水蒸气和CO2对等离子体—催化还原NOx的影响

等离子体协助选择性催化还原(PF-SCR)可以促进富氧环境下NOx的有效脱除。为研究实际尾气中含有的水蒸气和CO2对PF-SCR脱除NOx系统的影响,以C2H4作为还原剂,Ag/γ-Al2O3为催化剂,考察了3种(N2/O2/NOx/C2H4,N2/O2/NOx/C2H4/H2O(气)和N2/O2/NOx/C2H4/H2O(气)/CO2)配气条件下PF-SCR脱除NOx效果的变化。试验结果表明,较低水蒸气含量(φ(H2O)=1%)对PF-SCR还原NOx具有明显的抑制作用,其原因除了Ag/γ-Al2O3的抗湿性能较差外,水蒸气对等离子体反应器中C2H4和NO氧化的抑制以及由此导致的活性中间产物生成抑制也是一个重要因素。另一方面,水蒸气的存在也抑制了PF-SCR过程中副产物CO的大量生成,这可能是由于PF-SCR对C2H4的氧化减弱以及等离子体氧化生成的中间产物减少造成的。有水蒸气存在时,体系中的CO对PF-SCR还原NO影响不大。     

等离子体辅助催化还原NOx的协同特性

以NO/NO2/C2H4/O2/N2为模拟反应气体系,研究了较低催化温度下介质阻挡放电等离子体辅助C2H4在Ag/γ-Al2O3催化剂上选择催化还原NOx的协同特性.结果表明,在催化温度为240℃时,等离子体辅助催化脱除NOx方面表现出明显的协同效应;等离子体"预活化"过程产生的协同"媒介"物质包括3类:NO2、醛类(HCHO,CH3CHO)和含氮有机物(CH3ONO2,C2H5ONO2,CH3NO2),放电过程脱除的NOx主要转化为含氮有机物;在等离子体"预活化"过程中,提高放电能量密度或初始C2H4浓度均可促使协同"媒介"NO2向低温催化活性更高的含氮有机物转化和醛类的生成,进一步提高等离子体辅助催化的NOx脱除效率.     

O3和C2H4在介质阻挡放电转化NO中的作用

放电等离子体结合选择催化还原脱除NOx是一项很有前景的贫燃尾气治理技术,其预处理过程中,尾气中NO会向NO2转化。为了解重要的活性中间产物O3的作用和生成特性以及常见的烃类添加剂C2H4的作用,在介质阻挡放电等离子体反应器内进行了相关实验研究。监测N2/O2,N2/O2/NO,N2/O2/C2H4,N2/O2/NO/C2H4共4个体系下的O3产生特性,并通过N2/O2/NO和N2/O2/NO/C2H4体系的比较考察C2H4对NO转化影响的结果表明:除N2/O2体系外,其它体系中都不会产生大量的O3;C2H4不但提高了NO的转化率,还明显地抑制放电过程NO的生成。可以推断,O3作为氧化剂能促进NO向NO2的转化,C2H4添加剂可以提高NO的转化率。     

等离子体辅助催化还原NO_x系统的优化

为研究等离子体辅助催化系统的优化,以NO/NO2/C2H4/O2/N2为模拟反应气体系,介质阻挡放电(DBD)反应器为等离子体反应器,Ag/γ-Al2O3为催化剂,实验考察了DBD反应器内填充石英介质小球对等离子体辅助催化系统的NOx脱除效率影响。结果表明:DBD反应器内填充石英介质小球,有利于DBD反应器在较低的放电能量密度下产生更多低温催化活性高的含氮有机物,促使等离子体辅助催化系统在较低的催化温度250°C时获得>80%的NOx脱除效率。     

还原剂对等离子体预处理NO的影响

等离子体辅助选择性催化还原技术是脱除汽车尾气中NOx的有效途径,不同的还原剂影响着最终的处理效果,为此通过填充床式反应器产生等离子体,处理分别添加甲烷和乙烯作还原剂的模拟汽车尾气,对不同电压等级、电源频率、填料粒径条件下的NO脱除率、NO2体积分数、NOx总体积分数变化、CO体积分数等进行研究,对比甲烷和乙烯的处理效果...     

C_2H_4对介质阻挡放电协同Ag/Al_2O_3脱除NO_x的影响及机理分析

在模拟实验系统上,利用介质阻挡放电(DBD)结合Ag/Al2O3催化剂进行烟气脱硝实验,分析了C2H4对脱除NOx的影响及脱除机理。结果表明:同样情况下,添加C2H4后,NO脱除率明显升高,并且随着C2H4浓度的升高而增加;同时,加载催化剂比未加载催化剂的NO脱除率高。在能量输入密度300J/L、C2H4体积分数1%时,DBD协同Ag/Al2O3催化,NO脱除率达61.3%。分析认为:在DBD发生器中,C2H4与O2反应生成CH3O2·、HO2等强氧化性基团,将NO氧化成NO2;在催化装置中,C2H4与O2在Ag/Al2O3表面发生反应,产生更多的CH2=CH-O·和CH3COO·等自由基,最终使NOx脱除率升高。     

含二氧化钛的脉冲气液放电特性及降解四环素研究

利用光催化剂耦合气液放电等离子体可以有效提高水中有机污染物的降解效率,而催化剂添加会影响放电特性进而影响等离子体的应用效果。为了探究TiO₂添加对气液放电特性的影响,该文采用脉冲电源激励大气压空气中的气液放电,通过电学和光学诊断研究含TiO₂和未添加TiO₂的放电特性及等离子体特性,并利用紫外可见分光光度计检测溶液中活性粒子浓度及四环素去除率,讨论TiO₂光催化对放电特性及其降解四环素的影响机制。结果表明,含TiO₂条件下,脉冲持续时间内的峰值电流较未添加TiO₂时有所增大,且电流增大幅度随着电压的增大而增大,当电压为10kV时,TiO₂的添加使峰值电流增强了2.8倍。含TiO₂条件下的发光强度、N2(C-B)、Hα和O(3p-3s)的光谱强度与溶液中活性粒子浓度相比于未添加TiO₂时也明显增强,在电压10kV和频率1kHz时,添加TiO₂后H2O2浓度增大了7倍。此外...     

氢氧等离子体合成过氧化氢过程的能效研究

为提高氢氧等离子体合成H2O2技术的能量效率,通过分析放电过程的反应器能效及电源能量注入效率,确定了影响合成总能效的主要因素。考察了反应器电极间距、电源放电频率及注入功率对反应器能效和电源能量注入效率的影响。发现减小电极间距、提高放电频率和注入功率有利于提高反应器能效,但不利于提高电源能量注入效率。本研究中可以得到150 gH2O2/kWh的反应器能效,但由于较低的电源能量注入效率,致使合成H2O2的总能效不超过9 gH2O2/kWh。因此,提高等离子体法合成H2O2过程的总能效,不仅需要设计高能效的等离子体反应器,还需为反应器负载开发适配的电源,而后者是提升该技术能量效率的关键。     

填料表面形态对等离子体脱除NO_x的影响

填充床式等离子体反应器在NOx脱除方面有着显著的优势,其中填料的参数对处理效果有很大影响,以往报道多集中在填料尺寸方面的影响。为分析反应器能量利用效果,优化等离子体辅助催化系统,着重研究了填料表面形态对NOx脱除的影响情况,考查不同能量密度、电源频率条件下NOx的转化;测试了放电过程中的主要活性物种甲醛的含量,研究了表面形态对甲醛生产的影响,在此基础上得到甲醛生成量与NOx转化之间的关系。实验结果表明填料表面形态的改变会影响NOx的转化以及甲醛的生成;另外,NO的去除率与甲醛的生成量存在着正相关性。     

低温等离子体处理污水厂恶臭气体的应用研究

为控制某污水处理厂恶臭的污染,介绍了采用低温等离子体技术处理恶臭气体的技术原理和电源电压、电源频率和停留时间与降解效率的关系,用低温等离子体进行了分解特征恶臭气体氨气的试验,并从工程应用和试验研究方面说明了除臭设备的电参数、工艺流程。试验表明,增加电源电压、电源频率和停留时间可提高降解效率,但提高到一定程度后降解效率不明显;该技术在污水处理厂的运行结果表明,H2S、NH3、CH3—SH这类恶臭气体的去除率分别达到81.3%、88.1%、84.4%,可消除恶臭气体对周围环境的影响。     

粉煤灰小球协同低温等离子体处理汽车尾气

针对汽车尾气防治,自制了介质阻挡放电催化反应器,并以改性粉煤灰小球为催化剂对汽油机尾气进行处理,研究了脉冲电压、脉冲频率、放电间隙及气体流量qV等对NO、HC和CO去除率η的影响。结果表明:NO、HC和CO的η随脉冲电压、脉冲频率的增加而增加,随qV的增加而减小。当放电间隙G在2.5~3.5 mm变化时,3种污染物的η变化不大;但G增大到4 mm时,污染物η明显下降。当脉冲电压为20 kV、脉冲频率为15 kHz、G=3 mm、qV=0.05 m3/h,并以改性粉煤灰小球为催化剂时,NO、HC和CO的η分别能达到84.6%、87.7%和54.5%,比相同条件下不填充时分别增加了12.6%、7.2%和6.2%。研究表明:改性粉煤灰小球作为催化剂,能显著提高汽油机尾气中污染物的η。研究为等离子体催化技术提供了一种新型催化剂。     

介质阻挡放电产生低温等离子体除去NO_x的实验研究

低温等离子体技术对氮氧化物(NOx)及多种污染物实现同步净化已成为尾气净化方面的研究热点。为此,针对国内外大多数研究采用模拟气体放电的现状,以实际柴油机尾气中NOx为研究对象,采用介质阻挡放电技术,实验研究了电压幅值、电源频率、高压电极直径、反应器体积、放电间隙对NOx去除的影响。实验结果证明,采用该研究所建立的低温等离子体处理装置,柴油机尾气中的NOx的除去率随着电压幅值及其频率的增加先升高后降低,即出现一个最大值,随电压幅值的增加其能耗增加;NOx除去率随放电间隙的减小和高压电极直径的增加而升高,随着反应器体积增加而增加。该研究成果对低温等离子处理NOx装置的车载化应用有一定的指导意义。     

Pulsed electrical discharges assisted by dielectric pellets/catalysts for diesel engine exhaust treatment

This paper reports the study on gaseous pollutants (NOx, CO and HCs) using a combination of electric discharge plasma and catalysts. In this study, catalysts being used in conventional catalytic converters of gasoline engine were tried, for the first time, in diesel engine exhaust treatment assisted by electric discharge plasma. Initial studies investigate the effect of packed dielectric materials and catalysts on NOx removal. Both conventional and non-conventional catalysts were used in the studies. With plasma alone, the removal efficiency of oxides of nitrogen was around 75% and with a suitable combination of catalytic reactor the removal efficiency was as high as 90%. Among the catalysts studied, a new catalyst (CuMnAlO/sub 4/) was found to be as effective as the conventional expensive catalyst. The formation of byproducts like N/sub 2/O and HNO/sub 3/ have been studied and the results are discussed.     

Nitric oxide decomposition in air by using nonthermal plasmaprocessing with additives and catalyst

Catalyst (copper-coated zeolite catalyst, i.e., Cu-ZSM-5) was used to enhance NO_x removal plasma chemical reactions. Two kinds of hydrocarbons (2-propane-1-ol, 2-propanol) were added to the synthesized flue gas before the nonthermal plasma process, and their effects on NO_x removal characteristics were investigated. Enhancement effects of NO_x removal by the nonthermal plasma process with hydrocarbons as the additives were confirmed. Usually, the catalyst's working temperature is much higher than the room temperature. A catalytic reactor was installed after the plasma reactor. Catalytic effects on NO_x removal characteristics disappeared when the synthesized flue gas temperature was increased (~250°C). When the synthesized flue gas temperature was at room temperature, about 90% NO _x removal efficiency was realized with a combination of hydrocarbons, the catalytic reactor, and the pulsed discharge plasma     

Improvement of the energy efficiency in the decomposition of dilute trichloroethylene by the barrier discharge plasma process

In order to improve the energy efficiency in the dilute trichloroethylene (TCE) removal by the nonthermal plasma process, the barrier discharge reactor was studied experimentally. It is investigated by combining it with catalyst of manganese dioxide at the downstream of the barrier discharge reactor. Decomposition efficiency by the barrier discharge reactor was about 83% at the gas flow rate 2 L/min, where the dilute TCE concentration is 250 ppm. Decomposition efficiency with passing through manganese dioxide was improved about 99% at the specific energy of 40 J/L. However, other by-products including ozone and oxidation by-products such as DCAC and TCAA were detected by the gas chromatograph mass spectrometry or the Fourier transform infrared spectroscope measurement. DCAC is generated at the plasma reactor, but TCAA is generated at catalyst during ozone decomposition. CO/sub x/ yield increased about twice with passing through catalyst in the Direct Process. Nitric oxides such as NO, NO/sub 2/, and N/sub 2/O did not generate so much in this barrier discharge process. The dielectric barrier discharge process combined with manganese dioxide is considered as a very desirable way to improve the energy efficiency.     

选择性催化还原蜂窝状催化剂工业试验研究

以工业级药品为主要成分,制备选择性催化还原（selective catalytic reduction,SCR）蜂窝状催化剂,利用工业试验台对其活性进行测试,取得了催化剂在真实烟气情况下,不同空速、催化剂用量、温度、氨氮比、NO2初始浓度等因素对催化剂活性的作用效果。文中真实烟气环境下SCR脱硝系统运行存在最佳工况范围：SCR反应塔入口温度360～390℃,出口温度330～360℃,氨氮比为0．85～1,空速在4000-6000h-1。此工况下,催化剂脱硝效率可以达到84％。催化剂的75％活性温度窗口为320-400℃,且峰值在380℃处取得。催化剂的脱硝效率随氨氮比变化明显,当氨氮比达到0．9时,催化剂脱硝效率超过80％。催化剂对NO2浓度适应性较好,NO2初始浓度在615～3485mg．m-1范围内,催化剂的脱硝效率始终保持在70％以上。     

SCR催化剂在火电厂的应用

催化剂是选择性催化还原脱硝(SCR)系统的核心组成部分,催化剂性能的优劣直接关系到脱硝效率和经济性。现对3种不同结构形式的SCR催化剂进行性能比较,介绍了各种金属氧化物在催化脱硝过程中的作用。在SCR催化剂的运行过程中,分析了温度、氨氮摩尔比等参数对催化剂性能和寿命的影响。根据SCR系统的运行特点,提出了飞灰磨蚀、催化剂堵灰、碱金属和砷中毒、烧结是造成催化剂失活的主要原因。     

Simultaneous removal of NO/sub x/, SO/sub x/, and CO/sub 2/ at elevated temperature using a plasma-chemical hybrid process

In previous studies, the authors confirmed that the plasma-chemical combined hybrid process for controlling NO flue gas emission was extremely effective and economical in comparison with the conventional selective catalytic reduction (SCR) system and other technologies. In the present study, we carried out experiments on the simultaneous removal of NO/sub x/ and SO/sub x/ at elevated temperature using the plasma-chemical hybrid process. A series of experiments was performed to quantify all the reaction byproducts such as N/sub 2/O, CO, HNO/sub 2/, HNO/sub 3/, NO/sub 3//sup -/, and SO/sub 4//sup -/ to evaluate the simultaneous NO/sub x/ and SO/sub x/ removal efficiency. The oxidation from NO to NO/sub 2/ without decreasing NO/sub x/ concentration (i.e., minimum reaction byproducts) and with least power consumption is the key for the optimum operation of the plasma reactor. The produced NO/sub 2/ was totally converted to N/sub 2/ and Na/sub 2/SO/sub 4/ with Na/sub 2/SO/sub 3/ or Na/sub 2/S with and without NaOH using the barrier-type packed-bed plasma reactor followed by the packed-column chemical reactor. The NO/sub 2/ reduction was more effective for Na/sub 2/S than Na/sub 2/SO/sub 3/ but produces H/sub 2/S with Na/sub 2/S. For both cases at least five times the stoichiometric amount of chemicals were required for complete NO/sub 2/ reduction. Nearly 100% of NO/sub x/ and SO /sub 2/ and 40% Of CO/sub 2/ simultaneous removal were achieved with less than 5 ppm of N/sub 2/O and CO. The operating cost was less than 1/4 the SCR process. The additional SO/sub 2/ treatment system can be eliminated.     

Effects of reactor type and voltage properties in methanol reforming with nonthermal plasma

Reactor type and voltage properties affected the reforming behavior of 1% methanol in N/sub 2/ with nonthermal plasma. Methanol conversion increased with voltage frequency for both a ferroelectric packed-bed reactor (FPR) and a silent discharge reactor (SDR), but they showed different sensitivities to frequency change at fixed applied voltages. In the frequency range of 5 Hz-5 kHz, methanol conversion was expressed as a function of reactor energy density irrespective of the reactor type. Regarding the effect of voltage waveform with 50-Hz ac at the same applied voltage levels for FPR and SDR, methanol conversion decreased in the order: triangle>sine>square. H/sub 2/, CO, and CO/sub 2/ were obtained as the major products, and similar product distributions were observed in comparable methanol conversions irrespective of reactor type and the differences in frequency and waveform. Energy conversion efficiency increased to 40%/spl sim/60% at /spl sim/80% of MeOH conversions for FPR and SDR.     

Performance evaluation of nonthermal plasma reactors for NO oxidation in diesel engine exhaust gas treatment

The discharge plasma-chemical hybrid process for NO/sub x/ removal from the flue gas emissions is an extremely effective and economical approach in comparison with the conventional selective catalytic reduction system. In this paper we bring out a relative comparison of several discharge plasma reactors from the point of NO removal efficiency. The reactors were either energized by AC or by repetitive pulses. Ferroelectric pellets were used to study the effect of pellet assisted discharges on gas cleaning. Diesel engine exhaust, at different loads, is used to approximately simulate the flue gas composition. Investigations were carried out at room temperature with respect to the variation of reaction products against the discharge power. Main emphasis is laid on the oxidation of NO to NO/sub 2/, without reducing NO/sub x/ concentration (i.e., minimum reaction byproducts), with least power consumption. The produced NO/sub 2/ will be totally converted to N/sub 2/ and Na/sub 2/SO/sub 4/ using Na/sub 2/SO/sub 3/. The AC packed-bed reactor and pelletless pulsed corona reactor showed better performance, with minimum reaction products for a given power, when the NO concentration was low (/spl sim/100 ppm). When the engine load exceeds 50% (NO>300 ppm) there was not much decrease in NO reduction and more or less all the reactors performed equally. The total operating cost of the plasma-chemical hybrid system becomes $4010/ton of NO, which is 1/3-1/5 of the conventional selective catalytic process.