determination has been made of the lifetime of positive streamers produced in atmospheric air in a positive point-to-plane gap to which was applied a 40 nsec, 40 kV voltage pulse. The streamer tips have been detected at a given plane in the gap by means of a photomultiplier and high speed oscilloscope. It was found that the streamer tips continued to propagate in the gap, long (up to 35 nsec) after the voltage pulse was removed, in accordance with the predictions of a recently presented model of streamer propagation. Association of this long lifetime with the properties of an isolated tip was made possible by the detection of a new phenomenon at the anode. At the end of the voltage pulse a second luminosity was observed to leave the anode and to extend along the paths of the primary streamers for about one third of their length. This is shown to be the maximum extent of a more highly conducting trunk, behind and separated from the streamer tip, affecting both the propagation of the tip and the eventual transition of a streamer to a breakdown spark.     

Trace element analysis of fly ash samples by EDXRF technique

Trace element analysis of some fly ash samples and soil samples have been carried out by Energy Dispersive X-Ray Fluorescence technique. Fourteen elements namely K, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Se, Rb, Sr and Pb have been quantified in the fly ash samples by this technique. It was found that there is no huge concentration difference between the fly ash and soil samples as a result of which fly ash can be used as soil manure without any adverse impact on the plants.      

Deposition of Au/TiO2 film by pulsed laser

Au nanoparticles, which were photoreduced by a Nd:YAG laser in HAuCl₄ solution containing TiO₂ colloid and accompanied by the TiO₂ particles, were deposited on the substrate surface. The film consisting of Au/TiO₂ particles was characterized by the absorption spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The adhesion between the film and substrate was evaluated by using adhesive tape test. It was found that the presence of TiO₂ dramatically enhanced the adhesion strength between the film and the substrate, as well as the deposition rate of film. The mechanism for the deposition of Au/TiO₂ film was also discussed.     

脉冲偏压电弧离子镀CNx薄膜研究

用脉冲偏压电弧离子镀通过控制不同的氮流量在(100)单晶Si基片上制备了不同成分的CN_x薄膜.用光学显微镜,XPS,XRD,激光Raman和Nanoindenter等方法研究了薄膜的形貌、成分、结构和性能.结果表明,薄膜表面平整致密、氮含量随着氮流量的降低而降低、结构为非晶且为类金刚石薄膜;随着氮含量从18.9%降低到5.3%(摩尔百分比,全文同),薄膜的硬度和弹性模量单调增加而且增幅较大,其中硬度从15.0 GPa成倍增加到30.0 GPa;通过氮流量的调整能够敏感地改变薄膜中的sp³键的含量,是CN_x薄膜的硬度和弹性模量获得大幅度调整的本质原因. 关键词： x薄膜')" href="#">CN_x薄膜 脉冲偏压 电弧离子镀 硬度     

Mechanisms of radical removal by SO2

It is well established from experiments in premixed, laminar flames, jet-stirred reactors, flow reactors, and batch reactors that SO₂ acts to catalyze hydrogen atom removal at stoichiometric and reducing conditions. However, the commonly accepted mechanism for radical removal, SO₂ + H(+M) ? HOSO(+M), HOSO + H/OH ? SO₂ + H₂/H₂O, has been challenged by recent theoretical and experimental results. Based on ab initio calculations for key reactions, we update the kinetic model for this chemistry and re-examine the mechanism of fuel/SO₂ interactions. We find that the interaction of SO₂ with the radical pool is more complex than previously assumed, involving HOSO and SO, as well as, at high temperatures also HSO, SH, and S. The revised mechanism with a high rate constant for H + SO₂ recombination and with SO + H₂O, rather than SO₂ + H₂, as major products of the HOSO + H reaction is in agreement with a range of experimental results from batch and flow reactors, as well as laminar flames.     

Enhancement of surface properties of oil fly ash by chemical treatment

In this study, surface modification of oil fly ash (OFA), a by-product generated by oil power plants, was achieved by chemical treatment. A mixture of sulfuric and nitric acids was used to modify the surface in order to attach a carboxylic functional group to the surface of OFA. The goal of surface modification of OFA is to make its surface more compatible with nonpolar polymers in order to produce OFA/polymer composite materials with improved dispersion of OFA, and to increase OFA surface area in order to support its use as adsorbent materials in adsorptive separation and purification applications. Different acid compositions were used for treatment by gradually increasing the nitric acid concentration from 0 to 20%. Also, the effect of oxidation on surface modification was examined by introducing air to enhance the oxidation of OFA. FTIR analysis was performed to identify the different functional groups attached to OFA surface before and after the chemical treatment. Evaluation of different structural changes during the surface modification was investigated by XRD analysis. Surface morphology and spot analysis was studied by SEM technique to identify the composition of different elements present in the OFA such as carbon, oxygen and sulfur. BET analysis showed major increase in surface area after modification as well as pore size and micropore volume of OFA particles. The maximum increase in surface area was obtained with 15 vol.% HNO₃. Also, carboxylic functionalization of OFA was enhanced when air was injected.     

Laboratory studies of back-discharge in fly ash

The back-discharge is a type of discharge that takes place in the presence of corona discharge and occurs at an electrode covered with a dielectric layer of resistivity higher than about 10⁸ Ω m. Back-discharge can be observed in electrostatic precipitators when dust covering the collection electrode has low conductivity. In this paper, the studies of back-discharge generated in ambient air, in point-to-plane geometry with the plate electrode covered with fly ash are presented. The discharge is characterised in terms of its visual forms, current–voltage characteristics, and light emission spectra. Three forms of back-discharge were investigated: glow discharge, streamers, and low-current back-arc discharge. The current of the back-arc discharge was only a few milliamps. The discharge was stabilised by a high series resistance. It was noted that the voltage of ignition of the back-discharge for negative polarity is lower than for a positive one. Spectroscopic measurements of emission spectra provided information on elements present in the discharge column. The elements present in the fly ash, including toxic metals, can be re-entrained into the gas as particles or can be emitted as ions or neutrals during the discharge, and can decrease the collection efficiency of electrostatic precipitators. These elements were detected in the emission spectra. The effect of the discharge on the fly ash layer was also discussed. It was observed that sinter-like leftovers remain in the dust layer after a back-arc discharge.